XPS analysis of new lithium cobalt oxide thin-films before and after lithium deintercalation

Lithium cobalt oxides thin-films, prepared by radio frequency magnetron spu ttering and which could be used as positive electrode materials in microbat teries, were studied by X-ray photoelectron spectroscopy. The results have shown two formal oxidation numbers (+III and +IV) for cobalt ions and two e nvironments, octahedral and tetrahedral for lithium ions. A systematic over content of oxygen compared to crystalline LiCoO2 has been evidenced for the thin-films, this excess, attributed to unusual co-ordinations with metal a nd more covalent Co-O bonds, could be localised in the boundaries of the ra ndomly oriented nanodomains observed by transmission electron microscopy. T he evolution of these LixCoO2+y thin-films at different stages of their cyc le in experimental microbatteries has also been studied by an analysis of b oth core peaks and valence bands. The deintercalation of lithium has led to an increase of the proportion of 'Co4+' ions; in parallel an implication o f the anions has been observed. (C) 2001 Elsevier Science B.V. All rights r eserved.