Preparation of anhydrous iron fluoride with porous fusiform structure and its application for Li-ion batteries

Iron fluorides are drawing the attention of researchers for their high specific capacity as cathode materials of lithium ion batteries. In this work, we focus on the structural adjustment of iron fluorides themselves to improve the electrochemical performances. A kind of porous FeF₃ with a fusiform structure has been synthesized by a facile solvothermal method and subsequent heat treatment. The synthetic process of hydrated FeF₃ was performed by using simple and economic raw materials (iron salt and HF in absolute ethyl alcohol). The crystal water was removed through a mild drying in air, and porosity is given through the slow dehydration process. Electrochemical performance shows that the as-synthesized porous FeF₃ can deliver stable reversible capacities of 137.3 mA g⁻¹ for 100 cycles at 20 mA g⁻¹. Although the specific capacity is moderate among the current research results of iron fluorides, this open porous structure obviously enhance the cycling stability of iron fluorides, and it can be expected to be improved remarkably with further processing.