Solid polymer electrolytes (SPEs) based on plasticized sodium carboxymethyl cellulose/polyethylene oxide (CMC/PEO) were successfully prepared using solution casting method. The prepared SPEs were investigated using different spectroscopic techniques. Ultraviolet–Visible absorption spectra (UV–Vis) revealed that changing PEO content in the polymer matrix causes the optical band gap energy to change and decrease. These changes indicate that there is a transfer of charge carriers within the polymer matrix. The variations occurring in the major structural units within the prepared CMC/PEO SPEs are retraced using Fourier transform infrared spectroscopy (FTIR). FTIR results revealed that the polymeric materials suffer changes in their chemical structures and that complexation occurred between the individual polymers due to blending. Correlation between UV–Vis optical band gap and FTIR outcomes is established. Electrical impedance spectroscopy (EIS) was used to study the conduction mechanism for the prepared SPEs. Impedance results showed that the CMC/PEO sample with blending ratio of 80/20 wt% (sample named B2) possesses the highest ionic conductivity of 1.18E−06 S/cm and the lowest activation energy of approximately 0.67 eV at ambient temperature.
