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

Na-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 (R <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mover><mml:mn>3</mml:mn> <mml:mo>¯</mml:mo></mml:mover> <mml:annotation>$\bar 3$</mml:annotation></mml:semantics> </mml:math> m) 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 Na_1.67Mg_0.67Al_10.33O₁₇ (NMAO), which also suppresses the formation of the β' phase (P6₃/mmc) and decreases stacking faults. After sintering at 1550 °C for 2 h, Na_1.67Mg_0.67Al_9.33GaO₁₇ (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.