Fabrication and Electrochemical Performance of Br-Doped Na3PS4 Solid-State Electrolyte for Sodium–Sulfur Batteries via Melt-Quenching and Hot-Pressing

Room-temperature all-solid-state sodium–sulfur (Na-S) batteries are being regarded as a promising technology for large-scale energy storage. However, the low ionic conductivity of existing sulfide solid electrolytes has been hindering the potential and commercialization of Na-S batteries. Na3PS4 has garnered extensive attention among sulfide solid electrolytes due to its potential ionic conductivity (primarily predominated by vacancies) and ease of fabrication. Herein, we demonstrated a combined melt-quenching with Br doping technique to pre-generate abundant defects (vacancies) in the Na3PS4, which expanded ion transport channels and facilitated Na+ migration. The quenched Na2.9PS3.9Br0.1 holds an ionic conductivity of 8.28 × 10−4 S/cm at room temperature. Followed by the hot-pressed fabrication at 450 °C was conducted on the quenched Na2.9PS3.9Br0.1 to reduce interface resistance, the resultant Na2.9PS3.9Br0.1 pellet shows an ionic conductivity up to 1.15 × 10−3 S/cm with a wide electrochemical window and chemical stability towards Na alloy anodes. The assembled all-solid-state Na2S/Na2.9PS3.9Br0.1/Na15Sn4 cell delivers an initial reversible capacity of 550 mAh/g at a current density of 0.1 mA/cm2. After 50 cycles, it still maintains 420 mAh/g with a capacity retention of 76.4%. The integration of melt-quenching, doping, and hot-pressing provides a new strategy to enable sulfide electrolytes with high ionic conductivity and all-solid-state Na-S batteries with high performance.