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Structure of the polymer electrolyte poly(ethylene oxide)6:LiAsF6

Nature volume 398, pages 792–794 (1999)Cite this article

Abstract

Polymer electrolytes—salts (such as LiCF3SO3) dissolved in solid, high-molar-mass polymers (for example, poly(ethylene oxide), PEO)1,2,3—hold the key to the development of all-solid-state rechargeable lithium batteries4. They also represent an unusual class of coordination compounds in the solid state5. Conductivities of up to 10−4 S cm−1 may be obtained, but higher levels are needed for applications in batteries5,6,7. To achieve such levels requires a better understanding of the conduction mechanism, and crucial to this is a knowledge of polymer-electrolyte structure. Crystalline forms of polymer electrolytes are obtained at only a few discrete compositions. The structures of 3 : 1 and 4 : 1 complexes (denoting the ratio of ether oxygens to cations) have been determined5,8,9. But the 6 : 1 complex is of greater interest as the conductivity of polymer electrolytes increases significantly on raising the polymer content from 3 : 1 to 6 : 1 (refs 10, 11). Furthermore, many highly conducting polymer-electrolyte systems form crystalline 6 : 1 complexes whereas those with lower conductivities do not. Here we report the structure of the PEO:LiAsF6 complex with a 6 : 1 composition. Determination of the structure was carried out abinitio by employing a method for flexible molecular structures, involving full profile fitting to the X-ray powder diffraction data by simulated annealing12. Whereas in the 3 : 1 complexes the polymer chains form helices, those in the 6 : 1 complex form double non-helical chains which interlock to form a cylinder. The lithium ions reside inside these cylinders and, in contrast to other complexes, are not coordinated by the anions.

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Figure 1: Fitted X-ray powder diffraction pattern of PEO6:LiAsF6.
Figure 2: The structure of poly(ethylene oxide)6:LiAsF6, hydrogen atoms not shown.

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Acknowledgements

We thank D. Martin and D. Engberg for their help in collection and treatment of the OSIRIS data. P.G.B. thanks the EPSRC and the Leverhulme trust for financial support.

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  1. School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, Fife, UK

    Graham S. MacGlashan, Yuri G. Andreev & Peter G. Bruce

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  1. Graham S. MacGlashan
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  3. Peter G. Bruce
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Correspondence to Peter G. Bruce.

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MacGlashan, G., Andreev, Y. & Bruce, P. Structure of the polymer electrolyte poly(ethylene oxide)6:LiAsF6. Nature 398, 792–794 (1999). https://doi.org/10.1038/19730

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