Functionalized hierarchical porous carbon with sulfur/nitrogen/oxygen tri-doped as high quality sulfur hosts for lithium-sulfur batteries

Abstract

A novel tri-doped hierarchical porous carbon (PC) for sulfur host is prepared by pyrolysis of a commercial gelatin and a facile template process. And, sulfur-porous carbon (S@PC) composite as cathode material of lithium sulfur battery is synthesized by a melt diffusion method. The as-prepared PC has both strongly physical adsorption and tightly chemical bonding of polysulfides due to high porosity with the interlacement of micropores, mesopores and macropores/macrohollows, large surface area, and rich heteroatom tri-doping, resulting in an excellent electrochemical performance as a sulfur host for lithium sulfur battery cathodes. Among the synthesized S@PC composites, due to the optimum melting time, S@PC 12 h composite electrode has more effective nitrogen-containing and oxygen-containing groups, and stronger S–O bonds than other S@PC composites. As a result, S@PC 12 h composite electrode shows a high initial specific discharge capacity of 1471 mAhg−1 at 0.1C rate, a super rate capacity of 790 mAhg−1 at 1C after 20 cycles of low rate, an excellent long cycle stability at 1C. Appropriate macropores and/or macrohollows can not only provide charge transfer channels, but also effectively adsorb crystalline sulfur to a certain extent, result in the improvement of electrochemical performance for S@PC composites.