Insight to the synergistic effect of N-doping level and pore structure on improving the electrochemical performance of sulfur/N-doped porous carbon cathode for Li-S batteries

Abstract

Three nitrogen-doped porous carbons (NDPCs) with the ultrahigh specific surface areas are prepared via a one-step activation of the biomass waste. The as-prepared samples have different levels of nitrogen contents and pore structure. These sulfur hosting matrix materials are designed to systematically elaborate the effect of N-doping level and pore structure on the electrochemical performance of the S/NDPC nanocomposites. The higher volume ratio of marco-mesopores to micropores of the substrate can greatly enhance the rate capability of the S/NDPC cathodes. This is attributed to the improved electrolyte penetration via the rich marco-mesopores. Meanwhile, the higher nitrogen content of the NDPC contributes to improving the cycle stability of the S/NDPC cathode, which is assigned to the strong chemical adsorption and physical restriction of polysulfides by the interaction of nitrogen atom and polysulfides. Therefore, the S/NDPC-1 cathode, prepared by using a NDPC matrix with high nitrogen content, large specific surface area, and a moderate microporous volume percentage (VMicro/VT), displays an obvious enhancement in the electrochemical performance. It exhibits specific capacities of 926.1 and 815.8 mAh g−1 at 0.5 and 1.0 C rate, respectively, with a capacity fading rate of only 0.067% per cycle after 500 cycles at 1.0 C.