Influence of Atmospheric Gas Species on an Argyrodite-Type Sulfide Solid Electrolyte During Moisture Exposure.

Sulfide solid electrolytes have potential in practical all-solid-state batteries owing to their high formability and ionic conductivity. However, sulfide solid electrolytes are limited by the generation of toxic hydrogen sulfide and conductivity deterioration upon moisture exposure. Although numerous studies have investigated the hydrolysis degradation induced by "moisture," the influence of "atmospheric gases" during moisture exposure has not been extensively investigated despite the importance for practical fabrication. Therefore, in this study, we investigated the impact of atmospheric gases during moisture exposure on an argyrodite-type Li₆PS₅Cl via electrochemical impedance spectroscopy, X-ray diffraction, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. The electrolyte powder was exposed to various atmospheric gases, namely Ar, Ar+500 ppm CO₂, O₂, and O₂+500 ppm CO₂, with moisture at a dew point of -20 °C, and H₂S gas generation was monitored. As a result, the amount of H₂S gas did not depend on the atmospheric gases. However, the atmospheric gases had a significant effect on the decrease in conductivity. Spectroscopic analyses revealed that CO₂ facilitates the formation of carbonates and that O₂ promotes the formation of phosphates and sulfonates. The formation of these compounds leads to surface degradation, which further decreases the conductivity.