Modulating the d-band center of single-atom catalysts for efficient Li2S2-Li2S conversion in durable lithium-sulfur batteries

Abstract

Enhancing the conversion of insoluble Li2S2-Li2S to improve sulfur utilization has become an essential strategy for Lithium-Sulfur (Li-S) batteries. The proposed approach employs single-atom catalysts (SACs) known for their high atomic usage efficiency to enable in-situ reactions with Li2S2. However, the origin and mechanisms of various SACs involved in the Li2S2 to Li2S reduction reaction are not fully elucidated. Herein, we reveal the underlying mechanism of Li2S2-Li2S reduction catalysis on Mn atoms by examining the electronic structure of d orbitals. Theoretical calculations indicate that substituting a S atom for N in the first coordination structure of Mn SACs elevates the Mn d-band center and simultaneously enhances the hybridization between the Mn d orbitals and the p orbitals of sulfur species. This alteration not only improves the anchoring of lithium polysulfides, leading to better adsorption but also accelerates the conversion kinetics of Li2S2 to Li2S due to the improved intrinsic catalytic activity of SACs. As a result, the Li-S batteries equipped with the SAMn-based cathode deliver an impressive initial capacity of 1343.9 mAh g−1 at 0.1 C, exceptional rate capability of 782.4 mAh g−1 at 3 C, and maintain a low degradation rate of approximately 0.025% per cycle over 1000 cycles at 1.0 C. Furthermore, with a sulfur loading of 6 mg cm−2, the S/SAMn@NSC cathode achieves a reversible areal capacity of 4.4 mAh cm−2 at 0.1 C. This study significantly advances the kinetics of solid-solid transformation in Li-S battery cathodes through catalysis facilitated by single-atom d-band regulation.