Targeting new ways for large-scale, high-speed surface functionalization using direct laser interference patterning in a roll-to-roll process

Key words: 
• DLIP /
• lithium-ion battery /
• surface texturing /
• copper /
• aluminum

Abstract: 

Direct Laser Interference Patterning (DLIP) is used to texture current collector foils in a roll-to-roll process using a high-power picosecond pulsed laser system operating at either fundamental wavelength of 1064 nm or 2nd harmonic of 532 nm. The raw beam having a diameter of 3 mm @ 1/e² is shaped into an elongated top-hat intensity profile using a diffractive so-called FBS®-L element and cylindrical telescopes. The shaped beam is split into its diffraction orders, where the two first orders are parallelized and guided into a galvanometer scanner. The deflected beams inside the scan head are recombined with an F-theta objective on the working position generating the interference pattern. The DLIP spot has a line-like interference pattern with about 15 µm spatial period. Laser fluences of up to 8 J cm⁻² were achieved using a maximum pulse energy of 0.6 mJ. Furthermore, an in-house built roll-to-roll machine was developed. Using this setup, aluminum and copper foil of 20 µm and 9 µm thickness, respectively, could be processed. Subsequently to current collector structuring coating of composite electrode material took place. In case of lithium nickel manganese cobalt oxide (NMC 622) cathode deposited onto textured aluminum current collector, an increased specific discharge capacity could be achieved at a C-rate of 1 ºC. For the silicon/graphite anode material deposited onto textured copper current collector, an improved rate capability at all C-rates between C/10 and 5 ºC was achieved. The rate capability was increased up to 100% compared to reference material. At C-rates between C/2 and 2 ºC, the specific discharge capacity was increased to 200 mAh g⁻¹, while the reference electrodes with untextured current collector foils provided a specific discharge capacity of 100 mAh g⁻¹, showing the potential of the DLIP technology for cost-effective production of battery cells with increased cycle lifetime.