Study On Preparation And Performance Of Gel Ionic Liquid/Polymer Electrolytes

Commercialised supercapacitors and lithium-ion batteries usually contain liquid organic aprotic solvents plasticizing salts. This situation brings evaporation of the solvent or threat of possible leakage, what leads not only to decrease of the battery capacity, but also is environmentally hazardous. Ionic liquids meet the requirements of plasticizing salts and offer an improved thermal to gel polymer electrolytes. They have been developed and studied extensively during the last few years. But their ionic conductivity are most about 10^-4S·cm^-1, which cann't meet the request of conductivity of electrolytes, i.e.> 10^-3S·cm^-1. Evidently, the promising application of gel polymer electrolytes with high ionic conductivity and excellent thermal stability is brought forth.In This paper, a series of RTILs were synthesized by two-step method, which were identified by FT-IR. This RTILs are [BMIM]BF₄, [BMIM]PF₆, [BMIM]Cl-ZnCl₂ and [BMIM]H₂PO₄ .Firstly, gel polymer electrolytes comprising [BMIM]Cl-ZnCl₂ L-acid room temperature ionic liquid have been prepared and studied. The gel polymer electrolytes were formed by in situ free radical polymerization. While n([BMIM]Cl-ZnCl₂)/n(monomer) up to 7:3, the gel polymer electrolyte showed the maximum ionic conductivity of about 0.36×10^-3S·cm^-1 . They had greater thermal stability than the traditional electrolyte systems including liquid organic aprotic solvents plasticizing salts. In order to development of highly conductive electrolytes, gel polymer electrolytes with ionic liquid [BMIM]Cl-ZnCl₂ and aprotic solvents(PC and DMC) were prepared and studied, which showed highly ionic conductivity up to 2.83×10^-3S·cm^-1. And the activation energies of ions were calculated according to VTF equation. Gel polymer electrolytes exhibited high decomposition temperatures above 275℃.Gel polymer electrolytes with ionic liquid [BMIM]BF₄ or [BMIM]PF₆ and aprotic solvents(PC and DMC) were prepared and studied, which showed highly ionic conductivity over 10^-3S·cm^-1 at room temperature. The electric conductivity of the polymer electrolytes are increased with increasing temperature, and fit the Vogel-Tamman -Fulcher(VTF) equation. Gel polymer electrolytes PHEMA+LiBF₄+PC+ [BMIM]BF₄ and PHEMA+LiBF₄+PC+DMC+[BMIM]BF₄ showed highly ionic conductivity about 1.33×10^-3S·cm^-1 and 1.46×10^-3S·cm^-1 respectively. They exhibited high decomposition temperatures above 260℃. The weight loss were found less than 0.87wt.% up to 80℃. The transference number of lithium ion in the polymer electrolytes containing lithium salts are above 0.34. And the electrochemical window are up to 4.3. Gel polymer electrolytes PMMA+PC+[BMIM]PF₆ and PMMA+ LiPF₆+PC+DMC+[BMIM]PF₆ showed highly ionic conductivity about 3.44×10^-3S·cm^-1 and 10.05×10^-3S·cm^-1 respectively. They exhibited high decomposition temperatures above 250℃. And the weight loss found less than 0.97wt.% up to 80℃. The transference number of lithium ion in the polymer electrolyte containing lithium salts are about 0.3. And the electrochemical window are up to 5.1.Firstly, gel polymer electrolytes comprising B-acid room temperature ionic liquid [BMIM]H₂PO₄ have been prepared and studied. The conductivity of membranes with [BMIM]H₂PO₄ has been found to depend upon the concentration of ionic liquid, phosphoric acid and temperature. While n([BMIM]H₂PO₄)/n(HEMA) or n([BMIM]H₂PO₄)/n (MA) up to 7:3, the gel polymer electrolyte showed the maximum conduc -tivity of about 6.20×10^-3S·cm^-1 and 5.94×10^-3S·cm^-1 respectively. The gel polymer electrolytes without H₃PO₄ had greater thermal stability than the traditional electrolyte systems including liquid organic aprotic solvents plasticizing salts. They exhibited high decomposition temperatures above 258℃.