N/O dual coordination of cobalt single atom for fast kinetics sodium‐sulfur batteries

Abstract Room‐temperature sodium‐sulfur batteries are promising grid‐scale energy storage systems owing to their high energy density and low cost. However, their application is limited by the dissolution of long‐chain sodium polysulfides and slow redox kinetics. To address these issues, a cobalt single‐atom catalyst with N/O dual coordination was derived from a metal‐organic framework precursor (denoted as Co–N 2 O 2 /MOFc) for sulfur storage. Theoretical analysis demonstrates that, compared with the Co–N 4 structure, the introduction of oxygen atoms can further tune the d‐electron density of Co atoms via the coordinative effect, which enhances d‐p hybridization after Na 2 S x adsorption on Co–N 2 O 2 /MOFc. This leads to higher adsorption energy for Na 2 S x , lower Gibbs free energy for the rate‐limiting process and a decreased Na 2 S decomposition energy barrier, thereby promoting the polysulfide conversion reaction kinetics. When used as a sulfur host, the Co–N 2 O 2 /MOFc/S cathode exhibits excellent performance with a capacity of 590 mAh·g −1 (983 mAh·g −1 normalized by the sulfur mass) after 100 cycles at 0.1 A·g −1 and an excellent rate capability of 350 mAh·g −1 at 10 A·g −1 .