Dresden 2014 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 3: Ionic Liquids

CPP 3.2: Vortrag

Montag, 31. März 2014, 09:45–10:00, ZEU 260

The influence of different ion-species on ionic conductivity in polymer electrolytes mixed with ionic liquids — •Joyjit Chattoraj and Andreas Heuer — Institut für Physikalische Chemie, Westfälische Wilhelm Universität Muenster, Corrensstr. 28/30, 48149 Münster , Germany

We perform molecular dynamics (MD) simulations on a system of poly(ethylene oxides) PEO chains mixed with Li-cations and TFSI-anions and additionally the MPPY-TFSI ionic liquid over a broad range of temperatures and varying ionic liquid concentrations. This is a prototype of the solid polymer electrolyte which promises an improved ionic conductivity for Li-metal batteries at room temperature. Here we investigate the influence of different ion-species associations on ionic conductivity. In general for MD simulations ionic conductivity is estimated from the mean square displacement MSD of ions using the Nernst-Einstein equation. The collective MSD is expressed as a sum of self and cross terms. We show that the cross terms have peculiar characteristics due to the conservation of momentum. To be specific we find that the cross MSD of similar ions lowers the collective MSD and the cross MSD of different type of ions enhances the MSD and so ionic conductivity. The peculiarity in the cross MSD values is then investigated via looking upon the directional and mobility correlations of ions over space and time. A phenomenological model is proposed to further explain the influence of ion associations on the ionic conductivity and the results are compared with experiments.