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

Fluoride ferrous (FeF 2 ) 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 FeF 2 in high-energy cathodes. Here, a pressure-induced morphology control method is designed to prepare coralloid-like FeF 2 nanocrystals with nitrogen-rich carbon coating (c-FeF 2 @NC). The coralloid-like interconnected crystal structure of c-FeF 2 @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-FeF 2 @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-FeF 2 @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-FeF 2 @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.