Symposium ES1 : Materials Science and Chemistry for Grid-Scale Energy Storage

Grid-tied energy storage systems (ESS) are becoming more prevalent in the electricity infrastructure and are seen as critical to improve grid stability and reliability, and to accommodate large scale integration of renewables. When properly integrated, energy storage will improve the quality, flexibility, reliability, resiliency, and cost effectiveness of the existing electric utility systems. The enabling technology for grid-tied energy storage systems is the power conversion system (PCS). The PCS provides the bi-directional power conversion necessary to connect energy storage devices, such as batteries, flywheels, and other storage devices, to the grid. An optimized system would provide for maximum power transfer and control to and from the grid, while maintaining reliable and safe operation of the storage device. The integral part of the PCS is power electronics, which dominates the overall cost, and determines the overall reliability and performance of the converter. Most PCSs currently used in energy storage systems utilize silicon-based power semiconductor devices. PCSs using wide-bandgap (WBG) power semiconductors, such as Silicon Carbide and Gallium Nitride, are beginning to find greater use. SiC and GaN power modules allow for higher switching frequencies, higher breakdown voltages, and higher junction temperatures, while reducing the size of power modules enabled by advanced packaging techniques. Utilizing these types of switches will improve system performance by increasing the power density and efficiency by an order of magnitude, compared to traditional silicon-based designs. This presentation will give an overview of power electronics and power conversion systems, and highlight recent advances in associated component technologies, such as solid state transformers (SSTs) and high-frequency converters and advanced magnetics; along with their impact on the development of lower cost, high performance PCS for grid energy systems.

Aqueous energy storage systems, e.g. aqueous lithium ion batteries (ARLIBs), are becoming increasingly important for its high theoretical specific power and safety, while the practical performance has been critically constrained by its narrow voltage window due to the electrochemical water splitting side reactions.^{[1, 2]} Although the sluggish oxygen evolution usually requires a large overpotential, the hydrogen evolution reaction (HER) can easily take place when the applied potential increases, and critically constrains the battery voltage window as well as the Coulombic efficiency.^[3] The rational design of anode materials, where the hydrogen evolution also takes place, may suggest a new avenue for developing ARLIB with enhanced voltage window and power density.
Inspired by the high efficient hydrogen evolution catalysts,^{[4, 5]} we designed an opposite strategy instead, aiming to create a large HER overpotential for inhibiting water reduction and subsequently boosting both the battery output voltage and Coulombic efficiency in aqueous solutions. Moreover, the electrode surface passivated with hydrogen evolution further enables high current density during battery cycling, leading to both an ultrahigh power density and an excellent energy density. Density functional theory calculations indicate polyimide nanosheets provide limited sites for hydrogen atom binding and large activation barriers for HER, especially for Li⁺ associated polyimides. After improving their electronic conductivity by carbon nanotube (CNT) networks, the polyimides/CNT aqueous lithium-ion battery anode exhibits hydrogen evolution onset overpotential as large as 820 mV in neutral aqueous electrolytes, an outstanding reversible capacity of 133.0 mA h g^-1, and ultrafast charge-discharge capability (13.6 sec per cycle at 128C). Moreover, an aqueous polyimide-CNT//LiMn₂O₄ battery exhibits top-level performance, including a wide voltage window (> 2 V), exceptional capacity (68.8 mA h g^-1), energy density (76.1 W h kg^-1) and power density (12,610 W kg^-1), and excellent cycling stability over 1000 cycles when fast operated within ~ 5 min.

Reference
1. Luo, J.; Cui, W.; He, P.; Xia, Y. Nat. Chem. 2010, 2, 760-765.
2. Kim, H.; Hong, J.; Park, K.; Kim, H.; Kim, S.; Kang, K. Chem. Rev. 2014, 114, 11788-11827.
3. Suo, L.; Borodin, O; Gao, T; Olguin, M; Ho, J; Fan, X; Luo, C; Wang, C; Xu, K. Science 2015, 350, 938-943.
4. Zhang, X.; Meng, F.; Mao, S.; Ding, Q.; Shearer, M. J.; Faber, M. S.; Chen, J.; Hamers, R. J.; Jin, S. Energy Environ. Sci. 2015, 8, 862-868.
5. Wang, D.; Gong, M.; Chou, H.; Pan, C.; Chen, H.; Wu, Y.; Lin, M. C.; Guan, M.; Yang, J.; Chen, C.; Wang, Y.; Hwang, B.; Chen, C.; Dai, H. J. Am. Chem. Soc. 2015, 137, 1587-1592.

As an alternative to metal-based electroactive materials, quinone-based organic redox species represent one of the most promising electrode materials owing to features including material sustainability and tailorable properties. Here we systematically study quinones for liquid batteries in both aqueous and non-aqueous electrolyte. As an emerging battery technology, this organic liquid battery inherits the advantageous features of modular design of flow batteries and high voltage and energy efficiency of Li ion batteries. With the help of rotating disk electrode and cyclic voltammetry measurements, the redox chemistries of quinones are investigated comprehensively. Moreover, a combined experimental and computational study reveals that the redox properties of quinones are strongly dependent on the molecular aromaticity and electronic structures. As quinones play a pivotal role in bioelectrochemical process, a fundamental understanding of their reaction mechanisms in electrochemical energy storage devices can pave the path towards bio-inspired sustainable energy technologies.

With the growth of sustainable energy generation, there is an increased demand for large-scale energy storage to secure the grid system. Lithium-ion battery is considered as one of the most attractive energy storage solution due to its high energy density and efficiency. However, the high cost of the electrode materials hinders its application in such price sensitive market. Here, we report a low-cost, large-scalable waste tire-derived carbon and metal oxide composite anode for lithium ion batteries. Carbon composite powders were prepared with carbon recovered from used tire powders and 25 wt. % of the select metal oxides to form composite electrodes. With such controlled amount of the metal oxide and the unique pore size distribution of the tire-derived carbon as the absorbing matrix, the volume change and the degradation of the electrodes are minimized. The composite anode shows a very stable electrochemical performance with a capacity of over 650 mAh g^-1 after 300 cycles at a current density of 40 mA g^-1. We will report in detail about the synthesis and characterization of the carbon composite electrodes. This study provides a new pathway for inexpensive, environmentally benign and value-added waste tire-derived products towards large-scale energy storage applications.

Lithium-ion batteries (LIBs) are the key components of portable electronic devices and electric vehicles. High energy density lithium ion batteries are required for their future applications in electronic market, as the needs of the market are more demanding. Graphene and graphene based materials have gained the interest due to their good properties such as mechanical flexibility and high electrical conductivity, surface area and chemical diffusivity of Li. Graphene has been studied in the batteries in the past and their challenge has been demonstrated over the past couple of years [1, 2]. On the other hand metallic Tin based materials have also attracted great attention due to their good electrochemical properties when used as anode for LIBs, mainly due to theoretical specific capacity (993 mAh g^-1) of Sn, low cost and low toxicity [2]. However, Sn shows several problems: i) large volume changes during the lithiation/delithiation process (which can be up to 300 %); ii) high degradation and low cyclability due to these volume changes; iii) high decomposition of the electrolyte due to high reactivity of Sn nanoparticles. Different Sn/C composites have been developed to overcome these problems and improve the stability of Sn anodes. These carbon matrixes are reported to buffer the volume change of Sn during charge/discharge. [2]
The aim of this work, was to evaluate reduce graphene oxide (rGO) and a novel composite of SnO₂@rGO (binder free) aerogels as self-standing anodes for LIBs. SnO₂@rGO composites were synthesized in two steps: i) freeze-drying and ii) thermal reduction of a mixture of SnSO₄ and graphene oxide suspension, previously prepared by modified Hummer method. [3] The pure rGO was prepared following the same procedure. The materials have been characterized by XRD, XPS and SEM. Homogeneous distribution of 50–200 nm particles of SnO₂ in the graphene matrix has been observed.
CR2032 type coin cells were used to analyze the electrochemical properties of the composite cathode. Cells were fabricated inside a glove box under Argon atmosphere with H₂O and O₂ level < 0.1 ppm. 1.2 M LiPF₆ solution in ethylene carbonate and dimethyl carbonate 1:1 (v/v) solution with VC as additive was used as electrolyte. Lithium metal foil was used as counter/reference and glass fiber as separator. Self-standing rGO and Sn/SnO₂@rGO composite (without any binder and any support) were used as anodes. The reversible specific capacity of Sn/SnO₂@rGO was 650 mAh g^-1 at 50 mA g^-1 after 40 cycles and 420 mAh g^-1 at 1A g^-1. The pure rGO specific capacity was 298 mAh g^-1 after 40 cycles at 50 mA g^-1.[4]

[1] Z. Wu, G. Zhoua, L.Yina, W. R., F. Lia, H. Cheng. Nano Energy, 1 (2012) 107.
[2] J. Qin, C. He, N. Zhao, Z. Wang, C. Shi, E. Liu, J. Li. ACS Nano, 8 (2014) 1728.
[3] C. Botas, P. Álvarez, C. Blanco, R. Santamaría, M. Granda, et al. Carbon, 50 (2012) 275.
[4] C. Botas, D. Carriazo, G. Singh, T. Rojo, J. Mater. Chem. A, 3 (2015) 13402.

In this presentation novel ambient temperature electrolytes for application inn lithium-ion and post lithium-ion (e.g. sodium, magnesium, Li-S etc.) batteries will be presented. New fluorine and fluorine free salts which can easily be synthesized in the form required for various applications will be presented and their properties discussed from the viewpoint of particular applications. Some examples of the performance of batteries with electrolytes based on newly developed salts will also be included. In particular we would like to highlight some new ideas of the preparation of polymer solid, gel and ionic liquid electrolytes leading to their superior properties compared with currently commercially available electrolytes.

High-capacity Si-based anode is an advanced anode material to improve the energy density of Li-ion battery. In order to pair with commercial cathode, the areal capacity of Si-based anode should be increased to 3-4 mAh/cm². However, high-areal-capacity Si-based anode still encounters fast capacity fading issue and poor cycling stability, because huge volume change of Si active material upon repeated charge/discharge cycles will lead to damage of electrode structure integrity (like particle pulverization, electrode cracking/delamination, and loss of conducive network) and accumulative growth of SEI (solid electrolyte interface) layer. Here we develop an elastic and stretchable gel polymer electrolyte (GPE) coating strategy to improve the long-term cycling stability of high-areal-capacity SiO electrode. The polymer coating can swell and uptake 75 w% carbonate electrolyte, providing a moderate ionic conductivity of 2.4*10^-4 S/cm at room temperature. The GPE shows great chemical and electrochemical stability with lithium metal. At the electrode level, the GPE coating is elastic and stretchable, and it can improve electrode adhesion strength and alleviate electrode thickness change during charge/discharge process. For long-term cycling, the GPE coating can restrict the pulverized particles in a localized space to prevent loss of conductive network and maintain the electrode structure integrity. In half cell test, the SiO electrode with GPE coating shows a reversible capacity of 3.0 mAh/cm² (or specific capacity of 1200 mAh/g) for 280 cycles. In full cell test, the cell of NCM/prelithiated SiO electrode with GPE coating has a reversible capacity of 2.1 mAh/cm² (or specific capacity of 150 mAh/g) for 300 cycles, with an improved Coulombic efficiency of above 99.9%.

Although silicon has higher reversible capacity than graphite as a lithium storage material, its large volume expansion during lithium insertion causes poor capacity retention. To address this technical issue, melt-spun Si based alloy materials have been suggested as a promising materials for lithium ion batteries because of their high capacity and relatively low production cost. However, their long-term cycle performance should be further improved for the commercial success. In this work, it was demonstrated that mechanical deformation can improve the electrochemical performances of melt-spun Si alloy material. With the help of high-energy mechanical milling, Si/TiFeSi₂ nanocomposite was successfully tuned with a size of few nanometers based on the results of X-ray diffraction analysis and transmission electron microscopy observation. As a result, the microstructurally tuned Si/TiFeSi₂ showed a reversible capacity of more than 1000 mAh g^-1 with stable capacity retention up to 100 cycles. More detailed studies on the reasons for better cycle performance of milled Si/TiFeSi₂ will be discussed in this presentation.

The increasing demand for energy storage nowadays requires both high power and high energy density devices. Hybrid batteries are good candidates to meet the requirements by marrying battery and super-capacitor electrodes. In this work, Li₄Ti₅O₁₂ (LTO), as battery electrode, and activated carbon (AC), as supercapacitor electrode, are combined into one hybrid battery. Prior to the hybrid battery assembly, LTO electrodes were cycled three times against lithium chip in a Swagelok cells and then charged or discharged to non-lithiated or pre-lithiated states. We compared the charge/discharge capacity, cyclic voltammetry graphs, impedance, diffusion efficiency and other characteristic to discuss the impact of the pre-lithiation on the LTO/AC hybrid batteries. From charge/discharge and cyclic voltammetry tests, both kinds of hybrid batteries exhibit physical-absorption-domain CV curves and have similar performance. However, with the pre-lithation process, the hybrid battery has higher specific capacity, reduced electrode resistance and higher capacitive reactance.
This research is supported by NSF, a US government agency which supports fundamental research and education in all the non-medical fields of science and engineering, under Award Number 1318202.

The urgent need to increase the share of renewable sources in the energy scenario, as well as of environmentally compatible vehicles, either hybrid electric vehicles (HEVs) or electric (EVs), requests the fast development of improved energy storage systems. Lithium Ion Batteries (LiBs) are presently viewed as the most promising candidates due to their high specific energy density. However, the current LiB technology based on a C/LiCoO₂ chemistry is not yet at such a level to meet the requirements for HEVs and, in particularly EVs. Therefore, the development of alternative chemistries assuring decrease in cost and enhancement in energy density is a mandatory step. A promising example of a cathode alternative to the high cost and partially toxic LiCoO₂ is the LiNi_0.5Mn_1.5O₄ (LNMO) spinel, since it is characterized by higher theoretical energy density, about 660 Wh kg^-1, environmental compatibility and lower cost. However, several issues still prevent the practical implementation of LNMO cathodes in lithium batteries. Furthermore, the severe requirements of the battery manufacturers triggered the replacement of the metallic anode by alternative materials characterized by higher safety. In this contribution we present Li-ion batteries (LiBs) exploiting spinel cathodes and TiO₂-nanotubes anodes. The LiBs showed outstanding properties in terms of fast charge (about 5 minutes), high energy (230 Wh kg^-1) and long cycle life (extending to over 400 cycles). Moreover, by the addition of an ionic liquid to the carbonate-based electrolyte solution we demonstrated an enhanced safety content of the LiBs developed.

A simple methodology is developed for the in-situ preparation of flexible, three-dimensional ordered macroporous (3DOM) TiO₂ electrodes with greatly enhanced mass transfer. The 3DOM electrode is fabricated using a polystyrene colloidal crystal templated carbon cloth, and provides significant improvements over conventional nanoparticle electrodes without the use of binder or other additive. When evaluated as an anode in a Li-ion battery, the 3DOM electrode provides outstanding high rate performance. The electrode provides a specific capacity of 174 mAh g^-1 at a current density of 2 A g^-1, which is 2.6 times greater than that achieved with a nanoparticle electrode (68 mAh g^-1). The 3DOM electrode also achieves excellent cycling stability, with a capacity retention of 94.8% (181 mAh g^-1) over 1000 cycles at 10C (1.7 A g^-1) compared to 93.7% (67 mAh g^-1) for the nanoparticle electrode. To the best of our knowledge, the performance of our 3DOM electrode is among the highest of binder-free, flexible TiO₂ electrodes. We believe that this methodology is highly useful and is easily transferable to other materials and applications.

Disruptions in periodicity are extremely common in all kinds of solid materials and can manifest in multiple ways. Indeed solids often exhibit point defects (such as antisites, interstitials or vacancies), stacking faults, grain boundaries, pores, intergrowths or microstrains, just to name a few. While some technologies require the use of crystals that are nearly perfect, polycrystalline solids are usually the norm in most applications. This is the case of electrochemical storage systems, for which a proper understanding of the underlying thermodynamics and kinetics unavoidably requires the framework of both structure and microstructure.
Diffraction techniques (XRD, NPD) are typically used to characterize average structural features of functional materials. Thanks to the recent development of advanced tools for diffraction data treatment (either implemented in Rietveld refinement programs such as FullProf, or available as independent refinement programs such as FAULTS), powder diffraction can now be also used for the quantitative characterization of extended defects. Several examples corresponding to different battery materials will be shown to illustrate how, besides classic structural determination, quantitative information regarding microstructural features such as anti-phase domains, stacking faults, twinning or intergrowths or microstrains can now be extracted from diffraction data to establish correlations with materials’ properties and monitor their evolution upon cycling through the use of in situ or operando data.

Li-rich layered oxides, either as a solid solution or as a nano-composite of layered Li₂MnO₃ and Li(TM)O₂ (TM=Ni, Co, Mn), draw significant attention as the next-generation cathode materials for high-energy-density lithium ion batteries in electric vehicles. Over the past twenty years, the discharge capacity at room temperature of these cathode materials has been improved from 200 mAh g^-1 to over 320 mAh g^-1 today, even higher at elevated temperatures. While the research has continued to push the limit of the available capacity of the materials throughout the years, there are many issues still unclear. And numerous scientific challenges, especially voltage degradation during cycling of these materials, that must be overcome to realize their utilization in commercial lithium ion batteries.

Here, we report a design of modified co-precipitation method without ammonia addition to synthesize morphology controlled Li-rich material Li_1.2Ni_0.2Mn_0.6O₂ as high energy density cathode for lithium ion batteries. The obtained material has spherical secondary particles with uniform dispersion. The secondary particles are dense, and have an average diameter of approximately 3 μm. These secondary spherical particles consist of primary particles with particle size approximately 150 nm. The morphology controlled sample can minimize voltage decay as well as improve capacity retention during cycling. The successful implementation of this morphology controlled Li-rich material as the cathode for lithium ion batteries can increase the overall energy density of the state-of-the-art lithium ion batteries by 20-25%. And furthermore, the influence of morphology control on the cycling performance has been investigated through Transmission X-ray Microscope.

Recently, Ni-rich layered structure cathode materials LiNi_xMn_yCo_zO₂ (NMC, x ≥ 0.6) have received great attention as a promising cathode due to their high achievable discharge capacity (200~220 mAh g^-1), representing a significant enhancement in energy density (~800 Wh kg^-1) in comparison with traditional LiCoO₂ (~570 Wh kg^-1) and spinel LiMn₂O₄ (~440 Wh kg^-1). Ni-rich cathode materials also have much higher lithium ion diffusion coefficients, indicating a superior power capability as compared to other NMC cathodes with lower Ni contents. The other advantage of Ni-rich cathode materials is the reduction of production cost due to the reduced Co content. However, there are still some technical challenges hindering the mass applications of Ni-rich cathode materials, mainly including (i) micro strain and crack formation because of the significant volume variation during lithium ion de/intercalation processes, (ii) safety concern ascribed to the aggressive thermal reactions between the delithiated Ni-rich NMC materials and the organic carbonate electrolyte.
A lot of effort has been dedicated to improving the electrochemical performances and thermal stability of the Ni-rich NMC cathode materials. Representative approaches include lattice doping, surface treatment/modification, tuning the material compositions, a smart design of core-shell or concentration gradient structures, structural stabilization with a low content of Li₂MnO₃, and so on. In addition to the solution-based coating method, surface coating via atomic layer deposition (ALD) has attracted increasing attention in the development of high performance electrode materials for LIBs, due to its exclusive advantages including low deposition temperature and extremely uniform and conformal deposition of thin films with precisely controlled thickness. ALD surface coating of various oxide has proved to be effective in improving the long-term cycle life of a variety of cathode materials. Herein, we report for the first time ALD coating of a new solid-state electrolyte Li₃PO₄ on a Ni-rich cathode material LiNi_0.76Mn_0.14Co_0.10O₂ with. Coating with solid-state electrolyte Li₃PO₄ gives rise to a significant enhancement in the interfacial and structural stability, and the electrochemical performances of LiNi_0.76Mn_0.14Co_0.10O₂ even under harsh testing conditions of charge cut-off 4.5 V and at 60 ^oC. The functioning mechanism of solid electrolyte coating was investigated in detail by electrochemical measurements, impedance analysis in conjunction with systematic electron microscopic observations.

We report a solvent-free dry powder coating process for making a LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathodes in lithium-ion batteries. Comparing with the conventional wet slurry-based electrode manufacturing method, the dry powder coating method is a lower cost, higher throughput, and more environmentally friendly manufacturing process. This process lowers electrode fabrication cost by 90%, eliminates volatile organic compound emission, and reduces electrode drying time from hours to minutes. A dry mixture of NMC, carbon black, and poly(vinylidene difluoride) was sprayed onto an aluminum current collector to form a uniformly distributed electrode of controlled thickness and porosity. The composition, structure, thermal stability, and electrochemical performance of the electrodes were analyzed. Excellent electrochemical performance was obtained with a discharge specific capacity of 155 mAh g^-1 and capacity retention of 96% over 80 cycles from 3 to 4.3 V at 0.2 C/5 charging rate in lithium half cells. The electrodes have similar long-term cycling performance and durability to those made by the conventional web slurry process.

The composite of Fe₂SiO₄ with carbon nanotubes and Fe₃O₄ (Fe-Si-O/CNT) are fabricated by a simple one-step pyrolysis of ferrocene and tetraethyl orthosilicate mixture. The composite utilized as anode material for Li-ion storage exhibits ever-increasing capacities when cycled at a current density of 100 mA g^-1, and after 280 cycles, a stable capacity of 588 mAh g^-1 is achieved. When cycled at 200, 400, 800 and 1600 mA g^-1, the reversible capacities are 364, 323, 281, 235, and 186 mAh g^-1, respectively. Even cycled at 500 mA g^-1, a reversible capacity of 350 mAh g^-1 is retained after 600 cycles. The excellent performance is much superior to that of the carbon-coated Fe₃O₄ prepared under the similar conditions and mechanically mixed Carbon Nanotube@Fe₃O₄. The Fe-Si-O/CNT active material is characterized by structural analysis, such as XRD, TEM, Raman and FTIR, and electrochemical tests, such as Cyclic Voltammetry and Electrochemical Impedance Spectra. Outstanding performance of Fe-Si-O/CNT could be ascribed to improved conductivity by CNTs, stable structure of Fe₂SiO₄, enhanced capacity by Fe₃O₄ and significant activation effect during cycling.

Energy storage designs that include lithium-ion transport between electrodes require increased understanding of basic materials science that promotes mechanical degradation of the electrodes and reduced charge storage capacity of the energy storage device. Chemically induced stress in Li-ion battery (LIB) electrodes often leads to fracture of electrode particles during cycling and is commonly believed to be a key origin of decreased LIB lifetime and late-life performance. Here we identify the role of fracture on capacity and impedance in Li_XMn₂O₄ cathodes using a novel electrochemical shock approach combined with detailed analysis of impedance spectra and post-test microscopy and spectroscopic analysis. Specific charge-time cycles and conditions were used to induce discrete fracture events verified by in situ monitoring of acoustic emissions and post-test microscopy. We find that the discrete fracture events correlate with increased impedance, consistent with surface film growth and active particle-carbon contact resistance. Among the myriad number of potential LIB degradation mechanisms, this study demonstrates directly the relationship between electrochemically driven electrode fracture and performance loss, critical for well-informed design of Li-ion batteries with improved longevity and late-life performance required of expanded applications including grid-scale energy storage.

The high inactive materials content (e. g., separators, current collectors, conductive additives, binder and packaging) of current battery designs leads to high materials and manufacturing cost and reduces the overall energy density (both gravimetric and volumetric) of the battery. Increasing battery electrode thickness and/or density would be a simple and straightforward approach to increasing energy density and reducing cost, but is limited by transport limitations. In the limit of high density and large thickness, lithium salt depletion within the electrolyte-filled porosity typically becomes rate-limiting. To overcome this limitation and deliver high energy density at practical C-rates, it is critical to lower tortuosity through rational design and tailoring of the topology of the electrode pore structure.
We report magnetic alignment methods that produce low tortuosity porosity from sacrificial pore formers, and that are rapid, scalable, and naturally produce aligned porosity favorably oriented normal to the electrode plane. These methods are not limited to certain electrode materials and can be generally used to make both battery cathode and anode. We also report electrochemical measurement results of the low-tortuosity electrodes under both standard galvanostatic and model EV duty cycle tests. The low-tortuosity electrodes show overall faster charge transport kinetics and deliver more than threefold higher areal-capacity (e.g., >12 mAh/cm² vs <4 mAh/cm² in conventional electrodes) at practical charge-discharge rates.
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. 7056592 under the Batteries for Advanced Transportation Technologies (BATT) Program. J.S Sander thanks the Swiss National Science Foundation for financial Support (Grant Number P300P2_154584 and P2EZP2_148768).

Nowadays, Lithium-ion batteries are not only used in simple portable devices, but also its usage has been expanded into large scale applications such as electronic vehicle (EV) and hybrid electronic vehicle (HEV) owing to its high economic feasibility and high energy density compared to other types of energy storage devices. Currently, commercialized LIBs can maintain 80% of its initial capacity after 500 cycles in proper usage, which corresponds to a cycle efficiency of 99.93% per cycle. The irreversible capacity of 0.07% at every 1 cycle seems to be trivial but the small difference in cycle efficiency brings out a big difference upon cycles; reducing the irreversible capacity of cells by half (0.07% to 0.03%) corresponds to extending lifespans by double. Therefore, deeper understandings of the capacity fading mechanism of LIBs are necessary to realize the next generation LIBs.
In this study, the relationship between oxygen vacancy and structure degradation of lithium transition metal oxides is investigated. Herein, we have demonstrated that the cathode degradation process can be started from the inside of a single crystal due to an inevitable existence of oxygen vacancies and their diffusion in metal oxides, which is an opposite idea to the conventional fading mechanisms where the fading starts from the particle surface.

With the increasing demands of rechargeable batteries in electric vehicles and grid storage, the layer-structured ternary material LiNi_xCo_yMn_(1−x−y)O₂ (0 < x, y < 1) has been one of the most promising cathode materials in the market. Li_1.03(Ni_0.5Mn_0.35Co_0.2)_0.97O₂ (NMC-532) is a representative ternary material for the nickel rich layered structure and is expected to be promising due to its high discharge capacity and low cost, compared to those of LiCoO₂ and LiMn₂O₄. However, cycling at high working voltage accelerates the inferior side reactions between the electrode surface and the organic electrolyte, which leads to decomposition of the organic electrolyte, reconstruction of the surface of cathode, and finally capacity and cell voltage degradation. Aluminum oxide (Al₂O₃) atomic layer deposition (ALD) has been proven effective in protecting electrode surfaces and mitigating the unwanted interfacial reactions in many circumstances. This research focuses on the investigation of ALD Al₂O₃ coating effects on the electrochemical performance of NMC-532/graphite full cells. Both NMC-532 powder and the laminated electrodes made from NMC-532 powder have been used for ALD Al₂O₃ coating experiments, and characterized through complex electrochemical analysis methods. Moreover, the laminated electrodes with different porosity have also been studied to identify the coating effect on high-voltage cycling performance. Initial results show negligible effect of coating on the cycling behavior of thick electrodes after calendering. However, improvement in cycling performance has been observed for the porous electrodes without calendering. The divergent impacts of ALD coating are attributed to the coating coverage and quality for different electrode architectures. In addition, this presentation will compare the results from the coated NMC powder and the coated laminated-electrodes, systematically analyze the impact of coating on the electrochemical properties, and determine the most effective electrode structure for improved performance.

Recently, flexible and wearable electronic devices and their associated technologies have significantly increased in demand, thereby attracting much interest in development of flexible and wearable energy storage systems. However, flexible and stretchable energy storage system must address design issues such as the selection of suitable flexible, stretchable active material, as well as supporting substrate and current collector. Textile based supercapacitors have the ability to maintain electrochemical performance under mechanical strain and have high power density due to fast charge−discharge rates, which are characteristic of electrostatic double-layer capacitance. One disadvantage of supercapacitors, however, is their low energy density compared to other energy storage systems such as the Li-ion battery. To compensate for the low energy density, many researchers have deposited nanostructured pseudocapacitor materials such as metal oxides MnO₂ and RuO₂, as well as conductive polymers that can enhance the capacity by 200−300%. However, the metal oxide nanostructures result in large volume changes during charge−discharge cycles that cause delamination of the active materials and hence a decrease in electrochemical reliability.
To prevent the delamination of nanostructured pseudocapacitor materials, Yu et al¹ reported use of a thin layer of conductive polymer PEDOT:PSS(200 F/g) coated on top of the MnO₂ pseudocapacitor. Our aim is to use an alternative material for polymer coating that can serve as a conductive and adhesive layer while also enhancing capacitance. Polypyrrole is favorable due to its high energy capacity(620 F/g)², chemical stability, electrical conductivity (50−100 S/cm), and thermal stability. The high conductivity of polypyrrole can result in enhanced power density when coated on top of MnO₂ loaded CNT textile, and high power and energy densities can be expected. In addition, polypyrrole can prevent delamination of active materials during charge−discharge cycles.
In this study, polypyrrole was coated on top of MnO₂ nanoparticles that are deposited on CNT textile supercapacitor to prevent delamination of MnO₂ nanoparticles. An increase of 38% in electrochemical energy capacity to 461 F/g was observed, while cyclic reliability also improved, as 93.8% of energy capacity was retained over 10,000 cycles. An in-situ electrochemical and mechanical study revealed that polypyrrole−MnO₂ coated CNT textile supercapacitor can retain 98.5% of its initial energy capacity upon application of 21% tensile strain and showed no observable energy storage capacity change upon application of 13% bending strain. After imposing cyclic bending of 750,000 cycles, the capacitance was retained to 96.3%.

Hybrid electrodes of electrochemically active organic and inorganic components are often capable of delivering higher energy and power densities compared to single component electrodes for electrochemical capacitors (ECs) and batteries. Rational design of hybrid electrodes with nanostructured building blocks to maximize electronic and ionic conductivity and minimize mechanical failure are the most important factors for achieving high capacitance, rate capability, and cycle life performance in these types of electrodes. In this study, we have explored hybrid electrodes of MXenes (a family of 2D conductive transition metal carbides) and various conductive polymers. We have demonstrated that by a controlled deposition of nanoscale films of polyaniline (PANI) and polypyrrole (PPy) on individual sheets of Ti₃C₂ (one of the MXene family members), flexible and freestanding electrodes can be fabricated. These electrodes deliver unprecedented volumetric capacitances in excess of 1100 Fcm^-3 and excellent cycling stabilities when tested as electrodes for ECs. Moreover, they show high volumetric capacity and cyclic stability as electrodes for Li and Na ion capacitors. X-ray Diffraction (XRD) results show the increased interlayer spacing of MXene sheets after the intercalation and polymerization process which increases the accessibility of the electrolyte ions to Ti₃C₂ sheets and improves the ionic conductivity of the electrodes. In addition, electrochemically active polymers contribute to charge storage and excellent energy density of the electrode materials. The hybrid materials are further characterized by scanning electron microscopy (SEM), Fourier transform Infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and various electrochemical characterization methods to understand the mechanism of the in-situ polymerization and the effects of various synthesis parameters on the performance of the electrodes.

Capacitive energy storage from carbon-based systems offers a number of attractive features for grid applications including high power capability, fast response times, reliability and long-term cycling. As a result, these materials, generally known as supercapacitors, show great promise in the areas of load-leveling, peak-shaving and various grid stabilization functions. The principal limitation with current supercapacitor technology is their low energy density. Increasing the level of energy storage would expand the opportunities for capacitive energy storage in grid applications and in energy storage systems for intermittent energy sources.

The interest in using pseudocapacitor-based materials for electrochemical capacitors is that the energy density associated with faradaic reactions is much greater, by an order of magnitude, than the electrical double layer capacitance of carbon electrodes. Pseudocapacitance occurs when reversible redox reactions occur at or near the surface of an electrode material and are fast enough so that the device's electrochemical features are similar to those of a carbon-based capacitor, but with significantly higher levels of energy storage. One material which meets this criterion is Nb₂O₅. In our studies of Li⁺ insertion in Nb₂O₅, we have established a basis for intercalation pseudocapacitance, where a key feature is that the rate of charge storage is determined by surface-like kinetics rather than semi-infinite diffusion as occurs with battery materials. Another consideration with this mechanism is that the structure does not undergo a phase transformation upon Li⁺ insertion. In addition, when materials are reduced to nanoscale dimensions, they may begin to exhibit pseudocapacitive characteristics because of the large number of surface sites or because phase transitions which occur in the corresponding bulk materials are suppressed. MoO₂ is a good example of this behavior as micron-sized particles exhibit battery-like properties while nanosized materials exhibit pseudocapacitive responses. The ensemble of these results suggests that over the next few years we can expect that there will be a growing number of pseudocapacitive materials which can be considered for grid storage applications.

Carbon nanotubes (CNTs) and graphene sheets can be formed into yarns, forests and film enabling miniature high performance supercapacitors with power densities exceeding those of electrolytics, while achieving energy densities equaling those of batteries [1]. CNTs and graphene can act as both great EDL supercapacitor electrode materials or conductive scaffolds for deposition of pseudocapacitive materials such conductive polymers (PEDOT, PPY, PA, etc) or metal oxides (e.g. MnO₂, RuO₂, etc) [1]. In this work we show that high power, energy density and capacitance in yarn form are not unique to carbon materials, and introduce niobium nanowires as an alternative. Fast charging/discharging supercapacitors are made from Niobium nanowires both in form of long twisted yarns and nanowire forest. Niobium nanowire yarns show higher capacitance and energy per volume, are stronger and 100 times more conductive than similarly spun carbon multi-walled nanotube (MWNT) and graphene yarns [2].
Niobium nanowire yarns achieve device volumetric peak power and energy densities of 55 MW/m³ (55 W/cm³) and 25 MJ/m³ (7 mWh/cm³), 2 and 5 times higher than for state-of-the-art CNT yarns, respectively [1]. Device volumetric peak power and energy densities of 750 MW/m³ (750 W/cm³) and 1.5 MJ/m³ (0.42 mWh/cm³) are achieved for supercapacitors made of niobium nanowires in form of nanowire forest electrodes. Thanks to the high electrical conductivity of the niobium nanowires, ESR of less than 0.5 Ω was achieved. The capacitance per volume of Nb nanowire yarn is lower than the 158 MF/m³ (158 F/cm³) reported for carbon-based materials such as reduced graphene oxide (RGO)/CNT wet-spun yarn, but the peak power and energy densities are higher [1]. Achieving high power in long yarns is made possible by the high conductivity of the metal, while high energy density is possible thanks to the high internal surface area. By infiltrating the yarn with pseudo-capacitive materials such as PEDOT the energy density is further increased to 10 MJ/m³ (2.8 mWh/cm³). Similar to CNT yarns, niobium nanowire yarns are highly flexible and show potential for weaving into textiles and use in wearable devices.
[1] S. M. Mirvakili, M. N. Mirvakili, P. Englezos, J. D. W. Madden, and I. W. Hunter, “High-Performance Supercapacitors from Niobium Nanowire Yarns,” ACS Appl. Mater. Interfaces, vol. 7, no. 25, pp. 13882–13888, Jul. 2015.
[2] S. M. Mirvakili, A. Pazukha, W. Sikkema, C. W. Sinclair, G. M. Spinks, R. H. Baughman, and J. D. W. Madden, “Niobium Nanowire Yarns and their Application as Artificial Muscles,” Adv. Funct. Mater., vol. 23, no. 35, pp. 4311–4316, 2013.

Dynamic development of supercapacitors technology especially regarding electrode materials design requires a novel and more in-depth approach for their investigation. Hence, there is a need for their investigation during device operation, to recognize the major aspects of charge accumulation and aging phenomena as well as the performance failure. Conventional electrochemical techniques used allow the typical parameters (capacitance, resistance) to be determined, however, the mechanism of performance degradation requires a novel insight on the overall chemistry in the system.
The cycle life of electrochemical capacitors is by definition unlimited, as there is no structural change of the electrode material and charge is accumulated only in the electrostatic manner. On the other hand, several additional processes occurring during device operation cause that cycle life is somewhat limited.
This study is majorly focused on the employment of in-situ techniques such as Raman spectroscopy or Quartz Crystal Microbalance (EQCM) for determination of charge storage phenomena and recognition of aging factors in activated carbon-based supercapacitors.
In-situ Raman investigation for activated carbon electrodes operating in neutral aqueous media like Li₂SO₄ or LiNO₃ solutions indicated that there is a mild oxidation of positive electrode during cycling (vibration modes from oxygen-based functionalities found) whereas the surface chemistry of negative electrode is rather stable. Extended voltage, i.e. above 1.4V caused serious oxidation of the positive electrode and hydrogen storage in negative one followed by its further recombination. EQCM study confirmed significant frequency/mass variation on the positive side, whereas negative electrode remained almost constant. More interesting results were obtained for carbon electrodes operating in redox active electrolytes, like KI or KBr solutions. It has been confirmed that iodide anion undergoes several redox processes and strongly interacts with activated carbon surface; formation of -I bond, as well as polymeric forms of iodine/iodide species (triiodides, pentaiodides, etc.), have been observed. Moreover, oxidation of carbon surface has been identified near to iodide/iodine redox activity potentials. EQCM study confirmed the presence of various iodine specimen in the electrolyte solution with the strong dependence of the potential and polarization-exposure time. Carbon ‘corrosion’ has been observed especially for more concentrated iodide solutions. However, we have proved that IO₃^- anion does not contribute significantly to this process; it has a significant influence on the cyclability. In the case of bromide-based solutions, it has been observed that bromide has similar affinity to carbon surface as iodide, but typical -Br bonds have not been found to date.
Finally, the discussion will concern the cyclability issues of carbon electrodes, supported by typical electrochemical investigations.

Matrices/fabrics which can simultaneously generate and store energy are very attractive for charging electronic wearables as well as harvesting renewable energy for electric vehicles. Such an energy-smart (self-sufficient) matrix/fabric can be highly beneficial for military and civilian applications. Based on this novel concept, we recently developed a ribbon which can harvest solar energy and directly store in it. An encapsulated highly efficient solar cell is used as the energy harvesting device and a symmetric supercapacitor with high energy density and power density serves as the energy storage device. Under solar illumination, the energy harvested by the textile/matrix is directly stored in the supercapacitor through a shared electrode. The ribbons so developed are used as the filaments for weaving an energy-smart textile/matrix which can be used to power wearable devices.

Graphene materials are regarded as one promising candidate for next-generation electrochemical energy storage devices due to its unique properties, such as high specific surface area and electrical conductivity. However, most of the up-to-date methodologies for producing graphene, such as chemical vapor deposition, mechanical exfoliation and reduction of graphite oxide, involve several severe drawbacks including heavy ion pollution, low yield and labor-intensive processes, which raise the cost and limit the scalability of graphene production. Therefore, a facile and cost-saving pathway for high-quality graphene synthesis is urgently needed.
Combustion of fossil oil still represents a major energy source for electricity generation around the world, which releases a tremendous amount of CO₂ to cause detrimental global warming. As a result, a prospective method for graphene production is to use the available CO₂ as feedstock gas. But due to the inherent chemical stability of C=O bond, it is a great challenge to reduce CO₂ into carbon materials by conventional techniques. It is well-established that magnesiothermic reaction is capable of dissociating strong chemical bonds, which offers a potential way for effective utilization of CO₂.
Herein, we present an ultra-fast magnesiothermic reaction to fabricate few-layer graphene with highly developed mesoporosity from CO₂ and magnesium/magnesium oxide mixture. It is demonstrated that magnesium oxide acts as the crucial template to guide graphene formation and provide mesopores after acid rising. The quality of our graphene is guaranteed by its high specific surface area (710 m2 g^-1), high purity (~100 % weight loss by thermogravimetric analysis in air), few-layered feature (less than 5 layers), low oxygen content (C/O atomic ratio is 82) and high electrical conductivity (13, 000 S m^-1). Supercapacitors based on our graphene shows a high energy density up to 136 Wh kg^-1, and still keeps 60 Wh kg^-1 even at an ultra-high operating power density of 1, 000 kW kg^-1. The maximum power density of our graphene also reaches an unprecedented 9, 851 kW kg^-1. More significantly, a high capacitance retention of 90 % is obtained after 1 million charge/discharge cycles. To the best of our knowledge, the power capability and cyclic stability of our graphene represent the highest reported value for graphene-based supercapacitors.

Flexible, lightweight and wearable supercapacitors have attracted great interests in energy storage because of their potential applications in portable electronic devices, flexible displays, electronic paper and mobile phone.[1-3] The development of supercapacitors has focused on the use of graphene, due to its excellent electric and mechanical properties, chemical stability, high specific surface area up to 2675 m²/g, and feasibility for large-scale production.[4-5] Graphene-based nanocomposites have been achieved by incorporating guest nanoparticles onto 2D graphene sheets.[6] However, most of these structures suffer from graphene aggregation, which causes inferior ionic accessibility and thus obtains low electrochemical performance. Therefore, macroscopic graphene framework with three-dimensional interpenetrating structures can solve the issue of poor ionic and electronic transport. In our paper, freestanding three-dimensional hierarchical porous reduced graphene oxide foam (RGO-F) was first fabricated by “dipping and dry” method using nickel foam as the template. Three-dimensional (3D) RGO-F with high conductivity provides a large porosity than that of conventional graphene films. Polyaniline (PANI) nanowire arrays aligned on the foam (RGO-F/PANI) were synthesized by in situ polymerization. A symmetric supercapacitor with high energy and power densities was fabricated using RGO-F/PANI electrode. The highly flexible and mechanically foam can directly serve as an electrode with no binders and conductive additives. Owing to its well-ordered porous structure and high electrochemical performance of RGO-F/PANI composite, the symmetric device exhibits high specific capacitance (790 F g ^-1) and volumetric capacitance (205.4 F cm ^-3), showing maximum energy density and power density of 17.6 Wh kg ^-1 and 98 kW kg ^-1. Moreover, the device possesses excellent cycle life with 80% capacitance retention after 5000 cycles. Therefore, the 3D lightweight and freestanding symmetric supercapacitor is a promising candidate in the application of high-performance energy storage systems.
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[4] A. K. Geim, Science 324 (2009) 1530.
[5] Y. Zhu, S. Murali, M. D. Stoller, K. J. Ganesh, W. Cai, P. J. Ferreira, A. Pirkle, R. M. Wallace, K. A. Cychosz, M. Thommes, D. Su, E. A. Stach, R. S. Ruoff, Science 332 (2011) 1537.
[6] G. Wang, X. Sun, F. Lu, H. Sun, M. Yu, W. Jiang, C. Liu, J. Lian, Small 8 (2012) 452.

Lignin extracted from trees is one of the most common biopolymers on Earth. Recently lignin is explored as a promising energy storage material due to its high charge capacity, natural abundance, and low cost. The quinone group in lignin is used for electron and proton storage and exchange during charging and discharging. However, practical use of renewable lignin energy storage is hindered by several issues including short cycle life, low cycling efficiency, and a high self-discharge rate. All of these issues are related to electrode dissolution and the insulating nature of lignin. To address these critical challenges we use a reconfigurable graphene microfiber to capture the lignin, inspired by prey trapped by the Venus flytrap. The graphene provides efficient electron transport paths during the electrochemical reactions, efficiently addressing the insulating problem of lignin and playing a function as three dimentional current collector. Meanwhile, the reconfigurable graphene trap the lignin within the electrode to solve the dissolution problem. This biomimic design enables a best cycling performance of lignin reported so far of 91% capacitance retention for 4000 cycles and 197 F/g capacitance under 0.92 A/g current density. The present study demonstrates a feasible and effective strategy to solve the long-term cycling difficulty and insulating properties for lignin-based renewable energy storage.

Strongly variable energy demand with daily fluctuations and seasonal differences requires adequate energy storage solutions. In recent years electrochemical supercapacitors have attracted considerable attention due to their ability to both store and deliver electrical energy efficiently. Our efforts are focused on developing sustainable organic electrode materials for supercapacitors based on renewable bioorganic materials, offering a cheap, environmentally friendly and scalable alternative to store energy. In particular, we are using the second most abundant biopolymer in nature, lignin (Lig), which is an insulating material, in combination with electroactive and conducting polymers such as polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT). These biopolymer composites PPy/Lig¹ and PEDOT/Lig display significantly enhanced energy storage performance compared to the pristine conducting polymers without lignin. Redox cyclic voltammetry and galvanostatic charge/discharge measurements indicate that the enhanced performance is due to the additional pseudocapacitance generated by the quinone moieties in the lignin. These electrochemically generated quinones undergo a two-electron, two-proton redox process within the biopolymer electrodes as revealed by FTIR spectroelectrochemistry.² We further demonstrate that the PEDOT/Lig biocomposite is also highly stable, retaining ≈83% of its electroactivity after 1000 charge/discharge cycles. The high stability of PEDOT/Lig suggest that an important synergistic effect exists between the two polymers, in stark contrast to PPy/Lig composites where strong degradation is observed upon cycling. As the chemical synthesis of the PEDOT/Lig biocomposite is relatively simple, inexpensive and environmentally friendly these findings open up the possibility of scalable production of PEDOT/Lig composites.³ Moreover a new conjugated polymer poly(aminoanthraquinone) PAAQ which exhibits intrinsic quinone functions and excellent stability, has been combined with PEDOT in order to enhance the conductivity of the system and as a result the specific capacitance of PAAQ increases from 90 to 383 F g⁻¹.⁴ We now work on the next combination of biopolymer based polymer electrodes by incorporating lignin into the PAAQ/PEDOT composite. Optimization of the system parameters could lead to a low cost electrical storage application, a supercapbattery, possibly one order of magnitude lower than for present day Li-ion batteries.

References

1. G. Milczarek, O. Inganas,Science 2012, 355, 1468.

2. F. N. Ajjan, M. J. Jafari, T. Rebis, T. Ederth and O. Inganäs, J. Mater. Chem. A, 2015, 3, 12927.

3. F. N. Ajjan, N. Casado, T. Rebis, A. Elfwing^a N. Solin, D. Mecerreyes and O. Inganas J. Mater. Chem. A, 2016, 4, 1838.

4. S. Admassie, A. Elfwing and O. Inganas Adv. Mater. Interfaces 2016, 1500533.

High energy densities electrochemical capacitors can be achieved by using high purity carbon electrodes (> 98 atomic%) with controlled pore size distribution. Conventional activated carbon has a significant volume of microporosity which leads to high surface area. However, having very high microporosity without presence of mesoporisity can limit mass transfer when the electrodes are made thicker or the electrolyte consists of larger ions. In order to overcome the transport limitations in thicker carbon electrodes (>100μm), designing carbon with hierarchical porous architecture is essential. In this research work, hierarchical porous carbon that has both ultramicropores and mesopores was synthesized by blending polyfurfuryl alcohol with either polyethylene glycol or phloroglucinol. This pore size distribution can provide good accessible double layer specific area in lithium based electrolytes. By using this polymer blend approach, we were able to develop a lithium ion capacitor with specific cell capacitance of 78 F/g resulting in an energy density of 160 Wh/kg, based on total mass of both the electrodes when cycled between 2.2V – 4.5V with good cycling stability. The synthesized carbons were then characterized using nitrogen and CO₂ adsorption isotherms. Nitrogen isotherm was used to measure the total pore volume and surface area. The micropore volume was calculated using t-plot method.

To sustainably power electronics by harvesting mechanical energy using nanogenerators, energy storage is essential to supply a regulated and stable electric output, which is traditionally realized by a direct connection between the two components through a rectifier. However, this may lead to low energy-storage efficiency. Here, we rationally design a charging cycle to maximize energy-storage efficiency by modulating the charge flow in the system, which is demonstrated on a triboelectric nanogenerator by adding a motion-triggered switch.[1] Both theoretical and experimental comparisons show that the designed charging cycle can enhance the charging rate, improve the maximum energy-storage efficiency by up to 50% and promote the saturation voltage by at least a factor of two. This represents a progress to effectively store the energy harvested by nanogenerators with the aim to utilize ambient mechanical energy to drive portable/wearable/implantable electronics. [1]: Y. Zi, et al, Nature Communications, 7:10987, 2016.

We have developed transformational, and intrinsically safe, all-solid-state Li-ion batteries (SSLiBs), by incorporating high conductivity garnet-type solid Li-ion electrolytes into tailored tri-layer microstructures, by low-cost solid oxide fuel cell (SOFC) fabrication techniques to form electrode supported dense thin-film (~10μm) solid-state electrolytes. The microstrucurally tailored porous garnet scaffold support increases electrode/electrolyte interfacial area, overcoming the high impedance typical of planar geometry SSLiBs resulting in an area specific resistance (ASR) of only ~2 Ωcm^-2 at room temperature. The unique garnet scaffold/electrolyte/scaffold structure further allows for charge/discharge of the Li-metal anode and cathode scaffolds by pore-filling, thus providing high depth of discharge ability without mechanical cycling fatigue seen with typical electrodes. Moreover, these scalable multilayer ceramic fabrication techniques, without need for dry rooms or vacuum equipment, provide for dramatically reduced manufacturing cost.

Fabrication of supported dense thin-film garnet electrolytes, their ability to cycle Li-metal at high current densities with no dendrite formation, and results for Li-metal anode/garnet-electrolyte based batteries with a number of different cathode chemistries will be presented.

High capacity and low potential anode materials like lithium metal are preferred for high energy densities in all solid-state batteries. Due to the highly reducing potential of lithium metal, the electrochemical and thermodynamic stability of a solid ion conductor at the interface plays a crucial role for the performance of all solid-state batteries.

When a solid electrolyte is in contact with lithium metal, three different types of interfaces may occur:¹ (I) A stable interface may form with electrolytes that are thermodynamically stable against Li contact. (II) A reaction occurs and a mixed ionic-electronic conducting (MCI) new interphase forms,² which rapidly growths due to the electronic percolation pathways. (III) A reaction occurs and a solid electrolyte interphase (SEI) forms,³ which only conducts ions. While (I) may be preferred and (II) is exclusively detrimental, due to a proceeding reaction front, the impact of (III) on the battery performance depends on the type of forming SEI.

Here we will shortly introduce the types of possible interphases/interfaces and discuss the expected effects on the overall resistance and performance of an all-solid-state battery. Using time-resolved impedance spectroscopy and time-resolved cyclic voltammetry we introduce a guideline to characterize solid electrolytes for their stability against metal interfaces. The solid electrolyte Li₁₀GeP₂S₁₂ will be shown as an example of an instability,⁴ as has been theoretically predicted.^5,6 SEI formation occurs, affecting the overall cell resistance detrimentally.

Using a novel in situ X-ray photoelectron technique we study the resulting interphase formation when Li₁₀GeP₂S₁₂ is in contact with Li. Using the observed chemical species, in combination with time-resolved electrochemical measurements, we suggest a reaction mechanism for the interphase formation as well as provide an understanding of the growth kinetics.

¹Wenzel S., Leichtweiss T., Krüger D., Sann J., Janek J. Solid State Ion. 2015, 278, 98-105
²Hartmann P., Leichtweiss T., Busche M., Schneider M., Reich M., Sann J., Adelhelm P., Janek J. J. Phys. Chem. C 2013, 117, 21064-21074
³ Wenzel S., Weber D., Leichtweiss T., Busche M., Sann J., Janek J. Solid State Ion. 2016, 286, 24-33
⁴Wenzel S., Randau S., Leichtweiss T., Weber D., Sann J., Zeier W.G., Janek J. Chem. Mater. 2016, 28, 2400-2407
⁵Zhu Y., He X., Mo Y. ACS Appl. Mater. Int. 2015, 7, 23685-23693
⁶Zhu Y., He X., Mo Y. J. Mater. Chem A 2016 DOI: 10.1039/C5TA08574H.

We describe cathodes, modified Li anodes, and separator comprising engineered particles, which are combined to fabricate hybrid solid-state/ liquid electrolyte lithium ion batteries. These materials are fabricated by low cost aqueous spray deposition method and produce extremely safe batteries with long-cycle life and high specific energy. The spray-on porous inorganic solid-state-electrolyte film separator is imbued with LiPF6 liquid electrolyte to achieve Li-ion conductivity as high as 10^-3 S/cm. The separator comprises insulating inorganic nanoparticles that effectively block electron conduction. With melting temperature exceeding 1000 C, it is immune to high storage temperatures and overcharge heating. Our separator is far thinner, giving higher capacity, than any plastic separator, yet it is more mechanically robust, is chemically inert, and is immune to dendrite growth. Our separator works in conjunction with innovative composite cathode and anode to provide high energy density, power capability, safety, and life exceeding 1000 cycles. Fabrication is cheap, fast, environmentally benign, and scalable.

We have used time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to analyze the products formed after charge-discharge on the LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cathode for all solid-state lithium-ion batteries (ASSBs) based on Li₂S-P₂S₅ glass-ceramics. Although there have been several reports on improvements of the performance of ASSBs using lithium metal oxide coatings on the cathode active material, the mechanism of the performance improvement remains unclear. To better understand the effect of the surface coatings, we analyzed two different coatings and compared with bare and plasma treated sample. The first coating is a lithium zirconium oxide (LZO) compound. The second is diamond-like carbon (DLC). Both coating were deposited on LiNi_0.8Co_0.15Al_0.05O₂ (NCA) by spray chemical method and chemical vapor deposition (CVD) respectively. The effect of the thickness of both coatings was also analyzed. After 1 and 100 cycles the samples were analyzed by X-ray photo spectroscopy (XPS), and TOF-SIMS. The TOF-SIMS analysis has revealed that the coating layers prevents the interfacial reactions after charge-discharge, in particular, PO₃^-, PO₄^-, SO₃^-, SO₄^- formation at the interface. The coated NCA showed better cycle ability and rate performance than the bare and plasma treated samples. Those results are further supported by reduction of the interfacial resistance of the cathode and electrolyte observed in impedance spectroscopy for both coating. The relative amounts of these species are calculated and its possible relation with the electrochemical properties are discussed. Both coating layer were acting to hinder the side reactions between the cathode particle and the solid electrolyte. As a result, the interfacial resistance between the sulfide electrolyte and the cathode particles was suppressed, and the cell performance improved. The results of this study will provide useful insights for understanding the nature of the buffer layer for the cathode materials. This work demonstrates that the use of TOF-SIMS provides a new important insight for the development of ASSBs.

Sodium nickel chloride (Na/NiCl₂) battery is one of the most promising candidates as a large scale electrochemical energy storage device. The battery comprises molten Na and NiCl₂ as negative and positive electrodes, respectively, in its charged state, separating them by a β”-Al₂O₃ solid electrolyte (BASE). In order to facilitate fast sodium ion transport in the cathode compartment, molten NaAlCl₄, as a secondary electrolyte (or catholyte), is infiltrated into the cathode materials powder. The battery typically operates at 250~300^oC so as to maximize the ionic flux in the NaAlCl₄ and through the solid electrolyte, and to minimize the dissolution of NiCl₂ into the melt. However, this efficient battery is yet to be widely used in grid scale energy storage applications since it is still expensive and hard to dramatically reduce the cell price mainly due to its use of expensive sealing technologies.
The presentation introduces Korea-US collaborative efforts to develop a lower temperature operating sodium beta-alumina battery (LT-NBB) with a Na/NiCl₂ chemistry. Since the novel battery runs at below 200^oC, it can be fabricated at an ultra low manufacturing cost by introducing a new planar cell design with a greatly reduced number of cell components, and by eliminating expensive conventional sealing technologies. Enhanced degradation resistance of cathode materials is another important advantage of this technology. This presentation will start with stating the problems found in traditional sodium beta-alumina batteries, and possible solutions to resolve the issues will be described. Technical challenges and progress in materializing prototype LT-NBB cells, and related core technologies, including cell design, highly toughened BASE, enhanced wetting agent, and inexpensive sealing method, will be discussed.

Alkali borohydrides have recently emerged as highly promising solid electrolyte candidates due to liquid-like conductivities exceeding 0.1 S/cm^–1 at temperatures approaching room temperature. Despite the rapid advances in improving the superionic conductivity in these materials, an understanding of the exact mechanisms driving the transport remains unknown. Here we use extensive ab initio molecular dynamics calculations to address this issue by characterizing the diffusivity of the Li and Na species in a representative set of closoborane ionic conductors that include anionic species of B₁₂H₁₂, B₁₀H₁₀, and their carbon-doped analogs. We identify a set of mechanisms underpinning ionic transport in these materials that suggests the importance of both short- and medium-ranged interactions in controlling the cation diffusivity. Our results support the borohydrides as a subset of a larger family of very promising solid electrolytes and identify strategies to improving the conductivity in these materials.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Stationary electric energy storage is a crucial element to enable greater penetration of renewable energy resources and to improve the reliability of electric power grids. Sodium-metal halide (Na-MH) battery systems have gained interest for large-scale energy storage devices due to its higher voltage and energy density, safe cell failure mode, and easiness of assembly in discharged state. A major obstacle in commercialization of the technology is the relatively high manufacturing cost. Our research at PNNL has been primary focused on developing advanced Na-MH battery technologies capable of operating at temperatures less than 200°C with low cost cathode materials. This presentation will focus on our most recent progresses in Na-MH battery technology development.

As the importance of renewable energy grows, Sodium/β”-alumina(BASE) cell has been recognized as one of the most effective energy storage device because of its high specific energy, high efficiency of charge/discharge and long cycle life. For better operation of Sodium-BASE cell, poor wettability, which is caused by moisture and impurity in the BASE such as calcium, of electrolyte on liquid sodium anode should be enhanced. However, the formation of the oxide film, which is related to moisture absorbed on the BASE surface, impedes sodium dissolution, thereby hindering an accurate determination of wetting behavior. In this study, the sessile drop technique under controlled moisture and O₂ environment is used as a type of an artificial Sodium-BASE cell system to study the issue of water interface formed onto the BASE. To separate water interface, BASE surface need to be coated by metal that can form an alloy with sodium and therefore completely isolate its’ surface in a way that emulate the sealed and complete real cell. Bi is chosen as protect layer and sodium alloy with Bi is impervious to water yet does not interfere with sodium conductivity. By the enhanced wettability, the Sodium-BASE batteries can be operated at lower temperature with solving the safety issues and to use low cost polymeric seals.

Na-NiCl₂ chemistry is commonly implemented in the molten Na-beta alumina batteries (NBB) that use a beta alumina solid electrolyte (BASE) between anode and cathode. A Na-NiCl₂ NBB is typically operated at relatively high temperature (over ~270 °C) because the active Na-ions must be maintained in their molten state with expedited mobility. The cathode chamber of Na-NiCl₂ NBB features by a mixture of solid NaCl particles and Ni granules impregnated with liquid NaAlCl₄ catholyte. During the charge-discharge cycles, complicated electrochemical reactions take place in the cathode, including the transportation of Na-ions through NaAlCl₄ catholyte, the dissolution/coarsening of NaCl particles, the formation/decomposition of NiCl₂ layers on the active surfaces of Ni granules, and the electron transfer through the Ni granules. The thermodynamic and kinetic processes in the cathode area, therefore, play a vital role in controlling the electrochemical performance of Na-NiCl₂ NBBs. Upon repeated charge-discharge cycles, the cell degradation in the cathode area is often observed at the nominal high cell operation temperature primarily due to the incomplete reversible reactions for the Ni, NiCl₂, and NaCl materials, which can prevent a deeper and wider penetration of Na-NiCl₂ NBBs into the market. Therefore, one of the current trends is to develop advanced lower temperature Na-beta alumina batteries (LT-NBB) that can operate at intermediate temperatures (lower than ~200 °C) with a much lower degree of cell degradation. However, the diffusion and the migration kinetics of active Na-ions in the cathode chamber would be much limited at these intermediate temperatures. In seeking the fundamental understanding of such temperature effects on the electrochemical performance of Na-NiCl₂ LT-NBBs, the presentation introduces a mesoscopic computational model to capture the reaction thermodynamics and transport kinetics in the cathode area of Na-NiCl₂ NBBs. The mesoscopic model was developed based on the realistic cathode microstructures comprised of NaCl, Ni, NiCl₂, and catholyte materials. The model was applied to characterize the Na-ion diffusion, the particle coarsening/dissolution, and the resultant electrochemical performance of a novel planar cell, which was designed adopting a disc-shaped BASE instead of a conventional cloverleaf-shaped BASE. The planar cell geometry was intended to lower the cell operation temperature by optimizing the cell performance. For this multi-physics mesoscopic computational model, relevant physicochemical, thermodynamic, and kinetic material properties of active materials have been incorporated. The mesoscopic computation results were used to quantitatively elucidate the effects of (1) cell operation temperature, (2) charge-discharge rate, (3) cathode active materials to catholyte ratio, and (4) cell dimension on the structural changes of cathode materials and the Na-ion diffusion kinetics for the prototype planar Na-NiCl₂ NBBs.

Lithium–sulphur batteries (LSBs) with a high theoretical energy density are being pursued as highly promising next generation large-scale energy storage devices. However, its launching for practical application is still shackle by poor conductivity, limited sulfur loading and most seriously by polysulfides dissolution in organic electrolyte. To date, 3D porous carbon nanostructures (3D-PCNs) are attractive candidates for rechargeable batteries because they can integrate multiple advantages of unique collective effects and great potential electrochemical applications. We demonstrated a simple carbonization method to make novel 3D highly micro-mesoporous, vertically aligned and interconnected carbon nanosheets (3D-VCNs) for solving the hurdles associated with LSBs to bring high performance at low cost. The present 3D nanostructures with very high surface area of 1750 m²g^-1 are highly particular for enhancing the performance of LSBs in the terms of capacity, rate ability, and cycling stability. The developed porous structure is beneficial in facilitating the easy access of electrolyte through the structure of 3D-VCNs infiltered with sulfur (3D-S-VCNs) during the cycling process. As a consequence, the unique 3D-S-VCNs show high initial discharge capacity of 1240 mAh g⁻¹ at the current density of 167 mA g⁻¹ with excellent Coulombic efficiency of ≈100% and presents a long stability up to 300 cycles with high reversible specific capacity of 844 mAh g^-1 and capacity retention of ≈80.3% (a capacity decay of only 0.082% per cycle) at the current density of 837 mA g^-1. Furthermore, the electrode bears the excellent rate capability and maintains a high reversible capacity of 738 mAh g^-1 at the high current density of 3340 mA g^-1.


References:
S. Rehman, K, Khan S. Guo and Y. Hou, 3D Vertically Aligned and Interconnected Porous Carbon Nanosheets as Sulphur Immobilizers for High Performance Lithium-Sulphur Batteries, Advanced Energy Materials (DOI:10.1002/aenm.201502518).

All-solid-state-batteries are the next generation technology as they promise higher energy densities and more safety when using an ionic conducting solid electrolyte. In order to achieve the set goals for this technology, good ionic conductors are necessary, as a low ionic conductivity will ultimately lead to large overvoltages and slow attainable charge-discharge rates. The class of Li-conducting thiophosphates has recently been identified as a promising class due to the high conductivity and low mechanical stiffness. However, the diffusion pathways in some of these materials are still unknown and even the crystal structures have not been solved unequivocally.

Here we will present the structural properties of two ionic conductors, namely Li₁₀GeP₂S₁₂ and Li₄P₂S₆.
In the case of Li₁₀GeP₂S₁₂ it has long been believed to be a purely one-dimensional ion conductor with channels of migrating Li within the structure, despite theoretical predictions of a three-dimensional conduction. Using neutron diffraction in combination with the maximum-entropy-method, we are able, for the first time, to elucidate a three-dimensional conduction mechanism within Li₁₀GeP₂S₁₂. In addition, we use a combination of temperature dependent diffraction and speed of sound measurement to understand the mechanical properties of the lattice and its anisotropic thermal expansion, providing an understanding for the reported temperature dependent transport in this material.^[1]
In the case of Li₄P₂S₆, we will quickly present the newly solves crystal structure of this system. Previously, there have been reports corroborating possible space groups and structures. Here, we will present a combination of Bragg diffraction and pair distribution function analysis to elucidate the underlying structure. ^[2]


[1] D.A. Weber, et al. submitted
[2] C. Dietrich, et al. submitted

High surface area anode has been conceived as a critical component for high performance lithium-ion batteries (LIBs), which augments the insertion/extraction rate of electrons and Li⁺ during the charging/discharging processes. Different anode structures have been developed such as 3D carbon nano-network, carbon nanopipes, multi-walled carbon nanotubes and porous carbon electrode. The chemical vapor deposition (CVD) method has been extensively exploited for fabricating electrodes by researchers. A 3D C/TiO₂ electrode LIB has achieved a specific capacity of ~240 mAh g^-1 on a large area of 20 cm². However, most of the reported methods are thought to be expensive and rare for industrial manufacturing. In this research, a simple and cost-effective fabrication technique is developed for fabricating micro and nanoscale carbon electrodes without the use of expensive equipment and fabrication processes such as CVD. The performance of LIB with developed carbon electrode is evaluated and the results are compared with the published results.
The polyvinylidene fluoride (PVDF) solution was dissolved in an organic solvent of N-Methyk-2-pyrrolidone (NMP) at weight ratio of 2:9. Varying polydimethylsiloxane (PDMS) molds were used in the fabrication process. These PDMS molds featured with the same diameter of micro-holes but different spacing. For obtaining the micro pillar structure, the PVDF solution was first spin coated on metallic copper sheet as substrate and then left on a hotplate for solvent evaporation for 10 min. Then the Teflon coated PDMS mold was pressed into the PVDF in a nanoimprintor (NX-2600, Nanonex) at certain pressure and temperature. Once processed, the PDMS mold was removed from the substrate and the micro patterns were formed in the copper sheet. Before the pyrolysis process for carbon, dehydrofluorination was carried out with 4 mole aqueous sodium hydroxide (NaOH) solution containing 0.25 mmole of tetrabutylammonium bromide at 70 °C for 1 hour. This dehydrofluorinated process maintained its geometry during heat-treatment. The carbon pillars were achieved without causing any crumpling or fragmentation. At last, a similar pyrolysis process is conducted to form nanoscale carbon structures. After forming micro and nanoscale carbon electrodes, LIBs are made by assembling a separator between carbon and lithium metal electrode with an electrolyte containing 1 M LiPF₆ in ethylene carbonate (EC) / dimethyl carbonate (DMC) (1:1 volume ration) in an argon-filled glove box system. A copper and aluminum foil tapes were used for anode and cathode current collectors, respectively. In this study, the fabrication method is compatible with existing LIBs manufacturing process. Varying nanoparticles and different nano/micro carbon pillar spacing of electrodes will be conducted in the experiments for demonstrating the efficiency of energy storage. Finally, a discussion for low cost and compatible manufacturing process will be presented.

Metallic surfaces exposed to intense electric fields demonstrate surface evolution in response to the applied field. In scenarios where strong fields are applied in vacuum, this can lead to field breakdown as a result of plasma formation above the surface. This type of mechanism is a main failure mechanism for various application such linear accelerators, voltage breakers and other high voltage vacuum cavities.

We describe a stochastic model for surface evolution under intense electric fields based on writing master equations for the evolution of dislocation population within the sample. From this model we derive critical transition times and their dependence on drive conditions. Model results are compared to observed breakdown rates and other macroscopic measurements, such as dark current evolution as well as microscopic observations using TEM of post-breakdown samples.

Rechargeable Li-S batteries represents advanced battery system offering high energy density with low cost and environmentally benign electrochemical energy storage. The basic principle of Li-S systems involving sulfur and Li as a cathode and anode material (theoretical specific capacity ~ 1675mAh/g) has been investigated for decades, but the inherent cell chemistry hampers the commercial realization of this alluring technology. The critical limitations including capacity fading and low cycling stability, which are mainly associated with the insulating nature of sulfur (5 x 10-30 S/m), and formation and dissolution of intermediate polysulfides (Li2Sx) into the electrolyte during charge/discharge processes results in irreversible loss of the active material. Most of the previous strategies reported in trapping polysulfides considered the areal density of the sulfur in the cathode to be less than 2mg/cm2. However, in order to obtain superior electrochemical performance (high volumetric and gravimetric energy density) compared to currently available state-of-the art Li-ion batteries, the sulfur loading amount has to be atleast 6mg/cm2. 3D CNTs also provides interconnected conducting framework promoting effective utilization of sulfur particles, high electrolyte absorbability facilitating well-localized polysulfides within the 3D CNTs, and maintaining good structural integrity during volume expansion. Here in, we fabricated free standing 3D CNTs and strategically designed the cathode structure to accommodate higher loading amount of sulfur to enhance the areal capacity. Consequently, the cathode electrode shows outstanding electrochemical performance in terms of cyclic stability and high sulfur utilization with areal density of sulfur exceeding 8mg/cm2.

Supercapacitors are promising energy storage devices due to their higher energy density than the dielectric capacitors and higher power density and long cycle life time (> millions) compared with the conventional batteries. Carbon based materials such as activated carbon (AC) and carbon nanotubes (CNTs), owing to the high specific surface area and high electronic conductivity, have been extensively investigated as active electrode materials for supercapacitors. Nevertheless, carbon based electrodes suffer from the fact that the charge storage is through the electric double layers (EDL) which are limited on the surface of the porous electrodes, limiting the capacitance and energy density of the supercapacitors. In contrast, redox reactions occur throughout the entire volume of conducting polymers (CP), allowing for significantly higher energy storage capability. However, CP electrodes typically have poor mechanical stability because of volume changes during the doping/dedoping process, which causes failure of the electrode during long cycling. Recent experiments have demonstrated that the composite approach, in which CP layers are deposited on conductive porous networks such as CNTs, can lead to supercapacitors with significantly improved cycling stability. In such a conductive composite approach, the CNT networks provide electron transport pathways as well as mechanical support to the CP while the deposited CP layers enhance the charge storage capacity of the electrodes.
In this abstract, an oxidative chemical vapor deposition (oCVD) was employed to fabricate CP/A-CNTs electrodes in which a conducting polymer, P3MT, layer forms a conformal coating on very high aspect ratio A-CNTs (0.2 mm long). The oCVD allows precise control of the PEDOT layer thickness from sub-nanometer to tens of nanometers. The A-CNTs in this study were grown by a modified thermal CVD method at atmospheric pressure. These as-grown CNTs have a highly aligned structure with approximately 1% volume fraction (Vf) corresponding to ~80 nm inter-CNT spacing and an average CNT diameter of 8 nm. The conformal coated composite shows the specific capacitance as high as 300 F/g.

Growing concerns in reducing dependency on fossil fuels and searching for green energy have led to the development of renewable energy sources, such as solar and wind. But these energy sources are fluctuating and unpredictable by nature and therefore it’s necessary to make the volatile energy sources more consistent, resilient, and efficient. Energy Storage Systems (ESS) have been attracting much attention as an intermediate buffering reservoir as well as backup power supply¹. Traditionally, pumped hydroelectric storage (PHS) has been major ESS worldwide; c.a. 95% of entire ESS². Meanwhile, several assessments have shown that there will be huge increase in needs for high-energy and cost-effective ESS, where PHS would not be able to satisfy the demands. Recently, lithium-ion batteries (LIBs) with high-energy density and stable long-term cycle life have been widely studied as a promising candidate for future ESS³. Among the researches, silicon as an anode host material is believed to be very attractive due to its high theoretical specific capacity (3,579 mAh/g at ambient temperature) which is an order of magnitude higher than that of conventional graphite anode⁴. Although commercially available LIBs are well-developed and undeniably essential part in small, portable electronic devices, the integration of LIBs with ESS requires other crucial factors; how to lower the relevant costs (initial cost, operating cost, and end-of life cost). In this regard, using costly methods to synthesize silicon materials with delicate nano-structures would not be a tangible pathway for ESS. Instead, here we report, starting with easily accessible precursors, clay or sand (silica), a simple and effective heat scavenger aided-magnesiothermic redox process to synthesize micron-sized silicon powder with controlled porosity, which can be effectively achieved via a simple heat-treatment followed by scarification of magnesium oxides (or sulfide). Additionally, effects of surface chemistry that could stabilize Solid-Electrolyte Interphase (SEI) layer for stable, long-term cycling performance will be investigated. This cost-effective, scalable approach of manufacturing porous silicon would lower the critical barrier to the commercial deployment of large scale electrochemical energy storage systems.

1.Dunn, B., Kamath, H. & Tarascon, J.-M. Electrical Energy Storage for the Grid: A Battery of Choices. Science 334, 928-935, doi:10.1126/science.1212741 (2011).
2.Imre Gyuk, M. J., John Vetrano, Kevin Lynn, William Parks, Rachna Handa, Landis Kannberg, Sean Hearne, Karen Waldrip, Ralph Braccio. Grid Energy Storage. U.S. Department of Energy (2013).
3.Qian, H., Zhang, J., Lai, J. S. & Yu, W. A high-efficiency grid-tie battery energy storage system. IEEE Transactions on Power Electronics 26, 886-896, doi:10.1109/TPEL.2010.2096562 (2011).
4.Chan, C. K. et al. High-performance lithium battery anodes using silicon nanowires. Nature Nanotechnology 3, 31-35, doi:10.1038/nnano.2007.411 (2008).

The utilization of renewable energy is becoming increasingly necessary as rising CO₂ emissions threaten our environment. Without energy storage, current solar PV technologies are not able to provide solar power at night, when power demand is high, thus causing a gap between supply capabilities and demand. Solar thermochemical energy storage (TCES) has the potential to resolve the critical temporal issue between supply and demand, utilizing large energy storage densities inherent of chemical reactions to address intermittency of renewable energy. Strontium carbonate decomposition is used as a means to densely store high temperature thermal energy via chemical reaction, ideal for its high heat of reaction and high equilibrium temperature. In this work, two TCES subsystems have been designed and evaluated with respect to exergy and energy efficiency, and cost. Such parameters are explored via probabilistic analyses to determine the practical feasibility of utilizing sorbents for storage. The resulting figures show promise in developing an energy storage technology to pacify our current energy demands.

The sodium beta-alumina battery (NBB), which employs molten sodium as an anode and sodium-ion conducting β"-alumina as a solid electrolyte, is an attractive device for grid scale energy storage thanks to its long lifetime with negligible self-discharge and potentially low cost by use of naturally abundant elements. Commercialized NBBs, such as sodium sulfur (Na/S) and sodium nickel chloride (Na/NiCl₂) batteries, are typically being operated at 280~350^oC in order to facilitate ionic conduction through the solid electrolyte. However, this high operation temperature disturb additional cell cost reduction, which is continuously exacted by demanding forecast, since it is difficult to replace conventional expensive sealing technologies (such as glass sealing, thermal compression bonding, electron beam welding and so on) with lower cost substitutes. If the cell operation temperature is lowered down to below 200^oC, a wider range of choices for sealing technology can be considered such as inexpensive polymer sealing. Suppressed cell degradation at lower temperatures would be another important benefit.
One of the most difficult challenges to lower the cell operation temperature is an issue regarding the insufficient mechanical strength with increased size and exponential resistance rise of the solid electrolyte with decreased temperature, which can result in substantial performance loss. One can consider that the reduced thickness of the β"-alumina solid electrolyte (BASE) to resolve the resistance issue. However, as the BASE thickness decreases below 1.5~2.0 mm, its flexural strength becomes not acceptable to be used in cell fabrication. Therefore, our target has set to develop a BASE (1) to be thin to compensate the resistance increase at lower temperatures, (2) with enhanced mechanical properties to avoid unwanted cell failure. The target can be achieved by fabricating highly toughened thin composite electrolytes. It turns out that the flexural strength of this novel electrolyte could be greatly increased maintaining its area specific resistivity (ASR) as low as that of a conventional BASE. In this presentation, our on-going efforts on developing thin composite electrolytes made of β"-alumina and oxygen conducting oxides will be discussed.

We verified the electrochemical electrode properties with regard to an electrochemical double-layer capacitor electrode of activated carbon produced by performing the following methods in a sequential order: (1) a hydrothermal synthesis using starch as a starting material, (2) a KOH-solution vacuum impregnation method, and (3) chemical activation. The produced biostarch-activated carbon was investigated by conducting pore size distribution and specific surface area analyses, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. We also verified the electrochemical properties through an AC impedance measurement and a cyclic voltammetry measurement with regard to the supercapacitor electrode. Spherical carbon particles of diameter <2 µm were obtained by hydrothermal synthesis. The biostarch-activated carbon was produced at an activation temperature of 900 °C and had a specific surface area of 1579.4 m²/g, an average pore size of 2.9663 nm, and a pore distribution of 1.3–3.5 nm. The organic electrolyte (34 wt% 5-azoniaspiro-[4,4]-nonane tetrafluoroborate/7 wt% dimethyl sulfone/59 wt% sulfolane) exhibited specific capacitance of 151.2 F/g (@5 mV/s), 139.6 F/g (@50 mV/s), and 130 F/g (@200 mV/s).

Two sodium sulfur (NaS) cells, one with a planar design and the other with a tubular design, were subject to discharge-charge cycles in order to investigate the effect of cathode felt geometries on electrochemical characteristics of NaS cells. Their discharge-charge behaviors over 200 cycles were evaluated at the operation temperature of 350 °C with the current densities of 100 mA cm⁻² for discharge and 80 mA cm⁻² for charge. The results showed that the deviation from theoretical open circuit voltage changes of a planar cell was smaller than those of a tubular cell resulting in potential specific power loss reduction during operation. In order to understand the effect, a three dimensional statistically representative matrix for a cathode felt has been generated using experimentally measured data. It turns out that the area specific fiber number density in the outer side area of a tubular cathode felt is smaller than that of a planar felt resulting in occurrence of larger voltage drops via retarded convection of cathode melts during cell operation.

In this contribution, I’ll introduce our work on the nanostructures control of electrode materials for improved battery performance in lithium ion batteries (LIBs). Different structure design strategies and synthetic protocols has been applied due to different practical necessities：For cathode materials, I’ll report our research progress on the formation of nanoshells with their thickness being precisely-controlled achieving one nanometer accuracy. Different shell materials will be illustrated here including Al₂O₃, ¹ carbon and AlPO₄.² The cathode materials with an optimized core-shell structure shows improved cyclability and thermal stability benefiting from the delicate surface control. For anode materials, typically metal oxides such as Li4Ti5O12, I’ll introduce our work on the design and synthesis of hollow hybrid microspheres (HHMs).³ An interesting progressive-inward-crystallization process was developed for the morphology control. We also confirmed such a structure control is promising for its application as promising anode materials in lithium ion battery.

REFs :
Li-Ping Yang, An-Min Cao*, et al., J. Am. Chem. Soc., 2016, 138, 5916–5922
Fen-Li Yang, An-Min Cao*, et al., Chem. Commun., 2015, 51, 2943 – 2945
Wei Zhang, An-Min Cao*, et al., Angew. Chem. Int. Ed. 2014, 53, 12776 –12780

The use of an ionic liquid as a precursor for producing activated carbon offers a number of known benefits, not least of which is the fact that introduces nitrogen atoms into the final structure. Using this knowledge, we have demonstrated that the chemical activation of carbon derived from an ionic liquid (EMIM-dca) creates a structure that combines the high surface area of micro/mesopores with the excellent electrical conductivity of a graphitic structure due to the removal of nitrogen. These properties are attributed to the removal of nitrogen, which causes a rearrangement of atoms to create a new structure. To evaluate the potential of ionic liquid derived activated carbon (IL-AC) for use as an electrode material, it was used to assemble a two-electrode system for a supercapacitor. The rate performance was assessed through plots of specific capacitance versus current density for devices based on either IL-AC or commercial activated carbon. Note that despite this decrease in specific capacitance with increasing current density, 92% of the capacitance at 1.0 mA cm^-2 is still retained at 30 mA cm^-2; a result which shows a consistently higher specific capacitance at increased current density than commercial activated carbon. As this material could be applied in other high-power energy storage systems, we believe that the findings of this study are relevant to the scope of your journal and will be of interest to its readership.

Designing macroscopic, three-dimensional (3D) porous conductive materials with high mechanical strength are of great importance in many fields, including energy storage, catalysis, etc. Here we report a novel approach to fabricate polyaniline-coated 3D carbon x-aerogels, a special type of aerogels with mechanically strong, highly cross-linked structure that allows the originally brittle aerogels machinable. This approach is accomplished by introducing a small amount of graphene into the sol–gel process of resorcinol and formaldehyde, followed by chemical activation and subsequent cross-linking with polyaniline via electropolymerization. The resulting x-aerogels are not only porous and conductive, but also mechanically robust with high compressibility and fast recovery. The strong combination of these properties makes the x-aerogels promising for high performance supercapacitors that are designed to provide additional functionality for wearable and portable electronics. Such multi-functionality leads to a significant increase in electrochemical performance, in particular high volumetric capacitance, which results from the more densely packed electroactive structure in three dimensions. More importantly, monoliths of carbon x-aerogels are machinable into thin slices without losing their properties, thus enabling effective integration into devices with different sizes and shapes.

Surface (and interfacial) chemistry is found in various environments of scientific significance including biomembranes, ocean and atmospheric chemistry and applied electrochemistry. In fact, molecular redox behavior on the surface and at the interfaces can be drastically different than their bulk counterpart. Scanning electrochemical microscopy (SECM) is a analytical powerful tool to monitor various surface and interfaces in wide ranging industries and determining charge or ion transfer kinetics rate, diffusion phenomena and diffusion constant, imaging electrochemical redox reactions and topography in liquid and fabricating microstructures. The most significant advantage offered by SECM is its capability of probing chemical information of interfacial electron and ion transfer processes at the solid, air, liquid/liquid interfaces irrespective of substrates which is the focus of the present study. A constant potential is applied to the tip and electrochemical working electrode (i.e. the substrate in electrolyte) independently to drive reaction in bulk electrolyte solution of redox species (known as the mediator) and to probe the surface of certain thickness of graphene-based hybrids. The local or microscopic cyclic voltammograms (CV), probe approach curves (current versus tip–substrate distance) and 2D and 3D micrographs in feedback mode, were chosen to characterize the single bilayer of graphene/carbon nanotube, graphene/conducting polymer, graphene/MnO_x and graphene/CoO as supercapacitor cathodes to probe the ion adsorption and map highly electroactive (‘hot spots’) sites. The SECM setup has a resolution and repeatability of ~40 nm and can locate and relocate areas of interest precisely after a coarse image. We present our findings from viewpoint of reinforcing the roles played by heterogeneous electrode surfaces comprised of graphene nanosheets (conducting) / nanomaterials (semiconducting) via higher/lower probe current distribution maps. SECM approach curves as well as two dimensional scans elucidated the existence of regions of different conductivity and the imaging data is analyzed in terms of defects density sites distribution within the probes regions and determining diffusion and rate transfer constants via modeling tip ion current. We gratefully acknowledge financial support from NSF KY EPSCoR, NASA KY EPSCoR and WKU Research Foundation grants.

Lithium ion batteries have undergone tremendous development due to their high energy density [[i],[ii]]. However the need to look for cheaper and safer high energy density electrochemical devices able to sustain the large scale storage of renewable energy sources is moving the focus of research from the lighter lithium ion into the cheaper and more abundant sodium ion based systems. While many lithium ion analogues are able to operate as cathodes in sodium ion batteries [[iii]], in the quest for optimized anode materials, the metal Sn [[iv]], semimetal Sb[[v]], and non-metal P [[vi]] showed the highest capacities so far. In the field of metal-organic compounds, the presence of >C=N- and -C≡N- functionalities seems to be beneficial for sodium ion batteries in poly-Schiff bases as anodes [[vii]] and Prussian Blue related systems as cathodes [[viii]]. We observed for the first time that -(N=C=N)- containing compounds are electrochemically active as well [[ix]] as it was later confirmed by other group [[x]]. Carbodiimides are metal-organic compounds with a (N=C=N)^2- group bridging transition metal ions [[xi]]. Carbodiimides have many similarities with oxides: same charge (-2), electronegativity value and similar structures with the difference of the presence of the NCN chains.
In this communication we will show the electrochemical performance of transition metal carbodiimides as anode materials for lithium and sodium-ion batteries. The reaction mechanism responsible of high capacity values will be also discussed.


[i] Tarascon J.M. and Armand M.; Nature, 2001, 414, 359.

[ii] Goodenough J.B. and Kim Y.; Chem. Mater.,2010, 22 (3) 587.

[iii] Palomares V., Serras P., Villaluenga I., Hueso K., Carretero-Gonzalez J. and Rojo T.; Energy Envirom. Sci. 2012, 5, 5884.

[iv] Xu Y., Zhu Y., Liu Y. and Wang C.; Adv. Energy Mater., 2013, 3, 128.

[v] Slater M.D., Kim D., Lee E. and Johnson C.S; Adv. Funct. Mater., 2013, 23, 947.

[vi] Kim Y., Park Y., Choi A., Choi N-S., Kim J., Lee J., Ryu J. H., Oh S. M. and Lee K. T.; Adv. Mater., 2013, 25, 3045.

^[vii] Castillo-Martinez E., Carretero-Gonzalez J., Armand M; Angew. Chem. Int. Ed. 2014, 126, 5445.

^[viii] Lu Y., Wang L., Cheng J. and Goodenough J.B., Chem. Commun., 2012, 48, 6544.

^[ix] Eguía-Barrio A., Castillo-Martínez E., Liu X., Dronskowski R., Armand M., Rojo T., J. Mater. Chem. A 2016, 4, 1608.

^[x] Sougrati M. T., Darwiche A., Liu X., Mahmoud A., Hermann R. P., Jouen S., Monconduit L., Dronskowski R. and Stievano L., Angew. Chem. Int. Ed. 2016, 55, 5090.

^[xi] Jürgen Meyer H.; Dalton Trans., 2010, 39, 5973.

Hard-carbon materials derived from waste tires are considered as one of the most promising anodes for the emerging sodium-ion batteries. The tire-derived carbons obtained by pyrolyzing the acid-treated tire at 1100 °C, 1400 °C and 1600 °C. The carbon interlayer distances for crystalline carbon areas were determined to be 4.7 Å, 4.5 Å, and 4.0 Å for 1100, 1400 and 1600, respectively. These values are ideal for sodium intercalation. When the pyrolysis temperature is increased from 1100 to 1600°C, the capacity of the plateau below 0.2 V increases dramatically and this could help increase the full cell energy density. The 1600°C treated carbon shows a capacity of 203 mAh g^-1 after 100 cycles. We will report the current status of the tire-derived carbon powder scale up efforts and its use in energy storage applications.

We employed an in-situ electrochemical cell in the transmission electron microscope (TEM) together with ex-situ time-of-flight, secondary-ion mass spectrometry (TOF-SIMS) depth profiling, and FIB - helium ion scanning microscope (HIM) imaging to detail the structural and compositional changes associated with Na/Na⁺ charging/discharging of 50 and 100 nm thin films of Sb. TOF-SIMS on a partially sodiated 100 nm Sb film gives a Na signal that progressively decreases towards the current collector, indicating that sodiation does not proceed uniformly. This heterogeneity will lead to local volumetric expansion gradients that would in turn serve as a major source of intrinsic stress in the microstructure. In-situ TEM shows time-dependent buckling and localized separation of the sodiated films from their TiN-Ge nanowire support, which is a mechanism of stress-relaxation. Localized horizontal fracture does not occur directly at the interface, but rather at a short distance away within the bulk of the Sb. HIM images of FIB cross-sections taken from sodiated half-cells, electrically disconnected and aged at room temperature, demonstrate non-uniform film swelling and the onset of analogous through-bulk separation. TOF-SIMS highlights time-dependent segregation of Na within the structure, both to the film-current collector interface and to the film surface where a solid electrolyte interphase (SEI) exists, agreeing with the electrochemical impedance results that show time-dependent increase of the films’ charge transfer resistance. We propose that Na segregation serves as a secondary source of stress relief, which occurs over somewhat longer time scales.

Lithium-ion batteries (LIBs) have dominated portable electronics industry and solid-state electrochemical R&D for the past two decades. In light of possible concerns over the cost and future availability of lithium, sodium-ion batteries (SIBs) and other new technologies have emerged as candidates for large-scale stationary energy storage. Research in these technologies has increased dramatically with focus on the development of new materials for both the positive and negative electrodes that can enhance the cycling stability, rate capability, and energy density. Two-dimensional materials are showing promise for many energy-related applications and particularly for energy storage, because of the efficient ion transport between the layers and the large surface areas available for improved ion adsorption and faster surface redox reactions. In this talk we will discuss some recent research advances on the use of 2D materials in future ‘beyond Li-ion’ battery systems, especially SIBs, as well as the remaining challenges and possible strategies to address them.

SnSe₂ is a member of two dimensional layered transition metal dichalcogenide family, which has been predicted to have high theoretical capacity as anode material for sodium ion batteries (756 mAh g^-1), thanks to its layered crystal structure. Yet, there have been no reports on using SnSe₂ as Na ion battery anode. Here, we report a simple synthesis method to prepare pure SnSe₂ nanosheets, employing N₂ saturated NaHSe solution as a new selenium source. The SnSe₂ 2D sheets achieve theoretical capacity during the first cycle, and a stable and reversible specific capacity of 515 mAh g^-1 at 0.1 A g^-1 after 100 cycles, with excellent rate performance. A combination of ex-situ high resolution transmission electron microscopy (HRTEM) and X-ray diffraction show that the sodiation and desodiation process in this anode material occur via a combination of conversion and alloying reactions, which helps to explain high capacity of SnSe₂ for Na ions compared to other binary selenides. Density functional theory calculations were also used to elucidate the volume changes take place in this important 2D material.

Matured lithium ion battery technology has shown a great potential for the portable electronics. However, uneven distribution and high cost of lithium has raised concerns for developing alternative battery technologies. An alternative could be ‘revisiting’ sodium ion technology which offer low-cost, and scalability advantage due to earth abundance of sodium while exhibiting similar chemistry and suitable redox potential (E^ο_(Na⁺_/Na)= –2.71V versus the standard hydrogen electrode) as that of lithium. Nonetheless, large size (1.06 Å vs. 0.76 Å of Li⁺) and coordination preference of sodium ion may require new electrode materials which could accommodate large sodium ions, while being robust enough to endure volume changes. Therefore, design of electrode architectures and fundamental understanding of sodium ion interaction with host structure is required for the development of sodium ion battery technology.
MXenes, a new family of two-dimensional transition metal carbides and nitrides, have shown a great promise as a potential anode material in sodium ion batteries. However, the surface functional groups of Ti₃C₂T_x MXene (–O, -OH and –F) may act as barriers for sodium ion adsorption and further intercalation. Herein, a novel strategy was developed for confined polymerization of pyrrole between the MXene sheets without any oxidant followed by carbonization at moderate temperatures (400-500 °C). This led to unique binder-free self-standing MXene-carbon electrode architectures which served as an anode material for sodium ion half-cells. Carbonized Ti₃C₂ MXene/polymer composite exhibited excellent rate capabilities, cycling stability and superior specific sodiation capacity up to 200 mAh/g over pristine Ti₃C₂ MXene (30 mAh/g at a current density of 25 mA/g). The MXene/carbon composite is capable of reversible intercalation/de-intercalation of sodium ions without structural degradation. This study may open up new avenues for developing MXene-nanocarbon electrode architectures for metal-ion batteries/capacitors.

There is much interest in Na-ion batteries for grid storage because of the lower projected cost compared with Li-ion. Identifying Earth abundant, low cost and safe materials that can function as intercalation cathodes in Na-ion batteries is an important challenge facing the field. Layered oxides, NaMO₂, where M is one or more transition metals, represent an attractive class of cathodes for Na batteries. Here we report excellent performance from Na_0.67MnO₂ with the P2 structure, which exhibits a high capacity (175 mAhg^-1) with good capacity retention. The presence of Jahn–Teller active Mn³⁺ in Na_0.67MnO₂ leads to a sequence of structural transitions and voltage steps in the charge/discharge profile. Substituting Mn³⁺ ions with electrochemically inactive Mg²⁺, which have a strong preference for octahedral sites, leads to the formation of a highly stable framework with a smooth charge/discharge profile even for a substitution level as low as 5%.¹
b-NaMnO₂, with a structure quite different from the NaMnO₂ polymorphs and other compounds studied previously, exhibits high capacities to store Na of ca. 190 mAhg^-1 at a rate of C/20 with good rate capability (142 mAhg^-1 at 2C) and capacity retention (100 mAhg^-1 after 100 cycles at 2C). Powder XRD, HRTEM and ²³Na NMR studies show that this compound exhibits a complex intergrowth of a-NaMnO₂ and b-NaMnO₂ structures. The long-range structure collapses on Na extraction, which would be expected to compromise function, yet stable, reproducible and reversible Na intercalation occurs.²
References
[1] J. Billaud, G. Singh, A. R. Armstrong, E. Gonzalo, V. Roddatis, M. Armand, T. Rojo and P. G. Bruce, Energy Environ. Sci., 2014, 7, 1387.
[2] J. Billaud, R. J. Clément, A. R. Armstrong, J. Canales-Vázquez, P. Rozier, C. P. Grey, and P. G. Bruce, J. Amer. Chem. Soc., 2014, 136, 17243.

One important class of potential battery electrode materials are the Na-ion intercalating layered oxides and sulfides. Studying phase transitions and cation ordering are important steps for better understanding mechanical properties and degradation mechanisms in these materials. We have modeled the phase diagram and Na-ion orderings at finite temperatures for Na transition-metal oxides and sulfides in the O1/P3/O3 system. Using density functional theory and grand canonical Monte Carlo in conjunction with cluster expansions, we show that Na intercalation is fundamentally different from Li intercalation. In the studied Na system, several structural phase transitions are predicted at room temperature between O3, P3, O1, and hybrid phases that combine features of O1, O3, and P3. We further explore ordering of Na ions in P3 and O3, showing that these structures order in very distinct patterns with important consequences for diffusion mechanisms. Ordering on the honeycomb in the P3 structure forms triangular islands with vacancies along antiphase boundaries, which results in a devil’s staircase of ground states. Knowing the consequences of Na (de)intercalation can help us better design materials that will increase the lifetime of grid energy storage devices.

All-solid-state battery with inorganic electrolyte is believed to be the safest battery, since it does not suffer from volatile and flammable issues that coming with batteries using organic liquid electrolyte. Sodium-ion batteries show greater potential in large-scale application than lithium-ion batteries due to the abundance and low price of sodium sources. However, current sodium-ion conductors are not suitable for room-temperature application due to their low ionic conductivity (< 1 mS cm^-1) or incompatibility with electrodes at room temperature. Here we report a new sodium-ion conductor, Na₃P_1-xAs_xS₄ (0<x<1), which shows an extremely high ionic conductivity of 1.46 mS cm^-1 at ambient temperature. To the best of our knowledge, this is the highest ionic conductivity reported for a sodium-ion superior conductor in the sulfides system. The pressed pellet also shows dense microstructure and good compatibility with electrode materials. Synchrotron X-ray diffraction and first-principle analysis are involved to study the crystal structure evolution of Na₃P_1-xAs_xS₄ (0<x<1) upon As-substitution and uncover the mechanism behind the dramatic conductivity improvement. It is demonstrated the operation of all-solid-state rechargeable sodium-ion battery with the Na₃P_1-xAs_xS₄ electrolyte. Considering the facile synthesis method, ball-mill following by low-temperature heat treatment (< 300 °C), the solid-state electrolyte Na₃P_1-xAs_xS₄ (0<x<1) is believed to be the promising candidate for all-solid-state sodium-ion battery.

I will present my group recent research for the grid scale energy storage. The topics include: 1) Prussian blue open framework materials for ultrafast and low cost storage; 2) Zn anodes with a new concept of backside plating to overcome the problem of dendrites and their matching with Mn- and Ni-based cathodes; 3) New aqueous battery chemistries with long cycle life and low-cost. 4) Li metal polysulfide semiflow batteries. The low-cost chemistries afford potential solutions for grid scale energy storage.

Rechargeable batteries, more specifically lithium-ion batteries, are one of the best options as high energy density energy storage option. However, as the use of large format Li batteries becomes widespread, the cost of Li raw material has roughly doubled from the first application in 1991 to present. Sodium-ion batteries have been developed as alternatives to lithium-ion batteries since sodium is the most electronegative and the lightest material after lithium as well as one of the elements found abundantly in the Earth’s crust.
Safety and the cost per stored energy (in €/kWh) are the key-points of large scale energy storage systems. Aqueous rechargeable batteries have potential to fulfil these criteria as compared with organic batteries. The first aqueous rechargeable battery in the field of Li-ion batteries was documented by Dahn et al. in 1990 based on VO₂ and LiMn₂O₄ electrode materials¹. On the other hand, the work on sodium system is quite new and developing aqueous Na-ion batteries is more meaningful and practical because of the huge abundance of Na resources².
One of the challenging issues is to find proper anode materials in aqueous electrolyte batteries since most of the negative electrode materials are electrochemically active below the thermodynamic stability of water (~ -1.0 vs SHE). Thus, most used negative electrodes in the field of aqueous electrolyte sodium ion batteries are NaTi₂(PO₄)₃ and activated carbon. Apart these, recently we have proposed a new type anode material option^3,4 which can be potentially used as negative electrode in the field of Na-ion batteries; dissolved polysulfides, so called anolyte, whose potential is in the range of water stability of water (-0.5 V vs SHE).
Herein this contribution, we will be evaluating the electrochemical performance of aqueous electrolyte sodium batteries; to do so, Na₀.₄₄MnO₂ or NaFePO₄ positive electrodes together with dissolved Na-polysulphide negative electrode were assembled in a full cell configuration. All battery experiments were carried out in the range of voltage stability window of water, which provide secure and reliable operating conditions. One of the handicaps of such a full cell configuration is that the dissolved polysulfides need to be separated from the positive electrolyte. Thus, an ion-selective polymer membrane, was used which prevent the leakage of the polysulfides during battery operation.
References
W.Li, J.R.Dahn, D.Wainwright, Science 1994, 264, 1115–1118
Whitacre, J.F., A. Tevar, and S. Sharma, Electrochemistry Communications, 2010. 12(3): p. 463-466
Demir-Cakan, R., M. Morcrette, J.M. Tarascon, Journal of Materials Chemistry A, 2015. 3(6): p. 2869-2875
Demir-Cakan, R., M. Morcrette, J.B. Leriche, J.M. Tarascon, 2014. 2(24): p. 9025

Acknowledgements
This work is supported by TUBITAK 1001 Project (TUBITAK contact No. 114Z920) and joint research project between CNRS-TUBITAK bilateral (TUBITAK contact No. 214M272)

Wide-scale deployment of solar and wind resources places a burden on electricity grids and requires solutions in the form of grid-scale energy storage. In this context, interest in sodium-ion and potassium-ion batteries is growing as these lithium-ion battery alternatives have the promise of being more cost-effective and less resource limited. However, the graphite anode that enabled the development of the lithium-ion battery has been shown to exhibit almost no capacity for the storage of sodium ions and extremely slow kinetics and fast degradation in the storage of potassium ions. Accordingly, it has proven difficult to transition to sodium-ions or potassium-ion systems for grid-scale storage where fast response times and long cycle lives are necessary to provide power-balancing and load-leveling grid support. In order to meet these requirements, we report the use of a cointercalation reaction to enable the storage of both sodium and potassium ions in graphitic carbon electrodes to achieve exceptionally high-rate capability and long lifespans. We demonstrate capacities up to 150 mAh/g, stable performance over 8,000 cycles, and rates up to 30 A/g (200 C or 12 second charging times) using gylme solvents. Galvanostatic intermittent titration technique measurements support the high-rate capability showing that the electrodes operate near equilibrium conditions with fast diffusion through the lattice. Despite the large cycle-to-cycle volumetric change that occurs, X-ray diffraction and Raman characterization of post-cycled electrodes reveal negligible degradation of the carbon crystallinity—a counterintuitive finding that we attribute to weak ion-lattice interactions due to the electrostatic screening by the solvent shell. Finally, to gain a better understanding of the cointercalation reaction, in-situ Raman spectroscopy was utilized, providing further evidence of the weak interaction between the ion and the host while highlighting the sequential formation of stage 4, 3, 2, and 1 intercalation compounds that occurs without the initial signature of a dilute stage 1 compound. Overall, this system overcomes rate and durability bottlenecks that limit current alternative ion battery electrodes, and gives promise to cointercalation for durable, fast, and low-cost storage systems.


A.P. Cohn, K. Share, R. Carter, L. Oakes, and C.L. Pint, Nano Letters, vol. 16, pgs. 543-548, 2016.
A.P. Cohn, N. Muralidharan, K. Share, R. Carter, L. Oakes, and C.L. Pint, submitted.

This presentation will cover the scaling and implementation of large-scale energy storage electrochemical batteries that use largely unexplored electrode interactions that exploit muti-cation interactions simultaneously, and have a high electrode mass to electrolyte mass ratio. The core devices use a configuration wherein the active anode material consists of a blend of NaTi₂(PO₄)₃ and activated carbon and the cathode is Li-inserted cubic spinel l-MnO₂, and the electrolyte is a blend of Li⁺ and Na⁺ and hydrogen cation species (at some states of charge) solvated in an aqueous electrolyte with SO₄^- and OH^- (at some states of charge) as the countering anions. The basic function of the battery will be discussed, and data from units ranging in capacity from mAh to hundreds of Ah will be offered. Observations from the materials scale up process will be offered, with comparative materials process, property, and performance data from bench and full-scale materials production being offered.

NaMn₂O₄ is of the CaFe₂O₄ type structure which contains unique one-dimensional tunnels along the c-axis. Since this structural characteristic is appropriate for Na ions transportation, it can be one of candidates for the cathode materials for a sodium ion battery. The first synthesis of NaMn₂O₄ has been recently reported and carried out in high pressure and temperature conditions. NaMn₂O₄ was performed the charge–discharge test in the voltage range of 2.0–4.0 V. The discharge capacity is 65 mA h/g at a current density of 5mA/g. It should be noted that the capacity retention of NaMn₂O₄ was found to be 94% after 200 cycles at room temperature. In this study, we focus on the synthesis and characterization of Na(Mn_1-xFe_x)₂O₄ solid solutions because Fe is a so-called common metal and late 3d-transition metal such as Fe, Co and Ni, are often used as a component of the positive electrode materials. Na(Mn_1-xFe_x)₂O₄ (x=0~0.5) ones have been successfully synthesized at 4.5 GPa and 1273 K using a multi-anvil type high pressure generation apparatus. The SEM images of synthesized samples indicated that they were all obtained as aggregates of needle-like crystals. It should be noted that the crystal size depends on the Fe content and is 100-250 nm in diameter and 3-15 μm in length. The local structures, especially around Na ions: i.e. one-dimensional tunnels, have been refined by the Rietveld method using synchrotron X-ray diffraction profiles. It was found that the tunnel sizes which directly relate to the Na ions transportation depend on the Fe content and their charge/discharge capacities increase with increasing Fe content when x > 0.2. The details of thessexperimental results as a function of the Fe content will be discussed from viewpoints of the crystal morphology and chemistry in the presentaion.

The natural abundance and widespread distribution of sodium resources make sodium battery chemistries an attractive alternative to lithium-ion batteries, especially for grid-scale storage applications where cost is paramount. However, decreased electrode capacities and decreased cell voltages reported for sodium-ion systems mean that a significant sacrifice in performance is required to transition away from lithium. To maximize the energy density of sodium systems to compete with lithium-ion battery performance, stable sodium metal anodes need to be realized. Leveraging the thermodynamic advantages of sodium, we explore sodium-ion plating and stripping on aluminum current collectors using carbon seeding layers in diglyme solvent. This approach allows us to replace the copper foil conventionally used on the anode side with lighter and more cost-effective aluminum. Promising performance is shown with the reductive stability of diglyme facilitating stable cycling with >99% coloumbic efficiency. The sodium metal anode is demonstrated in a full cell using a pyrite (FeS₂) cathode with aluminum foil current collectors on both sides to realize a high-performance, cost-effective alternative to lithium-ion batteries.

The Na-ion battery is an increasingly attractive rechargeable electrochemical system for energy storage due to the low cost, high abundance, and global distribution of sodium. However, the larger size and weight of Na⁺ ions compared to Li⁺ ions cause increased hindrance for intercalation and diffusion. As a result, Na-ion electrode materials often exhibit lower overall capacities, poor power densities, and shorter cycle lives.

Bilayered vanadium pentoxide (δ-V₂O₅) has previously shown one of the highest cathode capacities in Na-ion batteries.^{1, 2} In this work, we demonstrate the use of chemical pre-intercalation to insert Na⁺ ions into the crystal structure of the δ-V₂O₅ phase prior to electrochemical cycling. Single phase bilayered Na_xV₂O₅ nanowires have been chemically synthesized through the inclusion of an aging step followed by hydrothermal treatment in the presence of NaCl. The formed nanowire morphology is advantageous for Na-ion battery electrodes as it minimizes diffusion distances and maximizes surface area exposed to the electrolyte. This bilayered V₂O₅ exhibits an initial capacity of 365 mAh/g in Na-ion batteries. We believe the high initial capacity of this material is achieved due to the large interlayer spacing of 10-13 Å, typical for the bilayered vanadium oxide phase, which allows for the facile diffusion of Na⁺ ions through the crystal structure of the electrode material. However, poor capacity retention of the aged and hydrothermally treated bilayered Na_xV₂O₅ was observed over extended cycling. Here, we have for the first time investigated the effect of low-temperature thermal annealing on electrochemical stability of the Na_xV₂O₅ nanowires with bilayered crystal structure. Annealing was conducted at 260°C under vacuum in order to prevent the phase transformation of the bilayered crystal structure to the Na_xV₂O₅ bronze phase, which does not possess the 2D, open layered structure desirable for Na⁺ ion diffusion. Low-temperature thermal treatment improves the crystallinity of the bilayered Na_xV₂O₅ nanowires, which we believe leads to enhanced structural stability during sodium ion cycling. Upon annealing, the high initial capacity is achieved and an improvement in the capacity retention is observed through multiple discharge/charge cycles. This work demonstrates that low-temperature annealing improves the electrochemical stability of chemically pre-intercalated, high capacity bilayered Na_xV₂O₅ nanowire cathodes in Na-ion batteries.

1. Clites, et al. Journal of Materials Chemistry A 2016, 4, (20), 7754-7761.
2. Tepavcevic, et al. ACS Nano 2012, 6, (1), 530-538.

Rechargeable metal-air batteries have emerged as a possible alternative to lithium ion batteries due to their potential to provide high energy density [1]. Understanding the oxygen reduction and evolution reaction kinetics is, however, key to achieving these high volumetric energy densities. Nonaqueous Na-O₂ batteries are receiving growing attention for their demonstration of highly reversible formation of NaO₂ as the discharge product, with energy efficiencies during the first cycle greater than 90% [2]. This performance is in stark contrast with more heavily investigated Li-O₂ batteries, for which analogous efficiencies of <70% are routinely achieved for carbon–based cathodes [3]. While Na-O₂ batteries represent a possible alternative route to the development of rechargeable nonaqueous metal-air batteries, the decomposition mechanisms of the discharge products and the charging mechanism are poorly understood.
One technique capable of providing great insight into electrochemical behavior is electrochemical impedance spectroscopy (EIS), which is widely used in the field of Li-ion batteries. Its application to metal-air batteries is, however, limited to a small number of investigations performed by a few research groups, and its potential in metal-air battery technology has yet to be fully exploited. In this work, a model of the discharge and charge reaction mechanisms is proposed, which allows the development of new approaches to better understand these mechanisms and their relation to material and morphological properties through EIS, X-ray diffraction and scanning electron microscopy analysis and appropriate interpretation. This fundamental knowledge is critical in understanding Na-O₂ batteries and will facilitate the development and engineering of novel electrode materials with appropriate porous structure and pore size. Further insight into the charge/discharge mechanisms, especially those pertinent to the reversibility of the electrochemical reactions, will be gleaned through the study of the growth process of NaO₂.

REFERENCES

1. D. G. Kwabi, N. Ortiz-Vitoriano, S. A. Freunberger, Y. Chen, N. Imanishi, P. G. Bruce, Y. Shao-Horn, MRS Bull. 39 (2014) 443-452.
2. N. Ortiz-Vitoriano, T. P. Batcho, D. G. Kwabi, B. Han, N. Pour, K. P. C. Yao, C. V. Thompson, Y. Shao-Horn, J. Phys. Chem. Lett. 6 (13) (2015) 2636–2643.
3. Y.C. Lu, B. M. Gallant, D. G. Kwabi , J. R. Harding , R. R. Mitchell, M. S. Whittingham, Y. Shao-Horn. Energy and Environ. Sci. 6 (2013) 750-768.

Throughout the many years dedicated to the discovery of stable, Earth-abundant photoelectrodes and catalysts for solar fuels generation, the anode and cathode components have often been optimized independently. Since most cathode and anode materials are acid-stable and base-stable, respectively, the long-term viability of such photoelectrochemical cells (PECs) is contingent on stable buffered electrolytes. Furthermore, robust separators will likely be a necessity to ensure maximum collection of gaseous products and overall electroneutrality. Here, a systematic study of the potential losses associated with employing a PEC with buffered electrolytes and commercial ion exchange membranes is presented. In particular, the ohmic drops caused by membrane resistivities, solution conductivity and the formation of a pH gradient were measured in a current density range up to 25 mA/cm². We identified that buffer concentration polarization is the most detrimental potential loss in monopolar ion exchange membranes, which can be greater than 300 mV.¹ However, this loss is somewhat mitigated by back-diffusion of neutral species when the cell is turned off. Furthermore, implementing bipolar membranes in a pH-polarized cell appears to provide an opportunity to de-couple the optimization and solution requirements of the materials for the anodic and cathodic reactions and minimizes overall overpotential losses in PECs .²
References:
(1) Hernandez-Pagan, E. A.; Vargas-Barbosa, N. M.; Wang, T.; Zhao, Y.; Smotkin, E. S.; Mallouk, T. E. Energy Environ. Sci. 2012, 5 (6), 7582.
(2) Vargas-Barbosa, N. M.; Geise, G. M.; Hickner, M. A.; Mallouk, T. E. ChemSusChem 2014, 7 (11), 3017.

Advance of energy storage technology led to convenience of human life due to its many applications including sensor, mobile device, electric car and grid-scale energy storage. In particular, grid scale energy storage devices require high capacity and reliability. This study examined the enhancement of cycling reliability of Si alloy-based anode electrode for large-scaled energy storage. We used active-inactive materials as silicon-based alloy anode electrode in order to obtain the buffer effect against stress which involved volume change during charging and discharging. Si alloy-based anode electrodes were grown on Cu foil current collector by co-sputtering deposition with Ta adhesion layers. The electrochemical properties of half-cell with silicon alloy based electrode as the working electrode and Lithium as the counter electrode were tested in the form of coin cell. The electrolytes were used in the form of liquid electrolyte of 1M LiPF₆ in a 1:1 mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DEC). A careful characterization of the structure changes after cycling has been carried out using various characterization tools such as scanning electron microscope (SEM) and transmission electron microscope (TEM). The series of SEM images show that the loss of the electrode is quite small even after 500 cycles. In TEM analysis, electrochemically driven elemental segregations inside the Si alloy-based anode electrode were observed during cycling. These results show that the morphology and microstructure of the electrode critically determine the electrochemical properties of the electrode. The capacity retention shows a significant improvement up to 500 cycles compared with our previous result of Si alloy-based anode electrode. The coulombic efficiency was 75% for the first cycle, while about 99.3% was maintained for the successive 500 cycles. The excellent rate capability of the Si-alloy benefits from the strain-released active-inactive structure and the transition metal atoms that provide improved electrical conductivity.

Intercalation cathode materials are mature and main commercialized cathodes for lithium-ion batteries in the market. However, normally only one Li ion involved in the electrochemical reaction limits the accessible capacity to < 200 Ah/kg, which greatly hinders the application of lithium-ion batteries, especially in the electric vehicles. To get higher energy density, one way is using high-voltage cathode materials, but this generally requires a compatible stable high-voltage electrolyte to get the full capacity, which is very challenging. Another feasible approach is finding a cathode material that can react with multi-Li ions (>1) within the voltage window of the present electrolyte system. Li_xVOPO₄ is a very good candidate, which can reversibly react with 2 Li at around 4.0 and 2.5 V respectively and give a theoretical capacity > 300 Ah/kg and energy density > 1000 Wh/kg. Our group have done many studies on this material and already proved that about 1.65 Li can be reversibly extracted and inserted, contributing to a capacity of ~ 260 Ah/kg at low current rate.
To improve the rate performance of the material, sol-gel synthesis was attempted in our study. Two different phases of LiVOPO₄ (orthorhombic and triclinic) can be easily synthesized in the air atmosphere with the same precursors but at different temperatures. A phase transformation from triclinic to orthorhombic then back to triclinic with gradually increased synthetic temperature was observed. Compared to the direct solid-state synthesis, the sol-gel synthesized samples give better electrochemical performance, especially rate performance, where ~ 250 Ah/kg can be obtained at 0.1C and up to 0.5C, the capacity can be still maintained above 200 Ah/kg. In addition, the orthorhombic sample shows better performance than the triclinic one, which may be due to the different kinetics caused by their different crystal structures. Furthermore, the effect of conductive coating or doping on the electrochemical performance will be also discussed. This work is supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) program under Award No. DE-EE0006852.

Thermochemical Energy Storage (TCES) is one of the major classes of using heat to charge energy storage, alongside sensible and latent energy storage. The superior energy density, and more importantly lower cost per unit energy, of TCES implies it has the potential to be the most technoeconomically viable form of thermal energy storage as the technology matures. Furthermore TCES is likely the thermal storage method most suitable for long-term storage as well as regional transportation. Despite this potential, TCES technology has the most remaining development hurdles (whereas sensible molten salts are commonly deployed commercially).
To overcome obstacles created by the growing capacity of intermittent resources on the grid, since 2008 the United States Department of Energy (USDOE) Solar Office has supported nearly 20 initiatives with over $30MM in funding. These programs have sought to research, develop, and demonstrate suitable complimentary endothermic and exothermic reactions in a closed system that could be coupled to a power cycle and deliver power when energy is at its greatest demand. Despite the incredibly wide range of chemical reactions considered, these endeavors have demonstrated clear themes. Specific materials, heat transfer, reactor and process engineering, scale, and lifetime challenges must be simultaneously overcome to achieve temperatures of a relevant power cycle and a value competitive with other energy sources. To this end the state of the art TCES demonstrations and conclusions are systematically evaluated in comparison to the needed technical and cost goals that, when achieved in tandem, would demonstration sufficient value to be desirable for the existing and future U.S. energy grid. The value of several scenarios in which TCES could be implemented are evaluated, including daily, seasonal, and geographic grid stability through either an independent power source (likely the sun) or using the grid directly as the charging force. In particular, technical targets for TCES systems are presented which complement a next generation sc-CO₂ Brayton cycle operating above 700°C.

CaCu₃Ru₄O₁₂ of ordered perovskite-type structure shows excellent electrical conductivity, and is expected to be chemically stable at high temperature in air. We focus on this material as a substitute for platinum in various applications of electrical devices such as gas sensors and a new cathode material in the Solid Oxide Fuel Cell (SOFC).
As CaCu₃Ru₄O₁₂ was found to be sintering-resistant in our preliminary experiment, we have investigated sintering additives for densification. Insulating metal oxide additive was found to improve the densification of CaCu₃Ru₄O₁₂ maintaining electrical conductivity high. In the presence of 25 vol.% sintering additive, sintered bulk CaCu₃Ru₄O₁₂ still maintained the electrical conductivity of pure sample (0.5 mΩcm at room temperature). The porosity and grain size of the bulk sample was controlled by the amount of the sintering additive. We have also investigated the applicability of the sintering additive for the thick film prepared by screen printing process. The sintering additive improved the density of the CaCu₃Ru₄O₁₂ thick film, and also the adhesion to alumina substrate.
We will present and discuss the electrical transport properties of the CaCu₃Ru₄O₁₂ bulks and thick films with the sintering additive for wide temperature range as well as microstructure.

We report the synthesis, characterization, and performance of a Si-based composite electrode, consisting of renewable biopolymer lignin and silicon nanoparticles, for lithium ion batteries. By mixing, coating, and subsequent heat treatment at various temperatures, we fabricated uniformly interconnected core-shell composite films of Si/C/polymer directly on the current collector, allowing for the assembly of coin-cells without the need for extra binder and conductive carbon. Excellent electrochemical performance was observed with a high specific initial capacity of 3100 mAh g^-1 and stable rate performance. Moreover, this Si-based composite electrode can be reversibly cycled at 1 A g^-1 with 78% capacity retention over 100 cycles. We found that the partially carbonizing lignin obtained at moderate temperatures of 500-600 C could facilitate both high electronic conductivity and mechanical flexibility in the nano-Si/C/polymer electrodes, leading to high capacity and long durability. This concept of converting a biopolymer to an electrically conducting and flexible scaffold for high capacity electrodes can be readily extended to other battery systems such as sodium ion batteries.

Sodium based rechargeable batteries have attracted interest for next-generation energy storage systems because of their potentially low cost and abundant resource materials. In particular, sodium metal halide (Na–MH) batteries using β″-alumina solid-state electrolyte represent compelling candidates owing to their long cycle life, high energy density, and superior battery safety that can fulfill the demands of applications from microgrids to large-scale stationary energy storage systems.

Despite the significant advantages of Na–MH batteries, several issues limit their practical application, including high operating temperature (> 280 °C), the use of a relatively high cost nickel (Ni) cathode, and limitations of cell design. We have recently demonstrated a Na-MH battery that can be operated at a lower temperature (< 200 °C) with much higher energy density and longer cycle life than those of a conventional tubular type of Na–MH batteries.

In order to further investigate the cycling performance and cell degradation mechanisms at the intermediate temperature of 190 °C, we carried out more detailed examinations on Na–MH batteries using Ni cathodes under various conditions, i.e., different cathode formulas and various battery testing protocols. Our results show that lowering operation temperature with less Ni content in the cathode could give substantial advantages, such as reducing the cost of cathode materials and manufacturing without sacrificing battery performance. Moreover, we demonstrate for the first time the possibility of applying conventional polymer sealing technologies in Na-MH battery systems, which could offer cost-effective and affordable solutions for large-scale manufacturing of the batteries.

Our results suggest great promise for the development of both sealing technologies and cathode materials at 190 °C. These advances can significantly reduce battery materials and manufacturing costs, and also expand the role of Na–MH battery technologies in stationary energy storage systems.

Sodium sulfur (NaS) batteries have been lauded as one of the most promising candidates for advanced grid scale energy storage systems (ESS). Within a NaS cell, there are heterogeneous joint parts comprised of different types of materials such as metallic alloys or glasses to bond between insulating ring/metals and insulating ring/electrolytes, respectively. Upon the freeze (cooling) and thaw (heating) processes, the ambient temperature change can result in the interfacial decohesion or the bulk fractures of these joint parts, which may lead to a catastrophic failure of NaS cells. Such thermo-mechanical stress concentration within the cell structure during the cell assembly or operation processes typically increases as the cell size increases. Therefore, the thermo-mechanical stability and safety in these joint parts is one of the critical issues in developing commercialized NaS cells. In this presentation, we will first review the current thermo-mechanical stability problem of contemporary NaS cells, and then we will introduce the computational approach to address the quantitative assessment of such thermo-mechanical stress concentrations in these metallic and glass joints area of NaS batteries. Specifically, the impacts of the cell sizes and the cell container material types on the thermo-mechanical behavior of contemporary planar-type NaS battery will be explored based on the finite-element analysis (FEA) computations. In contrast to the conventional tubular type cells, we will introduce a planar-type of NaS structure, as it has numerous advantages over the tubular cells. In developing the computational model, we have incorporated relevant stress-strain curves of each cell compartment assuming that the constituent cell materials would follow the J2 flow theory with isotropic hardening. A prototype of planar-type geometries of the NaS battery structure has been digitally transferred to the FEA solver using sophisticated mesh-generation software. The computation includes all of the experimental cell assembly procedures with corresponding temperature changes. After imposing the temperature changes onto the 3D NaS cell structures, a comprehensive analysis including the tangential and the normal stress concentrations at the interfaces and the bulk sections of the joint areas has been performed. The results of the FEA computations show that the thermo-mechanical stress concentration in the joint areas is strongly influenced by the cell size and the cell container material types. In this presentation, we will also show quantitative analyses on the probable fracture scenarios in the heterogeneous cell joints. It is expected that the outcomes obtained from the developed prediction tool employing FEA can guide to secure the stability and safety of the NaS cell systems with optimized material and geometrical designs.

CeO₂ has received considerable interest as an electrolyte for intermediate temperature solid oxide fuel cells. [1] Unfortunately, within this temperature range (~600-800°C), CeO₂ displays poor ionic conductivity, while at high temperatures and low oxygen partial pressures Ce⁴⁺ can be reduced to Ce³⁺, due to facile oxygen vacancy formation, [2] which results in electronic conductivity. In an attempt to improve the ionic conductivity of CeO₂ aliovalent doping is commonly employed, with trivalent species (e.g. Gd³⁺, Sm³⁺) a particular focus due to their creation of charge compensating vacancies which forms an O^2- diffusion pathway without the presence of Ce³⁺. Experimental evidence [3] has corroborated the increased ionic conductivity from trivalent dopants, however a detailed understanding on the effect of the dopant on the electronic structure of CeO₂ and a full exploration of the range of trivalent dopants has been lacking.

This study considers two aspects of trivalent doping using density functional theory simulations: (i) the formation of charge compensating vacancies and their role in O^2- conductivity, and (ii) their effect on the reducibility of CeO₂. These aspects are explored for a range of p-, d- and f-block ions. The first part of the study focusses on the position of the dopant ions to the vacancies, as dopant-vacancy association can limit ionic diffusion. The results indicate a clear relationship between the dopant species ionic radius and its position relative to the vacancy. In addition, some rare earth dopants (e.g. Dy, Nd) are found to have low dopant-vacancy association energies, suggestive of better ionic conductivity. The second aspect of the study, which is largely ignored in the literature, shows that the reduction energy correlates with the defect structure, therefore being only indirectly influenced by the ionic radius.

[1] Brett et al., Chem. Soc. Rev., 37, 1568 (2008).
[2] Scanlon et al., J. Phys. Chem. C, 113, 11095 (2009).
[3] Fu et al., Int. J. Hydrogen Energy, 35, 745 (2010).

Sodium-ion batteries (SIB) are emerging as an excellent alternative to the lithium-based counterpart. The Na resources come with advantages such as abundance in the earth crust, uniform geographic distributed, and low prices in comparison to lithium, offering an avenue of possibilities to develop cheaper and sustainable devices mainly for applications where energy density and specific energy are not the main concern. In this spirit, the mineral eldfellite, NaFe(SO4)2, was recently proposed as an inexpensive candidate for the next generation of cathode application in Na-based batteries. Employing the density functional theory framework we have investigated phase stability, electrochemical properties and ionic diffusion in the eldfellite material. We showed that the crystal structure undergoes volume shrinkage of ≈ 8% upon full removal of Na ions with no imaginary frequencies at Γ point of the phonon dispersion. It evokes the stability of the host structure. According to this result, we proposed structural changes to active greater specific energies by inserting two Na ions per redox-active metal. Our calculations indicate NaV(SO4)2 as the best candidate with the capability to reversely insert two Na ions per redox center and producing an excellent specific energy. The main bottleneck to the application of the eldfellite as a cathode is the high activation energies for Na⁺ ions hop, which can reach values even higher than 1 eV for the charged state. This effect produces finally low ionic insertion rate.

Device miniaturization and development of flexible and wearable technologies require compatible energy storage devices. Micro-supercapacitors based on interdigitated electrodes printed on or embedded within flexible polymer supports are a promising architecture to power these devices. Compared to thick sandwich-type cells, such micro-supercapacitors are thinner and can be made flexible and robust. Furthermore, the planar geometry of the interdigitated electrodes leads to the potential for coupling the electrode array to other materials to create new electrically-driven devices. However, the high cost of the fabrication process and the sub-optimal performance in terms of energy and power density limit their practical application. This study focuses on the fabrication and development of improved micro-supercapacitors using a renewable biomass source and a scalable laser patterning process to create a high performance, eco-friendly, mechanically robust, flexible, inexpensive and easily fabricated energy storage device.

Laser-induced carbonization and patterning of graphene oxide and, more recently, commercially available polyimide tapes, have emerged as a promising method to create such patterned electrodes. This is a direct-write process with many advantages over traditional photolithographic patterning. However, the energy density of the laser-induced supercapacitors is significantly lower than traditional supercapacitors due to a low areal capacity of 10-20 mF/cm² compared to state-of-the-art supercapacitors that are able to achieve > 1000 mF/cm². This discrepancy has motivated us to engineer more suitable materials for this laser patterning process and to develop and understanding of the important factors limiting device performance.

In the current study, a CO₂ infrared laser is used to pattern and convert polymer/graphene oxide (GO) composites into the high surface area, interdigitated electrodes used to boost the performance of micro-supercapacitors. The polymer used is poly (furfuryl alcohol) (pFA), a thermoplastic that is easily produced via homopolymerization of a monomer obtained from biomass such as sugarcane, corn etc. It is known to carbonize into dense, nanoporous hard carbon upon heat treatment which we will demonstrate can be induced by the CO₂ laser. In this talk we will discuss our efforts to optimize the polymerization procedure, casting approach and laser parameters to create a superior micro-supercapacitor technology. We expect this new material to accelerate the development of various technologies such as micro-supercapacitors in micro-electromechanical systems (MEMs), micro-robots, solar cells and flexible electronics.

Energy storage must be cost effective and scalable to meet future energy demands. Polymer-nanoparticle composites are attractive because of their relatively low cost and potentially high energy storage, based on the high breakdown strength of polymers and the high dielectric constant of ceramic nanoparticles. The incoherent nature of the interface between the nanoparticle and polymer has been shown to be an impediment to these composites’ development. We have created inkjet printable nanoparticle-polymer composites that have mitigated many of these interface effects. We detail multiple techniques that we have used to optimize the interface of our polymer-nanoparticle composites. We demonstrate a clear correlation of the breakdown of the composite and the dielectric gradient between nanoparticle and polymer through finite element analysis and experiment guided by this modeling. By utilizing multiple layers of ceramics and polymers of decreasing dielectric constant from nanoparticle to polymer, we have increased the overall breakdown field of our composites while utilizing the high dielectric constant of the nanoparticles. We also extend past work utilizing click chemistry to reduce the incoherent interface between polymer and nanoparticle filler by screening different surface functionalizations using density functional theory. By choosing the correct surface functionalization we are able to create dipole traps which further increase the breakdown strength of our composites. Our nano-scale understanding has allowed us to create the highest energy density composites currently available (>40 J/cm3). Future work that will take energy density in these composites to an order of magnitude greater to where they are today will also be detailed.

The ability to store energy during times of low demand, and utilize this stored energy during peak demand, is a critical necessity for existing power plants as well as future renewable energy driven power plants. Dispatchable electricity is an issue that most renewable energy power plants struggle with, given the intermittency of their sources, e.g. wind, solar, geothermal, etc. Pumped hydro and compressed air energy storage (CAES) have been the main method of energy storage for fossil fuel fired power plants, however these methods are not available for every plant, due to its dependency on geographic location. Even though the idea of storing electricity by first converting into heat followed by converting back into electricity intrinsically does not seem to be attractive from second law perspective, cost analysis shows that this approach is competitive, especially if phase change latent heat is used. This work carries out cost-analysis and preliminary design of a power plant storing electricity via latent heat. We utilize the high energy storage density of PCMs to develop a low cost and material compatible design for storing electricity as heat and generating supercritical steam to generate electricity at the megawatt-scale, compatible for power plants

Lithium-sulfur (Li-S) batteries are among the most promising next generation batteries to realize in the near future to meet the demands of electric vehicles and grid storage. However, the direct use of lithium anode and sulfur cathode confronts safety concerns due to the dendrite growth of lithium metal. An alternative is to use lithium sulfide (Li₂S) nanomaterials. However, the commercially available Li₂S exists only as micro-powders, due to the high temperature processes used in the industrial synthesis.
Herein we report a thermodynamically favorable method by taking the advantage of hydrogen sulfide (H₂S), a major industrial waste gas. Considering the fact that H₂S traditional abatement methods are energy intensive and cost ineffective due to the thermodynamic limitations and low values of the products sulfur and water, it is mutual beneficial to combine the alkali sulfide synthesis with the H₂S abatement. The synthetic reaction developed is spontaneous and irreversible at ambient temperature and pressure, proceeding to completion very rapidly.
Specifically, lithium naphthalenide (Li-NAP) in dimethoxyethane (DME) was used to react with H₂S, producing anhydrous Li₂S nanocrystals, and 1,4-dihydronaphthalene, itself a value-added chemical that could be used as liquid fuel. The phase purity, morphology, and homogeneity of the resulting Li₂S nanopowder was confirmed by X-ray diffraction and scanning electron microscopy. The synthesized Li₂S nanoparticles (100 nm) were assembled into cathodes and their performance was compared to cathodes fabricated using commercial Li₂S micropowders (1 - 5 µm). Electrochemical analyses demonstrated that the synthesized Li₂S nanoparticles were superior in terms of (dis)charge capacity, cycling stability, output voltage, and voltage efficiency.

In the commercial fabrication method of lithium-ion battery electrodes, N-Methyl-2-pyrrolidone (NMP) is necessary as the solvent to make slurry. After uniformly mixing, the resulting slurry that contains active material, conductive carbon, binder and solvents, is cast onto the surface of current collector and undergoes a drying process to evaporate the solvent and finishes the manufacture. Due to the high cost and potential pollution problem of NMP, NMP have to be recovered by the drying procedure, which can take up to 24 hours at 120 °C for some electrodes. Therefore, electrodes fabricated in a completely dry processing way represent an ideal development orientation of manufacturing, thereby eliminating the usage of solvents and the disadvantages that come with using them.

Here we fabricated lithium ion battery electrodes using a new, completely dry powder painting process. No solvents are applied, which are essential in the conventional slurry-casting manufacture. Thermal activation time has also been tremendously reduced due to a lowered time and resource requirement when the evaporation process is no long needed and replaced by a hot rolling process. It has been found that inducing the mechanical bonding of the thermoplastic polymer to the remaining active electrode particles only takes a few seconds for the thermal activation step. Furthermore, skipping the traditional drying process allows large-scale Li-ion battery production to be more economically viable in markets. Electrochemical results also show that our tested dry-painted electrodes outperform conventional slurry processed electrodes, which are due to their unique binder distribution based on our analysis. Bonding tests of the dry-deposited particles onto the current collector show that the bonding strength of them are greater than the ones of slurry-cast electrodes, 127.14 kPa as compared to 84.29 kPa. In addition, more electrodes design and optimization possibility on this new fabrication method are conducted and tested, and the fundamental researches on its specific electrode microstructure during manufacture and cycling are studied and recognized.

Zinc electrodeposition is a complex phenomenon and is known to form various morphologies under different electrochemical growth conditions. The overall morphology of electrodeposited Zn should be precisely controlled to suppress dendritic growth. In spite of the huge literature, majority of the work in this field is limited to studies at less than or equal to limiting potentials. In our recent work we reported a new morphology of Zinc, called Hyper Dendrite Zinc (HDZn), at high overpotentials (-2.0 V vs. Hg/HgO), in alkaline electrolyte. HDZn is a highly ramified conductive morphology and is shown to exhibit unique cycling properties with fast kinetics, better utilization, slower rate of passivation and conformal growth at micron scale. These properties make it an excellent anode material but the underlying physical mechanism of HDZn formation and cycling is not well understood.
In this work we report the results from ex-situ transmission electron and X-ray microscopy studies on the structural transformation of HDZn during growth and electrochemical cycling. Zinc is grown electrochemically on a Cu TEM grid at different overpotentials in 8.9 M KOH and 0.61M ZnO solution. Scanning EM is first used to identify the dominant morphology that best represents the sample. Subsequent TEM characterization is done on the same region. Interesting differences in the crystallographic orientations of Zinc at different potentials are found. Preliminary results suggest, transition from face dominated structure, with aggregated crystallites to edge dominated structure, with fiber like columnar growth and much smaller crystallite size. The goal is to establish basic understanding of crystal growth and its evolution during cycling at high over-potentials.

The reduction of pollutants under solar or UV radiation is highly attractive for an economical and environmental point of view and can be increased with a suitable photocatalyst. Nowadays, the requirements for a good photocatalyst involve being inexpensive, reliable, easily recycled and produced on flexible platforms adaptable for several surfaces. Titanium dioxide (TiO₂) fulfils these requirements as it is non-toxic, chemically stable, earth-abundant and shows remarkable photocatalytic activity in the decomposition of organic pollutants [1, 2]. In this study, titanium dioxide nanorod spheres in the powder form and nanorod arrays grown on polyethylene terephthalate (PET) substrates were simultaneously synthesized through microwave irradiation. The syntheses were performed in water or ethanol with limited temperature at 80 ^oC and 200 ^oC. A simple and low cost approach was used for the arrays growth, which involved a PET substrate with a ZnO seed layer deposited by spin-coating. X-Ray diffraction (XRD) and Raman spectroscopy revealed that the TiO₂ synthesis in water result in a mixture of brookite and rutile phases, while using ethanol as solvent it was only observed the rutile phase. Scanning electron microscopy (SEM) showed that the synthesized spheres were in the micrometer range appearing as aggregates of fine nanorods. The arrays maintained the sphere nanorod aggregate structures and the synthesis totally covered the flexible substrates. Transmission electron microscopy (TEM) was used to identify the brookite structure. The photoluminescence behaviour of the TiO₂ powders was investigated and the optical band gaps of all materials have been determined from diffuse reflectance spectroscopy. Photocatalytic activity was assessed from rhodamine B degradation with remarkable degradability performance under UV radiation. Reusability experiments were carried out for the best photocatalyst, which also revealed notable photocatalytic activity under solar radiation.

[1] D. Nunes, A. Pimentel, J.V. Pinto, T.R. Calmeiro, S. Nandy, P. Barquinha, L. Pereira, P.A. Carvalho, E. Fortunato, R. Martins, Photocatalytic behavior of TiO₂ films synthesized by microwave irradiation, Catalysis Today.
[2] K. Nakata, A. Fujishima, TiO₂ photocatalysis: Design and applications, Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 13 (2012) 169-189.

The increasing demands on battery storage system make it necessary to move away from the concept of traditional lithium-ion batteries and the lithium sulfur (Li-S) system is considered a promising candidate to achieve this. However, so far the Li-S battery still suffers from short cycle life, low sulfur utilization and safety concerns connected to the use of lithium metal anodes and flammable electrolytes. We here present three approaches for advanced carbon-sulfur composite materials, including ordered mesoporous carbons, carbon nanofibers and graphene-oxide based aerogels, which all have the potential to address the shortcomings of current technologies.
We have successfully improved the capacity retention in ordered mesoporous electrodes by functionalizing the conductive carbon matrix with covalently bonded sulfur to prevent migration of soluble polysulfide species. The approach relies on carbonizing a sulfur-containing precursor, furfuryl mercaptan, inside a silica hard template and we can achieve a doping level of up to 10 wt% sulfur in the structure. The sulfur functionalities do not only increase capacity retention by 8 % over 50 cycles compared to non-functionalized ordered mesoporous carbon but also influence the electrochemical reactions occurring during charge and discharge.
Helical carbon nanofibers (HCNFs), a subspecies of carbon nanofibers, have successfully been employed as sulfur host in cathodes for Li-S batteries. We show that for helical carbon nanofibers a thermal activation utilizing potassium hydroxide significantly increases the sulfur utilization whereas the same activation only results in a minor improvement of the performance for stacked graphene nano fibers (SGNFs) and carbon nanotubes (CNTs). The results show that HCNFs can be a highly suitable candidate as advanced sulfur carrier for Li-S cathodes
We developed a new method to synthesize high sulfur loading reduced graphene oxide based aerogels. The approach is a simple one-pot synthesis creating light-weight carbon, high sulfur loading structures which can be cut and used directly as electrodes in a Li-S cell. The cathodes are self standing (i.e. they contain no binder or additional conducting agent) and have therefore a true sulfur loading of around 70 wt%. The electrodes show excellent capacity retention over more than 200 cycles. Even at high C-rates, 1 C discharge/charge, the cells can maintain 75 % of the capacity compared to slow discharge/charge, 0.1 C. The areal capacity can be significantly increase to 3.5 mAh/cm² or more by simply increasing the thickness of the electrodes without sacrificing the performance in terms of sulfur utilization.
We conclude that the design of appropriate carbon composites for lithium sulfur batteries is of very high importance and can increase both capacity retention, sulfur utilization, and most importantly the practical energy density of a Li-S battery.

Owing to the increasing demands of energy storage in portable electronics, vehicle electrification and grid-scale stationary storage, advanced batteries with high energy density have recently attracted intensive interests. Among the existed myriad energy-storage technologies, lithium–sulfur batteries (LSBs) show the appealing potential for the ubiquitous growth of next-generation electrical energy storage application, owing to their unparalleled theoretical energy density of 2600 Wh/kg that is almost sixth fold larger than that of conventional lithium-ion batteries (LIBs). Despite holding high theoretical capacity, practical applications of lithium-sulphur batteries (LSBs) are plagued because of poor conductivity and low capacity release of sulphur as well as severe capacity fading over cycling. To tackle the hurdles associated with LSBs, exciting progress has been made, however still it is great challenge to solve the hurdles associated with LSBs and enhance its electrochemical performance. In order circumvent the aforementioned challenges, we design an innovative nanostructure, namely silicon/silica (Si/SiO₂) crosslink with hierarchical porous carbon spheres (Si/SiO₂@C), and use it as a new and efficient sulfur host to prepare Si/SiO₂@C-S hybrid spheres to solve the hurdle of the polysulfides dissolution. We employ the concept of both physical and chemical adsorptions of polysulfides via the carbon and Si/SiO₂ of developed hybrid spheres, respectively. Different from the traditional porous carbon structures, the developed hybrid spheres afford the intriguing structural advantages. As a results of multitude structural advantages of the developed hybrids spheres, it acts as efficient polysulfides reservoir for enhancing lithium sulfur battery (LSB) in the terms of capacity, rate ability and cycling stability via combined chemical and physical effects.
The present work highlights the vital role of the introduction of new class of hybrid nanostructure cathodes in boosting the performance of LSBs.

References:
S. Rehman, S. Guo and Y. Hou, Rational Design of Si/SiO₂@Hierarchical Porous Carbon Spheres as Efficient Polysulfide Reservoirs for High-Performance Li–S Battery, Advanced Materials.2016, 28, 3167–3172.
S. Rehman, S. Guo and Y. Hou, 3D Vertically Aligned and Interconnected Porous Carbon Nanosheets as Sulphur Immobilizers for High Performance Lithium-Sulphur Batteries, Advanced Energy Materials (DOI:10.1002/aenm.201502518).

Lithium-sulfur (Li-S) batteries have attracted great attention because of the very high theoretical specific energy of sulfur cathodes, ~2,600 Wh kg^-1. Dissolution, diffusion and side-reaction of lithium polysulfide intermediates and irreversible deposition of Li₂S are known to be the main technical barriers to achieving high-energy-density, long-cycling Li-S batteries. As one important component of sulfur cathodes, the carbon host plays a key role in the electrochemical performance of lithium-sulfur batteries. The talk will first present development of Li-S batteries with emphasis on applications of new carbon-sulfur composite with capability of chemical adsorption of sulfur/polysulfides to increase capacity, improve cycling stability, as well as demonstration of improved performances in Li-S batteries. Fundamental reaction mechanism in the new electrode materials and electrolyte to address the challenges will be also presented. Second, organo-sulfide electrolyte will be studied showing a new electrochemical pathway for Li-S batteries. organo-sulfide promotes the discharge of sulfur by formation and subsequent reduction of soluble dimethyl polysulfide species to new intermediates/products including lithium organosulfides. This largely avoids formation of soluble lithium polysulfides. The organo-sulfide boosts cell capacity while avoiding the extreme increase in electrolyte viscosity and cell resistance associated with lithium polysulfide dissolution, enabling high performance with much less electrolyte. Third, with use of new fluorinated electrolyte, the sulfur cathode can be paired with graphite to enable Li-ion Sulfur batteries with superior cycling stability and rate performance. The work enclosed here makes major inroads on the technical issues for Li-Sulfur and Li-ion Sulfur batteries, presenting a new electrochemical pathway for greatly enhancing their energy density and cycle life.

The lithium sulfur battery suffers from the shuttling of long-chain polysulfides during cycling, which results in low coulombic efficiency and reduced cycle life of the battery (typically <100 cycles). To enable high energy density and to reduce the cost of the battery, low electrolyte/sulfur ratio (electrolyte-starved-electrode), high cycle-life (~1000 cycles), and high loading of sulfur (at least 7 mg/cm²) have been identified through techno-economic modeling[i]. Recently, polymer encapsulated sulfur nano-composites have been used[ii]^-,[iii],[iv],[v] to prevent polysulfides from shuttling, with polypyrrole as the most tried polymer owing to its high electronic conductivity and ease of synthesis. However, the polypyrrole encapsulated sulfur composites studied, thus far, have shown no major successes (still <100 cycles). Here, we have demonstrated that by controlling the morphology of the encapsulating porous polypyrrole through intercalation of metal oxides nanoparticles (e.g. MnO₂) into the pores of the polymer, the cycle-life of the sulfur/polypyrrole nano-composite can be significantly improved. Conceptually, by intercalating metal oxide particles into the nanoscale pores of the encapsulating membrane, polysulfides can be blocked while electrolyte and lithium ions can still penetrate.

We show that the encapsulated sulfur nanoparticles made in this way have remarkable specific capacity between 0.2C – 0.5C rates. Self-discharge tests will be compared sulfur nanoparticles encapsulated in polypyrrole intercalated with MnO₂ nano-particles (SPPyMnO₂) with the unencapsulated sulfur nanoparticles at room-temperature to demonstrate that the encapsulated sulfur has both lower self-discharge and greater retained capacity in subsequent cycles. The Galvanostatic cycling performance of the SPPyMnO₂ will be compared to the uncoated sulfur nanopowder for proof of the enhancement in the capacity retention sulfur after encapsulation.


[i] D. Eroglu, K.R. Zavadil, K.G. Gallagher, J. Electrochem. Soc. 162, A982–A990 (2015).

[ii] J. Wang, J. Chen, K. Konstantinov, L. Zhao, S.H. Ng, G.X. Wang, Z.P. Guo, H.K. Liu, Electrochimica Acta 51 (2006) 4634-4638.

[iii] Y. Fu, and A. Manthiram, RSC Adv. 2, 5927-5929 (2012).

[iv] Z. W. Seh, W. Li, J. J. Cha, G. Zheng, Y. Yang, M. T. McDowell, P.-C. Hsu, and Y. Cui, Nature Communications 4 (2013) 1331.

[v] G. Yuan, and H. Wang, Journal of Energy Chemistry 23 (2014) 657-661.

The hybrid nanostructured materials have unique properties and provide a large volume conductive network for electron transfer, open chennels for ion diffusion and strong confinement of polysulfides. Herein we design a novel hybrid nanostructured Microporous carbon-mesoporous carbon doped TiO₂ nanotube host materials for sulfur using one step green synthesis approach by hydrothermal and annealing process.The process is facile, cheap, scalable and environmentally friendly. The materials were characterized and examined by XRD, BET, XPS, SEM, TEM, Raman, TGA, CV, EIS and galvanostatic charge-discharge tastes. It is found that the materials show both the characteristics of microporous and mesoporous behavior and contain large pore volume to encapsulate large amount of sulfur. Moreover, the presence of microporous carbon can effectively adsorb smaller sulfur (S_2-4) molecules in their narrow pores as well as increase the electrical conductivity of the cathode by decreasing the resistance of sulfur and enhance active material utilization. Meanwhile, mesoporous carbon doped TiO₂ nanotube were placed on the surface to prevent the overflow of sulfur as well as the dissolution of polysulfieds in the electrolyte effectively and improve the strength of the entire electrode thereby enhancing the electrochemical performance. As a result, using the hybrid nanostructured-sulfur nanocomposite as a cathode material, we demonstrated excellent cycle stabilty with initial discharge capacity of 882 mAh g^-1 with coulombic efficiency of over 97.1% at a current density of 0.1 C after 140 cycles.

The ever-growing demand on high energy storage systems for electrification of transportation has stimulated extensive research in high energy battery technologies throughout the world. Among them, the lithium-sulfur (Li-S) battery is one of the most promising candidates due to its extremely high theoretical electric capacity that is ten times higher than the current state-of-art batteries in the market, much lower manufacturing cost and environmental benignity. Significant investments, both from governmental agencies and from private sectors, are devoted to this field. However, the commercialization of this system still has significant obstacles. The most challenges are the limited cycle-life and the low practical sulfur utilization of this battery. More severely, the battery reactions involve complexed multi-steps electron transfer processes and phase transitions that are far from fully understood, and formation of soluble and insoluble polysulfide intermediates that are very difficult to control is facing serious challenges. So far, relatively little is known about the effective control of battery chemistry for the rational design of Li-S battery technology.
Herein, we conducted symmetric research in the understanding and controlling of the solubility of polysulfide species in Li-S batteries, which plays a key role in the long term cycling performance. Lithium trifluoromethanesulfonate (LiTf) and ammonium-based salts were identified as effective additives to tune the solvating properties of solution and thus significantly modify the chemical behavior of polysulfide species and cell performance. On the other hand, we show clear evidence that the electrochemical performance of lithium-sulfur battery is closely related to the growth pathway and morphology of sulfur species in the sulfur cathode. Large agglomerate of sulfur species rather than a thin layer precipitation is more favorable for high capacity. Through controlling sulfur species nucleation and growth pathway on low surface area carbon from a polysulfide catholyte, they form micro-sized ‘flower-like’ agglomerates. Under this condition, a 100% utilization of sulfur can be reached with stable cycling and good rate capability, and >99% coulombic efficacy at high area capacity of 4-5 mAh cm^-2. This finding opens a fundamentally new approach of using a low surface area carbon host for designing high energy Li-S battery by controlling the nucleation and growth pathway and morphology of sulfur species.
Acknowledgements
This work was supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES). The SEM images were performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL).

With a theoretical specific energy of 2500 W h kg^-1 and energy density of 2800 W h L^-1, the Li-S battery system is believed to provide the step-up in energy density necessary for lithium-based battery technologies to expand from portable electronics to transportation and grid-storage applications. However, the growth of dendrites during repeated Li plating/stripping and the low coulombic efficiency (CE) of these processes have limited application of rechargeable Li metal batteries. For example, a 300% excess amount of lithium often used in these batteries would directly result in halving the theoretical specific energy of the Li/S cells. In this presentation, the design of new electrolyte systems which enable high CE of lithium metal plating/stripping and high stability in the sulfur environment will be discussed. Tailoring of electrolyte properties for the lithium negative electrode has proven to be a successful strategy for improving the capacity retention and cycle life of Li-S full cells. This also enables lower electrolyte/sulfur mass ratios to be used and a lower excess of lithium metal; ultimately increasing the energy density of the system. A new class of electrolytes based on a high concentration of selected lithium salt provides a CE for lithium plating/stripping of greater than 99% for over 100 cycles. In contrast, lithium metal cycles for less than 40 cycles at high CE in the standard 1 M LiTFSI + 2wt% LiNO₃ in DOL:DME electrolyte. The inexpensive sulfur cathode paired with a low excess of lithium metal and the low-cost salt/solvent system may accelerate the applications of high energy density Li-S batteries in both electrical vehicles and large-scale grid energy storage markets.

Efficient energy storage is essential for the success of renewable energies, and electrochemical cells are among the best options to address this challenge. Electrochemical cells are complex systems integrated by several materials and their corresponding interfaces whose physical-chemical behavior is dominated by highly coupled mass and electron transport and chemical reactions.
In this talk we will discuss physical, chemical, and electrochemical phenomena occurring at solid/electrolyte interfaces of Li-ion batteries and how the methods of first-principles computational analysis may be used to understand them and suggest strategies for practical solutions.
In particular, we will refer to the solid electrolyte interphase (SEI) occurring due to electrolyte reduction on anode surfaces and the role of the nature of the solvents and additives on the resultant SEI properties and battery performance. Also, we will analyze the effect of chemical species generated at the cathode and migrating to the anode during cycling on the battery performance especially for Li/S batteries.

Lithiation of sulfur cathodes in Li-S batteries starts with the formation of Li₂S crusts on the outer surfaces of sulfur particles and continues via a two-phase growth process, during which nucleation and growth of Li₂S occurs at the Li₂S/S₈ interfaces. It has been shown that discharge capacity is limited due to the incomplete conversion of S₈ cores to Li₂S which is because of slow Li diffusion within Li₂S crusts [1].
In the present work, by using density functional theory calculations together with thermodynamics and kinetics considerations, we study formation of different types of ionic defects and ionic conductivity in Li₂S.
Results show that the ionic conductivity in Li₂S occurs by both positive interstitial Li (exchange mechanism) and negative Li vacancy (hopping mechanism) migrations with high activation energies (1.47 and 1.42 eV, respectively), leading to very low ionic conductivity in Li₂S at room temperature.
Moreover, we studied Li diffusion in Li₂S using AIMD simulations at different temperatures. It is shown that Li₂S has high ionic conductivity at temperatures higher than 750 K, which is due to a thermally-induced disorder in the crystal [2,3].

[1] R. Xu, I. Belharouak, X. Zhang, R. Chamoun, C. Yu, Y. Ren, A. Nie, R. Shahbazian-Yassar, J. Lu, J. C. M. Li, and K. Amine, “Insight into sulfur reactions in Li-S batteries,” ACS Appl. Mater. Interfaces 6, 21938–21945 (2014).
[2] A. Moradabadi and P. Kaghazchi, Thermodynamics and kinetics of defects in Li2S, APPLIED PHYSICS LETTERS 108, 213906 (2016).
[3] S. Panahian Jand and P. Kaghazchi, "Temperature-induced high Li-ion conductivity of Li2S", in preparation.

Sulfur has been considered as a potential cathode material for cost-effective, high-energy batteries due to its low cost, high theoretical specific capacity (1,675 mAh/g) and energy density (2,600 Wh/kg) ^[1]. However, the rate-capability and cycling lifespan of lithium-sulfur batteries are still problematic due to the insulating nature of sulfur and shuttling effects during cycling. Selenium is a congener of sulfur and shares similar electrochemical characteristics with sulfur. Although its gravimetric capacity (675 mAh/g) is lower, selenium is a potential cathode material for rechargeable batteries due to its higher conductivity (1 x 10^-3 S/m) than sulfur (5 x 10^-28 S/m) and comparable volumetric capacity (3,253 Ah/L) to sulfur (3,467 Ah/L) ^[2,3].
Due to better cycling stability (in conventional carbonate electrolyte systems) of selenium and higher capacity of sulfur, it is desirable to develop a cathode material that combines the advantages of both sulfur and selenium. Thus, the development of selenium sulfide (SeS₂) as a cathode material is highly desired to obtain good electrochemical performance. While there have been some successful demonstration of selenium sulfide-based electrodes ^[4], both capacity retention as well as reversible capacity still need to be improved. In our research, a novel selenium sulfide-carbon composite with high SeS₂ content (>60 wt%) has been developed, which can deliver a high discharge capacity of ~1100 mAh/g and maintain good cycling performance. The as-prepared SeS₂ composite cathodes also showed good rate capability. The effects of molecular structure as well as reaction mechanisms in different electrolytes (solvents, additives and salts) will be further investigated and compared to the performance of sulfur and selenium electrodes.

Reference:
[1] M.K. Song, Y.G. Zhang, J. Cairns Elton. Nano Lett., 2013, 13 (12), 5891-5899.
[2] A. Abouimrane, D. Dambournet, K.W. Chapman, et al. J. Am. Chem. Soc., 2012, 134 (10), 4505-4508.
[3] K. Han, Z. Liu, J.M. Shen, Y.Y. Lin, F. Dai, H.Q. Ye. Adv. Funct. Mater. 2015, 25, 455-463.
[4] C. Luo, Y.J. Zhu, Y. Wen, J.J. Wang, C.S. Wang, Adv. Funct. Mater. 2014, 24, 4082-4089.
[5] Z.A. Zhang, S.F. Jiang, Y.Q. Lai, et al. J. Power Sources, 2015, 284, 95-102.

The lithium-rich layered composite oxide, xLi₂MnO₃●(1-x)LiNi_1/3Mn_1/3Co_1/3O₂, is a promising cathode material with high capacity in lithium ion batteries (LIBs). An unusual charging-discharging feature for this material with sloping and plateau regions in the first run has been reported; however, mechanistic interpretations for this phenomenon are controversial in literature. In this work, ab initio calculations based on density functional theory were performed to examine the lattice stability of xLi₂MnO₃●(1-x)Li(Ni_1/3Mn_1/3Co_1/3)O₂ composite layered cathode materials during charging. The atomistic models of pristine Li₂MnO₃, Li(Ni_1/3Mn_1/3Co_1/3)O₂, and xLi₂MnO₃●(1-x)Li(Ni_1/3Mn_1/3Co_1/3)O₂ with x = 0.0, 0.3, 0.5, and 0.7 were constructed. The optimized structures agree closely with experiments. With these proposed atomistic models, the charging process of the 0.5Li₂MnO₃●0.5Li(Ni_1/3Mn_1/3Co_1/3)O₂ cathode was investigated through a detailed analyses on the defect formation energy of Li or O vacancies and Bader charge at various state of charge (SOC). The mechanisms of delithiation process as well as oxygen evolution during the charging process are revealed, which provides fundamental understandings as a guide for experimentally developing high-capacity cathode materials in LIBs.

Lithium-Sulfur batteries are thought to be the future of Li-ion batteries thanks to their high theoretical specific capacity (1675 mAh.g^-1) and low-cost. However, the real-life application of Lithium-Sulfur batteries is still hindered by limitations in their functioning. One of the main issues is the formation of Li₂S - an insulating and insoluble species - on the cathode upon discharge. It is crucial for the development of Lithium-Sulfur batteries to gain a better understanding on the chemical and microstructural changes which take place at the electrodes during discharge/charge cycles. To this end, we have used electron microscopy to investigate the microstructural, crystallographic and chemical properties of the species formed at the cathode during galvanostatic cycling. The studied cathode is formed by carbon nanoparticles 30 to 50 nm in diameter which have either solid or a hollow morphology. The carbon nanoparticles were uniformly coated with amorphous sulfur and discharged at different rates (from 1C to 0.05C) using a Swagelok type cell with Li metal anode with 1M LiTFSI-TEGDME/DIOX electrolyte. All materials were handled in oxygen-free conditions.
Scanning Electron Microscopy (SEM) highlights that the morphology of the discharge products is C-rate dependent. After full discharge at fast rate (1C) an amorphous discharge product was locally concentrated on the C/S composite while at faster rate (0.05C), a porous rosette cluster deposit was observed. A careful analysis of the discharge products was performed by means of High- to Atomic- Resolution Transmission Electron Microscopy (TEM) associated with Electron Energy Loss Spectroscopy (EELS). At the nanometric scale, both fast and slow cycling result in the deposition of a 1 to 2 nm thick Solid Electrolyte Interphase (SEI) onto the carbon particles. Moreover, in the case of slow cycling, the discharge product crystalized as cubic Li₂S nanocrystals up to 30 nm in size. They were observed either as isolated particles or aggregate clusters. The macroscopic morphology of the Li₂S agglomerates is compatible with the needles which form the rosette cluster structures observed with SEM. These observations suggest that changing the discharge rate allows controlling the formation of Li₂S from an amorphous to a 3D crystalline phase.

Rechargeable Li-ion batteries (LIBs) have been the predominant energy storage for a wide range of portable devices like cell phones, laptops and digital electronics. LIBs are now being considered for larger scale systems such as the electric grid and electric vehicles (hybrid, plug-in, pure) that require different types of specifications in terms of size, weight and most importantly lifetime or cyclability. We have recently developed a nondestructive method to visualize and quantify Li atom position in real-time using neutrons by a method referred to as neutron depth profiling (NDP). The NDP technique used in this work is developed in collaboration with Lei Cao. In situ NDP is an ideal technique for probing Li complex formation, accumulation and transport within the battery material during charge/discharge. Currently, our work is focused on understanding the effect of an electrochemical event to the materials’ storage properties. Specifically we report our recent work on the preferential Li nucleation, Li trapping and Li transport in intermetallic materials like Li_xSn_y, Li_xSi_y and Li_xAl_y and intercalating materials like LiNiMnCoO₃.

Operando diffraction is an extremely powerful technique for investigating reaction mechanisms in battery materials. To date, the vast majority of these experiments have been performed using synchrotron X-ray diffraction, predominantly due to the fast data collection times possible. However, operando neutron diffraction experiments are becoming increasingly popular due to a range of new cell designs increasing the accessibility of the technique [1], [2]. This contribution will present two different approaches to operando neutron diffraction, a larger format wound cell and a cheaper modified a coin type cell. The wound cell design contains a large quantity of active material (up to 4 g) enabling high quality diffraction patterns to be collected down to small d-spacings. When used to investigate the positive electrode material LiMn_1.5Ni_0.5O₄, reflections arising from Mn/Ni ordering could be observed to change during battery cycling. Further, due to the large d-space range accessed on the POLARIS neutron diffractometer, structural parameters such as ADPs were able to be tracked as a function of charge. The modified coin cell design utilizes a completely different approach to operando neutron diffraction experiments. The modified cells contain a large quantity of active material (300-400 mg) to a much smaller amount of electrolyte (0.01-0.05 ml), separator and lithium metal. The smaller volume of electrolyte is particularly vital as it substantially reduces the cost of the experiment, as deuteration may no longer be necessary. The modified coin cell exhibited favourable electrochemistry when cycled at C/10 and enabled unit cell and phase fraction information to be extracted from operando data collection conditions (5-15 min data sets).

[1] M. Bianchini, E. Suard, L. Croguennec, C. Masquelier, J. Phys. Chem. C, 2014, 118, 25947. [2] R. Petibon, J. Li, N. Sharma, W.K. Pang, V.K. Peterson, J.R. Dahn, Electrochim. Acta, 2015, 174, 417.

Synchrotron-based high-energy X-ray Compton scattering is a unique tool for characterizing energy materials. The technique has been applied to various materials and the results have shown that the energy spectra of Compton scattered X-rays can probe the orbital characters and occupancies of chemically active electrons [1,2]. Moreover, it is a non-destructive tool since it uses high energy X-rays that have high penetration power into the material. These advantages enable quantum chemical analysis of energy storage materials and products under in-situ and operando conditions. In this paper we present our recent studies of battery materials, including Li_xMnO₄ [3], Li_xCoO₂ and Li_xFePO₄.

Experiments have been performed with 115 keV X-rays at the High Energy Inelastic Scattering (BL08W) beamline, SPring-8. The energy spectra of Compton scattered X-rays are transformed into electron momentum density distributions, which are directly accessible via first-principles electronic structure calculations. Based on comparisons between experiment and theory, we discuss the character of redox orbitals and how they change during the lithium insertion / extraction process. Orbital occupation is closely linked with issues of lattice distortion, and electron and ion mobilities, all of which are essential factors in battery engineering.

We focus on the spinel material Li_xMn₂O₄ for 0 < x < 2. Here our analysis shows that the active orbital involved in lithium insertion / extraction process is mainly the oxygen 2p orbital, although the manganese 3d states also undergo spatial delocalization and involves 0.16 electron per Mn site. Our studies provide a new approach for an advanced characterization of lithium-ion batteries in which the redox orbital becomes the focus of materials design and engineering effort.

This work is supported by the Development of Systems and Technology for Advanced Measurement and Analysis program under Japan Science and Technology Agency and the U.S. Department of Energy.

[1] Y. Sakurai et al., Science 332 (2011) 698-702.
[2] Y. Kobayashi et al., J. Phys. Soc. Jpn 84 (2015) 114706.
[3] K. Suzuki et al., Phys. Rev. Lett. 114 (2015) 087401.

Layered lithium transition metal oxides are promising high-capacity cathode materials for Li-ion batteries. However, a substantial amount of the theoretical capacity is still not utilized in practice due to rapid capacity fading when cycled to high voltages, thus limiting its practical use for long-term applications such a grid energy storage. Understanding the structural changes leading to the capacity fade would help us design strategies to alleviate or eliminate this problem. As capacity fading is an accumulative effect that aggravates after each charge-discharge cycle, it would be very difficult to discern the small changes contributing to the capacity fading from a background of more substantial changes due to lithium (de)intercalation. Therefore, it is more beneficial to monitor the structural changes over extended multiple cycles rather than just a few so that trends in structural evolution could be discerned. In this work, we performed in-situ X-ray scattering measurement on a LiNi_0.8Co_0.15Al_0.05O₂ electrode to track the structural changes over multiple charge-discharge cycles. Trends in the structural evolution will be discussed in relation to capacity degradation.

Among the efforts to develop high-energy cathode materials for lithium-ion batteries, adding a second or even third cation to form solid solutions has been identified as an effective strategy for tailoring the structure and electrochemical properties of the electrodes. One notable example is the NCM transition metal oxides (i.e., Li-Ni-Co(Mn)-O), the subject of intense investigation in the last decade. Nevertheless, the study of this system is still far from complete due to the richness of the phases in the temperature-composition space and the complexity of the synthesis reactions. In addition to those known single phases (layered or spinel), there are a large number of composite phases and even new phases at the phase boundaries. Among the NCM phases, Ni-rich layered oxides LiNi_1-xM_xO₂ (M=Co, Mn, …; x≤ 0.4) are particularly interesting for the high capacity (>200 mAh/g) and low cost. However, synthesis of stoichiometric Ni-rich layered oxides has been recognized as a great challenge attributed to cationic disordering (namely mixing of Li⁺/Ni²⁺ in octahedral sites). In order to better understand the effect of Co, Mn-substitution on the cationic ordering during synthesis, in-situ X-ray diffraction (XRD) and neutron powder diffraction (NPD) measurements, combined with quantitative structure analysis, were performed to track the structural evolutions during solid-state synthesis of LiNi_1-xM_xO₂ (M=Co, Mn). Through detailed studies of kinetics and thermodynamics of cationic ordering, we show that highly ordered layered oxides with excellent electrochemical performance could be achieved through precise control of the synthesis conditions. The findings shed light on designing Ni-rich layered oxide cathodes with high structural ordering and long cycling stability for next-generation lithium-ion batteries.
The work is supported by DOE-EERE under the Advanced Battery Materials Research (BMR) program, under Contract No. DE-SC0012704.

The performance of Li-ion all-solid-state batteries is still limited by the control of the solid-interphases that form during lithiation. Thus, understanding the chemical composition and electrical properties changes that takes place during cycling are crucial for the design of next-generation long lifetime energy storage devices. To elucidate the origin of the degradation mechanism in Al anodes, we use real-time scanning electron microscopy in ultra-high vacuum (oxygen free environment) with in situ electrochemical cycling. An AlLi alloy capped by a stable Al-Li-O is formed on the top surface of the anode, trapping Li, which results in a rapid capacity fade, from 48.0 to 41.5 μ.Ah/cm² in two cycles [1]. The addition of a Cu capping layer is insufficient to prevent the device degradation because of the ultra fast Li diffusion within Al. Nevertheless, Si electrodes present extremely stable cycling: >92% of capacity retention after 100 cycles, with average Coulombic efficiency of 98% [2]. The in situ imaging method presented here can be expanded to other battery systems, including Na+ and Mg+, and nanostructured energy storage devices.

[1] C. Gong, D. Ruzmetov, A. Pearse, D. Ma, J. N. Munday, G. Rubloff, A. A. Talin, and M.S. Leite. Surface/Interface Effects on High-Performance Thin-Film All-Solid-State Li-Ion Batteries. ACS Applied Materials and Interfaces 7, 26007 (2015). Front COVER.

[2] M.S. Leite, D. Ruzmetov, Z. Li, L. Bendersky, A. Kolmakov, N. Bartelt, and A. Alec Talin. Insights From In-Situ Electron Microscopy into Capacity Loss Mechanisms in Li-Ion Batteries with Al Anodes. J. Materials Chem. A 2, 20552 (2014). Inside COVER.

Na₂Ti₆O₁₃ is an appealing negative electrode for lithium-ion batteries in view of its low intercalation voltage (ca. 1.5 V), reversibility of lithium insertion and specific capacity (ca. 100 mAh/g) (1-4). Therefore, is a potential alternative to the Li₄Ti₅O₁₂ spinel (4,5). However, though several studies have reported the effect of lithium insertion on the structure aiming for a better understanding of the electrochemical behavior, no conclusive evidences of the mechanism have been found.
We have carried out high resolution in situ synchrotron X-ray diffraction experiments as well as ex situ , neutron diffraction and solid-state ⁷Li-NMR spectroscopy of lithiated samples (Li_xNa₂Ti₆O₁₃) . The former revealed a two-step solid solution reaction in the approximate compositional ranges 0 ≤ x ≤ 1 (3.0-1.18 V) and 1 < x ≤ 2.36 (1.18-1.0 V). However, the capacity, and hence lithium composition, developed in the latter range is overestimated due to the side reactions likely related with electrolyte-electrode interfacial reactions. The nature of the solid solution has been investigated on chemically prepared samples, using n-butyllithium, with composition LiNa₂Ti₆O₁₃ and Li₂Na₂Ti₆O_13. Structural refinement shows that lattice parameters variation is very small indicating that Na₂Ti₆O₁₃ suffers only minor structural changes.
The ²³Na MAS-NMR analysis showed that Na cations remain at specific structural positions but Li ions preferentially occupy fourfold structural sites with reasonable Li-O bond distances. The shift of lines in the corresponding ⁷Li NMR spectra is related to the oxidation states of Ti cations.

(1) Dominko, R.; Baudrin, E.; Umek, P.; Arčon, D.; Gaberšček, M.; Jamnik, J. Electrochemistry Communications 2006, 8, 673
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Sodium alanates have attracted particular attention as active electrode materials for rechargeable batteries because these materials undergo electrochemical conversion which often yields higher energy density than intercalation reactions.
The NaAlH₄ conversion reaction occurs in a potential range between 0.7-0.01V vs Li. This is a multistep process involving the formation of hexa-alanate (LiNa₂AlH₆ and Na₃AlH₆) phases followed by their decomposition to LiH, metallic Na and Al. Mechanochemical treatments have been reported to improve the electrochemical reactivity and reversibility of sodium and lithium alanates. In this work, we focused our studies on the effect of mixing with carbon and ball milling on electrochemically converted samples, and we used ²³Na and ²⁷Al static and high resolution MAS nuclear magnetic resonance (NMR) to gain insights on the structural properties of NaAlH₄.
Static ²³Na NMR experiments were conducted on: a pristine sample, a ball milled one, a sample mixed with carbon and a sample ball milled with carbon. Through a comparison of the quadrupolar powder lineshapes, it was observed that ball milling affects the distribution in the asymmetry parameter and increases the ²³Na quadrupolar coupling constant. In addition, due to ball milling, there is an increase in the nanostructural disorder (i.e. nearest neighbors about Na) in these materials. The effect of carbon mixing on the other hand disperses ²³Na moments to the extent that magnetic dipolar interactions are lessened.
Similar analyses were attempted on the ²⁷Al NMR, but quadrupolar satellite transitions were observed in the powder pattern only for the pristine sample. Ball milling affects the structure of these materials with regard to the ²⁷Al environment as well, reducing second order quadrupolar and chemical shift anisotropy effects
²³Na and ²⁷Al MAS NMR experiments on fully discharged (0.01 V vs Li) and charged (2.5 V vs Li) materials were performed in order to confirm the reversibility of the conversion mechanism and highlight once more the effect of the mechanochemical treatment.

Recently emerging potassium ion batteries offer a lower-cost alternative to lithium ion batteries but unlike sodium ions, potassium ions form a high capacity stage 1 graphite intercalation compound enabling the use of a graphite anode. In this work, in-situ Raman spectroscopy is used to show the electrochemical staging of potassium in graphite. This provides the first in-situ characterization for electrochemical intercalation of K⁺ in graphite. The rate capability and capacity are improved using nitrogen doped few layer graphene (FLG) with a high capacity of 350 mAh/g, above the theoretical capacity for K⁺ in graphite. Electrochemical testing reveals additional reactions in nitrogen doped FLG that account for the improved rate capability and capacity and are likely due to defect mediated storage. Electrochemical testing and in-situ Raman spectroscopy are used to examine this defect mediated process and differences in staging between nitrogen doped and undoped FLG.

The Li-ion batteries are the most efficient devices in term of energy storage; however most of them suffer from a low energy density to envision using them in future mobile applications. The spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising positive electrode for lithium-ion batteries (LIBs) thanks to its high energy density (690 Wh/kg) and high voltage ( ~4.7 V vs. Li/Li⁺).
Two LNMO polymorphs whose structural stabilities strongly depend on their synthesis conditions have been reported: ordered LNMO (P4₃32) and disordered LNMO (Fd-3m) on Ni/Mn atomic sites^[1],[2]. Unfortunately, conventional X-ray diffraction cannot easily differentiate these arrangements. An easy and efficient way to do that is to use Raman scattering. Nevertheless difficulties were encountered to properly assign the observed vibration modes. Disordered LNMO is a typical case for which different approaches were used in the literature and conclusions were drawn based on only assumptions. Some people postulate for a discernible, other no-discernable Ni-O and Mn-O vibration bond in the Raman spectrum with no real poof to support their approach.
Up to this time, the theoretical modelisation of Raman spectra was impossible due to intensities calculations cost. Thus determining a relationship between the intensity of a peak associated with a vibrational mode is hardly feasible from a crystal simulation point of view. Therefore, attempts to assign spectra based only on the vibrational mode are often unreliable.
The relatively new feature of modeling the Raman intensity in crystal within DFT codes,^[₃] allow us to resolve the last bottleneck of the understanding the vibrational properties the spinel LNMO.
The results of the simulated Raman intensities prove for the first time the major contributions of Ni-O or Mn-O vibration for different Raman signals and confirm the assumption of discernible Ni-O and Mn-O vibration bonds. All these results will be discussed, to demonstrate that Raman spectroscopy coupled to calculated Raman intensities is a tool of choice to investigate LNMO as future cathode material for Li-ion batteries and more generally to follow the reaction mechanisms and possible intermediate species during lithiation/delithiation (sodiation/desodiation).^[4]


[1] M. Kunduraci, G. G. Amatucci, J. Electrochem. Soc. 2006, 153, A1345.
[2] D. Liu, W. Zhu, J. Trottier, C. Gagnon, F. Barray, a. Guerfi, a. Mauger, H. Groult, C. M. Julien, J. B. Goodenough, K. Zaghib, RSC Adv. 2014, 4, 154
[3] A) Maschio, L.; Kirtman, B.; Rérat, M.; Orlando, R.; Dovesi, R. I. Theory. J. Chem. Phys. 2013, 139 (16), 164101. B) Maschio, L.; Kirtman, B.; Rérat, M.; Orlando, R.; Dovesi, R. -J. Chem. Phys. 2013, 139 (16), 164102.
[4] L. Boulet-Roblin, C. Villevieille, P. Borel, C. Tessier, P. Novák, and M. Ben Yahia, submitted to J. Phys Chem C

Rechargeable lithium-ion batteries have been widely used for various portable electronics and even electric vehicle. However, there are various issues; such as lifetime, cost, and safety; that manifest when the capacity of a battery is extended either by modifying traditional materials or incorporating novel materials.[1] Among various cathode materials, LiCoO₂ and other layered oxides are widely studies due to their high energy density and performance. Yet, there is discrepancy between theoretical capacity and practical capacity in the cathode. Even though the theoretical capacity of LiCoO₂ is 274 mAh/g when Li is fully removed, only ~140 mAh/g can be used in practical application, which correspond to ~Li_0.5CoO₂ when it is charged to 4.2 V vs. Li. When more than half of Li is removed (overcharged), faster capacity fade with cycling is observed.[2] The structural changes of Li_1-xCoO₂ (0In this work, we examine the structural changes of LiCoO₂ cathodes in the cycle following overcharging in order to more completely understand the consequences of operating these cathodes across a larger voltage window. We use synchrotron-based X-ray diffraction (XRD) for the characterization of LiCoO₂ to measure the changes in crystal structure with high resolution and high throughput analysis while charging and discharging. To ensure a robust in situ cell capability of cycling for many cycles over many days, we employ an Al coated pouch cell and two X-ray transparent Be plates to apply uniform pressure across the cell. Results are compared with normally charged LiCoO₂ (charged to 4.2 V vs. Li) to show how the overcharging affect the evolution of the crystal structure in the following cycle and how these effects change the electrochemical properties and lifetime of LiCoO₂.

[1] J. B. Goodenough Accounts of Chemical Research (2013) 1053
[2] G. Ceder et al. Journal of Electrochemical Society (2007) A337
[3] J. R. Dahn et al. Journal of Electrochemical Society (1992) 2091
[4] J. McBreen et al. Electrochemistry Communications (2000) 100

Maryam Ghalkhani¹, Farid Bahiraei², Mehrdad.Saif³, Gholam-Abbas Nazri⁴, and Amir. Fartaj<sup>5

1,3</sup>Department of Electrical and Computer Engineering, University of Windsor 401 Sunset Ave. Windsor, Ontario, Canada N9B 3P4
^2,5Department of Mechanical, Automotive and Materials Engineering, University of Windsor 401 Sunset Ave. Windsor, Ontario, Canada N9B 3P4
⁴ Department of Electrical and Computer Engineering, Wayne State University, Detroit, Michigan 48202, USA

¹[email protected], ²[email protected], ³[email protected], ⁴[email protected], ⁵[email protected],

Abstract
The Lithium-ion (Li-ion) batteries are the preferred energy storage system for electric vehicles, because of their high potential, high energy and power densities and their good cycle life. Extension of the service life, safety, and reliability of the battery on board of an electric vehicle are the main concerns of the consumers. In addition to the battery chemistry, these concerns strongly depend on the quality and efficiency of battery thermal management system. A lithium-ion battery containing high energy materials may undergo thermal runaway if overcharged, due to the decomposition of battery components (electrolyte and electrodes) that generates flammable gaseous species. The experimental and simulation studies of the charge-discharge behavior and heat generation rate of a 10 Ah battery containing LiFePO4 cathode and mixed graphitic anode at different C-rates were reported in this work. In the experiments, the battery temperature was recorded using three T-type thermocouples attached to the battery surface while the battery was located in a chamber with fixed temperature, and the heat distribution in the battery was monitored using IR camera. In the numerical model, a one-dimensional (1D) electrochemical model of battery cross section was proposed which indicates that edge effects in the length and height of the battery were neglected. The model consists of three 1D computational domains i.e. negative porous electrode, polymer electrolyte, and the positive porous electrode. A time-dependent 3D electrochemical–thermal coupled model was then developed to estimate heat generation inside the active material and the cell temperature variation. The geometry and the mesh were generated in COMSOL MULTIPHYSICS v5.2 software. The variation of cell potential, load and temperature variation with time were presented. The numerical results revealed that in the case of assuming a uniform low current density through the cell the temperature will be rather uniform, mainly because of the uniform heat generation and low heat transfer to outside of the cell the maximum temperature rise was at the center of the cell. However, the cell under load with high current densities exceeding 1C showed non-uniform heat distribution with high heat close to the battery tabs. The modeling outcome was validated by the data collected by the IR camera.

Lithium-ion batteries, the dominant power source in portable devices, consist of two different electroactive materials as anodes and cathodes, which require two individual synthetic processes and increase the fabrication cost.^{[1, 2]} Additional efforts are required to match the mass and capacity of both electrodes to optimize the capacity of the full cell, and the polarity of battery needs to be connected correctly. Conceptually, these limitations can be solved by a symmetric LIB with identical electroactive material and fabrication procedure for both electrodes.
To realize such a symmetric battery, a material with several highly reversible redox processes in the voltage range of 0—5 V (vs. Li⁺/Li) is needed. To date, various types of symmetric LIBs based on different active materials have been developed.^[3-5] NASICON-type Li₃V₂(PO₄)₃ (LVP) is regarded as a promising high energy density cathode candidate for LiCoO₂.^[6] It can also be used as an anode with a comparative capacity when operated from 1.0 to 3.0 V with the intercalation of two Li⁺.^[7] These features offer the potential of utilizing LVP as the electroactive materials for a symmetric battery. Nonetheless, previous efforts in developing LVP-based symmetric LIBs encountered substantial challenges with continuous changing of the charge/discharge plateaus that indicate complex electrode reactions.^[4] Although the detailed mechanism is still under debate, it is generally believed to be attributed to the dissolution of LVP and subsequent shuttle through the separator to form new vanadium-containing materials on the electrodes.^[8]
Herein, we develop a separator-integrated, reversely connectable, symmetric lithium-ion battery, based on carbon-coated LVP nanoparticles and polyvinylidene fluoride-treated separators. Both the carbon and the polyvinylidene fluoride treatments substantially improve the cycling life of the symmetric battery, by preventing the dissolution and shuttle of the electroactive LVP. The obtained symmetric full cell exhibits a reversible capacity of ~ 87 mA h g^-1, good cycling stability, and capacity retention of ~ 70% after 70 cycles. In addition, this type of symmetric full cell can be operated in both forward and reverse connection modes, without any influence on the cycling of the battery. A 10-tandem-cell battery assembled without differentiating the electrode polarity exhibits a low thickness of ~ 4.8 mm and a high output voltage of 20.8 V.

To increase the energy density of current commercialized lithium-ion batteries, the challenge of maintaining structural reversibility of multiple electron transfer cathodes for the intercalation process must be resolved. ε-VOPO₄ is currently a promising cathode material with two redox transitions of V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺. However, the reversibility is compromised with only ~1.2 lithium inserted. The goal of this work is to investigate whether transition metal substitution can enhance the electrochemical performance of ε-VOPO₄. We have substituted ε-VOPO₄ with different molar percentages of transition metals into the vanadium positions in attempt to improve the capacity. We have focused on the transition metals that are predicted by first-principle calculations to display multiple redox potentials in useful voltage window and to form relatively stable substituted ε-VOPO₄ phases. Combing the analysis of X-ray diffraction, and inductively coupled plasma mass spectrometry, we have determined the limits of transition metal substitution in the structure. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy were also used to investigate the oxidation states of the transition metals and the mechanism of charge compensation. The effects of the substitution on the electrochemical performance will also be discussed. This research is supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0012583. CS gratefully acknowledges the financial support from Graduate Assistance in Areas of National Need (GAANN) Fellowship and Binghamton University Provost's Doctoral Summer Fellowship.

The use of low-cost and light-weight aluminium as current collectors in aqueous Li-ion batteries with water-based electrolytes is restricted by corrosion reactions caused by the aggressive ions in the aqueous environments. Here we report for the first time using highly corrosion-resistant Al foil with the chromate conversion coating (CCC Al) as current collector for cathodes in aqueous Li-ion batteries. Coating aluminium with chromium compounds is currently the most effective way to inhibit corrosion of aluminium and its alloys. The protection with the CCC is two-fold: (1) an impervious hydrated chromium(III) oxide serving as a physical barrier on the surface and (2) the chromium(VI) ions stored in the coating provide active corrosion protection.
We have experimentally demonstrated that CCC Al foil is resistant to corrosion when used as the current collector of LiMn₂O₄ electrodes. The cyclability of these electrodes are on par with or better than those observed for electrodes fabricated on stainless steel and titanium substrates. In contrast, electrodes fabricated on untreated Al foil saw serious corrosion of the substrate within the initial 10 cycles. Interestingly, CCC also effectively suppress oxygen evolution reaction at high potentials, leading to improved Coulombic efficiency of up to 99%. The increased overpotential for oxygen evolution was attributed to the occupation of active chemisorption sites and inhibition of electron transfer on the substrate surface by the chromium compounds. These results may open a new insight into the design of high-performance and high-stability cathode electrodes for aqueous Li- and Na-ion batteries with a higher cell-level energy density.

Electrospinning is an efficient route to synthesize highly porous and interconnected polymer fiber based separators. To study the effect of amorphous electroactive separator on the battery performance, the separator is fabricated with poly(vinyledene flouride) (PVDF) through electrospinning technique. In the current work, we propose an amorphous electroactive electrolyte separator system (ESS) for sodium ion batteries. The electroactive separator is immersed in 1M NaClO₄-EC: DEC(1:1 by weight) solution to make it amorphous.The physicochemical characteristics of the ESS are investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and Sodium ion conductivity. The electrochemical studies of the sodium half-cell (Na_0.66Fe_0.5Mn_0.5O₂ as cathode and pure sodium as anode) conducted from ESS are demonstrated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The inherent phases of the electroactive ESS are determined in the XRD and FTIR. The ionic conductivity is found to be in the order of 10^-4 S cm^-1at room temperature. CV of the sodium cell has revealed its pseudocapacitive nature. EIS of the cell promotes the non-interacting dipoles during an external electric field.

Finding a solution to effectively use renewable energy is one of the most important issues that one needs to overcome in order to achieve a sustainable society.¹ Renewable energies such as solar and wind energy do not produce electricity consistently with consumption demands. Thus, a large-scale energy storage system is essential to integrate the intermittent energy into a stable power supply. High-energy Li-ion batteries (LIBs) are expected to contribute to the solution; however, the high cost of LIBs raw materials prohibits wide application in this area. Recently, the attention was refocused on room-temperature Na-ion batteries (NIBs) as a potential low-cost alternative technology compared to LIBs.^2,3 The wide abundancy and low cost of Na make it suitable to the grid storage applications.
A large number of materials have been examined as candidates for cathode and anode in the NIBs.⁴ Herein, we show our studies on the Sn-based composite materials for the anode and the sodium layered oxides for the cathode. Sn and Sn-based compounds have drawn much attention as high-capacity NIB anodes because of the theoretical stoichiometry of Na₁₅Sn₄ (847 mAh g^-1) and low redox potential. By coupling with 2D carbon materials, the Sn-based composite material exhibits extraordinary performance as the battery anode. Meanwhile, we work on layered oxides (Na_xTMO₂) for cathode studies, due to their simple structures, high capacities, and ease of synthesis. Advanced material characterization tools (XAS, STEM/EELs, etc) are applied to assist the material design and optimization, more importantly, unveil the Na storage mechanisms in these materials. Sodium full cells have been designed and fabricated; yielding excellent results that shows good promise for energy storage applications.

Acknowledgement
The authors acknowledge the support by the National Science Foundation under Award Number DMR-1057170. Also thanks goes to AGEP GSR fellowship, which is the supplement fund to the DMR1057170.

References
(1) Armand, M.; Tarascon, J.-M. Building Better Batteries. Nature 2008, 451, 652–657.
(2) Slater, M. D.; Kim, D.; Lee, E.; Johnson, C. S. Sodium-Ion Batteries. Adv. Funct. Mater. 2013, 23, 947–958.
(3) Han, M. H.; Gonzalo, E.; Singh, G.; Rojo, T. A Comprehensive Review of Sodium Layered Oxides: Powerful Cathodes for Na-Ion Batteries. Energy Environ. Sci. 2015, 8, 81–102.
(4) Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba, S. Research Development on Sodium-Ion Batteries. Chem. Rev. 2014, 114 (23), 11636–11682.

Sodium-ion batteries are the next generation commercially and environmentally viable candidates for automobiles. Anode is an integral part of sodium-ion battery. Safety issues and formation of unstable passivating layers with most organic electrolytes prevent sodium metal being used as negative electrode directly. Moreover, graphite being a good anode for LIBs lags in intercalating sodium efficiently owing to larger Na⁺ radius. Silicon is an excellent anode material for lithium but it shows less sodiation voltage and also fails to intercalate sodium effectively. So there is an urgent need in development of anode material that can adress these problems. MnO₂ is currently under extensive investigations as an anode material for both lithium-ion and sodium-ion batteries. MnO₂ crystallizes into several crystallographic structures, namely, α, ß, R, γ, δ, and λ structures. Herein, we report thin film deposition of manganese oxide (ß-MnO₂, R-MnO₂) on stainless steel used as a negative electrode in the sodium-ion battery. The electrochemical behavior, structure, morphology and composition and of manganese oxide thin films were characterized by galvanostatic cycling, cyclic voltammetry (CV), field emission scanning electron microscopy (FESEM) and Raman spectroscopy. Nanocrystalline and binder free nature of the manganese oxide thin film deposited by PLD favours towards the electrochemical performance. Stable and long cyclic performance can be achieved by nano crystalline iron oxide thin film as negative electrode. Both ß-MnO₂, and R-MnO₂ showed excellent rate capability.

Over the past 5 years, the search for solid electrolytes enabling safer, more energy dense all-solid-state-batteries has led to the revival of sulfide glass-ceramics. As such, Na₃PS₄ has been highly touted for its high ionic conductivity and excellent electrochemical stability. With its suitable conductivity first reported by Hayashi et al.,¹ Na⁺ conductivities as high as 0.74 mS/cm have been reported through improvements in synthesis and the introduction of favorable dopants.² Though aliovalent doping pertinent to Na-excess structures (M⁴⁺, M = Si, Ge, Sn) has been explored extensively in pursuit of LGPS-like analogs,³ less effort has been dedicated to Na-vacant (X^-, X = F, Cl, Br, I) counterparts.^4,5 In this work, we investigate a doping strategy to further enhance the Na⁺ conductivity of Na₃PS₄ through induced Na-vacancies, with an integrated computational and experimental approach. We explore the effects of anion doping in the t-Na_3-xPS_4-xCl_x system. For x = 6.25%, the material exhibits an exceptional room temperature Na⁺ conductivity of 1.14 mS/cm at room temperature, which is in remarkable agreement with the computationally predicted 1.40 mS/cm. Additionally, we demonstrate the electrochemical stability of this material in a full-cell architecture. These results pave the way to further optimization of this highly promising superionic conductor in the pursuit of viable all-solid-state batteries.

References:

[1] Hayashi, A.; Noi, K.; Sakuda, A.; Tatsumisago, M., Nat. Commun, (2012), 3, 856.
[2] Tanibata, N.; Noi, K.; Hayashi, A.; Tatsumisago, M., RSC Adv., (2014), 4, 17120.
[3] Zhu, Z.; Chu, I.-H.; Deng, Z.; Ong, S. P., Chem. of Mater., (2015), 27 (24), 8318.
[4] Hibi, Y.; Tanibata, N.; Hayashi, A.; Tatsumisago, M., Solid State Ionics., (2013), 270, 6.
[5] de Klerk, N. J.J.; Wagemaker, M., Chem. Mater., (2016), 28, 3122.

Even though lithium-sulfur battery (LSB) has been widely used as an attractive energy storage device, the poor conductivity of sulfur (5x10^-3 S cm^-1 at 25^oC) limits electronic charge transfer during the charging/discharging processes. In addition, the shuttle mechanism of Li₂S₂/Li₂S reacting with polysulfide (PS) yields the soluble chains, which cause the rapid capacity decay limiting the practical use of LSB. Furthermore, when sulfur (S₈) is reduced to Li₂S (the final product) during the discharging process, the volume will expand up to 80%. In the LSB research area, (meso)porous carbon materials were chosen as the sulfur host for solving these problems due to its high conductivity, stability, and diversity. Herein, the sulfur was loaded into the mesopores of nitrogen-doped reduced graphene oxide aerogel (N-doped rGO aerogel) host using a melt adsorption method at 155^oC for 6 h. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and electrochemical techniques were investigated to investigate the as-prepared materials. It was found that the 3D porous structure of N-doped rGO aerogel can trap the soluble polysulfides and buffer the volume change of the sulfur during cycling and provide a high specific capacity of 957 mAh g^-1. In addition, the nitrogen-containing groups are beneficial for the redox reaction leading to high charge storage capacity and also increase the diffusivity of the electrolytes.

The development of advanced energy storage systems is one of the major challenges, which the humanity faces today. Lithium-ion batteries can be considered as a technology-driving tool, since they enable the rise of super-slim and flexible smartphones, long-running electric cars and other devices and applications including renewable energy, determining the technological progress and sustainability of our society. However, the emerging smart technologies highly require a significant advancement of performance of the present batteries and restriction of use of toxic materials. Therefore, scientists worldwide have been intensively working on making such progress to advance the electrochemical properties of the battery components [1]. The main concept is the development of novel electrode materials that are capable of storing large amount of Li-ions with better safety and higher stability. Currently, silica (SiO₂) is one of the most studied materials for Li-ion storage and the results from many laboratories confirm its potential to change today's energy-storage landscape. Silica could bring the biggest breakthrough yet due to its abundance on the Earth’s crust. It was also discovered that it is capable of storing Li-ions with a theoretical capacity of 1965 mAh g^-1 [2]. However, its capacity fading during cycling and poor electronic conductivity are critical issues that need to be addressed [3, 4]. In this work, a novel three-dimensional SiO₂/Carbon nanotubes (CNT)/graphene (G) hybrid material is proposed and extensively investigated as a potential safe and high capacity anode material for Li–ion batteries. The unique hybrid SiO₂/CNT/G composite was synthesized by a chemical free method. The hollow structure of silica spheres confined in the 3D conductive network was employed with the purpose to enhance specific capacity and cycling performance through accommodating and buffering volume changes of SiO₂ during lithium – ion insertion/extraction process. Physical and electrochemical properties of ternary composites SiO₂/CNT/G were extensively studied. Galvanostatic charge/discharge measurements were tested at a current density of 50 mA g^-1 between 0.01 and 3 V range versus Li/Li⁺. All detailed result analysis will be provided at the conference.

Acknowledgements
This research was funded under the target program N^o0115PK03029 "NU-Berkeley strategic initiative in warm-dense matter, advanced materials and energy sources for 2014-2018" from the Ministry of Education and Science of the Republic of Kazakhstan.

References
[1] Guozhong Cao, Part. Part. Syst. Charact., 2016, 33, 110-117.
[2] Guozhong Cao, J. Mater. Chem. A, 2015, 22739-22749.
[3] P. Chen, J. Mater. Chem. A, , 2015, 3, 1476-1482.
[4] A. Lisowska-Oleksiak, Int. J. Electrochem. Sci. 11, 2016, 1997 – 2017.

Lithium-oxygen (Li-O₂) batteries have an extremely high theoretical specific energy density when compared with conventional energy-storage systems. However, practical application of the Li-O₂ battery system still faces significant challenges. In this work, we report a new approach for synthesis of ultrafine metal oxide nano-catalysts through an electrochemical pre-lithiation process. This process reduces the size of NiCo₂O₄ (NCO) particles from 20~30 nm to a uniformly distributed domain of ~2 nm and significantly improves their catalytic activity. Structurally, the pre-lithiated NCO nanowires feature ultrafine NiO/CoO nanoparticles that are highly stable during prolonged cycles in terms of morphology and particle size, thus maintaining an excellent catalytic effect to oxygen reduction and evolution reactions. A Li-O₂ battery using this catalyst demonstrated an initial capacity of 29,280 mAh g^-1 and retained a capacity of >1,000 mAh g^-1 after 100 cycles based on the weight of the NCO active material. Direct in situ transmission electron microscopy (TEM) observations conclusively revealed the lithiation/delithiation process of as-prepared NCO nanowires and provided in-depth understanding for both catalyst and battery chemistries of transition-metal oxides. This unique electrochemical approach could also be used to form ultrafine nanoparticles of a broad range of materials for catalyst and other applications.
Acknowledgements
This work was supported by the Office of Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, of the U.S. Department of Energy (DOE) under Contract no. DEAC02-05CH11231 for PNNL and under DEAC02-98CH10886 under the Advanced Battery Materials Research (BMR) program. The microscopic and spectroscopic characterizations were conducted in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL)-a national scientific user facility located at PNNL, which is sponsored by DOE’s Office of Biological and Environmental Research. PNNL is operated by Battelle for DOE under Contract DE-AC05-76RLO1830.

Lithium-sulfur batteries (LSB) have been attracted attention as one of the most interesting energy storage technologies due to their high theoretical specific capacity (1675 mAh g⁻¹) and energy (2500 Wh kg^-1). However, the practical application of LSB is still hindered because of some drawbacks including low electronic conductivity of sulfur (5 × 10⁻³⁰ S cm⁻¹ at 25 °C) and shuttling effect of lithium polysulfides (Li₂S_x, 4 ≦ x ≦ 8) leading to poor columbic efficiency, utilization, and cycling stability. To overcome this issue, carbon black (CB) and oxidized carbon black (OCB) were encapsulated layer-by-layer on the surface of sulfur microparticles for which CB and OCB were coated on the sulfur core as the first and second shells, respectively namely S@CB@OCB. For the first shell, it was produced via a mechanofusion technique. For the second shell, the colloidal coating technique was used to coat the third OCB shell on the S@CB particle. A uniform spherical shape of the as-prepared double shell material contains high sulfur loading content of 57 wt.%. The S@CB@OCB delivers the first discharge capacity of 1,313 mAh g^-1 at 0.1C. After 400 cycles, the LSB exhibits a good capacity retention of 77% and high coulombic efficiency over 98%. After charged/discharged, the double shell materials were carefully characterized using an ex situ SEM and RAMAN. It is clearly observed that the shells covering the sulfur particles can improve the stability of sulfur particle. The CB can infuse inside the sulfur particles, which can reduce volume expansion and improve electronic conductivity of sulfur. Whilst, the OCB behaves as the passivation layer trapping the dissolved polysulfide species.

There have been numerous reports on flexible and stretchable energy storage devices in planar structures within the past decade. Nevertheless, energy storage devices in 1D forms such as wires for higher flexibility, bio-compatibility and wearability have been required for more extensive application of energy storage systems. As a result of these sharp demands, wire-type systems among the state-of-the-art technologies in energy storage field are attracting enormous efforts and interests from diverse applications, not only postmodern electronics, but also various fields such as fashion and culture.
Wires in 1D structure have an omnidirectional serpentine structure in the other axes. In contrast to 2D planes, it is much easier for wires to be constructed into more sophisticated structures such as woven textiles that can be used in our daily life.
Although 1D structures have broad potentials of structural deformation, some fundamental issues blur the way to use wire-type energy storage devices. Energy storage performances of wires are still much less competitive than those of 2D plane devices. Many researchers have made efforts to overcome these barriers of wire-type energy storage devices. Most of them have not broken the prototype fabrication rules of wire-type energy storage, such as construction of electrodes into cylindrical wires and a choice of superb material to maximize the performance. In this research, we did not depend on material choice, but theoretically analysed the origins of superior electrochemical property of 2D plane over 1D wire. Based on these analyses we confirmed the fundamental limits of wire-type supercapacitors compared with 2D. This is called “energy lag effect.” With these derivation, we have simultaneous integrated both favorable electrochemical performance of 2D system and high deformability of 1D system into one device. To eliminate the verified limitations of cylindrical electrodes, we fabricated a supercapacitor wire in unique structure totally different from conventional wire-type energy storage devices. The supercapacitor wire was designed as a dual plane-helix structure. Electrochemical properties of this system without energy lag effects were proved analytically and experimentally as well.

While known for a higher power density than batteries, electrochemical capacitors are limited by their energy density for some energy storage applications. Since the energy density is proportional to the square of operating potential window, an effective way to increase energy density of the device is by increasing this voltage window. Ionic liquid (IL) electrolytes are beneficial for this reason since they can theoretically operate at up to 6 V, though experimentally, the value is between 3-4 V, depending on the properties of electrode materials. By employing a novel electrochemical technique to study symmetric supercapacitors with carbon electrodes and IL electrolytes, we have found one of the possible reasons for the observed smaller operating potential window of ILs in practical applications. We observed that even for a symmetric device, the different properties of the cation and anion results in an asymmetric performance of the two electrodes. However, a solution to this asymmetry is found by mixing two ILs with the same cation, which ultimately results in a higher operating potential window of the device and therefore a higher energy density.¹ In this model system, onion-like carbon (OLC) was used as the electrode material due to its outer surface structure. However, electrode materials can also be made from high surface area carbons that contain a network of pores (activated carbon, carbide-derived carbon). Though they boast a large operating potential window, ILs are known to contain large and bulky ions. This can make it difficult to use an IL on a porous carbon with a range of pore sizes, even though the specific surface area of the electrode material is higher. It has also been shown that the capacitance of porous electrodes is maximized when the ion size and pore size are equal.² In this case, the ion is small enough to fit inside the pores while still large enough to take advantage of the surface area within the pore walls. While the outer surface materials allow a more accessible surface for adsorbing large ions, their capacitance is limited by their specific surface area. By designing an electrolyte based on mixed ILs, we can match the ions in the mixture to the multiple pore sizes of the electrode material. Recently, it was found that the capacitance of porous carbon could be increased with the presence of multiple ions in the electrolyte mixture. Finally, it has been shown previously that IL mixture electrolytes can be used to increase the operating temperature window of a supercapacitor to -50 °C – 100 °C.³ IL mixtures have therefore been shown to improve the potential window, the capacitive performance, and the temperature window of supercapacitors, becoming an important area of study in the field of energy storage.

Van Aken, et al. Angew. Chemie 127, 4888–91 (2015).
Lin, R. et al. Electrochim. Acta 54, 7025–32 (2009).
Lin, R. et al. J. Phys. Chem. Lett. 2(19), 2396-401 (2011).

Lithium-sulfur batteries (LSBs) are promising energy storage device due to its high theoretical specific energy (2,567 Wh kg^-1), high theoretical capacity (1675 mAh g^-1), low cost and abundant. However, there are some drawbacks that limit the practical use of LSB, which are polysulfide shuttle during the charging/discharging process, volume expansion of sulfur into Li₂S, and poor conductivity of sulfur. To address these problems, we introduce various types of carbon-based materials with different pore characteristics i.e. carbon hollow spheres (EC300J), activated carbon (AC), mesocarbon microbeads (MCMB), graphene oxide (GO) and N-doped incorporated-carbon aerogel (GO/MCMB/AC) as the hosts for sulfur loading and then use as the cathode materials. Sulfur was loaded into carbon hosts depending on the pore volume of each material. The results showed that different surface area and pore volume of carbon-sulfur composite significantly affect to the different Li-storage mechanism. Due to the open-pore structures of carbon materials that cannot accumulate the polysulfides efficiently, the activated-carbon fiber paper (A-CFP) was also used as an interlayer inserted between the cathode and the separator to increase bulk electronic, ionic conductivity, and also trap the polysulfides that dissolved into the electrolyte.

Li ion rechargeable batteries are of interest from last few decades due to its wide range applications from kids’ toys to hybrid electric vehicles. There are many issues related to environmental and performance of Li ion rechargeable batteries. We are working towards the process optimization of cathode materials for Li ion rechargeable batteries.
We have synthesized LiMn_2-xFe_xO₄ (0 ≤ x ≤ 0.5) cathode materials by sol-gel method. The synthesized materials were characterized using XRD, DSC and TGA. Our objective is to optimize the synthesis conditions to synthesize the cathode materials in bulk. In this study we are finding the correlation between the DSC/TGA and XRD data. The synthesized materials were annealed at various temperatures based upon the peaks observed from DSC and TGA. After annealing the materials at a particular temperature, XRD were recorded. The relation between DSC and XRD data and optimum annealing temperature will be discussed.

Sodium vanadium fluorophosphates have recently shown very good electrochemical performance vs. Na/Na⁺ providing high working voltages (3.6 and 4 V vs. Na/Na⁺) and good specific capacity values.
The vanadyl (IV) Na₃V₂O₂(PO₄)₂F compound which belongs to the Na₃V₂O_2x(PO₄)₂F_3-2x family of compounds can be successfully synthesized by a novel single-step hydrothermal method. However the absence of in-situ carbon in the final product makes necessary to employ an ex-situ carbon coating impregnation method, usually using sucrose. This carbon has demonstrated to increase the electronic conductivity and Na⁺ diffusion ability, enhancing the electrochemical performance of the sodium-vanadium fluorophosphate material. The derived composites exhibit good rate capability for charging rates up to 5C and excellent cycling stability .
On the other hand, Hydrothermal Carbonization (HTC) process is a widely used method for the synthesis of functional carbonaceous materials from biomass , so it can be an alternative way to get a carbonaceous coating during the hydrothermal synthesis of the fluorophosphate. The biomass usually used for this process includes crude plant materials like agricultural residues, wood and herbaceous energy crops, and carbohydrates like sugars, starch, or cellulose. Moreover, organic electroactive materials derived from biomass are promising candidates for the next generation of rechargeable batteries, due to the low cost, sustainabi lity and environmental benefits. However their application for electrodic materials in batteries is still a field under development.
In this work, two different carbon sources have been employed in the hydrothermal synthesis in order to obtain a carbon containing vanadyl (IV) Na₃V₂O₂(PO₄)₂F phase in a unique step by HTC. The employed carbon sources consisted on waste vine shoots and eucalyptus wood from vineyard and forest pruning. The samples were also subjected to a flash thermal treatment under nitrogen flux to improve the quality of the carbon generated in the sample.
Obtained samples have been characterized by X-ray diffraction, elemental analysis, transmission electron microscopy and Raman spectroscopy. The vanadium oxidation state of the compounds has been estimated by analyzing electron paramagnetic resonance spectra.
Electrochemical evaluation of the sodium vanadium fluorophosphates has been made on laminate cathodes in Swagelok cell vs. a metallic sodium anode. Differences in obtained specific capacities, rate capability and cycle life will be analyzed and related to the compositional, crystallographic and morphological changes induced by the use of different carbon sources, different synthesis temperatures and the use of a flash thermal treatment on the prepared materials.

Manganese oxide (MnO₂) is one of the promising candidate materials for pseudocapacitors due to its high theoretical specific capacitance (1370 F g^-1), low cost, and less toxicity. However, various morphologies of MnO₂ significantly affect the charge storage performances of the supercapacitors. In order to identify the appropriate structure of MnO₂ to be used as the supercapacitor electrode, a number of MnO₂ morphologies including nanospheres, nanorods, nanowires and nanosheets were synthesized and investigated extensively by FESEM, TEM, XRD, XPS, XAS, BET, TGA, RAMAN, FTIR, and electrochemistry techniques. Among these structures, the Mg-birnessite MnO₂ synthesized by a double-aging method presents two-dimensional (2D) layer structure with an interlayer spacing of 7 Å providing the highest charge storage capacity when compared with other morphologies. The symmetric supercapacitor of Mg-birnessite MnO₂ exhibits the highest specific capacitance of 194.3 F g^-1 at 1 A g^-1, specific energy of 23.4 Wh kg^-1, maximum specific power of 4009.2 W kg^-1 with a capacitance retention over 80 % after 3000 cycles in 0.5 M Na₂SO₄ aqueous electrolyte. The lamellar structure of Mg-birnessite MnO₂ can enhance the diffusion of Na⁺ (hydrated size of 4.0 Å) into the interlayer region leading to the superior capacitive behavior. In addition, the effect of pH in 0.5 M Na₂SO₄ electrolyte was further investigated using in situ X-ray adsorption near-edge structure (XANES) in order to identify the charge storage mechanism of MnO₂.

Although graphite anode has been commonly used in commercial Li-ion batteries (LIBs). However, the maximum configuration of graphite anode is one lithium for six carbon atoms (LiC₆) which limited the theoretical capacity of graphite to 372 mAh g^-1, hampering it for the future energy storage applications. This problem can be addressed by developing high reversible capacity, energy and power density of anode materials which are carbon-based materials, alloy/de-alloy materials and transitional metal oxides/sulphides/phosphides/nitrides. Among these, carbon-based materials have attracted the most attention due to their ease of synthesis, high conductivity, stability and low cost. Herein, we design the N-doped graphene aerogel and used as an anode in LIBs with the functionalized-carbon fiber paper substrate. The 3D nanostructured networks of graphene aerogel which has large surface area and pore volume can increase the rate of lithium ions insertion/extraction and decrease the diffusion path length of both lithium ions and electrons. The nitrogen doping introduces the defects and active sites, thus increasing the electronic properties of graphene aerogel. The results show a reversible capacity of 2462 mAh g^-1 at an applied current of 0.1 A g^-1. To the best of our knowledge, this value exhibits the highest specific capacity of N-doped carbon anode materials.

Flexible, portable and wearable electronic devices such as smart clothes are emerging in the mainstream and represent promising directions for future lifestyles. The rapid development strongly demands indispensable power systems that can be miniaturized, flexible, and adaptable. Lithium ion batteries have been used as one of the most ubiquitous types of power supplies. However, conventional lithium ion batteries, including both rigid bulk and flexible film, cannot satisfy the above requirements. These batteries have limited flexibility and cannot effectively adhere to soft substrates such as our bodies under deformation. Besides, they are not breathable, which is also a major consideration for wearable electronics. A revolution in lithium ion battery structure is necessary to ultimately solve these problems.

Herein, we have developed a new family of fiber-shaped lithium ion batteries with high performance based on carbon nanotube hybrid fiber electrodes. The energy density is approximately 3 times of previous thin-film lithium ion batteries, and the power density is approximately 140 times of thin-film lithium ion batteries. Besides, these unique fiber architecture allow batteries to be deformable in all dimensions. They are scaled up and further woven into breathable, light-weight, flexible, stretchable and shape-memory textiles to effectively meet the requirements of the modern electronics such as wearable products.

The electrochemical performance of rechargeable intercalation-based batteries, including Li-ion and Na-ion systems, is often limited by the cathode active material. Vanadium pentoxide (V₂O₅) has a high theoretical capacity, but rapid capacity fading is often experimentally observed. One reason for capacity decay is the degradation of the V₂O₅ crystal structure upon extended cycling. Therefore, the development of techniques to improve the structural stability of high capacity V₂O₅ cathodes leading to extended lifetimes is crucial for their use in batteries.

Chemical pre-intercalation is a wet chemistry method that allows for the insertion of positively charged ions into the crystal structure of electrode materials. Previously, this technique was used to insert alkali ions into a V₂O₅ bronze for improved electrochemical stability in Li-ion batteries.¹ Pre-intercalated immobile ions acted as pillars to hold structural layers, preventing phase transformations. While ion pre-intercalation resulted in lower charge storage ability compared to the pristine V₂O₅, relatively high capacities of 140-240 mAh/g were still achieved.¹ More importantly, an increase in capacity retention of the vanadium oxide was observed after alkali ion pre-intercalation. In addition, authors hypothesized that the inserted positively charged ions in the structure created electrostatic repulsions that facilitated the diffusion of charge-carrying Li⁺ ions, increasing power density.¹

In this work, chemical pre-intercalation of immobile ions was used to stabilize the crystal structure of bilayered vanadium oxide (δ-V₂O₅). This phase is of particular interest due to its large interlayer spacing, 10-13 Å,² that can be readily used for the intercalation of a large amount of positively charged ions. We have for the first time investigated performance of this material as a cathode in Li-ion batteries. Using a chemical pre-intercalation technique developed in our laboratory, we have synthesized Li-, Na-, K-, Mg-, and Ca-stabilized δ-V₂O₅. We demonstrate that ion-stabilization improves the electrochemical stability of the bilayered phase in Li-ion batteries. In addition, the effect of ion valence was investigated by comparing materials stabilized with monovalent (Na⁺ and K⁺) and divalent (Mg²⁺ and Ca²⁺) cations. Li-intercalated V₂O₅ was used as a reference material. Ion-stabilized phases showed increased capacity retention, with Na-stabilized δ-V₂O₅ demonstrating highest initial capacities (~385 mAh/g) and Mg-stabilized δ-V₂O₅ achieving highest capacity retentions (91% after 20 cycles). In this presentation we will demonstrate the effect of ion-stabilization on capacity retention of the bilayered V₂O₅ electrodes in Li-ion batteries after extended cycling.

1. Zhao, et al. Nano Letters 2015, 15, 2180−2185.
2. Clites, et al. Journal of Materials Chemistry A 2016, 4, (20), 7754-7761.

This work is focused on carbon materials received from biopolymers such as lignin, cellulose, and chitosan as precursors. Carbonization in nitrogen atmosphere followed by chemical activation in KOH was chosen as a synthesis method. The resulting carbon materials were characterized by well-developed surface area and microporous structure, beneficial in terms of electric double-layer capacitors (EDLCs). Capacitive characteristics were determined from electrochemical measurements conducted in Swagelok-type cells. At this stage, materials have shown capacitance at the level of 50 F g^-1 for acidic medium and 60 F g^-1 for the alkaline environment (values expressed per mass of both electrodes). The second stage of the study concerned the assembling of capacitors based on synthesized carbon materials in pouch cells. This part of the research was important from the application point of view. Although materials have shown similar properties in laboratory scale, their performance in real systems was no longer the same. The main drawback results from their structure. The specific surface area determined by the BET method (from nitrogen sorption) in the case of carbonized cellulose was vary from the real active surface involved in the charge storing (2DNLDFT model) by more than 1500 m² g^-1. Such parameter influence on material implementation, as well as on the content of other additives in the electrode. In this stage of the investigation, electrodes were prepared in the form of films deposited on metal foils constituting the current collectors. The composition of electrodes have varied depending on the type of the active material, and results from the need of good mechanical strength of the applied film as well as adhesion to the current collector. Nevertheless, as a result of conducted research was capacitor built of carbonized lignin with an alkaline electrolyte. This cell received stable capacitance c.a. 20 F (9 g) during over 60,000 cycles with 2A current load.
The authors acknowledge the financial support from the Polish Ministry of Science and Education – Grant No 3787/E-138/S/2015.

In recent years, transparent devices have attracted substantial attention. However, all components of transparent batteries, a key component in fully integrated transparent devices, have not yet been reported. The key factor in obtaining a transparent LIB resides mainly in the preparation of the cathode material. A general method of making transparent devices is to reduce their thicknesses much less than the optical absorption length, as in carbon nanotubes, graphene. Thus, we expect that the fabrication of battery with fully covered thin film materials allows the battery to possess highly transparency. Another important factor for thin-film materials to possess large transparency is their band gap energies. The thin-film materials with wide band gap energies, such as olivine compounds, are highly transparent, thus they are good candidates for transparent cathode materials. Olivine compound has advantages of excellent structural and thermal stabilities, non-toxicity, low cost and excellent electrochemical properties. Among this compound of materials, LiFePO₄ is remarkably stable even in rough operating condition, nontoxic and possible intensive. However, still the problem of the low energy density of LiFePO₄ resulting from its relatively low potential (~3.4V) remains unresolved. We found that the formation of a solid solution between LiFePO₄ and LiMPO₄ is energetically favored, and each transition metal actively participates in the electrochemical reaction within a reasonable voltage range. Our group previously studied exploration of composition by thin film cathode materials of olivine compound proved as LiFePO₄ without carbon. However, there are numerous limitations related to its intrinsic electrochemical properties, mainly coming from the slow kinetics. Hence, the electrical conductivity is improved through carbon coating, Ag-embedded or the decrease in particle sizes in recent works. In this study, we find that the formation of a solid solution between LiFePO₄ and LiMPO₄ is energetically favored, and each transition metal actively participates in the electrochemical reaction within a reasonable voltage range. Its electrochemical properties and phase stability are explored with continuous composition spread (CCS) radio frequency (RF) magnetron sputtering. We describe for Ag-doped olivine based cathode materials deposition on a transparent conducting oxide (TCO) substrate. The CCS RF sputtering is a feasible method to deposit various compositions on a substrate with two targets. Two independent RF magnetron sputtering guns installed with LiFePO₄ and LiMPO₄ targets are located vertically to a TCO substrate. Consequently, we have investigated the full range of LiFePO₄ and LiMPO₄ compositions to find optimized composition with continuous composition spread RF magnetron sputtering.

Along with the rapid progress in the electric vehicles technology, lithium ion battery (LIB) has faced newly required technical issues such as high energy density and fast charging capability. Graphite, currently used anode material for commercial LIB, has limits to be used for electric vehicles in terms of energy density and fast charging capability. To solve these problems, various anode materials have been suggested as alternatives to replace graphite anode material. In this work, titanium oxide coated graphite was investigated as an alternative anode material to improve the fast charging capability. The proposed core-shell structure, titanium oxide coated graphite anode electrode exhibited an excellent rate capability even at a high rate of 10 C without any degradation of reversible capacity and long-term cycle performance. The electrochemical properties of the titanium oxide coated graphite will be discussed in more detail.

Solid oxide fuel cells are an attractive technology for energy generation, due to fuel flexibility and high efficiency in fuel conversion, which can be greater than 80% in combined heat and power systems. Due to the high costs and performance degradation associated with high temperature SOFCs, further research is required to reduce the operating. In intermediate temperature solid oxide fuel cells (600 – 1000 K), due to poor ionic conductivity of the cathode, the oxygen reduction reaction is often limited to the interface between the cathode, electrolyte, and the air (the three-phase boundary). The region in which the oxygen reduction reaction can take place, mixed ionic and electronic conductors can be used as cathode materials. Ruddlesden-Popper materials, A_n+1B_nO_3n+1, have shown promise as mixed ionic and electronic conducting cathode materials for intermediate temperature solid oxide fuel cells.[1-3] They consist of n ABO₃ perovskite layers, which can accommodate oxygen vacancies, separated by AO rocksalt layers. The main focus has been on the n = 1 series, which possess K₂NiF₄-based structures. La₂NiO₄-based materials are of interest due to their good conductivity in the required temperature range, and compatibility with ceria-based electrolytes.

The structure and electronic properties of orthorhombic La₂NiO₄ have been calculated using PBEsol + U.[4] Oxygen vacancy and interstitial formation, and their dependence on temperature, oxygen partial pressure and chemical potential, in bulk La₂NiO₄ and at its low index surfaces has been examined. Formation energies of the defects have been calculated under solid oxide fuel cell operation conditions, with oxygen interstitial formation significantly lower in energy than oxygen vacancy formation. Nudged elastic band calculations have been carried out to examine the mechanism of oxygen diffusion within the LaO layers and across the LaNiO₃ layers.

[1] A. M. Hernandez et al., Int. J. Hydrogen Energy, 2010, 35, 6031 – 6036
[2] M. Rieu et al., J. Electrochem. Soc., 2010, 157, B477 – B480
[3] R. J. Woolley and S. J. Skinner, Solid State Ionics, 2014, 255, 1 – 5
[4] J. P. Perdew et al., Phys. Rev. Lett., 2008, 100, 136406

In this study, we reported a novel method to synthesize highly porous nitrogen-doped hard carbon spheres (NCS) by using Ammonium sulphate as nitrogen precursor and sucrose as carbon precursor. This NCS exhibited an high specific BET surface area (1830 m2 g–1), large pore volume (1.3 cm3 g–1), good nitrogen content (8.6 at %), and with good thermal stability. Thus with above features NCS as anode materials for lithium ion batteries delivered a good rate capacity, high reversible capacity and excellent cycling performance due to the enhanced electrochemical activity of doped nitrogen carbon spheres and the high porosity. Therefore, the highly porous NCS hold promise in the fields of energy storage.

In this study, we investigate the frequency response of micro-pseudocapacitors (MPCs) based on conducting polymer electrodes such as poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPY) and polyaniline (PANI). It is shown that by proper choice of polymeric material and device structure, miniaturized micro-pseudocapacitors can match the frequency response of commercial bulky electrolytic capacitors. Specifically, we show that PEDOT-based micro-pseudocapacitors exhibit phase angle of -80.5° at 120 Hz which is comparable to commercial bulky electrolytic capacitors, but with an order of magnitude higher capacitance density (3 FV/cm³). The trade-off between the areal capacitance (CA) and frequency response in the 2D architecture (CA = 0.15 mF/cm², phase angle of -80.5° at 120 Hz) is improved by designing 3D thin film architecture (CA = 1.3 mF/cm², phase angle of -60° at 120 Hz). Our work demonstrates that fast frequency response can be achieved using electroactive polymer electrodes.

Sodium-ion batteries are promising alternatives to lithium-ion batteries due to similar electrochemical properties of sodium and lithium and also the abundancy of sodium metal. However, current Na-ion batteries exhibit poor cycling stability and lower energy density which inhibit their practical use in applications. Tin dioxide (SnO₂) emerged as a promising candidate as anode material for Na-ion batteries due to its excellent sodium storage capacity. However, SnO₂ suffers large volume expansions upon cycling and inevitably pulverization occurs. This volume expansion followed by pulverization is the fundamental concern for SnO₂. In order to compensate the volume expansion, highly porous SnO₂ nanofibers (SnO₂ PNFs) were synthesized by electrospinning technique by adding mineral oil into precursor solution. Additionally, to stabilize the solid electrolyte interface (SEI) and thus improve the cycling performance, nanoscale amorphous carbon layer was coated on the surface of SnO₂ PNFs by hydrothermal process. In a typical process, as-prepared electrospun SnO₂ PNFs were added to sucrose solution and transferred to stainless steel autoclave. After that, carbonization of the sucrose coating on SnO₂ PNFs was carried out at 500 ^oC in Ar atmosphere. Electrochemical performance of the introduced anode was tested assembling coin-type half cells. Electrochemical test results demonstrated that carbon coating of SnO₂ PNFs led to better SEI formation and increased capacity retention. Capacity retention of carbon coated SnO₂ PNFs was 90.5% after 50 cycles, whereas the capacity retention of bare SnO₂ PNFs was only 11.4% after 50 cycles.

Lithium-ion battery (LIB) has been utilized in variety applications as energy source. Structural battery is a new approach that employs multifunctional material concept to use LIB with load-bearing capability to minimize the weight of the complete energy consumption system and maximize the efficiency. LIB usually consists of cathode, polymeric separator, and anode; in face, the separator has been known as the weakest part of the conventional LIB. This work aims at creating electrospun polymer membranes (at room temperature) with nanostructures as next generation LIB separator with improved thermal resistance and mechanical properties. Electrospinning (ES) is simple, flexible also cost-effective at all scales. ES employs the electrostatic force to control the production of nanofibers from polymer solutions. Solution and process parameters, such as type of polymer, concentration of solution, ES voltage, and solution feed rate, have been studied to achieve the desirable membrane properties. Many characteristics of electrospun polymer membrane would affect the performance of it as the separator in LIB, including surface morphology, microstructure, thermal stability, mechanical property, and electrochemical performance. In this study scanning electron microscopy, dynamic scanning calorimetry, tensile testing and electrochemical testing have been used to characterize the electrospun membranes. Design of experiments techniques has also been utilized to optimize the parameters in creating an improved separator for structural batteries.

Understanding the crystallization process during annealing of Li-V-O thin films can provide potential new avenues to control of electrode microstructure in thin film battery systems. Our goal is to correlate different microstructures during crystallization with electrochemical performance and degradation during extended cycling using in-situ transmission electron microscopy(TEM).
In-situ thermal annealing in the TEM was used to study the crystallization of amorphous Li-V-O thin films (50nm) deposited by RF Magnetron sputtering from LiV₃O₈ target material, in Ar and Ar+O₂ (Ar:O₂=3:1) atmospheres. X-Ray diffraction studies showed that- thicker films (1μm) synthesized in the Ar atmosphere formed LiV₂O₅, and those synthesized in the Ar+O₂ atmosphere formed primarily LiV₃O_8. From the in-situ TEM annealing experiments, we learned that the thin film microstructure and phases during recrystallization are sensitive to the original deposition parameters, and to the annealing conditions in the TEM. Exposure to the TEM electron beam in the Ar+O₂ sputtered LiVO thin films was also observed to influence the crystallization process. Annealing at 400^oC and 500^oC of the Li-V-O thin films deposited in Ar and Ar+O₂ atmospheres revealed complex diffraction patterns, differing from other and could not be indexed to a single Li-V-O phase. The sample deposited in Ar+O₂ and annealed in the TEM to 500^oC showed uniform V₂O₃ phase, indicating reduction of the vanadium center and almost complete delithiation. Lithium compositional measurements using Nuclear Reaction Analysis showed that diffusion of Li from the Li-V-O into the substrate is playing a substantial role in delithiation of the films. Our current work focuses on crystallizing desired Li-V-O phases by inhibiting the Li diffusion into the substrate using Ni coatings.
Further comparisons were made between in-situ TEM annealing and ex-situ annealing in an Ar atmosphere for Li-V-O films deposited in an Ar+O₂ atmosphere to understand the effect of annealing ambient on phase formation. It was observed that the phases formed after annealing in the two environments were different. After annealing at 400^oC in the Ar atmosphere, the film formed predominantly VO₂ which is different from phase formed in TEM annealing. In-situ TEM annealing experiments were also performed on LiV₃O₈ precursor material to check their evolution in TEM annealing conditions. We observed phase transformation from initial LiV₃O₈ phase when annealed at 500^oC.
In summary, we observed that deposition conditions, annealing temperatures, annealing environments and electron beam irradiation affected the crystallization process and formed different microstructures during in-situ annealing of thin Li-V-O films.
Acknowledgements: -The work was supported as part of the Center for Mesoscale Transport Properties (m2M), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award # DE-SC0012673.

RuO₂ has been identified as the key electrode material to make high specific capacitance supercapacitors. However, the application of RuO₂ was limited due to its high cost, another problem is that the cycling stability of RuO₂ is lower than that of activated carbon electrodes. 2D transition metal sulfide CuS nanosheets have good electrochemical performance and cycle stability, which was due to their unique layered structure, large specific surface area and fast electron transfer rate. In this paper, CuS doped RuO₂ composites were prepared by sol-gel and low-temperature annealing processes. XPS, TEM and XRD were used to examine the morphology and crystalline type of the synthesized material. The experiment results show that CuS doping increases the number of imperfections in the RuO₂ lattice, the composites have a lose and disordered structure. Cyclic voltammetry (CV), electrochemical impedance spectrometry (EIS), and galvanostatic charge-discharge tests indicated that when the loading level of CuS reaches 30%, the RuO₂ nanoparticles in the nanocomposite achieve a specific capacitances of 519 F/g， compared with the bare RuO₂, the RuO₂-CuS nanocomposites also exhibit the enhanced rate capability, more excellent electrochemical stability(about 94% retention after 1000 cycles).

Li-ion batteries (LIBs) with high energy and power densities are highly demanding to meet the requirements of next generation electric vehicles and stationary energy storage. Transition-metal oxides (TMOs), with high theoretical specific/volumetric capacity originated from the conversion reactions (M_xO_y + 2yLi⁺ + 2ye^- ↔ yLi₂O + xM), are very promising candidate as alternative electrode materials to carbonaceous anodes. However, its practical application is largely hindered by the poor reaction kinetics and the large volume variation during the lithium insertion and extraction processes, which lead to unsatisfied cycling performance and poor rate capability of the electrode. Here, we report a polymo-mediated route for the synthesis of hierarchical metal ion-containing precursors assembled from nanosheet or nanowire building blocks. The hierarchical structures are maintained upon subsequent calcination, and in most cases the building blocks are converted to be porous, yielding fascinating merits of large exposed surface, short diffusion distance and abundant electron/ion transport pathways for the obtained product, which would effectively boost the electrochemical activity. As a result, these hierarchical structures delivery excellent Li-ion storage performance in terms of high specific capacities, long cycle stabilities and good rate capabilities.A typical case is the formation of Fe₃O₄ hollow microspheres, which delivered special capacities of 992, 853, 716, 548 and 457 mA h g^-1 at 1, 2, 4, 8 and 10 A g^-1, respectively, and high capacity retention upon 100 cycles. In addition, the electrochemical properties of these transition metal oxide hierarchical structures can be further improved by in-situ metal doping or carbon coating. For example, Fe₂O₃ with highly conduction CuFe₂O₄ nanocrystals exhibits enhanced cycling performance (0.02% capacity loss per cycle) than that of bare Fe₂O₃.

Nowadays, one of the most interesting research in the renewable energy field is to design lignocelluosic biomass structure to produce higher valuable products. The valorization of waste is very attractive for both sustainable and material chemistries. Recently, waste-derived biomasses including glucose, cellulose, starch, lignin, or biochar has been used as a natural and abundant precursor to synthesize functional carbon nanomaterials. Among various biomass materials, the lignocellulosic biomass consisting of cellulose, hemicellulose and lignin is the most abundant renewable resource.
In this study, we report a high-performance sodium ion energy storage and highly selective CO₂ adsoprtion using novel phosphorous (P), sulfur (S) and nitrogen (N) doped nanoporous carbon via a one-step hydrothermal method. In addition, during hydrothermal process cellulose and lignin were simultaneously separated from lignocellulosic biomass without any pre-treatment. The doped nanoporous carbons have highly active sites and well-developed pores with the high surface area and pore volume of 1154 m² g^-1 and 2.47 cm³ g^-1, respectively, 330 times greater than those of raw lignocellosic biomass. In particular, P doped porous carbons exhibited the high specific capacitance of 298.43 F g^-1 at 10 m V^-1 and cycle retention of 90.67% after 1000 cycles in 1M KOH. For the CO₂ adsorption test, N doped porous carbon showed the highest CO₂ adsorption capacity of 10.79 mmol g^-1 among the doped porous carbons and excellent cycle retention of 88.90 % after 10 cycles. Consequently, this chemical synthesis can be an important opportunity for the transformation of raw biomass to valuable materials.

Magnesium metal is a promising anode choice for the next generation rechargeable energy storage device. The merits are featured as high volumetric energy density, low electrochemical potential and non-dendritic nature during plating. The development of full battery, however, faces two major hurdles: the lack of suitable cathode and the limited stability of electrolyte. Traditional intercalation chemistry suffers from the sluggish diffusion of the Mg²⁺ cation while novel O₂ and sulfur conversion cathodes exhibit poor rechargeability and low cell voltage. Bromine species-based conversion chemistry could potentially provide a promising cathode with fast kinetics, good cyclablility and reasonable capacity. Most of the existing studies of bromine based batteries are in aqueous electrolyte which renders incompatibility with the Mg anode, while non-aqueous electrolytes usually exhibit poor stability toward Br₂. Here we present the first proof-of-concept Mg-Br₂ battery, by employing a non-aqueous dual electrolyte system without employing solid state electrolyte, open circuit voltage of 3.0 V vs Mg²⁺/Mg was observed and continuous charge/fully discharge cycle was demonstrated over 20 cycles with 96 % coulombic efficiency and 70% round trip efficiency. This study provides fundamental knowledges for bromine cathode in non-aqueous electrolyte and brings new opportunity for Mg metal based rechargeable battery.

Although Lithium-ion batteries have made significant impacts on portable electronics and electric vehicle industries, the feasibility of wide deployment of lithium-based batteries in grid-scale energy storage may be questionable due to the relatively limited lithium resource, the resource geographic distribution, and the cost of lithium mining and recycling. Therefore, alternative rechargeable battery technologies based on abundant elements need to be developed. Among the potential candidates, aluminum (Al) may be the ultimate choice as the anode material: it is not only the third most abundant element and the most abundant metal in earth’s crust, but also has attractive capacity due to its trivalency. Al has the second highest specific capacity of 2980 mAh/g (Li = 4634 mAh/g) and the highest capacity density of 8046 mAh/cm³ (Li = 2456 mAh/cm³) among all metal anodes.
We hereby demonstrate the reversible Al intercalation-extraction in metal sulfides, particularly Chevrel phase molybdenum sulfide (Mo₆S₈), layered titanium sulfide (TiS₂) and thiospinel titanium sulfide (c-TiS₂) in ionic liquid electrode composed of aluminum chloride and 1-butyl-3-methyimidazolium chloride (AlCl₃-[BmIm]Cl). Electrochemical characterizations including cyclic voltammetry and galvanostatic charge-discharge demonstrate unambiguous Al intercalation-extraction in the Mo₆S₈. The X-ray diffraction analysis further indicates the crystal structure change of Mo₆S₈ after Al intercalation. Based on Rietveld refinement, the crystal structure of Al intercalated Mo₆S₈ (Al₂Mo₆S₈) and the theoretical capacity are proposed. The Al intercalation-extraction in the titanium sulfides is less facile, which may due to the more restraining crystal structures of the TiS2 comparing to Mo6S8. Nevertheless, electrochemical and spectroscopic results clearly indicate the reversible Al intercalation into the titanium sulfides, and 50 mAh/g specific capacity of TiS2 was demonstrated without particle size optimization.

The rapid growth of renewable energy from solar and wind power has created a strong demand for low-cost, safe, high-energy density energy storage systems to enable the integration of renewable energy into grid and peak shifting in energy demand. To meet the cost target of less than $100/kWh, earth-abundant materials have been actively explored for beyond-lithium-ion batteries. For example, Prussian blue analogues (PBAs) have attracted significant attention due to their unique open framework structures for Na and K ion storage in aqueous and non-aqueous batteries. However, the full cell rate performance is limited by the choices of anode.
Magnesium metal has recently attracted considerable attention as a safe anode due to the fact that Mg has a low standard potential (-2.37 V vs. SHE), fast deposition-stripping kinetics, and dendrite-free deposition behavior. However, the challenge is the lack of stable high-voltage cathode material due to the slow solid-state diffusion of highly polarizing Mg²⁺ ions in host.
In this work, a unique material combination is meticulously selected to demonstrate a hybrid Mg−Na-ion battery with the highest reported operating voltage (2.2V) and power performance (1.67 kW kg^-1). The excellent performance is due to the selection of open framework Berlin Green nanoparticle based cathode and a high-voltage Mg-Na dual salt electrolyte (3.2 V vs Mg/Mg²⁺), as well as a Mg metal with dendrite-free fast deposition-stripping behavior. The cathode shows reversible capacity of 143 mAh g^-1 and stable cycling for 50 cycles. The unit cell of BG has only 5.3 % volume increases than the pristine compound and slight non-uniform structural distortion when 1.52 Na inserts into the framework. X-ray absorption near edge structure (XANES) study shows a clear reversible shift of Fe K-edge to lower energy and a small hump around 7118 eV. At the anode side, EDX and SEM confirm fast and reversible Mg-only deposition mechanism. Therefore this work opens the door to many Na-ion cathode materials for high voltage Mg-Na hybrid batteries that could become a viable candidate for stationary energy storage.

There is a need for reliable, low-cost energy storage for electric vehicle applications. While advanced Li-ion batteries may possess sufficient power and energy density to be useful for electric vehicles, their high manufacturing and materials costs make them unsuitable outside of a relatively small market niche. Alkaline batteries, one of the most common modern forms of primary battery, are potentially ideal for electric vehicles. These cells depend on a reaction between zinc (Zn) and manganese dioxide (MnO2) to generate energy. This reaction gives alkaline batteries a relatively high energy density and a low cost per kilowatt-hour, but phase transformations occurring during deep discharge, particularly the formation of the electrochemically inactive ZnMn2O4 phase, prevent recharge. In a typical alkaline battery, useful rechargeability with minimal capacity losses can only be achieved if no more than 10% of the cathode’s capacity is used.
We have developed a new, low-cost electrolyte based on a combination of multiple different cations which prevents the formation of electrochemically inactive phases, even during deep discharge. A capacity of 360 mAh/g on a cathode basis has been achieved cycling against zinc for more than 60 stable cycles, without evidence of ZnMn2O4 formation. We have also characterized the effects of this electrolyte as well as more conventional alkaline battery electrolytes using both conventional and in-operando synchrotron XRD techniques. We will discuss the impact of electrolyte formulation, charging and discharging protocols, and conductive additives on the performance of the system, and hypothesize on the mechanism by which this electrolyte prevents formation of electrochemically inactive phases.