FeF₃@Thin Nickel Ammine Nitrate Matrix: Smart Configurations and Applications as Superior Cathodes for Li-Ion Batteries

Iron fluorides (FeFx) for Li-ion battery cathodes are still in the stage of intensive research due to their low delivery capacity and limited lifetime. One critical reason for cathode degradation is the severe aggregation of FeFx nanocrystals upon long-term cycling. To maximize the capacity and cyclability of these cathodes, we propose herein a novel and applicable method using a thin-layered nickel ammine nitrate (NAN) matrix as a feasible encapsulation material to disperse the FeF3 nanoparticles. Such core-shell hybrids with smart configurations are constructed via a green, scalable, in situ encapsulation approach. The outer thin-film NAN matrix with prominent electrochemical stability can keep the FeF3 nanoactives encapsulated throughout the cyclic testing, protecting them from adverse aggregation into bulk crystals and thus leading to drastic improvements of electrode behaviors (e.g., high electrode capacity up to ∼423 mA h g(-1), greatly prolonged cyclic period, and promoted rate capabilities). This present work may set up a new and general platform to develop intriguing core-shell hybrid cathodes for Li-ion batteries, not only for FeFx but also for a wide spectrum of other cathode materials.