Laser cutting method and pole piece manufacturing method

Abstract

The embodiment of the invention provides a laser cutting method and a pole piece manufacturing method. The laser cutting method comprises the steps that a pole piece base material is cut off through a laser device along a cutting path, the cutting path is perpendicular to the moving direction of the pole piece base material, and the number of times of cutting is 60-100; and after the cutting step, the pole piece base material is repaired through the laser device along the cutting path, and the number of times of cutting is 40-100. According to the laser cutting method, the same cutting path of the pole piece is repeatedly cut through the laser device, and in the continuous cutting process, burrs and molten beads on the cutting section of the pole piece are gradually melted till disappearing at the high temperature. And the cutting quality of the pole piece is improved, so that the production yield of the battery monomer can be improved.

Description

Technical Field

[0001] The disclosed embodiments relate to the technical field of battery production, and in particular to a laser cutting method and a pole piece manufacturing method. Background Art

[0002] With the rapid development of the battery industry in recent years, the requirements for battery production quality have become increasingly stringent. A battery cell is the smallest unit that provides an energy source in a battery, which includes a battery cell. The battery cell includes a pole piece, which is a lithium iron phosphate or lithium iron cobalt oxide material evenly coated on both sides of a copper foil (negative electrode) and an aluminum foil (positive electrode), and then the pole piece is cut into a specific shape by a cutting device. At present, some domestic manufacturers mostly use hardware knife dies to cut pole pieces. The pole pieces cut by hardware knife dies have more burrs, severe powder loss during cutting, and more dust, which greatly affects the application of battery pole pieces. The maintenance cost of hardware knife dies is high, and there is also a risk of material loss on the edges. During maintenance, the machine needs to be shut down to repair the knife, which increases the maintenance cost of the equipment in the later stage. In addition, the hardware knife die device occupies a large space in the factory and has high labor costs. Summary of the invention

[0003] The embodiments of the present application provide a laser cutting method and a pole piece manufacturing method, which can improve the cutting quality of the pole pieces of a battery, thereby improving the production yield of battery cells.

[0004] In a first aspect, an embodiment of the present application provides a laser cutting method comprising: a step of cutting a pole piece substrate along a cutting path by a laser, wherein the cutting path is perpendicular to a direction in which the pole piece substrate moves, and the number of cutting times is 60 to 100 times;

[0005] After the cutting step, the electrode substrate is repaired along the cutting path by the laser, and the number of cutting times is 40 to 100 times.

[0006] The laser cutting method of the present application utilizes a laser to repeatedly cut the same cutting path of the pole piece substrate. During the continuous cutting process, the uneven cut section of the pole piece substrate is gradually flattened under the high temperature of the laser, thereby improving the cutting quality of the pole piece substrate, thereby improving the production yield of the battery cell.

[0007] On the other hand, an embodiment of the present application provides a method for manufacturing a pole piece, including: applying a slurry to a substrate, drying and rolling to form a pole piece substrate, and cutting the pole piece substrate using the above-mentioned laser cutting method. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The accompanying drawings exemplarily illustrate the embodiments and constitute a part of the specification, and together with the text description of the specification, are used to explain the exemplary implementation of the embodiments. The embodiments shown are for illustrative purposes only and do not limit the scope of the claims. In all drawings, the same reference numerals refer to similar but not necessarily identical elements.

[0009] Figure 1 A schematic diagram of a laser cutting method according to an embodiment of the present application;

[0010] Figure 2 A schematic diagram of laser cutting of a pole piece substrate provided in one embodiment of the present application;

[0011] Figure 3 A schematic flow chart of a method for manufacturing a pole piece provided in accordance with an embodiment of the present application.

[0012] Reference numerals:

[0013] 100 - laser; 1 - cutting path; 200 - pole piece substrate; 201 - first edge; 202 - second edge. DETAILED DESCRIPTION

[0014] In order to make the objectives, technical solutions and advantages of the present application more clear, the present application is further described in detail below with reference to the accompanying drawings.

[0015] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to be limiting of the present application. As used in the specification and appended claims of the present application, the singular expressions "a", "an", "said", "above", "the" and "this" are intended to also include expressions such as "one or more", unless there is a clear contrary indication in the context.

[0016] References to "one embodiment" or "a specific embodiment" in this specification mean that one or more embodiments of the present application include a particular feature, structure or characteristic described in conjunction with the embodiment. The terms "include", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized.

[0017] In some related technologies, the battery cell mainly includes a positive electrode sheet, a negative electrode sheet and a separator assembled together in a wound or stacked manner, and a Mylar coating film used to insulate and protect the battery cell assembly. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer, the positive electrode active material layer is coated on the surface of the positive electrode collector, and the positive electrode collector not coated with the positive electrode active material layer is stacked as a positive electrode tab for electrical connection to the positive terminal. The negative electrode sheet includes a negative electrode collector and a negative electrode active material layer, the negative electrode active material layer is coated on the surface of the negative electrode collector, and the negative electrode collector not coated with the negative electrode active material layer is stacked as a negative electrode tab for electrical connection to the negative terminal.

[0018] During the production process, the pole piece needs to be cut according to the battery design structure and specifications. Generally, for wound batteries, the pole piece is divided into strips according to the design width; for laminated batteries, the pole piece is cut into pieces accordingly. At present, the following three processes are mainly used for cutting lithium-ion battery pole pieces: disc shear cutting, die punching and laser cutting.

[0019] During the electrode cutting process, the quality of the electrode cutting edge has an important impact on the battery performance and quality, including: burrs and impurities will cause short circuits in the battery, causing self-discharge or even thermal runaway; poor dimensional accuracy, unable to ensure that the negative electrode completely wraps the positive electrode, or the diaphragm completely separates the positive and negative electrode pieces, causing battery safety problems; thermal damage to the material, coating shedding, etc., causing the material to lose activity and be unable to function; uneven cutting edges cause uneven charging and discharging of the electrode. Therefore, the electrode cutting process needs to avoid these problems and improve process quality.

[0020] In view of this, the embodiments of the present application provide a laser cutting method and a pole piece manufacturing method to improve the pole piece cutting quality and reduce the number of burrs and molten beads. The embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0021] Figure 1 A schematic diagram of a laser cutting method according to an embodiment of the present application is provided. Figure 2 A schematic diagram of laser cutting of a pole piece substrate provided in one embodiment of the present application. Figure 1 and Figure 2 As shown, a laser cutting method provided in an embodiment of the present application includes the following steps:

[0022] S1: cutting the pole piece substrate 200 along a cutting path 1 by a laser 100, the number of cuttings being 60 to 100. The cutting path 1 is perpendicular to a moving direction M of the pole piece substrate 200.

[0023] S2: After the cutting step, the pole piece is repaired along the cutting path 1 by the laser 100, and the number of cutting times is 40 to 100 times to obtain a pole piece.

[0024] The principle of laser cutting is to use a high-power density laser beam 101 to irradiate the surface of the material to be cut, so that the material quickly melts, vaporizes or reaches the ignition point, and at the same time blows away the melted or burning material with a high-speed airflow, thereby realizing the cutting process. During the laser cutting process, the laser beam is focused into a very small light spot by a lens. The power density at the focus is very high, which can quickly heat the material to the vaporization temperature and evaporate to form holes. As the laser beam and the material move relative to each other, the holes continuously form narrow slits, completing the cutting of the material.

[0025] The cutting step in S1 above can be understood as rough cutting of the pole piece substrate 200, and the repairing step in S2 above refers to fine-tuning of the pole piece obtained after rough cutting. Among them, the cutting path 1 is perpendicular to the direction of movement of the pole piece substrate 200. In step S1, after one cutting, the cross-section of the pole piece substrate 200 is uneven, and there are obvious melt beads and burrs on the uneven cross-section. After 60 to 100 cuttings, the surface melt beads and burrs are greatly reduced, but still exist. In step S2, after another 40 to 100 cuttings, the melt beads and burrs are significantly reduced, and the cross-section of the pole piece is more delicate.

[0026] In the above embodiment, the same cutting path 1 of the electrode substrate 200 is repeatedly cut by the laser 100. During the continuous cutting process, the burrs and molten beads on the uneven cross-section of the electrode are gradually melted and disappear at high temperature, thereby improving the cutting quality of the electrode and thus improving the production yield of the battery cell.

[0027] In one embodiment, in both the cutting step and the repairing step, the laser 100 cuts back and forth along the cutting path 1. Specifically, the pole piece substrate 200 includes a first edge 201 and a second edge 202 opposite to each other, and the cutting path 1 is a line connecting any point A on the first edge 201 and any point B on the second edge 202, and the line is perpendicular to the moving direction of the pole piece substrate 200. The light spot formed by the laser beam 101 emitted by the laser 100 moves back and forth between point A and point B, that is, from point A to point B, and then from point B to point A.

[0028] The product quality of the laser cutting method of the present application is 180PPM to 200PPM. PPM (Parts Per Million) is a unit of measurement used to evaluate the quality level in a product or process. It indicates the number of defects per million units. The lower the PPM value, the higher the quality of the product and the higher the production efficiency. Compared with the product quality of 180PPM using a hardware die cutter, the pole piece production yield rate cut by the laser cutting method of the present application is higher.

[0029] It is worth noting that each cutting in the above laser cutting method completely cuts off the pole piece. Repeated cutting along the same cutting path 1 can gradually eliminate the molten beads and burrs, making the cut section smooth.

[0030] In one embodiment, the pole piece substrate 200 remains stationary during cutting. After the repairing step is completed, the conveyor belt drives the pole piece substrate 200 to move at a speed of 140 m / min to 160 m / min, thereby improving the processing efficiency of the pole piece.

[0031] Since the lithium-ion battery pole piece is a combination of a double-sided coating and an intermediate current collector metal layer, and the properties of the coating and the metal foil are very different, the response to the laser is also different. When the laser acts on the negative electrode graphite layer or the positive electrode active material layer, they have a high laser absorption rate and a low thermal conductivity. Therefore, these coatings require relatively low melting and vaporization laser energy, while the metal current collector has a reflective effect on the laser and has fast heat conduction, so the melting and vaporization laser energy of the metal layer increases. When the laser acts on the graphite layer, due to the characteristics of the material, the graphite is mainly vaporized. When the laser invades the metal copper foil, the copper foil begins to melt and form a molten pool. When the process parameters are not appropriate, the cutting edge coating may fall off, exposing the metal foil; or a large amount of cutting chips and foreign matter may appear around the cutting edge. These will lead to performance degradation, safety and quality problems of the battery.

[0032] In one embodiment, the above-mentioned electrode substrate 200 includes a positive electrode substrate and a negative electrode substrate. The positive electrode substrate is often made of lithium nickel cobalt manganese oxide (LiNiCoMnO2), lithium iron phosphate (LiFePO4), lithium acid (LiCoO2), and lithium manganese oxide (LiMn2O4). The negative electrode substrate is often made of graphite, soft carbon, and hard carbon. Therefore, the positive electrode substrate requires higher laser energy to achieve vaporization and melting. The negative electrode substrate requires lower laser energy to achieve vaporization and melting. The above-mentioned laser 100 includes a picosecond laser and a nanosecond laser. The positive electrode substrate is cut by a picosecond laser, and the negative electrode substrate is cut by a nanosecond laser. In this way, both types of electrode substrates 200 can form good cutting edge quality without residual metal chips and impurities. In addition, due to the high cost of picosecond lasers, only the positive electrode substrate is cut by a picosecond laser, which can reduce production costs.

[0033] In other embodiments, the negative electrode substrate may also be cut using a picosecond laser.

[0034] To improve cutting efficiency, the positive electrode substrate and the negative electrode substrate can be respectively arranged on both sides of the workbench, with a picosecond laser being arranged on the side where the positive electrode substrate is located and a nanosecond laser being arranged on the side where the negative electrode substrate is located. The positive electrode substrate and the negative electrode substrate are cut simultaneously.

[0035] In one embodiment, the total number of cutting times in the cutting step and the repairing step is 120 to 180. After reaching the above number of cutting times, a pole piece with a relatively flat and smooth cross section can be obtained.

[0036] Cutting speed refers to the length that a laser cutting machine can cut per unit time. The faster the speed, the higher the efficiency. Cutting speed is related to the type, thickness, hardness, etc. of the material, and is also affected by factors such as laser power and spot diameter. Under certain power conditions, the thicker the pole piece, the slower the cutting speed. There is a parabolic relationship between the surface roughness of the cut and the cutting speed (the parabola opens upward). There is an optimal cutting speed for the surface roughness of the cut and the cutting speed, which minimizes the surface roughness of the cut.

[0037] In one embodiment, the cutting speed of the picosecond laser in the cutting step may be 28000 mm / s to 32000 mm / s, and the cutting speed of the picosecond laser in the repairing step may be 22000 mm / s to 26000 mm / s.

[0038] In one embodiment, the cutting speed of the nanosecond laser in the cutting step is 18000 mm / s to 22000 mm / s, and the cutting speed of the nanosecond laser in the repairing step is 12000 mm / s to 16000 mm / s.

[0039] In some of the above embodiments, the cutting speed of the laser in the repairing step is slower than that in the cutting step, which is conducive to the solidification of the molten beads. After the molten beads solidify, the size is smaller. During the blowing, it is easy to be blown away by the auxiliary gas.

[0040] Laser power is an important factor in determining the cutting effect. The higher the power, the faster the cutting speed and the greater the cutting depth. In one embodiment, the output power of the picosecond laser in the cutting step is 280W to 320W, and the output power in the repairing step is 260W to 280W. The output power of the nanosecond laser in the cutting step is 180W to 220W, and the output power in the repairing step is 160W to 180W. In the repairing step, the laser power is small, the heat generated is weak, and no more molten beads are generated.

[0041] In one embodiment, the defocus of the picosecond laser is -2mm to 2mm, and the defocus of the nanosecond laser is -1mm to 1mm. The defocus range of the picosecond laser is set to be larger because the picosecond cutting speed is faster and the defocus has less effect on the picosecond cutting.

[0042] In a specific embodiment, the defocus amount of the picosecond laser and nanosecond laser is preferably 0.

[0043] In one embodiment, during the laser cutting process, blowing auxiliary gas helps to blow away the molten or vaporized material, protect the cutting head from smoke and dust, and thus improve the cutting quality. The gas type and flow rate vary depending on the material and thickness. For example, air, oxygen, and nitrogen can be used. The gas pressure is 0.5 MPa to 0.8 MPa, which can improve the cutting quality and efficiency.

[0044] The spot diameter refers to the diameter of the laser beam on the object. The smaller the diameter, the finer the focus and the higher the precision. In one embodiment, the spot diameter is 0.1 mm to 0.4 mm.

[0045] The focal position has a great influence on the incision width. Generally, the focal point is selected to be about 1 / 3 of the thickness below the pole piece surface to obtain the maximum cutting depth and the minimum incision width.

[0046] In one embodiment, for pulse laser cutting, the selection of pulse frequency and duty cycle will affect the cutting quality and efficiency. Appropriate pulse frequency and duty cycle can optimize the cutting process. The pulse frequency used by the above laser 100 can be 3000khz-5000khz, and the duty cycle can be 40% to 50%.

[0047] Figure 3 A schematic diagram of a process flow of a pole piece manufacturing method provided in one embodiment of the present application. Figure 3As shown, on the other hand, an embodiment of the present application further provides a method for manufacturing a pole piece, the method for manufacturing a pole piece comprising:

[0048] S10: Apply the slurry to the substrate.

[0049] The substrate can be copper foil or aluminum foil. The slurry is a mixture of electrode active material and binder. The slurry is applied to the substrate by a coating machine.

[0050] Among them, the electrode active material includes a positive electrode active material and a negative electrode active material. The positive electrode active material may include one or more of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese oxide, nickel cobalt aluminum, lithium cobalt oxide, and lithium titanate. The negative electrode active material may include one or more of a graphite active material, a silicon carbon active material, or a silicon oxide active material. The binder may include one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinyl alcohol, polyacrylate, silicone resin, epoxy resin, polyurethane, phenolic resin, polyimide resin, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, and acrylonitrile multipolymer.

[0051] S20: Drying and rolling the substrate coated with the slurry to form a pole piece substrate.

[0052] The drying temperature can be 40° C. to 100° C., and the thickness of the electrode substrate after rolling is in the range of 30 μm to 200 μm.

[0053] S30: using the laser cutting method in any of the above embodiments to cut the pole piece substrate to obtain the pole piece.

[0054] Although the embodiments or examples of the present disclosure have been described with reference to the accompanying drawings, it should be understood that the above methods are merely exemplary embodiments or examples, and the scope of the present application is not limited by these embodiments or examples, but is limited only by the authorized claims and their equivalents. Various elements in the embodiments or examples may be omitted or replaced by their equivalents. In addition, each step may be performed in an order different from that described in the present application. Further, the various elements in the embodiments or examples may be combined in various ways. It is important that with the evolution of technology, many of the elements described herein may be replaced by equivalent elements that appear after the present disclosure.

Claims

1. A laser cutting method, characterized in that: The laser cutting method comprises: The step of cutting the pole piece substrate along a cutting path by a laser, wherein the cutting path is perpendicular to the direction in which the pole piece substrate moves, and the number of cutting times is 60 to 100 times; After the cutting step, the pole piece substrate is repaired along the cutting path by the laser, and the number of cutting times is 40 to 100 times.

2. The laser cutting method according to claim 1, characterized in that: The electrode substrate includes a positive electrode substrate and a negative electrode substrate, the laser includes a picosecond laser and a nanosecond laser, the positive electrode substrate is cut by the picosecond laser, and the negative electrode substrate is cut by the nanosecond laser; The positive electrode sheet substrate and the negative electrode sheet substrate are cut simultaneously.

3. The laser cutting method according to claim 1, characterized in that: The total number of cuttings in the cutting step and the repairing step is 120 to 180 times.

4. The laser cutting method according to claim 2, characterized in that: The cutting speed of the picosecond laser in the cutting step is 28000 mm / s to 32000 mm / s; the cutting speed of the picosecond laser in the repairing step is 22000 mm / s to 26000 mm / s.

5. The laser cutting method according to claim 2, characterized in that: The cutting speed of the nanosecond laser in the cutting step is 18000 mm / s to 22000 mm / s; the cutting speed of the nanosecond laser in the repairing step is 12000 mm / s to 16000 mm / s.

6. The laser cutting method according to claim 2, characterized in that: In the cutting step, the laser cuts back and forth along the cutting path; in the repairing step, the laser cuts back and forth along the cutting path.

7. The laser cutting method according to claim 2, characterized in that: The output power of the picosecond laser in the cutting step is 280W to 320W, and the output power in the repairing step is 260W to 280W.

8. The laser cutting method according to claim 2, characterized in that: The output power of the nanosecond laser in the cutting step is 180W to 220W, and the output power in the repairing step is 160W to 180W.

9. The laser cutting method according to claim 2, characterized in that: The defocusing amount of the picosecond laser is -2 mm to 2 mm, and the defocusing amount of the nanosecond laser is -1 mm to 1 mm.

10. The laser cutting method according to claim 1, characterized in that: After the repairing step is completed, the pole piece substrate moves at a speed of 140 m / min to 160 m / min.

11. A method for manufacturing a pole piece, characterized in that: The slurry is applied to a substrate, dried and rolled to form a pole piece substrate, and the pole piece substrate is cut by the laser cutting method according to any one of claims 1 to 10.

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