Conductivity study of porous plasticized polymer electrolytes based on poly(vinylidene fluoride) - A comparison with polypropylene separators

The novel porous plasticized poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF/HFP)-based electrolytes, compared with conventional polypropylene (PP) separators (Celgard(R) 2400), were studied via electrochemical impedance spectroscopy, gas adsorption/desorption method, differential scanning calorimetry, and a simple wettability test. The obtained impedance spectra of the electrolytes and separators are extensively discussed, inclusive of the effect of poor wetting upon them. The average pore diameter and Brunauer-Emmett-Teller surface area of PVDF/HFP-based electrolyte membranes are 16.4 nm and 128. m(2) g(-1),respectively. Ionic conductivity and electrolyte retention characteristic of these electrolyte membranes are superior to conventional PP separators. Moreover, PVDF/HFP-based electrolyte membranes are free from the problem of wetting whereas the poor wetting of PP separators in some electrolytes may cause its effective conductivity to decrease by at least one order of magnitude. The enhanced wettability may be achieved by virtue of the swelling phenomenon between the polymer and the electrolytes. However, the activation energy for the conduction of PVDF/HFP-based electrolytes (ca. 17 kJ mol(-1)) is still larger than that of their parent neat electrolytes (< 8.0 kJ mol(-1)), which may imply that the influence of PVDF/HFP upon ionic mobility still exists even if they have been made nanoporous. (C) 2000 The Electrochemical Society. S0013-4651(99)11-025-5. All rights reserved.