Study and optimization of the solid-electrolyte interphase on silicon anodes for lithium-ion batteries

This thesis contains a concise overview of the research in the framework of a PhD study in the field of Chemistry carried out in three and a half years, between October 2013 and February 2017. The research is situated in the field of lithium-ion batteries and the general goal is to study and improve the solid electrolyte interphase on silicon-based anode materials. Such study and improvement are crucial for introducing the silicon-based anode materials in commercial lithium-ion batteries. This introduction would drastically improve the energy density of lithium-ion batteries, opening the door to major market breakthrough of electrical vehicles. The widely used lithium-ion battery has improved continuously since its commercial introduction in the ‘90s by Sony. However, these improvements were mainly focussed on novel cathode materials and an improved battery management. The most-used anode today is graphite, a material that was already included in the first Sony lithium-ion battery. The capacity of silicon is almost 10 times higher than graphite, making them one of the most investigated future anode material. Such high capacity is however accompanied by large volume expansions, leading to fractures and capacity fading. By using nano-silicon, this problem was resolved, but the most crucial issue for silicon anodes is not: the solid electrolyte interphase. The solid electrolyte interphase forms because lithium insertion into the anode occurs at potentials below the electrolyte reduction potential. The electrolyte decomposes and precipitates at the surface of the anode, forming a nanoscopic layer. This layer protects the electrolyte from the extremely low potentials at the anode. Due to the large volume changes during cycling, this protection layer will break and more electrolyte is decomposed. During this decomposition, lithium-ions are immobilized in this solid electrolyte interphase, and the capacity fades. The main goal of this work is to identify crucial parameters and mechanism during the formation of the solid electrolyte interphase, and exploiting these findings to improve the cycling performance of silicon-based anode materials. In the first part of the thesis, an introduction is given on batteries, silicon-based anode materials and the solid electrolyte interphase. The next three chapters contain three papers (of which two unpublished) which present the study of the electrolyte behaviour prior to cycling on the anode in confined spaces (paper I), the investigation focussing on the mechanical aspects of the solid electrolyte interphase (paper II) and the results of adding a polymer forming additive to the electrolyte which improves the solid electrolyte interphase and leads to lithium-ion battery testing that outperforms current state-of-the-art electrolytes. (paper III)

Publication year:2017

Keywords:lithium-ion battery, lithium, silicon, anode, solid electrolyte interphase

Accessibility:Closed