XPS investigations of TiOySz amorphous thin films used as positive electrode in lithium microbatteries

The electrochemical properties of several TiOySz thin films prepared by radio frequency magnetron sputtering in a pure argon or mixed oxygen/argon plasma were investigated. The two thin layers prepared in absence of oxygen presenting the compositions TiO0.6S2.8 and TiO0.9S1.7 exhibit very interesting electrochemical properties. Their behaviour was extensively studied during the first cycle and upon cycling by means of XPS (X-ray photoelectron spectroscopy). Beside titanium ions, this study evidences the contribution of the sulfur anions to the redox processes. This study also displays an analogy between the electrochemical mechanisms occurring into the TiO0.6S2.8 and TiO0.9S1.7 thin films and bulk TiS3. Furthermore, the growth of an interface between the cathode and the liquid electrolyte was evidenced upon the discharge as well as a partial dissolution upon the charge. This paper highlights the correlations that exist between the composition, the structure, the morphology of the thin films and their electrochemical performances.