Method for joining electrode taps and metal leads and lithium secondary battery

Abstract

To provide a method for bonding electrode taps and a metal lead, and a lithium secondary battery including a bonding structure formed by the method which can resolve the problems of conventional technology, form the outer peripheral shape of a lithium electrode tab uniformly, form the thickness of the lithium electrode tabs uniformly, easily adjust the bonding strength and specifications of the joint between the lithium electrode tab and the metal lead because the bonding area can be reliably adjusted, minimize resistance deviation between cells, and significantly improve process efficiency.SOLUTION: The present invention provides a method for bonding lithium electrode taps and a metal lead using a forming frame for the lithium electrode tap, and a lithium secondary battery including a bonding structure of the lithium electrode tap and the metal lead.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0079944 filed on June 21, 2021 and Korean Patent Application No. 10-2022-007,4655 filed on June 20, 2022, and all the contents disclosed in the corresponding Korean patent application documents are incorporated herein by reference in their entirety.

[0002] The present invention relates to a method for joining an electrode tap and a metal lead and a lithium secondary battery.

Background Art

[0003] As interest in energy storage technology increases, the application fields have expanded to mobile phones, tablets, laptops, camcorders, and even to the energy of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and research and development on electrochemical devices have been gradually increasing.

[0004] Among these electrochemical devices, the development of lithium secondary batteries that can be charged and discharged, and more specifically, lithium secondary batteries has become the focus of interest. Recently, in developing such batteries, in order to improve the capacity density and specific energy, research and development on new electrode and battery designs have been actively conducted.

[0005] The lithium metal battery developed as a next-generation battery by such a development trend has a negative electrode composed only of lithium. However, lithium has a lower melting point than other metals, is easily cut, and when exposed to air, there are potential risks such as explosion, and it is known to be difficult to develop as a battery.

[0006] In particular, joining the lithium electrode tap of the lithium negative electrode and the metal lead is known as a very difficult operation due to the soft nature of the lithium electrode tap.

[0007] In other words, in conventional lithium-ion batteries, tap welding is performed by ultrasonic welding, laser welding, or resistance welding between the negative electrode (copper) or positive electrode (aluminum) tap and the lead (copper, nickel, etc.). However, these techniques are not applicable to welding the lithium electrode tap of the lithium negative electrode to the metal lead.

[0008] Therefore, conventional techniques, as shown in Figure 1, utilize a method of joining metal leads and lithium electrode taps by pressing them together in a stacked state. However, when using such a method, because lithium electrode taps are soft, the degree to which they are pressed and expanded varies depending on the magnitude of the pressing pressure and the pressing time, making it difficult to adjust the bonding strength and the specifications of the joint. In other words, the shape of the outer circumference of the lithium electrode tap is formed differently each time the work is done, and the ends of the outer circumference are formed with many protrusions and intrusions, making it difficult to form a joint with a uniform shape. Furthermore, it was difficult to form the thickness of the lithium electrode tap and the area of ​​the joint to be constant.

[0009] Furthermore, the conventional method described above has the disadvantage of low battery production efficiency because lithium adheres to the pressing device that presses the lithium electrode tap, causing poor bonding and increasing the time required for the bonding process. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Korean Patent Publication No. 10-2020-0009230 [Overview of the project] [Problems that the invention aims to solve]

[0011] This invention was devised to solve the aforementioned problems of the prior art, The objective is to provide a method for joining electrode taps and metal leads, and a lithium secondary battery including a joining structure formed by the method, which allows for the uniform formation of the outer periphery of the lithium electrode tap, the uniform formation of the thickness of the lithium electrode tap, and the reliable adjustment of the joining area, thereby easily adjusting the joining strength and specifications of the joining part between the lithium electrode tap and the metal lead, minimizing resistance deviations between cells, and greatly improving process efficiency. [Means for solving the problem]

[0012] To achieve the above objective, the present invention, (a) The step of preparing the mold for the lithium electrode tap; (b) Positioning one end of the lithium electrode tap in the molding groove of the molding frame; (c) The step of stacking one end of a metal lead on top of the lithium electrode tap located in the molding groove; and (d) A method for joining a lithium electrode tap to a metal lead is provided, which includes the step of pressing the upper part of the stacked metal leads.

[0013] Furthermore, the present invention is A lithium secondary battery comprising an electrode junction structure of lithium electrode taps and metal leads, The present invention provides a lithium secondary battery characterized in that both longitudinal sides of the lithium electrode tap, which is joined to the metal lead, are formed to be flat. [Effects of the Invention]

[0014] The present invention's method for joining a lithium electrode tap and a metal lead allows for the uniform formation of the outer periphery of the lithium electrode tap, the uniform formation of the thickness of the lithium electrode tap, and the reliable adjustment of the joining area, thereby enabling easy adjustment of the joining strength and specifications of the joining portion between the lithium electrode tap and the metal lead.

[0015] In addition, the method for joining the electrode tap and the metal lead of the present invention significantly improves the process efficiency, provides the effect of minimizing joint defects, and provides the effect of minimizing the resistance deviation between cells.

[0016] Since the lithium secondary battery of the present invention includes a joint structure of a lithium electrode tap and a metal lead with excellent joint strength, it provides improved quality.

Brief Description of the Drawings

[0017] [Figure 1] It is a perspective view schematically showing a method for joining a lithium electrode tap and a metal lead of the prior art. [Figure 2] It is a perspective view schematically showing an embodiment of a method for joining a lithium electrode tap and a metal lead of the present invention. [Figure 3] It is a perspective view schematically showing an embodiment of a method for joining a lithium electrode tap and a metal lead of the present invention. [Figure 4] It is a perspective view schematically showing an embodiment of a molding frame used in a method for joining a lithium electrode tap and a metal lead of the present invention. [Figure 5] It is a drawing schematically showing the joining mechanism of a method for joining a lithium electrode tap and a metal lead of the present invention.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, the present invention can be embodied in several different forms and is not limited to the embodiments described herein. The same reference numerals are given to similar parts throughout the specification.

[0019] The method for joining the lithium electrode tap and the metal lead of the present invention is, as shown in FIGS. 2, 3 and 5, (a) Preparing the molding frame 10 of the lithium electrode tap; ](b) Positioning one end of the lithium electrode tap 22 in the molding groove 12 of the molding frame; (c) The step of stacking one end of the metal lead 30 on top of the lithium electrode tap 22 located in the molding groove 12; and (d) The step of pressing the upper part of the stacked metal lead 30; is characterized by including this step.

[0020] In the conventional technology, as shown in Figure 1, one end of the lithium electrode tap 22 and one end of the metal lead 30 were stacked together without using a molding frame, and then pressed to join the lithium electrode tap and the metal lead.

[0021] However, when using this method, the soft nature of lithium electrode taps meant that the degree to which they expanded varied depending on the magnitude of the pressing pressure and the pressing time, making it difficult to adjust the bonding strength and the specifications of the joint. In other words, the shape of the outer circumference of the lithium electrode tap was formed differently each time the work was done, and the ends of the outer circumference were also formed unevenly, making it difficult to form a joint with a uniform shape. Furthermore, it was difficult to form the thickness of the lithium electrode tap and the area of ​​the joint to be constant.

[0022] Furthermore, the joints between lithium electrode taps and metal leads formed by this method have inconsistent thickness and area, leading to a problem of large resistance deviations between cells. If the joint area is insufficient, the joints can easily break, resulting in many defects during cell assembly.

[0023] On the other hand, the conventional method described above caused lithium to stick to the pressing device that presses the lithium electrode tap, resulting in poor bonding. Furthermore, it increased the time required for the bonding process, thus contributing to a decrease in battery production efficiency.

[0024] The present invention is characterized by easily adjusting the bonding strength and specifications of the joint by using a molding frame 10 to join a lithium electrode tap 22 and a metal lead 30. In other words, the bonding method of the present invention, by using the molding frame 10, allows the shape of the outer circumference of the lithium electrode tap 22 to be uniformly formed by the shape of the molding groove 12 formed in the molding frame 10, and this effect makes it possible to reliably adjust the bonding area between the lithium electrode tap and the metal lead. Furthermore, the thickness of the lithium electrode tap 22 can also be formed uniformly by the action of the molding frame 10. That is, since the wall that forms the molding groove 12 in the molding frame 10 functions as a stopper when pressed, the thickness of the electrode tap 22 can be formed uniformly without having to delicately adjust the pressure on the metal lead 30 when pressed.

[0025] Furthermore, in the joining method of the present invention, the lithium electrode tap 22 does not directly contact the pressing device, but only contacts the molding groove 12 of the molding frame. Therefore, the problem of lithium sticking to the pressing device and causing bonding defects does not occur, and the problem of lithium sticking to the pressing device and increasing the time required for the joining process does not occur.

[0026] In one embodiment of the present invention, the molding groove 12 in step (a) can be formed in a continuous form from the tip to the end of the molding frame 10 in the direction of the metal lead 30, as shown in Figures 2 and 4(a).

[0027] This type of molded groove 12 is preferable because it allows for uniform control of the shape of both longitudinal side surfaces of the lithium electrode tap 22.

[0028] In one embodiment of the present invention, the molding groove 12 in step (a) may be a rectangular groove with one side open, as shown in Figures 3 and 4(b). In this case, the open side can be positioned toward the electrode 20 connected to the lithium electrode tap 22.

[0029] This type of molded groove 12 is preferable because it allows for uniform control of the shape of not only the longitudinal sides of the lithium electrode tap 22 but also the end portion.

[0030] In one embodiment of the present invention, the molding groove 12 can have a width of 0.5 to 1 times the width of the metal lead 30. If the width of the molding groove is greater than the width of the metal lead, a portion may be formed in the lithium electrode tap 22 that does not join with the metal lead 30 during joining. This is undesirable because, during pressing, the lithium electrode tap 22 may lift in the portion where the metal lead 30 is not present, potentially causing a resistance deviation between cells.

[0031] In one embodiment of the present invention, it is preferable that the depth of the molding groove 12 be shallower than the thickness of the lithium electrode tap 22. This is because when the metal lead 30 is pressed to join the metal lead 30 with the lithium electrode tap 22, the thickness of the lithium electrode tap 22, which has become softer, becomes thinner and spreads laterally. However, in order to form a uniform thickness for the lithium electrode tap 22, as shown in Figure 5(a), the wall forming the molding groove 12 in the molding frame 10 must act as a stopper to stop the pressing of the metal lead 30.

[0032] In one embodiment of the present invention, it is preferable that the molding groove 12 is formed wider than the width of the lithium electrode tap 22. This is because the lithium electrode tap 22 stretches laterally when pressed in the thickness direction, and therefore, there must be a space in the molding groove that can accommodate this stretched portion.

[0033] In one embodiment of the present invention, the step of welding the lithium electrode tap and the metal lead after step (d) may be further included. However, the welding step is not a required step. That is, since the metal lead and the lithium electrode tap can be joined without welding by various bonding structures, the welding step can be performed selectively.

[0034] In one embodiment of the present invention, step (b) may further include the step of applying a release agent to the molding groove 12 or covering the molding groove 12 with a release film, before the step of positioning one end of the lithium electrode tap 22 in the molding groove 12 of the molding frame 10.

[0035] Figure 5 illustrates the joining mechanism of the lithium electrode tap and metal lead joining method of the present invention. Figure 5(a) shows the cross-section of the lithium electrode tap 22 and metal lead 30 in the lateral direction, before and after joining. As shown in Figure 5(a), when pressure is applied in one or more directions to the metal lead 30 and the molding frame 10, the soft lithium electrode tap 22 expands laterally and is formed in the shape of the molding groove 12, and at the same time joins with the metal lead 30.

[0036] Figure 5(b) shows the longitudinal (vertical) cross-sections of the lithium electrode tap 22 and the metal lead 30, separated into before and after joining. As shown in Figure 5(b), when pressure is applied in one or more directions to the metal lead 30 and the molding frame 10, the soft lithium electrode tap 22 expands laterally as shown in (a) above, and at the same time, its thickness decreases as shown in (b), forming the shape of the molding groove 12. It is then joined to the metal lead 30 by this mechanism.

[0037] Figure 5(c) shows the deformation behavior of the lithium electrode tap 22 due to pressure, viewed from above the lithium electrode tap 22. As shown in Figure 5(c), when pressure is applied in one or more directions from either the metal lead 30 or the molding frame 10, the lithium electrode tap 22, which is soft, expands laterally and is formed in the shape of the molding groove 12.

[0038] The present invention also, A lithium secondary battery comprising a laminated junction structure of lithium electrode taps and metal leads, This invention relates to a lithium secondary battery in which both longitudinal sides of the lithium electrode tap, which is joined to the metal lead, are formed to be flat.

[0039] The aforementioned plane may be a surface formed by a molding frame.

[0040] The method for joining the electrode tap and metal lead described above can be similarly applied to the lithium secondary battery. Therefore, any content that overlaps with what has been previously stated will be omitted.

[0041] In one embodiment of the present invention, the end surface of the lithium electrode tap joined to the metal lead in the direction of the metal lead may be formed as a flat surface.

[0042] The aforementioned uniform surface may be a surface formed by a molding frame.

[0043] In one embodiment of the present invention, the upper and lower surfaces of the lithium electrode tap joined to the metal lead may be formed as flat surfaces of uniform thickness.

[0044] In one embodiment of the present invention, the laminated bonding structure may include a configuration in which a lithium electrode tap 22 with a step formed thereon is bonded to a metal lead 30 laminated on the lower part of the step, as shown in Figure 5(b).

[0045] In one embodiment of the present invention, the laminated bonding structure includes a configuration in which a lithium electrode tap 22 with a step is bonded to a metal lead 30 laminated on the lower part of the step, as shown in Figure 5(b), and the opposite side of the lithium electrode tap 22 from the metal lead 30 lamination also includes a step.

[0046] In one embodiment of the present invention, the step may be formed by positioning one end of the lithium electrode tap 22 in the molding groove 12 of the molding frame 10 of the lithium electrode tap, stacking one end of the metal lead 30 on top of the lithium electrode tap 22, and pressing the upper part of the stacked metal lead 30, as shown in Figure 5(b).

[0047] The end surfaces of the metal leads joined to the lithium electrode tap 22 can form a laminated bond structure in which they are joined seamlessly to the stepped surface of the lithium electrode tap. Here, "no gap" means that there is virtually no gap.

[0048] In one embodiment of the present invention, the lithium secondary battery may include a freestanding lithium electrode.

[0049] In one embodiment of the present invention, the lithium secondary battery can be manufactured comprising a negative electrode, a positive electrode, an electrolyte interposed between the negative electrode and the positive electrode, and a separation membrane, all of which are free-standing lithium electrodes.

[0050] The lithium secondary battery of the present invention can be manufactured by known methods using configurations known in the art, except for the junction structure of the lithium electrode tap and the metal lead. Specific examples of the positive electrode, electrolyte, and separator membrane will be described below.

[0051] positive electrode The positive electrode included in the lithium secondary battery of the present invention may include a positive electrode active material, a binder, and a conductive material. The binder is a component that assists in the bonding of the positive electrode active material to a conductive material and to the current collector, and may, but is not limited to, one or more selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene-butylene rubber, fluororubber, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, and mixtures thereof.

[0052] The binder can typically be added in an amount of 1 to 50 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode.

[0053] The conductive material contained in the positive electrode is not particularly limited as long as it has excellent electrical conductivity without causing side reactions in the internal environment of the lithium secondary battery or causing chemical changes in the battery. Typically, graphite or conductive carbon can be used, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and thermal black; carbon-based materials whose crystalline structure is graphene or graphite; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives; which can be used alone or in mixtures of two or more, but are not necessarily limited to these.

[0054] The conductive material can usually be added in an amount of 0.5 to 50 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode.

[0055] The positive electrode of the present invention can be manufactured by dispersing and mixing the positive electrode active material, binder, and conductive material in a dispersion medium (solvent) to create a slurry, applying this slurry to a positive electrode current collector, and then drying and rolling it. The dispersion medium can be, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof.

[0056] The positive electrode current collector may be made of platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In-doped SnO2), FTO (F-doped SnO2), and alloys thereof, as well as aluminum (Al) or stainless steel with a surface treatment of carbon (C), nickel (Ni), titanium (Ti), or silver (Ag), but is not necessarily limited to these. The positive electrode current collector may take the form of foil, film, sheet, punched, porous, or foamed material.

[0057] Separation membrane The separation membrane is interposed between the positive and negative electrodes, preventing short circuits between them and providing a pathway for lithium ions to move. The separation membrane can be made of polyethylene, polypropylene or other olefin polymers, glass fibers, etc., in the form of sheets, multilayer membranes, microporous films, woven fabrics, and nonwoven fabrics, but is not limited to these. On the other hand, if a solid electrolyte such as a polymer (e.g., organic solid electrolyte, inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte can also serve as the separation membrane.

[0058] electrolyte The electrolyte can be a solid electrolyte or a liquid electrolyte, and the liquid electrolyte can be, for example, a non-aqueous electrolyte (non-aqueous organic solvent). The non-aqueous electrolyte can be a carbonate, ester, ether, or ketone, either alone or in a mixture of two or more, but is not necessarily limited to these. For example, aprotic organic solvents such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butylloractone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, triesters phosphate, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxyethane, tetrahydroxyfuran (Franc), tetrahydrofuran derivatives such as 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, dioxolane and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, methyl propionate, and ethyl propionate can be used, but are not necessarily limited to these.

[0059] The electrolyte can be used with the addition of a lithium salt (a so-called lithium salt-containing non-aqueous electrolyte), and the lithium salt can be one of known ones that dissolves easily in non-aqueous electrolytes, such as LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 Examples include LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiPF3(CF2CF3)3, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, and lithium imide, but are not necessarily limited to these.

[0060] The lithium secondary battery of the present invention can be manufactured by conventional methods in the art. For example, it can be manufactured by placing a porous separation membrane between the positive electrode and the negative electrode and adding a non-aqueous electrolyte.

[0061] Although the present invention has been described in relation to the preferred embodiments mentioned above, various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the appended claims include such modifications and variations, insofar as they fall within the spirit of the invention. [Explanation of symbols]

[0062] 10: Molding frame 12: Molding groove 20: Lithium electrode 22: Lithium electrode tap 30: Metal Lead 40: Electrode lead film

Claims

1. A lithium secondary battery comprising a laminated junction structure of lithium electrode taps and metal leads, The lithium electrode tap portion joined to the aforementioned metal lead is It has a thickness thinner than the lithium electrode tap portion that does not make contact with the metal lead. A lithium secondary battery characterized by having a wider width in the lateral direction based on the direction of contact with the metal lead than the lithium electrode tap portion that is not in contact with the metal lead.

2. The lithium secondary battery according to claim 1, characterized in that the end edge with a wider width in the lateral direction is in a planar form.

3. A step exists between the lithium electrode tap portion that is not joined to the metal lead and the lithium electrode tap portion that is joined to the metal lead, due to the difference in thickness. The lithium secondary battery according to claim 1, characterized in that it has a structure in which metal leads are stacked on the lower part of the step.

4. The lithium secondary battery according to claim 3, characterized in that the step of the lithium electrode tap also exists on the opposite side of the surface on which the metal leads are stacked.

5. The lithium secondary battery according to claim 3, characterized in that the end surface of the metal lead joined to the lithium electrode tap in the direction of the lithium electrode tap is joined to the step-forming surface of the lithium electrode tap.

6. The lithium secondary battery according to claim 1, characterized in that the end surface of the lithium electrode tap joined to the metal lead in the direction of the metal lead is planar.

7. The lithium secondary battery according to claim 1, characterized in that the upper and lower surfaces of the lithium electrode tap joined to the metal lead are planar in shape with a uniform thickness.

8. The lithium secondary battery according to claim 1, characterized in that the lithium secondary battery includes a free-standing lithium electrode.

Images