Rechargeable lithium sulfur battery. I. Structural change of sulfur cathode during discharge and charge

In this paper, the structural change of the sulfur cathode during the electrochemical reaction of a lithium sulfur battery employing 0.5 M LiCF3SO3-tetra(ethylene glycol) dimethyl ether (TEGDME) was studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and wave dispersive spectroscopy (WDS). The discharge process of the lithium sulfur cell could be divided in the first discharge region (2.4-2.1 V) where the reduction of elemental sulfur to form soluble polysulfides and further reduction of the soluble polysulfide occur, and the second discharge region (2.1-1.5 V) where the soluble polysulfides are reduced to form a nonuniform Li2S solid film covered over the carbon matrix. It was also found that the charge of lithium sulfur cell leads to the conversion from Li2S to the soluble polysulfide, resulting in the removal of Li2S layer formed on carbon matrix. However, the oxidization of the soluble polysulfide to solid sulfur hardly occurs and few Li2S are left on carbon matrix even at 100% depth of charge.