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-hexafluoropropylen e) (PVDF/HFP)-based electrolytes, compared with conventional polypropylene (PP) separators (Celgard(R) 2400), were studied via electrochemical impedan ce spectroscopy, gas adsorption/desorption method, differential scanning ca lorimetry, and a simple wettability test. The obtained impedance spectra of the electrolytes and separators are extensively discussed, inclusive of th e 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 re tention characteristic of these electrolyte membranes are superior to conve ntional PP separators. Moreover, PVDF/HFP-based electrolyte membranes are f ree from the problem of wetting whereas the poor wetting of PP separators i n some electrolytes may cause its effective conductivity to decrease by at least one order of magnitude. The enhanced wettability may be achieved by v irtue of the swelling phenomenon between the polymer and the electrolytes. However, the activation energy for the conduction of PVDF/HFP-based electro lytes (ca. 17 kJ mol(-1)) is still larger than that of their parent neat el ectrolytes (< 8.0 kJ mol(-1)), which may imply that the influence of PVDF/H FP 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 r eserved.