Sulfonic group modified carbon nanotubes: the decorative strategy for enhancing the performance of lithium-sulfur batteries

Porous carbon nanotubes can not only provide a large surface area for anchoring sulfur and restraining polysulfides, but also provide continuous conductive networks to facilitate ion transport in lithium-sulfur batteries (LSBs). In order to improve the performance of LSBs, surface-modified groups can be exploited to restrict the shuttle effect of polysulfides. Therefore, thin-walled porous carbon nanotubes with low cost and high yield were successfully prepared from polymer nanotubes. Sulfonic groups were modified on the walls of the thin-walled porous carbon nanotubes by reacting with concentrated sulfuric acid. The sulfonic group-modified thin-walled porous carbon nanotubes were utilized as a sulfur-deposited cathode matrix for LSBs, and the discharge capacity of 617.7 mA h g⁻¹ is obtained after 100 cycles at 0.5 C, showing a good rate performance. Based on DFT calculation, sulfonic groups can enhance the binding energy between porous carbon nanotubes and sulfur, and strengthen the adsorption capacity of porous carbon nanotubes for polysulfides as well, which further proves the effectiveness of the system in optimizing the performance of LSBs.