Preparation Of Functional-imidazoled Ionic Liquids And Their Ultracapacitor Properties Study

In recent years, ionic liquids are viewed as “Green designer solvent for future”. The uniquephysicochemical properties of ionic liquids have attracted increasing interests due to their potentialapplications in various areas. Imidazoles ionic liquid is currently the best comprehensive performance ofionic liquids.Ionic liquids are manufactured by the modification of cationic or are changed anionicfunctional to be adjusted. We still can design and synthesize special functional groups ionic liquids to meetspecial various needs. Synthetize of special functional ionic liquid has gradually become the hot spot in thestudy of ionic liquid all over the world.Supercapacitor is a new environmental energy storage device, and has some important electrochemicalparameters, such as the rated voltage, charge/discharge efficiency, and cycle life etc. In order to adapt to theinvestigation and production of supercapacitors with large specific capacity and power, the research anddevelopment of high-performance electrolyte is the important alternative method. So, we design andsynthesize a series of functional-imidazoled ionic liquid（salt）and researched their properties and applicationas a electrolyte for supercapacitor. Our research work were focused on three aspects as follow:1. We synthesized an amino acid ionic liquid [Bmim]Asp （1-butyl-3-methylimidazole aspartate） and aseries of new type of alkyl imidazole ionic liquid. They were [Pmim]HCO₃（1-propyl-3-methylimidazolehydrogen carbonate）、[Bmim]HCO₃（1-butyl-3-methylimidazole hydrogen carbonate）、[Amim]HCO₃（1-pentyl-3-methylimidazole hydrogen carbonate）、[Pmim]H₂PO₄（1-propyl-3-methylimidazole dihydrogenphosphate）、[Bmim]H₂PO₄（1-butyl-3-methylimidazole dihydrogen phosphate）、[Amim]H₂PO₄（1-pentyl-3-methylimidazole dihydrogen phosphate）、[Pmim]SCN（1-propyl-3-methylimidazolethiocyanate）、[Bmim]SCN （1-butyl-3-methylimidazole thiocyanate）、[Amim]SCN（1-pentyl-3-methylimidazole thiocyanate），They were characterized by FT-IR,1HNMR andthire structure were confirmed accordingly.2. Thire physical properties，such as density，surface tension and viscosity is measured at differenttemperatures. According to the results, with the temperature increasing，the density and viscosity becomesobviously lower, while surface tension slightly decline. The length of Cationic alkyl chain significantlyeffects the physicochemical properties of ionic liquids. The chain alkyl cationic with the increase of CH₂will result in density and surface tension of ionic liquids reduce, viscosity increases. Therefore, changinglength of the cationic alkyl chain or the structure of cationic size may control the physicochemical properties of ionic liquids.3. These ionic liquids act as liquid electrolytes, respectively. Then the simulated supercapacitorthree-electrode electrochemical systems were assembled.The electrochemical analysis of the simulatedsupercapacitor was examined using AC impedance, cyclic voltammetry, and constant currentcharging/discharging tests. The tests results can provide valuable references for the preparation andassembly of products. According to the results, these electrolytes has the better electrochemistryperformance. The electrochemical window of these electrolytes in supercapacitor has reached to4.0V.Among these, when the voltage is3.3V, the single-electrode capacity of the supercapacitor based on[Amim]SCN electrolyte was as high as421.05F/cm³. The charge-discharge efficiency was96.3%.Compared with the initial capacitance, the supercapacitor capacitance weakened by2%after300cycles. Itis indicated that the supercapacitor electrolyte possessed stable electrochemical character, long cycle lifespan, working long hours under the design of voltage. This kind of ionic liquid is appropriate for electrolytein supercapacitor to further research.