A Quinonoid-Imine-Enriched Nanostructured Polymer Mediator for Lithium-Sulfur Batteries.

The reversible formation of chemical bonds has potential for tuning multi-electron redox reactions in emerging energy-storage applications, such as lithium-sulfur batteries. The dissolution of polysulfide intermediates, however, results in severe shuttle effect and sluggish electrochemical kinetics. In this study, quinonoid imine is proposed to anchor polysulfides and to facilitate the formation of Li2 S2 /Li2 S through the reversible chemical transition between protonated state (NH+ ) and deprotonated state (N). When serving as the sulfur host, the quinonoid imine-doped graphene affords a very tiny shuttle current of 2.60 × 10-4 mA cm-2 , a rapid redox reaction of polysulfide, and therefore improved sulfur utilization and enhanced rate performance. A high areal specific capacity of 3.72 mAh cm-2 is achieved at 5.50 mA cm-2 on the quinonoid imine-doped graphene based electrode with a high sulfur loading of 3.3 mg cm-2 . This strategy sheds a new light on the organic redox mediators for reversible modulation of electrochemical reactions.