Highly efficient and conductive in-situ assembled VS₄-VO₂ on reduced Graphene-oxide as advanced cathode materials for thermal batteries

Thermal batteries are a type of thermally activated reserve batteries, where the cathode material significantly influences the operating voltage and specific capacity of the battery. In this work, VS₄-VO₂ has been synthesized through the hydrothermal method and used as the cathode material for thermal batteries. Firstly, the material with the VS₄ crystallinity is obtained at 170 °C and the mass percentages of VS₄/VO₂ are 63.1 % and 36.9 %, respectively. The formation mechanism of VS₄-VO₂ has been proposed based on in-situ ultraviolet (UV) spectrum, which shows that the hydrolysis product S^2- under alkaline conditions promotes the formation of VS₄. To further improve the conductivity of the material, the reduced graphene oxide (rGO) has been introduced into VS₄-VO₂ nanomaterials. When applied in thermal batteries, the rGO-VS₄-VO₂ composite exhibits a voltage plateau of approximately 2.4 V and a discharging specific capacity of 327 mAh/g with the cut-off voltage of 1.5 V at 50 mA and 350°C, which are higher than those of VS₄-VO₂. Furthermore, the discharge mechanisms of rGO-VS₄-VO₂ in thermal batteries have been analyzed, which indicates that VS₄-VO₂ involves two processes of phase transformation, including the intercalation process and conversion process. The results confirm rGO-VS₄-VO₂ as a promising cathode material for thermal batteries.