Full-Range Redox Mediation on Sulfur Redox Kinetics for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li−S) battery is considered as a promising energy storage system because of its high theoretical energy density of 2600 Wh kg⁻¹, whose practical performance is limited by the sluggish sulfur redox kinetics. Homogeneous redox mediators (RMs) are effective promotors to propel the sulfur redox kinetics. However, most of the RMs only focus on a single reaction process. Herein, a strategy of mixed redox mediators (mixed-RM) is proposed for full-range redox mediation on the sulfur redox kinetics in working Li−S batteries. Concretely, one of the mixed-RM mainly mediates the liquid-solid reduction from polysulfides (LiPSs) to Li₂S during discharge, while the other aims to promote the solid-liquid conversion from Li₂S to LiPSs and the liquid-solid conversion from LiPSs to S₈ during charge. Consequently, 2.5 Ah Li−S pouch cells with the mixed-RM achieve an actual initial energy density of 354 Wh kg⁻¹ alongside stable 20 cycles. This work provides an effective strategy on promoting the sulfur redox kinetics for high-energy-density Li−S batteries and inspires rational combination of novel functional molecules for practical energy storage systems.