Interfacial Structure Design for High-Voltage and Safe Polymer Solid-State Lithium Batteries

Solid polymer electrolytes (SPEs) have garnered significant attention as key enablers for next-generation lithium metal batteries (LMBs), offering the potential for enhanced safety and higher energy density. However, critical challenges persist at the interfaces between SPEs and both lithium metal anodes and high-voltage cathodes, where electrochemical, mechanical, and chemical instabilities severely limit long-term performance. This review focuses on the fundamental origins and manifestations of these interfacial issues and summarizes recent progress in addressing them through materials design and interface engineering. Particular emphasis is placed on the underlying ion transport behaviors, interfacial reactions, and their implications for electrochemical stability. By identifying shared principles and distinct mechanisms at both interfaces, this review aims to provide a cohesive understanding of the challenges and opportunities in SPE-based LMBs. Finally, we highlight future research directions toward the development of durable and high-voltage-compatible solid-state battery systems.