Orbital interactions and high spin states: Unlocking the potential of Co-Single-Atom catalysts for Li-S batteries

Abstract

Single-atom catalysts (SACs) have been widely utilized in lithium-sulfur (Li-S) batteries. However, their sluggish reaction kinetics and serious shuttling effects remain major challenges. Current research on SACs focuses on adjusting their coordination structure to bolster the adsorption and conversion of polysulfides while overlooking their enhancement through modulation of the electronic structure of the metal centers. This study proposes a novel approach for synthesizing nitrogen-doped Co-SACs (Co-SAC@NC). Theoretical calculations and experimental results indicate that nitrogen doping leads to a high Fermi energy level within Co-SAC@NC, signifying an elevated average energy of the electrons. This elevation results in significant splitting and lifting of degeneracy among d-orbitals in Co metal, which ultimately leads to a high-spin configuration. This configuration enhances the orbital interactions between the polysulfides and the catalyst, causing a decrease in the energy barrier and fast conversion from polysulfides to lithium sulfide. Thus, it improves the polysulfide kinetics. As a result, the batteries with the Co-SAC@NC modified separator exhibit a remarkable initial discharge capacity of 1465 mAh g−1 at 0.1C and excellent rate performance (736 mAh g−1 at 4C), outperforming most Co-SAC-based Li-S batteries.