Flexible Sulfide Electrolyte Thin Membrane with Ultrahigh Ionic Conductivity for All-Solid-State Lithium Batteries

Dry-processed technology for flexible and high-performance FeS2-based all-solid-state lithium batteries at low stack pressure

All-solid-state lithium batteries (ASSLBs) are considered promising energy storage systems due to their high energy density and inherent safety. However, scalable fabrication of ASSLBs based on transition metal sulfide cathodes through the conventional powder cold-pressing method with ultrahigh stacking pressure remains challenging. This article elucidates a dry process methodology for preparing flexible and high-performance FeS2-based ASSLBs under low stack pressure by utilizing polytetrafluoroethylene (PTFE) binder. In this design, fibrous PTFE interweaves Li6PS5Cl particles and FeS2 cathode components, forming flexible electrolyte and composite cathode membranes. Beneficial to the robust adhesion, the composite cathode and Li6PS5Cl membranes are tightly compacted under a low stacking pressure of 100 MPa which is a fifth of the conventional pressure. Moreover, the electrode/electrolyte interface can sustain adequate contact throughout electrochemical cycling. As expected, the FeS2-based ASSLBs exhibit outstanding rate performance and cyclic stability, contributing a reversible discharged capacity of 370.7 mAh g-1 at 0.3C after 200 cycles. More importantly, the meticulous dQ/dV analysis reveals that the three-dimensional PTFE binder effectively binds the discharge products with sluggish kinetics (Li2S and Fe) to the ion-electron conductive network in the composite cathode, thereby preventing the electrochemical inactivation of products and enhancing electrochemical performance. Furthermore, FeS2-based pouch-type cells are fabricated, demonstrating the potential of PTFE-based dry-process technology to scale up ASSLBs from laboratory-scale mold cells to factory-scale pouch cells. This feasible dry-processed technology provides valuable insights to advance the practical applications of ASSLBs.

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.

Fast Kinetics Design for Solid-State Battery Device

Fast kinetics of solid-state batteries at the device level is not adequately explored to achieve fast charging and discharging. In this work, a leap forward is achieved for fast kinetics in full cells with high cathode loading and areal capacity. This kinetic improvement is achieved by designing a hierarchical structure of electrode composites. In the cathode, the authors' design enables high areal capacities above 3 mAh cm-2 to be stably cycled at high current densities of ≈13-40 mA cm-2, yielding a C-rate from 5 to 10 C. In the anode, the authors' design breaks the common rule of the negative correlation between critical C-rate and the discharge voltage that is observed in most other anodes. The overall design enables the fast cycling of such batteries for over 4000 cycles at room temperature and 5 C charge-rate. The design principles unveiled by this work help to understand critical kinetic processes in battery devices that limit the fast cycling at high cathode loading and speed up the design of high-performance solid-state batteries.

Designing Reliable Cathode System for High-Performance Inorganic Solid-State Pouch Cells

All-solid-state batteries (ASSBs) based on inorganic solid electrolytes fascinate a large body of researchers in terms of overcoming the inferior energy density and safety issues of existing lithium-ion batteries. To date, the cathode designs in the ASSBs achieve remarkable achievements, adding the urgency of scaling up the battery system toward inorganic solid-state pouch cell configuration for the application market. Herein, the recent developments of cathode materials and the design considerations for their application in the pouch cell format are reviewed to straighten out the roadmap of ASSBs. Specifically, the intercalation compounds and the conversion materials with conversion chemistries are highlighted and discussed as two potentially valuable material types. This review focuses on the basic electrochemical mechanisms, mechanical contact issues, and sheet-type structure in inorganic solid-state pouch cells with corresponding perspectives, thus guiding the future research direction. Finally, the benchmarks for manufacturing inorganic solid-state pouch cells to meet practical high energy density targets are provided in this review for the development of commercially viable products.

Jet-Printable, Low-Melting-Temperature Ga-xSn Eutectic Composites: Application in All-Solid-State Batteries

Low-melting-point Ga-xSn eutectic composites and natural silicate mineral powders were used as the electrode and solid-state electrolyte, respectively, in all-solid-state batteries for green energy storage systems. The influences of the Sn content in the Ga-xSn composite electrode on the electrochemical performance of the batteries were evaluated, and liquid composites with a Sn concentration of up to 30 wt.% demonstrated suitability for electrode fabrication through dip coating. Sodium-enriched silicate was synthesized to serve as the solid-state electrolyte membrane because of the abundance of water molecules in its interlayer structure, enabling ion exchange. The battery capacity increased with the Sn content of the Ga-xSn anode. The formation of intermetallic compounds and oxides (CuGa2, Ga2O3, Cu6Sn5, and SnO2) resulted in a high charge-discharge capacity and stability. The Ga-Sn composite electrode for all-solid-state batteries exhibits a satisfiable capacity and stability and shows potential for jet-printed electrode applications.

Efficient Ion Percolating Network for High-Performance All-Solid-State Cathodes

All-solid-state lithium batteries (ASSLBs) face critical challenges of low cathode loading and poor rate performances, which handicaps their energy/power densities. The widely-accepted aim of high ionic conductivity and low interfacial resistance seems insufficient to overcome these challenges. Here, it is revealed that an efficient ion percolating network in the cathode exerts a more critical influence on the electrochemical performance of ASSLBs. By constructing vertical alignment of Li0.35 La0.55 TiO3 nanowires (LLTO NWs) in solid-state cathode through magnetic manipulation, the ionic conductivity of the cathode increases twice compared with the cathode consisted of randomly distributed LLTO NWs. The all-solid-state LiFePO4 /Li cells using poly(ethylene oxide) as the electrolyte is able to deliver high capacities of 151 mAh g-1 (2 C) and 100 mAh g-1 (5 C) at 60 °C, and a room-temperature capacity of 108 mAh g-1 can be achieved at a charging rate of 2 C. Furthermore, the cell can reach a high areal capacity of 3 mAh cm-2 even with a practical LFP loading of 20 mg cm-2 . The universality of this strategy is also presented showing the demonstration in LiNi0.8 Co0.1 Mn0.1 O2 cathodes. This work offers new pathways for designing ASSLBs with improved energy/power densities.

Spray-Printed Flexible Li2S Cathode with Inorganic Ion-Conductive Binder Nano-Li3PS4

Flexible solid-state batteries fabricated by printing techniques are promising integrated power supplies for miniaturized and customized electronic devices. While typically these batteries use polymer solid electrolytes, a flexible Li2S cathode with sulfide solid electrolyte is spray-printed in this work, by using solvated Li3PS4 nanoparticles as inorganic ion-conductive binder. This benefits from a novel low-temperature-sintering property of these nanoparticles, which can be pressure-free densified, along with the desolvation process, and thus bind the cathode at 250 °C. The battery can be stably charged and discharged for 300 cycles with no stacking pressure, and the capacity maintains at 840 mA h gLi2 S-1. We believe this low-temperature-sintering phenomenon of solid electrolyte nanoparticles will open a new path toward the application of sulfide solid electrolytes in printed solid-state batteries.

Self-Assembly of Ultrathin, Ultrastrong Layered Membranes by Protic Solvent Penetration

Flexible membranes with ultrathin thickness and excellent mechanical properties have shown great potential for broad uses in solid polymer electrolytes (SPEs), on-skin electronics, etc. However, an ultrathin membrane (<5 μm) is rarely reported in the above applications due to the inherent trade-off between thickness and antifailure ability. We discover a protic solvent penetration strategy to prepare ultrathin, ultrastrong layered films through a continuous interweaving of aramid nanofibers (ANFs) with the assistance of simultaneous protonation and penetration of a protic solvent. The thickness of a pure ANF film can be controlled below 5 μm, with a tensile strength of 556.6 MPa, allowing us to produce the thinnest SPE (3.4 μm). The resultant SPEs enable Li-S batteries to cycle over a thousand times at a high rate of 1C due to the small ionic impedance conferred by the ultrathin characteristic and regulated ionic transportation. Besides, a high loading of the sulfur cathode (4 mg cm-2) with good sulfur utilization was achieved at a mild temperature (35 °C), which is difficult to realize in previously reported solid-state Li-S batteries. Through a simple laminating process at the wet state, the thicker film (tens of micrometers) obtained exhibits mechanical properties comparable to those of thin films and possesses the capability to withstand high-velocity projectile impacts, indicating that our technique features a high degree of thickness controllability. We believe that it can serve as a valuable tool to assemble nanomaterials into ultrathin, ultrastrong membranes for various applications.

A Fluoride-Rich Solid-Like Electrolyte Stabilizing Lithium Metal Batteries

To address the problems associated with Li metal anodes, a fluoride-rich solid-like electrolyte (SLE) that combines the benefits of solid-state and liquid electrolytes is presented. Its unique triflate-group-enhanced frame channels facilitate the formation of a functional inorganic-rich solid electrolyte interphase (SEI), which not only improves the reversibility and interfacial charge transfer of Li anodes but also ensures uniform and compact Li deposition. Furthermore, these triflate groups contribute to the decoupling of Li+ and provide hopping sites for rapid Li+ transport, enabling a high room-temperature ionic conductivity of 1.1 mS cm-1 and a low activation energy of 0.17 eV, making it comparable to conventional liquid electrolytes. Consequently, Li symmetric cells using such SLE achieve extremely stable plating/stripping cycling over 3500 h at 0.5 mA cm-2 and support a high critical current up to 2 mA cm-2 . The assembled Li||LiFePO4 solid-like batteries exhibit exceptional cyclability for over 1 year and a half, even outperforming liquid cells. Additionally, high-voltage cylindrical cells and high-capacity pouch cells are demonstrated, corroborating much simpler processibility in battery assembly compared to all-solid-state batteries.

3D Printing Manufacturing of Lithium Batteries: Prospects and Challenges toward Practical Applications

The manufacturing and assembly of components within cells have a direct impact on the sample performance. Conventional processes restrict the shapes, dimensions, and structures of the commercially available batteries. 3D printing, a novel manufacturing process for precision and practicality, is expected to revolutionize the lithium battery industry owing to its advantages of customization, mechanization, and intelligence. This technique can be used to effectively construct intricate 3D structures that enhance the designability, integrity, and electrochemical performance of both liquid- and solid-state lithium batteries. In this study, an overview of the development of 3D printing technologies is provided and their suitability for comparison with conventional printing processes is assessed. Various 3D printing technologies applicable to lithium-ion batteries have been systematically introduced, especially more practical composite printing technologies. The practicality, limitations, and optimization of 3D printing are discussed dialectically for various battery modules, including electrodes, electrolytes, and functional architectures. In addition, all-printed batteries are emphatically introduced. Finally, the prospects and challenges of 3D printing in the battery industry are evaluated.

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.

A Dynamically Stable Sulfide Electrolyte Architecture for High-Performance All-Solid-State Lithium Metal Batteries

All-solid-state batteries employing sulfide solid electrolyte and Li metal anode are promising because of their high safety and energy densities. However, the interface between Li metal and sulfides suffers from catastrophic instability which stems the practical use. Here, a dynamically stable sulfide electrolyte architecture to construct the hierarchy of interface stability is reported. By rationally designing the multilayer structures of sulfide electrolytes, the dynamic decomposing-alloying process from MS4 (M = Ge or Sn) unit in sulfide interlayer can significantly prohibit Li dendrite penetration is revealed. The abundance of highly electronic insulating decompositions, such as Li2 S, at the sulfide interlayer interface helps to well constrain the dynamic decomposition process and preserve the long-term polarization stability is also highlighted. By using Li6 PS5 Cl||Li10 SnP2 S12 ||Li6 PS5 Cl electrolyte architecture, Li metal anode shows an unprecedented critical current density over 3 mA cm-2 and achieves the steady over-potential for ≈900 hours. Based upon the merits, the Li||LiNi0.8 Co0.1 Mn0.1 O2 battery delivers a remarkable 75.3% retention even after 600 cycles at 1 C (1C-0.95 mA cm-2 ) under a low stack pressure of 15 MPa.

PVDF-HFP via Localized Iodization as Interface Layer for All-Solid-State Lithium Batteries with Li6 PS5 Cl Films

All-solid lithium (Li) metal batteries (ASSLBs) with sulfide-based solid electrolyte (SEs) films exhibit excellent electrochemical performance, rendering them capable of satisfying the growing demand for energy storage systems. However, challenges persist in the application of SEs film owing to their reactivity with Li metal and uncontrolled formation of lithium dendrites. In this study, iodine-doped poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) as an interlayer (PHI) to establish a stable interphase between Li metal and Li6 PS5 Cl (LPSCl) films is investigated. The release of I ions and PVDF-HFP produces LiI and LiF, effectively suppressing lithium dendrite growth. Density functional theory calculations show that the synthesized interlayer layer exhibits high interfacial energy. Results show that the PHI@Li/LPSCl film/PHI@Li symmetrical cells can cycle for more than 650 h at 0.1 mA cm-2 . The PHI@Li/LPSCl film/NCM622 cell exhibits a distinct enhancement in capacity retention of ≈26% when using LiNi0.6 Mn0.2 Co0.2 O2 (NCM622) as the cathode, compared to pristine Li metal as the anode. This study presents a feasible method for producing next-generation dendrite-free SEs films, promoting their practical use in ASSLBs.

Toward Sustainable All Solid-State Li-Metal Batteries: Perspectives on Battery Technology and Recycling Processes

Lithium (Li)-based batteries are gradually evolving from the liquid to the solid state in terms of safety and energy density, where all solid-state Li-metal batteries (ASSLMBs) are considered the most promising candidates. This is demonstrated by the Bluecar electric vehicle produced by the Bolloré Group, which is utilized in car-sharing services in several cities worldwide. Despite impressive progress in the development of ASSLMBs, their avenues for recycling them remain underexplored, and combined with the current explosion of spent Li-ion batteries, they should attract widespread interest from academia and industry. Here, the potential challenges of recycling ASSLMBs as compared to Li-ion batteries are analyzed and the current progress and prospects for recycling ASSLMBs are summarized and analyzed. Drawing on the lessons learned from Li-ion battery recycling, it is important to design sustainable recycling technologies before ASSLMBs gain widespread market adoption. A battery-recycling-oriented design is also highlighted for ASSLMBs to promote the recycling rate and maximize profitability. Finally, future research directions, challenges, and prospects are outlined to provide strategies for achieving sustainable development of ASSLMBs.

NaF-Rich Multifunctional Layers toward Stable All-Solid-State Sodium Batteries

NASICON oxide solid electrolytes are considered promising candidates for all-solid-state sodium batteries due to their extremely high ionic conductivity and favorable electrochemical stability. However, the practical application of NASICON electrolytes is greatly impeded by poor electrolyte-electrode interfacial contact and continuous sodium dendrite propagation. Herein, a NaF-rich multifunctional interface layer on the surface of a Na anode (Na@NaF-rich), containing NaF, amorphous carbon, and an unreacted C-F bond species, is developed in situ by the reaction between Na and commercial poly(tetrafluoroethylene). This NaF-rich interface layer is proven to reduce the diffusion barriers at the Na/NASICON electrolyte interface and homogenize Na deposition as well as suppress Na dendrite growth, thus achieving a high critical current density of 4 mA cm-2. The resultant Na3V2(PO4)3@C/Na@NaF-rich all-solid-state cell showed a high initial specific capacity of 117.6 mAh g-1 at 0.1 C with a Coulombic efficiency of 94.8%. Even at 0.5 and 1 C, it still exhibited high capacity retentions of 83.3% and 80.4%, respectively, after 750 cycles.

Dry-Electrode All-Solid-State Batteries Fortified with a Moisture Absorbent

For realizing all-solid-state batteries (ASSBs), it is highly desirable to develop a robust solid electrolyte (SE) that has exceptional ionic conductivity and electrochemical stability at room temperature. While argyrodite-type Li6PS5Cl (LPSCl) SE has garnered attention for its relatively high ionic conductivity (∼3.19 × 10-3 S cm-1), it tends to emit hydrogen sulfide (H2S) in the presence of moisture, which can hinder the performance of ASSBs. To address this issue, researchers are exploring approaches that promote structural stability and moisture resistance through elemental doping or substitution. Herein, we suggest using zeolite imidazolate framework-8 as a moisture absorbent in LPSCl without modifying the structure of the SE or the electrode configuration. By incorporating highly ordered porous materials, we demonstrate that ASSBs configured with LPSCl SE display stable cyclability due to effective and long-lasting moisture absorption. This approach not only improves the overall quality of ASSBs but also lays the foundation for developing a moisture-resistant sulfide electrolyte.

Elucidating Ion Transport Phenomena in Sulfide/Polymer Composite Electrolytes for Practical Solid-State Batteries

Despite the enormous interest in inorganic/polymer composite solid-state electrolytes (CSEs) for solid-state batteries (SSBs), the underlying ion transport phenomena in CSEs have not yet been elucidated. Here, we address this issue by formulating a mechanistic understanding of bi-percolating ion channels formation and ion conduction across inorganic-polymer electrolyte interfaces in CSEs. A model CSE is composed of argyrodite-type Li6PS5Cl (LPSCl) and gel polymer electrolyte (GPE, including Li+-glyme complex as an ion-conducting medium). The percolation threshold of the LPSCl phase in the CSE strongly depends on the elasticity of the GPE phase. Additionally, manipulating the solvation/desolvation behavior of the Li+-glyme complex in the GPE facilitates ion conduction across the LPSCl-GPE interface. The resulting scalable CSE (area = 8 × 6 (cm × cm), thickness ~ 40 μm) can be assembled with a high-mass-loading LiNi0.7Co0.15Mn0.15O2 cathode (areal-mass-loading = 39 mg cm-2) and a graphite anode (negative (N)/positive (P) capacity ratio = 1.1) in order to fabricate an SSB full cell with bi-cell configuration. Under this constrained cell condition, the SSB full cell exhibits high volumetric energy density (480 Wh Lcell-1) and stable cyclability at 25 °C, far exceeding the values reported by previous CSE-based SSBs.

Interface Engineering of All-Solid-State Batteries Based on Inorganic Solid Electrolytes

All-solid-state batteries (ASSBs) based on inorganic solid electrolytes (SEs) are one of the most promising strategies for next-generation energy storage systems and electronic devices due to the higher energy density and intrinsic safety. However, the poor solid-solid contact and restricted chemical/electrochemical stability of inorganic SEs both in cathode and anode SE interfaces cause contact failure and the degeneration of SEs during prolonged charge-discharge processes. As a result, the increasing interface resistance significantly affects the coulombic efficiency and cycling performance of ASSBs. Herein, we present a fundamental understanding of physical contact and chemical/electrochemical features of ASSB interfaces based on mainstream inorganic SEs and summarize the recent work on interface modification. SE doping, optimizing morphology, introducing interlayer/coating layer, and utilizing compatible electrode materials are the key methods to prevent side reactions, which are discussed separately in cathode/anode-SE interface. We also highlight the constant extra stack pressure applied during ASSB cycling, which is important to the electrochemical performance. Finally, our perspectives on interface modification for practical high-performance ASSBs are put forward.

Progress and Prospects of Inorganic Solid-State Electrolyte-Based All-Solid-State Pouch Cells

All-solid-state batteries have piqued global research interest because of their unprecedented safety and high energy density. Significant advances have been made in achieving high room-temperature ionic conductivity and good air stability of solid-state electrolytes (SSEs), mitigating the challenges at the electrode-electrolyte interface, and developing feasible manufacturing processes. Along with the advances in fundamental study, all-solid-state pouch cells using inorganic SSEs have been widely demonstrated, revealing their immense potential for industrialization. This review provides an overview of inorganic all-solid-state pouch cells, focusing on ultrathin SSE membranes, sheet-type thick solid-state electrodes, and bipolar stacking. Moreover, several critical parameters directly influencing the energy density of all-solid-state Li-ion and lithium-sulfur pouch cells are outlined. Finally, perspectives on all-solid-state pouch cells are provided and specific metrics to meet certain energy density targets are specified. This review looks to facilitate the development of inorganic all-solid-state pouch cells with high energy density and excellent safety.

Regulating the Solvation Shell Structure of Lithium Ions for Smooth Li Metal Deposition in Quasi-Solid-State Batteries

Gel polymer electrolytes (GPE) are promising next-generation electrolytes for high-energy batteries, combining the multiple advantages of liquid and all-solid-state electrolytes. Herein, we a synthesized GPE using poly(ethylene glycol)acrylate (PEGDA) in order to understand how the GPE efficiently inhibits lithium dendrite formation and growth. The effects of PEGDA on the solvation shell structure of the lithium ion are investigated using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, which are also supported by Raman spectroscopy. The GPE electrolytes with optimal PEGDA concentration exhibit high transference numbers (t Li + ${{_{{\rm Li}{^{+}}}}}$ =0.72) and ionic conductivity (σ=3.24 mS cm^-1 ). A symmetric lithium ion battery using GPE can be stably cycled for 1200 h in comparison to 320 h in a liquid electrolyte (LE), possibly owing to the high content of LiF (17.9 %) in the solid-electrolyte interphase film of the GPE cell. The observed concentration/electric field gradient observed through the finite element method also accounts for the good cycling performance. In addition, a LiCoO₂ |GPE|Li cell demonstrates excellent capacity retention of 87.09 % for 200 cycles; this approach could present promising guidelines for the design of high-energy lithium batteries.

Interface Design Enabling Stable Polymer/Thiophosphate Electrolyte Separators for Dendrite-Free Lithium Metal Batteries

Organic/inorganic interfaces greatly affect Li⁺ transport in composite solid electrolytes (SEs), while SE/electrode interfacial stability plays a critical role in the cycling performance of solid-state batteries (SSBs). However, incomplete understanding of interfacial (in)stability hinders the practical application of composite SEs in SSBs. Herein, chemical degradation between Li₆ PS₅ Cl (LPSCl) and poly(ethylene glycol) (PEG) is revealed. The high polarity of PEG changes the electronic state and structural bonding of the PS₄ ^3- tetrahedra, thus triggering a series of side reactions. A substituted terminal group of PEG not only stabilizes the inner interfaces but also extends the electrochemical window of the composite SE. Moreover, a LiF-rich layer can effectively prevent side reactions at the Li/SE interface. The results provide insights into the chemical stability of polymer/sulfide composites and demonstrate an interface design to achieve dendrite-free lithium metal batteries.

Enhancing the Interfacial Stability of the Li2S-SiS2-P2S5 Solid Electrolyte toward Metallic Lithium Anode by LiI Incorporation

Chalcogenide solid-state electrolytes (SEs) have been regarded as promising candidates for lithium dendrite suppression due to their high ionic conductivity, suitable mechanical strength, and large Li⁺ ion transference number. However, the wide applications of SEs in pragmatic all-solid-state batteries are still retarded by their limited interface stability, which leads to lithium dendrite growth and formation of interphase with high resistance. In addition, the interphase evolution mechanism between SEs and metallic Li anodes remains unclear. Herein, this work demonstrates that the interfacial stability of Li₂S-SiS₂-P₂S₅ SEs can be effectively enhanced by tuning the interphase through LiI incorporation. This strategy contributes to a high ionic conductivity of the SEs and electronic insulation interphase containing LiI. Thus, the 70(60Li₂S-28SiS₂-12P₂S₅)-30 LiI SEs prepared by melt-quenching exhibit a high ionic conductivity of 1.74 mS cm^-1 at room temperature and a larger critical current density of 1.65 mA cm^-2 at 65 °C. The cycling life of the symmetric Li|SEs|Li cell is up to 200 h without significant resistance growth at 0.1 mA cm^-2 at room temperature. This enhanced interface stability is revealed to originate from the in situ-formed LiI within the interphase, which prevents continual SEs degradation and suppresses lithium dendrite growth. This work provides a vital understanding of interphase evolution, which is valuable for designing SEs with long cycling stability.

Toluene Tolerated Li9.88GeP1.96Sb0.04S11.88Cl0.12 Solid Electrolyte toward Ultrathin Membranes for All-Solid-State Lithium Batteries

Sulfide solid electrolyte membranes employed in all-solid-state lithium batteries generally show high thickness and poor chemical stability, which limit the cell-level energy density and cycle life. In this work, Li_9.88GeP_1.96Sb_0.04S_11.88Cl_0.12 solid electrolyte is synthesized with Sb, Cl partial substitution of P, S, possessing excellent toluene tolerance and stability to lithium. The formed SbS₄^3- group in Li_9.88GeP_1.96Sb_0.04S_11.88Cl_0.12 exhibits low adsorption energy and reactivity for toluene molecules, confirmed by first-principles density functional theory calculation. Using toluene as the solvent, ultrathin Li_9.88GeP_1.96Sb_0.04S_11.88Cl_0.12 membranes with adjustable thicknesses can be well prepared by the wet coating method, and an 8 μm thick membrane exhibits an ionic conductivity of 1.9 mS cm^-1 with ultrahigh ionic conductance of 1860 mS and ultralow areal resistance of 0.68 Ω cm^-2 at 25 °C. The obtained LiCoO₂|Li_9.88GeP_1.96Sb_0.04S_11.88Cl_0.12 membrane|Li all-solid-state lithium battery shows an initial reversible capacity of 125.6 mAh g^-1 with a capacity retention of 86.3% after 250 cycles at 0.1 C under 60 °C.

In Situ Formed LiI Interfacial Layer for All-Solid-State Lithium Batteries with Li6PS5Cl Solid Electrolyte Membranes

Sulfide-based solid electrolytes are considered ideal materials for all-solid-state Li metal batteries owing to their high ion conductivity and satisfactory mechanical stiffness. However, the interfacial reaction between the sulfide electrolyte membrane and Li anode severely limits the commercial application of such membranes. Herein, a lithium iodide (LiI) layer is synthesized at the Li metal-sulfide electrolyte membrane interface via chemical vapor deposition. The synthesized LiI layer exhibits satisfactory ionic conductivity and high interfacial energy, as confirmed via density functional theory calculations. Consequently, the LiI@Li/Li₆PS₅Cl membrane/LiI@Li symmetric cell can cycle for >150 h at 0.1 mA cm^-2. The as-prepared all-solid-state batteries exhibit a high discharge capacity of 107 mA h g^-1 and an excellent capacity retention of 76% after 800 cycles at 1 C. This work offers a simple and effective method to improve the interface between the Li anode and sulfide electrolyte membranes that facilitates the mass production and practical application of high-energy-density sulfide-based all-solid-state batteries.

An Ultrathin, Flexible Solid Electrolyte with High Ionic Conductivity Enhanced by a Mutual Promotion Mechanism

The pursuit of strong endurance and nonflammable performances has promoted demand for solid-state batteries (SSBs). Meanwhile, the reduction of electrolytes' thickness is the key to improving battery performance. However, a large-scale feasible method to fabricate an ultrathin solid electrolyte exhibiting high ionic conductivities is still a challenge. Here, we show a large-scale feasible method to prepare a succinonitrile/polyacrylonitrile(SN/PAN)-coated Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) with flexibility and high ionic conductivity by tape-casting. The unique dual polymer-coated garnet electrolytes exhibit structural stability through mutual promotion, constructing soft interparticle contact that provides fast lithium-ion transfer channels. In essence, the mutual promotion mechanism is that SN can improve the Li⁺ conductivity of PAN, while PAN can protect SN from aggregation. Therefore, the flexible SN/PAN-coated LLZTO provides high structural stability and satisfactory electrochemical performance, contributing to a high ionic conductivity of 4 × 10^-4 S cm^-1 at room temperature (RT). In this way, a long lifespan of over 500 cycles and a high discharge capacity (163 mAh g^-1) are achieved based on LiFePO4 (LFP) cathodes at 0.2 C.

A Silica-Reinforced Composite Electrolyte with Greatly Enhanced Interfacial Lithium-Ion Transfer Kinetics for High-Performance Lithium Metal Batteries

Developing quasi-solid-state electrolytes with superior ionic conductivity and high mechanical strength is urgently desired to improve the safety and cycling stability of lithium-metal batteries. Herein, a novel solid-like electrolyte (SLE) with enhanced Li⁺ interfacial transfer kinetics is rationally designed by soaking bulk nanostructured silica-polymer composites in liquid electrolytes. Benefiting from the high content of inorganic silica and abundant interfaces for fast Li⁺ -transport channels, the prepared SLE exhibits superb ionic conductivity and high mechanical strength. Furthermore, fumed silica with a high specific area in the SLE can homogenize Li⁺ flux and electrical field gradient. More importantly, a Li₂ S-rich solid electrolyte interphase (SEI) is constructed on the lithium metal due to the intimate ion coordination in the SLE. Therefore, the lithium-metal anode exhibits excellent electrochemical performance in symmetric Li-Li cells due to the merits of superior ionic conductivity, high modulus, Li₂ S-rich SEI, as well as the homogeneous Li⁺ flux. Full cells with LiFePO₄ cathode can still display a capacity retention of 98% at 0.2 C after 400 cycles. The proposed strategy on quasi-solid-state electrolytes provides a promising avenue for next-generation metal-based batteries.

Room-Temperature Anode-Less All-Solid-State Batteries via the Conversion Reaction of Metal Fluorides

All-solid-state batteries (ASSBs) that employ anode-less electrodes have drawn attention from across the battery community because they offer competitive energy densities and a markedly improved cycle life. Nevertheless, the composite matrices of anode-less electrodes impose a substantial barrier for lithium-ion diffusion and inhibit operation at room temperature. To overcome this drawback, here, the conversion reaction of metal fluorides is exploited because metallic nanodomains formed during this reaction induce an alloying reaction with lithium ions for uniform and sustainable lithium (de)plating. Lithium fluoride (LiF), another product of the conversion reaction, prevents the agglomeration of the metallic nanodomains and also protects the electrode from fatal lithium dendrite growth. A systematic analysis identifies silver (I) fluoride (AgF) as the most suitable metal fluoride because the silver nanodomains can accommodate the solid-solution mechanism with a low nucleation overpotential. AgF-based full cells attain reliable cycling at 25 °C even with an exceptionally high areal capacity of 9.7 mAh cm^-2 (areal loading of LiNi_0.8 Co_0.1 Mn_0.1 O₂  = 50 mg cm^-2 ). These results offer useful insights into designing materials for anode-less electrodes for sulfide-based ASSBs.

Self-Powered Lithium Niobate Thin-Film Photodetectors

Thin-film lithium niobate platform, namely lithium-niobate-on-insulator (LNOI), brings new opportunities for integrated photonics, taking advantages from both outstanding crystalline properties and special structural features. The excellent properties of LNOI have triggered development of a variety of on-chip photonic devices for light generation and manipulation. However, as an indispensable component for photonic circuit with full functionalities, the thin-film photodetector lacks in portfolios of LNOI-based devices due to standing obstacles of low electrical conductivity and poor photoelectric conversion ability. Here, a self-powered broadband LNOI photodetector based on enhanced photovoltaic effect, benefitting from encapsulated plasmonic nanoparticles and doped silver ions, is reported. Maximum responsivity of 0.25 A W^-1 and detectivity (1.56 × 10¹⁴ Jones) are achieved. First-principle calculations and electric-field simulation reveal intrinsic mechanisms and crucial roles of plasmonic nanoparticles and silver ions on photocurrent generation and collection. This work opens an avenue to develop high-performance on-chip LNOI photodetectors, offering a conceivable means toward multiple-functional photonic circuits.

Priority and Prospect of Sulfide-Based Solid-Electrolyte Membrane

All-solid-state lithium batteries (ASSLBs) employing sulfide solid electrolytes (SEs) promise sustainable energy storage systems with energy-dense integration and critical intrinsic safety, yet they still require cost-effective manufacturing and the integration of thin membrane-based SE separators into large-format cells to achieve scalable deployment. This review, based on an overview of sulfide SE materials, is expounded on why implementing a thin membrane-based separator is the priority for mass production of ASSLBs and critical criteria for capturing a high-quality thin sulfide SE membrane are identified. Moreover, from the aspects of material availability, membrane processing, and cell integration, the major challenges and associated strategies are described to meet these criteria throughout the whole manufacturing chain to provide a realistic assessment of the current status of sulfide SE membranes. Finally, future directions and prospects for scalable and manufacturable sulfide SE membranes for ASSLBs are presented.

Enhancing Moisture Stability of Sulfide Solid-State Electrolytes by Reversible Amphipathic Molecular Coating

The all-solid-state battery (ASSB) is a promising next-generation energy storage technology for both consumer electronics and electric vehicles because of its high energy density and improved safety. Sulfide solid-state electrolytes (SSEs) have merits of low density, high ionic conductivity, and favorable mechanical properties compared to oxide ceramic and polymer materials. However, mass production and processing of sulfide SSEs remain a grand challenge because of their poor moisture stability. Here, we report a reversible surface coating strategy for enhancing the moisture stability of sulfide SSEs using amphipathic organic molecules. An ultrathin layer of 1-bromopentane is coated on the sulfide SSE surface (e.g., Li₇P₂S₈Br_0.5I_0.5) via Van der Waals force. 1-Bromopentane has more negative adsorption energy with SSEs than H₂O based on first-principles calculations, thereby enhancing the moisture stability of SSEs because the hydrophobic long-chain alkyl tail of 1-bromopentane repels water molecules. Moreover, this amphipathic molecular layer has a negligible effect on ionic conductivity and can be removed reversibly by heating at low temperatures (e.g., 160 °C). This finding opens a new pathway for the surface engineering of moisture-sensitive SSEs and other energy materials, thereby speeding up their deployment in ASSBs.

Argyrodite Solid Electrolyte-Integrated Ni-Rich Oxide Cathode with Enhanced Interfacial Compatibility for All-Solid-State Lithium Batteries

All-solid-state lithium batteries (ASSLBs) paired with an argyrodite sulfide solid electrolyte have become a candidate to take the world by storm for achieving high energy and safety. However, the undesirable interface design between a sulfide solid electrolyte and cathode is difficult to address its scalability production challenge. Particularly, the inferior interfacial contact between a sulfide solid electrolyte and cathode is an intractable obstacle for the large-scale commercial application of ASSLBs. Herein, an elaborately designed conformally in situ integration of a sulfide solid electrolyte onto a Ni-rich oxide cathode is proposed to overcome this issue through a facile tape casting method. In this unique integrated electrode structure, the sulfide solid electrolyte intimately makes contact with the Ni-rich oxide cathode, which significantly strengthens the solid-solid interfacial compatibility, as well as decreases the interfacial reaction resistances, thereby enabling rapid Li+ transportation and a stable interfacial structure. As a result, ASSLBs consisting of a sulfide solid electrolyte-integrated Ni-rich oxide cathode and Li anode exhibit high discharge capacity, excellent cyclic stability, and remarkable rate performance, which are superior to the cells with segregated structures composed of a Ni-rich oxide cathode, sulfide solid electrolyte, and Li anode. The features clearly indicate that the advanced interfacial contact between the cathode and solid electrolyte is responsible for ASSLBs with low polarization and fast reaction kinetics. Therefore, this work provides a rational proof-of-concept fabrication protocol for the reliable interfacial structure design of high-performance ASSLBs.

Cl-Doped Li10SnP2S12 with Enhanced Ionic Conductivity and Lower Li-Ion Migration Barrier

All-solid-state lithium batteries based on sulfide solid electrolytes have attracted much attention because of their high ionic conductivity. Li₁₀SnP₂S₁₂ (LSPS) has the same structure as Li₁₀GeP₂S₁₂, and there is little difference in ionic conductivity between them, but the preparation cost of LSPS is lower. Here, Cl doping is used to improve the electrochemical stability of the LSPS to the anode and the Li-ion transport performance. Among them, Li_9.9SnP₂S_11.9Cl_0.1 had a high ion conductivity of 2.62 mS cm^-1 after cold pressure. On the crystal structure, X-ray diffraction Rietveld refinement indicated that the Cl-substituted portion S is successfully incorporated into the lattice of the LSPS, increasing Li-ion vacancies and reducing the distance between adjacent Li-ion distributed along the c-axis, these are conducive to Li-ion transmission. The temperature-dependent AC impedance experiment and density functional theory calculation show that doping with Cl makes Li_9.9SnP₂S_11.9Cl_0.1 have a lower activation energy. The assembled lithium symmetric batteries show that the doping of Cl promotes the stability of the interface between LSPS and the lithium metal anode. The charge-discharge tests of all-solid-state batteries using Li_9.9SnP₂S_11.9Cl_0.1 as electrolyte have confirmed that Cl doping can improve the electrochemical performance of LSPS, which have a higher specific capacity and cycle life.

Stabilizing Interface between Li2S-P2S5 Glass-Ceramic Electrolyte and Ether Electrolyte by Tuning Solvation Reaction

Using solid-liquid hybrid electrolytes is an effective strategy to overcome the large solid/solid interfacial resistance in all-solid-state batteries and the safety problems in liquid batteries. The properties of the solid/liquid electrolyte interphase layer (SLEI) are essential for the performance of solid-liquid hybrid electrolytes. In this work, the solvation reactions between Li₂S-P₂S₅ glass-ceramic solid electrolytes (SEs) and ether electrolytes were studied, and their influence on the SLEI was examined. Although 1,2-dimethoxyethane (DME) reacted with the Li₂S-P₂S₅ glass-ceramic SE to form a dense SLEI, 1,3-dioxolane (DOL) severely corroded the SE, resulting in a loose SLEI. Consequently, a stable SLEI formed with DME. Using a combination of the Li₂S-P₂S₅ glass-ceramic SE and the DME-based liquid electrolyte (LE), stable lithium plating/stripping cycles over 1000 h and a hybrid Li-S battery that retained a specific capacity of 730 mAh g^-1 after 200 cycles were demonstrated. The knowledge of the reactions between the sulfide electrolytes and the organic LEs is instructive for the design of stable sulfide-liquid hybrid electrolytes for advanced batteries.