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

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. 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.