Preparations And Properties Of PVA-based And PEO-based Ionic Liquid Polymer Electrolytes

Polymer lithium ion battery has high energy density, long cycle life,flexible processing and safety performance characteristics， widely used inelectric vehicles, mobile communications, and other fields of the business.It has become one of research hot spots at present. PVA-based, PEO-basedpolymer electrolytes have better electrical conductivity, and polymerfeatures such as good mechanical properties, which provides a new directionfor the solid-state, safe,ultra-thin lithium ion battery. However, one of themain factors which limits PVA-based, PEO-based polymer electrolytes formass production application is its low room temperature conductivity.As the representative of green chemistry, ionic liquids are entirelycomposed of anion and cation at room temperature, which are non-volatile,having dissolving ability, high conductivity, good thermal stability and wideelectrochemical stability window, but when used as the electrolyte which iseasy to flow. When the ionic liquid is introduced into the good mechanicalperformance polymer system, made of new type of ionic liquid polymerelectrolyte, can be the advantages of both ionic liquids and polymer, whichhas a good application prospect.Through the studying of the grafting, composite, plastic modification ofpolymer matrix, this paper prepares a series of new type of PVA-based,PEO-based ionic liquid polymer electrolyte. On this basis, using FTIR, DSC,TGA, SEM, AC impedance, cyclic voltammetric test methods, the ionic liquidpolymer electrolytes were characterized. Briefly as follows:（1） With PVA as base, a series of poly （vinyl alcohol）/phosphotungsticacid/ionic liquid （PVA/PTA/BMIMCl） polymer electrolytes were prepared viasolution casting method. PTA in the electrolyte system has always maintained a Keggin type of PW₁₂O₄₀^3-anion feature structure, which can increase thecontent of amorphous phase system and reduce the glass transition temperatureof the polymer electrolyte. Moreover BMIMCl can increase the carrierconcentration of system, which is beneficial to the improvement of theconductivity.Using infrared spectra to characterize the structure of ionic liquidpolymer electrolyte; using DSC and TGA to studying thermal property of ionicliquid polymer electrolyte. The electrochemical performance of polymerelectrolyte membrane was studied by alternating current impedance and cyclicvoltammetry. Relationships between content of phosphotungstic acid, ionicliquid and conductivity were also studied.（2） A new kind of imidazoles ionic liquid polymer electrolyte: poly （vinylalcohol） graft N-vinyl imidazole fluoroboric acid salt （PVA-g-VyImBF₄）graft copolymer was synthesized via the free radical graft copolymerizationreaction for the first time. With the structural features of ionic liquid,the graft copolymer PVA-g-VyImBF₄is a kind of high density charge imidazolepolycation electrolytes, having the good practical performance. In order toimprove the practicability of the polymer electrolyte,PVA-g-VyImBF₄/PTA/PEG400IMBF₄Ionic liquid polymer electrolyte was preparedvia solution casting method.The results of Infrared spectroscopy（FTIR） and scanning electronmicroscopy （SEM） confirmed that the PVA-g-VyImBF₄graft copolymer wassynthesized. To determine the grafting rate of the best conductivity, studyrelationships between content of PTA、ionic liquid and conductivity.The results show that when m（PVA-g-VyImBF₄）:m（PTA）:m（PEG400IMBF₄） was4:2:1.8,the conductivity of the PVA-g-VyImBF₄/PTA/30%PEG400IMBF₄polymerelectrolyte membrane could get to3.27×10^-3S/cm while the electrochemicalstability window could get to4.2V, having good thermal stability and goodpractical performance. （3） With PEO as base, LiBF₄as lithium salt, homemade TEGIMBF₄ionic liquidas a plasticizer, a series of new type P （EO）_xLiBF₄-yTEGIMBF₄ionic liquidpolymer electrolytes were prepared by solution casting method for the firsttime. Ionic liquid TEGIMBF₄could not only serve as the ion source, but alsohave ether oxygen bond structure which is similar to the PEO, and have thesame anion with lithium salt LiBF₄.So with TEGIMBF₄as compositeplasticizer,PEO-based compositing polymer electrolyte was prepared in orderto stronger ion complexing ability and be provided with good mechanicalproperties and high conductivity.Structure characteristicization of ionic liquid polymer electrolyte wasstudied using infrared spectroscopy（FTIR） and DSC analysis techniques.Complexation-dissociation effects of lithium ions and the ether oxygen groupwere analysed. The crystallinity of the ionic liquid polymer electrolyte wasstudied. Conductivity of P（EO）15LiBF₄-yTEGIMBF₄ionic liquid polymerelectrolyte composite membrane with different TEGIMBF₄content was researched.The thermal stability and electrochemical window of the ionic liquid polymerelectrolyte was measured.