ELECTROCHEMICAL PROPERTIES OF AMORPHOUS V2O5

Pure amorphous vanadium pentoxide can be obtained by splat-cooling from the melt. The characterization of this amorphous oxide was carried out by X-ray diffraction, DTA, ESR, magnetic susceptibility, 51V NMR and electrical resistivity. This nonstoichiometric oxide exhibits electronic conductivity arising from a small-polaron hopping process between V4+ and V5+ ions. The amorphous oxide is able to give LixV2O5 phases via chemical or electrochemical insertion of Li+ ions into the oxide network. Electrochemical experiments performed with LiAsF6 in cyclic ether as an electrolyte show that 1.8 Li+ per V2O5 can be reversibly inserted between 3.5 v and 2 v (versus Li+/Li). Contrary to crystalline V2O5, the open-circuit voltage continuously decreases with the amount of inserted Li+, suggesting that no phase transition occurs in amorphous LixV2O5 up to x=1.8.