Homogeneous Redox Mediators Applied to Li–S Batteries

Lithium–sulfur (Li–S) batteries are promising as next‐generation energy storage, primarily due to their high theoretical specific energy density combined with a low‐cost cathode active material. However, incomplete sulfur utilization, polysulfide (PS) shuttling, sluggish redox kinetics, etc. still limit their practical performance. Employing homogeneous redox mediators (RMs) to the electrolyte is one strategy to improve charge transfer and facilitate key solid–liquid transitions. While both metallocene and quinone‐based RMs have shown promise, their reactivities with sulfur, PSs, and electrolyte components in general remain poorly understood. Here, we systematically investigate two metallocene RMs, decamethylferrocene (DmFc) and decamethylmanganocene (DmMn), and two quinone RMs, anthraquinone (AQ) and 1,4‐bis(methylamino)‐9,10‐anthraquinone (NHQ), across various Li–S battery designs including sulfur‐, PS catholyte‐, and Li ₂ S‐based active materials, and weakly solvating electrolytes. We show that the efficacy of these RMs is highly sensitive to sulfur speciation and electrolyte composition and that AQ is most versatile with suitable redox potential, high chemical stability, and efficient regeneration. Together, these findings provide guidelines for selecting RMs for specific Li–S battery technologies.