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

ABSTRACT 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 FeF ₃ 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‐FeF ₃ 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‐FeF ₃ 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.