Electrode assembly, lithium secondary battery including the same, manufacturing method of electrode assembly, and method for managing electrode sliding specifications

Abstract

The electrode assembly according to the present invention includes a negative electrode including a sliding region, and a thickness T of the negative electrode mixture layer at the center of the negative electrode. NC The thickness T of the negative electrode mixture layer at the first facing position where the negative electrode faces the lower end of the positive electrode N1 The ratio of the first negative electrode thickness ratio RT N1 (=T N1 / T NC ), and the thickness T of the positive electrode mixture layer at the center of the positive electrode PC The thickness T of the positive electrode mixture layer at the lower end of the positive electrode P1 The ratio of the first positive electrode thickness ratio RT P1 (=T P1 / T PC ) satisfies the following condition 1 and can effectively prevent the risk of local reversal of the NP ratio in the sliding region. [Condition 1] RT N1 ≧(RT P1 / NP ratio) × 100.1 (In the above condition 1, the NP ratio is a preset value and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0098524, dated August 8, 2022.

[0002] The present invention relates to an electrode assembly for preventing lithium deposition, a lithium secondary battery including the same, a method for manufacturing the electrode assembly, and a method for managing electrode sliding specifications. [Background technology]

[0003] As technological development and demand for mobile devices, automobiles, energy storage devices, and other industrial fields increase, the demand for batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and discharge voltage, have been the subject of much research and are now commercially available and widely used.

[0004] Secondary batteries are classified into cylindrical batteries and prismatic batteries, in which the electrode assembly is housed in a cylindrical or prismatic metal case depending on the shape of the battery case, and pouch batteries, in which the electrode assembly is housed in a pouch-shaped case made of an aluminum laminate sheet.

[0005] The electrode assembly housed in the battery case is a chargeable and dischargeable power generating element having a laminated structure of a positive electrode / separator / negative electrode. Examples of such an electrode assembly include a jelly-roll type electrode assembly in which a separator is interposed between a long sheet-shaped positive electrode and a negative electrode coated with an electrode mixture containing an electrode active material and the electrode is wound up; a stack type electrode assembly in which a number of positive electrodes and negative electrodes punched and notched in predetermined sizes are sequentially stacked with a separator interposed between them; and a stack / fold type electrode assembly in which a bi-cell or full cell in which a predetermined number of positive electrodes, negative electrodes, and a separator interposed between them is wound up.

[0006] The positive and negative electrodes that make up the electrode assembly are manufactured by applying the electrode mixture slurry, which is prepared in the mixing process, to an electrode current collector in a predetermined pattern and thickness through a slot die, followed by drying. However, since the electrode mixture slurry is a fluid, the electrode mixture layer after the application process of the electrode mixture slurry has fluidity, causing the electrode mixture slurry to flow out, a phenomenon known as sliding.

[0007] Fig. 1 shows an electrode sheet in which an electrode mixture is applied to a sheet-like current collector, and Fig. 2 shows a cross-sectional view of the electrode sheet cut along the cutting line (dotted line) in Fig. 1. Referring to these drawings, in the electrode mixture-applied portion 2 where the electrode mixture is applied, the thickness of the electrode mixture layer gradually decreases in the direction toward the electrode mixture-non-applied portion 1 at both side edges in the width direction x of the electrode sheet, forming an inclined surface on the current collector plane. This is called a sliding region S, and such a sliding region can be formed within 30 mm or 20 mm from the boundary line between the electrode mixture-non-applied portion where the electrode mixture is not applied and the electrode mixture-applied portion where the electrode mixture is applied, along the inward direction of the electrode mixture-applied portion.

[0008] 3, the positive electrode 10 and negative electrode 20 constituting the electrode assembly face each other with a separator (not shown) interposed therebetween, and the lengths of the positive electrode sliding region S and the negative electrode sliding region S' may differ from each other, and the inclination shape of the sliding region may be various, such as an upwardly convex shape, a downwardly convex shape, a linear shape, or an S-shape. Even if the inclination shape is the same, the slope may vary. Therefore, depending on the facing position of the positive electrode and negative electrode, there may be a localized imbalance in the NP ratio. This imbalance in the NP ratio can cause lithium to precipitate from the negative electrode, potentially leading to safety hazards such as a short circuit.

[0009] Therefore, technology development is needed to prevent imbalances in the NP ratio during the manufacturing process of positive and negative electrodes. However, conventionally, there have been limitations to managing the NP ratio in each unit process, such as the electrode slurry application process, drying and rolling process, and punching and notching process, due to the cumbersome task of measuring the thickness of the electrode mixture layer in the sliding area and the lack of a standardized method. Therefore, there is a need for technology development for an electrode assembly that prevents localized imbalances in the NP ratio in the sliding area during the electrode manufacturing process, and a method for managing electrode sliding standards to prevent imbalances in the NP ratio. Summary of the Invention [Problem to be solved by the invention]

[0010] The first problem to be solved by the technical idea of ​​the present invention is to provide an electrode assembly that prevents the risk of N / P ratio reversal even when the positive electrode and the negative electrode are in the same facing position as before when at least one of the positive electrode and the negative electrode includes a sliding region, a secondary battery including the same, and a manufacturing method thereof.

[0011] The second problem that the technical concept of the present invention aims to solve is to provide a standardized method for managing sliding specifications to prevent the risk of NP ratio reversal in the manufacturing process of electrodes that include sliding regions. [Means for solving the problem]

[0012] According to one embodiment of the present invention, there is provided an electrode assembly for a lithium secondary battery, in which a positive electrode and a negative electrode face each other with a separator interposed therebetween, and the positive electrode tab and the negative electrode tab protrude in opposite directions. The negative electrode tab includes a negative electrode shoulder line portion where a negative electrode mixture is applied to a negative electrode current collector, and a negative electrode uncoated portion where the negative electrode mixture is not applied. The negative electrode shoulder line portion includes a negative electrode sliding region where the thickness of the negative electrode mixture layer decreases along the protruding direction of the negative electrode tab, forming an inclined surface on the negative electrode current collector plane.NC the thickness T of the negative electrode mixture layer at the first facing position where the negative electrode faces the lower end of the positive electrode N1 The ratio of the first negative electrode thickness ratio RT N1 (=T N1 / T NC ), and the thickness T of the positive electrode mixture layer at the center of the positive electrode PC the thickness T of the positive electrode mixture layer at the lower end of the positive electrode P1 The ratio of the first positive electrode thickness ratio RT P1 (=T P1 / T PC ) can satisfy the following condition 1.

[0013] [Condition 1] RT N1 ≧(RT P1 / NP ratio)×100.1 (In the above condition 1, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0014] In the electrode assembly according to one embodiment, the thickness T of the negative electrode mixture layer at the center of the negative electrode NC the thickness T of the negative electrode mixture layer at the second facing position where the negative electrode faces the upper end of the positive electrode. N2 The second negative electrode thickness ratio RT N2 (=T N2 / T NC ), and the thickness T of the positive electrode mixture layer at the center of the positive electrode PC the thickness T of the positive electrode mixture layer at the upper end of the positive electrode P2 The ratio of the second positive electrode thickness ratio RT P2 (=T P2 / T PC ) can satisfy the following condition 2.

[0015] [Condition 2] RT N2 ≧(RT P2 / NP ratio)×100.1 (In the above condition 2, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0016] In the electrode assembly according to one embodiment, the ratio of the length L1 of the negative electrode shoulder line portion to the length L3 from the first facing position to the end of the negative electrode shoulder line portion may be 0.5 to 0.9.

[0017] In the electrode assembly according to one embodiment, the first positive electrode thickness ratio RT P1 (=T P1 / T PC ) can be between 0.6 and 1.

[0018] In an electrode assembly according to one embodiment, the positive electrode tab of the positive electrode may include a positive electrode shoulder line portion in which a positive electrode mixture is applied on a positive electrode current collector, and a positive electrode uncoated portion in which the positive electrode mixture is not applied. The positive electrode shoulder line portion may include a positive electrode sliding region in which the thickness of the positive electrode mixture layer decreases along a protruding direction of the positive electrode tab and which forms an inclined surface on a plane of the positive electrode current collector.

[0019] According to another embodiment of the present invention, a lithium secondary battery is provided, which may include one or more of the electrode assemblies described above.

[0020] According to another embodiment of the present invention, there is provided a method for manufacturing an electrode assembly, the method comprising the steps of: preparing an electrode sheet including an electrode mix coated portion on an electrode current collector sheet, where an electrode mix is ​​coated, and an electrode mix non-coated portion located on at least one side edge of the electrode mix coated portion and where the electrode mix is ​​not coated; a thickness measuring step of measuring the thickness of the electrode mix layer at each of a plurality of points selected at the boundary between the electrode mix coated portion and the electrode mix non-coated portion, and measuring the thickness of the electrode mix layer at a center of the electrode mix coated portion; a calculation step of calculating a ratio of the thickness of the electrode mix layer at each of the plurality of points to the thickness of the electrode mix layer at the center of the electrode mix coated portion; and a positive electrode / negative electrode notching step of setting planned notching lines for notching the positive electrode sheet and the negative electrode sheet in the form of individual positive electrodes and individual negative electrodes based on the calculated positive electrode thickness ratio and negative electrode thickness ratio values. a notching step of notching along the set planned notching line; and a joining step of joining the notched positive electrode and negative electrode with a separator interposed between them, wherein the setting step of the planned positive electrode / negative electrode notching line includes a step of determining a first planned positive electrode facing line P3 on a positive electrode sheet and a first planned negative electrode facing line P1 on a negative electrode sheet, a step of determining the first planned positive electrode facing line P3 as a planned notching line for a positive electrode lower end portion, and a step of determining a planned notching line for a negative electrode upper end portion based on the first planned negative electrode facing line P1, wherein the first planned negative electrode facing line P1 and the first planned positive electrode facing line P3 are determined such that a negative electrode thickness ratio at the first planned negative electrode facing line P1 and a positive electrode thickness ratio at the first planned positive electrode facing line P3 satisfy the following condition 3.

[0021] [Condition 3] Negative electrode thickness ratio ≥ (positive electrode thickness ratio / NP ratio) x 100.1 (In the above condition 3, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0022] In one embodiment of the manufacturing method for an electrode assembly, the step of setting the planned positive electrode / negative electrode notching line may further include a step of creating a table of combinations of positive electrode thickness ratios and negative electrode thickness ratios that satisfy Condition 3 according to a preset NP ratio value.

[0023] In a method for manufacturing an electrode assembly according to an embodiment, in the step of determining a planned notching line for the upper end portion of the negative electrode, the planned notching line for the upper end portion of the negative electrode may be determined as a virtual line connecting points spaced apart from the first planned negative electrode facing line by a distance G1 on the plane of the positive and negative electrodes along the width direction of the negative electrode sheet.

[0024] In one embodiment of a manufacturing method for an electrode assembly, the step of setting the planned positive / negative notching line may further include a step of determining a second planned positive electrode facing line P4 on the positive electrode sheet and determining a second planned negative electrode facing line P2 on the negative electrode sheet, and the second planned negative electrode facing line P2 and the second planned positive electrode facing line P4 may be determined such that the negative electrode thickness ratio at the second planned negative electrode facing line P2 and the positive electrode thickness ratio at the second planned positive electrode facing line P4 satisfy condition 3.

[0025] In one embodiment of a manufacturing method for an electrode assembly, the second negative electrode facing planned line P2 may be determined as a virtual line connecting points spaced apart from the first negative electrode facing line P1 by a length C in the overall length direction of the positive electrode along the width direction of the negative electrode sheet.

[0026] In the manufacturing method of an electrode assembly according to an embodiment, the step of setting the planned positive electrode / negative electrode notching line may further include a step of determining the second planned positive electrode facing line P4 as a planned notching line for an upper end portion of the positive electrode, and a step of determining, as a planned notching line for a lower end portion of the negative electrode, a virtual line connecting points spaced apart from the planned notching line for an upper end portion of the negative electrode along the width direction of the negative electrode sheet by a length A in the overall length direction of the negative electrode.

[0027] In the manufacturing method of an electrode assembly according to an embodiment, the step of setting the planned positive / negative electrode notching lines may further include the step of determining a planned positive electrode tab notching line and a planned negative electrode tab notching line, and the step of determining the planned positive electrode tab notching line and the planned negative electrode tab notching line may include setting the planned positive electrode tab notching line so that a positive electrode shoulder line portion where a positive electrode mixture is applied is included in the positive electrode tab, and determining the planned negative electrode tab notching line so that a negative electrode shoulder line portion where a negative electrode mixture is applied is included in the negative electrode tab.

[0028] In one embodiment of a manufacturing method for an electrode assembly, the joining step may include joining the positive electrode such that a planned notching line at a lower end of the notched positive electrode is positioned on a first planned facing line of the notched negative electrode.

[0029] In one embodiment of a manufacturing method for an electrode assembly, the joining step may include joining the positive electrode such that a planned notching line at an upper end of the notched positive electrode is positioned on a second planned facing line of the notched negative electrode.

[0030] According to another embodiment of the present invention, there is provided a method for controlling the electrode sliding specification. The method for controlling the electrode sliding specification is a method for controlling the sliding specification of an electrode including a sliding region in which the thickness of the electrode mixture layer gradually decreases and forms an inclined surface with respect to the plane of the current collector, the method comprising: PC and the thickness T of the positive electrode mixture layer at the planned lower end portion of the positive electrode P1 Measure each of the above T PC T for P1 The ratio of the first positive electrode thickness ratio RT P1 (=T P1 / T PC ) calculating a thickness T of the negative electrode mixture layer at the center of the negative electrode on the negative electrode sheet; determining a negative electrode first planned facing line P1 that faces the planned portion of the positive electrode lower end on the negative electrode sheet; NC and the thickness T of the negative electrode mixture layer at the first negative electrode facing planned line P1. N1Measure each of the above T NC The above T N1 The ratio of the first negative electrode thickness ratio RT N1 (=T N1 / T NC ) and the step of calculating the first positive electrode thickness ratio RT P1 and the first negative electrode thickness ratio RT N1 and confirming whether the relationship satisfies the following condition 1:

[0031] [Condition 1] RT N1 ≧(RT P1 / NP ratio)×100.1 (In the above condition 1, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0032] In the method for managing the electrode sliding standard according to one embodiment, the thickness T of the positive electrode mixture layer at the intended upper end portion of the positive electrode is P2 Measure the above T PC The above T P2 The ratio of the second positive electrode thickness ratio RT P2 (=T P2 / T PC ) calculating a thickness T of the negative electrode mixture layer at the second planned negative electrode facing line P2; determining a second planned negative electrode facing line P2 that faces the upper end of the positive electrode in the negative electrode sheet; N2 Measure the above T NC The above T N2 The second negative electrode thickness ratio RT N2 (=T N2 / T NC ) and the second positive electrode thickness ratio RT P2 and the second negative electrode thickness ratio RT N2 and confirming whether the relationship satisfies the following condition 2:

[0033] [Condition 2] RT N2 ≧(RT P2 / NP ratio)×100.1 (In the above condition 2, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0034] In one embodiment of a method for managing electrode sliding standards, in the step of determining the negative electrode first planned facing line, the negative electrode first planned facing line P1 can be determined as a virtual line connecting a point that is spaced apart along the width direction from the boundary line between the negative electrode mixture coated portion and the negative electrode mixture non-coated portion by the length L1 of the negative electrode shoulder line portion and the gap G1 on the plane of the positive electrode and the negative electrode.

[0035] In one embodiment of a method for managing electrode sliding standards, in the step of determining the negative electrode second planned facing line, the negative electrode second planned facing line P2 may be determined as a virtual line connecting points spaced apart from the negative electrode first planned facing line P1 along the width direction by a length C in the overall length direction of the positive electrode. [Effects of the Invention]

[0036] The electrode assembly and the manufacturing method of the electrode assembly according to the exemplary embodiment of the present invention have the effect of preventing the phenomenon of localized NP ratio inversion in the electrode sliding region.

[0037] According to an exemplary embodiment of the present invention, the positive electrode thickness ratio and the negative electrode thickness ratio calculated at a specific facing position where the positive electrode and the negative electrode face each other satisfy a predetermined condition, thereby ensuring prevention of the risk of local NP ratio reversal, and thereby enabling management of the sliding region where the risk of NP ratio reversal exists in a standardized manner. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 1 is a top view of an electrode sheet in which an electrode mixture is applied onto a current collector. [Figure 2] FIG. 2 is a cross-sectional view of the electrode sheet taken along the cutting line (dotted line) in FIG. [Figure 3] FIG. 10 is a conceptual diagram for explaining the concept of the appearance of an imbalance phenomenon of the NP ratio in the electrode sliding region. [Figure 4]1 is a cross-sectional view of an electrode assembly according to an embodiment of the present invention. [Figure 5] 5 is an enlarged cross-sectional view of the electrode assembly of part A in FIG. 4. [Figure 6] FIG. 5 is a top view of part A in FIG. 4. [Figure 7] 5 is an enlarged cross-sectional view of the electrode assembly of part B in FIG. 4. [Figure 8] FIG. 5 is a top view of part B of FIG. 4. [Figure 9] 4 is a flowchart illustrating a method for manufacturing an electrode assembly according to an embodiment of the present invention. [Figure 10] 4 is a flowchart illustrating a method for manufacturing an electrode assembly according to an embodiment of the present invention. [Figure 11] 1 is a view illustrating a method for manufacturing an electrode assembly according to an embodiment of the present invention; [Figure 12] 1 is a flowchart illustrating a method for managing an electrode sliding standard according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be described in detail below. Before that, the terms and words used in the specification and claims are not to be interpreted as being limited to their ordinary or dictionary meanings, but are to be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of the terms in order to best describe his own invention.

[0040] In the present invention, terms such as "comprise" and "have" are intended to specify the presence of a feature, numeral, step, operation, component, part, or combination thereof described in the specification, and may be understood as not excluding the presence or addition of one or more other features, numerals, steps, operations, components, parts, or combinations thereof. Furthermore, when a layer, film, region, plate, or other part is described as being "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part between them. Conversely, when a layer, film, region, plate, or other part is described as being "under" another part, this includes not only the case where it is "directly under" the other part, but also the case where there is another part between them. Furthermore, in this application, being "located on" can include not only the case where it is located on top, but also the case where it is located on bottom.

[0041] In this specification, the NP ratio is a preset value, and refers to the ratio of the negative electrode capacity to the positive electrode capacity per unit area. This can be determined according to the product specifications, and the NP ratio has a value of 100% or more, and the % unit is omitted in Conditions 1 to 3. Specific numerical ranges for the NP ratio can be greater than 100 and less than 200, greater than 100 and less than 180, greater than 100 and less than 160, or 101 to 140.

[0042] In this specification, the sliding region refers to a region around the boundary between an electrode mixture non-coated portion where the electrode mixture (positive electrode mixture layer and negative electrode mixture layer) is not coated and an electrode mixture coated portion where the electrode mixture is coated, where the thickness of the electrode mixture layer is not constant but gradually decreases as it approaches the electrode mixture non-coated portion, forming an inclined surface with respect to the plane of the current collector.

[0043] In this specification, the term "positive electrode upper end" refers to the end of the edge of the positive electrode from which the positive electrode tab protrudes, and the term "negative electrode upper end" refers to the end of the edge of the negative electrode from which the negative electrode tab protrudes.

[0044] In this specification, the term "positive electrode lower end" refers to the end of the positive electrode edge facing the positive electrode edge from which the positive electrode tab protrudes, and the term "negative electrode lower end" refers to the end of the negative electrode edge facing the negative electrode edge from which the negative electrode tab protrudes.

[0045] In this specification, the central part of the negative electrode (positive electrode) is a region excluding the sliding region, and is a broad concept referring to a region of the negative electrode (positive electrode) mixture layer where the negative electrode (positive electrode) mixture layer is parallel to the plane of the current collector and the thickness of the negative electrode (positive electrode) mixture layer is constant and does not refer to only a specific point in the central part of the negative electrode (positive electrode) in the overall length direction x.

[0046] In this specification, the width direction of the electrode sheet and the overall length direction of the electrode are defined as the y-axis direction, the transport direction MD of the electrode sheet and the overall width direction of the electrode are defined as the x-axis direction, and the thickness direction of the electrode and the thickness direction of the electrode assembly are defined as the z-axis direction.

[0047] (First embodiment) The present invention provides an electrode assembly as a first embodiment.

[0048] FIG. 4 is a cross-sectional view of an electrode assembly according to one embodiment of the present invention, FIG. 5 is a cross-sectional view of the electrode assembly enlarging part A of FIG. 4, FIG. 6 is a top view of part A of FIG. 4, FIG. 7 is a cross-sectional view of the electrode assembly enlarging part B of FIG. 4, and FIG. 8 is a top view of part B of FIG. 4.

[0049] 1 and 2, in an electrode assembly 100 for a lithium secondary battery according to one embodiment of the present invention, a positive electrode 110 and a negative electrode 120 face each other with a separator 130 therebetween, and the positive electrode tab 111 and the negative electrode tab 121 protrude in opposite directions. The negative electrode tab 121 includes a negative electrode shoulder line portion 121a in which a negative electrode mixture is applied to a negative electrode current collector 121, and a negative electrode uncoated portion 121b in which the negative electrode mixture is not applied. The negative electrode shoulder line portion 121a includes a negative electrode sliding region S' in which the thickness of a negative electrode mixture layer 122 decreases in the protruding direction of the negative electrode tab 121, forming an inclined surface on the negative electrode current collector plane.

[0050] Generally, electrode assemblies for lithium secondary batteries are controlled to maintain an N / A ratio of 1 or greater to prevent lithium precipitation during charge and discharge, and to prevent rapid battery degradation, especially during high-rate charge and discharge. However, when the positive and negative electrodes include sliding regions, an N / A ratio reversal phenomenon, in which the N / A ratio is locally less than 1, can occur depending on the length of the sliding region, the slope of the sliding (S-shaped or linear), and the slope. In particular, the thickness of the negative electrode mixture layer is relatively small in the negative electrode sliding region, so the risk of N / A ratio reversal can be greater.

[0051] According to one embodiment of the present invention, a negative electrode is manufactured by notching a negative electrode sheet so that the negative electrode shoulder line is included within the negative electrode tab. This means that the negative electrode sliding region is removed during the negative electrode notching. As a result, the length of the sliding region of the negative electrode mixture layer around the negative electrode upper end 120T according to the present invention is shorter than the length of the negative electrode sliding region according to conventional technology, in which notching is performed so that the negative electrode shoulder line does not exist within the negative electrode tab. Therefore, the electrode assembly according to the present invention can reduce the risk of NP ratio reversal due to the shorter length of the negative electrode sliding region. Here, the length of the negative electrode sliding region refers to the length of the negative electrode sliding region extending along the entire length (x-axis direction) of the negative electrode.

[0052] 4, the locations in the electrode assembly 100 where the NP ratio reversal may occur are location A where the positive electrode lower end 110B faces the negative electrode upper end 120T from which the negative electrode tab 121 protrudes, and location B where the positive electrode upper end 110T faces the negative electrode lower end 120B. Of the locations A and B, the NP ratio reversal is more likely to occur in location A where the positive electrode lower end 110B faces the negative electrode upper end 120T.

[0053] 5 and 7, the length of the negative electrode sliding region AS' in the facing region A is longer than the length of the negative electrode sliding region BS' in the facing region B. This is because, when the negative electrode sheet, which serves as the base material for the negative electrode, is notched into an individual negative electrode, the negative electrode shoulder line portion located within the negative electrode tab includes the sliding region as is, but a portion of the sliding region is cut away from the lower end of the negative electrode. Meanwhile, the length of the positive electrode sliding region AS in the facing region A is shorter than the length of the positive electrode sliding region BS in the facing region B. As a result, a negative electrode with a relatively long sliding region faces a positive electrode with a relatively short sliding region in the facing region A, which increases the likelihood of an NP ratio reversal occurring in the facing region A.

[0054] Therefore, the electrode assembly according to one embodiment of the present invention is characterized by being designed to preferentially satisfy the following condition 1 in the facing region A. Specifically, the electrode assembly 100 according to one embodiment has a thickness T of the negative electrode mixture layer at the center of the negative electrode. NC the thickness T of the negative electrode mixture layer at the first facing position where the negative electrode faces the lower end of the positive electrode N1 The ratio of the first negative electrode thickness ratio RT N1 (=T N1 / T NC ), and the thickness T of the positive electrode mixture layer at the center of the positive electrode PC the thickness T of the positive electrode mixture layer at the lower end of the positive electrode P1 The ratio of the first positive electrode thickness ratio RT P1 (=T P1 / T PC ) can satisfy the following condition 1.

[0055] [Condition 1] RT N1 ≧(RT P1 / NP ratio)×100.1 (In the above condition 1, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0056] The positive and negative electrodes face each other with a separator between them, and to prevent the NP ratio from being reversed, the capacity of the negative electrode must be greater than the capacity of the positive electrode facing it. However, since it is practically difficult to measure the capacity of the positive electrode in the positive electrode sliding region and the capacity of the negative electrode in the negative electrode sliding region, it is easy to control the NP ratio by measuring the thickness of the positive electrode mixture layer and the negative electrode mixture layer, respectively, instead of the capacity in the sliding region. This is because the capacity of the electrode is proportional to the thickness of the electrode mixture layer.

[0057] Nevertheless, it is practically impossible to apply to a mass production process a method of controlling the NP ratio by measuring the thickness of the positive electrode mixture layer and the thickness of the negative electrode mixture layer at all locations where the positive electrode and the negative electrode face each other and checking whether the NP ratio is satisfied based on the measured values.

[0058] Therefore, in order to present an electrode assembly model in which NP ratio reversal does not occur, the present invention calculates the values ​​of the first negative electrode thickness ratio and the first positive electrode thickness ratio from the thicknesses of the positive electrode mixture layer and the negative electrode mixture layer measured at specific facing positions, without the need to measure the thickness of the electrode mixture layer at all locations where the positive electrode and negative electrode face each other, and guarantees that an electrode assembly in which these relationships satisfy Condition 1 does not cause NP ratio reversal. The first facing position P1, which is the thickness measurement position for calculating the thickness ratio, is specified as the position facing the lower end portion 110B of the positive electrode in the case of the negative electrode 120, and as the lower end portion 110B of the positive electrode in the case of the positive electrode 110.

[0059] In other words, the electrode assembly according to the present invention is an electrode assembly designed using a thickness ratio at the "first facing position P1" where the positive electrode lower end 110B and the negative electrode 120 face each other, and has the effect of preventing the risk of reversal of the NP ratio.

[0060] In the present invention, the NP ratio is controlled using the thickness ratio rather than the absolute thickness value because the thickness ratio can further ensure prevention of the risk of NP ratio reversal. Although the thickness of the positive electrode mixture layer or the negative electrode mixture layer measured at a specific facing position cannot predict the level of sliding, the positive electrode thickness ratio or the negative electrode thickness ratio at a specific facing position can predict the level of sliding. Therefore, the method of controlling the NP ratio using the thickness ratio can further ensure prevention of the risk of NP ratio reversal.

[0061] In one specific example, the first positive electrode thickness ratio RT P1 (=T P1 / T PC ) may be 0.6 to 1, specifically 0.65 to 0.99, 0.7 to 0.98, 0.75 to 0.95, or 0.8 to 0.95. It is preferable that the sliding region of the lower end 110B of the positive electrode in the facing region A be minimized in order to increase the energy density of the positive electrode, and as a result, the first positive electrode thickness ratio, which is the thickness ratio of the lower end of the positive electrode, falls within the above numerical range.

[0062] 6, in one specific example, the ratio of the length L1 of the negative electrode shoulder line portion 121a to the length L3 from the first facing position P1 to the end of the negative electrode shoulder line portion may be 0.5 to 0.9, specifically 0.65 to 0.8, 0.6 to 0.9, 0.7 to 0.9, or 0.7 to 0.8. In order to prevent reversal of the NP ratio, it is preferable that the length of the negative electrode shoulder line portion is long.

[0063] The electrode assembly 100 according to an embodiment of the present invention has a thickness T NC the thickness T of the negative electrode mixture layer at the second facing position where the negative electrode faces the upper end of the positive electrode. N2 The second negative electrode thickness ratio RT N2 (=T N2 / T NC ), and the thickness T of the positive electrode mixture layer at the center of the positive electrode PC the thickness T of the positive electrode mixture layer at the upper end of the positive electrode P2 The ratio of the second positive electrode thickness ratio RT P2 (=TP2 / T PC ) can satisfy the following condition 2.

[0064] [Condition 2] RT N2 ≧(RT P2 / NP ratio)×100.1 (In the above condition 2, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0065] The above condition 2 can be a condition for ensuring prevention of the risk of reversal of the NP ratio at the facing site B. As described above, the possibility of reversal of the NP ratio at the facing site B is smaller than that at the facing site A, so the above condition 2 can be meaningful as an auxiliary means of NP ratio management.

[0066] 7 and 8, the facing portion B is a portion where the positive electrode upper end portion 110T and the negative electrode lower end portion 120B face each other. The positive electrode tab 111 may include a positive electrode shoulder line portion 111a where the positive electrode mixture layer 112 is applied on the current collector, and a positive electrode uncoated portion 111b where the positive electrode mixture is not applied. The positive electrode shoulder line portion 111a may include a positive electrode sliding region S where the thickness of the positive electrode mixture layer 112 decreases along the protruding direction of the positive electrode tab 111, forming an inclined surface on the plane of the positive electrode current collector.

[0067] (Second embodiment) The present invention provides a method for manufacturing an electrode assembly as a second embodiment.

[0068] 9 and 10 are flowcharts illustrating a method for manufacturing an electrode assembly according to one embodiment of the present invention, and FIG. 11 is a diagram illustrating a method for manufacturing an electrode assembly according to one embodiment of the present invention.

[0069] Referring to FIG. 9, a method of manufacturing an electrode assembly according to an exemplary embodiment of the present invention includes a step (P110) of preparing an electrode sheet including an electrode mixture application portion and an electrode mixture non-application portion, a thickness measurement step (P120) of measuring the thickness of each electrode mixture layer at a plurality of points selected at the boundary between the electrode mixture application portion and the electrode mixture non-application portion, and measuring the thickness of the electrode mixture layer at a center of the electrode mixture application portion, and an electrode thickness ratio calculation step (P120) of calculating the ratio of the thickness of each electrode mixture layer at each of the plurality of points to the thickness of the electrode mixture layer at the center of the electrode mixture application portion. a setting step (P140) of planned positive / negative electrode notching lines for notching the positive electrode sheet and the negative electrode sheet in the form of individual positive electrodes and individual negative electrodes based on the calculated positive electrode thickness ratio value and negative electrode thickness ratio value; a notching step (P150) of notching along the set planned notching lines; and a joining step (P160) of joining the notched positive electrode and negative electrode with a separator interposed between them.

[0070] According to an exemplary embodiment of the present invention, before setting the planned notching lines of the positive and negative electrodes, a plurality of points are selected at the boundary between the electrode mixture coated portion and the electrode mixture non-coated portion, the thicknesses of the electrode mixture layer are measured at the selected plurality of points, and the thickness ratios at the respective plurality of points are calculated. Then, an electrode assembly is designed based on the calculated thickness ratios, thereby preventing a phenomenon in which the NP ratio is locally inverted in the electrode sliding region.

[0071] The electrode sheet preparation step (P110) may be a step of preparing an electrode sheet including an electrode mixture application portion on an electrode collector sheet where an electrode mixture is applied, and an electrode mixture non-application portion located on at least one side edge of the electrode mixture application portion and where the electrode mixture is not applied.

[0072] Specifically, the electrode sheet preparation step (P110) may include a step of preparing a negative electrode sheet and a step of preparing a positive electrode sheet, which may be performed by applying an electrode slurry containing an electrode active material onto a sheet-shaped current collector, followed by drying and rolling.

[0073] 10 , the negative electrode sheet 20 may include a negative electrode mixture coated portion 22 to which the negative electrode mixture is applied, and a negative electrode mixture non-coated portion 21 to which the negative electrode mixture is not applied. The negative electrode mixture non-coated portions 21 may be located on both side edges of the negative electrode mixture coated portion in the width direction (x-axis direction) of the negative electrode sheet. However, this is not limited thereto, and the negative electrode mixture non-coated portion 21 may be located on one side edge of the negative electrode mixture coated portion 22. Similar to the negative electrode sheet 20, the positive electrode sheet 10 also includes a positive electrode mixture coated portion 12 to which the positive electrode mixture is applied, and a positive electrode mixture non-coated portion 11 to which the positive electrode mixture is not applied, and the positive electrode mixture non-coated portion 11 may be located on both side edges of the positive electrode mixture coated portion 12 or on one side edge of the positive electrode mixture coated portion 12.

[0074] The thickness measurement step (P120) may include the steps of selecting a plurality of points on the boundary between the electrode mixture application portion and the non-application portion and measuring the thickness of each electrode mixture layer at the selected points, and measuring the thickness of the electrode mixture layer at the center of the electrode mixture application portion. Here, the boundary between the electrode mixture application portion and the non-application portion may be a region where a sliding region exists.

[0075] The thickness measuring step (P120) can include a step of measuring the thickness of the positive electrode mixture layer on the positive electrode sheet, and a step of measuring the thickness of the negative electrode mixture layer on the negative electrode sheet.

[0076] Specifically, the step of measuring the thickness of the positive electrode mixture layer in the positive electrode sheet may include a step of measuring the thickness of the positive electrode mixture layer in the center of the positive electrode sheet 10, and a step of arbitrarily selecting a plurality of points in a boundary peripheral region between the positive electrode mixture-applied portion 12 and the positive electrode mixture-unapplied portion 11, including a sliding region, in the positive electrode sheet 10, and measuring the thickness of the positive electrode mixture layer at each of the points. In this case, the plurality of points may be selected at regular intervals along the width direction (x-axis direction) of the positive electrode sheet 10.

[0077] Furthermore, the step of measuring the thickness of the negative electrode mixture layer in the negative electrode sheet may include a step of measuring the thickness of the negative electrode mixture layer in the center of the negative electrode sheet 20, and a step of arbitrarily selecting a plurality of points in a boundary peripheral region between the negative electrode mixture coated portion 22 and the negative electrode mixture non-coated portion 21, including the sliding region, in the negative electrode sheet 20, and measuring the thickness of the negative electrode mixture layer at each of the points. In this case, the plurality of points may be selected at regular intervals along the width direction (x-axis direction) of the negative electrode sheet 20.

[0078] The thickness measurement step (P120) is followed by the thickness ratio calculation step (P130). The thickness ratio calculation step may include a positive electrode thickness ratio calculation step and a negative electrode thickness ratio calculation step.

[0079] The positive electrode thickness ratio is the thickness T PC The negative electrode thickness ratio can be defined as the ratio of the thickness T of the positive electrode mixture layer at each of the plurality of points to the thickness T of the negative electrode mixture layer at the center of the negative electrode mixture application area. NC The thickness ratio of each of the negative electrode mixture layers at the plurality of points can be defined as the ratio of the thickness of each of the negative electrode mixture layers at the plurality of points to the thickness of each of the positive electrode mixture layers at the plurality of points. Therefore, the thickness ratio calculation step (P130) can calculate the thickness ratio of each of the positive electrode mixture layers at the plurality of points and the thickness ratio of each of the negative electrode mixture layers at the plurality of points.

[0080] The step (P140) of setting the planned positive / negative electrode notching lines may be a step of setting planned positive electrode notching lines in the form of individual positive electrodes 110 on the positive electrode sheet 10, and setting planned negative electrode notching lines in the form of individual negative electrodes 120 on the negative electrode sheet 20, based on the positive electrode thickness ratio and negative electrode thickness ratio calculated in the electrode thickness ratio calculation step (P130).

[0081] The step of setting the planned positive / negative notching line occurs before the positive electrode, negative electrode, and separator are joined, and therefore it is not yet determined which portion of the positive electrode sheet will face which portion of the negative electrode sheet, and in this state it is unclear whether the relationship between the negative electrode thickness ratio and the positive electrode thickness ratio satisfies Condition 3. Therefore, the step (P140) of setting the planned positive / negative notching line may include steps of determining the portion of the positive electrode sheet that will face the negative electrode, and determining the portion of the negative electrode sheet that will face the positive electrode.

[0082] 4 to 5 and 11, with respect to the x-axis direction, the upper part of the positive electrode sheet 10 may be notched as the positive electrode lower end part 110B, and the lower part of the positive electrode sheet 10 may be notched as the positive electrode tab 111 and the positive electrode upper end part 110T. The positive electrode lower end part 110B and the positive electrode upper end part 110T may be specific facing positions of the positive electrode according to the present invention. That is, the positive electrode lower end planned line may be the positive electrode first facing planned line P3, and the positive electrode upper end planned line may be the positive electrode second facing planned line P4.

[0083] Here, the positive electrode upper end refers to the end of the edge of the positive electrode from which the positive electrode tab protrudes, and the positive electrode lower end refers to the end of the edge of the positive electrode facing the positive electrode edge from which the positive electrode tab protrudes.

[0084] According to the present invention, the electrode assembly may be designed such that each positive electrode thickness ratio on the first planned positive electrode facing line P3 and the second planned positive electrode facing line P4 satisfies Condition 3. That is, among the multiple positive electrode thickness ratio values ​​calculated in the thickness ratio calculation step (P130), a point having a positive electrode thickness ratio that satisfies Condition 3 may be located on the first planned positive electrode facing line P3 and the second planned positive electrode facing line P4.

[0085] 6 to 7 and 11, the negative electrode 120 is generally cut to be larger than the positive electrode 110, so that when the positive electrode 110 is placed on top of the negative electrode 120, a portion of the negative electrode 120 is visible from the outer periphery of the positive electrode 110. Based on the x-axis direction, the upper portion of the negative electrode sheet 20 may be notched as the negative electrode tab 121 and the negative electrode upper end portion 120T, and the lower portion of the negative electrode sheet 20 may be notched as the negative electrode lower end portion 120B. A first planned negative electrode facing line P1 may be set on the upper portion of the negative electrode sheet 20, and a second planned negative electrode facing line P2 may be set on the lower portion of the negative electrode sheet 20.

[0086] Here, the negative electrode upper end refers to the end of the negative electrode edge from which the negative electrode tab protrudes, and the negative electrode lower end refers to the end of the negative electrode edge opposite to the negative electrode edge from which the negative electrode tab protrudes.

[0087] According to the present invention, an electrode assembly may be designed such that each negative electrode thickness ratio on the first planned negative electrode facing line P1 and the second planned negative electrode facing line P2 satisfies Condition 3. That is, among the plurality of negative electrode thickness ratio values ​​calculated in the thickness ratio calculation step (P130), a point having a negative electrode thickness ratio that satisfies Condition 3 may be located on the first planned negative electrode facing line P1 and the second planned negative electrode facing line P2.

[0088] In the electrode assembly 100 assembled through the bonding step (P160), the negative electrode first planned facing line P1 and the positive electrode first planned facing line P3 may overlap with each other based on the horizontal direction xy of the electrode assembly, and the negative electrode second planned facing line P2 and the positive electrode second planned facing line P4 may overlap with each other based on the horizontal direction xy of the electrode assembly.

[0089] 10 and 11 , the positive / negative electrode planned notching line setting step (P140) according to one embodiment may include the steps of: determining a positive electrode first planned facing line P3 on the positive electrode sheet 10 and determining a negative electrode first planned facing line P1 on the negative electrode sheet 20 (P141); determining the positive electrode first planned facing line P3 as a planned notching line for a positive electrode lower end portion (P142); and determining a planned notching line for a negative electrode upper end portion based on the negative electrode first planned facing line P1 (P143). In this case, the negative electrode first planned facing line P1 and the positive electrode first planned facing line P3 may be determined such that the negative electrode thickness ratio at the negative electrode first planned facing line P1 and the positive electrode thickness ratio at the positive electrode first planned facing line P3 satisfy the following condition 3.

[0090] [Condition 3] Negative electrode thickness ratio ≥ (positive electrode thickness ratio / NP ratio) x 100.1 (In the above condition 3, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0091] That is, among a plurality of negative electrode thickness ratio values, a point having a negative electrode thickness ratio that satisfies the above-mentioned condition 3 can be determined as the negative electrode first facing planned line P1, and among a plurality of positive electrode thickness ratio values, a point having a positive electrode thickness ratio that satisfies the above-mentioned condition 3 can be determined as the positive electrode first facing planned line P3.

[0092] Condition 3 above is a criterion for ensuring prevention of reversal of the NP ratio of the positive electrode / negative electrode in the sliding region, and a method for manufacturing an electrode assembly according to an embodiment of the present invention can ensure prevention of reversal of the NP ratio by setting planned positive electrode / negative electrode notching lines and joining the positive electrode / negative electrode based on a specific facing position that satisfies condition 3. Furthermore, an electrode assembly manufactured in this manner can ensure prevention of reversal of the NP ratio at region A where the positive electrode lower end portion 110B faces the negative electrode upper end portion 120T from which the negative electrode tab 121 protrudes.

[0093] According to one embodiment of the present invention, the step (P140) of setting the planned positive / negative notching lines may further include a step of creating a table of combinations of positive electrode thickness ratios and negative electrode thickness ratios that satisfy Condition 3 according to a preset NP ratio value. In this case, there is an effect that the planned positive electrode first opposing line, planned positive electrode second opposing line, planned negative electrode first opposing line, and planned negative electrode second opposing line that satisfy Condition 3 can be easily determined.

[0094] For example, when the NP ratio is set to 108, combinations of positive electrode thickness ratios and negative electrode thickness ratios that satisfy Condition 3 above can be generated as shown in Table 1. Then, based on the combinations in Table 1, the positive electrode first planned opposing line P3, the positive electrode second planned opposing line P4, the negative electrode first planned opposing line P1, and the negative electrode second planned opposing line P2 that serve as references for the planned notching line can be determined.

[0095] [Table 1]

[0096] 11, the planned notching line (dotted line 120) of the negative electrode in the negative electrode sheet 20 may be set larger than the size of the positive electrode (dotted line 110) to be notched. The planned notching line of the negative electrode tab may be located on one side of the negative electrode mixture application portion 22. The planned notching line of the negative electrode may be determined based on the length L1 of the negative electrode shoulder line portion, the length A of the negative electrode in the overall length direction (x-axis direction), and the length W1 of the negative electrode in the overall width direction (y-axis direction).

[0097] In one embodiment, the length A of the negative electrode in the overall length direction and the length W1 of the negative electrode in the width direction may be preset lengths, and in determining the length L1 of the negative electrode shoulder line portion 121a included in the negative electrode tab 121 region, the length L1 of the negative electrode shoulder line portion may be determined naturally based on the negative electrode first planned facing line P1 that satisfies the above condition 3. Here, the length of the negative electrode shoulder line portion may be defined as the length in the extension direction of the negative electrode shoulder line portion 121a to which the negative electrode mixture is applied, in the negative electrode tab planned region.

[0098] Referring to FIG. 11, in the step (P143) of determining the planned notching line of the upper end portion of the negative electrode, the planned notching line of the upper end portion of the negative electrode may be determined as a virtual line connecting points spaced apart by a distance G1 on the plane of the positive and negative electrodes along the width direction (x-axis direction) of the negative electrode sheet from the first planned negative electrode facing line P1.

[0099] 10 and 11, the planned notching line 110 of the positive electrode in the positive electrode sheet 10 may be set to be smaller than the size of the negative electrode 120 to be notched. The planned notching line of the positive electrode may be set so that a positive electrode tab 111 is formed on one side of the positive electrode mixture application portion 12. The planned notching line of the positive electrode may be determined based on the length L2 of the positive electrode shoulder line portion, the length C of the positive electrode in the overall length direction (x-axis direction), and the length W2 of the positive electrode in the overall width direction (y-axis direction).

[0100] In one embodiment, the overall length C of the positive electrode and the overall width length W2 of the positive electrode may be preset lengths, and in determining the length L2 of the positive electrode shoulder line portion 111a included in the positive electrode tab region, the length L2 of the positive electrode shoulder line portion may be naturally determined based on the positive electrode second facing planned line P4 that satisfies the above condition 3.

[0101] According to one embodiment, the step (P140) of setting the planned positive / negative notching line may further include a step (P144) of determining a second planned positive electrode facing line P4 on the positive electrode sheet and determining a second planned negative electrode facing line P2 on the negative electrode sheet. In this case, the second planned negative electrode facing line P2 and the second planned positive electrode facing line P4 may be determined such that the negative electrode thickness ratio at the second planned negative electrode facing line P2 and the positive electrode thickness ratio at the second planned positive electrode facing line P4 satisfy Condition 3.

[0102] The electrode assembly manufactured in this manner can ensure that the NP ratio is prevented from reversing at the portion B where the upper end portion 110T of the positive electrode and the lower end portion 120B of the negative electrode face each other. However, as described above, the possibility of the NP ratio reversal occurring is higher at the above-mentioned facing portion B than at the facing portion B, so the step (P144) of determining the second planned facing line P2 can serve as a supplement to the step of determining the first planned facing line P1.

[0103] Referring to FIG. 11, the second negative electrode facing planned line P2 may be determined as a virtual line connecting points spaced apart from the first negative electrode facing line P1 by a length C in the overall length direction of the positive electrode along the width direction of the negative electrode sheet.

[0104] In one embodiment, the step (P140) of setting the planned positive electrode / negative electrode notching lines may further include a step (P145) of determining a planned notching line for the upper end of the positive electrode, and a step (P146) of determining a planned notching line for the lower end of the negative electrode.

[0105] Referring to FIG. 11, the planned notching line at the upper end of the positive electrode may be determined as the planned second facing positive electrode line P4, and the planned notching line at the lower end of the negative electrode may be determined as an imaginary line connecting points spaced apart from the planned notching line at the upper end of the negative electrode by a length A in the overall length direction of the negative electrode along the width direction of the negative electrode sheet.

[0106] In one embodiment, the step of setting the planned positive / negative electrode notching lines may further include a step (P147) of determining a planned positive electrode tab notching line and a planned negative electrode tab notching line. Referring to Fig. 11, the step of determining the planned positive electrode tab notching line and the planned negative electrode tab notching line may include setting the planned positive electrode tab notching line so that the positive electrode tab 111 includes a positive electrode shoulder line portion 111a where the positive electrode mixture is applied, and setting the planned negative electrode tab notching line so that the negative electrode tab 121 includes a negative electrode shoulder line portion 121a where the negative electrode mixture is applied.

[0107] Specifically, the shoulder line portion 121a of the negative electrode tab 121 extends from an imaginary line connecting points spaced apart from the first planned negative electrode facing line P1 by a predetermined distance G1 on the positive and negative electrode planes toward the negative electrode tab uncoated portion 121b, and may be included in an inner region of the negative electrode tab 121. The boundary line between the negative electrode shoulder line portion 121a and the negative electrode uncoated portion 121b may coincide with the boundary line between the negative electrode mixture coated portion 22 and the negative electrode mixture uncoated portion 21 of the negative electrode sheet 20, which is the base material of the negative electrode 120.

[0108] The shoulder line portion 111a of the positive electrode tab 111 extends from the second planned positive electrode facing line P4 toward the positive electrode tab uncoated portion 111b and may be included in the inner region of the positive electrode tab 111. The boundary line between the positive electrode shoulder line portion 111a and the positive electrode uncoated portion 111b may coincide with the boundary line between the positive electrode mixture coated portion 12 and the positive electrode mixture uncoated portion 11 of the positive electrode sheet 10 that serves as the base material of the positive electrode 110.

[0109] The notching process (P150) may include a positive electrode notching process in which the positive electrode sheet 10 is notched along the planned positive electrode notching line set by the process described above to obtain individual positive electrodes 110, and a negative electrode notching process in which the negative electrode sheet 20 is notched along the planned negative electrode notching line set by the process described above to obtain individual negative electrodes 120.

[0110] The bonding step (P160) may be a step of bonding the notched positive electrode and the negative electrode with a separator interposed therebetween.

[0111] The joining step (P160) may include joining the notched positive electrode 110 so that the planned notching line of the lower end of the notched positive electrode 110 is positioned on the first planned facing line P1 of the notched negative electrode 120.

[0112] The bonding step (P160) may include bonding the positive electrode 110 so that the planned notching line at the upper end of the positive electrode 110 is positioned on the second planned facing line P2 of the notching negative electrode 120.

[0113] The manufacturing method of the electrode assembly according to the exemplary embodiment of the present invention can control the electrode sliding specification in a standardized manner using a specific facing position and electrode thickness ratio of the positive electrode / negative electrode in the electrode sheet including the sliding region. Also, the reversal control of the NP ratio of the electrode sliding region can be more simply performed, thereby improving production efficiency.

[0114] (Third embodiment) The present invention provides a lithium secondary battery as a third embodiment.

[0115] A lithium secondary battery according to an exemplary embodiment of the present invention may include one of the electrode assemblies or a stack of a plurality of the electrode assemblies.

[0116] According to one embodiment, the electrode assembly is an electrode assembly for a lithium secondary battery in which a positive electrode and a negative electrode face each other with a separator interposed therebetween, and the protruding direction of the positive electrode tab and the protruding direction of the negative electrode tab are opposite to each other. The negative electrode tab includes a negative electrode shoulder line portion in which a negative electrode mixture is applied on a negative electrode current collector, and a negative electrode uncoated portion in which the negative electrode mixture is not applied. The negative electrode shoulder line portion includes a negative electrode sliding region that forms an inclined surface on the negative electrode current collector plane as the thickness of the negative electrode mixture layer decreases along the protruding direction of the negative electrode tab. NC the thickness T of the negative electrode mixture layer at the first facing position where the negative electrode faces the lower end of the positive electrode N1 The ratio of the first negative electrode thickness ratio RT N1 (=T N1 / T NC ), and the thickness T of the positive electrode mixture layer at the center of the positive electrode PC the thickness T of the positive electrode mixture layer at the lower end of the positive electrode P1 The ratio of the first positive electrode thickness ratio RT P1 (=T P1 / T PC ) can satisfy the following condition 1.

[0117] [Condition 1] RT N1 ≧(RTP1 / NP ratio)×100.1 (In the above condition 1, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0118] (Fourth embodiment) The present invention provides a method for managing electrode sliding specifications as a fourth embodiment.

[0119] FIG. 12 is a flowchart illustrating a method for managing an electrode sliding standard according to an embodiment of the present invention.

[0120] Referring to FIG. 12 , the method for controlling the electrode sliding specification according to the exemplary embodiment of the present invention is a method for controlling the sliding specification of an electrode including a sliding region in which the thickness of the electrode mixture layer gradually decreases to form an inclined surface with respect to the current collector plane, and the thickness T PC and the thickness T of the positive electrode mixture layer at the planned lower end portion of the positive electrode P1 Measure each of the above T PC T for P1 The ratio of the first positive electrode thickness ratio RT P1 (=T P1 / T PC ), a step (P220) of determining a negative electrode first facing planned line P1 that faces the planned portion of the positive electrode lower end portion of the negative electrode sheet, and a step (P230) of calculating a thickness T of the negative electrode mixture layer at the center of the negative electrode of the negative electrode sheet. NC and the thickness T of the negative electrode mixture layer at the first negative electrode facing planned line P1. N1 Measure each of the above T NC The above T N1 The ratio of the first negative electrode thickness ratio RT N1 (=T N1 / T NC ) and the step (P230) of calculating the first positive electrode thickness ratio RT P1 and the first negative electrode thickness ratio RT N1 and a step (P240) of checking whether the relationship satisfies the following condition 1.

[0121] [Condition 1] RT N1 ≧(RT P1 / NP ratio)×100.1 (In the above condition 1, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0122] In one embodiment, the electrode sliding standard control method is to measure the thickness T P2 Measure the above T PC The above T P2 The ratio of the second positive electrode thickness ratio RT P2 (=T P2 / T PC ) calculating a thickness T of the negative electrode mixture layer at the second planned negative electrode facing line P2; determining a second planned negative electrode facing line P2 that faces the upper end of the positive electrode in the negative electrode sheet; N2 Measure the above T NC The above T N2 The second negative electrode thickness ratio RT N2 (=T N2 / T NC ) and the second positive electrode thickness ratio RT P2 and the second negative electrode thickness ratio RT N2 and confirming whether the relationship satisfies the following condition 2:

[0123] [Condition 2] RT N2 ≧(RT P2 / NP ratio)×100.1 (In the above condition 2, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.)

[0124] Referring to FIG. 11 , in a step of determining a negative electrode first planned facing line according to one embodiment, the negative electrode first planned facing line P1 can be determined as a virtual line connecting a point that is spaced apart along the width direction from the boundary line between the negative electrode mixture coated portion and the negative electrode mixture non-coated portion by the length L1 of the negative electrode shoulder line portion and the gap G1 on the plane between the positive electrode and the negative electrode.

[0125] In addition, in the step of determining the negative electrode second planned facing line according to one embodiment, the negative electrode second planned facing line P2 can be determined as a virtual line connecting points spaced apart from the negative electrode first planned facing line P1 along the width direction by a length C in the overall length direction of the positive electrode.

[0126] A method for controlling electrode sliding specifications according to an exemplary embodiment of the present invention can control electrode sliding specifications in a standardized manner using specific facing positions of positive and negative electrodes and electrode thickness ratios in an electrode sheet including a sliding region.

[0127] Hereinafter, the present invention will be described with reference to examples, but these are for easier understanding of the present invention and are not intended to limit the scope of the present invention.

[0128] Example 1 A negative electrode slurry containing artificial graphite, SBR (styrene butadiene) binder, CMC (carboxymethyl cellulose) thickener, and carbon black was applied to copper foil, dried, and rolled to prepare a negative electrode sheet. 0.8 Co 0.1 Mn 0.1 A positive electrode slurry containing O2, PVDF (polyvinylidene fluoride) binder, and carbon black is applied to an aluminum foil, which is then dried and rolled to prepare a positive electrode sheet.

[0129] The overall length of the positive electrode, the overall width of the positive electrode, the overall length of the negative electrode, the overall width of the negative electrode, and the distance G1 on the plane between the upper end of the negative electrode and the lower end of the positive electrode are set so that the NP ratio of the electrode assembly to be assembled is 108.

[0130] In the prepared negative electrode sheet, a plurality of measurement positions were arbitrarily selected at the boundary between the negative electrode mixture coated portion and the negative electrode mixture uncoated portion, and the thickness of each negative electrode mixture layer was measured at the selected plurality of positions. The thickness of the negative electrode mixture layer at the center of the negative electrode mixture coated portion was also measured. Thereafter, the value of the negative electrode thickness ratio, which is the ratio of the thickness of the negative electrode mixture layer measured at each of the plurality of positions to the thickness of the negative electrode mixture layer at the center of the negative electrode, was calculated.

[0131] For the prepared positive electrode sheet, the thickness of the positive electrode mixture layer was measured in the same manner as for the negative electrode sheet, and the value of the positive electrode thickness ratio was calculated.

[0132] A first negative electrode facing planned line P1 was determined on the negative electrode sheet with a negative electrode thickness ratio of 0.94, a first positive electrode facing planned line P3 was determined on the positive electrode sheet with a positive electrode thickness ratio of 0.99, a second negative electrode facing planned line P2 was determined on the negative electrode sheet with a negative electrode thickness ratio of 0.96, and a second positive electrode facing planned line P4 was determined on the positive electrode sheet with a positive electrode thickness ratio of 0.94.

[0133] An imaginary line connecting points spaced apart from the negative electrode first planned opposing line P1 by a predetermined distance G1 on the plane of the positive electrode and negative electrode was determined as the planned notching line for the negative electrode upper end. An imaginary line connecting points spaced apart from the negative electrode upper end planned notching line by a predetermined length A in the overall length direction of the negative electrode was determined as the planned notching line for the negative electrode lower end. The positive electrode first planned opposing line P3 was determined as the planned notching line for the positive electrode lower end, and the positive electrode second planned opposing line P4 was determined as the planned notching line for the positive electrode upper end.

[0134] The positive and negative electrodes were notched along the thus-set planned notching lines, and the positive electrodes were joined such that the planned notching line of the lower end of the notched positive electrode was positioned on the first planned negative electrode facing line P1 of the notched negative electrode, and the planned notching line of the upper end of the notched positive electrode 110 was positioned on the second planned negative electrode facing line P2 of the notched negative electrode, thereby completing the manufacture of the electrode assembly.

[0135] <Example 2> In Example 1, when determining the first and second planned negative electrode facing lines and the first and second planned positive electrode facing lines, the first planned negative electrode facing line P1 was determined in the negative electrode sheet with a negative electrode thickness ratio of 0.89, and the first planned positive electrode facing line P3 was determined in the positive electrode sheet with a positive electrode thickness ratio of 0.94. The second planned negative electrode facing line P2 was determined in the negative electrode sheet with a negative electrode thickness ratio of 0.93, and the second planned positive electrode facing line P4 was determined in the positive electrode sheet with a positive electrode thickness ratio of 0.90. Except for this, an electrode assembly was manufactured in the same manner as in Example 1.

[0136] <Comparative Example 1> In Example 1, when determining the first and second planned negative electrode facing lines and the first and second planned positive electrode facing lines, the first planned negative electrode facing line P1 was determined in the negative electrode sheet with a negative electrode thickness ratio of 0.90, and the first planned positive electrode facing line P3 was determined in the positive electrode sheet with a positive electrode thickness ratio of 0.99. Then, the second planned negative electrode facing line P2 was determined in the negative electrode sheet with a negative electrode thickness ratio of 0.85, and the second planned positive electrode facing line P4 was determined in the positive electrode sheet with a positive electrode thickness ratio of 0.94. Except for this, an electrode assembly was manufactured in the same manner as in Example 1.

[0137] <Comparative Example 2> In Example 1, when determining the first and second planned negative electrode facing lines and the first and second planned positive electrode facing lines, the first planned negative electrode facing line P1 was determined in the negative electrode sheet with a negative electrode thickness ratio of 0.80, and the first planned positive electrode facing line P3 was determined in the positive electrode sheet with a positive electrode thickness ratio of 0.94. Then, the second planned negative electrode facing line P2 was determined in the negative electrode sheet with a negative electrode thickness ratio of 0.82, and the second planned positive electrode facing line P4 was determined in the positive electrode sheet with a positive electrode thickness ratio of 0.90. Except for this, an electrode assembly was manufactured in the same manner as in Example 1.

[0138] <Experimental example: Observation of lithium deposition> Each electrode assembly of the above examples and comparative examples was housed in a pouch-type battery case made of a PP (polypropylene) / Al / nylon laminate sheet, and an electrolyte solution was injected and sealed, followed by an activation process to manufacture a secondary battery.

[0139] The produced secondary battery was subjected to 200 charge / discharge cycles, and then the battery was disassembled to visually check whether or not lithium had precipitated from the negative electrode, and the results are shown in Table 1. In Table 1, conditions 1, 2, and 3 are as described above, and "◯" means that the condition was met or lithium precipitated, and "×" means that the condition was not met or lithium did not precipitate.

[0140] [Table 2]

[0141] As described above, the electrode assembly manufactured by the method according to the embodiment of the present invention satisfied conditions 1, 2, and 3, and no lithium deposition occurred in the negative electrode after 200 charge-discharge cycles. On the other hand, lithium deposition was observed in the secondary battery including the electrode assembly of the comparative example after 200 charge-discharge cycles.

[0142] As described above, according to the present invention, a facing position having a positive electrode / negative electrode thickness ratio that satisfies the above conditions 1 to 3 is identified, and the planned notching line is set based on that position. Therefore, it is possible to easily prevent a local reversal of the NP ratio without changing the preset positive electrode / negative electrode spacing. [Explanation of symbols]

[0143] 10: Positive electrode sheet 11: Positive electrode mixture non-coated area 12: Positive electrode mixture coating section 20: Negative electrode sheet 21: Negative electrode mixture non-coated area 22: Negative electrode mixture coating section 100: Electrode assembly 110: Positive electrode, positive electrode notching planned line 120: Negative electrode, negative electrode notching planned line 111: Positive electrode tab 121: Negative electrode tab 111a: Positive electrode shoulder line part 111b: Positive electrode plain area 121a: Negative electrode shoulder line part 121b: negative electrode uncoated portion P1: Negative electrode first facing planned line P2: Negative electrode second facing planned line P3: Positive electrode first facing planned line P4: Positive electrode second facing planned line

Claims

1. An electrode assembly for a lithium secondary battery in which a positive electrode and a negative electrode face each other with a separator interposed therebetween, and the protruding directions of the positive electrode tab and the negative electrode tab are opposite to each other, The negative electrode tab includes a negative electrode shoulder line portion in which a negative electrode mixture is applied on a negative electrode current collector, and a negative electrode uncoated portion in which the negative electrode mixture is not applied, the negative electrode shoulder line portion includes a negative electrode sliding region in which a thickness of the negative electrode mixture layer decreases along a protruding direction of the negative electrode tab, forming an inclined surface on a plane of the negative electrode current collector; Thickness T of the negative electrode mixture layer at the center of the negative electrode ＮＣ the thickness T of the negative electrode mixture layer at the first facing position where the negative electrode faces the lower end of the positive electrode Ｎ１ The first negative electrode thickness ratio RT Ｎ１ (=T Ｎ１ / T ＮＣ ), and the thickness T of the positive electrode mixture layer at the center of the positive electrode ＰＣ the thickness T of the positive electrode mixture layer at the lower end of the positive electrode Ｐ１ The first positive electrode thickness ratio RT Ｐ１ (=T Ｐ１ / T ＰＣ ) satisfies the following condition 1, [Condition 1] RT Ｎ１ ≧(RT) Ｐ１ / NP ratio) × 100.1 In the condition 1, the NP ratio is a preset value and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area, An electrode assembly in which no other layer is formed on the surface of either the negative electrode mixture layer or the positive electrode mixture layer.

2. The thickness T of the negative electrode mixture layer at the center of the negative electrode ＮＣ the thickness T of the negative electrode mixture layer at the second facing position where the negative electrode faces the upper end of the positive electrode Ｎ２ The second negative electrode thickness ratio RT Ｎ２ (=T Ｎ２ / T ＮＣ ), and the thickness T of the positive electrode mixture layer at the center of the positive electrode ＰＣ the thickness T of the positive electrode mixture layer at the upper end of the positive electrode Ｐ２ The second positive electrode thickness ratio RT Ｐ２ (=T Ｐ２ / T ＰＣ ) satisfies the following condition 2, [Condition 2] RT Ｎ２ ≧(RT) Ｐ２ / NP ratio) × 100.1 2. The electrode assembly of claim 1, wherein in condition 2, the NP ratio is a preset value and means a ratio of a negative electrode capacity to a positive electrode capacity per unit area.

3. 2. The electrode assembly of claim 1, wherein a ratio of a length L1 of the negative electrode shoulder line portion to a length L3 from the first facing position to an end of the negative electrode shoulder line portion is 0.5 to 0.

9.

4. The first positive electrode thickness ratio RT Ｐ１ (=T Ｐ１ / T ＰＣ 2. The electrode assembly according to claim 1, wherein ρ is 0.6 to 1.

5. the positive electrode tab of the positive electrode includes a positive electrode shoulder line portion in which a positive electrode mixture is applied on a positive electrode current collector, and a positive electrode uncoated portion in which the positive electrode mixture is not applied, 3. The electrode assembly of claim 2, wherein the positive electrode shoulder line portion includes a positive electrode sliding region in which the thickness of the positive electrode mixture layer decreases along a protruding direction of the positive electrode tab and in which an inclined surface is formed on a plane of the positive electrode current collector.

6. A lithium secondary battery comprising one or more electrode assemblies according to claim 1.

7. preparing an electrode sheet including an electrode mixture-applied portion on an electrode current collector sheet where an electrode mixture is applied, and an electrode mixture-unapplied portion located on at least one side edge of the electrode mixture-applied portion and where the electrode mixture is not applied; a thickness measuring step of measuring the thickness of the electrode mixture layer at each of a plurality of points selected at the boundary between the electrode mixture applied portion and the electrode mixture non-applied portion, and measuring the thickness of the electrode mixture layer at a center of the electrode mixture applied portion; a calculating step of calculating a ratio of the thickness of the electrode mixture layer at each of the plurality of points to the thickness of the electrode mixture layer at a center of the electrode mixture application portion; a planned notching line setting step of setting planned notching lines for notching the positive electrode sheet and the negative electrode sheet in the form of individual positive electrodes and individual negative electrodes based on the calculated positive electrode thickness ratio value and negative electrode thickness ratio value; a notching step of notching along a set notching planned line; a bonding step of bonding the notched positive electrode and the negative electrode with a separator interposed between them, The notching planned line setting step includes: determining a positive electrode first planned opposing line P3 on the positive electrode sheet and a negative electrode first planned opposing line P1 on the negative electrode sheet; determining the positive electrode first opposing planned line P3 as a planned notching line of a lower end portion of the positive electrode; determining a planned notching line at an upper end portion of the negative electrode based on the first planned negative electrode facing line P1; the negative electrode first planned opposing line P1 and the positive electrode first planned opposing line P3 are determined such that the negative electrode thickness ratio at the negative electrode first planned opposing line P1 and the positive electrode thickness ratio at the positive electrode first planned opposing line P3 satisfy the following condition 3, [Condition 3] Negative electrode thickness ratio ≧ (positive electrode thickness ratio / NP ratio) × 100.1 In the condition 3, the NP ratio is a preset value and means a ratio of the negative electrode capacity to the positive electrode capacity per unit area.

8. 8. The method for manufacturing an electrode assembly according to claim 7, wherein the planned notching line setting step further includes a step of creating a table of combinations of positive electrode thickness ratios and negative electrode thickness ratios that satisfy Condition 3 according to a preset NP ratio value.

9. 8. The method for manufacturing an electrode assembly according to claim 7, wherein in the step of determining the planned notching line of the upper end portion of the negative electrode, the planned notching line of the upper end portion of the negative electrode is determined as a virtual line connecting points spaced apart from the first planned negative electrode facing line by a distance G1 on the plane of the positive electrode and the negative electrode along the width direction of the negative electrode sheet.

10. the planned notching line setting step further includes a step of determining a second planned positive electrode facing line P4 on the positive electrode sheet and a step of determining a second planned negative electrode facing line P2 on the negative electrode sheet, 8. The method for manufacturing an electrode assembly according to claim 7, wherein the negative electrode second planned facing line P2 and the positive electrode second planned facing line P4 are determined such that the negative electrode thickness ratio at the negative electrode second planned facing line P2 and the positive electrode thickness ratio at the positive electrode second planned facing line P4 satisfy condition 3.

11. 11. The method of manufacturing an electrode assembly according to claim 10, wherein the second negative electrode facing planned line (P2) is determined as a virtual line connecting points spaced apart from the first negative electrode facing planned line (P1) by a length (C) in the overall length direction of the positive electrode along the width direction of the negative electrode sheet.

12. The notching planned line setting step includes: determining the positive electrode second opposing planned line P4 as a planned notching line at an upper end portion of the positive electrode; determining, as a planned notching line for a lower end of the negative electrode, a virtual line connecting points spaced a distance A in the overall length direction of the negative electrode from the planned notching line for the upper end of the negative electrode along the width direction of the negative electrode sheet.

13. the planned notching line setting step further includes a step of determining a planned positive electrode tab notching line and a planned negative electrode tab notching line, 8. The method for manufacturing an electrode assembly according to claim 7, wherein in the step of determining the planned positive electrode tab notching line and the planned negative electrode tab notching line, the planned positive electrode tab notching line is set so that a positive electrode shoulder line portion where the positive electrode material mixture is applied is included in the positive electrode tab, and the planned negative electrode tab notching line is set so that a negative electrode shoulder line portion where the negative electrode material mixture is applied is included in the negative electrode tab.

14. 8. The method for manufacturing an electrode assembly according to claim 7, wherein the joining step includes joining the positive electrode such that a planned notching line of a lower end portion of the notched positive electrode is positioned on a first planned facing line of the notched negative electrode.

15. 8. The method for manufacturing an electrode assembly according to claim 7, wherein the joining step includes joining the positive electrode such that a planned notching line of an upper end portion of the notched positive electrode is positioned on a second planned facing line of the notched negative electrode.

16. A method for controlling the sliding specification of an electrode including a sliding region in which the thickness of an electrode mixture layer gradually decreases and forms an inclined surface relative to a current collector plane, comprising: The thickness T of the positive electrode mixture layer at the center of the positive electrode in the positive electrode sheet ＰＣ and the thickness T of the positive electrode mixture layer at the intended lower end portion of the positive electrode Ｐ１ Each of the T ＰＣ The T Ｐ１ The first positive electrode thickness ratio RT Ｐ１ (=T Ｐ１ / T ＰＣ ) and determining a negative electrode first intended facing line P1 that faces the positive electrode lower end intended portion of the negative electrode sheet; The thickness T of the negative electrode mixture layer at the center of the negative electrode in the negative electrode sheet ＮＣ and the thickness T of the negative electrode mixture layer at the first negative electrode facing planned line P1 Ｎ１ Each of the T ＮＣ The T Ｎ１ The first negative electrode thickness ratio RT Ｎ１ (=T Ｎ１ / T ＮＣ ) and The first positive electrode thickness ratio RT Ｐ１ and the first negative electrode thickness ratio RT Ｎ１ and confirming whether the relationship satisfies the following condition 1: [Condition 1] RT Ｎ１ ≧(RT) Ｐ１ / NP ratio) × 100.1 In the condition 1, the NP ratio is a preset value, and means the ratio of the negative electrode capacity to the positive electrode capacity per unit area.

17. Thickness T of the positive electrode mixture layer at the intended upper end portion of the positive electrode Ｐ２ Measure the T ＰＣ The T Ｐ２ The second positive electrode thickness ratio RT Ｐ２ (=T Ｐ２ / T ＰＣ ) and determining a negative electrode second facing planned line P2 that faces an upper end of a positive electrode in the negative electrode sheet; The thickness T of the negative electrode mixture layer at the second negative electrode facing planned line P2 Ｎ２ Measure the T ＮＣ The T Ｎ２ The second negative electrode thickness ratio RT Ｎ２ (=T Ｎ２ / T ＮＣ ) and The second positive electrode thickness ratio RT Ｐ２ and the second negative electrode thickness ratio RT Ｎ２ and confirming whether the relationship satisfies the following condition 2: [Condition 2] RT Ｎ２ ≧(RT) Ｐ２ / NP ratio) × 100.1 17. The method of claim 16, wherein in the condition 2, the NP ratio is a preset value and means a ratio of the negative electrode capacity to the positive electrode capacity per unit area.

18. 17. The method for managing an electrode sliding standard according to claim 16, wherein in the step of determining the negative electrode first planned opposing line, the negative electrode first planned opposing line P1 is determined as a virtual line connecting points along the width direction from a boundary line between a negative electrode material mixture coated portion and a negative electrode material mixture non-coated portion, the points being spaced apart by a length L1 of a negative electrode shoulder line portion and a gap G1 on a plane between the positive electrode and the negative electrode.

19. 18. The method for managing an electrode sliding standard according to claim 17, wherein, in the step of determining the negative electrode second planned opposing line, the negative electrode second planned opposing line (P2) is determined as a virtual line connecting points that are spaced apart from the negative electrode first planned opposing line (P1) along the width direction by a length (C) in the overall length direction of the positive electrode.

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