Promoting Bidirectional Conversion of Li₂S with Single-Atom Cobalt Coordinated Gel Catalyst for High-Rate Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries exhibit extraordinary advantages owing to their high theoretical capacity and the natural abundance of sulfur. However, their practical applications are hindered by sluggish redox kinetics, particularly during the Li₂S₂−Li₂S conversions. Here, we propose a novel metal-coordinated gel strategy to develop a Co-SAs/NC (Co-N5-C) single-atom catalyst for efficient insoluble sulfur conversion. By crosslinking cobalt into a polyacrylonitrile matrix via Co-N coordination, a nitrogen-coordinated Co single-atom structure with high Co contents embedded in a layered carbon framework is achieved. Experimental and theoretical results reveal that the unfilled 3d orbitals of Co-N5 sites enhance d-p hybridization via Co-S binding, facilitating the bidirectional conversion between Li₂S₂ and Li₂S, Reducing the barrier for reducing Li₂S₂ to Li₂S from 1.33 for NC carbon to 0.64 eV for Co-N5-C, and that for oxidizing Li₂S from 2.12 for NC carbon to 1.62 eV for Co-N5-C. With the Co-N5-C-modified separator, the Li-S battery delivers a high discharge capacity of 780 mAh g⁻¹ at 5 C, and an unprecedented areal capacity of 9.0 mAh cm⁻² under a high sulfur loading of 8.97 mg cm⁻². This work provides an efficient single-atom catalysis approach for achieving stable high-rate Li-S batteries by redefining the sulfide conversion kinetics.