Sodium ion conducting nanocomposite polymer electrolyte membrane for sodium ion batteries

The paper reports effect of dispersion of titanium dioxide (TiO2) nanofiller on the sodium ion conducting nanocomposite polymer electrolyte membranes consisting of TiO2 dispersed membranes of poly(vinylidenedifluoride-co-hexafluoropropylene) (PVdF-HFP) soaked in a liquid electrolyte of sodium hexafluorophosphate (NaPF6) in ethylene carbonate (EC) and propylene carbonate (PC). The TiO2 dispersed membranes have been prepared by phase inversion technique. The structural and morphological properties of the polymer electrolyte membranes have been investigated using x-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The membranes have been found to be highly porous with maximum porosity ~ 72% and liquid electrolyte uptake ~ 270%. Ionic conductivity of the electrolyte membranes containing different concentrations of TiO2 has been measured by complex impedance spectroscopy. The maximum room temperature ionic conductivity has been found to be ~ 1.3 × 10−3 S cm−1. The ionic conductivity measured with temperature has been found to follow VTF behavior. The ion transport numbers of the membranes have been studied using dc polarization, complex impedance, and cyclic voltammetry. The membranes have been found to be predominantly ionically conducting with Na+ transport number ~ 0.31. The electrochemical stability window of the membranes has also been measured using cyclic voltammetry and found to be 3.5 V.