Multilayer structured negative electrode for secondary battery, method of manufacturing multilayer structured negative electrode for secondary battery, and secondary battery including same

Abstract

Provided is a multilayer structured negative electrode for a secondary battery. The multilayer structured negative electrode for a secondary battery comprises a current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer sequentially stacked on the current collector, the first negative electrode active material layer contains a first negative electrode active material and a first binder, the second negative electrode active material layer contains a second negative electrode active material and a second binder, the mass% content of the first binder in the first negative electrode active material layer is greater than the mass% content of the second binder in the second negative electrode active material layer, and the ratio of the thickness of the second negative electrode active material layer to the thickness of the first negative electrode active material layer is 8 to 10.

Description

A negative electrode for a secondary battery having a multilayer structure, a method for manufacturing a negative electrode for a secondary battery having a multilayer structure, and a secondary battery including the same

[0001] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0084454, dated June 27, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a negative electrode for a secondary battery having a multilayer structure, a method for manufacturing a negative electrode for a secondary battery having a multilayer structure, and a secondary battery including the same.

[0003] The electrode of a secondary battery is manufactured by coating an active material on the surface of a metal electrode current collector. The electrode current collector may be, for example, a metal foil made of aluminum or copper, and the active material is coated on one or both sides of the electrode current collector in the form of a slurry.

[0004] The purpose of the present invention is to provide a secondary battery negative electrode having a multilayer structure having excellent adhesive strength between a negative electrode active material layer and a current collector.

[0005] The purpose of the present invention is to provide a secondary battery negative electrode having a multilayer structure in which the loading amount of negative active material in the negative active material layer is increased, thereby improving battery performance such as cell life and output.

[0006] The purpose of the present invention is to provide a multilayer structured secondary battery negative electrode having excellent adhesion between a negative electrode active material layer and a current collector while improving battery performance such as cell life and output.

[0007] The purpose of the present invention is to provide a method for manufacturing a negative electrode for a secondary battery having the above-described multilayer structure.

[0008] The purpose of the present invention is to provide a secondary battery utilizing the above-described multilayer structured secondary battery negative electrode.

[0009] The objectives of the present invention are not limited to those mentioned above. Other objectives and advantages of the present invention not mentioned above can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the objectives and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0010] In one embodiment of the present invention, a multilayer structure negative electrode for a secondary battery is provided, the negative electrode including a current collector and a negative electrode active material layer, the negative electrode active material layer including a first negative electrode active material layer and a second negative electrode active material layer sequentially laminated on the current collector, the first negative electrode active material layer including a first negative electrode active material and a first binder, the second negative electrode active material layer including a second negative electrode active material and a second binder, a mass% content of the first binder in the first negative electrode active material layer is greater than a mass% content of the second binder in the second negative electrode active material layer, and a ratio of a thickness of the second negative electrode active material layer to a thickness of the first negative electrode active material layer is 8 to 10.

[0011] The total content of the first negative electrode active material and the second negative electrode active material may be 92 parts by weight or more, based on 100 parts by weight of the entire negative electrode active material layer.

[0012] The total content of the first binder and the second binder may be 5 parts by weight or less relative to 100 parts by weight of the entire negative electrode active material layer.

[0013] The thickness of the first negative electrode active material layer may be 5 µm to 50 µm.

[0014] The thickness of the second negative electrode active material layer may be 100 µm to 300 µm.

[0015] The weight ratio of the second binder to the first binder in the entire negative electrode active material layer may be greater than 1:1 to 10.

[0016] Among the entire negative electrode active material layer, the mass ratio of the first negative electrode active material to the second negative electrode active material may be greater than 0: less than 100 to 20:80.

[0017] The ratio of the mass% content of the first binder in the first negative electrode active material layer to the mass% content of the second binder in the second negative electrode active material layer may be 1 to 50.

[0018] The first negative electrode active material and the second negative electrode active material are each independently artificial graphite, natural graphite, hard carbon, soft carbon, graphitized carbon fiber, graphitized mesocarbon microbead, petroleum coke, resin sintered body, carbon fiber, pyrolytic carbon, Si, SiOx(0 <x≤2)로 표시되는 규소산화물, 리튬티타늄산화물(LTO), 리튬 금속 또는 이들의 조합으로 이루어진 군으로부터 선택된 적어도 하나를 포함할 수 있다.

[0019] The above first negative electrode active material may be natural graphite, and the above second negative electrode active material may be artificial graphite.

[0020] The first negative electrode active material layer may be formed by a gravure coating method, and the second negative electrode active material layer may be formed by a slot die coating method.

[0021]

[0022] In one embodiment of the present invention,

[0023] A step of preparing a composition for a first negative electrode active material layer including a first negative electrode active material, a first binder, and a first dispersion medium;

[0024] A step of preparing a composition for a second negative electrode active material layer including a second negative electrode active material, a second binder, and a second dispersion medium;

[0025] A step of forming a first negative electrode active material layer by coating the composition for the first negative electrode active material layer on one surface of a negative electrode current collector using a gravure coating method; and

[0026] A step of forming a second negative electrode active material layer by coating a composition for the second negative electrode active material layer on the first negative electrode active material layer using a slot die coating method;

[0027] In the above method, the ratio of the coating thickness of the second negative electrode active material layer to the coating thickness of the first negative electrode active material layer may be greater than 8 and less than 10.

[0028] In the above method, the first negative electrode active material layer can be coated to a thickness of 5 μm to 50 μm.

[0029] In the above method, the second negative electrode active material layer can be coated to a thickness of 100 μm to 200 μm.

[0030] In the above method, the mass% content of the first binder in the first negative electrode active material layer may be greater than the mass% content of the second binder in the second negative electrode active material layer.

[0031] In the above method, the total content of the first negative electrode active material and the second negative electrode active material may be 92 parts by weight or more, and the total content of the first binder and the second binder may be 5 parts by weight or less, based on 100 parts by weight of the total content of the first negative electrode active material layer and the second negative electrode active material layer.

[0032] In the above method, among the entire first negative electrode active material layer and the second negative electrode active material layer, the mass ratio of the first negative electrode active material to the second negative electrode active material may be greater than 0: less than 100 to 20:80.

[0033] In the above method, the weight ratio of the second binder to the first binder in the entire negative electrode active material layer may be greater than 1:1 to 10.

[0034]

[0035] In one embodiment of the present invention, a secondary battery including a negative electrode, a positive electrode, and a separator having the multilayer structure is provided.

[0036] The above positive electrode includes a positive electrode active material, and the positive electrode active material may be a lithium composite transition metal compound represented by the following chemical formula 1.

[0037] Secondary battery:

[0038] [Chemical Formula 1]

[0039] Li a Ni (1-x-y) Co x M1 y M2 w O2

[0040] In the above chemical formula 1,

[0041] 1.0≤a≤1.5, 0 <x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0<x+y≤0.2 이고,

[0042] M1 is at least one metal among Mn and Al,

[0043] M2 is at least one metallic element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

[0044] A negative electrode for a secondary battery having a multilayer structure according to one embodiment of the present invention has excellent adhesion between the negative electrode active material layer and the current collector.

[0045] A multilayered secondary battery negative electrode according to one embodiment of the present invention has a high loading amount of negative electrode active material in the negative electrode active material layer, and thus can improve battery performance, such as cell life and output, of a secondary battery using the negative electrode.

[0046] A multilayered secondary battery negative electrode according to one embodiment of the present invention can improve battery performance, such as cell life and output, of a secondary battery using the negative electrode by maintaining excellent adhesiveness between the negative electrode active material layer and the current collector, while also having a high loading amount of the negative electrode active material within the negative electrode active material layer.

[0047] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0048] FIG. 1 is a graph showing a cross-section of a negative electrode for a secondary battery having a multilayer structure according to one embodiment of the present invention.

[0049] Figure 2 is a perspective view of a battery can that can be applied to the battery cell of the embodiment.

[0050] FIG. 3 and FIG. 4 are perspective views showing the states before and after lamination of the first electrode, the second electrode, and the separator for manufacturing an electrode assembly to be accommodated in a battery can, respectively, and FIG. 5 is a plan view of the lamination state of FIG. 4.

[0051] Figures 6 and 7 are perspective and side views of an electrode assembly manufactured by winding the laminate of Figures 4 and 5 into a jelly-roll shape.

[0052] Figures 8 and 9 are perspective views showing a state in which a current collector plate is attached to the upper portion of the electrode assembly and no current collector plate is attached to the lower portion.

[0053] Fig. 10 is a cross-sectional view showing the process of accommodating the electrode assembly of Figs. 8 and 9 into a battery can.

[0054] Figure 11 is a cross-sectional view showing the process of welding the first electrode terminal and the current collector plate.

[0055] Figure 12 is a drawing showing the process of pressing a cap into a battery can.

[0056] Figure 13 is a cross-sectional view showing a state in which the electrode connection part of the cap is joined to the tab of the second electrode of the electrode assembly and the mating surface of the cap is joined to the mating wall surface of the battery can.

[0057] The above-described objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily practice the technical idea of ​​the present invention. In describing the present invention, if a detailed description of a known technology related to the present invention is judged to unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0058] Hereinafter, the phrase "any configuration is placed on (or below)" a component or "on (or below)" a component may mean that any configuration is placed in contact with the upper surface (or lower surface) of said component, and that other configurations may be interposed between said component and any configuration placed on (or below) said component.

[0059] Additionally, when it is described that a component is "connected," "coupled," or "connected" to another component, it should be understood that the components may be directly connected or connected to one another, but that other components may also be "interposed" between the components, or that each component may be "connected," "coupled," or "connected" through another component.

[0060]

[0061] In one embodiment of the present invention, a negative electrode for a secondary battery having a multilayer structure is provided, which includes a current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer sequentially laminated on the current collector.

[0062] The above multilayered secondary battery negative electrode forms a multilayered structure of a first negative electrode active material layer having a high binder content ratio to improve the adhesive strength between the negative electrode active material layer and the current collector, and a second negative electrode active material layer having a composition advantageous for improving cell performance.

[0063] Fig. 1 shows a cross-sectional structure of the negative electrode (100) for a secondary battery having the above multilayer structure. In Fig. 1, the negative electrode (100) for a secondary battery having the above multilayer structure has a structure in which a first negative electrode active material layer (121) and a second negative electrode active material layer (122) are sequentially laminated on a current collector (110), and the negative electrode active material layer (120) has a structure formed by a multilayer of the first negative electrode active material layer (121) and the second negative electrode active material layer (122).

[0064] In one embodiment, the mass% content of the first binder in the first negative electrode active material layer is greater than the mass% content of the second binder in the second negative electrode active material layer. For example, the ratio of the mass% content of the first binder in the first negative electrode active material layer to the mass% content of the second binder in the second negative electrode active material layer, i.e., (mass% of the first binder in the first negative electrode active material layer) / (mass% of the second binder in the second negative electrode active material layer), may be 1 to 50, specifically, 10 to 50, for example, 20 to 50.

[0065] As long as the first negative electrode active material layer secures a certain level of adhesive strength, the thicker the second negative electrode active material layer is compared to the first negative electrode active material layer, the more advantageous it is in terms of battery performance.

[0066] The negative electrode for a secondary battery having the above multilayer structure can improve battery performance such as cell life and output by increasing the thickness ratio of the second negative electrode active material layer to the first negative electrode active material layer.

[0067] In one embodiment, the first negative electrode active material layer includes a first negative electrode active material and a first binder, the second negative electrode active material layer includes a second negative electrode active material and a second binder, a mass% content of the first binder in the first negative electrode active material layer is greater than a mass% content of the second binder in the second negative electrode active material layer, and a ratio of a thickness of the second negative electrode active material layer to a thickness of the first negative electrode active material layer may be 8 to 10. The mass% content of the second binder in the second negative electrode active material layer may be low, and the content ratio of the second negative electrode active material in the second negative electrode active material layer may be relatively high, so that as the thickness of the second negative electrode active material layer becomes thicker, the content of the negative electrode active material in the entire negative electrode active material layer increases, which may result in improved performance of the battery.

[0068] When manufacturing the negative electrode for a secondary battery having the above multilayer structure, the first negative electrode active material layer may be formed by a gravure coating method, and the second negative electrode active material layer may be formed by a slot die coating method.

[0069] If all of the multilayer negative electrode active material layers are formed by the slot die coating method, it is difficult to form the first negative electrode active material layer and the second negative electrode active material layer at the desired thickness ratio because both the first negative electrode active material layer and the second negative electrode active material layer must have a thickness of a certain level or more during the slot die coating.

[0070] In order to control the coating thickness in the slot die coating process, the gap between the substrate and the die lip can be adjusted, or the flow rate of the pump supplying the slurry can be adjusted. However, although the coating thickness can be reduced when the coating gap is reduced, the thicknesses of both the first and second negative electrode active material layers also become reduced. On the other hand, when the pump flow rate is reduced, the flow rate is lowered, but due to the decrease in the internal pressure of the die, a deviation in the flow rate in the width direction of the discharged slurry occurs, making it difficult to form a uniform coating layer in the coating width direction. Therefore, there is a limit to reducing the thickness by reducing the pump flow rate.

[0071] Therefore, when forming both the first negative electrode active material layer and the second negative electrode active material layer using a slot die coating process, a predetermined thickness ratio cannot be formed.

[0072] Since the negative electrode for a secondary battery having the above multilayer structure forms a negative electrode having a multilayer structure including a first negative electrode active material layer and a second negative electrode active material layer by combining slot die coating and gravure coating methods, it is not subject to the limitations of the case where only the slot die coating process as described above is applied, and it is possible to form the first negative electrode active material layer and the second negative electrode active material layer at a predetermined thickness ratio, that is, the ratio of the thickness of the second negative electrode active material layer to the thickness of the first negative electrode active material layer is 8 to 10. The negative electrode for a secondary battery having the above multilayer structure formed at the above thickness ratio has excellent adhesion of the negative electrode active material layer to a current collector, and can load the negative electrode active material at a relatively high content, thereby improving battery performance.

[0073] In one embodiment, the total content of the first negative electrode active material and the second negative electrode active material may be 92 parts by weight or more, specifically, 95 parts by weight or more to less than 100 parts by weight, more specifically, 96 parts by weight or more to less than 100 parts by weight, and even more specifically, 97 parts by weight or more to less than 100 parts by weight, relative to 100 parts by weight of the entire negative electrode active material layer. As described above, the negative electrode for a secondary battery having a multilayer structure can load a high content of the second negative electrode active material by increasing the thickness of the second negative electrode active material layer compared to the first negative electrode active material layer, and as a result, the content of the negative electrode active material in the entire negative electrode active material layer (i.e., the total content of the first negative electrode active material and the second negative electrode active material. In the present specification, the negative electrode active material is a general term including both the first negative electrode active material and the second negative electrode active material) can be implemented within the above numerical range. By including a negative electrode active material in a content ratio within the above numerical range, the negative electrode for a secondary battery having a multilayer structure can improve battery performance by loading the negative electrode active material at a relatively high content while having excellent adhesion of the negative electrode active material layer to the current collector.

[0074] In one embodiment, the total content of the first binder and the second binder may be 5 parts by weight or less, specifically, more than 0 and 3 parts by weight or less, more specifically, more than 0 and 2 parts by weight or less, and even more specifically, more than 0 and 1 part by weight or less, based on 100 parts by weight of the entire negative electrode active material layer. As described above, the negative electrode for a secondary battery having a multilayer structure can load the first binder at a low content by reducing the thickness of the first negative electrode active material layer, and as a result, the binder content (i.e., the total content of the first binder and the second binder. In the present specification, binder is a general term including both the first binder and the second binder) in the above numerical range can be implemented. By including a binder in a content ratio within the above numerical range, the negative electrode for a secondary battery having the multilayer structure can improve battery performance by loading the negative electrode active material at a relatively high content while having excellent adhesion of the negative electrode active material layer to the current collector.

[0075] In one embodiment, the thickness of the first negative electrode active material layer may be 1 μm to 50 μm, specifically, 1 μm to 30 μm, and more specifically, 1 μm to 10 μm. As described above, in the case of slot die coating, it is difficult to form with a low thickness, but the first negative electrode active material layer can be formed with the above thickness range by forming it with a gravure coating method. The negative electrode for a secondary battery having the multilayer structure including the first negative electrode active material layer with the above thickness range can excellently maintain the adhesion of the negative electrode active material layer to the current collector.

[0076] In one embodiment, the thickness of the second negative electrode active material layer may be 100 μm to 300 μm, specifically, 150 μm to 200 μm. As described above, when the second negative electrode active material layer together with the first negative electrode active material layer are both formed by slot die coating, it is difficult to form only the second negative electrode active material layer thick. However, the first negative electrode active material layer is formed by gravure coating, and only the second negative electrode active material layer can be formed in the above thickness range by applying slot die coating. The negative electrode for a secondary battery having the multilayer structure including the second negative electrode active material layer in the above thickness range can improve battery performance by loading the negative electrode active material at a relatively high content while having excellent adhesion of the negative electrode active material layer to a current collector.

[0077] In one embodiment, the weight ratio of the second binder to the first binder in the entire negative electrode active material layer may be greater than 1:1 to 10. As described above, the negative electrode for a secondary battery having a multilayer structure has a low thickness of the first negative electrode active material layer and a high thickness of the second negative electrode active material layer relative to the first negative electrode active material layer, so that even if the first binder is in a relatively high content in the first negative electrode active material layer, the thickness of the first negative electrode active material layer is small, so that the relative content ratio of the first binder and the second binder can be implemented within the above numerical range. The content ratio of the first binder and the second binder within the above numerical range ultimately means that the thickness of the first negative electrode active material layer is reduced and the second negative electrode active material layer is formed thickly. Therefore, the negative electrode for a secondary battery having such a multilayer structure can improve battery performance by loading the negative electrode active material at a relatively high content while having excellent adhesion of the negative electrode active material layer to the current collector.

[0078] In one embodiment, the negative electrode for a secondary battery having a multilayer structure may have a mass ratio of the first negative electrode active material to the second negative electrode active material among the entire negative electrode active material layers of more than 0: less than 100 to 20:80, specifically, a mass ratio of more than 0: less than 100 to 15:85, and more specifically, a mass ratio of more than 0: less than 100 to 12:88. As described above, the negative electrode for a secondary battery having a multilayer structure may have a lower thickness of the first negative electrode active material layer or a higher thickness of the second negative electrode active material layer compared to the first negative electrode active material layer, so that even if the first negative electrode active material has a relatively low content in the first negative electrode active material layer, the relative content ratio of the first negative electrode active material and the second negative electrode active material can be implemented within the above numerical range because the thickness of the first negative electrode active material layer is small. The content ratio of the first negative electrode active material and the second negative electrode active material within the above numerical range ultimately means that the thickness of the first negative electrode active material layer is reduced and the second negative electrode active material layer is formed thickly. Therefore, the negative electrode for a secondary battery having such a multilayer structure can improve battery performance by loading the negative electrode active material at a relatively high content while having excellent adhesion of the negative electrode active material layer to the current collector.

[0079] As the first negative electrode active material and the second negative electrode active material, known materials used as negative electrode active materials can be used. For example, the first negative electrode active material and the second negative electrode active material can be, independently, artificial graphite, natural graphite, hard carbon, soft carbon, graphitized carbon fiber, graphitized mesocarbon microbead, petroleum coke, resin sintered body, carbon fiber, pyrolytic carbon, Si, SiO. x (0 <x≤2)로 표시되는 규소산화물, 리튬티타늄산화물(LTO), 리튬 금속 또는 이들의 조합으로 이루어진 군으로부터 선택된 적어도 하나를 포함할 수 있고, 이에 한정되지 않는다.

[0080] The above artificial graphite can generally be manufactured by carbonizing raw materials such as coal tar, coal tar pitch, and petroleum heavy oils at temperatures above 2,500°C. After graphitization, the particles are adjusted through grinding and secondary particle formation to be used as a negative electrode active material. In the case of artificial graphite, crystals are randomly distributed within the particles, and compared to natural graphite, the sphericity is lower and the shape is somewhat pointed.

[0081] Artificial graphite includes MCMB (mesophase carbon microbeads), MPCF (mesophase pitch-based carbon fiber), artificial graphite graphitized in block form, and artificial graphite graphitized in powder form, which are widely used commercially. Artificial graphite having a sphericity of 0.91 or less, for example, 0.6 to 0.91, or another example, 0.7 to 0.9, can be used.

[0082] The above sphericity may be a value obtained by dividing the circumference of a circle having the same area as the projected image when the graphite-based active material is projected by the perimeter of the projected image, and may be specifically expressed by the following mathematical formula 1. The above sphericity may be measured using a particle shape analyzer, such as a sysmex FPIA3000 manufactured by Malvern.

[0083] [Mathematical Formula 1]

[0084] Sphericity = Circumference of a circle with the same area as the image projected on the active material / Perimeter of the projected image

[0085] In one embodiment, the artificial graphite may have an average particle size of 5 to 30 μm, specifically, 10 to 25 μm.

[0086] The above natural graphite is generally in the form of plate-shaped aggregates before being processed, and the plate-shaped particles can be manufactured into a spherical shape with a smooth surface through post-processing such as particle crushing and reassembly processes in order to be used as an active material for manufacturing electrodes.

[0087] The above natural graphite may be used having a sphericity of more than 0.91 and less than or equal to 0.97, for example, 0.93 to 0.97, or another example, 0.94 to 0.96.

[0088] The above natural graphite may have an average particle diameter of 5 µm to 30 µm, specifically, 10 µm to 25 µm.

[0089] The first negative electrode active material layer and the second negative electrode active material layer may each include different negative electrode active materials, and each layer may include two or more types, and may form a concentration gradient depending on the distance from the current collector, or even if the negative electrode active material is the same type of material, it may be included in a form with different average particle diameters or shapes.

[0090] For example, the first negative electrode active material layer may include only natural graphite, or may include both natural graphite and artificial graphite, and the second negative electrode active material layer may include only artificial graphite, or may include both natural graphite and artificial graphite. Even when negative electrode active materials of the same material are used in the first negative electrode active material layer and the second negative electrode active material layer (for example, when both natural graphite and artificial graphite are included), the first negative electrode active material layer may include a negative electrode active material having a small average particle diameter, and the second negative electrode active material layer may include a negative electrode active material having a large average particle diameter.

[0091] In one embodiment, a mixing region (intermixing) in which the negative electrode active materials of both layers are mixed with each other may exist between the first negative electrode active material layer and the second negative electrode active material layer.

[0092] In one embodiment, the first negative electrode active material may be natural graphite, and the second negative electrode active material may be artificial graphite. The multilayered secondary battery negative electrode may use a material with excellent adhesiveness, such as natural graphite, as the first negative electrode active material, and artificial graphite, which is advantageous for improving battery performance, as the second negative electrode active material, thereby realizing excellent adhesiveness with a current collector while increasing the thickness of the second negative electrode active material layer to increase the loading amount of artificial graphite, thereby realizing excellent battery performance.

[0093] The above current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used.

[0094] The thickness of the above-mentioned collector is not particularly limited, but may have a thickness of 3 to 500 ㎛, which is typically applied.

[0095] The first binder and the second binder may each independently be one or more types of binder polymers, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), fluororubber, and various copolymers.

[0096] The composition for the negative electrode active material layer can be typically formed into a slurry by mixing the negative electrode active material and a binder with a dispersion medium. The composition for the negative electrode active material layer can further include a thickener, which is a polymer that increases the viscosity of the composition for the negative electrode active material layer and contributes to the dispersion stabilization of the slurry.

[0097] The thickener may be, for example, carboxymethylcellulose (CMC), starch, polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, etc.

[0098] Among these thickeners, there are examples (polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, etc.) that are used alone without other binders to simultaneously act as a binder within the active material layer and as a thickener for stabilizing the dispersion of the slurry, and there may also be examples (carboxymethyl cellulose, starch, etc.) that are used together with other binders to further contribute to the dispersion stability of the slurry.

[0099] The above negative electrode active material layer may optionally further include a conductive material. For the convenience of distinction, the first negative electrode active material layer may be referred to as including a first conductive material, and the second negative electrode active material layer may be referred to as including a second conductive material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorocarbon, aluminum, and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0100] In one embodiment, the ratio of the first binder to the first conductive material may be greater than the ratio of the second binder to the second conductive material, and the ratio of the first negative electrode active material to the first conductive material may be less than the ratio of the second negative electrode active material to the second conductive material.

[0101]

[0102] In one embodiment of the present invention,

[0103] A step of preparing a composition for a first negative electrode active material layer including a first negative electrode active material, a first binder, and a first dispersion medium;

[0104] A step of preparing a composition for a second negative electrode active material layer including a second negative electrode active material, a second binder, and a second dispersion medium;

[0105] A step of forming a first negative electrode active material layer by coating the composition for the first negative electrode active material layer on one surface of a negative electrode current collector using a slot die coating method; and

[0106] A step of forming a second negative electrode active material layer by coating a composition for the second negative electrode active material layer on the first negative electrode active material layer using a gravure coating method;

[0107] A method for manufacturing a negative electrode for a secondary battery having a multilayer structure is provided.

[0108] The above-described multilayered secondary battery anode can be manufactured by the method for manufacturing the multilayered secondary battery anode. Accordingly, the detailed description of the multilayered secondary battery anode can be equally applied to the method for manufacturing the multilayered secondary battery anode.

[0109] In one embodiment, the ratio of the coating thickness of the second negative electrode active material layer to the coating thickness of the first negative electrode active material layer may be greater than 8 and less than 10.

[0110] In one embodiment, the mass% content of the first binder in the first negative electrode active material layer may be greater than the mass% content of the second binder in the second negative electrode active material layer.

[0111] In one embodiment, the total content of the first negative electrode active material and the second negative electrode active material may be 92 parts by weight or more, and the total content of the first binder and the second binder may be 5 parts by weight or less, based on 100 parts by weight of the total content of the first negative electrode active material layer and the second negative electrode active material layer.

[0112] In one embodiment, among the entire first negative electrode active material layer and the second negative electrode active material layer, the mass ratio of the first negative electrode active material to the second negative electrode active material may be greater than 0: less than 100 to 20:80.

[0113] In one embodiment, the weight ratio of the second binder to the first binder in the entire negative electrode active material layer may be greater than 1:1 to 10.

[0114] The dispersion medium that can be used as the first dispersion medium and the second dispersion medium may be a known material used for manufacturing a fluid composition containing a negative electrode active material to form a coating layer, and examples thereof include, but are not limited to, N-methylpyrrolidone, acetone, water, etc.

[0115] The composition for the negative electrode active material layer may be coated to form a coating layer, and then dried to form a negative electrode active material layer. After this drying step, a step of rolling the negative electrode active material layer may be further performed. Rolling may be performed by a known method such as roll pressing, and may be performed, for example, at a pressure of 1 to 20 MPa and a temperature of 15 to 30°C.

[0116]

[0117] In one embodiment of the present invention, a secondary battery is provided, which includes a negative electrode, a positive electrode, and a separator for a secondary battery having a multilayer structure. For example, the secondary battery can be manufactured by injecting an electrolyte into an electrode assembly including a positive electrode, a negative electrode having a multilayer structure, and a separator interposed therebetween.

[0118] The above positive electrode can be manufactured by mixing a positive electrode active material, a conductive material, a binder, and a solvent to prepare a composition for the positive electrode active material, and then directly coating the composition on a current collector, or by casting the composition on a separate support and laminating a positive electrode active material film peeled from the support onto a current collector to manufacture a positive electrode including a positive electrode active material layer.

[0119] In one embodiment, the positive electrode active material layer includes a positive electrode active material, and for example, the positive electrode active material layer may include 80 to 99 wt% of the positive electrode active material, for example, 85 to 99 wt%, or for another example, 90 to 99 wt%, based on the total weight of the positive electrode active material layer.

[0120] The above cathode active material may be a lithium composite transition metal compound represented by the following chemical formula 1.

[0121] [Chemical Formula 1]

[0122] Li a Ni (1-x-y) Co x M1 y M2 w O2

[0123] In the above chemical formula 1,

[0124] 1.0≤a≤1.5, 0 <x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0<x+y≤0.2 이고,

[0125] M1 is at least one metal among Mn and Al,

[0126] M2 is at least one metallic element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

[0127] Detailed descriptions of the conductive agent, binder, and dispersion medium in the composition for the above positive electrode active material are as described in the above negative electrode.

[0128] The above separator may use a porous polymer film, and for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer may be used alone or in a laminated manner. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The above separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator. In addition, a typical porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

[0129] The above electrolyte can be injected as an electrolyte solution including a lithium salt and an organic solvent for dissolving the same.

[0130] The above lithium salt can be used without limitation as long as it is one commonly used in electrolytes for secondary batteries, and for example, the anion of the above lithium salt is F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N -, F3CF2(CF3)2CO - , (CF3SO2)2CH-, (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , H3CO2 - , SCN - , (CF3CF2SO2)2N - and one selected from the group consisting of combinations thereof may be used.

[0131] As the organic solvent included in the above electrolyte, a known substance may be used, and for example, one selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, and combinations thereof may be used, but is not limited thereto.

[0132] Among the above carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are high-viscosity organic solvents with high dielectric constants, which can be utilized to facilitate the dissociation of lithium salts within the electrolyte. For example, by mixing low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate with cyclic carbonates in a predetermined ratio, an electrolyte with high electrical conductivity can be produced.

[0133] The secondary battery can be manufactured by forming an electrode assembly by placing a separator between the positive and negative electrodes, placing the electrode assembly in, for example, a pouch, a cylindrical battery case, or a square battery case, and then injecting an electrolyte. Alternatively, the secondary battery can be manufactured by stacking the electrode assemblies, then impregnating them with an electrolyte, and then placing the resulting product in a battery case and sealing it.

[0134]

[0135] Hereinafter, with reference to FIGS. 2 to 13, the structure of a cylindrical battery cell according to one embodiment of the present invention will be described.

[0136] The battery cell of the embodiment may be, for example, a cylindrical battery cell having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of the cylindrical battery cell) of greater than about 0.4.

[0137] Here, the form factor refers to a value indicating the diameter and height of a cylindrical battery cell. Cylindrical battery cells to be applied to a pressure tester may be, for example, 46110 cells, 48750 cells, 48110 cells, 48800 cells, and 46800 cells. In the numerical value indicating the form factor, the first two numbers indicate the diameter of the cell, the next two numbers indicate the height of the cell, and the last number 0 indicates that the cross-section of the cell is circular.

[0138] The battery cell to be applied to the pressure tester may be a cylindrical battery cell having a roughly cylindrical shape, a diameter of approximately 46 mm, a height of approximately 110 mm, and a form factor ratio of 0.418.

[0139] According to another embodiment, a battery cell may be a cylindrical battery cell having a generally cylindrical shape, a diameter of approximately 48 mm, a height of approximately 75 mm, and a form factor ratio of 0.640.

[0140] According to another embodiment, a battery cell may be a cylindrical battery cell having a generally cylindrical shape, a diameter of approximately 48 mm, a height of approximately 110 mm, and a form factor ratio of 0.418.

[0141] According to another embodiment, a battery cell may be a cylindrical battery cell having a generally cylindrical shape, a diameter of approximately 48 mm, a height of approximately 80 mm, and a form factor ratio of 0.600.

[0142] According to another embodiment, a battery cell may be a cylindrical battery cell having a generally cylindrical shape, a diameter of approximately 46 mm, a height of approximately 80 mm, and a form factor ratio of 0.575.

[0143] The pressure tester of the present invention can of course be applied to battery cells having a form factor ratio of approximately 0.4 or less, such as 18650 cells, 21700 cells, etc. For 18650 cells, the diameter is approximately 18 mm, the height is approximately 65 mm, and the form factor ratio is 0.277. For 21700 cells, the diameter is approximately 21 mm, the height is approximately 70 mm, and the form factor ratio is 0.300.

[0144] Referring to FIG. 2 and FIG. 10, the battery can (10) includes a cylindrical side wall portion (11) and a bottom portion (12) connected to one axial end of the side wall portion (11).

[0145] The above-mentioned bottom portion (12) and side wall portion (11) can be manufactured by forming a metal sheet with a nickel plated surface using a deep drawing process, and trimming the front end of the side wall portion (11) with a punch while holding it with a blank holder. Of course, the material of the can (10) is not limited to this.

[0146] A hole is formed in the center of the bottom portion (12), and a first electrode terminal (13) can be fitted into the hole. The first electrode terminal (13) can be riveted and fixed to the bottom portion (12) while a terminal gasket (14) is interposed therebetween. The terminal gasket (14) is interposed between the first electrode terminal (13) and the bottom portion (12), thereby sealing the inside and outside of the battery can (10) to prevent leakage of the electrolyte, and electrically insulating the first electrode terminal (13) and the bottom portion (12).

[0147] However, the method of connecting the first electrode terminal (13) and the bottom part (12) is not limited to this. For example, if the structure can seal between the first electrode terminal (13) and the bottom part (12) and electrically insulate the first electrode terminal (13) and the bottom part (12), various other fixing methods, such as a bolt-nut joint method, a glass seal method, or a chrome coating & PP-MAH thermal bonding method, can also be applied.

[0148] The first electrode terminal (13) above may have a first polarity, and the battery can (10) may have a second polarity. Accordingly, both the bottom portion (12) of the battery can (10) and the side wall portion (11) connected thereto may have a second polarity.

[0149] Accordingly, the battery can (10) can have both the first electrode terminal (13) and the second electrode terminal (15) positioned at one axial end. Then, the battery can (10) can have both the bus bar connected to the first electrode terminal (13) and the bus bar connected to the second electrode terminal (15) positioned at one axial end of the battery can (10), i.e., the upper end.

[0150] In one example, the first electrode terminal (13) may be a positive terminal and the second electrode terminal (15) may be a negative terminal. Of course, the opposite may also be true.

[0151] An electrode assembly (20) is accommodated within the battery can (10). The electrode assembly (20) is prepared by preparing a first electrode (21), a second electrode (22), and a separator (28) having a predetermined width and extending in the longitudinal direction as illustrated in FIG. 3, and then forming a laminated body by sequentially stacking the first electrode (21), the separator (28), the second electrode (22), and the separator (28) as illustrated in FIGS. 4 and 5, and then winding this around a core shaft to form a jelly roll.

[0152] The above first electrode (21) may be an anode, and the above second electrode (22) may be a cathode. Of course, the opposite may also be the case.

[0153] The above first electrode (21) and second electrode (22) are manufactured in the form of sheets. The electrode sheet is manufactured in the form in which an active material layer (24) is applied to the surface of a current collector (23). The electrode sheet has a holding portion (25) region where the active material layer (24) is applied, and a non-coated portion (26) region where the active material layer (24) is not applied. The positive electrode sheet has a non-coated portion (26) region on one side in the width direction, and the negative electrode sheet has a non-coated portion (26) region on the other side in the width direction.

[0154] The non-conductive portion (26) is exposed or protrudes in the width direction of the laminate. The non-conductive portion (26) itself functions as an electrode tab.

[0155] In the above-mentioned blank portion (26), notches can be formed at a predetermined interval to form flag-shaped notching tabs (27).

[0156] In the embodiment, the notching tabs (27) are exemplified as having an equilateral trapezoidal shape. However, their shapes may be various, such as a semicircle, a semi-ellipse, a triangle, a rectangle, a parallelogram, etc.

[0157] In addition, in the embodiment, a form in which the notching tabs (27) arranged along the longitudinal direction have the same width is exemplified. However, the width of the notching tabs may be gradually or stepwise widened from the core side to the outer periphery side.

[0158] In addition, in the embodiment, a form in which the height of the notching tabs (27) gradually increases from the core side to the outer circumference side is exemplified. However, the height of these notching tabs may be implemented in a form in which they are constant or gradually decrease.

[0159] In addition, in the embodiment, a structure is exemplified in which a notching tab (27) is deleted in a predetermined section of the centrifugal end of the non-conductive portion (26) and a predetermined section of the centrifugal end. However, it is of course possible that the notching tab may not be deleted in the centrifugal end of the non-conductive portion, and that the notching tab may not be deleted in the centrifugal end of the non-conductive portion.

[0160] In the jelly roll-shaped electrode assembly (20), the notched tab (27) may be bent radially and flattened. The notched tab (27) may be bent radially inward or outward. In the embodiment, a structure in which the notched tab (27) is bent radially inward as illustrated in FIGS. 6 and 7 is exemplified.

[0161] The above-mentioned notched tabs (27) can be bent one by one during the process of forming a jelly roll-shaped electrode assembly (20) by winding the laminate. Alternatively, the above-mentioned notched tabs (27) can be bent all at once after the laminate is wound to form a jelly roll-shaped electrode assembly.

[0162] The notching tabs (27) of the first electrode (21) and the notching tabs (27) of the second electrode (22), which are bent and overlapped in the radial direction in this way, can provide a plane substantially perpendicular to the axial direction at both axial ends of the electrode assembly (20), as illustrated in FIG. 7.

[0163] A current collector plate (31) can be joined to a substantially flat surface provided by bending the notched tabs (27) exposed at both axial ends of the electrode assembly (20), as shown in FIG. 8.

[0164] The above-mentioned collector plate (31) can be manufactured by punching, trimming, piercing, and bending a metal sheet.

[0165] Referring to Fig. 8, the current collector plate (31) has a terminal connection portion (32) extending radially from the center, a ring portion (33) connecting the centrifugal edge of the terminal connection portion (32) in a circumferential direction, and an electrode connection portion (34) extending centripetally from the ring portion (33) but not connected to the terminal connection portion (32). The center of the terminal connection portion (32) covers at least a portion of the core hollow portion of the electrode assembly (20).

[0166] The above electrode connection part (34) is joined to the notched tab (27) of the first electrode (21) of the electrode assembly (20) by laser welding or the like before the electrode assembly (20) is placed in the battery can (10).

[0167] Referring to Fig. 9, a collector plate may not be connected to the notched tab (27) of the second electrode (22) of the electrode assembly (20). Of course, the present invention is not limited to a structure in which a collector plate is not connected to the notched tab (27) of the second electrode (22).

[0168] As illustrated in FIGS. 10 and 11, the electrode assembly (20) is accommodated in the battery can (10) in a state where the current collector plate (31) is aligned so as to face the bottom portion (12) of the battery can (10). At this time, an insulator (19) is interposed between the current collector plate (31) and the bottom portion (12) of the battery can (10) so as to electrically insulate the current collector plate (31) from the bottom portion (12).

[0169] And, the terminal connection part (32) of the current collector plate (31) is joined to the first electrode terminal (13) fixed to the battery can (10) by a method such as resistance welding, ultrasonic welding or laser welding. The welding device for forming the welding part (W) of the current collector plate (31) and the first electrode terminal (13) can approach the back surface of the center of the terminal connection part (32) of the current collector plate (31) through the core hollow part of the electrode assembly (20) from the other axial end of the electrode assembly (20) and perform welding. Of course, in addition to this, the current collector plate (31) and the first electrode terminal (13) can also be joined by a brazing or soldering method. In other words, various methods can be applied to the current collector plate (31) and the first electrode terminal (13) as long as they are a joining method that can electrically connect them and fix them to each other.

[0170] Referring to FIGS. 12 and 13, when the electrode assembly (20) is accommodated in the battery can (10) and the first electrode (21) is connected to the first electrode terminal (13), the notched tab (27) of the second electrode (22) can be directly connected to the cap (40) that is press-fitted through the open end of the battery can (10). Accordingly, the second electrode (22) is electrically connected through the welding portion (W) of the notched tab (27) and the cap (40). Of course, other joining methods such as brazing or soldering can be applied to the notched tab (27) and the cap (40) in addition to the welding method.

[0171] The edge of the cap (40) is electrically connected to the side wall (11) of the battery can (10) and sealed and fixed. Accordingly, the second electrode (22) can be electrically connected to the cap (40) and the battery can (10). Various methods, such as welding, brazing, and soldering, that can electrically connect and seal the joint between the cap (40) and the battery can (10) can be applied to the processing of the joint (M).

[0172]

[0173] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely exemplary of the present invention, and the present invention is not limited to the examples described below.

[0174]

[0175] (Example)

[0176] Example 1

[0177] <Manufacturing of the cathode>

[0178] A composition for a first negative electrode active material was prepared in the form of a slurry by mixing natural graphite as a first negative electrode active material, carbon black as a first conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a first binder in a weight ratio of 90.5:1:1:7.5.

[0179] A composition for a second negative electrode active material was prepared in the form of a slurry by mixing artificial graphite as a second negative electrode active material, carbon black as a second conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a second binder in a weight ratio of 97.72:1:1:0.28.

[0180]

[0181] Using a coater capable of sequentially performing gravure coating and slot die coating, the composition for the first negative electrode active material was coated with a thickness of 20 μm using a gravure coater to form the lower layer of a multilayer electrode, and the composition for the second negative electrode active material was sequentially coated with a thickness of 180 μm using a slot die coater to form the upper layer of a multilayer electrode, and after drying at once, the composition was rolled to manufacture a negative electrode having a multilayer structure as shown in FIG. 1.

[0182] The thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer formed by coating the first negative electrode active material composition and the second negative electrode active material composition was 1:9, and the weight ratio of the negative electrode active material: conductive material: CMC: binder in the entire negative electrode active material layer (120) in the manufactured multilayer structure electrode was 97:1:1:1, and the weight ratio of the first binder: second binder in the entire negative electrode active material layer (120) was 0.75:0.25. The content of the negative electrode active material refers to the total content of the first negative electrode active material and the second negative electrode active material, the content of the binder refers to the total content of the first binder and the second binder, and the content of the conductive material refers to the total content of the first conductive material and the second conductive material.

[0183] <Manufacturing of the positive electrode>

[0184] Li(Ni) as a cathode active material 0.6 Mn 0.2 Co 0.2 )O2(NCM-622), carbon black as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) as a solvent at a weight ratio of 96:2:2 to prepare a composition for a positive electrode active material in the form of a slurry. The slurry was coated on one side of an aluminum current collector having a thickness of 15 μm, and drying and rolling were performed under the same conditions as the negative electrode to prepare a positive electrode. The loading amount based on the dry weight of the positive electrode active material layer was 28.1 mg / cm 2 It was.

[0185] <Manufacturing of Lithium Secondary Batteries>

[0186] A non-aqueous electrolyte was prepared by dissolving LiPF6 in an organic solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a ratio of 1:2:1 (volume ratio) to a concentration of 1.0 M.

[0187] A polyolefin separator was interposed between the positive and negative electrodes manufactured above, and this was inserted into a cylindrical battery can, and the electrolyte was then injected to manufacture a 4680 cell lithium secondary battery.

[0188]

[0189] Comparative Example 1

[0190] A composition for a first negative electrode active material was prepared in the form of a slurry by mixing natural graphite as a first negative electrode active material, carbon black as a first conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a first binder in a weight ratio of 90.5:1:1:7.5.

[0191] A composition for a second negative electrode active material was prepared in the form of a slurry by mixing artificial graphite as a second negative electrode active material, carbon black as a second conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a second binder in a weight ratio of 97.72:1:1:0.28.

[0192] The first negative electrode active material composition was sequentially coated as a first negative electrode active material layer (121) and the second negative electrode active material composition was sequentially coated as a second negative electrode active material layer (122) using a slot die coater to a thickness of 100 μm, and then dried and rolled to manufacture a negative electrode having a multilayer structure as shown in FIG. 1.

[0193] The thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer formed by coating the first negative electrode active material composition and the second negative electrode active material composition was 5:5, and the weight ratio of the negative electrode active material: conductive material: CMC: binder in the entire negative electrode active material layer (120) in the manufactured multilayer structure electrode was 94.11:1:1:3.89, and the weight ratio of the first binder: second binder in the entire negative electrode active material layer (120) was 3.75:0.14. The content of the negative electrode active material refers to the total content of the first negative electrode active material and the second negative electrode active material, the content of the binder refers to the total content of the first binder and the second binder, and the content of the conductive material refers to the total content of the first conductive material and the second conductive material.

[0194] A 4680-cell lithium secondary battery was manufactured by manufacturing the positive electrode in the same manner as in Example 1, except that the negative electrode was manufactured as described above.

[0195]

[0196] Comparative Example 2

[0197] A composition for a first negative electrode active material was prepared in the form of a slurry by mixing natural graphite as a first negative electrode active material, carbon black as a first conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a first binder in a weight ratio of 96.5:1:1:1.5.

[0198] A composition for a second negative electrode active material was prepared in the form of a slurry by mixing artificial graphite as a second negative electrode active material, carbon black as a second conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a second binder in a weight ratio of 97.5:1:1:0.5.

[0199] The first negative electrode active material composition was sequentially coated as a first negative electrode active material layer (121) and the second negative electrode active material composition was sequentially coated as a second negative electrode active material layer (122) using a slot die coater to a thickness of 100 μm, and then dried and rolled to manufacture a negative electrode having a multilayer structure as shown in FIG. 1.

[0200] The thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer formed by coating the first negative electrode active material composition and the second negative electrode active material composition was 5:5, and the weight ratio of the negative electrode active material: conductive material: CMC: binder in the entire negative electrode active material layer (120) in the manufactured multilayer structure electrode was 97:1:1:1, and the weight ratio of the first binder: second binder in the entire negative electrode active material layer (120) was 0.75:0.25. The content of the negative electrode active material refers to the total content of the first negative electrode active material and the second negative electrode active material, the content of the binder refers to the total content of the first binder and the second binder, and the content of the conductive material refers to the total content of the first conductive material and the second conductive material.

[0201] A 4680-cell lithium secondary battery was manufactured by manufacturing the positive electrode in the same manner as in Example 1, except that the negative electrode was manufactured as described above.

[0202]

[0203] Comparative Example 3

[0204] A composition for a first negative electrode active material was prepared in the form of a slurry by mixing natural graphite as a first negative electrode active material, carbon black as a first conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a first binder in a weight ratio of 96.125:1:1:1.875.

[0205] A composition for a second negative electrode active material was prepared in the form of a slurry by mixing artificial graphite as a second negative electrode active material, carbon black as a second conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a second binder in a weight ratio of 97.58:1:1:0.42.

[0206] The first negative electrode active material composition was sequentially coated as a first negative electrode active material layer (121) and the second negative electrode active material composition was sequentially coated as a second negative electrode active material layer (122) using a slot die coater to a thickness of 80 μm and 120 μm, respectively, and then dried and rolled to manufacture a negative electrode having a multilayer structure as shown in FIG. 1.

[0207] The thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer formed by coating the first negative electrode active material composition and the second negative electrode active material composition was 4:6, and the weight ratio of the negative electrode active material: conductive material: CMC: binder in the entire negative electrode active material layer (120) in the manufactured multilayer structure electrode was 97:1:1:1, and the weight ratio of the first binder: second binder in the entire negative electrode active material layer (120) was 0.75:0.25. The content of the negative electrode active material refers to the total content of the first negative electrode active material and the second negative electrode active material, the content of the binder refers to the total content of the first binder and the second binder, and the content of the conductive material refers to the total content of the first conductive material and the second conductive material.

[0208] A 4680-cell lithium secondary battery was manufactured by manufacturing the positive electrode in the same manner as in Example 1, except that the negative electrode was manufactured as described above.

[0209]

[0210] Comparative Example 4

[0211] A composition for a first negative electrode active material was prepared in the form of a slurry by mixing natural graphite as a first negative electrode active material, carbon black as a first conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a first binder in a weight ratio of 95.5:1:1:2.5.

[0212] A composition for a second negative electrode active material was prepared in the form of a slurry by mixing artificial graphite as a second negative electrode active material, carbon black as a second conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a second binder in a weight ratio of 97.64:1:1:0.36.

[0213] The first negative electrode active material composition was sequentially coated as a first negative electrode active material layer (121) and the second negative electrode active material composition was sequentially coated as a second negative electrode active material layer (122) using a slot die coater to a thickness of 60 µm and 140 µm, respectively, and then dried and rolled to manufacture a negative electrode having a multilayer structure as shown in FIG. 1.

[0214] The thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer formed by coating the first negative electrode active material composition and the second negative electrode active material composition was 3:7, and the weight ratio of the negative electrode active material: conductive material: CMC: binder in the entire negative electrode active material layer (120) in the manufactured multilayer structure electrode was 97:1:1:1, and the weight ratio of the first binder: second binder in the entire negative electrode active material layer (120) was 0.75:0.25. The content of the negative electrode active material refers to the total content of the first negative electrode active material and the second negative electrode active material, the content of the binder refers to the total content of the first binder and the second binder, and the content of the conductive material refers to the total content of the first conductive material and the second conductive material.

[0215] A 4680-cell lithium secondary battery was manufactured by manufacturing the positive electrode in the same manner as in Example 1, except that the negative electrode was manufactured as described above.

[0216]

[0217] Comparative Example 5

[0218] A composition for a first negative electrode active material was prepared in the form of a slurry by mixing natural graphite as a first negative electrode active material, carbon black as a first conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a first binder in a weight ratio of 94.25:1:1:3.75.

[0219] A composition for a second negative electrode active material was prepared in the form of a slurry by mixing artificial graphite as a second negative electrode active material, carbon black as a second conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a second binder in a weight ratio of 97.69:1:1:0.31.

[0220] The first negative electrode active material composition was sequentially coated as a first negative electrode active material layer (121) and the second negative electrode active material composition was sequentially coated as a second negative electrode active material layer (122) using a slot die coater to a thickness of 40 µm and 160 µm, respectively, and then dried and rolled to manufacture a negative electrode having a multilayer structure as shown in FIG. 1.

[0221] The thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer formed by coating the first negative electrode active material composition and the second negative electrode active material composition was 2:8, and the weight ratio of the negative electrode active material: conductive material: CMC: binder in the entire negative electrode active material layer (120) in the manufactured multilayer structure electrode was 97:1:1:1, and the weight ratio of the first binder: second binder in the entire negative electrode active material layer (120) was 0.75:0.25. The content of the negative electrode active material refers to the total content of the first negative electrode active material and the second negative electrode active material, the content of the binder refers to the total content of the first binder and the second binder, and the content of the conductive material refers to the total content of the first conductive material and the second conductive material.

[0222] Except for manufacturing the negative electrode as described above, an attempt was made to manufacture a lithium secondary battery by manufacturing the positive electrode in the same manner as in Example 1. However, the loading in the coating width direction of the first negative electrode active material layer composition was uneven, so the electrode could not be manufactured normally.

[0223]

[0224] Comparative Example 6

[0225] A composition for a negative electrode active material was prepared in the form of a slurry by mixing natural graphite as a negative electrode active material, carbon black as a conductive material, carboxymethyl cellulose (CMC) as a thickener, and styrene butadiene rubber (SBR) as a binder in a weight ratio of 97:1:1:1.

[0226] The above composition for the negative electrode active material was coated with a thickness of 200 μm using a slot die coater as a negative electrode active material layer, dried, and then rolled to manufacture a negative electrode having a single-layer structure.

[0227] A 4680-cell lithium secondary battery was manufactured by manufacturing the positive electrode in the same manner as in Example 1, except that the negative electrode was manufactured as described above.

[0228]

[0229] (Experimental example)

[0230] The adhesive strength of the electrodes of Example 1 and Comparative Examples 1 to 6 manufactured above was evaluated, and the output and life characteristics of the manufactured 4680 cell lithium secondary battery are shown in Table 1 below.

[0231]

[0232] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Composition of the first negative electrode active material layer (weight ratio) 90.5 : 1 : 1 : 7.59 0.5 : 1 : 1 : 7.59 6.5 : 1 : 1 : 1.59 6.125 : 1 : 1 : 1.8759 5.5 : 1 : 1 : 2.59 4.25 : 1 : 1 : 3.7597 : 1 : 1 : 1 Composition of the second negative electrode active material layer (weight ratio) 97.72 : 1 : 1 : 0.289 7.72 : 1 : 1 : 0.289 7.5 : 1 : 1 : 0.59 7.58 : 1 : 1 : 0.429 7.64 : 1 : 1 : 0.3697.69 : 1 : 1 : 0.31 Total negative electrode active material layer composition (weight ratio) (negative electrode active material : conductive material : CMC : binder) 97 : 1 : 1 : 195.4 : 1 : 1 : 2.697 : 1 : 1 : 197 : 1 : 1 : 197 : 1 : 1 : 197 : 1 : 1 : 197 : 1 : 1 : 1 Thickness ratio (first negative electrode active material layer : second negative electrode active material layer) 1 : 95 : 55 : 54 : 63 : 72 : 8 Single-layer coating Total binder weight ratio of negative electrode active material layer (first binder : second binder) 0.75 : 0.25 3.75 : 0.14 0.75 : 0.25 0.75 : 0.250.75 : 0.250.75 : 0.251Weight % of artificial graphite as the second negative electrode active material among the total negative electrode active material90.751.950.360.470.580.6100Coating methodGravure / slot dieSlot die / slot dieSlot die / slot dieSlot die / slot dieSlot die / slot dieSlot die coating not possibleSlot dieAdhesion (gf / 10mm)3347313232-9Output characteristics (1C / 0.2C)87%69%74%77%79%-87%Life characteristics (%, 100 th cycle / 1 st cycle)91%77%84%86%87%-92%

[0233] Example 1 has the same composition ratio of the first negative electrode active material layer composition and the second negative electrode active material layer composition as Comparative Example 1, but the first negative electrode active material layer composition has a high first binder content ratio and includes natural graphite with high resistance, and is coated as a thin film at a low thickness ratio to form the first negative electrode active material, and the second negative electrode active material layer composition has a low second binder content ratio and includes artificial graphite with excellent performance, and is coated at a high thickness ratio, so that the binder ratio can be designed low and the artificial graphite ratio can be designed high throughout the negative electrode active material layer, and it can be confirmed that the output and life characteristics are relatively excellent. In addition, Example 1 has the same composition of the entire negative electrode active material layer as Comparative Examples 2 to 4, that is, active material: conductive agent: CMC: binder 97: 1: 1: 1, but the second negative electrode active material layer can be designed and coated at a higher thickness ratio than the first negative electrode active material layer by continuous coating of gravure coating and slot die coating. According to the number of possible uses, the proportion of artificial graphite in the overall negative active material layer design composition is high, and the same level of adhesion and better output and life characteristics are exhibited compared to Comparative Examples 2 to 4.

[0234] Comparative Example 6 has the same output and life characteristics as Example 1 by applying artificial graphite in a single layer, but the electrode adhesive strength is low, which may lower the electrode manufacturing processability.

[0235]

[0236] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the exemplary embodiments disclosed herein, and that various modifications may be made by those skilled in the art within the scope of the technical spirit of the invention. Furthermore, even if the operational effects of the configurations of the invention have not been explicitly described and explained while describing the exemplary embodiments of the invention, it is also to be understood that the effects predictable by the configurations should be acknowledged.

[0237]

[0238] [Explanation of symbols]

[0239] 10: Battery can

[0240] 11: Side wall

[0241] 12: Bottom

[0242] 13: Positive terminal (first electrode terminal)

[0243] 14: Terminal gasket

[0244] 15: Negative terminal (second electrode terminal)

[0245] 19: Insulator

[0246] 20: Electrode assembly

[0247] 21: First electrode

[0248] 22: Second electrode

[0249] 23: Whole house

[0250] 24: Active material layer

[0251] 25: Maintenance Department

[0252] 26: Ministry of Immigration

[0253] 27: Notching tab

[0254] 28: Membrane

[0255] 31: Current collector board

[0256] 32: Terminal connection

[0257] 33: Ringbu

[0258] 34: Electrode connection

[0259] 40: Cap

[0260] 100: Multilayer cathode

[0261] 110: Whole house

[0262] 120: Negative electrode active material layer

[0263] 121: First negative electrode active material layer

[0264] 122: Second negative electrode active material layer

Claims

1. Contains a current collector and a negative electrode active material layer, The negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer sequentially laminated on the current collector, The first negative electrode active material layer includes a first negative electrode active material and a first binder, The second negative electrode active material layer includes a second negative electrode active material and a second binder, The mass% content of the first binder in the first negative electrode active material layer is greater than the mass% content of the second binder in the second negative electrode active material layer, The ratio of the thickness of the second negative electrode active material layer to the thickness of the first negative electrode active material layer is 8 to 10. A multilayer structured negative electrode for secondary batteries.

2. In paragraph 1, The total content of the first negative electrode active material and the second negative electrode active material is 92 parts by weight or more compared to 100 parts by weight of the entire negative electrode active material layer. A multilayer structured negative electrode for secondary batteries.

3. In paragraph 1, The total content of the first binder and the second binder is 5 parts by weight or less compared to 100 parts by weight of the entire negative active material layer. A multilayer structured negative electrode for secondary batteries.

4. In paragraph 1, The thickness of the first negative electrode active material layer is 5 ㎛ to 50 ㎛. A multilayer structured negative electrode for secondary batteries.

5. In paragraph 1, The thickness of the second negative electrode active material layer is 100 ㎛ to 300 ㎛. A multilayer structured negative electrode for secondary batteries.

6. In paragraph 1, The weight ratio of the second binder to the first binder among the entire negative electrode active material layer is greater than 1:1 to 10. A multilayer structured negative electrode for secondary batteries.

7. In paragraph 1, Among the entire negative electrode active material layer, the mass ratio of the first negative electrode active material to the second negative electrode active material is greater than 0: less than 100 to 20:

80. A multilayer structured negative electrode for secondary batteries.

8. In paragraph 1, The ratio of the mass% content of the first binder in the first negative electrode active material layer to the mass% content of the second binder in the second negative electrode active material layer is 1 to 50. A multilayer structured negative electrode for secondary batteries.

9. In paragraph 1, The first negative electrode active material and the second negative electrode active material are each independently artificial graphite, natural graphite, hard carbon, soft carbon, graphitized carbon fiber, graphitized mesocarbon microbead, petroleum coke, resin sintered body, carbon fiber, pyrolytic carbon, Si, SiOx(0 <x≤2)로 표시되는 규소산화물, 리튬티타늄산화물(LTO), 리튬 금속 또는 이들의 조합으로 이루어진 군으로부터 선택된 적어도 하나를 포함한 A multilayer structured negative electrode for secondary batteries.

10. In paragraph 1, The above first negative electrode active material is natural graphite, and the above second negative electrode active material is artificial graphite. A multilayer structured negative electrode for secondary batteries.

11. In paragraph 1, The first negative electrode active material layer is formed by a gravure coating method, and the second negative electrode active material layer is formed by a slot die coating method. A multilayer structured negative electrode for secondary batteries.

12. A step of preparing a composition for a first negative electrode active material layer including a first negative electrode active material, a first binder, and a first dispersion medium; A step of preparing a composition for a second negative electrode active material layer including a second negative electrode active material, a second binder, and a second dispersion medium; A step of forming a first negative electrode active material layer by coating the composition for the first negative electrode active material layer on one surface of a negative electrode current collector using a gravure coating method; and A step of forming a second negative electrode active material layer by coating a composition for the second negative electrode active material layer on the first negative electrode active material layer using a slot die coating method; A method for manufacturing a negative electrode for a secondary battery having a multilayer structure.

13. In paragraph 12, The ratio of the thickness of the second negative electrode active material layer to the thickness of the first negative electrode active material layer is greater than 8 and less than 10. A method for manufacturing a negative electrode for a secondary battery having a multilayer structure.

14. In paragraph 12, The first negative electrode active material layer is coated with a thickness of 5 μm to 50 μm. A method for manufacturing a negative electrode for a secondary battery having a multilayer structure.

15. In paragraph 12, The second negative electrode active material layer is coated with a thickness of 100 μm to 200 μm. A method for manufacturing a negative electrode for a secondary battery having a multilayer structure.

16. In paragraph 12, The mass% content of the first binder in the first negative electrode active material layer is greater than the mass% content of the second binder in the second negative electrode active material layer. A method for manufacturing a negative electrode for a secondary battery having a multilayer structure.

17. In paragraph 12, The total content of the first negative electrode active material layer and the second negative electrode active material layer is 92 parts by weight or more, and the total content of the first binder and the second binder is 5 parts by weight or less, based on 100 parts by weight of the total content of the first negative electrode active material layer and the second negative electrode active material layer. A method for manufacturing a negative electrode for a secondary battery having a multilayer structure.

18. In paragraph 12, Among the entire first negative electrode active material layer and the second negative electrode active material layer, the mass ratio of the first negative electrode active material to the second negative electrode active material is greater than 0: less than 100 to 20:

80. A method for manufacturing a negative electrode for a secondary battery having a multilayer structure.

19. In paragraph 12, The weight ratio of the second binder to the first binder among the entire negative electrode active material layer is greater than 1:1 to 10. A method for manufacturing a negative electrode for a secondary battery having a multilayer structure.

20. A secondary battery comprising a negative electrode, a positive electrode, and a separator having a multilayer structure according to any one of claims 1 to 11.

21. In paragraph 20, The above positive electrode includes a positive electrode active material, and the positive electrode active material is a lithium composite transition metal compound represented by the following chemical formula 1. Secondary battery: [Chemical Formula 1] The a Nor (1-x-y) Co x M1 y M2 w O2 In the above chemical formula 1, 1.0≤a≤1.5, 0 <x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0<x+y≤0.2 이고, M1 is at least one metal among Mn and Al, M2 is at least one metallic element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

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