An oxazole-linked donor-acceptor covalent organic framework as an efficient electrocatalyst for lithium-sulfur batteries

Covalent organic frameworks (COFs) with ordered channels and light weight are regarded as promising separator modifications for lithium-sulfur (Li-S) batteries. However, they typically suffer from stability issues and limited electrocatalytic activity, resulting in unsatisfactory battery performance. Herein, a donor-acceptor (D-A) COF (BTT-DABD) featuring oxazole linkages is developed through a one-step solvothermal route and then coated on a commercial separator, acting as an efficient electrocatalyst for Li-S batteries. Note that BTT-DABD exerts better chemical stability than its traditional imine-linked counterpart (BTT-DA). Moreover, the heterocyclic structure of oxazole linkage not only regulates the electronic structure of active N sites to enhance the chemical affinity for polysulfides but also gives rise to extended pi-conjugation and enhanced D-A interaction to facilitate electron transport along the framework, thus endowing BTT-DABD with excellent electrocatalytic activity in the bidirectional sulfur redox processes. The assembled Li-S batteries using BTT-DABD separator exhibit an impressive electrochemical performance, including high incipient discharge capacity (1383 mA h g-1 at 0.1C), outstanding rate capability (674 mA h g-1 at 5C), and excellent long-term cycling performance (decay rate of 0.061% per cycle over 500 cycles at 3C). This work provides novel insights into the rational design of COF-based electrocatalysts for advanced Li-S batteries.