Advancing Lithium-Sulfur Batteries through the study of the Quasi-Solid Sulfur Conversion
Lithium–sulfur batteries are widely seen as one of the most promising candidates for the next generation of energy storage, offering the potential for significantly higher energy density than today’s batteries while using abundant and inexpensive sulfur. However, several scientific and technological challenges still prevent their large-scale industrial deployment.
One key issue is the formation of soluble lithium polysulfides during battery operation, which can migrate inside the cell and lead to rapid capacity loss. Recent research suggests that a different reaction pathway, known as a “quasi-solid mechanism”, could limit this dissolution and significantly improve battery stability.
This PhD project aims to design and study lithium–sulfur pouch cells operating through this quasi-solid mechanism. The work will combine materials development, electrochemical testing, and advanced characterization techniques to better understand the processes governing battery performance and durability.
The project will focus on two complementary research directions:
1. Design of advanced sulfur cathodes
The first part of the work will involve developing optimized sulfur-based cathodes. This includes exploring different conductive host materials and tuning their structure and surface properties to better confine sulfur and reduce unwanted reactions.
2. Development of improved electrolytes
The second part of the project will focus on electrolyte formulations that reduce the solubility of polysulfides while maintaining good battery performance. Current solutions often rely on dense, fluorinated solvents that increase cost and environmental impact. This project will explore alternative solvent systems and investigate how salt composition and concentration influence cell behaviour.
To gain deeper insight into the quasi-solid reaction mechanism, the project may also involve operando or in-situ characterization techniques, such as Raman spectroscopy, X-ray diffraction, and high-resolution X-ray tomography.
Advancing All-Solid-State Microbatteries: Interface Stabilization and Degradation Mitigation for Long-Term Reliability
This PhD project focuses on advancing all-solid-state microbatteries for miniaturized energy storage applications, such as wearable electronics, IoT systems, and implantable medical technologies. The research aims to stabilize and mitigate degradation at the electrode/electrolyte interfaces, which are critical bottlenecks in solid-state microbattery performance. The project involves two main research axes: (1) the study and optimization of ultrathin films (sub-nanometer to nanometer scale deposited by ALD) for engineering the interfaces in LiCoO2/LiPON/Li stacks, and (2) a fundamental investigation of the mechanisms responsible for interface degradation. The study will involve the fabrication and characterization of partial and complete stacks using techniques like cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The incorporation of alloying metals (e.g., Ag, Au) between the buffer layer and lithium will also be explored to enhance lithium-metal interface stability. The expected outcomes include an optimized microbattery stack capable of exceeding 1,000 cycles with minimal increase in interfacial resistance and a comprehensive framework describing degradation mechanisms and buffer layer effects.
Study of mechanical stress on Solid State Micro-batteries
CEA-Leti provides integrated microstorage solutions, including solid state (or solid electrolyte) microbatteries. Solid-state micro-batteries are among the most promising microstorage technologies for applications in several fields such as the internet of things and implantable devices for medical use. The objective of this thesis is to study the impact of mechanical stresses on microbatteries, particularly during microbattery charge/discharge cycles. To this end, two approaches will be considered: experimental study with the development of mechanical test benches and numerical simulation.
The PhD student's work will begin with the development of test benches, the first of which will apply variable pressure to the surface of a microbattery during charge/discharge cycles. He/she will be required to develop the pressure measurement equipment. Once the mechanical test bench is operational, other characterizations, such as measuring anode deformations, will be considered. In parallel with this experimental work, a mechanical model will be developed. This model will be progressively refined using the experimental results obtained with the mechanical test bench, and new characterizations may be implemented in order to obtain the mechanical properties of the different materials used. Ultimately, the objective will be to propose the integration of new layers to improve the mechanical performance of microbatteries during cycling.
Exploring the Strategic Benefits of 0V Storage for Na-ion Batteries
Recently deployed on a commercial scale, the Na-ion battery technology demonstrates excellent behaviour during medium or long-term storage at zero voltage. This characteristic offers numerous safety advantages during the transport, assembly and storage of cells and modules, as well as during emergency shutdowns in the event of external issues. But are there no consequences for battery performance?
This research project aims to study and better understand the electrochemical mechanisms at play when the potential difference across the terminals is maintained at 0 V.
Initially, advanced dynamic characterisation techniques will be used to analyse and compare the electrochemical, thermal and mechanical properties of battery materials. The results will enrich calendar and cycling ageing models at the cell scale, thereby improving their accuracy and reliability. Subsequently, tests will be conducted on mini-battery modules assembled in various electrical architectures to study cell behaviour during cycling and ageing, particularly in response to the application of negative voltage. Specific battery management system (BMS) solutions could then be proposed to address these issues.
The scientific approach will involve implementing advanced characterisation and instrumentation techniques, conducting ageing and safety tests to identify mechanisms, and developing ageing models. This approach will draw on the expertise and testing facilities of CEA-Liten at the Bourget du Lac site in Savoie.
Understanding Lithium Recovery Mechanisms through the Application of Electrochemical Pumping on Battery Leachates
The economical, environmental and geopolitical context recently pushed Europe to issue a regulation on battery recycling. By 2031, 80% of lithium in batteries should be recovered. In this context, CEA is interested in Electrochemical Lithium-Ion Pumping (ELIP): this process uses battery electrodes to selectively insert and disinsert lithium, allowing to extract it from a complex solution. Unlike more common lithium recovery processes, ELIP allies a high selectivity towards lithium, does not require the use of toxic chemicals during the process and offers the possibility to be used in a continuous flow mode, practical for industrial applications. A first PhD work on the subject, in our team, evidenced for the relevance of such a process for the separation of lithium from other alkali cations (sodium and potassium). Real battery leachates are however more complex and can include transition metal cations and organic species besides alkaline cations. The proposed PhD subject has the aim to precisely understand the effect of these solutions on the ELIP process in order to choose the best position in the recycling loop (upstream or downstream), and to adapt to adverse effects encountered in such conditions. The impact of the other species present in solution will be evaluated on selectivity, efficiency and durability at different scales: material, electrode and membrane. Chemical (ICP-AES, EDX), structural (XRD) and morphological (SEM, TEM) characterizations will be correlated with electrochemical results in order to identify side reactions and species which impact the most the performances. Based on these results, the PhD student will have to test different improvement protocols (additive incorporation, pH control, change of the electrochemical method, etc...) and to understand the physico-chemical reasons governing these improvements. The PhD work will allow to propose a thoughtful integration of the ELIP process in conventional battery recycling steps, as well as highlighting the relevance, or not, of such a process for lithium extraction from real leachates.
Physics-Informed Deep Learning and Multi-Modal Sensor Fusion for Li-Ion and Na-Ion Battery degradation mechanisms predictive monitoring
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 (internal sensors using optical fiber modality, and external sensors Embedded on the cell packaging) 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.
Development of Zinc Sodium-ion batteries for stationary storage of renewable energy
In the global context of massive renewable energy deployment, production and storage are becoming increasingly intertwined. Battery electrochemical energy storage systems (BESS) are currently experiencing strong market growth. These systems differ radically from electric mobility solutions due to their specific characteristics (cost, safety, durability). Faced with the limitations of Li-ion batteries (fire risks, the criticality of lithium and cobalt, production costs), aqueous zinc/sodium-ion technology presents a disruptive alternative. Based on abundant, non-toxic, and inherently safe materials, it offers unique potential for long-term storage with a low environmental impact. The zinc battery sector faces scientific challenges that limit reversibility and cycle life, notably the formation of zinc dendrites and cathode instability. This doctoral thesis project proposes to overcome these obstacles through a research and development strategy for innovative electrodes based on the reversible transformation of zinc into zinc phosphate in an aqueous sodium phosphate medium. This choice of electrolyte allows the use of sodium-ion positive electrodes as well as AGM (absorptive glass mat) separators, developed notably for lead-acid batteries.
The thesis work will focus on experimental electrochemical studies combined with multiphysics modeling of the system at the cell scale, taking into account the thermodynamics and kinetics of the included reactions. This approach will allow for the rapid exploration of a vast design space to identify the conditions enabling scaling up and transfer to industry, meeting the imperatives of energy sovereignty and the circular economy.
Fast charging of lithium-ion batteries : Study of the lithium plating phenomenon using operando NMR
The focus of the thesis is the fast-charging process of lithium-ion batteries and, more specifically, the phenomenon of lithium plating, which will be studied using operando NMR. The target application is electric mobility. The objective of the thesis is to study the dynamics of lithium insertion and lithium metal deposition at the graphite or graphite/silicon-based negative electrode in order to understand the mechanisms leading to plating formation.
Operando NMR is an ideal technique for this study because it offers the unique possibility of simultaneously tracking the signals of the lithiated graphite phases and of deposited lithium during the electrochemical processes. The coupling of electrochemistry and operando NMR will allow us to determine the onset of plating, i.e. the potential of the negative electrode at which deposition begins, and the kinetics of lithium metal deposition and reinsertion at different temperatures and different charging current regimes. We will study Li-ion batteries with a pure graphite negative electrode, but also with graphite-silicon electrodes, in order to investigate the impact of silicon on this phenomenon. The data obtained on the onset mechanisms and the kinetics of lithium metal deposition and reinsertion will be used in a multiphysics model that has already been developed in the laboratory to improve the prediction of plating onset. We will then be able to evaluate the chargeability gains on an NMC 811 // Gr+Si system incorporating optimized electrodes and propose innovative charging protocols.
Exploration of VACNTs in Anode-less Batteries: Mechanism and Cell Optimization
Anode-less or anode-free batteries are getting increasing attention owing to their excellent energy density, cost efficiency, and ease of process upscaling. Exploring anode-less battery will offer a breakthrough in energy storage devices by using the lithium reserve already present in the NMC cathode to reversibly cycle after an initial formation process, which will reduce the overall thickness, processing steps, and cost of materials, and provide excellent energy density. Vertically aligned CNTs (VACNTs) on metal substrates can be an interesting choice for this application due to their low thickness, reproducible synthesis process, and uniform surface properties, which have already proven their applicability in supercapacitors. In this PhD project, we will investigate their newer avenue of applications- anode-less batteries, where VACNTs act as the lithium or sodium plating substrate. We will study the electrochemistry of VACNT in lithium anode-less batteries (in liquid and solid electrolytes) and in sodium anode-less batteries in a liquid electrolyte. The PhD student will work on the synthesis optimizations of VACNT to tune the thickness and density to match their electrochemistry. Post-cycling studies (Raman and SEM) will be carried out to study the effect of cycling and the electrolytes on the VACNT layers. The project aims to explore the possibility of the application of VACNTs in various energy storage systems, which can open up new application possibilities and valorization