Abstract :
[en] The PhD was focused on the development of metal oxides thin films using sol-gel process, for various applications. It is part of the overall context of the European EnSO (Energy for Smart Objects) project, funded by the Electronic Components and Systems for European Leadership Joint Undertaking (ECSEL-JTI), in collaboration with the European Union's H2020 Framework Programme (H2020/2014-2020) and national authorities. The project aimed at developing autonomous micro energy sources, including both an energy harvesting system and a storage system. As the ULiège NCE laboratory was involved in the development of both parts, and following a general reorientation of the project at mid-term, the candidate was led to work on two different types of materials. This PhD thesis is thus presented in two distinct parts.
The first part concerns the optimisation of a process for the growth of zinc oxide nanowires (ZnO NWs) for piezoelectric nanogenerator application. The objective was to develop a process for the synthesis of NWs on a substrate, with a growth rate compatible for industrial scale-up (minimum 20 nm min-1). A combined process including (i) the deposition of a seed layer made of ZnO crystallites followed by (ii) ZnO NW growth using wet chemistry was developed at the NCE laboratory. The study of the different steps of the process, as well as the growth kinetics of the NWs, made it possible to optimise the conditions of deposition and to obtain a growth speed compatible with industrial scale (70 nm min-1). By combining the results with those obtained by other researchers in the project, it was possible to obtain materials that can be used for the manufacture of piezoelectric nanogenerators, as shown by the characterisations after assembly, in collaboration with the Greman laboratory (Tours).
The NWs were also characterised as photocatalysts for the potential decomposition of pollutants in water, thus showing the diversity of possible applications.
The second part focuses on the optimisation of porous layers for positive electrodes of Li-metal batteries. Optimisation was based on the use of Li7La3Zr2O12 (LLZO), an ionic conductor synthesised by sol-gel process, as nanostructured solid electrolyte within the electrode. The final objective of the project, carried out mainly in collaboration with Prayon s.a. and CEA-Leti (Grenoble), was to produce solid-state Li-metal/LCO microbatteries. The aim of the thesis, which is based on the work of another researcher from the NCE laboratory, was to improve the ionic conductivity of the positive electrode layers by filling their porosity with the nanostructured LLZO. Hybrid LCO-LLZO layers preserving the electrochemical properties of the active electrode material were prepared and the characterisations carried out by adding a liquid electrolyte showed that the LCO does not undergo any alteration in the presence of LLZO. Finally, preliminary encouraging results were obtained when replacing the liquid electrolyte with the gel polymer electrolyte (GPE) developed at NCE: the addition of LLZO to the LCO electrode resulted in a microbattery that is stable when cycling at 1C.
