Electrocatalysis of polysulfide conversion via sulfur–cobalt CoS2 on a carbon nanotube surface as a cathode for high-performance lithium–sulfur batteries

Abstract

Lithium–sulfur batteries received intense attention because of their high-energy density and inexpensive active material. However, the poor electrical conductivity of sulfur, shuttle effect, and slow electrochemical kinetics hinder their application. Herein, cobalt disulfides uniformly in situ grow on the surface of carbon nanotubes to prepare a three-dimensional carbon nanotubes-cobalt disulfide composite material as the sulfur host. The in situ growth cobalt disulfides on the carbon nanotube is confirmed to play the role of electrocatalyst, triggering the oxidation reaction of Li2S6 and Li2S4 at a higher potential, which promotes the conversion of Li2S6 to Li2S4 and Li2S4 to Li2S2, respectively, and significantly enhances the electrochemical reaction kinetics during the charge and discharge process. Particularly, the carbon nanotubes-cobalt disulfide-20 composite provides a suitable number of active sites for Li2S6 and Li2S4 and exerts an initial discharge capacity of 1253 mA h g−1 at 0.1 C and a retentive capacity of 84% after 200 cycles at 0.2 C.