Low temperature structures and phase behaviour of solvents and liquids for lithium-ion batteries crystallized in-situ
Jeudi 25 octobre 2012 15:00
- Duree : 1 heure
Lieu : ILL 4, Salle de Séminaires, 1er étage - 6 rue Jules Horowitz 38042 Grenoble Cedex 09
Orateur : Dr Pamela WHITFIELD (National Research Council Canada - Ottawa)
Lithium-ion batteries tend not to function well in cold conditions. This fact is very well known during a Canadian winter, where keeping a camera or mobile phone in an inside pocket to keep warm is common practice when the temperature starts to plunge. In addition to the familiar limitations of chemical kinetics with decreasing temperatures, the freezing point of the common electrolytes and their constituent solvents are unfortunately much closer to 0°C than -50°C. Consequently, the low temperature phase behaviour of existing and new electrolytes and electrolyte components is an area of considerable interest when considering the real-world performance of a lithium-ion cell. On a simplistic phase-ID level, low temperature in-situ measurements need to identify any electrolyte components that may appear, and such basic data does not yet exist.
There are already a number of low temperature crystal structures of various organic solvents and liquids in the Cambridge Structure Database and elsewhere. Common solvents such as acetone [1] and THF [2] have been studied together with some less mainstream compounds such as dithiols [3], but the structures of other important solvents such as isopropyl alcohol and dimethyl carbonate have never been published. Most of the structures in the published literature have either been solved using single crystal techniques (often at a single temperature) or neutron powder diffraction (sample crushed at low T into powder after cooling). Crystallizing the sample as a fine-grained solid inside a capillary would seem to be the easiest approach allowing for easy lab-based non-ambient studies, but tends to produce datasets exhibiting orientation to a greater or lesser degree. A generalized approach to overcome the problem was demonstrated in 2009 [4]. Phase behaviour studies and structure solutions from quenched and crystallized solvents have become routine in our laboratory, although not every solvent has been successfully crystallized. The additional uncertainties/variables introduced by possible orientation effects on the relative intensities and the technique to overcome them, means that computational validation using VASP is carried out on all candidate crystal structures where possible
The methodology used and a selection of behaviour and structures of solvents and additives for existing and potentially novel lithium-battery electrolytes will be described. Additionally, some interesting behaviour from other solvents will be mentioned.
Pamela Whitfield, Yvon Le Page, Yaser Abu-Lebdeh, Nuha Salem & Isobel Davidson
[1] D.R. Allen et al, Chem. Commun., (1999) p.751-752
[2] W.I.F. David & R.M. Ibberson, Acta Cryst., C48 (1992), p.301-303
[4] V.R. Thalladi, R. Boese & H-C. Weiss, J.Am.Chem.Soc., 122 (2000) p.1186-1190
[4] P.S. Whitfield, J.Appl.Cryst., 41 (2009) p.134-136
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