Crown Ether Electrolyte Additive Enables High‐Rate and Stable Polyviologen Cathode Material for Chloride Ion Batteries

Abstract A variety of inorganic and inorganic cathode materials for chloride ion storage are reported. However, their application in chloride ion batteries (CIB) is hindered by poor rate capability and cycling stability. Herein, an organic poly(butyl viologen dichloride) (PBVCl₂) cathode material with significantly enhanced rate and cycling performance in the CIB is achieved using a crown ether (18‐Crown‐6) additive in the tributylmethylammonium chloride‐based electrolyte. The as‐prepared PBVCl₂ cathodes exhibit impressive capacity increases from 149.4 to 179.1 mAh g⁻¹ at 0.1 C and from 57.8 to 111.9 mAh g⁻¹ at 10 C, demonstrating the best rate performance with the highest energy density among those of various reported cathodes for CIBs. This impressive performance improvement is a result of the great boosts in charge transfer, ion transport, and interface stability of the battery by the use of 18‐Crown‐6, which also contributes to a more than twofold increase in capacity retention after 120 cycles. The electrode reaction mechanism of the CIB based on highly reversible chloride ion transfer is revealed by Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy.