Sonderforschungsbereiche
Sonderforschungsbereich 458 - Ionenbewegung in Materialien mit ungeordneten Strukturen -
vom Elementarschritt zum makroskopischen Transport -
B12 - PD Dr. N. Stolwijk / Prof. Dr. H.-D. Wiemhöfer

Ionic Transport in Polymer Electrolytes of Variable Composition

Diffusion experiments with radiotracers allow for the ion-specific determination of transport properties in polymer electrolytes (PE). Especially for this class of electrolytes there is a strong need to measure the mobility of cations and anions individually since both species contribute substantially to the total ion conduction. Moreover, comparing the sum of the cation and anion diffusion coefficient with conductivity data may reveal the occurrence of mobile ion pairs or other electrically neutral complexes. However, the few published radiotracer studies on PE materials date back to the 1980s.

We investigated ion motion in an amorphous electrolyte consisting of poly(ethylene oxide) and sodium iodide by using the radioactive isotopes ²²Na and ¹²⁵I. Radiotracer penetration profiles were measured by means of microtome sectioning after isothermal diffusion annealing in a temperature range from 70 °C to 180 °C. Self-diffusion coefficients determined from the observed (near-)Gaussian or (near-)erfc-type profile shapes can be described by Arrhenius equations with activation energies of 0.39 eV for sodium and 0.29 eV for iodine. It is observed that iodine migrates roughly a factor of 3 faster than sodium which is more accurately expressed by the increase of the cation transference numbers from 0.16 at 70 °C to 0.32 at 180 °C. This finding agrees with earlier reports on the mobility of cations and anions in polymer electrolytes.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft

Beteiligte Wissenschaftler:

Dipl. Phys. Sh. Obeidi, PD Dr. N.A. Stolwijk (project leader), Prof. Dr. H.-D. Wiemhöfer (Anorganisch-Chemisches Institut, WWU), Dipl. Phys. B. Zazoum

Veröffentlichungen:

Sh. Obeidi, B. Zazoum, N.A. Stolwijk: Radiotracer diffusion in polymer electrolytes, 53^rd Annual Meeting of the International Society of Electrochemistry, 15. -  20. September 2002, Düsseldorf, Germany

Sh. Obeidi, B. Zazoum, N.A. Stolwijk: Radiotracer diffusion of sodium and iodine in a PEO₃₀NaI polymer electrolyte, Verhandl. DPG (VI) 38, 5/64 (2003)