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Reference : UMR6502-NICDUP-001
Workplace : NANTES
Date of publication : Friday, January 14, 2022
Scientific Responsible name : Nicolas Dupré
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 April 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Thanks to their very high energy densities and their long lifetime, lithium-ion (Li-ion) batteries are one of the most promising energy storage technologies. Developing applications, such as the electric vehicle or intelligent power grids, require higher energy densities and retention of cycling capacities but also increased safety requirements.
Among the negative electrode candidate materials, silicon is one of the most attractive alternatives to graphite due to its natural abundance and its high energy density (3579 mAh.g-1 vs 372mAh.g-1 for graphite). For the past 10 years, silicon has been at the center of a growing number of studies. Previous studies have shown the continuous and uncontrolled degradation of the liquid electrolyte on the surface of silicon particles, playing a significant role in the failure mechanism and responsible the end of battery life. It appears therefore necessary to understand and control the parasitic side reactions degrading the salt and the solvents of the electrolyte as well as the composition of the passivation layer on the surface to optimize the behavior of the batteries.
The proposed PhD thesis is part of an ANR project, in collaboration with CEA-LITEN (Grenoble) and LIST (Luxembourg). During this thesis work, the dynamics of formation and evolution of passivation layers will be characterized by following the mobility and the trapping of Li ions, in the case of silicon and silicon-graphite half-cells. The impact of the pre-lithiation of silicon on the evolution of the passivation layer and electrochemical performance will then be evaluated for silicon/NMC full cells. The main objective of this thesis will be to combine different characterization techniques (liquid and MAS-NMR but also XPS, impedance measurements, microscopy and electrochemical measurements) to obtain both qualitative and quantitative information on the chemical composition and the physicochemical properties. of the passivation layer. The aim of the proposed research is to develop a methodology based on solid and liquid 7Li and 6Li NMR techniques and the tracing of lithium to better understand its mobility in the passivation layer / material of electrode and study its trapping through a detailed description of the phenomenon. XPS spectroscopy and profilometry analyzes will be carried out on the surface of the electrodes in order to obtain additional information concerning the chemical structure of the passivation layer. ToF-SIMS will also be used on the surface of samples and in cross sections (obtained by in situ FIB), in order to characterize the lithium isotopic ratio in different parts of the analyzed electrodes. Operando NMR will also be considered to study Li mobility in real time during cycling. This will lead to a better understanding of the failure mechanism of Si-based electrodes for lithium batteries cycled in full-cell configuration.
IMN is a joint CNRS / University of Nantes laboratory (UMR CNRS 6502) on the chemistry and physics of materials in the solid state, and is made up of 5 teams with 75 permanent researchers, 40 technical and administrative staff and 75 doctoral students and post-docs. The doctoral student will be enrolled in the 3M doctoral school (Matériaux Matières Molécules) and will be attached to the Storage and Electrochemical Transformation of Energy (STEE) team. The research work will take place at IMN (Nantes, https://www.cnrs-imn.fr/) for 18 months then at CEA-LITEN during the second half of the thesis. Short stays at LIST are also planned. The student will be able to train and work with the following techniques: preparation and cycling of electrodes, electrochemical measurements, liquid and MAS NMR, XPS, ToF-SIMS, TEM, SEM.
Constraints and risks
Short stays at LIST are also planned.
The candidate must hold a Masters in Materials Science or Materials Chemistry.
He or she should also have the following skills: fluency in English, have knowledge of electrochemical cycling and battery testing and have experience in characterization of materials, be able to work in a team and be proactive.
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