Electronegativity-Induced Jahn-Teller Distortion Boosts Li-S Conversion on Asymmetric Cu Single-Atom Catalysts

A series of Cu-based single-atom catalysts (SACs) with asymmetric coordination were designed to accelerate lithium-sulfur (Li-S) chemistry. The electronegativity contrast from the dopant induces a localized electronic asymmetry that amplifies Jahn-Teller distortion at the Cu center. This distortion profoundly modulates the Cu 3d electronic structure and its interaction with Li-S intermediates. Among the series, the CuN₃F site exhibits the strongest Cu(II) Jahn-Teller distortion and the lowest free-energy step (ΔG ≈ 0.19 eV) for sulfur reduction, indicating superior catalytic activity. To rigorously capture the underlying electronic and structural effects, we establish a quantitative Jahn-Teller distortion index (Q_JT), defined as the product of the local spin magnetic moment and the standard deviation of integrated crystal orbital Hamilton population (iCOHP) values among Cu-ligand bonds. This descriptor effectively distinguishes true electronic Jahn-Teller activity from mere geometric or steric asymmetry, providing a physically grounded metric to assess and engineer the active site electronic structure. Mechanistic analysis reveals that the dynamic Jahn-Teller distortion at CuN₃F leads to an ideal alignment of Cu d orbitals with the LUMO of key Li-S intermediates, enhancing electronic coupling and reaction kinetics. This work demonstrates a novel Jahn-Teller distortion engineering strategy for Li-S catalysis, wherein electronegativity-driven local asymmetry is harnessed to tune the electronic structure and boost catalytic performance in energy storage system technologies.