Conductivity Study on PEO Based Polymer Electrolytes Containing Hexafluorophosphate Anion: Effect of Plasticizer

PEO based polymer electrolytes containing ammonium hexafluorophosphate (NH₄PF₆) and hexafluorophosphoric acid (HPF₆), both with PF anion have been studied. The effect of the addition of propylene carbonate (PC) to PEO-NH₄PF₆ and PEO-HPF₆ has been observed to increase in ionic conductivity which is attributed to an increase in free ion concentration due to the dissociation of ion aggregates present at higher acid/salt concentrations. The plasticized polymer electrolytes containing HPF₆ show relatively higher conductivity (σ_max = 1.02 × 10^?4 S/cm at 10 wt% HPF₆) as compared to electrolytes containing NH₄PF₆ (σ_max = 1.09 × 10^?5 S/cm at 10 wt% NH₄PF₆). Presence of free ions, ion aggregates and their dissociation with the addition of PC has been studied by Fourier Transform Infrared Spectroscopy (FTIR). The change in amorphous phase with PC content was also studied by X-Ray Diffraction (XRD). The variation of conductivity with temperature shows Vogel–Tammen–Fulcher (VTF) behavior, which is associated with the highly amorphous nature of electrolytes. ¹H Nuclear magnetic Resonance (NMR) spectra at different temperatures shows line narrowing and suggests the onset of long range ion diffusional motion. Change in surface morphology of polymer electrolytes with the addition of PC is also checked by Scanning Electron Microscopic (SEM) studies.