<p>Solid polymer electrolytes (SPEs) are promising alternatives to liquid electrolytes, offering improved stability and design flexibility. However, their practical application is hindered by low ionic conductivity. This study focuses on enhancing PEO-NaCl-based polymer electrolyte films through the incorporation of glycerol as a plasticizer to reduce crystallinity and improve electrochemical performance. Characterization techniques, including Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS), were employed to evaluate structural, spectroscopic, and electrochemical changes with varying glycerol content. The results revealed that the ionic conductivity increased dramatically from 2.7 × 10⁻⁹ S/cm for the pristine sample to 3.41 × 10⁻⁵ S/cm with 32 wt% glycerol an enhancement of over 12,629 times. The relaxation time also dropped significantly from 1514.665 μs to 5.09 μs, indicating faster ion transport. Moreover, the charge carrier density rose from 2.98 × 101³ cm⁻3 to 2.56 × 1015 cm⁻3. The dielectric loss tangent (tan δ) peak shifted from 243.83 Hz to 31,231.8 Hz, with its magnitude increasing nearly ninefold, suggesting enhanced dielectric behavior. These improvements are attributed to glycerol's ability to reduce polymer rigidity, promote ion dissociation, and increase polymer chain flexibility. The findings confirm that glycerol is an effective plasticizer for optimizing the performance of solid-state polymer electrolytes.</p>