WEB Microstructural investigation of Al-current collector foils after the compression of electrodes for Li-ion-batteries
Highly compressed electrode foils are used to increase the capacity and volumetric energy density in Li-ion batteries. During the calendering the microstructure of the electrodes undergo tremendous changes. For instance, the volume fraction of pores is reduced while the fraction of binder and active material increases during compaction. The compression process also influences the microstructure of the Al-foil of the cathode current collector and the functional interface to the electrode coating with active materials. Depending on size and morphology of the active material, the particles are pushed into the Al-foil. Due to deformation and embedded particles, the adhesion of the electrode coating, the mechanical stability and the electric conductivity of the electrode is increased. Depending on the design concept and production techniques used, not all areas of the Al-foil are coated and covered with the slurry paste. These uncovered regions partly remain after electrode cutting and are used to connect the current collectors to the battery pins. The Al-foil consists of highly deformed and coated regions, as well as undeformed and uncoated regions at the edges. This leads to the formation of wrinkles in the uncoated areas, which decrease the processability and can lead to unusable electrodes due to structural damages.
We remove the NMC coating to get access to the Al-foil surface and apply different inspection technologies. Confocal laser scanning microscopy (LSM) provide high-resolution surface profiles of the Al-foil surface. It is shown, how the number, depth and morphology of the imprints of the active material particles can be quantified and correlated with the deformation. Additionally, SEM and Focussed Ion Beam (FIB) investigations reveal information about the internal microstructure and changes of grain orientation due to current collector deformation. By combination of these different investigation technologies, it is possibly to quantify the microstructural changes occurring during the calendering process. These changes have a significant influence on the mechanical properties of the electrodes and the performance of the battery cell. Therefore, it is relevant to develop reliable investigation techniques to analyse these microstructural changes to get a deeper knowledge of the battery microstructure and help to improve production technologies.
|Category||Short file description||File description||File Size|
|Extended Abstract||Picture 1||FIB cross section of Li-ion battery - Interface of current collector is influenced by imprint of active material particles||1,018 KB||Download|
|Extended Abstract||Picture 2 - SEM and LSM||comparision of current collector Al-foils before and after calendering. Surface morphologie is investigated with SEM and with Laser Scanning Microscopy||2 MB||Download|