Cooperation of Multifunctional Redox Mediator and Separator Modification to Enhance Li-S Batteries Performance under Low Electrolyte/Sulfur Ratios.

Sluggish reaction kinetics of sulfur species fundamentally trigger the incomplete conversion of S↔LiS and restricted lifespan of lithium-sulfur batteries, especially under high sulfur loading and/or low electrolyte/sulfur (E/S) ratios. Developing redox mediators (RMs) is an effective strategy to boost the battery reaction kinetics, yet their multifunctionality and shuttle inhibition are still not available. Here, a unique ethyl viologen (EtV) RM with two highly reversible redox couples (EtV/EtV, EtV/EtV) is demonstrated to well match the redox chemistry of sulfur species, in terms of accelerating the electron transfer in S reduction, LiS nucleation and the LiS oxidation.