Surface roughness and chemistry of battery foil, key to better battery

During battery manufacturing, thin metallic foils are coated with a slurry that contain binders, conductive material and the active material. The role of the foil is to both mechanically act as a substrate for the slurry and as a conductor of the electricity to the outside of the battery. The foil does not add to the capacity of the battery which is why it is made as thin as possible, about 12 - 18 micrometre is common. This put fairly high demands on the mechanical properties of the foil and the interactions between slurry and foil.

By increasing the surface roughness the foil can increase the surface area without increasing the size of the foil. This has potential to both increase the adhesion of the slurry to the foil and to reduce the contact resistance in the interface. This could be achieved in an environentally friendly manner by laser techniques or during rolling by utilizing patterned rollers.

The adhesion of the slurry to the foil is a challenge for many batteries, especially newer more environmentally and worker friendly chemistries. Atmospheric plasma is a well tested technique that improve wettability and adhesion, in for example adhesive bonding. It also has promising potential to improve the wettability and adhesion of the slurry to surface activated battery foils.

Some distinctive results from the project are that surface structuring with laser can provide improved surface energy and can affect the mechanical properties of the aluminum foil. Surface activation with atmospheric plasma increased surface energy and showed little impact on mechanical properties. The wettability was also increased with atmospheric plasma even when the treatment was carried out directly on the foil without removing the roller oil available from the production of the foil. The surface activation also showed that different functional groups were formed, which can have positive effects on the function of the battery. Finally, initial impedance measurements on test cells with water-based LFP electrodes also showed promising results with better contact between battery foil and electrode material, i.e. showing potential to improve battery function. This result needs to be verified in a larger study.

With the knowledge we have built up in the field of laser surface structuring, atmospheric plasma surface activation, and the impact of roller oil, we intend to continue the development in the field and investigate how the surface properties affect battery performance. Additional projects are needed to enable larger-scale testing and to be able to proceed with scale-up at both battery foil and battery manufacturers.