Preparation And Electrochemical Properties Of Carbon/Sulfur Composites

ABSTRACT:Lithium sulfur battery is rich in sulfur electrode resources, non-toxic, environmental friendly and low in price. It is one of the most promising battery systems. Sulfur and the final reduction products Li2S2and Li2S are poor in electrical and ionic conductivity. Long chain sulfur ions are easy to dissolve in the electrolyte. In order to solve the above two problems, a large number of carbon/sulfur composites have been researched. General nanoporous carbon spheres (NCs) and hierarchical nanoporous carbon spheres (HNCs) were synthesized by using one-step reflux method and simple hydrothermal method in this paper. NCs/S and HNCs/S were preparaed through in situ deposition method. In order to improve the electrochemical properties of NCs/S, CNTs were mixed with NCs in physical or chemical way respectively getting NCs/CNTs/S and NCs@CNTs/S. Besides, the morphology and the electrochemical properties of multi-walled carbon nanotubes etched by KOH (etching wCNTs) in hydrothermal solution were studied. The main contents are as follows:The effects of CNTs on the morphology and the electrochemical properties of NCs/S were researched. The results revealed that NCs/CNTs/S (CNTs:NCs=1:8) showed a better cycling performance. Its initial discharge capacity was1304.0mAh·g-1, and maintained above500mAh·g-1after80cycles. NCs@CNTs showed a new flower-like morphology with a larger specific surface area, so sulfur could be distributed more uniformly. The initial discharge specific capacity of NCs@CNTs/S at0.5C was up to1716.8mAh·g-1, and remained598.1mAh·g-1after50cycles, which was higher than that of NCs/CNTs/S. This research has a significant reference value for multiple carbon/sulfur materials.The influences of template agent, carbon/silicon source ratio and melt treatment to the morphology and the performance of HNCs/S were respectively studied. Results showed that HNCs-1synthesized using SiO2sol as template had the smallest particle size. HNCs/S was synthesized in hydrothermal situ deposition method. HNCs-1@S showed excellent electrochemical performance, which was obtained after melting treatment of HNCs/S. Its initial specific capacity was1541.0mAh·g-1at0.2C, and remained at721.2mAh·g-1after50cycles.Etching wCNTs with shorter length, nanoporous wall, larger specific surface area could be generated in KOH hydrothermal etching method. The impacts of hydrothermal temperature on the morphology and the properties of carbon nanotubes were studied. The results revealed that wCNTs-160etched under160℃had the best morphology. The length of wCNTs-160was about30nm, and tube walls were rich in microporous which were about4nm. WCNTs-160was a good carrier for sulfur. The initial discharge specific capacity of wCNTs-160/S was717.6mAh·g-1,695.7mAh·g-1at0.2C and0.5C within1.5-2.8V. And the capacity remained about400mAh·g-1at0.5C after190cycles.