Enhanced immobilization and accelerated conversion of polysulfides by functionalized separator for advanced lithium sulfur batteries

Abstract

Lithium-sulfur (Li–S) batteries have attracted much attention due to high energy density and low cost. However, some vital issues, especially the notorious shuttle effect of polysulfides has greatly hindered the practical development of Li–S batteries. Reasonable design of electrocatalysts to improve the electrochemical performance of Li–S batteries by enhancing the chemical immobilization and catalytic conversion of polysulfides is considered as a promising solution. Herein, an integrated structure consisting of reduced graphene oxide (RGO) nanosheets modified with Co9S8 nanoparticles is reported, which is expected to be used as a mediator for Li–S batteries to improve the anchoring and catalyzing of polysulfides. The Co9S8 nanoparticles not only have excellent chemisorption capability to capture polysulfides, but also can be used as catalysts to accelerate the conversion of polysulfides. Highly conductive RGO nanosheets can provide appropriate ion/electron diffusion path length, facilitate interfacial reaction kinetics and physically limit polysulfide diffusion. Accordingly, the as-assembled Li–S battery has excellent cycling stability with a low capacity decay rate of 0.041% per cycle over 1000 cycles at 3 A g−1. Importantly, it enables the device to operate over a wide temperature range, with an area specific capacity of 6.4 mAh cm−2 at a sulfur load of 5.8 mg cm−2.