Symposium EC2 : Facilitating Charge Transport in Electrochemical Energy Storage Materials

Microstructures strongly affect transport phenomena in electrode materials and their performance. However, explicit consideration of the complex structures such as the grain boundary network poses a challenge in simulations. In this work, we develop an innovative method for incorporating the surface and interface diffusion with the bulk diffusion based on the smoothed boundary method. Complex grain structures are described using multiple domain parameters, where the value of domain parameter is uniformly one inside the corresponding grain, and zero outside. As such, the grain boundaries are implicitly defined by the transition regions of domain parameters, and the diffusion equations can be straightforwardly solved on a standard Cartesian grid system. This method is applied to simulate the diffusional impedance of polycrystalline electrode materials. The simulations show that both grain boundary diffusivity and grain size affect the diffusional impedance. With high grain boundary diffusivities, the concentration of ions along the grain boundaries is similar to that at the electrode particle surfaces, such that radial diffusion within each primary particle dominates the impedance behavior. Conversely, with low grain boundary diffusivities, the overall radial diffusion in the secondary particle determines the impedance behavior. In coordination with the modeling effort, electrochemical impedance spectroscopy measurements of polycrystalline single secondary cathode particles are conducted. The simulations and experiments are combined to reveal the impact of interfacial transport on electrode materials’ performance. In turn, the insight gained through this work opens a new avenue for extracting microstructural characteristics (e.g., the grain size) from its impedance behavior.

Current Li-ion batteries suffer from problems caused by the chemical instability of their organic electrolyte. Therefore a lot of research focuses on replacing the organic electrolyte by inorganic solid ion conductors. Cubic Li₇La₃Zr₂O₁₂ (LLZO) garnets and its variants are among the most promising candidates for next generation all solid state Li-ion batteries ^[1,2]. They provide a high Li-ion conductivity and combine chemical and electrochemical stability. One crucial aspect is the doping of the material, in order to stabilize its cubic phase but also in terms of diffusion paths and mobile defects. Different dopants have been investigated, but the specific effect of each dopant, the importance of the exact Li-ion stoichiometry, as well as degradation phenomena are still not completely understood. For nominally identical dopant content, for example, rather different conductivities were reported.
In this contribution, we present a combined study of electrochemical impedance spectroscopy (EIS) and elemental analysis (inductively coupled plasma mass spectrometry, ICP-MS) has been used to determine the effects of varying lithium and dopant content on the Li-ion conductivity. The roles of sintering temperature and preparation procedure, but also effects of the sample dimension are considered and reasons behind severe variations of effective Li-ion conductivities are discussed. Besides overall Li-ion conductivity measurements using blocking electrodes and analysis of the bulk composition, measurements on microelectrodes of different sizes (20 – 300 µm) were performed to obtain information on local Li-ion conductivities. Within one and the same sample, conductivity variations up to almost one order of magnitude were found. Laser ablation (LA) ICP-MS was employed to obtain local information on the exact composition and thus of stoichiometric variations in the samples. For example, a correlation between spatially varying Al content and local conductivities was found, with higher conductivities primarily in the outer regions of the ceramics. These studies provide a deeper understanding for the variation of Li-ion conductivity in publications on nominally similar samples. Furthermore they help in finding optimal dopant contents, Li contents and preparation procedures of LLZO.

^[1] Murugan, R.; et al.; Angew. Chem. 2007, 119, 7925-7928
^[2] Thangadurai, V.; et al.; Chem. Soc. Rev. 2014, 43(13), 4714-4727

LiMn_1.5Ni_0.5O₄ is a high voltage cathode material for lithium ion batteries which has attracted great attention within the battery community due to its potential for high energy and power density. This compound can be ordered or disordered depending on the arrangement of Mn and Ni in the spinel structure. The charge-discharge behavior of ordered and disordered structures has been tested by several research groups. However still it is not clear which structural composition is suitable for a high performance battery. It is also not clearly understood if the rate performance of the material is limited by bulk transport properties or interfacial reactions. Here we report on the electronic and ionic conductivity and diffusivity of ordered (P4₃32) and disordered LiMn_1.5Ni_0.5O₄ which has been determined separately by using ion and electron blocking cell configurations as a function of lithium concentration on sintered dense pellets. The disordered phase exhibits about fifteen time higher electronic conductivity than the ordered phase at room temperature in the lithiated state. The conductivities of the partially delithiated ordered phase measured at a given temperature increase monotonically with increasing delithiation at x = ~0.3 and beyond that the electronic conductivity is almost leveled up. In contrast, the electronic conductivity of disordered phase initially decreases with delithiation and comes down to the level of lithiated ordered phase. After that it exhibits almost the same electron conducting behavior as of ordered phase. The lithiated ordered and disordered phases exhibit the same order of magnitude of ionic conductivity and diffusivity. The measurements of lithium ion diffusivity (conductivity) as function of lithium content in electron-blocking cells, is found to be consistent with AC and DC technique. Chemical diffusion during electrochemical use is limited by lithium transport, but is fast enough over the entire state-of-charge range to allow charge/discharge of micron-scale particles at practical C-rates. Furthermore, measurements of exchange current density of the two phases as a function of lithium concentration are in progress. The measurements are being also performed on sintered dense pellets with a defined surface area.

The first part of the contribution refers to ionic and mixed ionic/electronic transport in the constituent phases of Li- or Na-based batteries. Adjusting screws for tuning mass transport in electrolyte and electrode phases are discussed using recent materials examples.
The second part of the talk addresses interfacial phenomena and the influence of interfacial resistances and capacitances. Here the job-sharing mechanism is of particular relevance as it has the potential to lead to artificial electrodes. Interfacial anomalies are not only relevant for nanostructured electrodes but also for composite electrolytes with single ion conduction.
The third part refers to the important issue of electrochemical networks and the transport therein. Such network issues that may comprise electrode and electrolyte phases, are especially important when adjusting screws to optimize transport properties of the individual phases are exhausted.

A critical challenge for electric energy storage is understanding the basic science associated with the gap between the usable output of energy storage systems and their theoretical energy contents. The goal of overcoming this inefficiency is to achieve more useful work (w) and minimize the generation of waste heat (q). Minimization of inefficiency can be approached at the macro level, where bulk parameters are identified and manipulated, with optimization an ultimate goal. However, such a strategy may not provide insight towards the complexities of electric energy storage, especially the inherent heterogeneity of ion and electron flux contributing to the local resistances at numerous interfaces found at several scale lengths within a battery. Thus, the ability to predict and ultimately tune these complex systems to specific applications, both current and future, demands not just parameterization at the bulk scale, but rather specific experimentation and understanding over multiple length scales within the same battery system, from the molecular- to the meso-scale. This presentation will be structured as a case study examining the insights and implications from multiscale investigations of a prospective iron oxide based battery material.

A solid electrolyte interphase is generated on the anode of lithium ion batteries during the first few charging cycles. The presence and stability of the SEI is critical to the performance of the battery. Despite thorough investigation of the SEI for over 20 years, the mechanism of formation and function are still relatively poorly understood. We have investigated the structure of the SEI on graphite and silicon electrodes along with changes which occur to the SEI upon additional cycling. In addition, we have been using the one electron reducing agent, lithium napthalenide to independently prepare the reduction products which constitute the SEI. The reduction products and their subsequent decomposition products have been thoroughly investigated via a combination of NMR, XPS, IR-ATR, TGA, and GC-MS. The investigation of SEI via different methods of generation and evolution provides significant insight into the structure and properties of the anode SEI.

Electrochemical energy storage is an important issue for future technology development. For lithium ion batteries, graphite is the most popular anode material, but its theoretical capacity is only 372 mAh/g. This capacity is not high enough for future electronics. By contrast, the theoretical capacity of silicon is 4200 mAh/g. In addition, silicon anode can be charged at a higher rate with sufficient cycle stability. Silicon is therefore regarded as one of the most potential anode materials for next generation batteries. However, there is a large volume expansion (about 300%) when lithium ions are inserted into silicon; besides, the poor capacity retention due to the formation of solid electrolyte interface (SEI) makes silicon unfavorable for practical applications. In our recent TEM observations of the anode made of Si nanoparticles in lithium ion battery, the size of Si nanoparticles reduces from 100 nm to 5 nm after 20 charge/discharge cycles. The silicon nanoparticles are also wrapped by SEI. In order to understand the evolution of Si nanoparticles and the formation of SEI during lithiation, we use the electrochemical liquid cell holder for in-situ TEM analysis. The configuration of the electrochemical system includes the silicon nanoparticles as the working electrode, Pt reference electrode, LiCoO₂ powder at the counter electrode to provide lithium ions. The electrolyte is LiClO₄ in EC/DMC (vol% 1:1), which is stable in air. We use the Omniprobe manipulator in a focused-ion beam system to prepare the nano battery on a silicon nitride membrane window, which is pre-patterned with Pt electrodes, on a Si chip. Another Si chip with a silicon nitride membrane window covers on the system to seal the electrolyte. The cell is mounted on a TEM holder. We cycle the voltage on the cell to intercalate lithium ions into silicon nanoparticles and deintercalate the lithium ions for in-situ observations of the volume change of the silicon nanoparticles and the formation of SEI.

During initial battery cycling carbonate electrolytes undergo reduction at the negatively polarized electrode surface. This generates a passivating layer consisting of inorganic and organic electrolyte decomposition products usually referred to as the Solid Electrolyte Interphase (SEI). These passivation films undergo substantial deformations when the underlying electrode particles expand and contract during electrochemical cycling. While there has been considerable speculation about the relationships between SEI formation and mechanical failure, observing and probing these phenomena directly is extremely challenging. In this study we demonstrate a new approach for applying controlled strains to SEI films with patterned Si electrodes, in conjunction with direct observations of SEI growth and mechanical degradation using in situ atomic force microscopy (AFM). This provides an excellent platform for investigating the deformation and failure of SEI films, in response to controlled mechanical strains that are induced by lithiation and delithiation of the underlying Si. This approach enabled in operando monitoring of SEI growth, strain, and mechanical failure in SEI films during electrochemical cycling. This work provides a wealth of new information about relationships between SEI formation and the mechanical degradation of SEI films. For example, the results verify that crack formation occurs during lithiation (this has been predicted previously, but not directly observed). Additional SEI formation at low potentials did not fill these cracks, which directly contradicts prior speculation by some previous researchers. Also, analysis of these measurements make it possible to obtain the fracture toughness of the SEI, a key value which has not been previously measured..

The new methodology reported here makes it possible to obtain critical information about the chemo-mechanical stability of SEI films. These carefully controlled experiments also provide important information for chemical-mechanical degradation models that are used to predict capacity fade in Li-ion batteries. These models, combined with our direct experimental observations of key failure mechanisms will ultimately be used to design improved SEI passivation layers.

Lithium-Ion batteries are important devices for present and future electric energy storage, offering high energy density and durability. Positive electrodes (cathode) materials are predominantly transition metal oxides containing exchangeable lithium. The electronic and ionic structure of these materials in the bulk as well as on their surfaces/interfaces are key factors for their properties, such as electrode potential, charge transfer intercalation reactions, as well as degradation and reactivity.
This contribution gives an overview of our surface science studies to investigate layered-oxide cathodes and Li addressing their electronic structure and cathode-electrolyte interface formation. In a surface science approach, well-defined surfaces/interfaces are prepared and analyzed with surface sensitive analytical techniques such as electron spectroscopy (XPS, UPS, XAS) using emersed electrodes after electrochemical treatment and modelling experiments by adsorbing/depositing contact materials as solvents (H₂O, DEC) or solid electrolytes (LiPON). With this approach the electronic and chemical structure of surfaces and interfaces can be analysed allowing conclusions on the electronic structure of the bulk, on reactivity with other phases, and on electrochemical interface properties.
The obtained results on the interaction can be addressed to charge transfer reactions of electrons and ions and related defect formation which will be discussed on the basis of energy level diagrams extracted from the experimental data. The results indicate that presently available concepts should be improved in considering electron induced effects on bulk properties and possibly occuring electron induced side reactions.

The nature of the surface electrolyte interphase (SEI) is critical to proper electrode and battery function. Characterization of this layer is difficult, especially when it is desired to do so in situ. Although Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) have been demonstrated in situ, the sensitivity typically does not allow one to measure the SEI directly. We describe here NMR methodology based on ⁶Li/⁷Li exchange, by which the formation and the properties of the SEI can be probed indirectly.

The technique involves tracking particular isotopes of lithium over time. A model based on ion diffusion and diffusion through the SEI, as well as the skin effect of the radiofrequency signals is developed. The technique provides a unique, time resolved “window” into the lithium ion dynamics at the metal-SEI-electrolyte interfaces. We will describe how this “window” can be used to extract information about the growth of the SEI layer and measure the diffusion of lithium ions through it using NMR experiments on well-designed, isotopically-enriched systems.

A thin amorphous coating of Al₂O₃ obtained via atomic layer deposition (ALD) has demonstrated the ability to improve cycle-life for several cathode materials in rechargeable Li-ion batteries [1]. However, due to the insulating nature of Al₂O₃, the coatings on cathode particles impede the transport of Li-ion and electrons during the battery cycling. Therefore, a large overpotential on the cathode surface can develop leading to significant capacity loss at higher C-rates and for thicker coatings. In this work, we describe a method to estimate the overpotential of amorphous ALD Al₂O₃ coatings on Li[Ni_0.5Mn_0.3Co_0.2]O₂ (NMC) cathode and can be extended to any other coating materials. At 1C-rate (2.062mA), the estimated Al₂O₃ overpotential is about 0.82 mV/nm yielding an estimation of effective resistivity 6.3 MWm and Li-ion diffusivity of 1.7x10^-14 cm²/s.

We found that the Al₂O₃ overpotential varies linearly with coating thickness and also with driving current, implying an “Ohmic” behavior. Based on the theoretical model [2], these observations lead to conclude that coatings acts like an electrolyte, consisting of positively charged Li ions and negatively charged electrons. In such a mechanism, Li-ions take part in the ionic transport across coating and the counter-balancing negative charges (electrons) remain trapped in localized electronic states within the coating. Those electrons are originally donated by protons incorporated in the coating resulting from the ALD process and then ion-exchanged with Li⁺ during battery operation. Since the resistivity is inversely proportional to Li⁺ concentration, the concentration of the protons in the original coatings determines the resistivity and overpotential value. We support this hypothesis by demonstrating a higher overpotential for Al₂O₃ coatings of a lower proton concentration.

[1] Y. S. Jung, A. S. Cavanagh, A. C. Dillon, M. D. Groner, S. M. George, S. H. Lee, J. Electrochem. Soc. 157, A75-A81 (2010)
[2] S. Xu, R. M. Jacobs, H. M. Nguyen, S. Hao, M. Mahanthappa, C. Wolverton, and D. Morgan, J. Mat. Chem. A 3, 17248-17272 (2015)

Superionic conductivity was recently found in salts comprised of Li⁺ or Na⁺ cations and large cage-like polyhedral closo-borate-based anions, such as B₁₂H₁₂^2-, B₁₀H₁₀^2-_, CB₁₁H₁₂^-, and CB₉H₁₀^-, upon their entropically driven transformations to disordered phases [1-5]. This dramatically high conductivity (e.g., ~0.03 S cm^-1 for NaCB₉H₁₀ at 297 K [4]) is enabled by the emergence of a vacancy-rich cation sublattice and possibly further aided by the concomitant onset of high reorientational mobility (typically >10¹⁰-10¹¹ reorientational jumps s^-1) of the quasi-spherical anions. Furthermore, these superionic-conducting phases can be better stabilized at device-relevant temperatures via additional strategies such as ball-milling and anion-mixing [5,6]. Neutron scattering techniques are invaluable for elucidating the structures and bonding potentials associated with these hydrogenous materials and the dynamical nature of the reorienting anions. This talk will focus on what quasielastic neutron scattering measurements can tell us about the reorientational behaviors and mobilities of the different divalent and monovalent polyhedral anions within the various disordered salt structures that coincide with the unusually rapid cation translational diffusion in these materials. The possible relationship between the high anion reorientational mobilities and the impressive cationic conductivities will be discussed.

[1] T. J. Udovic, M. Matsuo, A. Unemoto, N. Verdal, V. Stavila, A. V. Skripov, J. J. Rush, H. Takamura, S. Orimo, Chem. Commun. 50, 3750−3752 (2014).

[2] T. J. Udovic, M. Matsuo, W. S. Tang, H. Wu, V. Stavila, A. V. Soloninin, R. V. Skoryunov, O. A. Babanova, A. V. Skripov, J. J. Rush, A. Unemoto, H. Takamura, S. Orimo, Adv. Mater. 26, 7622−7626 (2014).

[3] W. S. Tang, A. Unemoto, W. Zhou, V. Stavila, M. Matsuo, H. Wu, S. Orimo, T. J. Udovic, Energy Environ. Sci. 8, 3637−3645 (2015).

[4] W. S. Tang, M. Matsuo, H. Wu, V. Stavila, W. Zhou, A. A. Talin, A. V. Soloninin, R. V. Skoryunov, O. A. Babanova, A. V. Skripov, A. Unemoto, S. Orimo, T. J. Udovic, Adv. Energy Mater. 6, 1502237 (2016).

[5] W. S. Tang, M. Matsuo, H. Wu, A. Unemoto, V. Stavila, S. Orimo, T. J. Udovic, Energy Storage Mater. 4, 79−83 (2016).

[6] W. S. Tang, K. Yoshida, A. V. Soloninin, R. V. Skoryunov, O. A. Babanova, A. V. Skripov, M. Dimitrievska, V. Stavila, S. Orimo, T. J. Udovic, ACS Energy Lett. 1, 659–664 (2016).

Solid electrolytes, where Li⁺ can migrate fast in their crystal lattice, are the key materials for realization of high performance all-solid-state lithium batteries. From the early stage of the research, most of the works have focused on compounds containing Li⁺ in themselves. Some of the Li compounds show extremely high Li⁺ conductivity comparable to that in liquid electrolytes and are so-called Li⁺ superionic conductors [1]. In addition to high Li⁺ conductivity, excellent sinterability, intimate electrochemical contact with active materials and wide potential window, etc. are also required for practical applications.
Pure Li⁺ ion conductors can also be synthesized from “Li-free” compounds via doping of Li salts [2]. According to the latter methods, we can fabricate a desirable solid electrolyte by choosing a “Li-free” compound (or solid solvent) having above-mentioned properties. For example, by selecting KI as a solid solvent, we have synthesized a pure Li⁺ conductor with small grain boundary resistance [2]. In this work, the ionic conduction properties of NaI slightly doped with LiBH₄ are investigated.
All the experiments were conducted in an Ar atmosphere. The reagents were mixed in an alumina mortar at a given molar ratio. Using an air tight chrome steel pot (45 ml) and 10 pieces of balls (10 mm in diameter), they were milled at 400 rpm. To confirm the crystal and local structure of the samples, XRD measurement with Cu Kα radiation and ⁷Li NMR were performed, respectively. For electrochemical measurement, the powder was pelletized at 100 MPa and Li and/or stainless steel plates were fixed at the both sides of the pellets. An electrical conductivity was measured by AC impedance methods between 303 K and 393 K. Transference number of Li⁺ was determined by DC polarization measurement.
Diffraction peaks assigned to NaI structure are observed without other pronounced peaks. A lattice parameter of the sample is decreased by increasing the concentration of the Li salts. Therefore, it can be said that Na⁺ and I^- are substituted with Li⁺ and BH₄^-, respectively. An electrical conductivity of NaI doped with 6 mol% LiBH₄ is 1.7 × 10^-6 S/cm at 303 K, which is comparable to that of pure LiI. However, the conductivity is decreased after keeping the cell at 393 K for one night. An activation energy of Li⁺ conduction is 0.68 eV / 0.32 eV at the heating / cooling cycle, respectively. These discrepancies of the results between heating and cooling cycle would originate from transient lattice defects introduced by milling, which are thermally relaxed during heating cycle. A transference number test confirmed that the mobile ion in NaI lattice was Li⁺. These results indicate that pure Li⁺ conductors can be synthesized not only from KI and NaI but other alkali halides can also be used as a solid solvent for Li⁺ conductors.

References
[1] Knauth P, Solid State Ionics 180 (2009) 911.
[2] Miyazaki R et al., APL Materials 2 (2014) 056109

All-solid-state lithium ion batteries employing solid-state electrolytes promise potentially improved operational safety compared to standard lithium ion batteries using flammable liquid electrolytes. So far, only a few oxide- and thiophosphate-based solid-state electrolytes exhibit lithium ion conductivities near room temperature comparable to liquid organic electrolytes. However, none of these electrolytes has enabled the fabrication of a competitive all-solid-state battery yet. Here we report the discovery of a superionic phase near room temperature in the class of lithium amide-borohydrides, enabling ionic conductivities of 8 mS/cm, comparable to values of common organic liquid electrolytes. We further demonstrate excellent rate performance up to 5C and stable cycling over 400 cycles at 1C of our solid-state electrolytes in half-cell battery configuration representing an important step towards a viable solid-state battery technology.

The need for new battery concepts shifts solid Li-ion conductors into the focus of research. Li-stuffed oxide garnets such as Li₇La₃Zr₂O₁₂ (LLZO) are among the most promising candidates. LLZO does not only show a very high Li-ion conductivity; also its electrochemical inertness over a wide potential window and its stability against Li metal makes LLZO exceptionally well suited to be used as an electrolyte for Li-metal based batteries.^{1, 2}

Pure LLZO has a tetragonal low-temperature phase with space group (SG) I4₁/acd (no. 142) that shows a comparatively poor Li-ion conductivity of ~10^-6 S cm^-1. For use as solid-state electrolyte, the cubic “high-temperature” modification with SG Ia-3d (no. 230) is much more desirable, as it shows a Li-ion conductivity in the order of 10^-4 – 10^-3 S cm^-1. Fortunately, the cubic high-temperature modification can be stabilized at room temperature by the introduction of small amounts of supervalent cations such as Al³⁺, Ta⁵⁺ and Nb⁵⁺.²

Recent studies show that the introduction of certain cations such as Ga³⁺ and Fe³⁺ causes the formation of a different cubic structural modification showing the acentric cubic SG I-43d (no. 220).^{3, 4} The reduced symmetry compared to the Ia-3d modification results from the site preference of Ga³⁺ and Fe³⁺.

These new garnet-similar materials show exciting electrochemical properties. ⁷Li NMR relaxometry experiments revealed an additional dynamic process for Ga-stabilized LLZO with SG I-43d compared to Al-stabilized LLZO with SG Ia-3d.³ The Li-ion conductivity of both LLZO modifications with SG I-43d is higher than 1.0 × 10^-3 S cm^-1 and therefore among the highest values for garnet-type materials, exceeding Al-stabilized LLZO.^{4, 5} These results highlight the impact of structure-property relationships for these kind of materials.

¹ Murugan, R.; Thangadurai, V.; Weppner, W.; Angew. Chem. Int. Ed. 2007, 119, 7925–7928
² Thangadurai, V.; Narayanan, S.; Pinzaru, D.; Chem. Soc. Rev. 2014, 43 (13), 4714–4727
³ Wagner, R.; Redhammer, G. J.; Rettenwander, D.; Senyshyn, A.; Schmidt, W.; Wilkening, M.; Amthauer, G.; Chem. Mater. 2016, 28 (6), 1861–1871
⁴ Wagner, R.; Redhammer, G. J.; Rettenwander, D.; Tippelt, G.; Welzl, A.; Taibl, S.; Fleig, J.; Franz, A.; Lottermoser, W.; Amthauer, G.; Chem. Mater. 2016, 28 (16), 5943–5951
⁵ Rettenwander, D.; Redhammer, G. J.; Preishuber-Pflügl, F.; Cheng, L.; Miara, L.; Wagner, R.; Welzl, A.; Suard, E.; Doeff, M. M.; Wilkening, M.; Fleig, J.; Amthauer, G.; Chem. Mater. 2016, 28 (7), 2384–2392

Solid-state lithium batteries (SSLiBs) have temendous potential to mitigate battery safety/flammability issues as well as allow high enegy density Li metal anodes. Unfortunately progress on SSLiBs has been limited due to high interfacial impedance. To overcome these limitations we have pursued an integrated theoretical and experimental approach based on addressing the intrinsic anode-electrolyte and cathode-electrolyte interfaces, as well as dramaitically extending the 3D electrode-electrolyte interfacial area through multi-layer ceramic fabrication techniques. The resulting modified garnet interface in a microstrucurally tailored porous Li-garnet scaffold support increases electrode/electrolyte interfacial area and overcomes the high impedance typical of planar geometry SSLiBs. For Li-metal-anode/garnet-electrolyte cycling this results in an area specific resistance (ASR) of only ~2 Ωcm^-2 at room temperature. Similar results are also being developed for cathode/garnet interfaces.

The competition of Na⁺ ion versus K⁺ ion transport in a mixed alkali borosilicate glass has been investigated by low energy bombardment induced ion transport employing Cs⁺ ions as the foreign ion [1]. Electrodiffusion causes the replacement of Na⁺ and K⁺ down to about 200 nm below the surface of the glass. Beyond this electrodiffusion front (in the direction of ion transport) K⁺ ions accumulate to a density above the bulk concentration while Na⁺ is further depleted towards the backward platinum electrode. At the backward electrode only Na is electrodeposited since the electrical potential does not allow for K electrodeposition. A full simulation of the electrodiffusion profiles reveals the complete concentration dependence of the diffusion coefficients of the Na⁺ and K⁺ ions. As a consequence of the ion transport in the bulk material the former internal glas / platinum interface is turned into a Na interphase. Subsequently, this interphase has been analyzed by means of FIB-TEM.
[1] Johannes Martin, Sarah Mehrwald, Martin Schäfer, Thilo Kramer, Christian Jooss, Karl-Michael Weitzel, Electrochimica Acta, 191, 616-623, (2016)

Metal/oxide interfaces have long been studied for their fundamental importance in material microstructure. However, the challenge involved in characterizing the relation between structure and electron transport of a large number of metal/oxide combinations inhibits the search for interfaces with improved functionality. Therefore, we develop a novel high-throughput screening approach that combines computational and theoretical techniques. We use a Density Functional Theory + U (DFT+U) quantum mechanical formalism to produce effective Schrödinger equations, which are solved by wave packet propagation to simulate charge transport across the metal/oxide interface. We demonstrate this method on α-Fe2O3/Mt interfaces, for Mt = Ag, Al, Au, Ir, Pd, or Pt metals. We use this novel method to screen for binary alloys of these metals at the α-Fe2O3/Mt interface and perform a successful validation test of the methodology. Finally, we correlate the interface potential energy and the charge transport permeability through the interface. Counterintuitively, among the interfaces studied, we find that higher mismatch interfaces have better charge transport permeability. We anticipate that this method will be useful as a computationally tractable strategy to perform high-throughput screening for new metal/oxide interfaces.

References:
1. O. Neufeld and M. Caspary Toroker, “A novel high-throughput screening approach for functional metal/oxide interfaces”, J. Chem. Theo. Comp. 12, 1572 (2016).
2. O. Neufeld and M. Caspary Toroker, “Can we judge an oxide by its cover? The case of platinum over alpha-Fe2O3 from first principles”, Phys. Chem. Chem. Phys. 17, 24129 (2015).

Space-charge layers at heterointerfaces of ionic-conducting materials drastically modify the conducting properties of a system. Although such interfaces play key roles in electrochemical devices, including solid-state lithium batteries and fuel cells, quantitative investigations into a depth of the space-charge layers are still unsatisfactory. Consequently, the evaluation of the depth profiles of Li ions in a solid electrolyte along the perpendicular axis to the heterointerfaces is of great importance.
Here we report applied-voltage-dependent Li-ion distributions at the interface between a Li-ion solid electrolyte and a metal electrode, measured using Rutherford backward scattering (RBS) and nuclear reaction analysis (NRA). Ni thin films with a typical thickness of 200 nm were deposited as blocking electrodes on both sides of a 0.18 mm thick Li_1.5Al_0.5Ge_1.5P₃O₁₂ (LAGP, Toshima Co. Ltd.) solid electrolyte substrate, using a DC magnetron sputtering method. A proton (H⁺) beam accelerated at 1 MeV was used for both the RBS and NRA measurements. We developed an original sample holder that enabled us to apply voltages (V= 0 V, +5 V and -5V, defined at the Ni electrode on the side irradiated with the H⁺ beam) between the electrodes during the RBS and NRA measurements.
Surprisingly, the NRA measurements revealed that the space charge layer in the Li-ion solid electrolyte is in the order of micro-meters. We stress that the Li density is depressed more than 40% at V = +5 V compared to that at V = 0 V. The depth of Li-depressed region exceeds 8 micro-meters. This result is in striking contrast to the liquid electrolyte case; the electric double layer is in the order of nano-meters. The understandings of the space-charge layer at metal/solid-electrolyte interfaces would open the way to improve ionic conductivity at the heterointerfaces and to eliminate the interface resistivity by controlling the space-charge layer.
This study was supported by JST-CREST, JST-ALCA, and KAKENHI.

Recently, all-solid-state batteries (ASSBs) with NASICON-based electrolytes are expected to use the new generation of energy storage devices because of their high energy density and safety. However, one of the problems of ASSBs is large interfacial resistance between active material and solid electrolyte. Factors of interfacial resistance are attributed to high contact resistance due to solid-solid interface, formation of mutual diffusion layer at the interface, and formation of space charge layer (SCL) at the interface. In these cases, surface modification of solid electrolyte by ionic conductive materials that have the low melting point has been suggested to as an effective method. However, a detailed study on the interfacial resistance and SCL has been not really investigated. In this work, a Li_2.2C_0.8B_0.2O₃ (LCBO) was coated by ball-milling on the surface of Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) as highly conductive solid electrolyte particles because it has a low meting point (> 700 °C) and then the structure and ionic conductivity of the surface-modified solid electrolyte were studied. We optimized the ball-milling process by using the results. The enhanced ionic conductivity of solid electrolyte with surface modification was been explained by three plausible mechanisms. One is related to packing of particles with reduce of size by ball-milling. The second mechanism is the formation of surface layer such as change in phase, crystalline structure, and distribution of ions. The last is change in ion distribution by space charge layer effect. The conductivity enhancement with the surface modification of solid electrolytes could be indicated by the type of charge carrier: Li vacancy for LCBO and interstitial Li⁺ for other high ionic conductors. The surface modification of solid electrolyte can be used to decrease considerably interfacial resistance and thus improve the power density of ASSBs.

Transition metal fluorides (such as FeF3, FeF2, CoF2) are promising cathode materials for the lithium ion batteries due to the significantly high theoretical capacities (> 571 mA h g-1). However, the transition metal fluorides have to be mixed with carbon due to the low electronic conductivity, and have to be prelithiated to couple with Li-free anodes. It is very challenging to homogeneously distribute transition metal (TM) and LiF nanoparticles in carbon matrix. In this study, the unique TM/LiF/C (TM=FeCo, FeNi) pomegranate-like nano-spheres, where 2~3 nm carbon coated TM-nanoparticles (~10 nm in diameter) and LiF nanoparticles (~ 20 nm) are uniformly embedded in a carbon sphere matrix (100~1000 nm), was synthesized in aerosol-spray process due to the extremely short pyrolysis time (~ 1 s) preventing the growth of Fe and LiF. The role of Ni or Co in TM/LiF/C is to prevent the formation of Fe3C and reduce the particle size of Fe. The constructed architecture ensures the intimate contact among Fe, LiF and C, thus greatly enhance the reaction kinetics. Therefore, TM/LiF/C shows an impressive high specific capacity of ~ 300 mAh g-1 and stable cycling performances, which is one of the best among the prelithiated FeF3-based cathodes reported so far. The present fluoride cathode materials with built-in Li source can pave the way for the practical application of transition metal fluorides in the next generation of high energy density LIBs.

References:
1) X. Fan, Y. Zhu, C. Luo, L. Suo, Y. Lin, T. Gao, K. Xu, C. Wang. ACS Nano, 2016, DOI: 10.1021/acsnano.6b02309.
2) X. Fan, Y. Zhu, C. Luo, T. Gao, L. Suo, S.C. Liou, K. Xu, C. Wang. J. Power Sources, 2016, 307, 435-442.

Silicon alloys have the highest specific capacity when used as anode material for lithium-ion batteries; however, the drastic volume change inherent in their use causes formidable challenges toward achieving stable cycling performance. Large quantities of binders and conductive additives are typically necessary to maintain good cell performance. In this report, only 2% (by weight) functional conductive polymer binder without any conductive additives was successfully used with a micron-size silicon monoxide (SiO) anode material, demonstrating stable and high gravimetric capacity (>1000 mAh/g) for ∼500 cycles and more than 90% capacity retention. Prelithiation of this anode using stabilized lithium metal powder (SLMP) improves the first cycle Coulombic efficiency of a SiO/NMC full cell from ∼48% to ∼90%. The combination enables good capacity retention of more than 80% after 100 cycles at C/3 in a lithium-ion full cell.

The amount of electrical power generated by lithium-ion batteries (LIBs) is constrained by the transport of lithium (Li) in the composite electrode structure composed of an active material and an electrolyte. Therefore, Li-ion conduction in the electrolyte materials and the intercalation in the active material are the keys to determine the performance of the batteries. It is thus necessary to understand the microstructure of the electrode and its correlation to the performance of LIB. The effects of the microstructure on Li-ion conduction are not yet clearly and completely understood owing to difficulties involved in an experimental assessment of the conduction pathway. In this context, a simulation model provides insightful information about how much an appropriately design of the electrode structure could change Li-ion transport properties and improve overall performance of the battery. The present paper describes development of two distinctive numerical simulation techniques for investigating the fundamental constitutive relationship between the Li conduction phenomena and the quantitative microstructural features of the positive electrode microstructure such as grain size, spatial distribution of active material particles and electrolyte particles, and material properties inside the particles. First, the phase-field method, in which the temporal evolution of the microstructure is calculated based on a free-energy function, is used for constructing a wide range of composite particle distributed 3D microstructures. Second, the regression models such as neural network are used as tools to obtain the overall picture of the Li transport landscape for the microstructural parameters based on the above dataset. Conventional apparent conduction evaluation methods such as potentiostatic intermittent titration technique (PITT) are used to investigate the effects of electrode microstructures on electrode performance. As a result, the simulation results clearly demonstrated that the apparent ionic conductivity notably affects the discharge properties at a high discharge rate by modifying the overpotential. The present simulation provides an estimation of the material properties required prior to the experimental procedure under the specific discharge condition.

Hollandites (K_xMn₈O₁₆ or OMS-2) have a tunneled structure permitting one-dimensional insertion and deinsertion of ions along the c direction. Synthetically, we have demonstrated that it is possible to control size, composition and morphology of the structure. Specifically, the electroactive, K_xMn₈O₁₆, was prepared in a fibrous form using a scalable, moderate temperature, aqueous synthesis. Binder-free self-supporting (BFSS) paper-like cathodes could be prepared from the redox-active, high aspect ratio K_xMn₈O₁₆ nanofibers eliminating the need for binder and current collector. Electrochemical performance of BFSS cathodes and OMS-2 conventional cathodes was evaluated by galvanostatic charge/discharge, GITT, and EIS. The electrochemical performance of BFSS cathodes showed several advantages compared to conventional cathodes in the electrochemical tests. Elimination of the binders and current collectors resulted in 3 fold increase in specific energy at lower rate and 10 fold increase in specific energy at higher rate relative to conventional electrodes, providing opportunity for 2.5 fold cathode mass savings at the lower rate and 14 fold cathode mass savings at the higher rate. This approach could provide a path toward high capacity large form factor cell designs, as required for applications demanding high energy content.

Motivated by heterogeneous catalyst thermal regeneration strategies, a facile cathode recycling process was demonstrated. In this approach, previously used BFSS cathodes are removed from a cell, heat treated, then inserted into a new cell restoring delivered capacity and cycle life. After 200 discharge-charge cycles, the recycled BFSS electrodes display restored crystallinity and oxidation state of the manganese centers with resulting electrochemistry (capacity and coulombic efficiency) reminiscent of freshly prepared BFSS cathodes. This approach demonstrates a conceptually new approach for regenerating active materials where a thermal treatment method previously employed in catalyst systems can fully restore the average oxidation state of the manganese centers, crystallinity, and the battery electrochemical performance.

Current lithium ion battery technology is insufficient for high energy/power applications, such as electric transportation. Conventional lithium ion battery graphite anodes provide stable cycling but a limited specific capacity (372 mAh/g). Replacing graphite with silicon could enable a tenfold increase in capacity with a theoretical limit of 4200 mAh/g. However expansion and contraction of silicon during lithiation and delithiation leads to an unstable solid electrolyte interface, causing degradation of the anode and severe loss in capacity over time. To understand how to stabilize this solid electrolyte interface, we have conducted model studies using thin film silicon anodes. We have achieved successful, stable cycling of 100nm silicon anodes in lithium ion half cells by functionalizing the anode surface with poly(methyl methacrylate) brushes via a facile and robust atom transfer radical polymerization method. The layer of brushes acts as a hydrolytically stable artificial solid electrolyte interface that is able to withstand the large volume changes of silicon during charging and discharging. The electrochemical performance of coated Si anodes were evaluated in half cells (against Li counter electrodes) using 100μL 1.0M LiPF₆ in 1:1:1 EC:DMC:DEC electrolyte and a galvanostatic C/5 rate. Our initial findings show that with very thick polymer layers (>400nm) cycling is stable (>100cycles), but capacity is sacrificed (600 mAh/g). Thus future research is required to investigate minimum polymer thicknesses required to yield stable cycling.

Nanosizing is a promising approach to increase the rate capability of the cathode material in Li-ion batteries [1]. In the present work, we have investigated atomic and electronic structures, magnetic properties, formation energies, and energy barriers for diffusion of Li in single vacancies, divacancies, and missing rows in bulk and surface of LiCoO₂.
Our DFT-PBE results indicate that there is a very low energy barrier for Li-ion deintercalation/intercalation from/into the topmost surface of LiCoO₂. However, we find that Li hopping with PBE+U calculations is accompanied by polaron hopping between nearby Co cations. Therefore PBE+U barriers, which are for both Li and polaron hopping, are higher than the corresponding PBE barriers which are only for Li hopping. We also have found that the ionic bond character between Co and O atoms at the topmost layer of the LiCoO₂(10-14) surface is weaker than that in bulk LiCoO₂, as there are unpaired electrons on O atoms at the surface.
This study helps us to understand the role of surface in the rate capability of nanostructured LiCoO₂ cathodes in Li-ion batteries. Moreover our work provides a qualitative approach to study polaron hopping in semiconductors [2].

[1] M. Okubo, E. Hosono, J. Kim, M. Enomoto, N. Kojima, T. Kudo, H. Zhou and I. Honma, Nanosize Effect on High-Rate Li-Ion Intercalation in LiCoO2 Electrode J. Am. Chem. Soc., 2007, 129, 7444.
[2] A. Moradabadi and P. Kaghazchi, Mechanism of Li Intercalation/Deintercalation into/from the Surface of LiCoO₂, Phys. Chem. Chem. Phys., 2015, 17, 22917

Numerous studies have established that coating high voltage Li battery cathode materials with a protective film can provide enhanced cycling stability and even enhance rate performance. While the exact mechanism by which these coatings lead to enhanced performance is still not clear, it is likely that many coatings require some ability to intercalate and diffuse Li. We have therefore investigated the Li solubility and transport properties of several coating materials (bulk phases), such as Al₂O₃, AlF₃, MgO, ZrO₂, SiO₂, and related those properties to coating overpotential. Furthermore, as many coatings are just a few nanometers or fewer thick, we have also studied the influence of interfaces on the Li intercalation properties between materials with different intercalation voltages. In our studies of coating properties and their relation to overpotential, we propose an Ohmic continuum model for understanding the connection between the coating overpotential and Li solubility, diffusivity, coating thickness, and current density. We use this model and previous studies of Li in amorphous Al₂O₃ and AlF₃ to predict that Atomic Layer Deposited (ALD) Al₂O₃ coatings have a resistivity of 1789 MOhmm (10⁶Ohm●m), which value is qualitatively consistent with that extracted from multiple ALD experiments (ranges from 7.8 MOhm●m to 913 MOhm●m). In order to model the effects of interfaces on the Li energetics we explore the Li intercalation voltage profile across an interface of two materials with different bulk intercalation voltages. The olivine-structured FePO₄-MPO₄ (M=Co, Ti, Mn) and layered-structured LiNiO₂-TiO₂ interfaces provide model cases to understand the physics governing Li intercalation energetics across material interfaces. We find that across the interface from a high to low voltage material (i.e. low to high Li intercalation energy), the Li site energy remains constant in the high voltage material and decays approximately linearly in the low voltage region, approaching the Li site energy of the low voltage material. This effect indicates that the existence of a high intercalation voltage material at an interface can significantly enhance the Li intercalation voltage in a low voltage region over a 1-2 nm scale. We explore possible implications of this interfacial voltage enhancement for the design of novel cathode superlattice structures.

The study of new electrode material with high energy density is crucial for the development of Li-ion batteries, in particular high energy density application such as EV/HEV. Silicon is one of the most promising anode materials for the next-generation Li-ion batteries because of its highest theoretical specific capacity (3590mAh/g, Li₁₅Si₄) which is ten times higher than that of current graphite anode (372mAh/g), low charge/discharge voltage profile and its abundance. Although silicon has many advantages, it suffers from volume expansion during alloying with lithium resulting in pulverization, loss of contact with current collector and capacity fading and from complex and expensive usual growth processes (chemical vapour deposition (CVD) and physical vapour deposition (PVD)). Regarding the first issue, the promising solution relies on Silicon composites, in which “hard material” can preserve from volume expansion and hence improve the cyclic stability.
In this work, we are addressing both previous issues, knowing the volume expansion and the growth process. To do so, we have developed an innovative low cost and large scale two step electrochemical process to synthesize noble nanostructured composite electrodes. This composite is made of self-organized titania (TiO₂) nanotubes coated with different silicon loading on both amorphous and crystalline titania. TiO₂ nanotubes have been chosen to play the role of silicon volume expansion buffer.
Firstly, self-organized TiO₂ nanotubes array are synthesized by simple anodization process. Secondly, we have fabricated Si/TiO₂ nanotubes composite anode by electrodeposition from ionic liquid, a room temperature operating process which exhibits many benefits for controlling the morphology and structure of the nanostructured silicon growth.
Silicon is deposited on amorphous and crystalline TiO₂ nanotubes from electrolyte solution of SiCl₄ in 1-butyl-1-methylpyrrolidium bis (trifluoromethylsulfonyl) imide ([Py_1,4]TFSA) ionic liquid. The morphology and the structure of the nanostructured electrodes have been studied by SEM, TEM and XRD. The charge/discharge performances of the electrodes have been tested in Li-ion coin cell by electrochemical test. Both components of the composite are electrochemical active for lithiation/delithiation delivering a total first charge capacity of 0.26mAh/cm² and 0.21mAh/cm² retained to 0.22mAh/cm² and 0.17mAh/cm² for Si/amorphous-TiO₂ and Si/crystalline-TiO₂ after 5 cycles respectively.
Si/TiO₂ composites, directly grown on current collector, provide an easy electron transport without any need of adding binder or conductive additives. Besides, free space inside and in between nanotubes can give a free space for silicon volume expansion preventing from pulverization. Finally the roughness of the titania wall enhances the adhesion of silicon, and by the way the advantage of the composite. All of this demonstrate the performances of the composite as anode for Li-ion battery.

LiNi_0.8Co_0.15Al_0.05O₂ (NCA) has been widely used as cathode in commercialized lithium-ion batteries (LIBs), but its fundamental electrokinetic properties are still poorly understood. Studies of diffusivity and conductivity of bulk NCA at different states of charge (SOC) have previously been investigated using single-phase dense samples¹. Based on that, we attempt to understand the electrochemical charge-transfer reaction at the liquid electrolyte/NCA interface, and determine the rate-limiting transport factors for NCA cathode as a function of state-of-charge.
The rate of interfacial reaction rate at solid/electrolyte interface is characterized by an exchange current density, which is the materials-specific parameter encompassing the effects from solid structure and interface composition. Herein, we applied two methods - electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT) to study the exchange current density of NCA at different SOC using the same dense samples². The exchange current density as measured by both EIS and PITT decreases by over an order of magnitude upon delithiation.
Based on the measured exchange current density and bulk diffusion coefficients, the relative rates of diffusion and interfacial reaction can be determined as an electrochemical Biot number. In the case of 75% SOC, with decreasing particle size, the maximum C-rate when limited by either diffusion or interfacial reaction decreases. For typical commercial NCA particle sizes of 5-30 µm, the interfacial reaction is clearly rate-limiting.

This work was supported as part of the North East Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012583.

[1]. R. Amin, D.B. Ravnsbaek, Y.-M. Chiang, J. Electrochem. Soc. 2015, 162, A1163-A1169.
[2]. J. Li, X. Xiao, F. Yang, M. W. Verbrugge, Y.-T. Cheng, J. Phys. Chem. C. 2012, 116, 1472–1478.

The development of durable and high capacity lithium-ion batteries requires a deep understanding of the reactivity at the electrode/electrolyte interface and the impact on the battery performance. The composition, properties and mechanisms behind electrolyte/electrolyte interface on positive electrode are still unknown for most of the lithium ion battery materials, whereas the EEI layer on negative electrodes (also referred as Solid Electrolyte Interphase) is well known especially for graphite and lithium metal [1]. In particular, at high voltages, when the limit of the oxidative stability of the electrolyte is reached, new mechanisms, such as the evolution of oxygen from the oxide lattice or the formation of active oxygen intermediates like surface peroxide or superoxide, can also contribute to the interfacial reactivity and change the nature of the EEI layer.
By using X-ray Photoelectron Spectroscopy (XPS) on LiCoO₂, and NMC electrodes with different Ni content we show how the nature of the EEI layer depends on the chemistry of the oxide and on the applied voltage. We highlight the importance of using model electrodes containing only the active material, without conductive agents and polymeric binders that can modify the EEI layers on the electrode [2]. The comparison of different XPS results points to a strong dependency of the surface reactivity on the electrode composition and lithiation state.

[1] M. Gauthier, T. Carney, A. Grimaud et al., J. Phys. Chem. Lett. 6, 4653 (2015).
[2] M. Gauthier et al., in preparation.

Lithium ion batteries (LIB) have drawn significant attention for the past decades as the primarily energy storage units in portable electronics. However, they barely meet the ever increasing performance demands for recent applications such as electric vehicles (EV). While the overall energy density of the battery is limited by the capacity of the cathode materials, prolonged safe application of the LIB systems suffered from the performance of anode materials. Most commercial cathodes in EV, i.e. LiCoO₂ and LiFePO₄, exhibit electrode energy between 560 mWh/g to 600 mWh/g. which could deliver battery energy density between 150 mWh/g to 300 mWh/g when combining with carbon anode. This number is smaller when safer Li₄Ti₅O₁₂ is used as carbon anode suffer from structure instability and rapid solid electrolyte interface (SEI) layer formation. To fulfill the US government’s standards of future EVs, energy density of the cathode material will have to be enhanced and a safer anode is also required.
Herein with our research, we were able to activate Ni²⁺/Ni³⁺ redox couple above 5.1 V within olivine type LiNi_xFe_1-xPO₄ solid solution materials by chemical delithiation. Combined with high voltage electrolyte this material can potentially increase the mainstream cathode capacity by as much as 40%. On the other hand, anatase TiO₂ based anode materials with high structure stability for safe applications were studied. TiO₂ and TiO₂/CNT core-shell nanofibers were prepared using eletrospinning. Interwoven morphology of fibers built a hollow framework through which the ternary interface of anode, electronic conductor and electrolyte were increased. Specific capacity as high as of 249 mAh/g at C/10 and 32.5% capacity retention at the 10C rate were obtained from as synthesized fiber in a coin cell setup. Enhancement in electrochemical performance was attributed to the increase of electronic conductivity and lithium diffusivity, as confirmed by impedance spectroscopy and GITT method. Trace amount CNT loading was found to be most effective in enhancing the electrode performance. Post hydrogen treatment also proved to be beneficial for high current operations.

In the design and manufacture of a Li-ion battery, an electrically conducting binder is added to the slurry in order to facilitate a conductive charge pathway. While it is clear from empirical experiments that this binder plays an important role in the charge transport between the active materials, the binder distribution and the corresponding function of its actual 3D assembly remains largely a mystery, especially in graphite electrodes. This is due, in part, to difficulties in imaging and segmentation of the carbon-rich conductive binder from the graphite particles typically used in a positive electrode, which present a unique characterization challenge for 3D analysis.

The present study has been designed to reveal the 3D nature of the binder distribution by means of a contrast enhancement method. Functionalized iron nanoparticles were added to the typical conductive carbon. 3D imaging was performed using a pair of X-Ray microscopes (XRMs) employing the method of X-Ray computed tomography, in which the Fe nanoparticles were easily visualized because of iron’s much higher atomic number. Sub micron-scale XRM was initially employed in order to survey the pore networks and identify the appropriate representative volume element based on porosity, and then nano-scale XRM was used to image that volume with higher resolution and segment the conductive (Fe-doped) binder.

Analysis of the results yielded a 3D map of the binder thickness distribution, contact surface area, and porosity. Employing an effective diffusion coefficient simulation allowed the pore-space tortuosity to be measured, and electrical conductivity simulations yielded a 3D measurement of electrical conductivity as well as a 3D visualization of the potential gradient across the electrode. Furthermore, the role of conductive additive was studied by simulating a uniform coating of conductive binder around the particles with two different thicknesses, comparing this to the case of no binder. By further comparing these results to the electrical conductivity from the actual pathway as prepared with contrast enhancement, we were able to show, for the first time, the influence of slurry preparation procedures on electronic conduction with a Li-ion battery, and study the deviations between actual electrodes and theorized models that are based on assumptions of uniformity.

A novel and simple strategy to synthesize cobalt oxide decorated reduced graphene oxides (CoO-rGO) nanocomposites was successfully developed as the anode materials for lithium ion battery (LIB) application. The CoO-rGO nanocomposites are prepared by simultaneous reduction of GO and Co²⁺ in the presence of NaBH₄. Addition of 15 wt% rGO can produce a narrow size distribution of ultra-fine CoO nanoparticles with mean particles size of 4.5 nm, which exhibits the closely nano-dimensional contact between CoO and rGO for the excellent electrochemical performance. The first reversible capacity of CoO-rGO nanocomposites ranges between 1140 and 1260 mAh/g at the current density of 150 mA/g and maintains at 473 mAh/g at 2400 mA/g. In addition, a reversible capacity of 652 mAh/g is achieved at 600 mA/g after 60 cycles. The electrochemical impedance spectra shows that the charge transfer resistance decreases significantly after 60 charge-discharge cycles, resulting in the increase in reversible capacity when the current density recovers to 150 mA/g. In addition, XPS spectra and XRD patterns of CoO-rGO after cycling clearly indicate the involvement of electrolyte into CoO nanoparticles during intercalation-deintercalation cycling, and then transforms the Co species from Co²⁺ to Co³⁺ for the enhancement of electrochemical performance at high current density. Results obtained in this study provide a new avenue to fabricate metal oxide-rGO based nanocomposites as the anode materials for high performance of LIB application.

The applications of lithium-ion batteries (LIBs) is expanding toward macroscale energy storage systems such as electric energy-based transportation and smart grids, to replace the existing fossil fuels-based energy industries. However, safety issues on LIBs are still exist and accidental explosions of batteries are occasionally reported. The high voltage anode materials have greatly relieved the unstable state of LIB during operation because they circumvent the uneven plating of lithium and oxidative electrolyte decomposition. Although various titanium based oxides have been developed as high voltage anodes, low capacity or poor potential flatness still severely hinder their wide commercialization.
H₂Ti₁₂O₂₅ (HTO) was recently discovered as an anode material for LIB and has outstanding electrochemical performance compared to other high voltage materials (e. g., Li₄Ti₅O₁₂). However, its thermodynamic/kinetic properties as a lithium ion host have not been thoroughly investigated yet. In this study, the Li storing behavior of HTO was intensively characterized with theoretical and experimental studies. In addition, the close dependence of electrochemical performance on Li diffusion kinetics stimulates the development a nanostructured HTO which provides incorporated Li with a short diffusion length inside a nano-crystal. As a result, the nanostructured HTO showed improved Li storage performance. This work suggests the HTO as one of the most competitive anode material found to date for the construction of advanced LIB with enhanced safety and stability.

Since the introduction of Li-ion batteries carbonaceous materials have been used as commercial anode materials. Graphite anodes exhibit excellent capacity retention, high Columbic efficiency, good rate capability, low voltage hysteresis, and low volume expansion during the charge-discharge process but a low theoretical capacity of 372 mAh g^-1. However, the rapid advances in the energy storage industry vigorously demand further gravimetric and volumetric energy density increases for Li-ion batteries. In this regards, group IVA materials (e.g., Si, Ge, and Sn) have attracted much attention as promising alternative to graphite anode due to their high specific capacities. Among them, Si has recently gained attention as promising anode materials because of its high specific capacity and low discharge potential. Despite attractive features, the use of Si alloy anode in practical Li-ion cells is still limited by the severe capacity fading due to a volume change that occurs during Li-ion insertion and extraction. To solve this problem, many studies have focused on buffering the volume expansion to overcome the drawback associated with Li-ion anodes. The nanostructured materials are expected to provide voids to accommodate volume changes and to allow effective strain relaxation during cycling. In addition, the formation of a carbon shell around the active nanoparticles significantly improves the electrochemical performance. In this case, the carbon shell prevents the aggregation of active materials and increases the chance of electrical contact, which may occur during cycling. On the basis of its preparation, thermal decomposition of a carbonaceous polymeric precursor on the surface of active particles is a common preparation method. Better cycling performances can be achieved by using homogeneous carbon layers with an appropriate thickness on the active nanoparticles for composite anodes than that achieved by using pure metal anodes.
In this study, we will present surface modification of Si nanoparticles modified with nitrogen doped carbon layers to enhance the electrochemical performance. The surface modified Si have been prepared by using a simple pyrolysis of nitrogen containing ionic liquid to provide structural stability against the volume expansion-contraction and offered improved electrochemical conduction path ways. Furthermore, we have investigated the possibility of usage in anode material for lithium-ion battery applications.

NASICON-type structured materials (Na Super-Ionic Conductor, with space group R-3c) are promising solid electrolytes with total ion conductivity of about 10^-4 to ~10^-2 S cm^–1. [1]
Due to the very high bulk Li⁺/Na⁺ conductivity in this class of materials the corresponding arc in the complex impedance plane response in the high MHz range and can be only resolved at very low temperatures. [2,3] Determination of the ionic bulk conductivity is strongly simplified when large sized single crystals are available; as for polycrystalline pellets macroscopic electrodes may be used in electrical measurements and electrical properties can be determined without being restricted by the need for a proper separation of partly large grain boundary resistances. Here, a modification of conventional impedance spectroscopy comes into play: microelectrodes deposited on large single crystals or grains of a polycrystalline sample still allow impedance measurements which are unaffected by the resistivity of grain boundaries. [4-6] This is caused by the spatially very constricted current distribution between neighboring microelectrodes. However, so far this technique of local impedance measurements was rarely applied to determine bulk Li⁺/Na⁺ conductivities.
In this contribution microcontact impedance spectroscopy and single crystal X-ray diffraction were applied to small Li_1+xAl_xTi_2-x(PO₄)₃, and Na₃Sc₂(PO₄)₃ single crystals to exactly determine the ionic bulk conductivity and crystal structure, respectively. [7,8] This enables a precise analysis on transport properties and a better understanding of the structure–property relationship of Li⁺/Na⁺-based NASICON-structured materials.

[1] Aono, H., Sugimoto, E., Sadaoka, Y., Imanaka, N., Adachi, G. J. Electrochem. Soc., 1990, 137, 1023.
[2] Breuer, S.; Epp, V.; Ma, Q.; Tietz, F.; Wilkening, M. J. Mater. Chem. A, 2015, 3, 21343.
[3] Wang, S.; Ben, L.; Li, H.; Chen, L. Solid State Ionics, 2014, 268, 110.
[4] Fleig, F.; Rodewald, S.; Maier, J. J. Appl. Phys., 2000, 87, 2372.
[5] Rodewald, S.; Fleig J.; Maier, J. J. Am. Ceram. Soc., 2001, 84, 521.
[6] Fleig, J.; Rodewald S.; Maier, J. Solid State Ionics, 2000, 136-137, 905.
[7] Rettenwander, D.; Welzl, A.; Pristat, S.; Tietz, F.; Redhammer, G.; Fleig. J. J. Mater. Chem. A, 2016, 4, 1506.
[8] Redhammer, G. J.; Rettenwander, D.; Pristat, S.; Dashjav, E.; Kumar, C. M. N.; Topa, D.; Tietz, F. Solid State Chem., 2016, under review.

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising electrolyte material for all-solid-state battery due to its high ionic conductivity and air stability with metallic lithium. LiNi_0.5Mn_1.5O₄ (LNM) is an attractive candidate for the practical preparation of 5 V cathodes due to its good stability on repeated Li-ion deintercalation and intercalation. In the present work, we fabricated Li/LLZO/LNM all-solid-state lithium battery using RF magnetron sputter deposition and thermal evaporation. The crystal structure of each thin film was investigated by X-ray diffraction (XRD). The microstructure and surface morphology of thin films were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ion-conductivity of the thin film was measured by an AC impedance method. The electrochemical properties of the thin films were studied with cyclic voltammetry (CV) and charge-discharge cycling test.

Electronic and ionic transport properties of single particles of existing and future electrode materials such as Li(Mn,Fe)PO₄ or Li₂(Mn,Fe,Co)SiO₄ are of great interest for optimizing energy storage devices. Especially systematic studies on the single particle level are needed to yield further insights into the influence of grain boundaries or structural changes during cell operation on the transport processes in electrodes prepared from slurries containing the active material. Hence, we present a design for an electrochemical cell which in combination with micro- and nano-patterning techniques can be used to measure electronic and ionic transport in single particles of active electrode materials, which typically exhibit diameters of about 20 µm. During charging and discharging the cell or performing electrochemical impedance spectroscopy (EIS), in situ Raman spectroscopy can be applied to obtain additional information about structural changes. The particles are arranged by patterning an SU-8 layer on top of a TCO-electrode and remain accessible for Raman spectroscopy during cell operation. By adjusting the pattern transferred into the SU-8 layer, measurements on defined arrangements of few particles can be performed to characterize their transport and structural properties. This allows us to correlate electric transport properties with structural changes of single particles or with the contacts between particles itself in different particle arrangements as well as contacts between particles and the electrode surface. Such a systematic study should yield a full microscopic understanding of the complex transport behaviour in these materials, which is necessary for optimizing and developing future battery materials.

Lithium rich layered cathodes, which offer increased capacity, have, for several years, been regarded as one of the next major advances, able to store charge by invoking transition metal and oxygen redox processes in the same material. However, they are still challenged by problems such irreversible first cycle capacity, voltage fade on cycling related to changes in the structure. Recently important work has been carried out to better understand the origin of the high capacity and the voltage fade.
In this contribution we shall present data probing the nature of the O redox states in Li rich 3d transition metal oxides, on the nature of O loss probed by isotopic substitution and on the degree of oxygen loss vs oxygen redox. We shall also report on a new sol-gel synthesis for Li_1.2Mn_0.54Ni_0.13Co_0.13O₂. The electrochemical performance is shown in Figure 1. The cycling stability of the material is good with a capacity of ~250 mAh g^-1 maintained after 100 cycles.

Sn as an anode in lithium ion batteries offers large theoretical charge capacity, but also exhibits irreversible capacity loss through mechanical degradation. This occurs due to the large volume changes associated with the formation of different phases during lithiation. To relate the volume changes to the corresponding stress, it is necessary to know the elastic modulus of each phase. Here, we report measurements of the elastic modulus of a Sn anode at different state of charge. The modulus is determined from the elastic response of the lithiated Sn film to a small-scale delithiation as measured by in situ substrate curvature during the electrochemical treatment. Ex situ X-ray diffraction (XRD) is used to identify the lithiated phases formed. Focused ion beam (FIB) milling is done after the experiments to measure the thicknesses of the lithiated phase, which are used to interpret the curvature data in terms of stress evolution from the lithiation experiments. The analyzed bulk modulus of the lithiated phases is compared with the simulation results reported in the literature.

Solid-state electroreduction of metal oxides is critical since it relates to the charge/discharge of various energy storage devices. In the electroreduction of some oxides with aqueous electrolyte, such as NiO₂ and MnO₂, H⁺ ions diffuse inside oxides, and the reaction is shown in equation (1):
MO₂ + H⁺ + e^- = MOOH (M = Ni or Mn) (1) Researchers have reached a consensus that H⁺ diffusion from outside to inside of the particles is the rate-limiting step. In the electroreduction of some oxides with non-aqueous solvent and Li salt such as Nb₂O₅, V₂O₅, MoO₃ and Fe₃O₄, Li⁺ diffusion inside oxides is the rate limiting step and these electroreductions are intercalation reaction. However, for some metal oxides, H⁺ ions do not diffuse inside particles during their reduction in aqueous electrolyte; or Li⁺ ions do not insert the particles in non-aqueous electrolyte. For instance, during the electroreduction in alkaline based aqueous solution, Fe₂O₃ is first reduced to Fe₃O₄ and CuO is reduced to Cu₂O or Cu; in non-aqueous electrolyte, MO (M = Ni, Co, Cu, Fe, and Mn) is reduced to metal and O^2- from the cleavage of M-O combines with Li⁺ to form Li₂O. These electroreduction reactions are conversion reaction. To the best of our knowledge, there is no consensus about the reaction mechanism of this kind of reactions, which have no ion (such as: Li⁺ and H⁺) diffusion into particles. Which step is their limiting step is no determined. Understanding the limiting step is critical because one of the obstacles to utilize these metal oxides in energy storage system is their low rate performance. Determining the reaction mechanism, especially the rate-limiting step of the reduction reaction, can provide some clue to overcome the obstacle.
A type of metal oxide electroreduction reaction is summarized in this study, and the characteristic is no ion diffusion from electrolyte into oxide particles during their reduction. A common rule is generalized about the reaction process: reduction process includes five elementary steps, and O^2- diffusion from their bulk toward outside is the limiting step, especially at the high scan rate. The relationship between peak current density in the CV profile and scan rate supports this point directly. The particle size of metal oxides can affect the shape of CV profile, cathodic peak potential and reduction reaction rate, because all these electrochemical properties depend on ionic overpotential associated with O^2- diffusion distance inside oxides. The O^2-diffusion efficient inside a-Fe₂O₃, γ-Fe₂O₃, Fe₃O₄, CuO and Bi₂O₃ are estimated in the study. The rule is suitable for all the metal oxides, when no H⁺ ions diffuse into particles during reduction process in aqueous electrolyte, or the reduction is the conversion reaction with Li⁺ containing non-aqueous electrolyte during their reduction process.

A unique multi-shelled SnCuO₃ nanosphere is successfully synthesized using carbon sphere as sacrificial template. This ternary metal oxide is found to be very suitable for solving the critical volume expansion problem and mass transfer property due to its high surface area and hollow structure, which is critical for high capacity metal oxide electrodes for lithium ion batteries. Then covalently interconnected three-dimensional graphene foams encapsulated multi-shelled SnCuO₃ nanospheres are successfully obtained through chemical cross-linking and self-assembly of graphene oxide nanosheets and SnCuO₃ nanospheres. The three-dimensional graphene networks could greatly improve the cycling stability and rate capability of the multi-shelled SnCuO₃ spheres electrodes due to the flexible buffering matrix and highly conductive networks. As a result, the three-dimensional graphene encapsulated triple-shelled SnCuO₃ spheres anodes exhibit a high reversible capacity of 650 mAh g^-1 even after 500 cycles at the current density of 200 mA g^-1. These excellent electrochemical performances are ascribed to the large specific surface area of the multi-shelled SnCuO₃ spheres that facilitate lithium diffusion and storage, while the porous thin shells and the flexible graphene sheets could buffer mechanical stresses that accompany volume changes. Furthermore, this strategy using covalently interconnected three-dimensional graphene foams encapsulate the multi-shelled SnCuO3 spheres not only develops a high performance anode material with long cycle life but also holds great promise for flexible binder-free for lithium ion batteries.

Micron-scale, high aspect ratio cathodes (LiMn₂O₄, or LMO) and anodes (Li₄Ti₅O₁₂, or LTO) for 3D Li-ion microbatteries were fabricated by the solution-based soft imprinting lithography. LMO and LTO nanopowders were well dispersed to form homogeneous inks stabilized by polymer surfactants or small molecule acids and directly patterned into micron-scale lines with 10 μm pitch, 2 μm line width and 5 μm height on gold coated substrate, which serves as a current collector, and annealed at elevated temperature. A full battery was assembled by spincoating the opposite electrode ink onto the imprinted one, forming a microbattery with an interdigitated electrode architecture. The high aspect ratio of the electrode provides efficient packing of functional materials in the out-of-plane z-direction and the interdigitated architecture ensures a short ionic path between electrode fingers, which enables enhancement of the energy and power densities at the same time. Cyclic voltammetry and galvanostatic charge/discharge tests were conducted on both the half cell and full battery. Excellent electrochemical response was measured and the microbattery is promising to serve in many applications including on-chip power sources for MEMS.

The electrode-electrolyte interfaces (EEIs) play important roles in lithium ion batteries, often determining the capacity retention, safety and lifetime. The EEI of the positive electrode is far less understood than its negative counterpart. In addition to possible electrolyte oxidation products, layered cathodes often exhibit pronounced surface phase transformations that can also limit the performance of the battery. For example, recent experiments have correlated charge-transfer impedance growth with surface phase transformations at Li_1-xNi_0.80Co_0.15Al_0.05O₂ (NCA) surfaces, which result from surface oxygen loss.[1] Alumina coatings are often employed to suppress surface oxygen loss in layered oxides, but the exact mechanism remains unclear since even a single monolayer of alumina can result in 90% capacity retention for LiCoO₂ cathodes over 100 cycles.[2] Density functional theory (DFT) studies have since suggested that autocatalytic HF reactions are responsible for degrading the surface of LiCoO₂, and that partially fluorinated alumina surface species can scavenge HF thereby halting the degradation mechanism.[3]

Here we report on our surface studies of NCA, to examine the evolution of the intrinsic surface aluminum for electrochemically and thermally stressed NCA electrodes. In addition to conventional x-ray photoelectron spectroscopy (XPS) and soft x-ray absorption spectroscopy (XAS), we employ hard x-ray photoelectron spectroscopy (HAXPES) of the Al 1s core-level to uniquely study the local chemical environment of the surface aluminum. As a result, we are able to correlate chemical changes and phase transformations with the evolution of the surface aluminum. We present evidence supporting autocatalytic reactions involving HF as being responsible for degrading the NCA surface. Furthermore, we show that the degradation is suppressed by the formation of Al-O-F species. Our work provides insight into how alumina coatings improve the capacity retention of layered cathodes.

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

[1] S. Sallis et al., App. Phys. Lett. (2016) in press
[2] I. D. Scott et al., Nano Letts. 11 (2011) 414
[3] J. T. Tebbe et al., ACS Appl. Mater. & Interfaces 7 (2015) 24265

Recent studies on Li₄Ti₅O₁₂ (LTO) have converged into overcoming its poor conductivity through employing conducting surface layers such as graphene. Most commonly used graphene can be obtained by the reduction of graphene oxide that is prepared through Hummers' method, however, often shows ionic impurities and remains unexfoliated. Such irregularly deposited thick graphene layers impeding Li⁺ diffusion stand detrimental to the rate capability. To tackle this drawback, high purity graphene oxide was prepared by thorough cleaning and dialysis, which enables a facile Li-ion diffusion. The resulting single-layer graphene-wrapped LTO synthesized via solid state reaction exhibits an excellent specific capacity of 130 mAh g^-1 even at a lithiation/delithiation of 30 C. In this study, decoupling of electric conduction and Li⁺ diffusion was investigated by layer by layer control of graphene wrapping process, thereby leading to high battery performance of graphene wrapped LTO.

[1] Y. Oh, S. Nam, S. Wi, J. Kang, T. Hwang, S. Lee, H. H. Park, J. Cabana, C. Kim, and B. Park, J. Mater. Chem. A 2, 2023 (2014).
[2] S. Nam, S. J. Yang, S. Lee, J. Kim, J. Kang, J. Y. Oh, C. R. Park, T. Moon, K. T. Lee, and B. Park, Carbon 85, 289 (2015).

Corresponding Authors: Byungwoo Park: [email protected]
Sang Ouk Kim: [email protected]
Chunjoong Kim: [email protected]

In recent years, lithium ion battery has been widely used on portable electronic devices and electric/hybrid vehicles because of its high energy density and cycling stability. As an anode material for the lithium ion battery, Silicon(Si) is getting attention for its high theoretical specific capacity (about 4200mAh/g) and its proper potential range for lithium insertion and extraction. However, Si has properties that could be obstacles for its practical use as the lithium ion battery anode. Si not only has low intrinsic electric conductivity but also undergos severe volume changes during the lithium ion insertion/extraction process which results in pulverization of the electrode materials, causing the capacity to fade. To overcome these problems and enhance the electric conductivity, we synthesized Silicon/Carbon composites as an anode material. Si/C composites were prepared by two step method, including magnesiothermic reduction of SBA-15(Santa Barbara Amorphous material No. 15) and carbonization of phenol resin. The electrochemical performances of Si/Carbon composites were investigated to find the effect of binders and an electrolyte additive by charge/discharge, cyclic voltammetry and impedance tests. The anode electrode of Si/C composite with PAA binder appeared better capacity(1,899 mAh/g) and the capacity retention ratio(92%) than that of other composition coin cells during 40 cycles. Also, Vinylene carbonate(VC) was tested as an electrolyte additive. The influence of this additive on the behavior of Si/Carbon anodes was very positive(3,049 mAh/g), since the VC additive is formed passivation films on Si/C surfaces and suppresses irreversible changes in electrolyte solution.

Silicon is a promising anode material with a high theoretical specific capacity (~4200 mAh g^-1) for lithium-ion battery applications. However solid silicon particles suffer the breakdown due to the large volume change during the lithiation/delithiation. One way to overcome the shortcoming is to utilize porous silicon from metallothemic reactions. Nature provides us a lot of porous bio-derived silica materials (e.g., diatom frustules, rice husk). Metallothermic reactions, including magnesiothermic and aluminothermic reductions, could convert them into silicon and corresponding metal oxides. After subsequent removal of the metal oxides in hydrochloric acid solution, porous silicon with hierarchical porosity was finally obtained. The formed hierarchical porosity could facilitate the charge/mass transfer, enhance the utilization of the active material and promote its electrochemical performance. Nonfilling coating could further improve its performance. The optimized specific capacity could reach 1800 mAh g^-1 at 1 A g^-1 even after 100 cycles. Since temperature of metallothemic reactions spanned a wide range (300-700 ^oC), silicon materials with various porous structures could be synthesized. Their electrochemical performance was summarized and compared, and the influence of hierarchical porosity on the performance was analyzed. The study will promote the design of electrode materials for energy storage.

Inorganic solid Li ion conductors have attracted great interests for new electrolytes in Li ion batteries because of its superior properties compared with current commercial polymeric Li ion conductors, i.e., electrochemical and thermal stability, resistance to vibrations, and compact manufactures. However, the ionic conductivity of solid electrolytes is usually two or three orders of magnitude lower than that of liquid electrolytes, and hence further improvement is necessary for the actual lithium battery application. One of the best inorganic solid lithium ion conductors is Li_3xLa_2/3-xTiO₃ (LLTO) (0The LLTO specimen was prepared by sintering method, where a powder mixture of Li₂CO₃, TiO₂ and La₂O₃ was annealed at 1250°C for 12 h. The chemical composition of the resultant pellet was determined to be Li_0.33La_0.56TiO₃ using inductively coupled plasma analysis. For the measurement of Li ion conductivity, ESM imaging was performed, where we can obtain two dimensional conductivity map with sub-micrometer spatial resolution. At first, we identified crystal orientation of grains by using EBSD and then measured Li ion conductivity by ESM method at the corresponding area. The experimental results show that Li ion conductivity becomes lower along the grain orientation close to [111]. We also revealed that Li ion conductivity becomes lower along the random grain boundaries, while the higher symmetric grain boundaries such as Σ5 does not prevent ionic conductivity (along the boundary). Detailed discussion will be given in this presentation.


Acknowledgement. A part of this work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING2) project of the New Energy and Industrial Technology Development Organization (NEDO), Japan, and was also conducted in the Research Hub for Advanced Nano Characterization, The University of Tokyo, under the support of "Nanotechnology Platform" (Project No.12024046) by MEXT, Japan.

We prepared elongated ZnO nanowire (NW) with length up to 1 mm by a simple selective adsorption surfactant to the polar surface of ZnO. We found that the mechanism of elongated ZnO NW growth was attributed to the acceleration of the growth rate of the Zn²⁺ terminated (0001) face of ZnO by the attachment of cation on the (000) O^2--terminated face. During the ZnO NW in the hydrothermal reaction, the cation surfactant, tetraethylammonium tetrafluoroborate (TEFB), was strongly adsorbed on the (000) O^2--terminated face, which result in the acceleration of stacked ZnO hexagonal subunits in the direction of c axis. The LIB devices based on the ZnO NW stacking of ZnO nanocrystal network electrode materials, from alternating binding of charged crystal, exhibits superior electrochemical performance with high-rate capacity with a high reversible specific capacity as well as an excellent cycling performance, corresponding to a Coulombic efficiency of 99.9%.

Carbon coated hexagonal polycrystalline Co-ZnO nanosheet (Co-ZnO NS) have been fabricated as a anode for the Li ion batteries by the simple carbonization of shape controller at 350 ^oC in argon gas. The hexagonal Co-ZnO NS has been synthesized by acceleration of lateral direction of initial hexagonal Co-ZnO nanocrystal using an anion surfactant, sodium dodecyl sulfate (SDS). The structure of Co-ZnO NS was consisted of the interconnection of the single crystal of Co-ZnO, which gives the porous structure to accommodate the volume expansion of Co-ZnO during the charge process. The carbon coating on the Co-ZnO to increase the electrical conductivity was directly accomplished by the carbonation of shape controller, SDS, followed by the calcination at 350 ^oC. Carbon-coated-Co-ZnO NS (thickness of 10 nm carbon) exhibits the remarkable high specific capacity and improved cycle performance. It shows a superior initial specific capacity of 300 mAhg^-1 compared to a current density of 100 mAhg^-1. The initial capacity was maintained 80% after 100 cycles at the 1C rate and Coulombic efficiencies of 99% over 50 cycles. The high performance is attributed to robust Co-ZnO micro-porous structure and high electrical conductivity due to the connectivity of the Co-ZnO nanoparticles.

The transition metal oxides have been extensively explored to replace carbonaceous anodes in Li-ion batteries because of their potential physicochemical properties. They can define two different mechanism by reaction with lithium, such as intercalation and conversion reactions, by reaction with lithium. The first, the intercalation-type materials (e.g, Li₄Ti₅O₁₂, TiO₂, MoO₂) with multiple-dimensional structure can reversibly insert lithium-ion into the lattice without destroying the crystal structure but specific capacity is limited. While conversion-type materials, such as CuO, NiO, Co₃O₄, Fe₃O₄, are usually decomposed as metallic particles embedded in an insulating Li₂O matrix. However, these materials have higher gravimetric specific capacity than that of already-commercialized graphite, structural instability and poor electrical conductivity during the cycling are the drawback. Among the transition metal oxides, niobium-based oxide as intercalation-type materials have been extensively investigated as anode materials for Li-ion batteries. They can offer safety advantage that surface reactivity with the electrolyte occurs less to form solid-electrolyte interphase (SEI) layer. Case of orthorhombic Nb₂O₅, on addition, a stable charge–discharge process can permit by crystal structure because empty octahedral sites between (001) planes provides Li-ion transport tunnels. However, it has poor electrical conductivity and reduces the charge transfer. Interestingly, the lithium insertion/extraction kinetics could be enhanced significantly by several approaches. The electronic conductivity can be effectively improved by conductive material (i.e., carbon) or cation/anion doping. In addition, the nano-structured materials with a large surface area are expected to increase lithium-ion insertion/extraction kinetics by shorter diffusion pathway, resulting in excellent power density.
We will present here a solvothermal synthesis without any surfactant assistance to obtain carbon-decorated dual-type niobium-based spherical particles with nanosize building-block morphology. The as-synthesized samples are explored as negative electrode materials for Li-ion batteries that exhibits superior electrochemical properties compared to pristine Nb₂O₅ and TiNb₂O₇ sphere. Also the effect of the amorphous carbon layer thickness for as-synthesized samples on the electrochemical performances is investigated.

There is growing interest in lightweight, flexible, thin and safe energy storage devices to meet the strong needs for wearable devices. Paper is lightweight, flexible, low-cost and environmentally friendly, so it can be a suitable substrate for flexible electronics. In addition, by utilizing the roughness of paper, the reaction area of active materials can be maximized. Here we report paper-based flexible battery through facile fabrication process. Electrodes were made by solvent-free method, and all the fabrication process was conducted in ambient condition. The resulting freestanding cell showed mechanical stability, and the performance was maintained under bending condition. In-series structure utilizing novel origami method was successfully realized in small area, thereby high output voltage was achieved. This work suggests that paper can be efficient solution for low-cost energy storage devices.

It is well-known that LiNi_0.80Co_0.15Al_0.05O₂ (NCA) is useful cathode material of rechargeable lithium-ion batteries for large-sized devices such as EVs because of its high power density, thermal stability and chemical stability. Generally their positive electrodes are fabricated by coating a cathode electrode ink paste on a metal sheet. The ink paste is produced through mixing, kneading and dispersing of cathode material powder, conductive powder and binder with solvent. However, the ink paste using NCA has a water resisting problem; Li ion in NCA easily is dissolved in water containing in the solvent, leading to a crosslinking reaction of the binder, namely, gelling. It prevents production with stable quality. Moreover, life elongating of the lithium ion battery has been required for the vehicle uses. In this study, to address these issues, we synthesized NCA having Al-rich surface layer. Its characteristics, water resistivity and electrochemical performance were investigated and compared with the pristine NCA.
Powder of NCA was prepared in a laboratory scale by a solid state reaction between lithium hydroxide and hydroxide co-precipitate of transition metals. Then, fluidized NCA powder and mist of solution containing aluminum triisopropoxide were mixed in a chamber, followed by a heat treatment in oxygen atmosphere, resulting in NCA with Al-rich surface layer. Accelerated water resisting test was performed using cathode electrode ink paste with additive water and confirmed that the NCA with Al-rich surface layer showed better waterresisting property than the pristine NCA. The positive electrode fabricated using the cathode materials were assembled into 2032-type coin cell with graphite negative electrode and LiPF₆ in ethylene carbonate-diethyl carbonate as the electrolyte in an argon-filled glove box. The electrochemical measurement revealed that the Al-rich surface layer effectively contributed to improvement of charge-discharge cycle life performance. SEM observation of cathode materials after the cycling test revealed that the pristine NCA had many gaps among primary particles in the secondary particle, while the NCA having Al-rich surface layer did not. Therefore, the Al-rich surface layer improved the breakdown strength of the secondary particles during the charge-discharge cycling, leading to prevent the formation of isolated primary particles which do not contribute to the charge-discharge behavior.

Recently, all-solid-state batteries (ASSBs) have received much attention due to their high safety, reliability, and long cycle life. For the last two decades conventional ASSBs fabricated by using thin film technologies have been thoroughly investigated. They have been also developed as micro-batteries because of their low specific capacity. Their specific capacities depend on the thickness of the cathode electrode.
One of the main challenges of ASSBs is to increase its specific capacity for application in electric vehicles and energy storage systems (ESS). However, many attempts to increase the electrode thickness have not been successful because micro-cracks between the components are formed as a result of stress generated at the solid electrode-electrolyte interface during sintering process. In this case, the control of the thermal expansion coefficient of solid electrolyte or active material has been suggested as an effective method.
In this work, the thermal expansion coefficient of solid electrolyte with sintering temperature has been investigated. A NASICON-type Li_1.6Al_0.5Ti_0.95Ta_0.5(PO₄)₃ (LATTP) solid electrolyte as a super ionic conductor at room temperature has been selected because of its high conductivities combined with low activation energies according to previous reports. And monoclinic Li₃V₂(PO₄)₃ (LVP) was used as both the negative and positive electrode materials to build symmetric battery. The thermal expansion coefficients of the LATTP and LVP were determined with sintering temperature to find the optimal condition for preparation of the composite electrode. The assembly of symmetric composite-LVP/LATTP/composite-LVP all-solid-state batteries are fabricated. In order to analyze the applicability of the LATTP to all-solid-state batteries, electrochemical performance was discussed in detail.

Silicon is the current research interest in electrochemical storage field because it has the highest theoretical capacity for Li ions uptake. In this work a silicone septum which is an inorganic polymer of silicon, available in laboratory is treated to get nanosized silica particles. This silica is further reduced with Mg powder at high temperatures under Argon atmosphere to get elemental silicon. This process had a conversion yield of 90-95 %. The obtained silicon has the 3-10 % oxygen on the surface as characterised. TEM showed the particle size in the range of 10-30 nm and obtained particles were interconnected. To overcome the volume expansion related issues of silicon during lithiation and de-lithiation, Silicon particles were coated by in situ polymerisation of phytic acid doped polyaniline. This gel was coated on the current collector making the electrode binder free. This silicon was further tested against Li metal as the reference electrode. Electrochemical Impedance study showed the lowering the charge transfer resistance during cycling. The prominent formation of Li₁₅Si₄ phase during lithiation was observed by cyclic voltammetry measurements. This cell yielded ~2000 mAh g-1 at current density of 100 mA g-1 and cell was stable for more than 200 cycles. The obtained material promises to be a good anode material for Li ion battery.
1. Favors et al, Scientific Reports 05623 2014.
2. Bao et al, Nature Letters, 446, 2007
3. Wu et al, Nature Communication, 2941, 2013

It has been proposed as a potential cathode materials for next generation of lithium ion batteries the LiFePO₄ .
A good cathode materials must meet the following properties: high charge-discharge, high cycles (1000 cycles); thermodynamic stability during energy process, high charge storage capacity per mole of material and compatible with the environment.
LiFePO₄ electrode , which has a structure of type "olivine " mixed with a conductive material, as reported by Goodenough et al. in 1997 [1] , appears to meet many of these requirements. However, its low electronic conductivity has prevented their widespread use. Several studies have investigated the effect of doping agents [2] in the structure, and consequently in its elctroquímica response.
The LiFePO₄ can be synthesized by high temperature reactions [ 1] or using hydrothermal conditions [2]. As this material has low conductivity at room temperature , it can reach the theoretical capacity only if a current density low is used [3] or at elevated temperatures [4], as a consequence of the low diffusion of lithium in the interface electrode / electrolyte. Ravet et al. [5] demonstrated that a covering of carbon significantly improves the electrochemical performance of the material .
In this work we have synthesized by hydrothermal method , LiFePO₄ doped yttrium using as a source the yttrium oxide . The synthesis was carried out in an acid digestion bomb, Parr . The imposed temperature is 170°C for 5 hours and then increased to 180°C for another 5 hours. He was subsequently dried under vacuum at 80°C for 24 hours under these experimental conditions should present a theoretical capacity of 169 mAh / g. Both the LiFePO₄ as LiFePO₄-Y was characterized by XRD and TEM, their electrochemical properties were recorded in a potential range between 2.0 V and 4.5 V at a rate of capacity of C/20 . The curve of specific capacity versus cycle number realize the stability over time to a constant value of specific capacity of about 65 mAh / g.

The heat signature of a cell, during charge or discharge, at different temperatures and varying SOCs can provide useful information about the internal resistance, SOH, entropic changes in transport phenomena, and related efficiencies. Non-calorimetric methods to look at entropic changes can be determined based on montioring changes in OCV over short pulses in well controlled tests. Typically it has been difficult to do such shorter pulse tests on a cell and at the same the calorimetry is conducted because the thermal transport properties of the cell are slow compared to the desired rate of pulsing. However, careful measurement of the heat flow from a coin cell under charge or discharge can result in a much more rapid measurement of heat and simultaneous testing is more fruitful. In the same vein, internal resistance as a function of SOC can also be much more easily determined through calorimetric means where heat transfer is rapid and the relative loss or gain through the conencting wires is minimized. Several examples of this combined approach are provided on standard commerical coin cells.

The energy storage capability of a battery scales with the potential difference between its electrodes. Yet operation of positive electrode materials at high potentials introduces challenges of stabilization of charged states. As of today, no positive electrode material has been demonstrated to durably and safely operate above 4.5 V vs. Li⁺/Li⁰. LiCoPO₄-based electrodes theoretically offer high specific capacity and high potentials of operation, around 4.8V vs. Li+/Li0, but these electrodes are prone to failure during cycling. Failure occurs through chemical and structural degradation in the bulk of the active material or at its interfaces with cell components, especially the electrolyte. The development of Li-ion battery electrodes operating at high potential is indispensable to meet the specific energy target of 250 kWh/kg at the packaged cell level.
Changes in the electronic structure and chemical stability of olivine-type LiCoPO₄ and Fe-substituted LiCoPO₄ were explored as both a function of ion substitution and oxidation state. Soft Ex situX-Ray absorption spectroscopy (XAS) made it possible to compare the changes in chemical bonding between electrode bulk and surface as a function of lithium content. This technique can probe the density of states at the transition metal and O levels. The evolution of these levels revealed changes in the metal-oxide covalence when lithium was deintercalated from the structure. An increase in covalence can lead to the destabilization of the anions. If this process takes place in the bulk of the material, this destabilization can lead to thermal degradation via oxygen loss. At the surface, even small degrees of destabilization are sufficient to produce oxidizing species that attack the electron-rich solvent molecules in the electrolyte, leading to irreversible capacity loss.
Increased metal-oxygen covalence was universally observed in the spectroscopy in the form of a rising pre-O K-edge peak at ~530 eV as a function of lithium deintercalation in both bulk and surface. However, accompanying changes in the Co spectroscopy were only observed in the Fe-substituted sample. These changes are also indicative of increased hybridization between Co 3d and O 2p orbitals. Co K-edge XANES and EXAFS experiments further corroborated these findings, in which virtually no changes in the Co K-edge were observed upon oxidation of unsubstituted LiCoPO₄. Additionally, the presence of Fe³⁺ measured on the surface of pristine Fe-substituted LiCo_1-xFe_xPO₄ electrodes which may assist in the facilitation of Li⁺ leaving the structure. Furthermore, Fe doping appears to play a substantial role in getting Co to participate in redox chemistry, and the mechanism by which it occurs is currently being explored using Density Functional Theory. Fe-substituted LiCoPO₄ is an exciting new positive electrode material that may prove useful in advancing Li-ion battery technology.

Increased energy density is required for rechargeable batteries to keep up with the consumer demand for electronic devices, electric vehicles, and smart grids. Current lithium ion battery technology utilizes cathodes with high voltage and capacity against a carbon anode, shuttling Li ions back and forth on charge and discharge in a non-aqueous electrolyte. No new commercially viable cathodes with greater capacity than those identified by Goodenough and co-workers�¹� have been yet found, with no real increase in capacity over the original LiCoO₂ composition since 1980. Options to increase energy density in Li-ion batteries can be summarized by increasing the voltage or lowering the molar mass of the active material in the cathode. Families of compounds that have yet to be investigated are scarce, however one such family are those containing fluorides. By introducing a more electronegative anion, higher oxidation states of transition metals can be stabilized which opens up the opportunity of higher redox potentials as well as the possibility of more than one Li⁺ ion deintercalation per transition metal; a phenomenon yet to be observed in Li-ion batteries. Lithium-transition metal-fluorides have potential as candidates for high voltage, low molar mass cathode materials, resulting in high energy density.
Thus far, it has only been shown that lithium intecalation into Li₃MF₆ (M^III to M^II) structures has been possible�^2,3�, while the elusive reversible deintercalation (M^III to M^IV) has not been achieved. Our preliminary studies show that in certain conditions, reversible deintercalation of these family of compounds is possible providing the synthetic methods are carefully controlled. Changes in the oxidation state of the central transition metal were confirmed by hard x-ray absorption spectroscopy and changes in the crystal structure were shown using high resolution x-ray diffraction. We are currently investigating this family of materials with other transition metals and anticipate these compounds will show similar results.
These promising results have given hope to redox chemistry at much higher operating voltages than has been previously observed for fluoride compounds.


1. K. Mizushima, P. C. Jones, P. J. Wiseman, and J. B. Goodenough, Mater. Res. Bull., 15, 783–789 (1980).
2. A. Basa, E. Gonzalo, A. Kuhn, and F. García-Alvarado, J. Power Sources, 207, 160–165 (2012).
3. G. Lieser et al., J. Power Sources, 294, 444–451 (2015).

Stable cycling performance with high power density in lithium ion battery (LIBs) is required to meet the criteria for the power source such as electric vehicles. But generally, high power density is hindered by slow diffusion of lithium ions in micrometric electrode materials. [1] From this perspective, nanoparticle electrode materials can enhance the rate of lithium ions because of shortened diffusion pathway of lithium ion. Besides, high surface area of electrode induces facile access of charge via large contact area with electrolyte and conducting additives like carbon. However, at the same time, chemical degradation at electrode-electrolyte interface is facilitated by large contact area with nanoparticle electrode. Unfavorable interfacial reactions such as dissolution of cathode species and decomposition of electrolyte mainly occur through energetically unstable surfaces of the active material. [2] In order to minimize side reactions that can negatively affect electrochemical performance, introducing electrochemically inactive ions on the surface of active materials can improve the interfacial stability. However, such ions should be introduced as thin passivating layers on individual particles to avoid excessively reducing the capacity of the electrode. [3] A strategy toward the stabilization of electrode-electrolyte interfaces has been devised by introducing core-shell nanocrystals, consisting of electroactive lithium transition metal oxide cores and ultra-thin inactive epitaxial oxide shells on the surface. Layered Li_xCoO₂ nanocrystals were used as a core component, with an Al-rich shell as passivation layer to minimize unfavorable reaction on the surface of cathode particles. The electrochemical performance shows that Li_xCoO₂ nanoparticle with conformal shell reveals improved capacity retention and rate capability compared to bare Li_xCoO₂.

Reference
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Synchrotron based soft x-ray spectroscopy, including soft x-ray absorption spectroscopy (sXAS), X-ray emission spectroscopy (XES), and resonant inelastic X-ray scattering (RIXS), is one of the incisive tools for detecting the critical electron states that are relevant to the chemical and electrochemical properties of battery materials. Compared with hard x-ray techniques, soft X-ray spectroscopy does not provide the long-range structural information directly, however, it is sensitive to almost anything that is related with electron state configurations, especially on the surface or at the interface. For example, different chemical bonding of the same element leads to different electron distribution, and thus distinct soft x-ray spectra; 3d transition-metal valence is determined by the 3d electrons that could be directly measured with soft X-ray; the redox of an electrode material, especially at the charged state, is fundamentally regulated by the electron state configurations of the cations and anions.

Besides the intrinsic electron states in the bulk materials, soft x-ray spectroscopy is inherently elemental, orbital, and even site sensitive with two different probe depth of about 10 nm and more than 100 nm depending on the techniques. With the rapid instrumentation developments based on high brightness synchrotron light sources, soft X-ray experiments could now be performed under in-situ/operando conditions. This provides us a unique opportunity for studying the surface and interface of battery materials in both ex-situ and in-situ sample environments.

This presentation will cover the aforementioned topics with recent demonstrations and examples. We show that the high sensitivity of soft x-ray spectroscopy to the chemical state allows comparative studies of the surface and bulk chemical evolutions of battery materials during cycling. We show that the stability issues and optimization potentials often lie in the surfaces and interphases of an electrochemical device. We will also discuss how the resonance effect in RIXS could be utilized to enhance the subtle chemical bond differences in both solid state and liquid systems.

The Li-ion technology still needs improvements to fulfil the requirements for electric mobility, especially in terms of energy density. LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode material thanks to its high potential during cycling and thus its high energy density [1]. However, it suffers from stability problems in long-term applications, especially in full-cell configuration against a graphite electrode. The understanding of the main and side reaction mechanisms is crucial to develop this cathode and to this, operando techniques are the most suitable ones to follow the structural and/or surface changes occurring during cycling.
For the structural changes and especially to follow lithium distribution, a cylindrical cell for neutron powder diffraction measurements was developed (Figure 1, left). During cycling, LNMO undergoes a solid-solution reaction from pristine to half-delithiated states followed by a two-phase reaction occurring from half to fully delithiated states. Similar results were obtained from our in house operando XRD measurements.
The near-surface region of the LNMO was investigated using operando Raman spectroscopy measurements (Figure 1, right). The assignment of the peaks and their intensities were confirmed by first principle calculations. All these results, combining information from bulk and surface, will be discussed, to demonstrate that LNMO could be a cathode of choice for future of Li-ion batteries.

Electrochemical energy storage, specifically lithium ion batteries (LIBs), are often touted as an ideal candidate for large scale power grid applications for sustainable usage of renewable energy sources such as solar and wind generation. To this end there are still major limitations in terms of energy density, overall cost, battery cycling rate and capacity fade that limit implementation en masse. The majority of improvements to LIB technology have come through the development of new novel cathode materials. One promising cathode material is Li₂FeSIO₄ (LFS), desirable for its low cost and high theoretical (and recently achieved [1]) capacity of ca. 330 mAh/g. However, the ionic conduction and transport mechanisms within this material are still not well understood, and require further investigation to improve upon cycling rate performance. To this end combined measurements of XRD & XANES have been performed in operando on LFS during electrochemical cycling, i.e. at selected electrochemical states of charge during the formation cycle the crystalline structure and the transition metal oxidation state/site symmetry were characterized via the two aforementioned techniques. The XANES & XRD data were collected near simultaneously at the 06ID-1 Hard X-ray Micro-Analysis (HXMA) beamline at the Canadian Lightsource using a novel experimental setup [2]. Through these studies further insight into the complex polyvalent and structurally assisted transport properties of LFS have been elucidated and are presented here.

[1] T. Masese, et al. J. Phys. Chem. C, 119 (2015) 10206-10211.
[2] Z. Arthur, et al. J. Phys.: Conference Series, 712 (2016) 012124.

In a conventional lithium ion cell, in which electrodes are composed of active materials, binders, conductive agents, and current collectors, the mixtures of different materials result in a complex architecture, posing a great challenge to extracting the intrinsic kinetic parameters of the electrode materials. In this work, single-particle experiments are conducted to directly measure the particle-level kinetics, and elucidate the factors limiting rate performance and reversibility capacity.
In this work the single-particle kinetic parameters of Li_1-xNi_0.8Co_0.15Al_0.05O₂ (NCA), a Li-ion cathode that is widely used in Li-ion batteries for electric vehicles and other applications, are investigated as a function of charge voltage (and state-of-charge). An electrochemical cell has been designed in which single cathode particles of 10-30 µm diameter can be interrogated with electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration tests (PITT). In addition, the internal structure and morphology of the particles is characterized using transmission X-ray microscopy (TXM). We also evaluate the effects of binder and electrolyte composition on the particle-level kinetic parameters. In coordination with the experiments, single-particle electrochemical simulations that take into account the particle geometry, interfacial transport, and surface reactions are performed.

Keywords: Lithium; batteries; single-particle measurements; transport; kinetics; interfaces; NCA

Acknowledgments
This work was supported as part of the North East Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012583. P-c T thanks the Ministry of Science and Technology, Taiwan (MOST 104-2917-I-006-006), for financial support.

The electrochemical reactions in an operating battery system may proceed via intercalation process, namely insertion of Li⁺ ions into interstitial sites without breaking the crystal lattice of the host, or via conversion that involves local migration/re-ordering of transition metal (TM) ions, and eventually, the extrusion of metallic TMs. Broadly speaking, these two types of reactions both involve ionic transport and ordering of cations (Li⁺ and TM ions) in a close-packed anion framework. This process is the basis of the battery operation. However, probing the local transport and ordering of cations, Li⁺ ions in particular, poses an extreme challenge to traditional X-ray or electron scattering techniques, largely due to their weak scattering power and vulnerability to radiation damage. Herein, electron energy-loss spectroscopy (EELS) was developed for probing Li and its bonding states by taking the advantage of high inelastic cross-section of Li K-edge [1]. Alternative imaging techniques of high-angle annular dark field (HAADF) and annular bright field (ABF), using aberration-corrected scanning transmission electron microscopy (STEM), were shown capable of simultaneously visualizing cations and anions (TMs ions, Li⁺, O^2-, F^-) with atomic-level resolution [2, 3]. And the development of in-situ electrochemical cells specialized for TEM measurements enables real time tracking of ionic transport and electrochemical dynamics in single nanoparticles using advanced S/TEM imaging and EELS spectroscopy techniques [4]. Examples from our recent research will be given, to show how these studies could help to identify the fundamental limits to the electronic/ionic transport and electrochemical dynamics in intercalation and conversion electrodes, thereby offering insights into designing new high-energy electrodes [5-7]. References [1] F. Wang, et al., ACS Nano 3, 1201 (2012);[2] F. Wang, et al., Nanotechnology 24, 424006 (2013); [3] W. Zhang, et al., Adv. Energy Mater. (in press): [4] F. Wang, et al., Nat. Commun. 3, 1201 (2012); [5] S-W. Kim, et al., ACS Nano 9, 10076 (2015); [6] F. Wang, et al., Nat. Commun. 8, 6668 (2015); [7] W. Zhang, H-C Yu, L. Wu, H. Liu, A. Abdellahi, B. Qiu, J. Bai, B. Orvananos, F. C. Strobridge, X. Zhou, Z. Liu, K. Thornton, Y. Zhu, G. Ceder, C. P. Grey, and F. Wang, (submitted). Acknowledgement This work was partially supported by the North Eastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, under Award Number DE-SC0001294, and by the Laboratory Directed Research and Development (LDRD) program at Brookhaven National Laboratory, under Contract No. DE-SC0012704. Research carried out in part at the Center for Functional Nanomaterials and the National Synchrotron Light Source at Brookhaven National Laboratory, is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0012704.

The increasing demand for smaller, lighter, cheaper, and more stable power sources for portable electronics, vehicles and aircrafts has stimulated intensive research on lithium ion batteries. Rational battery engineering, including design of smart electrode materials, is impossible without in-depth understanding of the chemical and physical processes in galvanic cells at the microscopic, nanoscopic, and eventually, molecular levels. Reaction mechanisms, cathode expansion, formation of cracks and solid-electrolyte-interface (SEI) layers, electrolyte decomposition, etc. are being extensively studied with a variety of ex and in situ microscopic, spectroscopic and electrochemical techniques. However, one of the limitations of the existing methodologies is their inability to deliver Li⁺ ions and control their concentration at the nanoscale level. In addition, the classic electrochemical techniques necessarily involve liquid-solid interfaces and inevitable formation of a SEI layer. This is a significant impediment for studying lithium diffusion and associated morphological changes in cathode materials. We have recently introduced a new tool – lithium focused ion beam (Li-FIB) microscopy – which allows precise dosage and spatial implantation of Li⁺ ions by controlling the ion beam spot size, beam positioning, current and exposure time. The Li-FIB technique allows in vacuo lithiation without exposing the sample to liquids and formation of SEI. In previous work¹ we studied lithiation of tin, a potential battery anode material that easily alloys with lithium. Here we report on Li-FIB studies of single-crystal V₂O₅ nanowires, which undergo classical intercalation process. The topochemistry of vanadium pentoxide bronzes is well studied macroscopically, giving us an opportunity to directly compare intercalation processes after Li implantation with the Li-FIB tool with standard wet electrochemical processes. The lithium diffusion process, concurrent phase transitions, structural and morphological transformations are studied and characterized by in situ Li-FIB and post mortem TEM. It is shown that V₂O₅ nanowires can intercalate lithium without structural integrity failure or crack formation.

ES acknowledges support under the Cooperative Research Agreement between the University of Maryland and the National Institute of Standards and Technology Center for Nanoscale Science and Technology, Award 70NANB10H193, through the University of Maryland.

1 Takeuchi, S. et al. Editors' Choice Communication—Comparison of Nanoscale Focused Ion Beam and Electrochemical Lithiation in β-Sn Microspheres. Journal of The Electrochemical Society 163, A1010-A1012, doi:10.1149/2.1161606jes (2016).

The development of durable and high capacity lithium-ion batteries requires a deep understanding of the reactivity at the electrode/electrolyte interface and the impact on the battery performance. While the electrolyte decomposition and formation of a Solid Electrolyte Interphase (SEI) at the negative electrode has been extensively studied [1,2], less is known on the reactivity at the positive electrode, where a thin Electrode Electrolyte Interface (EEI) layer is also observed [3,4]. At voltages where the batteries usually operate the electrolyte is expected to be stable against oxidation and the formation of the EEI layer is attributed to chemical reactions of solvent molecules or solvated salt at the oxide surface. At high voltages, when the limit of the oxidative stability of the electrolyte is reached, also other mechanisms, such as the evolution of oxygen from the oxide lattice or the formation of active oxygen intermediates like surface peroxide or superoxide, can also contribute to the interfacial reactivity and change the nature of the EEI layer.
By combining X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption and Emission Spectroscopy (XAS/XES) and Density Functional Theory (DFT) on LiCoO₂, and NMC electrodes with different Ni content we show how the nature of the EEI layer depends on the chemistry of the oxide and on the applied voltage. We highlight the importance of using model electrodes containing only the active material, without conductive agents and polymeric binders that can modify the EEI layers on the electrode [5].
The comparison of XPS results with the stability of reaction intermediates of solvent decomposition computed by DFT points to a strong dependency of the surface reactivity on the electrode composition and lithium content. These trends are rationalized in terms of the oxide electronic structure as computed by DFT and measured by XAS/XES.

In the past three decades, research is focusing on lithium-ion batteries and has expanded significantly. In order to respond to the development of new portable devices or electric vehicles, energy and power densities but also safety must be increased. The safety issue requires new electrode materials and electrolytes and combination of them. Currently used organic electrolytes are toxic and can possibly have a negative impact on the environment. Therefore, aqueous electrolytes with their associated safety and environmental friendliness have been investigated as alternative. However with the problem of limited stability voltage window, new electrolytes must be developed to decrease water reactivity. Electrolytes remain one of the most critical elements that affect the cycling stability of anode material. Indeed, interaction between electrolyte and electrode material may affect and consume both of materials.
With the goal to preserve the electrode materials and the electrolyte, in this study various electrolytes were combined with electrode materials to enhance the efficiency of aqueous lithium-ion batteries. A series of concentrated electrolytes including “water-in-salt electrolyte” were evaluated. The electrochemical activity of anode and cathode electrode materials was found to significantly dependent on the nature of the electrolyte and more specifically the concentration of the salt dissolved in water.

Specific energy and specific power are the main parameters of batteries. Achieving high values of both parameters in the same device is a challenging task. Electrode materials with high redox potentials are necessary to achieve high specific energy. High conductivity of all battery components is necessary to achieve high specific power. These two requirements often contradict each other.
Aqueous electrolytes are characterized by high conductivity whereas their electrochemical window is only 1.2 V. On the other hand, ionic liquids (IL) and electrolytes on the base of organic aprotic solvents possess large electrochemical window whereas their conductivity is a few orders of magnitude lower than the conductivity of aqueous electrolytes. Thus, specific energy is limited for aqueous electrolytes and specific power is limited for IL and organic-based electrolytes.
The aim of this study was to create a battery that combines high specific power and high specific energy. Our approach consists in using the overpotential phenomenon to widen the electrochemical window of aqueous electrolytes by selecting the electrodes, electrolyte composition, and electrode reaction conditions that inhibit water electrolysis and catalyze the target electrochemical reactions.
We have studied concentrated aqueous solutions of LiClO4 and NaClO4 as the electrolyte. Hg, Pb, Bi, In, Sn, their alloys, and composites with graphite foam were used as the negative electrode. The choice of these metals was defined not only by high values of the overpotential, but also by their ability to form intermetallic compounds with alkali metals and low melting point. We think that these three factors inhibit the by-reaction of hydrogen reduction on one hand and catalyze the target reaction of alkali metal reduction on the other hand. Porous cellular material on the base of graphite was used as the positive electrode. Graphite is characterized by high overpotential of oxygen evolution during water electrolysis. Under the conditions of positive polarization, oxidation reaction results in graphite intercalate formation. Thus, stabilization of the oxidized state of the electrode is achieved. In the cells prepared, potential-forming reactions are the following. Anode reaction is A⁺(aq) + M + e^- ↔AM, where A is Na or Li and M is Hg, Pb, Bi, In, Sn or their alloys. Cathode reaction is ClO₄^-(aq) + graphite - e^- ↔ ClO₄^-@graphite⁺. The potential of 3.5 V was achieved in the cell with Hg anode and LiClO₄-based aqueous electrolyte. Analogous cell with NaClO₄-based electrolyte demonstrates the voltage of 3.2 V and Coulomb efficiency of 90%.
To summarize, we have shown that using the electrodes with high overpotential of water electrolysis allows achieving the battery operational voltage similar to the voltage of the batteries based on nonaqeous aprotic electrolytes. Owing to high conductivity of the elements of the cell proposed, high specific power comparable to that of supercapacitors could be achieved.

Li metal anodes are needed to realize the high energy densities promised by advanced electrochemical cell designs. However, Li metal has a tendency to form dendritic structures upon cycling and is highly reactive in the atmosphere or various electrolytes. Lithium superionic conductors are being developed to address these challenges. These solid materials have high ionic conductivities, suppress dendrites and are impermeable to liquids. In this study, the electrochemical stability of lithium aluminum titanium phosphate, Li_1+x+yAl_xTi_2-xSi_yP_3-yO₁₂ (LATP) was characterized in deionized water and HCl solutions (aq) supported with LiCl. X-ray diffraction (XRD) displayed no significant changes in the structure of the material regardless of the treatment received. Electrochemical impedance spectroscopy (EIS), showed that the conductivity of LATP membranes immersed in DI water remained stable over a one month period. However, the resistance increased significantly in aqueous HCl solutions. The grain and grain boundary impedances showed only a small increase, but a second RC semicircle appeared at low frequencies, which has been tentatively attributed to a reaction between H+ and the LATP. Based on previous studies [1, 2], we believe this reaction creates a surface layer with reduced Li⁺ conductivity, which impedes Li⁺ transport. This is supported by the fact that a pH 2 solution showed lower conductivities than at pH 4 (1.4x10^-5 and 3.9x10^-5 S/cm at 20 °C, respectively). Adding LiCl salt in the solution reduced the surface layer impedances. Especially, in high salt concentrations the Nyquist plots were indistinguishable from the pristine LATP plates. Morphological analysis with scanning electron microscopy (SEM) confirms EIS results. The grains of the pristine LATP sample were sharp and clearly defined. This definition decreased after soaking the material in pH 4 HCl solution. Adding LiCl salt in the acidic solution and by increasing the salt concentration, the morphology of the LATP gradually returned to the pristine conditions. These results lead to the hypothesis that the excess amount of Li⁺ introduced by the salt may inhibit the exchange between Li⁺ from the ceramic and H⁺ from the liquid.

References:
S. Hasegawa, N. Imanishi, T. Zhang, J. Xie, A. Hirano, Y. Takeda, O. Yamamoto, J. Power Sources 189 (2009) 371
F. Ding, W. Xu, Y. Shao, X. Chen, Z. Wang, F. Gao, X. Liu, JG. Zhang, J. Power Sources 214 (2012) 292

Batteries with specific energy and energy density higher than that of state-of-the-art Li-ion batteries are considered critical for mass adoption of electric automobiles. Metal-oxygen batteries, Li- and Na-O₂ batteries in particular, offer the highest theoretical specific energy among all known battery types. In Na-O₂ batteries, NaO₂ is the discharge product and is an electronic insulator. However, surprisingly, the electrochemical deposition of NaO₂ does not lead to battery electrode passivation. We will present experimental results backed by theoretical calculations that suggest NaO₂ solvation chemistry plays a dominant role in the electrochemical deposition (during discharge) and dissolution (during charge) of NaO₂ in Na-O₂ batteries. This mechanism leads to a higher specific energy than that limited by electrode passivation and enables recharge at low overpotentials unlike the high charge overpotentials for Li₂O_2, the discharge product in the closely related Li-O₂ battery. Furthermore, we present experimental data that suggests near theoretical specific energy can be achieved in Na-O₂ batteries employing electrode structures that maximize mass transport while this is not possible in the Li-O₂ system. We will discuss the electrochemical differences between Li-O₂ and Na-O₂ batteries that lead to the experimentally observed differences in the two electrochemical systems.

To meet the future demands for sustainable energy supply and storage, novel systems needs to be considered. The materials challenges span both solid as well as liquid bulk and interfaces, and a comprehensive approach, which addresses the relevant as well as connection between different length scales, is needed. In this talk we will highlight our work in uncovering charge transport limitation in future high energy storage systems; such as Li excess materials, multivalent (Mg, Ca, Al, Y and Zn) cathodes and liquid electrolytes. By employing density-functional-theory to both bulk, interface and electrolytes, we can elucidate the transport bottlenecks for each case and guide experimental efforts towards accelerated improvement strategies. The methods and methodology developed use a range from first-principles to classic atomistic modeling with experimental verification to understand and design cathode and electrolytes with improved properties.

Features of low cost, multi-valence enabled high energy density, and non-dendritic formation on the surface makes Magnesium (Mg) battery an attractive energy storage method that can replace the lithium ion batteries. It has been reported that reversible stripping and plating of Mg metal has been enabled in Grignard reagents and hydride based electrolytes. However, these electrolytes are reduction-resistant but oxidation vulnerable, and only stable at much lower operation voltages than lithium ion batteries. Here, we report that an Mg²⁺-conducting artificial interphase formed on the Mg surface protects the surface from reacting with electrolytes while maintaining efficient Mg²⁺ migration, thus allows for the reversible Mg stripping and plating in not ethereal-based and more oxidation-resistant electrolytes, such as carbonate based electrolytes. This novel approach was proved with the reversible Mg stripping and plating tests with the electrolyte of Mg(TFSI)₂ in propylene carbonate (PC) and remarkable extended cycle life was observed with the artificial interface on the Mg surface. Full cell capabilities were also examined with V₂O₅ cathode, and reversible Mg intercalation with an artificial interface tailored Mg electrode was observed while rapid capacity degradation was found with the bare Mg electrode. TEM, XPS, TGA and TOF-SIMS analyses were adopted to study the structures of an artificial interface and will be presented in detail. This concept creates a new strategy that circumvents the obstacles to realize the high-voltage Mg batteries by using oxidation-resistant electrolytes and high-voltage cathodes that have been excluded in the state-of-art Mg batteries.
Acknowledgement: This work was supported by the Laboratory Directed Research and Development (LDRD) Program at the National Renewable Energy Laboratory. NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy operated by the Alliance for Sustainable Energy, LLC.

New secondary batteries are intensively studied by many researchers in order to meet the energy demands required for portable devices, vehicular or for stationary applications. As the performance of lithium ion battery continuously improves, the battery approaches the limits of its theoretical energy density. Multivalent battery systems, especially those comprising of magnesium metal anodes have been enthusiastically studied for over few decades as possible high energy density alternatives to Li ion. This is combined with the added benefit of lower risks related to the occurrence of common issues, such as formation of dendrites which is typically observed in metal electrodes.
A typical magnesium ion battery (MgB) constitutes of a magnesium metal anode, a Chevrel phase Mo6S8 cathode and an electrolyte consisting of Grignard based salt in tetrahydrofuran solvent[1]. One of the key challenges in this battery system is the development of highly conductive, non-corrosive, and chemically stable electrolyte with a wide potential range[2-4]. Recently our group developed a new electrolyte using monocarborane; a boron cluster Mg salt that meets the aforementioned demands[5,6]. Here, we show Mg battery feasibility using magnesium-carborane/tetraglyme electrolyte with magnesium metal anode and Chevrel phase Mo6S8 cathode.These studies will be mostly focused on the charge- and discharge behavior observed under constant current conditions, where the electrochemical properties of each component using electrochemical impedance will be discussed.

References:
[1] D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, E. Levi, Nature 2000, 407, 724.
[2] J. Muldoon, C. B. Bucur, and Th. Gregory, Chem. Rev. 2014, 114, 11683.
[3] C. Wall, Z. Zhao-Karger, and M. Fichtner, ECS Electrochem. Lett 2015, 4, C8
[4] F. Wang, Y. Guo, J. Yang, Y. Nuli, and S. Hirano, Chem. Commn. 2012, 48, 10763.
[5] O. Tutusaus, R. Mohtadi, ChemElectroChem 2015, 2, 51.
[6] O. Tutusaus, R. Mohtadi, T. S. Arthur, F. Mizuno, E. G. Nelson, Y. V. Sevryugina, Angew. Chem. Int. Ed. 2015, 54, 7900.

The widespread integration of renewable, intermittent energy sources is dependent upon the development of efficient large-scale energy storage systems for load-levelling the electric grid. Similarly, the acceptance of electric vehicles hinges on the availability of intermediate scale, safe, low-cost energy storage batteries. It is acknowledged that traditional Li-ion batteries are approaching their limits for both applications. This presentation will present an in-depth view on the challenges, opportunities and perceived limits for future strategies for electrochemical energy storage that go “beyond Li-ion”, based on intercalation of multivalent cations. Here, we present new materials that intercalate either Mg²⁺ or Zn²⁺ at the positive electrode, which are coupled with metallic negative electrodes to maximize energy density. The contrast between intercalation in aprotic vs aqueous media and the role of water will be highlighted for both multivalent cations using examples from our most recent studies on sulfide and oxide positive electrode materials, and new developments in electrolytes for aprotic Mg batteries will be presented. Guiding materials development for both the positive electrode and the electrolyte also requires developing an understanding of the underlying chemistry of redox processes. The talk will address fundamental investigations involving structural changes on redox cycling, and diffusion coefficient measurements that permit direct comparison with Li⁺ intercalation systems, in addition to exploring multifunctional nanostructured electrode materials which allow us to control processes at the electrolyte interface.

Research into aluminum ion battery systems began several decades ago, but the success of lithium ion systems lead to a loss in interest. Now that there is renewed interest in “beyond lithium” systems, aluminum ion batteries have seen a resurgence in research. The system of interest here is the aluminum ion cell which uses an ionic liquid as the electrolyte. It has recently been found that graphene can serve as an intercalation material for the aluminum tetrachloride anions in batteries which use ionic liquid electrolytes, which were found to have stable discharge plateaus and stable cycling performance.
Building upon this work, we have introduced nitrogen dopants and pores into the graphene based cathode in order to probe the effects on cell performance. We have previously found that such dopants dramatically increase the capacitance of supercapacitors and the pores allow better ion access to the interior structure of few-layered graphene, and we now hope to leverage defect engineering to improve the cathode. In this presentation, I will explore the implications these defects and pores have for the performance of aluminum ion batteries using an ionic liquid electrolyte. The effects on ion mobility will also be examined.

Ion-selective or permselective separators allow the transport of the electrolyte with desired ions while restricting the passage of certain ions/species. The efficiency of the process depends on the ability of the membrane to block the unwanted ions/species while enabling free transport of the other ion. Ion – selectivity although not desired in Lithium-ion battery could be harnessed advantageously in certain electrochemical systems where redox-active species are dissolved or dispersed in the electrolyte, such as redox flow batteries, fuel cells and Lithium-Sulfur (Li-S) batteries. Utilizing permselective membranes holds tremendous promise for mitigating the polysulfide migration issue facing Li-S battery technology, but it has received small attention. One promising material which could serve effectively as permselective membrane is graphene oxide (GO). It is well known that the negatively charged oxygen functional groups present on GO can repel the negatively charged polysulfide species back to the cathode, acting as an effective shuttle inhibitor to the sulfur and polysulfides. However, the insertion of a GO membrane or any other permselective membrane would naturally bring extra resistance to the battery system, degrading the energy efficiency of the Li-S battery, particularly at high rates. To overcome this issue, we report the facile fabrication of a high flux graphene oxide membrane directly onto the sulfur cathode by shear alignment of discotic nematic liquid crystals of GO. We show that the high degree of order and alignment imparted to graphene sheets upon applying shear to nematic GO results in a permselective membrane with minimum transfer resistance. We demonstrate that there is a negligible compromise between selectivity and permeability of the shear-aligned GO membrane we introduced in our Li-S cell, resulting in a significantly improved rate performance compared to the functional membranes reported to date.

Lithium-sulfur battery is now one of the promising rechargeable battery systems among the next-generation energy storage systems. However, several intrinsic drawbacks of sulfur such as poor electronic conductivity, huge volume change during the cycling, dissolution of intermediates, which hinder its progress to be commercialized. In order to overcome those problems, a combination of sulfur and carbon-based material, Sulfur-polyacrylonitrile (SPAN) compound ¹was studied. It shows an outstanding ability to prevent the dissolution of intermediates and largely enhances its long-cycle stability, which has been seen a potential material for the lithium-sulfur battery.
Although many groups reported different synthesis of the SPAN materials with good cycling abilities, the reaction mechanism of SPAN during the cycling is rarely discussed and still unclear. The structure has been reported by several groups, which the sulfur is in favor of small size (S_x, x = 1~3) and connects with carbon on the dehydrated PAN structure. However, the lithiation reaction is still lacking in direct observation. Therefore, in this study, the SPAN is studied by in situ Raman spectroscopy to further elucidate the reaction mechanism.
For the Raman spectrum of as-prepared SPAN, peaks found at 171, 301, and 803 cm⁻¹ are assigned as C-S bonds, and peaks found at 481, and 940 cm⁻¹ are related to S-S bonds. This feature is different from S/C composite, which only observed peaks same as elemental sulfur at 150, 216, and 470 cm⁻¹, showing the formation of covalent C-S bonds between sulfur and PAN backbone rather than simple physical absorption between sulfur and carbon composite.
The assembled cell using S-PAN cathode was analyzed by in situ Raman spectroscopy during charging and discharging processes. In the lithiation process, as the lithium content increases, the S-S bonds are observed the decrease of peak intensity at first, and the C-S bonds are observed to decrease after, indicating lithium ions react with S-S bonds prior to the C-S bonds. This observation is supported by the dissociation energy of C-S bond (272 kJmol^-1) and S-S bond (251 kJmol^-1) as well. In the delithiation process, the peaks of C-S and S-S have slightly increased to the end of charge. However, the intensity is not as intensive as the initial SPAN, which may indicate the formation of nano-sized sulfur in PAN backbone.
The reaction mechanism of S-PAN during the lithiation/delithiation process is further discussed and understood in this work, which could contribute to design and enhance better sulfur-polymer based material for lithium-ion battery use.

Reference
1. Kim, J.-S.; Hwang, T. H.; Kim, B. G.; Min, J.; Choi, J. W., A Lithium-Sulfur Battery with a High Areal Energy Density. Advanced Functional Materials 2014, 24 (34), 5359-5367.

The fast depletion of fossil fuels and deterioration of environment have led to increasing demand for renewable energies and efficient energy storage technologies. Lithium-sulfur (Li-S) batteries have been regarded as one of the most promising high-energy power sources in broad applications ranging from electric vehicles to large-scale grid energy storage. Li-S batteries deliver a theoretical energy of 2600 W h kg-1 that is an order of magnitude higher than that of the current lithium-ion batteries (LIBs), and utilize naturally abundant sulfur as the cathode material which significantly reduces the cost. The major challenge for the practical implementation of Li-S batteries resides in the dramatic capacity decay. The intermediate lithium polysulfides (Li_xS_n, 3≤n≤8) formed during cycling dissolve in the liquid electrolyte, migrate through the separator, and deposit on Li metal anode, causing “shuttle effect”. In addtion, the utilization of the active material is strongly hampered by the intrinsic insulating of S and its discharge product Li2S, leading to a low capacity and poor rate capability. Furthermore, the S cathode suffers from the volume variation (~80%) during lithiation/de-lithiation, causing the loss of electrical contact and the structure instability.
Herein, we demonstrate an innovative strategy to efficiently entrap Li_xS_n from synergistic effect of structural restriction and chemical encapsulation using metal oxide-decorated hollow sulfur spheres. The significance of this strategy lies in that we purposely design a material architecture with both structural and chemical encapsulation effect, and that the material architecture provides a prolonged cycling stability. MnO₂ is selected as a model and the MnO₂ nanosheets-decorated hollow S spheres (hollow S-MnO₂) nanocomposites are achieved through a facile synthesis. The nanocomposites with unique structure possess several features favoring highly stable S electrodes: i) the hollow spheres with inner void space not only alleviate the volume expansion of S on lithiation but also structurally restrict soluble Li_xS_n within the spherical structure; ii) the decorated MnO₂ nanosheets with large surface area efficiently and chemically minimize the polysulfides dissolution by forming strong bonding; iii) the small dimensions of hollow S-MnO₂ nanocomposites facilitate both ion and electron transport, leading to a better utilization of the S. This design presents a new strategy to prevent loss of polysulfides by structural and chemical dual-encapsulation, and can be expanded to other metal oxides or metal hydroxides. The unique material architecture enables high-performance S cathodes with high capacity, high sulfur loading and extremely low capacity decay of only 0.028% per cycle over 1500 cycles at 0.5 C-rate.

The Lithium-sulfur (Li-S) battery has a theoretical specific energy of 2600 W h kg^-1 that is 3-5 times that of Li-ion batteries, therefore, has the potential to serve as the next generation of high energy batteries. However, in the cathode the low electrical conductivity of sulfur and dissolution of polysulfides result in a poor specific power and fast capacity decay on cycling, and in the anode the use of lithium metal foil leads to dendritic growth that raises serious safety issues, which have long been identified as major issues for the development of Li-S batteries.
Most researches have focused on the cathode materials by filling porous discrete carbon nano/micro-particles with sulfur and then coating a mixture of the sulfur/carbon powder and additives on a current collector made of aluminum foil to form an electrode. However, sulfur/carbon composites are usually in the form of discrete particles tens of nanometers to micrometers in size. The electrons generated during charging/discharging have to transfer from particle to particle until they reach the current collector and inter-particle boundaries are the major cause of the poor electrode kinetics at a high current density.
We suggested optimizing the Li-S battery performance by engineering the current collector,^[1],[2] and reported a three-dimensional current collector composed of hundreds of micrometer-long carbon nanotube bundles that are connected by covalent carbon-carbon bonds to an ultrathin-graphite foam (CNT-UGF).^[3] When filling the CNT-UGF current collector with elemental sulfur without any additional binder or carbon black, the cathode contains 43 wt.% (areal loading density of 2.4 mg cm^-2) sulfur, delivers a capacity decay rate of 0.06 % per cycle after 400 charge/discharge cycles at 0.5 C rate. When the CNT-UGF is electroplated with lithium metal, the anode cycles with a voltage hysteresis of 14 % of that of the lithium foil for more than 800 hours without short circuiting, although a short circuit occurs in a lithium foil anode after 260 hours. A Li-S cell assembled with the S/CNT-UGF cathode (47 wt.% sulfur content, areal loading density of 2.6 mg cm^-2) and the Li/CNT-UGF anode (20 wt.% lithium content) delivers a remarkable high-rate capacity of 860 mAh g^-1 at 12 C rate.^[3] Thus a Li-S cell assembled with a S/CNT-UGF cathode would be able to deliver a specific power of 2890 W kg^-1 with a specific energy of 240 W h kg^-1 with respect to the mass of the whole cell. This result allows the Li-S cell to be charged with an energy comparable to that of a fully charged Li-ion battery in 5 minutes.

References
[1] Ji, H. X.and Ruoff. R. S.* et al. Nano Letters 12, 2446-2451 (2012)
[2] Xu, J.; and Ji, H. X.* et al. Advanced Materials 2016, Online, DOI:10.1002/adma.201600586.
[3] Jin, S.; Ji, H. X.* and Ruoff, R. S. et al. Submitted.

Solid polymer electrolytes based on poly(ethylene glycol) and cardanol, a renewable resource from cashew nut shell liquid, were prepared and their properties were investigated. UV-induced self-crosslinkable polymer matrix were synthesized by free radical copolymerization of poly(ethylene glycol) methyl ether methacrylate and 2-hydroxy-3-cardanylpropyl methacrylate. Solid polymer electrolytes were prepared by simple solution casting method followed by UV irradiation, which induces cross-linking reaction of cardanol moieties. The obtained electrolytes were dimensionally stable, free-standing, and thermally stable. Maximum ionic conductivities of 2.6 X 10^-5 S/cm at 30 ^oC and 2.5 X 10^-4 S/cm at 60 ^oC were obtained when cardanol content in the matrix polymer was 8 mol% and lithium salt doping concentration ([Li⁺]/[EO unit]) was 0.05. The feasibility of the prepared electrolytes to solid polymer electrolytes for lithium secondary batteries was examined by linear sweep voltammetry and galvanostatic charge-discharge cell test.

A multivalent battery system using Mg ions has gained a great interest as an alternative to the Li-ion battery due to its high volumetric capacity almost twice that of Li. As one of a very few high energy-density anode materials, nano-structured Sn is capable of delivering good operating voltage and capacity for a rechargeable Mg ion battery. However, understanding of how the nanostructures change during magnesiation is still lacking. Here, we demonstrate for the first time how Mg ions insert into and alloy with Sn nanoparticles, observed in real time inside a transmission electron microscope. Magnesiation was performed via a chemical route using electron beam irradiation on Sn nanoparticles immersed in a diglyme-Mg(TFSI)₂ salt complex electrolyte, all of which were encapsulated inside a graphene liquid cell. Magnesiation of Sn, along with a large volumetric expansion (> 200%), induced phase coexistence between disintegrated Sn and newly formed crystalline Mg₂Sn before being pulverized entirely into amorphous Mg₂Sn.

Conversion-type lithium ion batteries (LIB) using electrodes such as transition metal oxides, hydrides, and sulfides are capable of utilizing all possible oxidation states of a compound, and thus can provide large specific capacity for advanced applications such as electrical vehicles. Understanding the atomistic conversion mechanism is fundamentally important in searching for new conversion-type electrode materials and the application of these materials. Unfortunately, the conversion mechanism has not been explicitly established mostly because the process is wrapped in a nanoscale narrow reaction front. WO₃ is an ideal model system to study the intercalation initiated conversion reaction, and the interplay between these two chemical processes. In this presentation, we report our in-situ TEM direct atomic level observation of the structural and chemical evolution across a conversion reaction front with high spatial resolution in WO₃ upon electrochemical ions (Li, Na, Ca) insertion. An intercalation step right prior to conversion is explicitly revealed at atomic scale for the first time for Li, Na, Ca. Nanoscale diffraction and ab initio molecular dynamic simulations found that going beyond intercalation, the inserted ion-oxygen bonding formation destabilized the transition-metal framework which gradually shrunk, distorted and finally collapsed to amorphous W and M_xO (M = Li, Na, Ca) composite structure. This study provides a full atomistic picture on the transition from intercalation to conversion, which is of essential importance for both secondary ion batteries and electrochromic devices.

Rechargeable metallic lithium batteries such as lithium-sulfur, lithium-air and lithium-solid state batteries, have attracted great attention in recent years because of their high energy density, which could be used as next generation power supplier for consumer electronics, electric vehicle, grid energy storage and other fields. However, the obstacles of the application for metallic lithium anode includes at least five factors: 1) inhomogeneous deposition and dissolution of lithium upon cycling; 2) reaction with the electrolyte during storage; 3) unstable SEI on lithium anode during storage and electrochemical cycles; 4) volume variation; 5) low melting temperature (~ 180 ^oC). Numerous strategies have been proposed to overcome these fences: using ceramic/polymer solid electrolyte¹ to inhibit the lithium dendrite growth, treating the separators to inducing a more uniform plating², coating buffer layer³, searching the electrolyte-salt-additive ⁴, using the composite lithium anodes⁵ and sealing the lithium anode in electrolyte package boxes.
In this work, we have investigated the morphology evolution of the lithium metal anode during the electrochemical plating and stripping process. And then we studied the lithium reaction with atmosphere during storage. It is found a SEI-like composition with Li₃N and Li₂CO₃ can modulate the interfacial stabilization between the lithium foil and the ether electrolyte. Besides, the physical/chemical properties of the SEI on metal lithium anode has also been studied. We also prepared the lithium thin film on the conductive substrate. Then the thin film was used as anode in Swagelok-type cell with two kinds of electrolyte: one is ester-based electrolyte LiPF₆-DMC&EC; the other is ether-based electrolyte LiTFSI-DME, LiTNFSI-DME, LiBETI-DME. The cathode is LiCoO₂ or LiFePO₄. SEM, SPM, SIMS, XPS have been used to characterize the surface structure of the lithium metal anode before and after cycling or soaking. Different mechanical and potential and composition distribution on lithium anode have been obtained. A preliminary mechanism of SEI formation on lithium have been proposed accordingly.

Acknowledgements
Financial supports from the NSFC project (51325206), “973” project (2012CB32900), Beijing S&T Project (Z13111000340000), and “Strategic Priority Research Program” of the Chinese Academy of Sciences, Grant no. (XDA09010000) are appreciated.

(1) Lu, Y.; Tu, Z.; Archer, L. A. Nature materials 2014, 13, 961.
(2) Zhai, Y.; Xiao, K.; Yu, J.; Ding, B. Electrochim. Acta 2015, 154, 219.
(3) Ma, G.; Wen, Z.; Wu, M.; Shen, C.; Wang, Q.; Jin, J.; Wu, X. Chem Commun (Camb) 2014, 50, 14209.
(4) Zhang, Y.; Qian, J.; Xu, W.; Russell, S. M.; Chen, X.; Nasybulin, E.; Bhattacharya, P.; Engelhard, M. H.; Mei, D.; Cao, R.; Ding, F.; Cresce, A. V.; Xu, K.; Zhang, J. G. Nano letters 2014, 14, 6889.
(5) Liu, Y.; Lin, D.; Liang, Z.; Zhao, J.; Yan, K.; Cui, Y. Nature communications 2016, 7, 10992.

Lithium ion batteries (LIBs) are used to portable energy source for many electronic systems from portable electronic devices to electric vehicles. Meanwhile Li ion batteries have some limitations which are energy density, high temperature stability and high manufacturing cost. Thus, next generation power source should be studied in non-Li ion batteries. The Mg is the most attractive materials for energy storage system due to low cost and abundance. Especially, Mg is a fascinating element which can have some advantages. One is the storage of up to 2 electrons per one Mg atom. It can result in a high volumetric energy comparable with Li. Moreover, the atomic radius of Mg is comparable with Li which means smaller atom size can lead high diffusion rate and rate capability. The others are a low cost and abundance. However, Mg is much heavier than Li that it can not insert into host materials as well as Li ion. Accodingly, Mg ion was diffused into host-material through the high energy barrier. Nanomterials can proposed candidate electrode with short ion diffusion path. In LIB system, group IV elements(Si. Ge, Sn) have studied intensively.
In this study, we fabricated Si nanosheets for Magnesium ion batteries. The Si nanosheets with thickness and diameter of < 5 nm and > 5 mm, were directly grown on graphite foil using chemical vapor deposition process. A half-cells tests were carried out using Si nanosheet as anode. The half-cells test showed cycle performance and electrochemical properties. We investigated structural changes during magnesiation using synchrotron XRD. Theses in-situ XRD were carried out electrochemical reaction by potentiostat. The silicon nanosheets will be discussed in terms of their structural changes with Mg+ intercalation.

A number of research for development of novel electrode with high capacity, stable cyclability and low cost for Lithium-ion battery (LIB) have been carried out to applicate to various portable electronic devices (e.g, mobile phones, tablet computers). Furthermore, recently, as electric vehicles and hybrid electric vehicles have attracted tremendous interests, faster charging speed, higher capacity and more stable cyclability have been demanded. To develop more enhanced battery, various in-situ studies have been carried out to understand reaction mechanism of lithiaition and de-lithiation.
CuS was one of the promising LIB anode materials during the early stage of LIB development due to its high capacity (~ 560mah/g) and high electronic conductivity (~ 10³/S). However, it has been found that capacity fading is dramatically sharp in various structure with formation of soluble lithium poly sulfide. Eventually, poor cyclability is the main issue to be solved. Here, we report in-situ observation of lithiation of CuS hexagonal paticles to discover possible reasons why it goes through sharp capacity drop. Real time transmission electron microscopy (TEM) observation has provided unique information on lithiation process of various LIB anode materials. To make proper environment for lithiation in a conventional TEM, CuS and LiF particles were dispersed on graphene-coated Au grid. In real time TEM observation, LiF was decomposed by electron-beam irradiation, generating Li metal. In the case of a particle, as lithiated, copper dendrite was formed at the opposite area from LiF. In terms of particles, as CuS particles were chemically impregnated with Li, interparticular copper movement was observed. Finally, CuS particles were fully lithiated, forming copper dendrite on only (001) plane of a CuS particle which is located at edge side among particles. During the whole lithiation process, general hexagonal particle shape retained due to replacement of copper with Li with just little change of sulfur lattice. This study suggest that type of lithiation of CuS is belong to displacement reaction and that formation of copper dendrite during lithiation could make negative effects on cyclability such as exfoilation from current collector.

Many researches and applications of lithium ion (Li-ion) devices have confirmed their excellent performance in a variety of conditions. However, liquid Li-ion electrolytes increase the risk of leakage although they have higher ionic conductivity. The development of polymeric solid electrolytes have improved the safety of electrochromic devices and batteries besides the creation of different shapes and their reduction of size. This work describes a novel segmental motion-decoupled polymer chain that can result in lithium-ion hybrid solid polyelectrolytes with superior ionic conductivity. They were synthesized by a simple chemical route of a polymer chain containing germanium as a central atom using the polymeric precursor method. The main purpose of preparing a hybrid polymer is to enable a higher ion mobility with a rigid polymer chain due to the electronegativity of germanium. FTIR (Fourier Transform Infrared) and FT-Raman (Fourier Transform Raman Spectroscopy) analysis confirmed the polymerization of the metallic citrate and the formation of a polymer chain. From the FTIR results, it was identified that the region between 1020 and 1080 cm^-1 contains the stretching vibration of O-C-C. DSC (Differential Scanning Calorimetry) and XRD (X-Ray Diffraction) analysis confirmed the presence of only one glass transition temperature for the polyelectrolyte made of germanium at -29°C, which confirms the amorphous behaviour of the material at ambient temperature, increasing its ionic conductivity. It was confirmed that the polyelectrolyte synthesized is a Single Phase Hybrid Polyelectrolyte (SPHP), which its charge transfer mechanism occurs by “hopping”, i.e. lithium ions move independent of the polymer chain movement. Thus these results indicated the material developed is promising to a fast ion conduction of Li⁺ and Na⁺. Impedance spectroscopy analysis of this electrolyte will be performed to confirm the fast conductivity. Finally, the developed SPHP can be a promise material for several electrochemical devices application.

Acknowledgements
We gratefully acknowledge financial support from the Brazilian agencies of CNPq (Grants no. 128243/2015) and FAPESP (Grants 2011/19924-2 and 2014/50516-6).

Sulfur, S, is one of the promising active materials for Li batteries because of its high theoretical capacity (1672 mAh g^-1). However, the both ionic and electronic conductivities are too low and the lithium polysulfide dissolves into the electrolyte solution during charge/discharge process. To overcome the disadvantages, composites with metals and carbon have been investigated. Recently, we developed a heat-treated mixture of polyethylene glycol and sulfur, sulfurized polyethylene glycol (here after denoted as SPEG), and found to show excellent charge-discharge cycles in a coin cell. In this study, we synthesized SPEG at various conditions and investigated local structure and chemical state of S in SPEG to discuss electrochemical properties of SPEG.
SPEG was prepared through refluxing at 723 K under N₂ flow. The obtained product was pulverized and heat-treated at 573 ~ 1073 K under N₂ flow for at least 2 h to remove residual S. The electrode was prepared by mixing the active materials, acetylen black as a conductive additive and polytetrafluoroethylene as a binder in a weight ratio of 50:45:5. The electrode was tested in IEC R2032 coin-type cell assembled with separator, lithium foil as a counter electrode, and 1 M lithium bis(trifloromethanesulfonyl)amide (LiTFSA) in tetraglyme as electrolyte. The electrochemical properties were examined by battery testing system at a current density of 30 mA g^-1 in the potential range of 1.0 ~ 3.0 V vs. Li/Li⁺at 303 K. The crystallographic structure was investigated by the synchroton X-ray diffraction (SR-XRD) and the chemical state was examined by Raman spectroscopy and S K-edge X-ray absorption spectroscopy (XAS).
SPEG heat-treated at 573 K shows a second discharge capacity of 488 mAh g(SPEG)^-1 and is kept at 433 mAh g(SPEG)^-1 even after the 10^th cycle. While, the second discharge capacity of SPEG gradually decreases from 488 to 10 mAh g(SPEG)^-1 with increasing the heat-treated temperature. The SR-XRD profiles of SPEG show wide broad profiles such as low-crystalline or amorphous materials, and do not show crystalline S and carbon phases. The XANES spectrum of the composite shows three distinct peaks at around 2469, 2472 and 2473 eV, which do not correspond to profiles of pure S and Li₂S. The strongest Raman peak of SPEG appears at 1441 cm^-1 between G (1600 cm^-1) and D (1300 cm^-1) bands of graphite, and this peak intensity gradually becomes weak with increasing the heat-treated temperature. The other peaks appear at 1279, 1066, 846, and 772 cm^-1. These peaks are not assigned to various vibration modes of pure S and carbon. From the results obtained in this study, we speculate that free S is absent in the composite. The new chemical states are formed between S and C in SPEG, which are destroyed at high temperature. We will discuss the relationship between the electrochemical properties and the local structural parameters of SPEG such as S-C and S-S distances and coordination number.

The next generation of deformable and shape-conformable electronics devices will need to be powered by batteries that are not only flexible but also foldable. Here we report a foldable Lithium-Sulfur (Li-S) rechargeable battery, with the highest areal capacity (~3 mAh cm^-2) reported to date among all types of foldable energy-storage devices. The key to this result lies in the use of fully-foldable and super-elastic carbon nanotube current-collector films and impregnation of the active materials (S and Li) into the current-collectors in a checkerboard pattern, enabling the battery to be folded along two mutually orthogonal directions. The carbon nanotube films also serve as the sulfur entrapment layer in the Li-S battery. The foldable battery showed < 12% loss in specific capacity over 100 continuous folding and unfolding cycles. Such shape-conformable Li-S batteries with significantly greater energy density than traditional lithium-ion batteries could power the flexible and foldable devices of the future including laptops, cell-phones, tablet computers, surgical tools and implantable bio-medical devices.

Li-O₂ batteries have garnered significant attention in recent years due to their high theoretical energy density (3505 Wh/kg), which is almost 5 times larger than those of current Li-ion batteries. Although, a lot of effort has been put into this field to develop viable Li-O₂ batteries, they are still in their infancy. A typical non-aqueous Li-O₂ batteries is composed of lithium anode, porous cathode (open to the air) and Li⁺-conductive liquid electrolyte between the electrodes. However, using liquid electrolytes in Li-O₂ batteries causes serious problems, including electrolyte evaporation/degradation during cycling, unstable Li metal interface due to Li dendrite growth or uncontrolled oxygen penetration, and limited choices in cell design. Therefore, many attempts have been made to replace liquid electrolytes with solid-state electrolytes to address these problems. Among solid-state electrolytes, gel polymer electrolytes (GPEs) composed of liquid electrolytes and polymer have been studied due to their impressive ionic conductivity and mechanical flexibility. However, little improvements have been reported for GPEs on recyclability and discharge capacity of Li-O₂ batteries. The aim of this study is to develop practical composite gel polymer electrolytes by combining different electrolytes, polymer and ceramic fillers. Electrochemical characterization including electrochemical impedance spectroscopy and Galvanostatic charge/discharge along with scanning electron microscopy (SEM), X-ray diffraction (XRD) have been performed.

Ag_0.50VOPO₄ (silver vanadium phosphate, SVOP) demonstrates a counterintuitive higher initial loaded voltage under higher discharge current. SVOP is a multi-mechanism material as it displays two reduction mechanisms, reduction of the vanadium center accompanied by lithiation of the structure, or reduction-displacement of the silver cation to form silver metal. Synchrotron radiation based energy dispersive X-ray diffraction (EDXRD) was used to create tomographic-like profiles of the active material and reaction products within the cathode at various depths of discharge for cells discharged under two rates. The EDXRD experiments were conducted where unmodified coin cells were probed through the stainless steel housings. Thus, in-situ EDXRD allowed for analysis of the cathode crystal structure changes during the battery discharge process. At the C/170 discharge rate the reduction of V⁵⁺ was the preferred initial pathway over reduction- displacement of Ag⁺. However, at a rate of C/400 the formation of conductive Ag⁰ could be detected at an earlier depth of discharge. Additionally, the discharge rate influenced the location of the reduction reaction and formation of silver metal within the cathode. Cells discharged at a faster rate showed a non-uniform reduction process resulting in an uneven distribution of Ag⁰ in the cathode near the current collector. A slower discharge rate resulted in a more homogeneous distribution of Ag⁰. This study assists in the elucidation of the roles of electronic and ionic conductivity limitations within a cathode at the mesoscale and how they impact the course of the reduction processes and the loaded voltage.

Ag₇Fe₃(P₂O₇)₄ is an example of an electrochemical displacement material which contains two different electrochemically active metal cations, where one cation (Ag⁺) forms metallic silver nanoparticles external to the crystals of Ag₇Fe₃(P₂O₇)₄ via an electrochemical reduction displacement reaction, while the other cation (Fe⁺³) is electrochemically reduced with retention of iron cations within the anion structural framework concomitant with lithium insertion. These contrasting redox chemistries within one pure cathode material enable high rate capability and reversibility when Ag₇Fe₃(P₂O₇)₄ is employed as cathode material in a lithium ion battery (LIB). Further, pyrophosphate materials are thermally and electrically stable, desirable attributes for cathode materials in LIBs. In this work, a bimetallic pyrophosphate material Ag₇Fe₃(P₂O₇)₄ is synthesized and confirmed to be a single phase by Rietveld analysis. Electrochemistry of Ag₇Fe₃(P₂O₇)₄ is reported for the first time in the context of lithium based batteries using cyclic voltammetry and galvanostatic discharge-charge cycling. The reduction displacement reaction and the lithium (de)insertion processes are investigated using x-ray absorption spectroscopy of electrochemically reduced and oxidized Ag₇Fe₃(P₂O₇)₄. Ag₇Fe₃(P₂O₇)₄ exhibits good reversibility at the iron centers and excellent rate capability. Mechanistic details and implications will be discussed.

Non-aqueous electrolytes with oxygen moieties (i.e. ethers, esters, sulfoxides) are known to coordinate with Li+ cations in solution. This coordination has been theorized to reduce the Lewis acidity of Li+ and thereby modify the reduction mechanism in lithium-oxygen/lithium-air batteries. The family of compounds known as room temperature ionic liquids (RTILs) is an interesting sandbox for designing selective coordination into electrolytes while maintaining good electrochemical stability, low vapor pressure, non-flammability and hydrophobicity. In this work, ionic liquids were modified to contain oxygen moieties that coordinate with Li+ in a variety of motifs. The physical properties of these species were determined and correlated to their behavior as electrolytes in Li-Air batteries.

All-solid-state Li-ion battery based on solid electrolyte materials is a promising next-generation Li-ion battery technology with intrinsic safety, high energy density, and enhanced cyclability. In particular, the high-energy Li metal anode may be enabled by the solid-state electrolyte. The key problem in enabling this new battery technology is the high interfacial resistance and interfacial degradation at the solid electrolyte-electrode interfaces. In this presentation, I will show how we use computational modeling to provide unique insights into the fundamental mechanisms at these buried interfaces, which are difficult to access in experiments. I will first demonstrate using first principles computation to predict various materials properties of the solid electrolyte materials with little experimental input. In addition, we systematically investigate and compare the electrochemical stability and chemical stability of the solid electrolyte-electrode interfaces, and study how these interfaces affect the interfacial resistance, low cyclability, and mechanical failure in all-solid-state Li-ion batteries. Our computation results suggest the formation of decomposition interphase layers in all-solid-state Li-ion batteries and the significant effects of the interphase layers on the electrochemical performance of the all-solid-state Li-ion batteries. Different interfaces between solid electrolyte and electrode materials may have different problems at the interfaces, which require different interfacial engineering strategies to resolve. The mechanisms of artificial layers to improve the interfacial properties are revealed by our computation. This computational study provides novel insights and general guidance for interfacial engineering in all-solid-state Li-ion batteries.

Most of our portable electronic devices currently rely on a lithium-ion battery as means of energy storage due to its remarkable cycle life and energy density. Over the years, the growing demand for larger energy storage capacity has been fulfilled by technical advances in lithium-ion battery, but this system is now getting close to its theoretical limits. Rechargeable Mg batteries have been proposed as candidates for post lithium-ion batteries due to their higher volumetric capacity, lower cost, and absence of dendrite formation.^[1]
Our group recently introduced a new family of electrolytes for Mg battery based on anions incorporating the B-H motif.^[2] Among them, magnesium monocarborane (MMC) stands out as the first simple-salt magnesium compound stable to Mg metal, providing high anodic stability, non-corrosive and chemically robust.^[3] Here, we will share our latest results aimed at gaining further understanding of the unique properties of MMC that are relevant to its use as electrolyte for Mg battery.

References:
[1] D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, E. Levi, Nature 2000, 407, 724.
[2] O. Tutusaus, R. Mohtadi, ChemElectroChem 2015, 2, 51.
[3] O. Tutusaus, R. Mohtadi, T. S. Arthur, F. Mizuno, E. G. Nelson, Y. V. Sevryugina, Angew. Chem. Int. Ed. 2015, 54, 7900.

Lithium-ion batteries are widely used for portable electronics, particularly laptops and mobile phones, due to their superior energy and power densities. In order to improve safety, flexibility in packaging, and energy densities, polymer gel electrolytes are used in lithium-polymer batteries, providing several important advantages over conventional liquid electrolyte systems, i.e. LiPF₆ in alkyl carbonates.[1] Typical thicknesses of gel electrolytes are on the order of 50 µm.[2] In this study, novel thin film gel electrolytes are being developed to replace conventional gels to reduce ohmic resistances and increase effective energy/power densities. These thin gels are synthesized using initiated chemical vapor deposition (iCVD) - a proven method to readily deposit polymer thin films with exquisite control over chemical compositions and physical properties for gel applications. Moreover, thickness can be tuned from 10nm to several micrometers, and the polymer film can be synthesized directly on the exposed surface area of LiCoO₂ composite cathodes. In this study, cross-linked poly (butyl acrylate) was synthesized by iCVD and combined with 1M LiPF₆ in EC:DMC:DEC (1:1:1). Crosslinking densities of the films were varied to modulate the liquid fraction in the gels, which govern mechanical properties and ionic conductivity. Conductivity was measured by electrochemical impedance spectroscopy (EIS). Characterizations by Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy demonstrated that the gel was stable on the cathode after imbibing the liquid electrolyte solutions. The coated cathodes were assembled into full cells against graphite anodes and cycled galvanostatically. High coulombic efficiencies and capacity retention over 100 cycles were observed, consistent with conventional cell chemistries. The effect of these gel coatings on the high voltage stability of LiCoO₂ and other state-of-the-art cathodes (e.g. LiMn_1.5Ni_0.5O₄) will be reported.

1. Hallinan, D.T. and N.P. Balsara, Polymer Electrolytes. Annual Review of Materials Research, 2013. 43(1): p. 503-525.
2. Santos, C.S.D., Polymer Electrolytes: Fundamentals and applications. 2010: Woodhead Publishing.

Although Li-ion battery technology has benefited from steady incremental improvements since its commercial introduction in 1991, the market demand for smaller, lighter, and less costly batteries remains strong. Over the past several years R&D efforts focused on next generation battery technology have covered a broad spectrum of alternative anodes and cathodes as well as the possibility of all solid-state structures and it is not yet clear which of these strategies will lead to commercial success. With regards to lithium-based technologies, there is little doubt that replacing the carbon anode in Li-ion cells with a lithium metal electrode that exhibits highly efficient cycling and safe behavior would lead to a dramatic increase in energy density (Wh/l and Wh/kg). In this presentation we will examine a number of development paths for solid-state anodes, as well as the evolution from Li-ion to safe, rechargeable Li metal batteries.

Solid electrolytes are generally claimed to have better resistance to growth and penetration of lithium dendrites than liquid electrolytes. The absence of clear and direct imaging of dendrites inside solid state batteries has led the field to speculate about their behavior. In this work, the first in situ images of naturally grown dendrites inside of a solid electrolyte allow conclusions about the growth behavior of dendrites in a solid. An analytical model based on the present observations shows that once initiated, the growth of dendrites is nearly unstoppable. Although the initiation of dendrites has been proposed to be suppressed if the shear modulus of the solid electrolyte is high enough, our results suggest that this criterion may be less important than the initial flaw population at the electrolyte interface, particularly in polycrystalline solid electrolytes.
The work was supported by the grant DE-SC0002633 funded by the U.S. Department of Energy, Office of Science.

Solid state electrolytes (SEs) in Li batteries are believed to be the ultimate solution to the electrode dissolution problems and safety hazards of liquid electrolyte (LE) systems. Sulfur based bulk type SE attracts great interest due to their relatively high ionic conductivities. Besides the bulk lithium ion conductivity, physical contact, structural evolution and redox reaction kinetics at SE and electrode interface during battery processes are other key factors that dictate the efficiency of battery cycling performances. The current challenge of studying the interfacial processes in operando in all solid battery systems is the difficulty of assembling an air-tight spectro-electrochemical cell with good electrical contact and optical accessibility to the interface of interest. In this work, a spectro-electrochemical cell is designed for an in operando Raman measurement at SE/Au interface during Li deposition and stripping processes. Three representative sulfur based SEs (β-Li₃PS₄, 70Li₂S-30P₂S₅ glass ceramic (LPS-GS) and Li₁₀GeP₂S₁₂ (LGPS)) were investigated. Spectroscopic data shows that, in general, partially reversible structural interconversion occurs among PS₄^3-, P₂S₆^3-, P₂S₇^3- and other unidentified P-S anion species. Corresponding variations in cell impedance also supports these interfacial structural evolutions. Result reveals that in all solid Li battery systems, oxidation/reduction of Li⁺ occurs along with breaking and reformation of the Li⁺-Anion interactions, which are usually accompanied by some unexpected, partially irreversible structural evolution of the counter ions. The resulted byproducts are later accumulated at the electrode/electrolyte interfaces. This result not only help build the electrochemical fundamentals of the molecular details at solid-solid interface but also guide the choice of materials and interfaces in all solid Li battery systems.

A rechargeable lithium metal battery (LMB), which uses metallic lithium at the anode, is among the most promising technologies for next generation electrochemical energy storage devices due to its high energy density, particularly when Li is paired with energetic conversion cathodes such as sulfur, oxygen/air, and oxygen-carbon dioxide mixtures. Practical LMBs in any of these designs remain elusive due to multiple stubborn problems, including parasitic reactions of Li metal with liquid electrolytes, unstable/dendritic electrodeposition at the anode during cell recharge, and chemical reaction of dissolved cathode conversion products with the Li anode. The solid electrolyte interface (SEI) formed between lithium metal and liquid electrolytes plays a critical role in all of these processes. We report on the chemistry and interfacial properties of artificial SEI films created by in-situ reaction of a strong Lewis Acid AlI₃, Li metal, and aprotic liquid electrolytes. We find that these SEI films impart exceptional interfacial stability to a Li metal anode. We further show that the improvements come from at least three processes: (i) in-situ formation of an Li-Al alloy; (ii) formation of a LiI salt layer at the interface; and (iii) creation of a stable oligomer thin film on the Li anode.
When the pretreated lithium metal is used as the electrode in symmetric Li/Li cells or as anode in Li-S cells, the stability of the electrode is shown to be greatly improved by multiple synergistic processes. These processes include the effect of LiI and Li-Al in stabilizing electrodeposition of Li against dendrite formation and protection of the Li anode in the Li-S cell from reaction with soluble LiPS and therefore reducing shuttling and anode surface passivation. The promising electrochemical results and scientific understanding made possible by the study, underscore the promise of AlI₃ and other strong Lewis acids as initiators for the formation of stable, self-limited polymer films that provide artificial SEI coatings to stabilize performance of electrochemical cells based on high-capacity conversion cathodes and metallic anodes.

Maintaining dimensional control of the lithium anode in a liquid electrolyte and eliminating parasitic reaction with the liquid electrolyte would enable lithium metal batteries for a variety of applications. Graphene is an attractive two dimensional material with which to form protective membranes for lithium. Graphene is readily functionalized, forms laminar freestanding films defined by a two dimensional pathway for ion transport, and, in an oxidized form, exhibits high shear modulus and fracture toughness. The key challenges in creating a stable graphene-based scaffold that can be placed in direct contact with lithium include insulating the scaffold from reductive decomposition by lithium, preventing electrolyte solvent permeation into and transport through the inter-sheet channels, and chemical functionality that supports Li cation transport. In this paper, we describe a systematic effort to address these challenges resulting in a Li cation conductive membranes. We demonstrate several examples where laminar nanocomposites based on either inorganic fast ion conductors with graphene oxide or ion conductive polymers with cross-linked graphene oxide. We demonstrate that these membranes can be integrated into coin and pouch cells supported onto standard commercial separators or as free-standing membranes. The membranes yield measureable increases in coulombic efficiency by blocking solvent access to the lithium surface.

Supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE’s NNSA under contract DE-AC04-94AL85000.

We will describe our work on the development of techniques for assessing Li-ion batteries and battery materials via magnetic resonance imaging (MRI). The goal of these studies is to analyze battery degradation and energy storage mechanisms in situ by imaging changes in both the electrolyte and the electrodes in a noninvasive fashion while a cell is charged or discharged. We have used this approach on a functioning lithium metal battery to correlate the behavior of the electrolyte concentration gradient to the type and rate of dendrite growth on the surface of the Li electrode, confirming the existence of separate growth mechanisms in different charging regimes. The methodology is extremely sensitive to Li dendrite formation, opening up the possibility of testing a broad range of materials and operating conditions to understand when dendrites grow and how they can be prevented.

The impact that the dendrites have on their surroundings through local magnetic fields also allow them to be measured indirectly using fast ¹H imaging techniques that can detect the ‘shadows’ of dendrites growing through the electrolyte. The result is a real-time, 3D movie showing dendrites growing across the electrodes in the cell, shedding light on the growth behavior, rate and morphology of the structures formed.

The poor performance and safety concerns of Li metal anodes represents a critical challenge to enable high energy density rechargeable batteries beyond Li-ion^1,2. This is attributed to the evolution of Li metal morphology during cycling, which leads to dendrite growth and surface pitting. Herein, we present a comprehensive understanding of the voltage variations observed during Li metal cycling, which is directly correlated to morphological evolution through the use of operando video microscopy³. A custom-designed visualization cell was developed to enable in situ synchronized observation of Li metal electrode morphology and electrochemical behavior during cycling. A mechanistic understanding of the complex behavior of these electrodes is gained through correlation with continuum-scale modeling, which provides insight into the dominant surface kinetics. This work provides a comprehensive explanation of (1) when dendrite nucleation occurs, (2) how those dendrites evolve as a function of time, (3) when surface pitting occurs during Li electrodissolution, (4) kinetic parameters that dictate overpotential as the electrode morphology evolves, and (5) how this understanding can be applied to evaluate electrode performance in a variety of electrolytes. An understanding of how the impedance of reaction pathways change during cycling is used to provide predictive insight into the behavior lithium metal anodes. This provide detailed insight into the interplay between morphology and the dominant electrochemical processes occurring on the Li electrode surface through an improved understanding of changes in cell voltage, which represents a powerful new platform for analysis.
References:
(1) Bruce, P. G.; Hardwick, L. J.; Abraham, K. M. MRS Bull. 2011, 36 (07), 506.
(2) Gallagher, K. G.; Goebel, S.; Greszler, T.; Mathias, M.; Oelerich, W.; Eroglu, D.; Srinivasan, V. Energy Environ. Sci. 2014, 7 (5), 1555.
(3) Wood, K. N.; Kazyak, E.; Chadwick, A. F.; Chen, K.-H.; Zhang, J.-G.; Thornton, K.; Dasgupta, N. P. Submitted 2016.

Lithium batteries (LBs) have been widely utilized to alternate the previous energy storage devices due to high energy density and good cycle life, however, a new approach is required to improve the performance of the batteries. Introduction of lithium (Li) metal is one of the most challenging anode material to increase the energy density of LBs. In spite of attractive properties, there are several limitations to use the Li metal in LB due to poor cycle life and safety problem from dendrite formation on the surface. Herein, we introduce polymerized ionic liquid (PIL)-based random copolymers comprising styrene and pyrrolidinium-based ionic liquid as the monomers to improve electrochemical performances of Li metal anode in Li metal batteries (LMBs). The PIL-based random copolymer, polystyrene-co-polyvinylbenzyl-methyl-pyrrolidinium bis(fluorosulfonyl)imide (PS-VBMP FSI), contains both strengthen part and Li ion-balancing part, which can effectively prevent the formation of dendrite on the surface of Li during charge/discharge process causing performance deterioration of LMBs. NMR, MALDI-TOF, and GPC are used to confirm the molecular structure of the obtained polymer followed by synthetic process of the polymer.
First of all, we introduce PS-VBMP FSI-based protective layer on the surface of Li metal anode followed by fabrication of Li/Li symmetry coin cell and Li-LCO coin cell with ether-based electrolyte. The results of electrochemical performance indicate 35% and 10% improved cycle stability compared to bare Li/Li symmetric and bare Li/LCO cells, respectively. This trend is directly reflected in depressed dendrite formation by PS-VBMP FSI-based protective layer on the surface of Li metal anode. Additionally, we prepare PS-VBMP FSI-based solid polymer electrolyte (SPE) using simple solvent casting method. The prepared freestanding SPE shows great Li ion transfer property, such as 1.93x10^-5 S/cm (25 °C) and 1.56x10^-4 S/cm (60 °C) of enhanced ionic conductivities and 0.55 of lithium transference number. For evaluation of the electrochemical performance, we figure out the cycle test of the Li/PS-VBMP FSI-based SPE/LiFePO₄ coin cell at 60 °C of operation temperature. This all solid-state LMB is well performed at 0.1 mA/cm² of C/D rate with 130 mAh/g of specific capacity and 99.2% of Coulombic efficiency without shortage and/or cell-resistance increasing problems. To understand the effects of PS-VBMP FSI on the surface of Li metal in charge/discharge process, we investigate molecular dynamics computer simulations indicating depressed dendrite formation due to Li ion shielding effect of PIL parts on the dendrite initiation point. Through this work, we systemically demonstrate the potential of the PIL-based random copolymer to improve cycle stability of Li metal in not only liquid system but also all-solid system due to depression of the dendrite formation, leading to the assembly of Li metal anode in the LMBs.

We describe some of the developments in solid electrolytes accomplished in our laboratory in recent years under the categories nanoporous gel electrolytes and plastic crystal proton and alkali metal ion conductors.

Room temperature ionic liquids are attractive to numerous applications and particularly, to renewable energy devices. As solvent free electrolytes, they demonstrate a paramount connection between the material morphology and Coulombic interactions: the electrode/RTIL interface is believed to be a product of both polarization and spatiotemporal bulk properties. Yet, theoretical studies have dealt almost exclusively with independent models of morphology and electrokinetics [1]. Introduction of a distinct Cahn−Hilliard−Poisson type mean-field framework for pure molten salts (i.e., in the absence of any neutral component), allows a systematic coupling between morphological evolution and the electrokinetic (inter-diffusion) phenomena, such as transient currents [2]. Specifically, linear analysis shows that spatially periodic patterns form via a finite wavenumber instability and numerical simulations demonstrate that while labyrinthine type patterns develop in the bulk, lamellar structures are favored near charged surfaces. The results demonstrate a qualitative phenomenology that is observed empirically and thus, provide a physically consistent methodology to incorporate phase separation properties into an electrochemical framework.

[1] A. Yochelis, M. B. Singh, and I. Visoly-Fisher, Coupling bulk and near-electrode interfacial nanostructuring in ionic liquids, Chem. Mater. 27, 4169 (2015).
[2] N. Gavish and A. Yochelis, Theory of phase separation and polarization for pure ionic liquids, J. Phys. Chem. Lett. 7, 1121 (2016).

Ionic liquids (ILs) are pure solutions of charged organic molecules with no solvent. These molecular electrolytes show a property original for a pure liquid: they self-organize in nanometric fluctuating aggregates [1]. When probed at the macroscopic scale, ILs behave as highly dissociated (i.e. strong) electrolytes [2] while, at the molecular scale, they show clear characteristics of weak ionic solutions [3]. In this talk, we report a multi-scale analysis that reconciles these apparently at odd behaviors.
We investigate by Quasi-Elastic Neutron Scattering (QENS) and Neutron Spin-Echo (NSE), the nanometer/nanosecond dynamics of BMIM-TFSI and OMIM-BF₄, two imidazolium based ILs showing respectively low and strong nanostructuration. We also probe the same ILs on the microscopic (mm and ms) scales by Pulsed Field Gradient NMR. To interpret the neutron data, we introduce a new physical appealing model to account for the dynamics of the side-chains and for the diffusion of the whole molecule. We take advantage of specific deuteration to show that this modelization is robust enough to describe the observables over the whole and unprecedented investigated Q ([0.15 - 2.5] Å^-1) and time ([0.5 - 2000 ] ps) ranges.
We reach a coherent and unified structural/dynamical description of the local cation dynamics: a localized motion within the ILs nanometric domains is combined with a genuine long-range translational motion. The QENS-NSE and NMR experiments describe a same long-range translational process, but probed at different scales. Depending on the IL level of nanostructuration, the associated diffusion coefficients can be up to one order of magnitude different. We show how this apparent discrepancy is a manifestation of the ILs nanostructuration.
Due to their remarkable chemical and electrochemical stability, ILs have been identified as prime candidates electrolytes for the development of new safe and sustainable energy storage systems. We show [4] a noticeable enhancement (by a factor 3) of the transport properties of Ils under CNT (Carbon NanoTube) confinement in a 1D situation. A patent [5] has been filed on the use of CNT membranes as a possible solution to boost the transport properties and hence the specific power of lithium batteries.

[1] R. Hayes, G. G. Warr and R. Atkin, Chem. Rev. 115, 6357 (2015).
[2] A. A. Lee, D. Vella, S. Perkin and A. Goriely, J. Phys. Chem. Lett. 6, 159 (2015).
[3] M. A. Gebbie et al., Proc. Natl. Acad. Sci. 110, 9674 (2013).
[4] Q. Berrod et al., Nanoscale 8, 7845 (2016).
[5] Q. Berrod, F. Ferdeghini, P. Judeinstein and J.-M. Zanotti, Patent FR1552572 (2016).

Ionic liquids show potential for use as electrolyte materials in Li-ion batteries. They possess desirable characteristics such as non-volatility, non-flammability, and high ionic conductivity. Additionally, they can be "tuned" to achieve different properties by altering the anion or cation used.
Multinuclear (¹H, ⁷Li, ¹⁹F) NMR measurements are to be completed on a family of pyrrolidinium-bis(trifluoromethane)sulfonimide (Pyrr-TFSI) ionic liquids. The chain length on the Pyrr cations were varied with 3, 5, 6, 7, 8, or 9 carbons in the chain. Variable pressure (ambient to 250 MPa) diffusion (D) and spin-lattice relaxation (T₁) measurements were undertaken.
In addition to the pure ionic liquids, measurements are also being made with the addition of Li-TFSI salt at a 15%/wt concentration. Measurements for T₁ and diffusion can elucidate information on localized motion and translational motion, respectively. The nucleus specific nature of NMR allows us to probe the motions of the Pyrr cation, TFSI anion, and Li cation independently. Of particular interest here is the effect of chain length on both long and short range motion of all the ions in the IL/Li-salt mixtures.
With this information, we can expand current knowledge on the transport properties of these "designer solvents" in order to create better electrolytes for Li-ion batteries.

Liquid crystals are molecular self-assembled materials, which can provide nanoscale functional structures. Our intention is to use these bicontinuous cubic, smectic, and columnar liquid-crystalline (LC) states for the development of new transport materials because well-controlled 3D, 2D, and 1D ionic nano-channels are formed in these materials.[1,2] Herein we describe design of ion conductive nanostructured liquid crystals and approaches to applications of these materials.[3-7] Lithium-ion batteries have been developed based on smectic LC electrolytes consisting of polar mesogenic molecules and lithium salts.[4] Smectic LC electrolytes have also been used for the fabrication of dye-sensitized solar cells (DSSCs).[5] They can be used as thermally stable electrolytes for DSSCs.
Partial financial support by CREST, JST is gratefully acknowledged.
References
[1] Kato, T. Angew. Chem. Int. Ed. 2010, 49, 7847.
[2] Kato, T. Science, 2002, 295, 2414.
[3] Ichikawa, T.; Yoshio, M.; Hamasaki, A.; Taguchi, S.; Liu, F.; Zeng, X,; Ungar, G.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2012, 134, 2634.
[4] Sakuda, J.; Hosono, E.; Yoshio, M.; Ichikawa, T.; Matsumoto, T.; Ohno, H.; Zhou, H.; Kato, T. Adv. Funct. Mater. 2015, 25, 1206.
[5] Hogberg, D.; Soberats, B.; Uchida, S.; Yoshio, M.; Kloo, L.; Segawa, H.; Kato, T. Chem. Mater. 2014, 26, 6496.
[6] Soberats, B.; Yoshio, M.; Ichikawa, T.; Taguchi, S.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2013, 135, 15286.
[7] Soberats, B.; Yoshio, M.; Ichikawa, T.; Zeng, X.; Ohno, H.; Ungar, G.; Kato, T. J. Am. Chem. Soc. 2015, 137, 13212.

After a remarkable evolution over the last 30 years, nowadays Ionic Liquids (ILs) play an essential role in a wide variety of application, as in chemical industry, medicine, and even space technology. However, their low viscosity often precludes them from being used as macroscopic stable components, for instance, in battery electrolytes or gas separator membranes. In order to overcome this constraint (and to satisfy the processing industry), the outstanding features of neat ILs are combined with the well controllable macroscopic properties of polymers, which leads to a novel class of materials known as Polymeric Ionic Liquids (PILs). Although PILs have already demonstrated remarkable performance in electrochemical devices (such as in dye-sensitized solar-cells, actuators, or field effect transistors), their most fundamental properties are basically not yet understood. In the current study, the chemical structure of PILs is systematically varied and, on the other hand, the measurement techniques of Broadband Dielectric Spectroscopy (BDS), Transmission Electron Microscopy (TEM) as well as Differential Scanning (DSC) and AC-Chip Calorimetry are strategically employed. Hence, one is able to investigate in detail the underlying charge transport mechanism(s), molecular dynamics, polarization effects, and mesoscopic structures in PILs.

References:
[1] Frenzel, F.; Folikumah, M. Y.; Schulz, M.; Anton, A. M.; Binder, W. H.; Kremer, F. Molecular Dynamics and Charge Transport in Polymeric Polyisobutylene-Based Ionic Liquids. Macromolecules, 2016
[2] Frenzel, F.; Binder, W. H.; Sangoro, J. R.; Kremer, F. Glassy dynamics and Charge Transport in Polymeric Ionic Liquids. Springer 'Dielectric Properties of Ionic Liquids', 2016
[3] Sangoro, J. R.; Iacob, C.; Agapov, A. L.; Wang, Y.; Berdzinski, S.; Rexhausen, H.; Strehmel, V.; Friedrich, C.; Sokolov, A. P.; Kremer, F. Decoupling of ionic conductivity from structural dynamics in polymerized ionic liquids. Soft Matter, 2014
[4] Choi, U. H.; Mittal, A.; Jr., T. L. P.; Gibson, H. W.; Runt, J. & Colby, R. H. Polymerized Ionic Liquids with Enhanced Static Dielectric Constant. Macromolecules, 2013

Ionic liquids (ILs) offer the potential to replace volatile aqueous- and organic-based electrolytes due to their moderate room temperature ionic conductivity (1-10 mS/cm), negligible vapor pressure, and high electrochemical stability (3-5 V). Solvate ionic liquids (SILs) are an emergent subclass of IL electrolytes that offer the advantages of traditional ILs while incorporating an inorganic cation (or anion) species, which is coordinated by a neutral ligand to form a complex ion. For example, lithium cation-containing SILs have previously been demonstrated by complexing the Li⁺ cation of an appropriate lithium salt with oligoether ligands (such as tetraglyme) to form a nonvolatile liquid electrolyte that is suitable for lithium-based electrochemical energy storage devices. While SIL/IL electrolytes hold great promise for many future applications, incorporating these liquids into solid-state gel electrolytes is a compelling direction of investigation due to the leakproof nature and robust flexibility of gels. Here, mechanically robust solvate ionogel electrolytes have been fabricated via in situ free-radical polymerization/cross-linking of poly(ethylene glycol) diacrylate (PEGDA) to immobilize the solvate ionic liquid [Li(G4)][TFSI], which consists of an equimolar mixture of lithium bis(trifluoromethanesulfonyl)imide (Li[TFSI]) and tetraglyme (G4). Solvate ionogels with varying PEGDA content have been prepared, and their electrochemical, ion transport, and mechanical properties have been measured. Lithium ion diffusivity values measured by pulsed-field gradient spin-echo NMR spectroscopy demonstrate an increase from 6.0 x 10^-12 m²/s to 10.0 x 10^-12 m²/s as the PEGDA content is increased from the minimum gelation point (8 vol.%) up to 21 vol.% polymer; the corresponding Li⁺ transport numbers increase from 0.510 to 0.575, respectively. Meanwhile, room temperature ionic conductivity measurements reveal high conductivities, up to 0.89 mS/cm at 8 vol.% PEGDA. Compression testing verifies a widely tunable elastic modulus of these solvate ionogels, varying from 2 kPa to 1.6 MPa. Importantly, analogous solvate ionogels containing a polymer network lacking ethylene oxide chains (cross-linked poly(methyl methacrylate)) exhibited lower ionic conductivities and lower Li⁺ transport numbers. These results suggest that a chemically cross-linked polymer network containing ethylene oxide moieties includes additional conductive pathways to facilitate enhanced lithium ion transport. In the case of a 21 vol.% PEGDA solvate ionogel, an exceptionally high Li⁺ transport number (0.575) was achieved while still maintaining good room temperature ionic conductivity (0.39 mS/cm), making these novel gel electrolytes strong candidates for solid-state lithium-based electrochemical energy storage applications.

Single-ion conducting ionomers offer enormous potential advantages as battery electrolyte materials. By covalent attachment of anions to polymers, polarization of anions during charge and discharge can be greatly reduced, allowing faster charging, raising the power limits for battery use and potentially avoiding dendrite growth across the electrolyte that shorts the battery. The most successful ionomers thus far are based on poly(ethylene oxide) (PEO) because lone electron pairs on each ether oxygen provide strong specific solvation of small cations (Li and Na), greatly diminishing ion aggregation. We have recently reported Li diffusion in PEO-based single-ion conducting ionomers. To our surprise, we find that the diffusion is orders of magnitude faster than expected by measured ionic conductivity using the Nernst-Einstein equation! That result means that the majority of Li diffusion occurs by ion pairs moving with the polymer segmental motion. Segmental motion only contributes to ionic conduction in the rare event that one of these ion pairs has an extra Li (a positive triple ion). This leads us to a new metric for ion-conducting soft materials, the product of the cation number density p₀ and their diffusion coefficient D_NMR; p₀D_NMR is the diffusive flux of lithium ions. This new metric has a maximum at intermediate ion content that corresponds to the overlap of ion pair polarizability volumes. At higher ion contents, the ion pairs interact strongly and form larger aggregation states that retard segmental motion of both mobile ion pairs and triple ions. Since the ion pair polarizability volume overlap parameter is proportional to the dielectric constant, this picture also explains our counter-intuitive observation that raising the dielectric constant of the polymer actually forces stronger ion aggregation, since the polarizability volumes of ion pairs then overlap more. This conundrum appears to be ubiquitous to this class of materials and we close with some suggested paths forward.

Commercial Li ion batteries use liquid electrolytes between the electrodes to obtain good Li ion conductivity and thus good energy density. However, the liquids are highly flammable, which presents a great challenge in designing large scale batteries. Solid polymer electrolytes (SPEs) based on poly(ethylene oxide) (PEO) have been widely explored as an alternative of all-solid-state Li ion batteries. However, their wide adoption is prohibited due to their low conductivity at room temperatures (lower than 10^-5 S cm^-1), presumably because PEO is semicrystalline and crystals may not be available for ion conductivity. The goal of this study is to design and prepare series of polymers containing amorphous PEO with high free volume, achieving higher Li ion conductivity than the semi-crystalline PEO. Specifically, polymers were prepared using UV photopolymerization from poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) methyl ether acrylate (PEGMEA). The addition of PEGMEA in PEGDA increases the free volume and polymer chain flexibility. Polymer electrolytes based on PEGDA-co-PEGMEA and lithium perchlorate (LiClO₄) have been prepared and characterized using DSC, WAXD and electrochemical impedance spectroscopy (EIS). At PEGMEA content of 90% in the polymer with an O:Li ratio of 14, the conductivity approaches the current industrial targeted value (10^-5 S/cm), which is two orders of magnitude higher than that of pure PEO. The value of 10^-5 S/cm is also one of the highest values reported for SPEs at room temperature. This presentation will also compare the results with those based on the PEO-containing materials using the Vogel-Fulcher-Tammann (VFT) equation.

Electrochemical energy storage devices are increasingly desired for consumer vehicle electrification and renewable power utilization. Safety and performance of batteries is strongly dictated by the performance of the electrolyte. Polymer electrolytes offer advantages over liquid and ceramic/inorganic electrolytes, as they are non-leakable and non-volatile while flexible. Single-ion conducting electrolytes that eliminate ion concentration gradients offer further advantages: greater electrochemical stability allowing for higher voltage cells, lower interfacial impedance, and higher theoretical charge/discharge rates. Single-ion conducting polymer electrolytes may simply be created by titration of an ionomer with the active ion – Li+ in a Li-ion battery, for example. Unfortunately, the drastically low ionic conductivity of single-ion conducting polymer electrolytes without added solvent has precluded their commercial application thus far. Improved understanding of lithium ion transport mechanisms is critical for the development of high performance electrolytes. Our investigations of Li+ transport in various lithiated side-chain ionomers will be detailed.

In the realm of host materials for polymer electrolytes, polyethers – particularly poly(ethylene oxide) (PEO) – has long been the sole ruling class and ever since the initial discovery of ionic conductivity in polymeric solids, it is PEO that has seen the bulk of the research effort. Despite the well-known limitations of PEO, [1] alternative materials have historically received only limited attention. [2] Following recent research progress, however, this has begun to change, and particularly electrolytes based on polycarbonates have been actively investigated by several research groups. [3–5]
We have applied materials based on polycarbonates and polyesters in Li batteries as well as in light-emitting electrochemical cells (LECs) – two applications wherein PEO has been the traditional choice of ion transport material, but that in several respects have widely differing demands regarding the materials characteristics. Here, the synthetic flexibility of these materials platforms has proven highly valuable to enable materials specifically tailored for each of these applications.
In the context of Li batteries, we have successfully developed materials with ionic conductivity in excess of 4×10⁻⁵ S cm⁻¹ at room temperature [6] and cation transference numbers that widely exceed those seen for polyether electrolytes. [7] This has enabled the construction of Li polymer batteries operational at ambient temperature. For LECs we have, in contrast, recently shown that the ionic conductivity, while related to the turn-on kinetics, is not critical for the operational characteristics. [8] Instead, ion release kinetics and compatibility between the electrolyte and the light-emitting material [8,9] are important characteristics to consider for the device performance. Here, we present new polycarbonate-based ion transporter materials that give unprecedented performance in terms of brightness and efficiency for polymer LECs, with devices that show a record-breaking maximum current efficacy of 13.4 cd A⁻¹ at a brightness of 1063 cd m⁻².
Altogether, these results usher in a new era of polymer electrolyte development to enable realization of the full potential of solid-state electrochemical devices beyond the polyether paradigm.

References

[1] O. Buriez et al., J. Power Sources, 89 (2000) 149–155.
[2] K. Xu, Chem. Rev., 114 (2014) 11503–11618.
[3] Y. Tominaga, K. Yamazaki, Chem. Commun., 50 (2014) 4448–4450.
[4] B. Sun et al., Electrochem. Commun., 52 (2015) 71–74.
[5] M. D. Konieczynska et al., ACS Macro Lett., 4 (2015) 533–537.
[6] J. Mindemark et al., J. Power Sources, 298 (2015) 166–170.
[7] B. Sun et al., Phys. Chem. Chem. Phys., 18 (2016) 9504–9513.
[8] J. Mindemark et al., Chem. Mater., 28 (2016) 2618–2623.
[9] S. Tang et al., Chem. Mater., 26 (2014) 5083–5088.

Glymes have demonstrated desirable characteristics as solvents in a variety of Li-ion batteries. We report here a comprehensive Nuclear Magnetic Resonance (NMR) characterization of variable chain length glymes with lithium triflate salt. Pulsed-field gradient diffusion measurements (of ¹H to track the solvent, ⁷Li to track the cation, and ¹⁹F to track the anion) were performed, as well as natural abundance ¹⁷O chemical shift measurements. These measurements, along with comparisons to previous measurements using other techniques, allow us to identify ion association, mobility of the separate species, and small changes in the electronic environment of the oxygen members of each group. We discuss mechanisms driving some aspects of the performance of these electrolytes. We also discuss extending these solvents for use with other lithium- and sodium-based salts, measurements of which are in progress.

Intense research in renewable energy is stimulated by global demand of electric energy. Electrochemical energy storage and conversion systems namely, supercapacitors and batteries, represent the most efficient and environmentally benign technologies. Moreover, controlled nanoscaled architectures and surface chemistry of electrochemical electrode materials is enabling emergent next-generation devices approaching theoretical limit of energy and power densities and deliver electrical energy rapidly and efficiently. In this work we develop graphene-inorganic hybrid assembly highlighting the impacts of nanoscale internal microstructure producing tailored interfaces for improved electrochemical and electroanalytical properties. Molecular electrodeposition and facile hydrothermal synthesis techniques followed by thermal treatment are demonstrated to be effective approaches for nanoengineered electrochemical electrodes. The electrode assembly consists of supercapacitive graphene nanosheets and pseudocapacitive nanostructured transition metal oxides (TMeOs) synthesized on two- and three-dimensional graphene nanosheets facilitate chemically bridged (covalently and electrostatically anchored) yet tunable graphene-TMeO interfaces. The intrinsic microstructure and surface of these hybrids were characterized by electron microscopy combined with elemental mapping, X-ray diffraction and Raman spectroscopy. The electrochemical properties are investigated as asymmetric hybrid supercapacitors. We demonstrated that hybrids show improved electrochemical performance as compared with constituents by themselves. We attribute the remarkable findings due to interplay of (a) open pore system beneficial to ion diffusion and transport kinetics owing to larger accessible geometric surface area, (b) three-dimensional topologically multiplexed and highly conductive pathways provided by multilayer graphene, electrochemically reduced graphene oxide and hydrothermal processed reduced graphene oxide nanoscaffold architectures to ensure rapid charge transfer and electron/ion conduction (< 10 ms), and (c) synergistic integration of functional nanomaterials devoid of graphene sheets agglomeration with optimal transition metal (oxides) nanoparticles loading. Computational simulations via periodic density functional theory (DFT) with and without transition metal adatoms on graphene and graphene oxide sheets are performed. These calculations determine the total and hybridized partial electronic density of states (DOS) in the vicinity of Fermi level thereby complementing and synergizing experimental work in terms of various contributions toward surface/interfacial charge transfer sites on heterogeneous electrodes, electron/ion transport, pseudocapacitive and electric double layers.

Supercapacitors (SCs), also called electrochemical capacitors, are promising energy-storage system due to their high power density, short charging times, simple energy-storage mechanism, and long cycle stability. However, practical application of SCs has been limited by their low energy density as opposed to that of batteries and fuel cells. The energy density of SCs can be improved by adjusting the operating voltage range and capacitance. For example, a combination of two different electrode materials significantly improves the operating voltage range. Additionally, nanomaterials applied to the active material have been shown to improve the capacitance of SCs. From a material viewpoint, innovative active electrode materials that have a high surface area, high theoretical capacitance, and high conductivity should enhance the capacitance.
One-dimensional (1D)-nanostructured electrically conductive materials are candidates for working electrode materials because of their design simplicity and fast charge-transportation network. Among the 1D materials, carbon-based forms offer excellent cyclability, good electrical conductivity, a high surface area, and long service life. The hollow 1D tubular structure of CNTs, for example, offers several beneficial features. First, the 1D structure facilitates efficient electron transport along the longitudinal direction. Second, the 1D hollow inner-pore structure increases the ion flux owing to the large surface-to-volume ratio with the electrolyte. In this regard, a 1D structure with a more complicated inner hollow structure might provide the advantages of more accessible electrolyte ion diffusion and faster charge transport. Enhanced electrochemical performance requires optimization and simplification of the fabrication processes of 1D nanostructures with complicated inner-pore configurations to take full advantage of the porous features.
In this presentation, we propose the facile mathod of manganese oxide (MnO₂) coated 1D hollow multichannel CNF for SCs electrode material. The hollow multichannel structured CNFs (MCNFs) were gained from single nozzle co-electrospinning of two immiscible polymer solutions, followed by carbonization. To maximize the capacitance of the active material, the surface of MCNFs and their inner hollow channels were coated with MnO₂. The amount of MnO₂ on the MCNFs was controlled by adjusting the reaction time, and the Mn_MCNFs of various reaction times were applied to the SC electrode material. The optimized Mn_MCNF for this study (Mn_MCNF_60 corresponding to a 60 min reaction time for optimal MnO₂ growth) exhibited a specific capacitance of 837 F g^–1. The synergetic effect of the hollow structure and MnO₂ resulted in enhanced electrolyte diffusion for better rate capability and charge–discharge performance.

Supercapacitors have attained a large attention due to its potential energy storage capacity [1] in the recent years. Among the available metal oxide based materials, MnO₂ is considered as a promising material due to its exceptionally high theoretical specific capacitance (1370 F/g), robust thermal operating range, high cyclic stability, low cost and eco-friendliness. However the low electronic conductivity of the material is an important issue to be addressed to tap the maximum specific capacitance. Various methods have been adopted by different groups include metal doping, carbon coating, sizing down to nano range and morphological variation etc. [2, 3]. In the attempt to increase the performance of MnO₂ based electrode material, we have synthesized pristine and 3 mol% Zn doped MnO₂ nanoflakes by a low temperature hydrothermal method. The Zn doped MnO₂ shows a superior performance compared to the pure case which is due to the increment in the electronic conductivity of the material upon Zn doping. An asymmetric supercapacitor assembly has been made by using the doped MnO₂ as positive electrode and activated carbon as the negative electrode. Supercapacitor device is showing a good specific capacitance ~ 60 F/g with an extended voltage window (~ 2.6 V) in 1 M Na₂SO₄ aqueous electrolyte. We will present structural, spectroscopic, thermal, microscopic and electrochemical studies for the pure and doped MnO₂ and the build up of a supercapacitor assembly along with its performance evaluation.
References
1) B.E. Conway, Electrochemical Supercapacitors: Scientific, Fundamentals, and Technological Applications.
Kluwer, (New York), 1999.
2) J. W. Lee, A. S. Hall, J.-D. Kim and T. E. Mallouk, Chemistry of Materials 24 (6), 1158-1164 (2012).
3) Y. Qiao, Q. Sun, H. Cui, D. Wang, F. Yang and X. Wang, RSC Advances 5 (40), 31942-31946 (2015).

This work introduces a facile electrochemical method that can substantially improve the capacitance of graphene-based electrodes while still retains their excellent rate capability. This method involves two ion-intercalation steps (lithium-ion intercalation and perchlorate-ion intercalation), followed by hydrolysis of perchlorate ion intercalation compounds. Lithium ion intercalation mainly leads to surface exfoliation, whilst the hydrolysis of perchlorate ion intercalation compounds functionalizes graphene surface with oxygen moieties. Electrochemically treated graphitic paper electrode shows 1000 times enhancement in areal capacitance. Without the need of post-treatment annealing, the treated graphitic paper maintains an outstanding rate capability of 84% (0.5 mA/cm² to 5 mA/cm²). The same strategy can also be extended to boost the gravimetric capacitance of lightweight 3D printed graphene aerogels. The treated graphene aerogel achieved an outstanding gravimetric capacitance of 101.7 F/g (10 A/g) with an excellent rate capability of 81.6% (0.5 A/g to 10 A/g).

Materials with the ability to rapidly store and release charge offer great opportunities for energy storage technologies. Producing well-defined electrode architectures with efficient electron conduction pathways is a promising target for fast charge transport, while maintaining the structural integrity of these electrodes under operating conditions is critical for practical use. Co(OH)₂ is a strong candidate energy storage material due to its high theoretical specific capacity and electrical conductivity. We have synthesized a hierarchical electrode composed of 30 nanometer diameter tubes with concentric layers of Co(OH)₂ and 1-pyrenebutyric acid (PyBA). The nanotubular structure with perpendicular orientation to the current collector provides efficient electron transport along the length of the tubes, while the large spacing between the Co(OH)₂ layers allows for better electrolyte access and higher electrochemical activity. However, Co(OH)₂ structures with large interlayer spacing are fundamentally unstable in the alkaline electrolytes required for optimum performance. A rapid dissolution-reprecipitation process occurs after immersion in such strong alkaline electrolytes, resulting in formation of small β-cobalt oxyhydroxide platelets with lower electrochemical activity and poor interparticle electrical conductivity. We discovered that adding high concentrations of PyBA into the alkaline electrolyte prevents decomposition of the hybrid structure with negligible loss of charge storage capacity. We also present further experiments with other small molecules and polymer electrolyte additives to elucidate the role of supramolecular interactions versus covalent bonding in passivation of the Co(OH)₂ dissolution.

In this work, we report on the fabrication and characterization of symmetric supercapacitors with nanocomposite electrodes of polypyrolle (PPy) and silver nanowires (Ag NW). Ag NWs provided high surface area, high conductivity and a template for the attachment of PPy. In-situ chemical oxidation polymerization was utilized for the deposition of PPy onto Ag NWs and resulted in the formation of a core-shell structure. PPy created a porous 3D network attaching core-shell Ag NW/PPy nanocomposites at the junction points. Electrochemical properties, such as specific capacitance and cycle life of the supercapacitors with these nanocomposite electrodes were then investigated through cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. A specific capacitance of 70.4 F g^-1 and remarkable capacity retention with almost no degradation upon 10000 cycles was obtained for Ag NW/PPy nanocomposite supercapacitor devices, which was higher than that of bulk PPy control devices. We will present a detailed analysis of charge transfer properties of the fabricated supercapacitors to underline their capacitive behavior. Our obtained results show the potential of the use of Ag NW/PPy nanocomposites in energy storage devices and the method investigated herein can be simply adapted to various other metallic nanowire systems.

In this work, we report on the fabrication and characterization of vertically aligned carbon nanotube (VACNT) - polyaniline (PANI) nanocomposite supercapacitor electrodes on aluminum foils. 5 μm long VACNTs were grown using chemical vapor deposition method, which is followed by the electrodeposition of PANI onto the VACNTs to finalize the nanocomposite electrodes. Electrochemical properties such as specific capacity and capacity retention of the fabricated nanocomposite electrodes were examined through cyclic voltammetry, chronopotentiometry, electrochemical impedance spectroscopy by three electrode system and compared to that of control sample fabricated simply by depositing PANI onto aluminum foils. The effect of deposited PANI thickness to the electrochemical properties of the electrodes were also examined. Produced supercapacitor electrodes showed encouraging results with a specific capacitance of 80 F g^-1. Highly conducting VACNTs modified the surface of the aluminum electrodes by translating the conventional 2D interface to a 3D interface and enhanced the charge transport from PANI to current collecting aluminum electrode. A comprehensive analysis on the electrochemical properties of the fabricated supercapacitor electrodes will be presented. The structure presented in this work is highly plausible and can be easily extended to other conducting polymer systems.

This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Grant No: 113E596.

Three-dimensional (3D) hierarchical Co3O4@Co3S4 nanoarrays (NAs) were synthesized via a stepwise hydrothermal method involving precipitation and in-situ sulfurization of Co3O4 nanoneedle arrays (NNAs). By controlling both anion exchange and ostwald ripening reactions during the sulfurization process, 3D hierarchical Co3O4@Co3S4 NAs with tailored Co3S4 nanostructures have been fabricated as electrode materials for electrochemical capacitor applications. Owing to an interconnected matrix within the 3D architecture, the as-prepared Co3O4@Co3S4 NAs exhibit excellent electrical conductivity, high specific capacity and high cycling stability. It can deliver a high capacitance of 1284.3 F g-1 at 2 mV s-1 and maintained a capacitance retention of 93.1 % after 5000 cycles. Moreover, a flexible solid-state asymmetric supercapacitor (ASC) composed of Co3O4@Co3S4 NAs as the positive electrode and activated carbon (AC) as the negative electrode exhibited an energy density of 1.5 m Wh cm-3 and a power density of 6.1 W cm-3 at a high operating voltage of 1.6 V. Our result not only presents the 3D hierarchical nanostructure of Co3O4@Co3S4 NAs, but it also demonstrates the potential of electrodes for future generation supercapacitors.

Although layered double cobalt hydroxides (LDCHs) have been well known as a promising pseudocapacitive materials, the unsatisfactory conductivity and unstable structure are seriously concerned for practical applications with long cycle life. To address this issue, here, silver is for the first time incorporated to the LDCHs via a simple one-step co-electrodeposition process. A simultaneous growing silver-doped layered double cobalt hydroxide (Ag-LDCHs) nanosheets on a reduced graphene oxide (rGO)-coated functionalized carbon fiber paper (f-CFP) was carried out in 1 mM AgNO₃ + 100 mM Co(NO₃)₂ in 0.5 M NaNO₃ at -0.5 V vs. Ag/AgCl for 10 min. Ag-LDCHs consist of high porosity LDCHs decorated with silver nanoparticles. Silver doping can give rather high areal capacitance of 1,161 mF cm^-2 at a scan rate of 10 mV s^-1 in 1 M NaOH aqueous electrolyte. To further understand the influence of Ag doping, the charge storage mechanism during the charge/discharge process was investigated by an in-situ X-ray Absorption Spectroscopy (XAS). The results showed that the oxidation number of Co in the Ag-LDCHs can reversibly return to its initial oxidation state after discharged. Whilst, Ag metal was found after charged and discharged indicating that Ag enhances the charge transfer inside the materials. For practical applications, the symmetric supercapacitor of Ag-LDCHs was fabricated using an ionic-liquid electrolyte with a wide working potential. The device exhibits ultrahigh maximum specific power of 20.31 kW kg^-1 and specific energy of 114.37 Wh kg^-1 with a wide operating voltage of 3.8 V. The incorporation of Ag into LDCH structures significantly enhances electrical conductivity, ion transportation and reversibility of the material.

Micro-scale energy storage devices are of great importance to the advancement of low maintenance, high power devices. They can easily be used in applications that extract energy from mechanical, solar, thermal and thermoelectric sources. Several of these devices have achieved mean areal capacitance of 1.5 mF cm^-2 and maximal energy and power densities of 6.6 mJ cm^-2 and 44.9 mW cm^-2, respectively. It has been demonstrated that a smaller gap enhances the performance. Currently, these types of devices are only made possible by using several micro-fabrication steps and techniques that are cost prohibitive and have limit the larger scale manufacturing of such devices. We present a simple but highly scalable method that is cost effective in fabricating high power interdigitated micro energy storage devices using binder free carbon nanotubes and laser irradiation to obtain gap width of the order of approximately 5 μm. The binder free electrodes devices show higher power density and an improved frequency response, compared to what have been reported in the literature. Additionally, we observed significantly reduction in cell resistance leading to enhancement in cell capacitance, consequently, an increase in energy density.

Electric double layer capacitor (EDLC) has been attracted much attention as one of the most promising high power and durable energy storage devices. However, low energy density is the major drawback, therefore, the optimization of specific surface area, nanoscale and mesoscale pore volume should be necessary to improve electrostatic capacity and reliability.
In this study, we carburized furfural resin (10 µm in diameter) in N2 atmosphere in three hour (temperature rising rate 1 °C /min) at 400°C or 600°C . Then, we treated carburized particle by three kinds of methods, KOH activation (KOH: samples = 4: 1 in weight ratio), CO2 activation or a combination of KOH and CO2 activation (KOH+CO2 activation). All activation methods were performed for 30 minutes from 800 to 850°C (temperature rising rate 10 °C /min). Specific surface area/pore size distribution measurement was performed by N2 adsorption method. Elemental analysis was done by using to determine CHNO fraction. We prepared coin shaped carbon electrode (12 mm in diameter, from 8:1:1 mixture of active carbon, carbon black, and PTFE), and investigated the electrostatic characteristics of the capacitors in 6M KOH to elucidate the relationship between characteristic structure properties and electrochemical.
We obtained large specific surface area as 1161 m2/g, 699 m2/g and 418 m2/g with furfural resin by KOH activation, KOH+CO2 activation and CO2 activation, respectively. The mesopore volume to total pore volume ratio (35.1 %) of KOH+CO2 activation method is larger than KOH activated method (21.4 %). CO2 activation after the KOH activation drastically enhanced the mesopore volume to total pore volume ratio, with decreasing the specific surface area. Electrostatic capacity was 137 F/g, 121 F/g, and 20 F/g with KOH activation, KOH+CO2 activation, and CO2 activation at 20 mA/g. Even if specific surface area of the KOH activated carbon became 60% after CO2 activation, the electrostatic capacity remained more than 85%, suggesting mesopore yielded by CO2 activation was effective for electrolyte diffusion.

Supercapacitors are become essential power sources in transportation and passive electronic components. Our group has done extensive work on supercapacitor based on nanocomposite (polyaniline-graphene (G), polypyrrole (PPY)-graphene, MWCNT-PPY, RuO₂-graphene, MnO₂ –G, polyethylenedioxythiophene (PEDOT)–G etc.) based electrode materials [1-4]. Recently, two-dimensional (2D) molybdenum disulphide (MoS₂) has been shown to be a promising electrode material for supercapacitor applications. We have studied supercapacitor on PEDOT-MoS₂ nanocomposite electrode material. The MoS₂-PEDOT nanocomposite was synthesized in aqueous based system under controlled condition. The PEDOT-MoS₂ nanocomposite was characterized using Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray-diffraction, and Transmission Electron Microscopy (TEM) techniques. Cyclic voltammetry, chronoamperometry, electrochemical impedance, charging –discharging etc., electrochemical measurements were performed to understand the specific capacitance, power and energy of supercapacitor. The supercapacitor fabricated from PEDOT-MoS^₂ based electrode has shown high energy density compared to graphene based nanocomposite electrodes. This study provides a fundamental understanding for high performance supercapacitor based on MoS₂-PEDOT based nanocomposite electrode material.
References
[1] P.A. Basnayaka, M.K. Ram, E.K. Stefanakos, A. Kumar, Nanostructured Hybrid Graphene-Conducting Polymers for Electrochemical Supercapacitor Electrodes, Handbook of Nanoelectrochemistry: Electrochemical Synthesis Methods, Properties, and Characterization Techniques, (2016) 479-501.
[2] P.A. Basnayaka, M.K. Ram, L. Stefanakos, A. Kumar, High performance graphene-poly (o-anisidine) nanocomposite for supercapacitor applications, Materials Chemistry and Physics, 141 (2013) 263-271.
[3] H. Gómez, M.K. Ram, F. Alvi, P. Villalba, E.L. Stefanakos, A. Kumar, Graphene-conducting polymer nanocomposite as novel electrode for supercapacitors, Journal of Power Sources, 196 (2011) 4102-4108.
[4] F. Alvi, M.K. Ram, P.A. Basnayaka, E. Stefanakos, Y. Goswami, A. Kumar, Graphene–polyethylenedioxythiophene conducting polymer nanocomposite based supercapacitor, Electrochimica Acta, 56 (2011) 9406-9412.

The bulk of work in transparent electronics is focused on transparent displays. Works on transparent power sources are limited and for supercapacitors concern thinned down carbon electrodes. Such devices offer effective capacitances around 1 mF/cm² at a transparency of 60% or lower. Our group pursues an approach where an intrinsically transparent material, namely wideband gap semiconductor zinc oxide (ZnO) forms the transparent electrodes with highly developed surfaces. Since we know that ZnO exhibits capacitances related to double layer formation, to increase the effective capacitances, we add MnO₂ nanostructures, known for its redox properties.
In this communication we discuss the ZnO/MnO₂ nanostructure system applied for transparent electrodes in symmetric supercapacitors with a LiCl/PVA gel electrolyte. Nanostructured ZnO is fabricated by reactive magnetron sputtering with post deposition annealing. Pure ZnO electrodes yield capacitances of 20 μF/cm² at transparencies over 70% in the visible light. MnO₂ nanostructures are fabricated using two approaches: (1) magnetron sputtering of 10 nm thin films, (2) nanoparticle synthesis based on reactions of KMnO₄ with manganese acetate or poly(alliloamine hydrochloride). We assess their performance by electrochemical measurements including cyclic voltammetry and impedance spectroscopy. We correlate these results with high resolution electron transmission microscopy to assess the structural and interfacial properties of the ZnO/MnO₂.
A different behavior of sputtered and solution-grown MnO₂ was observed. It is related not only to the crystalline phase of the oxide but also to the type of electrode coverage. In sputter deposition, the thin film deposited on top of the electrode at different process conditions lowered the capacitance of the ZnO electrodes in all cases, except when containing the λ-MnO₂ phase (C_eff = 80 μF/cm²). The mechanism was that of pore filling, reducing the available surface as well as penetration of the electrolyte. The λ-MnO₂ phase, while still covering the pores, contains also nano-channels in the unit cell, where Li⁺ ions intercalate.
On the other hand, the sensitization of ZnO with MnO₂ nanoparticles always increased the capacitances of the devices in the ranges 35 – 84 μF/cm². Even though the individual nanoparticles are significantly larger than the 10 nm deposited by sputtering which, especially in the case of nanoparticle complexes should lead to even more efficient pore coverage. The nanoparticles and their complexes penetrate the macroporous ZnO more effectively than the deposited film, yielding more surface coverage of the electrode, at the same time facilitating charge transport from the electrolyte.
This research was supported by the National Centre for Research and Development in the frames of the Lider V Programme through the project ‘Nanocoral zinc oxide-based supercapacitors for transparent electronics (NACZO)’, contract: LIDER/030/615/L-5/NCBR/2014.

The present work elucidates synthesis and electrocapacitive performance of cobaltites viz. Co₃O₄, NiCo₂O₄, ZnCo₂O₄ and MnCo₂O₄ nanostructured particles synthesized using template free urea assisted hydrothermal method at 180^OC for 10 hrs. Morphology and size of the synthesized cobaltites were examined by using scanning electron microscopy. Hierarchical structures namely fibrous and urchin-like microsphere were observed for the cobaltites. The electrochemical measurements were performed using standard three electrode system with 3M KOH electrolyte via cyclic voltammetry and galvanostatic charge-discharge methods. Amongst the cobaltite studied, NiCo₂O₄ displayed high surface area (46.05 m²/g), high specific capacitance (350 F/g at 5mA/s) and energy density (7 Wh/kg). The specific capacitance of all the cobaltites decreased with the increase in scan rate. Furthermore, specific capacitance showed invariance with the current density up to 5A/g. The cyclic stability of NiCo₂O₄ was studied up to 5,000 cycles and about 76% retention in charge storage capacity was observed. The superior electrocapacitive behavior of the NiCo₂O₄ is attributed to high surface area urchin like structure and high electrical conductivity amongst studied cobaltites. Density of states calculation was performed using hybrid density functional theory. The calculations showed that the bandgap falls in order of 4.1eV > 3.7eV >2.9eV >1.4eV for ZnCo₂O₄, Co₃O₄, MnCo₂O₄ and NiCo₂O₄ respectively. This further confirms the fact that NiCo2O4 has lowest band gap, highest conductivity and hence superior electrocapacitive behavior amongst all cobaltites.

Recent years, increasing demand of energy looks for alternative energy sources and energy storage mechanism. Supercapacitors stand out best devices for energy storage because of its high specific power, long life and fast charge–discharge process which make them attractive as power resources in high power electric devices. Because of their cost effectiveness and abundance, recently spinel oxides have been heavily explored for their potential supercapacitive material. The supercapactive behavior of material largely depends on morphology, surface area, porosity, electrolyte etc. In view of the above, the present work delineates systematic study of synthesis of Fe₃O₄ hollow nanospheres in presence and absence of hydrolyzing agent and explore the electrocapacitive performance of the same. Two set of Fe₃O₄ hollow nanostructured were prepared one with hydrolyzing agents such as urea (Fe₃O₄-Urea) and ammonium bicarbonate (Fe₃O₄-ABC) and other with glucose (Fe₃O₄-Glucose) via hydrothermal method. The x-ray diffraction show presence of spinel phase Fe₃O₄ without any presence of impurity.The scanning electron microscopy images show presence of Fe₃O₄ hollow nanostructures of average diameter 150 nm. The BET surface area for Fe₃O₄-Urea is 17.08 m²/g, Fe3O4-ABC is 23.08 m²/g, and Fe₃O₄-Glucose is 67.59 m²/g. The magnetic properties measured using vibrating sample magnetometer shows that Fe₃O₄-Urea (Ms ~ 83 emu/g), Fe₃O₄-ABC (Ms ~ 85 emu/g,), ferromagnetic behavior while Fe₃O₄-Glucose show superparamagnetic behavior at room temperature (Ms ~ 60.55 emu/g).The electrode material (Fe₃O₄, PVDF, and N-methyl pyrrolidinone) was pasted on Ni foam and cyclic voltammograms (with 3M KOH, LiOH, NaOH electrolyte) were recorded in the potential window of 0 to 0.6 V. The anodic/cathodic peaks were observed and are related to the formation of redox couple Fe⁺²/Fe⁺³ during charge transfer reaction. The specific capacitance at 0.5 A/g for Fe₃O₄-Glucose was highest (49.48 F/g) while Fe₃O₄- ABC was 42.34 F/g and Fe₃O₄-Urea was 41.9 F/g. Furthermore, the specific capacitance for Fe₃O₄-Glucose for one cycle was found to be 64.31 F/g while 34.52 F/g for 5000 numbers of cycles. Similarly, Specific capacitance for Fe₃O₄-Glucose, Fe₃O₄-Urea and Fe₃O₄- ABC hollow spheres was 107.16, 90.84 and 94.95 F/g for 5 mV/s scan rate and decrease slowly for increasing of scan rate and it is due to the chemical reaction occurs for higher scan rate. It is suggested that the Fe₃O₄ hollow sphere synthesized by this method is a promising anode material for high energy-density lithium-ion batteries. Furthermore, best electrocapacitive performance of Fe₃O₄ was measured in KOH electrolyte, which has smallest hydroxyl ion radii as compared to LiOH and NaOH. This leads to easy intercalation of KOH in the electrode material. In conclusion the study shows that with high surface area and proper choice of electrolyte, high specific capacitance in Fe₃O₄ system can be attained.

Among oxides, Spinel Co₃O₄ has recently been shown to exhibit remarkable photo- and electro-chemical properties as well as an excellent stability during oxygen reduction and evolution reaction processes. These properties, combined with its cost effectiveness and wide abundance, have promoted this material as a promising candidate for pseudocapacitor, fuel cell, lithium ion batteries, water splitting and energy applications. It is well documented in the literature that the pseudocapactive performance of oxides depends on many factors such as type of oxide, surface area and morphology, electrolyte, temperature etc. In view of this work delineates efforts to understand the effect of morphology on the electrocapacitive behavior of Co₃O₄ nanostructure particles. The systematic morphological changes in Co₃O₄ is achieved using hydrolyzing agent urea during the hydrothermal synthesis of particles. Co₃O₄ nanostructures were prepared with cobalt nitrate salt along with different urea concentration viz. 2.99 gram,1.49 gram,0.37 gram,0.22 gram and 0.11 gram via hydrothermal method at 180^OC for 10 hrs. Morphology and size of the different synthesized Co₃O₄ were examined by using scanning electron microscopy (SEM). Hierarchical structures namely plate like architecture and brush like structures were observed. The electrochemical measurements were performed using standard three-electrode system with 3M KOH electrolyte via cyclic voltammetry and galvanostatic charge-discharge methods. Amongst the Co₃O₄ studied, Co₃O₄-U0.37 displayed moderate surface area (50.10 m²/g), highest specific capacitance (764 F/g at 5mV/s) and energy density (19.56 Wh/kg). The specific capacitance of all Co₃O₄ decreased with the increase in scan rate. The cyclic stability of Co₃O₄-U0.37 was studied up to 5,000 cycles and about 64% retention in charge storage capacity was observed. The superior electro-capacitive behavior of the Co₃O₄-U0.37 was attributed to high surface area, brush like structure, and high electrical conductivity amongst studied Co₃O₄. In conclusion, it was demonstrated that high specific capacitance is achievable in the same oxide material by the tight control of morphology of the material. The low hydrolyzing concentration aided in producing high surface area architecture.

Due to the increasing concerns about the environment protection and limited fossil stock, it is time to develop materials from renewable resources for energy generation and storage. Among various energy devices, batteries, fuel cells and capacitors are most attractive. Capacitors provide high power density whereas batteries deliver high energy density. Supercapacitors serve as a bridge between the capacitors and batteries. Various materials such as metal oxides, conducting polymers and carbons from various sources have been used for these applications. However, most of these materials often suffer from low capacitance and high cost, so in this we attempted to use orange peel, a bio-waste, for electrochemical charge storage applications. The bio-waste was carbonized and chemically activated to have better electrochemical performance. The electrochemical properties of the chemically activated orange peel were studied using cyclic voltammetry and galvanostatic charge–discharge methods. The effect of chemical activation of the charge storage capacity of the orange peels was investigated. It was observed that 1:1 ratio of orange peel and KOH showed the most promising results by yielding maximum specific capacitance of 489 F/g in 3 M KOH at a current density of 0.4 A/g. The effect of different electrolytes such as LiOH, NaOH and KOH on electrochemical properties of the carbonized orange peel was also investigated. The flexibility and cyclic stability of the activated orange peels displayed almost 100% capacitance retention over 5,000 cycles of charge-discharge. The effect of temperature on the electrochemical properties of supercapacitor device was studied. About 35 % improvement in the charge storage capacity of the device was observed by increasing temperature from 10 to 80 ^oC. Our studies indicate that bio-waste such as orange peel could be used electrode materials for flexible and high performance energy storage devices.

Electronic products have been asked to be small, light, safe, eco-friendly and even flexible. Supercapacitors are one of the great candidates of the next generation rechargeable energy storage devices for the portable electronic devices. Here, we have proposed a new scalable fabrication approach for making a thin film supercapacitor using submicron-size activated carbon that achieved moderate areal capacitance of ~12 mF/cm² and showed superior long-term thermal stability for for 2,000 hours under 60 °C. The total thickness of a packaged device was ~0.3 mm. The fabricated devices had the electrode dimension of 5x5 cm² and 10x10 cm², respectively. They showed good mechanical flexibility with no change in the capacitance of the device after 1000 bending cycles with the bending radius of 10 mm.

Wearable and flexible electronic devices have continuously attracted increasing attentions and represented a new family of energy storage devices ^[1]. Amongst them, the developing fiber-shaped supercapacitors are increasingly appreciated as a reliable strategy to leap over the geometrical restrictions of traditional planar supercapacitors ^{[2, 3]}. However, the academic achievements have not been translated to industrial success because of the complex fabrication process. Although many attempts are made to realize the scale-up production of fiber-shaped supercapacitors ^{[4, 5]}, it remains challenging to achieve a continuous fabrication.

Here, we design a synchronous deposition strategy to continuously fabricate fiber-shaped supercapacitors based on aligned carbon nanotube (CNT) composite fibers ^[6]. As a demonstration, we continuously prepared a CNT/graphene composite fiber through a synchronous electrochemical reduction and deposition process. After being coated with polymer gel electrolyte, two fibrous electrodes are twisted to directly fabricate fiber-shaped supercapacitor. This continuous fabrication strategy can be extended to other pseudocapacitive active materials such as manganese dioxide, polyaniline and polypyrrole to fabricate various fiber-shaped supercapacitors.

Reference
[1] L. Li, Z. Wu, S. Yuan, X. B. Zhang, Energy Environ. Sci. 2014, 7, 2101-2122.
[2] D. S. Yu, Q. H. Qian, L. Wei, W. C. Jiang, K. L. Goh, J. Wei, J. Zhang, Y. Chen, Chem. Soc. Rev. 2015, 44, 647-662.
[3] J. Ren, W. Y. Bai, G. Z. Guan, Y. Zhang, H. S. Peng, Adv. Mater. 2013, 25, 5965-5970.
[4] D. S. Yu, K. Goh, H. Wang, L. Wei, W. C. Jiang, Q. Zhang, L. M. Dai, Y. Chen, Nat. Nanotechnol. 2014, 9, 555-562.
[5] L. Kou, T. Q. Huang, B. N. Zheng, Y. Han, X. L. Zhao, K. Gopalsamy, H. Y. Sun, C. Gao, Nat. Commun. 2014, 5, 3754.
[6] B. J. Wang, X. Fang, H. Sun, S. S. He, J. Ren, Y. Zhang, H. S. Peng, Adv. Mater. 2015, 27, 7854-7860.

A simple and scalable method is developed to prepare highly wrinkled graphene sheets – carbon nanospheres (WG-CN) composite for ultra high energy density supercapacitor application. Here, we introduce a novel simple wax candle flame technique for the simultaneous reduction of graphene oxide (GO) and deposition of carbon nanospheres on the graphene sheets. This is followed by introducing permanent wrinkles to the composite. The WG-CN composite exhibit the high specific capacitance values of 290 F g^-1 and 253.7 F g^-1 (138.5 F ^cm-3) for 6M KOH and EMIMBF₄ ionic liquid electrolytes respectively. The ultra high energy density values of 108 Wh Kg^-1 and 58.9 Wh L^-1 has been obtained at the power density of 3955 W Kg^-1 and 2157 W L^-1 simultaneously. These attractive performances exhibited by the WG-CN composite supercapacitor electrode make them potential candidate for future energy storage devices. The key to success of this composite is the ability to make full utilization of the high intrinsic specific surface area of the nanocomposite. The wrinkled morphology and carbon nanospheres enable the formation of mesopores by environmentally benign ionic liquids capable of operating at high current density.

Supercapacitors have unique advantages over lithium-ion batteries in high power delivery and long cycling life, and are emerging as attractive electrochemical energy storage devices for future energy storage application. Since the charges are stored at the electrode surface, newly developed graphene have been selected owing to their large specific surface area, high electrical conductivity and chemical stability. However, the irreversible stacking due to the strong π–π interactions significantly decreases accessible surface area.
We firstly present a sea-urchin-shaped template approach for fabricating highly crumpled graphene balls. Simultaneous chemical etching and reduction process of graphene oxide (GO)-encapsulated iron oxide particles results in dissolution of the core template with spiky morphology and conversion of the outer GO layers into reduced GO layers with increased hydrophobicity which remain in contact with the spiky surface of the template. After completely etching, the outer graphene layers are fully compressed into the crumpled form. The crumpled balls exhibit significantly larger surface area and good water-dispersion stability with high electrical conductivity. These crumpled graphene networks with compression still maintain their crumpled morphology, thus high gravimetric and volumetric capacitance of supercapacitive electrode can be realized.
For the second part, using a ice-templated self-assembly process with reduced graphene sheets and vanadium phosphate (VOPO₄) nanosheets, we realize a vertically porous nanocomposite of layered VOPO₄ and graphene nanosheets with high surface area and high electrical conductivity. The resulting 3D VOPO₄–graphene nanocomposite has a much higher capacitance of 527.9 F/g with solid cycling stability. The enhanced pseudocapacitive behavior mainly originates from vertically porous structures from directionally grown ice crystals and simultaneously inducing radial segregation and forming inter-stacked structures of VOPO₄–graphene nanosheets. This VOPO₄–graphene nanocomposite electrode would provide the short diffusion paths of electrolyte ions and fast transportation of charges within the conductive frameworks. In addition, an asymmetric supercapacitor (ASC) is fabricated by using vertically porous VOPO4–graphene as the positive electrode and vertically porous 3D graphene as the negative electrode; it exhibits a largely enhanced energy density of 108 Wh/kg.
In the last part, we also used the ice-templated vertically porous graphene nanostructures as a stretchable supercapacitor electrode. Radially compressed honeycomb structures exhibited nearly-zero poission ratio structures and maintained their structure and electrical conductivity even at 50 % of starched states. The capacitive performance of these compressed honeycomb structures also shows fairly high over 130 F/g and these high performance still be maintained at highly stretched condition.

Supercapacitors plays important roles in transportation, electronics, military and renewable power sources. We have fabriacted supercapacitor based on ruthenium oxide (RuO₂)-graphene (G), G-polyaniline (PANI), G-poly(ortho-anisidine), G-polypyrrole, G-thiophene in symmetric and asymmetric configurations in aqueous and solvent based electrolytes, and have obtained specific capacitance from 160 F/g to 500 F/g [1-3]. The specific capacitance of supercapacitor is dependent on high surface area, conductivity, wider potential window and asymmetric configuration based electrodes. Recently, 2D-chalcodenide (MoS₂) has been shown to be promising electrode material for supercapacitor due to higher intrinsic ionic conductivity than oxides and graphitic electrode materials.
We have studied the layered structure of MoS₂ and layered MoS₂-self-assembled PANI electrode for supercapacitor applications. The MoS₂ layer was peeled from crystal using the commercially available adhesive tape. The peeled MoS₂ layer was placed on graphite electrode by our developed method. Later, PANI film of PANI was deposited on MoS₂ surface using in-situ self-assembled technique. The electrode were characterized using FTIR, SEM, X-ray diffraction techniques. The cyclic voltammetric, charging discharging, Nyquist, Bode plot, open circuit studies were performed to understand the specific capacitance, specific power and energy on various electrodes materials. The presence of the sulfur group in dichalcogenide nanocomposite enhances the charging/discharging processes. The MoS₂ –self assembled PANI film has shown very high specific capacitance, power and energy as well shown interesting photoelectrochemical capacitance properties.

[1] H. Gómez, M.K. Ram, F. Alvi, P. Villalba, E.L. Stefanakos, A. Kumar, Graphene-conducting polymer nanocomposite as novel electrode for supercapacitors, Journal of Power Sources, 196 (2011) 4102-4108.
[2] F. Alvi, M.K. Ram, P.A. Basnayaka, E. Stefanakos, Y. Goswami, A. Kumar, Graphene–polyethylenedioxythiophene conducting polymer nanocomposite based supercapacitor, Electrochimica Acta, 56 (2011) 9406-9412.
[3] P.A. Basnayaka, M.K. Ram, E.K. Stefanakos, A. Kumar, Supercapacitors based on graphene–polyaniline derivative nanocomposite electrode materials, Electrochimica Acta, 92 (2013) 376-382.

The development of materials with the capacity to rapidly store and release large amounts of energy is a great contemporary challenge. In these materials charge storage reactions occur at interfaces, and generated charges need to be channeled efficiently to electrodes. For these reasons, high surface area and oriented structures are two key features for optimal materials. Co(OH)₂ is a strong candidate material for such supercapacitor function due to its high theoretical specific capacity and electrical conductivity. We synthesized a Co(OH)₂-organic hybrid material by electrodeposition on a stainless steel substrate, which acts as the current collector. We found that the dominant feature of this hybrid material is a hierarchical structure consisting of microns-long, 30 nanometer diameter tubes with concentric, curved layers of Co(OH)₂ and 1-pyrenebutyric acid. The nanotubular structure offers high surface area as well as macroscopic orientation perpendicular to the substrate for efficient electron transfer. The energy storage performance of this material is among the highest reported without the use of conductive additives. Hybrid materials synthesized with surfactants lacking the pyrene core form lamellar flat films with less accessible surface area and electron conduction pathways oriented parallel to the substrate, resulting in electrodes with 70% lower specific capacity. We found that the pyrene surfactants used to template nanotubular growth also enhance the structural integrity of the hybrid when added to the alkaline electrolyte solution necessary for redox-based energy storage.

The semiconducting properties of certain ferroelectric materials, partially caused by the interactions among ferroelectric polarizations, charged domain walls, and conducting point defects, pose a threat to the reliability of ferroelectrics used as dielectric material in capacitor devices, and is not yet fully understood. Here we proposed a physical model combining the phase-field method for ferroelectric domain structures and diffusion equations for defect transport to study the resistance degradation behavior in multi-domain tetragonal BaTiO₃ capacitors. We considered a hypothetical Ni/BaTiO₃/Ni single parallel plate capacitor configuration subject to 0.5V dc bias at 25°C. It is found that 90° domain walls are charged, induce local space charge segregation, and form local electric potential barriers upon external bias that significantly influence the ionic transport behavior. Additionally, the 180° domain walls remain nearly charge neutral and have much less influence on ionic transport. The effect of domain wall and polarization orientations on the leakage current evolution is investigated. Our study could necessitate further understanding on the influence of ferroelectric state, ionic interactions, transport barriers, spatial distributions, and breakdown phenomena.

This study was supported by the U.S. DOE, Office of Basic Energy Sciences (BES), Materials Sciences and Engineering Division (MSED) through FWP Grant No. ERKCZ07 (Y.C., S.V.K.). The work at Penn State was supported by U.S. Department of Defense, Air Force under FA9550-14-1-0264 (Chen) and FA9550-14-1-0067 (Randall), and the National Science Foundation as part of the IUCRC Center for Dielectrics and Piezoelectrics under Grant No. IIP-1361571 at Penn State.

This present study demonstrates an exclusive and cost efficient hydrothermal protocol to synthesize grass-like tangled cobalt vanadium oxide hydrate (CVO) nanocanes array. Decoration of CVO by iron oxide nanospheres was successfully accomplished by similar facile hydrothermal method. Finally, a high performance mesoporous composite electrode material was fabricated through in-situ oxidative polymerization of pyrrole at a low temperature in presence of iron oxide decorated CVO (FeO@CVO) that results in wrapping up of polypyrrole over iron oxide decorated CVO (PPy/FeO@CVO). All the as prepared electrode materials was characterized by WAXD, FTIR in order to determine the exact crystal structure and bonding. FESEM and TEM investigation suggests the formation of grass-like CVO nanocanes, decoration of spherical iron oxides on the surface of CVO and PPy wrapping over FeO@CVO. Electrochemical measurements of PPy/FeO@CVO in 1 M aqueous KOH exhibit a maximum specific capacitance of ~1202 F/g as compared to pure CVO (~708 F/g) and FeO@CVO (~968 F/g) together with exceptionally high energy and power density value of 41.73 Wh/Kg and 250 W/Kg at 1 A/g, accordingly. Moreover, PPy/FeO@CVO retains~96.5% of its initial specific capacitance even after 3000 consecutive charge-discharge cycles at 1 A/g current density, exploring its high stability and robustness required for advance supercapacitor applications.

Conductive polymers have been considered promising candidate materials for supercapacitors due to their fast charge-discharge kinetics, tunable morphology, relative low cost and fast doping/de-doping processes. The stability in the oxidized state and the moderate band gap make poly(3,4-ethylenedioxythiophene) (PEDOT) one of the most successful conductive polymer materials. More efforts are still needed to develop a simple and low cost method to fabricate the supercapacitor cells with active materials like PEDOT. In this study, a simple “dip and dry” process was used to deposit graphene nanoplatelets onto commercially available open cell polyurethane sponge by the vapor-phase polymerization of PEDOT. The result PEDOT/graphene composite sponges showed high capacitve performance. Graphite nanoplatelets were also employed to study the effects of the different carbon materials on this kind of composite electrodes. VPP temperatures variation (50 and 110 °C) was used to optimize the capacitive behavior of the final electrodes. The chemical composition and surface morphology were characterized by Raman spectroscopy and scanning electron microscopy (SEM) respectively. To evaluate the electrical performance, a series of electrical measurements including cyclic voltammetry (CV), charge-discharge (CD) and electrochemical impedance spectroscopy were carried out on symmetric supercapacitor cells with two-electrode configuration. The optimal capacitance obtained with the PEDOT/graphene composite electrodes was 758.8 mF cm^-2 from CV measurement at 10 mV s^-1 and 798.2 mF cm^-2 from CD at 0.1 mA cm^-2.

Transition metal dichalcogenide (TMD) nanolayers show potential as high performance catalysts in energy conversion and storage devices. Synthetic TMDs produced by chemical vapor deposition (CVD) methods tend to grow parallel to the growth substrate. Here we show that with the right precursors and appropriate tuning of the CVD growth conditions, ReS₂ nanosheets can be made to orient perpendicular to the growth substrate. This accomplishes two important objectives- first, it drastically increases the wetted or exposed surface area of the ReS₂ sheets and second, it exposes the sharp edges and corners of the ReS₂ sheets. We show that these structural features of the vertically grown ReS₂ sheets can be exploited to significantly improve their performance as electrochemical catalysts in Lithium-Sulfur (Li-S) batteries and in hydrogen evolution reactions (HER). After 300 cycles, the specific capacity of the Li-S battery with vertical-ReS₂ catalyst is retained above 750 mA h g⁻¹ with only ~0.063% capacity decay per cycle, much better than the baseline battery (without ReS₂) which shows ~0.184% capacity decay per cycle under the same test condition. As a HER catalyst, the vertical-ReS₂ provides very small onset over-potential (< 100 mV) and an exceptional exchange current density (~67.6 µA/cm²), which is vastly superior to the baseline electrode without ReS₂.

Redox polymers are characterized by a dense population of the electron-releasing and -gaining site that allows efficient redox gradient-driven electron- or charge-transport and -storage throughout the polymer layers via self-exchange reactions. The redox sites in our research are radicals, quinones, viologen, and terephthalate. Requisites to allow high power and energy density and cyclability in the electrode performance are discussed, in focusing on both the redox species and the polymer backbone designing. A new trend in battery fabrication will be illustrated, using bendable and burst-power polymer batteries for an example.

To meet future energy needs and to minimize our CO₂-emissions, a higher share of produced electricity must come from renewable resources. Renewable energy sources are however often intermittent and as the renewable energy production varies in time it does not correlate with the time dependency of electricity demand. For this reason, high capacity storage systems are needed to utilize renewable energy sources fully. A functioning and sustainable energy storage system in this context, based on renewable resources, does not exist today. Thus, new technologies are needed to develop materials for electrical energy storage (EES). Concerning the manufacturing of batteries, which today rely on metals, the benefits of converting to carbon based materials are several, e.g. lower weight and cost, flexible materials and better recycling possibilities. In addition, the total energy consumption in the production chain will most likely be reduced due to avoidance of high temperatures when extracting and processing metals. Conducting redox polymers (CRPs), i.e. conducting polymers with redox active side groups, are currently investigated as possible organic electrode materials. In this work we focus on finding stable side groups with high charge storage capacity. Quinones function as charge carriers in natural energy conversion systems, i.e. during photosynthesis and respiration, and these molecules have captured our attention as attractive side-group alternatives due to their high gravimetric capacity. For a functioning battery application the redox group and the polymer backbone must be active in the same potential window. The quinone potential can be effectively tuned over a wide potential range by substitution on the quinone ring, hence various quinone derivatives could match different polymer backbones.
In this work, copolymers utilizing the high potential of hydroquinones as organic high charge capacity materials have been synthesized. Further, functioning batteries with cathodes produced from these novel copolymers have been assembled and characterized. The results take us a leap forward in the work targeting renewable organic batteries for a future of sustainable energy storage.

A comprehensive understanding of how local surface (de)activation and site-specific differential reactivity impacts the dynamic ion-transfer capabilities of ion-battery electrode interfaces has yet to be fully elucidated [1,2]. Exploring quantitatively local ionic reactivity is of paramount importance for the design of efficient storage materials. New in-situ analytical tools are required to address present and future battery challenges by incorporating versatile platforms capable of imaging surface redox reactivity and ionic transfer reactions for species such as Li⁺, Na⁺ and K⁺ at interfacial and bulk nanostructures in non-aqueous electrolytes [2].

Here, we introduce an experimental approach for detecting redox reactivity and quantifying and imaging ionic reactivity on operating ion-battery electrodes using scanning electrochemical microscopy (SECM). The measurement principle is based on SECM probes that integrate mercury mirco- and nano- cap electrodes on which alkaline ions can be detected by means of fast-scan anodic stripping voltammetry (Figure 1A and B). In a first application, these probes were used for the detection of Na⁺, Li⁺ and K⁺ in propylene carbonate, as well as the deposition of Li⁺ on operating Au electrodes [3]. The probe potential provided chemical specificity while the probe limiting current permitted to measure ionic fluxes with excellent stability and linearity for concentrations in the molar to sub-millimolar range. We also demonstrated the possibility of carrying out analysis on electrodes of ~100 nm.

In following studies, [4] we demonstrated the utility of our approach for elucidating ion insertion in ~10-layer graphene as well as the role of surface patterns as points of entry for ions into its bulk structure. Currently, we are using simultaneous ionic and redox probing of redox active polymer interfaces to understand the effects of charge trapping and specific interactions between the electrolyte composition and charge accessibility. The described SECM technique represents an unprecedented step in the analysis of ion insertion mechanisms into highly localized electrode structures and ultra-thin samples. SECM mapping reveals aspects of surface reactivity that are lost during averaging in conventional battery testing.

References
[1] S.J. Harris, P. Lu. J. Phys. Chem. C 117 (2013) 6481.
[2] Z. J. Barton, J. Rodríguez-López. Anal. Bioanal. Chem. 408 (2016) 2707.
[3] Z.J. Barton, J. Rodríguez-López. Anal. Chem. 86 (2014) 10660.
[4] J. Hui, M. Burgess, J. Zhang, J. Rodríguez-López. ACS Nano 10 (2016) 4248.

Understanding material interactions in restricted size domains (i.e. nanoscale) has been a focused research effort for decades and the knowledge acquired has facilitated the development of new nano- and meso- scale materials, such as low density, and high surface area composites. These composites have an emerging niche in numerous technology-related applications due to their enhanced physicochemical behavior compared to bulk materials. Commonly, low-density materials are synthesized through the utilization of methodologies that allow the uniform generation of voids throughout a sample. However, in prevailing synthetic techniques the pore distribution is discontinuous, which negatively impacts the mass transport and diffusion of analytes of interest through the pores. This contribution proposes to overcome current limitations by developing bicontinuous materials through the arrest of a natural thermal-induced unmixing that undergoes spinodal decomposition. The surface properties of amphiphilic particles are designed such that the particles are trapped in an energy-well at the interface of a binary mixture. Thus, during spinodal decomposition as the two phases grow, the interface containing particle shrinks until the particles physically jam and prevent further phase growth. This arrested state contains two bicontinuous phases that can be selectively exchanged, which facilitates the development of bicontinuous and hierarchical composites with enhanced transport properties and mechanical integrity. This research is expected to lead to final materials entailing a network of continuous macroporous channels that connect to smaller pores of low-density material enhancing substance transport through these channels and pores. This presentation will focus on various electrode materials that we have developed and some preliminary results towards enhanced charge transport, as well as other energy-derived applications.

*This abstract has been approved for public release LA-UR-16-24202

Conversion reactions in batteries, such as the electrochemically-driven phase separation of a metal oxide into Li₂O and reduced metal nanoparticles, are well-known to have specific capacities far beyond typical intercalation materials. However, conversion materials have been commercially limited by several factors, including: (i) its slow, diffusion-limited kinetics, (ii) poor cycling performance driven by substantial structural re-organization and corresponding large volume changes, and (iii) Coulombic inefficiency—especially during the first cycle. Oxides also tend to have substantially lower redox potentials than thermodynamically expected values. The nanoscale network of metal-rich and lithia-rich phases that form during conversion suggests that interfaces between these species play a critical role in the mass/charge transport properties that define the overall properties of the electrode.

To understand and control the reaction kinetics, we have prepared and studied model oxide nanostructures with tunable, periodic geometries to better correlate electrochemical reactivity with the morphology of the electrode. In particular, the interparticle void space can be designed to accommodate fast lithium diffusion and constrain the volume expansion of oxides during lithiation. We have examined structures containing arrays of spherical particles or periodic holes in the oxide matrix with tunable size and spacing. These electrodes were prepared by 1) combining the rich phase-space of self-assembled block copolymers (BCP) with sequential infiltration synthesis via atomic layer deposition and 2) utilizing complexation in solution between metal ions and functional units in the core domain of BCP micelles. Traditional scanning probe methods have combined with both ex-situ and in-situ grazing incidence small angle X-ray scattering and diffraction to investigate the controlled phase separation of a conversion reaction. These results provide deeper knowledge of the reaction kinetics of the conversion process while providing insight into the broader loss mechanisms and strategies for improving its viability.

Tradition graphene anodes in lithium ion batteries (LIBs) suffer significant performance loss due to the restacking of graphene layers. In this work, we have demonstrated a facile synthesis of preparing a series of graphene-based nanomaterials for LIBs with excellent cyclic duarbility and much enhanced capacity. Moreover, theoretical charge capacity of these nanographenes exceeds 2000 mAh/g due to an increased edge to surface ratio and oxygen containing functional groups. These exceptional metrics observed within the novel assemblies is primarily due to the robust structure with high surface areas along with the optimal d-spacing allowing for facilitated Li adsorpiton/desorption and diffusion. Development of nanomaterials anode suggests that the optimal design of graphene materials with high-surface areas and robust structures is very important for next generation LIBs with high-energy storage efficiencies.

Nowadays, it is obviously expected for flexible and stretchable electronics to be next generation electronics and dominate the world market. Most of flexible electronics are certainly supplied electrical power by energy sources which are even capable of being flexible. Unfortunately, flexible energy storages for flexible electronics are demanded to have same properties as before; high power density, high specific capacity, stability, and safety. [1] However, the traditional electrode structure in commercialized battery has limited both its flexibility because the structure are composed coating of slurry mixture which contain active materials, binders and conductor on metal current collector. Furthermore, in that electrode only active material could contribute to capacity which means electrochemically active with lithium ion in electrolyte, that is, eliminating weight of binder, conductor, and current collector helps increasing gravimetric capacity. Therefore, next generation power sources must overcome the limited points of traditional electrode.
Here, we demonstrate, as a model study, hybrid structure of direct synthesizing of vertically aligned Li₄Ti₅O₁₂ (LTO) nanowire on freestanding graphene (FSG). For synthesizing the hybrid electrode, vertically aligned LTO nanowires were directly synthesized on FSG without any additives. That hybrid structure combining vertical nanowire and flexible FSG facilitate high flexibility without any deformation at low bending radius. In addition, the morphology of vertically aligned nanowire could maximize high power capability due to the enlarged surface area,[3] and FSG could have electrical pathway to completely support the high power capability of LTO as a current collector. In contrast with traditional electrode, FSG, which material is graphite, acts as both current collector and anode material. Finally, the hybrid electrode was successfully demonstrated to satisfy several demand of the future flexible lithium ion battery, i.e. high power performance, cycling efficiency, gravimetric capacity, and flexibility.

Electric double layer capacitors are playing an increasingly important role in a number of vital applications such as energy storage and capacitive deionization for desalination. Recent advances in electrode materials have dramatically increased the potential energy density of these systems based on increases in material capacitance and pseudo-capacitance. This increase, however, leads to the potential of substantial electrolyte depletion due to intrinsic electrolyte solubility limits (e.g. in organic electrolytes for supercapacitors) or desired operational regimes (e.g. capacitive deionization of brackish water). As a result, the response of these systems involves a complex interplay of electromigration and diffusive transport of electrolyte species throughout the porous structures of the electrodes and spacer. Here we present a parametric model of electrolyte species transport including electrolyte depletion, which is capable of accounting for variations in cell geometry, electrolyte composition, and electrode material capacitance, resistivity, and structure. We show that electrolyte depletion can play an important role in cell performance for a range of relevant cases, and we consider material and cell design choices as well as operating conditions that minimize detrimental effects of electrolyte depletion.

Increasing demand for portable electronic devices calls for the need of light-weight power source. Electrical double layer capacitors (EDLCs) are promising candidates due to their high power density and outstanding charge/discharge cycling stability. Three-dimensional (3D) carbon materials have been extensively studied for EDLCs. Yet, a major challenge for 3D carbon electrodes is the limited ion transport rate in their internal space. To address this limitation, preparation of hierarchical porous 3D structures that provides additional channels to facilitate internal ion transport is favorable. In my presentation, I will talk about a new template-free method for synthesis of ultralight (9.92 mg/cm3) 3D porous carbon foam (PCF) involving carbonization of glutaraldehyde cross-linked chitosan aerogel in the presence of potassium carbonate. Electron microscopy images reveal that the carbon foam is an interconnected network of carbon sheets with uniformly dispersed macro-pores, while Brunauer–Emmett–Teller measurements confirm the existence of hierarchical porous structure. Electrochemical data show that the PCF electrode can achieve an outstanding gravimetric capacitance of 246.5 F/g at a current density of 0.5 A/g, and a remarkable capacitance retention of 67.5% when current density increases from 0.5 A/g to 100 A/g. A quasi-solid-state symmetric supercapacitor fabricated via assembly of two pieces of PCF is able to deliver an ultrahigh power density of 25 kW/kg at an energy density of 2.8 Wh/kg.

One-Dimensional nanomaterials with large surface area, more surface active sites and better permeability can significantly increase the energy density, power density and cycling performance for the energy storage. Such hierarchical structure can also be used as targeted intracellular recording for its facile synthesis route. In our present work, a series of hierarchical nanomaterials have been obtained, including kinked hierarchical nanowires, hierarchical heterostructured nanowires and hierarchical scrolled nanowires which shows great electrochemical performance.
To improve the electrochemical performance, V₃O₇ nanowire templated semi-hollow bicontinous graphene scrolls architecture is designed and constructed through “oriented assembly” and “self-scroll” strategy. The V₃O₇ nanowire templated semi-hollow bicontinous graphene scrolls with interior cavities provide continuous electron and lithium ion transfer channel and space for free volume expansion of V₃O₇ nanowires during cycling, thus representing a unique architecture for excellent lithium ion storage capacity and cycling performance.¹ Besides, we have designed and synthesized hierarchical MnMoO₄/CoMoO₄ heterostructured nanowires by combining "oriented attachment" and "self-assembly". The asymmetric supercapacitors based on the hierarchical heterostructured nanowires show a high specific capacitance and good reversibility with a cycling efficiency of 98% after 1,000 cycles.² We also established spiral-shaped three-dimensional micropseudocapacitors with the area of ≈1.67 mm² and height of 1.7 μm, which deliver both ultrahigh energy density of 34.9 mWh cm^-3 at the scan rate of 10 mV s^-1 and high power density of 193.4 W cm^-3 at the ultrahigh scan rate of 200 V s^-1.³ Recently, we also constructed the hierarchical zigzag Na_1.25V₃O₈ nanowires,⁴ K₃V₂(PO₄)₃ bundled nanowire,⁵ and Li₃V₂(PO₄)₃ mesoporous nanotubes⁶ with enhanced electrochemical performance. Our work presented here can inspire new thought in constructing novel one-dimensional structures and accelerate the development of energy storage appilications.
References
(1) Yan, M. Y. et al., J. Am. Chem. Soc. 2013, 135, 18176-18182.
(2) Mai, L. Q. et al., Nature Commun. 2011, 2, 381.
(3) X. C. Tian. et al., Adv. Mater. 2015, 27, 7476.
(4) Dong, Y. F. et al., Energy Environ. Sci. 2015, 8, 1267.
(5) Wang, X. P. et al., Adv. Energy Mater. 2015, 5(17).
(6) Niu, C. J. et al., Nature Commun. 2015, 6, 7402.

Synthesis and crystal engineering of metal oxides typically focuses on the creation of single-phase materials; we present syntheses of multi-component, conformal manganese oxide thin films on carbon nanofoams that can be engineered via ion exchange and thermal processing [1]. These composite solid-state materials function as advanced electrodes for pseudocapacitive and Faradaic (battery-like) charge storage; however, the amorphous and/or nanoparticulate phases are difficult to characterize via neutron or X-ray scattering because of broad Bragg peaks. Total scattering analyses allow atomistic modeling of these difficult to characterize—but functionally important—composites via differential pair distribution functions (DPDFs). We use Raman spectroscopy to track the effect of crystal engineering on the carbon nanofoam [2].

We find that electroless deposition of sodium permanganate on mesoporous carbon nanofoams (CNFs) generates a lamellar sodium birnessite phase (NaMnOx@CNF). Exchange of Li⁺ for Na⁺ of NaMnOx@CNF in a 1 M aq. LiNO₃ solution for 8 h generates LiMnOx[8]@CNF with no increase in pseudocapacitance in a nonaqueous electrolyte compared to the bare CNF. Immersion of LiMnOx[8]@CNF in 1 M aq. LiNO₃ for an additional 16 h creates a registered birnessite phase in LiMnOx[24]@CNF with an observable (001) peak by PXRD. This registry increase is concomitant with a doubling of the nonaqueous pseudocapacitance of the electrode compared to LiMnOx[8]@CNF or NaMnOx@CNF. Further heat processing of the LiMnOx[24]@CNF in an argon environment followed by an air environment generates nanoscale cubic LiMn₂O₄ conformally affixed to the CNF (LiMn₂O₄@CNF). This processed LiMn₂O₄@CNF composite retains one layer of LiMnOx as discerned by the DPDF analyses; we posit this layered phase is the initial MnOx slab affixed to the CNF as the carbon is oxidized by the precursor permanganate and serves as the foundation slab on which the five overlayers of AMnOx are engineered into 3D crystal structures. The tunability of this system for pseudocapacitance and/or faradaic electrochemical behavior will be discussed in context of the materials’ (non)crystalline structures.

[1] M.B. Sassin, S.G. Greenbaum, P.E. Stallworth, A.N. Mansour, B.P. Hahn, K.A. Pettigrew, D.R. Rolison, J.W. Long, J. Mater. Chem. A, 1 (2013) 2431–2440.
[2] M.D. Donakowski, J.M. Wallace, M.B. Sassin, K.W. Chapman, J.F. Parker, J.W. Long, D.R. Rolison, Cryst. Eng. Commun. (2016) doi:10.1039/c6ce00861e.

The increase in the consumption of portable electronic devices such as cell phones, notebooks, and tablets, among others, has necessitated an increase in battery production. The alkalline batteries, or Zn-MnO₂ batteries, are know as primary batteries, once they cannot be recharged after it's exausts. In 2010, the EU discarded approximately 1,720,000.00 tons of primary and secondary batteries. In the U.S., the Rechargeable Battery Recycling Corporation (RBRC) estimates that approximately 5,400.00 tons of batteries were collected in the landfills of US. In Brazil, ABINEE (Brazillian Association of Eletric and Electronic Industries) estimates that 1.4 billions of primary and secondary batteries are consumed per year. So, the development of new recycling methods are extremely importante on a social and ecological point of view.
Herein, an electrochemical recycling method for manganese present in the cathode of spent alkalline batteries is presented. First, the cathode of a spent Zn-MnO₂ was leached using a mixture of H₂SO₄ and H₂O₂, then the pH was set to 3,0 and buffered using H₃BO₃ 0.1 mol.L^-1. Then, manganese were recovered as MnO₂, using galvanostatic electrodeposition. The electrochemical measurements were made using a potentiostat/galvanostat Autolab 128n, with a typical three electrode cell. Satured calomelan electrode was used as reference electrode, a platinum electrode as counter electrode and 304L stainless steel, with an area of 0.5 cm² as working electrode. A current density of 10 mA.cm^-2 were applied during 100 seconds, in two different temperatures, 25 and 80 ^oC. After the electrodeposition, the films were weighed for means of charge efficiency calculation. A charge efficiency of 80 and 88.00 % were obtained for the films grown at 25 and 80 ^oC, respectively.
For films characterization, Scanning Electron Microscopy (SEM) and Raman Spectroscopy were used.
SEM images reveals a lamelar structure for both films, nevertheless, the film obtained at 80 ^oC showed greater porosity and a more effective substrate coating. Raman spectras detected principal MnO₂ vibrational bands.
To evaluate electrochemical properties, cyclic voltammetry were performed, for both electrodeposits, in a Na₂SO₄ 0.5 mol.L^-1 solution. A good cycle stability and reversibility was obtained for both electrodeposits. At 1.0 mV.s^-1 a specific capacitance of 66.80 and 367.30 F.g^-1, for films grown at 25 and 80 ^oC, respectively, was found. The greater specific capacitance at 80 ^oC can be explained due the higher filme porosity, showed in SEM images. Galvanostatic charge-discharge cycles were also performed, using a current of 1.1 A.g^-1, in this case, a specific capacitance of 34.00 and 460.13 F.g^-1 for 25 and 80 ^oC, respectively, was obtained.
So, the recycling mechanism here proposed shows a good charge efficiency and also an interesting method for the production of electrochemical capacitors.

Rechargeable batteries and double-layer capacitors are two representative types of electrochemical energy storage devices. The former generally delivers high energy density and moderate power density, while the later features high power density but low energy density. Such a gap could be filled by pseudocapacitive materials, which enable charge storage based on fast redox reaction with a capacitor-like behavior. In particular, ion-capacitors operating based on ultrafast pseudocapacitive ion insertion-deinsertion are expected to simultaneously deliver high energy density and high power density. Several transition metal oxides are capable of pseudocapacitive Li ion storage once they are prepared in a suitable form, such as TiO₂, V₂O₅, Nb₂O₅ etc [1-3]. Replacing Li with more abundant elements, for example, Na, would largely reduce the cost of these energy storage devices. However, due to the larger size of Na, the available host materials for Na ions are much rarer compared to those for Li ions, not to mention host materials with pseudocapacitive capability.
We recently develop a nanostructured composite material based on graphene and mesoporous TiO₂ mesocrystals by using a microwave-assisted solvothermal method. The TiO₂ mesocrystals exhibit anatase structure with abundant mesopores, and they are intimately anchored on graphene sheets. We found that the Na ions insertion and de-insertion processes in such TiO₂/graphene nanocomposite exhibit an ultrafast pseudocapacitive behavior, similar to the pseudocapacitive Li insertion reported in anatase TiO₂ thin film. However, fast insertion/de-insertion of the large Na ions has not yet been observed in the pure anatase TiO₂ phase. The TiO₂/graphene nanocomposite delivers a reversible capacity of 125 mAh g^-1 at a high rate of 10 C, and almost no capacity fading after 18000 cycles. Such exceptional fast Na storage capability and stability could be related to the unusual mesoporous structure of TiO₂ and the strong coupling with the conductive graphene sheets. To demonstrate the advantages of such pseudocapacitive-type electrode, we assemble an asymmetric Na-ion capacitor using a TiO₂/graphene-based negative electrode and a carbon-based positive electrode, delivering a high energy density of 67 Wh kg^-1 at a power density of 121 W kg^-1 and 20 Wh kg^-1 at 1554 W kg^-1.

Reference
1. T. Brezesinski, J. Wang, J. Polleux, B. Dunn, S. H. Tolbert, J. Am. Chem. Soc., 2009, 131 (5), 1802–1809.
2. M. Sathiya, A. S. Prakash, K. Ramesha, J−M. Tarascon, and A. K. Shukla, J. Am. Chem. Soc., 2011, 133 (40), 16291-16299.
3. V. Augustyn, J. Come, M. A. Lowe, J. W. Kim, P.-L. Taberna, S. H. Tolbert, H. D. Abruña, P. Simon, B. Dunn, Nature Materials, 2013, 12 (6), 518-522.

High-energy supercapacitors have potential applications in electrical energy storage. While binder-free supercapacitors with heteroatom-doped reduced graphene oxide (rGO) are efficient, their fabrications are complex and expensive. Herein we describe a simple, ultrafast method to fabricate these supercapacitor electrodes in situ without thermal or chemical treatments. Ultrasonic spray deposition (USD) was used for activating rGO, whose collision with the nitrogen carrier gas molecules introduced nitrogen dopant into rGO (N-rGO). Meanwhile, two-dimensional N-rGO and one-dimensional carbon nanotubes (CNTs) were deposited layer-by-layer to form periodic, nanoporous and interdigitated electrodes. In the resulting electrode, the nitrogen doping improved the access of ion species, and the surface area was much higher than electrodes using only rGO. A record high specific capacitance (areal, 62.1 mF cm^-2; gravimetric, 612 F g^-1 at 10 mV s^-1) and ultrafast response (below 0.992 ms) were achieved. The electrodes also displayed high cycling stability and structural flexibility.

The increased number of lithium ion batteries and supercapacitor technologies utilized in everyday products demands more reliable and safer technologies enabling high energy densities with faster response times over an extended range of temperatures. A design strategy for device configuration along with fabrication of a thermally stable lithium ion supercapacitors are described. We report the performance of a symmetric activated carbon electrode supercapacitor with LiFTSI in a glycerol carbonate electrolyte compared to a similar device configuration in an EC/DMC electrolyte. Electrochemical measurements, based on the total weight of electroactive materials, gave a specific capacitance of 162 F/g at 1 mV s^-1, an energy density of 14.2 Wh kg^-1 at 2 A/g, and a power density of 7.5 KW kg^-1 at 10 A/g at a temperature of 100 °C. Cyclic voltammetry (CV), charge discharge (CD), and electrochemical impedance spectroscopy (EIS) were performed to investigate the electrochemical properties of the fabricated coin cells.

Porous carbon nanostructure have their unique structural characteristics and potential applications in many different fields. Especially, their novel structural properties as the electrode materials, such as abundant active sites and high ion accessibility, are important in realizing high capacitance with robust cycle life in electrochemical energy storage applications. In this research, we demonstrate various nitrogen-rich carbon nanostructure having multiporosity for electrochemical energy storage with high performances.
Nitrogen-rich carbon nanostructures are fabricated with various approaches to have a 0D sphere, 0D hollow sphere, and biomimetic 1D nanotube structures. These N-rich carbon based materials shows various N-configurations in carbon matrix, porosity, and open channels for the ion-pathway. Basically, the porous nature of N-rich carbon spheres buffers the volume change of silicon and thus resolves critical issues in Si anode operations in lithium-ion batteries (LIBs) such as unstable solid-electrolyte-interphase formation and vulnerable contacts between Si and carbon. Moreover, by introducing a template-free process, we developed N-rich hollow carbon spheres, where micropores increase active sites to store redox ions and mesopores enhance their diffusivity to encapsulated nickel oxide. This unique structure shows a high-performance full-cell type capacitor showing excellent energy and power densities. Furthermore, using both hard and soft template, we also fabricated a N-rich nanotube structure, in which internal compartments enable the accommodation of numerous metal nanocrystals and open mesoporous channels enable fast ion insertion/desertion. Metal nanoparticles (NP) encapsulated N-rich nanotubes can be applied to high performances LIBs and the N-rich nanotube itself shows high capacities in anion storage. In addition, this metal with N-rich nanotubes composite was assembled into the Li-ion battery type anode of a full-cell hybrid capacitor device and combined with a N-rich nanotubes electrochemical-double-layer-type cathode with excellent rate capability and robust cycle life. Consequently, we expect that the method demonstrated here for the fabrication of N-rich carbon based nanocomposites could pave a route to realize advanced type materials for high-performance energy storage devices.

Pseudocapacitors are newly emerging energy storage systems that bridge the gap between batteries and electric double layer capacitors. Unlike the more commonly known redox pseudocapacitance, which offers near surface faradaic charge transfer, intercalation pseudocapacitance occurs when ions intercalate into the channels or layers of a redox-active material accompanied by a faradaic charge-transfer. Recently, it has been proposed that suppression of phase transformations in intercalation pseudocapacitors, which can be achieved through nanostructuring, is required in pseudocapactive charge storage because the nucleation and growth of new phases is kinetically slow. Here, we demonstrate intercalation pseudocapacitance charge storage through MoS₂ nanocrystals (n-MoS₂) using both Li⁺ and Na⁺ ions accompanied by phase transition suppression. MoS₂ is an attractive material because of the large van der Walls gaps between its layered structure that allows highly reversible intercalation. Eighty-three and ninety-four percent of the charge storage in n-MoS₂ was found to be capacitive during Li⁺ and Na⁺ insertion respectively, while bulk MoS₂ (b-MoS₂) is largely diffusion limited. In agreement with this fact, b-MoS₂ has previously been shown to display phase change upon ion intercalation. To examine phase stability in n-MoS₂, we use in-situ X-ray diffraction (XRD) during electrochemical cycling. b-MoS₂ shows a phase transition with new peaks emerging accompanied by a continuous lattice expansion in c-axis. Starting from the trigonal structure, b-MoS₂ is transformed to a triclinic phase as ions intercalate into the layers. During deinsertion, the lattice spacing relaxes back to its original state and b-MoS₂ is converted back to the trigonal phase. Meanwhile, no phase change is found in n-MoS_2, which suggests that phase transition suppression is the reason for its high capacitive response. Only a slight peak shift is observed in n-MoS₂ due to the expanded inter layer spacing in the c-axis. This same trend is observed in both Li⁺ and Na⁺. This is unexpected because Na⁺ is larger in ionic radius and has a unique staging intercalation mechanism in the bulk, where Na⁺ first intercalates every other layer. Despite the bulk behavior in MoS₂, n-MoS₂ has demonstrated fast charging behavior as a result of phase transition suppression and can be set as another example of extrinsic pseudocapacitive materials.

Asymmetric capacitors composed of a battery-type electrode and a high surface area carbon electrode merge the advantages and reduces the drawback of redox and capacitive based systems; namely, the asymmetric design offers the advantages of supercapacitors (power rate, cycle life) and batteries (energy density).
This work is focused on lithium-ion capacitors (LICs) utilizing graphite (G) and reduced graphite oxide (RGO) as negative electrode materials and activated carbon (AC) with the well-developed surface area as positive one. Our results reflect the different behavior of pure and modified graphite material applied as an anode in a hybrid device. The electrode with the slowest response (involving redox process) will determine the power of the total system. Since intercalation of lithium ions into graphite material occurs relatively slow, the power of LIC with graphite as the anode will be lower. For this reason, the chemically reduced graphite oxide seems to be promising material as the anode in LIC. A merged mechanism of the energy storage in RGO allows the good power rate to be achieved. In this investigation, the hybrid cells with graphite and RGO anodes showed the energy density at mild current regimes of ca. 80-90 Wh kg^-1, but this tendency was maintained only for AC/RGO(Li) capacitor at higher rates. Moreover, this system demonstrated the energy density of 30 Wh kg^-1 at a power density of 25 kW kg^-1, i.e. at the current load of 20C (calculated per mass of both electrodes). Good cyclability of LIC has been retained for 1000 cycles as well as the high state of charge after 20h of OCV (around 93% of the full state of charge). Electrochemical techniques such as cyclic voltammetry, galvanostatic charging/discharging and electrochemical impedance spectroscopy, were applied to record responses of individual electrodes (positive and negative) by measurements carrying in three-electrode systems.
Financial support from the project DEC-2013/09/D/ST5/03886 is gratefully acknowledged.

We report a facile method for grafting of 1-nitropyrene (Pyr-NO₂) onto highly graphitized carbon onion. This is achieved through lowering of the onset potential of the pyrene unit polymerization via in-situ reduction of the NO₂ group. The additional redox activity associated with the NO₂ redox activity allows to surpass the faradic capacity solely associated with the p-doping of the grafted pyrene backbone, as it is observed for the pyrene, 1-aminopyrene, and unreduced Pyr-NO₂. Upon 20 wt % grafting of Pyr-NO₂ the capacity of the electrode jumps from 20 mAh/g_electrode to 38 mAh/g_electrode which corresponds to 110 mAh/g_Pyr-NO2 per mass of Pyr-NO₂. Altogether, this results in a striking increase of the energy density vs. the Li counter electrode by 90 % (29 to 55 Wh/Kg_electrode), while the average potential is increased by 18 %. Very interestingly, such high performance comes together with outstanding retentions of both the initial capacity for more than 4000 cycles and power characteristics demonstrating the superior advantages of the present in-situ grafting technique. Lastly and most importantly, a full cell is demonstrated by combining Li-terephthalate/carbon as anode.

Synthetic pore templates provide an easy way to create porous structures, but their usage for large scale production is limited due to the process complexity and prohibitive cost of material. Here we investigate use of bacteria, a naturally abundant and environmentally friendly material, as a pore template and demonstrate their applicability in Li-oxygen battery cathode fabrication. Bacteria are approximately a million times cheaper, require no chemical synthesis, are available in different morphologies, and degrade easier than conventional pore templates. We fabricate free standing porous multiwalled carbon nanotube (MWCNT) films using bacteria as pore templates, and demonstrate the performance impact of porosity control on cathodes for Li-oxygen batteries. Film porosity as well as the shape of pores in the cathodes were easily tuned to achieve a 30% improvement in oxygen evolution efficiency and double the full discharge capacity in repeated cycles when compared to the compact MWCNT films. The interconnected pores effectively improved the accessibility of reactants throughout the cathode matrix allowing the porous MWCNT cathodes to achieve 8,649 Wh/kg of gravimetric energy density at a power of 4,942 W/kg under 2 A/g_e (1.7 mA/cm²).