Poly(Ionic Liquid)\nElectrolytes at an Extreme Salt\nConcentration for Solid-State Batteries

Polymer-in-salt electrolytes were introduced three decades\nago\nas an innovative solution to the challenge of low Li-ion conductivity\nin solvent-free solid polymer electrolytes. Despite significant progress,\nthe approach still faces considerable challenges, ranging from a fundamental\nunderstanding to the development of suitable polymers and salts. A\ncritical issue is maintaining both the stability and high conductivity\nof molten salts within a polymer matrix, which has constrained their\nfurther exploration. This research offers a promising solution by\nintegrating cationic poly(ionic liquids) (polyIL) with a crystallization-resistive\nsalt consisting of asymmetric anions. A stable polymer-in-salt electrolyte\nwith an exceptionally high Li-salt content of up to 90 mol % was achieved,\nproviding a valuable opportunity for the in-depth understanding of\nthese electrolytes at an extremely high salt concentration. This work\nexplicates how increased salt concentration affects coordination structures,\nglass transitions, ionic conductivity, and the decoupling and coupling\nof ion transport from structural dynamics in a polymer electrolyte,\nultimately enhancing electrolyte performance. These findings provide\nsignificant knowledge advancement in the field, guiding the future\ndesign of polymer-in-salt electrolytes.