Regensburg 2013 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 23: Polymer Dynamics

CPP 23.10: Talk

Wednesday, March 13, 2013, 12:15–12:30, H39

A Simulation Study of the Lithium Transport Mechanism in Ternary Polymer Electrolytes – The Critical Role of the Segmental Mobility — •Diddo Diddens and Andreas Heuer — Institut für physikalische Chemie, Westfälische Wilhelms-Universität Münster

Polymer electrolytes – typically consisting of PEO and a lithium salt such as LiTFSI – are promising candidates for light-weighted but powerful energy storages. However, at ambient temperatures, the conductivity of most polymer electrolytes is still too low for an efficient technological use. Among several other remedies, the incorporation of an ionic liquid (IL) seems to be a fruitful improvement of these materials. Here, it was observed that depending on the ratio of PEO ether oxygens to lithium ions, the lithium diffusion coefficient significantly increases with the IL concentration or, alternatively, is roughly constant [Passerini et al., Electrochim. Acta, 2012]. In order to unravel the microscopic scenario giving rise to these observations, we use MD simulations in combination with a Rouse-based analytical transport model, which has originally been devised for classical polymer electrolytes. It turns out that the mobility of the PEO segments plays a decisive role for the precise value of the macroscopic lithium diffusion constant due to the cooperative motion of the lithium ions with the polymer segments. For the latter, two opposing effects are present in the ternary systems: the slowing-down due to the coordinating lithium ions and the plasticizing effect of the IL. Thus, for the design of novel battery materials, one should ensure that the latter effect dominates.