UV-visible and IR spectroelectrochemical properties of V2O5 crystalline films charged/discharged in extended potential range

Electrochemical properties of amorphous and crystalline V2O5 films, dip-coated from V-oxoisopropoxide sols and thermally treated at various temperatures (100, 150, 200 and 300 degreesC), have been studied in extended potential range, i.e. from 1.4 to -1.6 V vs. Ag/AgCl in 1M LiClO4/propylen carbonate (PC) electrolyte. The formation of various lithiated (alpha-, delta-, epsilon- and gamma -LixV2O5) phases was correlated with the values of insertion coefficient x obtained from cyclic voltammograms (CV) of crystalline V2O5 films (300 degreesC). Reversible charging was observed when films were cycled up to -1.0 V vs. Ag/AgCl, while the extension of the potential to -1.3 V vs. Ag/AgCl change the CV of films irreversibly. Charging of crystalline V2O5 films was followed by the help of in-situ UV-visible spectroscopy, that revealed the intensity variations of the polaron absorption above 600 nm and the presence of the absorbing V3+ species between 550 and 650 nm. Ex-situ IR spectra of the crystalline films charged/discharged at -1.6V/1.4V vs. Ag/AgCl confirmed the amorphisation of the films' structure.