Accelerating Sulfur Redox Chemistry by Atomically Dispersed Zn-N₄ Sites Coupled with Pyridine-N Defects on Porous Carbon Sheets

Single-atom catalysts (SACs) with specific N-coordinated configurations immobilized on the carbon substrates have recently been verified to effectively alleviate the shuttle effect of lithium polysulfides (LiPSs) in lithium-sulfur (LiS) batteries. Herein, a versatile molten salt (KCl/ZnCl2)-mediated pyrolysis strategy is demonstrated to fabricate Zn SACs composed of well-defined Zn-N4 sites embedded into porous carbon sheets with rich pyridine-N defects (ZnN/CS). The electrochemical kinetic analysis and theoretical calculations reveal the critical roles of Zn-N-4 active sites and surrounding pyridine-N defects in enhancing adsorption toward LiPS intermediates and catalyzing their liquid-solid conversion. It is confirmed by reducing the overpotential of the rate-determining step of Li2S2 to Li2S and the energy barrier for Li2S decomposition, thus the ZnN/CS guarantees fast redox kinetics between LiPSs and Li2S products. As a proof of concept demonstration, the assembled LiS batteries with the ZnN/CS-based sulfur cathode deliver a high specific capacity of 1132 mAh g(-1) at 0.1 C and remarkable capacity retention of 72.2% over 800 cycles at 2 C. Furthermore, a considerable areal capacity of 6.14 mAh cm(-2) at 0.2 C can still be released with a high sulfur loading of 7.0 mg cm(-2), highlighting the practical applications of the as-obtained ZnN/CS cathode in LiS batteries.