Metalated Covalent Organic Frameworks as Electrocatalytic Sulfur Cathodes for High-Performance Lithium–Sulfur Batteries

High Resolution Image Download MS PowerPoint Slide Lithium–sulfur batteries (LSBs) hold significant potential as a next-generation, high-energy-density, and cost-effective battery technology. However, the low cycling stability and sulfur utilization continue to be significant challenges to the large-scale adoption of LSBs. This study focuses on the use of isoreticular two-dimensional (2D) porphyrin and cobalt porphyrin-based covalent organic frameworks (COFs) as cathodic materials for LSBs. By integrating cobalt into the porphyrin-based COF, we observed a significant improvement in the electrochemical performance at high current rates. The X-ray photoelectron spectroscopy (XPS) analysis revealed the interaction of S@COF-366-Co with lithium polysulfides (LiPS) during different stages of battery cycling. The results indicated the efficient conversion of longer-chain polysulfides into shorter-chain polysulfides, demonstrating the potential of COF-366-Co in addressing the shuttle effect and improving battery performance. Although the specific capacities of both S@COFs were very similar at low discharge rates (1250–1194 mA h g –1, 0.05 C), S@COF-366-Co excelled in rate capability and long-term stability. S@COF-366-Co outperformed at high C-rates, maintaining 50% of its original capacity (495 mA h g –1 ) at 2 C. In contrast, S@COF-366 was not operational beyond 1.5 C, reaching only 55 mA h g –1 . Over 1000 cycles at 0.5 C, S@COF-366-Co exhibited enhanced cycling stability, retaining 493.3 mA h g –1 with a decay rate of 0.0345% per cycle and a lower charge transfer resistance. These results highlight the critical role of cobalt as electrocatalytic centers in improving the efficiency and durability of COF-based LSBs.