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Gilles Brenet

Multi-scale simulations of kinetics in energy materials: Solar silicon and intercalation compounds for Li-ion batteries

Published on 16 May 2016


Thesis presented May 10, 2016

Abstract:
Energy production and storage is a big challenge in our society. The properties of some materials are mainly due to the defects therein. To improve the materials we use, it is necessary to be able to model them. This work focuses on the study of various defects in both materials, silicon and lithium graphite. Through the multi-scale simulation, we model the defects and their kinetics in order to predict their formation but also aging.
The first part focuses on the various methods we used. These methods are divided into three categories, each providing access to a simulation scale. By starting on electronic models with textit{ab initio} simulations, we were able to simulate defects behavior with atomistic simulations using stochastic algorithm. These results then led to macroscopic models, in order to compare our simulations with the experimental results. The second part develops our analysis of point defects in silicon: carbon, oxygen, vacancies and interstitials. These defects gather and form complexes in the irradiated silicon. By analyzing the behavior of these complexes at the atomic scale, we could build a model to simulate the kinetics of multiple defects, and the reaction chain, over several decades. Thus, it is possible to determine the conditions for greater control of the formation and aging of various complexes.
The last part presents the analysis of lithium graphite. This component of lithium-ion batteries is made of graphite in which lithium atoms intercalate during charging. The kinetics of the charging predicts the grouping of lithium atoms in islands, which move during charging. The lithium atoms diffusion from the edges of the electrode towards the center of the graphite is also analyzed.

Keywords:
Battery, Monte Carlo, Diffusion, Silicon

On-line thesis.