The capability to rapidly charge a Li-ion battery is important for widespread electricvehicle adoption, but fast charging can cause battery performance issues. The degradation of
Li-ion batteries during fast charging is not well understood; however, operando research on
Li-ion cells and batteries in general has rapidly grown in popularity in the past few years to
study fast charging among other battery-related phenomena, including chemical reactions in
the electrode, SEI layer formation, electrolyte transport, and other phenomena in real-time.
Operando research has proven to be valuable for elucidating the electrochemical mechanisms
at play inside cycling batteries. Fourier transform infrared spectroscopy (FTIR) used in
conjunction with attenuated total reflection (ATR) enables operando measurements of liquid
electrolytes, including the measurement of phenomena such as molecular degradation and the
transport of Li-ions through the cell. This research focused on solvation shifting of solvent
infrared absorption bands in the presence of lithium ions. The lithium-shifted and nonlithium-shifted infrared absorption peaks of ethyl methyl carbonate and ethylene carbonate
were compared to infer ion concentration changes during cycling. Lithium concentrations
were calibrated using EC/EMC/LiPF6 electrolytes with known lithium concentrations from
0.5 mol/liter to 1.75 mol/liter. A custom Li-ion liquid half-cell with a graphite anode and
EC/EMC/LiPF6 electrolyte was assembled in an argon-filled glove box and observed with
FTIR-ATR. The results showed a rapid and abrupt change in lithium concentration at
various charging rates. These measurements were the first operando measurements of lithium
ions using FTIR/ATR and the first measurements of this kind under fast-charge conditions.
The ability to observe lithium concentration within a Li-ion cell has significant implications
for the utility of future operando studies, as well as the potential to link lithium movement
to battery performance, especially at high charging rates.
Copyright of the original work is retained by the author.
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