Method for bonding electrode tap and metal lead 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 June 21, 2021, and Korean Patent Application No. 10-2022-0074655 filed June 20, 2022, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference.

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

[0003] As interest in energy storage technology continues to grow, the application fields are expanding to include energy storage in mobile phones, tablets, laptops, and camcorders, as well as electric vehicles (EVs) and hybrid electric vehicles (HEVs), and research and development into electrochemical devices is steadily increasing.

[0004] Among the electrochemical devices, lithium secondary batteries capable of being charged and discharged, and furthermore, the development of lithium secondary batteries, have been the focus of attention. Recently, in developing such batteries, research and development into new electrode and battery designs has been actively conducted in order to improve capacity density and specific energy.

[0005] As a result, lithium metal batteries, which are being developed as next-generation batteries, have a negative electrode made solely of lithium. However, lithium has a lower melting point than other metals, breaks easily, and there is a risk of explosion when exposed to air, making it difficult to develop into batteries.

[0006] In particular, joining the lithium electrode tab of the lithium negative electrode to the metal lead is known to be a very difficult task due to the soft nature of the lithium electrode tab.

[0007] That is, in the case of 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.), but it is difficult to apply such techniques to welding the lithium electrode tap and metal lead of the lithium negative electrode.

[0008] Therefore, in the prior art, as shown in Figure 1, a metal lead and a lithium electrode tab are laminated and then pressed together to bond them. However, when using this method, the lithium electrode tab is soft, and the degree to which it expands varies depending on the amount of pressure and the duration of pressure applied, making it difficult to control the bonding strength and the specifications of the bonded portion. That is, the shape of the outer periphery of the lithium electrode tab varies with each operation, and the end of the outer periphery also has many indentations and dents, making it difficult to form a bonded portion with a uniform shape. It is also difficult to form the lithium electrode tab with a uniform thickness and bonded area.

[0009] Furthermore, the conventional method described above has the drawback of low battery production efficiency because lithium sticks to the pressing device that presses the lithium electrode tab, 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 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been devised to solve the above-mentioned problems of the prior art, The present invention provides a method for joining an electrode tap and a metal lead, which allows the outer periphery of the lithium electrode tap to be uniformly shaped, the thickness of the lithium electrode tap to be uniform, and the joining area to be reliably adjusted, thereby easily adjusting the joining strength and specifications of the lithium electrode tap and metal lead, minimizing the resistance deviation between cells, and significantly improving process efficiency, and also provides a lithium secondary battery including a joining structure formed by the method. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides (a) preparing a molding frame for a lithium electrode tap; (b) positioning one end of a lithium electrode tab in the forming groove of the forming frame; (c) laminating one end of a metal lead on the upper portion of the lithium electrode tab positioned in the forming groove; and (d) pressing the upper part of the stacked metal lead;

[0013] The present invention also provides A lithium secondary battery including an electrode junction structure of a lithium electrode tap and a metal lead, The lithium secondary battery is characterized in that both longitudinal side surfaces of the lithium electrode tab joined to the metal lead are formed flat. [Effects of the Invention]

[0014] The method for joining a lithium electrode tap and a metal lead according to the present invention allows the outer periphery of the lithium electrode tap to be uniformly shaped, the thickness of the lithium electrode tap to be uniform, and the joining area to be reliably adjusted, thereby making it possible to easily adjust the joining strength and the specifications of the joining portion between the lithium electrode tap and the metal lead.

[0015] Furthermore, the method for joining an electrode tap and a metal lead according to the present invention significantly improves process efficiency, minimizes joint defects, and minimizes resistance deviations between cells.

[0016] The lithium secondary battery of the present invention provides improved quality since it includes a joint structure between the lithium electrode tap and the metal lead, which has excellent joint strength. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view schematically showing a conventional method for joining a lithium electrode tap and a metal lead. [Figure 2] 1 is a perspective view schematically showing one embodiment of a method for joining a lithium electrode tap and a metal lead of the present invention. FIG. [Figure 3] 1 is a perspective view schematically showing one embodiment of a method for joining a lithium electrode tap and a metal lead of the present invention. FIG. [Figure 4] 1 is a perspective view schematically showing one embodiment of a molding frame used in a method for joining a lithium electrode tap and a metal lead of the present invention. FIG. [Figure 5] 1 is a diagram schematically illustrating the joining mechanism of the method for joining a lithium electrode tap and a metal lead according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily understand the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein. The same reference numerals are used throughout the specification to refer to similar parts.

[0019] The method for joining a lithium electrode tap and a metal lead according to the present invention is as follows, as shown in FIGS. 2, 3 and 5: (a) preparing a molding frame 10 for a lithium electrode tap; (b) positioning one end of a lithium electrode tab 22 in the forming groove 12 of the forming frame; (c) laminating one end of a metal lead 30 on the upper portion of the lithium electrode tab 22 positioned in the forming groove 12; and (d) pressing the upper portion of the stacked metal leads 30;

[0020] As shown in FIG. 1, the prior art did not use a molding frame, but instead stacked one end of the lithium electrode tab 22 and one end of the metal lead 30 together, and then pressed to join the lithium electrode tab and the metal lead.

[0021] However, when using this method, since the lithium electrode tab is soft, the degree to which the lithium electrode tab is pressed and expanded varies depending on the magnitude of the pressing pressure and the pressing time, making it difficult to control the joining strength and the specifications of the joint. That is, the shape of the outer periphery of the lithium electrode tab varies each time it is worked, and the end of the outer periphery also becomes uneven, making it difficult to form a joint with a uniform shape. It is also difficult to form the lithium electrode tab with a uniform thickness and joint area.

[0022] In addition, the joint between the lithium electrode tap and the metal lead formed by this method has an inconsistent thickness and area, which causes a problem of large resistance deviation between cells. If the joint area is insufficient, the joint easily breaks, causing many defects during cell assembly.

[0023] However, the conventional method described above causes lithium to stick to the pressing device that presses the lithium electrode tab, resulting in poor bonding. Furthermore, it also increases the time required for the bonding process, thereby reducing the production efficiency of the battery.

[0024] The present invention is characterized by easily adjusting the bonding strength and bonding size by bonding the lithium electrode tab 22 and the metal lead 30 using the molding frame 10. That is, the bonding method of the present invention uses the molding frame 10 to uniformly form the outer periphery of the lithium electrode tab 22 according to 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 tab and the metal lead. In addition, the action of the molding frame 10 also makes it possible to form the lithium electrode tab 22 with a uniform thickness. That is, because the wall forming the molding groove 12 in the molding frame 10 functions as a stopper during compression, the electrode tab 22 can be formed with a uniform thickness without having to delicately adjust the pressure on the metal lead 30 during compression.

[0025] In addition, in the bonding method of the present invention, the lithium electrode tab 22 does not come into direct contact with the pressing device, but only comes into contact with the forming groove 12 of the forming frame, so there is no problem of lithium sticking to the pressing device, which causes bonding defects, and there is no problem of lithium sticking to the pressing device, which causes the bonding process to take longer.

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

[0027] Such a form of forming groove 12 is preferable because it is possible to uniformly control the shapes of both side surfaces in the longitudinal direction of lithium electrode tab 22 .

[0028] In one embodiment of the present invention, the forming 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 may be positioned toward the electrode 20 coupled with the lithium electrode tab 22.

[0029] Such a shaped groove 12 is preferable because it allows the shape of not only both side surfaces in the longitudinal direction of the lithium electrode tab 22 but also the end portion to be uniformly controlled.

[0030] In one embodiment of the present invention, the forming groove 12 may have a width that is 0.5 to 1 times the width of the metal lead 30. If the width of the forming groove is greater than the width of the metal lead, a portion of the lithium electrode tab 22 that does not bond with the metal lead 30 may be formed during bonding, and the lithium electrode tab 22 may lift up in the portion where the metal lead 30 is not present during compression, which may cause a resistance deviation between cells, which is undesirable.

[0031] In one embodiment of the present invention, the depth of the forming groove 12 is preferably shallower than the thickness of the lithium electrode tab 22. This is because, when the metal lead 30 is pressed to bond the metal lead 30 and the lithium electrode tab 22, the lithium electrode tab 22 becomes soft and thins, causing it to spread laterally. In order to make the lithium electrode tab 22 have a uniform thickness, the wall that forms the forming groove 12 in the forming frame 10 needs to act as a stopper that stops the pressing of the metal lead 30, as shown in Figure 5(a).

[0032] In one embodiment of the present invention, the forming groove 12 is preferably formed to be wider than the width of the lithium electrode tab 22. This is because the lithium electrode tab 22 expands laterally when pressed in the thickness direction, and a space capable of accommodating this expanded portion must be present in the forming groove.

[0033] In one embodiment of the present invention, the step of welding the lithium electrode tab and the metal lead may be further included after step (d). However, the welding step is not an essential step. That is, the metal lead and the lithium electrode tab can be joined without welding using various joining structures, so the welding step may be selectively performed.

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

[0035] The bonding mechanism of the method for bonding a lithium electrode tab and a metal lead according to the present invention is illustrated in Figure 5. Figure 5(a) shows cross sections of the lithium electrode tab 22 and the metal lead 30 in the explosion direction (horizontal direction) before and after bonding. As shown in Figure 5(a), when pressure is applied in at least one direction of the metal lead 30 and the molding frame 10, the soft lithium electrode tab 22 expands laterally and is molded into the molding groove 12, and is simultaneously bonded to the metal lead 30.

[0036] 5(b) shows longitudinal (vertical) cross sections of the lithium electrode tab 22 and metal lead 30 before and after bonding. As shown in FIG. 5(b), when pressure is applied from at least one direction of the metal lead 30 and the molding frame 10, the soft lithium electrode tab 22 expands laterally as shown in (a) above, and at the same time, its thickness is reduced as shown in (b) to form the molding groove 12. This is how the lithium electrode tab 22 is bonded to the metal lead 30.

[0037] 5(c) shows the deformation behavior of the lithium electrode tab 22 due to pressure from above the lithium electrode tab 22. As shown in FIG. 5(c), when pressure is applied from at least one direction of the metal lead 30 and the molding frame 10, the soft lithium electrode tab 22 expands laterally and is molded into the shape of the molding groove 12.

[0038] The present invention also provides a method for producing a semiconductor device comprising: A lithium secondary battery including a laminated joint structure of a lithium electrode tap and a metal lead, The present invention relates to a lithium secondary battery in which both longitudinal side surfaces of the lithium electrode tab joined to the metal lead are formed flat.

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

[0040] The details of the method for joining the electrode tap and the metal lead described above can be similarly applied to the lithium secondary battery, and therefore, the same details as those described above will be omitted.

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

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

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

[0044] In one embodiment of the present invention, the stacked junction structure may include a form in which a lithium electrode tab 22 having a step and a metal lead 30 are stacked and joined to a lower part of the step, as shown in FIG. 5(b).

[0045] In one embodiment of the present invention, the laminated junction structure may include a form in which a lithium electrode tab 22 having a step is joined to a metal lead 30 stacked below the step, as shown in FIG. 5(b), and the surface of the lithium electrode tab 22 opposite to the metal lead 30 stack may also include a step.

[0046] In one embodiment of the present invention, the step may be formed by a process of positioning one end of a lithium electrode tab 22 in a forming groove 12 of a lithium electrode tab forming mold 10, stacking one end of a metal lead 30 on the lithium electrode tab 22, and then pressing the upper part of the stacked metal lead 30, as shown in FIG. 5(b).

[0047] The end surface of the metal lead bonded to the lithium electrode tab 22 may be bonded without gaps to the stepped surface of the lithium electrode tab, forming a laminated bonded structure. Here, "without gaps" means that there are substantially no gaps.

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

[0049] In one embodiment of the present invention, the lithium secondary battery may be manufactured including a negative electrode, which is a freestanding lithium electrode, a positive electrode, an electrolyte interposed between the negative electrode and the positive electrode, and a separator.

[0050] The lithium secondary battery of the present invention may be fabricated by a known method using a known structure in the art, except for the joining structure of the lithium electrode tap and the metal lead. Specific examples of the positive electrode, electrolyte, and separator are 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, a conductive material, and the like. The binder is a component that aids in bonding the positive electrode active material to the conductive material and the current collector, and may be, for example, at least one 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, and mixtures thereof, but is not limited thereto.

[0052] The binder may 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 and does not cause side reactions in the internal environment of the lithium secondary battery or chemical changes to the battery. Representative examples include graphite or conductive carbon, and examples thereof include graphite such as natural graphite and 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 having a graphene or graphite crystal structure; 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. These may be used alone or in combination. However, the conductive material is not necessarily limited thereto.

[0054] The conductive material may 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 cathode of the present invention can be manufactured by dispersing and mixing the cathode active material, binder, and conductive material in a dispersion medium (solvent) to form a slurry, which is then coated on a cathode current collector, dried, and rolled. The dispersion medium can be, but is not limited to, NMP (N-methyl-2-pyrrolidone), DMF (dimethyl formamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or a mixture thereof.

[0056] The positive electrode current collector may be, but is not limited to, 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 SnO), FTO (F-doped SnO), alloys thereof, or aluminum (Al) or stainless steel surface-treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag). The positive electrode current collector may be in the form of a foil, film, sheet, punched, porous, foam, or the like.

[0057] Separation membrane The separator is interposed between the positive electrode and the negative electrode to prevent short circuits between them and provide a path for lithium ions to move. The separator may be made of an olefin polymer such as polyethylene or polypropylene, glass fiber, or the like, and may be in the form of a sheet, multi-layer membrane, microporous film, woven fabric, or nonwoven fabric, but is not limited thereto. Meanwhile, when a solid electrolyte such as a polymer (e.g., an organic solid electrolyte, an inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also serve as the separator.

[0058] electrolyte The electrolyte may be a solid electrolyte or a liquid electrolyte, and the liquid electrolyte may be, for example, a non-aqueous electrolyte solution (non-aqueous organic solvent). The non-aqueous electrolyte solution may be, but is not limited to, carbonate, ester, ether, or ketone, either alone or in combination. 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-butyl lactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxyethane, tetrahydroxyfuran, tetrahydrofuran derivatives such as 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, dioxolane and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, methyl propionate, and ethyl propionate may be used, but are not limited thereto.

[0059] The electrolyte may further contain a lithium salt (a so-called lithium salt-containing non-aqueous electrolyte). The lithium salt may be a known salt that is easily dissolved in a non-aqueous electrolyte, such as LiCl, LiBr, LiI, LiClO4, LiBF4, or LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiPF3(CF2CF3)3, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide, etc., but are not necessarily limited to these.

[0060] The lithium secondary battery of the present invention can be manufactured by a conventional method in the art, for example, by inserting a porous separator between a positive electrode and a negative electrode and then introducing a non-aqueous electrolyte solution.

[0061] Although the present invention has been described in connection with the preferred embodiments set forth above, various modifications and variations can be made without departing from the spirit and scope of the invention, and therefore, the appended claims are intended to cover all such modifications and variations as fall within the spirit and scope 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) preparing a lithium electrode tap molding form; (b) positioning one end of a lithium electrode tab in the forming groove of the forming frame; (c) laminating one end of a metal lead on the upper portion of the lithium electrode tab positioned in the forming groove; and (d) pressing the upper portion of the laminated metal lead.

2. 2. The method of claim 1, wherein the forming groove in step (a) is formed in a continuous form from the leading end to the trailing end of the forming mold in the direction of the metal lead.

3. 2. The method of claim 1, wherein the formed groove in step (a) is a rectangular groove having one side open, and the open side is located toward the electrode coupled to the lithium electrode tap.

4. 4. The method for joining an electrode tap and a metal lead according to claim 2, wherein the width of the formed groove is 0.5 to 1 times the width of the metal lead.

5. 2. The method of claim 1, further comprising the step of welding the lithium electrode tap and the metal lead after step (d).

6. 2. The method of claim 1, further comprising, before step (b), applying a release agent to the molding groove or covering the molding groove with a release film.

7. A lithium secondary battery including a laminated joint structure of a lithium electrode tap and a metal lead, A lithium secondary battery, characterized in that both longitudinal side surfaces of the lithium electrode tab joined to the metal lead are formed flat.

8. 8. The lithium secondary battery according to claim 7, wherein the laminated junction structure comprises a lithium electrode tab having a step and a metal lead laminated and joined to a lower portion of the step.

9. The lithium secondary battery according to claim 8 , wherein the surface of the lithium electrode tab opposite to the metal lead lamination also includes a step.

10. 10. The lithium secondary battery of claim 8, wherein the step is formed by a process of positioning one end of the lithium electrode tab in a forming groove of a lithium electrode tab forming mold, stacking one end of a metal lead on an upper portion of the lithium electrode tab, and pressing an upper portion of the stacked metal lead.

11. The lithium secondary battery according to claim 8, wherein an end surface of the metal lead joined to the lithium electrode tab is joined to a stepped surface of the lithium electrode tab without any gap.

12. 8. The lithium secondary battery according to claim 7, wherein the end surface of the lithium electrode tab connected to the metal lead in the metal lead direction is formed as a flat surface.

13. The lithium secondary battery according to claim 7 , wherein the upper and lower surfaces of the lithium electrode tab joined to the metal lead are formed as flat surfaces with a uniform thickness.

14. 8. The lithium secondary battery according to claim 7, wherein the lithium secondary battery comprises a free-standing lithium electrode.

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