Concentration Dependent Solution Structure and Transport Mechanism in High Voltage LiTFSI-Adiponitrile Electrolytes
Journal article, 2020

The physiochemical properties of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in adiponitrile (ADN) electrolytes were explored as a function of concentration. The phase diagram and ionic conductivity plots show a distinct relationship between the eutectic composition of the electrolyte and the concentration of maximum ionic conductivity in the 25 degrees C isotherm. We propose a structure-based explanation for the variation of electrolyte ionic conductivity with LiTFSI concentration, where the eutectic concentration is a transitionary region at which the structure changes from solvated contact ion pairs to extended units of [Li-z(ADN)(x)TFSIy](z-y) aggregates. It is found through diffusion coefficient measurements using pulsed-field gradient (PFG) NMR that both D-Li/D-TFSI and D-Li/D-ADN increase with concentration until 2.9 M, where after Li+ becomes the fastest diffusing species, suggesting that ion hopping becomes the dominant transport mechanism for Li+. Variable diffusion-time (Delta) PFG NMR is used to track this evolution of the ion transport mechanism. A differentiation in Li+ transport between the micro and bulk levels that increases with concentration was observed. It is proposed that ion hopping within [Li-z(ADN)(x)TFSIy](z-y) aggregates dominates the micro-scale, while the bulk-scale is governed by vehicular transport. Lastly, we demonstrate that LiTFSI in ADN is a suitable electrolyte system for use in Li-O-2 cells. (c) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.

Author

Christopher J. Franko

McMaster University

Chae-Ho Yim

National Research Council Canada

Fabian Årén

Chalmers, Physics, Materials Physics

Gustav Åvall

Chalmers, Physics, Materials Physics

Pamela S. Whitfield

National Research Council Canada

Patrik Johansson

Chalmers, Physics, Materials Physics

Yaser A. Abu-Lebdeh

National Research Council Canada

Gillian R. Goward

McMaster University

Journal of the Electrochemical Society

0013-4651 (ISSN)

Vol. 167 16 160532

Subject Categories

Inorganic Chemistry

Physical Chemistry

Materials Chemistry

DOI

10.1149/1945-7111/abcf17

More information

Latest update

1/8/2021 4