Method for Laser Cutting of Metal Foil

Abstract

To provide, for example, a new improved laser beam cutting method for metal foil.SOLUTION: In a laser beam cutting method for metal foil, for example, the metal foil being a laser beam machining object constituting a negative electrode of a battery, is intermittently irradiated with laser beam pulses at a frequency of 10 [MHz] to be thereby cut by the laser beam. In the method of laser beam cutting for metal foil, an overlap ratio R between an irradiation region of one pulse and an irradiation region of a next pulse may be larger than -22% and less than or equal to 96% when the overlap ratio R is defined as the following formula (1), R=L2 / L1 (1) where L1 is a length in a sweep direction of the irradiation region, and L2 is: a length in the sweep direction of the overlap area of the pulse and the next pulse when the pulse and the next pulse overlap in the sweep direction; otherwise, 0 when the pulse and the next pulse contact each other in the sweep direction; or -I when the pulse and the next pulse are separated from each other by a distance I (>0) in the sweep direction.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for laser cutting of metal foil.

Background Art

[0002] As one of the methods for cutting a workpiece made of a metal material, laser cutting by irradiation with a laser beam is known. Laser cutting is a method in which a laser beam is irradiated onto a portion to be cut of a workpiece, and the portion is melted by the energy of the laser beam to cut the workpiece (see, for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the workpiece is a metal foil, the metal foil is likely to be deformed or torn. Therefore, when various parameters in laser cutting are set in the same manner as in the case of a thicker metal member, it may be difficult to obtain the required quality.

[0005] In addition, when the metal foil is applied to the negative electrode of a battery, higher-quality laser cutting is required.

[0006] Therefore, one of the problems of the present invention is to obtain an improved and novel method for laser cutting of metal foil that enables laser cutting of, for example, a metal foil as a workpiece constituting the negative electrode of a battery.

Means for Solving the Problem

[0007] The laser cutting method of the metal foil of the present invention laser-cuts a processing target, for example, a metal foil serving as a processing target constituting a negative electrode of a battery, by intermittently irradiating the metal foil with laser light pulses at a frequency of 10 [MHz] or less.

[0008] In the laser cutting method of the metal foil, the overlap ratio R between the irradiation region of the pulse and the irradiation region of the next pulse is expressed by the following formula (1) R = L2 / L1 ··· (1) Here, L1: the length in the scanning direction of the irradiation region, L2: when the pulse and the next pulse overlap in the scanning direction, the length in the scanning direction of the overlapping region between the pulse and the next pulse, 0 when the pulse and the next pulse are in contact with each other in the scanning direction, and -I when the pulse and the next pulse are separated from each other by a distance I (>0) in the scanning direction. When defined as such, the overlap ratio R may be greater than -22 [%] and not more than 96 [%].

[0009] In the laser cutting method of the metal foil, the irradiation energy of the laser light may be 0.03 [J / mm] or more and less than 5.0 [J / mm].

[0010] In the laser cutting method of the metal foil, the thickness of the metal foil may be 500 [μm] or less.

[0011] In the laser cutting method of the metal foil, the metal foil may have a portion covered with a film and a portion not covered with a film.

[0012] In the laser cutting method of the metal foil, the spot diameter of the laser light may be 100 [μm] or less.

[0013] In the laser cutting method of the metal foil, the spot diameter of the laser light may be 50 [μm] or less.

[0014] In the laser cutting method of the metal foil, the spot diameter of the laser beam may be 28 [μm] or less.

[0015] In the laser cutting method of the metal foil, the peak output of the laser beam may be 200 [W] or more.

[0016] In the laser cutting method of the metal foil, the metal foil may have a metal layer made of a copper-based material.

[0017] In the laser cutting method of the metal foil, the frequency may be 1 [MHz] or less.

[0018] In the laser cutting method of the metal foil, the irradiation energy of the laser beam may be less than 1.0 [J / mm].

[0019] In the laser cutting method of the metal foil, the peak output of the laser beam may be 400 [W] or more.

[0020] In the laser cutting method of the metal foil, the overlap ratio R between the irradiation region of the pulse and the irradiation region of the next pulse is expressed by the following formula (1) R = L2 / L1 ··· (1) where L1: the length in the scanning direction of the irradiation region, L2: when the pulse and the next pulse overlap in the scanning direction, the length in the scanning direction of the overlapping region between the pulse and the next pulse, 0 when the pulse and the next pulse are in contact in the scanning direction, -I when the pulse and the next pulse are separated by a distance I (>0) in the scanning direction. When defined as such, the overlap ratio R may be 9 [%] or more.

[0021] In the laser cutting method of the metal foil, the overlap ratio R may be 78 [%] or less.

[0022] In the laser cutting method of the metal foil, the metal foil may have an active material layer applied to the surface of the metal layer.

[0023] In the laser cutting method of the metal foil, the frequency may be 500 [kHz] or less.

[0024] In the laser cutting method of the metal foil, the frequency may be 100 [kHz] or more.

[0025] In the laser cutting method of the metal foil, the irradiation energy of the laser beam may be 0.15 [J / mm] or less.

[0026] In the laser cutting method of the metal foil, the overlap ratio R between the irradiation region of the pulse and the irradiation region of the next pulse is expressed by the following formula (1) R = L2 / L1 ··· (1) Here, L1: the length in the scanning direction of the irradiation region, L2: when the pulse and the next pulse overlap in the scanning direction, the length in the scanning direction of the overlapping region between the pulse and the next pulse, when the pulse and the next pulse are in contact in the scanning direction, it is 0, when the pulse and the next pulse are separated by a distance I (>0) in the scanning direction, it is -I. When defined in this way, the overlap ratio R may be 24 [%] or more.

Advantages of the Invention

[0027] According to the present invention, it is possible to obtain a novel and improved laser cutting method for a metal foil capable of laser cutting a metal foil as a processing target constituting a negative electrode of a battery.

Brief Description of the Drawings

[0028]

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[0029] Exemplary embodiments of the present invention are disclosed below. The configurations of the embodiments shown below, as well as the actions and results (effects) brought about by those configurations, are examples. The present invention can also be realized by configurations other than those disclosed in the following embodiments. Further, according to the present invention, it is possible to obtain at least one of various effects (including derivative effects) obtained by the configuration.

[0030] The embodiments shown below have the same configurations. Therefore, according to the configurations of each embodiment, the same actions and effects based on those same configurations can be obtained. Further, in the following, the same reference numerals are given to those same configurations, and redundant explanations may be omitted.

[0031] 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 direction, Y direction, and Z direction intersect and are orthogonal to each other. The X direction and Y direction are directions along the surface Wa (machining surface) of the workpiece W to be machined, and the Z direction is the normal direction of the surface Wa. Note that in some figures, the X direction is illustrated as the sweeping direction SD, but the sweeping direction SD only needs to intersect the Z direction and is not limited to the X direction.

[0032] [First Embodiment] [Configuration of Laser Cutting Device] FIG. 1 is a schematic configuration 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.

[0033] The laser device 110 includes 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, 800 [nm] or more and 1200 [nm] or less, but is not limited thereto. Further, the laser device 110 can intermittently output a continuous-wave laser at a frequency of, for example, 10 [MHz] or less.

[0034] 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 single-mode laser light, the optical fiber 130 is configured to transmit single-mode laser light. In this case, the M 2 beam quality of the single-mode laser light is set to 1.2 or less. When the laser device 110 outputs multi-mode laser light, the optical fiber 130 is configured to transmit multi-mode laser light.

[0035] The optical head 120 is an optical device for irradiating the surface Wa of the workpiece W with the laser light input from the laser device 110. The optical head 120 includes a collimating lens 121, a focusing lens 122, and a DOE 123 (diffractive optical element). The collimating lens 121 and the focusing lens 122 can also be referred to as optical components. The optical head 120 may include optical components other than the collimating lens 121 and the focusing lens 122.

[0036] In the present embodiment, the optical head 120 is configured to be able to change the relative position with respect to the workpiece W in order to scan the laser light L while irradiating the surface Wa of the workpiece W with the laser light L. The relative movement between the optical head 120 and the workpiece W can be realized by the movement of the optical head 120, the movement of the workpiece W, or the movement of both the optical head 120 and the workpiece W.

[0037] The collimating lens 121 collimates the input laser light. The collimated laser light becomes parallel light. The focusing lens 122 focuses the laser light as parallel light and irradiates the workpiece W as the laser light L (output light). Further, the DOE 123 is disposed between the collimating lens 121 and the focusing lens 122 and shapes the beam shape (hereinafter referred to as the beam shape) of the laser light. The DOE 123 has, for example, a configuration in which a plurality of diffraction gratings with different periods are superimposed. The DOE 123 can shape a beam with a more suitable shape by bending or superimposing the parallel light in a direction affected by each diffraction grating. The DOE 123 can also be referred to as a beam shaper.

[0038] With such a configuration, the optical head 120 irradiates the surface Wa of the workpiece W with the laser light L in the direction opposite to the Z direction. The irradiation direction of the laser light L from the optical head 120 is the direction opposite to the Z direction. The optical head 120 can focus the laser light L so that the beam diameter is, for example, 10 [μm] or more and 100 [μm] or less.

[0039] The controller 140 can control the operation of the laser device 110, the operation of a relative movement mechanism (not shown) that relatively moves the optical head 120 and the workpiece W so that the laser beam L is scanned on the surface Wa, and the like.

[0040] [Workpiece] FIG. 2 is a cross-sectional view of the metal foil 10 as the workpiece W, and FIG. 3 is a plan view of the metal foil 10. In the present embodiment, the workpiece W of the laser cutting device 100 is the metal foil 10 that constitutes the negative electrode of the battery. The thickness of the metal foil 10 is, for example, 500 [μm] or less, but is not limited thereto.

[0041] As shown in FIG. 2, the metal foil 10 has a metal layer 11 and an active material layer 12. The active material layer 12 is a film formed on both sides in the thickness direction of the metal layer 11, that is, on the front and back surfaces of the metal layer 11. The active material layer 12 can also be referred to as a coating film, a coated substance, a surface layer, or a surface layer material. The metal foil 10 constitutes the negative electrode of a battery such as, for example, a lithium-ion battery. In that case, the metal layer 11 is made of a copper-based material such as, for example, oxygen-free copper or a copper alloy, and the active material layer 12 is made of an active material such as, for example, a carbon-based material or lithium titanate.

[0042] Also, as shown in FIG. 3, on the surface Wa of the metal foil 10 configured as an electrode of the battery, a covered portion Pc where the metal layer 11 is covered with the active material layer 12, that is, the film, and an exposed portion Pe where the metal layer 11 is exposed without being covered with the active material layer 12 are formed. The laser cutting device 100 can continuously cut both the covered portion Pc and the exposed portion Pe by scanning the laser beam L on the surface Wa of the metal foil 10 along a predetermined scanning path Pt. In this case, the controller 140 can control the laser device 110 and the relative movement mechanism so that the irradiation conditions of the laser beam L when cutting the covered portion while scanning the laser beam L on the surface Wa are switched from the irradiation conditions of the laser beam L when cutting the exposed portion.

[0043] [Laser cutting method] In laser cutting using the laser cutting device 100, first, the workpiece W is set so that the laser beam L is irradiated onto its surface Wa. Then, with the laser beam L irradiating the surface Wa, the laser beam L and the workpiece W move relative to each other. As a result, while the laser beam L irradiates the surface Wa, it moves (scans) in the scanning direction SD on the surface Wa. The portion irradiated with the laser beam L melts and is cut.

[0044] [Intermittent irradiation] In such laser cutting of the metal foil 10, when a strong laser beam L hits the metal foil 10, the cut edge 10a may bend or curl. However, if the output of the laser beam L is reduced, laser cutting will take a long time. Therefore, as a result of intensive research, the inventors have found that when the workpiece W is the metal foil 10, by intermittently (intermittently) irradiating the surface Wa with the laser beam L at a predetermined frequency, it is possible to perform higher-quality processing in a shorter processing time. From such a perspective, the inventors experimentally found that the frequency of the pulses of the laser beam L is preferably 10 [MHz] or less. Also, if the energy of the laser beam L per unit area, that is, the energy density, is low, it becomes difficult to obtain the required cutting state. From such a perspective, it has been found that the diameter of the spot (spot diameter) 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.

[0045] FIG. 4 is a graph showing a schematic time waveform of the pulses of the laser beam output from the laser device 110. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the output of the laser beam from the laser device 110. In intermittent irradiation, when the oscillation time of each pulse is Tp and the period of the pulse is Tc, the duty ratio Dr can be expressed as Dr = (Tp / Tc) × 100 [%]. Also, the frequency of the pulse is 1 / Tc.

[0046] [Overlap ratio] In addition, the inventors have found through experimental research that the overlapping state of the irradiation ranges of two consecutive pulses with a time interval on the surface Wa affects the cutting quality. FIG. 5 is a plan view showing a state where the irradiation ranges of two consecutive pulses partially overlap on the surface Wa, and FIG. 6 is a plan view showing a state where the irradiation ranges of two consecutive pulses are separated without overlapping on the surface Wa.

[0047] The overlap ratio R is defined as in the following formula (1). R = L2 / L1 ··· (1) Here, L1 is the length along the scanning direction SD on the center line C in the width direction of the scanning locus of the irradiation region Pn of the n-th pulse of the laser beam L and the irradiation region Pn+1 of the (n + 1)-th pulse of the laser beam L, and is the same value in the two irradiation regions Pn, Pn+1. n is a positive number. This L1 can be expressed by the following formula (2). L1 = Lo + d ··· (2) Here, Lo is the moving distance on the surface Wa accompanying the scanning of the spot of the laser beam L during the pulse oscillation time Tp (see FIG. 4), and d is the diameter of the spot of the laser beam L on the surface Wa (spot diameter).

[0048] On the other hand, L2 is the length indicating the overlapping state between the irradiation region Pn and the irradiation region Pn+1. As shown in FIG. 5, when the irradiation region Pn and the irradiation region Pn+1 overlap, L2 is the length along the scanning direction SD on the center line C of the overlapping region A between the irradiation region Pn and the irradiation region Pn+1. In this case, L2 > 0. Although not shown, when the irradiation region Pn and the irradiation region Pn+1 are in contact with each other in the scanning direction SD, L2 = 0. Also, as shown in FIG. 6, when the irradiation region Pn and the irradiation region Pn+1 are separated by a distance I (>0) in the scanning direction SD, L2 = -I. In this case, L2 < 0.

[0049] [Spot diameter] Figure 7 is an explanatory diagram of the definition of the spot diameter. In Figure 7, Ax is the optical axis, f1 is the focal length of the collimating lens 121, f2 is the focal length of the condenser lens 122, θ1 is the beam divergence angle, θ2 is the beam spread angle, D c is the beam diameter of the collimated light, D f is the focal position P f at the beam diameter, D a is the beam diameter (spot diameter) on the surface Wa as the defocus position, a is the distance between the focal position P f and the surface Wa. Note that the spot diameter D a can also be referred to as the theoretical spot diameter. In this case, the following equations (3) to (5) hold. D c = 2θ1f1 ···(3) D f =(4f2 / πD c )M 2 λ ···(4) D a = D f √{1 + (4aλ / πD f 2 ) 2} ···(5) Here, M 2 is the beam quality and λ is the wavelength.

[0050] In the laser cutting of this embodiment, each part of the laser cutting apparatus 100 is configured, adjusted, or controlled so that the spot diameter D a on the surface Wa becomes the desired value. As a result of the inventors' intensive research, it has been found that the spot diameter D a is preferably 28 [μm] or less to reduce the heat influence, and more preferably 21 [μm] or less. As an example, when the beam quality M 2 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], according to the optical head 120 with an optical magnification of 1.5 times, the spot diameter D a can be set to 21 [μm].

[0051] [Edge Quality Evaluation] As a result of intensive research on the case of laser-cutting the metal foil 10 as the negative electrode by intermittent irradiation of the laser beam L, the inventors have found that by appropriately setting the irradiation conditions of the laser beam L, various unfavorable events occurring in the vicinity of the edge 10a of the metal foil 10 cut by the laser beam L can be avoided, and the quality in the vicinity of the edge 10a can be further improved.

[0052] FIG. 8 is a front view of the cut edge 10a of the metal foil 10 as viewed in a direction perpendicular to the thickness direction (Z direction) and the sweeping direction SD of the metal foil 10 (opposite direction of the Y direction), FIG. 9 is a plan view of an example of the edge 10a as viewed in the thickness direction (opposite direction of the Z direction), and FIG. 10 is a plan view of the edge 10a of another sample as viewed in the thickness direction (opposite direction of the Z direction).

[0053] At the edge 10a of the metal foil 10, as shown in FIG. 8, there may occur protrusions D such as dross (lumps) that bulge in the thickness direction (Z direction) of the metal foil 10. Also, at the edge 10a, as shown in FIG. 9, there may occur protrusions P such as burrs that protrude from the edge 10a in a direction along the surface Wa. Further, at the edge 10a, as shown in FIG. 10, there may occur a discolored region H that extends along the edge 10a with a predetermined width.

[0054] [Copper foil with active material: protrusion in the thickness direction] An experiment was conducted on a copper foil with an active material (active material: graphite composite material, thickness 90 [μm]). The suitable processing conditions obtained from the experimental results of the copper foil with an active material can be applied to laser cutting at the coated portion Pc.

[0055] As a result of the experiment, it was found that the height of the protrusion D in the thickness direction (Z direction) at the edge 10a (see FIG. 8) changes depending on the irradiation energy and the pulse frequency of the laser beam L. FIG. 11 is a graph showing an example of the evaluation results of the height of the protrusion D in the thickness direction at the edge 10a when cutting a copper foil coated with an active material, with respect to the irradiation energy and the pulse frequency of the laser beam L.

[0056] The irradiation energy E [J / mm] is the energy irradiated per unit length of the surface Wa and can be expressed by the following formula (6). E = Pp × Dr / (100 × v) ···(6) Here, Pp: peak output [W], Dr: duty ratio [%], v: scanning speed [mm / s]. Note that the state where the frequency of the pulse is 0 indicates a state where the laser light is irradiated continuously rather than intermittently.

[0057] In FIG. 11, ○: best indicates the case where the height along the Z direction (hereinafter referred to as the first height) from the surface Wa of the protrusion D is 5 [μm] or less, ◇: good indicates the case where the first height is greater than 5 [μm] and 10 [μm] or less, and ×: poor indicates the case where the first height is greater than 10 [μm].

[0058] As shown in FIG. 11, it has been found that the frequency is preferably 0 [kHz] or more and 500 [kHz] or less (good or better), and the irradiation energy is preferably 0.03 [J / mm] or more and less than 5.0 [J / mm] (good), and more preferably 0.15 [J / mm] or less (best). This is presumably because protrusions D occur when the given energy amount exceeds a predetermined amount.

[0059] [Copper foil with active material: protrusion in the direction along the surface] By experiments, it has been found that for the protrusion P (see FIG. 9) in the direction along the surface Wa (Y direction) at the edge 10a, its height changes depending on the overlap ratio and the peak output of the pulse (Pp, see FIG. 4). FIG. 12 is a graph showing an example of the evaluation results of the height of the protrusion P in the direction along the surface Wa at the edge 10a when the copper foil coated with the active material is cut, with respect to the overlap ratio and the peak output.

[0060] In FIG. 12, ○ indicates the best case where the height along the Y direction from the edge 10a of the protrusion P (hereinafter referred to as the second height) is 10 [μm] or less, ◇ indicates the good case where the second height is greater than 10 [μm] and 20 [μm] or less, and × indicates the bad case where the second height is greater than 20 [μm].

[0061] As shown in FIG. 12, it was found that for the peak output, it is preferably greater than 200 [W] (good), and more preferably 400 [W] or more (best). For the overlap ratio, it is preferably 9 [%] or more and 96 [%] or less (good), and more preferably 24 [%] or more and 78 [%] or less (best). This is because the lower the overlap ratio and the more the region where the laser beam L is not irradiated occurs, the easier it is for the protrusion P to occur, and the larger the peak output, the larger the kerf width (cutting width) and the more difficult it is for the protrusion P to occur.

[0062] [Copper foil with active material: Color change region] By experiments, it was found that for the color change region H extending along the edge 10a with a predetermined width (see FIG. 10), the size of its width changes depending on the irradiation energy of the laser beam L and the frequency of the pulse. FIG. 13 is a graph showing an example of the evaluation results of the width of the color change region H at the edge 10a when cutting a copper foil coated with an active material with respect to the irradiation energy of the laser beam L and the frequency of the pulse.

[0063] In FIG. 13, ○ indicates the case where the width along the Y direction of the color change region H is 50 [μm] or less, ◇ indicates the good case where the width of the color change region H is greater than 50 [μm] and 100 [μm] or less, and × indicates the bad case where the width of the color change region H is greater than 100 [μm]. The color change region H is a region where the luminance in the photographed image is 45% or less compared to the general region in the vicinity of the edge 10a. The general region refers to a region in the metal foil 10 to be cut that is less affected by cutting with the laser beam L. For example, a location more than 1000 [μm] away from the edge 10a can be regarded as the general region.

[0064] As shown in FIG. 13, it has been found that the frequency is preferably (good) 0 [kHz] or more and 500 [kHz] or less, and more preferably (best) 100 [kHz] or more. Regarding the irradiation energy, it has been found that it is preferably (good) 0.03 [J / mm] or more and less than 1.0 [J / mm], and more preferably (best) 0.12 [J / mm] or less. This is presumably because discoloration due to thermal effects is likely to occur when the given energy amount exceeds a predetermined amount.

[0065] [Copper foil (without active material): protrusion in the thickness direction] For the copper foil (without active material, thickness 10 [μm]) as well, the same experiment as for the copper foil with active material was conducted. The suitable processing conditions obtained from the experimental results of the copper foil (without active material) can be applied to laser cutting at the exposed location Pe.

[0066] FIG. 14 is a graph showing an example of the evaluation results of the height of the protrusion D in the thickness direction at the edge 10a when cutting a copper foil without active material applied, with respect to the irradiation energy of the laser beam L and the frequency of the pulses. The criterion for the height of the protrusion D is the same as in the case of the copper foil with active material.

[0067] As shown in FIG. 14, it has been found that the frequency is preferably (good) 0 [kHz] or more and 1 [MHz] (1000 [kHz]) or less, and more preferably (best) 500 [kHz] or less. Regarding the irradiation energy, it has been found that it is preferably (good) 0.03 [J / mm] or more and less than 2.0 [J / mm], and more preferably (best) 0.2 [J / mm] or less.

[0068] [Copper foil (without active material): protrusion in the direction along the surface] FIG. 15 is a graph showing an example of the evaluation results of the height of the protrusion P in the direction along the surface Wa at the edge 10a when cutting a copper foil without active material applied, with respect to the overlap ratio and the peak output. The criterion for the height of the protrusion P is the same as in the case of the copper foil with active material.

[0069] As shown in FIG. 15, for the peak output, it is preferably (good) 200 [W] or more and 1000 [W] or less, and more preferably (best) 400 [W] or more. For the overlap ratio, it is preferably (good) greater than -22 [%] and 96 [%] or less, and more preferably (best) 9 [%] or more and 78 [%] or less.

[0070] [Copper foil (without active material): Color change range] FIG. 16 is a graph showing an example of the evaluation results of the width of the color change range H at the edge 10a when the copper foil without the active material is cut, with respect to the irradiation energy of the laser beam L and the frequency of the pulse. The color change range H is defined as the region where the luminance in the captured image is 53 [%] or less compared to the general region in the vicinity of the edge 10a. The general region refers to a region in the metal foil 10 to be cut that is less affected by the cutting with the laser beam L. For example, a location more than 1000 [μm] away from the edge 10a can be defined as the general region.

[0071] As shown in FIG. 16, for the frequency, it is found that it is preferably (good or better) 0 [kHz] or more and 1 [MHz] or less. For the irradiation energy, it is preferably (good) 0.03 [J / mm] or more and less than 1.0 [J / mm], and more preferably (best) 0.8 [J / mm] or less.

[0072] As described above, according to the present embodiment, in the laser cutting method of the metal foil constituting the negative electrode of the battery, by appropriately setting the frequency of the pulse, the irradiation energy, the peak output, the overlap ratio, etc., the protrusion D in the thickness direction at the edge 10a, the protrusion P in the direction along the surface Wa at the edge 10a, and the formation or increase of the color change range H can be suppressed. Therefore, according to the present embodiment, laser cutting of higher quality metal foil can be realized.

[0073] [Second Embodiment] FIG. 17 is a schematic configuration diagram of a laser cutting apparatus 100A according to the second embodiment. In this embodiment, the optical head 120 has a galvanometer scanner 126 between the collimator lens 121 and the condenser lens 122. The galvanometer scanner 126 has two mirrors 126a. The irradiation direction and irradiation position of the laser beam L change due to the change in the postures of these two mirrors 126a. That is, the laser cutting apparatus 100A can move the irradiation position of the laser beam L and scan the laser beam L without moving the optical head 120. The controller 140 can control the operation of the motor 126b corresponding to each mirror 126a so that the angle (posture) of the mirror 126a changes. Also according to this embodiment, the same operations and effects as those of the first embodiment can be obtained.

[0074] Although the embodiments of the present invention have been illustrated above, the above embodiments are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, replacements, combinations, and changes can be made without departing from the gist of the invention. Also, the specifications (structure, type, direction, type, size, length, width, thickness, height, number, arrangement, position, material, etc.) of each configuration, shape, etc. can be appropriately changed and implemented.

Description of Reference Numerals

[0075] 10... Metal foil 10a... Edge 11... Metal layer 12... Active material layer 100, 100A... Laser cutting apparatus 110... Laser device 120... Optical head 121... Collimator lens 122... Condenser lens 123... DOE 126... Galvanometer scanner 126a... Mirror 126b... Motor 130... Optical fiber 140... Controller A... Overlapping region Ax…Optical axis a…Distance C…Center line D…Projection D a …Beam diameter (spot diameter) D c ,D f …Beam diameter f1, f2…Focal length Dr…Duty ratio E…Irradiation energy H…Variable color range I…Distance L…Laser beam P…Projection Pc…Coated part Pe…Exposed part Pf…Focus position Pn, Pn+1…Irradiation area Pt…Scanning path R…Overlap ratio SD…Scanning direction Tp…Oscillation time W…Workpiece Wa…Surface X…Direction Y…Direction Z…Direction θ1…Beam divergence angle θ2…Beam spread angle

Claims

1. A method for laser cutting a metal foil, comprising intermittently irradiating a metal foil to be processed, which constitutes a negative electrode of a battery, with laser light pulses at a frequency of 500 [kHz] or less to laser cut the processing target, wherein the metal foil has a metal layer made of a copper-based material and an active material layer coated on the surface of the metal layer, wherein the irradiation energy of the laser light is set to 0.03 [J / mm] or more and 0.15 [J / mm] or less, and wherein the height of a protrusion protruding in the thickness direction of the metal foil at the cut edge of the metal foil is set to 5 [μm] or less.

2. The method for laser cutting a metal foil according to claim 1, wherein the frequency is 100 [kHz] or more.

3. The method for laser cutting a metal foil according to claim 1 or 2, wherein the thickness of the metal foil is 500 [μm] or less.

4. The method for laser cutting a metal foil according to any one of claims 1 to 3, wherein the metal foil has a portion covered with a film and a portion not covered with a film.

5. The method for laser cutting a metal foil according to any one of claims 1 to 4, wherein the spot diameter of the laser light is 100 [μm] or less.

6. The method for laser cutting a metal foil according to claim 5, wherein the spot diameter of the laser light is 50 [μm] or less.

7. The method for laser cutting a metal foil according to claim 6, wherein the spot diameter of the laser light is 28 [μm] or less.

8. When the overlap ratio R between the irradiation region of the pulse and the irradiation region of the next pulse is defined by the following formula (1): R = L2 / L1... (1) where: L1: the length in the scanning direction of the irradiation region, L2: when the pulse and the next pulse overlap in the scanning direction, the length in the scanning direction of the overlapping region between the pulse and the next pulse; when the pulse and the next pulse are in contact in the scanning direction, 0; when the pulse and the next pulse are separated by a distance I (>0) in the scanning direction, -I, the method for laser cutting a metal foil according to any one of claims 1 to 7, wherein the overlap ratio R is 24 [%] or more.

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