A methodology for evaluating electrode interface quality through contact area analysis of calendering-induced particle indentations

The global shift towards electromobility drives the demand for high-energy-density lithium-ion batteries. Gaining an in-depth knowledge of battery production steps is crucial to meet this demand. Electrodes, a key component in lithium-ion batteries, consist of a multi-material system coated on a metallic current collector foil. Calendering affects mechanical and electrochemical properties by compacting the electrodes and defining the volumetric energy density. The strive for higher energy densities and the associated high compaction rates during calendering lead to an increase in electrode deformations. The coated particles are pressed into the current collector foil during compaction, influencing the electrode's electrical and mechanical properties at the interface. A holistic understanding of particle behavior during compaction is essential for producing high-quality electrodes. In this work, an automated, model-based approach is adapted for the process analysis to determine the calendering-induced particle indentations and the resulting contact area for lithium-ion battery cathodes. The methodology presented in this study enables the quantification of the contact area and the associated calendering-induced microstructural deformations of the current collector foil. A strong correlation was identified between the contact area and the characteristic values for the electrical resistance and adhesion strength at the interface between the coating and the current collector foil. The particle indentations are dependent on the mechanical specification of the current collector foil used, as a softer aluminum foil leads to a larger contact area.