Synthesis and electrochemical properties of a sulfur-multi walled carbon nanotubes composite as a cathode material for lithium sulfur batteries

Abstract A sulfur-multi walled carbon nanotubes (MWCNTs) composite is prepared by the direct precipitation method as a cathode material for lithium sulfur batteries. The microstructure and morphology of the sulfur-MWCNTs composite are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS) mapping and thermogravimetric analysis (TGA). From these results, it is found that the synthesized sulfur has an orthorhombic phase and the MWCNTs are chemically well-dispersed over the whole surface of the synthesized sulfur. Electrochemical charge–discharge tests demonstrated that the sulfur-MWCNTs composite exhibits better capacity retention (63%) than that (16%) of the precipitated sulfur, which is also prepared by the direct precipitation method without MWCNTs. The enhanced cycle performance of the sulfur-MWCNTs is mainly attributed to the formation of highly conductive electron path due to the uniformly dispersed MWCNTs. Furthermore, in order to investigate the electrochemical reaction mechanism for the Li–S cell during the discharge process, the ac-impedance spectra as a function of the state of discharge are measured and analyzed.