New amorphous molybdenum oxysulfide thin films their characterization and their electrochemical properties

New amorphous molybdenum oxysulfides have been obtained by r.f. sputtering using an MoS2 target. Their chemical composition depends on the partial pressure of oxygen introduced in the plasma during the preparation. All the properties depend on their composition. By transmission electron microscopy some randomly oriented ordered domains were found and identified as a 2H---MoS2-like phase in which a partial substitution of oxygen for sulfur has been evidenced. The low oxygen content thin films have the best electrical conductivity but can intercalate only 1.7 lithium per molybdenum. On the opposite, the high oxygen content ones are able to intercalate up to 3.5 lithium. Whatever the composition of the material, the intercalation of the first lithium is never reversible. By X-ray photoelectron spectroscopy it was found that this phenomenon corresponds to the reduction of Mo6+ to Mo5+ and Mo4+, the reversible part is mainly due to the further redox process of Mo5+ and Mo4+ and also of disulfide pairs S22−.