I, N Co-doped hierarchical micro/mesoporous carbon modified separator for enhanced electrochemical performances of lithium-sulfur batteries

Although the high discharging capacity and coulombic efficiency can be obtained by impregnating sulfur into various conductive porous hosts in lithium-sulfur (Li-S) batteries, the low sulfur loading content and volumetric specific energy diminish their advantages. To solve this problem, a modified layer is prepared by coating I and N co-doped hierarchical micro/mesoporous kelp bio-carbon on surface of the polypropylene separator. Furthermore, the composite porous carbon is obtained by one-step thermal pyrolysis of edible dried kelp. The modified layer on separator can effectively prevent shuttle of polysulfides due to the synergistic effect from the micro/mesoporous carbon structures (physisorption effect) and I and N co-doped electrochemical active sites in carbon matrix (chemisorption effect), allowing high capacity and high coulombic efficiency. In this study, we developed Li-S batteries with 80% sulfur loading content and the area loading is higher than 2.0 mg cm −2 , which are better than previous published ones. In addition, the cathode electrode could stabilize at 760 mAh g −1 after 200 cycles at 0.5 C and delivers a high retention specific capacity of 498 mAh g −1 after 500 cycles with a slight capacity attenuation of 0.07% per cycle.