Aqueous-processable polymer binder with strong mechanical and polysulfide-trapping properties for high performance of lithium–sulfur batteries

Lithium–sulfur batteries (LSBs) are regarded as the next-generation high-performance energy storage devices due to their high energy density. However, the long-term use of LSBs in practical applications is limited by the shuttle effect resulting from the diffusion of lithium polysulfides (LiPS) in electrolyte. To address these challenges, a novel aqueous-processable polymer with multiple functional groups, catechol-conjugated chitosan sulfate (CCS), is developed as the binder of the sulfur cathode. The CCS binder demonstrates strong adsorption capability to trap LiPS, as evidenced by ultraviolet-visible (UV-vis) spectra and density functional theory (DFT) calculations. Its excellent mechanical and binding properties also result in stabilization of sulfur cathodes in long-term cycling. LSBs assembled with CCS exhibit remarkable improvement in cycling performance with high capacity retention of 80.14% after 400 cycles at 0.5C, and the electrodes maintain their integrity without any clear cracks. At a high rate of 2C, the LSBs can still maintain 77.30% capacity after 300 cycles with high coulombic efficiency of 99.37%. Our results provide new insights into the significance of sulfate and catechol groups in CCS binder for sulfur cathode and pave a new way for the tailoring of the chemical structures of natural polymers to realize LSBs with superior electrochemical performance.