Oxidation State and Local Structure of a High-Capacity LiF/Fe(V2O5) Conversion Cathode for Li-Ion Batteries
FeF3 + 3Li ↔ Fe + 3LiF E0 = 2.96 V (weighted average), Cth= 712 mAh/g
The traditional approach to enable metal fluorides as cathode materials for Li-ion batteries is to coat the insulating fluoride particles with a conducting carbon shell by high-energy ball milling . The FeF3/C nanocomposites show a very high capacity up to the theoretical maximum in the first few cycles, but cyclic stability is poor due to a pulverisation of the core-shell FeF3/C particles upon prolonged cycling.
We recently prepared an improved LiF/Fe(V2O5) nanocomposite by high-energy ball milling, which shows a high reversible capacity of 420 mAh/g in the first 20 cycles and 270 mAh/g after 50 cycles . The cyclic stability was much improved compared to FeF3/C composites due the addition of V2O5. We used in situ XAS, Mössbauer spectroscopy, ab initio calculation of model XANES spectra and principle component analysis to identify highly amorphous V[FeV]O4 nanograins, which form during ball milling . From the calculations we also identified LixVO2-xFx. Both phases have open crystal structures and the ability to reversibly store lithium in interstitial lattice sites. As the V[FeV]O4 and LixVO2-xFx nanograins are in close contact with LiF and Fe particles, they help to maintain electrical and ionic contact upon prolonged cycling.
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