Boosting Li–S Battery Performance by Regulating Microstructures of Porous Hollow Carbon Nanospheres from Lignites

Abstract

Li–S batteries with high energy density are considered to be some of the most promising energy storage devices. However, the shuttle effect, sluggish kinetics, and volume expansion problems of lithium polysulfides (LiPSs) have severely limited their industrial applications. In this work, porous hollow carbon nanospheres (HCNSs) with tunable microstructures were designed by replacing resorcinol with an ethanol-soluble portion (ESP) from lignites rich in heteroatoms and alkyl side chains and employed as cathodes for Li–S batteries. The results show that the specific surface area, defect, and heteroatoms significantly increase after introducing ESP, thus promoting the adsorption and conversion of LiPSs. S@HCNS-30 exhibits the best electrochemical performance with a high initial discharge specific capacity of 1253.2 and 782.7 mAh·g–1 at 0.1C and 2C, respectively, and a low decay rate of 0.075% per cycle after 500 cycles, which is much superior to S@HCNS from pure resorcinol and many other coal- or biomass-derived carbon materials. In addition, a high discharge specific capacity of 659.9 mAh·g–1 was achieved under challenging conditions of a depleted electrolyte (E/S = 10 μL·mg–1) and high areal density (5.3 mg·cm–2). This work not only contributes to the high-value utilization of lignites but also provides a facile approach for high-performance cathodes for Li–S batteries.