Cationic conductivity and relaxation processes in solid polymer electrolytes with lithium perfluoroalkyl sulfonate or sulfonato end-capped poly(ethylene oxide)

Abstract

Blends of lithium perfluorinated sulfonate, C 8F 17SO 3Li, or sulfonato end-capped poly(ethylene oxide), PEO(SO 3Li) 2, with high molecular weight PEO have been used as solid polymer electrolytes. In these materials, either the anion is bulky enough or is anchored to a polymer backbone to expect the anionic transport number to be equal to zero, so that only the cation contributes to the current transport. In addition, the fluorine atoms in the first anion would decrease the ion pairing whereas the second structure may be seen as a self-solvating anion, bringing the oxygen atoms required for the solvation of the lithium cation. PEO(SO 3Li) 2 has been synthesized by reaction of PEO alcoholate with propane sultone. These solid polymer electrolytes have been characterized by d.s.c., X-ray diffraction and complex impedance spectroscopy. The conductivities at room temperature are around 10 −7 S cm −1, of the same order of magnitude as solid polymer electrolytes with only one mobile ion. Beside the resistances, some relevant parameters of the electrochemical behaviour (relaxation times, dispersive indexes) have been derived from analysis of complex impedance spectra and tentatively interpreted in the framework of charge carrier transport in heterogeneous electrolytic media in order to yield information about the morphological state of the materials.