In Li-ion cells, several processes lead to reduced battery performance, e.g., one-dimensional Li-ion diffusion, the power loss due to diffusion overstress at high charge/discharge rates, ohmic resistance, or mechanical stresses in the active material due to Li-ion insertion/extraction processes. Three-dimensional (3D) battery architectures enable high surface energy densities as a result of the increased surface area. According to the state of the art, these surface structures in thin film batteries are introduced into the battery system via current dissipation patterning. However, these approaches are not transferable to standard and thick film electrodes.
In this work, copper and aluminum current conductor foils are structured by means of Direct Laser Interference Patterning (DLIP) to improve the layer adhesion for high-energy and thick-film electrodes. For this purpose, basic process parameters of DLIP structuring in combination with a UKP high-power laser source were investigated and the conductor foils were evaluated with respect to their performance characteristics. Furthermore, a upscaling concept for large-area surface structuring was developed. Therefore the process and system technology (lasers, optics, scanners) was adapted and implemented and in a roll-to-roll process.
A 12 ps laser system with 1064 nm wavelength was used for processing. By applying beam shaping components, an elongated spot with a top-hat energy distribution was used for patterning with a galvano-scan system with a focal length of f = 191 mm. With this lens, a spatial period of interference maxima of 15 µm was created in the elongated DLIP spot. The laser spot was guided directly on the current conductor foil, which was moved via an in-house developed roll-to-roll system. A structure depth of approx. 2 µm was ablated with a processing speed of the scan system of up to 5 m/s.