Photo-initiated crosslinking of a methacrylate/ionic liquid based gel polymer electrolyte: effect of the curing sequence on the electrochemical properties

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