Preparation of Carborane-Tailored Covalent Organic Frameworks by a Postsynthetic Modification Strategy as a Barrier to Polysulfide in Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) have attracted much attention due to their high energy density and theoretical specific capacity. However, the "shuttle effect" of polysulfides limits their application. Herein, we propose a postsynthetic modification (PSM) strategy to synthesize a fibrous carborane-tailored covalent organic framework (PMCB-COF). Benefiting from its amphiphilicity, strong adsorption ability, high specific surface area, and accessible Li transport channels, PMCB-COF could serve as a barrier to polysulfide to inhibit the shuttle effect. The cell assembled with PMCB-COF exhibits a high initial capacity of 926 mAh g at 1 C. A Coulombic efficiency of 98% and a fading rate of only 0.039% per cycle are exhibited even after 1500 cycles. So far as we know, PMCB-COF is one of the best materials as a separator of LSBs. This work provides a safe and efficient avenue for tailoring COFs with carborane and might help promote the development of secure, low-cost, and durable rechargeable batteries.