Ion conducting polymer-silica hybrid ionogels obtained via non-aqueous sol-gel route

Abstract

One pot synthesis of high ion-conducting polymer based organic-inorganic hybrid ionogels via non-aqueous sol-gel route is being reported here. These hybrid ionogel films have been obtained using copolymer, poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), silica precursor, tetraethyl orthosilicate (TEOS), salt, lithium trifluoromethanesulfonate (LiTf) and ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIMTf). The use of non-aqueous sol-gel route facilitates the confinement of large amount of electrolyte solution in the hybrid matrix. The highest value of ionic conductivity achieved at room temperature for these hybrid ionogels (encompassing 65 wt% of electrolyte solution) is 3 mS/cm (comparable to that of liquid electrolyte), which is a desirable value for many electrochemical applications. Deconvolution of the ATR-IR spectra in the range 980–1100 cm−1 has provided information about the varying concentration of free ions (CF3SO3−) in the hybrid ionogels and evidence of ion-pair formation while the spectra in the 2900–3300 cm−1 range throws light on the interaction of the electrolyte solution (trapped in the organic-inorganic matrix) with the other constituents of the hybrid film (i.e., polymer and silica). These hybrid ionogels exhibit a wide electrochemical stability window (~4.63 V) and high thermal stability (~320 °C) along with increased amorphisity. The value of tLi+ has been found to be in the range. The value of tLi+ has been found to be in the range ~0.41 to 0.48 for all the films. The maximum value of tLi+ ~ 0.48 has been obtained for the hybrid ionogel film containing 60 wt% of electrolyte solution (PVdF-HFP/silica/ES-60). Mechanical properties indicate that higher amount of the electrolyte solution in the matrix reduces the mechanical strength. However, for films with same amount of electrolyte solution, the film without SiO2 has higher mechanical strength as compared to the one with SiO2.