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

摘要

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 90 wt%, the tap density of CNT/sulfur increased from 0.4 to 1.98 g cm~(-3), and the mass/areal/volumetric capacities of the whole electrodes (CNT/sulfur composites and binders) was improved from 500.3 mAh g~(-1)/0.298 mAh cm~(-2)/ 200.1 mAh cm~(-3) to 563.7 mAh g~(-1)/0.893 mAh cm~(-2)/1116.0 mAh cm-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.