Electrochemical properties of tungsten oxysulphide thin films as positive electrodes for lithium microbatteries

[摘要] Several WO_ð‘�?S_ð‘�? tungsten oxysulphide thin films were tested as positive electrodes for lithium microbatteries. The amorphous WO_1.05S₂ thin film was found very promising. A capacity decrease occurred during the first few cycles, after which the films were able to intercalate reversibly up to 1.1 lithium ion per formula unit under high regime (75 𝜇A/cm²). They were tested for 250 chargeâ€�?�discharge cycles, between 3.0 V and 1.2 V.X-ray photoelectron spectroscopy measurements were performed on different compounds in both intercalated (Li₁WO_1.05S₂, Li_2.7WO_1.05S₂ and Li_3.8WO_1.05S₂) and partially de-intercalated (Li₁WO_1.05S₂) states in order to understand the redox processes occurring during the first dischargeâ€�?�charge cycle. The analysis of both the W4ð‘�?? and the S2ð‘�? peaks has shown that the redox processes involve not only the tungsten atoms but also sulphur atoms. At the beginning of the intercalation, W⁶⁺ was first partially reduced into W⁵⁺, and then into W⁴⁺, but the important stage was the reduction of W⁴⁺ into W⁰. In W⁰, the electron binding energy was very close to that of metallic tungsten. At the same time, S$^{2-}_2$ ions were partially reduced into S^2- ions. But only the reduction process of tungsten atoms appeared to be totally reversible.

[学科分类] 材料工程

[关键词] Lithium microbattery;tungsten oxysulphide;thin film;X-ray photoelectron spectroscopy (XPS);sputtering.