CoS2-NC@CNTs hierarchical nanostructures for efficient polysulfide regulation in lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries have received extensive attention in electrochemical energy storage systems due to their high theoretical energy density as well as natural abundance of sulfur and low cost. However, Li-S batteries exhibit rapid capacity decay and inferior rate performance due to polysulfides (LiPSs) shuttling and sluggish redox kinetics. Therefore, it is crucial that LiPSs are anchored and their conversion reactions are catalyzed in order to improve the performance of Li-S batteries. In this work, ZIF-67-derived carbon polyhedra decorated with ultrafine CoS2 nanoparticles are interconnected by carbon nanotubes (CNTs). The uniformly distributed CoS2 nanoparticles can immobilize LiPSs and catalyze their conversion of solid-to-liquid-to-solid reactions, which enhances the redox kinetics. Furthermore, the three-dimensional conductive network consisting of ZIF-67-derived carbon polyhedra and CNTs facilitates fast electron transport and thus leads to excellent rate and cycling performance. The cells were assembled using CoS2-NC@CNTs-pp and show a high initial discharge capacity of 1408.5 mAh g−1 at 0.1 C and 1186.7 mAh g−1 at 1 C, and they remain outstanding cycling stability for over 500 cycles. Even at a high C rate of 5 C, it still can deliver a high discharge capacity of 832.6 mAh g−1. This work provides an efficient route to accelerate redox conversion and suppress the shuttle effect by designing a multifunctional separator.