Hydrolysis mechanism of Li‐argyrodite Li 6 PS 5 Cl in air

All‐solid‐state lithium‐ion batteries (ASSLBs) with solid state electrolytes (SSE), regarded as next‐generation battery system, have attracted most of the research and industrial interest in the electrochemical storage field due to their higher energy density, wider voltage window, safety and other superior performance. Seeking promising solid‐sate electrolytes with high ionic conductivity and excellent electrochemical stability plays the key role in practicing ASSLBs. Li‐argyrodites show high ionic conductivity and stable electrochemical properties, which are advantageous to ASSLIBs. However, as most sulfide solid electrolytes show poor stability in air, Li‐argyrodites would react with H 2 O molecules in the air and release harmful H 2 S gas. We have carried out first‐principles calculations on the failure mechanism of Li‐argyrodites based on the hydrolysis of Li 6 PS 5 Cl. Two possible hydrolysis paths for H 2 O molecule on the Li 6 PS 5 Cl surface are found, with single or dual H 2 O molecules, respectively. The dynamic results show that both oxygen atoms and sulfur vacancies could diffuse on the surface. However, they are difficult to migrate in the bulk. Thermodynamic calculations show that the thermodynamic stability of Li 6 PS 5 Cl decreases gradually with the continuous hydrolysis reaction. The effect of doping Sn in Li 6 PS 5 Cl is further investigated, which explains the inhibiting mechanism of Sn‐doping in Li 6 PS 5 Cl from the perspective of kinetics. Our studies also show that Sn doping mainly inhibits the hydrolysis of Li 6 PS 5 Cl by preventing the decomposition of OH − when involving single H 2 O molecule, while it obstructs the decomposition of the absorbed H 2 O when involving dual H 2 O molecules.