Improving Lithium-Sulfur Batteries' Performance via Inverse Vulcanization of Vinylene-Linked Covalent Organic Frameworks

Covalent organic frameworks (COFs) with one-dimensional (1D) pores are capable of sulfur encapsulation; however, the physical absorption leads to an insufficient suppression on the shuttle of lithium polysulfides that ultimately cripples the performance of lithium-sulfur batteries (LSBs). Here, we prepared two vinylene-linked COFs bearing different pores, denoted as COF-1 and COF-2. Interestingly, COF-1 can only physically isolate sulfur to give S-COF-1, while the polysulfide chains can be covalently linked to the framework of COF-2 via inverse vulcanization to produce S-COF-2. S-COF-1 and S-COF-2 deliver superior capacities of 1179 and 1293 mAh g(-1) at 0.2C, an outstanding rate performance (331 and 692 mA h g(-1) at 3C), and a prolonged cycling life span (a low declining value of 0.09% per cycle at 1C for S-COF-2). Due to the synergistic effect of covalent linking and physical confinement of sulfur, S-COF-2 features a superior LSBs performance compared to S-COF-1. Our studies provide a strategy for improving the performances of LSBs by combining the chemical and physical installation of sulfur.