Iron Oxyfluorides as High Capacity Cathode Materials for Lithium Batteries

Abstract

Nanostructure iron oxyfluoride compounds of tunable oxygen content were fabricated by a solution process utilizing iron metal and fluorosilicic acid solutions as precursors. Simple adjustment of the synthesis atmosphere, temperature, and time enabled the fabrication of iron oxyfluoride materials with compositions spanning over the entire range from pure FeF2 to FeOF. Nanocomposites were fabricated from iron oxyfluorides of various oxygen content and activated carbon in order, for the first time, to evaluate the impact of oxygen on the iron fluoride electrochemical performance. The introduction of oxygen proved beneficial to cycling stability but at the expense of reversible capacity. A combination of electrochemical and structural characterization analyses was performed to identify the iron oxyfluoride reaction mechanism.