Preparation And Electrochemical Properties Of Sulfur-based Cathode Materials For Li-S Batteries

Lithium ion secondary battery plays an irreplaceable role in modern societyowning to the merits of high power density, high discharge voltage, long cycle life,environment friendly and so on, however, the low theoretical capacity of commercialcathode materials has restricted the further development of lithium secondary battery.Elemental sulfur is a kind of new cathode materials, which has the advantage of hightheoretical specific capacity, abundant resources, low cost and non-toxic, and it’sconsidered to be one of the most promising cathode materials. However, there are stillmany problems when sulfur used as the cathode material, such as electrically andironically insulated nature of sulfur, high solubility of reaction intermediate in organicelectrolyte and large volume expansion (80%) during the discharge process, etc. Thecommon method to solve above problems is coating or using strong adsorptionmaterials.Carbon nanotube is a new kind of carbonaceous materials, which has beenwidely used in lithium-ion batteries, and TiO2has strong chemical adsorption topolysulfide. Therefore, we used multi-walled carbon nanotubes and porous TiO2nanofibers as substrate separately to prepare sulfur-based composite, and theelectrochemical properties were tested. In this paper, the main research contents andresults are as follows:(1) We used potassium hydroxide to activate the multi-walled carbon nanotubes(MWCNTs), obtained the K-MWCNTs with abundant pores and opened tips, andfurther, we used the K-MWCNTs as substrate to prepare the K-MWCNTs-Scomposite. The electrochemical test results show that the composite has goodelectrochemical properties, the initial discharge capacity is741mAh g-1sulfur, and thecapacity retention of80%after50cycles at the current density of200mAg-1. (2) The porous TiO2nanofibers with anatase-rutile mischcrystal structure wereprepared by electrospinning technique. The results show that the TiO2nanofiberscomposed of small particles are about50-200nm in diameter. We prepared the TiO2-Scomposite by introducing sulfur into the TiO2nanofibers, and the electrochemicalproperties were tested. The initial discharge capacity is914mAh g-1sulfur, and thereversible capacity remains in530mAh g-1sulfurafter50cycles at the current densityof335mAg-1.(3) RGO-TiO2-S composites were successfully prepared. The electrochemicaltest results show that the initial discharge capacity is369mAh g-1compositeat the currentdensity of200mAg-1, and the coulomb efficiency is over99%during the cycles.