XPS analysis of the lithium intercalation in amorphous tungsten oxysulfide thin films

Amorphous thin films of tungsten oxysulfide have been prepared by radio frequency (RF) magnetron sputtering. The composition of thin films is varied by changing the pressure of the reactive gas (O2) and discharge gas (Ar+O2) in the sputtering chamber. The X-ray photoelectron spectroscopy (XPS) studies of the thin films have shown three different types of environment for tungsten atoms: W6+ surrounded by oxygen O2−, W4+ surrounded by sulphur S2− and W5+ in a mixed oxygen–sulphur environment consisting of O2−, S2− and S22− pairs. The electrochemical characterisation of the film was performed in the Li/LiPF6-EC-DMC/WOySz cell. The XPS during intercalation evidences the role of W6+ and S22− in the redox process.