Boosting the Structural and Electrochemical Stability of Chloride‐Ion‐Conducting Perovskite Solid Electrolytes by Alkali Ion Doping

Abstract The use of chloride‐based solid electrolytes derived from Lewis acid‒base reactions enables the construction of various new rechargeable batteries, such as chloride ion batteries (CIBs). However, a critical problem with these electrolytes is their poor stability under low‐temperature, moist, or electrochemical conditions, which can lead to deterioration of the phase structure and a loss of ion conduction. Herein, the robust cubic structure of tin‐based perovskite chloride—a chloride ion conductor—is achieved by alkali ion doping at the tin site via direct mechanical milling. The as‐prepared cubic CsSn_0.925Na_0.075Cl_2.925 (CSNC) electrolyte exhibits outstanding structural stability over a broad temperature range of 213−473 K or under a high relative humidity of up to 90%, at which the typical chloride electrolytes previously reported deteriorate because of moisture. Importantly, mild annealing can modify the microstructure of the CSNC, resulting in a two fold increase in ionic conductivity and an increase in electrochemical stability, which is superior to those of other chloride electrolytes reported in previous studies. The effective chloride‐ion transfer and wide electrochemical window of the CSNC are further demonstrated in different solid‐state CIBs.