Vanadium pentoxide thin films used as positive electrode in lithium microbatteries: An XPS study during cycling

Vanadium pentoxide thin films, usable as positive electrode in microbatteries, have been prepared by radio frequency magnetron sputtering in a pure argon or mixed argon/oxygen atmosphere using a V2O5 target. Depending on the oxygen partial pressure in the discharge gas, we have obtained either crystallized or amorphous thin films, with different morphologies. These two kinds of thin films having different electrochemical behavior, an extensive XPS study was carried out. The main redox processes and their reversibility occurring during the 1st, 10th, and 30th discharge-charge cycles were discussed in relation with the electrochemical properties. Our results have revealed a good reversibility of the redox process for amorphous thin films and degradation for crystallized ones, in agreement with the discharge capacity evolution. Furthermore, the growth of a surface layer between the cathode and the liquid electrolyte was evidenced upon the discharge as well as its partial dissolution upon the charge. (c) 2006 Elsevier Ltd. All rights reserved.