Description du sujet de thèse

Micro-supercapacitors are a promising solution for energy storage in embedded electronics, thanks to their high power and long lifespan [1]. Manganese dioxide (MnO₂) is an attractive pseudocapacitive material due to its low toxicity, abundance, and low cost. However, its application is limited by a narrow potential window in aqueous electrolytes.
Recent experiments have demonstrated that using an aprotic ionic liquid electrolyte based on sodium salt, such as sodium bis(fluorosulfonyl)imide (NaFSI) at 1 M dissolved in 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr₁₃FSI), significantly extends the MnO₂ potential window, well beyond the typical limits observed in aqueous solutions [2]. This phenomenon paves the way for higher energy density and enhanced efficiency of micro-supercapacitors.
However, the underlying electrochemical mechanisms responsible for this extension remain poorly understood. The objective of this PhD project is therefore to explore and model the interactions between MnO₂ and ionic liquids, combining both theoretical and experimental approaches.

PhD Project Objective
This project proposes a theoretical and experimental approach to understand and control charge storage mechanisms in MnO₂ in an ionic liquid environment.
1) Molecular Modeling
- Study of interactions between MnO₂ and ionic liquids using Density Functional Theory (DFT) and Reactive Molecular Dynamics (ReaxFF).
- Analysis of oxidation state evolution of Mn as a function of applied potential.
- Identification of mechanisms limiting the stability and cyclability of the material.
2) Electrochemical Measurements
- Investigation of the relative contribution of electrochemical double-layer capacitance (EDLC) and pseudocapacitance to charge storage in MnO₂ within an ionic liquid medium.
- In-situ characterization of manganese oxidation states beyond 2 V to analyze the evolution of charge storage mechanisms.
Six-month cycles of simulations and experimental validation will be alternated throughout the PhD to optimize experimental conditions and validate the developed models.

Candidate Profile: We are looking for a candidate with a background in numerical simulation, who is also interested in learning experimental electrochemistry.
Required Skills:
- Mandatory: Background in physics, theoretical chemistry, materials science, or related fields. Experience in atomistic modeling (DFT, molecular dynamics).
- Desired: Knowledge of electrochemistry and/or materials synthesis.
Additional Assets: Interest in experimentation and interdisciplinary research.
A specific training in electrochemistry will be provided during the PhD.

References
[1] N.A. Kyeremateng, T. Brousse, D. Pech, “Micro-supercapacitors as miniaturized energy storage components for on-chip electronics”, Nature Nanotechnology, vol. 12, p. 7-15 (2017).
[2] B. Bounor, J.S. Seenath, S.G. Patnaik, D. Bourrier, C.C.H. Tran, J. Esvan, L. Weingarten, A. Descamps-Mandine, D. Rochefort, D. Guay and D. Pech, “Low-cost micro-supercapacitors using porous Ni/MnO2 entangled pillars and Na-based ionic liquids”, Energy Storage Materials, vol. 63, 102986 (2023).

Contexte de travail

This PhD is funded by the Doctoral School GEET (Electrical Engineering, Electronics, Telecommunications) at Paul Sabatier University. The PhD candidate will be supervised by Alain Estève and David Pech at LAAS-CNRS (Toulouse), within the MRS team (Reactive Materials and Energy Storage). They will benefit from a dynamic research environment with access to the laboratory's experimental (cleanroom) and computational platforms.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

Constraints: Work in a controlled environment (cleanroom), requiring the wearing of specific protective clothing and strict adherence to protocols.
Risks: Possible exposure to chemical substances.