Photo-Initiated Cross-Linking of a Methacrylate/Ionic Liquid Based Gel Polymer Electrolyte: Effect of the Curing Sequence on the Electrochemical Properties

In\nthe present work, emphasis is given to the effect of the photocuring\nsequence on the electrochemical properties of a methacrylate/ionic\nliquid based gel polymer electrolyte (GPE). The reaction mixture consists\nof BEMA (30 wt %), LiTFSI (18 wt %), and PYR13TFSI ionic liquid (52 wt %) using Darocur1173 as photoinitiator.\nIn-situ photo-DSC analyses show that the radiation intensity has no\neffect on the final conversion rate (100% in all cases), whereas it\nconsiderably influences the polymerization rate and the final GPE\nstructure. Namely, the obtained GPE mechanical strength increases\nwith the radiation intensity (from 82 to 182 kPa). For the same initial\nprecursor solution, the GPE cured with the lower radiation intensity\npresents the highest ionic conductivity (up to +40%, 0.8 mS cm^–1 at 25 °C). The temperature dependence of the\nionic conductivity exhibits a VTF behavior for all considered cross-linking\nconditions. Particular attention is given to the investigation of\nthe transport properties in the GPE using diffusion measurements by\nnuclear magnetic resonance spectroscopy (PFG-NMR). It is found that\nfor the same initial precursor solution, the lower radiation intensities\ntend to provide low cross-linking density polymers with longer chains\nwhich lead to an ionic conductivity increase.