Surface-localized phase mediation accelerates quasi-solid-state reaction kinetics in sulfur batteries

Lithium-sulfur batteries promise high energy density storage but show poor stabilities owing to uncontrolled polysulfide dissolution. Although limiting polysulfide solvation to establish quasi-solid-state sulfur reaction can decouple electrode reactions from the electrolyte volume, this approach suffers from slow reaction kinetics. Here we propose a surface-localized polysulfide-solvation strategy to mediate the reaction of 'quasi-solid' polysulfide by leveraging an organic phase mediator with a weakly solvating electrolyte. This electrolyte restricts polysulfide dissolution globally while the phase mediator complexes with the surface polysulfide, promoting polysulfide solvation at the surface and facilitating fast surface-localized solution-phase sulfur reactions. Lithium-sulfur batteries using surface-localized phase mediation show excellent rate performance with 494 mA h g^-1_-sulfur at 16 C and stabilized cycling for 300 cycles with 90.2% capacity retention. The strategy enables steady operation of a 2.4 Ah 331 Wh kg^-1 pouch cell. Our work highlights the advantages of surface phase mediation in controlling electrode reaction pathways and kinetics via electrolyte rational design.