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Relaxation in polymer electrolytes on the nanosecond timescale

Nature volume 405, pages 163–165 (2000)Cite this article

Abstract

The relation between mechanical and electrical relaxation in polymer/lithium-salt complexes is a fascinating and still unresolved problem in condensed-matter physics1, yet has an important bearing on the viability of such materials for use as electrolytes in lithium batteries. At room temperature, these materials are biphasic: they consist of both fluid amorphous regions and salt-enriched crystalline regions. Ionic conduction is known to occur predominantly in the amorphous fluid regions. Although the conduction mechanisms are not yet fully understood2, it is widely accepted that lithium ions, coordinated with groups of ether oxygen atoms on single or perhaps double polymer chains, move through re-coordination with other oxygen-bearing groups3,4. The formation and disruption of these coordination bonds must be accompanied by strong relaxation of the local chain structure. Here we probe the relaxation on a nanosecond timescale using quasielastic neutron scattering, and we show that at least two processes are involved: a slow process with a translational character and one or two fast processes with a rotational character. Whereas the former reflects the slowing-down of the translational relaxation commonly observed in polyethylene oxide and other polymer melts, the latter appears to be unique to the polymer electrolytes and has not (to our knowledge) been observed before. A clear picture emerges of the lithium cations forming crosslinks between chain segments and thereby profoundly altering the dynamics of the polymer network.

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Figure 1: Variations of the inverse relaxation times τ-1 for pure PEO and P(EO)7.5LiClO4 electrolyte at 75 °C.
Figure 2: Coefficients of the slow (A) and fast (B) relaxation processes for the P(EO)7.5LiClO4 electrolyte at 75 °C.
Figure 3: Inverse relaxation times τ-11 and τ-12 for the P(EO)7.5LiTFSI electrolyte at 75 °C.
Figure 4: Coefficients of the slow (A) and fast (B1 and B2) relaxation processes for the P(EO)7.5LiTFSI electrolyte at 75 °C.

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Acknowledgements

This work was supported by The Divisions of Chemical Sciences and Materials Sciences, Office of Basic Energy Sciences, US Department of Energy. We thank M. B. Armand for pointing us to the PEO–LiTFSI electrolyte and for discussions, U. Buchenau for critical reading of the manuscript, the ISIS staff for experimental support, and D. S. Sivia for providing fitting routines.

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Authors and Affiliations

  1. Argonne National Laboratory, Argonne, 60439, Illinois, USA

    Guomin Mao, Ricardo Fernandez Perea, David L. Price & Marie-Louise Saboungi

  2. Rutherford-Appleton Laboratory, Chilton, OX11 0QX, Oxfordshire, UK

    W. Spencer Howells

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  1. Guomin Mao
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Correspondence to Marie-Louise Saboungi.

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Mao, G., Perea, R., Howells, W. et al. Relaxation in polymer electrolytes on the nanosecond timescale. Nature 405, 163–165 (2000). https://doi.org/10.1038/35012032

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