Aligned carbon nanotube/sulfur composite cathodes with high sulfur content for lithium-sulfur batteries

The use of conductive carbon scaffolds is efficient and effective to obtain advanced composite cathodes for lithium-sulfur batteries. However, the loading amount of mostly less than 70 wt% induces a limited energy density and the typical fabrication route involving high-temperature and elaborate process also limits the manufacturability of sulfur cathode, both of which hinder the practical application of lithium-sulfur batteries. Herein, a scalable, room-temperature, and one-step method is employed for carbon nanotube (CNT)/sulfur composite cathode, in which aligned CNTs served as interconnected conductive scaffolds to accommodate sulfur. When the loading amount of sulfur increased from 50 to 90wt%, the tap density of CNT/sulfur increased from 0.4 to 1.98gcm^-3, and the mass/areal/volumetric capacities of the whole electrodes (CNT/sulfur composites and binders) was improved from 500.3mAhg^-1/0.298 mAhcm^-2/200.1mAhcm^-3 to 563.7mAhg^-1/0.893 mAhcm^-2/1116.0mAhcm^-3, respectively. The rise of sulfur content in the composite cathode renders a dramatic increase of the energy density of lithium-sulfur cells. The ultra-high loading amount of sulfur is attributed to the open, ordered, straight pore structure of aligned CNT scaffolds for the uniform distribution of fine sulfur particles. The robust sp² carbon frameworks served as rapid pathways for electron transfer, and the large aspect ratio, good alignment, ordered packing of individual CNT in small bundles offer a low conductive percolation threshold. Consequently, the sulfur with a high loading content was efficiently utilized for a lithium-sulfur cell with a much improved energy density.