A combined X-ray and neutron Rietveld study of the chemically lithiated electrode materials Li2.7V3O8 and Li4.8V3O8

The lithium insertion in the positive electrode material Li1+αV3O8 (image close to 0.1–0.2) includes a phenomenon near 2.6 V (voltage vs. the Li metal electrode), the mechanism being a two-phase process with the transformation from ca. Li2.9V3O8 to ca. Li4V3O8. Near 2.4 V down to 2 V, Li is inserted in a single phase up to ca. Li5V3O8. Chemical Li insertions have been performed in a Li1.1V3O8 precursor prepared at 350 °C and the structures of the products Li2.7V3O8 (before the 2.6 V phenomenon) and Li4.8V3O8 (near the expected maximum) have been studied by a combined Rietveld refinement of X-ray and neutron diffraction data. The structure of Li4.8V3O8 is an ordered derivative of the rock-salt type, with all the Li and V ions in slightly distorted octahedral sites. Li2.7V3O8 has a poor crystallization state and, although the expected V3O8 layers are obtained, only a part of the Li sites have been reliably determined. Between adjacent V3O8 layers, several unidentified sites are likely weakly occupied, thus giving a markedly disordered character for the structure of the compound formed just before the transition at 2.6 V. The atomic shifts at the transition are briefly discussed.