Sulfur-containing soft Lewis base polymers for improved lithium-ion conductivity under polymer-in-salt conditions

Abstract

Solid polymer electrolytes have been intensively studied to improve the safety and energy density of lithium-ion batteries (LiBs). Although high-rate performance of LiBs has been reported in electrolytes under polymer-in-salt conditions with an excess of lithium salts and polymers, effective conditions for achieving high ionic conductivity have been unresolved. In this study, we elucidated the mechanism and high Li-ion transportability of poly(sulfone-thioether) under polymer-in-salt conditions. In particular, the composition of the polymer with an asymmetric Li salt, lithium(fluorosulfonyl)(trifluoromethane sulfonyl)imide (LiFTFSI), induced a high ionic conductivity above 10−5 S/cm, which was higher than that of the poly(ethylene oxide) (PEO)-Li salt system. Under polymer-in-salt conditions, the enhanced conductivity of poly(sulfone-thioether) contrasts with the conductivity drop observed in the conventional PEO system. These results showed the superiority of polymers with soft Lewis bases, such as sulfur donor atoms, for Li-ion transport under polymer-in-salt conditions.