3D hierarchical nitrogen-doped graphene/CNTs microspheres as a sulfur host for high-performance lithium-sulfur batteries

Abstract

The practical applications for Li–S batteries rely on the restriction of shuttle effect from polysulfides and the improvement of conductivity of sulfur and Li2S. 3D hierarchical nitrogen-doped graphene/carbon nanotubes (N-GCNTs) microspheres were prepared by one-step ultrasonic spraying deposition method. N-GCNTs microspheres are consisted of sucrose, graphene and water-soluble carbon nanotubes and are named according to different mass ratio, like N-GCNTs-1 (1:1:1), N-GCNTs-2 (1:3:1) and N-GCNTs-3 (1:5:1). N-GCNTs-2 microspheres have 3D porous structure with abundant of N atoms which is constituted by the intertwine of nanotubes and graphene, and maintained the characteristics of 1D and 2D nano-carbon. By contrast, N-GCNTs-1 microspheres shows broken microspheres connected by a few CNTs, and N-GCNTs-3 microspheres expose the smoother and integrated spheres which are hardly found CNTs. N-GCNTs-2 microspheres mainly manifest the eminent physical characterization for big BET specific surface area (575.8 m2g-1) and pore volumes (0.303568 cm3g-1) and high sulfur content (87.5%). Moreover, N-GCNTs-2 microspheres show the high initial discharge capacities of 1465.1 mAh g−1 at 0.1 C, good cycle stability of 1315.1 mAh g−1 after 200 cycles and outstanding long-term cycling performance of 849.1 mAh g−1 after 500 cycles at 2.0 C. The N-GCNTs-2 microspheres effectively enhance the electrochemical performance of cathodes for lithium-sulfur batteries due to 3D hierarchical porous structure and successful N-doping.