Solid Polymer Electrolytes for Advanced Lithium Batteries: Decoupling Ion Transport, Engineering Interfaces, and Enabling Sustainable Manufacturing.

Solid polymer electrolytes (SPEs) are promising materials for next-generation lithium batteries owing to their inherent safety, mechanical flexibility, and compatibility with advanced cell architectures. However, their practical implementation remains constrained by low room-temperature ionic conductivity, solid-solid interfacial resistance, and limited manufacturing scalability. This review critically examines recent advances in SPEs, with particular emphasis on fundamental Li+ transport mechanisms and the molecular factors governing ionic mobility, as well as strategies for decoupling ion transport from polymer segmental dynamics. Emerging design strategies, including architecture-engineered polymers, single-ion conductors, self-healing networks, and polymer-ceramic composites, are evaluated in terms of their ability to balance ionic conductivity, mechanical integrity, and interfacial stability. Particular attention is devoted to interfacial phenomena and mesoscale structural regulation that govern practical electrochemical performance. Recent progress in sustainable electrolytes, including fluorine-free salts, bio-derived polymers, and recyclable dynamic networks, is also highlighted. Finally, remaining challenges and future opportunities are discussed, emphasizing integrated molecular and interfacial design, standardized performance evaluation, and scalable manufacturing toward safe, sustainable, and high-performance solid-state batteries.