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X-ray photoelectron spectroscopy: A powerful tool for a better characterization of thin film materials

1999; Springer Science+Business Media; Volume: 22; Issue: 3 Linguagem: Inglês

10.1007/bf02749975

0973-7669

A. Levasseur, Philippe Vinatier, D. Gonbeau,

Advanced Battery Materials and Technologies

X-ray photoelectron spectroscopy (XPS) is one of the most powerful tools to characterize thin films materials. To illustrate the use of XPS, some examples will be given on materials used as positive electrode in microbatteries. Further analyses of the film to understand the redox process are quite difficult with conventional methods due to the amorphous nature of the cathode. Here surface methods like XPS are very useful. Two main kinds of information can be obtained from XPS analysis: the oxidation states, and the determination of atomic environments. Different kinds of positive electrode materials were studied, titanium and molybdenum oxysulfides (MO y S z , M=Ti, Mo) and lithium cobalt oxide (Li x CoO2+y ) and have been illustrated in the present work. In light of the binding energies obtained for the reference compounds, several types of environments and different formal oxidation states have been found for the transition elements. XPS is also very useful for folllowing the oxydo-reduction mechanisms occurring during the intercalation and the de-intercalation of lithium, corresponding respectively to the discharge and the charge of the battery. After strict identification of each species, the evolution of their binding energies could be followed very easily. The XPS analyses of oxysulfides thin films at different stages of their cycling process have shown apparently good efficiency of the oxygen-rich compositions. During the redox process, the results obtained have clearly shown the important contribution of the sulfur atoms beside the transition metal atom.