EFFECTS OF POLYMER MATRIX AND SALT CONCENTRATION ON THE IONIC-CONDUCTIVITY OF PLASTICIZED POLYMER ELECTROLYTES

Abstract

Two polar polymers with different dielectric constants, poly(vinylidene fluoride) (PVDF) and poly (ethylene oxide) (PEG), were each blended with a chlorine-terminated poly(ethylene ether) (PEG) and one of the two salts, LiBF4 and LiCF3CO2, to form PEC-plasticized polymer electrolytes. The room-temperature ionic conductivity of the PEC-plasticized polymer electrolytes reached a value as high as 10(-4) S/cm. The room-temperature ionic conductivity of the PVDF-based polymer electrolytes displayed a stronger dependence on the PEC content than did the PEG-based polymer electrolytes. In PVDF/PEC/LiBF4 polymer electrolytes, the dynamic ionic conductivity was less dependent on temperature and more dependent on the PEC content than it was in PEO/PEC/LiBF4 polymer electrolytes. The highly plasticized PVDF-based polymer electrolyte film with a PEC content greater than CF4 (CF4 defined as the molar ratio of the repeat units of PEC to those of PVDF equal to 4) was self-supported and nonsticky, while the corresponding PEG-based polymer electrolyte film was sticky. In these highly plasticized PVDF-based polymer elec trolytes, the curves of the room-temperature ionic conductivity vs. the salt concentration were convex because the number of carrier ions and the chain rigidity both increased with increase of the salt content. The maximum ionic conductivity at 30 degrees C was independent of the PEC content, but it depended on the anion species of the lithium salts in these highly plasticized polymer electrolytes. (C) 1995 John Wiley and Sons, Inc.