Positive electrode for secondary battery, method for manufacturing positive electrode for secondary battery, electrode assembly, secondary battery, battery module including secondary battery, and battery pack

Abstract

The present invention relates to a positive electrode for a secondary battery, a method for manufacturing a positive electrode for a secondary battery, an electrode assembly, a secondary battery, a battery module including a secondary battery, and a battery pack. The positive electrode includes a first thickness reduction part and a second thickness reduction part to reduce a step formed at a longitudinal end portion of the positive electrode, thereby improving a phenomenon in which a hollow portion of a core part does not maintain its circular shape and collapses due to deformation of the electrode assembly caused by contraction / expansion of an electrode during charging and discharging of a battery, and preventing damage to a negative electrode and a separator.

Description

A positive electrode for a secondary battery, a method for manufacturing a positive electrode for a secondary battery, an electrode assembly, a secondary battery, a battery module including a secondary battery, and a battery pack

[0001] The present application claims the benefit of the filing dates of Korean Patent Application No. 10-2024-0194154 filed with the Korean Intellectual Property Office on December 23, 2024, Korean Patent Application No. 10-2025-0190784 filed with the Korean Intellectual Property Office on December 4, 2025, and Korean Patent Application No. 10-2015-0190791 filed with the Korean Intellectual Property Office on December 4, 2025, the contents of which are all incorporated herein.

[0002] The present invention relates to a positive electrode for a secondary battery, a method for manufacturing a positive electrode for a secondary battery, an electrode assembly, a secondary battery, a battery module including a secondary battery, and a battery pack. Specifically, the invention relates to a positive electrode for a secondary battery with improved deformation of the core portion of an electrode assembly, a method for manufacturing a positive electrode for a secondary battery, an electrode assembly, a cylindrical secondary battery, a battery module including a cylindrical secondary battery, and a battery pack.

[0003] In the case of cylindrical batteries, a jelly-roll type electrode assembly is manufactured by rolling a long electrode of a fixed width into a roll. Cylindrical batteries manufactured by inserting such an electrode assembly into a battery case undergo repeated contraction and expansion of the electrodes during charging and discharging. In particular, if an in-tab is located in the core of the electrode assembly or if silicon-based active material is added to the negative electrode, increasing the degree of contraction and expansion, the pressure acting on the core of the electrode assembly increases significantly.

[0004] Meanwhile, the core portion of the cylindrical battery is a space where the winding core used for winding the electrode assembly is located, and there exists a hollow space, i.e., a core hollow, used during the cylindrical battery assembly process, such as the insertion process of the electrode assembly into the battery case and the welding process.

[0005] Recently, with the increase in low-resistance / high-capacity designs, there has been a growing trend of electrode assemblies containing multiple tabs or incorporating silicon-based active materials. Consequently, the possibility of core deformation due to shrinkage or expansion of the electrode assembly increases. In particular, battery life degradation occurs due to the core collapse, where the hollow core fails to maintain its circular shape. Furthermore, problems have arisen where the cathode end located in the core and the adjacent anode deform beyond a certain level, causing the separator between the anode and cathode to break (core impingement). This leads to direct contact between the anode and cathode, resulting in internal short circuits that cause heat generation and ignition.

[0006] In order to resolve the issues of battery life degradation, separator damage, and internal short circuits caused by the deformation of such electrode assemblies, it is necessary to develop technology that can improve the phenomenon where the hollow core in the relevant area fails to maintain its circular shape and collapses, and suppress internal short circuits caused by separator damage.

[0007] The present invention relates to a positive electrode for a secondary battery with improved core deformation, a method for manufacturing a positive electrode for a secondary battery, an electrode assembly, a secondary battery, a battery module including a secondary battery, and a battery pack.

[0008] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0009] One embodiment of the present invention is a positive current collector; A positive electrode for a secondary battery comprising a positive active material layer provided on at least one surface of the positive current collector, wherein at least one of the positive active material layers comprises a first flat portion, a second flat portion, a first thickness reduction portion located at one end of the first flat portion, and a second thickness reduction portion located at the other end of the second flat portion, wherein the first thickness reduction portion comprises (a) a first inclined portion in which the thickness is gradually reduced from the first flat portion toward a first end portion which is a longitudinal end portion of the positive current collector, and extends from the first flat portion and has a longitudinal end portion at the same position as the first end portion, or (b) a first non-contact portion in which the positive current collector is exposed from the first flat portion toward a first end portion which is a longitudinal end portion of the positive current collector, and the first non-contact portion has a longitudinal end portion at the same position as the first end portion, and the second thickness reduction portion comprises (a) a portion in which the thickness is gradually reduced from the second flat portion toward a second end portion which is a longitudinal end portion of the positive current collector. (b) a second inclined portion that extends from the second flat portion and has a longitudinal end at the same position as the second end, or (b) a second non-conforming portion in which the positive current collector is exposed from the second flat portion toward the second end, which is the other longitudinal end of the positive current collector, and the second non-conforming portion has a longitudinal end at the same position as the second end.

[0010] Another embodiment of the present invention provides a method for manufacturing a positive electrode for a secondary battery and a positive electrode for a secondary battery manufactured thereby, comprising the steps of: applying a positive active material slurry on at least one surface of a positive current collector to form a positive active material layer including a first flat portion, a loading reduction portion, and a second flat portion; stopping the application of the positive active material slurry to form a positive non-positive portion in which the positive current collector is exposed; and cutting the loading reduction portion, wherein the loading reduction portion is located between the first flat portion and the second flat portion and extends from the first flat portion and the second flat portion to form an area in which the thickness of the positive active material layer is reduced or the positive current collector is exposed, and the application is performed in a first direction from one end in the longitudinal direction of the positive current collector to the other end in the longitudinal direction of the positive current collector.

[0011] Another embodiment of the present invention provides an electrode assembly including the aforementioned positive electrode for a secondary battery, a secondary battery including the electrode assembly, a battery module including the secondary battery, and a battery pack.

[0012] The positive electrode for a secondary battery according to the present invention includes a first thickness reduction portion and a second thickness reduction portion to mitigate the step difference formed at the longitudinal end of the positive electrode, thereby improving the phenomenon in which the hollow core portion fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging, and preventing damage to the negative electrode and separator.

[0013] In the positive electrode for a secondary battery according to the present invention, since the positive electrode current collector is not exposed at the longitudinal end of the positive electrode due to the first thickness reduction portion and the second thickness reduction portion, internal short circuit between the positive electrode and the negative electrode is prevented even without a separate protective tape, thereby improving battery stability and lifespan characteristics.

[0014] The method for manufacturing a positive electrode for a secondary battery according to the present invention and the positive electrode for a secondary battery manufactured thereby can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging by mitigating the step difference formed at the longitudinal end of the positive electrode, thereby preventing damage to the negative electrode and separator, and can manufacture a positive electrode for a secondary battery with improved battery stability and lifespan characteristics in a simpler way.

[0015] The method for manufacturing a positive electrode for a secondary battery according to the present invention is suitable for a continuous process using existing roll-to-roll process equipment, and since it can prevent internal short circuits between the positive electrode and the negative electrode without the need for a separate protective tape, productivity and economic efficiency can be secured.

[0016] In addition, the electrode assembly according to the present invention and the secondary battery including the same can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging, prevent damage to the negative electrode and separator, and prevent internal short circuits between the positive and negative electrodes, thereby improving battery stability and lifespan characteristics.

[0017] The effects of the present invention are not limited to those described above, and unmentioned effects will be clearly understood by those skilled in the art from the present specification and the accompanying drawings.

[0018] FIGS. 1a to 1d are schematic drawings showing a positive electrode for a secondary battery according to one embodiment of the present invention.

[0019] FIGS. 2 to 5 are schematic diagrams illustrating a method for manufacturing a positive electrode for a secondary battery according to one embodiment of the present invention.

[0020] FIGS. 6 to 8 are schematic diagrams showing the components of an electrode assembly including a positive electrode for a secondary battery according to one embodiment of the present invention.

[0021] FIG. 9 is a schematic diagram showing an electrode assembly including a positive electrode for a secondary battery and a component of a secondary battery according to one embodiment of the present invention.

[0022] FIG. 10 is a perspective view illustrating a secondary battery according to one embodiment of the present invention.

[0023] Figure 11 illustrates an evaluation method according to an experimental example.

[0024] Figure 12 is a graph showing the evaluation results according to the experimental example.

[0025] FIG. 13 is a perspective view illustrating a battery pack according to one embodiment of the present invention.

[0026] FIG. 14 is a perspective view illustrating a moving means according to one embodiment of the present invention.

[0027] [Explanation of the symbol]

[0028] 1: Secondary battery

[0029] 2: Pack Housing

[0030] 3: Battery pack

[0031] 10: Electrode assembly

[0032] 20: Battery case

[0033] 100: Cathode

[0034] 200: Separator

[0035] 300: Anode

[0036] 310: Loading reduction section

[0037] 311: First thickness reduction section

[0038] 311s: 1st Slope

[0039] 311n: 1st unintelligible part

[0040] 311f: 1st auxiliary leveling section

[0041] 312: Second thickness reduction section

[0042] 312s: Second incline section

[0043] 312n: Second Undisclosed Division

[0044] 312f: Second auxiliary leveling section

[0045] 321: First level section

[0046] 322: Second level section

[0047] 330: Bipolar non-polar region

[0048] 330s: Medium slope

[0049] 301E: First end

[0050] 302E: Second end

[0051] 300T: Positive tab

[0052] 300P: Protective tape

[0053] C: Core section hollow

[0054] V: Means of transportation

[0055] E1: First extension line

[0056] E2: Second extension line

[0057] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0058] Throughout this specification, when a component is described as being located "on" another component, this includes not only cases where a component is in contact with another component, but also cases where another component exists between the two components.

[0059] Throughout this specification, the length, thickness, diameter, etc. of a positive electrode for a secondary battery, an electrode assembly, and a component included in a secondary battery refers to an average value unless otherwise specified. For example, the "average value" may be the average value of the length, thickness, and diameter, etc. measured by selecting 10 arbitrary points in each area after dividing the object to be measured into four areas of 1% to 25%, 25% to 50%, 50% to 75%, and 75% to 100%. Meanwhile, the "minimum value" and "maximum value" may be the minimum and maximum values ​​of the length, thickness, and diameter, etc. measured by selecting 10 arbitrary points in each area after dividing the object to be measured into four areas of 1% to 25%, 25% to 50%, 50% to 75%, and 75% to 100%.

[0060] Throughout this specification, the ‘flat section’ includes errors due to process capability, and, for example, may be a section in which the dispersion of thickness values ​​measured by selecting 10 arbitrary points in each section after dividing a continuously formed active material layer into four sections of 1% to 25%, 25% to 50%, 50% to 75%, and 75% to 100% is 5% or less. Meanwhile, the ‘sloping section’ may be a section in which the dispersion of thickness values ​​measured by selecting 10 arbitrary points in each section after dividing a continuously formed active material layer into four sections of 1% to 25%, 25% to 50%, 50% to 75%, and 75% to 100% is greater than 5%.

[0061] Throughout this specification, the length, thickness, and diameter, etc. of a positive electrode for a secondary battery, an electrode assembly, and a component included in the secondary battery may be measured after activation of the secondary battery including the positive electrode and the electrode assembly. Specifically, the length, thickness, and diameter, etc. of said component may be measured in a normal standby state and a state of normal use after activation of the secondary battery. For example, the length, thickness, and diameter, etc. of said component may be measured after 50 charge and discharge cycles under conditions of 25°C, 1C charge, and 1C discharge of the secondary battery, and in this case, the actual values ​​may be measured by physically disassembling the secondary battery, but are not limited thereto. For example, the length, thickness, and diameter, etc. of said component may be calculated values ​​derived using computed tomography (CT) images, and, if necessary, may be calculated values ​​derived using simulation.

[0062] Throughout this specification, the term "after activation" may mean after a predetermined cycle has been performed for the manufacture and product completion of the secondary battery. Specifically, the "after activation" may include storage conditions prior to the commencement of active use, including multiple cycles for the purpose of power supply, i.e., prior to and after sale, and may include a state in which self-discharge occurs during storage.

[0063] The above activation may refer to a step of verifying the stability of the battery by repeating aging and charging / discharging after the assembly of the electrode assembly and the battery case, and the 'state after activation' can be achieved in a simple manner by performing a predetermined cycle, for example, 50 cycles under the condition of 1C / 1C @25 ℃, on a battery obtained at any point after assembly. However, the above activation conditions are not limited to the scope used in the industry to achieve the same purpose.

[0064] The present invention will be described in detail below with reference to the drawings. However, the drawings are intended to illustrate the invention, and the scope of the invention is not limited by the drawings.

[0065] One embodiment of the present invention is a positive electrode for a secondary battery comprising: a positive current collector; and a positive active material layer provided on at least one surface of the positive current collector, wherein at least one of the positive active material layers comprises a first flat portion; a second flat portion; a first thickness reduction portion and a second thickness reduction portion.

[0066] The first thickness reduction portion includes a first inclined portion in which the thickness gradually decreases from the first flat portion toward the first end portion, which is a longitudinal end portion of the anode current collector, and has a longitudinal end portion extending from the first flat portion and having the same position as the first end portion.

[0067] Alternatively, the first thickness reduction portion includes a first non-exposed portion in which the anode current collector is exposed from the first flat portion to a first end portion, which is a longitudinal end portion of the anode current collector, and the first non-exposed portion has a longitudinal end portion at the same position as the first end portion.

[0068] The second thickness reduction portion includes a second inclined portion in which the thickness gradually decreases from the second flat portion toward the second end, which is the other end in the longitudinal direction of the anode current collector, and has a longitudinal end extending from the second flat portion and having the same position as the second end.

[0069] FIGS. 1a to 1d are schematic drawings illustrating a positive electrode for a secondary battery according to an embodiment of the present invention. Specifically, FIGS. 1a to 1d are schematic perspective views illustrating a positive electrode for a secondary battery according to an embodiment of the present invention, comprising a first flat portion, a second flat portion, a first thickness reduction portion, and a second thickness reduction portion including a second inclined portion, or a positive electrode for a secondary battery comprising a first flat portion, a second flat portion, a first thickness reduction portion including a first inclined portion, and a second thickness reduction portion including a second inclined portion.

[0070] More specifically, FIGS. 1a to 1c are perspective views showing an embodiment in which the first thickness reduction portion includes a first inclined portion. According to one embodiment of the present invention, the positive active material layer comprises a first flat portion (321); a second flat portion (322); a first inclined portion (311s) in which the thickness gradually decreases from the first flat portion (321) toward a first end (301E), which is a longitudinal end of the positive current collector, and a first thickness reduction portion (311) extending from the first flat portion (321) and having a longitudinal end at the same position as the first end (301E); It may include a second inclined portion (312s) in which the thickness gradually decreases from the second flat portion (322) toward the second end (302E), which is the other end in the longitudinal direction of the anode current collector, and may include a second thickness reduction portion (312) that extends from the second flat portion (322) and has a longitudinal end at the same position as the second end (302E).

[0071] In this case, the longitudinal length of the first inclined portion of the anode according to the present invention may be equal to or different from the longitudinal length of the first thickness reduction portion. Specifically, the longitudinal length of the first thickness reduction portion may be greater than or equal to the longitudinal length of the first inclined portion.

[0072] FIGS. 1a and 1c are perspective views showing an embodiment in which the length of the first thickness reduction portion is greater than the length of the first inclined portion and the length of the second thickness reduction portion is greater than the length of the second inclined portion, wherein the positive active material layer located on one side of the positive current collector is a first inclined portion.

[0073] That is, FIG. 1a and 1c may include a first thickness reduction section which is provided from the first inclined section to the first end side, which is one end in the longitudinal direction of the positive current collector, and a first auxiliary flat section (311f) in which the thickness of the positive active material is constant, and a second thickness reduction section which is provided from the second inclined section to the second end side, which is the other end in the longitudinal direction of the positive current collector, and a second auxiliary flat section (312f) in which the thickness of the positive active material is constant.

[0074] Meanwhile, FIG. 1b is a perspective view showing an embodiment in which the lengths of the first thickness reduction section and the first inclined section are the same, and the lengths of the second thickness reduction section and the second inclined section are the same.

[0075] Referring to FIG. 1b, when the positive electrode for the secondary battery is manufactured by the method for manufacturing a positive electrode for a secondary battery described later, the longitudinal ends of the first thickness reduction portion (311) and the first inclined portion (311s) may be provided at the same location by cutting the loading reduction portion (310), in which case the longitudinal lengths of the first inclined portion (311s) and the first thickness reduction portion (311) are equal to each other, and when the positive electrode for the secondary battery is manufactured by the method for manufacturing a positive electrode for a secondary battery described later, the longitudinal ends of the second thickness reduction portion (312) and the second inclined portion (312s) may be provided at the same location by cutting the loading reduction portion (310), in which case the longitudinal lengths of the second inclined portion (312s) and the second thickness reduction portion (312) may be equal to each other.

[0076] FIG. 1d is a perspective view showing an embodiment in which the first thickness reduction portion includes the first non-thick portion. Specifically, FIG. 1d is a perspective view schematically showing a positive electrode for a secondary battery according to one embodiment of the present invention, comprising a first flat portion, a second flat portion, a first thickness reduction portion including the first non-thick portion, and a second thickness reduction portion including the second inclined portion and the second non-thick portion.

[0077] According to one embodiment of the present invention, the positive active material layer comprises a first flat portion (321) and a second flat portion (322), and the positive electrode for the secondary battery may comprise a first non-flat portion (311n) in which the positive current collector is exposed from the first flat portion (321) toward a first end (301E), which is a longitudinal end of the positive current collector, and a first thickness reduction portion (311) having a longitudinal end at the same position as the first end (301E); and a second non-flat portion (312n) in which the positive current collector is exposed from the second flat portion (322) toward a second end (302E), which is a longitudinal end of the positive current collector, and a second thickness reduction portion (312) having a longitudinal end at the same position as the second end (302E).

[0078] And, FIG. 1a is a perspective view showing an embodiment in which a positive active material layer with a taper coating is provided on both sides of a positive current collector and the shape of the positive active material layer located on both sides of the positive current collector is the same, and FIG. 1c is a perspective view showing an embodiment in which a positive active material layer with a taper coating is provided on one side of a positive current collector and the positive active material layer including the first flat portion and the second flat portion is provided on the other side, and the shape of the positive active material layer provided on one side of the positive current collector is different.

[0079] In addition, the second end shape of the positive active material layer provided on one side of the positive current collector in FIG. 1d may be different from the second end shape of the positive active material layer provided on the other side. In FIG. 1d, a positive active material layer including a first thickness reduction portion including a first flat portion, a second flat portion, and a first non-flat portion, and a second thickness reduction portion including a second inclined portion and a second non-flat portion may be located on one side of the positive current collector, and a positive active material layer including a first flat portion and a second flat portion may be located on the other side of the positive current collector.

[0080] FIGS. 2 to 5 are schematic diagrams illustrating a method for manufacturing a positive electrode for a secondary battery according to one embodiment of the present invention. Specifically, FIG. 2(a) is a cross-sectional view illustrating a method for manufacturing a positive electrode for a secondary battery according to one embodiment of the present invention, and FIG. 2(b) is a cross-sectional view illustrating a positive electrode for a secondary battery manufactured by the above manufacturing method. FIG. 3(a) is a cross-sectional view illustrating a method for manufacturing a positive electrode for a secondary battery according to another embodiment of the present invention, and FIG. 3(b) is a cross-sectional view illustrating a positive electrode for a secondary battery manufactured by the above manufacturing method. FIG. 4(a) is a cross-sectional view illustrating a method for manufacturing a positive electrode for a secondary battery according to one embodiment of the present invention, and FIG. 4(b) is a cross-sectional view illustrating a positive electrode for a secondary battery manufactured by the above manufacturing method. FIG. 5(a) is a plan view showing a method for manufacturing a positive electrode for a secondary battery according to one embodiment of the present invention, and FIG. 5(b) is a plan view showing a positive electrode for a secondary battery manufactured by the above method.

[0081] Referring to FIG. 2(b), FIG. 3(b) and FIG. 4(b), the positive active material layer comprises a first flat portion (321); a second flat portion (322); a first inclined portion (311s) in which the thickness gradually decreases from the first flat portion (321) toward a first end (301E), which is a longitudinal end of the positive electrode, and a first thickness reduction portion (311) extending from the first flat portion (321) and having a longitudinal end at the same position as the first end (301E). It may include a second inclined section (312s) in which the thickness gradually decreases from the second flat section (322) toward the second end (302E), which is the other end in the longitudinal direction of the anode, and a second thickness reduction section (312) extending from the second flat section (322) and having a longitudinal end at the same position as the second end (302E).

[0082] As described below, a first thickness reduction portion (311) extending from the first flat portion (321) and having a longitudinal end at the same position as the first end (301E) may be provided by performing a cutting in the loading reduction portion (310) included in the positive active material layer in a second direction perpendicular to the first direction, i.e., in the YZ plane direction; and a second thickness reduction portion (312) extending from the second flat portion (322) and having a longitudinal end at the same position as the second end (302E).

[0083] At this time, the first thickness reduction section (311) includes a first inclined section (311s) in which the thickness gradually decreases from the first flat section (321) toward the first end (301E), which is one end in the longitudinal direction of the anode current collector, and the second thickness reduction section (312) includes a second inclined section (312s) in which the thickness gradually decreases from the second flat section (322) toward the second end (302E), which is the other end in the longitudinal direction of the anode.

[0084] Referring to FIG. 3(b), the positive active material layer includes a first flat portion (321) and a second flat portion (322). Additionally, the positive electrode for the secondary battery includes a first non-flat portion (311n) in which the positive current collector is exposed from the first flat portion (321) toward a first end (301E), which is a longitudinal end of the positive electrode, and a first thickness reduction portion (311) having a longitudinal end at the same position as the first end (301E) of the first non-flat portion (311n); and may include a second non-exposed portion (312n) in which the anode current collector is exposed from the second flat portion (322) toward the second end (302E), which is the other end in the longitudinal direction of the anode, and the second non-exposed portion (312n) may include a second thickness reduction portion (312) having a longitudinal end at the same position as the second end (302E).

[0085] As described below, a first thickness reduction portion (311) having a longitudinal end at the same position as the first end (301E) on one side of the first flat portion (321) and a second thickness reduction portion (312) having a longitudinal end at the same position as the second end (302E) on one side of the second flat portion (322) may be provided by performing a cutting in a second direction perpendicular to the first direction, i.e., the YZ plane direction, in the loading reduction portion (310) included in the positive active material layer.

[0086] At this time, the first thickness reduction portion (311) includes a first non-positive portion (311n) having a longitudinal end at the same position as the first end (301E), which is a longitudinal end of the anode current collector, and the second thickness reduction portion (312) includes a second non-positive portion (312n) having a longitudinal end at the same position as the second end (302E), which is a longitudinal end of the anode current collector, and the anode current collector is exposed on one side of the second flat portion (322).

[0087] The positive electrode for a secondary battery according to the present invention includes a first thickness reduction portion and a second thickness reduction portion to mitigate the step difference formed at the longitudinal end of the positive electrode, thereby improving the phenomenon in which the hollow core portion fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging, and preventing damage to the negative electrode and separator.

[0088] In addition, since the positive electrode for a secondary battery according to the present invention does not expose the positive electrode current collector at the longitudinal end of the positive electrode due to the first thickness reduction portion and the second thickness reduction portion, internal short circuit between the positive electrode and the negative electrode can be prevented even without a separate protective tape, thereby improving battery stability and lifespan characteristics.

[0089] In addition, since the positive electrode for a secondary battery according to the present invention does not expose the positive electrode current collector at the longitudinal end of the positive electrode due to the active material layer provided on the opposite side of the first thickness reduction portion and the second thickness reduction portion, internal short circuit between the positive electrode and the negative electrode can be prevented even without a separate protective tape, thereby improving battery stability and lifespan characteristics.

[0090] According to one embodiment of the present invention, the first thickness reduction portion and the second thickness reduction portion may have longitudinal ends at the same location as the anode current collector. In other words, the first thickness reduction portion and the second thickness reduction portion may be provided extending to the longitudinal end of the anode current collector.

[0091] When the first thickness reduction portion and the second thickness reduction portion have longitudinal ends at the same location as the anode current collector, it has the same advantages as the anode non-free edge structure in that it can mitigate the step difference caused by the total thickness of the anode, unlike the conventional anode free edge structure.

[0092] Specifically, by introducing first and second thickness reduction portions at the longitudinal end of the anode through a taper coating, or by introducing first and second thickness reduction portions including first and second uncoated portions at the longitudinal end of the anode through a cross-sectional coating, the thickness of the first end and the second end having a free edge structure can be adjusted, and the step difference caused by the thickness of the first end and the second end can be mitigated.

[0093] Meanwhile, when the first thickness reduction portion and the second thickness reduction portion have longitudinal ends at the same location as the positive current collector, it has the same advantages as a positive free edge structure. Specifically, since the positive current collector is not exposed at the first end and the second end, unlike a conventional non-free edge structure, internal short circuits between the positive and negative electrodes are prevented without the need for a separate protective tape, thereby improving battery stability and lifespan characteristics.

[0094] According to one embodiment of the present invention, the longitudinal length of the first inclined portion and the second inclined portion may be 1 mm or more and 10 mm or less. Specifically, the longitudinal length of the first inclined portion and the second inclined portion may be 2 mm or more, 3 mm or more, 4 mm or more, or 5 mm or more, and may be 9 mm or less, 8 mm or less, 7 mm or less, 6 mm or less, or 5 mm or less.

[0095] According to one embodiment of the present invention, the longitudinal length of the first thickness reduction portion and the second thickness reduction portion may be 1 mm or more and 20 mm or less. Specifically, the longitudinal length of the first thickness reduction portion and the second thickness reduction portion may be 2 mm or more, 3 mm or more, 4 mm or more, or 5 mm or more, and may be 19 mm or less, 18 mm or less, 17 mm or less, 16 mm or less, or 15 mm or less.

[0096] When the first and second thickness reduction sections and the first and second inclined sections have longitudinal lengths within the aforementioned range, the positive current collector is not exposed at the first and second ends by the first and second thickness reduction sections, and the slope and thickness of the first and second inclined sections have an optimized range, so the effect of preventing internal short circuits between the positive and negative electrodes can be superior.

[0097] According to one embodiment of the present invention, based on 100% of the average thickness of the first flat portion, the minimum thickness of the first inclined portion may be 5% to 75%. Specifically, based on 100% of the average thickness of the first flat portion, the minimum thickness of the first inclined portion may be 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more, and may be 70% or less, 65% or less, 60% or less, 55% or less, or 50% or less.

[0098] According to one embodiment of the present invention, based on 100% of the average thickness of the second flat portion, the minimum thickness of the second inclined portion may be 5% to 75%. Specifically, based on 100% of the average thickness of the second flat portion, the minimum thickness of the second inclined portion may be 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more, and may be 70% or less, 65% or less, 60% or less, 55% or less, or 50% or less.

[0099] According to one embodiment of the present invention, the minimum thickness of the first and second inclined portions may be equal to or different from the average thickness of the first and second ends. Specifically, the minimum thickness of the first and second inclined portions may be greater than or equal to the average thickness of the first and second ends.

[0100] According to one embodiment of the present invention, based on 100% of the average thickness of the first flat portion, the average thickness of the positive active material layer at the first end, i.e., the first auxiliary flat portion, may be 5% or more and 70% or less. Specifically, based on 100% of the average thickness of the first flat portion, the average thickness of the first auxiliary flat portion may be 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more, and may be 65% or less, 60% or less, 55% or less, or 50% or less.

[0101] According to one embodiment of the present invention, based on 100% of the average thickness of the second flat portion, the average thickness of the positive active material layer at the second end, i.e., the second auxiliary flat portion, may be 5% or more and 70% or less. Specifically, based on 100% of the average thickness of the second flat portion, the average thickness of the second auxiliary flat portion may be 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more, and may be 65% or less, 60% or less, 55% or less, or 50% or less.

[0102] According to one embodiment of the present invention, the average thickness of the positive active material layer at the first end and the second end may be the same. Referring to FIGS. 2 to 5, when the positive electrode for a secondary battery is manufactured by the method for manufacturing a positive electrode for a secondary battery described later, the first end (301E) and the second end (302E) may be provided by cutting the loading reduction portion (310), and in this case, the average thickness of the positive active material layer at the first end (301E) and the second end (302E) may be the same.

[0103] When the minimum thickness of the first and second inclined sections and the average thickness of the positive active material layer at the first and second ends have the aforementioned range, the positive current collector at the first and second ends is not exposed by the first thickness reduction section and the second thickness reduction section, and the slope and thickness of the first and second inclined sections have an optimized range, so the effect of preventing internal short circuits between the positive and negative electrodes can be better.

[0104] In addition, when the average thickness of the anode at the first and second ends has the aforementioned range, the anode current collector is not exposed by the active material layer provided on the opposite side of the first and second ends by the first and second thickness reduction sections, and the slope and thickness of the first and second thickness reduction sections have an optimized range, so the effect of preventing internal short circuit between the anode and the cathode can be better.

[0105] According to one embodiment of the present invention, between the first flat portion and the second flat portion, there may be an anode-free portion in which the anode current collector is exposed. Specifically, with reference to FIG. 2(b), FIG. 3(b), FIG. 4(b) and FIG. 5(b), the anode-free portion (330) may be an area in which the anode active material layer is not provided and the anode current collector is exposed.

[0106] When the anode-free portion is included between the first flat portion and the second flat portion, it may be easier to secure a space for an anode tab, which is a middle tab, to be provided on the anode current collector.

[0107] Here, the middle tab refers to an electrode tab provided on an electrode-free portion formed at a location other than the longitudinal end of the electrode. On the other hand, the electrode tabs provided on the electrode-free portions located at both longitudinal ends of the electrode may be referred to as a core tab or an out tab depending on the arrangement direction of the electrode.

[0108] According to one embodiment of the present invention, the anode may further include an intermediate slope portion in which the thickness gradually decreases from the first flat portion or the second flat portion to the anode-free portion. Specifically, the thickness of the intermediate slope portion may gradually decrease from the first flat portion or the second flat portion to the anode-free portion according to the coating direction of the anode active material slurry.

[0109] Referring to FIGS. 1a to 1d, the anode (300) may further include an intermediate sloped section (330s) in which the thickness gradually decreases from the first flat section (321) or the second flat section (322) to the anode-free section (330). Specifically, FIGS. 1a to 1c illustrate an embodiment including an intermediate sloped section (330s) in which the thickness gradually decreases from the first flat section (321) to the anode-free section (330). As described below, this may mean that the anode active material slurry is applied in the direction of the intermediate sloped section (330s) in which the thickness decreases from the first flat section (321) to the anode-free section (330), that is, in the X direction.

[0110] By further including the above-mentioned intermediate slope, the step difference formed at the longitudinal end of the anode-free portion is mitigated, thereby preventing damage to the cathode and separator and preventing internal short circuits between the anode and cathode, thus improving battery stability and lifespan characteristics.

[0111] According to one embodiment of the present invention, the intermediate slope may be a drag line. Here, the 'drag line' refers to a slope where the slope is not constant as the loading amount decreases at the point where the application of the positive active material slurry ends, that is, a slope that appears due to the dragging of the active material slurry application nozzle.

[0112] As described below, the application of the positive active material slurry may be performed in a first direction from one end in the longitudinal direction of the positive current collector to the other end in the longitudinal direction of the positive current collector. At this time, at the point where the first flat section or the second flat section, which is the point where the application of the positive active material slurry ends, meets the intermediate inclined section, an intermediate inclined section with an uneven slope may be formed as the loading amount decreases.

[0113] According to one embodiment of the present invention, the intermediate slope (330s) may have a thickness that gradually decreases from the first flat section (321) to the anode-free section (330). In this case, the intermediate slope (330s) adjacent to the first flat section (321) may be a drag line, and the application of the anode active material slurry may be performed from the first flat section (321) toward the anode-free section (330), that is, from the first end (301E) toward the second end (302E).

[0114] Referring to FIG. 2 (a) and (b), when the intermediate sloped section (330s) is adjacent to the first flat section (321) and is a drag line, the application of the positive active material slurry may be performed from the first end (301E) toward the second end (302E), i.e., in the X direction.

[0115] On the other hand, unlike (a) and (b) of FIG. 2, the intermediate slope (330s) may have a thickness that gradually decreases from the second flat section (322) to the anode-free section (330). In this case, the intermediate slope (330s) adjacent to the second flat section (322) may be a drag line, and the application of the anode active material slurry may be performed from the second flat section (322) toward the anode-free section (330), that is, from the second end (302E) toward the first end (301E). In other words, the first direction in which the application of the anode active material slurry is performed may be the opposite direction to the X direction.

[0116] If the intermediate slope (330s) is adjacent to the second flat section (322) and is a drag line, the application of the positive active material slurry may be performed from the second end (302E) toward the first end (301E), that is, in the opposite direction of the X direction. In other words, if the intermediate slope is a drag line, the coating direction of the positive active material layer can be determined.

[0117] According to one embodiment of the present invention, the anode may further include an anode tab provided on the anode-free portion. In this case, the anode tab may be a middle tab. That is, the anode tab may be formed at a location other than the longitudinal end of the anode. In this case, a protective tape, such as a protective tape made of polyimide (PI) material, may be attached to the anode tab, i.e., the middle tab, to prevent exposure of the anode-free portion.

[0118] On the other hand, the anode tab may not be provided at the longitudinal end of the anode, and since the anode current collector is not exposed at the longitudinal end of the anode, the battery stability and lifespan characteristics can be improved by preventing an internal short circuit between the anode and the cathode even without providing a separate protective tape at the longitudinal end of the anode.

[0119] According to one embodiment of the present invention, the longitudinal length of the anode-free portion may be 5 mm or more and 20 mm or less. Specifically, the longitudinal length of the anode-free portion may be 6 mm or more, 7 mm or more, 8 mm or more, 9 mm or more, or 10 mm or more, and may be 19 mm or less, 18 mm or less, 17 mm or less, 16 mm or less, or 15 mm or less.

[0120] When the above-mentioned anode-free portion has a longitudinal length within the aforementioned range, it may be easier to secure a space for an anode tab to be provided on the anode current collector, and by preventing an internal short circuit between the anode and the cathode, battery stability and lifespan characteristics can be improved. In addition, since the longitudinal lengths of the first flat portion and the second flat portion have an optimized range, battery capacity loss due to a reduction in the area facing the cathode can be prevented.

[0121] According to one embodiment of the present invention, the positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery. Specifically, the positive current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. That is, the positive current collector may be provided in the form of surface-treated stainless steel, aluminum foil, etc.

[0122] In addition, the positive current collector can typically have a thickness of 3 to 50 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0123] According to one embodiment of the present invention, the positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (0≤x≤0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-y M y Ni-site type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01≤y≤0.3); chemical formula LiMn 2-z M z Examples include lithium manganese composite oxides represented by O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01≤z≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4 in which part of the Li of the chemical formula is substituted with alkaline earth metal ions, but are not limited thereto. The anode may also be Li-metal.

[0124] According to one embodiment of the present invention, the positive active material layer may further include a positive conductive material and a positive binder. The positive conductive material is used to impart conductivity to the electrode and can be used without special limitations as long as it has electronic conductivity without causing chemical changes in the battery being constructed. Specifically, the positive conductive material may be graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0125] In addition, the anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0126] One embodiment of the present invention provides a method for manufacturing a positive electrode for a secondary battery, comprising the steps of: applying a positive electrode active material slurry on at least one surface of a positive electrode current collector to form a positive electrode active material layer including a first flat portion, a loading reduction portion, and a second flat portion (S100); stopping the application of the positive electrode active material slurry to form a positive electrode non-exposed portion where the positive electrode current collector is exposed (S200); and cutting the loading reduction portion (S300). The loading reduction portion is located between the first flat portion and the second flat portion and is an area extending from the first flat portion and the second flat portion where the thickness of the positive electrode active material layer is reduced or an area where the positive electrode current collector is exposed. The application is performed in a first direction from one end in the longitudinal direction of the positive electrode current collector toward the other end in the longitudinal direction of the positive electrode current collector.

[0127] The method for manufacturing a positive electrode for a secondary battery according to the present invention alleviates the step difference formed at the longitudinal end of the positive electrode, thereby improving the phenomenon where the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by the shrinkage / expansion of the electrode during battery charging / discharging, preventing damage to the negative electrode and separator, and enabling the manufacturing of a positive electrode for a secondary battery with improved battery stability and lifespan characteristics in a simpler manner.

[0128] In addition, the method for manufacturing a positive electrode for a secondary battery according to the present invention is suitable for a continuous process using existing roll-to-roll process equipment, and since it can prevent internal short circuits between the positive electrode and the negative electrode without the need for a separate protective tape, productivity and economic efficiency can be secured.

[0129] Here, the roll-to-roll method may refer to a method of processing multiple flexible metal foils, etc., by moving them between rollers, and, for example, may refer to a method of unwinding a roll that is winding a flexible and thin metal sheet-type electrode current collector to supply the electrode current collector, applying an electrode active material slurry containing an electrode active material to at least one surface of the electrode current collector and drying it to form an electrode active material layer, and then rewinding the processed electrode current collector on another roll to recover it.

[0130] According to one embodiment of the present invention, the step of forming the positive active material layer; and the step of forming the positive non-positive portion may be performed in a plurality of ways.

[0131] Specifically, referring to FIG. 2(a), FIG. 3(a), FIG. 4(a) and FIG. 5(a), the step of forming the positive active material layer; and the step of forming the positive non-positive portion may be performed in multiple steps, and subsequently, the step of cutting the loading reduction portion may be performed.

[0132] For example, a method for manufacturing a positive electrode for a secondary battery according to one embodiment of the present invention may include the step of forming a positive electrode active material layer including a first flat portion, a loading reduction portion, and a second flat portion by continuously applying a positive electrode active material slurry on at least one surface of a positive electrode current collector (S100); the step of forming a positive electrode non-exposed portion in which the positive electrode current collector is exposed by stopping the application of the positive electrode active material slurry (S200); and the step of forming a positive electrode non-exposed portion in which the positive electrode current collector is exposed by continuously applying a positive electrode active material slurry on one surface of a positive electrode current collector (S100) and the step of forming a positive electrode non-exposed portion in which the positive electrode current collector is exposed by stopping the application of the positive electrode active material slurry (S200), after which the step of cutting the loading reduction portion (S300) is performed.

[0133] When the step of forming the positive active material layer and the step of forming the positive non-positive portion are performed in multiple steps, it is suitable for a continuous process using existing roll-to-roll process equipment, and since internal short circuits between the positive and negative electrodes can be prevented without the need for a separate protective tape, productivity and economic efficiency can be secured.

[0134] According to one embodiment of the present invention, the coating may be performed on at least one surface of the positive current collector. Specifically, the coating may be performed on both surfaces of the positive current collector. More specifically, the coating may be performed such that the longitudinal lengths of the positive active material layers formed on one surface and the other surface of the positive current collector are equal or different, taking into account the curvature of the positive electrode included in the electrode assembly.

[0135] For example, based on the anode current collector, the longitudinal length of the anode active material layer provided on one side in the direction opposite to the winding axis of the electrode assembly may be 0 mm to 10 mm smaller than the longitudinal length of the anode active material layer provided on the other side in the direction opposite to the winding axis.

[0136] According to one embodiment of the present invention, the coating may be performed in a first direction from one end in the longitudinal direction of the anode current collector toward the other end in the longitudinal direction of the anode current collector.

[0137] Specifically, the coating may be performed from a coating start area, which is one end in the longitudinal direction of the positive current collector, toward a coating end area, which is the other end in the longitudinal direction of the positive current collector, and the coating may be performed in the same direction on one side and the other side of the current collector. In other words, the coating direction of the positive active material slurry applied on one side and the other side of the positive current collector may be the same.

[0138] If the loading reduction portion is a region where the thickness of the positive active material layer is reduced, the coating may be performed such that the loading reduction portion has a thickness of 5% or more and 75% or less, based on 100% of the average thickness of the first flat portion or the second flat portion. Specifically, based on 100% of the average thickness of the first flat portion or the second flat portion, the thickness of the loading reduction portion may be 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more, and may be 70% or less, 65% or less, 60% or less, 55% or less, or 50% or less.

[0139] According to one embodiment of the present invention, the coating may be performed to form a drag line from one end in the longitudinal direction of the first flat portion or the second flat portion. Here, the 'drag line' is as described above with respect to the positive electrode for a secondary battery.

[0140] Specifically, the coating may be performed in a first direction from one end in the longitudinal direction of the anode current collector toward the other end in the longitudinal direction of the anode current collector. At this time, at the point where the first flat section or the second flat section, which is the point where the coating ends, meets the intermediate slope section, an intermediate slope section with an uneven slope may be formed as the loading amount decreases.

[0141] Referring to FIG. 2 (a) and (b), the first direction in which the positive active material slurry is applied may be the direction from the first end (301E) to the second end (302E), i.e., the X direction. In this case, an intermediate inclined section (330s), i.e., a drag line, may be formed adjacent to the first flat section (321).

[0142] On the other hand, unlike (a) and (b) of FIG. 2, the first direction in which the anode active material slurry is applied may be the direction from the second end (302E) to the first end (301E), that is, the opposite direction of the X direction. In this case, an intermediate inclined section (330s), that is, a drag line, may be formed adjacent to the second flat section (322).

[0143] According to one embodiment of the present invention, the coating may be performed such that the loading reduction portion has a longitudinal length of 2 mm or more and 50 mm or less. Specifically, the coating may be performed such that the loading reduction portion has a longitudinal length of 3 mm or more, 4 mm or more, 5 mm or more, 6 mm or more, 7 mm or more, 8 mm or more, 9 mm or more, or 10 mm or more, and may be performed such that the longitudinal length is 49 mm or less, 48 ​​mm or less, 47 mm or less, 46 mm or less, 45 mm or less, 44 mm or less, 43 mm or less, 42 mm or less, 41 mm or less, or 40 mm or less.

[0144] When the above-mentioned loading reduction section is applied to have a longitudinal length within the aforementioned range, it is suitable for a continuous process using existing roll-to-roll process equipment, and since internal short circuits between the anode and cathode can be prevented without the need for a separate protective tape, productivity and economic efficiency can be secured.

[0145] According to one embodiment of the present invention, the cutting may be performed in a second direction perpendicular to the first direction at the loading reduction portion.

[0146] Specifically, with reference to FIG. 2(a), FIG. 3(a), FIG. 4(a) and FIG. 5(a), the coating of the positive active material may be performed in a first direction, i.e., in the X direction, from a first end (301E), which is one end in the longitudinal direction of the positive current collector, to a second end (302E), which is the other end in the longitudinal direction of the positive current collector.

[0147] At this time, by performing a cut in the loading reduction section (310) in a second direction perpendicular to the first direction, i.e., in the YZ plane direction, a first thickness reduction section (311) extending from the first flat section (321) and having a longitudinal end at the same position as the first end (301E); and a second thickness reduction section (312) extending from the second flat section (322) and having a longitudinal end at the same position as the second end (302E) may be provided.

[0148] According to one embodiment of the present invention, the cutting may be performed at a point spaced 0.5 mm or more and 29.5 mm or less from one end in the longitudinal direction of the loading reduction part. Specifically, the cutting may be performed at a point spaced 1 mm or more, 1.5 mm or more, 2 mm or more, 2.5 mm or more, or 3 mm or more from one end in the longitudinal direction of the loading reduction part in the opposite direction of the first flat part or the second flat part, and may be performed at a point spaced 29 mm or less, 28.5 mm or less, 28 mm or less, 27.5 mm or less, or 27 mm or less.

[0149] Referring to FIG. 2(a), FIG. 3(a), FIG. 4(a) and FIG. 5(a), the cutting may be performed at a point spaced from one end of the longitudinal direction of the loading reduction part, that is, one end of the longitudinal direction of the first flat part (321), by 0.5 mm or more and 29.5 mm or less in the opposite direction of the first direction, that is, in the opposite direction of the X direction.

[0150] Additionally, the above cutting may be performed at a point spaced from the other end in the longitudinal direction of the loading reduction part (310), that is, from the first end in the longitudinal direction of the second flat part (322), by 0.5 mm or more and 29.5 mm or less in the X direction.

[0151] When the above-mentioned cutting satisfies the aforementioned range, by mitigating the step difference formed at the longitudinal end of the anode, the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by the shrinkage / expansion of the electrode during battery charging / discharging is improved, damage to the negative electrode and separator is prevented, and a positive electrode for a secondary battery with improved battery stability and lifespan characteristics can be manufactured in a simpler way.

[0152] One embodiment of the present invention provides a positive electrode for a secondary battery that is manufactured by the above-described method for manufacturing a positive electrode for a secondary battery.

[0153] The positive electrode for a secondary battery manufactured by the method for manufacturing a positive electrode for a secondary battery according to the present invention may improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging by mitigating the step difference formed at the longitudinal end of the positive electrode, prevent damage to the negative electrode and separator, and improve battery stability and lifespan characteristics.

[0154] One embodiment of the present invention provides an electrode assembly comprising the aforementioned anode; a separator and a cathode.

[0155] The electrode assembly according to the present invention can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging, prevent damage to the negative electrode and separator, and prevent internal short circuits between the positive and negative electrodes, thereby improving battery stability and lifespan characteristics.

[0156] FIGS. 6 to 8 are schematic diagrams showing the components of an electrode assembly including a positive electrode for a secondary battery according to one embodiment of the present invention. Specifically, FIG. 6(a) schematically shows the components of an electrode assembly including a positive electrode for a secondary battery having a free edge structure, and FIG. 6(b) schematically shows the components of an electrode assembly including a positive electrode for a secondary battery according to one embodiment of the present invention.

[0157] Referring to FIG. 6 (a) and (b), an electrode assembly including a positive electrode for a secondary battery according to one embodiment of the present invention can adjust the thickness of the first end (301E) and the second end (302E) having a free edge structure by introducing a first thickness reduction portion (311) including a first inclined portion (311s) and a second thickness reduction portion (312) including a second inclined portion (312s) at the longitudinal end of the positive electrode through a taper coating, and can mitigate the step difference caused by the thickness of the first end (301E) and the second end (302E).

[0158] Meanwhile, when the first thickness reduction portion (311) and the second thickness reduction portion (312) have longitudinal ends (301E, 302E) at the same location as the positive electrode current collector, they have the same advantages as a positive electrode free edge structure. Specifically, since the positive electrode current collector is not exposed at the first end (301E) and the second end (302E), unlike the existing non-free edge structure, internal short circuits between the positive and negative electrodes can be prevented without providing a separate protective tape (300P), thereby improving battery stability and lifespan characteristics. In this case, as previously mentioned, the positive electrode (300) for the secondary battery may further include a positive electrode tab (300T) provided on the positive electrode non-part (330).

[0159] FIG. 6(a) schematically shows the components of an electrode assembly including a positive electrode for a secondary battery having a free edge structure, and FIG. 6(b) schematically shows the components of an electrode assembly including a positive electrode for a secondary battery according to one embodiment of the present invention.

[0160] Referring to FIG. 6 (a) and (b), an electrode assembly including a positive electrode for a secondary battery according to one embodiment of the present invention can adjust the thickness of the first end (301E) and the second end (302E) having a free edge structure by introducing a first thickness reduction portion (311) including a first non-thickness portion (311n) and a second thickness reduction portion (312) including a second non-thickness portion (312n) at the longitudinal end of the positive electrode through cross-sectional coating, and can mitigate the step difference caused by the thickness of the first end (301E) and the second end (302E).

[0161] Meanwhile, when the first non-positive portion (311n) and the second non-positive portion (312n) have longitudinal ends (301E, 302E) at the same location as the positive current collector, it has the same advantages as a positive free edge structure. Specifically, since the positive current collector is not exposed on one side of the first end (301E) and the second end (302E), unlike the existing non-free edge structure, internal short circuits between the positive and negative electrodes are prevented without providing a separate protective tape (300P), thereby improving battery stability and lifespan characteristics. In this case, as previously mentioned, the positive electrode (300) for the secondary battery may further include a positive tab (300T) provided on the positive non-positive portion (330).

[0162] Referring to FIG. 8, the electrode assembly (10) may be formed by stacking and winding an anode (300); a separator (200) and a cathode (100) in sequence. That is, the electrode assembly may be a jelly-roll type electrode assembly.

[0163] According to one embodiment of the present invention, the cathode may comprise a cathode current collector and a cathode active material layer provided on the cathode current collector. Specifically, the cathode may comprise a cathode current collector and a cathode active material layer formed on one or both sides of the cathode current collector, the cathode active material layer comprising a cathode active material. In other words, the cathode active material layer is formed on the cathode retaining portion of the cathode current collector, and the side not provided with the cathode active material layer may be described as a cathode-free portion.

[0164] According to one embodiment of the present invention, the negative current collector may include a negative retaining portion where a negative active material layer is formed and a negative non-negative portion where a negative active material layer is not formed, and may include a tab on the negative non-negative portion. Specifically, the negative current collector may include a negative non-negative portion and may include a negative tab formed on the negative non-negative portion. Accordingly, the electrode assembly manufactured may include one or more negative tabs.

[0165] According to one embodiment of the present invention, the negative electrode active material layer may comprise a negative electrode active material comprising one or more selected from the group consisting of silicon-based materials and carbon-based materials. Additionally, the negative electrode active material layer may further comprise a negative electrode conductive material and a negative electrode binder, and the negative electrode active material; the negative electrode conductive material; and the negative electrode binder may be any material used in the art without limitation. For example, the negative electrode active material may be Si, SiOx(0 <x≤2) 및 Si / C 중 적어도 어느 하나를 포함하는 것일 수 있다.

[0166] According to one embodiment of the present invention, the negative current collector may be conductive without causing chemical changes in the battery, and is not particularly limited. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used as the negative current collector. Specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used as the negative current collector. The thickness of the negative current collector may be 5 μm or more and 30 μm or less, but the thickness of the negative current collector is not limited thereto.

[0167] According to one embodiment of the present invention, the cathode binder may comprise at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also comprise various copolymers thereof.

[0168] According to one embodiment of the present invention, the cathode conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0169] According to one embodiment of the present invention, the electrode assembly may include a plurality of separators. For example, the electrode assembly may have a structure in which a separator / negative electrode / separator / positive electrode are stacked in sequence. The separator separates the positive electrode and the negative electrode and provides a pathway for the movement of lithium ions. It may be used without special limitations as long as it is typically used as a separator in a secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a stacked structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. In addition, the above-described separator may be a separator in which a slurry containing ceramic components or polymer materials is coated on the substrate layer to secure heat resistance or mechanical strength, using the aforementioned separator material as a substrate layer, and may optionally be used in a single-layer or multi-layer structure. The thickness of the separator may be 5 μm or more and 20 μm or less, but is not limited thereto.

[0170] One embodiment of the present invention provides a secondary battery comprising the aforementioned electrode assembly; a battery case with one side open; and a seal, wherein the battery case further comprises an electrolyte.

[0171] The secondary battery according to the present invention can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by the shrinkage / expansion of the electrode during battery charging and discharging, prevent damage to the negative electrode and separator, and prevent internal short circuits between the positive and negative electrodes, thereby improving battery stability and lifespan characteristics.

[0172] FIG. 10 is a perspective view illustrating a secondary battery according to one embodiment of the present invention.

[0173] Referring to FIGS. 8 to 10, the secondary battery (1) may include an electrode assembly (10) inside a battery case (20) with one side open, and after injecting an electrolyte into the battery case (20), the open end of the battery case (20) may be sealed with a sealant (not shown).

[0174] According to one embodiment of the present invention, the battery case may be cylindrical. Specifically, the battery case may be cylindrical, prismatic, or pouch-shaped depending on the application, and preferably cylindrical.

[0175] According to one embodiment of the present invention, the interior of the battery case may contain an electrolyte. Specifically, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0176] According to one embodiment of the present invention, the non-aqueous organic solvent may be, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. It can be used.

[0177] According to one embodiment of the present invention, the metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, as an anion of the lithium salt, 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 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more types selected from the group consisting of can be used.

[0178] According to one embodiment of the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0179] One embodiment of the present invention provides a battery module including the secondary battery and a battery pack including the same. Specifically, the battery module may include the aforementioned secondary battery as a unit cell, and the battery pack may include the battery module. If necessary, the battery pack may directly include the secondary battery as a unit cell.

[0180] Since the above battery module and battery pack include the above secondary battery with improved high capacity, high battery stability, and lifespan characteristics, they may be used as a power source for medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0181] FIG. 13 is a perspective view illustrating a battery pack according to one embodiment of the present invention.

[0182] Referring to FIG. 13, the battery pack (3) may include at least one secondary battery (1) inside the pack housing (2). Since the battery pack includes a secondary battery with improved battery stability and lifespan characteristics, the stability and lifespan characteristics may be improved.

[0183] One embodiment of the present invention provides a means of transport comprising the battery pack described above. Specifically, the means of transport may comprise the battery pack described above, and the battery pack may comprise a battery module comprising the secondary battery described above as a unit cell. If necessary, the battery pack may directly comprise the secondary battery as a unit cell.

[0184] FIG. 14 is a perspective view illustrating a moving means according to one embodiment of the present invention.

[0185] Referring to FIG. 14, the means of transport (V) may include at least one battery pack (3).

[0186] The above-mentioned means of transportation uses a battery pack with improved battery stability and lifespan characteristics, so it can be excellent in terms of stability and sleep characteristics.

[0187]

[0188] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0189] Preparation Example 1

[0190] Manufacturing of cathodes for secondary batteries

[0191] An Al foil with a thickness of 15 μm and a width of 63.9 mm was prepared as a positive current collector, and a positive active material slurry was prepared comprising the positive current collector, an NMCA (Ni-Mn-Co-Al) composite with a Ni content of 92% or more as a positive active material, and CNT as a conductive material. By applying and drying the positive active material slurry onto the positive current collector, a positive active material layer was formed to manufacture a positive electrode for a secondary battery having a thickness of 154 μm.

[0192] Specifically, a positive active material slurry was continuously applied to one surface of the positive current collector to form a positive active material layer including a loading reduction portion of 30 mm between a first flat portion and a second flat portion, and the application of the positive active material slurry was stopped to continuously form a positive non-flat portion of 15 mm, and then a point spaced 15 mm from one end of the loading reduction portion in the longitudinal direction was cut to manufacture a positive electrode for a secondary battery in the form of FIG. 1a.

[0193] At this time, the amount of positive active material slurry applied to the loading reduction section was adjusted so that the average thickness of the positive active material layer at the first and second sections was 5% of the average thickness of the first and second flat sections.

[0194] Preparation Example 2

[0195] A positive electrode for a secondary battery was prepared in the same manner as in Preparation Example 1, except that the amount of positive active material slurry applied to the loading reduction section was adjusted so that the average thickness of the positive active material layer at the first and second sections was 18% of the average thickness of the first and second flat sections.

[0196] Preparation Example 3

[0197] A positive electrode for a secondary battery was prepared in the same manner as in Preparation Example 1, except that the amount of positive active material slurry applied to the loading reduction section was adjusted so that the average thickness of the positive active material layer at the first and second sections was 36% of the average thickness of the first and second flat sections.

[0198] Preparation Example 4

[0199] A positive electrode for a secondary battery was prepared in the same manner as in Preparation Example 1, except that the amount of positive active material slurry applied to the loading reduction section was adjusted so that the average thickness of the positive active material layer at the first and second sections was 66% of the average thickness of the first and second flat sections.

[0200] Preparation Example 5

[0201] A positive electrode for a secondary battery was prepared in the same manner as in Preparation Example 1, except that the amount of positive active material slurry applied to the loading reduction section was adjusted so that the average thickness of the positive active material layer at the first and second sections was 77% of the average thickness of the first and second flat sections.

[0202] Preparation Example 6

[0203] A positive electrode for a secondary battery was prepared in the same manner as in Preparation Example 1, except that the amount of positive active material slurry applied to the loading reduction section was adjusted so that the average thickness of the positive active material layer at the first and second sections was 89% of the average thickness of the first and second flat sections.

[0204] Preparation Example 7

[0205] A positive electrode for a secondary battery was prepared in the same manner as in Preparation Example 1, except that the amount of positive active material slurry applied to the loading reduction section was adjusted so that the average thickness of the positive active material layer at the first and second sections was 0% of the average thickness of the first and second flat sections.

[0206] Preparation Example 8

[0207] A positive electrode for a secondary battery was prepared in the same manner as in Preparation Example 1, except that the amount of positive active material slurry applied to the loading reduction section was adjusted so that the average thickness of the positive active material layer at the first and second sections was 100% of the average thickness of the first and second flat sections.

[0208]

[0209] Example 1

[0210] Manufacture of electrode assemblies

[0211] A Cu foil with a thickness of 8 μm and a width of 65.1 mm was prepared as a cathode current collector, and a cathode active material slurry containing 50 parts by weight each of artificial graphite and natural graphite as cathode active materials was applied and dried on the cathode current collector to form a cathode active material layer, thereby manufacturing a cathode having a thickness of 187 μm.

[0212] Meanwhile, two sheet-type polyethylene separator membranes were prepared.

[0213] Subsequently, an electrode assembly was manufactured by placing a separator between the above-mentioned cathode and the anode according to Preparation Example 1, laminating them, and winding them.

[0214] manufacturing of secondary batteries

[0215] After inserting the above electrode assembly into a cylindrical battery case, an electrolyte solution was prepared by mixing ethylene carbonate (EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) in a volume ratio (vol%) of 20:5:75 and dissolving LiPF6 to contain 0.7 M, and the cylindrical battery case was sealed with a cap assembly to manufacture a secondary battery.

[0216] Examples 2 to 6

[0217] An electrode assembly and a secondary battery were manufactured using the same method as in Example 1, except that the electrode assembly and the secondary battery were manufactured using the cathode for a secondary battery according to Examples 2 to 6, respectively, instead of the cathode according to Example 1.

[0218] Comparative Example 1 and Comparative Example 2

[0219] An electrode assembly and a secondary battery were manufactured using the same method as in Example 1, except that the electrode assembly and the secondary battery were manufactured using the cathode for a secondary battery according to Example 7 and Example 8, respectively, instead of the cathode according to Example 1.

[0220] Experimental Example

[0221] Experimental Example - Core Impingement Evaluation

[0222] The secondary batteries of Examples 1 to 6 and Comparative Example 1 and Comparative Example 2 were prepared, and after 200 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the occurrence of Core Impingement was evaluated in the following manner, and the results are shown in Table 1 and Figure 12, respectively.

[0223] Figure 11 illustrates an evaluation method according to an experimental example. Specifically, Figure 11 schematically illustrates a method for evaluating whether core impingement occurs. Specifically, Figure 11 (a) schematically illustrates a method for evaluating whether core impingement occurs when deformation occurs in the cathode, and Figure 11 (b) schematically illustrates a method for evaluating whether core impingement occurs when deformation does not occur in the cathode.

[0224] 1) On the first surface, which is the surface opposite to the winding axis of the anode (300), a straight line connecting the longitudinal end of the anode, i.e., the first end (301E), and a point 5 mm away from the end is extended to form a first extension line (E1).

[0225] 2-1) Case where deformation occurs at the cathode

[0226] A second extension line (E2) is drawn by extending a straight line connecting two points where the curvature direction changes within a distance of 5 mm from the first end (301E) on the surface of the cathode (100) facing the first surface of the anode (300).

[0227] 2-2) Case where no deformation occurs at the cathode

[0228] A second extension line (E2) is drawn by extending a straight line connecting two points that are spaced 5 mm apart from the longitudinal end (301E) of the anode on the surface of the cathode (100) opposite to the first surface of the anode (300).

[0229] 3) Core Impingement was evaluated to have occurred when the angle from the first extension line (E1) to the second extension line (E2) in a counterclockwise direction, centered on the intersection point of the first extension line (E1) and the second extension line (E2), exceeded 10°.

[0230] Meanwhile, the above method for evaluating whether Core Impingement has occurred can be applied in such a way that, when an unknown secondary battery (Unknown Cell) is obtained, the occurrence of Core Impingement is evaluated at the time of initial acquisition, and the occurrence of Core Impingement is re-evaluated every 200 cycles and compared with the Core Impingement conditions of the secondary battery according to the embodiment of the present invention.

[0231] Ratio (%) of the average thickness of the positive electrode active material layer at the first and second ends to the average thickness of the first and second flat sections of the positive electrode for a secondary battery Secondary Battery Core Impingement Angle (˚) Core Impingement Evaluation Results Manufacturing Example 15 Example 11.3X Manufacturing Example 218 Example 22.8X Manufacturing Example 336 Example 34.7X Manufacturing Example 466 Example 48.0X Manufacturing Example 577 Example 510.9O Manufacturing Example 689 Example 616.1O Manufacturing Example 70 Comparative Example 10.8X Manufacturing Example 8100 Comparative Example 217.3O

[0232]

[0233] Figure 12 is a graph showing the evaluation results according to the experimental example.

[0234] Referring to Table 1, Fig. 11, and Fig. 12 above, it was confirmed that the Core Impingement Angle of the secondary batteries according to Examples 1 to 6 was reduced compared to the secondary battery according to Comparative Example 2, which includes a positive electrode having a free edge, i.e., the ratio of the average thickness of the positive electrode active material layer at the first end and the second end is 100%.

[0235] Specifically, it was confirmed that the Core Impingement Angle was reduced for all secondary batteries according to Examples 1 to 6, and in particular, for the secondary batteries according to Examples 1 to 4, the Core Impingement Angle was 10° or less, and it was confirmed that the possibility of Core Impingement occurring due to damage to the negative electrode and separator, i.e., shrinkage / expansion of the electrode assembly, was significantly reduced.

[0236] Meanwhile, in the secondary battery according to Comparative Example 1, which includes a positive electrode having a non-free edge, the ratio of the average thickness of the positive active material layer at the first and second ends is 0%, and since the positive current collector is directly exposed at the first and second ends, in order to prevent an internal short circuit between the positive electrode and the negative electrode, protective tape (300P) must be attached to both sides of the first and second ends respectively to have a structure as shown in FIG. 6 (a), making it impossible to secure productivity and economic efficiency. In other words, it was confirmed that the secondary battery according to Comparative Example 1, which includes a positive electrode having a non-free edge, is unsuitable for a continuous process using roll-to-roll process equipment.

[0237] Meanwhile, it was confirmed that the secondary battery according to Comparative Example 2, which includes a positive electrode having a free edge, has an inferior effect in preventing damage to the negative electrode and separator because it fails to alleviate the step difference formed at the longitudinal end of the positive electrode.

[0238] In other words, the electrode assembly according to the present invention and the secondary battery including the same can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging, prevent damage to the negative electrode and separator, and prevent internal short circuits between the positive and negative electrodes, thereby improving battery stability and lifespan characteristics.

[0239] The above detailed description is intended to illustrate and explain the present invention. Furthermore, the foregoing merely indicates and describes preferred embodiments of the present invention, and as described above, the present invention may be used in various other combinations, modifications, and environments, and may be modified or altered within the scope of the concept of the invention disclosed herein, the scope equivalent to the foregoing disclosure, and / or the scope of the art or knowledge. Accordingly, the above detailed description of the invention is not intended to limit the present invention to the disclosed embodiments. Additionally, the appended claims should be interpreted as including other embodiments.

Claims

1. A positive current collector; and a positive active material layer provided on at least one surface of the positive current collector, as a positive electrode for a secondary battery, At least one of the above positive active material layers is, It includes a first flat section, a second flat section, a first thickness reduction section located at one end of the first flat section, and a second thickness reduction section located at the other end of the second flat section. The first thickness reduction portion comprises (a) a first inclined portion in which the thickness gradually decreases from the first flat portion toward a first end portion, which is a longitudinal end portion of the anode current collector, and extends from the first flat portion and has a longitudinal end portion at the same position as the first end portion, or (b) a first non-exposed portion in which the anode current collector is exposed from the first flat portion toward a first end portion, which is a longitudinal end portion of the anode current collector, and the first non-exposed portion has a longitudinal end portion at the same position as the first end portion. The second thickness reduction portion comprises (a) a second inclined portion in which the thickness gradually decreases from the second flat portion toward the second end portion, which is the other end in the longitudinal direction of the positive current collector, and has a longitudinal end portion extending from the second flat portion and having a longitudinal end portion at the same position as the second end portion, or (b) a second non-exposed portion in which the positive current collector is exposed from the second flat portion toward the second end portion, which is the other end in the longitudinal direction of the positive current collector, and the second non-exposed portion has a longitudinal end portion at the same position as the second end portion, for a positive electrode for a secondary battery.

2. In Paragraph 1, A positive electrode for a secondary battery, wherein the first thickness reduction portion is provided from the first inclined portion toward the first end portion, which is one end in the longitudinal direction of the positive electrode current collector, and further includes a first auxiliary flat portion having a constant thickness of the positive electrode active material layer.

3. In Paragraph 1, A positive electrode for a secondary battery, wherein the second thickness reduction portion is provided from the second inclined portion toward the second end side, which is the other end in the longitudinal direction of the positive electrode current collector, and further includes a second auxiliary flat portion having a constant thickness of the positive electrode active material layer.

4. In Paragraph 1, The positive electrode for a secondary battery, wherein the second thickness reduction portion is provided from the second inclined portion to the second end side, which is the other end in the longitudinal direction of the positive electrode current collector, and includes a second non-exposed portion in which the positive electrode current collector is exposed.

5. In Paragraph 1, The positive electrode for the secondary battery is provided with a positive electrode active material layer comprising a first flat portion, a second flat portion, a first thickness reduction portion, and a second thickness reduction portion on one surface of the positive electrode current collector, and A positive electrode for a secondary battery, wherein the positive electrode active material layer including the first flat portion and the second flat portion is provided on the other surface of the positive electrode current collector.

6. In Paragraph 1, A positive electrode for a secondary battery, wherein the longitudinal length of the first thickness reduction portion is 1 mm or more and 20 mm or less.

7. In Paragraph 1, A positive electrode for a secondary battery, wherein, based on an average thickness of 100% of the first flat portion, the minimum thickness of the first inclined portion is 5% or more and 75% or less.

8. In Paragraph 1, A positive electrode for a secondary battery, wherein, based on 100% of the average thickness of the first flat portion, the average thickness of the positive electrode active material layer at the first end is 5% or more and 70% or less.

9. In Paragraph 1, A positive electrode for a secondary battery, further comprising a positive electrode-free portion in which the positive electrode current collector is exposed between the first flat portion and the second flat portion.

10. In Paragraph 9, A positive electrode for a secondary battery further comprising an intermediate inclined portion in which the thickness gradually decreases from the first flat portion or the second flat portion to the positive electrode non-existent portion.

11. In Paragraph 10, The above intermediate slope is a drag line for a positive electrode for a secondary battery.

12. A step of forming an anode active material layer comprising a first flat portion, a loading reduction portion, and a second flat portion by applying an anode active material slurry on at least one surface of an anode current collector; A step of stopping the application of the anode active material slurry to form an anode-free portion in which the anode current collector is exposed; and Step of cutting the above loading reduction section Includes, The loading reduction portion is located between the first flat portion and the second flat portion, and is an area extending from the first flat portion and the second flat portion where the thickness of the positive active material layer is reduced or the positive current collector is exposed. A method for manufacturing a positive electrode for a secondary battery, wherein the coating is performed in a first direction from one end in the longitudinal direction of the positive electrode current collector toward the other end in the longitudinal direction of the positive electrode current collector.

13. In Paragraph 12, The step of forming the above positive active material layer A step of applying an anode active material slurry on one surface of the anode current collector to form a first flat portion, a loading reduction portion, and a second flat portion; and A method for manufacturing a positive electrode for a secondary battery, comprising the step of continuously applying a positive active material slurry onto the other side of the positive electrode current collector to form a positive active material layer.

14. In Paragraph 12, A method for manufacturing a positive electrode for a secondary battery, wherein the step of forming the positive electrode active material layer and the step of forming the positive electrode non-positive portion are performed in a plurality of ways.

15. In Paragraph 12, The above coating is, A method for manufacturing a positive electrode for a secondary battery, wherein a drag line is formed from one end in the longitudinal direction of the first flat portion or the second flat portion.

16. In Paragraph 12, The above coating is, A method for manufacturing a positive electrode for a secondary battery, wherein the above-mentioned loading reduction portion is performed to have a longitudinal length of 2 mm to 50 mm.

17. In Paragraph 12, The above suspension is, A method for manufacturing a positive electrode for a secondary battery, wherein the above-mentioned positive electrode unoccupied portion is performed to have a longitudinal length of 5 mm to 20 mm.

18. In Paragraph 12, The above cut is, A method for manufacturing a positive electrode for a secondary battery, wherein the method is performed in a second direction perpendicular to the first direction in a region having an average thickness less than or equal to the average thickness of the loading reduction portion.

19. A positive electrode for a secondary battery manufactured by the manufacturing method according to Paragraph 12.

20. An electrode assembly comprising an anode according to any one of claims 1 to 11 and 19; a separator and a cathode.

21. A secondary battery comprising an electrode assembly according to paragraph 20; a battery case with one side open; and a seal, The above battery case is a secondary battery that further contains an electrolyte.

22. A battery module including a secondary battery according to paragraph 21.

23. A battery pack including a secondary battery according to paragraph 21.

24. A battery pack including a battery module according to paragraph 22.

Images