High Configuration Entropy Promises Electrochemical Stability of Chloride Electrolytes for High‐Energy, Long‐Life All‐Solid‐State Batteries

Solid‐state electrolytes (SSEs) with high ionic conductivity, stability, and interface compatibility are indispensable for high‐energy‐density and long‐life all‐solid‐state batteries (ASSBs), yet there are scarce SSEs with sufficient ionic conductivity and electrochemical stability. In this study, with a high‐entropy SSE (HE‐SSE, Li 2.9 In 0.75 Zr 0.1 Sc 0.05 Er 0.05 Y 0.05 Cl 6 ), we show the high configuration entropy has a thermodynamically positive relationship with the high‐voltage stability. As a result, the ASSBs with HE‐SSE and high‐voltage cathode materials exhibit superior high‐voltage and long‐cycle stability, achieving 250 cycles with 81.4 % capacity retention when charged to 4.8 V (vs. Li + /Li), and even 5000 cycles if charged to 4.6 V (vs. Li + /Li). Experimental characterizations and density functional theory calculations confirm that the HE‐SSE greatly suppresses the high‐voltage degradation of SSE at the interface, promoting the high‐voltage stability coordinately through high entropy and interface stability. The high entropy design offers a general strategy to simultaneously improve the high‐voltage stability and ionic conductivity of SSEs, creating an avenue to building high‐energy and long‐life ASSBs.