An Effective Single-Atom Catalytic Descriptor for Accelerating Sulfur Reduction Reaction in Lithium-Sulfur Batteries

The solid-solid Li₂S₂-to-Li₂S transition represents a fundamental bottleneck in sulfur electrochemistry, critically governing reaction kinetics and energy efficiency in lithium-sulfur batteries (LSBs). While single-atom catalysts (SACs) show promise in modulating this process, the absence of intrinsic descriptors linking atomic-scale electronic properties to macroscopic catalytic performance has hindered rational catalyst design. Here, we establish a universal electronic descriptor, θ-χ, defined as the difference between the valence electron count (θ) and electronegativity (χ) of transition metal (TM) centers. This descriptor quantitatively correlates d-band modulation and interfacial charge redistribution with catalytic activity, circumventing the conventional reliance on polysulfide adsorption configurations. Systematic screening across 3d/4d-TM@nitrogen-doped graphene (NG) systems reveals a strong θ-χ dependence of the energy barriers for the Li₂S₂-to-Li₂S conversion, with a correlation coefficient (R²) of about 0.90. Descriptor-guided screening not only identifies V@NG, Ti@NG, and Nb@NG as outperforming benchmark catalysts consistent with experimental validation but also uncovers the Mo@NG system, which exhibits superior catalytic activity. Notably, θ-χ exhibits transferability to sodium-sulfur batteries (NSBs), accurately predicting Na₂S₂-to-Na₂S kinetics trends without requiring system-specific recalibration. This work marks a paradigm shift from configuration-dependent simulations to electronic-structure-driven catalyst design, providing atomic-level insights into sulfur electrochemistry for both LSBs and NSBs catalysts.