Effect of Sulfur Vacancies of CoNi2S4 on Its Electrochemical Performance in Hybrid Supercapacitors

Ternary cobalt nickel sulfides are considered promising electrode materials due to their unique physical properties. However, its capacitive performance is still limited by the insufficient material utilization efficiency. Here, we design and fabricate CoNi2S4 with nanorods and hairy-petal-like nanosheets on nickel foam (NF) as an excellent self-standing electrode for a hybrid supercapacitor (HSC). The CoNi2S4 electrode material was synthesized on the NF substrate by cobalt organic framework (Co-MOF) conversion and introducing sulfur ion and nickel ion exchange. The CoNi2S4 electrode material with sulfur vacancies was controlled by regulating the reduction time, and then electrochemical analysis and comparison were performed. The results demonstrate that the synergistic effect of the MOF-derived CoNi2S4 skeleton and sulfur vacancies can significantly improve the electrochemical activity of nickel cobalt sulfide. The CoNi2S4 electrode exhibits a superior high specific capacitance of 5.24 F/cm2 at a current density of 3 mA/cm2. Furthermore, the assembled CoNi2S4-60//AC HSC displays a high energy density of 59.41 Wh/kg and a power density of 999.98 W/kg. Even after 10,000 continuous charge–discharge cycles, its initial capacitance was retained at 89.24%. These results demonstrate the feasibility and practicality of CoNi2S4-60 as an electrode material, showcasing its potential for real-world applications.