Solid state physics, chemistry and nanosciences - Ultra-divided matter, Physical sciences for materials

Beyong lithium microbatteries: new materials for Li-free systems

New families of miniaturized stand-alone and wireless devices are emerging, embarking their own energy-harvesting (photovoltaic, piezoelectric, thermoelectric) and energy storage (microbattery) systems. Lithium all-solid-state microbatteries are performant electrochemical systems. Nevertheless, their operation voltage is quite high for these specific applications which require quite low voltage (ca. 1V) to achieve improved energy recovery yields. This implies to consider new all-solid-state electrochemical cells free of lithium and potentially less reactive towards humidity (convenient for implantables sytems). The aim of this PhD thesis will be to prepare and evaluate new couples of electrode materials able to fullfill these requirements and compatibles with an integration in all-solid-state microbatteries.'Simple' systems based on a metallic anode and a intercalation compound of same metal ions (mono or divalent) will be studied at first. The study will deal with both powder and thin film materials (PVD). A wide panel of characterization techniques will be used to study these materials and all-solid-state cells including them: ICP, RBS, EPMA, XPS, Auger spectroscopy for determination of the chemical composition; XRD, Raman and Mössbauer spectroscopies,HRTEM to determine the structure; SEM to study the morphology and electrochemical methods (EIS, Galvanostatic cycling, cyclic voltammetry).

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Département : Département des Technologies des NanoMatériaux (LITEN) Laboratory : Laboratoire Composants micro stockage de l'Energie Start Date : 01-10-2013 ECA Code : SL-DRT-13-0689 Contact : frederic.lecras@cea.fr

Thermo-mechanicam modelling of the hydride breathing for a safe and efficient design of hydrogen solid state storage tanks

The thesis concerns the hydrogen storage through hydride materials. The team "Hydrogen Storage" in the laboratory of hydrogen technologies is responsible for developing this type of technology called solid storage, which has the advantage over the other two common storage route (as compressed gas or liquid form) to be more secure and compact. The hydride material is in the form of a dry granular medium. Hydrides that work well in a reversible manner are currently intermetallic materials, with a grain size of a few microns to several hundred microns. The generic phenomenon of hydride breathing (swelling/shrinking during the absorption/desorption of hydrogen) is a known phenomenon, but only empirically for the moment. Yet it is important to control it for two reasons: the efficiency of the heat exchanger in which the hydride is contained (as the hydriding/déhydruration phenomenon is exo/endothermic) and the mechanical integrity of the container. This topic closely implies the field of mechanics of granular media with an aspect that has been very little studied until now. The fundamental issue is to answer the question: how does a granular material behave knowing that each grain can see its volume change by 20% to 30% ? The main objective is to predict the level of load created on the walls of the container. The thesis aims firstly to better characterize the mechanical behaviour of a material during hydride cycles of absorption-desorption of hydrogen. For this, an experimental apparatus has just been developed in the laboratory that permits a mechanical characterization under tri-axial of revolution state of stress of the hydride under hydrogen with strain measurement by optical method. The bench is operational, but has not provided results yet. In a second time, the work consists in developing a predictive model of the mechanical behaviour of the hydride (or even a thermomechanical model, because coupling to the thermal effect is expected). The first method is to use the discrete element simulation that can take into account the physics of the phenomenon better, but we will also try to develop a continuum model type, more suitable for "engineer" design of real tanks, on the basis of existing models developed in the field of compaction of dry granular media (eg Drucker Prager Cap Model). It is also desirable to look at analytical models such as silo models (Jensen).

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Département : Département des Technologies Biomasse et Hydrogène (LITEN) Laboratory : Laboratoire des Technologies de l'Hydrogène Start Date : 01-09-2013 ECA Code : SL-DRT-13-0942 Contact : olivier.gillia@cea.fr

Synthesis and functionalization of 1D nanomaterials (metallic nanowires fabricated by solution synthesis and/or electrospinning). Fabrication of flexible transparent electrodes with low temperature printing techniques and integration into functional devices.

The transparent conductive layers currently used for photoelectric devices are essentially based on TCO (Transparent Conductive Oxides). These materials are made of indium, which is an expensive and poorly abundant metal, moreover ITO has no flexibility properties. For technical and economic reasons the development of new electrodes is the subject of considerable research. Some alternatives appear relevant today, including the use of conductive materials of nanometric size. For example, nanomaterials such as metallic nanowires, nanoparticles of zinc oxide or carbon nanotubes can be used for this purpose and the first results in this direction portend excellent development prospects. The metal nanowires appear particularly promising and will be the focus of this thesis. The study will address the entire process, from the synthesis of nanowires with different techniques up to their integration into functional materials.

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Département : Département des Technologies des NanoMatériaux (LITEN) Laboratory : Laboratoire Composants Récupération de l'Energie Start Date : 01-10-2013 ECA Code : SL-DRT-13-1003 Contact : jean-pierre.simonato@cea.fr