Study on ionic conductivity behavior of novel composite polymer electrolytes

Poly(ethylene glycol) 600 (PEG, M_n = 600) and CH ₂Cl₂ were polycondensated to form a soft main chain block polymer. H NMR measurement demonstrated that the polymer repeating unit was [CH₂O(CH₂CH₂O)₁₃] . A series of composite polymer electrolytes were prepared by using the polymer with an appreciable amount of LiN(CF₃SO₂)₂ blended with fumed silica (8wt% of the polymer). The conductivity was studied through measurements of AC impedance spèctra, and fitting the resulting equivalent circuits. The processability of the composite polymer electrolytes was improved very much, and its conductivity was 2-3 orders higher than that of pure PEO/Li salt system. The conductivity increased with the increase of temperature. At low temperature area, the conductivity increased dramatically, while it increased slowly at high temperature area and not coincided with Arrhenius formula. Within EO/Li = 13-34:1 (molar ratio), the plot of conductivity vs. salt content showed two peaks and the peak value in low salt content was higher. When EO/Li = 28:1 at 303 K, the highest ionic conductivity appeared and approached 10^-4 S/cm.