Aqueous sulfur/carbon nanotube composite material and nanostructure for the cathode of lithium-sulfur batteries

Abstract

The use of multi-wall carbon nanotubes (CNTs) in lithium sulfur batteries (LSB) provides advantages of structural integrity (to account for volume expansion) and better electronic conductivity (to aid the insulating nature of sulfur active material), however, how to efficiently utilise CNTs remains elusive. Here, sulfur/CNT composites are synthesised via scalable melt diffusion and cathodes are fabricated by a sustainable aqueous approach. CNTs are used as the carbon host and carbon black C65 as the electrical additive. Different ratios of CNT (in the melt diffusion step) and C65 (in the cathode coating step) are investigated. The formation of C–S bonds and thiophene-like sulfur in the sulfur/CNT composite material during melt diffusion promotes redox reactions and mitigates polysulfide dissolution. The CNT host forms a hierarchical nanostructure covering a range of pore widths to promote sulfur infiltration into the CNT matrix and increase surface area and porosity, resulting in improved ion diffusion kinetics, polysulfide confinement, and better ability to accommodate sulfur volume changes during (dis)charging. The initial discharge capacity is 1350 mA h g−1 at 0.05 C with the cathode containing 17.5 wt% CNT (capacity based on the total mass of the cathode including both active and inactive materials) and the capacity maintains at 550 mA h g−1 at 1 C