Accurate determination of optimal sulfur content in mesoporous carbon hosts for high-capacity stable lithium-sulfur batteries

Mesoporous carbon materials have been widely used as hosts for sulfur encapsulation to mitigate the low electrical conductivity of sulfur, lithium polysulfide shuttle, and drastic volume changes of sulfur species associated with lithium-sulfur batteries (LSBs). The ideal sulfur-host composite should have an optimal content of sulfur that partially fills the pores of the host and produces the exact amount of final discharged product Li2S that can be completely accommodated by the pores of the host. However, accurately determining this optimal content of sulfur is a challenge and no effective method has been established. In this work, we successfully determined the optimal sulfur content for the Ketjenblack EC-600 JD (KB) sulfur host by simply characterizing sulfur-KB (SKB) composites with different sulfur contents using X-ray diffraction (XRD) spectroscopy coupled with thermogravimetric analysis (TGA). The LSB using the SKB with the optimal sulfur content of 52.9% showed a high specific capacity of 1535 mAh g−1 at 0.1C and a capacity of 680 mAh g−1 even at the high rate of 5C. Furthermore, it also showed stable cycling stability with low capacity decay rates of 0.05% and 0.09% per cycle over 500 cycles at 2C and 5C, respectively.