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+alpha V3O8 (alpha 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 350degreesC and the structures of the products Li2.7V3O8 (before the 2.6 V phenomenon) and L4.8V3O8 (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. (C) 2004 Elsevier Inc. All rights reserved.