Carbon Nanotubes@Nickel Cobalt Sulfide Nanosheets for High‐Performance Supercapacitors

As new and alternative energy storage devices to batteries and traditional capacitors, supercapacitors exhibit both high power and high energy density as well as good cycle life. NiCo 2 S 4 , a spinel‐structured transition metal sulfide with a high specific capacity, is considered to be a promising electrode material for supercapacitors with great application potential. However, the poor electrical conductivity of NiCo 2 S 4 results in poor rate and cycle performance of the material, which limits its practical application. In this work, we design a composite by loading NiCo 2 S 4 on the surface of carbon nanotubes (CNTs) to enhance the conductivity. The best‐performing CNTs@NiCo 2 S 4 electrode materials were obtained after the optimized heat‐treatment of CNTs@SiO 2 precursors. At a current density of 1 A g −1 , the CNTs@NiCo 2 S 4 composite exhibits a specific capacity of 216.4 mAh g −1 and a capacity retention of 75 % after 2000 cycles. Even at a high current density of 5 A g −1 , the capacity can still retain 87 % of that under 1 A g −1 . It is demonstrated that the electrochemical performance of NiCo 2 S 4 can be effectively boosted by combining with conductive CNTs.