Beyond Boundaries: Redox Mediators as Dynamic Charge Carriers and Catalytic Hubs for Efficient Sulfur Conversion in Solid‐State Lithium–Sulfur Batteries

ABSTRACT Despite the exceptionally high theoretical energy density of all‐solid‐state lithium–sulfur batteries (ASSLSBs), their practical performance is severely limited by discontinuous interfacial contact and sluggish transport of electrons and lithium ions. These issues cause accumulation of locally electrochemically inactive sulfur, resulting in electrode passivation and uneven reaction distribution, which are critical bottlenecks to performance improvement. In recent years, redox mediators (RMs) have garnered significant attention due to their ability to effectively regulate complex multiphase reaction processes in liquid‐phase lithium–sulfur (Li–S) systems. However, whether RMs can enable efficient and closed‐loop redox cycling under solid–state conditions remains a central challenge. To address this issue, this review systematically summarizes and compares sulfur conversion pathways across different electrolyte systems, with a particular focus on the mechanistic roles of RMs in regulating the transformation of sulfur species in ASSLSBs. It further discusses the relationship between the molecular structures of representative RMs and their electrochemical performance. The key scientific problems and engineering challenges currently facing the field are identified. The review outlines future directions for molecular designs of tunable RMs and a deeper understanding of redox mechanisms in solid–state environments to provide theoretical guidance and design strategies for high–performance ASSLSBs.