Département Thermique Biomasse et Hydrogène (LITEN)
Thanks to a high efficiency, high temperature steam electrolysis has received an increasing interest in recent years. An originality of the technology is that it offers the possibility to coelectrolyze steam and carbon dioxide, thus valorizing CO2 into the production of a syngas composed of H2 and CO. However, significant degradation rates are still reported in electrolysis and coelectrolysis constituting a major limitation to the industrial deployment of this technology. Underlying mechanisms inducing the degradation phenomena are associated to local entangled processes happening within the electrodes. The combined effect of these elementary mechanisms on the degradation rates is not well understood and needs to be unraveled. The proposed PhD thesis will address this issue by using a coupled experimental and modelling multi-scale method. Thanks to this fundamental approach, technical solutions in terms of strategy of operation and/or cell architectures could be proposed.
Département des Technologies des NanoMatériaux (LITEN)
Laboratoire de Nanocaractérisation et Nanosécurité
We aim at developing a state-of-the-art method for characterization of the solid electrolyte interphase (SEI) on silicon electrodes and lithium life cycle. This SEI is the result of electrolyte reduction and degradation at the electrode surface, and is one of the main causes of performance loss and durability of Li-ion battery systems. Surface analysis methods such as X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) are particularly well-suited for such studies. In order to go even further, we also consider using isotopic labelling and benefit of the ToF-SIMS ability to separate elements and molecular fragments by their mass. There are still few studies described in literature. Cross-analysis protocols involving ToF-SIMS and XPS, and maybe also Auger spectroscopy, will be developed. This approach will allow a better description of the SEI structure developing on (or in) electrode materials during electrochemical cycling. This work will rely on the development of studies carried out in CEA Grenoble, in relation with 1) the prélithiation of silicon electrodes, which is a way to preempt the first irreversibility cycle and 2) the formation, which is the way to optimize the SEI before ageing. Prior and in parallel to these case studies, model cases such as thin silicon layers used in micro-batteries, will be considered in order to optimize the methodology. This work will take place at LITEN, in CEA Grenoble. Characterizations will be carried out at the Nanocharacterization Center at Minatec Campus, while battery cells and electrochemical analysis will be done in the Electricity and Hydrogen for Transport department. Complementary analysis will be considered as well, such as scanning or transmission electronic microscopy (SEM/TEM), nuclear magnetic resonance (NMR) or atomic force microscopy (AFM). By providing state-of-the-art materials, industrial partners will also be involved in this research project. The PhD student will have an excellent working environment with privileged access to various characterization techniques on state-of-the-art instruments. A strong interaction with different research teams is essential, so that communication and openness will be important assets for the success of this thesis work.