Solid polymer electrolytes (SPE) based on poly-(vinyl alcohol) (PVA)0.7 and sodium iodide (NaI)0.3 complexed with sulfuric acid (SA) at different concentrations were prepared using solution casting technique. The structural properties of these electrolyte films were
examined by X-ray diffraction (XRD) studies. The XRD data revealed that sulfuric acid disrupt the semi-crystalline nature of (PVA)0.7(NaI)0.3 and convert it into an amorphous phase. The proton conductivity and impedance of the electrolyte were studied with changing sulfuric acid
concentration from 0 to 5.1 mol/liter (M). The highest conductivity of (PVA)0.7(NaI)0.3 matrix at room temperature was 10−5S cm−1 and this increased to 10−3S cm−1 with doping by 5.1 M sulfuric acid. The electrical conductivity (σ) and dielectric permittivity (ε′) of the solid polymer electrolyte in frequency range (500 Hz– 1 MHz) and temperature range (300–400) K were carried out. The electrolyte with the highest electrical conductivity was used in the fabrication of a sodium battery with the configuration Na/SPE/MnO2. The fabricated cells give open circuit voltage of 3.34 V and have an internal resistance
of 4.5 kΩ.