We investigate the effect of blend host polymer on solid polymer electrolyte (SPE) films doped with ammonium iodide (NH4I) salt using a variety of experimental techniques. Structural studies on the composite SPEs show that the blending of Poly(ethylene oxide) (PEO)–Poly(vinylidene fluoride) (PVDF) polymers in a suitable ratio enhances the amorphous fraction of the polymer matrix and facilitates fast ion conduction through it. We observe that the addition of a small amount of PVDF in the PEO host polymer enhances the ion – polymer interaction leading to more ion dissociation. As a result, the effective number of mobile charge carriers within the polymer matrix increases. Systematic investigation in these blend SPEs shows that the maximum conductivity (1.01 × 10–3 S/cm) is obtained for PEO – rich (80 wt. % PEO, 20 wt. % PVDF) composites at 35 wt. % NH4I concentration at room temperature. Interestingly, at higher salt concentrations (above 35 wt. %), the conductivity is found to decrease in this system. The reduction of conductivity at higher salt concentrations is the consequence of decrease in the carrier concentration due to the formation of an ion pair and ion aggregates. PVDF–rich compositions (20 wt. % PEO and 80 wt. % PVDF), on the other hand, show a very complex porous microstructure. We also observe a much lower ionic conductivity (maximum ∼ 10–6 S/cm at 15 wt. % salt) in these composite systems relative to PEO-rich composites.

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The enhancement of conductivity of a composite polymer as a dielectric material is an essential requirement for electrostatic storage devices. We have modified the microstructure of the polymer matrix by introducing an insulating nanofiller SiO2. The effect of such a filler on the ionic conductivity of the composite polymer electrolyte has been investigated using a variety of experimental techniques along with the non-Debye type of relaxation functions. We have achieved optimum conductivity enhancement at a threshold filler concentration of 0.7 wt % in the blend polymer matrix composed of poly­(ethylene oxide), poly­(vinylidene fluoride) (80:20), and salt NH4 I (35 wt %). Such an enhancement of conductivity is a result of formation of a highly conducting interphase region around the nanofiller surface. The mobility of the conducting species is found to increase enormously in the presence of a filler. As a consequence, the ionic conductivity of the filler-induced blend polymer electrolyte increases 3 times of its magnitude (3.02 × 10–3 S/cm) compared to that without a filler. The occurrence of two different activation energies which decrease with increasing filler concentrations, as determined from temperature-dependent conductivity, has been well explained from the dynamics of free and contact ions. A non-Debye behavior of relaxation properties has been analyzed using a newly approached one-parameter Mittag-Leffler function. The experimental decay function fits very well using the Mittag-Leffler function as compared to the conventional non-Debye Kohlrausch–Williams–Watts function used in the literature.

A solid polymer electrolyte (SPE) film with improved mechanical and thermal stability has drawn significant attention in the field of polymer research due to their technological applications in energy storage devices. We have explored the electrical properties of the blend SPE composed of 20 wt. % poly(ethylene oxide), 80 wt. % polyvinylidene fluoride, and 35 wt. % NH4I by introducing a plasticizer ethylene carbonate (EC). A significant enhancement of electrical conductivity has been found in the composite SPE containing 80 wt. % of EC. We have confirmed the formation of a hydrogen bonding network between the carbonyl group (C=O) of EC and the cations NH4+. Therefore, EC facilitates the new coordination sites via the hydrogen bonding network with the cations NH4+, which eventually leads to the enhancement of conductivity up to a maximum value of 1.2 × 10−4 S/cm at 80 wt. % of EC. The increase in the relative percentage of contact ions over free ions at 80% of EC, as estimated from the FTIR study, is thus intriguing. Therefore, we have proposed an ion transport mechanism based on ion hopping through different coordinating sites mediated by EC. Dielectric relaxation of the composite SPE has been best delineated by a two-parameter Mittag-Leffler function. The exponents obtained from the fit of the experimental decay function with the two-parameter Mittag-Leffler function in the entire time domain are positive and less than one, suggesting non-Debye relaxation in the polymer composite system under investigation.