Catalysis

Engineering

Lithium (medication)

Polymer chemistry

Electrochemistry

Magic angle spinning

Materials science

Imide

Endocrinology

Nuclear magnetic resonance spectroscopy

Inorganic chemistry

Chemical engineering

Physical chemistry

Organic chemistry

Phosphonium

X-ray photoelectron spectroscopy

Medicine

Chemistry

Ionic liquid

Electrode

Electrolyte

ACS Applied Materials & Interfaces

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.

Spectroscopic Characterization of the SEI Layer Formed on Lithium Metal Electrodes in Phosphonium Bis(fluorosulfonyl)imide Ionic Liquid Electrolytes