Dual Optimization of Electrolyte and Interface in Na-β″-Al2O3 via Ga3+ Doping for Advanced Solid-State Sodium Batteries

Na- β ″-Al 2 O 3 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 3 ¯ $\bar 3$ 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 Ga 3+ into Na 1.67 Mg 0.67 Al 10.33 O 17 (NMAO), which also suppresses the formation of the β ′ phase ( P 6 3 / mmc ) and decreases stacking faults. After sintering at 1550 °C for 2 h, Na 1.67 Mg 0.67 Al 9.33 GaO 17 (NMA9.33GO) exhibits an ionic conductivity of 9.2 × 10 −4 S cm −1 at 30 °C, ≈1.7 times greater than NMAO. Furthermore, Ga 3+ 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 cm 2 . A quasi-solid-state battery assembled with Na 3 V 2 (PO 4 ) 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.