Sulfonated covalent organic framework modified separator suppressing shuttle effect in lithium-sulfur batteries.

Lithium-sulfur battery (LSB) has gained intense research enthusiasm due to its high energy density. Nevertheless, the "shuttle effect" of soluble polysulfide (discharge product) reduces the cycling stability and capacity, thus restricting the practical application of LSB. To tackle this challenging issue, we herein report a sulfonated covalent organic framework modified separator (SCOF-Celgard) that would alleviate the shuttling of polysulfide anions and accelerate the migration of Li+ ions. Specifically, the negatively charged sulfonate can inhibit the same charged polysulfide anion through electrostatic repulsion, thereby improving the cycle stability of the battery and preventing the Li-anode from being corroded. Meanwhile, the sulfonate groups may facilitate the positively charged lithium ions pass through the separator. Consequently, the battery assembled with the SCOF-Celgard separator exhibits a 81.1% capacity retention after 120 cycles at 0.5C, which is much superior to that (55.7%) of the battery with Celgard separator. It has a low capacity degradation of 0.067% per cycle after 600 cycles at 1C, and a high discharge capacity (576 mAh g-1) even at 2C. Our work proves that the modification of separator with SCOF is a viable and effective route for enhancing the LSB electrochemical performance.