Articles techniques et présentations

Lithium ion battery electrodes are porous composite film made up of two or three different types of solid material. Typically using the fabrication of the electrode, the solid powders (active material, binder and in most cases a conductive active) are dispersed in a solvent like NMP and made it into a slurry and cast of a metal foil. During the drying of this electrode, the solvent is evaporated to create the porous composite electrode. The drying process involves a complex interplay of different competing phenomena. The drying process to a large scale determines the microstructure of the electrode which in turn affects the battery performance.

In this work an attempt is made to model the drying process with the continuum approach. There are primarily two stages in the drying process. In the first stage the solvent evaporates and the film thickness shrinks and porosity is created. In this work the slurry coated on the foil is treated as a 1D geometry and changes along the thickness of the drying film is modeled. The film is dried at a constant temperature which is below the boiling point of the solvent. A coupled heat transfer, mass and momentum transport for solid, liquid are solved in this stage along with the reduction in thickness. Moving mesh feature of COMSOL Multiphysics® 5.4 is used to track the reduction in the thickness of the film. During the second stage of the drying, change in thickness reduces and the evaporation continues from within the pores and two phase transport (liquid and vapor) is modeled. The shrunken porous electrode geometry from the phase 1 is used as the initial geometry for phase 2 and Darcy’s law for two phase transport along with heat transfer process is modeled. Sedimentation and binder migration are ignored during this phase in this model. Thickness and porosity predicted from phase 1 of the model is used as the geometric parameter for modeling phase 2 of the evaporation process

The results from the model will be validated through controlled experiments for a set of materials used in lithium-ion battery. The drying kinetics during both the phases, thickness and weight loss and porosity predicted from the model will be experimentally verified.