Investigating energy storage ability of cobalt molybdenum hydroxide, sulfide and boride as active materials of battery supercapacitor hybrids

Transition metal compounds with multiple oxidation states and high electrical conductivity have been widely applied as the active material of battery supercapacitor hybrids (BSH). Cobalt-based compounds have large theoretical capacitances, and molybdenum has high electrical conductivity and long cycle life. Numerous bimetallic compounds based on cobalt and molybdenum (Co-Mo) have been proposed for energy storage applications, but limited reports study the influences of the anionic part on material and electrochemical features. In this work, three Co-Mo bimetallic compounds based on layered double hydroxide (LDH), sulfide and boride are synthesized using hydrothermal and soaking processes as the active material of BSH. The Co-Mo sulfide electrode presents the largest specific capacitance (CF) of 1655.1 F/g at 10 A/g, due to the high electronegativity of sulfur and the great pore structure. The BSH composed of Co-Mo sulfide and carbon electrodes shows the energy density of 37.14 Wh/kg at 0.7 kW/kg, and the CF retention of 93% and Coulombic efficiency of 94% after 7500 cycles. The result suggests that the intrinsic property of the anionic part plays more significant roles than the surface property like specific surface area on the electrochemical performance.