Regulating evolution of valence bonds on carbon surface to inhibit dissolution of polysulfides during production

Polysulfides (Li2Sx) have become key points that limit capacity improvement of lithium-sulfur batteries because of their high solubility. Oxygen-containing functional groups (such as C-O-H, C-O-C and C=O) can effectively relieve a large amount of polysulfide dissolution due to their strong polarity. However, their types and contents on polysulfide-capturing abilities are still unknown. Therefore, three kinds of electrodes containing different contents of hydroxyl (C-O-H), ether (C-O-C) and carbonyl (C=O) groups on carbon surface are controlled by changing pyrolysis times of dandelion. Electrochemical performance of lithium-sulfur batteries is tested to analyze influence of these groups on polysulfide-capturing abilities. It is discovered that C=O and C-O-H groups can obviously inhibit shuttle effects of polysulfides during their initial production. In addition, a large number of C=O bonds are converted to C-O-H bonds. More C-O-H bonds facilitate reversible capture of polysulfides and improve capacities. The introduction of C-O-C groups is not suitable for capturing more polysulfides rapidly and the appearance of ether groups limits conversion process of C-O-H groups. Both S load and discharging/charging process can effectively regulate evolution of three valence bonds, which is conducive to improving rate performance of lithium-sulfur batteries. (C) 2020 Elsevier Ltd. All rights reserved.