Study On Preparation And Performance Of Gel Ionic Liquid-Polymer Electrolyte

Ionic liquids, due to their excellent properties, such as high ionic conductivity, immeasurably low vapor pressure, good thermal and electrochemical stability, benign to environment, are suitable for incorporation into polymers. The obtained ionic liquid-polymers afford the completely compatible combination of ionic liquid and polymer, so the safety and stability of batteries will be improved further. Evidently, the promising application foreground of them in lithium batteries and capacitors is brought forth. In this paper, several kinds of imidazolium ionic liquids, 1-ethyl-3-methylimida- zolium tetrafluoroborate (EMIBF₄), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄), 1-ethyl-3-methylimidazolium hexfluorophosphate (EMIPF₆) and 1-butyl-3- methyl-imidazolium hexfluorophosphate (BMIPF₆), were synthesized. Furthermore a series of ionic liquid-polymer electrolytes based on them were prepared. The main study contents were as follows:Firstly, several kinds of imidazolium ionic liquids were synthesized. Through selecting reaction solutions and improving synthesis technology of several imidazo- lium ionic liquids were optimized. The middle products, 1-ethyl-3-methylimidazolium bromide (EMIBr) and 1-butyl-3-methyl-limidazolium bromide (BMIBr), were synthesized used low poisonous ethylacetate. The method possesses some advantages, such as operating more easily and higher yield. The synthetic route of sodium salt- silver salt method was brought forward for the water-soluble ionic liquids. As a result, the synthetic cost was decreased under guaranteeing the purity of products.Secondly, two kinds of room-temperature ionic liquids, EMIBF₄ ,BMIBF₄ ,EMIPF₆ and BMIPF₆ were incorporated into copolymer P(VDF-HFP). Then the gel ionic liquid-polymer electrolytes were studied by FTIR, TG and electrochemical measurement. Analysis of FTIR spectra showed that there existed an interaction between ionic liquid and polymer matrix. The resulting ionic liquid-polymer electrolytes had higher decomposition temperatures(305℃) and ionic conductivities (10^-3 S/cm). And the temperature dependence of the ionic conductivity followed Arrhenius equation, which enhanced with increasing mass fraction of ionic liquid. The gel electrolytes prepared with ionic liquid EMIBF₄: P(VDF-HFP) mass ratio of 2:1 exhibited excellent ionic conductivity up to 3.67×10^-3 S/cm.Thirdly, in situ free radical polymerization of compatible vinyl monomers (methyl methacrylate, MMA) in a room temperature ionic liquid (1-butyl-3-methylimidazolium...