Pressure-induced growth of coralloid-like FeF2 nanocrystals to enable high-performance conversion cathode

Fluoride ferrous (FeF2) is viewed as a promising conversion cathode material for next-generation lithium-ion batteries (LIBs) due to its high theoretical specific capacity and low cost. Unfortunately, issues such as poor intrinsic conductivity, iron dissolution, and phase separation hinder the application of FeF2 in high-energy cathodes. Here, a pressure-induced morphology control method is designed to prepare coralloid-like FeF2 nanocrystals with nitrogen-rich carbon coating (c-FeF2@NC). The coralloid-like interconnected crystal structure of c-FeF2@NC contributes to reducing interfacial resistance and enhancing the topotactic transformation during the conversion reaction, and the nitrogen-rich carbon (NC) coating can enhance interfacial stability and kinetic performance. When used as a conversion cathode for LIBs, c-FeF2@NC exhibits a high initial reversible capacity of 503.57 mA h g−1 and excellent cycling stability of 497.61 mA h g−1 with a low capacity decay of 1.19 % over 50 cycles at 0.1 A/g. Even at 1 A/g, a stable capacity of 263.78 mA h g−1 can still be retained after 200 cycles. The capability of c-FeF2@NC as a conversion cathode for sodium-ion batteries (SIBs) was also evaluated to expand its field of application. Furthermore, two kinds of full batteries have been assembled by employing c-FeF2@NC as cathodes and quantitative limited-Li (LLi) and pre-lithiated reduced graphene oxide (PGO) as anodes, respectively, to envisage the feasibility of practical applications of conversion materials.