Dual Cation- and Anion-Based Redox Process in Lithium Titanium Oxysulfide Thin Film Cathodes for All-Solid-State Lithium-Ion Batteries

A dual redox process involving Ti³⁺/Ti⁴⁺ cation species and S^2–/(S₂)^2– anion species is highlighted in oxygenated lithium titanium sulfide thin film electrodes during lithium (de)­insertion, leading to a high specific capacity. These cathodes for all-solid-state lithium-ion microbatteries are synthesized by sputtering of LiTiS₂ targets prepared by different means. The limited oxygenation of the films that is induced during the sputtering process favors the occurrence of the S^2–/(S₂)^2– redox process at the expense of the Ti³⁺/Ti⁴⁺ one during the battery operation, and influences its voltage profile. Finally, a perfect reversibility of both electrochemical processes is observed, whatever the initial film composition. All-solid-state lithium microbatteries using these amorphous lithiated titanium disulfide thin films and operated between 1.5 and 3.0 V/Li⁺/Li deliver a greater capacity (210–270 mAh g^–1) than LiCoO₂, with a perfect capacity retention (−0.0015% cycle^–1)