Optimization of Interfaces in High-Temperature Fuel Cells (SOFC) and Electrolyzers (SOEC) by Magnetron Sputtering Deposition

As part of the France 2030 Plan, hydrogen technologies and fuel cells are currently enjoying a major boom in both industry and research. Among the electrochemical systems being considered, ceramic technologies are particularly promising. Whether Solid Oxide Fuel Cells (SOFC) or Solid Oxide Electrolysis Cells (SOEC), also known as High Temperature Steam Electrolysers (HTSE), their high operating temperatures enable them to achieve high conversion efficiencies (Gas to Power and Power to Gas). What's more, these devices do not use precious metal catalysts such as platinum (Pt) or iridium oxide (IrO2). Although highly efficient in the short term, current cells are not sufficiently durable. In particular, a degradation rate of the order of 0.1%/k hour is targeted in the near future (which can be estimated at an operating life of the order of 10 years).
Although charge transfer and ion transfer properties at the interfaces are very important to ensure good electrochemical cell behavior, material stability is also crucial. At present, the main reasons for premature cell ageing are related to parasitic reactions between the constituent materials and a certain chemical instability of the latter with respect to the gases used. In the case of SOFCs and SOECs based on an O2- conductive electrolyte made of Yttria Stabilized Zirconia (YSZ), a so-called "barrier" layer is usually interposed between the electrolyte and the oxygen electrode to ensure proper transfer of O2- ions through the cell, but also to prevent diffusion of cations from the electrode and/or the interconnector metal material. In particular, this means avoiding reaction with ions such as La3+, Sr2+, Fe3+, Co3+ (in the case of La1-xSrxFe1-yCoyO3-d type electrodes) or others, or Cr3+, Ni2+ cations in the case of the interconnector metal.
In this context, gadolinium ceria barrier layers - Cerium Gadolinium Oxide (CGO) - are frequently used. This oxide crystallizes in a fluorine structure such as YSZ, which accommodates CGO/YSZ interfaces, and has good oxygen ionic conductivity thanks to the presence of vacancies. What's more, this material slows down the diffusion of cations into the electrolyte. However, the ionic conductivity of Zr1-x-y'-y "YxM'yM''y "O2-d mixed phases (where M 'and M'' are the metal cations) is poorly understood. In addition, the structural and microstructural parameters of this interfacial layer remain to be defined in order to optimize this interface and increase cell lifetime: grain size, thickness, porosity, etc.
The aim of this thesis will be to study and develop new barrier layers in order to improve their performance (stability, ionic resistance) and reduce the quantity of critical elements such as Gd. Magnetron sputtering, which enables the production of dense layers significantly thinner than those traditionally obtained by tape casting, will be chosen here as the synthesis process. This study will comprise 4 main components: (i) the synthesis of films by magnetron sputtering, (ii) their in-depth physico-chemical and structural characterization, (iii) the production of interfaces and architectural electrodes and (iv) the study of the influence of the coating on the electrochemical behavior of the oxygen electrode and the evolution of the interfaces over time. This will require the use of various characterization techniques, including SEM/EDS, SEM/FIB, X-ray diffraction, electrochemical impedance spectroscopy (EIS), confocal optical microscopy, ToF-SIMS, Auger nanoprobe.
This work will be carried out as part of the European SustainCell Project, which brings together 10 partners and aims to support European industry in developing the next generation of electrolyzers and fuel cell technologies (low and high temperature) by developing a sustainable European supply chain of materials, components and cells, with significantly lower dependence on critical raw materials (CRMs), a smaller environmental footprint and lower costs, and superior performance and durability to existing technologies. They will be carried out jointly at two laboratories in the Nouvelle Aquitaine region, in Pessac (CEA Tech's Plateforme Batterie and Bordeaux's Institut de Chimie de la Matière Condensée (ICMCB)).

Experimental study and thermo-hydraulical modelling of a heat and cold storage prototype coupling thermocline and latent heat technologies

Heating and cooling in residential buildings hold a 28% share in the total energy consumption of Europe, out of which 75% of the energy is still generated from fossil fuels, while only 19% comes from renewable energy sources. To increase the share of renewable energy in the near future, the French energy commission has identified 4th generation district heating networks as a plausible option. Key hardware components for next generation smart urban heating networks are heat and cold storages, which allows a shift between production and consumption as necessary.
The prototype that will be studied in this thesis couples in a same component heat and cold storage, in order to obtain significant gains in terms of compactness and cost. Cold storage is based on ice-water phase change transition around finned tubes in charging mode (-6°C), and on direct contact between water and ice in discharging mode (direct contact = water flow through the ice and directly exchange heat without any wall between water and ice). Heat storage is based on thermocline technology with water (60-70°C) as coolant.
The prototype is currently under manufacturing in the framework of a European Project and will be operational at the beginning of the thesis. The objective of the thesis is on the one hand to experimentally characterize the performances of the storage, on the other hand to work on a numerical modelling of the storage. The thermos-hydraulical modeling of the discharge in cold mode, with direct contact between ice and water, is particularly challenging. The study of the addition of Phase Change Material capsules for heat storage (50-60°C), in order to boost energy and power, will also be studied with potential implementation in prototype during the thesis.

High-throughput experimentation applied to battery materials

High throughput screening, which has been used for many years in the pharmaceutical field, is emerging as an effective method for accelerating materials discovery and as a new tool for elucidating composition-structure-functional property relationships. It is based on the rapid combinatorial synthesis of a large number of samples of different compositions, combined with rapid and automated physico-chemical characterisation using a variety of techniques. It is usefully complemented by appropriate data processing.
Such a methodology, adapted to lithium battery materials, has recently been developed at CEA Tech. It is based, on the one hand, on the combinatorial synthesis of materials synthesised in the form of thin films by magnetron cathode co-sputtering and, on the other hand, on the mapping of the thickness (profilometry), elemental composition (EDS, LIBS), structure (µ-DRX, Raman) and electr(ochim)ical properties of libraries of materials (~100) deposited on a wafer. In the first phase, the main tools were established through the study of Li(Si,P)ON amorphous solid electrolytes for solid state batteries.
The aim of this thesis is to further develop the method so as to enable the study of new classes of battery materials: crystalline electrolytes or glass-ceramics for Li or Na, oxide, sulphides or metal alloys electrode materials. In particular, this will involve taking advantage of our new equipment for mapping physical-chemical properties (X-ray µ-diffraction, Laser-Induced Breakdown Spectroscopy) and establishing a methodology for manufacturing and characterising libraries of thin-film all-solid-state batteries. This tool will be used to establish correlations between process parameters, composition, structure, and electrochemical properties of systems of interest. Part of this work may also involve data processing and programming the characterisation tools.
This work will be carried out in collaboration with researchers from the ICMCB and the CENBG

Development of thin film negative electrodes for Li-free all-solid-state batteries

The aim of this work is to develop 'Li-free' negative electrodes for new generations of high energy density all-solid-state lithium batteries. The function of this type of electrode is to provide a significant gain in energy density in the battery, to facilitate its manufacture by eliminating the need to handle lithium metal and, most importantly, to enable the formation of a homogeneous, dendrite-free lithium film when the battery is charged.
These electrodes will be based on the functionalisation of a metal collector with thin-film materials comprising at least one lithiophilic material (typically a compound that can be alloyed with lithium) and an inorganic ionic conductor. These electrodes are prepared by physical vacuum deposition processes such as sputtering or thermal evaporation. It will therefore be necessary to study the influence of the composition and structure of the lithiophilic layer on the nucleation and growth mechanism of the lithium film and on the evolution of the electrode during charge/discharge cycles. The role of chemical/mechanical interactions with the ionic conducting layer will also be investigated.
This work, which is part of a national CEA/CNRS joint project, will be carried out at the CEA Tech site in Pessac, which has a full range of vacuum deposition and thin film characterisation equipment, in close collaboration with ICMCB CNRS in Bordeaux. It will benefit from the many characterisation resources (confocal optical microscopy, SEM/cryo FIB, ToF-SIMS, SS-NMR, µ-XRD, AFM,...) available in the various partner laboratories involved in the project.

Enhancing micro-mobility battery pack lifetime by using proper and cost effective thermal management

Urban mobility options are diversifying, notably with the deployment of micro-mobility vehicles (electric bikes, cargo bikes, scooters, electric carts). Their usage poses increasing challenges for powertrains, especially for batteries. Li-Ion batteries are temperature-sensitive and require effective thermal regulation to maximize their lifespan. This constraint is well-considered in the automotive sector, which often employs onboard cooling systems to cool or warm batteries.

Micro-mobility vehicles often incorporate battery packs with a simple and cost-effective design, featuring minimal components and lacking a thermal management system. If these batteries are used in severe weather conditions or under high electrical loads, their lifespan can be significantly affected, directly impacting their overall environmental footprint. The development of new thermal management solutions tailored to usage patterns and industrial viability will be the central theme of this thesis.

We aim to achieve the following objectives:

- Investigation of typical usage profiles for these mobility devices (current profiles, external thermal constraints, charging and discharging conditions, integration constraints within the vehicle).
- Design and development of innovative thermal management systems.
- Prototyping and characterization of one or more solutions.
- Integration of thermal results into an aging model to analyze the effects on lifespan.

This thesis proposes an approach combining design, simulation/modeling, and prototyping/characterization. The laboratory is equipped with a dedicated platform for battery pack assembly, featuring rapid prototyping tools (3D printing, laser cutting and welding, mechanical workshop), as well as a testing platform enabling advanced characterizations of battery systems.

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.

Understanding flamability of Li-ion thermal runaway vent gases

The objective of the thesis is to characterize the ignition of vent gases resulting from the thermal runaway of lithium-ion cells. During the venting phase, the cell emits electrolyte vapours that mix with the air, and then during thermal runaway, a hot jet of gases and particles is formed that can enrich the mixture and ignite it. The underlying scientific questions concern the evolution of the fundamental characteristics of combustion (flame velocity and auto-ignition delay) with temperature, pressure and composition, ignition mechanisms and the impact of the environment on the preponderance of one of the mechanisms.
To answer this question, we will first use an approach based on the identification of a reaction kinetic model using existing results in the literature and complementary tests to be performed in the thesis at the cell level. Then, we will experimentally characterize the conditions of ignition of mixtures by a hot jet of gas and particles in a shock tube coupled to a combustion chamber. Finally, the mapping obtained on the basis of the knowledge acquired on the mechanisms and conditions of inflammation will be reinterpreted.

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.

Synthesis and electrochemical characterization of p-type organic electrode materials for anion-ion battery

Nowadays Li-ion batteries use mainly inorganic compounds as electrode materials especially transition metal based ones. Although their performances are satisfying, they present several important drawbacks. Indeed these compounds are expensive and leads to large environmental footprint because they are prepared due to energy-consuming techniques from rare mineral precursors. Moreover, this technology is based on the use of lithium leading to geostrategic issues.

Some organic redox compounds such as viologen based derivatives can reversibly react with anions. Consequently they appear as an interesting alternative to conventional active materials especially for negative electrode for battery in anion-ion configuration which not use metallic counter ions. Interestingly these organic molecules can be easily prepared using simple organic chemistry techniques from low cost precursors. However their redox potential is too high (~2-2.5V vs Li+/Li) for the development of high energy density batteries.

The work of this thesis will firstly focus on the synthesis of new insoluble structure based on viologen derivatives presenting a redox potential below 2V vs Li+/Li. Some fine characterizations in particular Electron Paramagnetic Resonance (EPR) will be applied in order to better understand their electrochemical 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.

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