Microstructures of reduced graphene oxide/sulfur nanocomposites and their impacts on lithium storage performances

Abstract

The lithium-sulfur (Li/S) concept has a theoretical specific capacity of 1672 mAh g-1 based on the complete reduction of S into lithium sulfide (Li2S). Practically, however, a pure S electrode encounters low deliverable capacity and poor charge/discharge cycle life owing to S's electrical insulation and problems associated with polysulfide dissolution. Here, we report our studies to couple S with reduced graphene oxide (rGO) prepared via either mechanical milling or chemical precipitation. The differences of the resulting rGO/S composites with respect to morphology, structure, composition, and phase transformations are extensively studied. Thermal analyses, X-ray diffraction, scanning electron microscopy, and Raman spectroscopic results on the chemical rGO/S consistently confirmed the existence of amorphous/nanocrystalline S and their homogeneous distribution as well as interaction with the rGO microstructure. The electrochemical performances of chemical rGO/S revealed a marked improvement in both capacity retention and S utilization compared to those of the mechanical rGO/S.