In situ sulfur deposition route to obtain sulfur-carbon composite cathodes for lithium-sulfur batteries

An in situ sulfur deposition route has been developed for synthesizing sulfur-carbon composites as cathode materials for lithium-sulfur batteries. This facile synthesis method involves the precipitation of elemental sulfur into the nanopores of conductive carbon black (CCB). The microstructure and morphology of the composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that most of the sulfur in the amorphous phase is chemically well-dispersed in the nanopores of the CCB. The sulfur content in the composites is confirmed using thermogravimetry analysis (TGA). The S-CCB composites with different sulfur content (52 wt%, 56 wt% and 62 wt%) deliver remarkably high initial capacities of up to 1534.6, 1357.4 and 1185.9 mA h g (1) at the current density of 160 mA g (1), respectively. Correspondingly, they maintain stable capacities of 1012.2, 957.9 and 798.6 mA h g(-1) with the capacity retention of over 75.1% after 100 cycles, exhibiting excellent cycle stability. The electrochemical reaction mechanism for the lithium-sulfur batteries during the discharge process is investigated by electrochemical impedance spectroscopy (EIS). The significantly improved electrochemical performance of the S-CCB composite is attributed to the carbon-wrapped sulfur structure, which suppresses the loss of active material during charging-discharging and the restrained migration of the polysulfide ions to the anode. This facile in situ sulfur deposition method represents a low-cost approach to obtain high performance sulfur-carbon composite cathodes for rechargeable lithium-sulfur batteries.