A parametric study on encapsulation of elemental sulfur inside CNTs by sonically assisted capillary method: Cathodic material for rechargeable Li-S batteries

Abstract

Encapsulation of elemental sulfur inside of carbon nanotubes is one of the best solutions to face the Lithium-Sulfur batteries challenges to get successful commercialization. In this work, the first parametric study of the capillary drawing-in dissolved materials in low surface tension solvents accompanying ultrasonic method is reported which has low heat consumption and convenient process. The optimized parameters are composite concentration (ratio of total composite material to solvent), ultrasonic irradiation power, ultrasonic irradiation time and initial sulfur concentration on the filling yield. A complete characterization were executed to investigate various characteristics of synthesized S@CNT composites. The results indicate that the elemental sulfur were successfully physically (no chemical bond) confined inside of the carbon nanotubes. The maximum amount of sulfur that confined inside the cavity of carbon nanotubes is 36.21 %wt. This synthesized composite as cathodic material for Li-S battery offers a stable cycling profile (81.68% capacity retention after 100 cycles at 2C) and sufficient capacity (725 mAh g(-1) at 2C) at high C-rate. These results indicate that carbon nanotubes provide a high electronic conductivity shell with a cavity that balances the volume expansion of the sulfur during charge and discharge of cycles in Li-S batteries and also supplies an excellent trap for the polysulfides, prevents the dissolution of them, and controls the shuttle effect. These excellent results are believed to contribute to improvements in this technology.