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

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.