Microstructure of Poly(vinylidene fluoride)-Based Polymer Electrolyte and Its Effect on Transport Properties

Poly(vinylidene fluoride- -hexafluoropropylene) (PVDF/HFP)-based membranes have been prepared using tri- -cresyl phosphate, dibutyl phthalate, propylene carbonate, or triethyl phosphate as plasticizers. Scanning electron microscopy and the gas adsorption/desorption method were used to reveal the microporous structure of the membranes. Results indicate that the boiling point and viscosity of the plasticizers are important factors during the membrane-forming process. The membrane prepared with a plasticizer of higher boiling point can achieve higher porosity, electrolyte uptake, and thus higher ionic conductivity. The pore sizes of the PVDF/HFP membranes obtained in this study are mostly below 40 nm while the average pore sizes are smaller than 20 nm. The conductivities at room temperature are higher than The transference numbers measured using the dc polarization method coupled with ac impedance spectra are found to be above 0.7 when 1 M in ethylene carbonate/γ-butyrolactone (1:1 v/v) was used as the liquid electrolyte counterpart. © 2002 The Electrochemical Society. All rights reserved.