Structural, optical, electrochemical, and ion transference characteristics of the PVA-based plasticized polymer composite electrolyte: LiI doped with plasticizer (D-sorbitol)

High ionic conductivity polymer electrolytes are now of considerable interest due to their prospective uses in several electrochemical devices such as batteries, fuel cells, solar cells, and supercapacitors. Several approaches have been used to improve their ionic conductivity, including adding plasticizers, polymer blends, and nanocomposites. This work examined how the plasticizer D-sorbitol affected the ion transport in solid polymer electrolyte membranes made of polyvinyl alcohol (PVA) complexed with 30 wt% of LiI. The membranes were created with a D-sorbitol concentration of up to 55 wt% using the solution casting technique. The XRD structural study showed that the membranes’ amorphousness increased when the sorbitol content increased. The complexation between PVA and the additives was studied using UV–vis and FTIR analysis. Electric methods such as ac-impedance spectroscopy and linear sweep voltammetry were used to investigate the conductivity, decomposition voltage, ion transference number, dielectric constant (ε′), dielectric loss factor (ε″), and electric modulus (M) of the investigated membranes. The results indicated the interactions between LiI, PVA, and D-sorbitol plasticizer. The increase in D-sorbitol concentration affected the electrical properties and electrochemical stability window. The highest ionic transfer number value of 0.997 was obtained with 55 wt% of D-sorbitol at 30 °C. The UV–vis optical study revealed a direct allowed transition band with an optical energy gap decreased from 3.92 eV (for PL) to 3.82 eV (for PLS5).