The mediated synthesis of FeF₃ nanocrystals through (NH₄)₃FeF₆ precursors as the cathode material for high power lithium ion batteries

The exploration of cathode materials with high electrochemical performances is critical to improve the energy and power densities of lithium ion batteries (LIBs). Iron fluoride (FeF₃) has been proposed as an ideal candidate of LIBs cathode material because of the high discharge plateau and theoretical capacity. In this study, a precursor-mediated method was proposed to synthesize FeF₃ nanocrystals (NCs) with different microstructures. These FeF₃ NCs were obtained through the thermal decomposition of the precipitated ammonium hexafluoroferrate [(NH₄)₃FeF₆] precursor, and the morphology and crystallinity could be adjusted by varying the ethanol/water volume ratio in the procursor precipitation process. Electrochemical studies demonstrated that FeF₃ NC, derived from (NH₄)₃FeF₆ precipitated from the solution with the ethanol/water volume ratio of 20, delivered the initial specific capacity of 217.6 mAh g⁻¹ at 0.2C, associated with excellent rate capability up to 20C (93.8 mAh g⁻¹), and showed the capacity retention of 80.6% after 500 cycles at 20C. These results indicate a tunable and convenient strategy towards nanostructured metals fluorides for high power LIBs.