Abstract
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.
Highlights
The development of highly-conductive solid electrolytes is crucial for innovative battery technology, such as lithium-ion and fuel-cell batteries [1,2,3,4], which are being applied to power sources of motor vehicles working at intermediate temperature of 373 to 573 K
MAImC1 -PW12 was revealed to be polymerized by a radical polymerization using AIBN as an initiator. Both hybrid monomer and polymers contained imidazolium moieties, and were expected to work as ionic or proton conductors [10,11,12,13,23]. These MAImC1 -PW12 hybrid monomer and polymers have an advantage to the generality on the selection of polyoxometalate anions and ionic liquid cations
The organic ionic liquid moiety can be flexibly designed in terms of organic syntheses, and the inorganic polyoxometalate anions can be variously selected, indicating more versatility than other polyoxometalate-polymer systems using polyoxometalate with the organic moiety grafted by covalent bonding [25,26,27,28,29,30,31,32,33,34,35,36]
Summary
The development of highly-conductive solid electrolytes is crucial for innovative battery technology, such as lithium-ion and fuel-cell batteries [1,2,3,4], which are being applied to power sources of motor vehicles working at intermediate temperature of 373 to 573 K. They demand highly-conductive solid electrolyte to overcome some drawbacks when used at Polymers 2017, 9, 290; doi:10.3390/polym9070290 www.mdpi.com/journal/polymers. Present solid electrolytes, to use proton-conducting fluorocarbon polymers (Nafion) exhibiting high conductivity only under date, humidified are insufficient in their conductivities
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