High-Entropy Design for Improving Ionic Conductivity and Air Stability of Lithium Argyrodites for All-Solid-State Lithium-Sulfur Batteries.

Lithium argyrodites hold great promise as solid electrolytes for all-solid-state batteries (ASSBs) owing to their high room-temperature ionic conductivity and soft mechanical properties. However, their poor air stability hinders large-scale commercial applications. To overcome this, we demonstrate herein a high-entropy design strategy by substituting the P-site in Li6PS5I with Ge, Sb, Si, and As, yielding Li6.5As0.25Si0.25Ge0.25Sb0.25S5I with a configurational entropy of 2.04R. Neutron powder diffraction (NPD) and various spectroscopic analyses indicate that the compositional complexity increases structural (occupational) disorder and facilitates lithium transport, resulting in room-temperature ionic conductivities of 8.0 mS cm-1 in cold-pressed state and 11.4 mS cm-1 for hot-pressed pellets, the latter being significantly higher compared to the glassy counterpart Li6PS5I (1.5 mS cm-1). HEA-As0.25 also demonstrates much improved chemical stability against moist air and toluene. When integrated into full cells with a sulfur cathode and an In/InLi anode, the respective all-solid-state lithium-sulfur batteries exhibit excellent cycling stability. Overall, this work provides a new approach for designing advanced sulfide solid electrolytes that simultaneously possess high ionic conductivity and air stability.