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Issue 33, 2011
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Ionic liquids and oligomer electrolytes based on the B(CN)4 anion; ion association, physical and electrochemical properties

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Abstract

The role of B(CN)4 (Bison) as a component of battery electrolytes is addressed by investigating the ionic conductivity and phase behaviour of ionic liquids (ILs), ion association mechanisms, and the electrochemical stability and cycling properties of LiBison based electrochemical cells. For C4mpyrBison and C2mimBison ILs, and mixtures thereof, high ionic conductivities (3.4 ≤ σion ≤ 18 mS cm−1) are measured, which together with the glass transition temperatures (−80 ≤ Tg ≤ −76 °C) are found to shift systematically for most compositions. Unfortunately, poor solubility of LiBison in these ILs hinders their use as solvents for lithium salts, although good NaBison solubility offers an alternative application in Na+ conducting electrolytes. The poor IL solubility of LiBison is predicted to be a result of a preferred monodentate ion association, according to first principles modelling, supported by Raman spectroscopy. The solubility is much improved in strongly Li+ coordinating oligomers, for example polyethylene glycol dimethyl ether (PEGDME), with the practical performance tested in electrochemical cells. The electrolyte is found to be stable in Li/LiFePO4 coin cells up to 4 V vs.Li and shows promising cycling performance, with a capacity retention of 99% over 22 cycles.

Graphical abstract: Ionic liquids and oligomer electrolytes based on the B(CN)4− anion; ion association, physical and electrochemical properties

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Supplementary files

Article information


Submitted
06 Apr 2011
Accepted
20 Jun 2011
First published
21 Jul 2011

Phys. Chem. Chem. Phys., 2011,13, 14953-14959
Article type
Paper

Ionic liquids and oligomer electrolytes based on the B(CN)4 anion; ion association, physical and electrochemical properties

J. Scheers, J. Pitawala, F. Thebault, J. Kim, J. Ahn, A. Matic, P. Johansson and P. Jacobsson, Phys. Chem. Chem. Phys., 2011, 13, 14953
DOI: 10.1039/C1CP21062A

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