Coupling Porous Architecture and Fe-F Coordination Engineering Enables Highly Reversible FeF3 Cathode Materials

Iron trifluoride (FeF3) is a promising conversion-type cathode material for next-generation lithium-ion batteries (LIBs) owing to its high theoretical capacity enabled by multielectron redox chemistry. However, its practical application is limited by sluggish reaction kinetics, large volume fluctuations, and unstable electrode/electrolyte interfaces. Herein, we develop a deep eutectic solvent strategy that enables controlled fluorination, constructing interconnected porous architectures and regulating the local Fe-F coordination environment. Benefiting from shortened Li+ diffusion pathways and reduced stress accumulation, the porous FeF3 delivers a reversible capacity of 551.5 mAh g-1 at 50 mA g-1 and excellent cycling stability with 66.4% capacity retention after 1000 cycles. Spectroscopic characterizations and COMSOL simulations reveal that the regulated Fe-F promotes the formation of a robust inorganic-rich cathode electrolyte interphase, thereby enabling stable interfacial chemistry. This work highlights the critical roles of both porous architecture design and local coordination chemistry in governing conversion-type cathode materials for LIBs.