A Versatile Sn‐Substituted Argyrodite Sulfide Electrolyte for All‐Solid‐State Li Metal Batteries

Sulfide‐based solid‐state electrolytes (SSEs) for all‐solid‐state Li metal batteries (ASSLMBs) are attracting significant attention due to their high ionic conductivity, inherently soft properties, and decent mechanical strength. However, the poor incompatibility with Li metal and air sensitivity have hindered their application. Herein, the Sn (IV) substitution for P (V) in argyrodite sulfide Li₆PS₅I (LPSI) SSEs is reported, in the preparation of novel LPSI‐xSn SSEs (where x is the Sn substitution percentage). Appropriate aliovalent element substitutions with larger atomic radius (R_<Sn> > R_<P>) provides the optimized LPSI‐20Sn electrolyte with a 125 times higher ionic conductivity compared to that of the LPSI electrolyte. The high ionic conductivity of LPSI‐20Sn enables the rich I‐containing electrolyte to serve as a stabilized interlayer against Li metal in sulfide‐based ASSLMBs with outstanding cycling stability and rate capability. Most importantly, benefiting from the strong Sn–S bonding in Sn‐substituted electrolytes, the LPSI‐20Sn electrolyte shows excellent structural stability and improved air stability after exposure to O₂ and moisture. The versatile Sn substitution in argyrodite LPSI electrolytes is believed to provide a new and effective strategy to achieve Li metal‐compatible and air‐stable sulfide‐based SSEs for large‐scale applications.     

Incorporating Solvate and Solid Electrolytes for All‐Solid‐State Li2S Batteries with High Capacity and Long Cycle Life

The development of all‐solid‐state lithium–sulfur batteries is hindered by the poor interfacial properties at solid electrolyte (SE)/electrode interfaces. The interface is modified by employing the highly concentrated solvate electrolyte, (MeCN)₂?LiTFSI:TTE, as an interlayer material at the electrolyte/electrode interfaces. The incorporation of an interlayer significantly improves the cycling performance of solid‐state Li₂S batteries compared to the bare counterpart, exhibiting a specific capacity of 760 mAh g^?1 at cycle 100 (330 mAh g^?1 for the bare cell). Electrochemical impedance spectroscopy shows that the interfacial resistance of the interlayer‐modified cell gradually decreases as a function of cycle number, while the impedance of the bare cell remains almost constant. Cross‐section scanning electron microscopy (SEM)/ energy dispersive X‐ray spectroscopy (EDS) measurements on the interlayer‐modified cell confirm the permeation of solvate into the cathode and the SE with electrochemical cycling, which is related to the decrease in cell impedance. In order to mimic the full permeation of the solvate across the entire cell, the solvate is directly mixed with the SE to form a “solvSEM” electrolyte. The hybrid Li₂S cell using a solvSEM electrolyte exhibits superior cycling performance compared to the solid‐state cells, in terms of Li₂S loading, Li₂S utilization, and cycling stability. The improved performance is due to the favorable ionic contact at the battery interfaces.     

Unraveling the Intra and Intercycle Interfacial Evolution of Li6PS5Cl‐Based All‐Solid‐State Lithium Batteries

High‐performance rechargeable all‐solid‐state lithium metal batteries with high energy density and enhanced safety are attractive for applications like portable electronic devices and electric vehicles. Among the various solid electrolytes, argyrodite Li₆PS₅Cl with high ionic conductivity and easy processability is of great interest. However, the low interface compatibility between sulfide solid electrolytes and high capacity cathodes like nickel‐rich layered oxides requires many thorny issues to be resolved, such as the space charge layer (SCL) and interfacial reactions. In this work, in situ electrochemical impedance spectroscopy and in situ Raman spectroscopy measurements are performed to monitor the detailed interface evolutions in a LiNi_0.8Co_0.1Mn_0.1O₂ (NCM)/Li₆PS₅Cl/Li cell. Combining with ex situ characterizations including scanning electron microscopy and X‐ray photoelectron spectroscopy, the evolution of the SCL and the chemical bond vibration at NCM/Li₆PS₅Cl interface during the early cycles is elaborated. It is found that the Li⁺ ion migration, which varies with the potential change, is a very significant cause of these interface behaviors. For the long‐term cycling, the SCL, interfacial reactions, lithium dendrites, and chemo‐mechanical failure have an integrated effect on interfaces, further deteriorating the interfacial structure and electrochemical performance. This research provides a new insight on intra and intercycle interfacial evolution of solid‐state batteries.     

High Capacity All‐Solid‐State Lithium Batteries Enabled by Pyrite‐Sulfur Composites

As the theoretical limit of intercalation material‐based lithium‐ion batteries is approached, alternative chemistries based on conversion reactions are presently considered. The conversion of sulfur is particularly appealing as it is associated with a theoretical gravimetric energy density up to 2510 Wh kg^?1. In this paper, three different carbon‐iron disulfide‐sulfur (C‐FeS₂‐S) composites are proposed as alternative positive electrode materials for all‐solid‐state lithium‐sulfur batteries. These are synthesized through a facile, low‐cost, single‐step ball‐milling procedure. It is found that the crystalline structure (evaluated by X‐ray diffraction) and the morphology of the composites (evaluated by scanning electron microscopy) are greatly influenced by the FeS₂:S ratio. Li/LiI‐Li₃PS₄/C‐FeS₂‐S solid‐state cells are tested under galvanostatic conditions, while differential capacity plots are used to discuss the peculiar electrochemical features of these novel materials. These cells deliver capacities as high as 1200 mAh g_(FeS2+S)^?1 at the intermediate loading of 1 mg cm^?2 (1.2 mAh cm^?2), and up to 3.55 mAh cm^?2 for active material loadings as high as 5 mg cm^?2 at 20 °C. Such an excellent performance, rarely reported for (sulfur/metal sulfide)‐based, all solid‐state cells, makes these composites highly promising for real application where high positive electrode loadings are required.     

Ultrathin,Flexible Polymer Electrolyte for Cost‐Effective Fabrication of All‐Solid‐State Lithium Metal Batteries

All‐solid‐state batteries are promising candidates for the next‐generation safer batteries. However, a number of obstacles have limited the practical application of all‐solid‐state Li batteries (ASSLBs), such as moderate ionic conductivity at room temperature. Here, unlike most of the previous approaches, superior performances of ASSLBs are achieved by greatly reducing the thickness of the solid‐state electrolyte (SSE), where ionic conductivity is no longer a limiting factor. The ultrathin SSE (7.5 µm) is developed by integrating the low‐cost polyethylene separator with polyethylene oxide (PEO)/Li‐salt (PPL). The ultrathin PPL shortens Li⁺ diffusion time and distance within the electrolyte, and provides sufficient Li⁺ conductance for batteries to operate at room temperature. The robust yet flexible polyethylene offers mechanical support for the soft PEO/Li‐salt, effectively preventing short‐circuits even under mechanical deformation. Various ASSLBs with PPL electrolyte show superior electrochemical performance. An initial capacity of 135 mAh g^?1 at room temperature and the high‐rate capacity up to 10 C at 60 °C can be achieved in LiFePO₄/PPL/Li batteries. The high‐energy‐density sulfur cathode and MoS₂ anode employing PPL electrolyte also realize remarkable performance. Moreover, the ASSLB can be assembled by a facile process, which can be easily scaled up to mass production.     

Solid‐State Prelithiation Enables High‐Performance Li‐Al‐H Anode for Solid‐State Batteries

Lithium alanates exhibit high theoretical specific capacities and appropriate lithiation/delithiation potentials, but suffer from poor reversibility, cycling stability, and rate capability due to their sluggish kinetics and extensive side reactions. Herein, a novel and facile solid‐state prelithiation approach is proposed to in situ prepare a Li₃AlH₆‐Al nanocomposite from a short‐circuited electrochemical reaction between LiAlH₄ and Li with the help of fast electron and Li‐ion conductors (C and P6₃mc LiBH₄). This nanocomposite consists of dispersive Al nanograins and an amorphous Li₃AlH₆ matrix, which enables superior electrochemical performance in solid‐state cells, as much higher specific capacity (2266 mAh g^?1), Coulombic efficiency (88%), cycling stability (71% retention in the 100th cycle), and rate capability (1429 mAh g^?1 at 1 A g^?1) are achieved. In addition, this nanocomposite works well in the solid‐state full cell with LiCoO₂ cathode, demonstrating its promising application prospects. Mechanism analysis reveals that the dispersive Al nanograins and amorphous Li₃AlH₆ matrix can dramatically enhance the lithiation and delithiation kinetics without side reactions, which is mainly responsible for the excellent overall performance. Moreover, this solid‐state prelithiation approach is general and can also be applied to other Li‐poor electrode materials for further modification of their electrochemical behavior.     

Exploiting Lithium‐Depleted Cathode Materials for Solid‐State Li Metal Batteries

Solid‐state lithium metal batteries (SSLMBs) may become one of the high‐energy density storage devices for the next generation of electric vehicles. High safety and energy density can be achieved by utilizing solid electrolytes and Li metal anodes. Therefore, developing cathode materials which can match with Li metal anode efficiently is indispensable. In SSLMBs, Li metal anodes can afford the majority of active lithium ions, then lithium‐depleted cathode materials can be a competitive candidate to achieve high gravimetric energy density as well as save lithium resources. Li_0.33MnO₂ lithium‐depleted material is chosen, which also has the advantages of low synthesis temperature and low cost (cobalt‐free). Notably, solid‐state electrolyte can greatly alleviate the problem of manganese dissolution in the electrolyte, which is beneficial to improve the cycling stability of the battery. Thus, SSLMBs enable practical applications of lithium‐depleted cathode materials.     

Interfacial Incompatibility and Internal Stresses in All‐Solid‐State Lithium Ion Batteries

Rechargeable Li‐ion batteries (LIBs) are electrochemical storage device widely applied in electric vehicles, mobile electronic devices, etc. However, traditional LIBs containing liquid electrolytes suffer from flammability, poor electrochemical stability, and limited operational temperature range. Replacement of the liquid electrolytes with inorganic solid‐state electrolytes (SSEs) would solve this problem. However, several critical issues, such as poor interfacial compatibility, low ionic conductivity at ambient temperatures, etc., need to be surmounted before the commercialization of all‐solid‐state Li‐ion batteries (ASSLIBs). In this review, a brief historical context for the inorganic SSEs is described first. Then, two critical issues in the ASSLIBs are highlighted: interfacial incompatibility of the electrodes and SSEs and internal stresses. For the interfacial incompatibility, the discussion is focused on the dynamic characterization of the electrode/SSE interfaces, the origin and evolution of the interfacial resistance, and interface engineering to minimize the interfacial resistance. The internal stresses in the ASSLIBs are another major concern because rigid contacts are introduced. Stress generation, stress evolution during battery cycling, stress measurement/simulation, and ways to alleviate the stresses are outlined in detail. Finally, current challenges and perspectives for future development of the inorganic SSEs and ASSLIBs are outlined.     

Enabling High‐Energy Solid‐State Batteries with Stable Anode Interphase by the Use of Columnar Silicon Anodes

All‐solid‐state batteries (ASSBs) with silicon anodes are promising candidates to overcome energy limitations of conventional lithium‐ion batteries. However, silicon undergoes severe volume changes during cycling leading to rapid degradation. In this study, a columnar silicon anode (col‐Si) fabricated by a scalable physical vapor deposition process (PVD) is integrated in all‐solid‐state batteries based on argyrodite‐type electrolyte (Li₆PS₅Cl, 3 mS cm^?1) and Ni‐rich layered oxide cathodes (LiNi_0.9Co_0.05Mn_0.05O₂, NCM) with a high specific capacity (210 mAh g^?1). The column structure exhibits a 1D breathing mechanism similar to lithium, which preserves the interface toward the electrolyte. Stable cycling is demonstrated for more than 100 cycles with a high coulombic efficiency (CE) of 99.7–99.9% in full cells with industrially relevant areal loadings of 3.5 mAh cm^?2, which is the highest value reported so far for ASSB full cells with silicon anodes. Impedance spectroscopy revealed that anode resistance is drastically reduced after first lithiation, which allows high charging currents of 0.9 mA cm^?2 at room temperature without the occurrence of dendrites and short circuits. Finally, in‐operando monitoring of pouch cells gave valuable insights into the breathing behavior of the solid‐state cell.     

Perovskite Membranes with Vertically Aligned Microchannels for All‐Solid‐State Lithium Batteries

Perovskite‐type solid‐state electrolytes exhibit great potential for the development of all‐solid‐state lithium batteries due to their high Li‐ion conductivity (approaching 10^?3 S cm^?1), wide potential window, and excellent thermal/chemical stability. However, the large solid–solid interfacial resistance between perovskite electrolytes and electrode materials is still a great challenge that hinders the development of high‐performance all‐solid‐state lithium batteries. In this work, a perovskite‐type Li_0.34La_0.51TiO₃ (LLTO) membrane with vertically aligned microchannels is constructed by a phase‐inversion method. The 3D vertically aligned microchannel framework membrane enables more effective Li‐ion transport between the cathode and solid‐state electrolyte than a planar LLTO membrane. A significant decrease in the perovskite/cathode interfacial resistance, from 853 to 133 Ω cm², is observed. It is also demonstrated that full cells utilizing LLTO with vertically aligned microchannels as the electrolyte exhibit a high specific capacity and improved rate performance.     

Recent Progress of the Solid‐State Electrolytes for High‐Energy Metal‐Based Batteries

Secondary batteries based on metal anodes (e.g., Li, Na, Mg, Zn, and Al) are among the most sought‐after candidates for next‐generation mobile and stationary storage systems because they are able to store a larger amount of energy per unit mass or volume. However, unstable electrodeposition and uncontrolled interfacial reactions occuring in liquid electrolytes cause unsatisfying cell performance and potential safety concerns for the commercial application of these metal anodes. Solid‐state electrolytes (SSEs) having a higher modulus are considered capable of inhibiting difficulties associated with the anodes and may enable building of safe all‐solid‐state metal batteries, yet several challenges, such as insufficient room‐temperature ionic conductivity and poor interfacial stability between the electrode and the electrolyte, hinder the large‐scale development of such batteries. Here, research and development of SSEs including inorganic ceramics, organic solid polymers, and organic–inorganic hybrid/composite materials for metal‐based batteries are reviewed. The comparison of different types of electrolytes is discussed in detail, in the context of electrochemical energy storage applications. Then, the focus of this study is on recent advances in a range of attractive and innovative battery chemistries and technologies that are enabled by SSEs. Finally, the challenges and future perspectives are outlined to foresee the development of SSEs.     

On the Functionality of Coatings for Cathode Active Materials in Thiophosphate‐Based All‐Solid‐State Batteries

The last decade has seen considerable advancements in the development of solid electrolytes for solid‐state battery applications, with particular attention being paid to sulfide superionic conductors. Importantly, the intrinsic electrochemical instability of these high‐performance separators highlights the notion that further progress in the field of solid‐state batteries is contingent on the optimization of component material interfaces in order to secure high energy and power densities, while maintaining device safety and a practical cycle life. On the cathode side, the need for a protective coating to inhibit solid electrolyte degradation is clear; however, a mechanistic understanding of the coating functionality remains unresolved, and there is still much room for improvement regarding the methodology and associated material properties. Herein, the essential requirements for a suitable coating are specified and fundamental considerations are discussed in detail. Additionally, this article will provide an overview of the various material classes, assessment protocols and practical coating methods, as well as an outlook on the development of coatings for cathode active materials in thiophosphate‐based solid‐state batteries.     

Solvent‐Free Synthesis of Thin,Flexible, Nonflammable Garnet‐Based Composite Solid Electrolyte for All‐Solid‐State Lithium Batteries

Thin solid‐state electrolytes with nonflammability, high ionic conductivity, low interfacial resistance, and good processability are urgently required for next‐generation safe, high energy density lithium metal batteries. Here, a 3D Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO) self‐supporting framework interconnected by polytetrafluoroethylene (PTFE) binder is prepared through a simple grinding method without any solvent. Subsequently, a garnet‐based composite electrolyte is achieved through filling the flexible 3D LLZTO framework with a succinonitrile solid electrolyte. Due to the high content of garnet ceramic (80.4 wt%) and high heat‐resistance of the PTFE binder, such a composite electrolyte film with nonflammability and high processability exhibits a wide electrochemical window of 4.8 V versus Li/Li⁺ and high ionic transference number of 0.53. The continuous Li⁺ transfer channels between interconnected LLZTO particles and succinonitrile, and the soft electrolyte/electrode interface jointly contribute to a high ambient‐temperature ionic conductivity of 1.2 × 10^?4 S cm^?1 and excellent long‐term stability of the Li symmetric battery (stable at a current density of 0.1 mA cm^?2 for over 500 h). Furthermore, as‐prepared LiFePO₄|Li and LiNi_0.5Mn_0.3Co_0.2O₂|Li batteries based on the thin composite electrolyte exhibit high discharge specific capacities of 153 and 158 mAh g^?1 respectively, and desirable cyclic stabilities at room temperature.     

Digital Twin‐Driven All‐Solid‐State Battery: Unraveling the Physical and Electrochemical Behaviors

The digital twin technique has been broadly utilized to efficiently and effectively predict the performance and problems associated with real objects via a virtual replica. However, the digitalization of twin electrochemical systems has not been achieved thus far, owing to the large amount of required calculations of numerous and complex differential equations in multiple dimensions. Nevertheless, with the help of continuous progress in hardware and software technologies, the fabrication of a digital twin‐driven electrochemical system and its effective utilization have become a possibility. Herein, a digital twin‐driven all‐solid‐state battery with a solid sulfide electrolyte is built based on a voxel‐based microstructure. Its validity is verified using experimental data, such as effective electronic/ionic conductivities and electrochemical performance, for LiNi_0.70Co_0.15Mn_0.15O₂ composite electrodes employing Li₆PS₅Cl. The fundamental performance of the all‐solid‐state battery is scrutinized by analyzing simulated physical and electrochemical behaviors in terms of mass transport and interfacial electrochemical reaction kinetics. The digital twin model herein reveals valuable but experimentally inaccessible time‐ and space‐resolved information including dead particles, specific contact area, and charge distribution in the 3D domain. Thus, this new computational model is bound to rapidly improve the all‐solid‐state battery technology by saving the research resources and providing valuable insights.     

Germanium Thin Film Protected Lithium Aluminum Germanium Phosphate for Solid‐State Li Batteries

Solid‐state Li batteries using Na⁺ superionic conductor type solid electrolyte attracts wide interest because of its safety and high theoretical energy density. The NASCION type solid electrolyte LAGP (Li_1.5Al_0.5Ge_0.5P₃O₁₂) shows favorable conductivity as well as good mechanical strength to prevent Li dendrite penetration. However, the instability of LAGP with Li metal remains a great challenge. In this work, an amorphous Ge thin film is sputtered on an LAGP surface, which can not only suppress the reduction reaction of Ge⁴⁺ and Li, but also produces intimate contact between the Li metal and the LAGP solid electrolyte. The symmetric cell with the Ge‐coated LAGP solid electrolyte shows superior stability and cycle performance for 100 cycles at 0.1 mA cm^?2. A quasi‐solid‐state Li–air battery has also been assembled to further demonstrate this advantage. A stable cycling performance of 30 cycles in ambient air can be obtained. This work helps to achieve a stable and ionic conducting interface in solid‐state Li batteries.     

A 3D Lithium/Carbon Fiber Anode with Sustained Electrolyte Contact for Solid‐State Batteries

To reconcile the energy storage ability and operational safety of lithium metal batteries (LMBs), a transformation from a liquid to a solid‐state system is required. However, Li volume variation, poor interfacial contact, and high operation temperatures hinder its practical applications. To address the above issues, here, an integral structure design for solid‐state LMBs is shown, in which a Li‐preinfused 3D carbon fiber (Li/CF) anode is ionically connected to a cathode via an autopolymerized gel electrolyte. The gel electrolyte helps to encapsulate the liquid electrolyte within the Li/CF anode and the cathode to improve the interfacial contact. The gel also serves as a reservoir that balances the liquid electrolyte supply during repeated Li stripping/plating process. As a result, the symmetrical cells and full cells with Li/CF electrodes exhibit improved cycling stability and effective suppression of dendrites at ambient temperature. This work facilitates the realization of solid‐state LMBs with high energy and high safety.     

Fluorine‐Free Noble Salt Anion for High‐Performance All‐Solid‐State Lithium–Sulfur Batteries

Amongst post‐Li‐ion battery technologies, lithium–sulfur (Li–S) batteries have captured an immense interest as one of the most appealing devices from both the industrial and academia sectors. The replacement of conventional liquid electrolytes with solid polymer electrolytes (SPEs) enables not only a safer use of Li metal (Li°) anodes but also a flexible design in the shape of Li–S batteries. However, the practical implementation of SPEs‐based all‐solid‐state Li–S batteries (ASSLSBs) is largely hindered by the shuttling effect of the polysulfide intermediates and the formation of dendritic Li° during the battery operation. Herein, a fluorine‐free noble salt anion, tricyanomethanide [C(CN)₃^?, TCM^?], is proposed as a Li‐ion conducting salt for ASSLSBs. Compared to the widely used perfluorinated anions {e.g., bis(trifluoromethanesulfonyl)imide anion, [N(SO₂CF₃)₂)]^?, TFSI^?}, the LiTCM‐based electrolytes show decent ionic conductivity, good thermal stability, and sufficient anodic stability suiting the cell chemistry of ASSLSBs. In particular, the fluorine‐free solid electrolyte interphase layer originating from the decomposition of LiTCM exhibits a good mechanical integrity and Li‐ion conductivity, which allows the LiTCM‐based Li–S cells to be cycled with good rate capability and Coulombic efficiency. The LiTCM‐based electrolytes are believed to be the most promising candidates for building cost‐effective and high energy density ASSLSBs in the near future.     

Stack Pressure Considerations for Room‐Temperature All‐Solid‐State Lithium Metal Batteries

All‐solid‐state batteries are expected to enable batteries with high energy density with the use of lithium metal anodes. Although solid electrolytes are believed to be mechanically strong enough to prevent lithium dendrites from propagating, various reports today still show cell failure due to lithium dendrit growth at room temperature. While cell parameters such as current density, electrolyte porosity, and interfacial properties have been investigated, mechanical properties of lithium metal and the role of applied stack pressure on the shorting behavior are still poorly understood. Here, failure mechanisms of lithium metal are investigated in all‐solid‐state batteries as a function of stack pressure, and in situ characterization of the interfacial and morphological properties of the buried lithium is conducted in solid electrolytes. It is found that a low stack pressure of 5 MPa allows reliable plating and stripping in a lithium symmetric cell for more than 1000 h, and a Li | Li₆PS₅Cl | LiNi_0.80Co_0.15Al_0.05O₂ full cell, plating more than 4 µm of lithium per charge, is able to cycle over 200 cycles at room temperature. These results suggest the possibility of enabling the lithium metal anode in all‐solid‐state batteries at reasonable stack pressures.