posted on 2024-03-18, 14:39authored byBonhyeop Koo, Sunwook Hwang, Kyoung Ho Ahn, Chulhaeng Lee, Hochun Lee
Acetonitrile (AN) electrolyte solutions
display uniquely high ionic
conductivities, of which the rationale remains a long-standing puzzle.
This research delves into the solution species and ion conduction
behavior of 0.1 and 3.0 M LiTFSI AN and propylene carbonate (PC) solutions
via Raman and dielectric relaxation spectroscopies. Notably, LiTFSI–AN
contains a higher fraction of free solvent uncoordinated to Li ions
than LiTFSI–PC, resulting in a lower viscosity of LiTFSI–AN
and facilitating a higher level of ion conduction. The abundant free
solvent in LiTFSI–AN is attributed to the lower Li-solvation
power of AN, but despite this lower Li-solvation power, LiTFSI–AN
exhibits a level of salt dissociation comparable to that of LiTFSI–PC,
which is found to be enabled by TFSI anions loosely bound to Li ions.
This work challenges the conventional notion that high solvating power
is a prerequisite for high-conductivity solvents, suggesting an avenue
to explore optimal solvents for high-power energy storage devices.