# Investigation of Laser Cutting Width of LiCoO\({}_{2}\) Coated Aluminum for Lithium-Ion Batteries
## 3 Result and Discussion
The material removal rates, when the laser scanning speed is 500 mm/s, 1000 mm/s, 1500 mm/s, and 2000 mm/s, are 32.14 mm\({}^{3}\)/min, 42.86 mm\({}^{3}\)/min, 48.21 mm\({}^{3}\)/min, and 55.71 mm\({}^{3}\)/min, respectively. When the results are examined from the laser ablation point of view, the laser power of 50 W can selectively ablate the active electrode material with the material removal rate of 32.14-55.71 mm\({}^{3}\)/min. The kerf width, depending on the laser scanning speed, is shown in Figure 5a. Figure 5b shows the variation of the kerf width depending on the volume energy. It is noted that the cathode is fully separated with the laser speed of 5 m/s and laser power of 150 W. As the scanning speed becomes faster, the kerf width decreases. When the laser power is greater than 100 W, the kerf width is observed under all laser scanning speeds applied in this study. It is obvious that no kerf width is observed with the laser power of 50 W since there is no melting and no ablation. With the laser power of 100 W, kerf width is observable when the laser scanning speed is less than 3000 mm/s. Therefore, the observation from Figures 4 and 5 lead to the conclusion that the threshold volume energy to fully penetrate the 50 \(\mathrm{\SIUnitSymbolMicro m}\)-thick current collector is between 9.62752 \(\times\) 10\({}^{10}\)-8.02293 \(\times\) 10\({}^{10}\) J/m\({}^{3}\). Figure 4: (a) Melting width VS. Scanning speed; (b) Volume energy. Figure 5: (a) Kerf width VS. Scanning speed; (b) Volume energy. All widths defined in this study are compared together with the fixed laser power, as shown in Figure 6. SEM images after laser cutting is shown in Figures 7-12. Although all widths decrease as the scanning speed increases, as shown in Figure 6a-c, the change rate is different. The changing rates of the top and melting width are greater than that of the kerf width. This means that the material removal rate of the active electrode material is greater than that of the current collector. From the observation of the changing rates, we can presume that the absorbed laser energy is transferred more rapidly in the region of the active electrode material than that of current collector. This can be explained by examining the material properties. The heat conductivity and thermal diffusivity of the LiCoO\({}_{2}\) is less than those of aluminum. However, the absorption coefficient of LiCoO\({}_{2}\) is 2.5 times greater than that of aluminum [2; 11]. The absorption coefficient of LiCoO\({}_{2}\) and aluminum is 0.17 and 0.07, respectively. The more laser energy is absorbed, the greater material removal is observed. Figure 7 shows this phenomenon more clearly. Figure 6: Width variation VS. Volume energy when laser power (**a**) 250 W; (**b**) 200 W; (**c**) 150 W; (**d**) 100 W; and, (**e**) 50 W.  
Figure 8: One-dimensional semi-infinite conduction model. Figure 1:0 Clearance width by laser power. Figure 1:1 Scanning Electron Microscope (SEM) image with a laser power of 250 W.  
Clearance width was observed previously by [PERSON] et al. [10]. The clearance width (\(w_{c}\)) can be derived from the measured top and kerf widths as follows  
Figure 1:2  
where \(W_{top}\) is the top width and \(W_{kerf}\) is the kerf width. The calculated clearance width is shown in Figure 1:3 All clearance width is less than 20 \(\upmu\)m. However, the clearance width interestingly exceeds 20 \(\upmu\)m when the laser power is 200 W. The clearance width is very closely related to the  
Figure 1:4 Result of one-dimensional semi-infinite conduction model. Figure 1:5 SEM image with a laser power of 150 W.  
Figure 1:6 SEM image with a laser power of 200 W.  
above-mentioned material properties. To explain the formation of the clearance width with the above-mentioned material properties, a simplified transient one-dimensional semi-infinite conduction model can be introduced and shown in Figure 1:7  
To see the effect of material properties on the clearance width, this model ignores the liquid and vapor phases.