Description du sujet de thèse

All-solid-state micro-devices represent a significant advance in the field of miniaturized energy storage devices (Li-ion micro-batteries, micro-supercapacitors or micro-capacitors). Unlike "traditional" devices, they eliminate liquid electrolytes in favor of solid materials, limiting leakage and improving safety, durability and performance. Schematically, the solid electrolyte ensures the conduction of ions between two electrodes of a micro-device. For example, it can be deposited as a photostructurable gel in which an ionic liquid is trapped, or as a thin film of a material with sufficient ionic conductivity, which is the limiting point of current solutions. This design allows for increased energy density, improved chemical stability and thermal resistance, and above all enables the encapsulation of a durable micro storage device. As a result, all-solid-state microdevices offer promising advantages for miniaturized electronics applications, such as implantable medical devices or flexible energy storage systems, i.e. for powering the Internet of Things. Although challenges remain, such as reducing production costs, these advances are attracting growing interest because of their potential to meet the growing need for efficient, compact energy storage.

Contexte de travail

The aim of the thesis is to fabricate a new line of efficient all-solid-state micro-devices based on new MSC and MB solid-state electrolytes for powering sensors (IoT). This thesis is divided into two phases: firstly, the manufacture of solid electrolytes for MSCs, of the ionogel/hydrogel type or ionic liquid deposition by CVD, and secondly, the combinatorial deposition of thin films by co-sputtering for MBs. It will add significant value to the electrode materials technology mastered by the UCCS / IEMN partnership. This project will benefit from the RS2E environment, the NanofuturX+ team, the PEPR battery and the RENATECH+ network. Alongside micro-batteries (MBs), micro-supercapacitors (MSCs) are lesser-known energy storage micro-devices, but very promising because they are very fast (t charge less than 30 seconds), but their technological maturity remains at laboratory scale despite intensive research over more than 20 years. To date, there are no commercial micro-supercapacitors, whereas lithium micro-batteries (using planar technology) are already available from manufacturers. Micro-batteries, like MSCs, consist of two electrodes deposited in thin-film technology, separated by an electrolyte that conducts ions between the two electrodes. Whatever the type of micro-device under consideration, the ionic conductivity of the electrolyte must be as high as possible, especially for MSCs, which are high-power micro-devices. The electrolyte's electrochemical stability window must also be high, and it must be capable of "absorbing" the potential difference between 2 electrodes of an MB, for example, without degrading or decomposing. To date, the most effective electrolytes are liquid electrolytes (aqueous, organic or ionic liquids): these electrolytes have high ionic conductivity, but are liquid and therefore difficult to handle for miniaturized components. One of the main technological obstacles to the industrial development of MSCs or MBs lies in the creation of a SOLID electrolyte with high ionic conductivity. Several approaches can be considered, depending on the type of device under consideration. For MSCs, "gel" electrolytes in which a confining matrix traps a liquid appear to be an attractive solution, but it is necessary to select the most relevant liquids and to have a photostructurable gel to enable the manufacture of miniature MSCs with a surface area of just a few mm2. Hydrogels are aqueous gels (PVA/KOH, PVA/H2SO4) in which a base or acid is circulated to ensure ionic conduction between the two electrodes: these gels degrade rapidly, however, as the water evaporates. Ionogels are solid electrolytes in which an ionic liquid flows through the pores of a solid or flexible gel. The low vapor pressure of ionic liquids prevents evaporation. For MBs, we want to study the properties of thin-film solid electrolytes, whose performance in a "bulk system" based on Li4Al0.33Si0.165Ge0.165P0.33O4 powder has demonstrated exceptional ionic conductivity (10-2 S/cm at RT). To form multi-element thin films, a combinatorial approach to optimizing deposition conditions will be implemented based on the co-sputtering of multiple binary or ternary targets (Li3PO4, Li4SiO4....) in confocal mode. The possibility of using several targets with different chemical compositions will enable us to create gradients of compositions, enabling us to optimize these in a single deposit. Mapping techniques on 10 cm diameter substrates (micro-diffraction, micro-fluorescence, micro-Raman, conductivity, etc.) will then be used to characterize the deposited films at substrate scale. The development and optimization of thin films of solid electrolyte will require a lot of to-ing and fro-ing between synthesis and characterization. The CMNF (Couches Minces et Nanofabrication, hosted by IEMN) and PCA (Plateforme de Caractérisation Avancée, hosted by Institut Chevreul) platforms, accredited by the University of Lille, will be used extensively. The IEMN's new deposition cluster will also be used to develop the combinatorial copulverization approach. The study of electrode material/electrolyte material interfaces is particularly important, but also particularly complex to characterize, and will also be undertaken as part of this project.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.