Electrolytic Preparation and Application of Iron Based Fluoride As Cathode Materials in Lithium Ion Batteries

The iron-based fluorides with different fluorine iron ratios and particle sizes could be obtained by controlling the concentration of fluorine ions when electrolyzing carbon steel in the HF system using graphite as the cathode in this article. X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle size measurement techniques were used to describe the products, and the reaction mechanism of the electrolytic preparation process was investigated using a polarization curve and an impedance test. A lower concentration of F^– enhanced the oxidation of Fe²⁺ to Fe³⁺ during the anodic dissolution process, and Fe³⁺ rapidly chelated with F^– in the solution. When the HF concentration was 0.2–0.6 mol/L, single Fe₃F₈⋅2H₂O with a micrometer size was successfully synthesized. FeF₃⋅0.33H₂O/FeF₂ crystalline grains were obtained by heat treatment of Fe₃F₈⋅2H₂O at 250°C for 2 h in a tubular furnace under air atmosphere. When FeF₃⋅0.33H₂O/FeF₂ crystalline grains were further used as the cathode material of lithium-ion batteries (LIBs), the cathode material exhibited a high discharge capacity of 153 mA h g^–1 in the first cycle and 131.6 mA h g^–1 after 50 cycles under the voltage range of 2–4.2 V and the current density of 20 mA g^–1.