Symmetry-Broken Coordination of Single-Atom Catalysts Unlocks Spin- and Orbital-Regulated Sulfur Redox in Lithium–Sulfur Batteries

Abstract Sulfur cathodes are considered promising candidates for next-generation energy storage due to their high theoretical energy density, low cost, and elemental abundance. However, their practical deployment is limited by the polysulfide shuttle effect and sluggish sulfur redox reaction (SRR) kinetics. In this study, we design coordination-regulated cobalt single-atom catalysts (CoClNC) featuring an asymmetric Cl–Co–N3 coordination environment to investigate the relationship between SRR catalytic activity and spin state configuration. The incorporation of Cl atoms induces electron delocalization in Co(II), promoting a transition from a low-spin to higher-spin state. This spin-state modulation enhances dz2 orbital hybridization with the π* antibonding orbitals of polysulfides, thereby accelerating their redox conversion. Furthermore, the asymmetric coordination lowers the d-band electron occupancy, improving sulfur species adsorption and facilitating SRR kinetics. Lithium–sulfur batteries employing CoClNC/S cathodes demonstrate remarkable cycling stability, with an average capacity fade of only 0.023% per cycle. This work highlights a general strategy for spin and orbital engineering via coordination field modulation to boost SRR catalysis.