A novel approach to design sodium-ion conducting ternary solid polymer blend electrolytes (TSPBEs): structural, conductivity, and relaxation dynamics

In recent decades, research on solid polymer electrolytes (SPEs) has advanced significantly due to their natural abundance, cost-effectiveness, low toxicity, and biodegradability. Blending two or more biodegradable polymers is a potential method for enhancing ionic conductivity. This work presents the development of ternary blended biodegradable SPEs based on polyvinyl alcohol (PVA), chitosan (CS), and fish skin gelatin (FSG) as host materials, and sodium iodide (NaI) as an ionic source, via the solution casting technique. The polymer-salt complexation was confirmed through interactions between functional groups of polymers, such as OH, C = O, NH, and C-O-C and ions of the added salt using Fourier transformed infrared spectroscopy (FTIR). The enhancement of amorphous characteristics of ternary blend electrolytes is examined by X-ray diffraction (XRD). The ionic conductivity of the ternary blended electrolyte samples was evaluated through electrochemical impedance spectroscopy (EIS), where the sample incorporating 40 wt.% of NaI was found to have the optimum ionic conductivity. The sample with the maximum contribution of salt demonstrated a decrease in conductivity as a consequence of salt re-association, a reduction in the amorphous region, and a limitation on the accessible area for the movement of free ions. Ionic transport parameters, including the diffusion coefficient (D), ion mobility (μ), and carrier density (n), were determined from the Nyquist plot. An examination of dielectric properties revealed an improvement with the incorporation of salt, exhibiting dispersive relaxation features that confirmed the non-Debye behavior. This tendency was also supported by the emergence of a deformed arc in the Argand plot. The drop-in relaxation time is reflected by the displacement of loss tangent (tan δ) peaks toward higher frequency areas.