Electrode for secondary battery and method for manufacturing electrode for secondary battery

Abstract

The present disclosure relates to an electrode of a secondary battery and a method for manufacturing an electrode of a secondary battery. The electrode of a secondary battery according to one embodiment of the present disclosure includes: an electrode current collector including a coated portion and an uncoated portion; and an active material layer located on the coated portion of the electrode current collector, wherein a recessed portion is formed on the surface of the uncoated portion, and a plastic deformation layer is formed on the surface of the recessed portion.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2019-0160898 filed on December 5, 2019, and Korean Patent Application No. 10-2020-0143369 filed on October 30, 2020, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference.

[0003] The present disclosure relates to an electrode of a secondary battery and a method of manufacturing the electrode of a secondary battery, and more particularly, to a rolling device and a rolling method for a secondary battery that improve stress resistance of an uncoated portion. Background Art

[0004] A secondary battery may be formed by inserting an electrode assembly consisting of a positive electrode plate, a negative electrode plate, and a separator into a housing and then sealing the housing. A positive electrode plate or a negative electrode plate (hereinafter referred to as an "electrode plate") may be formed by coating an active material slurry to a predetermined thickness on a positive electrode conductive collector or a negative electrode conductive collector, and an electrode assembly may be formed by inserting a separator between the positive electrode plate and the negative electrode plate and winding the electrode plate multiple times in a jelly roll type or laminating the electrode plate in multiple layers.

[0005] The electrode plate may be formed of an active material coating layer coated with an active material slurry and an uncoated portion. The active material coating layer may be subjected to a rolling process to increase adhesion to an electrode current collector and increase the volume density of the active material. The rolled electrode plate may be cut into a predetermined size by passing through a cutter having a certain width for use after drying.

[0006] The rolling process has a problem in which a compression deviation occurs due to the thickness difference between the coating layer and the uncoated portion when rolling the electrode plate. Due to this deviation, unbalanced plastic deformation of the electrode current collector occurs, resulting in residual stress. In particular, tensile residual stress can cause a reduction in fatigue durability and a reduction in the fracture strength of the component.

[0007] Figure 1 is a schematic diagram showing a rolling process using a conventional rolling device. Figure 2 is a plan view showing the electrode plate after rolling.

[0008] Reference Figure 1 , a rolling process of rolling the coating layer 30 and the uncoated portion 40 formed on the electrode current collector 20 by rolling the rolling roller 10 may be performed. At this time, the pressure is concentrated on the coating layer 30, such as Figure 2As shown in FIG, a difference is generated between the stretching degree of the coating portion 30P and the stretching degree of the uncoated portion 40, and wrinkles may be generated in the uncoated portion 40. Due to the wrinkles of the uncoated portion 40 generated during rolling, process defects such as electrode disconnection may occur in subsequent processes. In particular, when a high tensile residual stress remains at the interface between the coating portion 30P and the uncoated portion 40, the electrode may continue to receive weak stress due to contraction and expansion, and may become easy to break. Summary of the invention

[0009] Technical issues

[0010] An object of the present disclosure is to provide an electrode for a secondary battery and a method of manufacturing the electrode for a secondary battery in which stress resistance of a non-coated portion is improved.

[0011] However, the problems to be solved by the embodiments of the present disclosure are not limited to the above-mentioned problems, and various extensions can be made within the scope of the technical concept included in the present disclosure.

[0012] Technical Solution

[0013] According to one embodiment of the present disclosure, a method for manufacturing an electrode for a secondary battery is provided, comprising the steps of: coating an active material onto an electrode current collector to form a coated portion and an uncoated portion; and applying compressive residual stress to a surface of the uncoated portion, wherein the step of applying compressive residual stress to the surface of the uncoated portion comprises: a step of performing a shot peening process on the surface of the uncoated portion.

[0014] A step of applying compressive residual stress to the surface of the uncoated portion is performed before a rolling process performed along the moving direction of the electrode current collector, and the rolling process may include at least one of the following processes: a process of rolling the coated portion and the uncoated portion of the electrode current collector, and a process of grooves in the coated portion and the uncoated portion of the electrode current collector.

[0015] The step of applying the compressive residual stress to the surface of the uncoated portion may include the step of performing a shot peening process.

[0016] The step of performing the shot peening process may include the step of forming a concave portion on a surface of the non-coated portion.

[0017] A plastic deformation layer is formed on the surface of the recessed portion such that the plastic deformation layer has a compressive residual stress and an interior of the uncoated portion located outside the plastic deformation layer has a tensile residual stress.

[0018] The step of applying the compressive residual stress to the surface of the non-coated portion may include the step of performing an ultrasonic peening process.

[0019] The step of performing the ultrasonic peening process may include the step of forming a recessed portion on the surface of the non-coated portion.

[0020] After performing the shot blasting process on the surface of the non-coated portion, the method of manufacturing an electrode for a secondary battery may further include heat-treating the electrode current collector.

[0021] According to another embodiment of the present disclosure, an electrode of a secondary battery is provided, comprising: an electrode current collector comprising a coated portion and an uncoated portion; and an active material layer located on the coated portion of the electrode current collector, wherein a recessed portion is formed on a surface of the uncoated portion, and a plastic deformation layer is formed on a surface of the recessed portion.

[0022] The electrode of the secondary battery further includes a plastic deformation layer on a surface of the recessed portion, wherein the plastic deformation layer may have a compressive residual stress, and an interior of the uncoated portion outside the plastic deformation layer has a tensile residual stress.

[0023] Beneficial Effects

[0024] According to an embodiment of the present disclosure, by applying compressive residual stress to the surface of the uncoated portion before the electrode rolling and / or grooving process, the fatigue durability and fracture strength of the material can be improved and the stress resistance can be improved. Therefore, the occurrence of fracture caused by fatigue fracture at the interface between the electrode and the uncoated portion can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram showing a rolling process using a conventional rolling device.

[0026] Figure 2 is a plan view showing the electrode plate after rolling.

[0027] Figure 3 is a perspective view showing a rolling device according to one embodiment of the present disclosure.

[0028] Figure 4 It is a schematic diagram showing the Figure 3 Schematic diagram of the state of the rolling device.

[0029] Figure 5 is a schematic diagram showing a slotting device according to one embodiment of the present disclosure.

[0030] Figure 6 It is shown Figure 4 and Figure 5 Schematic cross-sectional view of the shot peening process.

[0031] Figure 7 is a perspective view showing a shot peening process according to an embodiment of the present disclosure.

[0032] Figure 8 It is shown by Figure 7 A cross-sectional view showing a state where a concave portion is formed by a shot peening process.

[0033] Fig. 9 is a schematic cross-sectional view showing an aging process according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0034] Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement them. The present disclosure can be modified in various different ways and is not limited to the embodiments set forth herein.

[0035] Parts irrelevant to the description will be omitted to clearly describe the present disclosure, and like reference numerals denote like elements throughout the application.

[0036] In addition, in the drawings, for the convenience of description, the size and thickness of each element are arbitrarily shown, and the present disclosure is not necessarily limited to those shown in the drawings. In the drawings, for the sake of clarity, the thickness of layers, regions, etc. are exaggerated. In the drawings, for the convenience of description, the thickness of some layers and regions is exaggeratedly shown.

[0037] In addition, it will be understood that when an element such as a layer, film, region or plate is referred to as being "on" or "above" another element, the element may be directly on the other element or there may be intervening elements. Conversely, when an element is referred to as being "directly on" another element, it means that there are no other intervening elements. In addition, the term "on..." or "above..." refers to being disposed above or below a reference portion, and does not necessarily mean being disposed at the upper end of the reference portion facing the opposite direction of gravity.

[0038] Furthermore, throughout the application, when a part is referred to as “comprising” a certain component, it means that the part may further include other components, without excluding the other components, unless otherwise specified.

[0039] Furthermore, throughout the application, when referred to as a “plane”, it means when the target portion is viewed from the upper side, and when referred to as a “section”, it means when the target portion is viewed from one side of a vertically cut cross section.

[0040] Figure 3 is a perspective view showing a rolling device according to one embodiment of the present disclosure.

[0041] Reference Figure 3 , a method for manufacturing an electrode of a secondary battery according to one embodiment of the present disclosure includes the following steps: coating an active material onto an electrode current collector 300 to form a coated portion 400 and an uncoated portion 500; and applying compressive residual stress to the surface of the uncoated portion 500. At this time, the step of applying compressive residual stress to the surface of the uncoated portion 500 includes the step of performing a peening process on the surface of the uncoated portion 500. When the peening process is performed on the surface of the uncoated portion 500, it is desirable to minimize the physical deformation on the surface of the uncoated portion 500. That is, compressive residual stress must be applied to the surface of the uncoated portion 500 through an action such as quenching through a peening process, which is different from applying a tensile force. According to the present embodiment, through the peening process, there is no physical change on the surface of the uncoated portion 500, or even if there is a physical change, the change can occur uniformly.

[0042] A step of applying compressive residual stress to the surface of the uncoated portion 500 is performed before a rolling process performed along the moving direction of the electrode current collector 300, and the rolling process may include at least one of the following processes: a process of rolling the coated portion 400 and the uncoated portion 500 of the electrode current collector 300, and a process of grooved the coated portion 400 and the uncoated portion 500 of the electrode current collector 300.

[0043] Figure 4 It is a schematic diagram showing the Figure 3 Schematic diagram of the state of the rolling device. Figure 5 is a schematic diagram showing a slotting device according to one embodiment of the present disclosure.

[0044] Reference Figure 3 and Figure 4 , the electrode rolling device 100 according to the embodiment of the present disclosure includes: a first roller 101 for unwinding an electrode plate 250 having a coating portion 400 formed with a coating material on an electrode current collector 300 and an uncoated portion 500 corresponding to an uncoated portion; a second roller 102 for winding the electrode plate 250; and a rolling roller 109, which is located between the first roller 101 and the second roller 102 and rolls the coating portion 400 and the uncoated portion 500 of the electrode plate 250 along a moving direction of the electrode plate 250. The uncoated portion 500 may refer to a region other than the coating portion 400 formed on the electrode current collector 300.

[0045] The first roller 101 provides the electrode plate 250 to be rolled to the rolling device 100, and rotates clockwise along the Figure 4 The electrode plate 250 is moved in the direction of the arrow D1. The electrode plate 250 unwound from the first roller 101 passes between the rolling rollers 109 while moving in the direction of the arrow. The rolling rollers 109 are respectively located on both sides of the electrode plate 250 as a reference, and press the electrode plate 250 passing between the two rolling rollers 109. Thereafter, the electrode plate 250 passing between the two rolling rollers 109 is wound again on the second roller 102.

[0046] The method for manufacturing an electrode of a secondary battery according to an embodiment of the present disclosure includes the following steps: before the electrode plate 250 having the coated portion 400 and the uncoated portion 500 is unwound and then rolled by the rolling roller 109, a shot peening process is performed. The shot peening process can be performed by a shot peening device PN located between the first roller 101 and the rolling roller 109 in the electrode rolling device 100 according to the present embodiment. According to the present embodiment, the shot peening process can apply compressive residual stress to the uncoated portion 500.

[0047] Reference Figure 5 In a modified embodiment, the method for manufacturing an electrode of a secondary battery according to an embodiment of the present disclosure includes the following steps: before the electrode plate 250 having the coated portion 400 and the uncoated portion 500 is unwound and then grooved by the grooved upper mold 210 and the lower mold 220, a shot peening process is performed. The shot peening process can be performed by a shot peening device PN located between the first roller 201 and the grooved molds 210 and 220 in the electrode grooved device 200 according to the present embodiment.

[0048] Figure 6 It is shown Figure 4 and Figure 5 Schematic cross-sectional view of the shot peening process. Figure 7 is a perspective view showing a shot peening process according to an embodiment of the present disclosure. Figure 8 It is shown by Figure 7 A cross-sectional view showing a state where a concave portion is formed by a shot peening process.

[0049] Reference Figure 6 According to the present embodiment, the step of applying compressive residual stress to the surface of the uncoated portion 500 may include a step of performing a shot peening process or a step of performing an ultrasonic peening process. Hereinafter, the step of performing the shot peening process will be mainly described.

[0050] Reference Figure 7and Figure 8 , the shot 600 may be thrown onto the surface of the uncoated portion 500 at high speed, thereby hammering the surface of the electrode current collector 300. The shot 600 may be formed of a steel ball such as stainless steel. Specifically, in the shot peening process, the shot 600 impacts the surface of the uncoated portion 500 at high speed, the kinetic energy of the shot 600 instantly causes plastic deformation on the surface of the material, and the shot 600 detaches from the surface. At this time, a concave portion DP having a concave shape is formed on the surface of the uncoated portion 500. According to the present embodiment, a thin plastic deformation layer PDL is formed on the surface of the concave portion DP, and the plastic deformation layer PDL may have a compressive residual stress. In contrast, the inside of the uncoated portion 500 located outside the plastic deformation layer PDL may have a tensile residual stress. Thus, the plastic deformation layer PDL according to the present embodiment is applied with a force to keep the stretched surface in the state before stretching, and compressive residual stress and tensile residual stress are formed on the surface and inside of the uncoated portion 500 where the concave portion DP is formed, respectively, so as to achieve balance. The shot peening process leaves compressive residual stress on the surface of the uncoated portion 500. When repeated tensile force is applied, the compressive residual stress is gradually eliminated, thereby extending the fatigue life until the compressive residual stress disappears.

[0051] The above-mentioned compressive residual stress and tensile residual stress can be interpreted as the cosine value of the residual stress measured using a residual stress tester.

[0052] Refer again Figure 6 In a modified embodiment, the step of applying compressive residual stress to the surface of the uncoated portion 500 may include: performing an ultrasonic peening process. In the ultrasonic peening process, an ultrasonic device 700 is disposed at the upper end of the uncoated portion 500 so that ultrasonic waves impact the surface of the uncoated portion 500 at high speed, thereby causing plastic deformation. Specifically, in the ultrasonic peening process, compressive residual stress can be controlled when ultrasonic energy is transferred to the surface of the uncoated portion 500, and high and low cycle fatigue can be improved. Figure 6 The ultrasonic peening process is performed while controlling the height of the ultrasonic device 700 shown in FIG. By controlling the height, the surface roughness of the uncoated portion 500 can be controlled.

[0053] The step of performing the ultrasonic peening process may replace the step of performing the above-mentioned shot peening process. Even in the step of performing the ultrasonic peening process, a recessed portion may be formed on the surface of the uncoated portion 500, and a plastic deformation layer having a compressive residual stress may be formed on the surface of the recessed portion, and the inside of the uncoated portion located outside the plastic deformation layer may have a tensile residual stress. In the ultrasonic peening process, the physical deformation on the surface of the uncoated portion 500 may be relatively small compared to the above-mentioned shot peening process.

[0054] Fig. 9 is a schematic cross-sectional view showing an aging process according to an embodiment of the present disclosure.

[0055] Reference Fig. 9 , the method for manufacturing an electrode of a secondary battery according to an embodiment of the present disclosure may include: after performing a shot peening process on the surface of the uncoated portion 500, a step of heat treating the electrode current collector 300. In the step of heat treating the electrode current collector 300, a heat treatment device 800 is arranged at the upper end of the uncoated portion 500 so that ultrasonic waves impact the surface of the uncoated portion 500 at high speed, thereby causing plastic deformation. When aging such as heat treatment is performed in addition to the above-mentioned shot peening process, compressive residual stress may be further generated on the surface of the electrode current collector 300. Therefore, the level of unbalanced plastic deformation caused by the stress during rolling can be reduced, and the level of tensile residual stress generated on the surface can be significantly reduced.

[0056] According to an embodiment of the present disclosure, by applying compressive residual stress to the electrode current collector 300 through a shot peening process, the electrode current collector 300 can be heat-treated in a state where the fracture strength and fatigue durability are improved, thereby manufacturing an electrode of a secondary battery in which the internal grains of the electrode current collector 300 are stable. At this time, the heat treatment temperature can be set to a temperature and time within a range in which the physical properties of the material do not change greatly.

[0057] Although the preferred embodiments of the present disclosure have been described in detail above, the scope of the present disclosure is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present disclosure defined in the following claims also fall within the scope of rights.

[0058] Reference Signs

[0059] 300: Electrode current collector

[0060] 400: Coating part

[0061] 500: Uncoated part

[0062] 600: Projectile

[0063] DP: Depression part

[0064] PDL: Plastic deformation layer.

Claims

1. A method for manufacturing an electrode for a secondary battery, comprising the following steps: coating an active material onto an electrode current collector to form a coated portion and an uncoated portion; applying compressive residual stress to the surface of the uncoated portion, The step of applying compressive residual stress to the surface of the uncoated portion includes: performing a shot peening process on the surface of the uncoated portion to form a plastic deformation layer on the surface of the uncoated portion, wherein the plastic deformation layer has a compressive residual stress, and the interior of the uncoated portion outside the plastic deformation layer has a tensile residual stress, wherein after the step of performing a shot peening process on the surface of the uncoated portion, the electrode current collector is heat treated, and The shot peening process includes a step of applying compressive residual stress on the surface of the uncoated portion through a quenching effect to minimize physical deformation.

2. The method for manufacturing an electrode for a secondary battery according to claim 1, A step of applying compressive residual stress to the surface of the uncoated portion is performed before a rolling process is performed along the moving direction of the electrode current collector, and the rolling process includes at least one of the following processes: a process of rolling the coated portion and the uncoated portion of the electrode current collector, and a process of grooves the coated portion and the uncoated portion of the electrode current collector.

3. The method for manufacturing an electrode for a secondary battery according to claim 2, The step of applying compressive residual stress to the surface of the uncoated portion includes the step of performing a shot peening process.

4. The method for manufacturing an electrode for a secondary battery according to claim 3, The steps of performing the shot peening process include: A step of forming a recessed portion on a surface of the non-coated portion.

5. The method for manufacturing an electrode for a secondary battery according to claim 4, The plastic deformation layer is formed on the surface of the recessed portion.

6. The method for manufacturing an electrode for a secondary battery according to claim 2, The step of applying compressive residual stress to the surface of the uncoated portion includes the step of performing an ultrasonic peening process.

7. The method for manufacturing an electrode for a secondary battery according to claim 6, The step of performing the ultrasonic peening process includes the step of forming a recessed portion on the surface of the uncoated portion.

8. The method for manufacturing an electrode for a secondary battery according to claim 7, The plastic deformation layer is formed on the surface of the recessed portion.

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