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

ABSTRACT 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 Li 6 PS 5 I with Ge, Sb, Si, and As, yielding Li 6.5 As 0.25 Si 0.25 Ge 0.25 Sb 0.25 S 5 I with a configurational entropy of 2.04 R . 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 Li 6 PS 5 I (1.5 mS cm −1 ). HEA‐As 0.25 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.