Adaptive ionic moieties for electrolyte structural design

Abstract

Ionic liquids (ILs) are now an established and ubiquitous material class. In energy applications and electroresponsive lubrication, their interfacial self-assembly is crucial for their properties. This in turn is determined by chemical structure and a local hierarchy of Coulombic, van der Waals, and solvophobic interactions. We hypothesize that delocalization of the ionic charge permits the Coulombic interactions to adapt to other self-assembly imperatives, promoting both bulk and interfacial self-assembly structures and enhancing double layer responses. Novel chelated bis(catecholato)borate anion architectures are introduced, with [P66614] cations. Small/wide-angle x-ray scattering of the ILs indicates pronounced cation assemblies. In the electrolyte solvent propylene carbonate, small-angle neutron scattering shows marked anion-dependent self-assembly modulation. Neutron reflectivity reveals analogous response in the electrochemical double layer; the catechols form thicker and more electroresponsive interfacial layers. Density functional theory calculations demonstrate electronic resonance, modulating the anion polarizability. This direct self-assembly control broadly affects electrochemistry, lubrication, and formulation design.