Research Progress on Cathode Interface for All-Solid-State Lithium Batteries Based on Lithium-Rich Manganese-Based Layered Oxides Materials

All-solid-state lithium batteries (ASSLBs) emerge as a pivotal direction for next-generation energy storage systems due to their high energy density, intrinsic safety, and extended cycle life. Lithium-rich manganese-based layered oxides (LLOs) with their exceptional specific capacity (i.e., >300 mA·h/g) and cost-effectiveness are regarded as a promising cathode candidate for high-energy-density ASSLBs. However, critical challenges such as poor solid-solid interfacial contact between LLOs and solid electrolytes, irreversible lattice oxygen loss, and interfacial side reactions hinder their practical implementation. This review comprehensively analyzes the structural characteristics of LLOs, the anionic oxygen redox (OAR) mechanism, and interfacial challenges in ASSLBs, while systematically summarizing modification strategies across sulfide-, halide-, oxide-, and polymer-based solid electrolyte systems.

The high capacity of LLOs primarily originates from OAR, where reversible O^2-/O^- redox contributes to extra capacity. However, oxygen release and transition metal (TM) migration lead to voltage decay and structural degradation. To address these issues, gradient doping and surface coating are developed to stabilize lattice oxygen and suppress phase separation. Compared to polycrystalline materials, single-crystal LLOs exhibit superior mechanical stability and interfacial contact, effectively mitigating crack propagation caused by volume changes.

In sulfide-based systems, the space charge layer (SCL) effect and sulfur oxidation at high voltages are the main limiting factors. Strategies such as LLOs surface sulfurization, uniform dispersion by liquid-phase mixing, and functional coatings can effectively reduce the interfacial resistance and enhance the OAR reversibility. For halide electrolytes, the introduction of carbon additives and ion-conductive coatings can establish a continuous conductive transport network. Oxide-based systems benefit from co-sintering LLO with garnet-type Li₇La₃Zr₂O₁₂ and Li₃BO₃ sintering aids to improve interfacial densification, although Mn/La interdiffusion in co-sintering requires further attention. Polymer electrolytes, especially those formed by in-situ polymerization of propane sultone-based materials, are able to form a thin and uniform cathode-electrolyte interface (CEI), thereby widening the electrochemical stability window.

A critical finding across these systems is the importance of mechanical-electrochemical coupling at interfaces. "Soft-contact" interfaces with flexible ion-conductive layers are essential to accommodate volume changes. Halide electrolytes have a unique compatibility with LLOs via minimizing SCL effects, while sulfide systems demand a precise control of oxidation-prone components to prevent degradation.

Future research should prioritize advanced characterization techniques to elucidate dynamic structural evolution and interfacial degradation pathways during OAR. Material optimization, such as designing Co-free LLOs with gradient TM distribution and single-crystal morphology, can enhance intrinsic Li⁺/electronic conductivity and structural integrity. Innovations in electrolytes, including hybrid organic-inorganic composites or high-entropy sulfides can balance ionic conductivity (32 mS/cm) and interfacial stability. Scaling up production processes for sulfide/halide electrolytes and addressing their moisture sensitivity are also crucial steps toward commercialization. In summary, interfacial stability remains a cornerstone for high-performance LLOs-based ASSLBs. ASSLBs are poised to achieve energy densities of exceeding 1000 W·h/kg via synergizing material design, interface engineering, and mechanistic understanding, paving a way for their application in electric vehicles and grid-scale storage.