Silanol–branched covalent organic framework host structure for boosting sulfur electrochemistry of Li–S batteries

Lithium-sulfur batteries (LSBs) have been considered as ideal candidates for next-generation energy storage equipment. However, its development has been hindered by the shuttle effect exhibited by the intermediate lithium polysulfides (LiPSs). To address this problem, covalent organic frameworks (COFs) show great promises as sulfur hosts for LSBs. We devised and synthesized a covalent organic framework (TPAS–TPB–COF) that is rich in redox sites by solution polymerization. The reactive groups in the covalent organic framework nano–channels not only inhibit the shuttling of polysulfides, but also promote the migration of Li ions. Meanwhile, the abundant cavities as well as redox sites in the COF nano–channels achieve a high sulfur loading capacity (∼71 wt%), a strong LiPS adsorption capacity, and facilitate ion diffusion. Based on these advantages, when it is used as a sulfur host for LSBs, our COF system provides a high capacity of 1134 mAh g −1 at 0.2 C (1 C = 1675 mA g −1 ), an outstanding rate capability (560 mAh g −1 at 4 C), and excellent stability.