Ablation behaviour of electrode materials during high power and high repetition rate laser structuring

Abstract

Laser structuring is introduced to homogenize the wetting of electrodes with liquid electrolyte, to avoid or significantly shorten the process time of warm ageing, and to reduce the lithium-ion diffusion overpotential that occurs during highperformance operation or when thick-film electrodes are applied. For the integration of the laser structuring process into the cell production line, the process speed must be adapted to the electrode coating speed. Various strategies, including increasing the repetition rate and laser power, beam shaping, where the Gaussian beam is formed into a rectangular intensity profile (1D top-hat), and multibeam processing by beam splitting, are pursued here. In the presented study, a laser system providing an average pulse duration of 600 fs, repetition rates in the MHz range, and a maximum power of 300 W, was applied. The ablation results are compared to those of a ps laser system that operates at lower repetition rates. The ablation depth and width as well as the appearance of the structures depending on the applied maximum energy density, repetition rate, and structuring speed, were evaluated, while the pulse overlap was kept constant. It was shown that the use of very high repetition rates leads to a decrease in ablation depth as well as a widening of the manufactured grooves, as the developing of material vapor plasma and ejected particles modify the absorption of subsequent laser pulses. A maximal scanning speed of 1.7 m/s could be achieved for the laser structuring applying a Gaussian beam.