Symposium EN02—Materials for High-Energy and Safe Electrochemical Energy Storage

Li metal and Li-alloy based anode materials are the most promising anodes for next-generation Li batteries. The poor interfacial stability (unstable solid-electrolyte interphase (SEI)) in the battery and microstructural failure of Li metal into mossy or dendritic Li during its plating/stripping have been two primary issues hindering their practical application. In this talk, first, I will present a strategy to reinforce the SEI with desired properties including good tolerance to the Li-based material volume change and efficient surface passivation against electrolyte penetration. The strategy works via introducing multiple functional components bonded to the Li-based material surface into the SEI. The SEI reinforced shows much better stability than the SEI reinforced by electrolyte additive strategy, which is the current state-of-art and commercially used solution to SEI stability issue. Second, I will present an approach of structured host for Li metal to promoting uniform Li plating/stripping at high deposition capacity and current density. This approach uses a polymeric sponge with high zeta potential to promote electrokinetic effects so as to alter Li-ion transport properties and reduce concentration polarization for Li plating/striping. High efficiency cycling of Li metal was achieved and demonstrated in Li metal battery cells at low N/P ratio and high deposition capacity and current densities.

The path toward Li-ion batteries with higher energy-densities will likely involve use of thin lithium metal (Li) anode (<50 mm thickness), whose cyclability today remains limited by dendrite formation and low Coulombic efficiency (CE). Previous studies have shown that the solid-electrolyte-interface (SEI) of the Li metal plays a crucial role in Li electrodeposition and stripping behavior. However, design rules for optimal SEIs on Li metal are not well established. Here, using integrated experimental and modeling studies on a series of structurally-similar SEI-modifying model compounds, we reveal the relationship between SEI compositions, Li deposition morphology and CE, and identify two key descriptors (ionicity and compactness) for high-performance SEIs. Using this understanding, we design a highly ionic and compact SEI that shows excellent cycling performance in high specific energy LiCoO₂ or NCA-Li full cells (1.3 Ah pouch cells, > 300 Wh/kg) at practical current densities. Our results provide guidance for rational design of the SEI to further improve Li metal anodes.

Li-ion batteries are nowadays considered as the main source of energy for an electric vehicle (EV) application; however, the significantly longer “refueling” time compared to standard internal combustion engine vehicles is a substantial disadvantage from the perspective of the end-user. It is speculated that increasing the charging rate by a factor of three should significantly reduce the gap between EVs and conventional automobiles, promoting further penetration of EVs on the mass market. However, a significant drawback of very rapid charging is lithium plating on the negative electrode, which arises if the current exceeds the intercalation rate at which lithium diffuses into the negative electrode. In this case, a film of metallic Li will deposit on the surface, which subsequently reacts with electrolyte, leading to an increase of the cell internal resistance, a lower capacity, and potential short-circuiting in extreme cases.
Here we report an application of the parallel-plate RF probe to monitor in situ deposition of Li metal on a graphite anode during charging of a single layer prismatic cell, assembled with electrodes extracted from a commercial battery. We have demonstrated that part of the plated lithium was able to intercalate into the graphite after the current was turned off. Moreover, the signal of deposited Li metal consists of two resonances corresponding to (1) a “Li film” on the surface of the electrode, and (2) to dendrites orthogonal to electrodes’ planes. Our data demonstrate that the Li metal intercalation into the graphite is primarily happening from the former type of deposited metal, while the lithium stored in dendrites can partially dissolve into the electrolyte during the consecutive discharge of the cell. Importantly, we were able to quantify the amount of reversibly and irreversibly deposited lithium. Finally, a coexistence of three stages of intercalated into graphite Li (2L, 2 and 1) is demonstrated during a fast charge cycle, suggesting a non-uniform lithiation of the electrode in that case.

1. S.A. Krachkovskiy. J.Foster, D.J., Bazak, B.J. Balcom, and G.R. Goward, J.Phys.Chem. C., 122, 21784–21791 (2018).
2. A Ramírez Aguilera, B. MacMillan, G. Goward, B. Balcom, Concepts Magn. Reson. A, 47A, e21465 (2018).
3. M. Halse, D. J. Goodyear, B. MacMillan, P. Szomolanyi, D. Matheson, B. J. Balcom, J Magn Reson, 165, 219 (2003).

Silicon is one of the most promising materials for high energy density anodes in next generation Li-ion batteries. However, the long-term performance of Si anodes is currently limited due to large volumetric expansion and contraction upon lithiation and delithiation, as well as continuous solid electrolyte interface (SEI) formation. Understanding of this SEI is difficult due to its buried nature, rough sample morphology, as well as convolution of chemical and electrochemical formation processes. Another important aspect of the SEI formation that needs better understanding is the presence of native oxide SiOx at the Si surfaces exposed to ambient atmosphere.
Here, we report on our recent studies of lithium silicide (LixSi) and lithium silicate (LixSiOy) thin films, as model systems to study SEI formation on Si anode with SiOx native oxide in Li-ion batteries. The LixSi and LixSiOy thin films were deposited by combination of sputtering and thermal evaporation, on both Si and Cu foil substrates. The resulting samples were studies by a combination of electrochemical (charge-discharge profiles, impedance spectroscopy, etc), spectroscopic (x-ray photoemission spectroscopy XPS, Fourier-Transform Infrared Spectroscopy FTIR) techniques, with high accuracy enabled by flat homogeneous character of the thin film model samples.
The results of our studies indicate that the SEI can be formed simply by chemical reduction of electrolyte on lithium silicide surfaces, without any electrochemical driving force [1]. They also suggest that it may be possible to increase the lifetime of the next-generation Li-ion batteries using prelithiated Si anodes. On the other hand, it is determined that LixSiOy is not beneficial in stabilizing the Si anode surface during battery operation, due to large electronic conductivity, and despite its ductile mechanical properties [2]. These results also suggest future directions for design of artificial SEI layer coatings on Si anode surfaces.
[1] Y. Xu, A.K. Burrell, A. Zakutayev et al, J. Phys. Chem. C 123, 13219 (2019)
[2] Y. Xu, K. Persson, A.K. Burrell, A. Zakutayev et al ACS Appl Mat Int 10, 44 (2018)

Using an epitaxial thin-film model system deposited by physical vapor deposition, we study the lithium-ion conductivity of Li₄Ti₅O₁₂, a common anode material for Li-ion batteries, in the absence of grain boundaries [1]. Epitaxy, phase purity, and composition across the film thickness are verified employing out-of-plane and in-plane X-ray diffraction, transmission electron microscopy, time-of-flight mass spectrometry, and elastic recoil detection analysis. We find that epitaxial Li₄Ti₅O₁₂ grown on a single-crystal MgO(111) surface behaves like an ideal ionic conductor that is well described by a parallel RC equivalent circuit, with an ionic conductivity of 2.5 × 10^–5 S/cm at 230 °C and an activation energy of 0.79 eV in the measured temperature range of 205 to 350 °C [1]. To study lithium-ion conductivity as a function of state of charge, epitaxial Li₄Ti₅O₁₂ was also grown on an epitaxial Pt(111) surface functioning as current collector [2]. Epitaxial Li₄Ti₅O₁₂ was subsequently cycled galvanostatically in half-cell configuration vs lithium metal in 1m LiPF₆ in EC:DMC organic electrolyte. We find that epitaxial Li₄Ti₅O₁₂ shows stable cycling at least up to 50 C. We also study lithium-ion conductivity and lithium-ion diffusion as function of state of charge by impedance spectroscopy and galvanostatic intermittent titration technique and interpret our results in the theoretical framework developed for phase-transformation materials [3].


References:
1. F. Pagani, E. Stilp, R. Pfenninger, E. Cuervo Reyes, A. Remhof, Z. Balogh-Michels, A. Neels, J. Sastre-Pellicer, M. Stiefel, M. Doebeli, M. D. Rossell, R. Erni, J.L.M. Rupp, C. Battaglia, ACS Appl. Mater. Interfaces, 10 (2018), 44494−44500.
2. F. Pagani et al, in preparation
3. Y. Zhu, C. Wang, J. Phys. Chem. C, 114 (2010), 2830-2841.

Abstract: We are the first to examine the role of graphene host structure/chemistry in plating-stripping in lithium metal anodes employed for lithium metal batteries (LMBs). Structural and chemical defects are bad since highly defective graphene promotes unstable solid electrolyte interphase (SEI) growth. This consumes the FEC additive in the carbonate electrolyte and is correlated with rapid decay in CE and formation of filament-like Li dendrites. A unique flow-aided sonication exfoliation method is employed to synthesize "defect-free" graphene (df-G), allowing for a direct performance comparison with conventional reduced graphene oxide (r-GO). At cycle 1, the r-GO is better electrochemically wetted by Li than df-G, indicating that initially it is more lithiophilic. With cycling, the nucleation overpotential with r-GO becomes higher than with df-G, indicating less facile plating reactions. The df-G yields state-of-the-art electrochemical performance; stable plating at 0.5 - 4 mA/cm², areal capacity up to 2 mAh/cm², cycle 1 CE at 98% and cycle 100 CE at 94%. With df-G the post cycled metal surface is relatively smooth and dendrite-free. Conversely, r-GO templates have CE rapidly degrade from the onset, with extensive dendrites after cycling. Extensive SEI growth and associated FEC depletion with r-GO are further confirmed by electrochemical impedance analysis and surface science methods (XPS). We therefore propose the following design rule for next-generation supports for LMBs: An ideal architecture will promote copious heterogenous nucleation of the plating metal, shielding it from the electrolyte. In addition, it is essential that the host is itself non-catalytic towards SEI formation.

The lithium-rich transition metal oxides, e.g. Li[Li_0.2Ni_0.2Mn_0.6]O₂ can store charge on the oxide as well as the transition metal ions (oxygen redox). However, oxygen redox in these systems is almost always accompanied by substantial structural change and voltage hysteresis, limiting their application. Understanding the relationship between the oxidation of O^2- ions and the deleterious changes that are triggered by such oxidation is essential if we are to develop strategies for their mitigation and therefore unlock the high capacity of O-redox materials. Recent work on the relationship will be discussed.

Here we report the TEM, X-ray, and first-principle investigation of a promising high-capacity lithium-rich 3d-4d (Mn-Ru) transition-metal layered compound. The incorporation of 4d transition metals here offers an uncharted phase space for mechanistic exploration as compared to the well documented 3d transition metal (TM) oxides. Using state-of-the-art electron and X-ray based techniques, we find surprisingly, after cycling, ruthenium segregates out as metallic nanoclusters on the reconstructed surface. Our calculations show that the unexpected ruthenium metal segregation is due to its thermodynamic insolubility in the oxygen deprived surface. This insolubility can disrupt the reconstructed surface, which explains the formation of a porous structure in this material. The revealed mechanism allows us to provide predictive guidance for the future design of lithium-rich as well as stoichiometric layered cathode materials.
This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, and the Scientific Data and Computing Center, a component of the Computational Science Initiative, at Brookhaven National Laboratory under Contract No. DE-SC0012704. Dr. Enyuan Hu, Dr. Seongmin Bak, and Dr. Xiao-Qing Yang were supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program, including Battery500 Consortium under Contract DE-SC0012704. Work done by R.Z. is partially supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Award Number: DE-EE0008444. This research used resources 8-ID, 23-ID-2, and 28-ID-2 of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. This research used resources of beamline 8.0.1 of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. We acknowledge the technical support from beamline scientists Dr. Jianming Bai and Dr. Eric Dooryhee at the XPD beamline of NSLSII.

There is an imperative need for resource-friendly and high-energy-density cathode materials for Li-ion batteries to satisfy the rapidly increasing need for electrical energy storage. To replace the Ni and Co, which are limited resources and are associated with safety problems in current Li-ion batteries, high-capacity cathodes made of earth-abundant and safer metals have been intensively sought after by battery scientists [1]. In this regard, disordered-rocksalt lithium transition metal oxides (Li-TM oxides) have received much attention as the cathode materials for their large compositional space and high dimensional stability, allowing the development of high-energy-density cathodes made of inexpensive metals such as Mn and Ti [2-6].
It is now well understood that to operate the disordered rocksalt cathodes, so-called a ‘Li-excess’ (i.e., TM-deficient) composition (x>1.0 in Li_xTM_1-xO₂, e.g., Li_1.2TM_0.8O₂) is required, because otherwise, Li diffusion in the materials is very slow [2]. Meanwhile, the decreased TM-content due to ‘Li-excess’ often results in a limited amount of extractible electrons from TM-redox in the materials, for which a large number of electrons from oxygen (O-redox) are often additionally needed upon cycling [7]. Unfortunately, excessive O-redox activity triggers various O-redox-related side reactions, including (i) oxygen loss followed by metal densification and (ii) bulk crystal structure changes, all of which degrade the cycling performance of the disordered rocksalt cathodes [4,6]. Therefore, strategies to bypass the O-redox-related side reactions while maintaining the integrity of the disordered-rocksalt Li-excess framework should be highly important for the improvement of the disordered-rocksalt cathode materials.
In this talk, based on recent studies of fluorinated disordered-rocksalt compounds such as Li_1.15Ni_0.45Ti_0.3Mo_0.1O_1.85F_0.15, Li₂Mn_2/3Nb_1/3O₂F, and Li₂Mn_1/2Ti_1/2O₂F, I will discuss rational strategies to mitigate the O-redox-related side reactions in the disordered rocksalt cathodes [3,6]. In particular, I will show how the introduction of high valent cations (e.g., Nb⁵⁺, Ti⁴⁺, Mo⁶⁺) and fluorine (F^-) anion to the metal- and anion-sites, respectively, can lead to Mn²⁺/Mn⁴⁺-redox-based disordered-rocksalt cathodes with ultrahigh capacity and a low cost [3].

[1] K. Turcheniuk et al., Nature 559, 467-470 (2018)
[2] J. Lee et al., Science 343, 519-522 (2014)
[3] J. Lee et al., Nature 556, 185-190 (2018)
[4] J. Lee et al., Energy Environ. Sci. 8, 3255-3265 (2015)
[5] N. Yabuuchi et al., PNAS 112, 7650-7655 (2015).
[6] J. Lee et al., Nat. Commun. 8, 981 (2017)
[7] D. Seo et al., Nat. Chem. 8, 692-697 (2016)

The recent discovery of anionic redox chemistry in Li-ion batteries has already had promising implications for improving their capacity via increased electrochemical activity. Higher performance materials are now required to make this technology a reality and new strategies for designing compounds that exhibit this phenomenon are needed. Anionic redox activity requires a balance between the quantities U (d-d coulomb repulsion) and Δ (charge transfer), which in turn are sensitive to the d-metals present in the crystal structure.[1] We present a computational study in which d-metals are systematically substituted into a range of prototypical cathode crystal structures using materials informatics tools that we have previously applied in the context of solar energy materials.[2,3]

The resulting 250 compounds are subject to an automated density functional theory (DFT) screening workflow, using the open-source python package Atomate. Our workflow facilitates the assessment the thermodynamic stability of the new phases, as well as relating electronic energy levels calculated accurately using hybrid DFT to the key heuristics U and Δ, in order to identify the most promising candidates. Data-driven discovery tools powered by supervised machine learning algorithms, which require large, high quality datasets,[4] are then applied to the calculation results in order to suggest new candidate compounds.

[1] G. Assat, J.-M. Tarascon, Fundamental understanding and practical challenges of anionic redox activity in Li-ion batteries, Nature Energy, 2017; DOI: 10.1038/s41560-018-0097-0
[2] D. W. Davies et al., SMACT: Semiconducting materials by analogy and chemical theory, JOSS, 2019; DOI: 10.21105/joss.01361
[3] D. W. Davies et al., Computer-aided design of metal chalcohalide semiconductors: from chemical composition to crystal structure, Chem. Sci., 2018; DOI: 10.1039/c7sc03961a
[4] K. T. Butler, D. W. Davies, H. Cartwright, O. Isayev, A. Walsh, Machine learning for molecular and materials science, Nature, 2018; DOI: 10.1038/s41586-018-0337-2

Determining the fundamental properties affecting lithium metal plating is challenging because characterization methods are largely limited by the ease with which lithium metal is damaged, notably altering structure and morphology by the sources of probes. Recent work has demonstrated the ability of cryogenic transmission electron microscopy (cryo-TEM) to observe the morphology and surface chemistry of nanoscale electrochemically deposited lithium at atomistic scale. We have also demonstrated cryogenic focused ion beam (cryo-FIB) to characterize three dimensional and bulk morphology of electrochemically deposited lithium. This work depicts not only the importance of cryo-FIB for preparing sensitive battery materials, but also elucidate the impact of electrolyte and additive selection in the density and morphology of plated lithium, which directly impacts long term cycling performance. We further extend cryo-FIB to process and analyze TEM lamella of lithium metal and lithium metal solid-state batteries. The cryogeneic imaging techniques can enable a new paradigm for studying beam sensitive materials and electrochemically activated compounds.

The traditional host material of choice for Li⁺-conducting solid polymer electrolytes (SPEs) has long been poly(ethylene oxide) (PEO) and with this material most of what we today know about ion transport in SPEs has been revealed. [1,2] While PEO is an excellent material for solvating Li⁺ ions, the chelating ability of the oxyethylene repeating units in this material also result in excessive coordination strength, limiting the ability of the cation to shed its coordination shell and transfer between coordination sites. This ultimately restricts cation transport in this material and manifests as notably low cation transference numbers in PEO-based electrolytes. [3]
Hence, substantial interest has recently been raised in alternative host materials that show improvements in, e.g., cation transference number and room temperature ionic conductivity. [4] While materials such as polyesters and polycarbonates eliminate the strong coordination of oxyethylene repeating units, other interesting effects become relevant.
This presentation will account for our recent efforts into understanding ion transport in polyesters, polycarbonates, and copolymers thereof, using a combination of molecular dynamics simulations, NMR spectroscopy, IR spectroscopy, and electrochemical measurements. This has revealed important effects of preferential coordination, competing plasticization and steric hindrance of side chains, and correlation of cation transference number with the ion coordination strength. Of particular interest is also the differences observed when comparing Li⁺ and Na⁺ conduction in these materials.
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The ceramic-sulfide family of solid-electrolytes are amongst the most promising directions for achieving all-solid-state lithium ion batteries. While the ceramic-sulfides are celebrated for remarkably high ionic conductivity, even exceeding conventional liquid-electrolytes, they remain a narrow electrochemical stability window of approximately 1.7-2.1 volts vs lithium metal based on standard thermodynamic prediction. These electrochemical stability windows further narrow upon forming interfaces with many active materials. This talk will cover new approaches for enabling a largely expanded metastability window for both bulk ceramic-sulfides and interphases with common electrodes. 5V cells based on layered Li-Co-O and spinel Li-Mn-Ni-O will be presented that make use of these metastable widening techniques ceramic-sulfide voltages.

The underlying stabilization methods will be discussed from a detailed theoretical perspective. Ceramic-sulfides are known to undergo significant volume expansion during electrochemical decay. This volume expansion has been shown to be a viable means of substantial voltage widening for lithium ion battery cells [1,2]. The discussed theoretical framework will be used to evaluate experimental evidence of voltage-widening in both of the representative ceramic-sulfides Li10GeP2S12 and Li10SiP2S12.

Discussion on the interphases between ceramic-sulfides and common electrode materials will focus on our recent high-throughput computational work[3], in which over nearly 70,000 materials were evaluated for interfacial chemical and electrochemical stabilities with Li10SiP2S12. This work cataloged over 2,000 coating materials that were determined to form stable interfaces with Li10SiP2S12 in the cathode voltage range (2-4V). These coating materials, combined with widened bulk electrochemical stability, suggest the path forward for all-solid-state lithium ion batteries based on ceramic-sulfide electrolytes.

[1] Fan Wu*, William Fitzhugh*, Luhan Ye, Jiaxin Ning, Xin Li. Advanced Sulfide Solid Electrolyte by Core-Shell Structural Design. Nature Communications, (9), 4037 (2018)
[1] William Fitzhugh*, Fan Wu*, Luhan Ye*, Haoqing Su, Xin L. Strained Stabilized Ceramic-Sulfide Electrolytes. Under review
[3] William Fitzhugh*, Fan Wu*, Wenye Deng, Pengfei Qi, Luhan Ye, Xin Li. A High-Throughput Search for Functionally Stable Interfaces in Sulfide Solid-State Lithium Ion Conductors. Advanced Energy Materials, 1900817 (2019)

Next generation of energy storage may largely benefit from fast Li⁺ ceramic electrolyte conductors to allow for safe and efficient batteries. With recent discoveries in thin film processing solid-state lithium ion conductors, such as Li-garnets and LIPON or LiSICON-based solids, have been recently considered as candidate materials not only for next-generation solid-state batteries but also for gas sensors measuring environmental CO2 and memristors owing to the fast ionic transport in the solid-state electrolyte.
In the first part of this talk, we review and underline the advantages of various Li solid-state conductor materials and reflect on opportunities of thin film processing, being a requirement to define precisely the Lithium stoichiometries and related electronic state changes for transition metal ions, miniaturize the device, and reach high energy/information densities for energy storage, computation, and sensing.
In the second part, we focus on thin film processing and controlling Lithium stoichiometries to reach fast conductive phases for Li garnets and Li titanates as solid state battery, and memristive neuromorphic computing units. Insights on structure-phase-transport interaction and implications on performances will be exemplified for energy storage aiming high energy densities, and modulations of synaptic artificial weights through lithium induced metal-to-insulator transitions in lithium titanate memristors.

References
A low ride on processing temperature for fast lithium conduction in garnet solid-state battery films
R. Pfenninger, M. Struzik, I. Garbayo, E. Stilp, J.L.M. Rupp, Nature Energy, 1 (2019)
A Simple and Fast Electrochemical CO2 Sensor based on Li7La3Zr2O12 for Environmental Monitoring
M. Struzik, I. Garbayo, R. Pfenninger, J.L.M. Rupp, Advanced Materials, 30, 1804098 (2018)
Glass-Type Polyamorphism in Li-Garnet Thin Film Solid State Battery Conductors
I. Garbayo, M. Struzik, W.J. Bowman, R. Pfenninger, E. Stilp, J.L.M. Rupp, Advanced Energy Materials, 1702265 (2018)
Accelerated Ionic Motion in Amorphous Memristor Oxides for Non-Volatile Memories and Neuromorphic Computing
R. Schmitt, M. Kubicek, E. Sediva, M. Trassin, M.C. Weber, A. Rossi, H. Hutter, J. Kreisel, M. Fiebig, J.L.M. Rupp, Advanced Functional Materials, 1804782 (2018)
Lithium Titanate Anode Thin Films for Li-Ion Solid State Battery based on Garnets
R. Pfenninger, M. Struzik, I. Garbayo, S. Afyon, J.L.M. Rupp, Advanced Functional Materials, 28, 201800879 (2018)
Designing Strained Interface Heterostructures for Memristive Devices
S. Schweiger, R. Pfenninger, W.J. Bowman, U. Aschauer, J.L.M. Rupp, Advanced Materials, 1605049 (2017)
Interface-Engineered All-Solid-State Li-Ion Batteries Based on Garnet-Type Fast Li+ Conductors
J. van den Broek, S. Afyon, J.L.M. Rupp, Advanced Energy Materials, 1600736 (2016)

The experimental observation of Li dendrite growth inside mechanically hard solid electrolytes (SEs) raised an important question; can hard solid electrolytes mechanically stop Li-dendrite growth? Here we report a multiscale model coupling Density Functional Theory (DFT) calculations with the phase-field method to address the question. In particular, we investigate the roles of internal defects, such as pores and crack surfaces, inside a number of solid electrolytes including cubic Li₇La₃Zr₂O₁₂ (c-LLZO), β-Li₃PS₄, Li_1.17Al_0.17Ti_1.83 (PO₄)₃ (LATP), and Li₂PO₂N. It is shown that LLZO surfaces have a much smaller band gap than the corresponding bulk and thus could trap significant excess electrons, while the other three systems do not exhibit significant differences in the surface and bulk band gaps. A fully coupled phase-field model was then developed to further examine the impact of excess surface electrons on the Li dendrite growth morphology in polycrystalline LLZO. This model successfully explained the experimentally observed dendrite intergranular growth and revealed that the trapped electrons may produce isolated Li-metal nucleation, leading to a sudden increase of Li-dendrite penetration depth. Finally, we compared the basic material properties and found that the Li ranked dendrite resistance in these SEs, based on the surface electronic properties instead of mechanical properties, is consistent with a broad range of experimental observations. Therefore, surface band gaps can be used as new descriptors to screen SEs with high Li dendrite resistance.

The demand for rechargeable batteries with higher energy density than lithium-ion batteries that are commercially available has been ever increasing ^{1, 2}. Elemental lithium metal has thus come into the spotlight again as one of the most promising negative electrode materials owing to its exceptionally high theoretical capacity (3860 mAh g^-1) and the lowest negative electrochemical potential (-3.040 V vs. a standard hydrogen electrode) ^{3, 4}. Moreover, its stable utilization is pivotal in the success of the next-generation electrochemical systems. Nevertheless, the commercialization of rechargeable lithium metal electrode has been retarded due to the catastrophic safety issue arising from lithium dendrite formation. Even with a small irregularity in lithium metal deposition during the initial stage of charge, further selective and self-amplifying lithium deposition follows due to the presence of favorable deposition sites ^{5, 6}. The needle-like lithium dendrite can penetrate the polymer separator and possibly contact the opposite electrode, and such contact would result in a huge current flow through the internal circuit, triggering joule heating thermal runaway.
Unfortunately, it has been revealed that dendrite formation cannot be completely inhibited and some reported successes are only valid at low current densities and with low utilization levels of lithium metal. Batteries operating under extreme conditions might still be exposed to the potential risk of dendrite growth and internal short-circuit. Therefore, not only protective techniques for lithium metal but also sensing technologies to detect dendritic growth in advance are needed.
Herein, we introduce a lithium rechargeable battery system with a bifunctional auxiliary electrode that can detect the potential signs of an internal short-circuit and simultaneously prevent cell failure by inhibiting further dendritic growth of lithium metal. Based on this working principle, we provide guidelines for bifunctional auxiliary electrode design and demonstrate that it can act as both a safety sensor and a lithium scavenger. Finally, we show that our in-house designed cell, using a flexible and self-standing auxiliary electrode, can effectively alert the danger of a short circuit in real-time without additional dendrite growth. We expect that this finding will open up unexplored opportunities utilizing various auxiliary electrode chemistry for safe rechargeable lithium metal batteries.

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The Department of Energy (DoE) announced the energy density target of >500 Wh/Kg for next-generation lithium-ion batteries in the incoming 3-5 years, to meet the rapidly growing market in electrical vehicles (EVs) and portable electronic devices. Li metal, is considered as the most promising candidate as anode (Xu, Energy Environ Sci 2014). However, the dendrite forming, low Coulombic efficiency, and unstable solid electrolyte interphase (SEI) pose big challenges in applying Li metal in batteries (Chandrashekar, Nat Mater2012). Here we present a novel, single-side Li-infused carbon fiber fabric (LiCFF) with a controllable, minimized Li loading, which shows a highly reversible plating/stripping with an extremely low overpotential of less than 30 mV (Li foil: >1.0 V over 50 cycles) upon >3000 cycles (6000 and 2000 hours) at 1 and 3 mA/cm²in symmetric cells, respectively (Xi Chen et al, ACS Appl Mater Interfaces, 2019, in print). With a high areal capacity up to 10 mAh/cm²and a high current density of 10 mA/cm², the cell still shows a minimum overpotential of 150-175 mV after 250 cycles (500 hours). Full cell batteries using the LiCFF as ‘all-in-one’ anode without additional slurry-making process and nickel-manganese-cobalt oxide (NMC) as cathode exhibit an improved capacity retention when compared with Li foil: 32% at 0.5 C and 119% at 1.0 C capacity improved after 100 cycles. In parallel, the mossy/dendritic Li on the LiCFF was largely suppressed, which was confirmed using in-situobservations of Li plating/striping in a capillary cell. The excellent electronic conductivity of the carbon fabric leads to small contact/transfer resistances of 3.4/3.8 Ω (Li foil: 4.1/44.4 Ω), enabling a drastically lowered energy barrier for Li nucleation/growth. Thus a uniform current distribution results in forming a homogeneous Li layer instead of forming dendrite.The current LiCFF as anode with controllable Li (n/p ratio), improved cycling stability, mitigated dendrite formation, and flexibility displays promising applications in versatile Li-metal batteries such as Li-NMC and Li-S.
Keywords:Li metal; Carbon fiber fabric; Low overpotential; Dendrite; Lithium ion batteries

Increasing the energy density of sodium-ion batteries is of paramount importance toward achieving a sustainable society. The present limitation of the energy density is owing to the small capacity of cathode materials, in which the (de)intercalation of sodium ions is charge-compensated by transition-metal redox reactions. Although additional oxygen-redox reactions of oxide cathodes have been recognized as an effective way to overcome this capacity limit, the electronic structure during oxygen-redox reactions are yet to be fully understood.
In this work, we employed combined analyses of synchrotron X-ray diffraction, soft X-ray absorption spectroscopy, and DFT calculations to demonstrate how reversible oxygen-redox reactions occurs in transition-metal oxides. As an oxygen-redox compound, we studied Na2RuO3 and Na2Mn3O7, which exhibit highly reversible oxygen-redox reactions. Detailed analyses revealed that, while nonbonding oxygen 2p orbital plays a central role to trigger oxygen oxidation, hole generated on oxygen 2p orbital is stabilized by interaction with metal d orbitals.
Furthermore, we found a self-ordering phenomenon of stacking faults upon desodiation from an oxygen-redox layered oxide Na2RuO3, realizing much better reversibility of the electrode reaction. The cooperatively ordered vacancy in lithium-/sodium-rich layered transition-metal oxides is shown to play an essential role, not only in generating the electro-active nonbonding 2p orbital of neighbouring oxygen but also in stabilizing the phase transformation for highly reversible oxygen-redox reactions.

Ref.
1. B. Mortemard de Boisse, et al., M. Okubo and A. Yamada, Nature Commun. (2016) 7, 11397.
2. M. Okubo, et al., ACS Appl. Mater. Interfaces (2017) 9, 36463.
3. B. Mortemard de Boisse, et al., M. Okubo and A. Yamada, Adv. Energy Mater. (2018) 1800409.
4. B. Mortemard de Boisse, et al., M. Okubo and A. Yamada, Nature Commun. (2019) 10, 2185.

Layered transition oxides are the dominant cathodes in Li-ion batteries, and are the leading choice for electric vehicles, which require ever higher energy densities to extend the driving range. Most recently, there has been a drive to increase the nickel content, such as in LiNi_0.8Mn_0.1Co_0.1O₂ (NMC 811), as higher nickel contents lead to higher capacities and are lower in cost. The capacity can also be increased by raising the charging voltage, but that leads to greater instability with electrolyte. An optional key strategy to increase the energy density of the layered oxides is to overcome the loss in capacity experienced in the 1st cycle. This can range from 10-20% of the total capacity, and so its elimination or at least reduction could lead to a ~10% enhancement of energy density at the cell level. Our studies found that ~ 80% of the 1^st capacity loss of NMC 811 can be attributed to slow lithium diffusion at high lithium concentrations. Increasing the temperature to 45°C eliminates the kinetics limitation. The remaining 20% of the 1^st cycle capacity loss is likely caused by surface changes in the material and/or CEI formation during the charge process, which might be solved by coatings to protect the cathode surface and preform the CEI. Some surface and structural characterizations during the 1^st charge and discharge will be discussed to show the possible reasons causing the diffusion drop of Li ions at the high Li lithiation state. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy, through the Advanced Battery Materials Research Program (Battery500 Consortium).

Lithium ion batteries are ubiquitous in modern technology and are poised to lead the electric vehicle revolution. Challenges such as lower cost, higher performance, safety, durability and recyclability are at the forefront of battery research and much attention is focused on layered oxide materials such as LiCoO₂ and LiNi_1/3Mn_1/3Co_1/3O₂ (NMC-111). By increasing the nickel content in these layered oxide materials, one can decrease the quantity of cobalt, thereby alleviating issues surrounding cost and ethical concerns as well as increase the energy density of the battery. For example, the practical discharge capacities increase from ~ 140 mAh g^-1 for LiCoO₂ to > 200 mAh g^-1 for LiNi_0.8Mn_0.1Co_0.1O₂ (NMC-811). The challenges with moving to these new cathode chemistries include degradation issues, routes to reliable synthesis and scale-up of promising materials for commercial viability.

In this work, we present a newly-developed sol-gel method for the synthesis of phase pure high nickel content NMC materials, which utilises microwave heating to reduce both reaction times and temperatures. These particles exhibit smaller sizes than those achieved with conventional heating methods and interestingly, by varying the synthesis conditions, these particles display faceted morphologies. We will present the implications of this on electrochemical performance. To circumvent the capacity fade typically observed for high-nickel content cathodes, we also present two avenues to mitigate electrode degradation. Firstly, aliovalent doping during synthesis of both the lithium and transition metal sites with cations such as Mg²⁺ and Al³⁺ respectively provides structural stability to the O3 unit cell during cycling, especially during deep delithiation, with our results revealing significant capacity retention. Secondly, the application of a thin coating of amorphous Al₂O₃ to the particles assists in the protection of the surface to parasitic reactions by fluorine-containing species in the electrolyte and electrochemical testing in half-cells reveals excellent capacity retention compared to uncoated materials. These results demonstrate the viability of this facile approach to faceted high-nickel content (doped) cathodes and we will finally discuss the potential scalability of this approach.

Increasing lithium-ion battery energy density and reducing cost without compromising lifetime or safety is an important goal for EV applications. While Co has been a critical constituent of Li-ion battery positive electrode materials such as NCA and NMC, instability of Co pricing and concerns about long-term availability motivate the reduction of Co content in these materials. This work pairs first-principles density functional theory (DFT) computations with experimental measurements to gain fundamental insight into how individual dopants influence the structural and electrochemical properties of LiNi_1-yM_yO₂ (y=0, 0.05; M=Al, Mg, Mn, Co) and makes comparison with NCA materials. Trends in capacity reduction as a function of dopant valence and concentration can be explained using simple oxidation state analysis, which is shown to hold on the atomic scale from DFT computations. Similarly, computations over various Li configurations at high states of charge demonstrate preferred structural arrangements for Al and Mg, which helps understand the effective suppression of phase transitions otherwise observed in LiNiO₂ and LiNi_0.95Co_0.05O₂ using dQ/dV analysis and in-situ XRD. Oxygen binding energy computations as a function of dopant type and Li content paired with TGA and ARC measurements further reveal the mechanism through which small dopant concentrations help reduce the reactivity of ultra-high Ni materials with electrolyte at elevated temperature, potentially leading to safer Li-ion cells.

Fluorinated electrolyte is a promising candidate to replace the regular carbonate-based electrolyte because of its impressive anodic stability, conductivity as well as thermo-stability. Yet, most of the fluorinated electrolyte studies focused on the interfacial reaction and electrochemical performance. Although it is equally critical in understanding the interaction between different electrolyte systems and the bulk cathode structure to improve the energy density of the whole cell, the research regarding this topic is limited. In this work, bulk electrode analysis via in-situ XRD technique was carried out to unveil the high Nickel cathode structural changes by using different electrolytes and the results indicate the use of fluorinated electrolyte can mitigate the electrolyte decomposition. Most importantly, it can also assist the preservation of the crystal structure of high Nickel cathode by inhibiting the loss of active Li ion and transition metal during cycling. All results converge to the conclusion that the use of fluorinated electrolyte can not only stabilize the interface but also conserve the bulk structure. Owing to its impressive anodic stability, conductivity as well as thermo-stability, fluorinated electrolyte is a promising candidate over the conventional regular carbonate-based electrolyte for next generation functional electrolyte. Currently, most of the fluorinated electrolyte studies have been focused merely on the interfacial reaction and electrochemical performance. Although it is equally critical in understanding the interaction between different electrolyte systems and the bulk cathode structure to improve the energy density of the whole cell, the research regarding this topic is still lacking. In this work, bulk electrode analysis via in-situ XRD technique was carried out to unveil the high Nickel cathode structural changes in different electrolyte systems and the results indicated the use of fluorinated electrolyte can mitigate the electrolyte decomposition. More importantly, it can also assist the preservation of the crystal structure of high Nickel cathode by inhibiting the loss of active Li ion and transition metal during cycling. All results converge to the conclusion that the use of fluorinated electrolyte can not only stabilize the interface but also conserve the integrity of the bulk crystal structure.

The advent of solid-state batteries has spawned a recent increase in interest in lithium conducting solid electrolytes, especially in the lithium thiophosphates. While current lithium electrolytes provide fast-ionic conduction to fundamentally study solid-state batteries, their ionic conductivities are not sufficient for thick electrode configurations, which will really allow high energy densities to be achieved.¹

In this presentation, we show how an understanding of the structure-transport properties of the lithium argyrodites Li₆PS₅X can help tailor the ionic conductivity. We show that an anion site-disorder between S^2-and X^-is beneficial²and that an induction of the site disorder in Li₆PS₅I leads to a significant improvement of the conductivity.³Having achieved the fastest lithium argyrodite so far with = 18 mS/cm, solid-state batteries with thick electrode configurations (150 – 350 ) can be built. Due to the optimized solid electrolyte, the solid-state battery can be cycled even at 1C with no capacity fade over 150 cycles. This work shows that optimizing solid electrolytes helps to achieve stable cycling at high rates in solid-state batteries with thick electrodes.

Further, we will show how the stability of thiophosphate electrolytes can be measured and that the operation window affects cell performance. Lastly, we show how volume changes, induced by electrochemical (de-)intercalation, affect the performance in solid state batteries providing an understanding of the underlying mechanochemical influences in Li-S solid-state batteries.^4–6

(1) Janek, J.; Zeier, W. G. A Solid Future for Battery Development. Nat. Energy2016, 16141.
(2) Kraft, M. A.; Culver, S. P.; Calderon, M.; Böcher, F.; Krauskopf, T.; Senyshyn, A.; Dietrich, C.; Zevalkink, A.; Janek, J.; Zeier, W. G. Influence of Lattice Polarizability on the Ionic Conductivity in the Lithium Superionic Argyrodites Li6PS5X (X = Cl, Br, I). J. Am. Chem. Soc.2017, 139(31), 10909–10918.
(3) Kraft, M. A.; Ohno, S.; Zinkevich, T.; Koerver, R.; Culver, S. P.; Senyshyn, A.; Indris, S.; Morgan, B. J.; Zeier, W. G. Inducing High Ionic Conductivity in the Lithium Superionic Argyrodites Li6+xP1-XGexS5I for All-Solid-State Batteries. J. Am. Chem. Soc.2018, 140, 16330–16339.
(4) Zhang, W.; Schröder, D.; Arlt, T.; Manke, I.; Koerver, R.; Pinedo, R.; Weber, D. A.; Sann, J.; Zeier, W. G.; Janek, J. (Electro)Chemical Expansion during Cycling: Monitoring the Pressure Changes in Operating Solid-State Lithium Batteries. J. Mater. Chem. A2017, 5(20), 9929–9936.
(5) Koerver, R.; Zhang, W.; de Biasi, L.; Schweidler, S.; Kondrakov, A.; Kolling, S.; Brezesinski, T.; Hartmann, P.; Zeier, W.; Janek, J. Chemo-Mechanical Expansion of Lithium Electrode Materials – On the Route to Mechanically Optimized All-Solid-State Batteries. Energy Environ. Sci.2018, 11, 2142–2158.
(6) Ohno, S.; Koerver, R.; Dewald, G.; Rosenbach, C.; Titscher, P.; Steckermeier, D.; Kwade, A.; Janek, J.; Zeier, W. G. Observation of Chemomechanical Failure and the Influence of Cutoff Potentials in All-Solid-State Li–S Batteries. Chem. Mater.2019, 31(8), 2930–2940.

The demand from portable electronics and electric vehicles call for high energy batteries beyond the current lithium ion batteries. Here I will present our recent progress on materials and interfacial design to enable much high energy density batteries, which include 1) High capacity Si anodes with success together commercialization; 2) Li metal anodes: host and interface design to over the lithium metal dendrite formation and interfacial instability; 3) Our pioneering development of cryogenic electron microscopy for understanding the battery materials and solid-electrolyte interphase down to atomic scale resolution.

In situ diagnosis appears to be one of the essential methods for gaining insights as how an electrode material failure, therefore feeding back for designing and creating new materials with enhanced battery performances. In this presentation, I will highlight recent progress on ex-situ, in-situ and operando S/TEM for probing into the structural and chemical evolution of energy storage materials. Both ex-situ and in-situ high resolution imaging enables direct observation of structural evolution, phase transformation and their correlation with mass, charge and electron transport, providing insights as how active materials failure during the cyclic charging and discharging of a battery. In particular, I will broadly cover the frontier of the current understanding of the fading mechanism of layer structured cathode and Li dendrite growth and interaction with separators. Subsequently, I will discuss some recent breakthrough experiments and observations for correlating the structural and chemical evolution with the electrochemical properties of both layered cathode and Li metal. In perspective, my presentation will target to stimulate this field of research to re-check what has been understood and what need to be done to tackle the technical challenges facing the application of the layer structured cathode and Li metal anode.

The applications of rechargeable battery are growing in various field for the efficient energy systems [1]. To expand the application of the rechargeable battery, the developments of innovative rechargeable batteries which overcome the performances of current batteries are required. Fluoride shuttle batteries (FSBs) which is based on the shuttle of fluoride ions in electrolyte and fluorination/defluorination reactions on electrodes [2, 3] contains higher theoretical energy densities than current rechargeable batteries. We have developed organic electrolyte and electrodes from metal fluorides for FSBs [2, 4-10]. However, the reaction mechanisms on the electrode in FSB are not understood. For the further developments of FSB, the analysis of the reaction at the interface between electrode and electrolyte were performed by using atomic force microscopy (AFM) [1, 11-13]. In the presentation, we will show the investigation on the effects of electrolyte composition on the reaction mechanisms.
This research was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING) and Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2) projects of the New Energy and Industrial Technology Development Organization (NEDO), Japan.

[1] Taketoshi Minato et al., Prog. Surf. Sci., 92, 240–280 (2017).
[2] Hiroaki Konishi et al., J. Electrochem. Soc. 164, A3702-A3708 (2017).
[3] Ken-ichi Okazaki et al, ACS Energy Lett., 2, 1460–1464 (2017).
[4] Hiroaki Konishi et al., J. Electroanal. Chem. 826, 60-64 (2018).
[5] Hiroaki Konishi et al., Chem. Lett., 47, 1346-1349 (2018).
[6] Hiroaki Konishi et al., J. Appl. Electrochem., 48,1205–1211 (2018).
[7] Hiroaki Konishi et al., Mater. Chem. Phys. 226, 1-5 (2019).
[8] Hiroaki Konishi et al., J. Electroanal. Chem., 839, 173-176 (2019).
[9] Asuman Celik Kucuk et al., J. Mater. Chem. A, 7, 8559-8567 (2019).
[10] Hiroaki Konishi et al., J. Phys. Chem. C, 123, 10246–10252 (2019).
[11] Taketoshi Minato et al., J. Chem. Phys. 147, 124701 (2017).
[12] Kenichi Umeda et al., Langmuir, 34, 9114–9121 (2018).
[13] Kenichi Umeda et al., Phys. Rev. Lett., 122, 116001 (2019).

Lithium-sulfur (Li-S) batteries are a beyond Li-ion battery technology that provides large theoretical capacity (1672 mAh/g) while also being earth-abundant and low cost. In this study, we investigate the behavior of lithium polysulfides (LiPS; Li2Sx, x = 4, 6 ,8) and lithium salt (LiTFSI; Li bis(trifluoromethane)sulfonimide) in model electrolyte solutions using small angle X-ray scattering (SAXS). A concentration series of polysulfides (ranging from 100 to 1500 mM depending on the solution) in solvents relevant to Li-S battery electrolytes (DOL:DME, acetonitrile) with a range of polysulfide solvation were selected after an initial screening of common solvents. Some aggregation of LiPS was observed at high concentrations (> 1000 mM based on the mass of sulfur) in both solvents, but DOL:DME-based solutions exhibited aggregation even at low concentrations. Fitting the data with a unified model yielded two distinct populations in the DOL:DME solutions – one with a radius of gyration (Rg) of about 5 Å and one with a Rg of about 12 Å. In the 1 M LiTFSI in DOL:DME solutions, the SAXS data showed a peak at all polysulfide concentrations, indicating quasi-periodic nanostructuring in the solution that is induced by the presence of the LiTFSI salt. This nanostructuring is also present in the 1 M LiTFSI in acetonitrile solutions, confirming that the effect originates from the LiTFSI salt. We will compare experimental results with those from molecular dynamics calculations. These results add molecular level insight into Li-S electrolytes and a better understanding of electrolyte-salt interactions.

The rapid growth in popularity of battery devices has brought energy storage and conversion to the spotlight of materials research. Bringing together researchers from a variety of disciplines spanning science and engineering, it is now a common goal to build batteries that are safe, long-lasting, and powerful enough to serve today’s most demanding applications. In order to meet these goals, a methodical development approach is needed, including material synthesis, processing, characterization, and design iteration.

In recent years, X-ray analysis has become a popular choice for electrochemical device characterization, including X-ray microscopy (XRM), X-ray fluorescence (XRF), and X-ray absorption spectroscopy (XAS). Owing to the high penetrating power of X-rays and non-destructive nature of X-ray interactions with matter, these techniques provide unique insight into electrochemical devices such as batteries, fuel cells, and catalysts. XRM employs the technique of computed tomography (X-ray CT or XCT), yielding 3D models of a material’s microstructure, while XRF provides elemental identification and XAS reveals chemical states. Combining these three techniques together results in a powerful characterization approach that compliments conventional electrochemical measurements and other analysis methods, while delivering new information about the material under study. However, while the use of XRM, XRF, and XAS for electrochemical device characterization continues to rise, the techniques are traditionally limited to synchrotron facilities only, which has limited the reach of these techniques for widespread use.

In our work, we have developed a suite of laboratory X-ray instrumentation, designed with battery, fuel cell, and catalyst research in mind. Our laboratory nano-XRM is capable of providing spatial resolutions down to 40 nm, creating a high-resolution model of material microstructures for time-evolved (4D) characterization and computational simulation incorporating fine features within the specimen. In tandem with this, our laboratory micro-XRF system provides sub-parts-per-million (sub-ppm) elemental detection sensitivities with < 10 um spatial resolutions, and pairs elemental identification with optical and x-ray radiographic imaging for spatially-resolved spectroscopic analysis. The most recent addition to this set of tools is the laboratory X-ray absorption spectrometer, which provides sub-eV energy resolution in a matter of minutes and yields oxidation state, coordination number, and bond length information non-destructively and without extensive specimen preparation. These three systems carry with them performance characteristics that begin to mirror those of synchrotron.

Non-aqueous lithium oxygen(air) battery has been considered as a promising next-generation energy storage system because of its highest theoretical energy density among all the battery chemistries which have been introduced so far. However, there are many hurdles in practical demonstration of the high energy density of lithium oxygen battery.¹ One typical and serious problem is that premature passivation of insulating Li₂O₂ inevitably occurs on the surface of the cathode. Using redox mediators such as 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ), coenzyme Q10 (CoQ10), and Vitamin K2, that change the reaction pathway of producing Li₂O₂ from surface of electrode to bulk liquid phase is now suggested as a key solution to circumvent such passivation problems.^2-4 However, such engineering is somewhat empirical with limited mechanistic understanding since most of previous experimental analyses for studying working principles of lithium oxygen battery are based on ex situ experiments. In this work, we implement a liquid TEM holder to capture real time status of the lithium oxygen battery while discharging with a typical redox mediator of DBBQ, which is one of recent emerging electron microscopy techniques for examinations of liquid samples.^5,6 We successfully obtain a real time TEM movie presenting growth of Li₂O₂ on the solution phase and analyze the growth rate, morphology transformation of Li₂O₂. Interestingly, growth of Li₂O₂ in electrolyte solution during discharge involves distinct two-step pathway. Our findings can provide the answer for the unsolved question regarding the redox mediation mechanism, growth kinetics of discharge products, and morphology evolution of Li₂O₂ in lithium oxygen batteries.

References
[1] H. D. Lim^† and B. Lee^† et al. Chem. Soc. Rev. 46, 2873 (2017)
[2] X. Gao et al. Nat. Mater. 15, 882 (2016)
[3] Y. Zhang et al. Adv. Mater. 30, 1705571 (2018)
[4] Y. Ko et al. Adv. Funct. Mater. 29, 1805623 (2019)
[5] J. Park et al. Science 349, 290 (2015)
[6] B. H. Kim et al. Adv. Mater. 30, 1703316 (2018)

Lihthium hexafluorophosphate (LiPF₆) is adopted almost exclusively as the conducting salt of the electrolyte in current commercial lithium-ion (Li-ion) batteries because of the high ionic conductivity, good electrochemical stability and lower cost. However, thermal instability of LiPF₆, which could lead to the generation of detrimental byproduct hydrogen fluoride (HF) through LiPF₆ hydrolysis, raises challenges for LiPF₆ based electrolytes to function well at elevated temperatures (>55°C) and in presence of inevitable moisture or alcohol impurities. Lithium bis(fluorosulfonyl)imide (LiFSI), with higher ionic conductivity and thermal stability, could be a promising alternative to LiPF₆ since it bypasses the hydrolysis of PF₅^- that generates HF. However, a major technical challenge for LiFSI to be employed as a primary conducting salt is aluminum current collector corrosion generally seen from around 4.2 (vs. Li/Li⁺) which is within the operating voltage of Li-ion batteries with lithium nickel manganese cobalt oxide (NMC) cathode. Lithium iron phosphate (LiFePO₄)/graphite Li-ion batteries have an operating voltage between 2.0 and 3.6 V (vs. Li/Li⁺), and therefore, could utilize LiFSI as the primary conducting salt without running into the aluminum corrosion issue.

The intent of this study was to evaluate a series of LiFSI based electrolytes in the LiFePO₄/graphite chemistry. It was found that the calendar life of LiFePO₄/graphite Li-ion batteries was significantly improved in high temperature storage when LiPF₆ was completely or partially substituted by LiFSI. Batteries using LiFSI based electrolytes also demonstrated improved power performance largely due to the superior ionic conductivity of these electrolytes. It was further confirmed that aluminum corrosion is not occurring within the operating voltage of LiFePO₄/graphite Li-ion batteries with LiFSI based electrolytes. This study reveals a promising path forward to produce LiFePO₄/graphite Li-ion batteries with much improved performance so as to meet OEM’s stringent requirements for next-generation Li-ion batteries.

Bisiminoacenaphthene (BIAN) has been an important ligand structure for a variety of metal complex and widely employed as a ligand for olefin polymerization catalysts. However, in spite of their unique electrochemistry, it has not been widely utilized for energy devices. In the present work, firstly BIAN based novel conjugated polymer was prepared by Sonogashira-coupling polymerization and the obtained polymer (P-BIAN)¹ was employed as anode binder in Li/EC:DEC/C type anodic half cells. Second, novel additive material bearing BIAN structure (BIANODA) was synthesized by condensation of acenaphthequinone with 2 eq. of dianiline compound, which was used as additive to improve the characteristics of MNC cathode material (LiMn_1/3Ni_1/3Co_1/3O₂)².
Electrochemistry of these materials along with characteristics of fabricated Li ion battery cells under these design protocol will be presented in detail.
The structures of P-BIAN and BIANODA were supported by NMR, IR spectra etc. Mn of P-BIAN was found to be 40000 when measured by gel permeation chromatography (THF as an eluent, PSt standards)
The BIAN based polymer, P-BIAN shows lower LUMO level in comparison with ethylene carbonate (EC). This means reductive doping of P-BIAN takes place prior to reductive decomposition of EC at anode surface, which will restrict thick SEI formation at anode. When cyclic voltammetry measurements were carried out for coin cell with P-BIAN, peak due to reductive decomposition of EC was not observed, unlike the case of PVDF. Further, after charge-discharge cycles, coin cell with P-BIAN exhibited much smaller internal resistance when compared with PVDF. This indicates that reductive doping of P-BIAN and restriction of SEI decomposition had synergistically decreased internal resistance of battery cells. As a result, coin cell with P-BIAN showed 1.5 times higher discharging capacity in comparison with coin cell with PVDF.
On the other hand, BIANODA has higher HOMO level than that of EC, which enables oxidative polymerization of BIANODA prior to oxidative decomposition of EC. This will restrict thick SEI formation at MNC cathode surface. Use of Schiff base can trap HF generated during the cycling, and strong binding property of BIAN can stabilize MNC cathode for long term use. Consequently, BIANODA additive had enhanced the discharging performance of MNC/EC:DC/Li cathodic half cells.

1. S. G. Patnaik, R. Vedarajan, N. Matsumi. J. Mater. Chem. A. 5, (2017) 1790
2. S. G. Patnaik, R. Vedarajan, N. Matsumi. Mol. Syst. Des. Eng. (2019) in press

Silicon (Si) and its derivatives (Si/C composite, SiO_x) have garnered enormous attention as anode materials for next-generation high-capacity lithium-ion batteries (LIBs). However, despite the prodigious beneficial features of pure Si, its large-scale commercialization is still hindered due to the existence of numerous inevitable defies such as colossal volume change during (de-)alloying, inherent low electric conductivity, low Coulombic efficiency, unstable/dynamic solid electrolyte interphase (SEI), electrode swelling, electrolyte drying etc. Among proposed mitigating strategies, the use of a fraction dose of molecular additives is hailed as the most effective, economic and scalable approach to realize Si and its derivative anode based LIBs. Additives can modify the nature and chemical composition of the SEI layer, which in turn dictates the obtainable capacity, rate capability, Coulombic/energy efficiency, thermal reactivity etc. of the battery system. Thus, we report a systematic and comparative investigation of various electrolyte additives, namely tetraethoxysilane (TEOS), (2-Cyanoethyl)triethoxysilane (TEOSCN), vinylene carbonate (VC), fluoroethylene carbonate (FEC), and a blend of TEOSCN, VC and FEC (i.e. VC/FEC/TEOSCN) using electrochemical analysis, X-ray photoelectron spectroscopy (XPS), Density Functional Theory (DFT) calculation and differential scanning calorimetry (DSC). The ternary mixture (FEC/VC/TEOSCN) results in a thinner SEI layer consisting of high shear modulus SEI-building species (mainly LiF). It also provides much improved thermal stability amid all tested additives, evidencing its potentiality to boost high capacity and safer Si anode-based LIBs. Pouch cells fabricated using Si anode, NMC cathode and LiPF₆/EC-DEC electrolyte doped with TEOSCN-based additives demonstrated excellent electrochemical cycling performance for over 400 cycles with nearly 100% Coulombic efficiency. The improvement could be explained due to the fact that –C≡N group can undergo a polymerization reaction by decreasing the bond order from triple (C≡N) to double (C=N) and single (C-N) bonds, thus forming a chemically stable and highly ionically conductive material and also possibly Li₃N as precipitates on Si surface. Moreover, strong nucleophiles formed by the reduction of the C≡N could attack FEC and/or LiPF₆ stripping of –F to form LiF, as evidenced from XPS analysis.

Thus, nitrile-functionalized silanes are highly promising electrolyte additives to boost the electrochemical performance and safety-induced risks of Si anode-based LIBs, emanating from the formation of a robust SEI layer.

We believe that this study gives a valuable understanding and provides new insights on the use of electrolyte additives for highly-energy density and reversible Si and Si-derivative anodes in Li-ion batteries.

Electrolytes control battery recharge time and efficiency, anode/cathode stability, and ultimately safety, consequently electrolyte optimization is crucial for the design of modern energy storage device. Electrolytes containing ionic liquids (ILs) are often regarded as attractive candidates to replace the currently-adopted organic solvents thanks to their superior chemical stability, however, poor transport properties are hindering their applicability. Given the ionic nature, these systems possess high degrees of ion-ion correlation, therefore posing a non-trivial yet crucial and interesting challenge to understanding their transport properties.

Here we present molecular dynamics analysis of transport properties in IL-based electrolytes. First, the strong ionic interactions result in significant correlations and deviations from ideal solution behavior. By adopting rigorous concentrated multicomponent solution theory, we show that when accounting for intra- and inter-species correlation, beyond the commonly used uncorrelated Nernst-Einstein-based approach, an anomalously low and even negative Li transference number emerges. Second, we computationally confirm the recently measured negative Li transference number in Li-containing IL-based electrolytes, and extend this surprising result to a vast range of different chemistries, suggesting a universal behavior of this class of electrolytes. Additionally, we characterize the atomistic nature of the anion-cation clusters, formulate a way to compute the effective lithium charge, and show that lithium-containing clusters carry a negative charge in a remarkably wide range of compositions and concentrations. Third, we leverage our microscopic understanding to suggest and test modifications to increase the cation transference number. Our results have significant implications for the adoption of ionic liquid-based electrolytes as they provide a recipe for optimizing transport properties in next-generation highly correlated electrolytes.

An all-solid lithium-ion battery (ASLIB) consisting of a polyethylene oxide (PEO)-based polymer electrolyte with a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, lithium titanate (LTO)-based anode and lithium iron phosphate (LFP)-based cathode has been fabricated. The solid polymer electrolyte has an ionic conductivity of ~10-4 S/cm at 40 °C). The electrolyte is prepared using a solvent free hot-pressing method. The electrodes consist of the active materials (LTO or LFP), carbon black, small amounts of PEO, LiTFSI, and a PVDF binder. A coin cell is assembled using these electrodes and electrolyte. The cell shows stable electrochemical performace over 20 charge/discharge cycles.

Two-dimensional (2D) layered materials are increasingly studied in effort to discover new compounds and the fascinating properties engineered by their sheet-like structure. Graphene, atomic layer of carbon, is the most researched among 2D materials, albeit limited to just carbon in its composition. Recently, a new emergent family of 2D transition metal carbides and carbonitrides – so called “MXene” – are synthesized that may have wide-ranging applications, including energy storage, polymer nanocomposite fillers, water purification, transparent optical conductive coatings and electronic devices. Nevertheless, before the best application is identified, the fundamental chemical physics of these materials must be understood and therefore synthesis-structure-property relationships must be established. To our expanding interests in this emerging class of materials, we investigate the structure and properties of layered transition metal carbides (Ti₃C₂T_x) MXenes phases for renewable energy prepared by collaborator. We employed electron microscopy, optical absorption spectroscopy, Raman spectroscopy and advanced electrochemistry including SECM to determine surface morphology, nanoscale structure, lattice vibrational properties and surface sensitive electrochemical properties and physicochemical processes at solid/liquid interface.

With the increasing demand for lithium-ion batteries in electronics and vehicles, great efforts have been drawn on promoting both the energy and power densities. The electrochemical properties of electrode materials directly affect the performance of lithium-ion batteries, and therefore it is the primary issue to develop and optimize new-type electrode materials. The performance of high-capacity anode materials can be improved by constructing nanostructures and combining with carbon materials of high conductivity. How to develop effective and practical methods for the design and synthesis of anode materials for lithium-ion batteries is challenging.
Bionic design has been playing an important role in the invention of new tools. In recent years, a variety of bionic-designed anode materials with hierarchical structures have been developed, but they all share some defects: on the one hand, in most cases only the biological macro appearances were selected to emulate, while the microstructures of plants and animals were neglected; on the other hand, the bionic-designed composites are all based on amorphous carbon, which cannot satisfy the design requirements of anode materials with high rate performance, and therefore other materials with higher conductivity (e.g. graphene) are to be introduced in high-performance anode materials. Herein, this research focuses on bioinspired designing and constructing nanostructured graphene-based anode materials of high performance. By modifying the shape and chemical properties of graphene and controlling the bionic structures of the composites, a series of metal oxide/graphene composite anode materials with high capacity, high rate performance, are prepared and the mechanism is investigated.

References:
[1] Chengling Zhu, Shenmin Zhu, Kai Zhang, Zeyu Hui, Hui Pan, Zhixin Chen, Yao Li, Di Zhang, Da-Wei Wang, Confined SnO₂ Quantum-Dot Clusters in graphene sheets as High-Performance Anodes for Lithium-Ion Batteries. Sci. Rep. 2016, 6, 25829.
[2] Xianghong Lou¹, Chengling Zhu¹, Hui Pan, Jun Ma, Shenmin Zhu, Di Zhang, Xueliang Jiang, Cost-Effective Three-Dimensional Graphene/Ag Aerogel Composite for High-Performance Sensing. Electrochim. Acta 2016, 205, 70.
[3] Chengling Zhu, Zhixin Chen, Shenmin Zhu, Yao Li, Hui Pan, Xin Meng, Muhammad Imtiaz, Di Zhang, Construction of SnO₂−Graphene Composite with Half-Supported Cluster Structure as Anode toward Superior Lithium Storage Properties. Sci. Rep.2017, 7, 3276.
[4] Chengling Zhu, Zeyu Hui, Hui Pan, Shenmin Zhu, Qing Zhang, Jianfeng Mao, Zaiping Guo, Yao Li, Muhammad Imtiaz, Zhixin Chen, Ultrafast Li-Ion Migration in Holey-Graphene-Based Composites Constructed by a Generalized Ex Situ Method towards High Capacity Energy Storage. J. Mater. Chem. A 2019, 7, 4788.

The use of correlated materials in applications that aim to harness electronic phase transitions or mitigate charge-localization altogether requires synthetic techniques wherein electron migration barriers can be modulated with some meaningful degree of tunability. Vanadium oxides represent an attractive model system owing to the relative narrowness of V 3d-derived bands. V₂O₅ can further intercalate metals (Mⁿ⁺) spanning the periodic table that trigger rearrangement of the V₂O₅5 lattice giving rise to a structurally diverse family of mixed-valence compounds (M_xV₂O₅). The extent of electron correlation can be chemically tuned by careful selection of the intercalated metal ion (M) which introduces new electronic states, by stoichiometric control of the mixed oxidation state of the vanadium oxide framework (x), and by low-temperature topochemical modification of the vanadium oxide framework. The utility of this approach is demonstrated by its application to three materials design challenges. First, modulation of the thermally-driven metal-insulator transition in β’-Cu_xV₂O₅ is achieved through precise control of Cu stoichiometry. Diffusion of copper between two distinct crystallographic sites is shown to modulate the thermal energy threshold for the melting of a self-trapped polaronic state on the vanadium-oxygen lattice as observed in the broadening of hybridized Cu 3d/O 2p states near the upper edge of the valence band. Notably, precise control is a critical requisite for designing materials for brain-inspired computing applications. In a second example, the copper atoms are topochemically leached from the β/β’-Cu_xV₂O₅ compound to stabilize a metastable ζ-V₂O₅ phase with a unique quasi-1D structure. The broader dispersion of d-bands stemming from the lower symmetry crystal structure mitigates self-trapping of polarons relative to the thermodynamically-stable α-V₂O₅ phase, thereby increasing its Mg-ion storage capacity (from 50 to 92 mAhg^-1). Finally, the empty ζ-V₂O₅ phase is topochemically intercalated with Sn²⁺ to form a metastable β-Sn_xV₂O₅ phase. As a result, hybridized Sn 5s/V 3d/O 2p states are introduced at energetic positions close near the valence band of photoabsorbing quantum dots. By tuning this overlap in β-Sn_xV₂O₅/CdX heterostructures, we have achieved sub-picosecond hole transfer from quantum dot to vanadium oxide and demonstrated highly efficient hydrogen evolution.

The emerging market of autonomous microsystems such as Internet of Things and (implantable) medical devices has drawn attention to the need for new energy storage devices. Key features for such power sources are integration in the component architecture, footprint, and performance. Amongst several technical solutions, thin film solid-state lithium batteries (TFBs) appear to be a promising candidate to fulfill these requirements.
We present here the recent advances in our group regarding the development of excellent performance, highly-integrable TFBs. The fabrication process flow was carried out in a clean room environment using the TINY platform. The LiCoO₂/LiPON based TFBs are deposited on 8’’ silicon wafers in a pilot-line scale environment and subsequently patterned using specifically developed, microelectronics-compatible, photolithography processes. Using micromanufacturing techniques, the 0.75 mm substrate is thinned down to 50 µm and the dies are then laser-diced. The 5.3 mm² TFBs demonstrated discharge capacity above 600 µAh/cm² under C/5 galvanostatic cycling condition in the 4.2-3.0 V potential range. The average capacity loss over 30 cycles is around 0.1 %/cycle at 1 C current density in the stabilized regime.
Despite these state-of-the-art performances, when comparing the same electrode in liquid cell configuration, we notice capacity losses for the TFB and irreversible losses between first charge and first discharge, whichever the configuration. In the present work we use the TFB as an electrode-oriented system model to investigate on the possible phenomena which could account for these losses. We propose to examine the LiCoO₂ electrode and its interface with the electrolyte in various configurations and state-of-charge by means of 2D, cross-sectional Raman spectroscopy mappings. In the TFB configuration, the LiCoO₂ layer is well and homogeneously crystallized at open-circuit voltage (out of fabrication). The Raman mapping image after the first charge (4.2V) indicates that the Li extraction is uniform throughout the whole cathode thickness and no specific interfacial phenomenon is evidenced. Performing the same measurement after the first charge and first discharge reveals a fairly uncomplete relithiation with poor crystalline quality in the partially reliathied areas, which could account for the first-cycle irreversibility.

With the recent trend of rampant development of modern portable electronic devices, their power requirement is changing rapidly, and so it is indispensable to redefine their energy storage systems from all the aspects of science and technology. The new age energy storage devices should store an ample amount of electronic charge even with fast charge transfer rate. The device should have a long lifetime and safe to use. Battery-capacitor hybrid system somehow solves the primary objective, i.e. energy and power density. However, it can not be a perfect choice because of the probable energy loss at the bridging circuit. Also, safety, flexibility and lifetime issues associated with conventional batteries make the hybrid system inferior compared to its electrochemical counterpart; i.e. supercapacitor, which could be a better choice. EDLCs are the fastest and long lasting supercapacitor, but they have poor energy density as compared to pseudocapacitor.
The redox reaction dominated pseudocapacitors suffer from poor lifetime, charge transfer rate and self-discharge through the high ESR. To improve energy density, and lifetime, we prepare flower like V₂N dominated V₂N@V₂C nanocomposite, to be used as a pseudocapacitive electrode material with extremely low ESR. The CV nature of this material confirms that the charge storing is not dominated by redox reaction and the trends of low ESR (about 6 Ω) and higher coloumbic efficiency also supports the finding. Three electrode measurement shows 31.38 mFcm^-2 specific capacitance at 1 mAcm^-2 current density. The less redox dependency and lower ESR improves its capacitance retention rate and coloumbic efficiency by 98% and 95.86% even after 3 thousand charge-discharge cycles. Although the use of lithium based electrolyte may improve energy density but the use of KOH as the electrolyte, makes the device highly safe as compared to lithium based energy storage device. A flexible supercapacitor prototype was fabricated using PVA-KOH gel electrolyte, and that too is performing well in terms of stability, ESR and coloumbic efficiency.

The commercialization of Na metal anode is largely hindered by several long-lasting challenges, namely metallic Na dendrite growth and unstable SEI formation. Meanwhile, these challenges can be effectively resolved by employing non-flammable solid Na conductor as an electrolyte. Solid electrolytes not only can eliminate severe safety concerns, they can also enhance electrochemical stability and prolong cycling life. However, solid ceramic electrolyte NASICON is subjected to high electrolyte/electrode interfacial resistance a, leading to poor interface conductivity that results in non-uniform Na ion flux. The pairing of pristine NASICON with high-capacity metallic Na anode gives rise to large NASICON/Na interfacial resistance and poor interface conductivity that result in non-uniform Na ion flux across the interface. Specifically, Na tends to plate preferentially along the grain boundaries of NASICON where the Na ion flux is locally intensified, leading to detrimental dendrite-like nucleation on Na anode over repeated charge/ discharge cycles. Theoretically, a homogeneous and stable interlayer with superior Na anode compatibility and ion conductivity can facilitate uniform Na ion flux across the interface, therefore effectively decrease the interfacial resistance and suppress unregulated dendrite-like Na formation during cycling.

In this work, we proposed the direct coating of an ultrathin graphene layer on NASICON by CVD. The Raman spectrum surface-modified NASICON reveals the three characteristic graphene peaks of D band, G band and a relatively weak and broad 2D band. The thickness of graphene-like layer coating on NASICON was estimated by both XPS depth profiling and TEM to be around 4 nm. This interlayer acts as a uniform and conductive network for Na ion transport. As a result, the surface-modified NASICON significantly decreased the interfacial resistance by more than 10-fold (524 Ω cm² to 46 Ω cm²), improved Na plating/stripping stability (at 1 mA/cm² current density with a 1 mAh/cm² capacity) with much smaller voltage overpotential and enabled uniform Na plating with minimized uncontrolled dendrite formation after 1000 cycles. This Na metal cycling with surface-modified NASICON is, to the best of our knowledge, the best performing all-solid-state Na symmetric cells reported. Moreover, SEM images revealed Na electrodes cycled with surface-modified NASICON remained smooth on the surface, while Na electrodes cycled with pristine NASICON exhibited dendrite morphology.

To evaluate the electrochemical performance of surface-modified NASICON as a solid ceramic electrolyte, solid-state batteries were assembled with Na3V2(PO4)3 (NVP) as cathode and bare metallic Na as anode. At 1C current density, NVP/Na battery delivered a high reversible initial capacity of 108 mAh/ g with 85% capacity retention (~92 mAh/g) after 300 cycles at nearly 100% Coulombic efficiency. In contrast, the control experiment of NVP/Na with pristine NASICON showcased inferior performance with rapid capacity decay and very unstable voltage profiles.

Subsequently, this surface-modified NASICON was incorporated into an optimized PEO based solid polymer electrolyte, and the synergetic effects of the modified ceramic and optimized polymer electrolytes lead to great improvement in both interfacial wettability and ionic conductivity, leading to great reduction in Na cycling overpotential, facilitating uniform Na plating, and enabling superior Na-S and Na/NVP batteries. Overall, these works can provide valuable insights for all-solid-state dendrite-free battery development.

E. Matios, H. Wang, W. Li, “Graphene Regulated Ceramic Electrolyte for Solid-State Sodium Metal Battery with Superior Electrochemical Stability.” (2019) ACS Applied Materials & Interfaces.

E. Matios, H. Wang, W. Li, “Enabling Safe Sodium Metal Batteries by Solid Electrolyte Interphase Engineering: A Review.” (2019) Industrial and Engineering Chemistry Research.

To overcome the low electrical conductivity, manganese oxide (MnO_x) is coupled with reduced graphene oxide (rGO), and it can be significantly overcome through the hybridization. Moreover, the oxidation state and structural properties of MnO_x are precisely adjusted to further enhance the electrochemical performance for practical electrochemical energy storages. In this work, MnO_x/rGO hybrid films possess different crystallinity and oxidation states compared with bare Mn oxides_, and they are produced by a simple strategy with combining a solution based synthesis and post-thermal annealing process. The oxidation state and crystallinity (degree of hydrous states) of MnO_x in the composite film is easily controlled by tuning annealing conditions such as temperature and atmosphere. The resulting MnO_x/rGO film not only has a high mechanical flexibility, but also the hybrid film based electrochemical capacitors shows remarkably enhanced electrochemical performances such as high specific capacitances and prolonged cycle-life after 10k cycles. Our work indicates that well-adjusted material properties of MnO_x (crystallinity and oxidation states) are highly correlated with its energy storage ability. From the hybridization with rGO, our optimized MnO_x/rGO hybrid film is potentially utilized as a promising electrode material for high performance flexible energy storage devices, and our proposed strategy can give a new insight for the fabrication of other transition-metal oxides/rGO based composites for flexible and wearable energy storage applications.

While interest in rechargeable batteries has increased due to widespread usage of all-electric vehicles and drones, the locality and cost competitiveness of lithium and transition metal sources are prompting researchers to find alternative battery chemistry that can replace conventional lithium ion batteries (LIBs). As one of the most abundant elements in the Earth’s crust, aluminium has been of interest because it is a widely used commodity material in global commerce and has one of the highest theoretical capacities (8,056 mAh cm^-3) on account of its multiple charge storage with trivalent ions. However, despite these advantages, research on aluminium ion batteries (AIBs) has not progressed significantly due to the limited electrolytes different from conventional non-aqueous and aqueous electrolytes. In addition, it is highly challenging to design cathode materials for AIBs, because trivalent aluminium ions (Al³⁺) normally have a very low ionic conductivity in most oxide or sulfide-based materials.
Herein, we demonstrate a triangular macrocycle as a potential cathode material for AIBs, in which three redox-active organic units of phenanthrenequinone (PQ) are covalently linked. The PQ unit was firstly revealed to react with AlCl₂⁺ complex ions, and the formation of layered stacks of the triangular macrocycles allowed them to alleviate the strain induced during the insertion and extraction of the complex ions, showing high stability over thousands of cycles. Also, the use of cationic complex ions of AlCl₂⁺ increased the energy density of the whole cell by utilizing less chloride from electrolytes than that of anionic complex ions of AlCl₄^-. These results constitute significant advances in the design of rechargeable aluminium batteries and provide a good starting point for the development of affordable large-scale energy storage devices.

Sodium based batteries are emerging as a viable beyond Li-ion battery technology for future energy storage. Sodium has certain advantages such as greater abundance than lithium, great intrinsic safety and potentially a relatively high energy density. Currently, much research is focussed on the electrode materials (hard carbon anodes and new cathodes) however the electrolyte component is an important enabler of the technology. Ionic liquids and organic ionic plastic crystals (OIPCs) have been shown to be good electrolyte candidates for Na batteries, enabling Na metal anodes.
Organic ionic plastic crystals (OIPCs) are a unique class of solid state electrolyte material that are increasingly drawing attention due to their negligible volatility and increased safety in contrast to electrolytes based on organic, flammable solvents that are typically used in electrochemical cells. Moreover, many OIPCs are characterized by high thermal and electrochemical stability that makes them a perfect candidate for many electrochemical device applications. Tailoring the materials properties can be achieved by pairing various anions and cations. In order to enable use of OIPCs in sodium batteries a source of Na⁺ (as a second component) needs to be added to the neat plastic crystal. Addition of “dopants’’ to OIPCs may also result in enhanced mobility of ions in the electrolyte material by increasing the number and size of defects.
In this work we focus on a new OIPC - hexamethylguanidinium bis(fluorosulfonyl)imide (HMG FSI) - and the effect of doping with sodium salt (NaFSI). All electrolytes and neat OIPC were evaluated in terms of thermal properties, ionic conductivities, ion diffusion and electrochemical stabilities. HMG FSI displays excellent properties such high conductivity and a wide electrochemical stability window that makes it a promising material as a starting point for new solid state electrolytes. All compositions of OIPC with NaFSI resulted in solid-state electrolytes, and a phase diagram is proposed.

The organic liquid electrolyte for lithium-oxygen battery has been mainly used because of its high ionic conductivity and wide electrochemical stability window. Despite these great electrochemical properties, the electrolyte depletion under semi-open system operation and electrolyte decomposition by highly reactive oxygen radical have been major obstacles to successful development of lithium-oxygen battery. The use of gel polymer electrolyte can effectively encapsulate organic solvent in the cell, suppress the electrolyte decomposition by superoxide anion radicals and provide stable interfacial characteristics with lithium electrode. These unique characteristics make gel polymer electrolyte a desirable electrolyte system for enhancing the cycling performance of the lithium-oxygen batteries. In this work, poly(methyl methacrylate) (PMMA)-based gel polymer electrolyte with non-volatile ionic liquid was synthesized. A chemical cross-linking reaction has been induced in the presence of divinylbenzene as a cross-linking agent by free radical reaction to obtain the three-dimensional cross-linked polymer network. As the non-volatile electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide was added in order to improve the ionic conductivity of the gel polymer electrolyte. In addition, a zwitterion was synthesized and added as a functional additive to increase both dissociation of lithium salt and transport properties of Li⁺ ions as well as enhance the interfacial stability toward the lithium electrode. Our results demonstrate that the cycling stability of a lithium-oxygen cell assembled with gel polymer electrolyte could be remarkably improved by employing zwitterion additive due to its beneficial effects in the gel polymer electrolyte.

Recently, Lithium-ion batteries are widely utilized for a variety of applications, such as consumer electronics and electrical vehicles. Silicon monoxide (SiOx) is one of the most promising candidates for next generation anodes because of the high capacity and excellent cyclability. One of the remained issues for SiOx is the poor first-cycle Coulombic efficiency, in the range of 50-70%. In order to improve the first-cycle Coulombic efficiency, several prelithiation methods have been reported. Here we propose a facile prelithiation method by using a catalytic reaction between SiOx and lithium metal with naphthalene in ether solutions. The reaction continues until the electrochemical potential of SiOx equals to that of lithium naphthalenide. The catalytic reaction with naphthalene offers the practical implementation of highly scalable prelithiation for active materials in lithium-ion batteries. We demonstrate electrochemical performance of the prelithiated SiOx as well as the mechanism of the prelithiation method.

Li-metal batteries (LMBs) with composite polymer electrolytes (CPEs) have attracted considerable attention compared with conventional Li-ion batteries. However, the uncontrolled Li deposition and the flammability of CPEs are still pressing issues. Here, a non-flammable CPE is fabricated by composing of a flame-retardant trimethyl phosphate as the solvent, a poly(vinylidene) matrix, Li_6.4La₃Zr_1.4Ta_0.6O₁₂ fillers, and a LiClO₄ salt. The CPE exhibits unique characteristics including non-flammability, high ionic conductivity, flexibility, and good thermal stability. More importantly, a fluoroethylene carbonate (FEC) additive is used on the surface of Li metal to facilitate the formation of a LiF-rich solid electrolyte interphase layer. The FEC-coated Li|CPE|LiPFeO₄ battery exhibits excellent cycling stability (at room temperature) with a discharge capacity of 152 mAh g^-1 and nearly 100% Coulombic efficiency over 500 cycles at 0.2 C. The non-flammable CPE has a high rate capability of 109 mAh g^-1 at 4 C. To potentially improve the energy density of the LMB, the LiPFeO₄ cathode is replaced with a high-voltage material LiNi_1/3Mn_1/3Co_1/3O₂. The obtained Li|CPE|LiNi_1/3Mn_1/3Co_1/3O₂ cell exhibits a discharge capacity of 109 mAh g^-1 after 100 cycles at 0.2 C. Consequently, the strategy offers guidelines for the future development of safe batteries with high energy density.

Mixed ionic-electronic conductors (MIECs), which simultaneously conduct Li ions and electrons, can play a pivotal role when employed in the electrodes of solid-state batteries to achieve high energy and power densities. Both conductive agent and solid electrolyte can be substituted with MIEC catholyte in order to overcome the limitation of the conventional composite cathode such as lithium depletion on the electrolyte surface and CO₂ formation during the sintering. Furthermore, it is simpler to build a continuous conduction network between MIEC catholyte and the active material than conventional composite cathode which needs uniformly distributed network of two separate pathways for electrons (carbon) and Li ions (solid electrolyte).
In this study, we proposed new MIECs having perovskite structure. For the systematic materials design, the percolation for the macroscopic lithium conduction has been analyzed, moreover, oxygen vacancy formation and lithium diffusion barrier energies have been calculated with a density functional theory (DFT) and nudged elastic band (NEB) to estimate the electronic and lithium ion conductivities. In perovskites, high oxygen vacancy concentration can lead to high electronic conductivity owing to a large amount of carriers. Specifically, we have explored Li_xLa_yMO_3-δ compositions with varying 3d transition metals and Li/La/vacancy configuration. With this strategy, we could achieve high lithium ion (8.8 x 10^-5 S/cm) and high electronic (2.0 x 10^-3 S/cm) conductivity together in the designed MIEC perovskite.

Acknowledgment
S. Bak and X.-Q. Yang at Brookhaven National Laboratory was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technology Office of the U.S. Department of Energy through the Advanced Battery Materials Research (BMR) Program, including Battery500 Consortium under contract DE-SC0012704.

The lithium-sulfur (Li-S) battery has been considered one of the promising post-lithium-ion battery systems due to its high gravimetric energy density and environmentally benignity. However, there remain unresolved issues such as the insulating nature of active material and an irreversible loss of polysulfide anions during cycling. In this study, conceived from multi-layer spin coating process in the film technology, a novel double-layered electrode structure comprised of a bottom sulfur cathode and an upper protecting layer (PrL) was developed by using orthogonal pairs of solvent and binder. While two different pairs of the binder and solvent, PVDF-NMP and PE-chloroform, were attentively selected based on Hansen solubility parameters (HSPs) to avoid intermixing between the sulfur cathode and PrL during the electrode fabrication process. Two distinctive carbon materials, mesoporous carbon sheet (MCS) and carbon paper (CP), were adopted as respective conductive media for each layer. This rationally designed electrode showed superior electrochemical performances in cycle life and rate capability. We believe our strategy is one of the key findings to the practical application of Li-S battery.

The push towards self-powered electronics through energy harvesting, calls for the development of high-performance supercapacitors that can enable sustained, autonomous operation of electronic devices for applications such as wearable electronics, biomedical implants and internet-of-things. Low cost supercapacitors with high energy density can potentially work as stand-alone and maintenance-free power sources when combined with energy harvesters. Therefore, great efforts have been devoted to extend the energy density of these storage systems by using pseudocapacitive transition-metal oxides, which store energy by fast surface redox reactions, enhancing the storage ability of the system, while keeping the energy/cost ratio low. The limited electronic conductivity of most pseudocapacitive oxides leads to high electrode resistance and, consequently, lower power densities. As a result, pseudocapacitive devices with high energy density and high-rate handling ability remain a major challenge. Considering the pressing need for high-power and high-energy density storage devices through low-cost fabrication strategies, our work focuses on the fabrication and integration of high performance, fully solution processed, co-planar NiO micro-supercapacitors through inkjet printing. In this study, the phenomenon of electrical conductivity enhancement of NiO when the material is processed at the nanoscale, was exploited through a developed nanoparticle-based, inkjet-printable ink that was used to produce highly porous NiO electrodes that demonstrated up to 14 orders of magnitude higher electrical conductivity compared to single crystal NiO. The enhanced conductivity of the electrodes was reflected in the ultra-high charge/discharge rate handling ability of up to 50,000 mV s^-1 and the low relaxation time constant of just 30 ms of the devices, which is among the lowest achieved for any supercapacitors. A surfactant-based saturated magnesium perchlorate aqueous gel electrolyte with extended operating voltage window was developed to enable the operation of the devices up to 1.5 V. The devices showed remarkable areal and volumetric specific capacitances of up to 155 mF cm^-2 and 705 F cm^-3 at 5 mV s^-1 respectively, surpassing the best micro-supercapacitors known. The superior energy and power density of the devices bridges the gap between lithium-ion batteries and electrolytic capacitors, opening new exciting opportunities in the field of electrochemical energy storage and harvesting.

Li₈ZrO₆, because of its high lithium content, has been considered as a CO₂ absorber, a blanket material for fusion reactors, and as a solid electrolyte for high temperature applications. In this presentation we examine the synthesis, structure, and electrochemical properties of Li₈ZrO₆/carbon nanocomposites as potential cathode materials for lithium-ion batteries with high specific capacity. These nanocomposites were synthesized by the reaction between zirconyl chloride and lithium benzoate as the source of both lithium and conductive carbon. Li₈ZrO₆ is a pseudolamellar compound with high lithium content and containing zirconium as a relatively abundant, low cost transition metal. Although Li₈ZrO₆ is intrinsically a poor conductor its intimate contact with in-situ produced carbon and its small grain size enabled by mechanical delamination allow for reversible electrochemical delithiation. Quantum mechanical calculations suggest that removal of 2 Li/formula unit is topotactic with only 1–2% volume change, but removal of more Li involves a distortion with possible loss of oxygen, although this may be kinetically prevented. In fact, coin half-cells containing Li₈ZrO₆/C as the cathode and Li-metal as the anode exhibited a capacity of 221 mAh/g (which corresponds to extracting 2 Li per formula unit) over at least 140 cycles. By applying a higher capacity limit, a discharge capacity of 331 mAh/g (which corresponds to extracting 3 Li per formula unit) was maintained over 15–20 cycles. Ex-situ and operando X-ray diffraction (XRD) studies of galvanostatically cycled cells showed that at these levels of charge, delithiation follows a reversible path with only small distortions around Zr atoms. During this process, crystalline grain sizes decrease continuously, shortening diffusion lengths within grains but increasing the number of grain boundaries and electrode/electrolyte interfaces. Given that Zr is already in its highest oxidation state in Li₈ZrO₆, charge storage appears to involve partial oxidation of oxygen atoms and production of small-polaron holes, as supported by XRD, X-ray photoelectron spectroscopy, and pair-distribution function studies and predicted by quantum mechanical calculations. At higher depths of charge, delithiation results in amorphization of the active electrode material. The charge storage mechanism in Li₈ZrO₆ is unusual among lithium-ion battery electrode materials and involves a combination of mechanisms that resemble intercalation and conversion reactions, as well as some capacitive storage at higher charge rates. With further refinement, Li₈ZrO₆/C based materials open up opportunities to develop new cathode materials for lithium-ion batteries that may improve on currently existing capacity barriers.

With the increase in the usage demands of lithium-ion batteries (LIBs) as power sources, it is imperative to further improve the LIB performance. In particular, cathode materials in LIBs must exhibit a high energy density, long lifetime, and safety. For enhancement of energy densities in LIBs, use of reactions not involving redox of heavy transition metal ions is effective. Recently, using redox reactions of oxide ions in cathode materials has attracted much attention. In cathode materials referred to so-called Li-rich oxides, such as layered-rock-salt which a part of transition metal is substituted by lithium and cation-disordered-rock-salt which transition metal and lithium are located randomly in the same cation sites, an additional high capacity has been reported via the utilization of charge compensation by oxygen in addition to the transition-metal redox.
Antifluorite-type Li₅FeO₄, Li₆CoO₄, and Li₆MnO₄ have potentials as high-capacity cathode materials due to the rich lithium content which can be intercalated/deintercalated. Cathode performances of these materials were first reported in 1999 (S. Narukawa et al., Solid State Ionics 1999,122, 59.), and very recently observation of oxygen redox in Li₅FeO₄ was confirmed (C. Zhan et al., Nat. Energy 2017, 2, 963.). However, the amount of reversible capacity with antifluorite-type materials were attributable to only redox of transition metals (Fe³⁺/Fe⁴⁺ in Li₅FeO₄ with 173 mAh g^–1 or Co²⁺/Co⁴⁺ in Li₆CoO₄ with 326 mAh g^–1).
Here we demonstrate reversible oxygen redox in antifluorite-type materials using mechanochemically treated Li₆CoO₄. After ball-mill treatment, tetragonal Li₆CoO₄ changed to cubic antifluorite phase. Since no decomposition of Li₆CoO₄ into CoO and Li₂O was observed, the cubic phase was attributed to cation-disordered Li₆CoO₄. This material exhibited charging capacity of 489 mAh g^–1 without O₂ gas evolution reaction and reversible capacity of 400 mAh g^–1, indicating more than 2 electrons were transferred reversibly. Co K-edge and O K-edge XANES spectra revealed that both redox of Co²⁺/Co⁴⁺ and O^2–/O₂^2– proceeded during charge/discharge. According to XRD patterns, reversible transformation between cubic antifluorite phase and cubic rock-salt phase was observed. Since pristine Li₆CoO₄ was tetragonal, reversible reaction between tetragonal antifluorite and cubic rock-salt hardly proceed. The large reversible capacity with mechanochemically treated Li₆CoO₄ was probably derived from both downsizing effect of particles and transformation from tetragonal phase to cubic phase by cation-disordering.

Lithium metal anodes have been considered as the ultimate choice for anode electrodes for rechargeable batteries because of the high theoretical specific capacity (3860 mAh/g), the lowest electrode potential (3.040 V versus standard hydrogen electrode) and low density (0.534 g/cm³). The safety problem caused by the uncontrollable lithium dendrite and the poor cycling performance has limited the application of lithium second batteries several decades. Here the lithium plating/stripping (P/S) behavior are investigated respectively with non-aqueous electrolyte and solid-state electrolyte by combining interfacial modification and ordered three-dimensional structure methods. Lithium plating/stripping (P/S) behavior is regulated by both the interfacial conductivity and distribution of electric field induced by the structure. It was demonstrated that homogenous surface electronic conductivity and ordered three-dimensional structure could be beneficial to significantly improve lithium plating-stripping behavior and reach a high performance lithium metal anode.

All-solid-state lithium-ion batteries (ASLBs) are receiving considerable attention due to their safety superiority and high energy density. Inorganic solid electrolytes are explored as a key enabling material of the ASLBs. However, their critical challenges, including grain boundary resistance, interfacial instability with electrode materials and complicated processability, remain yet unresolved. Here, we demonstrate a new class of gel electrolyte with reversible thixotropic transformation and abuse tolerance to address the aforementioned longstanding issues. The gel electrolyte consists of fluoropolymer/cellulose derivative blend and liquid electrolyte. The reversible thixotropic transformation is realized via sol-gel transition based on Coulombic interaction of the polymer matrix with liquid electrolyte. This unusual rheological feature allows the gel electrolyte to be printed in various forms. In addition, the gel electrolyte shows low crystallinity, thus playing a viable role in delivering high ionic conductivity. Based on understanding of rheological/electrochemical characteristics of the gel electrolyte, we fabricate a form factor-free pouch-type cell assembled with the gel electrolyte using sequential screen-printing process. The resultant cell shows exceptional safety upon exposure to various harsh abuse conditions, along with decent electrochemical performance.

Elemental phosphorous is emerging as one of the most intriguing anode materials for Li, Na, and K rechargeable batteries due to its specific capacity of 2596 mAhg^-1. (1) At the same time, the performances obtained from different tests are far from the theoretical values (~600-1000 mAhg^-1). Moreover, no clear indications about the phosphorous form most suitable for electrochemical applications is emerged until now. Elemental phosphorous exists as different allotropes, including white phosphorous, WP, red phosphorous, RP, and black phosphorous, BP. Orthorhombic BP, the most stable polymorph, presents a 2D structure, making it particularly intriguing as anode material. The preparation of ortho-BP is thus a central issue in development of anodes based on elemental P. Among the variety of complex synthesis approaches, high energy ball milling, HEBM, starting from the commercially available RP appears to be the most convenient. Even if HEBM is one of the most diffuse preparation method and several experimental procedures have been proposed, no systematic exploration of the synthesis parameters has been tackled to date.
In this work, starting from the mathematical model of energy transfer during the ball milling process, we investigate the effects on RP → BP conversion of three experimental parameters, the rotation speed, the milling time, and the weight ratio between the spheres and the milled material (BtPw ratio). The efficiency of the conversion process was verified by solid-state NMR, Raman spectroscopy, and X-ray diffraction. Whereas the first two parameters have a minor importance, the BtPw ratio plays a primary role in the RP → BP conversion. Yields approaching 100% can be obtained also with short milling times (15 min) and adequate rotation speed (e.g., 500 r.p.m.), provided that the BtPw ratio >40:1 is used. These results confirm the energy sustainability of the mechanochemical synthesis approach. (2)
(1) Xu, G.-L.; Amine, R.; Abouimrane, A.; Che, H.; Dahbi, M.; Ma, Z.-F.; Saadoune, I.; Alami, J.; Mattis, W.L.; Pan, F.; Chen, Z.; Amine, K. Challenges in Developing Electrodes, Electrolytes, and Diagnostics Tools to Understand and Advance Sodium-Ion Batteries. Adv. Energy Mater. 2018, 1702403.
(2) Ferrara, C.; Vigo, E.; Albini, B.; Galinetto, P.; Milanese, C.; Tealdi, C.; Quartarone, E.; Passerini, S.; Mustarelli, P. Efficiency and Quality Issues in the Production of Black Phosphorus by Mechanochemical Synthesis: A Multi-Technique Approach. ACS Applied Energy Materials 2019, 2, 2794-2802.

The combination of electrochemical techniques with bulk and advanced spectroscopic ones is a powerful tool to investigate the processes occurring in the novel electrochemical energy storage systems based on lithium metal anode. NMR exploits the magnetic properties of atoms nuclei to find out information on the chemical environment in molecules and solids, as well as on its changes over time. The combination of ⁷Li and ¹⁷O (at natural abundance) nuclear magnetic resonance (NMR) [1] and electrochemical characterization is here proposed as an effective approach to investigate the Li⁺ solvation structures and properties of electrolytes featuring tetraethylene glycol dimethyl ether and lithium-bis(trifluoromethane sulfonyl) imide. The NMR results, also supported by physico-chemical characterizations such as thermal gravimetric analyses, differential scanning calorimetry, specific conductivity and viscosity, provide information about the association of Li⁺ ions with anion and solvent molecules, so allowing a deeper knowledge on the relationships among structure and functional properties of super-concentrated solutions. The increase of the electrolyte concentration is, indeed, a multi-effective strategy to improve the performance of high energy batteries featuring Li metal anode [2, 3].

[1] J. Peng, L. Carbone, M. Gobet, J. Hassoun, M. Devanye, and S. Greenbaum, Electrochim. Acta 2016, 213, 606–612.
[2] L. Suo, Y.-S. Hu, H. Li, M. Armand, and L. Chen, Nat. Commun. 2013, 4, 1481
[3] F. Messaggi, I. Ruggeri, D. Genovese, N. Zaccheroni, C. Arbizzani, and F. Soavi, Electrochim. Acta 2017, 245, 296–302.

The use of lithium metal as the anode for Lithium Metal Batteries (LMB) requires having solid or quasi-solid electrolytes able to block dendrites formation during cell cycling. Here we reported on a hybrid electrolyte membrane based on nanostructured yttria-stabilized-zirconia, sintered by means of High Pressure-Field Assisted Sintering Technique (HP-FAST) in order to retain proper nano-porosity, and activated with a standard LiPF₆-EC-DMC solution. By a thorough physico-chemical and functional characterization, we demonstrated that the liquid is effectively nano-confined in the ceramic membrane, and the resulting quasi-solid electrolyte is non-flammable. A remarkable conductivity value of 0.91 mS cm^-1 was observed at room temperature, with activation energy of 0.2 eV, and cation transference number, t⁺ =0.55, substantially higher than that of the pure liquid electrolyte. The hybrid electrolyte showed electrochemical stability up to 6 V vs. Li⁺/Li, and excellent resistance to dendrite formation for more than 350 cycles in a Li/electrolyte/Li symmetrical cell. A full cell Li/electrolyte/LiMn₂O₄ showed more than 90 mAh g^-1 at 2C for more than 120 cycles. These very promising results indicated that nano-porous ceramic hybrid electrolytes may be conveniently used in LMB.

The use of redox mediator (RM) effectively reduces the high polarizations of lithium-oxygen batteries by mediating the electrochemical formation and decomposition of the discharge products. As the electrochemical reactions are mediated by RMs, the power capability of the system would be critically dependent on the intrinsic kinetic properties of RM in mediating the reaction. Herein, we performed comparative kinetic study for several reported oxygen evolution reaction RMs by probing RM-assisted charging process with respect to the rate of chemical decomposition of discharge product and the diffusivity of RM in the controlled lithium-oxygen cells. It is found that the overall kinetics of RMs have a positive correlation with the redox potential of RMs, and, multi-redox RMs can display distinct properties depending on its oxidation states. Among RMs investigated, DMPZ²⁺ (5,10-dihydro-5,10-dimethylphenazine) exhibit the highest reaction rate of lithium peroxide decomposition, while the mass diffusion rate is the highest for TEMPO⁺ (2,2,6,6-tetramethyl-1-piperidiny). Additionally, the choice of electrolyte is shown to greatly affect the rate capability of RM-assisted charge, and thus be carefully considered. This study suggests the importance of understanding the kinetics of RMs and provides guidelines for achieving an optimized RM/electrolyte combination to realize high-power lithium–oxygen batteries.

Lithium nickel manganese cobalt oxide (NMC) has become the most promising cathode material for next generation lithium-ion batteries due to high specific capacity and low cost. However, the fast capacity decay and DCIR growth during cycling still limit its practical application. Bulking doping approach can increase the cycling performance, while the specific capacity is sacrificed due to the electrochemically inactivity of dopants. The surface of cathode materials is exposed to the electrolyte and therefore more vulnerable to the lattice volume change and phase change, which greatly contributes to the capacity degradation. Therefore, restricting the doping to cathode surface may minimize the sacrifice in capacity while stabilizing the structures.
In this work a unique dry process has been developed to achieve surface doping. This dry process eliminates the contact between the cathode materials with water or organic solvent and the possible damage of the cathode surface. In addition, this process eliminates the multi-step drying process to remove the solvent and the necessity of waste management.
The dry surface doping technique significantly improves the cycling performance and reduces the DCIR increase during cycling. Meanwhile the crack formation and growth in cathode materials during cycling is suppressed. The result suggests great promise of using the cost-efficient process to improve the cycling performance and reducing DCIR of NMC cathode materials.

Polymer electrolytes show promise as alternatives to energy storage and electrochemical devices but have been limited due to their inverse correlation between ionic conductivity and shear modulus. Recently, we have discovered a new class of electrolyte material, termed a molecular ionic composite (MIC), through the combination of poly(2,2’)-disulfonyl-4,4’benzidine terepthalamide (PBDT), a rigid-rod (aspect ratio ~ 1000) sulfonated polyelectrolyte,¹ and ionic liquids (ILs). MICs are thermally stable materials with simultaneous high conductivity and high modulus.^2,3 However, the mechanisms underlying this fortuitous combination of properties remain unknown. In this study, we use rheology, dielectric spectroscopy and NMR diffusometry to measure the temperature dependences over a wide temperature range (-90^oC to 200^oC) of the linear viscoelastic response, ionic conductivity, dielectric constant, and ion diffusion coefficients in a series of non-crystalline MICs of varying PBDT concentration with the ionic liquid 1-butyl- 3-methylimidazolium tetrafluoroborate (BMIm BF₄). We show that as the PBDT concentration in the MICs increases, the shear modulus increases into the MPa range while maintaining ionic conductivity within a factor of two of the neat IL. Additionally, by comparing the ionic conductivity with ionic diffusion, we show that increasing PBDT concentration in the MICs leads to more ions contributing to the conductivity.

References:
[1] Wang, Y.; He, Y.; Yu, Z.; Gao, J.; Brinck, S. T.; Slebodnick, C.; Fahs, G. B.; Zanelotti, C. J.; Hegde, M.; Moore, R. B.; Ensing, B.; Dingemans, T. J.; Qiao, R.; Madsen, L. A. Double Helical Conformation and Extreme Rigidity in a Rodlike Polyelectrolyte. Nature Communications 2019, 10, 1–8.
[2] Wang, Y.; Chen, Y.; Gao, J.; Yoon, H. G.; Jin, L.; Forsyth, M.; Dingemans, T. J.; Madsen, L. A. Highly Conductive and Thermally Stable Ion Gels with Tunable Anisotropy and Modulus. Advanced Materials 2016, 28 (13), 2571–2578.
[3] Yu, Z.; He, Y.; Wang, Y.; Madsen, L. A.; Qiao, R. Molecular Structure and Dynamics of Ionic Liquids in a Rigid-Rod Polyanion-Based Ion Gel. Langmuir 2017, 33 (1), 322–331.

This study aims to create controlled fine space by electrospinning, and to develop the electrode materials for high-performance energy devices.

With the popularization of mobile devices, household appliances, hybrid vehicles, electric vehicles, and the like, the use of power storage devices is expanding, and further performance improvements are required. Its performance is dependent on the capacity of the electrode. Particulate graphite has been used for the anode materials of currently widely used lithium-ion rechargeable batteries (LIBs), but the battery characteristics close to the theoretical capacity (372 mAh/g) have been realized previously. Therefore, the study of new anode materials is essential to achieve further high performance of storage devices. There is silicon (Si) with a theoretical capacity of 4200 mAh/g as an anode material to replace graphite, but there are many challenges for practical applications, such as the destruction of Si structures due to the large volume expansion rate (300-400%) upon the intercalation of Li ions. In this study, a novel electrode material was developed by compositing Si with carbon nanofibers derived from polyacrylonitrile (PAN).

The nanofibers have a large surface area because of thin nanofibers in complex entanglement with each other by electrospinning. The bulk density of nonwoven fabrics composed of nanofibers is small, and about more than 90 vol.% of them are occupied by space. We tried to absorb the expansion of Si by the space of nanofibers.

Solutions of solvents N,N-dimethylformamide (DMF) mixed with PAN, and Si particles were used for electrospinning. The ratio of PAN to Si particles is 2:1 by weight. Nanospaces are created by the binding of heteromorphic molecules in which different substances are combined at the molecular size level. The voltage from 20 to 30 kV was applied between the nozzle and the collector for electrospinning. Ultrasonic vibration was also applied to the needle tip, which is the nozzle of electrospinning, to forcibly mix the materials during spinning. The texture and structure of the nanofibers were observed and analyzed by SEM and transmission electron microscopy (TEM) combined with image processing.

In order to stabilize the nanofibers produced by electrospinning, they were heat-treated at 280°C in the air. Carbon nanofibers (CNF’s) were made from them by heat-treatment at 700 to 1000°C in the nitrogen atmosphere. The prepared sample and polyimide (PI) and N-methyl-2-pyrrolidone (NMP) were kneaded, coated on a copper foil, and fired to prepare an electrode material.

Nano spaces were created in the CNFs and Si particles were able to be contained in the CNFs. Not only large Si particles but also small Si particles were found to contain CNT. In the second cycle of the charge/discharge experiment of LIB electrode made from the materials, a discharge capacity at 500mAh/g was obtained, which was 1.3 times the theoretical capacity using graphite. Although the decrease in capacity from the second cycle to the fifth cycle was small, the capacity decreased to the same level as the theoretical capacity of graphite near 15 cycles. The capacity at the first cycle charge reached 900 mAh/g, resulting in large irreversible capacity. It is considered that electrode breakage occurs, such as Si particles on the CNF surface exfoliate from the fiber due to the volume change. It may be because the energy was used to form organic film (called a solid electrolyte interface (SEI)) on the electrode surface. In order to put the LIB using the present anode material into practical use, it is necessary to suppress the irreversible capacity at the first cycle.

Mixing and electrospinning PAN with Si particles and the like to fabricate functional porous carbon materials with micropore and mesopore connected multidimensional structure leads to the development of next generation energy devices．

The application of lithium-ion batteries (LIBs) has extended from portable devices to smart grid and energy storage system, resulting in the advancement of energy infrastructure in our society today. Yet further improvement, especially in volumetric density, is still required. Among various types of layered cathode materials (LiNi_1−x−yCo_xMn_yO₂) for LIBs, conventional LiCoO₂ (LCO) still holds the record for practical volumetric energy density (2500 Wh L⁻¹ when charged to 4.30 V vs. Li⁺/Li) due to its high compressed electrode density (4.0-4.2 g/cc). For LCO cathode, charging above 4.3 V is a viable method to increase the energy density of LIBs. However, at the voltage limit exceeding ~4.35 V, it is plagued with a rapid capacity fading issue coupled with structural and surface deformations.
Herein, we have demonstrated surface-stabilized LiCo_0.95Ni_0.05O₂ (denoted as S-LCNO) with superior cycle stability at high charge voltage of 4.45 V under practical conditions (loading density ~15 mg cm⁻², electrode density ~4.0 g cm⁻³ with both coin-type half-cell and pouch-type full-cell testing). Interestingly, the doped-Ni with oxidation state gradient (from 3+ to 2+) in S-LCNO only modestly changed the bulk chemistry, yet significantly modified the surface properties, such as decreasing surface reactivity to electrolyte decomposition in the close-to-surface region. Using spatially-resolved electron energy loss spectroscopy (EELS), we have found that the doped-Ni in Co-rich cathode, which redox potential (Ni^2+/3+ and Ni^3+/4+:e_g band) located above Co^3+/4+:t_2g band with respect to the O^2-:2p band, is likely to mitigate the hole transfer to the O site at charged state, a crucial factor determining the degree of surface reactivity. Indeed, by measuring the leakage current during a floating test, we further observed that S-LCNO stably sustained a mild surface reactivity upon cycling, compared to commercial LCO. As a result, the interfacial degradations, such as surface structure transformation and side reactions from catastrophic EC dissociation, were effectively suppressed. This study would suggest the potential feasibility of facile doping strategy to enhance the surface stability with a comprehensive understanding of the kinetic origin of capacity decay in Co-rich cathode.

The advancement of the flexible electronic system is crucial for the development of electronic products including mobile, computers and many other related products. A major requirement to such electronics is the implementation of physically flexible high-performance energy storage system. The rechargeable thin films solid-state Li-ion batteries are key to power-drive such modern devices due to their properties such as high energy/power density and/or high efficiency and long cycle life. Though these batteries are very attractive and promising both in terms of storage capacity and performance, the large scale production of the particle is quite expensive. A new innovative production, process optimization, and automation engineering of the large-scale battery production are important for economic viability. The current industrial Li-ion battery production route carries three major steps including (1) slurry-based electrode preparation (2) cell assembly (3) formation and aging. The recent electrode manufacturing procedure is a very complex and labor-intensive process warranting a new fabrication procedure to fulfill the market demand.

In the present work, the electrode fabrication was carried out following (1) traditional electrode manufacturing procedure with the phase pure Li₄Ti₅O₁₂ powder produced using high throughput screening of the precursor-solvent combinations¹ (2) material transfer from the collecting unit to the electrode substrate via role-to-lamination techniques (3) in-situ double flame direct deposition technique for C coating.² During the production process, the C aerosol stream from one individual flame was mixed with the stream of LTO active material to deposit either on the substrate or the collecting unit. While the in-situ direct deposition technique avoids the use of any solvent or binder for electrode preparation, the lamination technique allows studying the influence of lamination pressures on the electrochemical performance. All the powders/layers were characterized using advanced physiochemical techniques such as XRD, BET, and TEM imaging. The overall performance from role-to-role lamination technique for layer transfer showed enhanced specific discharge capacities compared to reference electrodes prepared using traditional electrode manufacturing procedure. The discharge capacity of 146.5mAh/g for 450 cycles at 1C with the charge retention of 85%, reveal high rate and efficient charge reversibility. This work clearly shows (1) a paradigm shift from labor-intensive electrode fabrication process to directly aerosol deposition (2) possibility of electrode deposition on a flexible/nonflexible polyimide substrate. To test this hypothesis, Li₄Ti₅O₁₂ electrodes were covered with a solid electrolyte and tested against lithium metal electrodes. The battery performance both at flat and physically bent conditions showed feasibility and uniqueness of the electrode fabrication procedure opening a new research opportunities for manufacturing flexible miniaturized thin film batteries.³

References
1. F. Meierhofer, Haipeng Li, M. Gockeln, R. Kun, T. Grieb, A. Rosenauer, U. Fritsching, J. Kiefer, J. Birkenstock, L. Mädler, S. Pokhrel, ACS Appl. Mater. Interfaces, 2017, 9 (43), 37760–37777
2. M. Gockeln, S. Pokhrel, F. Meierhofer, J. Glenneberg, M. Schowalter, A. Rosenauer, Udo Fritsching, M. Busse, L. Mädler, R. Kun, J. Power Sources, 2018, 374, 97-106
3. M. Gockeln, J. Glenneberg, M. Busse, S. Pokhrel, L. Mädler, R. Kun, Flame aerosol deposited Li₄Ti₅O₁₂ layers for flexible, thin film all-solid-state Li-ion batteries, Nano Energy, 2018, 49, 564-573

Lithium metal is an ideal replacement for graphite anodes in lithium batteries due to its 10 fold higher capacity; however, it suffers from safety and efficiency problems that have so far prevented it from being commercialized. In particular, the tendency of Li metal to form dendritic structures presents a major safety hazard as dendrites can lead to short circuit, thermal runaway, and battery fires. However, the causes of dendrite nucleation are numerous and complex. In order to disentangle these causes we studied the factors affecting dendrite nucleation using an array of analytical techniques, allowing us to examine the surface chemistry and topography with simultaneous ultra-high spatial resolution and chemical selectivity. From this, we developed a 3D picture of the chemical make-up of the native Li surface, the corresponding topography, and the subsequent solid electrolyte interphase (SEI) with better than 200 nm resolution. We find that, contrary to the general understanding, it is the initial surface chemistry rather than the topography that is the dominant factor leading to dendrite nucleation in this system. Specifically, the untreated native Li surface contains inhomogeneously distributed organic material which promotes the formation of LiF-rich SEI in those regions after exposure to electrolyte. These localized LiF-rich regions become preferential locations for dendrite nucleation, leading to inhomogeneous Li deposition on the surface. This has significant implications for battery research as it elucidates a mechanism for inhomogeneous SEI formation, something that is widely accepted, but not well understood. It also highlights the importance of lithium surface preparation prior to cell assembly, which is implicit in much of the literature, but not directly addressed. By homogenizing the native Li surface, we were able to homogenize the SEI and therefore, the Li deposition, leading to smaller dendrites and longer cycle life.

Rechargeable lithium-ion batteries (LIBs) became an important part of human life because of unmatchable combination of their properties. In our days graphite is one of the most widespread anode materials, but, its small reversible capacity of 372 mAh g^-1 significantly reduces the energy density of LIBs. [1] Thus, an alternative anode material with higher reversible capacity, safety, and low cost needs to be found. Transition metal oxides with relatively high capacity and cycle stability are potential candidates to replace conventional graphite anodes. Tungsten oxide (WO₃) with a theoretical capacity of 693 mAh g^-1 stands out against other transition metal oxides due to combination of low cost and very large volumetric capacity of 5274 mAh cm^-3. [2,3] However WO₃ struggles from the large volume changes upon lithiation / delithiation leading to disintegration of the electrode and fast capacity fade at high charging rates. [4] To address this issue we used a glancing angle deposition technique [5] to create array of vertically aligned WO₃ nanorods (NRs) directly onto current collector. Such anode configuration enables directional electronic/ionic transportation, leading to high electron collection efficiency. [6] Controlled geometry of NRs also enables us to minimize effect of volumetric expansion on the mechanical stability of electrode. [1] As a result, coin cells with WO₃ nanorodes as anode exhibited stable cycle performance up to 3C rates, without disintegration of the electrode. To clarify the lithiation mechanism upon cycling we studied the phase transformations in the active material during the first two cycles. Ex-situ X-Ray diffraction analysis, scanning and transmission analytical electron microscopy in combination with the first principles calculations suggested that conversion reaction plays a very important role in the formation of solid electolyte interphase (SEI) and further transformation of initial WO₃ material into lithium tungstate. Formation of lithium tungstate at the very first lithiation may cause a large specific capacity drop after the first cycle, previously reported [7] for WO₃-based anodes. More experimental results will be presented and discussed during the conference.

This work was financially supported by ALCA-SPRING (JST) and Yazaki Memorial Foundation for Science and Technology.

[1] W. Qi, et al., J. Mater. Chem. A, 5, 19521–19540 (2017).
[2] S. Yoon, et al., Phys. Chem. Chem. Phys., 13, 11060–11066 (2011).
[3] US Geological Survey, “Mineral Commodity Summaries”, (2019).
[4] F. Liu, et al., Appl. Surf. Sci., 316, 604–609 (2014).
[5] Y. Pihosh, et al., Small, 10, 3692–3699 (2014).
[6] P. Roy and S.K. Srivastava, J. Mater. Chem. A, 3, 2454–2484 (2015).
[7] P. Li, et al., Electrochim. Acta, 192, 148–157 (2016).

Fluorine modification of lithium-ion (Li-ion) battery cathodes exhibits promising advantages compared to today's materials, including improved electrode stability, higher discharge/charge voltages, and higher energy density. However, practical applications of fluorinated cathodes are still limited by their synthesis methods. These rely currently on chemical reactions with F-containing reactants (e.g., NH₄HF₂ or NH₄F), or solid-state reactions via high-energy ball milling. These methods require highly toxic or corrosive chemicals or consume a significant amount of energy. Here, we demonstrate a non-toxic, energy-efficient, electrochemical method to achieve lithium fluoride (LiF) coatings on electrode materials by reduction of a fluorinated gas: sulfur hexafluoride (SF₆). By discharging the Li-SF₆ cell, a uniform LiF coating can be formed on the substrate materials (oxides or carbon). The discharge potential of the cell (~2.3 V) is fully within the stability window of the electrolyte, and thus, guarantees the formation of a "clean" LiF coating without contribution from contaminants, such as electrolyte reduction products. By tuning the discharge conditions, the morphology of the LiF coating can be precisely controlled. Additionally, the LiF coating formed in this approach is conformal, nano-scale and in intimate contact with the substrate, making it suitable for applications in battery materials. To demonstrate the practical feasibility of this method, we first applied LiF coating on various transition metal monoxides (MO, M = Mn, Ni) as model substrates for studying the LiF-splitting reaction and resulting phases formed upon cycling. The LiF-coated MO exhibited high reversible capacities (~200 mAh/g) when used as Li-ion cathodes, which can be attributed to successful LiF splitting and F-incorporation. In addition to the electrochemical performance, the morphology of LiF coating, the structural change of LiF-coated MnO during the activation (first charge) process, and the redox reaction mechanism will be discussed. This work develops an electrochemical “soft” synthesis approach for fluorinated cathodes, which is more practical and controllable than most of the currently investigated methods.

Mg-Air batteries have been receiving much attention in the recent years. Due to their high theoretical energy density and relatively low cost, they can be used as promising electrochemical energy storage and conversion devices. The theoretical voltage of the Mg–air battery is 3.1 V and the specific energy density is 6.8 kWhkg-1. However, Mg-air batteries are facing a number of challenges, including high self-corrosion properties and low discharge performance. In the present research, new magnesium alloys have been designed for improving the discharging performance. Microstructure and phase composition of alloys before discharge and after battery testing have been characterised by OM, XRD, SEM, TEM and STEM techniques. The electrochemical properties of these Mg alloys have been analyzed using a three-electrode electrochemical workstation

Vanadium pentoxide, V₂O₅, is an interesting cathode material as the extraction/intercalation of Li is feasible without the need of carbon additives. Its theoretical capacity ranges from 294 to 437 mAh/g for two and three Li-ions, respectively. Its drawbacks are well known. It is accepted that nanostructuring the material enhances the battery performance, but it has not been yet explored how the geometry of the cathode can contribute to this matter. In this work, we investigate the electrochemical performance of V₂O₅ thin films (2D systems) and those with a quasi-fractal structure (D < 2), that are proposed as well as a potential scalable solution for Li-ion batteries (LiB) in view of all solid-state batteries.
V₂O₅ was obtained from the thermal oxidation of vanadium layers. The qualification of the oxidation process was done using P-doped Si(100) substrates. The vanadium films were 25-200 nm thick. The oxidation annealing were carried out in air for 1 h at 350-600 °C; the time condition assures that the metal film is fully oxidized. The thickness conversion factor between the metal and the oxide was ~1.3.The quasi-fractal patterning was fabricated via lift-off of the metal layer using cracked white-egg templates ~300 nm thick, following the methodology of B. Han et al [DOI:10.1038/ncomms6674]. In the quasi-fractal systems, the effective area covering the substrate ranged from 10% to 60%. The oxidation procedure is then transferred to stainless steel substrates that are the cathode collector in Swagelok LiB cells. This oxide procedure formation avoids chemical impurities typically found upon wet chemical synthesis, rendering the obtained V₂O₅ as a simple model system to understand the influence of the cathode microstructure on the battery performance.
The oxidation temperature plays an important role in the crystallinity and morphology of the V₂O₅ and thus the electrochemical performance. At 500 and 600 °C, we produce single phase V₂O₅, with an orthorhombic crystalline structure. The 2D oxide films are polycrystalline while the quasi-fractal layers are strongly (010) textured. This is in turn reflected in the topography of the grains, formed by terraces with plateaus: the oxide films consist of rounded grains of a few hundreds of nm‘s in diameter while the quasi fractal pattern is formed by elongated rhomboid shapes with lengths as large as 3.5 µm. The cyclability of the films was evaluated in the potential window of 2.0-4.0 V where V₂O₅ could intercalate 2 mol of Li. We found that the optimum capacity is observed for 50 nm vanadium films oxidized at 500 °C, producing excellent rate capability of 180 mAh/g at 2C and 120 mAh/g at 20C. The quasi-fractal patterns are currently being evaluated.
Our Density Functional Theory modelling of the Li insertion into bulk V₂O₅ allowed to reproduce the unit cell parameters and obtaining the voltage profile for Li-intercalation, which shows a good agreement with potential difference measured experimentally.

Lithium-ion capacitors (LICs) are regarded as the promising energy storage devices owing to their balanced energy and power characteristics compared to both batteries and supercapacitors. To effectively couple the charge storage kinetics of the battery-typed anodes and capacitive cathodes, it is essential to employ high-capacity and high-rate anode materials. Moreover, as one aspect of the sustainable synthesis, the use of heavy metal and critical elements should be avoided. Currently, the mainstream anode material—graphite—suffers from sluggish charge transfer kinetics and potential safety issues due to the unfavorably low Li⁺ intercalation potential (0.01 V vs. Li/Li⁺). To overcome these adverse effects, intercalative Li₄Ti₅O₁₂ (LTO) with outstanding rate capability and higher insertion potential is used. Nevertheless, the low capacity (175 mAh g^-1) and excessively high (1.55 V vs. Li/Li⁺) insertion potential renders it also unsuitable for high-energy LICs. In view of such dilemma between high-energy and safety, and further inspired by the discovery of novel polyanionic material Li₂TiSiO₅ (LTSO) [Liu et. al., Energy Environ. Sci., 2017, 1456-1464], we rationally design a conductive 3D structure consisting of uniformly distributed and aggregation-free LTSO nanoparticles into nanofibrous carbon skeleton [Wang et al., Nano Energy, 2019, 173-181]. The synthetic procedures mainly involve facile and sustainable electrospinning process, followed by a morphology-preserved thermal transformation to convert organic Li, Ti, Si salts in-situ to LTSO and polymer nanofibers to carbon. It should also be noticed that such strategy adopts biocompatible polymer precursors and gets rid of heavy metal and critical elements. As-fabricated LTSO/C electrodes exbibit high-capacity (241.9 mAh g^-1 at 0.2 A g^-1, higher than 217.2 mAh g^-1 of graphite and 158 mAh g^-1 of LTO), superior rate capability (50% retention from 0.1 to 10 A g^-1, significantly higher than graphite and similar to LTO), and suitable Li⁺ insertion potential (0.1-1 V vs. Li/Li⁺ to balance between high full-cell voltage and safety). Subsequent kinetic analysis suggests that the high-rate performance probably derives from the pseudocapacitive mechanism, which is highly related to the unique 3D nanoarchitecture based on dispersive LTSO nanoparticles and interconnected conductive carbon framework. As a device level demonstration, the LICs employing LTSO/C anodes with high working potential of 4.2 V are fabricated, which exhibit a high energy density of 105.8 Wh kg^-1 and high power density of 28500 W kg^-1, effectively bridging the gap between lithium-ion batteries and supercapacitors. We believe that this work may be an essential reference for the rational design and sustainable synthesis of the desired LIC anodes for high-energy, fast, and safe energy storage.

Acknowledgement: This work was supported by General Research Fund (GRF) from the Research Grants Council (RGC) of Hong Kong (No.: 14203715 and 14218516). Shijie Wang is currently supported by Hong Kong Ph.D. Fellowship Scheme (HKPFS).

The current lithium-ion battery technology relies on intercalation-type materials which are highly stable but are limited in storage capacity [1]. Conversion-type materials are a way to greatly increase the energy density of a lithium-ion battery [2]. Molybdenum disulfide (MoS₂) is one material that can act as both an intercalation- and conversion-type (via lithium sulfide) anode by controlling the voltage window of cycling [3]. However, it is plagued by problems of pulverization due to the large volume expansion during lithiation [4], poor electrical conductivity [5], and electrolyte dissolution [6], leading to poor cyclability [7]. In this work, we first synthesize MoS₂ via a solvothermal route with nanoporous carbon, for strong electrical contact and mechanical support. We further improve the contact between MoS₂ and the nanoporous carbon via a thermal treatment. The electrochemical performance shows a long cycling life (800 cycles), due to the structural stability of the nanoporous carbon matrix that minimizes the pulverization and loss of active material via polysulfide shuttling. The improved electrical contact and mechanical support also allowed for high utilization of the active materials. An exceptionally high capacity is achieved due to the lithium sulfide from the conversion of MoS₂ and a capacitive contribution from the nanoporous carbon. In addition, an increasing electrochemical activation during cycling results in a significant capacity increment. Detailed material characterization such as scanning electron microscopy (SEM) will also be used to elucidate the origin of the high cyclability.

References:
[1] Y. Lu, L. Yu, and X. W. (David) Lou, “Nanostructured Conversion-type Anode Materials for Advanced Lithium-Ion Batteries,” Chem, vol. 4, no. 5, pp. 972–996, 2018.
[2] S. H. Yu, S. H. Lee, D. J. Lee, Y. E. Sung, and T. Hyeon, “Conversion Reaction-Based Oxide Nanomaterials for Lithium Ion Battery Anodes,” Small, vol. 12, no. 16, pp. 2146–2172, 2016.
[3] T. Stephenson, Z. Li, B. Olsen, and D. Mitlin, “Lithium ion battery applications of molybdenum disulfide (MoS₂) nanocomposites,” Energy Environ. Sci., vol. 7, no. 1, pp. 209–231, 2014.
[4] J. Zhou et al., “2D space-confined synthesis of few-layer MoS₂ anchored on carbon nanosheet for lithium-ion battery anode,” ACS Nano, vol. 9, no. 4, pp. 3837–3848, 2015.
[5] R. Fang, S. Zhao, Z. Sun, D. W. Wang, H. M. Cheng, and F. Li, “More Reliable Lithium-Sulfur Batteries: Status, Solutions and Prospects,” Adv. Mater., vol. 29, no. 48, pp. 1–25, 2017.
[6] A. Rosenman, E. Markevich, G. Salitra, D. Aurbach, A. Garsuch, and F. F. Chesneau, “Review on Li-Sulfur Battery Systems: An Integral Perspective,” Adv. Energy Mater., vol. 5, no. 16, pp. 1–21, 2015.
[7] S. H. Yu, X. Feng, N. Zhang, J. Seok, and H. D. Abruña, “Understanding Conversion-Type Electrodes for Lithium Rechargeable Batteries,” Acc. Chem. Res., vol. 51, no. 2, pp. 273–281, 2018.

Current research on improving state of the art anode technology for Lithium-ion rechargeable batteries is focused heavily on the development of silicon and graphite/silicon composite anodes. However, for beyond lithium-ion research, such as sodium-ion batteries, both silicon and graphite perform poorly. Due to this, anodes that are tin-, phosphorous-, and antimony- based are at the forefront of potential sodium-ion anodes. Of these materials, SnSb has been shown to be a promising material, with a mixture of stable cycling and high energy density.

We have developed the electrodeposition of pure phase, crystalline SnSb from an ethaline solution at room temperature. Electrodeposition is an interesting process as it allows for the study of the anode material’s intrinsic properties without the presence of carbon and binders that are typically used in the slurry-based production of anodes. We will present the sodium battery cycling studies of the electrodeposited SnSb and compare them to Sn-rich containing SnSb electrodes described in other previously reported electrodeposition processes. The incorporation of Sn is detrimental to the lifetime of battery material, which is a main motivation for the production of pure phased SnSb. We will present and discuss a suite of electrochemical characterization data used to understand the performance of the phase pure material.

Lithium Sulfur batteries (LSBs) are of a great scientific and commercial interest with potentially five times the energy density of current Li-ion technologies and lower cost. However, the technology suffers problems that have so far prevented their commercialization and wide scale adoption. These include poor cycle-life, limited sulfur utilization, and severe self-discharge during rest and charge. Compounding the problem is the rather complex, multistep reaction pathway that involves reduction from elemental sulfur to form shorter chain species of polysulfides and lithium-polysulfides (LiPS), which can be soluble or insoluble in the electrolyte. So far, modeling has helped to illustrate the processes and species that can be formed inside the cell at various states of charge. However, much more effort is needed to verify these results and supply the models with better data, as many parameters are assumed or fitted. The self-discharge phenomena is the focus of the present study which aims to validate a numerical model with experimental data over long periods of cycling and rest. We shed light on the nature of the LSB’s reversible and irreversible losses and predict their evolution over time.
References
Pope, Michael A., and Ilhan A. Aksay. "Structural design of cathodes for LiS batteries." Advanced Energy Materials 5.16 (2015): 1500124.
Rehman, Sarish, Shaojun Guo, and Yanglong Hou. "Rational Design of Si/SiO₂@ Hierarchical Porous Carbon Spheres as Efficient Polysulfide Reservoirs for High Performance LiS Battery." Advanced Materials 28.16 (2016): 3167-3172.

Novel honeycomb-like N-doped carbon three-dimensional (3D) nanowebs (HCNs) have been synthesized through a facile aqueous solution route for use as cathode materials in lithium sulfur batteries. The Li₂S@HCN cathode delivers a high discharge capacity of 815 mAh g^-1 after 65 cycles at 0.1 C, along with a superior rate capacity of 568 mAh g^-1 even at 2 C. The outstanding electrochemical rate performance is ascribed to their unique 3D honeycomb-like nanoweb structure, consisting of nanowires derived from polypyrrole. These properties greatly enhance the electrochemical reaction kinetics by providing continuous electron pathway and hollow channels for electrolyte transport. Nitrogen doping in the carbon nanowebs also considerably improves the chemisorption properties by tuning the affinity between sulfur and oxygen functional groups on the carbon framework. The simple synthesis strategy and resulting unique electrode structure provide a new aspect of nanostructure research for high performance lithium sulfur batteries.

Dendritic growth plagues the development of rechargeable lithium metal anodes. Recently, it has been reported that self-heating of the cell provides a mitigation strategy for suppressing dendrites. In order to study this phenomenon, we extend our recently developed nonlinear phase-field model to incorporate an energy balance equation allowing a full thermally coupled electrodeposition model using the open-source software package MOOSE. In this work, we consider the interplay between ionic transport and electrochemical reaction rate as a function of temperature and explore the possibility of using thermal shock induced dendrite suppression. We discover that, depending on the electrochemical reaction barrier and ionic diffusion barrier, self-heating could accelerate (larger reaction barrier) or decelerate (larger diffusion barrier) dendrite formation. Given that the electrolyte constituents can be used to tune both barriers, this study could provide an important avenue to exploit the self-heating effect favorably through electrolyte engineering.

Use of flammable organic electrolytes in secondary batteries possesses a safety threat and also it add to the cost of the battery in terms of battery fabrication. This force us to revisit the possible application of aqueous electrolytes where not only the toxicity is reduced but rate kinetics are also enhanced as there is a two-fold increase in the ionic conductivity. However, the limited working voltage window range to avoid water splitting makes it difficult to test all electrode materials in aqueous media especially high voltage materials. Hence, it is important to look for efficient and stable electrode materials compatible with aqueous electrolytes. Herein, we present two such case studies using earth-abundant Fe-based compounds. In the first case, performance of Na₂FePO₄F in aqueous electrolytes is demonstrated. The half-cell delivered a discharge capacity of 85 mAh g^-1 at 1 mA cm^-2 current density using a three electrode setup with excellent rate kinetics. A full cell assembled using NaTi₂(PO₄)₃ anode delivered a reversible capacity of 85 mAh g^-1 at a voltage of 0.8 V battery (Sharma et al, ChemElectroChem, 2018, 6, 444-449). The second work is based on LiFePO₄OH anode for aqueous lithium-ion batteries. In organic electrolytes, it delivered a stable discharge capacity of 140 mAh g^-1 at 2.6 V vs. Li⁺/Li. However, the half-cell configuration in aqueous electrolyte delivered a discharge capacity of 153 mAh g^-1 with very good rate kinetics. Interestingly, it was found to be working in the anodic range for aqueous batteries (Sharma et al, J. Power Sources, 2019, 429, 17-21). A full cell assembled with LiFePO₄ cathode delivered discharge capacity of 120 mAh g^-1 at 0.8 V. The structural characterization along with electrochemical studies will be presented for both case cases.

The search for next-generation solid-state superionic conductors has attracted significant attention. Among Na superionic conductors, Na₁₁Sn₂PS₁₂ has been reported to have a room temperature ionic conductivity of 1.4 mS/cm. In this study, we employ density functional theory to study the stability of Na₁₁Sn₂PS₁₂ and further explore the substitution of Sn with Ge. Our results indicate that Na₁₁Ge₂PS₁₂ is more stable than Na₁₁Sn₂PS₁₂. Furthermore, substituting Sn with Ge increases the band gap, improves the room temperature ionic conductivity by a factor of 2, and lowers the activation energy of Na hopping. Statistical analysis suggests that Na₁₁Ge₂PS₁₂ has a faster diffusion along the ab-plane compared to the c-axis. The Na diffusion in Na₁₁Ge₂PS₁₂ appears to occur with two different mechanisms depending on temperature: 1) an ion hopping process at lower temperatures (<800 K); 2) a fluid-like distribution of Na ions at higher temperatures (>1000 K). The computations suggest that Na₁₁Ge₂PS₁₂ is a promising candidate as a solid Na electrolyte due to its high room temperature ionic conductivity and phase stability. In light of these simulation results, we expect to stimulate further experimental studies on Na₁₁Ge₂PS₁₂.

Development of sodium-ion based energy storage devices is becoming more popular on account that the excessive consumption of lithium resources, which will be expected more in the electrical vehicle and grid scale energy storage fields. However, the design and construction of safer sodium ion based devices are still hindered owing to lack of high performance electrodes materials and high ionic conductive solid state separators.
Here, we will report a new type of quasi-solid sodium ion capacitor with high safety and enhanced high-energy density by using flake-shaped MoS₂ nanohybrids and sodium-ion ionogel electrolyte. The optimized quasi-solid state sodium ion capacitor could deliver a high energy density up to 115 W h kg⁻¹ at 70 °C, and excellent durability up to 8000 cycles. The relationship between microstructure and performances was systemically evaluated. Energy storage mechanisms were also exploited by using electrochemical analysis and molecular simulation methods in order to disclose the temperature effects. Our study suggests that high performance capacitors with enhanced energy density and cyclability can be achieved by carefully programmed nanoarchitectures and optimized ionic liquid gel separators.

Lithium-sulfur batteries become one of the most promising batteries due to the high theoretical specific energy density. However, practical applications are currently hindered by a few obstacles, such as poor cycle performance notoriously caused by the shuttle effect of lithium polysulfides. Herein, we design a micro/nano-structure VO₂/carbon nanofibers composite via a hierarchical control method. And we utilize this self-supporting membrane as the interlayer in lithium-sulfur batteries. The VO₂ microsheets with a porous structure introduce an immobilization process of polysulfides, controlling the deposition of Li₂S₂ or Li₂S on the designed interlayer. An arranged relocation of sulfur species is induced during cycling, resulting in a shortened electron passage and an improved utilization of active material. The exposing VO₂ nanoparticles on carbon nanofibers provide a large amount of active sites for polysulfide conversion, which can effectively improve the redox kinetics. With a sulfur loading of 2.4mg cm^-2 and a sulfur content of 80% at the whole electrode level, the cell with micro/nano-structure VO₂/carbon nanofibers interlayer delivers an initial discharge capacity of 1411 mAh g^-1, 1230 mAh g^-1, and 602 mAh g^-1 at 0.1C, 1C and 5C. It can maintain a reversible capacity of 748 mAh g^-1 after 100 cycles at 1 C and maintain a specific capacity of 507 mAh g^-1 after 1000 cycles at 5 C with a fade rate of 0.02% per cycle. Our research provides a new fabrication method and structure design of interlayer toward the rational design of long-life lithium sulfur batteries.

MoS₂ is a promising 2D material which could serve as anode for fabricating lithium ion batteries with high energy and power densities.^1,2 Crystallinity (ordered layer structure) and defects (mainly edge and planar defects) in MoS₂ are shown to have significant role in deciding the electrochemical performance.³ In an effort to disentangle and understand the role of individual contributions on the electrochemical properties, we have synthesized planar and edge defect-rich MoS₂ (MoS₂-D) nanosheets and defect-suppressed ordered layers of MoS₂ (MoS₂-C) nanosheets from a wet chemically synthesized precursor. MoS₂-D are obtained upon annealing at 500 °C and MoS₂-C nanosheets are obtained upon annealing at 900 °C for 1 h. For MoS₂-D anodes, the crystallite size is small (∼3 nm) with an average 5 layers of S-Mo-S stack within a nanosheet. The nanosheets are mostly curled, resulting in large number of dislocations, edge and planar defect regions. MoS₂-C nanosheets have larger crystallite size (∼10 nm) with an average of 15 S-Mo-S layers. These crystalline nanosheets are mostly flat with less defects and the defects are mostly from the edge terminations and surface regions. Lithiation and delithiation characteristics, effective charge storage capability, rate capability and cycling stability are analyzed in the intercalation regime (1 to 3 V vs Li/Li⁺). During initial lithiation, MoS₂-D nanosheets exhibit large Li intake (x~1.9) and show an initial lithiation capacity of 319 mAh/g (~Li_1.9MoS₂). The MoS₂-C nanosheets in contrast show smaller intake of Li (x~1.22) and has a capacity of 204 mAh/g (~Li_1.22MoS₂). The excess lithium intake is attributed to the interaction of lithium ions with planar and edge defect sites in MoS₂ nanosheets. The first reversible capacities are found to be 166 mAh/g (x~0.99) and 138 mAh/g (x~0.82) for MoS₂-D and MoS₂-C nanosheets, respectively, suggesting that a large fraction of initial Li intake for MoS₂-D nanosheets is electrochemically irreversible. At 10C current rate, the MoS₂-D and MoS₂-C nanosheets show reversible capacity of 37 mAh/g and 67 mAh/g, respectively. This indicates that the rate capability of well crystalline nanosheets is better. Interestingly, when tested for cycling stability at 10C-rate for 1000 cycles, at the end of 1000 cycles a ~30% increase in capacity is noted for MoS₂-D anodes. Contrastingly, MoS₂-C nanosheets show capacity fading, with final capacity ~80% of initial capacity. The decrease in capacity of MoS₂-C is due to the increasingly defiant Li diffusion upon continuous cycling. The gain in capacity in MoS₂-D nanosheets is attributed to the excess lithium retained at defects during the first lithiation. These excess lithium at defect sites shuttle around, reducing the diffusion lengths for lithium ions, thus effectively activating the electrode over repeated cycling. These results indicate that crystallinity and defects play complementary role in deciding the electrochemical properties of 2D MoS₂ in the intercalation regime. Thus, defect-rich nanosheets, MoS₂-D, exhibit large capacity at low current rates and better cycling stability. Defect-suppressed nanosheets, MoS₂-C, on the other hand have better rate capability at high current rates and reasonable cycling stability.

References:
1. Stephenson, T., Li, Z., Olsen, B. & Mitlin, D. Lithium ion battery applications of molybdenum disulfide (MoS₂) nanocomposites. Energy Environ. Sci. 7, 209–231 (2014).
2. Wang, T., Chen, S., Pang, H., Xue, H. & Yu, Y. MoS₂-Based Nanocomposites for Electrochemical Energy Storage. Adv. Sci. 4, 1600289 (2016).
3. Budumuru, A. K., Rakesh, B. & Sudakar, C. Enhanced high rate capability of Li intercalation in planar and edge defect-rich MoS₂ nanosheets. Nanoscale 11, 8882–8897 (2019).

Dielectric capacitors are very attractive for high power energy storage. However, the low energy density of these capacitors, which is mainly limited by the dielectric materials, is still the bottleneck for their applications. In this work, lead-free single-phase perovskite Sr_x(Bi_1-xNa_0.97-xLi_0.03)_0.5TiO₃ (x=0.30 and 0.38) bulk ceramics, prepared using solid-state reaction method, were carefully studied for the dielectric capacitor application. Polar nano regions (PNRs) were created in this material using co-substitution at A-site to enable relaxor behavior with low remnant polarization (P_r) and high maximum polarization (P_max). Moreover, P_max was further increased due to the electric field induced reversible phase transitions in nano regions. Comprehensive structural and electrical studies were performed to confirm the PNRs and reversible phase transitions. And finally, a high energy density (1.70 J/cm³) with an excellent efficiency (87.2%) was achieved using the contribution of field-induced rotations of PNRs and PNR-related reversible transitions in this material, making it among the best performing lead-free dielectric ceramic bulk material for high energy storage.

Asymmetric supercapacitor (ASC) devices are emerging as effective high-performance energy storage systems. We report on the synthesis of novel and green electrode materials and their use to construct high-performance ASCs. The assembled ASCs are based on 3D porous graphene-wrapped V2O5 nanospheres as the positive electrode and Fe3O4@graphene as the negative electrode. The optimal ratio of the
V2O5 nanospheres intercalated graphene sheets in the composite electrodes were identified. Compared to all positive electrode formulations, the V2O5@3DGr (33%) hybrid electrode achieved the highest specific capacitance (612.5 Fg-1) at a current density of 1.0 A g-1. Based on the excellent electrochemical behavior of the fabricated electrodes, the assembled asymmetric supercapacitor devices of V2O5@3DGr// Fe3O4@3DGr exhibited a maximum energy density of 54.9Wh kg-1 with a power density of 898 Wkg-1 with an extended voltage of 1.8 V in 1.0M Na2SO4 aqueous electrolyte. Furthermore, the ASC device demonstrated excellent cycling stability with 89.6% capacitance retention over 10,000 cycles. The outstanding electrochemical performance of the fabricated electrodes can be attributed to the synergic effect between graphene sheets and metal oxides (V2O5, Fe3O4) sandwich network structures. Interestingly, the proposed asymmetric electrode materials provide a promising strategy for integrating low-cost transition metal, green electrolyte, high energy, and power densities of supercapacitor devices and that can bridge the gap with commercial batteries.

The huge volume change of high-capacity active materials has hindered their practical application for Li-ion batteries. Although various kinds of surface coating materials were applied to address this issue so far, the suitable coating sources satisfying both low cost and high mechanical strength have not still confirmed. Here, a cheap carbonaceous material, pitch, as a qualified coating source for Si anodes is thoroughly investigated. Specifically, from in situ lithiation and indentation tests, we discovered that pitch-coated Si nanoparticles could withstand both internal and external force without any mechanical failure. Through various physicochemical analysis, we elucidated the distinctive structural properties after its carbonization can support the outstanding mechanical strength. By applying pitch coating on the Si-nanolayer-embedded graphite (SG), pitch was homogeneously distributed on the SG, and it improved the electrochemical performance. Furthermore, in both half- and full-cell tests, pitch-coated SG exhibited higher capacity retention and cycling Coulombic efficiencies than acetylene- and sucrose-coated SG by effectively mitigating the volume change and suppressing the continuous formation for solid electrolyte interphase. For more details, pitch-coated silicon nanolayer–embedded graphite (SG) exhibits superior capacity retention (81.9%) compared to that of acetylenecoated SG (66%) over 200 cycles in a full-cell by effectively mitigating volume expansion (< 50%), even under industrial electrode density conditions (1.6 g cc⁻¹). Thus, this work presents new possibilities for the development of high capacity anodes for industrial implementation.

Multi-electron redox processes are attractive charge storage mechanisms for next-generation, high energy density batteries. Multi-electron redox can be achieved via >1 electron redox per transition metal in conventional intercalation-type materials or through conversion mechanisms using divalent cations. Electrodeposition of divalent cations, for example, yield smooth metal deposits compared to Li metal deposited at the same current densities suggesting that divalent metal batteries could be a viable next-generation chemistry. Many challenges remain for divalent-based chemistries, however, including developing and understanding materials that support solid-state divalent ion conductivity. Divalent ion conductivity is an essential fundamental process employed by intercalation electrodes, solid-state electrolytes, and solid-state interfacial layers. To begin understanding the fundamental mechanisms of divalent ion conductivity, we aim to probe divalent ion conductivity in electronically insulating solid-sate host matrices. We will discuss our first attempt at this with a case-study on ZnPS₃. ZnPS₃ supports Zn²⁺ conductivity with unexpectedly low activation energies (~350 meV) thanks to the flexible [P₂S₆]^4- polyanion that we suggest distorts into the van der Waals gap at the transition state.

Amongst known families of solid electrolytes of potential interest for solid-state batteries, the anti-perovskites (A₃BX) are of interest for the high ionic conductivities observed in certain compositions, and, like perovskites, the compositional flexibility provided by the possibility for ion substitution onto multiple lattice sites. For example, variations in the relative size of ions A, B and X result in changes in the Goldschmidt tolerance factor, or extent of disorder, that are accompanied by changes in the distribution of lithium migration energies. [1]

In surveying transport in this family of ion conductors, we observed a trend wherein numerous compositions show upwards curvature on an Arrhenius plot, indicating a non-constant activation energy. This is unusual as most solids exhibiting non-Arrhenius behavior exhibit a negative deviation. We have synthesized a wide range of Li and Na antiperovskites, and have confirmed non-Arrhenius conductivity with a positive deviation in compositions such as Na₃OBr_0.6I_0.4. This talk will discuss compositional trends related to this behavior, and our attempts to understand the structural origin(s) of this behavior through temperature-dependent X-ray and neutron scattering, calorimetry, and other methods. Implications for the design of solid electrolytes for solid state batteries will be discussed.

This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.

[1] Kwangnam Kim and Donald J. Siegel. "Correlating lattice distortions, ion migration barriers, and stability in solid electrolytes." Journal of Materials Chemistry A 7, no. 7 (2019): 3216-3227.

While a recent fervor for the commercialization of electric vehicle applications has steered the battery industry’s efforts toward high energy density batteries, another significant path for research and development lies with grid-scale energy storage systems (ESSs). ESSs are pivotal in that they can be used to stabilize the power grid through frequency regulation operations. Ideally, power supply should match demand in order to maximize efficiency. However, this is hardly the case in reality because fluctuations in both supply and demand occur due to various reasons. For example, the sporadic nature of renewable energy sources such as wind often results in oscillations in power supply, while certain times during the day demand high levels of power. This mismatch is balanced through the use of ESSs. In order to accommodate such real-time changes, however, ESSs must be highly responsive to perturbations. In other words, high charge/discharge rate capability is critical for such responsiveness, where ESSs can store extra power and discharge when needed in a short period of time. Furthermore, as ESSs are composed of multiple battery modules, a fire may have devastating consequences on its surroundings and/or human lives. Thus, batteries that target ESS applications must meet two crucial requirements: high power density and safety.

In this respect, aqueous zinc ion batteries (AZIBs) are being tapped as potential candidates for ESS applications. AZIBs are promising systems for ESSs in several ways. First, the use of aqueous electrolytes significantly lowers the risk of fire hazards. Second, the inherently high ionic conductivity of water creates an environment amicable for high rate battery operation. Third, zinc (Zn) is known for its stability in water, rendering its metallic form employable as an anode. Finally, the bivalence of the Zn²⁺ ion opens up possibilities for high capacity. Unfortunately, the use of water as the primary electrolyte solvent ironically entails a critical disadvantage: water splitting. This consists of hydrogen/oxygen evolution reactions at their respective electrodes, the potentials of which sum up to 1.23 V as determined by thermodynamics. Evidently, it is within this narrow voltage window the AZIB must operate. Beyond these boundaries, the irreversible HER/OER steps not only deplete the electrolyte, but also may degrade the electrodes.

In this sense, recent research efforts in AZIBs have primarily focused on discovering new cathode materials suitable for aqueous applications. With Zn generally established as the anode, the cathode becomes the key performance factor. The ideal cathode for AZIBs must meet the following conditions; i) a redox potential within the voltage window, ii) good intercalation kinetics, iii) well-defined ion diffusion channels, and iv) structural stability. Having taken such conditions into account, we have discovered that a mixed-valence vanadium oxide, V₆O₁₃, exhibits promising electrochemical traits such as 93% capacity retention after 2,000 cycles and high rate capabilities of up to 24.0 A g^-1. These results were correlated with synchrotron in situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) experiments to reveal a single phase reaction pathway and reversible redox of vanadium upon Zn (de)intercalation. Interestingly, water plays a crucial role in this process, whereby Zn intercalation is significantly enhanced by means of hydrated intercalation. This intriguing phenomenon was probed via experiments and density functional theory calculations, which highlight the importance of the desolvation energy penalty at the electrode/electrolyte interface as well as the structural implications of co-intercalated water. These results show that V₆O₁₃ is not only a promising candidate for AZIB cathodes, but the reaction mechanisms responsible for such performance could also be extended to future investigations to pave the way for AZIBs.

Aprotic lithium-oxygen batteries (LOBs) have much higher energy density compared to today’s lithium ion batteries. However, highly reactive superoxide, the discharge intermediate of LOBs, triggers side reactions to deteriorate LOB performances. Also, high overpotential is required to oxidize the discharge product Li₂O₂ during charge due to the non-conductive nature of Li₂O₂. Herein, we present 4-carboxy-TEMPO as a bifunctional mobile catalyst soluble in LOB electrolytes for improving LOB performances. The roles of 4-carboxy-TEMPO is two-fold: (1) the chemo-catalyst to catalyze superoxide disproportionation reaction for suppressing the superoxide-triggered side reactions; and (2) the redox mediator to oxidize the discharge product Li₂O₂ in a kinetically effective way for reducing the overpotential during charge. As expected, the use of the mobile catalyst in LOB cells resulted in the 4-fold increase in cycle life from 50 cycles to 200 cycles, significantly reducing the overpotential during charge. Also, the discharge capacity increased 4-fold.

A water-miscible anthraquinone with polyethylene glycol (PEG)-based solubilizing groups is introduced as the redox-active molecule in a negative electrolyte (negolyte) for aqueous redox flow batteries, exhibiting the highest volumetric capacity among aqueous organic negolytes. We synthesized and screened a series of PEG-substituted anthraquinones (PEGAQs) and carefully studied one of its isomers, namely 1,8-bis(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)anthracene-9,10-dione (AQ-1,8-3E-OH), which has high electrochemical reversibility and is completely miscible in water of any pH. A negolyte containing 1.5 M AQ-1,8-3E-OH, when paired with a ferrocyanide-based positive electrolyte across an inexpensive, non-fluorinated permselective polymer membrane at pH 7, exhibits an open-circuit potential of 1.0 V, a volumetric capacity of 80.4 Ah/L, and an energy density of 25.2 Wh/L.

The urgent need for safer batteries is leading research to all-solid-state lithium-based cells. To achieve energy density comparable to liquid electrolyte-based cells, ultrathin and lightweight solid electrolytes with high ionic conductivity are desired. However, solid electrolytes with comparable thicknesses to commercial polymer electrolyte separators (~10 μm) used in liquid electrolytes remain challenging to make because of the increased risk of short-circuiting the battery. Here, we report on a polymer–polymer solid-state electrolyte design, demonstrated with an 8.6-μm-thick nanoporous polyimide (PI) film filled with polyethylene oxide/lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI) that can be used as a safe solid polymer electrolyte. The PI film is nonflammable and mechanically strong, preventing batteries from short-circuiting even after more than 1,000 h of cycling, and the vertical channels enhance the ionic conductivity (2.3 ×10^−4 S/cm at 30 °C) of the infused polymer electrolyte. All-solid-state lithium-ion batteries fabricated with PI/PEO/LiTFSI solid electrolyte show good cycling performance (200 cycles at C/2 rate) at 60 °C and withstand abuse tests such as bending, cutting and nail penetration.

As devices requiring lithium-ion batteries become more diverse and more numerous, not only the energy density but also the customer's demand for power density are increasing.With reported in several papers, the charge rate of a lithium ion battery depends heavily on anode due to the kinetic and thermodynamic reasons such as electrochemical reaction in the vicinity of the interface between the active material and the electrolyte, the low diffusivity and conductivity of lithium ions into inner active materials(Graphite,Si).However, because charging performance (charging rate capability) of Lithium ion batteries decreases drastically with increasing charging rate. In fact, Most researches focused on numerical improvements in charging rate capability, but there was given less consideration for analytic explanation of how the improvement was originated from some reason. Conceptually, in this study, We has been demonstrated that the charging rate capability is improved by designing of the anode active material (SIN@IGnB) and qualitative and quantitatively tried to elucidate how this improvement corresponds with the physicochemical and electrochemical results. As with the step above, we have endeavored to compare the capacity composition on the individual lithiated components which are Graphite and Si or SiN (each capacity contribution of Graphite parts /Si part) of the promising the Si nanolayer embedded Graphite by deconvoluting the lithiated peaks and integrating the peak area through the differential capacity analysis. As a result, at 5C C-rate, there was a remarkable reversal in the Graphite to Silicon capacity ratio which it was 6 to 4, at 5C charged whereas the ratio was 3 to 7 in case of formation C-rate (0.2C) The reversal in this ratio was originated from the drastic reduction in the capacity of the graphite, which was due to the fact that for the same reasons as overpotential(so-called staging kinetics) related to the high resistance and low electronic/ionic conductivity of lithiated Si in itself the anode capacity is more favorable to exhibited by the Stage 2,2L, 3, 4) than the Stage 1 of graphite and. We have strategically designed the SiN@IGnB (SiN nanolayer coated Graphene lumps growth on MCMB).This architecture greatly increases electron / ion migration near the surface by graphene lump ,through the SiN nanolayer, and further accelerates migration of lithium ions toward graphite by the formed Li-Si-N ternary phase, In verification of the materials design strategies by the same method as above, we have demonstrated that there was not reversal of Graphite to Si-N ratio, which was 55 to 45. A differential capacity (dQ/dV) analysis results also showed that the exhibited capacity by stage 1 and 2 was higher than that of Si, which facilitated the capacity utilization of graphite. Furthermore, by introducing the concept of “effective thickness expansion ratio” and comparing it according to the charging rate, graphite shows a rapid irreversible expansion (~ 20%) which means the lithium plating at 3C while SiN@IGnB shows the (~7%) negative value of the effective thickness expansion ratio,which means that there was less susceptible to lithium plating on the harsh condition of anode.

Replacing the traditional graphite anodes by Si electrodes can greatly improve the energy density of lithium-ion batteries. However, the large volume expansion and the formation of highly reactive Li-Si binary phases during battery operations can cause continuous lithium and electrolyte consumptions as well as the fast decay of Si anodes. In this work, by adding a second metal cation (M) into the electrolyte, we stabilize the Si anodes during the lithiation process through in situ formation of Li-M-Si ternary phases. Firstly, using solid-state nuclear magnetic resonance spectroscopy, we show that the doping of M can dramatically suppress the chemical reactions between the Li-M-Si model compound and common electrolyte solvents. Guided by this discovery, new mixed-salt electrolytes with M cations were prepared and tested with graphite-free Si electrodes, which demonstrated higher capacity, better cyclability, and higher efficiencies in both half-cell and full-cell tests. Post-electrochemistry characterizations demonstrate that adding M salts leads to the co-insertion of M cations along with Li into Si during the lithiation, which stabilized the lithiated silicon anodes by forming more stable Li-M-Si ternaries. The new electrolytes fundamentally change the traditional Li-Si binary chemistry formed during operations while minimally affecting silicon electrochemical profiles and theoretical capacities. This study provides a new and simple approach to stabilize silicon anodes, which can enable the commercial application of Si as the next-generation anodes in lithium-ion batteries.

Lithium metal batteries are promising due to its high energy density and low density. But lithium dendrite caused by the lithium vertical deposition at high current density and energy density could penetrate the separator and the direct contact between lithium anode and cathode causes short circuit of cell, which impede its utilization. To address this challenge, we design a 3D Li metal anode composite with high surface energy artificial framework, which realizes the faster and uniform lithium ions transfer at high current density and a large amount of lithium deposition horizontally inside the artificial framework at high capacity without any lithium dendrite growth.The dendrite-free electrode has long cycle term of over 120 h at high current density of 30 mA/cm² and capacity of 30 mAh/cm². This work provides new ways to address the lithium dendrite issue and get longer lifespan at high current and energy density toward the next generation of Li metal batteries.

Rechargeable lithium (Li) metal batteries (LMBs) with intercalation cathodes have been revived as promising battery chemistry in recent years due to their superior theoretical energy-densities comparing to the state-of-the-art Li -ion batteries. However, there is still significant barriers to be overcome before large scale commercialization of LMBs because of their limited cycle life and potential safety concerns. Li pulverization during cycling is one of the most critical barriers for safe operation of LMBs. Here we report a new approach to prevent Li pulverization in high-energy LMBs with a Ni-rich LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathode during long-term cycling by a highly stable SEI layer enabled by a novel electrolyte. A homogeneous solid electrolyte interphase layer on Li anode is generated in this electrolyte, which is rich in inorganic species and robust against cycling. It successfully minimizes Li loss and pulverization. Furthermore, this electrolyte also enabled the formation of a good cathode electrolyte interphase on the NMC811 cathode, which effectively stabilizes the NMC811 structure. Therefore, very high Li Coulombic efficiency and great stability has been demonstrated in Li||NMC811 cells adopting this electrolyte. The details of the electrolyte together with post-mortem analysis on Li||NMC811 cells using this electrolyte will be discussed at the presentation.

Solid state batteries with Lithium metal anodes have huge potential as the next high energy-density cells. However, the development of solid state batteries has been hindered by new failure modes not seen in liquid and semi-solid electrolyte systems. A greater understanding of the physical properties of the component parts and the mechanical interaction between them during cycling is required for real battery applications. In order to investigate this we have developed a methodology to test the microstructural and mechanical properties of air sensitive battery-specific materials.
This new approach focuses on in-situ observation of plastic deformation with reference to crystallographic orientation. To demonstrate this we use the example of Li metal, which has previously been shown to have anisotropy in elastic and yield properties. Large single crystal tests and Density Functional Theory (DFT) modelling of the crystal structure have shown the anisotropy but the role of the microstructure and texture has yet to be explored for materials used in Li metal batteries.
In-situ nanoindentation and Electron Backscatter Diffraction (EBSD) allows for testing the mechanical properties of Li metal in specific crystallographic directions. The physical response to load measures elastic modulus, hardness and creep behaviour of the material. Observing the real time development of sink-in around indents is indicative of the dislocation activity caused by the highly localised stress in soft materials.

Li-metal batteries (LMBs) and Na-metal batteries (NMBs) are considered as the promising candidates to replace the conventional Li-ion batteries (LIBs) due to their high theoretical energy density. For LMBs and NMBs, Li metal and Na metal are the ultimate choices to achieve their high energy density due to the high specific capacity, low electrochemical potential and lightweight [1]. However, as alkali metals, both Li and Na metal anodes suffer from serious challenges including 1) Li/Na dendrite formations and short circuits; 2) Low Coulombic efficiency (CE) and poor cycling performance; and 3) Infinite volume changes. This presentation mainly focuses on the design of multiple strategies for the stabilization of Li and Na metal anode for LMBs and NMBs.
Solid electrolyte interphase (SEI) layer is one of the key factors for the Li and Na deposition behaviors [2]. We developed different approaches to fabricate artificial SEI with significantly improved electrochemical performances. Firstly, we have demonstrated different ultra-thin protective layers for Li and Na metal anodes by advanced atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques, including Al₂O₃, alucone, and polyurea, et al [3]. More recently, we designed a natural SEI-inspired dual-protective layer for Li metal anode with precisely controlled thicknesses, compositions and mechanical properties [4]. Secondly, we developed the in-situ solution-based methods to fabricate the Li₃PS₄ and Na₃PS₄ as protective layers for both Li and Na metal anodes with significantly enhanced performances and reduced dendrite growth [5].
To address another challenge of volume change, 3D conductive interlayers and hosts have been designed for Li and Na metal anodes. Carbon paper (CP) and modified CP with carbon nanotubes have been used as host/interlayer with excellent electrochemical performance under high current density and high capacity [6].
In conclusion, we developed the different approaches, including protective layers fabricated by ALD/MLD and solution methods, interlayers, and 3D skeleton design, for Li and Na metal anodes with enhanced electrochemical performances and reduced dendrite growth. Meanwhile, the ideas have been also applied to solve the practical issues for testing Li and Na metal batteries.

[1] Y. Zhao, X. Sun, Energy & Environmental Science, 2018, 11, 2673
[2] Y. Zhao, X. Sun, Joule, 2018, 2, 2583
[3] Y. Zhao, X. Sun et al, ACS Energy Letters, 2018, 3, 899; Y. Zhao, X. Sun et al, Small Methods, 2018, 2, 1700417; Y. Zhao, X. Sun, et al, Advanced Materials, 2017, 29, 1606663; Y. Zhao, X. Sun et al, Nano Letters, 2017, 17, 5653; Y. Sun⁺, Y. Zhao⁺, X. Sun, et al, Advanced Materials, 2019, 31, 201806541
[4] Y. Zhao, X. Sun et al, 2019, submitted
[5] Y. Zhao, X. Sun et al, Journal of Materials Chemistry A, 2019, 7, 4119; J. Liang, X. Sun et al, Advanced Materials, 2018, 30, 1804684
[6] Y. Zhao, X. Sun et al, Nano Energy, 2018, 43, 368; Y. Zhao, X. Sun et al, Energy Storage Materials, 2018, 15, 415; Y. Zhao, X. Sun et al, Small, 2018, 14, 1703717

The state-of the-art rechargeable Lithium-ion batteries (LIBs) use liquid electrolytes and are the major choice for current EVs and portable electronic applications. However, these LIBs still suffer from many issues related to safety, lifespan and energy density. Accordingly, solid-state lithium batteries (SSLBs) have recently emerged as a promising alternative energy storage device due to their ability to overcome the intrinsic disadvantages of liquid-electrolyte LIBs and possess a greater volumetric energy density due to the use of solid-state electrolytes (SSEs). However, the interfacial issues between SSEs and electrodes (both cathode and anode) have a significant impact on the stability and lifetime of SSLBs [1-2]. The origin of these interfacial phenomena is the unstable contact and chemical reactions between electrodes and electrolytes to form an interlayer with extremely low electronic and/or ionic conductivities, which restricts the performance of the SSLBs. An artificial, uniform and ultrathin interfacial layer is critical to address these challenges [2]. Atomic layer deposition (ALD) and molecular layer deposition (MLD) are unique coating techniques that can realize excellent coverage and conformal deposition with precisely controllable at the nanoscale level due to its self-limiting nature, which are ideal for addressing the challenges of interface in SSLBs [2].
Our work apply ALD/MLD to rationally design novel coatings to address the interfacial challenges in SSLBs. The goal is to prevent capacity degradation of SSLBs caused by high interfacial resistance and chemical/electrochemical reactions between electrodes and electrolytes (e.g. sulfide-based). We will demonstrate to (i) stabilize the interface between cathode electrodes and electrolytes and prevent the formation of intrinsically high resistance layers, (ii) suppress elemental inter-diffusion during the operation of SSLBs, (iii) fabricate facile ionic transportation channels to facilitate ion exchange between different components of SSLBs, and (iv) buffer volume changes during cycling of SSLBs.

References:
Y. Zhao, X. Sun. Molecular Layer Deposition Technique for Energy Conversion and Storage. ACS Energy Lett. (2018),3,899-914.
Y. Zhao, X. Sun .Addressing Interfacial Issues in Liquid-based and Solid-State Batteries by Atomic and Molecular Layer Deposition. Joule.2018, in press.
Y. Zhao, X. Sun, et al., Robust Metallic Lithium Anode Protected by Molecular Layer Deposition Technique, Small Methods, (2018),1700417. DOI: 10.1002/smtd.201700417
C. Wang, X. Sun, et al., Stabilizing interface between Li10SnP2S12 and Li metal by molecular layer deposition. Nano Energy.53 (2018) 168–174.
C. Wang, X. Sun, et al., Boosting the performance of lithium batteries with solid-liquid hybrid electrolytes: Interfacial properties and effects of liquid electrolytes. Nano Energy.48 (2018) 35-43.
J. Liang, X. Sun, et al., In-Situ Li3PS4 Solid-State Electrolyte Protection Layers for Superior Long Life and High Rate Li-Metal Anodes. Adv. Mater. 2018, 30,1804684.
X. Li, X. Sun, et al., High-performance all-solid-state Li–Se batteries induced by sulfide electrolytes, Energy Environ. Sci., 2018, 11,2828-2832.
X. Li, J. Liang, J. Luo, C. Wang, X. Li, Q. Sun, R. Li, L. Zhang, R. Yang, S. Lu, H. Huang, X. Sun, High-Performance Li-SeSx All-Solid-State Lithium Battery, Adv. Mater, 2019, 1808100.

Lithium ion batteries have become the dominant form of energy storage used in consumer electronics and, recently, electric vehicles. However, high costs have prevented widespread deployment of lithium ion batteries for applications other than portable electronics, and the safety issues associated with liquid organic electrolytes remain to be addressed. In order to enable the greater utilization of electric vehicles, allow for grid scale energy storage, and meet the demands of new electronic applications, new materials for high energy density batteries must be developed. High capacity electrode materials like lithium metal have the potential to facilitate these technologies, but lithium metal electrodes are presently limited by significant side reactions, poor quality deposition, and the potential to form hazardous dendrites. Therefore, it is important to develop a clear understanding of the surface reactivity and growth behavior of the lithium metal at the interface with the electrolyte in order to enable stable long-term cycling.

The products that form as a result of electrolyte decomposition reactions at the electrode interface are known to be extremely important in determining the final cell performance. Specifically, fluorinated salts and solvent additives have been shown to enable stable cycling of Li metal anodes. This improvement is ascribed to the formation of LiF in the solid electrolyte interphase (SEI), yet the understanding of how LiF and other SEI compounds are formed and how they affect battery cycling is not complete. In this presentation, in situ spectroelectrochemical techniques including infrared spectroscopy (FTIR), differential electrochemical mass spectrometry (DEMS), and electrochemical quartz crystal microbalance (EQCM), are used to clearly identify components of the Li metal SEI. An understanding of SEI formation with respect to electrochemical potential and time will be discussed. With this understanding we provide new insights into the formation and chemical nature of SEI components that promote stable cycling of lithium metal electrodes.

Room Temperature Ionic Liquids (RTILs) are emerging materials for application in energy storage because of their wide physical stability, and large electrochemical window enabling the use of high voltage difference when used as electrolyte in capacitors. From a mechanical point of view, due to their solvent-free nature, the behaviour of RTILs strongly deviates from classical liquid description. The confinement of RTILs down to the nanoscale gives rise to exotic interfacial features resulting from the strong fluid-surface electrostatic interactions, thus highly dependent on the electronic nature of the surfaces. Then the exotic interfacial structural properties of RTILs confined with insulating surfaces have been extensively studied, but still need to be explored for metallic surfaces which are relevent for supercapacitors purposes. Furthermore, with the development of electrodes made of nanoporous materials in order to enhance the capacitance of RTILs based systems, it gets important to take into account the properties of RTILs under strong confinement.

Here, we use a tuning-fork based dynamic Surface Force Tribometer to experimentaly probe the mechanical properties of RTILs confined between extended gold surfaces. Our model sphere-plane geometry enables to probe the mechanical properties of RTILs confined in a 'slit' for which the size is controlled with nanometric resolution. For strong confinement, 'slit' size under some tens of nanometers, the RTILs undergo a dramatic confinement induced phase transition from a liquid to a solid state. Thus the overall ionic dynamics within this solid interfacial phase may be reduced as the ionic mobility sinks from the liquid to the solid state. By further measuring the mechanical properties of the nanoconfined RTILs, the system exhibits a glassy nature and eventually a shear induced fluidization. Eventually, exploring the mechanical properties of nanoconfined RTILs may enable to provide insights into the dynamics of such solvent-free electrolytes to be used in capacitive applications.

Ceramic solid-state electrolytes could potentially enable Li metal anodes, leading to safer and more energy dense Li-ion batteries. However, it has been hypothesized that electric field amplification at electrode edges can destabilize the interface and lead to short-circuiting under extended cycling. In this study, symmetric Li/ Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZO) cells were assembled with Li electrodes of varying geometries to observe the effects on Li electrodeposition. Modeling of the electric field distribution at the electrode/electrolyte interface showed that areas of high electric field were localized at sharp corners but uniformly distributed along regions of low, gradual curvature. To verify this, cells with varying electrode geometries were cycled under galvanostatic conditions until failure and spatial distribution of the degradation was analyzed using optical and electron microscopy. Critical current density was also measured to determine how electric field amplification caused by geometric effects impacts the cell performance. According to the models, isolated regions of high current density/curvature were shown to act as preferred sites for Li filament nucleation. This was experimentally confirmed by localized electrochemical impedance spectroscopy measurements. Non-uniform electric field distributions at the Li/LLZO interface could play a major role in determining cycling capabilities and failure modes of solid-state batteries. This may also have important implications for the manufacturing of Li-ion battery electrodes with geometry being a key consideration for increasing longevity.

Electrochemical stability windows of electrolytes largely determine the limitations of operating regimes of lithium-ion batteries, but the degradation mechanisms are difficult to characterize and poorly understood. Using computational quantum chemistry to investigate the oxidative decomposition that govern voltage stability of multi-component organic electrolytes, we find that electrolyte decomposition is a process involving the solvent and the salt anion and requires explicit treatment of their coupling. We find that the ionization potential of the solvent-anion system is often lower than that of the isolated solvent or the anion. This mutual weakening effect is explained by the formation of the anion-solvent charge-transfer complex, which we study for 16 anion-solvent combinations. This understanding of the oxidation mechanism allows to formulate a simple predictive model that explains experimentally observed trends in the onset voltages of degradation of electrolytes near the cathode. This model opens opportunities for rapid rational design of stable electrolytes for high-energy batteries.

Fire-retardant electrolyte formulations have attracted vivid attention recently given the surprising properties observed, with also the potential to solve the grand challenges of alkali-ion batteries: safety, use of metallic anodes and elevated anodic stability. Whereas these chemistries are still extensively studied and correlations are drawn to explain the enhanced electrochemical stability, one essential property - the redox potential - remains poorly characterized.
In this contribution we will report how the strong solvation (or coordination) of lithium cations by organic phosphates, the widely used flame-retardant constituents, induces a negative redox potential shift by as much as half of a volt (-0.5 V). Through a series of complementary 2- and 3-electrode measurements, with different reference electrode chemistries, we demonstrate that the redox potential shift is characteristic of mainly Li-cation (de)solvation processes whereas the redox potential shift of other, non Li-cation (de)solvation processes is negligible. Solvent coordination ratio, cation valence number as well as self-diffusion coefficients are determined via complementary NMR/DOSY methods and correlated with the electrochemical measurements. We will in particular highlight how these processes can impact the developments on high-energy hybrid battery concepts such as higher voltage dual-carbon (dual-ion) or organic batteries as well as the apparent enhancement of the anodic stability. These findings may also trigger the re-evaluation of the electrochemical stability mechanisms of the non-conventional battery electrolyte formulations towards a more realistic picture.
B. Ernould, (...), A. Vlad, 2019, submitted.

Ni-rich materials were used as cathode materials for lithium-ion batteries in electric vehicles(EV), plug-in hybrid vehicles(PHEV) and energy storage systems(ESS) due to their high energy density and rate characteristics. Ni-rich cathode materials were prepared by co-precipitation using ammonia. However, ammonia is highly toxic and corrosive, which is considered hazardous when exposed to humans. To resolve the above problems, it is necessary to replace ammonia with an eco-friendly chelating agent. Another problem with Ni-rich materials were related to LiOH/Li₂CO₃ impurities formed on the surface of cathode material upon exposure to air. The LiOH/Li₂CO₃ impurities reacts with the LiPF₆ electrolyte to form HF, which directly dissolves the transition metal ions of the cathode material, resulting in gas evolution and phase transition from layered to spinel.
In this study, spherical Ni_0.9Co_0.1(OH)₂ precursors were prepared by co-precipitaion using citric acid as a chelating agent. The cathode material was prepared by mixing precusor and LiOH H₂O and sintering at 680, 700, 720 and 740 °C. The excessive Li on the surface of the synthesized material was removed by washing and the electrochemical performance was investigated. Also, in order to improve the crystallinity of the prepared cathode materials, it was recalcined at 700 °C to investigate its electrochemical characteristics. The particle size distribution, particle shape and crystal structure of the cathode materials were analyzed by SEM and XRD. The prepared precursor had spherical shape and average particle size of Dv(50)=6 µm. The electrochemical performance of the coin cell using a cathode material fabricated by co-precipitation method using citric acid as a chelating agent in LiPF₆(EC:DEC=1:1 vol%) electrolyte was evaluated by the initial charge/discharge, cycle stability, rate capability, and electrochemical impedance spectroscopy(EIS). The initial charge/discharge efficiency of LiNi_0.9Co_0.1O₂ cathode materials prepared by recalcination was decreased, but the cycle capacity(187 mAh/g) and stability(85%) were improved and showed excellent rate capability.

Li₂MnO₃, a layered lithium-rich manganese oxide, is one of the potential high-capacity positive electrode materials among the Li containing transition metal oxide materials but its low electrical conductivity restricts its electrochemical activity. We recently found that Li–Mn cation disordering of the Li₂MnO₃ resulting in the formation of a NaCl-type structure improves electrochemical activity of the Li₂MnO₃ , i.e., a high initial discharge capacity of 320 mA h g⁻¹. However, its cycling performance is still poor probably due to structural instability, especially, oxygen emission during charging. In this study, we found that the structural stability of NaCl-type Li₂MnO₃ was significantly improved by forming a composite with spinel-type LiMn₂O₄ by mechanical milling. The initial discharge capacity of the composite of Li₂MnO₃ and LiMn₂O₄ in molar ratio of 1 : 2, was 379 mA h g⁻¹ (more than 1100 Wh kg^-1 per active material) which is much higher than those of precursor NaCl-type Li₂MnO₃ (320 mAhg^-1) and spinel-type LiMn₂O₄(298 mAhg^-1). This capacity corresponds to about 1.4 and 1.5 mol eq. Li ion insertion, i.e., the obtained electrochemical capacity of the sample cannot be explained by the redox reaction of Mn^3+/4+.
The 50th discharge capacity of the composite electrode showed more than 70% of the initial one, while less than 50% for NaCl-type Li₂MnO₃ electrode.
The LiMn₂O₄ component in the composite enhanced the structural stability of NaCl-type Li₂MnO₃, resulting in a restricted oxygen emission from the Li₂MnO₃ domain during charging confirmed by ex-situ XRD analysis and GC-MS. Such a structural stability leads to a better cycling stability and effective utilization of the oxygen redox reaction compared to pure NaCl-type Li₂MnO₃ resulting in the higher reversible capacity.

It is widely known that the crystal structures of the most of alkali halides are the rock-salt type. For alkali borohydrides (MBH₄), the rock-salt structures are also stable at room temperature. Because of the high affinity between halide and BH₄^- ions, alkali borohydrides form the solid solution with alkali halides for the whole compositional range (for example, NaI-NaBH₄ systems [1]). However, only lithium borohydride is the exceptional; the crystal structure of LiBH₄ is wurtzite [2]. Furthermore, the solid solution of LiI-LiBH₄ is not the rock-salt type but high temperature phase (H.T. phase) of LiBH₄ (wurtzite) is stabilized at room temperature, which is clear difference from the other MBH₄-MI systems [3].
At the present stage, the solubility limit of LiBH₄-LiI systems is under controversial. The solubility limit of LiI into LiBH₄ was reported to be 33 mol% when the samples was synthesized by sintering at 543 K [3]. On the other hand, 50 mol% of LiI could dissolve in H.T. phase of LiBH₄ by mechanical milling [4]. Although, the rock salt structure is the stable phase of LiI at room temperature, it was reported that hexagonal phase of LiI was observed at the temperature below 273 K [5], which is the same structure with H.T. phase of LiBH₄. Thus, it is expected that the solubility limit highly depends on the fabrication procedure and/or temperature. The purpose of this research is investigating the solubility limit of LiI-LiBH₄ systems fabricated by low temperature milling.
All of the samples were fabricated in Ar filled glove box. LiI-LiBH₄ systems were fabricated by ball-milling at low temperature. LiBH₄ and LiI were purchased from Aldrich Co. Mechanical milling was carried out by using chrome steel pot (45ml) and 10 pieces of balls (10 mm in diameter). First, the given molar ratio of LiI and LiBH₄ were mixed in the mortar and encapsulated in the air-tight milling pot. Subsequently, the samples were kept at 213 K for one hour. Then, mechanical milling was performed at 400 rpm for 5 minutes. After milling, samples were cooled at 213 K again. Above cooling and milling cycles were repeated for 60 times, which resulted in the total milling time of 5 hours. The crystal structures of the samples were characterized by XRD measurement. The measurement was conducted at room temperature. The Li⁺ ion conductivities were measured by AC impedance method with Li electrodes. For the conductivity measurement, the powder samples were pelletized at ca. 150 MPa for 30 seconds. The thickness and diameter of the pellets were ca. 2 mm and 10 mm, respectively.
From XRD measurements, it was indicated that 2LiI･LiBH₄ (LiI : 67 mol%) is single phase of the hexagonal structure. Because LiI concentration is larger than 50 mol%, it can be said that LiBH₄ is not the host lattice but BH₄^- ions were introduced to the hexagonal modification of LiI. More specifically, this result indicates that wurtzite-type LiI was stabilized at room temperature. Further increase of the LiI concentration yielded to the two phase mixture of hexagonal (LiBH₄-LiI system) and rock-salt (unreacted LiI) structures. It should be noted that relative peak intensity of rock-salt LiI was reduced when LiI-LiBH₄ systems were fabricated by low temperature ball milling. Therefore, it is suggested that low temperature milling is the effective method for the stabilization of the hexagonal phase of LiI at room temperature.

References
[1] M. Matsuo et al., Applied Physics Letters, 100 (2012) 203904.
[2] J-Ph. Soulie et al., J. Alloys and Compounds, 346 (2002) 200-205.
[3] R. Miyazaki et al., Solid State Ionics., 192 (2011) 143-147.
[4] H. Oguchi et al., Applied Physics Letters, 94 (2009) 141912.
[5] B. Wassermann et al., Solid State Communications, 65 (1988) 561-564.

Since the commercialization of Li-ion battery (LIB) in 1990s, it has been an essential energy storage technology for powering advanced portable electronics and now has been becoming a key enabler for transforming our society into sustainable energy paradigm by deploying electric vehicles and grid-scale applications for renewable energy sources. To realize this transformation, tremendous efforts have gone to develop high capacity electrode materials with low cost and high abundant raw materials. From now on, almost all Li-ion cathode materials are composed of only few transition metals such as Ni and Co, which are electroactive in layered cathode materials such as LiCoO₂ and Li(Ni, Mn, Co)O₂, causing constraints on their resources and availability. To replace Ni or Co with cheap and abundant Mn, developing Mn-rich electrode materials with high energy density will be very attractive. Recent study reports that Mn-rich electrode materials with disordered-rocksalt structure can achieve higher energy density than conventional layered materials by using Mn²⁺/Mn⁴⁺ double redox that was enabled by a fluorination process and high valent dopants. However, they still suffer from sluggish Li diffusion caused by fully cation-disordered structure and can be still lack of practical implementation.
In a departure from previous approaches, we take a strategy of enhancing reversible oxygen redox reaction for increasing energy density in Mn-rich materials by controlling of the atoms solubility. The resulting Mn-rich material can achieve the highest energy density, ~1100 Wh/kg among reported Mn-rich materials and deliver superior rate capability, up to 10C rate (3A/g). Interestingly, the superior rate capability with very high discharge capacity in the resulting material indicates that the Co-free Mn-rich material can be kinetically comparable to other only TM redox materials, contrary to previous observation in Mn-based materials.
We believe that the findings in this study can unlock the potential of Mn-rich electrode materials and will provide new avenues for the design of electrode materials that have high energy density and that can be practically implemented for high performance Li-ion batteries.

High Li⁺ mobility in electrode materials is required for high power Li-ion battery applications, enabling rapid charging and discharging rates. However, many conventional Li-ion electrode materials display slow ionic diffusion rates, leading to low capacity at high (dis)charging rate in bulk particles. Understanding and realising high ionic mobility in solids is also crucial for emerging sodium-ion and magnesium battery technologies, due to the larger size and high charge density of Na⁺ and Mg²⁺ respectively. For instance, mobility of Mg²⁺ in many oxides is extremely poor, and achieving reversible Mg²⁺ intercalation in oxide cathodes with both high capacity and high voltage at room temperature represents a major challenge in Mg battery development.

Transition metal oxides built from corner-sharing octahedra and the tetragonal/hexagonal tungsten bronze structure, but with empty interstitial sites reminiscent of ReO₃, have emerged as exceptional high-power Li-ion intercalation electrodes. Some materials in this family exhibit excellent capacity retention at high rates, which can be achieved in bulk particles without nanosizing. [1]

The corner-sharing framework of ReO₃ undergoes correlated distortions and rotations upon Li⁺ intercalation, which stabilise the Li⁺ ions and limit their mobility. [2] In contrast, bronzes that allow high-rate intercalation comprise some degree of edge-sharing among polyhedra in the ab crystallographic plane. These provide structural rigidity, limiting framework distortions, and leading to ions occupying ‘frustrated’ intercalation sites. [1,3] Mobility of ions is enhanced when moving between frustrated sites, due to a smoothing of the potential energy surface. [4]

Here we present results of hybrid-exchange DFT calculations on a range of materials with bronze-type structures, including ReO₃, T-Nb₂O₅, V₂O₅, V₄Nb₁₈O₅₅, and Mo_2.5+yVO_9+δ. [5] These materials display a range of structural features and connectivity including differently sized channels, c-axis separation, and elemental composition. We compare the behaviour of Li⁺, Na⁺ and Mg²⁺ ions, thus exploring the effects of both varying ionic size and charge on intercalation and mobility.

Our calculations reveal that the smaller Li and Mg ions adopt frustrated coordination sites in some of the frameworks, whilst Na ions typically occupy stable sites with high coordination number due to their larger size. Low energy migration pathways exist between some sites for Li⁺ and Mg²⁺, indicating bronzes can be used to achieve high mobility for these ions. We also identify high energy regions in certain structures through which ions are unlikely to move, and thus represent bottleneck for ionic mobility under ambient temperature conditions. We can therefore begin to establish design principles for achieving high ionic mobility in bronzes for Li-ion battery materials and intercalation chemistries employing other charge-carrying ions.

[1] Griffith, K. et al., Nature, 559, 556–563 (2018)
[2] Bashian, N. H. et al., ACS Energy Lett., 3, 10, 2513-2519 (2018)
[3] Chen, D. et al., J. Am. Chem. Soc., 139 20 7071-7081 (2017)
[4] McColl, K. and Corà, F., J. Mater. Chem. A, 7, 3704-3713 (2019)
[5] McColl, K. and Corà, F., Phys. Chem. Chem. Phys., 21, 7732-7744 (2019)

Lithium-ion batteries have remained a state-of-the-art electrochemical energy storage technology for decades now, but their energy densities are limited by electrode materials and conventional liquid electrolytes can pose significant safety concerns. Lithium metal batteries featuring Li metal anodes, solid polymer electrolytes, and high voltage cathodes represent promising candidates for next
generation devices exhibiting improved power and safety, but no solid electrolytes have been identified that exhibit the requisite electrochemical properties and thermal stability. Here, we report an interpenetrated network polymer with weakly coordinating anion nodes that functions as a high-performing single-ion conducting electrolyte, with a wide electrochemical stability window, a high room temperature conductivity of 1.5 × 10⁻⁴ S cm⁻¹, and exceptional selectivity for Li-ion conduction (t_Li+= 0.95). Importantly, this material is also flame retardant and highly stable in contact with lithium metal. Significantly, a lithium metal battery prototype containing this solid electrolyte is shown to outperform a conventional battery featuring a polymer electrolyte.

An area of growing interest in electrolyte research for electrochemical devices is Deep Eutectic Solvents (DES), which are formed from two different components whose mixture has a lower melting point compared to its components and one of them (essentially, the halide salt part) acts as a hydrogen bond donor (HBD) and the other as acceptor (HBA) [1,2]. Understanding the relation between chemical structure and physical-electrochemical properties of DES is of paramount importance in the design of new electrolytes. In this work, fast field cycle nuclear magnetic resonance (FFC NMR) relaxometry techniques are used to study the molecular dynamics of DES composed of choline chloride (ChCl) and glycerol. By measuring proton spin lattice relaxation rate dispersions at different molar concentrations of ChCl and at different temperatures with regular and deuterated glycerol, we investigate factors such as hydrogen bond disruption which may be involved in ionic conduction. Dynamics extracted from the relaxation profiles are compared with results obtained by other techniques, including broadband dielectric spectroscopy data obtained by collaborators.

References
[1] Q. Zhang, K. De Oliveira Vitier, S. Royer, and F. Jerome. Chemical Society Reviews 41, 7108 (2012).
[2] M. H.Chakrabarti, F. S. Mjalli, I. M. AlNashef, M. A. Hashim, Hussain, M. A., Bahadori, L. & Low, C. T. J., Renewable and Sustainable Energy Reviews 30, 254 (2014).

This work was supported by Breakthrough Electrolytes for Energy Storage (BEES) - an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409.

The application of high-energy lithium-ion batteries (LIBs) has been expanded from mobile electronics to electric vehicles (EVs) and energy storage systems (ESSs). However, accidents of the explosion of LIBs not only for small-scale ones but also large-scale ones such as EVs happened frequently in recent years. Accordingly, the safety issue of conventional LIBs, originating from the use of organic liquid electrolytes, has emerged as a serious concern. In this regard, all-solid-state batteries (ASSBs) are one of the most promising next-generation battery systems. Especially, ASSBs employing sulfide solid electrolytes show outstanding performance, compared with those fabricated using oxide or polymer solid electrolytes. Sulfide solid electrolytes have a critical advantage of deformable property besides the high ionic conductivity, enabling intimate contacts with active materials by the simple cold pressing process. Furthermore, several sulfide solid electrolytes such as Li₆PS₅Cl and LiI-Li₄SnS₄ are reported to be fully dissolved in solvents without side reactions and to be recovered by eliminating solvents and the subsequent heat-treatment, i.e., solution-processable, which allows to directly coat solid electrolytes onto active materials or to infiltrate conventional LIB composite electrodes with solid electrolytes. Thus, the solution process of solid electrolytes could be an effective protocol to realize the scalable production of ASSBs with high energy density. Unfortunately, only a few candidates of solution-processable sulfide solid electrolytes (e.g., (LiI-)Li₄SnS₄, Li₆PS₅X (X = Cl, Br, I), (NaI-)Na₃SbS₄, Na_4-xSn_1-xSb_xS₄) have been reported so far. Moreover, the decrease of ionic conductivity after the solution process by approx. an order of magnitude is common.
In this presentation, compositional tuning of argyrodite sulfide SEs via the solution process and its resulting electrochemical performances for ASSBs are presented.

The accelerating development of portable electronic devices and electric vehicles increases the demand for better secondary batteries. Rechargeable Li-ion battery (LIB) is a representative secondary battery system, displaying a large energy density and high power. On the other hand, because conventional graphite anodes have a small theoretical capacity and slow rate-capability, the development of Li-alloy-based anodes is required for the realization of high-performance LIBs. Therefore, various Li-alloyable materials have been pursued for increasing the anode capacity. Among the Li-alloyable materials, many studies have focused on Sb-based systems because of its high gravimetric (Li₃Sb: 660 mAh g^-1) and volumetric capacities (~4370 mAh cm^-3). Although Sb-based systems have a higher energy density, they suffer from poor cycling behavior because a large volume change occurs during discharge/charge. Therefore, many studies have focused on Sb-based intermetallics and their nanostructured composites to alleviate or minimize the volume change that occurs during cycling.
In this study, to enhance the electrochemical behavior of the Sb, the intermetallic Nb₅Sb₄ compound was synthesized by a simple solid-state method and tested its electrochemical properties for use as LIB electrodes. The reaction mechanism of intermetallic Nb₅Sb₄ compound was examined during Li insertion/extraction using various ex-situ analytical tools, such as X-ray diffraction (XRD) and Nb K-edge extended X-ray absorption fine structure (EXAFS) and differential capacity (dQ/dV) plot. Additionally, the intermetallic Nb₅Sb₄ compound was tested as high performance Sb-based anodes for Li-ion battery.
Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) grant, funded by the Korea Government (MSIP) (NRF-2018R1A2B6007112, NRF-2018R1A6A1A03025761).

As the development of electric vehicles and portable electronic devices accelerates, the needs for improved secondary batteries have risen considerably. A rechargeable Li-ion batteries (LIBs) are a representative energy storage system due to its high operating voltage and energy density. However, commercial graphite anodes in LIBs show relatively good electrochemical performance, it has a low theoretical capacity and slow rate capability. Among the representative Li-alloy-materials (Si, Ge, Sn, P, and Sb), which exhibit higher theoretical capacities than commercial graphite anodes, the Sn-based anodes are considered as alternative anode materials due to higher conductivity and volumetric capacity than that of the other anode materials.
To design an easily manufactured, large energy density, highly reversible, and fast rate-capable Li-ion battery (LIB) anodes, Fe-Sn intermetallic compounds were synthesized, and their potential as anode materials for LIBs were investigated, including ex situ X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) analyses at the Fe K-edge, along with a differential capacity plots (DCPs). Among the Fe-Sn intermetallic compounds, FeSn₂ was selected on the basis of the electrochemical performances. To improve the electrochemical performance of FeSn₂, it was modified using various transition metal carbides of TiC, WC, and SiC, which acted as a buffer matrix against the volume expansion during cycling. Furthermore, carbon black was used to manufacture FeSn₂/TiC/C nanocomposite for stable cycling. The easily manufactured FeSn₂/TiC/C nanocomposite for the Sn-based Li-ion battery anodes showed large energy density (first reversible capacity of 572 mAh g^-1), high reversibility (first coulombic efficiency of 74.3%), long cycling behavior (95% capacity retention after 200 cycles), and fast rate capability (approximately 458 mAh g^-1 at 3C rate).

Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) grant, funded by the Korea Government (MSIP) (NRF-2018R1A2B6007112, NRF-2018R1A6A1A03025761).

To meet increasing demands for energy storage, many recent battery researches are devoted to new electrode chemistries and reaction mechanisms that promise substantial increase in energy density. Traditional positive electrode materials for lithium-ion batteries such as LiCoO₂ and LiFePO₄ rely on the redox reaction of the transition metal within the structure for charge-discharge. Though, the capacity is low because of their small charge-to-mass ratio. To break away from conventional thinking, here, we turn inexpensive Cu and Al foils, the common current collectors, into active materials as positive and negative electrodes, respectively, that undergo electrochemical reactions and charge transfer to store energy. The electrochemical reactions at the electrodes are given by
Cathode: Cu (s) ↔ Cu⁺ + e^-
Anode: Al (s) + e^- + Li⁺ ↔ AlLi (s)
Here, we are successful in constructing a 3 V Cu-Al full cell the battery by coupling a Cu foil as the positive electrode with an Al foil as the negative electrode in LiTFSI-based aprotic electrolyte. During cycling, the charge transfer on the Cu electrode is achieved by stripping and deposition of Cu/Cu⁺, while that on the Al electrode is carried out by the alloying and dealloying reactions between Li and Al. TFSI^- anions migrate through the anion exchange membrane to balance the charge. Stable cycle performance is possible with the use of a highly concentrated electrolyte - a 3 V cell exhibits excellent cycle stability for more than 200 cycles in 6M LiTFSI DMC electrolyte.
Raman spectroscopy, electrochemical impedance spectroscopy (EIS), field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) were conducted on the Cu-Al cells and electrodes to further understand the reasons for the improved performance in the highly concentrated electrolyte. We found that the highly concentrated electrolyte suppresses Cu cross-over with the formation of large solvation structure, which also promotes smooth and non-dendritic Cu-metal plating, enhancing the long-term stability of the cell. XPS measurements show that an SEI derived from TFSI^- effectively passivates the surface of the Al electrode during initial cycling, leading to excellent capacity retention. Besides AEM, other common membranes, for example polypropylene, are also being examined as alternatives. More investigations on the interactions between the membrane and the solvation structure of electrolyte are underway.
Our findings demonstrate a novel 3 V battery that can be easily fabricated by putting two common metal foils (Cu and Al) together without any active material coating. Our Cu-Al battery can give a volumetric energy density of the range of 79-156 Wh L^-1, comparable to that of state-of-the-art all-vanadium redox flow batteries, and has potential to be used for future grid storage applications.

Lithium-ion capacitors (LICs) incorporate the fundamental features of intercalation battery materials and double-layer capacitor materials, to bring together the desirable combination of high energy and power densities, long cycle life and materials stability. But, the presence of battery materials in anode also contribute towards LIC’s long-term capacity fade, based on its extent of utilization. This work studies the importance of anode to cathode capacity ratio, and its influence on the electrodes potential variation and capacity decay behaviors. In a LIC system based on activated carbon (AC) and hard carbon (HC), we show that increasing the HC:AC capacity ratio from 1.1 to 3, boosts the capacity retention of the LIC by 10% after 2,000 cycles at 1C rate, and by 28% after 20,000 cycles at 60C rate. During the intermittent EIS and 3-electrode galvanostatic tests at 0.25C rate, lower anode over-potential is observed for LIC with larger anode to cathode capacity ratio. Pointing towards a reduced charge transfer and Warburg diffusion resistances, based on the potential at which the anode was operating. We show that for LICs with different anode to cathode capacity ratios, the difference in cell impedances originates from the difference in anode potential or degree of lithiation, and anode inter-planar distance expansions and contractions. The 1C and 60C rates long term tests , and intermittent EIS and 3-electrode tests at 0.25C rate were all in agreement that LIC with larger HC:AC capacity ratio had a better electrochemical performance.

As the most expensive and important part of Li-ion batteries (LIB) is the cathode, developing high performance cathode material is vital for large-scale application of next generation LIB. NCM cathode materials have been used commercially due to its high energy density. For example, LiNi_0.6Mn_0.2Co_0.2O₂, a kind of Ni-rich NCM cathode, has higher capacity, which have emerged as an ideal cathode material for LIB. However, its capacity is not high enough to reach the theoretical capacity, so the capacity of NCM622 still needs to be improved. Element doping is an efficient way to improve the electrochemical properties of cathode materials, and several mono- and multi-valent doping cations have been used to dope NMC622. Here, Cu-doped NCM622 cathode (CuNCM) was prepared by a coprecipitation process. The cyclic voltammetry profile showed the obvious wider peak than the virgin NCM. From XRD results, the strongest peak shifted to higher angle and the lattice parameter is smaller in the refinement. The specific capacity of CuNCM is 186 mAhg^-1 and 180.5 mAhg^-1 in first cycle at 0.1C and 0.33C between 3 to 4.3 V, which is 14 mAhg^-1 higher and 17 mAhg^-1 than the virgin NCM respectively.

In the context of Lithium Batteries (LB), Lithium Metal Batteries (LMBs), are considered a promising technology for meeting increased capacity and power demands, both for intermittent, renewable energy sources, and Electric Vehicles (EVs). With LMBs come particular challenges and obstacles, among which dendrite growth has been a significant concern for the LB research community. Fruits of research efforts have included exploring general strategies for preventing/stopping dendrites. This has been traditionally attempted with solid electrolytes that are either strong enough to halt dendrite advancement (high modulus materials), or prevent excessive concentration gradiens (single-ion conductors).

In the latter category the highest Li+ conductivities are often found in inorganic materials such as ceramics, glasses or glass-ceramics. Conductivities are usually 1-2 orders of magnitude below traditional liquid electrolytes, though some systems have comparable conductivities. With the choice of a hard, inflexible electrolyte comes the challenge of impedance contributions from the electrode-electrolyte interface, as well as instability against the anode and even cathode.

A possible solution to the larger issue of ceramic electrolytes’ brittleness and fragility is to use them in a pulverized form, and combine with an appropriate binder. Binders generally are softer and able to conformally adhere to the electrodes, solving the electrode-electrolyte interface, and grain boundary problems.

While this should be a straightforward solution, binders and ceramics tend to have dissimilar properties, such that there is lack of intimate contact, thus shifting the interfacial problem to the ceramic-binder interface. If unaddressed, ionic conduction happens preferentially in the organic binder, which almost inevitably has inferior ionic conductivity, and the ironically supposed compatibilizing component becomes the rate-limiting step. It is within this smaller context that this work takes place, seeking to develop a suitable electrolyte-binder interface.

Currently, a silica (SiO₂) mediated electrolyte-binder coating is being developed for a commercial, proprietary lithium ion conducting glass-ceramic (LICGC^TM) electrolyte, functionalized with opportune moieties. A silylated SiO₂ layer includes Li-solvating poly(ethylene oxide) (PEO) chains, as well as 2 different immobilized, pendant anion groups. The plan is to explore these moieties' effects on maintaining suitable conductivity values and minimizing concentration gradients at the interface, as well as avoiding dual ion conduction, as would be the case for LiX-based systems.

The formation of the silylated coating is achieved by a modified sol-gel method, starting with hydrolyzable silicon alkoxides (also known as silanes), with at least one group being non-hydrolyzable, and incorporating one of the above mentioned moieties.
In the case of silanes with PEO, these are referred to as monopodal (one silane group on one end of PEO) or dipodal (one silane group on both ends) PEG-silanes, while silanes with pendant anions (PA) are referred to as PA-silanes. Combinations of different silanes in different feed ratios have been explored, along with the incorporation of LiTFSI as a lithium source in select compositions. The alkoxides employed are either commercially available, or synthesized.

In this initial work, the bulk properties of these coatings have been explored. These have included thermal characterization by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), as well as electrochemical characterization by temperature-dependent conductivity through electrochemical impedance spectroscopy (EIS). Ongoing work has included bulk EIS characterization LICGC^TM wafers with different thicknesses of SiO₂.

In this work, Nuclear Magnetic Resonance (NMR) Diffusometry was used to investigate the transport properties of sodium electrolytes for two different materials systems. Variable-Temperature PFG NMR was performed on samples of NaPF6 salt dissolved in glycol dimethoxy ethers (glymes), a novel electrolyte for use in Electric Double-Layer Capacitors (EDLCs), as well as NaPF6 in mixtures of Ethyl Carbonate (EC), Propylene Carbonate (PC), Diethyl Carbonate (DEC), and Fluoroethylene Carbonate (FEC), at various concentrations. Self-diffusion Measurements for ¹H, ¹⁹F, and ²³Na were taken from 0-60°C, and ionic conductivities were calculated from the Nernst-Einstein relation:

σ_NMR = F²[C]/RT * (D_cation + D_anion)


Where is the ionic conductivity, F is Faraday’s constant, R is the ideal gas constant, T is the temperature in Kelvin, C is the molar concentration ,and D_cation and D_anion are the self- diffusion coefficients for the cation and anion, respectively. The results indicate significant ion pairing effects which increase with both increasing temperature and decreasing glyme molecular mass. We have also investigated ionic liquid-based Na electrolytes, and these results will be discussed in the context of practical use for Na-ion electrolytes for commercial energy storage.

Li-ion battery (LIB) has promoted the growth of global market such as portable electronic devices, personal mobilities, unmanned aerial vehicles and long-range electric vehicles. Over two decades of dedicated researches and developments, the energy density of LIB has increased about 2 times since its commercial release. However, it has been mostly achieved by the improvement in battery manufacturing technologies, and only little change has been made in active materials and their chemistry, reaching their own theoretical limitations. In this regard, exploring next-generation energy storage materials that satisfies high energy density and low cost is essential. Extensive studies on next-generation energy storage materials have narrowed down some candidate materials and sulfur has shown the most promising results among them. Its advantages such as its high theoretical capacity, natural abundance, non-toxicity and low cost render sulfur an attractive choice. However, lithium-sulfur battery suffers from rapid capacity fading and shuttling phenomena caused by reaction intermediates called lithium polysulfides (Li₂S_x, 4 ≤ x ≤ 8). Low electronic conductivity of sulfur and reaction products also compels introduction of large amount of conducting carbon, lowering practical energy density of lithium-sulfur battery. Many efforts for encapsulating sulfur using polar conductive matrices (doped carbon, conducting polymers) have been made to alleviate these problems, however, most of the approaches are proven to be effective only for few hundreds of cycles. Instead of exploring bulky heavy materials for lithium-sulfur battery, we propose highly reactive electrolyte additive, which can immediately react with lithium polysulfides to form thin solid layer and results in effective blocking of migration of lithium polysulfides to anode side. Chemical composition of the material formed in-situ as well as its electrochemical property was investigated and possible reaction mechanism, corresponding cell performance and desirable structure of additive will be suggested.

All solid-state supercapacitors (SCs) have received significant research interest as a shape deformable power supply device owing to the recent progress in portable, lightweight, and flexible electronics/optoelectronics. SCs typically exhibit fast power delivery rates, long life cycles, a wide range of operating temperatures, and good operational safety compared to rechargeable batteries. However, their low energy density limits the use of SCs in broader applications. To overcome the low energy density of the SCs, we employed three-dimensionally interconnected large mesoporous carbons (49 nm) to electrochemically stable ionic-liquid (IL) based solid polymer electrolytes (referred to as ionic gels). Precisely designed large mesopores interconnected through windows provide effective transport pathways for the electrolyte ions, while the well-developed micropores render a large active area for capacitive charge storage. The resulting SCs showed excellent energy storage performance such as specific capacitance of 323 F g^-1 and record-high energy density of 179 Wh kg^-1. Furthermore, the high energy and power densities obtained in this work exceed the upper bound of Ragone plots constructed based on aqueous-, organic-, and IL-based EDLCs reported to date. We also demonstrated the flexible all-solid-state SCs with an outstanding energy storage density (115 Wh kg⁻¹) that are suitable for bendable and foldable electronic devices. We believe these results provide design principles for developing high-performance SCs using electrochemically stable but dynamically slow ILs or IL-based solid electrolytes.

Owing to their highest energy density compared to other commercially available energy storage devices, rechargeable lithium-ion batteries (LIBs) are indispensable device in modern society. In addition to the daily applications, LIBs are also expected to be used for cutting-edge fields such as deep-see, space, and other planets. In order to extend the application filed of LIBs, understanding of electrochemical behavior of LIBs at extreme environments is required. In addition, basic understanding of effects of pressure for battery operation is very important to improve reliability and safety of LIBs. Here, we report Li-ion storage properties of LiMn₂O₄ electrodes under extremely high-pressure condition up to 100 MPa.
In order to perform electrochemical experiments under high-pressure condition, we developed a two-electrode-type cell in this study. The cell was immersed in an insulating silicone-oil (pressure medium) and hydrostatic pressure generated by a hand-pump was applied through a free-piston. Galvanostatic charge-discharge tests, galvanostatic intermittent titration measurements (GITT), and electrochemical impedance spectroscopy (EIS) were performed. In the measurements, a Li-metal foil, and LiMn₂O₄ coated on Al foil (LiMn₂O₄ : carbon black : PVdF = 6 : 3 : 1 in weight ratio) were used as anode and cathode, respectively. A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) solution (EC : DEC = 1 : 1 in volume ratio) containing LiClO₄ (1 mol L-1) was used as the electrolyte. A glass-fiber filter was used as separator. All test cells were constructed in high-purity Ar-filled glovebox.
We confirmed that the reversible capacity of LiMn₂O₄ electrode at 25°C was not changed up to 100 MPa. In the meantime, plateau potentials corresponding to Li-insertion/extraction reaction was changed by the pressure. It was found that charge transfer resistance of the LiMn₂O₄ was clearly decreased with increasing pressure. It was also found that the thermal stability of LiMn₂O₄ was dramatically improved under high pressure condition: Under 100 MPa condition, the LiMn₂O₄ electrode showed good cyclability even at 55°C. On the other hand, reversible capacity of the electrode was dropped within 2 cycles at 0.1 MPa-55°C condition. These results indicate that LiMn₂O₄ cathode has great potential for special batteries for high-pressure application (deep-sea exploration etc.).

Since its introduction, the research community has been engaged in efforts to replace the state-of-the-art graphite anode used in commercial Li-ion batteries with novel high-capacity materials. Among several candidates, silicon-core carbon-shell nanoparticles -NPs- are considered one of the most promising choices due to their good electrochemical performance and high gravimetric and volumetric storage capacities. Although a wide range of different Si-C nanocomposites have been proposed over the years, establishing a rational understanding of how the material structure and properties influence the battery performance is far from trivial. For instance, the influence of the presence and quality of the carbon (i.e. graphitization degree) on the electrochemical performance of the synthesized materials is still not well understood. We have investigated a novel approach to address this question through a modified Chemical Vapor Deposition -CVD- approach that enables a fine and precise tailoring of carbon coating graphitization degree on Si NPs. Our composite Si-C materials are produced by starting from the same raw silicon nano-powders, which allows for direct comparison of carbon shell contributions as the silicon cores are identical. The NPs are coated in a conformal layer of amorphous carbon resulting from the thermal cracking of C₂H₂ at 650 °C. After removing C₂H₂ from the reaction zone, the temperature is increased to 1000°C in Ar permitting controlled graphitization of the C-shell. Notably, both TEM and Raman analysis have shown no detectable presence of silicon-carbide in the synthesized materials. The as-produced composites have been tested in Li-ion battery half-cell assemblies. Both the amorphous-C-coated and graphitic-C-coated Si NPs exhibit a high first cycle coulombic efficiency of 87% with capacities around 1800 mAh g^-1. However, after 100 cycles the amorphous-C-shell rapidly decays to a capacity retention of 34% while the graphitic-C-shell drastically enhances the cycling stability showing a capacity retention above 71%. To explain this phenomenon, we then observed the lithiation process through in-situ TEM measurements. Highly graphitic carbon markedly improves the structural stability of the composite particles and strongly favours the passage of lithium ions into the silicon core with respect to a purely amorphous carbonaceous material. This interpretation is confirmed by EIS analysis, displaying a stark reduction of both SEI and Charge Transfer impedances for a carbon layers with high a graphitization degree. Finally, we demonstrate that the silicon-graphite composites produced also work as a functional “drop-in” additive in graphite dominant anodes. The addition of 10% in wt of the Si-based active material enables the fabrication of electrodes with areal capacity around 3 mAh/cm², gravimetric capacity 60% higher than the one of a pure graphite electrode, first cycle CE of 90% and capacity retention of 81% over 100 cycles.

Lithium-oxygen batteries (LOBs) can achieve a large energy density (> 3500 Wh/kg) through the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) during the discharge and charge processes. In the LOBs, the oxygen-cathodes can improve the efficiency of discharge-discharge cycle through effective ORR and OER. Carbon is used as a support for the catalyst applied to the conventional air electrode. However, the carbon-electrolyte interface causes side-reactions such as the formation of by-products and then exhibits a large overpotential between charge-discharge. Therefore, a carbon-free catalyst supports capable of suppressing side-reactions is required. Transition metal oxides have attracted interest to replace carbon-based catalyst supports.
This work investigated the Ti₄O₇ crystal structure as a chemically/physically stable catalyst support. Initially, anatase-TiO₂ was synthesized by sol-gel synthesis method. Thereafter, in order to control the anatase-TiO₂ phase to the Magnéli-Ti₄O₇ phase, reduction heat treatment was performed in an H₂ gas atmosphere. Magnéli-Ti₄O₇ has the best electrical conductivity among titanate crystal structures. The electric conductivity of Magnéli-Ti₄O₇ is improved due to oxygen vacancies with Ti³⁺ cations on the (110) surface plane. Therefore, since the characteristics that can efficiently transfer electrons to the catalyst are obtained, Magnéli-Ti₄O₇ can exhibit excellent charge-discharge performance with the stable charge-discharge overpotential than anatase-TiO₂.
We investigated the phase transition of Magnéli-Ti₄O₇ with anatase-TiO₂ through XRD, TEM, XPS, etc. In electrochemical properties such as cyclic voltammetry and galvanostatic cycle tests, Magnéli-Ti₄O₇ was proved an excellent catalyst support through the introduction of RuO₂ catalyst.

3D printing is an additive manufacturing (AM) technique that has attracted extensive attention for both industry and academia because it enables direct printing of multifarious, delicate, and complex structures in a low-cost, adjustable and scalable way. 3D printing also provides a facile route to fabricate advanced architectures and systems for a broad range of applications: energy, biotechnology, microfluidics, electronics, and engineered composites. In this work, we demonstrated electrical double layer supercapacitors using 3D printed activated carbon-based porous materials. Supercapacitors typically show intermediate characteristics of conventional electrolytic capacitors and secondary batteries and have outstanding advantages such as rapid charge/discharge rates, high efficiency, a wide operating temperature range, and a semi-permanent lifetime. The porous carbon-based electrode inks developed in this work were printable in various shapes: lattice, rectangular, circle, pyramid, spiral and so on. They can also be stacked in multiple layers to increase electrode surfaces for capacitive energy storage. For the device fabrication, multi-stacked/interdigitated electrodes were designed and generated and the resulting energy storage performance was studied. As an electrolyte layer solid-state polymer gel electrolytes consisting of ionic liquid and host polymer networks were employed. To evaluate the electrochemical performance, cyclic voltammetry measurements were performed at various scan rates and the devices showed the reversible energy storage characteristics in the investigated operating voltage window. In addition, galvanostatic charge/discharge properties of the supercapacitors were examined at various current densities and the devices exhibited triangular shaped charge/discharge profiles.

The constant technological development and the increasing mobility lead to the necessity of new ways of energy generation and storage [1].
Lithium ion batteries are increasingly used in portable devices and show some advantages when compared to other battery systems, due to higher energy storage, high capacity and higher number of charge-discharge cycles.
Membrane separators are one of the key components of battery systems, the most important characteristics of these membranes being porosity, ionic conductivity, good mechanical properties and chemical stability [2].
Poly(vinylidene fluoride) (PVDF) and (vinylidene fluoride) (VDF) copolymers such poly(vinylidene fluoride – co – trifluoroethylene) (PVDF-TrFE) are known for its excellent chemical resistance, mechanical properties and outstanding electroactive properties [3].
In the present work, porous poly(vinylidene fluoride-cotrifluoroethylene) (PVDF-TrFE) separators with different patterned surfaces constituted by arrays of hexagons, lines, zig-zags and pillars microstructures and their influence on battery performance. In addition, computer simulations allow to deeper understate the influence of the patterned surface on battery response.
The discharge capacity efficiency of batteries with zig-zag micropatterned separators is the largest among the patterned separators, being 804% higher than the one for batteries with non-patterned separators.

Si based anode materials for lithium-ion batteries have high theoretical capacity(3,580 mAhg^-1), but they have critical limit for commercial use because of their poor cycle performance associated with severe volume changes during lithium insertion and desertion. Our previous work, two-dimensional(2D) SiO_x nanosheets electrode showed highly stable cycle performance and excellent dimensional stability because of physical nature of 2D nanostructure such as short diffusion length and abundant pore formed between stacked 2D nanosheets. However, their low reversible capacity has been a drawback to compete with other commercial material. In this work, we suggested 2D SiO_x nanosheets and 0D Si nanoparticles hybrid materials using abundant intra-nanosheets pores in the stacked 2D SiO_x nanosheets. The hybrid material delivered much improved reversible capacity more than 825 mAhg^-1 with higher initial efficiency compared to those of 2D SiO_x nanosheets without sacrificing other anodic performances.

With the current target of numerous countries to push electro mobility to the mass market, the demand for high performance batteries has increased drastically. Currently, the next goals on the roadmap are to achieve sufficient mileage and to reduce charging time of electrical vehicles. To accomplish these goals, the energy density as well as rate capability of lithium-ion batteries (LIBs) needs to be increased.

Silicon is widely recognized as the most promising component in high-capacity anode materials for next-generation lithium-ion batteries (LIBs) owing to its natural abundance, relatively low working potential, and its high theoretical storage capacity of 3579 mAh/g. However, the practical application of Si-based anodes is severely hindered by its low intrinsic electrical conductivity and its large volume change (>300%) during charging and discharging. The resulting mechanical stress causes rapid pulverization of the silicon and insulation and disconnection of the active material from the current collector. These failure events can cause rapid degeneration of the Si electrode and is especially prominent for silicon particles exceeding the size of a few hundred nanometres. Thus, recent research mainly focusses on nanostructures and nanocomposites that can tolerate the volume change.

A very promising way to stabilize silicon in LIB anodes is the incorporation of nitrogen, which has been shown to significantly improve the cycle performance. We therefore developed a gas-phase synthesis method based on the pyrolysis of monosilane in ammonia-rich atmosphere. Production rates are as high as 30 g/h and can be easily scaled. Based on this technology we are able to synthesize high-performing SiN_x nanoparticles for lithium-ion battery anode. Moreover, their electrochemical properties can be designed by adjusting the synthesis parameters, thus affecting Si/N stoichiometry, particle morphology, size, and crystallinity.

We further demonstrate that SiN_x nanoparticles with medium nitrogen content show significantly enhanced cycling performance of LIB-electrodes compared to pristine silicon. They show an initial specific discharge capacity as high as 1400 mAh/g and a highly stable cycle performance with a capacity retention of 96% after 100 cycles and over 80% after 500 cycles. Rate capability tests show that more than 60% of their capacity can be retained at a charging/discharging rate of 10 C. These results imply that silicon-rich SiN_x based LIB electrodes are promising candidates for high-performance lithium-ion batteries with very high durability.

Although Lithium-ion batteries (LIBs) have been regarded as fascinating energy storage device, the scarcity and high cost of lithium resources intrigue researchers’ interest in the next-generation batteries such as Potassium-ion batteries (KIBs) which have similar electrochemical characteristic of LIBs and use abundant potassium resources. However, to date there are still significant problems about searching suitable anode materials for KIBs because of hazardous of potassium metals and unstable cycle performance of carbonaceous materials due to large ionic size of potassium. Herein, we report ordered mesoporous niobium nitride/N-doped carbon composites hybrids (m-NbN/NC) as anodes for KIBs with superior cyclability and rate capability. The electrode delivers reversible capacities of 143 mA h g^-1 at 0.01 A g^-1 and 49 mA h g^-1 at 1 A g^-1. More impressively, the capacity retention of 100% at 0.5 A g^-1 after 2000 cycles could be achieved. In situ X-ray diffraction and ex situ SEM analysis indicates that m-NbN/NC electrode retains its structural integrity during potassiation and is accompanied by small strain, which is ascribed to high proportion of surface-controlled reaction. This work may suggest feasible new class of anode materials for ultra-stable KIBs.

Coating silicon nanoparticles (nSi) with cyclized polyacrylonitrile (PAN) is one approach to address the large volume expansion of silicon when used as an electrode material in solid-state batteries. This also enables the use of industrial processing techniques and inexpensive materials that can provide high active material mass loading with large reversible capacity. While previous studies have demonstrated success in using these materials to maintain high energy densities over long cycling life, comprehensive characterization is still needed to supply critical details needed for further optimization and extension to different material systems. In this work we focus on analysis of solid-state sheet style electrodes (nSi-PAN) and the interface with the LPS (Li₂S-P₂S₅) solid electrolyte. This analysis was performed in cross-section after fracturing and polishing the exposed surface using Ar⁺ion milling. All sample preparation and subsequent characterization was performed without exposure to atmosphere so that no unintentional oxidation of the material would obscure true material properties. Devices were studied in the initial uncycled state and also at full delithiation after extensive cycling. SEM-based EDS mapping has revealed that there are changes in the spatial distribution of the nSi particles after cycling devices extensively. Additionally, sulfur from the solid electrolyte appears to have migrated into the nSi-PAN layer after cycling. No sulfur was observed in this layer prior to device cycling. A more complete understanding of how these changes relate to device performance was attained by correlation with electronic characteristics (scanning spreading resistance microscopy (SSRM)) and nano-scale evaluation of the structure and chemistry using scanning transmission electron microscopy (STEM). Through connecting the observed device characteristics with micro- to nano-scale structure, chemistry, and electrical properties, this work provides critical information regarding the cycling behavior of nSi-PAN based electrodes that can be used to further optimize these materials for use in all solid-state batteries.

To achieve improvement in the performance and energy density of lithium ion batteries, there is a high demand for novel electrolytes. Solid polymer electrolytes (SPEs) are now becoming increasingly attractive for LIBs because of their excellent properties such as high safety, easy fabrication, low cost, high energy density, good electrochemical stability and excellent compatibility with lithium salts. Polymers may also act as hosts for ions.
PEO is a polyether compound with low toxicity and is thus used in a variety of applications. PEO can complex with lithium salts (Li⁺) to form polymer electrolytes. Its ethylene oxide (EO) units have a high donor number for Li⁺ and high chain flexibility, which are responsible for ion transport. The ions can move in the space provided by the free volume of the polymer host, and conductivity is thus possible above the glass transition temperature (T_g) of the polymer where the polymer molecules are free to move. The ionic conductivity displays a diffusive liquid-like behavior in the solid electrolyte. The design criteria for PEO-based electrolytes is the suppression of PEO crystallinity to increase the percentage of amorphous phase of PEO for ion transport. Various strategies have been employed to improve the ionic conductivity of PEO based electrolytes.
The challenging and critical issue with solid polymer electrolytes are to improve the ionic conductivity, interfacial contacts between electrodes and electrolytes and electrochemical stability window
In order to above requirements, recent research in PEO-based solid-state electrolytes (SSEs) has focused on the design of additive for solid polymer electrolytes (SPEs). The additives include ionic liquid, oxide particles, etc. The addition of ionic liquid and organic solvent could serve as the plasticizers, which were found to be efficient on improving the ionic conductivities of SPEs. On the other hand, various modification methods of SPEs by introducing oxide particles have been published. It was reported that the addition of oxide nanoparticles to the SPEs, such as SiO₂, TiO₂, Al₂O₃, LAGP, YSZ can improve ionic conductivity. Researchers attributed the enhanced ionic conductivity to that the highly dispersed nanoparticles be able to inhibit the recrystallization of polymer segment and further accelerate Li⁺ transport. The nanoporous materials such as nanosized mesoporous SiO₂ and metal−organic framework (MOF) can be used to achieve high Li ion conductivities. One material containing porous channel was used as an additive to a high ionic conductivity composite electrolyte.
These results indicated the porous nanoparticles may be a relatively effective additive to increase the ionic conductivity than the nonporous particles, which is mainly attributed to the pores creating more space charge regions to facilitate Li⁺ transport. The implanted materials with rich nanoporous structure can effectively promote the formation of an Li⁺ enrichment area through the adsorption effect. In the newly formed percolated interface between additives and polymer, the continuous area could act as a high-speed pathway for fast lithium ion diffusion.
In this study, we mixed PEO and Si and Al based 3-dimensional nanoporous oxide structures(NOPSs) to make composite solid electrolytes. Because the choice of lithium salt also plays a crucial role in solid polymer electrolyte, lithium hydroxide (LiOH) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were used to investigate the effect of different kind of Li salt on the Li ion conductivity. The most important requirement of lithium salt is their solubility in polymer matrix. We varied the drying temperature of the composite solid state electrolytes. The drying temperature range is from 25 °C to 60 °C. We also changed the ration of EO:Li. Different molar concentration of PEO is utilized such as, EO:Li = 16:1 & 18:1 ratios. The best lithium ion conductivity was obtained in the temperature of 50 °C.

Lithium metal is an attractive material for use as anodes in batteries due to its high electronegativity, low density, and high energy density. Because it is unstable during recharging, with non-uniform Li deposition that leads to porosity, dendrites, and dead Li, rechargeable lithium metal batteries have been unrealistic for nearly fifty years with serious safety problems and low Coulombic efficiency. Over this time, research on electrolyte additives, solid-state electrolytes, artificial SEI modifications, and separators have produced modest improvements, but none that have justified considering lithium metal batteries over lithium-ion batteries in rechargeable applications. Battery stability, ionic conductivity, and interfacial issues remain key challenges.

Nonuniform lithium deposition during charging occurs due to a Li ion depletion layer adjacent to the anode, especially at modest to high charge rates of 1C or above. By including a small, 100 MHz surface acoustic wave device into the lithium metal battery that produces intense acoustic waves in the electrolyte, rapid submicron boundary layer mixing flow may be generated during charging. This flow largely eliminates the Li ion depletion layer, and because the SAW device is small, solid state, and requires only 10 mWh/cm² during battery charging, there is a realistic possibility of incorporating this technology into current batteries under consideration for an electric vehicle, consumer device, and medical applications. The elimination of the ion depletion layer furthermore allows high-rate charging, as we will demonstrate in our electrochemistry and morphological results. The underlying physics will be explained using a closed-form model formed from intermediate asymptotics, and will show the crucial impact of the Peclet number in avoiding the ion depletion layer.

Amorphous Li_0.35La_0.55TiO₃ (LLTO) shows great promise for solid electrolyte in all-solid-sate Li-ion batteries (ASSLiB), amorphous LLTO thin films have also been successfully synthesized by sol-gel process in our previous work. The ionic conductivity can reach up to 1.88*10^-5 S/cm at 30 °C. However, one key requirement for solid electrolyte is high ionic conductivity. In order to further increase the ionic conductivity to fit the demand of ASSLiB, doping method was applied in our research. In specific, Strontium (Sr) was introduced as dopant. The ionic conductivity of Li_0.35La_0.5Sr_0.05TiO₃ (LLSTO) is one order’s higher than LLTO. In this study, we successful prepared amorphous LLSTO thin film via sol-gel procedure, moreover, differences are introduced with Sr ratio in order to understand the relationship of ionic conductivity change and structure difference. We also proved the LLSTO came with promising electrochemical stability window and stability in contact with Lithium metal. In this case, we are able to better reveal the fundamental relationship between structure and ionic conductivity in a variety of solid-state electrolytes and Li-ion transport mechanism.

Solid electrolytes for the all-solid-state lithium batteries have been mainly developed based on Li compounds in which the host Li⁺ ions are the main conduction species. On the other hand, our group has been focused on the “Li-free” compounds as the base materials for the solid electrolytes, where the foreign ions, or “guest Li⁺ ions” play a major role for the ionic conduction. From our previous research, it has been shown that NaI, NaBr and KI become guest Li⁺ ion conductors via forming the solid solution with LiBH₄ (6 mol%) [1-3]. While the guest Li⁺ ions are the major conduction carriers, the contribution of the host Na⁺ ion conduction in NaI-LiBH₄ systems was proven to be quite small [4]. The solid solutions of NaI-LiBH₄ were fabricated by mechanical milling of NaI and LiBH₄, however, it was suggested that the as-milled samples include unreacted LiBH₄ as the secondary phase [5]. The difference of the crystal structures would be one of the reasons for the slow kinetics for the formation of the solid solution (rock-salt and wurtzite structures for NaI and LiBH₄, respectively). Therefore, it is expected that the fraction of the secondary phase can be reduced if the guest Li⁺ ions in NaI lattice are introduced by the doping of LiI (rock-salt structure). In the present work, both BH₄^- and Li⁺ ions are doped into NaI by the mechanical milling of NaI, NaBH₄ and LiI all of which are the rock-salt type compounds. The guest Li⁺ conduction properties in NaI-NaBH₄-LiI systems will be also presented.
NaI, NaBH₄ and LiBH₄ were purchased from Aldrich Co. The mechanical milling was conducted with 10 pieces of balls in a chrome still pot (45 ml). First, several composition of NaI-NaBH₄ solid solutions were fabricated with the different I^-/BH₄^- ratios. Subsequently, LiI was milled with NaI-NaBH₄ systems in a given molar ratio. The concentration of Li⁺ and BH₄^- ions were changed by adjusting the doping amount of LiI and NaBH₄, respectively. The crystal structures of the obtained samples were analyzed by XRD measurement using Cu Kα radiation source. The local structure around guest Li⁺ was investigated by ⁷Li NMR measurement. For the conductivity measurement, the powder sample was pelletized under ca. 400 MPa, resulting in the dense pellet with the thickness of 1 mm. Stainless steel was used as the both sides of electrodes and the three layered cell was sealed into air-tight cell. Electrical conductivity of the sample was measured by AC impedance methods from the frequency range between 1 MHz and 1 Hz.
From the results of ⁷Li NMR measurement for NaI-NaBH₄-LiI systems, it was clearly confirmed that the fraction of the secondary phase was successfully reduced by using LiI as the starting material. The Li⁺ conductivity is increased by the reduction of the secondary phase; the conductivity of 9(15NaI-NaBH₄)-LiI was reached to be 1.5 × 10^-5 S/cm at room temperature while the conductivity of the sample with unreacted LiBH₄ (9NaI-LiBH₄) was remained to 3.0 × 10^-6 S/cm. The conductivity results of the samples with the different cation and anion ratios will be presented at the meeting.

References
[1] R. Miyazaki, D. Kurihara, T. Hihara, J. Solid State Electrochem., 20 (2016) 2759.
[2] R. Miyazaki, H. Maekawa, H. Takamura, APL Materials, 2 (2014) 056109.
[3] R. Miyazaki, M. Shomura, R. Miyagawa, T. Hihara., MRS Communication 9 (2019) 304.
[4] R. Miyazaki, I. Sakaguchi, K-M. Weitzel, T. Hihara, Electrochimica Acta,. 283 (2018) 1188.
[5] R. Miyazaki et al., MRS Advamces., 20 (2017) 389.

The sharp growth of the energy storage business - 30 % in the US in 2018, dominated by lithium ion battery - urges to find new alternatives for fast, safe and reliable and devices. Existing solutions rely either on batteries or supercapacitors : the former stores energy with a high density but suffer from slow energy delivery and irreversible capacity fading; the latter stores less energy but higher power densities, with charging times of seconds to minutes and excellent cyclability.
But what if we could combine the best of both worlds ?

This promise may be kept by using new pseudocapacitive materials known as MXenes. They are a rapidly growing family of transition carbides and/or nitrides with the general formula M_n+1X_nT_x (n = 1, 2 or 3; M = transition metal, e.g. Ti, V, Nb, Mo; X = C and/or N; T = surface termination, e.g., -OH, -F, =O). Their potential in energy storage devices has already been intensively studied since their discovery in 2011. They exhibit a 2D layered structure, a very high conductivity, can intercalate ions or molecules in order to trigger or enhance ion insertion, show low diffusion barriers for Li⁺ ions or other multivalent ions. Another key aspect is that they use fast surface redox reactions to store more energy than traditional electrical double layer capacitors and at a higher rate than traditional batteries.

But the real potential of MXenes lies in their versatility. Researchers primarily focused on finding new M_n+1X_n chemistries, with great success. But another way to control their performances is to engineer surface terminations : they are introduced during the synthesis process and strongly influence Fermi's level density of state. Conductivity is thus strongly impactedas well as electrochemistry. Removing them or finding strategies to modify them is of great importance and can lead to boost performances.
In addition, intercalating molecules and/or ions between MXenes sheets is another mechanism that can be used. Interplanar distance and thus, storage capabilities, will be modified. We could think that 'the wider, the better' but this would be a false assumption. Indeed, as it has recently been proven, solvent plays a key role in this mechanism. A balance has to be found.

In this study, we demonstrate that for a given battery electrolyte, it is possible to enhance electrochemical storage in MXenes by choosing the right intercalant. Our results showed a 30 % improvement in performances by finding the correct balance between inter planar distance and ion insertion (with or without solvation shell). Moreover, we will also evaluate the impact of surface terminations modifications on battery performances and provide insight using electron microscopy.

The new technological breakthrough of battery systems is essential to spurring the development of energy-storage systems with a high energy density for electric vehicles and various electronic devices, albeit many advances since the commercialization of Li-ion batteries in 1991. At present, the employment of Li metal as a battery anode has attracted enormous attention because of its high capacity (3860 mA h g^-1), lightweight (0.59 g cm^-3), and a low working voltage as crucial factors to fabricate high energy density batteries (e.g., Li-air batteries, Li-S batteries, and Li-metal batteries). Nonetheless, there are serious problems hanging over the system including the volume expansion and dendrite growth of Li anodes, safety issue, unstable interphase between Li metal and electrolytes, low round-trip efficiency, and short cycle life. Thus, it is necessary to seek a solution for suppressing the Li dendrites and then finally leading to advancing the development of practical Li metal batteries. In this work, we propose practical approaches for enhancing the electrochemical performances of Li metal batteries using two ways. One is a Li₂TiO₃ layer,(LT) which has the 3D pathway inside the particles for Li-ions, along with a simple, secure, and scalable fabrication method. The other is a polymer layer on a Li metal surface, which transports Li ions and screens Li metal from oxygen and moisture. Additionally, these works include indisputable evidence for verifying the superiority of these ways and practical demonstrations of full cells using high-energy cathodes.

All solid-state thin film batteries are promising candidates for applications ranging from medical implants to micro-power sources for portable electronic devices. The structural durability and reliability of thin film batteries depend on the volume change in the electrodes. In order to make further improvements in the thin film battery technology, an in-depth understanding of the electro-chemo-mechanical processes involved in these batteries is necessary. To enhance the cyclic performance of thin film batteries, a fully coupled diffusion-stress modeling in continuum scale with various operating conditions are essential. In this work, we have incorporated coupling of diffusion and stress in a Si thin film and analyzed the impact of the nature of charging pulse on the evolution of hydrostatic and principal stresses.

Prussian blue analogs (PBAs) are polynuclear transition metal cyanides with the general chemical formula of AM_α[M_β(CN)_6^●xH₂O, where A represents monovalent cations and M transient metal cations. The PBAs have been considered as promising electrode materials for multivalent metal-ion batteries as well as monovalent metal-ion batteries because of their robust and large 3D channel framework.^[1] In particular, copper hexacyanoferrate (CuHCF) has shown promising performances in aqueous Zn-ion batteries with specific energy and power comparable to organic Li-ion batteries.^[2] However, the CuHCF suffers from decreasing capacity upon cycling. The exact mechanism of the CuHCF upon Zn ions insertion is still difficult to understand.
Here, we investigate the change of the CuHCF cathode in aqueous Zn-ion battery in terms of morphology, chemical composition, and oxidation state. Advanced electron microscopy techniques such as scanning electron microscopy, (scanning) transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy, and focused ion beam are applied in order to unravel the underlying mechanism. We observed the formation of wire and cubic morphologies of the Zn_xCu_1-xHCF upon cycling the CuHCF cathode in Zn ions-containing electrolytes. A substitution mechanism is proposed to explain the increasing Zn content of the cathode material while simultaneously the Cu content is lowered during the Zn-ion battery cycling. The detailed degradation mechanism and its relationship with the electrochemical performance will be discussed.

[1] J. Qian, C. Wu, Y. Cao, Z. Ma, Y. Huang, X. Ai, H. Yang, Adv. Energy Mater. 2018, 8, 1702619
[2] F. Mao, W. Guo, J. Ma, RSC Adv. 2015, 5, 105248-105258.

Layered transition metal oxide family of cathode materials for Lithium-ion battery(LIB) has been exclusively studied due to their high theoretical capacities and chemical stability. Their performance is limited by the capacity degradation during cycling as irreversible reaction occurs. The irreversible reaction resulting from the crystal structural change of the cathode materials is due to the movement of lithium ions between electrodes while cycling at different rates. As a result, different phases can be observed by X-ray Powder Diffraction (PXRD). In order to understand the mechanism of different phases formation during cycling, it is necessary to locate the regions where the inhomogeneity is formed within the cathode . LiNi_0.80Co_0.15Al_0.05O₂(NCA) was used as an example to develop an ex-situ methodology by using X-ray Microdiffraction (µ-XRD) at the scale from 1mm to 100µm to visualize the distribution of inhomogeneity within the cathode by generating a map of distribution of unit cell parameters of crystal lattice. Applying this approach, NCA has been examined under different discharging rates (C/10,C/5,C/2,1C and 5C) with different sizes of lithium anode. The maps clearly show the distribution patterns of rate-depend inhomogeneities due to kinetic limitation within the cell . This methodology will be further developed to investigate the inhomogeneity formation on secondary particles.

Lithium phosphorus oxynitride (LiPON) has attracted significant interest in solid-state batteries, due its wide potential window, high ionic conductivity, and fairly good mechanical stability. However, several issues which are associated with the formation of an interfacial layer between LiPON and battery electrodes (e.g. LiCoO₂) and the structural degradation of electrodes significantly affect the electrochemical performances in solid-state batteries.
Several techniques (such as HRTEM, STEM, SEM etc.) have been employed to look into the interfacial layer between solid-state electrolytes and electrodes; but it was technically difficult to analyze the same spot of sample without damage, due to its high energy beam. In operando neutron reflectometry (NR) is a non-destructive technique which enables the investigation of the evolution of nanometer-scaled interfacial layers as a function of working potential. In addition it is very sensitive to the light elements such as Li and H, which facilitates the qualitative analysis of thin films. Due to these fascinating characteristics, it has been used to study the by-products (e.g. solid electrolyte interphase) formed at the interface of battery electrodes.
Through this study, we investigated the interface of LiCoO₂ electrode before and after sputtering LiPON via NR and studied how Li-impregnated solid-state electrolyte affects the structural characteristics of LiCoO₂ electrode. Morevoer, we looked into the structure and composition of the co-diffused layer between LiPON and LCO using NR. These results may expain the reason for the capacity fade and power fade of solid-state-batteries. In future work, we will explore the possibility that a thin layer of Al₂O₃ can improve the structural integrity of each LiPON and LCO. These fundamental studies will lead us to understand the inherent problem of solid-state batteries and provide guidelines to design the suitable electrode for thin film solid-state batteries.

Lithium sulfide (Li₂S) is one of the most promising cathode materials for the next-generation advanced lithium-ion batteries as it allows for the use of lithium-free metal-based high capacity lithium-ion anodes such as silicon-based anode etc. It has high theoretical capacity (1167 mA h g^-1) and large energy density to match with high capacity metal anodes. However, Li₂S suffers from poor rate performance and short cycle life due to its insulating nature (very low electronic and ionic conductivity) and shuttle effect of lithium polysulfides during charge-discharge cycles. In this work, we report a facile and scalable ball milling synthesis method to synthesize nitrogen-doped graphene/carbon nanotubes (CNTs)/Li₂S composites with 80 wt% Li₂S loading. In this composite cathode, two-dimensional (2D) N-doped few layer graphene nanosheets and one-dimensional (1D) CNTs provides efficient channels for electron transfer and ionic diffusion, and leads to a low solubility of polysulfides in electrolytes during charge-discharge cycles. The N-doped Graphene/CNTs/Li₂S composites cathode yields an exceptionally high initial capacity of 847 mAh g^-1 after 3 cycles at the C/20 rate based on the mass of Li₂S. The mass loading of active material (Li₂S) was ~4 mg cm^-2 in the cathode. The cell also shows good cycling stability with an average decay rate of 0.23% per cycle over 150 cycles at C/3 rate, and improved rate capability of 470 mAh g^-1 at C/2 rate. The reported facile and scalable synthesis method of N-doped Graphene/CNTs/Li₂S composites cathode with high Li₂S content presents promising application potentials in high-performance lithium-sulfur batteries.

Recently, iron based metal oxides have attracted much attention for advanced lithium ion batteries (LIBs) anode. However, rapid capacity fading and poor rate capability caused by drastic volume variations during cycling process hinder their practical applications. To circumvent these issues, one dimensional nanofibric architecture consisting voids/gap present in between individual nanoparticles may play a vital role to prevent the volume variation during long term cycling. In this regard, nanofibers of Ca₂Fe₂O₅ have been fabricated by facile, environment friendly and cost-effective electrospinning technique, and thoroughly characterized by FE-SEM, TGA, XRD, XPS and BET. Further, the advantages and importance of Ca₂Fe₂O₅ nanofibers as LIBs anode is demonstrated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). Ca₂Fe₂O₅ nanofibers exhibit remarkable lithium storage performance such as high initial reversible capacity (650(±10) mAh.g^-1), excellent cyclic stability (600(±10) mAh.g^-1 up to 100 cycles) and good rate capability_. Moreover, Nanoparticles of Ca₂Fe₂O₅ were also investigated as LIBs anode, however, nanoparticles performance are found to be inferior to the nanofibers. The better performance of Ca₂Fe₂O₅ nanofibers is attributed to the unique features of nanofibric architecture such as one dimension, porous, high aspect ratio and presence of voids/gap between interconnected nanoparticles.
References:
Y. Sharma, N. Sharma, G. V. S. Rao, and B. V. R. Chowdari, Adv. Funct. Mater., 17, 2855 (2007).
J. Bhagwan, A. Sahoo, K. L. Yadav, and Y. Sharma, J. Alloys and Compd., 703, 86 (2017).

Next-generation battery technologies with higher capacities and longer lifetimes compared to current lithium-ion batteries (LIBs) are vital for portable devices and electric vehicles. Lithium-sulfur batteries have received significant attention due to their ultrahigh theoretical capacity of 1675 mA g^-1 and the environmental availability and benignity of sulfur. However, several issues currently prevent their more widespread utilization, including the low electronic conductivity of sulfur (S₈) and its lithiated products (Li₂S). Additionally, the “shuttle effect” resulting from the soluble intermediate polysulfides Li₂S_n (4 ≤ n ≤ 8) formed during charging and discharging in organic electrolytes has been shown to cause rapid capacity fade and battery failure.

Various strategies have been utilized to mitigate these issues, such as forming composites with conductive and adsorptive hosts to confine sulfur. However, the shuttle effect and resulting electrode instability has yet to be eliminated. Herein, we designed a metal-organic framework (MOF) derived N-doped micropourous-carbon coated electrode consisting of sulfur and nanostructured titanium dioxide (S-TiO₂). The N-doped carbon coating is formed from the carbonization of an electrospray deposited Zn-MOF, and possesses a suitable pore size to prevent polysulfides from passing while not inhibiting the movement of Li⁺. Meanwhile, the TiO₂ nanostructures provide efficient electron pathways to enhance the high-rate performance of the electrodes. The resultant electrodes deliver a high specific capacity and excellent rate performance.

The high areal-energy and power requirements of advanced microelectronic devices favor the choice of a lithium-ion system, since it provides the highest energy density of available battery technologies. Several attempts have been made to produce primary and secondary thin film batteries utilizing printing techniques. These technologies are still at an early stage, and most currently printed batteries exploit printed electrodes sandwiched with self standing commercial polymer membranes, produced by conventional extrusion or papermaking techniques, followed by soaking in aqueous or non-aqueous liquid electrolytes.
In this work we report on the development and fabrication of novel 3D-printed solid-state or quasi-solid electrolytes by fused filament fabrication (FFF). The electrolytes are composed primarily of polyethylene oxide (PEO) and polyethylene glycol (PEG) which are known ionic conductors, and polylactic acid (PLA) for enhanced mechanical properties and high temperature durability. Flexible quasi-solid-state printed electrolyte plasticized by the ionic liquid (IL) 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI) with 0.3M concentration of LiTFSI exhibited an ionic conductivity of 2.8 × 10−4 S/cm at 60^oC.
The 3D printed electrolytes were characterized by means of SEM imaging, differential scanning calorimetry (DSC) and electrical impedance spectroscopy (EIS). We have also investigated the charge transport dynamics in this printed electrolyte material by pulsed field gradient diffusion nuclear magnetic resonance (NMR) using the probe nuclei ¹H, ⁷Li, and ¹⁹F, corresponding to the PYR₁₄, Li, and TFSI ions. All ionic diffusivities in the IL-plasticized PLA/PEO/PEG electrolyte were reduced compared to their values in the IL with 0.3M LiTFSI, even though the ionic conductivity exhibited an acceptable value. Interestingly, a sample consisting of the IL LiTSI mixture imbibed into the PLA matrix exhibited no reduction in ionic diffusivity compared to the liquid sample.
These results pave the way for a fully printed battery, which enables free-form-factor geometries and is far superior in terms of safety compared to standard Li ion batteries which contain volatile solvents.

Layered oxides are among one of the leading cathodes for lithium ion batteries due to their high energy density. They are one of the more attractive options for use in electric vehicles which makes their safety a top priority. It is well known that layered oxides produce oxygen upon heating which can lead to exothermic reactions within the cell aiding in thermal runaway. This presentation will discuss the thermal stability of the high nickel layered oxides Li_xNi_0.8Mn_0.1Co_0.1O₂ (NMC) and Li_xNi_0.8Co_0.15Al_0.05O₂ (NCA) in different charged states. The effect of composition of the layered oxides as well as their interaction with the electrolyte components will be explored in order to isolate the cause of the thermal output present upon heating. Differential scanning calorimetry (DSC) was used to study the exothermic reaction between the cathode materials and the electrolyte. To further understand these reactions, the individual components of both the cathode and the electrolyte were studied to identify what interactions were causing the heat release. X-ray diffraction (XRD) was used after DSC to identify products of the reaction to gain better insight on what is going on within the cell. While high nickel content in layered oxides is known to destabilize the material, the onset temperatures for these reactions is not below 200°C and the total heat released does not exceed 1400 J/g. By using a more stable electrolyte, the total heat released drops to roughly 400 J/g.

Acknowledgement: This research was funded by U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) program under BMR award no. DE-EE0006852

Composite solid electrolytes (CSEs), which are composed of inorganic fillers and organic polymers, show improved safety and suppressed lithium dendrite growth in Li-metal batteries, as compared to flammable liquid electrolytes. However, the performance of current CSEs is limited by the agglomeration effect, with low content of inorganic Li⁺-conducting fillers and ineffective Li⁺ transport between the inorganic fillers and the polymer matrix. We therefore set out to design a CSE toward high-performance, solid-state Li-metal batteries based mainly on inorganic Li-conductors, with supplementary polymer content for improving interfacial contact. A new type of CSE with enriched inorganic Li-conductors and well-percolated network was introduced utilizing one dimensional Li_6.28La₃Al_0.24Zr₂O₁₂ (LLAZO) nanofibers to provide long-range and fast Li⁺ conduction. Additionally, acrylate functional groups (CH₂=CHCOO^-) were covalently bonded on the surface of LLAZO nanofibers, which enabled the chemical grafting of functional monomers directly from the nanofiber surfaces. In the resultant composite electrolytes, silane-decorated LLAZO nanofibers (s@LLAZO nanofibers) were cross-linked along with polymerization of monomers. This controlled fabrication of composite structures led to a well-percolated network, forming continuous, 3-dimensional, and fast Li⁺ conductive pathways within the CSE. The silane coupling agent significantly prevented the inhomogeneous distribution of inorganic Li⁺ conductors and enhanced the interaction between the LLAZO nanofibers and the polymer matrix, which improved the mechanical strength of CSE, favored the amorphization of polymer, and reduced the activation energy of Li⁺ conduction between the filler and polymer. Consequently, the silane coupling agent successfully eliminated the agglomeration effect, and the introduced CSEs (LLAZO nanofibers > 60 wt.%) exhibited higher ionic conductivity, larger lithium transference number, and wider electrochemical stability window. Excellent cycling stability and extraordinarily high rate capability (up to 10C) was demonstrated in the all-solid-state Li-metal batteries with LiFePO₄ and high-voltage Li[Ni_1/3Mn_1/3Co_1/3]O₂ cathodes at ambient temperature. This novel design of CSEs with s@LLAZO nanofibers paves the way for a new generation of improved functioning all-solid-state Li-metal batteries.

Driven by safety concern and cost-efficient demand of the commercial market, Rechargeable aqueous zinc-ion batteries (ZIBs) has drawn many attentions in last few years due to high energy/powder hubs and eco-friendly features for facile massive production and large-scale applications. However, considering the highly reversible and superior capacity of ZIBs, the researches of vanadium-based cathode materials are still in its infancy and suffering from a deficient investigation of zinc ion diffusion kinetics and deep insight of intercalation mechanism within a crystallographic configuration. Herein, we elaborately fabricated tunable d-spacing expansion of ammonium vanadium oxide (NVO) with various amount of ammonium ions as cathode material in ZIBs. The hydrogen bond of NH₄⁺ within interlayer of V₂O₅ framework possesses superior behaviour on zinc ion diffusion as “lubricant” like water molecule which is highly different from metal pre-intercalated V₂O₅ in previous reports. Thus, the as-obtained NVO presented 252 mAh g^-1 at a high current density of 10A g^-1 with excellent retention of 95% after 1000 cycles. The electrochemical reaction kinetics, structure evolutions and zinc storage mechanism are discussed in detail. This work may stimulate future exploitation of vanadium-based cathodes in ZIBs and bring more insights into the mechanisms of zinc-ion storage.

During fast charging, the commonly used Li-ion battery anode material, graphite, has a significant shortcoming: its discharge potential is too low to guarantee the safety of batteries. Li₃VO₄ (LVO), an alternative anode material, has a safe discharge potential window of 0.5 V to 1.0 V vs. Li⁺/Li and high theoretical capacity (∼394 mAh/g). However, the poor conductivity of LVO (∼10⁻¹⁰ S/m) constrains its further applications. This presentation will show our recent efforts embedding LVO uniformly onto a multilayered material, Ti₃C₂T_x MXene, by a sol–gel method. The Ti₃C₂T_x MXene nanolayers with high electrical conductivity (2.4 × 10⁵ S/m) served as a scaffold to load LVO nanoparticles. The LVO/Ti₃C₂T_x MXene composite exhibited remarkable electrochemical performance in terms of rate capability and long-term cycle stability in comparison with bare LVO and commercial graphite anodes. The LVO/Ti₃C₂T_x MXene composite delivered an initial capacity of ∼187 mAh/g and 146 mAh/g after 1000 cycles at 5C, compared to bare LVO (an initial capacity of ∼41 mAh/g and ∼40 mAh/g after 1000 cycles at 5C) and graphite (∼71 mAh/g after 1000 cycles at 5C). We believe this work opens new possibilities of anode materials for safe and fast-charging Li-ion batteries.
This presentation is based on our recent publication:
J. Mater. Chem. A, 2019, 7, 11250-11256
https://doi.org/10.1039/C9TA02037C

Energy storage systems can be the most plausible solution since we are on the verge of a global energy crisis due to the rapid dissolution of fossil fuels. Finding environmentally benign fossil fuel replica with a broad performance spectrum is still a very encouraging field of research. In recent times, a tremendous effort related to the energy storage device has been put by our research groups. Few-layer graphene (FLG) achieved via mechanical exfoliation method from agricultural waste biomass: peanut shell. We have explored that the electrochemically deposited three-dimensional graphene oxide (ErGO) has a crucial role to act as binder-free electrode material for supercapacitor application. A facile electrochemical method can have advantages to grow reduced graphene oxide-polypyrrole hybrid platform on a pristine nanoporous gold chip for microsupercapacitor (MSC) application with outstanding cycle life.
Recently, electrochemical followed by laser-induction have shown the advancement for the fabrication of conductive and robust and flexible metal-free MSC. The LIG film on flexible substrate was patterned with the aim to develop on-chip flexible MSC, which offers large working voltage of 1.2 V in aqueous solid electrolyte. The MSC, without any metal current collector, interestingly shows unique electrical-double layer behavior and unprecedented cycling stability. Notably, the retention of initial capacitance after 1,00,000 continuous cycle was 100% and after 150 days was more than 99%, respectively. This study provides an effective strategy to build up metal-free supercapacitor with exceptional life cycle and facilitates progress toward a sustainable energy future.

References:
Energy & Environmental Science, 2019, DOI: 10.1039/C9EE01458F
J. Mater. Chem. A, 2018, 6, 22858 – 22869.
Sci. Rep., 2018, 8, 640.
Sci. Rep. 2017, 7, 15239

In the last few years the concept of self-powered systems (SPS) has gained momentum in the fields of portable flexible technology. SPS usually refers to devices that are powered up by harvesting energy from external sources, such as solar radiation and body movement.[1] In a society where portable devices become an indispensable part of modern life, the development of SPS is of major importance.[2] These systems not only reduce the pressure on the electrical grid, but also help society moving towards sustainable and renewable energy sources. When integrated with energy storage devices, such as batteries and supercapacitors, SPS are also capable of storing energy under normal circumstances, thus assuring energetic self-sufficiency, even when surrounding conditions are less favourable for energy harvest.[1] In fact, the development of energy autonomous SPS is anticipated to bring unforeseen ubiquitous innovations in our daily lives. Current thin-film batteries, still suffer from several technical disadvantages, as their energy per volume tends to rapidly decrease in the micrometre scale.[2] Moreover, they also raise safety concerns. On the other hand, micro-supercapacitors are highly desired as power sources for flexible devices as they present an enhanced power density, optimal cyclability, long shell life and capability of direct on-chip integration.[2–4] However, to be fully integrated into wearable and flexible technologies, supercapacitors need to be flexible enough to undergo large mechanical deformations, without compromising their performance.[5] Commercially available supercapacitors do not present the most suitable configuration for devices meant to be bent or even rolled up, due to the presence of rigid components and the constant risk of harmful electrolyte leakage. The transition from current supercapacitor technology to fully printed, planar, ultra-thin and light supercapacitors will be disruptive.

In this work, inks based on carbon nanotubes (CNTs) and two dimensional manganese oxide nanosheets (MnO₂) processed by liquid phase exfoliation will be used as promising material platforms for flexible in-plane printed micro-supercapacitors. Owing to their superior mechanical and electrical properties, CNTs were implemented as highly efficient current collectors, thus removing the need for bulky and heavy metallic components. UV-Vis analysis revealed that the electrical conductivity of CNT films, as thin as 12 nm, is suitable for supercapacitor applications. Energy storage active materials, such as 2D - manganese oxide nanosheets, were then printed on top of the CNT films. Preliminary cyclic voltammetry experiments exhibited a characteristic supercapacitor behaviour. In order to maximize the exploitation of these devices properties, optimized inks, formulations and printing patterns will be carefully designed and characterized.
The proposed combination of liquid phase exfoliation and printing technologies will open the venue for the large-scale manufacture of ultra-light and thin flexible energy storage devices.


References

1. Lin, Y., Gao, Y., Fang, F. & Fan, Z. Recent progress on printable power supply devices and systems with nanomaterials. Nano Res. 11, 3065–3087 (2018).
2. Huang, G. W. et al. Laser-Printed In-Plane Micro-Supercapacitors: From Symmetric to Asymmetric Structure. ACS Appl. Mater. Interfaces 10, 723–732 (2018).
3. Kyeremateng, N. A., Brousse, T. & Pech, D. Microsupercapacitors as miniaturized energy-storage components for on-chip electronics. Nature Nanotechnology 12, 7–15 (2017).
4. Yu, W., Zhou, H., Li, B. Q. & Ding, S. 3D Printing of Carbon Nanotubes-Based Microsupercapacitors. ACS Appl. Mater. Interfaces 9, 4597–4604 (2017).
5. Zou, M. et al. Flexible devices: From materials, architectures to applications. J. Semicond. 39, 011010 (2018).

In recent time transition metal oxide vanadium pentoxide (V₂O₅ ) is considered as an excellent energy storage device material for Li-ion batteries (LIBs) with reference to its high charge storing capacity, low cost, rich layered structure, and abundant material. With respect to its rich layered structure, which can reversibly accept the intercalation and deintercalation of Li-ions in the process of charging and discharging of LIBs. In this study, we report a simple hydrothermal procedure to synthesize the porous microstructure of V₂O₅ as a cathode for LIBs with subsequent annealing temperature. The structural analysis stands for the orthorhombic phase of V₂O₅ and other suboxides phase of vanadium are absent. The RAMAN analysis justifies the layered structure of V₂O_5. The morphological study of V₂O₅ shows the flower-like three-dimensional micro flowers (having diameter ~1.2 to 2.6µm) self-assembled by Nanorods. In electrochemical cyclic voltammetry measurement three cathodic peaks were observed corresponds to 3.27V, 3.05V, and 2.08V as Li/Li⁺ refer to three crystal phase α-V₂O₅ to β- Li_0.5V₂O₅; β-Li_0.5V₂O₅ to δLiV₂O₅ and δ -LiV₂O₅ to γ –Li₂V₂O₅ respectively_, And also three anodic peaks correspond to Li-ion deintercalation. Which indicate the good reversibility of the electrode. In this report, V₂O₅ micro flowers deliver very high specific discharge capacity of 290mAhg^-1 and after 50cycles the capacity reduced to 198mAhg^-1 cycled between the voltage range 2.0-4.0V at the current rate 0.1C.

Recently, aqueous rechargeable zinc-ion batteries (ARZIBs) have attracted great attention as compared to commercial lithium-ion batteries due to their unique advantages of high intrinsic safety (non-flammable water-based electrolyte) and low cost. [1-3] Over the past few decades, much progress has been focused on the exploration of suitable cathode materials. Among them, vanadium dioxide (B) has been considered as a potential cathode for ARZIBs owing to its unique double layers of V₄O₁₀ type with tunnels, which can facilitate rapid zinc-ions de/insertion processes. [4] However, the reported VO₂ (B) displays a high initial capacity but noticeable capacity fading and especially declines drastically at a high current rate. Compositing VO₂ (B) with an electrically conductive matrix has recently been introduced as an effective way to improve the power capability. However, it can only improve the external electric conductivity and the usage of expensive carbon (graphene) negates the cost advantage of vanadium oxides. Therefore, it is of great importance to construct novel VO₂ (B) electrode materials with excellent electrochemical performance.

Herein, we report an alternative approach to designing and engineering a hierarchical porous Ni-doped vanadium dioxide (B) nanobelts for ARZIBs. The as-synthesized samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). The existence of Ni dopant was confirmed by the X-ray absorption near-edge structure studies (XANES) and X-ray photoelectron spectroscopy analysis. Electrochemical studies indicate that the Ni-doped VO₂ nanobelts electrode exhibits superior cycling stability and ultrahigh rate capability with long cycle life, which is significantly higher than that of the undoped VO₂ (B). This can be attributed to the utilization of Ni dopant to electrical wiring the electroactive material, the intrinsic conductivity of VO₂ can be effectively increased. In-operando XRD measurements coupled with ex-situ TEM micrographs taken at specific potentials were exploited to gain a further understanding into the structural evolution upon cycling and ions storage mechanism. The results of the study can potentially open the doors for the widespread application of constructing other elemental doping materials as cathodes with high rate capability and long cycle life for aqueous rechargeable batteries.

References:
[1] Fang G, Zhou J, Pan A, et al. Recent advances in aqueous zinc-ion batteries[J]. ACS Energy Letters, 2018, 3(10): 2480-2501.
[2] Pan H, Shao Y, Yan P, et al. Reversible aqueous zinc/manganese oxide energy storage from conversion reactions. Nature Energy, 2016, 1(5): 16039.
[3] Li H, Ma L, Han C, et al. Advanced rechargeable zinc-based batteries: Recent progress and future perspectives[J]. Nano Energy, 2019.
[4] Mai L, Wei Q, An Q, et al. Nanoscroll buffered hybrid nanostructural VO₂ (B) cathodes for high-rate and long-life lithium storage. Advanced Materials, 2013, 25(21): 2969-2973.

Sodium-based battery chemistries have potential for use as competitive energy storage alternatives to Li-ion batteries (LIBs), largely due to the low cost and wide availability of raw sodium materials compared to their lithium counterparts (150 USD t^-1 vs 5000 USD t^-1 for Na and Li carbonate respectively).¹ Unfortunately, the development of Na-ion batteries (NIBs) has been limited by the intrinsic gravimetric barriers that come from moving toward Na-based intercalation. Na-air batteries (NABs) on the other hand, do not suffer from these barriers, reaching high theoretical capacities of 1108 Wh kg^-1.² The comparatively high energy density of the NAB arises from a fundamentally different cell chemistry, where energy is gained through chemical synthesis rather than intercalation. Typically, a sodium metal anode is oxidized upon discharge to give Na⁺ ions which travel across a liquid electrolyte toward a porous carbon cathode, where O₂ gas is reduced to form either sodium superoxide (NaO₂) or sodium peroxide (Na₂O₂) in competing oxygen reduction pathways. Although theoretical gravimetric capacity is high in these batteries, cell lifetime is hindered by the oxidative instability of the carbon cathode toward NaO₂, forming sodium carbonate in a parasitic side reaction (Na₂CO₃).³
In this work, titanium dioxide (TiO₂) is investigated as a starting material for alternative cathode substrates in long cycle life, chemically stable, NABs. Electrically insulating TiO₂ is reduced via hydrogen gas to produce highly conductive single phase Ti₄O₇. The stability of Ti₄O₇ toward NaO₂ is confirmed by monitoring a ground mixture of the two by solid state ²³Na magic angle spinning nuclear magnetic resonance (MAS NMR), where no reaction is observed. A comparison mixture of NaO₂ and graphitic carbon is also monitored, and a distinct reaction to form Na₂CO₃ is seen.
Porous, carbon-free, Ti₄O₇ electrodes are fabricated and tested in Swagelok style Na-air cells. Cells are discharged, halted, stripped, and have their cathodes removed to examine the electrochemical products formed. ²³Na MAS NMR is used at spinning speeds of up to 40 kHz and at fields of up to 19.9 T in tandem with the multiple quantum MAS (MQMAS) pulse sequence to give optimal separation of the complex electrochemical mixture. Both NaO₂ and Na₂O₂ are found to form on the Ti₄O₇ cathode, and are found to be relatively stable over time when compared to the carbon-based system. Continuous wave, x-band, electron paramagnetic resonance (EPR) is also used to characterise NABs. Both NaO₂ and Ti₄O₇ resonances are visible in the EPR spectrum of discharged cathodes. The EPR signature of Ti₄O₇ is measured before and after an oxidative stress test where the cathode is kept at 4 V (Na/Na⁺) in an oxygen atmosphere to mimic the most extreme conditions faced in the NAB, and little to no change is observed.
The long-term cycle life of Ti₄O₇ NABs is tested by monitoring capacity retention of cells over 50 charge/discharge cycles with varying cut-off voltage windows. Measurable improvement is seen over the carbon system. Ti₄O₇ is shown to be a highly stable cathode material for NAB systems, while tandem ²³Na MAS NMR and EPR are proven to be an encompassing toolkit for the disentanglement of the complex chemistries found in metal-air batteries.

1. Slater, M. D., Kim, D., Lee, E. & Johnson, C. S. Sodium-Ion Batteries. Advanced Functional Materials 23, 947-958, doi:10.1002/adfm.201200691 (2013).
2. Lutz, L. et al. Role of Electrolyte Anions in the Na–O2 Battery: Implications for NaO2 Solvation and the Stability of the Sodium Solid Electrolyte Interphase in Glyme Ethers. Chemistry of Materials 29, 6066-6075, doi:10.1021/acs.chemmater.7b01953 (2017).
3. Reeve, Z. E. et al. Detection of Electrochemical Reaction Products from the Sodium-Oxygen Cell with Solid-State (23)Na NMR Spectroscopy. J Am Chem Soc 139, 595-598, doi:10.1021/jacs.6b11333 (2017).

A novel and facile polymer-assisted chemical solution (PACS) method is successfully developed for the synthesis of LiMn₂O₄, LiMn_1.5Ni_0.5O₄ and LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) with unique morphology and nanoparticle nature as cathodes for lithium-ion batteries. PACS uses polymers polyethyleneimine and ethylenediaminetetraacetic acid to bind with metal salts, such as metal nitrate. PACS is unique compared with other solution methods in that water-soluble polymers bind with the metal ions to prevent them from hydrolysis. Therefore, these metal-polymer solutions are stable for years. The compositions and particle sizes of cathode materials can be tuned by simple controlling different heating temperatures from metal-polymer solutions. At low heating temperature of 550 °C, LiMn_2-xNi_xO₄ nanoparticles are covered by a thin layer of carbon from in situ incomplete depolymerization of the polymers. The LiMn_2-xNi_xO₄ cathode exhibited better durable rate capability with 100 % of the capacity retained (∼100 mAhg^-1) after 400 cycles at 10 C rate. However, for NCM materials, higher calcination temperature of above 800 °C is necessary for layered structure formation with a lower degree of Ni/Li cation mixing thus for better electrochemical performance. As compared with the NCM prepared at 800 °C, the sample heated at 900 °C exhibits a higher initial discharge specific capacity of 189 mAh g^-1 being charged to 4.5 V at a current rate of 0.05 C, and better cyclability at 4.3 V cutoff voltage and a current density of 1 C.

The discovery of Li-excess disordered rocksalt (DRX) materials has opened up a diversified chemical space for the development of low-cost high-energy-density cathodes. However, because of the Li excess, DRX oxide materials typically suffer from unsatisfactory capacity retention due to irreversible oxygen loss, a problem which can be mitigated by fluorination as it lowers the average cation charge states and makes more transition metal capacity available. In this work, we use ab-initio models to understand the short-range order and Li transport in fluorinated DRX (F-DRX) across different cation chemistries and fluorine contents. We find that the percolation of Li in F-DRX is governed by both Li-F attractions and cation mixing. To provide rational design principles for F-DRX, a synthesis map that combines expected electronic capacity, 0-TM percolation, and synthetic accessibility of fluorinated DRX materials is presented. Finally, we experimentally verify the fluorination effect in DRX materials and propose several promising F-DRX systems that combine high capacity and good cycle life.

There has been considerable interest in developing low-cost, high-energy electrodes for batteries. However, synthesizing materials with the desired structure and properties has proven difficult due to the complexity of the reaction involved in chemical synthesis. Additional challenge comes from the fact that synthesis is often undertaken under non-equilibrium conditions and, hence, the process is hard to be predicted by theoretical computations. In situ, real-time probing of synthesis reaction allows for identification of intermediates and determination of thermodynamic/kinetic parameters governing kinetic reaction pathways, thereby enabling synthetic design of materials with desired structure and properties. In this presentation, we will report our recent results from in situ probing and synthetic control of local structural ordering during synthesis of high-Ni layered LiNi_1-x (MnCo)_xO₂ (x>0.7). Findings from this study, along with its implication to designing surface-stabilized high-Ni layered oxide cathodes, will be discussed.

As batteries are employed in larger numbers and for increasingly diverse applications, there is interest in alternative electrode materials, especially with improved safety, availability, and cost relative to the layered materials employed in commercial Li-ion batteries (LIBs). Early transition-metal oxides, one class of promising alternatives, have demonstrated compelling performance for high-rate LIBs and even multivalent-ion-based energy storage. However, as this family of compounds is chemically and structurally distinct from the layered and olivine materials employed in commercial LIB electrodes, we are just beginning to understand the origins of their promising charge storage capabilities.

To bring new understanding to this class of materials and how they store charge, we analyze the cycling and structural evolution of KNb₃O₈ and related NaNb₃O₈, which comprise complex layers of edge- and corner-sharing [NbO₆] octahedra. On the first discharge, these materials react with 2 moles of Li per mole of Nb, resulting in relatively disordered products. Only half of the first discharge capacity is reversible on charge, yet long-range order is recovered and the structures of charge products resemble the initial materials. Using ex situ and operando XRD and PDF, we describe the evolution of the structure, focusing on changes in the [NbO₆] layers during cycling and the role of the countercation.

Our findings on how these materials store charge and their unexpected recovery of long-range order can inform the selection and design of new materials for energy storage, with relevance for early transition-metal oxides as well as conversion electrodes.

Lithium ion battery (LIB) has been intensively investigated in recent years for vehicle electrification and its cost has been significantly reduced.¹For the long-range electrical vehicles, however, the cell energy and durability still need to be further improved to go beyond that of conventional Li-ion batteries. Among different cathode materials, Ni-rich NMC (LiNi_xMn_yCo_1-x-yO₂, x ≥ 0.6) has a specific capacity greater than 200 mAh g^-1, high operating voltage (ca. 3.8 V) and low cost, and is therefore deemed as one of the most promising cathode candidates for next-generation Li-ion batteries.

Unlocking the full potentials of Ni-rich NMC cathodes demands to push the limit of this class of materials to achieve good cycling stability at elevated voltages to extract maximum reversible capacity, prevent Ni-catalyzed electrolyte decomposition, structural degradation and cracking during cycling, improve thermal stability and reduce moisture sensitivity, as well as overcome practical limitations to maximize the accessible capacity in the full cells.²Although fundamental understandings of Ni-rich cathode have been deepened, an effective method to address the cathode problems is still lacking and even the failure mechanism of Ni-rich cathode is arguable. There is still a significant knowledge gap between materials research and cell-level need of the materials properties. For example, although many attractive attributes have been displayed from nano-sized cathode materials, the direction towards higher energy cathode is the opposite i.e., micron-sized large particles with high tap density and press density when being calendered into electrodes. The desired particle size, morphology and tap density of Ni-rich NMC that will benefit the porosity control and the electrochemical performances of the thick electrodes are not well studied from the synthesis point of view. The synthesis approach that help to extract greater than 210 mAh/g capacity from Ni-rich NMC without increasing the cutoff voltage is also critical and a necessity in improving the energy of next-generation Li-ion batteries which are, however, not well studied.

This talk will discuss the synthesis, understanding and implementation of single crystal Ni-rich cathode in lithium ion batteries. While polycrystalline is the common form of traditional LiNi_1/3Mn_1/3Co_1/3O₂, single crystal is preferred when Ni content becomes dominant (>70%) in the cathode material. Single crystal Ni-rich cathode may have reduced gas evolution, reduced sensitivity to moisture, lower surface area and increased tap density, all of which will play a key role for high performance advanced Li-ion batteries.

Electric vehicles, consumer electronics, and the possibility of electric aviation demand energy storage with extremely high specific and volumetric energy densities. Incorporating Li metal as the anode in a Li ion battery to make Li metal batteries has the potential to fill this demand. To integrate Li metal into a battery, an electrolyte that is chemically stable with Li, and can suppress Li dendrites is required. Some of the most promising electrolytes are the ceramic electrolyte which have good ionic conductivity and electrochemical stability but are particularly prone to penetration by Li filaments. The glassy electrolyte Lipon on the other hand has a moderate ionic conductivity but can completely suppress Li filaments. The aim of this research is to answer the question: if ceramic electrolytes had a glassy interface like Lipon could they suppress Li dendrites at high current densities? To test this hypothesis, we deposited a Lipon layer on the surface of lithium lanthanum zirconium oxide (LLZO) and lithium aluminum titanium phosphate (LATP) ceramic electrolytes and cycled Li metal at increasing current densities. The answer to this question gives us great insight into the origin of Li filament formation and what is needed to suppress them in solid-state electrolytes with high ionic conductivities.

Requirements for higher energy density and better safety in demanding applications such as grid storage and electric vehicles call for next-generation battery technologies. All Solid State Batteries (ASSBs) might enhance the safety and the energy density of conventional LIBs by removing flammable organic electrolytes and allowing the use of metallic lithium anodes [1]. In this context, solid sulfide-based solid electrolytes have drawn a lot of attention owing to their high ionic conductivities (10^-2 – 10^-4 Scm^-1 at RT) [2–5]. Few compositions in the Li₂S – P₂S₅ binary system, particularly Li₃PS₄ and Li₇P₃S₁₁, are being heavily investigated as glass-ceramic materials synthesized by mechano-chemistry and subsequent annealing [4]. However, varying ball-milling parameters and annealing procedures were rarely systematically investigated [5].

In this work, we will report on the synthesis of various materials in the Li₂S – P₂S₅ system (Li₃PS₄, Li₇P₃S₁₁, Li₂P₂S₆, …) via a systematic synthesis approach: the individual effects of pre-selected ball-milling and subsequent annealing parameters will be presented, as characterized in details through X-ray and neutron diffraction, and various techniques of spectroscopy such as Raman, NMR and complex impedance. The latter technique is quite powerful to discriminate between crystalline and amorphous contributions to the total ionic conductivity, which may be strongly affected as well by the relative amounts of local units such as P₂S₆^4-, P₂S₇^4- and PS₄^3- in the material. Additionally, the chemical stabilities in air and the electrochemical stability windows of the aforementioned materials were assessed with the help of specialized experimental setups. These results will be comparatively presented along with the discussion of the link between the electrochemical and the chemical stabilities and the structure.

[1] J. Janek, W.G. Zeier, Nat. Energy., 1 (2016) 16141.
[2] S. Chen, D. Xie, G. Liu, J.P. Mwizerwa, Q. Zhang, Y. Zhao, X. Xu, X. Yao, Energy Storage Mater., 14 (2018) 58–74.
[3] M. Tatsumisago, S. Hama, A. Hayashi, H. Morimoto, T. Minami, Solid State Ionics, 154 (2002) 635–640.
[4] A. Hayashi S. Hama, T. Minami, M.Tatsumisago, Electrochem. Commun., 5 (2003) 111–114.
[5] Ö.U. Kudu, T. Famprikis, B. Fleutot, M.D. Braida, T.L. Mercier, M.S. Islam, C. Masquelier, J. Power Sources, 407 (2018) 31–43.
[6] R. Mercier, J.P. Malugani, B. Fahys, R. Guy, Acta Crystallogr. Sect. B, (1982) 1887–1990.
[7] K. Homma, M. Yonemura, T. Kobayashi, M. Nagao, M. Hirayama, R. Kanno, Solid State Ionics, 182 (2011) 53–58.
[8] H. Stöffler, T. Zinkevich, M. Yavuz, A. Senyshyn, J. Kulisch, P. Hartmann, T. Adermann, S. Randau, F. Richter, J. Janek, S. Indris, H. Ehrenberg, J. Phys. Chem. C., 122 (2018) 15954–15965.

The vast majority of solid-state electrolyte (SSE) materials are unstable in contact with lithium metal, and (electro)chemical reactions between SSEs and lithium result in the formation of an interphase region [1]. Understanding the growth kinetics and chemo-mechanical consequences of interphase formation is key for controlling solid-state interfaces, which may enable the use of a wider variety of SSE materials within lithium metal batteries. Here, we investigate NASICON-structured L_1+xAl_xGe_2-x(PO₄)₃ (LAGP), as well as sulfide-based SSEs. For LAGP, multi-modal in situ investigation of interfacial reactions combined with electrochemical experiments reveal how the formation of the interphase is linked to cell failure. In situ transmission electron microscopy (TEM) shows that the reaction of LAGP with lithium is similar to a conversion reaction, in which lithium insertion causes amorphization and volume expansion of ~130% [2]. The interphase is a mixed ionic-electronic conductor, resulting in continuous growth. In situ X-ray tomography experiments of operating LAGP-based cells reveal that the growth of the interphase causes fracture of the SSE, and quantification of the crack network shows that the extent of fracture with time is directly correlated to impedance increases within the cell [3]. Finite-element analysis is used to model stress evolution during interphase formation, and the initial fracture locations predicted from modeling correspond well to experimental observations. Interestingly, we have found that interphase growth trajectories can be modulated through the deposition of interfacial protection layers. Controlling the morphology of the interphase with protection layers results in the ability to extend cycling stability of symmetric cells from ~30 hours with unprotected SSEs to >1000 hours with protected materials. Overall, these results provide fundamental insight into interfacial transformations in SSEs, and they show that control over interfacial transformation processes could enable a wider variety of materials to be used in solid-state lithium metal batteries.

1. V. Augustyn, M. T. McDowell, A. Vojvodic “Towards an Atomistic Understanding of Solid-State Electrochemical Interfaces for Energy Storage,” Joule, 2018, 2, (11), 2189-2193.

2. J. A. Lewis, F. J. Q. Cortes, M. G. Boebinger, J. Tippens, T. S. Marchese, N. Kondekar, X. Liu, M. Chi, M. T. McDowell “Interphase Morphology Between a Solid-State Electrolyte and Lithium Controls Cell Failure” ACS Energy Letters, 2019, 4, (2), 591-599.

3. J. Tippens, J. C. Miers, A. Afshar, J. A. Lewis, F. J. Q. Cortes, H. Qiao, T. S. Marchese, C. V. Di Leo, C. Saldana, M. T. McDowell “Visualizing Chemo-Mechanical Degradation of a Solid-State Battery Electrolyte” ACS Energy Letters, 2019, DOI: 10.1021/acsenergylett.9b00816.

As all-solid-state batteries (SSBs) develop as an alternative to traditional cells, a thorough theoretical understanding of driving forces behind battery operation is needed. We present a fully first-principles-informed model of potential profiles in SSBs and apply the model to the Li/LiPON/Li_xCoO₂ system. Starting from the assumption of open-circuit equilibrium, the model predicts interfacial potential drops driven by both electron transfer and Li⁺ space-charge layers that vary with the SSB’s state of charge (SOC). Li⁺ ions tend to move from LiPON to LCO at high SOC but in the opposite direction at low SOC. This explains conflicting experimental observations of the direction of Li⁺ transfer at this interface. Predicted band bending at the interfaces is also in agreement with SXPS data from the literature. The results suggest that a lower electronic ionization potential in the solid electrolyte favors Li⁺ transport into the cathode, leading to higher discharge power. A detailed exploration of the interfaces, including the space-charge layers and decomposition products which may mediate the interfacial potential drop, contributes to the understanding of interfacial lithium transport barriers and can provide guidance to reduce interfacial resistance in SSBs.

This work was supported by the Nanostructures for Electrical Energy Storage (NEES) center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award number DESC0001160.

One of the key challenges in the development of high energy-density solid-state lithium batteries is the development of an electrolyte that is chemically stable with respect to a lithium metal anode. Lithium-rich garnets have been shown to possess the required electrochemical stability window to interface with lithium during battery cycling and consequently are highly promising candidate solid-state battery electrolytes [1,2]. Despite this, garnet-based batteries are yet to achieve commercialisation. Questions remain around how best to optimise lithium conductivity in the garnet framework to make them truly competitive with conventional liquid electrolytes, and how to prevent the formation and propagation of lithium dendrites, which cause batteries to fail by short circuit.

A number of recent works have suggested that defect chemistry of lithium garnets is non-trivial, with experimental evidence for the presence of oxygen vacancies in the as-synthesised materials [2]—This raises questions about both the native defect chemistry, and how native defect chemistry interacts with extrinsic dopants used to control lithium content in an attempt to optimise conductivity. Other work has suggested that electronic conductivity in lithium garnets is the reason behind ruinous dendrite formation [3]; in this work it was proposed that electronic conductivity facilitates the reduction of lithium within the garnet structure, causing dendrites to nucleate within the electrolyte, rather than propagating out from the anode. As the defect and electrical properties of semiconductors are inextricably linked, we have used first principles techniques to investigate both in this work, in an attempt to determine to what extent these can be controlled by synthetic design.

We have used hybrid density functional theory calculations to determine defect formation energies in the prototypical lithium garnet Li₇La₃Zr₂O₁₂ (LLZO). We use these defect formation energies to solve for grand canonical defect and carrier concentrations self-consistently as a function of chemical growth conditions [4].

Analysis of these results suggests that the defect chemistry of LLZO is indeed more complex than previously suggested. We report potential synthesis regimes in which the charge introduced by donor doping to control lithium content is compensated by the formation of Li_Zr anti-sites as opposed to the expected lithium vacancy [6]. Calculation of electronic charge carrier concentrations, in addition to further first principles analysis of dielectric response and charge carrier effective mass, allow for us to estimate electronic conductivities using the Feynman polaron mobility model [7]. These results provide insight into the nature of electronic conductivity and the extent to which synthetic control can be used to minimise electronic conductivity, finding that under the range of temperatures LLZO is typically synthesised under, charge carrier concentrations can vary by 6 orders of magnitude. This work may aid in understanding what synthesis regimes reduce electronic conductivity, with the potential consequence of inhibiting dendrite formation.

References
[1] Thompson, T. et al., ACS Energy Lett., 2017, 2, 2, 462-468
[2] Thangadurai, V. et al., Chem. Soc. Rev., 2014, 43, 4714.
[3] Kubicek, M. et al., Chem. Mater., 2017, 29, 7189–7196.
[4] Han, F. et al. Nat. Energy, 2019, 4, 187–196
[5] Github Page for sc-fermi. https://github.com/jbuckeridge/scfermi.
[6] Pesci, F. et al., J. Mater. Chem. A, 2018, 6, 19817-19827
[7] Frost, J., Phys. Rev. B, 2017, 96, 195202

The application of solid-state ionic conductors is vast, ranging from next generation solid-state Li-ion batteries, to solid oxide fuel cells and different families of sensors. However, the realization of these applications is mostly impeded by the slow diffusion of ions in the lattice. One of the factors that directly impact the conduction of ions in solid materials is the vibration of atoms in the lattice. In the classical theory of diffusion, the effect of these vibrations only enters the formulations through a set of proxy parameters such as the attempt frequency. Such oversimplification of the vibrational effects neglects all the individual contribution that each phonon/mode of vibration can have on the hopping of ions between different lattice sites. In this study, we introduce a formalism that allows us to better understand the effect of individual phonons on the diffusion of ions through the lattice. Specifically, after calculating the modes of vibration for different configurations of the system using lattice dynamics calculations, we determine their contribution to the ionic diffusion using (i) molecular dynamics simulations and (ii) Nudge Elastic Band calculations. Our obtained results on the example structure of Ge-doped Li₃PO₄ revealed that >90% of the Li-ion diffusion in the lattice originates from the vibrational modes with frequencies in the 10-15THz region. Analyzing the distribution of eigen-vectors for these contributing modes shows that the P atom in all these vibrations is frozen and does not participate in the vibrations. Such a high resolution understanding of the contribution of phonons to the ionic conduction opens new gates for (i) improving the performance of the existing electrolytes by engineering the vibrations of phonons in their respective structures, and (ii) searching for better performing solid-state ionic conductors, using methods such as high-throughput computational approaches.

New battery materials hold the key for an electrified future by enabling electrification of transportation and integration of storage on the electric grid. While there is a robust and growing effort to accelerate the discovery of new materials, the next frontier is identifying synthesis pathways to ensure that these materials can be made. Recently, new approaches focused on precision synthesis have gained a lot of attention in the materials field, including battery materials. While the focus of much of these efforts is around developing predictive routes to synthesis materials of a specific crystal structure, it has been clear for decades that the morphology of the material plays an equally crucial role in its behavior. An example is the layered LiNi_xMn_yCo_xO₂(NMC) layered oxide. In these materials the high reactivity of the cathode with respect to the electrolyte remains a key challenge that impedes their performance. It is well-established that the reactivity of these materials depends strongly on crystal facet, suggesting that shielding some primary particle facets from solution could be critical. Cathode secondary particle porosity can aid with fast-charging but also expose greater surface area to reaction. Graded secondary particles, wherein the outer regions are designed to be less reactive while the interiors are designed to be more energetic, have been advanced as an approach, but ensuring that the right gradation is achieved and the right structure is exposed to the electrolyte requires careful morphology control. Finally, while coatings (e.g., Al₂O₃) are known to protect the cathode surface, their coverage tends to differ on different facets. Controlling the reactivity of these materials requires control over the morphology of the cathode material in addition to the structure. Therefore, synthesis routes need to be tuned to achieve the right morphology, in addition to obtaining the right crystal structure.

Over the last two years we have been developing a methodology to link synthesis conditions to particle morphology with the aim of using predictive approaches to guide synthesis. The focus of the research has been around (i) linking synthesis conditions to morphology during the co-precipitation of the NMC-hydroxide precursor and the sintering to the lithiated oxide and (ii) linking the sintering of Li₇La₃Zr₂O₁₂(LLZO) solid electrolytes to the density of the final structure. The methodology involves simulations at multiple scales to bring focus to preferred crystal orientation during synthesis, growth of primary and secondary cathode particles, understanding grain growth and grain boundary movement, and the formation of dense structures as a function of process conditions. The models are complemented with in situsynchrotron x-ray methods and other techniques to provide physical insights and use as comparisons to the models.

This talk to summarize the approach, and describe the physical insights that have been gained in these two material classes. Further, the talk will describe the various opportunities in this emerging new area in battery synthesis.

Lithium ion batteries (LIBs) are todays state-of-the-art power supplies for portable electronic devices as well as for electrical and hybrid vehicles. In addition, LIBs are a promising technology to store the excess energy generated from renewable energy sources which would otherwise be wasted. To meet the requirements of such applications, an optimization of the overall performance, i.e. life-time, cyclability, and energy as well as power density, of such batteries is crucial [1]. A deeper understanding of the transport in the active material used in the electrodes of the LIBs is key to such optimizations. State-of-the-art LIBs usually contain layered structured transition metal oxides, such as Li(Ni_xCo_yMn_1−x−y)O₂ (NCM), as cathode active material (CAM) [2] [3]. To investigate the properties of such CAMs conventionally composite electrodes are prepared. In this composite electrodes micrometer sized spherical secondary particles (diameter of 10 to 30 µm) of the CAM, built from a complex porous network of nanometer sized single crystalline primary particles, are embedded in a network of organic binder and conductive agents. These additives might influence or superpose the properties of the pure active material [4].
To investigate the transport properties in the pristine active material we developed a technique that allows to perform electrochemical measurements on single particles of CAMs. The investigated NCM material was of the composition Li(Ni_1/3Co_1/3Mn_1/3)O₂ (NCM111). The particles were arranged in trap holes, formed via photolithographical structuring a photoresist, on top of a noble metal coated substrate. The setup, on one hand, allowed us to perform experiments with ion-blocking electrodes [5] and, on the other hand, to assemble Lithium ion batteries, that contain a single secondary particle of NCM as cathode active material (SCAMP-LIB). We performed cycling experiments, cyclic voltammetry, and impedance spectroscopy on single secondary particles and agglomerates of NCM111 secondary particles. To resolve the influence of the measurement set-up systematically, different set-ups have been investigated. We found clear evidence, that the secondary particle’s diameter, and therefore its porosity, has an influence on the impedance of the cell system. Furthermore, it was possible to estimate the diffusion coefficient of Lithium ions in the bulk NCM111 during delithiation. This estimated diffusion coefficient was a few orders of magnitude lower than those reported by other groups [6][7]. We found clear evidence, that the investigated material undergoes severe surface degradation during cyclization.
Nevertheless, the presented method is a promising way to study the transport in pristine CAMs. The technique can be further improved by the application of solid electrolytes in the cell system or a controlled arrangement of many single secondary particles to achieve a better model of a real electrode.
References:
[1] J. Wang et al. Phys. Chem. Chem. Phys., 2015, 17, 32033-32043.
[2] L. Li et al. J. Alloys Compd., 2015, 638, 77-82.
[3] T. Ohzuku et al. Solid State Ion., 1994, 69, 201-211.
[4] M. Levi et al. J. Phys. Chem., 2004, 108, 11693-11703.
[5] J. Maier Z. Phys. Chem., 1984, 140, 191-215.
[6] R. Amin et al. J. Electrochem Soc., 2016, 163, A1512-A1517.
[7] J. Li et al. Nano Energy, 2013, 2, 1249-1260.

In-situ exploration of Venus is seriously hampered by its severe environment, which is benign (28^oC) at an altitude of 55 km, but rapidly becoming more hostile at lower altitudes, with temperature increasing initially at ~10oC/km eventually to reach ~465°C and the pressure attaining 90 bars at the surface. These challenging conditions have limited Venus in-situ exploration missions to high altitude balloons at 55 km (above the clouds) that lasted for 48 h, or even shorter duration of 2h for surface missions, even when the batteries were enclosed in thermal chamber. Both these types of missions were implemented using primary batteries. There is a need for more long-duration in-situ missions for a better understanding of the Venus atmosphere across the cloud layers and below, and even to the surface, as recommended by the Venus Exploration Analysis Group (VEXAG). Two types of mission concepts, i.e., i) long-duration variable-altitude balloons with extended range below the clouds, and ii) landers with lifetimes of a few days have gained particular interest. This talk will describe new power technology for a variable altitude balloon (VAB) that we have been developing under NASA-NIAC (NASA Innovative and Advanced Concepts) program for sustained Venus atmospheric exploration. The probe mission concept utilizes: i) Photovoltaics (PV), regenerative solid oxide fuel (SOFC), hydrogen storage bed for on-demand storage or release of hydrogen, and a balloon filled with hydrogen and with hydrogen buoyancy-based altitude control system. This novel architecture enables generation of fuel from in-situ resources at high altitudes, power at low altitudes, and provides transport gas for the balloon. In addition to this VAB, we have been developing high-temperature primary batteries for Venus surface missions under NASA’s HOTTech program. These batteries are based on lithium alloy (e.g., Li-Al) anodes, molten salt electrolytes based on binary/ternary mixtures of alkali metal halides, cathodes consisting of transition metal sulfides and designs similar to the aerospace thermal batteries.

There is tremendous interest in making the next super battery, but state-of-the-art Li-ion technology works well and has inertia in several commercial markets. Supplanting Li-ion will be difficult. Recent breakthroughs in Li metal solid-state electrolytes could enable a new class of non-combustible solid-state batteries (SSB) delivering twice the energy density (1,200 Wh/l) compared to Li-ion. Garnet-type ceramic electrolyte with the nominal formula Li₇La₃Zr₂O₁₂ (LLZO) satisfies many of the criteria necessary to enable Li metal electrodes. However, technological and manufacturing challenges remain. The discussion will consist of recent milestones and attempts to bridge knowledge gaps to include:

Stability and kinetics of the Li metal-LLZO interface
Stability and kinetics of the catholyte-LLZO interface
Manufacturing and scale-up of thin film ceramic constructs and cells.

Despite the challenges, SSB technology is rapidly progressing. Multi-disciplinary research in the fields of materials science, solid-state electrochemistry, and solid-state mechanics will play an important role in determining if SSB will make the lab-to-market transition.

The extension of Internet connectivity and interrelating physical devices, known as Internet of Things (IoT), has become an increasingly growing topic of research over the past few years. Because of rapid progresses in this filed, it is expected that successful implementation of IoT will revolutionize everyday human life within the coming decades. Therefore, it has become inevitably necessary to redesign the current power supplies to integrate them directly into the production line [1]. This has motivated many researchers for enhancing solid-state and on-chip storage systems, such as supercapacitor and lithium-ion battery [2]. In this respect, the significant specific capacity (4200 mAh/g) and high lithium-ion diffusion coefficient of silicon (Si) made it an attractive candidate for storage applications. However, it has been extensively discussed and proved that Si suffers from a low life cycle and large volume expansion. Nanostructuring of Si has been one of the viable solutions to reduce the stress during lithiation. As a matter of fact, porous silicon has been a favourable candidate as on-chip anode for supercapacitor [3], high power density [4] and high energy density device [5]. Although downsizing the active material can prevent volume expansion stress, it also increases specific surface, leading to formation of solid electrolyte interface, which is the origin of irreversible capacity. On this subject, functionalization of the semiconductor surface by carbon has been one of the most compelling alternatives for limiting SEI formation and the first cycle irreversible capacity. Compared to silicon, germanium (Ge) has better electrons and holes mobilities, faster Li-ion diffusion rate, lower charge/discharge potential, and an isotropic volume expansion less significant than silicon during lithiation process. Similar to porous silicon, macro- and mesoporous Ge anodes have shown outstanding performances, but they have been produced by an unscalable and expensive process; the thermal reduction synthesis. In parallel, progresses in the electrochemical etching of Ge provided conditions for the synthesis of low-cost and scalable porous layers [6]. Concerning graphene functionalization based on CVD technique, Ge offers a good catalytic surface, because of the low miscibility of carbon into Ge, to grow a graphene-like coating with higher quality compares to silicon.
In this study, we have investigated a mesoporous Ge on-chip anode that was synthesized by electrochemical etching, and we have compared the improvement of the electrode life cycle and rate capability once the active material was coated with graphene-like layer grown by CVD. A coulombic efficiency above 98% was achieved and 1000 mAh/g capacity was reached during over 400 cycles for the graphene-coated porous Ge nanocomposite on-chip anode. In this presentation, we will discuss the crucial parameters and experimental conditions that allowed us to achieve such high-performance devices and will present a new type of anode which can reach a wide range of power density value.
[1] S. Comello, The emergence of cost effective battery storage, Nat. Commun., pp. 1–9, 2019.
[2] J. M. Tarascon and M. Armand, Issues and challenges facing rechargeable lithium batteries., Nature, vol. 414, no. 6861, pp. 359–67, 2001.
[3] L. Oakes et al., Surface engineered porous silicon for stable, high performance electrochemical supercapacitors, Sci. Rep., vol. 3, pp. 1–7, 2013.
[4] A. S. Westover et al., On-chip high power porous silicon lithium ion batteries with stable capacity over 10000 cycles, Nanoscale, vol. 7, no. 1, pp. 98–103, 2015.
[5] X. Sun, H. Huang, K. L. Chu, and Y. Zhuang, Anodized macroporous silicon anode for integration of lithium-ion batteries on chips, J. Electron. Mater., vol. 41, no. 9, pp. 2369–2375, 2012.
[6] Y. A. Bioud et al., Fast growth synthesis of mesoporous germanium films by high frequency bipolar electrochemical etching, Electrochim. Acta, vol. 232, pp. 422–430, 2017.

Lithium (Li) metal anodes promise to provide high energy density for Li-ion batteries, but are limited by poor cycle life. Among many strategies reported for extending Li metal lifetime for commercial application, polymeric coatings have been investigated as a low-cost and scalable method. So far, viscoelasticity, self-healability, and single-ion conductivity have been proposed as beneficial properties for polymer coatings, but a systematic study of these properties is lacking. Furthermore, previous works exploring coatings with such properties utilize synthetically complex and expensive polymers. In this work, we report the synthesis of a new class of low-cost and scalable coordination polymers based on anionic crosslinking centers that form dynamic bonds with connector ligands. By controlling the chemical nature of the crosslinking center in these coordination polymers, networks with self-healability, viscoelasticity, and single-ion conductivity can be created. By systematically tuning the coordination chemistry, we found that the properties of dynamic self-healability and singe-ion-conductivity both drastically improve the life of Li metal anodes, and that these properties are synergistic.

The final structure for use as a Li metal coating is a dynamic, single-ion-conducting network (DSN) with room temperature Li ion conductivity of 3.5 * 10^-5 S cm^-1. When cut, the material self-heals at room temperature in 12 hours. Molecular dynamics simulations combined with DFT calculations show that the labile bonding between the anionic centers and the coordination ligands impart the dynamic self-healability and high ionic conductivity. When used as a coating on Li metal, 1 mAh cm^-2 of lithium can be reversibly plated and stripped at rate of 0.5 mA cm^-2 for a record high 300 cycles with a high coulombic efficiency of 96.5%. In contrast to other lithium coatings, synthesis of DSN emerges from a facile, scalable, one-pot process with only hydrogen gas as the by-product. Furthermore, the coating can be directly applied to Li metal via a dip-coating process at a cost of only 0.02 $ cm^-2. Using this scalable approach, a DSN-coated Li metal anode was used in a high-voltage NMC-532 full-cell with all commercial components. The coated Li metal anodes show dramatically increased cycle life (160+ cycles) over uncoated Li (<100 cycles). The rational design of these scalable coordination polymers offers a promising approach to enable next-generation batteries with Li metal anodes.

Li-garnets have been considered as the candidate ionic conductors for multiple new technological applications, including all-solid-state batteries¹ and very recently, electrochemical gas sensors,² owing to their wide electrochemical stability window, high room temperature Li-ion conductivity, and good thermal stability. Very recently, research advancements have demonstrated the possibility of transferring Li-garnets to their thin-film forms with various crystalline and poly-amorphous states,³ giving room for researchers to redesign the structural and transport properties with alternatives of low-temperature film processing for grain-boundary-free polyamorphous Li-garnets to compete with state-of-the-art electrolytes, such as LiPON, and prevent dendrite penetration.^3-4 Despite the promises, there is still a lack of understanding on the crystallization kinetics and its effects on Li-ion transport properties. In this study, garnet-type Li₇La₃Zr₂O₁₂ (LLZO), is processed as thin films by spray pyrolysis. The crystallization and phase transitions of the LLZO thin films were studied by DSC together with Raman spectroscopy and in situ TEM. Johnson-Mehl-Avrami-Kolmogorov (JMAK) crystallization theory and Kissinger analysis are applied here, for the first time, to study the fundamentals of the crystallization involving chemical reactions and enthalpy changes during the phase formation process of LLZO. We develop Time-Temperature-Transformation-Conductivity (TTTC) diagrams for Li-garnet films to connect the transport properties with phase formation kinetics. Inspired by the TTTC diagram, crystallization temperature for the cubic phase LLZO is successfully lowered via an isothermal annealing step. Role of structural compaction on ionic conductivity is discussed for the crystalline and poly-amorphous LLZO and compared to the structure-transport characteristics of other Li-glass conductors. Our methodology and results highlight a new opportunity of tuning Li motion and lowering the crystallization temperature by precisely controlling the processing history with a cost-effective processing method.
The insights from this work are expected to serve as fundamental guidelines for understanding the processing-structure-property relationships of amorphous and crystalline Li-garnet. Technologically, the work demonstrates new opportunities to stabilize amorphous and crystalline cubic films at low temperatures, and sets process temperature windows for next-generation solid-state batteries.

Acknowledgments
This work was sponsored by Samsung Electronics.

References
[1] R. Pfenninger, et al., J.L.M. Rupp, Lithium Titanate Anode Thin Films for Li-Ion Solid State Battery Based on Garnets. Advanced Functional Materials 2018, 28 (21).
[2] M. Struzik, et al., J.L.M. Rupp, A Simple and Fast Electrochemical CO2 Sensor Based on Li7La3Zr2O12 for Environmental Monitoring. Advanced Materials 2018, 30 (44).
[3] I. Garbayo, et al., J.L.M. Rupp, Glass-Type Polyamorphism in Li-Garnet Thin Film Solid State Battery Conductors. Advanced Energy Materials 2018, 8 (12).
[4] R. Pfenninger, et al., J.L.M. Rupp, A Low Ride on Processing Temperature for a Fast Li Conduction in Garnet Solid State Battery Films. Nature Energy 2019, 1.

Over the last years, the continuous miniaturization of nomadic electronic systems such as sensors, actuators or medical devices, has put a focus on the growing need for miniaturized energy sources with high power densities. All solid-state thin film batteries have proved to be of particular interest for such applications as they can be directly integrated onto the device. Moreover, the absence of liquid electrolyte is particularly advantageous in terms of safety, particularly for the numerous medical applications that are emerging today.
In this work we propose to present our latest progress on microfabrication process for thin film batteries.
Microbatteries are manufactured on 8 inches silicon wafers using standard semiconductors processes such as physical vapor deposition, photolithography and etching. The fabrication process flow is carried out in a clean room environment using the TINY platform. Lithium based materials are particularly challenging when it comes to patterning processes due to their high reactivity. Moreover, the need for higher battery capacity induces an increase of the materials thickness, which brings also great challenges in terms of process development.
Microfabricated thin film batteries presented in this work are composed of the following layers (bottom-up): Platinum as current collector, LiCoO₂ as the cathode, LiPON as solid electrolyte, Silicon as anode and Titanium as anodic current collector and redistribution layer.
In order to improve the capacity of the battery, the thickness of the LiCoO₂ cathode is increased up to 20 µm, leading to a high defectivity in the film due to coating process limitations. We propose to optimize the patterning process to cope with the high defect density.
After fabrication, the wafer is thinned down to about 50 µm in order to obtain a total thickness of less than 100 µm for the battery. Wafer dicing is then carried out to obtain single batteries ready to be tested and integrated in the final component.
The 5.3 millimeter square batteries demonstrate excellent electrical performances with a discharge capacity of 20µAh (680 µAh.cm^-2, galvanostatic cycling, 3-4.2V potential range, 0.2C rate). The average capacity loss is limited to 0.1%/cycle, with a state of the art coulombic efficiency of 99%.

Lithium metal is considered one of the most promising anode materials for realizing high volumetric and gravimetric energy density, owing to the high specific capacity (∼3860 mAh g−1) and the low electrochemical potential of lithium (−3.04 V vs. the standard hydrogen electrode)[1]. However, undesirable dendritic or mossy lithium growth and corresponding instability of the solid electrolyte interphase prevent safe and long-term use of lithium metal anodes[2-3]. This work presents an easy electrolyte approach to improve the performance of lithium metal batteries by tuning the dielectric constant of the liquid electrolyte. Electrolyte formulations are designed by changing the concentration of ethylene carbonate to have various dielectric constants. This study confirms that high ethylene carbonate content in a liquid electrolyte enhances the cycling performance of lithium metal batteries because the electric field intensity applied to the electrolyte is reduced in relation to the polarization of the electrolyte and thus allows smooth lithium plating by the formation of stable solid electrolyte interphase. We believe that this approach provides an important concept for electrolyte system design suitable for lithium metal batteries.
1. D. Lin et al., Reviving the Lithium Metal Anode for High-Energy Batteries. Nat. Nanotech. 12 (2017), 194-206.
2. K.-H. Chen et al., Dead Lithium: Mass Transport Effects on Voltage, Capacity, and Failure of Lithium Metal Anodes. J. Mater. Chem. A 5 (2017), 11671-11681.
3. P. Bai et al., Transition of Lithium Growth Mechanisms in Liquid Electrolytes. Energy Environ. Sci. 9 (2016), 3221-3229.

Recently, the achievement of newly designed carbon−sulfur composite materials has attracted a tremendous amount of attention as high-performance cathode materials for lithium−sulfur batteries. Compared with commercialized lithium-ion batteries, the Li-S batteries possess a characterisitic advantage in storing an electrical energy (2.6 kWh/kg). To date, sulfur materials have been generally synthesized by a sublimation technique in sealed containers. This is a well-developed technique for the synthesizing of well-ordered sulfur materials, but it is limited when used to scale up synthetic procedures for practical applications. In this study, we design a room-temperature, ambient-pressure chemical synthetic method by which to obtain multistacked, amine-functionalized carbon−sulfur composite materials. By an aqueous chemical conversion from sodium thiosulfate (Na₂S₂O₃), sulfur layers are deposited on preformed two-dimensional carbon templates, which are synthesized through the electrostatic interaction between negatively charged graphene oxides and positively charged amine-terminated multiwalled carbon nanotubes. It is demonstrated that stable cycling performance outcomes are achievable with a capacity of 730 mAhg⁻¹ at a current density of 1 C with good cycling stability by a virtue of the characteristic chemical/physical properties of composite materials. The critical roles of conductive carbon moieties and amine functional groups inside composite materials are clarified with combinatorial analyses by X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy.

To develop high-performance cathode materials in Li-ion batteries, diverse synthetic methods have been explored with the overall goal of producing a product with controlled morphology and without local compositional and crystallographic inhomogeneities. Polyol method is a promising synthetic technique, when properly designed, that can offer these advantages. The unique properties of polyol solvent allow for monodispersed nanoparticle morphology while maintaining scalability for industrial applications. In this work, we introduce this novel synthesis method to produce cathode materials with three different crystal structures - layered LiNi_0.4Mn_0.4Co_0.2O₂, spinel LiNi_0.5Mn_1.5O₄, and olivine LiCoPO₄. Each of the synthesized material shows high crystallinity and competitive electrochemistry due to stable surface structure. After confirming the versatility of this synthetic method, our study extends to the detailed synthesis reaction mechanism that explores nanoscale dynamics occurring during polyol synthesis. With a combination of in situ and ex situ characterizations, including STEM/EELS, soft XAS, synchrotron XRD, and pair distribution functions (PDF) analysis, we directly observe the structural and chemical transformation during each step of the reaction. Our work highlights the deep insights in designing and optimizing synthesis procedure for cathode materials and possibly a wide range of intercalation compounds in the future.

Polymer electrolytes for lithium ion batteries offer superior mechanical stability and lower risks than liquid organic solvents, but are challenged by a lower ionic conductivity. The addition of secondary modifications to the polymer backbone opens up an additional degree of freedom for design to enhance the transport properties, by modulating the polymer-ion and counterion interactions. In this work, we explore how non-covalent interactions govern the interplay between conductivity and viscosity of a series of ethylene-oxide oligomers with secondary modifications. DFT calculations were used to quantify the additional non-covalent interactions introduced by the secondary modifications. A multi-dimensional regression was then fit to experimental conductivity and viscosity data at different temperatures. The binding energies of the secondary site towards lithium ion, counteranion, glyme, and the same secondary site through intermolecular interaction were used as the inputs to the regression. Since all inputs to the predictor are available from affordable simulations, this multi-dimensional free energy relationship was then used to screen for new secondary sites that maximize conductivity, which were then realized in the lab and shown to have 13% higher molar conductivity than baseline at room temperature.

All-solid-state batteries have received significant attention around the world because of high safety, reliability and energy density. Up until now, all-solid-state batteries are produced by vacuum deposition techniques, such as RF-sputtering like physical vapor deposition (PVD) or pulsed laser deposition (PLD), and thermal evaporation. These batteries are developed to use micro-batteries because their specific capacities are only between 5 and 100 μAh cm^-2, depending on the thickness of electrode.
The main challenge facing all-solid-state batteries is to enhance the surface capacity influenced by the thickness of electrode. However, many attempts to increase the electrode thickness have not been successful because of micro-cracks between the components by stress generated at the solid electrode-electrolyte interface. In addition, strong kinetic limitations due to the low mobility of the ions and electrons in the increased electrode is also another problem. To overcome these problems, a composite-electrode made of multifunctional materials should be used as electrode. The composite-electrode contains the electrochemically active material, solid electrolyte, and conducting additive to transport electrons and ions in the electrode.
In this study, a Li_2.2C_0.8B_0.2O₃ solid electrolyte is used for Li⁺ conduction pathway in the composite-electrode because it has a low melting point (> 500 °C) and is expected to act as a bonding material at the interface resulted from liquid phase sintering. Moreover, the composite-electrode with a strong mechanically framework was fabricated by a simple one-step spark plasma sintering (SPS) technique. To apply composite-electrode of all-solid-state batteries, optimized parameters are scrutinized, such as SPS conditions to protect decomposition of active material and the composite-electrode formulation (active material/solid electrolyte/electrical conductor ratio) to ensure good ionic and electronic percolation. The composite-electrode was very dense with very few voids as a result of the microstructure analysis. The Li_2.2C_0.8B_0.2O₃ solid electrolyte was in close contact with the active materials due to liquid phase sintering. A Li-ion conduction path was formed along the electrode particles. In order to analyze the effects of liquid phase sintering systematically, the electrochemical performance of the composite-electrode is discussed in detail.

A separator is a key component for the safety of batteries. The conventional separator is made of polypropylene (PP), that has a shut-down function by closing its pores at an elevated temperature. But its fundamental thermal stability is low; it shrinks largely over melting point (PP: 160 °C), resulting in direct contact and short circuit between cathode and anode. We here propose and report a highly heat-resistant separator based on boron nitride nanotube (BNNT), which has high chemical and thermal stabilities (stable in air up to 900 °C) [1].
Self-supporting BNNT papers (thickness: 25 µm) were fabricated by dispersion and filtration without using binder. Similarly, self-supporting electrodes based on carbon nanotube (CNT) with lithium cobalt oxide (LCO) and graphite for cathode and anode, respectively, were fabricated [2]. The cathode/separator/anode stack was prepared, heated to and kept at a given temperature for 10 min. After cooled down, the insulation between the cathode and anode was checked. Then the charge-discharge test was performed by fabricating a 2032-coin cell using the stack and fresh electrolyte.
The PP separator shrank significantly, resulting in short-circuit at 225 °C. In contrast, the BNNT separator showed little thermal shrinkage and kept insulation even at 500 °C. Furthermore, the stack with BNNT showed no degradation after heating in the charge-discharge test. This showed that BNNT separator as well as the CNT-based electrodes worked without problem after heating at 500 °C.
[1] Y. Chen, et al., Appl. Phys. Lett. 84 (2004) 2430.
[2] K. Hasegawa, S. Noda, J. Power Sources 321 (2016) 155.

Efficient operation of batteries at low temperature is crucial to enable technological development in the areas of electric aircraft, interplanetary space exploration, and advanced robotics. For these high energy applications, Li metal batteries are the superior choice as they can deliver significantly higher specific energy than conventional Li-ion cells with graphite anodes. However, the electrochemical behavior of Li metal anodes at low temperatures is largely unknown. In this work, we investigate the effect of sub-zero temperatures on electrochemical behavior, morphological evolution, and solid-electrolyte interphase (SEI) formation of Li metal anodes in carbonate and ether solvents. We find that electrolytes containing carbonates tailored for low-temperature operation exhibit severe transport limitations at low temperatures, while ether-based electrolytes show promising Li cycling ability down to -80 °C. Interestingly, ex situ investigation after cycling revealed that distinct Li morphologies form at different temperatures, which is likely due to different nucleation and growth behavior, as well as differences in SEI chemistry and structure. Detailed SEI characterization by x-ray photoelectron spectroscopy and cryogenic electron microscopy reveal distinct structures of the SEI formed at room temperature compared to temperatures less than -40 °C . These results provide a fundamental understanding of how Li metal anodes behave at low temperatures, which could enable high-energy batteries for a range of operating conditions and environments.

Utilizations of metal-organic frameworks (MOFs) for electrochemical applications are significantly limited by insulating nature and mechanical/chemical instability. One promising approach for the deployment of conventional MOFs in electrochemical applications is to fabricate MOF-based hybrids (MBHs) with conductive materials, which facilitate effective electron transfer via conductive additives between MOFs. Herein, we present a facile method for effective filling of Cu- and Ni-HKUST-1 (Cu-/Ni-MOF) inside 3D ordered mesoporous carbon (24nm, mC), 3D ordered N-doped macroporous carbon (300 nm, NMC), and 3D ordered macroporous carbon (300 nm, MC), denoted as MOF@mC, MOF@NMC, and MOF@MC, respectively. The MOF@carbon matrix (MOF@CM) composites were intended for use as electrodes for electrical double layer capacitors (EDLCs) and Li-S battery (LSB) and as electrocatalysts for the oxygen reduction reaction (ORR). EDLC performance of MOFs can be significantly improved by facilitating electron transfer through 3D conductive CM, reducing the electron pathway within insulating MOF using CM with small pores, and choice of metal center with pronounced faradaic nature. Ni-MOF@mC exhibited superior specific surface area normalized are capacitance (26.5 uF/cm²), exceeding most carbons and MOF-based EDLCs and outstanding long-term stability (91%@5000th). Furthermore, Cu-MOF@mC resulted in pronounced ORR activities, excellent methanol tolerance, and long-term stability. For LSB, Cu-MOF@mC presented superior performances compared to Ni-MOF@mC probably due to more preferential coordination bonding of S toward Cu center. It is clearly demonstrated that conventional MOFs can be utilized for EDLC, ORR, and LSB when conjugated with a 3D-connectednano-sized CM.

Garnet-type solid electrolytes are suitable for solid-state batteries with a lithium metal anode due to their high ionic conductivity, good stability against the lithium metal, and wide electrochemical window. The interfaces between the garnet electrolytes and the anode/cathode play an important role in the performance of garnet-based lithium metal batteries. In this study, at first, we applied some metal or alloy coating layers on the surface of garnet-type Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO) pellets that were synthesized by pressureless solid-state sintering and assembled LiFePO₄|| LLZTO||Li cells. These LLZTO-based cells showed a long cycle life with a large current density of a few hundreds of μA/cm² at room temperature and an excellent rate performance, because the interfacial resistance between the electrolyte pellets and the Li anode was significantly reduced by 1-2 orders and the lithium dendrite growth was suppressed. The microstructure and composition of the interfacial layers formed at the LLZTO/Li interfaces were systematically investigated by high-resolution TEM and XPS. Next, based on the optimized LLZTO/Li interface above, the interface between the garnet electrolytes and the cathode was studied. Ionic liquid was adopted to improve the contact between the LiCoO₂-based cathode and LLZTO. With an optimal cathode composition, LiCoO₂||LLZTO||Li solid-state cells were fabricated and the influence of the concentration and type of Li salts in the ionic liquid on the performance of these cells was studied. The cells can be steadily cycled at room temperature. It is worth noting that our cathode design is applicable for other active materials when they are combined with garnet electrolytes. Our work provides proper interfacial optimization methods for garnet-based lithium metal batteries and paves the way for developing high-performance solid-state batteries.

Studies on the high specific capacity of silicon (Si) based anodes for lithium ion batteries (LiBs) have recently been conducted, despite a large volume being expanded during electrochemical cycling^[1], which is a significant problem. Although a variety of Si structures have been incorporated into the anode to prevent this problem^[2], such structures have difficulties in terms of mass production. Herein, we present a new way to repetitively produce micron Si rods at different boron (B) doping levels using laser interference lithography (LIL) and metal assisted chemical etching (MACE), enabling the mass-production of multiple Si rods at low cost. The micron rod shaped Si anodes showed a higher rate capability and capacity retention than powdery Si particles. These characteristics are attributed to an increase in the surface-to-volume ratio, and a short radial lithium (Li) ions diffusion path, leading to alleviated pulverization during the de/lithiation process. In addition, the effects of the B-doping level on the electrochemical battery performance are studied for the first time. In particular, lightly B-doped Si rod (~10¹⁵ atoms cm^-3) anodes exhibit the highest capacity and cycling performance, showing a high initial coulombic efficiency (CE) of 98.1% and a capacity fading rate of 0.11% during 500 cycles owing to the high kinetics of de/lithiation relevant to the phase transition and diffusion. Through a CV analysis, it was confirmed that the lightly B-doped Si rod have a low over-potential, implying outstanding kinetics for the de/lithiation process. Whereas the heavy B doping hinders the de/lithiation kinetics because a number of Li atoms are trapped from the outermost side of the Si rods even after being fully delithiated with an increase in B-doping densities. This study provides a new approach for easy and rapid preparation of the electrode material and elucidates the dependence of the electrochemical performance on the level of B doping.

References
[1] Jerliu, B.; Hüger, E.; Dörrer, L.; Seidlhofer, B. K.; Steitz, R.; Oberst, V.; Geckle, U.; Bruns, M.; Schmidt, H. Volume Expansion during Lithiation of Amorphous Silicon Thin Film Electrodes Studied by In-Operando Neutron Reflectometry. J. Phys. Chem. C 2014, 118 (18), 9395–9399.
[2] Feng, K.; Li, M.; Liu, W.; Kashkooli, A. G.; Xiao, X.; Cai, M. Silicon-Based Anodes for Lithium-Ion Batteries : From Fundamentals to Practical Applications. Small 2018, 14, 1702737.

Over last few decades, lithium ion battery (LIB) has been extensively explored and has dominated the power source market for portable electronic devices since Sony Co launched their first LIB in 1992. Recently, as a result of depletion of coal fuels, it triggered cleaner and more sustainable energy technology development including the invention of electrical vehicles (EVs), hybrid electrical vehicles (HEVs) and plug-in hybrid electrical vehicles (PHEVs). The challenges of developing EV, HEV and PHEV are short calendar and cycle lifetime, high weight, high volume and safety issues. LIBs provide the solutions for these technologies due to its high gravimetric and volumetric energy density, rechargeability, temperature stability and capability of scale-up. In most cases, a certain number of cells are packed together in various configurations (parallel and/or series connected) to form a module. Several modules are then combined in series or parallel to provide the required voltage and capacity for EVs or HEVs. The large amount of heat generated by large number of Li-ion batteries packed together during high power charging/discharge, in some cases, can shorten the battery life or posing a safety hazard. Traditional cooling mechanisms such as air cooling and liquid cooling are not favoured in EVs due to the large volume that the components take up and the extra power consumption provided for accessories like pumps and fans. Developing a light-weight high-efficiency cooling system remains challenging to both researchers and companies.
Herein, a novel battery thermal management system (BTMS) based on phase change material (PCM) encapsulated reduced graphene aerogel beads (rGOAB) and silicone rubber has been investigated. Graphene oxide aerogel beads (GOAB) were wet-spun from aqueous GO slurry with a concentration of 15 mg/ml, followed by overnight freeze drying and thermal annealing at 1200 °C for 1 h. Tetradecanol (TD) and octadecane (OD), two paraffin waxes with different phase change temperature (38°C and 28°C), were absorbed into rGOAB via capillary forces at liquid state. Thermal properties of rGOAB infiltrated with TD (rGOAB/TD) and OD (rGOAB/OD) were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Then rGOAB/TD and rGOAB/OD were dispersed in ceramic sillicone rubber and injected into a mold to form a battery pack. 9 Sony 18650 LIBs were connected in series forming a 3 times 3 square, inserted into the pack and put into a thermal insulated box. The batteries were discarged at 1C, 2C and 3C rate, respectively and the temperature was monitored. The effects of rGOAB/paraffin concentration, thermal conductivity of ceramic silicone rubber and phase change temperature were investigated. Comparison of paraffin encapsulated silica capsules were also conducted. The results showed that with 10 wt% of rGOAB/TD in silicone rubber, temperature decreases were up to 8°C, 11°C and 13°C at 1C, 2C and 3C discharge rate, respectively. Silica capsules showed lower temperature decrease compared with rGOAB due to its lower encapsulation efficiency and lower heat transfer property. Moreover, temperature decrease per unit mass increased with the concentration of rGOAB, which is a critical factor for energy density in EVs, HEVs and PHEVs. It was also found that, with comparable latent heat, the phase change temperature of PCM does not affect the overal performance.

Recently, researches on the production and utilization of renewable energy (solar, wind, geothermal, etc.) have attracted attention as environmental pollution problems caused by depletion and use of fossil energy are emerging. The development of the renewable energy sector is essential to build an energy storage system (ESS) to secure the elasticity of energy production and consumption. Therefore, although lithium-ion battery systems widely used today are in the spotlight, the development of new material-based battery systems is required for long-term demand response and stability of supply and demand. Na-ion batteries have similar electrochemical mechanisms to Li-ion batteries and are actively being studied as candidates for energy storage systems due to their abundant amount and price stability.
Na₃V₂(PO₄)₃ (NVP) is one of the promising cathode materials among Na ion storage materials due to its excellent structural and thermal stabilities due to its strong polyanion network. However, it is difficult to secure a reversible capacity close to the theoretical capacity (117.6 mAh g^-1 at 3.4 V vs. Na/Na⁺) owing to NVP's poor electrical conductivity. There have been many attempts to improve the mass and charge transport of NVP materials by decreasing the NVP particles size or introducing conductive materials. In particular, many attempts have been made to synthesize carbon-NVP composites by forming carbon coatings using hydrocarbons, organic solvents, organic acids and surfactants on the surface of NVP. However, these methods require a high carbon weight of at least 10% to achieve high rate performance. Recently, the use of graphene or graphene oxides enabled ultra-high speed movement with a relatively small amount of carbon (less than 5%), but the use of related materials limits the practicality of using Na-ion battery systems instead of lithium.
In this study, we have developed carbon-containing Na₃V₂(PO₄)₃ (NVP) as an active cathode material for Na-ion batteries using carbon-methyl cellulose (CMC) and sucrose as dual carbon sources. The interaction between CMC and sucrose formed a porous structure (surface area: 58.998 m² g^-1) with increased sp² carbon species, promoting mass and charge transport. The specific capacity (104.99 mAh g^-1) of the carbonized CMC/sucrose NVP (CS-NVP) was obtained close to the theoretical capacity (117.6 mAh g^-1). Also, CS-NVP exhibited stable cyclability with a specific capacity of 75.04 mA g^-1 at a rate of 20 C.

Fluoride-ion batteries using solid-state electrolytes are expected as one of the candidates for next-generation rechargeable batteries [1]. For fluoride-ion batteries, the ion carrier is monovalent fluoride ion, which can realize the multi-electron reactions of counter cations in active materials of fluoride compounds. However, it is far from practical use mainly due to lack of solid electrolytes which has high ionic conductivity and a wide electrochemical potential window like lithium-ion conductors. The previously reported fluoride-ion conductors such as PbSnF₄ [2] and La_0.9Ba_0.1F_2.9 [3] contain one type of anion, fluoride ions. To our best knowledge, there is no report on the solid electrolyte materials containing multiple-anion compounds. Fluoride-based multiple-anion compounds have the potential to exhibit abundant functionality (electrical, optical, and magnetic properties, etc.) because of a variety of crystal structures [4]. However, their stability of fluoride compounds is low because the activity of fluorine in the air is extremely low compared to that of oxygen. Therefore, in many cases, controlling the synthesis atmosphere is required, resulting in few research examples of multiple-anion compound using fluoride ion.
In this study, we prepared Yb-F-S compounds containing fluoride and sulfides ions as anions by solid-state reaction under vacuum. In order to identify the phase of the prepared samples, powder XRD measurement was performed. F K-edge and O K-edge XAS measurements were performed at BL-2 in Ritsumeikan University SR Center. Electrochemical impedance spectroscopy and the two-probe conductivity measurement were performed. In addition, the charge-discharge properties of the prepared compounds were examined.
The synthesized sample contains the ytterbium fluoride sulfide as the main phase and ytterbium oxyfluoride as an impurity. One of the reasons for the appearance of this impurity is that the oxygen source which was initially contained in the starting materials could not be removed during the synthesis process and remained in the resulting sample. Electrochemical measurements indicate that the prepared compound exhibits electric conductivity. This is because ytterbium ion in this compound is a mixed valence state with divalent and trivalent.

Reference:
[1] M.A. Reddy and M. Fichitner, J. Mater. Chem, 21, 17059–17062 (2011).
[2] N. I. Sorokin, P. P. Fedorov, O. K. Nikol’skaya, O. A. Nikeeva, E. G. Rakov, and E. I. Ardashinikova, Inorg. Chem., 37, 1178-1182 (2017)
[3] C. Rongeat, M. A. Reddy, R. Witter and M. Fichtner, Appl. Mater. Interfaces, 6(3), 2103-2110 (2014).
[4] M. Leblanc, V. Maisonneuve, A. Tressaud, Chem. Rev., 115, 1191-1254 (2015).

Dense thin films of Li₂O and Li₂S grown by r.f. sputtering are found to exhibit ionic conductivities at 25 °C that are multiple orders of magnitude higher than expected from the bulk defect chemistry. The enhancement appears not to be due to the substrate - film interface, nor to doping, nor to the presence of impurity phases. Instead, the evidence points to higher-dimensional defects as enabling the faster ion transport. The resulting conductivity values are consistent with those typically observed from composite SEI layers that contain Li₂O or Li₂S. This work may help explain the rate-limiting process for ion transport through some SEI layers.

Lithium-ion batteries(LIBs) have been successfully utilized as a main power source for various energy storage applications owing to their high energy density and excellent power characteristics. Unfortunately, current LIBs cannot fulfill the requirements of the rapidly growing electric vehicle(EV) market due to their limited energy density based on conventional electrode materials [1]. Therefore, the development of advanced materials for LIBs has become very important. In practice, graphite is the most popular anode material of commercialized LIBs owing to a low reaction potential(~0.2V vs. Li/Li⁺) and a high reversibility toward Li⁺ intercalation and de-intercalation. However, the practical use of graphite in EV applications is hindered by poor rate capability and cycle performance because Li⁺ intercalation into graphite is allowed only through the edge-plane of graphite so that uncontrollable metallic Li is deposited on the surface of graphite anode under high-rate cycles [2]. In this respect, it is crucial to develop a robust design of graphite to make it more suitable for EV applications. With a purpose of improving the rate capability and cycle performance of graphite, herein, we propose a bi-phasic graphite decorated with N-doped nanoporous carbon(NPC) nanoparticles. It can be obtained by a direct growth of ZIFs(Zeolitic Imidazolate Framework) on the surface of graphite followed by a carbonization process. The large specific area and high electrical conductivity of NPC offer additional reaction sites of Li⁺ as well as promote charge-transfer reactions [3-4]. Furthermore, the porous structure of NPC is advantageous for securing the tortuosity of electrode and facilitating Li⁺ migration in the electrode during cycles. Based on the electrochemical and structural analyses, further discussion on the positive effects of NPC decoration on the rate capability and cycle performance of graphite will be presented.

References
[1] Lu, L. Han, X. Li, J. Hua, J. & Ouyang, M. J. Power Source. 226, 272-288 (2013).
[2] Zhang, S. S. J. Power Source. 161, 1385-1391 (2006).
[3] Qie, L. Chen, W. -M. Wang, Z. -H. Shao, Q. -G. Li, X. Yuan, L. -X. Hu, X. -L. Zhang, W. –X. & Huang, Y. -H. Adv. Mater. 24, 2047-2050 (2012).
[4] Zheng, F. Yang, Y. & Chen, Q. Nat. Commun. 5, 5261 (2014).

Fluctuation of oil prices and the effects of global warming have resulted in increased research in alternative energy storage and conversion systems, especially in battery technologies. Development of cost effective and environmentally safe battery technologies for a variety of applications ranging from small portable electronic devices to electric vehicles are also driven by increased public awareness of fire, explosion and toxicity risks associated with today’s Li-ion batteries. Metal-air batteries are considered as cheaper and safer alternative to Li-ion batteries due to their theoretically higher energy densities (1000-13000 Wh kg^-1) for a wide range of applications. However, metal-air batteries have not reached their full potentials as they suffer from limited capacity and lifetime mostly due to catalyst corrosion, anode passivation and corrosion, electrolyte loss and pore clogging leading to performance loss and reduced cycle life.

Here we present an improved Gas Diffusion Electrode (GDE) based on CVD deposited hydrophobic and oxygen selective polymeric thin films as gas diffusion layers to increase energy and power densities of metal-air batteries. Oxygen selective and highly hydrophobic copolymer thin films containing tetravinyltetramethylcyclotetrasiloxane (V4D4), 2-(perfluorohexylethyl) acrylate and 2-(perfluoroalkyl)ethyl methacrylate were fabricated via Initiated-CVD. Fabricated copolymer films minimize the accumulation of excess water and prevent flooding of GDE during battery operation. In addition, higher oxygen permeability leads to higher current densities resulting in improved battery performance.

Both distribution and composition of Lithium in a charged cathode affect the capacitance and the efficiency of Lithium ion battery (LIB). Auger Electron Microscopy (AES) is one of the common methods to analyze distribution and composition of Lithium in the battery with high spatial resolution by using focused electron beam for surface analysis of the specimen. Since the energy of Auger electrons is a few electron volts, it is possible to analyze with surface sensitive information. In addition, AES is also capable of providing depth profiling by using Ar ion sputtering, making AEM a quite useful method for LIB analysis. However, there are issues with AES analysis for LIB. The Auger electrons are very sensitive to the electrostatic field on the surface. The user should therefore create a condition of ‘floating’ Cathode with respect to the specimen holder during AES analysis. Otherwise, the Cathode will discharge Lithium ion during the analysis.
Currently we are focusing our efforts on using SXES (Soft X-ray Emission Spectrometer) method, which was recently developed. This method allows analysis of characteristic X-ray of Lithium by charging on the sample surface.
The SXES is installed on Field Emission SEM (Scanning Electron Microscope) that is able to detect soft X-rays with high spatial resolution. The acquisition energy range of SXES is less than 250 eV, which means that this SXES enables the use of low landing voltage with small interaction volume for X-ray excitation such as 2 kV or below. Such setup makes SXES a surface analysis method like an AES. In addition, using SXES is sufficient to generate soft X-rays with low landing energy such as 2 kV, which suppresses the charging of the sample by the irradiated electrons.
JEOL FE-SEM (JSM-7200F) equipped with SXES (SS-94000) was used for analyzing Lithium distribution in LIB Cathode. Sample was prepared in a glove box and transferred without air exposure into the SEM to avoid any oxidation. The soft X-ray spectra were acquired at an accelerating voltage of 2 kV and a beam current of 40 nA. As a result, a characteristic X-ray of a Lithium peak around 48 eV was detected from the surface of fully charged LIB cathode.
In this study, we will report that we examined the distribution of Lithium by direct analysis from the surface of charged Lithium ion battery cathode using SEM-SXES.

Recently, lithium ion batteries (LIBs) have been considered as the most suitable power source for various energy storage applications. In the LIBs, graphite is widely used as a commercial anode material because it offers a low reaction potencial (~0.2 V vs. Li/Li⁺) and high theoretical capacity (~372 mAh/g) [1]. However, because of the layered structure of the graphite, graphite does not offer sufficient cycle performance and rate-capability for practical use in electric vehicles (EV) applications [2]. Therefore, it is of great importance to develop advanced anode materials with improved electrochemical performance in this research field. To overcome these technical limitations, various structural modifications of the graphite have been proposed to make it more favorable for securing a long term cycle stability as well as excellent power characteristic. In this respect, we focused on advantages of non-stoichiometric metal oxides with distinctive electronic propreties because they can play an important role as a functional additive for improving the electrochemical performance of the graphite [3]. Herein, we propose a new material design with a core-shell structure in which graphite core is encapsulated by a functional surface layer (shell) composed of non-stoichiometric MeO_x and amorphous carbon. The functional layer can be successfully introduced on the surface of graphite by a simple solution process combined with a carbothermal reduction using MeO₂ nanoparticles and coal-tar pitch precursors. Tailoring the surface structure of graphite with a functional layer is effective for suppressing structural degradation and lowering the overpotential at the surface of graphite even at high current densities. In addition, cycle performance of the proposed anode material can be notably improved compared with commercial graphite. Based on a range of structural and electrochemical analyses, fundamental roles of the functional layer on the surface of graphite will be discussed.

References
[1] Shu, Z. X. McMillan, R.S. & Murray, J. J. J. Electrochem. Soc. 140, 922-927 (1993).
[2] Terada, N. J. Power sources.100, 80-92 (2001).
[3] Karen, P. J. Solid State Chem. 179, 3167-3183 (2006).

During the last decade, lithium ion batteries (LIBs) have shown great promise as a potential power source for various application such as portable electronic devices and electric vehicles (EVs) [1]. Responding to growing demand for high-energy LIBs, it is crucial to develop materials which provide a higher energy density than commercial materials currently available.

Li metal has been considered as a future anode material for LIBs because of its extremely high theoretical capacity (~3,860mAh/g) and low redox potential. Despite these benefits, the practical use of Li metal is limited by several technical issues as follow; i) inevitable growth of dendritic Li and ii) infinite volume changes during cycling are regarded as drawbacks causing rapid performance degradation and safety issues [2]. Recently, porous carbon materials with well-distributed pore that can serve as Li storage reservoir have been proposed to suppress unfavorable volume changes [3-4]. Herein, we design a disordered mesoporous carbon (DPC) as a potential Li storage material, allowing a dual-phase reaction (i.e. lithiation and metallization). It can be synthesized via a direct carbonization of silica-embedded zeolitic imidazolate frameworks (SEZIFs) combined with a chemical etching process. The DPC exhibits a great potential for accommodating a large amount of metallic Li thanks to its highly mesoporous structure. In practice, we confirm that Li can be reversibly stored in the structure based on various electrochemical and structural analyses. Furthermore, a correlation between pore structure and Li storage behavior is thoroughly investigated to examine the feasibility of DPCs as the next generation anode for high-energy LIBs.

References
[1] Nitta, N. Wu, F. Lee, J. T. & Yushin, G. Mater. Today. 18, 252-264 (2015).
[2] Xu, W. Wang, J. Ding, F. Chen, X. Nasybulin, E. Zhang, Y. & Zhang, J. -G. Energy Environ. Sci. 7, 513-537 (2014).
[3] Li, A. Tong, Y. Cao, B. Song, H. Li, Z. Chen, X. Zhou, J. Chen, G. & Luo, H. Sci. Rep. 7, 40574 (2017).
[4] Vu, A. Qian, Y. & Stein, A. Adv. Energy Mater. 2, 1056-1085 (2012).

Recently, demands of renewable energy are increasing with against lack of energy resources. However, power generation of renewable energies (solar and wind-power) drastically change with meteorological variation, and have poor stability of output performances. Therefore, large-scale and high-energy-density energy storage devises are strongly desired for power system stabilization, and lithium-sulfur (Li-S) batteries are expected as the one candidates. Main advantages of Li-S batteries are low-cost of elemental sulfur (S₈) and their high capacity (1,672 mAhg^-1). On the other hand, intermediate compound of positive electrode material with charge-discharge process (Li₂S_x) can be easily dissolved into electrolyte solution with significant degradation of cells. Moreover, lithium dendrite grows up at the Li metal and causes internal short-circuit. In this study, to prevent the Li dendrite, Li-incorporated negative electrode, such as C₆Li_x (Li-doped graphite electrode) was proposed as a stable electrode.
C₆Li_x electrodes were prepared by reconstructed process of electrochemical cells (C₆ | electrolyte | Li). In order to improve the efficiency of Li dope process, we investigated the electrolyte species (glyme and sulfolane) and composition dependencies for electrochemical performances. Moreover, preparation process of cells (annealing temperature) affected electrical coulombic efficiency. In the presentation, we will also report Li-S battery performances of [S₈ | electrolyte | Li-doped C₆ (C₆Li_x)] cells, and their related applied systems.

In recent years, lithium-ion cells have been introduced into electric vehicles. Presently, one of the most promising cathode materials for lithium batteries industry are mixed manganese nickel cobalt oxides (NMCs) due to their high specific capacity and high cycle stability.
In this work, we present how the application of different electrolyte mixtures influences safety and stabilizes the NMC cathode material with upper cutoff potential exceeding 4.2 V. Next, we will demonstrate all-solid-state battery (ASSB) design using S-based solid electrolyte. The structure and morphology of the materials will be examined using Raman spectroscopy, scanning electron microscopy, X ray powder diffraction and specific surface area by (BET). Electrochemical measurements are carried out in three-electrode Swagelok® systems with Li metal as counter and reference electrodes and a working electrode composed of NMC active material. In order to determine the optimal potential window of NMC without a significant specific capacity drop electrolytes based on LiPF6, LiTFSI, LiTDI and LiBOB in various organic solvents were tested. Those cells are characterized by chronopotentiometry and cyclic voltammetry.
As most of the batteries with liquid electrolyte are flammable and unstable and therefore are not a reliable solution for various applications, especially in higher voltage systems, we present an alternative design characterized by higher safety and energy density thanks to application of S-based solid electrolytes to our exemplary ASSB system. Thin layered ASSB design will be possible thanks to our recently discovered liquid synthesis approach of producing lithium thiophosphates.^1–3 This new generation of all-solid-state batteries creates new possibilities. It may be attractive, efficient and safer for several energy storage systems, especially for automotive industries due to the large potential window, higher energy density, and its inflammability.



1. Wang, H., Hood, Z. D., Xia, Y. & Liang, C. Fabrication of ultrathin solid electrolyte membranes of β-Li 3 PS 4 nanoflakes by evaporation-induced self-assembly for all-solid-state batteries. J. Mater. Chem.A 4, 8091–8096 (2016).
2. Ziolkowska, D. A., Arnold, W., Druffel, T., Sunkara, M. K. & Wang, H. Rapid and Economic Synthesis of Li7PS6 Solid Electrolyte from Liquid Approach. ACS Appl. Mater. Interfaces (2019).
3. Hood, Z. D. et al. Fabrication of Sub-Micrometer-Thick Solid Electrolyte Membranes of β-Li3PS4 via Tiled Assembly of Nanoscale, Plate-Like Building Blocks. Adv. Energy Mater. 1800014 (2018).

Solid State Batteries offer safe alternatives to classical Lithium-ion batteries (LIBs) due to the non-liquid nature of the electrolyte and give perspective to assure both, high energy and power densities^1–3. Despite the fast-growing field of solid-state batteries, the high-temperature manufacturing of the battery cell components and co-assembly of solid electrolyte/cathode interfaces define largely by structures and kinetics the battery characteristics for technology. Till date, interface fabrication in Li-garnet (LLZO) based cathode/electrolyte interface is reported for high-temperature sintering (600-1050 ^oC)^4–8 and also implicate its electrochemical storage capability. However, interfacial resistances for the Li⁺ transfer between the active material and the LLZO electrolyte and corresponding overpotential are still high which limits overall performance. Through this work, we focus on fabrication and characterization of all solid state cathode/LLZO electrolyte interfaces using most popular oxide cathode material, LiFePO_4, and LiCoO₂. Critical discussion is placed on how to enhance contact quality at low temperature in the co-assembly manufacturing vs. phase stability. We highlight the need to control the number of the reaction site and assure efficient electro-ionic percolation pathway by comparing classic co-sintered and infiltration manufactured cathode/electrolyte assemblies, and also discuss the findings towards other three-dimensional composite cathodes processed with and without additives. Ultimately, this work provides guidelines on the phase stability of LLZO and cathode interfaces, and temperature window for processing depending on the manufacturing route (classic sintering vs. infiltration) for the engineering of future solid-state batteries based on Li-garnets for safe energy storage.

(1) van den Broek, J.; Afyon, S.; Rupp, J. L. M. Interface-Engineered All-Solid-State Li-Ion Batteries Based on Garnet-Type Fast Li+Conductors. Adv. Energy Mater. 2016, 6 (19), 1–11.
(2) Hänsel, C.; Afyon, S.; Rupp, J. L. M. Investigating the All-Solid-State Batteries Based on Lithium Garnets and a High Potential Cathode-LiMn1.5Ni0.5O4. Nanoscale 2016, 8 (43), 18412–18420.
(3) Pfenninger, R.; Struzik, M.; Garbayo, I.; Stilp, E.; Rupp, J. L. M. A Low Ride on Processing Temperature for Fast Lithium Conduction in Garnet Solid-State Battery Films. Nat. Energy 2019.
(4) Han, F.; Yue, J.; Chen, C.; Zhao, N.; Fan, X.; Ma, Z.; Gao, T.; Wang, F.; Guo, X.; Wang, C. Interphase Engineering Enabled All-Ceramic Lithium Battery. Joule 2018, 2 (3), 497–508.
(5) Liu, T.; Zhang, Y.; Zhang, X.; Wang, L.; Zhao, S. X.; Lin, Y. H.; Shen, Y.; Luo, J.; Li, L.; Nan, C. W. Enhanced Electrochemical Performance of Bulk Type Oxide Ceramic Lithium Batteries Enabled by Interface Modification. J. Mater. Chem. A 2018, 6 (11), 4649–4657.
(6) Liu, T.; Ren, Y.; Shen, Y.; Zhao, S.; Lin, Y.; Nan, C. Achieving High Capacity in Bulk-Type Solid-State Lithium Ion Battery. J. Power Sources 2016, 324, 349–357.
(7) Tsai, C. L.; Ma, Q.; Dellen, C.; Lobe, S.; Vondahlen, F.; Windmüller, A.; Grüner, D.; Zheng, H.; Uhlenbruck, S.; Finsterbusch, M.; et al. A Garnet Structure-Based All-Solid-State Li Battery without Interface Modification: Resolving Incompatibility Issues on Positive Electrodes. Sustain. Energy Fuels 2019, 3 (1), 280–291.
(8) Shoji, M.; Munakata, H.; Kanamura, K. Fabrication of All-Solid-State Lithium-Ion Cells Using Three-Dimensionally Structured Solid Electrolyte Li7La3Zr2O12 Pellets. Front. Energy Res. 2016, 4 (August), 1–7.

Lithium-sulfur batteries have been actively studied as one of the future energy storage devices because they have higher theoretical capacity values compared to commercial lithium-ion batteries. Since sulfur is abundant in nature, it is low in price and environmentally safe. However, when sulfur is used as an anode material for lithium-sulfur batteries, it often lowers the conductivity and the reaction intermediates (ex. Li₂S, Li₂S₂) cause expansion in volume. The reaction intermediates also show high solubility in electrolytes reducing the cell cycles. Porous structured carbon with high content of sulfur can suppress volume expansion and also improve conductivity. Porous carbon can easily be synthesized by carbonization of metal-organic framework (MOF) with controllable porosity facilitating charge transfer. Heteroatom doping can also enhance the conductivity and prevent dissolution of polysulfide into electrolytes due to an electronegativity of the doped atoms.
Herein, we synthesized MOF-5 derived N, S-codoped porous carbon via microwave-assisted solvothermal method. The microwave-assisted solvothermal process can drastically reduce the time (<30min) required for heteroatom (N, S) doping compared to conventional solvothermal methods (several hours). When thiourea was used as a doping source, 1~3 at% and 2~5 at% of N and S in porous carbon were obtained, respectively. Furthermore, when it was used as a cathode of Li-S battery, it showed high initial capacity of ~1300 mAhg^-1 and excellent cell cycle retention of 60% at 0.1 C after 150 cycles. In addition, the crystal size of MOF was controlled by stirring speed. As a result of controlling the stirring speed from 0 to 300 rpm, it was confirmed that the crystal size of the MOF changed to a size of about 10 μm to 100 μm (higher speed results in smaller crystal size). As a result of reduced-size crystal applied to Li-S battery, the initial capacity was improved to ~1400 mAhg^-1 at 0.1C compared to ~1000 mAhg^-1 at 0.1C for non-stirred MOF. Therefore, we can greatly improve the performance of Li-S batteries by optimizing structure and composition of porous carbon which can contribute to commercialization of Li-S batteries.

Na-ion batteries (NIBs) [1] are attracting widespread interests as convenient alternatives to current state-of-the-art Li-ion batteries (LIBs) [2] for large-scale grid energy storage applications [3]. Despite similar working principles, the larger sodium ion needs different component materials than LIBs, especially at the negative electrode [4]. In this context, recent studies have proposed new electrodes based on nano-structured materials like TiO₂ anatase nanoparticles, and the reported results are very promising in terms of both performance and stability [5]. However, a deep comprehension of the surface-related mechanism for insertion/de-insertion of Na into the specific materials surface/interface termination is still missing. Within this context, in this contribution we report state-of-the-art first-principles calculations on two prototypical systems that can be applied as nano-electrodes in NIBs, namely the TiO₂ anatase nanoparticles, and the MoS₂-Graphene hybrid 2D heterojunction [6].
First, we rationalize the adsorption and insertion of Na at the different (101), (100) and (001) surface termination of TiO₂ anatase nano-particles: our results provide an unambiguous explanation of recent relevant experiments. Second, we will highlight the potentiality of molybdenum disulfide 2D nano-layer supported on Graphene for the inclusion and diffusion of the sodium cation at such hybrid interface.
In conclusion, the new insights on the structural features that determine the observed electrochemical behavior can be easily exploited further for the design of new and more effective nano-structured electrodes for NIBs.
Authors wish to thank European Union (FSE, PON Ricerca e Innovazione 2014-2020, Azione I.1 “Dottorati Innovativi con caratterizzazione Industriale”), for funding a Ph.D. grant to Arianna Massaro.

REFERENCES:
[1] J-Y. Hwang, S-T. Myung, Y-K. Sun “Sodium-ion batteries: present and future” Chem. Soc. Rev., 46 (2017), 3529-3614.
[2] B. Scrosati, J. Garche, “Lithium batteries: Status, prospectus and future” J. Power Sources, 195 (2010), 2419-2430.
[3] D. Larcher, J.M. Tarascon “Towards greener and more sustainable batteries for electrical energy storage” Nature Chem., 7 (2015), 19-29.
[4] L. P. Wang, L. Yu, X. Wang, M. Srinivasan, Z. J. Xu “Recent developments in electrode materials for sodium-ion batteries” J. Mater. Chem. A, 3 (2015), 9353-9378.
[5] F. Bella, A.B. Muñoz-García, G. Meligrana, A. Lamberti, M. Destro, M. Pavone, C. Gerbaldi, “Unveiling the controversial mechanism of reversible Na storage in TiO₂ nanotube arrays: Amorphous versus anatase TiO₂”, Nano Res., 10(8) 2017, 2891-2903.
[6] H. Hwang, H. Kim, J. Cho, “MoS₂ Nanoplates Consisting of Disordered Graphene-like Layers for High Rate Lithium Battery Anode Materials”, Nano Lett., 11 (2011), 4826.

Grid-scale implementation of redox flow batteries (RFBs) has been hindered by the availability of cost-effective redox couples within the solvent window of aqueous electrolytes. Vanadium is the predominant active species in RFBs because it is highly reversible over many cycles and it possesses multiple oxidation states, allowing it to be used in both sides of the battery (positive electrolyte: V⁵⁺↔V⁴⁺, negative electrolyte: V²⁺↔V³⁺). However, the cost of vanadium is too high, resulting in a high capital cost that is not competitive for grid-scale energy storage. While other redox active species are frequently reported, such as Fe, Cr, and Br, there are few that are compatible with the aqueous solvent window while utilizing graphite electrodes, commonly used in the standard RFB configuration.

In this presentation, boron-doped diamond (BDD) is shown to be an exceptional alternative to the standard graphite electrode by enabling a wide range of redox couples that are more cost effective, environmentally friendly, and sustainable, while also offering improved efficiencies and energy densities than the current state-of-the-art. Diamond has proven itself to be a superior material for a variety of applications and its utility in electrochemistry has become increasingly apparent over the past decade. In addition to diamond’s ability to resist fouling and corrosion in extreme environments, it’s most critical advantage for flow batteries is it’s extremely high overpotential for both hydrogen and oxygen evolution (-1 V to 2.5 V, respectively). This large solvent window enables the use of redox couples that would occur with common electrodes, such as graphite or platinum, in either the hydrogen or oxygen evolution regime. Despite these advantages, it has not been until now, that BDD has been considered for use in RFB technology. This has led to the identification of several additional relevant redox couples that were previously out of reach. This research represents a monumental advancement of RFB technology and could be the solution to grid-scale energy storage challenges.

Secondary Li-ion batteries are the battery concept with the highest energy density both per volume and weight currently on the market and have driven the electric mobility transition.
A difficult compromise between energy density and safety has to be found for electric vehicle (EV) Li-ion chemistries. The most common positive electrode for EV applications is based on the LiNi_xMn_yCo_zO₂(NMC) system, as this is the only system that can meet the power and range requirements. Increasing the Ni content with NMC oxides results in higher capacity values but is detrimental to the capacity retention and the thermal stability.
This work explores a simple acidic co-precipitation route as a "one-pot" synthesis for high energy layered oxide cathodes by oxalate precipitation, adapted from a method described by Zhen Chen et al. [1]. This versatile synthesis route allows for the preparation of single phase high Nickel oxides such LiNi_0.8Mn_0.1Co_0.1O₂ (NMC 811), and more complex composites such as LiNi_0.8Co_0.15Al_0.05O₂ decorated LiNi_0.84Mn_0.08Co_0.08O₂ in core-shell structure with improved capacity retention compared to NMC 811. This study further includes the implementation of protective surface coatings to further improve the cycle-life and increase the thermal stability of Ni rich layered oxides by lowering the reactivity of the material surface. Most reported coating methods rely on expensive fluidised bed atomic layer deposition. [2-4] Here we compare FB-ALD with wet chemical methods that can be implemented into the material synthesis.

[1] Noh, Hyung-Joo., et al., Comparison of the structural and electrochemical properties of layered Li[Ni_xCo_yMn_z]O₂ (x= 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) cathode material for lithium-ion batteries. Journal of power sources , 2013, 233, 121-130.
[2] Laskar, M.R., et al., Atomic Layer Deposition of Al2O3-Ga2O3 Alloy Coatings for Li[Ni0.5Mn0.3Co0.2]O2 Cathode to Improve Rate Performance in Li-Ion Battery. ACS Appl Mater Interfaces, 2016, 8(16), 10572-80.
[3] Wise, A.M., et al., Effect of Al2O3 Coating on Stabilizing LiNi0.4Mn0.4Co0.2O2 Cathodes. Chemistry of Materials, 2015, 27(17),6146-6154.
[4] Han, B., et al., From Coating to Dopant: How the Transition Metal Composition Affects Alumina Coatings on Ni-Rich Cathodes. ACS Appl Mater Interfaces, 2017, 9(47), 41291-41302.

In recent years, a new class of high entropy materials has gained scientific interest besides the already known high entropy alloys, namely, the “high entropy oxides” (HEOs).^1,2 These compounds are based on the concept of entropy stabilization of crystal structures in oxide systems by embedding multiple metal cations into single-phase crystal structures. The interactions among the various metal cations lead to interesting and often unexpected characteristics. Some of the compounds show electrochemical and structural properties, which improve the capacity retention of conversion materials for Li-ion batteries.^3,4 Another promising material class are the high entropy oxyfluoride systems (HEOFs), showing great potential to be part of next generation cathode materials.⁵ The modular building approach for these high entropy materials allows tailoring the composition to develop customized electrode materials, e.g. with reduced Co content.
In our report we present different approaches, which utilize the high entropy concept, for novel high entropy electrode materials.^3,5 The compounds (Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)O and Li(Co_0.2Cu_0.2Mg_0.2Ni_0.2Zn_0.2)OF are used as anode and cathode materials, respectively. By replacing, adding or subtracting elements, the electrochemical properties can be tailored and the influence of different elements evaluated.
References:
1. Sarkar, A. et al. High-Entropy Oxides: Fundamental Aspects and Electrochemical Properties. Advanced Materials (2019). doi:10.1002/adma.201806236
2. Rost, C. M. et al. Entropy-stabilized oxides. Nat. Commun. 6, 1–8 (2015).
3. Sarkar, A. et al. High entropy oxides for reversible energy storage. Nat. Commun. 9, (2018).
4. Sarkar, A. et al. Nanocrystalline multicomponent entropy stabilised transition metal oxides. J. Eur. Ceram. Soc. 37, 747–754 (2017).
5. Wang, Q. et al. Multi-anionic and -cationic compounds: new high entropy materials for advanced Li-ion batteries. Energy Environ. Sci. 17–19 (2019). doi:10.1039/c9ee00368a

Li-ion secondary batteries are widely used in many applications from various of electric devices, including mobile phones and electric vehicle to large scale power storage system due to high capacity, cycle ability and in/out put ability. Conventional electrolytes of Li-ion battery are mainly used flammable organic liquid electrolyte such as ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC). Not only performance improvement of batteries but also securing of essential safety of Li-ion batteries are also important. All solid-state Li ion battery can solve the safety problem and higher energy density by stacking, weight saving of device by thinning of electrolyte layer are also possible. Our group focused on solid polymer electrolyte with high flexibility and oxide-based inorganic solid electrolyte with high ionic conductivity and chemical stability in air.
We prepared polymer/inorganic composite solid electrolyte has high autonomy at thinning by using polyether-based solid polymer electrolyte and cubic-Li₇La₃Zr₂O₁₂(LLZO), one of the most candidate Li-ion conductive inorganic electrolyte with garnet structure.
Preparation of samples and cell were carried out in Ar-filled grove box. LiN(SO₂CF₃)₂ and DMPA (photo initiator) were dissolved in polyether-based macromonomer solution ([Li] / [O] =0.1, amount of O was based on oxide unit from polyether and DMPA is 1000ppm based on weight of macromonomer). Cubic-LLZO were mixed in weight ratio of macromonomer: LLZO = 1: x (x =0, 0.2, 0.33, 0.42, 0.5, 0.6, 0.66) and a little acetonitrile were added to the solution to obtain homogeneous solution. The solutions were vacuum dried over 12h. The solutions were casted on glass plate and covered by two glass plate and 0.5mm teflon spacer. Composite solid electrolyte films were fabricated by radical polymerization under UV at 5 min.
Ionic conductivity, Li/electrolyte interfacial behavior using Li/Li symmetrical cell, Li ion transport number were measured by AC impedance method (VSP, Bio-logic). Temperature dependence of ionic conductivity and Li/electrolyte resistance were carried out and Li-ion transport number were also measured at 333K. We consider that there are two Li ion conduction pass of polymer phase and LLZO particle in polyether/LLZO composite system from changing of impedance spectra. Li-ion conduction in LLZO particle and grain boundary is more preferentially than polymer phase because of ionic conductivity and amount of Li-ion career are much higher than polymer phase.
Thermal properties of polyether/LLZO composite solid electrolytes were measured by differential scanning calorimetry (THRMO PRO EVO2, Rigaku). Heat capacity changes with glass transition of polymer electrolyte were observed -243K.
All solid-state Li batteries were prepared using LiCoO₂ for positive electrolyte and Li metal for negative electrolyte. Charge-discharge measurements were performed in the operating voltage 4.2~2.5V and 0.05C rate at 333K and showed initial capacity of 120mAh/g. We will present about charge-discharge property and ionic conduction mechanism of polyether/LLZO composite system in detail on conference.

Prussian blue analogues (PBA) are some of the most promising cathode materials for sodium-ion and potassium-ion batteries operated in both aqueous and non-aqueous electrolytes.¹ They have an open-framework structure that exhibits minimal structural change during ion insertion/extractionand enables fast ionic conduction. This leads to high power and long cycle life electrodes. However, the excellent properties of PBA cathodes can only be fully utilised in a full cell with an anode of comparable performance. One pathway to high performance anodes is to develop low-potential PBA materials by tuning the composition.² This has successfully led to the development of anodes based on manganese hexacyanomanganate with a reduction potential of – 0.70 V vs. SHE.³

In search for lower potential PBA compositions we recently reported a thorough characterisation of manganese hexacyanochromate which has a reduction potential of – 0.86 V vs. SHE, giving full cell voltages against common PBA cathodes approaching 2 V.⁴ This material had a modest specific capacity of 63 mAh g^-1, much lower than its theoretical value (~170 mAh g^-1) due to high vacancy and water content, and only one transition metal being electrochemically active. Improving its capacity is a scientific challenge as the material is unstable in the reduced state in water, which prevents the use of common strategies to reduce the vacancy and water content during synthesis. In my talk, I will present our efforts to improve the specific capacity and stability of low-potential Prussian blue analogues by exploring the wider transition-metal hexacyanochromate composition space and by developing novel synthetic strategies.


(1) Hurlbutt, K.; Wheeler, S.; Capone, I.; Pasta, M. Prussian Blue Analogs as Battery Materials. Joule 2018, 2 (10), 1950–1960.
(2) Pasta, M.; Wessells, C. D.; Liu, N.; Nelson, J.; McDowell, M. T.; Huggins, R. A.; Toney, M. F.; Cui, Y. Full Open-Framework Batteries for Stationary Energy Storage. Nat. Commun. 2014, 5, 3007.
(3) Firouzi, A.; Qiao, R.; Motallebi, S.; Valencia, C. W.; Israel, H. S.; Fujimoto, M.; Wray, L. A.; Chuang, Y.-D.; Yang, W.; Wessells, C. D. Monovalent Manganese Based Anodes and Co-Solvent Electrolyte for Stable Low-Cost High-Rate Sodium-Ion Batteries. Nat. Commun. 2018, 9 (1), 861.
(4) Wheeler, S.; Capone, I.; Day, S.; Tang, C.; Pasta, M. Low-Potential Prussian Blue Analogues for Sodium-Ion Batteries: Manganese Hexacyanochromate. Chem. Mater. 2019, 31 (7), 2619–2626.

Ab initio modelling is a useful tool in the study of battery electrodes, able to support experimental findings and predict new phases and behaviours, providing a suitable and accurate method is used. Regular Density Functional Theory (DFT) functionals such as the commonly used PBE, however, are impacted by the ‘self-interaction error’ which severely impacts the accuracy of calculations involving the highly-correlated 3d valence electrons in transition metals.¹
Historically, the study of battery cathodes using DFT has been improved through the addition of ‘U’ parameters, which correct for the self-interaction error,² however these parameters require tuning to experimental measurements on the specific system in question, while also need to be varied during intercalation (with changes in oxidation state) and can be highly sensitive to changes in transition metal composition. This makes them unideal for the description of complex cathode systems such as NMCs and as a predictive tool for new systems.
Additionally, with the increased development behind the theory of anionic redox, accurate assessment of the charge transfer transition, which standard DFT tends to underestimate, is crucial.³ Minimally-parameterised hybrid DFT functionals such as HSE06 are routinely used to accurately predict the band gaps of semiconductors, however previous studies have highlighted disagreement between hybrid DFT and the band gap of LiCoO2 recorded from XPS-BIS, as well as overestimation of its predicted intercalation voltage.^4,5
In this study, we address this issue, demonstrating through a combination of HSE06 and high-level quasiparticle self-consistent GW calculations that the perceived value of the LiCoO2 charge transfer transition is underestimated, and that HSE06 represents an accurate, transferable standard method for describing the structural and electronic properties of LiMO2 cathode materials (M=Mn, Co, Ni). We also consider the issue of dispersion effects on estimated intercalation voltages, and explore the impact of the reassessed charge transfer gap on the defect chemistry of these materials, with a view to wider study of degradation and anionic redox in NMC cathodes.

1) Urban, A.; Seo, D.-H.; Ceder, G. npj Comput. Mater. 2016, 2 (October 2015), 16002.
(2) Zhou, F.; Cococcioni, M.; Marianetti, C. A.; Morgan, D.; Ceder, G. Phys. Rev. B - Condens. Matter Mater. Phys. 2004, 70 (23), 235121.
(3) Ben Yahia, M.; Vergnet, J.; Saubanère, M.; Doublet, M. L. Nat. Mater. 2019, 18 (5), 496.
(4) Seo, D. H.; Urban, A.; Ceder, G. Phys. Rev. B - Condens. Matter Mater. Phys. 2015, 92 (11), 115118.
(5) Aykol, M.; Kim, S.; Wolverton, C. J. Phys. Chem. C 2015, 119 (33), 19053.

Porous carbon is known for its strong mechanical stability, excellent electrical conductivity, high surface area and porosity. Therefore, it is utilized in various fields such as electrodes for electrochemical reactions or supports for gas storage. When applied as an electrode, its porous structure provides increased active sites and efficient electrolyte infiltration resulting in an enhanced performance of batteries. More specifically, porous structure reduces volume expansion of a cathode minimizing deformation and shuttle effect caused by migration of intermediates during reduction-oxidation reaction via sequestrating intermediates inside the pores. Furthermore, multiscale porous structure with macro-, meso-, and micro-pores allows an effective ion diffusion and charge transfer by shortening the ion diffusion path.
Herein, we synthesized metal organic framework (MOF) derived multiscale porous carbon by varying the ratio of more than one solvent and MOF-5 precursor, respectively. Dimethylformaide(DMF) and water were used as solvents, whereas benzene-1,4-dicarboxylic acid (BDC, C₆H₄(COOH)₂) and zinc nitrate hexahydrate (Zn(NO₃)₂6H₂O) were MOF-5 precursors. Varying the ratios of solvents and ligand to metal led to changes in morphology of MOF via competition between water and BDC ligands for coordination with [Zn(NO₃)₂]⁶⁺ units. Afterwards, carbonization of MOF resulted in porous carbon with high specific surface area (837~2990 m²/g) and porosity (pore volume of 0.582~3.281 cc/g). Batteries with the controlled porous carbon as an electrode showed a broad range of performances: an initial capacity was 1123 mAh/g when water to DMF ratio was 11: 1 and the metal-ligand ratio was 1: 6, and the coulombic efficiency maintained over 98% even after 200 cycles. We believe a facile way to synthesize multiscale porous carbon with both meso- and micro-pores can pave a way for many other application areas including energy/conversion devices, catalysis, and gas storage.

There has been much effort to develop solid-state electrolytes, including polymer electrolytes, with high energy and power densities, long cycle lives, and safety for next-generation lithium batteries. However, the ionic conductivities of current polymer electrolytes are orders of magnitude less than those of liquid electrolytes, and they are still insufficient for practical battery applications.
In this study, a series of polyether-based polymers having different number of cyanoethoxy side chains are newly synthesized and compared. The contribution of the cyanoethoxy group to the Li⁺ coordination structure as well as electrolyte properties, such as the ionic conductivity and lithium transference number, are studied by various (electro)chemical and spectroscopic techniques. Here, we verify that the molecular structure of the repeating monomer unit of the polymers (i.e. the number of the cyanoethoxy group on the main chain) alter the Li⁺ coordination structure, which in turn affects the thermal stabilities and ionic transport properties. The result thus indicates the importance of the Li⁺ coordination structure in the polymer electrolyte in order to understand electrolyte properties. Our findings pave the way toward a design strategy for polymer electrolytes with improved conductivity, based on the Li⁺ coordination structure that has been experimentally identified.

Polymer solid electrolyte such as polyethylene oxide (PEO) could influence solid-state battery chemistries with desirable performance and safety due to their high ionic conductivity of 10^-4 S.cm^-1 (65^oC -78 ^oC), low glass transition temperature, flexibility and its stability with lithium metals and conductive with lithium salt. In addition, it is environmentally stable and has an electrochemical window wide enough to overpower surplus electronic transport.
However, limited thermal stability of PEO makes it more challenging for commercial use, which consequently, hinders the fast charging and discharging behavior of the battery. This work investigates the synthesis of polyethylene oxide solid electrolyte by a simple melting technique. A remarkable reduction of the interfacial impedance was noticed at room temperature. The structure and surface morphology of PEO was characterized by X-ray diffraction (XRD) and FESEM, respectively. Interestingly, field emission scanning electron microscope (FESEM) images show a porous nature of the electrolyte which promotes the movement of lithium ions through the electrolyte. The electrochemical performance of the battery shows outstanding performance with large charge storage capability. The battery shows improved capacitance with higher number of charging and discharging cycles. This improvement in the rate ability is a result of the reduction in the interfacial impedance.
This work is supported by the NSF-CREST (CREAM) Grant Number HRD 1547771, and NSF-CREST1 (CNBMD) Grant number HRD 1036494.

Composite solid electrolytes consisting of a processible soft polymer phase and a highly conductive hard ceramic phase are promising in enabling lithium metal anode to achieve high energy and power density. In order to achieve energy density goals, the electrolyte film must be thin (< 30 μm). In previous work, we discovered that composite electrolytes with high ceramic loadings suffer from low ionic conductivity due to a large interfacial resistance for ion transport across the polymer-ceramic interface.^1-2 In a composite electrolyte where discrete ceramic particles are dispersed in the polymer host, ions do not transport through the ceramic phase due to large interparticle resistance.

Here we introduce an approach that creates a 3D interconnected structure of the ceramic with greatly reduced interparticle resistance.³ Furthermore, we fabricate a solid composite electrolyte film that is thin (20-30 μm in thickness), ionically conductive, and mechanically robust. Without the use of plasticizers, our composite film has an ionic conductivity of approximately 0.03 mS/cm at 30°C. Ion conduction path in the composite electrolyte is investigated by synchrotron X-ray tomography and finite element analysis.

Acknowledgements: This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE), under contract DE-AC05-00OR22725, was primarily sponsored by the Office of Energy Efficiency and Renewable Energy for the Vehicle Technologies Office’s Advanced Battery Materials Research program and partially sponsored by the Laboratory Directed Research and Development Program (LDRD) of ORNL.


1. Chen, X. C.; Liu, X.; Pandian, A. S.; Lou, K.; Delnick, F. M.; Dudney, N. J., Determining and Minimizing Resistance for Ion Transport at the Polymer/Ceramic Electrolyte Interface ACS Energy Letters 2019, 4, 1080-1085.
2. Pandian, A. S.; Chen, X. C.; Chen, J.; Lokitz, B. S.; Ruther, R. E.; Yang, G.; Lou, K.; Nanda, J.; Delnick, F. M.; Dudney, N. J., Facile and scalable fabrication of polymer-ceramic composite electrolyte with high ceramic loadings. Journal of Power Sources 2018, 390, 153-164.
3. Kalnaus, S., Tenhaeff, W.E., Sakamoto, J., Sabau, A.S., Daniel, C., Dudney, N.J., Analysis of composite electrolytes with sintered reinforcement structure for energy storage applications, Journal of Power Sources, 2013, 241, 178-185.

Cocrystals of adiponitrile (ADN)₂ LiXF₆ (X = P, As, Sb) can be formed by dissolving the LiXF₆ salts in excess ADN at elevated temperature and cooling to room temperature, resulting in the formation of cocrystals. The cocrystals all have the same crystal structure. Temperature-dependent ionic conductivities, (σ) and lithium ion transference numbers, t_Li+, show that t_Li+ (Sb) > t_Li+ (As) > t_Li+ (P), that is there is a greater contribution from the Li⁺ ion to the conductivity as the anion becomes larger (greater mass). Thermogravimetric analysis data indicate that the ADN is removed first (T_d ~ 100 ^°C) and that it comes off at the same temperature as ADN for LiPF6 but at a higher temperature (T_d ~ 150 ^°C) for LiAsF₆ and LiSbF₆. Further, the residual weight loss of the anion increases as the anion size increases in mass. DSC data for (ADN) LiXF₆ indicates no melting of the sample below the T_d. However, there is a small melt and crystallization of the ADN. As previously observed, this is attributed to liquid regions around the co-crystallites. Similar DSC results are observed for the LiAsF₆ and LiSbF₆.

High-nickel NMCs are very attractive high capacity cathode material for practical applications, especially in automotive industry. However, many obstacles caused by the high nickel content, such as high surface reactivity, structural instability, etc., must be overcome before this type of compounds can become the material of choice for application. Through a wet chemistry method, a Li-Nb-O coated and substituted co-modified NMC 811 was prepared by single step treatment. The Li-Nb-O coating/substitution not only supplies a protection on surface but also optimize the material itself by Nb⁵⁺ incorporation. With this treatment, the 1^st capacity loss was significantly reduced (13.7 vs. 25.1 mAh/g), which can contribute at least 5% increase on the energy density of full-cell level. In addition, both rate (158 vs. 135 mAh/g at 2C) and cycling (89.6 vs. 81.6% after 60 cycles) performance were greatly enhanced as well.

Acknowledgement: This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy, through the Advanced Battery Materials Research Program (Battery500 Consortium).

Aryl diazonium salts have been widely reported in the research of surface chemistry and they are believed to increase the specific capacitance of pristine graphene electrodes by introduction of pseudocapacitance as well as increased surface area due to prevention of graphene restacking. In this work functionalized graphene for use in supercapacitors was prepared by a two-step process, where graphene was functionalized with two different aryl diazonium salts (4-nitrobenzenediazonium tetrafluoroborate (NBD) or 4-bromobenzenediazonium tetrafluoroborate (BBD)) simultaneously during electrochemical exfoliation. Characteristic peaks identified from Raman and X-ray photoelectron spectroscopy demonstrate that the simultaneous functionalization and exfoliation of the graphene with NBD and BBD was successful. Cyclic voltammetry, galvanostatic charge-discharge measurements and electrochemical impedance spectroscopy were performed to study the electrochemical properties of the functionalized graphene electrodes. It was found that graphene NBD functionalized for 30 minutes (N30) exhibited superior energy storage properties with 5 times increase in specific capacitance compared to pristine graphene.

With the increasing demands of the green energy and fresh water, it is necessary to develop a more efficient approach to provide sustainable resources for human use. Seawater is an abundant resource to produce clean water and to store energy by desalination process. Among several types of desalination, electrochemical salt removal is a promising approach to separate dissolved salt ions from seawater and to selectively store sodium and chloride ions in cathode and anode. The development of desalination batteries depends critically on the discovery of high performance chloride-storage electrodes. Among all types of anode materials, bismuth-based electrodes, with a comparable theoretical specific capacity, as new high efficient electrode materials for chloride storage.
In this study, we designed and fabricated bismuth nanowire arrays with various aspect-ratios serving as chloride-storage electrodes by a template-assisted process. Chloride ions can be efficiently stored in the high-aspect-ratio bismuth nanowire structures in the form of BiOCl. We characterized and evaluated the bismuth nanowire array electrodes for application of seawater desalination. We carried out linear sweep voltammetry (LSV) and galvanostatic charging/discharging tests for half-cell reactions of bismuth nanowire array electrode to examine its chlorination/dechlorination behavior. In addition, we discussed the effects of the dimensional parameters of the bismuth nanowire arrays and the surface treatments on the bismuth nanowire arrays.

The choice of an anode material for Li-Ion batteries is critical, since the formation of dendrites, which will result in safety problems and self-discharge, usually occurs on the anode. Thus, the choice of anode materials, the charge-discharge conditions and the additives inside of the electrolyte is critical to the formation of dendrites. Here, we focus our study on the use of Li metal anodes. To study the process of dendrite formation on Li anodes, we have developed a Lattice Boltzmann model. The model is used to
study the mechanism of these processes, and the effects of applied potential and
morphological features on the local concentration distribution and structure
evolution. Our model is also able to capture the effect of charge-discharge cycles on the morphology of the anode. We also study the effect of pulsing on the formation of dendrites in the battery. These results can be used to build a relationship between design parameters and battery performance in order to improve the stability and the capacity of the battery.

Rechargeable Li-ion batteries with energy density ≥ 300 Wh/kg (650 Wh/L) have become increasing important to extend driving range beyond 250 miles per charge for electric vehicles. While cell level energy density target may be achieved with commercial grade high nickel content (≥80%) NCM cathode when paired with Si/graphite composite anode, how to ensure such high nickel chemistry can deliver on cell safety requirements is a major hurdle to the vehicle electrification roadmap. Therefore, a number of techniques have been studied in order to improve Li ion battery safety at component level, such as active materials engineering and safer electrolyte formulation.
The main purpose of this research is to demonstrate a technology path which can deliver cell level energy density of 300 Wh/Kg as well as meet very stringent abuse tolerance tests including nail penetration, overcharge, hotbox and crush. Due to intrinsically low first cycle columbic efficiency of the Si/graphite anode, prelithiation emerges as an indispensable process to reach 300 Wh/Kg energy density target. Cell safety is primarily achieved by combining A123’s for proprietary safety technologies with commercially available cathode materials such as NCM 811. As expected, the composite cathode materials exhibited improved thermal stability as onset temperature shifted to higher degree with split exothermal peaks as revealed by differential scanning calorimetry (DSC) characterization. Subsequent validation experiments conducted through production intent large format cell testing confirmed the effectiveness of the A123 safety technologies while maintaining target energy density, as cells without those safety additives failed nail penetration (Hazard level 5.0) whereas those with safety additives passed convincingly (Hazard Level 3.0). Not surprisingly, this study also demonstrates that nail penetration, the most challenging one among all abuse tolerance tests, shows a strong dependence on testing conditions such as size and speed of the nail. Those results shed light on how high energy density Li ion batteries (≥300 W/kg) can be made safe through innovative engineering of commercial NCM cathode materials.

Li_1-xCoO₂ (LCO) is a promising material for the application in lithium batteries as cathodes as well as the new type of transistor devices. Fabricating the epitaxial LCO thin films is considered to be a potentially effective method to raise the ionic conductivity and to optimize the interface between the solid electrolyte and electrode. In order to improve the performance of the LCO, the high-quality epitaxial thin films with different orientations, e.g. (104), (110), and (001) were grown on (100), (110), and (111) – oriented SrTiO₃ substrates utilizing the Pulsed Laser Deposition (PLD) technique with deposition temperature of 650 – 700 ^oC, respectively. By tuning the oxygen pressure and laser repetition precisely, the epitaxial LCO thin films with different grain sizes were fabricated. As shown in the X-ray diffraction results, the crystallization varies with changing oxygen pressure, e.g. intensity of the LCO diffraction peaks of each orientation firstly increases with raising oxygen pressure from 50mTorr to 150mTorr and then decreases at higher pressure. The surface geometry mapped by AFM and SEM also reveals that the grain size is the maximum at 150mTorr and would decrease with both raising and reducing the oxygen pressure. This may be related to the different growth modes: the level of interaction between the ablated material and the oxygen environment effectively enhanced the diffusion and growth of the film until the interactions increased past a critical point to change the growth mode leading to smaller uncoalesced grains at higher pressure. In order to maximize the grain size, the laser frequency is then carefully tuned at the most promising oxygen pressure of 150 mTorr. There exists approximately an order of magnitude change in the grain size with changing repetition. The grain size could be almost 1 micron with the laser frequency of 2Hz. Recently, the Lithiation and de-lithiation process is taken in a sealed cell at room temperature to investigate the function of the LCO with different grain sizes.

In this study, the thermal properties of a group of zwitterionic copolymers containing ionic liquid designed for electrochemical energy storage are investigated using temperature modulated differential scanning calorimetry (TMDSC) and thermogravimetry (TG). Investigating the thermal properties will reveal how the zwitterionic moieties affect transition phenomena and interact with ionic electrolytes. Sulfobetaine vinylimidazole (SBVI) and 2-methacryloyloxyethyl phosphorylcholine (MPC) were dissolved in the commercial ionic liquid EMI TFSI in varying molar ratios and subsequently polymerized to produce fully zwitterionic random copolymers. TG reveals two degradation steps at 290 ^oC and 390 ^oC due to MPC degradation, and one step at 350 ^oC due to SBVI degradation. TMDSC at 5 ^oC /min was used to identify the glass transition of these materials, showing a decrease in T_g from 60 ^oC to 10 ^oC with increasing addition of SBVI. A melting endotherm at -18 ^oC was observed on heating, attributed to the presence of residual ionic liquid. The solid state heat capacity of the polyzwitterions with ionic liquid was measured and compared to predictions assuming additivity of the heat capacities of the ionic liquid and polyzwitterions. The assumption of additivity was valid for only a few of the polyzwitterion compositions, suggesting that some of these materials were still in the liquid or partially liquid state, even down to -80 ^oC.

Transition metal (TM) substitution has been widely applied to tune the complex oxides crystal structures to create high energy density electrodes materials in high performance secondary rechargeable lithium-ion batteries. The LiNi_0.5Mn_1.5O₄ spinel, which is obtained by substituting one fourth of the Mn with Ni in the LiMn₂O₄ spinel, is a candidate cathode material for electric vehicle applications because of its high operating voltage and large energy density. The distribution of Ni and Mn at the octahedral sites plays a key role in the electrochemical performances such as capacity and cyclability, and it brings complexity in the material synthesis, thermal treatment and structure tuning. Thanks to its high sensitivity in detecting lithium ions and distinguishing transition metals, in-situ neutron scattering is used here to study the TM-mediated structure transition during the synthesis, as well as crystal structures in global and local scales, which is correlated with the electrochemical behaviors. In-situ neutron diffraction monitors the TM activities at elevated temperature, which are found to be significantly influenced by the atmosphere. In air, Ni and Mn reversibly exchange at the octahedral sites between 700~750 °C, mediating the “ordered” and “disordered” TM arrangement. The spinel-to-rocksalt structural transition occurs at higher temperatures, and it is reversible upon cooling. In contrast, in oxygen-deficient atmosphere it is found that the TM atoms not only exchange at the octahedral site but also migrate to the Li tetrahedral sites, resulting in the formation of a tetragonal spinel phase with the cubic spinel phase reserved. In-situ neutron diffraction reveals the kinetics of the TM migration, and the in-situ neutron pair distribution function evidences the TM valence change during the phase transition. The results will further guide and accelerate the novel material finding for high performance Li ion batteries.

Significant interest has arisen in all-solid-state lithium-ion batteries due to benefits in safety and cost. The electrolyte compounds used have many other benefits over traditional liquid electrolytes. One solid-state electrolyte of interest is the NASICON-like solid compound lithium aluminum titanium phosphate (Li_1+xAl_xTi_2-x(PO₄)₃, LATP), due to its demonstrated high ionic conductivity of ~3x10^-3S cm^-1. In this study, LATP thin films weresuccessfully prepared through RF-magnetron sputtering of a 99.9% pure single LATP target onto a variety of substrates. LATP thin films (~100-150nm) were deposited at a range of temperatures varying from room temperature to 300^oC, and annealed post-deposition at a variety of temperatures ranging from room temperature to 400^oC. These alterations in process temperature have a significant impact on the resulting crystal structure of the thin films, as well as affecting both its ionically conductive and electrically resistive properties. The films’ structural and compositional properties were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) and secondary ion mass spectroscopy (SIMS). The resulting XRD spectra depict a primarily polycrystalline structure with peaks at 35^oand 50^o, which can be attributed to the presence of LiOTi and AlTi alloy, respectively. SEM analysis shows crack-free films with clear surface morphology, which is ideal for minimizing electrolyte-electrode interface resistance, and SIMS analysis shows films with uniform composition.

Lithium ion batteries are becoming an increasingly important part of everyday life with diverse applications from low emission electric vehicles to consumer electronics. Si anodes offer the potential for approximately ten times higher capacity than the presently used graphite electrodes. However, Si anodes have several challenges that have so far prevented their commercial application on a large scale. These include high capacity fade, a poor shelf life, and the long-term stability of the electrode materials. Solid electrolyte interphase (SEI) formation and stability is poorly understood in Si anodes as compared to graphite anodes. Problems faced include the large volume expansion/contraction on lithiation/delithiation and extensive gas formation during cycling.

In this work, we report on analytical scanning transmission electron microscopy (STEM) studies of the lithiation behavior and SEI formation on various model Si electrode structures. These include bare wafer Si and wafer Si with different thickness native and thermally grown SiO_x layers. We report data on the structure and chemistry of the lithiated electrodes and SEI layers formed. The results are correlated with results obtained by other techniques on the same samples including electrochemical cycling data and scanning spreading resistance microscopy (SSRM) measurements on SEI thickness and resistivity. We have observed that resistance changes of the SEI measured by SSRM correlate with compositional differences in the SEI as determined by STEM electron energy loss spectrometry (EELS) and energy dispersive x-ray spectrometry (EDS) measurements.¹

1. “Three-dimensional electronic resistivity mapping of solid electrolyte interphase on Si anode materials” C Stetson, T. Yoon, J. Coyle, W. Nemeth, M. Young, A. Norman, S. Pylypenko, C. Ban, C.-S, Jiang, M. Al-Jassim, and A. Burrell, Nano Energy 55 (2019) 477.

Recent studies on lithium-ion batteries (LIBs) have focused on satisfying the electrochemical performance that required for their applications such as electric vehicles and energy storage systems. Along with this research trend, there is also growing interest in preventing the risk factors on present LIBs caused by excessive improvement. In this respect, all-solid-state lithium-ion batteries (ASLBs) are one of the attractive candidate for next generation batteries that can improved both performance and safety compared to conventional LIBs.

Among various types of solid electrolyte (SE) candidates, sulfide-based SEs are promising due to high ionic conductivity which is comparable to commercial liquid electrolytes (~10^-2 S cm^-1 at room temperature) and high-formability which enables favorable inter-particles contact on composite electrode for ASLBs. Despite the advantages of sulfide-based SEs, there are several problems that should be solved such as chemical and oxidation instability, diffusion of mutual elements on interface with cathode materials.

In this work, we synthesized Li₇P₃S₁₁ and Li₆PS₅Cl sulfide-based SEs which have been widely studied, and we have conducted a comparative study on their chemical and thermal stability. To compare them, we performed optical observation and advanced X-ray diagnostics. Further more, we also confirmed the conformity between sulfide-based SEs and commercialized cathode material. The details will be discussed at the conference.

Sodium (Na) metal is one of the most appealing anode materials for grid-scale energy storage systems owing to the high earth abundance and low cost of Na resources. Nevertheless, the implementation of Na metal anode is hindered by two primary issues associated with Na dendrite growth and volume expansion, resulting in low Coulombic efficiency and poor cycle life. Herein we present a facile and scalable method to synthesize tin (Sn) nanoparticles (NPs) that are uniformly embedded within carbon network (denoted as Sn@C composite), which can address the two issues simultaneously. Specifically, Sn NPs can serve as preferential nucleation sites to guide Na nucleation and thereby lower the Na deposition overpotential, while the carbon network can act as buffer layer to effectively minimize the volume change and alleviate the exfoliation of Sn NPs over repeated cycles. Consequently, high-capacity Na anodes can be realized with long-term reversibility and stability. Moreover, a room-temperature Na-sulfur battery based on the Sn@C composite as anode coupled with commercial sodium sulfide as cathode was demonstrated with significantly improved electrochemical performance. We believe this work provides a new pathway in designing high-energy Na metal batteries.

To improve the safety of Lithium Ion Batteries (LIBs) more desirable, non-flammable, highly conductive solid-state electrolytes are needed for commercial use. One promising alternative is the synthesis of highly conductive and flexible polymer electrolytes. Current polymers often suffer from low ionic conductivities that cannot meet current standards for operation in LIBs. In order to increase performance and longevity, materials that only admit the electrochemically active cation are desirable. For this reason, synthetic efforts toward single-ion conducting polymers are necessary. A promising synthetic pathway is with the exploitation of the Lewis basic nature of borane compounds. With matching salts with Lewis basic anions to Lewis acidic boron-containing polymers, the interaction of the anions with the boron-containing polymer backbone are likely to hinder anionic movement. Meanwhile this allows the cations to be the most likely ionic conductor and help improve overall ionic conductivity of the system. The preparation of step-growth or Ziegler-Natta catalyzed boron-containing electrolyte polymers will be synthesized and analyzed via thermal gravimetric analysis, differential scanning calorimetry and electrochemical impedance spectroscopy for preliminary characterization.

One of the major problems with the Li metal batteries is the safety issues associated with dendrite growth when using metallic Li⁰ anode. There has been extensive research on the prevention of dendritic growth, including mechanical inhibition and limiting concentration gradients that result in anion depletion near the anode. The latter can be achieved by the use of electrolytes with high ionic conductivities and low anion mobility, i.e. high Li⁺ ion transference numbers (t_Li⁺). Concentration gradients are avoided in polymer single ion conductors (SICs) with t_Li⁺ ~ 1. However, conductivities of polymer SICs have remained low (< 10^-5 S cm^-1). One of the reasons for low conductivity in polymer SICs is extensive ion aggregation. In this work we proposed the use of multi-ionic polyhedral oligomeric silisquioxane (POSS) with dissociative lithium salts [POSS-(LiNSO₂CF₃)₈] dissolved in tetraglyme (G₄), CH₃-O-(CH₂CH₂O)₄-CH₃, as electrolytes having both high ionic conductivity and high lithium ion transference numbers. [POSS-(LiNSO₂CF₃)₈] can be dissolved at very high loadings into G₄ , where they can be considered solvent-in salt electrolytes. Two systems were investigated, neat [POSS-(LiNSO₂CF₃)₈] in G₄ and mixtures of [POSS-(LiNSO₂CF₃)₈] with LiPF₆ or lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI). PFG-NMR indicates that Li can be un-dissociated, completely dissociated and surrounded by G₄ molecules, or as contact ion pairs (in which there are 3–4 ether oxygen contacts and one contact with the oxygen from the anion). Equilibria exist between the species of [POSS-(LiNSO₂CF₃)₈] and if there is rapid equilibration between the Li states and close enough proximity between the POSS-(LiNSO₂CF₃), then the Li⁺ ions can migrate by a Grotthus-type coordinated hopping mechanism, as well as by a purely diffusive motion. Unlike polymer single ion conductors, where the backbone flexibility permits cluster/aggregate formation, which inhibits escape and mobility of the Li⁺ ions, the rigid POSS cube and its colloidal structure in G₄ prevents formation of POSS-(NSO₂CF₃^-)^…. Li^{+ ….}(^-CF₃NSO₂)-POSS triplets. Instead, the solvated Li⁺ in POSS-(NSO₂CF₃^-)^…Li^+…G₄ can be more easily removed to form conductive G₄^…Li^+…G₄. Good ionic conductivities (< 10^-4 S cm^-1) and lithium ion transference numbers of t₊^PP = 0.65 can be achieved in these systems. Mixtures of 80 wt% LiTFSI and 20 wt% [POSS-(LiNSO₂CF₃)₈] in G₄ at an O/Li ratio of 20/1, yield both high conductivity (3.3 x 10^-3 S cm^-1) and high (t₊^PP = 0.65) transference number. Stable cycling at C/4 with high capacity retention was achieved using Li⁰/[G₄/80 wt% LiTFSI/20 wt% [POSS-(LiNSO₂CF₃)₈]/LiFePO₄ half-cells.

S.Chereddy et.al., Materials Horizons, 2018 , 5, 461