Cooperation of Multifunctional Redox Mediator and Separator Modification to Enhance Li‐S Batteries Performance under Low Electrolyte/Sulfur Ratios
Weihua Jin, Yunpeng Guo, Taorong Gan, Zhengyuan Shen, Xuebing Zhu, Peng Zhang, Yong Zhao, Yong Zhao
Abstract
Abstract Sluggish reaction kinetics of sulfur species fundamentally trigger the incomplete conversion of S 8 ↔Li 2 S 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 2+ ) RM with two highly reversible redox couples (EtV 2+ /EtV + , EtV + /EtV 0 ) is demonstrated to well match the redox chemistry of sulfur species, in terms of accelerating the electron transfer in S 8 reduction, Li 2 S nucleation and the Li 2 S oxidation. When coupling with a functionalized separator with electronegative ‐SO 3 Li groups, a synergetic chemistry is established to ensure the substantial inhibition of the shuttle effect and the acceleration of charge transfer. As a result, the activation energies during sulfur species conversion (S 8 →Li 2 S 4 →Li 2 S/Li 2 S 2 →Li 2 S 4 →S 8 ) are decreased, especially for Li 2 S nucleation step. The correspond lithium‐sulfur batteries achieve a high specific capacity of 1006.9 mAh g− 1 (0.1 C; sulfur loading of 5 mg cm −2 ; E/S ratios of 6 μL mg s −1 ), and an outstanding cycling stability. This study provides a paradigm of solving complex problems via multifunctional molecule engineering and strategic cooperation towards Li−S batteries and other battery communities.