Polypyrrole-coated iron oxychloride cathode material with improved cycling stability for chloride ion batteries

Iron oxychloride has been regarded as a promising cathode material for chloride ion batteries (CIBs). However, it suffers a severe capacity decay during repeated conversion reactions based on chloride ion transfer. Herein, we report an iron oxychloride composite material with a polypyrrole coating (FeOCl@PPy), which is prepared by a facile and efficient chemical vapor phase polymerization method, as cathode for CIB. The as-prepared FeOCl@PPy cathode material with drastically enhanced charge transfer and chloride ion diffusion shows a stable core-shell structure, which can prevent the FeOCl particles from pulverization during cycling. As a result, a maximum capacity of 187 mA h g⁻¹ and significantly improved cycling stability with 82.9% capacity retention after 30 cycles are obtained. In contrast, the neat FeOCl cathode fades fast and shows only 13.2% capacity retention.