Degradation phenomena in anion exchange membrane electrolysers
The production of hydrogen using anion exchange membrane water electrolysis (AEMWE) is a promising technology for the storage of large quantities of electricity. Some AEMWE systems are already commercially available, but their deployment is hindered by the lack of understanding of the factors which limit their durability. The proposed work aims therefore to study, at single-cell level, degradation phenomena given rise to by, among other factors, the intermittant nature of electrolyser operation when powered using renewable energy sources. This study will focus on the mechanisms (thermal, fluidic, (electro)chemical) responsible for degradation of the various cell components. It will utilise test facilities available at CEA, and be enriched by the modelisation of physical degradation mechanisms for integration into a digital code. Real electrolysers need to be able to function for several years, so an early task in this work will be the definition of accelerated stress test (AST) protocols which will precipitate degradation in a targeted fashion, and in a relatively short space of time. Electrochemical data produced during these ASTs will be followed by post-test physical characterisation (XPS, XRD, SEM) of component microstructure, in order to elucidate degradation mechanisms.
Development of Single-Ion Eutectogel Electrolytes through Polymerization of Deep Eutectic Solvents (DES)
The proposed PhD thesis focuses on the development of innovative polymer electrolytes for next-generation batteries, aimed at improving the safety and performance of energy storage systems.
Polymer electrolytes represent a promising solution to replace traditional liquid electrolytes. However, their development is limited by challenges related to ionic conductivity and low ion transport numbers. The addition of Deep Eutectic Solvents (DES) into the polymer matrix enhances ionic conductivity. Furthermore, the "single-ion" approach, based on grafting the counter-ion onto the polymer chain, leads to unipolar conduction.
CEA has recently developed "single-ion eutectogel" electrolytes, obtained by polymerizing a DES composed of a single-ion monomer and a hydrogen bond donor (HBD). These electrolytes exhibit very promising performance, achieving unipolar ionic conductivities greater than 0.1 mS/cm at room temperature. However, it is essential to further explore the relationships between formulation, structure, and properties, as well as the conduction mechanisms within these materials, in order to continue their development.
The thesis will be structured in three main phases:
Study of the reference system: Establish a research methodology to link polymerizable formulations, polymer structure, and their electrochemical properties. This will include the study of the starting DES and the electrolyte resulting from its polymerization. The study of conduction mechanisms within these electrolytes will be a central focus of this phase.
Optimization of properties: Based on the results from the previous phase, optimize the properties of the electrolytes through formulation work to select the most promising electrolyte for the next phase.
Integration into a complete system: Explore the integration of the electrolyte into a battery cell, using the in situ polymerization process to synthesize the electrolyte directly within the cell.
Physicochemical techniques (NMR, DSC, TGA, FTIR, RAMAN, SEC, SAXS, ...) and electrochemical techniques (EIS, CV, GCPL, ...) will be used throughout the project.
The PhD will be carried out in collaboration with CEA and LEPMI, providing access to state-of-the-art infrastructures and recognized expertise in formulation, polymer chemistry, and polymer electrolyte electrochemistry.
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.
Predictive Diagnosis and Ageing Trajectory Estimation of New Generation Batteries through Multi-modalities Fusion and Physics-Informed Machine Learning
Context:
Lithium-ion and emerging Sodium-ion batteries are crucial for energy transition and transportation electrification. Ensuring battery longevity, performance, and safety requires understanding degradation mechanisms at multiple scales.
Research Objective:
Develop innovative battery diagnostic and prognostic methodologies by leveraging multi-sensor data fusion (acoustic sensors, strain gauge sensors, thermal sensors, electrical sensors, optical sensors) and Physics-Informed Machine Learning (PIML) approaches, combining physical battery models with deep learning algorithms.
Scientific Approach:
Establish correlations between multi-physical measurements and battery degradation mechanisms
Explore hybrid PIML approaches for multi-physical data fusion
Develop learning architectures integrating physical constraints while processing heterogeneous data
Extend methodologies to emerging Na-Ion battery technologies
Methodology:
The research will utilize an extensive multi-instrumented cell database, analyzing measurement signatures and developing innovative PIML algorithms that optimize multi-sensor data fusion and validate performance using real-world data.
Expected Outcomes:
The thesis aims to provide valuable recommendations for battery system instrumentation, develop advanced diagnostic algorithms, and contribute significantly to improving the reliability and sustainability of electrochemical storage systems, with potential academic and industrial impacts.
CTC electrolyte pour LiS system
Lithium-Sulfur (Li-S) Batteries are among the most promising energy storage technologies for the fifth generation of batteries, often referred to as post-Li-ion. With a theoretical energy density five times higher than that of conventional Li-ion batteries and an abundant availability of sulfur, the Li-S system offers a unique potential to meet the growing demand for sustainable energy storage. However, current technology is limited by major challenges related to the dissolution of polysulfides in the electrolyte, leading to active sulfur loss, poor cycle life, and insufficient electrochemical performance. These limitations currently hinder the market deployment of this technology.
This thesis aims to explore an alternative approach based on an all-solid electrochemical sulfur conversion mechanism. To achieve this, a next-generation organic solid electrolyte developed in the laboratory will be implemented. This electrolyte features a unique lithium-ion conduction mechanism within a crystalline lattice, preventing polysulfide solubilization. The main objectives are:
1. To understand and control the ionic conduction mechanisms in these electrolytes.
2. To integrate this solid electrolyte into an innovative Li-S system.
3. To optimize the cathode structure for the solid-state mechanism and evaluate the electrochemical performance on a representative prototype scale.
The PhD candidate will use a wide range of characterization and analysis techniques to carry out this project:
• Formulation and characterization of the organic solid electrolyte: Techniques such as FT-IR and NMR to analyze chemical structures and identify the properties of synthesized materials (DSC, TGA, XRD, etc.).
• Electrochemical characterization: Analyses using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and symmetric cell cycling tests to study ionic conduction properties and electrolyte stability.
• Formulation and performance study of the cathode: Formulation of carbon/sulfur composites and sulfur cathodes integrating the solid electrolyte; galvanostatic cycling tests and advanced interface analyses to understand and optimize solid-state sulfur conversion.
The research will progress in three main phases:
1. Development and characterization of the solid electrolyte: Material development, analysis of conduction mechanisms, and optimization of ionic and mechanical properties.
2. Design and optimization of the cathode structure: Improving electrolyte/cathode interfaces for solid-state sulfur conversion.
3. Electrochemical performance evaluation: Experimental validation of prototypes through in-depth tests, including cyclability and power performance.
Multiphe hydrogen injection at anode side of PEMFC
The alternating feeding architecture (known as Ping-Pong) was developed by the CEA. This architecture emerged in 2013 and has been implemented in several fuel cell systems. Following the latest tests on this architecture, questions remained unanswered. First, it is a question of understanding how species (hydrogen, nitrogen, liquid and gaseous water) move in cells operating with alternating feeding. Control laws influences these movements, it will be necessary to identify the levers to make the most out of it and then to propose methods to promote the evacuation of water and nitrogen while avoiding the evacuation of hydrogen.
The thesis work will aim to optimize the anode architecture with alternating feeding and to bring this architecture to maturity. The key points are the search for an optimum control of this architecture, the achievement of a hydrogen rejection rate of less than 1%. Finally, this optimization will also have to maximize the durability of the stack.
The doctoral student will have to model the movements of species at different time scales (10ms to 10 minutes), understand the mechanisms, adapt the control laws and validate the new control laws on a test bench.
This work will identify solutions to efficiently evacuate liquid water and nitrogen and minimize H2 rejection and then obtain superior performance compared to conventional architectures.
For high-performance, safe, and long-lasting batteries: understanding the role of an additive in liquid electrolytes
The trade-off between performance, aging, and safety remains a major challenge for Li-ion batteries [1]. Indeed, the incorporation of certain additives into the 3rd-generation electrolyte aims to delay or reduce the consequences of thermal runaway, thus reducing the risk of fire or explosion. However, this approach can have negative effects on other key parameters, such as ionic conductivity [2,3]. Therefore, this thesis proposes to study the coupled effects of these additives in order to better understand and potentially predict their impact on each of these indicators.
At the beginning of this work, an additive will be selected to study its role in an NMC 811/Gr-Si chemistry and a 3rd-generation liquid electrolyte, in terms of performance, long-term stability, and safety. The additive will be chosen based on the state of the art and post-mortem analysis of commercial cells representative of the current market. In parallel, new commercial cells of a few Ah will be used. These will be equipped with a reference electrode, internal temperature measurement, and ionic conductivity monitoring. The cells will then be activated with the selected electrolyte at different additive concentrations. Electrochemical performance, along with chemical and morphological characterization of the materials present, will be studied. Key safety parameters (thermal stability, release of reducing gases, O2, released energy, flammability of the electrolyte) for these new cells will be measured at different additive concentrations. The internal instrumentation, including the reference electrode, will also be used innovatively to study the onset of thermal runaway under these conditions.
A full aging campaign will be conducted over a maximum period of one year. At regular intervals, a sample of cells will be studied to characterize the impact of aging on chemical, electrochemical, and morphological changes, as well as on key safety parameters. The most important mechanisms, along with simplified laws governing safety as a function of additive quantity and aging, will be proposed.
[1] Batteries Open Access Volume 9, Issue 8, August 2023, Article number 427
[2] Journal of Energy Storage 72 (2023) 108493
[3] Energy Storage Materials 65 (2024) 10313
Numerical optimisation of internal safety devices of batterry cells depending on chemistry
Thermal runaway (TR) of a battery pack's elementary accumulator is a key factor that can lead to various safety issues, such as fires or explosions, involving both property and people. Several safety devices can prevent and/or mitigate the consequences of thermal runaway, including the PTC (Positive Temperature Coefficient) to limit short-circuit current, the CID (Current Interrupt Device) to disconnect the external electrical terminals from the internal active elements, and the Safety Vent for cell depressurization. Internal gas pressure is the main triggering factor. However, since the gas quantity strongly depends on the chemistry involved, these safety devices should be optimized for future battery generations.
In this PhD thesis, we will develop a methodology for sizing these safety devices through numerical simulations, incorporating all characterizations from the material scale to abusive cell testing. This research will therefore focus on both numerical and experimental aspects in parallel, in collaboration with other laboratories in our department
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.
Multi-physical characterization of potassium hybrid supercapacitors for performance improvement
The PhD subject focuses on the optimization of potassium hybrid supercapacitors (KIC), which combine the properties of supercapacitors (power, cyclability) and batteries (energy). This system, developed at the CEA, represents a promising technology, low cost and without critical/strategic materials. However, performance optimization still requires overcoming various obstacles observed in previous work, in particular on the intercalation of potassium in graphite and the heating phenomena of cells during operation. In order to explore in depth the operating mechanisms of the KIC system, an essential part of the thesis project will include experiments conducted at the ESRF (European Synchrotron Radiation Facility), where advanced diffraction and imaging techniques will be used to analyze the structure of the materials and their behavior in real operating conditions. The processing of the data collected will also be crucial in order to establish correlations between the physicochemical properties of the materials and the overall performance of the system. This thesis will contribute to the fundamental understanding of the multi-physical mechanisms at stake in KIC to develop innovative design strategies and thus improve their capacity, energy efficiency and lifetime.