Hierarchical free-standing carbon-nanotube paper electrodes with ultrahigh sulfur-loading for lithium-sulfur batteries

The rational combination of conductive nanocarbon with sulfur leads to the formation of composite cathodes that can take full advantage of each building block; this is an effective way to construct cathode materials for lithium-sulfur (Li-S) batteries with high energy density. Generally, the areal sulfurloading amount is less than 2.0 mg cm ^-2, resulting in a low areal capacity far below the acceptable value for practical applications. In this contribution, a hierarchical free-standing carbon nanotube (CNT)-S paper electrode with an ultrahigh sulfur-loading of 6.3 mg cm ^-2 is fabricated using a facile bottom-up strategy. In the CNT-S paper electrode, short multi-walled CNTs are employed as the short-range electrical conductive framework for sulfur accommodation, while the super-long CNTs serve as both the long-range conductive network and the intercrossed mechanical scaffold. An initial discharge capacity of 6.2 mA·h cm ^-2 (995 mA·h g ^-1), a 60% utilization of sulfur, and a slow cyclic fading rate of 0.20%/cycle within the initial 150 cycles at a low current density of 0.05 C are achieved. The areal capacity can be further increased to 15.1 mA·h cm ^-2 by stacking three CNT-S paper electrodes - resulting in an areal sulfur-loading of 17.3 mg cm ^-2 - for the cathode of a Li-S cell. The as-obtained free-standing paper electrode are of low cost and provide high energy density, making them promising for flexible electronic devices based on Li-S batteries.