Electrical, mechanical, structural, and thermal behaviors of polymeric gel electrolyte membranes of poly(vinylidene fluoride‐co‐hexafluoropropylene) with the ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate plus lithium tetrafluoroborate

Polymeric gel electrolyte membranes based on the polymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF- HFP)) with different weight percentages of the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate plus 0.3M lithium tet- rafluoroborate (LiBF4) salt were prepared and characterized by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, complex impedance spectroscopy, pulse echo techniques, and Vickers hardness (H) testing. After the incorporation of the IL plus the salt solution in the P(VdF-HFP) poly- mer, the melting temperature, glass-transition temperature (Tg), degree of crystallinity, thermal stability, elastic modulus (E), and hardness (H) gradually decreased with increasing content of the IL-salt solution as a result of complexation between the P(VdF- HFP) and IL. This was confirmed by FTIR spectroscopy. A part of the IL and LiBF4 were found to remain uncomplexed as well. The ionic conductivity (r) of the polymeric gel membranes was found to increase with increasing concentration of the IL-salt solution. The temperature-dependent rs of these polymeric gel membranes followed an Arrhenius-type thermally activated behavior. V C 2014