Achieving stable and high-rate quasi-solid-state sodium batteries through strengthened P-O covalency and interface modification in NaZrSiPO.

Solid-state sodium metal batteries have attracted great interest because of their improved safety and abundant Na resources. However, the interfacial resistances and instabilities induced by parasitic reactions, together with Na dendrite issues, result in reduced rate capability and poor cycling stability. Here, we address these challenges by intrinsically inhibiting parasitic interfacial redox reactions through enhanced P-O covalency in NaZrSiPO (NZSP) with NaSiF incorporation, wherein the high electronegativity of F strengthens P-O covalency. Additionally, SnF coating provides a sodiophilic surface and stabilizes the NZSP interface, which is essential for effective electrochemical cycling. This integrated approach significantly reduces interfacial impedance to 2.0 Ω cm, enabling stable Na plating/stripping for 3600 hours at 0.5 mA cm/0.25 mAh cm. The full cell with NaV(PO) positive electrode demonstrates stable cycling with high-rate capability (87.5% capacity retention after 2500 cycles at 1 C and 96.1% capacity retention after 1200 cycles at 5 C). This study sheds light on the development of high-performance quasi-solid-state sodium batteries.