Solid‐state polymer electrolytes: Decoupling lithium‐ion transport from relaxation dynamics of polymer chain segments

Abstract The pursuit of high‐energy‐density energy storage systems has induced significant safety risk in lithium metal batteries, particularly due to the lithium dendrite growth and flammability of liquid electrolytes. Solid‐state electrolytes (SSEs) have emerged as a promising alternative, among which solid‐state polymer electrolytes (SPEs) stand out due to their lightweight, flexibility, and excellent interfacial compatibility with electrodes. Despite these advantages, conventional SPEs, particularly those based on poly(ethylene oxide) (PEO), suffer from low room‐temperature ionic conductivity, low transference numbers, and insufficient mechanical strength. Recent advancements have introduced decoupled SPEs (DSPEs), a novel class of SPEs that decouple ionic conduction from polymer chain segment motion. This decoupling mechanism, akin to that observed in superionic crystals and glasses, enables simultaneous achievement of high ionic conductivity and robust mechanical properties at room temperature. DSPEs represent a significant departure from traditional SPEs, offering a new paradigm for designing high‐performance SSEs. This review provides a comprehensive examination of DSPEs, covering their fundamental ion transport mechanisms, key performance evaluation criteria, and advanced characterization techniques. We discuss various design strategies and materials that have been employed to develop DSPEs, highlighting their unique ion conduction mechanisms and comparative advantages. Furthermore, the review raises several critical challenges that must be overcome to advance DSPEs toward commercialization, including scalability, cost reduction, and optimization of electrode‐electrolyte interfaces. By systematically analyzing the current state of DSPE research, this review aims to provide a roadmap for future developments in this field, ultimately contributing to the realization of next‐generation, high‐performance solid‐state lithium metal batteries.