Reactivity-guided formulation of composite solid polymer electrolytes for superior sodium metal batteries

Solid-state electrolytes (SSEs) can effectively address the dendrite growth and safety concerns associated with current battery technologies, but their implementation is still plagued by low ionic conductivity and high interfacial impedance. Herein, we report a reactivity-guided strategy towards the synthesis of a composite solid polymer electrolyte (SPE) with optimized compositions of polyester PPC, ceramic NASICON and the PEO host to simultaneously improve ionic conductivity, interfacial impedance, electrochemical stability, and mechanical properties. We formulate a novel synergistic approach that effectively increases the amorphousness of the composite SPE and forms anin situsodium-ion conductive wetting layer upon contacting and reacting with the metallic sodium electrode to enable solid-state sodium metal batteries with superior performance. Compared to the conventional PEO electrolyte, the proposed composite SPE exhibits 25 times higher Na⁺conductivity (0.12 mS cm⁻¹) and 10 times lower interfacial impedance. Solid-state full cells are further demonstrated with nearly 90% capacity retention after cycling at 1C rate for 500 cycles.