The present work is concerned with the electrochemical chacteristics of plasticized network polymer electrolyte based on poly(ethylene oxide)(PEO). The polymer was synthesized by condensation polymerization of poly(ethylene glycol)(PEG, $M_n$=1000) and 3-chloro-2-chloromethyl-1-propene(CCMP), followed by cross-linking reaction. And plasticized polymer electrolytes were prepared by adding the plasticizers.
These studies are classified in three categories concerned with one another. First the ionic conductivity with the contents of ethylene carbonate(EC) in network PEO(NPC) was investigated. The ionic conductivity was saturated with the increase of EC contents. The ionic conduction is affected by the mobility and the number of carrier ions. As a qualitatively measure of the mobility of polymer electrolyte, DSC experiments were conducted, and then infrared(IR) spectroscopy was measured to quantify the number of charge carriers. As a results, it was found that the ionic conductivity was dependent strongly on the mobility of polymer electrolyte rather than the number of charge carriers. Also the ionic conductivity at room temperature showed very high value $(10^{-3} S/cm)$ even in the small EC contents(100wt%) in comparison with other system such as PMMA. That result was because of the different viscosity in polymer electrolyte resulted from the intrinsically chain mobility of polymers.
Second, the interfacial resistances were studied under storage time and the electrical stress respectively using Li/Li symmetric cell. Plasticized polymer electrolytes formed much more stable interface in two conditions. These phenomena were explained with the variation of contact area and properties of interphase.
Third, electrochemical stability could be guaranteed by obtaining linear sweep voltammogram. And charge-discharge properties of this system were investigated using charge-discharge instrument. Plasticized polymer electrolyte showed even higher peak current than solvent-free polymer electrolyte. It was found that these facts resulted from the better bulk conductivity, more stable interfacial resistance and better contact with Li electrode.
