## 4 Result and Discussion  
Since various physical phenomena such as melting, molten pool formation, sublimation, evaporation, and re-solidification exist together, the above-mentioned widths were defined and used to explain the laser cutting process of electrodes for lithium-ion batteries. The top width indicates that heat conduction and sublimation play a major role in removing the active electrode material or graphite due to sublimation. Hence, laser energy is absorbed on the top surface and transferred by conduction from the top surface to the body of graphite in the radial direction. When the body of the graphite reaches the sublimation temperature, the graphite is sublimated and the mass is removed. These heat transfer and material removal mechanisms are observable by investigating the top width. The physical phenomena such as melting, molten poolformation, and re-solidification are related to the melting width. From the kerf width, material removal caused by evaporation can be clearly observed. Figure 4 shows the top width, melting width, and kerf width. From the figures, the \(x\)-axis is depicted with two variables--laser scanning speed (Left) and line energy (Right). The definition of line energy \(\left(=\frac{P_{0}}{\pi w^{2}\cdot p}\right)\) can be referred to [2; 11]. Figure 4a shows that increasing the scanning speed decreases the top width. With a laser power of 50 W, no top width is shown when the scanning speed is faster than 2000 mm/s. The top width is always observed when the laser power is greater than 50 W. In addition, increasing line energy increases top width. However, no active electrode material is removed when the line energy is less than 4.814 \(\times\) 10\({}^{10}\) J/m\({}^{3}\). Therefore, it is 4.814 \(\times\) 10\({}^{10}\) J/m\({}^{3}\) that is the line energy required to remove an active electrode material. Figure 4b shows the melting width. Increasing scanning speed decreases the melting width. No melting width is formed when the laser power is less than 150 W. When the scanning speed is faster than 2000 mm/s, the melting width is not formed with a laser power of 150 W. A melting width is always observable when the laser power is greater than 150 W. According to the line energy, a line energy greater than 0.963 \(\times\) 10\({}^{10}\) J/m\({}^{3}\) is required to form the melting width. The comparison of the kerf width is shown in Figure 4c. Increasing the scanning speed decreases the kerf width. No kerf width is observed when the laser power is less than 150 W. To fully penetrate the anode, a scanning speed less than 1500 mm/s is required with a laser power of 150 W. Furthermore, scanning speeds less than 2000 mm/s and 2500 mm/s are required to fully penetrate the anode with laser powers of 200 W and 250 W, respectively. Full penetration can be achieved when the line energy is greater than 3.009 \(\times\) 10\({}^{10}\) J/m\({}^{3}\). Figures 4 and 5 show the variation of widths depending on laser power. SEM images are taken after the cutting is completed using the laser power of 250-50 W. Five types of classification with regard to physical phenomena are introduced and shown in Figure 6: (1) full penetration with wider top width of electrode; (2) partial penetration of current collector; (3) partial melting of current collector; (4) full ablation of active electrode material; and (5) partial ablation of active electrode material. It is interesting that full penetration with a narrower top width of the electrode is hardly observable. Figure 7 shows SEM images with a laser power of 250 W and these show very significant changes in terms of physical phenomena from the full penetration to the partial penetration to the partial melting. With a laser scanning speed of 500 mm/s to 2000 mm/s, full penetration with a wider top width of the electrode is observed. The melting widths are clearly observed and these are relatively wide compared to the widths observed for cathode materials.