Synthesis of High‐Sodium‐Content Oxythiosilicate Glass Electrolytes Via Sodium Polysulfide

Sulfide glass electrolytes with high ionic conductivities and formabilities are key materials for practical use in all‐solid‐state sodium secondary batteries. Both sealing and quenching are considered to be necessary for producing high‐alkali‐content sulfide glass electrolytes. In this study, the glass‐forming ability of sodium thiosilicate glasses is enhanced by adding a small quantity of SiO 2 . Consequently, high‐sodium‐content oxythiosilicate glass is synthesized without sealing and quenching processes under Ar atmosphere. The prepared Na 4 SiS 4 ·0.200SiO 2 (molar ratio) glass exhibits ionic conductivity of 4.0 × 10 −5 S cm −1 at 25 °C, surpassing that of Na 4 SiS 4 glass. The Na 4 SiS 4 ·0.200SiO 2 glass shows high reduction stability to sodium metal. The all‐solid‐state Na metal/Na 4 SiS 4 ·0.200SiO 2 glass/Na 2.88 Sb 0.88 W 0.12 S 4 /TiS 2 cell shows a reversible capacity of 140 mAh g −1 for 5 cycles. The amount of H 2 S gas generated in Na 4 SiS 4 ·0.0830SiO 2 and Na 4 SiS 4 ·0.200SiO 2 glasses is one‐tenth that of the Na 4 SiS 4 glass, suggesting increased chemical stability to humidity by incorporating oxygen in the structure. High‐sodium‐content oxythiosilicate glass with high ionic conductivity, high chemical stability against humidity, and high reduction stability is successfully prepared under ambient pressure without sealing and quenching processes.