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Thin films of poly(ethylene oxide) (PEO) doped with sodium iodide (NaI) were prepared by casting method. The films have an average thickness of 70 mm and contain different NaI concentrations, that is 1, 2, 4, 6, 8, 10, and 15% by weight (wt%). The dielectric constant, alternating current (AC)-conductivity, and thermal conductivity of the electrolytic composites were studied as a function of applied frequency, temperature, and NaI concentration. The AC conductivity and dielectric constants were determined from the impedance data, and the thermal conductivity was measured using the transient electric pulse method. It was found that the dielectric constants and AC conductivity increase with increasing temperature and NaI concentration. The percolation threshold of the observed AC conductivity occurs at about 1 wt% NaI dispersed in the PEO matrix. The charge transfer in the electrolytic films is dominated by ions transport and creation of more localized energy states due to high amorphous phase in the solid electrolyte. The formed iodide complexes also contribute in increasing the AC quantities. It was found that the thermal conductivity of the polymer electrolyte films increases with both temperature and NaI concentration. Empirical models were used to describe the dependence of electrical and thermal conductivities on the dopant content, frequency, and temperature.

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