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, LiSO3CF3, 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 Δ(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 Δ(1/T) as a quantity describing the correlation.

Coupled Ion Conduction Mechanism and Dielectric Relaxation Phenomenon in PEO20–LiCF3SO3-Based Ion Conducting Polymer Nanocomposite Electrolytes

“…According to this mechanism, beyond the dispersive regime, the observed constancy in the crossover angular frequency causes the non-Arrhenius behavior of the dc conductivity. According to this model, the dc conductivity, σ dc , is expressed by the following expression where α and γ are the pre-exponential factors and E * is the elementary displacive step activation energy. Figure shows a comparative study between VTF and MIGRATION-based concepts for PEO 20 –LiCF 3 SO 3 –8 wt % TiO 2 PNCE composition.…”

Spectral deconvolution in electrophoretic NMR to investigate the migration of neutral molecules in electrolytes

“…Assuming validity of the Nernst–Einstein equation, transference numbers and thus the contributions of particular ion species to the conductivity can be determined . In concentrated electrolytes, however, ion correlations such as ion pair formation may play a large role, as shown for a range of different systems . In that case, the information content of diffusion coefficients is limited, and an interpretation in terms of single ions, pairs, or clusters requires complex models …”

Ion Transport Effects in a Solid Polymer Electrolyte Due to Salt Substitution and Addition Using an Ionic Liquid

“…This situation leads to a strong correlation between the mobility of Li or Na and the motion of the polymer segments. 21 By contrast, the anions are not directly bound to the polymer, so that they commonly exhibit a higher diffusivity than the cations in classical SPE systems, such as PEO−NaI. 7,22,23 In PEO−IL systems, however, the bulky organic cations only weakly coordinate to the polymer.…”

“…Surveying the literature on polymer electrolytes, it has been established that small alkali-metal cations, such as Li and Na, form strong coordinative bonds with the oxygen atoms in the PEO chains. , As a result, the conformational freedom of the polymer is constrained, which is reflected by an increase of T g . This situation leads to a strong correlation between the mobility of Li or Na and the motion of the polymer segments . By contrast, the anions are not directly bound to the polymer, so that they commonly exhibit a higher diffusivity than the cations in classical SPE systems, such as PEO–NaI. ,, …”