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Spectroscopic characterization of the SEI layer formed on lithium metal electrodes in phosphonium bis(fluorosulfonyl)imide ionic liquid electrolytes

journal contribution
posted on 21.02.2018, 00:00 authored by Gaetan Girard, Matthias HilderMatthias Hilder, Nicolas Dupre, Dominique Guyomard, Donato Nucciarone, Kristina Whitbread, Serguei Zavorine, Michael Moser, Maria ForsythMaria Forsyth, Douglas R MacFarlane, Patrick HowlettPatrick Howlett
The chemical composition of the solid electrolyte interphase (SEI) layer formed on the surface of lithium metal electrodes cycled in phosphonium bis(fluorosulfonyl)imide ionic liquid (IL) electrolytes are characterized by magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray photoelectron spectroscopy (XPS), fourier transformed infrared spectroscopy, and electrochemical impedance spectroscopy. A multiphase layered structure is revealed, which is shown to remain relatively unchanged during extended cycling (up to 250 cycles at 1.5 mA·cm-2, 3 mA h·cm-2, 50 °C). The main components detected by MAS NMR and XPS after several hundreds of cycles are LiF and breakdown products from the bis(fluorosulfonyl)imide anion including Li2S. Similarities in chemical composition are observed in the case of the dilute (0.5 mol·kg-1 of Li salt in IL) and the highly concentrated (3.8 mol·kg-1 of Li salt in IL) electrolyte during cycling. The concentrated system is found to promote the formation of a thicker and more uniform SEI with larger amounts of reduced species from the anion. These SEI features are thought to facilitate more stable and efficient Li cycling and a reduced tendency for dendrite formation.

History

Journal

ACS applied materials and interfaces

Volume

10

Issue

7

Pagination

6719 - 6729

Publisher

American Chemical Society

Location

Washington, D.C.

eISSN

1944-8252

Language

eng

Publication classification

C1 Refereed article in a scholarly journal

Copyright notice

2018, American Chemical Society