Three-Dimensional\nCovalent Organic Framework Serving\nas Host and Electrocatalyst in the Cathode of Li–S Battery

Lithium–sulfur\nbatteries (LSBs), as very promising lithium-ion\nbatteries, have received widespread attention from researchers. However,\nthe low conductivity of sulfur in lithium sulfur batteries and the\nsignificant volume expansion during charging and discharging seriously\naffect the high rate performance of the battery, hindering its practical\napplication. In this study, we designed bifunctional 3D covalent organic\nframeworks (COFs) with interconnected nanostructures and significant\ncatalytic activity by connecting flexible cycloocta thiophene blocks\nwith porphyrin units. 3D COFs act as catalytic nanotraps in the cathode\nof LSBs, providing confinement and chemical adsorption of lithium\npolysulfides, thereby improving the redox kinetics of sulfur. The\nacceleration of Li<sub>2</sub>S nucleation by Ni-porphyrin active\ncenters, as confirmed through in situ X-ray diffraction and Raman\nspectroscopy, enhances polysulfide conversion kinetics, further improving\nbattery performance. The constructed battery that incorporates the\n3D COF exhibits a minor fading trend of only 0.05% per cycle over\n500 cycles at 1 C, outperforming commercial carbon nanotubes. Additionally,\nunder lean electrolyte conditions and high sulfur loading, the 3D\nCOF shows promise as a practical solution for high-energy-density\nLSBs, achieving an actual area capacity of 7.0 mAh cm<sup>–2</sup> at 0.2 C. This research sets a solid foundation for the tailored\ndesign of COFs-based bifunctional catalytic nanotraps that can serve\ndual roles as both host materials and electrocatalysts in Li–S\nbatteries.