Covalently Bonded Sulfur Anchored with Thiol-Modified Carbon Nanotube as a Cathode Material for Lithium–Sulfur Batteries

The lithium–sulfur (Li–S) battery as a promising energy storage system has attracted intensive attention, but its development is still restricted by the electrical insulation of elemental sulfur and the severe shuttle effect caused by lithium polysulfides (LiPS) in ether electrolytes. In this work, a functional sulfur cathode using thiol-modified carbon nanotubes (CNTSH) is synthesized as the host material. Experimental and theoretical calculation results show that the thiol groups attached to carbon nanotubes can covalently bond with soluble sulfur species during cycling. Meanwhile, the conductive matrix of the carbon nanotubes provides a facile pathway for electron transport. The fabricated functional cathode material shows improved electrochemical performance. The discharge capacity still maintains 669.2 mAh g–1 after 300 cycles, accompanied with a low-capacity fading rate of 0.166% per cycle at 0.1 C, whereas the sulfur cathode material without thiol modification only exhibits 328.3 mAh g–1 under the same conditions. This work indicates the significance of forming chemical bonds between sulfur species and host materials during the redox process and may provide a new way to design excellent Li–S batteries.