DIFFUSION AND IONIC-CONDUCTIVITY IN LI(CF3SO3)PEG(10) AND LIN(CF3SO2)(2)PEG(10)

Self-diffusion of the cation, the anion and the polymer chain in the l ow-molecular-weight polymer electrolyte systems Li(CF3SO3)PEG(10) and LiN(CF3SO2)(2)PEG(10) has been studied as a function of temperature us ing nuclear magnetic resonance spectroscopy. The diffusion behaviour i s very similar in the two systems, where the cation is diffusing attac hed to the polymer chain, while the anion is moving slightly decoupled . However, all species are slightly more mobile in LiN(CF3SO2)(2)PEG(1 0) than in Li(CF3SO3)PEG(10), due to the plasticizing effect of the N( CF3SO2)(2)(-) ion, which also explains the higher conductivity for the LiN(CF3SO2)(2)PEG(10) to system. The temperature dependence of the di ffusion coefficients is of Arrhenius type while the ionic conductivity follows the Vogel-Tammann-Fulcher relation. The diffusion has been co mpared with the conductivity by applying the Nernst-Einstein relation: a slight discrepancy is found for Li(CF3SO3)PEG(10), while the agreem ent is very good for LiN(CF3SO2)(2)PEG(10). Spin-lattice relaxation ex periments have shown that the polymer chains undergo local conformatio nal transformations, providing an additional diffusion mechanism for t he ions. Copyright (C) 1996 Elsevier Science Ltd.