(23e) Ionic Liquid Electrolytes for Lithium Ion Batteries—Effect of Lithium Salts On Thermal and Transport Properties

Ionic liquids (ILs) are of significant interest as non-volatile and non-flammable electrolytes for lithium ion batteries.¹ Towards developing more stable and more conductive Li-ion battery electrolytes, the thermal and transport properties of the solutions of two different lithium salts (lithium iodide and lithium bistriflamide) in six different ILs [1,3-dialkylimidazolium iodide,² 1,3-dialkylimidazolium bistriflamide, PEGylated imidazolium iodide,² PEGylated imidazolium bistriflamide,³ (ω-perfluoroalkyl)PEG-derivatized imidazolium iodide,³ and (ω-perfluoroalkyl)PEG-derivatized imidazolium bistriflamide³] were characterized using differential scanning calorimetry, viscometry, electrochemical impedance spectroscopy, and pulsed field gradient nuclear magnetic resonance diffusion experiments. PEGylation improved lithium salt solubility in the ILs. Complexation of lithium ions with the ether oxygen atoms of the PEG moieties strongly affected thermal properties, such as the glass transition temperature, and transport properties such as viscosity, self-diffusion coefficient, and ionic conductivity. The properties of the IL–salt blends were analyzed using a recently reported mathematical framework relating viscosity, diffusion coefficient, and conductivity.⁴ Structure–property correlations were also investigated through molecular dynamics simulations conducted using Materials Studio.

References

1) Rock, S.; Lin, W.; Crain, D.; Krishnan, S.; Roy, D. Interfacial Characteristics of a PEGylated Imidazoliujm Bistriflamide Ionic Liquid Electrolyte at a Lithium Ion Battery Cathode of LiMn₂O₄. ACS Appl. Mater. Interfaces 2013, 5, 2075-2084.

2) Ganapatibhotla, L. V. N. R.; Zheng, J.; Roy, D.; Krishnan, S. PEGylated Imidazolium Iodide Ionic Liquid Electrolytes: Thermophysical and Electrochemical Properties. Chem. Mater. 2010, 22, 6347-6360.

3) Ganapatibhotla, L. V. N. R.; Wu, L.; Zheng, J.; Jia, X.; Roy, D.; McLaughlin, J. B.; Krishnan, S. Ionic Liquids with Fluorinated Block-oligomer Tails: Impact of Self-assembly on Transport Properties. J. Mater. Chem. 2011, 21, 19275-19285.

4) Lebga-Nebane, J. L; Rock, S.; Franclemont, J.; Roy, D.; Krishnan, S. Thermophysical Properties and Proton Transport Mechanisms of Trialkylammonium and 1-Alkyl-1H-imidazol-3-ium Protic Ionic Liquids. Ind. Eng. Chem. Res. 2012, 51, 14084-14098.