Oxidation state and local structure of a high-capacity LiF/Fe(V2O5) conversion cathode for Li-ion batteries

• Published in: Acta materialia Vol. 68; pp. 179 - 188
• Main Authors: Pohl, A.H., Guda, A.A., Shapovalov, V.V., Witte, R., Das, B., Scheiba, F., Rothe, J., Soldatov, A.V., Fichtner, M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.04.2014
• Subjects: Extended X-ray absorption fine structure (EXAFS, XANES); Iron fluoride; Li-ion battery; Mixed conductor; Nanocomposite; Nanocomposite; Extended X-ray absorption fine structure (EXAFS, XANES); Mixed conductor; Li-ion battery; Iron fluoride
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2014.01.016

[Display omitted] We prepared LiF/Fe(V2O5) nanocomposites with varying (0–20wt.%) V2O5 by high-energy ball milling and found a stable specific capacity of 450mAhg−1 for a period of 20 cycles without a noticeable reduction in capacity for the composite with 15wt.% V2O5. X-ray diffraction was unable to identify new phases present in the nanocomposite. To identify the phases formed during ball milling and cycling, we collected in situ X-ray absorption spectra at the Fe K- and VK-edges. During the first charge, LiF/Fe was converted to ∼35% FeF2, and during the second discharge, the initial V3.9+ oxidation state was reduced to V3.5+. Using principal component analysis, we decomposed the series of Fe K-edge spectra into three components consisting of Fe, FeF2 and a new phase, which was identified by comparison with theoretical X-ray absorption near edge structure spectra of model compounds with tetrahedral and octahedral V coordination and 57Fe Mössbauer spectroscopy to be the inverse spinel V[FeV]O4. From the calculations, we also identified the lithium vanadate LixVO2−xFx. Both LixVO2−xFx and V[FeV]O4 have open crystal structures with the ability to reversibly store lithium in interstitial lattice sites, and the effect of these compounds on capacity and cyclic stability of the LiF/Fe(V2O5) nanocomposites is discussed.