Synergistic Electrolyte Solvation and Mediation Engineering for Quasi-Solid-State Sulfur Electrochemistry

Lithium-sulfur (Li-S) batteries are currently hindered by the notorious polysulfide shuttling and lithium dendrite formation, despite their high theoretical energy density and low cost. These challenges are fundamentally rooted in the electrolyte chemistry, as the electrolyte environment critically influences both sulfur redox reactions and lithium plating/stripping behavior. Here, we report a synergistic electrolyte design that integrates solvation structure engineering and redox mediation to simultaneously address these bottlenecks. The well-designed siloxane-based electrolyte features a weakly solvating nature that enables an anion-rich Li+ solvation structure. This electrolyte design not only suppresses polysulfide dissolution through a quasi-solid-state sulfur reaction mechanism but also promotes stable lithium deposition to mitigate dendrite growth. Furthermore, isopropylxanthic disulfide (DIP) is introduced as a reaction mediator to chemically modulate sulfur conversion via targeted interactions with polysulfides. The resulting Li-S cells achieve superior electrochemical performance, exhibiting a specific capacity of 576.1 mAh g-1 at 4 C and 85% capacity retention after 100 cycles at 2 C. The 3 Ah and 6 Ah pouch cells fabricated under an ultralow electrolyte loading of 2 μL mg-1 deliver gravimetric energy densities of 391.7 Wh kg-1 and 453.8 Wh kg-1, respectively. This study presents a dual-functional electrolyte design that integrates solubility control with kinetic regulation, providing critical insights toward the development of practical Li-S batteries.