JP7746101B2 - Laser cutting method for metal foil - Google Patents

Description

The present invention relates to a method for laser cutting metal foil.

Laser cutting, which involves irradiating a metal workpiece with laser light, is known as one method for cutting the workpiece. Laser cutting involves irradiating the part of the workpiece to be cut with laser light, melting that part with the energy of the laser light, and cutting the workpiece (see, for example, Non-Patent Document 1).

Patwa, Rahul, et al. "High speed laser cutting of electrodes for advanced batteries." International Congress on Applications of Lasers & Electro Optics. 2010.

When the object to be processed is metal foil, the foil is prone to deformation and tearing, so if the various laser cutting parameters are set in the same way as for thicker metal components, it can be difficult to achieve the required quality.

In addition, when metal foil is used as the positive electrode of a battery, higher quality laser cutting is required.

Therefore, one of the objectives of the present invention is to provide an improved, novel method for laser cutting metal foil, which makes it possible to laser cut metal foil as a processing target that constitutes, for example, the positive electrode of a battery.

The metal foil laser cutting method of the present invention laser-cuts a metal foil, which serves as a processing target, for example, a battery positive electrode, by intermittently irradiating the metal foil with pulses of laser light at a frequency of 10 MHz or less.

In the metal foil laser cutting method, the overlap rate R between the irradiation area of the pulse and the irradiation area of the next pulse is calculated by the following formula (1):
R=L2/L1... (1)
Here, when L1 is defined as the length in the sweep direction of the irradiation region, L2 is defined as the length in the sweep direction of an overlap region between the pulse and the next pulse when the pulse and the next pulse overlap in the sweep direction, 0 when the pulse and the next pulse are in contact with each other in the sweep direction, and −I when the pulse and the next pulse are spaced apart by a distance I (>0) in the sweep direction, the overlap rate R may be −21% or more and 99% or less.

In the metal foil laser cutting method, the irradiation energy of the laser light may be less than 5.0 [J/mm].

In the metal foil laser cutting method, the thickness of the metal foil may be 500 μm or less.

In the metal foil laser cutting method, the metal foil may have areas covered with a coating and areas not covered with a coating.

In the metal foil laser cutting method, the spot diameter of the laser light may be 100 μm or less.

In the metal foil laser cutting method, the spot diameter of the laser light may be 50 μm or less.

In the metal foil laser cutting method, the spot diameter of the laser light may be 28 μm or less.

In the metal foil laser cutting method, the peak output of the laser light may be 150 W or more.

In the metal foil laser cutting method, the metal foil may have a metal layer made of an aluminum-based material.

In the metal foil laser cutting method, the frequency may be 1 MHz or less.

In the metal foil laser cutting method, the peak output of the laser light may be 200 W or more.

In the metal foil laser cutting method, the metal foil may have an active material layer applied to the surface of the metal layer.

In the metal foil laser cutting method, the irradiation energy of the laser light may be 0.03 [J/mm] or more and 0.8 [J/mm] or less.

In the metal foil laser cutting method, the metal foil may have a metal layer made of an aluminum-based material and a ceramic insulating layer made of ceramic and applied to the surface of the metal layer.

In the metal foil laser cutting method, the frequency may be 300 kHz or higher.

In the metal foil laser cutting method, the irradiation energy of the laser light may be 0.05 [J/mm] or more and less than 1.0 [J/mm].

In the metal foil laser cutting method, the overlap rate R between the irradiation area of the pulse and the irradiation area of the next pulse is calculated by the following formula (1):
R=L2/L1... (1)
Here, when L1 is defined as the length in the sweep direction of the irradiation region, L2 is defined as the length in the sweep direction of the overlap region between the pulse and the next pulse when the pulse and the next pulse overlap in the sweep direction, 0 when the pulse and the next pulse are in contact with each other in the sweep direction, and −I when the pulse and the next pulse are spaced apart by a distance I (>0) in the sweep direction, the overlap rate R may be greater than 21%.

In the metal foil laser cutting method, the frequency may be 100 kHz or more, and the irradiation energy of the laser light may be less than 0.4 J/mm.

In the metal foil laser cutting method, the metal foil may have a metal layer made of an aluminum-based material and a polymer insulating layer made of a polymer and applied to the surface of the metal layer.

In the metal foil laser cutting method, the peak output of the laser light is 600 [W] or more and 800 [W] or less, and an overlap rate R between an irradiation area of the pulse and an irradiation area of the next pulse is set to be equal to or less than the following formula (1):
R=L2/L1... (1)
Here, when L1 is defined as the length in the sweep direction of the irradiation region, L2 is defined as the length in the sweep direction of an overlap region between the pulse and the next pulse when the pulse and the next pulse overlap in the sweep direction, 0 when the pulse and the next pulse are in contact with each other in the sweep direction, and −I when the pulse and the next pulse are spaced apart by a distance I (>0) in the sweep direction, the overlap rate R may be 70% or more and 80% or less.

In the metal foil laser cutting method, the peak output of the laser light may be greater than 300 W and the overlap rate may be 40% or greater.

In the metal foil laser cutting method, multiple sweeps may be performed along the same path.

In the metal foil laser cutting method, the multiple sweeps may include two or more sweeps each having different laser light irradiation conditions.

The present invention provides a novel and improved method for laser cutting metal foil, which is capable of laser cutting metal foils that constitute the positive electrodes of batteries.

FIG. 1 is an exemplary schematic configuration diagram of a laser cutting device according to a first embodiment. FIG. 2 is an exemplary schematic cross-sectional view of a metal foil as an example of an object to be processed by the laser cutting device of the embodiment. FIG. 3 is an illustrative and schematic plan view of a metal foil as an example of an object to be processed by the laser cutting device of the embodiment. FIG. 4 is a schematic diagram showing an example of a time waveform of the output of the light source of the laser cutting device according to the embodiment. FIG. 5 is a schematic plan view showing an example of an irradiation area on the surface of an object to be processed of two temporally consecutive pulses of laser light output from the laser cutting device of the embodiment. FIG. 6 is a schematic plan view showing another example of an irradiation range on the surface of the object to be processed of two temporally consecutive pulses of laser light output from the laser cutting device of the embodiment. FIG. 7 is an explanatory diagram showing the definition of the spot diameter in the laser cutting device of the embodiment. FIG. 8 is a photographed side view of an example of a cut edge of a metal foil as a processing object. FIG. 9 is a photographed image in plan view of an example of a cut edge of a metal foil as a processing object. FIG. 10 is a photographed image in plan view of another example of a cut edge of a metal foil as a processing object. FIG. 11 is a graph showing an example of an evaluation result of the height of protrusions in the thickness direction at the cut edge when uncoated aluminum foil is cut by the laser cutting device of the embodiment, relative to the irradiation energy of the laser light and the pulse frequency. FIG. 12 is a graph showing an example of an evaluation result of the pulse overlap rate and the output from the light source with respect to the height of protrusions in the direction along the surface of the cut edge when uncoated aluminum foil is cut by the laser cutting device of the embodiment. FIG. 13 is a graph showing an example of an evaluation result of the width of the discolored area at the cut edge when uncoated aluminum foil is cut by the laser cutting device of the embodiment, as a function of the irradiation energy of the laser light and the pulse frequency. FIG. 14 is a graph showing an example of an evaluation result of the height of protrusions in the thickness direction at the cut edge when an aluminum foil with an active material layer is cut by the laser cutting device of the embodiment, relative to the irradiation energy of the laser light and the pulse frequency. FIG. 15 is a graph showing an example of evaluation results for the pulse overlap rate and the output from the light source with respect to the height of protrusions in the direction along the surface at the cut edge when an aluminum foil with an active material layer is cut by the laser cutting device of the embodiment. FIG. 16 is a graph showing an example of the evaluation results for the width of the discolored area at the cut edge when an aluminum foil with an active material layer is cut using the laser cutting device of the embodiment, versus the irradiation energy of the laser light and the pulse frequency. FIG. 17 is a graph showing an example of the evaluation results for the height of protrusions in the thickness direction at the cut edge when aluminum foil with a ceramic insulation layer is cut by the laser cutting device of the embodiment, versus the irradiation energy of the laser light and the pulse frequency. FIG. 18 is a graph showing an example of the evaluation results for the pulse overlap rate and the output from the light source with respect to the height of protrusions in the direction along the surface at the cut edge when aluminum foil with a ceramic insulation layer is cut by the laser cutting device of the embodiment. FIG. 19 is a graph showing an example of the evaluation results for the pulse overlap rate and the output from the light source with respect to the height of protrusions in the direction along the surface at the cut edge when aluminum foil with a polymer insulation layer is cut by the laser cutting device of the embodiment. FIG. 20 is an exemplary schematic configuration diagram of a laser cutting device according to the second embodiment.

The following describes exemplary embodiments of the present invention. The configurations of the embodiments described below, as well as the actions and results (effects) achieved by these configurations, are merely examples. The present invention can also be realized using configurations other than those disclosed in the following embodiments. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derivative effects) achieved by the configurations.

The embodiments shown below have similar configurations. Therefore, the configurations of each embodiment provide similar actions and effects based on the similar configurations. Furthermore, below, similar configurations will be assigned similar reference numerals, and duplicate explanations may be omitted.

In addition, in each figure, the X direction is represented by arrow X, the Y direction is represented by arrow Y, and the Z direction is represented by arrow Z. The X, Y, and Z directions intersect and are perpendicular to each other. The X and Y directions are directions along the surface Wa (machining surface) of the workpiece W, and the Z direction is the normal direction to the surface Wa. Note that in some figures, the X direction is shown as the sweeping direction SD, but the sweeping direction SD need only intersect with the Z direction and is not limited to the X direction.

[First embodiment]
[Configuration of laser cutting device]
1 is a schematic diagram of a laser cutting device 100 according to the first embodiment. The laser cutting device 100 includes a laser device 110, an optical head 120, an optical fiber 130, and a controller 140.

The laser device 110 is equipped with a laser oscillator as a light source and is configured to output, for example, single-mode laser light with a power of several kW. The wavelength of the laser light output by the laser device 110 is, for example, not less than 800 nm and not more than 1200 nm, but is not limited to this. The laser device 110 can also output a continuous wave laser intermittently at a frequency of, for example, not more than 10 MHz.

The optical fiber 130 optically connects the laser device 110 and the optical head 120, and guides the laser light output from the laser device 110 to the optical head 120. When the laser device 110 outputs a single-mode laser light, the optical fiber 130 is configured to transmit the single-mode laser light. In this case, the ^M2 beam quality of the single-mode laser light is set to 1.2 or less. When the laser device 110 outputs a multimode laser light, the optical fiber 130 is configured to transmit the multimode laser light.

The optical head 120 is an optical device for irradiating the laser light input from the laser device 110 onto the surface Wa of the workpiece W. The optical head 120 has a collimating lens 121, a condensing lens 122, and a DOE 123 (diffractive optical element). The collimating lens 121 and the condensing lens 122 may also be referred to as optical components. The optical head 120 may have optical components other than the collimating lens 121 and the condensing lens 122.

In this embodiment, the optical head 120 is configured to be able to change its position relative to the workpiece W, in order to sweep the laser light L while irradiating it over the surface Wa of the workpiece W. Relative movement between the optical head 120 and the workpiece W can be achieved by moving the optical head 120, moving the workpiece W, or moving both the optical head 120 and the workpiece W.

The collimating lens 121 collimates the input laser light. The collimated laser light becomes parallel light. The condensing lens 122 condenses the parallel laser light and irradiates the workpiece W with it as laser light L (output light). The DOE 123 is positioned between the collimating lens 121 and the condensing lens 122 and shapes the shape of the laser light beam (hereinafter referred to as the beam shape). The DOE 123 has, for example, a configuration in which multiple diffraction gratings with different periods are superimposed. The DOE 123 can shape a beam with a more suitable shape by bending the parallel light in a direction influenced by each diffraction grating or by superimposing the gratings. The DOE 123 can also be called a beam shaper.

With this configuration, the optical head 120 irradiates the surface Wa of the workpiece W with laser light L in the opposite direction to the Z direction. The irradiation direction of the laser light L from the optical head 120 is the opposite direction to the Z direction. The optical head 120 can focus the laser light L so that the beam diameter is, for example, greater than or equal to 10 μm and less than or equal to 100 μm.

The controller 140 can control the operation of the laser device 110 and the operation of a relative movement mechanism (not shown) that moves the optical head 120 and the workpiece W relative to each other so that the laser light L is swept over the surface Wa.

[Processing target]
Fig. 2 is a cross-sectional view of the metal foil 10 as the processing object W, and Fig. 3 is a plan view of the metal foil 10. In this embodiment, the processing object W of the laser cutting device 100 is the metal foil 10 that constitutes the positive electrode of a battery. The thickness of the metal foil 10 is, for example, 500 μm or less, but is not limited to this.

As shown in FIG. 2, the metal foil 10 includes a metal layer 11, an active material layer 12, and an insulating layer 13. The active material layer 12 is a coating formed on both sides of the metal layer 11 in the thickness direction, i.e., on both the front and back surfaces of the metal layer 11. The insulating layer 13 is a coating formed on both sides of the metal layer 11 in the thickness direction, i.e., on both the front and back surfaces of the metal layer 11, at a position separate from the active material layer 12. The active material layer 12 and the insulating layer 13 may also be referred to as coatings, coating materials, surface layers, or surface layer materials. The metal foil 10 constitutes the positive electrode of a battery, such as a lithium-ion battery. In this case, the metal layer 11 is made of an aluminum-based material, such as pure aluminum or an aluminum alloy. The active material layer 12 is made of an active material, such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, or a ternary material (nickel-manganese-cobalt). The insulating layer 13 is made of, for example, a ceramic such as alumina or a polymer such as ABS resin.

Also, as shown in FIG. 3, the surface Wa of the metal foil 10 configured as a battery electrode is formed with coated portions Pc1 and Pc2, where the metal layer 11 is covered with the active material layer 12 and the insulating layer 13, i.e., a coating, and exposed portions Pe, where the metal layer 11 is exposed and not covered with the active material layer 12. The laser cutting device 100 sweeps the laser beam L along a predetermined sweep path Pt over the surface Wa of the metal foil 10, thereby continuously cutting both the coated portions Pc1 and Pc2 and the exposed portion Pe. In this case, the controller 140 can control the laser device 110 and the relative movement mechanism to switch between the irradiation conditions of the laser beam L when cutting the coated portions and the irradiation conditions of the laser beam L when cutting the exposed portions while sweeping the laser beam L over the surface Wa.

[Laser cutting method]
In laser cutting using the laser cutting device 100, first, the workpiece W is set so that the laser light L is irradiated onto its surface Wa. Then, while the laser light L is irradiating the surface Wa, the laser light L and the workpiece W move relative to each other. As a result, the laser light L moves (sweeps) over the surface Wa in a sweeping direction while being irradiated onto the surface Wa. The portion irradiated with the laser light L is melted and cut.

[Intermittent irradiation]
When laser cutting such a metal foil 10, if a strong laser beam L strikes the metal foil 10, the cut edge 10a may bend or turn over. However, reducing the output of the laser beam L increases the time required for laser cutting. Therefore, the inventors conducted extensive research and found that when the workpiece W is a metal foil 10, intermittent irradiation of the laser beam L at a predetermined frequency on the surface Wa can achieve higher quality processing in a shorter processing time. From this perspective, the inventors experimentally found that the pulse frequency of the laser beam L is preferably 10 MHz or less. Furthermore, if the energy per unit area of the laser beam L, i.e., the energy density, is low, it becomes difficult to achieve the desired cutting state. From this perspective, it was found that the diameter (spot diameter) of the spot of the laser beam L is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less.

Figure 4 is a graph showing a schematic time waveform of the laser light pulses output by the laser device 110. In Figure 4, the horizontal axis represents time, and the vertical axis represents the laser light output from the laser device 110. In intermittent irradiation, when the oscillation time of each pulse is Tp and the pulse period is Tc, the duty ratio Dr can be expressed as Dr = (Tp/Tc) x 100 [%]. The pulse frequency is 1/Tc.

[Overlap rate]
Furthermore, the inventors have found through experimental research that the overlapping state of the irradiation areas on the surface Wa of two successive pulses spaced apart in time affects the cutting quality. Fig. 5 is a plan view showing a state in which the irradiation areas of two successive pulses partially overlap on the surface Wa, and Fig. 6 is a plan view showing a state in which the irradiation areas of two successive pulses do not overlap on the surface Wa but are spaced apart.

The overlap rate R is defined as in the following equation (1).
R=L2/L1... (1)
Here, L1 is the length along the sweep direction SD of the irradiation area Pn of the nth pulse of laser light L and the irradiation area Pn+1 of the (n+1)th pulse of laser light L on the center line C in the width direction of the sweep locus, and is the same value for the two irradiation areas Pn and Pn+1. n is a positive number. This L1 can be expressed by the following equation (2):
L1=Lo+d... (2)
Here, Lo is the distance traveled by the spot of the laser light L on the surface Wa as it sweeps during the pulse oscillation time Tp (see Figure 4), and d is the diameter (spot diameter) of the spot of the laser light L on the surface Wa.

On the other hand, L2 is the length indicating the overlap between irradiation area Pn and irradiation area Pn+1. As shown in Figure 5, when irradiation area Pn and irradiation area Pn+1 overlap, L2 is the length along the sweep direction SD on the center line C of the overlap area A between irradiation area Pn and irradiation area Pn+1. In this case, L2 > 0. Although not shown, when irradiation area Pn and irradiation area Pn+1 are in contact with each other in the sweep direction SD, L2 = 0. Furthermore, as shown in Figure 6, when irradiation area Pn and irradiation area Pn+1 are separated by a distance I (> 0) in the sweep direction SD, L2 = -I. In this case, L2 < 0.

[Spot diameter]
7 is an explanatory diagram of the definition of spot diameter. In FIG. 7, Ax is the optical axis, _f1 is the focal length of the collimator lens 121, _f2 is the focal length of the condenser lens 122, _θ1 is the beam divergence angle, _θ2 is the beam spread angle, _Dc is the beam diameter of the collimated light, _Df is the beam diameter at the focal position _Pf , _Da is the beam diameter (spot diameter) on the surface Wa as the defocus position, and a is the distance between the focal position _Pf and the surface Wa. Note that the spot diameter _Da can also be referred to as the theoretical spot diameter. In this case, the following equations (3) to (5) hold:
D _c =2θ ₁ f ₁ ...(3)
D _f = (4f ₂ /πD _c )M ² λ (4)
D _a = D _f √{1+(4aλ/πD _f ² ) ² } ...(5)
where ^M2 is the beam quality and λ is the wavelength.

In the laser cutting of this embodiment, each component of the laser cutting device 100 is configured, adjusted, or controlled so that the spot diameter _Da on the surface Wa is a desired value. Through extensive research, the inventors have found that a spot diameter _Da of 28 μm or less is preferable because it can reduce thermal effects, and a spot diameter Da of 21 μm or less is even more preferable. As an example, if the beam quality ^M2 of the laser light is less than 1.1, the core diameter of the optical fiber 130 is 14 μm, and the wavelength of the laser light is 1070 nm, the spot diameter _Da can be set to 21 μm using an optical head 120 with an optical magnification of 1.5.

[Edge quality evaluation]
As a result of extensive research into laser cutting of metal foil 10 as a positive electrode by intermittent irradiation of laser light L, the inventors discovered that by appropriately setting the irradiation conditions of laser light L, it is possible to avoid various undesirable phenomena that occur near the edge 10a of the metal foil 10 cut by laser light L, and to further improve the quality near the edge 10a.

Figure 8 is a front view of the cut edge 10a of the metal foil 10, viewed in the thickness direction (Z direction) of the metal foil 10 and in a direction perpendicular to the sweep direction SD (opposite the Y direction); Figure 9 is a plan view of an example of the edge 10a, viewed in the thickness direction (opposite the Z direction); and Figure 10 is a plan view of the edge 10a of a different sample from Figure 9, viewed in the thickness direction (opposite the Z direction).

As shown in Figure 8, protrusions D, such as dross (lumps), bulging in the thickness direction (Z direction) of the metal foil 10 may occur at the edge 10a of the metal foil 10. Also, as shown in Figure 9, protrusions P, such as burrs, may occur at the edge 10a, protruding from the edge 10a in the direction along the surface Wa. Furthermore, as shown in Figure 10, a discolored area H may occur at the edge 10a, extending a predetermined width along the edge 10a.

[Aluminum foil (no coating): protrusions in the thickness direction]
An experiment was conducted on uncoated aluminum foil (A1050, thickness: 20 μm) as the active material layer 12 or insulating layer 13, i.e., the metal layer 11 not covered with a coating. The preferable processing conditions obtained from the experimental results of the uncoated aluminum foil can be applied to laser cutting at the exposed portion Pe.

Experiments have shown that the height of protrusions D (see Figure 8) in the thickness direction (Z direction) at the edge 10a varies depending on the irradiation energy and pulse frequency of the laser light L. Figure 11 is a graph showing an example of the evaluation results for the height of protrusions D in the thickness direction at the edge 10a when cutting uncoated aluminum foil, as a function of the irradiation energy and pulse frequency of the laser light L.

The irradiation energy E [J/mm] is the energy irradiated per unit length of the surface Wa, and can be expressed by the following equation (6).
E=Pp×Dr/(100×v)...(6)
where Pp is the peak power [W], Dr is the duty ratio [%], and v is the sweep speed [mm/s]. Note that a state where the pulse frequency is 0 indicates that the laser light is irradiated continuously, not intermittently.

In Figure 11, ○: Best indicates that the height of the protrusion D from the surface Wa along the Z direction (hereinafter referred to as the first height) is 10 μm or less, ◇: Good indicates that the first height is greater than 10 μm and less than 20 μm, and ×: Poor indicates that the first height is greater than 20 μm.

As shown in Figure 11, it was found that a frequency of 0 kHz or more and 1000 kHz (1 MHz) or less is preferable (good or better), and that an irradiation energy of less than 5.0 J/mm is preferable (good), and less than 1.5 J/mm is more preferable (best). This is thought to be because protrusions D occur when the amount of energy applied exceeds a predetermined amount.

[Aluminum foil (no coating): protrusions along the surface]
Experiments have shown that the height of protrusions P (see FIG. 9) in the direction along the surface Wa at the edge 10a (Y direction) varies depending on the overlap rate and the pulse peak output (Pp, see FIG. 4). Figure 12 is a graph showing an example of the evaluation results for the height of protrusions P in the direction along the surface Wa at the edge 10a when cutting uncoated aluminum foil, with respect to the overlap rate and peak output.

In Figure 12, ○: Best indicates that the height of the protrusion P from the edge 10a in the Y direction (hereinafter referred to as the second height) is 20 μm or less, ◇: Good indicates that the second height is greater than 20 μm and less than 30 μm, ×: Poor indicates that the second height is greater than 30 μm, and △: Uncuttable indicates that cutting was not possible.

As shown in Figure 12, it was found that the peak power is preferably 200 W or more and 1000 W or less (good), with a value of more than 500 W being more preferable (best), and the overlap rate is preferably -21% or more and 99% or less (good), with a value of -8% or more being more preferable (best). This is thought to be because the lower the overlap rate and the more areas are left unirradiated by the laser light L, the more likely protrusions P are to occur, and the greater the peak power, the larger the kerf width (cut width) and the less likely protrusions P are to occur.

[Aluminum foil (no coating): discolored area]
Experiments have shown that the width of the discoloration region H (see FIG. 10 ), which extends a predetermined width along the edge 10 a, varies depending on the irradiation energy and pulse frequency of the laser light L. FIG. 13 is a graph showing an example of the evaluation results for the width of the discoloration region H at the edge 10 a when cutting an uncoated aluminum foil, as a function of the irradiation energy and pulse frequency of the laser light L. The discoloration region H is defined as a region near the edge 10 a where the brightness in the captured image is 250% or more compared to the general region. The general region refers to a region of the metal foil 10 to be cut that is less affected by cutting with the laser light L. For example, the general region can be a location 1000 μm or more away from the edge 10 a.

In Figure 13, ○ indicates that the width of the discoloration area H along the Y direction is 20 μm or less, ◇ indicates that the width of the discoloration area H is greater than 20 μm and less than 50 μm, and × indicates that the width of the discoloration area H is greater than 50 μm.

As shown in Figure 13, it was found that a frequency of 0 kHz or more and 1 MHz or less is preferable (good), with 200 kHz or less being more preferable (best), and that the irradiation energy is preferably 0.05 J/mm or more and less than 5.0 J/mm (good), with 2.0 J/mm or less being more preferable (best). This is thought to be because discoloration due to thermal effects is more likely to occur if the amount of energy applied exceeds a certain amount.

[Aluminum foil (with active material layer): protrusions in the thickness direction]
The same experiment as for the uncoated aluminum foil was also carried out on an aluminum foil (thickness: 150 μm) with an active material layer 12 made of iron phosphate (LiFePO4) on both sides of the metal layer 11 (aluminum foil). The preferable processing conditions obtained from the experimental results of the aluminum foil with an active material layer can be applied to laser cutting at the coated portion Pc1.

Figure 14 is a graph showing an example of the evaluation results for the height of protrusions D in the thickness direction at the edge 10a when an aluminum foil with an active material layer is cut, as a function of the irradiation energy and pulse frequency of the laser light L. The criteria for determining the height of protrusions D are the same as for uncoated aluminum foil.

As shown in Figure 14, it was found that a frequency of 10 kHz or more and 1 MHz or less is preferable (good), with a frequency of more than 200 kHz being more preferable (best), and that irradiation energy is preferably 0.03 J/mm or more and less than 0.8 J/mm (good), with a frequency of 0.25 J/mm or less being more preferable (best).

[Aluminum foil (with active material layer): protrusions along the surface]
15 is a graph showing an example of the results of evaluation of the height of protrusions P in the direction along the surface Wa at the edge 10 a when an aluminum foil with an active material layer is cut, with respect to the overlap rate and peak output. The criteria for determining the height of protrusions P are the same as those for uncoated aluminum foil.

As shown in Figure 15, it was found that a peak output of 200 W or more and 1000 W or less is preferable (good), with a peak output of more than 400 W being more preferable (best). It was also found that an overlap rate of -21% or more and 99% or less is preferable (good), with a peak output of more than 10% being more preferable (best) in the range of more than 400 W.

[Aluminum foil (with active material layer): discoloration area]
16 is a graph showing an example of the evaluation results of the width of the discoloration region H at the edge 10a when cutting an aluminum foil with an active material layer, as a function of the irradiation energy and pulse frequency of the laser light L. The discoloration region H is defined as a region near the edge 10a where the brightness in the captured image is 80% or less compared to the general region. The general region refers to a region of the metal foil 10 to be cut that is less affected by cutting with the laser light L. For example, a location 1000 μm or more away from the edge 10a can be defined as the general region.

As shown in Figure 16, it was found that a frequency of 0 kHz or more and 1 MHz or less is preferable (good), with a frequency of more than 300 kHz being more preferable (best), and that irradiation energy is preferably 0.05 J/mm or more and less than 1.0 J/mm being more preferable (good), with a frequency of 0.75 J/mm or less being more preferable (best).

[Aluminum foil (with ceramic insulating layer): protrusions in the thickness direction]
Experiments similar to those for uncoated aluminum foil were conducted on ceramic insulating layer-coated aluminum foil (thickness: 130 μm), in which both sides of the metal layer 11 (aluminum foil) were covered with insulating layers 13 made of ceramic, such as alumina-based ceramic. The preferred processing conditions obtained from the experimental results for the ceramic insulating layer-coated aluminum foil can be applied to laser cutting at the coated portion Pc2.

Figure 17 is a graph showing an example of the evaluation results for the height of protrusions D in the thickness direction at the edge 10a when cutting aluminum foil with a ceramic insulation layer, as a function of the irradiation energy and pulse frequency of the laser light L.

In Figure 17, ○ (good) indicates that the first height is 20 μm or less, and × (poor) indicates that the first height is greater than 20 μm.

As shown in Figure 17, it was found that a frequency of 100 kHz or more and 200 kHz or less is preferable (good), and that an irradiation energy of less than 0.4 J/mm is preferable (good) when the frequency is in the range of 100 kHz or more.

[Aluminum foil (with ceramic insulating layer): protrusions along the surface]
FIG. 18 is a graph showing an example of evaluation results for the overlap rate and peak output with respect to the height of the protrusion P in the direction along the surface Wa at the edge 10a when cutting an aluminum foil with a ceramic insulation layer.

In Figure 18, ○ (good) indicates that the second height is 20 μm or less, and × (poor) indicates that the second height is greater than 20 μm.

As shown in Figure 18, it was found that a peak output of 150 W or more and 1000 W or less is preferable (good), and an overlap rate of greater than 21% is preferable (good). This is because if the overlap rate is low, small pieces of ceramic will remain in areas not irradiated by the laser light L.

[Aluminum foil (with polymer insulating layer): protrusions along the surface]
Experiments similar to those for uncoated aluminum foil were conducted on aluminum foil with a polymer insulation layer (thickness: 110 μm), in which both the front and back sides of the metal layer 11 (aluminum foil) were covered with an insulating layer 13 made of a polymer such as ABS resin. The preferred processing conditions obtained from the experimental results for the aluminum foil with a polymer insulation layer can be applied to laser cutting at the coated portion Pc2.

Figure 19 is a graph showing an example of the evaluation results for the overlap rate and peak output in relation to the height of protrusions P in the direction along the surface Wa at the edge 10a when aluminum foil with a polymer insulation layer is cut.

In addition, experiments were conducted on laser cutting of aluminum foil with a polymer insulation layer, not only in a single sweep, but also in two sweeps along the same path. This is because the insulating layer 13 made of polymer has a low heat absorption rate, making it difficult to cut in a single sweep.

In Figure 19, ○: Good indicates that the second height of the protrusion P was 30 μm or less when cut with one sweep, ×: Poor indicates that the second height was greater than 30 μm when cut with one sweep, □: Good indicates that the second height was 30 μm or less when cut with two sweeps, and △: Poor indicates that the second height was greater than 30 μm when cut with two sweeps.

As shown in Figure 19, it was found that for a single sweep, when the peak power is in the range of 600 W or more and 800 W or less, the overlap rate is preferably 70% or more and 80% or less (good), and for a double sweep, when the peak power of either the first or second sweep is in the range of greater than 300 W, the overlap rate is preferably 40% or more (good). Note that in a double sweep, the peak power and overlap rate may be the same or different between the first and second sweeps. Furthermore, sweeps may be performed more than once, and multiple sweeps may be performed when laser cutting aluminum foil with an active material or aluminum foil with a ceramic insulation layer. Multiple sweeps may also include two or more sweeps with different laser beam irradiation conditions, such as pulse frequency, irradiation energy, peak power, and overlap rate.

As explained above, according to this embodiment, in a method for laser cutting metal foil that constitutes a battery positive electrode, by appropriately setting the pulse frequency, irradiation energy, peak output, overlap rate, etc., it is possible to suppress the formation or increase of protrusions D in the thickness direction at the edge 10a, protrusions P in the direction along the surface Wa at the edge 10a, and discolored areas H. Therefore, this embodiment makes it possible to achieve higher quality laser cutting of metal foil.

Second Embodiment
FIG. 20 is a schematic diagram of a laser cutting device 100A according to the second embodiment. In this embodiment, the optical head 120 has a galvanometer scanner 126 between a collimator lens 121 and a condenser lens 122. The galvanometer scanner 126 has two mirrors 126a. The irradiation direction and irradiation position of the laser light L change depending on the position of these two mirrors 126a. In other words, the laser cutting device 100A can move the irradiation position of the laser light L and sweep the laser light L without moving the optical head 120. The controller 140 can control the operation of the motors 126b corresponding to each mirror 126a so as to change the angle (position) of the mirror 126a. This embodiment also provides the same functions and effects as the first embodiment.

The above describes exemplary embodiments of the present invention, but the above embodiments are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in a variety of other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, the specifications of each configuration, shape, and the like (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be modified as appropriate.

10...metal foil 10a...edge 11...metal layer 12...active material layer 13...insulating layer 100, 100A...laser cutting device 110...laser device 120...optical head 121...collimating lens 122...condensing lens 123...DOE
126... Galvano scanner 126a... Mirror 126b... Motor 130... Optical fiber 140... Controller A... Overlapping area Ax... Optical axis a... Distance C... Center line D... Projection D _a ... Beam diameter (spot diameter)
_Dc , _Df ...beam diameters _f1 , _f2 ...focal length Dr...duty ratio E...irradiation energy H...discoloration area I...distance L...laser light P...protrusions Pc1, Pc2...coated area Pe...exposed area Pf...focal position Pn, Pn+1...irradiation area Pt...sweeping path R...overlap ratio SD...sweeping direction Tp...oscillation time W...processing object Wa...surface X...direction Y...direction Z...direction _θ1 ...beam divergence angle _θ2 ...beam spread angle

Claims (24)

Laser cutting the target by intermittently irradiating a metal foil as a processing target constituting a positive electrode of a battery with pulses of laser light at a frequency of 10 MHz or less ;
A method for laser cutting a metal foil, wherein the peak output of the laser light is 150 W or more . Laser cutting the target by intermittently irradiating a metal foil as a processing target constituting a positive electrode of a battery with pulses of laser light at a frequency of 10 MHz or less ;
the metal foil has a metal layer made of an aluminum-based material;
A method for laser cutting a metal foil, wherein the peak output of the laser light is 200 W or more . Laser cutting the target by intermittently irradiating a metal foil as a processing target constituting a positive electrode of a battery with pulses of laser light at a frequency of 10 MHz or less ;
A method for laser cutting a metal foil , wherein the metal foil has a metal layer made of an aluminum-based material and a ceramic insulating layer made of ceramic and applied to the surface of the metal layer . Laser cutting the target by intermittently irradiating a metal foil as a processing target constituting a positive electrode of a battery with pulses of laser light at a frequency of 10 MHz or less ;
A method for laser cutting a metal foil , wherein the metal foil has a metal layer made of an aluminum-based material and a polymer insulating layer made of a polymer and applied to the surface of the metal layer . 5. The method for laser cutting a metal foil according to claim 3 , wherein the peak output of the laser beam is 150 W or more. 2. The method of claim 1 , wherein the metal foil has a metal layer made of an aluminum-based material. 7. The method for laser cutting a metal foil according to claim 6 , wherein the peak output of the laser beam is 200 W or more. 8. The method for cutting a metal foil with a laser according to claim 2, wherein the frequency is 1 MHz or less. 9. The method for laser cutting a metal foil according to claim 2 , wherein the metal foil has an active material layer applied to the surface of the metal layer. 10. The method for laser cutting a metal foil according to claim 2 , wherein the irradiation energy of the laser light is 0.03 [J/mm] or more and 0.8 [J/mm] or less. The method for laser cutting metal foil according to claim 3 , wherein the frequency is 300 kHz or higher. 12. The method for laser cutting a metal foil according to claim 3 or 11 , wherein the irradiation energy of the laser light is 0.05 [J/mm] or more and less than 1.0 [J/mm]. The overlap rate R between the irradiation area of the pulse and the irradiation area of the next pulse is calculated by the following formula (1):
R=L2/L1... (1)
Here,
L1: length of the irradiation area in the sweep direction,
L2: the length in the sweep direction of the overlapping region between the pulse and the next pulse when the pulse and the next pulse overlap in the sweep direction, 0 when the pulse and the next pulse are adjacent in the sweep direction, and −I when the pulse and the next pulse are separated by a distance I (>0) in the sweep direction;
13. The method for laser cutting a metal foil according to claim 3 , wherein the overlap rate R is greater than 21% when the overlap rate R is defined as follows: 14. The method for laser cutting a metal foil according to claim 13 , wherein the frequency is 100 kHz or more and the irradiation energy of the laser light is less than 0.4 J/mm. The peak output of the laser light is 600 [W] or more and 800 [W] or less,
The overlap rate R between the irradiation area of the pulse and the irradiation area of the next pulse is calculated by the following formula (1):
R=L2/L1... (1)
Here,
L1: length of the irradiation area in the sweep direction,
L2: the length in the sweep direction of the overlapping region between the pulse and the next pulse when the pulse and the next pulse overlap in the sweep direction, 0 when the pulse and the next pulse are adjacent in the sweep direction, and −I when the pulse and the next pulse are separated by a distance I (>0) in the sweep direction;
5. The method for laser cutting a metal foil according to claim 4 , wherein when the overlap rate R is defined as follows, the overlap rate R is 70% or more and 80% or less. The overlap rate R between the irradiation area of the pulse and the irradiation area of the next pulse is calculated by the following formula (1):
R=L2/L1... (1)
Here,
L1: length of the irradiation area in the sweep direction,
L2: the length in the sweep direction of the overlapping region between the pulse and the next pulse when the pulse and the next pulse overlap in the sweep direction, 0 when the pulse and the next pulse are adjacent in the sweep direction, and −I when the pulse and the next pulse are separated by a distance I (>0) in the sweep direction;
The method for laser cutting a metal foil according to any one of claims 1 to 12 , wherein, when the overlap rate R is defined as: The method for laser cutting a metal foil according to any one of claims 1 to 9, 11, 15 and 16 , wherein the irradiation energy of the laser light is less than 5.0 [J/mm]. The method for laser cutting a metal foil according to any one of claims 1 to 17 , wherein the thickness of the metal foil is 500 μm or less. 19. The method for laser cutting a metal foil according to claim 1, wherein the metal foil has a portion covered with a film and a portion not covered with a film. 20. The method for laser cutting a metal foil according to claim 1 , wherein the spot diameter of the laser light is 100 μm or less. 21. The method for laser cutting a metal foil according to claim 20 , wherein the spot diameter of the laser light is 50 μm or less. 22. The method for laser cutting a metal foil according to claim 21 , wherein the spot diameter of the laser light is 28 [μm] or less. A method for laser cutting metal foil according to any one of claims 1 to 22, in which multiple sweeps are performed along the same path. The metal foil laser cutting method described in claim 23, wherein the multiple sweeps include two or more sweeps each having different laser light irradiation conditions.