Electrode cutting is a significant process step in the production of lithium ion batteries. Different cutting technologies exist to singularize electrode sheets out of electrode coils e.g. mechanical and laser cutting.
The laser cutting process combines the conventional notching of the current collector and cutting out electrode sheets. This process provides a high cutting flexibility regarding electrodes with different materials and properties. Furthermore, it is a non-contact and high flexible production step with low maintenance.
However, this innovative process also includes new challenges in view of producing high quality electrode sheets without any cutting defects in combination with high production speed. We had been investigating this technology using a modulated continuous-wave laser for singulation of cathode electrodes based on lithium iron phosphate (LFP).
It appeared in the study that LFP is more prone to cause cutting defects like welding beads and frayed-like edges along the edges of the laser cut electrodes compared to electrodes with lithium nickel cobalt manganese oxide (NCM). The use of inappropriate process parameters can massively impact the electrode quality and hence the quality of the final assembled cell. These artefacts may cause damage to the separator after cell assembly and therefore can lead to short-circuits.
The defect patterns had been systematically investigated by varying the laser parameters such as cutting speed, frequency, maximum and average power.
The parameter study shows that laser cutting parameters need to be optimized to each electrode material and properties. High heat input is needed in order to reach full sublimation of LFP electrode materials. Furthermore, high pulse frequency is necessary with the aim of high heat input into the electrode in short time to reduce the heat affected zone.
However, due to limited frequency range low cutting speed is required when using modulated continuous-wave laser for LFP electrode cutting. Our results show that process defects increase at high cutting speeds beyond 4.7 m min-1. By reducing the process speed at higher laser frequency, welding beads and frayed-like edges could be completely eliminated.
Compared to values used in this study, cutting speed must be further increased with respect to potential industrial applications.