Dielectric polarization and relaxation processes of the lithium-ion conducting PEO/PVDF blend matrix-based electrolytes: effect of TiO2 nanofiller

Abstract

The effect of TiO2 nanofiller concentration on the dielectric polarization and relaxation processes of (75PEO/25PVDF)/25 wt% LiClO4–x wt% TiO2 (x = 0, 2, 5, 10, 15, and 20) compositions based nanocomposite solid polymer electrolyte (NSPE) films has been investigated by employing the dielectric relaxation spectroscopy. The SEM micrographs demonstrate that the dispersion of TiO2 nanoparticles enormously alters the spherulitic morphology with the development of some cracks, pores, and wrinkles of these solution-cast prepared NSPE films. The X-ray diffraction study confirms that the heterostructures of these NSPE materials are semicrystalline and their degree of crystallinity increases irregularly with the increase of TiO2 concentration, however the crystallinity of host polymer blend matrix of these electrolytes decreases. The complex dielectric permittivity spectra of these NSPE materials in the frequency range from 20 Hz to 1 MHz at 27 °C reveal that there is a dominant contribution of electrode polarization and interfacial polarization at lower frequencies, whereas the high frequency permittivity values attribute to dipolar and ionic polarizations. Four types of relaxation processes have been probed by the ‘master curve representation’ of the dielectric and electrical spectra of these solid ion–dipole complexes. It is observed that the addition of TiO2 nanoparticles up to 10 wt% in these electrolytes influences the dielectric properties anomalously, but a huge decrease in the dielectric polarization and increase in the relaxation times are noted resulting in a significant decrease in the ionic conductivity of the film at 20 wt% TiO2 concentration. The dependence of dc ionic conductivity of these lithium-ion conducting NSPE materials on the chain segmental relaxation time and also the degree of crystallinity has been explored. The results of these NSPE materials have also been compared with the TiO2 nanoparticles loaded different polymer matrices and salts based electrolytes and discussed appropriately. These lithium-ion based electrolyte films are accredited for the solid-state ion-conducting energy storing devices from their electrochemical parameters characterized by LSV, CV, and CA techniques.