Description du sujet de thèse

The objective of this thesis is to use optical characterization techniques to study chemical and electrochemical processes within energy storage systems, particularly batteries. Specifically, fiber evanescent wave spectroscopy will be employed to monitor not only the reduction of the electrolyte, but also the formation of parasitic products, whether soluble or solid. This technique will be employed to monitor not only electrolyte reduction, but also the formation of parasitic products, whether soluble or solid. Such an approach will enable a more holistic understanding of the mechanisms at play in these systems.
The spectroscopic data obtained will then be correlated with long-term cycling data in order to elucidate the factors influencing battery longevity and performance.
As part of the SENSIGA project, this work will be carried out in collaboration with theoretical chemists from the PHENIX laboratory, who will complement the experimental results with theoretical calculations. In addition, expertise on infrared optical fibers will be provided by the Institut des Sciences Chimiques de Rennes (ISCR), while the CEA will contribute expertise in battery degradation modeling.
Through a synergistic approach combining experimental data generation and modeling, the project aims to develop a technology capable of bridging the gap between complex chemical and electrochemical degradation phenomena and the long-term performance of energy storage systems.

Contexte de travail

As global energy demands escalate, and the use of non-renewable resources becomes untenable, renewable resources and electric vehicles require more advanced batteries to stabilize the new energy landscape. To optimize battery performance and extend their lifespan, it is essential to understand and monitor the fundamental mechanisms that govern their operation throughout their lifecycle. Since 2020, the Solid-State Chemistry and Energy Lab at Collège de France has become one of the leaders in the operando characterization of batteries. Utilizing optical sensors, which are both small and versatile, we could track thermal, mechanical and chemical properties of batteries in real time1. Notably, the integration of infrared fiber evanescent wave spectroscopy (IR-FEWS) into commercial 18650 sodium-ion cells has enabled live monitoring of battery electrolyte reduction under real-world conditions. Those fibers made of chalcogenide glass (Te2As3Se5 or TAS), enable efficient transmission of infrared light from 3 to 13 µm and the generation of an evanescent wave at the fiber surface. Like classic absorption spectroscopy, this wave can be absorbed by the molecules located in the proximity of the fiber, enabling their investigation inside cells.

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