Controllable Substitution of S Radicals on Triazine Covalent Framework to Expedite Degradation of Polysulfides.

Lithium-sulfur (Li-S) batteries are facing a significant barrier due to the diffusion of intermediate redox species. Although some S doped covalent framework cathodes have been reported with outstanding reversibility, the low content of sulfur (less than 30%) limits the practical applications. To overcome the issue, the sulfur and nitrogen co-doped covalent compounds (S-NC) as a host-type cathode have been developed through the radical transfer process during thermal cracking amino groups on the precursor, and then plentiful positively charged sulfur radicals can be controllably introduced. The experimental characterization and DFT theoretical calculation certificate that the sulfur radicals in S-NC/S can expedite redox reactions of intermediate polysulfides to impede their dissolution. Moreover, the energy barriers during ions transfer also obviously decreased after introducing S radicals, which lead to improved rate performance.