Studies On Synthesis And Properties Of Solid Polymer Electrolytes

Solid polymer electrolytes (SPE) have many advantages such as: light weight, easier to fabrication, good viscoelasticity and thermal stability. They have potential applications in solid state secondary lithium batteries, fuel cells, electrochromic display devices, electrochemical sensors, capacitors and so on. In recent years, researches on SPE have received considerable attention from people. To improve electrolyte efficiency , various methods have been applied to modify the structure and morphology of polyether hosts. There are two means to increase the ionic conductivity of the SPE : ( I ) suppression of crystallization of polymer chains to improve polymer chain mobility; (II) increase in the carrier concentration. The suppression of crystallization of polymer chains to improve polymer chain mobility can be realized by ( i )cross-linking; (ii )co-polymerization; (iii)comb formation (side chains and dendritic polymers); (iv)polymer alloy(including Inter Penetrating Network(IPN)), and (v )inorganic filler blend. The gel electrolytes are promising because of their high room temperature conductivities (the ionic conductivity can be about 10²S/cm). Scientists have become increasingly interested in polymer electrolytes. Weston and Steele first demonstrated the idea of incorporating electrochemically inert particulate fillers into polymer matrixes as a means to increase mechanical stability of the polymer. Since then, with a view to making dimensionally stable polymer electrolytes for lithium batteries, high surface area particulate fillets such as TiO₂, ZrO₂, Al₂O₃, and fiber glass were introduced into polymer matrixes to obtain the so called 'composite polymer electrolytes' or 'composite ceramic electrolytes'. Composite formation was also found to enhance the ionic conductivities of the electrolytes leading to their potential use in lithium batteries. In this paper, three new sorts of composite polymer electrolytes were designed and synthesized. For these synthesized SPE, we studied their chemical structure, microcosmic morphology, thermal stability and ionic conductivity.In recent years, mixed ionic-electronic conductors (MIECs) based on composites have found wide applications in solid-state ionic devices such as batteries, fuel cells, and chemical sensors, and in electrochemical processes such as electrosynthesis and gas separation. The greatest advantage of a composite MIEC over a homogeneous, single phase MIEC is that the transport properties of a composite can be readily tailored for a particular application. For membrane applications, a desired composite MIEC consists of two continuously distributed phases, one being predominantly ionically conductive and the other being predominantly electronically conductive. Accordingly, it is possible to integrate a highly electronically conductive phase with a highly ionically conductive phase to achieve high ambipolar conductivities. In this paper, two new series of mixed ionic-electronic conductors were designed and synthesized. The microstructure, ionic conductivity and thermal stability of these mixed conductors were investigated by means of Fourier transform infra-red spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric (TG) analysis and a. c. impedance. Topics considered are:1. For SPE, the developing history, the categories, ion-transport mechanism, technique of characterization and advances of polymer electrolytes were reviewed. Some tentative conclusions are made about future short-term trends. For conductive polymer, the definition, characteristic, classify, electric mechanism, application were reviewed. We also expound the basis of this thesis topic, quoted 150 references.2. Ionic-electronic conductors were prepared by oxymethylene-linked polyoxyethylene multiblock polymer, LiClO₄, and Polypyrrole (PPy) in solution. The structural and complexation behaviour have been studied by FT-IR and X-ray diffraction(XRD) analyses. The results show that the synthesized products are consistent with designs. The thermal stability of the electrolyte is ascertained by using TG and DSC. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) were used to investigate microcosmic structure. The ionic conductivities of the electrolytes have been measured by an a.c. impedance technique at room temperature. According to analysis and calculating of the imitated equivalent circuit, the conductivity optimum value is 10^-6 S/cm. An imitating equivalent circuit is proposed in this paper, in terms of the device structure. A.C. impedance test conductance, which can imitate the data better, and has certain general suitableness.3. Composite polymer electrolytes have been prepared from three inorganic particles and LiClO₄ using oxymethylene-linked polyoxyethylene multiblock polymer as the polymer host. The chemical structure of polymers was characterized by FT-IR. Microcosmic morphology and model of molecule accumulation were observed by SEM and TEM. X-ray diffraction analysis proves that the kind of SPE is amorphous, and which is helpful for ionic conductivity. The results of the thermal analysis indicate that they have better thermal stability. The ionic conductivity could reach 10^-6 S/cm at room temperature.4. From oxymethylene-linked polyoxyethylene multiblock polymer, PPy/SiO₂ composite materials and LiClO₄ , we get a new series of mixed conductors of electron-ion. The designed chemical structure of product can be proved by means of the FT-IR analysis. SEM and TEM photograph showed microcosmic morphology and structure. X-ray diffraction analysis demonstrated that this kind of mixed conductor is amorphous solid, which is favorable for ionic conductivity. TG and DSC show that thermal stability of synthesized polymer is very good. The conductivity was studied by using A.C. impedance at room temperature. The highest ionic conductivity of the complexes polymers is 10^-5 S/cm.5. In this part of paper, we summarized the full text, analysesed the difference of a variety of family in conductivity and other performance, and explored the reasons.