Of Peo-based Composite Solid Polymer Electrolyte Preparation, Structural Characterization And Electrical Conductivity Enhancement Mechanism

Firstly, in order to overcome the problem of aggregation and not uniform dispersion of ceramic fillers in composite polymer electrolytes, a simple and effective method is the blending in situ which is used usually to prepare nano-polymer composite materials. (PEO)₈LiClO₄-TiO₂ composite polymer electrolytes were prepared through the blending in situ and mechanical blending. The key to mechanical blending is the preparation of TiO₂ powders by the method of sol-gel beforehand. The analysis of particle diameter shows the mean diameter of TiO₂ powders is 23 μm. From the result of SEM, the morphology of TiO₂ powders is not sphericity rather than ruleless congregate. There is great effect of the method of adding tetrabutyl titanate on the conductivity of composite polymer electrolytes prepared through the bleding in situ. At the condition of same temperature and TiO)2 content, the conductivity of (PEO)₈LiClO₄-TiO₂ composite polymer electrolytes prepared through the blending in situ is higer than that of composite polymer electrolytes prepared through mechanical blending.Secondly, in order to clarify the role of ceramic fillers especially on the mechanism of enhancement of conductivity, the structure of (PEO)₈LiClO₄-TiO₂ composite polymer electrolytes prepared through the blending in situ was examined by differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy and alternating current impedance. IR shows that the interaction of Li⁺-O-Li⁺ is weakened by the interaction between -OH from the surface of TiO₂ and PEO chain. The surface of (PEO)₈LiClO₄ composite polymer electrolytes is smoothy and flat from the result of SEM. TiO₂ particles are distributed uniformly in (PEO)₈LiClO₄-5%TiO₂ composite polymer electrolytes and the basic diameter of TiO₂ particles is about 400 nm. The result of the first DSC heating curves shows that the glass transition temperature and the crystallinity of composite polymer electrolytes are decreased by addition of TiO₂. The changes of the glass transition temperature and the crystallinity are observed from the second DSC heating curves of composite polymer electrolytes compared with the first DSC heatingcurves. The third DSC heating curves is accordant to the second DSC heating curves, indicating that the stucture and properties of composite polymer electrolytes are steady after the samples are heated twice. AC impedance spectra of (PEO)8LiClO4 and (PE0)8LiC104-5%Ti02 composite polymer electrolytes show a semicircle at the range of higher frequency and a inclined line at the range of lower frequency. The temperature dependence of conductivity of composite polymer electrolytes is accordant to Arrhenius equation. The maximum of conductivity of composite polymer electrolytes is observed with 5% TiO2 content. The conductivity is increased obviously by addition of TiO2 at room temperature, which can be assumed that the glass transition temperature and the crystallinity are decreased by addition of TiO2. The mechanism of the enhancement of conductivity above the melting temperature of PEO is the formation of the new conductive passport on the surface of TiO2 particle.Lastly, the effect of SiO2 and surface modified SiO2 on the conductivity of composite polymer electrolytes was examined. The results of IR and TGA of SiO2 before and after surface modification show that the modification reaction is successful. The enhancement of conductivity of composite polymer electrolytes by addition of surface modified SiO2 is higher than the prisine SiO2, which is maybe resulting from better interfacial interaction between surface modified SiO2 and polymer matrix.