Correlations of ion motion and chain motion in salt-in-polysiloxane-g- oligoether electrolytes

Abstract

The transport properties of salt and chains in a salt-in-polymer electrolyte consisting of polysiloxane-g-oligoether with different concentrations of lithium triflate, LiSO 3CF 3, are investigated. Temperature-dependent impedance spectroscopy, viscosity, and multinuclear self-diffusion NMR characterize the mobility of the chains and the different salt species, i.e., ion pairs or single ions. Comparison of different transport parameters allows conclusions about the motions of different species and correlations between them. For example, comparing diffusion coefficients and conductivities via the Nernst-Einstein equation, the fraction of undissociated ion pairs is concluded to be larger than 90%. Macroscopic and microscopic viscosities describe chain and small species motions, respectively. Distinct differences are observed between the temperature-dependence of the transport parameters of ion pairs, which is of Arrhenius-type, and that of the transport of chains or single ions, which deviates from Arrhenius, indicating a strong correlation with the chain dynamics for the latter. Most interestingly, the comparison of conductivity and fluidity data shows that their temperature dependence can be fully superimposed to a master curve in an Arrhenius plot, if shifted by a small value ?(1/T) along the inverse temperature axis. This novel master curve scaling is a proof of the strong correlation of matrix and charge carrier dynamics. It is observed here for the first time in a macromolecular system, with the shift value ?(1/T) as a quantity describing the correlation. © 2012 American Chemical Society.