Enhancing Li Ion Conduction in Argyrodite Solid Electrolytes through Anion Site-Exchange

The superionic solid electrolyte Li₆PS₅Cl (LPSC), featuring ionic conductivity on par with those of liquids, has gained intense interest in the development of all-solid-state batteries. However, the mechanisms behind such extraordinarily high ionic conductivity remain unclear. In previous works, a phenomenon involving positional exchange between S and Cl anions was observed, which we referred to as "S/Cl site-exchange." We disclosed the correlation between Li ion conduction and the S/Cl site-exchange by integrating DFT, AIMD and NEB simulations, along with ⁷Li PFG NMR diffusivity measurements for the first time. A remarkable increase of ~10² times in Li ionic conductivity and a substantial reduction of ~160 meV in energy barriers are observed when the S/Cl site-exchange is introduced. We found out that transportation bottlenecks of Li ions are overcome through beneficial neighboring Li configuration induced by the S/Cl anion exchange. The comprehensive understanding of ion transport mechanisms in LPSC would help the design of solid-state fast ion conductors.