Nitrogen-doped graphene/sulfur composite as cathode material for high capacity lithium-sulfur batteries

摘要

Two types of nitrogen-doped graphene sheets (NGS) synthesized by a facile hydrothermal method are used to immobilize sulfur via an in situ sulfur deposition route. The structure and composition of the prepared nitrogen doped graphene/sulfur (NGS/S) composites are confirmed with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) images shows the porous sulfur particles are well wrapped by NGS. Compared with graphene/sulfur (GS/S) composite, the NGS-1/S composite with high loading (80 wt%) of sulfur presents a remarkably higher reversible capacity (1356.8 mAh g~(-1) at 0.1 C) and long cycle stability (578.5 mAh g~(-1)remaining at 1 C up to 500 cycles). Pyridinic-N rich NGS-1/S exhibits a better electrochemical performance than pyrrolic-N enriched NGS-2/S. The improvement of electrochemical properties could be attributed to the chemical interaction between the nitrogen functionalities on the surface of NGS and polysulfide as well as the enhanced electronic conductivity of the carbon matrix.