Effect of reduced graphene oxide reduction degree on the performance of polysulfide rejection in lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries are considered as a promising candidate for large-scale applications such as electrical vehicles (EVs) because of their high theoretical capacity, large energy density and low cost. However, due to the shuttling effect of polysulfides, the continuous capacity fading during cycling remains a substantial bumper for the practical use of Li-S batteries. Here, reduced graphene oxide (rGO) materials with different reduction degrees were used as the polysulfide inhibitor and were coated onto glass fiber separators to minimize the shutting of polysulfides. The influence of reduction degree on the effort of polysulfide rejection was investigated. The incorporation of rGO coating with higher reduction degree largely minimized the polysulfide shuttling, thus the Li-S cells with separators modified with high-reduction degree rGO was able to maintain a capacity of 733 mAh g−1 after 100 cycles and delivered a high capacity of 519 mAh g−1 at 2C, which were 42% and 90% higher than those of cells with separators coated with low-reduction degree rGO. Therefore, it was found that rGO with higher reduction degree demonstrated better polysulfide rejection performance than rGO with lower reduction degree. This study provides a promising strategy in the rGO selection for high-performance Li-S batteries.