Multifunctional Chitosan-Covalent Bonded Multi-Walled Carbon Nanotubes Composite Binder for Enhanced Electrochemical Performances of Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are considered as one of the most promising next-generation energy-storage devices because of their high energy density. However, the long-term use of LSBs is mainly limited by polysulfide shuttling and cathode structural degradation caused by volume changes during charging and discharging. To address these issues, a multifunctional, high-performance aqueous binder is developed by modifying a natural polysaccharide with multi-walled carbon nanotubes (MWCNTs). Specifically, the catechol-conjugated chitosan (CCS) acts as the binder, showing strong polysulfide adsorption, while the MWCNTs covalently bonded to CCS enhance the mechanical toughness and electronic conductivity. The resulting CCS-MWCNTs composite binder exhibits a tensile strength of 40 MPa and a strain at break of 300%, which are higher than those of CCS. As a binder for sulfur cathodes, the CCS-MWCNTs binder demonstrates superior cyclic stability and rate capability. At a sulfur loading of 2.0 mg cm⁻², it delivers an initial capacity of 1016 mAh g⁻¹ at 0.2 C and retains 690 mAh g⁻¹ after 100 cycles, significantly outperforming commercial polyvinylidene difluoride (PVDF), sodium carboxymethylcellulose/styrene butadiene rubber (CMC/SBR), and CCS binders. This study demonstrates the potential applications of polysaccharide binders in metal-sulfur batteries by innovatively incorporating carbon nanotubes into the biopolymer binder, providing a promising alternative for environmentally friendly energy storage.