Formation of iron oxyfluoride phase on the surface of nano-Fe ₃O₄ conversion compound for electrochemical energy storage

We have investigated a novel approach wherein we undertake surface fluorination of nanometer sized Fe₃O₄ conversion compound into corresponding oxyfluoride with the goal toward enhancing their energy density as well electrochemical performance stability. This is achieved by using direct fluorination of nano-Fe₃O₄ in a fluidized bed reactor under controlled reaction atmosphere and temperature. X-ray photoemission spectroscopy analysis shows conclusive evidence of the surface fluorination of Fe₃O₄ particles at a reaction temperature of 100 C and higher forming a surface oxyfluoride phase that can be nominally described as FeOF. Formation of oxyfluoride phase is confirmed by the appearance of a higher potential intercalation plateau during the electrochemical charge-discharge cycling. Based on the experimental results, various pathways are discussed for the formation of oxyfluoride species on the surface.