Lithium cobalt oxides thin-films, prepared by radio frequency magnetron sputtering and which could be used as positive electrode materials in microbatteries, were studied by X-ray photoelectron spectroscopy. The results have shown two formal oxidation numbers (+III and +IV) for cobalt ions and two environments, octahedral and tetrahedral for lithium ions. A systematic overcontent of oxygen compared to crystalline LiCoO2 has been evidenced for the thin-films, this excess, attributed to unusual co-ordinations with metal and more covalent Co-O bonds, could be localised in the boundaries of the randomly oriented nanodomains observed by transmission electron microscopy. The evolution of these LixCoO2+y thin-films at different stages of their cycle in experimental microbatteries has also been studied by an analysis of both core peaks and valence bands. The deintercalation of lithium has led to an increase of the proportion of 'Co4+' ions; in parallel an implication of the anions has been observed.