China Nonferrous Metallurgy

Iron fluoride (FeF₃) has emerged as a promising cathode material for lithium-ion batteries due to its high voltage, high capacity, and low cost. However, its highly insulating nature severely limits the effective utilization of its lithium storage capabilities. Nanostructuring can shorten lithium-ion diffusion pathways and effectively enhance the electrochemical activity of iron-based fluorides. Nevertheless, current synthesis methods rely on complex liquid-phase reactions and high-temperature treatments, making industrial-scale production challenging. This study employed constant potential electrolysis in an ammonium hydrogen fluoride (NH₄HF₂) solution to directly synthesize nanostructured iron fluoride cathode material. The electrochemical oxidation pathway of metallic iron in the NH4HF2 solution was elucidated using polarization curves and cyclic voltammetry techniques. The main conclusions are as follows: Polarization curves and cyclic voltammetry tests revealed characteristic oxidation potential peaks at -0.58V (Fe-2e→Fe²⁺) and 0.01V (Fe²⁺-e→Fe³⁺). Controlling the anode potential at 0.01V for 1 hour of constant potential electrolysis at 25℃ successfully synthesized iron fluoride material. The primary particles of the synthesized material exhibited granular and needle-like morphologies, with particle sizes below 100nm. This material delivered an initial discharge specific capacity of 220.2mAh/g at 0.1C within the voltage range of 2.0~4.5V. It demonstrated a capacity retention rate of 91.5% after 100 cycles, reaching a performance level comparable to carbon-coated materials.