Design and characterization of one-dimensional carbon-based cathode for lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) battery has been pursued as the most promising high energy battery that alternates current lithium-ion batteries (LIB). In the virtue of a high theoretical specific capacity of elemental sulfur $(1,675 mAh g^{-1})$, the Li-S battery has a remarkable theoretical energy density (2,500 Wh $kg^{-1}$) which is ~7 times larger than that of LIB (387 Wh $kg^{-1}$). Despite their benefit, the Li-S battery suffers from the low conductivity of sulfur, volume expansion of cathode, and shuttle mechanism of polysulfide. An enormous number of carbon materials have been investigated to mitigate the obstacles. It has been reported that the zero-dimensional porous carbon particles have trouble with a contact resistance and limited pore volume, and the two-dimensional graphene has disadvantages of restacking and limited transport of lithium ion across the graphene sheets. Furthermore, a concern for high sulfur loading $(>3 mg cm^{-2})$ has rapidly grown to improve the practical performance of Li-S battery with a high areal capacity. Herein, we investigated two different composites consist of one-dimensional carbon materials such as carbon nanotube (CNT) or carbon nanofiber (CNF). Due to the benefits of the carbon network including high surface area per volume, great electron path and capillary action, both composite accomplished enhanced cycle performance and sulfur loading. The sulfur composite with CNT (CNT-S) achieved a high sulfur loading $(~6 mg cm^{-2})$ and retained stable reversible capacity over 650 mA h $g^{-1}$. The other sulfur composite with CNF (CNF-S) realized a superior sulfur loading $(>10 mg cm^{-2})$ with a good reversible capacity $(~700 mAh g^{-1})$. This values correspond to an outstanding areal capacity over 7 mAh $cm^-2 which surpasses that of recently reported lithium-ion batteries (1~3 mAh $cm^{-2}$) and it is meaningful performance to be practically used.