Nanoarchitectured graphene/CNT@porous carbon with extraordinary electrical conductivity and interconnected micro/mesopores for lithium-sulfur batteries

Abstract

The sp2-hybridized nanocarbon (e.g., carbon nanotubes (CNTs) and graphene) exhibits extraordinary mechanical strength and electrical conductivity but limited external accessible surface area and a small amount of pores, while nanostructured porous carbon affords a huge surface area and abundant pore structures but very poor electrical conductance. Herein the rational hybridization of the sp2 nanocarbon and nanostructured porous carbon into hierarchical all-carbon nanoarchitectures is demonstrated, with full inherited advantages of the component materials. The sp2 graphene/CNT interlinked networks give the composites good electrical conductivity and a robust framework, while the meso-/microporous carbon and the interlamellar compartment between the opposite graphene accommodate sulfur and polysulfides. The strong confinement induced by micro-/mesopores of all-carbon nanoarchitectures renders the transformation of S8 crystal into amorphous cyclo-S8 molecular clusters, restraining the shuttle phenomenon for high capacity retention of a lithium-sulfur cell. Therefore, the composite cathode with an ultrahigh specific capacity of 1121 mAh g-1 at 0.5 C, a favorable high-rate capability of 809 mAh g-1 at 10 C, a very low capacity decay of 0.12% per cycle, and an impressive cycling stability of 877 mAh g-1 after 150 cycles at 1 C. As sulfur loading increases from 50 wt% to 77 wt%, high capacities of 970, 914, and 613 mAh g-1 are still available at current densities of 0.5, 1, and 5 C, respectively. Based on the total mass of packaged devices, gravimetric energy density of GSH@APC-S//Li cell is expected to be 400 Wh kg-1 at a power density of 10 000 W kg-1, matching the level of engine driven systems. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.