Zwitterionic covalent organic framework as a multifunctional sulfur host toward durable lithium-sulfur batteries

The shuttle effect and slow redox kinetics of sulfur cathode are the most significant technical challenges to the practical application of lithium-sulfur (Li-S) battery. Herein, a novel zwitterionic covalent organic framework (ZW-COF) wrapped onto carbon nanotubes (CNTs), labeled as ZW-COF@CNT, is developed by a reversible condensation reaction of 1,3,5-benzenetricarboxaldehyde (BTA) and 3,8-diamino-6-phenylphenanthridine (DPPD) with CNTs as a template and a subsequently-one-step post-synthetic grafting reaction with 1,3-propanesultone. The experimental results showed that, after loading active material sulfur, zwitterionic ZW-COF@CNT can effectively suppress the shuttle effect of the soluble lithium polysulfides (LiPSs) in Li-S batteries, and exhibits better cycling behavior than the as-developed neutral COF@CNT. Specifically, the as-obtained ZW-COF@CNT based sulfur cathode can maintain a discharge capacity of 944 mAh/g after 100 cycles, while that of COF@CNT based sulfur cathode drops to (665 mAh/g) after 100 cycles. Moreover, the ZW-COF@CNT based sulfur cathode delivers an attractive prolonged cycling behavior with a low capacity decay rate of 0.046 % per cycle at 1 C. This work sheds new light on rational selection and design of functionalized COFs based sulfur cathode in the Li-S battery.