Regensburg 2007 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 15: Diffusion and Transport Processes

CPP 15.6: Talk

Tuesday, March 27, 2007, 16:00–16:15, H47

Diffusion and local dynamics in polysiloxane-based polymer electrolytes — Miriam Kunze¹, Yunus Karatas², Hans-Dieter Wiemhöfer², Hellmut Eckert¹, and •Monika Schönhoff¹ — ¹Institut für Physikalische Chemie und SFB 458, WWU Münster, Germany — ²Institut für Anorgansiche und Analytische Chemie und SFB 458, WWU Münster, Germany

A new improved Li ion conducting salt-in-polymer electrolyte system consisting of a polysiloxane backbone with oligoether side chains and added LiCF₃SO₃ (Li triflate = LiTf) is studied concerning the mechanisms governing ion dynamics. Conductivity values at 30 C reach up to 7.8×10⁻5 S cm⁻1 after crosslinking, which is employed to enhance mechanical stability. We characterize this system by a combination of pulsed field gradient(PFG)-NMR diffusion and spin relaxation (R₁ and R₂) of ⁷Li, ¹9F and ¹H in dependence on T and salt content. Comparing diffusion coefficients of Li and Tf with conductivity data by the Nernst-Einstein-equation reveals that transport is dominated by diffusion of neutral ion pairs and clusters, while only a low fraction of free ions exists. Evaluating activation energies from diffusion coefficients and relaxation rates, respectively, shows that the underlying activation processes governing ionic mobility can be discussed by their relevant length scale rather than by the ion involved: Activation energies of diffusion, a long range process, are much larger than those of R₂, which describe local mobility. An important conclusion is that the relatively high ionic conductivity could even be increased, if salt dissociation can be enhanced further.