Positive electrode for secondary battery and method for manufacturing the same

Abstract

The present invention proposes a positive electrode for a secondary battery, the positive electrode including a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, the positive electrode including: a coated portion at which the positive electrode mixture layer is formed in a uniform thickness; an uncoated portion provided on at least one edge of the coated portion on the positive electrode current collector and at which the positive electrode mixture layer is not formed; and a buffer portion between the coated portion and the uncoated portion, at which the positive electrode mixture layer is formed in a thickness smaller than that of the coated portion.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2020-0142435, filed on October 29, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a positive electrode for a secondary battery and a method for manufacturing the same, and more specifically, to a positive electrode structure for a secondary battery that minimizes irregular wrinkling or folding, electrode breakage, etc., and a method for manufacturing the positive electrode structure. Background Technology

[0004] Rechargeable and dischargeable secondary batteries are widely used as energy or auxiliary power devices for mobile devices. Furthermore, secondary batteries have attracted attention as a power source for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), and have been proposed as a measure to address air pollution from existing gasoline and diesel vehicles that use fossil fuels. Recently, there has been a need to develop secondary batteries with higher energy density to increase the remaining fuel-to-empty driving range of electric vehicles.

[0005] During the manufacturing of secondary batteries, the electrode assembly and electrolyte are placed together in the electrode housing. Electrode assemblies, which consist of a positive electrode, a negative electrode, and a separator, are classified according to their manufacturing methods into stacked, folded, and stacked-folded types, among others.

[0006] A method is needed for manufacturing the cathode and anode of an electrode assembly by applying an electrode active material to one or both sides of a metal current collector, manufacturing an electrode sheet by drying the electrode active material, winding the electrode sheet, and cutting the electrode sheet into an electrode interval.

[0007] The positive electrode current collector consists of a coated portion containing the positive electrode active material to be coated and uncoated portions disposed on both sides of the coated portion along its longitudinal direction, without the positive electrode mixture layer being coated. The positive electrode mixture layer is applied to the coated portion of the current collector and rolled to the desired thickness.

[0008] For rolling, electrode sheets are typically rolled continuously using cylindrical rolls, and this process is repeated to obtain the desired electrode thickness and density. Electrodes are rolled at high rolling ratios to manufacture secondary batteries with high energy density.

[0009] However, when the electrode sheet is rolled by rollers, especially when the electrode is rolled at a high rolling ratio, very little pressure is applied to the uncoated portion of the current collector. As a result, due to the difference in elongation between the coated and uncoated portions of the current collector, ripples or wrinkles are generated on the current collector, and in severe cases, breakage occurs.

[0010] When corrugations or wrinkles form on the electrode, a gap is easily created between the cathode mixture layer and the current collector, and this gap significantly degrades the electrode performance due to the separation of the cathode mixture layer. Furthermore, if the corrugations or wrinkles are severe, the entire electrode may break during rolling. When breakage occurs, productivity and yield can be significantly reduced, and in severe cases, it may be impossible to roll to the desired thickness.

[0011] Related technologies have been developed to reduce the elongation difference between coated and uncoated portions during rolling by softening the uncoated portion with IHA heating. However, the IHA output should be increased to adequately address the breakage issue. However, in this case, there is a problem of excessive softening of the current collector, leading to quality degradation in subsequent processes such as welding.

[0012] Therefore, there is a great need to develop a technology that can fundamentally solve this problem.

[0013] Related technical documents

[0014] (Patent Document 1) KR10-2016-0141448A Summary of the Invention

[0015] This application aims to solve the above-mentioned problems, and its purpose is to optimize the thickness of the active material layer in the longitudinal direction of the current collector after the rolling process by minimizing the elongation difference between the coated and uncoated portions, and to minimize the elongation difference between the coated and uncoated portions during the rolling process by optimizing the design of the cushioning section between the coated and uncoated portions before the rolling process.

[0016] According to an embodiment of this application, the positive electrode for a secondary battery includes a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector. The positive electrode includes: a coated portion, on which a positive electrode mixture layer is formed with a uniform thickness; an uncoated portion, which is disposed on at least one edge of the coated portion on the positive electrode current collector and on which no positive electrode mixture layer is formed; and a buffer portion, which is located between the coated portion and the uncoated portion, on which a positive electrode mixture layer is formed with a thickness less than that of the coated portion.

[0017] In the positive electrode of a secondary battery according to an embodiment of the present invention, the thickness of the buffer portion can gradually increase from a first point, which is the boundary between the uncoated portion and the buffer portion, toward a second point, which is the boundary between the buffer portion and the coated portion.

[0018] In the positive electrode of a secondary battery according to an embodiment of the present invention, a third point may exist between the first and second points in the buffer portion, and the thickness of the positive electrode mixture layer at the third point in the buffer portion may be 30%-80% of the thickness of the positive electrode mixture layer in the coating portion.

[0019] In the positive electrode of a secondary battery according to an embodiment of the present invention, the distance between the third point and the first point can be 20%-60% of the length from the first point to the second point on the current collector.

[0020] In the positive electrode of the secondary battery according to an embodiment of the present invention, a fourth point may exist between the second and third points in the buffer portion. The thickness of the positive electrode mixture layer at the third point may be 20%-50% of the thickness of the positive electrode mixture layer in the coating portion. The thickness of the positive electrode mixture layer in the buffer portion may gradually increase from the third point to the fourth point, and the thickness difference between the third point and the fourth point may be within 30% of the thickness of the positive electrode mixture layer in the coating portion.

[0021] In the positive electrode of the secondary battery according to an embodiment of the present invention, a fourth point may exist between the second and third points in the buffer portion, the thickness of the positive electrode mixture layer at the third point may be 50%-60% of the thickness of the positive electrode mixture layer in the coating portion, the thickness of the positive electrode mixture layer in the buffer portion may gradually increase from the third point to the fourth point, and the thickness difference between the third point and the fourth point may be within 20% of the thickness of the positive electrode mixture layer in the coating portion.

[0022] In the positive electrode of the secondary battery according to an embodiment of the present invention, a fourth point may exist between the second and third points in the buffer portion, the thickness of the positive electrode mixture layer at the third point may be 60%-70% of the thickness of the positive electrode mixture layer in the coating portion, the thickness of the positive electrode mixture layer in the buffer portion may gradually increase from the third point to the fourth point, and the thickness difference between the third point and the fourth point may be within 15% of the thickness of the positive electrode mixture layer in the coating portion.

[0023] In the positive electrode of a secondary battery according to an embodiment of the present invention, the distance between the third and fourth points on the current collector can be 20%-80% of the distance between the first and second points on the current collector.

[0024] In the positive electrode of a secondary battery according to an embodiment of the present invention, the distance between the first point and the third point on the current collector can be 10%-30% of the distance between the first point and the second point on the current collector.

[0025] In the positive electrode of a secondary battery according to an embodiment of the present invention, the density of the positive electrode mixture layer in the coated portion is 3.5 g / cc (grams per cubic centimeter) or higher.

[0026] In the positive electrode of a secondary battery according to an embodiment of the present invention, the loading of the positive electrode mixture layer in the coated portion is 16.0 mg / cm³. 2 above.

[0027] In the positive electrode of a secondary battery according to an embodiment of the present invention, the thickness of the positive electrode current collector can be less than 15 μm.

[0028] In the positive electrode of a secondary battery according to an embodiment of the present invention, the tensile strength of the current collector corresponding to the uncoated portion can be 12 kgf / mm². 2 above.

[0029] A method for manufacturing a positive electrode for a secondary battery according to an embodiment of the present invention includes: preparing a positive electrode current collector; and applying a positive electrode mixture layer onto the positive electrode current collector, wherein a positive electrode is formed during the application of the positive electrode mixture layer, the positive electrode including a coated portion in which the positive electrode mixture layer is formed at a uniform thickness in a predetermined region of the positive electrode current collector; an uncoated portion disposed on at least one edge of the coated portion on the positive electrode current collector and where no positive electrode mixture layer is formed; and a buffer portion in which the positive electrode mixture layer is applied between the coated portion and the uncoated portion at a thickness less than the thickness of the coated portion.

[0030] The method for manufacturing a positive electrode for a secondary battery according to an embodiment of the present invention may further include rolling a coated portion and a buffer portion under the same level of pressure after applying a positive electrode mixture layer.

[0031] As described above, the positive electrode for a secondary battery and the method for manufacturing the positive electrode according to the present invention minimize the difference in elongation between the coated portions and minimize wrinkles, fractures, etc. generated during the rolling of the positive electrode, thereby achieving the effect of manufacturing a high-quality positive electrode by reducing the defect rate of the electrode. Attached Figure Description

[0032] The above and other objects, features and advantages of the present invention will become clearer from the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0033] Figure 1This is a perspective view of the positive electrode of a secondary battery after a rolling process, according to the first embodiment of the present invention.

[0034] Figure 2 for Figure 1 The diagram shows a cross-sectional view of the positive electrode of the present invention for a secondary battery;

[0035] Figure 3 This is a perspective view of the positive electrode for a secondary battery after a rolling process according to the second embodiment of the present invention.

[0036] Figure 4 for Figure 3 The diagram shows a cross-sectional view of the positive electrode of the present invention for a secondary battery;

[0037] Figure 5 This is a measured 3D cross-sectional view of the positive electrode of a secondary battery after a rolling process according to the second embodiment of the present invention. Invention Details

[0038] The objects, specific features, and novel features of the present invention will become more apparent from the following detailed description and embodiments in relation to the accompanying drawings. It should be noted that when components in the drawings are given reference numerals, the same components are assigned the same numbering, even if they are shown in different drawings. In this specification, the terms "one surface," "another surface," "first," "second," etc., are used to distinguish one component from another, and the components are not limited to these terms. In the following description, well-known related techniques that would unnecessarily obscure the spirit of the invention may no longer be described.

[0039] In the following description, embodiments of the invention will be described in detail with reference to the accompanying drawings, and the same reference numerals are assigned to the same parts.

[0040] To obtain a secondary battery with high energy density, a high-density positive electrode is required. To apply a high-density positive electrode, the positive electrode current collector 10 coated with a positive electrode mixture layer 20 needs to be rolled. This invention relates to the shape of a secondary battery electrode 1 and a method for manufacturing the secondary battery electrode 1, wherein the positive electrode mixture layer 20 is rolled at high density, and the current collector 10 does not break during the rolling process.

[0041] The positive electrode for a secondary battery according to the present invention will be described by illustrating, respectively, the positive electrode for a secondary battery after the rolling process and the positive electrode for a secondary battery before the rolling process. First, the positive electrode for a secondary battery after the rolling process is obtained by rolling a positive electrode designed to prevent current collector breakage, corresponding to Embodiments 1 and 2 described below. The positive electrode for a secondary battery before the rolling process is a positive electrode obtained by coating the current collector with a positive electrode mixture layer before rolling, and this positive electrode will be described in the method for manufacturing the positive electrode for a secondary battery described in Embodiment 3 below.

[0042] The positive electrode for a secondary battery according to the present invention comprises a positive electrode current collector and a positive electrode mixture layer. The positive electrode current collector is not particularly limited, as long as it has high conductivity and does not cause chemical changes in the battery. It can be made of aluminum, stainless steel, nickel, titanium, baked carbon, or aluminum or stainless steel, with a surface treated with carbon, nickel, titanium, silver, etc. The positive electrode mixture layer may include a positive electrode active material, conductive additives, binders, etc. The positive electrode active material can be a layered compound, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals, but is not limited thereto. As a conductive additive, conductive carbon is generally used, and various conductive carbon materials such as graphite, carbon black, acetylene black, Ketjen black, Super-P, and carbon nanotubes can be used.

[0043] Figure 1 and Figure 2 A secondary battery electrode 1 according to an embodiment of the present invention is shown.

[0044] According to an embodiment of the present invention, the positive electrode 1 for a secondary battery includes a positive electrode current collector 10 and a positive electrode mixture layer 20 on the positive electrode current collector 10. The positive electrode 1 for the secondary battery includes: a coated portion 100, on which the positive electrode mixture layer 20 is formed with a uniform thickness; an uncoated portion 200, which is disposed on at least one edge of the coated portion 100 on the positive electrode current collector 10, and on which the positive electrode mixture layer 20 is not formed; and a buffer portion 300, which is located between the coated portion 100 and the uncoated portion 200, on which the positive electrode mixture layer 20 is formed with a thickness less than that of the coated portion 100.

[0045] refer to Figure 1 and Figure 2 The positive electrode 1 of the present invention comprises a positive electrode current collector 10 and a positive electrode mixture layer 20 coated on the current collector 10. The positive electrode 1 is divided into a coated portion 100, an uncoated portion 200, and a buffer portion 300. The coated portion 100 is the portion on which a positive electrode mixture layer 20 of a predetermined thickness is coated on the positive electrode current collector 10. Figure 1It is understood that the coated portion 100 is formed to have a uniform thickness. The uncoated portion 200 may be disposed along the longitudinal direction of the coated portion 100 on both sides or one edge of the coated portion 100. The uncoated portion 200 is the portion on which the positive electrode mixture layer 20 is not formed on the current collector 10. The buffer portion 300 is formed with a thickness less than the thickness of the positive electrode mixture layer 20. (Reference) Figure 1 The buffer portion 300 is located between the coated portion 100 and the uncoated portion 200, and minimizes the difference in elongation between the coated portion 100 and the uncoated portion 200 when the electrode 1 is rolled. The buffer portion 300 can be formed such that the positive electrode mixture layer 20 has two or more different thickness slopes. That is, the buffer portion 300 can be formed with two thickness slopes, such as... Figure 1 As shown, it can also be formed with three thickness slopes, such as Figure 3 As shown, it can also be formed as a slope with greater thickness. The length of the buffer section 300 is much greater than its thickness, although the ratio is not accurately shown. Figures 1-4 For example, if the thickness of the buffer portion 300 is 110 μm, its length can be approximately 5 mm. That is, the width length between the coated portion 100 and the uncoated portion 200 is significantly greater than the thickness between the coated portion 100 and the uncoated portion 200, thereby enabling the buffer portion 300 to perform buffering that minimizes the difference in elongation between the coated portion 100 and the uncoated portion 200.

[0046] In the positive electrode 1 of the secondary battery according to an embodiment of the present invention, the thickness of the buffer portion 300 can gradually increase from a first point 310, which is the boundary between the uncoated portion 200 and the buffer portion 300, toward a second point 320, which is the boundary between the buffer portion 300 and the coated portion 100.

[0047] The boundary between the uncoated portion 200 and the buffer portion 300 is called the first point 310. That is, the first point 310 is the boundary between the portion on the current collector where the positive electrode mixture layer 20 is formed and the portion where the positive electrode mixture layer 20 is not formed. Accordingly, the thickness of the positive electrode mixture layer 20 at the first point 310 is 0. The second point 320 is the boundary between the portion of the coated portion 100 where the thickness of the positive electrode mixture layer 20 is uniform and the buffer portion 300 where the thickness is less than that of the positive electrode mixture layer 20 in the coated portion 100. Therefore, the thickness of the positive electrode mixture layer 20 at the second point 320 is the same as the thickness of the positive electrode mixture layer 20 in the coated portion 100.

[0048] The thickness of the positive electrode mixture layer 20 at the first point 310 is 0% of the thickness of the positive electrode mixture layer 20 in the coating portion 100, while the thickness of the positive electrode mixture layer 20 at the second point 320 is 100% of the thickness of the positive electrode mixture layer 20 in the coating portion 100. Therefore, from the first point 310 to the second point 320, the thickness of the positive electrode mixture layer 20 in the buffer portion 300 gradually increases from 0% to 100% relative to the thickness of the positive electrode mixture layer 20 in the coating portion 100.

[0049] In the positive electrode 1 of a secondary battery according to an embodiment of the present invention, a third point 330 may exist between the first point 310 and the second point 320 in the buffer portion.

[0050] In the following description, 'a' is the gap between the first point 310 and the third point 330 on the plane of the positive electrode current collector 10, and 'c' is the gap between the second point 320 and the third point 330 on the plane of the positive electrode current collector 10. Furthermore, 'x' is the thickness difference between the first point 310 and the third point 330 in a direction perpendicular to the plane of the positive electrode current collector 10, and 'z' is the thickness difference between the second point 320 and the third point 330 in a direction perpendicular to the plane of the positive electrode current collector 10.

[0051] [Table 1]

[0052]

[0053] [Table 2]

[0054]

[0055] The embodiments corresponding to Scheme 1 of the present invention are represented by 1-1 to 1-5, and the instances corresponding to Scheme 1' are represented by 1'-1' to 1'-4'.

[0056] The comparative examples show test results without the buffer portion of the present invention. As can be seen from the comparative examples, the number of breaks is higher than in other embodiments. That is, the breakage of the positive electrode can be significantly reduced by forming the buffer portion of the present invention.

[0057] In the positive electrode 1 for a secondary battery according to the embodiment of this application, the third point 330 may exist between the first point 310 and the second point 320 of the buffer portion 300, and the thickness of the positive electrode mixture layer 20 at the third point 330 in the buffer portion 300 may be 30%-80% of the thickness of the positive electrode mixture layer 20 in the coating portion.

[0058] In the positive electrode 1 of the secondary battery according to an embodiment of the present invention, the distance between the third point 330 and the first point 310 can be 20%-60% of the length of the current collector 10 from the first point 310 to the second point 320.

[0059] refer to Figure 1 and Figure 2 When the gap between the first point 310 and the third point 330 on the current collector 10 is 'a' and the gap between the third point 330 and the second point 320 on the current collector 10 is 'c', the condition 0.2≤a / (a+c)≤0.6 is satisfied.

[0060] As shown in Table 1, a / (a+c) is between 0.2 and 0.6. When the positive electrode is conveyed for 2000m and rolled based on this value, the density of positive electrode 1 can be above 3.69g / cc without breakage.

[0061] Considering that the number of breaks during the 2000mm transport period in Implementation Scheme 1 is 0 and the density is above 3.69g / cc, it can be concluded that the positive electrode mixture layer 20 is fully compressed and the current collector 10 is not broken.

[0062] Referring to No. 1'-3' and No. 1'-4' in Implementation Scheme 1', a / (a+c) are 0.09 and 0.82, respectively. When 'a' increases and a / (a+c) exceeds 0.6, as in No. 1'-4', the capacity of the positive electrode mixture layer 20 may be significantly reduced. However, when 'c' increases and a / (a+c) is less than 0.2, as in No. 1'-3', the effect of preventing breakage may be significantly reduced. Therefore, in terms of battery capacity and density, a / (a+c) is preferably between 0.2 and 0.6.

[0063] When the thickness difference between the first point 310 and the third point 330 is 'x', and the thickness difference between the third point 330 and the second point 320 is 'z', it can satisfy 0.3≤x / (x+z)≤0.8.

[0064] In the positive electrode 1 for a secondary battery according to an embodiment of the present invention, x / (x+z) can be between 0.3 and 0.8, and when the positive electrode is rolled by conveying it for 2000m based on this value, the density of the positive electrode 1 can be above 3.69 g / cc without breakage.

[0065] Referring to Table 1, x / (x+z) in Implementation Scheme 1 is between 0.3 and 0.8. In Implementation Scheme 1, considering that the number of breaks during the 2000mm transport period is 0 and the density is above 3.69g / cc, it can be seen that the positive electrode mixture layer 20 is fully compressed and the current collector 10 is not broken.

[0066] Referring to No.1'-1' and No.1'-2' in Implementation Scheme 1', x / (x+z) are 0.89 and 0.18, respectively. When the ratio x / (x+z) is too large, as in No.1'-1', the positive electrode mixture layer 20 loaded on the buffer section 300 becomes thicker, and the effect of minimizing the elongation difference disappears, thus causing breakage (occurring twice during the 2000m transport). When the ratio x / (x+z) is too small, as in No.1'-2', the positive electrode mixture layer 20 is too thin, making coating virtually impossible. Therefore, when the ratio of x / (x+z) is between 0.3 and 0.8, unlike No.1'-1' and No.1'-2' in Implementation Scheme 1', the number of breaks during the 2000m transport can be kept at 0, ensuring ease of coating.

[0067] In the positive electrode 1 of the secondary battery according to the second embodiment of the present invention, the buffer portion 300 may have three different slopes. That is, a fourth point 340 may exist in the buffer portion 300 between the second point 320 and the third point 330.

[0068] In the following description, 'a' is the distance between the first point 310 and the third point 330 on the plane of the positive electrode current collector 10, 'b' is the distance between the third point 330 and the fourth point 340 on the plane of the positive electrode current collector 10, and 'c' is the distance between the fourth point 340 and the second point 320 on the plane of the positive electrode current collector 10. Furthermore, 'x' is the thickness difference between the first point 310 and the third point 330 in a direction perpendicular to the plane of the positive electrode current collector 10, 'y' is the thickness difference between the third point 330 and the fourth point 340 in a direction perpendicular to the plane of the positive electrode current collector 10, and 'z' is the thickness difference between the fourth point 340 and the second point 320 in a direction perpendicular to the plane of the positive electrode current collector 10.

[0069] Figure 5 A measured 3D cross-sectional view of the positive electrode 1 for a secondary battery after the rolling process according to the second embodiment of the present invention. Figure 5 The cross-section between 10mm and 20mm on the horizontal axis in the 3D view shows that as the thickness of the positive electrode mixture layer 20 changes, the slope of the positive electrode mixture layer 20 changes, thus forming the first point 310, the second point 320, the third point 330, and the fourth point 340. Therefore, from... Figure 5 As can be seen from this, the structure of the positive electrode 1 for secondary batteries of the present invention is a substantially formable structure.

[0070] [Table 3]

[0071]

[0072] [Table 4]

[0073]

[0074] In the positive electrode 1 for a secondary battery according to the second embodiment of the present invention, a fourth point 340 may exist between the second point 320 and the third point 330 in the buffer portion. The thickness of the positive electrode mixture layer 20 at the third point 330 may be 20%-50% of the thickness of the positive electrode mixture layer 20 in the coating portion 100. The thickness of the positive electrode mixture layer 20 in the buffer portion 300 may gradually increase from the third point 330 to the fourth point 340, and the thickness difference between the third point 330 and the fourth point 340 may be within 30% of the thickness of the positive electrode mixture layer 20 in the coating portion 100.

[0075] The boundary between the uncoated portion 200 and the buffer portion 300 can be referred to as the first point 310, while the boundary between the buffer portion 300 and the coated portion 100 can be referred to as the second point 320. That is, the first point 310 is the boundary between the portion on the current collector where the positive electrode mixture layer 20 is formed and the portion where the positive electrode mixture layer 20 is not formed, respectively. Therefore, the thickness of the positive electrode mixture layer 20 at the first point can be 0. The second point 320 is the boundary between the portion of the coated portion 100 where the thickness of the positive electrode mixture layer 20 is uniform and the buffer portion 300 where the thickness is less than that of the positive electrode mixture layer 20 in the coated portion 100. Therefore, the thickness of the positive electrode mixture layer 20 at the second point 320 can be the same as the thickness of the positive electrode mixture layer 20 in the coated portion 100.

[0076] In the positive electrode 1 for a secondary battery according to the second embodiment of the present invention, 0.2≤x / (x+y+z)≤0.5 can be satisfied, and the thickness change (y) from the third point 330 to the fourth point 340 can satisfy y / (x+y+z)≤0.3.

[0077] Referring to the data in Scheme 2, No. 2-6 and No. 2-8 in Table 4, it can be seen that x / (x+y+z) is between 0.2 and 0.5, and in this case, y / (x+y+z) is below 0.3. Considering that the number of breaks during the 2000mm transport period in the data of No. 6 and No. 8 is 0 and the density is above 3.69g / cc, it can be concluded that the positive electrode mixture layer 20 is sufficiently compressed and the current collector 10 is not broken.

[0078] That is, when the thickness difference between the first point 310 and the third point 330 is 20%-50% of the thickness of the positive electrode mixture layer 20 in the coating portion 100, preferably, the thickness difference between the third point 330 and the fourth point 340 formed in the middle of the buffer portion 300 is within 30% of the coating portion 100. Since the thickness of the buffer portion 300 should not change rapidly in order to achieve its main function of suppressing breakage during the rolling of the positive electrode 1, the thickness change from the third point 330 to the fourth point 340 is limited based on the thickness change between the first point 310 and the third point 330.

[0079] In the positive electrode 1 of the secondary battery according to the second embodiment of the present invention, a fourth point 340 may exist in the buffer portion 300 between the second point 320 and the third point 330. The thickness of the positive electrode mixture layer 20 at the third point 330 may be 50%-60% of the thickness of the positive electrode mixture layer 20 in the coating portion 100. The thickness of the positive electrode mixture layer 20 in the buffer portion 300 may gradually increase from the third point 330 to the fourth point 340, and the thickness difference between the third point 330 and the fourth point 340 may be within 20% of the thickness of the positive electrode mixture layer 20 in the coating portion 100.

[0080] In the positive electrode 1 for a secondary battery according to the second embodiment of the present invention, 0.5 ≤ x / (x+y+z) ≤ 0.6 can be satisfied, and the thickness change (y) from the third point 330 to the fourth point 340 can satisfy y / (x+y+z) ≤ 0.2.

[0081] Referring to the data in No. 2-9 of Implementation Scheme 2 in Table 4, x / (x+y+z) is between 0.5 and 0.6, at which point y / (x+y+z) is below 0.2. Considering that the number of breaks during the 2000mm transport period in the data of No. 2-9 is 0 and the density is above 3.69g / cc, it can be concluded that the positive electrode mixture layer 20 is sufficiently compressed and the current collector 10 is not broken.

[0082] That is, when the thickness difference between the first point 310 and the third point 330 is 50%-60% of the thickness of the positive electrode mixture layer 20 in the coating portion 100, preferably, the thickness difference between the third point 330 and the fourth point 340 formed in the middle of the buffer portion 300 is within 20% of the coating portion 100. Since the thickness of the buffer portion 300 should not change rapidly to achieve its main function of suppressing breakage during the rolling of the positive electrode 1, the thickness change from the third point 330 to the fourth point 340 is limited based on the thickness change between the first point 310 and the third point 330. Compared with No. 2-6 and No. 2-8 in Embodiment 2, in No. 2-9, x / (x+y+z) becomes larger, and the thickness change of the buffer portion 300 from the first point 310 to the third point 330 increases, therefore the range of y / (x+y+z) decreases to suppress the rapid increase of the thickness change of the entire buffer portion 300.

[0083] In the positive electrode 1 for a secondary battery according to the second embodiment of the present invention, a fourth point 340 may exist between the second point 320 and the third point 330 in the buffer portion. The thickness of the positive electrode mixture layer 20 at the third point 330 may be 60%-70% of the thickness of the positive electrode mixture layer 20 in the coating portion 100. The thickness of the positive electrode mixture layer 20 in the buffer portion 300 may gradually increase from the third point 330 to the fourth point 340, and the thickness difference between the third point 330 and the fourth point 340 may be within 15% of the thickness of the positive electrode mixture layer 20 in the coating portion 100.

[0084] In the positive electrode 1 for a secondary battery according to the second embodiment of the present invention, 0.6≤x / (x+y+z)≤0.7 can be satisfied, and the thickness change (y) from the third point 330 to the fourth point 340 can satisfy y / (x+y+z)≤0.15.

[0085] Referring to the data in Implementation Scheme 2, No. 7 in Table 4, x / (x+y+z) is between 0.6 and 0.7, at which point y / (x+y+z) is below 0.15. Considering that the number of breaks during the 2000mm transport period in No. 7 is 0 and the density is above 3.69g / cc, it can be concluded that the positive electrode mixture layer 20 is sufficiently compressed and the current collector 10 is not broken.

[0086] That is, when the thickness difference between the first point 310 and the third point 330 is 60%-70% of the thickness of the positive electrode mixture layer 20 in the coated portion 100, preferably, the thickness difference between the third point 330 and the fourth point 340 formed in the middle of the buffer portion 300 is within 15% of the coated portion 100. Since the thickness of the buffer portion 300 should not change rapidly to achieve its main function of suppressing breakage during the rolling of the positive electrode 1, the thickness change from the third point 330 to the fourth point 340 is limited based on the thickness change between the first point 310 and the third point 330. Compared with No. 2-9 in Embodiment 2, in No. 2-7, x / (x+y+z) becomes larger, and the thickness change of the buffer portion 300 from the first point 310 to the third point 330 increases, therefore the range of y / (x+y+z) is reduced to suppress the rapid increase of the thickness change of the entire buffer portion 300.

[0087] In the positive electrode 1 of the secondary battery according to the present invention, the distance between the third point 330 and the fourth point 340 on the current collector 10 can be 40%-80% of the distance between the first point 310 and the second point 320 on the current collector 10.

[0088] In the positive electrode 1 of the secondary battery according to the present invention, the distance between the first point 310 and the third point 330 on the current collector 10 can be 10%-30% of the distance between the first point 310 and the second point 320 on the current collector 10.

[0089] refer to Figure 3 and Figure 4 In the positive electrode 1 of the secondary battery according to the second embodiment of the present invention, when the distance between the first point 310 and the third point 330 is 'a', the distance between the third point 330 and the fourth point 340 is 'b', and the distance between the fourth point 340 and the second point 320 is 'c', it can satisfy 0.2≤b / (a+b+c)≤0.8. That is, the distance between the third point 330 and the fourth point 340 on the current collector 10 can be 20%-80% of the distance between the first point 310 and the second point 320 on the current collector 10.

[0090] Referring to Table 3, it can be seen that in Scheme 2, Nos. 6-9, b / (a+b+c) is between 0.2 and 0.8. That is, when the positive electrode 1 is rolled based on the b / (a+b+c) between 0.2 and 0.8 in Scheme 2, the density of the positive electrode 1 is above 3.69 g / cc and there are no breaks. Considering that the number of breaks during the 2000 mm conveying in Scheme 2 is 0 and the density is above 3.69 g / cc, it can be seen that the positive electrode mixture layer 20 is sufficiently compressed and the current collector 10 is not broken. Therefore, it is preferable that b / (a+b+c) is between 0.2 and 0.8 in Scheme 2.

[0091] refer to Figure 3 and Figure 4 In the positive electrode 1 for a secondary battery according to the second embodiment of the present invention, when the distance between the first point 310 and the third point 330 is 'a', the distance between the third point 330 and the fourth point 340 is 'b', and the distance between the fourth point 340 and the second point 320 is 'c', it can satisfy 0.1≤a / (a+b+c)≤0.3.

[0092] Referring to Table 3, in Scheme 2, the ratio of a / (a+b+c) in Nos. 6-9 is between 0.1 and 0.3. That is, when the positive electrode 1 is rolled using a feed rate of b / (a+b+c) between 0.2 and 0.8 in Scheme 2, the density of the positive electrode 1 is above 3.69 g / cc and there are no breaks. Considering that the number of breaks during the 2000 mm feed in Scheme 2 is 0 and the density is above 3.69 g / cc, it can be seen that the positive electrode mixture layer 20 is sufficiently compressed and the current collector 10 does not break. Therefore, it is preferable that a / (a+b+c) is between 0.1 and 0.3 in Scheme 2.

[0093] In the positive electrode 1 for a secondary battery according to the first and second embodiments of the present invention, the density of the positive electrode mixture layer 20 in the coating portion 100 can be 3.5 g / cc or more, and the loading of the positive electrode mixture layer 20 in the coating portion 100 can be 16.0 mg / cm³. 2 The thickness of the positive electrode current collector can be less than 15 μm, and the tensile strength of the current collector 10 corresponding to the uncoated portion 200 can be 12 kgf / mm². 2 above.

[0094] In order to form a high-density positive electrode, the density of the positive electrode mixture layer 20 should be relatively high. The minimum density of the positive electrode mixture layer 20 of the present invention can be 3.5 g / cc or higher.

[0095] The loading of the positive electrode mixture layer 20 indicates how much of the positive electrode active material is coated relative to the area of ​​the current collector 10. Since the positive electrode 1 of the present invention should not only have a high density but also be able to generate energy above a predetermined level, the loading of the positive electrode mixture layer 20 can be 16.0 mg / cm³. 2 above.

[0096] The thickness of the positive electrode current collector 10 can be less than 15 μm, and the tensile strength of the current collector 10 can be 12 kgf / mm². 2 The above measures ensure that the material is not thermally bonded during welding after the rolling process.

[0097] A method for manufacturing a positive electrode 1 for a secondary battery according to an embodiment of the present invention includes: preparing a positive electrode current collector 10 and applying a positive electrode mixture layer 20 onto the positive electrode current collector 10. When applying the positive electrode mixture layer 20, a positive electrode 1 is formed, comprising a coated portion 100, an uncoated portion 200, and a buffer portion 300. The positive electrode mixture layer 20 is formed at the coated portion 100 in a predetermined region of the positive electrode current collector 10 with a uniform thickness. The uncoated portion 200 is disposed on at least one edge of the coated portion 100 on the positive electrode current collector 100, and no positive electrode mixture layer 20 is formed at the uncoated portion. A buffer portion 300 is formed, which applies the positive electrode mixture layer 20 between the coated portion 100 and the uncoated portion 200 with a thickness less than the thickness of the coated portion 100.

[0098] The method for manufacturing the positive electrode 1 for a secondary battery according to an embodiment of the present invention may further include rolling the coated portion 100 and the buffer portion 300 under the same level of pressure after applying the positive electrode mixture layer 20.

[0099] After the positive electrode mixture layer 20 is applied, the electrode 1 can be rolled. Since the coated portion 100 and the buffer portion 300 are rolled under the same force, even after rolling, the thickness of the buffer portion 300 can be less than the thickness of the coated portion 100.

[0100] Depending on the coating method, the positive electrode mixture layer 20 can be applied as having a small slope or stepped structure on the buffer portion 300. After rolling, the positive electrode 1 can have a shape in which the thickness of the positive electrode mixture layer 20 in the buffer portion 300 gradually increases from the uncoated portion 200 located on at least one or both sides of the positive electrode current collector 10 toward the coated portion 100.

[0101] The application of the positive electrode mixture layer 20 can be achieved by the following steps: providing a coating portion-slurry outlet for forming the positive electrode mixture layer 20 in the coating portion 100 and a buffer portion-slurry outlet for forming the positive electrode mixture layer 20 in the buffer portion 300, and then coating the positive electrode current collector 10 with the positive electrode mixture layer 20 through the two slurry outlets. The two slurry outlets can be operated simultaneously or sequentially.

[0102] Furthermore, the application of the positive electrode mixture layer 20 can be achieved by the following steps: forming the positive electrode mixture layer 20 on the coating portion 100 using a slurry outlet, and then forming the positive electrode mixture layer 20 on the buffer portion 300 to have a small slope or stepped structure by removing a portion of the positive electrode mixture layer 20 at at least one edge of the coating portion on which the positive electrode mixture layer 20 is formed.

[0103] Although the invention has been described in detail with reference to specific embodiments, these embodiments are provided for the purpose of describing the invention in detail only, and the invention is not limited to these embodiments. Furthermore, it will be apparent to those skilled in the art that changes and modifications can be made to the invention without departing from its spirit.

[0104] Any simple modifications or alterations to this invention are included within the scope of protection of this invention, and the detailed scope of protection of this invention is defined by the claims.

Claims

1. A positive electrode for a secondary battery, the positive electrode comprising a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, the positive electrode comprising: The coating portion, wherein the positive electrode mixture layer is formed at the coating portion with a uniform thickness; An uncoated portion, wherein the uncoated portion is disposed on at least one edge of the coated portion on the positive electrode current collector and the positive electrode mixture layer is not formed at the uncoated portion; and A buffer portion, located between the coated portion and the uncoated portion, is where the positive electrode mixture layer is formed with a thickness less than that of the coated portion. The thickness of the buffer portion gradually increases from a first point, which is the boundary between the uncoated portion and the buffer portion, toward a second point, which is the boundary between the buffer portion and the coated portion. In the buffer section, there is a third point between the first point and the second point, and the thickness of the positive electrode mixture layer at the third point in the buffer section is 30%-80% of the thickness of the positive electrode mixture layer in the coating section. The distance between the third point and the first point is 20%-60% of the length of the current collector from the first point to the second point.

2. A positive electrode for a secondary battery, the positive electrode comprising a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, the positive electrode comprising: The coating portion, wherein the positive electrode mixture layer is formed at the coating portion with a uniform thickness; An uncoated portion, wherein the uncoated portion is disposed on at least one edge of the coated portion on the positive electrode current collector and the positive electrode mixture layer is not formed at the uncoated portion; and A buffer portion, located between the coated portion and the uncoated portion, is where the positive electrode mixture layer is formed with a thickness less than that of the coated portion. The thickness of the buffer portion gradually increases from a first point, which is the boundary between the uncoated portion and the buffer portion, toward a second point, which is the boundary between the buffer portion and the coated portion. In the buffer section, there is a third point between the first point and the second point, and a fourth point between the second point and the third point. The thickness of the positive electrode mixture layer at the third point is 20%-50% of the thickness of the positive electrode mixture layer in the coated portion, and the thickness of the positive electrode mixture layer in the buffer portion gradually increases from the third point to the fourth point. The thickness difference between the third point and the fourth point is within 30% of the thickness of the positive electrode mixture layer in the coated portion. The distance between the third point and the fourth point on the current collector is 20%-80% of the distance between the first point and the second point on the current collector. The distance between the first point and the third point on the current collector is 10%-30% of the distance between the first point and the second point on the current collector.

3. A positive electrode for a secondary battery, the positive electrode comprising a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, the positive electrode comprising: The coating portion, wherein the positive electrode mixture layer is formed at the coating portion with a uniform thickness; An uncoated portion, wherein the uncoated portion is disposed on at least one edge of the coated portion on the positive electrode current collector and the positive electrode mixture layer is not formed at the uncoated portion; and A buffer portion, located between the coated portion and the uncoated portion, is where the positive electrode mixture layer is formed with a thickness less than that of the coated portion. The thickness of the buffer portion gradually increases from a first point, which is the boundary between the uncoated portion and the buffer portion, toward a second point, which is the boundary between the buffer portion and the coated portion. In the buffer section, there is a third point between the first point and the second point, and a fourth point between the second point and the third point. The thickness of the positive electrode mixture layer at the third point is 50%-60% of the thickness of the positive electrode mixture layer in the coated portion, and the thickness of the positive electrode mixture layer in the buffer portion gradually increases from the third point to the fourth point. The thickness difference between the third point and the fourth point is within 20% of the thickness of the positive electrode mixture layer in the coated portion. The distance between the third point and the fourth point on the current collector is 20%-80% of the distance between the first point and the second point on the current collector. The distance between the first point and the third point on the current collector is 10%-30% of the distance between the first point and the second point on the current collector.

4. A positive electrode for a secondary battery, the positive electrode comprising a positive electrode current collector and a positive electrode mixture layer on the positive electrode current collector, the positive electrode comprising: The coating portion, wherein the positive electrode mixture layer is formed at the coating portion with a uniform thickness; An uncoated portion, wherein the uncoated portion is disposed on at least one edge of the coated portion on the positive electrode current collector and the positive electrode mixture layer is not formed at the uncoated portion; and A buffer portion, located between the coated portion and the uncoated portion, is where the positive electrode mixture layer is formed with a thickness less than that of the coated portion. The thickness of the buffer portion gradually increases from a first point, which is the boundary between the uncoated portion and the buffer portion, toward a second point, which is the boundary between the buffer portion and the coated portion. In the buffer section, there is a third point between the first point and the second point, and a fourth point between the second point and the third point. The thickness of the positive electrode mixture layer at the third point is 60%-70% of the thickness of the positive electrode mixture layer in the coated portion, and the thickness of the positive electrode mixture layer in the buffer portion gradually increases from the third point to the fourth point. The thickness difference between the third point and the fourth point is within 15% of the thickness of the positive electrode mixture layer in the coated portion. The distance between the third point and the fourth point on the current collector is 20%-80% of the distance between the first point and the second point on the current collector. The distance between the first point and the third point on the current collector is 10%-30% of the distance between the first point and the second point on the current collector.

5. The positive electrode according to any one of claims 1-4, wherein the density of the positive electrode mixture layer in the coated portion is 3.5 g / cm³ or more.

6. The positive electrode according to any one of claims 1-4, wherein the loading of the positive electrode mixture layer in the coated portion is 16.0 mg / cm². 2 above.

7. The positive electrode according to any one of claims 1-4, wherein the thickness of the positive electrode current collector is less than 15 μm.

8. The positive electrode according to any one of claims 1-4, wherein the tensile strength of the current collector corresponding to the uncoated portion is 12 kgf / mm². 2 above.

9. A method for manufacturing a positive electrode for a secondary battery according to any one of claims 1-4, the method comprising: Preparation of positive electrode current collector; Apply the positive electrode mixture layer to the positive electrode current collector, and Rolling the positive electrode mixture layer, The positive electrode is formed during the application of the positive electrode mixture layer, the positive electrode including a coated portion in which the positive electrode mixture layer is formed at a uniform thickness in a predetermined region of the positive electrode current collector; an uncoated portion disposed on at least one edge of the coated portion on the positive electrode current collector, where the positive electrode mixture layer is not formed; and a buffer portion in which the positive electrode mixture layer is applied between the coated portion and the uncoated portion at a thickness less than the thickness of the coated portion. The positive electrode mixture layer is rolled by rolling the coated portion and the buffer portion under the same level of pressure.

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