Ionic Motion in Materials with Disordered Structures
Ionic Transport in Polymer Electrolytes of Variable Composition
Polymer electrolytes are used as ion conducting materials in batteries for laptops and cellular telephones. Necessary improvements in the performance of the polymer electrolytes are hindered by a lack of basic knowledge about the ion transport mechanisms. The project determines the diffusion behaviour of each individual ion species and the overall electrical conductivity with the aid of radiotracer techniques and impedance spectroscopy, respectively.
We studied ion transport in amorphous
PEO30NaI consisting of polyethylene oxide (PEO) and sodium iodide in a Na-to-O ratio
of 30. Depth profiles of 22Na and 125I were measured by means of microtome
sectioning after diffusion annealing in the temperature range from 67 to 180oC. The
125I diffusivity exceeds the 22Na diffusivity at all temperatures investigated. In
contrast to both tracer diffusivities, the dc conductivity exhibits a pronounced Vogel-Tamann-Fulcher
behavior reflected by a downward curvature in the Arrhenius plot. As a consequence, the charge diffusivity as
calculated from the dc conductivity increasingly falls below the sum of the Na and I tracer diffusivity with
increasing temperature. Evaluating simultaneously all experimental data within a combined single-ion/ion-pair
diffusion model yields not only the true diffusion coefficient of all individual species but also the ion-pairing
reaction constant as a function of temperature.
Drittmittelgeber:
Beteiligte Wissenschaftler:
Veröffentlichungen:
| 
