Description du sujet de thèse

Context: 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 time. 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.

Objective: Based on these preliminary results, the objective of the thesis project is to utilize infrared fiber evanescent wave spectroscopy to go much further in the diagnostic of battery chemical reactions and interface formations in real-time. Specifically, the focus will be on studying by IR-FEWS the evolution of electrolytes and the formation of parasitic products—whether soluble, solid (at the interface), or gaseous— during battery operation. Coupled with quantification methods such as inductively coupled plasma mass spectrometry (ICP-MS) and titration gas chromatography (TGC), this approach will enable obtaining a more holistic understanding of the chemical dynamics within the battery. We will then correlate these observations with long-term battery cycling data to elucidate the factors that affect battery longevity and performance. The methodology will be used for pushing the development of new electrolyte formulations and formation protocols, which are shorter, optimized, more reliable, and suitable for different active materials and electrolytes.

Profile of the candidate: Degree in engineering or a master's in physics or chemistry. The candidate must have a strong aptitude for experimentation and be capable of adapting to problems from different fields. Proficiency in English and programming skills in Python are required.

Contexte de travail

The CSE lab is a renowned expert in the field of batteries, with its major achievements including the search for new Li reactivity mechanisms, the mastery of interfaces, the assembly of cells, and the exploration of chemistries beyond Li-ion such as Na-ion and all-solid-state batteries. The laboratory is also pioneer in integrating optical fibers into batteries for monitoring physicochemical processes under real conditions.

The doctoral work is part of the SENSIGA project, which is part of the Battery2030 initiative. In this context, collaborations will be carried out with the PHENIX laboratory to complement the experimental results with theoretical calculations. Additionally, expertise on infrared fibers will be provided by the Institute of Chemical Sciences of Rennes (ISCR), while expertise in modeling battery health will be offered by the CEA.