Effect of morphological variation in three-dimensional multiwall carbon nanotubes as the host cathode material for high-performance rechargeable lithium–sulfur batteries

Abstract

Lithium–sulfur batteries (LSBs) demonstrate potential as next-generation energy storage systems due to the high theoretical capacity and energy density of the sulfur cathode (1672 mAh g⁻¹ and 2600 W h kg⁻¹, respectively) in addition to the low-cost, natural abundance, and environmentally benign characteristics of sulfur. However, the insulating nature of sulfur requires an efficient conductive and porous host material such as three-dimensional carbon nanotubes (3D CNTs). Identifying parameters that provide high conduction pathways and short diffusion lengths for Li-ions within the CNT structure is essential for a highly efficient CNT-S cathode in a LSB. Herein, the effect of morphological variation in 3D CNTs as a sulfur host material is studied, and parameters that affect the performance of a CNT-S cathode in LSB are investigated. Four different 3D CNTs are synthesized via the chemical vapor deposition (CVD) technique that vary in specific surface area (SSA), CNT diameter, pore sizes, and porosity. The superior 3D CNT-S (CNT-S-50) cathode, which possessed high surface area and porosity as compared to the rest of the 3D CNT-S cathodes, with ∼38 wt% (6.27 mg cm⁻²) sulfur loading, demonstrated an areal and specific discharge capacity of 8.70 mAh cm⁻² and 1387 mAh g⁻¹ at 0.1C, respectively. Results from this work demonstrate that the combination of high surface area and porosity are two crucial parameters in 3D CNTs as an efficient sulfur host material for LSB cathodes.