Rechargeable Lithium Metal Batteries with an In-Built Solid-State Polymer Electrolyte and a High Voltage/Loading Ni-Rich Layered Cathode

Solvation Regulation Reinforces Anion-Derived Inorganic-Rich Interphase for High-Performance Quasi-Solid-State Li Metal Batteries

Solid-state polymer lithium metal batteries are an important strategy for achieving high safety and high energy density. However, the issue of Li dendrites and inherent inferior interface greatly restricts practical application. Herein, this study introduces tris(2,2,2-trifluoroethyl)phosphate solvent with moderate solvation ability, which can not only complex with Li+ to promote the in-situ ring-opening polymerization of 1,3-dioxolane (DOL), but also build solvated structure models to explore the effect of different solvation structures in the polymer electrolyte. Thereinto, it is dominated by the contact ion pair solvated structure with pDOL chain segments forming less lithium bonds, exhibiting faster kinetic process and constructing a robust anion-derived inorganic-rich interphase, which significantly improves the utilization rate of active Li and the high-voltage resistance of pDOL. As a result, it exhibits stable cycling at ultra-high areal capacity of 20 mAh cm-2 in half cells, and an ultra-long lifetime of over 2000 h in symmetric cells can be realized. Furthermore, matched with LiNi0.9Co0.05Mn0.05O2 cathode, the capacity retention after 60 cycles is as high as 96.8% at N/P value of 3.33. Remarkably, 0.7 Ah Li||LiNi0.9Co0.05Mn0.05O2 pouch cell with an energy density of 461 Wh kg-1 can be stably cycled for five cycles at 100% depth of discharge.

Perspective on Lewis Acid-Base Interactions in Emerging Batteries

Lewis acid-base interactions are common in chemical processes presented in diverse applications, such as synthesis, catalysis, batteries, semiconductors, and solar cells. The Lewis acid-base interactions allow precise tuning of material properties from the molecular level to more aggregated and organized structures. This review will focus on the origin, development, and prospects of applying Lewis acid-base interactions for the materials design and mechanism understanding in the advancement of battery materials and chemistries. The covered topics relate to aqueous batteries, lithium-ion batteries, solid-state batteries, alkali metal-sulfur batteries, and alkali metal-oxygen batteries. In this review, the Lewis acid-base theories will be first introduced. Thereafter the application strategies for Lewis acid-base interactions in solid-state and liquid-based batteries will be introduced from the aspects of liquid electrolyte, solid polymer electrolyte, metal anodes, and high-capacity cathodes. The underlying mechanism is highlighted in regard to ion transport, electrochemical stability, mechanical property, reaction kinetics, dendrite growth, corrosion, and so on. Last but not least, perspectives on the future directions related to Lewis acid-base interactions for next-generation batteries are like to be shared.

Interface Modifications of Lithium Metal Anode for Lithium Metal Batteries

Lithium metal batteries (LMBs) enable much higher energy density than lithium-ion batteries (LIBs) and thus hold great promise for future transportation electrification. However, the adoption of lithium metal (Li) as an anode poses serious concerns about cell safety and performance, which has been hindering LMBs from commercialization. To this end, extensive effort has been invested in understanding the underlying mechanisms theoretically and experimentally and developing technical solutions. In this review, we devote to providing a comprehensive review of the challenges, characterizations, and interfacial engineering of Li anodes in both liquid and solid LMBs. We expect that this work will stimulate new efforts and help peer researchers find new solutions for the commercialization of LMBs.

Alleviating Structure Collapse of Polycrystalline LiNixCoyMn1-x-yO2 via Surface Co Enrichment

The structure collapse issues have long restricted the application of polycrystalline LiNixCoyMn1-x-yO2 (NCM) at high voltages beyond 4.4 V vs Li/Li+. Herein, for LiNi0.55Co0.12Mn0.33O2 (P-NCM), rapid surface degradation is observed upon the first charge, along with serious particle fragmentation upon repeated cycles. To alleviate these issues, a surface Co enrichment strategy is proposed [i.e., Co-enriched NCM (C-NCM)], which promotes the in situ formation of a robust surface rock-salt (RS) layer upon charge, serving as a highly stable interface for effective Li+ migration. Benefiting from this stabilized surface RS layer, Li+ extraction occurs mainly through this surface RS layer, rather than along the grain boundaries (GBs), thus reducing the risk of GBs' cracking and even particle fragmentation upon cycles. Besides, O loss and TM (TM = Ni, Co, and Mn) dissolution are also effectively reduced with fewer side reactions. The C-NCM/graphite cell presents a highly reversible capacity of 205.1 mA h g-1 at 0.2 C and a high capacity retention of 86% after 500 cycles at 1 C (1 C = 200 mA g-1), which is among the best reported cell performances. This work provides a different path for alleviating particle fragmentation of NCM cathodes.

In Situ Polymerization Facilitating Practical High-Safety Quasi-Solid-State Batteries

Quasi-solid-state batteries (QSSBs) are gaining widespread attention as a promising solution to improve battery safety performance. However, the safety improvement and the underlying mechanisms of QSSBs remain elusive. Herein, a novel strategy combining high-safety ethylene carbonate-free liquid electrolyte and in situ polymerization technique is proposed to prepare practical QSSBs. The Ah-level QSSBs with LiNi0.83Co0.11Mn0.06O2 cathode and graphite-silicon anode demonstrate significantly improved safety features without sacrificing electrochemical performance. As evidenced by accelerating rate calorimetry tests, the QSSBs exhibit increased self-heating temperature and onset temperature (T2), and decreased temperature rise rate during thermal runaway (TR). The T2 has a maximum increase of 48.4 °C compared to the conventional liquid batteries. Moreover, the QSSBs do not undergo TR until 180 °C (even 200 °C) during the hot-box tests, presenting significant improvement compared to the liquid batteries that run into TR at 130 °C. Systematic investigations show that the in situ formed polymer skeleton effectively mitigates the exothermic reactions between lithium salts and lithiated anode, retards the oxygen release from cathode, and inhibits crosstalk reactions between cathode and anode at elevated temperatures. The findings offer an innovative solution for practical high-safety QSSBs and open up a new sight for building safer high-energy-density batteries.

In Situ-Initiated Poly-1,3-dioxolane Gel Electrolyte for High-Voltage Lithium Metal Batteries

To realize high-energy-density Li metal batteries at low temperatures, a new electrolyte is needed to solve the high-voltage compatibility and fast lithium-ion de-solvation process. A gel polymer electrolyte with a small-molecular-weight polymer is widely investigated by combining the merits of a solid polymer electrolyte (SPE) and liquid electrolyte (LE). Herein, we present a new gel polymer electrolyte (P-DOL) by the lithium difluoro(oxalate)borate (LiDFOB)-initiated polymerization process using 1,3-dioxolane (DOL) as a monomer solvent. The P-DOL presents excellent ionic conductivity (1.12 × 10-4 S cm-1) at -20 °C, with an oxidation potential of 4.8 V. The Li‖LiCoO2 cell stably cycled at 4.3 V under room temperature, with a discharge capacity of 130 mAh g-1 at 0.5 C and a capacity retention rate of 86.4% after 50 cycles. Moreover, a high-Ni-content LiNi0.8Co0.1Mn0.1O2 (NCM811) cell can steadily run for 120 cycles at -20 °C, with a capacity retention of 88.4%. The underlying mechanism of high-voltage compatibility originates from the dense and robust B- and F-rich cathode interface layer (CEI) formed at the cathode interface. Our report will shed light on the real application of Li metal batteries under all-climate conditions in the future.

Long-cycling and High-voltage Solid State Lithium Metal Batteries Enabled by Fluorinated and Crosslinked Polyether Electrolytes

Solid-state lithium metal batteries (LMBs), constructed through the in situ fabrication of polymer electrolytes, are considered a critical strategy for the next-generation battery systems with high energy density and enhanced safety. However, the constrained oxidation stability of polymers, such as the extensively utilized polyethers, limits their applications in high-voltage batteries and further energy density improvements. Herein, an in situ fabricated fluorinated and crosslinked polyether-based gel polymer electrolyte, FGPE, is presented, exhibiting a high oxidation potential (5.1 V). The fluorinated polyether significantly improves compatibility with both lithium metal and high-voltage cathode, attributed to the electron-withdrawing -CF3 group and the generated LiF-rich electrolyte/electrode interphase. Consequently, the solid-state Li||LiNi0.6Co0.2Mn0.2O2 batteries employing FGPE demonstrate exceptional cycling performances of 1000 cycles with 78 % retention, representing one of the best results ever reported for polymer electrolytes. Moreover, FGPE enables batteries to operate at 4.7 V, realizing the highest operating voltage of polyether-based batteries to date. Notably, our designed in situ FGPE provides the solid-state batteries with exceptional cycling stability even at practical conditions, including high cathode loading (21 mg cm-2) and industry-level 18650-type cylindrical cells (1.3 Ah, 500 cycles). This work provides critical insights into the development of oxidation-stable polymer electrolytes and the advancement of practical high-voltage LMBs.

From Liquid to Solid-State Batteries: Li-Rich Mn-Based Layered Oxides as Emerging Cathodes with High Energy Density

Li-rich Mn-based (LRMO) cathode materials have attracted widespread attention due to their high specific capacity, energy density, and cost-effectiveness. However, challenges such as poor cycling stability, voltage deca,y and oxygen escape limit their commercial application in liquid Li-ion batteries. Consequently, there is a growing interest in the development of safe and resilient all-solid-state batteries (ASSBs), driven by their remarkable safety features and superior energy density. ASSBs based on LRMO cathodes offer distinct advantages over conventional liquid Li-ion batteries, including long-term cycle stability, thermal and wider electrochemical windows stability, as well as the prevention of transition metal dissolution. This review aims to recapitulate the challenges and fundamental understanding associated with the application of LRMO cathodes in ASSBs. Additionally, it proposes the mechanisms of interfacial mechanical and chemical instability, introduces noteworthy strategies to enhance oxygen redox reversibility, enhances high-voltage interfacial stability, and optimizes Li+ transfer kinetics. Furthermore, it suggests potential research approaches to facilitate the large-scale implementation of LRMO cathodes in ASSBs.

Computational approach inspired advancements of solid-state electrolytes for lithium secondary batteries: from first-principles to machine learning

The increasing demand for high-security, high-performance, and low-cost energy storage systems (EESs) driven by the adoption of renewable energy is gradually surpassing the capabilities of commercial lithium-ion batteries (LIBs). Solid-state electrolytes (SSEs), including inorganics, polymers, and composites, have emerged as promising candidates for next-generation all-solid-state batteries (ASSBs). ASSBs offer higher theoretical energy densities, improved safety, and extended cyclic stability, making them increasingly popular in academia and industry. However, the commercialization of ASSBs still faces significant challenges, such as unsatisfactory interfacial resistance and rapid dendrite growth. To overcome these problems, a thorough understanding of the complex chemical-electrochemical-mechanical interactions of SSE materials is essential. Recently, computational methods have played a vital role in revealing the fundamental mechanisms associated with SSEs and accelerating their development, ranging from atomistic first-principles calculations, molecular dynamic simulations, multiphysics modeling, to machine learning approaches. These methods enable the prediction of intrinsic properties and interfacial stability, investigation of material degradation, and exploration of topological design, among other factors. In this comprehensive review, we provide an overview of different numerical methods used in SSE research. We discuss the current state of knowledge in numerical auxiliary approaches, with a particular focus on machine learning-enabled methods, for the understanding of multiphysics-couplings of SSEs at various spatial and time scales. Additionally, we highlight insights and prospects for SSE advancements. This review serves as a valuable resource for researchers and industry professionals working with energy storage systems and computational modeling and offers perspectives on the future directions of SSE development.

PDOL-Based Solid Electrolyte Toward Practical Application: Opportunities and Challenges

Polymer solid-state lithium batteries (SSLB) are regarded as a promising energy storage technology to meet growing demand due to their high energy density and safety. Ion conductivity, interface stability and battery assembly process are still the main challenges to hurdle the commercialization of SSLB. As the main component of SSLB, poly(1,3-dioxolane) (PDOL)-based solid polymer electrolytes polymerized in-situ are becoming a promising candidate solid electrolyte, for their high ion conductivity at room temperature, good battery electrochemical performances, and simple assembly process. This review analyzes opportunities and challenges of PDOL electrolytes toward practical application for polymer SSLB. The focuses include exploring the polymerization mechanism of DOL, the performance of PDOL composite electrolytes, and the application of PDOL. Furthermore, we provide a perspective on future research directions that need to be emphasized for commercialization of PDOL-based electrolytes in SSLB. The exploration of these schemes facilitates a comprehensive and profound understanding of PDOL-based polymer electrolyte and provides new research ideas to boost them toward practical application in solid-state batteries.

Contributing to the Revolution of Electrolyte Systems via In Situ Polymerization at Different Scales: A Review

Solid-state batteries have become the most anticipated option for compatibility with high-energy density and safety. In situ polymerization, a novel strategy for the construction of solid-state systems, has extended its application from solid polymer electrolyte systems to other solid-state systems. This review summarizes the application of in situ polymerization strategies in solid-state batteries, which covers the construction of polymer, the formation of the electrolyte system, and the design of the full cell. For the polymer skeleton, multiple components and structures are being chosen. In the construction of solid polymer electrolyte systems, the choice of initiator for in situ polymerization is the focus of this review. New initiators, represented by lithium salts and additives, are the preferred choice because of their ability to play more diverse roles, while the coordination with other components can also improve the electrical properties of the system and introduce functionalities. In the construction of entire solid-state battery systems, the application of in situ polymerization to structure construction, interface construction, and the use of separators with multiplex functions has brought more possibilities for the development of various solid-state systems and even the perpetuation of liquid electrolytes.

Enabling Scalable Polymer Electrolyte with Dual-Reinforced Stable Interface for 4.5 V Lithium-Metal Batteries

Hitherto, it remains a great challenge to stabilize electrolyte-electrode interfaces and impede lithium dendrite proliferation in lithium-metal batteries with high-capacity nickel-rich LiNx Coy Mn1- x-y O2 (NCM) layer cathodes. Herein, a special molecular-level-designed polymer electrolyte is prepared by the copolymerization of hexafluorobutyl acrylate and methylene bisacrylamide to construct dual-reinforced stable interfaces. Verified by X-ray photoelectron spectroscopy depth profiling, there are favorable solid electrolyte interphase (SEI) layers on Li metal anodes and robust cathode electrolyte interphase (CEI) on Ni-rich cathodes. The SEI enriched in lithiophilic N-(C)3 guides the homogenous distribution of Li+ and facilitates the transport of Li+ through LiF and Li3 N, promoting uniform Li+ plating and stripping. Moreover, the CEI with antioxidative amide groups can suppress the parasitic reactions between cathode and electrolyte and the structural degradation of cathode. Meanwhile, a unique two-stage rheology-tuning UV polymerization strategy is utilized, which is quite suited for continuous electrolyte fabrication with environmental friendliness. The fabricated polymer electrolyte exhibits a high ionic conductivity of 1.01 mS cm-1 at room temperature. 4.5 V NCM622//Li batteries achieve prolonged operation with a retention rate of 85.0% after 500 cycles at 0.5 C. This work provides new insights into molecular design and processibility design for polymer-based high-voltage batteries.

Hybrid Crosslinked Solid Polymer Electrolyte via In-Situ Solidification Enables High-Performance Solid-State Lithium Metal Batteries

Solid-state lithium-metal batteries constructed by in-situ solidification of cyclic ether are considered to be a critical strategy for the next generation of solid-state batteries with high energy density and safety. However, the poor thermal/electrochemical stability of linear polyethers and severe interfacial reactions limit its further development. Herein, in-situ ring-opening hybrid crosslinked polymerization is proposed for organic/inorganic hybrid polymer electrolyte (HCPE) with superior ionic conductivity of 2.22 × 10-3 S cm-1 at 30 °C, ultrahigh Li+ transference number of 0.88, and wide electrochemical stability window of 5.2 V. These allow highly stable lithium stripping/plating cycling for over 1000 h at 1 mA cm-2 , which also reveal a well-defined interfacial stabilization mechanism. Thus, HCPE endows assembled solid-state lithium-metal batteries with excellent long-cycle performance over 600 cycles at 2 C (25 °C) and superior capacity retention of 92.1%. More importantly, the proposed noncombustible HCPE opens up a new frontier to promote the practical application of high safety and high energy density solid-state batteries via in-situ solidification.

Efficiencies of Various in situ Polymerizations of Liquid Electrolytes and the Practical Implications for Quasi Solid-state Batteries

In situ polymerization of liquid electrolytes is currently the most feasible way for constructing solid-state batteries, which, however, is affected by various interfering factors of reactions and so the electrochemical performance of cells. To disclose the effects from polymerization conditions, two types of generally used in situ polymerizing reactions of ring-opening polymerization (ROP) and double bond radical polymerization (DBRP) were investigated on the aspects of monomer conversion and electrochemical properties (Li+ -conductivity and interfacial stability). The ROP generated poly-ester and poly-carbonate show a high monomer conversion of ≈90 %, but suffer a poor Li+ -conductivity of lower than 2×10-5  S cm-1 at room temperature (RT). Additionally, the terminal alkoxy anion derived from the ROP is not resistant to high-voltage cathodes. While, the DBRP produced poly-VEC(vinyl ethylene carbonate) and poly-VC(vinylene carbonate) show lower monomer conversions of 50-80 %, delivering relatively higher Li+ -conductivities of 2×10-4  S cm-1 at RT. Compared two polymerizing reactions and four monomers, the VEC-based F-containing copolymer possesses advantages in Li+ -conductivity and antioxidant capacity, which also shows simultaneous stability towards Li-metal with the help of LiF-based passivating layer, allowing a long-term stable cycling of high-voltage quasi solid-state cells.

A Thin Composite Polymer Electrolyte Functionalized by a Novel Antihydrolysis Additive to Enable All-Solid-State Lithium Battery with Excellent Rate and Cycle Performance

Composite solid-state electrolyte (CSE) incorporated with fluorine-containing functional additives usually endows the assembled cell with improved electrochemical performance by forming stable electrode/electrolyte interfaces. However, most of fluorine-containing additives are prone to hydrolysis, which is not suitable for the large-scale preparation of CSEs. In this work, an antihydrolysis and fluorine-containing additive of magnesium 2,3,4,5,6-pentafluorophenylacetate (MgPFPAA) is successfully synthesized and then used to regulate the properties of the electrode/electrolyte interfaces of the all-solid-state lithium batteries (ASSLBs). The antihydrolysis property of MgPFPAA facilitates the large-scale preparation of the ultrathin CSEs in atmospheric environment. Both theoretical calculations and experimental results indicate that MgPFPAA can effectively improve the composition and structure of the generated solid electrolyte interface film by providing rich F sources and Mg2+ , thus leading to a stable CSE/Li interface. Furthermore, an ultrathin PEO/PVDF-based CSE (≈30 µm) functionalized by this novel MgPFPAA additive enables the assembled LiFePO4 -based ASSLB with greatly enhanced electrochemical performances, with high discharge specific capacity of 93.7 mAh g-1 at 10 C and a high capacity retention of 74.9% after 1500 cycles at 5.0 C. Also, this MgPFPAA functionalized CSE can be compatible with the high-areal-capacity LiFePO4 and the high-voltage LiNi0.8 Co0.1 Mn0.1 O2 cathodes.

In-Situ-Polymerized 1,3-Dioxolane Solid-State Electrolyte with Space-Confined Plasticizers for High-Voltage and Robust Li/LiCoO2 Batteries

In-situ-polymerized solid-state electrolytes can significantly improve the interfacial compatibility of Li metal batteries. Typically, in-situ-polymerized 1,3-dioxolane electrolyte (PDOL) exhibits good compatibility with Li metal. However, it still suffers from the narrow electrochemical window (4.1 V), limiting the application of high-voltage cathodes. Herein, a novel modified PDOL (PDOL-F/S) electrolyte with an expanded electrochemical window of 4.43 V and a considerable ionic conductivity of 1.95 × 10-4 S cm-1 is developed by introducing high-voltage stable plasticizers (fluoroethylene carbonate and succinonitrile) to its polymer network. The space-confined plasticizers are beneficial to construct a high-quality cathode-electrolyte interphase, hindering the decomposition of lithium salts and polymers in electrolytes at high voltage. The as-assembled Li|PDOL-F/S|LiCoO2 battery delivers superior cycling stability (capacity retention of 80% after 400 cycles) at 4.3 V, superior to that of pristine PDOL (3% after 120 cycles). This work provides new insights into the design and application of high-voltage solid-state lithium metal batteries by in situ polymerization.

Diagnosing and Correcting the Failure of the Solid-State Polymer Electrolyte for Enhancing Solid-State Lithium-Sulfur Batteries

Solid-state polymer electrolytes (SPEs) attract great interest in developing high-performance yet reliable solid-state batteries. However, understanding of the failure mechanism of the SPE and SPE-based solid-state batteries remains in its infancy, posing a great barrier to practical solid-state batteries. Herein, the high accumulation and clogging of "dead" lithium polysulfides (LiPS) on the interface between the cathode and SPE with intrinsic diffusion limitation is identified as a critical failure cause of SPE-based solid-state Li-S batteries. It induces a poorly reversible chemical environment with retarded kinetics on the cathode-SPE interface and in bulk SPEs, starving the Li-S redox in solid-state cells. This observation is different from the case in liquid electrolytes with free solvent and charge carriers, where LiPS dissolve but remain alive for electrochemical/chemical redox without interfacial clogging. Electrocatalysis demonstrates the feasibility of tailoring the chemical environment in diffusion-restricted reaction media for reducing Li-S redox failure in the SPE. It enables Ah-level solid-state Li-S pouch cells with a high specific energy of 343 Wh kg^-1 on the cell level. This work may shed new light on the understanding of the failure mechanism of SPE for bottom-up improvement of solid-state Li-S batteries.

Natural Pyranosyl Materials: Potential Applications in Solid-State Batteries

Solid-state batteries have become one of the hottest research areas today, due to the use of solid-state electrolytes enabling the high safety and energy density. Because of the interaction with electrolyte salts and the abundant ion transport sites, natural polysaccharide polymers with rich functional groups such as -OH, -OR or -COO^- etc. have been applied in solid-state electrolytes and have the merits of possibly high ionic conductivity and sustainability. This review summarizes the recent progress of natural polysaccharides and derivatives for polymer electrolytes, which will stimulate further interest in the application of polysaccharides for solid-state batteries.

Durable and Adjustable Interfacial Engineering of Polymeric Electrolytes for Both Stable Ni-Rich Cathodes and High-Energy Metal Anodes

Achieving stable cycling of high-voltage solid-state lithium metal batteries is crucial for next-generation rechargeable batteries with high energy density and high safety. However, the complicated interface problems in both cathode/anode electrodes preclude their practical applications hitherto. Herein, to simultaneously solve such interfacial limitations and obtain sufficient Li⁺ conductivity in the electrolyte, an ultrathin and adjustable interface is developed at the cathode side through a convenient surface in situ polymerization (SIP), achieving a durable high-voltage tolerance and Li-dendrite inhibition. The integrated interfacial engineering fabricates a homogeneous solid electrolyte with optimized interfacial interactions that contributes to tame the interfacial compatibility between LiNi_x Co_y Mn_z O₂ and polymeric electrolyte accompanied by anticorrosion of aluminum current collector. Further, the SIP enables a uniform adjustment of solid electrolyte composition by dissolving additives such as Na⁺ and K⁺ salts, which presents prominent cyclability in symmetric Li cells (>300 cycles at 5 mA cm^-2 ). The assembled LiNi_0.8 Co_0.1 Mn_0.1 O₂ (4.3 V)||Li batteries show excellent cycle life with high Coulombic efficiencies (>99%). This SIP strategy is also investigated and verified in sodium metal batteries. It opens a new frontier for solid electrolytes toward high-voltage and high-energy metal battery technologies.

Effective transport network driven by tortuosity gradient enables high-electrochem-active solid-state batteries

Simultaneously achieving high electrochemical activity and high loading for solid-state batteries has been hindered by slow ion transport within solid electrodes, in particular with an increase in electrode thickness. Ion transport governed by 'point-to-point' diffusion inside a solid-state electrode is challenging, but still remains elusive. Herein, synchronized electrochemical analysis using X-ray tomography and ptychography reveals new insights into the nature of slow ion transport in solid-state electrodes. Thickness-dependent delithiation kinetics are spatially probed to identify that low-delithiation kinetics originate from the high tortuous and slow longitudinal transport pathways. By fabricating a tortuosity-gradient electrode to create an effective ion-percolation network, the tortuosity-gradient electrode architecture promotes fast charge transport, migrates the heterogeneous solid-state reaction, enhances electrochemical activity and extends cycle life in thick solid-state electrodes. These findings establish effective transport pathways as key design principles for realizing the promise of solid-state high-loading cathodes.

Tailoring polymer electrolyte ionic conductivity for production of low- temperature operating quasi-all-solid-state lithium metal batteries

The stable operation of lithium-based batteries at low temperatures is critical for applications in cold climates. However, low-temperature operations are plagued by insufficient dynamics in the bulk of the electrolyte and at electrode|electrolyte interfaces. Here, we report a quasi-solid-state polymer electrolyte with an ionic conductivity of 2.2 × 10^-4 S cm^-1 at -20 °C. The electrolyte is prepared via in situ polymerization using a 1,3,5-trioxane-based precursor. The polymer-based electrolyte enables a dual-layered solid electrolyte interphase formation on the Li metal electrode and stabilizes the LiNi_0.8Co_0.1Mn_0.1O₂-based positive electrode, thus improving interfacial charge-transfer at low temperatures. Consequently, the growth of dendrites at the lithium metal electrode is hindered, thus enabling stable Li||LiNi_0.8Co_0.1Mn_0.1O₂ coin and pouch cell operation even at -30 °C. In particular, we report a Li||LiNi_0.8Co_0.1Mn_0.1O₂ coin cell cycled at -20 °C and 20 mA g^-1 capable of retaining more than 75% (i.e., around 151 mAh g^-1) of its first discharge capacity cycle at 30 °C and same specific current.

Molecular Self-Assembled Ether-Based Polyrotaxane Solid Electrolyte for Lithium Metal Batteries

Poly(ethylene oxide) has been widely investigated as a potential separator for solid-state lithium metal batteries. However, its applications were significantly restricted by low ionic conductivity and a narrow electrochemical stability window (<4.0 V vs Li/Li⁺) at room temperature. Herein, a novel molecular self-assembled ether-based polyrotaxane electrolyte was designed using different functional units and prepared by threading cyclic 18-crown ether-6 (18C6) to linear poly(ethylene glycol) (PEG) via intermolecular hydrogen bond and terminating with hexamethylene diisocyanate trimer (HDIt), which was strongly confirmed by local structure-sensitive solid/liquid-state nuclear magnetic resonance (NMR) techniques. The designed electrolyte has shown an obviously increased room-temperature ionic conductivity of 3.48 × 10^-4 S cm^-1 compared to 1.12 × 10^-5 S cm^-1 without assembling polyrotaxane functional units, contributing to the enhanced cycling stability of batteries with both LiFePO₄ and LiNi_0.8Co_0.15Al_0.05O₂ cathode materials. This advanced molecular self-assembled strategy provides a new paradigm in designing solid polymer electrolytes with demanded performance for lithium metal batteries.

Dual fluorination of polymer electrolyte and conversion-type cathode for high-capacity all-solid-state lithium metal batteries

All-solid-state batteries are appealing electrochemical energy storage devices because of their high energy content and safety. However, their practical development is hindered by inadequate cycling performances due to poor reaction reversibility, electrolyte thickening and electrode passivation. Here, to circumvent these issues, we propose a fluorination strategy for the positive electrode and solid polymeric electrolyte. We develop thin laminated all-solid-state Li||FeF3 lab-scale cells capable of delivering an initial specific discharge capacity of about 600 mAh/g at 700 mA/g and a final capacity of about 200 mAh/g after 900 cycles at 60 °C. We demonstrate that the polymer electrolyte containing AlF3 particles enables a Li-ion transference number of 0.67 at 60 °C. The fluorinated polymeric solid electrolyte favours the formation of ionically conductive components in the Li metal electrode's solid electrolyte interphase, also hindering dendritic growth. Furthermore, the F-rich solid electrolyte facilitates the Li-ion storage reversibility of the FeF3-based positive electrode and decreases the interfacial resistances and polarizations at both electrodes.

Constructing an In Situ Polymer Electrolyte and a Na-Rich Artificial SEI Layer toward Practical Solid-State Na Metal Batteries

Sodium is one of the most promising anode candidates for the beyond-lithium-ion batteries. The development of Na metal batteries with a high energy density, high safety, and low cost is desirable to meet the requirements of both portable and stationary electrical energy storage. However, several problems caused by the unstable Na metal anode and the unsafe liquid electrolyte severely hinder their practical applications. Herein, we report a facile but effective methodology to construct an in situ polymer electrolyte and Na-rich artificial solid-electrolyte interface (SEI) layer concurrently. The obtained integrated Na metal batteries display long cycling life and admirable dynamic performance with total inhibition of dendrites, excellent contact of the cathode/polymer electrolyte, and reduction of side reactions during cycling. The modified Na metal electrode with the in situ polymer electrolyte is stable and dendrite-free in repeated plating/stripping processes with a life span of above 1000 h. Moreover, this method is compatible with different cathodes that demonstrate outstanding electrochemical performance in full cells. We believe that this approach provides a practical solution to solid-state Na metal batteries.

Research Progress and Perspective on Lithium/Sodium Metal Anodes for Next-Generation Rechargeable Batteries

With the development of consumer electronic devices and electric vehicles, lithium-ion batteries (LIBs) are vital components for high energy storage with great impact on our modern life. However, LIBs still cannot meet all the essential demands of rapidly growing new industries. In pursuance of higher energy requirement, metal batteries (MBs) are the next-generation high-energy-density devices. Li/Na metals are considered as an ideal anode for high-energy batteries due to extremely high theoretical specific capacity (3860 and 1165 mAh g^-1 for Li and Na, respectively) and low electrochemical potential (-3.04 V for Li and -2.71 V for Na vs. standard hydrogen electrode). Unfortunately, uncontrolled dendrite growth, high reactivity, and infinite volume change induce severe safety concerns and poor cycle efficiency during their application. Consequently, MBs are far from commercialization stage. This Review represents a comprehensive overview of failure mechanism of lithium/sodium metal anode and its progress for rechargeable batteries through (i) electrolyte optimization, (ii) artificial solid-electrolyte interphase (SEI) layer formation, and (iii) nanoengineering at materials level in current collector, anode, and host. The challenges in current MBs research and potential applications of lithium/sodium metal anodes are also outlined and summarized.

Challenges and Modification Strategies of Ni-Rich Cathode Materials Operating at High-Voltage

Ni-rich cathode materials have become promising candidates for lithium-based automotive batteries due to the obvious advantage of electrochemical performance. Increasing the operating voltage is an effective means to obtain a higher specific capacity, which also helps to achieve the goal of high energy density (capacity × voltage) of power lithium-ion batteries (LIBs). However, under high operating voltage, surface degradation will occur between Ni-rich cathode materials and the electrolytes, forming a solid interface film with high resistance, releasing O₂, CO₂ and other gases. Ni-rich cathode materials have serious cation mixing, resulting in an adverse phase transition. In addition, the high working voltage will cause microcracks, leading to contact failure and repeated surface reactions. In order to solve the above problems, researchers have proposed many modification methods to deal with the decline of electrochemical performance for Ni-rich cathode materials under high voltage such as element doping, surface coating, single-crystal fabrication, structural design and multifunctional electrolyte additives. This review mainly introduces the challenges and modification strategies for Ni-rich cathode materials under high voltage operation. The future application and development trend of Ni-rich cathode materials for high specific energy LIBs are projected.

Stabilizing the Li1.3 Al0.3 Ti1.7 (PO4 )3 |Li Interface for High Efficiency and Long Lifespan Quasi-Solid-State Lithium Metal Batteries

To tackle the poor chemical/electrochemical stability of Li_1+x Al_x Ti_2-x (PO₄ )₃ (LATP) against Li and poor electrode|electrolyte interfacial contact, a thin poly[2,3-bis(2,2,6,6-tetramethylpiperidine-N-oxycarbonyl)norbornene] (PTNB) protection layer is applied with a small amount of ionic liquid electrolyte (ILE). This enables study of the impact of ILEs with modulated composition, such as 0.3 lithium bis(fluoromethanesulfonyl)imide (LiFSI)-0.7 N-butyl-N-methylpyrrolidinium bis(fluoromethanesulfonyl)imide (Pyr₁₄ FSI) and 0.3 LiFSI-0.35 Pyr₁₄ FSI-0.35 N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄ TFSI), on the interfacial stability of PTNB@Li||PTNB@Li and PTNB@Li||LiNi_0.8 Co_0.1 Mn_0.1 O₂ cells. The addition of Pyr₁₄ TFSI leads to better thermal and electrochemical stability. Furthermore, Pyr₁₄ TFSI facilitates the formation of a more stable Li|hybrid electrolyte interface, as verified by the absence of lithium "pitting corrosion islands" and fibrous dendrites, leading to a substantially extended lithium stripping-plating cycling lifetime (>900 h). Even after 500 cycles (0.5C), PTNB@Li||LiNi_0.8 Co_0.1 Mn_0.1 O₂ cells achieve an impressive capacity retention of 89.1 % and an average Coulombic efficiency of 98.6 %. These findings reveal a feasible strategy to enhance the interfacial stability between Li and LATP by selectively mixing different ionic liquids.

Toward Sustainable Solid Polymer Electrolytes for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are the most widely used energy storage system because of their high energy density and power, robustness, and reversibility, but they typically include an electrolyte solution composed of flammable organic solvents, leading to safety risks and reliability concerns for high-energy-density batteries. A step forward in Li-ion technology is the development of solid-state batteries suitable in terms of energy density and safety for the next generation of smart, safe, and high-performance batteries. Solid-state batteries can be developed on the basis of a solid polymer electrolyte (SPE) that may rely on natural polymers in order to replace synthetic ones, thereby taking into account environmental concerns. This work provides a perspective on current state-of-the-art sustainable SPEs for lithium-ion batteries. The recent developments are presented with a focus on natural polymers and their relevant properties in the context of battery applications. In addition, the ionic conductivity values and battery performance of natural polymer-based SPEs are reported, and it is shown that sustainable SPEs can become essential components of a next generation of high-performance solid-state batteries synergistically focused on performance, sustainability, and circular economy considerations.

Facile, Atom-Economic, Chemical Thinning Strategy for Ultrathin Lithium Foils

Metallic lithium is considered as the ultimate anode material for lithium-based batteries due to its highest energy density. However, as an anode, commercial Li metal foils are too thick, with a large amount of trouble to balance its exorbitant areal capacity with common cathodes in full cells. Here, a new chemical thinning strategy is proposed via a simple surface dissolving reaction between lithium and naphthalene, which enables scalable, continuous, and roll-to-roll preparation of ultrathin Li foil. A Li foil less than 15 μm with a clean surface can be successfully obtained within 20 min. The thinning rate and thickness of the lithium foil can be easily adjusted by changing the concentration, temperature, and operation mode. The produced Li-Naph solution after thinning can also be used as a multifunctional reagent of great value, and the Li ions in the final waste solution can be further extracted in the form of Li₂CO₃, showing superior lithium atom economy of our strategy.

Self-Healing Polymer Electrolyte for Dendrite-Free Li Metal Batteries with Ultra-High-Voltage Ni-Rich Layered Cathodes

Practical applications of polymer electrolytes in lithium (Li) metal batteries with high-voltage Ni-rich cathodes have been hindered by the dendrite growth and poor oxidative stability of electrolytes. Herein, a self-healing polymer electrolyte is developed by in situ copolymerization of 2-(3-(6-methyl4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate (UPyMA) and ethylene glycol methyl ether acrylate (EGMEA) monomers. With the electrolyte, the dendrite growth is inhibited by spontaneously repairing dendrite-induced defects, cracks, and voids at the Li/electrolyte interface; the suppressed dendrite growth and associated electro-chemo behaviors are visualized by the kinetic Mont-Carlo simulation. Benefitting from the high ionic conductivity, wide electrochemical window and good interfacial stability, the self-healing polymer electrolyte enables stable cycling of the LiNi_0.8 Mn_0.1 Co_0.1 O₂ (NMC811) cathode under 4.7 V, achieving a high specific capacity of ≈228.8 mAh g^-1 and capacity retention of 80.4% over 500 cycles. The new electrolyte is very promising for developing highly safe and dendrite-free Li metal batteries with high energy density.

Solid Electrolyte Interphase Growth in Lithium Metal Cells With Normal Electrolyte Flow

In high energy density lithium metal batteries (LMBs), dendrite and solid electrolyte interphase (SEI) growth reduce safety and longevity, respectively. A stable SEI layer enables high efficiency cycling but continued SEI growth can lead to reduced capacity and coulombic efficiency. In this paper, we develop a steady-state model that predicts the effect of small advective electrolyte flow towards the lithium metal electrode on SEI growth during charging. For a fixed current density, increasing the electrolyte flow rate improves the coulombic efficiency and decreases SEI layer growth rate. Decreasing the charging current density at a constant flow rate also decreases the SEI layer growth rate. Low flow rates (μm/s) can increase coulombic efficiency by up to 6%. The sensitivity of the coulombic efficiency to plating and SEI layer reaction rates is also explored.

Self-Enhancing Gel Polymer Electrolyte by In Situ Construction for Enabling Safe Lithium Metal Battery

Lithium metal battery (LMB) possessing a high theoretical capacity is a promising candidate of advanced energy storage devices. However, its safety and stability are challenged by lithium dendrites and the leakage of liquid electrolyte. Here, a self-enhancing gel polymer electrolyte (GPE) is created by in situ polymerizing 1,3-dioxolane (DOL) in the nanofibrous skeleton for enabling safe LMB. The nanofiber membrane possesses a better affinity with poly-DOL (PDOL) than commercial separator for constructing homogeneous GPE with enhanced ion conductivity. Furthermore, polydopamine is introduced on nanofiber membrane to form hydrogen bonding with PDOL and bis((trifluoromethyl)sulfonyl)imide anion, dramatically improving the mechanical strength, ionic conductivity, and transference number of GPE. Besides, molecular dynamic simulation is used to reveal the intrinsic factors of high ionic conductivity and reinforcing effect in the meantime. Consequently, the LiFePO4 //Li batteries using self-enhancing GPE show extraordinary cyclic stability over 800 cycles under high current density of 2 C, with a capacity decay of 0.021% per cycle, effectively suppressing the growth of lithium dendrites. This ingenious strategy is expected to manufacture advanced performance and high safety LMBs and compatible with the current battery production.

Solid electrolytes for solid-state Li/Na–metal batteries: inorganic, composite and polymeric materials

This feature article presents the electrolyte synthetic approaches, design strategies, and merging materials that may address the critical issues of solid electrolytes for solid-state Li/Na–metal batteries.

Progress in Solid Polymer Electrolytes for Lithium-Ion Batteries and Beyond

Solid-state polymer electrolytes (SPEs) for high electrochemical performance lithium-ion batteries have received considerable attention due to their unique characteristics; they are not prone to leakage, and they exhibit low flammability, excellent processability, good flexibility, high safety levels, and superior thermal stability. However, current SPEs are far from commercialization, mainly due to the low ionic conductivity, low Li⁺ transference number (t_Li+ ), poor electrode/electrolyte interface contact, narrow electrochemical oxidation window, and poor long-term stability of Li metal. Recent work on improving electrochemical performance and these aspects of SPEs are summarized systematically here with a particular focus on the underlying mechanisms, and the improvement strategies are also proposed. This review could lead to a deeper consideration of the issues and solutions affecting the application of SPEs and pave a new pathway to safe, high-performance lithium-ion batteries.

Hybrid Electrolyte with Dual-Anion-Aggregated Solvation Sheath for Stabilizing High-Voltage Lithium-Metal Batteries

Lithium (Li)-metal batteries (LMBs) with high-voltage cathodes and limited Li-metal anodes are crucial to realizing high-energy storage. However, functional electrolytes that are compatible with both high-voltage cathodes and Li anodes are required for their developments. In this study, the use of a moderate-concentration LiPF₆ and LiNO₃ dual-salt electrolyte composed of ester and ether co-solvents (fluoroethylene carbonate/dimethoxyethane, FEC/DME), which forms a unique Li⁺ solvation with aggregated dual anions, that is, PF₆ ^- and NO₃ ^- , is proposed to stabilize high-voltage LMBs. Mechanistic studies reveal that such a solvation sheath improves the Li plating/stripping kinetics and induces the generation of a solid electrolyte interphase (SEI) layer with gradient heterostructure and high Young's modulus on the anode, and a thin and robust cathode electrolyte interface (CEI) film. Therefore, this novel electrolyte enables colossal Li deposits with a high Coulombic efficiency (≈98.9%) for 450 cycles at 0.5 mA cm^-2 . The as-assembled LiǁLiNi_0.85 Co_0.10 Al_0.05 O₂ full batteries deliver an excellent lifespan and capacity retention at 4.3 V with a rigid negative-to-positive capacity ratio. This electrolyte system with a dual-anion-aggregated solvation structure provides insights into the interfacial chemistries through solvation regulation for high-voltage LMBs.

SnF2 -Catalyzed Formation of Polymerized Dioxolane as Solid Electrolyte and its Thermal Decomposition Behavior

Polymerized-dioxolane(P-DOL) is of potential as a solid-polymer-electrolyte(SPE) due to its high Li⁺ -conductivity, good compatibility with Li-metal and desired preparation method of in situ polymerization in cells. In this study, SnF₂ was demonstrated not only to be an efficient catalyst for the polymerization of DOL at room temperature, but also an effective additive for improving interfacial wettability and suppressing dendrite through the reaction with Li-metal and the formation of LiF/Li_x Sn based composite solid electrolyte interlayer(SEI). Using the SnF₂ polymerized P-DOL containing 1 M LiTFSI as SPE(P-DOL-SPE), obviously denser Li-deposition was obtained, and the all-solid-state(ASS) Li/LiFePO₄ cell delivered stable cycling over 350 cycles at 45 °C. At the same time, the irreversible decomposition of P-DOL-SPE into formaldehyde and small molecule epoxides are observed at 110 °C, which is even initiated at lower temperature of 40 °C under vacuum. This thermal decomposition of P-DOL-SPE in pouch cell causes huge volume swell, and therefore putting a strict limitation on the operating temperature window for the P-DOL based electrolytes.

Commercialization-Driven Electrodes Design for Lithium Batteries: Basic Guidance, Opportunities, and Perspectives

Current lithium-ion battery technology is approaching the theoretical energy density limitation, which is challenged by the increasing requirements of ever-growing energy storage market of electric vehicles, hybrid electric vehicles, and portable electronic devices. Although great progresses are made on tailoring the electrode materials from methodology to mechanism to meet the practical demands, sluggish mass transport, and charge transfer dynamics are the main bottlenecks when increasing the areal/volumetric loading multiple times to commercial level. Thus, this review presents the state-of-the-art developments on rational design of the commercialization-driven electrodes for lithium batteries. First, the basic guidance and challenges (such as electrode mechanical instability, sluggish charge diffusion, deteriorated performance, and safety concerns) on constructing the industry-required high mass loading electrodes toward commercialization are discussed. Second, the corresponding design strategies on cathode/anode electrode materials with high mass loading are proposed to overcome these challenges without compromising energy density and cycling durability, including electrode architecture, integrated configuration, interface engineering, mechanical compression, and Li metal protection. Finally, the future trends and perspectives on commercialization-driven electrodes are offered. These design principles and potential strategies are also promising to be applied in other energy storage and conversion systems, such as supercapacitors, and other metal-ion batteries.

Vertical Channels Design for Polymer Electrolyte to Enhance Mechanical Strength and Ion Conductivity

Polymer electrolytes are the key candidates for solid-state batteries benefiting from their intrinsic advantages over inorganic electrolytes in terms of flexibility and easy processability. However, they suffer from low ionic conductivity and poor mechanical strength, which restrict their wide utilization. Conventional ceramic fillers are used to improve the mechanical properties of polymer electrolytes but lack sufficient Li⁺ conductivity. In this work, a framework with vertical channels that possess fast Li⁺ movement is designed. It is found that the poly(ethylene oxide) (PEO) compound in the vertical channel framework benefits to improve the ionic conductivity and mechanical strength synchronously. The framework in which ionic liquids are loaded on a zirconium dioxide surface (ZrO₂@ILs) helps to improve ionic conductivity by 2 orders of magnitude compared with PEO, which is due to the enhanced orientation of ion transport. By optimizing the content of ZrO₂@ILs, the elastic modulus is also tripled. Therefore, the symmetric lithium battery can cycle stably for more than 800 h at a current density of 0.25 mA cm^-1, whereas the lithium metal battery has a specific capacity of 135 mAh g^-1 at a current density of 2C and can cycle stably for more than 200 cycles at 60 °C.

Lithium-Ion Battery Operation, Degradation, and Aging Mechanism in Electric Vehicles: An Overview

Understanding the aging mechanism for lithium-ion batteries (LiBs) is crucial for optimizing the battery operation in real-life applications. This article gives a systematic description of the LiBs aging in real-life electric vehicle (EV) applications. First, the characteristics of the common EVs and the lithium-ion chemistries used in these applications are described. The battery operation in EVs is then classified into three modes: charging, standby, and driving, which are subsequently described. Finally, the aging behavior of LiBs in the actual charging, standby, and driving modes are reviewed, and the influence of different working conditions are considered. The degradation mechanisms of cathode, electrolyte, and anode during those processes are also discussed. Thus, a systematic analysis of the aging mechanisms of LiBs in real-life EV applications is achieved, providing practical guidance, methods to prolong the battery life for users, battery designers, vehicle manufacturers, and material recovery companies.

Mechanically Strong and Electrochemically Stable Single-Ion Conducting Polymer Electrolytes Constructed from Hydrogen Bonding

Herein, composite membranes based on a single-ion conducting polymer electrolyte (SIPE) and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) were prepared by an electrospinning technology. The SIPE with hydrogen bonding was obtained via reversible addition-fragmentation chain transfer (RAFT) copolymerization of 2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate (UPyMA), poly(ethylene glycol) methyl ether methacrylate (PEGMA), and lithium 4-styrenesulfonyl (phenylsulfonyl) imide (SSPSILi). The obtained composite membrane exhibited a highly porous network structure, superior thermal stability (>300 °C), and high mechanical strength (17.3 MPa). The fabricated SIPE/PVDF-HFP composite membrane without lithium salts possessed a high ionic conductivity of 2.78 × 10^-5 S cm^-1 at 30 °C, excellent compatibility with the lithium metal electrode, and high lithium-ion transference number (0.89). The symmetric Li//Li cell exhibited a superior cycle performance without short circuit, indicating the generation of a stable interface between SIPE and the lithium metal electrode during the process of lithium plating/stripping, which could inhibit lithium dendrite growth in lithium metal batteries (LMBs). The Li//LiFePO₄ cell also exhibited superior cycle life and excellent rate capability at 60 or 25 °C. In consequence, the composite membrane exhibits a considerable future prospect for advanced LMBs.

Designing Polymer-in-Salt Electrolyte and Fully Infiltrated 3D Electrode for Integrated Solid-State Lithium Batteries

Solid-state lithium batteries (SSLBs) are promising owing to enhanced safety and high energy density but plagued by the relatively low ionic conductivity of solid-state electrolytes and large electrolyte-electrode interfacial resistance. Herein, we design a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymer-in-salt solid electrolyte (PISSE) with high room-temperature ionic conductivity (1.24×10^-4  S cm^-1 ) and construct a model integrated TiO₂ /Li SSLB with 3D fully infiltration of solid electrolyte. With forming aggregated ion clusters, unique ionic channels are generated in the PISSE, providing much faster Li⁺ transport than common polymer electrolytes. The integrated device achieves maximized interfacial contact and electrochemical and mechanical stability, with performance close to liquid electrolyte. A pouch cell made of 2 SSLB units in series shows high voltage plateau (3.7 V) and volumetric energy density comparable to many commercial thin-film batteries.

Stamping Flexible Li Alloy Anodes

Li metal holds great promise to be the ultimate anode choice owing to its high specific capacity and low redox potential. However, processing Li metal into thin-film anode with high electrochemical performance and good safety to match commercial cathodes remains challenging. Herein, a new method is reported to prepare ultrathin, flexible, and high-performance Li-Sn alloy anodes with various shapes on a number of substrates by directly stamping a molten metal solution. The printed anode is as thin as 15 µm, corresponding to an areal capacity of ≈3 mAh cm^-2 that matches most commercial cathode materials. The incorporation of Sn provides the nucleation center for Li, thereby mitigating Li dendrites as well as decreasing the overpotential during Li stripping/plating (e.g., <10 mV at 0.25 mA cm^-2 ). As a proof-of-concept, a flexible Li-ion battery using the ultrathin Li-Sn alloy anode and a commercial NMC cathode demonstrates good electrochemical performance and reliable cell operation even after repetitive deformation. The approach can be extended to other metal/alloy anodes such as Na, K, and Mg. This study opens a new door toward the future development of high-performance ultrathin alloy-based anodes for next-generation batteries.

Interface Issues and Challenges in All-Solid-State Batteries: Lithium, Sodium, and Beyond

Owing to the promise of high safety and energy density, all-solid-state batteries are attracting incremental interest as one of the most promising next-generation energy storage systems. However, their widespread applications are inhibited by many technical challenges, including low-conductivity electrolytes, dendrite growth, and poor cycle/rate properties. Particularly, the interfacial dynamics between the solid electrolyte and the electrode is considered as a crucial factor in determining solid-state battery performance. In recent years, intensive research efforts have been devoted to understanding the interfacial behavior and strategies to overcome these challenges for all-solid-state batteries. Here, the interfacial principle and engineering in a variety of solid-state batteries, including solid-state lithium/sodium batteries and emerging batteries (lithium-sulfur, lithium-air, etc.), are discussed. Specific attention is paid to interface physics (contact and wettability) and interface chemistry (passivation layer, ionic transport, dendrite growth), as well as the strategies to address the above concerns. The purpose here is to outline the current interface issues and challenges, allowing for target-oriented research for solid-state electrochemical energy storage. Current trends and future perspectives in interfacial engineering are also presented.

Electrolytes and Interphases in Potassium Ion Batteries

Potassium ion batteries (PIBs) are recognized as one promising candidate for future energy storage devices due to their merits of cost-effectiveness, high-voltage, and high-power operation. Many efforts have been devoted to the development of electrode materials and the progress has been well summarized in recent review papers. However, in addition to electrode materials, electrolytes also play a key role in determining the cell performance. Here, the research progress of electrolytes in PIBs is summarized, including organic liquid electrolytes, ionic liquid electrolytes, solid-state electrolytes and aqueous electrolytes, and the engineering of the electrode/electrolyte interfaces is also thoroughly discussed. This Progress Report provides a comprehensive guidance on the design of electrolyte systems for development of high performance PIBs.