Nitrogen Rich Hierarchically Organized Porous Carbon/Sulfur Composite Cathode Electrode for High Performance Li/S Battery: A Mechanistic Investigation by Operando Spectroscopic Studies

The physiochemical properties of the carbon host matrix and their sulfur loadings play a major role in the electrochemical performance of lithium-sulfur batteries. A highly sulfur (S) loaded (75 wt%) carbon matrix (S/nitrogen rich carbon host matrix (NGC)) has been designed, with hierarchically organized micro/mesopore structures containing nitrogen and oxygen functional groups, and using metal oxide nanostructured templates. The S/NGC electrodes give reversible capacities of 868 and 666 mAh g(-1) at C/5 current rates, with sulfur loading of 2.2 and 3.4 mg cm(-2), respectively. Based on the advantages of the hierarchically organized porous structure and heteroatom doping, S/NGC electrode shows long cycling stability (0.03% capacity decay per cycle in the first 1000 cycles) with high coulombic efficiency (>99%), which is an improvement by a factor of two compared with a sulfur/graphene cathode. Further, the charge/discharge mechanism of the cell is investigated in detail by in situ Raman and ex situ X-ray photoelectron spectroscopy. The presence of nitrogen on the carbon support is found to make the bond formation easier between sulfur and oxygen functional groups existing at the carbon support, which is supposed to play a major role along with hierarchically organized porous structure, for the prevention of sulfur/polysulfides species dissolution to the anode side.