Composite Polymer Electrolytes for Sodium-Ion Batteries: From Material Design to Interfacial Engineering and Future Perspectives

Abstract

The escalating need for sustainable and safe energy storage systems has positioned sodium-ion batteries (SIBs) as a viable substitute for lithium-ion batteries, considering the lower expense and natural abundance of sodium. However, the flammability and dendrite-related safety concerns of traditional liquid electrolytes necessitate the advancement of durable solid-state electrolytes.Among these, composite polymer electrolytes (CPEs), which integrate inorganic fillers within a polymer matrix, have arisen as a leading alternative to tackle the drawbacks of individual solid polymer and inorganic ceramic electrolytes. This review provides a comprehensive and up-to-date insight into the design, preparation, and performance of CPEs for SIBs. We systematically discuss the fundamental ion migration mechanisms, the critical role of active (Na-ion conductive) and passive (inert) fillers in enhancing ionic conductivity, electrochemical stability, and mechanical strength, and the various fabrication techniques employed. A significant focus is placed on interfacial engineering strategies to mitigate the substantial interface resistance between solid electrolytes and electrodes. Finally, we address the prevailing challenges and offer future perspectives, highlighting the need for integrated design from mechanics to materials science to accelerate the practical application of high-performance, safe, and durable CPEs in next-generation SIBs.