| Research Abstract |
Ion-conducting materials are essential for electrochemical energy-storage and energy-conversion devices, such as batteries, capacitors, fuel cells, and solar cells. Recently, the ion-conducting materials are also utilized in soft actuators that can be applicable to medical use, micro-machine, and nano-technology, Conventionally, electrolyte solutions have been used as the ion-conducting materials. For instance, Sulfuric acid is used for lead-acid car batteries, flammable organic electrolyte solutions are used for lithium-ion batteries that are main power source of cellar phones and lap-top computers. As a result, the most of the electrochemical devices are not solid devises but liquid devices that include volatile liquids. Thus, it has been a subject of many researchers to make the ion-conducting materials non-volatile, non-flammable, and solid.
Ionic liquids are room temperature molten salts and of great interest as new electrolyte materials, because of their unique properties such as
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non-volatility, non-flammability, thermal and chemical stability, high ionic conductivity, and wide potential window. We have directed out attention to the combination of the ionic liquids and polymers as new polymer electrolytes and proposed that in situ radical polymerization of common vinyl monomers in these ionic liquids affords compatible combinations of the ionic liquids and the resulting network polymers. Completely compatible combinations are new polymer electrolytes and named "ion gels" that are solid electrolytes with the characteristic properties of the ionic liquids. If task-oriented properties are molecularly designed in the ionic liquids, he scope of the utility of ionic liquids and ion gels may greatly expand. In this project we have aimed at exploring the following fundamental and task-oriented properties.
1)Ion dynamics in ionic liquids and ion gels
2)Design of anhydrous proton-conducting ionic liquids and their ion gels that are stable at the temperatures higher than 100℃
3)Design of mixed-conducting ionic liquids and their ion gels that can conduct both ions and electrons
The ion dynamics has been mainly explored by using PGSE-NMR technique combined with electrochemical impedance technique. From the diffusivity for both of the cations and anion, consisting the ionic liquids, from he NMR, the ionic conductivity can be calculated from Nernst-Einstein equation (λ_<NMR>), while he experimental conductivity (λ_<imp>) can be obtained by the impedance measurements. We newly proposed that the ratio, λ_<NMR>/λ_<imp>, could be a measure of he state-of ions in the ionic liquids. As for the design of he anhydrous proton conducting ionic liquids, we have found for he first time that novel Bronsted acid-base ionic liquids, derived from a simple combination of a wide variety of organic amines with bis(trifluoromethane sulfonyl)imide, are anhydrous proton conductors, following the combination of the vehicle and Grotthuss mechanisms. Electrons are also mobile in the ionic liquids when a redox couple is dissolved in them at a high concentration. We have revealed that charge transport of an I^-/I_3^-redox couple in an ionic liquid nonlinearly increases with increasing the concentration by using microelectrode technique. This anomaly of the charge transport at high concentrations of the redox couple with comparable [I^-] and [I_3^-] can be attributed to the exchange reaction of I^-+I_3^-→I_3^-+I^-. Less
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