Hydrogen Components of a Sulfide-based Argyrodite-Type Solid Electrolyte after Moisture Exposure

In all-solid-state lithium-ion battery research, sulfide-based solid electrolytes (SEs) have been intensively studied because of their attractive properties, such as high lithium ionic conductivity, plasticity, and thermal stability. The most significant problem with SEs is the toxic hydrogen sulfide (H2S) gas generation upon their exposure to moisture. While many studies have developed new materials to improve the ionic conductivity and moisture durability of SEs, only a few have elucidated the degradation mechanism and surface state by moisture exposure at the molecular and atomic levels. In this study, we investigated the moisture-exposed argyrodite-structured sulfide-based Li6–xPS5–xClx SE by 1H magic angle spinning nuclear magnetic resonance spectroscopy to analyze the hydrogen species generated from the undesirable surface degradation reactions in the air with a dew point of −20 °C (0.9 g m–3 of H2O). The spectra showed peaks from surface hydrogen components such as LiOH, LiOH·xH2O, thiol groups, and unreacted H2O cluster adsorbates. Additionally, we conducted temperature-programmed desorption mass spectrometry measurements on moisture-exposed SE samples to confirm the desorption of H2O clusters upon heating.