Mechanochemical synthesis and characterization of Na3–P1–W S4 solid electrolytes

All-solid-state sodium batteries are attracting attention as next-generation batteries, owing to their improved safety and abundance of sodium resources. To realize all-solid-state sodium batteries, solid electrolytes with high sodium-ion conductivities are required. In this study, Na3PS4 electrolytes with partial substitution of P5+ with W6+ were investigated. The Na3–xP1–xWxS4 sulfide-based solid electrolytes were prepared via a mechanochemical process and consecutive heat treatment. The Na2.85P0.85W0.15S4 electrolyte with Na vacancies exhibited an ionic conductivity of 8.8 × 10−3 S cm−1 at 25 °C, which was higher than that of Na3PS4 solid electrolyte. The all-solid-state batteries (Na-Sn/Na2.85P0.85W0.15S4/TiS2) exhibited a reversible capacity of 140 mA h g−1 at a current density of 0.038 mA cm−2 and retained the capacity of 115 mAh g−1 for 40 cycles at 0.130 mA cm−2 at 25 °C. The Na3–xP1–xWxS4 samples prepared via mechanochemistry are homogeneous electrolytes free of crystalline WS2 impurities and are effective for application to all-solid-state sodium batteries.