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

Abstract

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. Lithium–sulfur batteries are a promising electrochemical energy storage technology; however, they are limited by the dissolution of polysulfide intermediates. Now, it has been shown that sparingly solvating electrolytes containing a phase mediator can avoid polysulfide dissolution and accelerate surface-localized solution-phase sulfur reaction to improve battery performances.