Broad Band Dielectric Behaviour of Plasticized PEO-based Solid Polymer Electrolytes

The conductivity and dielectric response of poly(ethylene oxide) (PEO) based plasticized polymer electrolyte systems were studied in the broad frequency range from 5 Hz to 1.8 GHz and in the temperature range from 248 K to 353 K. Propylene carbonate (PC) and ethylene carbonate (EC) were used as conventional plasticizers while poly(perfluorinated ethylene methylene oxide) (M03) was used as a new type of plasticizer. PEO-LiN(CF(3)SO(2))(2) plasticized with M03 shows high enough conductivity values to be used as electrolyte in rechargeable lithium polymer batteries. At high frequency a dielectric relaxation is observed for pure PEO as well as for the salt containing systems in the GHz region that is assumed to be due to segmental motion of the polymer chains. In the salt containing systems, this relaxation is shifted to lower frequencies relative to that of pure PEO, this is attributed to transient cross-linking. However, at lower frequencies another dielectric response peak was detected in all samples containing salts. The effect of the plasticizer on this relaxation is complex.