Sealed pre-carbonization to regulate the porosity and heteroatom sites of biomass derived carbons for lithium-sulfur batteries.

Ultrathin carbon sheets with high surface area, abundant mesoporous structure and rich N, O heteroatom doping sites were prepared from puffed rice through unique sealed pre-carbonization. By utilizing them as cathode materials for lithium-sulfur batteries, the in-operando Raman spectra and electrochemical tests indicated that the polysulfides shuttling effect could be substantially suppressed by the physical confinement and chemical adsorption due to these structural advantages. In addition, the well-developed hierarchical porous structure and ultrathin thickness were found to enhance the mass diffusion in the electrode, which increased the ion conductivity within the carbon framework. Therefore, the as-designed cathode was observed to accommodate the high sulfur loading amounts and demonstrated a high reversible capacity of 920.8 mAh g-1 after 100 cycles at 0.2C with high coulombic efficiency (~100%). Moreover, the long-term stability test at 1C indicated that the cathode achieved a high reversible capacity of 702.1 mAh g-1 after 300 cycles with low decay rate of 0.07% per cycle.