Deciphering Physical Versus Chemical Contributions to the Ionic Conductivity of Functionalized Poly(methacrylate)-Based Ionogel Electrolytes. Supporting Information
Tufts University, Department of Chemical and Biological Engineering Medford United States
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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 bistrifluoromethylsulfonylimide 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 ethacrylate TFEMA, or 2-dimethylaminoethyl methacrylate DMAEMA and a small amount of the cross-linker pentaerythritol tetra acrylate. 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 ionogels 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 ionogels electrolytes.