Unveiling the Ion Conduction Mechanism in Imidazolium-Based Poly(ionic liquids): A Comprehensive Investigation of the Structure-to-Transport Interplay

Polymerized ionic liquids (poly(ILs)) are considered highly promising for the realization of high-performance and intrinsically safer electrolytes for rechargeable batteries due to their high charge density. However, to date little is known about the ion conduction mechanism for this class of solid polymer electrolytes (SPEs). Herein, we performed an in-depth characterization of a homologous series of 1-alkyl-3-vinylimidazolium bis(trifluoromethane)sulfonimide-derived homopolymers, i.e., p(CnVIm-TSI) with n = 2, 4, 6, 8, and 10, serving as a model compound family. A particular focus was set on the interplay of the physicochemical properties, nanostructure, and ionic conductivity as well as on the impact of the additional incorporation of a lithium salt, LiTFSI. The results reveal that the nanostructure of these self-assembling poly(ILs) plays a decisive role for the ion conduction mechanism, allowing for a (partial) decoupling of charge transport and segmental relaxation of the polymer backbone.