Understanding of corrosion mechanisms and means of mitigating corrosion in a NaCl-ThCl4-UCl3 salt. Application to future molten salt fuel and coolant reactors

The molten salt reactor concept is based on dissolving the fuel in a molten salt. This liquid fuel concept is highly innovative and in many respects represents a break with current reactors, which are all based on the use of a solid fuel and a fluid coolant. Recently, the emergence of American start-ups proposing this innovative concept and the major effort made in China have revived interest worldwide in studying this technology, which offers a number of advantages, both real and potential, over the use of solid fuel, particularly in terms of incineration and intrinsic safety. To build a feasibility demonstrator for this breakthrough concept, extensive research is needed to acquire data and justify the behaviour of the containment barriers, primarily the metal barrier in contact with the salt. In the case of molten salt reactors, the structural materials, nickel-based alloys, are chosen to optimise their behaviour in terms of corrosion and high temperature. Corrosion of the materials is one of the critical points to be overcome when building this reactor. A detailed understanding of the corrosion mechanisms of the alloy chosen as the structural material, on the one hand, and of the chemistry of the ternary salt NaCl-ThCl4-UCl3 envisaged, on the other hand, are necessary to predict the material corrosion rate over the lifetime of the demonstrator. These studies will enable several corrosion mitigation methods to be developed. Each of these processes will be tested and evaluated under nominal conditions and then aggravated.
The first part will be devoted to understanding the corrosion mechanisms of the alloy and the chemistry of the NaCl-ThCl4-UCl3 salt. To this end, tests will be carried out at the IPN in Orsay and the corrosion mechanisms and chemistry studies will be established using electrochemical techniques and microstructural characterisation of corroded samples (thermogravimetry, SEM, TEM, XPS, Raman, GD-OES, etc.). Secondly, material protection tests using different types of salt redox control will be carried out and then tested in nominal and aggravated environments.
This approach will make it possible to meet a major and ambitious corrosion control challenge for an innovative energy process.

Protection by self-decontaminating coatings against biocontamination of surfaces

The proposed PROBIO-ES project falls within the scope of the priority defense theme « biologie, santé, NRBC », and in particular the sub-themes of protection and decontamination. Its aim is to develop self-decontaminating surfaces for a number of terrestrial and space applications. The project has been shortlisted by CNES for the award of a 1/2 thesis grant. In the context of manned spaceflights to distant destinations such as low Earth orbit, the Moon, and potentially Mars, biological contamination poses a significant threat to the health of the crew and the preservation of space equipment. The microflora carried by the crew in enclosed habitats is an unavoidable concern, heightened by prolonged periods of isolation and dependence on closed-loop life support systems. Beyond risks to astronaut health, biocontamination can damage critical equipment aboard spacecraft. Microorganisms 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 limiting bacterial proliferation must be implemented. The MATISS experiment (2016-2024) explored the use of hydrophobic coatings to reduce biocontamination aboard the ISS, but improvements are needed. This collaborative thesis between SyMMES and CEA-Leti in Grenoble aims to develop durable antimicrobial layers without harmful substances, using a new method of deposition through cold atmospheric plasma, suitable for large surfaces. The PROBIO-ES project is therefore fully in line with the « biologie, santé, NRBC » thematic priorities of AID 2024 call for projects.

Hierarchically conducting polymer coated on 3D ALD/Silicon nanostructures for integrated solid and flexible micro-supercapacitors

The objective of this thesis is to develop and high performance and durable all-solid state flexible micro-supercapacitors (micro-SC). These new solid-state micro-generators will operate over a wide temperature range (-50°C to +120°C) and exhibit exceptional lifetime and performance. The ?-SCs proposed in this thesis project are based on i) the elaboration by CVD growth of electrodes composed of silicon nanowires and nanotrees followed by a nanometric deposition of a dielectric and new electronically conductive polymer, ii) the elaboration and characterization of new copolymers based on n-type EDOTs derivativesiii) the synthesis of polymeric solid electrolytes (ESPs) based on poly(siloxane)s and ionogels iv) performance tests of different electrodes and electrolytes in three-electrode system configuration, v) elaboration of nanocomposites based on EDOT-based electronically conductive polymers and silicon nanowires covered with nanometric layers of alumina and HfO2, and v) assembly and tests of devices in rigid and flexible sandwich type configuration

Development of high-halogen argyrodites for all-solid all-sulfide systems

All-solid-state batteries have been enjoying renewed interest in recent years, as this technology offers the prospect of higher energy densities due to the use of lithium as a negative electrode, as well as increased battery safety compared with Li-ion technology. The use of sulfides as positive electrode materials coupled with argyrodite as solid electrolyte are interesting systems to develop. The argyrodites achieve ionic conductivities close to those of liquid electrolytes. Moreover, the electrochemical stability window of sulfides is close to that of argyrodite, making all-sulfide technology a promising one for the development of all-solid batteries.
In order to improve the conduction properties of argyrodites, recent studies have shown that ionic conductivity is highly dependent on their local structure. Solid-state NMR thus appears to be a promising technique for probing the local environments of the nuclei mentioned, and in particular for quantifying the variety of different local environments favoring an increase in ionic conductivity. Some compositions enriched in halides appear to promote ionic conduction, and the synthesis of corresponding materials and their structure will be studied.
The thesis will focus on two main areas: the study of all-sulfide batteries and the fine characterization of argyrodite with controlled local structures. Halogen-rich argyrodites will be developed and studied to determine the influence of different local environments on conduction properties.

Relationships between surface reactivity, composition and deformation of Silicon-based negative electrodes for sulfide-type solid electrolyte batteries

All-solid-state batteries using sulfide-based electrolytes are among the most extensively studied, in order to improve energy density, safety and fast charging. Although lithium metal was initially the preferred choice for the anode, the difficulties encountered in its implementation and the performance achieved suggest that alternatives should be proposed. Silicon offers an interesting compromise in terms of energy density and lifetime. However, further improvements are still needed. An initial thesis on the subject highlighted the benefits of using silicon nanomaterials in combination with argyrodite L6PS5Cl. This work also enabled us to switch from 0.8 mAh cells made from compacted powders to 16 mAh cells made from coated electrodes, while significantly reducing cycling pressure from over 125 MPa to 1 MPa and improving lifetime (90% capacity retention after 160 cycles). However, several questions remain unanswered. The reactivity between argyrodite and silicon, which depends on the surface chemistry, and the mechanisms that enable coated electrodes to cycle at pressures as low as 1 MPa need to be elucidated
To answer these questions, we propose to use XPS to characterize the interfaces between the electrolyte and various silicon materials during the life of the battery. Secondly, to measure cell deformation during cycling. These characterizations, coupled with standard physico-chemical and electrochemical characterizations, will help to improve cell performance. These improvements will be based on the use of high-performance silicon nanowire/graphite composites synthesized at IRIG for the anode, NMC with a coating for the cathode, and electrode formulation development work. Initial tests with silicon/graphite composites have been conclusive, but the impact of these materials' characteristics on performance remains to be assessed, in particular wire diameter, silicon content, surface chemistry and choice of graphite. The production of coated electrodes, initiated in the thesis of M. Grandjean in collaboration, remains to be developed. In particular, there is a need to increase surface capacity and power performance, and to do this we need to increase the proportion of active material and evaluate different types of carbon for the electrical conductive network.
This work will help maintain CEA's momentum on the subject and propose a solution for generation 4a batteries, which could succeed current batteries thanks to a better understanding of operating and degradation mechanisms.

Operando gas analysis for Li-ion batteries at small and large scales: investigation of key parameters and correlation of results to real-life aging and safety performance

This PhD project will focus on the development of Online Electrochemical Mass Spectrometry (OEMS) method for operando analysis of gases evolved during operation of Li-ion batteries (LIBs). LIBs represent the most relevant energy storage devices for the wide commercialization of electric vehicles. However, among the most important challenges for modern LIBs, cyclability and safety are the key issues that need to be addressed to increase the driving range and mitigate numerous hazardous risks. In this regard, there is a huge demand for efficient and representative characterization methods capable of predicting aging and safety performances of new battery materials and cells in a reliable manner based on relatively short experimental duration. OEMS is such a powerful and versatile method providing information on mechanisms of chemical reactions taking place in LIBs at different experimental conditions.

The main objectives of the present project are: 1) identification of a few key parameters affecting the gas evolution in LIBs quantitatively and qualitatively during OEMS measurements at different scales; 2) unraveling the interplay between the key parameters and proposing new cell architectures or test protocols to tackle issues; 3) understanding the correlations between safety, aging tests and OEMS results obtained for the same/similar Li-ion battery.

The project will take place at The French Alternative Energies and Atomic Energy Commission (CEA) located in Grenoble, France. CEA is widely known for its technological and scientific excellences, as well as for its outstanding equipment resources and its expertise in the research and development of greener energy, notably in batteries. This center offers a great opportunity to join a dynamic team and to conduct a high-level research in a multidisciplinary environment. Additionally, there might be a possibility to take part in experiments using synchrotron radiation at ESRF and to explore battery chemistries beyond LIBs. We are looking for a highly motivated and pro-active candidate to start the Ph.D internship in autumn 2024 for 3 years. Good oral and written English skills are required. The student will conduct thorough literature reviews, publish his/her scientific findings in high-level peer-reviewed journals and communicate them at international conferences. The experience acquired by the student during his/her Ph.D study will be undoubtedly of high interest for further employment. Health insurance is provided for foreigners. Grenoble’s area is a famous hiking and skiing playground in the heart of the French Alps.

High energy density Li-Ion and Na-Ion Positive Electrodes with reduced critical material content

This PhD subject will aim at developing new positive electrode materials based on glasses for high Energy Density Li-Ion and Na-Ion cells with reduced critical material content. These developments will be held jointly between the laboratory of materials for batteries from CEA-Grenoble and LDMC lab from CEA-Marcoule that is specialized in the formulation and characterization of glass materials.
The work will be focused on the optimization of the complex formulation of the glass cathodes to solve the issues related to first cycle irreversible loss and low cycling performances. The main objective will be to obtain one composition without critical raw materials exhibiting more than 1000Wh/kg at active material level vs 700 for state-of-the-art materials. This target will be reached with the support of advanced characterization techniques such as X-Ray Diffraction and RAMAN and FTIR spectroscopies. A dedicated effort will concern the development of operando or in-situ measures to be able to explain the link between electrochemical performances and glass characteristics, what has never been reported in the litterature.
This thesis will allow the candidate to gain valuable professional experience in the glass and energy sectors. He or she will develop skills in materials science and electrochemistry. In addition, thanks to his work environment, he will be able to assimilate a culture of nuclear waste conditioning.

Hybrid solid electrolytes for "all-solid" batteries: Formulation and multi-scale characterization of ionic transport

Lithium-ion batteries, widely present in our daily lives, have revolutionized portable applications and are now used in electric vehicles. The development of new generations of batteries for future applications in transport and storing electricity from renewable sources is therefore vital to mitigating climate change. Lithium-ion technology is generally considered as the preferred solution for applications requiring high energy density, while sodium-ion technology is particularly attractive for applications requiring power.

However, the intrinsic instability of liquid electrolytes results in safety issues. Faced with the requirements concerning the environment and safety, solid-state batteries based on solid electrolytes can provide an effective solution while meeting battery energy storage needs. The barriers to overcome allowing the development of all-solid-state battery technology consist mainly in the research of new chemically stable solid electrolytes with good electrical, electrochemical and mechanical performance. For this goal, this thesis project aims to develop “polymer/polymer” and “ceramic/polymer” composite solid electrolytes with high performance and enhanced safety. Characterizations by electrochemical impedance spectroscopy (EIS) will be carried out in order to understand the cation dynamics (by Li+ or Na+) at the macroscopic scale in composite electrolytes, while the local dynamics will be probed using advanced techniques of Solid-state NMR (23Na / 7Li relaxation, 2D NMR, in-situ NMR & operando). Other characterization techniques such as X-ray and neutron diffraction, XPS, chronoamperometry, GITT ... will be implemented for a perfect understanding of the structure of electrolytes as well as aging mechanisms at the electrolyte / electrolyte and electrolyte/electrode interfaces of the all-solid battery.

Key words: composite solid electrolyte, all-solid-state battery, interfaces, multiscale characterization, dynamics of Li + and Na + ions, electrochemical performance, solid-state NMR, X-ray / neutron diffraction.

Elucidation of the Correlation between the Electrochemical Activity of Oxygen Reduction and the Molecular Structure of the Platinum/Ionomer Interface in Proton Exchange Membrane Fuel Cells

This thesis focuses on the Proton Exchange Membrane Fuel Cell (PEMFC), used in the transportation sector to generate electricity and heat from hydrogen and oxygen. Although promising for reducing CO2 emissions through the use of green hydrogen, the PEMFC needs to enhance its performance and durability to compete with combustion engines and batteries. The electrode plays a crucial role, but the molecular complexity of the electrochemical interface between the platinum-based catalyst and the ionomer makes characterization challenging. Currently, the qualitative understanding of this interface is limited, impeding progress and model predictability. The thesis aims to establish a correlation between the molecular structure of the electrochemical interface and the electrochemical kinetics, focusing on platinum oxidation and ionomer adsorption. A unique device developed at CEA allows simultaneous electrochemical and spectroscopic characterizations. The novelty lies in using Atomic Force Microscopy (AFM) coupled with Raman spectroscopy and synchrotron-based micro-infrared spectroscopy as original techniques to obtain crucial information for PEMFC applications.

Physics-based ageing model of Li-ion batteries

In recent years, Li-ion batteries have become the benchmark technology for the global battery market, supplanting the older Nickel-Cadmium and Alkaline technologies. Although slightly inferior to fossil fuels in terms of massic energy capacity, Li-ion batteries have a major advantage for the development of electric vehicles: their exceptional lifespan. It has recently been demonstrated that particular electric vehicle technologies can exceed one million km. Beyond the promising performance of ideal prototypes, the question of battery lifespan is linked to industrial, economic and environmental issues that are crucial to the ecological transition and energy sovereignty of our country.

One of the major challenges in developing these long-life batteries is to anticipate and control the various internal degradation phenomena that occur during actual use. Although most degradation phenomena have been identified in laboratory on common battery materials, the question of their kinetics in a battery pack in real use remains open, as does the prediction of the battery's state of health and end-of-life.

CEA's teams draw on a unique expertise combining experimental data and modeling to build a predictive physico-chemical model of Li-ion battery degradation. As part of this thesis, you will design and carry out basic characterization experiments on battery degradation mechanisms in the laboratory, using a wide range of advanced experimental techniques (electrochemical titration, impedance spectroscopy, operando gas measurements, DRX, etc.). Your work will also involve integrating your results into aging models, and studying the predictions and validation of these models.

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