Toward High Energy Density FeFx (x=2 and 3) Cathodes for Lithium-Ion Batteries

It has been challenging to develop next-generation higher energy density cathode materials to satisfy the incremental demand for lightweight and miniaturization for lithium-ion batteries (LIBs). The iron-based fluoride (FeFx) cathodes may be highly competitive due to abundant resources as well as high theoretical capacity. However, the complex multiphase conversion reactions of the FeFx cathodes cause limited battery performance hindering its commercialization. Herein, this review focuses on the multi-electron conversion processes involved in solid-solid reactions. More importantly, the scientific strategies of enhanced FeFx performance are mainly addressed in view of four critical aspects, i. e., conductive matrix, heteroatom doping, surface modification, and electrolyte engineering. It is demonstrated that the optimized strategies can mitigate the challenges of the FeFx cathodes during multi-electron conversion processes. It is believed that this review has been a guidance for improving the cycling performance of the FeFx cathodes for high energy density LIBs.