Preparation And Characterization Of Compounds And Inorganic Particles Of The Plastic Crystal Doped Peo-based Composite Polymer Electrolyte

In recent years, the ionic conductivity of polymer electrolytes was too low to be satisfied for practical applications at room temperature. Through doping lithium salt to the plastic crystal at room temperature, ionic conductivity of plastic crystal has reached 10^-3 S ? cm^-1, but the plastic crystal material has poor mechanical properties. We are trying to find an optimal balance point for the contradiction between ionic conductivity and mechanical properties. Two kinds of PEO based CSE (PECO)₈LiClO₄/SN (PLS) and (PEO)₈LiClO₄/SiO₂/SN (PLSS) composite polymer electrolyte were prepared by a solution cast technique. The morphology, thermal performance, crystallinity and ionic conductivity of the CSPE were investigated by SEM, IR, DTA, TG, DSC, XRD and A.C impedance spectroscopy.(1) From the A.C. impedance spectra we can see that the conductivity of CSPE adding SN or SiO₂ was higher than PEO/LiClO₄; Compared with the SiO₂, the addition of SN in PEO/LiClO₄ leads to higher enhancement in ionic conductivity. But PLSS composite polymer electrolyte obtained the highest conductivity; the conductivity is increased obviously by addition of SiO₂ at room temperature. When SiO₂ concentration is at about 10wt%, the conductivity of PLSS attains the maximum value, 3.44×10^-4 S / cm. The temperature dependence of conductivity of PLS and PLSS CSPE are accordant to Arrhenius equation.(2) It's indicated that there are certain interactions among PEO, succinonitrile and lithium salt by IR. For the sake of the existence of the interactions, the different properties of CSPE have improved. Especially the cyano-group on succinonitrile is both faveorable to dissociation of the LiClO₄ and transferring of Li⁺.(3) DSC and XRD show that the crystallinity is observed to decrease greatly by addition of SiO₂ and SN. The glass transition temperature (T_g) of PLSS decrease by filling with SN and inorganic particle SiO₂. TG and DTA show that initial decomposition temperature of PLSS is increased. The movement of polymer chain is restricted by SiO₂ particle, thereby enhanceng the energy of polymer chain in the heating process, improving the thermal stability of PLSS polymer electrolyte when adding SiO₂ and SN.(4) The results of contact angle testing show the surface energy is increased by addition of SN. PLS polymer electrolyte has a good mechanical property. The ionic conductivity is related to the surface free energy, the smaller the surface energy is, the bigger the ionic conductivity is; the bigger the surface energy is, the smaller the ionic conductivity is.(5) Based on the experimental study, the research on the mechanism of enhancement of conductivity of CSPE was discussed. Decrease in crystallinity of electrolyte and the existence of a highly conducting layer or grain boundary at the electrolyte/filler interface and decrease of crystallinity can account for the reason of the enhancement in ionic conductivity by the addition of ceramic fillers and SN.