One-step solvothermal synthesis and electrochemical properties of graphene-supported dendritic CoNi₂S₄ nanostructures

One of the main challenges for the high-performance energy storage device is to develop advanced electrode materials with a high energy density at a high power. In this study, a facile one-step route was designed for the synthesis of graphene-supported dendritic CoNi₂S₄ nanostructures constructed by abundant nanorods. The investigation showed that the introduction of graphene oxide (GO) could efficiently restrain the production of the impurity, α-NiS, and could affect the shape of CoNi₂S₄ and improve the electrochemical properties of CoNi₂S₄. When the reaction was carried out in the system containing the Ni²⁺/Co²⁺/GO mass ratio of 133/67/60, the as-prepared sample (labeled as CoNi₂S₄/rGO-60) exhibited the best electrochemical properties. At a current density of 1 A g⁻¹, the specific capacitance reached 1224 F g⁻¹; and at a high current density of 20 A g⁻¹, the specific capacitance still achieved 768 F g⁻¹, indicating the excellent rate capability of the as-obtained electrode. After 3000 cycle at a current density of 4 A g⁻¹ in a three-electrode system, the specific capacitance of 81% was still kept, implying the good cycle stability. The enhanced electrochemical performance could be attributed to the synergistic effect between CoNi₂S₄ and rGO. Furthermore, the electrochemical performances of the asymmetric device assembled by CoNi₂S₄/rGO and activated carbon (AC) were also investigated.