Synthesis and Electrochemical Performance of NiCo₂O₄@CC Nanoparticles and Needle-Shaped NiCo₂S₄@CC and Their Application to Supercapacitors

Due to faster charging, longer charge–discharge cycles, and broader operating temperature ranges, electrochemical supercapacitors (ES’s) can be used in electric vehicles, electronic devices, and smart grids. NiCo2O4@CC and NiCo2S4@CC composites were synthesized using a two-step hydrothermal method without organic binders on a carbon cloth substrate. NiCo2O4@CC was successfully synthesized through a hydrothermal reaction at 160 °C for 16 h and annealing at 350 °C for 2 h. NiCo2S4@CC was successfully synthesized through a hydrothermal reaction at 160 °C for 16 h, followed by a reaction at 120 °C for 14 h and annealing at 350 °C for 2 h. Annealing was found to make the structure of the loaded compound more stable, which was beneficial in preventing shedding of the active substance. The synergistic effect between polymetals, nanoparticles, porosity and high conductivity of carbon cloth improved the electrochemical performance. The specific capacitance of the NiCo2S4@CC sample at the current density of 1 A/g was about 1.5 times that of the NiCo2O4@CC sample. The electrolyte entered the voids due to the irregular arrangement of needle-like NiCo2S4, which enlarged the contact area between the ions in the solution and NiCo2S4@CC, resulting in an increase in the specific capacitance. A preferred irregular arrangement of nanostructure, sulphur substitution for oxygen atom, and the formation of more active sites can be assumed to be the underlying mechanism. The high flexibility of NiCo2S4@CC enables it to be further used to provide a stable power supply for wearable and portable electronic devices.