Embedding Zn single-atom catalysts into pyrrolic-N defect enriched multilayer carbon sheets boosts sulfur redox kinetics

Abstract

Lithium–sulfur (Li–S) batteries have been considered as one of the most promising rechargeable energy storage systems on account of their impressive theoretical capacity of 1675 mA h g⁻¹ and low cost. Nevertheless, the shuttle effect of soluble polysulfides resulting from the sluggish reaction kinetics has severely hindered their practical applications. Herein, a novel ZnCl₂-assisted pyrolysis strategy was presented to synthesize Zn single-atom catalysts (SACs) embedded into nitrogen (N)-doped multilayer porous carbon nanosheets (Zn-NMPC-x, x is the mass ratio of ZnCl₂ to coal tar pitch) by using low-cost coal tar pitch as precursors, with the purpose of boosting redox kinetics in Li–S batteries. During the pyrolysis process, the generated multi-phase interfaces from molten ZnCl₂ and precursors contribute to the formation of pyrrolic-N defect enriched multilayer carbon sheets with the help of urea and in situ anchoring of atomically dispersed Zn with N sites within carbon frameworks. The theoretical calculations and experimental results indicate that Zn SACs coupled with pyrrolic-N defects can effectively capture polysulfides and accelerate the redox kinetics of sulfur species. Further, the assembled Li–S battery with the optimized Zn-NMPC-5@S cathode delivers a high discharge capacity of 1288 mA h g⁻¹ at 0.1C, excellent rate performance of 683 mA h g⁻¹ at 2C, and long-term cycling stability with 0.026% capacity decay per cycle over 500 cycles at 1C. Impressively, a high reversible areal capacity of 5.2 mA h cm⁻² for Zn-NMPC-5@S cathode with a sulfur loading of 6.3 mg cm⁻² can be still obtained. This work provides a convenient and feasible strategy to prepare Zn SACs with N-doped multilayer carbon structures for advanced Li–S batteries.