Negative electrode, method for manufacturing the same, secondary battery containing the same, and method for manufacturing a secondary battery

Abstract

The present invention relates to a negative electrode, a manufacturing method thereof, a secondary battery including the same, and a manufacturing method thereof, and more particularly to a negative electrode including a metal foil and a negative electrode active material layer coated thereon, wherein an upper end and a lower end of the negative electrode are coated with a binder, a manufacturing method thereof, a secondary battery including the same, and a manufacturing method thereof. According to the present invention, there is provided a negative electrode and a manufacturing method thereof that prevents the folding phenomenon of the separator during the manufacture of a stack cell by having excellent adhesion to the separator without impairing battery performance, and further, there is provided a secondary battery and a manufacturing method thereof that reduces the reduction in manufacturing yield and the occurrence of accidents due to low voltage defects.

Description

[Technical Field]

[0001] [Cross-reference with related applications] This application claims priority under Korean Patent Application No. 10-2022-0038662 dated March 29, 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a negative electrode, a method for manufacturing the same, a secondary battery containing the same, and a method for manufacturing a secondary battery. More specifically, it relates to a negative electrode and a method for manufacturing the same that do not impair battery performance, have excellent adhesion to the separation membrane, and prevent the folding phenomenon of the separation membrane during the manufacturing of stack cells, and to a secondary battery and a method for manufacturing the same that, due to the absence of folding of the separation membrane, reduce the reduction in manufacturing yield due to low voltage defects and the occurrence of accidents. [Background technology]

[0003] A lithium secondary battery generally consists of a positive electrode, in which the positive electrode active material layer is coated with a metal foil such as aluminum; a negative electrode, in which the negative electrode active material layer is coated with a metal foil such as copper; a separation membrane that prevents the positive and negative electrodes from mixing with each other; and an electrolyte that allows lithium ions to move between the positive and negative electrodes.

[0004] Lithium-ion secondary batteries are classified into winding and stacking methods depending on the manufacturing method, and the stacking method is further classified into stack and folding method (Lamination and Stacking method), Z-folding method (Zigzag Stacking method), and so on.

[0005] The aforementioned winding method, which involves winding cells to produce lithium secondary batteries, results in empty spaces and low energy density, and has the problem of distortion and swelling occurring during long-term charging and discharging.

[0006] On the other hand, the aforementioned stacking method has the advantage of minimizing empty space, resulting in high energy density, and less strain and swelling, because it creates lithium secondary batteries by stacking cells.

[0007] However, in the aforementioned stacking method, intermediate assemblies such as a half-cell composed of a separator membrane / negative electrode / separator membrane / positive electrode, or a monocell composed of a separator membrane / negative electrode / separator membrane, are first manufactured, and then these intermediate assemblies are stacked and attached to produce a stack cell. However, in this case, because the adhesion force between the negative electrode and the separator membrane is low, folding of the separator membrane occurs inside the stack cell. Such folding of the separator membrane leads to low voltage defects in lithium secondary batteries, reduces the manufacturing yield, and if the defect is not detected during the manufacturing stage, an accident may occur during consumer use.

[0008] Therefore, there is an urgent need to develop secondary batteries that have high energy density, do not experience problems such as strain or swelling, and do not suffer from membrane folding or low-voltage failures. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Korean Published Patent No. 10-2017-0103208 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] To solve the problems of the conventional technology described above, the present invention aims to provide a negative electrode that does not impede battery performance, has excellent adhesion to the separation membrane, and prevents the folding phenomenon of the separation membrane during the manufacturing of stacked cells, as well as a method for manufacturing the same.

[0011] Furthermore, the present invention aims to provide a secondary battery that reduces the decrease in manufacturing yield and the occurrence of accidents due to low voltage failures caused by folding of the separation membrane, and a method for manufacturing the same.

[0012] The above-mentioned and other objectives of the present invention can all be achieved by the present invention as described below. [Means for solving the problem]

[0013] To achieve the above objective, I) one embodiment of the present invention provides a negative electrode comprising a metal foil and a negative electrode active material layer coated on the metal foil, wherein a binder is coated on the upper and lower ends of the negative electrode.

[0014] II) The binder may preferably be a PVdF-based binder.

[0015] III) In I) and II) above, the negative electrode active material layer may preferably contain an SBR-based binder.

[0016] IV) In I) to III) above, preferably, the coating area of ​​the binder at the lower end of the negative electrode may be larger than that at the upper end of the negative electrode.

[0017] V) In I) to IV) above, the negative electrode active material layer may preferably include a silicon-based active material.

[0018] VI) In I) to V) above, the negative electrode active material layer may preferably include a carbon-based conductive material.

[0019] VII) One embodiment of the present invention provides a method for manufacturing a negative electrode, which includes the steps of forming a negative electrode active material layer on a metal foil and pattern coating the upper and lower ends of the negative electrode active material layer with a binder.

[0020] VIII) In the above I) - VII), the pattern coating may preferably be dual die coating.

[0021] IX) In the above I) - VIII), the method for forming the negative electrode active material layer may preferably be a strip continuous coating method.

[0022] X) In the above I) - IX), the method for manufacturing the negative electrode may preferably include a notching step after the pattern coating step.

[0023] Further, XI) An embodiment of the present invention provides a secondary battery including a negative electrode including a metal foil and a negative electrode active material layer coated on the metal foil, a positive electrode including a metal foil and a positive electrode active material layer coated on the metal foil, and a separator, wherein the negative electrode has a PVdF - based binder coated on its upper and lower ends.

[0024] XII) In the above I) - XI), the separator may contain a PVdF - based binder.

[0025] Further, XIII) An embodiment of the present invention provides a method for manufacturing a secondary battery, including steps of forming a negative electrode active material layer on a metal foil, pattern - coating a binder on the upper and lower ends of the negative electrode active material layer, notching to manufacture a monocell after the pattern - coating step, laminating a separator on the monocell, and stacking a positive electrode including a metal foil and a positive electrode active material layer coated on the metal foil on the separator.

[0026] XIV) In I) - XIII), the pattern coating is preferably dual die coating, or the formation of the negative electrode active material layer can be by a strip continuous coating method.

Advantages of the Invention

[0027] The present invention provides a negative electrode that does not impair battery performance, has excellent adhesion to the separation membrane, and prevents the folding phenomenon of the separation membrane during the manufacturing of stacked cells, as well as a method for manufacturing the same.

[0028] Furthermore, the present invention has the effect of providing a secondary battery that reduces the decrease in manufacturing yield and the occurrence of accidents due to low voltage defects, as well as a method for manufacturing the same. [Brief explanation of the drawing]

[0029] [Figure 1] This plan view schematically shows, in order, a negative electrode sheet in which a negative electrode active material layer is continuously coated onto a metal foil (strip); a negative electrode sheet in which a binder is coated on the upper and lower ends of the upper layer of the negative electrode active material layer; and a negative electrode plate that has been notched from the negative electrode sheet, projected onto a horizontal plane. [Figure 2] This is a simplified process diagram showing the assembly process of a stack cell from electrode preparation to the taping step. [Figure 3] This is a simplified cross-sectional view showing the cross-section of the intermediate assembly where the separation membrane has folded. [Modes for carrying out the invention]

[0030] The inventors confirmed that when the upper and lower edges of the surface of the negative electrode active material layer are thinly coated with a predetermined binder, the battery performance is not reduced and the folding phenomenon of the separation membrane does not occur, thereby greatly improving the productivity and stability of lithium secondary batteries. Based on this, they continued their research and completed the present invention.

[0031] The negative electrode, its manufacturing method, the secondary battery containing it, and the manufacturing method of the secondary battery will be described in detail below.

[0032] However, the terms and words used in this specification and in the claims shall not be interpreted to be limited to their ordinary or dictionary meanings, but rather to be interpreted in a sense and concept consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their invention. Accordingly, it should be understood that the embodiments and configurations shown in the drawings described herein are merely embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can substitute for them, and that they may be arranged, substituted, combined, separated or designed in various other configurations.

[0033] All technical or scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention pertains, unless otherwise defined.

[0034] negative electrode The negative electrode of the present invention is a negative electrode comprising a metal foil and a negative electrode active material layer coated on the metal foil, characterized in that a binder is coated on the upper and lower ends of the negative electrode. In this case, it does not impede battery performance and has excellent adhesion to the separation membrane, thus having the advantage of preventing the folding phenomenon of the separation membrane during the manufacture of stacked cells.

[0035] The binder is preferably a PVdF-based binder, and specific examples of the PVdF-based binder include poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), polyvinylidene fluoride-co-trichloroethylene (PVdF-TCE), poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVdF-CTFE), poly(vinylidene fluoride-co-tetrafluoroethylene) (PVdF-TFE), and poly(vinylidene fluoride-co-trichloroethylene). It is one or more selected from the group consisting of oloethylene (PVdF-TrFE), in which case it does not impair battery performance and has even better adhesion to the separation membrane, thus having the effect of preventing the folding phenomenon of the separation membrane during the manufacture of stacked cells. In particular, when the negative electrode active material layer contains an SBR-based binder and the binder is a PVdF-based binder, the adhesion between such a negative electrode and a separation membrane that generally contains a PVdF-based binder is very good, so there is the advantage that the folding phenomenon of the separation membrane does not occur during the manufacture of stacked cells.

[0036] The upper end of the negative electrode coated with the binder may preferably be 0.01 to 0.2 times the area of ​​the entire negative electrode active material layer, more preferably 0.01 to 0.1 times, even more preferably 0.015 to 0.05 times, and even more preferably 0.02 to 0.04 times. In this case, the battery performance is not hindered, and the adhesion to the separation membrane is even better, which has the effect of preventing the folding phenomenon of the separation membrane during the manufacturing of stacked cells.

[0037] The lower end of the negative electrode coated with the binder may preferably be 0.01 to 0.3 times the area of ​​the entire negative electrode active material layer, more preferably 0.05 to 0.2 times, even more preferably 0.1 to 0.2 times, and even more preferably 0.1 to 0.15 times. In this case, there is the advantage that it can be applied to the manufacture of various stack cells with different notching lengths, and it does not impede battery performance and does not reduce the adhesion strength with the separation membrane, thus preventing the folding phenomenon of the separation membrane during the manufacture of the stack cell.

[0038] The lower end portion of the negative electrode coated with the binder preferably has an area that is not smaller than, more preferably larger than, the upper end portion of the negative electrode coated with the binder. In this case, there is an advantage that it is applicable to the manufacture of various stack cells with different notch lengths, does not inhibit battery performance, has an even better adhesive force with the separator, and thus has the effect of preventing the folding phenomenon of the separator during the manufacture of the stack cell.

[0039] The layer (hereinafter referred to as the "pattern coating layer") in which the binder is pattern-coated on the upper end portion and the lower end portion has a thickness of, for example, 1 μm to 30 μm, preferably 1 μm to 5 μm, more preferably 2 to 4 μm. Within this range, it does not inhibit battery performance, has an even better adhesive force with the separator, and thus has the effect of preventing the folding phenomenon of the separator during the manufacture of the stack cell.

[0040] In this description, the method for measuring the thickness of the layer is not particularly limited as long as it is a method for measuring the layer thickness commonly used in the technical field to which the present invention pertains.

[0041] The negative electrode active material layer preferably contains an SBR-based binder. The SBR-based binder is, as a specific example, one or more selected from the group consisting of styrene-butadiene rubber and acrylated styrene-butadiene rubber. In this case, it does not inhibit battery performance, has an even better adhesive force with the separator, and thus has the effect of preventing the folding phenomenon of the separator during the manufacture of the stack cell.

[0042] The negative electrode active material layer preferably contains a silicon-based active material. The silicon-based active material may be, as a specific example, one or more selected from the group consisting of Si, SiO x (0 < x < 2), and SiC. In this case, it has an even better adhesive force with the separator, and thus has the effect of preventing the folding phenomenon of the separator during the manufacture of the stack cell. Also, it has the advantage of excellent discharge capacity of the secondary battery.

[0043] The negative electrode active material layer preferably contains a conductive material, and the conductive material is not particularly limited as long as it is used as a conductive material in the art to which the present invention belongs. Specific examples include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; conductive metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; and conductive organic compounds such as polyphenylene derivatives. Preferably, the conductive material is a carbon-based conductive material, in which case it does not impede battery performance and has even better adhesion to the separation membrane, thus preventing the folding phenomenon of the separation membrane during the manufacture of stacked cells.

[0044] The negative electrode active material layer may further contain, if necessary, thickeners, surfactants and / or solvents commonly used in the art to which the present invention belongs.

[0045] Negative electrode manufacturing method The method for manufacturing a negative electrode according to the present invention is characterized by including the steps of forming a negative electrode active material layer on a metal foil and pattern coating the upper and lower ends of the negative electrode active material layer with a binder. In this case, it does not impede battery performance and has excellent adhesion to the separation membrane, thus having the advantage of preventing the folding phenomenon of the separation membrane during the manufacturing of stacked cells.

[0046] The binder may preferably be applied to the pattern coating in the form of a slurry or solution mixed with water or an organic solvent. In this case, the coating process can be easily controlled, and there is an advantage in that the pattern coating layer has excellent reproducibility.

[0047] The organic solvent is not particularly limited as long as it is an organic solvent that can turn the binder into a slurry or solution. For example, it may be an organic solvent that is commonly used as a binder in the art to which the present invention belongs. Specifically, it may be one or more selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), tetrahydrofuran (THF), acetone, N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0048] The pattern coating is preferably slot die coating, more preferably dual die coating. In this case, multiple layers can be coated using a single coating apparatus, which simplifies the process, reduces costs, and allows for arbitrary adjustment of the slot width, thus enabling coating of various widths without replacing the entire coating apparatus.

[0049] The dual-die coating includes, as a specific example, a slot die and a shim fitted into the slot, in which case the shim obstructs a portion of the slot, thereby adjusting the width or division of the coating layer as the coating liquid passes through the slot and coats the surface of the substrate.

[0050] The shims can be fitted into desired positions in the slots, and there may be one or more of them, and they may be selected to be of a desired length. In this case, multiple layers can be coated using a single coating apparatus, or coating layers of various widths can be formed. This eliminates the need to replace the coating apparatus due to changes in the coating shape, simplifies the coating process, and reduces coating costs.

[0051] The pattern-coated upper end may preferably be coated with an area of ​​0.01 to 0.2 times the total area of ​​the negative electrode active material layer, more preferably 0.01 to 0.1 times, even more preferably 0.015 to 0.05 times, and even more preferably 0.02 to 0.04 times. Within this range, the binder, even after the notching step, matches the height of the pattern-coated upper end of the negative electrode, which does not impede battery performance and provides even better adhesion to the separation membrane, thus preventing the folding phenomenon of the separation membrane during the manufacturing of stacked cells.

[0052] The lower end portion to be pattern-coated may preferably be coated with an area of ​​0.01 to 0.3 times the total area of ​​the negative electrode active material layer, more preferably 0.05 to 0.2 times, even more preferably 0.1 to 0.2 times, and even more preferably 0.1 to 0.15 times. Within this range, there is the advantage that it can be applied to the manufacture of various stack cells with different notching lengths. Since there is no damage or loss of the binder layer even after the notching step, the excellent adhesion to the separation membrane is maintained, which has the effect of suppressing the folding phenomenon of the separation membrane during the manufacture of the stack cell.

[0053] The aforementioned area or width ratio can be interpreted as the height ratio from the bottom end across the top end when the coating is applied in a "-" shape or horizontally with respect to the top and bottom ends of the negative electrode.

[0054] The foil may, for example, be copper foil.

[0055] The method for manufacturing the negative electrode may preferably include a notching step after pattern coating. In this case, the adhesion to the separation membrane is further improved without hindering battery performance, thus preventing the folding phenomenon of the separation membrane during the manufacturing of stacked cells.

[0056] In this description, notching refers to a process of machining an electrode or similar object using a device capable of cutting along the intended cutting area.

[0057] The method for forming the negative electrode active material layer may preferably be a method of continuously coating a slurry-like negative electrode active material composition onto a metal foil in strip form. In this case, battery performance is not hindered, and the adhesion to the separation membrane is even better, which has the effect of preventing the folding phenomenon of the separation membrane during the manufacture of stacked cells.

[0058] The following describes specific examples in detail based on the attached drawings.

[0059] Figure 1 below is a schematic plan view showing, in order, a negative electrode sheet in which a negative electrode active material layer is continuously coated onto a metal foil (strip), a negative electrode sheet in which a binder is coated on the upper and lower ends of the upper layer of the negative electrode active material layer, and a negative electrode plate that has been notched from the negative electrode sheet, projected onto a horizontal plane.

[0060] Referring to Figure 1, first, a negative electrode sheet is prepared by continuously coating a negative electrode active material layer (inner part; gray area) onto a metal foil (outer part; yellow area), which is the negative electrode current collector. Next, a predetermined binder is pattern-coated onto the upper end (narrow, thin gray area) and lower end (wide, thin gray area) of the upper layer of the negative electrode active material layer. Here, the height of the pattern coating layer can be adjusted by the width of the dual-disim. Then, the negative electrode sheet pattern-coated with the binder is notched to finally produce a negative electrode that does not fold the separation membrane according to the present invention. In the drawing, four negative electrodes are produced. In a preferred embodiment, the negative electrode active material layer and / or pattern coating layer may be dried immediately after formation and rolled before notching without a separate drying step to produce the negative electrode sheet. However, if necessary, such as when the boiling point (bp) of the solvent used is high, the negative electrode sheet may be produced by forming the negative electrode active material layer and / or pattern coating layer, drying the produced negative electrode sheet at a temperature above the boiling point of the solvent, and then rolling it before notching.

[0061] secondary battery The secondary battery of the present invention comprises a negative electrode including a metal foil and a negative electrode active material layer coated on the metal foil, a positive electrode including a metal foil and a positive electrode active material layer coated on the metal foil, and a separation membrane, wherein the negative electrode is coated with a PVdF-based binder at its upper and lower ends. In this case, while having excellent battery performance, there is no folding of the separation membrane, which has the advantage of providing a secondary battery that reduces the reduction in manufacturing yield due to low voltage defects and the occurrence of accidents.

[0062] The aforementioned negative electrode may include all of the above-described details relating to the negative electrode and the method for manufacturing the negative electrode.

[0063] The positive electrode active material layer may preferably include a positive electrode active material, a binder, and a conductive material.

[0064] The positive electrode active material is preferably at least one selected from the group consisting of lithium cobalt oxides such as LCO; lithium manganese oxides such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). More preferably, it is a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof. In this case, there is an effect of excellent reversible capacity and thermal stability.

[0065] As another specific example, the positive electrode active material has the following Chemical Formula 1 [Chemical Formula 1] Li a Ni x Mn y Co z M w O 2+δ (In Chemical Formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, and 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented by this.

[0066] The positive electrode active material may preferably be a high nickel (High Ni) positive electrode active material having a Ni content of 65 mol% or more based on the total weight of its metal elements.

[0067] The conductive material can be selected as needed from the conductive materials described above, for example, and may preferably be a carbon-based conductive material, more preferably carbon black, graphite, or a mixture thereof.

[0068] The binder may, for example, be a polymer binder, preferably a PVdF-based binder, an SBR-based binder, or a mixture thereof as described above, more preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, and even more preferably polyvinylidene fluoride.

[0069] As the separation membrane, an insulating thin film having high ion permeability and mechanical strength may be used. The pore diameter of the separation membrane is generally 0.01 μm to 10 μm, and the thickness may be 5 μm to 300 μm. Non-limiting examples of such separation membranes include sheets or nonwoven fabrics made of olefin polymers such as polypropylene with chemical resistance and hydrophobicity, glass fibers, or polyethylene.

[0070] The separation membrane can preferably contain a PVdF-based binder. In this case, while maintaining excellent battery performance, it interacts with the pattern coating layer to prevent folding of the separation membrane, thereby providing a secondary battery with reduced manufacturing yield due to low voltage failures and fewer accidents.

[0071] The secondary battery may preferably contain an electrolyte, which may, for example, include an organic solvent and a lithium salt.

[0072] The organic solvent may be, for example, an aprotic solvent. Specific examples include N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate, and may be one or more selected from the group consisting of them.

[0073] The lithium salt may be, for example, one or more selected from the group consisting of LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4-phenylboric acid, and imide.

[0074] The secondary battery may include, for example, an electrode assembly in which the positive electrode and the negative electrode are alternately laminated with the separator, and the electrolyte is housed / sealed together with an exterior material such as a battery case.

[0075] Further, the secondary battery may include, for example, a unit cell, a battery module including the same, or a battery pack including the same.

[0076] The secondary battery may preferably be used as a power source for an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

[0077] Manufacturing method of secondary batteries The method for manufacturing a secondary battery according to the present invention is characterized by comprising the steps of forming a negative electrode active material layer on a metal foil, pattern coating the upper and lower ends of the negative electrode active material layer with a binder, notching after the pattern coating step to manufacture a monocell, laminating a separation membrane onto the monocell, and stacking a positive electrode, which includes a metal foil and a positive electrode active material layer coated on the metal foil, on the separation membrane. In this case, there is an advantage in providing a secondary battery that has excellent battery performance while having no folding of the separation membrane, thus reducing the yield of production due to low voltage failures and the occurrence of accidents.

[0078] The aforementioned pattern coating may preferably be a dual die coating. In this case, while the battery performance is excellent, there is no folding of the separation film, which has the effect of reducing the reduction in manufacturing yield due to low voltage failures and the occurrence of accidents.

[0079] The negative electrode active material layer may preferably be formed by a continuous strip coating method. In this case, while the battery performance is excellent, there is no folding of the separation membrane, which has the effect of reducing the yield of production due to low voltage failures and the occurrence of accidents.

[0080] The method for manufacturing the secondary battery described above may include all of the above-mentioned negative electrode, method for manufacturing the negative electrode, and contents of the secondary battery.

[0081] The method for forming the positive electrode active material layer may preferably involve continuously coating a metal foil with a slurry-like positive electrode active material composition in strip form.

[0082] The metal foil of the positive electrode may be, for example, aluminum foil.

[0083] The positive electrode active material composition slurry may preferably contain a positive electrode active material, a binder, a conductive material, and a solvent, and may further contain a dispersant and / or a thickener as needed.

[0084] The solvent, dispersant, and thickener are not particularly limited as long as they are substances commonly used in the art to which the present invention pertains.

[0085] The following describes specific examples in detail based on the attached drawings.

[0086] Figure 2 below is a simplified process diagram illustrating a lithium secondary battery manufacturing method using the stacking method, showing the assembly process of stacked cells from electrode preparation to the taping step.

[0087] Referring to Figure 2, in the electrode step, a positive electrode sheet is manufactured by coating both sides of a long sheet-like positive electrode current collector with a positive electrode active material layer containing positive electrode active material, conductive material, binder, etc., and then cutting this sheet to a certain size to prepare the positive electrode. Although not shown in Figure 2, after forming the positive electrode active material layer, the positive electrode sheet can be dried at a predetermined temperature (for example, 135°C) for several hours (for example, 3 hours or more) before cutting, i.e., notching, and then rolled (pressed) to manufacture the positive electrode sheet.

[0088] Alternatively, a negative electrode sheet is manufactured by coating both sides of a long, sheet-like negative electrode current collector with a negative electrode active material layer containing negative electrode active material, conductive material, and binder, and then coating a pattern coating layer containing binder on top of that. This sheet is then cut to a certain size to prepare the negative electrode. Although not shown in Figure 2, after forming the negative electrode active material layer and / or pattern coating layer, the negative electrode sheet can be rolled (pressed) before cutting, i.e., notching, to manufacture the negative electrode sheet.

[0089] Finally, prepare the separator membrane for lithium secondary batteries, which has been cut to a specific size.

[0090] Next, as an intermediate assembly step, the prepared separation membrane is stacked on both sides of the prepared negative electrode to prepare a separation membrane / negative electrode / separation membrane monocell, and the positive electrode is stacked on one side of the prepared monocell to prepare a separation membrane / negative electrode / separation membrane / positive electrode halfcell.

[0091] Next, in the stack cell step, multiple prepared half cells are stacked and attached together, and then finished with a prepared mono cell to produce a stack cell. Finally, in the taping step, the produced stack cell is secured with tape.

[0092] Figure 3 below is a simplified cross-sectional view of the intermediate assembly where the separation membrane has folded.

[0093] Referring to Figure 3, in some monocells and halfcells, the adhesive force between the negative electrode and the separator membrane is weak, causing the edges of the separator membrane to become entangled as they lift up. This leads to folding of the separator membrane when these are stacked to manufacture stacked cells. Folding of the separator membrane results in low voltage failure in the secondary battery, reduces the manufacturing yield, and can cause accidents during use. However, the negative electrode and secondary battery containing the same according to the present invention do not experience folding of the separator membrane, thus preventing low voltage failures caused by this.

[0094] Folding test of separation membrane The stacked cells and secondary batteries according to the present invention can, for example, be used to indirectly confirm that folding of the separator membrane has not occurred by using conventional methods such as methods for detecting damage to the separator membrane, methods for confirming insulation failure of a battery, or methods for selecting low-voltage defective cells.

[0095] The aforementioned conventional methods are not particularly limited as long as they are methods disclosed in the art to which the present invention pertains. For example, when a constant voltage (CV) of 30 to 100V is applied to a stack cell, if a leakage current above a reference value or an insulation resistance value below a reference value is detected, it can be evaluated that folding of the separator membrane has occurred. In this case, the leakage current measuring device and the insulation resistance measuring device are not particularly limited, and commercially available measuring devices are acceptable. For example, the ST5540 (manufactured by Hioki Corporation) may be used.

[0096] In this document, the reference value refers to the value obtained by measuring a normal stack cell with no folding of the separation membrane.

[0097] As a result, in the stack cell including the negative electrode on which the pattern coating layer according to the present invention is formed (Example), folding of the separation film does not occur, so the resistance value becomes an ideal infinite value, and a large value of several hundred MΩ or more can be obtained. In contrast, in the stack cell including the negative electrode without the pattern coating layer according to the present invention (Comparative Example), folding of the separation film occurs, and the insulation between the positive and negative electrodes is destroyed, resulting in a low insulation resistance value.

[0098] Furthermore, in describing the negative electrode of the present invention, its manufacturing method, a secondary battery containing it, and a method for manufacturing a secondary battery, other conditions, processes, or equipment not explicitly described can be appropriately selected within the range of practices commonly carried out in the art to which the present invention pertains, and are not particularly limited.

[0099] The configurations, elements, or complete assemblies described above for carrying out the present invention, as well as the methods and elements thereof, and variations of the embodiments of the present invention, can be combined with and modified from one another in any combination.

Claims

1. The steps include forming a negative electrode active material layer on a metal foil, The step includes pattern coating the upper and lower ends of the negative electrode active material layer with a binder, The upper end portion of the negative electrode active material layer coated with the binder is 0.01 to 0.2 times the area of ​​the entire negative electrode active material layer. The lower end portion of the negative electrode active material layer coated with the binder is 0.05 to 0.3 times the total area of ​​the negative electrode active material layer, and the coating area of ​​the binder is larger than that of the upper end portion of the negative electrode active material layer. A method for manufacturing a negative electrode, characterized by including a notching step after the step of pattern coating.

2. The method for manufacturing a negative electrode according to claim 1, characterized in that the pattern coating is a dual die coating.

3. The method for producing a negative electrode according to claim 1, characterized in that the method for forming the negative electrode active material layer is a strip continuous coating method.

4. The negative electrode includes a first metal foil and a negative electrode active material layer coated on the first metal foil, the positive electrode includes a second metal foil and a positive electrode active material layer coated on the second metal foil, and a separation membrane. The negative electrode has a PVdF-based binder coated on its upper and lower ends. The upper end portion of the negative electrode coated with the binder is 0.01 to 0.2 times the area of ​​the entire negative electrode active material layer. The lower end portion of the negative electrode coated with the binder is 0.05 to 0.3 times the total area of ​​the negative electrode active material layer, and the coating area of ​​the binder is larger than that of the upper end portion of the negative electrode. A secondary battery characterized in that the separation membrane contains a PVdF-based binder.

5. The steps include forming a negative electrode active material layer on a first metal foil, The steps include pattern coating the upper and lower ends of the negative electrode active material layer with a binder, The process involves the step of notching after the pattern coating step, in order to manufacture a monocell. The steps include stacking a separation membrane on the monocell, The step of stacking a second metal foil and a positive electrode including a positive electrode active material layer coated on the second metal foil onto the separation membrane, The upper end portion of the negative electrode active material layer coated with the binder is 0.01 to 0.2 times the area of ​​the entire negative electrode active material layer. A method for manufacturing a secondary battery, characterized in that the lower end portion of the negative electrode active material layer coated with the binder is 0.05 to 0.3 times the total area of ​​the negative electrode active material layer, and the coating area of ​​the binder is larger than that of the upper end portion of the negative electrode active material layer.

6. The method for manufacturing a secondary battery according to claim 5, characterized in that the pattern coating is a dual die coating, or the negative electrode active material layer is formed by a strip continuous coating method.

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