Résumé
For many years, humans have produced energy from fossil fuels such as oil, coal and natural gas. Combustion of these fuels produces a large amount of greenhouse gases that contribute to global warming. Other, more environmentally friendly sources of energy exist, such as sunlight and wind. However, the production of energy from these sources is intermittent and their development requires devices that allow significant storage during the production in order to release it at off-peak production times. The performance of the current lithium-ion battery systems does not allow optimum energy storage.Lithium-oxygen (Li-O2) batteries are one of the most promising energy storage and conversion technologies due to their ultra-high energy density (almost ten times higher than current Li-ion systems). Despite these promising characteristics, high efficiency Li-O2 batteries development is still challenging. Some of these challenges include low round-trip efficiency, poor rechargeability, and high polarisation. One way to overcome these challenges is to focus on the cathode. This electrode is the site of the electrochemical reactions during cycles; therefore, it is essential to optimise it.
The objective of this work is to design cathodes for efficient lithium oxygen batteries. Two strategies have been used, the first consists of tuning the composition of the cathode in order to modulate the reaction kinetics and the second of creating a hierarchical structure in order to increase the diffusion within the electrode.
First, we designed a cathode structure with hierarchical micro/meso/macro porosity based on Murray’s law. The hierarchically porous cathode is formed using a bottom-up, layer-by-layer evaporation-driven self-assembly process. This specific gradient porous cathode was tested in a non-aqueous lithium-oxygen battery and exhibited a higher discharge capacity compared with a slurry-based carbon powder cathode demonstrating the positive impact of this structure on the performances.
Then, a second study focused on the use of 3d transition metals as cathode material, and the relation between the electrochemical properties of the material on the performance of the battery was established.
Carbon being a source of degradation in Li-O2 batteries, AB2O4 nanowire arrays carbon-free cathodes were synthetised and allowed good Li2O2 formation decomposition, resulting in improved performances.
| la date de réponse | 30 août 2021 |
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| langue originale | Anglais |
| L'institution diplômante |
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| Sponsors | Université de Namur |
| Superviseur | BAO LIAN SU (Promoteur), Alexandru Vlad (Jury), Yann Garcia (Jury), Luca Fusaro (Jury), Alain KRIEF (Jury) & Guillaume Berionni (Jury) |