Cationic Covalent-Organic Framework as Efficient Redox Motor for High-Performance Lithium-Sulfur Batteries.

The shuttle effect of soluble lithium polysulfides (LiPSs) leads to the rapid decay of sulfur cathode, severely hindering the practical applications of lithium-sulfur (Li-S) batteries. To this point, a covalent-organic framework (COF) with proper cationic sites, which can be utilized as the cathode host of high-performance Li-S batteries, is reported. The chemical sulfur anchoring within micropores effectively suppresses the dissolution of LiPSs into the electrolyte. During the discharge step, the cationic sites can accept electrons from anode and deliver them to polysulfides to facilitate the polysulfides' disintegration. Meanwhile, the cationic sites can receive electrons from polysulfides and then send them to the anode during the charge process, which promotes the polysulfides oxidation. Thus, both experiments and computational modeling show that the cationic COF can effectively inhibit the shuttle effect of LiPSs and improve the batteries' performances. Compared with electrically neutral COFs, the cationic COF-based batteries show much better cycling stability even at high current density, for instance, a high specific capacity of 468 mA h g-1 is retained after 300 cycles at a current density of 4.0 C.