Template-Free Preparation of Hierarchical Porous Carbon Nanosheets for Lithium-Sulfur Battery.

Porous carbon nanosheets have the advantages of longitudinal continuity, transverse ultrathin, high specific surface area, and surface atomic activity, as well as the synergistic effect of micro and nanoproperties, so the research on their preparation, structure, and properties has attracted wide attention. A series of ultrathin hierarchical porous carbon nanosheets (HPCNs) is fabricated through carbonization of precursors obtained through the Friedel-Crafts reaction-assisted loading of polystyrene on graphene oxide. Hierarchical pore structures consist of three parts: (1) the micropores (1.3 nm), which were provided by porous polystyrene through the Friedel-Crafts reaction; (2) the mesopores (3.8 nm), which were provided by slab pores from the stack of carbon nanosheets; and (3) the pores (>5 nm) formed from the random stack of carbon nanosheets. Controlling the carbonization time and temperature adds to a prominent increase in specific surface area from 405.8 to 1420 m2 g-1. It was found that excessive carbonization would destroy the hierarchical pore structure. These porous carbon materials were used as cathode materials for lithium-sulfur battery and showed good performance. HPCN/sulfur cathode has good rate performance and cycle performance, and the capacity retention rate is 87% after the current density rises from 1 to 3 C and 91% after 200 cycles.