Yolk–Shell Structured Nickel Cobalt Sulfide and Carbon Nanotube Composite for High-Performance Hybrid Supercapacitors

Optimizing electrode materials performance and improving the energy density of supercapacitors is a hot research topic. The complex hollow sphere structure material, as a supercapacitor electrode material, provides more redox active sites and volume expansion space during the electrochemical energy storage process, which has the potential to assemble high performance supercapacitors. Herein, a novel nickel cobalt sulfide and carbon nanotube composite are successfully prepared by the Kirkendall effect. The yolk–shell-structured nickel cobalt sulfide and carbon nanotube composite exhibits superior electrochemical performance as the positive electrode of the hybrid supercapacitor. The hybrid supercapacitor has a specific capacity of 603 C g–1 at 1 A g–1, and the capacity retention rate is as high as 67.4% from 1 to 15 A g–1. Moreover, the assembled hybrid supercapacitor has an energy density of 45.35 Wh kg–1. After 8000 cycles, the capacitance retention rate is 91.33%, and the columbic efficiency is 96.15%. Its excellent electrochemical performance is mainly attributed to the excellent conductivity of carbon nanotubes as the supporting skeleton and conducting network, which effectively inhibits the aggregation of nanospheres, exposes more active sites, and facilitates the rapid transmission of ions/electrons, thereby obtaining high specific capacity and rate performance.