## 4 Result and Discussion
Moreover, the difference between the top width and melting width is narrower than the difference between the melting width and kerf width. With a laser scanning speed of 2500 mm/s to 3500 mm/s, partial penetration of the current collector is observed. This may have occurred due to sporadic evaporation as illustrated in Figure 8. Thus, partial penetration occurs at the point where the evaporation occurs. On the other hand, more frequent evaporation occurrence may lead to full penetration. The physical mechanism of partial penetration was explained by [PERSON] et al. [27]. The forces caused by surface tension and recoil pressure are in a state of equilibrium and maintain a metastable state. When the force caused by surface tension increases, it leads to the formation of a connecting bridge as shown in Figure 8. On the other hand, increasing force caused by the recoil pressure results in full penetration. With a scanning speed of 4000 mm/s to 5000 mm/s, partial melting of the current collector is observed. The given laser parameters provide enough energy to remove the active electrode, but not enough energy to fully penetrate the current collector. Figure 4: Comparison of (**a**) Top width; (**b**) Melting width; (**c**) Kerf width. Figure 5: Variation of widths depending on laser power: (**a**) 250 W, (**b**) 200 W, (**c**) 150 W, (**d**) 100 W, (**e**) 50 W.  
Figure 6: Category of five physical phenomena: (**a**) full penetration with a wider top width of the electrode; (**b**) the partial penetration of current collector; (**c**) the partial melting of the current collector; (**d**) full ablation of active electrode material; (**e**) partial ablation of active electrode material. SEM images with a laser power of 200 W are shown in Figure 9. This also shows three types of physical phenomena such as full penetration of the electrode (laser scanning speed of 500 mm/s to 1500 mm/s), partial penetration of the current collector (laser scanning speed of 2000 mm/s to 2500 mm/s), and partial melting of the current collector (laser scanning speed of 3000 mm/s to 5000 mm/s). Under this laser power, a wider connecting bridge width is observed compared to the case of 250 W laser power. The full penetration and partial penetration of the current collector occur due to a combination of multiphysical phenomena such as heat conduction, heat convection, evaporation, melting, and re-solidification. On the contrary, the full and partial ablation of the active electrode material occurs with relatively simple physical phenomena such as heat conduction and the sublimation of graphite. Figure 8: Evaporation points for (**a**) partial penetration and (**b**) full penetration. Figure 7: SEM images with a laser power of 250 W.  
According to the analysis of the cutting efficiency discussed above, the cutting efficiency with appropriate material properties [15] for the case of full penetration is shown in Figure 10. The cutting efficiency varies from 14.6% to 37.7%. It is interesting that the cutting efficiency increases as the laser scanning speed increases. This is because losses due to thermal conduction make up a smaller portion of the absorbed energy [28]. Therefore, a higher laser cutting speed providing full penetration leads to higher cutting efficiency and productivity. SEM images with a laser power of 150 W are shown in Figure 8.0 In this figure, full penetration of the electrode and full ablation of the active electrode material are observed. Moreover, SEM images with a laser power of 100 W, as shown in Figure 12, show only one type of physical phenomenon--the full ablation of the active electrode material.