Preparation Of Gel Electrolytes Based On Ionic Liquids And Their Electrochemical Behavior

Due to their unique properties, such as low volatility, non-flammability, high thermal stability, wide electrochemical window and excellent conductivity, ionic liquids （ILs） have shown broard application prospects in various fields, like lithium secondary batteries, actuators, fuel cells and so on. However, it should be noted that devices based on ionic liquids are still demonstrating leakage problems in practical use, as ionic liquid （IL） is a kind of liquid. Thus to employ ILs in real application, it is preferable that the ILs are solidified without disrupting their unique properties. Moreover, such solidification can enhance the performance, safety, long-term stability, and reliability of the devices. As kinds of solidified ILs, ionogles and poly（ionic liquid）s have been intensively studied and are popular research topics. As two important branches of ILs, ionogles and poly（ionic liquid）s have shown broarder application prospects in practice compared with ILs.In this dissertation, we carried out the following works:（1） Fabrication of supermolecular ionogels via metal coordination interactions and characterized their properties as solid electrolytes. （2） Preparation of a novel kind of poly（ionic liquid）s hydrogels with excellent mechanical properties and characterized their properties as flexible electrolytes. The whole paper contains three sections, which are summarized as following:Section Ⅰ:Briefly introduced the research background and applications of ionic liquids, ionogels and poly（ionic liquid）s.Section Ⅱ:A facile strategy to prepare supramolecular conducting ionogels was developed based on two commercially available and inexpensive compounds: benzenetricarboxylic acid （H₃BTC） and iron（III） nitrate nonahydrate （Fe（NO₃）₃9H₂O）. Gelators can form stable ionogels in bmimBsa and bmimCl via metal coordination interaction within several seconds. Via this method, the time required for producing ionogels was reduced significantly. The prepared ionogel Fe-H₃BTC-bmimBsa can even remain in the gel state at 150℃. This is the first example of a supramolecular conducting ionogel prepared by low molecular weight gelators that can remain in the gel state at such a high temperature. The high gel-sol transition temperature of the ionogel Fe-H₃BTC-bminBsa may result from the strong π-π stacking interaction between the scaffolds and the ionic liquids. The high thermal durability were further characterized by TG and DSC. Then, we investigated the microstructures of these ionogels and their formation mechanisms. Moreover, these supramolecular ionogels exhibited high conductivity and relatively low activation energy characterized by impedance analysis. These results help to promote the applications of supramolecular ionogels in the area of the electrolyte.Section Ⅲ:One-step synthesis of poly（ionic liquid） hydrogel electrolytes was developed. Both cations and anions of these ionic liquids contained carbon-carbon double bonds and can be polymerized. To the best of our knowledge, this is the first work on preparing hydrogels based on poly（ionic liquid）s with polymerized cations and anions. The FT-IR and SEM were used to certify the successful polymerization of double bonds, and the compressive tests and impedance analysis were used to characterize their mechanical and electrochemical properties, respectively. The presence of strong and weak crosslinks made these hydrogels tough, stretchable, flexible and self-recoverable. Notably, these poly（ZIW/AMPS） hydrogels exhibited superior electrochemical properties, which could remain stable under different bending angles and successive bending, folding, compressing and twisting. We believe that these poly（ionic liquid） hydrogel electrolytes will facilitate the development of high-performance flexible energy storage and conversion devices and thus boost the advent of next-generation flexible electronic devices.