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

Abstract

Optimizing electrode materials performance\nand improving the energy\ndensity of supercapacitors is a hot research topic. The complex hollow\nsphere structure material, as a supercapacitor electrode material,\nprovides more redox active sites and volume expansion space during\nthe electrochemical energy storage process, which has the potential\nto assemble high performance supercapacitors. Herein, a novel nickel\ncobalt sulfide and carbon nanotube composite are successfully prepared\nby the Kirkendall effect. The yolk–shell-structured nickel\ncobalt sulfide and carbon nanotube composite exhibits superior electrochemical\nperformance as the positive electrode of the hybrid supercapacitor.\nThe hybrid supercapacitor has a specific capacity of 603 C g^–1 at 1 A g^–1, and the capacity retention rate is\nas high as 67.4% from 1 to 15 A g^–1. Moreover, the\nassembled hybrid supercapacitor has an energy density of 45.35 Wh\nkg^–1. After 8000 cycles, the capacitance retention\nrate is 91.33%, and the columbic efficiency is 96.15%. Its excellent\nelectrochemical performance is mainly attributed to the excellent\nconductivity of carbon nanotubes as the supporting skeleton and conducting\nnetwork, which effectively inhibits the aggregation of nanospheres,\nexposes more active sites, and facilitates the rapid transmission\nof ions/electrons, thereby obtaining high specific capacity and rate\nperformance.