Design Principles for Covalent Organic Frameworks to Achieve Strong Heteroatom-Synergistic Effect on Anchoring Polysulfides for Lithium-Sulfur Batteries.

The shuttle effect is still a notorious issue hindering commercial applications of lithium-sulfur batteries. Recently, covalent organic framework (COF) nanomaterials have been employed as cathode materials, especially because of their polar linkages, which can induce strong anchoring capacity to impede the shuttle of polysulfides. To investigate the structure-activity relationship between COF composition and anchoring performance, eight representative linkages composed of high-electronegativity elements are selected and constructed to be eight linkage-benzene-linkage COFs. Through the analyses of adsorption energy, charge transfer, atomic density of states, and so forth, the synergistic effect of O atoms in the secondary amine linkage and the "clamp" structure (N1-N2-C-O1) can both make significant contributions to improve the anchoring capacity on polysulfides. The promising effect of nucleophilic group branches is demonstrated. The solvent effect is also considered while selecting favorable COF scaffoldings in DME or DOL solvents. These results can provide helpful guidance for designing ideal cathode scaffoldings of lithium-sulfur batteries.