Enhancing Argyrodite Electrolyte Conductivity and Air Stability via Anion Entropy–Enthalpy Tuning

Lithium argyrodite compounds stand out as highly attractive solid electrolytes for all-solid-state batteries (ASSBs), owing to their promising ion transport properties and inherent mechanical flexibility. However, their large-scale application is mainly restricted by the poor air stability and narrow electrochemical window. Herein, structural engineering of argyrodite sulfide electrolytes by finely tuning the anion entropy and reaction enthalpy of Li 6 PS 5 Cl 1− x Br x is reported. Through substituting Cl − with 50% of Br − , the structure of the argyrodite shows the maximum anion entropy and weakened P–S bonds that reduce the existence of P 2 S 7 4− , which ensures the lowest lithium-ion migration energy barrier and the highest hydrolysis enthalpy. Consequently, with proper adjustment, the ionic conductivity of Li 6 PS 5 Cl 1− x Br x ( x = 0.5) can reach 3.67 mS/cm, and maintain ~35%/72% of its ionic conductivity after humid-air/dry-room exposure, respectively, much higher than those of mono-halide argyrodites. ASSBs with the Li 6 PS 5 Cl 0.5 Br 0.5 electrolyte, a ZrO 2 -coated LiNi 0.9 Mn 0.05 Co 0.05 O 2 cathode, and Li-In anode result in enhanced capacity output and stable long-term performance across a range of temperatures (retention of 93% and 92% at 60 and −20 °C, respectively). This study provides a guidance for the development of sulfide-based ASSBs toward practical applications.