Asymmetric Coordination Induced d‐Band Center Upshift of Ti Single Atoms for Accelerated Sulfur Conversion in Aqueous Zn─S Batteries

ABSTRACT

In aqueous Zn‐S batteries (AZSBs), sulfur cathodes based on conversion reactions offer ultrahigh theoretical capacity; however, sulfur redox chemistry is fundamentally constrained by sluggish solid‐solid reaction kinetics. Here, a single‐atom catalyst, characterized by a designed asymmetric Ti‐N ₃ S coordination configuration embedded in a conductive carbon matrix, was precisely exploited and served as a catalyst enhancing the electrochemical activity of sulfur redox kinetics. Partial substitution of N ligands by S disrupts the symmetric Ti‐N ₄ coordination, leading to increased electron density in the Ti 3d orbitals. This electronic redistribution upshifts the d‐band center of Ti, which elevates the energy of antibonding orbitals and reduces their occupation states. Consequently, Ti‐S interactions are strengthened, and the adsorption capacity toward sulfur species is enhanced in AZSBs. Meanwhile, the interfacial charge transfer is accelerated, leading to a lower energy barrier for the reversible S/ZnS conversion in AZSBs. As a result, the S@Ti‐N ₃ S/C cathode delivers a high initial capacity of 1375 mAh g ⁻¹ at 0.2 A g ⁻¹ and retains a reversible capacity of 570 mAh g ⁻¹ after 300 cycles at 5 A g ⁻¹ in AZSBs. This work highlights d‐band center engineering via asymmetric coordination as an effective strategy for regulating sulfur conversion kinetics in AZSBs.