Dual Optimization of Electrolyte and Interface in Na‐<i>β</i>″‐Al₂O₃ via Ga³⁺ Doping for Advanced Solid‐State Sodium Batteries

Abstract

AbstractNa‐β″‐Al2O3 is a highly promising solid‐state electrolyte (SSE) for solid‐state sodium batteries (SSSBs) with a wide electrochemical stability window and excellent stability against metallic sodium. However, its practical application is hindered by the instability of β″ phase (Rm) during sintering, low polycrystalline ionic conductivity at room temperature, and poor interfacial contact with sodium anodes. In this study, a stablized SSSB is obtained via doping Ga3+ into Na1.67Mg0.67Al10.33O17 (NMAO), which also suppresses the formation of the β′ phase (P63/mmc) and decreases stacking faults. After sintering at 1550 °C for 2 h, Na1.67Mg0.67Al9.33GaO17 (NMA9.33GO) exhibits an ionic conductivity of 9.2 × 10−4 S cm−1 at 30 °C, ≈1.7 times greater than NMAO. Furthermore, Ga3+ doping enhances the wettability with sodium, achieving superior contact stability and the formation of Na‐Ga alloys at the interface significantly improves electrode‐electrolyte contact stability, achieving a high critical current density (CCD) of 0.8 mA cm−2 and a low interfacial impedance of 16 Ω cm2. A quasi‐solid‐state battery assembled with Na3V2(PO4)3 (NVP) as the cathode demonstrates excellent cycling stability and rate performance, retaining a high discharge capacity of 91 mAh g−1 at 5 C, and maintaining 87% capacity retention after 1000 cycles at 1 C. This work provides new insights into improving electrolyte performance and interfacial engineering through doping strategies, thereby promoting the development of efficient and long‐term SSSBs.