Flotation for Li-ion active materials recycling : limitations and influence of hydrodynamics and interfacial physico-chemistry on their selective separation
Battery recycling is now a major geopolitical, economic and environmental issue for the EU. Graphite, which makes up the anode of Li-ion batteries, is very rarely recycled. It is concentrated in a fraction called blackmass, where it is mixed with metal oxides of high commercial value. This graphite is then considered as an impurity and causes oversizing of hydrometallurgical operations. Since natural graphite is considered critical by EU and in order to reduce the operating and investment costs of hydrometallurgical processes, it is proposed to carry out a pre-treatment step on the blackmass in order to valorize the graphite directly. This stage is carried out by flotation. This process for separating solids suspended in water uses gas in the form of air bubbles to separate the particles according to their difference in wettability and therefore their attachment to the air bubbles. The complexity of the flotation process, linked to the dependence on both the nature of the interfaces and the hydrodynamic conditions, requires in-depth understanding of the mechanisms involved.
The aim of the proposed project, which follows on from two internal projects, is to identify the mechanisms at work during flotation, using methods of interfaces characterization, stability and rheology of foam fraction, imaging, etc., with a view to improving the performance of the flotation stage and extending it to other recycling challenges.
The PhD thesis work will be carried out at the Laboratoire des technologies de Valorisation des procédés et des Matériaux pour les ENR (LVME) at CEA Grenoble and in close collaboration with the Laboratoire de Caractérisations Avancées pour l'Energie (LCAE) at CEA Grenoble, the Laboratoire des Procédés Supercritiques et décontamination (LPSD) and the Laboratoire de développement des procédés de recyclage et valorisation pour les systèmes énergétiques décarbonnés (LRVE) at CEA Marcoule (30). In parallel with the experimental work, the models and mechanisms involved and the associated technical solutions will have to be proposed.
The scientific and industrial interest of the subject guarantees that the work will be promoted through international communications. After the PhD, you can join one of the best academic or applied research teams, or pursue an R&D career directly in industry.
The development of surfaces that limit microbial proliferation is a crucial public health issue. In the context of manned flights to remote destinations such as low Earth orbit, the Moon and possibly Mars, biological contamination represents a significant threat to crew health and the preservation of space equipment. The microflora carried by the crew in enclosed habitats constitutes an unavoidable risk, accentuated by prolonged periods of isolation and dependence on closed environment life support systems. In addition to the risks to astronauts' health, biocontamination is known to damage critical equipment on board spacecraft. Furthermore, micro-organisms exposed to the space environment can develop resistance and mutate, transforming benign microbes into pathogens. To mitigate these risks, effective measures, such as filtration systems and self-decontaminating surfaces that limit bacterial proliferation, need to be put in place. The MATISS experiment (2016-2025), in which the SyMMES and PRISM laboratories were involved, explored the use of hydrophobic coatings to reduce biocontamination on board the ISS, but further improvements are needed, in particular to find alternative solutions to perfluorinated agents and antibiotics, but also applicable to a wide range of materials. Such advances could have a wide range of applications beyond space, including food safety (packaging), implantable materials, drinking water treatment, public transport hygiene, etc. The aim of this collaborative thesis between SyMMES and CEA-Leti in Grenoble is to develop sustainable antimicrobial coatings free from harmful substances, by exploring different functionalization methods, such as the formation of self-assembled monolayers, electropolymerization on conductive materials, and in a highly original way by implementing a new cold atmospheric plasma deposition method, suitable for large surfaces, and above all applicable to a wide range of different materials.
Monte Carlo methods for sensitivity to geometry parameters in reactor physics
The Monte Carlo method is considered to be the most accurate approach for simulating neutron transport in a reactor core, since it requires no or very few approximations and can easily handle complex geometric shapes (no discretisation is involved). A particular challenge for Monte Carlo simulation in reactor physics applications is to calculate the impact of a small model change: formally, this involves calculating the derivative of an observable with respect to a given parameter. In a Monte-Carlo code, the statistical uncertainty is considerably amplified when calculating a difference between similar values. Consequently, several Monte Carlo techniques have been developed to estimate perturbations directly. However, the question of calculating perturbations induced by a change in reactor geometry remains fundamentally an open problem. The aim of this thesis is to investigate the advantages and shortcomings of existing geometric perturbation methods and to propose new ways of calculating the derivatives of reactor parameters with respect to changes in its geometry. The challenge is twofold. Firstly, it will be necessary to design algorithms that can efficiently calculate the geometric perturbation itself. Secondly, the proposed approaches will have to be adapted to high-performance computing environments.
Influence of delayed neutron precursors losses resulting from fission gas evacuation on molten salt reactors dynamics
Over the past twenty years, molten salt reactors (MSRs) have been the focus of renewed interest in the international nuclear community (national programs, start-ups, including one from the CEA). Modern MSR concepts feature a system for evacuating fission gases, which accumulate in the expansion tank. Some of these gases will consist of radionuclides that are delayed neutron precursors, which will therefore be lost for the fission chain reaction. This should further reduce the effective fraction of delayed neutrons in these reactors, already reduced by the circulation of the fuel salt outside the critical zone. The aim of this thesis is to assess the extent of this reduction, and its influence on reactor dynamics.
Such an assessment may involve numerical simulations that take into account 1) a differentiation of delayed neutron precursor groups into “liquid phase groups” and “gas phase groups”, and 2) two-phase flow models (where each type of group joins its corresponding phase). In order to differentiate the groups, we need to evaluate the “liquid” and “gas” fractions for each of them, based for example on the branching ratios of the nuclear evaluations and knowledge of the chemical elements joining each of the phases. Once this has been done, simulations can be carried out with the CATHARE “system” code (already able to use two-phase models) and the TRUST-NK “core” code (whose two-phase calculation functions may require further development) to assess the influence of precursor loss on reactor dynamics.
Methodology for studying the deployment of a fleet of innovative nuclear reactors driven by grid needs and constraints
Power grids are to a society what the blood system is to the human body: the providers of electrical energy essential to the daily life of all the organs of society. They are highly complex systems that have to ensure balance at all times between consumer demand and the power injected onto its lines, via mechanisms on different spatial and temporal scales.
The aim of this thesis is to develop a methodology for optimizing the deployment of innovative nuclear reactors in power grids, adapted to their specific needs and constraints. This approach should be applicable to a wide variety of grids, from island to continental scale, and to various levels of penetration and technologies of Variable Renewable Energies (VREs). Network constraints will need to reflect stability requirements in the short term (location and capacity of inertial reserves, participation in ancillary services), medium term (controllability and load following), and long term (seasonal availability and load factor of generation resources). Innovative nuclear reactors can be of any technology, and are characterized by macroscopic parameters such as load ramp-up/down kinetics, partial power levels, time before restart, cogeneration capacities, etc., as well as the technical and economic data required for dispatching. The aim is then to be able to draw up a profile (i.e. location, power, kinetics) of nuclear reactor fleets guaranteeing stabilized operation of power grids despite a high VREs penetration rate. Two main contributions are expected:
- Academic contribution: to propose an innovative methodology for optimizing the deployment of large-scale energy systems comprising innovative nuclear reactors, by integrating both the physics of power grids and their operational constraints;
- Industrial contribution: develop recommendations for the optimal deployment of innovative nuclear reactors in power systems incorporating VREs, taking into account aspects such as reactor power and inertia, location, reserve requirements for system services, load-following capability and availability.
The PhD student will be based in an innovative nuclear systems research unit. At the intersection of the study of nuclear reactor dynamics, power system physics and optimization, this energetics thesis will offer the PhD student the opportunity to develop in-depth knowledge of tomorrow's energy systems and the issues associated with them.
Low temperature selective epitaxial growth of SiGe(:B) for pMOS FD-SOI transistors
As silicon technologies for microelectronics continue to evolve, processes involved in device manufacturing need to be optimized. More specifically, epitaxy, a crystal growth technique, is being used to fabricate 10 nm technological node FD-SOI (Fully Depleted-Silicon On Insulator) transistors as part of CEA-Leti's NextGen project. Doped and undoped Si and SiGe semiconductor epitaxy is being developed to improve the devices' electrical performances. The thesis will focus on selective SiGe(:B) epitaxy for channels and source/drains of pMOS transistors. A comparison of SiGe and SiGe:B growth kinetics will be made between growth under H2, the commonly used carrier gas, and N2. Innovative cyclic deposition/etching (CDE) strategies will also be evaluated, with the aim of lowering process temperatures.
Impact of synthesis on the modeling of sodium storage mechanisms in hard carbon
Sodium-ion (Na-ion) batteries are attracting considerable interest as a credible alternative to the lithium-ion batteries widely used today. The abundance of sodium, together with the potential use of electrode materials without critical elements in their composition, has led to intensified research into Na-ion batteries. Hard carbon (HC) has been identified as the most suitable negative electrode for this technology. However, there is no consensus on the mechanisms for storing sodium in HC, because the many precursors and synthesis methods lead to singularly different HCs, which obviously do not function in the same way. A large database provides relationships between synthesis parameters (precursor, washing, pre-treatment, pyrolysis, grinding) and HC properties (porosity, structure, morphology, surface chemistry, defects), but it does not explain them. Consequently, the approach envisaged in this thesis is a multiphysics modeling of HC performance to understand the influence of precursor and synthesis method, exploiting the large existing characterization database.
Advanced Surface Analysis of Ferroelectrics for memory applications
CEA-Leti has a robust track record in memory technology. This PhD project aims to contribute to the development of HfO2-based ferroelectric devices. One of the major challenges in this field is to stabilize the orthorhombic phase while reducing film thickness and thermal budget. To gain a deeper understanding of the underlying mechanisms, a novel sample preparation method will be adapted from a previous PhD project and further developed for application to ferroelectric memories. This method involves creating a beveled crater that exposes the entire thickness of the film, allowing for access by multiple characterization techniques (XPS, TOF-SIMS, SPM) on the same area. This approach will enable the correlation of compositional and chemical measurements with electrical properties. Furthermore, heating and biasing within advanced surface characterization instruments (TOF-SIMS, XPS) will provide insights into how device performance is influenced by compositional and chemical changes.
You possess strong experimental skills and a keen interest in state-of-the-art surface analysis instruments. You excel in team environments and will have the opportunity to collaborate with experts across a wide range of techniques on the nanocharacterization platform, including advanced numerical data treatment. Proficiency in Python or similar programming languages is highly desirable.
Analyzis and modelling of ions-catalyst-ionomer interactions in an AEM electrolyzer cell
CEA/Liten is a research organization on new energies. It offers a PhD on the production of green hydrogen by electrolysis of water using a new technology. The 3 types of water electrolysis to produce hydrogen from electricity are: high temperature electrolysis, low temperature alkaline electrolysis, low temperature PEM electrolysis (proton exchange membrane). All these types of electrolysis have their advantages and disadvantages. Very recently, a new type of electrolysis was born: low temperature electrolysis with AEM membrane (OH- anion exchange). It is a compromise between PEM and alkaline electrolysis to benefit from the advantages of these 2 technologies. First prototypes of such a device exist at the CEA and are studied at the cell or stack scale but the mechanisms involved in the electrochemical and chemical reactions at smaller scales within the electrodes are still poorly understood. In particular, the interactions (ion exchanges, ionic potentials) between the ionomer of the active layer, the membrane and the solution of water and diluted KOH are poorly understood. The objective of the thesis is 1/ to study these mechanisms and to quantify them by developing elementary experiments then, 2/ to model them and implement these models in an existing in-house electrolyzer code and finally 3/ to simulate polarization curves to validate all the models of the code including those developed by the doctoral student.
This thesis will span 2 laboratories: an experimental laboratory and a simulation laboratory in which the student will find all the skills necessary to achieve these objectives. This thesis is linked to several projects involving people from the CEA and other French university laboratories. The student will therefore be in a working environment where this theme is booming.
The candidate is required to have good knowledge of electrochemistry and polymer chemistry and to have notions of modeling and use of software such as Comsol.
ALD materials for FE and AFE capacitances
Ultrathin HfO2-based materials are regarded as promising candidates for embedded non-volatile memory (eNVM) and logic devices. The CEA-LETI has a leadership position in the field of BEOL-FeRAM memories ultra-low consumption (<100fj/bit) at low voltage (<1V). In this context, the developments expected in this thesis aim to evaluate the impact of HfO2-based ferroelectric FE and antiferroelectric AFE layers (10 to 4 nm fabricated by Atomic Layer Deposition ALD) on the FeRAM properties and performances.
In particular, the subject will permit a deep understanding of the crystallographic phases governing the FE/AFE properties using advanced measurements techniques offered by the CEA-LETI nano-characterization platform (physico-chemical, structural and microscopy analysis, electrical measurements). Several integration solutions for ferroelectric capacitances FeCAPs using ALD FE/AFE layers will be studied including doping, interface layers, sequential fabrication w/wo air break…
Thus, the developments based on FeCAPs stack fabricated using 300mm ALD deposition tool aspires to explore the following items:
1-Doping incorporation in FE/AFE layers (La, Y…)
2-Engineering of the interface between FE/AFE layers and top/bottom electrode
3-Plasma in-situ treatment of bottom electrode surface
4-Sequential deposition with and without air break
[1] S. Martin et al. – IEDM 2024
[2] Appl. Phys. Lett. 124, 243508 (2024)