Preparation And Characterization Of Ionic Liquid Polymer Electrolyte

Ionic liquids, due to their excellent properties, such as high ionic conductivity, good thermal and electrochemical stability, negligible vapor pressure, nonflammability, are suitable for incorporation into polymers as plasticizer. The incorporation of ionic liquid into polymer electrolytes can distinctively increases the ionic conductivity of the polymer electrolytes and can solve safety problems, such as explosion, which are evoked by volatile nature of small molecular solvent, particularly when short circuits create localized heating, using in large-scale batteries or at high temperature. The promising application foreground of them in lithium batteries is brought forth.In this study, 1-butyl-3-methylimidazolium hexaflurophosphate (BMIMPF₆) was incorporated into PVdF-HFP-LiPF₆ and PEO-LiTFSI system respectively to synthesize ionic liquid-polymer elctrolytes (IGPEs) for rechargeable lithium batteries. The results show that ionic conductivity of PVdF-HFP-LiPF₆ or PEO-LiTFSI electrolytes were both increased by incorporation of ionic liquid and when there are same amount of ionic liquid and lithium salt in the two kinds of ionic liquid-polymer electrolytes, PEO-LiTFSI-BMIMPF₆ shows higher ionic conductivity than PVdF-HFP-LiPF₆-BMIMPF₆ does. Emission FT-IR at different temperature was used to study the ion-conducting mechanism of IGPE. Combining the results of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimerty (DSC), scanning electron microscopy (SEM), it can be known that the incorporation of ionic liquid can increase ionic conductivity by (1) decreasing the crystallinity of polymer electrolyte; (2) the interaction between ionic liquid and polymer matrix, accelerates the decoupling of the ion transport from polymer segmental motion; (3) providing more transfer tunnels for lithium ions.Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were applied to investigate the effect of SBA-15 on compatability between IGPE and lithium anode and LiFePO₄ cathode, and the performance of charge and discharge gel polymer electrolytes with and without SBA-15 were compared. The results demonstrate that the addition of SBA-15 to ionic liquid-polymer electrolyte results in a better interface stability and a better compatibility with lithium anode and LiFePO₄ cathode. The test performed on Li metal/LiFePO₄ batteries contains SBA-15 shows a better capacity performance.The innovation of this theme is based on the synthesizing of ionic liquid-polymer electrolyte, in which BMIMPF6 was chosen as plasticizer because it is the most common kind of ionic liquid and for its easy synthesis, the physical and chemical characterization of polymer electrolyte was studied systemically. Fourier transform infrared spectroscopy and emission FTIR were used to investigate the effect of ionic liquid on the structure of polymer matrix at molecule level; the exploratory experiments demonstrated that the FTIR spectroscopy is an important method to be applied in the study of lithium batteries. The addition of SBA-15 results in a better capacity performance, and to our knowledge, it is the first time that this kind of ionic liquid tested in Li metal/LiFePO₄ batteries.