Electrical and Thermal studies on Sodium based polymer electrolyte

Abstract

Polymer electrolytes (PEs) have attracted much attention due to their numerous applications such as rechargeable batteries, sensors, electro chromic devices, super capacitors, etc. A series of poly(ethylene oxide) (PEO) and sodium iodide (NaI) based PEs were prepared with different concentrations, hereafter referred to as the number of oxygen atoms (n) to a sodium (n:1). In this study samples with n = 7.5,10,15,20,30,40,50,60 and 80 were prepared. In this study, PEO was used as the polymer. Acetonitrile, sodium iodide was used as solvent and salt, respectively. Free standing films of polymer electrolytes were prepared using solvent casting method. Samples were characterized by different experimental techniques like complex impedance spectroscopy, DC conductivity, polarized light microscopy and Differential Scanning Calorimetry (DSC). The dependence of salt concentration on ionic conductivity of PEO-NaI PEs was investigated using complex impedance spectroscopy whereas the changes in the spherulite formation of PEs, was observed using Polarized light microscopy. DC polarization test was used to calculate ionic transference numbers. The melting temperature and melting enthalpy were studied using DSC. The ionic conductivity increased with increasing salt concentration and the sample temperature. The amorphous nature was increased with the increasing salt concentration. This is evident from the slight reduction in the onset and the maximum temperature of the pure PEO melting peaks in samples with high salt concentrations. This is supported by the images of spherulites obtained using the polarized light microscope. Fourier Transform Infrared (FTIR) spectroscopy studies show the cation polymer interactions an important concept in ionic transport mechanism.