A study of the electrochemical mechanisms involved during lithium insertion into TiO0.6S2.8 thin film used as positive electrode in lithium microbatteries

Amorphous thin films were prepared by radio-frequency magnetron sputtering from TiS2 target under pure argon atmosphere. Two complementary techniques, X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS), were used to investigate the local and electronic structure of the asprepared sample and to study the electrochemical mechanisms occurring during the first cycle. The results exhibit that the as-prepared TiO 0.6S2.8 thin film is close to bulk TiS3 (which may be viewed as Ti4+S22-S2-) with regard to the local and electronic structure. The electrochemical characterization of the film was performed in the Li/LiAsF6 (IM in EMC)/TiO0.6S2.8 cell. Upon lithium insertion, sulfur is first involved into the electrochemical reduction followed by titanium. The reduction of S22- to S2- is concomitant with the elongation of the distance between the two sulfur ions of the disulfide pair. At the end of the charge, the electrochemical processes appear to be reversible. This study clearly evidences the major contribution of sulfur atoms beside titanium.