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Role of Li concentration and the SEI layer in enabling high performance Li metal electrodes using a phosphonium bis(fluorosulfonyl)imide ionic liquid

journal contribution
posted on 05.10.2017, 00:00 authored by Gaetan Girard, Matthias HilderMatthias Hilder, D Nucciarone, K Whitbread, S Zavorine, M Moser, Maria ForsythMaria Forsyth, D R MacFarlane, Patrick HowlettPatrick Howlett
In this study the performance of the lithium (Li) anode is characterized in two alternative ionic liquid electrolytes: (i) a solution of 0.5 mol·kg-1of lithium bis- (fluorosulfonyl)imide (LiFSI) in trimethyl(isobutyl)- phosphonium FSI (P111i4FSI) and (ii) an equimolar mixture of these two salts, effectively an inorganic-organic mixture IL. We have investigated the formation of the solid electrolyte interphase (SEI) at the lithium electrode and its influence on the polarization potential, the electrode surface impedance and deposition morphologies. Lithium metal cycling is revealed to be significantly more stable in the electrolyte with high lithium salt concentration due to the creation of a more uniform SEI. Stable and effective cycling was demonstrated at high applied currents (up to 12 mA·cm-2) with large areal capacities being transferred with each polarization cycle (up to 6 mAh·cm-2at 50 °C). An average Coulombic efficiency of not less than 99.2% was demonstrated under these conditions and SEM observations of the cycled electrode surfaces show a uniform and compact deposit. Combined with spectroscopic characterization of the electrolyte and electrode surface, these observations indicate a role for the speciation and transport properties of these high concentration ionic liquid electrolytes in modifiying the physicochemical properties of the SEI which result in enhanced cycling performance of the Li metal electrode.

History

Journal

Journal of physical chemistry C

Volume

121

Issue

39

Pagination

21087 - 21095

Publisher

ACS Publications

Location

Washington, D.C.

ISSN

1932-7447

eISSN

1932-7455

Language

eng

Publication classification

C1 Refereed article in a scholarly journal

Copyright notice

2017, American Chemical Society