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Electrical and spectroscopic characterization of PVdF-HFP and TFSI-ionic liquids-based gel polymer electrolyte membranes. Influence of ZnTf<inf>2</inf> salt

Abstract:

Three different ionic liquids (ILs), 1-ethylpyridinium bis(trifluoromethylsulfonyl)imide (EPy TFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI), and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide (P6,6,6,14 TFSI), with the same anion, TFSI-, were added, with or without ZnTf2 salt, to the host polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) in order to obtain Gel Polymer Electrolytes (GPEs). The incorporation of IL or IL+ZnTf2 salt to the polymer produces more amorphous and more ionic membranes when compared to pristine PVdF-HFP films. Ionic conductivity values, impedance spectra, dielectric measurements, voltammograms and results of potential stability depend clearly on the IL cation type used in the GPE. Also, the incorporation of ZnTf2 salt inside the film increased the ionic conductivity for all GPEs, which can be related to the existence of free triflate anions. The participation of Zn2+ cations on the conduction process has been demonstrated by cyclic voltammetry and EDX measurements. Among the six GPEs analyzed, the PVdF-HFP+EMIM TFSI+ZnTf2 membrane exhibits the best results: maximum value of ionic conductivity, 1.73×10-1Sm-1, low activation energy value, and a highly reversible and high current density voltammetric behavior. © 2014 Elsevier B.V.