Superior electrochemical performance of N-doped nanocrystalline FeF₃/C with a single-step solid-state process

FeF₃ is a promising cathode material for lithium ion batteries but its poor electronic conductivity makes it non-practical. Here, we significantly improve the electrochemical activity of FeF₃ by reducing the strong ionic character of Fe-F with the replacement of some F with N atoms. N-doped nanocrystalline FeF₃/C achieves the best electrochemical performance among FeF₃ compounds reported to date: ∼95 mA h g^-1 at 21.1C discharge rate for 250 cycles. The results illustrate that the poor electronic conductivity of metal fluorides can be controlled by doping and this enables FeF₃ or metal fluorides to be practically utilized in possible applications including energy conversion and storage.