Alkali Metal Anodes Research Articles

Heterogeneity in Point Defect Distribution and Mobility in Solid Ion Conductors.

Alkali metal anodes paired with solid ion conductors offer promising avenues for enhancing battery energy density and safety. To facilitate rapid ion transport crucial for fast charging and discharging of batteries, it is essential to understand the behavior of point defects in these conductors. In this study, we investigate the heterogeneity of defect distribution in two prototypical solid ion conductors, Li3OCl and Li2PO2N (LiPON), by quantifying the defect formation energy (DFE) as a function of distance from the surface and interface through first-principles simulations. To simulate defects at the electrode-electrolyte interface, we perform calculations of Li+ vacancy in Li3OCl near its interface with lithium metal. Our results reveal a significant difference between the bulk and surface/interface DFE which could lead to defect aggregation/depletion near the surface/interface. Interestingly, while Li3OCl has a lower surface DFE than the bulk in most cases, LiPON follows the opposite trend with a higher surface DFE compared to the bulk. Due to this difference between bulk and surface DFE, the defect density can be up to 14 orders of magnitude higher at surfaces compared to the bulk. Further, we reveal that the DFE transition from surface/interface to bulk is precisely characterized by an exponentially decaying function. By incorporating this exponential trend, we develop a revised model for the average behavior of defects in solid ion conductors that offers a more accurate description of the influence of grain sizes. Surface effects dominate for grain sizes ≲1 μm, highlighting the importance of surface defect engineering and the DFE function for accurately capturing ion transport in devices. We further explore the kinetics of defect redistribution by calculating the migration barriers for defect movement between bulk and surfaces. We find a highly asymmetric energy landscape for the lithium vacancies, exhibiting lower migration barriers for movement toward the surface compared to the bulk, while interstitial defects exhibit comparable kinetics between surface and bulk regions. These insights highlight the importance of considering both thermodynamic and kinetic factors in designing solid ion conductors for improved ion transport at surfaces and interfaces.

Enhanced electrochemical cyclability of composite sodium metal anode with inorganic-rich solid electrolyte interphase

The practical application of sodium (Na) metal anode in rechargeable batteries is impeded by inferior electrochemical properties and safety hazards arising from uneven Na plating/stripping behaviors. The Na-ion diffusion within the solid electrolyte interphase (SEI) plays a pivotal role in influencing these behaviors and the electrochemical performance of the Na metal anode. In this study, we leveraged the spontaneous reaction between red phosphorus (P) and metallic Na to fabricate a Na/Na3P (NNP) composite foil using a straightforward folding and mechanical rolling method at room temperature. The in-situ formed Na3P phase fosters the formation of an inorganic-rich SEI layer with high ionic conductivity, effectively enhancing the Na-ion diffusion kinetics and curbing the formation of Na dendrites. Moreover, the Na3P present in the NNP composite can continually replenish the functional component and promptly repair the fracture of the SEI layer, thereby ensuring the stability of its structure and properties. Consequently, the NNP composite electrode significantly extends the Na plating/stripping cyclic lifespan compared to a bare Na anode. As a demonstration, the Na3V2(PO4)3||NNP full cell exhibits stable performance over 400 cycles with 96.7 % capacity retention at 5C. This work paves the way for designing stable SEI layers with fast ion diffusion capability for alkali metal anodes, and the findings are anticipated to propel the development of alkali metal batteries.

Stable Hydroborate Solid-State Lithium Battery with High-Voltage NMC811 Cathode

Hydroborate solid electrolytes offer high ionic conductivity and are stable in contact with alkali metal anodes, but are challenging to integrate into batteries with high-voltage cathodes [1-3]. Here, we demonstrate stable dis-/charge cycling of solid-state lithium-ion batteries combining a Li3(CB11H12)2(CB9H10) hydroborate electrolyte with a 4 V-class LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode, exploiting the enhanced kinetic stability of the LiCB11H12-rich and LiCB9H10-poor electrolyte composition [4]. Cells with lithium metal and indium/lithium anodes achieve a discharge capacity at C/10 of ~145 mAh g–1 at room temperature and ~175 mAh g–1 at 60 °C. Indium/lithium cells retain 98% of their initial discharge capacity after 100 cycles at C/5 and 70% after 1000 cycles at C/2. Capacity retention of 97% after 100 cycles at C/5 and 75% after 350 cycles at C/2 is also achieved with a graphite anode without any excess lithium. The energy density per cathode composite weight of 460 Wh kg–1 is on par with the best solid-state batteries reported to date.[1] L. Duchêne, A. Remhof, H. Hagemann, D. Battaglia, Energy Storage Materials, 2020, 225, 782[2] L. Duchêne, R.-S. Kühnel, E. Stilp, E. Cuervo Reyes, A. Remhof, H. Hagemann, C. Battaglia, Energy & Environ. Science, 2017, 10, 2609[3] R. Asakura, D. Reber, L. Duchêne, S. Payandeh, A. Remhof, H. Hagemann, C. Battaglia, Energy & Environ. Science, 2020, 13, 5048[4] H. Braun, Ryo Asakura, A. Remhof, C. Battaglia, ACS Energy Lett. in press

Development of Pentablock Copolymer Membranes for a Sodium Polysulfide Hybrid Redox Flow Battery

Long duration energy storage devices, such as redox flow batteries (RFBs), are critical for enabling the widespread adoption of renewable energy sources such as wind and solar on the electric grid. Non-aqueous RFBs (NARFBs) have emerged as a possible alternative to aqueous RFBs (e.g., all-vanadium and Zn/Br systems), as they have the potential to use supporting electrolytes with wide operating voltage windows (>3 V) and a variety of redox couples. One NARFB of interest is a hybrid RFB that utilizes an alkali metal anode, such as sodium, and a polysulfide catholyte. However, the realization of a hybrid NARFB for long duration energy storage requires the development of new membranes with robust mechanical properties, good (electro)chemical stability, high ionic conductivity, and low polysulfide permeability. In this work, we have utilized a cation exchange pentablock copolymer membrane with sodium sulfonate and sodium trifluoromethanesulfonimide (TFSI) functionalities. We studied various crosslinking methods with the goal of reducing electrolyte uptake and polysulfide crossover of the membrane, while maintaining high ion transport. One lightly crosslinked membrane exhibits a 40% reduction in electrolyte uptake compared to the uncrosslinked membrane, but at the expense of a reduction in ionic conductivity from 2.5 x 10-4 S/cm to 4.2 x 10-5 S/cm at 20 °C. Our continued efforts in developing techniques to improve membrane properties will also be discussed.

Constructing Three-Dimensional Architectures to Design Advanced Copper-Based Current Collector Materials for Alkali Metal Batteries: From Nanoscale to Microscale.

Alkali metals (Li, Na, and K) are deemed as the ideal anode materials for next-generation high-energy-density batteries because of their high theoretical specific capacity and low redox potentials. However, alkali metal anodes (AMAs) still face some challenges hindering their further applications, including uncontrollable dendrite growth and unstable solid electrolyte interphase during cycling, resulting in low Coulombic efficiency and inferior cycling performance. In this regard, designing 3D current collectors as hosts for AMAs is one of the most effective ways to address the above-mentioned problems, because their sufficient space could accommodate AMAs' volume expansion, and their high specific surface area could lower the local current density, leading to the uniform deposition of alkali metals. Herein, we review recent progress on the application of 3D Cu-based current collectors in stable and dendrite-free AMAs. The most widely used modification methods of 3D Cu-based current collectors are summarized. Furthermore, the relationships among methods of modification, structure and composition, and the electrochemical properties of AMAs using Cu-based current collectors, are systematically discussed. Finally, the challenges and prospects for future study and applications of Cu-based current collectors in high-performance alkali metal batteries are proposed.

Superior electrochemical performance of alkali metal anodes enabled by milder Lewis acidity

Weak Lewis acidity of potassium-ions promotes enhanced anion incorporation into the solvation shell, facilitating the formation of a more stable and dissolution-resistant solid electrolyte interphase for K metal compared with that for Li and Na metals.

A Comprehensive Study of the Parameters Affecting Magnesium Plating/Stripping Kinetics in Rechargeable Mg Batteries

Beyond the lithium ion battery (LIB) technology, alkali and alkaline earth metal (Li, Na, Mg, Ca etc.) anodes boost the prospect of next generation battery chemistry through their highly promising theoretical specific capacities.1,2 Mg metal anode based battery is thus one of the strong contenders for sustainable and alternative rechargeable battery systems, with its natural abundance and eco-friendly resources.3 Despite the first proof-of-concept of a Mg battery established back in 2000,4 its complete rechargeability still remains elusive due to the lack of suitable conventional electrolytes and low mobility of Mg2+ ions in typical intercalation cathodes. Although potentially safer than Li metal (less prone to dendritic growth), reversible Mg electrodeposition in non-aqueous liquid electrolytes is a challenge due to poor salt solubility and formation of ionically blocking surface passivation films.5,6 The study of the interphase between a Mg metal anode and electrolyte is therefore of critical worth as it can dictate stability and reversibility for a particular electrode/electrolyte combination.7 In this work, we explore the role of various parameters, including electrolyte composition, concentration, solvent and substrate nature (various metals and carbon based substrates) and their impact on Mg plating/stripping kinetics and coulombic efficiency. The deposit morphology was investigated via ex situ scanning electron microscopy (SEM) and the reductive stability of the electrolytes was studied by cyclic voltammetry (CV), X-ray Photoelectron Spectroscopy (XPS) and electrochemical quartz crystal microbalance (EQCM). Overall, a comprehensive discussion about the relationship between cation solvation structure, composition and stability of passivation layer (if any) and the degree of reversibility of Mg electrodeposition will be presented. Keywords: Beyond LIB chemistry, metal anode, magnesium, EQCM, plating/stripping.

Electrochemical Signatures of Potassium Plating and Stripping

Alkali metals are attractive anodes for high energy density batteries, but practical utilization of these materials in rechargeable cells has so far been hindered by safety concerns, limited Coulombic efficiencies and short cycle lives. These issues are all connected to the uneven electrodeposition and stripping of alkali metals; dendritic metal deposits can short circuit the cell and deposits with large surface areas consume more electrolyte and active material in side reactions.[1] To circumvent these problems, one of the approaches which have been attempted is electrolyte engineering. For instance, electrolytes with higher salt concentration, so called highly concentrated electrolytes, have been shown to suppress both dendrite growth and increase the Coulombic efficiency of metal anodes.[2,3] When different metal anode stabilization strategies are evaluated, it is common to perform galvanostatic cycling experiments in symmetric or asymmetric cells. This allows the cycling stability and Coulombic efficiency of the plating/stripping to be analyzed. Additionally, it is common to use features of the voltage profile as signatures on the mechanisms responsible for changes in electrochemical performance. For instance, a sharp decrease in (over)voltage during plating/stripping is a sign of a short circuit. A gradually increasing overvoltage during cycling on the other hand can be a result of continuous solid electrolyte interphase (SEI) buildup. However, several processes often occur in parallel when symmetric/asymmetric cells are cycled galvanostatically, each giving different contributions to the voltage profile which need to be deconvoluted to make sense of the data. In this contribution, we use three-electrode cells in combination with simple electrochemical experiments like cyclic voltammetry, chronoamperometry and chronopotentiometry to disentangle the contributions to different features in the galvanostatic voltage profiles of alkali metal anodes.In particular, we dissect the voltage profiles of potassium-copper (K-Cu) cells with highly concentrated electrolytes. Due to the higher reactivity of K compared to other alkali metals, certain features in the voltage profiles of these cells become exaggerated compared to lithium or sodium metal cells. We show that during galvanostatic deposition on a fresh Cu substrate, SEI formation and nucleation occur partly in parallel. If an SEI-formation step is performed prior to the galvanostatic deposition, a much sharper ‘nucleation peak’ in the voltage profile can be observed, indicative of the higher rate of nucleation that needs to occur in this case. Further, the potassium metal anode exhibits a steplike voltage profile from the second cycle and onwards. We confirm that this feature arises because bulk K is covered by a resistive native layer, whereas another type of, less resistive, interphase covers the freshly deposited K. This inhomogeneous interphase will inevitably promote preferential and inhomogeneous plating/stripping.

In-Situ Probing the Origin of Interfacial Instability of Na Metal Anode

The chemical-mechanical stability of solid–electrolyte interphase (SEI) is probably the most critical factor determining the performance of alkali metal anode (Li, Na, etc.) in secondary batteries. Although extensive advanced characterization methods have been carried out to study SEI layers of Na metal anode, including solid state nuclear magnetic resonance1, 2, cryogenic transmission electron microscopy3, etc., the structural/componential evolution of SEI is still an uncharted territory due to its transient formation process and complicated components. In this work, we systematically analyze the SEI formation and dissolution processes via jointly combining multiple in-situ characterization technologies. By revealing spatial-temporal resolved information of SEI evolution, the buried origin of chemical-mechanical instability of SEI in Na anode is further clarified, which provides valuable guidelines for SEI engineering. A dynamic SEI formation/dissolution model of Na metal anode is demonstrated as follow:Quantitative evaluation methods for the chemical instability (i.e., solubility) and mechanical instability (i.e., modulus) are designed. According to the mass variation in EQCM and the modulus measurement in in-situ AFM, we firstly quantitatively observe the chemical and mechanical stability evolution during SEI formation process.The dynamic evolution picture of SEI formation has been explicitly established. We discover the instantaneous electrochemical formation process of SEI is obviously divided into two stages based on the potential. It is revealed that the formation of efficient passivation layer anchored on Na surface during the 1st (passivating) stage (2.3 – 1 V vs Na/Na+) (Scheme 1 a-b) is the critical factor to construct stable SEI. In absence of passivation layer, the Na mental surface will trigger unrestricted electrolyte decomposition and homogenous components distribution during the subsequent (growing) stage.The dissolution model of SEI was revealed related to its spatial distribution of organics and inorganics. SEI with layered structure evolved from a compact passivation layer is found to have higher stability than that with homogenously distributed components. The inorganic species in the latter structure tend to detach from the SEI with the dissolution of organics, resulting in poor SEI chemical stability (Scheme 1 c and e). By contrast, SEIs with hierarchical structure growing based on the top of a passivation layer exhibits lower dissolution tendency (Scheme 1 d and f).The dynamic analysis of SEI evolution of Na anode presented in this work not only sheds light on how to construct a stable SEI, but also provides guiding significance in unveiling the seemingly complicated interfacial chemistry in batteries via a concerted characterization approach.References Gao, L.N., Chen, J.E., Chen, Q.L. et al. The chemical evolution of solid electrolyte interface in sodium metal batteries. Science Advances 8, 4606 (2022).Xiang, Y., Zheng, G., Liang, Z. et al. Visualizing the growth process of sodium microstructures in sodium batteries by in-situ 23Na MRI and NMR spectroscopy. Nat. Nanotechnol. 15, 883–890 (2020). Han, B., Zou, Y., Zhang, Z. et al. Probing the Na metal solid electrolyte interphase via cryo-transmission electron microscopy. Nat Commun 12, 3066 (2021). Figure 1

Advances in Electrochemical Energy Storage over Metallic Bismuth-Based Materials.

Bismuth (Bi) has been prompted many investigations into the development of next-generation energy storage systems on account of its unique physicochemical properties. Although there are still some challenges, the application of metallic Bi-based materials in the field of energy storage still has good prospects. Herein, we systematically review the application and development of metallic Bi-based anode in lithium ion batteries and beyond-lithium ion batteries. The reaction mechanism, modification methodologies and their relationship with electrochemical performance are discussed in detail. Additionally, owing to the unique physicochemical properties of Bi and Bi-based alloys, some innovative investigations of metallic Bi-based materials in alkali metal anode modification and sulfur cathodes are systematically summarized for the first time. Following the obtained insights, the main unsolved challenges and research directions are pointed out on the research trend and potential applications of the Bi-based materials in various energy storage fields in the future.

Interaction Mechanisms Between Nitrogen‐Containing Groups and Alkali Metals with Molecular Model System of HATCN**

AbstractTo enable the practical implementation of alkali metal batteries (AMBs), significant endeavors have been focused on enhancing the stability of alkali metal anodes (AMAs) using a range of strategies, such as optimizing electrolyte compositions, constructing anode deposition hosts, and establishing artificial protective layers. Despite significant progress in enhancing battery performance, limited attention has been given to comprehending the interaction mechanisms between alkali metals and protective materials, which is pivotal for the informed development of novel protective materials. Thus, aiming to enhance the comprehension of interaction processes between AMAs and organic protective materials containing various nitrogen groups, we conducted a mechanism study utilizing 1,4,5,8,9,11‐hexaazatriphenylenehexacarbonitrile (HATCN) as the model material, based on in‐situ x‐ray and ultraviolet photoelectron spectroscopy (XPS/UPS), and near edge x‐ray absorption fine structure (NEXAFS), as well as density functional theory (DFT) calculations. Through the investigation of interaction processes between HATCN and Li/Na, we find that Li or Na interacts with the two different nitrogen‐containing groups of HATCN in the same order: preferentially interacts with the inner imine groups of HATCN before interacting with the outer nitrile groups. Interestingly, our findings also reveal that the two distinct nitrogen‐containing groups exhibit a smaller difference in their sodiophilicity compared to their difference in lithiophilicity. These valuable insights shed light on the intricate interactions between nitrogen‐containing protective materials and AMAs, paving the way for the development of more effective protective materials in the future.

Green Ether Electrolytes for Sustainable High-voltage Potassium Ion Batteries.

Ether-based electrolytes are promising for secondary batteries due to their good compatibility with alkali metal anodes and high ionic conductivity. However, they suffer from poor oxidative stability and high toxicity, leading to severe electrolyte decomposition at high voltage and biosafety/environmental concerns when electrolyte leakage occurs. Here, we report a green ether solvent through a rational design of carbon-chain regulation to elicit steric hindrance, such a structure significantly reducing the solvent's biotoxicity and tuning the solvation structure of electrolytes. Notably, our solvent design is versatile, and an anion-dominated solvation structure is favored, facilitating a stable interphase formation on both the anode and cathode in potassium-ion batteries. Remarkably, the green ether-based electrolyte demonstrates excellent compatibility with K metal and graphite anode and a 4.2 V high-voltage cathode (200 cycles with average Coulombic efficiency of 99.64 %). This work points to a promising path toward the molecular design of green ether-based electrolytes for practical high-voltage potassium-ion batteries and other rechargeable batteries.

Green Ether Electrolytes for Sustainable High‐voltage Potassium Ion Batteries

AbstractEther‐based electrolytes are promising for secondary batteries due to their good compatibility with alkali metal anodes and high ionic conductivity. However, they suffer from poor oxidative stability and high toxicity, leading to severe electrolyte decomposition at high voltage and biosafety/environmental concerns when electrolyte leakage occurs. Here, we report a green ether solvent through a rational design of carbon‐chain regulation to elicit steric hindrance, such a structure significantly reducing the solvent‘s biotoxicity and tuning the solvation structure of electrolytes. Notably, our solvent design is versatile, and an anion‐dominated solvation structure is favored, facilitating a stable interphase formation on both the anode and cathode in potassium‐ion batteries. Remarkably, the green ether‐based electrolyte demonstrates excellent compatibility with K metal and graphite anode and a 4.2 V high‐voltage cathode (200 cycles with average Coulombic efficiency of 99.64 %). This work points to a promising path toward the molecular design of green ether‐based electrolytes for practical high‐voltage potassium‐ion batteries and other rechargeable batteries.

Nano to macro-scale elastic and plastic characteristics of calcium metal and implications for rechargeable battery applications

Multivalent metals (Ca, Mg, Al, etc.) are promising for anodes of rechargeable batteries owing to their high theoretical capacity that stems from multiple electron transfer per redox center. Among these multivalent metals, calcium exhibits a low electrochemical potential of −2.87 V (relative to the standard hydrogen electrode) and is the fifth most abundant element in the earth’s crust. In addition to resolving electrochemical issues, prior to practical use it remains critical to fully understand calcium’s mechanical properties to mitigate any potential degradation and failure mechanisms. To this end, we have conducted mechanical testing of Ca at the nano- and macro-scale through nanoindentation and bulk compression testing. Nanoindentation tests indicate an elastic modulus that ranges from 25.2 to 21.7 GPa and a hardness that ranges from 0.88 to 0.46 GPa as the indentation depth increases from 0.25 to 10 μm. Bulk compression tests show a yield strength of 107 ± 4.6 MPa (average ± standard deviation). These tests demonstrate a minimal sensitivity of calcium’s mechanical properties to strain rate or “size effects”, which differs from previous studies of alkali metal anodes, likely stemming from Ca’s relatively high melting point compared to the alkali metals. We conclude the manuscript by discussing the implications of these measured mechanical properties in the context of energy storage applications.

Ultrastable Sodium/Potassium Metal Anode Enabled by a Multifunctional Interphase Layer with Enhanced Ion Transport Kinetics

AbstractNa (K) metal batteries (NMB and KMB) have gained tremendous attention as large‐scale energy storage systems because of their high specific capacity, low working potential, and natural abundance. However, severe Na dendrite growth hinders the practical application of Na (K) anode. Here, a multifunctional interphase layer consisting of fast‐ion conductive Na–Bi (K–Bi) alloy and sodiophilic (potassiophilic) Na3VO4 (K3VO4) phases, which i derived from a spontaneous reaction (denoted as BVO@Na or BVO@K), is proposed and prepared. The designed electrode exhibits enhanced ion transport kinetics and homogenous Na (K) deposition behavior, and finally achieving dendrite‐free Na (K) growth. Accordingly, the BVO@Na displays a high Na plating/stripping reversibility of 960 h at 1.0 mA cm−2, 1.0 mAh cm−2, and the BVO@K electrode can be operated a cycle lifespan of 870 h under 1.0 mA cm−2, 2.0 mAh cm−2 in symmetric cells. In BVO@Na||Na3V2(PO4)3 full battery, it shows remarkable cycling stability (91% of capacity retention after 1900 cycles) and a high energy density of 281 Wh kg−1 at a power density of 16.2 kW kg−1. The findings lend credence to the prospect of the multifunctional interface layer contributing to the design of a protective layer for alkali metal anodes.

Fast cycling of “anode-less”, redox-mediated Li-S flow batteries

Redox flow batteries (RFBs) that incorporate solid energy-storing materials are attractive for high-capacity grid-scale energy storage due to their markedly higher theoretical energy densities compared to their fully liquid counterparts. However, this promise of higher energy density comes at the expense of rate capability. In this work we exploit a ZnO nanorod-decorated Ni foam scaffold to create a high surface area Li metal anode capable of rates up to 10 mA cm−2, a 10× improvement over traditional planar designs. The ZnO nanorods enhance Li metal wettability and promote uniform Li nucleation, allowing the RFB to be initially operated with a prelithiated (charged) anode, or with a safety-conscious, Li-less, fully discharged anode. 5 mgS cm−1 were cycled using a mediated S cathode, whereby redox mediators help oxidize and reduce solid S particles. At 2.4 mgS cm−2 and 10 mA cm−2, the RFB becomes limited by the mediation of solid S. Nevertheless, a respectable energy density of 20.3 Wh L−1 is demonstrated, allowing considerable increase if the S mediation rate can be further improved. Lessons learned here may be broadly applied to RFBs with alkali metal anodes, offering an avenue for safe, dense, grid-scale energy storage.

(Invited) Multi-Scale Implications of Material Heterogeneity on Solid State Battery Performance

Solid state batteries are comprised of an ensemble of materials with varying structural, mechanical, chemical, and transport properties1,2. Orchestrating these materials to act synergistically and enable high power and high energy densities requires understanding how solid state electrodes and electrolytes can be engineered to enable: (1) efficient ion and electron transport and (2) maintain uniform contact between components during electrochemical cycling. Bulk processing approaching (e.g. coating, sintering, densification, etc.) do not lead to much control over material properties across various length scales (nano-to-meso). Material heterogenities exist within the cathode, solid electrolyte, and anode. In the cathode, the solid electrolyte and active material can be non-uniformly distributed leading to bottlenecks for transport and non-uniform active material utilization. In the solid electrolyte, active and passive heterogenities can influence how the ion moves between the anode and cathode and cause deleterious current focusing dynamics3,4. Finally, at the anode voiding and contact loss can occur in alkali metal anodes. This talk discusses our recent work combining operando synchrotron studies, electrochemical characterization, and advanced material characterization to unravel the implications of heterogenity on performance and degradation mechanism in solid state batteries.[1] Zaman, Wahid, and Kelsey B. Hatzell. "Processing and manufacturing of next generation lithium-based all solid-state batteries." Current Opinion in Solid State and Materials Science 26.4 (2022): 101003.[2] Ren, Yuxun, and Kelsey B. Hatzell. "Elasticity-oriented design of solid-state batteries: challenges and perspectives." Journal of Materials Chemistry A 9.24 (2021): 13804-13821.[3]Dixit, Marm B., et al. "Polymorphism of garnet solid electrolytes and its implications for grain-level chemo-mechanics." Nature Materials 21.11 (2022): 1298-1305.[4]Ren, Yuxun, Nicholas Hortance, and Kelsey B. Hatzell. "Mitigating Chemo-Mechanical Failure in Li-S Solid State Batteries with Compliant Cathodes." Journal of The Electrochemical Society 169.6 (2022): 060503.

An Exploration of the Sodium Solid Electrolyte Interphase in Glyme Electrolytes with Carbonate Additives

The utilization of alkali metal anodes is hindered by an inherent instability in organic electrolytes. Sodium (Na) is of growing interest due to its high natural abundance, but the carbonate electrolytes that are popular in lithium systems are unable to form a stable solid electrolyte interphase (SEI) with a sodium metal electrode. However, the glyme (chain ether) electrolytes produce thin, predominantly inorganic SEI at sodium metal interfaces. Using half-cell and symmetric cell analysis, we identify diglyme (G2) as the best performing of the glymes, balancing the high nucleation barrier of the short glyme (G1) and the high plateau overpotential of the long glyme (G4). Based on mesoscale modeling, we capture the critical dependence of the nucleation and early-stage growth morphology on a competing set of mechanisms, including the reduction kinetics on the substrate/newly deposited Na and the surface mobility of these deposits. Through in situ optical microscopy, the onset and growth of Na dendrites is revealed in glyme electrolytes, and the addition of small quantities (~10% volume/volume) of ethylene carbonate (EC) and fluoroethylene carbonate (FEC) to G2 is shown to facilitate uniform sodium plating characteristics in the optical cell, presumably through alterations to SEI composition. X-ray photoelectron spectroscopy (XPS) analysis reveals that the FEC additive results in an SEI with similar atomic composition to that formed in G2 alone, whereas addition of EC to G2 results in an entirely different SEI composition, despite the molecular similarity of the carbonate additives. We have determined that the SEI formed by glyme alone may not support extensive or extreme cycling conditions, but the addition of FEC provides a much more robust SEI at the Na metal surface to facilitate numerous consistent sodium plating and stripping cycles.

Toward the Formation of the Solid Electrolyte Interphase on Alkaline Metal Anodes: Ab Initio Simulations**

AbstractThe transition from lithium‐based energy storage to post lithium systems plays a crucial part in achieving an environmentally sustainable energy infrastructure. Prime candidates for the replacement of lithium are sodium and potassium batteries. Despite being critical to battery performance, the solid electrolyte interphase (SEI) formation process for Na and K batteries remains insufficiently understood, especially compared to the well‐established lithium systems. Using ab initio molecular dynamics (AIMD) simulations based on density functional theory (DFT) calculations, we study the first steps of SEI formation upon the decomposition of typical solvent molecules on lithium, sodium and potassium metal anodes. We find that two dominant products form during the early SEI formation of cyclical carbonates on alkali metal anodes, carbon monoxide and alkali‐carbonate. The carbonate‐producing reaction is thermodynamically favorable for all tested metals, however, Na and K exhibit a much stronger selectivity than Li towards carbonate formation. Furthermore, we propose a previously unknown reaction mechanism for the CO polymerization on metallic lithium.

Unravelling the conductivity behaviour of thermally stable Li2O– Bi2O3–B2O3–P2O5 glasses embedded with V2O5

Solid state batteries are becoming more in demand owing to the advancement of EV technology. However, use of liquid electrolytes has become problematic due to their explosive nature. As a result, a lot of research is being done on solid electrolyte-based batteries (also known as “solid state batteries”) that employ glasses and alkali metal anodes consisting of Li+, Na+, K+. Herein we demonstrate the influence of V2O5 content on the conductivity characteristics along with their structural and thermal properties of melt-quenched V2O5-substituted lithium-bismuth-boro-phosphate glasses. The produced glasses were meticulously examined using XRD, FTIR, DTA, 11B-NMR, EPR, and impedance analyzer methods. Structural studies reveal the formation of non-crystalline/amorphous glasses having thermal stability up to 800 °C. Both FTIR and 11B-NMR results reveals the presence of borate groups, i.e., both BO4 and BO3. Additionally, EPR results exhibits hyperfine splitting of tetragonal V2O5, whose distortion varies with the content of V2O5 in the host glass. Furthermore, impedance and dielectric spectroscopy were used to explore the ac and dc conductivities in the frequency and temperature ranges 10 Hz - 3 MHz and 473–623 K respectively. The analyzed results show that both ac and dc conductivities increase with V2O5 content and the conductivity is more ionic in nature. Overall, the investigated results will enhance the fundamental understanding of conducting behaviour of glasses containing alkali and transition metal ions for the development of solid-state batteries.