Electrochemical Mechanisms during Lithium Insertion into TiO0.6 S 2.8 Thin Film Positive Electrode in Lithium Microbatteries

Amorphous thin films were prepared by radio frequency magnetron sputtering from TiS 2 target under pure argon atmosphere. Two complementary techniques, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, were used to investigate the local and electronic structure of the as-prepared sample and to study the electrochemical mechanisms occurring during the first cycle. The results exhibit that the as-prepared TiO 0 . 6 S 2 . 8 thin film is close to bulk TiS 3 [which may be viewed as Ti 4 + (S 2 - 2 )S 2 - ] with regard to the local and electronic structure. An electrochemical characterization of the film was performed. Upon lithium insertion, sulfur is first involved in the electrochemical reduction, followed by titanium. The reduction of S 2 - 2 to S 2 - 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.