Polymerizable Ionic Liquid Crystals Comprising Polyoxometalate Clusters toward Inorganic-Organic Hybrid Solid Electrolytes.

Solid electrolytes are crucial materials for lithium-ion or fuel-cell battery technology due to their structural stability and easiness for handling. Emergence of high conductivity in solid electrolytes requires precise control of the composition and structure. A promising strategy toward highly-conductive solid electrolytes is employing a thermally-stable inorganic component and a structurally-flexible organic moiety to construct inorganic-organic hybrid materials. Ionic liquids as the organic component will be advantageous for the emergence of high conductivity, and polyoxometalate, such as heteropolyacids, are well-known as inorganic proton conductors. Here, newly-designed ionic liquid imidazolium cations, having a polymerizable methacryl group (denoted as MAImC₁), were successfully hybridized with heteropolyanions of [PW12O40]3- (PW12) to form inorganic-organic hybrid monomers of MAImC₁-PW12. The synthetic procedure of MAImC₁-PW12 was a simple ion-exchange reaction, being generally applicable to several polyoxometalates, in principle. MAImC₁-PW12 was obtained as single crystals, and its molecular and crystal structures were clearly revealed. Additionally, the hybrid monomer of MAImC₁-PW12 was polymerized by a radical polymerization using AIBN as an initiator. Some of the resulting inorganic-organic hybrid polymers exhibited conductivity of 10-4 S·cm-1 order under humidified conditions at 313 K.