Frozen slab method mediated sulfur-affinitive single-atom catalysts for efficient reversible sodium storage

Carbon-supported single-atom catalysts (C-SAMs) have recently emerged as a frontier strategy to address the issue of irreversible reactions in MoS₂-based sodium-ion batteries. However, conventional C-SAMs designed solely considering the d-p orbital coupling theory often yield distorted adsorption energy predictions for Na₂S, as it overlooks the roles of Na-N bond interactions and structural deformation. Herein, we introduce the frozen slab method to evaluate the influence of C-SAMs' affinities toward Na and S on Na₂S adsorption. Based on their relative adsorption strengths, C-SAMs are classified into three categories: S-affinitive, amphiphilic, and Na-affinitive. Theoretical calculations reveal that S-affinitive C-SAMs strongly adsorb S atoms, thereby weakening the Na-S bond in Na₂S and facilitating bond cleavage during charging. This reduces the decomposition energy barrier of Na₂S and enhances the reversibility of the conversion reaction. Experimental results confirm that S-affinitive C-SAV can accelerate Na⁺ storage kinetics in MoS₂, enabling highly efficient reversible conversion during charging. As a result, after 1000 cycles at a high current density of 5 A g^-1, the MoS₂/C-SAV electrode exhibits a specific capacity of 332.8 mAh g^-1, with a capacity retention rate as high as 98.87% and an average capacity decay of only 0.001% per cycle.