Polymer electrolytes based on ethylene oxide-epichlorohydrin copolymers

In this work we studied the ionic conductivity for three copolymers of the title co-monomers as a function of LIClO4 content, temperature and ambient relative humidity. We also investigated the interactions between the salt and the co-monomer blocks in the copolymers and its effect on the morphology and thermal properties of the copolymer/salt complexes. Our data indicate that the Li+ ion predominantly interacts with the ethylene oxide repeating units of the copolymers. The copolymer with the highest ionic conductivity was obtained with an ethylene oxide/epichlorohydrin ratio of 84/16 containing 5.5% (w/w) of LiClO4. It showed a conductivity of 4.1 X 10(-5) S cm(-1) (30 degrees C, humidity < 1 ppm) and 2.6 X 10(-4) S cm(-1) at 84% relative humidity (24 degrees C). The potential stability window of the copolymer/salt complex is 4.0 V, as measured by cyclic voltammetry. For comparison, we also prepared a blend of the corresponding homopolymers containing LiClO4; it showed higher crystallinity and lower ionic conductivity. (C) 2000 Elsevier Science B.V. All rights reserved.