Gel electrolytes based on crosslinked tetraethylene glycol diacrylate/poly(ethylenimine) systems

Gel electrolytes were prepared by crosslinking low molecular weight poly(ethylenimine) (PEI) with tetraethylene glycol diacrylate (TEG) in the presence of 2-methoxyethyl ether (diglyme) and lithium triflate (LiTf). Impedance and infrared (IR) spectroscopies were used as complimentary tools for studying the mode of ion conduction in these gel electrolytes. Ionic conductivity measurements for all samples tested exhibited significant LiTf and diglyme composition dependency. The maximum ionic conductivity at 20 °C was 2×10⁻⁴ S/cm with moderate LiTf and high diglyme compositions. The calculated molal concentration of non-ionically bound ‘free’ triflate ion was found to vary directly with ionic conductivity with the highest molality ‘free’ triflate samples yielding the highest ionic conductivity. Lithium ion interactions with the triflate ion, diglyme and the crosslinked polymer matrix were observed with IR spectroscopy. A lower frequency shoulder on the v_s(CO) vibrational mode increases in intensity as LiTf composition is increased. Curve fitting and molar calculations suggest that over 85% of the total lithium ions available are coordinated to the TEG carbonyl at dilute LiTf compositions.