Sodium Ion-Conducting Polyvinylpyrrolidone (PVP)/Polyvinyl Alcohol (PVA) Blend Electrolyte Films

We report the synthesis of sodium ion-conducting polymer-blend electrolyte (NIPBE) thin films prepared by a standard solution-casting technique based on polyvinylpyrrolidone (PVP)/polyvinyl alcohol (PVA) and sodium bicarbonate (NaHCO₃). The as-synthesized NIPBE thin films were flexible, free-standing and displayed good mechanical stability. The prepared films were characterized using various experimental techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), AC impedance spectroscopy, linear sweep voltammetry (LSV), cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR) and UV–visible spectroscopy. The SEM, XRD and DSC studies revealed a reduction in the crystallinity of the polymer-blend electrolyte with an increase in the content of NaHCO₃ due to the plasticization effect of Na-salts. The FTIR spectra show the complexation behavior of our as-prepared NIPBEs. The optical properties (i.e., direct and indirect optical energy bandgaps, optical absorption edge) were estimated using UV–visible spectroscopy studies. The dynamic ion behavior of all the as-prepared samples was assessed by the frequency-dependent AC conductivity of the NIPBEs. Also, the dielectric constant and dielectric loss (ε′ and ε″), and electric modulus (M′ and M″) vs. frequency plots at different concentrations and at room temperatures, were reported. The relaxation frequency (τ_s) of the NIPBE films was determined from the loss tangent spectra (tanδ). The ionic conductivity of NIPBE films was found to increase with sodium salt concentration, with maximum conductivity of the order of ∼10⁻⁵ S/cm at 30 °C. CV measurements showed good electrochemical stability of the sample containing a high concentration of Na salts. The optimized NIPBEs showed ionic conductivity and electrochemical voltage stability which is good for application in energy storage devices.