Effects of Oxide Precursors on the Structure and Properties of Na₃PS_4–xO_x Glassy Solid Electrolytes

Solid-state sodium batteries based on sulfur cathodes offer the advantage of both sustainability due to the abundance of sodium and sulfur and the safety offered by solid electrolytes. However, they are hampered by the challenges associated with the sodium solid-state electrolytes, sodium–metal anodes, and sulfur cathode. We present here the synthesis of Na 3 PS 4– x O x glassy solid electrolytes (GSEs) through a facile mechanochemical reaction of various oxide precursors and milling conditions, aiming to identify the relationship between the stability of the oxide precursor and the extent of oxygen integration. Structural motifs unique to each oxygen precursor are identified with 23 Na and 31 P magic-angle spinning nuclear magnetic resonance and Raman spectroscopies to identify anion mixing and oxygen incorporation. Additionally, the degree of unreacted Na 2 S during the synthesis is quantified and correlated with the transport properties. The cycling stabilities of solid-state Na–S cells assembled with Na 3 PS 4 and Na 3 PS 3.8 O 0.2 electrolytes are compared at room temperature. Notably, cells assembled with the Na 3 PS 4– x O x GSE that was prepared with P 2 O 5 exhibit 980 mA h g –1 after 50 cycles at 25 °C with an areal capacity of 0.5 mA h cm –2 . This study demonstrates the potential of safer, sustainable solid-state batteries with earth-abundant sodium and sulfur.