IN-SITU DETECTION OF ELECTRICAL-CONDUCTIVITY VARIATION OF AN A-WO3 THIN-FILM DURING ELECTROCHEMICAL REDUCTION AND OXIDATION IN LICLO4(M)-PCELECTROLYTE

The in situ detection of electrical conductivity variation of amorphou s tungsten trioxide (a-WO3) thin films during insertion and extraction of Li+ ions was carried out by microwave techniques coupled to electr ochemical measurements. The techniques were applied to an electrochemi cal cell containing lithium electrolyte. The intensity of the transmit ted microwave was measured, together with the potential of the cell du ring galvanostatic polarization. As expected, the electrical conductiv ity of a-WO3 increases during insertion and decreases during extractio n of Li+ ions. The in situ study shows that if O2 evolution occurs at the a-WO3-electrolyte interface during oxidation after Li+ ions have b een completely extracted, then a sudden decrease of conductivity is ob served in the oxide layer, suggesting that oxidation of the sub-stoich iometric a-WO3 thin film into a more stoichiometric oxide may be under gone by an electrochemical process at room temperature.