Materials Design Principles for Air‐Stable Lithium/Sodium Solid Electrolytes

Sulfide solid electrolytes are promising inorganic solid electrolytes for all-solid-state batteries. Despite their high ionic conductivity and desirable mechanical properties, many known sulfide solid electrolytes exhibit poor air stability. The spontaneous hydrolysis reactions of sulfides with moisture in air lead to the release of toxic hydrogen sulfide and materials degradation, hindering large-scale manufacturing and applications of sulfide-based solid-state batteries. In this work, we systematically investigate the hydrolysis and reduction reactions in Li- and Na-containing sulfides and chlorides by applying thermodynamic analyses based on a first principles computation database. We reveal the stability trends among different chemistries and identify the effect of cations, anions, and Li/Na content on moisture stability. Our results identify promising materials systems to simultaneously achieve desirable moisture stability and electrochemical stability, and provide the design principles for the development of air-stable solid electrolytes.