Structural characterization of Li1.2v3o8 insertion electrodes by single-crystal x-ray-diffraction

Abstract

The crystal structures of Li1.2V3O8 and a lithiated product Li4.0V3O8 have been determined by single-crystal X-ray diffraction methods. The structure refinement of Li1.2V308 confirms that of Li1+xV3O8(x almost-equal-to 0) reported by Wadsley thirty-six years ago. However, unlike Wadsley's data, the refinement of Li1.2V3O8 demonstrates that the lithium ions are distributed over two independent crystallographic sites. One lithium ion, Li (1), is octahedrally coordinated; the other, Li(2), has tetrahedral coordination. Lithiation of LiL2V308 with an-butyl lithium at room temperature displaces Li(1) through an octahedral face into a neighbouring octahedral site, whereas Li(2) shifts its position very slightly to adopt octahedral coordination. During lithiation, the packing of the oxygen-ion array is adjusted slightly to adopt an arrangement that approaches cubic-close-packing. The lithiated product Li4V3O8 has a defect rock salt structure. The structural data provide a greater insight into the discharge mechanism that occurs in Li/Li1+xV3O8 electrochemical cells.