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 (QJT), 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.