Evaluation of nanoscale surface coatings on high energy density positive electrodes for lithium-ion batteries.
Nickel-rich layered oxides LiNi1-x-yMnxCoyO2 (NMC) and LiNi1-x-yCoyAlzO2 (NCA) are exceptional materials for the positive electrode of lithium batteries due to their high reversible storage capacity. However, under real conditions, undesired reactions can lead to the dissolution of transition metals and electrodes cracking, thus affecting their electrochemical properties. This phenomenon is linked to the presence of hydrofluoric acid (HF) in the electrolyte, mainly due to the degradation of the LiPF6 salt. To address this problem, surface treatments are needed to protect the active material and improve performance. The EVEREST project proposes an innovative, flexible, and affordable method for creating inorganic coatings at the nanoscale. This method is based on a recent technique, coaxial electrospinning, which allows the production of nanofibers with a well-defined core-sheath structure. For this project, we propose to evaluate the impact of nanofiber shaping parameters on morphology, electrochemical performance and the underlying mechanism. The electrochemical performances of the coated and the pristine positive electrodes will be compared in a half-cell with Li metal as a counter electrode. Redox processes, charge transfer mechanisms and structural modifications will be studied in the operando mode using the synchrotron radiation beam.
Silver nanowires synthesized from end-of-life solar panels for CO2 reduction and transparent electrodes
Silver nanowires (AgNW) networks are remarkable materials with both the highest electrical and thermal conductivity at ambient temperature, and a good chemical stability. They are used in transparent electrodes, for instance in organic solar cells, heating films or electrochromic devices. Their synthesis has been upscaled at the industrial level with high yield and reproducibility. More recently, they also found promising applications in low-emissivity layers on windows, and in catalysis of CO2 reduction at ambient temperature as a selective electrocatalyst.
In this PhD project, we will turn to recycled sources of silver from dismantled end-of-life silicon solar panels for the synthesis of AgNWs, in a “green chemistry” approach. The quality of the nanomaterial will be checked directly in two relevant devices, namely IR-low-emissivity films for reduction of heat loss, and electroreduction of CO2 for the production of e-fuels. The project will focus on understanding the fundamental basis of the impact of impurities on the synthesis of AgNWs, the physical properties of the AgNW networks, their stability under electrical stress or chemical wear, and their performance as active material in the devices.
The work will take place in Grenoble, the second scientific hub in France. The PhD student will be hired by CEA, a major French research institution with a high focus on alternative energies. He/she will join the fundamental research lab SyMMES, expert in nanomaterial design and energy devices such as solar cells, batteries and electrolyzers. She/he will work in co-supervision in the partner lab LMGP expert in materials science, synthesis and implementation at Grenoble INP. SYMMES and LMGP belong to University Grenoble Alpes and host widely international teams. The project will be actively supported by a local industrial recycling company.
Applicants should hold a Master 2 degree in chemistry, physics or materials science with skills in nanomaterials, electrochemistry or physical chemistry and in basic science for energy. Good English proficiency and a strong interest for innovation and collaborative work are expected.
Monitoring the electrode-electrolyte interface and redox activity in aqueous water-in-salt Na-ion batteries
Using concentrated aqueous electrolytes (Water-In-Salt aqueous Electrolytes), a significant increase in the potential window of aqueous Li batteries can be achieved. This is due to the absence of free water molecules while the interfaces seem to play a crucial role. While WISEs pave the way for sustainable systems, the Li-based solutions use expensive and toxic salts. To look for more sustainable elements, one can envision sodium, which is less expensive and more abundant. While the systems based on Li imide salts have been quite thoroughly investigated, a fundamental understanding of the reactions at stake in sodium batteries based on WISEs, particularly at the interfaces, is needed. The project aims at identifying the reactions occurring at the interphase between the electrodes and the electrolyte in aqueous water-in-salt Na-ion batteries as well as the redox behavior of electrodes in these solutions. To do so, we propose to use cutting-edge in situ/operando techniques, namely infrared spectroscopy (IR) and X-ray absorption spectroscopy (XAS) at SOLEIL. The PhD student will first develop/adapt dedicated cells to perform these measurements. He/she will then conduct in-depth investigation of
the electrodes and interfaces reactivity in aqueous water-in-salt Na-ion batteries. This will provide insights into electrodes behavior in the bulk and also on the chemical composition of the interfaces, on their formation mechanisms and their stability upon cycling.
Relationship between the nature of hard carbons and the properties of electrodes for Na-ion batteries
Hard carbons are the most commonly used negative electrode materials in Na-ion batteries. Their capacity exceeding 300 mAh/g, low operating voltage, long lifespan, and power performance make them the best option for commercializing Na-ion batteries. However, several challenges remain to approach the performance of low-impact Li-ion technologies like LF(M)P/graphite. One major limitation is their low volumetric density. Their disordered nature and resulting microporosity lead to a lower skeletal density compared to graphite. This significantly affects both the volumetric and gravimetric energy densities due to the difficulty of compressing the electrodes.
The main objective of this thesis is to establish a link between the material's skeletal density and the electrode's calendering capability to reduce its porosity. First, we will evaluate the relationship between the structure, morphology, and surface state of hard carbon and the electrode's density. We will attempt to understand the impact of calendering on the material’s properties. Then, we will assess the tortuosity and conductivity of hard carbon electrodes to predict their performance. Finally, we will work on improving and optimizing the electrodes in terms of energy densities, focusing particularly on electrode formulations.
Reactive metals corrosion in innovative binders – Experimental study and hydro-chemo-mechanical modelling
Nuclear waste management requires the packaging of several kinds of metal wastes for long-term storage. These wastes, which can be very reactive metals, are prone to corrosion and commonly immobilised into containers with hydraulic binders as embedding matrices. Innovative binders (low carbon cements, alkali activated materials) are thus developed to increase the packaging performances. The main objective of the European project STREAM (in the frame of the Eurad-2 program) is to evaluate the interactions between these metal wastes and the selected cement matrices. The PhD thesis purpose is to investigate the reactive metal corrosion in the selected binder with electrochemical techniques. A generic experimental protocol will be developed in order to determine the impact of the corrosion products growth at the metal/binder interface on the global mechanical behaviour of the binder-waste composite and possible micro-cracks occurrence. A post-mortem characterisation will be performed on the metal/binder microstructure with mechanical properties measurements of the materials at the interface, especially the corrosion products. Afterwards, these results will feed a simplified Hydro-Chemo-Mechanical (HCM) model aiming the simulation of corrosion consequences on the composite material behaviour. Subsequently, this model will be used for long-term simulation at the waste package scale.
This research project is aimed at a PhD student wishing to improve his/her skills in materials science both in the experimental field and in the modelling/simulation of coupled physicochemical phenomena.
Optimization of the catalytic layer for CO2 electroreduction integrated into a PEM electrolyzer
This thesis focuses on optimizing the catalytic layer for CO2 electroreduction in an acidic medium, integrated into a proton-exchange membrane (PEM) electrolyzer. The aim is to upgrade CO2 by converting it into valuable chemicals, such as carbon monoxide. The acidic environment inherent to PEM electrolyzers helps limit carbonate formation, improving CO2 conversion efficiency. However, CO2 reduction in acidic media competes with the hydrogen evolution reaction, which reduces the selectivity of electroreduction products. This work seeks to develop noble-metal-free catalysts inspired by those used for oxygen reduction in fuel cells, improve the properties of carbon supports, and optimize the design of the catalytic layer, in particular thickness, porosity and hydrophobicity, to maximize CO2 conversion into target molecules. Finally, the active layer will be integrated into a 16 cm² PEM electrolyzer to assess overall performance and gain insights into the mechanisms involved through electrochemical characterization.
Microemulsion model: Towards the prediction of liquid-liquid extraction processes
This multi-scale modeling thesis aims to develop innovative theoretical approaches and numerical tools to revolutionize strategic metal extraction processes, such as liquid-liquid extraction, whose underlying mechanisms remain poorly understood. To address these challenges, solvent phases will be represented as microemulsions through a synergy of mesoscopic and molecular modeling approaches.
The mesoscopic approach will involve the development of a code based on microemulsion theory using a random wavelet basis. This code will enable the characterization of the structural and thermodynamic properties of the solutions. The molecular approach will rely on classical molecular dynamics simulations to evaluate the curvature properties of the extractants, which are essential for bridging the two scales.
The new high-performance computational code may integrate artificial intelligence techniques to accelerate the minimization of the system’s free energy while accounting for all chemical species present with a minimal number of parameters. This will pave the way for new research directions, such as predicting speciation and calculating thermodynamic instabilities in ternary phase diagrams, thereby identifying unexplored experimental conditions.
This PhD thesis, conducted at the Mesoscopic Modeling and Theoretical Chemistry Laboratory at the Marcoule Institute for Separation Chemistry, will have applications in the recycling domain and extend to the broader field of nanoscience, thereby expanding the impact of this work.
The PhD candidate, with an academic background in physical chemistry, theoretical chemistry, or physics, and a strong interest in programming, will be encouraged to disseminate his/her scientific results through publications and presentations at national and international conferences. Upon completion of the thesis, the candidate will have acquired a wide range of skills in modeling and physical chemistry, opening numerous professional opportunities in both academic research and industrial R&D.
Study of the amorphous intermediate states during the precipitation of actinides oxalate
Growing energy needs and the climate emergency require a rapid transition to completely carbon-free energy, by mixing renewable energies and sustainable nuclear power. In this context, the precipitation of plutonium and uranium in the form of oxalate constitutes a key step in the industrial process of recycling spent fuel. A detailed understanding of the crystallization mechanisms of these oxalates thus constitutes a major challenge for better management of these operations.
However, it is now widely accepted that ions in solution assemble into crystals via a series of non-crystalline transient states, which fundamentally contradicts all classical nucleation theories used in precipitation models. In particular, we have demonstrated in recent years that rare earth oxalate crystals (Eu, Nd, Ce, Tb), some used to experimentally simulate the recycling of uranium and plutonium, form via liquid, reagent-rich nanodroplets which separate from the aqueous solvent. This behavior modifies the view hitherto retained for the precipitation of these oxalates and leads us to question the behavior of actinide oxalates.
The aim of this thesis is to confirm or refute that transient mineral droplets also form during the formation of uranium and plutonium oxalates, and to determine whether crystallization transients impact the precipitation models used to calibrate the recycling process of nuclear fuel. This study will not only impact precipitation processes used in recycling, but will also advance a fundamental question about long-debated “non-classical” crystallization.
Online analysis of actinides surrogates in solution by LIBS and AI for nuclear fuel reprocessing processes
The construction of new nuclear reactors in the coming years will require an increase in fuel reprocessing capacity. This evolution requires scientific and technological developments to update process monitoring equipment. One of the parameters to be continuously monitored is the actinide content in solution, which is essential for process control and is currently measured using obsolete technologies. We therefore propose to develop LIBS (laser-induced breakdown spectroscopy) for this application, a technique well suited for quantitative online elemental analysis. As actinide spectra are particularly complex, we shall use multivariate data processing approaches, such as several artificial intelligence (AI) techniques, to extract quantitative information from LIBS data and characterize measurement uncertainty.
The aim of this thesis is therefore to evaluate the performance of online analysis of actinides in solution using LIBS and AI. In particular, we aim to improve the characterisation of uncertainties using machine learning techniques, in order to strongly reduce them and to meet the monitoring needs of the future reprocessing plant.
Experimental work will be carried out on non-radioactive actinide simulants, using a commercial LIBS equipment. The spectroscopic data will drive the data processing part of the thesis, and the determination of the uncertainty obtained by different quantification models.
The results obtained will enable publishing at least 2-3 articles in peer-reviewed journals, and even to file patents. The prospects of the thesis are to increase the maturity level of the method and instrumentation, and gradually move towards implementation on a pilot line representative of a reprocessing process.
Electrolyte ceramics for oxygen potentiometric sensors in aggressive media of advanced nuclear reactor
The solid electrolytes are thought to play major role in future energetic systems (SOFC, SOEC). Among them, oxide ceramics with fluorite structure are particularly important. Correctly doped, their ionic conductivity is high and they are suitable for applications in aggressive media or at high temperatures. However, these properties are closely related to their microstructure, thus to their fabrication route. At CEA IRESNE, we develop fluorite based-potentiometric sensors for oxygen monitoring of advanced reactors coolants.
This thesis proposed to study the relation between the microstructure of two fluorite materials, doped hafnium or thorium oxides, and their behavior in liquid sodium or molten chlorides. The influence of grain size, density and impurity contents on the corrosion kinetic in sodium would provide insights on the corrosion mechanisms. The ultimate aim is to optimize the service life of these ceramics in oxygen sensors for sodium based energetics systems and to test them. The electrolyte will be used in sensors to characterize the behavior of oxygen in these complex media.
The student should be graduated in materials science. The thesis work will take place at the CEA/IRESNE Institute on the Cadarache site (France, Provence) in collaboration with the Institute of separative chemistry of Marcoule (France, Occitanie).