A MnO₂/Graphene Oxide/Multi-Walled Carbon Nanotubes-Sulfur Composite with Dual-Efficient Polysulfide Adsorption for Improving Lithium-Sulfur Batteries

Abstract

Lithium-sulfur batteries can potentially be used as a chemical power source because of their high energy density. However, the sulfur cathode has several shortcomings, including fast capacity attenuation, poor electrochemical activity, and low Coulombic efficiency. Herein, multi-walled carbon nanotubes (CNTs), graphene oxide (GO), and manganese dioxide are introduced to the sulfur cathode. A MnO₂/GO/CNTs-S composite with a unique three-dimensional (3D) architecture was synthesized by a one-pot chemical method and heat treatment approach. In this structure, the innermost CNTs work as a conducting additive and backbone to form a conducting network. The MnO₂/GO nanosheets anchored on the sidewalls of CNTs have a dual-efficient absorption capability for polysulfide intermediates as well as afford adequate space for sulfur loading. The outmost nanosized sulfur particles are well-distributed on the surface of the MnO₂/GO nanosheets and provide a short transmission path for Li⁺ and the electrons. The sulfur content in the MnO₂/GO/CNTs-S composite is as high as 80 wt %, and the as-designed MnO₂/GO/CNTs-S cathode displays excellent comprehensive performance. The initial specific capacities are up to 1500, 1300, 1150, 1048, and 960 mAh g^-1 at discharging rates of 0.05, 0.1, 0.2, 0.5, and 1 C, respectively. Moreover, the composite cathode shows a good cycle performance: the specific capacity remains at 963.5 mAh g^-1 at 0.2 C after 100 cycles when the area density of sulfur is 2.8 mg cm^-2.