Elucidation of degradation mechanism of a Li-argyrodite solid electrolyte against moisture and proposal of design principles for robust stability

As sulfide solid-state electrolytes advance toward commercialization, unresolved safety issues like structural degradation in humid air persist. This study elucidates atomistic degradation mechanisms using first-principles calculations with Li-argyrodite as a model. Among air components, oxygen molecules suppress H 2 S generation by binding to the argyrodite surface through hybridization with sulfur's non-bonding orbitals. Substituting P 5+ with cations like V 5+ , Mo 6+ , and W 6+ , which have d-orbitals and high oxidation states, enhances stability by reducing sulfur's non-bonding orbitals and weakening reactions with H 2 O. However, their composition must be controlled to prevent increased electronic conductivity. Group 15 elements (As 5+ , Sb 5+ , and Bi 5+ ) also improve moisture stability through PS 4 distortion due to large ionic sizes and by promoting new S–S bond formation without interacting with sulfur's non-bonding orbitals. This work provides valuable insights into degradation mechanisms and offers design principles for fabricating moisture-resistant solid electrolytes for promising Li-ion batteries.