Practical Application of Li-Rich Materials in Halide All-Solid-State Batteries and Interfacial Reactions between Cathodes and Electrolytes

Unveiling Incompatibility of High Nickel Cathode With p-xylene Solvent for Facile Wet-Slurry Process in All-Solid-State Batteries

All-solid-state batteries (ASSBs) are considered one of the most promising next-generation batteries due to their outstanding safety and superior energy density. For the commercial success of ASSBs, developing a scalable wet-slurry-based electrode manufacturing process is essential. In this regard, non-polar solvents have been generally used in the wet-slurry process with sulfide-based solid electrolytes (SEs) to avoid their chemical crosstalk. Although many studies on the chemical compatibility between sulfide-based SEs and non-polar solvents have been conducted, to the best of the knowledge, an in-depth understanding of the interfacial chemistry between those solvents and active materials is not fully elucidated. In this study, the chemical incompatibility of LiNi0.8Co0.1Mn0.1O2 (NCM) cathode with p-xylene, a representative non-polar solvent, through in-depth analyses of cation mixing, Ni dissolution, and surface reconstruction is revealed. Contrary to expectations, severe interfacial challenges arise from the side reactions between NCM and p-xylene, resulting in poor electrochemical properties in ASSBs. The origin of the decrease in electrochemical performances of the wet-slurry-based electrodes in ASSBs is unveiled, which can be addressed by employing a surface protective coating layer on NCM cathodes.

Understanding the Electrochemical Window of Solid-State Electrolyte in Full Battery Application

In recent years, solid-state Li batteries (SSLBs) have emerged as a promising solution to address the safety concerns associated. However, the limited electrochemical window (ECW) of solid-state electrolytes (SEs) remains a critical constraint full battery application. Understanding the factors that influence the ECW is an essential step toward designing more robust and high-performance electrochemical systems. This review provides a detailed classification of the various "windows" of SEs and a comprehensive understanding of the associated interfacial stability of SEs in full battery application. The paper begins with a historical overview of SE development, followed by a detailed discussion of their structural characteristics. Next, examination of various methodologies used to calculate and measure the ECW is presented, culminating in the proposal of standardized testing procedures. Furthermore, a comprehensive analysis of the numerous parameters that influence the thermodynamic ECW of SEs is provided, along with a synthesis of strategies to address these challenges. At last, this review concludes with an in-depth exploration of the interfacial issues associated with SEs exhibiting narrow ECWs in full SSLBs.

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.

Fundamentals, Status and Promise of Li-Rich Layered Oxides for Energy-Dense Li-Ion Batteries

Li-ion batteries (LIBs) are the dominant electrochemical energy storage devices in the global society, in which cathode materials are the key components. As a requirement for higher energy-dense LIBs, Li-rich layered oxides (LLO) cathodes that can provide higher specific capacity are urgently needed. However, LLO still face several significant challenges before bringing these materials to market. In this Review, the fundamental understanding of LLO is described, with a focus on the physical structure-electrochemical property relationships. Specifically, the various strategies toward reversible anionic redox is discussed, highlighting the approaches that take the basic structure of the battery into account. In addition, the application for all-solid-state batteries and consider the prospects for LLO is assessed.

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.

Recent Progress and Challenges of Li-Rich Mn-Based Cathode Materials for Solid-State Lithium-Ion Batteries

Li-rich Mn-based (LRM) cathode materials, characterized by their high specific capacity (>250 mAh g-¹) and cost-effectiveness, represent promising candidates for next-generation lithium-ion batteries. However, their commercial application is hindered by rapid capacity degradation and voltage fading, which can be attributed to transition metal migration, lattice oxygen release, and the toxicity of Mn ions to the anode solid electrolyte interphase (SEI). Recently, the application of LRM cathode in all-solid-state batteries (ASSBs) has garnered significant interest, as this approach eliminates the liquid electrolyte, thereby suppressing transition metal crosstalk and solid-liquid interfacial side reactions. This review first examines the historical development, crystal structure, and mechanisms underlying the high capacity of LRM cathode materials. It then introduces the current challenges facing LRM cathode and the associated degradation mechanisms and proposes solutions to these issues. Additionally, it summarizes recent research on LRM materials in ASSBs and suggests strategies for improvement. Finally, the review discusses future research directions for LRM cathode materials, including optimized material design, bulk doping, surface coating, developing novel solid electrolytes, and interface engineering. This review aims to provide further insights and new perspectives on applying LRM cathode materials in ASSBs.

Boosting Anionic Redox Reactions of Li-Rich Cathodes through Lattice Oxygen and Li-Ion Kinetics Modulation in Working All-Solid-State Batteries

The use of lithium-rich manganese-based oxides (LRMOs) as the cathode in all-solid-state batteries (ASSBs) holds great potential for realizing high energy density over 600 Wh kg-1. However, their implementation is significantly hindered by the sluggish kinetics and inferior reversibility of anionic redox reactions of oxygen in ASSBs. In this contribution, boron ions (B3+) doping and 3D Li2B4O7 (LBO) ionic networks construction are synchronously introduced into LRMO materials (LBO-LRMO) by mechanochemical and subsequent thermally driven diffusion method. Owing to the high binding energy of B─O and high-efficiency ionic networks of nanoscale LBO complex in cathode materials, the as-prepared LBO-LRMO displays highly reversible and activated anionic redox reactions in ASSBs. The designed LBO-LRMO interwoven structure enables robust phase and LBO-LRMO|solid electrolyte interface stability during cycling (over 80% capacity retention after 2000 cycles at 1.0 C with a voltage range of 2.2-4.7 V vs Li/Li+). This contribution affords a fundamental understanding of the anionic redox reactions for LRMO in ASSBs and offers an effective strategy to realize highly activated and reversible oxygen redox reactions in LRMO-based ASSBs.

Pre-Lithiated Silicon-Based Composite Anode for High-Performance All-Solid-State Batteries

Silicon is widely recognized as a promising anode material for all-solid-state batteries (ASSBs) due to exceptional specific capacity, abundant availability, and environmental sustainability. However, the considerable volume expansion and particle fragmentation of Si during cycling lead to significant performance degradation, limiting its practical application. Herein, the development of a pre-lithiated Si-based composite anode (c-Li1Si) is presented, designed to address the key challenges faced by Si-based anodes, namely severe volume changes and low electrochemical stability. The c-Li1Si anodes are prepared by incorporating Li₁Si powders with Li6PS5Cl (LPSCl) sulfide solid electrolyte (SSE), forming a dense structure that enhances conductivity and mitigates structural degradation. The ASSBs with c-Li1Si-60 anode exhibit outstanding electrochemical performance, including excellent rate capability and capacity retention of 84.4% after 1000 cycles at 1 C and exceptional performance even at low anode-to-cathode capacity ratios (N/P ratio) of 1.68. EIS and pressure measurements reveal improved reaction kinetics and reduced volume expansion. X-ray micro-CT and SEM further confirmed the introduction of LPSCl effectively alleviated volume changes and maintained electrode structural integrity, contributing to enhanced electrochemical performance. These results underscore the potential of the c-Li1Si anode to overcome the intrinsic limitations of Si-based anodes, offering a promising pathway toward high-energy-density ASSBs.

Bulk/Interfacial Structure Design of Li-Rich Mn-Based Cathodes for All-Solid-State Lithium Batteries

Li-rich Mn-based cathode materials (LRMO) are promising for enhancing energy density of all-solid-state batteries (ASSBs). Nonetheless, the development of efficient Li+/e- pathways is hindered by the poor electrical conductivity of LRMO cathodes and their incompatible interfaces with solid electrolytes (SEs). Herein, we propose a strategy of in-situ bulk/interfacial structure design to construct fast and stable Li+/e- pathways by introducing Li2WO4, which reduces the energy barrier for Li+ migration and enhances the stability of the surface oxygen structure. The reversibility of oxygen redox was improved, and the voltage decay of the LRMO cathode was addressed significantly. As a result, the bulk structure of the LRMO cathodes and the high-voltage solid-solid interfacial stability are improved. Therefore, the ASSBs achieve a high areal capacity (∼3.15 mAh/cm2) and outstanding cycle stability of ≥1200 cycles with 84.1% capacity retention at 1 C at 25 °C. This study offers new insights into LRMO cathode design strategies for ASSBs, focusing on ultrastable high-voltage interfaces and high-loading composite electrodes.

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

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

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

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