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 low-molecular-weight polymer electrolyte systems Li(CF3SO3)PEG(10) and LiN(CF3SO2)(2)PEG(10) has been studied as a function of temperature using nuclear magnetic resonance spectroscopy. The diffusion behaviour is very similar in the two systems, where the cation is diffusing attached to the polymer chain, while the anion is moving slightly decoupled. However, all species are slightly more mobile in LiN(CF3SO2)(2)PEG(10) 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 diffusion coefficients is of Arrhenius type while the ionic conductivity follows the Vogel-Tammann-Fulcher relation. The diffusion has been compared with the conductivity by applying the Nernst-Einstein relation: a slight discrepancy is found for Li(CF3SO3)PEG(10), while the agreement is very good for LiN(CF3SO2)(2)PEG(10). Spin-lattice relaxation experiments have shown that the polymer chains undergo local conformational transformations, providing an additional diffusion mechanism for the ions. Copyright (C) 1996 Elsevier Science Ltd.