Positive electrode and battery containing the same

Abstract

The present invention relates to a positive electrode and a battery including the same, and more particularly to a positive electrode including a metal foil and a positive electrode active material layer coated thereon, characterized in that the upper and lower ends of the positive electrode are coated with a binder, and a battery including the same. According to the present invention, by inserting a resin layer of a predetermined thickness at a predetermined position between the positive electrode active material layers, it is possible to provide a positive electrode and a battery including the same that can ensure excellent stability even in the case of an abnormally large current flow without impairing the performance of the battery, and enable both high energy density and high electrode loading.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0038663, filed on March 29, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode and a battery including the same, and more particularly to a positive electrode and a battery including the same, which ensure excellent stability even when an abnormally large amount of current flows without impairing battery performance by inserting a resin layer at a predetermined position between positive electrode active material layers, thereby enabling both high energy density and high electrode loading. [Background technology]

[0003] A lithium secondary battery is generally composed of a positive electrode in which a positive electrode active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative electrode active material layer is coated on a metal foil such as copper, a separator to prevent the positive electrode and negative electrode from mixing with each other, and an electrolyte to allow lithium ions to move between the positive electrode and negative electrode.

[0004] Such lithium secondary batteries are classified into a winding type and a stacking type according to the manufacturing method, and the stacking type is further classified into a stack and folding type (lamination and stacking type), a Z folding type (zigzag stacking type), etc.

[0005] In the winding method, cells are wound to form a lithium secondary battery, which results in empty spaces, resulting in low energy density, and also in distortion and swelling during long-term charging and discharging.

[0006] On the other hand, the stacking method has the advantage that the empty space is minimized, the energy density is high, and distortion and swelling are reduced because the cells are stacked to form a lithium secondary battery.

[0007] Recently, the use of lithium secondary batteries has expanded to electric vehicles and other devices that require high output. As a means of further increasing the energy density, the negative electrode loading per unit area (g / cm 2 ) and positive electrode loading (g / cm 2 ) has increased significantly.

[0008] However, if the energy density of a lithium secondary battery becomes excessively high, an abnormally large amount of current may be generated, which may lead to a serious accident.

[0009] Therefore, there is an urgent need to develop lithium secondary batteries that can significantly improve output characteristics such as energy density while ensuring safety under abnormal conditions. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent Publication No. 10-2017-0103208 Summary of the Invention [Problem to be solved by the invention]

[0011] In order to solve the above-mentioned problems of the conventional art, the present invention aims to provide a cathode and a battery including the same, which can ensure excellent stability even when an abnormally large amount of current flows without impairing battery performance by inserting a resin layer at a predetermined position between cathode active material layers, thereby enabling both high energy density and high electrode loading.

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

[0013] To achieve the above object, I) the present invention provides a positive electrode including a positive electrode current collector, a first positive electrode active material layer coated on the positive electrode current collector, a resin layer coated on the first positive electrode active material layer, and a second positive electrode active material layer coated on the resin layer.

[0014] II) In I), when the thickness of the first positive electrode active material layer is T1, the thickness of the second positive electrode active material layer is T2, and the thickness of the resin layer is Tr, the following formula 1 can preferably be satisfied. [Formula 1] Tr <T1≦T2

[0015] III) In I) or II), it is preferable that the first positive electrode active material layer has a thickness of more than 0 μm and less than 200 μm, the second positive electrode active material layer has a thickness of more than 0 μm and less than 200 μm, and the resin layer has a thickness of 5 to 50 μm.

[0016] IV) In the above I) to III), the resin layer may preferably contain a base resin, a conductive material, and an adhesive.

[0017] V) In I) to IV), the resin layer may preferably contain 10 to 90% by weight of a base resin, 5 to 50% by weight of a conductive material, and 5 to 40% by weight of an adhesive.

[0018] VI) In the above I) to V), the base resin may preferably be a resin that has a melting temperature of 60 to 180° C. and expands in volume when melted.

[0019] VII) In the above I) to VI), the base resin may preferably be one or more selected from the group consisting of polyethylene, polypropylene, and polyethylene vinyl acetate.

[0020] VIII) In the above I) to VII), the conductive material can preferably contain carbon or a metal.

[0021] IX) In the above I) to VIII), the adhesive is preferably polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, or polytetrafluoroethylene. ,workman The rubber may be one or more selected from the group consisting of ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

[0022] X) In the above I) to IX), the first and second positive electrode active material layers may preferably contain a high-nickel positive electrode active material.

[0023] XI) In the above I) to X), the high-nickel active material may preferably be an NCM (nickel cobalt manganese) or NCMA (nickel cobalt manganese aluminum) positive electrode active material.

[0024] XII) In the above I) to XI), the positive electrode preferably has a loading amount, defined as the weight of the positive electrode active material coated on the positive electrode current collector per unit area, of 10 mg / cm. 2 It may be more than that.

[0025] XIII) The present invention also provides a method for manufacturing a positive electrode, including the steps of coating a first positive electrode active material layer on an upper portion of a positive electrode current collector, coating a resin layer on the upper portion of the coated first positive electrode active material layer, and coating a second positive electrode active material layer on the upper portion of the coated resin layer.

[0026] In addition, XIV) the present invention provides a battery comprising: a positive electrode according to any one of I) to XIII); a negative electrode comprising a negative electrode current collector and a negative electrode active material layer coated thereon; and a separator.

[0027] XV) In the above I) to XIV), the negative electrode preferably has a loading amount, defined as the weight of the negative electrode active material coated on the negative electrode current collector per unit area, of 10 mg / cm. 2 It may be more than that. [Effects of the Invention]

[0028] According to the present invention, by inserting a resin layer at a predetermined position between positive electrode active material layers, it is possible to provide a positive electrode that ensures excellent stability even when an abnormally large amount of current flows without impairing battery performance, thereby enabling both high energy density and high electrode loading, and a battery including the same. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a cross-sectional view simply showing a vertical cross section of a positive electrode according to the present invention. [Figure 2] This is a schematic diagram showing the principle that the resin layer according to the present invention maintains a conductive network made of conductive material under normal conditions, but under abnormally high temperature conditions, the base resin (thermoplastic resin) melts and expands, destroying the conductive network made of conductive material. [Figure 3] 1A is a cross-sectional view showing a vertical cross section of a battery in which the resin layer according to the present invention is omitted, and FIG. 1B is a cross-sectional view showing a vertical cross section of a battery in which the resin layer according to the present invention is inserted between positive electrode active material layers. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present inventors have confirmed that, in a high electrode loading secondary battery, when a predetermined resin layer is inserted at a predetermined position between positive electrode active material layers, the resistance increases when an abnormally large amount of current flows without impairing the battery performance, thereby preventing accidents. Based on this, they have continued their research and have completed the present invention.

[0031] The positive electrode of the present invention and the battery including the same will be described in detail below.

[0032] However, the terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of terms in order to best describe his or her invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely one embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and therefore various equivalents and modifications that can be substituted for them may be present, and they may be arranged, substituted, combined, separated, or designed in various other configurations.

[0033] Unless otherwise defined, all technical or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0034] positive electrode The positive electrode of the present invention includes a positive electrode current collector, a first positive electrode active material layer coated on the positive electrode current collector, a resin layer coated on the first positive electrode active material layer, and a second positive electrode active material layer coated on the resin layer. In this case, the positive electrode has the effect of ensuring excellent stability even in the event of a sudden, abnormally large current flow without impairing battery performance, thereby enabling both high energy density and high electrode loading.

[0035] When the thickness of the first positive electrode active material layer is T1, the thickness of the second positive electrode active material layer is T2, and the thickness of the resin layer is Tr, the following formula 1 can be preferably satisfied. Within this range, there is an advantage that both the performance and stability of the battery are excellent. [Formula 1] Tr <T1≦T2

[0036] The positive electrode more preferably satisfies the following formula 1a, and within this range, the battery has excellent performance and stability. [Formula 1a] Tr <T1<T2

[0037] In the positive electrode, preferably, the first positive electrode active material layer has a thickness of more than 0 μm and less than 200 μm, the second positive electrode active material layer has a thickness of more than 0 μm and less than 200 μm, and the resin layer has a thickness of 5 to 50 μm; more preferably, the first positive electrode active material layer has a thickness of 10 μm to 190 μm, the second positive electrode active material layer has a thickness of 10 μm to 190 μm, and the resin layer has a thickness of 5 to 50 μm; even more preferably, the first positive electrode active material layer has a thickness of 50 to 120 μm, the second positive electrode active material layer has a thickness of 80 to 150 μm, and the resin layer has a thickness of 5 to 50 μm; within these thickness ranges, there is an advantage that both the performance and stability of the battery are excellent.

[0038] The sum of the thicknesses of the first positive electrode active material layer and the second positive electrode active material layer may be, for example, 200 μm or less, or 1 μm to 200 μm, preferably 20 μm to 200 μm, and more preferably 130 μm to 200 μm. Within this range, there is an advantage that both the performance and stability of the battery are excellent.

[0039] For example, the resin layer may include a base resin and a conductive material, and preferably may include a base resin, a conductive material, and an adhesive. In this case, the resin layer has advantages of excellent durability and output characteristics due to excellent adhesion to the positive electrode active material layer while providing excellent battery performance and stability.

[0040] The resin layer preferably contains 10 to 90 wt % of a base resin, 5 to 50 wt % of a conductive material, and 5 to 40 wt % of an adhesive; more preferably, 20 to 90 wt % of a base resin, 5 to 50 wt % of a conductive material, and 5 to 30 wt % of an adhesive; even more preferably, 30 to 90 wt % of a base resin, 5 to 50 wt % of a conductive material, and 5 to 20 wt % of an adhesive; and even more preferably, 30 to 80 wt % of a base resin, 15 to 50 wt % of a conductive material, and 5 to 20 wt % of an adhesive. Within these ranges, the battery has excellent performance and stability, and also has excellent adhesion to the positive electrode active material layer, resulting in excellent durability.

[0041] The base resin preferably has a melting temperature of 60 to 180°C and may expand in volume when melted, more preferably has a melting temperature of 70 to 170°C, and even more preferably has a melting temperature of 75 to 160°C. Specific examples of melting temperatures within this range include 70 to 140°C and 110 to 170°C. Within these ranges, there are advantages in that the battery performance is not impaired, excellent stability is ensured even in the event of a sudden, abnormally large current flow, and both high energy density and high electrode loading are possible.

[0042] In this description, the melting temperature may be measured by a method or device commonly used in the technical field to which the present invention pertains, for example, by DSC analysis, specifically, the maximum point of the endothermic peak measured during the second heating after the first heating and cooling using a differential scanning calorimeter (DSC, device name: DSC2920, manufacturer: TA Instruments) at a rate of 10°C / min in a nitrogen atmosphere.

[0043] The base resin may preferably be one or more selected from the group consisting of polyethylene, polypropylene, and polyethylene vinyl acetate, and more preferably polyethylene, which has the advantage of providing an excellent balance between battery performance and stability.

[0044] The conductive material may include, for example, a carbon-based conductive material or a metallic conductive material, and preferably includes a carbon-based conductive material. In this case, the conductive network within the resin layer operates well under normal conditions, but when an abnormal condition is suddenly reached, the conductive network is easily broken, thereby ensuring stability.

[0045] Specific examples of the conductive material include graphite such as natural graphite and artificial graphite; graphene; 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.

[0046] The adhesive is preferably polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene. ,workman The material may be one or more selected from the group consisting of ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber. In this case, the battery has excellent performance and stability, and also has excellent adhesion to the positive electrode active material layer, resulting in excellent durability and output characteristics.

[0047] The first and second positive electrode active material layers may preferably be high nickel positive electrode active materials, more preferably NCM (nickel cobalt manganese) - based or NCMA (nickel cobalt manganese aluminum) - based positive electrode active materials. In this case, even with high energy density or high electrode loading, there is an advantage of ensuring excellent stability against sudden abnormal large - current flows without inhibiting the performance of the battery.

[0048] In this description, the high nickel positive electrode active material can preferably mean a high nickel (High Ni) positive electrode active material with a Ni content of 65 mol% or more based on the total weight of its metal elements.

[0049] As another example, the positive electrode active material is as follows, the following Chemical Formula 1 [Chemical Formula 1] Li a Ni x Mn y Co z M w O 2+δ (In the Chemical Formula 1, M contains one or more 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 thereby.

[0050] As an example, the loading amount of the positive electrode, which is defined by the weight of the positive electrode active material coated on the positive electrode current collector per unit area, is 10 mg / cm 2 or more, preferably 20 mg / cm 2 or more, more preferably 30 mg / cm 2 or more, further preferably 50 mg / cm 2 or more, even more preferably 60 mg / cm 2 or more. The upper limit value is not particularly limited, but as an example, it may be 200 mg / cm 2 or less, preferably 180 mg / cm 2 or less, more preferably 160 mg / cm 2Within this range, the performance and stability of the battery according to the present invention are advantageously maximized.

[0051] The positive electrode current collector is not particularly limited as long as it is a positive electrode current collector commonly used in the technical field to which the present invention pertains, and may be, for example, a metal foil for a positive electrode, specifically, an aluminum foil.

[0052] Each of the first and second positive electrode active material layers may further include, for example, a conductive material and / or a binder.

[0053] The conductive material is not particularly limited as long as it is a conductive material for a positive electrode commonly used in the technical field to which the present invention belongs, and may also include conductive materials for a negative electrode described below unless otherwise limited. For example, the conductive material may be a metal-based conductive material or a carbon-based conductive material, preferably a carbon-based conductive material, and specific examples thereof may include carbon black, graphene, carbon nanotubes, or graphite.

[0054] The binder is not particularly limited as long as it is a binder for a positive electrode commonly used in the technical field to which the present invention pertains. For example, the binder may be a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile butadiene rubber (NBR), or a mixture thereof, and more preferably polyvinylidene fluoride.

[0055] The first and second positive electrode active material layers may further include a thickener, a surfactant, and / or a solvent, which are commonly used in the technical field of the present invention, if necessary.

[0056] Hereinafter, specific embodiments will be described in detail with reference to the accompanying drawings.

[0057] FIG. 1 below is a cross-sectional view showing a simplified vertical cross section of a positive electrode according to an embodiment of the present invention.

[0058] Referring to FIG. 1, a first positive electrode active material layer is coated on an aluminum foil having a thickness of 15 to 20 μm, which serves as a positive electrode current collector. Then, a resin layer containing a base resin, a conductive material, and an adhesive is coated on the first positive electrode active material layer. Then, a second positive electrode active material layer is coated on the resin layer, thereby producing a positive electrode having a resin layer inserted between the positive electrode active material layers.

[0059] Figure 2 below is a schematic diagram showing that the resin layer of the present invention maintains a conductive network of conductive materials under normal conditions, but under abnormally high temperatures, the base resin melts and expands, destroying the conductive network of conductive materials, i.e., functioning as a resistor.

[0060] Referring to FIG. 2, the left side diagram is a schematic cross-section of the resin layer in a normal state, showing that the base resin inside is shrunk and fixed, while the conductive material forms a conductive network connecting the upper (second positive electrode active material layer (not shown)) and lower (first positive electrode active material layer (not shown)). In contrast, the right side diagram is a schematic cross-section of the resin layer in an abnormally high temperature state, showing that the base resin inside expands and melts, destroying the conductive network of the conductive material, thereby insulating the upper (second positive electrode active material layer (not shown)) and lower (first positive electrode active material layer (not shown)).

[0061] Positive electrode manufacturing method The method for manufacturing a positive electrode of the present invention includes the steps of coating a first positive electrode active material layer on an upper portion of a positive electrode current collector, coating a resin layer on the upper portion of the coated first positive electrode active material layer, and coating a second positive electrode active material layer on the upper portion of the coated resin layer. In this case, there is an advantage in that it provides a secondary battery that has excellent battery performance and ensures excellent stability even when a sudden, abnormally large current flows.

[0062] The step of coating the positive electrode current collector with a first positive electrode active material layer may, for example, be a step of coating the positive electrode current collector with a slurry containing a positive electrode active material, a conductive material, a binder, and a solvent. The coating method may be any method commonly used in the art, including, for example, a strip continuous coating method or a roll-to-roll method, which has the advantage of enabling economical electrode production. The solvent may, for example, be an organic solvent, water, or a mixture thereof, and may be, for example, one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylacetamide, dimethylformamide, dimethyl carbonate, acetone, methanol, ethanol, and water.

[0063] The slurry for forming the first positive electrode active material layer contains, as a specific example, 85 to 98 wt % of the positive electrode active material (for example, LiNi 0.6 Mn 0.2 Co 0.2 The binder may be a slurry in which 1 to 10% by weight of a conductive material (for example, carbon black) and 1 to 10% by weight of a binder (for example, PVdF) are mixed in a solvent (for example, NMP).

[0064] The amount of the solvent used is not particularly limited as long as it is within a range commonly used in the technical field to which the present invention pertains. For example, the amount may be an amount that allows the positive electrode active material, conductive material, and binder to be dissolved or dispersed, and then uniformly coated on a positive electrode current collector, taking into consideration the coating thickness of the slurry, production yield, etc.

[0065] The step of coating the first positive electrode active material layer on the positive electrode current collector may preferably further include a step of drying the coating.

[0066] The step of coating a resin layer on the coated first positive electrode active material layer may, for example, be a step of coating a slurry containing a base resin, a conductive material, and a solvent on the first positive electrode active material layer. The coating method may be any method commonly used in the technical field of the present invention, for example, a strip continuous coating method or a roll-to-roll method. The solvent may be any solvent that can be used to mix the base resin and the conductive material to form a slurry, and may preferably be at least one selected from the group consisting of acetone, methyl ethyl ketone, N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

[0067] The slurry for forming the resin layer may be, for example, a slurry prepared by mixing 30 to 80% by weight of a base resin (e.g., polyethylene), 15 to 50% by weight of a conductive material (e.g., carbon black), and 5 to 20% by weight of an adhesive (e.g., PVdF) with a solvent (e.g., water), based on the total combined weight of the base resin, conductive material, and adhesive. In this case, the base resin, conductive material, and adhesive may be mixed by being added to the solvent, respectively, or the conductive material and adhesive may be mixed by being added to a base resin dispersion (e.g., polyethylene dispersion) prepared by mixing the base resin with the solvent.

[0068] The step of coating a resin layer on the coated first positive electrode active material layer may preferably further include a step of drying the resin layer after coating.

[0069] The step of coating the second positive electrode active material layer on the coated resin layer may, for example, be a step of coating the resin layer with a slurry containing a positive electrode active material, a conductive material, a binder, and a solvent. The coating method may be any method commonly used in the art, including, for example, a strip continuous coating method or a roll-to-roll method. The components of the second positive electrode active material layer may be the same as those of the first positive electrode active material layer, for example, the same components.

[0070] The slurry for forming the second positive electrode active material layer contains, as a specific example, 85 to 98 wt % of the positive electrode active material (for example, LiNi 0.6 Mn 0.2 Co 0.2 The binder may be a slurry in which 1 to 10% by weight of a conductive material (for example, carbon black) and 1 to 10% by weight of a binder (for example, PVdF) are mixed in a solvent (for example, NMP).

[0071] The step of coating a second positive electrode active material layer on the coated resin layer may preferably further include a step of drying the second positive electrode active material layer after coating.

[0072] Drying after coating the first positive electrode active material layer, after coating the resin layer, and / or after coating the second positive electrode active material layer can be performed in a vacuum oven at a temperature of, for example, 100 to 140°C, preferably 110 to 130°C, more preferably 115 to 125°C, and even more preferably around 120°C.

[0073] For example, the method for manufacturing the positive electrode may include a step of pressing after coating the first positive electrode active material layer, after coating the resin layer, and / or after coating the second positive electrode active material layer.

[0074] As an example, the method for manufacturing the positive electrode may include a step of cutting the positive electrode plate into a certain size after coating the second positive electrode active material layer.

[0075] Negative electrode The negative electrode of the present invention can include a metal foil and a negative electrode active material layer coated thereon. The negative electrode active material layer can include a negative electrode active material, and optionally, can further include a conductive material and / or a binder.

[0076] The loading amount defined by the weight of the negative electrode active material coated on the negative electrode current collector per unit area of the negative electrode is, as an example, 10 mg / cm 2 or more, preferably 20 mg / cm 2 or more, more preferably 30 mg / cm 2 or more, still more preferably 50 mg / cm 2 or more, even more preferably 60 mg / cm 2 or more. The upper limit value is not particularly limited, but as an example, it may be 200 mg / cm 2 or less, preferably 180 mg / cm 2 or less, more preferably 160 mg / cm 2 or less. Within this range, there is an advantage that the performance and stability effects of the battery according to the present invention are maximized.

[0077] The negative electrode current collector is not particularly limited as long as it is a negative electrode current collector commonly used in the technical field to which the present invention belongs. As an example, it is a metal foil for a negative electrode, and as a specific example, it can be a copper foil.

[0078] The negative electrode active material preferably includes a silicon-based active material. The silicon-based active material is not particularly limited as long as it is used as a silicon-based active material in the technical field to which the present invention belongs. As specific examples, it may be one or more selected from the group consisting of Si, SiO x (0 < x < 2), and SiC.

[0079] The conductive material is not particularly limited as long as it is used as a conductive material in the technical field to which the present invention pertains, and examples include carbon-based conductive materials and metal-based conductive materials. Specific examples include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; graphene; 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, and preferably the carbon-based conductive material.

[0080] The binder is not particularly limited as long as it is used as a binder for a negative electrode in the technical field to which the present invention pertains. For example, the binder may include an SBR-based binder, a PVdF-based binder, or a mixture thereof.

[0081] Specific examples of the PVdF-based binder include one or more selected from the group consisting of 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-trifluoroethylene (PVdF-TrFE).

[0082] Specific examples of the SBR binder include at least one selected from the group consisting of styrene-butadiene rubber (SBR) and acrylated styrene-butadiene rubber.

[0083] The negative electrode active material layer may further include a thickener, a surfactant, and / or a solvent, which are commonly used in the technical field of the present invention, if necessary.

[0084] Negative electrode manufacturing method The method for manufacturing a negative electrode according to the present invention may include a step of coating a negative electrode active material layer on a negative electrode current collector.

[0085] The step of coating the negative electrode current collector with a negative electrode active material layer may, for example, be a step of coating the negative electrode current collector with a slurry containing a negative electrode active material, a conductive material, a binder, and a solvent. The coating method may be any method commonly used in the art, including, for example, a strip continuous coating method or a roll-to-roll method, which has the advantage of enabling more economical production of the negative electrode. The solvent may, for example, be an organic solvent, water, or a mixture thereof, and may be, for example, one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylacetamide, dimethylformamide, dimethyl carbonate, acetone, methanol, ethanol, and water.

[0086] The negative electrode current collector is not particularly limited as long as it is a negative electrode current collector commonly used in the technical field to which the present invention pertains, and may be, for example, copper foil, specifically, copper foil having a thickness of 15 to 20 μm.

[0087] The slurry for forming the negative electrode active material layer may be, for example, a slurry in which 85 to 98 wt % of a negative electrode active material (e.g., artificial graphite), 1 to 10 wt % of a conductive material (e.g., carbon black), and 1 to 10 wt % of a binder (e.g., SBR) are mixed in a solvent (e.g., distilled water), based on the total weight of the negative electrode active material, conductive material, and binder.

[0088] The amount of the solvent used is not particularly limited as long as it is within a range commonly used in the technical field to which the present invention pertains. For example, the amount may be an amount that allows the negative electrode active material, conductive material, and binder to be dissolved or dispersed, and then uniformly coated on a negative electrode current collector, taking into consideration the coating thickness of the slurry, production yield, etc.

[0089] For example, the step of coating the negative electrode active material layer on the negative electrode current collector may be dried immediately after coating, so a separate drying process may be omitted. However, if the boiling point (bp) of the solvent used is high, the step of drying the negative electrode active material layer at a temperature equal to or higher than the boiling point of the solvent until the solvent is removed may be further included after coating the negative electrode active material layer, as necessary.

[0090] The drying can be carried out in a vacuum oven under a temperature condition of, for example, 100 to 140°C, preferably 110 to 130°C, more preferably 115 to 125°C, and even more preferably around 120°C.

[0091] For example, the method for manufacturing the negative electrode may include a step of coating a negative electrode active material layer and then pressing the coated layer.

[0092] For example, the method for manufacturing the negative electrode may include a step of coating a negative electrode active material layer and then cutting the coated negative electrode into negative electrode plates of a predetermined size.

[0093] secondary battery The secondary battery of the present invention is characterized by including a positive electrode according to the present invention; a negative electrode including a negative electrode current collector and a negative electrode active material layer coated thereon; and a separator. In this case, it has the advantage of ensuring excellent stability even when a sudden, abnormally large current flows at high energy density and high electrode loading.

[0094] The separation membrane is not particularly limited as long as it is a separation membrane commonly used in the technical field to which the present invention pertains. Preferably, the separation membrane has a pore diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm. Specific examples include olefin polymers such as polypropylene; sheets or nonwoven fabrics made of glass fiber or polyethylene; and the like. In this case, the separation membrane has advantages such as high ion permeability, mechanical strength, insulating properties, chemical resistance, and hydrophobicity.

[0095] In this description, the pore diameter can be measured by a measurement method commonly used in the technical field to which the present invention pertains.

[0096] The secondary battery may include, for example, an electrolyte, specifically, an electrolytic solution, and the electrolytic solution may include, for example, an organic solvent and a lithium salt.

[0097] The organic solvent may be, for example, an aprotic solvent, and specific examples thereof may be one or more selected from the group consisting of N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0098] Examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, and (CF3SO2)2NLi.

[0099] For example, the secondary battery may include an electrode assembly in which the positive electrode and the negative electrode are alternately stacked with the separator, and the electrode assembly is housed and sealed together with the electrolyte in an exterior material such as a battery case.

[0100] The secondary battery may be preferably used as a power source for electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0101] Secondary battery manufacturing method A method for manufacturing a secondary battery according to the present invention includes the steps of: laminating a negative electrode and a separator; and laminating a positive electrode on the separator. The manufacturing of the positive electrode includes the steps of: coating a first positive electrode active material layer on a positive electrode current collector; coating a resin layer on the coated first positive electrode active material layer; and coating a second positive electrode active material layer on the coated resin layer. This has the effect of providing a secondary battery that ensures excellent stability even when a sudden, abnormally large current flows at high energy density and high electrode loading.

[0102] The step of stacking the negative electrode and the separator may be, for example, a step of stacking the separator on both sides of the negative electrode to manufacture a separator / negative electrode / separator monocell.

[0103] The step of stacking the positive electrode on the separator may be, for example, a step of stacking a positive electrode on one side of the manufactured mono-cell to manufacture a separator / negative electrode / separator / positive electrode half cell.

[0104] For example, the method for manufacturing the secondary battery may include a step of manufacturing a stack cell by stacking and attaching a plurality of manufactured half cells and completing the mono cell.

[0105] For example, the method for manufacturing the secondary battery may include the steps of placing the stack cell in a battery case, injecting an electrolyte solution, and then sealing the battery case. A specific example of the electrolyte solution may be a solution of 1M LiPF6 dissolved in a solvent of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate mixed in a weight ratio of 1:1:1.

[0106] The details regarding the positive electrode, negative electrode, separator, and electrolyte are the same as those described above, and therefore will not be described here.

[0107] Hereinafter, specific embodiments will be described in detail with reference to the accompanying drawings.

[0108] FIG. 3 below is a cross-sectional view showing a vertical cross section (a) of a battery in which the resin layer according to the present invention is omitted, and a vertical cross section (b) of a battery in which the resin layer according to the present invention is inserted between positive electrode active material layers.

[0109] Referring to Figure 3, the right diagram corresponds to a secondary battery according to the present invention, and when a large amount of current flows in the direction of the arrow during abnormal overcharge, the temperature rises rapidly. Therefore, it can be seen that the resin layer inserted into the positive electrode active material layer acts as a resistor, as described in Figure 2, and charging is carried out only through the second positive electrode active material layer, thereby significantly improving the stability of the secondary battery. Here, the secondary battery according to the present invention has a structure in which a first positive electrode active material layer, a resin layer, a second positive electrode active material layer, a separator, a negative electrode active material layer, and a copper foil negative electrode current collector are sequentially stacked on an aluminum foil positive electrode current collector.

[0110] On the other hand, the left diagram in FIG. 3 corresponds to a comparative example of the secondary battery according to the present invention, in which a resin layer is omitted between the positive electrode active material layers. Therefore, if a large amount of current flows in the direction of the arrow in an abnormal overcharge situation, there is no means to immediately stop this, and there is a risk of serious accidents such as fires and explosions due to a sudden increase in current and temperature.

[0111] In the description of the positive electrode, negative electrode, secondary battery, and methods for producing the same of the present invention, other conditions, steps, equipment, and the like that are not explicitly described can be appropriately selected within the range commonly used in the technical field to which the present invention pertains, and are not particularly limited.

[0112] Overcharge and performance test The cathode according to the present invention and a secondary battery including the cathode can be confirmed to be capable of both high energy density and high electrode loading by ensuring excellent stability even when an abnormally large amount of current flows without deteriorating battery performance through, for example, an overcharge test, a life performance test, and an output performance test.

[0113] The overcharge test may be any method disclosed in the technical field of the present invention, and is not particularly limited thereto. For example, the battery may be charged to a full charge voltage (4.25 V) at 0.3 C, charged at a 0.05 C cutoff, and then rested for three hours to stabilize the voltage. The battery may then be overcharged at 1 C and 6.4 V, and evaluated based on the increase (%) in remaining capacity (SOC) up to the overcharge termination voltage. The smaller the increase in remaining capacity, i.e., the more rapidly the electrical resistance increases, the more stable the secondary battery is even when an abnormally large current flows.

[0114] In conclusion, the overcharge test confirmed that the cathode according to the present invention and the battery including the same (Example) have excellent stability even during overcharge due to the inclusion of a resin layer at a predetermined position between the cathode active material layers, whereas the cathode and battery not including the resin layer according to the present invention (Comparative Example) do not experience a rapid increase in resistance during overcharge and the remaining capacity continues to increase, resulting in a significant risk of accidents.

[0115] The life performance test is not particularly limited as long as it is a method disclosed in the technical field to which the present invention pertains. As a specific example, after 50 charge / discharge cycles at room temperature (25°C) and a driving voltage range of 2.5 to 4.2V under a condition of 0.5C / 0.5C, the capacity retention rate (%) is calculated using the following Equation 3. It can be evaluated that the higher the capacity retention rate, the better the life performance. [Formula 3] Capacity retention rate (%) = (discharge capacity after 50 cycles / discharge capacity after 1 cycle) x 100

[0116] In conclusion, through the life performance test, it can be confirmed that the positive electrode including the resin layer according to the present invention and the battery including the same (Example) do not have a reduced life performance compared to the positive electrode and battery not including the resin layer according to the present invention (Comparative Example).

[0117] The output performance test is not particularly limited as long as it is a method disclosed in the technical field to which the present invention pertains. For example, a voltage difference is measured after discharging at a rate of 1C for 10 seconds under conditions of room temperature (25°C) and SOC 50%, and then the resistance is calculated using the following Equation 4. If the resistance is large, it can be evaluated that the output performance is excellent. [Formula 4] R(resistance)=(Vmax-Vmin) / I (In the formula, I means current.)

[0118] In conclusion, through the output performance test, it can be confirmed that the output performance of the positive electrode including the resin layer according to the present invention and the battery including the same (Example) is not reduced compared to the positive electrode and the battery not including the resin layer according to the present invention (Comparative Example).

Claims

1. a positive electrode current collector; a first positive electrode active material layer coated on the positive electrode current collector; a resin layer coated on the first positive electrode active material layer; and a second positive electrode active material layer coated on the resin layer, the resin layer includes a base resin, a conductive material, and an adhesive; the first positive electrode active material layer has a thickness of 50 to 120 μm, the second positive electrode active material layer has a thickness of 80 to 150 μm, the resin layer has a thickness of 5 to 50 μm, and the sum of the thicknesses of the first positive electrode active material layer and the second positive electrode active material layer is 130 μm to 200 μm; the base resin is at least one selected from the group consisting of polyethylene, polypropylene, and polyethylene vinyl acetate; the adhesive is at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber; When the thickness of the first positive electrode active material layer is T1, the thickness of the second positive electrode active material layer is T2, and the thickness of the resin layer is Tr, the following formula 1a is satisfied: [Formula 1a] Tr<T1<T2 That is, the positive electrode.

2. 2. The positive electrode of claim 1, wherein the resin layer comprises 10 to 90% by weight of a base resin, 5 to 50% by weight of a conductive material, and 5 to 40% by weight of an adhesive.

3. 2. The positive electrode according to claim 1, wherein the base resin has a melting temperature of 60 to 180° C. and expands in volume when melted.

4. 10. The positive electrode of claim 1, wherein the conductive material comprises carbon or a metal.

5. The positive electrode of claim 1 , wherein the first positive electrode active material layer and the second positive electrode active material layer comprise a high-nickel positive electrode active material.

6. 6. The positive electrode of claim 5, wherein the high-nickel positive electrode active material is a nickel-cobalt-manganese (NCM)-based or nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material.

7. The positive electrode has a loading of 10 mg / cm, which is defined as the weight of the positive electrode active material coated on the positive electrode current collector per unit area. ２ The positive electrode according to claim 1 , wherein

8. coating a first positive electrode active material layer on an upper portion of a positive electrode current collector; coating a resin layer on the coated first positive electrode active material layer; and coating a second positive electrode active material layer on the coated resin layer, the resin layer includes a base resin, a conductive material, and an adhesive; the first positive electrode active material layer has a thickness of 50 to 120 μm, the second positive electrode active material layer has a thickness of 80 to 150 μm, the resin layer has a thickness of 5 to 50 μm, and the sum of the thicknesses of the first positive electrode active material layer and the second positive electrode active material layer is 130 μm to 200 μm; the base resin is at least one selected from the group consisting of polyethylene, polypropylene, and polyethylene vinyl acetate; the adhesive is at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber; When the thickness of the first positive electrode active material layer is T1, the thickness of the second positive electrode active material layer is T2, and the thickness of the resin layer is Tr, the following formula 1a is satisfied: [Formula 1a] Tr<T1<T2 This is a method for manufacturing a positive electrode.

9. A battery comprising: the positive electrode according to claim 1 ; a negative electrode comprising a negative electrode current collector and a negative electrode active material layer coated on the negative electrode current collector; and a separator.

10. The negative electrode had a loading of 10 mg / cm, defined as the weight of the negative electrode active material coated on the negative electrode current collector per unit area. ２ The battery according to claim 9, wherein

Images