Conditions Extrêmes et Matériaux : Haute Température et Irradiation
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2021

These
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Ludivine Afonso de Araujo, 'Étude du mécanisme de dépôt de lithium par Résonance Magnétique Nucléaire operando pour optimisation de la charge rapide des batteries Li-ion', These 22 Fév 1-354 (2021)

As recognized by the 2019 Nobel Prize of chemistry, the Li-ion battery technology is nowadays ubiquitous. One of its technological limitations for the generalization of transport electrification is the reduction of the charging time. This thesis focuses on metal lithium plating on the negative electrode (graphite), a degrading mechanism related to quick charge and/or charge at low temperature. We use operando Nuclear Magnetic Resonance (NMR) to detect it at an earlier stage than with electrochemical techniques: 7Li NMR spectra of a Li-ion functioning full cell are measured in real time. NMR sensitivity is a key point for early detection of metallic lithium. The first part of this study involves the optimization of the experimental setup to attenuate the electric noise generated by cycling on the NMR spectra. Concomitantly the setup was modified, and a three-electrode cell prototype was designed to correlate the negative electrode potential to the onset of metallic lithium deposition. Moreover, a pouch cell setup was developed to achieve low temperature experiments, down to -30°C. In a second part, the protocol for data treatment (synchronization with electrochemical data, baseline treatment, signal integration, smoothing) was optimized to achieve the detection of plated lithium. Finally, the metallic lithium deposit, its chemical stability, its (electro)stripping was characterized in a battery assembled with commercial NMC and graphite electrodes. The effect of overlithiation for several charging rates, the effect of overcharge and the effect of low temperature were also all studied in a model Li-ion battery.