Metalated Covalent Organic Frameworks as Electrocatalytic Sulfur Cathodes for High-Performance Lithium–Sulfur Batteries
Mohammad K. Shehab, Mahmoud M. Kaid, Shiraj Pokhrel, Omar K. Farha, Hani M. El‐Kaderi
Abstract
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.