Concerted Influence of HO and CO: Moisture Exposure of Sulfide Solid Electrolyte LiSnS.

Although moisture-induced deterioration mechanisms in sulfide solid electrolytes to enhance atmospheric stability have been investigated, the additional impact of CO exposure remains unclear. This study investigated the generation of HS from LiSnS under HO and CO exposure. LiSnS was exposed to Ar gas at a dew point of 0 °C with and without 500 ppm of CO, and its ion conductive properties were evaluated. Although the lithium-ion conductivity of LiSnS decreased regardless of the presence of CO, the amount of HS generated with CO was five times higher. To elucidate the underlying mechanism, X-ray diffraction and Raman spectroscopy were used. Without CO, hydrate LiSnS·4HO formation markedly increased, whereas, with CO, it increased a little. The difference revealed distinct deterioration mechanisms leading to a decrease in lithium-ion conductivity: without CO, adsorbed HO and LiSnS·4HO contributed to the decrease, while with CO, a weak acid dissociation reaction could reduce the thermodynamic stability of the moisture-exposed LiSnS surface including LiSnS·4HO and adsorbed HO, promoting HS release and carbonate formation. This was supported by the recovery of lithium-ion conductivity after vacuum heating. The concerted influence of HO and CO provides valuable insights into the fundamental deterioration mechanisms in sulfide solid electrolytes that could be applied in battery manufacturing processes.