Hiring Institution
Centre National de la Recherche Scientifique – ICMCB (CNRS-Ubx)

PhD-Awarding Institutions
Université de Bordeaux
The University of Sydney (USYD)

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Option 1

NEW OXIDES WITH A CaFe₂O₄-TYPE STRUCTURE USED AS POSITIVE ELECTRODE FOR SODIUM-ION BATTERIES

This project is primarily a fundamental research project whose main goal is the exploration of new materials and new potentialities of electrochemical deintercalation and intercalation of sodium for a family of oxides that has thus far received little attention and that could be used as positive electrode materials in sodium ion batteries. More specifically, its objectives are:

– Exploring new Na(M,M’)₂O₄ systems with CaFe₂O₄-type structure by targeting ambient pressure synthesis conditions. Titanium- and ruthenium-based compounds will be selected as titanium and ruthenium can both help to stabilize this structure-type at ambient pressure. In order to explore more systems and/or to compare the structural and electrochemical properties of the new synthesized materials to those of existing ones (for example, NaMn₂O₄), HP-HT syntheses might also be necessary. All the syntheses could be performed at the ICMCB.

– Evaluating the electrochemical performance of all synthesized systems as positive electrode materials in a sodium battery. This task will provide a comprehensive state of the art appraisal of the most promising CaFe₂O₄-type Na(M,M’)₂O₄ oxides candidates. In situ or operando X-ray powder diffraction experiments will also be performed during the charge/discharge of sodium batteries in order to study the structural mechanisms occurring in these materials during sodium electrochemical deintercalation and intercalation, as they have been the subject of a single publication. In particular, the structural mechanisms occurring during the discharge have never been studied. The electrochemical tests could all be performed at the ICMCB. In situ or operando experiments could be implemented either in the same laboratory or at large scale facilities.

– Understanding Na(M,M’)₂O₄ structural details in order to elucidate mechanisms for sodium transport combining experimental and theoretical tools such as the Maximum Entropy Method (MEM) and Molecular Dynamics (MD). MEM analyses will rely on the analyses of high resolution powder diffraction patterns recorded at various temperatures at synchrotron or neutron sources. Optimization of electrochemical properties for any of the Na(M,M’)₂O₄ systems will require a complete comprehension of percolation paths within their three-dimensional channel-type structures.

Option 2

COMPOSITION OPTIMISATION OF THE SPINEL-TYPE LiNi_0.5Mn_1.5O₄ COMPOUND USED AS POSITIVE ELECTRODE FOR LITHIUM-ION BATTERIES

This project is primarily a fundamental research project whose main goal is the composition optimization of a well-known compound used as positive electrode in lithium-ion batteries to improve it electronic and ionic conductivity. More specifically, its objectives are:

– Limiting the amount of nickel in the spinel-like compound LiNi_0.5Mn_1.5O₄ by gradually replacing a total number of Ni₂₊ and Mn₄₊ ions by an equivalent number of Fe₃₊ ions until the composition LiNi_1/3Mn_4/3Fe_1/3O₄ which exhibits an excellent thermal stability and which is able to deliver a high energy density. The syntheses will be carried out by sol-gel route in order to promote a homogeneous distribution of the three transition metal cations at the atomic scale.

– Analysing in detail the average structure of the as-synthesised compounds by synchrotron X-ray diffraction and by neutron diffraction. Neutron diffraction will indeed be of great scientific benefit, not only for locating lithium ions in the crystalline structure, but also for scattering factors. The synthesis conditions may affect the composition, the oxygen stoichiometry and the cationic order in the different octahedral and/or tetrahedral sites. This order is sometimes difficult to quantify by diffraction techniques which essentially provide information on the average structure. Therefore, the local structure of will also by studied by the analysis of the pair distribution functions (PDF).

– Understanding Li(Ni,Mn,Fe)₂O₄ structural details in order to elucidate mechanisms for lithium transport combining experimental and theoretical tools such as the Maximum Entropy Method (MEM) and Molecular Dynamics (MD). MEM analyses will rely on the analyses of high resolution powder diffraction patterns recorded at various temperatures at neutron sources. Optimization of electrochemical properties for any of the Li(Ni,Mn,Fe)O₄ systems will require a complete comprehension of percolation paths within their three-dimensional channel-type structures.

Option 3

MORPHOLOGY OPTIMISATION OF SPINEL-TYPE Li(Ni,Mn,Fe)O₄ COMPOUNDS USED AS POSITIVE ELECTRODE FOR LITHIUM-ION BATTERIES

This project is primarily a fundamental research project whose main goal is the morphology optimization of spinel-like Li(Ni,Mn,Fe)₂O₄ compounds used as positive electrode in lithium-ion batteries to improve it electronic and ionic conductivity. More specifically, its objectives are:

– Exploring a wide range a particle morphology for the spinel-like compound LiNi_1/3Mn_4/3Fe_1/3O₄ by synthetising it in different conditions (solid-state route, sol-gel route, molten-salt route…). The morphology of electrode material particles can dramatically affect lithium-ion transport properties in them. A meticulous study will be carried out in order to understand the relationship between morphology and transport properties.

– Analysing in detail the average structure of the as-synthesised compounds by synchrotron X-ray diffraction and by neutron diffraction. Neutron diffraction will indeed be of great scientific benefit, not only for locating lithium ions in the crystalline structure, but also for scattering factors. The synthesis conditions may affect the composition, the oxygen stoichiometry and the cationic order in the different octahedral and/or tetrahedral sites. This order is sometimes difficult to quantify by diffraction techniques which essentially provide information on the average structure. Therefore, the local structure of will also by studied by the analysis of the pair distribution functions (PDF).

– Understanding Li(Ni,Mn,Fe)₂O₄ structural details in order to elucidate mechanisms for lithium transport combining experimental and theoretical tools such as the Maximum Entropy Method (MEM) and Molecular Dynamics (MD). MEM analyses will rely on the analyses of high-resolution powder diffraction patterns recorded at various temperatures at neutron sources. Optimization of electrochemical properties for any of the Li(Ni,Mn,Fe)O₄ systems will require a complete comprehension of percolation paths within their three-dimensional channel-type structures.

Marie Guignard
Maxim Avdeev

Solid-state chemistry, Materials science