Symposium EN05—Emerging Materials for Electrochemical Energy Storage Devices—Degradation and Failure Characterization—From Composition, Structure and Interfaces to Deployed Systems

Solid-state batteries (SSB), consisting of inorganic solid electrolytes and energy-dense lithium metal anode, are promising candidates as next-generation energy storage devices. The high intrinsic thermal stability of inorganic solid electrolytes and their ability to mechanically restrain the growth of lithium dendrites can potentially address critical thermal safety challenges encountered in lithium-ion batteries. Due to the high reactivity of lithium and other mechanistic aspects (e.g., high-voltage cathode), the overall thermal stability of SSBs is predicated on the chemical, electrochemical, and mechanical interactions at various solid-solid interfaces and underlying crosstalk mechanisms involving the cathode, solid electrolyte, and metal anode. Chemo-mechanical interactions such as filament growth through the solid electrolyte (e.g., via grain boundaries) may lead to additional stability challenges. In this presentation, we will assess the intrinsic thermo-electrochemical mechanisms that could be responsible for potential thermal instability in solid-state batteries.

Accelerating Rate Calorimetry (ARC) has previously been used to evaluate differences observed in various active materials with a typical comparison shown in the figure below. This evaluation is usually performed on small cells of roughly the same capacity (~1 AH) to allow for an easy comparison of active materials as they are developed. However, this and similar calorimetry methods present a means to perform more quantitative measurements of the heat generated and kinetics of thermal runaway. Sandia National Laboratories has performed testing on cells in the 10s of amp hours and analyzed the thermal runaway behavior of these cells.
This work uses accelerating rate calorimetry to evaluate the impact of cell chemistry, state of charge, cell capacity, and ultimately cell energy density on the total energy release and peak heating rates observed during thermal runaway of Li-ion batteries. This work seeks to better understand how applicable small cell data is to understand the thermal runaway behavior of large cells as well as determine if thermal runaway behaviors can be more generally tied to aspects of lithium-ion cells such as total stored energy and specific energy. We have found a strong linear correlation between the total enthalpy of the thermal runaway process and the stored energy of the cell, apparently independent of cell size and state of charge. We have also shown that peak heating rates and peak temperatures reached during thermal runaway events are more closely tied to specific energy, increasing exponentially in the case of peak heating rates.
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.

Li-ion batteries exhibit transient thermal profiles during charge/discharge behaviors. These profiles are dictated by active material type, C-rate, and ambient temperature. Isothermal battery calorimetry (IBC) allows us to maintain Li-ion batteries in isothermal conditions while performing charge/discharge processes and reports heat flux from the cell. Portions of cell charge and discharge that produce the most heat deliver the lowest power efficiency. Therefore, with quantification of power efficiency at distinct C-rates and ambient temperatures we can create “smart” charge/discharge protocols that avoid the inefficient regions of cell operation, facilitating optimal performance and long cycle life. We demonstrate the heat flux on high energy Samsung 50E cells in the 21700 form factor at various C-rates and ambient profiles over 100% DOD cycles and then truncate charge and discharge in various ways to demonstrate the impact of heat generation on cell efficiency. Opportunities for IBC measurements to inform operational protocols and battery design concepts to protect materials and electrodes will be presented.

Battery degradation depends not only on component chemistry but also complex physical-chemical processes during diverse operating conditions, including dynamic cycles, temperature/thermal effects, time between operations, and other environmental factors. In this work, the thermal effect during battery operation is proposed to play a critical role in the degradation of Li-ion batteries. Specifically, the heat generated in commercial Li-ion batteries under grid services (frequency regulation and peak shaving) is measured by using electrochemical-calorimetric method such as accelerating rate calorimetry (ARC), aiming to disclose the relationship between thermal characteristics and the degradation/reliability of Li-ion batteries in stationary applications.

Solid-state batteries (SSBs) offer the promise of increased safety, high energy density, and reduced charge time. Interfacial resistance between the solid electrolyte and the electrodes remains a critical challenge, significantly impacting rate capability and performance. One solution to this challenge is the inclusion of a small amount of liquid electrolyte at the interface. However, there are concerns regarding the impact of liquid electrolyte on safety. To date, no experimental data has been presented on the safety implications of liquid electrolyte use to facilitate interfacial ion transfer in SSBs.

The results of thermal stability testing and characterization on SSB components, including Ta-doped LLZO, with liquid electrolyte, will be presented. Thermal characterization was carried out on individual and combinations of components utilizing a differential scanning calorimeter (DSC). This allowed for the determination of the components’ and component combinations’ exothermic and endothermic heat release values and the temperatures at which those heat releases occurred. Testing the thermal stability of different component combinations offered the ability to elucidate side reactions that occurred in response to material interactions, due to contact and/or gases generated, and their respective heat releases. In addition, coin cells were assembled to obtain various states of charge (SOC) and the subsequent materials were harvested and tested with DSC. This gave the heat release as a function of SOC. For all thermal stability tests, scanning electron microscopy (SEM) was used to determine morphological changes in the SSB components. X-ray diffraction (XRD) was used to examine changes in the solid electrolyte crystal structure and chemical composition. The thermal stability testing of SSB components and characterization of those components presented here offers insight into the safety benefits provided by the utilization of solid electrolytes in Li-ion batteries.



Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and 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.

Current techniques for experimentally measuring heat capacity and latent heats, such as differential scanning calorimetry, are not suited for precise characterization of thin films. The majority of the difficulties in applying current techniques to nanoscale material systems is due to the large dimensionality of the heat flux source and monitor systems; the ‘depth’ resolution of thermal-based techniques is directly related to the width of these heat flux components (e.g., a 100 nm film requires thermometers on the order of hundreds of nanometers for precise measurements of thermophysical properties). However, the thermophysical properties of nanoscale materials can be drastically different than their bulk counterparts, increasing the necessity for accurate determination of their thermal storage properties and thus the need for new techniques. Further, due to the cost and time required to produce bulk quantities of novel material systems, the ability to measure the specific heat of materials at the nanoscale is of increasing interest to industries spanning from energy to pharmaceuticals.

In this work, we introduce a novel optical pump-probe technique for simultaneous measurement of numerous thermal parameters including thermal conductivity, volumetric heat capacity, and the latent heat of thin films on the order of tens of nanometers thick. More specifically, we implement a nanosecond-resolved moving boxcar averaging detection scheme to allow for monitoring of the transient temperature rise and decay of the sample surface with a focused laser “probe” beam (e.g., detector) as it is periodically heated by a high power “pump” beam (e.g., source). By measuring the laser-induced heating over multiple modulation frequencies, we are able to decouple the material’s thermal properties, and calculate its specific heat capacity, thermal conductivity, and thermal boundary conductance. We demonstrate the application of this new measurement technique by analyzing a variety of thin films including a collection of phase change materials.

Phosphorus-doped silicon has been reported to exhibit improved cycling stability and/or higher capacity retention than pure silicon as the anode in lithium-ion batteries. However, crystallite size and particle morphology are difficult to decouple from compositional tuning during chemical modification. In this work, we explore direct solid-state routes to phosphorus doping of silicon powders relevant to electrochemical applications. A wide range of compositions are assessed, from 0.01-3.0 at% P, as well as a wide range of silicon starting materials of varying crystallinity, particle size, and particle morphology. Successful incorporation of phosphorus into the silicon lattice is best confirmed by X-ray diffraction; the Si (111) reflection shifts to higher angles roughly consistent with the known lattice contraction of 0.002 Å per 1 at% phosphorus. The addition of phosphorus to Si nanoparticles (50-100 nm) in the high doping regime causes grain coarsening and catalyzes an increase in crystallinity that is difficult to prevent. On the other hand, dilute doping of phosphorus can be carried out without a great alteration of the nanoparticulate morphology. The opposite effect occurs for very large microparticles (>10 μm) whereby doping is concomitant with a disruption of the crystal lattice and reduction of crystallite size. These effects are borne out in both the electrochemical stability over long-term cycling in a lithium-ion half-cell as well as in the thermal stability under high-temperature decomposition. By comparison across a wide range of pure and P-doped materials of varying particle and crystallite size, the independent effects of doping and structure on thermal and electrochemical stability are decoupled.

Despite particle cracking has been considered as one of the root causes for Ni-rich NMC cathode deterioration and limited long-term cycle stability, the detrimental effects from crack formation have not been completely resolved. The search for efficient approaches to prevent particles from cracking represents one of the most critical technological challenges facing Ni-rich cathodes at present. In this work, through deep understanding of the effects of Co and Mn on mechanical properties, we successfully mitigate the particle cracking issue in Ni-rich cathodes via dual gradient concentration design without sacrificing the high capacity. Our result reveals that the Co-enriched surface design in Ni-rich particles benefits from its low stiffness, which can effectively suppress the formation of particle cracking. Meanwhile, the Mn-enriched core not only limits internal expansion but also increases structural reversibility. Together, these two aspects of the gradient concentration design significantly strengthen the morphological stability and enhance the cycle reversibility in Ni-rich NMC. These results provide new insights on the roles of Co and Mn on mechanical properties and the alleviation of lattice strain in Ni-rich NMC, which can serve as essential design principles to help facilitate the future discovery of structurally stable cathode materials in lithium-ion batteries.

Lithium-ion batteries do not reversibly operate below 0 C, with complete failure below about -30 C. The poor low-temperature behavior is largely due to sluggish diffusion of lithium within the graphite anode, along with electrolyte transport limitations and freezing. Thus, even with improved electrolytes, new anode materials with high specific capacities and fast lithium diffusion must be developed and understood to enable high-energy, low-temperature batteries. Here, we investigate the performance and structural evolution of various alloy anodes (antimony, silicon, and tin) at temperatures as low as -40 C, using a tailored ether electrolyte. Galvanostatic cycling reveals that antimony can be used as an anode material at -40 C and still provide a specific capacity of over 400 mAh g^-1 on the first cycle. Tin and silicon can only be reversibly cycled at -30 C and 0 C, respectively, due to increased overpotential causing simultaneous lithium plating. While all materials tested provide high initial capacities at low temperatures, only antimony exhibits relatively stable capacity retention over tens of cycles. To gain insight into electrochemical mechanisms, the galvanostatic intermittent titration technique (GITT) is used to extract thermodynamic and kinetic contributions to the materials’ behavior as a function of temperature. GITT reveals that the kinetic overpotential makes up a larger portion of the overall voltage hysteresis for tin and antimony at low temperatures, while the opposite is true for silicon at all temperatures. Additionally, the thermodynamic voltage hysteresis for silicon and tin become larger at lower temperatures, while they stay relatively constant for antimony after the first cycle. Finally, ex-situ X-ray diffraction of antimony electrodes shows that, despite large kinetic overpotentials, antimony is still able to form crystalline Li₃Sb on lithiation and reform crystalline Sb on delithiation at low temperatures, but with smaller crystallite sizes. Overall, these results provide new fundamental insight into the electrochemical alloying and dealloying processes at low temperatures and are a vital first step in developing this promising class of anode materials for low temperature lithium-ion batteries.

Laser structuring has a huge impact on performances and operational lifetime of lithium-ion batteries. Optimized cell architectures including current collectors, separators, and electrodes are flanked by material concepts for the development of next-generation 3D lithium-ion batteries. Recently a new approach was established by merging 3D electrode, high-energy material and thick film electrode concepts. For this purpose ultrafast laser structuring for upscaling including roll-to-roll processing was established. Performance, degradation and failure processes were studied and correlated to the 3D electrode architectures. Post-mortem studies using laser-induced breakdown spectroscopy (LIBS) were carried out to illustrate the formation of new lithium diffusion pathways in 3D electrodes. In addition, 3D elemental mappings by LIBS were used to indicate starting points of cell degradation in coin and pouch cell designs. The studies were performed with NMC 622 as cathode and graphite as well as graphite/silicon as anode. Those materials are commonly used in lithium-ion batteries (LIBs). Due to the demand for a significantly increased energy density for xEVs (electromotive vehicles), there is worldwide a strong effort to increase the energy density on the battery level. Silicon has the benefit to provide one order of magnitude higher gravimetric energy density than graphite. However, a bottleneck of silicon as anode material is its huge volume change of about 300 % during electrochemical cycling. Volume change induces high compression and tension, which results in crack formation, continuous reformation of solid electrolyte interphase (SEI) layers, and subsequent electrode delamination from the current collector. Especially the compressive stress can restrict a complete fully lithiation in silicon and graphite and accelerates chemical degradation of the battery. In this study, thick film graphite, silicon, and silicon/graphite composite electrodes on the anode side and nickel-enriched NMC on the cathode side were developed. Subsequently, hole, grid, and line patterns were generated on electrodes by ultrafast laser ablation in order to reduce compressive stress during electrochemical cycling, to shorten the electrolyte diffusion distance and to reduce diffusion overpotential. The latter one is a critical issue in elevated power densities of the thick film electrodes, i.e., high mass loading. 3D elemental mapping by using LIBS could demonstrate that new lithium-ion diffusion pathways were generated along the structure's sidewalls and are activated with increasing power densities. It was shown that batteries with laser structured electrodes benefit from a homogenous lithiation as well as delithiation, reduced compressive stress, an overall improved electrochemical performance, and cell lifetime in comparison to batteries with unstructured electrodes. Cells with 3D micro-structured electrodes demonstrate an improved high rate capability and an increased battery lifetime. Laser structuring of electrodes offers a new manufacturing tool for next-generation battery production to overcome current limitations in electrode design and cell performance.

Aqueous rechargeable lithium (Li) batteries (ARLB) were recently highlighted owing to low cost and safety issues. However, the narrow electrochemical potential window of water and instability of the electrode surface remained significant challenges. One of the promising solutions to mitigate these challenges is the use of extremely high concentrations of electrolyte salts, called water-in-salt electrolyte (WiSE). The predominant aggregated-ion pairs in the WiSE widened the potential window to ~3.0 V and protected the electrode surface by forming solid-electrolyte interphase (SEI). However, the possible precipitation and the high cost of the salts may lose the advantages of using the aqueous medium.
In this presentation, I focus on the interfacial reaction of positive electrodes with a low concentration of lithium salt (0.5~3 mol kg^-1 (m)) to improve the performance of the aqueous Li-ion cells. The LiCoO₂ (LCO) with the layered structure was used, which typically showed rapid deteriorations in an aqueous medium. It was attributed to the dissolution of cobalt ion in the presence of O₂ gas and the intercalation of H⁺ through the water dissociation.^1-3 Soft X-ray absorption near-edge structure (XANES) spectroscopy exhibited a distorted oxide layer of LCO with 1 m LiTFSI (Li(NSO₂CF₃)₂) (aq) after 30 cycles tested in an argon-filled glove box. It indicated the irreversible Li⁺ (de)intercalation due to the inserted H⁺ effect. In sharp contrast, the deterioration of the LCO electrode was considerably suppressed by using 0.5 m Li₂SO₄ (aq). Since there was no evidence of SEI formation and negligible pH effect in the mild alkaline solutions, we attributed the different cell performances to the role of the anion. In addition, 1 m NO₃^–, and ClO₄^– showed better performances than TFSI^-. Interestingly, the order of capacity retentions, SO₄^2- > NO₃^- > ClO₄^- > TFSI^-, was related to the strength of kosmotrope, the water-structure-making property of ion. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra revealed the increased ice-like O-H bond vibration at 3200 cm^-1 with increasing SO₄^2– concentration, as the hydrogen-bonding network nearby SO₄^2– becomes rigid. In contrast, NO₃^–, ClO₄^–, and TFSI^– showed the intense signals at 3600 cm^-1 with increasing anion concentrations, indicating enlargements of the disordered hydrogen bond and the free water. Therefore, superior cyclability with SO₄^2– was caused by the strong hydrogen-bonding network, which harnessed the intercalation of H⁺ into the LCO electrode at the interface. In addition, molecular dynamics (MD) simulation envisioned the locally concentrated SO₄^2– paring with Li⁺ at the interfacial region, suggesting the predominant ice-like water at the LCO surface. The LCO cathode coupled with Li_xNb_2/7Mo_3/7O₂ anode showed 74% capacity retention for 500 cycles with 3 m Li₂SO₄(aq) for full cells. By comparison, 3 m LiTFSI and 9 m LiNO₃ only maintained <40% capacity. I will discuss the anions’ propensity according to the strength of kosmotrope and their correlation with cell performances in the presentation.
References
1. Ramanujapuram, A.; Gordon, D.; Magasinski, A.; Ward, B.; Nitta, N.; Huang, C.; Yushin, G., Degradation and stabilization of lithium cobalt oxide in aqueous electrolytes. Energy & Environmental Science 2016, 9 (5), 1841-1848.
2. Yong-gang Wang, J.-y. L., Cong-xiao Wang, and Yong yao Xia, Hybrid Aqueous Energy Storage Cells Using Activated Carbon and Lithium-Ion Intercalated Compounds II. Comparison of LiMn₂O₄, LiCo_1/3Ni_1/3Mn_1/3O₂, and LiCoO₂ Positive Electrodes. Journal of Electrochemical Society 2006, 153 (8), A1425-A431.
3. Byeon, P.; Bae, H. B.; Chung, H.-S.; Lee, S.-G.; Kim, J.-G.; Lee, H. J.; Choi, J. W.; Chung, S.-Y., Atomic-Scale Observation of LiFePO₄ and LiCoO₂ Dissolution Behavior in Aqueous Solutions. Advanced Functional Materials 2018, 28 (45).

During cycling of lithium batteries, irreversible side reactions, changes in morphology, and loss of active material degrades battery capacity. For example, impurities in cell components and high cell voltages can cause significant gas evolution. Gas buildup in lithium batteries is proposed to cause failure by swelling and rupture which can be catastrophic given the flammable nature of evolved gases. However, little is known about how evolved gases impacts the cycling of lithium batteries. Aurbach et al. first commented on the possibility that hydrogen could react at the anode of lithium batteries to form LiH – a reaction that typically needs high temperatures (> 600°C) to proceed to completion. Given the unfavorable conditions and high reactivity of LiH, the possibility of LiH in lithium batteries has long been ignored. Recently, competing hypotheses for the role of hydrogen in lithium batteries include the formation of a LiH rich solid-electrolyte interphase (SEI) and dendritic growth of LiH. Given the conflicting reports of LiH in lithium batteries and the unlikely conditions for reaction, it remains uncertain if LiH exists in lithium batteries. Furthermore, if LiH does exist, it is unclear if it is an important SEI component which can improve reversibility or a capacity loss mechanism that reduces cycle life. In either case, a convincing mechanism for how LiH forms in lithium batteries has not been proposed. In this talk, we discuss the phase coexistence of lithium metal with LiH in lithium batteries. Using the latest techniques in cryogenic scanning/transmission electron microscopy, electron energy loss spectroscopy, x-ray diffraction, and electrochemistry we aim to better understand the role of hydrogen in lithium batteries.

Ni-rich LiNi_1-xCo_x/2Mn_x/2O₂ (NMC) layered cathode materials have attracted great interest for electric vehicle (EV) applications due to their high gravimetric and volumetric energy densities. However, the Ni-rich NMC cathodes still experience a series of degradation issues, especially when their charging voltage exceeds 4.3 V_vs.Li. Therefore, current cell operating conditions limits their usage, which corresponds to about 60 – 70 % of their theoretical capacities. Current understanding on the degradation mechanism of Ni-rich NMC at high voltages (e.g., > 4.3 V_vs.Li) includes; (1) Ni²⁺ migration to vacant Li⁺ layer, leading to an irreversible phase transformation from layered structure to rock-salt structure; (2) oxidative decomposition of electrolytes and unwanted parasitic reactions at cathode/electrolyte interfaces (CEI), increasing the internal impedance and consumption of Li-ions; (3) large volumetric changes and subsequent mechanical stresses inducing surface cracking and particle pulverization during extended cycling.
One of the most prominent approaches to improve the high-voltage stability is coating the surface of the Ni-rich NMC with inorganic materials such as Al₂O₃, ZrO₂, and Li₃PO_4. However, the commonly used coating techniques involve extra processing steps and/or unwantedly increase CEI impedance due to sluggish Li-ion transportation properties of the coated materials. Therefore, in this work, we will present solid-electrolyte (SE) implemented composite NMC cathodes prepared without any extra process, by relying on conventional electrode fabrication processes in Li-ion battery cells. This simple process offers advantages over the conventional coating methods in terms of manufacturing friendliness, energy saving, and cost effectiveness.
Among various solid electrolytes, Li_6.7La₃Zr_1.7Ta_0.3O₁₂ (LLZT) with garnet structure showed great promises based on its wide electrochemical stability window, good mechanical properties, and reasonable Li-ion conductivity (10^-3 – 10^-4 S/cm). Based on these promising properties, we examined the effect of LLZT on the NMC + LLZT. First, the NMC + LLZT composite cathode significantly improved specific capacity and its retention during cycling at high voltages (e.g., 4.5 V_vs.Li). Compared with the baseline data (i.e., simple NMC cathode), the composite cathode showed 22% improved specific capacity and 11% improvement cycle life after 200 cycles at C/3-rate in full-cells (i.e., using graphite anode). Microscopy of the NMC + LLZT cathode revealed (i) a dispersion of LLZT nanoparticles on the surface of the NMC and (ii) LLZT microparticles interconnecting the NMC particles within the electrode microstructures. The X-ray photoelectron spectroscopy (XPS) data showed that LLZT-NMC cathode had thinner CEI than that of bare NMC, suggesting that LLZT coating could passivate the NMC and reduces parasitic reactions occurring at high voltages. Meanwhile, the high Li-ion conductivity of LLZT can provide facile lithium-ion conduction pathway via the NMC-LLZT-NMC network inside cathode microstructures, as evidenced by lower cell impedance from electrochemical impedance spectroscopy (EIS) combined with distributed time relaxations (DRT) techniques. As a result, the LLZT-NMC also deliver improved rate capabilities: e.g., ~ 5 times improved capacity at 5C-rate. The results suggest that tailoring the surfaces of Ni-rich NMC by using SE materials will be a promising approach to stabilize CEI of any types of high-voltage cathodes for next-generation EVs.

The recent development that printing technologies have experienced, combined with the increasing demand for miniaturized wearables and portable electronics, has boosted the interest in compact and high energy density freeform energy storage devices. At the moment, emerging applications and devices such as biomedical sensors or micro-electro-mechanical systems, are limited in shape, size and price by the energy storage devices that power them.
In this regard, printing technologies propose an affordable and adaptable alternative of creating complex architectures that could maximize the energy density of batteries and supercapacitors[1].
Although a substantial effort has been done to push forward the application of printing strategies for energy storage devices, especially by additive manufacturing, this field is still in its infancy and a lot of challenges remain[2].
A recurrent problem in this field is the lack of information on how the microstructure of the composites is affected by the selected fabrication method and how this impact the performance of the final device. This makes it difficult to translate results and isolate problems, as well as optimize designs and composites.
In this work, we present a systematic study of the changes that occur on the electrode materials when we move from traditional techniques to printing based methods. We give special attention to the correlation of the electrochemical performance of the devices with the microstructure shown by the electrodes fabricated by each technique.
The selected techniques encompass traditional battery fabrication methods such as slurry casting and filtration and more advanced ones used in printed devices, including extrusion printing, spray coating and aerosol jet printing. To fairly compare these methods, the same ink formulations were used across all techniques. For each technique, three different percentages of conductive additive were used to assess the behaviour shown by each fabrication method. The main active material used for this work was LTO in combination with CNTs, but to prove that the results can be extrapolated to any materials, silicon was also used to back up the findings.
The methodology used for the electrochemical analysis, was mainly the comparison of their rate performance. The results were fitted to physical models[3] and the differences were correlated to the observations made by morphological and structural based techniques, such as TEM, SEM and BET.
It was found that significant differences in the network arrangement can be induced by the deposition technique, creating segregated[4] or randomly arranged networks depending on the processes involved. It was also found that porosity is another factor that is massively affected by the fabrication technique and its effect on the electrochemical performance is influenced by the network arrangement.
In summary, our work is a systematic and insightful study of how the deposition techniques affect each of the physical parameters of the electrodes and how those interplay with the device performance. Additionally, we highlight the main issues in each technique and ways to mitigate them.
[1] Y. Pang, Y. Cao, Y. Chu, M. Liu, K. Snyder, D. MacKenzie, C. Cao, Additive Manufacturing of Batteries, Adv. Funct. Mater. 30 (2020). doi:10.1002/adfm.201906244.
[2] P. Chang, H. Mei, S. Zhou, K.G. Dassios, L. Cheng, 3D printed electrochemical energy storage devices, J. Mater. Chem. A. 7 (2019). doi:10.1039/c8ta11860d.
[3] R. Tian, S.-H.H. Park, P.J. King, G. Cunningham, J. Coelho, V. Nicolosi, J.N. Coleman, Quantifying the factors limiting rate performance in battery electrodes, Nat. Commun. 10 (2019). doi:10.1038/s41467-019-09792-9.
[4] S.-H.H. Park, P.J. King, R. Tian, C.S. Boland, J. Coelho, C. (John) Zhang, P. McBean, N. McEvoy, M.P. Kremer, D. Daly, J.N. Coleman, V. Nicolosi, High areal capacity battery electrodes enabled by segregated nanotube networks, Nat. Energy. 4 (2019). doi:10.1038/s41560-019-0398-y.

Lithium (Li) metal has been regarded as one of the most promising anodes to achieve a high-energy-density battery due to its ultrahigh theoretical specific capacity (3860 mAh g^–1) and low redox potential (– 3.04 V vs. standard hydrogen electrode). However, the practical usage of Li metal anode is hindered by several challenges including the generation of heterogeneous/non-uniform solid electrolyte interphase (SEI) layer, “dead” Li formation during repeated cycling causing volume change and loss of active Li, continuous consumption of electrolyte triggering low Coulombic efficiency (CE). To address these problems, we have developed a double-layer coating to protect Li metal anode. It is well known that PEO is stable with Li metal and has a high donor number for Li-ion and high chain flexibility, which are important for promoting ion transport and considered a suitable candidate for the ionic conductive protection layer for Li metal anode. However, PEO is dimensionally unstable in liquid electrolytes due to dissolution or swelling. To maintain the integrity of PEO in liquid electrolyte, a double layer (DL) concept is proposed. The DL consists of a PEO-based bottom layer and a top layer which is stable in organic solvent. A uniform double-layer (less than 1 μm thick) was obtained as shown by scanning electron microscope. DL-coated Li metal anode (DL@Li) enabled a long cycling lifespan of 1000 h without a significant increase in polarization of Li||Li symmetric cells when cycled in a capacity of 1 mAh cm^–1 at a current density of 1 mA cm^–1. In comparison, the bare Li anode is shorted at around 960 h under the same condition. Furthermore, the DL@Li showed smooth and stable Li deposition/stripping profiles at a high current density (2 mA cm^–1) while the bare Li presented the sudden voltage changes which were caused by continuously building up and breaking down of SEI layers at the electrolyte/Li interface. Therefore, the DL@Li may alleviate electrolyte consumption which induces interface reaction during cycling. In addition, the DL@Li enables stable deposition/stripping behavior with a slightly higher average Li Coulombic efficiency value of 99.5% than the bare Li (99.4%). Benefitting from the advantage of the DL protection, the DL@Li||Ni-rich cathode cell showed a much better long cycling stability than the bare Li||Ni-rich cathode at a high current density of 2.1 mA cm^–2 (C/2 rate). After cycling, the DL@Li exhibited a flat and smooth surface without Li dendrites while the bare Li anode illustrated a rough and porous surface with massive dendritic Li. In addition, the DL protection improved the fast-charging capability of the DL@Li||Ni-rich cathode cell (4.6 mAh cm^–1) and led to a stable Li deposition even at a current density of 6.9 mA cm^–2 based on its remarkable promotion of uniform Li-ion flux. This study provides an efficient approach to protect Li metal anode and enhance the performance of high-performance Li-metal batteries.

Owing to their high theoretical energy density, lithium (Li) metal batteries (LMBs) have drawn extensive attention from both industry and academia. However, the relatively short cycle life and poor safety performance of LMBs still impede their large-scale practical applications. To extend the cycle life and enhance the safety performance, we focus on the modification of a previously neglected component in LMBs, the separator. The conventional polyolefin separators used in today’s Li-ion batteries have low melting points, ca. 110 ?C for polyethylene (PE) and ca. 160 ?C for polypropylene (PP). When the battery temperature increases rapidly in case of short and/or abusive conditions, the polyolefin separators shrink drastically due to their low thermal stability, leading to the direct contact between negative and positive electrodes. Consequently, the internal short-circuiting leads to immense heat generation, thermal runaway or even explosion of the batteries. Such thermal instability of polyolefin separators may result in severer safety issues when applied to high energy density LMBs. To address this concern, we fabricated a composite separator that contains a layer of high-melting point polymer membrane and a layer of polymer which is highly stable with Li metal anode. Such composite separator maintains its morphology when stored at high temperatures, whereas the polyolefin separator itself shrinks significantly. Therefore, the composite separator is expected to enhance the thermal stability of LMBs since it can block the direct contact between Li and positive material when thermal runaway takes place. When tested in LMBs with a nickel-rich cathode, the composite separator also enables the cells to exhibit higher capacity retention and much less deviation than the polyolefin separator in the long-term cycling. Detailed information will be discussed at the presentation.

Electrolyte engineering improved cycling of Li metal batteries and anode-free cells at low current densities; however, high-rate capability and tuning of ionic conduction in electrolytes are desirable yet less-studied. Herein, we design and synthesize a family of fluorinated-1,2-diethyoxyethanes as electrolyte solvents. The position and amount of F atoms functionalized on 1,2-diethyoxyethane were found to significantly impact electrolyte performance. Partially-fluorinated, locally-polar –CHF₂ is identified as the optimal group rather than fully-fluorinated –CF₃ in common designs. Paired with 1.2 molar LiFSI, these developed single-salt-single-solvent electrolytes simultaneously enable high conductivity, low and stable overpotential, >99.5% Li || Cu half-cell efficiency (up to 99.9%, ±0.1% fluctuation), and fast activation (Li efficiency >99.3% within two cycles). Combined with high-voltage stability, these electrolytes achieve ~270 cycles in 50-μm-thin-Li || high-loading-NMC811 full batteries and >140 cycles in fast-cycling Cu || microparticle-LFP pouch cells under realistic testing conditions. The correlation of Li⁺-solvent coordination, solvation environments, and battery performance is investigated to understand structure-property relationships.

Lithium metal is the most promising anode active material candidate for the next-generation lithium secondary batteries, attributed by its high electrochemical potential of –3.04 V (vs. SHE) and theoretical energy density of 3860 mAh/g. However, commercialization of lithium metal batteries is challenging due to the dendrite formation of lithium, which eventually causes the battery failure. Diverse micro- or nanostructured current collectors have been proposed, which can reduce the current density and therefore suppress the formation and growth rate of lithium dendrite, yet the limitations of each structures are clear. The microscale structures are limited in the amount of current density reduction, whereas the nanostructure have less structural stability. Herein, we introduce a structurally hierarchical current collector containing nanorods on the inner surface of the structurally optimized microcavities. We design and fabricate the micro- and nanostructures independently which can take different roles, yet their synergic effect contributes in suppressing the lithium dendrite growth and therefore increase the battery life time. Arrays of microcavities on a copper surface are fabricated by the photolithography and the electroforming, to have a high reproducibility, uniformity between patterns, and freedom of the shape adjustment. The nanorods are fabricated by the diffusion-limited electrodeposition in aqueous solution, and the overgrown nanorods outside the microcavities are removed by mechanical polishing. We observe the lithium deposition behavior via SEM and conduct electrochemical simulation, which show that the microcavities not only perform a role as a stable host for the lithium agglomerates but also complement the structural vulnerability of nanorods. Meanwhile, the nanorods can significantly reduce the current density owing to the increased surface area, therefore suppress the generation of lithium dendrites. We characterize and compare the coulombic efficiency and the cycle life time of planar, micro-structured, and hierarchical Cu current collectors, and show that the hierarchical Cu current collector has a cycle life of 1300 h and sustains CE > 90 % even after 230 cycles in the Cu||Li half-cell, which is 260 % longer lifetime than the planar Cu and 83 % longer than the microstructured Cu. Finally, we discuss different routes for realizing the hierarchical Cu collectors, which can improve the productivity for practical use and can further enhance the battery life time.

Li metal anode batteries are regarded as the ultimate battery system for the high energy density compared to graphite anode batteries. However, the practical usage of Li metal anode is hindered by various reasons like safety concerns, Li dendrite growth, the poor lifespan, and so on. Here, we introduce copper nitride nanowires(Cu₃N NWs) coated Li metal that could give us outstanding cyclability even at a high current density. A roll pressing method was adopted for its simplicity. When we roll-press Cu₃N NWs and Li metal, Cu₃N NWs turn to Li₃N which exhibits high Li-ion conductivity and Cu by the conversion reaction, and this additional layer can give homogeneous Li-ion flux with dendrite-free Li plating behavior. The Li₃N@Cu NWs coated Li metal symmetric cells exhibit reversible and stable cycling performances at a high current density of 5.0 mA cm^-2. This layer also exhibits outstanding performance at the full cells when we use the LiCoO₂ and Li₄Ti₅O₁₂ cathode as counter electrodes, the long-term cyclability could be realized over 300 cycles and 1000 cycles where the current densities were 1.7 mA cm^-2 and 2.0 mA cm^-2 each.

Complex devices like batteries, fuel cells or organic sensors and solar cells are commonly assembled from multiple functional components with different materials properties. To gain a fundamental understanding of the microstructure-property relations of such complex macroscopic structures, their degradation and failure mechanisms by complementary scale-bridging microscopic and spectroscopic techniques, it is desirable to prepare cross sections of entire devices or parts. Most challenging is the generation of electron transparent cross-sectional samples for investigation by advanced transmission electron microscopy (TEM); preparing TEM samples of devices consisting of different material classes may be utmost difficult. Therefore, TEM sample preparation is often preceded by the disassembly of a device down to individual components rendering an investigation of relations between the individual components impossible.
(Cryo-)ultramicrotomy as well as plasma-FIB as advanced cross-sectioning techniques for challenging samples may solve those issues. Both are capable to generate ultra-thin, electron transparent cross sections of hundreds of micrometers in size being larger than the typical thickness of modern devices.
In this contribution, we demonstrate the capabilities of modern (cryo-)ultramicrotomy in conjunction with advanced TEM characterization of sensitive or reactive and thus challenging devices down to the atomic scale. Examples include battery parts, PEM fuel cells and novel flexible all-organic electronics. The achieved thickness of those cross sections is commonly of the order of a few 10 nm, which even allows for atomic-resolution imaging and advanced spectroscopy for microstructure and defect analyses as well as compositional and chemical-bond investigation, respectively.

Li metal anode has been considered as a promising constituent for next-generation Li-ion batteries with higher power- and energy-densities due to its low chemical potential and high specific capacity. However, Li dendrite formation under high current-density and inhomogeneous Li-ion flux results in limited performance as well as significant capacity degradation. To mitigate the dendrite formation problem, various efforts have been made such as building artificial solid-electrolyte-interface, coating lithiophilic materials on the electrode, and a three-dimensional host structure for Li plating. In particular, host structures including metal nanowires, carbon fibers, and Cu foams have demonstrated improved cycling performances by reducing effective current density. However, these host structures require additional pre-lithiation step by electroplating of Li or uncontrolled Li-infusion, which often result in lower process throughput or excessively thick Li layer, respectively.
In this study, we fabricate super-lithiophilic three-dimensional host structure for improving performance of lithium metal anode. We develop a scalable fabrication process for uniform and thin Li metal anode by enhancing wicking of molten Li into porous Cu current collector. The porous Cu current collector is fabricated by the dynamic hydrogen bubble template to tailor the pore structure and Li-wettability. Brunauer-Emmett-Teller measurement reveals that the structure possesses a large surface to volume ratio, which can reduce the effective current density significantly. Furthermore, we fabricate a super-lithiophilic structure by introducing an interfacial layer with a high Li-affinity on the porous Cu structure while minimizing the impact on hydrodynamic resistance. As molten Li contacts the surface of the lithiophilic current collector, the capillary effect causes molten Li to permeate rapidly into the Cu structure, forming a uniform and thin Li metal anode. Furthermore, the evolution of the Li morphology during cycling is characterized by in-situ visualization cell and ex-situ FIB-SEM, and modeled by finite element method simulation. Finally, symmetric- and full-cell tests show stable electrochemical performance at a current density over 4 mA/cm², demonstrating a potential for high-power Li-ion batteries.

Lithium dendrite growth and poor Coulombic efficiency lead to a safety issue and inferior electrochemical properties, which are the major obstacles that impede high energy density Li metal battery development in practical applications. Here, it is demonstrated that the Ge interlayer deposited on commercial polyethylene (PE) separator (Ge@polyethylene, Ge@PE) induces the formation of a pleated solid electrolyte interphase (SEI) layer, which can effectively prevent the Li dendrites formation. The optimized Ge@PE configuration enables obvious improvement in Li plating/stripping behavior in Li||Ge@PE|| Cu battery due to the robust and efficient SEI layer. The Li||Ge@PE||LCO(LiCoO₂) full battery also endows enhanced highly reversible cyclability and exhibits Li dendrite-free generation during the repeated Li plating/stripping process.

Rechargeable alkali metal batteries including Li, Na, and K as anodes are the ultimate choice for the next generation batteries. However, because of their very negative reduction potentials and reactivity, electrolytes always react with the anodes, leading to the formation of solid electrolyte interphase (SEI). The stability and lifetime of these batteries are not still sufficient because the nonstable SEIs cause dendrite formation, which can eventually lead to battery short-circuits and fire issues. Although many characterization tools have been used to study the anodes and their failure mechanisms, such highly reactive materials generally present challenges for characterization. This is because ambient air exposure leads to contamination during sample transfer, and because they can be damaged by both electron and X-ray radiation. Therefore, it is important to develop a method for reliable characterization of alkali anodes.
To characterize these reactive materials, one of the strategies is to obtain embedded cross-sections of the battery system as this can directly visualize dendrite morphology. Focused ion beam (FIB) microscopy is a suitable technique to achieve this goal, as it can be used to prepare sight-specific sample through sputtering. However, at room temp temperature, cross-sectional analysis is usually hindered as the ion beam causes deleterious effects, significantly changing the chemical and morphological properties of the metal surfaces. In addition, new emerging cryogenic techniques such as cryogenic transmission microscope (cryo TEM) and cryogenic atomic probe microscopy (cryo APT) require a high level of sample preparation with minimal sample damage by the FIB technique. As such, developing a “damage-free” method for alkali metals on FIB is not only necessary for morphological analysis in the FIB/SEM itself but also provides an important step for advanced analysis such as cryo TEM.
Cryogenic focused ion beam scanning microscope (cryo FIB) has been shown to be a promising characterization tool for alkali metals, as it reduces deleterious effects such as Ga/O implantation and mechanical deformation by the ion beam. The extremely low temperature sufficiently reduces the kinetics of any side reactions and Ga⁺ cryo FIB has been used to obtain Li metal cross-sections in its pristine state. The recent development of Xe⁺ plasma FIB (PFIB) /SEM systems enables a large amount of materials to be removed in a given time at high currents (a few microamps) compared to Ga based liquid metal FIB, which can further promote battery research and its sample preparation efficiency.
Here, we have used cryogenic Xe⁺ PFIB to explore the capability for the characterization of alkali metal anodes in liquid and solid electrolytes. We found that -170 C^o is no longer necessary for damage-free samples from reactive materials: this will significantly simplify and shorten the processes involving cross-sectional SEM analysis and cryo TEM sample preparation for the metal anodes. Furthermore, because of the large currents produced in the PFIB, it is possible to create tomographic reconstructions of the entire morphology of alkali metal batteries, including each electrode in a coin cell. This allows the structures to be identified throughout the distance between the electrodes. We believe this cryo PFIB technique will significantly aid alkali battery research by increasing the volume and area of analysis far beyond what is possible to accomplish with liquid Ga ion-based FIB.

Innovation in transportation is key to stopping climate change. Undoubtedly, a true enabler of zero-emission electric vehicles (EVs) is rechargeable batteries. Among many types of the batteries, Li-ion batteries dictate the modern EV battery technology. Meanwhile, the need for high-energy-density batteries also continues to grow as the market for EVs rapidly expands. One of the effective ways to increase energy storage capacity of a battery is to engineer its anode. In this regard, anode-free batteries that do not require a physical anode material in the cell can be a promising next-generation system with high volumetric energy density.
The anode-side of anode-free batteries often consist of a plain current collector. Thus, understanding the effect of current collectors on reversible Li plating and stripping will be key to enabling anode-free batteries. In this presentation, I will discuss how to shift energetics of Li plating and stripping in anode-free batteries by employing three-dimensional frameworks on current collector. First, I will introduce electro-writing, the unique 3D manufacturing technique developed in my group. Electro-writing is capable to form periodic 3D structures made of functionalized polymer composites on a copper foil. Second, electrochemical properties of anode-free batteries assembled with the manufactured 3D current collectors will be demonstrated, and the effect of 3D configurations on reversible Li cycling will be discussed. It was found that mechanical stabilization in the anode-side is critical to stabilizing Li plating and stripping. Mechanically robust 3D polymer structures enables reversible Li cycling by suppressing volume change over the extended number of cycles. In the context, the practical applications of anode-free batteries will also be discussed.
This study was supported by the LG Energy Solution company through the Battery Innovation Contest (BIC) program. The authors also thank the generous support of the PSEG Foundation.

Developing new high-performance anodes is highly desired to meet the ever-increasing demands for lithium-ion battery (LIB) systems with large capacity, high-rate capability, and long cycling life. Herein, we present an effective solution for the insufficient reversible capacity issues of titanium oxides largely attributable to the slow Li-ion diffusion, intrinsic low electrical conductivity, and narrow reversible half-cell working potential window, through new material design strategy of unique titanium oxide heterostructure. We report a uniquely integrated hybrid structure of rutile TiO₂ (r-TiO₂) nanothorns in-situ grown over a new porous and conductive TiO core, which is generated from pyrolysis of anatase TiO₂ with Mg metal at 650 degree in centigrade. The TiO is controllably in-situ oxidized to generate r-TiO₂ nanothorns over the TiO surface to form the r-TiO2-TiO hybrid.
The new hybrid exhibits superb LIB performance as an anode with a high reversible capacity and almost no capacity decay during 1000 cycles at a high current density of 20 C (4000 mA g^-1). Two independent reactions of intercalation and interfacial pseudocapacitive interaction are confirmed to occur in the composite of the r-TiO₂ and TiO, respectively. In particular, the excellent rate capability along with long cycle life enables the new hybrid to have ultrafast charging of the system. Furthermore, the hybrid with the job-sharing property exhibits stable charge-discharge performance over a wider potential window range of 0.01 to 3.0 V, particularly even in the low potential range of 1 and 0.01 V, which usually causes irreversible Li-intercalation and rapid capacity decay for pristine TiO₂. All the properties including the wider potential window allows the hybrid to realize the highest electrochemical performance that titanium oxides have ever achieved so far.

Energy storage is a topic that has become central to progress in applications ranging from cell phones to grid storage for renewable energies. As a result, any incremental progress in the field has the potential to instigate profound global impact and why so much effort is being put into improving the current industry leader of lithium-ion battery technology. Soon after the introduction of graphite as the standard anode material in the 1990’s, it was noted that silicon’s theoretical 4200 mAh/g capacity dwarfed graphite’s 372 mAh/g.^[1] Unfortunately, silicon’s problems of limited electrical conductivity, excessive solid electrolyte interphase (SEI) formation, and volume change during cycling have been problems preventing its commercial adoption. However, silicon’s volume expansion of ~300% upon lithiation has demonstrated that a critical scale of 150 nm, beyond which lithiation causes the particle to fracture itself.^[2] This learning has somewhat limited the structure of materials being researched to being below that scale. Some work has looked beyond these size restrictions with macrostructures,^[3] thus gaining some beneficial properties like reduced SEI formation afforded to larger structures. This naturally leads to the question of whether a macrostructure like a mesoparticle, particle made up of smaller particles, can benefit from both its large cumulative scale and the scale of its components.
To perform this investigation, mesoparticles on the scale of 5 mm were produced through spray drying using a solution of 12% PVP to 88% Si by weight. The silicon particles themselves were selected to have 100 nm, 20 nm, and 10 nm in average diameter. After the spray drying process the mesoparticles underwent a CVD process developed by our lab to both coat the individual nanoparticles in a conformal carbon shell, and then graphitize the carbon shell without impacting the silicon or the macrostructure.^[1] The final result being identically produced mesoparticles of the same size, composed of individually graphite coated nanoparticles of three different sizes. For direct comparison between mesoparticles and single particles, the aforementioned CVD process was performed on the un-clustered silicon at each size. These materials were then analyzed through SEM, TEM, EDS, and XRD, while also undergoing standard half-cell testing and additional 3^rd party full cell testing as an additive to standard graphite anodes.
Experimental results show both a clear beneficial impact of the mesoparticle macrostructure with regards to cycling stability, as well as an obvious influence in C-rate and general stability by the nanoparticle size. Less anticipated benefits of higher C-rate stability were observed with the mesoparticle structures being able to supply up to 4x the capacity of their un-structured counterparts when cycled at 0.5 C, despite near identical capacities when cycled at 0.1 C. The trend of general improvement in cycling stability was also observed in full-cell testing. Overall, we show that the mesoparticle macrostructure improves electrochemical stability in general, while simultaneously the size of its nanoparticle components express both the benefits and drawbacks of their size.

Lithium ion battery (LIB) is widely used in elctric vehicle (EV) and hybrid electric vehicle (HEV) market. In LIB, low practical capacity of positive electrode material compared to anode electrode materials blocks achieving high energy density of a full cell. In this regard, Ni-rich layered (Ni>60%) materials such as NCM and NCA were studied because of their higher practical capacity than conventional LiCoO_2. Recently, LiNiO₂, an end member of NCM and NCA material receives a lot of attention because of its high theoretical capacity (275 mAh/g).
In this study, electrochemical activity of LiNiO₂ at 1st cycle and factors affecting its activity were understood. Even though LiNiO₂ can achieve almost its theoretical charge capacity, it cannot deliver the theoretical discharge capacity and 1^st coulombic efficiency (CE) of LiNiO₂ is low in all voltage cut-off. Given that the H2-H3 phase transition occurs at ~ 4.2V, the low 1^st CE with the 4.1V cut-off voltage is not caused by this phase transition. The low 1^st CE of LiNiO₂ is a result of the additional 3.5V discharge reaction, which is kinetically limited and thereby not activated even at reasonable discharge current density. Under a GITT (Galvanostatic Intermittent Titration Technique) condition, the LiNiO₂ can achieve 100% CE even with 4.3V cut-off voltage by fully activating the 3.5V reaction.
Using neutron diffraction and ⁶Li nuclear magnetic resonance (NMR) measurements, the sluggish kinetics of the 3.5V reaction can be ascribed to difficult insertion of Li at the end of the discharge, because this reaction can be accompanied by the rearrangement of cations or local structure change in the structure. To achieve high discharge capacity in LiNiO₂ with the 4.3V cut-off voltage, this 3.5V sluggish reaction should be improved. In this talk, we will discuss about the mechanism of the electrochemical activity of LiNiO₂ and its low coulombic efficiency.
1. Bae, C., Dupre, N., & Kang, B. (2021). Further Improving Coulombic Efficiency and Discharge Capacity in LiNiO2 Material by Activating Sluggish∼ 3.5 V Discharge Reaction. ACS Applied Materials & Interfaces.

As the era of electric devices, EV and renewable energy start to flourish, lithium ion battery(LIB) has been considered as one of the promising energy storage system. However, current status of LIBs has struggled to meet the increasing demand of cheaper, smaller and lighter energy storage systems. Since conventional cathodes utilize intercalation chemistry to accomodate charges in electrode materials, their theoretical maximum capacities are restricted by the number of interstitial sites of host structure. Unlike intercalation chemistry, conversion reaction accomodates lithium ions and electrons in sepereated phase whose capacity is not limited by interstitial sites. In this respect, exploiting both intercalation and converison reaction provide electrode material double or triple capacities of conventional cathode materials by taking advantage of multi redox(TM^0/2+/3+). However, conversion based cathode materials shows severely poor cyclic reversibility compared to commercialized cathode materials (LCO, LFP, NCA, ...). Conversion reaction carries substantial structural changes which is detrimental for maintaining facile diffusion path of intercalation reaction. Furthermore, conversion reaction has insufficient cycle reversibility of itself. Regarding these struggles, enlarging the range of various insertion/conversion type materials will give us in-depth understanding about those type material and effective cycle enhancing strategies. Herein, we report a mechanochemically derived iron fluorosulphate material, a-LiFeSO4F with high energy density, cycle stability and rate capability. This newly derived phase exploits both insertion and conversion reaction for charge storage mechanism with abnormal cycling performances compared to reported conversion type materials. a-LiFeSO4F demonstrates 370 mAh/g specific capacity with 89 % capacity retention after 200 cycles even at elevated temperature (40 mA/g, 333 K). These superior electrochemical performances are originated from its amorphous structure which induces facile kinetics of re/conversion reaction. Consequently, we provide a new insertion/conversion type electrode material as well as potentials of which a method for excavating new insertion/conversion type electrode materials which might lead us to comprehensive understanding of those type materials.

Most conventional cathode materials, such as LiCoO₂ and Li(Ni,Co,Mn)O₂ (NMC), have layered structures and require Co and Ni to keep the cathode stable upon cycling. The rapid market growth of Li-ion batteries will demand that one moves away from the typical Co- and Ni-based cathode materials. Spinel-type cathode are good candidates to enable the future growth of Li-ion as, unlike the NMC materials, they can utilize inexpensive and earth-abundant Mn as redox active element. However, the detrimental two-phase reaction at ~ 3 V limits its usable capacity. Here, we demonstrate a series of well-selected partially-(dis)ordered spinel cathodes in which different degrees of cation disorder are used to suppress the two-phase reaction. Our results reveal that the over-stoichiometry of cations in the synthesis is the key to control the amount of Mn 16c/16d disorder in the structure and its electrochemical performance. The varying degree of cation disorder can also modify the voltage profile, rate capability and charge-compensation mechanism in a rational and predictable way. Our findings reveal an important tuning handle for achieving high energy and power in the vast space of partially ordered cathode materials.

Introduction
It has been well established that nanostructured materials for energy applications (cathodes, anodes, solid electrolytes) perform better than their coarse-grained polycrystalline counterparts. Most of these nanomaterials were obtained by solid state reaction techniques. Our group, however, has systematically explored thermal crystallization of glasses as a simpler alternative way to synthesize nanostructured materials for energy storage. We have carried a series of studies on thermal nanocrystallization [1] of glassy analogues of cathode materials for sodium and lithium batteries (e.g. V₂O₅ [2], LiFePO₄ [3], Na₃V₂(PO₄)₂F₃ [4]) and solid electrolytes (e.g. Bi₂O₃ – oxygen ion conductor [5]). Thanks to this alternative technique, it was possible to synthesize nanostructured cathodic and electrolytic materials exhibiting interesting morphology and unique physical properties [6].

Nanocrystalline cathode materials
In the case of the cathode materials, nanocrystallization was used to improve the poor conductivity of those materials without introducing carbon additives. A giant and irreversible increase of the conductivity (even by a factor as high as 10⁹) was obtained. The microstructure of the samples consisted of 5–50 nm nanocrystallites. The conductivity increase has been attributed to appearance of highly disordered shells around such small grains (cores), which facilitated the electron hopping, e.g. between aliovalent V⁵⁺ / V⁴⁺ or Fe³⁺ / Fe²⁺ centers.

Nanocrystalline electrolytes
Crystalline δ–Bi₂O₃ is the best O^2– ion conductor, but it is stable in a relatively narrow temperature range 729–825 °C only. Its very high ionic conductivity (1 S/cm at 750 °C) has motivated many researchers to look for a method to stabilize this fluorite-type structure to lower temperature. So far the successful strategies to achieve the stabilization of the delta phase have included doping (e.g. by rare-earth elements) or synthesis in form of thin films.
By thermal nanocrystallization of Bi₂O₃-based glasses, we have succeeded to stabilize nanosize grains of δ–like phase confined in a glassy matrix down to RT [7]. The phase remained stable for at least one year of storage at ambient conditions. This method may be used to stabilize other phases in the future.

Acknowledgments
This research was funded by POB Energy and POB TechMat of Warsaw University of Technology within the Excellence Initiative: Research University (IDUB) program.

References
1. T.K. Pietrzak et al., Materials Science and Engineering B 213 (2016) 140–147.
2. T.K. Pietrzak et al., Journal of Power Sources 194 (2009) 73–80.
3. J.E. Garbarczyk et al., Solid State Ionics 272 (2015) 53–59.
4. T.K. Pietrzak et al., International Journal of Applied Glass Science 11 (2020) 87–96.
5. T.K. Pietrzak et al., Solid State Ionics 323 (2018) 78–84.
6. T.K. Pietrzak et al., Nanomaterials 11 (2021) 1321.
7. T.K. Pietrzak et al., Scientific Reports 11 (2021) 19145.

Due to its high capacity and low cost, LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) is considered as the next promising cathode for commercial lithium-ion batteries. However, it is still suffering from serious performance degradation and safety hazard before large-scale commercialization. These existing issues are usually reflected as cation mixing, oxygen evolution, irreversible phase transition, transition metal ion dissolution, and microcracking. Aimed at addressing these problems, surface coating has been proven to be a widely accepted and effective approach. Among a variety of coating methods, atomic layer deposition (ALD) has emerged as a unique tool to deposit uniform and conformal coatings over NMCs, which have shown remarkable effects on improving battery performance.^1-4 Herein, for the first time we deposited ultrathin sulfide ALD coatings⁵ over NMC811 composite electrodes. It was found that the sulfide coatings enable to noticeably enhance the cyclability and rate capability of NMC811 cathodes. To clarify the effects of the ALD sulfide coatings, we utilized a suite of characterization techniques, and the results revealed that the sulfide coatings can perfectly maintain the NMC structure during long cycling, consequently suppressing the crack formation. Furthermore, the sulfide layer has been verified to react with trace H₂O in electrolyte and O₂ released from the NMC structure, forming oxidized sulfide layers. In addition, the measurements of electrochemical impedance spectroscopy confirms that the sulfide coatings physically protect the NMC surface from the electrode/electrolyte interfacial reactions. Based on our results, it can be foreseen that sulfides would be a new class of coating materials for addressing NMC issues.

References:
1. Meng, X.; Yang, X. Q.; Sun, X. L., Advanced Materials 2012, 24 (27), 3589-3615.
2. Liu, Y.; Wang, X.; Cai, J.; Han, X.; Geng, D.; Li, J.; Meng, X., Journal of Materials Science & Technology 2020, 54, 77-86.
3. Wang, X.; Cai, J.; Liu, Y.; Han, X.; Ren, Y.; Li, J.; Liu, Y.; Meng, X., Nanotechnology 2020, 32 (11), 115401.
4. Gao, H.; Cai, J.; Xu, G.-L.; Li, L.; Ren, Y.; Meng, X.; Amine, K.; Chen, Z., Chem. Mater. 2019, 31 (8), 2723-2730.
5. Meng, X.; Comstock, D. J.; Fister, T. T.; Elam, J. W., ACS Nano 2014, 8 (10), 10963-10972.

In the past decade, cobalt-free LiNi_0.5Mn_1.5O₄ (LNMO) spinel has been considered as a next generation cathode because of its high operating voltage (~4.7 V vs. Li/Li⁺), low cost, and good power capability. However, the main challenge for a commercialization of LNMO cathode lies in parasitic reactions occurring at cathode-electrolyte interface (CEI) due to oxidative decomposition of electrolytes. Resulting side-reaction products migrate and attack solid-electrolyte interphase (SEI) layer on graphite anodes, which in turn leads to an unwanted consumption of active Li-ion and consequent capacity fading.
Significant R&D efforts have been dedicated to finding strategies to overcome the electrolyte instability issues at high-voltage battery cells. One of the most effective pathways is adopting electrolyte additives. Among various additives, triethyl borate (TEB) has been reported as an effective additive that can passivate the LNMO CEI in half-cells (i.e., LNMO/Li). However, there is a lack of literature data proving that TEB is still useful in LNMO/graphite full-cells. In particular, the most critical barrier for the commercialization of LNMO is electrolyte oxidation and concurrent parasitic reactions at SEI on graphite anodes, which in turn leads to a poor cycle life of LNMO/graphite full-cells.
In this work, we investigated the role of TEB additive on the interfacial stabilities of electrodes in full-cells. Electrochemical measurement results indicated that TEB additive greatly improve full-cells cycle life by lower active Li⁺ loss during cell formation cycles. By Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses, we confirmed that TEB participated in formations of both CEI and SEI layers. However, combinatorial study of the TEB-treated graphite and LNMO electrodes revealed that the performance improvement of the full-cells was mostly attributed to an improved SEI stability on graphite anodes. For example, dQ/dV profiles showed the reductive decomposition of TEB earlier than EC during the SEI formation on graphite anodes.
In addition, TEB additives suppressed the formation of LiF on the cycle-aged graphite SEI as evidenced by XPS analysis. This result indicates that TEB inhibited electrolyte decomposition and suppress the Li-ion consumption by maintaining a thinner SEI on graphite. As a result, the full-cells with TEB additive delivered 10% improved cycle life compared with the baseline data (i.e., no additive). Among the various TEB compositions (0 – 4 wt%) investigated, 1 wt% TEB offered both improved capacity retention and low cell resistance (50% decrease from the baseline data at 50^th cycle) as evidenced by electrochemical impedance spectroscopy (EIS) analysis. Results from this work offered a fundamental understanding on the improvement mechanisms of TEB additive at electrode-electrolyte interphases.

The global energy crisis coupling with the consumption of fossil fuels and the associated environmental issues, has stimulated extensive interest in searching for clean, efficient and sustainable energy storage and conversion systems. In this talk we are going to introduce a novel chemical solution approach for epitaxial thin film deposition and oxide nanoparticle network synthesis. The use of water soluable polymer to bind the metal ions has several advantages. The formation of covalent complexes between the lone pairs on the nitrogen atoms of the polymer and the metal cations make it possible to prepare almost any metal polymer precursor solutions. The unique chemistry and processing design of this technique deliver stable and homogeneous solutions at a molecular level that allows epitaxial growth of high-quality thin films and oxide nanoparticle network materials. Oxygen electrocatalysis, including both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), dominates the performance of the devices. However, the sluggish kinetics of these two reactions limits their performance. Therefore, development of non-precious metal-based oxygen electrocatalysts is greatly demanded. Metal oxides have attracted extensive interest as alternative electrocatalysts due to their low price and good endurance under relatively high temperature, which can be doped with a wide range of cations attributed to their flexible compositions and structures, leading to easy manipulation of their electrocatalytic properties. We study the nanoscale engineering of perovskite oxides and layered oxides in energy conversion/storage devices and focus on the electrode catalyst design and fabrication for boosting ORR and OER electrocatalysis.

We have identified CrOF₄ and NbFe₃(PO₄)₆ as candidate cathodes with density functional theory (DFT) calculations which suggest a useful balance of low chemical expansion and gravimetric energy density. Low chemical expansion is a likely requirement for high cycle batteries and the employment of solid electrolytes. CrOF₄ and NbFe₃(PO₄)₆ have predicted average voltages of 5.1 and 4.0 V and chemical expansion less than 3% and 1% within the stoichiometric range of 0 to 1 Li per formula unit, respectively, significantly outperforming commonly used cathode materials. While practical energy densities can be challenging to estimate with DFT calculations, DFT suggests that these exhibit gravimetric capacity densities in excess of 200 and 100 Ah/kg and gravimetric energy density in excess of 1020 and 400 Wh/kg, respectively, depending on irreversible processes during cycling. These were identified by screening approximately 38,000 compounds using statistical models trained on available data and physically motivated descriptors. We also assessed ease of synthesizablity in our selection of these materials, and will provide an update on efforts of experimental validation.

The development of lithium-ion batteries (LIBs) with high specific capacity and long lifespans has become a research hotspot in recent years due to rapidly growing energy demands in many fields such as electric vehicles, hybrid electric vehicles, and portable electronic devices. At present, graphite is the most widespread anode material for LIBs owing to low working potential and superior cyclability with high coulombic efficiency, but its unsatisfying theoretical capacity (372 mAh g^-1) has led researchers to seek for alternative anode materials with high specific capacity and rate performance. Silicon based anode material, which has extremely high theoretical capacity (4200 mAh g^-1) and low working potential (<1.0 V vs. Li/Li⁺), has attracted great interests in the energy storage area. However, the huge volume expansion up to 400% during the alloying/dealloying process of Si with lithium seriously restrict its widespread application. In order to overcome the issue, SiO₂ based material, which has smaller volume expansion (100%) compared to Si, has been proposed as alternative anode material for LIBs. Moreover, SiO₂-carbon composites are highly attractive as promising anode materials owing to their improved electrical conductivity induced by carbon species. It has been found that introduction of nitrogen and phosphorus co-doping into the carbon structure can further accelerate electron transfer, which is attributed to strong dipole effect originated from difference of electronegativity of the elements (P: 2.2, C: 2.6, and N: 3.0).
Herein, yolk-shell structured SiO₂@N, P co-doped carbon (SiO₂@NPC Y.S.) was fabricated by in situ thermal phosphidation and carbonization of SiO₂@PPy, followed by the partial etching of SiO₂ using dilute HF. The core-shell structured SiO₂@PPy was synthesized using hydrothermal method to conduct thermal polymerization of polypyrrole on the surface of SiO₂ sphere. The prepared SiO₂@NPC Y.S. nanospheres exhibited superior initial capacity of 1261 mAh g^-1 at the current density of 0.1 A g^-1 owing to improved electrical conductivity from heteroatom doping on carbon shell. Furthermore, the long-cycle reversible capacity can be preserved at 705 mAh g^-1 even after 300 cycles stemming from highly controlled yolk-shell structure. The unique yolk-shell structure with sufficient void space between yolk and shell has been demonstrated to be effective in alleviate the volume swelling, thereby improving the cycling performance during repeated lithium insertion/extraction process. Furthermore, the unique structure can not only prevent the aggregation of active materials but also reduce diffusion length of Li⁺ and facilitate the infiltration of electrolyte. Accordingly, this research will provide valuable insights into the future direction for the facile preparation of yolk-shell structured anode materials with highly controlled yolk size and heteroatom doped carbon shell for practical energy storage and conversion devices.

Silicon has been intensively studied as an anode material due to the high theoretical capacity (3572 mAh g^-1, Li₁₅Si₄) and a relatively low working voltage (~0.5 V vs Li/Li⁺) in lithium-ion batteries (LIBs). However, poor electrochemical properties caused by the large volume change (~ 300%) and low electronic conductivity of silicon have limited its practical use. In this regard, a carbon coating is introduced to mitigate the volume expansion of Si and improve the cycle performance of Si-based anode. However, scalable processing with a low-cost process should be developed for the practical use of silicon. Here, we report carbon-coated silicon/graphite composite (C@SGC) as an attractive anode material to control the swelling behavior and achieve improved electrochemical properties. SGC was synthesized through spray drying and the carbon layer was uniformly coated on the surface of SGC through the mechanical coating method. C@SGC shows a reversible charging capacity of ~ 1150 mAh g^-1 at the initial cycle, improved initial coulombic efficiency of 85% at 0.1C, and exhibits stable cycle performance with the capacity retention of 71% over 500 cycles at 1C. The inner buffer space and outer uniform carbon coating layer released stress, which enables the controlled swelling behavior of the C@SGC electrode during cycling.

Lithium metal anode is a promising candidate for an all-solid-state battery for exceptional traditional lithium-ion battery capabilities. Nevertheless, unwanted Li dendrite thickening, and low Coulombic efficiency hinder their feasibility. Carbonaceous materials are used as a host of Ag nanoparticles which have been proved to increase specific capacity of Lithium-ion batteries anodes. Recent research has shown the advantage of using Ag nanoparticles due to the solubility of Ag nanoparticles in Lithium which lower nucleation energy and improves the uniform deposition of Li ion improving cyclability observing a long-life cycle life. Different composition of C-Ag has been studied with different forms of carbon as graphene, carbon single and multi-wall carbon nanotubes, carbon black and graphite. Ag_(5-x) C_x (x= 1, 2, 3) among them C: Ag = 1:3 revealed high specific capacity and long cyclability performance for a range of voltage 0.001 V - 2.5 V. The ability of silver regarding formation of alloys with high lithium percentage gave the mentioned nanocomposite an excellent electrochemical stability for possible exploration in thin film batteries. Preliminary result of electrochemical studies showed high capacity and cycle retentions of composites.

The popular conducting polymers such as polyaniline and polypyrrole have been sometimes described as a potential candidate binder for high silicon anode materials due to its low price, high conductivity, and simple synthesis. However, the manufacturing process of conducing polymer-based electrodes requires environmental-unfriendly organic solvents such as n-methylpyrrolidone. In this study, a new design on polymeric binder is proposed for the high-capacity anodes. The effective addition of conductive aniline oligomers to adhesive alginate-graft-polyacrylamide binder improves the performance of the silicon/graphite composite electrodes. To do this, three-step in situ polymerization is adopted to synthesize adhesive and conductive alginate-graft-poly(acrylamide-co-acrylamide aniline tetramer). A small amount of aniline tetramer added to the binder, of 1.25 wt.%, is enough to enhance electronic and ionic transport through the silicon-based anode, while maintaining electrode adhesion. Consequently, the silicon/graphite electrode containing the alginate-graft-poly(acrylamide-co-acrylamide aniline tetramer) binder shows 701.2 mAh g^-1 after 200 cycles with excellent cyclic stability. This is significantly greater performance than that of commercial graphite electrodes.

Two dimensional (2D) materials have promising properties to regulate the ion transport across interfaces and within the electrolyte, act as substrate for metal deposition, and reduce the occurrence of dendrites. In this presentation, I will showcase our efforts in utilizing graphene, graphene oxide, phosphorene, and boron nitride nanosheets in design of rechargeable Zn and Li metal batteries. We have observed that graphene oxide materials coated on separators can regulate the transport of Li ions across the Cu-electrolyte interface evident by far less dendritic deposition of Li in comparison to non-coated Cu cells. In addition, graphene is shown to control the deposition of Zn due to minimal lattice mismatch with Zn and the zincophilic properties (strong bonding with Zn). The utilization of phosphorene in PEO-based polymer electrolytes also is shown to increase the fraction of free Li ions resulting in better ionic conductivity and low interfacial resistance. In another work, we have shown the BN nanosheets are effective in controlling the thermal conductivity in solid polymer electrolytes leading to the lesser chance of local hot spots creation in polymer batteries.

Li-ion batteries are considered as the most suitable electrochemical energy storage systems for a wide range of applications including stationary applications, when combined with renewable energy harvested systems, and automotive applications with the electrification of transportation, in order to contribute to the reduction of CO₂ emissions responsible for climate change.
Indeed, Li-ion batteries combine high specific energy and power, long cyclelife, high efficiency, high charge/discharge rate capability and low self-discharge. In addition, it is a versatile technology easily adaptable to the application by playing with the electrode materials and electrolyte composition.
However, most commercial Li-ion batteries widely use organic carbonates electrolyte containing Li salt which is volatile, flammable and can induce thermal runaway in case of inner short-circuit. In order to make the battery safer, CEA-Liten and Solvay have developed a new technology based on hybrid polymer lithium battery, where the organic carbonates electrolyte is confined in a hybrid polymer membrane as well as in gelled electrodes from their manufacturing.
Hybrid polymer membrane is prepared by using a non-aqueous sol–gel route. A new Solvay proprietary functionalized PVdF is able to react and create a stable network able to trap fully the organic carbonate electrolyte. The membrane elaborated by a two-step cross-linking method and implemented by using roll-to-roll coating machine, shows homogeneous structure coupled with high ionic conductivity and high flexibility when LiPF₆ (1M) in a carbonate mix is used.
The gelled electrodes are prepared by using a second Solvay proprietary functionalized PVdF as binder, which is able to trap the organic carbonate electrolyte in the electrode microstructure. Gelled electrodes are produced according to conventional electrode manufacturing process (i.e using mixing, coating and calendering machines). Thus, gelled graphite based anode and gelled NMC622 based cathode are produced at the pilot line scale in anhydrous atmosphere, using LiPF₆ (1M) in a carbonate mix. In addition, the technology allows producing high loading electrodes (5mAh/cm2 typically for the gelled cathode) with suitable mechanical properties adapted for winding. No damage was observed regarding the integrity of the gelled electrodes at each manufacturing step.
Proof of concept of the technology was carried out by assembling the gelled electrodes with the hybrid polymer membrane (without any addition of additional electrolyte) in various cell sizes and formats: from single layer pouch to 1 Ah stacked cell, prismatic cell or even 18650 cylindrical cell, leading to relevant electrochemical performances. In addition, the retention of the organic carbonate electrolyte has shown unequivocally a benefit effect on the safety, highlighted by calorimetry analysis and some abusive tests.
New process is today under investigations in order to manufacture the hybrid polymer membrane as well as the gelled electrodes without the any process solvent, than those used in the organic carbonate electrolyte. This way allows simplifying considerably the cell manufacturing process, increasing the safety and reducing the cost and the environmental footprint because no solvent is evaporated and recovered, as it is the case with conventional Li-ion batteries.

CEA-Liten and Solvay have developed a battery technology operating at room temperature called SOLGAIN™. In this technology, the liquid electrolyte is already contained in the components (electrodes and membrane) before the cell assembly. After having developed the preparation process of a hybrid polymer membrane retaining electrolyte, CEA-Liten and Solvay have imagined then to use this technology with bipolar architecture. The bipolar technology is based on the use of bipolar electrode(s) and requires that each compartment is perfectly isolated: no exchange of electrolyte between adjacent compartments is acceptable. At each extremity of the stacked assembly is positioned a terminal electrode: a negative one and a positive one separated from the adjacent bipolar electrode by an ion-conducting separator. The physical contact between the terminal electrodes and the bipolar one is mainly prevented by the presence of the membrane but also by electronic insulation adhesive tape positioned on aluminium tab.
A bipolar SOLGAIN™ battery have been performed in soft pouch cell using LiNi_xMn_yCo_zO₂ (NMC) and negative electrode Li₄Ti₅O₁₂ (LTO). Due to the potential of LTO vs Li₊/Li, aluminium can be used as current collector for both electrodes (negative and positive). The bipolar SOLGAIN™ were then cycled at low C-rate between [2.0-6.0V] with a cut-off voltage for each compartment between [1.0-3.0V]. The voltage curves of the two compartments are rigorously similar a long time, such a behavior proves that there is no ionic short circuit. SOLGAIN® technology allows keeping the electrolyte inside each compartment and thus making possible the working of bipolar LTO/NMC based batteries in cycling. This promising result evidences the interest of the SOLGAIN® technology in bipolar architecture.
Moreover, as the proof of feasibility was made for two lithium-ion systems, there is no reason that it was not also applicable for other electrochemical couples of Li-ion or Li metal technology, even for other metal-ion technologies.

With the global economy pushing towards a greener and cleaner energy future for the world, renewable energy storage technologies must continue to develop and improve to allow for a seamless transition from the ways of the past to a carbon neutral future. To this end, renewable battery technology and in particular that of the capacity of the anode must be improved. Furthermore these improvements must be made across various battery technologies (Lithium/Sodium-ion) and be cost-effective to allow for its widespread implementation and use worldwide.

In this work, Tin(II) Oxide (SnO)/single wall carbon nanotube (SWCNT) composite electrodes are analysed as a possible alternative anode material for both lithium (LIB) and sodium-ion batteries (NIB). The LIB is limited by the current commercial anode material of graphite with a relatively low theoretical capacity of 372 mAh g^-1 whilst NIB’s use hard carbon with a capacity of roughly 300 mAh g^-1. Alloy/de-alloy materials are envisioned to be a suitable candidate for next generation LIBs/NIBs due to their large specific capacities although major drawbacks concern the poor cycling life associated with the volume change and the associated irreversible capacity. To overcome such issues the downsizing of materials from the micro to the nanoscale and the fabrication of composites which incorporate both lithium active and inactive material are viewed as the most promising solutions. Nanostructured transition metal oxides, forming an inactive lithium oxide matrix are appealing candidates.

Through the implementation of a solvent engineered wet chemistry synthesis, various layered SnO microparticles are produced with several morphologies well-suited to energy storage applications whilst also being scalable and cost-effective. While SWCNTs are themselves not suited towards energy storage applications, their incorporation in the electrodes allows them to act as a conductive additive at a lower weight loading than other conventional carbon sources (carbon black/graphite), presenting a more effective strategy to form an effective electrical percolation network while also removing the need for polymer binders.

Four morphologies were selected as promising towards LIB/NIB technology and binder free electrodes were produced via filtration, removing the need for a copper current collector. The four morphologies were “thick squares” (SnO produced in H₂O), “nanoflowers” (ethanol), “platelets” (methanol:water, 70:30) and “perforated thick squares” (1-hexanol). All morphologies of SnO tested produced high capacity anodes in both LIBs/NIBs after mass loading optimization of CNTs. The thinner “platelet” like morphologies formed in ethanol and 70% methanol produced the highest capacities at low C-rates, with initial discharges of 960 and 985 mAh g^-1 recorded respectively in LIBs. The reduced dimensions and significantly increased surface area of the platelet-like structures permit greater contact between electrode and electrolyte resulting in higher Li⁺ ion flux across the interface and thus greater charge capacity. A maximum capacity of 670 mAh g^-1 was recorded for the nanoflower morphology in NIB with testing currently occurring on the remaining morphologies. Furthermore, using the “nanoflower” morphology and a mass loading of 5 mg cm^-2, an areal capacity of 5.41 mAh cm^-2 was recorded which is far in excess of commercial graphite anodes. Issues still remain regarding the cycling performance of the material due to the larger volumetric change associated with the charge/discharge process (360%) and this is where current work is focused.

References:
[1] S. Jaskaniec, S. R. Kavanagh, S. Ryan, J. Coelho, C. Hobbs, A. Walsh, D. O. Scanlon and V. Nicolosi, npj 2D Mater. Appl., 2021, 5, 27.
[2] J. H. Shin and J. Y. Song, Nano Converg., 2016, 3(1), 9.
[3] F. Zhang, J. Zhu, D. Zhang, U. Schwingenschlögl and H. N. Alshareef, Nano Lett., 2017, 17, 1302–1311.

The increasing energy demands of the 21^st century will require fundamental improvements to existing battery technology. One strategy is the improvement of the specific capacity of currently used carbonaceous anodes in Li- and next-generation Na-ion batteries. Phosphorus shows promise as an alternative anode material, with its ability to reversibly form lithium- or sodium-phosphorus compounds during electrochemical cycling, resulting in a potential capacity 6 times greater than that of standard graphite or hard carbons.^1,2 However, the conductivity, stability and safety of elemental P as an anode prevents the technology from reaching real-world applications.³ Whilst previous attempts have been made to utilize carbon-phosphorus composites (i.e., with separate carbon and phosphorus domains),^4,5,6 the incorporation of phosphorus into the graphitic lattice and subsequent use of these materials in electrochemical applications has not been explored. Our single-precursor, single-step pyrolysis synthesis allows the production of stable phosphorus-doped carbon materials. Interstitial incorporation of phosphorus into the turbostratic graphitic lattice gives greater stability than pure phosphorus and improved capacity in Li-ion batteries compared to an undoped graphite. The Na insertion chemistry is similarly explored. Moderate control of the phosphorus content, which is also present in a variety of allotropes, provides some control over capacity and stability. Via a thorough structural, compositional and electrochemical analysis, including the use of ex situ solid-state NMR, the insertion mechanisms of these materials may be explored. Identification of the preferential sites used for ion storage within phosphorus-doped graphite gives an improved understanding of the further alterations needed to develop it as a future anode material.

The development of energy dense and environmentally friendly secondary batteries is central to meeting the ever-increasing global energy demand. Consequently, sodium (Na)-ion batteries are promising candidates to replace traditional Li-based technology due to their greater relative abundance, lower cost, and ease of processing. Polyanionic alluaudite structures are potential intercalation compounds for Na-ion cathodes. In particular, the sulfate alluaudite variant Na₂Fe₂(SO₄)₃ exhibits the highest ever Fe^2+/3+ redox voltage (3.8V vs Na) observed in any cathode material, which is attributed to the unique edge-sharing MO₆ (M = Fe, Mn, Ni, Co) octahedra in the alluaudite structure.¹ However, sulfates are chemically unstable and suffer from low theoretical capacities. Although phosphate alluaudites can reach high (~140 mAh/g) capacities, they exhibit lower (2.7 V vs Na) Fe^2+/3+ redox potentials, limiting their energy densities.² The development of alluaudite cathodes has been limited by the number of electrochemically active transition metals in this structure type. Barring just a few compositions, only the low voltage Fe^2+/3+ redox has been harnessed, even though structures containing multiple transition metal species have been reported. Herein we successfully apply a set of design principles to activate the Mn^2+/3+ redox couple in alluaudites. First, vanadate compounds were explored in order to increase the electrical conductivity of typically insulating polyanionic structures. Secondly, Al substitution was employed to buffer Jahn-Teller distortions in MnO₆ octahedra, resulting in more facile Mn^2+/3+ redox. We report the synthesis of a new redox active Mn-based alluaudite composition and employ synchrotron X-ray diffraction (SXRD), solid-state nuclear magnetic resonance, density functional theory, X-ray absorption spectroscopy, and scanning electron microscopy to characterize the structure and morphology of this material.³ The electrochemical Na-ion de(intercalation) processes of the alluaudites were probed through galvanostatic cycling, galvanostatic intermittent titration technique, and ex-situ SXRD. The Mn alluaudite compositions were found to be electrochemically active, with Al substitution resulting in a more than twofold increase in discharge capacity. The successful activation of a higher voltage Mn^2+/3+ redox couple via compositional design opens up a new compositional space for alluaudites, paving the way for high energy density Na-ion cathodes.
References:
1) Barpanda, Prabeer, et al. "A 3.8-V earth-abundant sodium battery electrode." Nature communications 5.1 (2014): 1-8.
2) Huang, Weifeng, et al. "Self-Assembled Alluaudite Na2Fe3− xMnx (PO4) 3 Micro/Nanocompounds for Sodium-Ion Battery Electrodes: A New Insight into Their Electronic and Geometric Structure." Chemistry–A European Journal 21.2 (2015): 851-860.
3) Wu, V.; Giovine, R.; Foley, E. E.; Finzel, J.; Balasubramanian, M.; Sebti, E.; Mozur, E.; Clément, R.J. Unlocking new redox activity in alluaudite cathodes through compositional design. In preparation

One effective solution to improve energy and power densities and reduce the cost of batteries is to reduce the ratio of inactive components, such as current collector, separator, cell container, by increasing mass loading of electrodes. However, the conventional film electrode fabrication cannot produce high mass loading electrodes mainly for two reasons: sluggish ion transport inside the thick film and migration of binder to the electrode surface during the drying process. Here, we produced the 3D carbon microlattices with periodic micropore structures that enhance ion transport by using a liquid crystal display-SLA (LCD-SLA) 3D printer costing 300USD. Carbon microlattices with an average beam width of 32.8µm reached the record-high areal capacity of 21.3 mAh cm^–2 at high mass loading of 98 mg cm^–2 without sacrificing performance, overcoming the limit of mass-loading that conventional electrodes suffer (~30 mg cm^–2). Furthermore, binder-free, pure-carbon elements of microlattices enable us to detect structural changes in HC that endorse hypothesized intercalation of Na ions at plateau regions by temporal ex-situ XRD measurements. Our results will advance development of high-performance and low-cost anodes for SIBs as well as understanding on Na ion storage mechanisms in HC, expanding the utilities of 3D-printed carbon architectures in both applications and fundamental studies.

With a growing need for clean water worldwide, interest in capacitive deionization (CDI) is growing as a potentially low energy desalination methodology. Current commercial technologies are using activated charcoal at both electrodes, but these materials suffer from low capacity and poor durability.
Inspired by the recent advances in sodium-ion batteries, several studies have proposed to use intercalation materials to increase the desalination potential of electrodes. Among the proposed materials for desalination batteries, hexacyanoferrate Prussian blue analogue materials (PBAs) are especially interesting because of their open framework structure that allow insertion of Na with high reversibility and fast kinetics.
This study focused on the development of heterostructured NaM_xN_y(HCF) PBs with M and N being Ni, Mn or Fe, with an optimization for performance and durability in 1M NaCl electrolyte. Materials were synthesized using a simple, cost-effective and scalable coprecipitation synthesis process at room temperature. Different compositions and electrode architecture were tested and salt absorption above 75 mg/g of electrode at rates above 100 mg/g/min will be reported for PBAs containing Ni and Mn.

Low-cost, long-duration energy storage is critically needed for the resilience of the electric grid powered by renewables like wind and solar. Low-temperature (<130 °C) molten sodium (Na) batteries with NaI-metal halide molten salt catholytes have been developed to address this requirement. This technology avoids the safety concerns caused by metal dendrites and flammable organic solvents found in Li-metal or Li-ion batteries. One of the remaining challenges for molten Na batteries is to achieve high current density performance while cycling at temperatures just above the melting point of Na (98 °C). In particular, catholyte stability under high rates and wide capacity windows presents the greatest hurdle for practical applications. To optimize the catholyte compositions under phase restrictions and conductivity requirements, our group has examined a variety of chemistries, including mixtures of NaI with AlCl₃, AlBr₃, and GaCl₃. To better understand the failure modes within the catholyte, we have performed electrochemical kinetics studies and mathematical modeling of the iodide-triiodide speciation. Results reveal the equilibrium speciation limitations to usable capacity and current densities for the given catholyte compositions. Additional experiments, including cyclic voltammetry and chronoamperometry, probe the influence of the electrode material on electrochemical kinetics and stability during cycling. Insights from these fundamental studies provide guidance for the future design of robust catholyte chemistries and cathode materials.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and 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.

Sodium ion batteries (NIBs) are seen as key to sustainable energy storage. NIBs based on earth-abundant materials offer efficient, safe, and environmentally sustainable solutions for a decarbonized society. However, to compete with mature energy storage technologies such as lithium ion batteries, further progress is needed, particularly in the areas of energy density and operational lifetime. Considering these aspects as well as a circular economy perspective, we use biodegradable cellulose nanoparticles for the preparation of a gel polymer electrolyte that offers a high liquid electrolyte uptake of 2985%, an ionic conductivity of 2.32 mS/cm, and a Na⁺ transference number of 0.637. A balanced ratio of mechanically rigid cellulose nanocrystals and flexible cellulose nanofibers results in a mesoporous hierarchical structure that ensures close contact with metallic Na. This architecture offers stable Na plating/stripping at current densities up to ±500 μA/cm², outperforming conventional fossil-based sodium-ion batteries having separator-liquid electrolyte systems. Paired with an environmentally sustainable and economically attractive Na₂Fe₂(SO₄)₃ cathode, the battery reaches an energy density of 240 Wh/kg, delivering 69.7 mAh/g after 50 cycles at a rate of 1C. In comparison, Celgard in liquid electrolyte delivers only 0.6 mAh/g at C/4. Such gel polymer electrolytes may open up new opportunities for sustainable energy storage systems beyond lithium ion batteries.

With the increasing research interest in rechargeable batteries, avoiding structure degradation in cathode material is crucial to prolong the lifecycle of a battery. Structure degradation often occurs during deep charging phase as anionic redox activity causes irreversible structure reordering that accompanies oxygen gas release. This makes balancing capacity and stability of a cathode material incredibly difficult. Recently studies have shown an exceptional reversibility and low-voltage hysteresis of oxygen-redox active cathode, Na₂Mn₃O₇ (NMO), as the material shows little transition metal migration and structure reordering in deep charging phases. In this work, we utilize ground state and excited state calculation to determine the redox mechanism of different sodium-based cathode material and investigate how defect structures can impact the stability of different cathode materials.

Ambient sodium-sulfur battery operation is desirable due to the low cost and abundance of active materials but is not realized due to the poor fundamental understanding and system optimization. We identify chemical and physical parameters that strongly influence performance using in-situ optical microscopy. With optical microscopy we can chart average polysulfide speciation in the cell electrolyte as polysulfide dissolution occurs and visualize morphological changes to the anode and cathode. When comparing glyme ether (monoglyme-G1, diglyme-G2, and tetraglyme G4) based electrolytes with 1M NaPF₆, we identify that G1 minimizes polysulfide dissolution, while G2 provides the most sodium metal anode stability. Further investigation of the G2 based electrolyte, reveals that orientation of the electrodes dramatically influences performance, emphasizing the operational need to position the sulfur cathode face-up. We also demonstrate that co-solvent blends of G2 and FEC at 1:0.1 v:v ratios stabilize sodium metal plating and stripping processes and prevent dendrite formation. However, this blend limits the sodium-sulfur reaction to a primary cell or single discharge. In order to investigate why the FEC additive prohibits cyclability, we use ultrafast spectroscopy to elucidate the interactions between the solvents and constituents including salt ions and polysulfide.

Having dominated the market for over the past three decades, Li-ion batteries (LIBs) are now faced with a challenge for the use in grid-scale energy storages because of the rarity of Li resources. To meet the growing demands of power sources, Na-ion batteries (NIBs) have emerged as a promising alternative for LIBs owing to the high abundance of sodium. Despite the considerable attention to NIBs, their overall electrochemical performance remains inferior to LIBs because of the less negative redox potential and larger ionic radius of Na ^[1,2]. Thus, the development of Na-ion cathodes with high energy densities and long cycle lives are critical for NIBs to be widely applied as an alternative to LIBs. Anionic redox, which was discovered early in LIBs with extraordinary energy densities ^[3], has been widely reported as an effective method for high performance Na-ion cathodes. One representative example is Na₂Mn₃O₇, of which exhibits superior rate performance with high theoretical capacity of 150 mAhg^{-1 [4]}.
In addition to introducing anionic redox reactions, another effective approach to promote the cycle lives of Na-ion cathodes is doping redox-inactive cations. Among various dopants available, Al, with its natural abundance and low cost, has shown to improve long-term cyclability of cathodes by widening Na layers ^{[5, 6]}. Above two strategies imply that the combination of redox-inactive dopants and anionic redox-based Na-ion cathodes will lead to enhanced performance suitable for future cathodes. Despite such promising aspects, doping strategies have mostly been employed mostly for NaTMO₂ (TM = transition metal elements) stoichiometries, where cationic redox prevails over anionic redox.
In this study, we investigate the influence of Al dopants on the electrochemical performances of Na₂Mn₃O₇. Using Na_2.4Al_0.4Mn_2.6O₇ as a testbed chemical formula, we predicted the additional active Na sites that improves capacity while smoothening voltage profiles. Furthermore, the addition of Al dopants with higher electronegativity and lower oxidations states causes the structural changes beneficial for fast charging batteries. Lastly, by employing Ti dopants with opposing properties to Al, we also discuss the relationship between the dopant properties (e.g. electronegativity, oxidation state) and electrochemical performance (e.g. cyclability, voltage), which can enable the development of high performance sodium manganese oxide cathodes.
References
[1] Tapia-Ruiz, Nuria, et al., Journal of Physics: Energy 3.3 (2021): 031503
[2] Park, Young-Uk, et al., Journal of the American Chemical Society 135.37 (2013): 13870-13878
[3] Sathiya, Mariyappan, et al., Nature materials 12.9 (2013): 827-835
[4] Song, Bohang, et al., Chemistry of Materials 31.10 (2019): 3756-3765
[5] Pang, Wei-Lin, et al., Journal of Power Sources 356 (2017): 80-88
[6] Ramasamy, Hari Vignesh, et al., The journal of physical chemistry letters 8.20 (2017): 5021-5030

Unsustainable mining and limited availability of lithium-ion battery materials have created a driving need to develop alternatives such as sodium hosts.^1-4 The development of suitable anode materials remains a major challenge facing sodium-ion battery development.² Efforts into studying charge storage of sodium in transition metal sulfides have gained traction due to improved kinetics compared with oxides.⁵ Van der Waals CrS₂ has been predicted to be a good intercalation host for Na⁺ but has not been isolated as a bulk phase. Rather, [CrS₂]^- layers exist in delafossite-related materials such as NaCrS₂, which has only a moderate reversible capacity of about 100 mAh/g.⁶ Here we present a new material, H_xCrS₂ formed by proton-exchange of NaCrS₂ which has a measured capacity of 728 mAh/g with significant improvements to capacity retention, sustaining over 700 mAh/g during cycling experiments. This is the highest reported capacity for a sulfide electrode and exceeds the capacity of antimony (576 mAh/g) which has been the most promising anode to date, pairing high capacity with high rates.⁷ These capacity improvements are facilitated by fast sodium-ion diffusion with diffusion constants in H_xCrS₂ of ~10^-9 cm²/s. Pretreatment by proton-exchange offers a route to materials such as H_xCrS₂ which provide fast diffusion and high capacities for sodium-ion batteries.
References:
(1) Tarascon, J.-M. Is Lithium the New Gold? Nature Chemistry 2010, 2, 510-510.
(2) Hwang, J.-Y.; Myung, S.-T.; Sun, Y.-K. Sodium-ion Batteries: Present and Future. Chemical Society Reviews 2017, 46, 3529-3614.
(3) Jaskula, B. W. Minerals Yearbook: Lithium. US Geological Survey (Reston, VA: US Department of the Interior and US Geological Survey, 2011) 2010, 44-1.
(4) Agusdinata, D. B.; Liu, W.; Eakin, H.; Romero, H. Socio-environmental Impacts of Lithium Mineral Extraction: Towards a Research Agenda. Environmental Research Letters 2018, 13, 123001.
(5) Hannah, D. C.; Sai Gautam, G.; Canepa, P.,; Ceder, G. On the Balance of Intercalation and Conversion Reactions in Battery Cathodes. Adv. Energy Mater. 21018, 8, 1800379.
(6) Shadike, Z.; Zhou, Y.-N.; Chen, L.-L; Wu, Q.; Yue, J.-L; Zhang, N.; Yang, X.-Q; Gu, L.; Liu, X.-S; Shi, S.-Q; Fu, Z.-W. Antisite Occupation Induced Single Anionic Redox Chemistry and Structural Stabilization of Layered Sodium Chromium Sulfide. Nat Commun 2017, 8, 566.
(7) Tapia-Ruiz, N.; Armstrong, A. R.; Alptekin, H.; Amores, M.A.; Au, H.; Barker, J.; Boston, R.; Brant, W. R.; Brittain, J.M. Chen, Y., et al. 2021 Roadmap for Sodium-ion Batteries. Journal of Physics: Energy 2021, 3, 031503.

Along with the rapid growth of the electric vehicle and other electronic device markets, ever-increasing demands on rechargeable batteries are expected shortly. As the cathode materials play a critical role in the performance and the price of the battery, the research on different aspects of cathode materials is conducted by different companies and research institutes.
So far, layered transition metal oxides are promising cathode materials due to their high theoretical capacity. However, an irreversible phase transition with the electrochemical cycling occurred in the conventional layered materials due to the migration of the transition metals hinders the performance of the battery. For instance, only 70 % of the theoretical capacity is utilized for NCM to ensure structural stability. This issue of the transition metal migration might be aggravated with the current trend of increasing nickel content to increase the electrochemical performance. Therefore, many research attempts to suppress the transformation by doping different cations or coating the surface. On the other hand, the sustainability issue related to the low abundance and the high price of cobalt and nickel, which are the key atoms of the current cathode materials, must be incorporated in the future research direction of cathode materials.
Herein, we report low-cost birnessite-type layered manganese oxide as cathode materials vs. Li⁺/Li and Na⁺/Na. Manganese oxide usually shows Mn migration leading to the irreversible transition to spinel-type phase. In this study, this irreversibility was alleviated by controlling the content of interlayer species such as crystal water and cations. Furthermore, we attempted to elucidate the triggers and mechanisms of the reversible phase transition according to the variables. We expect this work to suggest not only a low-cost cathode materials with high cyclability but also a reversible electrochemical phase transition mechanism to solve the irreversibility issue of the layered cathode materials.

Long-duration energy storage (LDES) continues to emerge as a critical necessity in the evolving sustainable, carbon-free global energy infrastructure. While batteries are expected to play key roles in meeting select LDES demands, both current and developing technologies will be challenged to safely and reliable store energy at unprecedented levels. The required increases in battery scale, durability, and longevity needed for these very large systems introduces new issues associated with safety and reliability that must be considered. Here, we describe how molten salt-based batteries, formulated from earth-abundant reagents, may offer promise for safe and reliable storage from several different perspectives including long discharge duration (e.g., >6-10 hours), long storage duration between charge and discharge (long shelf-life), or long battery lifetime (>10-15 years). We will describe here the structure and chemistry of emerging molten-salt based batteries and highlight why they may be well-suited for LDES. For example, we will consider emerging low temperature (near 100°C) molten sodium-halide batteries, comprising a molten sodium anode, a fully inorganic, molten sodium iodide-based metal halide salt catholyte, and an efficient solid state sodium ion-conducting separator. These batteries show high voltage (>3.5V) and promising cycle life at 110°C. Importantly, in simulated failures, these molten salt-based batteries do not exhibit thermal runaway or generate hazardous gas overpressure. For LDES applications, these fully inorganic systems are projected to be scalable for long-duration discharge, they have historically long lifetimes, and they can be utilized for long shelf-life storage and seasonal storage, as charged batteries can be “frozen,” providing reliable energy storage with extremely low self-discharge. Continued advances in this class of batteries will further open the door to additional, low-cost battery chemistries.

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.

The physicochemical properties of hard carbon can vary significantly depending on the precursor used during its synthesis. Among various precursors for hard carbon, cellulose has been getting significant attention because of the excellent electrochemical performances of the hard carbon obtained from its decomposition. However, the correlation between the microstructure or crystal structure of the resultant hard carbons from cellulose and their electrochemical properties looks still elusive. Hence, this study compares the sodium-ion storage behaviors of fiber cellulose-based hard carbon composed of crystalline and amorphous grains with those of microcrystalline cellulose (MCC)-based hard carbon without any amorphous grains. The presence or absence of amorphous regions affects the pore size and distribution of hard carbons significantly. Particularly, the hard carbon obtained from a thermal decomposition of MCC exhibited a high capacity reaching 300 mA h g^–1 thanks to plenty of open pores, whose size is primarily less than 2 nm. Additionally, ²³Na MAS NMR analysis revealed that the characteristic pore structure from MCC played a key role in extending the reversible sodium storage of hard carbon. This study provides a meaningful insight into understanding the effect of the microstructure and crystal structure on the sodium storage mechanism of hard carbons with different cellulose precursors.

High energy long life rechargeable battery is considered as key enabling technology for deep de-carbonization. Energy storage in the electrochemical form is attractive because of its high efficiency and fast response time. Besides the technological importance, electrochemical devices also provide a unique platform for fundamental and applied materials research since ion movement is often accompanied by inherent complex phenomena related to phase changes, electronic structure changes and defect generation. In this seminar, I will discuss a few new perspectives for energy storage materials including new fast ion conductors, new intercalation compounds and their interfacial engineering. With recent advances in characterization tools and computational methods, we are able to explore ionic mobility, charge transfer and phase transformations in electrode materials in-operando, and map out the structure-properties relations in functional materials for next generation energy storage and conversion. Moreover, I will discuss a few future priority research directions for electrochemical energy storage.

Lithium (Li) metal has been highly regarded as an ultimate anode for high-energy rechargeable batteries, ascribed to its extremely high capacity (3860 mAh/g) and the lowest negative electrochemical potential (-3.04 V versus the standard hydrogen electrode). However, Li metal has been hindered from commercialization, due to its high reactivity and dendritic growth. To this end, uncountable efforts have been invested to address these issues and they can be categorized into two main strategies: (i) architecting Li anodes and (ii) Li interface engineering. In the past decade, atomic layer deposition (ALD) has emerged as a new technique for engineering battery interfaces, featuring inorganic coating materials.^1-3 Following ALD, molecular layer deposition (MLD) recently has been employed to develop polymeric coatings for lithium-ion batteries and beyond.⁴ Owing to their same operational principle and similar working mechanisms, ALD and MLD share some unrivaled capacities, such as enabling extremely uniform and conformal coatings, atomic/molecular preciseness, low deposition temperature, and so on.^4-5 Using MLD, in a recent study we developed three new lithium-containing polymers, lithicones.⁶ Among them, we found that LiGL (GL = glycerol) is particularly superior, showing high ion conductivity and flexibility. As a consequence, the LiGL-coated Li metal anodes could achieve extremely long-life cyclability (over 15,000 cycles) without having any sign of failure at 5 mA/cm² and 1 mAh/cm². We found that the LiGL coating could protect the Li metal from corrosion, significanlty mitigate electrolyte decomposition and formation of solid electrolyte interphase, and therefore dramatically extend the lifetime of Li||Li symmetric cells. Thus, this work paves a new avenue for developing safety-reliable high-performance lithium metal anodes.

References:
1. Meng, X.; Yang, X. Q.; Sun, X. L., Emerging applications of atomic layer deposition for lithium-ion battery studies. Adv. Mater. 2012, 24 (27), 3589-3615.
2. Meng, X., Atomic layer deposition of solid-state electrolytes for next-generation lithium-ion batteries and beyond: Opportunities and challenges. Energy Storage Materials 2020, 30, 296-328.
3. Meng, X., Atomic-scale surface modifications and novel electrode designs for high-performance sodium-ion batteries via atomic layer deposition. J. Mater. Chem. A 2017, 5, 10127-10149.
4. Meng, X., An overview of molecular layer deposition for organic and organic-inorganic hybrid materials: Mechanisms, growth characteristics, and promising applications. J. Mater. Chem. A 2017, 5 (35), 18326-18378.
5. Sun, Q.; Lau, K. C.; Geng, D.; Meng, X., Atomic and molecular layer deposition for superior lithium-sulfur batteries: Strategies, performance, and mechanisms. Batteries Supercaps 2018, 1 (2), 41-68.
6. Meng, X.; Lau, K. C.; Zhou, H.; Ghosh, S. K.; Benamara, M.; Zou, M., Molecular Layer Deposition of Crosslinked Polymeric Lithicone for Superior Lithium Metal Anodes. Energy Material Advances 2021, 2021, 9786201.

Lithium (Li) metal has drawn a special attention especially from battery researchers investigating next-generation anodes, due to to its excellent properties: high specific capacity (3860 mAh/g), the most negative standard potential (around -3.04 V vs. SHE), and low density. However, inherent challenges associated with inhomogeneous Li plating/stripping and low Coulombic efficiency impede the practical use of Li anode for conventional batteries. As one of the promising approaches, the functionalized battery separators have received a significant attention from big battery companies and academics to improve the intrinsic weaknesses of polyolefin-based separators and the battery safety. In general, polyolefin-based separators have two major problems: 1) relatively poor electrolyte wettability and 2) huge thermal shrinkage. By coating/depositing a functional material layer over the polyolefin separator, both problems originating from the material properties of polyolefins can be dramatically improved.
Separator-functionalizing materials are systematically classified into six categories, in order to show how each type of materials affects the morphology of deposited Li and the electrochemical performances of Li metal batteries. The detailed research direction for functionalized battery separators will be given in this talk.

Materials informatics (MI), a data-driven approach for materials discovery, has attracted significant recent attention in the field of rechargeable batteries. Instead of relying on the experience and intuition of researchers for exploring new materials, the MI approach employs data science techniques that can, in principle, reduce the time and cost of the discovery of new materials with superior battery performance. In fact, virtual screening of compounds has been a particularly active research field; new solid-state materials (primarily crystalline) have been successfully discovered using this strategy by applying computational techniques to conveniently predict desirable properties. By contrast, the MI-based approach has not been frequently employed for liquid-state materials (primarily liquid electrolytes). This is primarily because of the difficulties involved in obtaining sufficient datasets for applying MI techniques. The properties of the SEI film formed at the electrode/electrolyte interface and those of the bulk electrolyte, such as Li-ion conductivity and electrochemical stability, must be considered in the material design of liquid electrolytes. However, the complicated mechanism of the formation of the SEI film can induce significant computational costs for preparing the numerous datasets required to apply MI techniques. An effective approach for MI-driven materials discovery for liquid electrolytes involves the use of an automated robotic high-throughput experimental setup. Although high-throughput experiments have been effectively used to acquire large datasets, these methods have not yet been extensively applied for MI-driven materials discovery of liquid electrolytes, owing to difficulties in performing automated sequential electrochemical analysis in conjunction with big data processing.
An automated robotic experimental system was recently developed by our group for discovering new multicomponent electrolytes for Li-metal-based batteries (ref). Although superior searching throughput more than 400 samples per day was achieved, adequate experimental design is essential to realize high-throughput exploration of electrolyte composition from large searching space. For example, when considering a combination of selecting 5 types from 30 types of chemicals, the candidates are up to 305 (2.43 × 10⁷). Thus, it is not realistic to comprehensively evaluate all the possible combination even using such high throughput experimental setup. Therefore, a specific electrolyte composition that realises a superior battery performance must be determined with only a limited number of experimental trials. In the present study, the effectiveness of a data-driven high-throughput screening method was investigated to discover multicomponent electrolyte additives for lithium metal batteries. Established machine-learning methodologies using Bayesian optimisation were employed to solve combinatorial optimisation problems for analysing datasets obtained from the automated robotic experiments, thereby minimising the number of trials required to identify the ideal electrolyte composition. As a result, we identified the specific electrolyte composition that enhanced the discharge/charge performance of the lithium metal batteries. Studies empowered by data-driven high-throughput screening methods offer new opportunities for efficiently identifying electrolyte compositions and accelerating the development of next-generation rechargeable batteries.
Refereces:
S. Matsuda, K. Nishioka, S. Nakanishi, Scientific Reports, 2019, 9, 6211

The increasing demand for next-generation energy storage systems necessitates the development of high-performance lithium batteries. Unfortunately, the current Li anode exhibits rapid capacity decay and short cycle life due to the continuous generation of solid electrolyte interface and isolated Li (i-Li). The formation of i-Li during the nonuniform dissolution of Li dendrites leads to a significant capacity loss in lithium batteries under most of the testing conditions. Since i-Li loses electrical connection with the current collector, it has been considered electrochemically inactive or “dead” in batteries. Contradictory to this commonly accepted presumption, we discover that i-Li is highly responsive to battery operations because of their dynamic polarization to the electric field in the electrolyte. Simultaneous Li deposition and dissolution occur on two ends of the i-Li, leading to its spatial progressions toward cathode (anode) during charge (discharge). Revealed by our simulation results, the progression rate of i-Li is mainly affected by its length, orientation, and the applied current density. Moreover, we successfully demonstrate the recovery of i-Li in Cu-Li cells with >100% Coulombic efficiency and NMC-Li full cells with extended cycle life.

Unregulated lithium (Li) growth is the major cause of low Coulombic efficiency, short cycle life, and safety hazards for rechargeable Li metal batteries. Strategies aiming to achieve large granular Li deposits have been extensively explored; yet, it remains a challenge to achieve the ideal Li deposits, which consist of large Li particles that are seamlessly packed on the electrode and can be reversibly deposited and stripped. Here we report a dense Li deposition (99.49% electrode density) with an ideal columnar structure that is achieved by controlling the uniaxial stack pressure during battery operation. Using multi-scale characterization and simulation, we elucidate the critical role of stack pressure on Li nucleation, growth and dissolution processes and propose a Li-reservoir testing protocol to maintain the ideal Li morphology during extended cycling. The precise manipulation of Li deposition and dissolution is a critical step to enable fast charging and low temperature operation for Li metal batteries.
Ref: C.Fang. et al, Nature Energy, 6, 987–994 (2021)

Rechargeable FeS₂ has recently re-emerged as a cathode candidate for high energy density batteries. With a theoretical capacity of 894 mAh g^-1 combined with being the most abundant metal sulfide on earth, FeS₂ holds great promise to provide a means toward higher energy density batteries in a sustainable manner. However, the complex reaction pathways of FeS₂ after the initial lithiation are not well understood and discrepancies over the intermediate and charge products formed still remain. Improved understanding of these reactions is key for combatting the pervasive capacity fade problems experienced by Li/FeS₂ secondary batteries.

In our work, we combine a suite of techniques (XRD, XANES, XPS) to investigate the lithiation and delithiation reaction pathways under a wide temperature range (RT to 100 ^oC), enabled by the use of an ionic liquid electrolyte. In particular, we report two features, which have been largely overlooked in prior studies. First, from the initial lithiation reaction, we identify hexagonal FeS and Li₂S as the intermediates formed in the two-step reaction, in contrast to the often cited Li₂FeS₂. The detection of hexagonal FeS as an intermediate phase suggests that the electrochemical pathways for FeS and FeS₂ are more similar than previously thought, with both iron sulfides exhibiting an irreversible lithiation. To emphasize the similarity between hexagonal FeS and FeS₂, we demonstrate that a composite of Li₂S: hexagonal FeS (1:1 mol) presents an electrochemically equivalent system to Li/FeS₂.

Second, upon charging to 3.0 V (vs Li/Li⁺) at various temperatures, we report, for the first time, the electrochemical formation of greigite (Fe₃S₄) as a charge product. The formation of this sulfur-rich iron sulfide compound is found to be highly dependent on both temperature (appearing at ~40 ^oC) and the availability of sulfur to drive FeS to Fe₃S₄. Interestingly, this reaction has been reported in the geology literature as a pathway to pyrite formation. While Fe₃S₄ forms reversibly for the first few cycles at 60 ^oC, its long-term formation is inhibited by the availability of sulfur due to the solubility of sulfur and polysulfides in the electrolyte as indicated by UV-VIS. After 5 cycles, this loss of sulfur inhibits Fe₃S₄ formation and the room temperature charge product, nanocrystalline tetragonal FeS, is formed instead, accounting for the capacity degradation observed within the first few cycles. Upon further cycling, we find that the Li/FeS₂ capacity stabilizes to 500 mAh g^-1 after 50 cycles. The insights presented here underscore the importance of understanding the reversibility of each of these charge products to improve capacity retention. These features are also likely to impact the emerging interest in solid-state FeS₂ systems.

Solid electrolytes have the potential to be safe replacements for the liquid electrolytes used in lithium-ion batteries. For the most part, solid electrolytes are based on ceramic materials and while there has been significant progress in this field, it is always interesting to consider alternative approaches. This presentation emphasizes the synthesis, properties and versatility of ionogels, pseudo-solid state materials that represent an emerging direction for designing and creating solid electrolytes. Ionogels are based on the confinement of an ionic liquid electrolyte within a mesoporous sol-gel derived silica matrix. The resulting material possesses the wide electrochemical window, rapid ion transport and thermal stability properties of the ionic liquid despite becoming a macroscopic solid. Because of their unique architecture, ionogels maintain a nanoscale fluidic state and thus mitigate the interfacial resistances which commonly arise at solid-solid interfaces. The use of sol-gel synthesis enables the materials to be prepared as liquids and to penetrate porous electrodes before becoming solid, an especially beneficial property for solid-state batteries. In this presentation, we highlight the versatility of ionogels. First, we show the ease in readily obtaining either Li-ion and Na-ion conducting ionogel materials, simply by modifying the synthesis and the dissolved salt. Moreover, by moving away from ionic liquids and incorporating glyme-based electrolytes, the resulting ionogel exhibits excellent interfacial stability in contact with metallic Na, leading to sodium metal batteries which exhibit specific energies in excess of 400 Wh/kg. The versatility of liquid phase processing is shown by the integration of ionogels in non-planar electrode configurations. In this case, the ionogel was designed to function as an electrolyte whose conformality was required to cover 3D post arrays of the cathode material. The resulting microbattery offers high areal energy densities from the post array while the high conductivity ionogel solid electrolyte enables high power densities. In summary, ionogels possess a unique set of processing and ion transport properties which, when coupled with their thermal and electrochemical stability, makes these materials a very promising direction for a wide range of energy storage devices.

Disordered sodium vanadate (NaV₃O₈) is synthesized for use in an aqueous zinc-ion battery (ZIB) and showed a superior capacity of 450 mAh g^-1 with a good cyclability of 82% of the capacity after 500 cycles at 0.4 A g^-1 in full cell test. Disordered NaV₃O₈ features ample structural vacancies with a large interlayer distance of 9.35 Å. In this work, a complicated mechanism of conversion-intercalation of vanadyl ions in addition to the co-intercalation of zinc ions and protons is investigated via in operando x-ray diffraction spectroscopy (XRD) and x-ray absorption spectroscopy (XAS) technique. In addition to the reversible charge storage of Zn²⁺, H⁺, and VO²⁺, VO²⁺ ions are oxidized into V₂O₅ during charging and vice versa during discharge. Employment of VO²⁺ as a redox-active charge carrier simultaneously enhances capacity and cyclability compared to the conventional single-carrier charge storage systems. This study is expected to broaden the perspective of the synergistic energy storage mechanisms for the development of higher-capacity and longer-lasting aqueous batteries.

Aqueous zinc-ion batteries are receiving increasing attention as a cost-effective alternative to lithium-based systems, owing to their intrinsic safety, lower environmental impact and high theoretical capacity. Nonetheless, the commercialization of zinc-ion batteries is critically hindered by their inferior cycling stability and low coulombic efficiency, which can be attributed to the growth of dendrites during repeated charge and discharge cycles and to the corrosion of metallic zinc in aqueous electrolytes.
Structural re-design of the electrodes is a promising route to alleviate the degradation of zinc anodes, thus prolonging stability and cycle life. To this end, 3D Printing techniques like Direct Ink Writing allow the fabrication of thick electrodes with customized geometries via the layer-by-layer deposition of a suitable ink. 3D-structured electrodes present smaller local current densities and larger contact area with the electrolyte, which promote more uniform electric fields and enhance the reversibility of the device. At the same time, the rational design of 3D printed architectures promotes the efficient transport of ions and electrons via uninterrupted diffusive path, preventing the onset of large transport resistance in thick structures, which would be detrimental to electrochemical performance. 3D electrodes also present higher loading of active material and smaller fraction of inactive components when compared to conventional slurry-coated structures, which is beneficial to energy density.
Here we present the fabrication of 3D printed zinc-ion batteries based on mildly acidic aqueous electrolytes using Direct Ink Writing. Different ink formulations were investigated for the Zn-metal anode in order to achieve the optimal printability and longest cycling stability. The degradation of the 3D printed electrodes was studied via post-mortem characterization, finalized at investigating the morphology, spatial distribution and composition of the cycling by-products and their effect on the cycling performance. Finally, the Zn anodes were coupled with a 3D printed cathodes to assemble fully-3D printed aqueous Zn-ion batteries.

With lithium-ion batteries seemingly reaching their developmental limits, researchers are exploring new chemistries to obtain the higher energy densities needed for demanding applications. Batteries based on Mg chemistries could achieve these goals. Oxides with a spinel structure are predicted to provide a favorable combination of properties to function as magnesium cathodes, and are of interest to create a fundamental understanding of Mg²⁺ motion within the lattice. Traditionally, Mg²⁺ intercalation is thought to suffer from sluggish mobility, despite theory and experiments suggesting otherwise. Predicted energy barriers for the Mg²⁺ hops between tetrahedral sites via the vacant octahedral sites are low enough to enable sufficient room temperature transport. Experimental studies have shown Mg²⁺ motion at comparable timescales. While the activation barriers could be extracted, the path followed by the Mg²⁺ cation during a hop remains to be elucidated.
To better understand the trajectories for multivalent ion motion in spinel oxides, variable temperature neutron diffraction and pair distribution function (PDF) are used to examine the average and local structure as motion is induced and the ability to diffuse is increased. Reverse Monte Carlo (RMC) profiling is then used to map the ionic pathways and observe cationic motion, via large-box modeling of the crystal structure. Further contrast is provided by studying similarly structured samples where hopping is predicted to face higher activation barriers than Mg and, thus, show slower migration. Insight into how ion mobility is achieved in spinel structured oxides will better inform the design of new battery cathode host structures and electrolytes to help push Mg batteries into commercialization.

As the world transitions from fossil fuels to renewable energy sources, demand for energy dense battery materials will continue to rise. Today, the most common battery technology in electric vehicles and portable devices is based upon Li-ion transport between a transition metal oxide cathode and a graphite anode. Despite their popularity, graphite anode Li-ion batteries inherently offer lower capacities than metal anode batteries. Moreover, Lithium metal anode batteries raise concerns regarding the environmental impact of their disposal and potential to degrade upon dendrite formation^[1]. Li shortages have also highlighted the need for batteries based upon the ion transfer other than Li-ions ^[2]. A promising candidate material that has emerged from the search for next generation batteries are nanocrystal spinel vanadium oxides. Recent reports demonstrate that despite the presence of complex structural defects V₂O₄ nanocrystals are capable of cycling Mg²⁺ at capacities greater than Cr and Mn spinel counterparts ^[3]. In this contribution, we will present a characterization of spinel MgV₂O₄ using atomic resolution scanning transmission electron microscopy (STEM), nanoscale electron energy loss measurements (EELS) and x-ray energy dispersive spectroscopy (XEDS). The combination of these methods will allow us to correlate local structural changes to differences in electronic structure and chemical composition with nanoscale precision. The focus of this study will be to explore the effects that post-thermal annealing and structural defects have on electrochemical cycling performance of MgV₂O_4.
This study will be conducted using an aberration-corrected cold field emission JEOL ARM200CF operated at 200kV primary electron energy. Imaging and spectroscopic measurements will be conducted with the emission current at 12μA. The electron probe will be operated at 24 mrad convergence semi-angle. The inner angle detector will be set to 75 mrad for high angle annular dark imaging (HAADF); conversely the inner angle for low angle annular dark field (LAADF) will be 30mrad. To conduct nanoscale elemental identification and quantification the ARM200CF is equipped with an Oxford XMAX100TLE X-ray detector. EELS measurements will be conducted using a post-columns Gatan Continuum GIF spectrometer.
Using this approach, we can examine crystals at different stages of electrochemical cycling. We will demonstrate that crystals undergo structural transformations upon electrochemical charging and discharging. Additionally, we will show that electrochemical activity can be mapped locally within large single crystals. ^[4]
[1] Muldoon, J., Bucur, C. B., & Gregory, T. (2014). Quest for nonaqueous multivalent secondary batteries: magnesium and beyond. Chemical reviews, 114(23), 11683-11720.
^[2] Nitta, N., Wu, F., Lee, J. T., & Yushin, G. (2015). Li-ion battery materials: present and future. Materials today, 18(5), 252-264.
^[3] Hu, L., Jokisaari, J. R., Kwon, B. J., Yin, L., Kim, S., Park, H., ... & Cabana, J. (2020). High Capacity for Mg2+ Deintercalation in Spinel Vanadium Oxide Nanocrystals. ACS Energy Letters, 5(8), 2721-2727.
^[4] This work is solely supported by the Joint Center for Energy Storage Research (JCESR) and Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences.

Structural energy storage promises to merge the features of structural composites with that of batteries or capacitors, resulting in high-stiffness devices that can bear mechanical loads and resist impact. However, structural energy materials are often faced with tradeoffs in stiffness and energy. This is because structural electrodes and electrolytes are often composites of materials that either store energy or bear loads alone, meaning that simple mixing rules may apply. This talk will examine structural electrodes and electrolytes that provide a synergistic path toward the simultaneous improvement of both mechanical and electrochemical behavior. Structural battery lithium iron phosphate cathodes and silicon anodes based upon a reduced graphene oxide (rGO)/aramid nanofiber (ANF) matrix are examined. The rGO sheets provide conductivity and mechanical stiffness, and the ANFs provide Kevlar-like stiffness and toughness. Further, ANFs assembled into thermally stable, high-stiffness membranes provide robust battery separators. Besides batteries, that same rGO/ANF electrode platform provides a path toward high-stiffness capacitor electrodes, in which chemical modification of the rGO surface yields non-covalent interactions with the ANFs that lead to a dramatic enhancement in stiffness. However, these electrodes may undergo dimensional changes during charging and discharging, leading to the generation of internal stresses. To quantify this, the electrochemo-mechanical coupling of rGO electrodes is analyzed using a custom-built instrument, showing clear trends in the stress evolution during operation. Taken together, this work provides insight molecular-level strategies that address both mechanical properties and electrochemical performance for improved structural energy storage devices.

Large-scale energy storage devices need to be safe, reliable, and rechargeable. Redox flow batteries are a technology that could meet large-scale energy requirements. Unfortunately, current technologies suffer from low energy density, which has inhibited widespread application. Furthermore, capacity fade from the redox material crossover between the negalyte and posalyte makes them unreliable with limited rechargeability. In general, aqueous RFBs typically suffer from low energy density while having high conductivity; additionally, many aqueous systems employ acidic environments that accelerate degradation. Conversely, nonaqueous systems usually have the opposite problems of an aqueous system: low conductivity, high energy density. Furthermore, nonaqueous systems have no acidic environment; instead, hazardous solvents are used like acetonitrile. Therefore, RFB researchers face many challenges finding an appropriate electrolyte with high energy density and high conductivity, non-toxic, and compatible with the RFB components.
Microemulsions are an emerging alternative to traditional RFB electrolytes because of their ability to produce thermodynamically stable, homogeneous solutions of polar and non-polar molecules. This property of microemulsions allows them to accommodate organic redox species with fast electron transfer rates that are not soluble in the aqueous phase while still offering the high conductivity of an aqueous salt electrolyte. Microemulsion electrolytes consist of a non-polar phase, which solubilizes the redox material—or the redox material can be the entire oil phase, an aqueous brine phase, and a surfactant that stabilizes the two immiscible liquids. Moreover, each component can be environmentally and biologically safe; for example, the aqueous phase only consists of salt and water, polysorbate-20—the surfactant used in this study—is found in many cosmetics and food products. Some of the redox materials being investigated in our lab are vitamins such as menadione (vitamin K3) and tocopherol (vitamin E).
Microemulsions form many self-assembled nanoscale structures, such as oil-in-water or water-in-oil droplets and bicontinuous. Understanding these bulk structures is critical to understanding a material's properties, such as conductivity and diffusion to an electrode surface. Understanding the changes in the bulk structure with composition variation provides a clear path to optimizing the balance between acceptable conductivity levels in the electrolyte and the high volume of an oil phase bearing the redox-active species in a µE. This optimization is critical to achieving high-performing electrochemical systems using µEs. This talk will discuss the evolution of a microemulsion electrolyte nanoscale structure with small-angle neutron scattering and relate this to how the structural changes affect the cyclic voltammetry response

Developing low-cost aqueous electrolytes with high water stability and reversible Li storage in a wide voltage window (> 3.0 V) is a critical step towards high-energy aqueous Li-ion batteries. Emerging approaches exploiting highly-concentrated salts (21m-55m) successfully create artificial solid-electrode-interfaces and improve water stability^1-3, however, they also raise concern of cost and toxicity. A new concept of aqueous electrolyte, polyethylene glycol (PEG)-based molecular crowding electrolyte uses low-concentration salts (2m) to achieve 3.2V-voltage window. However, PEG molecular crowding electrolyte⁴ is limited by low conductivity (0.8 mS cm^-1) resulting from the high viscosity of PEG. More importantly, the lack of comprehensive understanding on how crowding agent structure affects the key properties of electrolyte prevents rational design of molecular crowding electrolyte for high-power and high-voltage aqueous batteries.
In this work, we developed a new crowding agent and substantially improved ionic conductivity 3 times compared to PEG 400 without sacrificing voltage window. A high-power and high-voltage aqueous Li₄Ti₅O₁₂/LiMn₂O₄ cell using this newly designed electrolyte showed stable cycling for 800 times at 5C achieving. No hydrogen evolution reaction (HER) was detected during battery operation as confirmed by online electrochemical mass spectroscopy (OEMS). This work demonstrates rational material design strategies for advanced molecular crowding electrolytes and high-energy and high-power aqueous battery applications.
Acknowledgment:
The work described in this paper was fully supported by a grant from the Research Grant Council of the Hong Kong Special Administrative Region, China (project no. CUHK14304520).
Reference:
(1) Droguet, L.; Grimaud, A.; Fontaine, O.; Tarascon, J.-M. Water-in-Salt Electrolyte (WiSE) for Aqueous Batteries: A Long Way to Practicality. Advanced Energy Materials 2020, 10 (43), 2002440.
(2) Suo, L.et al. Advanced High-Voltage Aqueous Lithium-Ion Battery Enabled by “Water-in-Bisalt” Electrolyte. Angewandte Chemie International Edition 2016, 55 (25), 7136.
(3) Suo, L.; Oh, D.; Lin, Y.; Zhuo, Z.; Borodin, O.; Gao, T.; Wang, F.; Kushima, A.; Wang, Z.; Kim, H.-C.et al. How Solid-Electrolyte Interphase Forms in Aqueous Electrolytes. Journal of the American Chemical Society 2017, 139 (51), 18670.
(4) Xie, J.; Liang, Z.; Lu, Y.-C. Molecular crowding electrolytes for high-voltage aqueous batteries. Nature Materials 2020, 19 (9), 1006.

Fuel cells (FCs) and battery technologies are renewable options that may prevail in the vehicle industry, replacing fossil fuel dependence. This has led to the design and manufacture of electrocatalysts for energy conversion reactions in the mentioned technologies, such as the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR). These reactions can be improved with new methods to obtain accessible, active and high-performance electrocatalysts. This study used a new Pb electroless (e-less) monolayer deposition approach to design electrocatalysts. This process is surface selective, surface controlled, and self-terminating, leading to a better design of active and accessible materials. We synthesized Pt/C, Pt/Au/C and Pt/NbN/C catalysts to catalyze the ORR in alkaline and acid mediums. We found that the e-less deposition approach placed a pseudo-monolayer (ML) of Pb on the selected supports (C, Au/C and NbN/C) and then Pt was placed on the support via spontaneous galvanic displacement (SGD) without the need of using an applied reduction potential. Our cyclic voltammograms results demonstrated the presence of hydrogen adsorption and desorption peaks associated to Pt on the C, Au/C and NbN/C supports. These materials were further tested for ORR generating oxygen polarization curves and the Pt/NbN/C provided half-wave potentials (E_1/2) vs. RHE of 750 mV in 0.1M HClO₄ and 810 mV in 0.1M KOH. Additional experiments will be held to characterize the placement of Pt on the supports using transmission electron microscopy (TEM) and addres the catalysts' performance by exposing them to numerous cyclic voltammogram cycles in both mediums.

Pseudocapacitors harness unique charge storage mechanisms to enable high-capacity, rapidly cycling devices. Fully organic pseudocapacitors are an inexpensive and green alternative, but until now, they have underperformed their inorganic counterparts. These limitations are especially salient for electron-accepting materials used in negative electrodes, which are required for pairing with electron-donating materials in positive electrodes to achieve maximum performance in asymmetric cells. In this talk, I will describe an organic system composed of perylene diimide and hexaazatrinaphthylene exhibiting a specific capacitance of 689 F/g at a rate of 0.5 A/g, stability over 50,000 cycles, and unprecedented performance at rates as high as 75 A/g. We incorporate the material into two-electrode devices for a practical demonstration of their potential as next-generation energy storage systems. We identify the source of this exceptionally high-rate charge storage as surface-mediated pseudocapacitance, through a combination of spectroscopic, computational, and electrochemical measurements. By underscoring the importance of molecular contortion and complementary electronic attributes in the selection of molecular components, these results provide a general strategy for the creation of organic high-performance energy storage materials.

The fast-growing energy demand of applications such as electric vehicles and stationary storage requires next-generation batteries with improved energy density and lower cost.Magnesium-ion batteries (MIBs) have received considerable attention during the last few years as an alternative battery chemistry to Li-ion technologies thanks to the advantages of Mg over Li.Mg has a significantly larger volumetric capacity (3832 mAh cm⁻³ vs 2061 mAh cm⁻³ for Li), higher natural abundance and lower cost than Li [1]; Mg also has a relatively low redox potential (-2.37 V vs. SHE [1]).Furthermore, being Mg²⁺ a divalent cation, for the same amount of ions stored in a host material, the specific capacity is doubled in comparison with monovalent cations such as Li⁺.Thanks to these key advantages MIBs can theoretically achieve higher energy densities at a lower cost than LIBs [2] making MIBs a very attractive battery technology. However, one of the main fundamental challenges in MIBs is the slow Mg²⁺ ion solid state diffusion into the cathode active material’s lattice. This is attributed to the high charge/radius ratio of the Mg²⁺ ion, which results in strong interactions with the anions and cations of the host structures [2].As consequence, cathode materials for MIBs usually show low specific capacities and high overpotentials. In addition, such strong interactions leads to the disruption of the crystalline structure and Mg ions entrapment during cycling, resulting in a poor cycling stability.
Vanadium-based oxides are a promising class of cathode materials for MIBs due to their relatively high potential of 2.5 V vs Mg²⁺/Mg, and the possibility to explore multiple oxidation states of V, i.e. V⁵⁺/V⁴⁺ and V⁴⁺/V³⁺, resulting in higher theoretically achievable specific capacities [3]. Within this family, the H₂V₃O₈ (HVO) phase shows promising structural and morphological characteristics which could favour Mg²⁺ intercalation. Specifically, H₂V₃O₈ has a relatively large interlayer distance of 8.4 Å and crystallizes in a nanowire morphology. However, H₂V₃O₈ has only recently been tested in a MIB, showing a capacity of around 80 mAh g^-1 at room temperature, even though its theoretical capacity is 190 mAh g^-1, for the intercalation of 1 eq. of Mg²⁺ [4].
Our study aimed to investigate the changes in structure, morphology and chemistry of the electrode/electrolyte interphase, occurring in HVO upon Mg²⁺ intercalation. Therefore, a post-mortem analysis, combining bulk and surface characterization, was carried out on HVO electrodes upon charge and discharge at specific cycle numbers. For the first time, we demonstrate that HVO in TFSI-based electrolytes can approach a specific capacity of 200 mAh g^-1 at room temperature. Depending on the cycle number, Mg²⁺ intercalation upon discharge resulted in a 0.5% to 4% change in the unit cell parameters compared to the pristine electrode, and a shrinkage of the interlayer distance. The intercalation caused a change in the V⁵⁺/V⁴⁺ ratio, with a lower ratio (i.e. higher amount of V⁴⁺) associated with cycle numbers showing the highest capacity values. However, Mg²⁺ ions could not be completely extracted upon charge, resulting in lattice parameters which do not return to their original values. Although the nanowires did not change dimensions over cycling, a surface roughening was observed at high cycle numbers, indicating formation of a surface layer. Such layer contained organic (i.e. TFSI) and inorganic components (i.e. MgF₂). Its thickness varied upon cycling, increasing during discharge, which correlated with the excess of capacity. Evidence of V dissolution could also be confirmed, resulting in capacity fading after about 35 cycles.
[1]C. Kuang et al., J. Nanosci. Nanotechnol., vol. 19, no. 1, pp. 12, 2019.
[2]Y. Tian et al., Chem. Rev., vol. 121, no. 3, pp. 1623, 2021.
[3]H. Tang et al., Electrochem. Energy Rev., vol. 1, no. 2, pp. 169, 2018.
[4]M. Rastgoo-Deylami et al., Chem. Mater., vol. 30, no. 21, pp. 7464, 2018.

The lithium ion batteries are dominating rechargeable battery market with advantages of long cycle life, adaptability, and high energy density; however, disadvantages including lithium resource shortage, high processing cost arising from the other battery components (Co-based cathode, electrolyte), safety concerns due to flammable organic electrolytes, and highly reactive lithium species hinder grid-scale Li ion battery applications to be realized.
The zinc ion batteries have been proposed to substitute Li ion batteries owing to suitable electrochemical properties of large specific capacity (820 mAh/g), high volumetric capacity (5854 mAh/cm³), and low redox potential (-0.76 V). Also, Zinc’s low cost and environmental abundance, inexpensive mass production, and safety due to usage of aqueous electrolyte make Zn ion battery extremely promising for future grid-scale battery applications.
Prior to the commercialization of Zn ion batteries, a critical issue remains with rapid battery performance degradation mainly due to dendrite formation and additional side reactions during charging and discharging process. Dendrite growth in association with the reduction of zinc ions during discharging process causes capacity decrease by unceasing water/electrolyte decomposition with fast electrolyte depletion as well as lifespan shortening by short circuit due to separator piercing. Side reactions between electrode and electrolyte result production of hydrogen and zinc sulfate hydroxide. These reactions reduce a Coulombic efficiency and prohibit reaching theoretically expected electrochemical performances. To suppress the dendrite growth, several strategies have been proposed such as interfacial electrode modification through an increase of surface area of zinc anodes, insertion of electrolyte additive, modification of crystallographic orientation.
Here, we propose additional ferroelectric layer coating onto Zn anode for the compression of dendrite growth and the hindrance of side reaction. The ferroelectric layer can suppress the dendrite formation by inducing a uniform electric field between anode and cathode from compensation of accumulated charges at the dendrite tip. Among the ferroelectric materials, we selected poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) due to cost-effective fabrication, compatibility with battery components, and non-toxicity. To enhance the ferroelectricity of P(VDF-TrFE), nanocomposites are prepared using BaTiO₃ nanoparticles, one of the typical lead-free ferroelectric materials with high ferroelectricity. The 800 nm-thick ferroelectric layer was spin-coated onto Zn electrode. Along with the increase of ferroelectricity via addition of BaTiO₃ nanoparticles to P(VDF-TrFE) layer, we observed about three times extended cycle life and a decrease of side reaction products(dendrites, hydrogen, zinc sulfate hydroxide)to the half value or less.

As safety issue of the battery system emerges, aqueous zinc ion batteries (AZIBs) using safe water-based electrolytes are considered to replace lithium-ion batteries (LIBs). Aqueous electrolytes used in AZIBs have higher ionic conductivity (0.1-6 S/cm) compared to organic electrolytes of LIBs (10^-3-10^-2 S/cm). In addition, the high theoretical capacity and cost competitiveness of zinc metal anode are big merits. Manganese and vanadium-based transition metal oxides are the mainstream cathode materials for AZIBs. In particular, vanadium oxide-based cathode materials have been studied intensively due to their high capacity and charge store reversibility through the mechanism of intercalation reaction to the layered structure. However, they face many hurdles for commercialization, such as the trapping phenomenon that hinder electrochemical reversibility and the low electrical conductivity. In this study, we designed conducting polymers-intercalated vanadate system via the simple sonochemical method to overcome their shortcomings. In addition, various in-situ and ex-situ analyses were performed to understand the charge storage mechanisms and electrochemical behaviors of conducting polymer-intercalated vanadates. This unique cathode system not only improves the electrical conductivity and mitigates the zinc ion trapping phenomenon by intercalating the conducting polymers but also expands the interlayer, providing large reaction sites and effective ion channels.

Aqueous rechargeable zinc-ion batteries are often regarded as an attractive alternative to lithium-ion batteries, mainly because of their low cost, material abundancy and environmental friendliness. While metallic zinc has been demonstrated to be a suitable anode material with high theoretical energy density, the research for a cathodic material which has a high capacity and long-term stability in aqueous electrolytes is still ongoing.
Prussian blue analogues (PBA) are a noteworthy class of cathodic materials with an open framework structure and generic formula A_xM’[M’’[CN]₆]_y●nH₂O, where A are guest cations M’ and M’’ are transition metals. In the crystalline lattice, the M’ atoms are coordinated to the nitrogen atoms of the CN group, while M’’ atoms are coordinated to the carbon atoms.[1]
Zinc-ion batteries featuring PBAs as cathode materials exhibit good specific capacity and outstanding operating voltage. For example, in 2015 R. Trócoli et al.[2] reported an operating voltage of 1.73V for a zinc-ion battery based on CuFe[CN]₆. After 100 cycles in 20mM ZnSO₄, the device was able to retain 96.3% of its maximum capacity of 55 mAh g^-1. More recently, L. Ma et al. [3] developed a zinc-ion battery based on CoFe[CN]₆ which operated above 1.7V. The device was able to sustain a current as high as 6 A g^-1 with a high capacity of 109 mAh g^-1.
One of the main advantages of PBAs is their easy synthetic route, which involves a simple coprecipitation reaction. By partially substituting some of the M' transition metal atoms in the precursor solution, it's possible to tune of the electrochemical properties and cyclability. For instance, G.Kasiri et al. [4] increased the capacity retention at 1000 cycles of CuFe[CN]₆ from 74.35% to 85.54% by introducing zinc, with the best results being achieved by Cu_0.93Zn_0.07Fe[CN]₆.
The aim of this work is to highlight the properties of Co_1-xMn_xFe[CN]₆ obtained by of the introduction of Mn atoms during the synthesis of CoFe[CN]₆. As shown by M. Li et al. [5] in their recent work on MnFe[CN]₆, Mn can dissolve in the ZnSO₄ electrolyte. In the long term, this phenomenon leads to material degradation, but in the short term the Mn dissolution reduces the diffusion resistance and increases the capacity of the battery. By reducing Mn dissolution to involve only a small fraction of the material, we can reduce the diffusion resistance of CoFe[CN]₆, without capacity loss in the long run.
The material is synthesized with a co-precipitation reaction, where the Mn and Co precursors are mixed in the appropriate stoichiometric ratio. For the material characterization XRD, SEM, EDS, ICP-OES and TGA analysis on the dried powders are carried out. Electrochemical characterization is performed with CV in a three electrode cell, by drop casting an ink with the active material on a glassy carbon electrode. Coin cells are assembled with the PBA ink as the cathodic material, zinc as the anodic material and their performance is assessed in charge-discharge cycles at different C-rates.

Bibliography:
[1] G. Zampardi and F. La Mantia, “Prussian blue analogues as aqueous Zn-ion batteries electrodes: Current challenges and future perspectives,” Curr. Opin. Electrochem., vol. 21, pp. 84–92, Jun. 2020.
[2] R. Trócoli and F. La Mantia, “An Aqueous Zinc-Ion Battery Based on Copper Hexacyanoferrate,” ChemSusChem, vol. 8, no. 3, pp. 481–485, Feb. 2015.
[3] L. Ma et al., “Achieving High-Voltage and High-Capacity Aqueous Rechargeable Zinc Ion Battery by Incorporating Two-Species Redox Reaction,” Adv. Energy Mater., vol. 9, no. 45, p. 1902446, Dec. 2019.
[4] G. Kasiri, J. Glenneberg, A. Bani Hashemi, R. Kun, and F. La Mantia, “Mixed copper-zinc hexacyanoferrates as cathode materials for aqueous zinc-ion batteries,” Energy Storage Mater., vol. 19, pp. 360–369, May 2019.
[5] M. Li et al., “Electrochemical performance of Manganese Hexacyanoferrate cathode material in aqueous Zn-ion battery,” Electrochim. Acta, p. 139414, Oct. 2021.

Metal batteries have been considered the most promising approaches to next generation high energy density batteries because using metal anode could provide low voltages and large specific capacities, and thus increase the battery energy density. Among metal batteries, Zn batteries attract the increased research attention for commercial application especially the large-scale energy storage because of its safety, low-cost, environmental benign nature, and the high capacity as the anode material. However, similar as other metal anode, the dendrite growth can pierce the separator and cause the sudden death of the Zn battery. The diffusion limitation and the depletion of ions at high current density are the main reasons for dendrite growing. In this work, a nanoporous polymer coating on Zn anode was developed and studied to investigate the ion transport and Zn deposition on the anode. The incorporation of the nanoporous polymer coating promotes the electro kinetic phenomenon such as electro surface conduction and electro osmosis, which enhances the mass transport under electric field and thus mitigates the dendrite growth. The Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electrochemical Impedance Spectroscopy (EIS) and other characterization were carried out to investigate the morphology evolution and electrochemical performance of the electrodes. The understanding learned from this research can be used to design and develop high energy density Zn battery with decreased dendrite problem and longer life.

Electrochemical energy conversion and storage devices such as fuel cells, metal-air batteries play an important role in solving environmental and energy crises. Especially, rechargeable zinc-air batteries (ZABs) have attracted considerable attention as a sustainable and eco-friendly device. However, the electrochemical efficiency of ZABs has been hindered by a sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) to discharge and charge reaction, respectively. Although noble metal-based materials such as platinum and ruthenium oxides are considered as state-of-the-art electrocatalysts for ORR and OER, practical application has been hampered by high cost, scarcity, and poor electrochemical durability. Thus, the researches for earth-abundant non-noble metal based bifunctional electrocatalysts with high durability, reasonable cost, and high activity for ORR and OER are needed to enhance the performance of ZABs. Transition metal-based spinel oxides (AB₂O₄, A, B = Ni, Co, Fe, and Cu) are regarded as promising electrocatalysts for ZABs owing to their low cost, high redox property, and superior stability. Furthermore, the introduction of oxygen vacancy into spinel type metal oxide can increase the electrocatalytic activity by leading to optimize absorption/desorption energy of oxygen-containing reactants.
In this study, N-doped hollow carbon sphere coated with oxygen vacancies rich CoFe/CoFe₂O_4-x (V_o-CoFe/CoFe₂O_4-x@NC) was synthesized via a facile polymerization process and a subsequent annealing procedure. Briefly, melamine-formaldehyde resin sphere (MF) was prepared as a self-sacrificial template through polymerization of melamine and formaldehyde. And then, MF, dopamine, Co²⁺, and Fe³⁺ species were mixed in tris-HCl buffer solution to acquire polydopamine, Co²⁺, and Fe³⁺ coated with MF sphere (CoFe/PDA@MF). As prepared CoFe/PDA@MF annealed in Ar atmosphere at high temperature to obtain hollow structure N-doped carbon coated with CoFe/CoFe₂O₄ (CoFe/CoFe₂O₄@NC). Finally, CoFe/CoFe₂O₄@NC was reduced by 10% H₂/Ar flow at 300 °C for 2 h to induce oxygen vacancy into CoFe₂O₄, denoted V_o-CoFe/CoFe₂O_4-x@NC. The hollow structure not only provides a short ion diffusion distance but also increases exposed active sites owing to the large surface area. Furthermore, heteroatom (such as N, S, and P) doped carbon materials regulate the adsorption energy between oxygen related intermediates and active sites by adjusting the electronic structure, thereby effectively enhancing electrocatalytic performance. As a result, the bifunctional V_o-CoFe/CoFe₂O_4-x@NC catalysts show the better ORR catalytic activity (half-wave potential of 0.858 V and Tafel slope of 56 mV dec^-1) than state-of-the-art Pt/C (half-wave potential of 0.855 V and Tafel slope of 62 mV dec^-1). It also displays outstanding OER kinetics (Tafel slope of 64 mV dec^-1), compared to commercial RuO₂ (Tafel slope of 72 mV dec^-1) in alkaline solution. In rechargeable ZABs, V_o-CoFe/CoFe₂O_4-x@NC has a superior open circuit voltage (OCV) of 1.53 V and power density of 139.5 mW cm^-2 than Pt/C and RuO₂ (OCV of 1.49V, power density of 121.7 mW cm^-2).

The severe crisis of environmental pollution and depletion of fossil fuels has stimulated an urgent demand for developing efficient, clean, and sustainable energy devices. Recently, rechargeable zinc-air batteries (ZABs) have emerged as promising renewable energy devices for next-generation owing to their high theoretical energy densities, cost-effectiveness, and zero-carbon emissions. The main obstacles of ZABs are the sluggish kinetic behaviors of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) involving a complex four-electron process. Precious metal-based electrocatalysts (e.g., Pt/C, IrO₂, and RuO₂) with high electrocatalytic performances for ORR and OER are commonly used as the state-of-the-art electrocatalysts. However, their high cost, scarcity, inferior multifunctionality, and low stability limit the large-scale commercialization of ZABs. Therefore, the development of effective non-precious metal-based electrocatalysts (NPMCs) is a key for enhancing the energy conversion efficiency and utilization of ZABs. Among various candidates, the transition metal-containing N-doped carbon (M-N-C, M = Fe, Co, Ni, etc. and their alloys) materials with enhanced electric conductivity and outstanding durability are considered as the most competitive electrocatalysts.
Herein, we fabricated CoFe alloy nanoparticles embedded in N-doped carbon supported on highly defective ketjenblack (FeCoNC/D) via simple hydrothermal and impregnation method, followed by a high-temperature annealing process. First, the defect-rich ketjenblack (D-KB) was prepared by partial oxidation and etching of carbon atoms in ketjenblack during the hydrothermal procedure using H₂O₂, thereby introducing abundant carbon vacancies and nanopores. After that, metal ions and dicyandiamide (DCD) which has a high content of nitrogen were mixed and adsorbed on the D-KB. Finally, DCD was transformed to an N-doped carbon matrix with homogeneously embedded CoFe alloy nanoparticles on D-KB via in-situ thermal polymerization into g-C₃N₄, followed by the high-temperature carbonization process. The synthesized FeCoNC/D exhibits superior bifunctional electrocatalytic activity with a half-wave potential of 901 mV (vs. RHE) for ORR and an overpotential of 362 mV at a current density of 10 mA cm^-2 for OER. Moreover, the FeCoNC/D showed outstanding long-term durability for both of ORR and OER compared to commercial Pt/C and RuO₂. The excellent bifunctional oxygen electrocatalytic activity of FeCoNC/D encouraged us to assess its potential for air-cathode in rechargeable ZABs. The ZABs with FeCoNC/D display a narrow discharge/charge gap of 0.7 V, the higher power density of 157 mW cm^-2 at 240 mA cm^-2, and superior stability than Pt/C-RuO₂. The improved electrocatalytic performances toward ORR, OER, and ZABs of FeCoNC/D can be attributed to these advantages : a) outstanding properties of defect rich carbon support exhibiting excellent electric conductivity, abundant edge defects with high charge densities, and large surface area promoting exposure of catalytic active sites; b) uniform distribution of CoFe alloy nanoparticles, which can not only induce the internal electron redistribution but decrease the reaction energy barrier owing to synergistic effects induced by the inherent polarity of the alloy components; c) the encapsulated alloy nanoparticles inside the N-doped carbon layer, which are strongly coupled with outer carbon nanosheets, thereby preventing corrosion of metal during the electrocatalytic reaction.

Energy storage systems combined with renewable energies have drawn a lot of attention in the energy sector as a solution to deal with the energy crisis. Among the available energy storage systems, redox flow batteries have risen as one of the most promising technologies due to the efficiency, ease of scalability and their ability to separate energy and power [1]. However, most redox flow batteries are based on aqueous electrolytes, as the well-known vanadium redox flow batteries, which limits their cell potential due to the restricted electrochemical stability window of water [2]. In this regard, non-aqueous redox flow batteries (NARFBs) using organic solvents for the electrolytes offer wider electrochemical window. Also, vanadium acetylacetonate (V(acac)₃) based redox chemistry provides excellent reversibility for these energy storage systems [3, 4]. So far, NARFB research has mainly focused on electrolytes and redox couple development, while little attention has been paid to improvements in membrane. A membrane is a crucial component in NARFBs, which prevents electrolytes cross mixing while retaining the physicochemical properties.
Therefore, we tested three available commercial membranes in a non-aqueous vanadium redox flow batteries. The studied membranes were a porous separator (Celgard 4560) and two dense anion exchange membranes. First, we were able to stably charge/discharge V(acac)₃ species over hundreds of cycles at current densities between 10 – 50 mA cm^-2 with Celgard 4560 porous separator. Further, we studied the AEMs’ performance in the similar set-up, which showed very different performance trend in NARFBs. It was found that the conductivity and chemical compatibility of membranes play vital role for achieving high performance in NARFBs. The outcome of this study will be discussed in detail during the presentation.
Acknowledgements:
Los Alamos National Laboratory is operated by Triad, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy (Contract No. 89233218NCA000001). SM and RM would like to thank Dr. Imre Gyuk and financial support from the U.S. Department of Energy’s Office of Electricity for the publication of this work is gratefully acknowledged. SD also acknowledges the grant 2018/12504 from University of Castilla-La Mancha, the FEDER funds and the European Union.
References:
[1] C. Choi, S. Kim, R. Kim, Y. Choi, S. Kim, H.-y. Jung, J.H. Yang, H.-T. Kim, Renewable and Sustainable Energy Reviews, 69 (2017) 263-274.
[2] S.-H. Shin, S.-H. Yun, S.-H. Moon, RSC Advances, 3 (2013).
[3] J.D. Saraidaridis, C.W. Monroe, Journal of Power Sources, 412 (2019) 384-390.
[4] Jae-Hun Kim, Sandip Maurya, Jae-Suk Lee and Seung-Hyeon Moon, RSC Advances, 10 (2020) 5010.

With the increasing interest of renewable energy sources, the electrical energy storage (EES) system has received great attention to solve uncertainty of power input and output. Among many EES systems, a redox flow battery is the most promising candidate due to design flexibility for large scale. Recently, low cost and earth abundant transition metal based redox couples have attracted significant attention to replace the expensive vanadium redox couples. Conventional Mn-based aqueous zinc-ion battery is highly safe energy storage system, but low operating voltage (<1.5V) and low energy density limits its broad application in large-scale energy storage system. Recently, a novel aqueous zinc-manganese dioxide redox flow battery is reported. This battery is composed of Mn²⁺ based acidic catholyte and Zn²⁺ based alkaline anolyte, respectively, exhibiting an open circuit voltage of 2.66 V. Also, a neutral electrolyte was located between two different membranes to prevent the cross contamination of acidic and alkaline electrolytes, maintaining the charge balance. However, Mn³⁺ ions suffer from the disproportionation side reaction, lowering battery performance. Thus, the low reversibility of Mn/MnO₂ redox couple should be improved for broad application of Zn-Mn redox flow batteries. In addition, the formation of zinc dendrite should be suppressed when the zinc-based anolyte was used, which could deteriorate the cell performance.
In this work, we report a high voltage aqueous Zn−Mn hybrid redox flow battery with a high operating voltage of >2.0 V. This work is a significant step forward by exploring the pH differential hybrid flow cell with the double-membrane, three-electrolyte configuration. The manganese cathode was deposited on carbon felt electrode with bismuth using carbothermal reduction process. Moreover, two metal ions of Ni²⁺ and Mg²⁺ are added as solution catalysts. We found that the reversibility of Mn was improved, and side reactions were suppressed by adding the transition metal catalysts, maintaining a higher oxidation state of Mn ions. As a result, our works suggest that the zinc-manganese dioxide redox flow battery can be operated at high voltage with the excellent reversibility. We also optimized the double membrane system in hybrid redox flow batteries, showing the improved deposition and dissolution kinetics of manganese ions by introducing transition metal catalysts. Considering zinc dendrite issues, we introduced the tin and copper doped zinc carbon felt in the negative electrode. The zinc nucleation overpotential was lowered by surface modified carbon felt electrode, also minimizing hydrogen evolution.
Acknowledgements
This research was supported by Pusan National University BK21 Four Education and Research Division for Energy Convergence Technology. This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (No.2021R1C1C1008349)

Redox flow batteries are a promising candidate for grid energy storage due favorable scaling and cyclability but are limited by low energy density due to poor solubility of active species in both aqueous and organic solvent. To increase the energy density we investigate the use of a solvent free liquid quinone electrolyte, resulting in high active species concentration (>10M). Well studied in aqueous and organic solvents, the electroreduction of quinones has been shown to strongly depend on the solvent and supporting electrolyte. The absence of inert solvent poses additional challenges due to mass transport and reaction effects in highly concentrated solutions. Here we characterize the physical and electrochemical properties of eutectic quinone electrolytes, ranging in concentration from a dilute solution in inert organic solvent to a highly concentrated solvent-free liquid quinone, and investigate the performance of this material for use as a solvent-free electrolyte.

According to the increased demand for wearable devices, there has been extensive research on flexible energy storage devices including batteries and supercapacitors. Among them, flexible supercapacitors based on hydrogel electrolytes can be facilely applied to various wearable electronic devices. However, hydrogel easily freezes at sub-zero temperatures and evaporates at high temperatures due to water contents, limiting the operation temperatures for the supercapacitors. As an alternative to hydrogels, organohydrogels with anti-freezing and evaporation resistance have been paid a vast attention.
We report on the fabrication of a temperature-resistant, anti-drying, flexible supercapacitor based on polyacrylamide/poly(2-acrylamido-2-methyl-1-propanesulfonic acid) PAAM/PAMPS organohydrogel. The organohydrogel electrolyte is synthesized via UV initiated one-pot polymerization of a precursor solution containing acrylamide, 2-acrylamido-2-methyl-1-propanesulfonic acid, water, ethlyene glycol, LiCl, a cross-linker of N,N‘-methylenebisacrylamide and an initiator of ammonium persulfate. As temperature tolerant conductive electrodes, polyaniline/multi-walled carbon nanotubes deposited on a flexible graphite substrate is used. Using such prepared electrodes and organohydrogel electrolyte, a stack-type supercapacitor is assembled, exhibiting a high areal capacitance of 50 mF cm^-2, energy density of 8 μWh cm^-2 and power density of 90 μW cm^-2 at room temperature. The initial capacitance at room temperature remains at over 75% in the temperature range between -20 and 80 °C. Three repeated cycles of cooling and heating from -20 to 80 °C recovers the capacitance at room temperature, indicating the high temperature tolerance of our fabricated supercapacitor. Furthermore, 80% of the initial capacitance also remains even after 5,000 cycles of charging/discharging in the whole temperature range. These results demonstrate the potential application of our PAAM/PAMPS organohydrogel based supercapacitor to wearable electronics as an integrated energy storage device under extreme temperature conditions.

The increasing demand for clean energy is a main force driving the energy storage industry’s innovations and the search for cost-affordable materials with high specific energy. Developing novel materials and scalable production processes is essential for the advancement of supercapacitor technologies in both scientific exploration and practical applications. To this end, transition metal selenides (TMSes) are a class of materials that can provide the required specs to realize such technology due to the two-dimensional (2D) nature and conductivity of the materials. Herein, we demonstrate the synthesis of binary metal selenides (Co-W-Se) via carbonization of zeolitic imidazolate framework (ZIF-67), a subclass of metal−organic frameworks. The morphology and surface functional groups of the as-synthesized Co-W-Se composite are characterized via FESEM, HRTEM, and FTIR spectroscopy. Furthermore, the crystal structure and elemental composition of the fabricated Co-W-Se composite are elucidated by XRD and XPS analyses. Upon testing its electrochemical performance as a supercapacitor electrode, the fabricated Co-W-Se shows exceptional specific capacitance (1061 F g^-1 at 2 A g^-1). Furthermore, the constructed asymmetric supercapacitor device using Co-W-Se displays superior energy density of 33.4 Wh kg^-1 with high Columbic efficiency over 10 000 charge/discharge cycles at 10 A g^-1.

The development of clean, sustainable and zero-carbon emission energy conversion and storage technologies has become an urgent demand to cope with the technological advancements. In this regard, Metal Organic Frameworks (MOFs) have emerged as outstanding materials for supercapacitors due to their high porosity, diverse structures and their ability to host other active species within its cages and prevent its dissolution. Herein, we report on a facile one pot synthesis of zeolitic imidazolate framework encapsulated with vanadium substituted polyoxometalates (V₂POM@ZIF-67). The morphological and structural properties of the as synthesized materials were investigated via FESEM, EDS, XRD and FTIR techniques. Moreover, N₂ adsorption/desorption isotherms and XPS measurements were carried out to elucidate the textural properties and composition of the fabricated materials. Upon their use as supercapacitor electrodes, the V₂POM@ZIF-67 electrode exhibited a maximum specific capacitance of 475 F g^-1 at 2 A g^-1. Furthermore, a supercapacitor device was constructed using activated carbon as the negative electrode and V₂POM @ZIF-67 as the positive electrode, delivering energy density and power density of 20.9 Wh kg^-1 and 702 W kg^-1, respectively. Furthermore, the device demonstrates an excellent long term stability and high Columbic efficiency over 5000 charging/discharging cycles at 5 A g^-1.

The miniaturization and surge in the use of consumer electronics have led to an increased demand for energy storage devices that can absorb and deliver high amounts of energy quickly and efficiently. Electrochemical Supercapacitors (ES) are devices that achieve this criterion along with providing longer cycle life than batteries. Since many applications of these devices require the ES to perform reliably in extreme temperatures, researchers have shifted towards all-solid-state supercapacitors. Solid-state supercapacitors not only expand the temperature stability window of ES but also eliminate problems associated with hazardous electrolyte leakage and provide structural stability at extremely low thicknesses.
We recently developed an atomic layer deposition (ALD) process for thermal lithium phosphorus oxynitride (LiPON) solid-state electrolyte [1]. ALD deposited thermal LiPON shows an ionic conductivity of 5.5 × 10-7 S/cm at room temperature. In this study, we present thin-film thermal LiPON as a solid-state electrolyte for ES. 50nm of LiPON is deposited between thermally evaporated gold electrodes, and the MIM stack is characterized electrochemically. LiPON exhibits an EDLC behavior with a capacitance of 15uF/cm2 when cycled between 0-2V. The cutoff frequency reported is 10k Hz at room temperature and increases with temperature to 50k Hz at 65C. High energy and power density are achieved, and the capacitor shows long cyclic stability when cycled between 0-2V for 10,000 cycles at 50uA/cm2. The energy density of the capacitor is enhanced by adding a thin layer of (50-100nm) ALD TiN between the gold and LiPON layers. The ALD deposited TiN has 10-15 percent oxygen which enhances the capacitance of the ES due to intercalation and fast faradic reaction at the ALD TiN-LiPON interface. The voltage stability in the new stack increases from 2V to 3V, and it shows 100X energy density compared with the Au-LiPON-Au stack.
LiPON exhibits high voltage and cyclic stability with a wide frequency window for a large set of applications. Using LiPON as a solid-state electrolyte highlights how battery materials can enhance the energy density of the existing ES. Since ALD enables conformal deposition of layers, the energy density of ES can be further enhanced in 3D architecture [2].

1) Nanoscale Solid State Batteries Enabled by Thermal Atomic Layer Deposition of a Lithium Polyphosphazene Solid State Electrolyte, Alexander J. Pearse, Thomas E. Schmitt, Elliot J. Fuller, Farid El-Gabaly, Chuan-Fu Lin, Konstantinos Gerasopoulos, Alexander C. Kozen, A. Alec Talin, Gary Rubloff, and Keith E. Gregorczyk, Chemistry of Materials 2017 29 (8), 3740-3753
2) Three-Dimensional Solid-State Lithium-Ion Batteries Fabricated by Conformal Vapor-Phase Chemistry, Alexander Pearse, Thomas Schmitt, Emily Sahadeo, David M. Stewart, Alexander Kozen, Konstantinos Gerasopoulos, A. Alec Talin, Sang Bok Lee, Gary W. Rubloff, and Keith E. Gregorczyk, ACS Nano 2018 12 (5), 4286-4294

Todays, flexible and wearable electronic devices have a great attraction for their wide-range applications. Hence, high demands for these products have stimulated the fast development of flexible energy storage devices such as supercapacitors (SCs) and Lithium-Ion batteries (LIBs). In contrast to LIBs, supercapacitors have high power density, long cycle life, and fast charging.
Currently, most energy storage devices are rigid and bulky for the next generation of flexible electronics. Hence, it is crucial to develop a high-performance and reliable supercapacitor which is flexible, light, and thin. Moreover, these SCs need to be functional at high temperatures (600 C) and under various mechanical deformations, such as bending, twisting, and stretching.
In this study, a high-performance flexible supercapacitor with gel-polymer electrolyte (GPE) was fabricated with optimal properties in terms of design, fabrication, mechanical, safety, and electrochemical performance. The optimum materials for gel electrolytes were determined for durable, long cycle life, high performance, flexible, and environmentally friendly supercapacitors (SCs). Since the electrolyte was ultrathin and the electrodes were composed of activated carbon with a high specific area, the fabricated supercapacitor was lightweight, flexible, and low cost with high electrochemical performances.
Moreover, different mechanical testing of the electrolyte, as stretchability, flexibility, yield stress, and ultimate tensile strength (UTS), was conducted by the MARK-10 apparatus. The elongation of the gel-polymer electrolyte (GPE) was 355%. Besides flexibility, different design strategies were adopted to provide additional stretchability in the supercapacitors.
Furthermore, electrochemical tests, including cyclic voltammetry (CV) and galvanostatic charge and discharge (GCD), has been conducted to evaluate the performance of the supercapacitors in different bending angle and temperature.

To keep up with the ever-growing modern technological markets, such as consumer electronics and electric vehicles, it is essential to develop energy storage devices with high energy and power density as well as long cycle life. The conducting polymers have been extensively applied in energy storage owing to their favorable features, including superior electrochemical activity and intrinsic electrical conductivity, yet they suffer from low cycling stability due to the volumetric degradation through repeated charge–discharge processes. Herein, aniline tetramer, the basic building block of polyaniline, with short chain length is employed, and with the assistance of 3D carbon materials, the covalently linked hybrid electrode materials are formed. The as-prepared electrodes as well as the fabricated symmetric supercapacitors deliver remarkable long-term cycling stability. Furthermore, clear evidence from the cyclic voltammetry, galvanostatic charge–discharge profiles and impedance spectroscopy confirms greatly enhanced electrochemical performance in this proposed design compared with noncovalently linked, long-chain polyaniline based hybrid materials.

Supercapacitors have become one of the leading energy-storage technologies because of their merits such as high power density and long cycle life. Due to their unique charge-storage mechanism, supercapacitors bridge the gap between conventional electrical capacitors and batteries in energy-power metrics; however, the state-of-the-art energy density is undesirably low. Hybrid pseudocapacitive electrodes based on nanosized transition metal oxides and carbonaceous materials are considered as promising candidates to overcome this limitation. Herein, we present a VO_x/graphene electrode that incorporates vanadium oxides with multiple valence states onto three-dimensional graphene scaffolds. The fast photothermal synthesis can simultaneously oxidize VCl₃ and reduce the graphite oxide in the precursor mixture. It enables the large-area fabrication of pseudocapacitive electrodes that can be integrated with various substrates. The as-prepared thin-film VO_x/graphene electrodes exhibit a wide potential window with a high three-electrode specific capacitance. The aqueous VO_x/graphene symmetric supercapacitors (SSCs) can reach a high energy density with hardly any capacitance loss after 20,000 cycles. Moreover, the flexible quasi-solid-state VO_x/graphene SSCs can also reach an exceptionally high energy density and near 100% Coulombic efficiency, with an extended voltage window and over 90% capacitance retention after 20,000 cycles. Both supercapacitors outperform many systems in literature and some commercial devices. Therefore, the pseudocapacitive VO_x/graphene electrode can potentially enable highly desirable energy storage features such as fast charging and grid storage.

Micro-supercapacitors are poised to work as energy conversion and storage unit for on-chip electronics. However, their practical application was limited by the low areal power and energy densities and high leakage current due to the self-discharge process. Here, layer-by-layer electro-deposition of an open-shell conjugated polymer and reduced graphene oxide was developed to fabricate hierarchical composite electrode materials with high areal capacitance up to 145 mF cm^-2 (460.3 F cm^-3) and 3 V potential window. The extended delocalization within the conjugated polymer facilitates the wide potential window and high areal capacitance. The hierarchical electrode promotes ultrafast kinetics during the charging/discharging process. Thus, the fabricated device reached 12.7 mF cm^-2 areal capacitance at the fast scan rate of 10 V s^-1, and enable a record energy density of 21.9 μWh cm^-2 at power density of 227 mW cm^-2. Meanwhile, a novel separator that contained sulfonate ion-exchange resin was employed to trap impurities in electrolyte and thereby suppress the self-discharge in supercapacitors. Compared to devices using commercially available separators, the device here exhibited a lower leakage current and higher charging efficiency. These attributes allow the fabricated device to work with radio frequency energy-harvesting circuits and serve as high-endurance energy storage for wireless electronics

Laser-induced graphene (LIG) has been one of promising materials that can substitute for conventional graphene or graphene-like electrode materials due to its simple fabrication, mechanical flexibility, and electrochemical properties tantamount to three-dimensional graphene materials. LIG is produced by irradiating polymer, being represented by polyimide (PI), with a laser ranging from UV to near-IR lasers. While numerous studies demonstrated the promises of typical LIG for electrodes of energy storage devices such as supercapacitors, this as-obtained LIG suffered from inherently limited surface area. The small surface area of LIG is critically related to limited energy storage performance, which should be overcome for practically applying LIG in energy storage devices.
In this study, we present three strategies for boosting electrochemical capacitance of LIG: densification, doping, and the incorporation of pseudocapacitive metal oxide. The duplicate laser-induced pyrolysis method has been developed to simultaneously implement these goals. Unlike typical methods for LIG fabrication, as implied by “duplicate”, laser irradiation is conducted twice in this method. First, LIG is produced by irradiating a PI sheet with a CO₂ laser beam, which corresponds to typical LIG. Then, the LIG is coated with a polyamic acid (PAA) layer that contains precursors for dopants and (or) pseudocapacitive metal oxides. The PAA layer is treated with heat for imidization, and the additional PAA layer is converted into PI. Finally, this sample is irradiated with the laser again, and a high-performance LIG electrodes is obtained. Because of the additional loading of PI and its pyrolysis into LIG, densification of LIG is achieved, and interestingly doping of LIG and (or) decoration of LIG with metal oxide nanoparticles are observed.
Based on the duplicate laser pyrolysis of PI, LIG could be doped with nitrogen only, simultaneously with nitrogen and boron, or simultaneously with nitrogen and phosphorus. These LIG electrodes are denoted by N-LIG, NB-LIG, and NP-LIG, respectively. While the electrochemical properties of these doped LIG varied with laser processing parameters and the concentration of doping solutions, the optimally doped LIG electrodes all exhibited remarkably improved electrochemical capacitance superior to those of typical LIG. For instance, the specific capacitances of N-LIG, NB-LIG, and NP-LIG were 49.0, 104.3, and 163.6 mF/cm² at 0.2 mA/cm² in 1 M H₂SO₄ electrolyte, whereas that of undoped LIG was only ~9 mF/cm². These doped LIG maintained the excellent flexibility of LIG, showing negligible capacitance change by bending. Moreover, when a metal precursor was additionally loaded in the doping solution, metal oxide nanoparticles was generated on the surface of doped LIG, which potentially further boost the capacitance of the doped LIG because of pseudocapacitance of metal oxides.
In summary, the duplicate laser-induced pyrolysis enabled the facile fabrication of heteroatom-doped LIG. While this method requires additional coating process and laser irradiation, densification and (co)doping of LIG were simultaneously achieved, and the resulting LIG electrodes exhibited starkly increased capacitance. We envision the use of this method for doping of other energy-storage carbon nanomaterials.

Polymorph MoS₂ attracts great attention for supercapacitor and Li-ion battery applications. Although the capacitance origin is usually attributed to the intercalation process, MoS₂ exhibits a well-defined electrical double layer (EDL) behavior. Nonetheless, the nature of the EDL behavior of MoS₂ is yet to be revealed. Herein, we investigate the quantum capacitance (C_Q) of the three main phases of MoS₂ (the semiconductor 2H and 3R phases and the metallic 1T phase). Interestingly, the number of MoS₂ layers greatly affects the C_Q of the material. In addition, the absence of Van der Waals (VdW) interactions overestimates the bandgap and C_Q, emphasizing the importance of the VdW correction in the C_Q calculations. As MoS₂ usually stores charges via the intercalation of cations, the effect of H⁺, Na⁺, Li⁺, and K⁺ intercalation on the C_Q of the three phases of MoS₂ is thoroughly investigated. The intercalation of all studied alkali metal cations leads to the transformation of the 2H and 3R phases into the metallic 1T phase and increases its stability. Importantly, the K⁺ and Na⁺ intercalations show the greatest impact in enhancing the C_Q of the studied phases. However, the charging process of K⁺ and Na⁺ ions is not as reversible as that of Li⁺ as revealed from the estimated binding energies. To this end, herein, we demonstrate the co-intercalation of Li⁺/Na⁺ ions as a strategy to enhance the overall capacitance performance. The Li⁺/Na⁺ co-intercalation shows a C_Q of 3163 F/g with a more thermodynamically stable adsorption process. Finally, the study recommends the use of 2H–MoS₂ only as a positive electrode and 1T-MoS₂ as a negative and/or positive electrode in energy storage devices. Also, K⁺ intercalation is recommended to achieve the highest C_Q and the Li⁺/Na⁺ co-intercalation for the best overall performance.

The higher charge density, cheaper cost and relative stability over lithium-ion batteries have driven the development of Rechargeable Magnesium batteries (RMBs) [1,2]. However, at electrode/electrolyte interfaces (called Solid-Electrolyte Interfaces, SEIs), the high charge
density of Mg²⁺ ions trigger the formation of ion impermeable deposits. Electrolytes need to remain stable against reductive reactions at the electrode/electrolyte interface to overcome the stability and reversibility issues caused by SEIs [3,4]. Ethereal solvents containing Magnesium
halide salts provide an exciting prospect towards development of stable electrolytes for RMBs.The primary charge carriers in solution are a variety of electroactive species (EAS) formed due to complex equilibria of the Mg-halide system balanced with a counter-ion such as AlCl₄^-. The
existence of larger ionic architectures formed by the anion bridged ionic agglomerations have been previously shown [5].

Here we investigated ion agglomeration and transport of several such EAS in MgCl₂ salts dissolved in five ethereal solvents and in the presence of two anions under both equilibrium and operating conditions using large scale atomistic simulations. We find that clusters were discovered irrespective of the anion used, the rate of ionic clustering is affected by the nature of the anion present. Highly interacting anions such as Cl^- tend to enhance clustering rates while weakly interacting anions lower clustering rates in all solvent environments. Solvents
and anions perform complementary roles in enhancing the clustering of the EAS, with clustering in heavier solvents being significantly affected by the solvents. We further illustrate that ionic transport in the electrolytes are affected by the weight of the solvent used with heavier solvents
showing significantly lowered diffusivities. We highlight the role of the solvent in determining cluster morphology and ion mobility by controlling ion diffusion pathways and ion coverage. Our findings of the solvent and anion controls on cluster formation and kinetics can provide useful insight into the electrochemical reactions at the anode/electrolyte interface in RMBs.

References
1. C. B. Bucur, T. Gregory, A. G. Oliver and J. Muldoon, The Journal of Physical Chemistry Letters, 2015, 6, 3578-3591.
2. M. John, B. C. B. and G. Thomas, Angewandte Chemie International Edition, 2017, 56, 12064-12084.
3. P. Baofei, H. Jinhua, H. Meinan, B. S. M., V. J. T., Z. Lu, B. A. K., Z. Zhengcheng and L. Chen, ChemSusChem, 2016, 9, 595-599.
4. K. A. See, K. W. Chapman, L. Zhu, K. M. Wiaderek, O. J. Borkiewicz, C. J. Barile, P. J. Chupas and A. A. Gewirth, Journal of the American Chemical Society, 2016, 138, 328-337.
5. V. Vasudevan, M. Wang, J. A. Yuwono, J. Jasieniak, N. Birbilis and N. V. Medhekar, The Journal of Physical Chemistry Letters, 2019, 10, 7856-7862.

Iron-based alkaline battery systems such as iron-nickel or iron-air batteries exhibit the potential for large scale stationary energy storage due to the high abundancy of iron and its low cost.
Iron electrodes have a high lifespan and are insensitive to overcharging, partial and deep discharge. High energy densities, which come close that of today's lithium-ion batteries, can be achieved. In an iron-based alkaline battery system, it is assumed that iron is oxidized to iron hydroxide during the first discharge step, which correspondents to a capacity of 960 mAh/g_Fe. This can then be further oxidized to magnetite with a theoretical capacity of up to 1280 mAh/g_Fe. There are however two limiting factors in conventional iron electrodes. Typical iron electrodes that are manufactured on the basis of iron powder, have experimentally determined capacities that are in the range of only 100 - 300 mAh/g_Fe, which is therefore significantly lower than the theoretical capacity. It is assumed that the low experimental capacity is related to a buildup of a passivating layer and thus hinders the charge/discharge reaction. However, it has not yet been clearly proven what exactly leads to this passivation and how it can be mitigated. Another bottleneck of iron electrodes is the low discharge rate, which makes it inferior compared to other types of batteries.
To overcome these limitations, we have developed a thin film iron electrode, that delivers high capacities of 500 mAh/g_Fe at a discharge rate of 1C. The coating was first carried out on planar substrates, to investigate how different deposition parameters such as e.g. pH value, precursors/additives, deposition time, current density, substrate material, etc. affect the morphology and adhesion of the iron layers as well as the electrochemical properties, in particular the iron-related capacity to be achieved. These properties were examined with methods of SEM / EDX, chronoamperometry, chronopotentiometry and cyclic voltammetry. In addition, material changes of the electrodes depending on the state of charge and cycle were analyzed in order to identify the cause of the as aforementioned low capacities achieved in practice with typical iron electrodes. For this purpose, scanning electron microscopy/EDX, FTIR, X-ray diffractometry and Raman spectroscopy were used to examine material phases.
The produced planar electrodes have shown good performance. But to increase the active mass to substrate ratio, electrodes have to be 3 dimensionally structured. For this purpose, iron has been deposited onto 3-dimensionally structured carbon layers. The challenge in fabricating these types of electrodes was to obtain a homogenous coating, which goes deep into the material without clogging the pores. Similar to the case of planar electrodes, this has been achieved through a variation of deposition parameters.

To date, a majority of battery technologies rely on metal-ion charge carriers. Surprisingly, non-metal cations, particularly proton-containing cations, i.e., H⁺ , H₃O⁺, and NH⁺⁴ , have received exceedingly little attention. The simplest form of hydrogen cation, a single proton, is nearly "invisible" with a measured radius of ∼0.89 fm or ∼2.1 fm, using muon or e⁻ spectroscopy, respectively. Due to the negligible strain of hosting protons, the rate capability and cycle life of proton batteries have the potential to be far superior to those of existing batteries. In this talk, I will describe the hierarchy of structural ingredients that permits fast proton transport and storage. These include a percolating nanoscale pipework containing a constrained network of hydrogen bonded water. We have abstracted topology of this bonding network as a graph and show that the network remains robust as it is filled with additional protons.

One-dimensional tunnel manganese oxides (TuMOs) such as hollandite α–MnO₂ are attracting considerable interest in the context of intercalation batteries because its unique structure induces a robust framework for ion insertion and deinsertion. However, practical deployment of TuMOs still encounters critical challenges such as poor rate capability due to long-distance 1D diffusion and performance degradation induced by structural instability during charge/discharge cycling. Through an integration of experiment and simulation, we show that Mn and O vacancy complexes can be effectively introduced in the tunnel wall through elaborated acid leaching and open additional pathways to enhance ion diffusion. Through first-principles calculations, it is found that the cross-tunnel diffusion barrier for Li⁺ ions through Mn-O vacancy complexes is significantly lower than that by crossing the intact wall without vacancies. Moreover, we show that the vacancy-enriched hollandite α–MnO₂ can be effectively stabilized via Li₂O incorporation to significantly improve its capacity retention. Experimentally, Li₂O incorporation into α–MnO₂ structure is achieved via wet mixing of α-MnO₂ with LiOH in methanol, followed by drying and heat treatment. After 100 intercalation/extraction cycles, the Li₂O-stabilized α–MnO₂ electrode exhibits 53% capacity retention, compared to 17% and 40% shown by the acid-leached only and pristine α–MnO2. Computationally, atomic structural evolutions during intercalation/deintercalation cycles are comprehensively studied via first-principles calculations to provide fundamental understandings of the observed capacity retention improvements.

Hydrogen production has gained popularity due to being an excellent energy carrier, with the capabilities of being stored and used with sustainable energy sources like fuel cells. However, hydrogen does not exist in nature and needs to be produced using non-environmentally friendly methods. These methods have led to the development of new sustainable hydrogen production alternatives, like alkaline water splitting for clean energy production. The development of new earth-abundant electrocatalysts for the Oxygen Evolution Reaction (OER) could help the efficiency of water splitting processes by reducing the energy barrier and improving its reaction kinetics. We used in this work a Nickel/Vulcan XC-72R (Ni/V) electrocatalyst for the OER in an alkaline medium. The Rotating disk slurry electrodeposition (RoDSE) methodology was explored to prepare nickel nanocatalysts supported on Vulcan XC-72R. The Ni/V electrodeposition was performed in 0.1 M KClO₄ at three different potentials (-0.40 V, -0.67 V, -0.75 V) vs. RHE. We found that Ni/V was deposited on the Vulcan support at -0.67 V and -0.75 V vs. RHE using cyclic voltammetry (CV). Linear sweep voltammograms (LSV) experiments demonstrated an overpotential of 480 mV vs. RHE at 10 mA/cm²disk in 0.1M KOH for the OER using the Ni/V catalyst obtained by electrodeposition at -0.75 V vs. RHE. Future experiments will focus on measuring our remaining Ni/V electrocatalyst and determining their specific activity and mass activity for the OER in alkaline electrolyte.

Clay is one of the oldest known silicate-based materials to humans and has been an integral part to our civilization from the prehistoric era, that includes pottery, tiles, art objects, bricks, tools, medicinal properties, ceramics and ancient batteries (Baghdad batteries). The layered structures of clay with interchangeable ions can be tuned for various applications that include energy storage, sensing, wastewater treatment, polymer composites, fire-resistant materials, cosmetics, and biomedical materials. Additionally, its abundant supply, low cost, high porosity, high surface area, and good thermal barrier and mechanical properties make clay a highly deserving material for high-valued applications. Among various energy storage and conversion materials, functionalized natural clays display significant potentials as electrodes, electrolytes, separators, and nanofillers in energy storage and conversion devices. In addition, natural clays deliver the advantages of high ionic conductivity and hydrophilicity, which are beneficial properties for solid-state electrolytes. Herein, we show a unique approach to engineer hybrid clay films using simple precursors viz. earth-abundant clay, water, and a quaternary ammonium salt. The quaternary ammonium salt arranges in monolayer, bilayer, and pseudo-tri-layer structure into the clay gallery, allowing to tune the basal spacing of the material. In the present study, we have varied the carbon chain length of the quaternary ammonium salt from lower to higher carbon chain length. The low-carbon chain quaternary ammonium salts arranged themselves in a pseudo-tri-layer configuration, increasing the basal spacing to a higher value compared to high-carbon chain modifications. The above parameters have been well characterized using powder X-ray diffraction and infrared spectroscopy studies. In addition, the engineered clay films have also been characterized using x-ray photoelectron spectroscopy, scanning electron microscopy, and x-ray fluorescence techniques to explore the films' structural and morphological parameters. Furthermore, we have analyzed for impedance spectra of the engineered clay films in non-aqueous electrolyte solutions. The spectra exhibit lower electrochemical series resistance (ESR) values for the non-metallic and monometallic clay films against the parent clay material. Moreover, a bimetallic analogue of the clay films showed a further decrease in the ESR values, which show glimpses of new ventures into non-lithiated and non-sulfur based materials used in energy application, esp. batteries, electrodes. Additionally, using the right chemical modifications, newly developed hybrid clay films can be engineered as cost-effective battery separators and capacitors. The unique methodology could address the challenges posed by energy industries, agencies and researchers, and usher new pathways for developing a sustainable and biocompatible materials energy applications using a cost-effective approach.

The development of a clean and renewable energy carrier is necessary owing to the tremendous devastation of the environment and exhaustion of fossil fuel resources. Due to the high energy density and renewability of hydrogen gas, it is regarded as one of the energy alternatives to traditional fossil fuels. Electrochemical water splitting, which consists of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), is considered as sustainable technology for high-purity hydrogen gas production. However, the thermodynamically sluggish kinetics of electrochemical reaction at each electrode have hampered the practical applications in the industrial fields. To overcome this issue, ruthenium- and platinum-based materials are generally used for electrocatalysts for improving OER and HER performances, respectively. However, their high cost, scarcity, and insufficient durability have limited their large-scale applications. Recently, transition metal-based oxide, sulfide, phosphide have been considered as promising electrocatalysts for water splitting owing to their remarkable advantages such as low cost, abundance, rich redox properties, and outstanding chemical stability. Among them, transition metal phosphides (TMPs) are emerging as a promising bifunctional electrocatalyst for both of OER and HER. However, their intrinsic low electrical conductivity still remained as a challenge
Herein, core-shell structured nickel cobalt alloy-nickel cobalt phosphide (NiCo@NiCoP) nanorod directly grown on nickel foam (NF) was synthesized by hydrothermal, thermal reduction, electrochemical oxidation, and phosphidation process. First, NiCo carbonate hydroxide (NiCoCH) was synthesized by hydrothermal method, and then it was calcined under the H₂ flow to form NiCo alloy core. The core-shell structured NiCo@NiCo hydroxide (NiCo@NiCoOH) was obtained by electrochemical oxidation at an anodic current density of 300 mA cm^-2 for 60 min in 1 M KOH solution. Finally, NiCo@NiCoP was prepared by the annealing method which was placed NaH₂PO₂ and NiCo@NiCoOH in a tube furnace under Ar atmosphere. The metallic core encourages the charge transport to the surface phosphide, and the phosphide shell provides abundant active sites for HER and OER. Also, such a homogeneous 1D structure can easily absorb a liquid-phase solution onto the electrode surface owing to the strong capillary force, thus reducing the gas-solid interface friction and enhancing the release of generated oxygen gas bubbles. As a result, the NiCo@NiCoP nanorods on NF require the low overpotentials of 146 mV (vs. RHE) and 340 mV (vs. RHE) for HER and OER, respectively, at a current density of 100 mA cm^-2 in alkaline condition. Moreover, the NiCo@NiCoP nanorods show superior long-term stability for 50 h, compared to commercial Pt/C and RuO₂ on NF.

Organic electrolytes, an essential component in today’s energy storage technologies, inherently suffer from safety, cost and non-eco-friendly issues. Water-based electrolytes have proven out to be a better alternative to organic electrolytes because of their much superior ionic conductivities. Ionic transport constitutes part of the bottleneck for the total resistance of the devices which limit the power. Moreover, aqueous electrolytes are cost-effective and non-flammable. The major challenge of aqueous electrolytes in organic batteries is that they lead to drastic self-discharge.
Herein, we have utilized the concept of “water-in-salt electrolyte” with polyelectrolytes, more especially potassium polyacrylate (PAAK). This is a new class of electrolyte that we called “water-in-polymer salt electrolyte”. It is non-flammable and displays a high ionic conductivity (70-90 mS/cm). The ionic conductivity is mostly governed by the ionic mobility of K⁺ ions as polyacrylate is immobile and it is found to be independent of the viscosity of the PAAK electrolytes. Since this electrolyte solely transports cations, the organic battery concept that suits it is a “cation rocking chair” battery including two types of polymeric quinones: lignin and polyimide redox polymers as a positive and negative electrode, respectively. The advantage of these redox polymers is that they are electrochemically active with K⁺ ions at neutral pH.[1] Neutral pH is advantageous to avoid corrosion in metal collectors.
The sustainable organic battery displayed a high specific power of 6.8 kW/kg owing to the high ionic conductivity of the PAAK electrolyte and the fast redox quinone redox chemistry. The organic redox polymers were also stable in this electrolyte as the specific capacity degrades to only 35% in 2500 cycles. Moreover, we achieved an extremely low self-discharge rate as open circuit potential (OCP) drops from 1V (faradic peak) to 0.75V in >100 h. This is the world record for the self-discharge of organic electrodes in aqueous electrolytes. We believe this study opens a new avenue for efficient lignin-based truly safe, non-flammable and large-scale high-power energy storage solutions.
References
[1] Z.Khan et.al. Water-In-Polymer Salt Electrolyte for Slow Self-discharge in Organic Batteries. Advanced Energy and Sustainability Research submitted

Polymer Electrolyte Membrane Fuel Cell (PEMFC) technology is an advantageous solution for clean energy applications due to its zero-emission, high efficiency, low maintenance cost, and high energy density. The maturity of this technology has been the product of considerable scientific and industry efforts devoted to developing highly efficient and reliable systems increasingly adopted in the transportation and energy generation sectors. PEMFCs produce electricity by converting the electrochemical reactions of hydrogen oxidation and oxygen reduction into electrical energy. However, fabricating catalysts materials with high performance at scale is still a challenge that needs to be tackled to enable a marketable increase in the energy generated from this technology. For this reason, tunability of the catalyst materials at the core of this technology is more than essential to meet certain energy demands. Here we investigate commercially available catalysts based on platinum nanoparticles (Pt NPs) supported on Engineered Carbon Supports (ECS)^TM produced by Pajarito Powder, LLC.
Heat treatments (HT) were performed on base catalyst materials containing 30 wt% Pt supported on two different types of ECS, labeled as 3701 and 4601 (both made with similar materials and procedures, 4601 has more pore formers). The treatments were performed at temperatures ranging from 400 to 1000 °C in 7% H₂/N₂, N₂, He, and Ar atmospheres for 1hr. The main goal of this study is to understand the effects and the properties of these types of ECS (having different degrees of porosity) on the stability of the Pt NPs, to get a clearer vision of how those different environments and temperatures affect the sintering processes taking place on the Pt NPs which can be correlated to the catalyst performance.
Our preliminary results by X-ray diffraction (XRD) have shown an increase of the Pt crystallite size as temperature increases and 1000 °C in an atmosphere of 7% H₂/N₂ appears to have a stronger effect on Pt crystallite growth when compared to N₂ or Ar, while such growth seems to have the same trend in both N₂ and Ar atmosphere. Additionally, CO chemisorption showed a reduction of the active metallic surface area with increasing temperature, verifying the trend measured by XRD. For every treated sample, Raman characterization did not show a dramatic change in the ratios between the G-mode peak (representing crystalline sp² hybridized carbon), and the D-mode peak (attributed to disordered sp³ diamond-like carbon). This can shed a light on the amorphization or graphitization processes taking place under these conditions and the degree of graphitization of the carbon support. Transmission Electron Microscopy (TEM) will be performed to further clarify any conclusion. X-ray Photoelectron Spectroscopy (XPS) surface characterization revealed that there is a reduction in the Pt NPs oxidation from 600 to 1000 °C. Treatments in N₂, the O 1s spectra were different than the other conditions possibly due to the lower presence of atmospheric oxygen during this treatment. On the other hand, the C 1s spectra show a minor shift to higher binding energy in the main peak as a result of the treatments, indicating a slight increment in the amount of sp³ and a decrease in the amount of sp² carbon nature.
This research will be expanded with TEM imaging and physisorption data to get a more quantitative and qualitative interpretation of the phenomena taking place in the mobility and sintering processes of Pt NPs on the ECS surfaces and the role of the porosity and carbon morphology. Finally, direct measurements of the mass transport from which surface diffusivity can be determined during the process of Pt sintering will be also performed using in-situ TEM, simulating the furnace conditions using a methodology that would allow us to scrutinize how the nanoscale characteristics of these powders influence the coalescence and sintering processes in these nanoparticles.

Recently, a tremendous upsurge in the research of Solid oxide fuel cells (SOFCs) has been documented due to cheap electricity production and without harming the environment. The development of efficient SOFCs requires more robust cathode for oxygen reduction. Until yet a copious amount of research has been done on varieties of materials including LSCF. In this work, Ruthenium is doped on the LSCF forming nanostructured Ru-LSCF with various Ru stoichiometric quantities. The Ru-LSCF catalyst is prepared via simplistic technique “Glycine combustion process”, producing evenly embedded Ru in LSCF perovskite materials leading to increased oxygen reduction reaction (ORR). The nanostructured Ru-LSCF cathode showed polarization resistance of approximately 0.031 Ωm² at 750 ⁰C. The peak powers of approximately 1760.5, 1480.1, 893.3 mW/cm² were recorded at 750, 700, and 650 ⁰C, respectively. Ru LSCF was quantitatively optimized for enhanced power production with high precision calculation. The results show that the Ru-LSCF optimum fabricated nanostructured cathode is promising catalyst for the reduction of oxygen at the cathode side for highly durable SOFCs.

Polymer Electrolyte Membrane Fuel Cell (PEMFC) is an electrochemical cell which undergoes oxygen reduction reaction to produce energy. Platinum (Pt) metal has been used for catalysis since its inception but expensiveness is the major obstacle in commercialization of fuel cell. Herein a non-precious group metal (NPGM) is employed instead of Pt to reduce the cost of PEMFCs. Manganese dioxide based carbon nanotubes (MnO₂ CNTs) is a catalyst having excellent electrochemical properties and offers a better alternative to the Platinum based PEMFC. The catalyst is synthesized by impregnating the transition metal on large surface carbonaceous CNTs by hydrothermal synthesis techniques. To enhance the catalytic activity and increase the volumetric current density, the sample was pyrolyzed at 800 ⁰C temperature under nitrogen atmosphere. During pyrolysis, the nitrogen was doped in the framework of CNTs. The material is then treated with acid for removing the unreacted metals and adding oxygen functional group to the CNT framework. This process ameliorates the catalytic activity of the manganese based catalyst. The catalyst has been characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and the catalyst activity has been examined by Rotating Disc Electrode (RDE) experiment. The catalyst was strong enough to withstand austere alkaline environment in experimental conditions and had high electro catalytic activity for oxygen reduction reaction (ORR). Linear Sweep Voltammetry (LSV) depicts a current density of -4.0 mA/cm² and an over potential of -0.3V vs. Standard Calomel Electrode (SCE) in 0.1M KOH electrolyte. Rotating Disk Electrode (RDE) was conducted at 400, 800, 1200, and 1600 rpm. The results of MnO₂CNT uphold the proponent of desirable and low cost catalyst to supplant the Pt metal in fuel cell.

Metallic nanoparticles have been intensively studied as catalytic materials [1] significant understanding of their physio-chemical properties has been achieved to date, paving the way for their usage in wide range of industrial applications, from pharmaceuticals to sensing and energy. Over time, the importance of nanoparticle shape in defining its performance has been recognised; the rate of catalytic activity also depends on the shape and size of nanoparticles and therefore the synthesis of well-controlled shapes and sizes of colloidal nanoparticles can significantly improve catalytic performance [2]. Given the increasing demand for durable platinum catalysts for applications such as fuel cells and electrolysers, shaped nanoparticles offer an effective solution with minimal or no cost differences.
Sub-5 nm shaped noble metal nanoparticles with high fraction of {111} surface domains have been shown to demonstrate significantly superior resistance to surface dissolution and rearrangement [3]. Hence, are of fundamental and practical interest as electrocatalysts, especially in fuel cells. The nanoparticles surface structure dictates its catalytic properties, including kinetics and stability [4]. However, unlike their bimetallic analogues that typically deliver poor durability, the synthesis of size-controlled, pure Pt shaped nano-catalysts has remained a formidable chemical challenge. Therefore, there is great need for an industrially scalable and greener synthetic method for the production of ultra-small, size-controlled nano-catalysts. We report a green innovative one-step approach used for the preparation of ultra-small pyramidal nano-catalysts with a high fraction of {111} surface domains. This is achieved by harnessing the shape-directing effect of citrate molecules, together with a strict control of oxidative etching whilst avoiding polymers, surfactants, and organic solvents. The low costs and green synthetic method can also be easily scaled up, as it is simple, low temperature, ‘one-pot’ and fast. The procedure yields single-crystal 3.4 nm Pt NPs with pyramidal shape and prevalent extended {111} facets, as proved by HR-TEM and electrochemical characterization. This was followed by Pt pyramidal NPs deposition on Vulcan carbon, ink formation and spray deposition to create gas diffusion electrodes. In a preliminary study, these pyramidal Pt catalysts are shown to offer significantly enhanced stability, using the standardised US Department of Energy (DoE) accelerated stress tests (ASTs) metrics, as cathode catalysts in full polymer electrolyte fuel cells, both compared to non-faceted equivalents and highly optimised commercial Pt/C catalysts, while providing equivalent current and power densities. Post mortem HR-TEM images of the catalyst show reduced agglomeration for the pyramidal Pt NPs compared to the commercial Pt NPs. Demonstrating that the {111} surface domains in pyramidal Pt NPs (as opposed to spherical Pt NPs) can improve aggregation/corrosion resistance, leading to a significant improvement in membrane-electrode assembly (MEA) stability and lifetime.
[1] Iben Ayad, A.; Belda Marín, et all. “Water Soluble” Palladium Nanoparticle Engineering for C-C Coupling, Reduction and Cyclization Catalysis. Green Chem. 2019, 21 (24), 6646–6657.
[2] Stepanov, A. L.; Golubev, et all. A Review on the Fabrication and Properties of Platinum Nanoparticles. Rev. Adv. Mater. Sci. 2014, 38 (2), 160–175.
[3] Fuchs, T.; Drnec, J.; Calle-Vallejo, et all. Structure Dependency of the Atomic-Scale Mechanisms of Platinum Electro-Oxidation and Dissolution. Nat. Catal. 2020, 3 (9).
[4] Lopes, P. P.; Li, D.; et all. Eliminating Dissolution of Platinum-Based Electrocatalysts at the Atomic Scale. Nat. Mater. 2020, 19 (11), 1207–1214.

The growing demand for energy and serious environmental problems have promoted the urgent development of sustainable energy conversion and storage devices. Metal-air batteries and fuel cells are regarded as one of the most promising energy storage and conversion device for the next-generation owing to competitive benefits such as zero-carbon emissions, high energy density, and operating safety. Despite the numerous efforts to utilization of fuel cells, sluggish oxygen reduction reaction (ORR) involving four-electron transfer on the air cathode limit the overall electrochemical kinetics. Until now, although the platinum-based materials have been used as electrocatalysts for ORR owing to outstanding activity, their high cost, scarcity, and low stability have hindered the large-scale commercialization. Thus, enormous research endeavours have been dedicated to exploring efficient and inexpensive electrocatalysts for next-generation energy devices using various transition metal-based materials. Transition metal-nitrogen-doped carbon (M-N-C) have been studied to replace the platinum-based electrocatalysts because of their abundance, various redox property, and durability. Among them, iron-nitrogen-doped carbon (Fe-N-C) electrocatalysts with the locally modified electronic structure and optimal O₂ adsorption/desorption energy are considered as attractive alternatives.
In this study, we proposed hollow-structured Fe-, N-, and S-tridoped carbon spheres (FeNSC) synthesized by hydrothermal polymerization of polypyrrole on the surface of SiO₂ nanosphere, impregnation of Fe ions, chemical etching of a metallic Fe and a SiO₂ template, followed by the carbonization with sulfur source. The hollow-structured FeNSC nanospheres showed excellent ORR onset-potential (0.971 V vs. RHE) and half-wave potential (0.877 V vs. RHE), which is superior to hollow-structured Fe-N-doped carbon nanosphere, hollow-structured N-S-doped carbon nanospheres, and state-of-the-art Pt/C electrocatalyst in 0.1 M KOH electrolyte. Furthermore, the current density of FeNSC degraded only by 4.3% after the chronoamperometry measurements for 50h, showing excellent durability compared to Pt/C (28.3%). These outstanding ORR performance of FeNSC are mainly originated from abundant Fe-Nx sites, which are generally considered as the highly active sites for ORR. Additional S dopant with high electron spin density can not only enhance the electric conductivity of carbon matrix but adjust the adsorption/desorption energy of oxygen related intermediates. Also, as the sacrificial SiO₂ cores are etched by HF solution, the uniform hollow structure of FeNSC possess reduced ion-diffusion length, large specific area, and abundant active sites, thereby improving electrocatalytic ORR performance.

As the Pt loading in proton exchange membrane fuel cell cathodes is driven down to reduce costs, catalyst utilization becomes increasingly important. Here, we report an atomic layer deposition-facilitated electrode fabrication technique designed to improve the catalyst-ionomer interface. The ionomer solvent environment and carbon support nanoporosity were studied independently, and it was found that the combination of an agglomerated ionomer dispersion and a mesoporous support gave access to a high catalytic activity (MA = 0.31 A/mg_Pt with pure Pt) that could be maintained at high current densities. We hypothesize that the formulation results in Pt sufficiently withdrawn from the ionomer such that poisoning and transport losses are reduced. When paired with a low-resistance dispersion-cast membrane, a 0.1 mg_Pt/cm² cathode could deliver an unprecedented 0.65 V power density of 1.0 W/cm² at 150 kPa and 80°C. Due to the enhanced durability of Pt nanoparticles prepared via atomic layer deposition, the assembly also demonstrated impressive resistance to dissolution/corrosion, losing only 33 mV after 30k cycles and thereby meeting the stability targets of the US DOE.

Supercapacitors (SCs) are drawing great attention as highly efficient and pollution-free electrochemical energy storage (EES) due to their high power density, fast rates of charging/discharging within seconds, infinite cycle life, low cost, low self-discharging, and safe operation against batteries. SCs come in all shapes and sizes with the advances in carbon nanomaterials and fabrication methods. The general assembly of SCs is based on two-dimensional planar architecture sandwiched by two flat-facing conductive electrodes that are separated by a porous separator sealed in liquid electrolyte. It shows great potential in a wide range of applications such as large grid-scale energy storage facilities, hybrid electric vehicles, consumer electronics, and military/defense devices. However, a major challenge of commercial SC technologies lies in the development of rational design in a range of form factors for applications such as energy backup systems, portable electronics, roll-up displays, smart skins, and wearable electronics. Recent advances in the field of SCs have been made not only to improve power/energy delivery and ion/electron kinetics but reduce total device volume through adopting microarchitecture to the SCs. Besides, in the aspects of rational cell configuration, many efforts are being directed towards the development of lightweight and flexible devices that can meet power and energy demands in spatial-limited applications such as energy backup systems, portable/wearable electronics, and electric vehicles. The demand for on-chip power sources in a range of form factors drives considerable efforts on high-performance, flexible miniature energy storage. Micro-supercapacitors (MSCs) afford high power capability due to fast ion kinetic during charging/discharging. In this regard, the development of mechanically robust MSCs is important as they have the potential for wearable and flexible energy storage systems. Among MSCs, fiber supercapacitors are attracting significant attention for wearable and portable electronics. Here, we report flexible and/or even wearable fiber electrodes via colloidal self-assembly for high-performance fiber MSCs. When assembled into symmetrical two-electrode cells, the fiber MSC electrodes deliver exceptional volumetric capacitance even at a high current density and long cycle lives even when deformed. Based on electrochemical impedance spectroscopy analysis, it is revealed that high electrochemical properties are attributed to fast response kinetics. The fiber electrodes also demonstrate excellent storage performance under mechanical deformation—for example, bending-straightening cycles.

In recent years, the metal-CO₂ battery has been demonstrated as a novel approach to capture CO₂ from gas streams and to generate electricity, particularly using high energetic metallic Lithium, Sodium, Magnesium and Aluminum anodes. Aluminum is the most abundant metal in the earth’s crust and is less reactive than alkali metals. Aluminum also participates in a three-electron process during electrochemical charge/discharge reactions, which gives its attractive gravimetric capacity (2980 Ah/kg) and competitive volumetric capacity (804 Ah/cm³) compared to single-electron lithium and sodium redox reactions. A rechargeable metal-CO₂ battery based on aluminum metal is advantageous in terms of cost-effectiveness, manufacturability and safety handling. In this work, we developed an Al-CO₂ battery that is rechargeable and can deliver high capacity and high energy. The battery utilizes an aluminum metal anode, a commercial carbon cathode and an ionic liquid electrolyte containing AlCl₃/1-ethyl-3-methyl imidazolium chloride with a redox mediator as the electrolyte additive. Al-CO₂ cells with this design are shown to achieve excellent rechargeability with less than 50 mV overpotential. Reversible storage capacity of 500 mAh/g based on the active carbon mass on the cathode for over 13th cycles is reported. An ultra-high energy density of 9930 Wh/kg and specific capacity of 9411 mAh/g can be achieved when performing a full discharge at 100% CO₂ gas environment. Importantly, an energy density of 910 Wh/kg and specific capacity of 901 mAh/g can still be reached when the cell is discharged in 5% CO₂ mixed with argon gas. This indicates the cell can probably capture and convert CO₂ directly from the flue gases, while generating and storing electricity. We have been activity studying the fundamental reaction mechanism of the Al-CO₂ batteries by using spectroscopic and electrochemical tools at the cathode during the charge and discharge processes. On that basis, we plan to discover the carbon capture mechanism and improve the electrochemical performance of the rechargeable Al-CO₂ battery.

The potassium-oxygen battery (KOB) is a promising energy storage technology with high theoretical specific energy of 935 Wh/kg and long cycle life. In recent years, the KOB has distinguished itself from other alkali metal-oxygen batteries by its facile cathodic cell chemistry that enables thousands of cycles with negligible performance loss. Capacities relevant for practical applications are achieved using affordable carbon paper as cathode material without need for precious metal catalysts. In addition, operation in dry ambient air has been demonstrated.
The cathode chemistry of KOB is based on the highly reversible interconversion of oxygen and potassium superoxide (KO₂). Formation of KO₂ is thermodynamically and kinetically favored over potassium peroxide (K₂O₂) and potassium oxide (K₂O). A distinctive chemical stability renders KO₂ unreactive towards cell components and is the driver for the remarkable cycling stability of KOB. Recently, it was found that a further reduction of KO₂ towards K₂O₂ and K₂O occurs in the absence of oxygen, which induces currently unknown parasitic side reactions. In consequence, the coulombic and round-trip efficiencies are diminished. These findings raise several questions: How does oxygen partial pressure p(O₂) influence the cell chemistry? Can K₂O₂ formation during discharge be prevented? How does p(O₂) affect the performance and what role does the cathode structure play?
We tackled these questions in an experimental approach. The influence of p(O₂) on the discharge performance was investigated by extensive battery testing over a wide range of p(O₂). Analytical techniques were used in situ and post-mortem to study the effects of p(O₂) on product formation, parasitic side reactions and cell failure mechanisms.
We find that higher p(O₂) is all around beneficial for the discharge performance of KOB and substantially improves the maximum discharge capacity and rate capability. Furthermore, we show that proper design of the cathode structure allows for fast, gaseous transport of oxygen throughout the entire cathode, which drastically improves the rate capability by enabling the homogeneous deposition of KO₂ and high degrees of pore volume filling. Our findings emphasize the critical importance of efficient mass transport for high performance KOB.

Due to recent energy crises and global climate change, there is a global push to reduce the carbon footprint of the transportation industry. One of the numerous approaches people are taking is by using more efficient means of transportation like electric vehicles (EV). The EVs still haven’t flooded the market, mainly because consumers are not encouraged to invest in EVs given the time it takes to charge a car and how many miles it can run before 100% discharge. Hence there is an incentive to make efficient and fast-charging batteries. Lithium-ion batteries (LIBs) are prominently used in EVs because of their cyclability, ease of production, high energy density, and power density compared to other electrochemical systems. However, there is a limitation to LIB: we seek higher energy density batteries but there is substantial pressure to increase the power density – which is limited by Li-ion transport within the electrolyte and anode/cathode system. This rate-limiting process is highly influenced by the tortuosity of intergranular regions in the electrodes and separator. LIBs with fast-charge capability are more prone to dendrite growth and potentially could be hazardous. Improving LIBs ability to charge faster requires high through-plane diffusion of Li ions. Currently, researchers have proposed using dual-layer electrodes. However, implementing the proposed methodology in an industry setting might not be economically feasible. In this work, we propose a model with various patterns that can be imprinted using lithographic or templating techniques onto the electrode. We use COMSOL Multiphysics to evaluate how various geometrical structures and dimensions influence the current density inside the electrode and around the microstructures. Imprinting microstructures can create a secondary pore channel which will help allow faster Li-ion migration.

Net zero will only be achieved with decarbonisation of a wide range of sectors, including those that implementing other electrochemical systems is expected to be more difficult to, such as aviation and shipping. Fuel cells are positioned to exploit this opportunity, and their commercial relevance is becoming increasingly clear.^1,2 Despite this, costs remain high, partly due to the use of expensive platinum catalysts. If costs can be offset by long device lifetimes than fuel cells may start to see widespread uptake, particularly in automotive and shipping sectors, which in turns allows for economies of scale to significantly reduce the costs. Significant worldwide research effort has focused on developing new catalyst systems, with costs, durability and scalability being some of the most important factors for success. However, the other components such as support material and ionomer distribution of the catalyst layer also play a significant role in determining device lifetime.^3–5
Graphene has been suggested to have great potential as catalyst support material due to its theoretical high surface area and carbon corrosion resistance. However, in practice graphene typically forms low porosity and poor performing electrodes, although this can be mitigated with introduction of spacers or sacrificial additives.^6–9 In this work, we report the degradation behaviour of mixed graphene/carbon nanotube catalyst layers. The nanomaterials were synthesised by a scalable method utilising layer charging with sodium naphthalene to allow exfoliation, allowing functionalisation of the resultant material. This was followed by Pt deposition, ink formation and spray deposition to create the electrodes. The catalyst layers were characterised via cross sectional SEM, EDS, polarisation curves, CV and EIS before and after being degraded via the DoE carbon corrosion protocol. The initial performance of high ratio CNT based electrodes tested in this study were found to be lower than commercial PtC based electrodes. However, after the durability testing the loss of power density of high ratio CNT based electrodes was found to be less than 10%, at which point they outperformed the less durable carbon black based electrodes.

Li-ion batteries are complex systems whose long-term performance is still the subject of much research. Of particular interest is the degradation of electrode materials during long-term cycling under a variety of operating conditions. Several mechanisms for degradation of Li-ion batteries have been proposed in recent years. These proposed mechanisms have not been tied to performance of commercial cells during long-term cycling under a variety of operating conditions. Determining and understanding systematic trends in degradation is crucial to further improvement of Li-ion battery performance and safety.
Previously, researchers at Sandia National Labs conducted a systematic study of commercially available battery cycling behavior. Dozens of commercial NCA (LiNixCoyAl1-x-y¬O2) and NMC (LiNixMnyCo1-x-yO2) cells were cycled to 80% capacity and end of life across a range of temperatures, discharge rates, and depth of discharge windows. To better understand the reasons for the observed degradation trends, electrochemical characterization and materials postmortem characterization was carried out on cells in their as received condition, and 80% capacity. This allowed for the linking of degradation modes to specific cycling conditions and chemistries.
Analysis of electrochemical characterization via Electrochemical Impedance spectroscopy (EIS) and Incremental Capacity Analysis (ICA) was combined with post-mortem materials characterization consisting of X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Electron Dispersive Spectroscopy (EDS), Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP), and X-ray Computed Tomography (XCT), to generate a relatively complete picture of a cell’s state of health when it was disassembled. Seven NCA and seven NMC cells (total of 14) were selected to be analyzed in this way. For both chemistries an as received cell was selected along with cells that were cycled at different ambient temperatures and between different state of charge (SOC) ranges. In total, this work correlated 164 sets of data to understand similarities and differences in cell degradation during cycling at different conditions.
Two key conclusions have been drawn from this data. First, the degradation of cells to 80% capacity is path dependent based on cycling conditions and cell chemistry. Second, rapid capacity fade was correlated to cells with evidence of multiple degradation mechanisms occurring and it appears that multiple mechanisms can interact to amplify their effects on the cell.
This work was funded by the DOE Office of Electricity under the direction of Dr. Imre Gyuk.
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. SAND2021-13303 A

Studying degradation processes in lithium-ion batteries provides beneficial information for further improvement of electrode concepts and cell design. One specific characteristic, which is strongly connected to a homogeneous lithium distribution within entire electrodes, is a uniform intercalation / deintercalation process of lithium-ions, which in turn assigns cell properties such as lifetime, combined with failure mechanisms during electrochemical cycling. The homogeneity of lithium distribution was investigated for three types of thick film electrodes: (i) electrodes after manufacturing, (ii) electrochemically cycled electrodes with locally compressed porosity regions, and (iii) electrochemically cycled electrodes with laser-generated electrode architectures. 3D mapping of lithium in thick film electrodes was performed by laser-induced breakdown spectroscopy (LIBS), which is an analytical tool offering a full 3D elemental analysis of the entire electrode surface and volume. Within a few seconds, a chemical map including quantitative lithium concentration values could be obtained. Additionally, post-mortem LIBS analyses were correlated with electrochemical data, offering new perspectives in studying and visualizing degradation processes during battery operation. Briefly, critical points of cell failure were reliable localized on electrodes. It is worth mentioning that one main mechanism of cell failure was attributed to the electrical short cut at cathode side indicated by an enormous increase in lithium concentration which we assign to the metallic phase. Using the information obtained by LIBS, the continuous evolution of degradation processes could be illustrated. This enabled a model-like description of the degradation behaviour of thick-film electrodes, which in final consequence follows the scenario of spontaneous cell failure. Four characteristic electrode segments were detected in which the lithium concentration and its distribution showed a strong deviation from electrochemically uncycled reference electrodes (after manufacturing). The significant increase in lithium content - as starting point for degradation - could be initiated by mechanical compression inside the cell or dendrite grow processes. Depending on the electrode design and properties such as porosity, tortuosity, or film adhesion, design criteria for optimized 3D electrodes could be derived.

In lithium-ion batteries, internal mechanical defects can be caused by a variety of production processes. Extensive research has shown that these defects are accompanied by a massive loss of capacity, are vastly limiting the fast charging capability, or can even lead to a safety-critical state. Therefore, it is of great interest to avoid unwanted artifacts in production processes or quantify whether these will have a detrimental impact on the lifetime or performance of the cell. Unfortunately, this is usually done by tedious and destructive post-mortem analyses in the chemistry laboratory.
In this work, we present an open-hardware apparatus that non-destructively images the internal condition of the battery. This is achieved with a method where ultrasonic waves are emitted and received at each point of the surface of a battery cell with ultrasound transducers (also called scanning acoustic microscopy). The ultrasonic waves change some of their core properties like velocity or amplitude depending on the medium they are traveling through. This effect is used to detect the mechanical properties of the cell components at each position approached by the transducers. Combined with a robust signal processing toolchain, this method produces an image of the inside of the battery in less than 5 minutes with an image resolution in the micrometer range. The significant advantage of this technology compared to other imaging techniques is that it is non-destructive, cost-effective and fast. This makes it suitable for integration into existing production and battery testing processes.
Using the developed apparatus, we demonstrate the effect of a locally clogged separator on battery aging. For this purpose, three cells with known locally clogged separators were clamped and cycled down to 80% residual capacity. The apparatus was able to non-destructively image both the clogged separators and the resulting local covering layer formation and gassing in all investigated cells. Post-mortem analysis revealed that the covering layer was lithium plating, which was plausibly caused by local increased current density at the edge of the clogged separator sites.
The developed apparatus is published as open hardware to increase the availability of scanning acoustic microscopy for further research activities in academia and industry.

Recent years have seen a surge in the demand for high-performance battery electrode materials for automotive, and various electronic device applications. Improving battery performance requires precise knowledge on the structure-composition properties of active electrode materials. To this effect, quantitative and precise estimation of the composition of advanced electrode materials, containing trace amounts of dopants provide immense value towards developing next generation high-capacity battery materials. Herein, we demonstrate the application of calibration-free Laser Induced Breakdown Spectroscopy (LIBS) as a powerful analytical tool for rapid and reliable quantitative spectrochemical characterizations of layered Li metal oxide cathodes containing Mo and Cr dopants (<5 at%). Specifically, we employ LIBS using an internal calibration methodology to establish the quantitative elemental ratios of major (Ni, Mn, Co) and trace dopant (Cr, Mo) transition metals to the bulk Li contents in diverse cathode material samples such as, LiNi_0.5Mn_0.5O₂ (NM-50/50), LiNi_0.33Mn_0.33Co_0.33O₂ (NMC), LiNi_0.317Mn_0.317Co_0.317Cr_0.05O₂ (Cr doped NMC), and LiNi_0.5-x/2Mn_0.5-x/2Mo_xO₂ (x = 0.03, 0.04, 0.05) (Mo doped NM-50/50) that were synthesized via sol-gel routes. Our results indicate good agreement between the LIBS estimated elemental compositions and the nominal stoichiometric values. Ex-situ LIBS characterizations presented here paves the path for future high-efficacy application of calibration-free quantitative LIBS for rapid in-situ analyses of elemental composition changes in battery electrode materials under operation that need not resort to off-site analytical techniques requiring cumbersome sample preparations and/or, external standards.

The high specific capacities of Ni-rich transition metal oxides have garnered immense interest for improving the energy density of Li-ion batteries (LIBs). Despite the potential of these materials, Ni-rich cathodes suffer from interfacial instabilities that lead to crystallographic rearrangement of the active material surface as well as the formation of a cathode electrolyte interphase (CEI) layer on the composite during electrochemical cycling. While changes in crystallographic structure can be detected with diffraction-based methods, probing the chemistry of the disordered, heterogeneous CEI layer is challenging. In this work, we use a combination of ex situ solid-state nuclear magnetic resonance (SSNMR) spectroscopy and X-ray photoemission electron microscopy (XPEEM) to provide chemical and spatial information on the CEI deposited on LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) composite cathode films. Specifically, XPEEM elemental maps offer insight into the lateral arrangement of the electrolyte decomposition products that comprise the CEI. Separately, paramagnetic interactions (assessed with electron paramagnetic resonance (EPR) and relaxation measurements) in ¹³C SSNMR provide information on the radial arrangement of the CEI from the NMC811 particles outward. Using this approach, we find that LiF, Li₂CO₃, and carboxy-containing structures are directly appended to NMC811 active particles, whereas soluble species detected during in situ ¹H and ¹⁹F solution NMR experiments (e.g., alkyl carbonates, HF, and vinyl compounds) are randomly deposited on the composite surface. We show that the combined approach of ex situ SSNMR and XPEEM, in conjunction with in situ solution NMR, allows for spatially-resolved, molecular-level characterization of paramagnetic surfaces and new insights into electrolyte oxidation mechanisms in porous electrode films.

Commercial off the shelf (COTS) Li primary batteries are an attractive candidate for many civilian and military applications due to their long-term stability and batch-to-batch consistency. Unfortunately, little is known about variations in internal cell chemistry and aging characteristics of these cells, making it difficult to predict the long-term performance of systems with embedded COTS cells. In this study, we probe electrochemical performance, electrolyte composition, and bulk/surface electrode chemistry across ~10 years of COTS Li/MnO₂ cells, ultimately determining that both discharge characteristics and bulk cell chemistry remain largely unchanged as a function of age, whereas electrode surface chemistry exhibits significant variation. Based on changes observed in surface chemistry between new vs aged cells, we also explore a new approach to accelerated aging whereby humidity, pressure and vacuum are implemented as aging accelerants as opposed to more traditional methods such as heat and electrical stressors. We find that major changes in electrode surface chemistry can be observed within the first 6 months of accelerated aging. Finally, we investigate chemical changes which occur during the first few months of aging in more controlled Li/MnO₂ systems.
This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and 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-NA-0003525.

Although LiNi_0.8Co_0.1Mn_0.1O₂ (NMC-811) materials have attracted increasing attention in Li-ion batteries, owing to their high capacity, their shorter lifetime during cycling hinders their practical application. A deeper understanding of the capacity fade mechanisms is required to increase cells lifetime. In this study, we investigate the influence of single crystal (SC) and polycrystalline (PC) morphologies of Ni-rich NMC-811 electrodes with respect to their cycling stability in graphite/ NMC-811 cells, to elucidate the corresponding degradation mechanisms. Long-term cycling tests showed that cells with single crystal NMC-811 outperformed PC NMC-811 cells, showing an excellent capacity retention after 500 cycles at both 25°C and 40°C, when tested to upper cut-off voltage of 4.2 and 4.3 V. Electrochemical impedance spectroscopy measurements indicated a huge growth of charge transfer resistance for PC NMC-811, particularly for the PC cells cycled at more stressed conditions. Our post-mortem investigations via SEM, SIMS and HAXPES/XAS highlighted the correlation between the structure/surface reduction (degradation) and electrochemical performance of SC and PC NMC-811 as a function of the different cycling conditions. Our results point to the necessity of enhancing the surface structural stability of Ni-rich NMC cathode materials to mitigate degradation phenomena.

Lithium-ion batteries are pervasive power sources for portable electronics and transportation electric vehicles. As such, the ambient environment in which these batteries operate is not static, but ever changing. Our research group has been working to understand how the operating environment and external conditions, effect material properties, electrochemical performance and instability, leading to a decrease in overall safety. We have demonstrated how dynamic external conditions, specifically thermal gradients and transients, can induce differing degradation modes of the positive and negative electrodes. For instance, a modest directionally-dependent thermal gradient throughout can induce electrode-centric degradation of the NMC-composite electrode as particle cracking and delamination and graphite degradation manifest as SEI growth, pore clogging and metallic lithium plating. Under stressful operating conditions, we have observed strong electrochemical-mechanical coupling where lithium plating on the negative electrode causes a physical deformation and collapse of the cylindrical cell jellyroll. In this talk, we will present in-operando optical microscopy and X-ray computed tomography data to show how dynamic electrical and external thermal conditions can irreversibly effect the chemistry, structure and subsequent safety of lithium-ion battery materials, components and cells. We will discuss the importance of testing materials and cells outside of controlled laboratory static conditions in favor of operating in dynamic thermal environments, to include austere and stressful operating conditions. Last, we harness this understanding of battery materials and cell degradation to propose an accelerated aging technique to replicate real world degradation at a fraction of calendar runtime and show how these data support the development of remaining-useful-life machine learning models.

Most state-of-the-art rechargeable lithium-ion batteries (LiBs) for electric vehicles use high-nickel content cathodes based on lithium nickel manganese cobalt oxide, LiNi_1-xMn_xCo_xO₂ (x ≤ 0.2). In order to meet increasing energy capacity demands and attain oxide energy densities > 800 Wh kg^-1, it is desirable to increase the Ni content even more; however, the higher capacity usually comes at the cost of decreased stability.^{1, 2} Furthermore, the inclusion of cobalt is problematic as it is a security-critical material with associated high cost, so there is much effort to reduce or eliminate Co.^{3, 4} Next-generation cathodes are being developed with these goals in mind, but must be thoroughly characterized and understood before commercial adoption occurs. Recently, we have developed in situ infrared spectroscopy techniques (Raman and FTIR) to probe the electrode-electrolyte interphase during the electrochemical operation of cells.^5,6 In the case of cathodes, we have shown that changes in the vibration signatures from both the electrolyte and electrode are indicative of the redox chemistry of the transition metals and the related local structural changes of the cathode.
Here, we present an in situ study of the interfacial phenomena occurring during galvanostatic cycling of the electrochemical cell that uses a high-nickel, low-cobalt LiNi_1-xMn_xCo_xO₂, with x =0.05 (NMC9055) cathode (vs. a lithium metal anode). The in situ cells we designed provide both reliable electrochemical performance and strong spectroscopic signals near the cathode surface. In situ ATR-FTIR was used to investigate the voltage-dependent electrolyte solution structure changes (e.g., near-surface Li⁺ ion (de)solvation by solvent molecules) and cathode-electrolyte interphase formation and evolution at various upper cutoff voltages (above 4.0 V vs. Li/Li⁺). In addition, in situ ATR-FTIR revealed near-surface local cathode structure changes mostly correlated to the Ni transition metal redox. These changes were further corroborated using X-ray absorption and diffraction studies, XAS and XRD, respectively. Our studies using the development of in situ ATR-FTIR characterization methods provide new insight into interfacial failure in battery systems, and we demonstrate our approach is useful to evaluate novel electrode materials and new electrolyte formulations.

References:
1. Schipper, F.; Erickson, E. M.; Erk, C.; Shin, J.-Y.; Chesneau, F. F.; Aurbach, D., Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes: I. Nickel-Rich, LiNi_xCo_yMn_zO₂. J. Electrochem. Soc. 2017, 164 (1), A6220-A6228.
2. Croy, J. R.; Abouimrane, A.; Zhang, Z., Next-generation Lithium-ion Batteries: The promise of near-term advancements. MRS Bull. 2014, 39 (5), 407-415.
3. Croy, J. R.; Long, B. R.; Balasubramanian, M., A Path toward Cobalt-free Lithium-ion Cathodes. J. Power Sources 2019, 440, 227113.
4. Kim, Y.; Seong, W. M.; Manthiram, A., Cobalt-free, High-nickel Layered Oxide Cathodes for Lithium-ion Batteries: Progress, Challenges, and Perspectives. Energy Storage Mater. 2021, 34, 250-259.
5. Ha, Y.; Tremolet de Villers, B. J.; Li, Z.; Xu, Y.; Stradins, P.; Zakutayev, A.; Burrell, A.; Han, S.-D., Probing the Evolution of Surface Chemistry at the Silicon-Electrolyte Interphase via In Situ Surface-Enhanced Raman Spectroscopy. J. Phys. Chem. Lett. 2020, 11 (1), 286-291.
6. Tremolet de Villers, B. J.; Bak, S. M.; Yang, J.; Han, S.-D., In Situ ATR-FTIR Study of the Cathode–Electrolyte Interphase: Electrolyte Solution Structure, Transition Metal Redox, and Surface Layer Evolution. Batter. Supercaps 2021, 4, 778-784.

Lithium (Li) metal is considered as the ultimate anode choice for the next generation rechargeable Li batteries due to its ultrahigh theoretical specific capacity (3860 mAh g−1) and the most electronegative potential (−3.04 V vs standard hydrogen electrode). As the Li metal anode is highly reactive to carbonate electrolytes, a solid-electrolyte interphase (SEI) at the Li metal anode is formed. The as-formed SEI can prevent Li metal anode from further reactions. However, the fragile SEI is not stable upon the huge volume change during Li plating/stripping cycles. The sacrifice and reformation processes of the SEI result in rapid capacity fade and also raises safety issues. Electrolyte engineering is considered a promising strategy to improve the cycling stability of LMBs. By tuning the electrolyte composition, the electrochemical and mechanical properties of SEI can be regulated. In this work, an electrolyte with additives will be studied for high-energy-density Li metal batteries, pairing Li metal anode with high nickel layered structure metal oxide cathode. A comprehensive characterization including electrochemical evaluation, XPS, SEM, TEM, and quantitative NMR to illustrate the role of each component in SEI formation on Li metal anode and CEI on the cathode surface. The understanding of decomposition product and SEI structures contributed from additives in electrolytes can help to design new high-performance electrolytes for next-generation Li metal batteries. This newly developed electrolyte enables Li metal anode to achieve a high CE (>99.0%), and Li/NCM811 coin cell to retain more than 80% capacity after 240 cycles under practical conditions (high areal capacity of NCM811, 3.5 mAh/cm²@0.5 C for discharging, ultrathin 50 μm Li, and low E/C ratio ~3.0 g/Ah).

Despite the important role that the solid electrolyte interface (SEI) formation process plays in determining long-term cycle life of lithium-ion batteries, accurate methods to track the quantity of lithium consumed during formation remain time-intensive and require the usage of high-precision cyclers [1]. In this work, we further investigate a scalable and facile method that was proposed in [2] to estimate the amount of lithium consumed during SEI formation based on a measurement of the full cell resistance at low states of charge (R_LS). Using a model of the electrode-specific stoichiometries and resistances, we show that R_LS correlates to the quantity of lithium consumed during SEI formation.
To study R_LS experimentally, we built and analyzed a set of forty 2.37 Ah prismatic nickel manganese cobalt (NMC) / graphite prismatic pouch cells which were formed using two different formation protocols [3] and cycled at two different temperatures. With this dataset, we demonstrate that lifetime prediction models trained using R_LS are more accurate than the state-of-the-art [4] while requiring fewer cycles of data. We discuss the generalizability and limitations of applying the proposed technique towards other lithium-ion chemistries (e.g. lithium iron phosphate cathode and silicon anodes) and degradation modes (e.g. active material losses).

References

[1] Fathi, R., Burns, J.C., Stevens, D.A., Ye, H., Hu, C., Jain, G., Scott, E., Schmidt, C., and Dahn, J.R. (2014). Ultra high-precision studies of degradation mechanisms in aged LiCoO 2 /graphite Li-ion cells. J. Electrochem. Soc. 161, A1572–A1579. https://doi.org/10.1149/2. 0321410jes.
[2] A. Weng, P. Mohtat, P. M. Attia, V. Sulzer, S. Lee, A. Stefanopoulou (2021). Predicting the impact of formation protocols on battery lifetime immediately after manufacturing. Joule 5, 1-22, doi: 10.1016/j.joule.2021.09.015.
[3] An, S.J., Li, J., Du, Z., Daniel, C., and Wood, D.L. (2017). Fast formation cycling for lithium ion batteries. J. Power Sources 342, 846–852.
[4] Severson, K.A., Attia, P.M., Jin, N., Perkins, N., Jiang, B., Yang, Z., Chen, M.H., Aykol, M., Herring, P.K., Fraggedakis, D., et al. (2019). Data-driven prediction of battery cycle life before capacity degradation. Nat. Energy 4, 383–391. https://doi.org/10.1038/s41560-019- 0356-8.

As the demand for high performance lithium-ion batteries grows, the use of nickel-rich cathodes is becoming more widespread. Of particular focus, due to its high theoretical capacity of 275mAh g-1, and low cobalt percentage, is nickel-manganese-cobalt-oxide LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811). However, this materials is plagued with unavoidable degradation mechanisms associated with volume changes that lead to particle cracking(1). Moreover, this cracking is particularly problematic at higher voltages(2), limiting the usable capacity. These defects can be detected via ex-situ nano-scale X-ray Computed Tomography (CT) (3), however, resolution limitations associated with micro-scale methods lead to defect analyses often being qualitative, rather than quantitative.
A solution is to combine the in-situ tomographic data, with quantitative algorithms, which can determine the state-of-health (SoH) for hundreds of particles within a single scan. This has multiple benefits over traditional approaches. Firstly, defects that cannot be directly visualized due to particle averaging of data can be deconvoluted and extracted, allowing tracking and quantification. This enables more accessible, lower resolution scans (micro-CT) to replace time consuming, high resolution characterisation (nano-CT). Secondly, the large number of particles (hundreds or even thousands per scan) enable higher statistical confidence in the results compared to nano-scale work (where typically an order of magnitude fewer particles are examined). Thirdly, this methodology can overcome signal-to-noise issues commonly experienced with in-situ work, and can therefore be achieved within the laboratory without necessitating access to synchrotron facilities. And finally, due to in-situ measurements, the cause of defects within a particle can be explicitly revealed, removing the uncertainty over damage sustained during fabrication.
The work combines lab-scale micro-scale imaging (spatial resolution ca. 200µm), with a novel algorithm, to quantitatively assess the SoH for particles as they are charged to increasingly higher voltages. This enables the voltage at which cracking initiates to be confirmed, alongside the degree of reversibility of such degradation to be measured. This knowledge will enable a deeper insight into how particles behave not only during standard conditions, but at the extreme voltages, paving the way for batteries with higher useable capacities and better capacity retention. Finally, due to the large datasets and imaging throughput, this methodology lends itself well for machine learning algorithms for automatic crack detection systems.
1. Li H, Liu A, Zhang N, Wang Y, Yin S, Wu H, et al. An Unavoidable Challenge for Ni-Rich Positive Electrode Materials for Lithium-Ion Batteries. Chem Mater. 2019;31(18):7574–83.
2. Li W, Asl HY, Xie Q, Manthiram A. Collapse of LiNi1- x- yCoxMnyO2 Lattice at Deep Charge Irrespective of Nickel Content in Lithium-Ion Batteries. J Am Chem Soc. 2019;141(13):5097–101.
3. Heenan TMM, Wade A, Tan C, Parker JE, Matras D, Leach AS, et al. Identifying the Origins of Microstructural Defects Such as Cracking within Ni-Rich NMC811 Cathode Particles for Lithium-Ion Batteries. 2020;2002655.
4. Tan C, Daemi S, Taiwo O, Heenan T, Brett D, Shearing P. Evolution of Electrochemical Cell Designs for In-Situ and Operando 3D Characterization. Materials (Basel) [Internet]. 2018;11(11):2157. Available from: http://www.mdpi.com/1996-1944/11/11/2157

In recent years, much attention has been paid to isotropic deformation in alloy-type battery electrodes [1]. Such isotropic deformations usually give rise to large dimensional changes such as a linear change of ~45% or a volumetric change of ~300%. However, much less attention has been paid to non-isotropic deformations, which are significantly more severe than isotropic deformations. In this talk, I will present our work on a new buckling deformation phenomenon that occurs in monolithic nanoporous films used as lithium-ion battery electrodes. This non-isotropic deformation occurs out-of-the plane of the material, and the corresponding linear strain can be as high as ~500 %, which is 11 times higher than the ~45% linear deformation commonly encountered during (de)lithiation-induced isotropic deformation. In our research, in situ electrochemical dilatometry techniques, and electron microscopy characterizations in combination with focus-ion beam based on Xe plasma, are used to thoroughly investigate this (de)lithiation-induced buckling deformation phenomenon.
Reference:
[1] J.S. Corsi, S.S. Welborn, E.A. Stach, and E. Detsi: “Insights into the Degradation Mechanism of Nanoporous Alloy-Type Li-Ion Battery Anodes.” ACS Energy Letters 6 (2021).

Lithium–sulfur batteries are key energy storage enablers in sectors such as transportation and grid storage due to the low cost and high theoretical energy density of sulfur as a cathode material. However, significant challenges exist with cathode degradation during cycling, including mechanical failure via cracking or detachment of insulating active material lithium sulfide (Li₂S) from the conductive matrix in the cathode, causing irreversible capacity fade. Additive manufacturing is a promising route towards the development of mechanically resilient 3D electrodes with complex architectures, high active material loadings, and large areal capacities relative to conventional 2D film electrodes. Additive manufacturing processes for fabricating lithium-sulfur (Li-S) cathode materials are beginning to be explored; currently only extrusion methods have been reported, which are limited in resolution to >150 µm and offer limited control over the final morphology and microstructure of the printed material.

We report an additive manufacturing process which enables fabrication of 3D architected lithium sulfide (Li₂S) carbon composite cathodes for Li-S batteries via digital light processing stereolithography and subsequent pyrolysis. The composites have feature sizes of ~50 µm and are comprised of a porous glassy carbon matrix containing crystalline Li₂S deposits within the pores. We 3D print porous polymer composites using water-in-oil emulsions of aqueous lithium sulfate dispersed in a UV-curable photopolymer resin. Pyrolysis then converts the porous polymer matrix to glassy carbon and the lithium sulfate deposited within the pores to lithium sulfide via carbothermal reduction. We investigate the effects of surfactant concentration and emulsion composition on pore size, pore connectivity, and Li₂S morphology via SEM image analysis and show that pore size and Li₂S crystal size can vary from ~10 nm to ~5 µm and are related to the size of aqueous domains in the emulsion.
Such architected cathode materials have promise for mitigating mechanical degradation in high volume-change battery materials such as the sulfur cathode. We additionally performed nanomechanical compression experiments, making use of a Hertzian elastic contact model, on lithium sulfide powders to determine how this material yields, deforms, and fails due to volume-change-induced stress during battery cycling. We place these measurements into the context of in-situ stress evolution measurements in literature and discuss design considerations for 3D-architected battery materials to enable the rational design of high energy density, long-cycling, and mechanically robust sulfur cathodes.

Today’s Li-ion technology is highly optimized for performance at relatively slow charging operation. However, significant challenges still present for extreme fast-charging conditions (> 6C). These challenges include large kinetic polarizations, concentration gradients, and Li metal plating. In state-of-the-art Li-ion batteries (LIBs) with high energy densities, the electrodes are relatively thick (> 100 μm), which leads to a tradeoff between energy density and high-power performance. In addition, the electrochemical potential of the anode can easily become more negative than Li/Li⁺ during fast charging, resulting in Li plating. Therefore, new approaches are needed to overcome these energy/power tradeoffs in LIBs

In this talk, I will introduce two strategies to enable fast charging LIBs, using industrially-relevant pouch cells with thick (>3 mAh/cm²) electrode loadings. In the first strategy, vertical channels are introduced into post-calendared electrodes using laser ablation patterning [1]. The resulting 3-D anode architecture consists of a hexagonal close-packed array of vertical channels that serve as linear pathways for rapid ionic diffusion through the electrode thickness. This allows for a more homogeneous flux of Li throughout the volume of the electrode and decreased ionic concentration gradients, in comparison to slow/tortuous diffusion paths in the conventional anode, thus improving the accessible capacity of the electrode during fast charging. As a result, the accessible capacity of the electrode during fast charging increases, and Li plating is eliminated. The laser-patterned electrodes facilitate 6C fast charging with <20% loss in capacity after 500 cycles, which exceeds the U.S. Department of Energy (DOE) goals for fast charging.

In the second strategy, we overcome the energy/power tradeoffs in carbonaceous anode materials by forming hybrid blends of graphite and hard carbon [2]. This allows for a balance between the higher energy density of graphite with the faster rate performance of hard carbon. By controlling the graphite/hard carbon ratio, we identify an optimal blend which maintains >80% of capacity retention after 500 cycles at 6C. The improved fast-charging performance is described by a continuum-scale model, which illustrates the benefits of the hybrid electrode architecture to improve the homogeneity of the Li intercalation flux throughout the thick electrode volume. This reduced current focusing effectively eliminates Li plating during fast charging. This scalable process is directly compatible with existing Li-ion manufacturing, as illustrated by roll-to-roll processing of multi-layered, multi-Ah pouch cells.

[1] K.-H. Chen, M. Namkoong, V. Goel, C. Yang, S. Kazemiabnavi, S. M. Mortuza, E. Kazyak, J. Mazumder, K. Thornton, J. Sakamoto, N. P. Dasgupta, J. Power Sources 471, 228475 (2020).
[2] K.-H. Chen, V. Goel, M. J. Namkoong, M. Wied, S. Müller, V. Wood, J. Sakamoto, K. Thornton, N. P. Dasgupta, Adv. Energy Mater. 11, 2003336 (2020).

The ability to achieve fast charge rates has become a pragmatic issue for timely implementation of advanced batteries in numerous applications. Recent guidance from the U.S. DOE has put forth a 10-minute charge (denoted 6C) as the target for Li-ion cell chemistries being designed for extreme fast charging (XFC) of electric vehicles [1]. The choice of electrolyte is a central consideration to achieve XFC goals. The design of new electrolytes for XFC chemistries may involve moving to solvents that are less viscous, more diffusive and yet that might be more volatile, calling for balanced considerations in applications. Additionally, the choice of stabilizing additives is a key metric because of more extensive redox behavior at the surface of electrodes under XFC [2].
The primary target for this study is development of electrolytes for XFC Li-ion cells based on an effective combination of modeling approach using the Idaho National Laboratory Advanced Electrolyte Model (INL-AEM) and parallel laboratory techniques. First, AEM provides rapid early screening of multi-solvent electrolyte candidates for XFC based on an assortment of cell-relevant properties, such as transport properties (e.g., conductivity and diffusivity), lithium desolvation energies, and electrode pore wetting rates. Multi-solvent systems provide a balanced set of properties, wherein lower molecular-weight solvents offer reduced viscosity, increased species diffusivity, and mitigation of concentration polarization at high charge rates. Then, performance of selected electrolytes is tested using coin and pouch cells having NMC532 cathodes with graphite electrodes. Lab testing results coincides with property predictions from the AEM and a macro-scale cell model. Results indicate combinations of low-molecular weight solvents are key for fast-charge electrolytes as they extend the useful conductivity range to both low and higher salt concentrations, and possess higher self-diffusivities compared to conventional solvents. One of selected electrolytes, called B26 (EC:DMC:DEC:EP:PN (20:40:10:15:15, wt.) w/ 3% VC and FEC) + LiPF₆), outperformed other tested electrolytes in conditions including capacity cycle life and fast charging ability. Under fast charging conditions, B26 shows increased charge acceptance, decreased lithium metal plating at the anode, decreased concentration polarization, and decreased aging.

Reference
[1] Michelbacher et al., J. Power Sources, 367 (2017)
[2] Ning et al. Energy Storage Materials, 44, 296-312 (2022)

Fast charging of lithium-ion batteries (LIBs), being developed for electric vehicles, is needed to meet customer demands of time-parity with today’s gasoline-powered cars. The U.S. Department of Energy (DOE) has set a target charging time of 15 minutes (4C rate) as a near-term goal, further indicating that a 5-minute charge (12C rate) could be a long-term goal. This presentation is an overview of extreme fast charge studies being conducted at Argonne National Laboratory as part of projects funded by the U.S. DOE. This talk will discuss modes of cell aging during repeated exposure to high currents, with particular focus on electrode behavior. Results from cells containing layered oxide cathodes and graphite anodes will be highlighted. The use of a microprobe reference electrode to monitor electrode polarization, onset of Li plating and develop charging protocols will be examined. Methodologies to detect Li-plating, examine lithium concentration gradients that develop in the electrodes and investigate changes in the electrode materials will also be discussed.
For details and additional information, the reader may look up the following references:
Pidaparthy et al., J. Electrochem. Soc. 168, 100509 (2021).
Rodrigues et al., ACS Appl. Energy Mater. 4, 1063 (2021).
Raj et al., J. Power Sources 484, 229247 (2021).
Rodrigues et al., J. Electrochem. Soc. 166, A996-A1003 (2019).
Rodrigues et al., ACS Appl. Energy Mater. 2, 873−881 (2019).
Shkrob et al., J. Electrochem. Soc. 166, A4168-A4174 (2019).
Yao et al., Energy & Environmental Science 12, 656-665 (2019).

The rapidly growing electric vehicle market is increasing the demand for fast charging capability of high-energy-density Lithium (Li)-ion batteries. However, state-of-art Li-ion batteries with thick graphite electrodes suffer from Li plating when charged at >4C rates. This undesired Li plating can lead to electrolyte consumption, internal electrical shorting, gas evolution, capacity loss, and thermal runaway. To inform mitigation strategies for Li plating under fast-charging conditions, there is a need to improve our fundamental understanding of the Li plating process.
In this work, plan-view operando video microscopy was performed on >3 mAh cm^-2 calendared graphite electrodes during and after 6C charging [1]. This technique enables time-synchronization of the graphite working electrode voltage with the morphological evolution of the electrode. During a 6C charging half cycle, this platform was applied to visualize the spatial heterogeneity of graphite SoC across the electrode surface and the nucleation and growth of the plated Li. During the subsequent open circuit voltage (OCV) rest and discharge steps, the interaction between the plated Li and graphite was also studied. Furthermore, a 3D understanding of the changes across the electrode volume was developed by performing ex situ cross-sectional microscopy. Finally, pouch cells were fabricated to confirm the voltage signature associated with dead Li formation in a commercially relevant cell format.
The results of this study demonstrate that: 1) during fast-charging, spatial heterogeneity in the local SoC of individual graphite particles develops; 2) preferential nucleation of plated Li occurs on the graphite particles that had the fastest lithiation rate; 3) the onset of Li plating correlates with a voltage minimum of the graphite electrode; 4) after fast-charging, galvanic corrosion currents are the primary driving force for Li re-intercalation and graphite SoC re-equilibration; and 5) during OCV rest or discharge steps, electrochemical signatures can be associated with the re-intercalation of plated Li.
[1] Y. Chen, K.-H. Chen, A. J. Sanchez, E. Kazyak, V. Goel, Y. Gorlin, J. Christensen, K. Thornton, N. P. Dasgupta “Operando video microscopy of Li plating and re-intercalation on graphite anodes during fast charging” J. Mater Chem. A, In Press (2021).

Lithium-ion batteries have revolutionized the possibilities for electrified transportation, as recognized by the 2019 Nobel Prize in chemistry. However, lithium-ion batteries suffer from a critical slow charging limitation, contributing to range anxiety amongst consumers and inhibiting adoption of electric vehicles. Recently, it has been demonstrated that under white light illumination LiMn₂O₄ cathodes undergo photo-accelerated fast charging, essentially improving the kinetics of delithiation without use of low electrode loadings or nanostructured active materials. In this work, using LEDs to select discrete wavelengths of light, it is shown that d-d transitions in Mn are largely responsible for the increased charging rate. This excitation is possible by absorption of red light; however, in UV light the absorption process is dominated by excitation of electrons from O-2p into available Mn-t_2g states, which is ineffective in promoting enhanced electrochemistry. It is further demonstrated through X-ray absorption spectroscopy methods that LiMn₂O₄ undergoes a reduction in Mn-Mn distance as a result of d-electron excitation which leads to improved kinetics of delithiation. The results presented here set forth a road map for facile identification of future materials with potential for photo-accelerated fast charging.

Increasing the achievable charging rate of lithium-ion batteries (LIBs) is critical to the widespread commercialization of electric vehicles (EVs).¹ The primary factor limiting the fast-charge ability of state-of-the-art LIBs is the propensity for Li metal to plate out on the graphite surface during charging.² The poor reversibility of Li metal in LIB electrolytes leads to rapid capacity fade, consumption of the electrolyte (cell drying), and possibly even short-circuit from dendrites penetrating the separator. This problem is exacerbated in high-energy density cells with thicker electrodes, leading to energy-power tradeoffs.
To prevent/mitigate these effects, in this work³ we implement an atomic layer deposition (ALD) surface coating on calendered graphite anodes. We demonstrate that this artificial solid electrolyte interphase (a-SEI) that outperforms the natural SEI in fast-charging ability. A large majority of ALD coatings that have been investigated as electrode coatings are simple binary metal oxides that have very low ionic conductivity. In contrast, the ALD coating used here is a lithium borate-carbonate (LBCO) solid electrolyte. This ALD single-ion conductor has previously been shown to exhibit ionic conductivities above 2*10^-6 S/cm and excellent electrochemical stability, including with Li metal.⁴
In comparison to uncoated control electrodes, the LBCO a-SEI coating: 1) eliminates natural SEI formation during formation cycles, 2) decreases interphase resistance by >75% compared to that of the natural SEI, and 3) extends cycle life under 4C-charging conditions, enabling retention of 80% capacity after 500 cycles (compared to 12 cycles in the uncoated control) in pouch cells with >3 mAh-cm^-2 loading. Not only is this a promising approach to enable fast-charging of LIBs, but it also challenges the prevailing thinking that mass-transport limitations in the liquid electrolyte must be addressed to enable fast charging. Since the a-SEI approach focuses on the solid surface, not the liquid phase, this method could work synergistically with other fast-charging methodologies.
References
(1) Zeng, X.; Li, M.; Abd El Hady, D.; Alshitari, W.; Al Bogami, A. S.; Lu, J.; Amine, K. Commercialization of Lithium Battery Technologies for Electric Vehicles. Adv. Energy Mater. 2019, 9 (27), 1900161. https://doi.org/10.1002/aenm.201900161.
(2) Gallagher, K. G.; Trask, S. E.; Bauer, C.; Woehrle, T.; Lux, S. F.; Tschech, M.; Lamp, P.; Polzin, B. J.; Ha, S.; Long, B.; Wu, Q.; Lu, W.; Dees, D. W.; Jansen, A. N. Optimizing Areal Capacities through Understanding the Limitations of Lithium-Ion Electrodes. J. Electrochem. Soc. 2016, 163 (2), A138–A149. https://doi.org/10.1149/2.0321602jes.
(3) Kazyak, E.; Chen, K.-H.; Chen, Y.; Cho, T. H.; Dasgupta, N. P. Enabling 4C Fast Charging of Lithium-Ion Batteries by Coating Graphite with a Solid-State Electrolyte. Adv. Energy Mater. 2021, In Press.
(4) Kazyak, E.; Chen, K. H.; Davis, A. L.; Yu, S.; Sanchez, A. J.; Lasso, J.; Bielinski, A. R.; Thompson, T.; Sakamoto, J.; Siegel, D. J.; Dasgupta, N. P. Atomic Layer Deposition and First Principles Modeling of Glassy Li3BO3-Li2CO3 Electrolytes for Solid-State Li Metal Batteries. J. Mater. Chem. A 2018, 6 (40), 19425–19437. https://doi.org/10.1039/c8ta08761j.

Enabling fast charging in lithium-ion batteries (LIBs) is critical for future electric vehicles, with the U.S. goal of charging to 80% of full capacity in 15 minutes by 2023 ^[1]. Fast charge rates induce irreversible lithium (Li) plating that adversely impacts battery performance and safety. External stack pressure can improve electrical contact, minimize delamination, and an understanding of the impact of pressure on capacity fade can provide insight into the degradation mechanisms ^[2,3]. In this work, we investigate the extreme fast charging (XFC) regime, focusing on cell degradation and parasitic Li plating using single-layer pouch cells with graphite anodes, LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathodes, and 1.2 M LiPF₆ in 3:7 weight % ethylene carbonate and diethyl carbonate. Cells are tested between 10 – 150 psi, and the cells cycled at higher pressures show a strong reduction in capacity fading after 150 cycles. We performed synchrotron radiation-based operando XRD and in situ 2D XRD mapping in a novel pressure cell during fast charge to study Li plating, parasitic reactions, and Li intercalation into graphite under controlled, uniform pressure. This was complemented with ex situ XPS to study the composition of parasitic reaction products and corrosion to correlate local Li plating to pressure and heterogeneity. Our data reveals the emergence of Li_xC₆ and Li metal during cycling at XFC, with a reduction in plated parasitic Li at elevated pressure. These results show that the observed improvement on performance is due to more homogenous reaction conditions across the anode and less polarization through the electrode thickness. We emphasize the importance of electrode stack pressure in XFC batteries and quantify Li plating and intercalation yielding critical insight into the degradation mechanisms that cause capacity fade for better battery engineering.
References
[1] USABC Goals – Lithium Electrode Based Cell and Manufacturing for Automotive Traction Applications, USABC (United States Advanced Battery Consortium), http://www.uscar.org/guest/article_view.php?articles_id=85
[2] C. Cao et al. Influence of Controlled Pressure on Fast-Charging Li-ion Batteries (in preparation)
[3] J. Cannarella and C. B. Arnold, J. Power Source, 2014, 245, 745-751.

As a society, we continue to advance our technology and with it, bringing a greater demand for available energy. In recent times we are seeing a shift toward renewable energy sources to provide power, such as wind, solar and hydro, and new technological innovations are being commercialized such as electric vehicles and more advanced computational devices. The combination of these technological advances is putting a large demand for technologies to store electrical energy, either on grid or in your pocket. In previous generations energy storage came in the form of coal, oil, or biomass, however with new direction for a cleaner, more renewable energy economy, new storage technologies are required, the most common at the moment being batteries and hydrogen.
Batteries, in particular Lithium ion, have become extremely popular for their high energy density making them ideal for portable energy devices such as cell phones or even passenger vehicles. However, these energy devices are still being heavily researched for improvements in performance, cost and lifetime. As such, many variations of the constituent materials are being investigated. Similarly, hydrogen fuel cells are also becoming more integrated into commercial and industrial machines, such as trains, buses, trucks and even marine vehicles as the lifetime and cost continue to be improved [1, 2, 3].
A key aspect in materials science is the ability to generate new material designs with specific characteristics to provide a particular function that improves performance and lifetime in a working device. Energy devices rely on specific material arrangements and microstructures to achieve this. As such, changes to this microstructure with repeated use can lead to significant performance degradation and shorten the usable lifetime. Understanding these microstructural evolutions and their linkages to device performance is critical in designing the next generation of energy storage and conversion devices but faces substantial challenges because of the closed nature of these devices. An emerging, but powerful method for investigating these effects is the combination of non-destructive 3D imaging with computational material simulation methods.
With its non-destructive 3D imaging capabilities, X-ray microscopy (XRM) provides unique insight into material microstructure and is ideal for imaging energy materials, which are often comprised of an interconnected 3-dimensionsal microstructures spanning orders of magnitude. Repeated imaging at various temporal stages enables powerful in situ investigations of dynamic material properties, often termed as 4-dimensional CT, and is particularly well suited to study dynamic and evolutionary processes in energy devices such as batteries and fuel cells.
From these accurate 3D sample geometries and morphologies, the segmented datasets can be used as input to computational methods available in software packages such as GeoDict, enabling accurate quantification of the true fabricated material morphology and simulating device performance. This understanding can help link microstructure and performance, even as degradation and operation cause changes in the material morphology and composition.
Here we present several applications of in situ imaging of batteries and fuel cells utilizing 3D XRM with examples of how this data can be used in material and device simulations to advance our understanding of these complex aging and degradation phenomena.
References:
[1] Few transportation fuels surpass the energy densities of gasoline and diesel. US Energy Information Administration. https://www.eia.gov/todayinenergy/detail.php?id=9991
[2] C.E. Thomas, Fuel Cell and Battery Electric Vehicles Compared. US Department of Energy. https://www.energy.gov/sites/default/files/2014/03/f9/thomas_fcev_vs_battery_evs.pdf
[3] Cano, Z.P., Banham, D., Ye, S. et al. Batteries and fuel cells for emerging electric vehicle markets. Nat Energy 3, 279–289 (2018).

In recent years, cryogenic transmission electron microscopy (cryo-TEM) has enabled high-resolution characterization of sensitive battery materials by minimizing electron beam-induced artifacts and damage. Success of this technique relies on the preparation of thin, rapidly frozen samples, generally by disassembling batteries under inert atmosphere, transferring materials of interest to a TEM grid, and finally plunge freezing into a cryogen. In material degradation studies, this extensive time between electrochemical cycling and cryo-TEM characterization leaves room for structural relaxation, diffusion, and other dynamic processes that make it difficult to precisely correlate the imaged structure with the native structure that evolves during battery cycling or aging. Here, we present a method to integrate battery cycling with fast preparation of electrode samples for cryo-TEM. This enables higher fidelity between the structures characterized and the electrochemical state of interest, which we use to study deformation in silicon nanoparticle anodes for lithium-ion batteries.

Spinel LiMn₂O₄ has historically been a highly appealing Li-ion cathode due to its use of Mn over resource-scarce Co and Ni as well as its favorable voltage profile, with significant plateaus that allow access to higher capacity within a limited voltage range. However, the advantage of the plateau is curbed by the large, non-homogeneous volume change associated with significant Jahn-Teller distortion across the LiMn₂O₄-Li₂Mn₂O₄ plateau, which causes particle cracking. In this work, we apply ab-initio modeling to investigate whether it is possible to reduce or even completely remove the two-phase plateau. Specifically, a topological analysis of the spinel shows that there are no possible low-lying solid-solution pathways in well-ordered spinel. We will show that adding disorder between the 16d Mn and 16c octahedral sites can potentially result in a shortened LiMn₂O₄-Li₂Mn₂O₄ plateau. We will also show results of an analysis how inactive elements can help to reduce the two-phase region.

Si-based anodes have received considerable research attention for high-density Li-ion batteries (LiBs) due to its exceptionally high volumetric and gravimetric energy density. In terms of theoretical specific capacity, LiSi alloy phase can attain 3579mAh/g while graphite only exhibits 372mAh/g. In particular, the micro-Si anodes are promising for high energy anode due to its advantages of high tap-density and low manufacturing cost. The main technical challenge for micro-Si anodes, however, is its large volumetric changes (310% for fully lithiated Si) during Li insertion and extraction which leads to pulverization of the Si particles and subsequent fast capacity fading.
Researchers have investigated various model system samples (e.g., Si thin films and etched Si islands) to reveal the Si degradation mechanisms dominated by various types of mechanical failure. However, Si model systems differ from actual Si-based electrodes over multiple aspects including their extremely large impedance and limited cycle capability. To overcome the limitations imposed by theses model system, we developed an Atomic Force Microscopy (AFM)-based characterization method to observe and quantify the micro-sized Si-based anode in a LiB half-cell configuration during cycling. A special unit battery cell was designed and fabricated by stacking micro-Si electrode, separator, and Li counter-electrode, imitating the actual battery cell configuration. The unit cell is placed in a modified AFM environmental cell with its cross section exposed to an AFM tip and its electrodes accessed by an electrochemical test workstation.
Using this setup, we collected real-time morphological AFM images depending on the state-of-charge (SOC) during the electrochemical cycling. Then we implemented a novel image processing approach to precisely identify the Si boundaries from AFM amplitude maps and further quantify the volume of Si particles corresponding to each SOC. We found the micro-Si went through an initial pulverization forming circular sub-particles, and these Si sub-particles expanded until reaching up to 180% of its original volume. Then Si surface fractures were generated during the subsequent de-lithiation process. At the fractured areas, new SEI layer was produced immediately. As a result of the Si surface fracture, the battery cell gained large impedance and its performance degraded quicky. We demonstrated that the physical properties and electrochemical performance of micro-Si were directly controlled by the electrochemical cycling conditions.
Based on the observation and analysis, we proposed optimal cycling conditions to mitigate micro-Si anode degradation. Our method comprehensively probed the electro-chemo-mechanical coupling behaviors of the micro-Si electrode during cycling, providing in-depth understanding of the micro-Si degradation mechanisms. Our unique characterization also provided unlimited possibilities in studying and optimizing other multi-physics-coupling systems.

While Li-ion is the prevailing commercial battery chemistry, development of batteries using earth abundant alkali metals (e.g., Na and K) alleviates reliance on Li with potentially cheaper technologies. While electrolyte engineering has been a major thrust of Li-ion battery (LIB) research, it is unclear if the same electrolyte design principles apply to K-ion batteries (KIBs). Fluoroethylene carbonate (FEC) is a well-known additive used in Li-ion electrolytes, because the products of its sacrificial decomposition aid in forming a stable solid electrolyte interphase (SEI) on the anode surface. Here, we show that FEC addition to KIBs containing hard carbon anodes results in a dramatic decrease in capacity and cell failure in only two cycles, whereas capacity retention remains high (> 90% over 100 cycles at C/10 for both KPF₆ and KFSI) for electrolytes that do not contain FEC. Using a combination of ¹⁹F solid-state nuclear magnetic resonance (SSNMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS), we show that FEC decomposes during galvanostatic cycling to form insoluble KF and K₂CO₃ on the anode surface, which correlates with increased interfacial resistance in the cell. Our results strongly suggest KIB performance is sensitive to accumulation of an inorganic SEI, likely due to poor K transport in these compounds. This mechanism of FEC decomposition was confirmed in two separate electrolyte formulations using KPF₆ or KFSI. Interestingly, the salt anions do not decompose themselves, unlike their Li analogues. Insight from these results indicates that electrolyte decomposition pathways and favorable SEI components are significantly different in KIBs and LIBs, suggesting that entirely new approaches to KIB electrolyte engineering are needed.

Potassium vanadium fluorophosphates, KVPO₄F, is one of the most promising cathode candidates for K-ion batteries because of its high specific capacity, voltage, and energy density.^[1] However, reducing its capacity fade remains an important challenge. In this study, we leveraged structure and electrochemical analysis to understand the capacity degradation mechanism of the KVPO₄F cathode.^[2] Interestingly, we find that the KVPO₄F cathode remains mostly intact even after 200 charge-discharge cycles in a K-half cell. Instead, we observe that the K-electrolyte is severely decomposed at high voltage (> 4.5 V vs. K/K⁺) and causes drying of the cell and the formation of resistive layers on the cathode surface, which significantly increase cell polarization. In addition, we compare the cycling stability of KVPO₄F/K cells using four distinct KPF₆- and carbonate-based electrolytes (0.7 M KPF₆ in EC/DEC, EC/DMC, EC/PC, and PC). Among these electrolytes, EC/PC delivers the highest capacity retention (~63%) after 200 cycles (0.185% fade per cycle), which is attributed to its high oxidation stability. Therefore, this study clearly demonstrates that KVPO₄F is a highly promising cathode material, but further efforts should be dedicated to the development of novel K electrolytes with high oxidation stability to improve the cycling stability of KVPO₄F cathode for practical use.
References
[1] H. Kim et al. Adv. Energy Mater. 8, 1801591, 2018
[2] H. Kim et al. J. Electrochem. Soc. 167, 110555, 2020

The development of safe, rechargeable, and environmentally benign batteries is crucial to transforming our energy systems towards carbon neutrality. Zinc metal batteries (ZMBs) offer a high theoretical volumetric capacity and increased safety, while using Zn metal as an anode, a low cost, Earth abundant material [1,2]. Thus, ZMBs are excellent candidates for grid-level energy storage. Though promising, the anodes in ZMBs suffer from several loss mechanisms that hinder reversibility, such as dendrite formation, parasitic reactions, and the formation of dead zinc [3]. How these loss mechanisms occur, to what degree, and what variables impact them have not been thoroughly characterized, preventing rationale development of methods to minimize these losses.

In this talk, we present synchrotron radiation-based operando X-ray diffraction (XRD) to follow, in real time, the Zn metal diffraction intensity and crystalline reaction products. From these data, we quantify the rate of change of the XRD intensity vs time (rate of metal deposition) and compare this to the charge passed, and we find an unexpected nonlinear dependence. This suggests that the efficacy of Zn metal plated decreases with deposit thickness. Ex situ XPS is used to detect amorphous products and confirm XRD findings. Our results provide insight into loss mechanisms for aqueous zinc batteries that can be extended for other multivalent anodes and to non-aqueous ZMBs.

References
1. Yaroshevsky, A. A. Abundances of chemical elements in the Earth’s crust. Geochemistry Int. 44, 48–55 (2006).
2. Li, H. et al. Advanced rechargeable zinc-based batteries : Recent progress and future perspectives. Nano Energy 62, 550–587 (2019).
3. Ma, L. et al. Critical Factors Dictating Reversibility of the Zinc Metal Anode. Energy Environ. Mater. 1–6 (2020).

Solid oxide electrolysis cells (SOECs) represent one of the most environmentally clean technologies and has great potential as means to efficiently convert the excess heat and electrical energy into various chemicals such as H₂ and/or CO for energy storage. However, different operating conditions lead to diverse degradation phenomena which are not yet fully understood in SOEC mode even though many efforts have been spent to understand the degradation mechanism of SOECs recently. SOEC degradation was classified into three categories including mechanical failure due to thermal stress, electrochemical/chemical degradation and structural degradation. Among them, structural degradation represented one to the most critical degradation during SOEC long-term operation. In this study, we tried to understand the structural degradation mechanism of the delamination at the interface region of the symmetric cells composed of yttria-stabilized zirconia (YSZ) electrolyte and strontium-doped lanthanum manganite (La_0.8Sr_0.2MnO₃, LSM) electrodes, particularly using transmission electron microscope (TEM).
For half-cell fabrication, 8 mol% YSZ discs with 8 mm diameter and 2-3 mm thickness were fabricated by die pressing and sintering at 1500 °C for 5 hrs. The LSM ink was prepared by mixing the commercial LSM powder with solvent, binder and dispersant in a desired ratio. The LSM oxygen electrodes were screen-printed on both sides of the YSZ disc in symmetric geometry and sintered at 1150 °C for 3 hrs. Electrochemical measurements were performed in the alumina tube reactor at 700 °C. Dry air was supplied with the flow rate of 200 sccm, and constant current (1.5 A/cm²) was applied for 200 hrs between the working and counter electrodes, and the voltage response was monitored. Micro-cracks near interface between the electrolyte and air electrode were observed using scanning electron microscopy (SEM, Regulus 8230, Hitachi). And TEM samples were prepared using focused ion beam (FIB, Ethos NX5000, Hitachi) equipped with Ar+ ion gun. In order to analyze the microstructure near the interfacial region where the micro-cracks appear, TEM (TEM, Talos F200X, FEI) equipped with energy dispersive spectroscopy (super-EDX) with four SDD detectors were used.
We compared the microstructures of non-working cells and working cells with commonly applied current densities (1.5 A/cm²). A remarkable feature in the working-cells was the pore formation. We observed a few nanometer-sized pores at the interfaces as well as hundreds nanometer-sized pores in YSZ grain boundary which was reported in the previous researches. Another interesting microstructural defect was dislocations observed in YSZ just below the interface. They are assumed to be the products of the YSZ lattice shrinkage. The lattice strain could be induced by accumulation of oxygen ions, which was confirmed by selected area diffraction pattern (SADP) analysis. Also we will provide direct evidence how the dislocations evolve pores and cracks in the end.

Solid oxide fuel cell (SOFC) electrodes are regularly subjected to changes in temperature and oxygen partial pressure during startup, shutdown, and normal operation, causing large changes in the oxygen stoichiometry of the electrodes. The lattice expansion resulting from this change in stoichiometry is known as chemical expansion, which can cause device failure in the form of cracking or delamination. Naturally, it is desirable to develop strategies to minimize the chemical expansion and design low-strain electrodes. When oxygen is removed from these materials, the electrons left behind by the removed oxide ions typically reduce the cations, resulting in an increase in cation radius that causes the chemical expansion. An empirical model by Marrocchelli et al.¹ predicts that the coefficient of chemical expansion (CCE) would be larger if a given increase in cation radius occurs at the B-site than at the A-site of the perovskite. Motivated by this, we chose to study² two acceptor-doped Pr-based perovskite materials, PrGa_0.9Mg_0.1O_3−δ (PGM) and BaPr_0.9Y_0.1O_3−δ (BPY), placing the multivalent Pr ion either on the A- or B-site. However, both materials were measured to exhibit near-zero CCEs regardless of Pr site placement. To investigate this unusual result, we performed density functional theory (DFT) calculations to study the chemical expansion of these two materials. Our calculations suggest that redox on the anions, instead of the cations, can lead to significantly smaller chemical expansions. By varying the degree of electron localization of the Pr-4f electrons via adjustment of the Hubbard U parameter in DFT+U, we were able to study the chemical expansion with redox occurring on either Pr or O. At low U values, Pr holes were formed with acceptor doping; at high U values, O holes were formed instead. For both materials, the CCE was found to be significantly smaller when O holes, rather than Pr holes, were filled during reduction. We show that the O hole states are more delocalized than the Pr hole states, which can lead to smaller CCEs when the hole states are filled. These results suggest that redox on O may be occurring to some extent in BPY and PGM, contributing to their anomalously low CCEs. Based upon our findings, we propose designing materials that can achieve redox on anions as a potential route to attaining low CCEs in SOFC electrodes.

References:
1. Marrocchelli, D.; Perry, N. H.; Bishop, S. R., Understanding chemical expansion in perovskite-structured oxides. Physical Chemistry Chemical Physics 2015, 17 (15), 10028-10039.
2. Anderson, L. O.; Yong, A. X. B.; Ertekin, E.; Perry, N. H., Toward Zero-Strain Mixed Conductors: Anomalously Low Redox Coefficients of Chemical Expansion in Praseodymium-Oxide Perovskites. Accepted for publication in Chemistry of Materials on 22 October 2021.

Electrochemically-accelerated corrosion of support materials and dissolution of active materials in proton exchange membrane fuel cell (PEMFC) catalyst layers are two degradation modes that represent key challenges to the long-term performance and cost effectiveness of fuel cell systems. Comparisons between microporous and mesoporous carbon materials as high surface area (HSA) supports for precious metal catalysts (e.g., Pt) has conventionally focused on their respective effects on the electrochemical performance or I-V curves of membrane electrode assemblies (MEAs). Specifically, different carbon materials have been extensively studied for their roles in dispersing nanoparticles and ionomer molecules, electron conductivity, gas transport, and water management—properties largely relevant to PEMFC performance. Here, we examine carbon support materials of varying mesoporosities, and instead compare their effects on PEMFC durability, in the context of the two aforementioned degradation modes. Using accelerated stress tests (ASTs) of single-cell MEAs, we find that, while Pt dissolution resistance in highly-microporous HSA carbon blacks can be moderately enhanced via surface functionalization/doping, highly-mesoporous carbon support materials can be tailored to strongly modulate Pt dissolution resistance whilst offering comparable MEA performance. Similarly, by performing graphitization treatments to modulate carbon corrosion AST durability, we show that mesoporous carbons are able to offer significantly different performance-durability tradeoffs than their microporous counterparts. Ex situ characterization of both microporous and mesoporous carbon-containing catalyst layers, before and after undergoing ASTs, gives us mechanistic insights into the relationship between mesoporosity and the generally-accepted physical models underlying the two degradation modes.

The demand for batteries to deliver high capacities at fast charge/discharge rates is rapidly increasing. Electric vehicles are required to cover large distances and to have short recharge times between stops. These types of applications seek to simultaneously maximise capacity and power. While the charging rate can be increased without impacting the capacity, this is only possible until a threshold charge/discharge rate, R_T, is reached. Past R_T the capacity begins to rapidly decline. Understanding the factors influencing this capacity-rate trade-off is crucial for designing systems with exceptional rate performance.

In this work, we use a simple semi-empirical model to extract a characteristic time, τ for charge/discharge which quantifies the rate behaviour of the investigated system. It has been proposed by Tian et al. that τ is linked to electrode kinetics and the physical parameters (e.g. out-of-plane electrode conductivity, σ_E, electrode thickness, L_E) of the system.[1] This multi-mechanistic model is based on solid- and liquid-phase diffusion processes, as well as electrical and electrochemical effects. The equation for τ has been demonstrated to accurately describe a large variety of electrodes found in literature, for both Na and Li-ion batteries. Since τ is a function of common physical parameters, it is possible to predict how rate performance will be affected by a given property. We investigated the rate performances of model battery systems in which only one parameter is varied (L_E, and separator thickness, L_S), and we found that the outputs of the rate model are in close agreement with experimental data.

To gather rate data, we used chronoamperometry (CA), a recently reported alternative to traditional galvanostatic charge-discharge (GCD) measurements.[2] Current transients are converted to capacity-rate curves, which were fitted with the previously described fitting method. We firstly investigated the effects of L_E on rate performance by obtaining τ-L_E curves over a wide L_E range (10-252 μm).[3] The results clearly show a quadratic dependence of τ on L_E, a result that is not explained by simple models that only incorporate solid or liquid-phase diffusion, but is in full agreement with our rate equation. Furthermore, electrochemical impedance spectroscopy measurements indicate that the electrochemical and solid-state diffusion contributions to τ are in line with our model.
In a similar manner, we examined the rate behaviour of systems where only L_S is varied through stacked separator films. The rate model predicts a linear τ-L_S curve, which is confirmed by experimental data at separator thicknesses <100 μm. Our results highlight the potential of the rate equation proposed by Tian et al. We used the equation to describe how rate performance varies with L_E and L_S and it has been used to analyse τ-σ_E data as well.[4] This in-depth analysis further builds the understanding of rate performance and importantly, quantifies the effects which influence it. We believe it is a tool that can be used for designing electrodes for high-rate applications and for identifying emerging materials for energy storage.

In the future, our aim is to apply the rate equation to battery systems and to design electrodes which have very small values of τ and thus, excellent rate performance. For a given system we aim to use optimization techniques such as design of experiments to minimize τ. The insights gained from the equation would provide use with the necessary instructions on what parameters to tune for maximised rate performance.

[1] – https://doi.org/10.1038/s41467-019-09792-9
[2] – https://doi.org/10.1016/j.jpowsour.2020.228220
[3] – https://dx.doi.org/10.1021/acsaem.0c01865
[4] – https://doi.org/10.1021/acsaem.0c00034

The functionality and proper handling of lithium-ion batteries have a significant impact on achieving environmental goals and contributing to the widespread distribution of battery electric vehicles (BEV). The battery management system (BMS) monitors and controls the lithium-ion battery, making it a key component for the reliable and efficient operation of BEVs.
Present condition monitoring is limited to current, voltage and temperature measuremenents, hence the BMS must estimate various battery states with sufficient accuracy as part of the diagnostics. Moreover, the remaining driving range of the BEVs needs to be predicted precisely in order to maximize user-friendliness and overcome range anxiety. Physically, the remaining driving range correlates with the residual usable energy that requires knowledge of the future load profile and environmental factors until the complete discharge of the battery. Due to these challenges, it is common to estimate the usable energy with the help of the State of Charge (SoC) without considering the driving profile and the environmental conditions. However, by definition, the SoC reflects the charge and not the energy drawn from a battery. Thus, determining the usable energy with that method has several drawbacks, which lead to inaccuracies in range prediction: First, the energy dissipation due to battery cycling is neglected. Second, the SoC spares the non-linearity of the voltage curve. However, since the energy is defined as the integration of power over time, the extractable energy is not constant over a fixed-size SoC interval. For those aforementioned reasons, it is helpful to introduce the more practically relevant key figure, State of Energy (SoE), which inherently provides information about the remaining energy and thus represents a vital state for the user management and energy optimization of the battery system.
In this work, two physically motivated definitions for the SoE are mathematically derived and analyzed: a theoretical SoE, which correlates with the energy inherently stored in the battery, and a practical SoE, which correlates with the remaining energy from the user's point of view. The theoretical SoE is of interest for limiting the operating range of each cell, whereas the practical SoE can be used in particular to predict the remaining driving range. Based on a literature review, common definitions of the SoE in several publications are critically investigated regarding their feasibility and are distinguished from the definitions of the SoE that are proposed in this work. In addition, the SoE metrics are systematically differentiated from the SoC. It is shown that the dissipated energy increases with larger average current, progressive aging, and low temperatures causing an increase in the difference between SoC and the practical SoE. Especially under dynamic environmental influences, the SoC differs significantly from the practical SoE, which justifies the need for range prediction based on the State of Energy in the application.

The service life of lithium-ion batteries (LIBs) targeted for battery electric vehicle (BEV) applications is limited by the performance degradation such as capacity and power fades due to the various aging mechanisms including lithium deposition, electrolyte decomposition, active material dissolution, phase changes in the insertion electrode materials, and passive film formation over the electrode and current collector surfaces among others. The performance degradation of LIB does not originate from a single aging mechanism, but from multiple mechanisms and their interactions. It is, therefore, very challenging to predict the performance degradation of LIBs by including the multiple causes that occur simultaneously in the process of battery aging in the modeling and simulation tools of LIB for the optimal design and management of the vehicle electrical system in BEV applications.
In this work, two aging mechanisms of the cyclable lithium loss and electrolyte depletion induced by various unwanted “side reactions” occurring during the operation and storage of LIBs are chosen to demonstrate the feasibility of the modeling methodology to estimate the combined effects of the multiple aging mechanisms on the performance degradation of LIBs. A one-dimensional model based on a finite element method is presented to calculate the discharge behaviors of an LIB cell during galvanostatic discharge for various levels of the cyclable lithium loss and electrolyte depletion. Modeling results are compared with experimental measurements during galvanostatic discharge at various discharge rates for 9 different levels of the cyclable lithium loss and electrolyte depletion to validate the model. The calculation results obtained from the model are in good agreement with the experimental measurements. On the basis of the validated modeling approach, the combined effects of the cyclable lithium loss and electrolyte depletion on the discharge capacity and available discharge power of the LIB cell are estimated.

Lithium metal has been challenged in its implementation as an anode for Li secondary batteries due to its uncontrollable large volume change and dendritic growth during plating/stripping processes. The geometric changes of lithium metal surface cause degradation in a cell’s lifetime and lead to short-circuits and explosions. Here, we report producing a LiF-rich phase on the lithium anode surface by adapting a ‘‘bi-phase” separator. We coated PVDF-HFP onto a cellulose separator. The coverage of coating was controlled by adjusting its concentration in the coating solution. The combination of PVDF-HFP and cellulose produced a LiF-rich SEI(solid-electrolyte interphase) layer on the Lithium surface via an "alkyl halide nucleophile exchange" in facing with the bi-phase separator during plating. Symmetric cell tested that the bi-phase separator extends the life-time by more than 300 h, with overpotentials of less than 100 mV under plating/stripping for a capacity of 2 mAh cm2 @ 2 mA cm2.

Acknowledgement:
This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MOE)(NRF-2021R1A6A3A01086448).

Dendritic growth of lithium and corresponding parasitic reactions are intrinsic vulnerability of lithium metal anodes, limiting practical application. Herein, we report a stable artificial solid electrolyte interphase (SEI) layer composed of Li2Se and LiCl with high Li ion conducting and insulating properties fabricated through a facile and low-cost approach. The designed artificial SEI layer on lithium blocks direct contact with the electrolyte and allows Li plating without dendritic growth through the artificial SEI layer. With these advantages, Li metal anodes with an artificial SEI layer indicate dendrite-free Li plating behaviors with a lower porosity of 30% compared to that of bare Li, 43% at a high current density of 5.0 mA* and a high capacity of 40 mAh* . In addition, these modified anodes exhibit stable cyclability with lower overpotentials in Li symmetric cells. The significant improvement is achieved in cycling performance over hundreds of cycles using LiCoO2 and LiFePO4 cathodes. Furthermore, we realized higher average Coulombic efficiency of 96.4% in a full cell composed of a high-capacity 3.5 mAh* Ni0.8Co0.1Mn0.1O2 and thin, 50 μm modified Li metal anodes compared to that of bare Li metal anodes, 94.3%.

Correlation of structure with ionic conductivity in a range of newly developed fast ion Li conductors helps inform how cation disorder and a frustrated energy landscape impacts conductivity and activation energy. These considerations lead to exciting new classes of solid state electrolytes (SEs) with high ionic conductivity and very low electronic conductivity. Owing to the excellent interfacial stability of the SEs against un-coated high-voltage cathode materials, ASSBs utilizing LiNi_0.85Co_0.1Mn_0.05O₂ exhibit superior rate capability and long-term cycling (up to 4.8 V vs Li⁺/Li) compared to state-of-the-art ASSBs. These studies highlight the role of designing SE's with a low electronic/ionic conductivity ratio. Decomposition (oxidation) of any SE at high voltage can only occur via electron diffusion through the interface between the SE and NCM, leading to sluggish kinetics and thus a higher stability window than predicted by thermodynamics. Low-resistance "clean" solid-solid interfaces enable room temperature cells with capacities close to their liquid Li-ion counterparts at practical discharge rates, and high cathode loadings are also demonstrated in ASSBs with stable capacity retention of > 4 mAh/cm2.

Most next generation Li battery materials suffer from severe interfacial instabilities that prevent commercial application. Unfortunately, most approaches to monitoring interfacial degradation require cell disassembly and may not capture transient/unstable intermediates that are critical to battery performance. Here, I will discuss recent efforts in our group to use nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) as a non-destructive tool to detect electrolyte redox reactions and interphase formation during electrochemical cycling of Li metal batteries, Ni-rich cathode materials, and all solid-state batteries. Insight from this work provides some of the first atomistic descriptors of electrode/electrolyte interfacial decomposition pathways in their native operating environment that may enable safe and efficient battery operation.

Lithium metal batteries (LMBs) offer higher energy density, but the uncontrollable growth of lithium throughout cycling limits the electrochemical performance of LMBs in liquid electrolytes. The morphology of electrodeposited lithium is strongly correlated to the Coulombic efficiency (CE) and is dictated by the nature of the substrate. Further investigation is required to understand the nucleation and growth of lithium, as well as degradation processes in lithium electrodes, especially in the context of methods designed to spatially control growth of lithium. Here, we investigate how lithium alloy layers affect the electrochemical growth and evolution of lithium during deposition and stripping using electrochemical methods and operando optical microscopy. We find that silver thin films enable improved CE for lithium cycling compared to bare current collectors and other alloy layers (antimony) in a variety of liquid electrolyte systems. Specifically, silver-coated electrodes exhibit an average CE of 93.8% (compared to 82.2% for bare stainless steel) in an ether-based electrolyte. Performance degradation is investigated within the alloy electrodes, and ex situ SEM indicates that the differing mechanical properties of alloy layers play a key role in enabling higher CE. Operando optical microscopy reveals reduced dendritic growth of lithium on silver-coated current collectors at higher current densities (4 mA cm^-2) compared to bare current collectors, and image analysis enables direct correlation between electrochemical signatures and observed dendritic growth dynamics. The microscopy experiments also show different stripping behavior between alloy and non-alloy electrodes, with spatially non-uniform stripping dominating on bare stainless steel current collectors. This work provides new understanding of the interaction of lithium metal with alloy substrates and highlights the importance of interfacial layers at the current collector that can potentially enable anode-free configurations with long cycle life.

Li metal anodes represent the ultimate in energy density for battery materials but are plagued with safety issues caused by dendrite formation during lithium plating. To mitigate this, it is critical to understand the solid–electrolyte interphase (SEI) layer which mediates the transport of lithium to the metal surface. Significant strides have been made to study the SEI with NMR spectroscopy, which can give detailed information on local structure and dynamics; however, as a bulk technique, it is challenging to selectively observe the SEI using NMR, especially in the presence of electrolyte.
Dynamic nuclear polarisation is a promising approach to enhance the signal in NMR experiments, by exploiting the ~10³ times greater gyromagnetic ratio of paramagnetic electrons to hyperpolarise the nuclear spins. Previously the SEI has been studied by exogenous DNP, whereby organic radicals are added to the system which is then cooled to cryogenic temperatures (100 K or below). This approach has several limitations: (i) the addition of organic radicals may alter the nature of SEI; (ii) the organic radicals are external to the SEI so cannot be readily used to probe the SEI–metal interface; (iii) exogenous DNP is not selective to the SEI and can also enhance any impurities in the system; and (iv) the use of cryogenic temperatures means that the experiments cannot be coupled with in-situ electrochemical cycling or used to study Li⁺ dynamics.
In this work, the Pauli paramagnetism of the lithium metal itself was exploited to hyperpolarise nearby nuclear spins via Overhauser DNP and investigate the lithium microstructures and SEI of lithium metal batteries [1]. Since the lithium metal is in direct contact with the SEI, this allows the buried SEI–metal interface to be selectively and non-destructively probed, which would be extremely challenging via other techniques. Furthermore, since the electron relaxation in lithium metal is temperature independent, the experiments can be performed at room temperature, paving the way for the investigation of dynamic processes and in-situ methodologies.
First, significant hyperpolarisation of the ⁷Li metal signal was demonstrated at high magnetic field, as required for high-resolution experiments. The hyperpolarisation was then harnessed to selectively enhance, and thus identify, the diamagnetic components of the SEI via the ⁷Li, ¹H and ¹⁹F NMR spectra. The relative DNP enhancements allow the proximity of different species in the SEI to the metal surface to be inferred, while double resonance experiments (⁷Li→¹H/¹⁹F cross polarisation and ⁷Li{¹⁹F} rotational echo double resonance) were further used to reveal minor components such as polymeric organic species and LiF. The chemical composition and structure of the SEI layer is highly dependent on the electrolyte system used, so we compared samples prepared from electrolytes with and without the common additive fluoroethylene carbonate (FEC). This showed that the addition of FEC reduces the amount of trapped ethylene carbonate in the SEI and promotes the formation of poly-vinylene carbonate species at the expense of poly-ethylene oxide-like species. Overall, we present a new technique to study the lithium–SEI interface, which is of key interest for the development of safe lithium metal batteries.
1. Hope, M. A.; Rinkel, B. L. D.; Gunnarsdóttir, A. B.; Märker, K.; Menkin, S.; Paul, S.; Sergeyev, I. V.; Grey, C. P. Nat. Commun. 2020, 11 (1), 2224.

Improving the energy density and cycling stability of battery systems are inevitable for fulfilling the targeted climate goals.¹ Interfaces between different materials, which are present in all types of lithium-based batteries, play a crucial role in reaching these goals. At these interfaces, degradation and charge-transfer resistances occur. When the degradation mechanism and the fundamentals of ion transport across the interfaces are distinctively understood, the development of proper countermeasures can sustainably improve future batteries.
Besides electrode–electrolyte interfaces, those between different types of electrolytes—which we call here “heteroionic” interfaces—are much less investigated, but equally as important. They occur, for example, in hybrid all-solid-state batteries, where the malleability and ionic conductivity of sulfide-based solid electrolytes (SEs) is combined with the chemical stability of oxide-based ones. Composites of polymer electrolytes (PEs) with added SE particles for improved ionic conductivity also involve heteroionic interfaces. And lastly, liquid electrolytes (LEs) are often applied for improved contact between electrodes and SEs as well as formation of a stable SEI on lithium metal, preventing degradation during contact to the SE. Additionally, SE separators can prevent detrimental chemical cross-talk in next-generation Li–S or Li–O₂ batteries and dendrite propagation.²
Herein, we analyze charge-transfer across heteroionic interfaces and interfacial degradation for multiple different SEs using a combined approach of state-of-the-art in situ and ex situ techniques. Thereby, the formation of an interphase of degradation products (solid/liquid electrolyte interphase, SLEI) is detected on the SE surface, mainly contributing to the high interfacial resistance. SLEI formation is investigated by in situ neutron reflectometry and quartz crystal microbalance studies, while its resistance is monitored in situ via time-resolved four-point impedance spectroscopy. Combined with surface analysis and depth profiling by X-ray photoelectron spectroscopy, secondary-ion mass spectrometry, and atomic force microscopy, an in-depth understanding of the composition and formation mechanism of the interphase is obtained.^3–5
Evaluating different combinations of LE and SE, the material selection is optimized and the importance of surface morphology highlighted. Consequently, NASICON-based SEs are found to exhibit lower interphase resistances than LiPON when combined with ethereal LEs commonly used in next-generation batteries.^2,5
Literature:
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[2] M. Weiss, F. J. Simon, M. R. Busche, T. Nakamura, D. Schröder, F. H. Richter, J. Janek, Electrochem. Energ. Rev. 2020, 3, 221.
[3] M. R. Busche, T. Drossel, T. Leichtweiss, D. A. Weber, M. Falk, M. Schneider, M.-L. Reich, H. Sommer, P. Adelhelm, J. Janek, Nat. Chem. 2016, 8, 426.
[4] M. Weiss, B.-K. Seidlhofer, M. Geiß, C. Geis, M. R. Busche, M. Becker, N. M. Vargas-Barbosa, L. Silvi, W. G. Zeier, D. Schröder et al., ACS Appl. Mater. Interfaces 2019, 11, 9539.
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Lithium(Li) metal is consider as promising anode for high energy density batteries. However, lithium dendrite growth during Li plating/striping cause low columbic efficiency and safety issues. The above problems can be controlled by the engineering of interface between Li metal and electrolytes for better Li-ion kinetics and interface stability. In this study, we fabricate a thin LiF/defluorinated polymer(LiF@Po) composite as an artificial SEI layer. This LiF@Po artificial layer is formed by a roll-pressing process using polytetrafluoroethylene (PTFE) and Li metal. With this facile and scalable method, the artificial SEI layer is composed of lithium metal side LiF rich and electrolyte side polymer rich layer. This LiF@Po artificial SEI layer improve cyclability even in a carbonate-based electrolyte. More than 1000h at 1mA/cm2 in lithium symmetric cell and capacity retention of 80% for >200cycles with an average columbic efficiency of 99.7% in Li/LiCoO2 full cell.

Localized high concentration electrolytes (LHCEs) are a promising class of electrolytes to enable stable cycling of the lithium metal anode. Here, we report the use of operando nuclear magnetic resonance (NMR) spectroscopy to observe electrolyte decomposition during Li stripping/plating and identify the influence of individual components in LHCEs on Li metal battery performance. Data from operando ¹⁹F solution NMR indicates that both bis(fluorosulfonyl)imide (FSI^–) salt and bis(2,2,2-trifluoroethyl)ether (BTFE) diluent molecules play a key role in solid electrolyte interphase (SEI) formation, in contrast to prior reports that suggest diluents are inert. Using a combination of solution ¹⁷O NMR and cyclic voltammetry (CV), we assess differences in solvation and electrochemical reduction in LHCEs and compare to low concentration electrolytes (LCEs). We find that BTFE diluents are chemically (rather than electrochemically) reduced during Li metal battery operation, which can be detected with operando NMR, but not conventional electrochemical methods. Solid-state NMR (SSNMR) and X-ray photoelectron spectroscopy (XPS) measurements confirm that LHCEs decompose to form a SEI on Li metal that contains organic BTFE reduction products as well as high quantities of lithium fluoride from both BTFE and FSI^– reduction. Insight into the (electro)chemical reduction mechanisms underpinning SEI formation in LHCEs suggests that fluorinated ethers exhibit tunable reactivity that can be leveraged to control Li deposition behavior.

Cobalt-free LiNi_0.5Mn_1.5O₄ (LNMO) spinel is a promising candidate for the next generation cathode material based on its high operating voltage (4.75 V_{vs Li}), low material cost, and excellent rate capability. However, recent studies reported that the most critical barrier for the commercialization of LNMO is electrolyte oxidation and concurrent parasitic reactions at electrode/electrolyte interfaces, which led to a poor cycle life of LNMO/graphite full-cells. To mitigate the issue, various approaches have been proposed such as coating LNMO, tuning chemical compositions of LNMO, coating graphite anodes, using electrolyte additives, and adopting functional binders for LNMO. However, there is no simple solution to resolve all the complex issues occurring in the high-voltage cells. For example, physical coating on electrode materials will eventually fail due to mechanical cracking of cathode particles due to its repeated volume changes during cycling. In addition, not only LNMO but carbon conductors (e.g., acetylene black) inside a cathode leads to unwanted electrolyte oxidation prompted by its high electronic conductivity and large surface area. Considering that such parasitic reactions originate from cathode-electrolyte interphase (CEI) and propagate to anode solid-electrolyte interphase (SEI), there is a dire need of multimodal strategies that can create synergistic effect on stabilizing the electrode-electrolyte interphases in cell level.
To address these complex interfacial issues, we developed a strategy to innovate the LNMO CEI by endowing critical functionalities – (i) in-situ formation of CEI, (ii) self-healing CEI, (iii) passivation of all LNMO, carbon conductor, and Al-foil. After screening candidates of CEI elements on LNMO, titania was selected as the main ingredient of CEI based on its slow dissolution kinetic at the presence of hydrofluoric acid and its capability to form LiNi_0.5Mn_1.5-xTi_xO₄ (LNMTO) solid-solution phase. Since increasing amount of Ti-substitution (x) in LNMTO reduces bulk electrical conductivity and specific capacity, we designed and synthesized a core (LNMO) – shell (LNMTO) structured cathode powders. This core-shell cathode can produce Ti-enriched CEI layer in-situ through a partial dissolution of Mn and Ni into electrolyte during cycling. If the existing CEI was damaged by a crack, the freshly revealed cathode surface can be recovered by a new, local CEI via the same interfacial reaction (i.e., partial metal dissolution), which can be referred to the “self-healing” mechanism. At the same time, lithium polyacrylate binder was adopted to passivate all LNMO, carbon conductor, and Al-foil against oxidative decomposition reactions at CEI. The combination of inorganic CEI (i.e., Ti-enriched oxides) and organic CEI (i.e., lithium polyacrylate) mimics the physical distribution and functionality of the graphite SEI.
This presentation will also focus on the effect of the multifunctional CEI on battery performances. To avoid a corrosion issue of coin-cell parts made with stainless steel, which critically degraded the full-cell performance at high-voltages, battery performances was examined by using pouch-type cells. The full-cells having the multifunctional CEI retained > 90 % of its half coin-cell capacity at C/3-rate with much improved cycle life compared to baseline performance obtained from the conventional LNMO cathode. AC impedance spectroscopy combined with the distribution of relaxation times (DRT) technique revealed a suppression of cell interfacial resistance during cycling, suggesting the enhanced stability of the multifunctional CEI. Finally, microscopy and spectroscopy data obtained from cycle-aged CEI and graphite SEI will be corelated to the cell performance data to identify the CEI property-performance relationship. This unique multifunction CEI strategies will be applicable to various cathode materials for the next-generation Li-ion batteries.

As Li-ion batteries approach practical performance limits and Li metal batteries grapple with issues such as dendrite formation, batteries based on multivalent (MV) metal anodes such as Ca and Mg are gaining increased research attention. Such systems are attractive because of high gravimetric and volumetric energy densities, high natural abundance, and seemingly low propensity for dendrite formation [1,2]. Implementation of MV metal anodes is challenging due to sluggish transport of Ca²⁺ and Mg²⁺ and thermodynamically favored electrolyte decomposition, often to ionically insulating products. To achieve high (>99.9%) coulombic efficiencies (CE) required for long-term cycling, MV anodes require a robust solid-electrolyte interphase (SEI) that suppresses parasitic reduction of electrolyte components while permitting cation transport at appreciable rates. The study of MV SEIs is in its infancy; little is known about interphase composition and structure and their correlation to anode performance [3].

We recently discovered that a nanometric heterogeneous oxide [4] enables reversible Ca electrodeposition in a model electrolyte, Ca(BH₄)₂ in THF [5]. Cryogenic focused ion beam (cryo-FIB) liftout and transmission electron microscopy (cryo-TEM) techniques enabled analysis of Ca electrodeposits with the liquid electrolyte vitrified in place, thereby preserving the native SEI formed during electrodeposition and open-circuit holds. Electron energy loss spectroscopy mapping, selected-area diffraction, energy-dispersive X-ray spectroscopy, and high-resolution cryo-TEM imaging were used to map the structure and chemistry of nanometric heterogeneous interphases formed on calcium anode surfaces.
In this contribution, we build on our accomplishment by intentionally engineering SEIs for MV metals. We rationally design electrolytes to control interphase chemistry, structure, and heterogeneity, and we then correlate such properties with electrochemical performance enhancements. One case study we discuss is the addition of weakly coordinating calcium salts, such as calcium carba-closo-dodecaborate [Ca(CB₁₁H₁₂)₂], to Ca(BH₄)₂ in THF. This addition modifies the Ca²⁺ coordination in the bulk electrolyte, which enhances interfacial reactivity and, in tandem with CB₁₁H₁₂^- anions, increases oxide interphase heterogeneity. Another case study, aimed at generalizing SEI engineering principles to other MV systems, utilizes an electrolyte of mixed Mg salts in ether solvents. For both cases, we use cryogenic techniques to map the native phases and chemistry of the deposited and cycled structures, correlate morphological and chemical features of engineered SEI layers with the accommodation of newly deposited metal, and highlight potential mechanisms contributing to degradation and failure of MV metal anodes. Our results are a critical step towards the design of ideal SEIs for high-efficiency rechargeable MV metal batteries.
This work was supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy (DOE) and was performed, in part, at the Center for Integrated Nanotechnologies (CINT), an Office of Science User Facility operated for the U.S. DOE Office of Science. 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. DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in the article do not necessarily represent the views of the U.S. DOE or the United States Government.
References:
[1] X. Zhang et al. Advanced Functional Materials 2020, 30(45), 2004187.
[2] Y. Liang et al. Nature Energy 2020, 5(9), 646-656.
[3] H. Wang et al. ChemElectroChem 2021, 8(16), 3013-3029.
[4] S. A. McClary et al. Submitted.
[5] D. Wang et al. Nature Materials 2018, 17(1), 16-20.

The transition to net zero carbon emission will require a step change in performance of energy devices. Batteries based on new chemistries that overcome the fundamental limitations of lithium-ion batteries will play an important role in enabling the energy transition. Lithium-sulfur (Li-S) batteries have attracted attention because of their high theoretical energy density, low materials cost and safety¹. However, fundamental challenges such as low sulfur utilization, sluggish reactions and capacity fading due to polysulfide shuttling have hampered their development. In this presentation, I will describe the realization of Li-S batteries using metallic 1T phase of two-dimensional molybdenum disulfide. Our previous work has shown that compact electrodes assembled from monolayered nanosheets of metallic 1T phase MoS₂ are highly conductive, lyophilic, and are catalytically active^2-4. These attributes lead to > 85% utilization of sulfur due to improved adsorption of lithium polysulfides, enhanced Li⁺ diffusivity, accelerated electrochemical reaction kinetics and superior electrocatalytic activity for polysulfide conversion. We have translated these properties into practical pouch cells, achieving performance compared exceptionally favourably with current state-of-the-art in Li-S batteries^1,5. Our results provide unique insights into new designs for Li-S cathodes based on electrocatalytically active and conducting two-dimensional (2D) materials.

Reference
1. Manthiram, A., Fu, Y., Chung, S. H., Zu, C. & Su, Y. S. Rechargeable lithium-sulfur batteries. Chem. Rev. 114, 11751–11787 (2014).
2. Eda, G. et al. Photoluminescence from chemically exfoliated MoS₂. Nano Lett. 11, 5111–5116 (2011).
3. Chhowalla, M. et al. The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nat. Chem. 5, 263–275 (2013).
4. Voiry, D. et al. The role of electronic coupling between substrate and 2D MoS2 nanosheets in electrocatalytic production of hydrogen. Nat. Mater. 15, 1003–1009 (2016).
5. Zhao, C. et al. A high-energy and long-cycling lithium–sulfur pouch cell via a macroporous catalytic cathode with double-end binding sites. Nat. Nanotechnol. 16, 166–173 (2021).

Lithium-Ion Batteries (LIBs) have received increasing attention due to their crucial role in the transition from fossil fuel to renewable energy. In supporting the energy transition process, LIBs play an essential role in a wide range of energy storage applications from the transport sector (e.g. Electric Vehicles) to the energy market, where LIBs help to improve the power grid stability [1, 2]. This high demand opens up a need to improve LIB technology, such as increasing the energy density, capacity efficiency, and safety of LIBs. One cause of the latter issue is the formation and degradation of the passivation layer called Solid Electrolyte Interphase (SEI). The SEI results from organic solvent degradation and deposition [3]. However, uncontrolled SEI growth causes an undesired and irreversible capacity fade, battery self-heating, and in the worst case to thermal runaway and explosion. Understanding SEI formation and growth is one of the main challenges for LIBs' further development [4]. The SEI's highly reactive nature and complexity of in-situ techniques make the experimental observation of such phenomena very challenging. A possible solution to these obstacles is using a more theoretical approach, but even this approach is not trivial because the SEI requires consideration of all the different phenomena with different time scales [5]. With this work, we propose an innovative protocol to reconstruct the morphology of the SEI polycrystalline layer with an atomic resolution. In our approach, we combine Reactive Force Field MD (ReaxFF) [6] simulations with an in-house routine for statistical generation and positioning in the computational box of several SEI crystalline grains. A consistent computational protocol has been developed to impose the appropriate mass density of the polycrystalline structure as well as the reactive formation of amorphous formation among the several SEI grains. Initially, the SEI grains are scattered in the simulation box, so the system undergoes a slow compression to allow the approach and orientation of the particles. Then, the formation of grain boundaries is obtained by relaxing the system with an annealing simulation. Finally, our procedure delivers consistent configurations of the SEI structure along and attached to the anode slab. Upon generation of the above SEI and SEI+Anode structures, we perform an enhanced sampling simulations campaign to extract the Free Energy Landscape (FEL) and lithium transport properties. Furthermore, our protocol is wrapped and interactively managed with the user-friendly and easy-to-use interface of Jupyter Notebooks. Thanks to python libraries and our in-house codes, we achieved a flexible simulation environment where the user can apply major changes to the studied system with minimal effort. In conclusion, with this protocol, we aim to pave the way for a new computational platform allowing an in-silico experimental campaign to shed light on the SEI formation mechanism and a more rational design of the next generation LIBs.
[1] Chu, Steven, Yi Cui, and Nian Liu. "The path towards sustainable energy." Nature materials 16.1 (2017): 16-22.
[2] Cano, Zachary P., et al. "Batteries and fuel cells for emerging electric vehicle markets." Nature Energy 3.4 (2018): 279-289.
[3] Pinson, Matthew B., and Martin Z. Bazant. "Theory of SEI formation in rechargeable batteries: capacity fade, accelerated aging and lifetime prediction." Journal of the Electrochemical Society 160.2 (2012): A243.
[4] Goodenough, John B., and Youngsik Kim. "Challenges for rechargeable batteries." Journal of Power Sources 196.16 (2011): 6688-6694.
[5] Wang, Aiping, et al. "Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries." npj Computational Materials 4.1 (2018): 1-26.
[6] Van Duin, Adri CT, et al. "ReaxFF: a reactive force field for hydrocarbons." The Journal of Physical Chemistry A 105.41 (2001): 9396-9409.

Developing an industry standard for determining the battery state-of-stability after a potentially abusive condition (e.g., a car crash) remains a key challenge for transportation energy storage systems due to the complexity of the problem. Monitoring a battery pack using traditional techniques can be misleading. A pack may appear healthy, even though it contains a single problematic cell. That problematic cell has the potential to cause cascading failure, leading to thermal runaway in other cells within the pack. Abusive conditions can also be created unintentionally, such as voltage imbalance resulting in overcharge and overdischarge. Even a poor thermal design can create thermally abusive conditions. These problems present a clear need to detect and mitigate catastrophic cell failure under normal use and abuse conditions for transportation energy storage systems.

This research aims to enhance the safety, reliability, and stability of energy storage systems by integrating novel sensors and measurement tools into a battery management system for advanced diagnostics and reporting. This presentation details a collaborative project between Sandia and Idaho National Laboratories to develop a diagnostic demonstration platform. The scope of the project includes characterizing battery performance during normal and off-normal operations using novel sensor technology and embedding these sensors into battery management systems. The capability of these sensors to identify markers of imminent failure in cells and battery packs is a critical component of the project and, it will be the main topic of discussion during this presentation.

Improved battery intelligence is critical to increase penetration of electric vehicles and grid-tied storage systems. Reaching accurate diagnosis and prognosis is complex due to the intricate, nonlinear, and path-dependent nature of battery degradation. Data-driven models are anticipated to play a significant role in the behavioral prediction of dynamical systems such as batteries. However, they are often limited by the amount of training data available.
In this work, we will present the application of a digital twin methodology to generate synthetic big data training datasets for intercalation batteries. We will show how a mechanistic approach that combines both modeling and experimental techniques can provide a universal tool for the creation of synthetic voltage curves practically indistinguishable from real data. The approach offers the benefits of the broad applicability of the model to various cell chemistries, designs, and operating modes, as well as the high fidelity. The methodology could be applied to the generation of training datasets encompassing the entire degradation spectrum as well as different operating conditions such as rate and temperature. Scenarios leading to lithium plating with adjustable reversibility can also be added and the addition of random noise on the data could be considered to make the datasets even more realistic and consider the impact of real-life testing machines' precision and accuracy.
The already available public proof-of-concept datasets are over three orders of magnitude larger than what is currently available in the literature. When used for transfer learning, these datasets expend critical capabilities of current AI algorithms, tools, and techniques to predict scientific data. The synthetic datasets will cover the entire spectrum of possible degradations and degradation paths for several battery chemistries. These complete datasets are unprecedented and they will be used to identify meaningful learning parameter by comparing and evaluating different features of interest on the voltage curves to understand the relationship between data and model. For example, early prognosis conditions were tested to establish whether a single point early prognosis is possible.

With the US economy incurring $200 billion annual losses due to corrosion, there is still a significant need for effective a priori models which enable the prediction of materials’ corrosion behavior¹. Within the field of energy storage, accurately predicting corrosion resistance is a critical first step in evaluating whether emerging theoretical materials found through materials discovery can be used within electrochemical energy storage applications, such as batteries and fuel cells. While most current predictive corrosion models use fully empirical parameters, there is a value in the development of high-throughput kinetic models which utilize solely quantum-mechanics-derived inputs. Therefore, as a first step in this direction, we develop an ab initio-kinetic model by applying the Pilling-Bedworth Rule (PBR), a metric commonly used to predict the passivation protectiveness of a given material based on mechanical driving forces^2-4. By automating this methodology for all single-element, binary, and ternary materials currently in the Materials Project database, we propose that this model can serve as a preliminary, low-cost screening step which can be applied to a wide range of potential energy storage materials for predicting their electrochemical stability. We then extend our methodology for a smaller subset of materials by also considering more complex kinetic models which incorporate a chemical transport driving force, with the aim to enable the creation of higher-accuracy ab initio models for predicting the corrosion behavior of energy storage materials.

*This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 026257-001.
References:
[1] Jacobson, G. A., Nace international’s impact study breaks new ground in corrosion management research and practice. The Bridge 2016, 46.
[2] Xu, C.; Gao, W., Pilling-Bedworth ratio for oxidation of alloys. Material Research Innovations 2000, 3 (4), 231.
[3] McCafferty, E., Introduction to corrosion science. Springer Science & Business Media: 2010.
[4] Pilling, N., The oxidation of metals at high temperature. J. Inst. Met. 1923, 29, 529

NMC electrodes typically consist of primary particles aggregated to form polycrystalline secondary particles. Electrodes composed of polycrystalline NMC particles have high gravimetric capacity and good rate capabilities but do not perform as well as single crystal equivalents in terms of volumetric energy density and cycling stability. This has prompted research into well-dispersed single-crystal NMC products as an alternative solution for high-energy-density batteries.
There has also been a move towards the application of new characterisation techniques to better understand the degradation processes and extend lifetime. Of these, acoustic techniques have rapidly increased in popularity, with electrochemical acoustic time-of-flight (EA-ToF) spectroscopy being used to study various degradation phenomena in LiBs such as severe gas formation^[1], cell stiffness ^[2], and cathode dissolution^[3]. In addition, studies have commonly coupled EA-ToF spectroscopy with complementary characterisation tools including X-ray diffraction (XRD)^[4] and X-ray computed tomography (CT) ^[1] to further enhance understanding of the structural changes taking place in the materials and architectural changes at the device level. Progress in EA-ToF investigations of LiB thermal expansion can provide a greater understanding of these dynamic processes, something which will help to overcome limitations in current density, battery lifetime and capacity fade and ultimately minimise the total cost of battery systems. Furthermore, EA-ToF spectroscopy is a non-invasive, non-destructive technique that can be applied to batteries with minimal cost and high time-resolution results, making it an attractive proposition for detailed on-board diagnostics of operating batteries.
Here, we will discuss the underlying principles of EA-ToF spectroscopy and report EA-ToF spectrograms collected for pouch cells containing either single-crystal NMC811 (SC-NMC811) or polycrystalline NMC811 (PC-NMC811) electrodes. For the first time known to the authors, EA-ToF spectroscopy has been shown to be effective in distinguishing between LiBs composed of either SC-NMC811 or PC-NMC811 electrodes. Cells composed of PC-NMC811 electrodes had a higher degree of gas evolution compared to cells containing SC-NMC811 electrodes and underwent larger changes in the acoustic signal’s time-of-flight (ToF) during constant current cycling at a range of C-rates indicating expansion, fracture or dislocation of the reflective interfaces inside the cell. In addition, X-ray CT was used to confirm significant differences in morphology between SC-NMC811 and PC-NMC811 electrodes such as particle sphericity and particle diameter that may have a direct effect on acoustic signal interaction with these electrode interfaces. However, there was no noticeable difference in the internal architecture of the SC-NMC811/Gr cell and PC-NMC811/Gr cell, suggesting that the variation in acoustic response between the cells was principally due to the difference in crystallinity and morphology of the NMC811 electrodes.
References
[1] M. T. M. Pham, J. J. Darst, D. P. Finegan, J. B. Robinson, T. M. M. Heenan, M. D. R. Kok, F. Iacoviello, R. Owen, W. Q. Walker, O. V. Magdysyuk, T. Connolley, E. Darcy, G. Hinds, D. J. L. Brett, P. R. Shearing, J. Power Sources 2020, 470, 228039.
[2] C. Bommier, W. Chang, J. Li, S. Biswas, G. Davies, J. Nanda, D. Steingart, J. Electrochem. Soc. 2020, 167, 020517.
[3] J. B. Robinson, R. E. Owen, M. D. R. Kok, M. Maier, J. Majasan, M. Braglia, R. Stocker, T. Amietszajew, A. J. Roberts, R. Bhagat, D. Billsson, J. Z. Olson, J. Park, G. Hinds, A. Ahlberg Tidblad, D. J. L. Brett, P. R. Shearing, J. Electrochem. Soc. 2020, 167, 120530.
[4] C. Bommier, W. Chang, Y. Lu, J. Yeung, G. Davies, R. Mohr, M. Williams, D. Steingart, Cell Reports Phys. Sci. 2020, 1, 100035.

With the increase in deployment of Li-ion batteries for uses in energy storage and electric vehicles, the risk of thermal runaway and subsequent fires must be mitigated. As the energy density of cells and assembled systems of cells increases, the risk of cascading failure also rises. However, experimental investigations of thermal runaway in large systems are difficult and costly, which necessitates supplementing experimental data with simulation predictions. To reliably predict propagation and the performance of mitigation strategies, the rate of thermal runaway in a range of thermal conditions must be well-understood. One challenge that arises in cascading failure is that failing cells are rapidly heated by previously failed cells to react at higher temperatures, and fundamental kinetics measurements are not available under these conditions.

Kurzawski et al. (Proc. Combust. Instit., 38(3): 4737–4745, 2020) identified the need to limit high temperature rates in cell-stack and pack-scale thermal-runaway predictions as literature models over-predicted the propagation speed. They proposed intra-particle diffusion as a solution to poor predictions of legacy models at these scales. As thermal runaway progresses, species (Li⁺ or O^2-) must diffuse to the surface of the electrode particles to react with the electrolyte. The particles can be represented as spherical shells with active material in the core, where species diffuse through a shell with some diffusivity constant. Diffusion is found to be limiting at high temperatures because the kinetic rates surpass diffusion rates due to differing activation barriers. Combining the diffusion rate and electrode-electrolyte rate in serial results in transition between the previously identified thermal runaway kinetics and the new diffusion-limited rate that becomes relevant at high temperatures.

The current work explores in greater detail the formulation of an intra-particle diffusion limiter on propagating thermal runaway predictions. These predictions are validated against experimental thermal runaway propagation data for a range of thermal dilution scenarios.

Acknowledgements:
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and 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-NA-0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.
SAND No: SAND2021-13655 A

Lithium-ion batteries are indispensable in the automotive sector as energy storage devices due to their high energy and power density. With the increasing energy capacity of automotive battery systems, safety requirements have become even more critical.
However, present condition monitoring of lithium-ion batteries is limited to current, voltage, and sporadic temperature measurements on the outside of the cells. Since temperature dependencies are critical for all known measurement setups, a more direct measurement of internal temperature by integrating sensors offers new insight into the operating conditions of battery cells. This is particularly important as the volume of cells used in automotive applications is increasing, and thus gradients between the surface and the cell's core are becoming more relevant. Integrating electronics and sensor technologies into the inside of the cell enables direct and unaltered measurements and extends battery monitoring to a new scale. This could also lead to a new era of an overall BMS design. However, it must be taken into account that current battery cell formats have little functional space left inside, and the electrolyte is a chemically aggressive environment for electrical components.
In this work, the use of a glass fiber sensor and the use of a fiber optic measurement method of coherent optical frequency domain reflectometry (C-OFDR) is investigated as a novel method for measurements of thermal effects in batteries. Those fibers enable spatially resolved temperature measurement on or even after integration in cells. The use of chemically robust glass fibers, which are also unaffected by electric fields, makes them suitable for integration into batteries and opens up new fields of application. In contrast to previously in literature used fiber bragg grating (FBG) sensors, the presented measurement method enables direct measurement over the entire length of the glass fiber without prior time-consuming and expensive preparation of the fiber, resulting in considerable equipment savings and cost reduction.
Glass fibers as a sensor show a direct correlation to external thermal and mechanical impacts. Prior determination and knowledge of the strength of those effects isolated are essential before using in an undefined environment such as inside of the battery. It was found that fiber optic measurement techniques are suitable for spatially resolved temperature measurements and that the measurement results are sufficiently precise for cell monitoring. Due to the high sampling rate and low response time, the recorded measurement values can also be potentially used to give prior warning against thermal runaway in a live evaluation.
As a proof-of-concept, battery cells were equipped with glass fibers as a sensor and already showed promising results such as a correlation with the temperature during the cycling of the battery cell. Thus, an advanced characterization of battery cells can be achieved with the integration of such a sensor technology.

With the pursuit of high energy density of lithium ion batteries (LIBs), the safety of LIBs is raising intensive concerns. The high flammability of the liquid electrolytes used in state-of-the-art LIBs is one critical link of the overall safety property of LIBs. The conventional approach to reduce the flammability of the liquid electrolytes is to introduce a certain amount of a miscible flame retardant (FR) as additive or co-solvent into the LiPF₆/carbonates electrolytes. However, the added FRs, normally organic phosphate compounds, are incompatible with the graphite electrodes, hence they actually induce severe deterioration in battery performance. Meanwhile, the continuous consumption of FR molecules at the electrode/electrolyte interfaces by the parasitic reactions, the flame retarding effectiveness of the FR gradually decreases. In response to these challenges, new safe electrolytes based on the concept of localized high-concentration electrolyte (LHCE) were developed by using common FRs, organic phosphorus-containing solvents. The incompatibility issue between phosphorus-containing solvents and graphite has been successfully resolved by the unique solvation structure of LHCEs and the incorporation of a small amount of electrolyte additives. Ignition tests show that these LHCEs are much less flammable than the conventional LiPF₆/carbonate electrolyte. Moreover, the graphite-based LIBs using such phosphorus-solvent-based LHCEs can achieve long cycle life, similar to or much better than those of conventional LiPF₆/carbonate electrolyte depending on cell chemistries. More details will be reported during the presentation.

Nowadays’ research on lithium-ion batteries, especially for electric drive applications, focuses on either Ni-rich layered oxides, namely lithium nickel manganese cobalt oxide (NMC), or high voltage spinel cathode chemistries. Besides cost and cobalt reduction, Ni-rich NMC promises higher cut-off voltages and increased energy densities, while unfortunately, the reactivity increases with increasing Ni-content, leading to irreversible structural changes and correlated reduced cyclability, safety, and thermal stability [1]. The Ni-amount in the NMC cathode particles can be directly related to the compounds’ stability, which leads to difficulties and significant capacity decay when being stored under ambient conditions [2].
In addition to their high reactivity and correlated structural instability, layered oxide cathodes suffer from low capacity retention, especially at high charging/discharging currents. To increase the high rate stability while maintaining high energy density, more sophisticated electrode designs such as 3D electrode architectures via incorporation of carbon nanotubes [3] or laser generated patterns [4] are currently under investigation.
Recently, we have presented two promising strategies for improvements of NMC811 containing Li-ion batteries [5],[6]:
- Particle coating via different approaches (physical vapor deposition and atomic layer deposition) with different protective coatings (ZrO₂ and Al₂O₃) at nanometer scale.
- Ultrafast laser ablation of high energy thick film electrodes to create channels for accelerated and homogenized electrolyte wetting, improved Li⁺-diffusion kinetics, and reduced overpotentials at elevated C-rates.
The resultant pouch cells not only show increased cycling stability, but also promises higher safety and NMC811 powder stability for storage under ambient conditions. It was also shown that the transport kinetics of the electrodes where enhanced via laser patterning of the NMC811 electrode sheets.
The structured thick film electrodes show increased rate stability compared to unstructured NMC811 at 2C charge/discharge with specific discharge capacities larger than 130 mAhg^-1 in multilayer cell configuration. To further evaluate the optimisation strategies, we have performed standardised cell safety tests (short circuit, nail penetration) in 2 Ah pouch cells. It was shown that the proposed optimisation strategies not only result in improved but also safer NMC811 cathode containing batteries with high energy density for future xEV applications.
References
[1] R. Jung, M. Metzger, F. Maglia, C. Stinner, and H. A. Gasteiger, ‘ Oxygen Release and Its Effect on the Cycling Stability of LiNi x Mn y Co z O 2 (NMC) Cathode Materials for Li-Ion Batteries ’, J. Electrochem. Soc., vol. 164, no. 7, pp. A1361–A1377, 2017, doi: 10.1149/2.0021707jes.
[2] R. Jung et al., ‘Effect of Ambient Storage on the Degradation of Ni-Rich Positive Electrode Materials (NMC811) for Li-Ion Batteries’, J. Electrochem. Soc., vol. 165, no. 2, pp. A132–A141, 2018, doi: 10.1149/2.0401802jes.
[3] A. Shah et al., ‘A Layered Carbon Nanotube Architecture for High Power Lithium Ion Batteries’, J. Electrochem. Soc., vol. 161, no. 6, pp. A989–A995, 2014, doi: 10.1149/2.052406jes.
[4] W. Pfleging, ‘A review of laser electrode processing for development and manufacturing of lithium-ion batteries’, Nanophotonics, vol. 7, no. 3, 2018.
[5] K. Froehlich, W. Pessenhofer, H. Besser, Pfleging Wilhelm, and Jahn Marcus, ‘Strategies enhancing the electrochemical performance of NMC811 high energy electrodes for xEV applications’, in The 21st International Conference on Advanced Batteries,Accumulators,Fuel Cells and Special Electrochemical Technologies, 2020.
[6] K. Froehlich, B. Eschelmueller, W. Pessenhofer, H. Besser, W. Pfleging, and Jahn Marcus, ‘Realisation of stable and high power capable NMC811 pouch cells for future xEV applications’, Nanomaterials, no. planned, 2021.

Battery Energy Storage Systems (BESSs) can facilitate renewable energy sources integration onto the grid. For grid-storage applications, BESSs are expected to last for a decade or more but the actual battery degradation under different real-world conditions is still largely unknown. In this work, more than seven years of usage for a Hawai'i based BESS comprising cells made of a lithium cobalt and lithium nickel cobalt oxides blended positive electrode and a titanate negative electrode were analyzed.
The BESS was found to be operational 90% of the time and it stored a cumulative 2.3 GWh of energy, which represented more than 7500 equivalent full cycles on the cells. An initial estimate of BESS degradation and a representative duty cycle were derived from an analysis of the first three years or usage. The battery duty cycle was characterized based on 5 parameters: pulses duration, pulses intensity (current), state of charge (SOC) swing range, SOC event ramp rate, and temperature.
Laboratory testing and analysis, in conjunction with a more thorough SOH estimation protocol, resulted in a detailed description of degradation that improved the predictions of the remaining useful battery life. Based on the BESS representative usage profile, cycle-aging and calendar-aging experiments were designed to test the degradation of the associated Li-ion cells in a controlled fashion. It was proven that cell temperature had the strongest impact on battery degradation followed by the C-rate and the state of charge. Interestingly, the impact of SOC, both on the cycle-aging and the calendar-aging experiments, was revealed to be counterintuitive. During cycle aging, small SOC swings were more detrimental than larger ones. During calendar aging, batteries lost capacity faster at low SOC than at high SOC. Moreover, the different stress factors were shown to affect the two components of the positive electrode blends differently.
The associated degradation mechanisms and their path dependency were analyzed using incremental capacity analysis using in-depth understanding of the different crystallographic and electrochemical reactions in the battery electrodes active materials.

If energy stored within a battery is inadvertently released in an uncontrolled manner, the battery can go into thermal runaway, and for high energy density lithium-ion systems thermal runaway is quite hazardous. There are two main classes of exothermic processes that might initiate thermal runaway in lithium-ion batteries. If an electrical short circuit develops, often initiated through mechanical failure of the separator, the electrochemical reactions associated with discharge can release the cell’s energy. If the short circuit is internal, the full stored energy can be released as heat within the cell, raising temperatures many hundreds of degrees. Alternately, a series of thermochemical reactions can occur if lithium-ion cells are heated through some means. These involve the anode and cathode materials decomposing together with the electrolyte and possibly other materials and can also raise temperatures many hundreds of degrees. We show that thermodynamics forces key reactant species for both paths to be in common. This modeling study considers interactions between these chemical pathways for heat release, including limiting reactant effects and the relative thermal contributions from each reaction pathway. An effective oven temperature concept is introduced as a method to compare thermal runaway initiation via internal short circuits versus direct heating of a cell. For localized internal short circuits, temperature and reaction inhomogeneities lead to variations in the balance between electrochemical and thermochemical reactions through the cell. The more detailed inhomogeneous analysis is contrasted with a homogeneous analysis common in thermal runaway modeling. Mitigation effectiveness via external cooling during an internal short circuit event is also investigated.

With increasing energy density the safety and the thermal management of Li-ion batteries is becoming more and more important, because the thermal runaway can cause an ignition or even explosion of the battery with simultaneous release of toxic gases. In the last ten years, we have established battery calorimetry as a versatile characterization technique, which allows advancements for the thermal management and the safety of batteries. With six adiabatic Accelerating Rate Calorimeters of different sizes and two sensitive Tian-Calvet calorimeters combined with cyclers we operate Europe’s largest battery calorimeter center, which enables the evaluation of thermodynamic, thermal and safety data on material, cell and pack level under quasiadiabatic and isoperibolic environments for both normal and abuse conditions (thermal, electrical, mechanical). Calorimetry allows the collection of quantitative data required for optimum battery performance and safety. This information is applied to define the requirements for thermal management. It will be explained how calorimeters can be used for studies on heat generation and dissipation of Li-ion cells. It will be shown that by measuring the specific heat capacity and the heat transfer coefficient the measured temperature data during cycling can be converted into generated and dissipated heat data, which are needed for the adjustment of the thermal management systems. It will be presented how battery calorimeters allow to perform safety tests on cell and pack level by applying thermal, mechanical or electrical abuse conditions. For the advanced Li-ion technology, a holistic safety assessment is in the focus, because the thermal runaway can have multiple interacting causes and effects. A test in the calorimeter reveals the entire process of the thermal runaway with the different stages of exothermic reactions. As a result of the different tests quantitative and system relevant data for temperature, heat and pressure development of materials and cells are provided. In addition it will be explained how calorimeters allow studying the thermal runaway propagation in order to develop and qualify suitable countermeasures, such as heat protection barriers, which is currently becoming a very hot topic.

Li-ion batteries are used for energy storage in a variety of applications such as smartphones, laptop computers, power tools, stationary energy storage, unmanned aerial vehicles (UAV), light electric vehicles (LEV), as well as electric cars (EV, HEV, PHEV). Besides costs, high energy density, and fast-charging capability, a high safety level is one of the most important properties during the whole life of a battery.
For Li-ion cells, safety relevant incidents can happen due to abusive conditions. Such conditions are tested in the lab, for example by nail penetration, overcharge, or overheating experiments. Especially, at elevated temperatures exothermic reactions can occur, generating substantial heat and gas in the cells. If the heat transfer from the cell to the surrounding is insufficient, the rate of the undesired chemical reactions inside the cell accelerate which can lead to venting and thermal runaway.
In this study, we coupled accelerating rate calorimetry (ARC) with on-line mass spectrometry (MS), resulting in a new method (ARC-MS). ARC-MS allows measuring the thermal properties of the cell under quasi-adiabatic conditions with simultaneous analysis of the emitted gases after venting [1]. Additionally, data from gas and audio sensors as well as resistance and voltage are recorded at the same time.
This method is applied to different commercial Li-ion cells at different state-of-charge (SOC) and state-of-health (SOH) for overheating as well as overcharging to gain insights into the safety critical mechanisms. It turns out that safety of aged cells depends not only on the value of the SOH. Moreover, safety also depends on the aging mechanism as determined by Post-Mortem analysis [2] and in case of Li plating on the rest time between the end of cycling and the start of the ARC test [3]. Cells with Li deposition on the anode and overcharged cells show an early onset of self-heating. The organic solvent signals are predominant at the time of cell venting whereas the C₂H₄, CO₂, and POF₃ signals are more common at cell explosion.
Due to electrolyte decomposition by anodic and cathodic exothermic reactions, the amount of the detected species by MS are depending on the chemical composition and history of the cell, e.g. SOC, aging mechanism, and overcharging.
References
[1] A.A. Abd-El-Latif, P. Sichler, M. Kasper, T. Waldmann, M. Wohlfahrt-Mehrens, Batteries & Supercaps 4 (2021) 1135–1144. https://doi.org/10.1002/batt.202100023.
[2] T. Waldmann, J.B. Quinn, K. Richter, M. Kasper, A. Tost, A. Klein, M. Wohlfahrt-Mehrens, J. Electrochem. Soc.164 (2017) A3154-A3162. https://doi.org/10.1149/2.0961713jes
[3] T. Waldmann, M. Wohlfahrt-Mehrens, Electrochim. Acta 230 (2017) 454-460. http://dx.doi.org/10.1016/j.electacta.2017.02.036
Acknowledgment
Funding of the AnaLiBa project (03XP0347C) by the German Federal Ministry of Education and Research (BMBF) and the TEESMAT project (n° 814106) (http://www.teesmat.eu) by European Community's Horizon 2020 Framework are gratefully acknowledged.

At its essence, energy is the sum of heat and work: △E = q + w. As such, the ultimate goal for any energy storage system is to maximize useful work (w) and minimize the generation of waste heat (q). Ideal batteries would provide energy that can be efficiently converted to useful electrical work over many reversible cycles, however, degradation inevitably occurs. Operando isothermal microcalorimetry (IMC) is a precise technique that can monitor real-time heat flow released during battery operation and can thus be utilized as a diagnostic tool for quantifying the heat flow. Our detailed analysis of the thermal profiles enabled determination of thermodynamic reversibility as well as the contributions of parasitic reactions to total heat flow.
Specifically, IMC was used to probe electrolyte interactions on conversion materials used as negative electrodes as a function of state of charge and voltage. The heat flow analysis separated the contributions from polarization, entropic changes, and parasitic reactions where the onset and magnitude of the electrolyte reaction could be determined. Further, IMC was used to probe insertion positive electrode materials also as a function of state of charge and associated voltage. Study of the heat flow under conditions of increased delithiation achieved through the use of higher charge voltage revealed differences in thermodynamic reversibility. The examples provided will illustrate the important mechanistic insights that can be gained through in depth analysis of thermal data.

The lithium-ion battery family (LCO, LMO, LFP, NMC) suffer thermally accelerated failure, making thermal management of the batteries and the batteries thermal properties important. At higher temperatures, the degradation of active phases accelerates, and thermal runaway becomes a safety concern. Battery degradation can be identified by analyzing the thermal properties of the cathode material. In this presentation, the transient hot wire method (THW) is applied to gauge the thermal conductivity of polycrystalline lithium nickel manganese cobalt oxide (NMC 811) as a function of the state of charge and cycles. The thermal properties of the uncycled baseline NMC811 electrode will also be discussed. Applications of this work to thermal management and battery diagnostics will be discussed.

The physico-chemical properties of solid–electrolyte interphase (SEI) dominate the interfacial reactions and charge-carrier-transportation, both being crucial to the lithium/sodium battery performance. The detailed understanding of SEI chemistry and structure, especially for the new generation batteries such as sodium-ion-batteries (SIBs) [1] is still under debate, to great extent due to the lack of adequate in-situ nanoscale characterisation tools [2]. The progress is further complicated by the diversity of surface reactions taking place in interlinked sequences varying for different battery formation protocols, the state of charge/discharge and the type of anode active materials and electrolytes.
To understand the nanoscale details of the formation mechanism behind different SEI structures, here we introduce a novel approach of scanning probe microscopy based “3D operando nanorheology” [3]. It allows direct nanoscale characterisation of SEI formation by revealing 3D structure (organic/inorganic moieties within the SEI layer), quantifying the nanomechanical properties of SEI organic and inorganic components, and providing a common denominator for evaluating the SEI properties (mechanical, thermal, electrical) formed on lithium/sodium battery anodes.
By using new methodology, we were able to directly observe that the SEI formation on the non-intercalation graphitic carbon basal plane follows the impurity adsorption nucleation and precipitation mechanism resulting in a 3D nano-mosaic and multilayer hybrid structure with randomly mixed organic and inorganic SEI layer. This was very different to the intercalation-active graphitic carbon edge planes where the ion intercalation assisted electrolyte salt decompositions resulted in a single inorganic layer. On the other hand, the SEI formation on the electrochemical deposition based new-generation Li/Na anodes showed more complicated and dynamic structures. In this case, the interface structure varies during the Li/Na plating and stripping, and highly depends on the electrolyte solvent structures within the inner Helmholtz layer. By further comparing the nanomechanical/rheology properties of SEI formed on various carbon, lithium and sodium metal anodes, we deduce the intrinsic material properties of SEI layers such as elastic moduli, plasticity and relaxation time, predicting the SEI quality in commercial batteries after their formation by correlating quantitatively measured nanoscale SEI properties with the battery performance. This novel “3D operando nanorheology” characterization methodology provides a novel paradigm for battery community, that can be effectively used for SEI measurements in different type of battery electrode-electrolyte systems. Predicting the SEI quality based on this new methodology will be extremely beneficial for selecting a new electrolyte, optimising formation process and reducing the time and cost of battery formation process.
This work was supported by the Faraday Institution (grant number FIRG018), EU Graphene Flagship Core 3 project and EPSRC project EP/V00767X/1 and EP/P009050/1.
Contact: y.chen102@lancaster.ac.uk / o.kolosov@lancaster.ac.uk
Reference
1. Bommier, C. and X. Ji, Electrolytes, SEI Formation, and Binders: A Review of Nonelectrode Factors for Sodium-Ion Battery Anodes. Small, 2018. 14(16): p. 1703576.
2. Liu, D., et al., Review of Recent Development of In Situ/Operando Characterization Techniques for Lithium Battery Research. Advanced Materials, 2019. 31(28): p. 1806620.
3. Chen, Y., et al., Controlling Interfacial Reduction Kinetics and Suppressing Electrochemical Oscillations in Li4Ti5O12 Thin-Film Anodes. Advanced Functional Materials, 2021. 31(43): p. 2105354.

Electrolytes are an essential component of energy storage devices. Electrolyte composition has a significant impact on the safety, price and performance of the battery. Intrinsically nonflammable aqueous electrolytes can offer safer battery operation and decreased associated toxicity but suffer from a smaller electrochemical stability window (and hence energy density) co