Molten-Perfusion-Fluorination Strategy To Enable Graphite Layer Confined Pyrochlore-Phase Iron Hydroxy Fluoride as Sustainable Conversion-Type Cathode

Abstract Multielectron-conversion type and economically friendly iron fluorides are labeled as potential cathode candidates over single electron-redox intercalation oxides for Li-driven batteries. Herein, we propose a molten-perfusion-fluorination strategy to introduce pyrochlore-phase iron hydroxy fluoride into nature graphite layers. The macroscopic coralloid-like morphology, sandwich-packing with Fe–C chemical bonds, and 3D open framework endow FeF3 with abundant (surface/bulk) reactive sites and self-adaption ability against consecutive conversion reactions. The microscopic hydroxy anion replacement against F– framework also reduces the Fe–F coordination strength while partially substituting “tough” LiF by “soft” LiOH in discharge products. Consequently, the optimized cathode delivers a good cycling performance (255 mAh g–1 after 150 cycles) at 100 mA g–1 and outstanding capacity retention from 200 to 1000 mA g–1 (with reversible capacity of 327 mAh g–1). Such structural design method also reveals new perspectives for the expansion and exfoliation of graphite and its confinement effect and hybridization with electrode active species.