The 2-EHA-AA-MMA terpolymer binder realizes a long-chain sulfur SPAN cathode via S-O covalent anchoring to construct high-capacity and shuttle-free Li-S batteries

Among various cathode materials, sulfurized polyacrylonitrile (SPAN) is considered a highly promising cathode for Lithium-sulfur (Li-S) batteries due to its unique covalent sulfur fixation mechanism, which fundamentally suppresses polysulfide dissolution and the shuttle effect. However, conventional SPAN materials typically limit sulfur chains to short S 2 -S 4 structures to maintain a solid-solid reaction, restricting their theoretical capacity. Moreover, the material's insulating nature and significant volume changes during cycling greatly limit its electrochemical performance and practicality. To address these issues, this study designed and synthesized a high-elasticity water-based binder based on a 2-ethylhexyl acrylate/acrylic acid/methyl methacrylate (2-EHA-AA-MMA) terpolymer. Abundant carboxyl groups (-COOH) in its molecular chain form stable S-O covalent bonds with sulfur chains in SPAN. Combined with PAN's terminal fixation of sulfur chains, this achieves a synergistic “long-chain capacity enhancement and strong anchoring shuttle suppression” effect. It stabilizes long S 6 chains, improving cycling stability and reversible capacity, while also directing S 6 conversion directly to Li 2 S 3 , bypassing soluble Li 2 S 4 intermediates to suppress shuttle effects at the source. Experimental results show that the SPAN cathode with this binder delivers a high specific capacity of 850.3 mAh g −1 at 0.1 C, with 68.4% capacity retention after 100 cycles and effective polysulfide shuttle suppression.