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Molecular Dynamics simulation of the LiPF6∙PEO6 structure
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry.
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2005 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 15, no 14, 1422-1428 p.Article in journal (Refereed) Published
Abstract [en]

Molecular dynamics (MD) simulations have been performed for the crystalline LiPF6·PEO6 system at ambient temperature in an effort to model the detail of its atomic-level structure and dynamics. Start coordinates were taken from the neutron powder diffraction analysis of Gadjourova et al., Chem. Mater., 2001, 13, 1282 (ref. ). Polymer-chain conformation, Li+-ion coordination and thermal displacement parameters are compared with experimentally determined values; the differences found are rationalised in terms of differences between the infinite-chain models investigated (both experimental and theoretical) and the finite chain-length material studied.

Place, publisher, year, edition, pages
2005. Vol. 15, no 14, 1422-1428 p.
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-92856DOI: 10.1039/b417232aOAI: oai:DiVA.org:uu-92856DiVA: diva2:166161
Available from: 2005-03-31 Created: 2005-03-31 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Understanding Ionic Conductivity in Crystalline Polymer Electrolytes
Open this publication in new window or tab >>Understanding Ionic Conductivity in Crystalline Polymer Electrolytes
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polymer electrolytes are widely used as ion transport media in vital applications such as energy storage devices and electrochemical displays. To further develop these materials, it is important to understand their ionic conductivity mechanisms.

It has long been thought that ionic conduction in a polymer electrolyte occurs in the amorphous phase, while the crystalline phase is insulating. However, this picture has recently been challenged by the discovery of the crystalline system LiXF6∙PEO6 (X=P, As or Sb) which exhibits higher conductivity than its amorphous counterpart. Their structures comprise interlocking hemi-helical PEO-chain pairs containing Li+ ions and separating them from the XF6- anions.

The first Molecular Dynamics (MD) simulation study of the LiPF6∙PEO6 system is presented in this thesis. Although its conductivity is too low for most applications at ambient temperature, it can be enhanced by iso- and aliovalent anion doping.

It is shown that the diffraction-determined structure is well reproduced on simulating the system using an infinite PEO-chain model. The Li-Oet coordination number here becomes 6 instead of 5; minor changes also occur in the polymer backbone configuration. The crystallographic asymmetric unit and diffraction profiles are also reproduced. On simulating a shorter-chain system (n=22), more resembling the real material, the structure retains its double hemi-helices, but the polymer adopts a more relaxed conformation, facilitating the formation of Li+-PF6- pairs.

Infinite-chain simulation shows the ionic conduction to be dominated by anion motion, in contrast to earlier NMR results. The effects of doping are also reproduced. Shortening the polymer chain-length has the effect of raising the transport number for lithium, thereby bring it into better agreement with experiment. It can be concluded that it is critical to take polymer chain-length and chain-termination into account when modelling ionic conductivity mechanisms in crystalline polymer electrolytes.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 63 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 34
Keyword
Chemistry, Polymer electrolyte, molecular dynamics, conductivity mechanism, aliovalent anion substitution, smectic, nematic, polymer chain length, Kemi
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-5734 (URN)91-554-6204-9 (ISBN)
Public defence
2005-04-21, Häggsalen, Ångström Laboratory, Uppsala, 13:15 (English)
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Available from: 2005-03-31 Created: 2005-03-31 Last updated: 2010-03-03Bibliographically approved

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