When solid polymers meet Na-ions: unraveling solvation dynamics and molecular design principles for next-generation high-energy sodium metal batteries

Abstract

In the pursuit of safer and next-generation high-energy batteries, solid polymer electrolyte (SPE)-based systems have emerged as leading contenders. The absence of volatile organic solvents, combined with outstanding thermo-mechanical stability and resistance to freezing or electrolyte leaching, underscores their superiority over conventional electrolytes. Despite these advantages, the implementation of SPEs in high-energy sodium-metal batteries remains limited compared with their liquid counterparts. Low room-temperature ionic conductivity, interfacial incompatibility with sodium metal, and poor electrode–electrolyte contact continue to impede their widespread adoption. This review provides a comprehensive overview of how solvation dynamics govern ion coordination, salt dissociation, and interfacial stability through the molecular design of SPEs. Distinct from prior reviews, this work directly correlates solvation behavior with molecular-level design strategies, encompassing approaches such as in situ generation to engineer robust electrode–electrolyte interfaces, polymer-blend SPEs, and nanofiller-incorporated SPEs. Temperature-dependent ionic transport mechanisms and kinetic models are systematically discussed to elucidate the relationships between structure, properties, and practical battery performance. Furthermore, current progress and remaining challenges are critically analyzed, with future directions emphasizing green synthesis methodologies, operando analytical techniques, the integration of artificial intelligence and machine learning, along with advanced sensor technologies for real-time battery monitoring. By bridging solvation dynamics and molecular design principles, this review establishes a conceptual roadmap to accelerate the realization of safe, highly-conductive, and commercially viable SPE-based sodium metal batteries—capturing the core theme of “When Solid Polymers Meet Na-ions”.