Na‐K Interlayer Driven Na‐NASICON Solid‐State Batteries

Abstract Solid‐state sodium batteries are deemed as a highly promising candidate for medium and long‐term stationary energy storage. But, the solid‐state electrolyte with desirable ionic conductivity and high stability against solid metal electrodes remains a significant challenge for the research and development of solid‐state sodium metal batteries. In this research, the approach of in‐situ formed Na‐K interlayer is put forward, wherein K⁺ electrochemically migrates from the K‐substituted NASICON‐structure ceramic electrolyte toward the interface of ceramic electrolyte and Na metal electrode, locally and dynamically forming a Na‐K interlayer with Na metal. Therefore, the compatibility between ceramic electrolytes and the Na electrode is obviously enhanced. Accordingly, the area specific resistance of the solid/solid interface contact gets reduced to 29.9 Ω cm² and a high room temperature critical current density of 1.3 mA cm⁻² is achieved. In the meantime, the Na/Na₃Zr₂Si₂PO₁₂‐0.005K/Na can steadily operate for 1400 h at 0.2 mA cm⁻². Moreover, NASICON‐structure ceramic electrolyte‐based solid‐state sodium metal batteries paired with polyanion and layered sodium ion cathodes are constructed to highlight the superiority of this well‐designed ceramic electrolyte/metal electrode interface.