Symposium EN06 : Safer and More Energy-Dense Rechargeable Batteries

Intercalation compounds form the basis of essentially all lithium rechargeable batteries. They exhibit a wide range of electronic and crystallographic structures. The former varies from metallic conductors to excellent insulators. Today’s lithium batteries are limited in capacity, because less than one lithium ion is reversibly intercalated per transition metal redox center. There may be an opportunity to increase the storage capacity by utilizing redox centers that can undergo multi-electron reactions. This might be accomplished by intercalating multiple monovalent cations or one multivalent cation. In this talk we will review the key theoretical and experimental results on lithium and magnesium reversible intercalation into two prototypical materials: titanium disulfide, TiS₂, and vanadyl phosphate, VOPO₄. Both of these materials exist in two or more phases, which have different molar volumes and/or dimensionalities and thus are expected to show a range of diffusion opportunities for battery active guest ions such as lithium, sodium, and magnesium. A major conclusion of this research is that reversibly intercalating two lithium or sodium ions into a host lattice whilst maintaining it’s crystal structure is possible. A second major conclusion is that theoretical studies are now sufficiently mature that they can be relied upon to predict the key free energy values of simple intercalation reactions, i.e. the energy that might be stored. This could help to focus future choices of battery couples.
This work was supported as part of NECCES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0012583.

All-solid-state rechargeable Li or Na batteries attract much attention because of their high safety, long cycle life, versatile geometry and high energy density. Sulfide solid electrolytes based on the system Li₂S-P₂S₅ have several advantages of high conductivity, wide electrochemical window, and appropriate mechanical properties suitable for forming close solid-solid interfaces with electrode active materials. Dense sulfide electrolyte pellets with about 90% relative density are prepared by only mold-pressing at room temperature without any sintering at high temperatures. To increase energy density of the batteries, the use of positive electrode active materials with high capacity and the increase of their content in a positive electrode layer are desired. Formation of favorable and large contact areas between electrode and electrolyte is achieved by electrolyte coating on electrode particles via gas-phase or liquid-phase techniques. Sulfide amorphous electrolyte coating on LiCoO₂ particles by pulsed laser deposition is effective in increasing reversible capacity of all-solid-state batteries. Closely-attached electrolyte-LiCoO₂ interfaces with large contact area are achieved by electrolyte coating. The coating reduces the volume of electrolyte content in an electrode layer, and energy density of solid-state batteries is thus increased. Preparation of nanocomposite electrodes with solid electrolytes and nano-carbons by high-energy ball milling is useful for sulfur or Li₂S active materials. Conductivity enhancement of Li₂S by the combination of LiI contributes to the improvement of utilization of Li₂S active material in all-solid state batteries. Amorphous transition metal sulfides such as amorphous TiS₃ are attractive as a mixed conductor with large capacity, and all-solid-state Li and Na batteries with high energy density are achieved.

Ref. A. Hayashi, A. Sakuda and M. Tatsumisago, Front. Energy Res., 4, 25 (2016).

With recent industry-wide investments into electric vehicles, much research & development has focused on designing safer, lighter, fast-charging batteries. In particular, researchers search for an electrolyte that is manufacturable, mechanically robust, dendrite-resistant, and ionically conductive. The success of LiPON thin films indicates promise in glassy and amorphous materials, which are known to have different transport properties than their crystalline counterparts.
With computational atomistic study of ionic transport mechanisms, we develop mechanistic understanding and design rules for new glassy electrolytes. Using molecular-dynamics simulations, we model Li-ion conduction in various families of crystalline and amorphous materials. In particular, we identify the effects of structure amorphization on ionic conductivity and correlation.

This work is partially supported by the Advanced Projects Research Agency - Energy (ARPA-E), U.S. Department of Energy, and by the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy.

Recent computation and experimental works have discovered a remarkable array of materials with superionic conductivities that rival or exceed the conductivity of conventional liquid electrolytes such as Li and Na conducting NASICON-type oxides, Li garnets, lithium-rich anti-perovskites, and thiophosphate materials. Unfortunately, the high ionic conductivity often is associated with a penalty of high impedance at interfaces between electrolyte and electrodes; this interfacial impedance can dominate the internal resistance in many systems. High impedance is found both in thiophosphate electrolytes in contact with oxide cathodes and during high temperature processing of oxide electrolytes cosintered with oxide cathodes. Because of the necessity of maintaining low interfacial impedance for high power applications, we have focused on understanding the reactions occurring at the various interfaces. This talk will focus on the development and implementation of computational thermodynamic methods to predict trends in reactivity and types of reaction products formed at the interfaces of a number of commonly investigated electrolyte systems, cathode materials, and cathode coatings. We use these results to identify combinations of materials that are thermodynamically stable over the range of processing and operating conditions experienced in high voltage all solid state battery systems.

Advances in solid electrolytes and their interfaces represent major challenges for the development of future energy storage. An ideal solid electrolyte material must not only be highly ionically conductive but also exhibit desirable stability with metallic lithium and cathodes. While several new solid electrolyte materials have been developed that demonstrate high conductivity, little is known about their integration with electrodes. Unexpected high resistivity is often observed at solid electrolyte-electrode interfaces. Understanding how solid-solid interfaces are formed and how mass transport and charger transfer occur at these interfaces are crucial to the design of interfaces with high electrochemical performance. Many solid electrolytes are polycrystalline and contain significant amounts of grain boundaries that often exhibit completely different structure and chemistry from that of bulk grains. Particular attention has to be paid to the electrochemical stability of the grain boundaries that are exposed to the interfaces with electrodes. However, experimentally probing these embedded interfaces is challenging. Here, in situ and atomic-resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) are used to study these interfaces. Al-Li₇La₃Zr₂O₁₂ (LLZO) and LLTO were used as model systems. In order to understand the crystalization mechanism of amorphous LCO on LLTO, phase evolution and chemical diffusion at the interface of LLTO with sputtered amorphous LiCoO₂ were monitored in situ during thermal annealing. The competing elemental diffusion and crystallization were vividly revealed. At the interface of LLZO with Li metal, we focused on understanding how different types of grain boundaries response to the contact of Li metal both in a static state and upon an electrical bias. Our microscopy results provide valuable insights into the design and synthesis of solid electrolyte – electrode interfaces.

Acknowledgement
Research sponsored by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Microscopy performed as part of a user project at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. DOE User Facility.

The recent resurgence of electrified vehicle product introductions seen in recent years has been enabled by meaningful advances in lithium ion batteries. This technology’s specific energy (Wh/kg) has improved steadily at nearly 8% per year. The achievement and maintenance of this specific energy growth rate has been the result of large, long term investment in improved battery research, development and manufacturing. However, to significantly promote the displacement of petroleum fuels from the transportation sector, a step increase in battery performance is necessary.

Solid state (SS) batteries are one of the most versatile and promising approaches of the various technologies under development for next generation energy storage. By enabling the use of high energy lithium metal anodes, SS batteries can enable major improvements in energy density. An approximately 50% gain in cell energy density is possible if SS electrolytes of comparable thickness to incumbent polyolefin separators could be developed to use metallic lithium anodes [1]. However, despite research efforts for more than 50 years, the mechanical properties of lithium metal are not well known.

A SS electrolyte material must fulfil various physical and chemical requirements to perform successfully in the battery environment. For example, some SS electrolytes have shown a tendency to allow for lithium dendrites to penetrate its structure once a critical charge density (CCD) has been reached [2]. Main of these requirements are driven by the need to conduct and contain lithium metal anodes and yet relatively little is known of the physical properties of this metal. A review of previous efforts to characterize the mechanical elastic constants, elastic and plastic deformation limits of metallic will be shown and compared to new bulk empirical results [3]. Additionally, the particular mechanical requirements of the battery environment will be discussed and future mechanical targets introduced.

REFERENCES
[1] McCloskey, B. et al. J Phys. Chem. Lett. 6 (2015) 4581-4588.
[2] Sharafi, A. et al. J. Power Sources, 302 (2016) 135-139.
[3] Masias, A et al. ECS Fall Conf. (2017) Abs #205.

Li⁺ and Na⁺-ion conductors not only control the performance of all-solid-state-batteries but are also key components in large-scale metal-air, metal-sulfur, and alkali-redox flow batteries. Therefore, designing new and optimizing known ion conductors is crucial for enabling large-scale energy storage systems with high rate performance. The redevelopment of the crystal chemical bond valence approach into our energy-scaled “bond valence site energy” method [1] allows for computationally cheap predictions of ion migration pathways and migration barriers from static structure models and thus for high-throughput screening of wide ranges of candidate compounds as alkali ion or mixed conductors with balanced conductivity and stability. As a transferable effective forcefield for MD simulations it helps to analyze ion transport mechanisms, as exemplified here by a discussion of differences between alkali ion migration in superionic Li₁₀GeP₂S₁₂ and Na₁₀GeP₂S₁₂, explaining why the latter is, despite contrary predictions from ab initio MD simulations, only a moderate Na⁺ conductor. To overcome fundamental limitations of two-body forcefields, it will also be discussed how the approach can be augmented to an EAM-type multibody forcefield with bond valence sum-based embedding function.
As the ionic conductivity in mixed conductors also controls the achievable rate performance of insertion electrode materials, we extended our combined ab initio and empirical bond valence analyses to alkali-ion cathode material structures,[2] demonstrating a simple structure property relationship that yields from the structure a quantitative prediction of the characteristic (dis)charge rate up to which a material (with given particle size) can be expected to deliver high capacity.
Experimentally we aim to establish rationally optimized processing for solid electrolytes and electrode materials by in situ X-ray or neutron monitoring of the formation process.[3] Thereby we not only achieve phase pure high performance materials with well-controlled dopant contents in a cost and energy-efficient way, but provide deeper understanding of the formation mechanisms and kinetics of the desired phase as well as of potential impurities. We tested our predictions by the realization of all solid state Na⁺-ion batteries with high rate performance at room temperature [4] and of high energy efficiency aqueous Li-air batteries (LABs) using scalable fast-ion conductor membranes.[5,6]
References
[1] H. Chen, S. Adams, IUCrJ 4 (2017) 614-625.
[2] L.L. Wong, H. Chen and S. Adams; Phys. Chem. Chem. Phys. 19 (2017) 7506.
[3] R. Prasada Rao, W. Gu, N. Sharma et al.; Chem. Mater. 27 (2015) 2903.
[4] R. Prasada Rao, H. Chen, L.L. Wong and S. Adams; J. Mater. Chem. A 5 (2017) 3377.
[5] D. Safanama, S. Adams, J. Power Sources 340 (2017) 294; ACS Energy Lett. 2 (2017) 1130.
[6] Y.G. Zhu, Q. Liu, Y. Rong, H. Chen et al.; Nature Comm. 8 (2017) 14308.

Rechargeable sodium-ion batteries have received growing attention as promising alternatives to lithium-ion batteries because of the abundance of Na resources as well as its high theoretical capacity of 1165 mAh/g, and low electrochemical potential (-2.71 V vs. standard hydrogen electrode). However, the safety issues remain as the most critical problems for its application. The rise of sulfide-based solid state electrolytes (SSEs) with high Na-ion conductivity have brought about new opportunities for the development of sodium metal batteries. Compared to organic electrolytes, the inorganic SSEs have an increased Young's modulus, which suppress stress points in the metal anode to prevent dendrite formation. Additionally, the SSEs are non-flammable, which addresses the safety concern posed with the organic electrolyte.
Despite the high ionic conductivities of sulfide-based SSEs, most of them are not stable with a metallic sodium anode. The recently investigated tetragonal Na₃SbS₄ having a superior Na-ion conductivity up to 3 mS/cm at room temperature is a good candidate for SSE, but it also suffers from poor chemical stability with Na. Based on theoretical calculation and experimental results, we find Na₃SbS₄ is not stable with Na metal and will decompose into Na₂S and Na₃Sb, resulting in a significant increase of interfacial resistance. Our approach for stabilizing the Na₃SbS₄/Na interface is to introduce a cellulose-supported poly(ethylene oxide) (CPEO) layer between Na₃SbS₄ and Na. Owing to the high stability of the CPEO layer and the enhanced interfacial contact with Na, the Na/CPEO/Na₃SbS₄/CPEO/Na symmetric cell shows a stable Na stripping/plating over 800 hours under 0.1 mA/cm² at 60 ^oC. This simple and scalable polymer protecting approach provides a solution to improve the anode stability of sulfide-based electrolyte.

Garnet-based lithium ion conducting solid electrolyte, with nominal composition Li₇La₃Zr₂O₁₂, is a promising solid electrolyte for all solid-state batteries due to its high Li-ion conductivity and stability with lithium metal anode [1]. However, lithium dendrite growth during lithium deposition on the negative electrode causes short-circuit with increasing current density [2, 3]. In this work, we prepared garnet-based Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZT) pellets, with different synthesis conditions, and investigated correlation between the pellet structure and short-circuit prevention.
LLZT powder and pellets were prepared using a solid-state reaction and spark plasma sintering technique, respectively, as reported in our previous work [2]. The prepared pellets are designated as LLZT-air (conventional method), LLZT-w/o-air (without exposing to air), and LLZT-2calc (calcined twice with addition of LiOH) [4]. A combination of structural and chemical characterization techniques, such as scanning electron microscopy and fourier transform infrared spectroscopy, revealed presence of LiOH and Li₂CO₃ on the LLZT powder and effects of excessive lithium salt on the microstructure of the pellets. To investigate the short-circuit prevention, symmetric cells of Li | LLZT | Li were assembled. The cells were cycled at various current densities (1 hour per cycle) at 25°C, which were gradually increased until the cells showed voltage drop [2, 3]. Direct current (DC) polarization curves demonstrate that the voltage fluctuation during cycling increased, as the current density increased. This is due to reduced effective electrode area because voids were formed by the Li dissolution at the Li | LLZT interface. The critical current density (CCD), at which voltage drop occurred, depended on the specimens. LLZT-2calc exhibited the highest CCD of 0.6 mA cm⁻², while LLZT prepared without exposing to air showed rather poor short-circuit prevention (CCD of 0.15 mA cm⁻²). This suggests that Li₂CO₃ and/or LiOH on surface of starting LLZT powder is effective to improve density of grain boundaries in the pellets to suppress the short circuit. Microstructural analysis and detailed electrochemical impedance analysis demonstrated that Li₂CO₃ and LiOH not only facilitate sintering on the grain boundary, but also physically suppress the lithium growth by filling voids among LLZT grains [4].

References
[1] R. Murugan, V. Thangadurai, W. Weppner, Angew. Chem. Int. Ed. 46 (2007) 7778.
[2] H. Yamada, T. Ito, R. Hongahally Basappa, Electrochim. Acta 222 (2016) 648.
[3] R. Hongahally Basappa, T. Ito, H. Yamada, J. Electrochem. Soc. 164 (2017) A666.
[4] R. Hongahally Basappa, T. Ito, T. Morimura, R. Bekarevich, K. Mitsuishi, H. Yamada, J. Power Sources 363 (2017) 145.

Recently, sodium has reattracted scientists' interest in using in rechargeable battery for its low cost and abundant amount compared with lithium. All-solid-state sodium metal battery is doomed to have promising future for its theoretically high capacity (1166mAh/g), non-flammability and low cost. Here, we fabricated a polyethylene oxide (PEO) based hybrid solid electrolyte which showed low glass transition temperature, absence of crystallization and ionic conductivity greater than 1×10^-4 S/cm at 80 °C. The solid electrolyte showed low interface resistance (~100ohms at 80C) with sodium metal and high stability in cycling test, with Cd reaching 3000C/cm² at current density 0.5mA/cm². All-solid-state sodium metal battery using thermal-treated vanadium oxide as active material, the hybrid polymer as the electrolyte and separator, and pristine sodium metal as the anode. The battery showed excellent capacity (300mAh/g) and good coulombic efficiency. Detailed sodium dendrite growth and electrolyte depletion in have also been systematically studied. Our work showed that the hybrid network is promising for all-solid-state sodium battery applications.

We present a study to understand the role of defects in enhancing the charge capacity of many layered graphene by gradually increasing the defect concentration in a pristine graphene sample by ion beam irradiation. An Ar⁺ ion beam with energies of 50-105 KeV was used to engineer defects by varying the penetration depth of the ion beam in the sample. Electrochemical cycling of these defective graphenic layers against Li metal foil showed a correlation between the specific charge capacity and the energy of the irradiated ion beam used to create defects. The charge capacity was found to increase to 440mAh/g compared to the charge capacity of a pristine many layered graphene sample of 250mAh/g after 100 cycles. The charge capacity however, doesn't increase linearly with the energy of the Ar⁺ ion beam but tends to decrease after an optimum value that can be attributed to the distribution of the created defects in the sample.

Rechargeable lithium-ion batteries are widely used in mobile devices, hybrid, plug-in hybrid, and electric vehicles. The performance of batteries strongly depends on the structure, morphology, and properties of electrode materials. A great effort has been made to synthesize a variety of electrode materials and to understand the role of the electronic structure of redox active materials to improve the energy density, rate capability, and cycling stability. It is generally considered that positive electrode determines the specific capacity and the energy density of batteries. Li(Ni,Co,Mn)O₂, a layered material, has gained considerable attention as the positive electrode due to its high specific capacity and thermal stability. To understand the nature of the electrochemical reaction, it is expected that single crystal-like electrode materials may offer better understanding of its effects on crystallographic orientation on the electrochemical properties. To this end, epitaxial Li(Ni,Co,Mn)O₂ thin films of different orientations have been successfully grown on SrTiO₃ substrates from a solution method, called polymer-assisted deposition. The films have been characterized by x-ray diffraction, atomic force microscope, and cross-section high resolution transmission electron microscope.

Development of electrode materials with high capability and long cycle life are central issues for lithium ion batteries (LIBs). Here, we report an architecture of three-dimensional (3D) flexible silicon and graphene/carbon nanofibers (FSiGCNFs) with atomic-scale control of the expansion space as the binder-free anode for flexible LIBs. The FSiGCNFs with Si nanoparticles surrounded by accurate and controllable void spaces ensure excellent mechanical strength and afford sufficient space to overcome the damage caused by the volume expansion of Si nanoparticles during charge and discharge processes. This 3D porous structure possessing built-in void space between the Si and graphene/carbon matrix not only limits most solidelectrolyte interphase formation to the outer surface, instead of on the surface of individual NPs, and increases its stability but also achieves highly efficient channels for the fast transport of both electrons and lithium ions during cycling, thus offering outstanding electrochemical performance (2002 mAh g−1 at a current density of 700 mA g−1 over 1050 cycles corresponding to 3840 mAh g−1 for silicon alone and 582 mAh g−1 at the highest current density of 28 000 mA g−1).

Single-phase, nano-sized Li₃V₂(PO₄)₃/C materials with the monoclinic structure were prepared by a modified sol-gel method, in which the precursor materials were sintered at 750, 800, 850 and 900 °C, respectively. The X-ray diffraction(XRD) patterns of all the materials were consistent with the monoclinic structure without any impurities. The LVP/C composite sintered at 800 °C was selected as the most promising material on the basis of the lattice parameters (a = 8.605 Å, b = 8.596 Å, c = 14.732 Å, b = 125.20 °, V = 890.59 ų), crystallite size (99 nm), and morphology (5−6 nm carbon layer). The LVP/C composite sintered at 800 °C showed a high specific capacity with excellent kinetic properties (capacity of 130 and 170 mAh*g^-1 at voltages of 3.0-4.3 and 4.8 V at 0.1 C, 25 °C ), which showed about 98%, 86% of its theoretical capacity, respectively.

There has been a considerable interest in the battery system beyond lithium-ion. Magnesium-based systems remain the stronger candidate because of their earth abundance, and their ability to use Mg-metal as anode, which has been shown to deposit non-dendritically, a major impediment for realization of Li-metal system. However, the role of the surface passivating film (SEI) in the deposition/stripping of Mg at the anode/electrolyte interface during the reversible charge/discharge cycle has not been fully explored. For example, some borohydride-based electrolytes such as Mg(BH₄) suffer from lower oxidative potential (1.7v vs. Mg), and are prone to undergo electrochemical changes in the anode/electrolyte interface during cycling. Combined operando approaches using electrochemical-synchrotron soft X-ray absorption (sXAS) and transmission electron microscopy (TEM) provide perfect platforms to observe such representative electrochemical processes in great details.
Both sXAS and TEM utilize operando electrochemical cell consisting of microfabricated Si₃N₄ window and Pt electrode contacts. In sXAS, two additional electrode – Mg foil and a platinum wire are inserted, and the electrochemical interface at the thin Pt layer is probed. In TEM, the enclosed liquid cell consisting of Pt electrode electrochemistry chips is supplied with a continuous flow of electrolyte with a gas tight syringe, and cyclic voltammograms are recorded at 2 mV/s. All TEM analysis are performed using a JEOL JEM-2100 operating at 200kV, and a liquid electrochemistry is performed using a Hummingbird Scientific liquid-electrochemistry TEM holder.
Here, we present operando cross-platform sXAS/TEM methods to study the electrochemical studies of Mg-metal in Mg(BH₄)-based electrolytes to gain insights into the role of anode/electrolyte interface and interphase during Mg deposition and stripping processes. We use extended X-ray absorption fine structure (EXAFS) to investigate the solvent coordination of the as-prepared Mg(BH₄)₂: 3LiBH₄/DME electrolyte and after one reduction/oxidation cycle. The decrease in the intensity of Mg-O bond after the first cycle suggested the loss in solvent coordination at the interphase. Upon studying the oxidation/reduction processes in liquid TEM, we observe the formation of passivating surface SEI layer and H₂ gas beneath the magnesium metal deposit. Further study of B K-edge XAS indicated that [BH₄]- anion promoted the reductive formation of H₂ gas, and the reduction of Mg²⁺. These results present a new paradigm into using magnesium borohydride-based electrolytes for rechargeable magnesium batteries.

A critical bottleneck in the development of a high power battery material is to overcome the rate-limiting de-solvation step associated with intercalation of an alkali ion into graphite. Here, I will discuss results focused on utilizing co-intercalation as a method to enable fast charging and high power batteries. This concept pivots on the strong interaction between linear ether solvent molecules and alkali metal ions that results in a solvent shell which chelates the metal ion. This strong interaction leads the ion to maintain its solvent shell through insertion and extraction from graphite, bypassing the normal rate-limiting kinetics associated with desolvation. I will specifically discuss high-rate potassium and sodium co-intercalation into natural graphite that exhibits specific capacities above 100 mAhg^-1 at currents of 5 Ag^-1. To pair this into a full-cell battery architecture, I will discuss cathode options including Prussian blue nanoparticles that exhibit similar capacities at rates up to 10 C. The results from this work demonstrates how cointercalation of alkali ions poses an exciting option for high power batteries that rely on strategies where moderate energy density and low-cost make them an excellent option for emerging areas of grid storage, electric vehicles, and other high-power applications.

Nano layered double hydroxides Ni-Al-Li-LDHs was firstly introduced into Lithium-ion battery to modify LiFePO₄ (LFP) cathode. The 3D "Silk flower" like Ni-Al-Li-LDHs were in-situ grown on the surface of LFP by hydrothermal method with specific mole ratios of LFP/LDHs. A series of structural characterization have been carried out on these composites. The XRD, SEM, FT-IR and TEM test results reveal that Ni-Al-Li-LDHs was truly grown on the surface of LFP and formed a core-shell like structure. Then these LFP/LDHs composite were taken as cathode materials in lithium battery. Their electrochemical performance were detected by electrochemical impedance spectroscopy (EIS), cyclic voltammetry(CV), galvanostatic charge-dischage cycling. Both electrochemical activity and stability of LFP have obtained significant progress by Ni-Al-Li-LDHs optimizing. The highest specific capacity was obtained by LDHs/LFP (mole ratio 1:4) as 180 mAhg^-1, which is much higher than that of pure LFP cathode (120 mAhg^-1) . Moreover, the stability of these composites cathode were also outstanding by 200 cycling evaluation. The excellent performances of LFP/LDHs cathode in lithium ion battery were due to the enhancement of lithium ion mobility by Ni-Al-Li-LDHs. Which based on the unique layered by layered structure and ion exchangeable ability of Ni-Al-Li-LDHs. Besides, LDHs also enlarge the specific surface area of LFP by N₂ adsorption-desorption experiment. Which have provided more active site for electrochemical reaction. Modifying LFP by Ni-Al-Li-LDHs was a novelty attempt and achieved some positive results.

Current commercial lithium-ion batteries have reached their capacity limit due to the materials in use. To improve the capacity of lithium-ion batteries, researchers have started to use new electrode materials such as sulfur and silicon. Sulfur, although being a high capacity cathode material, suffers from conductivity and expansion problems. To increase the conductivity of sulfur electrodes, a high percentage of carbon is usually added to the electrode, resulting in low sulfur loading. A common method to improve the conductivity and the sulfur loading of an electrode is to calendar or densify the electrode, resulting in a more intimate contact between active material and the conductive additive. Herein we look at the positive effects of calendaring sulfur electrodes at different temperatures, varying from room temperature to as high as 120C. By elevating the electrode temperature, the heat softens the sulfur, allowing the sulfur particles to better come into contact with the conductive network and improving the conductive network. The increase in calendar temperature increases cycle life, capacity, and rate capability of the lithium-sulfur battery.

Multivalent batteries, such as rechargeable Mg-ion batteries, may be able to overcome the safety and cost limitations of Li-ion batteries. They are promising candidates for applications in large-scale stationary energy storage as well as in transportation. Finding high-voltage electrolytes which are compatible with the Mg-ion battery chemistry continues to be a research focus. In this work, we present electrochemical analysis of a a fluorinated dialkoxide-based magnesium-ion electrolyte. The electrolyte is stable at high voltages (>2V) and shows good performance in full battery cells using Chevrel phase Mo₆S₈. Its performance in other sulfide-based cathodes is also reported.

The Lithium-Sulfur (Li-S) batteries have been extensively investigated for next energy storage applications due to its great advantages such as much higher energy density and lower cost than current Lithium-ion batteries. Li-S batteries still suffer from several key performance issues (e.g., poor cycle life, self-discharge and rate capability) associated with polysulfide shuttling effect and slow kinetics. To tackle these problems, various approaches including the C-S nanocomposite and the interlayer concept have been suggested. For C-S composites, the structural parameters of the carbon hosts (i.e., pore size and porosity) proved to be very crucial to Li-S battery performance. In addition, a porous carbon interlayer inserted between the cathode and the separator to confine soluble polysulfides has been found effective in mitigating the polysulfide shuttling phenomena. However, most of approaches might not be suitable for mass production of cheap Li-S batteries. In this study, we propose a novel design of Li-S battery integrating a protective cathode incorporating a porous polysulfide adsorbent and a functional separator, which can be applied to current process and facilities. We focused on mitigating the polysulfide loss and further improving practical energy density of Li-S battery by investigating the electrochemical behavior of Li-S batteries under high sulfur loading conditions.

Lithium-sulfur (Li-S) batteries have received considerable attention owing to their unique features such as high capacity, non-toxicity and natural abundance. Despite recent significant performance improvement, several key performance issues (e.g., cycle life, rate property, self-discharge, safety) still remain unsolved. Recently, many researchers have focused on the development of new cathode materials along with the carbon-sulfur (C-S) concept to tackle poor cycle life and rate problems of Li-S batteries. A huge number of porous carbon materials have been applied to the sulfur cathode until now. Mostly, C-S composites have been found very effective in improving cycle performance. However, their practical application would be considered very hard since the synthesis process is so complex and expensive.
In this study, we present a highly sustainable sulfur cathode which can maintain its structural integrity and minimize polysulfide diffusion out of the cathode during cycling. Integration of inorganic porous materials within a sulfur cathode would be highly helpful for confining soluble polysulfides. We demonstrate enhancement of structural stability of sulfur cathode by incorporating porous inorganic materials and suggest a rational design of sulfur cathode ensuring long cycle life and high sulfur loading.

Lithium ion batteries have penetrated into our daily lives ranging from mobile phones to electric vehicles. This prompted considerable efforts toward the development of high-energy density lithium batteries, with a focus on designing new electrode active materials. In this context, elemental sulfur has been regarded as one of the promising candidates for next generation cathode materials owing to their high theoretical specific capacity (1672 mAh/g) and high energy density (2567 Wh/kg）based on 2-electron redox chemistry. In addition, low-cost, low-toxicity, and natural abundance of sulfur are another advantages. In spite of aforementioned strengths, sulfur cathodes suffer from critical limitations to be used in practical applications, such as volumetric changes during cycling, irreversible relocation of charge/discharge products, intrinsic insulating nature of sulfur, and dissolution of lithium polysulfide intermediates into the polar electrolyte. In the present study, we report the development of new sulfur cathodes based on inverse-vulcanized polymers. A new strategy is the use of functional linkers for the vulcanization process to enhance the electrochemical properties upon modulating electronic structures of the resultant polymers. Inverse-vulcanized polymers with 2,3,5,6-Tetra(allyloxy)benzoquinone linker showed amorphous morphology with improved redox activity, low band gap, and enhanced electric conductivity. By taking advantages of these benefits, the lithium-sulfur batteries can deliver high reversible discharge capacity of 1100 mAh/g with good capacity retention and decent rate capability up to 10 C.

Lithium ion battery (LIB) with high energy and power densities are actively investigated to enhance the competitiveness and extensive development of electric vehicles (EVs) and energy storage system (ESS), and for facilitating novel portable devices. The energy density of a battery is primarily determined by the charge-discharge capacities of the electrode materials and the operating potential of the battery. Due to the low theoretical capacity of graphite (372 mAhg^-1 for LiC₆), the commercialized anode material for LIBs, development of alternative anode materials for LIBs is strongly required for future applications. Certain metals and metalloids that alloy with lithium is particularly promising, such as Sn and Sb which both show several times higher energy densities than that of graphite (e.g. 993 mAhg^-1 for Li_4.4Sn; 660 mAhg^-1 for Li₃Sb). The choice of the SnSb from several synergistic effects between the Sn and Sb: 1) both components of alloy distribute to its high theoretical capacity of 824 mAhg^-1; 2) alloying/dealloying of Sn and Sb occur at different potentials, which smoothens the mechanical stress.
SnSb + xLi⁺ + xe^- ↔ Li_xSnSb (0≤x≤1.6)
Li_1.6SnSb + 1.4Li⁺ + 1.4e^- ↔ Li₃Sb + Sn
Sn + 4.4Li⁺ + 4.4e^- ↔ Li_4.4Sn
In the present work, nanoporous SnSb alloy with 3-D pore system and well-developed crystalline framework was successfully obtained via nano-casting method by using a 3-D porous silica as a hard-template. The nanoporous SnSb exhibits high specific surface area of 115 m²g^-1, large pore volume of 0.5 cm³g^-1 and dual nanopore sizes of 4 and 22 nm. Thus, 3-D nanoporous SnSb showed outstanding rate capabilities up to 2 C as well as high reversible lithium storage capacity of 810 mAhg^-1 with excellent coulombic efficiency of 99.3 %.

Sn-based alloy materials have gained popularity to replace commercial graphite anodes due to their higher gravimetric and volumetric capacity for next generation rechargeable lithium-ion batteries. Here a series of Sn_xFe alloys with nanosized derived from chemical transformation of pre-formed Sn nanoparticles as templates were successfully prepared. The morphology, crystal structure and composition of Sn_xFe intermetallic are greatly influenced by temperature, surface stabilizer and reagent molar ratio. The optimized Sn-Fe anode with core-shell structure could deliver 541 mAh/g after 200 cycles at the C/2 rate, corresponding to nearly 100 % initial capacity and 90.2% of the maximum charging capacity. The calculated volumetric capacity was about two times than that of commercial carbon. It also has excellent rate performance, delivering 94.8%, 84.3%, 72.1%, and 58.2% of the 0.1C capacity (679.8 mAh/g) at 0.2C, 0.5C, 1C and 2C, respectively. When it went back from 1 C to 0.1 C, the charge capacity recovered to 513.3, 603.2, 662 and 692.8 mAh g⁻¹. The exploring of Fe-Sn alloy from this work also provides insight for the designing other Sn-M (Co, Ni, Cu, Mn etc.) system.

Acknowledgement: This work is supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) program under Award No. DE-EE0006852.

Li₄Ti₅O₁₂ (LTO) is regarded as the most promising oxide negative electrode material for lithium ion batteries (LIB), with excellent charge-discharge cyclability and a flat plateau in potential-charge properties. However, the insulating nature of LTO hinders high-speed charge-discharge processes. Generally, the strategies to improve the conductance of a material include the enhancement of the conductivity by doping, and the mixing with a conducting material. The approach for the commercial oxide active materials is to use a carbon-based conductor, whereas studies on substitution of the tetravalent (4+) Ti ions with trivalent (3+) or pentavalent (5+) metal ions are ongoing in the laboratory level.
In the present study, we attempted to introduce oxygen deficiency to LTO thick films, expecting partial valence change of Ti ions. Amorphous LTO films that were deposited by an electrostatic spray deposition method in air at 250°C were post-annealed at 700°C in various ambient gases. A film annealed in Ar still showed sharp charge and discharge peaks in its current-potential properties, suggesting the possibility of reduction in an inert gas without the collapse of its crystal structure. Coating an LTO thick film with a glass-like carbon ultrathin layer, that also requires a post-treatment in the inert ambient gas, has been also attempted. Comparison of these films in conductivity is presented.

Engineering higher-performing lithium-ion batteries may be key to meeting the ever-growing demand for energy storage. Commonly used in battery cathodes because of its high theoretical capacity, thermal stability, and ecological friendliness, lithium iron phosphate (LFP) still has one major flaw, its low conductivity, both electronic and ionic. Technology is limited by this property of LFP, but several methods have been developed to increase battery performance, such as carbon additives and controlled porosity. Previous studies have established the importance that these two factors play in battery performance, and this project investigates the relationship between performance and pore size.

In lieu of a more common carbon black/graphite additive, graphene was chosen in this research due to its higher surface area and electronic conductivity. Additionally, four polymers (polyethylene terephthalate, polyvinyl chloride, polystyrene, and polypropylene) were tested as porous media, all with different particle surface-area-to-volume ratios, allowing us to manipulate pore surface area while keeping porosity (%) constant. Cathode slurries were mixed with LFP as the active material and with varying polyvinylidene difluoride (PVDF) to graphene weight ratios in an N-methylpyrrolidone (NMP) solvent. Then, the mixtures were spread on non-conducting plates, dried, and their electronic conductivities were measured using a four-point probe.

The PVDF/Graphene ratio yielding the highest conductivity was determined, and then slurries were prepared with the added polymers in order to achieve porosities between 20% and 40%. The slurries were spread onto non-conducting plates, dried, and calcinated. The four-point probe method was used to determine each sample’s conductivity, and coin cell batteries were assembled. Lastly, an Arbin battery tester was used to perform cycling tests on each of the prepared batteries. Imaging of each cathode material was also taken using a scanning electron microscope (SEM), and the crystallinity of the material was analyzed by dispersive spectroscopy (EDS).

Synthetic graphite is still the standard anode material for lithium ion battery industry. Herein, we introduce a scalable, recycled Polyethylene Terephthalate (PET)–derived graphite anode for lithium-ion battery. PET-derived anodes were obtained through electrospinning process. Formation of graphite tubes with diameter of 0.5 – 2 micrometers was confirmed through Raman analysis and Scanning Electron Microscopy (SEM) images respectively. Additionally, X-ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDS) and Brunauer-Emmett-Teller (BET) analysis were applied as well. Electrochemical properties of PET-derived graphite anodes were tested through Galvanostatic Cycling with Potential Limitation (GCPL), Galvanostatic Intermittent Titration Technique (GITT), Electrochemical Impedance Spectroscopy (EIS) and Constant Voltage (CV). Obtained PET-derived carbons show high surface area with good lithium diffusivity and capacity of 264 mAh/g after 500 cycles. The study provides a novel pathway to fabricate high capacity energy storage device from recycled waste plastic.

The market for electric vehicles (EVs) has gained significant popularity over recent years. However, in order for that market to continue to expand relative to consumer demands, lithium ion technologies need to be improved to withstand the common stresses encountered in EV applications. An example of such stresses is unanticipated fluctuations in internal and ambient temperatures. Currently, optimal performance of lithium ion batteries is limited to a specific operating temperature, subsequently, batteries that are exposed to temperatures outside of the operating range will exhibit detrimental performance effects such as a loss in capacity, life cycle degradation, and more concerning safety hazards. These effects are attributed to the decomposition of the solid electrolyte interphase (SEI) layer during stressed cycling. The common approach towards improving robustness of SEI is to utilize various electrolyte additives. This approach, however, is prone to adverse effects such as rapid self-discharge and a decrease in energy density. Herein, we propose a noninvasive approach towards developing robust SEI layer in lithium sulfur batteries to improve thermal stability at high temperatures. Robustness of SEI layers is modified via controlled conditioning of lithium sulfur (LiS) batteries within specified voltage regions. This work explores conditioning of LiS batteries at low temperatures within 8 – 17 degrees Celsius in attempt to slow down the kinetics involved in SEI formation and hence, develop robust SEI layers within the first cycles. The batteries are then evaluated for aging at elevated temperatures within 30 - 60 degrees Celsius, and assessed via GCPL, CV, EIS, and GITT.

The galvanostatic intermittent titration technique (GITT) is an electroanalytical tool commonly used in lithium ion technologies which uses transient and steady state measurements to obtain kinetic and thermodynamic properties of electrodes materials. The GITT procedure involves applying short current pulses followed by relaxation periods. In conventional lithium ion cells, when we apply current pulses, we induce concentration changes within the host electrodes. In lithium sulfur batteries however, the concentration change occurs in the electrolyte due to the reduction process of sulfur to electrolyte-soluble polysulfides. Hence, it is a complex procedure to quantify values such as, chemical diffusivity coefficient of lithium ions and the resistivity through the electrolyte in lithium sulfur cells, as opposed to conventional solid state lithium ion cells. Accordingly, research efforts to utilize GITT for lithium sulfur cells, omit the polysulfide shuttle mechanism to obtain a semi-solid state model. Herein, we explore a complete lithium sulfur model that enables more accurate quantitative depictions for mass transport rates, chemical reaction rates, and sulfur utilization.

Electrochemical storage has gained momentum amid increasing concerns for a cleaner, more environmentally friendly future. Currently, lithium ion battery systems do not meet the requirements to quell the increasing concerns and it is therefore imperative to move in a new direction. Top contenders for ‘beyond lithium’ is lithium-sulfur (Li-S) and silicon (Si). In order to scale up these new materials, it is crucial to study the effects of densification on their performance. Densification may alter the robustness of the electrode’s conductive network and ability of the electrolyte to penetrate the electrode. Through altering the electrode's density, it possible to improve network conductivity while also maintaining electrolyte penetration. Silicon and Sulfur electrodes were set to different densities and then characterized using gravimetric cycling, galvanostatic intermittent titration technique, cyclic voltammetry, and material utilization.Herein we report the fabrication of simple sulfur and silicon electrodes at different densities and their long term positive effects on cycling, rate performance and capacity.

Over the past two decades, lithium ion battery chemistries have enabled the practical development of many new products and technologies. Today, rechargeable Li-ion batteries are often the primary means of providing electrical power to a diverse and growing number of devices, from mobile phones to electric vehicles. Despite many advances and widespread adoption, Li-ion battery technologies have limitations. Battery chemistries based on lithium ions have a high theoretical gravimetric capacity of 3829mAh/cm³ only a modest volumetric capacity of 2044mAh/cm³ [1]. Volumetric capacity is anticipated to be especially important in IoT devices and wearables, where thin, flexible batteries which can cover large areas are ideal. By comparison, divalent batteries based on zinc or magnesium ions have theoretical volumetric capacities of 5854mAh/cm3 and 3882mAh/cm3 respectively [1]. In addition to somewhat a somewhat modest volumetric capacity, lithium is far less common in the earth’s crust than magnesium or zinc and possesses higher reactivity [2]. Because of this, lithium-ion batteries are anticipated to be less environmentally friendly and cost effective than divalent metal-ion batteries for applications requiring many large battery cells. It should also be noted that over the past year, the safety of lithium-ion batteries in consumer products has been called into question after a high-profile recall involving lithium-ion batteries in smartphones.

One means of addressing the shortcomings of lithium ion-battery technologies is to develop new battery chemistries based on divalent metal ions such as magnesium. Divalent metal-ion batteries could be made of flexible materials that allow for safe operation in the event of mechanical damage. Here we present an experimental magnesium ion half-cell constructed from flexible materials. A magnesium-ion cell was chosen due to its low material cost, good theoretical volumetric capacity, simple fabrication steps, and separator-free reaction chemistry. Flexible, insertion-type anodes and cathodes were fabricated using bismuth nanotubes and tungsten disulfide respectively. A polymer-based electrolyte made of PVDF-HFP and magnesium perchlorate was chosen for its demonstrated high ionic conductivity and mechanical flexibility. Each interface of the half-cell was characterized though the use of cyclic voltammetry and Raman spectroscopy, while a complete cell was examined using a commercial battery tester. Cell fabrication, component/interface electrochemistry, electrode materials, and overall cell performance will be described in detail.

[1] R.K. Guduru, J.C. Icaza. “A Brief Review on Multivalent Intercalation Batteries with Aqueous Electrolytes”. Nanomaterials, vol. 6, pp. 1-19, Feb 2016
[2] N. Nitta, F. Wu, J.T. Lee, and Gleb Yushin. “Li-ion battery materials: present and future”. Materials Today, vol. 18, pp. 252-264, June. 2015

Lithium iron phosphate (LiFePO₄, LFP) is the driving technology for battery energy storage applications due to its high theoretical capacity (170 mAh g^-1), cost-effectiveness, long cycle life, good thermal stability, and environmental friendliness in comparison to other traditional cathode materials such as lithium cobalt oxide (LiCoO₂) and lithium manganese oxide (LiMn₂O₄). However, key limitations of LFP are a low intrinsic electronic conductivity (~10^-9 S cm^-1) as well as limited ionic conductivity at room temperature. Several methods have been used to enhance electronic conductivity, such as carbon coating, super-valence ion doping on the Li-site, and nano-networking of electronic conductive metal-rich phosphides. On the other hand, enhancement of ionic conductivity has been researched to a less extend.
Theoretically, Chen et al. determined that the best conductivity for LFP cathode is achieved by a combination of 30% active material, 7.5% graphite, 10.15% carbon black, and 12.35% polyvinylidene fluoride (PVDF) by volume, to achieve a 40% porosity. In this work, we used polyvinyl chloride (PVC) and Polystyrene (PS) powders to experimentally optimize the size of pores and control the porosity of prepared cathodes. LFP cathodes are prepared in a slurry composed of lithium iron phosphate powder as the active material, carbon black and graphite as conductive additives, PVDF as a binder, and N-methyl-2-pyrrolidone (NMP) as the solvent. To create a matrix of pores, the cathodes are heated at 300°C and 360°C to evaporate PVC and PS, respectively. To calculate pore volume of the cathodes, their morphology is characterized by a scanning electron microscope (SEM) an image processing. To determine battery performance, coin-cells were assembled with cathodes containing various percentage of porosity. Cycling testing was performed using an Arbin tester.

Amorphous carbons such as hard carbon are being developed as anode materials for next generation sodium ion batteries. These materials have a structure composed of nanoscale domains of twisted, rumpled, and vertically disordered graphene stacks. Compared to graphite anodes, the dilated morphology makes insertion of large sodium ions into the galleries between graphene layers more energetically favourable. However, there is a disparity between the average gallery spacing observed experimentally during Na intercalation and the ab initio predicted local dilation necessary for favourable intercalation. In this work sinusoidally rippled bilayer graphene is used as a model for amorphous hard carbon. Using this it is demonstrated that the rippled graphene morphology creates local regions with large d-spacing, and in these geometrically dilated regions Na storage is highly favorable.

LiFePO₄ has been proved as a promising cathode material for LIBs because of its cost effective, high thermal stability, environmental friendly, and theoretical capacity of 170 mAh/g. Previously our group demonstrated that LiFePO₄ is able to be synthesized in a limited air environment. By doing this, it lowers the requirement of equipment, gas environment, and decrease the synthesis time needed in compare to traditional solid state method. And by applying a closed crucible designed to limit the amount of oxygen participating in the reaction, the quality of produced materials was improved and so decrease the cost of LiFePO₄ synthesis. However, the oxidation of the LiFePO₄ is still an issue that limit the quality of synthesis. In order to further improve the quality of the LiFePO₄, a time study on the synthesis is conducted. In our method, pre-dried iron phosphate (FePO₄) and lithium acetate (CH₃COOLi) are mixed. The mixture is placed in a sealed crucible and heated in a muffle furnace. The crucible is inserted in to the furnace after it reaches the designed temperature and removed from the furnace once designed heating time is reached to limit the byproduct reaction. Multiple experimental runs are conducted with various heating time to optimize the time needed for the reaction. The time study allows toward the understanding of the reaction evolution, especially the type of the oxide formed during the reaction and the oxidation development base on time. Several techniques are applied to characterize the properties of synthesized LiFePO₄. The crystal structure and chemical composition of the synthesized material are characterized by X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS). The grain size of resulted materials is determined by scanning electron microscopy (SEM). Raman spectroscopy is applied to detect the type of oxidization and oxidization level inside the materials. The synthesized LiFePO₄ is assembled into a half coin cell for electrochemical characterization. The cycleability and electrochemical performance of the cells under different C-rates are tested using an Arbin tester.

Silicon is considered as one of promising electrode materials for lithium-ion batteries (LIBs), thanks to its high energy density, high theoretical specific capacity and low discharge potential. Note that the strong volume expansion (~300%) of silicon during lithiation and delithiation is one of the main issues for its applications. To solve this issue, we develop silicon-carbon nanospheres (SCNSs) as LIB anodes by a simple and scalable method. Firstly, silicon nanospheres (SNSs) are synthesized via magnesium reduction of silica nanospheres, which are produced by an in-situ acid catalyzed polymerization of tetraethyl orthosilicate (TEOS). The SNSs with 3D nanoporous spheres have an average diameter of ~100 nm. To fully extract the real performance of the SNSs, carbon coating is further performed to enhance the electronic conductivity of SNSs. We obtain the SCNSs LIB anodes exhibiting excellent lithium storage performance, which have a reversible capacity of ~3170 mAh g⁻¹, high rate capability (C/2) and cyclic stability (capacity of ~1010 mAh g^-1 after 500 cycles). Our results demonstrate that the spherical nature and high nanoporosity of the SCNSs significantly improves the electrochemical stability by accommodating the volume changing.

VOPO₄ is a promising cathode material in Li-ion batteries due to its ability to hold multiple Li-ions per redox center. Specifically, the V⁵⁺/V⁴⁺ and V⁴⁺/V³⁺ redox couples allow for the insertion of two Li-ions into VOPO₄, LiVOPO₄ and Li₂VOPO₄. These phases also exhibit polymorphism, with VOPO₄ and LiVOPO₄ having seven and three different polymorphic phases, respectively. A thorough comparison of the physical and electrochemical properties of these polymorphs will help determine the mechanisms by which these phases form and how they perform electrochemically. This study focuses on the three most promising LiVOPO₄ phases: α₁ (layered, tetragonal), β (orthorhombic), and ε (triclinic). All phases are synthesized from a single precursor, LiVOPO₄-2H₂O, reducing the effects of synthesis methods on the physical and electrochemical properties of the products, allowing for more accurate comparisons. The transformations between the different phases are studied using x-ray diffraction and differential scanning calorimetry. The electrochemical performance of each phase is evaluated using galvanostatic discharge-charge between 1.5 to 4.5 V at various current rates. The lithium diffusion coefficients are calculated using cyclic voltammetry and galvanostatic intermittent titration technique.

Titanium dioxide has recently attracted focus as a potential anode material in lithium-ion rechargeable batteries (LiBs) because of the low cost, abundant source, light weight, safety, and high theoretical capacity. However, the practical application of TiO₂ is restricted by its poor electronic conductivity and inefficient lithium diffusion. Previous experimental studies have demonstrated that the incorporation of oxygen vacancy into TiO₂ nanostructures as a strategy to enhance anode material performances. In this work, three most common polymorphs of TiO₂ were investigated for potential as lithium-ion battery anode materials: anatase, rutile and TiO₂(B). Each phase was modeled and first-principles study based on density functional theory (DFT) calculations were employed to investigate the intercalation and diffusion behavior of lithium at dilute concentrations in TiO₂ with/without an oxygen vacancy. Total energies of possible intercalation sites were first calculated to determine favorable sites among the three phases. Furthermore, all lithium diffusion pathways form one stable site to another were examined by climbing image nudged elastic band method. To understand the effect of oxygen vacancy on the lithium diffusion mechanism, energy barriers of lithium diffusion for pristine and oxygen-defective TiO₂ structures were calculated and compared. In addition, the electronic structures of TiO₂ with oxygen vacancy were compared to pristine TiO_2. The results indicate that among the three polymorphs, TiO₂(B) may the better choice for use as anode material after oxygen vacancy creation because of lower diffusion energy barrier change and larger band gap reduction.

In recent years, cubic lithium garnets, Li₇La₃Zr₂O₁₂ (LLZO) in particular, have attracted much attention due to reasonable ionic conductivity (>10^-4 S cm^-1 at room temperature), good chemical stability with lithium metal, and near-to-unit transference number. It has been reported that small amount of Al₂O₃ dopant can act as sinter aid to yield dense and cubic phase, the fast Li-ion conducting phase. This talk first introduces our efforts to synthesize such lithium garnets. We investigated the effect of preparation parameters including Al₂O₃ doping amount, crucibles, and heating schedule on the materials properties such as ionic conductivity and air stability, using various characterization techniques such as XRD, ICP-OES, SEM-EDS, NMR, Raman and EIS. We optimized the preparation process and obtained lithium garnets with good air stability and room-temperature conductivity in the range of 4~6 x 10^-4 S cm^-1 [1]. Then the reaction mechanisms of LLZO in ambient air are discussed [2,3,4]. This talk ends with the applications of LLZO in novel lithium batteries such as solid lithium batteries, hybrid lithium battery and Li-S batteries [5,6].
References:
[1] Biyi Xu, Huanan Duan, Wenhao Xia, Yiping Guo, Hongmei Kang, Hua Li, Hezhou Liu, Journal of Power Sources, 302 (2016) 291-297.
[2] Wenhao Xia, Biyi Xu, Huanan Duan, Yiping Guo, Hongmei Kang, Hua Li, Hezhou Liu, ACS Appl. Mater. & Interfaces, 8 (2016) 5335-5342.
[3] Wenhao Xia, Biyi Xu, Huanan Duan, Xiaoyi Tang, Yiping Guo, Hongmei Kang, Hua Li, Hezhou Liu, Journal of the American Ceramic Society (2017) 1-8.
[4] Huanan Duan, Hongpeng Zheng, Ying Zhou, Biyi Xu, Hezhou Liu, accepted by Solid State Ionics.
[5] Biyi Xu, Wenlong Li, Huanan Duan, Haojing Wang, Yiping, Guo, Hua Li, Hezhou Liu, Journal of Power Sources 354 (2017) 68-73.
[6] Biyi Xu, Huanan Duan, Hezhou Liu, Chang-An Wang, Shengwen Zhong, ACS Applied Materials & Interfaces 9 (2017) 21077-21082.

ABSTRACT:
Insight into relationship between Crystal/Interface structure and properties of capacity, stability and rate capability are important for developing advanced Li-ion batteries. Using theoretical calculations combined with experimental in-situ tests, we did extensive studies on the kinetic of Li-ion diffusion for two representative cathode materials: layered Li(Ni_xMn_yCo_z)O₂ (NMC) (x + y + z = 1) and LiFePO₄. We not only focus on the bulk kinetics, but also the kinetics across electrode/electrolyte solid-liquid interface and in the electrolytes. For example, we first proposed that "Janus" solid-liquid interface would facilitate the Li-ion transport in battery and introducing some disordering in non-active cathode materials would activate them for Li-ion storage. Finally, we also developed some in-situ technologies for battery studies. For example, using electrochemical quartz crystal microbalance (EQCM), we achieve an in situ experimental investigation of the LiFePO4 (LFP) and NaFePO4 (NFP)/electrolyte interfacial kinetics for Li(Na)-batteries. （Ref. 1）
For high energy and power density applications (e.g., EVs), the safety becomes especially important. Using ab initio calculations combined with experiments, we clarified how the thermal stability of NMC materials can be tuned by the most unstable oxygen, which is determined by the local coordination structure unit (LCSU) of oxygen (TM(Ni, Mn, Co)₃-O-Li_3-x’): each O atom bonds with three of transition metal (TM) from the TM-layer and three to zero of Li from fully discharged to charged states from the Li-layer. Under this model, how the lithium content, valence states of Ni, contents of Ni, Mn, and Co, and Ni/Li disorder to tune the thermal stability of NMC materials by affecting the sites, content, and the release temperature of the most unstable oxygen is proposed. (Ref. 2)

Ref.
(a)F. Pan el al., “Kinetics Tuning of Li-ion Diffusion in Layered Li(NixMnyCoz)O2”, J. Am. Chem. Soc., 2015, 137, 8364; (b) Adv. Energy Mater., 2015, 1501309(1-9).(c) Nano Lett,2015, 15 (9), pp 6102 (d) Adv. Energy Mater., (Front page ) 2016, 1601894 (e)F. Pan el al., Excess Li-ion storage on reconstructed surfaces of nanocrystals to boost battery performance, Nano Lett, 2017, 17, 6018−6026, (f) Nano Energy 2017 37, 90 (g) Nano Lett., 2017, 17 (8), 4934–4940, (h) Inorg. Chem. 2017 DOI: 10.1021/acs.inorgchem.7b02150
(a) F. Pan el al., “Tuning of Thermal Stability in Layered Li(NixMnyCoz)O2”, J. Am. Chem. Soc., 2016, 138 (40), 13326, (b) Nano Letters 2016, 16 (10), pp 6357; (c) Nano Letters, 2015, 15, 5590; （d） J. Phys. Chem. Lett., 2017, 8 (22), 5537–5542

We report on a particularly stable 3 V all-solid-state sodium–ion battery built using a closo-borate based electrolyte, namely Na₂(B₁₂H₁₂)_0.5(B₁₀H₁₀)_0.5. The battery employs a sodium metal anode and a NaCrO₂ cathode. Battery performance is enhanced through the creation of an intimate cathode–electrolyte interface resulting in reversible and stable cycling with a capacity of 85 mAh/g at C/20 and 80 mAh/g at C/5 with more than 90% capacity retention after 20 cycles at C/20 and 85% after 250 cycles at C/5. We also discuss the effect of cycling outside the electrochemical stability window and show that electrolyte decomposition leads to faster though not critical capacity fading. Our results demonstrate that owing to their high stability and conductivity closo-borate based electrolytes could play a significant role in the development of a competitive all-solid-state sodium–ion battery technology.

[1] L. Duchêne, R.-S. Kühnel, E. Stilp, E. Cuervo Reyes, A. Remhof, H. Hagemann, C. Battaglia, Energy & Environmental Science 10, 2609 (2017)

Driven by the promise of high safety and reliability for all-solid Li ion battery applications, many research efforts have since been performed for developing oxide-type solid electrolytes with a garnet framework. This is made evident by the large number of research works found in the literature, particularly on ionic conductivity optimization by way of doping at the cation sub-lattice of the garnet crystal structure. Some of these doping strategies result to direct blockage of the Li ion conduction pathway and could cause profound impacts on the structure and overall conductivity behavior of the material. To elucidate what these impacts exactly are, we carried out atomistic-level computational modelling on two specific doping or cation incorporation in the Li sub-lattice of the garnet structure: i) Ga doping¹ which has been reported to reach 10^-3 S/cm order of Li ionic conductivity (among the highest reported so far for garnet compounds²) and ii) proton exchange which occurs upon exposure to air or moisture during synthesis or powder handling.

References:
1. Jalem et al., Chem. Mater. 2015, 27, 2821−2831.
2. Bernuy-Lopez et al., Chem. Mater. 2014, 26, 3610−3617.

To meet the future demands of future hybrid, plug-in hybrid, and all electric vehicles, advances in energy storage for transportation is indispensable. Additionally, energy diversification is vital to tailor electrification requirements to optimize the cost, range and size of the application. Recently, post Li-ion batteries, such as Li-O₂, multivalent and anion batteries, have garnered much attention. The lithium metal sulfur (Li-S) battery is an exciting system due to its high theoretical capacity (1673 mAh/g-S) and the potential of low cost.¹ However, realizing Li-S batteries relies on solving key challenges such as dissolution and shuttling of polysulfides, low sulfur utilization at high-areal loading levels, lithium metal dendrite formation, and continuous electrolyte decomposition on the Li metal surface.
The potential benefits of solid-state electrolytes, such as polymer electrolytes, gel electrolytes and ion-conducting ceramics electrolytes, are wide-operating windows, active material dissolution prevention and metal dendrite inhibition. However, low ionic conductivity and interfacial stability require continued development to achieve a viable energy storage system. Recently, ionic conductivities rivaling liquid based-systems have been observed for the sulfide-based, glass-ceramic L₁₀GeP₂S₁₂ (LGPS),² encouraging continued research into solid-state batteries using sulfide-based solid-electrolytes. Tatsumisago et al.³ illustrated and impressive initial cycling results using lithium-indium alloy anode, a lithium iodide/lithium sulfide solid-solution cathode, and a solid sulfide electrolyte: over 1000 mAh/g at 2C cycling for over 2000 cycles. Inspired by the results, developing all solid Li-S batteries presents hope for a high-energy density battery.
Here, we will present the electrochemical discharge mechanism of solid state Li-S batteries using glass-ceramic, sulfide-based solid-electrolyte and a lithium metal anode. The solid-state reactions of the active materials with the solid-electrolyte are evidenced through X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and thermal analysis. Our results reveal that the electrochemical properties are closely tied to the fabrication of the solid-state cathodes. Additionally, researchers have recently observed the decomposition of sulfide electrolytes in contact with lithium metal^4,5. We will discuss protection strategies to inhibit undesired reactions at the anode-electrolyte interface as potential solutions to further improve all-solid Li-S batteries for vehicle electrification.

[1] Manthiram, A. et al. Chem. Rev. 2014, 114, 11751-11787.
[2] Kanno, R. et al. Nat. Mater. 2011, 10, 682-686.
[3] Tatsumisago, M. et al. Adv. Sustainable Syst. 2017, 1700017, 1-6.
[4] Sakamoto, J. et al. Electrochimica Acta 2017, 237, 144-151.
[5] Janek et al. Solid-State Ionics 2016, 286, 24-33.

By virtue of their high specific energy, energy density and long cycle life, lithium-ion batteries have contributed to a significant enhancement or even enablement of several space missions and defense applications. However, NASA’s future missions, e.g., Astronaut’s Portable Life Support System (PLSS) for Extra-Vehicular Activities (EVA), small planetary rovers, planetary probes, CubeSats etc., require battery technologies with higher specific energies and energy densities, for short cyclic lifetimes. Similarly, Department of Defense (DoD) is interested in the development of a high energy rechargeable battery system for soldier and navy applications. The lithium/sulfur system is deemed the most viable future technology, because of its high theoretical specific energy (3-4x vs Li-ion). However, despite several years of development, this system hasn’t matured yet, mainly due to the challenges from the soluble polysulfides, which results in a ‘redox shuttle’ and a deposition of lithium sulfides and impedance growth at the lithium anode. Several attempts were reported in the literature with novel cathode designs, e.g., hierarchical porous carbon structures to sequester sulfur and its reduction products, and also with electrolyte solutions to minimize their solubility. ^1-3 Good cycle life was achieved in some of these cases, but the sulfur loadings in the cathodes are much lower (1-2 mg/cm²) than desired. To realize high specific energy from a Li/S cell, sulfur loading will need to be high, i.e., > 12 mg/cm² per side or >6 mAh/cm² areal capacity. Recently, our group⁴ and several others^6-8 have been developing new sulfur composite cathodes blended with transition metal sulfides (e.g., titanium and molybdenum disulfide), which assist in the trapping of polysulfides within the cathode and improve the cycle life of Li-S cells. In addition, we have demonstrated similar improvements in the cycle life with the use of ceramic-coated separators, e.g., Tonen separators coated with alumina and aluminum fluoride,⁸ and with protected Li anodes. In this paper, we will describe our recent studies with the high-areal-capacity composite sulfur cathodes, coated separators and protected Li anodes for improved cyclic stability of our laboratory Li-S cells.

Lithium-ion batteries are crucial to the future of energy storage. However, the energy density of current lithium-ion batteries is insufficient for future applications. Sulfur cathodes have garnered a lot of attention in the field due to their high capacity potential. Although recent developments in sulfur cathodes show exciting results in half-cell formats, there has been minimal progress in utilizing sulfur cathodes in full cells. This is because current lithium-ion cathodes are expected to act as the lithium source in a lithium full-cell, and sulfur cathode cannot do so. Current methods for incorporating lithium in full cells utilizing sulfur cathodes involves prelithiating the anode or using lithium sulfide, the lithiated form of sulfur. These methods, however, complicate material processing and creates safety hazards. Herein, we present a novel full-cell battery architecture that bypasses the issues associated with current methods. This battery architecture gradually integrates controlled amounts of pure lithium into the system by allowing lithium the access to the external circuit. A high specific energy density of 350 Wh/kg after 250 cycles at C/10 was achieved in a sulfur-silicon full cell using this method. This work should pave the way for future researchers into sulfur full cells.

This work provides novel insights into the oxygen activity and its correlation with the chemical environment of transition metals at the surfaces , sub-surfaces and bulk of layered transition metal oxides in lithium ion and sodium ion batteries. The oxygen activity in battery materials are historically challenging to be analyzed due to the lack of proper techniques that can simultaneously probe the unoccupied oxygen 2p and transition metal 3d orbitals. The energy range of soft X-ray covers both the oxygen K-edge and transition metal L-edges, the combination of which can provide precise information on the local transition metal-oxygen (TM-O) octahedral crystal field. We take advantage of unique features of soft X-ray absorption spectroscopy (s-XAS) and electron energy loss spectroscopy (EELS) to investigate the differences in the oxygen activity between the classical layered oxides and Li rich layered oxides and the impact of such difference on the surrounding TM-O environment, during the first cycle and after a number of high voltage cycles. The experimental data will be carefully interpreted with the help of first principles computation. With a quantitative comparison between the classical layered oxides and lithium rich layered oxides, we hope to provide a strategy to effectively control the oxygen activities in layered oxides, especially when guest ion (Li+ and Na+) concentrations are low (high voltage range). Last but not least, we will demonstrate the important role of defects in anion redox active materials.

The energy density of many lithium metal oxide battery cathodes is limited by redox reactions associated with the transition metal alone. Anionic redox reactions are affording new opportunities to increase this energy density. Here, we present results from first-principles density functional theory (DFT) calculations aimed at understanding the combined cation/anion redox of Li-rich materials, and designing new materials that will enable high-capacity, reversible cycling with minimal oxygen evolution. We illustrate this approach on three Li-rich compounds: Li₅FeO₄, Li₄Mn₂O₅, and Li₂MnO₃.

Li₅FeO₄: Initial removal of Li is accompanied by Fe migration to form a disordered rocksalt structure. A local Li₆-O coordination of oxygen, identified by DFT calculations, raises the O 2p band and enables reversible O-/O^2- redox behavior, previously unknown in this material. This insight leads to the prediction and subsequent experimental demonstration of anionic and cationic redox reactions with good reversibility and without any obvious O₂ gas release.

Li₄Mn₂O₅: We study the recently-reported, high-capacity, disordered rocksalt-type Li₄Mn₂O₅ compound and also determine the ground state ordered structure of Li4Mn2O5 via a DFT-based enumeration method. DFT calculations show that the delithiation process occurs via a three-step reaction pathway involving the complex interplay of cation and anion redox reactions: i) Mn3+→ Mn4+ (Li_xMn₂O₅, 4 > x > 2), ii) O²⁻ →O¹⁻ (2 > x > 1), and iii) Mn⁴⁺ →Mn⁵⁺ (1 > x > 0) concomitant with Mn migration from the original octahedral site to the adjacent tetrahedral site. Finally, we predict that alloying with M = V and Cr in Li₄(Mn,M)₂O₅ would produce new stable compounds with substantially improved electrochemical properties.

Li₂MO₃: We catalog the family of Li₂MO₃ compounds as active cathodes or inactive stabilizing agents using high-throughput density functional theory (HT-DFT). With an exhaustive search based on design rules that include phase stability, cell potential, resistance to oxygen evolution, and metal migration, we predict a number of new Li₂M^IO₃–Li₂M^IIO₃ active/inactive electrode pairs, in which M^I and M^II are transition- or post-transition metal ions, that can be tested experimentally for high-energy-density lithium-ion batteries.

Na-ion battery is an emergent technology beyond Li-ion chemistries with very attractive properties for grid scale energy storage. However, the limited energy density comparing to Li-ion batteries has been a major argument against its wide applications. One of the main reasons is from the cathode material, which usually has limited specific capacity and low charge cut-off voltage. Here, we introduce our recent work on the development of high energy density Na-ion battery cathodes and the fundamental understanding behind that. In particular, a cathode material synthesized showed >180 mAh/g specific capacity between 2-4.2V and very good cycling stability. The corresponding energy density of the cathode is ~600 Wh/kg. Good air stability was also demonstrated. It is a big leap for the field making Na-ion battery potentially promising as competitive to Li-ion batteries.

Achieving the energy limit of LiNi_1-2xCo_xMn_xO₂ (NCM) (x=0~1/3) cathodes has raised great research interests in recent years. In order to obtain longer cycle and calendar life, current NCM cathodes deliver far less than their theoretical energy density, even after intense modifications such as cation/anion doping, coating, core-shell structure, and concentration-gradient design. By a throughout and careful literature survey, we summarized five individual phenomena observed at the end of charge: O3-O1 phase reaction, crack propagation, Li-Ni exchange, layered-spinel phase transition, and Oxygen evolution. These five phenomena have been reported independently by different researchers using novel ex situ and in situ characteristic techniques, and which one leads to the degradation of NCM cathode is not clear.
In this study, we perform a comprehensive study of LiNi_1-2xCo_xMn_xO₂ (NCM) (x=0~1/3) cathodes, using first-principle calculations within the DFT+U framework and a bond model based on the effective interaction of transition metal (TM) ions. Based on our results, we have located the obstacles toward unity efficiency and revealed that the degradation strongly depends on the Ni concentration and the depth of charge (DOC). Based on our findings, the optimal composition for a good electrochemical performance of NCM cathode materials is found within the region of 1/10<x<1/4 (50-80% of Ni). We also proposed separate solutions for each Ni concentration to prevent degradation at high voltage/capacity. For 1/4≤x≤1/3, a feasible way to reduce the Oxygen evolution during charge would be through doping with high valence TM ions, in order to reduce strongly covalent Co-O bonds. On the other hand, for 0≤x≤1/4, the use of coating materials or novel materials design like core-shell and concentration-gradient structures could restrict the lattice distortion along the charge process. The key factors found in present work will help researchers, especially the newcomers to understand the obstacles toward unity efficiency, and also help them to rationally design NCM cathode materials with high-energy density through possible solution mechanisms, such as doping, coating or novel nanostructures, like core-shell or concentration gradient cathodes.

Related publications:
C. P. Liang, Roberto C. Longo, et al. Obstacles toward unity efficiency of LiNi_1-2xCo_xMn_xO₂ (x=0~1/3) (NCM) cathode materials: Insights from ab initio calculations. Journal of Power Sources, 2017, 340: 217-228.
C. P. Liang, F.T. Kong, et al. Unraveling the Origin of Instability in Ni-Rich LiNi_1−2xCo_xMn_xO₂ (NCM) Cathode Materials. The Journal of Physical Chemistry C, 2016, 120 (12): 6383–6393.
C. P. Liang, F.T. Kong, et al. Site Dependent Multicomponent Doping Strategy for Ni–rich LiNi_1–2yCo_yMn_yO₂ (y = 1/12) Cathode Materials for Li–Ion Batteries. In revision.
C. P. Liang, Roberto C. Longo, et al. Ab initio study on Surface Segregation and Anisotropy of Ni-rich LiNi_1-2xCo_xMn_xO₂ (NCM) (x ≤ 0.1) Cathodes. Submitted.

To cope with global warming and ever-increasing energy demands, there has been a great effort to develop an efficient energy storage system (ESS) for electric vehicles (EVs) and grid-scale ESSs. Li-ion batteries (LIBs) have the greatest potential to be used such applications on their high energy and power densities, however, as the size of battery packs is getting larger, there is a growing concern on the battery safety issues.^[1-2] Battery safety is closely related to the thermal stability of the cathode materials because the structural transition or decomposition of charged cathode generally involves O₂ evolution, which increase the risk of thermal explosion of battery packs.^[3-4] In this regards, in-situ monitoring the structural evolution of cathode materials at various conditions (i.e. temperature, state of charge, C-rates, etc.) is a critical issue to develop safer electrode materials.^[5]

Neutron diffraction techniques have been widely used to investigate the crystal structure of electrode materials for rechargeable batteries on the merit of the direct interaction of neutron with atomic nucleus, which enable us to investigate detailed structure of electrode materials containing light elements such as Li, Na and O.^[6] Furthermore, quantitative discussion on neighborhood elements in the periodic table such as Mn, Fe, Co, and Ni are comparably easy, which is difficult with X-ray. For this reason, neutron diffraction researches on electrode materials for rechargeable batteries have been significantly increased for several years.^[6]

In this presentation, we will demonstrate the effect of transition metal ions in Ni-Co-Mn-based oxide (NCM) electrode materials upon phase transition at high temperature using combined in-situ high temperature neutron diffraction and gas analyses. We believe that this research can provide a new insight into atomic migration and phase evolution in NCM materials and intuition for the design of cathode materials with high thermal stability.

References
[1] J. Zheng, T. Liu, Z. Hu, Y. Wei, X. Song, Y. Ren, W. Wang, M. Rao, Y. Lin, Z. Chen, J. Lu, C. Wang, K. Amine, F. Pan, J. Am. Chem. Soc. 2016, 138, 13326-13334.
[2] D. Larcher, J. M. Tarascon, Nat. Chem. 2015, 7, 19.
[3] K.-W. Nam, S.-M. Bak, E. Hu, X. Yu, Y. Zhou, X. Wang, L. Wu, Y. Zhu, K.-Y. Chung, X.-Q. Yang, Adv. Funct. Mater. 2013, 23, 1047.
[4] S.-M. Bak, K.-W. Nam, W. Chang, X. Yu, E. Hu, S. Hwang, E. A. Stach, K.-B. Kim, K. Y. Chung, X.-Q. Yang, Chem. Mater. 2013, 25, 337.
[5] C. P. Grey, J. M. Tarascon, Nat. Mater. 2017, 16, 45.
[6] A. M. Balagurov, I. A. Bobrikov, N. Y. Samoylova, O. A. Drozhzhin, E. V. Antipov, Russ. Chem. Rev. 2014, 83, 1120.

Electrophoretic deposition (EPD) is a technique widely used for high throughput industrial processes. Here we show EPD as a route to manufacture low-cost, high areal capacity battery electrodes. Using non-toxic, quick-drying acetone as a solvent, we use EPD to fabricate lithium iron phosphate cathodes with high areal loadings of 50 mg/cm². Higher electrode mass loadings substantially contribute to increasing the energy density while minimizing the overall cost of the battery materials by decreasing the ratio of inactive to active components. This work highlights the electrochemical performance of high areal loading EPD manufactured electrodes with capacities up to ~8 mAh/cm². EPD is a promising technique to manufacture the next generation of nanoarchitecture electrodes with high energy density at reduced manufacturing costs.

Development of low-cost cathodes with high energy density and long cycle life is critical to enable advanced Li-ion batteries for transportation applications. Traditional layered LiMO₂ (M = Mn, Co, Ni, etc.) cathodes cannot reversibly cycle their entire Li supply (e.g., x ≤ 0.5 in Li_1-xCoO₂). When charged beyond ~4.3 V vs. Li/Li⁺, many lithium-transition metal oxides undergo irreversible structural changes with concomitant oxygen gas evolution, resulting in irreversible capacity loss and voltage fade during cycling.^[1-3] Understanding and addressing these structural instabilities is necessary to design new cathode materials which can better utilize their Li supply without sacrificing cycle life.

Li₂MoO₃ has recently received attention as a cathode material due to the unique properties of Mo which can access several oxidation states (e.g., Mo⁴⁺ in Li₂MoO₃ and Mo⁶⁺ in MoO₃), allowing for the possibility to store multiple Li per transition metal. Our previous work showed that Li₂MoO₃ also has excellent oxidative stability and thus may be useful to stabilize the oxygen sublattice of conventional cathode materials. This presentation will detail the synthesis and characterization of layered-layered composite Mo-based cathodes with the general formula xLi₂MoO₃-(1-x)LiMO₂ (M = Ni, Mn, and/or Co). Various synthesis routes including solid-state reactions and sol-gel chemistry will be explored to understand the effect of synthesis conditions on the structure and electrochemical properties of these materials. The structural evolution of these cathodes over several charge/discharge cycles will be studied using Raman spectroscopy and X-ray diffraction (XRD). In-situ mass spectrometry will be used to monitor the composition and quantity of gas evolved during battery operation. The effect of fluorine doping on the operating potential and oxidative stability of these materials will also be discussed.

Acknowledgements
Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy.

References
[1] R. E. Ruther, H. Zhou, C. Dhital, K. Saravanan, A. K. Kercher, G. Chen, A. Huq, F. M. Delnick, J. Nanda, Chem. Mater. 2015, 27, 6746-6754.
[2] M. Sathiya, G. Rousse, K. Ramesha, C. P. Laisa, H. Vezin, M. T. Sougrati, M. L. Doublet, D. Foix, D. Gonbeau, W. Walker, A. S. Prakash, M. Ben Hassine, L. Dupont, J. M. Tarascon, Nat Mater 2013, 12, 827-835.
[3] R. E. Ruther, A. S. Pandian, P. Yan, J. N. Weker, C. Wang, J. Nanda, Chem. Mater. 2017, 29, 2997-3005.

Although photo-patterning has been used extensively in the semiconductor industry for the fabrication of low cost structures, it has hardly been utilized in the battery community. The photo-patterning of solid electrolytes offers several potential advantages as the ability to achieve spatial control with micron and sub-micron resolution enables one to form electrolytes in non-planar geometries as well as to develop new battery fabrication routes, especially ones that offer better integration with microelectronics and on-chip batteries. The present paper describes our work in photo-patterning two different lithium-ion conducting electrolytes, silica-based ionogels and an epoxy-based gel electrolyte.

Ionogels are pseudo-solid-state electrolytes in which an ionic liquid electrolyte confined in a mesoporous inorganic matrix leads to a material that possesses the electrochemical properties of the ionic liquid despite being a macroscopic solid. In the work reported here, we used UV cross-linking to induce hydrolysis and condensation of a sol-gel silica network. The resulting materials retained the ion transport and electrochemical stability of the confined ionic liquid electrolyte and demonstrated photolithographic patterning of simple structures. The photoresist used in this study, SU-8, was modified with LiClO₄ to form a gel electrolyte. The presence of the lithium salt reduces the degree of cross-linking during UV exposure, leading to increased conductivity but without sacrificing photo-patterning properties. The material also exhibits good thermal and electrochemical stability, excellent mechanical integrity and micron-scale patterning. Thin films of both UV cross-linked electrolytes were evaluated in electrochemical half cells and exhibited good interfacial stability.

The safety concerns originating from the use of flammable organic liquid electrolytes have impeded widespread of conventional Li-ion batteries for the large-scale energy storage applications such as battery-driven electric vehicles and energy storage systems. In this regard, solidifying electrolytes with inorganic superionic conductors is considered as an ideal solution. Among various inorganic solid electrolyte (SE) candidates, sulfide materials are suitable to achieve high performance for all-solid-state batteries as the conductivities for the-state-of-the-art sulfide materials (e.g., Li_9.54Si_1.74P_1.44S_11.7Cl_0.3: 25 mS cm^-1) are comparable to that for liquid electrolytes and the sulfide materials are soft. The softness of sulfide materials allows surface contacts with active materials by simple pressing procedure at room temperature, avoiding deteriorating high-temperature sintering process which is the critical limitation for oxide SE materials.
Despite the extensive progresses in the SE materials, the test protocols for all-solid-state batteries are poorly developed. In most previous literatures, the performances of working electrodes for all-solid-state batteries have been assessed by using In or Li-In as reference and counter electrodes without any verification. Moreover, analysis of all-solid-state full-cells, which is crucial for practical applications, has been unprecedented so far. In this regard, development of all-solid-state three-electrode cells is of prime importance. Unfortunately, the unique fabrication protocol of all-solid-state batteries make the development of all-solid-state three-electrode cells extremely challenging.
In this presentation, our recent results on development of the first all-solid-state three-electrode cells and its application to diagnoses on failure modes of several battery systems.

References
[1] Y. S. Jung, D. Y. Oh, Y. J. Nam, K. H. Park, Israel J. Chem. 55 (2015) 472-485.

In the advent of fast charging and high voltage storage devices, thermal runaway followed by meltdown of lithium ion battery is a cause of concern. Prior experiments on lithium battery modules have shown issues of high thermal generation in high energy storage electrodes. Theoretical and numerical analysis have focused on either the factors causing heat generation from electrode particles at microscale or the possible thermal management techniques to mitigate thermal failure in fullscale battery. We report a multiscale thermomechanical model which bridges heat generation by the electrode particle to thermal runaway in a multilayered electrode separator system. The thermal analysis is coupled with an elasto-plastic diffusion induced stress model to compare the thermal and mechanical performance under different design and operating parameters. A parametric analysis is performed for combination between three cathode and anode materials and the performance of the model is studied over a range of particle radius and charging rates. Higher charging rate and larger particle size are found to push the electrode into plastic deformation. Four modes of heat generation are considered including three conventional heating modes, i.e. polarization heating due to surface over-potential, entropic heating due to entropy release during lithiation, resistive heating due to electrical resistivity of the electrodes; and heat generation from the plastic deformation of electrode particles under faster charging condition. The results present a conflicting scenario where reducing the particle size diminishes the stress field but increases the volumetric heat generation, and vice-versa. The paper concludes with a set of optimum design parameters and limiting charging rate for different electrode material combinations in a battery and proposes thermal management techniques to permit faster charging of the battery.

Here we show a two-step electrodeposition process to fabricate a high volumetric and areal capacity 3D-structured Sn/C anode starting from a commercial mesostructured thick 3D Ni scaffold. An anode with 20% Sn loading exhibits a volumetric/areal capacity of ∼879 mAh/cm³ and 6.59 mAh/cm² after 100 cycles at 0.5C and a good half-cell rate performance of about 750mAh/cm³ and 5.5 mAh/cm² (charge) at 10C. The 3D Sn/C anodes also show good compatibility with commercial LCO cathodes. EIS and finite element simulation are applied to verify the effects of Sn loading and carbon coating on the cycling and power performance of the 3D Sn/C anodes. We find that while higher loadings of Sn will cause a larger capacity decay with cycling, the addition of the carbon coating significantly improves the structural stability of the 3D-structured anodes. The combination of the high volumetric and areal capacity these anodes provide may make them of interest for next generation energy storage systems.

The market for lithium ion batteries (LIBs) has been rapidly grown with exponentially increasing demands for electric vehicles and portable information technology devices. However, the current materials are still limited in capacity and energy density. A feature common to the current materials is that less than one electron participates in the redox reaction. To increase the chemical energy stored, a multielectron redox reaction would be preferred. Recently, researchers have reported LiVOPO₄ as a promising multi-electron material to incorporate two electrons. There are two redox couples in this material, V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺, per vanadium, which enables two Li ions to be reversibly inserted/extracted, leading to a high theoretical capacity of 305 mAh g^-1 based on the weight of Li₂VOPO₄. However, LiVOPO₄ has both poor lithium diffusivity and electronic conductivity, which can cause polarization and poor utilization of active material. To overcome these challenges, we propose a mechanical method to nanosize LiVOPO₄ and coat carbon on the surface of particles meanwhile, which shortens diffusion pathway for Li ions and increases the electronic conductivity. Whereas the structural disorder and poor crystallinity were detected in LiVOPO₄ after the mechanical treatment, which impeded the migration of Li ions in the diffusion passages and resulted a poor cycling stability. A following thermal method was adopted to reconstruct the structure of LiVOPO₄ under a controlled condition with keeping particles nanosizing and without reducing LiVOPO₄. The resulting LiVOPO₄ gave superior electrochemical performance in terms of rate capability and cycling stability, with the highest stable cycling capacity, 260 mAh g^-1 at C/5, of any two electrons redox phosphate system reported to date.

This research is funded by (1) U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) program under BMR Award No. DE-EE0006852, and (2) NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. DE-SC0012583.

The development of novel high-capacity and high-energy cathode materials for lithium ion batteries is a focus of the energy storage technology. Different from LiMO₂ and LiFePO₄, which only one Li⁺ can be reversibly cycled, Li₂CoSiO₄ would allow reversible extraction of two Li⁺ in principle thus delivering a higher theoretical capacity of 325 mAh/g. Moreover, it has been proved to show a high voltage plateau above 4.0 V, which makes it among the few candidates having theoretical energy density above 1200 Wh/kg.
However, poor electronic conductivity seriously hinders its electrochemical performance. Unfortunately, carbon-coating, which has significantly enhanced the electronic transportation of many polyoxyanion materials, is usually fruitless and frustrating in Co-silicates. In the past decade, the reversible capacity of Li₂CoSiO₄ has been staying 75 mAh/g above 3.0 V or 107 mAh/g above 1.5 V despite extensive efforts.
To break the development bottleneck of Co-silicates, first-principles calculations had been performed by our group to investigate the changes of lattice and electronic structure for understanding electrochemistry of Li₂CoSiO₄. With the guidance of theoretical calculations, we had evaluated several mechanisms that may control the electronic structures of Co-silicates in doping. At the same time, a series of innovations in material synthesis were also carried out to improve the conductivity of the materials. Under such a joint effort, a P-doped Li₂CoSiO₄, whose discharge capacity up to 144 mAh/g above 2.5 V, was successfully synthesized for the first time in 2016. Recently, we develop a novel Mn-doped Li₂CoSiO₄ with more advance performance. This new scheme not only reduces the proportion of Co, thus enhancing the cost competitiveness, but also improves the electrochemical performance effectively, resulting in a more highly leveraged possibility for the application of cobalt based silicates as high energy cathode materials. The synthesized Li₂Mn_xCo_1-xSiO₄/C could deliver a reversible capacity up to 208 mAh/g in the voltage window of 1.5-4.8 V, which is almost double of the highest record in the last ten years. Moreover, we are surprising to find that the Mn involves in the redox reaction during charging and discharging. This is in contrast to that of the LiNi_xCo_yMn_1-x-yO₂ and Mn-silicates. The introduction of Mn may bring a synergistic effect with Co redox, leading to the significant increase in reversible capacity.
In summary, with the joint theoretical and experimental studies, we design and synthesis a capacity record-breaking Li₂Mn_xCo_1-xSiO₄ and for the first time realize a reversible capacity above 200 mAh/g for Co-silicates. This on the one hand opens a new window for the further research of silicate material, on the other paves an avenue to a new prototype of advanced high energy cathode materials from tetrahedral groups.

The demands of sustainable high-energy-density rechargeable batteries have led to the exploration of high-capacity and low-cost electrode materials. Based on reversible alloying-dealloying reactions, silicon stores 10 times more lithium (Li₂₂Si₅, 4,200 mAh g^-1; Li₁₅Si₄, 3,579 mAh g^-1, 8,343 Ah L^-1) than the current commercial graphite anode (LiC₆, 372 mAh g^-1, 804 Ah/L). However, unlike the topotactic intercalation of Li into carbonaceous materials, the alloying/dealloying reaction causes much more dramatic, three-dimensional chemical and structural rearrangements on the surface and bulk structure, and results in a fast degradation in cycling performance. Moreover, the formation of solid electrolyte interphases on the Si surface results in the loss of lithium inventory and low Coulombic efficiency. Besides of using sophisticated design of nanostructure silicon materials and electrodes, our research has concentrated on surface modification strategies to stabilize the surface of the reactive silicon materials, but also accommodate the volumetric changes during lithaition/delithiation of silicon materials. The effects of the surface modification have been investigated through morphology, structure, mechanical and electrochemical characterization and analysis methods. The research has elucidated the important role of surface modification in stabilizing the cycling performance and enable a high level of material utilization at high mass loading. This talk will focus on reviewing the surface modification approaches used for improving electrochemical performance, and elaborate the effects of surface modification on the surface chemistry and electrochemistry of silicon-based anodes, and also discuss the strategies towards developing practical silicon-based anodes for high-energy-density lithium-ion batteries.

Understanding the battery degradation requires identifying the “irreversible” chemical and structural changes – from atomic to meso-scale – that appear during battery cycling. To design nanostructures mitigating these degradation mechanisms, will further rely on our ability to quantify and predict these irreversible changes. This talk will focus on recent modeling methodology developed to compliment in situ observations in order to elucidate the underlying factors contributing to mechanistic failures. For example, most experimental techniques are not sufficiently sensitive to reveal the amorphous Si and SiO characteristics change upon cycling. Reactive molecular dynamics, along with a new lithiation and delithation algorithm, simultaneously tracks and correlates the lithiation-delithiation rate, compositional change, mechanical property evolution, stress distributions, and fracture. Thus the model can quantify the irreversible volume change of Si and SiO nanostructures, the amount of trapped Li, the generation and distribution of inner pores and coating delamination, and the atomistic structural difference in the amorphous structures, upon cycling. These findings lead to design criteria for mechanically stable coated Si nanostructures and battery operating guidelines to mitigate capacity loss due to trapped Li and coating delamination.

Rechargeable batteries based on lithium (Li) metal chemistry are attractive for next-generation energy storage. Nevertheless, dendritic growth, infinite relative dimension change, severe side reactions and limited power output, greatly impede their practical applications. The presented work for the first time introduces an electrolyte-proof design of three-dimensional Li metal anode where most of the Li domains are embedded in a Li-ion conductive matrix. In the new architecture, the Li-ion conductive matrix isolate the embedded Li domains from liquid electrolyte and thus prevent severe initial side reactions, while the matrix can simultaneously transport Li-ion and maintain the electrochemical activity of the embedded Li. This composite electrode was obtained by reacting over-stoichiometry of Li with SiO above Li melting temperature. The unique reaction dynamics results in a structure of Li embedded in the Li_xSi-Li₂O matrix with one-pot synthesis. Since uniform Li nucleation and deposition can be fulfilled owing to the high-density active Li domains, the as-obtained nanocomposite electrode exhibits low polarization, stable cycling and high-power output (up to 10 mA/cm²) even in carbonate electrolytes. The Li-S prototype cells further exhibited highly improved capacity retention under power-intersive operation (~600 mAh/g at 6.69 mA/cm²). The all-round improvement on electrochemical performance sheds light on the effectiveness of the new design principle for developing safe and stable Li metal anodes with high-power capability.

Silicon with its ~10 times theoretical Li capacity compared with carbon-based electrodes, becomes one of the most promising alternative anode materials in lithium-ion batteries. However, its application is challenging due to the more than 400% volume expansion during lithiation, and the subsequent volume reduction during de-lithiation. Nanostructured Si materials have been studied to accommodate the volume change and to mitigate the issues, including Si nanowires, Si nanotubes and nano-porous Si. Here we investigate a novel form of nano-porous Si structure prepared by a liquid metal de-alloying method. The nanopores effectively prevent electrode cracking and therefore ensure long-term durability and stable performance within batteries. However, morphological changes and degradation of the Si nanoporous electrode during charging and discharging are still not fully understood, which limit utilizing this novel electrode with its full capacity. We apply synchrotron-based x-ray nano-tomography to quantify the three-dimensional morphological changes of the nanoprous Si anodes under different cycling conditions. We quantify the evolution of the electrode thickness and the material density distribution within the electrode as a function of electrochemical cycling. The delamination process, the morphological evolution and the degradation of the batteries will be discussed.

Conventional positive (cathodes) electrode materials for lithium-ion batteries, use mixed-conducting lithium containing transition metal oxides, metal phosphates etc. which are able to store both lithium and electrons by changing their oxidation state. In this presentation, we discuss the synthesis of materials suitable for alternative electrode concepts including transition metal fluorides that operate by a conversion type mechanism (1) and a promising new type of alternative nanocomposite composite cathodes, where the storage of lithium and of charge is distributed over two components of a nanocomposite containing LiF and or metal oxides, MO (M= Mn, Fe, Co, Ni, Cu) (2,3).
Transition metal fluorides MF₂ (M=Fe, Mn, Zn) were derived from one dimensional metal organic frameworks (MOF) by a polymer (PVDF) assisted decomposition at 600°C, 6h in Ar gas. The MOF were initially prepared by a simple chimie douce method. Incorporation of the MOF with a fluorinated polymer (PVDF) and the eventual decomposition lead to carbon coated metal fluoride nanoparticles of high surface area of >200 m²/g. Electrochemical studies were carried out in the voltage, range 4 to 1.0 Vs. Li, at current rate of 50 mA/g (0.1 C) and preliminary galvanostic cycling of FeF₂ demonstrates that the material exhibit stable and good reversible capacity of 580 mAh/g during the initial cycles and slight capacity fading has been observed after 20 cycles. Further optimization of the performance is being carried out. Whereas MnF₂ and ZnF₂ showed reversible capacity of 220 and 200 mAh/g and retained a capacity around 100 mAh/g after 20 cycles.
Nanocomposites of divalent transition metal oxides MO (M= Mn, Fe, Co, Ni, Cu) and LiF were prepared ball-milling method. The obtained materials will be characterized in detail by X-ray diffraction; Scanning and Transmission electron microscope (SEM/TEM) are used study the morphology. Raman, X-ray photoelectron spectroscopy are used understand structure, vibrational bands and oxidation state of the materials and BET surface area method. Structural and microstructural variations during charge-discharge cycling were characterized by in operando X-ray diffraction for elected promising compositions. Electrochemical properties will be evaluated voltage, range 4 to 1.0 vs. Li in the voltage using cyclic voltammetry at scan rate of 0.075 mV/sec, galvanostatic cycling at a current rate of 0.1C, and electrochemical impedance spectroscopy. Preliminary electrochemical studies yield a reversible capacity of 100 mAh/g. Further long term cycling studies of the nanocomposites are in progress.

References
(1) Cabana, J etal. .; . Adv. Mater. 2010, 22, E170.
(2) Jung, S.-K.; etal. Lithium-free transition metal monoxides for positive electrodes in lithium-ion batteries. 2017, 2, 16208.
(3) Poizot, P. etal Nano-sized transition-metaloxides as negative-electrode materials for lithium-ion batteries. Nature 2000, 407, 496.

With the lowest chemical potential and highest energy density among anode materials, lithium metal becomes the most promising candidate for next-generation rechargeable batteries with high energy density. However, its non–uniform electrodeposition behaviors and spontaneous side–reactions with electrolyte components have caused numerous safety concerns and constrained its applications. Through vapor deposition, a hermetic coating layer of silicate can be readily formed on lithium foil under ambient conditions. Such coatings consist of a “hard” inorganic moiety that helps to suppress lithium dendrites and a “soft” organic moiety that enhances the toughness. Lithium–metal batteries, including Li–LiFePO₄ and Li–S batteries, made with such coated anodes show significantly improved lifetime. This work provides a simple yet effective approach stabilizing the interface of lithium metal anodes for advanced rechargeable batteries.

Energy density (energy per volume) is a key consideration for portable, automotive and stationary battery applications. We created selenium (Se) lithium and sodium metal cathodes that are monolithic and free-standing, and with record Se loading of 70 wt%. The carbon host is derived from nanocellulose, an abundant and sustainable forestry product. The composite is extremely dense (2.37 g cm^-3), enabling theoretical volumetric capacity of 1120 mAh cm^-3. Such architecture is fully distinct from previous Se – carbon nano or micropowders, intrinsically offering up to 2X higher energy density. For Li storage, the cathode delivered reversible capacity of 1028 mAh cm^-3 (620 mAh g^-1) and 82% retention over 300 cycles. For Na storage 848 mAh cm^-3 (511 mAh g^-1) was obtained with 98% retention after 150 cycles. The electrodes yield superb volumetric energy densities, being 1727 Wh L^-1 for Li-Se and 980 Wh L^-1 for Na-Se normalized by total composite mass and volume. Despite the low surface area, over 60% capacity is maintained as the current density is increased from 0.1 to 2 C (30 min charge) with Li or Na. Remarkably, the electrochemical kinetics with Li and Na are comparable, including the transition from interfacial to diffusional control.

The lithium-ion battery is the rechargeable power source for nearly all modern portable electronics and electric vehicles, due to its relatively high energy density, negligible memory effect, and minute self-discharge. Despite its widespread use in modern electronics, the drive for a sustainable energy future and applications such as all-electric vehicles, robots, and drones require future batteries to possess much higher energy densities. A major limitation faced by lithium-ion batteries stems from the graphite anode, commonly used due to its stability upon lithiation, which possesses a relatively low capacity compared to next-generation anode materials such as lithium, silicon and lithium alloy materials. Switching to these materials could significantly boost the energy density of lithium-ion batteries and would also enable high capacity next-generation chemistries beyond lithium-ion. Lithium metal in particular is considered the ideal anode material, as it possesses the lowest electrochemical potential and an extremely high theoretical capacity. Still, the implementation of lithium metal anodes is currently impeded by their significant volume change upon charging and discharging, lithium metal’s propensity to grow dendritic structures that can cause dangerous short circuits, and the instability of the solid electrolyte interface that forms upon exposing the anode to electrolyte. Unique nanomaterials can provide a key advancement in the development of high capacity lithium anodes by controlling the transport and storage of ions at the nanoscale. In this work, we investigate several non-porous carbon-based thin films that can act as selectively-permeable lithium-ion membranes and as protective intermediaries between the lithium metal anode and the electrolyte. These coatings serve to block electrolyte, form a stable solid electrolyte interface, and limit the formation of dendrites. We demonstrate the performance of the protected lithium metal anodes in symmetric lithium-lithium cells and in lithium-sulfur batteries, signifying the ability of these protection layers to provide a key step towards safe and highly energy-dense next-generation rechargeable batteries.

The ability to directly utilize Lithium (Li) metal anodes in rechargeable batteries presents itself as an ideal, albeit challenging, situation. Li metal used as an anode would provide Li batteries with the maximum possible specific capacity (3860 mAh/g) in comparison to currently used anodes (e.g. graphite – 380 mAh/g). Nonetheless, Li metal anodes remain rare in commercial devices due to inherent safety concerns associated with the formation of Li dendrites during practical rate cycling, as well as Li metals’ susceptibility to exhibit high reactivity towards commercially available organic electrolytes. Due to possibilities of thermal runaway, such concerns have adversely affected the potential use of Li metal. Additionally, Li metal reacts negatively with water which can be found as an impurity in commercially available organic solvents; or passivate in the presence of small quantities of moisture rendering it un-rechargeable. This presents a significant hurdle when water-tolerant Li cycling is warranted (e.g. Li-air). Hence, significant efforts in recent rechargeable battery literature have targeted the development of robust electrolytes, capable of better stability when used with Li metal.
To date, various strategies have been employed to overcome such concerns; the use of solid electrolytes as a mechanical barrier, or the use of specific organic solvent-based electrolytes which control the properties of the solid-electrolyte interface (SEI), being noted observations. Amongst the various classes of Li battery electrolytes developed to date, ionic liquids (ILs) have been utilized as electrolytes which can facilitate enhanced Li cycling efficiencies and favorable Li plating morphologies while being inherently non-volatile/non-flammable alternatives to commercially available organic electrolytes. Through the capability to combine various cations (Imidazolium, Ammonium, etc.) and anions (TFSI, DCA, etc.); the use of such ILs could produce a more adept SEI, resulting in the improved cycling behaviors reported in literature.
Recently, we reported that certain ILs allowed for successful Li metal cycling in the presence of water mixed into the IL. To our knowledge, no reports have shown the capability to sustain morphologically friendly Li deposition upon application of practical cycling rates while allowing for stable cycling in water containing electrolytes. In recognition of this unique capability, we analytically probed the characteristics of the IL SEI’s to understand their protective capability. Based on such understanding, we now introduce a new method to artificially form these SEI’s on Li metal via the screening of various IL combinations. The electrochemical results, along with fundamental analytical analyses of the ILs capable of Artificial SEI Transplantation on Li metal, while sustaining commercially feasible Li morphologies at practical cycling rates in the presence of water containing electrolytes will be presented and discussed.

Lithium ion battery (LIB) cells are established electrochemical energy storage systems with high Coulombic and energy efficiencies and high energy and power densities [1-3]. Four performance parameters are considered key for the success of future applications: High energy density, fast charging, long cycle life and enhanced safety.
The controlled safe behavior of LIBs is a critical performance requirement for commercial use, especially in large batteries for automotive and stationary energy storage (“grid”) application. In the past years several incidents occurred, that caused public attention to the safety of the technology in general, raising doubts on the implementation of LIBs in large battery applications. Moreover, the progressive development of new materials and advanced cell designs improves the cell performance continuously, but unfortunately the growing energy densities and increasing battery pack sizes raise the safety risks, too.
Measures can be taken on various levels of battery hierarchy to improve safety of LIBs. On battery system level, housing, packaging, thermal and battery management play important roles. On module level, temperature control of sensors and an intelligent battery management system help to improve safety. The cell design has a major influence on the safety of LIB cells. The heat dissipation rate during an exothermal reaction largely influenced by the cell design. If the heat dissipation rate is larger than the heat generation rate of the exothermic reaction, the cell will cool down and not reach a critical state. If the cell gets into a critical state, different safety measures like current interruption devices (CID), positive temperature coefficient elements (PTC) or burst discs are the last measures before the cell chemistry comes into play. The latest incidents with smartphones clearly prove, that we also have to address the cell chemistry. The intrinsic safety of LIBs is influenced by the anode and cathode active materials, as well as the inactive materials, like electrolyte and separator. The usually used liquid electrolyte is the most critical compound as it is volatile, flammable and in contact with every part of the LIB cell [4]. In addition, the electrolyte does decompose forming toxic components [5].
In this presentation, we will focus on intrinsic cell safety and the prominent role of the electrolyte. We will show how different additives influence the different components of a LIB cell and cell safety.
References:
[1] Wagner R, Winter M, et al., J. Appl. Electrochem., 2013, 43 (5), 481-496
[2] Placke T, Winter M, et. al. J. Solid State Electrochem., 2017, 1-26, DOI: 10.1007/s10008-017-3610-7
[3] Meister P, Winter M, Placke T, et. al. Chem. Mater., 2016, 28, 7203-7217
[4] Schmitz R W, Winter M, et. al. Prog. Solid State Ch., 2014, 42, 65-84
[5] Nowak S, Winter M, J. Electrochem. Soc., 2015, 162, A2500-A2508

Lithium-ion layered structure continues to have immense appeal as a promising electrode material for rechargeable batteries owing to its superior capability of intercalation and deintercalation of lithium-ions per compound unit. However, this type of electrode suffers from the irreversible capacity loss resulting from solid-electrolyte interphase (SEI) formation and surface reconstruction by electrolyte reactions. To overcome the inherent limitations relevant to the layered structure, a multi-layer of stacked-graphene (8-layers) grown by chemical vapour deposition (CVD) is introduced perpendicular to the basal planes. Although the basal planes are generally regarded as a physical barrier to the lithium-ion diffusion, lithium-ions are likely to be intercalated into the planes through defect sites of the CVD grown graphene. The clap-net like design of the graphene treatment effectively isolates the inward environment, where the electron conduction takes place, from the outer system where the undesired redox reactions occur by the electrolyte. This engineered interface with the stacked-graphene not only preserves the initial local-atomic environment of the active material, but also renders the electrode/electrolyte interface to be stable for dynamic charge rates change. The current study sheds some light on developing battery electrodes that suppresses the surface reconstruction of the active material, leading to stable SEI formation.

Titanium dioxide (TiO₂) polymorphs are promising electrode materials for Li-ion and Na-ion batteries, due to their potentially high capacity, cycling stability and charge/discharge rate. The mechanistic understanding of redox processes, involving compounds like TiO₂, in terms of formally defined charge transfers between the involved reactants is, by definition, based on the change of the oxidation states of the involved species. Although the way formal oxidation states are determined can be justified by a variety of valid arguments, the implications that come with them, especially with regard to redox processes, might be counter-intuitive and of little practical use. The charge state of titanium in titanium dioxide is commonly assumed to be +4, which is the basis for any description of redox processes involving this material. Previous investigations on the other hand (e.g. Nature 453 (2008) 763) showed that the physical charges on transition metal atoms are generally little affected by changes in their formal oxidation states. We concluded in comprehensive investigations on TiO₂ molecules and TiO₂ bulk crystals, using different quantum theory of atoms in molecules (QTAIM) approaches like Bader charge analysis or delocalization indices, a lower charge state (+3).
Moreover, a recent investigation (Organometallics 36 (2017) 622) using charge reporter molecules concluded a remarkable stability/similarity of charge states of many transition metal atoms, including titanium, in different environments corresponding to very different formal oxidation states. Ab initio investigations carried out by us on titanium carbonyl complexes support this experimental findings. Furthermore, our QTAIM charge analyses on titanium for its intercalation into p-doped crystals and in titanium halides confirm the similarity of the Ti charge in different environments and do not suggest that the charge state of titanium reaches the ideally assumed Ti⁴⁺ in other common Ti(IV) compounds commonly classified as ionic. All of this makes the possibility of further Ti oxidation or O reduction in terms of charge density increase or depletion around the corresponding nuclei, at least in a theoretical framework, possible, as it was seen in our analyses on simple model systems.

Silicon is an ideal anode material for Li-ion batteries, provided it can accommodate the large volume changes between charging and discharging. We present a method, based on Plasma Enhanced Chemical Vapor Deposition (PECVD), to create self-organized nano-structured silicon layers, which can accommodate the large volume changes. Large advantage of this method is that it does not require any pre- or posttreatment of the silicon to obtain the nano-structuring and high porosity. The nanometer scale porosity of these layers can be tuned between 30 and 70%, leading to specific areas of more than 200 m²/g (as measured by BET analysis).
The layers are deposited in a pilot roll-to-roll PECVD deposition system, in which we can handle foils with a width up to 30 cm. The linear plasma sources, however, can be easily extended to a width of more than 1 meter, offering perspectives to cost-effective high throughput mass production of the silicon layers.
We tested this material both in half cells with Li counter electrode and in full cells with an NMC cathode, with a silicon mass load of approximately 1 mg/cm². Half cells, charged at 1000 mAh/g at C/5 show no capacity fading and a CE of 99.5% after more than 350 cycles, using a standard electrolyte LiPF₆ containing FEC. Small pouch cells (3x3 cm²) could be charged/discharged more than 100 cycles at 1000 mAh/g_Si without capacity fading but with a CE of about 98%. Further improvement of the lifetime is expected through modifications of the electrolyte to increase the Coulombic efficiency in full cells.

Recently, the fast-growing market for portable electronic devices, electric vehicles (EVs) and flexible devices has placed great demands on rechargeable batteries with high energy/power density, security and flexibility. Tellurium, an element in the chalcogen family, which possesses the highest electronic conductivity among all non-metallic elements, has more advantages over sulfur and selenium, such as high utilization rate and better kinetics during charge/discharge process. However, the conventional carbonate electrolyte for Li-Te batteries does not work well and faces many inevitable security problems, such as inflammability and explosion. In this paper, single crystalline tellurium (Te) nanotubes grown on carbon fiber cloth (Te/CFC) conductive substrates have been prepared by a chemical vapor deposition (CVD), which are used as the cathode for flexible all-solid-state lithium-tellurium (Li-Te) rechargeable batteries with high safety. A high gravimetric capacity of 316 mA h g^-1 and a volumetric capacity of 1979 mA h cm^-3 after 500 cycles at a current density of 100 mA g^-1 can be obtained, respectively.

Owing to its high energy density and light weight, Li-ion batteries have taken away over half of the worldwide rechargeable battery market. However, the safety issues of Li-ion batteries that originate from the combustible organic electrolyte are of great concern recently. Solid-state batteries using powder compact solid electrolytes (PCSE) are promising options toward safer and higher energy density batteries due to the utilization of inorganic electrolyte and metal lithium as anode, however, the high solid-solid interfacial resistance between the lithium metal and the solid electrolyte is still a challenge.
In this work, we demonstrate reversible plating and stripping of dendrite-free metallic-lithium with a reduced anode/PCSE interfacial resistance by introducing a thin interfacial layer formed by heating. First, the PCSE which has an ionic conductivity of ~ 10^-4 S/cm at room temperature, was synthesized by mechanical milling, and characterized using NMR, DSC, IR spectroscopy, and Raman spectroscopy. Next, the PCSE was tested in symmetric cells for electrochemical impedance spectroscopy and cycling. To address the high solid-solid interfacial resistance and short-circuiting dendrite problems, we demonstrate a simple strategy to engineer the lithium-PCSE interface by forming an in-situ interlayer via a heat treatment. The area specific resistance of 573.6 Ω/cm² has been successfully achieved with a 0.9 mm thickness pellet under a current density of 0.1 mA/cm². These results provide a promising PCSE membrane that can be applied to lithium metal battery and other energy storage application, such as lithium sulfur batteries.

Engineering of composite electrode for silicon anode materials plays an important role in the practical application of Si-based lithium-ion batteries (LIB). In this work, a hybrid composite anode of silicon-carbon-polyimide was in-situ fabricated by proper heat treatment of the slurry coat containing silicon power and polyamic acid polymer, without any carbon agent. The resulted film shows three components (silicon-carbon-polymer) composite structure wherein the hybrid carbon-polyimide is in-situ generated from polyamic acid by proper heat treatment. The hybrid Si composite exhibits robust binding and conductive properties, and also meso/macroporous internal structure enabling it to buffer Si volume expansion. When applied as LIB anode, it deliveres promising battery performance with little volume change even under high content of Si (>96wt%), which implies that the in-situ fabricatoin method could be another effective way for Si anode engineering for high energy density LIB.

Electrochemical Impedance Spectroscopy (EIS) has been proved to be a very powerful technique to investigate the interfacial electrochemical dynamics within various kinds of electrochemical systems. However, using EIS to study the lithium-ion battery systems is not mature and reliable enough to analyze the State of Charge (SOC) and State of Health (SOH) of the batteries alone. Since EIS is a frequency related technique and the elements inside the battery system are also frequency related, by monitoring the internal temperature profile during the EIS period, more detailed and accurate analysis of the EIS results can be attained without adding any other time consuming and cycling techniques. In our study, temperature variation pattern has been found for different EIS tests during the whole aging process, and improvement for EIS analysis has been reached.

High energy density, thin and flexible batteries are a critical component of flexible electronics. Metal air chemistries are particularly attractive for flexible electronics applications as they eliminate the need for thickness-adding packaging and capacity-limiting cathode volumes. Here we demonstrate the first fully printed ultrathin metal air batteries from solution processed cell layer materials that enable monolithic layer by layer stencil printing. Printed cell layers include the current collector, a zinc alloy composite electrode, a solid ionic liquid/polymer electrolyte and an oxide nanocatalyst-decorated reduced graphene oxide(r-GO) /carbon nanotube(CNT) composite cathode. The carbon nanotube/graphene catalyst mixture layer self aseembles into hierarchical porous structure with MnCo₂O₄ nanoparticles(~10nm) decorated r-GO flakes(2-4 layers) covering the surface of CNT bundles(~50μm). We utilized the hierarchical nanostructures to maximize the number of reaction active sites while maintaining sufficient electrical percolation and air access to the catalytic sites in the cathode. The The low vapor pressure of ionic liquid enables thermal processing temperatures of 80°C. The printed metal air batteries exhibit high thin cell volumetric capacities of 170 mAh/cm³, areal capacities of 2.0 mAhr/cm² from a total cell thickness of 150 micron. This is among the very highest areal capacity batteries demonstrated to date and relies on air stable, low cost and low toxicity printed Zn air / solid polymer electrolyte chemistry. The batteries are bendable and lightweight and are well positioned as a promising power source of flexible electronics and next generation wearable and on-body electronics.

Despite the outstanding potential for high energy densities, lithium-oxygen (Li-O₂) batteries are not yet widely used in ultrahigh energy density devices such as electric vehicles, owing to various challenges, including poor cyclability, low efficiency, and poor rate capability at high capacities. For the past few years, many researchers have tried to solve these problems, and the issues related to the low reaction kinetics, especially for an oxygen evolution reaction (OER), has been tackled by adopting proper electrocatalysts. Unfortunately, however, in those systems using solid catalysts and conventional carbon materials, the instabilities associated with solid catalysts and carbon electrode materials are one of the challenges that prevent Li-O₂ batteries from achieving a truly rechargeable high energy density. Here we seek to achieve reversible Li-O₂ battery operations with high energies by tackling these instabilities through the synergistic integration of dual soluble catalysts for both discharging and charging with antimony tin oxide (ATO) non-carbon electrodes with a porous inverse opal structure. The dual redox mediators showed a synergistic combination without any negative interference with one another, leading to higher capacity and rechargeability. The stability against degradation of redox mediators and the effect of surface characteristic on the discharge mechanism are also discussed.

The rechargeable lithium-oxygen (Li-O₂) battery, providing theoretically high specific-energy-density calculated as ~3 kWh kg^-1_cell, is a promising future energy storage system. However, the over-potential is considerably severe during charge due to difficulty of Li₂O₂ decomposition (Li₂O₂(s) = 2Li⁺ + O₂(g) + 2e⁻, E_rev = 2.96 V vs. Li⁺/Li), which is one of the greatest challenges for implementation of practical battery systems. Much effort has been devoted by incorporation of metal oxide promoters and soluble redox mediator. However, these additive materials give rise to side reactions and require high cost. Here I present a new strategy for decrease in charge over-potential by tailoring carbon electrodes. The oxygen functional groups implemented in carbon electrodes allow for growth of conformal and amorphous Li₂O₂ film during discharge, which rapidly decomposes in the following charge. In contrast, seamless and graphitized carbon electrode provides crystalline Li₂O₂ requiring higher overpotential for decomposition. This result is attributed to O₂ and LiO₂ adsorption affinity with respect to surface property of carbon, determining nucleation and growth pathway of Li₂O₂ during discharge. Further, morphological and structural characteristics of Li₂O₂ may greatly affect its ionic and electronic conductivities, enabling facile decomposition of Li₂O₂ toward amorphous structure. This study gives insights into design of carbon electrode surface toward the enhancement of discharge capacity, charge potential and cycling stability. It also paves the way for improvement of Li-O₂ cell performance in the absence of additional promoters.

Lithium ion batteries are today’s state-of-the-art energy storage technologies. Due to high volumetric and energy densities, they have become the industry standard for portable applications such as consumer electronics and hybrid vehicles. However, lithium ion batteries also have large capital costs, which make them prohibitively expensive for grid-based energy storage. Therefore, there is a clear need for new innovative energy storage systems which are able to meet the required performance standards as well as the necessary economic benchmarks that make them commercially viable. Compared to lithium ion batteries, magnesium and sodium batteries provide a very attractive low-cost alternative. However, establishing suitable electrode chemistries for non-lithium batteries remains a crucial challenge. In this talk, I will highlight our group’s recent work on identifying suitable electrode materials for Sodium and Magnesium batteries using advanced computational techniques. Our analysis establishes the electrochemical performance of these materials as well as their viability as electrodes in next generation, low cost batteries.

[1] J. Yuwono, N. Birbilis and N. V. Medhekar, Aqueous electrochemical activity of Mg surfaces: the roles of group 14 /15 microalloying elements, in review (2017).
[2] J. Yuwono, N. Birbilis, K. Williams and N. V. Medhekar, Electrochemical stability of magnesium surfaces in an aqueous environment, Journal of Physical Chemistry C 120, 26922 (2016).
[3] M. Mortazavi, Q. Ye, N. Birbilis and N. V. Medhekar, High capacity group-15 alloy anodes for Na-ion batteries: electrochemical and mechanical insights, Journal of Power Sources 285, 29 (2015).
[4] M. Mortazavi, C. Wang, J. Deng, V. B. Shenoy and N. V. Medhekar, Ab initio characterization of layered MoS2 as anode for sodium-ion batteries, Journal of Power Sources 268, 279 (2014).
[5] M. Mortazavi, J. Deng. V. B. Shenoy and N. V. Medhekar, Elastic softening of alloy negative electrodes for Na-ion batteries, Journal of Power Sources 225, 207 (2013).

Metal-oxygen batteries have been paid attention to one of the promising next-generation batteries owing to their higher energy densities than current lithium-ion batteries. In particular, sodium-oxygen (Na-O₂) batteries are a promising candidate applied for electric vehicles, because they provide far higher round-trip efficiency than lithium-oxygen (Li-O₂) batteries. The critical problems in Li-O₂ cells typically arise from the positive electrode side where O₂ gas is injected. The oxygen reduction reaction occurring in discharging produces the superoxide (O₂^–) species, which is chemically reactive and is susceptible to degradation on non-aqueous electrolyte solution and carbonaceous electrode in the presence of Li⁺ ion. By contrast, the O₂^– may be more stable with Na⁺ ion caused by favorable soft base and soft acid interaction. The main discharge product of sodium superoxide (NaO₂) and insignificant amount of side product in Na-O₂ cells demonstrate highly stable superoxide species at the positive electrode side. Nevertheless, cycling stability has still underperformed in Na-O₂ cells, which have not as yet been fully understood.
Here we improve cycling performance of Na-O₂ cells by increasing stability of negative electrode, Na metal. Na metal is highly reactive and easily forms solid electrolyte interphase (SEI) layer through chemical reduction of electrolyte solution. The sodium triflate (NaOTf) salt in diglyme (G2) has been widely used as the electrolyte solution in Na-O₂ cells[1], while dead Na powders and electrical short have been often observed after a couple of cycles due to instability of SEI and negative electrode[2]. In addition, the observations of color change of electrolyte solution and severe precipitates that cover the positive carbon electrode at even open circuit voltage (OCV) state allow us to hypothesize that soluble SEI causes continuous decomposition of electrolyte solution from Na metal. To mitigate this problem and establish stable SEI layer protecting Na metal, we have examined various sodium salts to Na-O₂ cells. Among them, sodium hexafluorophosphate (NaPF₆)/G2 exhibits the preeminent results such as negligible color change of electrolyte solution and insignificant precipitates on positive electrode surface. It indicates the formation of highly stable and uniform SEI layer, and X-ray photoelectron spectroscopy (XPS) reveals the main species of layer to sodium fluoride (NaF). The stable SEI layer improves cycling performance in Na-O₂ cells. The capacity retention with NaPF₆/G2 is superior to others, which is attributed to trivial dead Na and dendrite at separator after 10 cycles. In the presentation, I will discuss detailed chemical and electrochemical analyses of SEI layers with different electrolytes and the correlated cycling performance in Na-O₂ cells using online-electrochemical mass spectroscopy and XPS analysis.


[1] Nature Materials, 2013, 12, 228–232
[2] Phys. Chem. Chem. Phys., 2014, 16, 15646-15652

All-solid-state sodium-ion batteries promise to simultaneously yield higher energy density, improved safety, and lower cost as compared to state-of-the-art lithium-ion technologies based on organic liquid electrolytes. A competitive all-solid-state battery requires a solid-state electrolyte with high ionic conductivity near room temperature and high thermal and electrochemical stability. Meeting these three requirements simultaneously represents a major challenge. In fact, research focus has recently shifted from merely conductivity improvement of the electrolyte to interface engineering for the implementation in all-solid cells.
In this regard, we will present a new sodium-ion conductor, namely Na₂(B₁₂H₁₂)_0.5(B₁₀H₁₀)_0.5, that simultaneously offers high sodium ion conductivity of 0.9 mS cm^-1 at 20 °C, excellent thermal stability up to at least 300 °C, and importantly a large electrochemical stability window of 3 V including stability versus metallic sodium enabling long-term striping and plating and the use of a sodium metal anode [1]. In addition, we will discuss strategies to enable a 3 V all-solid-state battery based on Na₂(B₁₂H₁₂)_0.5(B₁₀H₁₀)_0.5 and demonstrate first cycling results (85% capacity retention after 250 cycles at C/5).
Our results demonstrate that closo-borate based electrolytes and particularly Na₂(B₁₂H₁₂)_0.5(B₁₀H₁₀)_0.5 could pave the way towards safe and long-life all-solid-state batteries.

[1] Duchêne, L.; Kühnel, R.-S.; Rentsch, D.; Remhof, A.; Hagemann, H.; Battaglia, C. A Highly Stable Sodium Solid-State Electrolyte Based on a Dodeca/deca-Borate Equimolar Mixture. Chem. Commun. 2017, 53 (30), 4195–4198.

Developing new earth-abundant materials has been attracted more and more attention for energy storage applications. In this talk, I would like to talk about our recent work related to development of Aluminum ion battery (AIB). AIB was demonstrated recently based on Al foil anode, graphite cathode and ionic liquid electrolyte. Much remains to be done to increase the cathode capacity and to understand details of the anion-graphite intercalation mechanism. Here, we developed a freestanding film of natural graphite flakes bound by a binder as AIB cathode. The specific capacity and Coulombic efficiency of the battery was achieved ~110 mAh/g and ~98% respectively, at a current density of 99 mA-g^-1 with clear discharge voltage plateaus ~2V. The cycle stability of the battery exceeded 6000 cycles with a capacity of 60 mAh/g at a current density of 660 mA/g. Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy data elucidated chloroaluminate intercalation in natural graphite. Finally, theoretical calculations were employed to investigate the intercalation behavior of choloraluminate anions in the graphite electrode.

High-energy all-solid-state lithium (Li) batteries are of great promises as the next-generation energy storage devices. Among all choices of electrolytes, polymer-based systems have attracted wide-spread attention due to their low density, low cost, and excellent processability. However, they are generally mechanically too weak to effectively suppress Li dendrites, with relatively low ionic conductivity for reasonable kinetics at ambient temperature. In fact, there is a mechanical strength versus ionic conductivity dilemma in solid polymer electrolytes, where higher ionic conductivity generally brings about more mobile polymer chains and thus lower modulus. Herein, we developed for the first time a new design principle to mechanically reinforced composite polymer electrolyte (CPE) by introducing a stiff mesoporous backbone. As a result, over one order of magnitude higher modulus than the conventional polymer electrolytes (~0.43 GPa) and high ionic conductivity of ~0.6 mS cm^-1 (30 °C) were simultaneously achieved. Furthermore, stable Li symmetric-cell cycling for >450 cycles and full cells with cathode areal capacity up to 2.1 mAh cm^-2 were demonstrated. The mechanically reinforced CPE represents a new design methodology for solid-state electrolytes and offers opportunities for viable all-solid-state Li batteries.

Rechargeable lithium metal batteries (LMBs) are regarded as the “holy grail” of energy storage systems, but the electrolytes that are highly stable with both a lithium metal anode and high-voltage cathodes still remain a great challenge. Here we report a novel “localized high concentration electrolyte (LHCE)” that enables dendrite-free cycling of lithium metal anodes with high coulombic efficiency (99.5%) and excellent capacity retention (>80% after 700 cycles) of Li||LiNi1/3Mn1/3Co1/3O2 batteries. Unlike the high concentration electrolytes reported before, the electrolyte reported in this work exhibits low concentration, low cost, low viscosity, improved conductivity, and good wettability. With selected Li salt and solvent, we further demonstrated a fire-retardant LHCE that exhibits excellent anodic stability even up to 5.0 V and greatly enhances the cycling performance of LMBs. A Li||LiNi0.6Mn0.2Co0.2O2 battery using this electrolyte can retain > 97% capacity after 600 cycles at 1C rate, corresponding to a negligible capacity decay of < 0.005% per cycle. Therefore, this novel electrolyte can enable safe operation of high-energy LMBs for practical applications. Similar electrolytes can also be used in Li-ion batteries and other batteries to largely improve their safety and cyclability.

Conversion-type materials like transition metal (TM) oxides and sulfides exhibit the possibility to take advantage of all the valence states of the TM and can thus achieve much higher capacity compared to the intercalation-type materials. However, the conversion-type electrodes, suffer from drawbacks such as huge volumetric expansion, inadequate reversibility, and large voltage hysteresis which have been hindering their practical applications. Thus, in order to push these materials and reactions towards real practical use, there is a large need to obtain a thorough understanding of the conversion reaction mechanisms. Different hypotheses have been suggested, but some critical issues like the origin of the large hysteresis during charge/discharge of these materials is still not well-understood. In this study, we design and utilize a novel computational mechanistic approach that provides, for the first time, a detailed explanation of the hysteresis and non-equilibrium reaction pathways associated with these conversion-type electrodes. We firstly apply this methodology to investigate various lithiation reaction pathways of typical conversion-type electrode materials as picked: Co₃O₄ and NiO by exploring the energetics of a large number of equilibrium and non-equilibrium structural configurations using first-principle calculations.^1,2 The overall value of the voltages from our mechanistically-constructed, non-equilibrium pathway is in much better agreement with experimental lithiation than the calculated equilibrium voltage while the overall value of the latter reasonably agrees with experimental delithiation. We propose, therefore, that the charge and discharge processes proceed through very distinct equilibrium and non-equilibrium pathways which contribute significantly to the experimentally observed voltage hysteresis for Co₃O₄ and NiO. The methodology we have developed is not specific to these particular compounds, the application of this methodology has been extended to diverse conversion-type materials including (Co,Cu)₃O₄,³ CuS,⁴ MoS₂,⁵ and CuBi.⁶ Our study thus provides new insights on the lithiation process of conversion-type electrodes and could help future experiments to overcome the current limitations of them promoting the development of more advanced LIBs.
Reference:
(1) Yao, Z.; Kim, S.; Aykol, M.; Li, Q.; Wu, J.; He, J.; Wolverton, C. Chem. Mater. 2017, 29 (21), 9011.
(2) Li, Q.; Wu, J.; Yao, Z.; Thackeray, M. M.; Wolverton, C.; Dravid, V. P. Nano Energy 2017, 44, 15.
(3) Liu, H.; Li, Q.; Yao, Z.; Li, L.; Li, Y.; Wolverton, C.; Hersam, M. C.; Dravid, V. P. Adv. Mater. 2017, 1704851.
(4) He, K.; Yao, Z.; Hwang, S.; Li, N.; Sun, K.; Gan, H.; Du, Y.; Zhang, H.; Wolverton, C.; Su, D. Nano Lett. 2017, 17 (9), 5726.
(5) Li, Q.; Yao, Z.; Wu, J.; Mitra, S.; Hao, S.; Sahu, T. S.; Li, Y.; Wolverton, C.; Dravid, V. P. Nano Energy 2017, 38, 342.
(6) Amsler, M.; Yao, Z.; Wolverton, C. Chem. Mater. 2017, 29 (22), 9819.

Lithium ion batteries (LIBs) have been the most prominent electrochemical energy storage technology over the past decades and enabled the wireless evolution of portable electronic devices. Conventional cathode materials used are typically lithium-containing transition metal oxides and phosphides (e.g., LiCoO₂, LiFePO₄, LiMn₂O₄) which store (release) electrical energy via (de-)insertion of Li⁺ ions, accompanied by redox reactions of the transition metal cation. The specific capacity of the cathode is therefore limited by the number of electrons per transition metal cation that can participate in the redox reaction. This exclusive dependence on the transition metal cations as the redox center has been challenged by the recent discovery of oxygen redox reactivity in Li-excess cathode materials. The opportunity has thus arisen to boost the capacity and energy density of LIBs if the anionic and cationic redox activity can be enabled at the same potential. However, it is challenging to develop anionic-redox-based cathodes with acceptable cycle performance. Here in this study, we report the realization of simultaneous anionic and cationic redox in the super lithium-rich Li₅FeO₄ based cathode materials.¹ Highly reversible anionic redox reactivity with no obvious oxygen release was realized in this low-cost and earth-abundant iron oxide under a controlled voltage range. We then present a clear and quantitative picture of the structural, composition, and oxidation state evolution by first-principles density functional theory (DFT) calculations and various experimental measurements. We identify one special anionic redox active Li-excess configuration “Li₆-O” by exclusively examining the local atomistic environments of O ions involved in the anionic redox. The O^2-/O^1- ions in the “Li₆-O” configurations can give/uptake one extra electron on further oxidation/reduction enabling the reversible O^2-↔ O^1- during the charging/discharging. Our findings provide insights into the electrochemical oxygen redox reactivity and shed light on the design of low-cost transition metal oxide-based high-energy-density cathode materials.
Reference:
(1) Zhan, C.; Yao, Z.; Lu, J.; Ma, L.; Maroni, V. A.; Li, L.; Lee, E.; Alp, E. E.; Wu, T.; Wen, J.; Ren, Y.; Johnson, C.; Thackeray, M. M.; Chan, M. K. Y.; Wolverton, C.; Amine, K. Nat. Energy 2017, 2 (12), 963.

Electronic products have become the essential part of our daily life, and Li-ion battery is of particular interest because of their high power and energy density and long cycle life. Noval electronic devices with multiple shapes require configuration designable energy storage which can be integrated seamlessly into their limited space. While 3D printing of rechargeable batteries has received immense interests to advance the next generation of 3D energy storage devices, challenges of 3D printed electrolyte still exist. Additional processes, especially for solvent evaporation, are required for previous studies of electrolyte fabrication, which hinders the simultaneous production of electrode and electrolyte in all 3D printed batteries.

Herein, we developed an elevated-temperature DIW 3D-printing technique, and designed a solid-state electrolyte ink, enabling 3D printing of hybrid solid-state electrolyte batteries. In the proposed elevated-temperature DIW process, the hybrid electrolyte ink is directly printed on electrodes without any surface treatment for the substrate and post-processing for the electrolyte, through which the preparation of electrolyte and its incorporation within a battery will be of higher efficiency and lower cost. The hybrid solid-state electrolyte consists of solid polymer matrices and ionic liquid. The porous solid polymer matrix provides plentiful channels for Li-ion diffusion and improves the mechanical properties of the battery. The ionic liquid maintains its liquid form, preserving its ionic conductivity and electrochemical properties. TiO₂ nanoparticles were added into the PVDF-co-HFP based polymer inks to modify their viscosity, tune the contact angles and improve the electrochemical performances. In addition, the hybrid electrolyte printed by the elevated-temperature DIW process shows a lower interfacial resistance due to a unique dense interface formed between the electrolyte and electrode. Interestingly, the interfacial resistance in this method was reduced significantly compared with the traditional method of stacking electrolyte on an electrode.

Fe-based cathode materials are quite suitable for sodium ion batteries (SIBs) owing to the abundance and low cost of iron resources. ¹ However, poor electrochemical reaction kinetics and low cyclic stability limited the practical application of most iron based oxides. ^2-3 Among various Fe-based materials, sodium ferrous sulfate (NFS) shows relatively high operating voltage (average discharge voltage at 3.8 V) with superior Na intercalation kinetics, but the theoretical electrochemical capacity is hard to achieve because of the inherently low electronic conductivity like other polyanion type materials. ^4-6 Herein, a type of nano-sized Na_2.4Fe_1.8(SO₄)₃/C (NFS/C) composite with high-performance is reported. Carbon is used both to restrict the grain size and to obtain high-efficient electron transport among nano-sized particles. Propylene carbonate (PC) is used as electrolyte medium to achieve wider electrochemical reaction window (2.0 V–4.5 V) for stable battery performance. The NFS/C composite shows high capacity (100.2 mAh g^-1 at 1 C), great cyclability (76.5 mAh g^-1 after 500 cycles at 1 C) and excellent rate performance (95.1 mAh g^-1 at 5 C, 91.3 mAh g^-1 at 10 C, 80.5 mAh g^-1 at 20 C). The outstanding performance of as-prepared material proved that NFS is a very competitive candidate for high energy density SIBs.

Acknowledges: The authors greatly acknowledge the financial support from National Natural Science Foundation of China (No. 21405053), the Specialized Research Found for the Doctoral Program of Higher Education of China (No. 20130142120036) and the National Thousand Talents Program of China.

References:
1. Barpanda P, Oyama G, Nishimura S, et al. Nature Communications, 2014, 5(5):4358.
2. Dwibedi D, Ling C D, Araujo R B, et al. Acs Appl Mater Interfaces, 2016, 8(11):6982-6991.
3. Yu M, Yu T, Zhang S, et al. Journal of Materials Chemistry A, 2016, 4(5):1624-1631.
4. Yu T, Lin B, Li Q, et al. Physical Chemistry Chemical Physics, 2016, 18(38):26933.
5. Goñi A, Iturrondobeitia A, et al. Journal of Power Sources, 2017, 369:95-102.
6. Oyama G, Pecher O, Griffith K J, et al. Chemistry of Materials, 2016, 28(15).

Scientists have made numerous attempts to stabilize the Sn alloy geometry by constructing nano-structures with carbon nanotubes, graphene, nanorods and metal alloy scaffold. However, most of these Sn particles can’t long survive due to severe agglomerations, leading to a limited cyclic capability. A rapid capacity decay and a low rate performance are usually detected, posing an urgent need in preventing pulverization and contact loss upon a long cycling. Here by making a wide-size-ranging hybrid composite of Sn kernel and TiO₂ skin, with a tunable interspace, we have achieved a long life of >10000 cycles at fast rates of 5.0 C and 10.0 C charge/discharge rate with reversible capacity exceeding 662 (double times of graphite) and 360 mAh/g, respectively (Nano Letters, 2018, in print, DOI: 10.1021/acs.nanolett.7b04416). At 1.0 C, the capacity exceeds 727 mAh/g with a Coulombic efficiency of >99.8% after 3000 cycles. Our ‘Skin Grafting’ route is simple and industrially scalable. The long cycling and fast charge/discharge performance makes this battery a high potential in replacing graphite based lithium-ion batteries (LIBs) for practical applications in electric vehicles (EVs).

With the current proliferation of Li-ion batteries (LIB) beyond mobile devices there is a great need to develop inexpensive and safe cathode materials with high energy and power densities. Li₂FeSiO₄ (LFS) is a promising LIB cathode candidate because of its high theoretical energy density, nontoxicity, abundance of iron and silicon in the earth’s crust, and structurally safe polyanionic framework. However, challenges with full attainment of 2Li capacity, reversibility and conductivity have not allowed for the full potential of these interesting intercalation compounds to be achieved. In search of deeper understanding of the structural chemistry of LFS towards overcoming some of these challenges in this study the effect of dopants is investigated via theoretical modelling and experiment. In terms of modelling, we apply density functional theory (DFT) calculations to examine the viability of several divalent dopants selected from alkali earth metals and 3d transition metals. Computational results suggest that the formation of Li₂Fe_1-xM_xSiO₄ solid solution (M = Mg²⁺, Ca²⁺, Sr²⁺, Co²⁺, and Ni²⁺, x = 0 – 6.25%) is energetically favourable. For the lithiation/delithiation of the first Li⁺, which corresponds to the redox couple Fe²⁺/Fe³⁺, less than 3.0% volume variation is calculated indicating that good structural stability can be maintained in all the doped LFS materials. Cell voltage is found to increase slightly after doping and shows a linear relation with the doping concentration. The intercalation of the second Li⁺, on the other hand, requires a voltage higher than 4.5 V vs. Li/Li⁺ but more importantly is accompanied by a large volume change (around 21%) even with the help of Fe-site substitution. Experimentally, doped-LFS was synthesized with crystal formation control via hydrothermal method. The use of low temperature (e.g. 200^oC) provides us the chance to explore the rarely studied low-temperature orthorhombic phase with S.G. Pmn2₁ as opposed to previous works that have looked the high-temperature monoclinic phase with S.G. P2₁/n. Magnesium and cobalt substitution of iron in the LFS framework were achieved from sulfate precursor systems, whereas calcium and strontium were doped out from chloride systems due to the limited solubility of their sulfate salts. Nickel, however, was not miscible with LFS, which agrees with previously reported results. Electrochemical performances of doped-LFS as cathode material were investigated in detail via galvanostatic charge/discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements.

Layered lithium mixed-transition-metal oxides (NCM: LiNi_1-x-yCo_xMn_yO₂) with high nickel content (i.e., Ni-rich NCM) offer high electrochemical storage capacity, high operating potential, low toxicity, and relatively low cost. These compounds, however, exhibit poor structural and electrochemical stability. Zirconium, which has been studied as a substitutional element for transition metal in the layered NCM cathode materials, can stabilize the layered structure and improve the cyclability. However, the fundamental mechanism of the Zr-dopant is still unclear, especially in Ni-rich NCMs.

In this research, we synthesized Zr-doped LiNi_0.8Co_0.1Mn_0.1O₂ (Zr-NCM811) with a variety of dopant concentrations and systematically examined their structure, composition, phase, morphology, chemical state and electrochemical performance using XRD, ICP, SEM, TEM, and XPS. The 1 at.% Zr-NCM811 [Li(Ni_0.8Co_0.1Mn_0.1)_0.99Zr_0.01O₂] achieved the most stable cycling performance and the best high-rate capability with 165.2 mAh×g^-1 at 2C (400 mA×g^-1) cycling and 83.1% of retention after 60 cycles in contrast to 163.8 mAh×g^-1 and 71.4% for the un-doped NCM811. The excellent high-rate performance of Zr-NCM811 can be attributed to the enhanced lithiation/delithiation kinetics, evidenced by conductivity and diffusivity measurements on the Zr-NCM811 materials.