Elaborate interface design of CoS2/Fe7S8/NG heterojunctions modified on a polypropylene separator for efficient lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered as the most promising energy storage system due to their high specific capacity and resource abundance. However, the low electronic conductivity of S8 and Li2S, shuttle effects of lithium polysulfides (LiPSs), and sluggish reaction kinetics hinder the advance of Li-S batteries. The key to addressing the issues mentioned above is to improve the electrical conductivity of the cathode, enhance the absorption of LiPSs and accelerate the conversion. Nevertheless, it is a great challenge to simultaneously optimize them all. In this study, by incorporating the virtues of the large lamellar structure and strong nonpolar adsorption of reduced graphene oxide (rGO), strong polar polysulfide adsorption of Fe7S8 and excellent catalytic polysulfide activity of CoS2, a CoS2/Fe7S8 heterostructure grown on the nitrogen-doped rGO (CoS2/Fe7S8/NG) was prepared. Besides, the experiments demonstrate that the designed CoS2/Fe7S8/NG possesses strong absorption and superior catalytic ability towards LiPSs. Subsequently, when applied as a modification layer for the polypropylene (PP) separator, the CoS2/Fe7S8/NG-PP coupled with CNT/S cathode exhibits a high initial discharge capacity (1459 mAh g−1 at 0.1 A g−1), a reversible capacity of 731 mAh g−1 after 100 cycles at 0.2 A g−1, and a robust cycling stability (0.058 % flowing rate at 1.0 A g−1). Moreover, the cathode with a high sulfur mass loading of ∼ 3.8 mg cm−2 can still display a reversible capacity of 663 mAh g−1 after 100 cycles at 0.2 A g−1. More importantly, the study shown herein shed light for the design of heterojunction to improve the electrochemical performance of Li-S batteries.