Bismuth and Chlorine Dual‐Doped Perovskite Chloride as a Phase‐Structure‐Stable and Moisture‐Resistant Solid Electrolyte for Chloride Ion Batteries

Abstract Perovskite chloride, an anion conductor, is a promising candidate to be a solid electrolyte for high‐energy and sustainable chloride ion batteries (CIB). However, it suffers from poor structural stability at low temperature and in ambient conditions, which leads to its transformation from an ionic conductor to an insulator. Herein, a bismuth and chlorine dual doping strategy is developed to stabilize the cubic structure of CsSnCl 3 in harsh environments. The as‐prepared dual‐doped CsSn 0.9 Bi 0.1 Cl 3.1 material with an optimized composition maintains its cubic structure at the extremely low temperature of 213 K for 10 days and at 40% relative humidity for 50 days, while the undoped cubic material deteriorates and transforms to a monoclinic phase under these conditions in less than 1 day. Consequently, the dual doping achieves efficient chloride ion conduction that is superior to single bismuth doping due to the introduction of interstitial chlorine facilitating chloride ion transport. Importantly, the practicality of the as‐prepared solid electrolyte is demonstrated in different symmetric solid cells and by various CIBs using the organic electrode couple, a multivalent metal chloride cathode, or a new high‐voltage metal oxychloride cathode.