Improving the cycle stability of FeCl₃-graphite intercalation compounds by polar Fe₂O₃ trapping in lithium-ion batteries

FeCl₃-intercalated graphite intercalation compounds (GICs) with high reversible capacity and high volumetric energy density are attractive anode material alternatives of commercial graphite. However, the rapid capacity decay, which was induced by chloride dissolution and shuttling issues, hindered their practical application. To address this problem, here, we introduce flake-like Fe₂O₃ species with inherently polar surface on the edge of FeCl₃-intercalated GICs through microwave-assisted transformation of a fraction of FeCl₃ component. Theoretical simulations and physical/electrochemical studies demonstrate that the introduced Fe₂O₃ component can afford sufficient polar active sites for chemically bonding the soluble FeCl₃ and LiCl species based on the polar-polar interaction mechanism, further inhibiting the outward diffusion of the chlorides and immobilizing them within the GIC material. In a lithium ion cell, the FeCl₃-intercalated GIC with a suitable Fe₂O₃ content shows remarkably improved cycling stability with a high reversible capacity of 1, 041 mAh∙g^-1 at a current density of 200 mA∙g^-1. Capacity retention of 91% is achieved at a high current density of 1, 000 mA∙g^-1 over 300 cycles. This work opens up the new prospect for immobilizing chlorides by introducing inorganic species in GIC for long-cycle electrochemical batteries.