(28h) Structure and Transport in Pyrrolidinium- and Imidazolium- Tfsi Ionic Liquids Doped with Litfsi | AIChE

(28h) Structure and Transport in Pyrrolidinium- and Imidazolium- Tfsi Ionic Liquids Doped with Litfsi


Borodin, O. - Presenter, University of Utah
Smith, G. D. - Presenter, University of Utah

We present structure and dynamics of pure and doped with
0.25 mol LiTFSI N-methyl-N-propyl pyrrolidinium+TFSI- (mppy+TFSI-)
and ethyl-methyl-imidazolium+TFSI- ionic liquids. The
liquid density, ion self-diffusion coefficients and conductivity predicted by
MD simulations were found to be in good agreement with experimental data, where
available. The Li+ cations were found to be coordinated on average
by slightly less than four oxygen atoms with each oxygen atom being contributed
by a different TFSI- anion in both imidazolium and pyrrolidinum-based ionic
liquids.  Significant lithium aggregation through up to three TFSI-
anions bridging lithiums was observed (Li+?(O=S=O)m?Li+),
m=1,2,3, particularly at lower temperatures where the lithium aggregates were
found to be stable for tens of nanoseconds. Polarization of TFSI-
anions is largely responsible for the formation of such lithium aggregates.  Li+
transport was found to occur primarily by exchange of TFSI- anions
in the first solvation shell with a smaller (~30%) contribution also due to Li+
cations diffusing together with their first solvation shell. Conductivity contribution
due to the Li+ cation in LiTFSI doped mppy+TFSI-
ionic liquids was found to be greater than that for a model poly(ethylene
oxide)(PEO)/LiTFSI polymer electrolyte but significantly lower than that for
ethylene carbonate/LiTFSI liquid electrolyte.   Finally, the time-dependent
shear modulus for the ionic liquids is compared with that for polymers and
nonionic liquids


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