Direct XRD observation of oxidation-state changes on Li-ion insertion into transition-metal oxide hosts

It is demonstrated here that the electron redistribution occurring as lithium becomes incorporated into or extracted from a crystalline transition-metal oxide (TMO) host can be studied experimentally by single-crystal X-ray diffraction (XRD) for the case of V6O13. The crystals pass through a sequence of LixV6O13 phases (x = 0, 0.5, 1, 2, 3 and 6) as lithium ions are incorporated into the V6O13 structure on discharging a [Li\liquid electrolyte\V6O13] cell from 3.2 to 1.8 V. The so-called deformation electron-density refinement of the electron distribution is exploited to extract the number of electrons associated with the Li, V and O atoms in the structure, and hence the electron rearrangement taking place on lithium insertion. This type of study is ultimately capable of identifying the complete sequence of oxidation-state changes occurring during the entire lithium insertion process in V6O13. (C) 1999 Elsevier Science S.A. All rights reserved.