Deciphering Physical versus Chemical Contributions to the Ionic Conductivity of Functionalized Poly(methacrylate)-Based Ionogel Electrolytes

Abstract

Polymer-supported ionic liquids (ionogels) are emergent, nonvolatile electrolytes for electrochemical energy storage applications. Here, chemical and physical interactions between the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI) and three different cross-linked polymer scaffolds with varying chemical functional groups have been investigated in ionogels fabricated via in situ UV-initiated radical polymerization of methyl methacrylate (MMA), 2,2,2-trifluoroethyl methacrylate (TFEMA), or 2-(dimethylamino)ethyl methacrylate (DMAEMA) and a small amount of the cross-linker pentaerythritol tetraacrylate. Experimental findings demonstrate that the chemical functionality of the polymer side groups can significantly affect the degree of ion dissociation within the ionic liquid component of the ionogel and that the fraction of dissociated ions is the dominant factor in determining relative ionic conductivity in these materials, rather than any large differences in ion diffusivity. The MMA-based polymer scaffold exhibits a stronger attractive interaction with EMI TFSI (as evidenced by a higher activation energy of ionic conductivity) compared to the TFEMA- and DMAEMA-based scaffolds, resulting in consistently lower ionic conductivity values for MMA-based ionogels. These results may offer guidance toward the rational selection of future polymer-ionic liquid pairings in order to maximize the fraction of dissociated ions, thereby yielding highly conductive ionogel electrolytes.

Chemically Cross‐Linked Poly(2‐hydroxyethyl methacrylate)‐Supported Deep Eutectic Solvent Gel Electrolytes for Eco‐Friendly Supercapacitors

“…PGSE NMR spectroscopy is a powerful experimental technique used to quantify the molecular self‐diffusion of species in liquid mixtures or liquid‐rich gels, and it has been broadly applied to measure the mobility of ions in both DESs and ILs in several previous studies ,,. Here, PGSE NMR spectroscopy was employed to measure the diffusivities of both the choline cation (Ch + ) and ethylene glycol (EG) in several DES gel electrolytes, as well as in the neat DES.…”

“…The molecular structures of the polymer scaffold‐forming materials used here (HEMA and PEGDA) are displayed in Figure (c). HEMA was selected due to the facile nature of methacrylate free radical polymerization in ionic liquids and its −OH functional group, which was expected to facilitate its good miscibility with the DES. Indeed, no HEMA/DES solubility issues were observed during this investigation (up to 50 wt.% HEMA added to the DES).…”

First examples of organosilica-based ionogels: synthesis and electrochemical behavior

“…The slight deviation between the energy of activation and the energy of dielectric relaxation is probably due to the inner structure with the migration in the vicinity of silicate walls compared to the porous structure, as already observed in other composites [55]. The relative ion conductivity considering the physical versus chemical contributions was recently addressed in polymer-ionic liquid pairing [56]. …”

Zwitterionic Copolymer‐Supported Ionogel Electrolytes: Impacts of Varying the Zwitterionic Group and Ionic Liquid Identities

“…[34] While the mobile ion concentration is easily controlled within aqueous electrolytes featuring well-solvated ions, it is known that extensive ion pairing or clustering can limit the number of effectively mobile ionic species within highly ion-dense ionic liquid electrolytes. [25] Due to their extremely large dipole moments, [37] zwitterionic (ZI) moieties have been demonstrated to interact strongly with ions and promote ion pair dissociation, boosting electrolyte ionic conductivity, [38][39][40][41] which makes ZI (co)polymers especially interesting scaffold materials for gel electrolytes. [25] Due to their extremely large dipole moments, [37] zwitterionic (ZI) moieties have been demonstrated to interact strongly with ions and promote ion pair dissociation, boosting electrolyte ionic conductivity, [38][39][40][41] which makes ZI (co)polymers especially interesting scaffold materials for gel electrolytes.…”