Dual-Interface Fluorination Stabilizing Rechargeable Na-NASICON Solid-State Batteries

Solid-state metal batteries promise next-generation energy storage with inherent safety and high energy density. However, instability at grain boundaries and surfaces critically hinders practical deployment in solid polycrystalline ion conductors. This work proposes a dual-interface fluorination strategy through the incorporation of fluoride-based grain boundary phases in solid electrolytes to simultaneously address these issues. The resulting NZSP-MgF₂ electrolyte exhibits a low electronic conductivity of 6.0 × 10⁻⁹ S cm⁻¹ and a widened bandgap, effectively suppressing the formation and growth of internal dendrites. Meanwhile, the interfacial contact impedance of the ceramic electrolyte against the metallic Na electrode is significantly reduced to 11 Ω cm². Crucially, the fluorinated polycrystalline Na₃Zr₂Si₂PO₁₂ ceramic electrolyte retains exceptional stability even after 30 days of exposure to air: symmetric sodium metal cells still exhibit low interfacial contact impedance (12 Ω cm²), high critical current density (1.0 mA cm⁻²), and stable cycling over 1100 h at 0.2 mA cm⁻². Furthermore, full cells paired with Na₃V₂(PO₄)₃ cathode demonstrate outstanding electrochemical performance with a capacity retention of 98.1% after 2000 cycles at 2 C. This work provides a general strategy to enhance air stability, dendrite suppression, and electrode compatibility of polycrystalline electrolyte, promoting the practical realization of solid-state metal batteries.