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Sciences pour l'ingénieur >> Chimie physique et électrochimie
8 propositions.

Synthesis of new electro-active polymers and use as electrode materials for lilthium battery

Actual lithium batteries use transition metal (Fe, Mn, Co, Ni) based compounds as electrode materials. Although their performances are satisfying, they present several important drawbacks. First these materials are expensive because they are prepared using energy-consuming techniques from expensive and rare mineral precursors. Moreover they have an important environmental footprint as some metals (Co, Ni) are toxic and hard to recycle at the end of life. Recently some new compounds which are able to reversibly form complexes with lithium have been identified: stable organic radicals in particular nitroxide radicals (TEMPO). These molecules have also the advantage to present very fast electrochemical reaction kinetics which enables to use them for high power application. The main problem of this kind of molecules is related to their important solubility in organic solvents used in electrolytes which leads to rapid drop of batteries performances along cycles of charge/discharge. To solve this issue, we propose to graft these molecules on a polymer backbone in order to limit their dissolution into electrolytes. The main interest of these organic radical functionalized polymers is that they can be easily prepared using simple organic synthesis techniques form cheap precursors. Moreover they could be easily implemented into electrodes as they can themselves act as binder mandatory to obtain electrodes with good mechanical properties.

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Département : Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN) Laboratory : Start Date : 01-10-2015 ECA Code : SL-DRT-15-0276 Contact : thibaut.gutel@cea.fr

Electrodes microstructural optimisation of Solid Oxide Cells for co-electrolysis operation

Because of its great potential, hydrogen production by high temperature steam electrolysis has received an increasing national and international interest in recent years. The hydrogen produced by water electrolysis if taking advantage of sustainable energy sources would constitute an energy carrier with low carbon footprint and would allow limit greenhouse gas emission. In this frame, co-electrolysis at high temperatures of steam and carbon dioxide constitutes a promising process. Indeed, it allows valorising CO2 by producing a syngas of H2 and CO. This mixture can be further transformed by chemical processes into methane or liquid fuel for both stationary and transport applications. However, the electro active components of electrolyser, i.e. the solid oxide cells, have been optimised for the classical operation under hydrogen. Electrodes microstructures as well as cell dimensions are not adapted for the specific operation in co-electrolysis. In the thesis, it is proposed to design electrodes microstructures and cell dimensional characteristics in order to improve the cell efficiency and reliability when operated in co electrolysis. The morphological optimisation will be carried out thanks to a ?multi physic? and ?multi scale? model, already available at CEA.

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Département : Département Thermique Biomasse et Hydrogène (LITEN) Laboratory : Laboratoire des Technologies de l'Hydrogène Start Date : 01-10-2014 ECA Code : SL-DRT-15-0364 Contact : guilhem.roux@cea.fr

Contribution of statistical tools and the methodology of design of experiments to the development of high energy density Li-ion batteries

The work will consist in evaluating the contribution of statistical tools and applying the design of experiment methodology (DOE) to optimize the working behavior of Lithium-Ion positive electrode materials. First, the work will be focused on NMC compounds and then will be enlarged to lithium rich layered oxides materials that have the potential to significantly increase the energy density of Li-Ion batteries. In both cases, the compounds will be synthesized by spray-pyrolysis route. The methodology of design of experiments will be used to optimize this synthesis and coupled with fine characterization to understand the link between synthesis parameters and the studied responses. With a DOE tool such as Minitab, the designs will be defined and will allow optimizing either their composition or their synthesis conditions or their electrochemical formation. Characterization techniques such as SEM, XRD, TGA, BET and electrochemical evaluation in coin cells will be performed for better understanding.

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Département : Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN) Laboratory : Start Date : 01-10-2015 ECA Code : SL-DRT-15-0485 Contact : david.peralta@cea.fr

Investigation of lithium/sulfur battery by means of in situ and operando X-ray tomography

This thesis will aim at studying and improving the understanding of the lithium/sulfur (Li/S) battery technology, its discharge and failure mechanisms, by means of various tomographic measurements. Indeed, this battery technology is quite promising in terms of energy density, costs and sulfur material abundance. However, the discharge mechanism and reasons for failures of this system are still unclear, and deserve further investigation. To this purpose, the sulfur electrode as well as full Li/S cells will be characterized thanks to in situ and operando tomographic measurements. This thesis will be held between two laboratories: CEA-LITEN and ESRF. The preparation of the cell components and the assembly of Li/S cells will be done in CEA-LITEN, as well as the electrochemical characterizations of the batteries, while the tomographic measurements will be performed in ESRF. The thesis will finally aim at better understanding the failure mechanisms of Li/S cells and sulfur electrodes during cycling, in order to propose innovative materials that could improve the electrochemical response of the system, in terms of discharge capacity and capacity retention.

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Département : Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN) Laboratory : Start Date : 01-10-2015 ECA Code : SL-DRT-15-0493 Contact : celine.barchasz@cea.fr

Metallic Lithium protection against alcaline electrolytes for very high energy density technologies

For automotive applications and more generally for mobility considerations, an increase in the energy density of the battery is mandatory to reach riding distance compatible with a general public use. With this objective, CEA-Grenoble developed since few years, electrochemical system of novel generation using metallic lithium coupled with Sulfur, Oxygen and soon with Nickel. These new systems will be able to reach very high energy density as high as respectively, 500Wh/kg, 1000Wh/kg and 900 Wh/kg. These technologies could be based on an alkaline electrolyte et therefore they required the development of an efficient protection on the Li-metal against water. To answer to this level of requirement, the PhD study will be based on two solutions probably complementary: a) the development of new ionically conductive solid polymer electrolytes AND b) the gelification of a electrolyte not immiscible to water. A multilayer approach could be developed starting from the studied elementary building blocks. Several experimental techniques, at the same time for the control of the synthesis (FTIR, NMR ?), for the electrochemical studies (EIS, cycling ?), for implementation (coating, spray, extrusion ?) will be implemented to bring the required level of comprehension of the charge-discharge mechanisms of the Li-metal electrode. At the end, we should be able to propose a functional prototype of Li-ion batteries with a very high energy density.

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Département : Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN) Laboratory : Start Date : 01-09-2015 ECA Code : SL-DRT-15-0531 Contact : lionel.picard@cea.fr

Multiscale modeling of aging mechanisms in Li-ion batteries. Analyses of the electrode/electrolyte interfaces evolution

The technology of lithium- ion batteries has a great success and is widely used in various portable technologies and for transport. However, battery performances decay with time with both capacity loss and resistance increase. The aim of the thesis is to develop a multi-scale battery model in order to study these performance losses and get a better vision of the parameters affecting the most the battery life-time. The muti-scale approach is necessary to finely describe the degradation mechanisms at electrode/electrolyte interfaces while taking into account the local conditions inside the cell which depends on the operating conditions. Experimental data obtained both at the cell scale during aging and at local scale from ante- and post-mortem characterizations will be used to support the model development.

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Département : Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN) Laboratory : Start Date : 01-10-2015 ECA Code : SL-DRT-15-0595 Contact : marion.chandesris@cea.fr

Real-time diagnosis of PEMFC performance and durability using impedance spectroscopy

PEMFC are very promising converters of chemical energy into electrical energy for stationary and transport applications. For many years, LITEN works on the development of MEA, stacks and PEMFC systems. This work led to the development of fuel cells based on bipolar plates stamped in perfect adequation with the market for this technology. At the same time, the development and testing of prototypes in actual operating conditions have allowed acquire, for LITEN, an important feedback on these systems and to highlight the impact of fuel cells operating conditions on their performances and their lifetime. It seems to be interesting to monitor in real time, the evolution of different operating parameters to quickly control the command-control and avoid degradations linked with extreme operation conditions. The PhD thesis deals with development of a diagnostic tool in real time based on fuel cell electrochemical impedance. In this work, the development of an electric model based on physical phenomena will be made. This model will then be streamlined in in order to online diagnosis system implementation. In a second step, electrochemical impedance spectroscopy measurements will be performed in nominal operating conditions and in degraded conditions (humidity, pressure and stoichiometry defects). The correlation between model and impedance measurements will be analysed. Finally, the impedancemeter will be implemented on a fuel cell system in order to validate the relevance of laboratory measurements and to evaluate the advantages of the embedded real-time diagnosis hardware for the command-control of fuel cell system.

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Département : Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN) Laboratory : Start Date : 01-09-2015 ECA Code : SL-DRT-15-0621 Contact : Sebastien.rosini@cea.fr

Multi-scale and multi-physic modeling of PEMFC fuel cell degradation mechanisms: upscaling from the micro-scale to the cell level

The Proton Exchange Membrane Fuel Cell (PEMFC) is considered by the automotive industry to offer solutions for a sustainable alternative to thermal propulsion. Even if today the automotive fuel cell car reach the target of 5000 hours durability, improvement on durability and cost are still necessary. In order to meet the reduction in the overall cost of a fuel cell, optimization of performance and sustainability of the membrane electrode assembly (MEA) is so complex that one must be assisted by the multi-physic and multi-scale simulation. The objectives of this thesis is to couple the different degradation mechanisms (catalyst dissolution, Ostawald ripening, carbon support corrosion, membrane and ionomer degradation) and by a bottom-up approach to upscale to a cell model. Models at the micro scale will be used and some specific libraries developed. Moreover, the simulation results will be tested and validated by different experiment tests. The final objective of this thesis is to predict the lifetime of a fuel cell on real operating automotive conditions (start/stop, cold start, peak power, idle mode).

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Département : Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN) Laboratory : Start Date : 01-10-2015 ECA Code : SL-DRT-15-0662 Contact : mathias.gerard@cea.fr
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