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Reference : UMR5085-CELMER-003
Workplace : TOULOUSE
Date of publication : Thursday, June 10, 2021
Scientific Responsible name : Céline Merlet
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 November 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Electrochemical Quartz Crystal Microbalance (EQCM) is a method of choice to study in situ the charge / discharge mechanisms in electrochemical energy storage systems such as batteries and supercapacitors. When conditions are adequate, it is possible to relate the frequency variations of a quartz crystal resonator to mass changes and ion fluxes at its surface with a sensitivity of a few ng/cm2 . At the CIRIMAT laboratory, this method was employed to study the interface between a carbon electrode and various electrolytes, and its evolution when applying a potential. One of the challenges associated with EQCM is that only one mass value is measured for each potential, resulting in fact from different ion and solvent fluxes. It is therefore necessary to make a number of hypotheses to interpret the results. Another difficulty is the existence of other phenomena, dissipative for example, which can affect the resonator frequency. To make the link between microscopic events and the macroscopic mass variation, it is possible to conduct atomistic molecular simulations. These simulations have been shown to provide a good agreement with experiments for a number of properties (quantities of ions adsorbed in the porous electrodes, capacitances, solvation numbers) but do not provide satisfactory interpretations for EQCM results to date. Due to long computation times and limited system sizes (simulations of carbon structures of a few nanometers for simulations, far from the micrometric particles used experimentally), molecular simulations alone are not necessarily the most suitable ones to interpret experiments. In particular, experimental carbons are often characterised by their pore size distribution, which is not correctly represented in small systems. So-called mesoscopic models, which can simulate micrometer-sized systems much faster (~ 10,000 times faster than molecular simulations), can then be developed. This has been done in the past to predict quantities of ions adsorbed in carbon materials and NMR spectra. Nevertheless, as for molecular simulations, the results of the mesoscopic simulations provide a good agreement with experiments for a number of properties but not for EQCM.
The objectives of the project are:
- to clearly establish the link between the microscopic properties of the electrode/electrolyte interface and the mass/frequency variations measured by EQCM;
- to improve the mesoscopic models based on this new knowledge in order to be able to simulate EQCM experiments more quickly and to help in the interpretation of these experiments.
While focused on carbon materials, the development of advanced modelling techniques to simulate EQCM experiments opens the door to a better understanding of many electrode materials used in batteries and supercapacitors. On the simulation side, there are a number of effects which can lead to discrepancies with experiments. In this project, we will use state-of-the-art molecular simulation techniques to explore the influence of several factors on the EQCM predictions. While modelling EQCM curves is the main objective, the simulations conducted will also be used to determine other properties, relevant to the performance of energy storage systems, bringing new fundamental insights into the charging mechanisms and the electrode/electrolyte interface.
This PhD is funded by the Réseau sur le Stockage Électrochimique de l'Énergie (RS2E) and is a joint project between the CIRIMAT laboratory in Toulouse (supervision by Céline Merlet) and the PHENIX laboratory in Paris (supervision by Mathieu Salanne). In the CIRIMAT laboratory, regular meetings with the experimentalists conducting the EQCM measurements, the team of Patrice Simon and Pierre-Louis Taberna, will be organised.
Constraints and risks
No constraints or specific risks.
Applicant's profile: The applicant should have (or be about to receive) a master in chemistry, materials science or physics and be interested in doing theoretical work. Some experience in programming and/or in molecular simulations and statistical physics would be appreciated.
For any additional information on the project and/or the recruitment process, it is possible to contact Céline Merlet (firstname.lastname@example.org). All applications must be sent through the “portail emploi CNRS” and must include a CV and a cover letter.
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