XPS and IR studies of transparent InVO4 films upon Li charge–discharge reactions

InVO4 belongs to the family of orthovanadates, oxides with attractive properties as Li insertion electrodes, indicated for electrochromic windows due to their transparency. The Li insertion reaction in indium vanadate films, deposited by the sol–gel dipping method onto conducting glass substrates, was performed electrochemically and the changes in physical properties of the material were studied by means of Infrared and X-ray Photoelectron spectroscopies. Results of photoelectron spectroscopy showed the reduction of V5+ to V4+ and V3+ upon Li insertion, and the onset of new structures in the valence band, related to the formation of Li carbonate on the electrode surface. The IR spectra for the Li-charged samples showed a drop in band intensities, which was associated with a decrease of the film electrical conductivity, and the appearance of new bands for x>0.6. The Li electrochemical de-insertion brought about the almost complete recovery of the oxide XPS initial spectrum, and the partial recovery of its IR spectrum. Such results confirmed the excellent chemical stability of this oxide material upon Li charge–discharge reactions (x<1), even when the long-range crystalline order has been perturbed by the electrochemical bulk insertion process. [Copyright &y& Elsevier]