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Investigation of Structure and Transport in Li-Doped Ionic Liquid Electrolytes: [pyr14][TFSI], [pyr13][FSI] and [EMIM][BF4]Ionic liquid electrolytes have been proposed as a means of improving the safety and cycling behavior of advanced lithium batteries; however, the properties of these electrolytes under high lithium doping are poorly understood. Here, we employ both polarizable molecular dynamics simulation and experiment to investigate the structure, thermodynamics and transport of three potential electrolytes, N-methyl-Nbutylpyrrolidinium bis(trifluoromethylsufonyl)imide ([pyr14][TFSI]), N- methyl-Npropylpyrrolidinium bis(fluorosufonyl)imide ([pyr13][FSI]), and 1-ethyl-3-- methylimidazolium boron tetrafluoride ([EMIM][BF4]), as a function of Li-salt concentration and temperature. Structurally, Li(+) is shown to be solvated by three anion neighbors in [pyr14][TFSI] and four anion neighbors in both [pyr13][FSI] and [EMIM][BF4], and at all levels of x(sub Li) we find the presence of lithium aggregates. Furthermore, the computed density, diffusion, viscosity, and ionic conductivity show excellent agreement with experimental data. While the diffusion and viscosity exhibit a systematic decrease and increase, respectively, with increasing x(sub Li), the contribution of Li(+) to ionic conductivity increases until reaching a saturation doping level of x(sub Li) is approximately 0.10. Comparatively, the Li(+) conductivity of [pyr14][TFSI] is an order of magnitude lower than that of the other liquids, which range between 0.1 - 0.3 mS/cm. The differences in Li(+) transport are reflected in the residence times of Li(+) with the anions, which are revealed to be much larger for [pyr14][TFSI] (up to 100 ns at the highest doping levels) than in either [EMIM][BF4] or [pyr13][FSI]. Finally, we comment on the relative kinetics of Li(+) transport in each liquid and we present strong evidence for transport through anion exchange (hopping) as opposed to the net motion of Li(+) with its solvation shell (vehicular).
Document ID
20140017741
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Haskins, Justin B. (Engineering Research and Consulting, Inc. Mountain View, CA, United States)
Bennett, William R. (NASA Glenn Research Center Cleveland, OH United States)
Hernandez-Lugo, Dione M. (NASA Glenn Research Center Cleveland, OH United States)
Wu, James (NASA Glenn Research Center Cleveland, OH United States)
Borodin, Oleg (Army Research Lab. Adelphi, MD, United States)
Monk, Joshua D. (Engineering Research and Consulting, Inc. Mountain View, CA, United States)
Bauschlicher, Charles W. (NASA Ames Research Center Moffett Field, CA, United States)
Lawson, John W. (NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
December 30, 2014
Publication Date
November 16, 2014
Subject Category
Chemistry And Materials (General)
Energy Production And Conversion
Report/Patent Number
ARC-E-DAA-TN15270
Meeting Information
Meeting: American Institute of Chemical Engineers Annual Meeting
Location: Atlanta, GA
Country: United States
Start Date: November 16, 2014
End Date: November 21, 2014
Sponsors: American Inst. of Chemical Engineers
Funding Number(s)
CONTRACT_GRANT: NNA10DE12C
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
lithium batteries
electrolytes
molecular dynamics

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