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Investigating Li-ion battery species dynamics with operando FTIR spectroscopy

Meyer, Lydia
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2025-06-24
Abstract
Lithium concentration polarization and slow ionic transport hinder fast charging of electric vehicle batteries and can cause cell degradation. Although pseudo-2D (P2D) models capture concentration polarization phenomena during fast charging, experimental measurements of Li-ion concentration have been limited. In this research, we collect operando optical measurements of Li-ion concentration in a graphite/NMC811 full cell with attenuated total reflection (ATR) and Fourier transform infrared spectroscopy (FTIR). To make these measurements, we have developed an optically accessible operando battery that enables real-time measurements of Li-ion concentration during cycling at fast charging rates. We measured significant Li-ion concentration changes during charging at 1C, 2C, and 3C, as well as discharging at C/2 and compared these results with a P2D model. Both the model and the experiments showed Li-ion depletion and rapid Li-ion concentration fluctuations that indicate non-ideal behavior during cycling. This research enables novel Li-ion concentration measurements with FTIR. This research also provides validation of P2D model physics for measuring and analyzing Li-ion concentration polarization at fast charging rates.
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