(130d) Facile Synthesis of Cos Nanoparticles Anchored on the Surface of Functionalized Mwcnts As Cathode Materials for Advanced Li-S Batteries

Lithium-sulfur (Li-S) batteries have been considered a promising candidate for the next generation of battery systems owing to their high specific capacity and energy density. However, some barriers hinder the application of Li-S batteries, such as the “shuttle effects” of lithium polysulfides (LPS), the poor electrical conductivity of sulfur, and lithium dendrite on lithium metal electrodes. The effects of CoS loading (10%, 20%, and 30%) on multi-walled carbon nanotubes (MWCNTs) on electrochemical performance for Li-S batteries were investigated. A facile hydrothermal method to grow CoS nanoparticles in-situ on the surface of multi-walled carbon nanotubes (MWCNTs) was used. In addition, CoS on functionalized multiwalled carbon nanotube (f@MWCNTs) was also investigated. SEM, TEM, XRD, and XPS were used to characterize the structure and electronic state of CoS on the surface of MWCNTs and f-MWCNTs. The initial discharge capacities and reversible specific capacities after 200 cycles were found to be 980 and 612 mAh/g, 990 and 707 mAh/g, and 959 and 658 mAh/g for the 10, 20, and 30% CoS samples, respectively. Interestingly, the 20% CoS@MWCNTs show the best initial discharge capacity and retention after 200 cycles. This finding can be attributed to the fact that high CoS loading (30%) may not be dispersed evenly on MWCNTs surface, while low CoS loading (10%) leads to fewer CoS and weaker adsorption for polysulfides. Moreover, the 20% CoS/f-MWCNTs show even higher initial discharge capacities of 1103 mAh/g and reversible specific capacities of 796 mAh/g after 200 cycles. This can be attributed to a rougher surface with more active sites on f-MWCNTs for trapping polysulfides, and for enhancing the electronic conductivity of cathode composite. XPS spectra show prominent peaks at 162.7 and 163.9 eV which correspond to Co-S and C-S bonds, respectively, suggesting CoS bonds well with MWCNTs. It is postulated that CoS/f-MWCNTs play a role to adsorb lithium polysulfides during the charge and discharge process and accelerating the kinetics of polysulfides conversion. This study provides a facile strategy to employ CoS@f-CNT/S in Li-S batteries and improve its performance.