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.

Study of NMC electrode materials for lithium-ion batteries by experimental and theoretical soft and hard X-ray photoemission spectroscopy

The photoemission spectroscopy (X-ray, XPS, or ultraviolet, UPS) is one of the direct probes of the electronic structure of materials change during redox processes involved in lithium ions-batteries at the atomic scale. However, it is limited by the extreme surface sensitivity, with a typical photoelectron path length of a few nanometers to the energies usually available in the laboratory , . Moreover, the spectra interpretation requires the ability to accurately model the electronic structure, which is particularly delicate in the case of transition metal based electrode materials. Upon lithium insertion and de-insertion, the charge transfer toward cations and anions induces local electronic structure changes requiring an adapted model that takes in account the electronic correlations between atoms.
In this thesis, we propose to use these limitations to our advantage to explore the electronic surface structure including the solid electrolyte interphase (SEI), and the bulk of the active cathode particle.
Thanks to the lab-based hard X-ray photoemission spectrometer (HAXPES), the electronic structure of the bulk of the electrodes (LiCoO2 and LiNiO2) materials have been studied up to about 30 nanometers , . To widen our picture on the role of cation and anion from surface to bulk in the lamellar metal oxide electrode for lithium-ion battery, this thesis will focus on mixed lamellar metal oxide Li(Ni1-x-yMnxCoy)O2 (NMC).
The comparison between the Soft-XPS and HAXPES spectra, during battery operation (operando) and post-mortem, will allow decoupling of the surface and core spectra for different NMC compositions and at different stages of the battery life cycle. The interpretation of the photoemission spectra will be done by direct comparison with ab-initio calculations combining density functional theory (DFT) with dynamical mean field theory (DMFT) , . This coupled approach will allow to go beyond the usual techniques based on cluster models, which do not take into account long-range screening, and to validate the quality of theoretical predictions on the effects of electronic correlations (effective mass, potential transfer of spectral weight to Hubbard bands) .
The thesis will include an instrumental (in particular, calibration of Scofield factor on model systems) and theoretical (prediction of core photoemission spectra based on DFT+DMFT calculations) development. The performance of electrochemical systems based on different cathode materials (NMC with different compositions) in combination with liquid and solid electrolytes and a Li metal anode will be studied in the frame of combined experimental and theoretical soft and hard X-ray photoemission spectroscopy.
The candidate will be hosted at the PFNC in the Laboratory of Characterization for the Energy of CEA Grenoble under the direction of Dr. Anass BENAYAD (department of Material) and LMP (Department of Electricity and Hydrogen for Transport) under the supervision of Dr. Ambroise Van Roekeghem.
Contact : anass.benayad@cea.fr et ambroise.vanroekeghem@cea.fr

Understanding the Impact of Operating Conditions and Utilization Profiles on Solid Oxide Electrolysis Stacks Lifetime

The shift to a low-carbon European Union (EU) economy raises the challenges of integrating renewable energy sources (RES) and cutting the CO2 emissions of energy intensive industries (EII). In this context, hydrogen produced from RES will contribute to decarbonize those industries, as feedstock/fuel/energy storage. Among the different technologies for low carbon H2 production, high temperature electrolysis (HTE) enables the production of green hydrogen with extremely high efficiency. The solid oxide cells (SOC) are typically operated in the 650-to-850°C temperature range, and arranged in pile-ups or stacks to increase the overall power density and address (pre-) industrial markets.
The technology has recently entered a phase of aggressive industrialization. However, significant efforts are still required to turn the high efficiencies into a competitive levelized cost of H2. As long as such cost remains largely controlled by that of stack manufacturing, stack degradation and the relationship with operating conditions remain a crucial subject of research and development. Moreover, recent advances have shown that to properly evaluate stack lifetimes, actual testing beyond 5 kh is critical [1,2]. A better understanding of degradation over the 5-to-10 kh range [3–5] could thus enable the development of both accelerated stress tests (AST) to reduce the necessary test duration, as well as optimized operational strategies to extend stack lifetimes.

Study of catalysis on stainless steels

The materials (mainly stainless steels) aging of the spent nuclear fuel reprocessing plant is the focus of an important R&D activity at CEA. The control of this aging will be achieved by a better understanding the corrosion mechanisms the stainless steels in nitric acid (the oxidizing agent used in the reprocessing steps).
The aim of the PhD is to develop a model of corrosion on a stainless steel in nitric acid as a function of temperature and the acid nitric concentration. This PhD represents a technological challenge because currently few studies exist on in situ electrochemical measurements in hot and concentrated nitric acid. The PhD student will carry out by coupling electrochemical measurements, chemical analyses (UV-visible-IR spectrometry...) and surfaces analyses (SEM, XPS,…). Based on these experimental results, a model will be developed, which will be incorporated in the future in a more global model of the industrial equipments aging of the plant.
The laboratory is specialized in the corrosion study in extreme conditions. It is composed of a very dynamic and motivated scientific team which has the habit to receive students.

Operando Bragg coherent diffraction imaging to probe CO2 Reduction

The imperative to capture and convert CO2 into high value-added chemicals or fuels represents one of the most significant challenges in achieving a sustainable society. This reaction can be performed in the gas phase at high temperature but also electrochemically, at low temperature, not only mitigating the greenhouse effect, but also providing a way to store energy by transforming intermittent renewable electricity into high added value chemicals. This project aims to investigate the structural evolution of individual nanocrystals during CO2 reduction reactions. Using the unique capabilities of Bragg coherent X-ray imaging, we can dynamically map, in situ and operando, the three-dimensional changes in lattice deformation, strain, composition, and crystallographic defects of nano-crystallites, establishing a comprehensive experimental framework for structure-chemistry-performance relationships. The experiments will be conducted at ESRF, the European synchrotron facility located in Grenoble, in close proximity to CEA-Grenoble, within a leading international scientific environment. The project will be in collaboration with LEPMI (Laboratory of Electrochemistry and Physico-chemistry of Materials and Interface, Grenoble-France), which has expertise in electrocatalysis, materials science, and energy storage and conversion systems.

Predicting new catalysts for fixing dinitrogen

New chemical approaches for conversion of N2 to NH3, as an alternative to the energy- and CO2-intensive Haber-Bosch process, are of high interest for improved fertilizer production and the potential of NH3 as a zero-carbon fuel. Catalytic N2 fixation, however, is an extremely difficult reaction with few successes. Previous attempts show low turnover rates, insufficient selectivity or too negative potentials required. A breakthrough in molecular N2 fixation was recently described (J. C. Peters and co. Nature, 2022). By combining coupled proton-electron transfer mediator, CPET, with simple Fe/Mo/W complexes in solution, selective catalysis was demonstrated (-1.2 V vs. Fc0/+). This proof-of-principle experiment implicates CPET mediation as a general N2 fixation strategy when combined with N2-binding metal complexes. However, design principles for improving catalytic N2 fixation activity under CPET conditions are not known. We propose here a multiscale simulation strategy to uncover these catalyst design principles and aid synthetic efforts. Our previous expertise in studying biological N2 fixation, multiscale modelling of redox processes and high-level calculations of redox mediators will be of benefit in this project.

Nanodiamond-based porous electrodes: towards photoelectrocatalytic production of solar fuels

Among nanoscale semiconductors, nanodiamonds (ND) have not been really considered yet for photoelectrocatalytic reactions in the energy-related field. This originates from the confusion with ideal monocrystalline diamond featuring a wide bandgap (5.5 eV) that requires a deep UV illumination to initiate photoreactivity. At the nanoscale, ND enclose native defects (sp2 carbon, chemical impurities such as nitrogen) that can create energetic states in the diamond’s bandgap decreasing the light energy needed to initiate the charge separation. In addition, the diamond electronic structure can be strongly modified (over several eV) playing on its surface terminations (oxidized, hydrogenated, aminated) which can open the door to optimized band alignments with the species to be reduced or oxidized. Combining these assets, ND becomes competitive with other semiconductors toward photoreactions. The aim of this PhD is to investigate the ability of nanodiamonds in reducing CO2 through photoelectrocatalysis. To achieve this goal, electrodes will be made from nanodiamonds with different surface chemistries (oxidized, hydrogenated and aminated), either using a conventional ink-type approach or a more innovative one that results in a porous material including nanodiamonds and a PVD-deposited matrix. Then, the (photo)electrocatalytic performances under visible illumination of these nanodiamond-based electrodes toward CO2 reduction will be investigated in terms of production rate and selectivity, in presence or not of a transition metal macrocyclic molecular co-catalyst.

Ab initio simulation of catalysts for green chemistry

Catalysis is today at the core of chemical industrial applications. For example, the conversion of nitrile to amide, which is relevant in pharmaceuticals, agrochemicals, synthetic chemistry and polymer chemistry, by hydration requires an efficient catalyst due to its slow kinetics. For environmental reasons, it is crucial to discover catalysts without transition metals, neither toxic nor corrosive, and cheap. One example of such catalyst is hydroxide choline.

During this thesis, the student will learn how to perform ab initio molecular dynamics simulations coupled with a method which can reconstruct the free-energy landscape of the hydration reaction for different aromatic nitriles in different in silico experimental conditions. He or she will also have to perform quantum chemistry calculations at a level that can describe all the required intra and intermolecular interactions. This theoretical approach has already been successfully used within our team to describe other chemical reactions in aqueous solution and will be applied to the innovative field of green chemistry.