In lithium-ion battery systems, there is a complex relationship between the lithium ion, the anion, and the electrolyte in two-solvent systems. Cyclic carbonates like ethylene carbonate are stable in the Li⁺ solvation sheath while linear carbonates like dimethyl carbonate move in and out frequently, reflecting a difference in coordinating stability with Li⁺. Because of this bias in Li⁺ coordinating ability, a correlation can be drawn between the composition of the Li⁺ solvation sheath and the resulting composition of the passivating solid electrolyte interphase (SEI) that forms on the graphitic anode of a Li-ion battery during the first charge. This interphase layer is crucial to the reversibility of the graphitic anode.
This work details the investigation into the solvation condition of the anion in the Li-ion electrolyte system. Evidence suggests that the anion plays a role in the formation of the anode SEI layer. It is hypothesized that the anion and its solvation structure may also influence the cathode SEI, either by participating in the chemistry of SEI formation, or by suppressing the formation of a cathode SEI altogether. Newer high-voltage cathode materials, such as LiNi_0.5Mn_1.5O₄ and LiCoPO₄, increase the likelihood of forming a cathode SEI.
Previous work indicated that although typical electrolyte anions are poorly coordinated, both PF₆^- and BF₄^- showed a preference for the low-permittivity linear carbonate ethyl methyl carbonate over the high-permittivity solvent ethylene carbonate. This work will attempt to show a correlation between the stability of anion-solvent clusters with the composition and formation of the cathode interphase layer.

Multivalent battery systems like rechargeable magnesium (Mg) batteries have recently gained more interest as candidate post-lithium (Li) battery systems, for possible applications in electric vehicles (EVs) and plug-in hybrid vehicles (PHVs). This is primarily due to concerns over the range performance of current Li battery systems, and the space requirements for future EVs and PHVs.^1-4 Mg, being divalent and denser, is theoretically capable of delivering a higher volumetric energy-density (3833 mAh cm^-3) than Li (2061 mAh cm^-3), making it a viable battery system for addressing current range and space concerns.^1-3 To date, various low voltage organohaloaluminate electrolytes have been utilized in Mg battery systems, due to the incompatibility of high voltage conventional battery electrolytes (TFSI^-, ClO₄^-, PF₆^-) with Mg metal anodes.^5-8
As we recently reported, it is however possible to use conventional battery electrolytes for Mg battery systems, by changing the type of anode, from a Mg metal anode to a Mg-ion insertion-type anode (e.g. Bi and Sn). This change enables Mg-ion transport through the anode/electrolyte interface during the use of conventional battery electrolytes.^3,9 Here, we report recent progress in the use of such insertion-type anodes for rechargeable Mg-ion batteries, via the application of a novel synthetic method. Further, we address specific issues related to the formation of various anode/electrolyte interfaces for Mg-ion batteries, which have recently been studied in some detail.¹⁰ Results from the application of the novel synthetic method and recent fundamental analytical analyses, focused on studying and understanding the nature of the anode/electrolyte interfaces, will be presented and discussed.
References:
1 J.-M. Tarascon and M. Armand, Nature, 2001, 414, 359.
2 P. Novak, R. Imhof and O. Haas, Electrochim. Acta, 1999, 45, 351.
3 T. S. Arthur, N. Singh and M. Matsui, Electrochem. Commun., 2012, 16, 103.
4 D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich and E. Levi, Nature, 2000, 407, 724.
5 D. Aurbach, J. Weissman, Y. Gofer and E. Levi, Chem. Rec., 2003, 3, 61.
6 Z. Lu, A. Schechter, M. Moshkovich and D. Aurbach, J. Electroanal. Chem., 1999, 466, 203.
7 T. D. Gregory, R. J. Hoffman and R. C. Winterton, J. Electrochem. Soc., 1990, 137, 775.
8 J. Muldoon, C. B. Bucur, A. G. Oliver, T. Sugimoto, M. Matsui, H. S. Kim, G. D. Allred, J. Zajicek and Y. Kotani, Energy Environ. Sci., 2012, 5, 5941.
9 N. Singh, T. S. Arthur, C. Ling, M. Matsui and F. Mizuno, Chem. Commun., 2013, 49, 149.
10 T. S. Arthur, P-A. Glans, M. Matsui, R. Zhang, B. Ma and J. Guo, Electrochem. Commun., 2012, 24, 43.

It has recently been demonstrated that the high solubility of lithium polysulfides in nonaqueous electrolytes can be exploited to make high energy density lithium-sulfur flow batteries with low raw cost [Fan et al. Nano Lett., 2014]. In particular, a new architecture was used in which a percolating network of nanoscale conductor particles (in this case carbon black) was incorporated within the electrode forming an embedded current collector which distributes electrochemical activity throughout the volume of the flow electrode, rather than being confined to the surfaces of stationary current collectors. Compared to the traditional approach, this architecture enables significantly higher capacity (~1200 mAh / g S) by allowing cycling of polysulfide solutions (2.0-2.5V) into the precipitation regime (~2V), where discharge proceeds via precipitation of insoluble Li₂S onto the conductor network.
The majority of the available capacity of this battery lies in this precipitation regime. Therefore, understanding the kinetics of the precipitation process is essential to improving the reversibility and rate capability of lithium-sulfur flow batteries. Here, we will discuss the nucleation and growth kinetics of the precipitates on various conductive substrates, including various carbon surfaces and conducting oxides, which were investigated by analyzing current transients from potential-step experiments.
Moreover, we will discuss the effects of cycling conditions and substrate on the morphology of the precipitates. For example, cycling at high rates results in small particles forming a conformal coating on the substrate, whereas lower rates result in much larger precipitates with less coverage of the substrate. The precipitation of lithium sulfide has long been a challenge for lithium-sulfur batteries due to its low electronic conductivity, so controlling the morphology of precipitates can reduce losses due to Ohmic polarization.

The performance of aromatic compounds as redox shuttles for overcharge protection in lithium-ion batteries is quite variable and is difficult to predict. Redox shuttles can decompose in battery electrolyte both in their neutral and radical cation forms, both of which are present during overcharge, and can lead to an inability to protect from overcharge or - even worse - an inability to fully charge a battery. While hundreds of compounds have been evaluated as redox shuttle candidates and a few have stood out as top performers (EPT, DBBB, ANL RS-2, and BCF3EPT), the reasons for increased stability over similar candidates with slightly different structures is often unclear, and the exploration of decomposition of redox shuttles has been severely limited, restricting our abilities to design improved versions of redox shuttles that do not suffer from the same reactions in lithium-ion batteries. To better understand the stability and reactivity of redox shuttles, which is also relevant to the improvement of positive electrode materials in non-aqueous redox flow battteries, our research has focused on measuring the stability of neutral and oxidized forms of redox shuttle candidates as well as using a variety of spectroscopic methods to analyze the byproducts of decomposition, both from radical cations generated in model solvents and electrolytes and from postmortem analysis of failed batteries. We generate radical cations by chemical oxidation with tris(4-bromophenylaminium) hexachloroantimonate or other oxidants or through bulk electrolysis in a solvent containing an electrolyte. We compared the lifetimes of radical cations in different solvents to determine which solvents lead to faster decomposition. Included in these solvents were small molecule carbonates that are used as the electrolyte solvents in lithium-ion batteries. We used UV-visible absorption spectroscopy to monitor radical cation lifetimes by following the intensity of the radical cation absorption, which is red-shifted in comparision to the absorption of the neutral equivalent. We have used EPR spectroscopy to monitor the formation of new radical species in solution and GCMS and ¹H NMR spectroscopy will be used to analyze decomposition products. We have compare different radical cations to see if decomposition pathways are similar and have identified multiple decomposition products, starting with N-alkylphenothiazine derivatives and are beginning to explore the reactions of different aromatic compounds like dialkoxybenzene derivatives, in which there is significant variation in stability.

We study the synthesis, electrochemical and mechanical performance of large area layered freestanding papers composed of acid functionalized few layer molybdenum disulfide (MoS₂) and reduced graphene oxide (rGO) flakes for use as a self-standing flexible electrode in sodium ion batteries. Synthesis was achieved through vacuum filtration of homogenous dispersions consisting of varying wt. % of exfoliated MoS₂ flakes in GO in DI water, followed by thermal reduction. The electrochemical behavior of the composite paper was evaluated as counter electrode against pure Na foil in a half-cell configuration. The papers showed good Na cycling ability with charge capacity of approx. 225 mAh.g^-1 with respect to total weight of the electrode and coulombic efficiency reaching 99%.

Graphite, as the most common anode for commercial Li-ion batteries, has been reported to have a very low capacity when used as a Na-ion battery anode. It is well known that electrochemical insertion of Na into graphite is significantly hindered by the insufficient interlayer spacing. Here we report expanded graphite as a Na-ion battery anode. Preparedt hrough a process of oxidation and partial reduction on graphite, expanded graphite has an enlarged interlayer lattice distance of 4.3 Å yet retains an analogous long-range-ordered layered structure to graphite.In situ transmission electron microscopy has demonstrated that the Na-ion can be reversibly inserted into and extracted from expanded graphite, which is different from other carbonaceous NIB anodes. The robustness of the long-range-ordered layered structure of EG during sodiation/desodiation has also been revealed by reproducible interlayer changes during multiple charge/discharge processes during in situ TEM observation. Galvanostatic studies show that expanded graphite can deliver a high reversible capacity of 284 mAh g-1 at a current density of 20 mA g-1, maintain a capacity of 184 mAh g-1 at 100 mA g-1, and retain 73.92% of its capacity after 2,000 cycles.The findings reported here are beneficial for the design and manufacture of rechargeable sodium-ion batteries, positioning EG as a promising anodic materials.
Sulfur can also been intercalated into expanded graphite and functions as cathode for Li-S batteries.Sulfur intercalated expanded graphite were synthesized by in-situ one-step sulfur reduction and intercalation of graphite oxide (GO) in vacuum at 600 oC. At 600 oC in vacuum, S vapors play dual roles: (1) assisted-reduction of GO into expended graphite (EG) and (2) simultaneous intercalation into EG interlayers. As cooling down to room temperature, the S molecules are physically and chemically confined by the interlayers of EG. The EG/S composites with 52% S loading showed high capacities, high rate capability and long cycling stability in the electrolyte of 1.0 M LiTFSI (TEGDME), in particular, undergoing the treatment of CS2, it exhibits extraordinary performances in Li-S battery. For instance, at a current density of 100 mA/g, the EG/S cathode shows that Coulumbic efficiency is close to 100% and capacity retains around 880 mAh/g with progressive cycling up to over 220 cycles. Moreover, even the current density increases 100 times (10.0 A/g), a capacity of more than 220 mAh/g can still be delivered. The exceptional performance of the EG/S cathode can be attributed to: (i) the S2 molecules are physically and chemically confined by the high surface RGO; (ii) the EG materials significantly improve the conductivity of the S and effectively buffer the structural strain/stress caused by the large volume change during lithiation/delithiation of S.

Very promising voltage profiles and specific capacities have been demonstrated for Na-ion battery cathodes based on honeycomb-ordered variants of the alpha-NaFeO₂ class of layered materials. Both ordered and disordered variants of this class of materials are known. The degree of perfection in the ordering of redox-active transition metal cations in this class of compounds has been investigated by a variety of bulk (synchrotron X-ray diffraction, neutron diffraction) and local (transmission electron microscopy, solid state nuclear magnetic resonance, pair distribution function analysis) structural probes in order to understand the influence of synthesis conditions on cation ordering, and the influence of cation ordering on electrochemical performance.

Lithium-metal anode degradation is one persistent challenge of lithium-sulfur (Li-S) batteries, hindering their practical utility as the next generation rechargeable battery chemistry. The polysulfide migration and shuttling associated with Li-S batteries deteriorate lithium metal, causing lithium dendrite formation and poor lithium cycling efficiency with complicated lithium-surface chemistry. Here, we show copper acetate as a surface stabilizer for lithium metal in a polysulfide-rich environment of Li-S batteries. The lithium surface is protected from parasitic reactions with the organic electrolyte and migrating polysulfides by an in situ chemical formation of a passivation film consisting of Li₂S/Li₂S₂/CuS/Cu₂S and electrolyte decomposition products. This passivation film suppresses lithium dendrite formation by controlling the lithium deposition sites, leading to a stabilized lithium surface characterized by a dendrite-free morphology and improved surface chemistry.
Polysulfide catholyte was added into a carbon nanofiber electrode and coupled with the lithium-metal anode. In order to suppress polysulfide shuttling prior to the formation of a stable passivation film, LiNO₃ was added into both the control cell and the experimental cell. Copper acetate was added only into the experimental cell. The experimental cell containing copper acetate outperformed the control cell without copper acetate in cycling stability. The control cell experienced a sudden capacity and Coulombic efficiency drop when approaching 100 cycles, possibly due to lithium dendrite development or depletion of electrolyte as a result of parasitic reactions. As indicated by scanning electron microscopy (SEM) results, the lithium-metal surface in the control cell after the first charge was characterized by bulk Li₂S/Li₂S₂ precipitates and non-uniformly deposited mossy lithium, confirming that LiNO₃ alone is not able to conserve the lithium morphology. In contrast, the experimental cell had a smoother lithium surface covered by a passivation film. After the 100^th charge, the lithium surface in the control cell exhibited clear dendritic morphology in contrast to the experimental cell where lithium deposition was uniform. X-ray photoelectron spectroscopy (XPS) data revealed that the lithium surface in the experimental cell had much less polysulfide adhesion after the first charge. The passivation film on the lithium surface in the experimental cell is comprised of Li₂S, Li₂S₂/CuS/Cu₂S, lithium salts, and electrolyte decomposition products. The concentration of electrolyte decomposition products did not increase with cycling in the experimental cell, indicating that fewer parasitic reactions occurred on lithium-metal surface. Superior battery performance is obtained when the protected lithium-metal anode is coupled with the cathode innovation. As far as we know, this is the first report of protecting lithium metal in a polysulfide-rich environment.

Hybrid Li-air batteries, in which the lithium-metal anode in a nonaqueous electrolyte is separated from the air cathode in an aqueous catholyte by a solid electrolyte membrane, show attractive properties for applications like electrical vehicles or grid-energy storage. They offer several advantages such as high cell voltage, high energy density, stability in ambient air, and reversibility in aqueous catholytes. However, the development of hybrid Li-air batteries is still at its infant stage. Many efforts have been made on extending the cycle life of rechargeable hybrid Li-air batteries. The research directions include development of highly active and stable bifunctional catalysts, suitable aqueous catholytes to maintain the stability of the solid electrolyte, and highly conductive solid electrolytes that are stable with lithium-metal anode and aqueous catholytes. The conventional bifunctional air cathode supports both the oxygen reduction reaction (ORR) during discharge and oxygen evolution reaction (OER) during charge. However, the ORR catalyst and carbon support suffer from corrosion and degradation under the highly oxidizing conditions during the charge process, resulting in rapid increase in overpotential upon cycling, which limits the cycle life of hybrid Li-air batteries.
We present here a novel hybrid Li-air battery with decoupled ORR and OER electrodes, which eliminates the corrosion problem and leads to high efficiency and long cycle life. Low-cost spinel NiCo₂O₄ nanoflakes grown onto a nickel foam (NCONF@Ni) in the decoupled configuration are found to exhibit higher OER activity and stability compared to NiCo₂O₄ powder (NCONF) in the conventional configuration. The decoupled configuration displays the best overall ORR and OER performances. This is because the ORR and OER require quite different electrochemical environments, which are fulfilled by separating these two functions into two independent electrodes with different properties. The Pt/C catalyst was loaded onto a hydrophobic carbon paper to maximize the three-phase boundary for ORR. The decoupled design also avoids the involvement of Pt/C in the oxidizing OER process. The NiCo₂O₄ nanoflakes were grown onto a three-dimensional (3-D) porous nickel foam and totally immersed in the electrolyte to ensure full contact of the OER catalyst with the electrolyte. Each nanoflake was directly connected to the conductive nickel foam substrate to achieve high catalytic efficiency.

Lithium-ion batteries (LIB) are complex multi-phase systems whose operation depends on ionic and electronic conduction across multiple interfaces. Recent modeling efforts suggest that the performance of LIBs is greatly dependent on characteristics which span multiple length-scales. Recent advances made with in-situ characterization tools have given insight into structural changes that occur during electrochemical cycling. However, often times the electrochemical cells used are designed with the experiment in mind and are not entirely representative of a fully-assembled commercial cell.
In our work, a fully-assembled commercial lithium iron phosphate battery is probed in situ using energy-dispersive x-ray diffraction. With the use of high-energy synchrotron x-rays, we are able to penetrate the battery and collect useful data across multiple length scales in three dimensions. Tomographic profiles are used to analyze the multi-layer structure on the millimeter-scale. Operando phase-mapping is used to analyze the discharge-evolution of lithiated phases on the micrometer-scale. In addition, a line profile analysis is used to analyze structural defects on the nanometer-scale. Observations will be connected across length-scales and insights into battery performance will be discussed.

Composite electrode structures with layered and spinel domains are of interest for arresting or suppressing the voltage fade that occurs when cycling high capacity, lithium- and manganese-rich ‘layered-layered&’ xLi₂MnO₃middot;(1-x)LiMO₂ (M=Mn, Ni, Co) electrodes in lithium-ion cells. Control of the spinel content in composite ‘layered-layered-spinel&’ structures and regulating the electrochemical voltage window of the lithium cells enhances the capacity of the electrode and significantly reduces voltage fade. In order to obtain capacities that exceed those of a conventional LiCoO₂ electrode, these composite electrode structures require an electrochemical activation step above 4.5 V that can involve the participation of the oxygen ions during the initial redox reactions of the cell. The reactions of these high capacity lithium-ion electrodes and their relationship to the functioning of transition metal oxide electrode/electrocatalyst materials in Li-O₂ cells will be discussed.
Acknowledgments
This work was funded by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357. The composite lithium-metal-oxide electrode research was supported by the Office of Vehicle Technologies, whereas the lithium-oxygen cell research was supported, in part, by the Center for Electrical Energy Storage, an Energy Frontier Research Center funded by the Office of Science, Office of Basic Energy Sciences.

Energy storage in hybrid supercapacitors (HSC) utilizing Li insertion electrode with battery like functionality and activated carbon (AC) electrode with electric double layer (EDLC) charge accumulation function is being intensively investigated. With ability for dense energy storage by Faradaic Li-ion insertion/extraction and high power density from reversible fast charge transfer at EDLC interface, HSCs are promising for powering electric and hybrid vehicles. A key factor for high energy density and cyclic stability is Li-insertion electrode. Li₄Ti₅O₁₂ (LTO) negative electrode in HSCs is ideal for Li ion intercalation without volume expansion. This research utilizes a unique surface sculpted LTO nanoplatelets engineered by a proprietary NanoScission process¹. The objective is to compensate for low electronic conductivity of LTO by creative nanostructure that enhances contact probability with electrolyte and electron transfer kinetics. A LTO electrode was formed by slurry coating with PVDF binder and carbon black on Cu and Timcal Super-P AC electrode on Al foils. HSC is assembled with LTO-AC electrodes in 2032 coin-type cells with 1M LiPF₆ electrolyte in EC:DEC and Celgard separator. LTO-AC HSCs with lithiated -LTO (Li₇T₅O₁₂) were also studied
Electrochemical performance of hybrid supercapacitor was recorded by cyclic voltammetry (CV) at scan rates 0.5 to 60 mV.s^-1 in 1-3.2 V range. Rectangular plots show pseudocapacitive behavior and current change in reverse at fast rate with undistorted fast scans CV indicates fast Faradaic kinetics. Nyquist impedance study show low charge transfer resistance from kinetically-controlled electron transfer and Li+ de-intercalation at LTO anode. At low capacity charge-discharge (0.2 C-1C) HSCs show high Coulomb efficiency and slightly lower at 5-10C due to limitation of adsorbed PF₆ anions at electrolyte-AC interface. Galvanostatic charge-discharge curves in 1-4.2V and 1-3.2V ranges at various C-rates show fast linear initial discharge due to capacitive storage across EDLC and plateau at 2.2 V due to Li+ ion intercalation reaction at LTO. The lithiated LTO electrode show stable capacity of 60-70 mA.g^-1 tested up to 30 cycles from initial high of 120 mA.g^-1. Loss in capacity due to electrochemical process induced structural changes in LTO were examined by x-ray diffraction and Raman line shifts. Reduction, broadening and shift of the Raman line at 678 cm^-1 from Ti-O bonds in TiO₆ octahedra after cycling indicates Li insertion reactions in the operation of HSC. Further, electrochemical induced changes in stretching Li-O bonds in LiO₄ and LiO₆ polyhedra were seen. This paper describes detailed electrochemical aspects of energy storage, charge stability, storage energy-power density through impedance, CV and galvanostatic CD measurements and induced structural changes in LTO by x-ray diffraction and Raman spectroscopy.
1. http://primetprecision.com/our-technology/

Understanding the reaction mechanism of olivine compounds as electrode materials for lithium ion batteries have received much attention recently. The question whether olivine LiFePO₄ undergoes two-phase or non-equilibrium single-phase reaction during electrochemical processes has taken center stage in the understanding of the faster reaction kinetics observed in this material. Here we report the lithiation/delithiation mechanism of Mg substituted LiFePO₄ using high resolution XRD, TEM and electrochemical measurements. Ex-situ partially (de)lithiated olivine-LiMg_0.2Fe_0.8PO₄ show the existence of stable equilibrium intermediate phases as characterized by the presence of more than two phases and broadness of diffraction peaks. EELS profiles across individual nanoparticles further confirm uniform lithiation with a constant Fe-L₃ energy measured across each nanoparticle. In addition, we observe continuous shift in diffraction peak position even in the “two-phase” region in the ex-situ electrochemical (de)lithiated electrodes.

Dissolution of manganese at surface is a long standing issue hindering the practical application of spinel LiMn₂O₄ cathode material, while few studies concerning the crystal structure evolution at surface area have been reported. Combining X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), scanning transmission electron microscopy (STEM), and density functional theory (DFT) calculations, we investigate the chemical and structural evolutions on the surface of LiMn₂O₄ electrode upon cycling. We found that an unexpected Mn₃O₄ phase was present on the surface of LiMn₂O₄ via the application of an advanced electron microscopy. Since the Mn₃O₄ phase contains 1/3 soluble Mn²⁺ ions, formation of this phase contributes significantly to the Mn²⁺ dissolution in LiMn₂O₄ electrode upon cycling. It is further found that the Mn₃O₄ appears upon charge, reaches a maximum at the end of the charge and disappears upon discharge, coincident with the valence change of Mn. Our results shed light on the importance of stabilizing the surface structure of cathode material, especially at charged state. The understanding of the manganese dissolution reaction that occurs in the LiMn₂O₄ can certainly be extended to other oxide cathodes.

Some of the most important performance characteristics of any composite battery electrode are the electronic and ionic conductivities. Moreover, heterogeneities in transport properties can accelerate failure mechanisms and require that the battery be overdesigned. Much work has been done, including by our group, researching electrode conductivity using a variety of methods, each with their own advantages and limitations.
Here we present the underlying theory, device fabrication details, and experimental measurements of an improved micro four-line probe that can quantify the conductivity and contact resistance of an intact battery electrode, meaning one still attached to the metallic current collector. Our probe is fabricated on a silicon wafer and mounted on an automated XYZ stage with force feedback. This allows repeated measurements at a single point with controlled pressure, as well as scans of conductivity across the surface with micron resolution. We present conductivity maps for multiple commercial-grade electrodes that would be used in lithium ion batteries including: lithium iron phosphate (LFP) cathode, nickel cobalt manganese (NCM) cathode, and graphite anode. The electrodes show significant variations in conductivity on a millimeter scale, which can significantly affect cell performance.

Lithium garnet oxides have become one of the most promising candidates as solid electrolytes for lithium-ion batteries, due to their high lithium ionic conductivity and high electrochemical stability. While most studies have been focused on different doping strategies to increase the conductivity values, mechanistic understanding of lithium ionic conduction in this class of materials remains limited. In this talk, we will present some of our recent results on the ionic conduction mechanisms in two model materials: tetragonal ordered composition Li7La3Zr2O12 (LLZ) and cubic disordered composition Li5La3Ta2O12 (LLT), studied by the classical molecular dynamics (MD) employing interatomic potentials. In lithium garnet oxides, there are two types of cages, i.e. tetrahedral (Td) and octahedral (Oh), to host lithium ions. These two cages are connected by triangular bottlenecks formed by three oxygen atoms. Our MD studies revealed that the tetragonal to cubic phase transition of LLZ happened at around 900 K, consistent with experimental observation by thermal analysis and x-ray diffraction. In addition, the phase transition is likely to be driven by the redistribution of lithium from one Td cage (8a), to another Td cage (16e), through one Oh cage (32g). Uneven nearest-neighbor Li-Li clusters can be identified in both model materials and such geometrical frustration leads to the local structure instability and fast ionic conduction. Our MD studies support that the lithium conduction path goes through the triangular bottleneck in a 3D continuous network of Td/Oh cages, without a direct Oh to Oh jump. However, the conduction mechanism should not be generalized as they are greatly influenced by the local environments or temperatures. Broadly speaking, lithium atoms hop through the bottleneck from an edge-passing mechanism at low temperatures to a center-passing mechanism at higher temperatures.

Carbon nanotubes are promising electrode materials for supercapacitors and batteries due to their high mechanical strength, electrical conductivity, and surface area. The energy density of carbon-based electrical double layer capacitors, however, is limited by the inactivity of inert carbon and the absence of Faradaic redox processes. Here, we show that residual Fe nanoparticles that remain within MWCNTs after synthesis can be “activated” using voltammetric cycling to positive potentials above the electrolysis limit in acidic electrolytes. The activation processes leads to anomalous electrochemical behavior associated with MWCNT rupturing in the regions surrounding the Fe nanoparticles along with rapid Fe oxidation. MWCNTs grown using a liquid injection chemical vapor deposited process can contain 5-10 wt. % residual Fe, which accounts for an increase in the peak capacitance (286 F/g) compared to MWCNTs with trace Fe (68 F/g). The increase in capacitance is a result of Faradaic charge transfer associated with the Fe²⁺/Fe³⁺ transition (E_1/2 = 0.48V vs Ag/AgCl) within confined Fe nanoparticles. Due to the additional Faradaic capacitance, a corresponding increase in charge capacity from 10 mAh/g to 16 mAh/g is also observed. These results provide motivation for further investigating the electrochemical activity of carbon nanomaterials with defects or impurities as a simple design approach to increasing the capacitance of electrode materials. This work is supported by NSF-CMMI scalable nanomanufacturing SNM # 1246800 award.

The large-scale deployment of renewable energy technologies critically depends on solving the intermittency of energy production methods with scalable and inexpensive energy-storage solutions. Lithium-ion battery (LIB) has been widely considered as the technology of choice to meet the future energy challenge. Conversion cathode materials represented by inexpensive iron fluorides (FeF₂ and FeF₃) and oxyfluorides hold the promise to significantly increase the energy density of current LIBs. However, despite significant experimental and theoretical efforts in recent years, this promise has yet to be realized due to the challenges of fast capacity decay and a large voltage hysteresis. Solving these challenges requires a better understanding of the electrochemical reaction mechanisms during battery operation, especially during recharge, which however has been surprisingly under-researched. Here we will report our comprehensive and integrated experimental and theoretical studies into the mechanisms controlling the nanoscale electrode conversion/reconversion. By holistically evaluating the results from in operando 2D X-ray absorption near-edge structure spectroscopy (XANES) microscopy, in operando X-ray absorption spectroscopy, in situ scanning transmission electron microscopy (STEM) and electron diffraction (ED), ex situ TEM/ED, synchrotron powder X-ray diffraction (PXRD), and density functional theory simulations, we will present new insights into the conversion mechanisms of these materials. We will also discuss our recent progress in developing long-cycle-life nanostructured iron fluoride conversion cathodes, which is built on the insights gleaned from the integrated experiments and modeling above.

The development of improved energy storage technologies with greater specific energies is critical to the success of future electric vehicles and renewable energy products. Among the different energy storage technologies under study, lithium-oxygen batteries are one of the most promising due to their greater gravimetric energies and capacities compared to other technologies such as conventional lithium-ion cells. The objective of this research is to develop a comprehensive understanding of how the anodic and cathodic parameters affect the discharge characteristics of lithium-oxygen cells through the use of the finite element method and computational fluid dynamics software ANSYS Fluent. Several major challenges remain in the development of a commercially available lithium-oxygen battery and many studies have been published that separately consider the effects of dendrite growth, species diffusivity, and electrode porosity on a cell&’s performance. The growth of dendrite structures on the anode surface can lead to shorts within the cell while the build-up of precipitate within the cathode can lead to pore clogging and capacity loss. Our finite element models consider each of these issues to gain an understanding of their collective effect on the performance of a lithium-oxygen cell. The model will aid in our understanding of the operating behaviors of lithium-oxygen cells and how species diffusivity, electrode porosity, and anode surface homogeneity affect the discharge performance of a lithium-oxygen cell. This comprehensive understanding will aid in the design of a commercially viable lithium-oxygen battery that could be used for a wide range of energy storage applications.

The prevention of capacity loss after electrochemical cycling is of paramount importance to the development of Lithium-ion batteries, especially for the application in the electric vehicle industry. The objective of this research is to investigate C-rate dependent diffusion-induced-stresses in a multi-particle system by adapting the thermal stress analysis approach. LiFePO₄ is selected as the model system in this study since it is one of the promising cathode materials used for the electric vehicle application. Three different concentration dependencies are incorporated in the finite element analyses: orthotropic elastic constants, volume expansion coefficients, and lithium diffusivities. Six different particle orientations are considered in calculating the average mechanical properties. Our simulation results show that the effect of concentration dependency on mechanical properties and lithium diffusivities cannot be neglected for the mechanical stress prediction. The results of lithium concentration profiles, total strain energies, normal stresses and shear stresses at different C-rates (1C, 2C, 6C and 10C) are compared and discussed. A higher maximum stress at a higher C-rate due to a steeper lithium concentration gradient suggests that particles inside the material may undergo fractures faster and lead to the capacity loss at higher C-rates.

Silicon is considered as a promising electrode material for next-generation, high-performance lithium-ion batteries (LIBs). However, silicon undergoes huge volumetric expansion of nearly 400% when fully lithiated. The expansion causes massive cracking and battery capacity fade, and remains one of the main obstacles to the development of advanced high-capacity LIBs. Recent studies have begun to examine the mechanistic aspect of the LIBs in search for a means to circumvent the problem of electrode cracking. In this talk, I will discuss our recent work on investigating the fracture behaviors of silicon electrodes under various electro-chemical conditions. This work provides quantitative fracture characteristics of lithiated silicon and will aid in the development of predictive models for microstructural optimization of silicon-based LIBs.

Despite intense investigation over the past decade, many details regarding the mechanism of lithiation and delithiation of Li-alloy forming anode materials remain unknown, thus hindering the replacement of graphite-based anodes with higher capacity alternatives. In this study we use all-solid-state thin film batteries with Al anodes to characterize the chemical and morphological changes that occur during lithiation and delithiation, in real time and with high spatial resolution. A unique characteristic of Al is that it reacts with Li⁺ producing an intermetallic compound, LiAl, which results in a single plateau voltage profile. We spatially resolve the composition changes of the Al anode that takes place upon cycling, and correlate these changes to the capacity loss observed. By combining micro-Raman spectroscopy with X-ray photoelectron spectroscopy (XPS) measurements we map the chemical composition of the anode surface with high spatial resolution. The anode top surface of the cycled batteries is formed by Li-Al-O ternary oxide, and the sub-surface layer is populated by LiAl Fd3m alloy mounds, as confirmed by TEM. Raman shift peaks at 1380 and 1585 cm^-1 were assigned to Li-Al-O, and a peak at 2890 cm^-1 corresponds to LiAl. XPS measurements have confirmed the presence of Li and Al on the top surface of the anode in an atomic ratio of 4:1, with binding energies equal to 56 and 74 eV, respectively. The local mapping of the composition changes of the anode was correlated to the morphology of the material. Based on our results, we propose that the Li-Al-O oxide acts as a cap around the LiAl mounds, preventing Li to diffuse back to the cathode during the battery discharge. To corroborate our experimental results, we calculated the electrochemical voltage profiles of the different Li-Al-O possible ternary oxides by density functional theory (DFT). LiAlO₂ and Li₅AlO₄ are formed at 3.35 V and 0.17 V, respectively. A detailed thermodynamic model of our system will be also presented.

Lithium oxygen battery is a promising energy storage technology owing to its high theoretical energy density. However, a number of challenges need to be addressed before this energy storage technology is ready for practical applications. Among them, short-term stability and low round-trip efficiency are major concerns with existing carbon based electrode materials. Recent research points towards issues of reactivity exhibited by the carbon cathode support that compromises the cyclability of Li-Oshy;₂ operation. A non-carbon cathode support has therefore become a necessity.
Our choice of material is the TiSi₂ nanonets, a high surface-area, and a highly conductive two-dimensional structure. To enable oxygen reduction and evolution reactions, Ru nanoparticles were deposited by Atomic Layer Deposition onto TiSi₂ nanonets. A surprising site-selective deposit of Ru nanoparticles onto only the b planes of TiSi₂ nanonets was observed. DFT calculations show that the selectivity is a result of different interface energetics. The resulting heteronanostructure proves to be a highly effective cathode material. It enables Li-O₂ test cells that can be recharged more than 100 cycles with average round-trip efficiencies greater than 70%. On a fundamental level, our study sheds light on what issues are truly connected with the carbon electrode. On a practical level, our material choice proves to be a highly effective cathode material that allows for the immediate advancement of Li-O₂ technology. In summary, our study promises to address key issues encountered in Li-O₂ battery research. A new door is now opened for the realization, to the full potential, of this new technology.

We report a dynamic particle packing (DPP) model capable of imitating the particle-level details of a porous Li-ion electrode formed by a slurry-coating process. Such a model is a first step in allowing us to predict electrode microstructure and therefore battery performance from fundamental fabrication conditions. In particular we simulate a cathode composed of nearly spherical active material particles (Toda 523), carbon black, and polymeric binder. The DPP model is based on using a superposition of spheres to imitate complex particle shapes and aggregates of carbon and binder. Equations of motion coupled to interparticle forces are solved to simulate particle motion and subsequent immobilization during fabrication steps. The resulting model structures are validated as follows. First, experimental microstructure data are determined by FIB/SEM sequential cross-sections of real composite electrodes. Image processing algorithms are used to segment the images into three phases also used in the model: active material, nanoporous carbon/binder domains, and macroscopic pores. The 3D segmented structures (model and experiment) are analyzed and compared using key metrics, such as volume fractions, contact probabilities, and Fourier spectra. Likewise, effective electronic and ionic conductivities of the model structures are compared to experimental values.

Graphene wrapped amorphous phosphorus nanocomposite was developed though facile conventional ball milling method. Nano-sized amorphous phosphorus was uniformly distributed within the high conductive carbon matrix, which was built up by graphene. Graphene not only enhanced the conductivity of the nanocomposite, but also served as a buffer layer on the surface of phosphorus particle stabilizing solid electrolyte interphase, suppressing volume expansion of phosphorus during lithiation and preventing contact loss between phosphorus and conductive matrix. Due to this unique structure, graphene wrapped amorphous phosphorus nanocomposite exhibited high specific capacity and excellent cycling stability used as anode for lithium ion battery both at ambient temperature and elevated temperature. High specific capacity of ~1800 mAh/g and satisfying Coulombic efficiency of 99.5% with excellent capacity retention of 80% within 200 cycles were achieved at room temperature, great specific capacity of ~2200 mAh/g and Coulombic efficiency of 99% with retention of 73% within 200 cycles were achieved at 60°C.Combing with the attractive rate performance at room temperature (~1080 mAh/g @ 3C), the P/G nanocomposite obtained from facile and general ball milling method would be a promising anode candidate for lithium ion battery.

Rechargeable Mg batteries present a promising technology to improve capacity of rechargeable batteries over those of Li-ion chemistries. Since the initial prototype was proposed in 2000 much work has been done on understanding/improving both electrolyte and cathode to work towards this goal of exceeding Li-ion capacity. In the present study, the performance of Chevrel phase Mo₆S₈ cathodes synthesized by both molten salt and high temperature synthesis were tested against both Mg Grignard salts (EtBuAlCl₂)₂- (dichloro complex, DCC) and second generation Mg(PhCl₃)(all phenyl complex, APC), in an attempt to understand how the synthetic method affects the performance of the cathode against various electrolytes. Three different cathode preparations, high temperature (HT) high temperature exposed to atmosphere (HTA) and molten salt (MS), were evaluated with XRD and XPS before and after cycling to ascertain the quality of the cathode crystal structure and surface structure as well as the effects of cycling on the cathode. Results show that the HT synthesis produces highly ordered crystallites free of contamination, while the MS synthesis produces less ordered crystallites with some contamination most likely acquired from the synthetic method. Full cells were assembled and tested vs. a Mg metal anode, and cycling data show that the maximum theoretical capacity of 121 mAh/g was achieved in both electrolytes for the HT synthesis, while the MS synthesis obtained a capacity of ~100 mAh/g with the decrease in performance caused by contamination acquired during cathode synthesis. An initial explanation of observed differences in performance attributable to synthetic route and electrolyte behavior will be presented, along with structure evolution data of the calcogenide before and after cycling.

High surface area carbons were derived from pyrolysis and physical activation of polyfurfuryl alcohol. The resultant carbon has high purity with oxygen content < 2 atomic%. Using emulsion polymerization and polymer blending, it is also possible to control the development of porosity in nano-, meso- and macroscale creating a hierarchical pore structure. The synthesized carbons demonstrated excellent voltage stability upto 4.5 V vs Li/Li⁺ in lithium electrolytes. With the help of fluorophosphate electrolyte additive, we were able to further improve the electrochemical stability from 4.8V to 1.2V vs Li/Li⁺ and specific capacitance as high as 120 F/g was achieved. The fabricated lithium ion capacitors demonstrated good cyclability and post-mortem analysis of the electrodes using X-ray photoelectron spectroscopy revealed formation of stable SEI layer on the high surface area carbon electrode.

Understanding the coupling between mechanics and electrochemical performance is of great importance for modern and future lithium-ion systems, all of which exhibit electrochemical-induced mechanical strains during operation. These strains result in the accumulation of mechanical stress at the cell level, which has previously been shown to accelerate chemical degradation of lithium-ion cells [1]. In this talk, we attribute the stress-accelerated chemical degradation to deformation of the polymer battery separator, which can cause spatially localized “hot spots” of high utilization. We present results from experiments and finite element simulations of cells containing purposely manufactured inhomogeneities to investigate their effects on degradation. Our results show that localized transport restrictions (e.g. separator deformation) can cause significant local increases in overpotential and current, both of which are known aggravators of cell ageing. We investigate the sensitivity of these localized phenomena to cell design parameters, materials properties, and operating conditions, and find that in certain cases localized lithium plating can occur in an otherwise well-functioning cell. We also discuss the reverse coupling, in which chemical degradation in the forms of plating and film formation can result in increased mechanical stress, presenting the possibility of a two way coupling with positive feedback between mechanics and degradation.
[1]. J. Cannarella, C. B. Arnold, J. Power Sources, 245 (2014) 745-751.

AlPO₄ nanoparticles were synthesized via chemical deposition method and used for the surface modification of MoO₂ to improve its structural stability and electrochemical performance. Structure and surface morphology of pristine and AlPO₄-coated MoO₂ anode material were characterized by electron microscopy imaging (SEM and TEM) and X-ray diffraction (XRD). AlPO₄ nanoparticles were observed, covering the surface of MoO₂. Surface analyses show that the synthesized AlPO₄ is amorphous, and the surface modification with AlPO₄ does not result in a distortion of the lattice structure of MoO₂. The electrochemical properties of pristine and AlPO₄-coated MoO₂ were characterized in the voltage range of 0.01-2.5thinsp;V versus Li/Li+. Cyclic voltammetry studies indicate that the improvement in electrochemical performance of the AlPO₄-coated anode material was attributed to the stabilization of the lattice structure during lithiation. Galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) studies reveal that the AlPO₄ nanoparticle coating improves the rate capability and cycle stability and contributes toward decreasing surface layer and charge-transfer resistances. These results suggest that surface modification with AlPO₄ nanoparticles suppresses the elimination of oxygen vacancies in the lattice structure during cycling, leading to a better rate performance and cycle life.

Ever increasing requirements to the lifetime, safety, energy density and cost of lithium-ion batteries for applications such as EVs require new strategies in material development. One such strategy is to develop core-shell positive electrode materials in which one composition, the “core”, is encapsulated in a micron scale coating, “the shell”, of another composition.¹ This is done so to hybridize the properties of materials with different compositions. Materials that show exceptional energy density, but not the best cell lifetime, due the oxidation of the organic carbonate electrolyte at the surface of the positive electrode are excellent candidates for the core material. Compatible materials that show less oxidation of the electrolyte at high potential are ideal candidates for the shell material.
Materials in the series Li_1+x(Ni_yMn_1-y)_1-xO₂ (x ge; 0, y le; 1), have been extensively studied for their crystallographic structure and electrochemical performance.^2,3 The electrochemical performance varies vastly with composition which makes some materials excellent candidates for the core of a core-shell material and others for the shell. The similarities in the compositions allows for a relatively simple synthesis of core-shell structures.
Synthesis and characterization of the core-shell mixed-transition metal hydroxide precursor materials have been previously explored⁴; however literature lacks a significant study of the electrochemical performance and characterization of the positive electrode material after lithiation and sintering. This presentation will explore the product after lithiation and calcination via high precision coulometry (HPC)⁵, powder XRD, EDS and SEM. When a Ni_0.6Mn_0.4(OH)₂:Ni_0.2Mn_0.8(OH)₂ core-shell precursor was mixed with Li₂CO₃ and sintered at 900#8304;C for 10 h, the core-shell motif was maintained as was confirmed using XRD and EDS. However when the same precursor and amount of Li₂CO₃ was sintered at 1000#8304;C for 10 h, the core-shell motif was virtually lost as the transition metals diffused together to form a more homogeneous composition throughout the particle. Electrochemical results from the HPC will also be discussed.
References:
1. S. T. Myung, H. J. Noh, S.J. Yoon, E. J. Lee, Y. K. Sun, J. Phys. Chem. Letters 5, 671 (2014).
2. E. McCalla, A. W. Rowe, R. Shunmugasundaram, J. R. Dahn, J. Chem. Mat. 6, 989 (2013).
3. Z. H. Lu, L.Y. Beaulieu, R.A. Donaberger, C. L. Thomas, J. R. Dahn J. Electrochemical Soc. 149, A778 (2002).
4. J. Camardese, D. W. Abarbanel, E. McCalla, J. R. Dahn, J. Electrochemical Soc. 161, A890 (2014).
5, A. J. Smith, J. C. Burns, S. Trussler, J. R. Dahn, J. Electrochemical Soc. 157, A196 (2010).

The study of high energy density electrode materials is central to the development of lithium-ion batteries; alternatives to carbonaceous anodes in lithium-ion batteries are being sought in recent years. Silicon has been considered as one of the most promising anode materials for the next generation lithium-ion batteries because it would afford a much higher capacity than the commonly used graphite (~4200 mAh/g vs. 372 mAh/g). However, the major obstacle to overcome is the electrode mechanical failure caused by the repeated significant volume change of Si when alloying/de-alloying with lithium during the lithium insertion/removal process. For the sake of alleviating this volume change impact and improving the electrochemical performance of Si, we developed a series of new silicon/silicon oxide/titanium composite anode materials which were prepared by the ball-milling method. The morphology, composition, structure and electrochemical properties of these materials were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), powder X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), magnetic analysis and galvanostatic charge-discharge tests. The results show that the theoretical capacity of Si in these composites can be achieved, and all the materials exhibit excellent electrochemical cyclability (with little capacity fading over 100 cycles). Such a cycling performance can be associated with the titanium particles which are found being evenly distributed in these composites, buffering the drastic volume change of silicon during the electrode reaction. This research is supported by DOE-EERE-BATT, DE-AC02-05CH11231 under Award Number 6807148, and by NYSERDA.

Mechanical degradation of solid electrode materials for energy storage devices has been correlated with capacity fade and impedance growth over repeated charging and discharging. Here, we consider whether -- and at what length scales -- the mechanical properties of electroceramic cathode materials in lithium-ion batteries are affected directly by electrochemical cycling, including lithium intercalation and deintercalation. We measured Young&’s modulus E, hardness H, and fracture toughness K_Ic via instrumented nanoindentation of single grains within polycrystalline Li_XCoO₂, a widely used cathode material, after different extents of electrochemical charging. During a single charge cycle, E and H decreased by up to 60%, while K_Ic decreased by up to 70%. This decreased fracture resistance is attributed to Li-depletion causing chemical expansion and phase transitions within the volume probed by nanoindentation. These results indicate that K_Ic reduction occurs during the first cycle of lithium deintercalation from polycrystalline aggregates of Li_XCoO₂. At the single crystal scale, such charge-dependent reduction in mechanical properties affects particle sizes resistant to electrochemical shock. Such reduced fracture toughness at the scale of individual grains can also facilitate intergranular and intragranular crack propagation within microscale, polycrystalline cathode particles over repeated electrochemical cycling. Both phenomena can plausibly promote extensive mechanical damage on the meso- to macroscale of battery electrodes. Thus, direct quantification of charge state-dependent mechanical properties of electroceramics in such energy storage devices can enable improved material and device performance.

Fluoride based materials have been studied as conversion-type cathode materials for lithium ion batteries because of their high specific and volumetric capacities, and high operating voltage. However, metal fluoride (MF) -based cathodes suffer large irreversible capacities and poor cycle stability, partly due to the formation of metal (M) nanoparticles during the conversion of MF into LiF and undesirable reactions of M with electrolyte. Such side reactions may include M dissolution as well as M-catalyzed decomposition of common electrolytes used in Li-ion and Li metal batteries. Electrolyte decomposition products may induce a significant barrier for the reversible formation of MF during Li extraction and thus lead to a rapid growth of polarization and capacity fading. Here we report on a surface passivation of MF nanoparticles, which greatly improve performance characteristics of MF cathodes by reducing cell polarization and enhancing cycle life. In addition, we report on a new type of MF-based nanocomposites, which overcomes some of the present limitations. Control over the size and microstructure of the produced composites at the nanoscale was found to be critical for optimizing their electrochemical performance and achieving hundreds of stable cycles. Structure-property relationships are studied by comparing results of electrochemical characterization with changes in physical and chemical characteristics of the electrodes before and after cycling.

The increased use of lithium ion batteries in hybrid electric vehicles and other automotive applications has driven the need for batteries that are capable of high discharge rates and long cycling lifetimes. The necessity of high ion mobility without loss of structural integrity places stringent demands on the crystalline structures of cathode materials.¹ The layered lithium transition metal oxide LiNi_xMn_xCo_1-2xO₂, is a promising cathode material because of its high capacity, excellent charge-discharge efficiency and almost no volume change under cycling.² However, such components still suffer from capacity fading and voltage instability problems, especially during high-voltage operation. Recent research has shown the localized structural rearrangement on the surface of active particles during the initial electrochemical cycling, which may contribute to the irreversible capacity and poor rate capability of the cell.³
In this work, a variety of electron microscopy techniques have been applied to investigate the structural changes and chemical evolution of the LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathode material in order to understand the charge-discharge mechanisms during electrochemical cycling. With a dual beam focused ion beam (FIB)/scanning electron microscope (SEM) system, hundreds of SEM images, each one produced after sectioning, were acquired to reconstruct the three-dimensional (3D) structure of the NMC cathode. The phase distribution of the active materials, polymer binder and pores is clearly visualized from the 3D structure, which can then be used to model transport properties.⁴ An increased number of cracks inside the NMC cathode was also observed by comparing the 3D structure of the cathode before and after cycling.
In addition, a detailed study using high-resolution electron energy loss spectroscopy (HREELS) has been carried out to investigate the charge-discharge mechanism by probing the valence changes of the transition metals (TMs) in the NMC cathode material. The combination of scanning transmission electron microscopy (STEM)-HREELS allows mapping the local valence changes of the TMs (Ni, Mn and Co) at different states of charge in order to identify the chemical evolution during the initial electrochemical cycle. The structural evolution of this cathode material following the electrochemical cycling is further studied using an aberration corrected scanning transmission electron microscopy (a/STEM) that allows for the atomic resolution.
References:
J.B. Goodenough, et al. Chemistry of Materials, 2010 (22): 587-603.
N. Yabuuchi, et al. Journal of Power Sources, 2003 (119): 171-174.
F. Lin, et al. Nature Communications, 2014, doi:10.1038/ncomms4529.
A Gully, et al. Journal of the Electrochemical Society, 2014 (161): E3066-E3077.

Rechargeable multivalent ion batteries can serve as next generation electrochemical energy storage systems for many prospective applications. Devices for grid scale storage will benefit from using abundant multivalent ions such as Cu²⁺, Zn²⁺, Fe³⁺, Al³⁺, and Mg²⁺. Among them, Mg is environmentally benign, earth abundant, stable in atmospheric conditions, and 24 times less expensive than Li. Mg is advantageous in higher theoretical specific volumetric capacity (3833 mAhcm^-3) in comparison to that of Li (2046 mAhcm^-3). However, there are many practical challenges that limit widespread utility of secondary Mg batteries. Two such challenges include (1) the design of electrolytes with large voltage stability windows with the appropriate interfacial stability that are able to solvate Mg salts sufficiently and (2) the availability of cathode materials that are capable of rapid and reversible Mg²⁺ insertion. Here we introduce the use of biologically-derived eumelanins as electrode materials for use in secondary Mg batteries.
Melanins are a broad class of pigments that can be found from many organisms including Homo sapiens and Sepia officinalis. Eumelanins are a subclass of natural melanins that mediate redox reactions and are composed of nano-sized granules. Eumelanins exhibit unique chemical signatures that support reversible cation binding including pendant carboxylates, aromatic amines, and catechols. Catechols participate in redox reactions via coordinated two-electron two-proton processes. Intermediates are stabilized by the formation of semiquinones. Concerted two-electron oxidation of eumelanin cathodes could be harmonized with extraction of divalent Mg²⁺ cations. Symmetric stoichiometry facilitates insertion and removal of Mg²⁺ cations during discharge cycles.
Eumelanin electrodes exhibit prominent stable cathodic and anodic peaks as assessed by cyclic voltammetry. These data suggest reversible insertion/extraction of Mg²⁺. Oxidation of catechols into quinones promotes the extraction of Mg²⁺ during discharge cycles with a voltage hysteresis of 0.7 V. Eumelanin cathodes exhibit stable discharge potential at around -0.3 V with charge storage capacities of >60 mAhg^-1 over 500 cycles when operating in half-cell configuration with aqueous electrolytes. High cycling stability in melanin cathodes is attributed to catechol groups. FT-IR and Raman spectroscopy corroborate that redox-active catechols form coordination bonds with divalent Mg²⁺ ions during half-cell discharge. Taken together, catechol-bearing melanins permit reversible Mg²⁺ extraction rendering this class of biologically-derived pigments potentially suitable for use as cathodes in secondary Mg batteries.

Due to its high theoretical specific capacity (4200 mAh/g), silicon has been the focal point of lithium ion battery (LIBs) anode research. However, major drawbacks prevent silicon from commercialization. Low electrical conductivity and large volume expansion in the lithiated state (up to 400%) lead to mechanical degradation, relatively low Coulombic efficiency, and high irreversible capacity losses.
Polyaniline doped silicon nanoparticles (SiNP-PANi) have been previously studied [1] demonstrating stable operation for over 5000 cycles at 6.0 A/g with almost zero irreversible capacity loss. The performance was explained by the “caged” PANi nanostructure which provides sufficient conductivity, reversible volume control, and limited growth of SEI throughout the electrode. However, these results were obtained using large submicron Si particles and low Si loading (0.3mg/cm), which does not satisfy the requirements for commercialization.
The objective of this study is in understanding the Li-ion transport and possible aging mechanisms within the SiNP-PANi architecture and at the liquid electrolyte interface.
The SiNP-PANi slurries were prepared by mixing SiNP (0.8g), aniline (0.008g), phytic acid (0.18g), and water (2mL) followed by sonication. Ammonium persulfate (0.009g) was added to the mixture, which then initiated radical polymerization of aniline. The green viscous slurry containing emeraldine salt of [([C₆H₄NH]₂[C₆H₄N]₂)_n]₂⁺ cation and phytic acid (C₆H₁₇O₂₄P₆)^- anion was deposited on an etched copper foil with a doctor blade. After drying in ambient conditions overnight, the electrodes were compressed at 25, 200, and 340^oC and a constant pressure of 100 psi#8729;cm^-2.
Our results indicate that SiNP-PANi anode heat-treated at 200^oC possess up to 3000mAh#8729;g^-1specific capacitance. Based on our results, it can be concluded that the cell performance largely depends on heat-treatment temperature and is significantly higher with PANI than with PAA. Heat treatment at constant pressure improves the SiNP-PAA electrode performance resulting in specific capacitance increase which is due to oxygen evolution and graphitization of PAA. Heat and pressure treatment with PANi electrodes mainly affects the morphology of the caged nanostructure. When heated, PANi-phytic acid salt redistributes itself in and around the SiNP, enhancing the architecture as well as the porosity and conductivity of the electrode. Heat treatment also induces decomposition of excess ammonium persulfate, as well as hydroxyl groups in excess phytic acid.
Data obtained from cyclic voltammetry, AC impedance spectroscopy, and extensive CC cycling will be discussed in combination with FESEM/EDX, HRTEM, TGA, DSC, FTIR and Raman spectroscopy for identification and correlation of temperature effects on cell performance, morphology, and the changes in chemical composition of PANi and PAA before and after heat treatment.
H. Wu, G. Yu, L. Pan, N. Liu, T. McDowell, Nature Communications, 4 (2013) 1943.

The partial graphitization of multiple activated carbons is herein shown to be directly dependent on the relative concentration of surface acidity. The relative density of total acidity (DTA) is shown to determine the graphitize-ability of independent carbon materials under progressive oxidation conditions. Powder X-ray diffraction, surface titrations and multiple optical techniques illustrate the dependence of crystallite size on the relative concentrations of specific surface oxygen groups (SOGs) for each carbon material presented—where the chemical graphitization method was shown to occur due to a transformation of π-bond density from aromatic to olefin type bonding—thereby enabling the proposed graphitization mechanism. The partially graphitized carbons were then analyzed for their Li-insertion utility. The carbon series were first treated with a long-chained fluorosurfactant to passivate outer-surface SOGs and then subjected to standard Li-insertion conditions. Reversible capacity was shown to increase over 10x after 50 charge/discharge cycles due to both increased pore-accessibility and a more homogenous, stronger SEI layer composed primarily of lithium ethylene dicarbonate. Electrochemical impedance spectroscopy (EIS) analysis of the extended cycled electrodes revealed further pertinent results concerning the integrity of the SEI layers developed on the oxidized and surfactant passivated electrodes. Such graphitization and passivation methods serve a unique utility for use as pre-lithiated electrode materials in hybrid battery type Li-ion capacitors.

Lithium-polysulfide batteries, which utilize the high solubility of lithium polysulfide in non-aqueous electrolytes to enable flowable electrodes, have high theoretical energy density and low raw materials cost. Our group recently demonstrated lithium polysulfide flow electrodes with an embedded current collector, enabled by low-volume-fraction percolating networks of nanoscale conductors¹. This approach resulted in a substantially higher capacity than a traditional carbon fiber flow battery current collector. To achieve greater electrode-level energy density, higher higher sulfur concentrations are needed.
In a given electrolyte system, sulfur utilization (e.g. mAh/g sulfur) decreases dramatically with increasing sulfur concentration at a fixed C-rate. We undertook a systematic investigation of the factors limiting the rate capability of higher concentration systems. In particular, we study the ionic conductivity and exchange current density of the lithium polysulfide solutions of varying concentration and in differing solvents. The electrolyte solvent is found to dramatically affect the solution ionic conductivity and exchange current density. Exchange current densities are measured using both impedance spectroscopy and galvanostatic polarization using glassy carbon working electrodes. In the concentration range of interest (1-8 M [S]), the ionic conductivity monotonically decreases with increasing sulfur concentration while exchange current density shows a more complicated response. The conductivity and current density results are used to interpret the rate capability of suspension-based cells. We also study non-carbonaceous electrode materials to understand how the electrode material can affect exchange current density and thus cell capacity.
Acknowledgements:
This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.
1. Fan, F. Y. et al. Polysulfide Flow Batteries Enabled by Percolating Nanoscale Conductor Networks. Nano Lett. (2014). doi:10.1021/nl500740t

As concerns over fossil fuel costs and associated greenhouses gas emissions continue to rise, the higher fuel efficiency (miles per gallon) requirements and controlled emissions are becoming a challenge for the transportation industry. The U.S. Federal Government is requiring new vehicle fleets to achieve an average fuel economy of at least 34.1 miles per gallon by 2016 and 56.2 mpg by 2025. Several types of electrified vehicles have emerged as potential solutions, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Batteries for these vehicles need to have high energy density, high power density, and low cost. The size of batteries required for each of these vehicles span from 1kWh in HEVs to 30-40kWh in EVs, making it economically impossible for one battery chemistry to meet all the requirements. Using a novel electrode construction and tailoring the active materials microstructure & morphology, we have achieved extremely high specific power approaching 2,000 W/kg at very low costs and life of the vehicle battery solution. This novel approach with unique design at EPS will allow all types of micro, mild, and strong hybrid, which typically require small size batteries up to 1 to 1.5 kWh battery, to offer the end users an attractive economic value proposition. By coupling this power performance with a high energy cell, e.g., lithium ion, the volume and cost of the resulting system can be reduced to half while its cycle life can be extended. This may allow development of electric and hybrid electric vehicles at a price that is competitive with ICE vehicles, a goal that has eluded the automotive industry for decades.

Achieving high performance with electrochemical energy-storage (EES) devices such as batteries and electrochemical capacitors (ECs) requires high mobility in long-range electron conduction (i.e., well-connected domains of ordered solid) and in long-range ionic and molecular transport (processes best optimized with some degree of structural disorder) [1]. Improved power/energy density and cycle life accrue using three-dimensional (3D) strategies to design the charge and mass transport function [2]—as seen by the leap in capability of 3D microbatteries [3]. Moving beyond the control exhibited on the small scale requires retaining and scaling transport. By realizing carbon-based ultraporous nanofoam papers with voids sized from 100 nm to 1 mm, we can now access batteries and ECs of all length scales, yet retain control of functionality on the nanoscale and in 3D [4,5]. Paper-supported architectures provide high surface area, a through-connected 3D network of porosity, a highly conductive carbon framework, and the mechanical properties (e.g., flexibility) of the paper mold in which the carbon nanofoam is synthesized. By using non-line-of-sight modification protocols, we “paint” the carbon surfaces with conformal, nanometer-thick skins of active materials of relevance in energy-storage devices. We can now design, fabricate, prototype, and build 3D electrodes for batteries and ECs that can be scaled to the desired macroscopic size to run devices requiring more energy than the > 1 J mm^-2 of microbatteries.
This work is supported by the Office of Naval Research.
[1] D. R. Rolison, J. W. Long, J. C. Lytle, A. E. Fischer, C. P. Rhodes, T. M. McEvoy, M. E. Bourg, A. M. Lubers, Chem. Soc. Rev. 2009, 38, 226.
[2] J. W. Long, B. Dunn, D. R. Rolison, H. S. White, Chem. Rev. 2004, 104, 4463.
[3] J. F. M. Oudenhoven, L. Baggetto, P. H. L. Notten, Adv. Energy Mater. 2011, 1, 10.
[4] J. C. Lytle, J. M. Wallace, M. B. Sassin, A. J. Barrow, J. W. Long, J. L. Dysart, C. H. Renninger, M. P. Saunders, N. L. Brandell, and D. R. Rolison, Energy Environ. Sci.2011, 4, 1913.
[5] J. W. Long, M. B. Sassin, C. N. Chervin, D. R. Rolison, Acc. Chem. Res. 2013, 46, 1062.

Not surprisingly, energy and materials are intimately related. Many forms of energy utilization, conversion and storage and generation are dominated by interfacial chemistry. Therein nanomaterials as an interfacial modifier can play a critical role in these processes. This talk will provide an overview of nanomaterial synthesis, integration and value in energy storage, conservation, transfer, efficiency, control and generation.
Highlights of our studies in each of the following will be presented:
Storage: Increased energy density in Li ion batteries and supercapacitors using carbon nanotubes
Efficiency: Reduced friction using nanolubricants between moving parts
Transfer: Improved thermal management using nanofluids in heat transfer applications
Conservation: Lightweight polymeric composites incorporating nanotubes, nanoclays and graphene oxide for vehicle composites
Control: Gas sensors based on nanoscale metal oxide semi-conductors for process control and monitoring
Generation: Catalysts and photocatalysts using nanostructured oxides for accelerated charge transfer and minimal recombination losses
Though synthesis of a host of carbon and metal oxide nanomaterials has been demonstrated, their integration into practical applications remains highly challenging. This talk will provide an overview of their synthesis, integration and value in energy storage, conservation, transfer, efficiency, control and generation. Alternative, scalable synthesis approaches such as flame synthesis and associated laser-based optical diagnostics will be touched upon.

High energy density lithium ion batteries have been developed and fabricated using LiMnBO₃ cathodes composed of nanometer-scale (~20 nm) particles, demonstrating capacities as high as 170 mAh/g, i.e. 70% higher than the published results. The material has a monoclinic lithium manganese borate (LiMnBO₃) structure synthesized in aqueous solution using M13 virus as a mediator. Among polyanion cathodes which have a highly stable structures against oxygen loss, borates have attracted great interests for lithium ion batteries (LIBs) because of the low atomic weight of boron resulting in high energy storage capacity ⁽¹⁾. One of the major challenges in achieving the full potential of the borate compounds, e.g. LiMnBO₃ with theoretical capacity of 222 mAh/g, is reducing the particle size of the active material to increase the surface to volume ratio of the cathode ⁽²⁾. Here we employed genetically-engineered multifunctional M13 virus as the template to promote formation of the nano-structured LiMnBO₃. Single wall carbon nanotubes (SWCNTs) self-assembled over the virus to improve the electronic characteristics of the cathode. Our novel synthesis method features two steps; 1) formation of the bio-templated nanowire manganese oxide with average particle size of ~5 nm as the seed structure; and 2) incorporating lithium and borate ions over the manganese oxide seed to produce nanometer-scale lithium manganese borate precursors. The post annealing condition was optimized by studying the structural evolution of the material at different temperatures. Monoclinic LiMnBO₃ structure was produced using an annealing process as short as 1 h at 400°C in 4% H₂ / 96% Ar ambient. We also studied the effect of annealing temperature on particle size and consequently on the electrochemical performance of the LIB. Monoclinic LiMnBO₃/SWCNT hybrid cathode achieved an initial capacity of 170 mAh/g cycled in voltage range of 2-4.5V. The cathode maintains 71% of the initial capacity after 50 cycles under C/20 charge and discharge rate. The presented method can be employed to synthetize various compounds, presenting a unique opportunity for producing nano-structured high-performance electrode materials.
V. Legagneur et.al. Solid State Ionics 139 37-46, 2001.
J-C Kim et.al. J. Electrochem. Soc. 158, 3, A309-A315, 2011.

Miniaturization of sensors and electronic devices demands their integration with power sources of comparable sizes to feed them with power. Thin film rechargeable microbatteries can be used to deliver small-scaled power and low current levels for various devices such as portable electronics and micro elecrto mechanical systems (MEMS). Many rechargeable thin film batteries features an intercalation cathode such as: TiS₂, V₂O₅, LiMn₂O₄ and LiCoO₂. Among those, LiCoO₂ present one of the best cathodes with its large operating voltage and high cycle life. Another key requirement for cathode material is its high Li-ion diffusivity. Li-ion diffusion in the cathode can be influenced by the microstructural properties of the synthesized film. Several techniques have been used to prepare LiCoO₂ such as: radio frequency (rf) magnetron sputtering, Sol-gel and pulsed laser deposition (PLD). LiCoO₂ films deposited by RF sputtering have a rhombohedral structure with R-m space group if it is annealed at temperatures above 400^oC. The quality of the post annealed film depends on the substrate, thickness, rf power. In particular, thickness variation of the film exhibit strong degree of preferred orientation or texture discrepancy. Smaller thickness films exhibit unfavorable texturing known to slow Li-ion diffusion through the cathode lattice. However, larger cathode thicknesses show better Li-ion diffusion characteristics. These concerns hinder the fabrication of high performance thin film batteries with a total thickness of 1 micron. We show deposition of high quality RF sputtered LiCoO₂ thin films of ultra-thin thicknesses with favorable Li-ion diffusion charectristics. We deposit LiCoO₂ films from a solid target using RF magnetron sputtering on thermally oxidized Si wafers. The target (2 inch in diameter and 0.25 mm in thickness) was sputtered in Ar/O₂ mixture of a 3:1 ratio and a pressure of 5 mtorr. A quartz crystal monitor positioned at the substrate plane with an automatic rf generator (approximately 90 watt RF power) were used to maintain the deposition at a constant rate of 0.2 A^o/s. Samples were annealed in air from 500-700 ^oC for 2 hours. X-ray diffraction (XRD) was used to characterize the texturing of the sputtered films. Surface morphology and film thickness were characterized by using scanning electron microscopy (SEM). Preliminary results of XRD show that none of the grains were oriented in the (003) unfavorable orientation. Diffraction peaks were observed in the (101), (104) and the (107) crystal orientations. Comparing the relative intensities, we find that about 70% of the grains were preferentially oriented to the (104) orientation parallel to the substrate. This is a pleasant texturing for ultra thin cathodes with high Li-ion diffusivity. Therefore, we believe our method for deposition produces high quality LiCoO₂ RF magnetron sputtered film for the use in thin film microbatteries.

Electrochemical conversion reactions of transition metal compounds create opportunities for large energy storage capabilities exceeding modern Li-ion batteries. However, for practical electrodes to be envisaged, a detailed understanding of their mechanisms is needed, especially vis-agrave;-vis the voltage hysteresis observed between reduction and oxidation. Data will be presented that provides such insight at scales from local atomic arrangements to whole electrodes. NiO was chosen as a simple model system. The most important finding is that the voltage hysteresis has its origin in the differing chemical pathways during reduction and oxidation. This asymmetry is enabled by the presence of small metallic clusters and, thus, is likely to apply to other transition metal oxide systems. The presence of nanoparticles also influences the electrochemical activity of the electrolyte and its degradation products and can create differences in transport properties within an electrode, resulting in localized reactions around converted domains that lead to compositional inhomogeneities at the microscale. The implications of these results vis-a-vis the viability of conversion reactions as practical solutions for energy storage will be discussed.

The design of novel Si-enhanced nanocomposite electrodes that will successfully mitigate mechanical and chemical degradation, is becoming increasingly important for next generation Li-ion batteries. Recently Si/C hollow core-shell nanoparticles were proposed as a promising anode architecture, which can successfully sustain thousands of cycles with high coulombic efficiency. As the structural integrity and functionality of these heterogeneous Si materials depend on the strength and fracture energy of the active materials, an in-depth understanding of the interface and their intrinsic mechanical properties, such as fracture strength and debonding, becomes critical for the successful design of such and similar composites. Here, we first perform ab-initio simulations to calculate these properties for lithiated a-Si/a-C interface structures and combine these results with linear elasticity expressions to model conditions that will avert fracture and debonding in these heterostructures. We find that the a-Si/a-C interface retains good adhesion even at high stages of lithiation. For average lithiated structures we predict that the strong Si-C bonding averts fracture at the interface; instead, the structure ruptures within lithiated a-Si. From the calculated values and linear elastic fracture mechanics we then construct a continuum level diagram, which outlines the safe regimes of operation in terms of the core and shell thickness and the state of charge. We believe that this multiscale approach can serve as a foundation for developing quantitative failure models, and for subsequent development of flaw-tolerant anode architectures.

Under the ARPA-E AMPED program for advanced battery management systems (BMS), PARC and LG Chem Power are developing SENSOR (Smart Embedded Network of Sensors with an Optical Readout), an optically based smart monitoring system prototype targeting batteries for hybrid and electric vehicles (EVs). The system will use fiber optic (FO) sensors embedded within Lithium (Li)-ion batteries to measure parameters indicative of cell state in conjunction with PARC's low-cost, compact wavelength-shift detection technology and intelligent algorithms to enable effective real-time performance management and optimized battery design. FO sensors are lightweight and thin, immune to electrostatic discharge, electromagnetic interference, can be protected with suitable coatings to withstand harsh environments, and can measure multiple parameters with high sensitivity, such as strain, temperature, pressure, and chemical composition in multiplexed configurations. All of these characteristics make them very attractive candidates for embedding as sensors in batteries. This paper will give an overview of the project, the underlying enabling technologies, and then cover some promising initial experimental results.
We have successfully fabricated initial functional prototypes of small format Li-ion pouch cells with embedded fiber optic sensors. Preliminary data indicates comparable performance and seal integrity of these cells to un-instrumented cells. We will present initial internal strain and temperature data recorded over charge-discharge cycles for various C-rates and operating conditions. The analysis of the measured strain data clearly exhibits a number of distinct characteristic features that provide information on Li-ion transport and intercalation stages. Our data clearly proves that fiber optic sensors provide a new in-situ and in-operando diagnostics tool that provide time-dependent information on Li-ion transport, stress and strain, and microstructural properties.
The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000274.

Unlike theoretical capacity, practical capacity of intercalation electrode materials depends on having appropriate Li-transport kinetics at multiple length scales. We have recently developed a model to assess the practical capacity of close-packed oxide materials for any cation arrangement, including cation-disordered systems [1]. We demonstrate how atomistic level detail of Li migration needs to be combined with higher length scale percolation theory to understand which materials can have large practical capacity.
Based on first-principles calculations, we identify two different atomic environments through which Li can migrate: 1-TM channels that pass along a transition metal (TM) atom, and 0-TM channels that only involve Li atoms. The activation energy for Li migration through 1-TM channels is highly sensitive to strain, lattice parameters and ordering, whereas 0-TM channels exhibit low diffusion barriers that are mostly independent of their local structure. Hence, structures that possess a percolating network of 0-TM channels can have large capacity as they provide good Li mobility over a large Li concentration range. With this insight we can explain the practical capacity of the four most common rocksalt-type Li-TM oxides: the layered structure provides very good Li mobility through 1-TM channels, but only over a limited Li extraction range. This explains why the practical capacity of stoichiometric layered materials is well below their theoretical capacity. The spinel-like (LT-LiCoO₂) structure supports good Li mobility over the entire range of Li concentrations. The Li mobility in the γ-LiFeO₂ structure is very low, which explains its poor performance as electrode material. Finally, the disordered rocksalt structure provides reasonable Li mobility over a very large Li extraction range, but only if the material contains sufficient Li excess. This understanding leads to new design concepts for high-capacity materials, including fully disordered rocksalts as recently discovered [2].
[1] A. Urban, J. Lee, and G. Ceder, Adv. Energy Mater. (2014) DOI: 10.1002/aenm.201400478.
[2] J. Lee, A. Urban, X. Li, D. Su, G. Hautier, and G. Ceder, Science 343 (2014) 519-522.

We developed a method of microwave-assisted hydrothermal process combined with carbothermal reduction to synthesize colloidal LiFePO₄ nanospheres, which possess the diameter about 200nm,to 1.5 mu;m, and mesoporous characteristic with Brunauer-Emmett-Teller (BET) surface area of 30.6 m² g^-1. The colloidal LiFePO₄ nanospheres were printed into thin thim with the thickness of 30 mu;m as the cathode for lithium ion battery. The electrolyte of LiOPN was deposited on cathode film by reaction RF-sputtering. The top anode of all-solid-state battery is lithium foil. The electrochemical performance of all-solid-state battery with LiFePO₄ colloidal cathode can achieve the capacity density of about 80~120 mAh/cm² at the 10C charge/discharge rate, promising for wearable power souce.

In lithium-ion intercalation cathode materials, which are often structurally and chemically complex transition-metal oxides, intrinsic point defects can be either essential or detrimental to their functioning and cycling stability. The lack of a detailed understanding of their defect thermodynamics and kinetics is hindering rational design of materials with improved performance for battery applications. First-principles defect calculations in the complex oxides are computationally challenging, yet they have been proven to be an important tool for detailed studies of the thermodynamics and kinetics, providing much needed insights into the materials&’ electrochemical performance [1]. In this presentation, we report our first-principles studies of the structure, energetics, and migration of intrinsic point defects in lithium manganese oxides, using hybrid Hartree-Fock/density functional theory calculations. On the basis of our results, we will discuss the materials&’ phase stability, defect thermodynamics, delithiation mechanisms, and electronic/ionic conduction mechanisms. We will also provide guidelines for defect-controlled synthesis and defect characterization and suggest solutions for reducing intrinsic defects (e.g., manganese antisites) that are detrimental to the materials&’ cycling stability. [1] K. Hoang and M. D. Johannes, J. Mater. Chem. A 2, 5224 (2014).

. In lithium ion and lithium metal batteries, electrochemically driven volume changes can lead to mechanical responses at interfaces that are generally not understood well, especially when a solid electrolyte is used. Since electrode-electrolyte interfacial contact and adhesion are important for long term stability and operation of batteries, a systematic study of the factors influencing the adhesion characteristics was undertaken. In the current study, adhesion between a solid electrolyte based on PEO and V₂O₅ electrodes of different surface morphologies (e.g. smooth films, patterned films, etc) was determined experimentally and compared to results from detailed finite element modeling of the experimental configuration. Methods (e.g. surface modification of electrode, tuning surface morphology of electrode) for improving the adhesion of this critical interface were also demonstrated. The height of islands and roughness of island sidewalls are believed to be critical factors for improving adhesion. Furthermore the electrochemical and mechanical properties of V₂O₅/PEO gel electrolyte system were investigated during electrochemical cycling. New insights obtained from this work have led to specific approaches for improving the electrolde-electrolyte interfacial robustness of PEO electrolyte/V₂O₅ system in solid state lithium batteries.
¹ School of Engineering, Brown University, Providence, RI 02912, USA.
² Medtronic Energy and Components Center, 6800 Shingle Creek Parkway, Brooklyn Center, MN 55430, USA.
^a [email protected], ^b [email protected], ^c [email protected], ^d [email protected], ^e [email protected], ^f [email protected] ^g [email protected].
* Corresponding author, B.W. Sheldon.

Improving Li transport and preventing electron leakage through the solid electrolyte interphase (SEI) are critical to Li-ion batteries capacity drop and power loss. Identification of the dominant diffusion carriers and their diffusion pathways in main components of SEI is a necessary step to understand the functionality of SEI before tailoring its properties. Therefore, dominant Li diffusion carriers and the ionic conductivity in perfect SEI components (such as Li₂CO₃ and LiF) were predicted over a broad voltage range of the electrode materials that the SEI component covers with density functional theory (DFT). It was predicted that the main diffusion carriers in Li₂CO₃ on anode are excess Li ion interstitials (Li_i⁺), however, above 3.98V, Li ion vacancies (V_Li^-) become the dominant diffusion carrier type. In contrast, the main diffusion carriers in LiF was predicted to be Schottky pairs (V_Li^- and V_F⁺), agreeing with experimental observations. While the V_Li^- diffuses through direct hopping, the Li_i⁺ diffuses by knocking off the Li⁺ ion from a lattice. Meso-scale Li⁺ ion diffusion equations were then formulated based on the diffusion mechanisms discovered by DFT and the boundary conditions of isotope exchange experiments in order to make direct comparison with TOF-SIMS measurements. Furthermore, by studying the point defect formation and diffusion, it is proposed that electron can be localized in a defect and transport via defect hopping or knocking off, such as Li_i⁰ interstitial, when the SEI is thicker than electron tunneling length. Ab initio molecular dynamics of SEI/electrolyte interface simulations further demonstrated that when a Li_i⁰ interstitial transports into the electrolyte, ethylene carbonate (EC) reduction is observed immediately. This is a possible mechanism to explain electron leakage through thick SEI films into the electrolyte.

Lithium-ion batteries (LIBs) are nowadays the predominant battery technology for portable electronics and are of growing importance in the area of electrical mobility. However, the limited abundance and uneven global distribution of lithium salts are raising concerns regarding future price development and supply security. In this regard, Sodium-ion batteries (SIBs) are recently gaining increasing attention as more economical alternative, due to the ubiquitous nature of sodium salts. In particular, for applications, where cost is more important than energy density, such as large-scale energy storage, SIBs might emerge as battery technology of choice.
However, especially due to the ~50% larger ionic radius of the Na-ion the electrochemistry of SIBs and LIBs is generally very different. Well studied materials for LIBs such as graphite or silicon perform only very poorly or not at all as anode material in SIBs, exemplifying that the development of new materials is essential in this field.
Tin and antimony are considered promising candidates as anode materials for both SIBs and LIBs based on their high specific capacities. However, these materials undergo upon charging and discharging drastic volume changes leading to rapid capacity fading after only a few cycles. In this regard, nanocrystals (NCs) are very advantageous electrode materials, since they can improve the cycling stability vastly by mitigating the impact of volume changes. Moreover, as a result of the reduced dimensions and higher surface area, nanocrystals offer faster kinetics compared to their bulk counterparts.
In this study we employed for the first time monodisperse NCs of Sn, Sb and SnSb as anode material studying the size-dependency of the electrochemical performance for SIBs and LIBs [1-3]. For both Na- and Li-ion storage NCs showed superior performance compared to bulk materials achieving enhanced cycling stability and rate capability. Most notably, Sb NCs show capacity retention of up to 80-85% even at 20C, which is comparable to the best Li-intercalation anodes and is unprecedented for Na-ion storage.
References
1) K. Kravchyk et al., JACS, 2013, 135, 4199.
2) M. He et al., Nano Letters, 2014, 14, 1255-1262.
3) M. He et al., submitted.

New positive and negative electrode materials store energy densely are in demand for high energy lithium-ion batteries enabling portable electronic devices, hybrid electric vehicles, and large scale energy storage. Silicon insertion anodes have received great attention, as the fully lithiated (ca. Li₂₂Si₅) alloy has the highest theoretical capacity of any known material at 4140 mAh g^minus;1. However, Si-based electrode has yet to find use in commercial application as typically suffering from poor capacity retention associated with huge volume swings (up to 300%) during lithium ion insertion and extraction, which leads to cracking and crumbling of active particles. Although reducing size of Si particle to nanoscale is known to help releasing mechanical stress and prevent the fracture of Si during Li insertion, handling difficulty, low coulombic efficiency and high production cost are still challenges. Hence cheaper process of Si anode is highly desired. This study presents a novel cost-saving Si material tackling poor capacity retention and high irreversible capacity which are typical and critical challenges most of Si anodes facing. We have tried to circumvent the limitations of typical top-down crushing nanoparticle production and paid attention to a bottom-up assembly using silane-based gas phase reactor. This method provides a chemical route for Si production offering excellent heat and mass transfer and operates at a lower temperature. Interestingly, in a practical granular poly-Si production, a certain amount of Si particles are derived homogeneously and have amorphous phase, called ASP (amorphous silicon particle). We employed it to prove the practical feasibility since the production cost is estimated to be many times lower than nano-sized Si from top-down crushing process as the mass production is already mature. After a short-time processing of particle disintegration using Air Flow Jet milling, ASP combines tailored properties as follows: 1) a highly porous structure offers buffer space accommodating volume swings by charge-discharge, 2) amorphous phase allows for homogeneous volume expansion provides reduced volumetric strains and 3) small oxygen content which adversely affects initial coulombic efficiency by consuming Li ion irreversibly. The electrochemical performance is proven to be outstanding compared to top-down crushed nano-size Si particle. ASP clearly shows superior initial coulombic efficiency (C.E) at various binder materials. The results are novel as 93% of 1st C.E is seldom reported in literature. The cycling performance is also excellent ASP shows stable cycling for 300 cycles. Materials characterization is performed through several different analytical methods including TEM, in-situ solid state lithiation, in-situ dilatometer to support the high electrochemical performance theoretically.

LiCoO₂ is the most widely utilized cathode material in the Li-ion battery industry due to its high energy density and good cycling performances. Although the capacity of LiCoO₂ has been improved, the limit in terms of the energy density still needs to be overcome to meet the demands for large-scale mobile devices and minimizing the portable electronics. It has been demonstrated that the cycling performances can be improved by doping of divalent and tetravalent ions such as Mg and Ti. In addition, the surface coating of metal oxides, TiO₂ and ZrO₂, improves the battery properties up to 4.4V (vs. Li). However, the use of 4.4V LiCoO₂ is still not enough to meet the requirement of high energy density applications.
In this study, we developed novel LiCoO₂ which can deliver 200 mAh/g within 3.0~4.55V (vs. Li) with excellent capacity retention by multi-elements doping and surface coating. The position of each dopant in the particles was identified by nano-SIMS technique. The structural stability was investigated using ex situ synchrotron XRD and XAS measurements.
XRD identified that a small amount of Li₃VO₄ and Co₃O₄ are present as separated phases. Due to deficient Li source which was used to form Li₃VO₄, unreacted Co₃O₄ is remained. The specific capacity of pristine and Mg/Mn/V doped compounds at the 1st discharge was 191 mAh/g and 198 mAh/g, respectively. It is obvious that the cycling performances were considerably enhanced by Mg/Mn/V doping. The capacity retention after 50 cycles were 84% in pristine and 95% in Mg/Mn/V doped LiCoO₂. The dQ/dV profiles indicate that the phase transformation of O3 to H1-3 was shifted to higher voltage in the LiCoO₂ with doping.
To confirm the structural stability, ex situ synchrotron XRD experiment was carried out. Pristine LiCoO₂ exhibited clear phase transformation to H1-3 and O1 at fully charged state. O3 phase, initial structure, became minor phase and H1-3 and O1 phases were grown considerably. In contrast, the phase transformation was suppressed in Mg/Mn/V doped LiCoO₂ showing small amount of H1-3 phase after 4.55V charge. We also analyzed the pre-edge of Co K-edge by XAS. The intensity of pre-edge was lower in Mg/Mn/V doped LiCoO₂ than pristine one at fully charged state indicating that local structural distortion is decreased in multi-elements doped compound. We believe that Mg/Mn doped into LiCoO₂ could improve the structural stability in the bulk resulting in decreased phase transformation at high voltage region. The surface of LiCoO₂ is possibly protected by Li₃VO₄ and Co₃O₄ phases.

Owing to a high volumetric capacity (3833 mAh cm^-3 vs. 2046 mAh cm^-3 for Li), absence of dendrites formation and lower cost of Mg metal (about 10 times cheaper than Li), rechargeable magnesium batteries have been receiving an increased attention. One major challenge facing these batteries is related to the electrolytes as they are restricted to a handful of corrosive, halogen-based magnesium reagents and complexes. Electrolytes based on conventional inorganic and ionic Mg salts were found unsuitable due to reductive electrochemical instability in the reducing environment of the Mg anode, which results in complete Mg passivation^[1]. To overcome these challenges, a new bottom up design strategy based on discovering Mg compatible electrolytes beyond state of the art is needed. Recently, motivated by the thermal stability and a presumed robustness of the BH₄^- anion against electrochemical reduction, we proposed magnesium borohydride as an electrolyte for rechargeable magnesium batteries^[2]. Owing to a high reductive stability, we discovered that magnesium borohydride could withstand this highly reducing environment making it the first and so far the only example of an inorganic, relatively ionic and halide free salt reported to date that could function as an electrolyte in Mg battery. This breakthrough has been the basis for creating a new family of highly performing electrolytes with wide electrochemical window which are far less corrosive that other existing electrolytes^[3]. Here, we will explain our bottom up design strategies, discuss fundamental properties obtained from systematic spectroscopic and electrochemical studies and share up-to-date results related to these new promising systems.
References
[1] H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy Environ. Sci. 2013, 6, 2265-2279.
[2] R. Mohtadi, M. Matsui, T. S. Arthur, S.-J. Hwang, Angew. Chem. Int. Ed. 2012, 51, 9780 -9783.
[3] T. J. Carter, R. Mohtadi, T. S. Arthur, F. Mizuno, R. Zhang, S. Shirai, J.W. Kampf, Angew. Chem. Int. Ed. 2014, doi: 10.1002/anie.201310317.

Interest in Li-ion batteries using lithium titanate (LTO) anode has increased in recent years due to LTO&’s characteristic power capability, long life, and safety. In particular, LTO has the potential to provide superior performance in applications such as advanced 12 V microhybrid battery systems that require hundreds of thousands of high power discharge pulses for starting a vehicle, dynamic charge acceptance for battery recharge, cold cranking at -30#8304;C, and sustaining hospitality loads. Developing any battery chemistry to meet all of these requirements over a wide temperature range is a challenge, especially when the battery is integrated in sustained high temperature environments such as an under-hood location where temperature can approach 75°C. This type of high temperature exposure for Li-ion cells can lead to power loss, gas generation, and decreased life.
LTO related high temperature performance degradation mechanisms have been the subject of study in the electrochemical literature and typically focus on the interfacial chemical reactivity of the LTO surface with electrolyte. One proposed mechanism includes catalytic electrolyte degradation involving the Ti³⁺-O sites leading to gassing and solid degradation products, while another proposes direct reduction of electrolyte at the LTO/electrolyte interface resulting in growth of thin surface films, LTO surface delithiation and LTO phase transformation. The presence of water and other impurities is believed to accelerate the above two mechanisms. Strategies to decrease this interfacial electrolyte activity typically include establishing a thin passivating, ionically conducting interface that reduces reactivity with the electrolyte. This can be accomplished through different methods including surface treatment of LTO powder, addition of functional additives to the electrolyte, and optimization of formation procedures. This presentation will review LTO high temperature performance degradation mechanisms and effective strategies to extend LTO&’s temperature range.

Abstract
The high inactive materials content (e. g., separators, current collectors, conductive additives, binder and packaging) of current nonaqueous battery designs contributes directly to high battery cost and reduces specific energy and energy density. Area specific capacity, which is perhaps the most objective measure of design performance, cannot be increased arbitrarily by increasing electrode thickness and/or density, due to kinetic limitations. In the limit of high density and large thickness, salt depletion within the electrolyte-filled porosity typically becomes rate-limiting. Thus, higher usable energy at practical C-rates can be achieved from thick, dense electrodes if the topology of the pore structure is tailored to lower tortuosity.
Here we report on the fabrication and electrochemical testing of thick, dense, low tortuosity electrodes by the freeze-casting of aqueous suspensions followed by sintering. This shaping technique allows design of oriented and interconnected structures that have a low tortuosity and high ionic transport. The electrochemical performance of the fabricated electrodes in half cells will be reported. We also report on the characterization of electronic and ionic conductivity in several candidate cathodes as a function of temperature and lithium content. These measurements were performed on additive-free sintered dense LiNi_0.8Co_0.15Al_0.05 (NCA) and Fe-doped and undoped LiMn_1.5Ni_0.5O_4-δ (LMNO and Fe-LMNO) plates using ion blocking and electron blocking cell configurations.
Acknowledgement
This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract No. 6920899 under the Batteries for Advanced Transportation Technologies (BATT) Program.

Assembling nanoparticles of active material into micron-sized spheres provides a means to combine the manufacturing and energy density benefits of micron-sized particles with the electrochemical properties of the constituent nanoparticles. We first perform electrochemical simulations on single, micron-sized particles with computer-generated multi-scale pore structure to develop design guidelines for the optimal internal structuring of the micron-sized active particles for specific applications (e.g. power or energy cells). We then demonstrate spray drying [1,2] as a method to assemble preformed nanoparticles into microspheres with controlled size, porosity, and hierarchical structure. Spray-drying is a simple, high-throughput, and scalable technique that involves drying of viscous slurry droplets in a hot air stream. It is generalizable to all material systems in which nanoparticles are assembled into microspheres.
In this work, we present experimental and computational results on lithium titanate (LTO). All slurries for the spray-drying process contain commercial LTO nanoparticles 40 nm in diameter. We can tune the porosity of the resulting LTO microspheres by varying the concentration of cellulose binder in the slurry and removing it during calcination of the micron-sized particles formed during the spray-drying process. To achieve microspheres with multi-scale porosities, we can add latex nanobeads ranging in diameter from 300 nm - 1 mu;m as templates into the slurry. Again, these templates are removed during calcination of the microspheres. The internal porosity of the different microspheres is measured with BET and the hierarchical structure is quantified by FIB-SEM tomography. The electrochemical performance as a function of C-rate is compared for microspheres of the same average particle size but with different internal porosities and structures. The experimental findings are compared against simulation.
This work highlights that it is possible to rationally design and then fabricate multi-scale structured materials for energy storage applications with industrially relevant techniques. Using spray-drying, the same starting nanoparticles along with low-cost, removable additives and templates can be used to tailor the internal structure of micron-sized materials the thereby control their electrochemical properties.
[1] K. Okuyama et al, “Preparation of nanoparticles via spray route”, Chem. Eng. Sc. 58, 537-547 (2003)
[2] G. Majano et al., “Assembly of a hierarchical zeolite-silica composite by spray drying”, Cryst. Eng. Comm. 18, 5985-5991 (2012)

In order to provide our daily lives with sufficient power and to fuel our transportation without compromising the environment, we must pursue new ideas to improve the current battery technology.The most commonly used electrode materials in battery are inorganic compounds prepared from limited mineralss. Lignin is composed of hydroxyphenol propane, and is a by-product generated in papermaking and biofuel fabrication. The quinone group in lignin can be used for electron and proton storage during redox processes. Redox-active abundant biomasses like lignin are promising as electrode-active materials for clean and low cost batteries. Biomass supplies an abundant and low-cost carbon source, which is a key material for energy storage. In this talk, we obtained conductive paper from a carbonization of biomass, and used the obtained paper as a conductive 3D scaffold for the lignin electrode. Rooted from the natural wood, we modified the different ingredients and integrated them into a sustainable, safe, and low cost energy storage device.
Natural wood fibers absorb ions and water as part of their growing process. The wood fibers are intrinsically porous and soft. Thin film Sn anodes deposited onto wood fibers sustain more than 400 charging/discharging cycles, a new record for Sn anodes in Na-ion batteries. Control experiments and chemomechanical modeling reveal that the wood fiber wrinkles to release the mechanical stress from sodiation/desodiation. Additionally, dual ion transport pathways within the mesoporous structure of wood cellulose fibers significantly improve the traditionally slow ion transport in Na-ion batteries.
In a summary, natural biomaterials were explored as new building blocks for energy storage. These studies could potentially introduce a new path for efficient energy storage based on sustainable wood-based materials.
Ref:
Zhu, H., ^sect; Jia, Z., ^sect; Chen, Y., Weadock, N., Wan, J., Vaaland, O., Han, X., Li, T., Hu, L. *. Tin Anode for Sodium-Ion Batteries Using Natural Wood Fiber as a Mechanical Buffer and Electrolyte Reservoir. Nano Letters, 2013(7): 3093-3100. (Reported in NPR news, Science Daily, Nanowerk et al. Most read paper in Nano Letters.)
Media coverage: NPR news, Frobes, msnbc News, CBS News, Discovery News, CNET News, Daily Mail, The Hindu, International Business Times, Science Daily, Science 2.0, etc.
2 Gui, Z., ^sect; Zhu, H., ^sect; Gillette, E., Han, X., Rubloff, G., Hu, L. *, Lee, S. *. Natural Cellulose Fiber as Substrate for Supercapacitor. ACS Nano, 2013, 7 (7): 6037-6046.
3 Chen, X., ^sect; Zhu, H., ^sect; Liu, C., Chen, Y., Weadock, N., Rubloff, G., Hu, L.*. Role of Mesoporosity in Cellulose Fiber for Paper-Based Fast Li-ion Batteries. Journal of Materials Chemistry A, 2013, 1, 8201-8208. (Featured in EFRC Newsletter)

Great interest exists in developing electrochemical energy storage that surpasses the current energy density and specific energy limits of Li Ion Battery technology. Success demands a transition to higher capacity electrodes, for which metal anodes will be required to achieve significant gains. The multivalent alkaline earth metals are attractive anodes from the perspective of energy density when combined with a high voltage cathode and a stable, functional electrolyte. High Coulombic efficiency is difficult to achieve with Mg, typically with a chloro-Mg complex in an ether solvent, and unreported for Ca. Chloride electrolytes are not suitable for envisioned high voltage oxide-based insertion cathodes. Additionally, an optimized Mg cell will require near unit Coulombic efficiency for Mg cycling onto itself over a wide range of deposition and stripping rates to suit the storage application.
Our goal is to understand how the Mg cation source and the solvent contribute to high Coulombic efficiency, morphologically controlled deposition and stripping. Electrochemical AFM/STM is employed to explore how Mg layer growth onto and dissolution from Mg occurs using inorganic sources of chloro-Mg complexes or weakly associated Mg salts in aprotic solvents. Chloro-Mg complexes result in highly textured Mg films that grow and dissolute by classical diffusive metal atom flux to and from step edges. Disruption of the growth or dissolution process with periods of electrolyte equilibration (static state of a battery anode) results in surface film formation. This film impedes both arriving and departing metal flux to the point that deposition and dissolution are re-initiated as localized processes, leading to the evolution of complex morphologies with cycling. The consequence of surface film induced defect structure on morphological evolution is tracked using electrochemical TEM providing information of growth dynamics. The net result is that electrochemical access to the metal itself can become compromised and lead to capacity loss for an initially optimized cell. Simple Mg salts capable of Mg deposition exhibit more complex behavior and provide insight on the differences between protective chloride versus alternate anions. Select alternate anion combinations are employed to explore structure-activity relationships over the range of minimally impeded to blocking layer formation, where ionic conductivity is eliminated in the latter case. We hypothesize that understanding how such films form and function will help establish the design rules necessary to create stable and active alkaline earth metal anodes.
This work is 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 multi-program 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.

Operation of rechargeable lithium ion batteries critically relies on repeated out/in migration of lithium ion in the lattice of the electrodes. It is often assumed, and for the most case it is indeed true, that other ions in the lattice appear to be immobile. However, in a long run, the lattice is subjected to gradual irreversible evolutions, which eventually lead to the failure of the structure. For layered lithium and manganese rich cathode materials, even though high capacity can be obtained, the continuous capacity and voltage fading upon cycling impedes its commercial applications. The layered to spinel-like phase transformation that occurred during cycling is believed to be one of the main reasons that contributes to the electrochemical degradation. However, it is far from clear how does this phase transformation happen. In this work, pristine and cycled Li_1.2Ni_0.2Mn_0.6O₂ (LNMO) cathode materials were studied in detail using aberration corrected scanning/transmission electron microscopy. We discovered that upon cyclic charge-discharge, the phase transformation initiates spatially from the surface of the particle and propagates into the bulk, featuring a transition sequence of C2/m → R-3m → spinel-like. Depending on the filling occupancy of the octahedral site by the transition metal cations in the Li-slabs, two spinel-like structures in the cycled samples were identified. Moreover, based on STEM-EELS analysis, we found that Ni concentration in the cycled sample is significantly reduced as compared with that in the pristine samples, demonstrating for the first time that accompanying the Li ion transport is the concurrent migration of Ni, which is corroborated by the observation of Ni-rich surface layer in the cycled samples. The present observation highlights Ni&’s role in structural transformation and cell degradation upon cycling. It also provides insight for designing of stable structure through tailoring of chemical composition.

Development of high energy density capacitors with fast discharge rates is essential to reduce the size, weight and cost of devices in future applications like hybrid vehicles and directed energy. Fundamentally, the dielectric material limits capacitor performance, with the energy density governed by the product of dielectric permittivity ε and breakdown strength V_bd. Polymer films are widely used as the dielectric medium in capacitors due to good processability, good breakdown strength, low loss and fast discharge speeds. Further improvements in capacitor energy density are greatly reliant on improving either ε or V_bd, or finding improvements through a combination of both properties. Experimental and simulation studies have shown that the presence of a barrier can significantly enhance the breakdown strength in polymers by hindering the electrical tree propagation. To exploit this effect, we use the directed self-assembly of block copolymers in thin films to form highly ordered nanostructures with sharp interfaces that create a highly tortuous path for electrical treeing, thus improving the breakdown strength. We observe a significant increase in the V_bd of an ordered block copolymer as compared to a non-ordered one. However, these polymers suffer from very low permittivities. Composite dielectrics offer a unique opportunity to combine high-permittivity nano-fillers with polymer matrices to improve the overall permittivity. To that effect, our highly ordered nanostructured block copolymers (BCP) also act as ideal templates to selectively sequester and organize high permittivity nano-fillers within polymer matrices. The results on impact of block copolymer morphology, orientation, molecular weight, nano-filler functionalization, loading level on the dielectric properties and overall energy density of the composite will be presented.

This study reports the electrical and mechanical behaviors of carbon nanofiber suspensions as a conductive component in semi-solid electrodes for redox flow batteries. Commonly, the suspensions show gel-like behavior implying the percolated network of nanofibers. The dependency of rheological plateau modulus on the nanofibers concentration surprisingly shows two percolating thresholds. Qualitatively, this trend is in accordance with the electronic conductivity which exhibits leveling off over 1-3 wt% nanofibers. This unusual double percolation may attribute to the network of fibers which turn into aggregates at higher concentration.
Under shear flow, the suspensions commonly exhibit three-regime flow curve: shear-thinning at low and high shear rates separated by a small plateau region over intermediate rates. The carbon nanofibers suspensions do not significantly lose their electronic conductivities under flow until a critical shear rate beyond which the conductivity increases. The fiber alignments under flow may explain such behavior. However, the saturated suspensions (at 7 wt%), in contrast, loses their conductivity as a result of possible breaking up of the aggregates. Eventually, an optimum concentration and suitable shear rate regime could be identified and compared to those of aggregated carbon black suspensions as an excellent electronically conductive medium for anolytes/catholytes of redox flow batteries.
The rheo-electrical behavior of an anolyte made up of lithium titanium oxide (Li₄Ti₅O₁₂)/carbon materials suspended in organic medium (1 M lithium bis(trifluoromethane)sulfonaimide; LiTFSI in propylene carbonate) was studied. Traces of carbon fibers mixed with conventional carbon black enabled: i) increasing the solid load of electrochemical active material (Li₄Ti₅O₁₂) without effect on the electronic conductivity of the anolyte, and ii) resisting the breaking up of the conductive pathway of carbon network via wiring by carbon nanofibers. These findings led to formulation of a promising anolyte for lithium redox flow battery application.

There has been an increasing demand for high-performance rechargeable lithium-ion batteries (LIBs) for electronic devices such as electric vehicles and hybrid electric vehicles. Considerable attentions have been paid to titanium dioxide (TiO₂) as anode materials because of its low cost, environmental friendliness, structural stability, and a high working potential of over 1.5 V versus Li⁺/Li. Although TiO₂ has substantial advantages, there are many challenges associated with its commercialization such as low theoretical capacity and poor electron transport. In this paper, a novel porous TiO₂ nanofibers in which Sn nanoparticles was encapsulated have been prepared by facile electrospinning and subsequent heat treatment. In situ TEM was used to study the charging/discharging processes of Sn-TiO₂ nanofiber. It was found that the porous TiO₂ can accommodate volumetric change of Sn nanoparticles and the morphology of Sn can also be changed after the delithiation process compared with the original one. As an anode, this material shows high capacity, long cycle life, and good rate capability. The exceptional electrochemical performance of the prepared materials can be ascribed to the novel structure in which the one-dimensional (1D) TiO₂ nanofiber can facilitate the lithium transport, the nano-scaled structure can reduce the diffusion length of Li ions, therefore, achieving a rapid charge-transfer reaction, pores in TiO₂ can buffer the volume expansion of Sn nanoparticles during charging/discharging processes, and TiO₂ nanofibers serve as a mechanical framework to further remain structure integrity.
Acknowledgements
The authors are grateful for the support received from the Research Grants Council of the Hong Kong Special Administration Region (grants: PolyU 5349/10E and PolyU 5312/12E) and the Hong Kong Polytechnic University (grants: G-YK47 and 1-BD08).

Because of the increasing demand of high energy electric devices, tons of lithium ion batteries are being produced all over the world, which indicating that lithium ion battery trash amount is growing rapidly year by year. From either environment protection or economic benefits point of view, recovering valuable materials from lithium ion batteries is highly desirable. In this work, a low cost, high efficiency process for recovering the metal values in spent lithium ion batteries is being developed. By undergoing a series of steps such as discharging the remaining capacities, mechanical treatment, acid leaching, as well as inorganic reactions, the Fe, Co, Ni, Mn, Cu Al metal values of 18650 lithium ion batteries collected from recycle bin will be recovered at a high recovery efficiency. Then Co, Ni and Mn are separated and recovered in the formation of metal hydroxides via a co-precipitation process involving NaOH and ammonia water, the spherical and dense Ni_1/3Mn_1/3Co_1/3(OH)₂ precursor particles will be synthesized. LiNi_1/3Mn_1/3Co_1/3O₂ cathode material is obtained by mixing precursor and Li₂CO₃ with 10 atom% excess of Li, followed by sintering at 450#8451; for 5h and 900#8451; for 12h. Electrochemical properties of C/10, C/5, C/3, C/2, C, 2C rate capacity and 0.5C cycle life were tested and will be discussed in details.

Solid particle pastes are widely used as electrochemical electrodes, but their dielectric and electrical conduction properties are seldom reported. This is because electrochemical characterization is conventionally conducted in the electrochemical cell level. Since the contributions to the cell behavior by the cell components are not decoupled, the properties of an electrode in the cell cannot be determined. Without knowing the electrode properties, electrode design cannot be rigorous. By using material-level rather than cell-level testing, this work has measured the properties of an electrode and has furthermore decoupled the contributions of the components of an electrode, thereby determining the relative dielectric constant and electrical resistivity of each component of an electrode. This work addresses electrodes in the form of electrolyte-based pastes containing a mixture of microscale manganese dioxide (MnO₂) particles (a common cathode material) and nanoscale carbon black (CB) particles (a common electrically conductive additive that is needed due to the non-conductivity of MnO₂). A 15 vol.% sulfuric acid aqueous solution is used as the electrolyte, which is the liquid component of the paste, since the electrolyte commonly penetrates a porous electrode. The dielectric constant (100.9) and electrical resistivity (5.7 Omega;.cm) of the electrolyte are determined in the absence of solid components. The relative dielectric constant (68) and resistivity (1960 #8486;.cm) of MnO₂ in the presence of the electrolyte are determined in the absence of CB and are assumed to be unaffected by the presence of CB. When the mass ratio of CB to MnO₂ is increased from 0 to 10%, the resistivity of the paste decreases from 600 to 40 Omega;.cm. The dielectric and conduction properties of the paste with MnO₂ and CB are obtained by using an equivalent circuit model in which the MnO₂ is in parallel with the series combination of CB and the electrolyte. It is thus found that, at a CB/MnO₂ mass ratio of 10%, the relative dielectric constants of the paste, MnO₂ and CB are 93, 68 and 64 respectively and the resistivities of the paste, MnO₂ and CB are 37, 1960 and 470 Omega;.cm respectively. The CB resistivity (470 Omega;.cm) is much higher than that in the absence of MnO₂ (11 Omega;.cm), due to the MnO₂ reducing the electrical connectivity of the CB in some directions. The CB dielectric constant (64) is higher than that in the absence of MnO₂ (31). Testing a dry MnO₂ compact without CB shows that the relative dielectric constant of MnO₂ is 62 (lower than the value of 68 when the MnO₂ is with the electrolyte) and the resistivity of MnO₂ is 14,000 #8486;.cm (much higher than the value of 1960 Omega;.cm when the MnO₂ is with the electrolyte). This means that the electrolyte increases the relative dielectric constant and greatly decreases the resistivity of MnO₂, due to the MnO₂ electrical connectivity promoted by the presence of the electrolyte.

Electrochemical efficiency of the cathode material is a key factor for developing lithium-ion battery technology for the next generation applications such as electric vehicles and electrical grids. Yet, the present technology has limitations in electrochemical performance, storage efficiency, safety and cost; which are current global research challenges [1, 2]. One of the potential ways to address such issues is by optimizing the constituents&’ proportion and developing nanostructured design of cathodes such as one-dimensional (1D) nanostructures by simple and scale-up electrospinning process [3]. Consequently in the present study, Li-rich, Co-free Li_1+x(Ni_1/3Mn_1/3Fe_1/3)O₂ electrospun nanofibers are fabricated with superior electrochemical performance (initial capacity ~126 mAh g^-1) with better cyclic stability (~92 % capacity retention after 100 cycles at 0.1 C) when compared to that of nanoparticles. On the other hand, owing to the interesting electrochemical performance with excellent structural stability of aforementioned material, in-situ neutron diffraction studies are performed to understand the phase evolution of the material in functional full-cell battery. This work revealed Li-intercalation/de-intercalation of the cathode to occur via a solid-solution reaction where the lattice response follows Vegard&’s law, differing to that observed for iso-structural commercial cathodes.
References
[1] J. -M. Tarascon and M. Armand, Nature, 2001, 414, 359-367.
[2] A. Manthiram, J. Phys. Chem. Lett., 2011, 2 (3), 176-184.
[3] S. Kalluri, K. H. Seng, Z. Guo, H. K. Liu and S. X. Dou, RSC Adv., 2013,3, 25576-25601.

Sodium-ion batteries are one of the best alternatives to lithium-ion batteries, because of similar electrochemistry, elemental rich, non-toxic nature, and most importantly, the low-cost of sodium [1]. Nevertheless, structurally and electrochemically stable cathode materials are still in need for the commercial dominance of the sodium-ion batteries. Global research focussed on various materials from polyanions to layered metal oxides. Layered metal oxides are prominent for their feasibility and high capacity values. Likely, P2-type Na_xFeO₂ is considered to be better option in terms of low-cost and eco-friendliness. Due to the stabilization issues of Fe⁴⁺ in the oxide-ion frameworks, ‘Mn&’ was partially doped for ‘Fe&’ to give P2-type Na_2/3(Fe_1/2Mn_1/2)O₂. Not only the doping aspects but also nanostructured design of the cathode materials plays a key role in enhanced electrochemical properties. One-dimensional nanostructures could have better effective contact areas with the electrolyte and offer improved electrochemistry and cycle life [2]. Accordingly, the present study [3] reports the first example of the preparation of Na_2/3(Fe_1/2Mn_1/2)O₂ hierarchical nanofibers by feasible and low-cost electrospinning technique. The nanofibers with aggregated nanocrystallites along the fiber direction have been characterized structurally and electrochemically; resulted in enhanced cyclability with initial discharge capacity of ~195 mAh g^-1, when compared to nanoparticles. This is attributed to the well-interconnections among the fibers with well-guided charge transfers and better electrolyte contacts. Inspired by these interesting features, in-situ synchrotron diffraction studies are performed in operational battery and suggests that sodiation/desodiation proceeds through a single-phase (solid-solution) reaction involving a minor (0.27%) volume change.
References
[1] M. D. Slater, D. Kim, E. Lee and C. S. Johnson, Adv. Funct. Mater, 2013, 23, 947-958.
[2] S. Kalluri, K. H. Seng, Z. Guo, H. K. Liu and S. X. Dou, RSC Adv., 2013,3, 25576-25601.
[3] S. Kalluri, K. H. Seng, W.K. Pang, Z. Guo, Z. Chen, H. K. Liu and S. X. Dou, ACS Appl. Mater. Interfaces, 2014, Article ASAP, DOI: 10.1021/am502343s.

Magnetite (Fe₃O₄) is a very promising candidate as an anode material in rechargeable lithium ion battery (LIBs) because of its ability to store up to eight Li per formula unit via reversible reactions, resulting in a high theoretical capacity of 924 mAh g^-1. Moreover, advantages such as low cost, ease of synthesis and environmental friendliness make it a promising candidate for large scale commercial applications for LIBs. However, Fe₃O₄ suffers from poor conductivity, large volume change and voltage hysteresis during the electrochemical reaction, which strongly limits its practical application. For the fact that carbon in its own feature exhibits several interesting properties, including electronic conductivity, high surface area, tunable porous structure, etc., the combination of Fe₃O₄ nanostructures and different forms of carbon materials show promising potential in the preparation of composite anode materials.
In this work, a high pressure and temperature based solvothermal route was developed for the synthesis of Fe₃O₄ with carbon as a composite anode for LIBs. The carbon in products was a result of the in situ carbonization of organic components under high pressure (24.0 MPa) and temperature (350 °C). Composites with different amounts of carbon were prepared by annealing the solvothermal products at different temperature. Taking advantage of the high theoretical capacity of Fe₃O₄ and favorable characteristics of carbon, a capacity of about 610 mAh g^-1 after 100 cycles was achieved for the composite with 54.6% carbon. The carbon amount depended electrochemical performance was also investigated. The Fe₃O₄@C composite can be used as an alternative anode material and the introduced synthetic strategy may provide further insights into the preparation of inorganic oxides coupled with carbon via in situ carbonization of organic components.

Despite the imminent commercial introduction of Li-ion batteries in electric drive vehicles and their proposed use as enablers of smart grids based on renewable energy technologies, an intensive quest for new electrode materials that bring about improvements in energy density, cycle life, cost, and safety is still underway. Besides, to understand the intrinsic reason of capacity fading, single nanowire device was designed for diagnosis of nanowire electrode. In this device, electrical transport of the single nanowire was recorded in situ to detect the evolution of the nanowire. Our results show that conductivity of the nanowire electrode decreased reversibly or irreversibly during the electrochemical reaction, limiting the cycle life.
We synthesized nano#64258;akes-assembled three-dimensional hollow porous V₂O₅. The resulting HP-V₂O₅ microspheres deliver promising Li-storage property with high speci#64257;c capacity, stable cyclability, and good rate performance. Employed as the cathode they attain a speci#64257;c capacity of 173 mAhg^minus;1 at 2 Ag^minus;1. More speci#64257;cally, the porous shell of the structure seems to facilitate the electrolyte penetration and increase the contact area between the HP-V₂O₅ electrode material and the electrolyte. Moreover, the hollow-porous structure might also be an advantage to accommodate the volume variation during the Li ions intercalation and deintercalation. Finally, the nanosized building blocks reduce the distance for Li ions diffusion and electron transport.
To increase the active sites, improve the stability and prevent the agglomeration of electrodes materials, 3D porous V₂O₅ hierarchical microplates have been fabricated by a one-step top-down strategy, and display excellent rate capability and stable capacity of 110 mAhg^-1 at 2000 mAg^-1 after 100 cycles. The porous structure would facilitate the electrolyte penetration and increase the contact area between the electrode and the electrolyte. Moreover, the nanosized building blocks reduce the distance for Li⁺ ions di#64256;usion and the electron transport.
Besides, to enhance stability of nanowire electrodes, VO₂ hollow microspheres showing empty spherical core with radially protruding nanowires, were synthesized through a facile and controllable ion-modulating approach. At high current density of 2 A/g, VO₂ hollow microspheres exhibit 3 times higher capacity than that of random nanowires. VO₂ hollow microspheres exhibit high surface area about twice higher than that of random nanowires and also provide an efficient self-expansion and self-shrinkage buffering during lithiation/delithiation, which effectively inhibits the self-aggregation of nanowires, thus representing a unique architecture for excellent lithium ion storage capacity and cycling performance.

The rapid progress in the field of flexible and portable electronics has triggered the development of cheap, lightweight, solid-state energy storage devices. Conducting polymers have become attractive candidate materials for supercapacitors due to their many striking attributes such as ease of solution-based processing, low cost, electrochemical stability, reversibility between redox states through doping/dedoping processes, and electrical conductivity. The performance of poly(3,4-ethylenedioxythiophene), PEDOT /paper based solid-state supercapacitors is optimized employing conducting poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) as a nucleation layer. These PEDOT/paper supercapacitors exhibited an areal capacitance of 242 mF/cm² and an energy density of 14.5 mWh/cm³ at a power density of 350 mW/cm³, the highest value so far achieved when compared to other PEDOT supercapacitors. The solid-state PEDOT device showed an energy density of 1.5 mWh/cm³ (normalised to the volume of whole cell including both the electrodes and the electrolyte), that is higher than the best reported ppy/paper (E = 1 mWh/cm³) and Pani/pencil/paper (E = 0.32 mWh/cm³) solid-state devices. Further, flexible microsupercapacitors of PEDOT are fabricated on a plastic substrate employing the top-down photolithography and bottom-up electrochemical polymerisation techniques. The cycling performance showed that capacitance retained up to 80% after 10000 cycles.

We increased the energy density and thermal stability of cathode materials by maximizing the pellet density using the bimodal distributed particles and removing the residual undesired small particles to minimize the electrolyte side-reaction. The mechanism of the implementation was investigated using the void fraction model, the particle size distribution control and surface area analysis. For the purpose of bimodal system, we specially designed the co-precipitation process using batch-type reactor and control the size and distribution of cathode material precursors. Also, the cathode surface reaction with electrolyte was analyzed to reveal the mechanism of improvement of thermal stability. The energy density of the large full cell of bimodal system was compared with mono-dispersed or commercial cathode materials with respect to low temperature power & resistance, cycle life, calendar life, and other cell performance. The thermal stability of the full cell was analyzed by ARC (Adiabatic Rate Calorimeter) and other safety test was conducted. Our main purpose in this research is to enhance the energy density of cathode materials without change the physical and chemical properties. As a result, the energy density of bimodal system is increased about 10% and the thermals stability was improved by reducing the heat flow of electrolyte surface reaction. This research will be applied to the high energy density and thermally stable cathode materials for the electric vehicle Li ion battery.

Silicon is considered one of the best candidates as an anode material for the next generation of lithium ion batteries due to its enormous capacity of 3579 mAh/g (Li₁₅Si₄) compared to that of graphite (372 mAh/g). However, lithium ion insertion and extraction results in a volumetric expansion of 300 ~ 400%, which can lead to fracture of the silicon anode during electrochemical cycling. In order to prevent capacity fade due to this mechanical degradation, a number of experiments have examined fracture of silicon electrodes during lithiation. An important parameter in these analyses is the fracture energy of the lithiated phase. However, most existing techniques for measuring fracture energy have limitations due in large part to the difficulty of determining the critical stress at which cracks are formed. Furthermore, experimental measurements of the fracture energy at various lithium concentrations are lacking.
In this study, we introduce a simple technique for measuring the fracture energy of thin-film silicon electrodes at various lithium concentrations. To do so, we have lithiated amorphous silicon thin-film electrodes on copper substrates to different states of charge. Subsequently, we performed a bending test by deforming the substrate to a customized shape, allowing for a variation in the curvature along the length of the sample. Finally, the electrodes were examined by focused ion beam (FIB) to obtain both the critical strain for crack initiation and the thickness of electrodes after lithiation. We also have measured the elastic modulus and stresses induced by lithiation in the electrodes using the substrate curvature technique. By determining the state of stress after lithiation and by performing the bending test, we have quantified the fracture energy through an analysis from fracture mechanics. The simple technique presented here is not only useful for silicon thin-film electrodes, but also can be applied to other thin-films or coatings.

Silicon nanowires (SiNWs) were uniformly decorated with ultrananocrystalline diamond (UNCD) by a novel route using paraffin wax as seeding source, which is more effective in the diamond nucleation than traditional methods. These one-dimensional UNCD decorated SiNWs (UNCD/SiNWs) exhibit diameters in the range of 100 to 150 nm and a UNCD grain size of ~5 nm. The films were used as anodes for lithium-ion battery (LIB) anodes, where UNCD coating provide effective conduction channels for both electrons and Li-ions and protect the integrity of SiNWs by featuring electrochemical inertness and mechanical strength. The cyclic voltammetry studies show redox peaks for Si consistent with lithium insertion/extraction, indicating good reversibility over extensive cycling. Electrochemical tests showed that UNCD/SiNWs electrodes can deliver an initial high discharge capacity of ~1500 mAh/g and a reversible capacity of ~1000 mAh/g over 50 cycles. After electrochemical cycling, the UNCD/SiNWs films showed negligible cracks formed due to high volumetric expansion of the silicon during lithiation. However, the film still had good contact with the Cu substrate and delamination was not detected. Therefore, UNCD/SiNWs hybrid structure grown directly on current collector (Cu), represents a promising anode material for rechargeable LIBs with high energy density and long cycling stability.

Alkaline batteries represent about a fourth of the worldwide primary/secondary battery market. In common with all types of batteries, the performance of alkaline batteries is strongly affected by the composition and microstructure of the electrodes. This work focuses on understanding and optimizing the cathode, which is composed of EMD (electrolytic manganese dioxide), graphitic carbon, and electrolyte-filled pores. Naturally, in trying to optimize an electrode there is a trade-off between the capacity or amount of active material (EMD) and amount of additive (carbon) and pores, which are needed to transport charge. Likewise, there is a tradeoff between the electronic and ionic conductivity. In this work we studied the effect of varying carbon type, carbon amount, and overall porosity on the electronic and ionic conductivity of EMD-containing cathodes in order to improve cell performance. The correlation between these transport properties and the microstructure was investigated as well. Tested carbons included a variety of common graphite additives as well as graphene. Multiple analysis tools were used, including SEM/FIB determination of microstructure, ion-transport experiments, and multi-probe determination of electronic conductivities. We quantify the significant effect of graphite additives on both electronic and ionic transport. The nanoporosity inherent in the EMD also has a significant effect.

A rechargeable battery that employs sulfur at the cathode and a metal (e.g. Li, Na, Mg or Al) at the anode provides perhaps the most promising path to a solid-state electrochemical storage device capable of high charge storage capacity. It is now understood that the dissolution of long-chain lithium polysulfides (Li₂S_x, x=2~8) into the electrolyte and the shuttling of polysulfides between cathode and anode has hindered the development of Li-S battery^[1].
Researchers have proposed different methods to prevent polysulfide dissolution and shuttling in Li-S batteries. Many of the most successful approaches focus on physically restraining polysulfide dissolution by using barrier materials^[2,3]. It is understood, however, that because the barrier to Li₂S_x dissolution in the electrolyte is kinetic, polysulfides physically trapped in the meso- or nanopores of a carbon host will eventually leach into the electrolyte, leading to premature cell failure.
In our work, we have developed a novel class of molecular sorbents for sulfur cathodes ((3-trimethoxysilylpropyl) diethylenetriamine and 1-methy-3-trimethoxysilane imidazolium chloride), which take advantage of strong lithium-nitrogen and lithium-chlorine interactions to sequester lithium polysulfides in the cathode. Additionally, the sorbent species are designed with anchoring groups (silane) such that they can cross-link within the cathode and bind to the surface of carbon.
Beginning with density-functional calculations of the structure and interactions of a generic lithium polysulfide species with nitrile and imidazolium containing molecules, we show that the Li₂S_x entrapment by our method is of thermodynamic origin and persists via strong lithium-electrophile interactions, and the interaction is also confirmed by DFT calculation of Raman. Other experimental techniques used include FTIR, ICP-AES, SEM and TEM.
Application of the concept to lithium-sulfur batteries leads to cells with potential profiles which show no noticeable changes even after 50 cycles, while the one without sorbent already show noticeable changes in peak positions and current amplitudes by the 10^th cycle. As an illustration of the effectiveness of the tethered sorbents, it is found that as little as 2w% of a nitrile-rich molecular species can increase the storage capacity of the sulfur cathode from effectively 100 mAh/g to at least 700 mAh/g after 100 charge/discharge cycles at a rate of 1C.
Our approach circumvents the need to apply coatings to the carbon or for thermal infusion of the sulfur into a porous carbon host. Preliminary thermodynamic analysis suggests that the method can also be used with oxygen-, chlorine-, fluorine-, and phosphorous-rich molecules.
Reference
[1] J. L. Wang, J. Yang, J. Y. Xie, N. X. Xu, Adv. Mater.2002, 14, 963.
[2] X. Ji, K. T. Lee, L. F. Nazar, Nat. Mater. 2009, 8, 500.
[3] G. Zheng, Y. Yang, J.J. Cha, S. S. Hong. Y. Cui, Nano Lett. 2011, 11, 4462.

Electrical energy storage devices are indispensable components in modern electronics, and it is always important but challenging to explore new dielectric materials to fulfill the demand of their continuous miniaturization and improved functionality. To maximize energy density, a desirable dielectric should exhibit high dielectric constant, high breakdown strength, and low loss during charge-discharge cycles. We conducted a systematic study on polythioureas as a prospective dielectric layer by implementation of a high throughput hierarchical modeling with combinatorial exploration and successive screening, followed by an evolutionary structure search based on density functional theory (DFT). From a down selection, a series of polythioureas were synthesized and investigated in terms of dielectric constant and loss, band gap, charge-discharge behavior and DC breakdown strength. The dielectric constant and band gap are in good correspondence with our DFT calculations. Dielectric constant of ~ 4.5 and a corresponding energy density of ~ 10 J/cc were achieved in accordance with Weibull characteristic breakdown voltage of ~ 700MV/m. With the incorporation of various chain segments, including aromatic, aliphatic and polyether, we were able to tune dielectric properties by means of introducing additional permanent dipole, altering conjugation length, controlling morphology, etc. Crystalline structures in solution processed films were observed by WAXD (Wide Angle X-ray Diffraction), which were in great agreement with DFT predicted diffraction patterns. The effects of crystalline structure, microstructure and surface roughness on high voltage conduction loss and breakdown strength were also investigated.

Graphite remains the most popular anode material in commercial lithium-ion batteries but it suffers from several drawbacks: (i) sluggish insertion kinetics on charging, (ii) low voltage vs. Li/Li⁺, (iii) limited capacity (~300mAh g^-1), (iv) low volumetric energy density, and (v) incompatibility with propylene carbonate electrolytes. The first two issues limit the overall charge rate of the cell. Using ethylene carbonate as opposed to propylene carbonate reduces the performance of cells in cold environments. For these reasons, much research over the last decade has been focused on finding new anode materials which seek to overcome some of these problems. Anode materials based on the alloying of Li with Sn, Sb, and Si have been heavily investigated, offering the promise of higher capacity. However, all of these nanoscale anodes suffer from huge first cycle irreversible capacity loss stemming from a significant SEI layer formation. When placed in full cells, this irreversible capacity robs lithium ions from the lithiated cathode, reducing the amount of Li available for cycling. To combat this phenomenon, it is a common practice in the laboratory to mix Li metal with the anode to provide the extra capacity needed to combat the first cycle loss. In practice, this technique is not economically efficient. We present here a novel microwave-assisted chemical lithiation technique used to over-lithiate the 4 V and 5V spinels and build a lithium reservoir in the cathode side of the full cell. The lithium reservoir concept is not new, but the method presented here relies on non-volatile, inexpensive chemicals and can be performed in an air atmosphere. The extra lithium ions inserted into the empty octahedral sites of the spinel are used to compensate for the first-cycle irreversibility of the anode. To demonstrate the effectiveness of this technique, we combine the over-lithiated spinel cathodes with a FeSb-TiC composite anode to produce a new high-voltage, high-rate lithium ion battery. The full cell employing the 5 V cathode has an energy density of ~ 260 mAh g^-1 (by total active mass) and maintains 85% of its capacity at 2C rate on charge and discharge. That being said, the batteries exhibit the same capacity fade seen in LMNO/graphite cells. Further modification of the cathode is needed to fully realize a practical cell. In theory, the over-lithiated spinel cathode can be used with any anode which suffers from high first-cycle irreversible capacity, such as nanoscale metal-oxides and TiO₂.

Sulfur is a very promsing positive electrode active material for lithium batteries, due to its high theoretical specific capacity (1675 mA h g^-1). Li-S cells generally experience low sulphur utilization, low Coulombic efficiency and poor long-term capacity retention. A major reason is the dissolution of LiPS intermediates in ether-based electrolytes, triggering a polysulfide-shuttle process. Porous carbons are typically used to conduct electrons to the insulating S/Li₂S, but they do not adsorb the polar LiPSs or adhere to discharged product Li₂S, resulting in active material loss and increased cell impedance.¹ Amphiphilic modifications on carbon frameworks have demonstrated enhanced LiPSs entrapment.¹ Insulating metal oxides² and metal-organic frameworks³ have also been applied to trap LiPSs via chemical interactions. However, these insulating materials cannot trigger the redox reactions of sulfur species, but serve only as LiPS reservoirs, sacrificing electrode conductivity and requiring high fractions of carbon additive.
Instead of relying on porosity to physically confine (or on insulating oxides to chemically trap) polysulfides, in this presentation we describe a different strategy based on a sulfur host that combines inherent metallic conductivity with the ability to chemically bind LiPSs and to facilitate sulfur reduction to Li₂S. A high-surface-area Magnéli phase Ti₄O₇ was synthesized that consists of nanocrystals of 8-20 nm with a very high surface area of 290 m²/g, essential for interfacial interaction. The strong adsorption ability towards LiPSs of this “sulphiphilic” host was probed via X-ray photoelectron spectroscopy (XPS). The Ti₄O₇/S composite demonstrate doubled capacity retention with respect to Vulcan carbon (VC) composite at C/2 over 250 cycles. Stable cycle performance with capacity fading as low as 0.06 % per cycle was demonstrated over 500 cycles.
More significantly, we demonstrate surface-enhanced sulfur redox reactivity using operando X-ray absorption near-edge structure (XANES), based on comparison of LiPSs/Li₂S speciation upon discharge between Ti₄O₇/S and VC/S electrodes. The strong adsorption of LiPS intermediates to the metallic oxide enhances the electron transfer between them, leading to much lower LiPSs fraction and gradual precipitation of Li₂S starting at the beginning of discharge. Adsorbed Li₂S precipitates uniformly on the metallic oxide, whereas in the case of VC/S, dissolved LiPSs cause formation of a detached Li₂S layer, as shown by SEM and impedance studies.
The concept of surface-enhanced sulfur redox extends not only to other Magneli phases, but also to other conductive - polar materials as will be presented here.
Reference
1. G. Zheng et al., Nano Lett. 13, 1265 (2013).
2. S. Evers et al., J. Phys. Chem. C.116, 19653 (2012).
3. J. Zheng et. al., Nano Lett. 14, 2345 (2014) .

Rechargeable batteries are widely used to convert chemical energy to electricity. In this talk we are going to demonstrate that batteries can also convert thermal energy to electricity. This is based on the fact that battery&’s voltage is a function of temperature. The temperature coefficient of full cell voltage is defined as alpha = dV/dT = ΔS/nF, where V is the full cell voltage, T is temperature, n is the number of electrons transferred in the reaction, F is Faraday&’s constant, and ΔS is the partial molar entropy change for the full cell reaction. Hence by discharging a battery at T1 and charging back at T2 with a lower voltage, thermal energy can be converted to electricity as the voltage difference in a thermal cycle. This strategy is called thermally regenerative electrochemical cycle (TREC). Recently we have demonstrated a system with high efficiency based on a copper hexacyanoferrate cathode and a Cu/Cu²⁺ anode¹. In this talk, recent progress on searching for materials with high temperature coefficient, improved cycling life and removing expensive ion-membrane will be discussed. Reference: 1. Seok Woo Lee, Yuan Yang, Hyun-Wook Lee, Hadi Ghasemi, Daniel Kraemer, Gang Chen, Yi Cui. Nature Communications 2014, 5, 3942.

Materials that undergo a conversion reaction with lithium have gained attention as promising candidates for high-capacity cathodes because of their ability to accommodate more than one Li atom per transition-metal cation. Among such conversion chemistries, FeS₂ represents a promising alternative to replace the conventional LiMO₂ (M = transition metal) intercalation mechanism. FeS₂ is inexpensive, highly energy dense, naturally abundant, and environmentally benign. Given that sulfur is one of the charge products of the FeS₂ conversion reaction, the most important factor determining the FeS₂ electrode's efficiency and reversibility lies in the dissolution of highly mobile polysulfide species (S_n^2-) produced during the reduction of sulfur, resulting in a parasitic redox shuttle, introducing unfavorable side reactions with a lithium metal negative electrode, reducing charging efficiency and quickly degrading cell performance. In this work, we exploit the polysulfide dissolution suppression by the bis(trifluoromethanesulfonyl)imide (TFSI^-) anion and the favorable electrochemical properties of the relatively small N-methyl-N-propylpyrrolidinium (PYR₁₃⁺) cation in order to enable a FeS₂ cathode with minimal use of auxiliary electrode components. We demonstrate the highly reversible cycling of a FeS₂/Li cell using a PYR₁₃TFSI (0.6M LiTFSI) electrolyte, yielding the highest energy-density FeS₂ composite cathode to-date, and confirm the TFSI^- anion's ability to suppress active material loss, along the way elucidating sulfur's role in the FeS₂/Li system's complex conversion mechanism.

Highly flexible, conducting thin polyethylenedioxythiophene (PEDOT) is made from in-situ polymerizing them on a paper via polymerisation at an interface of two immiscible solvent. The sheet resistance obtained is 3 Omega; for 43 µm thick paper in which PEDOT shows a conductivity of 390 S/cm. Uniform and conducting PEDOT is formed due the slow interfacial polymerization. The paper is used for making highly flexible supercapacitor and showing 0.65 Wh/cm3 for the whole device including electrolyte. A volumetric capacitance of 144 F/cm3 is obtained for PEDOT and these properties are highly reproducible in in flexible as well as twisted conditions. Excellent stability also found during continues charge-discharge 3000 cycles. 3 cells are patterned in single paper to form in series to achieve a potential of 3.6 V for higher energy requirements. The derived paper also used as counter electrode in DSSC&’s instead of TCO and Pt showing excellent conversion efficiency of 6.5 %.

In recent years the interest in high performance battery materials has increased due to the continuing demands for longer lasting electronic devices possessing increased power density. Lithium ion batteries provide a high theoretical capacity of 3860 mAh/g [1] and reasonable power densities, however with slower reaction kinetics than electrical double layer capacitors because of the activation barrier to lithium diffusion through the host material. However, faradaic electron transfer at a surface avoids excess activation energy such that Li insertion can proceed with capacitor-like kinetics through a phenomena known as pseudocapacitance.[2] In this presentation we will discuss strategies to over come the insulating nature of high surface area amorphous TiO₂ (up to 1000 m²/g)[3] in an effort to exploit the vast number of redox sites in the pores as a lithium battery cathode material with superior charge transfer kinetics.
We first discovered that it was possible to create conducting pathways in our mesoporous materials by directly polymerizing thiophene in the pores of the oxide using FeCl₃. This produced a significant increase in conductivity from 3.56 x 10^-2 to 5.79 mScm^-2 however, despite the increase in conductivity, the electrochemical performance was inhibited by poor lithium transport.[4] This problem was mitigated by use of pyrrole in place of thiophene, followed by investigating the effects of polymer loading levels and pore sizes of the oxide host. The most promising composites were those materials possessing the highest surface area, with 30 Å pores and the lowest loading levels (5 wt%) of conducing polymer. Despite the lower polymer content, the composites still displayed significantly improved conductivity (1.04 mScm^-2) while also displaying improved electrochemical performance, increasing the initial capacity of the pristine mesoporous oxide from 139 to 170 mAh/g with capacity retention from 28 to 58 % after 50 cycles.[5] Further investigations are probing into the development of a photopolymerization route to dismiss the requirement for a chemical oxidant and create an improved interface between the organic and inorganic phases.
[1] S.-L. Chou, J.-Z. Wang, J.-Z. Sun, D. Wexler, M. Forsyth, H.-K. Liu, D.R. MacFarlane, S.-X. Dou, Chem. Mater. 20 (2008) 7044.
[2] J. Wang, J. Polleux, J. Lim, B. Dunn, J. Phys. Chem. C 111 (2007) 14925.
[3] D.M. Antonelli, Microporous Mesoporous Mater. 30 (1999) 315.
[4] L.A.C. Smith, F. Romer, M.L. Trudeau, R.M. Souto Maior, M.E. Smith, J.V. Hanna, D.M. Antonelli, Microporous Mesoporous Mater. 194 (2014) 52.
[5] L.A.C. Smith, F. Romer, M.L. Trudeau, M.E. Smith, J.V. Hanna, D.M. Antonelli, Press (2014).

Scientific literature shows a substantial study-to-study variation in the electrochemical lithiation performance of "1-D" nanomaterials such as Si and Ge nanowires or nanotubes. In this study we varied the VLS growth temperature and time, resulting in nanowire arrays with distinct mass loadings, mean diameters and lengths, and thicknesses of the parasitic Ge films that are formed at the base of the array during growth. When all the results were compared, a key empirical trend to emerge was that increasing active material mass loading drastically degraded the electrochemical performance. For instance, GeNWs grown for 2 minutes at 320 °C (0.12 mg cm^-2 mass loading, 34 nm mean nanowire diameter, 170 nm parasitic film thickness) had a reversible capacity of 1405 mAh g^-1, a cycle 50 coulombic efficiency (CE) of 99.9%, a cycle 100 capacity retention of 98%, and delivered ~ 1200 mAh g^-1 at 5C. To contrast, electrodes grown for 10 minutes at 360°C (0.86 mg cm^-2, 115 nm, 1410 nm) retained merely 5.6% of their initial capacity after 100 cycles, had a CE of 96%, and delivered ~ 400 mAh g^-1 at 5C. Using TOF-SIMS we are the first to demonstrate marked segregation of Li to the current collector interface in planar Ge films that are 300 and 500 nm thick, but not in the 150 nm specimens. FIB analysis shows that the cycled higher mass loaded electrodes develop more SEI and interfacial cracks near the current collector.

Recent advances in high-resolution 3D X-ray computed tomography (CT) allow detailed, non-destructive 3D structural mapping of sub-surface structure across multiple length scales. Recent developments initiated at synchrotron beamlines have yielded a number of X-ray optical elements that have driven improvements in contrast and resolution down to 50 nm for laboratory-based (non-synchrotron) X-ray microscopes (XRM) to levels previously unachievable with conventional projection-based X-ray CT instrumentation. We will present detailed microstructural investigations of a commercially available Li-ion battery cathode characterized by XRM. Multiple length scale X-ray microscopy experiments reveal a wealth of microstructural information in three dimensions including phase fractions, volume specific surface area and tortuosity. Furthermore, the non-destructive imaging capabilities of high-resolution X-ray microscopes provide unique opportunities to study samples in their native environments (in situ) and to quantify how their microstructures evolve in 3D and over time (4D) from the meso- down to the nanoscale. By combining digital volume correlation (DVC) with successive 3D XRM images, the dimensional changes taking place during charge cycling are quantified in ‘4D&’ at the electrode level. After battery discharging, the extent of lithiation of the grains in the electrode is found to be a function of the distance from the battery terminal with grains. Lastly, XRM offers the capability to model batteries with realistic 3D morphologies. The nanoscale structure of the Li-ion battery cathode electrode was experimentally determined using XRM and a three dimensional numerical framework with finite volume method was employed to simulate heat generation during isothermal galvanostatic discharge processes. Heat generation in the Li-ion battery cell during the discharge processes from different mechanisms, such as electronic resistive heat, ionic resistive heat, contact resistive heat, reaction heat, entropic heat and heat of mixing, was investigated. Multiple length scale X-ray microscopy offers a unique and versatile characterization as well as increased multi-modal correlative opportunity with conventional electron microscopy.
Ref: Eastwood, D., .(2014). Adv. Eng. Matls. 4(4); Shearing, P. (2012). J. Elec. Soc., 159(7), A1023-A1027; Yan, B., (2012). J. Elec. Soc. 159(10), A1604-A1614.

The new generation of Li-ion batteries may only be obtained by achieving a further step in performance, which is majorly dependent upon the breakthrough of electrode materials. To this end, mechanochemically prepared iron phosphides with high phosphorus-content, i.e. FeP_y (2le;yle;4), have attracted much research attention. This is because this low-cost and environmental benign FeP_y can electrochemically react with multiple Li ions, thus providing a high specific capacity (e.g. the theoretical capacity of FeP₄ can reach from 596 up to 1787 mAh/g when the Li-ion transferable number ranges from 1 to 3). Although several publications have reported the electrochemical performance of FeP_y, little was known about the detailed structure evolution during cycling, key factors that govern the electrochemical performance, and most importantly, the detailed electrochemical reaction mechanism. We used a number of characterization techniques such as in-situ and ex-situ synchrotron X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and pair-distribution function (PDF) analysis to understand the chemical phase transition of FeP_y, along with probing its structural evolution during cycling. Our results suggest that FeP_y anode undergoes a conversion reaction (3yLi+FeP_y--yLi₃P + Fe) upon lithiation, and such a reaction is reversible but enables the formation of amorphous phases, which results in the crystallinity loss of FeP_y during cycling. Moreover, the reaction pathways of this material somewhat differ on discharge and charge; the recovery of FeP_y (upon delithiation) is always accompanying with the formation of small amount of inactive Fe phase. This research is supported by DOE-EERE-BATT, DE-AC02-05CH11231 under Award Number 6807148, and by NYSERDA. Guixin Wang is supported by the National Natural Science Foundation of China (Grant No.21206099) and the China Scholarship Council.

The extensive applications of mobile electronic devices have been greatly limited by the amount of energy provided by the storage devices. As one of the major energy storage devices, lithium ion batteries (LIB) have been identified as the best solution to power portable electronic devices.¹ Recently, research efforts have led to the discovery of a new storage mechanism (termed as conversion mechanism) in transition metal oxides and sulfides which are capable of storing 2 or more times the graphite anode (~372 mAh/g²) used in conventional LIBs.^3,4 Amongst these materials, cobalt sulfides have garnered much interest in the LIB research community.^5,6 In this research work, we present the first reported attempt to synthesize cobalt sulfide (CoS₂) on carbon nanotubes (CNT) for LIB application. The CoS₂ nanoparticles were coated on CNT via a simple one-pot solvothermal method. Different characterization methods are employed to analyze the morphology and crystal structures of the as-synthesized CoS₂/CNT composites. From the SEM images, it was seen that the originally smooth surface of the CNTs were uniformly covered with nanoparticles of ~10 - 30 nm. Diffraction patterns obtained from X-ray diffraction (XRD) have identified peaks that were well matched to both CNT and CoS₂, which is further confirmed by TEM image. Transmission electron microscopy (TEM) imaging showed the presence of ultra-fine nanoparticles of 2-5 nm along the surface of CNTs. In terms of electrochemical activity, initial galvanostatic charge-discharge cycling of the CoS₂/CNT versus Li/Li⁺ provided promising results. At 50 mA/g, the cobalt sulfide/CNT was able to deliver a higher 1297 mAh/g initial discharge with a coulombic efficiency of 60.7% followed by stable cycling of ~740 mAh/g with coulombic efficiency close to 100%. The dependence of loading for CoS₂ on CNT have also been investigated. The novel design of materials and its outstanding performance have opened a new way for synthesis of anode materials for LIB. This simple approach allows an easy access of highly capacitance CoS2 +CNT materials. On the other hand, we also foresee that the method could be easily extended to the growth of other transition metal sulfide and boost their applications in next generation LIB.
References
1. M. Arm and J. Tarascon, Nature, 2008, 451, 652-657.
2. J. Tarascon and M. Arm, Nature, 2001, 414, 359-367.
3. P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, and J. Tarascon, Nature, 2000, 407, 496-499.
4. P. Poizot, S. Laruelle, S. Grugeon, and J. Tarascon, Journal of the Electrochemical Society, 2002, 149, A1212-A1217.
5. Q. Bin, X. Zhao, and D. Xia, Journal of Alloys and Compounds, 2013, 579, 372-376.
6.J. Xie, S. Liu, G. Cao, T. Zhu, and X. Zhao, Nano Energy, 2013, 2, 49-56.

SnO₂ is a well know anode material in Li ion battery due to its physical and chemical stability, environmental benignity and low Li ion intercalation potential. The theoretical capacity of SnO₂ may be as high as 1493 mAh/g. SnO₂, however, suffers from large volume change (>300%) during discharging and charging cycles. This leads to continuous capacity fading. Several nanostructured SnO₂ materials together with its composites with different carbon materials, especially graphene were tried to minimize this problem. The results are quite impressive. Nevertheless, these materials show capacities which are still far away from the theoretical capacity of SnO₂.
In the present work, ternary composites of SnO₂ were made with reduced graphene oxide (rGO) and a conducting polymer, poly(3,4-ethylenedioxythiophene), PEDOT. PEDOT, in addition to rGO, in these composites was believed to accommodate the volume change of the main active material SnO₂. Transmission electron microscopy shows ~2 nm SnO₂ nanoparticles are uniformly dispersed over rGO sheets and covered with PEDOT. The specific capacities of the composites depend on the concentration of PEDOT in the hybrid. Galvanostatic discharge-charge characteristic of the composite with 5 wt% PEDOT shows first discharge and charge capacities of 1758.8 and 1028.8 mAh/g, respecitively, at a current density of 0.1C, with Coulombic efficiency 58.5%. The reversible capacity was 980 mAh/g after 160 cycles and a Coulombic efficiency more than 99%. This capacity is equivalent to 1300 mAh/g with respect to only SnO₂ in the composite. It is close to the theoretical capacity of SnO₂. The electrode material retained >94% of its initial capacity. Moreover, the composite shows an excellent rate performance. Galvanostatic intermittent titration technique (GITT) exhibits higher ionic mobility in the composites compared to SnO₂. The high capacity of the composite was attributed to the higher electronic and ionic mobility and maximum volume buffering effect offered by rGO and PEDOT.

Compared to the electrostatic storage of charge in electric double layer capacitors (EDLCs), could provide larger capacity and energy density through reversible redox reaction. In layered or tunneled materials, such as MoO₃ and MnO₂, ions can easily intercalate into the channels. However, due to their naturally poor conductivity and rate capability, the capacitance is largely hindered especially at high mass loading levels. In this context, we propose the following method to solve the poor conductivity issue and promote the electrochemical performance at high mass loading levels. First, we synthesis Al doped α-MnO₂ microspheres as positive electrode which show a specific capacitance of about 213 F g^-1 and 146 F cm^-3 and excellent cycling performance that maintained 91% after 15000 cycles under the high mass loading of 3-4 mg cm^-2. Second, hydrogenation method is applied to enhance the conductivity of MoO₃ which is demonstated by both of first principle calculation and single nanobelt measurement. Freestanding hydrogenated MoO₃ (MoO_3-x)/CNT electrodes (mass density 2.5 mg/cm²) were fabricated and showed much improved electrochemical performance, such as a specific capacitance of 337.5 F/g and a high volumetric capacitance of 291.4 F/cm³ with 64% initial capacitance at 10A/g. Finally, a SnO₂ coated H_xMoO₃ (SHMO) nanobelt was successfully fabricated under ambient room temperature through a facile reduction reaction. The highest specific capacitance of SHMO/CNT as negative electrode for pseudocapacitors is about 330 F/g with a volume capacitance of 415 F/cm³ at the current density of 1 A/g.
Acknowledgement
This work was financially supported by the National Natural Science Foundation of China (51322210), a Foundation for the Author of National Excellent Doctoral Dissertation of PR China (201035) and the Fundamental Research Funds for the Central Universities (HUST: 2012YQ025, 2013YQ049, 2013TS160).

Lithium-ion batteries combine highly energetic materials coupled with a flammable organic rather than aqueous electrolyte. They may experience severe failure if subjected to conditions for which they are never designed. Any thermal, mechanical or electrical abuse can trigger spontaneous heat-evolving reactions, which can lead to fire and explosion. A number of efforts have been underway to improve lithium-ion battery safety. They include use of safety vents, thermal fuses and circuit breakers. These techniques only use external devices and may not be able to response when the hazardous reactions happen in very high rate. Techniques using internal thermal fuse, e.g., positive temperature coefficient (PTC) layer integrated inside LIBs or shutdown separators, become promising research directions due to the fast and effective response to high rate hazardous reactions.
In the present study, two novel protective layers are designed and developed for the LIBs. Firstly, organic PTC ink is developed and applied to the current collector to serve as an internal fuse integrated in the battery structure. At normal operating temperatures, the conductive particles embedded in a crystalline polymer matrix provide a low resistance path for current flow. At elevated temperatures, the polymer&’s structure changes to an amorphous state. The accompanying expansion of the matrix breaks the conductive pathway between the embedded particles, rapidly increasing the device&’s resistance by several orders. This reduces the current to a relatively low and safe level. Secondly, a porous thermal sensitive protection layer is developed on top of the electrodes. The layer contains porous ceramic layer and thermoresponsive particle layer and undergoes a thermal transition at a predetermined trigger temperature on the ceramic surface.

The phase diagram of the Li-Mn-Ni-Oxide pseudoternary system¹ was used as a starting point to understand the influence of transition metal composition and lithium content in the series Li_1+x(Ni_y Mn_1-y)_1-xO₂ (y=0.2, 0.4, 0.5, 0.6 and 0.7, 0le;xle;0.34). A mixed transition metal hydroxide precursor (Ni_yMn_1-y (OH)₂ ) was synthesized through co#8209;precipitation in a continuously stirred tank reactor (CSTR)². The final products were achieved after sintering the precursor with the desired amount of Li₂CO₃ at 900^oC in air for 10 h. Samples were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements via coin cells.
One or two additional spinel rocksalt or layered phases were observed when the lithium content was less than required for a single layered phase in agreement with reference 1. Additionally, Li₂CO₃ residuals were detected in the SEM images when the lithium content exceeded that of the lower phase boundary. Contour plots of the lattice constants versus composition in the single phase region were generated. The maximum reversible capacity to 4.6 V was found at the lower extent (largest lithium content) of the single phase region when y > 0.5 while it was at the top (smallest lithium content) of the single phase region when y le; 0.5. The electrochemical measurements showed that multiphase samples had very low specific capacity for both 2.5-4.4 and 2.5-4.6 V cells. This work provides a careful baseline study for the rational selection of core and shell compositions for core-shell materials³.
References:
1. E. McCalla, A. W. Rowe, R. Shunmugasundaram, and J. R. Dahn, Chem. Mater. 25, 989minus;999 (2013).
2. A. V. Bommel and J. R. Dahn, J. Electrochem. Soc. 156(6), 362-365 (2009).
3. S. T. Myung, H. J. Noh, S.J. Yoon, E. J. Lee, Y. K. Sun, J. Phys. Chem. Lett. 5, 671 (2014).

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 active carbon to increase specific surface area and electrostatic capacity.
In this study, we prepared thermosetting resin-based active carbon particles (phenol resin and furfural resin, 10 mm in diameter) in N₂ atmosphere in one hour (rate 10C /min) at 6000C, then we activated those samples in 30 minutes at 8000C by KOH (KOH : samples = 4 : 1 in weight). Specific surface area/pore size distribution measurement was carried out and crystallographic evaluation by XRD and Raman spectroscopy was also performed. Finally we evaluated EDLC characteristics.
For both of carbonized phenol resin and furfural resin, specific surface area was less than 528 m²/g even after carburization, however, specific surface area increased and meso pore ratio decreased simultaneously after activating. We investigated the relationship between G-band (ca. 1590 cm^#8213;1) and D band (ca. 1350 cm^#8213;1) ratio (G/D ratio) by Raman spectroscopy and specific surface area, and found that smaller G/D ratio has an effect to increase specific surface area. EDLC characteristics measurements revealed that larger meso pore ratio increased electrostatic capacity per weight under 100 mA/g, and carbonized furfural resin had the largest capacity as 140 F/g at 20 mA/g.

Two-dimensional (2D) layered materials have attracted extensively research effort due to their extraordinary properties. Nature clay is one of them and has been widely studied in many areas due to its natural, abundant, and inexpensive characters. Unlike graphene related materials, electrochemical properties of nature clay has rarely been studied. Here we propose that nature clay could be a new green material for Li-ion battery/capacitor because of the lithium ion insertion ability of the layered structure.The performance of various status of clay will be exam. Both traditional slurry casting and electrostatic spray deposition (ESD) will be used to fabricate the electrode. TGA, XRD, BET, FTIR, SEM and TEM are carried out for examining the clay electrode. Cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) experiments are used to evaluate the electrochemical performance. More detailed results will be shown during the meeting.

Conducting polymers with a nanoporous morphology and as nanocopmposites with metal-oxides have emerged the materials system of great potential for high energy density storage. Based on these, electrodes structured at the nanoscale enable many fold enhancement of electroactive surface and interface with electrolyte facilitating absorption, ingress and diffusion of electrolyte ions which lead to increased energy and power density of supercapacitor devices. In this work we investigate nanocomposites in the 3-D nanoarchitecture using vertically aligned ZnO nanorods template to create conducting polymer Poly(3,4-ethylenedioxythiophene) (Pedot) nanotube and nanofibrous network structures using the facile electrochemical synthesis approach.
A hydrothermal technique is used to create free standing vertically aligned ZnO nanorod arrays of 60-120 nm diameter and 3-4 mu;m length on graphite substrate. Using ZnO nanorods as template, various 3-D nanostructures of Pedot are created by depositing doped-Pedot film by electropolymerization using ultra-short 10 ms current pulses of 4 mA.cm^-2 amplitude in the presence of surfactant to promote site selective filling. Pedot nanotubes are obtained by etching ZnO nanorods in 20% ammonia and nanofibres network by varying electropolymerization conditions and the ZnO nanorods array geometry.
Interaction and response of ZnO nanorod and various Pedot nanostructures was analyzed by electrochemical impedance, cyclic voltammetry and charge-discharge techniques. Impedance results for Pedot nanofibrous network structure showed creation of highly effective charge transfer interface structure with characteristic resistance ~5.4 #8486;.cm² significantly less in comparison to ZnO and Pedot. Ramanstudy show highly conjugated Pedot in oxidized state. Areal capacitance, 209 and 189mF cm^-2 is achieved in Pedot nanotubes formed with ZnO nanorods core of diameter 60 and 120nm, respectively. Pseudocapacitive behavior of electrodes is shown by rectangular feature of CVs and diffusion controlled process at electrode-electrolyte interface is confirmed by Randles-Sevcik plots. At fast CV scan rates, the charge storage through anions enhances in nanostructure created over 120 nm ZnO nanorods due increased access to larger surface regions. For 60 nm ZnO rod structures, ion diffusion limitation at higher scan rates is observed. Galvanostatic charge-discharge studies at different current densities conducted on Pedot nanostructures over ZnO nanorods are symmetrical and show capacitance consistent with CV results. In conclusion, this work shows that facilitated charge transfer and electron conduction achieved through structure control of the ZnO nanorods and Pedot nanotube and fiber network at the nanoscale has significantly improved the electrochemical redox processes and hence pseudocapacitive properties for efficient energy storage in a supercapacitor device.

Supercapacitor devices have emerged as preferred technology for electrochemical energy storage for high power applications in automotive transport and modern electronics. Conducting polymers like polypyrole (PPy) which exhibit pseudocapacitance by charge transfer reactions equivalent to doping-dedoping and nanocomposites with metal oxides with added contribution from fast surface redox reactions are actively investigated in microporous forms with focus on high surface area for accessible ions. Though, control of electrochemical interface, charge transfer and electron conduction in nanoscale structure can benefit energy storage, but received little attention. This work investigates electrodes with vertically aligned TiO₂ nanotubes ordered arrays as template to create PPy nanotube sheaths in 3-D nanoscale architecture. The strategy is to utilize nanoarchitecture of PPy for pervasive ion access and accelerated ion kinetics. This paper describes the synthesis and electrochemical properties of electrodes for energy storage in supercapacitor devices.
Vertical TiO₂ nanotube arrays forming core of 3-D nanoscaled electrode architecture were synthesized by anodization of Ti foil at +30 V dc in ethylene glycol with 0.25 wt % NH₄F. By addition of 2% water, close-packed 45-50 nm diameter TiO₂ nanotube arrays of 3-4 mu;m length are formed. The electrically conducting TiO₂ nanotubes are amorphous as XRD studies show. Redox active PPy sheath is created by ultra-short pulsed current electropolymerization under the action of surfactant to homogeneously nucleate and uniformly deposit conjugated polypyrrole around TiO₂ nanotubes.
Electrochemical properties of 3-D nanoscaled TiO₂ nanotube core-polypyrrole sheath electrodes were investigated. Cyclic voltammetry plots in -0.1 to 0.5 V range at 10-100 mV.s^-1 scan rates are rectangular and symmetrical about zero current axis testifying highly pseudocapacitive behavior and fast redox processes in nanostructured electrodes. Electrochemical processes during the evolution phases of polypyrrole sheath built-up over TiO₂ nanotube and electrolyte interface were elucidated using electrochemical impedance study through number of current pulses. High areal capacitance of 48 mF cm^-2 and low charge transfer resistance 12 ohm.cm^-2 with least ion diffusion limitation are realized at optimized polypyrrole sheath. Raman spectra studies reveal anion at specific chain locations involve in the redox process. Energy and power density of single electrode system evaluated by systematic charge-discharge plots generated at different 1-3 mA.cm^-2 current densities show cyclic stability of 3-D core-sheath electrodes. This paper reports pulsed electropolymerization synthesis, structure and electrochemical aspects of the polypyrrole sheath structured over TiO₂ nanotube core and describes energy storage performance of such structures in 3-D nanoarchitecture.

In the search for earth-abundant, high capacity lithium-ion anode materials, the significant advantages of germanium are often overlooked due to the focus given to silicon anodes. Both Ge and Si have significantly higher theoretical lithium capacity (1600 mAhg^-1 and 4200 mAhg^-1, respectively) compared to the carbon-based anodes (372 mAhg^-1) presently used in Li-ion batteries. However, Ge is more electronically conductive and has a higher room temperature Li-ion diffusivity. Due to their high capacities, Ge and Si anodes both suffer from large volume changes (up to 400%) during electrochemical cycling. Repeated expansion and contraction of these materials lead to fracturing and eventual pulverization resulting in the loss of electrical contact with the current collector and ultimately battery failure.
We will present in operando X-ray microscopy results, which directly track the morphology, electron density changes, and crack formation in micron-sized Ge anode particles during battery operation. By studying particles within a number of ~40 micron regions, we observe significant size dependence on the cycling characteristics of the Ge particles Only particles with diameters larger than a few microns display cracks during cycling. Small Ge particles experience volume expansion and cracking before their larger counterparts, but rapidly lose electrical contact. With in situ nanotomography, we demonstrate unambiguously the fracturing of alloying anode materials into completely unconnected pieces. Moreover, we show that the density changes due to lithiation are consistent with partial transformation into the Li15Ge4-like phase. Our results demonstrate the significant value in linking electrochemical performance studies with morphological evolution to understand failure mechanisms and encourage more systematic searches for a viable high capacity anode material

High capacity silicon (Si) anodes have received considerable attention because its high capacity could facilitate the advent of emerging lithium ion battery (LIB) applications, such as advanced mobile electronics and hybrid electrical vehicles. For this achievement, fading mechanisms from large volume change of Si should be resolved. Along this direction, polymeric binder has turned out to play a decisive role in stable cycling of Si anodes, as the binder could stabilize the electrode films even during the large volume change of Si. In this discussion, I will cover three of my recent binder studies: 1) Mussel-inspired wet-adhesive binder designed by conjugation of catechol functional groups can be a universal approach for various polymer backbones.¹ 2) Hydrogen bonding was found to be very useful for Si polymeric binder because it could generate intimate interaction with Si while allowing for self-healing mechanism. As an example, I will introduce hyperbranched multidimensional β-cyclodextrin polymer. This binder stabilizes Si electrodes by creating 3D hydrogen bonding.² 3) Finally, a more systematic binder study will be introduced. In this investigation, copolymer incorporating Meltrum&’s acid was designed to facilitate various binder functions such as self-healing, crosslinking, stiffness, etc. The systematic approach indicates that self-healing plays the most critical role in the Si anode performance among all the functions tested.
¹J. W. Choi et al., Adv. Mater., 2013, 25, 1571-1576. DOI: 10.1002/adma.201203981
² J. W. Choi et al., Nano Lett., 2014, 14, 864-870. DOI: 10.1021/nl404237j

Si is an attractive negative electrode material for lithium ion batteries due to its high specific capacity (~3600 mAh/g). On the other hand, the huge volume variation during cycling leads to several coupled issues at the material/electrode/cell level, including fracture of Si particles, unstable solid electrolyte interphase, and low Coulombic efficiency. In this work, we report that the breathing effect of the electrode caused by Si expansion is a major contributing factor to the degradation of electrode integrity, and we demonstrate that a Si-C yolk-shell structure with empty space between Si core and C shell can overcome this effect for improved electrode performance. The C shell stabilizes the solid-electrolyte interphase (SEI) layer and facilitates charge transfer, while the free space between Si and C accommodates the volume expansion of Si particles, reducing the variation in electrode thickness by an order of magnitude. The Si-C yolk-shell nanocomposite electrode exhibits excellent capacity retention as well as high cycle efficiency. In-situ transmission electron microscopy (TEM) and finite element (FEM) simulations were conducted to show how the C shell can constrain large volume expansion of the Si core and suppress the overall electrode expansion. The in-situ electrochemical dilatometer shows that the yolk-shell structure can reduce the electrode thickness change down to 5%, comparing with 100% of thickness variation in the electrode with Si nanoparticles as active materials.

Silicon has potential to greatly increase the capacity of negative electrodes in Li ion batteries, and like many of the new materials it has stability issues. This issue is particularly challenging in silicon, which has a high Li capacity and a correspondingly large volume expansion. Our work employs in situ AFM to investigate amorphous Si electrodes and Solid Electrolyte Interphase (SEI) formation on the surface, using lithographically patterned islands. The patterned films enabled direct in situ comparison between the Si and the copper current collector. These experiments were conducted in a closed electrochemical cell, and allowed us to investigate SEI behavior in different electrolytes and with different cycling conditions. An irreversible Si volume expansion was measured during the first cycle and is likely the product of lithiation induced changes to the silicon structure. The height of the electrodes during lithiation was modeled to extract diffusion and interface kinetics information. Both the electrolyte composition and the formation potential had significant effects on the SEI formation. Complimentary in situ stress measurements were performed to provide additional information. The cycled films were also examined with detailed TEM to characterize the SEI thickness and changes in Si. The results from this full range of experiments were used to characterize changes in Si electrodes and to develop a detailed model of SEI formation, which was then employed to develop strategies for designing more stable electrodes.

For future applications in portable electronics, electric vehicles and grid storage, batteries with higher energy storage density than current Li-ion need to be developed. Recent efforts in this direction have focused on high-capacity electrode materials such as lithium metal, silicon and tin as anodes, and sulfur and oxygen as cathodes. In particular, as an anode material, Li metal would be the optimal choice because it has the highest specific capacity (3860 mAh g^-1) and the lowest anode potential of all. However, Li anode forms dendritic and mossy metal deposits, causing serious safety concerns and low Coulombic efficiency during charge/discharge cycles. Though advanced characterization techniques have helped shed light on the Li growth process, effective strategies to improve Li metal anode cycling remain elusive. Here we show that coating the Li metal anode with a monolayer of interconnected amorphous hollow carbon nanospheres helps isolate Li metal depositions and facilitates the formation of a stable solid electrolyte interphase. We show that Li dendrites do not form up to a practical current density of 1 mA cm^-2. The Coulombic efficiency improves to ~99 % for more than 150 cycles. It is significantly better than the bare unmodified samples, which usually show rapid Coulombic efficiency decay in fewer than 100 cycles. Our results indicate that nanoscale interfacial engineering could be a promising strategy to tackle the intrinsic problems of Li metal anodes.

Silicon is one of the most promising electrode materials for high performance lithium ion batteries, since it possesses the highest known specific capacity of 4200 mAh/g, which is an order of magnitude higher than conventional graphite electrodes. One of the obstacles in achieving functioning Si battery electrodes is the sliding, cracking, and delamination of the Si electrodes from the Cu current collector. Attempts at elucidating these interface failure mechanisms have been hindered by the complex and unknown structure of the interface. Here, we present results from our recent Density Functional Theory (DFT) calculations to characterize the structure and deformation mechanisms at the interface bonding silicon and the copper substrate. Motivated by experimental studies which suggest that an inter-diffused region comprising of Cu, Li, and Si atoms exist between the crystalline Cu substrate and the lithiated Si film, we attempt to generate equilibrium inter-diffused Cu/Si/Li interface structures using ab-initio molecular dynamics (MD) simulations with varying lithium content to simulate the evolving interface structure with lithiation. The interfacial energies of the resulting structures suggest that the presence of Cu atoms in the inter-diffused region heavily influences the interfacial energy with a minimum of ~1 J/m². The low toughness is attributed to the strong directional bonding between Cu and Si in the inter-diffused region, which consequently results in weak bonding between the Si and Li atoms. Results from atomic simulations of tension and shear will also be presented, which provide insights into the interface sliding and delamination mechanisms observed during lithiation processes. In addition, the mechanical properties are extracted from those simulations and are able to serve as an effective tool for simulation of the interfacial behavior in other scales, leading us to a better design of the interface structures.

Despite high theoretical capacity in lithium-ion batteries, silicon (Si) anodes are still vulnerable to a severe capacity fading because of dramatic volume expansion and formation of solid-electrolyte interface (SEI) on their surfaces.^1,2 Herein, we directly prepared a novel hybrid anode of polyvinyl alcohol (PVA) polymer/Si nanoparticles/carbon nanotubes (CNTs) fibers on the battery current collector via water-based electrospinning. Such a feasible direct-deposit approach using water as solvent eliminates the use of toxic solvents like N-Methyl-2-pyrrolidone and by-passes conventional paste preparation steps such as sonication, blending, grinding, coating, and drying. The PVA/Si/CNTs fibers exhibited an excellent battery performance. The battery using hybrid fibers showed very outstanding reversible capacity of over 1,500 mAh/g at 1C. The capacity retention is over 85% after 300 cycles. In the rate capability performance from 0.1C and 5C, the hybrid fibers have an initial discharge capacity of 5,863 mAh/g at 0.1C due to the synergy between well-dispersed Si NPs and CNTs. The hybrid fibers also represented much high capacities of 1,675 mAh/g at 2C, 1,310 mAh/g at 3C and 950 mAh/g at 5C because the fiber anodes have a much less charge transport resistance by cooperating highly-conductive carbon nanostructures. Such excellent battery performance should be attributed to excellent dispersion of Si nanoparticles in PVA and supporting Si nanoparticles with CNTs, which prohibits not only the volume expansion but also the formation of SEI layers of silicon anodes.
References
[1] H. Wu, Y. Cui, Nano Today2012, 7, 414.
[2] Wu H.; Chan G.; Choi J. W.; Ryu I.; Yao Y.; McDowell M. T.; Lee S. W.; Jackson A.; Yang Y.; Hu L.; Cui Y. Nature Nanotech.2012, 7, 310.

Many high-energy-density lithium ion battery electrode materials have been studied to meet the requirements for smaller weight and longer battery life. Silicon is able to deliver 3600 mAh/g by forming Li₁₄Si₄, which is higher than the specific capacity of other known negative-electrode materials. However, Li-Si has poor cycle life and low cycle efficiency due to coupled mechanical and chemical degradation, which leads to quick capacity fading upon cycling.
The solid electrolyte interphase (SEI) is a passivation layer formed on the electrode surface to enable the long-term cyclability. An improved understanding of the relationships between the structure and properties of SEI is very important for unveiling the capacity fading mechanisms, predicting the cycling stability, and designing high performance and durable electrode-coatings. In this work, we tailor the structure of the SEI by controlling the formation voltages, and we establish a relationship between composition and mechanical properties of the resulting SEI through investigating the impact of mechanical and chemical properties of SEI the cycling history on the Li-Si electrode behavior. We found that the inorganic components in SEI led to higher elastic modulus and provided better mechanical protection and higher cycle efficiency. We envision this work can enable improvements in the design of artificial SEIs on electrodes that undergo large volume change, thereby leading to improvements in cell current efficiency and life of lithium ion batteries.

Silicon based hollow nanostructures are receiving significant scientific attention as potential high energy density anodes for lithium ion batteries. However their cycling performance still requires further improvement. Here we explore the use of atomic layer deposition (ALD) of TiO₂, TiN and Al₂O₃ on the inner, the outer, or both surfaces of hollow Si nanotubes for improving their cycling performance. We demonstrate that all three materials enhance the cycling performance, with optimum performance being achieved for SiNWs conformally coated on both sides with 1.5 nm of Li active TiO₂. Substantial improvements are achieved in the cycling capacity retention (1700 mAh/g vs. 1287 mAh/g for the uncoated baseline, after 200 cycles at 0.2C), steady-state coulombic efficiency (~100% vs. 97-98%), and high rate capability (capacity retention of 50% vs. 20%, going from 0.2C to 5C). TEM and other analytical techniques are employed to provide new insight into the lithiation cycling-induced failure mechanisms that turn out to be intimately linked to the microstructure and the location of these layers.

Li-ion-conducting solid electrolytes can circumvent many stubborn issues arising from the organic liquid electrolytes used in conventional Li-ion batteries, but their application is limited by the low ionic conductivities. The first step towards overcoming this drawback is to develop a proper understanding of the ionic transport mechanism; however, this knowledge is missing for many widely studied compounds. A typical example lies in the perovskite solid electrolyte (Li_0.33La_0.56)TiO₃. The material exhibits an alternate stacking of La-rich and La-poor layers along the [001] direction. Li migration is believed to primarily occur within the La-poor layer, where the relatively low La occupancy on the A-sites results in a higher chance of forming the percolative pathway for Li. However, this scenario cannot explain the conductivity optimization realized by high-temperature quenching, which completely disrupts the aforementioned cation ordering and should supposedly make the percolation of Li less likely. In the present study, this long-standing inconsistency has been reconciled. Using state-of-the-art scanning transmission electron microscopy imaging, we unambiguously visualized the Li migration pathways in the macroscopically disordered (Li_0.33La_0.56)TiO₃. It was the multiple, diverse directions of the pathways that gave rise to the larger conductivity. The present study pointed out that, when interpreting the ionic conduction behavior of solid electrolytes, the fluctuation of local atomic arrangement is no less important than the average crystal structures. This discovery would profoundly benefit future studies of ionic transport in solid electrolytes.

Silicon has attracted increasing attention as an ideal candidate for battery anode material because of its relatively low discharge potential and high theoretical gravimetric capacity of 4200mAh/g. However, traditional bulk and thin film Si anodes have poor cyclability because of severe mechanical degradation and capacity loss within several charge/discharge cycles due to the 400% volume expansion during Si lithiation. Nanoscale Si electrodes, such as nanowires and inverse opal lattices, have shown promising results of improved mechanical properties due to increased ductility in nano-sized Si and the availability of free spaces to absorb Si volume change. Moreover, nano-architectured electrodes also have improved rate capability because of a shorter solid phase diffusion length inside electrodes and a larger surface area.
We present a mechanically robust 3D Si nano-truss electrode with octect structure lattices, which provide high strength per weight. Two methods were designed to fabricate Cu-Si nano-trusses with Cu providing mechanical support and also functioning as current collector. In one method, 2-photon laser lithography was used to write a 3D polymer scaffold in the shape of the optimized lattice structure in which beams are 0.9 to 2 microns thick and 1 to 5 microns in length. Cu and then amorphous Si is deposited onto the polymer trusses using RF magnetron sputtering, with Si layer thickness under hundreds of nanometers in order to take advantage of the enhanced ductility due to nano-sizing effects. An alternative approach is also being developed where 2-photon lithography was used to create a polymer mold of the nano-trusses for direct Cu electroplating. The polymer photoresist was then removed and an amorphous layer of Si was deposited on solid Cu nano-trusses by CVD. The resulting Cu-Si nano-trusses have no polymer content and the Si layer will be more conformal.
In-situ lithiation inside a SEM was performed to directly observe volume change, mechanical deformation and electrochemical properties of the Si nano-truss anode during multiple cycles. A lithium electrode was mounted to the tungsten needle of the telescoping bar on the wall of the SEM chamber. Electrochemical testing was performed by contacting the lithium electrode, electrolyte and Si nano-truss electrode (located on the SEM sample stage) and applying a bias voltage across the electrodes. Two types of electrolytes were explored: one approach was directly contacting the Li electrode and the Si nano-trusses with the Li2O layer on Li as electrolyte, and alternatively ionic liquid was used as electrolyte wetting and thus connecting both the Li and the Si electrode. In-situ SEM observations shows that mechanical reliability of Si electrodes can be controlled and improved by nano-architecture. Optimization of the structure of the nano-architectured electrodes could potentially simultaneously increase cyclability, energy density and rate capability of Li batteries.

To meet the future demands for sustainable energy supply and storage, novel systems needs to be considered. The Joint Center for Energy Storage Research is leveraging start-of-the-art modeling, characterization and synthesis techniques to pursue and realize such ideas. The materials challenges span both solid as well as liquid bulk and interfaces, and a comprehensive approach, which addresses the connection between different length scales, is needed. In this talk we will highlight some of the work that is being done within JCESR, particularly pertaining to multivalent (Mg²⁺, Ca²⁺, Al³⁺, Y³⁺ and Zn²⁺) solid cathode development and liquid electrolytes. While many structure classes (layered, spinel, olivine, etc) are known to intercalate and transport monovalent ions (Na⁺, Li⁺, H⁺, etc), the only inorganic materials that has been conclusively proven to reversibly intercalate MV ions have been based upon the Chevrel structure. Furthermore, few electrolytes are known that can weaken the strong oxide passivation layer, formed on the metal anode site, enough for ion intercalation. Hence, enhanced understanding as well as innovation is needed for both electrode materials and electrolytes. 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.

Increasing demand of high energy density and high capacity batteries require development beyond Li-ion technology, such as multivalent batteries, and innovations in electrodes and electrolytes, alike. Magnesium has been considered as one of the most promising materials for multivalent batteries not only because it&’s cheaper than Li but because it could theoretically provide at least twice the energy density as compared to the Li-ion batteries that are currently being used in electric vehicles and other electronic devices. However development and commercialization of Mg batteries require not only improved electrode discovery and development but also novel electrolytes which are compatible with the Mg metal as conventional electrolytes fail to penetrate the Mg metal passivation layer. Thus a fundamental understanding of molecular level properties of these electrolytes is required to improve the electrochemical stability and the charge transfer properties. An automatic High-throughput infrastructure has been constructed for the electrolyte genome project supported by the US Joint Center for Energy Storage Research (JCESR). In this work, we present classical molecular dynamics simulations coupled with ab initio calculations for Mg salts in various solvents. We present structure, dynamics and energetics of Mg electrolytes benchmarked against available experimental results. We observed significant change in the properties of Mg electrolytes as compared to Li electrolytes in terms of mobility as well as desolvation of the ions at the electrode interface.

Significant progress has been made in Na-intercalation compounds for rechargeable Na batteries. P2 type layered oxides NaMO₂ have been shown to have high capacity, good cyclability, and improved rate capability. In this study, we present results of first-principles calculations and ab initio molecular dynamics simulations on the diffusion mechanism in P2-NaMO₂. Our computational results demonstrate that P2 sodium metal layered oxides are fast Na ionic conductors over a wide range of Na concentrations. We identify the Na diffusion mechanisms in P2 at non-dilute Na concentrations and compare them to diffusion in an O3-type layered compound. Our results suggest that P2 outperforms O3 in Na diffusion kinetics and that P2 is a promising cathode material with high rate capabilities. Methods to improve the rate performance in P2-type materials will be discussed.

Using synchrotron based advanced characterization techniques to study the new electrode materials for lithium-ion batteries
Yongning Zhou¹, Enyuan Hu¹, Xiqian Yu¹, Seong-Min Bak¹, Xiao-Qing Yang^1*, Hung-sui Lee¹, Jun Ma², Zhaoxiang Wang², Kyung-Wan Nam³, and Yijin Liu^4
1Brookhaven National Laboratory, Upton, NY 11973
²Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
³Dongguk University-Seoul, Seoul 100-715, Republic of Korea
⁴Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory
*Email: [email protected]
In developing high energy density cathode materials, layer structured Li₂MoO₃ is a very interesting model compound to study. Here we report the structural studies and charge compensation of Li₂MoO₃ during the initial charge and discharge. The close to fully reversible structural changes and Mo ion migration, originated from the charge compensation of Mo ions in both the Mo-O and Mo-Mo covalent bonds in the Mo₃O₁₃ cluster, make Li₂MoO₃ an appropriate alternative of Li₂MnO₃ in constructing new xLi₂MoO₃middot;(1-x)LiMO₂ cathode materials, which may have less irreversible transition metal migration and oxygen evolution.
Recently, LiNi_0.5Mn_1.5O₄, denoted as LNMO, has attracted a lot of research attention as a promising high-energy density cathode material based on its higher operating voltage at ~4.7V vs. Li+/Li compared to the parent material, LiMn₂O₄.On the other hand, the poor cycle and calendar life of LNMO, especially at elevated temperatures, still remain one of the major challenges in its widespread applications. Extensive research has addressed some key factors determining its capacity and rate performance, such as cation ordering, transition metal substitution, and the Li-insertion/extraction mechanism. A combination of in situ synchrotron time-resolved x-ray diffraction (TR-XRD) coupled with mass spectroscopy (MS) and in situ x-ray absorption spectroscopy (XAS) during heating, as well as transmission x-ray microscopy (TXM) were applied to study the thermal stability of this material. The effects of Fe doping on capacity and thermal stability were also studied.
Acknowledgement
The work at Brookhaven National Lab. was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies under Contract Number DE-AC02-98CH10886. The TXM at SSRL was supported by NIH/NIBIB under grant number 5R01EB004321. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Stanford University. The work at Institute of Physics, Chinese Academy of Sciences was financially supported by the National Natural Science Foundation of China (NSFC No. 51372268) and the National 973 Program of China (2009CB220100).

Li-ion batteries (LIBs) have been widely utilized as the power sources in numerous applications from small portable devices to large-scale transportation systems such as various forms of electric vehicles (EVs). The development of new electrode materials with higher capacity, higher power, longer cycle life, and especially lower cost and better safety characteristics is required for the next generation of LIBs for EV applications. Because of their higher energy density, less toxicity, and lower cost compared to LiCoO₂, Ni-based layered cathode materials are being considered as one of the prime candidates for alternative cathode materials. Despite these advantages, the thermal instability of Ni-rich materials is the largest hurdle that must be overcome before their widespread usage.
In this research, we take advantage of real time electron microscopy to directly investigate the process of thermal decomposition as it occurs at the surface of Li_xNi_0.8Co_0.15Al_0.05O₂ (NCA) and Li_xNi_yMn_zCo_1-y-zO₂ (NMC) cathode materials that have been charged to different state of charge (SOC). Previous studies using x-ray based techniques, such as x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS), have concluded that the substantial safety issues associated with Ni-rich materials are closely related to the existence of a structural instability. There have been quite a number of studies that have investigated the evolution of the average crystallographic structure of the cathode materials as a function of either temperature or degree of delithiation. However, because the degradation of electrode materials and the initiation of thermal runaway may start very locally within electrode materials, a complementary method is required to elucidate where and how these phenomena start and propagate at the nanoscale. Transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS) allowed us to gain information regarding both the crystallographic and electronic structure modifications occurring in NCA and NMC materials, as well as the morphology of a local area at high spatial resolution. All the details will be available at the meeting.
Acknowledgement
This work was supported by the Korea Institute of Science and Technology (KIST) Institutional Programs (Project No. 2E25086 and 2Z04020). Research partially carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

The development of room temperature sodium based batteries is currently a challenge in fundamental materials research. Along this line, we recently reported on Na₂Ti₃O₇, a well-known oxide previously studied for a wide range of applications, which turned out to reversibly uptake 2 Na ions per formula unit (200 mAh/g) at an average potential of 0.3 V vs Na⁺/Na⁰. [1] To our knowledge, this is the first ever reported oxide to reversibly react with sodium at such a low potential, which could tentatively be coupled to any developed high potential positive electrode material to build high energy density Na-ion cells. These preliminary results were inspiring and prompted to optimism in terms of technology.
The recently reported [2] investigation of the redox mechanism in A₂Ti₃O₇ (A=Li, Na) upon additional alkali ion intercalation concomitant to reduction of titanium is discussed in this contribution. Even if the low stability of the reduced phases (A_2+xTi₃O₇) precluded a direct study, DFT calculations allowed to propose structural models for the reduced phases (A_2+xTi₃O₇), which were further successfully confronted to the available experimental data. They crystallize in the P2₁/m space group with the same structure exhibiting both lithium and sodium ions occupying 2e Wyckoff sites with octahedral coordination, leading to a distorted rocksalt type structure. Both experimental and computational results indicate that for the same layered framework, one can get very different redox potentials depending on the alkali ion present between the layers and on the alkali ion which is inserted. We have determined that for the layered-A₂Ti₃O₇ hosts (A being either Li or Na), Li insertion voltages are about 0.7 V higher than Na insertion voltages. Calculated average intercalation potentials are 0.37 V for Na insertion in Na₂Ti₃O₇ and 1.46 V for lithium insertion in Li₂Ti₃O₇, in very good agreement with the values observed experimentally (0.3 V and 1.6 V respectively). In addition, the lower polarizing character of Na ion produces the expansion of the cell volume, while the more polarizing Li causes its contraction. A combination of computational and experimental methods also assisted to elucidate the origin of the poor cyclability of Na₂Ti₃O₇ electrodes_.
[1] Senguttuvan, P.; Rousse, G.; Seznec, V.; Tarascon, J.-M.; Palacín, M. R. Chem Mater 2011, 23, 4109.
[2] G Rousse, M. E. Arroyo-de Dompablo, P. Senguttuvan, A. Ponrouch, J.M. Tarascon, and M. R. Palacín, Chem. Mater 2013, 25, 4946

Rechargeable Li-ion cells are the most vital parts of the portable & consumer electronics, computing & telecommunication equipment required by the present modern information-rich, mobile society. It provides a very light weight energy solutions to various devices and equipments, therefore the drive for discovering new materials to address the issues related to electrochemical storage in Li ion batteries like irreversible capacity loss of the battery electrodes during the first cycle of its operation, low capacities of anode electrode etc. has become imperative. The new low-cost and safe cathodes for next-generation lithium batteries have sparked an increasing interest in silicate materials. Among various orthosilicates, Li₂FeSiO₄ has been the most attractive due its high capacity and superior performance. We have investigated the effects of Na substitution, on the structural parameters and electronic properties of orthosilicates using Density Functional Theory. Our comparative analysis on the delithiation process of the pure and Na substituted orthosilicate materials have suggested enhanced performance of lithium ion batteries using these cathodes. The effects of Na substitution on the electronic and structural properties along with diffusion pathways for Li ions will be discussed.

The Li-rich, Mn-rich (LMR) layered structure materials exhibit very high discharge capacities exceeding 250 mAh g^-1 and are very promising cathodes to be used in lithium ion batteries. However, significant barriers, such as voltage fade and low rate capability, still need to be overcome before the practical applications of these materials. Here we report a systematic investigation on the structure revolution of a typlical LMR material, Li[Li_0.2Ni_0.2Mn_0.6]O₂. The structures of LMR cathode were analyzed by aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The detailed phase transformation pathway in the LMR cathode during cycling will be analyzed. The fundamental findings provide new insights into capacity/voltage fading mechanism of this material. Several novel approaches designed to mitigate the volage and capacity fade will also be reported. In one approach, the voltage and energy fade of LMR cathodes has been significantly mitigated by inproving the atomic level spatial uniformity of the chemical species in LMR nano particles. It is found that LMR cathodes (Li[Li_0.2Ni_0.2M_0.6]O₂) prepared by co-precipitation and sol-gel methods are dominated by LiMO₂ R-3m phase, show significant Ni segregation at particle surfaces and exhibit large voltage/capacity fade. In contrast, an LMR cathode prepared by hydrothermal assisted method is dominated by Li₂MO₃ C2/m phase with minimal Ni segregation. It also demonstrates much smaller voltage fade and excellent capacity retention. In another approach, the effect of the precursors and electrolyte additives on the cycling stability of LMR cathode materials will also be reported.
Acknowledgement
This work is supported by the Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U. S. Department of Energy, under the Batteries for Advanced Transportation Technologies program.

Li-O₂ batteries have attracted much academic and technological attention due to their considerable capacity increasing comparing with widely used Li-ion batteries. One of the main issues for the Li-O₂ battery is the development of a cathode O₂ electrode with high capacity and cycle stability. Mesoporous materials have high surface area and pore volume and interconnection channels, which are very good aspects as candidates for O₂ electrode. In this report, mesoporous manganese oxides with different phases, such as β-MnO₂, α-MnO₂, Mn₃O₄ and Mn₂O₃, as catalysts of the O₂ electrode for rechargeable Li-O₂ batteries have been evaluated.
The surface area of as-prepared mesoporous β-MnO₂, α-MnO₂, Mn₃O₄ and Mn₂O₃ are 138, 89, 41 and 131 m²/g, respectively. The cathode for the Li-O₂ battery was prepared by casting a mixture of 10 mg of the mesoporous manganese oxide powder and 3 mg PEFE-coated acetylene black as the conducting binder. The resulting mixture was pressed onto a stainless steel mesh, and dried at 100 ^oC for 4 h in vacuum. A piece of lithium foil was used as the anode, and was separated by two glass fiber films. The assembled cell was gas-tight except for the stainless steel mesh windows to expose the porous cathode to the O₂ atmosphere. A mixed solution of 1 M lithium bis-(trifluoromethanesulfonyl)imide, ethylene carbonate (EC), and diethyl carbonate (DEC) with a volume ratio (EC:DEC) of 3:7 was used as the electrolyte. It has been widely accepted that carbonate electrolyte, especially propylene carbonate, is decomposed easily. However, the EC/DEC electrolyte is stable less than 4.0 V. Therefore, in this present study, the charge-discharge curves were measured in the voltage range of 4.0-2.0 V (0.1 mA/cm²) to avoid the decomposition of the electrolyte.
The cathode containing mesoporous β-MnO₂ showed highest discharge capacity. The discharge capacity for the cathodes containing mesoporous β-MnO₂, α-MnO₂, Mn₃O₄ and Mn₂O₃ were around 1900, 1600, 900 and 700 mAh/g_carbon. The β-MnO₂ without mesopore (BET surface area is around 6 m²/g), which was prepared using the same method with the preparation of mesoporous β-MnO₂ except the usage of KIT-6 as hard template, was also checked. The discharge capacity for the cathode containing the no porous β-MnO₂ was around 700 mAh/g_carbon, which was much lower than the value for mesoporous β-MnO₂. For the cathode containing mesoporous β-MnO₂, the charging potential was around 3.7 V. After ten cycling numbers, the capacity for the cathode containing mesoporous β-MnO₂ well retained. The increased current density, such as 0.2 and 0.5 mA/cm² have also been applied to check the discharge/charge performance for the cathode containing mesoprous β-MnO₂. The mesostructure was demonstrated to be a very positive factor to increasing the discharge capacity of corresponding Li-O₂ batteries.

Silicon (Si) is a promising anode material for lithium ion battery (LIB), due to its relatively high capacity. However, two serious intrinsic defects, i.e., the low electrical conductivity and large volume change occurring in lithiation-delithiation reaction, result in the poor cycling performance of silicon anode. Herein, by an electrostatic layer-by-layer assembly method to combine the high capacity of Si, high conductivity of copper/copper oxide (Cu), and excellent flexibility of polyurethane (PU), we get a PU/Cu/Si composite film. Because of the high electrical and mechanical properties, this film anode can afford great volume change during charge-discharge process, and therefore exhibits improved cycle performance for LIB.

Over the years, transition metal oxides (TMOs) have been demonstrated as a suitable replacement to graphite as anode in a li-ion battery due to their advantages such as high specific capacity, widespread availability and better safety [1]. Among various TMOs, iron oxide is particularly attractive as it is low cost, eco-friendly and has high theoretical capacity (1007 mA h g ^-1 for α -Fe₂O₃ and 926 mA h g ^-1 for Fe₃O₄) [2]. However, its major drawback is rapid charge/discharge capacity decay owing to high volumetric change associated with Li⁺ insertion and extraction [3]. In order to address this issue one approach is nanostructuring of iron-oxide [4]. Among various synthesis techniques to fabricate iron oxide based nanostructures, electrochemical anodization is particularly attractive due to its simplicity and cost-effectiveness [5]. Through anodization one-dimensional iron oxide nanotubes (NTs) arrays can be grown having unique vertical tubular morphologies. Such structures are helpful in increasing the electrode surface area for Li intercalation and also improvement in the surface electron transport properties.
In this work, high aspect ratio vertically oriented arrays of iron oxide NTs with a thickness of 5mu;m and pore diameter of around 100nm are fabricated by anodization of iron foil. The samples are then annealed in an oxygen atmosphere at 500 ^oC for 1 hour to obtain α-Fe₂O₃ and Fe₃O₄ crystalline phases. The FE-SEM images show the formation of well defined high aspect ratio one-dimensional nanotube arrays, while the X-ray diffraction and Reitveld analysis shows α-Fe₂O₃ phase as the dominating phase along with Fe₃O₄ phase. The electrochemical analysis shows a highly satisfying electrochemical response in terms of charge/discharge capacity, rate capability, cyclic performance and columbic efficiency. The enhanced performance is attributed to high surface area, short diffusion path and fast kinetics of the unidirectional oriented iron oxide nanotube arrays.
References:
[1] P. Poizot, et. al., Nature, 2000, 407, 496
[2] L. Taberna, et. al., Nat. Mater., 2006, 5, 567.
[3] C. Liu, et. al., Adv. Mater., 2010, 22, E28
[4] B.Wang, et. al., J. Mater. Chem., 2012, 22, 9466.
[5] K. Y. Xie, et. al., . Mater. Chem., 2012, 22, 5560.

In the light of the gradual depletion of conventional energy resources and the environmental crisis, the development of advanced energy storage devices including rechargeable batteries and supercapacitors is essential for the sustainable supply of power. Nickel hydroxides (Ni(OH)₂) are widely used as the electroactive material for batteries and pseudocapacitors due to their cost effectiveness and the well-defined redox process. Their limited electrical conductivity, however, has been addressed as the problem obstructing the ideal performance of Ni(OH)₂-based electrodes. In recent years, extensive research has been carried out to improve the electrode conductivity through chemical doping and morphology control of active materials in nanoscale. Here we discovered the competitive effects between morphology and chemical doping on the electrochemical performance of metal hydroxide electrodes. The morphology of Ni(OH)₂ was controlled and modified by adding glucose to the ethanol-mediated solvothermal synthesis. Ni(OH)₂ produced in this manner exhibited increased specific capacitance due to the reduced particle/flake size. In this size-reduced material, distance for mass transport can be shortened and thus, the internal resistance decreased. In addition, Ni(OH)₂ prepared with glucose showed high water content both on the surface and in the interlayer galleries, which is favorable for ion and electron mobility in the material. This high water content can be explained by the increased specific surface area of Ni(OH)₂, which is available for water molecule adsorption. During the alcohol-based solvothermal treatment, glucose undergoes ethanolysis through which α-hydroxyl groups are substituted by ethoxy groups. Unlike in the hydrothermal treatment of glucose, carbon formation was not observed due to the removal of α-hydroxyl groups, which participate in the condensation reaction for the polymerization of glucose prior to the carbonization. These glucose ethanolysis products can also serve as nucleation sites for Ni(OH)₂. They, especially at high concentrations of glucose, limit the diffusion of Ni precursors during synthesis and therefore, inhibit growth of Ni(OH)₂ particles into larger crystals. Additionally, we discovered that doping of materials with cobalt to form cobalt doped-nickel hydroxide (Co_xNi_1-x(OH)₂, x = 0 - 1) also improved specific capacitance. Interestingly, specific capacitance improvements by glucose is becoming less efficient at high cobalt contents and more efficient at low cobalt contents. This tendency revealed the existence of competitive effects between doping and morphology. The discussion on the origin of such observation will be presented in detail.

Lithium phosphates are promising candidates as lithium ionic conductor material for high-energy batteries and other related technologies. Indeed, they are materials permeable to lithium ions and impermeable to electrons, which serve as good candidate for a solid electrolyte. In addition, they have light weight and wide potential range of stability vs. lithium and lithium containing electrodes. Although lithium phosphate electrolytes have not been used in practical lithium-ion batteries because their ionic conductivities are generally too low to meet the required current densities, Li₃PO₄ nano-coatings have been reported as surface modifier to improve electrode stability upon cycling at fast kinetics.1-3 Chemical modifications of Li₃PO₄ might results in interesting ionic conductors. Moreover, the preparation of different Na-substituted Li₃PO₄ compounds could lead to novel sodium conductors. Note that Na₃PO₄ is a fast sodium ion conducting compound.
We expect to improve the ionic conductivity of Li₃PO₄ by partial replacement of Li⁺ by other ions. With this aim we have attempted to prepare several members of the Li_3-xNa_xPO₄ family to explore their ionic conductivity.4 A simple and cheap way for preparing orthorhombic Li₂NaPO₄ powder is successfully developed by wet-chemical method followed by optimal thermal treatment at 700 0C. It is the first time that the ionic conductivity of Li₂NaPO₄ is reported, leading to 6.5 10-6 and 1.5 10-5 S cm-1 at 25 and 700C, respectively. The conductivity value is higher than that of β- and γ-Li₃PO₄ phases by about two orders of magnitude, making very appealing candidate for future solid electrolytes in batteries.
The good ionic conductivity found in napiolite-Li₂NaPO₄ makes appealing exploring novel polymorphs of Li_3-xNa_xPO4 (0 < x < 3) compounds. With this aim, first principles calculation at the Density Functional Theory (DFT) level have been used to investigate the relative thermodynamic stability of Li_3-xNa_xPO₄ compounds within the crystal structures of nalipote, γ-Li₃PO₄ and β-Li₃PO₄.
1. S. X. Zhao, H. Ding, Y.C. Wang, B.H. Li, C.W. Nan, J. Alloys Compd. 2013, 566, 206.
2. M. C. Loacute;pez, G. F. Ortiz, J. R. González, R. Alcántara, J. L. Tirado, ACS Appl. Mater. Interfaces, 2014, 6, 5669.
3. X.B. Wu, S.H. Wang, X.C. Lin, G.M. Zhong, Z.L. Gong, Y. Yang, J. Mater. Chem. A. 2014, 2, 1006.
4. M.C. Loacute;pez, G.F. Ortiz, E.M. Arroyo-de Dompablo, J.L. Tirado, Inorg. Chem., 2014, 53, 2310.

The demand for improved energy and power densities necessitates the engineering of novel electrode architectures in lithium-ion batteries (LIBs). Nanocarbon materials (graphene and carbon nanotubes) are characterized by exceptional structural, mechanical, and electrical properties. Three-dimensional (3D), free-standing, highly porous, nano-engineered electrodes composed of nanocarbon materials are promising candidates for enhanced LIB performance. This study focuses on the controlled fabrication of high-quality 3D nanocarbon foams and their application as anode materials in LIBs. The results of the study have established connections between the properties of the 3D nanocarbon foam and the electrochemical behavior.

While lithium-ion batteries are the dominant technology in the energy storage market, a key challenge is the inability to meet the ever-increasing consumer demands for higher capacities and rapidly-emerging device features. Silicon nanoparticles, as one of the most promising candidates for the high-capacity anode materials offer a potential solution to address the problem. However, this technology is currently limited by the large volume expansion during discharge-charge cycles. This report describes recent results of an investigation of the preparation and characterization of different silicon-carbon nanocomposites as the anode materials. The morphological and structural features (e.g., nano-porosity, doping, etc.) of the nanocomposite materials can be controlled by a combination of the processing and treatment parameters, showing promises in increasing the charge-discharge cycle life and discharge capacity as high as ~3500 mAh/g(Si). The initial findings have significant implications to further refinements of the design parameters for better performances and different platforms, including flexible batteries.

As portable electronics such as smartphones and flexible displays rapidly emerge in the consumer electronics market, one of the biggest problems linked to the existing Li-ion batteries as power sources concerns the low capacity, large weight, and lack of conformal adaptivity. The combination of high capacity anode materials with light-weight and flexible platform may offer an effective way to address the problem. This presentation describes the development of flexible lithium-ion batteries featuring high capacity, light weight, low cost, and conformal integration as power sources for potential applications in portable electronics and medical devices. The basic approach couples the ability to engineer the flexible electrode devices by roll-to-roll manufacturing and printing/sintering processes, and the capability to process the anode materials by formulating silicon-based nanocomposites. Initial results demonstrating the feasibility of nanoparticles printing and laser sintering on flexible substrate for constructing flexible batteries will be discussed. Implications of the results for designing printable, rechargeable lithium-ion batteries with wearable, light-weight, and high-capacity features will also be discussed.

Li₂MnO₃-based composite materials have emerged as the most promising lithium-ion cathodes since they can deliver high discharge capacity (>250 mAh/g) and withstand at high operating voltage (>4.5 V). Among the composite cathode materials reported so far, layered-layered Li₂MnO₃-LiMO₂ composites exhibited good lithium-ion intercalation properties. This is possibly due to the structural compatibility between monoclinic Li₂MnO₃ and rhombohedral LiMO₂ components and electrochemical activation of Li₂MnO₃ ca. 4.45 V while charging the cells. The studies performed on various composite cathodes revealed that performances of LIBs highly depend on the composition of LiMO₂. In the present work, a novel xLi₂MnO₃-(1-x)LiNi_0.3Mn_0.16Co_0.04O₂ metal oxide having low content of cobalt is investigated as a safe cathode for lithium-ion batteries. Structural and electrochemical aspects of the material are investigated using advanced in-situ and ex-situ spectroscopic/microscopic techniques.
Sol-gel technique with suitable annealing conditions was employed to synthesize highly crystalline material. Phase purity of the prepared material was checked with powder X-ray diffraction and Raman spectroscopy. The analysis confirmed the existence of both monoclinic and rhombohedral components in the as-prepared material. From XRD studies the peaks observed in the 2theta; range of ~ 21 - 300 revealed the presence of short range ordering corresponding to monoclinic Li₂MnO₃ with space group. In Raman spectra the peaks present at 482 cm^-1 and 596 cm^-1 correspond to the rhombohedral LiMO₂ structure with space group R3/m and the peak at 420 cm^-1 corresponds to the monoclinic Li₂MnO₃ with space group C2/m. SEM studies were performed in order to check the morphology of the prepared material. XPS studies helps to find out the oxidation state of the transition metal ions present in the compound. The electrodes were prepared using active material, carbon black and PVDF in 8:1:1 ratio and spread over Al foil which acts as a current collector. Coin cells were fabricated inside Ar filled glove box using the coated material as cathode, Li metal foil as anode and 1.2M LiPF₆ in 1:2 ratio of EC: DMC used as electrolyte. Charge discharge, electrochemical impedance spectroscopy and cyclic voltammetry studies were carried out for these cells. The structural and electrochemical properties of this new cathode material will be presented in detail.

Graphite has been widely used as an anode material in lithium ion batteries. However, graphite does not have enough capacity for electric vehicle application. For higher capacity batteries, there is significant interest in the use of metal alloy anode materials which have higher theoretical capacity. Much research is focused on these materials, including tin (Sn). Tin material has almost three times higher capacity (944 mAh/g) than graphite (372 mAh/g). The major challenge to use this Sn-based material is volume expansion during lithium intercalation which results in insufficient solid electrolyte layer (SEI) formation and degradation of electrolyte and anode material. Many studies have introduced new fabrication techniques for Sn-based anodes to overcome problems of volume change. However, not many investigations have focused on SEI formation on Sn-based anode. To minimize the effect of surface area changes, a better understanding on SEI is required.
In this investigation, Sn-based anodes were prepared with Sn nano-particle and battery cycling performances were investigated with 1.2M LiPF₆ in EC/DEC electrolyte. The SEI stabilizing additives (FEC, VC and etc.) were added with different concentration and compared the performance. Best cycling performance was observed with FEC additive. VC containing electrolytes also have better performance than standard electrolyte. To characterize the structure of SEI, ex-situ surface analysis has been performed on cycled electrode with FTIR, XPS and SEM. This structural analysis provide exactly what components exist on SEI and provide the information for better SEI formation.

In an effort to reduce the cost of manufacturing lithium ion batteries, a novel layer by layer approach is being developed to prepare lithium ion batteries. The layer by layer approach offers a significant advantage over traditional rolling or stacking of multiple component cells by providing excellent contact and thinner separator layers. In addition, the method has the potential to conserve space and conserve energy density while also being a lower cost process.
The initial stacks used with this method were anode and cathode half stacks. Each half stack consists of a current collector, an electrode, and a 10 µm thick separator combined into a single component. The anode and cathode half stacks have been investigated in Li/anode and Li/cathode coin cells (half cells). The initial anode and cathode half cells were investigated at a low cycle rate (C/20) and provided excellent cycling performance. Variable rate performance was also utilized to investigate the rate capability of the cells. The anode and cathode half stacks were then used to construct full cells, where the separators of each stack stood face to face to simulate a layer by layer deposited full cell. The graphite/LMO cycled well possessing good performance both at low rates (C/20) and moderate rates (C/5). Cross sectional SEM images were acquired for fresh stacks and stacks cycled in full cells to investigate the mechanical stability of the novel electrodes. The SEM images reveal very little change in the anode and cathode materials upon cycling. Further optimization of the layer by layer deposited electrodes along with post-mortem analysis of the electrodes will be discussed.
Acknowledgement
Special thanks for the funding of this project go to Optodot and the U.S. Department of Energy grant number DE-EE0005433

Solid-state supercapacitors are promising candidates to fulfill today&’s requirements for portable, lightweight, and flexible energy storage systems. Activated carbon (AC) has been widely used as an electrode material because of its high surface area, chemical stability and low cost. Perfluorinated ionomers such as Nafion® are used as solid electrolytes, since they provide an ionic conducting electrode separator and binding substance. Various techniques have been used to further understand the electrode-electrolyte relationship in the storage mechanism of supercapacitors. There has been growing evidence that the mechanism depends strongly on the geometry, porosity and particle distribution throughout the electrode. Therefore, a precise characterization of these variables is of paramount importance. In this work we have studied supercapacitor electrodes as a function of AC concentrations by using scanning transmission electron microscopy. We have obtained maps of AC surface areas using x-ray and electron energy loss spectroscopies, with results correlated to the impedance of macroscopic capacitors.

Silicon (Si) has attracted considerable attention as an anode material in Li-ion batteries (LIB) because of its high theoretical capacity (4200 mAh/g), which is over 10 times higher than that of conventional graphite anodes. However, Si anode material suffers from large volume expansion (>300%) and the subsequent structural collapse of the electrode during lithiation-delithiation cycles, resulting in poor conductivity and drastic capacity fading. In order to circumvent this issue, alloy of Si with a Li-inactive element have been employed to minimize structural changes inside the anodes and improves electrochemical activity of the electrodes. But, Li-inactive metallic materials used to fabricate the Si alloys are prone to oxidation in the fabrication process and undermine its electrical properties compared to the element. In addition, due to the use of micro-size materials, to achieve uniform integration of metals into Si alloys, it usually requires a high temperature mechanical process for a long time. Keeping these problems in mind, in this work Siminus;Ti oxide/rGO nanocomposite was prepared by mild mechanical ball milling of Si nanoparticles, titanium (Ti) oxide nanoparticles, and rGO nanosheets, followed by thermal treatment to reduce TiO₂ (Ti⁴⁺) to Ti₂O₃ (Ti³⁺). In particular, Ti₂O₃ improved electrical characteristics on the basis of the phase, which is reduced by heat treatment. Therefore, Ti oxide in the Si-based alloy provides the role of the matrix to alleviate the stress caused by the volume change of the Si electrode and improves the conductivity of the composite electrode during the repeated cycling. As a result, the novel Si-Ti oxide/rGO nanocomposite achieves the significantly improved reversible capacity and steady cycleability. We anticipate that this system would further be extended to other nanocomposites as high-performance anode materials for Li-ion battery applications.

Rechargeable lithium-oxygen batteries are expected to have energy densities several times higher than those of state-of-the-art lithium-ion batteries. If successfully developed, therefore, they could enable electric vehicles with driving ranges similar to those of gasoline-powered vehicles. Carbon is the most widely used cathode material for non-aqueous Li-O₂ batteries. During discharge-charge cycles, however, carbon becomes unstable and promotes electrolyte decomposition, which results in large discharge-charge voltage gaps (low round-trip efficiency) and poor cycle life. In recent years, a carbon-free cathode design has been proposed as a promising strategy to mitigate the carbon-induced problems. In addition to making cathodes chemically and electrochemically stable, tailoring cathode structures in nanoscale is of vital importance for high-performance Li-O₂ batteries. Nanostructural engineering may be more critical for non-carbon cathodes that are usually made of much heavier and less porous materials (compared to carbon). Here, we report a new, carbon-free electrode design based on non-precious transition metal oxides. In particular, we propose a cathode architecture with a high porosity and a large surface area that consists of numerous one-dimensional nanoneedle arrays decorated with thin nanoflakes. The oxide-only cathodes show high specific capacities and remarkably reduced charge potentials as well as excellent cyclability, due to their unique design features: 1) the carbon- and binder-free cathode reduces the parasitic reaction with Li₂O₂ and thus promotes reversible formation and decomposition of Li₂O₂; 2) micro- and macro-pores among 1-D nanoneedles offer a large amount of open spaces for Li₂O₂ accumulation, while reducing mass transport limitations; and 3) the nanoflakes deposited on nanoneedles provide a large number of active reaction sites.

Geographical limitations and uncertainties about the availability of lithium resources have led researchers to develop alternative battery chemistries such as Na-ion battery. The Na-ion battery has great potential due to the abundance and low price of sodium precursor for large scale energy storage devices. Thus, recently considerable research interest in Na-ion batteries has been rapidly increasing. Spinel NiCo₂O₄ has been widely investigated as a promising alternative anode material for Li-ion batteries due to its several inherent advantages, including low cost, abundant resources and good environmental benignity. In particular, NiCo₂O₄ can offer at least twice the capacity of the most common intercalation anode materials and possesses much better electronic conductivity compared to the binary transition metal oxides. The high electronic conductivity is beneficial for fast electron transfer in an electrode, however, the practical applications to the anode material are largely hindered due to its poor cycling performance. Nanostructural engineering can provide facile ion kinetics by a shorter diffusion length, high surface area and better accommodation of the strains, which results in improving the electrochemical energy storage properties. In this work, NiCo₂O₄ nanoneeldes were fabricated by a hydrothermal route. The physicochemical properties of the NiCo₂O₄ were characterized and the sodium storage performances were investigated. This study suggests that the spinel NiCo₂O₄ nanoneedles can be used as a promising anode material in Na-ion batteries.

Silicon (Si) has been considered a promising electrode material for Li-ion batteries because of its high energy density. This property originates from incorporation of a high concentration of Li atoms, low discharge potential (~0.5 V versus Li/Li⁺), natural abundance, and environmental benignity. Even with these advantages, implementation of Si electrodes has been limited due to poor capacity retention resulting from large variations in its volume and its unstable solid-electrolyte interphase (SEI) during cycling. To resolve this inherent issue of Si, here, we report one dimensional (1D) Si-based multicomponent amorphous alloy nanofibers (Si₆₀Al₃Fe₅Ti₂Sn₁₂Ce₁₈ NFs) synthesized via electrospinning, followed by graphene-wrapping as an ultra-long cycle, high-performance anode material. Several characterizations showed that a web of 1D nanofiber exhibits little change in volume through compositional optimization in light of critical electrochemical parameters such as reversible and irreversible capacities. There was no active-metal-particle agglomeration (in particular for Sn nanoparticles, which melt at relatively low temperature (231.9 ^oC) and tend to be segregated into agglomerates at temperature higher than the melting point), or exclusion out of the fibers (resulting in stable SEI layers on the nanofibers, with graphene-shell suppressing direct growth of the SEI layer). Therefore, this unique anode, involving highly stable electrochemical surfaces and excellent dimensional stability, exhibited superior cell performance during charge/discharge. Its high specific capacity was maintained for up to 400 cycles (1,017 mAh/g at 50 mA/g) in Si₆₀Al₃Fe₅Ti₂Sn₁₂Ce₁₈NFs, with a graphene wrapping layer (Si₆₀Al₃Fe₅Ti₂Sn₁₂Ce₁₈ NFs at rGO); and it achieved a cycle-life of 2,100 cycles with capacity 556.47 mAh/g at current density of 0.5 A/g. Our novel concept for the Si anode suggests a new design principle for multicomponent amorphous alloys. This work demonstrates importance of choice of element in amorphous matrix and is particularly promising because it combines the structural advantages of Si-based amorphous alloy nanofibers, with the ubiquitous electrospinning technique, for the first time. This, we hope, will fuel development of amorphous Si-based and Sn-based anode materials that can be synthesized by electrospinning which has emerged as a powerful and versatile manufacturing method and will provoke quite a stir in fields of research related to amorphous alloys.

In the last few decades, successes of lithium ion batteries (LIB) on increasing energy density have allowed us to downsize of electronic devices and develop a wide variety of portable and wearable devices. With these successes, a next challenge is ongoing to apply LIB to large-scaled systems, such as electric vehicles, smart grid system. The development of large-scaled LIB is, however, rather slow, which are not only because of electrochemical performance (energy density, power density, cycle life) but also for cost, reliability and safety. All solid-state batteries employing nonflammable solid electrolytes are one of plausible solution to improve reliability and safety, but they suffer from poor rate capability mainly due to difficulty in fabricating interfaces for smooth ion transportation between solid electrolytes and active materials. In this paper, we report a novel energy storage device of a lithium-bromine battery (LBB) employing a solid electrolyte and aqueous active materials. This battery consists of nonflammable materials. And a good rate-capability is expected because of the liquid | solid interface.
A prototype of LBB was assembled using a NASICON-type lithium ion conducting solid electrolyte sheet in the system of Li-Al-Ti-Ge-P-Si-O (OHARA Inc.). Li metal and porous carbon were used as an anode and a cathode current collector, respectively. A glass filter soaked in an organic electrolyte solution was inserted between the Li anode and the solid electrolyte sheet to prevent the solid electrolyte from reduction. A catholyte was aqueous LiBr solution. Electrochemical performance of the cell was examined by cyclic voltammetry, galvanostatic charge-discharge tests and electrochemical impedance spectroscopy (EIS), respectively.
The prototype cell showed a discharge capacity of c.a. 100 mAh (g-LiBr)^minus;1, for the first cycle, which was smaller than theoretical capacity of 309 mAh (g-LiBr)^minus;1. This is due to large polarization, which was originated mainly from resistance between solid electrolyte and catholyte, according to EIS recorded on symmetrical cells. In this paper, origin of the interfacial resistance will be discussed in details.

Thin-film batteries have recently become the topic of widespread research for use as efficient energy storage devices. Spinel Li₄Ti₅O₁₂ has been considered as one of the most prospective anode materials for Li-ion batteries because of its excellent reversibility and long cycle life. We report here the sol-gel synthesis and coating preparation of spinel thin-film Li₄Ti₅O₁₂ electrodes for Li-ion microbatteries using lithium ethoxide produced in situ that reacts with titanium alkoxide to produce the precursor solution without particle precipitation. This synthesis procedure reduces the thermal treatment to obtain a pure phase at only 700 °C and 15 minutes. The physical and structural characterization of the 300 nm Li₄Ti₅O₁₂ coatings shows a very homogeneous distribution of elements and a pure spinel phase. Galvanostatic discharge-charge tests indicate maximum discharge capacities of 152 mA h g^-1 when the material is treated at 700 °C for 15 minutes. Results from this synthesis procedure will be compared with another one using titanium alkoxide and lithium acetate, the two more usual precursors.
This work has been supported by the Spanish Science and Innovation Ministry under project PLE2009-0074 from National Program for I+D internationalizing (ACI-PLAN E). J.M. thanks CSIC program JAEdoc.

Electrochemical capacitors or supercapacitors are new kind of energy storage devices which have high efficiency and outstanding properties such as high power density and long life cycle. In order to reach high capacitance, choosing the electrode material is very important. Porous carbon material is a great candidate because of its excellent properties such as high surface area, easy to process, flexibility of morphology design. Polybenzoxazine prepared via a sol-gel method was used as a carbon precursor. Cetyltrimethyl ammonium bromide (CTEB) was used as a soft template. Adjusting concentration of CTAB was required so as to find the best condition to obtain the highest amount of mesoporous porous carbon. In order to enhance the capacitance by faradic redox reaction, metal oxide (1, 3, and 5 wt.%) was incorporated into the electrodes. The electrochemical properties of electrode were investigated by electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge/discharge.

Li-La-Zr-O thin films were successfully fabricated using the sol-gel spin coating method and the effects of altering the annealing temperature and the number of layers of the films on electrolyte conductivity were studied. Using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), the characteristics of these films were investigated as a function of annealing temperature and the numbers of layers of the film. With these methods, an amorphous structure and smooth surface on the films was revealed. The thin film&’s ionic conductivity was investigated by impedance analysis. The results show that the ionic conductivity of the films decreases with an increase of the annealing temperature, from 1.67'10^-6 S cm^-1 for 600°C to 8.53'10^-7 S cm^-1 for 800°C. The influence of film thickness on conductivity was investigated and the conductivity followed an inverse u-shaped curve with increasing film thickness. We propose that Li-La-Zr-O thin films may be a promising solid electrolyte for thin-film lithium-ion batteries.

PilHo Huh^a, Bong-Soo Kim^b, Seong-Cheol Kim^c*
a Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, South Korea
^b Department of Advanced Materials & Applied Chemistry, Kyungnam College of Information & Technology , Busan 617-701, South Korea
^c Department of Nano, Medical and Polymer Materials, Yeungnam University, Gyeongsan, Gyeongbuk 712-749, South Korea
The chemical bonding of conjugated polymer and solid polymer electrolyte matrix was achieved as a supramolecular network structure by grafting-combination of poly (aminobenzyl alcohol) (PABA) with poly (ethylene glycol) (PEG). PABA was utilized as the frame for the ladder and the PEG as the rungs. The ion transport and backbone mobility of a PABA-PEG based Li⁺ ion conductor were investigated as a function of its structure, optical property, and ionic conductivity. The insertion of the ionic salts into the conjugated PABA-PEG supramolecular network led to the improvement of the ionic conductivity compared to that of PEG/LiClO₄. This synergic effect may preferentially be explained as more efficient segmental motion of the polymer chains or better ion mobility in the network due to the interrupted crystallization of the PEG chains. Positive charges could migrate within the string-like clusters without the cations actually moving. This may imply that when the ion clusters are able to be aligned along the polymer backbone, an ion conduction pathway could be well formed, which might potentially promote ion transport. The fine tuning of the conjugated polymer in supramolecular network structure might enable it to show a faster response to electrochemical stimuli.

Relaxor fluorinated polymers, polyvinylidene fluoride derivatives, are being actively explored as high dielectric materials for electrical energy storage applications^1),2). However, their high dielectric constants are accompanied by large dielectric losses due to ferroelectric hysteresis with transformation of molecular conformations, resulting in poor charge-discharge efficiencies. In order to reduce the dielectric losses while keeping the high dielectric constant, here we propose a new nanostructure-controlled PVDF based polymer films with tanδ < 1% (0.6%) and ε = 13 at frequency of 1kHz. We investigated crystalline-structures vs. dielectric-properties relationship by characterizing the representative PVDF based copolymers and terpolymers with different crystalline phases developed for energy storage application^1),3). We found that the large dielectric losses from 10¹ to 10⁵ Hz were mainly due to the α crystalline phase which is necessary to induce the high dielectric constant of the terpolymers. The large conformational changes during electric field-induced dipolar switching of β-phase through α-phase should be the origin for the large dielectric losses. Based on these understandings, we have developed a model nanostructure to realize low tanδ with high ε, and verified it by making cast films composed of newly-synthesized PVDF graft polymers with one-directional extension processes⁴⁾. Their nanostructures were characterized by using FTIR & XRD and it was found that surprisingly the α-phase still existed in the films with reduced dielectric losses. The microscopic mechanism and future prospect for further reducing the dielectric losses will be discussed as recently investigated by using theory and molecular dynamics simulation^5,6).
REFERENCES:
1) R. Su et al., Polymer 53, 728 (2012).
2) P. Khanchaitit et al., Nature Comm. 4, 2845 (26 Nov, 2013).
3) K. Tashiro: Crystal structure and phase transition of PVDF and related copolymers: H. S. Nalwa eds., Ferroelectric Polymers (Marcel Dekker, NY, 1995) Chapter 2, p.63.
4) J. Li et al., J. Mater. Chem. 22, 23468 (2012).
5) V. Ranjan et al., Phys. Rev. Lett. 108, 087802 (2012).
6) Philip Taylor et al., Abstract No. A33.00004 for the March 2013 APS Meeting (Mar 18, 2013, Baltimore MR, USA).

We demonstrate synthesis and electrochemical performance of novel molecular precursor-derived ceramic (PDC)/carbon nanotube embedded graphene self-supporting composite papers as Li-ion battery electrode. The papers were prepared through vacuum filtration of various PDC-graphene oxide (GO) dispersions in DI water followed by thermal reduction at elevated temperatures that resulted in a homogenous PDC/reduced GO papers that were highly crumpled, mechanically robust and consisted of a 3-D electrically conducting network. These electrodes showed electrochemical capacities as much as approx. 300 mAh.g^-1 with respect to total weight of the electrode (approx. 500 mAh.g^-1 w.r.t. active material), with negligible capacity loss for more than 1000 cycles. Boron-doped silicon carbon nitride (Si(B)CN/graphene) outperformed its un-doped counterparts (SiCN/graphene), both in terms of electrochemical capacity, cycling stability and coulombic efficiency.

With increasing demand of high energy storage capability, many researchers have developed various types of battery systems with optimized structure and materials. In particular, metal-air batteries are considered to be a strong candidate of next generation energy storage systems due to their potential advantages such as light weight and high energy storage capability. Among metal-air batteries, Li-air batteries offer the most promise for extremely high persistence applications. However, there still exist a lot of technical barriers to be overcome, and the challenges include low rate capability, a poor cycle life, and instability of electrochemical performances. The practical discharge capacity is far lower than the theoretical values because the reaction products (Li₂O or Li₂O₂) are difficult to be dissolved in the non-aqueous electrolyte and they can block the oxygen path for oxygen diffusion. Due to these reasons, the performance of the Li-air battery strongly depends on the characteristics of carbon-based cathodes.
Recently, there have been some attempts to produce carbon materials by simple carbonization of metal organic frameworks(MOFs) for energy storage systems.The sacrificial MOFs precursors were directly carbonized under inert atmosphere.The carbonized MOFs as cathode materials are known to have various advantages. Their structures can be designed and tunable in accordance with desired properties by selecting type of MOFs.
In this work, we demonstrate the application of the carbonized MOFs as thecathode material in non-aqueous Li-air battery. Various techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) were employed to characterize the morphology and crystalline structure of the framework system. The Brunauer-Emmett-Teller (BET) was utilized for the analysis of the surface area and porosity of the sample. The electrochemical properties of the carbonized MOF as the cathode electrode in Li-air battery were studied using the galvanostatic charge-discharge characterization method. The synthesized carbonized MOFs shows large specific surface area and narrow pore size distribution. It was shown that the open channel architecture of the MOF enhances the oxygen gas supply to the interface between the electrolyte and the cathode surface.
Acknowledgement
This research was supported by the MSIP(Ministry of Science, ICT and Future Planning), Korea, under the “IT Consilience Creative Program” (NIPA-2014-H0201-14-1002) supervised by the NIPA(National IT Industry Promotion Agency)

The properties of the solid-phase redox end-members (α-S, β-S, Li₂S, and Li₂S₂) are expected to strongly impact the performance of Li-S batteries, yet have not been widely studied. From a computational standpoint, the absence of this data can be partially explained by the molecular-crystal nature of elemental sulfur. That is, the omission of essential, long-ranged van der Waals interactions in conventional Density Functional Theory (DFT) complicates the analysis of S via first-principles methods. To address these limitations, here we apply state-of-the-art van der Waals augmented DFT (vdW-DFT) and quasi-particle methods (G₀W₀) to predict various structural, thermodynamic, spectroscopic, and electronic properties of these phases. These include: phase stability, bandgaps, surface energies, and equilibrium crystallite shapes. Special attention is given to the properties of Li₂S₂, whose presence in the discharge sequence remains a matter of debate.

Successful replacement of germanium with the isovalent ion silicon in the crystal Li₁₀SiP₂S₁₂ presents a cost effective constituent for a solid lithium superionic conductor. Tetragonal Li₁₀SiP₂S₁₂ displays a conductivity of 2.3 x 10^-3 S cm^-1 prior to sintering, the highest reported conductivity for a silicon-based solid electrolyte to-date. Performance, purity, and thermodynamic stability of Li₁₀SiP₂S₁₂ are correlated to the state of precursor amorphization prior to crystallization. The crystalline properties of Li₁₀SiP₂S₁₂ along with ionic conduction capabilities are in excellent agreement with the predictive modeling previously performed for this material. Li₁₀SiP₂S₁₂ presents one of the most enduring metastable crystals in contact with lithium - manifesting in an exceptionally cycling lithium metal secondary battery.

LiNi_1-x-yCo_xMn_yO₂ (NCM) cathode material has been a promising material for electric vehicle (EV) applications due to its safety, low cost, and high rate capability in lithium ion batteries (LIBs). However, the deposition of dissolved transition metals on the anode surface is a serious problem, because it can lead to further electrolyte decomposition, increase of impedance and deterioration of rate capability. Since the metal deposition is strongly related to the desolvation tendency of metal ions from solvents and additives, it was expected that the binding energy of additive with transition metal ions (Ni²⁺, Co²⁺, and Mn²⁺) is a key factor to suppress the desolvation of transition metal into anode surface. Thus, to compare the binding energies of various anions with metal ions, density functional theory (DFT) calculation was performed, and it showed that the novel electrolyte additive FC-211 has the strongest binding energy at the molecular level. Cyclic voltammetry (CV) and scanning electron microscope (SEM) results also supported that the deposition of transition metal was effectively suppressed by the addition of FC-211 as predicted by calculation. In addition, additional introduction of FC-220 effectively suppressed Cu dissolution from current collector which causes a negative effect on full cell performance. Electrochemical impedance spectroscopy (EIS) and direct current internal resistance (DCIR) tests revealed that a less resistive solid electrolyte interphase (SEI) layer was formed by introducing FC-211/FC-220 after cell cycling. This is mainly because FC-211/FC-220 prevents the additional electrolyte decomposition which can be caused by transition metal deposition on anode surface. Also, the FC-211/FC-220 derived SEI layer exhibited a relatively low resistance change even after high temperature (60^oC) storage at various state of charging (SOC) levels. As a result, the FC-211/FC-220 added electrolyte showed a significantly improved discharge capacity at high c-rates because of the enhanced lithium ion diffusion through the SEI layer.

Lithium-sulfur (Li-S) battery is one of the most promising advanced battery beyond the conventional lithium-ion battery due to the higher specific capacity with a theoretical value of 1675 mAhg^-1 and a resulting much higher energy density. However, Li-S batteries still suffer many challenges, one of which mainly comes from the dissolving of lithium polysulfides into the electrolyte. It would cause insoluble and insulating Li₂S₂ and Li₂S deposited on the Li metal as anode to impair the conductivity. Furthermore, it would lead to a “shuttle mechanism” that the redox reactions between the soluble lower-order and high-order polysulfides by diffusing back and forth between cathode and anode consumes more extra energy.¹ In consequence, these problems result in fast capacity decade, low Coulombic efficiency and poor rate capability. One efficient strategy to overcome these challenges is to incorporate sulfur molecules in a variety of carbon frameworks e.g. carbon fibers,² carbon nanotubes³ and graphenes⁴ that are able to constrain the polysulfide dissolution. On the basis of this method, many improvements including polymer modification, novel electrode architecture and intermediate blocking layer involvement have been developed to enhance the sulfur-constraint. Herein we will discuss a doping effect of three-dimensional (3D) carbon nanofoam (CNF ) doped by boron (B-doped CNF) and nitrogen (N-doped CNF) as the sulfur-matrix for Li-S batteries. We also propose a modification by fullerene (e.g. C₆₀) dissolved in tolunene via complete volatilization of the solvent as simple as the sulfur-anchoring in the same way. Last but not the least, we investigate the N-doped CNF modified by C₆₀ in combination with the single-walled carbon nanotube (SWNT) macrofilms as the interlayer between the sulfur composite electrode and separator to further restrain the polysulfide dissolving.
References:
Bruce, Peter G., Laurence J. Hardwick, and K. M. Abraham. "Lithium-air and lithium-sulfur batteries." MRS bulletin 36.07 (2011): 506-512.
Zheng, Guangyuan, et al. "Hollow carbon nanofiber-encapsulated sulfur cathodes for high specific capacity rechargeable lithium batteries." Nano letters11.10 (2011): 4462-4467.
Guo, Juchen, Yunhua Xu, and Chunsheng Wang. "Sulfur-impregnated disordered carbon nanotubes cathode for lithium-sulfur batteries." Nano letters11.10 (2011): 4288-4294.
Wang, Hailiang, et al. "Graphene-wrapped sulfur particles as a rechargeable lithium-sulfur battery cathode material with high capacity and cycling stability."Nano letters 11.7 (2011): 2644-2647.

Oxide-based all-solid-state battery (SSBs) has been expected as next-generation rechargeable batteries which can realize both high energy density and safety. Generally, those kinds of batteries have been investigated using a few micron-order thin film electrodes prepared by sputtering, pulsed laser deposition, sol-gel technologies, etc with heating process to crystallize the electrode materials. Here, we will show the electrochemical properties of SSBs with “thick-film” composite electrodes over 10 mm in thickness. The films are composed of LiNi_1/3Co_1/3Mn_1/3O₂ (NMC) electrodes and highly Li⁺ conductive solid electrolyte [LATP (Li_1.3Al_0.3Ti_1.7(PO₄)₃) powder, s_rt = 1 ' 10^-3 S cm^-1, Ohara Inc.] prepared by aerosol deposition (AD) “at room temperature”.
Well-mixed NMC (Nihon Kagaku, D50 = 10 mm) and LATP powders (~0.5 mm dia.) were used as the source materials of aerosol deposition [1], where the mixed ratios were 100:1 to 100:10 in weight. The resultant powders were ejected from a nozzle by Ar gas (5N) in an AD instrument, and the thick-film composite electrodes were fabricated on several kinds of substrates (Pt, stainless steel, SiO₂, polycarbonate, etc). The films were characterized by XRD, FE-SEM, EDX, and TEM. NMC amounts in the thick-film electrodes were estimated by ICP. The films prepared on SUS substrates were covered by LiPON films by RF magnetron sputtering [2], and later Li anode films by vacuum evaporation. Charge-discharge reactions of the resultant SSBs (NMC-LATP composite/LiPON/Li) were carried out at 60-100 °C at 10-1000 mu;A cm^-2.
The resultant films had almost uniform thickness and the thickness was controlled to be 10-50 mu;m by changing the deposition time and mixed ratio of starting powders. For the electrochemical measurements, 10-20 mu;m-thick films were tested mainly in this work. XRD analyses revealed that the film electrodes are well-crystallized film electrodes, although the films were prepared at room temperature. All the diffraction peaks were assigned to NMC or LATP powders in any cases. Cross-sectional TEM and EDX analyses revealed that the films have dense structures and the NMC-LATP submicron-networks were uniformly formed in the films.
The SSBs with 10-20 mu;m-thick composite electrodes were prepared. Energy densities of these batteries themselves (without substrates) are estimated to be over 300 Wh kg^-1. Charge-discharge reactions of the batteries were carried out at 10-1000 mu;A cm^-2 at 60 °C, and the battery delivered 150 mAh g^-1 at 10 mu;A cm^-2, almost equivalent with reported value in the liquid electrolyte. We will present the effects of thickness and LATP amount in the thick-film electrodes on the rate capability. (This work is financially supported by JST-ALCA and in part by NEDO-Post LiEAD project.)
1. J. Akedo, J. Am. Ceram. Soc.,89, 1834-1839 (2006).
2. Y. Iriyama, T. Kato, C. Yada, T. Abe, and Z. Ogumi, Solid State Ionics,176, 2371-2376 (2005).

Lithium-sulfur (Li-S) batteries have been regarded as one of promising candidates to replace current lithium-ion batteries due to their attractive features such as high theoretical capacity, high energy density, non-toxicity, natural abundance and low cost. Until now, a number of efforts have been devoted to improve poor cycle life and rate property of Li-S batteries which are relevant to the diffuse-out phenomena of long-chain polysulfides and the slow kinetics of chemical reaction between polysulfides, respectively. It has been recently suggested that the concept of mesoporous carbon-based sulfur composite would be effective for preventing the loss of electroactive materials and thereby enhancing cycle performance of sulfur cathodes. Herein, we present a simple approach to use mesoporous carbons as an adsorbent of polysulfides to address the poor cycle life issue. We found that the mesoporous carbons serves as an excellent adsorbent of highly soluble polysulfides, and structural properties of mesoporous carbons are essential to effective confinement of active materials in the cathodes.

Lithium-sulfur (Li-S) batteries have been considered as one of promising energy storages systems because of high theoretical energy density and natural abundance. World-wide researches have made a significant progress in terms of cycle life and energy density for the past decade. Despite considerable advances, there are crucial hurdles such as cycle life and rate capability for practical implementation of Li-S batteries. To solve these issues, a number of methods and ideas have been presented, including porous carbon-sulfur composites and functional interlayers between sulfur cathode and separator. In result, remarkable progress in cycle life has been made, but practical energy density has not been improved due to limited sulfur content within cathode. Actually, the concept of porous conducting material-sulfur composites has an obvious limitation in enhancing the energy density of Li-S battery systems.
In this study, we reexamine electrochemical reduction route of elemental sulfur and further present a simple and effective way to achieve Li-S batteries with high volumetric energy density.

Recently molybdenum oxide (MoO₂) nanoparticles have become a very promising anode material for Lithium-Ion batteries (LIBs). Once of the biggest problems with MoO₂ is it typically requires a long, complicated synthesis process. Using a method developed by Chen et al., the authors were able to synthesize MoO₂ nanoparticles for use in LIBs in a single step [1]. Another benefit of this particular synthesis technique is the reduction of expensive and potentially hazardous chemicals used in other synthesis techniques, since this technique only requires a MoO₃ precursor powder, ethylene glycol and DI water.
In the present work, we have synthesized MoO₂ nanoparticles which required no further processing of MoO₂. The MoO₂ nanoparticles were characterized using SEM, XRD, FTIR and Raman spectroscopy, techniques. XRD, FTIR and Raman spectroscopy confirmed the formation of MoO₂, while SEM confirmed uniformly sized nanoparticles. To determine the electrochemical properties, the MoO₂ nanoparticles were subjected to cyclic voltammetry, charge/discharge testing, and EIS, techniques, respectively. The investigation of a MoO2 battery indicates that not only we could achieve high energy density but also be economically cheaper and more environmentally friendly, which could make MoO₂ a potential anode material for lithium-ion battery application.
[1] X. Chen et al., “Selective synthesis of metastable MoO₂ nanocrystallites through a solution-phase approach,” Chemical Physics Letters 418 (2006) 105-108

Sodium ion batteries (SIBs) are gaining enormous interest as a promising alternative to lithium-ion batteries (LIBs); due to their eco-friendliness, sustainability and, in particular, the cost-effectiveness comes from the abundance of sodium. In several recent studies, anode materials for SIBs were proposed. Among these, anatase TiO₂ was attractive because of its abundant reserves, low cost and relatively high stability. However, the problem of the low electrical conductivity of anatase TiO₂ remains to be solved. For the first time, we propose the use of graphene-covered 1D anatase TiO₂ nanofibers (NFs) as an anode material for SIBs. The 1D anatase TiO₂ NFs were simple to synthesize using the electrospinning method, and their surfaces were covered with graphene sheets to improve conductivity and cell integrity. To prevent aggregation of the graphene sheets, and to provide strong interaction between them and the TiO₂ NFs; Poly(allylamine hydrochloride) (PAH) was used as a surface modifier of the TiO₂ NFs. After the graphene-wrapping treatment, we easily obtained graphene-covered anatase TiO₂ NFs (G-TiO₂ NFs). This material exhibits great cyclability, high-rate capability, and more capacity, with respect to pristine TiO₂ NFs. G-TiO₂ NFs showed significantly improved capacities; 217 mAhg^-1 at 0.2 C (67 mAg^-1), 181 mAhg^-1 at 1 C and 108 mAhg^-1 at 5 C. By contrast, TiO₂ NFs showed only about 131 mAhg^-1 at 0.2 C. After 200 cycles at 0.2 C, 1 C and 5 C, both G-TiO₂ NFs and TiO₂ NFs reached a coulombic efficiency of about 99%. This high coulombic efficiency is because anatase TiO₂ serves as a zero-strain anode material for SIBs. During cycling, even after 200 cycles, the anatase structure of TiO₂ was unchanged. For these properties of high cyclability and excellent capacity, we propose graphene-covered anatase TiO₂ NFs as a promising anode material for SIBs.

Conductive monoliths are expected to work sufficiently as both a current collector and support of electrode active materials in batteries, owing to their co-continuous frameworks with large surface area and pores which allows high permeability of electrolytes. In this work, we prepared the monolithic nickel phosphide (NiP) metal by using a polymer monolith template and evaluated its performance as battery electrodes. In order to prepare the metallic monolith, palladium (Pd) nanoparticles were supported on a polymer monolith template for performing Pd-mediated electroless plating of NiP metal. After the NiP metal was deposited on the monolithic framework, polymeric substances were removed by sintering at 600 ^oC under an inert atmosphere to obtain a conductive NiP monolith. Therefore, thus obtained NiP monolith had monolithic structure as a replica of the polymer monolith template. The NiP monolith possessed a specific surface area of 27.0 m²/g and a capacitance of ca. 4.0 F/g, which were measured by a nitrogen adsorption isotherm and a cyclic voltammetry in 1.0 M KOH aqueous solution at sweep rate 1.0 mV/s, respectively. We demonstrated two examples of the metallic monolith as battery electrodes, that is, a cathode of nickel metal hydride (Ni-MH) battery and an anode of lithium ion battery (LIB). The electrochemical deposition of nickel hydroxide (Ni(OH)₂) and tin (Sn) was performed on the monolithic current collectors to obtain a cathode of Ni-MH battery and an anode of LIB, respectively. In this presentation, we would like to discuss on their performance about their capacities and cycle characteristics.

In this study, we report the effect of metal coated silicon nanowires (SiNWs) on electrochemical performance as a negative electrode material which provides enhanced structural and electrical properties at the same time. We fabricated silver (Ag)- coated SiNWs by using one-step metal assisted chemical etching (MACE) process. Transmission electron microscopy (TEM) images show that SiNW arrays with Ag coating on a Si (100) substrate have been successfully prepared in a one-pot MACE process. To investigate the electrochemical performances of Ag-coated SiNWs, coin cells using SiNWs as negative electrodes by the slurry coating method were assembled with Li metal foil as the counter electrode. We show that the rate capability of Ag-coated SiNWs is greatly improved compare to bare NWs (a charge capacity of 580mAh/g^-1 at 5C rate). Also, the good cycling performances of the Ag-coated SiNWs were clearly observed. The enhanced electrochemical performance is attributed to the improvement of electrical conductivity of SiNWs. Furthermore, we suggest that the Ag layer is exposed to the electrolyte instead of bare Si, and it can prevent solid electrolyte interface (SEI) formation and deterioration of active materials.

LiMn_1/3+xCo_1/3+yNi_1/3-x-yO₂ (NMC) is being sought after as a promising alternative in the development of battery materials because of its comparable performance to LiCoO₂, lower price, enhanced stability, and more environmentally friendly characteristics.
In-depth structural analysis of bulk NMC particles using X-ray diffraction and neutron diffraction has been the main focus of many studies in the literature. However, micro-scale level structural changes have profound effects on the performance of the cathode material and cannot be captured with such bulk techniques. Therefore, nanometer level structural information must be explored with high spatial resolution chemical analysis techniques.
In this work, we have used quantitative analysis methods using energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS) in the SEM and Auger electron spectroscopy (AES) to provide compositional information on NMC to study compositional variations of the base material and compare this quantification with bulk analysis methods such as inductively coupled plasma mass spectrometry (ICP-MS). In order to do so, we have developed stable and reliable EDS quantification procedures to quantify the samples using standards. More accurate and precise data is demonstrated using WDS, as compared to EDS. We have also compared this quantification with AES analysis in order to detect and quantify Li. The optimal operating conditions for the quantification of Li with AES were investigated and detailed work was carried out to compare pristine samples with material that has been electrochemically cycled so as to quantify the Li content after operation of the cathode material.
This work allowed us to determine the accuracy and precision of quantification of the NMC composition both in primary and secondary particles and to study the evolution of the composition following cycling of the material. Further work was carried out with transmission electron microscopy and electron diffraction to correlate the compositional changes with structural information deduced at higher spatial resolution.

Conventional Li-ion battery electrodes are composites comprising electroceramic powder mixed with polymeric binder and conductive carbon additives. While these electrodes enable high power and performance, direct mechanical interrogation of the electrochemically active materials in these electrodes has remained difficult. Conversely, dense, monolithic sintered electrodes are ideal for measuring the charge-state-dependent micro-scale mechanical properties of cathode materials via instrumented nanoindentation. Such measurements are essential to understand the role of mechanical degradation in late-life degradation of electrode materials. Not surprisingly, the challenge of diffusing lithium through a dense, millimeters-thick electrode results in non-negligible solid-phase composition gradients, requiring independent measurement of the lithium content within the depth of indentation. In this work, a combination of X-Ray diffraction (XRD), Raman spectroscopy, and ICP-AES was used to characterize the depth-resolved composition and phase of mechanically characterized Li_xCoO₂ electrodes. Substantial composition gradients were found in the electrochemically charged samples by Raman spectroscopy and ICP-AES. From XRD peak shifts, material composition extending 9 µm from the free surface was determined for samples charged over varying durations. Raman peak shifts associated with a change in crystal symmetry were observed only at the charged surfaces, indicating that a thin layer of lithium-depleted monoclinic phase had formed during charging. These chemical characterization approaches are thus key components for interpreting the microscale gradients in Li content and in mechanical properties of materials used in energy storage electrodes.

Lithium ion batteries (LIBs) with great energy density and power density are desirable in electric vehicles and anode materials which can provide high charging rates equalling to high acceleration speeds are under constant research since decades. SnO₂ is one of the high capacity (782 mAh/g) anode materials used in LIBs with a tetragonal rutile structure which alloys at voltage of 0.5V vs Li. However cyclability for SnO₂/Sn based materials is very poor due to high volume expansion during alloying with Li ions (charging) and disintegration of structure during de-alloying (discharging) besides the formation of solid electrolyte interface (SEI) at lower operating voltage of the anode. Many attempts have been made to improve the cyclability and minimize the capacity losses of these materials by nanostructuring the material, making composites with graphene, CNTs, CNFs and even providing carbon coating. Even though the results are promising, reproducibility and the scaling up of the electrode material still remains as a major concern.
Here we present a new attempt of improving the cyclability of SnO₂ with minimum capacity loss using a composite electrode of SnO₂ and lithium titanate (LTO). LTO with a cubic spinal structure can intercalate reversibly with Li ions delivering a capacity of 175 mAh/g, theoretically. Low crystal strains during charging -discharging makes the material work even at high charging rates. The combination of SnO₂ and LTO can reduce the volume expansion experienced by bare SnO₂ during alloying de-alloying reaction as LTO material itself is a zero-strain material. We have synthesized SnO₂/LTO composite hollow fibers using combinational methods of sol-gel and electrospinning. This approach of nanomaterial fabrication opens the possibilities to obtain pure 1D inorganic nanomaterial. Further sol-gel/ electrospun based inorganic nanomaterials may be promising as electrodes for LIBs as diffusion path or volume expansion of electrode can be reduced to a greater extent due to the presence of nano grains in porous structures. In this work we present the fabrication of SnO₂/LTO composite hollow fibers prepared by sol-gel/electrospinning followed by measuring their electrochemical performance. LTO and SnO₂ sols in 1:1 composition were electrospun and the resulted SnO₂/LTO fibers were calcined in air at 750#730;C for the required phase formation. FESEM and XRD analysis revealed the formation of composite hollow fibers of phase pure SnO_{2 /}LTO with an average grain size of 25 nm. Surface area of 188±33 m²/cm³ was obtained for SnO₂/LTO fibers by SAXS studies. Electrochemical measurements such as galvanostatic charge-discharge studies, cyclic voltammetry and impedance spectroscopy were performed. Electrospun SnO₂/LTO based composite hollow fibers have shown excellent electrochemical performance as compared to only SnO₂ fibers with improved cycle stability and capacity retention even at high charging rates.

Fast development of portable electronic devices (such as a smart phone, iPad, and Galaxy Note) and electrified vehicles (such as EVs and HEVs) require better and smaller lithium ion batteries as their energy storages. What is needed for the cathode of the lithium ion battery is a material capable of higher energy density. However, not only the development of cathode material but also the commercialization of high energy density anode material has been limited due to the cathode material&’s much lower energy density compared to anode material. In this regard, Li-rich material (Li₂MnO₃-LiMO₂, M=Ni, Mn and Co) that has 150 % higher energy density than commercialized LiCoOshy;₂ is the unique next generation cathode material to solve the problem. In the past decade, many researches have focused on the surface stabilization method of this material to improve its intrinsic problems of poor cycle/ rate capability and such surface treatment methods have been demonstrated in a few examples, including AlF₃ coating and spinel heterostructures, yielding noticeable improvements in rate and cycle ability. Although such surface treatments showed improved rate and cycle performances, the realization of the Li-rich material&’s high volumetric energy density and long-term cycle life which are more critical factors for the commercialization of Li-rich material still remained unsatisfied. For instance, AlF₃ coated Li-rich LNCMO has abrupt capacity fade after 100 cycles, while it showed good rate and cycle capability within 100 cycles. Hence, new active material design, instead of simple surface modification methods such as coating or doping, is required to solve above previous limits.
Here we demonstrate a novel approach for lithium storage, which is a material design of a secondary structure which consists of large primary particle with a novel activation method using simple chemical treatment, to achieve superior long-term cycle life with high volumetric energy density. In this design, the large primary particle effectively reduced its surface area producing markedly decreased surface instability reaction as well as high tap density. Interestingly, the chemical approach activates only surface Li₂MnO₃ phase of large primary particle and the very surface activation effectively overcome the activation problem, which is limit of large primary particle have. This novel concept is very meaningful in that it is the first and unique method to achieve cathode material&’s high volumetric energy density with long-term cycle life. As a result, this novel designed material affords remarkable battery performance with high volumetric energy density of ~1980 Wh L^-1 and extremely high cycle retention of 90% during 300 cycles.

Spinel cathode materials have attracted much attention for applications of lithium ion batteries in electrical vehicles (EVs) and hybrid electrical vehicles (HEVs). The most interesting spinel cathodes are LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ due to their environmental friendliness, inexpensiveness and good electrochemical performance. The LiMn₂O₄ cathode has the same crystal structure to that of the LiNi_0.5Mn_1.5O₄ but shows completely different electrochemical performance, particularly at high cycling voltage of sim;5 V.The former shows significant capacity degradation, even cycled to high voltage for only one cycle. However, the latter can be cycled at high voltage for hundred of cycles without significant capacity degradation. The origin of this has not been fully explained.
Combined advanced scanning transmission electron miscopy (STEM), X-ray photoelectron microscopy (XPS), X-ray absorption microscopy (XAS), the local and average structure of these two cathode materials were investigated. The LiMn₂O₄ cathode shows significant levels of surface reconstruction (sim;5 nm) into a layered-like structure, which is bridged to the bulk spinel via an intermediate Mn₃O₄ structure, as observed directly under STEM. The surface also shows an increased amount of Mn²⁺ ions with charge voltage. In contrast, the LiNi_0.5Mn_1.5O₄ exhibits a relatively stable surface, though reconstruction also occurs in some nano regions. The Ni²⁺/Mn²⁺ ions in the surface of cycled LiNi_0.5Mn_1.5O₄ is negligible. Our results indicate that the surface structure is the origin of the difference of electrochemical performance for these two spinel cathode materials. A stable surface with limited migration of transition metal (TM) ions is responsible for stable charge transfer impedance and limited dissolution of TM ions, and consequently limited capacity degradation. We further suggest that to improve the electrochemical performance of spinel cathode materials cycled at high temperature, it is essential to stabilize the TM ions in the surface via doping or coating.

Lithium ion batteries are quickly becoming the mainstream power sources for environmentally friendly vehicles such as hybrid vehicles (HV), plug-in hybrid vehicles (PHV) and electric vehicles (EV) due to their high energy density. However, since a battery system with even higher energy density is required for the long-range PHV or EV applications, post lithium ion batteries (PLIB) such as Li-sulfur batteries or Li-air batteries have been getting more attention in recent years. Rechargeable magnesium batteries are also candidates for the PLIB due to the natural abundance of magnesium and the absence of dendrite formation when magnesium metal is used as the anode. In addition, a magnesium-metal electrode is expected to have high energy density, due to its divalent nature. However, there has been not much progress on the development of novel cathodes since the innovation of Chevrel phase materials such as MgMo₃S₄. The difficulty lies in the strong polarization character of the small and divalent Mg²⁺ and consequently the intercalation and diffusion of Mg²⁺ ions is somewhat difficult and complicated.
Recently, it has been found that calcium ferrite type (CF) AMn₂O₄ (A = Li, Na, or Mg) has potentially high cation mobility through the lattice. Especially, our simulation study indicated that the mobility of Mg²⁺ in this compound is fast enough to satisfy the requirements for a rechargeable Mg battery cathode. Followed by our theoretical investigation, this type of material has been successfully synthesized and excellent electrochemical performance was observed using as cathode material for Mg battery. The reaction mechanism and structural evolution upon Mg intercalation/deintercalation of CF-MgMn₂O₄ were investigated by multiple techniques, including powder synchrotron XRD, TEM, Raman, XPS, XAS.

Layered rocksalt-type lithium transition metal oxides (Li-TM oxides) are the dominating class of cathode materials for rechargeable lithium batteries due to their high energy density [1, 2]. In these materials, lithium and transition metal ions are well separated to form distinct layers that alternate in stacking [1, 2]. In general, this ordering in well-separated layers is believed to be necessary for high lithium mobility, and cation mixing between Li- and TM-layers has been observed and understood to cause poor cyclability by slowing down lithium diffusion [3, 4]. Such understanding and observations may have resulted in limited attention toward disordered rocksalt-type Li-TM oxides as potential cathode materials [5, 6].
In direct departure from this belief, our recent work on Li_1.211Mo_0.467Cr_0.3O₂ demonstrates that cation-disordered materials can be excellent intercalation electrodes as long as the Li excess content is high enough for low-activation energy paths to become percolating [7]. This material forms as a layered rocksalt, but transforms to a disordered rocksalt after just a few charge-discharge cycles. Nevertheless, it cycles very well, achieving a high specific capacity above 250 mAh/g. Using ab initio computations and Monte-Carlo simulations we explain the performance of Li_1.211Mo_0.467Cr_0.3O₂, and propose a guideline for designing high capacity electrodes from disordered rocksalt-type oxides [7]. The same design principle can also be extended to other rocksalt-type electrode materials [8].
References
[1] M. S. Whittingham, Chem. Rev. 104, 2004
[2] J. B. Goodenough, Y. Kim, Chem. Mater. 22, 2010
[3] K. Kang, Y. S. Meng, J. Breger, C. P. Grey, G. Ceder, Science 311. 2006
[4] A. Rougier, P. Gravereau, C. Delmas, J. Electrochem, Soc. 143, 1996
[5] C. Delmas, H. Cognac-Auradou, J. Power. Sources 54, 1995
[6] M. N. Obrovac, O. Mao. J. R. Dahn, Solid State Ion. 112, 1998
[7] J. Lee, A. Urban, X. Li, D. Su. G. Hautier, G. Ceder, Science 343, 2014
[8] A. Urban, J. Lee, G. Ceder, Adv. Energy Mater. 2014, 1400478

A series of transition metal oxides xA₂MnO₃#8901;(1-x)A_y(NiMn)O₂ (A=Li+, Na+ the mobile species) are capable of storing energy reversibly in lithium ion and sodium ion batteries. These oxides have intriguing and complex features including nanometer-scale phase separation upon cycling and dynamic cation redistribution at various state of charge, that significantly affect the mobility of the guest species. We investigate the high-energy cathode materials Li-excess layered oxide compounds by combining both computational and experimental methods. The bulk and surface structures of the compounds at different state of charge are characterized by synchrotron X-Ray diffraction, neutron diffraction together with aberration corrected Scanning Transmission Electron Microscopy (a-S/TEM). Electron Energy Loss Spectroscopy (EELS). We show clear evidence of transition metal ions migrations, oxygen electrochemical activity and a new spinel-like solid phase formed on the surface of the electrode materials after high-voltage cycling. We propose effective strategies to further improve this family of materials for future battery technologies.

LiNi_1/3Co_1/3Mn_1/3O₂ is considered to be one of the best cathode materials for power source system of HEV or EV, because of its high discharge capacity relatively low cost. But LiNi_1/3Co_1/3Mn_1/3O₂ for EV needs to achieve higher power performance, higher energy density, longer life, and high capacity under severe environment like high or low temperature. To improve these properties, we doped the elements M('A', 'B'), into LiNi_1/3Co_1/3Mn_1/3O₂ via solid-state reaction. We could maximize the improvement of electrochemical property by optimizing the particle size, distribution, type of doping materials and content of elements. We could confirm that the dopants were distributed homogeneously by EPMA and Nano-SIMS mapping measurement and XRD data showed no extra phase exists indicates the dopants can substitute Ni, Co, Mn equally at the 3a site and make solid solution. The electrochemical property can be improved by expansion of Li slab distance for LiNi_1/3-xCo_1/3-xMn_1/3-xM_xO₂ caused by the increase in the unit cell parameters. The doping into LiNi_1/3Co_1/3Mn_1/3O₂ increases c parameter and c/a value and the volume of the unit cell. It is suggested that relatively large ionic radii of doping elements compared to Co³⁺ (0.545Å) and Mn⁴⁺ (0.530 Å) causes unit cell parameters expand. Since I(003)/I(104) of the doped materials was higher compared with the undoped material at the XRD pattern, the degree of cation mixing of doped material decrease. EIS results demonstrated that both Li⁺ insertion resistance (Rct) and Li⁺ diffusion impedance (W) in doped LiNi_1/3Co_1/3Mn_1/3O₂ were lower than undoped at any depth of discharge (DOD). These results mentioned above lead to improve the electrochemical properties. The doped material not only shows the increase in discharge capacity by improvement of charge-discharge efficiency, but also improves capacity at the high C-rate(5C) and cycleability. Remarkably, discharge capacity at low temperature(-25#8451;) is improved as well as the capacity at room temperature. This property was observed when element "B" was doped especially .

The capacity fade of LiMn₂O₄-based Lithium ion battery is directly associated with the dissolution of Mn from the cathode/electrolyte interface and the subsequent deposition of Mn²⁺ onto the anode which leads to the active material loss and more importantly the impedance rising of the cell. Therefore, suppressing the dissolution of Mn from the cathode is critical to improve the cycle performance of LiMn₂O₄-based cells. Here, we report a novel nanoscale surface-doping approach that minimizes Mn dissolution from LiMn₂O₄, which exploits advantages of both bulk doping and surface coating methods. The surface doping layer protects the bulk of the spinel from the corrosion of the electrolyte while maintains the LiMn₂O₄ composition in the bulk. Moreover, the surface doping layer maintains spinel structure for the Li ion and electron transport, which minimizes the physical barrier between the bulk and surface of the particle. As a consequence, the surface-doped LiMn₂O₄ demonstrates significantly enhanced electrochemical performance in terms of cycleability and capacity at elevated temperature. This study provides encouraging evidence that surface doping could be a promising alternative to improve the cycling performance of lithium-ion batteries.

In the Lithium ion battery field, high rate capability, capacity and stability at high temperature for a range of applications from portable electronic devices to electric vehicles (EVs), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) and even energy storage systems (ESSs) are required to cathode material. Li-rich layered oxides material (Li₂MnO₃-LiMO₂, M=Ni, Mn and Co) with over 200mAhg^-1 discharge capacity is the most promising positive electrode material to satisfy the recent demand. However, Li-rich materials are limited by the instability of surface caused by the reaction with electrolyte, which deteriorates the rate performance, capacity retention. Moreover the side-reactions with electrolyte are accelerated at high temperatures. Many researchers have focused on the surface modifications to fulfill the encountered problems. Coating method using Al-precursors via sol-gel is one of the most common methods in surface modification. However, unique point of view makes them unique source and method to compensate the defect of Li-rich material.
Our synthesis strategy is a formation of sheet-like amorphous layer on the pristine material Li_1.12(Ni_0.2Co_0.2Mn_0.6)_0.88O₂ surface by using both acidic and basic atmosphere of sol-gel method for complete coating and overcome rate problem and thermal instability of Li-rich materials. After coating process, the amorphous layer coated on Li_1.12(Ni_0.2Co_0.2Mn_0.6)_0.88O₂ surface shows high reversible of 250mAhg^-1 and very excellent cycling stability at 60 celsius degree.

Engineering pore size distributions in porous carbon materials is essential to achieve high sulfur loadings without loss of capacity. A nanocasting approach was developed to generate highly hierarchical pore systems with specific surface areas up to 3000 m²/g and well controlled pore size in the micropore regime (< 2nm) but also well defined meso- (2-50 nm) or macroporosity (>50 nm) using preceramic polymers as precursors in combination with carbochlorination for the generation of micropores. Sulfur loadings up to 75 wt.% and high areal loadings were achieve with high sulfur utilization even at low electrolyte/sulfur ratios. Dry processing was identified as a beneficial and scalable production method for the electrodes.
The use of hard carbon anodes allows the investigation of cathode-intrinsic degradation effects since lithiated hard carbons were identified to sustain more than 1400 cycles in Li/S-systems. An additional benefit was generated by creating novel type of separators based on lithiated Nafion as an ion selective membrane to reduce shuttle effects.
S. Kaskel et al. J. Power Sources (2014), 251, 417-422; Adv. Funct. Mater. (2014), 24(9), 1283; Energy Mater. (2014), 4(2), 1300645/1-1300645/9, Chem. Commun. (2014), 50, 3208-3210; Angew. Chem. Int. Ed. (2013), 52(23), 6088-6091; Carbon (2012), 50(11), 3987-3994; Angew. Chem. Int. Ed. (2012), 51(30), 7577-7580.

To exceed the demands of current hybrid, plug-in hybrid and electric vehicles, new battery systems with high energy density are required. Magnesium (Mg) is an attractive alternative to current lithium-ion technologies because of the transfer of 2 electrons per magnesium-ion, higher volumetric capacity of magnesium metal compared to lithium metal (3833 mAh/cm³ Mg vs 2061 mAh/cm³ Li), and greater natural abundance [1]. However, to realize complete magnesium battery, cathodes capable of reversible Mg²⁺ reactions are required.
Recently, we proposed α-MnO₂ as a viable candidate for Mg batteries because of a large initial discharge capacity of 280 mAh/g [2]. However, the capacity faded to 70 mAh/g by the 10^th cycle, and a deep mechanistic investigation was required to determine the source of the capacity fade. We observed that instead of following the typical insertion reaction as with Li⁺ to produce LiMnO₂, magnesiation occurs through a conversion pathway to form an amorphous (Mg, Mn)O product. Through various transmission electron microscopy and soft X-ray absorption spectroscopy, we determined that magnesiation is partially reversible through the amorphous layer of the cathode [3]. From these results, we were encouraged to pursue amorphous materials as an avenue for magnesium battery cathodes.
The V₂O₅-P₂O₅ amorphous glass system has previously been shown to have good cycling and rate capabilities for lithium batteries [4]. Encouragingly, V₂O₅ has recently been highlighted as promising a cathode for magnesium batteries [5]. Here, we show the potential of amorphous V₂O₅-P₂O₅ cathodes for magnesium batteries. In a non-aqueous, full-cell system with a magnesium metal anode, we have observed a capacity of 164 mAh/g with good capacity retention. Importantly, we have identified the meta-stable phase which gives the amorphous V₂O₅-P₂O₅ system improved electrochemical properties over the bulk, crystalline V₂O₅.
Mg batteries have great potential as a post Li-ion technology, but finding a viable cathode material is vital to realizing a practical system. The V₂O₅-P₂O₅ system shows excellent potential as a cathode material, and provides us with an alternative, promising path for a complete magnesium battery.
[1] Aurbach et al. Nature 407 (2000) 724.
[2] Zhang et al. Electrochem. Comm. 23 (2012) 110.
[3] Arthur et al.ACS Appl. Mater. Interfaces 6 (2014) 7004.
[4] Sakurai and Yamaki J. Electrochem. Soc 132 (1985) 512.
[5] Aurbach et al. MRS Bulletin 39 (2014) 453.

Lithium-sulfur batteries (Li-S) are deemed as one type of the most promising candidates for next generation energy storage materials, owing to the high theoretical capacity (1675 mAh g^-1) and low cost. However, the practical application of Li-S battery is still hindered by the rapid capacity fading, mainly due to the dissolution of lithium polysulfides and the resulting shuttling effect. Two major structures that have been developed to solve these issues include (1) the mesoporous carbon-sulfur system and (2) the core-shell structures of graphene oxide or polymer coated sulfur. The sulfur@hollow carbon nanocomposite combines two above strategies and has been considered as a promising method, since it can confine sulfur in the porous carbon shell, increase the sulfur loading and maintain an intimate contact between carbon and sulfur. However, up to know, there has been no convincing evidence to show that the sulfur has really diffused into the internal void of the hollow carbon instead of only aggregating in/on the porous shell. If the sulfur just aggregated in/on the porous shell of the hollow carbon, it would easily be dissolved out during cycling. So, some critical questions emerged: was the hollow nanospheres really filled or partially filled with sulfur, or does sulfur simply aggregate on the external surface of the nanospheres? Of equal concern is, what is the best pore size for confining sulfur?
Here, we designed hollow carbon spheres with different pore sized mesoporous shell, which enable us to investigate the effect of pore size on the sulfur impregnation and polysulfides immobilization. We also introduced nitrogen into the porous carbon shell to further suppress the polysulfides shuttling through the coordination interaction between lithium polysulfides and nitrogen. We found that the pore size of the porous carbon shell, varied in a very narrow range, played a significant role in immobilizing the sulfur/polysulfide. The pore size around 3 nm would be a critical size, below which the sulfur could be well confined in the hollow carbon and the polysulfide shuttling could also be effectively suppressed.

The graphite co-intercalation model proposes that the lithium ion co-intercalates into graphite along with solvents which once inside graphite undergo reduction reactions setting off a series of reactions to form solid-electrolyte interface films on the graphite surface. Yet, little is known about the solvent reduction mechanisms inside graphite. In our report, we analyze the solvent reduction reactions inside graphite using density functional theory under periodic boundary conditions with the van der Waals correction term. We apply this approach to two ternary graphite interaction compounds (GICs) for lithium solvated by ethylene carbonate (EC) and by propylene carbonate (PC), the only difference of which is the methyl group of PC. Theoretical attempts to explain the well-known difference between EC- and PC-based electrolytes in the cycling behaviors of lithium-ion battery cells using models outside graphite have so far failed. Through the analysis of the ternary GICs, we discuss the effect of the methyl group of PC on the reaction kinetics of the solvent reduction and also on the mechanical stability of graphite in order to shed a light on the difference in the cycling behaviors.

Extending the lifetime of Li-ion cells to many decades is one of the most challenging problems remaining in battery technology. The use of electrolyte additives to reduce or eliminate the unwanted parasitic reactions at the electrolyte/electrode interfaces is the best known approach. There are hundreds of studies on electrolyte additives [1] [2] [3] however their exact roles in modifying the Solid Electrolyte Interphase (SEI) at both electrodes are barely understood.
Here, high precision coulometry, storage experiments, electrochemical impedance spectroscopy as well as measurements of gas evolution correlated to thorough X-ray Photoelectron Spectroscopy (XPS) analysis of the SEI films allow a more reliable understanding of the impact of electrolyte additives on parasitic reactions. Charge slippage, voltage drop during storage and gas formation during cycling can be better understood by a comparative ‘&’head to head&’&’ XPS study of the impact of several electrolyte additives on the SEI. Different sulfur-containing additives, that have recently shown promising performance in Li-ion cells [4] [5] were compared both singly and in combination with the commonly used vinylene carbonate (VC). Extremely reproducible machine-made Li[Ni_1/3Mn_1/3Co_1/3]O₂ (NMC)/graphite pouch cells were used to prepare electrodes for XPS study and to allow a direct comparison between additives and additive combinations thus ensuring highly reliable results.
[1] S.S. Zhang, J. Power Sources, 162, 1379 (2006).
[2] K. Xu, Chem. Rev., 104, 4303 (2004).
[3] G. Sarre, P. Blanchard, and M. Broussely, J. Power Sources, 127, 65 (2004).
[4] J. Xia, N. N. Sinha, L. P. Chen and J. R. Dahn, J. Electrochem. Soc., 161, A264 (2014).
[5] J. Xia, C. P. Aiken, L. Ma, G. Y. Kim, J. C. Burns, L. P. Chen and J. R. Dahn, J. Electrochem. Soc., 161, A1149 (2014).

A key challenge of the 21^st century involves miniaturizing on-board electrochemical energy storage systems to power autonomous systems in areas as diverse as sensing, actuation, communications, and medical implants. Traditional battery designs impose an unfortunate compromise between energy and power density and achieving appropriate energy levels to operate such microsystems requires increasing the areal footprint of the battery, which seriously impedes miniaturization. Three-dimensional (3D) battery architectures using non-planar designs (e.g. nanorod arrays) address this challenge by judiciously manipulating the electrode thickness using large surface area structures that increase energy within a small areal footprint while maintaining the short ionic transport distances necessary for high power densities. A key feature in a number of 3D battery architectures is the need to have a conformal electrolyte which covers the non-planar electrode. Here, we report the development of a new class of ultra-thin, conformal polymer electrolytes synthesized by initiated chemical vapor deposition (iCVD). We investigated a family of monomers that polymerize to form flexible, cross-linked network structures, with built-in channels for Li⁺ transport resulting in room temperature ionic conductivities approaching 10^-8 S/cm. We demonstrate that the conformal nature of the polymerization process results in complete coverage of complex geometries by a uniform, pin-hole free film, making these polymer electrolytes very attractive for 3D battery architectures. 10 - 30 nm thick polymer films were deposited by iCVD at deposition rate of 1-2 nm/min. Transmission electron microscopy (TEM) images of 160 nm diameter silver nanowire coated with 10 nm iCVD film shows that the film uniformly wraps around the nanowire, demonstrating excellent conformality over this high aspect ratio nanostructure. Atomic force microscopy (AFM) images show extremely smooth films with root mean square roughness of 0.46 nm. Ionic conductivity of the films was determined by Electrochemical Impedance Spectroscopy (EIS) using a hanging mercury drop electrode arrangement. Values in the range 10^-8 S/cm -10^-10 S/cm were obtained at room temperature, depending on choice of monomer and film thickness. Pin-holes in these films can act as shunting pathways that lead to battery failure. The pin-hole % in these films was found to be 0.72 - 1.02 % by calculation of diffusion coefficients for redox couples using cyclic voltammetry. These small pin-holes %, which are a measurement of the uncoated area of the substrate, suggest almost complete coverage of the substrate by the films. Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) quantifies the amount of Li⁺ present in the films to be ~ 10²¹ atoms/cm³. The solvent-free CVD approach used to engineer these ultra-thin, conformal, and pin-hole free ionic conductors is scalable and easily integrated with other techniques, such as roll-to-roll processing.

Lithium batteries with increased energy density are required for the fast growing markets of mobile electronic devices, electric vehicles, and smart grids. High-voltage cathodes delivers increased energy with same amount of charge, and can be designed relatively easily by cation substitution in existing compounds, without altering much the crystal structures or the intercalation chemistry. However, the practical use of high-voltage Lithium batteries is hampered by the narrow electrochemical window of the liquid electrolyte in conventional batteries. A solid electrolyte with a sufficiently wide electrochemical window does not decompose when cycled to high voltage, and thus possibly enables the full utilization of high-voltage cathodes.
Here we demonstrate the possibility to realize high-voltage lithium batteries in solid-state systems using an example of LiNi_0.5Mn_1.5O₄ cathode (operating potential: 4.7 V vs. Li/Li⁺), Lipon solid electrolyte, and Li metal anode. Lipon is used as the model solid electrolyte mainly because of its wide voltage window (0~5.5 V) and excellent interfacial compatibility with both cathodes and anodes. The high coulombic efficiency of this solid-state battery exceeds 99.98%, indicating that the decomposition of solid electrolyte is minimal. The reversible capacity delivered by the solid-state lithium battery with LiNi_0.5Mn_1.5O₄ cathode is stable for 10,000 cycles with 90.6% capacity retention, corresponding to a decay of less than 0.001% per cycle. For most applications, such a battery has a cycle life longer than most devices, and can be used for a lifetime without maintenance. The round trip energy efficiency is greater than 97%. After the first cycle, the voltage-capacity profiles are almost identical for the subsequent cycles through at least 10,000 cycles. The issues of transition metal dissolution and electrode/electrolyte interfacial stability are also solved. This work infuses a new life into existing chemistry of high-voltage lithium batteries.

As lithium-ion batteries evolve toward higher cell voltage and capacity, developing detailed knowledge of the electrolyte-electrode interface is critically important. While there is general agreement on solid electrolyte interphase (SEI) formation on graphitic anodes, clear evidence of passivation at the cathode interface remains elusive. This presentation discusses our efforts in investigating the interphases in Li ion batteries, on both cathodes and anodes. Primarily using in-situ electrochemical atomic force microscopy (EC-AFM), our studies focus on the live-formation of electrolyte-cathode interphases.

Among the many challenges to enable large scale commercialization of Li-ion batteries in plug-in hybrid electric vehicles (PHEVs) and full electric vehicles (EVs), formation of high quality solid electrolyte interphase (SEI) is one critical issue to achieve long term battery durability and safety. As a nano-meter scale thin film which natively forms on the negative electrode due to electrolyte reduction, SEI is a complex system composed of various lithium salts and organic reduction products. Most published works have focused on identifying the SEI composition, but the understanding of correlation between SEI properties and battery performance is still lacking.
Previously, we have identified that SEI impedance is closely related with its composition. Briefly, the inorganic components (e.g. Li₂O and Li₂CO₃, etc) constitute a low impedance and less porous part of SEI, while the organic reduction products tend to be more porous and resistive.¹ We will advance the findings and evaluate characteristic Li salts using isotope exchange method. Li ion exchange behaviors are measured with time-of-flight secondary ion mass spectrometry (TOF SIMS) and compared. Typical SEI components, e.g. Li₂CO₃, LiF, etc. are found to behave differently in passing Li. Such understandings of SEI facilitate the development of surface coating and modification as effective approaches to stabilize the electrolyte/electrode interface. We will demonstrate that the SEI chemistry on negative electrodes can be modified and better columbic efficiency can be achieved, through atomic layer deposition (ALD) coating and surface pre-treatment.
Reference 1. Lu, P., Li, C., Schneider, E. W., Harris, S. J., J. Phys. Chem. C, 2014, 118, 896-903

Electric double layer capacitors, conventionally known as supercapacitors, are increasingly being selected as energy storage systems of choice for high-power applications that may be unsuitable for conventional batteries. The physical charge storage mechanism, which relies on the electrosorption of ions on porous electrodes with high specific surface areas, allows for rapid charge/discharge loads and exceptionally long cycle lifetimes. Most research efforts to date have focused on maximizing accessible surface area and matching the pore and electrolyte ion diameters for maximum capacitance. Furthermore, theoretical simulations that have been the backbone of emerging research directions have treated the carbon electrode as a metallic, defect-free material. These approaches ignore the effect of the surface functional groups and graphitic structure of pore walls on the electrode-electrolyte interaction. Our efforts focus on the manipulation of chemistry and carbon ordering on electrode surfaces through high-temperature annealing and grafting of various functional groups on porous (e.g., carbide-derived carbons) and non-porous (e.g. carbon black) structures. We demonstrate the structural changes and resulting transformations in electrode hydrophobicity, thermal stability, and electrical conductivity that correlate with these modifications. By maintaining a consistent pore structure, we decouple the key properties that affect double layer charge storage and ion dynamics. We demonstrate the significance of specific surface properties and their effects to capacitance, rate performance, and electrochemical stability of ionic liquid electrolytes. In particular, the presence of defects, functional groups, and geometrical confinement of the ions all affect quantum capacitance contributions, high-voltage electrolyte breakdown, and ionophilicity. This understanding is critical for the development of high-performance supercapacitors with energy and power densities that make them suitable for applications such as microelectronics, MEMS power sources, hybrid battery/capacitor regenerative braking, and grid storage power systems.

Research in carbon nanomaterials has seen tremendous growth in recent years; however, technological advances are limited by the lack of continuous and scalable synthesis methods. The current industrial methods for producing carbon nanotubes are expensive and thereby increase the costs of energy storage to more than $10 Wh/kg. Here we present a scalable roll-to-roll process for synthesizing vertically#8209;aligned multi-walled carbon nanotubes (VACNTs) on Al foil ribbons, which are continuously drawn through a chemical vapor deposition (CVD) reactor operating at ambient pressure and a relatively low growth temperature (600 °C). Our method produces VACNTs with diameter (heights) between 50-100 nm (10-100 um), and a specific capacitance as high as 100 F/g. Electrodes comprised of VACNT forests synthesized in this process are directly assembled into supercapacitor cells, which yield high power densities (1270 W/kg) and energy densities (11.5 Wh/kg). These devices exhibit excellent cycle stability with no loss in performance over more than a thousand cycles. This work is supported by NSF-CMMI scalable nanomanufacturing SNM # 1246800 award.

Lithium ion batteries have been widely used in portable devices in the past twenty years. However, to be commercially implemented in the large-scale systems such as plug-in electric vehicles (PEV) or electric vehicles (EV), performance requirements are raised especially from the aspects of energy/power density, cycle life and safety issues. Besides searching for new materials, different optimization approaches are being applied, including doping, making nano particles, coating etc. Understanding surface and interface properties is of extreme importance for guiding the optimization.
Surface phase transformation has been found to be a common phenomenon in most layered oxide cathode material for lithium ion batteries, which is believed to deteriorate the performance. However, the mechanism of how it forms and how it can be improved is unclear. A combination effort of Scanning Transmission Electron Microscope / Electron Energy Loss Spectroscopy (STEM/EELS) and first principles calculations has been adopted to investigate the mechanism, especially focusing on the surface and interface properties. A novel oxygen vacancy assisted transition metal migration diffusion mechanism has been proposed. The effect of coating with AlF₃ as well as Lithium Lanthanum Titanium Oxide (LLTO) has also been studied.

The investigation of surface reactions of electrolytes with the electrodes of Lithium Ion Batteries (LIB) for Electric Vehicle (EV) applications will be presented. The beginning portion of the presentation will cover the mechanism of formation of the anode Solid Electrolyte Interphase (SEI) on graphite, silicon, and tin along with the effect of electrolyte additives on SEI structure and performance. Electrode surface analysis is conducted via a combination of microscopy and spectroscopy, including SEM, TEM, XPS, FT-IR, and NMR spectroscopy.
The latter portion of the presentation with cover a method for improving the energy density of lithium ion batteries by increasing the working potentials of positive electrode by employing lithium nickel manganese spinel LiNi_0.5Mn_1.5O₄ as the active material. The failure mechanism of graphite /LiNi_0.5Mn_1.5O₄ cells cycled at 25 ^oC and 55 ^oC (1.2 M LiPF₆ in 3:7 EC/EMC) have been analyzed by electrochemical methods and ex-situ surface analysis of the electrodes. We are using this mechanistic information about capacity fade in graphite/LiNi_0.5Mn_1.5O₄ cells to develop novel additives to improve the performance of LiNi_0.5Mn_1.5O₄ cycled to high voltage (4.9 V vs Li). The details of our experimental results and our mechanistic interpretation will be presented.

Lithium (Li) metal anode has been considered as the most promising anode for rechargeable batteries because of its significantly high theoretical capacity of 3860 mAh/g (10 times as large as that of graphite), the lowest electrochemical potential at -3.040 V vs. standard hydrogen electrode and the light density. However, the development and application of rechargeable Li-metal batteries has been hindered in the past four decades due to two major issuesfrac34;the Li dendrite growth on Li anode during repeated charge/discharge processes leading to serious safety hazards and the low Coulombic efficiency since Li metal is strongly reactive to organic solvents and salt anions. During the past four decades, several approaches have been reported to improve the stability of Li metal anode, including using Li alloy, adding electrolyte additives, modifying Li surface, and so on. However, the improvement on Li anode as far is not satisfactory.
In this work, we systematically investigated the effect of CsPF₆ as an electrolyte additive on Li morphology and battery performance of rechargeable Li|LiFePO₄ (or Li|LFP) batteries where the LFP loading of 2.4 mAh/cm² was used. When the charge current densities are less than 1 mA/cm², the effect of Cs⁺-additive has been clearly demonstrated in the studied cells where the cells can be cycled for more than 500 cycles with negligible capacity fading but the cells with the control electrolytes without Cs⁺-additive experienced fast capacity drop after less than 100 cycles. When the charge current densities are larger than 1 mA/cm², the effect of Cs⁺-additive is less dramatic in Li|LFP cells although the Cs⁺-additive does show a relatively slower capacity fade. The surface of Li metal anodes after cycling with the Cs⁺-additive also is smoother than that in control electrolytes. The fast growth of porous, dead Li on Li anode during high current-density charging/discharging cycles leads to dramatic resistance increase of tested coin cells confirmed by a.c. impedance analysis, and consequently severe capacity degradation. Details of the investigations will be reported and discussed in the presentation.
Acknowledgement
This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, of the U. S. Department of Energy.

The demand for a stable and compatible redox shuttle for use in lithium-ion batteries (LIBs) has prompted us to explore strategies to tune and improve the properties of redox shuttles and have studied over 50 new diarylamine derivatives synthesized in our laboratory. In one case, we introduced trifluoromethyl groups (minus;CF₃) at the positions para to the nitrogen atoms in N-ethylphenothiazine (EPT), a redox shuttle first reported by Dahn and coworkers. The high electronegativity of the CF3 group raises the oxidation potential of the phenothiazine and incorporation significantly increases solubility in battery electrolyte. Here we report 3,7-bis(trifluoromethyl)-N-ethylphenothiazine (BCF3EPT) as the redox shuttle with the highest reported solubility in battery electrolyte that nonetheless maintains the cell performance and stability of the shuttle molecule. We have compared its performance with 1,4-di-tert-butyl-2,5-dimethoxybenzene (DBBB), N-ethylphenothiazine (EPT), and other robust redox shuttles. Overcharge cycling of BCF3EPT far surpasses any reported redox shuttle and tolerates faster charging rates than DBBB and EPT. Our current work includes scale-up of BCF3EPT, which we have produced on multigram scales, and testing this compound in redox flow batteries, inspired by the work of Jansen, Vaughey, and Brushett who demonstrated that redox shuttles for overcharge protection can also be utilized as positive electrodes in all-organic non-aqueous redox flow batteries.

Characterization of solid electrolyte interphase (SEI) compounds in terms of ionic and electronic transport is critical for the understanding of rate-related issues in batteries, e.g. the bottlenecks in charge-discharge rates, electrode protection, overpotentials, metal plating etc. LiF is one of the most common SEI compounds, formed primarily when electrolyte contains fluorinated salts in Li batteries. It is a wide band gap material that favors the insulation of electrode surfaces by impeding further reduction of electrolyte. However, the details of ionic transport and the mediating defects in LiF are still in question. In this study, we conducted density functional theory (DFT) calculations of the defect formation energies and concentrations in a range of relevant Li chemical potentials. We considered several possible defect sites at different charge states. The close packing of the LiF makes it energetically unfavorable for interstitials to be present in considerable quantities. In accord, vacancies of the constituent elements are found to be predominant defects. Diffusion of Li is also evaluated by employing nudged-elastic band (NEB) method in defected structures. The activated states and the diffusion barriers of possible transport routes will be presented. The results will be verified using available experimental data. The gained information can be used to establish design criteria regarding LiF proportion in the SEI and cell chemistry to achieve target compositions.

Understanding the solution structural interactions within liquid electrolytes remains a daunting challenge. But this is just what is needed to intelligently design new electrolyte formulations for advanced battery chemistries and to better identify the limitations of existing electrolytes. Insight into the factors governing ion solvation and ionic association, in particular, enables mechanistic explanations to be made for the wide disparity often noted in electrolyte characteristics. Utilizing a methodology based upon a fusion of both experimental and computational techniques, the variations in electrolyte solution structure for differing solvents, lithium salts and concentrations—as well as the dynamics associated with solvate formation—will be detailed and the impact of this on salt solubility, transport properties and interfacial interactions delineated.

The development of rechargeable Mg batteries, driven by the desire to surpass the limiting specific energy density of Li ion batteries, is currently limited by the lack of stable, functional electrolytes compatible with high voltage cathodes. A functional electrolyte must deliver the Mg cation to the anode surface at nearly 100% Coulombic efficiency, requiring cation desolvation and accommodation without formation of a cation blocking film. Successful electrolytes have relied on Lewis acid - base reactions to form Mg cation-solvent complexes that include the traditional Grignard based and more recently reported inorganic MgCl₂ based complex electrolytes containing either BR₄^- or AlR_xCl_4-x^- species. However, organometallic species are considered undesirable from the standpoint of high voltage cathode compatibility, and novel approaches using inorganic Mg-salts are of tremendous interest despite their alleged propensity to form surface films, the functions of which are not well understood. We seek to provide more detailed fundamental insight into the nature of these films formed at the electrode/electrolyte interface and their impact on the electrodeposition and dissolution of Mg from inorganic salt electrolyte systems using in situ characterization techniques.
We first demonstrate the impact of surface film formation on Mg deposition and dissolution in an inorganic chloroaluminate electrolyte (MgCl₂-AlCl₃) in which the buildup of an impeding layer on the Mg surface enforces the re-nucleation of Mg on itself during subsequent deposition. The morphology and crystallographic texture of new Mg layers are altered, and restricted lateral mobility of Mg within the surface film leads to incomplete in-growth of depositing Mg and extensive interfacial void formation, the consequences of which will be discussed. We also demonstrate Mg plating and stripping characteristics of Mg(TFSI)₂ in diglyme, which exhibits kinetically facile but moderately reversible Mg deposition behavior due to passive film formation. Structurally, deposits generated in this electrolyte are radically different from those generated in chloroaluminate systems, yet the reasons for this are unknown. Using in situ imaging techniques (AFM, STM) we provide visualization of the presence and impact of surface films formed prior to and during Mg deposition as well as during dissolution. We will also provide complementary analyses of the electrode/electrolyte interface using QCM, vibrational spectroscopy and X-ray absorption spectroscopy to form a more complete picture of Mg surface films in this and other inorganic salt electrolytes.
This work is 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 multi-program 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.

With the intrinsic limit of energy density being approached in Li ion chemistry, there have been extensive efforts aiming at breaking out this limit set by the storage mechanism where only one Li⁺ could be accommodated per transition metal element. Among the so-called “beyond Li ion” chemistries, in which inert masses are kept at minimum, the electrode integrity is often sacrificed for high specific capacities, which presents severe challenge to the electrode/electrolyte interphases. Understanding the interactions between these new materials and electrolytes and the concomitant interphases would play significant roles in determining their future successes.
This presentation will only overview the electrolyte and interphase in these nascent battery chemistries, while emphasizing the most recent breakthroughs achieved in electrolytes and interphasial chemistry in Li/S system..

Rechargeable magnesium battery systems hold promise as candidates for post lithium-ion battery due to their high volumetric capacity (3833 mAh cm^-3 vs 2046 mAh cm^-3 for Li metal), lower cost, and absence of dendrite formation when compared to Li-based batteries. An added benefit of Mg metal as anode is the formation of a protective film on the metal surface upon exposure to air, providing safer energy storage devices. However, a number of challenges must be overcome before a fully competitive rechargeable Mg battery will be realized. In particular, a suitable electrolyte able operate a battery involving a Mg anode, a high voltage cathode and non-noble current collector still has not been identified. One of the major hurdles lies in the fact that the vast majority of the available electrolyte systems contain halides in their structure and renders the electroactive species corrosive to non-noble metals.^[1] Our group recently introduced magnesium borohydride as a novel unique electrolyte system,^[2] representing an end to the reign of halide-containing electrolytes and opened new horizons in the design space of magnesium battery electrolytes. Our main focus has been to expand the magnesium B-H electrolyte family and build systems that take advantage of the attractive properties of magnesium borohydride, but offer an enhanced oxidative stability. The magnesium carborane Grignard complex we recently reported represented the first proof-of-concept of our current research direction.^[3] In this talk, we will share our results on the development of magnesium boron cluster salts as magnesium electrolytes, which are fully compatible with Mg anode, offer a large electrochemical window, and are compatible with non-noble metals and high voltage cathodes.
References:
[1] J. Muldoon, C. B. Bucur, A. G. Oliver, J. Zajicek, G. D. Allred, W. C. Boggess Energy Environ. Sci.2013, 6, 482-487.
[2] R. Mohtadi, M. Matsui, T. S. Arthur, S.-J. Hwang, Angew. Chem. Int. Ed.2012, 51, 9780 -9783.
[3] T. J. Carter, R. Mohtadi, T. S. Arthur, F. Mizuno, R. Zhang, S. Shirai, J. W. Kampf Angew. Chem. Int. Ed.2014, 53, 3173 -3177.

The stability of the solid electrolyte interphase (SEI) is critical in rechargeable Li-ion batteries. A clear understanding of SEI formation, evolution and mechanical response will make it possible to tailor better passivation layers that can improve battery performance. In this work we present a novel approach that is based on patterned Si islands, with measurements that include galvanostatic cycling, electrochemical impedance spectroscopy (EIS), in situ optical microcopy, and in situ stress measurements. By calibrating the expansion and contraction of these islands, it is possible to systematically investigate the impact that large volume changes have on the SEI stability. Comparisons between these islands and continuous Si films then make it possible to correlate the irreversible capacity loss with expansion strain in the underlying Si. These galvanostatic experiments on island samples provide a novel mechanical testing configuration for investigating the stability of thin SEI layers. A comparison of SEI stability with different formation conditions and several common electrolytes will also be presented.

Engineering a stable solid electrolyte interphase (SEI) is important to improving the performance and durability of electrodes, such as silicon (Si) which is one of the most promising negative electrode materials for lithium ion batteries. Recently, it has been reported that the electrolyte additive fluoroethylene carbonate (FEC) improved the performance of Si electrodes and increased the presence of lithium fluoride (LiF) in the SEI. To understand this phenomenon, it is essential to study the properties of LiF as a SEI component.
In this study, we developed a theoretical method based on density functional theory to calculate the ionic conductivity of various defects in LiF in contact with electrode materials. In our model, the contacted electrode serves as a Li reservoir with adjustable Li chemical potential (mu;_Li). Since ionic conduction in LiF is a result of defect formation and transport, seventeen possible native defects with their relevant charge states in LiF were investigated to determine the dominant defect types on various electrodes. The diffusion barriers for dominant defects were calculated by the Climbed Nudged Elastic Band Method. The formation and transport of defects were then mapped to ionic conductivity by the Nernst-Einstein relationship as a function of mu;_Li.
Several defect formation reactions are observed as a function of mu;_Li in the reservoir in three regions: 1) intrinsic, 2) transitional, and 3) p-type region. In the intrinsic region (high mu;_Li, typically for the negative electrode), the main defects are Schottky pairs and in the p-type region (low mu;_Li, typically for the positive electrode) are Li ion vacancies. The ionic conductivity is calculated to be approximately 10^-31 S/cm when LiF is in contact with a negative electrode but it can increase to 10^-12 S/cm on a positive electrode. Comparing with other SEI components (e.g., Li₂CO₃) on the Si electrode, the ionic conductivity in LiF is about 18 orders magnitude lower than that in Li₂CO₃, which is not ideal as a component in SEI. However, due to the contribution of ionic transport to electronic conduction in LiF, this low ionic conductivity may help block electron leakage from the electrode, preventing electrolyte molecule decomposition and passivating the electrode surface.

Electrolytes based on the room-temperature molten salts known as ionic liquids (ILs) have great potential to improve both supercapacitor and battery devices. In supercapacitor devices, ILs offer stability over large voltages and high ionic conductivities. Lithium salts are highly soluble in many ILs, producing solutions that are of particular interest for lithium-based battery applications as ILs are non-flammable and therefore may mitigate or eliminate safety concerns stemming from thermal runaway. In order to maximize energy and power densities and eliminate the possibility of electrolyte leakage, ILs may be confined into a gel form called an "ionogel". Ionogels have been made using a variety of solid scaffold materials and fabrication techniques, with special emphasis on creating flexible and elastic materials that are nonetheless mechanically, chemically, and thermally robust.
This work introduces a new form of ionogel that combines high loadings of an IL or lithium-in-IL solution with a polydimethylsiloxane (PDMS) scaffold. This system is intriguing as PDMS offers excellent mechanical properties as well as high chemical and thermal stability. Importantly, however, PDMS is immiscible with many ILs of interest. Miscibility barriers have important implications for many forms of solid electrolytes, as they may impact the availability of suitable scaffold materials. In this work, a method to overcome the immiscibility between PDMS and ILs is demonstrated. By designing a process which surmounts this barrier, insight is also gained into the interactions between ILs and scaffold materials both during and after the process of gelation.
PDMS-supported ionogels with IL loadings of up to 80% by mass were realized using a simple sol-gel reaction at room temperature. A mixture of a functionalized PDMS oligomer, formic acid, and an IL (or lithium-in-IL solution) is stirred to produce a castable, one-phase resin that cures into a freestanding, flexible ionogel when left undisturbed for several hours. Because the formic acid, which acts as a catalyst, is dissolved in the IL phase, the reactive end groups of the PDMS oligomer must come into intimate contact with the IL for the reaction to proceed, resulting in a co-mingled mixture of the growing PDMS network within the IL. This approach stands in contrast to traditional cross-linking methods in which the catalyst resides in the polymer phase. PDMS-supported ionogels exhibit favorable ionic conductivity (~3 mS/cm) and excellent mechanical behaviour (elastic modulus ~60 kPa, fatigue life >5000 cycles, mechanically stable up to 200 °C). Moreover, the activation energy of ionic conductivity for PDMS-supported ionogels is found to be nearly identical to that of the neat IL, in contrast to ionogel systems wherein the scaffold material is miscible with the IL. This indicates that IL/scaffold chemical interactions are key to understanding ionogel electrical performance, especially at elevated temperatures.