Crystallinity, morphology, mechanical properties and conductivity study of in situ formed PVdF/LiClO4/TiO2 nanocomposite polymer electrolytes

Nanocomposite polymer electrolytes composed of poly(vinylidene fluoride) (PVdF), lithium perchlorate (LiClO₄) and TiO₂ nanoparticles were prepared by a solution-cast method. The nanosized ceramic filler, TiO₂, was synthesized in situ by a sol-gel process. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analysis revealed that the crystalline phase and crystallinity were slightly decreased with the addition of TiO₂ to the PVdF/LiClO₄ system. Scanning electron microscopy (SEM) micrographs showed that the PVdF/LiClO₄/TiO₂ solid polymer electrolyte (SPE) membranes had a porous structure to a certain extent, and that the pore size decreased with increasing TiO₂ content. The overfull nanoparticles tended to aggregate on the surface and inside the pores at TiO₂ content above 15 wt.% so that the porosity decreased. Regarding mechanical properties, the strength of the PVdF/LiClO₄/TiO₂ electrolytes decreased after the uptake of EC/PC solution. In contrast to the conductive behavior of wet PVdF/LiClO₄/TiO₂ membranes relative to the uptake of EC/PC solution, the conductive mechanism of the solid membranes, after the lithium ion of LiClO₄ had already been installed in the PVdF solid polymer network, was mainly influenced by the TiO₂ nanoparticles. At a TiO₂ content of 10 wt.%, the solid and wet PVdF/LiClO₄/TiO₂ systems had the maximum conductivity values of 7.1 × 10⁻⁴ and 1.8 × 10⁻³ S/cm, respectively.