Grafting polymeric sulfur onto carbon nanotubes as highly-active cathode for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are being explored as promising advanced energy storage systems due to their ultra-high energy density. However, fast capacity fading and low coulombic efficiency, resulting from the dissolution of polysulfides, remain a serious challenge. Compared to weak physical adsorptions or barriers, chemical confinement based on strong chemical interaction is a more effective approach to address the shuttle issue. Herein, we devise a novel polymeric sulfur/carbon nanotube composite for Li-S battery, for which 2, 5-dithiobiurea is chosen as the stabilizer of long-chain sulfur. This offers chemical bonds which bridge the polymeric sulfur and carbon nanotubes. The obtained composite can deliver an ultra-high reversible capacity of 1076.2 mAh g(-1) (based on the entire composite) at the rate of 0.1 C with an exceptional initial Coulombic efficiency of 96.2%, as well as remarkable cycle performance. This performance is mainly attributed to the reaction reversibility of the obtained polymeric sulfur-based composite during the discharge/charge process. This was confirmed by density functional theory calculations for the first time. (C) 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.