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

AbstractSulfide 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 SiO2. Consequently, high‐sodium‐content oxythiosilicate glass is synthesized without sealing and quenching processes under Ar atmosphere. The prepared Na4SiS4·0.200SiO2 (molar ratio) glass exhibits ionic conductivity of 4.0 × 10−5 S cm−1 at 25 °C, surpassing that of Na4SiS4 glass. The Na4SiS4·0.200SiO2 glass shows high reduction stability to sodium metal. The all‐solid‐state Na metal/Na4SiS4·0.200SiO2 glass/Na2.88Sb0.88W0.12S4/TiS2 cell shows a reversible capacity of 140 mAh g−1 for 5 cycles. The amount of H2S gas generated in Na4SiS4·0.0830SiO2 and Na4SiS4·0.200SiO2 glasses is one‐tenth that of the Na4SiS4 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.