In the IAD (Innovative Applications of Printing Technologies) research group at the HdM (Hochschule der Medien – Stuttgart Media University), the focus of the project research is on the thin, flexible printed Li-ion foil batteries that will be used to power the BEWELL skin patch. In addition to researching the printability of the electrochemically active materials, a comprehensive benchmarking study of substrates was carried out. The bendability of the battery is an important aspect, while at the same time sufficient barrier properties must be ensured. Ten substrate materials, mono films and composite films, were compared in terms of their mechanical, physical and surface properties. Modulus of elasticity, flexural rigidity, surface free energy, barrier properties (water vapour transmission rate WVTR), processability, dimensional stability and printability were determined. It turned out that a PET/Al/PET film with a total thickness of approx. 31µm had the best properties. Apart from the difficult handling in sheet-to-sheet screen printing presses (curling), the thicker PET films are advantageous there. In a final roll-to-roll process, however, the curling problem of the films does not play a role. The results (see diagrams below for examples) were presented at the IARIGAI (www.iarigai.org ) conference in Athens (at the University of West Attica) in September 2021. The paper was published at http://jpmtr.org/Advances_Vol_472021_online.pdf.
The contacting of the printed foil batteries was investigated and a riveting technique proved to be advantageous, see figures below.