Modified electron structure of CNT-CoSe2 (vs. CoSe2) with more Co2+ for improving catalytic effect in lithium sulfur batteries

Abstract

Currently, the great challenge of lithium sulfur (Li-S) batteries is the sluggish redox kinetics and the ineludible shuttle effect, which induce the rapid capacity fading. Regulating the electron structure of metal-based catalysts is regarded as a significant strategy to improve the catalytic effect of Li-S batteries, for accelerating the redox kinetics and enhancing the cathode performance. In this work, the valence of Co in CoSe2 is regulated by introducing carbon nanotube (CNT) during the preparation of ZIF-67. Compared with CoSe2, the ratio of Co2+/Co3+ increases, which boost the catalytic activity of CNT-CoSe2 both in discharging and charging process. Furthermore, the ratio of Co2+/Co3+ is reduced after discharging due to the electron transfer to sulfur species, and the ratio is increased again due to the inverse electron transfer. As a result, the CNT-CoSe2 with better catalytic properties endows the corresponding Li-S batteries more stable cycling performance, especially at high current density or high sulfur loading. The CNT-CoSe2 modified separator can endow Li-S batteries with a discharge capacity of 735.49 mAh g−1 at 2 C, and a retention ratio of 72.28% for 200 cycles at 0.1 C with sulfur loading of 4.60 mg cm−2.