Influence of carbon structure/porosity on the electrochemical performance in Li-sulfur batteries

The porous structure of three different, commercially available porous carbonaceous materials is investigated by the alpha S-plot method and by the t-plot method. Subsequently, the electrochemical properties of sulfur-free porous carbon electrodes from inspected materials are studied by cyclic voltammetry. The comparison of double-layer capacitances with the corresponding adsorption isotherms of N2 reveals the role of micropores during the capacitive charging of carbons by Li+. The studied carbons are added to the sulfur cathodes and evaluated. The cyclic voltammograms show no contribution of micropores in the carbon structure to the electrochemical processes taking place in the lithium-sulfur coin cell. The highest specific capacity of 816 mAh/g is observed for material with the lowest content of micropores in the structure (14%). The partially mesoporous and partially microporous (65%) sample and the predominantly microporous one (87%), show specific capacities of 664 mAh/g and 560 mAh/g, respectively. The galvanostatic cycling of lithium-sulfur coin cells with carbonaceous additives reveals that the mesopores and macropores in the carbon structure increase the specific charge capacity of the lithium-sulfur batteries and that the micropores improve the cycling stability of these batteries.