Diffusive solvent dynamics in a polymer gel electrolyte studied by quasielastic neutron scattering

Abstract

A quasielastic neutron scattering study has been performed on a polymer gel electrolyte consisting of lithium perchlorate dissolved in ethylene carbonate/propylene carbonate and stabilized with poly(methyl methacrylate). The dynamics of the solvent, which is crucial for the ion conduction in this system, was probed using the hydrogen/deuterium contrast variation method with nondeuterated solvent and a deuterated polymer matrix. Two relaxation processes of the solvent were studied in the 10-400 microeV range at different temperatures. From analysis of the momentum transfer dependence of the processes we conclude that the faster process ( approximately 100 microeV) is related to rotational diffusion of the solvent and the slower process ( approximately 10 microeV) to translational diffusion of the solvent. The translational diffusion is found to be similar to the diffusion in the corresponding liquid electrolyte at short distances, but geometrically constrained by the polymer matrix at distances beyond approximately 5 A. The study indicates that the hindered diffusion of the solvent on a length scale of the polymer network interchain distance ( approximately 5-20 A) is sufficient to explain the reduced macroscopic diffusivity and ion conductivity of the gel electrolyte compared to the liquid electrolyte.

Even Hard-Sphere Colloidal Suspensions Display Fickian Yet Non-Gaussian Diffusion

“…Diffusion of this sort is common in nature and technology. Examples include water diffusing through sand beds (a geology problem), solvents diffusing through polymer gels (a materials problem), and carbon diffusing through steel (a metallurgy problem) . A vast theoretical and experimental literature on diffusion and hydrodynamics focuses on the effective diffusivity. − To the best of our knowledge, these prior studies did not address the displacement distributions that are of primary concern here.…”

Trade‐offs between ion‐conducting and mechanical properties: The case of polyacrylate electrolytes

“…By virtue of the presence of fluidic media as well as their plasticization, ion transport in PA‐based GPEs is partially or entirely decoupled from the segmental motion of the polymer backbone 39,40 . Although the segmental dynamics of gelled PAs is enhanced, the long‐range diffusion of solvated Li + ions is inevitably hindered by PA skeletons 41 . The ion migration, a thermally activated diffusion process, follows the Arrhenius law: $$${\rm{\sigma }}={\sigma }_{0}\text{exp}\left(\frac{-\unicode{x02206}E}{{RT}}\right),$$$where σ is the conductivity, σ 0 is the preexponential factor, T is the thermodynamic temperature, R is the ideal gas constant, and ∆E (J mol −1 ) is the activation energy.…”

“…39,40 Although the segmental dynamics of gelled PAs is enhanced, the longrange diffusion of solvated Li + ions is inevitably hindered by PA skeletons. 41 The ion migration, a thermally activated diffusion process, follows the Arrhenius law:…”