Electrochemical Characterization of LiMnFeF 6 for Use as Positive Electrode in Lithium-Ion Batteries

Abstract

To replace common commercial lithium metal oxides or polyanionic cathode materials, lithium transition metal fluorides are of particular interest, as they potentially provide a high energy density, safety, and cyclability. The quaternary fluoride LiMnFeF6 that crystallizes in the Na2SiF6-type structure was synthesized without toxic chemicals by a sol-gel process with trifluoroacetic acid as fluorine source. After structural and morphological characterization, the as-synthesized material was ball-milled with carbon. The novel composite cathode material produced in this way was cycled versus lithium. The electrochemical potential range, cycling ability, and rate performance were investigated and the electrochemically active redox couple Fe3+/Fe2+ was confirmed by Mössbauer spectroscopy. Structural changes of the LiMnFeF6 host structure after Li insertion were investigated by X-ray powder diffraction.