Abstract

As part of the project "Engineering of electrode materials for the development of Li-ion batteries and supercapacitors with high energy density supported by the New Aquitaine authority", a PhD position is available to work on the charge storage mechanisms in Mn-Co nanocomposites for supercapacitors. The work will consist into:

- The study of lamellar oxide nanocomposites of Mn and Co for the development of more efficient hybrid supercapacitors. These composite materials are designed by stacking nano-objects of different compositions so as to combine complementary properties to go towards the optimization of performance in terms of power and energy,

- the understanding of the properties at solid/solid interfaces between nano-layers, which govern the physico-chemical properties of the composite and its performance during cycling. A large part of the research will focus on the study of these solid/solid and solid/electrolyte interfaces of these systems by purely computational approaches or combining experience and theory.

Scientific Context

This research project is part of the context of the electrochemical storage of energy by supercapacitors. The potential in terms of performance of supercapacitors, used for many years in small format devices (10 F / 2.5 V) for applications of the electronic power type, have led manufacturers to consider extending their applications to military, space, aeronautics or transport, to larger formats (several kW). However, supercapacitors still suffer from a too limited energy density (8Wh / kg approximately). In the context of hybrid vehicles, it is therefore necessary to increase energy densities, so that these systems can play their full role as a source of power, in addition to energy sources that are batteries. The performance of hybrid supercapacitor systems is closely related to the surface and interface phenomena of the materials that compose them, and more specifically it is the storage of charges and the insertion / de-insertion of surface ions which are at the origin of performance. A better understanding of the storage mechanisms of loads would better guide the optimization of materials for an increase in the density of power and energy. In this context, the development of materials with controlled morphologies associated with a thorough knowledge of the chemical mechanisms involved in surfaces and interfaces appears essential to meet the major challenges of hybrid supercapacitors.

Objectives

The project will focus on the identification and understanding of the differences in the reactivity of materials in relation to their morphology and the electronic structure of their surface for the improvement of electrochemical performances. The main objectives of the project are:

- the synthesis of nanocomposites based on A_xH_yMO₂ lamellar oxides / oxyhydroxides (M = Ni, Co, Mn) for hybrid supercapacitors, having morphologies, sizes, compositions and controlled structures,

- the study of the influence of surface modification of the active material on reactivity, by combining surface characterization methods and theoretical approaches at the atomic scale.

- control of surface phenomena and interfaces: the control of reactivity at the solid-solid and solid-liquid interfaces requires optimizing and understanding the mechanisms of charge storage on the surface of Mn oxyhydroxide particles and Co, and the respective role of these particles vis-à-vis the synergy of properties observed.

Litterature

• Quesne-Turin A., Flahaut D., Croguennec L., Vallverdu G., Allouche J., Charles-Blin Y., Chotard J.-N., Ménétrier M., Baraille I., The surface reactivity of Li2MnO3: First principles and experimental study Applied Materials and Interfaces. DOI 10.1021/acsami.7b14826
• Martin, L.; Vallverdu, G.; Martinez, H.; Cras, F. L.; Baraille, I. First Principles Calculations of Solid–solid Interfaces: An Application to Conversion Materials for Lithium-Ion Batteries. J. Mater. Chem. 2012, 22, 22063–22071
• Andreu N., Flahaut D., Dedryvère R., Minvielle M., Martinez H., Gonbeau D., XPS investigation of surface reactivity of electrode materials: effect of the transition metal, Applied Materials and Interfaces 2015, 7, 6629-6636.

Skills and knowledge

The candidates must have knowledge in:

• Physical chemistry and theoretical chemistry. Experience in supercapacitors will be appreciated.
• in characterization methods of materials in bulk (XRD, OCP, SEM and/or TEM) and/or surface (XPS, AES)

The candidates must demonstrate:

• a good organization;
• ability to present results issued from its research;
• ability to work in a team and to be capable of caring himself;

Contact

[email protected] [email protected] [email protected]