Effect of Plasticizer Addition to Poly(Ethylene Carbonate) Based Polymer Electrolyte

Properties of polymer solid electrolytes composed of poly(ethylene carbonate) [PEC], lithium bis(trifluoromethane sulfonimide) [LiTFSI, LiN(CF3SO2)(2)] and propylene carbonate [PC] as plasticizer have been analyzed using Raman spectroscopy and ac impedance spectroscopy. Including 14 wt% of PC in the PEC based polymer electrolyte with LiTFSI concentration of 0.2 mol per polymer repeat unit, made it possible to increase the ionic conductivity (sigma) by one order of magnitude to a practical-use level of 1.3 mS cm(-1) at 20 degrees C. The correlation between a and temperature fits well the Williams-Landel-Ferry equation, so it is considered that ionic conductivity depends on thermal activation of the polymer chains. From the correlation between sigma and temperature, it is concluded that PC (with greater mobility than the polymer chains) partly solvates with lithium ions, and sigma is improved by lowering its activation energy.