Promoting high-voltage stability through local lattice distortion of halide solid electrolytes

Investigation of ion diffusion in polyethylene oxide-based solid electrolyte with functionalized La(OH)3 nanofibers for high-rate all-solid-state lithium-metal batteries

Solid polymer electrolytes have emerged as promising materials for next-generation lithium metal batteries due to their enhanced safety and high energy density potential. However, their widespread adoption is hindered by slow ion transport and inefficient lithium-ion (Li+) selectivity. To overcome these limitations, this study introduces a composite electrolyte by incorporating functionalized La(OH)3 nanofibers with oxygen vacancies into a Poly(ethylene oxide) (PEO) matrix. These nanofibers, synthesized via a simple method, are designed to improve Li+ mobility by leveraging their oxygen vacancies to immobilize TFSI- anions from the bis(trifluoromethanesulfonyl)imide (LiTFSI). Simultaneously, amino groups on the nanofiber surface act as binding sites, facilitating lithium salt dissociation and creating supplementary ion transport pathways. Density functional theory (DFT) and molecular dynamics (MD) simulations reveal that the functionalized La(OH)3 nanofibers effectively suppress TFSI- anion movement while reducing the energy barrier for Li+ migration. This mechanism elevates the Li+ transference number to 0.51, a significant improvement over the conventional PEO-based electrolytes. The composite electrolyte exhibits excellent performance in Li||Li cells, maintaining stable cycling for over 600 h at a current density of 0.38 mA cm-2. Furthermore, a solid-state LiFePO4||Li battery demonstrates highly reversible capacities of 100.2 mAh g-1 after 600 cycles at 8C. By combining anion confinement strategies with tailored electronic interactions, this work provides a practical approach to advancing solid-state battery performance. The findings not only highlight the potential of La(OH)3-PEO composite electrolytes but also establish a new framework for optimizing ionic conductivity through targeted molecular design.

Cation-Anion-Engineering Modified Oxychloride Zr-Based Lithium Superionic Conductors for All-Solid-State Lithium Batteries

Within the family of halide solid electrolytes (SEs), Li2ZrCl6 demonstrates high oxidative stability, cost-effectiveness, and mechanical deformability, positioning it as a promising candidate for SEs. However, the application of Li2ZrCl6 as a SEs was hindered by its low ionic conductivity at room temperature. Current strategies to enhance the ionic conductivity of Li2ZrCl6 primarily are focused on single cation or anion sublattice-engineering, each with distinct advantages and limitations. Here, we propose a novel cation and anion-sublattice-engineering strategy, termed CASE, to increase the amorphous content and thus enhance ionic conductivity. The incorporation of Cu2+ and O2- induces distinctive structural modifications within Li2ZrCl6. This structure corroborated through analytic data of X-ray absorption spectroscopy, the neutron diffraction, and ab initio molecular dynamics. Consequently, the amorphous Li2.1Zr0.95Cu0.05Cl4.4O0.8 achieves an enhanced ionic conductivity of 2.05 mS cm-1 at 25 °C. Furthermore, all-solid-state lithium batteries utilizing the amorphous Li2.1Zr0.95Cu0.05Cl4.4O0.8 as an electrolyte and LiNi0.83Co0.11Mn0.06O2 as a cathode exhibit a superior long-term cycling stability retaining 90.3% of capacity after 1000 cycles at 2 C under room temperature, which are much higher than those of Zr-based halide electrolytes in publications. Such a result might stimulate the development of more amorphous structures with high ionic conductivity in the CASE strategy.

Rare-Earth Ions Regulating Lattice-Softened Bromide Solid Electrolytes for Highly Stable Fast-Charging Solid-State Batteries

All-solid-state lithium-based batteries (ASSLBs) with good safety and high energy density are valuable. To realize stable and high-efficiency ASSLBs, high-performance solid-state electrolytes (SEs) with good processability are necessary. Bromide (Br)-based rare-earth halide SEs (RE-HSEs) exhibit good deformability for large radii of RE and Br ions. Here, the influence of RE ions on the crystalline structure and mechanical properties of Br-based RE-HSEs (RE = Y, Gd, Tb, Ho, or Er) was analyzed in detail, and Li3GdBr6 (LGdB) showed the softest lattice and the best deformability due to having the longest RE-Br bond length. Furthermore, LGdB exhibits satisfactory ionic conduction ability (1.4 mS cm-1), and the assembled ASSLBs exhibit a reversible redox process, excellent fast-charging performance, and superior cycling stability for 6000 cycles at 10 C. This study indicates that the relationship between the RE and deformability of Br-based RE-HSEs is significant for the rational design and improvement of HSEs in ASSLBs.

A Perspective on the Origin of High-Entropy Solid Electrolytes

As the key material for the all-solid-state batteries (ASSBs), solid electrolytes (SEs) have attracted increasing attention. Recently, a novel design strategy-high-entropy (HE) approach is frequently reported to improve the ionic conductivity and electrochemical performance of SEs. However, the fundamental understandings on the HE working mechanism and applicability evaluation of HE concept are deficient, which would impede the sustainable development of a desirable strategy to enable high-performance SEs. In this contribution, the essence of HE-related approaches and their positive effects on SEs are evaluated. The reported HE strategy stems from complex compositional regulations. The derived structural stability and enhanced property are originally from the modulated system disorder and subtle local-structure evolutions, respectively. While HE ardently describes the increased entropy/disorder during the modification of prevailing SEs, rigorous experimental formulations, and direct correlations between the HE structures and desired properties are necessary to be established. This perspective would be a timely and critical overview for the HE approaches in the context of SEs, aiming to stimulate further discussion and exploration in this emerging research direction.

Stabilizing Halide Electrolytes against Lithium Metal with a Self-Limiting Layer for All-Solid-State Lithium Metal Batteries

Halide solid-state electrolytes (SSEs) with high ionic conductivity and high-voltage stability have attracted significant interest for application in all-solid-state batteries. However, they are not chemically stable against the lithium (Li) metal anode due to continuous side reduction reactions, hindering the application of halide SSEs in high-energy-density all-solid-state Li metal batteries (ASSLMBs). Here, we report a self-limiting layer (SLL) composed of InF3 and Li2ZrCl6 (LZC) to stabilize the halide SSEs and Li metal anode interface, where the in situ generated LiF-rich layer serves as a passivation layer to suppress ensuing reactions and kinetically stabilize the interface between LZC and Li metal anode. As a result, Li metal symmetric cells with LZC protected by the SLL exhibit excellent cycling performance for over 3000 h. The ASSLMBs with SLL achieve 99.2% capacity retention over 100 cycles at 0.5 C and 83.5% capacity retention after 250 cycles at 2 C. Density functional theory-computed thermodynamic data and postcycling experimental characterizations confirm the forming of a LiF-rich passivation layer between the SLL and the Li anode, which effectively prevents continuous side reactions. This self-limiting interface protection offers a feasible kinetical passivation strategy for halide SSEs and the Li metal anode toward high-performance ASSLMBs.

High-Voltage Cathode Materials for Sodium-Ion Batteries: Advances and Challenges

Sodium-ion batteries (SIBs) gain attention as a promising, cost-effective, and resource-abundant alternative, especially for large-scale energy storage. Cathode materials play a pivotal role in improving the electrochemical performance of SIBs, with high-voltage cathodes providing enhanced energy density and rate capacity, making SIBs suitable for high-power applications. Common cathode materials, such as layered transition metal oxides, polyanionic compounds, and Prussian blue analogs, each offer unique benefits. However, these materials face challenges under high-voltage conditions, such as phase transitions, metal cation migration, oxygen loss, and electrolyte degradation. This review discusses strategies to address these challenges, including elemental doping, surface coatings, modified synthesis methods, and interfacial adjustments, all aimed at enhancing the stability and electrochemical performance of high-voltage cathode materials. Here also explores how full-cell design optimizations can further improve energy and power density. By analyzing material degradation and failure modes, this review offers insights into the development of stable, high-performance SIBs with better safety and broader application potential in energy storage technologies.

Strategies for Advanced Solid Electrolytes toward Efficient Lithium-Ion Conduction in All-Solid-State Lithium Metal Batteries

All-solid-state lithium metal batteries (ASSLMBs) have currently garnered significant academic and industrial interest, due to their great potential to overcome intrinsic shortages of poor energy density and unsatisfactory safety of liquid-state lithium-ion batteries. Recently, many efforts have been made to move the progress of solid electrolytes (SEs) forward for ASSLMBs, especially on the understanding and optimization of lithium-ion conduction in SEs. Herein, we summarize a review of recent design strategies for rational SEs that display enhanced lithium-ion conduction, as well as the discussion on design principles and working mechanisms for boosted performance and stability of ASSLMBs. Given the intimate relationship between the lithium-ion conduction mechanism and the composition of SEs, the reported SEs can generally be classified into single-phase SEs and composite SEs. In detail, single-phase SEs contain three typical categories, e.g., polymer-based, inorganic, and plastic crystal-based SEs. For composite SEs, there are also three main kinds, including polymer-inorganic, plastic crystal-polymer, and plastic crystal-polymer-inorganic ternary composite SEs. The state-of-the-art literature and representative materials have been carefully discussed and analyzed, with the corresponding factors of enhancing lithium-ion conduction highlighted. Finally, an outlook for future directions to design advanced SEs with efficient lithium-ion conduction is presented for the development of ASSLMBs.

A Pre-Oxidation Strategy to Establish Stable Oxide Cathode/Halide Solid-State Electrolyte Interfaces for High Energy all Solid-State Batteries

All-solid-state lithium metal batteries (ASSLBs) are promising for high energy and safety. Halide-based solid-state electrolytes, characterized by high ionic conductivity and a notably wide electrochemical window exceeding 4.3 V, hold significant promise for compatibility with high-energy cathodes. However, oxygen in cathodes exhibits a strong tendency to interact with the central metal cation in halide solid-state electrolyte, forming an unstable cathode-electrolyte interface (CEI) and leading to cathodic degradations. Herein, a pre-oxidation strategy is proposed for Y based halide solid-state electrolytes, leveraging oxygen to pre-establish robust Y─O bonds within the halide electrolyte structure Li2YCl2.5Br1.5O0.5 (2LO-0.5). The robust Y─O bonds in 2LO-0.5 effectively hinder uncontrolled oxygen interactions with Y3⁺, which would otherwise lead to the formation of oxidizable YOCl. This stabilization promotes the formation of a thin, stable Y₂O₃-based CEI against LiNi0.83Co0.11Mn0.06O2 (NCM83). Therefore, the ASSLB assembled with 2LO-0.5 and NCM83 demonstrates an initial discharge-specific capacity of 208 mAh g-1 and retained 80.6% of its capacity after 1000 cycles, attributed to stable CEI film derived from pre-oxidized strategy. This work offers new insights for regulating the non-redox reaction between halide solid-state electrolytes and oxide cathodes, promoting the rational design of high-performance halide solid-state electrolytes.

Ductile Inorganic Solid Electrolytes for All-Solid-State Lithium Batteries

Solid electrolytes, as the core of all-solid-state batteries (ASSBs), play a crucial role in determining the kinetics of ion transport and the interface compatibility with cathodes and anodes, which can be subdivided into catholytes, bulk electrolytes, and anolytes based on their functional characteristics. Among various inorganic solid electrolytes, ductile solid electrolytes, distinguished from rigid oxide electrolytes, exhibit excellent ion transport properties even under cold pressing, thus holding greater promise for industrialization. However, the challenge lies in finding a ductile solid electrolyte that can simultaneously serve as catholyte, bulk electrolyte, and anolyte. Fortunately, due to the immobility of solid electrolytes, combining multiple types of solid electrolytes allows for leveraging their respective advantages. In this review, we discuss five types of solid electrolytes, sulfides, halides, nitrides, antiperovskite-type, and complex hydrides, and the challenges and superiorities for these electrolytes are also addressed. The impact of pressure on ASSBs has been systematically discussed. Furthermore, the suitability of electrolytes as the catholyte, bulk electrolyte, and anolyte is discussed based on their functional characteristics and physicochemical properties. This discussion aims to deepen our understanding of solid electrolytes, enabling us to harness the advantages of various types of solid electrolytes and develop practical, high-performance ASSBs.

Advanced High-Entropy Halide Solid Electrolytes Enabling High-Voltage, Long-Cycling All-Solid-State Batteries

Stable solid electrolytes are essential for advancing the safety and energy density of lithium batteries, especially in high-voltage applications. In this study, we designed an innovative high-entropy chloride solid electrolyte (HE-5, Li2.2In0.2Sc0.2Zr0.2Hf0.2Ta0.2Cl6), using multielement doping to optimize both ionic conductivity and high-voltage stability. The high-entropy disordered lattice structure facilitates lithium-ion mobility, achieving an ionic conductivity of 4.69 mS cm-1 at 30 °C and an activation energy of 0.300 eV. Integration of HE-5 into all-solid-state batteries (ASSBs) with NCM83 cathodes and a Li-In anode enables outstanding electrochemical performance, sustaining 70% capacity retention over 1600 cycles at a 4 C rate. Moreover, the high configurational entropy stabilizes the electrolyte's structure at elevated voltages, enabling stable operation at 5.0 V without significant degradation. Our work presents the dual advantages of high-entropy engineering in boosting high ionic conductivity and voltage stability, providing a broad roadmap for next-generation energy-dense ASSBs.

Regulating Chemical Bonds in Halide Frameworks for Lithium Superionic Conductors

Developing solid-state electrolytes (SSEs) is a critical task for advancing all-solid-state batteries (ASSBs) that promise a high energy density and improved safety. The dominant strategy in engineering advanced SSEs has been substitutional doping, where foreign atoms are introduced into the atomic lattice of a host material to enhance ionic conduction. This enhancement is typically attributed to optimized charge carriers' concentration or lattice structure alterations. In this study, we extend the concept of substitutional doping to explore its effects on chemical bond modulation and the resulting impact on ionic conduction in halide SSEs. As a case of study, we demonstrate that cation dopants with high charge density indices (e.g., Al3+ and Fe3+) can increase the covalency of metal-halide (M-X) bonds and induce the local asymmetric field of force, resulting in higher site energy and lower migration barriers, which significantly enhance the ionic conduction in halide frameworks. Specifically, we developed a series of halide SSEs with ionic conductivities exceeding the benchmark value of 1 mS cm-1 at room temperature. Detailed investigations, including neutron powder diffraction, pair distribution function analysis, and first-principles calculations, are performed to gain an insight into the mechanisms behind this adjustment. Furthermore, these materials exhibit enhanced deformability due to increased covalency of the metal halide framework, enabling high-performance ASSB prototypes operatable at low stacking pressures (<10 MPa). These advancements deepen our understanding of superionic conduction in halide SSEs and mark an important step toward the practical application of ASSBs in the future.

High Configuration Entropy Promises Electrochemical Stability of Chloride Electrolytes for High-Energy, Long-Life All-Solid-State Batteries

Solid-state electrolytes (SSEs) with high ionic conductivity, stability, and interface compatibility are indispensable for high-energy-density and long-life all-solid-state batteries (ASSBs), yet there are scarce SSEs with sufficient ionic conductivity and electrochemical stability. In this study, with a high-entropy SSE (HE-SSE, Li2.9In0.75Zr0.1Sc0.05Er0.05Y0.05Cl6), we show the high configuration entropy has a thermodynamically positive relationship with the high-voltage stability. As a result, the ASSBs with HE-SSE and high-voltage cathode materials exhibit superior high-voltage and long-cycle stability, achieving 250 cycles with 81.4 % capacity retention when charged to 4.8 V (vs. Li+/Li), and even 5000 cycles if charged to 4.6 V (vs. Li+/Li). Experimental characterizations and density functional theory calculations confirm that the HE-SSE greatly suppresses the high-voltage degradation of SSE at the interface, promoting the high-voltage stability coordinately through high entropy and interface stability. The high entropy design offers a general strategy to simultaneously improve the high-voltage stability and ionic conductivity of SSEs, creating an avenue to building high-energy and long-life ASSBs.

Building a Better All-Solid-State Lithium-Ion Battery with Halide Solid-State Electrolyte

Since the electrochemical potential of lithium metal was systematically elaborated and measured in the early 19th century, lithium-ion batteries with liquid organic electrolyte have been a key energy storage device and successfully commercialized at the end of the 20th century. Although lithium-ion battery technology has progressed enormously in recent years, it still suffers from two core issues, intrinsic safety hazard and low energy density. Within approaches to address the core challenges, the development of all-solid-state lithium-ion batteries (ASSLBs) based on halide solid-state electrolytes (SSEs) has displayed potential for application in stationary energy storage devices and may eventually become an essential component of a future smart grid. In this Review, we categorize and summarize the current research status of halide SSEs based on different halogen anions from the perspective of halogen chemistry, upon which we summarize the different synthetic routes of halide SSEs possessing high room-temperature ionic conductivity, and compare in detail the performance of halide SSEs based on different halogen anions in terms of ionic conductivity, activation energy, electronic conductivity, interfacial contact stability, and electrochemical window and summarize the corresponding optimization strategies for each of the above-mentioned electrochemical indicators. Finally, we provide an outlook on the unresolved challenges and future opportunities of ASSLBs.

Boosting the Structural and Electrochemical Stability of Chloride-Ion-Conducting Perovskite Solid Electrolytes by Alkali Ion Doping

The use of chloride-based solid electrolytes derived from Lewis acid‒base reactions enables the construction of various new rechargeable batteries, such as chloride ion batteries (CIBs). However, a critical problem with these electrolytes is their poor stability under low-temperature, moist, or electrochemical conditions, which can lead to deterioration of the phase structure and a loss of ion conduction. Herein, the robust cubic structure of tin-based perovskite chloride-a chloride ion conductor-is achieved by alkali ion doping at the tin site via direct mechanical milling. The as-prepared cubic CsSn0.925Na0.075Cl2.925 (CSNC) electrolyte exhibits outstanding structural stability over a broad temperature range of 213-473 K or under a high relative humidity of up to 90%, at which the typical chloride electrolytes previously reported deteriorate because of moisture. Importantly, mild annealing can modify the microstructure of the CSNC, resulting in a two fold increase in ionic conductivity and an increase in electrochemical stability, which is superior to those of other chloride electrolytes reported in previous studies. The effective chloride-ion transfer and wide electrochemical window of the CSNC are further demonstrated in different solid-state CIBs.

Research Progress on Solid-State Electrolytes in Solid-State Lithium Batteries: Classification, Ionic Conductive Mechanism, Interfacial Challenges

Solid-state lithium batteries exhibit high-energy density and exceptional safety performance, thereby enabling an extended driving range for electric vehicles in the future. Solid-state electrolytes (SSEs) are the key materials in solid-state batteries that guarantee the safety performance of the battery. This review assesses the research progress on solid-state electrolytes, including polymers, inorganic compounds (oxides, sulfides, halides), and organic-inorganic composites, the challenges related to solid-state batteries in terms of their interfaces, and the status of industrialization research on solid-state electrolytes. For each kind of solid-state electrolytes, details on the preparation, properties, composition, ionic conductivity, ionic migration mechanism, and structure-activity relationship, are collected. For the challenges faced by solid-state batteries, the high interfacial resistance, the side reactions between solid-state electrolytes and electrodes, and interface instability, are mainly discussed. The current industrialization research status of various solid electrolytes is analyzed in regard to relevant enterprises from different countries. Finally, the potential development directions and prospects of high-energy density solid-state batteries are discussed. This review provides a comprehensive reference for SSE researchers and paves the way for innovative advancements in regard to solid-state lithium batteries.

Tuning Ion Mobility in Lithium Argyrodite Solid Electrolytes via Entropy Engineering

The development of improved solid electrolytes (SEs) plays a crucial role in the advancement of bulk-type solid-state battery (SSB) technologies. In recent years, multicomponent or high-entropy SEs are gaining increased attention for their advantageous charge-transport and (electro)chemical properties. However, a comprehensive understanding of how configurational entropy affects ionic conductivity is largely lacking. Herein we investigate a series of multication-substituted lithium argyrodites with the general formula Li6+x[M1aM2bM3cM4d]S5I, with M being P, Si, Ge, and Sb. Structure-property relationships related to ion mobility are probed using a combination of diffraction techniques, solid-state nuclear magnetic resonance spectroscopy, and charge-transport measurements. We present, to the best of our knowledge, the first experimental evidence of a direct correlation between occupational disorder in the cationic host lattice and lithium transport. By controlling the configurational entropy through compositional design, high bulk ionic conductivities up to 18 mS cm-1 at room temperature are achieved for optimized lithium argyrodites. Our results indicate the possibility of improving ionic conductivity in ceramic ion conductors via entropy engineering, overcoming compositional limitations for the design of advanced electrolytes and opening up new avenues in the field.