One-pot fabrication of nitrogen and sulfur dual-doped graphene/sulfur cathode via microwave assisted method for long cycle-life lithium-sulfur batteries

Nitrogen and sulfur dual-doped graphene (NSG) synthesized by a simple and low-cost one-pot microwave assisted method is applied to immobilize sulfur by the mean of an in situ sulfur deposition approach. Images of scanning electron microscope (SEM) and transmission electron microscope (TEM) show that nano-sulfur (2-20 nm) is wrapped by the transparent NSG nanosheets with wrinkled and folded features. The application of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the structure and composition of the obtained nitrogen and sulfur dual-doped graphene/sulfur (NSG/S) composites as well. The heteroatom doping content was controlled by adjusting the amount of thiourea. The XPS analysis results indicate that pyridinic-N and pyrrolic-N are dominant among the product, thereby improving the cycle life of the lithium sulfur batteries. The NSG-4/S composites with sulfur loading of 68 wt% exhibits a remarkably higher reversible specific capacity of 1583 mAh g(-1), impressive rate capability, splendid specific discharge capacity of 819 mAh g(-1) at 0.1 C after 100 cycles and long cycle stability of 640 mAh g(-1) after 200 cycles at 1 C. (C) 2018 Elsevier B.V. All rights reserved.