Interface Stability between Na3Zr2Si2PO12 Solid Electrolyte and Sodium Metal Anode for Quasi-Solid-State Sodium Battery

Solid electrolytes are renowned for their nonflammable, dendrite-blocking qualities, which also exhibit stability over large potential windows. NASICON-type Na1+xZr2SixP3-xO12 (NZSP) is a well-known solid electrolyte material for sodium metal batteries owing to its elevated room temperature sodium-ion (Na+) conductivity and good electrochemical stability. Nevertheless, the strong electrode–electrolyte interfacial resistance restricts its implementation in sodium metal batteries and remains a significant challenge. In this work, we present an efficacious process to enhance the sodium wettability of Na3Zr2Si2PO12 by sputtering a thin gold (Au) interlayer. Our experimental investigation indicates a substantial reduction in interfacial resistance, from 2708 Ω cm2 to 146 Ω cm2, by employing a fine Au interlayer between the Na metal and the NZSP electrolyte. The symmetrical Na||NZSP||Na with a gold interlayer cell shows a steady Na stripping/plating at a high current density of 320 µA cm−2. A quasi-solid-state battery, with NaFePO4 (NFP) as a cathode, metallic sodium as an anode, and a Au-sputtered NZSP electrolyte with polypropylene (PP) soaked in electrolyte as an intermediate layer on the cathode, exhibited a discharge capacity of 100 mAh g−1 and a ~100% Coulombic efficiency at 50 μA cm−2 after the 50th charge/discharge cycle at room temperature (RT).