Interaction between Zn2+ cations and n-methyl-2-pyrrolidone in ionic liquid-based Gel Polymer Electrolytes for Zn batteries

Gel Polymer Electrolytes (GPEs) composed by 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM TFSI), ZnTf2 salt, and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) are synthesized using n-methyl-2-pyrrolidone (NMP) as solvent. Structural and Thermal characterization of GPEs with different ZnTf2 concentrations are analyzed by ATR-FTIR, XRD, DSC and TG. Ionic conductivity versus temperature plots obeys the Vogel-Tammen-Fulcher (VTF) behavior and activation energy values are deduced from the slopes. Use of NMP solvent turns out to be a key factor for improving the Zn2+ transport inside the GPE due to the interaction between Zn2+ cations and carbonyl groups of the NMP. High values of ionic conductivity and low activation energy values, together with the high reversibility and high current density obtained in the voltammograms reveal these GPEs as good candidates to be used in Zn batteries. Furthermore, ionic liquids-based GPEs are probed in Zn/MnO2 batteries, resulting specific capacities of 125 mAh g−1.