Promises, Challenges, and Recent Progress of Inorganic Solid-State Electrolytes for All-Solid-State Lithium Batteries

Li-Sb Alloy Formation Strategy to Improve Interfacial Stability of All-Solid-State Lithium Batteries

The solid electrolyte is anticipated to prevent lithium dendrite formation. However, preventing interface reactions and the development of undesirable lithium metal deposition during cycling are difficult and remain unresolved. Here, to comprehend these occurrences better, this study reports an alloy formation strategy for enhanced interface stability by incorporating antimony (Sb) in the lithium argyrodite solid electrolyte Li6PS5Cl (LPSC-P) to form Li-Sb alloy. The Li-Sb alloy emergence at the anodic interface is crucial in facilitating uniform lithium deposition, resulting in excellent long-term stability, and achieving the highest critical current density of 14.5 mA cm-2 (among the reported sulfide solid electrolytes) without lithium dendrite penetration. Furthermore, Li-Sb alloy formation maintain interfacial contact, even, after several plating and stripping. The Li-Sb alloy formation is confirmed by XRD, Raman, and XPS. The work demonstrates the prospect of utilizing alloy-forming electrolytes for advanced solid-state batteries.

A strategy involving the use of 3D self-supporting B·N co-doped carbon nanofiber composite solid polymer electrolytes to stabilize the interface between polymer electrolytes and lithium metal

All-solid-state batteries (ASSBs) have gained significant attention in the field of energy storage owing to their enhanced safety features based on the nonflammable solid-state electrolyte (SSE). To achieve high energy density, lithium metal is commonly considered the best choice as an anode material. However, the compatibility issues at the interface between polymer electrolytes and lithium metal pose significant challenges to their practical implementation. In this work, we present a new strategy to protect the typical polymer electrolyte polyethylene oxide (PEO) from significant decomposition and puncture caused by lithium dendrites, which is achieved through the combination of PEO and B·N co-doped carbon nanofibers (B·N-CNF) to modify the surface of the lithium anode. The stable cycling performance of the symmetric battery can last over 900 h at a high current density of 1 mA cm-2. The ASSBs (LiFePO4 is used as the cathode and Li metal is employed as the anode) exhibit a high capacity close to 120 mA h g-1 at 2C and cycle for over 300 cycles at 0.2C stably. This work provides inspiration for the rational design of a modification layer on the Li anode, enabling the development of high-performance ASSBs based on polymer electrolytes.

In Situ Analysis of Interfacial Morphological and Chemical Evolution in All-Solid-State Lithium-Metal Batteries

In situ analysis of Li plating/stripping processes and evolution of solid electrolyte interphase (SEI) are critical for optimizing all-solid-state Li metal batteries (ASSLMB). However, the buried solid-solid interfaces present a challenge for detection which preclude the employment of multiple analysis techniques. Herein, by employing complementary in situ characterizations, morphological/chemical evolution, Li plating/stripping dynamics and SEI dynamics were directly detected. As a mixed ionic-electronic conducting interface, Li|Li10GeP2S12 (LGPS) performed distinct interfacial morphological/chemical evolution and dynamics from ionic-conducting/electronic-isolating interface like Li|Li3PS4 (LPS), which were revealed by combination of in situ atomic force microscopy and in situ X-ray photoelectron spectroscopy. Though Li plating speed in LGPS was higher than LPS, speed of SSE decomposition was similar and ~85 % interfacial SSE turned into SEI during plating and remained unchanged in stripping. To leverage strengths of different SSEs, an LPS-LGPS-LPS sandwich electrolyte was developed, demonstrating enhanced ionic conductivity and improved interfacial stability with less SSE decomposition (25 %). Using in situ Kelvin probe force microscopy, Li-ion behavior at interface between different SSEs was effectively visualized, uncovering distribution of Li ions at LGPS|LPS interface under different potentials.

Disorder-Dependent Li Diffusion in Li6PS5Cl Investigated by Machine-Learning Potential

Solid-state electrolytes with argyrodite structures, such as Li6PS5Cl, have attracted considerable attention due to their superior safety compared to liquid electrolytes and higher ionic conductivity than other solid electrolytes. Although experimental efforts have been made to enhance conductivity by controlling the degree of disorder, the underlying diffusion mechanism is not yet fully understood. Moreover, existing theoretical analyses based on ab initio molecular dynamics (MD) simulations have limitations in addressing various types of disorder at room temperature. In this study, we directly investigate Li-ion diffusion in Li6PS5Cl at 300 K using large-scale, long-term MD simulations empowered by machine-learning potentials (MLPs). To ensure the convergence of conductivity values within an error range of 10%, we employ a 25 ns simulation using a 5 × 5 × 5 supercell containing 6500 atoms. The computed Li-ion conductivity, activation energies, and equilibrium site occupancies align well with experimental observations. Notably, Li-ion conductivity peaks when Cl ions occupy 25% of the 4c sites rather than at 50% where the disorder is maximized. In addition, Li-ion diffusion shows non-Arrhenius behavior, leading to different activation energies at high temperatures (>400 K). These phenomena are explained by the interplay between inter- and intracage jumps. By elucidation of the key factors affecting Li-ion diffusion in Li6PS5Cl, this work paves the way for optimizing ionic conductivity in the argyrodite family.

Wet Chemistry Route to Li3InCl6: Microstructural Control Render High Ionic Conductivity and Enhanced All-Solid-State Battery Performance

Thanks to superionic conductivity and compatibility with >4 V cathodes, halide solid electrolytes (SEs) have elicited tremendous interest for application in all-solid-state lithium batteries (ASSLBs). Many compositions based on groups 3, 13, and divalent metals, and substituted stoichiometries have been explored, some displaying requisite properties, but the Li+ conductivity still falls short of theoretical predictions and appealing sulfide-type SEs. While controlling microstructural characteristics, namely grain boundary effects and microstrain, can boost ionic conductivity, they have rarely been considered. Moving away from the standard solid-state route, here a scalable and facile wet chemical approach for obtaining highly conductive (>2 mS cm-1) Li3InCl6 is presented, and it is shown that aprotic solvents can reduce grain boundaries and microstrain, leading to very high ionic conductivity of over 4 mS cm-1 (at 22 °C). Minimized grain boundary area renders improved moisture stability and enhances solid-solid interfacial contact, leading to excellent LiNi0.6Mn0.2Co0.2O2-based full-cell performance, exemplified by stable room temperature (22 °C) cycling at a 0.2 C rate with 155 mAh g-1 capacity and 85% retention after 1000 cycles at 60 °C with a high 99.75% Coulombic efficiency. The findings showcase the viability of the aprotic solvent-mediated route for producing high-quality Li3InCl6 for all-solid-state batteries.

Inorganic Sodium Solid Electrolytes: Structure Design, Interface Engineering and Application

All-solid-state sodium batteries (ASSSBs) are particularly attractive for large-scale energy storage and electric vehicles due to their exceptional safety, abundant resource availability, and cost-effectiveness. The growing demand for ASSSBs underscores the significance of sodium solid electrolytes; However, the existed challenges of sodium solid electrolytes hinder their practical application despite continuous research efforts. Herein, recent advancements and the challenges for sodium solid electrolytes from material to battery level are reviewed. The in-depth understanding of their fundamental properties, synthesis techniques, crystal structures and recent breakthroughs is presented. Moreover, critical challenges on inorganic sodium solid electrolytes are emphasized, including the imperative need to enhance ionic conductivity, fortifying interfacial compatibility with anode/cathode materials, and addressing dendrite formation issues. Finally, potential applications of these inorganic sodium solid electrolytes are explored in ASSSBs and emerging battery systems, offering insights into future research directions.

Charge-Delocalized Triptycene-Based Ionic Porous Organic Polymers as Quasi-Solid-State Electrolytes for Lithium Metal Batteries

Ideal solid electrolytes for lithium (Li) metal batteries should conduct Li+ rapidly with low activation energy, exhibit a high Li+ transference number, form a stable interface with the Li anode, and be electrochemically stable. However, the lack of solid electrolytes that meet all of these criteria has remained a considerable bottleneck in the advancement of lithium metal batteries. In this study, we present a design strategy combining all of those requirements in a balanced manner to realize quasi-solid-state electrolyte-enabled Li metal batteries (LMBs). We prepared Li+-coordinated triptycene-based ionic porous organic polymers (Li+@iPOPs). The Li+@iPOPs with imidazolates and phenoxides exhibited a high conductivity of 4.38 mS cm-1 at room temperature, a low activation energy of 0.627 eV, a high Li+ transference number of 0.95, a stable electrochemical window of up to 4.4 V, excellent compatibility with Li metal electrodes, and high stability during Li deposition/stripping cycles. The high performance is attributed to charge delocalization in the backbone, mimicking the concept of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which facilitates the diffusion of coordinated Li+ through the porous space of the triptycene-based iPOPs. In addition, Li metal batteries assembled using Li+@Trp-Im-O-POPs as quasi-solid-state electrolytes and a LiFePO4 cathode showed an initial capacity of 114 mAh g-1 and 86.7% retention up to 200 cycles.

Microporous Materials in Polymer Electrolytes: The Merit of Order

Solid-state batteries (SSBs) have garnered significant attention in the critical field of sustainable energy storage due to their potential benefits in safety, energy density, and cycle life. The large-scale, cost-effective production of SSBs necessitates the development of high-performance solid-state electrolytes. However, the manufacturing of SSBs relies heavily on the advancement of suitable solid-state electrolytes. Composite polymer electrolytes (CPEs), which combine the advantages of ordered microporous materials (OMMs) and polymer electrolytes, meet the requirements for high ionic conductivity/transference number, stability with respect to electrodes, compatibility with established manufacturing processes, and cost-effectiveness, making them particularly well-suited for mass production of SSBs. This review delineates how structural ordering dictates the fundamental physicochemical properties of OMMs, including ion transport, thermal transfer, and mechanical stability. The applications of prominent OMMs are critically examined, such as metal-organic frameworks, covalent organic frameworks, and zeolites, in CPEs, highlighting how structural ordering facilitates the fulfillment of property requirements. Finally, an outlook on the field is provided, exploring how the properties of CPEs can be enhanced through the dimensional design of OMMs, and the importance of uncovering the underlying "feature-function" mechanisms of various CPE types is underscored.

Phonon Engineering in Solid Polymer Electrolyte toward High Safety for Solid-State Lithium Batteries

Extensively-used rechargeable lithium-ion batteries (LIBs) face challenges in achieving high safety and long cycle life. To address such challenges, ultrathin solid polymer electrolyte (SPE) is fabricated with reduced phonon scattering by depositing the composites of ionic-liquid (1-ethyl-3-methylimidazolium dicyamide, EMIM:DCA), polyurethane (PU) and lithium salt on the polyethylene separator. The robust and flexible separator matrix not only reduces the electrolyte thickness and improves the mobility of Li+, but more importantly provides a relatively regular thermal diffusion channel for SPE and reduces the external phonon scattering. Moreover, the introduction of EMIM:DCA successfully breaks the random intermolecular attraction of the PU polymer chain and significantly decreases phonon scattering to enhance the internal thermal conductivity of the polymer. Thus, the thermal conductivity of the as-obtained SPE increases by approximately six times, and the thermal runaway (TR) of the battery is effectively inhibited. This work demonstrates that optimizing thermal safety of the battery by phonon engineering sheds a new light on the design principle for high-safety Li-ion batteries.

Path ahead: Tackling the Challenge of Computationally Estimating Lithium Diffusion in Cathode Materials

In the roadmap toward designing new and improved materials for Lithium ion batteries, the ability to estimate the diffusion coefficient of Li atoms in electrodes, and eventually solid-state electrolytes, is key. Nevertheless, as of today, accurate prediction through computational tools remains challenging. Its experimental measurement does not appear to be much easier. In this work, we devise a computational protocol for the determination of the Li-migration energy barrier and diffusion coefficient, focusing on a common cathode material such as LiNiO2, which represents a prototype of the widely adopted NMC (LiNi1-x-y Mn x Co y O2) class of materials. Different methodologies are exploited, combining ab initio metadynamics, path sampling, and density functional theory. Furthermore, we propose a novel, fast, and simple 1D approximation for the estimation of the effective frequency. The outlined computational protocol aims to be generally applicable to Lithium diffusion in other materials and components for batteries, including anodes and solid electrolytes.

Research Progress on the Composite Methods of Composite Electrolytes for Solid-State Lithium Batteries

In the current challenging energy storage and conversion landscape, solid-state lithium metal batteries with high energy conversion efficiency, high energy density, and high safety stand out. Due to the limitations of material properties, it is difficult to achieve the ideal requirements of solid electrolytes with a single-phase electrolyte. A composite solid electrolyte is composed of two or more different materials. Composite electrolytes can simultaneously offer the advantages of multiple materials. Through different composite methods, the merits of various materials can be incorporated into the most essential part of the battery in a specific form. Currently, more and more researchers are focusing on composite methods for combining components in composite electrolytes. The ion transport capacity, interface stability, machinability, and safety of electrolytes can be significantly improved by selecting appropriate composite methods. This review summarizes the composite methods used for the components of composite electrolytes, such as filler blending, embedded framework, and multilayer bonding. It also discusses the future development trends of all-solid-state lithium batteries (ASSLBs).

Solvent-Mediated Synthesis and Characterization of Li3InCl6 Electrolytes for All-Solid-State Li-Ion Battery Applications

Superionic halides have attracted widespread attention as solid electrolytes due to their excellent ionic conductivity, soft texture, and stability toward high-voltage electrode materials. Among them, Li3InCl6 has aroused interest since it can be easily synthesized in water or ethanol. However, investigations into the influence of solvents on both the crystal structure and properties remain unexplored. In this work, Li3InCl6 is synthesized by three different solvents: water, ethanol, and water-ethanol mixture, and the difference in properties has been studied. The results show that the product obtained by the ethanol solvent demonstrates the largest unit cell parameters with more vacancies, which tend to crystallize on the (131) plane and provide the 3D isotropic network migration for lithium-ions. Thus, it exhibits the highest ionic conductivity (1.06 mS cm-1) at room temperature and the lowest binding energy (0.272 eV). The assembled all-solid-state lithium metal batteries (ASSLMBs) employing Li3InCl6 electrolytes demonstrate a high initial discharge capacity of 153.9 mA h g-1 at 0.1 C (1 C = 170 mA h g-1) and the reversible capacity retention rate can reach 82.83% after 50 cycles. This work studies the difference in ionic conductivity between Li3InCl6 electrolytes synthesized by different solvents, which can provide a reference for the future synthesis of halide electrolytes and enable their practical application in halide-based ASSLMBs with a high energy density.

Ternary Rotational Polyanion Coupling Enables Fast Li Ion Dynamics in Tetrafluoroborate Ion Doped Antiperovskite Li2OHCl Solid Electrolyte

Li-rich antiperovskite (LiRAP) hydroxyhalides are emerging as attractive solid electrolyte (SEs) for all-solid-state Li metal batteries (ASSLMBs) due to their low melting point, low cost, and ease of scaling-up. The incorporation of rotational polyanions can reduce the activation energy and thus improve the Li ion conductivity of SEs. Herein, we propose a ternary rotational polyanion coupling strategy to fasten the Li ion conduction in tetrafluoroborate (BF4 -) ion doped LiRAP Li2OHCl. Assisted by first-principles calculation, powder X-ray diffraction, solid-state magnetic resonance and electrochemical impedance spectra, it is confirmed that Li ion transport in BF4 - ion doped Li2OHCl is strongly associated with the rotational coupling among OH-, BF4 - and Li2-O-H octahedrons, which enhances the Li ion conductivity for more than 1.8 times with the activation energy lowering 0.03 eV. This work provides a new perspective to design high-performance superionic conductors with multi-polyanions.

Cold Sintering Enables the Reprocessing of LLZO-Based Composites

All-solid-state batteries have the potential for enhanced safety and capacity over conventional lithium ion batteries, and are anticipated to dominate the energy storage industry. As such, strategies to enable recycling of the individual components are crucial to minimize waste and prevent health and environmental harm. Here, we use cold sintering to reprocess solid-state composite electrolytes, specifically Mg and Sr doped Li7La3Zr2O12 with polypropylene carbonate (PPC) and lithium perchlorate (LLZO-PPC-LiClO4). The low sintering temperature allows co-sintering of ceramics, polymers and lithium salts, leading to re-densification of the composite structures with reprocessing. Reprocessed LLZO-PPC-LiClO4 exhibits densified microstructures with ionic conductivities exceeding 10-4 S/cm at room temperature after 5 recycling cycles. All-solid-state lithium batteries fabricated with reprocessed electrolytes exhibit a high discharge capacity of 168 mA h g-1 at 0.1 C, and retention of performance at 0.2 C for over 100 cycles. Life cycle assessment (LCA) suggests that recycled electrolytes outperforms the pristine electrolyte process in all environmental impact categories, highlighting cold sintering as a promising technology for recycling electrolytes.

Compact Solid Electrolyte Interface Realization Employing Surface-Modified Fillers for Long-Lasting, High-Performance All-Solid-State Li-Metal Batteries

The implementation of polymer-based Li-metal batteries is hindered by their low coulombic efficiency and poor cycling stability attributed to continuous electrolyte decomposition. Enhancement of the solid electrolyte interface (SEI) stability is key to mitigating electrolyte decomposition. This study proposes surface-functionalized silica mesoball fillers to fabricate a composite polymer electrolyte (MSBM-CPE). As a result of surface modification, the polyethylene oxide matrix benefits from the uniform distribution of the filler, which provides a large surface area and Lewis acid sites. Molecular dynamics simulations reveal that the dissociation energy of lithium bis(trifluoromethanesulfonyl)imide in the filler is fourfold higher (-1.95 eV) than that of the filler-free electrolyte. Consequently, the MSMB-CPE diffusivity is 30 times higher than its filler-free counterpart. The MSMB-CPE of ionic conductivity of 1.16 × 10-2 S cm-1 @60 °C and a venerable Li-ion transference number of 0.81. The excellent compatibility of MSMB-CPE with the Li anode is demonstrated by its stable symmetric cell performance under high current density (200 µA cm-2 @60 °C) for over 5000 h. Approximately 85.60% retention capacity of the [Li/MSMB-CPE/LiFePO4] full cell after 700 cycles. Furthermore, compositional analysis reveals that the SEI layer in MSMB-CPE is smooth with fewer by-products at the electrolyte/Li interface.

Side Reactions/Changes in Lithium-Ion Batteries: Mechanisms and Strategies for Creating Safer and Better Batteries

Lithium-ion batteries (LIBs), in which lithium ions function as charge carriers, are considered the most competitive energy storage devices due to their high energy and power density. However, battery materials, especially with high capacity undergo side reactions and changes that result in capacity decay and safety issues. A deep understanding of the reactions that cause changes in the battery's internal components and the mechanisms of those reactions is needed to build safer and better batteries. This review focuses on the processes of battery failures, with voltage and temperature as the underlying factors. Voltage-induced failures result from anode interfacial reactions, current collector corrosion, cathode interfacial reactions, overcharge, and over-discharge, while temperature-induced failure mechanisms include SEI decomposition, separator damage, and interfacial reactions between electrodes and electrolytes. The review also presents protective strategies for controlling these reactions. As a result, the reader is offered a comprehensive overview of the safety features and failure mechanisms of various LIB components.

Capacity Degradation of Zero-Excess All-Solid-State Li Metal Batteries Using a Poly(ethylene oxide) Based Solid Electrolyte

Solid-state polymer electrolytes (SPEs), such as poly(ethylene oxide) (PEO), have good flexibility when compared to ceramic-type solid electrolytes. Therefore, it could be an ideal solid electrolyte for zero-excess all-solid-state Li metal battery (ZESSLB), also known as anode-free all-solid-state Li battery, development by offering better contact to the Cu current collector. However, the low Coulombic efficiencies observed from polymer type solid-state Li batteries (SSLBs) raise the concern that PEO may consume the limited amount of Li in ZESSLB to fail the system. Here, we designed ZESSLBs by using all-ceramic half-cells and an extra PEO electrolyte interlayer to study the reactivity between PEO and freshly deposited Li under a real battery operating conduction. By shuttling active Li back from the anode to the cathode, the PEO SPEs can be separated from the ZESSLBs for experimental studies without the influence from cathode materials or possible contamination from the usage of Li foil as the anode. Electrochemical cycling of ZESSLBs shows that the capacities of ZESSLBs with solvent-free and solvent-casted PEO SPEs significantly degraded compared to the ones with Li metal as the anode for the all-solid-state Li batteries. The fast capacity degradation of ZESSLBs using different types of PEO SPEs is evidenced to be associated with Li reacting with PEO, residual solvent, and water in PEO and dead Li formation upon the presence or absence of residual solvent. The results suggest that avoiding direct contact between the PEO electrolyte and deposited lithium is necessary when there is only a limited amount of Li available in ZESSLBs.

Concurrent Crystallization Mechanism Leading to Low Temperature Percolation of LAGP Glass-Ceramic Electrolyte

Sintering of ceramic electrolytes (CE) is the most efficient way to obtain a dense, all ceramic solid-state battery with oxide-based materials. However, the high temperature required for this process leads to detrimental reactivity between CE and the active material. Crystalline ceramics are necessary for highly conductive oxide materials. Still, thermomechanical properties of glass-phase materials can be used to obtain a denser and more conductive CE. Glass-phase CE can be produced with Nasicon-type CE. Here, Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glass is used as a model to investigate the formability, densification, and conduction properties upon crystallization. A complete study of the crystallization mechanism is first performed to fully understand how a high conductivity of 6.3 × 10-5 S·cm-1 at 30 °C with 92% relative density is obtained at a sintering temperature of only 550 °C without pressure. This is approximately 200 °C below the usual sintering temperature of LAGP. X-ray diffraction is then used to calculate the amount of crystalline phase as a function of time. A combined study of reaction kinetics and conductivity evolution reveals an autocatalytic nucleation effect, which produces an early crystallization pathway. Density is studied to quantify the ability of the glass to flow during the crystallization process.

High-Performance 3D Stacked Micro All-Solid-State Thin-Film Lithium-Ion Batteries Based on the Stress-Compensation Effect

A novel all-solid-state thin-film lithium-ion battery (LIB) is presented to address the trade-off issue between the specific capacity and stabilities in a conventional LIB. Different from the conventional one, this LIB device consists of two same LIB components located at the front and back surfaces of the substrate, respectively. These two LIB components form parallel connection by using the conductive through vias distributed in the substrate. Compared with the conventional one, this LIB device doubles the areal specific capacity. More importantly, due to the stress-compensation effect, this device effectively suppresses the stress induced by its volume changes resulting from the lithiation/delithiation processes and thermal expansion. Consequently, this device shows good cycling and thermal stabilities even when working at an industrial-grade high temperature of 125 °C. To further improve the specific capacity without sacrificing the stabilities, a 3D stacked LIB is successfully realized by using this LIB device as the cell, in which each cell is parallelly connected by using the above-mentioned conductive through vias. This 3D stacked LIB is experimentally demonstrated to obtain high specific capacity (79.9 µAh cm-2) and good stabilities (69.3% of retained capacity after 100 cycles at 125 °C) simultaneously.

Tailoring Practical Solid Electrolyte Composites Containing Ferroelectric Ceramic Nanofibers and All-Trans Block Copolymers for All-Solid-State Lithium Metal Batteries

Ion transport efficiency, the key to determining the cycling stability and rate capability of all-solid-state lithium metal batteries (ASSLMBs), is constrained by ionic conductivity and Li+-migration ability across the multicomponent phases and interfaces in ASSLMBs. Here, we report a robust strategy for the large-scale fabrication of a practical solid electrolyte composite with high-throughput linear Li+-transport channels by compositing an all-trans block copolymer PVDF-b-PTFE matrix with ferroelectric BaTiO3-TiO2 nanofiber films. The electrolyte shows a sustainable electromechanical-coupled deformability that enables the rapid dissociation of anions with Li+ to create more movable Li+ ions and spontaneously transform the battery internal strain into Li+-ion migration kinetic energy. The ceramic framework homogenizes the interfacial potential with electrodes, endowing the electrolyte with a high conductivity of 0.782 mS·cm-1 and stable ion transport ability in ASSLMBs at room temperature. The batteries of LiFePO4/Li can stably cycle 1000 times at 0.5 C with a high capacity retention of 96.1%, and Ah-grade pouch or high-voltage Li(Ni0.8Mn0.1Co0.1)O2/Li batteries also exhibit excellent rate capability and cycling performance.

In Situ Constructing Robust and Highly Conductive Solid Electrolyte with Tailored Interfacial Chemistry for Durable Li Metal Batteries

Employing nanofiber framework for in situ polymerized solid-state lithium metal batteries (SSLMBs) is impeded by the insufficient Li+ transport properties and severe dendritic Li growth. Both critical issues originate from the shortage of Li+ conduction highways and nonuniform Li+ flux, as randomly-scattered nanofiber backbone is highly prone to slippage during battery assembly. Herein, a robust fabric of Li0.33La0.56Ce0.06Ti0.94O3-δ/polyacrylonitrile framework (p-LLCTO/PAN) with inbuilt Li+ transport channels and high interfacial Li+ flux is reported to manipulate the critical current density of SSLMBs. Upon the merits of defective LLCTO fillers, TFSI- confinement and linear alignment of Li+ conduction pathways are realized inside 1D p-LLCTO/PAN tunnels, enabling remarkable ionic conductivity of 1.21 mS cm-1 (26 °C) and tLi+ of 0.93 for in situ polymerized polyvinylene carbonate (PVC) electrolyte. Specifically, molecular reinforcement protocol on PAN framework further rearranges the Li+ highway distribution on Li metal and alters Li dendrite nucleation pattern, boosting a homogeneous Li deposition behavior with favorable SEI interface chemistry. Accordingly, excellent capacity retention of 76.7% over 1000 cycles at 2 C for Li||LiFePO4 battery and 76.2% over 500 cycles at 1 C for Li||LiNi0.5Co0.2Mn0.3O2 battery are delivered by p-LLCTO/PAN/PVC electrolyte, presenting feasible route in overcoming the bottleneck of dendrite penetration in in situ polymerized SSLMBs.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

Advances in All-Solid-State Lithium-Sulfur Batteries for Commercialization

Solid-state batteries are commonly acknowledged as the forthcoming evolution in energy storage technologies. Recent development progress for these rechargeable batteries has notably accelerated their trajectory toward achieving commercial feasibility. In particular, all-solid-state lithium-sulfur batteries (ASSLSBs) that rely on lithium-sulfur reversible redox processes exhibit immense potential as an energy storage system, surpassing conventional lithium-ion batteries. This can be attributed predominantly to their exceptional energy density, extended operational lifespan, and heightened safety attributes. Despite these advantages, the adoption of ASSLSBs in the commercial sector has been sluggish. To expedite research and development in this particular area, this article provides a thorough review of the current state of ASSLSBs. We delve into an in-depth analysis of the rationale behind transitioning to ASSLSBs, explore the fundamental scientific principles involved, and provide a comprehensive evaluation of the main challenges faced by ASSLSBs. We suggest that future research in this field should prioritize plummeting the presence of inactive substances, adopting electrodes with optimum performance, minimizing interfacial resistance, and designing a scalable fabrication approach to facilitate the commercialization of ASSLSBs.

Effects of H2O on Improving the Performance of a Solid Composite Electrolyte Fabricated via an Air-Processable Technique

Inert atmosphere is normally necessary for fabrication of solid composite electrolytes (SCEs) as a crucial part of solid-state Li-metal batteries in order to avoid undesirable reactions induced by ambient moisture. Herein, we developed an air-processable technique to fabricate SCEs by employing LiCF3SO3 (LiOTf) as the Li salt, which was combined with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) as the fast Li-conductor and polyvinylidene difluoroethylene/polyvinyl acetate (PVDF/PVAC) as the polymer matrix. With the assistance of trace H2O dissolved in electrolyte solution, the room-temperature Li+ conductivity of the obtained aSCE reached as high as 5.09 × 10-4 S cm-1, which was over 3 orders of magnitude higher than that of the one (iSCE, 1.93 × 10-7 S cm-1) cast by the electrolyte solution prepared in an inert atmosphere. The theoretical calculation results reveal that the oxygen atom of H2O exhibits a high propensity to interact with the Li atom in LiOTf (Li···O), thereby establishing a hydrogen bond with the oxygen atom (H···O) in N,N-dimethylformamide (solvent). Such interactions promoted the dissociation of LiOTf and led to the formation of uniform Li+ transportation channels. Simultaneously, the composition distribution was also altered, resulting in a smoother surface of aSCE and lowered crystallinity of PVDF. On this basis, the LiOTf/LLZTO/PVDF/PVAC solution at 60 °C was directly coated onto the surface of the LiFePO4 (LFP) cathode to fabricate the LFP-aSCE film after drying in an oven. The assembled LFP-aSCE/Li battery wetted by trace sulfolane exhibited an initial Coulombic efficiency of 94.7% and a capacity retention rate of up to 96% at 0.2 C (137 mAh g-1) after 180 cycles and a high capacity of 143.7 mAh g-1 at 0.5 C (150 cycles). Overall, this work could pave the way for the facile fabrication of solid electrolytes.

Enabling High-Performance Hybrid Solid-State Batteries by Improving the Microstructure of Free-Standing LATP/LFP Composite Cathodes

The phosphate lithium-ion conductor Li1.5Al0.5Ti1.5(PO4)3 (LATP) is an economically attractive solid electrolyte for the fabrication of safe and robust solid-state batteries, but high sintering temperatures pose a material engineering challenge for the fabrication of cell components. In particular, the high surface roughness of composite cathodes resulting from enhanced crystal growth is detrimental to their integration into cells with practical energy density. In this work, we demonstrate that efficient free-standing ceramic cathodes of LATP and LiFePO4 (LFP) can be produced by using a scalable tape casting process. This is achieved by adding 5 wt % of Li2WO4 (LWO) to the casting slurry and optimizing the fabrication process. LWO lowers the sintering temperature without affecting the phase composition of the materials, resulting in mechanically stable, electronically conductive, and free-standing cathodes with a smooth, homogeneous surface. The optimized cathode microstructure enables the deposition of a thin polymer separator attached to the Li metal anode to produce a cell with good volumetric and gravimetric energy densities of 289 Wh dm-3 and 180 Wh kg-1, respectively, on the cell level and Coulombic efficiency above 99% after 30 cycles at 30 °C.

Strategies for Enhancing the Stability of Lithium Metal Anodes in Solid-State Electrolytes

The current commercially used anode material, graphite, has a theoretical capacity of only 372 mAh/g, leading to a relatively low energy density. Lithium (Li) metal is a promising candidate as an anode for enhancing energy density; however, challenges related to safety and performance arise due to Li's dendritic growth, which needs to be addressed. Owing to these critical issues in Li metal batteries, all-solid-state lithium-ion batteries (ASSLIBs) have attracted considerable interest due to their superior energy density and enhanced safety features. Among the key components of ASSLIBs, solid-state electrolytes (SSEs) play a vital role in determining their overall performance. Various types of SSEs, including sulfides, oxides, and polymers, have been extensively investigated for Li metal anodes. Sulfide SSEs have demonstrated high ion conductivity; however, dendrite formation and a limited electrochemical window hinder the commercialization of ASSLIBs due to safety concerns. Conversely, oxide SSEs exhibit a wide electrochemical window, but compatibility issues with Li metal lead to interfacial resistance problems. Polymer SSEs have the advantage of flexibility; however their limited ion conductivity poses challenges for commercialization. This review aims to provide an overview of the distinctive characteristics and inherent challenges associated with each SSE type for Li metal anodes while also proposing potential pathways for future enhancements based on prior research findings.

An entanglement association polymer electrolyte for Li-metal batteries

To improve the interface stability between Li-rich Mn-based oxide cathodes and electrolytes, it is necessary to develop new polymer electrolytes. Here, we report an entanglement association polymer electrolyte (PVFH-PVCA) based on a poly (vinylidene fluoride-co-hexafluoropropylene) (PVFH) matrix and a copolymer stabilizer (PVCA) prepared from acrylonitrile, maleic anhydride, and vinylene carbonate. The entangled structure of the PVFH-PVCA electrolyte imparts excellent mechanical properties and eliminates the stress arising from dendrite growth during cycling and forms a stable interface layer, enabling Li//Li symmetric cells to cycle steadily for more than 4500 h at 8 mA cm-2. The PVCA acts as a stabilizer to promote the formation of an electrochemically robust cathode-electrolyte interphase. It delivers a high specific capacity and excellent cycling stability with 84.7% capacity retention after 400 cycles. Li1.2Mn0.56Ni0.16Co0.08O2/PVFH-PVCA/Li full cell achieved 125 cycles at 1 C (4.8 V cut-off) with a stable discharge capacity of ~2.5 mAh cm-2.

Exploring the Cathode Active Materials for Sulfide-Based All-Solid-State Lithium Batteries with High Energy Density

All-solid-state lithium batteries (ASSLBs) are considered promising alternatives to current lithium-ion batteries that employ liquid electrolytes due to their high energy density and enhanced safety. Among various types of solid electrolytes, sulfide-based electrolytes are being actively studied, because they exhibit high ionic conductivity and high ductility, which enable good interfacial contacts in solid electrolytes without sintering at high temperatures. To improve the energy density of the sulfide-based ASSLBs, it is essential to increase the loading of active material in the composite cathode. In this study, the Ni-rich LiNix Coy Mn1-x-y O2 (NCM) materials are explored with different Ni content, particle size, and crystalline form to probe suitable cathode active materials for high-performance ASSLBs with high energy density. The results reveal that single-crystalline LiNi0.82 Co0.10 Mn0.08 O2 material with a small particle size exhibits the best cycling performance in the ASSLB assembled with a high mass loaded cathode (active mass loading: 26 mg cm-2 , areal capacity: 5.0 mAh cm-2 ) in terms of discharge capacity, capacity retention, and rate capability.

Degradation Evolution for Li2 ZrCl6 Electrolytes in Humid Air and Enhanced Air Stability via Effective Indium Substitution

Superionic halides have aroused interests in field of solid electrolytes such as Li2 ZrCl6 . However, they are still facing challenges including poor air stability which lacks in-depth investigation. Here, moisture instability of Li2 ZrCl6 is demonstrated and decomposition mechanism in air is clearly revealed. Li2 ZrCl6 decomposes into Li2 ZrO3 , ZrOCl2 ·xH2 O and LiCl during initial stage as halides upon moisture exposure. Later, these side products evolve into LiCl(H2 O) and Li6 Zr2 O7 after longer time exposure. More importantly, structure of destroyed halides cannot be recovered after postheating. Later, Indium is doped into Li2 ZrCl6 (9.7 × 10-5 S cm-1 ) to explore its effect on structure and properties. Crystal structure of ball-milled In-doped Li2 ZrCl6 electrolytes is converted from the Li3 YCl6 -like to Li3 InCl6 -like with increasing In content and ionic conductivity can also be enhanced (0.768-1.13) × 10-3 S cm-1 ). More importantly, good air stability of optimal Li2.8 Zr0.2 In0.8 Cl6 is achieved since halide hydrates are formed after air exposure instead of total decomposition and the hydrates can be restored to Li2.8 Zr0.2 In0.8 Cl6 after postheating. Moreover, reheated Li2.8 Zr0.2 In0.8 Cl6 after air exposure is successfully applied in solid-state LiNi0.8 Co0.1 Mn0.1 O2 /halides/Li6 PS5 Cl/Li-In battery. The results in this work can provide insights into air instability of Li2 ZrCl6 and effective strategy to regulate air stability of halides.

Exploring the Underlying Correlation between the Structure and Ionic Conductivity in Halide Spinel Solid-State Electrolytes with Neutron Diffraction

The development of cutting-edge solid-state electrolytes (SSEs) entails a deep understanding of the underlying correlation between the structure and ionic conductivity. Generally, the structure of SSEs encompasses several interconnected crystal parameters, and their collective influence on Li+ transport can be challenging to discern. Here, we systematically investigate the structure-function relationship of halide spinel LixMgCl2+x (2 ≥ x ≥ 1) SSEs. A nonmonotonic trend in the ionic conductivity of LixMgCl2+x SSEs has been observed, with the maximum value of 8.69 × 10-6 S cm-1 achieved at x = 1.4. The Rietveld refinement analysis, based on neutron diffraction data, has revealed that the crystal parameters including cell parameters, Li+ vacancies, Debye-Waller factor, and Li-Cl bond length assume diverse roles in influencing ionic conductivity of LixMgCl2+x at different stages within the range of x values. Besides, mechanistic analysis demonstrates Li+ transport along three-dimensional pathways, which primarily governs the contribution to ionic conductivity of LixMgCl2+x SSEs. This study has shed light on the collective influence of crystal parameters on Li+ transport behaviors, providing valuable insights into the intricate relationship between the structure and ionic conductivity of SSEs.

Solid-State Electrolytes and Electrode/Electrolyte Interfaces in Rechargeable Batteries

Solid-state batteries (SSBs) are considered to be one of the most promising candidates for next-generation energy storage systems due to the high safety, high energy density and wide operating temperature range of solid-state electrolytes (SSEs) they use. Unfortunately, the practical application of SSEs has rarely been successful, which is largely attributed to the low chemical stability and ionic conductivity, ineluctable solid-solid interface issues including limited ion transport channels, high energy barriers, and poor interface contact. A comprehensive understanding of ion transport mechanisms of various SSEs, interactions between fillers and polymer matrixes and the role of the interface in SSBs are indispensable for rational design and performance optimization of novel electrolytes. The categories, research advances and ion transport mechanism of inorganic glass/ceramic electrolytes, polymer-based electrolytes and corresponding composite electrolytes are detailly summarized and discussed. Moreover, interface contact and compatibility between electrolyte and cathode/anode are also briefly discussed. Furthermore, the electrochemical characterization methods of SSEs used in different types of SSBs are also introduced. On this basis, the principles and prospects of novel SSEs and interface design are curtly proposed according to the development requirements of SSBs. Moreover, the advanced characterizations for real-time monitoring of interface changes are also brought forward to promote the development of SSBs.

Recent Progress on the Air-Stable Battery Materials for Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) offer numerous advantages in terms of safety and theoretical specific energy density. However, their main components namely lithium metal anode, solid-state electrolyte, and cathode, show chemical instability when exposed to humid air, which results in low capacities and poor cycling stability. Recent studies have shown that bioinspired hydrophobic materials with low specific surface energies can protect battery components from corrosion caused by humid air. Air-stable inorganic materials that densely cover the surface of battery components can also provide protection, which improves the storage stability of the battery components, broadens their processing conditions, and ultimately decreases their processing costs while enhancing their safety. In this review, the mechanism behind the surface structural degradation of battery components and the resulting consequences are discussed. Subsequently, recent strategies are reviewed to address this issue from the perspectives of lithium metal anodes, solid-state electrolytes, and cathodes. Finally, a brief conclusion is provided on the current strategies and fabrication suggestions for future safe air-stable SSLMBs.

Synergistic Interfacial Optimization for High-Sulfur-Content All-Solid-State Lithium-Sulfur Batteries

Improving the sulfur content in the cathode is essential for achieving high-energy-density all-solid-state lithium-sulfur batteries (ASSLSBs). However, the complex multiinterfaces, akin to the short wooden planks that consist of the cask, severely limit the performance of ASSLSBs with high sulfur content. Since singular approaches fail to optimize these interfaces simultaneously, we propose a synergistic approach using a dual-doped sulfide solid electrolyte (Y2S3 and LiI) and an SbSn alloy sulfur host in this work. The incorporation of Y2S3 in the solid electrolyte serves to improve the electrolyte-electrolyte interfaces and enhance the ionic conductivity, while the inclusion of LiI helps stabilize the electrolyte-anode interface and suppress dendrite formation. Meanwhile, the SbSn alloy sulfur host facilitates the transfer of Li+ at the electrolyte-cathode interfaces. Consequently, the solid-solid interfaces are significantly improved, leading to impressive specific capacities in ASSLSBs with high sulfur content (>44% in the cathode composite) at room temperature (1163.5 mAh g-1) and at 60 °C (1408.7 mAh g-1) during the 50th cycle at 0.05C. This work presents a promising strategy for achieving practical high-performance ASSLSBs.

Melt-casted Li1.5Al0.3Mg0.1Ge1.6(PO4)3 glass ceramic electrolytes: A comparative study on the effect of different oxide doping

The development of Li-ion conducting solid-state electrolytes (SSEs) is crucial to achieve increased energy density, operative reliability, and unprecedented safety to replace the state-of-the-art Li-ion battery (LIB). In this regard, we here present the successful melt-casting synthesis of a MgO-added NASICON-type LAGP glass-ceramic electrolyte with composition Li1.5Al0.3Mg0.1Ge1.6(PO4)3, namely LAMGP. The effects of three different additional oxides are investigated, with the aim to improve grain cohesion and consequently enhance Li-ion conductivity. Specifically, yttrium oxide (Y2O3, 5 mol%), boron oxide (B2O3, 0.7 mol%) and silicon oxide (SiO2, 2.4 %mol) are added, yielding LAMGP-Y, LAMGP-B and LAMGP-Si, respectively. Their effects are exhaustively compared in terms of thermal, crystalline, structural/morphological and ion conducting features. Among the three oxides, B2O3 is able to positively act on grain boundaries without bringing along grains deformation and insulating secondary phases formation, achieving enhanced ionic conductivity of 0.21 mS cm-1 at 20 °C as compared to 0.08 mS cm-1 for a commercial LAGP subjected to the same thermal treatment. A remarkable anodic oxidation stability up to 4.8 V vs Li+/Li is assessed by LAMGP-B system, which accounts for promising prospects for its use in combination with high-energy (high-V) cathodes.

Optimizing the Ion Conductivity and Mechanical Stability of Polymer Electrolyte Membranes Designed for Use in Lithium Ion Batteries: Combining Imidazolium-Containing Poly(ionic liquids) and Poly(propylene carbonate)

State-of-the-art Li batteries suffer from serious safety hazards caused by the reactivity of lithium and the flammable nature of liquid electrolytes. This work develops highly efficient solid-state electrolytes consisting of imidazolium-containing polyionic liquids (PILs) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI). By employing PIL/LiTFSI electrolyte membranes blended with poly(propylene carbonate) (PPC), we addressed the problem of combining ionic conductivity and mechanical properties in one material. It was found that PPC acts as a mechanically reinforcing component that does not reduce but even enhances the ionic conductivity. While pure PILs are liquids, the tricomponent PPC/PIL/LiTFSI blends are rubber-like materials with a Young's modulus in the range of 100 MPa. The high mechanical strength of the material enables fabrication of mechanically robust free-standing membranes. The tricomponent PPC/PIL/LiTFSI membranes have an ionic conductivity of 10-6 S·cm-1 at room temperature, exhibiting conductivity that is two orders of magnitude greater than bicomponent PPC/LiTFSI membranes. At 60 °C, the conductivity of PPC/PIL/LiTFSI membranes increases to 10-5 S·cm-1 and further increases to 10-3 S·cm-1 in the presence of plasticizers. Cyclic voltammetry measurements reveal good electrochemical stability of the tricomponent PIL/PPC/LiTFSI membrane that potentially ranges from 0 to 4.5 V vs. Li/Li+. The mechanically reinforced membranes developed in this work are promising electrolytes for potential applications in solid-state batteries.

State of Charge-Dependent Impedance Spectroscopy as a Helpful Tool to Identify Reasons for Fast Capacity Fading in All-Solid-State Batteries

Thiophosphate-based all-solid-state batteries (ASSBs) are considered the most promising candidate for the next generation of energy storage systems. However, thiophosphate-based ASSBs suffer from fast capacity fading with nickel-rich cathode materials. In many reports, this capacity fading is attributed to an increase of the charge transfer resistance of the composite cathode caused by interface degradation and/or chemo-mechanical failure. The change in the charge transfer resistance is typically determined using impedance spectroscopy after charging the cells. In this work, we demonstrate that large differences in the long-term cycling performance also arise in cells, which exhibit a comparable charge transfer resistance at the cathode side. Our results confirm that the charge transfer resistance of the cathode is not necessarily responsible for capacity fading. Other processes, such as resistive processes on the anode side, can also play a major role. Since these processes usually depend on the state of charge, they may not appear in the impedance spectra of fully charged cells; i.e., analyzing the impedance spectra of charged cells alone is insufficient for the identification of major resistive processes. Thus, we recommend measuring the impedance at different potentials to get a complete understanding of the reasons for capacity fading in ASSBs.

Advances in Inorganic Solid-State Electrolyte/Li Interface

The increasing demand for high-energy-density and high-safety energy storage devices has sparked a growing interest in all-solid-state lithium metal batteries (ASSLMBs). A high-quality inorganic solid-state electrolyte (ISE) is a fundamental requirement for ASSLMBs, and an effective ISE/Li interface is a key factor in attaining high-performance ASSLMBs. In this Concept, we initially summarize the challenges encountered by ISE/Li interfaces and delineate four commonly employed strategies for modifying the ISE/Li interface. Then, we explore the merits and drawbacks of coatings utilized as ISE/Li interfacial phases. We also delve into the commonly employed thermal bonding and innovative cold bonding methods utilized for in situ interface preparation. Lastly, we spotlight future directions for enhancing the functionality of ISE/Li interfaces and achieving high-performance ASSLMBs.

Highly Efficient Aligned Ion-Conducting Network and Interface Chemistries for Depolarized All-Solid-State Lithium Metal Batteries

Improving the long-term cycling stability and energy density of all-solid-state lithium (Li)-metal batteries (ASSLMBs) at room temperature is a severe challenge because of the notorious solid-solid interfacial contact loss and sluggish ion transport. Solid electrolytes are generally studied as two-dimensional (2D) structures with planar interfaces, showing limited interfacial contact and further resulting in unstable Li/electrolyte and cathode/electrolyte interfaces. Herein, three-dimensional (3D) architecturally designed composite solid electrolytes are developed with independently controlled structural factors using 3D printing processing and post-curing treatment. Multiple-type electrolyte films with vertical-aligned micro-pillar (p-3DSE) and spiral (s-3DSE) structures are rationally designed and developed, which can be employed for both Li metal anode and cathode in terms of accelerating the Li+ transport within electrodes and reinforcing the interfacial adhesion. The printed p-3DSE delivers robust long-term cycle life of up to 2600 cycles and a high critical current density of 1.92 mA cm-2. The optimized electrolyte structure could lead to ASSLMBs with a superior full-cell areal capacity of 2.75 mAh cm-2 (LFP) and 3.92 mAh cm-2 (NCM811). This unique design provides enhancements for both anode and cathode electrodes, thereby alleviating interfacial degradation induced by dendrite growth and contact loss. The approach in this study opens a new design strategy for advanced composite solid polymer electrolytes in ASSLMBs operating under high rates/capacities and room temperature.

A Review on Engineering Design for Enhancing Interfacial Contact in Solid-State Lithium-Sulfur Batteries

The utilization of solid-state electrolytes (SSEs) presents a promising solution to the issues of safety concern and shuttle effect in Li-S batteries, which has garnered significant interest recently. However, the high interfacial impedances existing between the SSEs and the electrodes (both lithium anodes and sulfur cathodes) hinder the charge transfer and intensify the uneven deposition of lithium, which ultimately result in insufficient capacity utilization and poor cycling stability. Hence, the reduction of interfacial resistance between SSEs and electrodes is of paramount importance in the pursuit of efficacious solid-state batteries. In this review, we focus on the experimental strategies employed to enhance the interfacial contact between SSEs and electrodes, and summarize recent progresses of their applications in solid-state Li-S batteries. Moreover, the challenges and perspectives of rational interfacial design in practical solid-state Li-S batteries are outlined as well. We expect that this review will provide new insights into the further technique development and practical applications of solid-state lithium batteries.

A Solid-State Electrolyte Based on Li0.95 Na0.05 FePO4 for Lithium Metal Batteries

Solid-state electrolytes (SSEs) play a crucial role in developing lithium metal batteries (LMBs) with high safety and energy density. Exploring SSEs with excellent comprehensive performance is the key to achieving the practical application of LMBs. In this work, the great potential of Li0.95 Na0.05 FePO4 (LNFP) as an ideal SSE due to its enhanced ionic conductivity and reliable stability in contact with lithium metal anode is demonstrated. Moreover, LNFP-based composite solid electrolytes (CSEs) are prepared to further improve electronic insulation and interface stability. The CSE containing 50 wt% of LNFP (LNFP50) shows high ionic conductivity (3.58 × 10-4 S cm-1 at 25 °C) and good compatibility with Li metal anode and cathodes. Surprisingly, the LMB of Li|LNFP50|LiFePO4 cell at 0.5 C current density shows good cycling stability (151.5 mAh g-1 for 500 cycles, 96.5% capacity retention, and 99.3% Coulombic efficiency), and high-energy LMB of Li|LNFP50|Li[Ni0.8 Co0.1 Mn0.1 ]O2 cell maintains 80% capacity retention after 170 cycles, which are better than that with traditional liquid electrolytes (LEs). This investigation offers a new approach to commercializing SSEs with excellent comprehensive performance for high-performance LMBs.

Additive-Derived Surface Modification of Cathodes in All-Solid-State Batteries: The Effect of Lithium Difluorophosphate- and Lithium Difluoro(oxalato)borate-Derived Coating Layers

Sulfide-based electrolytes, with their high conductivity and formability, enable the construction of high-performance, all-solid-state batteries (ASSBs). However, the instability of the cathode-sulfide electrolyte interface limits the commercialization of these ASSBs. Surface modification of cathodes using the coating technique has been explored as an efficient approach to stabilize these interfaces. In this study, the additives lithium difluorophosphate (LiDFP) and lithium difluoro(oxalato)borate (LiDFOB) are used to fabricate stable cathode coatings via heat treatment. The low melting points of LiDFP and LiDFOB enable the formation of thin and uniform coating layers by a low-temperature heat treatment. All-solid-state cells containing LiDFP- and LiDFOB-coated cathodes show electrochemical performances significantly better than those comprising uncoated cathodes. Among all of the as-prepared coated cathodes, LiDFP-coated cathodes fabricated using a slightly lower temperature than the phase-transition temperature of LiDFP (320 °C) show the best discharge capacity, rate capability, and cyclic performance. Furthermore, cells comprising LiDFP-coated cathodes showed significantly low impedance. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy confirm the effectiveness of the LiDFP coating. LiDFP-coated cathodes minimized side-reactions during cycling, resulting in a significantly low cathode-surface degradation. Hence, this study highlights the efficiency of the proposed coating method and its potential to facilitate the commercialization of ASSBs. Overall, this study reports an effective technique to stabilize the cathode-electrolyte interface in sulfide-based ASSBs, which could expedite the practical implementation of these advanced energy-storage devices.

Halogen chemistry of solid electrolytes in all-solid-state batteries

All-solid-state batteries (ASSBs) using solid-state electrolytes, replacing flammable liquid electrolytes, are considered one of the most promising next-generation electrochemical energy storage devices because of their improved, inherent safety and energy density. A family of solid electrolytes incorporating halogens has attracted attention because of their potentially high ionic conductivity, good deformability and wide electrochemical windows. Although progress has been made for halogen-containing solid electrolytes (HSEs) in ASSBs, challenges in the preparations, characterizations and low-cost industrial scalability remain. In this Review, we focus on the development of halide battery chemistry, the preparation, modification and properties of HSEs, and issues with HSEs in ASSBs. The chemical action of halogen and ion transport mechanisms are discussed. Moreover, the main challenges and future development directions of halide-based ASSBs are discussed to pave the way for practical applications of HSEs for next-generation rechargeable batteries.

Uniting Young's modulus and the flexibility of solid-state electrolytes for high-performance Li-batteries at room temperature

The use of solid-state composite electrolytes is a promising strategy to advance all-solid-state batteries. Great efforts have been devoted to improving the ionic conductivity of electrolytes, while little attention has been paid to studying the effect of their mechanical properties on electrochemical performance. The Young's modulus and flexibility are two important and contrary mechanical properties co-existing in electrolytes. Their effect on the electrochemical performance of all-solid-state batteries is important. Here, we study the effect of Young's modulus and flexibility based on a designed sandwich-structured solid-state composite electrolyte (SSCE) with high ionic conductivity (4.57 × 10-4 S cm-1 at 25 °C). In the SSCE, the middle layer with 9 : 1 : 0.5 mass ratio of Li6.4La3Zr1.4Ta0.6O12, poly(vinylidene fluoride-co-hexafluoropropylene) and bis(trifluoromethane)sulfonimide lithium is sandwiched by two outer layers with a 0.1 : 1 : 0.5 mass ratio among them, which can effectively suppress lithium dendrites and have intimate contact with the electrodes, leading to Li|SSCE|LiFePO4 with promising rate performance (155.5 mA h g-1 at 0.05 C and 124.4 mA h g-1 at 1 C) and excellent cycling stability with 98.8% capacity retention after 450 cycles at 25 °C. This work demonstrates that all-solid-state batteries have greatly enhanced electrochemical performance by uniting Young's modulus and flexibility via SSCEs, and provides a feasible strategy for the development of all-solid-state batteries.

Trigger of the Highly Resistive Layer Formation at the Cathode-Electrolyte Interface in All-Solid-State Lithium Batteries Using a Garnet-Type Lithium-Ion Conductor

Interfacial materials design is critical in the development of all-solid-state lithium batteries. We must develop an electrode-electrolyte interface with low resistance and effectively utilize the energy stored in the battery system. Here, we investigated the highly resistive layer formation process at the interface of a layered cathode: LiCoO2, and a garnet-type solid-state electrolyte: Li6.4La3Zr1.4Ta0.6O12, during the cosintering process using in situ/ex situ high-temperature X-ray diffraction. The onset temperature of the reaction between a lithium-deficient LixCoO2 and Li6.4La3Zr1.4Ta0.6O12 is 60 °C, while a stoichiometric LiCoO2 does not show any reaction up to 900 °C. The chemical potential gap of lithium first triggers the lithium migration from the garnet phase to the LixCoO2 below 200 °C. The lithium-extracted garnet gradually decomposes around 200 °C and mostly disappears at 500 °C. Since the interdiffusion of the transition metal is not observed below 500 °C, the early-stage reaction product is the decomposed lithium-deficient garnet phase. Electrochemical impedance spectroscopy results showed that the highly resistive layer is formed even below 200 °C. The present work offers that the origin of the highly resistive layer formation is triggered by lithium migration at the solid-solid interface and decomposition of the lithium-deficient garnet phase. We must prevent spontaneous lithium migration at the cathode-electrolyte interface to avoid a highly resistive layer formation. Our results show that the lithium chemical potential gap should be the critical parameter for designing an ideal solid-solid interface for all-solid-state battery applications.

Boosting lithium ion conductivity of antiperovskite solid electrolyte by potassium ions substitution for cation clusters

Solid-state electrolytes with high ionic conductivities are crucial for the development of all-solid-state lithium batteries, and there is a strong correlation between the ionic conductivities and underlying lattice structures of solid-state electrolytes. Here, we report a lattice manipulation method of replacing [Li2OH]+ clusters with potassium ions in antiperovskite solid-state electrolyte (Li2OH)0.99K0.01Cl, which leads to a remarkable increase in ionic conductivity (4.5 × 10‒3 mS cm‒1, 25 °C). Mechanistic analysis indicates that the lattice manipulation method leads to the stabilization of the cubic phase and lattice contraction for the antiperovskite, and causes significant changes in Li-ion transport trajectories and migration barriers. Also, the Li||LiFePO4 all-solid-state battery (excess Li and loading of 1.78 mg cm‒2 for LiFePO4) employing (Li2OH)0.99K0.01Cl electrolyte delivers a specific capacity of 116.4 mAh g‒1 at the 150th cycle with a capacity retention of 96.1% at 80 mA g‒1 and 120 °C, which indicates potential application prospects of antiperovskite electrolyte in all-solid-state lithium batteries.

Dry-Processable Polymer Electrolytes for Solid Manufactured Batteries

Designing a solid-state electrolyte that satisfies the operating requirements of solid-state batteries is key to solid-state battery applications. The consensus is that solid-state electrolytes need to allow fast ion transport, while providing better interfacial compatibility and mechanical tolerance. Herein, a simple but effective strategy is proposed, combining hard and soft component polymer systems, to exploit a solid polymer electrolyte (SPE) with a 3D network via an in situ graft polymerization. The 3D structure is constructed by a hard cellulose nanocrystal (CNC) as the skeleton and a soft polyacrylonitrile (PAN) as the filler through a dry-processing method. The reported systems have several advantages, including ease of processing, only requiring using an exceedingly small amount of solvent, light weight (ρ = 1.2 g cm-3), excellent mechanical stability (tensile strength of 9.5 MPa), and high ionic conductivity (3.9 × 10-4 S cm-1, 18 °C) and migration number (tLi+ = 0.8). In particular, the high conductivity is enabled: the efficient Li+ transportation path constructed between CNC-PAN powders and abundant sulfonate radicals and hydroxyl groups on the CNC surface acts as the bridge of Li+ transition. When the CNCs are grafted onto the PAN polymer, the dipole-dipole interaction between the nitrile groups of the PAN and the hydroxyl groups of the CNCs can help to improve the mechanical stability and ionic conductivity of the SPE. Moreover, a tightly formed interface between SPE and LiFePO4 (LFP)/carbon black/SPE cathode can be achieved in an assembled solid-state battery by hot pressing, thus further enhancing the battery's performance.

5D Analysis of Capacity Degradation in Battery Electrodes Enabled by Operando CT-XANES

For devices encountering long-term stability challenges, a precise evaluation of degradation is of paramount importance. However, methods for comprehensively elucidating the degradation mechanisms in devices, particularly those undergoing dynamic chemical and mechanical changes during operation, such as batteries, are limited. Here, a method is presented using operando computed tomography combined with X-ray absorption near-edge structure spectroscopy (CT-XANES) that can directly track the evolution of the 3D distribution of the local capacity loss in battery electrodes during (dis)charge cycles, thereby enabling a five-dimensional (the 3D spatial coordinates, time, and chemical state) analysis of the degradation. This paper demonstrates that the method can quantify the spatiotemporal dynamics of the local capacity degradation within an electrode during cycling, which has been truncated by existing bulk techniques, and correlate it with the overall electrode performance degradation. Furthermore, the method demonstrates its capability to uncover the correlation among observed local capacity degradation within electrodes, reaction history during past (dis)charge cycles, and electrode microstructure. The method thus provides critical insights into the identification of degradation factors that are not available through existing methods, and therefore, will contribute to the development of batteries with long-term stability.

Polymers with Intrinsic Microporosity as Solid Ion Conductors for Solid-State Lithium Batteries

Solid-state electrolytes (SSEs) with high ionic conductivity and superior stability are considered to be a key technology for the safe operation of solid-state lithium batteries. However, current SSEs are incapable of meeting the requirements for practical solid-state lithium batteries. Here we report a general strategy for achieving high-performance SSEs by engineering polymers of intrinsic microporosity (PIMs). Taking advantage of the interconnected ion pathways generated from the ionizable groups, high ionic conductivity (1.06×10-3  S cm-1 at 25 °C) is achieved for the PIMs-based SSEs. The mechanically strong (50.0 MPa) and non-flammable SSEs combine the two superiorities of outstanding Li+ conductivity and electrochemical stability, which can restrain the dendrite growth and prevent Li symmetric batteries from short-circuiting even after more than 2200 h cycling. Benefiting from the rational design of SSEs, PIMs-based SSEs Li-metal batteries can achieve good cycling performance and superior feasibility in a series of withstand abuse tests including bending, cutting, and penetration. Moreover, the PIMs-based SSEs endow high specific capacity (11307 mAh g-1 ) and long-term discharge/charge stability (247 cycles) for solid-state Li-O2 batteries. The PIMs-based SSEs present a powerful strategy for enabling safe operation of high-energy solid-state batteries.

Synergized Tricomponent All-Inorganics Solid Electrolyte for Highly Stable Solid-State Li-Ion Batteries

Garnet-type oxide Li6.4 La3 Zr1.4 Ta0.6 O12 (LLZTO) features superior ionic conductivity and good stability toward lithium (Li) metal, but requires high-temperature sintering (≈1200 °C) that induces high fabrication cost, poor mechanical processability, and high interface resistance. Here, a novel high-performance tricomponent composite solid electrolyte (CSE) comprising LLZTO-4LiBH4 /xLi3 BN2 H8 is reported, which is prepared by ball milling the LLZTO-4LiBH4  mixture followed by hand milling with Li3 BN2 H8 . Green pellets fabricated by heating the cold-pressed CSE powders at 120 °C offer ultrafast room-temperature ionic conductivity (≈1.73 × 10-3  S cm-1  at 30 °C) and ultrahigh Li-ion transference number (≈0.9999), which enable the Li|Li symmetrical cells to cycle over 1600 h at 30 °C with only 30 mV of overpotential. Moreover, the Li|CSE|TiS2  full cells deliver 201 mAh g-1  of capacity with long cyclability. These outstanding performances are due to the low open porosity in the electrolyte pellets as well as the high intrinsic ionic conductivity and easy deformability of Li3 BN2 H8 .