Coupling Electronic and Interfacial Engineering Unlocks Fast and Durable Iron Fluoride Cathodes

Iron fluoride is a promising conversion-type cathode for lithium-ion batteries owing to its high theoretical energy density, yet its practical application is hindered by poor electronic conductivity and limited cycling stability. Here, we report a synergistic strategy that integrates cobalt doping with binder engineering to simultaneously enhance the electronic structure and Li⁺ transport kinetics of FeF₃ cathodes. Cobalt incorporation modulates the Fe─F coordination environment, introduces defect sites, and redistributes charge density, thereby promoting electron transport and Li⁺ diffusion. In parallel, a sodium alginate-based graphene oxide (SAGO) binder with high ionic conductivity reduces interfacial resistance and facilitates ion transport. As a result of this dual modulation, the SAGO-Co-FeF₃ cathode delivers a reversible capacity of 356 mAh g^-1 after 50 cycles at 0.2 C and maintains 132 mAh g^-1 at 10 C. Comprehensive electrochemical measurements, kinetic analyses, in/ex situ characterizations, and density functional theory calculations elucidate the underlying enhancements in electronic and ionic transport. Notably, a full cell employing the SAGO-Co-FeF₃ cathode retains 86.5% of its initial capacity after 500 cycles. This work provides a generalizable strategy for designing high-energy, long-life conversion-type cathodes for practical lithium-ion batteries through coupled electronic and interfacial engineering.