Symposium EN01—Challenges in Battery Technologies for Next-Generation Electric Vehicles and Grid Storage Applications

Over the last decade, there has been a paradigm shift towards usage of earth abundant and cost effective materials in rechargeable batteries. A prominent example in this context, is sulfur. Sulfur delivers a high theoretical capacity of 1672 mAh g^-1, nearly one order higher compared to the best known intercalation cathodes (IOCs) used in Li/Na-ion batteries. The high theoretical capacity originates from the possibility of higher than one exchangeable Li-ion per S-atom (theoretically two exchangeable Li-ions per S-atom) as compared to only one Li-ion/formula unit of IOC. Additionally, S is cheap, highly abundant and non-toxic in nature. Despite these advantages, the chemical reactions determining the mechanism and quantum of electrical energy storage in a liquid electrolyte based Li-S battery pose several challenges. The main challenge is due to the various intermediate polysulfides formed during the reversible conversion of elemental S₈ to metal-sulfide. Bulk of the work related to metal-S rechargeable battery revolves around materials design strategies of a suitable carbon(/non-carbon)-host matrix targeted towards the entrapment of S and prevention of leaching out of polysulfides into the electrolyte. However, this limits the extent of S-loading and depending on the host may simultaneously increase the un-utilizable mass of S in the electrode. The presentation will discuss some of our important recent results in the context of M-S (M: Li, Na, Mg) highlighting the critical role of materials design and in operando monitoring studies for the development of highly stable metal-S bateries. The talk will discuss at length various ways for efficient anchoring of sulfur and the polysulfides at the S-cathode for various rechargeable metal-S batteries. Strategies will include (a) design of novel S-scaffolds based on molecular systems such as covalent organic frameworks (COFs), conducting carbon-based scaffolds, (b) additives and (c) interlayers based on non-carbonaceous nanoparticles. Our studies reveal several interesting fundamental insights related to the mechanism of storage which eventually have strong bearing on the metal-sulfur battery performance.

We have recently demonstrated the first definitive examples of dendrite formation in magnesium batteries and will additionally detail our progress towards design of metallic anodes which mitigate such growths. The utilization of metallic anodes holds promise for unlocking high gravimetric and volumetric energy densities for rechargeable batteries, however, lithium metal has a high propensity for dendrite formation, the plating of lithium as anisotropic fractal structures that can bridge across liquid and solid electrolytes to the cathode, thereby short circuiting the cell. Such catastrophic failure represents a major roadblock to this seemingly simple approach to achieving improved storage capacities. Magnesium-based batteries are considered a possible alternative, given the high earth-abundance of magnesium and the potential for higher volumetric energy density offered by its divalent charge. A promising advantage of switching to Mg-based batteries derives from the many reports which claim that Mg is inherently non-dendrite forming. Initial reports noted that Mg could be plated as relatively smooth deposits under charging conditions that resulted in dendritic growth for lithium. Since these reports, there has been substantial progress in development of cathodes and electrolytes, however, there has been little to no further vetting of the notion of metallic magnesium anodes. Through combining video microscopy studies of symmetric Mg-Mg cells with detailed 3D tomographic characterization of thin film morphologies and mesoscale modeling we demonstrate some of the first definitive examples of dendritic growth on magnesium anodes and elucidate mechanisms of formation. We have additionally designed metallic magnesium nanowire and nanotube arrays which have the potential for yielding low-volume expansion, lower current density anode materials. Our work opens the door for development of anode designs that mitigate dendrite growth, which will be crucial for further progression of Mg-based battery technology.

An advanced power-based spraying technology was developed by us to fabricate electrodes for the lithium-ion batteries to replace the conventional slurry cast method. The additive manufacturing technology is a low cost, highly efficient way to avoid toxic NMP solvent from electrode fabrication. The removal of solvents shortened the production time from days to seconds, analyzed to reduce 20% of production cost, and enabled a more precise control of electrode microstructure during manufacturing. With the continuous processing system, the technology has a good potential to be scaled up and commercialized. Beyond the current commercial materials, we can also demonstrate this technology with a wide range of compatibility on producing electrodes, including different types of cathodes (LCO, LMO, NCM), anodes (MCMB), advanced architecture designs (Ultra-low binder recipe (<1%), high-energy thick electrodes (>280um), hierarchical micro-structured). In addition, the flexible arrangement strategy of spraying guns promoted the development of hierarchical designs to be practically available to the lithium-ion market.

Wide deployment of electric vehicles (EVs) would greatly facilitate global de-carbonization, but achieving the emission targets depends on future battery prices. Conventional learning curves for manufacturing costs, used in many battery projections, unrealistically predict battery prices will fall below $100/kWh by 2030, pushing EVs to be economically competitive with internal combustion engine vehicles (ICEVs) in the absence of incentives. However, in reality, essential materials costs set practical lower bounds on battery prices.
Our 2-stage learning curve model projects the active material costs and NMC-based Lithium-ion battery pack price with mineral and material costs as the respective price floors. The learning rates are found to be 3.5% for chemical synthesis and 16.5±4.5% for battery production. The improved model predicts nickel-manganese-cobalt (NMC) battery prices will fall only to about $124/kWh by 2030 – much cheaper than today, but still too expensive to truly compete with ICEVs, due primarily to the high prices of cobalt, nickel, and lithium. Our results suggest that stabilizing raw materials prices and/or stimulating R&D activities on alternative battery chemistries will be important to achieve environmentally sustainable EV-based ground transportation at an attractive price.

Over the past several years, reports have emerged of ultrafast charging algorithms for lithium ion batteries [1,2] that in at least one instance [3] is attributed to megahertz frequency modulation of charging/discharging currents. Such algorithms are claimed to dramatically improve active material utilization as well as cycle life, but no mechanisms have been proposed in published work, nor, to our knowledge, have mechanistic studies have been conducted. In this work, we use a recently developed technique [4] in which single electrode particles having capacities of a few nAh can be interrogated with electrodynamic measurements (EIS, GITT, polarization-depolarization) while varying the state-of-charge. This capability allows clean separation of interfacial vs bulk transport limitations at the individual particle level, without complicating factors from typical composite electrode microstructures. To this capability, we have added AC pulse charging and discharging at ultra-low currents (down to picoA) with high-frequency waveforms (up to ~ MHz).
With this capability, we aim to answer a number of questions such as: Are these effects real? Are they significant? And, what are possible mechanisms by which ion transport kinetics in a lithium ion battery are responsive to megahertz frequency excitation?
This work was 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, Basic Energy Sciences under Award # DESC0012583.
References:
1. https://techcrunch.com/2015/05/05/nucleus-scientific-launches-to-revolutionize-batteries/
2. https://www.greencarreports.com/news/1121116_company-claims-to-harness-ai-for-quicker-electric-car-dc-fast-charging
3. Sherstyuk et al., Extended life battery, US Patent No. 9,966,780B2, May 2018.
4. P.-C. Tsai, B. Wen, M. Wolfman, M.-J. Choe, M. S. Pan, L. Su, K. Thornton, J. Cabana, Y.-M. Chiang, Single-particle measurements of electrochemical kinetics in NMC and NCA cathodes for Li-ion batteries. Energy Environ. Sci., 2018, 11, 860-871.

Replacing lithium ions with sodium ones in energy-storage systems is highly attractive due to the ~1300× enhancement in material abundance However, the 25% larger volume of sodium ions prevents a drop-in substitution. For example, the typical graphite-based anode used in Li-ion systems are not amenable to reversible Na-ion intercalation and cathodes designed for Li-S cannot accommodate the larger volume expansion. Herein, we employ a specially designed in-situ electrochemical cell developed at the Naval Research Laboratory¹ to probe the optical characteristics of electrodes under charge–discharge operation, yielding key information on electrochemical mechanisms.
For Sodium-ion anodes, disordered “hard carbon” anodes show more promise than graphitic carbons for Na-ion cells, but their charge-storage mechanisms are more complex, involving surface association, bulk cation-insertion reactions, and micropore-based deposition. Using the in-situ cell, we examine the sodiation of carbon nanofoam papers (CNFPs), which were recently reported for their high-capacity and high-rate charge-storage properties in nonaqueous Na-ion electrolytes.² Imaging the CNFP during galvanostatic “discharge” (reduction in half-cell configuration vs. Na metal) reveals distinct color changes from grey to black to bronze to blue, caused by carrier concentration variation with increasing Na-ion association/insertion at the carbon electrode. We correlate these optical changes with variations in the complex discharge profile of the CNFP, which arises from multiple defect- and porosity-enable Na+-storage mechanisms that are supported by this electrode. This fundamental understanding will enable optimization of defect concentration and porosity of this anode material for the realization of this system.
Alternatively, the RT Na-S system that boasts higher energy than Li-ion, in addition to high material abundance, is stalled by material challenges at the metal anode and conversion cathode. The soluble nature of discharge products and their interaction with the metal limit energy and cyclablity.³ However, using the in-situ cell, careful mapping of discharge mechanisms is achieved in conjunction with anode observation. The discharge products (Na₂S_n, 8<n<1) and relative quantities are determined, due to their distinct colors, with UV-vis spectroscopy. Since these behaviors prove strongly dependent on electrolyte solvent, the study is valuable to selection of optimal composition for anode stability and cathode performance.

1. Love, C. T.; Baturina, O. A.; Swider-Lyons, K. E., Observation of Lithium Dendrites at Ambient Temperature and Below. Ecs Electrochem Lett 2015, 4 (2), A24-A27.
2. DeBlock, R. H.; Ko, J. S.; Sassin, M. B.; Hoffmaster, A. N.; Dunn, B. S.; Rolison, D. R.; Long, J. W., Carbon nanofoam paper enables high-rate and high-capacity Na-ion storage. Energy Storage Materials 2019, 21, 481-486.
3. Carter, R.; Oakes, L.; Douglas, A.; Muralidharan, N.; Cohn, A. P.; Pint, C. L., A Sugar-Derived Room-Temperature Sodium Sulfur Battery with Long Term Cycling Stability. Nano Letters 2017, 17 (3), 1863-1869.

Li ion battery is one of suitable energy storage in our life, such as mobile electronic devices and electric vehicles. For delightful and convenient existence, high speed charging and long battery life are very important. Actually, charging time of smart phone is too long, which is about 5 hours to fully charge when the battery is empty. In this case, 0.2C is used for charging current, otherwise battery capacity is reduced “like broken” under higher C-rate (higher speed charging). This is because SEI layer, which is decomposed materials of electrolyte, LiF, organic solvent etc., is deposited on active cathode and anode materials. In this paper, we have achieved to obtain the ultrahigh speed charging and very tough cycling properties in LiCoO₂ cathode thin film battery decorated with dielectric BaTiO₃.^[1] The important point is the blocking of creating SEI on cathode surface. In details, we have investigated interface reaction between cathode and electrolyte using epitaxial thin film battery. We have tried to insert artificial SEI of high dielectric constant materials, BaTiO₃, on the cathode LiCoO₂ epitaxial thin film. The high rate performance and cyclability are enhanced by existence of triple phase interface, cathode LiCoO₂ – electrolyte LiPF₆ (EC:DEC)– dot BaTiO₃. The key point of this effect is that high dielectric constant material is better. We will discuss an effect of decolated dot materials. [1] S. Yasuhara, S. Yasui et al., Nano Lett. 19 (2019)1688.

Developing battery systems resilient to thermal runaway propagation is of great concern when designing resilience into large battery systems. This is particularly difficult when working with pouch format cells as the format exists primarily to drive increased energy density within systems, which itself makes failure propagation more likely to occur. Our work here focuses on module to module propagation and potential tools that might be used to mitigate this failure. We have constructed 3S3P configuration batteries with various mitigation strategies used to prevent module to module propagation. This has included conductive, insulating and advanced materials and is coupled with analysis of the heat transfer across these barriers to better understand the underlying mechanisms that can better improve propagation resistance in systems constructed with pouch format cells. We have used both mechanical and thermal initiation techniques to explore the different behaviors that might occur when the character of the initial failure changes as well. This includes the failure propagation from a single cell failure initiation as well as the failure of an entire 1S3P module within the pack. Finally, we look at the differing roles that both changes to energy density of the pack as well as changes to the heat transfer between cells might play in mitigating thermal runaway propagation.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Continuous improvements in lithium-based battery technology has facilitated the recent growth of personal electronics and the increasing introduction of electrified vehicles. Lithium-ion technology has evolved steadily since its introduction in 1991 with ever increasing specific energy. However, it is likely that more advancements in battery performance characteristics are necessary to enable the widespread adoption of electrified vehicles.

One of the leading candidates for next generation battery technology is the solid state (SS) battery, where a liquid electrolyte and polyolefin thin film separator are replaced by an ionically conducting solid. While SS battery technology replaces the flammable electrolyte of lithium-based technology with a non-flammable ceramic, glass or polymer, the addition of highly reactive lithium metal and potentially brittle separator materials may introduce different safety challenges. In this context, a safety assessment of lithium metal SS batteries is performed against existing international battery safety test standards and regulations, with an emphasis placed on water exposure and vibration.

Lithium/O₂ (air) batteries are promising exceptionally high specific energy, that can be theoretically 2-3 times higher than today Li-ion batteries.
Low cycling efficiency, low cycle life and slow discharge kinetics are still considered the main issues to be addressed for the development of high performance Li/O₂ batteries. The discharge product, lithium peroxide (Li₂O₂) which is formed on the cathode surface is an insulator that affects battery capacity and causes high overpotential during recharge and, thus, low recharge efficiency.
This process can be controlled by tailoring the electrolyte environment. Glyme-based solvent-in-salt (SIS) electrolytes have been recently proposed for Li-O₂ batteries. In SIS glyme-Li⁺ complexes are formed. They improve the electrochemical stability of the electrolyte and stabilize superoxide ion with a positive effect on cathode passivation.
An additional strategy for improving Li/O2 battery performannce is the use of a flowable catholyte ink. It is an organic dispersion of carbon particles which also acts as oxygen carrier, therefore improving Li/O₂ battery rate response. In this catholyte, ORR takes place on the solid phase of the carbon particles. Consequently, cathode surface passivation is limited, the battery cell death is delayed and the Li/O₂ battery energy increased. Such approach enabled areal capacity of 180 mAh cm^-2, energy of 500 mWh cm^-2 and current of 4 mA cm^-2
Here, we discuss about three strategies to improve semi-solid Li-O₂ battery cycling performance. Specifically, we report on i) a scanning electrochemical microscopy (SECM) investigation carried out to investigate the Li₂O₂ formation mechanism in salt-in-solvent and SIS electrolytes based on TEGDME and LiTFSI and in ionic liquids, iii) a semi-empirical modeling study that enables to predict the best cell design that improves the power gain of the flow Li/O₂ battery and iii) the study of the carbon composition of the semisolid catholyte that permits to achieve the exceptional high specific energy of 1 kWh kg^-1 .

Acknowledgments
Alma Mater Studiorum –Università di Bologna is acknowledged for financial support (RFO, Ricerca Fondamentale Orientata). We also thank the Italian Ministry of Education, University and Research (MIUR) for the “Dipartimento di Eccellenza 2018-2022” grant to the Department of Chemistry “Giacomo Ciamician” of the University of Bologna.

References

[1] F. Messaggi, I. Ruggeri, D. Genovese, N. Zaccheroni, C. Arbizzani, F. Soavi. Oxygen Redox Reaction in lithium-based electrolytes from salt-in-solvent to solvent-in-salt. Electrochim. Acta,
[2] I. Ruggeri; C. Arbizzani, F. Soavi. A novel concept of Semi-solid, Li Redox Flow Air (O₂) Battery: a breakthrough towards high energy and power batteries. Electrochim. Acta, 206 (2016) 291-300.
[3] F. Soavi, Ruggeri I., and C. Arbizzani, Design Study of a Novel, Semi-Solid Li/O₂ Redox Flow Battery. ECS Trans., 72 (2016) 1-9.
[4 ] I. Ruggeri, C. Arbizzani, F. Soavi, Carbonaceous catholyte for high energy density semi-solid Li/O₂ flow battery, Carbon, 130 (2018) 749e757
[5] F. Poli, L. K. Ghadikolaei, F. Soavi, Semi-empirical modeling of the power balance of flow lithium/oxygen batteries, Applied Energy, 248 (2019) 383–389
[6] I. Ruggeri, C. Arbizzani, S. Rapino, F. Soavi, Oxygen redox reaction in Ionic Liquid and Ionic Liquid-like based electrolytes: a scanning electrochemical microscopy study, J. Phys. Chem. Lett., Just Accepted Manuscript, DOI: 10.1021/acs.jpclett.9b00774

One of the most serious lifetime problems for established Li-ion and emerging “Beyond-Li” batteries is electrolyte degradation from unwanted side reactions. For many high-voltage and high-energy cathode materials, transition metal dissolution is known to accelerate capacity fade leading to unacceptably short battery lifetimes. Metals like Mn, Ni, and Co deposit at the anode and disrupt the formation and performance of the solid-electrolyte interphase (SEI), a vital battery interface responsible for protecting the electrolyte from the highly reductive anode. This results in continual Li loss and uncontrolled SEI growth. Understanding the role of each metal in undermining the passivation of the SEI is necessary to mitigate this degradation and enable commercialization of high-voltage Li-ion cathodes.

In this work, we interrogate the effects of transition metals on the SEI via in-situ electrochemical characterization. We apply generator-collector measurements and other electroanalytical techniques in order to probe mechanisms of transition metal incorporation into the SEI and their effect on through-film electron transport. By using convection to control electrode cross-talk, we observe the presence of metal contaminants from an upstream cathode at the downstream anode. Electrochemically interrogating the SEI with functionalized ferrocene mediators and interpreting voltammetry with continuum-scale models shows that incorporation of dissolved transition metals increases both the density and the activity of active sites within the SEI [2]. In a separate set of experiments, we compare Mn, Ni, and Co contaminants to explain the particularly detrimental effects of Mn [3-4]. We develop microkinetic models for an electron-tunneling mechanism and an electrocatalytic cycling pathway. Density functional theory is used to predict material parameters such as bandgap doping and redox potentials. Comparison of theory and experiment suggests that kinetic parameters dominate over thermodynamic redox potentials and point to the importance of the metal’s local coordination environment within the SEI.

[1] Gilbert et al, J. Electrochem. Soc. 164, A389, 2017.
[2] O. C. Harris, M.H. Tang, J. Phys. Chem C., 122, 20632, 2018.
[3] O. C. Harris, Y. Lin, Y. Qi, K. Leung, M.H. Tang, under review, 2019.
[4] O. C. Harris, K. Leung, M.H. Tang, under review, 2019.

Ti-based materials (e.g. Li₄Ti₅O₁₂ and TiO₂) have received considerable attention owing to their outstanding high-rate capacity and cycling stability, as well as their improved safety standards over graphite. Here we show there exist a series of lithium titanate hydrates with similar performance compared to most outstanding Ti-based electrodes (including the materials after modification) reported at present. That is, water promotes structural diversity (e.g. 2D layered) and nanostructuring of compounds, but does not necessarily degrade electrochemical cycling stability or performance in aprotic electrolytes. As new members in the Li-H-Ti-O material system, lithium titanate hydrates not only greatly expand the research scope of the Li-Ti-O and H-Ti-O material system, but also propose a new method for electrode materials modification. More significantly, they provide greater inspiration and guidance to other hydrated transition-metal compound systems in energy storage applications.

References:
S. Wang, et al. Nat Commun 2017, 8, 627.

Due to the large demand of electric vehicles and grid energy storage systems, many ongoing researches are focusing on the improvement of energy density, capacity, cycling stability and rate performance of Li-ion batteries. Lithium, Manganese-rich layered oxide cathode (LMR-NMC) is one of the promising cathode materials for the near future owing capacities of over 250 mAh g^-1 and energy density of over 1000 Wh kg^-1 between voltage range 2.0 – 4.8 V. Though, two main challenges still remain before these materials can be fully applied commercially; capacity fading and voltage fading. Here, we focus on the structure, properties and electrochemical performance of co-dope LMR-NMC, Na_xLi_1.2-xMn_0.54Ni_0.13Co_0.13]O_2-yF_y, synthesized via hydroxide co-precipitation followed by solid-state reaction. Initially, LMR-NMC with single dopant ratio was examined and best performance of each dopant was then selected in order to maximize the capability of co-dope material. Comparison among pristine, Na dope, F dope and co-dope samples were intensively analyzed. Regarding to the electrochemical studies, CD has the best performance in term of capacity (97%) and voltage retention (91%) after 100 cycles at 0.2 C with initial discharge capacity of 260 mAh g^-1 at 0.1 C. Based on this discovery, higher voltage and capacity retention LMR-NMC material are obtained allowing us to heighten the possibility of using LMR-NMC commercially in next-generation batteries.

Cobalt-free layered oxides with high specific capacity and low cost have emerged as promising candidates that can be used as next-generation cathodes for lithium ion batteries. Practical implenation of these materials, however, have been hindered by their low rate capability, structural instability, and fast capacity decay. Recent studies show the introduction of a small amount of cation dopants can strongly improve the electrochemmical performance of layered cathodes. But the underlying mechanisms remain illusive due to the lack of information at atomic scale. Here, with a combination of atomic-resolution STEM imaging and first principle calculations, we reveal the microcopic origin of enhanced electrochemical properties of LiNi_0.5Mn_0.5O₂ doped with ∼1 at % Mo. Our observations provide direct atomic-scale evidence that the small amount of Mo dopants distributed uniformly in the host lattice can significantly hinder the Li/Ni cation mixing. And such structral changes can strongly supress the detrimental phase transformations not only at the surfaces but also at the grain boundaries within the bulk of the cathode materials, leading to an enhanced capacity and cycling properties. These results provide useful insights into the fundamental understanding of doping effects on the structural stabilities of layered cathodes.

For the majority of cathodes in Li ion batteries, cationic doping offers an effective means to enhance electrochemical performance, in which the alien dopants are generally considered to operate via modifying bulk properties. In contact to the liquid electrolyte, the electrode surfaces often act as primary sites that suffer from structural and compositional degradation, however, the doping effects on the modification of electrode electrolyte interface (EEI) properties remain vague. By combining atomic level imaging, spectroscopic analysis and DFT simulation, we demonstrate that the dopant extends its effective domain from bulk to surface via dynamic evolution, which significantly improve the cathode/anode-electrolyte interface stability. Using Ni-rich cathode as a model system, we show that, during the materials synthesis stage, the trace amount of Al dopants migrate and accumulate beyond the surfaces and lead to the epitaxial growth of scattered Al₂O₃ nano-islands; upon cycling, the Al provides an additional physical barrier for slowing down the electrochemical degradation. The buffer zone developed by dopant evolution mitigates the electrode-electrolyte interactions and alleviates the performance decay during the battery operation.

Lithium-Sulfur batteries (LSB) are considered as high-potential candidate for next generation electrical energy storage technology due to the low cost and naturally abundant sulfur-based cathode, that endows the battery with a high theoretical energy density of 2600 Wh kg⁻¹ and specific capacity of 1675 mAh g⁻¹. However, rapid capacity fading due to the formation of soluble lithium polysulfide (LiPS) intermediates, electrically insulating property of sulfur and LiPS pose great challenges for the realization of long lasting LSBs for commercial applications. Present study dealt with the fabrication of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-sulfur@polyacrylonitrile electrospun nanofibers, which can be potentially used as flexible additives in the cathode of lithium-sulfur batteries. The unique architecture of thus fabricated nanofibers not only trap the intermediate LiPS and suppress their dissolution into liquid electrolyte but also provide rapid charge transfer pathway to improve the reaction kinetics. As a result, LSB with nanofiber incorporated cathode shows better cycle life and improved rate performance compared to the bare sulfur cathode owing to the adsorption effect of the nanofibers.

Intercalation compounds based on transition metal cation redox has been studied over a few decades, while their potential based on oxygen anion redox has been under heated debate recently. The richness of anionic redox chemistry in the solid state inspires the materials community to explore new systems for next generation electric energy storage. At the same time, advanced computational and experimental tools to quantify the anionic redox activities are under development to study the underlying science that triggers a reversible and stable anionic redox activity. Possible approaches are outlined to further improve electrochemical performance of anion redox, realizing its full potential. In this talk, we will showcase the new computational methodology that enbles the stabilization of oxidized lattice oxygen ions and follow up by demonstrating experimental evidence that is the true signal of oxidized lattice oxygen ions.

The emerging demands in large energy storage for portable electronic devices and transportations are attracting more interest in developing next-generation lithium-ion batteries (LIBs) with a series of new electrode materials, thus to achieve a 3-5 times higher capacity to meet a strategic perspective energy-density of 500 Wh/kg or higher. Silicon, with a theoretical capacity up to 4000 mAh/g, is considered as one of the promising anodes to achieve this goal. The industry R&D in Si-leaded anodes is widespread, and the release of commercial products for portable electronics seems imminent, although simultaneous achievement of high capacity and sufficient calendar life for automotive applications remains to be demonstrated due to a 360% volume expansion of silicon (Liu, Nano Lett 2011). The significant volume expansion makes the silicon not suitable for large amount loadings in actual batteries (Szczech, Energy Environ Sci 2011). The current ratio of silicon in graphite anode is typically less than 10%, which largely limits the overall energy density. Certain amounts of strategies have been tried to overcome this challenge by constructing various nano-structured configurations. Due to the light-weight, simple synthesis and low cost, recently scientists start to pay attention in applying polymeric materials in LIBs (Chao, Adv Mater 2014).
In this presentation, I will introduce a largely improved battery performance using micro-sized silicon skeleton caged by polypyrrole polymer as anode, which was synthesized via a facile wet-chemical strategy(Y Lv et al. 2019, under review). The industry available, micro-sized AlSi alloy was used as precursor, which ensures a scalable production with low cost. The hollow skeleton configuration provides sufficient spaces to accommodate the drastic volume expansion/shrinkage upon charging/discharging while the minimum amount of conductive polymer serves as a protective layer and fast channel for Li⁺/e^-transport. The battery with the micro-silicon cage as anode displays an excellent capacity retention upon long cycling at high charge/discharge rates and high material loadings. A specific capacity as high as 1660 mAh/g (>5X times graphite) with a high Coulombic efficiency of ~99.8% and 99.4 % were achieved after 500 cycles with 3 mg/cm² loading and 400 cycles with 4.4 mg/cm², respectively. At higher 1.0 C, the capacity close to 1150 mAh/g was remained after 500 cycles with such high loading. The areal capacity of as high as 6.4 mAh/cm² with 4.4 mg/cm² loading was obtained, which suffices a high battery energy density in powering large devices such as electric vehicles (EVs).

The performance and stability of lithium ion batteries (LIBs) depend on charge transfer processes and reactions at electrode-electrolyte interfaces (EEI), making interfaces design a key issue. Here we engineer this interface using conformal, functional polymer nanolayers via a novel vapor-based deposition technique. We demonstrate that poly(3,4-ethylenedioxythiophene) (PEDOT) nanolayer doubles the capacities of LiCoO₂ at high rates and extends its 4.5 V cycling life by 160%. The improved rate performance is enabled by high diffusion coefficient of Li⁺ in PEDOT measured from neutron depth profiling. Such behavior is further understood by density functional theory (DFT) calculation. The extended cycling stability comes from strong interactions between PEDOT and Co atoms, as suggested from X-ray photoelectron spectroscopy and DFT calculation. Additionally, in-situ synchrotron X-ray diffraction reveals that PEDOT uniformizes current distribution and improves LiCoO₂ structural stability during cycling tests. This work adds understanding and provides guidelines for designing the EEI for advanced LIBs.

Christine Hallquist, was CEO of a Vermont utility that was recognized for its leadership in transitioning to a 96% carbon-free electric supply by 2018. Christine spent 10 years as a member of a strategic advisory team to the National Rural Electric Association, which provided electricity to 56% of America’s land mass. The advisory group oversaw research projects with the Department of Energy, the National Laboratories, and industry. Christine was vice-chair of the advisory group and scheduled to move to chair when she left to become the democratic candidate for governor of Vermont in 2018. Her role in addressing climate change began in 2005 when the Vermont governor asked her to join an advisory group that traveled to Quebec to hear the report of the Intergovernmental Panel on Climate Change. She has now formed a Canadian Company, Cross Border Power, whose mission is to solve climate change and produce grid-scale storage as part of that mission.

Christine has been working with government and industry groups to carry out a North American Solution to Climate Change. This involves constructing a High-Voltage Direct Current (HVDC) transmission grid to interconnect North America, connecting as much solar and wind generation as possible, transitioning existing base-load hydro resources to peaking resources, buffering the grid with batteries and creating self-healing micro-grids using Smart Grid technology.

In order to understand the challenge ahead it is important to understand our current energy mix. According to the US Energy Information Administration, 81% of energy consumed in the US comes from fossil fuels. The per-capita daily use of electricity in 2018 was 11.6 kWh with 63% of the electricity generated from fossil fuels. In order to solve climate change, North America will need to transition its energy supply to 100% carbon-free sources of electricity 100% of the time. If we assume no improvement in efficiencies, this means the per capita use of electricity would rise to 61 kWh. That said, we can expect significant improvements in efficiency through transitioning to cold climate and geothermal heat pumps as well as electric transportation. We will increase the amount of electricity generated while transitioning. This will result in significant demand for additional wind and solar on the electric grid.

The electric grid was designed for rotating generators. The collective rotation of the interconnected generators provided system-wide inertia, which resulted in electrical stability. Eliminating those rotating generators and replacing them with wind and solar generation will require a tremendous amont of battery storage to inject the lost inertia and balance the supply with the load. While battery technology has been improving, from a cost and performance standpoint we have a long way to go.

The electric grid in Northern Vermont is already facing electrical stability problems from a large deployment of wind and solar. This area has become an ideal test case for studying impact and solutions. Presently, with all generation operating at peak output, the system is over capacity by at least 1/3, which means the wind projects are required to shut down due to grid stability issues, thus wasting the generation. These same stability issues are showing up all around the world, including California, Texas, Spain and Germany.

Christine’s presentation will address what is needed to solve the problems on the northern Vermont electric grid as well as what it will take to accomplish the North American Solution to Climate change. She will discuss the economics, physics and engineering challenges as well as the enabling policy changes that will can help accelerate the implementation. Included in her presentation will be the role of battery storage, the present state of storage and what developments are needed in order to fully decarbonize our energy portfolio.

Over the last decade the research community engaged in significant efforts to develop silicon-based anodes and boost the energy density of lithium-ion batteries. This goal is considered instrumental for the development of more efficient electric vehicles and stationary storage systems. While, from a material engineering standpoint, silicon-carbon nanocomposites have been demonstrated as one of the most promising strategies to produce electrodes with long-cycle life, overcoming the problem of silicon swelling upon lithiation, synthesis methods suitable for the low-cost industrial-scale manufacturing of these delicate and carefully engineered structures have still to be demonstrated. In this contribution, we present two innovative production systems purposely designed to be simple, cost-effective and suitable for future large-volume material production.
The first innovation is a method to produce silicon nanoparticles -NPs- with (i) high-purity (oxygen content <3%) and (ii) tailored nanoscale size. The system comprises a non-thermal radiofrequency plasma reactor serially connected to a tubular furnace. The plasma discharge quickly converts a silicon containing gas into silicon NPs and ensures a high precursor utilization (over 90%). The aerosol is then seeded into the furnace where the NPs are sintered into larger structures at high-temperature. The final particle size can be precisely adjusted between 5 nm and 60 nm (size distribution within 10% of the average value) by simply changing the temperature of this second thermal stage (800-1000°C).
The second innovation is chemical vapor deposition -CVD- method that allows growing highly graphitized and conformal layers of carbon directly onto the surface of silicon NPs. The NPs are introduced into a hot-wall furnace with an alumina combustion boat and are wrapped with a conformal coating of amorphous carbon resulting from the dissociation of acetylene -C₂H₂- at 650 °C. After removing C₂H₂, the furnace is ramped up to 1000°C in Argon -Ar- yielding a controlled graphitization of the carbon-shell with no detectable presence of silicon carbide.
The combination of the two aforementioned approaches achieves the production of a battery grade silicon-carbon nanomaterials with tunable properties (i.e. size, graphitic carbon content and carbon shell thickness). The as-produced composites demonstrate outstanding electrochemical performance as “drop-in” additives in graphite-dominant anodes. The addition of small amount of the Si-based active material (10% in wt) enables the fabrication of electrodes with a gravimetric capacity of around 600 mAh g^-1, first cycle CE of 90% and capacity retention of 81% over 100 cycles. The optimized composite material is used to fabricate a prototype 60 mm x 40 mm high-energy density pouch cell and its performance are compared to the one of a state-of-the-art commercial graphite-based battery.

As the era of electric vehicles arrives, it is necessary to develop li ion battery with high energy and power densities. Energy and power density, which are directly related to the performance of an electric vehicles and required by all electric devices. The commercial graphite anode li ion battery has limited gravimetric capacity of ~370 mAh g^-1, low charge rate and low retention stability due to the sluggish intercalation reactions during charging. Silicon are emerging as next-generation anode materials to solve these problems. Silicon has a high theoretical capacity (~ 4,200 mAh g^-1), which is ten times higher than commercial graphite anode materials. However it has a significant problem of stability due to the high expansion ratio (~ 400 %) and solid electrolyte interface that accompany the charging reaction. Silicon is classified as an alloy material that participates in direct bonding with li ions. Because of this, more than a certain amount of li ions are involved in the bonding with silicon, which causes expansion and pulverization at the same time. This is a typical retention stability degradation problem for silicon-based anode electrodes.
To avoid a degradation of a silicon anode for a lithium ion battery, we report new 2D multi-layered rGO/Si electrode prepared by a direct growth of Si into porous rGO film on current collector. The direct Si deposition method on the porous rGO film can intercalate Si layer into the rGO film by replacing oxygen related groups of GO with Si nanoparticles through in-situ thermal reduction of GO film. The thickness of rGO/Si thin-layered film can be controlled from a sub-nanometer to micrometer thickness Si electrode. Its rGO layers tightly hold Si layers and also were acted as a pre-volume against an expansion of Si layer with Li charging, leading to give a highly stable li ion battery. The 2D thin-layered film provided a short pathway for Li ion transport insertion and desertion process due to a nanometer thickness of Si and graphene. In addition, the 2D film gave a high conductivity even without binder and/or conductive agents, providing a high initial capacity of 2,978 mAh g ^-1 at 0.5C and a high reversible capacity at 0.5C (~ 1,791 mAh g ^-1 at 500 cycles).

In the past few years the lithium-ion batteries (LIBs) industry has expanded from consumer electronics to automotive industry. Lithium nickel manganese cobalt layered or NMC are state of the art cathode materials that have replaced the original lithium cobalt oxide cathode due to their promising high energy density. In NMC, Ni provides high capacity to the cathode material, while Co and Mn provide structure stability and safety over cycling. To further increase the energy density, current research is focused on nickel-rich oxides. The structure, morphology, and electrochemical performance of these oxides are highly dependent on the method of synthesis. Even slightest variations in the synthesis conditions can result in widely divergent characteristics when used as cathode material.
The presentation will discuss various reaction condition optimization for synthesis of NMCs like pH control, concentration of chelating and precipitating reagents and how does it affect the morphology and other properties of the material like tap density, electrochemistry and magnetic properties. In this work we have used Powdered X-ray Diffraction (PXRD), UV-Vis Spectroscopy, magnetic properties, Scanning Electron Microscopy (SEM) and tapped density to discuss various changes in physical and chemical properties of material with respect to reaction condition.

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

LiNi_0.5Mn_1.5O₄ cathode material which has a higher working voltage (4.8 v) and larger specific capacity (148 mAh/g) has been studied by high resolution transmission electron microscopy (TEM). The purpose of this work was focused on the battery failure mechanism through TEM observations and analysis of microstructural properties of LiNi_0.5Mn_1.5O₄ spinel material, meanwhile the samples before and after electrochemical cycling was compared. XRD and SEM/EDS were further used to evaluate the battery failure mechanism.

Comparing with fresh LiNi_0.5Mn_1.5O₄ particles before cycling, many LiNi_0.5Mn_1.5O₄ particles after cycling, which also called original single crystal grains, display a tendency of nano-polycrystalline. This kind of polycrystalline properties can be mainly represented by three major microstructural features in cycled LiNi_0.5Mn_1.5O₄ spinel material. First, many electron diffraction patterns that show FFT (Fast Fourier Transform) patterns got from TEM image area do not exhibit a regular single crystal diffraction pattern, but more complex patterns. 2^nd, lattice defects appeared in LiNi_0.5Mn_1.5O₄ particles, which are proved by lattice images and FFT patterns. And last major difference after cycling is that some smaller nano particles precipitated on the particle surface.

In order to compare and analyze LiNi_0.5Mn_1.5O₄ spinel material more efficiency, a detailed lattice structural model of spinel corresponding to the TEM lattice image and its FFT pattern is presented.

High capacity and cycling stability are two important key points in developing lithium-ion batteries. One of potential candidates as an anode material is MoO₃ is due to facile Li⁺ hosting in layered structure and thus resulting high theoretical capacity. Here, we present oxygen-vacancy-controlled MoO_3-x, where oxygen vacancies act as shallow donors and result improved electrical conductivity of the active materials. Without the use of additional binders and conductive materials, we were able to examine the Li-storage mechanism directly on MoO_3-x. We clearly demonstrate Li-storage capacity based on reversible formation/disruption of SEI films as an extra with the conjunction of Li ion intercalation as well as electrochemical reactions in the layered structures and surprisingly not resulting from the previously known conversion reactions in MoO_3-x. By conjugating the surface of MoO_3-x with Cu₂O via annealing process, we investigate the role of Cu₂O. According to our experimental results obtained by electrochemical analysis, ex-situ transmission electron microscopy and ex-situ X-ray absorption spectroscopy Cu₂O act as an effective catalyst for the formation of SEI films and reversible reaction of MoO_3-x with Li⁺ ions. As a result, Cu₂O@MoO_3-x exhibits a charge capacity of 1,100 mAh/g from the second cycle and maintains high reversible capacity, while MoO_3-x exhibits a charge capacity of 900 mAh/g and fades to 590 mAh/g for 100 cycles at 1 A/g. Cu₂O@MoO_3-x shows capacity of ~ 390 mAh/g at 10 A/g up to 1,000 charge/discharge cycles.

To date, nickel-rich cathode materials have been greatly developed by modification of surface and bulk morphology, structural design, and concentration gradients. However, the intrinsic problems originated from the morphological characteristics have not been completely prevented. The anisotropic expansion of each primary particles give rise to the morphological collapse upon the long-term cycling, resulting in a reaction inhomogeneity of the secondary particles.

Interestingly, we have investigated such reaction inhomogeneity induce the serious state-of-charge (SOC) heterogeneity in the thick electrode. We carried out 3-electrode full-cell test with an additional lithium metal electrode to track the LiNi_0.6Co_0.2Mn_0.2O₂ (NCM) cathode and graphite anode potential. These results show the cathode and anode potential steadily rise during the cycling at the high temperature of 45 °C. Noticeably, the cut-off potential was upraised from the 4.38 V to 4.47 V after 200 cycles, indicating that the additional lithium ions could be extracted from the cathode structure. We confirmed the potential was different according to the position in the thick electrode and the high potential distribution was concentrated on the surface particles from the Raman spectroscopy analysis using the cross-sectioned electrode. The Raman spectroscopy is a powerful and novel analysis tool for observing the degradation of metal oxide cathode materials in a microscale. The overutilization of the cathode particle in the surface accompanies severe morphological collapse with nickel dissolution, threatening the integrity of the graphite particles. In this regard, we suggest tuning the crystallinity of the NCM particles from the polycrystallinity to single grain. We intensively investigated the degradation mechanism of the single grain LiNi_0.8Co_0.1Mn_0.1O₂ and conventional NCM under the high temperature.

Research on “beyond lithium-ion” technology remains to be an ongoing challenge in identifying materials capable of reversibly storing multivalent ions, such as Mg²⁺, Ca²⁺, and Zn²⁺. For prospective Zn²⁺-based positive electrode materials, questions regarding the accommodation of Zn²⁺ remains largely unanswered. In the present study, we explore the charge-storage mechanism of a V-based Na⁺ superionic conductor (NASICON) framework, Na₃V₂(PO₄)₃ (NVP), by X-ray synchrotron characterization to unravel potential-dependent structure-property relationships. We ascribe the reversible electrochemical behavior of NVP cycled in a Zn²⁺-based electrolyte to a two-stage intercalation process involving both Na⁺ and Zn²⁺. The initial charging profile at C/20 indicates Na⁺ extraction from Na₃V₂(PO₄)₃ to NaV₂(PO₄)₃, observed by a single plateau in the galvanostatic charge/discharge profile, while subsequent discharge results in two plateaus corresponding to Na⁺, then Zn²⁺ insertion. Operando X-ray diffraction of the zinc-ion cells were collected to examine the changes associated with the first charge/discharge cycle, which showed reversible behavior based on shifts in X-ray reflections. To examine distinct changes linked with Na⁺ and Zn²⁺ two-stage intercalation process, electrodes were prepared ex situ for Rietveld refinement to understand variations in the crystal structure parameters. Furthermore, changes in V oxidation state, V-O coordination, and the presence of Zn²⁺ was studied by X-ray absorption spectroscopy. The results of this work present a thorough investigation of the multivalent charge-storage mechanism for a well-established NASICON framework, and may provide further insight into other related structures.

Potassium-ion battery (PIB) has recently attracted great attention, as a low-cost alternative to lithium-ion technology. PIB can be a high-voltage contender considering the significantly negative potential of the K⁺/K redox couple, which is close to or even lower than Li depending on the solvent [1]. Nonetheless, the large ionic radius of potassium coupled with significant strain accompanying potassium extraction / insertion, the number of potassium-based compounds (particularly, cathode materials) has greatly been undercut. In this work, we will highlight the electrochemical performance of honeycomb-based layered frameworks as potential cathode frameworks for rechargeable potassium-ion batteries [2].

References:
[1] Y. Marcus, Pure Appl. Chem., 57 (1985) 1129-1132.
[2] T. Masese, K. Yoshii, Y. Yamaguchi, T. Okumura, Z. –D. Huang, M. Kato, K. Kubota, J. Furutani, Y. Orikasa, H. Senoh, H. Sakaebe, and M. Shikano, Nat. Commun., 9 (2018) 3823.

Lithium–sulfur (Li–S) batteries are attracting substantial attention because of their high-energy densities and potential applications in portable electronics. However, an intrinsic property of Li–S systems, that is, the solubility of lithium polysulfide (LiPS), hinders the commercialization of Li–S batteries. Herein, a new material, that is, carbon nitride phosphorus (CNP), is designed and synthesized as a superior LiPS adsorbent to overcome the issues of Li–S batteries. Both the experimental results and the density functional theory (DFT) calculations confirm that CNP possesses the highest binding energy with LiPS at a P concentration of ∼22% (CNP22). The DFT calculations explain the simultaneous existence of Li–N bonding and P–S coordination in the sulfur cathode when CNP22 interacts with LiPS. By introducing CNP22 into the Li–S systems, a sufficient charging capacity at a low cutoff voltage of 2.45 V, is effectively implemented, to minimize the side reactions, and therefore, to prolong the cycling life of Li–S systems. After 700 cycles, a Li–S cell with CNP22 gives a high discharge capacity of 850 mAh g^–1 and cycling stability with a decay rate of 0.041% cycle^–1. A 4-stack pouch cell with a high-S-load of 6.1 mg cm⁻², which shows a capacity of 699 mAh g⁻¹ and CA of 93% after 74 cycles at 0.2 C. This is primarily ascribed to strong interactions between LiPS and CNP22, as well as a high S reutilization during cycling. The incorporation of CNP22 can achieve high performance in Li–S batteries without concerns regarding the LiPS shuttling phenomenon. The advantages of the Li–S cells with CNP22 are obvious, and therefore, CNP22 is a suitable material for constructing reliable Li–S batteries.

The challenges associated with integrating renewable resources, such as the intermittent solar and wind power, have placed substantial demands on the development of energy storage systems Sodium-based battery technologies that are economical (because Na is abundant) and have long cycle life are gaining importance especially for stationary energy storage applications. Intermediate-temperature Na batteries have demonstrated several advantages over their conventional high-temperature counterparts, including superior battery safety, lower operating temperature and manufacturing cost, potentially longer cycle life, and easier assembly. However, there is still a lack of cost-effective cathode materials with high energy density and rate capability suitable for large-scale applications. In this work, we will introduce some of our recent findings on advanced conversion-type cathodes for intermediate-temperature Na batteries with the emphasis on new cathode reaction mechanisms.

All-solid-state rechargeable batteries are expected to be used widely as post lithium-ion batteries. Recently, the ionic conductivity of the solid electrolyte has been dramatically improved to the similar order as organic electrolytes. However, to improve the performance of all-solid-state rechargeable batteries at the cell level, it is important to not only enhance the ionic conductivity of the solid electrolyte but also to understand the diffusion behavior of carrier ions in composite electrodes. Ion diffusion in composite electrodes is complicated during charging and discharging in all-solid-state rechargeable batteries. In the case of a liquid electrolyte using an organic solvent, the transport number is lower than 1.0[1], and it is known that ion concentration distribution is caused in the electrolyte[2, 3]. On the other hand, in principle, no ion concentration distribution occurs in the solid electrolyte since in the solid electrolyte, the transport number of carrier ions is approximately one. Therefore, it is considered that ion diffusion phenomena in solid electrolytes are different from liquid systems. Although ion diffusion in composite electrodes of bulk-type all-solid-state batteries proceeds through active materials and solid electrolytes, its diffusion path is very complicated, and its analysis is a challenge. Therefore, few observation examples of the dynamic behavior of carrier ions during the operation of the batteries have been reported. Another factor is that lithium ion, which is a general carrier ion, is a light element and it is difficult to detect the ions directly. In this research, as a model case of the all-solid-state rechargeable battery, the diffusion behavior in the composite electrode was directly observed by high energy synchrotron X-ray using the all solid secondary battery cell which uses silver ion as a carrier. Silver ion conductors have the advantage that solid electrolytes exhibiting high conductivity at room temperature have already been reported[4]. Also, silver ions are sensitive to X-ray. By using X-ray transmission imaging method with synchrotron X-ray with high transmittance, spatial resolution, and temporal resolution, the silver ion concentration distribution in the electrode during charging and discharging in the model battery was directly observed[5]. From the obtained results, the apparent diffusion coefficient in the composite electrode was calculated.
A silver-ion conductor, Ag₆I₄WO₄, was prepared as a solid electrolyte for all-solid-state silver battery. To observe the ion concentration distribution in the bulk-type all-solid-state rechargeable battery, an Ag | Ag₆I₄WO₄ | TiTe₂ cell was fabricated. Synchrotron X-ray radiography measurements were performed in SPring-8 (Hyogo, Japan). X-rays were irradiated during discharge with a constant potential at 72 mV, and transmission intensity was measured with a two-dimensional detector to obtain an image.
The apparent diffusion coefficient in the composite electrode was estimated from this imaging measurements. This result suggests that ion diffusion in the composite electrode governs the performance. Thus, it has been suggested that ion diffusion in the composite electrode is important at a scale of hundreds of microns of the actual electrode thickness.

References
[1] A. Nyman, M. Behm, and G. Lindbergh, Electrochim. Acta, 53, 6356 (2008).
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Advanced, next-generation lithium batteries play a key role in the market penetration of electrochemical energy storage systems that will boost the progress of sustainable alternative sources of energy and transport. The emerging flow lithium batteries (FLBs) are attracting great interest thanks to the combination in a unique solution of the high specific energy of lithium batteries and the design flexibility of redox flow batteries that, in turn, allow to decouple energy and power.
Different kinds of FLBs have been proposed, such as batteries featuring semi-solid anolytes and/or catholytes with Li-ion intercalation powders, such as LiFePO₄ or Li₄Ti₅O₁₂, dispersed in organic electrolyte, and Li/S, Na-ion and Li/O₂ flow batteries. However, advancements in materials, cell design and concepts are still mandatory to achieve the leap forward in next battery generation.
BETTERY is an Italian Innovative Startup that aims to bring into market a radically new battery concept, i.e. NEw Semi-Solid flow lithium OXygen battery (NESSOX) that combines the high energy density of Li/O₂ batteries with the flexible and scalable architecture of redox flow batteries. NESSOX, featuring a lithium metal anode and a semi-solid, flowable catholyte, displays the highest practical specific energy and energy density ever reported, up to 500 mWh cm^-2, allowing to extend the drive range of electric vehicles to consumer acceptable values. The flowable nature also permits a breakthrough in the battery field thanks to the fast recharge by “catholyte refueling”.
The main technology challenges faced by BETTERY to bring NESSOX into market are here presented and discussed.

Acknowledgements
The Authors would like to thank for financial support H2020 SME Instrument Phase 1, EIT Raw Materials Battery Challenge 2019, Climate-KIC Startup Accelerator Italy 2018, Stage 1 and Stage 2, The Gaetano Marzotto ‘Company Idea’ Prize (2018), PNI Cube 2017.

References
[1] I. Ruggeri, C. Arbizzani, F. Soavi, Electrochim. Acta 206 (2016) 291.
[2] F. Soavi, C. Arbizzani, I. Ruggeri, Semi-solid Flow Li/O₂ Battery. WO2017021840A1, 2017.
[3] M. Park, J. Ryu, W. Wang, J. Cho, Nature Reviews Materials 2 (2016) 16080.
[4] K. B. Hatzell, M. Boota, Y. Gogotsi, Chem. Soc. Rev. 44 (2015) 8664.
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Hole-rich carbon shells containing Iron(II) oxide (Fe₂O₃@NHC) were fabricated and exploited as electrocatalysts for rechargeable Zn-air battery. Fe₂O₃ particles were firstly synthesized by a hydrothermal reaction of Iron(III) nitrate, followed by wrapping glucose on the particles. The resulting glucose-coated Fe₂O₃ particles were annealed with urea to incorporate nitrogen on the carbon sp² structure, and then etched by hydrogen peroxide to form hole-rich structure. The formation of Fe₂O₃@NHC was confirmed by some analysis including HR-TEM, XPS, Raman and BET. The Fe₂O₃@NHC exhibited high specific surface area and high electrochemical surface area (ECSA) due to its hole-rich structure and incorporated N species. The electrocatalytic activity of the Fe₂O₃@NHC was confirmed by rotating ring disk electrode (RRDE). The Fe₂O₃@NHC exhibited outstanding oxygen reduction and evolution reaction activities in alkaline condition, which were comparable to noble-metal based catalysts. When the Fe₂O₃@NHC was used as a catalyst for the cathode of Zn-air battery, the battery showed outstanding energy density and good charge-discharge cycle stability. Therefore, the excellent catalytic activity and stability of Fe₂O₃@NPCs make them promising catalysts for rechargeable Zn-air battery.

Commercialized lihtium ion batteries(LIB) have applicated on electric vehicle running over 300 miles, but there is still a hazard of flammability due to liquid based electrolyte. Therefore, many researchers have been trying to ensure safety issues of flammable accident from liquid electrolyte. Solid electrolyte (SE), especially sulfide based SE, is expected that ionic conductivity in all-solid-state batteries (ASSBs) could catch up with liquid electrolyte level in LIB. Among the various sulfide-based SE, Li₆PS₅Cl (LPSCl) have been considered as promising SE because of its low cost, relatively stable with conventional cathode, and high ionic conductivity (1.3x10^-3 S cm^-1) at room temperature[1].
Average capacity have 140 mAh g^-1 using LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) active material as cathode and LPSCl as SE. However, the electrochemical performance of pellet-type cell consisting of NCM523 composite cathode/LPSCl/Indium foil shows that the capacity is rapidly decreased after 20 cycles, and the capacity retention falls down below 50% within 50 cycles. Janek’s group reported a side reaction of carbon-containing cathode composite which accelerates the oxidation of sulfide-based SE on cathode surface[2].
In this study, interestingly, we figured out that declined lifetime of cell is originated from not only side reaction in which an electrolyte is decomposed at interface between NCM523 active material and LPSCl but also cathode deterioration due to NCM523 phase transition. In particular, TEM analysis revealed that the Ni/Li cation mixing resulting in phase transition from layered R(-)3m phase to the spinel phase Fd(-)3m, and this result could be supported by confirming the change of Ni oxidation states analyzed by XANES. From above analysis, the similar mechanism as LIB has been observed to cause cathode deterioration, and we will discuss further more in detail which system is occurred the deterioration more quickly and what the reason is.
Reference
[1] C. Yu et al., Electrochimica Acta 215 (2016) 93–99
[2] W. Zhang et al., ACS Appl. Mater. Interfaces 2017, 9, 35888−35896

NMC811 (Ni_0.8Mn_0.1Co_0.1O₂) is a cathode material of significant commercial interest for next generation lithium ion batteries due to its higher capacity and lower cost compared to current LiCoO₂ cathodes (200mAh/g vs 140mAh/g). However, in the highly charged state (V > 4.3V vs Li/Li⁺), side reactions between high valence nickel and electrolyte jeopardize prolonged usage and stability. In this work, we address these issues by utilizing an industrially viable coprecipitation process to apply a chemically stable Mn_0.9Co_0.1O₂ spinel coating to protect the NMC material. After forming the metal hydroxide precursor, dilute solutions of manganese and cobalt sulfate are added in order to encourage coating formation while preventing supersaturation and the subsequent precipitation of separate crystals. The thin Mn_0.9Co_0.1O₂ spinel coating formed post-sintering is observed to improve capacity retention during electrochemical cycling at an upper voltage cutoff of 4.5V and at elevated temperatures of 55°C. In addition, electrochemical performance at high charge/discharge rates surpasses that of MnO₂-coated NMC811. The results suggest a method for an industrially viable process to synthesize and stabilize Ni-rich cathodes for improved lithium-ion batteries.

As demands for electric vehicles (EV) and mobile electronics are increased, energy storage device becomes important. Lithium ion Battery (LIB), currently one of the most promising solution to EV, has critical issue in terms of fast charging problem. Graphite material, currently used as anode materials for LIB, has prominent limitation in term of high rate capability. To overcome this limitation, many materials have been researched for alternative of commercialized graphite material. Herein, we prepared tungsten oxide coated graphite by facile sol-gel reaction. the prepared tungsten oxide coated graphite showed enhanced the high rate capability of LIB. Without any reversible capacity fading, the tungsten oxide coated graphite anode electrode showed an outstanding rate capability of 90.28 % of the capacity retention at a rate of 5C (1800 mA g^-1) compare to that tested at a rate of 0.2C (72 mA g^-1). In further characterization, microstructure and electrochemical performance of the tungsten oxide coated graphite will be discussed in more detail.

Currently, lithium cobalt oxide cathodes have been extensively used in personal electronic devices due to their light weight and high energy density. However, the high cost of cobalt due to its decreasing available resource limits its application in electric vehicles manufactures. We synthesized quaternary cobalt-free amorphous alloys through a high-throughput robotic synthesis system with machine learning. The amorphous materials promise high structural flexibility for tuning and a less-energy-intensive production. The sol-gel synthesis enabled us to obtain multicomponent homogeneous amorphous alloys. The properties of materials were easily tuned by adjusting procurers’ ratio, temperature, reaction time. The combination of high-throughput synthesis with machine learning helped us to avoid the guess-and-check method and fastened the research. Theoretical modelings revealed the working mechanism of amorphous materials. We obtained quaternary amorphous cathode with unprecedented performance while avoiding undesirable toxic or expensive components.

Alkali metal-ion batteries using metal anodes (Li, Na, K) are attractive because of their high specific capacities and low voltages. However, these anodes suffer from the dendrite growth issue, which causes short-circuiting of the cells and might lead to their ignition and even explosion. Recently, it has been proposed to use dendrite-free anodes based on potassium-sodium alloys (PSAs), which are liquids at temperatures down to −12.6 °C. However, there are no reports where asymmetric cells with PSA-based anodes show stable operation for >1000 charge-discharge cycles. This is likely due to the relative instability of the cathodes that have been utilized in these cells.
Here we developed a cell with the PSA-based anode and an organic polymer cathode, which is a derivative of hexaazatripenylene. The selected cathode material ensures excellent stability over >10000 cycles at 10 A g⁻¹ (>70 C rate, specific capacity 135 mA h g⁻¹) with 88% capacity retention after 10000 cycles. In addition, the organic cathode demonstrates exceptionally fast redox kinetics, showing the discharge capacity of 60 mA h g⁻¹ at 50 A g⁻¹ (>800 C rate), which is ~30% of the capacity reached at a relatively low current density of 0.2 A g⁻¹.

Li-ion batteries (LIBs) are one of the promising energy storage devices with diverse applications in portable devices, Electric Vehicles (EVs), Hybrid Electric Vehicles (HEVs) due to their impressive energy density and cycle life. However, the issues like abnormal temperature inside the LIBs leads to thermal runaway, material degradation, capacity fading and hence the performance deteriorates. In this work we have incorporated finite element method (FEM) based technique to couple thermal and electrochemical model in the battery electrode for safety and reliability. The FEM model explains about the quantification of heat generation inside the battery pack by integrating convection forced air cooling with the battery pack to maintain the temperature of the battery pack within the safety limits. Consequently, this model is tested with a real-time system for the superior battery health and performance.

Silica fume is an industrial by-product or solid waste of the manufacture of silicon metal and ferrosilicon alloys, which is collected from the smoke dust of electric arc furnaces. When the smelting temperature reaches 1700 °C or more in the electric furnace, bits of silicon reacts with oxygen in the air to form silicon monoxide, which can be further oxidized to silica. After cooling, silica fume is obtained by collecting the fine spherical particles via a dust collector. Recently, silica fume has been widely used as the admixtures to product concrete and cement. However, exploring high value-added utilization from silica fume is still expected for silicon smelters.

In this work, we synthesized a novel structural microspheres consisting of cross-linked CNT, porous Si/SiO_x nanoparticles, CNT, and carbon coating (CNT/SFDP-Si/SiO_x@C microspheres) by combining an inverse water-in-oil microemulsion approach with magnesiothermic reduction, in which silica fume, an inexpensive industrial by-product, is used as the porous Si precursor. The CNT/SFDP-Si/SiO_x@C microspheres features a unique secondary structure, providing multiple significant advantages for solving the problems associated with Si. (I) the nanosized primary particle size prevents fracture; (II) the internal luxuriant voids offer enough space for the expansion of Si; (III) the the internally and externally wired CNT construct a long distance electrically conductive networks and a electrical fast track to reinforce electron transport and acts as a structure protector to keep stability of the secondary microspheres without been destroyed; (IV) carbon exhaustively coats the outerface of the microspheres and inner nanosized Si particles, reducing SEI formation and retains the internal void space for silicon expansion; and (V) the space-efficient packing inside the secondary particles the micron-sized secondary microspheres possess low surface area and high tap density.

Thus, the CNT/SFDP-Si/SiO_x@C microspheres displays stable capacities of 576.2 mAh g^-1 at 2 C over 1000 cycles. The excellent electrochemical performance of CNT/SFDP-Si/SiO_x@C microspheres manifests its supremacy as widespread anode material for both LIBs.

Zinc metal anode possesses 3 times the volumetric capacity of Li metal anode, is compatible with non-flammable aqueous electrolyte, and remains on the same side of separator when discharged to ZnO in alkaline electrolyte. Indeed, primary zinc-air batteries have long been used for electronic devices requiring extremely high energy density (e.g. hearing aid). However, rechargeable zinc-air batteries have not been successful, preventing their entrance into larger markets such as electric vehicles, data center UPS, and indoor machinery. In this presentation, I will show my lab’s recent efforts towards making deeply (100% depth of discharge) rechargeable zinc-based batteries, via nanostructured material design. This presentation is based on the following six recent publications from my lab:
1. Nanoscale Design of Zinc Anodes for High-Energy Aqueous Rechargeable Batteries. Materials Today Nano 2019, 6, 100032.
2. Graphene oxide-modified zinc anode for rechargeable aqueous batteries. Chemical Engineering Science 2019, 194, 142-147. (Cover article)
3. Ion-sieving carbon nanoshells for deeply rechargeable Zn-based aqueous batteries. Advanced Energy Materials 2018, 8, 1802470.
4. A deeply-rechargeable zinc anode with pomegranate-inspired nanostructure for high-energy aqueous batteries. J. Mater. Chem. A 2018, 6, 21933-21940. (Included in “2018 Emerging Investigators” themed collection)
5. A Lasagna-inspired Nanoscale ZnO Anode Design for High-energy Rechargeable Aqueous Batteries. ACS Appl. Energy Mater. 2018, 1, 6345-6351.
6. Sealing ZnO nanorods for deeply rechargeable high-energy aqueous battery anodes. Nano Energy 2018, 53, 666-674.

Enabling the stable cycling of Li metal at rates and other metrics of practical significance is a key route to substantially increase the energy content of Li-based batteries beyond present Li-ion technology. Therefore, a careful analysis of lithium plating stability across a range of conditions and materials platforms is essential to understand and quantify the processes that lead to lithium growth through a separator and subsequent cell shorting. This talk will provide an overview of the current state of understanding of lithium plating stability, with a focus on both modeling and experimental methodologies. Emphasis will be placed on solid electrolyte systems, along with current gaps in knowledge and experimental validation of plating stability hypotheses. A number of practical issues and perspectives gained from the time the author served as a Program Director at ARPA-E working in the area of lithium metal batteries will also be included.

With the increasing demand for electric vehicles, there is an urgent need for Li-ion batteries (LIBs) with extreme fast charging (XFC) capabilities. A major challenge in such batteries is retention of battery capacity over cycling under XFC conditions when recharging times are comparable to traditional refueling times. Current literature states parasitic Li plating on the anode is the major factor contributing to decreasing battery capacity and therefore shortened battery life [1]. However, the techniques used for understanding Li plating under in situ conditions has primarily involved characterization of Li by averaging over entire specially built cells [2].

While this approach provides a good staring point, the plating process is expected to be heterogeneous across the cell. Therefore, we use X-ray diffraction to:
1. Study the spatial heterogeneity in Li plating across a full pouch cell at various length scales.
2. Correlate the total amount of plated Li to the capacity loss of the cell during cycling.
The non-destructive nature of X-ray based techniques enables characterization of the Li plating across multiple length scales on the same cell. Towards this, single layer pouch cells (4cm x 6cm) with a porous graphite anode, NMC (LiNi_xMn_yCo_zO₂) cathode and an EC:MC electrolyte were charged at different rates within the XFC regime and characterized using high energy x-rays.

At the mm-scale, powder diffraction was used to study the spatial heterogeneities and correlations between various species at the cell level.
The analysis showed that the intensity of plated Li was directly correlated to the intensity of Li-graphite staged phases (Li_xC), even after discharging. These Li-rich regions in the cell also corresponded directly to depleted anode (reduced graphite intensities), irrespective of the charging rate and regime. Additionally, the regions showing high Li intensity were analyzed for the orientation spread of plated Li. At the end of 450 cycles, the plated Li shows a random polycrystal orientation, without any direct evidence of a preferential texture, as suggested by some earlier studies [3]. Finally, the persistence of Li plating with increased number of XFC cycles as well as the effect of the cycling rate were examined in detail at the cell level. At the microscale, microdiffraction was used to study regions with significant Li plating, as found from the mm-scale scans. Such microscale analysis yields the size of plated Li crystallites as well as the local orientation/texture of plated Li, as a function of the charging rate and capacity fade.

The understanding gained from this study provides foundational knowledge of the conditions that promote and those that minimize parasitic Li plating. Based on this knowledge, parameters such as the XFC charging rate, charging protocol, electrolyte composition and anode architecture can be optimized, such that parasitic plating is minimized. This optimization will in turn help to guide the rational design of the next generation of XFC capable LIBs with a consistent performance.

[1] W. R. Brant, D. Li, Q. Gu, and S. Schmid. Comparative analysis of ex-situ and operando x-ray diffraction experiments for lithium insertion materials. Journal of Power Sources, 302:126–134, 2016.
[2] W. Li, U.-H. Kim, A. Dolocan, Y.-K. Sun, and A. Manthiram. Formation and inhibition of metallic lithium microstructures in lithium batteries driven by chemical crossover. ACS nano, 11(6):5853–5863, 2017.
[3] F. Shi, A. Pei, A. Vailionis, J. Xie, B. Liu, J. Zhao, Y. Gong, and Y. Cui. Strong texturing of lithium metal in batteries. Proceedings of the National Academy of Sciences, 114(46):12138–12143, 2017.

Inactive lithium (Li) formation is the immediate cause of capacity loss and catastrophic failure of Li metal batteries (LMBs). Differentiating and quantifying the Li⁺ in solid electrolyte interphase (SEI) components and the unreacted metallic Li, which together comprise the inactive Li, is the key to understanding the mechanisms leading to capacity decay. However, this has not yet been successful due to the lack of effective diagnosis tools that can accurately differentiate Li⁺ in SEI and the unreacted metallic Li. Here, by establishing a new analytical method, Titration Gas Chromatography (TGC), we accurately quantify the contribution from unreacted metallic Li to the total amount of inactive Li. We identify the unreacted metallic Li, rather than the (electro)chemically formed Li⁺ in SEI, as the dominating cause for the inactive Li and capacity loss in LMBs, clearing the long-term misconception in the field that the low CE is caused by the continuous repairing of SEI fracture. Using cryogenic electron microscopies to further reveal the micro- and nanostructure of inactive Li, we identified two ways for deposited metallic Li to lose electronic connections with the bulk electrode, thus becoming electrochemically inactive. Coupling the quantification of the global content of inactive Li to observations of its local atomic structure, we reveal the formation mechanism of inactive Li in different types of electrolytes, and determine the true underlying cause of low CE in Li metal deposition and stripping. We ultimately propose strategies for highly efficient Li deposition and stripping to enable Li metal anode for next generation high energy batteries.

Visualization of ion transport in electrolyte provides fundamental understandings of electrolyte dynamics and electrolyte-electrode interaction, shedding light on material designs to enhance device performance, such as batteries and fuel cells. However, this task is extremely challenging for existing techniques, since it is difficult to capture the low ionic concentration (<1 M) and the fast dynamics (1-10 s) of the electrolyte. Here we show that an emerging Stimulated Raman Scattering (SRS) microscopy offers the required spatial (sub-micrometer optical resolution), temporal (faster than 1 s per frame) and chemical (around mM) sensitivities to address this challenge.

The SRS microscopy has been used to study ion depletion and lithium dendrite growth in both liquid and polymer electrolyte, and distinct behaviors are observed. In liquid electrolyte, we observe a three-stage lithium deposition process, each corresponding to no-depletion, partial-depletion and full-depletion regime of Li⁺, respectively. A positive feedback mechanism between the inhomogeneous growth of lithium and the local ionic concentration or flux. In polymer electrolyte, we clearly see phase separation due to ion depletion and observe the accompanying transport of plasticizer inside, which was not observed in the past. These new understanding also leads to new strategies to suppress lithium dendrites. This study shows that SRS microscopy is a powerful technique for imaging ion transport and will open various applications in materials and energy fields.
References:
1. Qian Cheng et al., Operando and three-dimensional visualization of anion depletion and lithium growth by stimulated Raman scattering microscopy, Nature Communications 9, Article number: 2942 (2018).

Highly emerged electric vehicle (EV) market evokes the demands on advanced batteries with high energy density. Li-metal batteries, including Li-NMC and Li-S, have been recognized as promising candidates beyond conventional Li-ion for next generation EV application. However, besides the energy density, automotive industry has other critical requirements on specific parameters. In this talk we will first present the requirements for future electrical vehicle application and the impact of high energy density Li-metal batteries on automotive industry. Some recent development on Li-NMC and Li-S batteries will be reviewed. The concerns and challenges of using Li metal as anode in batteries will be discussed. Moreover, we will also compare the difference of Li-NMC and Li-S in the EV applications and their specific challenges. Lastly, we will introduce some strategies on how to solve these challenges from both materials and cell levels, and also show some of our recent progress on Li-metal batteries.

Interfacial stability is critical to the performance of solid-state batteries. Various promising solid electrolytes are unstable with either cathode or anode, such as sulfide electrolyte / LATP / LAGP with lithium metal, and polyethylene oxide (PEO) electrolyte with 4 V layered oxides. Such incompatibility limits the performance and commercialization of solid state batteries. In this talk I will present recent studies on improving interfacial stability of LATP/Li and 4 V cathode/PEO interface. At the LATP/lithium interface, a nanoscale boron nitride coating blocks electron transfer and can significantly enhance the stability between LATP and lithium. Long cycle life of 500 cycles is achieved in LiFePO4/LATP/BN(PEO)/Li cells. On the other side, we also enhance the stability between 4 V cathode and PEO electrolyte by surface modification. Long cycle life of 400 cycles is achieved, much better than previous reports.
References:
Qian Cheng, Aijun Li, Yuan Yang et al., Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating, Joule 2019.

The conduction mechanism and electrochemical stability of closo-borates, a particularly promising class of solid-state electrolytes for all-solid-state batteries [1,2], is investigated. We find from electrochemical impedance spectroscopy that the temperature dependent conductivity is characterized by three distinct regimes of conductivity. In the lowest temperature regime, conductivity remains low before a glass-like transition identified by X-ray diffraction and calorimetry causes a faster increase of cation conductivity through site disordering. Correlated ion diffusion evidenced by nuclear magnetic resonance originates from the coupling of the cation and anion motion due to short-range ion-ion interactions combined with background energy fluctuations, which we can associate through quasi-elastic neutron scattering experiment to fast librations of the anions. In the third regime, the thermal energy increases above the background energy fluctuations resulting in non-correlated ion diffusion.
I will further discuss recent progress in the fabrication of all-solid-state batteries based on closo-borate electrolytes and strategies to increase the electrochemical stability to enable a 4 V all-solid-state battery class bringing closo-borate-based all-solid-state batteries to a technology readiness level comparable to that of sulfide-based all-solid-state batteries.

[1] L. Duchêne, S. Lunghammer, T. Burankova, W.-C. Liao, J. P. Embs, C. Copéret, H. M. R. Wilkening, A. Remhof, H. Hagemann, C. Battaglia, Chem. Mater. 2019, 31, 3449
[2] R. Asakura, L. Duchêne, R.-S. Kühnel, A. Remhof, H. Hagemann, C. Battaglia, submitted

Advances in hybrid and electric technologies combined with a demand for green initiatives have motivated recent diversification in energy storage research for automotive electrification. To meet customer expectations for hybrid and electric vehicles, furthering the capability of existing battery systems remains critical. As such, new battery systems with higher energy density, power density and cycle life than the state-of-art Lithium (Li)-ion battery are needed. Post Li-ion battery systems, especially those focused on the utilization of Li metal have recently come to the forefront of research. The ability to directly utilize Li metal anodes in rechargeable batteries presents itself as an ideal, albeit challenging, situation. Li metal anodes could provide a maximum possible theoretical specific capacity (3860 mAh/g) in comparison to commercially used anodes (e.g. graphite – 380 mAh/g). Hence, significant efforts in recent literature have targeted the development of robust systems, capable of use with Li metal.
One such system is Li-sulfur which has attracted attention due to its high theoretical capacity (1673 mAh/g) and potential low cost. However, this system is hindered by polysulfide dissolution and electrolyte decomposition at the Li metal anode. Among the various strategies which have been employed to overcome such hurdles, the use of solid-state electrolytes (inclusive of polymers, gels and conducting ceramics) stands out, as the implementation of solid-state electrolytes can also serve as a mechanical barrier towards Li dendrite formation. However, these electrolytes exhibit relatively lower ionic conductivities and display poor interfacial stability towards Li metal anodes. While advances in solid-state electrolyte materials continue to improve their ionic conductivities, little is known about the interfacial interactions between sulfide-based solid-state electrolytes and Li metal which can greatly affect their electrochemical performance. Hence, studies into understanding the relationship properties between Li metal and these solid-state electrolytes is essential towards realizing a sulfide-based all-solid-state Li battery.
Here, we present the electrochemical properties of various sulfide-based solid-state electrolytes in contact with Li metal. Further, we present tandem analytical ex-situ and in-situ studies via transmission electron microcopy and X-ray tomography to reveal the interfacial interactions between Li metal and solid-state electrolytes, the deposition and dissolution properties of Li metal from these electrolytes, and the effects of the deposition and dissolution properties on the bulk electrolyte structure. The presented studies allow for comparisons of Li deposition and dissolution properties below and above the critical current densities for each solid-state electrolyte material and stand to help clarify both interfacial and morphological evolution mechanisms during Li cycling from them.

With wide liquid range, negligible vapor pressure, strong designability, high thermal and electrochemical stability, ionic liquids (ILs) are almost the ideal candidate for safe electrolyte in lithium ion or lithium metal batteries. While for one thing, most ILs are highly viscos, which may possibly reduce the electrolyte conductivity; and for the other, ILs are composed of large cations and ions, complicated interaction with lithium salt usually lead to reduced Li ion transference number (t_Li+). As a result, in spite of all the fascinating characteristics, most IL electrolytes still show limited conductivity and t_Li+, which hinder them far from application.^[1-3]
Combining the concept of ionic liquid and nanostructured materials, nanostructured ionic liquids (NIL) is a new type of matter that possess the properties of both IL and nano materials. By tethering IL structure onto nano particles such as SiO₂, Al₂O₃, we prepared several NILs and use them in lithium sulfur flow battery^[4], electrospun nano fiberous separator^[5], as well as electrolyte additive, we found that the NILs could increase the t_Li+ by anchoring the cation, and its strong interaction with anion could further regulate the transport of anions, on which enhanced electrochemical performance could be obtained.

[1] D.R. Macfarlane, N. Tachikawa, M. Forsyth, J.M. Pringle, P.C. Howlett, G.D. Elliott, J.H. Davis, M. Watanabe, P. Simon, C.A. Angell, Energy Environ. Sci. 7 (2014) 232-250.
[2] M.V. Fedorov, A.A. Kornyshev, Chem. Rev. 114 (2014) 2978-3036.
[3] Y.-S. Ye, J. Rick, B.-J. Hwang, J. Mater. Chem. A 1 (2013) 2719-2743.
[4] S. Xu, Y. Cheng, L. Zhang, K. Zhang, F. Huo, X. Zhang, S. Zhang, Nano Energy 51 (2018) 113-121.
[5] Y. Cheng, L. Zhang, S. Xu, H. Zhang, B. Ren, T. Li, S. Zhang, J. Mater. Chem. A 6 (2018) 18479-18487.

While inorganic nanoparticles have received great attention for solid-state lithium metal battery applications, rather less interest has been paid to all-polymeric nanoparticles despite the availability of easily up–scalable polymerization techniques for the synthesis of nanoparticles with functionalized surfaces. In this work, we report composite electrolytes based on all-polymeric methacrylic sulfonamide nanoparticles designed to provide transference numbers close to unity. Mixing the particles with conventional electrolytes, such as poly(ethylene oxide) or propylene carbonate, we obtained mechanically robust nanocomposite electrolytes with storage moduli values as high as 10⁶ Pa and ionic conductivity values up to 10^–4 S cm^–1. The comparison of lithium dynamics and mechanical properties suggest decoupling of these two antagonistic properties in our nanocomposite electrolytes. Pulsed–field gradient NMR showed that the mobility of lithium–ions exceeded by several orders of magnitude the mobility of the sulfonamide anions tethered to the particle surface. Finally, the electrochemical performance of symmetrical lithium cells are presented, showing promising results. Our findings suggest that all-polymer nanoparticles could represent a paradigm shift for solid-state lithium metal battery applications.

All-solid-state lithium (Li) metal batteries (LMBs) are considered good candidates for the next generation power sources because of their excellent safety compared to the liquid electrolyte-based batteries. However, the poor interfaces between the inorganic solid electrolyte and the two electrodes (cathode and anode) make the practical applications of all-solid-state inorganic batteries very challenging. Polymer electrolytes are more promising in processability due to their flexible characteristics. Polyethylene oxide (PEO) is the most widely studied polymer in Li metal polymer batteries (LMPBs). Nevertheless, the performance of conventional LMPBs remain limited by the poor room-temperature ionic conductivity of the PEO-based electrolytes. Conversely, the low oxidative resistivity of ethylene oxide (EO) segments (< 4 V vs. Li/Li⁺) of PEO restricts the utilization of 4 V class cathode materials in LMPBs, resulting in a low energy density of the batteries. Therefore, developing high voltage all-solid-state LMPBs is of high significance. In this work, polymer-in-salt electrolytes (PISEs) were developed by mixing PEO and lithium bis(fluorosulfonyl)imide (LiFSI) at high Li⁺/[EO] ratios. The optimal PISE exhibited a high oxidation voltage (4.38 V vs. Li/Li⁺ on Al) and moderate conductivity (0.07 and 0.27 mS cm^-1 at 60 and 80 °C, respectively). The all-solid-state Li|PISE|LiNi_1/3Mn_1/3Co_1/3O₂ cells were evaluated with a high cut-off voltage up to 4.4 V. Additional details will be reported during the 2019 Fall Materials Research Society (MRS) Meeting & Exhibit and ensuing presentation.


Acknowledgement

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, the Advanced Battery Materials Research (BMR) Program of the U.S. Department of Energy (DOE) under contract no. DE-AC02-05CH11231.

With an increase in demand for high energy dense storage devices for electric vehicles or intermittent energy sources, comes an increase for the need for efficient processing of materials that lead to safe and optimal-performing batteries. Safety can be enhanced with the incorporation of solid-state materials whereby an ion-conducting polymer matrix is established through the mixing and coating process of an electrode. These ion-conducting pathways are heavily dependent on the starting material sizes, the composition of the electrode, as well as the type of mixing profiles that are implemented. The efficacy of these ion-conducting pathways are quantified systematically from SEM images using existing computer packages in order to understand the best set of conditions that can lead to high-performing electrodes for safe solid-state lithium ion batteries.

Polymer electrolytes are considered to play a decisive role for the realization of safer rechargeable batteries and may, additionally, allow for the employment of lithium metal anodes, thus, paving the way for significantly higher energy densities.^[1,2] Beside mechanical strength, especially three characteristics appear to be of paramount importance: (i) Single-ion conduction to prevent the reversed cell polarization, negatively affecting the long-term cycling stability, (ii) suitable ionic conductivities at ambient temperature, and (iii) a homogeneous lithium deposition upon charge to avoid the dendritic metal deposition.^[2,3] While (i) has successfully been addressed already in literature, commonly by covalently tethering the anionic function to the macromolecular backbone,^[3] (ii) appears to be intrinsically limited by its dependency on the segmental relaxation of the polymer.^[4] Remarkably, the key to overcome the conductivity limitation and simultaneously address also (iii) may rely on introducing structure into polymer electrolytes.^[5,6]
Starting from a brief review, covering early and very recent work, selected strategies for this general approach will be highlighted. A particular focus will be set on fundamental insights into the charge transport mechanism and how this translates into enhanced electrochemical properties as well as selected results for high-energy lithium batteries comprising Ni-rich Li[Ni_1-x-yMn_xCo_y]O₂ cathodes – a cathode material that had commonly been considered incompatible with any polymer electrolyte due to its challenging interface chemistry.

References
[1] J. Kalhoff, G. G. Eshetu, D. Bresser, S. Passerini, ChemSusChem 2015, 8, 2154.
[2] D. T. Hallinan, N. P. Balsara, Annu. Rev. Mater. Res. 2013, 43, 503.
[3] H. Zhang, C. Li, M. Piszcz, E. Coya, T. Rojo, L. M. Rodriguez-Martinez, M. Armand, Z. Zhou, Chem. Soc. Rev. 2017, 46, 797.
[4] M. A. Ratner, P. Johansson, D. F. Shriver, MRS Bull. 2000, 25, 31.
[5] H.-D. Nguyen, G.-T. Kim, J. Shi, E. Paillard, P. Judeinstein, S. Lyonnard, D. Bresser, C. Iojoiu, Energy Environ. Sci. 2018, 11, 3298.
[6] D. Bresser, S. Lyonnard, C. Iojoiu, L. Picard, S. Passerini, Mol. Syst. Des. Eng. 2019, DOI: 10.1039/c9me00038k.

To reach a step change in energy density of rechargeable batteries new chemistries need to be considered as the current state-of-the-art, the Li-ion battery, is approaching its theoretical limit. Among potential chemistries for next generation batteries the LiS-battery has for some time been highlighted as one of the most promising. The interest stems from the high specific capacity of the reaction between Li and S and a theoretical energy density of a LiS-cell up to five times higher than current Li-ion technology. In addition, sustainability is more and more at focus in battery technology and being based on abundant materials LiS-technology has also the potential radically improve this aspect.

Despite the very promising characteristics LiS-technology has so far not been realized in large scale applications due to problems involving low utilization of active material, low practical energy density, slow kinetics resulting in poor rate capability, and capacity fading. Most of the problems are directly related to the conversion reaction between Li and S where polysulfide intermediates (Li₂S_n), which are soluble in many of the common battery electrolytes used, are produced. Whereas the solubility of polysulfides can be a problem in terms of loss of active material and side reactions if they migrate out of the cathode, it is also a prerequisite in order to have high active material utilization and fast kinetics. Thus, the key is to manage polysulfide dissolution, rather than preventing it, to prevent side reactions on the anode (most commonly Li-metal) and to maximize the fraction of active material in the cell, i.e. minimizing the amount of electrolyte as well as inactive components such as binders and conducting agents. New materials concepts are needed both for the electrode and the electrolyte in order to achieve this. Recently there has been considerable progress with the development of nanostructured and functionalized carbon structures on the cathode side as well as functional separators and new electrolytes.

In this contribution we present new materials concepts based on the use of self-supporting carbon structures and the use of catholytes, where a part of, or all, active material is dissolved in the electrolyte [1-3]. Carbon nanofiber membranes and self-standing graphene-based aerogels can be used directly as electrodes, without further processing or the addition of conducting agent, binders or metal current collector, thus maximizing the amount of active material in the cell [2-3]. The performance of these materials will directly depend on their nanostructure (surface areas, pore size and pore distribution) and on presence of functional groups being able to interact with the dissolved polysulfides. With a catholyte, on the other hand, we can both increase the amount of active material in the cell as well as help forming a stable interphase on the Li-anode [4]. We show that by these routes high practical energy density, high sulfur utilization, and stable cycling can be obtained in cells with high sulfur loading and very low amount of electrolyte. We also present result from operando experiments (Raman spectroscopy and x-ray imaging) where we directly follow the processes taking place during discharge and charge, as well as from complementary ex-situ techniques, in order to understand the reaction mechanism in these systems.

References
[1] M. Agostini, D-H. Lim, M. Sadd, J-Y. Hwang, S. Brutti, J. Heo, J-H. Ahn, Y-K. Sun, A. Matic, ChemSusChem 17, 2981 (2018)
[2] M. Agostini, J-Y. Hwang, H-M. Kim, P. Bruni, S. Brutti, F. Croce, A. Matic, Y-K. Sun, Adv. Energy. Mat. 1801560 (2018)
[3] C. Cavallo, M. Agostini, J. Genders, M. Abdelhamid, and A. Matic,Journal of Power Sources 146, 111 (2019)
[4] S. Xiong, J. Scheers, L. Aguilera, D-H. Lim, P. Jacobsson, A. Matic, RSC Advances 5, 2122 (2015)

There is an increasing need for high energy density batteries for achieving complete electrification of transportation. Batteries based on metal anodes like lithium can achieve energy densities much higher than the current state of the art. However, these batteries have been plagued by an unstable and uncontrollable growth of dendrites during electrodeposition leading to short circuit and loss of Coulombic efficiency. Here, we present a new approach using liquid crystalline electrolytes to suppress the growth of dendrites during electrodeposition in metal anode-based batteries. Liquid crystalline electrolytes provide fast ionic transport together with high cation transference number, wide temperature window, non-flammability and low-cost bulk manufacturing [1, 2]. However, the dendrite suppressing nature of liquid electrolytes due to their orientational order has not been explored. A nematic liquid crystalline electrolyte with a perturbed director field due to interface with lithium metal is associated with bulk distortion and anchoring free energy. This changes the free energy of lithium ions in the electrolyte leading to a change in the equilibrium overpotential and thereby the kinetics of metal electrodeposition when used in a metal anode-based battery. We employ a phase-field model to simulate the electrodeposition of lithium in the presence of a standard and liquid crystalline electrolyte. On comparison of metal surface growth metrics with a standard electrolyte, we find considerable suppression of dendrite growth using a liquid crystalline electrolyte. Finally, we propose some design guidelines for the properties of the liquid crystalline molecules/polymers in order to achieve dendrite suppression for practical applications in batteries.

[1] T Kato, From nanostructured liquid crystals to polymer-based electrolytes. Angewandte Chemie Int. Ed. 49, 7847–7848 (2010).
[2] J Sakuda, et al., Liquid-crystalline electrolytes for lithium-ion batteries: Ordered assemblies of a mesogen-containing carbonate and a lithium salt. Adv. Funct. Mater. 25, 1206–1212 517 (2015).

As the world faces a growing need to electrify and reduce carbon emissions, batteries offer much needed energy storage for electric cars, mobile devices, and the grid. For transportation and mobile devices, lightweight batteries are key, while non-toxicity is important for low environmental impact. The lithium-sulfur (Li-S) battery combines low weight, non-toxicity, low cost, and high capacity. With one of the highest theoretical capacities (1166 mAh/g) of any conversion-type cathode, the pursuit of low cost, long-lasting Li-S batteries is a global research focus. However, it is difficult to achieve the promised high theoretical capacity because of polysulfide dissolution in to the electrolyte and reaction at the Li anode surface, depleting the active material in the cathode. Current electrolytes are not effective enough at managing the polysulfide dissolution and have the negative side effects of high viscosity and high cost. In this study, we evaluate several new electrolytes with advantageous physical properties. We compare conventional sulfur cathodes to high-loading cathodes to look at the impact of wetting on performance. The impact of salt combinations and ratios on conductivity, viscosity, electrochemical performance, and SEI composition will be discussed in this talk.

Abstract: Lithium-sulfur batteries promise high energy density, but their poor cycling stability has been limiting their practical applications. The unstable performance is tightly associated with the insulating nature of sulfur and the dissolution and diffusion of the lithium polysulfide (LPS) intermediates with the subsequent parasitic reactions and low S utilization. These problems will be further aggravated in the cells with a high loading cathode at a lean-electrolyte condition, which, however, is critical for realizing the projected high energy of Li-S batteries in practice. Herein, to solve these issues, we introduce a new class of LPS trapping materials, conductive metal phosphides to the Li-S batteries. Using cobalt phosphide (CoP) as an example, we first explore the surface chemistry and demonstrate that the surface oxidation layer, naturally generated under ambient environment, plays a key role in absorbing the LPS species and promoting their conversion kinetics, thus the performance of lithium sulfur batteries is stabilized.¹ The CoP containing electrode with ultrahigh sulfur loading of 7 mg cm^-2 could deliver a striking areal capacity of ~5.6 mAh cm^-2 that is stable over 200 cycles. In another effort, we further verify that this distinct electrocatalytic and LPS binding effect could be applied to the lean electrolyte condition. The sulfur electrodes containing molybdenum phosphide (MoP) show the great decrease in the overpotentials for the charging and discharging reactions, giving rise to improvements in capacity, rate performance, and cycling stability.² As a result, high-performance sulfur electrodes, that are steadily cyclable at a high areal capacity of 5.0 mAh cm^-2 with a challenging electrolyte/sulfur (E/S) ratio of 4mL_E mg^-1_S, are successfully realized_.

1. Zhong, Y., Yin, L., He, P., Liu, W., Wu, Z., Wang, H., Surface Chemistry in Cobalt Phosphide-Stabilized Lithium-Sulfur Batteries. J. Am. Chem. Soc. 2018, 140, 1455-1459.
2. Yang, Y.,⁺ Zhong, Y.,⁺ Shi, Q., Wang, Z., Sun, K., Wang, H., Electrocatalysis in Lithium Sulfur Batteries under Lean Electrolyte Conditions. Angew. Chem. Int. Ed. 2018, 57, 15549-15552.

Low round-trip efficiency and poor cycle stability remain as major challenges of lithium oxygen (Li-O₂) batteries. These issues are primarily triggered by or correlated with the radical species that are produced during the operation of Li-O₂ cell, which significantly deteriorate the electrolytes and air-electrodes. Regulating the reactivity of radical species in an electrochemical cell would thus open up opportunities to mitigate such side reactions. Here, we introduce a dual functional superoxide carrier that is capable of quenching the reactive radical species produced in Li-O₂ cell into stable intermediate complexes both in discharge and charge processes. It leads to a significant suppression of side reactions with a remarkably improved oxygen efficiency. In addtion, it is found that the superoxide carrier is also capable of scavenging the superoxides from the surface of discharge products upon charging, thus substantially lowering the charging overpotential. The combined radical mediation and the scavenging of superoxides enables the cycle stability of a practical Li-O₂ cell employing the superoxide carrier over 200 cycles with 1,000 mAh/g specific capacity. Our findings indicate the importance of controlling the reactivity of radical species and suggest a new pathway to the stable and efficient Li-O₂ batteries.

Several grid energy services such as frequency regulation, demand charge management, and distribution upgrade deferral can be satisfied using energy storage systems with durations typically between 30 minutes and four hours. To enable deep penetration of renewable generators while maintaining grid reliability, however, long-duration energy storage (LDES) systems will be needed. To be cost-competitive, LDES systems require a unique optimization of various attributes--different than conventional lithium-ion battery systems--such as capital cost for energy, capital cost for power, and round-trip efficiency.

This presentation will introduce novel LDES technologies that are being funded by the Department of Energy, Advanced Research Projects Agency-Energy (ARPA-E) Duration Addition to electricitY Storage (DAYS) program that can cost-effectively provide 10 to 100 hours of power to the electric grid. The DAYS projects span a range of concepts, including electrochemical systems with low-cost active materials, pumped thermal storage via inexpensive storage media such as sand and concrete, thermophotovoltaics, and geo-mechanical storage. Key technical challenges and opportunities will be discussed. Although broad adoption of LDES for commercial applications will require policy changes, this presentation will also highlight potential early applications that can enable commercial scaling of these technologies.

Energy storage devices allow us to use energy in a flexible, high efficient and eco-benign way, which has profoundly shaped our everyday life. The most successful energy storage device is lithium-ion battery (LIB), which has dominated the portable electronic devices and are now penetrating deep into vehicle markets^[1]. However, the limited reserves of lithium^[2] and cobalt in the earth crust cannot fulfill the huge demand gap of electrochemical energy storage, and the fast expansion of LIB industry has already led to accelerated cost rising^[3]. Therefore, worldwide research programs strategically encourage the development of energy storage devices beyond LIB, among of which, sodium ion battery (SIB) is a very attractive one.
Electrochemically charging induced phase transition is a common and thermodynamically-driven phenomenon for variety of cathode materials, which couples with chemical and mechanical effects leading to performance degradation. Phase transition is particularly complex for layered sodium transition metal oxides and its related detrimental effects remain elusive. Doping electrochemically inactive elements is proven to be an effective approach to suppress the phase transition and Na-vacancy ordering to achieve improved electrochemical performance.
Herein, we take P2-type Na_2/3Ni_1/3Mn_2/3O₂ (P2-NNM) as an example to scrutiny the detrimental consequences upon high voltage cycling. We find that repeated P2-O2 phase transition breaks down cathode primary grains by generating high density of intragranular cracks, which is qualitatively proved to be the main cause of performance decay. Intriguingly, the nucleation and growth of intragranular crack is through loss of atoms rather than cleavage, resembling the stress corrosion cracking mechanism which preferentially nucleates at P2/O2 phase boundary. Moreover, we find the P2-structured cathode is not sensitive to surface degradation, which explains the superior performance of P2-NNM cathode when cycling at low voltage.^[4] we also investigate Mg-doped P2-structured Na_0.67Ni_0.33-xMn_0.67Mg_xO₂, and find doping electrochemciallly inactive elemnts is an effective method to suppress grain cracking, leading to improved cyclability^[5].

[1] M. Armand, J. M. Tarascon, Nature 2008, 451, 652.
[2] C.-X. Zu, H. Li, Energy Environ. Sci. 2011, 4, 2614.
[3] M. D. Slater, D. Kim, E. Lee, C. S. Johnson, Adv. Funct. Mater. 2013, 23, 947.
[4] K. Wang, P. Yan, M. Sui, Nano Energy 2018, 54, 148.
[5] K. Wang, P. Yan, M. Sui, submitted.

For modern society, energy storage and distribution are critical, with sodium ion batteries (SIB) potentially filling a critical role as a low-cost technology from earth abundant resources well-positioned to augment - or where suitable replace - lithium ion batteries (LIBs).[1] Thus, SIBs have gained prominence due to strong interest from both research and industry.
Here we explore current state-of-the-art Na-ion batteries in terms of both electrodes. Hard carbon-based materials are currently preferred due to their low cost and operating voltage (and hence high energy density). Meanwhile, the most promising cathodes include sodium manganese-rich layered oxides (with the formula Na_xMn_1-yM_yO₂; y ≤ 0.33, M is one or more transition metals, e.g. Ni, Ti, Fe, etc.), due to their potentially attractive physical, electrochemical, and commercial properties.[2] However, these suffer from Jahn–Teller distortion, which may cause loss of capacity and multiple step plateaus. Nevertheless, doping and substitution have been employed to stabilize the structure and/or increase the average Mn oxidation state – resulting in many new materials with improved performances.[3–5] Critically, it has been shown that even small quantities can affect a significant improvement without sacrificing the advantages of these systems.
Given that many of these first-generation technologies are approaching commercialisation, as highlighted in our prototyping and commercialisation section, it is important to consider which future areas of research will best unlock the potential of SIBs.
Improving the power density and rate capability of Na-ion systems has led to interest in nascent Na-ion hybrid capacitors (a coupled supercapacitor- and faradic-type electrode). We will discuss the topic, including remaining challenges (e.g. initial pre-metalation, safety and cost) and the promising development of low-cost hard carbon and high-performance intermetallic electrodes.[6,7]
High energy density, by contrast, is being targeted through advances in Na-air and Na-Sulfur (NaS) systems. Recent work has highlighted the great versatility offered by graphene-based aerogels as air-cathodes, thanks to their low density, high electronic conductivity, and adjustable porosity.[8] From this work, we will examine the specific role of this porosity on both cell capacity and efficiency - which has led to the development of a high-performance cathode, and represents a foundation for future Na-O₂ cathode design.

The challenges and advances in ambient-temperature sodium-sulfur (Na-S) batteries will also be presented. This system is a safe alternative to commercialized high-temperature Na-S batteries (working at 300-350 ^oC), offering high theoretical energy density and low cost. Different optimization approaches, such as applying fluorine-containing electrolyte solvents with redox mediator additives or gel polymer electrolytes, will be highlighted.[9,10]

Meanwhile, safety and cyclability (key factors for any energy storage system) are being addressed by the ongoing development of all solid-state systems, and advances in this area will be discussed briefly.

Through this presentation, we hope to highlight the benefits of sodium-based energy storage systems, provide context for the current state-of-art, and provide insights into the future pathways for development.

[1] V. Palomares et al., 2013, 6, 2312–2337.
[2] N. Ortiz-Vitoriano et al. Energy Environ. Sci., 2017, 10, 1051–1074.
[3] E. Gonzalo et al., J. Power Sources, 2018, 401, 117–125.
[4] M. H. Han et al., Chem. Mater., 2016, 28, 106–116.
[5] J. Billaud et al., Energy Environ. Sci., 2014, 7, 1387–1391.
[6] M. Arnaiz et al., Chem. Mater., 2018, 30, 8155–8163.
[7] J. Ajuria et al., J. Power Sources, 2017, 359, 17–26.
[8] M. Enterría et al., J. Mater. Chem. A, 2018, 6, 20778–20787.
[9] D. Zhou et al., Angew. Chemie, 2018, 130, 10325–10329.
[10] X. Xu et al., Nat. Commun., 2018, 9, 3870.

All-solid-state batteries have the potential to be safe and more energy dense than traditional rechargeable batteries. This emergent energy-storage technology, however, is still critically limited by the (electro)chemical issues at the solid electrolyte/electrode interface and low ionic conductivity of the solid electrolyte. To accelerate the discovery of new superionic conductors is essential to establish meaningful relations between ionic transport and simple materials descriptors. Recent experimental studies on lithium fast-ion conductor suggested that there exists a correlation between lattice dynamics and ionic transport. It has been shown that in lithium-based fast ionic conductor, the lattice softness correlates with low activation energies. Although, such findings highlight new strategies in controlling lattice dynamics to discover new lithium-ion conductors with enhanced conductivity, the universality of such lattice dynamics-based descriptors to understand and potentially control the ionic mobility of other ion conductors such as sodium is not clear. In this work, using an extensive ab initio molecular dynamics simulation based on density functional theory, we examine the applicability of the existing descriptors to a number of NASICON-like (sodium superionic conductors) and demonstrate the links between lattice dynamics and ionic transport in these structures. Finally, the correlation between lattice softness and pre-exponential factor of Na diffusivity, activation energy, and hopping attempt frequency will be obtained.

Two-dimensional transition metal carbide materials (termed MXenes) have attracted great research interest for electrochemical energy storage applications. Herein, with inspiration from the unique structure of pillared interlayered clays, our group demonstrated the fabrication of a series of pillar-structured MXene (Sn⁴⁺/S atoms pillared MXene) via a facile liquid-phase alkali metal ion/cationic surfactant pre-pillaring and Sn⁴⁺/S atoms pillaring methods. The interlayer spacing of Ti₃C₂MXene can be precisely controlled to be between 1 and 2.71 nm according to the size of the intercalated pre-pillaring agent (alkali metal ion, cationic surfactants). Because of the pillar effect, the obtained Sn⁴⁺ pillared MXene delivers a remarkable stable capacity of 765 mAh g^-1 at 0.1 A g^-1 for lithium-ion storage, and the obtained S atoms pillared MXene delivers an improved Na-ion capacity of 550 mAh g^-1at 0.1 A g^-1 (≈120 mAh g^-1 at 15 A g^-1, the best MXene-based Na⁺-storage rate performance reported so far), and excellent cycling stability over 5000 cycles at 10 A g^-1. We believe this pillared structure design of MXene will provide insight in synthesizing MXene-based nanostructures for high-performance energy storage devices.

Optimized carbon-coated Na₃V₂(PO₄)₂F₃ showed exceptional rate and electrochemical cycling capabilities, more than 4000 times at 1 C rate, as demonstrated by performance of the first hard carbon//Na₃V₂(PO₄)₂F₃ 18650 prototypes of 75 Wh kg⁻¹ prepared by our partner CEA.¹ These attractive results, among others, participate to a renewed interest in the field of Na-ion batteries considering vanadium fluorophosphates at the positive electrode.
The optimization of their electrochemical performance requires the control of the carbon coating,¹ and the careful tuning of the oxygen and thus vanadyle-type defects’ concentration through a deep understanding and control of the reaction synthesis. Indeed, the competition between the ionic V³⁺−F bond and the covalent V⁴⁺=O bond has a major effect on the structure of the pristine materials, and then on the phase diagram and redox mechanisms involved upon their cycling in batteries.^2,3 The influence of the anionic and cationic substitution will be illustrated for series of phases Na₃V_2-xM_x(PO₄)₂F_3-yO_y (M= transition metal) combining mainly Synchrotron X-ray diffraction and spectroscopic studies.^2-5

Acknowledgements:
The authors thank Loïc Simonin and Yvan Reynier from CEA-Liten (Grenoble, France) for their collaboration, as well as the European Union’s Horizon 2020 Research and Innovation Program (grant agreement No 646433-NAIADES) and the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01 and SODIUM Descartes Project ANR-13-RESC-0001-02) for funding.

References
1. T. Broux et al. Small Methods 2018, 1800215-1800226
2. T. Broux et al. - Chemistry of Materials 2016, 28(21), 7683-7692
3. H. B. L. Nguyen et al., Energy Storage Materials, 2019, https://doi.org/10.1016/j.ensm.2019.04.010
4. J. Olchowka et al. submitted
5. H. B. L. Nguyen et al. submitted

We report a directional flow-aided sonochemistry (FAS) exfoliation technique that allows for unparalleled control of graphene structural order and chemical uniformity. Depending on the orientation of the shockwave relative to the flow aligned graphite flakes, the resultant bilayer and trilayer graphene is nearly defect free (at-edge sonication graphene "AES-G") or is highly defective (in-plane sonication graphene "IPS-G"). AES-G has a Raman G/D band intensity ratio of 14.3 and an XPS derived O content of 1.3 at.%, while IPS-G has I_G/D of 1.6 and 6.2 at.% O. AES-G and IPS-G are then employed to understand the role of carbon support structure and chemistry in Na metal plating/stripping for sodium metal battery (SMB) anodes. The presence graphene defects and oxygen groups is highly deleterious: In a standard carbonate solution (1M NaClO₄, 1:1 EC:DEC, 5vol.%FEC), AES-G gives stable cycling at 2 mA/cm² with 100% CE (within instrument accuracy), and an area capacity of 1 mAh/cm². Meanwhile IPS-G performs on-par with the baseline Cu support in terms of poor CE, severe mossy metal dendrites, and periodic electrical shorts. We argue that SEI stability is the key for stable cycling, with defects IPS-G being catalytic towards SEI formation. For IPS-G, the SEI layer also shows F-rich "hot spots" due to accelerated decomposition of FEC additive in localized regions.

In the last years, black phosphorous has emerged as one of the most studied materials proposed as anode for rechargeable energy storage devices due to the high gravimetric and volumetric energy density, low cost and high availability. The 2D nature of this system makes it particularly intriguing and is the most studied and investigated form among the P allotropes. Two major drawbacks of the use of phosphorus as anode are under investigation. The first is the huge volumetric change due to the reaction P à R₃P (with R = Li, Na, K) that is of the order of 300-500% moving from Li to K. This colossal volume variation is consequence, of the poor cyclability of these electrodes. To overcome this problem, the strategy to develop P/C composites, has been recently explored. The other one is the optimal preparation of BP and relative composite.
Black phosphorus is typically prepared by high-energy ball milling starting from the commercially available red phosphorous. However, several combinations of parameters (mainly speed rotation, filling factor, and duration) must be considered to have reproducible syntheses.
Here, we present some recent results on the optimization approach of Black Phosphorus as anode for advanced batteries. Particular attention is devoted to address the role of Carbon on the electrode electrochemical performance.

The most promising candidate to replace lithium-ion batteries (LIB) are the Sodium ones (NIB). This is not only due to sodium abundance but also because of the main principles and cell structure, are very similar to LIB ones.
Due to these benefits, SIBs are expected for use in applications related to large-scale energy storage systems and other applications not requiring top-performance.^1,2.
The relevant issue that affect the large scale application of those battery systems is the anode material. Graphite and silicon, largely used in LIB, doesn’t show great performances in NIB.^3,4 Hard carbon looks very promising because of capacity, the abundance and cost⁵, but suffer of instability in particular at long term.
In this work we propose a carbon-coated TiO₂ that looks very promising in term of capability, abundance, low-cost, and most importantly, shows high stability during cycling.⁶
In this work we show a comprehensive structural characterization study that combine XRD and XANES and EXAFS techniques in order to have a complete electronical and structural overview of the modifications induced by sodiation and desodiation. This work also demonstrates for the first time a coherent explanation of the structural changes observed, where an electrochemical induced short-range ordering is revealed upon cycling.

1 Larcher, D.; Tarascon, J.-M. Towards Greener and More Sustainable Batteries for Electrical Energy Storage. Nat. Chem. 2015, 7, 19–29.
2 Hwang, J.-Y.; Myung, S.-T.; Sun, Y.-K. Sodium-Ion Batteries: Present and Future. Chem. Soc. Rev. 2017, 46, 3529–3614.
3 Hasa, I.; Dou, X.; Buchholz, D.; Shao-Horn, Y.; Hassoun, J.; Passerini, S.; Scrosati, B. A Sodium-Ion Battery Exploiting Layered Oxide Cathode, Graphite Anode and Glyme-Based Electrolyte. J. Power Sources 2016, 310, 26–31.
4 Dou, X.; Buchholz, D.; Weinberger, M.; Diemant, T.; Kaus, M.; Indris, S.; Behm, R. J.; Wohlfahrt-Mehrens, M.; Passerini, S. Study of the Na Storage Mechanism in Silicon Oxycarbide—Evidence for Reversible Silicon Redox Activity. Small Methods 2019, 3,
5 Dou, X.; Hasa, I.; Saurel, D.; Vaalma, C.; Wu, L.; Buchholz, D.; Bresser, D.; Komaba, S.; Passerini, S. Hard Carbons for Sodium-Ion Batteries: Structure, Analysis, Sustainability, and Electrochemistry. Mater. Today 2019, 23, 87–104.
6 Guo, S.; Yi, J.; Sun, Y.; Zhou, H. Recent Advances in Titanium-Based Electrode Materials for Stationary Sodium-Ion Batteries. Energy Environ. Sci. 2016, 9, 2978–3006.

Electrochemists understand that one electrode reacting in a more uniform manner allows more uniform reactivity at the countering electrode — unless that opposing electrode suffers from poor electrode kinetics or poor conductivity. This reactivity/conductivity mismatch under stress, such as deep depths of discharge or hundreds-to-thousands of charge–discharge cycles, is all too common between the positive and negative electrodes in batteries. Bringing an architectural perspective to the multifunctionality of energy-storing electrodes ensures wiring the critical per second reactions (electron transport, ion transport, and molecular transport) throughout the volume of the re-designed electrode, which concomitantly distributes the reacting surfaces in 3D, parcels out the imposed global current density to those surfaces rather than to a cross-sectional area, thereby lowering the local current density [1]. This concept will be explored with three case studies. The first two are enabled by zinc sponge anodes, which retain a metallic core that persists in 3D for direct wiring to the current collector even to >90% utilization of the metal [2,3]. When Zn sponges are cycled in alkaline electrolytes versus highly conductive silver oxide cathodes, high cycle life is obtained, even without relying on the cell engineering of additives and separator design typically required to thwart silver colloids spalling off during cycling [3]. When Zn sponges are cycled at high rate and to deep DOD in alkaline electrolytes versus harvested nickel hydroxide cathodes with the far lower conductivity and slower heterogeneous redox rates characteristic of NiOOH, 100% theoretical coulombic efficiency fades after 50+ cycles that can be immediately reversed by replacing the nickel electrode. We are thus currently redesigning the nickel cathode to develop better wiring to match the high performance of the monolithic zinc architecture. In the third case, we demonstrate that in neutral aqueous electrolytes of zinc sulfate and sodium sulfate, the discharge reaction at MnOx powder-composite cathodes can be transformed to hybrid capacitor+battery performance by using cathodes comprising nanoscale MnOx–painted carbon nanofoam paper [4].

[1] Multifunctional 3D nanoarchitectures for energy storage and conversion. D.R. Rolison, J.W. Long, J.C. Lytle, A.E. Fischer, C.P. Rhodes, T.M. McEvoy, M.E. Bourg, A.M. Lubers, Chemical Society Reviews 38 (2009) 226–252.
[2] Wiring zinc in three dimensions re-writes battery performance -- Dendrite-free cycling. J.F. Parker, C.N. Chervin, E.S. Nelson, D.R. Rolison, J.W. Long. Energy & Environmental Science 7 (2014) 1117–1124.
[3] Rechargeable nickel–3D zinc batteries: An energy-dense, safer alternative to lithium-ion. J.F. Parker, C.N. Chervin, I.R. Pala, M. Machler, M.F. Burz, J.W. Long, and D.R. Rolison, Science 356 (2017) 415–418.
[4] Combining battery-like and pseudocapacitive charge storage in 3D MnOx@carbon electrode architectures for zinc-ion cells. J.S. Ko, M.B. Sassin, D.R. Rolison, and J.W. Long, Sustainable Energy & Fuels 2018, 2, 626–636.

Rechargeable zinc (Zn) batteries are safe, sustainable, and energy-dense alternatives to Li-ion batteries. Recent advances, such as monolithic Zn-sponge electrodes, have enabled long cycle lives by suppressing the formation of short-circuiting dendrites even after deep levels of discharge and charge. A substantial barrier to their widespread adoption in large-format applications has been their insufficient mechanical integrity when scaled beyond 1 cm². While most approaches to fortify these electrodes involve adding supportive inactive materials, we enhance electrode strength by tuning the zinc architecture via electrode-emulsion and heat-treatment modifications that also increase energy density and obviate lengthy processing steps. This reformulation achieves an electrode tensile strength that maps to large-format electrode sizes while maintaining a rechargeable capacity and retaining high energy density when paired with a nickel electrode. This advance in scalability provides an opportunity for applications that require large electrodes such as batteries for grid-storage, personal electronics, and electric vehicles.

Rechargeable zinc-alkaline batteries are attractive candidates for stationary energy storage applications because of their high energy density, low cost, inherent safety, and environmental friendliness. However, widespread commercialization of these batteries has been prevented, in part, by the low cyclability of the zinc metal electrode. One reason for the limited cyclability is the accumulation of discharge product in the electrode resulting in passivation and loss of active material. In historical literature, various types of discharge species have been identified, and the discharge product has been treated as an inert species that simply occupies space and blocks ion transport to the active material. In this work, we demonstrate that the discharge product, zinc oxide, undergoes dynamic chemical changes as a function of electrode potential, which affect properties such as the color, composition, and conductivity of the electrode. The dynamic properties of the zinc discharge product must be considered when developing new architecture and additives for rechargeable zinc electrodes.
In this study, we used a combination of in operando and ex situ techniques to investigate the chemical structure of the discharge product in zinc-alkaline electrodes. Namely, in operando Raman spectroscopy was used to demonstrate that the vibrational modes of the discharge product change as a function of voltage, indicating a change in the composition or structure of the discharge product. Simultaneous optical microscopy revealed an accompanying color change in the discharge product as a function of voltage. Subsequently, quantitative ex situ solid-state ¹H and ⁷Li magic-angle spinning (MAS) NMR spectroscopy were used to observe local environments and dynamics of cations in the crystal structure of the discharge product. Our observations suggest that the zinc oxide discharge product in zinc-alkaline batteries is electrochemically active, and that the properties of the material have a dependence on electrode voltage. This talk will summarize the effects of voltage on the discharge product and demonstrate the importance of considering the dynamic behavior of the discharge product when developing future rechargeable zinc electrodes.

Zinc (Zn) anodes and manganese dioxide (MnO₂) cathodes are the electroactive components of alkaline cells which have dominated the market for single discharge disposable batteries for decades. They have high energy density, low cost, and outstanding safety and environmental characteristics. Transforming this non-rechargeable technology into a rechargeable system has the potential to provide very low-cost, safe and environmentally benign solutions for grid-scale energy storage. Howvever, poor charge-discharge reversibility, especially of the MnO₂ cathode at high depths of discharge (DOD) , has limited application of this otherwise very attractive technology.
Recent breakthroughs in obtaining excellent rechargeability of high DOD Zn anodes and MnO₂ cathodes achieved at the City University of New York Energy Institute (CUNY-EI) in partnership with Urban Electric Power, Inc. (UEP) will be reviewed. These developments, which received the 2019 ACS/EPA Green Chemistry Challenge Award, are now being commercialized to realize cell costs in the $40/kWh range.In this talk, the challenges in developing and manufacturing products based on such breakthroughs, e.g., into grid-scale rechargeable Zn/MnO₂ batteries for energy storage, will be discussed.

Grid scale energy storage requires high energy density, low-cost and safe systems. Semi-solid flow battery is attractive to achieve these objectives as its energy density not limited by the active species solubility, and also enables usage of wide range of cheap and safe solid active material and aqueous electrolyte. In this study, we have designed high energy density suspensions for Zn-Ni alkaline semi-solid flow battery. Firstly, stability of the suspension was ensured by suspending the solid particles in polymer and 7 M KOH electrolyte matrix. Then, effect of conductive additive concentration on the electrochemical performance of the suspension was studied in a static cell. By selecting suitable concentration of conductive additive (14 w% of carbon black), we were able to achieve high energy density semi-solid battery (134 Wh/L_catholyte, ~3 times of VRFB). Rheological study of these suspensions showed they have yield stress about ~200 Pa. As they don’t require high flow rate and narrow channels as VRFB, we found that the pumping loss in the flow channels for these suspensions is negligible (<1% w.r.t. energy output). Finally, scalability of this Zn-Ni semi-solid flow battery is tested in a 3-D printed flow cell.

Water-in-salt electrolytes have considerably expanded the electrochemical window of the electrolytes to 3 to 4 volts, making it possible to couple many high capacity anodes and high-voltage cathodes for Li-ion, Na-ion and Zn batteries. Since the water is strongly bonded to the salts, the low water activity in electrolytes allows the cell to be open to the air and operate in a wide temperature range. The high oxidation stability window also enables a halogen conversion–intercalation chemistry in graphite that produces composite electrodes with a capacity of 243 milliampere-hours per gram (for the total weight of the electrode) at an average potential of 4.2 volts versus Li/Li+.

A metal hydride/air battery (HAB) is an aqueous secondary battery consisting of a hydrogen storage alloy electrode, an air electrode, and an alkaline solution, of which the discharge reaction is water generation and the charge one is water decomposition. This unique system brings out the potential of air batteries which are no limitation on discharge capacity of the positive electrode unnecessary to storage the active mass, resulting in higher power density and energy density than the other types of secondary batteries. It is of importance that the discharge product is water, not solid, so that the plugging of the air electrode during discharge by solid products like lithium oxide in lithium/air batteries never occurs. The materials of HAB are further important in viewpoint of safety, because they are all non-flammable and are easily handled in air. Therefore, HAB is one of the promising candidates for next generation energy storage devices, which need that high performance and high safety should be compatible. Our project on the HAB development has been financially supported by Japan Science and Technology Agency (JST) from 2012 under the collaboration of two universities and three companies, in which the air electrode with bi-functional oxygen catalyst, the negative electrode using high capacity density of hydrogen storage alloy, and the cell design and configuration have been developed and modified. This paper presents the materials and performance of HAB including the preparation, characteristics, and activities of novel oxygen catalysts and the cell performance on energy density over 900 Wh/L and cycling behaviors of 500 cycles or more. A future plain for the application of HAB to stationary energy storage systems, which has been just started under Low Carbon Technology Research and Development Program by Ministry of the Environment (MOE), Japan, will be also indicated.

Large-scale energy storage is of significance to the integration of renewable energy into electric grid. Despite the dominance of pumped hydroelectricity in the market of grid energy storage, it is limited by the suitable site selection and footprint impact. Rechargeable batteries show increasing interests in the large-scale energy storage; however, the challenging requirement of low-cost materials with long cycle and calendar life restricts most battery chemistries for use in the grid storage. Recently we introduced a concept of manganese-hydrogen battery with Mn²⁺/MnO₂ redox cathode paired with H⁺/H₂ gas anode, which has a long life of 10,000 cycles and with potential for grid energy storage. We later expand this concept by replacing Mn²⁺/MnO₂ redox with a nickel-based cathode, which enables ∼10× higher areal capacity loading, reaching ∼35 mAh cm⁻². We also replace high-cost Pt catalyst on the anode with a low-cost, bifunctional nickel molybdenum cobalt alloy, which could effectively catalyze hydrogen evolution and oxidation reactions in alkaline electrolyte. Such a nickel-hydrogen battery exhibits an energy density of ∼140 Wh kg⁻¹ and estimated energy cost of ∼$83 per kilowatt-hour and excellent rechargeability with negligible capacity decay over 1,500 cycles. The excellent stability and the low cost of the rechargeable hydrogen batteries demonstrate attractive characteristics for large-scale energy storage.

Synthetic cost and long-term stability remain two of the most challenging barriers for the development of aqueous organic redox flow batteries for grid scale energy storage. In this work, we present a new method for synthesizing water-soluble anthraquinones from inexpensive starting materials. Two anthraquinones have been synthesized by the method at the time this abstract is being submitted. Both of them show remarkable chemical stability of both oxidized and reduced forms: no chemical decomposition at high temperature for two weeks. When paired with a Ferro/ferrycyanide posolyte, a full cell of 1 V is achieved, exhibiting a capacity fade rate of around 0.02% per day, which is among the most stable redox-active molecules reported. One of these species has a solubility of 1 M, corresponding to 53.2 Ah/L, at pH 12. This method may be extended to the synthesis of other redox-active aromatics.

The redox-flow battery has gained increased attention as an alternative to Li-ion batteries for grid-scale energy storage. While a number of flow battery chemistries have been developed and are undergoing commercialization, none satisfy the full set of requirements necessary for wide-scale deployment. For instance, the vanadium redox flow battery has impressive performance metrics, but is prone to fluctuating costs which are currently prohibitively high. Redox-active organics have recently emerged as promising alternatives to existing flow battery chemistries. These systems offer a level of tunability not available with transition-metal-based systems. A number of redox-active core structures have been reported and for each core structure selective functionalization can modulate the solubility, ionic charge, redox-potential, and a number of other properties, providing nearly endless possiblities for molecular design. Presented will be our recent work on phenazine-based anolytes, which yield cell voltages of over 1 V when coupled with ferrocyanide and can achieve solubilities up to 1.8 M. The effect of various molecular design approaches on solubility, redox potential, and stability will be discussed.

After years of silence, redox-active organic compounds are re-emerging in the energy storage community bringing with them interesting opportunities such as design flexibility and lightweight. Moreover, thanks to the use of abundant chemical elements, organic chemistry provides great opportunities for discovering innovative electrode materials, which could be prepared (i) from renewable resources (biomass) and (ii) via eco-efficient processes, making the concept of greener and sustainable batteries possible [1]. They can also integrate a wide variety of electrochemical device architectures operating both in aqueous or non-aqueous electrolytes. Interestingly, the past decade has seen significant progress in the design of new organic compounds and today a myriad of promising electroactive organic materials have been investigated [2]. In addition, very promising data are now also reported in redox flow cell configuration [3]. Some of them exhibit attractive electrochemical behaviors such as long-term cycling stability and high-rate capability. In addition, they offer different electrochemical activities including the common reversible cation uptake/release as well as access to anion-inserting process bringing to us another playground in designing organic electrochemical storage systems including the development, in principle, of molecular ion batteries [4]. However, several improvements are needed to further promote organic electrode materials especially in terms of energy density values and only few studies have been reported in the literature regarding the assembly of full organic cells.
This contribution aims at reporting recent electrochemical data obtained with crystallized organic materials [5] and explaining how it is possible to tune the electrochemical activity of redox-active organic moieties depending on the molecular assembly and its electrostatic environment. We hope that such findings can pave the way for designing novel chemistries for rechargeable batteries.

References:
[1] P. Poizot and F. Dolhem, Energy Environ. Sci., 2011, 4, 2003–2019.
[2] Y. Liang et al., Adv. Energy Mater., 2012, 2, 742–769; T. Janoschka et al., Adv. Mater., 2012, 24, 6397–6409; Q. Zhao et al., Ind. Eng. Chem. Res. 2016, 55, 5795−5804; Adv. Energy Mater. 2017, 7, 1601792.
[3] J. Winsberg et al., Angew. Chem. Int. Ed. 2017, 56, 686–711.
[4] M. Yao et al., Sci. Rep. 2015, 5, 10962; P. Poizot et al., Curr. Opin. Electrochem. 2009, 9, 70–80.
[5] A. Jouhara et al., Nat. Commun., 2018, 9, 4401; S. Perticarari et al., Adv. Energy Mater. 2018, 8, 1701988; S. Perticarari et al., Chem. Mater. 2019, 31, 1869–1880.

With significant growth in the clean energy sector (wind and solar), the search for an energy storage medium which is safe, durable and economical is at an all-time high and a variety of electrochemical systems are being evaluated; multiple flow battery chemistries and electrochemical hydrogen production (electrolysis). The efficiencies, lifetimes and costs of these electrochemical systems are tied to the membrane separator; however, commercially available membranes do not meet all the requirements. At Sandia National Laboratories, we have been developing both anion and cation exchange Diels Alder poly(phenylene) membranes as electrochemical separators. Since these materials are hydrocarbons they are excellent low-cost alternatives to perfluorinated materials, and since the polymer backbone consists of only aromatic benzene units it offers high chemical and thermal stability. For example, as most electrochemical systems operate in either an acid or alkaline environment to enhance the electrolyte conductivity and widen the operation voltage window, the membrane separator needs to be inert in these conditions. However, it has been found that hydrocarbon polymers that contain heteroatoms in the polymer backbone are attacked in alkaline environment (polymer degradation), while all aromatic DAPP is stable in alkaline environments, even at high temperatures. This presentation will discuss the development and synthesis of various cation and anion exchange materials employing the DAPP backbone, and its performance in a variety of electrochemical applications.

The scalability for an efficient process to fabricate electrodes with enhanced charge and mass transfer is still a challenge for flow batteries. For the first time, this work introduces a scalable and effective surface modification method of graphite felt (GF) electrode based on the controlled electrochemical exfoliation to enhance the mass and charge transfer of the electrode. Exfoliation of the GF was conducted in ammonium sulfate ((NH₄)₂SO₄) aqueous solution by breaking the weak van der Waals forces between the graphitic layers. This reaction occurred through anion intercalation and subsequent gas evolutions, causing expansion of the graphite layers at room temperature for 1 min. Consequently, the exfoliation incorporated sufficient oxygen functional groups that increase the active surface area, resulting in enhanced reaction kinetics at the electrode-electrolyte interface and improved hydrophilicity enabling better electrolyte accessibility. The Brunauer-Emmett-Teller (BET) results verified that the specific surface area of E-GF is 1.19 m² g⁻¹, which is two times larger than that of the pristine graphite felt (0.55 m² g⁻¹). Further, spin-polarized density functional theory was also employed to reveal the role of introduced oxygen functional groups in accelerating the vanadium redox reaction. Benefitting from the sufficient oxygen groups and superior wettability, the as-prepared exfoliated GF (E-GF) shows brilliant electrocatalytic activity with minimized overpotential, higher volumetric capacity, and improved energy efficiency. Finally, the RFB assembled with the E-GF electrode delivered voltage and energy efficiencies of ~ 90 and 86 % at the current density of 100 mA cm^-2, respectively. Remarkably, compared to the traditional GF treatment method, the elimination of the high-temperature, energy consuming, and longtime treatment processes make this approach much more energy and time efficient, scalable, and affordable.

Due to complex component and sensitive to the air and water of the lithium rechargeable battery, how to prepare a practical useful TEM (transmission electron microscopy) specimen from Li-ion cell has been critical to the TEM application in new generation batteries. We have developed an efficient way to prepare a TEM specimen from lithium ion cells that prevents electrode material contamination and chemical reaction from water or air and damage from mechanical stress.
By using our special technique for TEM specimen preparation the nano structural properties of SEI (solid-electrolyte-interphase) layer in Li(NiMnCo)O₂/graphite cell have been investigated. The MnF₂ nano-crystalnwith tetragonal structure in SEI layer was found and identified by HRTEM and EELS (electron energy loss spectrum). Furthermore, the morphology of MnF2 nano-grains, its nucleation, distribution and SEI layer thickness were studied.
By using our special technique for TEM specimen preparation LiNi_0.5Mn_1.5O₄ cathode material has also been studied on the battery failure mechanism, which will be reported in other project.

Redox flow batteries (RFBs) offer a number of advantages over current stationary energy storage technologies, such as the decoupling of power & energy and inherently safer designs. However, the energy density of commercially deployed RFB electrolytes is relatively low when contrasted with competing technologies, for example Li-ion battery installations. A significant amount of research has attempted to increase the energy density of the electrolyte by 1) employing non-aqueous electrolytes to improve voltage separation between redox events, 2) increasing the number of electrons transferred between half-cells by employing electroactive species with multiple redox couples, 3) increasing the concentration of the electrolyte by preparing highly soluble or liquid state redox active molecules, or 4) a combination of the previous three modifications. This talk will highlight Phillips 66 investigation of single component iron-based ionic liquids that may satisfy all roles of an energy dense RFB electrolyte: namely the solvent, supporting electrolyte, and redox active species. This presentation will cover the preparation, characterization, and electrochemical testing of the aforementioned energy dense materials.

The device performance characteristics of electrochemical energy storage (EES) technologies makes them suited to a broad range of applications spanning portable electronics and vehicle propulsion all the way to small-scale grid stabilization and remote power backup. With lithium-ion batteries (LIBs) currently the dominant chemistry in the market across all applications, there are now many opportunities to displace LIBs with new and emerging EES technologies that may be better suited to the particular device requirements or operating environment. The choice of electrolyte is one variable that can significantly alter the performance characteristics and desired operating environment of a given technology. Ionic liquids are an intriguing candidate to displace traditional electrolyte solvents owing to a number of favorable physicochemical and electrochemical properties, including thermal and electrochemical stability.

Recent work from within the group into the incorporation of ionic liquid electrolytes (ILEs) into three distinct battery types, namely lithium metal-based, sodium metal-based, and lithium anode redox flow, will be presented here. Investigations into the fundamental electrolyte properties, cycled electrode surface characterisations and device performance aspects have revealed a number of features which make ILEs a surprisingly attractive commercial prospect. The highlights of these features are the ability of ILEs to support high rate Li deposition (20 mA/cm²) through control of the Li nucleation process, and the ability to cycle Li metal with an average Coulombic efficiency of 99.0% over the first 100 cycles in a Cu|LFP configuration using a physical substrate modification approach. An understanding into these behaviors has been developed by considering the transport mechanisms in these electrolytes and the composition of the electrode surface deposits.

In an effort to bring ILEs into an industrially-relevant focus, device prototyping has been conducted at Deakin University’s Battery Technology Research and Innovation Hub (BatTRI-Hub). Here, we have demonstrated the capability of ILEs to enable high energy density pouch cell cycling in prototype devices capable of achieving a specific energy of 400 Wh/kg. Separator design has been identified as a primary factor which limits the cell cycle life and operational temperature range. Some of the key prototyping results will be presented and the implications for commercial application discussed.