Development of a new plasticizer for poly(ethylene oxide) based polymer electrolyte and the investigation of their ion-pair dissociation effect

摘要

One approach to increasing the ionic conductivity of polymer electrolyte is to add plasticizers to the polymer-salt complexes . Recently, we have synthesized a new plasticizer, modified carbonate (MC3), by attaching three ethylene oxide units to the 4-position of ethylene carbonate. AC impedance studies showed that an ionic conductivity of 5(x)10(sup (exp-5) S cm(sup (exp-1) could be achieved at room temperature, by adding 50 wt % of MC3 into PEO-LiCF(sub 3)SO(sub 3) complex. This is two orders of magnitude higher than that found in PEO-LiCF(sub 3)SO(sub 3) electrolyte without a plasticizer, and one order of magnitude higher than that found when using same amount of propylene carbonate (PC) as plasticizer. Temperature dependent conductivity measurement and thermal analysis show that this new plasticizer increased the ionic conductivity throughout the entire complex system, while the conventional plasticizers only create a high conductivity path way through the plasticizer itself. The samples are free standing films with good mechanical properties. When MC3 is used as a plasticizer, the ionic conductivity increase is much higher than using PC as a plasticizer at high temperature (65(degrees)C), implying an increase in the number of charge carriers. Therefore, we believe that MC3 has a stronger ion pair dissociation effect than PC, when used as a plasticizer. The ion pair dissociation effect was studied by Raman, FTIR, and near edge x-ray absorption fine structure (NEXAFS) spectroscopy.