Preparation of nanohybrid solid-state electrolytes with liquidlike mobilities by solidifying ionic liquids with silica particles

The novel ion-conducting properties of nanohybrid materials consisting of ionic liquids and nanosized silica were investigated. The nanohybrid materials can be prepared by a simple mechanical milling process, and their compositions can be controlled over a wide range of ratios of ionic liquid to nanosized silica particles. Interestingly, the hybrid materials remain in the solid state even when as much as 90 wt % of the ionic liquid is incorporated in the matrix, provided that nanosized silica with a particle size of 7 nm is used. The hybrid materials exhibit large conductivities from room temperature to the intermediate temperature region. For example, the conductivity of a [BMIm][TFSI]/silica (7 nm) hybrid containing 60 wt % ionic liquid increased to 1 × 10 ^-2S cm^-1 at 300°C, although the solid hybrids were stable even at the intermediate temperatures. The nanosize confinement of liquid molecules within the silica particles is presumed to be responsible for the liquidlike conductivities in the solid phase and for the stability of the ionic liquids to fluidity and evaporation. Nanosize effects of the ionic liquid on the conducting properties were also demonstrated.