Advances and Prospects of Sulfide All-Solid-State Lithium Batteries via One-to-One Comparison with Conventional Liquid Lithium Ion Batteries

Regenerative Solid Interfaces Enhance High-Performance All-Solid-State Lithium Batteries

The performance of all-solid-state lithium batteries (ASSLBs) is significantly impacted by lithium interfacial instability, which originates from the dynamic chemical, morphological, and mechanical changes during deep Li plating and stripping. In this study, we introduce a facile approach to generate a conductive and regenerative solid interface, enhancing both the Li interfacial stability and overall cell performance. The regenerative interface is primarily composed of nanosized lithium iodide (nano-LiI), which originates in situ from the adopted solid-state electrolyte (SSE). During cell operation, the nano-LiI interfacial layer can reversibly diffuse back and forth in synchronization with Li plating and stripping. The interface and dynamic process improve the adhesion and Li+ transport between the Li anode and SSE, facilitating uniform Li plating and stripping. As a result, the metallic Li anode operates stably for over 1000 h at high current densities and even under elevated temperatures. By using metallic Li as the anode directly, we demonstrate stable cycling of all-solid-state Li-sulfur batteries for over 250 cycles at an areal capacity of >2 mA h cm-2 and room temperature. This study offers insights into the design of regenerative and Li+-conductive interfaces to tackle solid interfacial challenges for high-performance ASSLBs.

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

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

Enhanced Electrochemical Stability and Extended Cycle Life in Sulfide-Based All-Solid-State Batteries: The Role of Li10 SnP2 S12 Coating on Ni-Rich NCM Cathode

Recently, sulfide-based all-solid-state batteries (ASSBs) have attracted great attention because of their excellent safety and high energy density. However, by-products formed from side-reactions between the oxide-based cathodes and sulfide-based solid electrolytes (SEs) increase the interfacial resistance and degrade the cell performance. Suppression of this interfacial resistance is thus critical. In this study, the extraordinarily high stability of the cathode/SE interface is discovered when a Li10 SnP2 S12 (LSnPS) is applied to a cathode buffer layer. The electrochemical properties of the cathode interface at high potential are improved by synthesizing a core-shell structure cathode using LSnPS. The synthesized LSnPS is uniformly coated on a Li2 ZrO3 -coated LiNi0.8 Co0.1 Mn0.1 O2 (LZO-NCM) surface using the cost-efficient mechano-fusion method. The ASSB with LSnPS-coated LZO-NCM as the cathode and Li6 PS5 Cl (argyrodite, LPSCl) as the SE exhibited a capacity of 192 mAh g-1 and excellent cycle retention of ≈75% after 500 charge/discharge cycles. In addition, the degradation mechanism at the cathode/SE interface is investigated. The results indicated that LSnPS stabilizes the interface between NCM and argyrodite, thereby inhibiting the decomposition of the SE. This technology is expected to contribute to the commercialization of cathode materials for sulfide-based ASSBs due to its enhanced cycle performance, low-cost material application, and eco-friendly process.

Preparation of Metal-Oxide-Doped Li7P2S8Br0.25I0.75 Solid Electrolytes for All-Solid-State Lithium Batteries

The all-solid-state lithium battery (ASSB) has received great attention due to its greater safety than the conventional lithium-ion battery (LIB). Sulfide-based inorganic solid electrolytes are an important component to fabricate the ASSB. But to attain a better performance, the ionic conductivity and electrochemical stability of the sulfide-based solid electrolytes need to be improved. In this work, we prepared the metal-oxide-doped/mixed Li₇P₂S₈I_0.75Br_0.25 lithium superionic conductors by a dry ball-milling process. The high ionic conductivity was achieved by a low-temperature (200 °C) heat-treatment process. The metal-oxide-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte exhibited a higher ionic conductivity value of 7.3 mS cm^-1 at room temperature than the bare Li₇P₂S₈I_0.75Br_0.25 solid electrolyte. The structural characteristics of the prepared solid electrolytes were studied by solid NMR and laser Raman analysis. The electrochemical stability of the prepared solid electrolyte was studied by cyclic voltammetry and DC charge-discharge analysis. The addition of metal oxide increased the electrochemical stability and dry-air stability of the Li₇P₂S₈I_0.75Br_0.25 solid electrolyte. The Ta₂O₅-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte was stable even after 300 charge-discharge DC cycles and also 100 h of dry-air exposure. Further, the Ta₂O₅-doped Li₇P₂S₈I_0.75Br_0.25 solid electrolyte-based ASSB exhibited a high discharge capacity value of 184 mA h g^-1 at 0.1 C rate with 66% initial cycle Coulombic efficiency.

Rational Design of High-Performance PEO/Ceramic Composite Solid Electrolytes for Lithium Metal Batteries

Composite solid electrolytes (CSEs) with poly(ethylene oxide) (PEO) have become fairly prevalent for fabricating high-performance solid-state lithium metal batteries due to their high Li+ solvating capability, flexible processability and low cost. However, unsatisfactory room-temperature ionic conductivity, weak interfacial compatibility and uncontrollable Li dendrite growth seriously hinder their progress. Enormous efforts have been devoted to combining PEO with ceramics either as fillers or major matrix with the rational design of two-phase architecture, spatial distribution and content, which is anticipated to hold the key to increasing ionic conductivity and resolving interfacial compatibility within CSEs and between CSEs/electrodes. Unfortunately, a comprehensive review exclusively discussing the design, preparation and application of PEO/ceramic-based CSEs is largely lacking, in spite of tremendous reviews dealing with a broad spectrum of polymers and ceramics. Consequently, this review targets recent advances in PEO/ceramic-based CSEs, starting with a brief introduction, followed by their ionic conduction mechanism, preparation methods, and then an emphasis on resolving ionic conductivity and interfacial compatibility. Afterward, their applications in solid-state lithium metal batteries with transition metal oxides and sulfur cathodes are summarized. Finally, a summary and outlook on existing challenges and future research directions are proposed.

A Review of Nonaqueous Electrolytes, Binders, and Separators for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are the most important electrochemical energy storage devices due to their high energy density, long cycle life, and low cost. During the past decades, many review papers outlining the advantages of state-of-the-art LIBs have been published, and extensive efforts have been devoted to improving their specific energy density and cycle life performance. These papers are primarily focused on the design and development of various advanced cathode and anode electrode materials, with less attention given to the other important components of the battery. The “nonelectroconductive” components are of equal importance to electrode active materials and can significantly affect the performance of LIBs. They could directly impact the capacity, safety, charging time, and cycle life of batteries and thus affect their commercial application. This review summarizes the recent progress in the development of nonaqueous electrolytes, binders, and separators for LIBs and discusses their impact on the battery performance. In addition, the challenges and perspectives for future development of LIBs are discussed, and new avenues for state-of-the-art LIBs to reach their full potential for a wide range of practical applications are outlined.

Graphic Abstract

Role of Interfaces in Solid-State Batteries

Solid-state batteries (SSBs) are considered as one of the most promising candidates for the next-generation energy-storage technology, because they simultaneously exhibit high safety, high energy density, and wide operating temperature range. The replacement of liquid electrolytes with solid electrolytes produces numerous solid-solid interfaces within the SSBs. A thorough understanding on the roles of these interfaces is indispensable for the rational performance optimization. In this review, the interface issues in the SSBs, including internal buried interfaces within solid electrolytes and composite electrodes, and planar interfaces between electrodes and solid electrolyte separators or current collectors are discussed. The challenges and future directions on the investigation and optimization of these solid-solid interfaces for the production of the SSBs are also assessed.

Ionically and Electronically Conductive Phases in a Composite Anode for High-Rate and Stable Lithium Stripping and Plating for Solid-State Lithium Batteries

Intensive efforts have been taken to decrease the over-potentials of solid-state lithium batteries. Lowering the anode-electrolyte interface resistance is an effective method. Compared to simply improving the interface contact, constructing both ionically and electronically conductive phases within the anode demonstrates superior improvement in reducing the interface resistance and promoting electrochemical stability. However, complex preparation procedures are usually involved in the construction of the conductive phases and the loading of metallic lithium. Herein, a composite anode containing metallic lithium and well-dispersed ionically conductive Li₃N and electronically conductive components (Fe, Fe₃C, and amorphous carbon) shows an effective decrease in lithium stripping/plating over-potentials at high current densities of up to 3 mA cm^-2. The unique dual ionically and electronically conductive phases exhibit good cycling stability for 3000 h. A full battery with the composite anode and a LiFePO₄ cathode also demonstrates decent performance. This work confirms the importance of constructing dual conductive phases that are electrochemically stable to Li and will not be consumed during the electrochemical reaction and provides a facile preparation method. The new knowledge discovered and the new methods developed in this work would inspire the future development of new Li-containing composite anodes.

Development of High-Energy Anodes for All-Solid-State Lithium Batteries Based on Sulfide Electrolytes

All-solid-state Li batteries (ASSBs) promise better performance and higher safety than the current liquid-based Li-ion batteries (LIBs). Sulfide ASSBs have been extensively studied and considerably advanced in recent decades. Research on identifying suitable cathode materials for sulfide ASSBs is currently well established, with great progress being made in the commercialization of layered cathodes in the liquid-based LIBs. Research on anode materials for sulfide ASSBs is of great importance for enhancing the battery energy density. However, it seems that little has been published that summarizes studies of anode materials for sulfide ASSBs and suggests future research directions. Thus, within this Minireview, we aim to provide an overview of previous and current research focused on anode materials for sulfide ASSBs and to suggest a future research direction for developing suitable anode systems for sulfide ASSBs.

Probing the Lithium Substructure and Ionic Conductivity of the Solid Electrolyte Li4PS4I

In search of high-performance solid electrolytes, various materials have been discovered in the past, approaching or even exceeding the ionic conductivity of conventional liquid electrolytes. Among the reported classes of superionic electrolytes for solid-state battery applications, lithium thiophosphates appear to be the most promising owing to their high ionic conductivity and mechanical softness. A recent example is the Li₄PS₄I phase (P4/nmm). Surprisingly, this material shows a comparatively low ionic conductivity at room temperature ranging from 10^-4 to 10^-5 S cm^-1 despite having favorable structural characteristics. Because of discrepancies between experiment and theory regarding the Li-ion conductivity and polymorphism in Li₄PS₄I, we herein examine the crystal structure over a broad temperature range using ex situ and in situ X-ray and neutron powder diffraction techniques. We demonstrate the absence of polymorphic transitions, with a lithium redistribution at low temperatures though, and confirm the relatively poor room-temperature ionic conductivity despite the presence of a three-dimensional (3D) percolation network for facile charge transport.

Ionic and Electronic Conductivities of Lithium Argyrodite Li6PS5Cl Electrolytes Prepared via Wet Milling and Post-Annealing

Lithium argyrodite Li₆PS₅Cl powders are synthesized from Li₂S, P₂S₅, and LiCl via wet milling and post-annealing at 500°C for 4 h. Organic solvents such as hexane, heptane, toluene, and xylene are used during the wet milling process. The phase evolution, powder morphology, and electrochemical properties of the wet-milled Li₆PS₅Cl powders and electrolytes are studied. Compared to dry milling, the processing time is significantly reduced via wet milling. The nature of the solvent does not affect the ionic conductivity significantly; however, the electronic conductivity changes noticeably. The study indicates that xylene and toluene can be used for the wet milling to synthesize Li₆PS₅Cl electrolyte powder with low electronic and comparable ionic conductivities. The all-solid-state cell with the xylene-processed Li₆PS₅Cl electrolyte exhibits the highest discharge capacity of 192.4 mAh·g⁻¹ and a Coulombic efficiency of 81.3% for the first discharge cycle.

Visualizing plating-induced cracking in lithium-anode solid-electrolyte cells

Lithium dendrite (filament) propagation through ceramic electrolytes, leading to short circuits at high rates of charge, is one of the greatest barriers to realizing high-energy-density all-solid-state lithium-anode batteries. Utilizing in situ X-ray computed tomography coupled with spatially mapped X-ray diffraction, the propagation of cracks and the propagation of lithium dendrites through the solid electrolyte have been tracked in a Li/Li₆PS₅Cl/Li cell as a function of the charge passed. On plating, cracking initiates with spallation, conical 'pothole'-like cracks that form in the ceramic electrolyte near the surface with the plated electrode. The spallations form predominantly at the lithium electrode edges where local fields are high. Transverse cracks then propagate from the spallations across the electrolyte from the plated to the stripped electrode. Lithium ingress drives the propagation of the spallation and transverse cracks by widening the crack from the rear; that is, the crack front propagates ahead of the Li. As a result, cracks traverse the entire electrolyte before the Li arrives at the other electrode, and therefore before a short circuit occurs.

A study on Li0.33La0.55TiO3 solid electrolyte with high ionic conductivity and its application in flexible all-solid-state batteries

As flexible all-solid-state batteries are highly safe and light weight, they can be considered as candidates for wearable energy sources. However, their performance needs to be first improved, which can be done by using highly conductive solid-state electrolytes. Herein, we prepare a crystallized and amorphous LLTO electrolyte through magnetron sputtering and investigate the effect of heat treatment on its ionic conductivity. The maximum ionic conductivity of the electrolyte is 9.44 × 10-5 S cm-1 at 140 °C. Electrode fracture after multiple cycles is the chief reason for the failure of solid-state batteries. To improve their cycle performance, we use LiNi0.5Co0.3Mn0.2O2 (NCM) with a volume change rate of 5% as the cathode and LTO with a volume change rate of 2% as the anode. A battery with a high output voltage using an internal series is prepared to enhance its application value. The output voltage of a single-layer NCM/LLTO/LTO battery is 2-2.4 V, while that of a two-layer NCM/LLTO/LTO battery can be 4.8 V in series. Owing to the small volume change rate of the electrode, the battery can be cycled up to 500 times, and the capacity of the battery remains at 89.2% of the initial state even after bending.

Combined wet milling and heat treatment in water vapor for producing amorphous to crystalline ultrafine Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte particles

Bulk-type all-solid-state batteries (ASSBs) consisting of composite electrodes of homogeneously mixed fine particles of both active materials and solid electrolytes (SEs) exhibit a high safety, high energy density, and long cycle life. SE nanoparticles are required for the construction of ion-conducting pathways as a response to the particle size reduction of active materials; however, simple and low-cost milling processes for producing nanoparticles cause a collapse in the crystal structure and eventually amorphization, decreasing the conductivity. This study develops a heat treatment process in water vapor for the low-temperature crystallization of ultrafine SE amorphous particles and the size control of crystalline nanoparticles. An ultrafine (approximately 5 nm) amorphous powder of Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), as a typical oxide-type SE, is produced via wet planetary ball milling in ethanol. The water vapor induces a rearrangement of the crystal framework in LATP and accelerates crystallization at a lower temperature than that in air. Further, since particle growth is also promoted by water vapor, depending on the heating temperature and time, this heat treatment process can be also applied to the size control of crystalline LATP nanoparticles. A combination of the wet planetary ball milling and heat treatment in water vapor will accelerate the practical application of bulk-type ASSBs.

The preparation of ultrafine particles through combined wet planetary ball milling and heat treatment in water vapor contributes to the fabrication of extensive composite electrodes with solid electrolytes for bulk-type all-solid-state batteries.

NiCo2S4 Bi-metal Sulfide Coating on LiNi0.6Co0.2Mn0.2O2 Cathode for High-Performance All-Solid-State Lithium Batteries

NiCo₂S₄ nanoparticles (NPs) were dry coated on LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode using a resonant acoustic coating technique to produce all-solid-state lithium batteries. The NiCo₂S₄ coating improved the electrochemical properties of the NCM622 cathode. In addition, NiCo₂S₄ eliminated the space-charge layer and the cathode showed an excellent affinity with the interface with a sulfide-based solid electrolyte as an inert material. X-ray diffraction patterns of NCM622 coated with NiCo₂S₄ showed the same peak separations and lattice parameters as those of bare NCM622. Field-emission scanning electron microscopy and electron dispersive spectroscopy mapping analyses showed that 0.3 wt% NiCo₂S₄-coated NCM622 had an evenly modified surface with NiCo₂S₄ NPs. X-ray photoelectron spectroscopy (XPS) revealed that the surface of 0.3 wt% NiCo₂S₄-coated NCM622 had two different S 2p peaks, a Co-S peak, and Ni and Co peaks, compared to those of bare NCM622. Electrochemical studies with electrochemical impedance spectroscopy and galvanostatic charge-discharge cycle performances showed that NiCo₂S₄-coated NCM622 retained a higher specific capacity over multiple cycles than bare NCM622. Especially, 0.3 wt% NiCo₂S₄-coated NCM622 exhibited a capacity retention of 60.6% at a current density of 15 mA/g for 20 cycles, compared to only 37.3% for bare NCM622. Finally, interfacial XPS and transmission electron microscopy-electron energy loss spectroscopy analyses confirmed the stable state of 0.3 wt% NiCo₂S₄-coated NCM622 with minimal side reactions.

Effect of surface carbonates on the cyclability of LiNbO3-coated NCM622 in all-solid-state batteries with lithium thiophosphate electrolytes

While still premature as an energy storage technology, bulk solid-state batteries are attracting much attention in the academic and industrial communities lately. In particular, layered lithium metal oxides and lithium thiophosphates hold promise as cathode materials and superionic solid electrolytes, respectively. However, interfacial side reactions between the individual components during battery operation usually result in accelerated performance degradation. Hence, effective surface coatings are required to mitigate or ideally prevent detrimental reactions from occurring and having an impact on the cyclability. In the present work, we examine how surface carbonates incorporated into the sol-gel-derived LiNbO3 protective coating on NCM622 [Li1+x(Ni0.6Co0.2Mn0.2)1-xO2] cathode material affect the efficiency and rate capability of pellet-stack solid-state battery cells with β-Li3PS4 or argyrodite Li6PS5Cl solid electrolyte and a Li4Ti5O12 anode. Our research data indicate that a hybrid coating may in fact be beneficial to the kinetics and the cycling performance strongly depends on the solid electrolyte used.

An Air-Stable and Li-Metal-Compatible Glass-Ceramic Electrolyte enabling High-Performance All-Solid-State Li Metal Batteries

The development of all-solid-state Li metal batteries (ASSLMBs) has attracted significant attention due to their potential to maximize energy density and improved safety compared to the conventional liquid-electrolyte-based Li-ion batteries. However, it is very challenging to fabricate an ideal solid-state electrolyte (SSE) that simultaneously possesses high ionic conductivity, excellent air-stability, and good Li metal compatibility. Herein, a new glass-ceramic Li_3.2 P_0.8 Sn_0.2 S₄ (gc-Li_3.2 P_0.8 Sn_0.2 S₄ ) SSE is synthesized to satisfy the aforementioned requirements, enabling high-performance ASSLMBs at room temperature (RT). Compared with the conventional Li₃ PS₄ glass-ceramics, the present gc-Li_3.2 P_0.8 Sn_0.2 S₄ SSE with 12% amorphous content has an enlarged unit cell and a high Li⁺ ion concentration, which leads to 6.2-times higher ionic conductivity (1.21 × 10^-3 S cm^-1 at RT) after a simple cold sintering process. The (P/Sn)S₄ tetrahedron inside the gc-Li_3.2 P_0.8 Sn_0.2 S₄ SSE is verified to show a strong resistance toward reaction with H₂ O in 5%-humidity air, demonstrating excellent air-stability. Moreover, the gc-Li_3.2 P_0.8 Sn_0.2 S₄ SSE triggers the formation of Li-Sn alloys at the Li/SSE interface, serving as an essential component to stabilize the interface and deliver good electrochemical performance in both symmetric and full cells. The discovery of this gc-Li_3.2 P_0.8 Sn_0.2 S₄ superionic conductor enriches the choice of advanced SSEs and accelerates the commercialization of ASSLMBs.

Li2ZrO3-Coated NCM622 for Application in Inorganic Solid-State Batteries: Role of Surface Carbonates in the Cycling Performance

All-inorganic solid-state batteries (SSBs) currently attract much attention as next-generation high-density energy-storage technology. However, to make SSBs competitive with conventional Li-ion batteries, several obstacles and challenges must be overcome, many of which are related to interface stability issues. Protective coatings can be applied to the electrode materials to mitigate side reactions with the solid electrolyte, with lithium transition metal oxides, such as LiNbO₃ or Li₂ZrO₃, being well established in research. In addition, it has been recognized lately that carbonates incorporated into the coating may also positively affect the interface stability. In this work, we studied the effect that surface carbonates in case of Li₂ZrO₃-coated Li_1+x(Ni_0.6Co_0.2Mn_0.2)_1-xO₂ (NCM622) cathode material have on the cyclability of pellet stack SSB cells with Li₆PS₅Cl and Li₄Ti₅O₁₂ as a solid electrolyte and an anode, respectively. Both carbonate-rich and carbonate-poor hybrid coatings were produced by altering the synthesis conditions. The best cycling performance was achieved for carbonate-deficient Li₂ZrO₃-coated NCM622 due to decreased degradation of the argyrodite solid electrolyte at the interfaces, as determined by ex situ X-ray photoelectron spectroscopy and in situ differential electrochemical mass spectrometry. The results emphasize the importance of tailoring the composition and nature of protective coatings to improve the cyclability of bulk SSBs.

Lithium and Chlorine-Rich Preparation of Mechanochemically Activated Antiperovskite Composites for Solid-State Batteries

Assembling all-solid-state batteries presents a unique challenge due to chemical and electrochemical complexities of interfaces between a solid electrolyte and electrodes. While the interface stability is dictated by thermodynamics, making use of passivation materials often delays interfacial degradation and extends the cycle life of all-solid cells. In this work, we investigated antiperovskite lithium oxychloride, Li₃OCl, as a promising passivation material that can engineer the properties of solid electrolyte-Li metal interfaces. Our experiment to obtain stoichiometric Li₃OCl focuses on how the starting ratios of lithium and chlorine and mechanochemical activation affect the phase stability. For substantial LiCl excess conditions, the antiperovskite phase was found to form by simple melt-quenching and subsequent high-energy ball-milling. Li₃OCl prepared with 100% excess LiCl exhibits ionic conductivity of 3.2 × 10⁻⁵ S cm⁻¹ at room temperature, as well as cathodic stability against Li metal upon the extended number of cycling. With a conductivity comparable to other passivation layers, and stable interface properties, our Li₃OCl/LiCl composite has the potential to stably passivate the solid-solid interfaces in all-solid-state batteries.

Li7GeS5Br-An Argyrodite Li-Ion Conductor Prepared by Mechanochemical Synthesis

In recent years, the search for glassy and ceramic Li⁺ superionic conductors has received significant attention, mainly due to the renaissance of interest in all-solid-state batteries. Here, we report the mechanochemical synthesis of metastable Li₇GeS₅Br, which is, to the best of our knowledge, the first compound of the Li₂S-GeS₂-LiBr system. Applying combined synchrotron X-ray diffraction and neutron powder diffraction, we show Li₇GeS₅Br to crystallize in the F4̅3m space group and to be isostructural with argyrodite-type Li₆PS₅Br, but with a distinct difference in the S^2-/Br^- site disorder (and improved anodic stability). Electrochemical impedance spectroscopy indicates an electrical (ionic) conductivity of 0.63 mS cm^-1 at 298 K, with an activation energy for conduction of 0.43 eV. This is supported by temperature-dependent ⁷Li pulsed-field gradient-nuclear magnetic resonance spectroscopy measurements. Overall, the results demonstrate that novel (metastable) argyrodite-type solid electrolytes can be prepared via mechanochemistry that are not accessible by conventional solid-state synthesis routes.

Revealing the Role of Liquid Metals at the Anode-Electrolyte Interface for All Solid-State Lithium-Ion Batteries

All-solid-state lithium-ion batteries (ASSLIBs) are receiving tremendous attention for safety concerns over liquid system. However, current ASSLIBs still suffer from poor cycling and rate performance because of unfavorable interfacial contact between solid electrolyte and electrodes, especially in the alloy-based anode. To wet the solid electrode/electrolyte interface, accommodate volume change, and further boost kinetics, liquid metal Ga is introduced into the representative Sb anode, and its corresponding role is comprehensively revealed by experimental results and theoretical calculations for the first time. In addition to interface contact and strain accommodation, with the aid of in situ generation of liquid metal Ga, the lithiation/de-lithiation activity of Sb is stimulated, showing outstanding rate and cycling performance in half cells. Furthermore, benefited from the in situ chemical reaction, TiS₂ powder can be directly used to construct a novel "Li-free" TiS₂|LiBH₄|GaSb full cell, which exhibits an outstanding capacity retention of 226 mA h g^-1 after 1000 cycles at a current density of 0.5 A g^-1. This work provides guidance for implementing future rational design of alloy anodes within ASSLIBs.

Sulfide and Oxide Inorganic Solid Electrolytes for All-Solid-State Li Batteries: A Review

Energy storage materials are finding increasing applications in our daily lives, for devices such as mobile phones and electric vehicles. Current commercial batteries use flammable liquid electrolytes, which are unsafe, toxic, and environmentally unfriendly with low chemical stability. Recently, solid electrolytes have been extensively studied as alternative electrolytes to address these shortcomings. Herein, we report the early history, synthesis and characterization, mechanical properties, and Li+ ion transport mechanisms of inorganic sulfide and oxide electrolytes. Furthermore, we highlight the importance of the fabrication technology and experimental conditions, such as the effects of pressure and operating parameters, on the electrochemical performance of all-solid-state Li batteries. In particular, we emphasize promising electrolyte systems based on sulfides and argyrodites, such as LiPS5Cl and β-Li3PS4, oxide electrolytes, bare and doped Li7La3Zr2O12 garnet, NASICON-type structures, and perovskite electrolyte materials. Moreover, we discuss the present and future challenges that all-solid-state batteries face for large-scale industrial applications.

Improving the Conductivity of Solid Polymer Electrolyte by Grain Reforming

Polyethylene oxide (PEO)-based solid polymer electrolyte (SPE) is considered to have great application prospects in all-solid-state li-ion batteries. However, the application of PEO-based SPEs is hindered by the relatively low ionic conductivity, which strongly depends on its crystallinity and density of grain boundaries. In this work, a simple and effective press-rolling method is applied to reduce the crystallinity of PEO-based SPEs for the first time. With the rolled PEO-based SPE, the LiFePO₄/SPE/Li all-solid li-ion battery delivers a superior rechargeable specific capacity of 162.6 mAh g^-1 with a discharge-charge voltage gap of 60 mV at a current density of 0.2 C with a much lower capacity decay rate. The improvement of electrochemical properties can be attributed to the press-rolling method, leading to a doubling conductivity and reduced activation energy compared with that of electrolyte prepared by traditional cast method. The present work provides an effective and easy-to-use grain reforming method for SPE, worthy of future application.

Co3S4@Li7P3S11 Hexagonal Platelets as Cathodes with Superior Interfacial Contact for All-Solid-State Lithium Batteries

Poor solid-solid contact between an electrode and solid electrolyte is a great challenge for all-solid-state lithium batteries (ASSLBs) which results in limited ion transport and eventually leads to rapid capacity fading. Two-dimensional (2D) materials have incomparable advantage in the construction of the desired interface because of their flat surface and large specific surface area. In order to realize intimate interfacial contact and superior ion transport, monodisperse 2D Co₃S₄ hexagonal platelets as cathodes for all ASSLBs are synthesized through a series of topological reactions followed with in situ coating of tiny Li₇P₃S₁₁ using a liquid-phase method. The unique 2D hexagonal platelets are favorable for in situ solid electrolyte coating. Moreover, the well-designed interfacial structure can make the electrode materials contact with solid electrolytes more closely, contributing to a remarkable improvement on electrochemical performance. ASSLBs employing the Co₃S₄@Li₇P₃S₁₁ composite platelets as a cathode deliver a large reversible capacity of 685.9 mA h g^-1 at 0.5 A g^-1 for 50 cycles. Even at a high current density of 1 A g^-1, the Co₃S₄@Li₇P₃S₁₁ composite cathode still exhibits a high capacity of 457.3 mA h g^-1 after 100 cycles. This work provides a simple strategy to design the composite electrode with intimate contact and superior ion transport via morphology controlling.

Influence of electronically conductive additives on the cycling performance of argyrodite-based all-solid-state batteries

All-solid-state batteries (SSBs) are attracting widespread attention as next-generation energy storage devices, potentially offering increased power and energy densities and better safety than liquid electrolyte-based Li-ion batteries. Significant research efforts are currently underway to develop stable and high-performance bulk-type SSB cells by optimizing the cathode microstructure and composition, among others. Electronically conductive additives in the positive electrode may have a positive or negative impact on cyclability. Herein, it is shown that for high-loading (pelletized) SSB cells using both a size- and surface-tailored Ni-rich layered oxide cathode material and a lithium thiophosphate solid electrolyte, the cycling performance is best when low-surface-area carbon black is introduced.

Low-surface-area carbon black helps to improve the performance of bulk-type all-solid-state batteries using NCM622 cathode material and argyrodite Li₆PS₅Cl solid electrolyte.

Building Better Batteries in the Solid State: A Review

Most of the current commercialized lithium batteries employ liquid electrolytes, despite their vulnerability to battery fire hazards, because they avoid the formation of dendrites on the anode side, which is commonly encountered in solid-state batteries. In a review two years ago, we focused on the challenges and issues facing lithium metal for solid-state rechargeable batteries, pointed to the progress made in addressing this drawback, and concluded that a situation could be envisioned where solid-state batteries would again win over liquid batteries for different applications in the near future. However, an additional drawback of solid-state batteries is the lower ionic conductivity of the electrolyte. Therefore, extensive research efforts have been invested in the last few years to overcome this problem, the reward of which has been significant progress. It is the purpose of this review to report these recent works and the state of the art on solid electrolytes. In addition to solid electrolytes stricto sensu, there are other electrolytes that are mainly solids, but with some added liquid. In some cases, the amount of liquid added is only on the microliter scale; the addition of liquid is aimed at only improving the contact between a solid-state electrolyte and an electrode, for instance. In some other cases, the amount of liquid is larger, as in the case of gel polymers. It is also an acceptable solution if the amount of liquid is small enough to maintain the safety of the cell; such cases are also considered in this review. Different chemistries are examined, including not only Li-air, Li-O2, and Li-S, but also sodium-ion batteries, which are also subject to intensive research. The challenges toward commercialization are also considered.

Argyrodite Solid Electrolyte with a Stable Interface and Superior Dendrite Suppression Capability Realized by ZnO Co-Doping

Despite the high ionic conductivity and good machinability, the application of sulfide solid electrolytes (SEs) is severely limited by the poor compatibility of oxide cathodes with Li metals. Herein, a ZnO co-doping strategy is proposed to enhance the chemical and electrochemical performance of sulfide SEs. Given the synergistic effect by incorporation of ZnO, the argyrodite electrolyte achieves superior interfacial stability and Li dendrite suppression capability. By in-depth ex situ analyses, the enhancement is ascribed to LiZn and Li₃OBr formed in the argyrodite/Li interface and a reduced electronic conductivity arising from the ZnO doping. In addition, O doping improves the air stability for argyrodite without degrading the ionic conductivity because of the compensation by Zn doping. Hence, all-solid-state batteries with ZnO-doped electrolytes achieve higher initial Coulombic efficiency and a larger specific capacity than those of the ZnO-free electrolyte. ZnO-doped sulfide SEs are promising to develop all-solid-state Li-metal batteries.