Secondary battery manufacturing apparatus and method for manufacturing secondary battery

Abstract

According to an embodiment of the present invention, there is provided an apparatus for manufacturing a secondary battery including a plurality of electrodes and separators stacked alternately, electrode tabs provided at ends of the plurality of electrodes, and electrode leads connected to the electrode tabs, the apparatus including: an upper fixed mold and a lower fixed mold that sandwich the electrode lead and contact upper and lower surfaces of the electrode lead, respectively, to fix the electrode lead; a plurality of lower roller dies disposed spaced apart from the lower fixed mold toward outer ends of the electrode leads; and a plurality of upper roller dies disposed spaced apart from the upper fixed mold toward the outer ends of the electrode leads.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0074849 dated June 20, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an apparatus for manufacturing a secondary battery and a method for manufacturing a secondary battery, and more particularly to an apparatus for manufacturing a secondary battery and a method for manufacturing a secondary battery that can reduce tensile stress applied to a joining portion between an electrode lead and an electrode tab, thereby preventing breakage. [Background technology]

[0003] The rapid increase in the use of fossil fuels has led to an increased demand for alternative and clean energy, and as part of this, the field of electrochemical power generation and storage is one of the most actively researched areas.

[0004] At present, a representative example of an electrochemical element that uses such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] Recently, with the increase in technological development and demand for portable devices such as portable computers, portable phones, and cameras, the demand for secondary batteries as energy sources has increased rapidly. In this context, much research has been conducted on lithium secondary batteries, which have high energy density and working potential, long cycle life, and low self-discharge rate, and they have been commercialized and widely used.

[0006] In addition, as interest in environmental issues grows, much research is being conducted on electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. Nickel-metal hydride secondary batteries are mainly used as the power source for such electric vehicles and hybrid electric vehicles, but active research is being conducted on the use of lithium secondary batteries with high energy density and discharge voltage, and some of them are already at the commercialization stage.

[0007] Such a lithium secondary battery is manufactured by coating a current collector with a positive or negative electrode active material, a binder, and a conductive material in the form of a slurry, drying the current collector to form an electrode mixture layer, manufacturing a positive electrode and a negative electrode, interposing a separator between the positive electrode and the negative electrode, and laminating the electrode assembly, and incorporating the laminated electrode assembly into a battery case together with an electrolyte. Electrode tabs extending from each cell of the electrode assembly incorporated into the battery case are collected and welded to be connected to an electrode lead. The electrode lead may be used for electrical connection to an external device.

[0008] 1 and 2 are diagrams illustrating an example of a secondary battery manufacturing apparatus according to the related art.

[0009] FIG. 1 is a diagram showing the state of an electrode lead before bending in a secondary battery manufacturing apparatus according to the conventional technology, and FIG. 2 is a diagram showing the state of the electrode lead after bending in a secondary battery manufacturing apparatus according to the conventional technology.

[0010] 1 and 2, an electrode assembly 1 is formed by stacking a plurality of positive and negative electrodes with a separator interposed therebetween, and a secondary battery can be manufactured by housing the electrode assembly 1 in a battery case 2. Electrode tabs 3 connected to each electrode included in the electrode assembly 1 are collected and welded as shown in the drawings, and then connected to an electrode lead 4. A lead film 5 surrounding the electrode lead 4 may be positioned on the electrode lead 4 to enhance sealing force with the battery case 2.

[0011] The electrode lead 4 may be electrically connected to an external device, and may be appropriately molded into various shapes depending on the environment of the connection state. In order to mold the electrode lead 4, a process of bending the electrode lead 4 into an appropriate shape is required. For this bending, as shown in FIG. 1 and FIG. 2, upper and lower molds 30 and 40 having the shape of the electrode lead 4 to be obtained are prepared, and the upper and lower molds 30 and 40 are combined to pressurize the electrode lead 4 while the joint portion between the battery case 2 and the electrode lead 4 is fixed by the upper fixed mold 10 and the lower fixed mold 20. At this time, a strong tensile force is applied to the joint portion A between the electrode lead 4 and the electrode tab 3 due to the force of pressing the electrode lead 4, and this may cause problems such as disconnection of the joint portion A between the electrode tab 3 and the electrode lead 4. In addition, according to the conventional technology, the electrode lead 4 can be molded into only one shape using the upper and lower molds 30 and 40 having a fixed shape, so it is impossible to manufacture electrode leads 4 of various shapes, and therefore there is a problem that individual molds corresponding to the shape of the electrode lead 4 are required depending on the type of product. Summary of the Invention [Problem to be solved by the invention]

[0012] The problem to be solved by the present invention is to provide a secondary battery manufacturing apparatus and a secondary battery manufacturing method that can prevent breaks from occurring at the joint between the electrode tab and the electrode lead due to tensile force generated in the electrode lead molding process, and can mold electrode leads of various shapes using a single manufacturing apparatus.

[0013] However, the problems to be solved by the embodiments of the present invention are not limited to the above problems, and can be variously expanded within the scope of the technical ideas included in the present invention. [Means for solving the problem]

[0014] According to an embodiment of the present invention, there is provided an apparatus for manufacturing a secondary battery including a plurality of electrodes and separators stacked alternately, electrode tabs provided at ends of the plurality of electrodes, and electrode leads connected to the electrode tabs, the apparatus including: an upper fixed mold and a lower fixed mold that sandwich the electrode lead and contact upper and lower surfaces of the electrode lead, respectively, to fix the electrode lead; a plurality of lower roller dies disposed spaced apart from the lower fixed mold toward outer ends of the electrode leads; and a plurality of upper roller dies disposed spaced apart from the upper fixed mold toward the outer ends of the electrode leads.

[0015] The lower roller die and the upper roller die may be capable of rotating and moving independently of each other.

[0016] The mold may further include a lower support mold disposed between the lower fixed mold and the lower roller mold, and configured to support a lower surface of the electrode lead.

[0017] The upper roller die may include a first upper roller die and a second upper roller die arranged sequentially along a direction toward the outer end of the electrode lead, and the lower roller die may include a first lower roller die and a second lower roller die arranged sequentially along a direction toward the outer end of the electrode lead.

[0018] The first lower roller die, the first upper roller die, the second lower roller die and the second upper roller die may be sequentially arranged along a direction toward the outer end of the electrode lead.

[0019] A method for manufacturing a secondary battery according to another embodiment of the present invention is a method for manufacturing a secondary battery including a plurality of electrodes and separators stacked alternately, electrode tabs provided at ends of the plurality of electrodes, and electrode leads connected to the electrode tabs, the method including the steps of: fixing the electrode lead between an upper fixed mold and a lower fixed mold; supporting a lower portion of the electrode lead with a lower support mold disposed adjacent to the lower fixed mold, and bending the electrode lead in a direction toward the lower support mold to form a first bent portion; and forming a second bent portion using a plurality of lower roller dies disposed spaced apart from the lower fixed mold toward an outer end of the electrode lead, and a plurality of upper roller dies disposed spaced apart from the upper fixed mold toward the outer end of the electrode lead.

[0020] The upper roller die may include a first upper roller die and a second upper roller die arranged sequentially along a direction toward the outer end of the electrode lead, and the lower roller die may include a first lower roller die and a second lower roller die arranged sequentially along a direction toward the outer end of the electrode lead.

[0021] The first lower roller die, the first upper roller die, the second lower roller die and the second upper roller die may be sequentially arranged along a direction toward the outer end of the electrode lead.

[0022] The step of forming the second bending portion may include a step of simultaneously lowering the first upper roller die and the second upper roller die to form a primary bending portion having a shape corresponding to the lower portion of the first upper roller die and a secondary bending portion having a shape corresponding to the upper portion of the second lower roller die.

[0023] The step of forming the second bending portion may include a step of lowering the first upper roller die to form a primary bending portion having a shape corresponding to a lower portion of the first upper roller die, and a step of lowering the second upper roller die to form a secondary bending portion having a shape corresponding to an upper portion of the second lower roller die.

[0024] The step of forming the second bent portion may include the steps of lowering the second upper roller die to contact the electrode lead, and lowering the first upper roller die to form a primary bent portion having a shape corresponding to the lower portion of the first upper roller die and a secondary bent portion having a shape corresponding to the upper portion of the second lower roller die. Effect of the Invention

[0025] According to an embodiment of the present invention, it is possible to prevent breakage at a joint between an electrode tab and an electrode lead by minimizing generation of tensile force during a molding process of an electrode lead. Also, it is possible to provide a secondary battery manufacturing apparatus and a secondary battery manufacturing method capable of molding electrode leads of various shapes using a single manufacturing apparatus without manufacturing an additional mold, etc.

[0026] The effects of the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram showing a state before electrode leads are bent in a secondary battery manufacturing apparatus according to the related art. [Diagram 2] FIG. 2 is a diagram showing a state after bending of an electrode lead in a secondary battery manufacturing apparatus according to the related art. [Diagram 3] FIG. 3 is a diagram showing a state before bending of an electrode lead in a manufacturing apparatus for a secondary battery according to an embodiment of the present invention. [Figure 4]FIG. 4 is a diagram showing a state after bending of the electrode lead in the secondary battery manufacturing apparatus of FIG. [Diagram 5] FIG. 5 is a diagram for explaining a method for manufacturing a secondary battery according to an embodiment of the present invention. [Figure 6] FIG. 6 is a diagram for explaining a method for manufacturing a secondary battery according to another embodiment of the present invention. [Figure 7] FIG. 7 is a diagram for explaining a method for manufacturing a secondary battery according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may be embodied in various different forms and is not limited to the embodiments set forth herein, but may be practiced in a variety of different ways, such as by way of example only, with reference to the accompanying drawings, in which: FIG.

[0029] In order to clearly describe the present invention, parts that are not relevant to the description will be omitted, and the same reference numerals will be used to refer to the same or similar components throughout the specification.

[0030] In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for convenience of explanation, and the present invention is not necessarily limited to those shown. In the drawings, thicknesses are enlarged to clearly show various layers and regions. In the drawings, thicknesses of some layers and regions are exaggerated for convenience of explanation.

[0031] In addition, when a part such as a layer, film, region, or plate is said to be "on" or "above" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between. Conversely, when a part is said to be "directly on" another part, it means that there is no other part in between. In addition, being "on" or "above" a reference part means being located above or below the reference part, and does not necessarily mean being located "on" or "above" the opposite direction of gravity.

[0032] In addition, throughout the specification, when a part is said to "comprise" a certain element, this does not mean to exclude other elements, but may further include other elements, unless specifically stated to the contrary.

[0033] Hereinafter, a secondary battery manufacturing apparatus according to an embodiment of the present invention will be described with reference to FIGS.

[0034] The secondary battery includes an electrode assembly 1 housed in a battery case 2 and an electrode lead 4 drawn out from the battery case 2 for electrical connection to the outside. The electrode assembly 1 is a power generating element capable of charging and discharging, and has a structure in which positive and negative electrodes are alternately stacked with a separator sandwiched therebetween. Electrode tabs 3 extend from the ends of the electrodes included in the electrode assembly 1. The electrode tabs 3 may be gathered at one point and welded, or the gathered electrode tabs 3 and the electrode lead 4 may be joined by means of welding or the like.

[0035] One end of the electrode lead 4 is electrically connected to the electrode tab 3 and extends through the sealing portion of the battery case 2, and the opposite end protrudes to the outside of the battery case 2. A lead film 5 may be positioned so as to surround the electrode lead 4 at least at one of the upper and lower parts of the electrode lead 4. The lead film 5 can prevent a short circuit from occurring in the electrode lead 4 during heat fusion and can improve the sealing between the sealing portion of the battery case 2 and the electrode lead 4.

[0036] 3 and 4, the secondary battery manufacturing apparatus according to one embodiment of the present invention is an apparatus for forming the aforementioned electrode lead 4, particularly the portion protruding outside the battery case 2, and includes an upper fixed mold 100 and a lower fixed mold 200 for fixing the electrode lead 4, an upper roller mold 300, a lower roller mold 400, and a lower support mold 500 for directly contacting the electrode lead 4 to form the shape of the electrode lead 4.

[0037] The upper fixed mold 100 and the lower fixed mold 200 are used to fix the electrode lead 4 during the molding process, and in particular, they support the portion where the electrode lead 4 is fixed to the battery case 2, and fix the electrode lead 4. To this end, as shown in Fig. 3, they are formed so that the overlapping portion of the battery case 2 and the electrode lead 4 is in contact with each other at the top and bottom and pressurized.

[0038] The lower support mold 500 is disposed adjacent to the lower fixed mold 200, spaced away from the outer end of the electrode lead 4. The lower support mold 500 is configured to contact the starting point of the electrode lead 4 where molding begins, and has a shape corresponding to the first bent portion 41 of the electrode lead 4. That is, the first bent portion 41 can be formed at a position corresponding to the lower support mold 500 by pressure applied by the upper roller mold 300 and the lower roller mold 400 described below.

[0039] The upper roller die 300 and the lower roller die 400 are respectively disposed away from the upper fixed die 100 and the lower fixed die 200 toward the outer end of the electrode lead 4, and are positioned such that the electrode lead 4 is disposed between the upper roller die 300 and the lower roller die 400. In particular, the lower roller die 400 is separated from the lower fixed die 200 with the lower support die 500 sandwiched therebetween.

[0040] The upper roller dies 300 and the lower roller dies 400 may each be provided in multiple numbers, and in this embodiment, an example including two upper roller dies 300 and two lower roller dies 400 is described; however, this is not limited to this, and the number and positions of the upper roller dies 300 and the lower roller dies 400 can be adjusted in various ways.

[0041] The upper roller die 300 includes a first upper roller die 310 and a second upper roller die 320, and the lower roller die 400 includes a first lower roller die 410 and a second lower roller die 420. As shown in Fig. 3 and Fig. 4, these roller dies are arranged in the order of the first lower roller die 410, the first upper roller die 310, the second lower roller die 420, and the second upper roller die 320 in the direction from the lower support die 500 toward the outer end of the electrode lead 4. In this state, the upper roller die 300 descends toward the electrode lead 4, and then descends while being disposed between the lower roller dies 400, thereby molding the electrode lead 4 while applying pressure to the electrode lead 4.

[0042] At this time, the upper roller die 300 and the lower roller die 400 are configured to be able to rotate independently. When the electrode lead 4 is pressed, the roller dies 300, 400 rotate to minimize friction with the electrode lead 4, and as a result, the tensile force applied to the electrode lead 4 can be reduced. In particular, when the tensile force is reduced, breakage can be prevented at the connection portion A between the electrode tab 3 and the electrode lead 4, which has a relatively weak connection strength. At the connection portion A between the electrode tab 3 and the electrode lead 4, breakage frequently occurs due to the tensile force applied to the connection portion during molding of the electrode lead 4. However, by using the roller dies 300, 400 instead of the conventional stamp type die as in this embodiment, it is possible to minimize the generation of friction and tensile force and prevent such breakage.

[0043] In addition, the positions of the upper roller die 300 and the lower roller die 400 can be changed independently. Therefore, it is possible to mold electrode leads 4 of various shapes without changing the die by adjusting the vertical and horizontal positions of the roller dies 300 and 400 so as to correspond to the shape required by the product. For example, when molding an electrode lead of the embodiment including the first bending portion 41 and the second bending portion 42, the bending angle of the first bending portion 41 may be determined by the vertical position and the pressure force of the first upper roller die 310. In addition, the second bending portion 42 may have two bending portions, that is, the primary bending portion 42a and the secondary bending portion 42b, but the shape of the primary bending portion 42a may correspond to the lower surface of the first upper roller die 310, or the upper surface of the second lower roller die 420 of the secondary bending portion 42b. The degree of bending of the primary bent portion 42a and the secondary bent portion 42b, i.e., the depth or width, can be changed by adjusting the lowering height of the upper roller die 300 and the separation distance between the upper roller die 300 and the lower roller die 400. In addition, the size and number of the roller dies 300, 400 are not limited to those in this embodiment, and may be appropriately determined depending on the required shape of the electrode lead 4, etc.

[0044] As described above, according to the manufacturing apparatus for a secondary battery according to one embodiment of the present invention, the tensile force applied to the electrode lead 4 and the electrode tab 3 during bending of the electrode lead 4 can be minimized to prevent breakage of the electrode lead 4. Furthermore, since it is possible to form various shapes of electrode leads 4 without changing the mold even with a single manufacturing apparatus, it is possible to reduce manufacturing costs.

[0045] Hereinafter, a method for manufacturing a secondary battery using the above-described secondary battery manufacturing apparatus according to one embodiment and another embodiment of the present invention will be described.

[0046] FIG. 5 is a diagram for explaining a method for manufacturing a secondary battery according to one embodiment of the present invention, and FIGS. 6 and 7 are diagrams for explaining a method for manufacturing a secondary battery according to another embodiment of the present invention.

[0047] 5, in the method for manufacturing a secondary battery according to an embodiment of the present invention, first, an electrode lead 4 is fixed between an upper fixed mold 100 and a lower fixed mold 200, and the electrode lead 4 is bent at a portion where the lower supporting mold 500 supports the electrode lead 4 to form a first bent portion 41. At this time, the electrode lead 4 may be bent downward, i.e., in a direction toward the lower supporting mold 500, while being supported by the lower supporting mold 500, so that the first bent portion 41 may have a shape corresponding to the upper surface of the lower supporting mold 500.

[0048] Next, the second bending portion 42 is formed using the upper roller die 300 and the lower roller die 400. In this embodiment, as shown in Fig. 5, the first and second upper roller dies 310, 320 included in the upper roller die 300 are simultaneously lowered to form the primary bending portion 42a and the secondary bending portion 42b included in the second bending portion 42. That is, the first and second upper roller dies 310, 320 are simultaneously lowered and the electrode lead 4 is pressed, thereby forming the primary bending portion 42a corresponding to the lower surface shape of the first upper roller die 310 and the secondary bending portion 42b corresponding to the upper surface shape of the second lower roller die 420.

[0049] 6, the method for manufacturing a secondary battery according to another embodiment of the present invention is different from the method for manufacturing the secondary battery according to the first embodiment in that the first and second upper roller dies 310, 320 are not lowered simultaneously, but the first upper roller die 310 is lowered first and then the second upper roller die 320 is lowered. That is, the first upper roller die 310 is lowered so that the electrode lead 4 comes into contact with the first lower roller die 410, the first upper roller die 310 and the second lower roller die 420, and then the second upper roller die 320 is lowered to press the electrode lead 4, thereby forming the first bent portion 42a and the second bent portion 42b.

[0050] 7, the manufacturing method for a secondary battery according to another embodiment of the present invention is different from the manufacturing method of the first embodiment in that the first and second upper roller dies 310, 320 are not lowered simultaneously, but the second upper roller die 320 is first lowered and then the first upper roller die 310 is lowered. In other words, the second upper roller die 320 is lowered so that the electrode lead 4 comes into contact with the second upper roller die 320, and then the first upper roller die 310 is lowered to press the electrode lead 4, thereby forming the primary bent portion 42a and the secondary bent portion 42b.

[0051] In this manner, in the manufacturing method for forming the electrode lead 4 using the secondary battery manufacturing apparatus according to one embodiment of the present invention, the electrode lead 4 can be manufactured in a desired shape by lowering and moving each roller die, particularly the upper roller die, in various orders.

[0052] In the following, the tensile forces generated in the method for manufacturing a secondary battery according to an embodiment of the present invention and the method for manufacturing a secondary battery according to a comparative example are measured, and the results are described.

[0053] In Example 1, the upper roller die 300 was moved by about 12 mm according to the manufacturing method of Fig. 5, and the maximum value of the tensile force applied to the joint portion A between the electrode tab 3 and the electrode lead 4 at this time was measured, in Example 2, the maximum value of the tensile force was measured similarly to the manufacturing method of Fig. 6, and in Example 3, the maximum value of the tensile force was measured similarly to Example 1 according to the manufacturing method of Fig. 7. On the other hand, in the comparative example, the upper die 30 was moved by about 12 mm similarly to Example 1 using the dies of Figs. 1 and 2, and the maximum value of the tensile force applied to the joint portion A between the electrode tab 3 and the electrode lead 4 at this time was measured. The results are shown in Table 1 below.

[0054] [Table 1]

[0055] As shown in Table 1 above, it was confirmed that the maximum tensile strength value was significantly lower than that of the comparative example in the embodiment of the present invention in which the electrode lead 4 was formed using the roller dies 300 and 400. Therefore, it was found that the embodiment of the present invention can prevent breakage of the electrode tab 3 and the electrode lead 4 during the process of forming the electrode lead 4.

[0056] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also belong to the scope of the present invention. [Explanation of symbols]

[0057] 3: Electrode tab 4: Electrode lead 100: Upper fixed mold 200: Lower fixed mold 300: Upper roller die 310: First upper roller die 320: 2nd upper roller die 400: Lower roller die 410: First lower roller die 420: Second lower roller die 500: Lower support mold

Claims

1. An apparatus for manufacturing a secondary battery, comprising: a plurality of electrodes and separators stacked alternately; electrode tabs provided at ends of the plurality of electrodes; and electrode leads connected to the electrode tabs, an upper fixed die and a lower fixed die for sandwiching the electrode lead and fixing the electrode lead; a plurality of lower roller dies spaced apart from the lower fixed die toward outer ends of the electrode leads; a plurality of upper roller dies spaced apart from the upper fixed die toward the outer ends of the electrode leads; A secondary battery manufacturing apparatus comprising:

2. The apparatus for manufacturing a secondary battery according to claim 1 , wherein the lower roller die and the upper roller die are capable of rotating and moving independently of each other.

3. The apparatus for manufacturing a secondary battery according to claim 1 , further comprising a lower support mold disposed between the lower fixed mold and the lower roller mold and supporting a lower surface of the electrode lead.

4. the upper roller die includes a first upper roller die and a second upper roller die sequentially arranged along a direction toward the outer end of the electrode lead, The secondary battery manufacturing apparatus according to any one of claims 1 to 3, wherein the lower roller die includes a first lower roller die and a second lower roller die arranged sequentially along a direction toward the outer end of the electrode lead.

5. 5. The secondary battery manufacturing apparatus of claim 4, wherein the first lower roller die, the first upper roller die, the second lower roller die, and the second upper roller die are sequentially arranged along a direction toward the outer end of the electrode lead.

6. 1. A method for manufacturing a secondary battery, comprising: a plurality of electrodes and separators stacked alternately; electrode tabs provided at ends of the plurality of electrodes; and electrode leads connected to the electrode tabs, Fixing the electrode lead between an upper fixed mold and a lower fixed mold; a lower support die disposed adjacent to the lower fixed die, the lower support die being supported at a lower portion of the electrode lead, and the electrode lead being bent in a direction toward the lower support die to form a first bent portion; forming a second bent portion using a plurality of lower roller dies spaced apart from the lower fixed die toward an outer end of the electrode lead, and a plurality of upper roller dies spaced apart from the upper fixed die toward the outer end of the electrode lead; A method for manufacturing a secondary battery comprising the steps of:

7. the upper roller die includes a first upper roller die and a second upper roller die sequentially arranged along a direction toward the outer end of the electrode lead, The method of claim 6 , wherein the lower roller die includes a first lower roller die and a second lower roller die sequentially arranged along a direction toward the outer end of the electrode lead.

8. 8. The method for manufacturing a secondary battery according to claim 7, wherein the first lower roller die, the first upper roller die, the second lower roller die, and the second upper roller die are sequentially arranged along a direction toward the outer end of the electrode lead.

9. The step of forming the second bent portion includes:

9. The method for manufacturing a secondary battery according to claim 7 or 8, further comprising a step of simultaneously lowering the first upper roller die and the second upper roller die to form a primary bent portion having a shape corresponding to a lower portion of the first upper roller die and a secondary bent portion having a shape corresponding to an upper portion of the second lower roller die.

10. The step of forming the second bent portion includes: lowering the first upper roller die to form a primary bent portion having a shape corresponding to a lower portion of the first upper roller die; and lowering the second upper roller die to form a secondary bent portion having a shape corresponding to an upper portion of the second lower roller die.

11. The step of forming the second bent portion includes: lowering the second upper roller die into contact with the electrode lead; and lowering the first upper roller die to form a primary bent portion having a shape corresponding to a lower portion of the first upper roller die and a secondary bent portion having a shape corresponding to an upper portion of the second lower roller die.

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