Ionogels based on ionic liquids as potential highly conductive solid state electrolytes

The preparation and properties of ionogels as potential highly conductive solid state electrolytes has been investigated. The ionogels have been prepared by a one-pot sol–gel synthesis using tetraethoxysilane (TEOS) in an ionic liquid, 1-butyl-3-methyl imidazolium tetrafluoroborate [BMIm][BF4]. The effect of silica content in the ionogels was characterized and analyzed in terms of chemical interactions, thermal stability and ionic conductivity. Immobilization of the IL in the silica network was observed even at high loading of IL (97 wt.%). Hydrogen bond networks between BF4− and the hydroxyl group in the silica was suggested as the mechanism of this immobilization, which was characterized by FTIR and solid-state NMR. TGA analysis shows that the prepared ionogels were stable up to around 450 °C, where a-final one-step degradation occurs. The ionic conductivity was found to decrease as the amount of silica increased. However, with high loading of IL (97 wt.%) the ionic conductivity was close to that of the pure IL. From the results obtained, these ionogels can be considered potential candidates for electrochemical devices where high ionic conductivity in solid state materials is desirable.