Porphyrin-Derived Graphene-Based Nanosheets Enabling Strong Polysulfide Chemisorption and Rapid Kinetics in Lithium-Sulfur Batteries

摘要

Lithium-sulfur (Li-S) batteries hold great promise as a next-generation battery system because of their extremely high theoretical energy density and low cost. However, ready lithium polysulfide (LiPS) diffusion and sluggish redox kinetics hamper their cyclability and rate capability. Herein, porphyrin-derived graphene-based nanosheets (PNG) are proposed for Li-S batteries, which are achieved by pyrolyzing a conformal and thin layer of 2D porphyrin organic framework on graphene to form carbon nanosheets with a spatially engineered nitrogen-dopant-enriched skin and a highly conductive skeleton. The atomic skin is decorated with fully exposed lithiophilic sites to afford strong chemisorption to LiPSs and improve electrolyte wettability, while graphene substrate provides speedy electron transport to facilitate redox kinetics of sulfur species. The use of PNG as a lightweight interlayer enables efficient operation of Li-S batteries in terms of superb cycle stability (cyclic decay rate of 0.099 during 300 cycles at 0.5 C), good rate capability (988 mAh g(-1) at 2.0 C), and impressive sulfur loading (areal capacity of 8.81 mAh cm(-2) at a sulfur loading of 8.9 mg cm(-2)). The distinct interfacial strategy is expected to apply to other conversion reaction batteries relying on dissolution-precipitation mechanisms and requiring interfacial charge- and mass-transport-mediation concurrently.