PhD offer: Correlating 3D electrode microstructure and transport modeling to enhance fast charging

Li-ion batteries are currently the most widely adopted technology for energy storage application, and the forthcoming E-mobility market leads to guide research for higher energy density and electrochemical performance. Li-ion battery is a very complex electrochemical system consisting of an electrolyte surrounding by two porous composite electrodes and two current collectors. The cell electrochemical performance relies solely on the intrinsic material properties as well as on the electrode microstructure, especially the electrode engineering that needs to consider the ionic and electronic percolation. Currently, most research are dedicated to the development of new materials. However, the transport and transfer phenomena occurring within the porous electrode are of utmost important and highly rely on the electrode microstructure. To achieve high electrochemical performance, manufactures are tuning the electrode engineering by increasing the electrode mass loading which directly impacts the percolation network and thus the electrode microstructure. In such case, mass and charge transport limitations will be exacerbated as well as additional issues will be popping up such as the electrode porosity/tortuosity hindering again the conductive pathways. These limitations are all the more restrictive during fast charging or low temperature operation conditions Thus, understanding the relationship between the electrode engineering, the electrode microstructure, and the transport properties is crucial for developing better batteries.

This thesis is then dedicated to understanding the effect from electrode microstructure on the electrochemical performance and aging of Li ion batteries. Several composite electrodes will be specifically designed by tuning the thickness of the electrode and the porosity which will be first link to their electrochemical performance. Then, advanced characterisation techniques at multiple length scale (from nanometre resolution of the micrometre one) will be carried out to collect information about the 3D microstructure of the electrode. Among the techniques to be used, X-ray absorption tomography as well as FIB-SEM will be state-of-the-art to reconstruct the local microstructure of the composite electrode and to collect information to develop specific transport models. Indeed, porous electrode models from Newman group’s has been used in research and industrial fields but they do not consider the microstructure of electrodes. By coupling our experimental approach based on electrochemical performance and 3D electrode microstructure, we will be able to propose alternative resolved models with explicit description of electrode microstructure taking into account the three phases: active material particles, electrolyte and carbon-binder domain.