Sulfur-impregnated 3D hierarchical porous nitrogen-doped aligned carbon nanotubes as high-performance cathode for lithium-sulfur batteries

• A rational HPNACNTs array is designed as scaffolds to infuse sulfur.
• The HPNACNTs array shows a hierarchical porous morphology and robust structure.
• The HPNACNTs-5-S electrode retains a high capacity of 817 mAh g−1 at 5 C.
• Its 3D structure with 1D conductive electron paths enables high-rate capability.

A rational 3D hierarchical porous nitrogen-doped aligned carbon nanotubes (HPNACNTs) with well-directed 1D conductive electron paths is designed as scaffold to load sulfur. The HPNACNTs have abundant micropores, mesopores and macropores with a relatively high specific surface area and a large total pore volume. The sulfur-HPNACNTs composite is synthesized for lithium–sulfur batteries by a melt-diffusion of sulfur powders into HPNACNTs scaffolds. Electrochemical tests reveal that the sulfur-HPNACNTs (68.8 wt% sulfur) composite exhibits a high initial discharge capacity of 1340 mAh g−1 at 0.1 C and retains as high as 979 mAh g−1 at 0.2 C after 200 cycles. More importantly, it shows high reversible capacity at high rates (817 mAh g−1 at 5 C). Its enhanced electrochemical performance can be attributed to the excellent electrical conductivity of aligned carbon nanotubes, the synergetic effect of its hierarchical porosity and the restraint of the shuttle effect due to the SxLi … N interactions via the N lone-pair electron.

HPNACNTs-S composites, whose 1D directed conductive electron path and the graphitic layers inside the cavities offered superior electrical conductivity to facilitate fast electronic transport and enhance reaction kinetics of sulfur, and the macropores facilitated the electrolyte penetration, and the intertube space and opened central canal provided avenues for electrolyte diffusion and ion transport, and the micropores facilitate the immobilization of sulfur and its intermediate polysulfides, have been successfully synthesized at 155 °C for 10 h by a typical melt-diffusion method. The as-synthesized HPNACNTs-S composites can greatly enhance the electrochemical performance when used as cathode for lithium-sulfur batteries.Figure optionsDownload as PowerPoint slide