A paper by Hongjun Liu (Hongjun Liu and Edward J. Maginn, “Effect of Ion Structure on Conductivity in Lithium-Doped Ionic Liquid Electrolytes: A Molecular Dynamics Study”, Journal of Chemical Physics, 2013, 139, 114508 http://jcp.aip.org/resource/1/jcpsa6/v139/i11/p114508_s1) was recently published. In this work, it is shown that ionic liquid electrolytes having planar anions that weakly coordinate with Li+ ions can lead to enhanced lithium conductivities relative to that observed in ionic liquids with more conventional anions such as bistrifylimide. This is due to the way in which Li+ organizes with respect to the anions in repeating manner, as shown in the figure below on the left. Lithium (shown as a pink sphere) coordinates with two pyrrolide anions in a planar orientation, while the cations (in this case, 1-n-butyl-4-methylpyridinum) are further away. In this figure, hydrogen atoms are omitted for clarity.
In the figure on the right, it is observed that the oxygen atoms of bistrifylimide strongly coordiante with the lithium ion, with four oxygen atoms binding in a combination of bidentate and monodentate orientations. This significalty slows the mobility of Li+, which is why ionic liquids hainvg bistrifylimide anions have poor conductivities. The calculations predict that anions such as pyrrolide have much better Li+ conductivities.