A method for relieving stress of a pole piece and a pole piece

Abstract

The present invention discloses a method for relieving stress of a pole piece, which belongs to the field of lithium battery manufacturing. The method comprises: opening and tensioning a warped pole piece; controlling a laser spot to act on a coating layer of the warped pole piece, wherein the spot is a non-focused spot. The pole piece stress relief method provided by the present invention removes stress by heating the pole piece with a laser, then applies the basic condition of physical tension, and then uses a customized laser to take different paths to achieve the release of the warping stress from local to overall. After thermal annealing to relieve stress, the pole piece warping degree is greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of lithium battery manufacturing, and in particular relates to a method for relieving stress of a pole piece and a pole piece. Background Art

[0002] Lithium-ion batteries have been widely used in consumer digital products, electric vehicles, energy storage and other fields in recent years due to their advantages such as high energy density, no memory effect and low environmental pollution.

[0003] In order to achieve the ultimate thinning of the thickness of the negative-pack positive battery during production, some battery manufacturers will perform a single-sided coating process on the two outermost non-reactive electrode layers. However, the electrode layers prepared by the single-piece coating process will usually suffer from severe warping after rolling due to uneven stress, which makes the subsequent battery packaging process more difficult.

[0004] In the prior art, the warpage of the pole piece is usually reduced by mechanical means, but the mechanical method can only control the failure rate of the pole piece to a certain proportion, and there is still a large warpage. Summary of the invention

[0005] The present invention provides a method for relieving stress of a pole piece and a pole piece, and the solution can effectively reduce the warping of the pole piece.

[0006] To achieve the above object, the embodiments of the present invention adopt the following technical solutions:

[0007] In a first aspect, the present invention provides a method for relieving stress of a pole piece, wherein the pole piece has a substrate layer and a coating layer, and the method for relieving stress of the pole piece comprises:

[0008] Open and tension the warped pole piece;

[0009] The laser spot is controlled to act on the coating layer of the warped pole piece, wherein the laser spot is a non-focused spot.

[0010] In some embodiments of the present invention, the parameters of the laser and the light spot include but are not limited to:

[0011] The spot size is 8-12mm, the power is 200-600W, the pulse width is 400-600ns, the frequency is 200-300KHZ and the spacing is 2-6mm.

[0012] In some embodiments of the present invention, the light spot acting on the coating layer of the warped pole piece includes:

[0013] The light spot moves along a preset path on the coating layer of the warped pole piece.

[0014] In some embodiments of the present invention, the moving along a preset path includes but is not limited to:

[0015] Move along a straight path in the length direction of the warped pole piece, move along the width direction of the warped pole piece, move along a grid path on the surface of the warped pole piece, move along an oblique path on the surface of the warped pole piece, and move along a composite path on the surface of the warped pole piece.

[0016] In some embodiments of the present invention, the movement speed of the pole piece is 0.5-3 m / s.

[0017] In some embodiments of the present invention, the opening and tensioning of the warped pole piece comprises:

[0018] The first tension roller and the second tension roller located on both sides of the warped pole piece are driven to tighten the warped pole piece.

[0019] In some embodiments of the present invention, after opening and tensioning the warped pole piece, the method further comprises:

[0020] A pressure different from the direction of the tensioning force is applied to the coating layer of the warped pole piece.

[0021] In some embodiments of the present invention, applying a pressure different from the direction of the tensioning force to the coating layer of the warped pole piece comprises:

[0022] A third tension roller is arranged on one side of the coating layer of the warped pole piece, and when the warped pole piece is tensioned, the coating layer of the warped pole piece presses the third tension roller.

[0023] In a second aspect, the present invention further provides a pole piece, which is prepared by the pole piece stress relief method as described in any one of the first aspects.

[0024] In the solution provided by the present invention, the pole piece is first mounted on the third roller, and the first roller as the main driving roller will give tension, so that the coating layer of the pole piece is close to the third roller and is tightened by the tension. The first roller and the second roller as tension devices can prevent lateral sliding and winding, and the third roller can better make the warped pole piece flat after being irradiated by the laser. After confirming that the pole piece is taut, the laser is turned on, and reverse stress is induced during the process of stress release, so that the pole piece can finally achieve the effect of improving warping.

[0025] According to some embodiments of the present invention, increasing the tension of the warped pole piece includes straightening the warped pole piece by applying mechanical tension on a tension roller.

[0026] In the solution provided by the present invention, a single-sided coated electrode roll is placed on a tension roller, the electrode is straightened using mechanical tension, and then moved at a constant speed. The relevant laser module is built so that the laser center acts vertically on the middle position of the electrode to ensure that the working area can reasonably cover the processing area.

[0027] In a second aspect, the present invention provides a pole piece obtained by the method described in any one of the first aspects.

[0028] The beneficial effects of the present invention compared with the prior art are:

[0029] The pole piece stress relief method provided by the present invention uses the basic principle of laser heating to remove stress, then adds the basic condition of physical tension, and then uses customized lasers to take different paths to achieve the release of warping stress from local to overall. After laser thermal annealing to remove stress, there is a great improvement in the pole piece warping.

[0030] The pole piece stress relief method provided by the present invention is highly flexible and can improve the pole piece warping phenomenon by changing different light spot energy distributions or scanning paths.

[0031] In the pole piece stress relief method provided by the present invention, the metal foil undergoes phase change and recrystallization during the heating and cooling process, and the stress release is solved from the root, without causing contact damage to the pole piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0033] Figure 1 A schematic diagram of the pole piece warping and laser irradiation direction provided in an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of a pole piece tension straightening structure provided in an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of different pattern paths of the laser spot provided in an embodiment of the present invention;

[0036] Figure 4 A schematic diagram of the physical bending structure of a pole piece provided in an embodiment of the present invention;

[0037] Figure 5 A schematic diagram of laser thermal annealing of a pole piece provided in an embodiment of the present invention;

[0038] Figure 6 A schematic diagram of a warped pole piece provided in an embodiment of the present invention;

[0039] Figure 7 This is a diagram showing the improvement effect of pole piece warpage after stress induction by a third tension roller and stress relief by laser irradiation provided in an embodiment of the present invention.

[0040] The reference numerals in the figures are:

[0041] 10. Warping pole piece; 1. Base material layer; 2. Coating layer; 3. First tension roller; 4. Second tension roller; 5. Third tension roller; 6. Laser module. DETAILED DESCRIPTION

[0042] The following description provides specific application scenarios and requirements of this specification, with the purpose of enabling those skilled in the art to make and use the contents of this specification. Various local modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of this specification. Therefore, this specification is not limited to the embodiments shown, but to the widest scope consistent with the claims.

[0043] The terms used herein are only used for the purpose of describing specific example embodiments and are not restrictive. For example, unless the context clearly indicates otherwise, as used herein, the singular forms "a", "an" and "the" may also include plural forms. When used in this specification, the terms "include", "comprise" and / or "contain" mean that the associated integers, steps, operations, elements and / or components exist, but do not exclude the existence of one or more other features, integers, steps, operations, elements, components and / or groups or that other features, integers, steps, operations, elements, components and / or groups may be added in the system / method.

[0044] In the present invention, the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal" and the like are based on the directions or positional relationships shown in the drawings. These terms are mainly used to better describe the present invention and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific direction, or to be constructed and operated in a specific direction.

[0045] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those skilled in the art, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

[0046] In addition, the terms "installed", "set", "provided with", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] In view of the following description, these and other features of the present specification, as well as the operation and function of the related elements of the structure, and the economy of the combination and manufacture of the parts can be significantly improved. Reference is made to the accompanying drawings, all of which form a part of this specification. However, it should be clearly understood that the drawings are for illustration and description purposes only and are not intended to limit the scope of this specification. It should also be understood that the drawings are not drawn to scale.

[0048] Lithium-ion batteries have been widely used in consumer digital products, electric vehicles, energy storage and other fields in recent years due to their advantages such as high energy density, no memory effect and low environmental pollution.

[0049] In order to achieve the ultimate thinning of the thickness of the negative-pack positive battery during production, some battery manufacturers will perform a single-sided coating process on the two outermost non-reactive electrode layers. However, the electrode layers prepared by the single-piece coating process will usually suffer from severe warping due to uneven stress after rolling, which makes the subsequent battery packaging process more difficult.

[0050] The existing technology uses mechanical means to reduce the pole piece warping, but the mechanical method can only control the pole piece dead bending defect to a certain proportion, and there is still a large warping, which cannot be completely eliminated.

[0051] like Figure 1-Figure 7 As shown, the present invention provides a method for relieving stress of a pole piece, comprising opening and tensioning a warped pole piece 10; controlling a laser spot to act on a coating layer 2 of the warped pole piece 10, wherein the laser spot is a non-focused spot.

[0052] The pole piece stress relief method provided by the present invention utilizes the principle of laser heating to remove stress. By controlling the laser spot to move along different paths on the coating layer 2 of the warped pole piece 10, the warped pole piece 10 is heated to achieve the release of the warping stress of the warped pole piece 10 from local to overall.

[0053] The following takes the warping of the electrode 10 with the single-sided coating layer 2 as an example. Figure 1 The figure shows the schematic diagram of the pole piece warping and the direction of laser irradiation. The pole piece 10 with the single-sided coating layer 2 warping will be stretched to a certain extent during the rolling process. The elongation rate of the active material and the elongation rate of the current collector are different. Due to the difference in elongation rate between the two, the side of the pole piece 10 with the single-sided coating layer 2 warping with the active material will be warped. The warping direction is from the coating layer 2 where the active material is located to the substrate layer 1 where the metal foil is located. Therefore, when laser stress relief is performed, the laser irradiation is best on the surface of the coating layer 2.

[0054] It should be noted that the above embodiment is described by taking the warped pole piece 10 with a single-sided coating layer 2 as an example. In other implementations, a warped pole piece 10 with double-sided coating but different elongation rates of active materials on both sides can also be selected. Correspondingly, the direction of laser irradiation can be selected to be the side where the warping occurs, thereby achieving stress release for the double-sided coated warped pole piece 10.

[0055] like Figure 2 As shown, it is a schematic diagram of the tension straightening structure of the warped pole piece 10. The single-sided coating layer 2 warped pole piece 10 is opened and placed on the tension roller. The tension roller includes a first tension roller 3 and a second tension roller 4. The first tension roller 3 is the main drive roller, which can provide tension to tighten the warped pole piece 10, and together with the second tension roller 4, realize the opening and tensioning of the warped pole piece 10. After the warped pole piece 10 is tensioned, the laser module 6 built above the tension roller controls the galvanometer to move on the tensioned warped pole piece 10 to achieve stress release of the warped pole piece 10. The movement speed of the pole piece on the tension roller is 0.5-3m / s. Preferably, in this embodiment, the movement speed of the pole piece is 1m / s. It can be understood that in other embodiments, other devices for providing tension can be selected, such as vacuum rollers, tension dual-loop controllers, hydraulic tensioning machines, etc., to achieve the opening and tensioning of the warped pole piece 10.

[0056] It should be noted that after the first tension roller 3 and the second tension roller 4 use mechanical tension to straighten the warped pole piece 10, the warped pole piece 10 moves uniformly on the tension roller at a certain speed. At the same time, the laser module 6 can control the spot of the laser center to act vertically on the middle position of the pole piece, ensuring that the working area of ​​the laser can reasonably cover the processing area of ​​the pole piece 10, and at the same time facilitate the control of the path and working area of ​​the laser spot.

[0057] In this embodiment, the laser module 6 uses a larger non-focused spot to disperse the energy. The spot cannot be too large or too small. The appropriate energy density can significantly release the stress of the metal foil after heating, and the warping is improved, while not causing damage to the metal foil or the coating layer 2. The parameters of the laser / spot are a laser spot size of 15mm, a laser power of 450W, a pulse width of 550ns, a frequency of 300KHZ, and a spacing of 5mm. The laser module 6 controls the laser to a non-focused spot and irradiates it on the warped pole piece 10, controls the heating time to be 1s, and the heat preservation time to be 10s.

[0058] like Figure 3As shown, it is a schematic diagram of different pattern paths. The pattern path refers to the preset path when the light spot moves on the coating layer 2 of the warped pole piece 10. Different pattern paths can be given a control card signal by the host computer, and the control card controls the galvanometer to move along the pattern path, and synchronously enables the laser to emit light synchronously. In this process, appropriate process parameters are adjusted to improve the warpage.

[0059] The movement of the galvanometer along the pattern path includes moving along a straight path in the length direction of the warped pole piece 10, moving along the width direction of the warped pole piece 10, moving along a grid path on the surface of the warped pole piece 10, moving along an oblique path on the surface of the warped pole piece 10, and moving along a composite path on the surface of the warped pole piece 10.

[0060] In order to make the warped pole piece 10 smoother after being irradiated by laser, after the warped pole piece 10 is tensioned by a tension roller, a stress-inducing operation is performed on the warped pole piece 10 .

[0061] It should be noted that stress induction refers to applying external stress to the warped pole piece 10 so that the internal structure of the warped pole piece 10 changes. Stress induction can be in various forms, for example, by torsion or preload. Figure 4 As shown, it is a schematic diagram of the physical bending structure of the warped pole piece 10, which is realized by the third tension roller 5. The warped pole piece 10 is placed on it. In order to better alleviate the warping, the bending direction of the warped pole piece 10 is opposite to the stress direction, that is, the third tension roller 5 contacts the coating layer 2 of the warped pole piece 10 and applies a pressure different from the direction of the tensioning force.

[0062] like Figure 5 As shown, it is a schematic diagram of laser thermal annealing of the pole piece, which combines the physically bent third tension roller 5 with laser heating, firstly sets the warped pole piece 10 on the third tension roller 5, then provides tension by the first tension roller 3 and the second tension roller 4, makes the material close to the third tension roller 5 and tightened by the tension, then pushes the galvanometer to move the coating layer 2 of the pole piece 10 to release the stress of the pole piece 10. In the process of stress release, the third tension roller 5 applies reverse stress induction, and finally makes the warped pole piece 10 have the effect of improving the warpage.

[0063] like Figure 6 and Figure 7 As shown, it is a schematic diagram of the warped pole piece and a diagram of the improvement effect of the pole piece warping after physical bending by the third tension roller and stress relief by laser irradiation. It can be seen that the warping phenomenon of the warped pole piece 10 after tensioning by the first tension roller, the second tension roller, stress induction by the third tension roller and laser stress relief treatment has been greatly improved, and the warping degree of the warped pole piece 10 after treatment has been significantly reduced.

[0064] In addition, the present invention also provides a pole piece, such as Figure 7 As shown, it is prepared by the above-mentioned pole piece stress relief method.

[0065] The pole piece provided by the present invention is prepared by the pole piece stress relief method described in the above embodiment, so its warping degree is smaller than that of the warped pole piece.

[0066] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for relieving stress of a pole piece, wherein the pole piece has a substrate layer and a coating layer, characterized in that: The method for relieving stress of the pole piece comprises: Open and tension the warped pole piece; The laser spot is controlled to act on the coating layer of the warped pole piece, wherein the laser spot is a non-focused spot.

2. The method for relieving stress of a pole piece according to claim 1, characterized in that: The parameters of the laser and the spot include but are not limited to: The spot size is 8-12mm, the power is 200-600W, the pulse width is 400-600ns, the frequency is 200-300KHZ and the spacing is 2-6mm.

3. The method for relieving stress of a pole piece according to claim 1, characterized in that: The light spot acts on the coating layer of the warped pole piece, including: The light spot moves along a preset path on the coating layer of the warped pole piece.

4. The method for relieving stress of a pole piece according to claim 3, characterized in that: The movement along the preset path includes but is not limited to: Move along a straight path in the length direction of the warped pole piece, move along the width direction of the warped pole piece, move along a grid path on the surface of the warped pole piece, move along an oblique path on the surface of the warped pole piece, and move along a composite path on the surface of the warped pole piece.

5. The method for relieving stress of a pole piece according to claim 3, characterized in that: The movement speed of the pole piece is 0.5-3m / s.

6. The method for relieving stress of a pole piece according to claim 1, characterized in that: The opening and tensioning of the warped pole piece comprises: The first tension roller and the second tension roller located on both sides of the warped pole piece are driven to tighten the warped pole piece.

7. The method for relieving stress of a pole piece according to claim 1, characterized in that: After opening and tensioning the warped pole piece, the method further comprises: A pressure different from the direction of the tensioning force is applied to the coating layer of the warped pole piece.

8. The method for relieving stress of a pole piece according to claim 7, characterized in that: The step of applying a pressure different from the tension force direction to the coating layer of the warped electrode comprises: A third tension roller is arranged on one side of the coating layer of the warped pole piece, and when the warped pole piece is tensioned, the coating layer of the warped pole piece presses the third tension roller.

9. A pole piece, characterized in that: The method for relieving stress of a pole piece as described in any one of claims 1 to 8 is prepared.

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