A Molecular Dynamics Study of Short-Chain Ordering in Crystalline LiPF6PEO6
2007 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 48, no 21, 6448-6456 p.Article in journal (Refereed) Published
Molecular dynamics (MD) simulations have been made of the crystalline short-chain LiPF6·PEO6 system to probe structural ordering for different chain-end arrangements for a methyl-terminated monodisperse poly(ethylene oxide) (EO23 Mw = 1059) host polymer. Five different start structures have been studied, two "smectic" and three "nematic", to represent different types of relative alignment of the end-groups between adjacent PEO chains, and different chain-end coordination situations to the Li-ions. One particular situation is found to result effectively in Li-ion bridging between PEO chains along the chain axes, thereby creating continuous ion transport pathways across the chain breaks. This situation is also found to give rise to Li+-PF6- ion-pairing and Li-O coordination instabilities in the end-group regions, where coordination to Li-ions would appear to have a more radical influence on local structure than the issue of smectic vs. nematic end-group alignment. It could be that such structural situations involving bridging Li-ions (in both smectic and nematic arrangements) are a necessary condition for the promotion of Li-ion transport in the chain direction. Comparison of simulated and experimental XRD profiles is concluded to be an inappropriately crude and uncertain technique for distinguishing between possible short-chain ordering models.
Place, publisher, year, edition, pages
2007. Vol. 48, no 21, 6448-6456 p.
End-group ordering, LiPF6·PEO6, Polymer electrolytes
IdentifiersURN: urn:nbn:se:uu:diva-95854DOI: 10.1016/j.polymer.2007.08.051ISI: 000250492000031OAI: oai:DiVA.org:uu-95854DiVA: diva2:170213