Formation of Iron Oxyfluoride Phase on the Surface of Nano-Fe3O4 Conversion Compound for Electrochemical Energy Storage

We have investigated a novel approach wherein we undertake surface fluorination of nanometer sized Fe 3 O 4 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-Fe 3 O 4 in a fluidized bed reactor under controlled reaction atmosphere and temperature. X-ray photoemission spectroscopy analysis shows conclusive evidence of the surface fluorination of Fe 3 O 4 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.