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.