Facile preparation of flexible porous carbon fibers as self-supporting sulfur cathode hosts for high-performance Li-S batteries.

Abstract

Lithium-sulfur batteries are expected to be prospective candidates of high-energy-storage systems due to their high theoretical specific capacity. However, poor electrical conductivity, severe polysulfide shuttle effect and low sulfur utilization generally cause inferior electrochemical performance, hence hindering the practical development. In this study, common makeup cotton derived self-supporting porous carbon fibers (SPCFs) are prepared by a facile simultaneous activation/pyrolysis process accompanied by the effectively regulation of a KHCO3activator. The as-prepared SPCF materials have mutually cross-linked porous skeletons with an ultrahigh specific surface area of 2124.9 m2 g-1 and a large pore volume of 1.01 cm3 g-1, whilst exhibiting robust flexibility. When directly used as a self-supporting carbon current collector for encapsulating sulfur, the interconnected and abundant porous carbon fibers can not only immobilize soluble polysulfides, but also form a highly conductive network for the favorable redox transformation of adsorbed polysulfides. Moreover, the voids between the carbon skeletons can alleviate the volume change of sulfur cathodes during charge/discharge. Owing to these structure merits, the optimized SPCF-based sulfur cathode with a sulfur loading of 3.0 mg cm-2 shows a high coulombic efficiency of approximately 99% and delivers a first discharge capacity of 778 mA h g-1 at 0.2 C. Even at a relatively high current rate of 0.5 C, the reversible capacity of 450 mA h g-1 can be obtained after 300 cycles. The above-mentioned self-supporting porous carbon current collectors provide a guidance for high-performance lithium-sulfur batteries.