Optimization of polymer electrolytes with the effect of concentration of additives in PEO-NH4HF2 polymer electrolytes

Abstract

In the present work, nanocomposite polymer electrolyte films were prepared by solution casting technique using nanosized fumed silica to polyethylene oxide (PEO)-based polymer electrolytes containing ammonium bifluoride (NH4HF2). The ionic conductivity of 1.19 × 10−5 S cm−1 has been observed at room temperature (25°C) for 3 wt% fumed silica in PEO-10 wt% NH4HF2 polymer electrolytes after which the conductivity was observed to decrease. Furthermore, the addition of high dielectric constant plasticizer propylene carbonate (PC) in the optimized composition of nanocomposite polymer electrolytes has increased the number of charge carriers by the large dissolution of ionic salt, amorphous content, and hence the ionic conductivity. Maximum ionic conductivity obtained at room temperature was found to be 1.55 × 10−4 S cm−1 in the case of PEO-10 wt% NH4HF2-3 wt% fumed silica-0.3 (ml) PC polymer electrolytes which is five orders of magnitude higher than that of the polymer host material. Temperature-dependent ionic conductivity, activation energy, and dielectric constant studies have been described for all the compositions of polymer electrolytes. Ionic conductivity and dielectric constant studies were determined from impedance data. Polymer electrolytes containing both fumed silica and PC highlight that there is no phase transition in the polymer electrolyte and temperature dependence of ionic conductivity in the temperature range is of almost Arrhenius type. The lowest activation energy value for the highest conducting polymer electrolyte was found to be 0.172 eV. Change in melting temperature, % crystallinity ( χ c), and mechanical properties have also been observed in polymer electrolytes containing fumed silica as well as PC as studied by Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TGA) and universal testing machine, respectively.