Sulfur Embedded in a Mesoporous\nCarbon Nanotube Network\nas a Binder-Free Electrode for High-Performance Lithium–Sulfur\nBatteries

Abstract

Sulfur-porous\ncarbon nanotube (S-PCNT) composites are proposed\nas cathode materials for advanced lithium–sulfur (Li–S)\nbatteries. Abundant mesopores are introduced to superaligned carbon\nnanotubes (SACNTs) through controlled oxidation in air to obtain porous\ncarbon nanotubes (PCNTs). Compared to original SACNTs, improved dispersive\nbehavior, enhanced conductivity, and higher mechanical strength are\ndemonstrated in PCNTs. Meanwhile, high flexibility and sufficient\nintertube interaction are preserved in PCNTs to support binder-free\nand flexible electrodes. Additionally, several attractive features,\nincluding high surface area and abundant adsorption points on tubes,\nare introduced, which allow high sulfur loading, provide dual protection\nto sulfur cathode materials, and consequently alleviate the capacity\nfade especially during slow charge/discharge processes. When used\nas cathodes for Li–S batteries, a high sulfur loading of 60\nwt % is achieved, with excellent reversible capacities of 866 and\n526 mAh g^–1 based on the weights of sulfur and electrode,\nrespectively, after 100 cycles at a slow charge/discharge rate of\n0.1C, revealing efficient suppression of polysulfide dissolution.\nEven with a high sulfur loading of 70 wt %, the S-PCNT composite maintains\ncapacities of 760 and 528 mAh g^–1 based on the weights\nof sulfur and electrode, respectively, after 100 cycles at 0.1C, outperforming\nthe current state-of-the-art sulfur cathodes. Improved high-rate capability\nis also delivered by the S-PCNT composites, revealing their potentials\nas high-performance carbon–sulfur composite cathodes for Li–S\nbatteries.