Monodispersed Poly(ethylene oxides) and Their Role in Conductivity Mechanism in Crystalline Polymer Electrolytes

Abstract

Previous research in the area of polymer electrolytes has been mainly focused on complexes prepared with alkali metal salts and polydispersed poly(ethylene oxides) (abbreviated to PEO).1 Previous studies have shown that polymer chain length may play a significant part in the ion transport in the crystalline phase but high distribution of molecular weight of the commercially available polymers complicates the understanding of the conductivity mechanism.2 By employing monodispersed polymers (with a discrete chain length) we attempt to reduce a number of variables that are likely to influence the ion transport process. However, monodispersed poly(ethylene oxides) are not readily available and therefore, a synthetic method has been developed to obtain a series of monodispersed homologues in a variety of chain lengths. These monodispersed polymers were used to prepare a series of crystalline complexes with a lithium salt (PEO6:LiPF6). Correlation between chain length of the polymer and unit cell parameters of the crystalline complexes in combination with molecular dynamics simulations3 revealed different structural arrangements at polymer chain-end regions. These arrangements and their role in coordination of lithium ions, ion mobility and transport, and the resulting conductivities will be presented. [1] P. G. Bruce, B. Scrosati and J. M. Tarascon, Angewandte Chemie-International Edition 2008, 47, 2930-2946. [2] E. Staunton, Y. G. Andreev and P. G. Bruce, Faraday Discussions 2007, 134, 143-156. [3]A. Liivat, D. Brandell, A. Aabloo and J. O. Thomas, Polymer 2007, 48, 6448-6456.