Effect of Porous Carbon Morphologies and Composite Manufacturing Processes on Long-Cycling Performance in High Sulfur Loading Li-S Batteries

Long-cycling performance of Li-S batteries was studied with the high-sulfur loading composites composed of 86% sulfur and 14% carbon. The composites are made by the physical mixing and S-liquefied pore-filling processes with nano sulfur powder and two kinds of porous carbons. The initial discharge capacities of the composite prepared by the physical mixing and liquefied pore-filling with 1-µm-sized carbon were 1060 mAh/g and 1121 mAh/g, respectively. On the other hand, the capacities of the composite using 5-µm-sized carbon were 705 mAh/g in physical mixing and 845 mAh/g in liquefied pore-filling process. The composite with the 1 µm carbon showed approximately ∼1.4 times higher than that of 5 µm. The reason for this difference is that the surface area of the sulfur wrapping the small particle carbon surface is larger than that of the composite wrapping the large particle carbon surface. Importantly, after 500 cycles, the cycle stability in the physical mixing process is 15∼30% higher than that in the S-liquefied pore filling process in both carbons, due to the decrease of electrolyte resistance by capturing polysulfide into the pores which are not filled by the sulfur during the process. In the case of high-sulfur loading composites, manufacturing process as well as the size and morphologies of the carbon are crucial factors that affect the capacity and cycle stability of the Li-S battery.