Properties And Applications Of Solid Electrolytes Based On Ionic Liquids And A Polymer

Generally, solid polymer electrolytes (SPEs) are formed by the dissolution of salts inion-coordinating macromolecules. SPEs have a number of beneficial properties such as theease of thin-film forming, good elasticity and light weight, which are free of issues likeliquid leakage and flammability in the case of liquid electrolytes. Moreover, the study ofthis class of materials will facilitate the understanding of ion transport in more complexsystems such as solvent-containing polyelectrolyte and biological membranes. So, thestudy on SPEs is very important for both scientific and technological interest. The aim ofthis work is to prepare membrane materials of SPE having some advantages, such as highionic conductivity, excellent electrochemical and thermal stabilities, good processibility.The interaction between the ionic liquid and the polymer in SPEs was researchedintensively. A knowledge of the ion transport mechanism in SPEs is essential to improveSPE conductivity and practical applications.In this work, eight novel ionic liquids (ILs) based on imidazolium/pyrrolidiniumcations and maleate/phthalate anions have been synthesized. The thermal property,viscosity, conductivity, electrochemical stability, and sparking voltage of these ILs havebeen investigated systemically. The conductivities and viscosities of these ILs weremeasured at different temperatures. The conductivities of imidazolium cation-based ILs arehigher than that of pyrrolidinium cation-based ILs and the conductivities of maleateanion-based ILs are higher than that of the corresponding phthalate anion-based ILs at acertain temperature. The temperature dependences of viscosity and conductivity werediscussed in this paper. The Vogel-Tammann-Fulcher (VTF) equation accurately describesthe dependence of both the conductivity and viscosity on temperature. In addition, thethermal properties of ILs were evaluated by DSC and TGA, which indicated these ILsbehave good thermal stability except for N-methylpyrrolidinium-based ILs. Theelectrochemical window values of the ILs range from 2.4V to 4.4V.Four ILs based on 1-ethyl-3-methylimidazolium and N, N-dimethypyrrolidiniumcations and maleate/phthalate anions were chosen as the complexing salt of SPEs. SomeSPE membranes of high conductivity, known as Polymer-in-Salt, have been prepared bycomplexing PVA/PVDF and the ILs. The dependence of SPE properties on the type of theILs, composition and polymer matrix were mainly discussed. The conductivities for SPEwere measured by a.c. impedance measurement at various temperatures. Similar to the IL case, the VTF equation accurately describes the dependence of the conductivity for SPE ontemperature. The interaction between the ILs and polymer matrix was investigated byinfrared spectra (IR) and X-ray Diffraction (XRD), which suggested a possible mechanismfor the influence of the ILs on the ionic conductivity for SPE. PVA has a strongcoordination interaction with the ILs and its SPEs are homogeneous and amorphoussystems. The electrochemical windows for the SPEs substantially depend on the content ofthe ILs, and are wider than that of the corresponding ILs.In order to improve the conductivity of SPEs, gamma-butyrolactone and ethyleneglycol were used as the plasticizers to add into the SPEs. The practical applications of thenew polymer gel electrolyte systems in the field of aluminum electrolytic capacitors andelectrochemical capacitors have been discussed. The results show that the aluminumelectrolytic capacitors utilizing the polymer gel electrolyte have satisfactory generalelectric properties, excellent shelf life and high resistance to soldering heat. Andelectrochemical capacitors utilizing the polymer gel electrolyte have goodcharge-discharge cycle life.