Nickel Sulfide/Carbon Nanotube Nanocomposites As High Performance Cathode Materials for Asymmetric Supercapacitors

Recently, supercapacitors have attracted extensive attention due to their unique properties of long cycling life, low maintenance cost, and high power density. Furthermore, supercapacitors show great potential applications for energy-storage systems in portable electronic devices and hybrid electric vehicles. Typically, supercapacitors have two mechanisms of the charge storage/delivery, namely the electric double-layer capacitors (EDLC) and psuedocapacitors. The pseudocapacitor usually shows a higher value of specific capacitance (C_m) than EDLC due to the presence of the Faradaic process. However, both EDLC and the pseudocapacitor show lower specific energy densities than batteries. Therefore, the development of the supercapacitors with high power and energy densities is still a challenge.

In this study, the Ni₃S₂/carbon nanotube composites were successfully developed by means of the glucose-assisted hydrothermal method. The composite electrode shows a high specific capacitance of 800 F/g and great cycling stability at a current density of 3.2 A/g. Furthermore, an asymmetric supercapacitor device was fabricated by using the composite of Ni₃S₂ and MWCNTs as the cathode and activated carbon as the anode. The fabricated device can be operated reversibly between 0 and 1.6 V, and obtain a high specific capacitance of 55.8 F/g at 1 A/g. It also delivers a maximum energy density of 19.8 Wh/kg with a power density of 798 W/kg. As a result, the asymmetric supercapacitor device based on the Ni₃S₂/MWCNTs cathode can be considered as a promising energy storage device.