Electrode assembly, method for manufacturing electrode assembly and secondary battery including electrode assembly

Abstract

The present invention relates to an electrode assembly, a method for manufacturing an electrode assembly, and a secondary battery including an electrode assembly. Specifically, the invention relates to an electrode assembly in which the deformation of the core portion is improved by changing the design of the electrode assembly, a method for manufacturing an electrode assembly, and a cylindrical secondary battery including an electrode assembly.

Description

Technology Field

[0001] The present invention relates to an electrode assembly, a method for manufacturing an electrode assembly, and a secondary battery comprising an electrode assembly. Specifically, the invention relates to an electrode assembly with improved core deformation by modifying the design of the electrode assembly, a method for manufacturing an electrode assembly, and a cylindrical secondary battery comprising the electrode assembly. The present application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0149964 filed with the Korean Intellectual Property Office on November 2, 2023, the contents of which are incorporated herein by reference. Background Technology

[0002] In the case of cylindrical batteries, a jelly-roll type electrode assembly is manufactured by rolling a long electrode of a fixed width into a roll. Cylindrical batteries manufactured by inserting such an electrode assembly into a battery case undergo repeated contraction and expansion of the electrodes during charging and discharging. In particular, if an in-tab is located in the core of the electrode assembly or if silicon-based active material is added to the negative electrode, increasing the degree of contraction and expansion, the pressure acting on the core of the electrode assembly increases significantly.

[0003] Meanwhile, the core portion of the cylindrical battery is a space where the winding core used for winding the electrode assembly is located, and there exists a hollow space, i.e., a core hollow, used during the cylindrical battery assembly process, such as the insertion process of the electrode assembly into the battery case and the welding process.

[0004] Recently, with the increase in low-resistance / high-capacity designs, there has been a growing trend of electrode assemblies including multiple tabs or the addition of silicon-based active materials. Consequently, the possibility of core deformation due to shrinkage or expansion of the electrode assembly increases. In particular, there have been problems where battery life deteriorates due to core collapse, where the hollow core fails to maintain its circular shape and collapses; and where the end of the first electrode located in the core and the adjacent second electrode deform beyond a certain level, causing damage to the separator located between the first and second electrodes (core impingement), which leads to direct contact between the first and second electrodes and subsequent heat generation and ignition due to an internal short circuit.

[0005] In order to resolve the issues of battery life degradation, separator damage, and internal short circuits caused by the deformation of such electrode assemblies, it is necessary to develop technology that can improve the phenomenon where the hollow core in the relevant area fails to maintain its circular shape and collapses, and suppress internal short circuits caused by separator damage. The problem to be solved

[0006] The present invention aims to provide an electrode assembly with improved core deformation by modifying the design of the electrode assembly, a method for manufacturing the electrode assembly, and a secondary battery including the electrode assembly.

[0007] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0008] One embodiment of the present invention may be defined by an independent claim, and additional features of a particular embodiment may be as described in each dependent claim.

[0009] One embodiment of the present invention provides an electrode assembly in which a first electrode, a separator, and a second electrode are laminated and wound around a winding axis. An extension line connecting the winding axis and the inner end of the first electrode; and an extension line connecting the winding axis and the point of maximum curvature of the first electrode may form an angle greater than 40° and less than or equal to 98°. Here, the angle may be determined in a plane perpendicular to the winding axis.

[0010] Throughout this specification, the terms "first electrode" and "second electrode" may be defined according to their meanings as used in the technical field related to secondary batteries, particularly in terms of battery design and manufacturing. The first electrode and / or the second electrode may be configured to receive and store charge carriers, such as electrons and / or ions, particularly lithium ions. Since the first electrode and the second electrode may have opposite polarities, they may receive and release charge carriers, respectively, during the charging process of the electrode assembly, and conversely, likewise release and receive charge carriers, respectively, during the discharging process of the electrode assembly. The materials and functions of the first electrode and the second electrode may be as known in the technical field unless otherwise specified.

[0011] For example, the first electrode may be a positive electrode and the second electrode may be a negative electrode. In another example, the first electrode may be a negative electrode and the second electrode may be a positive electrode. Generally, the positive electrode may include a current collector which may be provided as a plate, sheet, or film, and a positive active material is deposited thereon. For example, the positive active material may include a lithium metal oxide such as lithium cobalt oxide or lithium iron phosphate, or other suitable materials. The positive current collector may be made of an electrically conductive material such as aluminum, for example. Generally, the negative electrode may include a current collector which may be provided as a plate, sheet, or film, and a negative active material is deposited thereon. For example, the negative active material may include a carbon-based material such as graphite. The negative current collector may be made of an electrically conductive material such as copper, for example.

[0012] Separators are used in the field of secondary battery technology, particularly in terms of battery design and manufacturing. Specifically, the separator may be a porous membrane configured to be generally impermeable to solid materials but allowing charge carriers to pass through. The charge carriers may be, for example, ions, lithium ions, and / or electrons. The separator may be provided between a first electrode and a second electrode to prevent a short circuit between them.

[0013] The transfer of charge carriers between the first electrode and the second electrode may be made possible by an electrolyte that may exist at least partially between the first electrode and the second electrode. The electrolyte may be injected after the electrode assembly is housed in a battery case. Specifically, the electrode assembly may include the electrolyte such that the electrolyte exists between the first electrode and the second electrode.

[0014] The first electrode, the separator, and the second electrode may be provided as a layer (or sheet). The first electrode, the separator, and the second electrode may be stacked in a specific order. Specifically, the second electrode, the separator, the first electrode, and another separator are stacked in order to form a monocell. In another example, one or more monocells may be repeatedly stacked on top of the monocell in order to form a multicell.

[0015] The electrode assembly may include a monocell or a multicell wound in a roll form. The roll-shaped electrode assembly may also be referred to as a jelly roll. Specifically, in a monocell, a first electrode, a separator, a second electrode, and optionally another separator may be wound together around a winding axis. Thus, the electrode assembly may have a cylindrical shape, particularly a cylindrical shape having a spiral or vortex cross-section. Additionally, the first electrode, the separator, and the second electrode of the electrode assembly may be stacked in sequence and wound together around a winding axis. Therefore, the electrode assembly generally has cylindrical symmetry with respect to the winding axis. In cylindrical symmetry, the axial direction may be parallel to the winding axis of the electrode assembly. The radial direction may be perpendicular to the winding axis and perpendicular to the outer surface of the electrode assembly. Additionally, the circumferential direction may be perpendicular to the axial direction and the radial direction, and may refer to a direction following a circular path around the winding axis. Additionally, the winding direction of the electrode assembly may refer to a direction according to at least one of the first electrode, the separator, and the second electrode in the plan view, and accordingly, the winding direction may refer to a direction following a spiral path around the winding axis. Depending on the context, the winding direction may be approximated as a circle around the winding axis, similar to the circumferential direction in terms of the rotational direction.

[0016] Throughout this specification, unless otherwise specified, an azimuth may refer to the angle between two lines in a plane perpendicular to the winding axis. The two lines forming the azimuth may intersect at the winding axis.

[0017] Unless otherwise specified, geometric features regarding lines, angles, curvatures, etc., generally used throughout this specification may be defined in a planar view, that is, in a cross-section viewed parallel to the winding axis of the electrode assembly. Accordingly, unless otherwise specified, said geometric features may represent the approximate cylindrical geometry of the electrode assembly as it is wound around the winding axis. Additionally, unless otherwise specified, all lines used in this specification may represent straight lines.

[0018] Throughout this specification, cylindrical symmetry may be approximate in that the helical plan view and / or helical cross-section of the electrode assembly are each considered to be approximately circular plan view and / or circular cross-section. The plan view of the electrode assembly may represent a cross-section from a perspective parallel to the winding axis. Since the first electrode, the separator, and the second electrode are wound around the winding axis, the electrode assembly may have a helical cross-section opposite to the winding axis. Meanwhile, the cross-section of the electrode assembly may represent a cross-section perpendicular to the winding axis. Since the first electrode, the separator, and the second electrode are wound around the winding axis, the cross-section of the electrode assembly may be helical around the winding axis.

[0019] At least one of the first electrode, the separator, and the second electrode may have a rectangular shape in the plan view prior to winding. The winding axis may be parallel to at least one of the ends of the first electrode, the separator, and the second electrode. In a specific example, the first electrode, the separator, and the second electrode may each have a rectangular shape in their respective plan views, and may be arranged so that the ends of the second electrode, the separator, and the second electrode are aligned parallel to each other.

[0020] Throughout this specification, the term curvature may be used in the sense commonly used in mathematics. In particular, curvature may represent a measure of how much a curve deviates from a straight line. Additionally or alternatively, curvature may represent a measure of how much a surface deviates from a plane. Here, curvature may represent how much the direction of a curve changes for every infinitesimal distance, e.g., an angle per distance, for every part of the curve. Curvature may be a measure of the change in direction of a point along a curve. In particular, curvature may be a measure of the instantaneous rate of change of the unit tangent vector to the curve at point P as point P moves along the curve at a unit velocity. In a specific example, the position of the point P(s) may be a function of the parameter s, e.g., time or the length of an arc about a given origin. Additionally, T(s) may be the unit tangent vector at P(s) of the curve, which may be the derivative of P(s) with respect to s. Here, the derivative of T(s) with respect to s can be a vector perpendicular to the curve, and its length can be the curvature.

[0021] Throughout this specification, the curve may refer to a cross-section of the first electrode and / or a contour, outline, etc., in view of a plan view, i.e., parallel to the winding axis. In particular, since the first electrode may be provided as a sheet or a layer, the first electrode is recognized as a thick curve in the plan view. Additionally or alternatively, the same may apply to the second electrode and / or separator. Since the curve may be differentiated continuously near P, the tangent may vary continuously along the curve. Since the curve may be differentiated twice at any P, curvature may exist along the curve, for example, as the derivative of the aforementioned T(s) with respect to s.

[0022] Throughout this specification, curvature can be determined in terms of an oscillating circle on a curve. The oscillating circle of a curve at point P may be a circle having the same tangent and the same curvature as the curve. The tangent may be an approximation of the curve at point P. Additionally, the oscillating circle may be an approximation of the curve at point P. The curvature of a straight line may be zero. If the curvature of a point is not zero, the reciprocal of the curvature is considered to be the radius of curvature, i.e., the radius of the oscillating circle. The center of the oscillating circle is considered to be the center of the curvature, and can be constructed by indicating the radius of curvature perpendicular to the tangent of the curve in the direction in which the curve bends.

[0023] Additionally, the curvature used here may be determined as the derivative (or derivative value) of the central angle with respect to the arc of the contact circle at the center of the contact circle. As one method for determining the curvature of the first electrode described above, the curvature may be determined from a plan view or cross-sectional image of the electrode assembly taken from a viewpoint parallel to the winding axis. In particular, a curve may be determined using an image of the electrode assembly taken from a viewpoint parallel to the winding axis, that is, a visualized cross-sectional view of the first electrode, and the curvature may be determined from said curve.

[0024] Throughout this specification, the point of maximum curvature is a point where the curvature of the first electrode or the second electrode is maximum in a plan view of the electrode assembly, and may represent a point within a part or inside the first electrode or the second electrode. Thus, the point of maximum curvature may be a point on the first electrode where the first electrode exhibits the greatest curvature in a plan view of the electrode assembly. Additionally or alternatively, the point of maximum curvature may be a point on the first electrode where the contact circle of the first electrode is smallest. Additionally or alternatively, the same may apply to the second electrode and / or separator.

[0025] According to one embodiment of the present invention, the curvature of the first electrode may generally decrease as the first electrode extends from the winding axis toward the outer circumference of the electrode assembly. In other words, the curvature of the first electrode may generally decrease along the radial outer circumference of the first electrode, the helical outer circumference of the first electrode, or the winding direction. Since the first electrode, the separator, and the second electrode are wound together around the winding axis, the curvature of the first electrode may generally decrease along the radial outer circumference or the winding direction. Additionally or alternatively, the curvature of the second electrode and / or the separator may generally decrease along the radial outer circumference.

[0026] At the same time, the point of maximum curvature may be located closer to the winding axis than to the outer surface of the electrode assembly. In the plan view of the electrode assembly, the 'core portion' refers to the part closer to the winding axis than to the outer surface of the electrode assembly. The core portion may be additionally defined as described below. The point of maximum curvature may be provided inside or in a part of the core portion of the electrode assembly. The point of maximum curvature may be applied to the first electrode, but additionally or alternatively, the same may be applied to the second electrode and / or separator.

[0027] In the plan view, as the first electrode is wound in the winding direction around the winding axis, the first electrode extends from an inner end to an outer end. For example, the inner end of the first electrode may be located radially inward near the winding axis or in an adjacent area. For example, the outer end of the first electrode may be located radially outward near the outer surface of the electrode assembly or in an adjacent area. Alternatively or additionally, the same may be applied to the second electrode.

[0028] According to one embodiment of the present invention, a straight line connecting the winding axis and the inner end of the first electrode, i.e., a first straight line, can be drawn based on a cross-section perpendicular to the winding axis of the electrode assembly. For example, based on a cross-section perpendicular to the winding axis of the electrode assembly, the first straight line may be an imaginary line extending from the winding axis through the inner end of the first electrode. As described below, the first straight line may be drawn to determine the angle with the extension line connecting the winding axis and the point of maximum curvature, i.e., a second straight line.

[0029] According to one embodiment of the present invention, a second straight line, that is, a straight line connecting the winding axis and the point of maximum curvature of the first electrode, can be drawn based on a cross-section perpendicular to the winding axis of the electrode assembly. For example, based on a cross-section perpendicular to the winding axis of the electrode assembly, the second straight line may be an imaginary line extending from the winding axis through the point of maximum curvature of the first electrode. The second straight line may be drawn to determine the angle with the first straight line, that is, an extension line connecting the winding axis and the inner end of the first electrode.

[0030] According to one embodiment of the present invention, an extension line connecting the winding axis and the inner end of the first electrode from a viewpoint parallel to the winding axis; and an angle formed by an extension line connecting the winding axis and the point of maximum curvature, i.e., an angle formed by the first straight line and the second straight line, may be greater than 40° and less than or equal to 98°. Here, the angle may be one of the ranges of values ​​disclosed in this specification. As described above, a viewpoint parallel to the winding axis may refer to an axial viewing angle of cylindrical symmetry of the electrode assembly.

[0031] Alternatively or additionally, an electrode assembly is provided in which a first electrode; a separator and a second electrode are laminated and wound. In the core portion of the electrode assembly, an angle may be formed between the end of the first electrode and the point of maximum curvature of the first electrode, and may be greater than 40° and less than or equal to 98° with respect to the winding axis.

[0032] The above-mentioned core portion may be as described above or as described below. The longitudinal end of the first electrode may correspond to the inner end of the first electrode. The point where the curvature of the first electrode is maximum may correspond to the point of maximum curvature. The angle may be determined from a cross-sectional view of the electrode assembly or from a cross-section perpendicular to the winding axis of the electrode assembly, and may correspond to an azimuth angle where the vertex or apex lies on the winding axis or coincides with the winding axis.

[0033] An electrode assembly having the aforementioned features can achieve one of the technical effects mentioned in this specification. Specifically, one, part, or all of the electrodes of the electrode assembly may shrink and / or expand during battery charging and discharging, which may lead to deformation of the electrode assembly. Due to the deformation of the electrode assembly, the hollow core of the electrode assembly may fail to maintain its circular shape and collapse.

[0034] An electrode assembly according to one embodiment of the present invention can suppress the phenomenon in which the hollow core of the electrode assembly fails to maintain a circular shape and collapses due to deformation of the electrode assembly by adjusting the angle between the inner end of the first electrode and the maximum curvature point of the first electrode to a specific range.

[0035] Accordingly, an electrode assembly according to one embodiment of the present invention can contribute to preventing damage to the first electrode, the separator, and the second electrode. In addition, an electrode assembly according to one embodiment of the present invention can contribute to preventing an internal short circuit between the first electrode and the second electrode. Through this, it can contribute to improving battery stability and lifespan characteristics.

[0036] One embodiment of the present invention provides a method for manufacturing an electrode assembly. The manufacturing method enables a continuous manufacturing process by implementing an angle between the inner end of a first electrode and the point of maximum curvature of the first electrode in the manner described, for example using existing roll-to-roll process equipment, thereby increasing battery productivity and economic efficiency. This method can also achieve the technical effects described above and / or the technical effects described below.

[0037] According to one embodiment of the present invention, based on a cross-section perpendicular to the winding axis of the electrode assembly, the maximum point of curvature of the first electrode may be a point where the curvature of the first electrode is maximum. The maximum point of curvature of the first electrode may be determined in an azimuth angle of 0° to 180° extending from the inner end of the first electrode in the direction opposite to the winding direction, centered on the winding axis of the electrode assembly.

[0038] Throughout this specification, as defined above, the 'winding direction' may refer to the winding direction of the first electrode and / or the second electrode and the separator, and this may be a spiral path centered on the winding axis. That is, based on a plan view and / or a cross-section perpendicular to the winding axis, the winding direction of the first electrode may extend from the inner end of the first electrode to the outer end of the first electrode along the winding direction. However, in determining the azimuth angle, the winding direction of the first electrode may refer to a circular direction as a directional aspect of the rotational direction centered on the winding axis.

[0039] The azimuth angle may be determined from a cross-section perpendicular to the winding axis of the electrode assembly or from a plan view of the electrode assembly, wherein the vertex of the azimuth angle may coincide with the winding axis. In the aforementioned area, with respect to the cross-section perpendicular to the winding axis of the electrode assembly, one side of the azimuth angle may be an extension line connecting the winding axis and the inner end of the first electrode, i.e., a first straight line. With respect to the cross-section perpendicular to the winding axis of the electrode assembly, the other side of the azimuth angle may be given as an extension line connecting the winding axis to the boundary of the aforementioned area.

[0040] The above area may extend to or span an azimuth angle greater than 0° and less than or equal to 180°. In other words, the above area may cover the entire area between one boundary corresponding to an azimuth angle of 0° and another boundary corresponding to an azimuth angle of 180°. The one boundary corresponding to an azimuth angle of 0° and the other boundary corresponding to 180° intersect at the winding axis, and the above area may be the outer circumference of the electrode assembly, i.e., the interior of the additional boundary. The extension line connecting the winding axis and the inner end of the first electrode, i.e., the first straight line, may correspond to an azimuth angle of 0°. The above area may extend in a direction opposite to the winding direction. That is, it may cover an area opposite to a part of the first electrode extending from the inner end in the winding direction. If the above region extends over an azimuth range greater than 0° and less than or equal to 180°, the region may cover half of the cross-section perpendicular to the winding axis of the electrode assembly and / or half of the plan view of the electrode assembly, and may be bounded by an extension line connecting the winding axis and the inner end of the first electrode. That is, the region may be in the shape of a semicircle or a similar shape.

[0041] Alternatively or additionally, the point where the curvature is maximum may be a point where the curvature of the first electrode is maximum in an area greater than 0° and less than or equal to 180° in the direction opposite to the winding direction of the electrode assembly from the inner end of the first electrode.

[0042] In one embodiment of the present invention, the maximum curvature point of the first electrode may be provided within or in a part of the electrode assembly within 3 turns in the winding direction of the electrode assembly from the inner end of the first electrode.

[0043] The core portion may refer to a part of the electrode assembly enclosed by a third turn from the inner end of the first electrode. The core portion may correspond to the aforementioned core portion. The core portion may be implemented through some or all of the features described below.

[0044] Alternatively or additionally, the core portion may be an area within 3 turns from one longitudinal end of the first electrode of the electrode assembly. The longitudinal direction may be defined based on the state of the electrode assembly before winding and may correspond to the winding direction used in this specification after winding. One end may correspond to the inner end of the first electrode.

[0045] In one embodiment of the present invention, the first electrode comprises a first electrode current collector; and a first electrode active material layer provided on at least one surface of the first electrode current collector, wherein the first electrode active material layer extends to an inner end of the first electrode current collector, and the inner end of the first electrode current collector may correspond to an inner end of the first electrode.

[0046] In other words, the first electrode may comprise a first electrode current collector; and a first electrode active material layer provided on the first electrode current collector. The first electrode extends from one end in the longitudinal direction in a direction opposite to the winding direction, forming an inner end, which is the other end in the longitudinal direction, at the same position as the end in the longitudinal direction of the first electrode current collector. That is, with respect to the winding direction, the first electrode cannot extend beyond the first electrode current collector.

[0047] As described above, the active material layer may refer to a layer comprising an electrode active material or composed of an electrode active material. For example, the first electrode may be a positive electrode, and the first electrode active material layer may be a positive electrode active material layer.

[0048] Alternatively or additionally, the first electrode comprises a first electrode current collector; and a first electrode active material layer provided on at least one surface of the first electrode current collector, wherein the first electrode current collector and the first electrode active material layer may have longitudinal ends at the same location.

[0049] According to one embodiment of the present invention, the first electrode includes a first electrode non-active portion in which the first electrode active material layer is not provided. Additionally, the electrode assembly may include a first electrode tab provided on or physically connected to the first electrode non-active portion.

[0050] The first electrode non-existent portion may refer to a part of the first electrode, particularly the first electrode current collector, that is, a portion in which the first electrode active material layer, i.e., the first electrode active material or the active material of the first electrode, is not provided.

[0051] The electrode tab may be formed at least one from or on the first electrode blank portion, or provided at least one on the first electrode blank portion. The first electrode blank portion may be cut or notched. For example, at least one first electrode tab may be formed by forming one or more slits, notches, cuts, or similar elements from the edge of the first electrode blank portion to the first electrode blank portion. Alternatively or additionally, at least one electrode tab may be separately provided and attached to the first electrode current collector or the first electrode blank portion.

[0052] According to one embodiment of the present invention, the angle formed by the extension line connecting the winding shaft and the inner end of the first electrode, i.e., the first straight line, and the extension line connecting the point where the curvature of the winding shaft and the first electrode is 1 or less may be greater than 0°. The mathematical definition of curvature may be as described above or determined as described below. In particular, the point where the curvature of the first electrode is 1 or less may be located within 3 turns from the inner end of the first electrode, i.e., in the core portion of the electrode assembly. The above angle may refer to the aforementioned azimuth angle, and the vertex or apex may coincide with or correspond to the winding shaft.

[0053] According to one embodiment of the present invention, the angle formed by the extension line connecting the inner end of the winding shaft and the first electrode, i.e., the first straight line, and the extension line connecting the maximum curvature point of the winding shaft and the first electrode, i.e., the second straight line, may be determined after the activation of the electrode assembly.

[0054] Throughout this specification, activation may refer to the process of preparing an electrode assembly for use in a secondary battery by applying specific temperature and charge / discharge conditions to the electrode assembly or to a battery cell containing said electrode assembly. Activation may be referred to as formation. Activation may include an aging step, a charging step, and a discharging step, which may be performed in a specific order and optionally repeated in a specific order. The aging step may be performed to allow the electrolyte to penetrate into the first electrode and the second electrode. For example, the aging step may be performed by storing the electrode assembly at a specific temperature, e.g., 30°C, for a specific period, e.g., 30 minutes, 1 hour, 2 hours, or 3 hours. The charging step may be performed to allow the electrolyte to decompose on the surface of the negative electrode to form a Solid Electrolyte Interphase (SEI), i.e., a solid electrolyte interface. The charging step may include the process of charging the electrode assembly to a specific degree. After the charging step, a high-temperature aging process may optionally be performed at a high temperature, e.g., 40°C, 50°C, 60°C, or 70°C. Afterward, a discharge step may be performed on the electrode assembly at a specific C-rate, e.g., 0.1 C, 0.2 C, 0.5 C, or 1.0 C. Optionally, a degassing or degassing step may be performed to remove gas generated during the activation step.

[0055] The first electrode and / or the second electrode may contract and / or expand during the activation phase. Accordingly, the technical effect achieved by the present invention may be particularly advantageous in the electrode assembly after undergoing at least some of the activation phases.

[0056] Alternatively or additionally, the angle formed by the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum may be measured after activation.

[0057] According to one embodiment of the present invention, the angle formed by the extension line connecting the inner end of the winding shaft and the first electrode and the extension line connecting the maximum curvature point of the winding shaft and the first electrode may be determined after 50 cycles of charging and discharging under conditions of 25°C, 1 C charging and 1 C discharging.

[0058] Accordingly, throughout this specification, the angle formed by the first straight line and the second straight line may be determined after performing at least 50 repetitions of the charge and discharge cycles of the electrode assembly. Accordingly, the state or quality of the electrode assembly may be determined more accurately.

[0059] Alternatively or additionally, the angle formed by the inner end of the first electrode and the point where the curvature of the first electrode is maximum may be determined after 50 charge and discharge cycles under conditions of 25°C, 1 C charge and 1 C discharge.

[0060] According to one embodiment of the present invention, the circularity of the first electrode may be 89% or more within or in part of the electrode assembly within 3 turns in the winding direction from the inner end of the first electrode. As described above, a part of the electrode assembly within 3 turns from the inner end of the first electrode may be defined as the core part of the electrode assembly.

[0061] Alternatively or additionally, the roundness of the first electrode in the core portion of the electrode assembly may be 89% or more.

[0062] Throughout this specification, roundness may mean circularity or roundness according to mathematical or geometric principles. In particular, roundness may be determined according to ISO 1101. Throughout this specification, roundness may be determined as a two-dimensional parameter in the plan view of the electrode assembly. Alternatively or additionally, roundness may be determined as described below.

[0063] In one embodiment of the present invention, the first electrode may include a first surface facing the winding axis of the electrode assembly and a second surface opposite to the first surface. On the first surface of the first electrode, a first extension line may be drawn by extending a straight line connecting two points where the direction of curvature changes within a distance of 5 mm from the inner end of the first electrode. On the surface of the second electrode facing the first surface, a second extension line may be drawn by extending a straight line connecting two points that are spaced 5 mm from the inner end of the first electrode. The first extension line and the second extension line may form an angle of 25° or less. In particular, the first extension line and the second extension line may form an angle of 25° or less within 3 turns of the first electrode from the core portion, i.e., the inner end of the first electrode.

[0064] Alternatively or additionally, the first electrode may include a first surface facing the winding axis direction of the electrode assembly and a second surface opposite to the first surface. On the first surface of the first electrode, the first extension line may be drawn by extending a straight line connecting two points where the curvature direction changes within a distance of 5 mm from the longitudinal end of the first electrode. On the surface of the second electrode facing the first surface of the first electrode, the second extension line may be drawn by extending a straight line connecting two points at a distance of 5 mm from the longitudinal end of the first electrode, and may form an angle of 25° or less with the first extension line.

[0065] According to one embodiment of the present invention, the first electrode may not contain cracks or wrinkles. In particular, within 3 turns from the inner end of the first electrode, that is, within the core portion, the inside or part of the electrode assembly may not contain cracks or wrinkles.

[0066] According to one embodiment of the present invention, the flatness fraction of the first electrode may be within 3 turns from the inner end of the first electrode, that is, within the core portion, the inside or part of the electrode assembly, greater than 3% and less than or equal to 13.5%.

[0067] Throughout this specification, flatness may be determined according to the definition of flatness used in the fields of manufacturing and mechanical engineering. Flatness may be determined according to ISO 12781-1. Throughout this specification, the flatness ratio may be determined as described below.

[0068] Another embodiment of the present invention provides a method for manufacturing an electrode assembly. The manufacturing method comprises: (a) a placement process for forming a laminate by arranging a first electrode, a separator, and a second electrode in sequence; and (b) a winding process for winding the laminate around a winding axis using a winding core. The winding core may include a first winding core portion and a second winding core portion. The winding process may be performed such that an angle formed by an extension line connecting the winding axis and the inner end of the first electrode and an extension line connecting the winding axis and the maximum curvature point of the first electrode is greater than 40° and less than or equal to 98°, wherein a separator is inserted between the first winding core portion and the second winding core portion, and an extension line connecting the winding axis and the maximum curvature point of the first electrode is greater than 40° and less than or equal to 98°.

[0069] The above manufacturing method may be suitable for providing an electrode assembly according to one embodiment of the present invention. Accordingly, the manufacturing method according to one embodiment of the present invention may also be suitable for achieving technical effects such as those described above or those described below.

[0070] Alternatively or additionally, in a method for manufacturing an electrode assembly, the electrode assembly may be formed by winding a laminate comprising a first electrode, a separator, and a second electrode. The method for manufacturing an electrode assembly may include: (a) a supply process for supplying the first electrode, the separator, and the second electrode in a roll-to-roll manner; (b) a placement process for forming a laminate by arranging the supplied first electrode, the separator, and the second electrode in sequence; and (c) a winding process for winding the laminate.

[0071] Winding may be performed using a core comprising: a separation portion into which a separator is inserted; a first core portion provided on one side of the separation portion centered on the separation portion; and a second core portion provided on the other side of the separation portion and having a cross-sectional area different from that of the first core portion.

[0072] The batching process may be performed such that, centered on the winding axis, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is greater than 40° and less than or equal to 98°.

[0073] Throughout this specification, the roll-to-roll method or process may be defined according to the meaning used in the fields of manufacturing and industrial processing. In particular, the roll-to-roll method may include the step of starting from a roll wound with a flexible material, performing at least one process, and then winding the product back onto the roll to produce an output roll.

[0074] Specifically, the first electrode, the separator, and the second electrode may each be provided in a continuous manner, particularly in a roll-to-roll manner, and stacked in the order described above.

[0075] The separation portion may be used to fix the first electrode, the second electrode, and the separator and to wind them together. The above-mentioned winding core may form a hollow core portion of the electrode assembly after removal.

[0076] The cross-sectional areas of the first and second core sections may be determined in a plan view, that is, a view parallel to the winding axis and / or a cross-section perpendicular to the winding axis of the electrode assembly.

[0077] In one embodiment of the present invention, the first core and the second core may be asymmetric with respect to a cross-section perpendicular to the winding axis of the electrode assembly. In particular, with respect to a cross-section perpendicular to the winding axis of the electrode assembly, the first core and the second core may have different shapes and / or different sizes.

[0078] In one embodiment of the present invention, based on a cross-section perpendicular to the winding axis of the electrode assembly, the cross-sectional area of ​​the first core may be smaller than the cross-sectional area of ​​the second core, and the arrangement process of the first electrode, the separator, and the second electrode may be performed such that the inner end of the first electrode is arranged on the outer surface of the first core.

[0079] Alternatively or additionally, the cross-sectional area of ​​the first core may be smaller than the cross-sectional area of ​​the second core, and the arrangement process of the first electrode, the separator, and the second electrode may be performed such that the longitudinal end of the first electrode is placed on the outer surface of the first core.

[0080] Alternatively or additionally, the winding process is performed while maintaining a tension of 3.92 N or more, or 400 gf or more.

[0081] Furthermore, one embodiment of the present invention provides an electrode assembly manufactured by a manufacturing method according to one embodiment of the present invention.

[0082] One embodiment of the present invention provides a secondary battery. A secondary battery according to one embodiment of the present invention may include an electrode assembly according to one embodiment of the present invention.

[0083] According to one embodiment of the present invention, the secondary battery may include a battery case in which an electrode assembly is accommodated, in particular a cylindrical battery case.

[0084] One embodiment of the present invention provides an electrode assembly in which a first electrode, a separator, and a second electrode are laminated and wound, wherein, in the core portion of the electrode assembly, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, is 52° or greater and 68° or less.

[0085] Another embodiment of the present invention is a method for manufacturing an electrode assembly in which a first electrode, a separator, and a second electrode are laminated and wound, comprising: (a) a supply process for supplying the first electrode, the separator, and the second electrode in a roll-to-roll manner; (b) a placement process for forming a laminate by arranging the supplied first electrode, the separator, and the second electrode in sequence; and (c) a winding process for winding the laminate, wherein the winding comprises a spaced portion into which a separator is inserted; and a first winding core portion provided on one side of the spaced portion centered on the spaced portion. The present invention provides a method for manufacturing an electrode assembly and an electrode assembly manufactured by the above manufacturing method, wherein the method is performed using a core comprising a second core portion having a cross-sectional area different from that of the first core portion and provided on the other side of the above separation portion, and wherein the arrangement process is performed such that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is greater than 40° and less than or equal to 98° with respect to the winding axis.

[0086] Another embodiment of the present invention provides a secondary battery comprising the electrode assembly; and a battery case for accommodating the electrode assembly. Effects of the invention

[0087] An electrode assembly according to one embodiment of the present invention can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging by adjusting the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, and can prevent damage to the second electrode and the separator and prevent an internal short circuit between the first electrode and the second electrode, thereby improving battery stability and lifespan characteristics.

[0088] A method for manufacturing an electrode assembly according to one embodiment of the present invention can manufacture an electrode assembly in which the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is adjusted in a simpler manner, and can secure productivity and economic efficiency by being suitable for a continuous process using existing roll-to-roll process equipment.

[0089] In addition, the secondary battery according to the present invention can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by the shrinkage / expansion of the electrode during battery charging / discharging, prevent damage to the second electrode and separator, and prevent internal short circuits between the first electrode and the second electrode, thereby improving battery stability and lifespan characteristics.

[0090] The effects of the present invention are not limited to those described above, and unmentioned effects will be clearly understood by those skilled in the art from the present specification and the accompanying drawings. Brief explanation of the drawing

[0091] Figure 1 is a CT image of an electrode assembly according to Example 1 and an image showing the curvature of the first electrode extracted from the CT image. FIG. 2 is a CT image of an electrode assembly according to Example 2 and an image showing the curvature of the first electrode extracted from the CT image. Figure 3 is a CT image of an electrode assembly according to Comparative Example 1 and an image showing the curvature of the first electrode extracted from the CT image. Figure 4 is a CT image of an electrode assembly according to Comparative Example 2 and an image showing the curvature of the first electrode extracted from the CT image. Figure 5 is a CT image of an electrode assembly according to Comparative Example 3 and an image showing the curvature of the first electrode extracted from the CT image. Figure 6 is a CT image of an electrode assembly according to Comparative Example 4 and an image of a crack occurring in the first electrode core portion. Figure 7 is a CT image of an electrode assembly according to Comparative Example 5 and an image of a crack occurring in the first electrode core portion. Figure 8 is a graph showing the correlation between the flatness fraction of the first electrode and the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum. FIG. 9 shows the correlation between the angle formed by the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, the flatness fraction of the first electrode, and the deformation of the core portion according to the method of manufacturing an electrode assembly according to one embodiment of the present invention. FIG. 10 is a CT image of an electrode assembly according to Example 1 and an image showing the curvature of the first electrode extracted from the CT image and the arrangement relationship of the winding core. Figure 11 is a CT image of an electrode assembly according to Comparative Example 2 and an image showing the curvature of the first electrode extracted from the CT image and the arrangement relationship of the winding core. Figure 12 schematically illustrates a method for evaluating whether core impingement has occurred. Figure 13 is a CT image showing the sliding range of the longitudinal end of the first electrode of a secondary battery according to Reference Experimental Example 1 and Reference Experimental Example 2. Specific details for implementing the invention

[0092] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0093] Throughout this specification, when a component is described as being located "on" another component, this includes not only cases where a component is in contact with another component, but also cases where another component exists between the two components.

[0094] One embodiment of the present invention provides an electrode assembly in which a first electrode, a separator, and a second electrode are laminated and wound, wherein, in the core portion of the electrode assembly, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, is 52° or greater and 68° or less.

[0095] Here, the first electrode may include a first surface facing the winding axis of the electrode assembly and a second surface opposite to the first surface.

[0096] In addition, the above curvature may be calculated at a plurality of measurement points located on the first surface of the first electrode extracted from a computed tomography (CT) image as described below.

[0097] An electrode assembly according to one embodiment of the present invention can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging by adjusting the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, and can prevent damage to the second electrode and the separator and prevent an internal short circuit between the first electrode and the second electrode, thereby improving battery stability and lifespan characteristics.

[0098] Specifically, during battery charging and discharging, the electrode included in the electrode assembly repeatedly contracts and expands. Since outward expansion is restricted by the rigidity of the battery case surrounding the outer surface of the electrode assembly, stress may be concentrated in the hollow direction, which is the empty space located in the core. Accordingly, the possibility of core deformation of the electrode assembly may increase.

[0099] The deformation of the core portion described above may be classified into a phenomenon in which the hollow core portion of the electrode assembly fails to maintain its circular shape and collapses when internal stress reaches a certain level or higher, i.e., core collapse, and a phenomenon in which the end of the first electrode located in the core portion and the adjacent second electrode are deformed beyond a certain level, causing the separator located between the first electrode and the second electrode to break and the first electrode and the second electrode to come into direct contact, i.e., core impingement.

[0100] In particular, the collapse of the core portion may be concentrated in an area vulnerable to internal stress of the electrode assembly. Specifically, the collapse of the core portion may be concentrated in an area where the curvature of the first electrode is below a certain value, i.e., a flat area. That is, in the core portion of the electrode assembly, deformation due to internal stress may begin to occur starting from the area where the curvature of the first electrode is below a certain value, and after a certain point, the hollow of the core portion may no longer maintain its circular shape and completely collapse. In an electrode assembly where core portion collapse has occurred, the transfer of lithium ions between the first electrodes can no longer proceed smoothly, which may lead to a deterioration of battery life.

[0101] Here, the curvature of the first electrode may be influenced by the step difference caused by the thickness of the electrode, tab, etc., the shape of the core, and the tension acting on the electrode assembly during winding. For example, the core may include a pair of core sections separated by a spaced portion into which a separator is inserted, and when a certain level of tension is applied, twisting of the core may occur, and as a result, an area where the curvature of the first electrode is below a specific value, i.e., a flat area, may inevitably occur, and collapse of the core section may occur in the area where the curvature of the first electrode is below a specific value.

[0102] At this time, if the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is adjusted, the phenomenon in which the hollow core fails to maintain its circular shape and collapses, i.e., the core collapse phenomenon, may be improved. Through this, damage to the second electrode and the separator can be prevented, and internal short circuits between the first electrode and the second electrode can be prevented, thereby improving battery stability and lifespan characteristics.

[0103] According to one embodiment of the present invention, in the core portion of the electrode assembly, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, may be greater than 40° and less than or equal to 98°. Specifically, in the core portion of the electrode assembly, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, may be greater than 40° and less than 98°, greater than 45° and less than 95°, greater than 45° and less than 90°, greater than 45° and less than 80°, greater than 45° and less than 70°, greater than 45° and less than 65°, greater than 50° and less than 95°, greater than 50° and less than 90°, greater than 50° and less than 80°, greater than 50° and less than 70°, greater than 50° and less than 65°, greater than 60° and less than 95°, greater than 60° and less than 90°, greater than 60° and less than 80°, greater than 60° and less than 70°, or greater than 60° and less than 65°.

[0104] When the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum satisfies the aforementioned range, the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by the shrinkage / expansion of the electrode during battery charging / discharging can be improved, damage to the second electrode and separator can be prevented, and internal short circuits between the first electrode and the second electrode can be prevented, thereby improving battery stability and lifespan characteristics.

[0105] Hereinafter, regarding the angle formed between the longitudinal end of the first electrode of the present invention and the point where the curvature of the first electrode is maximum, the object of curvature measurement, the method of curvature measurement, and the time of curvature measurement will be explained in more detail.

[0106] According to one embodiment of the present invention, the curvature may be measured with respect to the first electrode in the core portion of the electrode assembly.

[0107] Here, the 'core portion' may be a region including a hollow located on the winding axis of the electrode assembly; and a portion of the stacked structure of the wound separator / second electrode / separator / first electrode.

[0108] In other words, the core portion may include a hollow located on the winding axis of the electrode assembly and an area extending to one end in the longitudinal direction of the first electrode located at the innermost angle where the winding of the electrode assembly begins, i.e., an area that does not include the first electrode. Additionally, the core portion may further include an area of ​​a predetermined length extending from one end in the longitudinal direction of the first electrode to the direction in which the winding of the first electrode takes place, which includes the first electrode.

[0109] According to one embodiment of the present invention, the core portion may be an area within 3 turns from one end in the longitudinal direction of the first electrode. Specifically, the core portion may be an area within 1 to 2.5 turns or within 1.5 to 2 turns from one end in the longitudinal direction of the first electrode.

[0110] Here, 1 turn may refer to the length required for 360° winding from a reference point of an electrode or separator included in an electrode assembly, and the length may be determined according to the outer diameter of the core used for winding the electrode assembly, the thickness of the separator and electrode, and the number of windings of the separator and electrode located inside the reference point. For example, 1 turn of the first electrode may refer to the length required to wind the first electrode 360° from the longitudinal end of the first electrode in the direction in which the winding of the electrode assembly takes place.

[0111] In other words, the core portion may refer to an area extending from one end of the longitudinal direction of the first electrode to a point spaced 3 turns or less away, or an area extending from one end of the longitudinal direction of the first electrode to a point spaced 1 to 2.5 turns away or an area extending 1.5 to 2 turns away.

[0112] Since the point where the curvature of the first electrode is maximum may be determined according to the range of the core portion, when the range of the core portion described above is satisfied, the point where the curvature of the first electrode is maximum can be determined more efficiently, and the reliability of the determined point where the curvature of the first electrode is maximum may be higher.

[0113] According to one embodiment of the present invention, the curvature may be measured at the core portion of the electrode assembly, may be measured for the first electrode at the core portion of the electrode assembly, or may be measured by extracting the first electrode from a CT image of the core portion of the electrode assembly.

[0114] When the object of measurement for the curvature is the first electrode located in the core portion of the electrode assembly, the reliability of the curvature measurement may be higher, and by adjusting the position of the longitudinal end of the first electrode, it may be easier to adjust the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum. Through this, deformation of the end of the first electrode located in the core portion and the adjacent second electrode is reduced, thereby achieving an effect of improving the phenomenon of core impingement, i.e., damage to the separator located between the first electrode and the second electrode.

[0115] According to one embodiment of the present invention, the curvature may be calculated at a plurality of measurement points located on the first surface of the first electrode extracted from a computed tomography (CT) image. Specifically, the curvature may be measured with respect to a first surface opposite to the winding axis of the electrode assembly of the extracted first electrode after extracting the first electrode from the CT image of the electrode assembly. More specifically, the curvature may be calculated at a plurality of measurement points having a constant interval located on the first surface of the first electrode. For example, the plurality of measurement points may be located at 2° intervals on the first surface of the extracted first electrode centered on the winding axis.

[0116] According to one embodiment of the present invention, the measurement points may be 180 or more. Specifically, the measurement points may be 180 or more and 720 or less. More specifically, the measurement points may be 240 or more and 660 or less, 300 or more and 600 or less, or 360 or more and 540 or less.

[0117] If the aforementioned range of measurement points is satisfied, the point where the curvature of the first electrode is maximum can be determined more efficiently, and the reliability of the determined point where the curvature of the first electrode is maximum can be higher.

[0118] According to one embodiment of the present invention, the curvature may be measured at separate measurement points at regular intervals or within a range of the number of measurement points arbitrarily selected from the aforementioned core part to determine the point where the curvature is maximum.

[0119] According to one embodiment of the present invention, the curvature may be a curvature according to the following Equation 1. Specifically, the curvature calculated at the measurement point may be calculated according to the following Equation 1 using coordinate values, i.e., x-coordinates and y-coordinates, obtained from a plurality of measurement points located on the first surface of the first electrode extracted from a CT image.

[0120] [Equation 1]

[0121] k=(x'y''-y'x'') / (x' 2 +y' 2 ) 3 / 2

[0122] In the above Equation 1, k is the curvature of the first electrode, x is the x-coordinate of the measurement point, y is the y-coordinate of the measurement point, x' is the first derivative of x, y' is the first derivative of y, x'' is the second derivative of x, and y'' is the second derivative of y.

[0123] In other words, the calculation of the curvature may mean measuring x-coordinate and y-coordinate values ​​at a plurality of measurement points spaced at regular intervals located on the first surface of the first electrode, and calculating the curvature value using the measured x-coordinates, y-coordinates, and Equation 1. Specifically, the curvature may be calculated as a parametric representation of a planar curve, and the curvature, i.e., the degree of bending, may increase as the value of k according to Equation 1 increases. More specifically, the curvature may be calculated using the equation through a Python program, and the x and y coordinate values ​​may have a range from -3 to +3. Meanwhile, x' and y' may represent the slope of the tangent line at each coordinate, and x'' and y'' may represent the rate of change of the slope.

[0124] If necessary, the above curvature value may be normalized using the radius of curvature of the electrode assembly according to each measurement point.

[0125] According to one embodiment of the present invention, in the core portion of the electrode assembly, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is 1 or less, centered on the winding axis, may be greater than 0°.

[0126] Specifically, in the core portion of the electrode assembly, the angle formed by the longitudinal end of the first electrode and the point where the curvature of the first electrode is 1 or less, centered on the winding axis, may be greater than 0° and less than 50°.

[0127] More specifically, in the core portion of the electrode assembly, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is 1 or less, centered on the winding axis, may be 5° or more and less than 50°, 10° or more and less than 45°, or 15° or more and less than 40°.

[0128] In other words, the region where the curvature of the first electrode is 1 or less, that is, the flat region, may be located between the point where the curvature of the first electrode is maximum and the longitudinal end of the first electrode, and may not overlap with the longitudinal end of the first electrode.

[0129] According to one embodiment of the present invention, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum may be measured in an area greater than 0° and less than or equal to 180° in the direction opposite to the direction in which the electrode assembly is wound, with respect to the longitudinal end of the first electrode. That is, the point where the curvature is maximum may be a point where the curvature is maximum in an area greater than 0° and less than or equal to 180° in the direction opposite to the direction in which the electrode assembly is wound, with respect to the longitudinal end of the first electrode.

[0130] In other words, the angle formed by the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum may be measured in an area greater than 0° and less than or equal to 180° with respect to the longitudinal end of the first electrode, in the direction opposite to the direction (W) in which the electrode assembly is wound, that is, in the rotation direction (R) of the core used for winding the electrode assembly.

[0131] Specifically, as the stress generated during the cycle progresses is concentrated in the hollow direction of the core due to the rigidity of the battery case, deformation of the core may occur in a flat area that is relatively vulnerable to stress. At this time, based on the longitudinal end of the first electrode, the area of ​​greater than 0° and less than 180° in the direction opposite to the winding direction (W) of the electrode assembly, that is, the rotation direction (R) of the winding core, has a relatively smaller number of turns of the first electrode up to the outermost layer compared to the area of ​​greater than 180° and less than 360°, and since the distance from the longitudinal end of the first electrode, which is capable of sliding, is relatively far, the concentrated stress is not relieved, so the possibility of deformation in the hollow direction of the core may be higher at that location.

[0132] In addition, as described below, the tension applied to the electrode assembly during winding causes twisting in the core, so when a gap is included in the core, a point where the curvature of the first electrode is maximum and a flat area may occur symmetrically in the gap; however, a flat area located in an area greater than 0° and less than 180° in the rotational direction (R) of the core with respect to the longitudinal end of the first electrode may be more susceptible to core deformation and may have a higher possibility of core deformation occurring even after an acceleration cycle.

[0133] Accordingly, if the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is measured in an area greater than 0° and less than or equal to 180° in the direction opposite to the winding direction of the electrode assembly relative to the longitudinal end of the first electrode, the point where the curvature of the first electrode is maximum can be determined more efficiently, and the effect of reducing deformation of the core part due to angle adjustment may be superior.

[0134] According to one embodiment of the present invention, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum may be measured after activation. Specifically, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum may be measured after activation in a normal standby state and a state where normal use has taken place, that is, before the occurrence of core deformation. For example, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum may be measured after 50 charge and discharge cycles under conditions of 25°C, 1C charge and 1C discharge.

[0135] Here, the meaning of "after activation" may refer to a state after a predetermined cycle has been carried out for the manufacture and product completion of the secondary battery. Specifically, "after activation" may include a storage state prior to the commencement of active use, including multiple cycles for the purpose of power supply, i.e., prior to and after sale, and may include a state in which self-discharge occurs during storage.

[0136] The above activation may refer to a step of verifying the stability of the battery by repeating aging and charging / discharging after the assembly of the electrode assembly and the battery case, and by performing a predetermined cycle, for example, 50 cycles under the condition of 1C / 1C @25 ℃, on a battery obtained at any point after assembly, the 'state prior to the occurrence of core deformation after activation' can be achieved in a simple manner. However, the above activation conditions are not limited to the scope used in the industry to achieve the same purpose.

[0137] Since the point where the curvature of the first electrode is maximum may be determined according to the above curvature measurement time, when the above curvature measurement time is satisfied, the point where the curvature of the first electrode is maximum can be determined more efficiently, and the reliability of the determined point where the curvature of the first electrode is maximum may be higher.

[0138] FIG. 8 is a graph showing the correlation between the flatness fraction of the first electrode and the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum. Specifically, FIG. 8 (a) is a scatter plot matrix quantifying arbitrary factors extracted from CT images before and after 27 acceleration cycles (1C / 1C 50 cycles) of the same cell, and FIG. 8 (b) is a graph showing the correlation between the flatness fraction of the first electrode and the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum.

[0139] Specifically, referring to FIG. 8, the location where deformation of the core part occurs may be determined by the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, or by the value of the flatness fraction of the first electrode, and the location where deformation of the core part of the electrode assembly occurs may coincide with the region where the curvature of the first electrode is 1 or less, that is, the flat region. In other words, the lower the flatness fraction, the lower the possibility of deformation of the core part occurring in the flat region, which is the location where deformation of the core part occurs.

[0140] Meanwhile, as an additional influencing factor related to the occurrence of deformation in the core portion, when the first electrode tab is positioned at 12 o'clock, it is preferable that the second electrode tab located at the outermost part be positioned between 5 o'clock and 8 o'clock or between 6 o'clock and 7 o'clock; it is preferable that the longitudinal end of the first electrode located in the core portion be positioned between 5 o'clock and 9 o'clock or between 6.5 o'clock and 8 o'clock; and it is preferable that the longitudinal end of the first electrode located at the outermost part be positioned between 4 o'clock and 6 o'clock or between 4.5 o'clock and 5.5 o'clock. Meanwhile, the area of ​​the hollow of the core portion is 10 mm 2 More than 40 mm 2 Less than or equal to 27 mm 2 More than 33 mm 2 It is desirable that it be less than or equal to the above. If the aforementioned additional influencing factors each satisfy the aforementioned range, the effect of reducing deformation in the core portion may be superior. In this case, the unit 'hour' represents the relative position of each factor in a clockwise direction when the first electrode tab is positioned at 12 o'clock on the CT image, and may be measured in the direction opposite to the direction (W) in which the electrode assembly is wound, that is, the rotation direction (R) of the winding core used for winding the electrode assembly. For example, 6 o'clock means forming a 180° angle with the first electrode tab located at 12 o'clock.

[0141] According to one embodiment of the present invention, in the core portion of the electrode assembly, the first electrode may not include cracks or wrinkles. Here, the crack may refer to a crack visible to the naked eye on the surface of the first electrode, and the wrinkle may refer to a case where a wrinkle or fold visible to the naked eye occurs on the surface of the first electrode.

[0142] When an electrode assembly including the first electrode with the above-mentioned crack is inserted into a battery case, the possibility of low voltage generation and short circuits caused by foreign substances increases significantly. On the other hand, since the electrode assembly according to one embodiment of the present invention does not include the first electrode with a crack or wrinkle in the core portion, battery stability can be improved.

[0143] According to one embodiment of the present invention, in the core portion of the electrode assembly, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum may have a positive correlation with the flatness fraction of the first electrode. Specifically, referring to FIG. 8(b), the correlation coefficient between the flatness fraction of the first electrode and the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum may be approximately 0.756.

[0144] Here, the flatness fraction (%) may mean the ratio of the flat area of ​​the first electrode to be measured, and the flat area may mean an area having a curvature less than or equal to a reference value.

[0145] That is, the flatness ratio may mean the ratio of an area showing a curvature value less than or equal to a reference curvature value in the first electrode being measured. For example, the flatness ratio may be the ratio (%) of the number of measurement points with a curvature of 1 or less, based on 100% of the number of measurement points.

[0146] Since the flatness ratio of the first electrode may be determined according to the above-mentioned standard curvature value, if the range of the above-mentioned standard curvature value is satisfied, the flatness ratio of the first electrode can be determined more efficiently, and the reliability of the determined flatness ratio of the first electrode may be higher.

[0147] According to one embodiment of the present invention, in the core portion of the electrode assembly, the flatness fraction of the first electrode may be greater than 3% and less than or equal to 13.5%. Specifically, in the core portion of the electrode assembly, the flatness fraction of the first electrode may be greater than 3% and less than or equal to 13.5%, greater than or equal to 5% and less than or equal to 13%, greater than or equal to 5% and less than or equal to 10%, greater than or equal to 7% and less than or equal to 10%, or greater than or equal to 7.5% and less than or equal to 10%.

[0148] When the flatness ratio range of the first electrode described above is satisfied, the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging can be improved, damage to the second electrode and separator can be prevented, and internal short circuits between the first electrode and the second electrode can be prevented, thereby improving battery stability and lifespan characteristics.

[0149] According to one embodiment of the present invention, in the core portion of the electrode assembly, the circularity of the first electrode may be 89% or more. Specifically, in the core portion of the electrode assembly, the circularity of the first electrode may be 89% or more or 90% or more, or 89% or more and 99% or less, or 90% or more and 98% or less.

[0150] Here, the circularity (%) may be the ratio of the minimum separation distance between the winding axis and the first electrode to the maximum separation distance between the winding axis and the first electrode, based on 100%. Specifically, the circularity is the maximum separation distance (R) between the winding axis and the first electrode. max The minimum separation distance (R) between the winding shaft and the first electrode for ) min It may mean the ratio (%) of ).

[0151] When the aforementioned range of roundness is satisfied, the shape of the electrode assembly can be closer to a circle, and the resistance to stress acting on the core part can be excellent. Accordingly, the phenomenon in which the hollow core part fails to maintain a circular shape and collapses due to deformation of the electrode assembly caused by the shrinkage / expansion of the electrode during battery charging / discharging can be improved, damage to the second electrode and separator can be prevented, and internal short circuits between the first electrode and the second electrode can be prevented, thereby improving battery stability and lifespan characteristics.

[0152] However, the above roundness may differ from the flatness fraction, which refers to the ratio of the area exhibiting a curvature below a reference value in the first electrode being measured. For example, depending on the shape of the electrode assembly, there may be cases where the roundness satisfies the aforementioned range, but the flatness fraction does not. In this case, by adjusting the flatness fraction to the aforementioned range in addition to the roundness, it is possible to exclude cases where the shape of the electrode assembly deviates from a circular shape at a specific location. Accordingly, shape control of the electrode assembly may be easier compared to simply adjusting the roundness, and the effect of reducing deformation in the core portion may be superior. In other words, the flatness fraction may serve as a more accurate standard for the degree to which the shape of the electrode assembly is 'close to a circular shape'.

[0153] According to one embodiment of the present invention, the first electrode comprises a first electrode current collector; and a first electrode active material layer provided on at least one surface of the first electrode current collector, and the first electrode current collector and the first electrode active material layer may have longitudinal ends at the same location. In other words, one longitudinal end of the first electrode may be in the form of a free-edge.

[0154] Through this, economic efficiency can be secured by reducing the area of ​​the unnecessary unused portion of the first electrode current collector, and since a slitting process can be performed after forming an active material layer on the electrode, a roll-to-roll process including a slitting process and a winding process can be carried out more efficiently.

[0155] Here, 'same position' means that the longitudinal ends are identical, and may include cases where the ends are formed at substantially the same position due to process errors that may occur during the slitting process, etc.

[0156] According to one embodiment of the present invention, the first electrode may include a first electrode non-existent portion in which a first electrode active material layer is not provided, and may further include a first electrode tab provided on the first electrode non-existent portion.

[0157] In other words, the first electrode current collector may include a first electrode retaining portion to which the first electrode active material is applied and a first electrode non-retaining portion to which the first electrode active material is not applied, and may include a tab on the first electrode non-retaining portion. Specifically, the first electrode current collector may include a first electrode non-retaining portion and may include a first electrode tab provided on the first electrode non-retaining portion.

[0158] That is, one end in the longitudinal direction of the first electrode may have a free-edge shape, the unoccupied portion of the first electrode may be located between both ends in the longitudinal direction of the first electrode, and the first electrode tab provided in the unoccupied portion of the first electrode may be a middle tab.

[0159] According to one embodiment of the present invention, the first electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery. Specifically, the first electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. That is, the first electrode current collector may be provided in the form of surface-treated stainless steel, aluminum foil, etc.

[0160] In addition, the first electrode current collector may typically have a thickness of 3 to 50 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the first electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0161] According to one embodiment of the present invention, the first electrode active material may be a commonly used first electrode active material. Specifically, the first electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (0≤x≤0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-y M y Ni-site type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01≤y≤0.3); chemical formula LiMn 2-z M zExamples include lithium manganese composite oxides represented by O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01≤z≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4 in which a portion of the Li in the chemical formula is substituted with alkaline earth metal ions, but are not limited thereto. The first electrode may also be Li-metal.

[0162] According to one embodiment of the present invention, the first electrode active material layer may further include a first electrode conductive material and a first electrode binder. The first electrode conductive material is used to impart conductivity to the electrode and can be used without special limitations as long as it has electronic conductivity without causing chemical changes in the battery being constructed. Specifically, the first electrode conductive material may be graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0163] In addition, the first electrode binder serves to improve adhesion between the first electrode active material particles and adhesion between the first electrode active material and the first electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0164] According to one embodiment of the present invention, the second electrode may comprise a second electrode current collector and a second electrode active material layer provided on the second electrode current collector. Specifically, the second electrode may comprise a second electrode current collector and a second electrode active material layer formed on one or both sides of the second electrode current collector, the second electrode active material layer comprising a second electrode active material. In other words, the second electrode active material layer is formed on the second electrode holding portion of the second electrode current collector, and the side not provided with the second electrode active material layer may be described as a second electrode non-retaining portion.

[0165] According to one embodiment of the present invention, the second electrode current collector may include a second electrode retaining portion where a second electrode active material layer is formed and a second electrode non-retaining portion where a second electrode active material layer is not formed, and may include a tab on the second electrode non-retaining portion. Specifically, the second electrode current collector may include a second electrode non-retaining portion and may include a second electrode tab formed on the second electrode non-retaining portion. Accordingly, the electrode assembly manufactured may include one or more second electrode tabs.

[0166] According to one embodiment of the present invention, the second electrode active material layer may comprise a second electrode active material comprising one or more selected from the group consisting of silicon-based materials and carbon-based materials. Additionally, the second electrode active material layer may further comprise a second electrode conductive material and a second electrode binder, and the second electrode active material; the second electrode conductive material; and the second electrode binder may be any material used in the art without limitation.

[0167] According to one embodiment of the present invention, the second electrode current collector may be conductive without causing chemical changes in the battery, and is not particularly limited. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used as the second electrode current collector. Specifically, transition metals that adsorb carbon well, such as copper or nickel, may be used as the second electrode current collector. The thickness of the second electrode current collector may be 5 μm or more and 30 μm or less, but the thickness of the second electrode current collector is not limited thereto.

[0168] According to one embodiment of the present invention, the second electrode binder may comprise at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which the hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also comprise various copolymers thereof.

[0169] According to one embodiment of the present invention, the second electrode conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fiber such as carbon fiber or metal fiber; conductive tube such as carbon nanotube; metal powder such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0170] According to one embodiment of the present invention, the electrode assembly may include a plurality of separators. For example, the electrode assembly may have a structure in which a separator / second electrode / separator / first electrode are stacked in sequence. The separator separates the first electrode and the second electrode and provides a pathway for the movement of lithium ions. It may be used without special limitations as long as it is typically used as a separator in a secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a stacked structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. In addition, the above-described separator may be a separator in which a slurry containing ceramic components or polymer materials is coated on the substrate layer to secure heat resistance or mechanical strength, using the aforementioned separator material as a substrate layer, and may optionally be used in a single-layer or multi-layer structure. The thickness of the separator may be 5 μm or more and 20 μm or less, but is not limited thereto.

[0171] According to one embodiment of the present invention, the angle formed by the first electrode and the second electrode may be 25° or less. Specifically, the first electrode includes a first surface in the direction of the winding axis of the electrode assembly and a second surface opposite to the first surface, and a first extension line drawn by extending a straight line connecting two points where the curvature direction changes within a distance of 5 mm from the longitudinal end of the first electrode on the first surface of the first electrode; and a second extension line drawn by extending a straight line connecting two points at a distance of 5 mm from the longitudinal end of the first electrode on the surface of the second electrode opposite to the first surface of the first electrode may form an angle of 25° or less. At this time, the angle formed by the first electrode and the second electrode may be measured, for example, after activation, after 200 or more additional charging and discharging cycles at 40° or higher.

[0172] When the aforementioned angle range is satisfied, the end of the first electrode located in the core and the adjacent second electrode are not deformed beyond a certain level, so the phenomenon in which the separator located between the first electrode and the second electrode is damaged and the first electrode and the second electrode come into direct contact, i.e., core impingement, may be suppressed. Through this, damage to the second electrode and the separator can be prevented and internal short circuits between the first electrode and the second electrode can be prevented, thereby improving battery stability and lifespan characteristics.

[0173] According to one embodiment of the present invention, the first electrode and the second electrode may each be an anode and a cathode. Specifically, the first electrode may be an anode, and the second electrode may be a cathode.

[0174] Another embodiment of the present invention is a method for manufacturing an electrode assembly in which a first electrode, a separator, and a second electrode are laminated and wound, comprising: (a) a supply process for supplying the first electrode, the separator, and the second electrode in a roll-to-roll manner; (b) a placement process for arranging the supplied first electrode, the separator, and the second electrode in sequence to form a laminate; and (c) a winding process for winding the laminate.

[0175] The above winding is performed using a core comprising: a spaced portion into which a separator is inserted; a first core portion provided on one side of the spaced portion centered on the spaced portion; and a second core portion provided on the other side of the spaced portion and having a cross-sectional area different from that of the first core portion, and the above arrangement process is performed such that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is greater than 40° and less than or equal to 98° centered on the winding axis, and the electrode assembly manufactured by the above manufacturing method is provided.

[0176] A method for manufacturing an electrode assembly according to one embodiment of the present invention can manufacture an electrode assembly in which the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is adjusted in a simpler manner, and can secure productivity and economic efficiency by being suitable for a continuous process using existing roll-to-roll process equipment.

[0177] In addition, the secondary battery according to one embodiment of the present invention can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging, prevent damage to the second electrode and separator, and prevent internal short circuits between the first electrode and the second electrode, thereby improving battery stability and lifespan characteristics.

[0178] Here, the core portion, the longitudinal end portion of the first electrode, and the curvature, specifically, the object of measurement of the curvature, the method of measurement of the curvature, and the time of measurement of the curvature may be as described above with respect to the electrode assembly.

[0179] According to one embodiment of the present invention, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, may be greater than 40° and less than 98°, greater than 45° and less than 95°, greater than 45° and less than 90°, greater than 45° and less than 80°, greater than 45° and less than 70°, greater than 45° and less than 65°, greater than 50° and less than 95°, greater than 50° and less than 90°, greater than 50° and less than 80°, greater than 50° and less than 70°, greater than 50° and less than 65°, greater than 60° and less than 95°, greater than 60° and less than 90°, greater than 60° and less than 80°, greater than 60° and less than 70°, or greater than 60° and less than 65°.

[0180] When the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum satisfies the aforementioned range, the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by the shrinkage / expansion of the electrode during battery charging / discharging can be improved, damage to the second electrode and separator can be prevented, and internal short circuits between the first electrode and the second electrode can be prevented, thereby improving battery stability and lifespan characteristics.

[0181] According to one embodiment of the present invention, the method for manufacturing the electrode assembly may be performed in a roll-to-roll manner. Specifically, steps (a) to (c) may be performed in a roll-to-roll processing manner in which a number of flexible metal foils are processed while moving between rollers. Here, the roll-to-roll method may mean a method of unwinding a roll that is winding a flexible and thin metal sheet-type electrode current collector to supply the electrode current collector, applying an electrode slurry containing an electrode active material to at least one surface of the electrode current collector and drying it to form an electrode composite layer, and then rewinding the processed electrode current collector on another roll to recover it.

[0182] A method for manufacturing an electrode assembly according to one embodiment of the present invention may be capable of producing an electrode assembly in a continuous process using existing roll-to-roll process equipment used in the industry, wherein the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is adjusted.

[0183] That is, the method for manufacturing an electrode assembly according to one embodiment of the present invention can secure productivity and economic efficiency by enabling the continuous production of an electrode assembly, in which the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is adjusted, using existing roll-to-roll process equipment.

[0184] FIG. 9 shows the correlation between the angle formed by the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, the flatness fraction of the first electrode, and the deformation of the core portion according to the method of manufacturing an electrode assembly according to one embodiment of the present invention.

[0185] Specifically, FIG. 9(a) schematically illustrates a method for manufacturing an electrode assembly according to an embodiment of the present invention, and FIG. 9(b) to (d) illustrate a winding core according to an embodiment of the present invention, a CT image of the electrode assembly, and the curvature of the first electrode extracted from the CT image. More specifically, FIG. 9(b) illustrates a flat region of the electrode assembly, FIG. 9(c) illustrates a point where the curvature of the electrode assembly is maximum, and FIG. 9(d) illustrates a CT image of the electrode assembly in relation to the winding core according to an embodiment of the present invention. Meanwhile, FIG. 9(e) is an image showing core deformation occurring in the flat region of the electrode assembly according to FIG. 9(b) to (d) after the cycle proceeds.

[0186] According to one embodiment of the present invention, the winding may be performed using a core comprising: a spaced portion into which a separator is inserted; a first core portion provided on one side of the spaced portion centered on the spaced portion; and a second core portion provided on the other side of the spaced portion and having a cross-sectional area different from that of the first core portion.

[0187] Specifically, the above-mentioned core may include a spaced portion (S) into which a separator is inserted, and a first core portion (A) may be provided on one side centered on the spaced portion (S), and a second core portion (B) with a cross-sectional area different from that of the first core portion (A) may be provided on the other side. By having the spaced portion of the above-mentioned core, a laminate such as a separator inserted in the spaced portion may be wound in a direction opposite to the rotation direction (R) of the core by the rotation of the above-mentioned core.

[0188] When the above-mentioned core comprises a first core portion and a second core portion having the same cross-sectional area as the first core portion, twisting of the core may occur due to tension during winding, and the roundness of the core portion of the manufactured electrode assembly may decrease. That is, the core portion is deformed into an elliptical shape due to tension during winding, which may be disadvantageous in terms of processability, outer diameter, and roundness.

[0189] On the other hand, if the above-mentioned core includes a first core portion; and a second core portion having a cross-sectional area different from that of the first core portion, the occurrence of core collapse may be minimized by minimizing the twisting and asymmetry of the core caused by tension during winding and increasing the average roundness of the core portion.

[0190] Specifically, the above-mentioned core comprises a first core portion and a second core portion having a cross-sectional area different from that of the first core portion, so that when high tension is applied to the core, twisting may occur in the relatively smaller core portion. Accordingly, centered on the separation portion, a point where the curvature of the first electrode is maximum may be located at a position adjacent to the relatively larger core, and a flat area of ​​the first electrode may be located at a position adjacent to the relatively smaller core.

[0191] In addition, regarding the longitudinal end of the first electrode, the region of greater than 0° and less than 180° in the direction opposite to the direction (W) in which the electrode assembly is wound, that is, the rotation direction (R) of the core, has a relatively smaller number of turns of the first electrode up to the outermost layer compared to the region of greater than 180° and less than 360°, and since the distance from the longitudinal end of the first electrode, which is capable of sliding, is relatively far, the concentrated stress is not relieved, so the possibility of deformation in the hollow direction of the core part at that location may be higher.

[0192] That is, the above-mentioned core may include a pair of core sections separated by a spaced portion into which a separator is inserted, and when a certain level of tension is applied, twisting of the above-mentioned core may occur, and as a result, an area where the curvature of the first electrode is below a specific value, i.e., a flat area, may inevitably occur, and collapse of the core section may occur in the area where the curvature of the first electrode is below a specific value.

[0193] At this time, the core collapse phenomenon may be improved when the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is adjusted in the region of greater than 0° and less than or equal to 180° in the direction opposite to the direction (W) in which the electrode assembly is wound, that is, in the rotation direction (R) of the winding core, with respect to the longitudinal end of the first electrode.

[0194] According to one embodiment of the present invention, the cross-sectional area of ​​the first core may be smaller than the cross-sectional area of ​​the second core, and the placement process may be performed such that the longitudinal end of the first electrode is placed on the outer surface of the first core.

[0195] Specifically, referring to FIG. 9 (a) to (d), the placement process may be such that the position of the longitudinal end of the first electrode is adjusted according to the insertion length of the separator, the insertion timing of the first electrode, etc., and the longitudinal end of the first electrode is placed on the outer surface of the first core. Even when the diameter of the core is different, the position of the longitudinal end of the first electrode can be adjusted by adjusting the insertion length of the separator, the insertion timing of the first electrode, etc.

[0196] According to one embodiment of the present invention, the placement process may be performed such that the longitudinal end of the first electrode is placed at a point spaced 40% or more and 60% or less from the spacing portion, based on 100% of the outer circumferential length of the first core portion. Specifically, the longitudinal end of the first electrode may be placed at a point spaced 40% or more and 50% or less from the spacing portion, or 50% or more and 60% or less from the spacing portion, based on 100% of the outer circumferential length of the first core portion, and for example, it may be placed at the 50% point. In other words, the longitudinal end of the first electrode may be placed on the outer circumferential surface of the first core portion at the point 1 / 2 of the outer circumferential surface of the first core portion, which is the point furthest from the spacing portion of the core.

[0197] When the above placement process is performed such that the longitudinal end of the first electrode is placed on the outer surface of the first core, the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is adjusted to a specific range. Furthermore, the manufactured electrode assembly can improve the phenomenon where the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging, prevent damage to the second electrode and separator, and prevent internal short circuits between the first electrode and the second electrode, thereby improving battery stability and lifespan characteristics.

[0198] According to one embodiment of the present invention, the winding process may be performed while maintaining a tension of 400 gf or more. Specifically, the tension may be 400 gf or more and 500 gf or less. More specifically, the tension may be 410 gf or more, 420 gf or more, 430 gf or more, 440 gf or more, or 450 gf or more, and may be 590 gf or less, 580 gf or less, 570 gf or less, 560 gf or less, or 550 gf or less.

[0199] When the above tension satisfies the aforementioned range, due to the high tension in the winding process, a point where the curvature of the first electrode is maximum may be located at a position adjacent to a relatively large core centered on the separation portion, and a flat area of ​​the first electrode may be located at a position adjacent to a relatively small core, and the positions of the point where the curvature of the first electrode is maximum and the flat area of ​​the first electrode may be formed consistently.

[0200] One embodiment of the present invention provides an electrode assembly manufactured by the aforementioned method for manufacturing an electrode assembly.

[0201] An electrode assembly according to one embodiment of the present invention can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by shrinkage / expansion of the electrode during battery charging / discharging by adjusting the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, and can prevent damage to the second electrode and the separator and prevent an internal short circuit between the first electrode and the second electrode, thereby improving battery stability and lifespan characteristics.

[0202] One embodiment of the present invention provides a secondary battery comprising: the electrode assembly; and a battery case for accommodating the electrode assembly. Specifically, the secondary battery may comprise the electrode assembly according to the above-described embodiment and the battery case for accommodating the electrode assembly.

[0203] The secondary battery according to the present invention can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by the shrinkage / expansion of the electrode during battery charging / discharging, prevent damage to the second electrode and separator, and prevent internal short circuits between the first electrode and the second electrode, thereby improving battery stability and lifespan characteristics.

[0204] According to one embodiment of the present invention, the battery case may be cylindrical. Specifically, the battery case may be cylindrical, prismatic, or pouch-shaped depending on the application, but is not limited thereto.

[0205] According to one embodiment of the present invention, the interior of the battery case may contain an electrolyte. Specifically, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0206] According to one embodiment of the present invention, the non-aqueous organic solvent may be, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. It can be used.

[0207] According to one embodiment of the present invention, the metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, as an anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN) 2- , BF4 - , ClO4 - , PF6- , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more types selected from the group consisting of can be used.

[0208] According to one embodiment of the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0209] One embodiment of the present invention provides a battery module comprising the secondary battery as a unit cell and a battery pack comprising the same. Since the battery module and the battery pack include the secondary battery with improved high capacity, high battery stability, and lifespan characteristics, they may be used as a power source for a medium-to-large device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0210] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention is not to be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present invention to those with average knowledge in the art.

[0211] Examples

[0212] Example 1

[0213] Electrode assembly manufacturing

[0214] Li(Ni as the first electrode active material 0.89 Co 0.07 Mn 0.04 A first electrode active material slurry was prepared by adding CNT as a first electrode conductive material and polyvinylidenefluoride (PVdF) as a first electrode binder to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.92:0.5:1.58. The first electrode active material slurry was coated onto an aluminum current collector having a thickness of 15 μm and a width of 63.9 mm, and then dried and rolled to form a first electrode active material layer, thereby preparing a first electrode having a thickness of 135 μm.

[0215] Next, natural graphite (C, average particle size 17 μm) was prepared as the second electrode active material, and a second electrode active material composition was prepared by mixing the second electrode active material, carbon black as the second electrode conductive material, and styrene butadiene rubber (SBR) as the second electrode binder in a weight ratio of 97.7:1.3:1.0. Subsequently, 7.8 g of distilled water was added to 5 g of the second electrode active material composition and stirred to prepare a second electrode active material slurry. The second electrode active material slurry was applied to a copper (Cu) metal thin film serving as the second electrode current collector, having a thickness of 8 μm and a widthwise length of 65.2 mm, and dried (drying temperature 120°C, 1 minute) to form a second electrode with an average thickness of 166 μm. At this time, the temperature of the circulating air was 60°C.

[0216] Subsequently, two separators were sequentially arranged and wound using a core with a diameter of 3.2 mm, and then the second electrode was inserted between the two separators and wound further. At this time, the core used included a gap where the separator is inserted, a first core section, and a second core section with a cross-sectional area different from that of the first core section, and the cross-sectional areas of the first and second core sections were each 15 mm 2 , 10 mm 2 was.

[0217] After the above separator and the second electrode are wound for about 3 turns, the first electrode is inserted and wound, and a PET seal tape is attached and finished to wrap around the upper and lower outer surfaces of the electrode assembly at the end where the winding ends.

[0218] At this time, based on the first core section located at the 6 o'clock position and the second core section located at the 12 o'clock position of the electrode assembly, the positions of the longitudinal ends and tabs located at the first electrode core section and the outermost section were adjusted as shown in Table 1 below. Here, FE (Free-edge) means that the electrode current collector and the electrode active material layer have longitudinal ends at the same position, and the unit 'hour' indicates the relative positions of each factor in a clockwise direction when the first electrode tab is positioned at the 12 o'clock position on the CT image.

[0219] The area and roundness of the core hollow measured from the computed tomography (CT) image were as shown in Table 1 below, and after 50 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the core of the electrode assembly was adjusted so that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, was 60.8°. At this time, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum was determined by comparing the curvature measured at each measurement point on the CT image, and identifying the measurement point where the curvature has a maximum value in the region greater than 0° and less than or equal to 180° in the direction opposite to the winding direction of the electrode assembly relative to the longitudinal end of the first electrode as the point where the curvature of the first electrode is maximum (Curvature Max.). The angle formed between the point where the curvature of the first electrode is maximum and the longitudinal end of the first electrode, centered on the winding axis, was measured and is shown in Table 2 below. In the following examples, comparative examples, and experimental examples, the point where the curvature of the first electrode is maximum (Curvature Max.) was measured using the same method.

[0220] Influencing factors Adjustment range 1st electrode core part FE position (time) 6.5-8 FE position (time) of the outermost part of the first electrode 4.5-5.5 Outermost second electrode tab position (time) 6-7 Area of ​​the hollow core (mm²) 2 ) 27-33 Roundness (%) 89-92

[0221] manufacturing of secondary batteries

[0222] After inserting the above electrode assembly into a cylindrical battery case, an electrolyte solution was injected by mixing ethylene carbonate (EC):ethyl methyl carbonate (EMC):diethyl carbonate (DEC) in a volume ratio of 20:5:75 and dissolving LiPF6 to a concentration of 1.4 M, and the cylindrical battery can was sealed with a cap assembly to manufacture a secondary battery.

[0223] Example 2

[0224] After proceeding with 50 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum in the core portion of the electrode assembly, centered on the winding axis, was adjusted to be 65°.

[0225] Comparative Example 1

[0226] After proceeding with 50 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, in the core portion of the electrode assembly was adjusted to be 98.9°.

[0227] Comparative Example 2

[0228] After proceeding with 50 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, in the core portion of the electrode assembly was adjusted to be 112.4°.

[0229] Comparative Example 3

[0230] After proceeding with 50 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis, in the core portion of the electrode assembly was adjusted to be 129.3°.

[0231] Comparative Example 4

[0232] After proceeding with 50 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum in the core portion of the electrode assembly, centered on the winding axis, was adjusted to be 40°.

[0233] Comparative Example 5

[0234] After proceeding with 50 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the electrode assembly and secondary battery were manufactured in the same manner as in Example 1, except that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum in the core portion of the electrode assembly, centered on the winding axis, was adjusted to be 20°.

[0235] Experimental Example

[0236] Experimental Example 1: Evaluation of Flatness Fraction

[0237] The flatness ratio of the secondary batteries of Example 1 and Comparative Examples 1 to 3 was evaluated by the following method, and the results are shown in Table 2 and Figures 1 to 4, respectively.

[0238] 1) The first electrode is extracted from the CT image of the electrode assembly.

[0239] 2) On the first surface of the first electrode, measurement points are set at 2° intervals from one end of the length direction of the first electrode, and the x and y coordinates of the measurement points are measured.

[0240] 3) Using the x and y coordinates of the above measurement points, the curvature (k) for each measurement point is calculated according to the following Equation 1.

[0241] [Equation 1]

[0242] k=(x'y''-y'x'') / (x' 2 +y' 2 ) 3 / 2

[0243] In the above Equation 1, k is the curvature of the first electrode, x is the x-coordinate of the measurement point, y is the y-coordinate of the measurement point, x' is the first derivative of x, y' is the first derivative of y, x'' is the second derivative of x, and y'' is the second derivative of y.

[0244] 4) If the curvature value calculated at each measurement point is 1 or less, the measurement point is evaluated as a flat area, and the ratio of the number of measurement points evaluated as a flat area to 100% of the total number of measurement points is evaluated as the flatness fraction (%).

[0245] Experimental Example 2: Evaluation of Core Collapse

[0246] The occurrence of Core Collapse in the secondary batteries of Example 1, Example 2 and Comparative Examples 1 to 5 was evaluated by the following method, and the occurrence of Core Impingement was re-evaluated every 200 cycles, and the results are shown in Table 2 and Figures 1 to 7, respectively.

[0247] 1) The first electrode is extracted from the CT image of the electrode assembly.

[0248] 2-1) The area of ​​the hollow core portion surrounded by the first electrode is measured from one end in the longitudinal direction of the first electrode to a point corresponding to one turn in the longitudinal direction of the first electrode.

[0249] 2-2) Based on 100% of the sum of the cross-sectional areas of the spacing portion, the first core portion, and the second core portion of the core used in winding the electrode assembly, if the area of ​​the hollow core portion is less than 100%, it was evaluated that Core Collapse occurred.

[0250] 3-1) On the first surface of the first electrode, the minimum value (D) of the diameter of the hollow core portion of the first electrode extracted min ) and maximum value(D max Draw extensions of the straight lines corresponding to ), and draw concentric circles using the intersection point of each straight line as the central axis, that is, the winding axis.

[0251] 3-2) Maximum separation distance (R) between the winding axis and the first electrode from one end in the longitudinal direction of the first electrode to a point corresponding to 1 turn in the longitudinal direction of the first electrode max ) and the minimum separation distance (R) between the winding shaft and the first electrode min Measure each ).

[0252] 3-3) Maximum separation distance (R) between the winding shaft and the first electrode max The minimum separation distance (R) between the winding shaft and the first electrode for ) min The ratio (%) of ) that is, the roundness of the hollow core part was calculated, and if the calculated roundness of the hollow core part was less than 89%, it was evaluated that Core Collapse had occurred.

[0253] Meanwhile, the above method for evaluating whether Core Collapse has occurred can be applied in such a way that, when an unknown secondary battery (Unknown Cell) is obtained, the occurrence of Core Collapse is evaluated at the time of initial acquisition, and the occurrence of Core Collapse is re-evaluated every 200 cycles and compared with the Core Collapse conditions of the secondary battery according to the embodiment of the present invention.

[0254] Experimental Example 3: Core Impingement Evaluation

[0255] The occurrence of Core Impingement in the secondary batteries of Example 1, Example 2 and Comparative Examples 1 to 5 was evaluated by the following method, and the occurrence of Core Impingement was re-evaluated every 200 cycles, and the results are shown in Table 2 and Figures 1 to 7, respectively.

[0256] FIG. 12 schematically illustrates a method for evaluating whether core impingement has occurred. Specifically, FIG. 12 (a) schematically illustrates a method for evaluating whether core impingement has occurred when deformation has occurred in the second electrode, and FIG. 12 (b) schematically illustrates a method for evaluating whether core impingement has occurred when deformation has not occurred in the second electrode.

[0257] 1) On the first surface of the first electrode (300), a straight line connecting the longitudinal end (310) of the first electrode and a point 5 mm away from the end is extended to draw a first extension line (E1).

[0258] 2-1) Case where deformation occurs in the second electrode

[0259] A second extension line (E2) is drawn by extending a straight line connecting two points where the curvature direction changes within a distance of 5 mm from the longitudinal end (310) of the first electrode on the surface of the core part of the electrode assembly that faces the first surface of the second electrode (100).

[0260] 2-2) Case where no deformation occurs in the second electrode

[0261] A second extension line (E2) is drawn by extending a straight line connecting two points that are spaced 5 mm apart from the longitudinal end (310) of the first electrode on the surface of the core part of the electrode assembly that is opposite to the first surface of the first electrode of the second electrode (100).

[0262] 3) Core Impingement was evaluated to have occurred when the angle from the first extension line (E1) to the second extension line (E2) in a counterclockwise direction, centered on the intersection point of the first extension line (E1) and the second extension line (E2), exceeds 25°.

[0263] Meanwhile, the above method for evaluating whether Core Impingement has occurred can be applied in such a way that, when an unknown secondary battery (Unknown Cell) is obtained, the occurrence of Core Impingement is evaluated at the time of initial acquisition, and the occurrence of Core Impingement is re-evaluated every 200 cycles and compared with the Core Impingement conditions of the secondary battery according to the embodiment of the present invention.

[0264] Experimental Example 4: Evaluation of Core Crack Occurrence

[0265] The occurrence of Core Crack in the electrode assemblies of Example 1, Example 2 and Comparative Examples 1 to 5 was evaluated by the following method, and the results are shown in Table 2 and Figures 6 and 7, respectively.

[0266] Specifically, the electrode assemblies of Example 1, Example 2 and Comparative Examples 1 to 5 were prepared, and the manufactured electrode assemblies were disassembled to visually check for the occurrence of cracks or wrinkles in the core portion. At this time, if cracks or wrinkles were found in the core portion, it was evaluated that a Core Crack had occurred.

[0267] First electrode FE - Curvature Max. Angle (°) Flatness Fraction (%) Core Collapse Evaluation Results Core Impingement Assessment Results Core Crack Occurrence Assessment Results Example 1 60.8 7.72 0 / 2 0 / 2 0 / 2 Example 2 65 9.6 0 / 2 0 / 2 0 / 2 Comparative Example 1 98.9 13.9 2 / 2 0 / 2 0 / 2 Comparative Example 2 112. 4 17.0 2 / 2 1 / 2 0 / 2 Comparative Example 3 129.3 16.49 2 / 2 1 / 2 0 / 2 Comparative Example 4 40 3.0 1 / 2 1 / 2 1 / 2 Comparative Example 5 20 1.0 1 / 2 1 / 2 1 / 2

[0268] FIG. 6 is a CT image of an electrode assembly according to Comparative Example 4 and an image of a crack occurring in the core portion of the first electrode, and FIG. 7 is a CT image of an electrode assembly according to Comparative Example 5 and an image of a crack occurring in the core portion of the first electrode. Specifically, FIG. 6(a) and FIG. 7(a) are CT images of the electrode assembly according to Comparative Example 4 and the electrode assembly according to Comparative Example 5, and FIG. 6(b) and FIG. 7(b) are exploded images showing a crack that occurred in the first electrode of the core portion of the electrode assembly according to Comparative Example 4 and Comparative Example 5, respectively. Here, the red circles represent the Core Impingement occurrence area corresponding to the longitudinal end of the first electrode and the crack occurrence area of ​​the first electrode of the core portion, respectively.

[0269] Referring to Table 2, Fig. 6(b), and Fig. 7(b), it can be seen that in the electrode assembly according to Comparative Example 4 and Comparative Example 5, the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum, centered on the winding axis in the core portion of the electrode assembly, is 40° or less, and the stress caused by the twisting of the winding core is concentrated at the longitudinal end of the first electrode, and as a result, wrinkles or cracks occur in the core portion.

[0270] If a crack in the first electrode and resulting foreign substances occur in the core portion of the electrode assembly during the winding process, the defect rate may increase and processability may deteriorate. Accordingly, by excluding the input of the first electrode, where cracking is expected, from the manufacturing process, a decrease in the productivity of the electrode assembly and the secondary battery can be prevented.

[0271] Specifically, when an electrode assembly with a crack is inserted into a battery case, the possibility of low voltage generation and short circuits caused by foreign substances on the first electrode within the battery case increases significantly. Accordingly, the possibility of cracking in the first electrode may be reduced by adjusting the range of the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum during the winding process. That is, it can be seen that the electrode assembly and the method for manufacturing the electrode assembly according to one embodiment of the present invention are suitable for a continuous process using existing roll-to-roll process equipment, thereby ensuring productivity and economic efficiency of the electrode assembly including the first electrode and the secondary battery.

[0272] Reference Experiment Example: Evaluation of Electrode Sliding Range

[0273] Reference Experiment Example 1

[0274] The secondary battery of Example 1 above was prepared and charged and discharged 50 times under conditions of 25°C, 1C charging and 1C discharging.

[0275] While performing 200 cycles from SOC 0% to SOC 100% under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, the position of the longitudinal end of the first electrode at SOC 0% and SOC 100% was extracted and recorded from CT images, and the sliding range of the longitudinal end of the first electrode was measured. Subsequently, the sliding range of the longitudinal end of the first electrode was evaluated from CT images before activation and at SOC 100% and is shown in Fig. 13 below.

[0276] Reference Experiment Example 2

[0277] Except for using the secondary battery of Example 2 above, the sliding range of the longitudinal end of the first electrode was measured in the same manner as in Reference Experiment 1. Subsequently, the sliding range of the longitudinal end of the first electrode was evaluated from CT images before activation and at SOC 100% and is shown in Fig. 13 below.

[0278] FIG. 13 is a CT image showing the sliding range of the longitudinal end of the first electrode of the secondary battery according to Reference Experimental Example 1 and Reference Experimental Example 2. Specifically, FIG. 13 is a CT image showing the sliding range of the longitudinal end of the first electrode before activation and at SOC 100% of the secondary battery according to Reference Experimental Example 1 and Reference Experimental Example 2.

[0279] Referring to Fig. 13, it was confirmed that in Reference Experimental Example 1, sliding occurred at 18.41° (SOC 100) - 16.72° (before activation) = 1.69°, and in Reference Experimental Example 2, sliding occurred at 55.08° (SOC 100) - 53.30° (before activation) = 1.78°. That is, in both Reference Experimental Example 1 and Reference Experimental Example 2, the measurement results confirmed that the longitudinal end of the first electrode slided within a range of 1° to 3° relative to its initial position.

[0280] Through this, it can be seen that in the secondary battery according to Example 1 and Example 2, sliding of the first electrode may occur due to contraction / expansion of the electrode before activation and at SOC 100%, but sliding occurs within a specific range (1° to 3°).

[0281] That is, the winding process is performed while maintaining tension greater than a certain value, so the position of the point where the curvature of the first electrode is maximum is maintained constant. Therefore, even when the cycle proceeds, it can be seen that the range of the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is maintained within the sliding range (1° to 3°) of the longitudinal end of the first electrode.

[0282] FIGS. 1 and 2 are CT images of an electrode assembly according to Example 1 and Example 2 and an image showing the curvature of the first electrode extracted from the CT image.

[0283] FIGS. 3 to 5 are CT images of electrode assemblies according to Comparative Examples 1 to 3 and images showing the curvature of the first electrode extracted from the CT images.

[0284] Specifically, FIGS. 1 to 5 represent, in color coordinates, the ratio of measurement points having a curvature less than or equal to an arbitrarily set reference value for the curvature measured at each measurement point. Here, the set reference value is a specific value within the range of 0.5 to 1.0, and the range of the color index expressed to the right of the color coordinates is 0 to 0.8 for FIGS. 1 to 5 (a) and 1 to 1.5 for FIGS. 1 to 5 (b).

[0285] More specifically, (a) of FIGS. 1 to 5 visualizes the flat area and flatness fraction by implementing the area where the k value is low in color coordinates when the color distribution range of the curvature measured at each measurement point is set to 0 to 0.8, and (b) of FIGS. 1 to 5 visualizes the point where the curvature is maximum by implementing the area where the k value is high in color coordinates when the color distribution range of the curvature measured at each measurement point is set to 1 to 1.5. At this time, each measurement point is extracted from the CT image of the first electrode as described above, and the longitudinal end of the first electrode located in the core part is adjusted to be positioned at the 6 o'clock direction.

[0286] Referring to Table 2, Figures 1 to 5, Figure 6 (a), and Figure 7 (a), it was confirmed that the electrode assembly according to Example 1 and Example 2 did not undergo core collapse or core impingement even after 500 cycles under conditions of 4.25 V-2.5 V 1 C / 1 C @25 ℃, and the angle between the longitudinal end of the first electrode extracted from the core CT image and the point where the curvature of the first electrode is maximum was 60.8° and 65°, respectively.

[0287] On the other hand, as in Comparative Examples 1 to 3, when the angle between the longitudinal end of the first electrode extracted from the CT image of the core part and the point where the curvature of the first electrode is maximum is greater than 98°, or as in Comparative Examples 4 and 5, when the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is 40° or less and does not satisfy the aforementioned angle range, it was confirmed that Core Impingement occurs when the angle formed by the first extension line and the second extension line is 25° or greater, or even if Core Impingement does not occur, Core Collapse occurs when the area of ​​the core hollow is less than 100% or the roundness of the core hollow is less than 89% based on 100% of the sum of the cross-sectional areas of the core used for winding.

[0288] Through this, it can be seen that the electrode assembly according to one embodiment of the present invention and the secondary battery including the same can improve the phenomenon in which the hollow core fails to maintain its circular shape and collapses due to deformation of the electrode assembly caused by contraction / expansion of the electrode during battery charging / discharging by adjusting the angle between the longitudinal end of the first electrode extracted from the CT image of the core part and the point where the curvature of the first electrode is maximum to a specific range, thereby preventing damage to the second electrode and the separator and preventing an internal short circuit between the first electrode and the second electrode, and thus improving battery stability and lifespan characteristics.

[0289] FIG. 10 is a CT image of an electrode assembly according to Example 1 and an image showing the curvature of the first electrode extracted from the CT image and the arrangement relationship of the winding core, and FIG. 11 is a CT image of an electrode assembly according to Comparative Example 2 and an image showing the curvature of the first electrode extracted from the CT image and the arrangement relationship of the winding core. Here, FIG. 10 and FIG. 11 (a) schematically shows the arrangement relationship of winding cores A and B used for winding, respectively, and the section corresponding to the section where the curvature of the first electrode is maximum, measured from FIG. 10 and FIG. 11 (b), is shown on the outer surface of winding core B indicated in FIG. 10 and FIG. 11 (a).

[0290] Referring to Table 2 and Figures 10 and 11 above, the electrode assembly according to Example 1 was configured such that the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is greater than 40° and less than or equal to 98° around the winding axis, and it was confirmed that no core collapse or core impingement occurred after 50 cycles under conditions of 4.2 V-2.5 V 1 C / 1 C @25 ℃ or after 500 cycles under conditions of 4.2 V (0.25 C)-2.85 V (0.33 C), @40 ℃.

[0291] On the other hand, as in Comparative Example 2, when the angle formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is greater than 98° centered on the winding axis—that is, when the angle range formed between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum as described above is not satisfied—it was confirmed that Core Impingement occurs when the angle formed by the first extension line and the second extension line is 25° or greater, or even if Core Impingement does not occur, Core Collapse occurs when the area of ​​the hollow core is less than 100% based on 100% of the sum of the cross-sectional areas of the core used for winding, or when the calculated roundness of the hollow core is less than 89%.

[0292] Through this, it can be seen that the method for manufacturing an electrode assembly according to one embodiment of the present invention can manufacture an electrode assembly in which the angle between the longitudinal end of the first electrode and the point where the curvature of the first electrode is maximum is adjusted in a simpler manner, and can secure productivity and economic efficiency by being suitable for a continuous process using existing roll-to-roll process equipment.

[0293] The above detailed description is intended to illustrate and explain the present invention. Furthermore, the foregoing merely illustrates and describes preferred embodiments of the present invention, and as described above, the present invention may be used in various other combinations, modifications, and environments, and may be modified or altered within the scope of the concept of the invention disclosed herein, the scope equivalent to the foregoing disclosure, and / or the scope of the art or knowledge. Accordingly, the above detailed description of the invention is not intended to limit the present invention to the disclosed embodiments. Additionally, the appended claims should be interpreted as including other embodiments. Explanation of the symbols

[0294] 100: Second electrode 300: First electrode 310: Longitudinal end of the first electrode E1: First extension line E2: Second extension line R: Direction of rotation of the winding core W: Winding direction of the electrode assembly A: First volume B: Volume 2 Heart S: Separation

Claims

Claim 1 In an electrode assembly in which a first electrode; a separator and a second electrode are laminated and wound around a winding axis, an extension line connecting the winding axis and the inner end of the first electrode; The angle formed by the extension line connecting the winding axis and the maximum curvature point of the first electrode is greater than 40° and less than or equal to 98°, and based on a cross-section perpendicular to the winding axis of the electrode assembly, the maximum curvature point of the first electrode is provided within or in part of the electrode assembly within 3 turns in the winding direction in which the electrode assembly is wound on the winding axis from the inner end of the first electrode, and is a point where the curvature of the first electrode is maximum in an area with an azimuth angle greater than 0° and less than or equal to 180° in the direction opposite to the winding direction of the electrode assembly from the inner end of the first electrode, and the flatness fraction, which is the ratio of the area where the curvature of the first electrode is 1 or less in the interior or part of the core portion of the electrode assembly, is greater than 3% and less than or equal to 13.5%. Claim 2 delete Claim 3 delete Claim 4 An electrode assembly according to claim 1, wherein the first electrode comprises a first electrode current collector; and a first electrode active material layer provided on at least one surface of the first electrode current collector, wherein the first electrode active material layer extends to an inner end of the first electrode current collector, and the inner end of the first electrode current collector corresponds to an inner end of the first electrode. Claim 5 An electrode assembly according to claim 4, wherein the first electrode comprises a first electrode non-part that is not provided with a first electrode active material layer, and further comprises a first electrode tab that is provided on or physically connected to the first electrode non-part. Claim 6 An electrode assembly according to claim 1, wherein an extension line connecting the winding shaft and the inner end of the first electrode; and an extension line connecting the winding shaft and the point where the curvature of the first electrode is 1 or less, and the angle formed by the extension line is greater than 0°. Claim 7 An electrode assembly according to claim 1, wherein the angle formed by the extension line connecting the winding shaft and the inner end of the first electrode; and the extension line connecting the winding shaft and the maximum curvature point of the first electrode is determined after activation of the electrode assembly. Claim 8 An electrode assembly according to claim 1, wherein the angle formed by the extension line connecting the winding shaft and the inner end of the first electrode; and the extension line connecting the winding shaft and the maximum curvature point of the first electrode is determined after 50 charge and discharge cycles under conditions of 25°C, 1C charge and 1C discharge. Claim 9 An electrode assembly according to claim 1, wherein the circularity of the first electrode is 89% or more in the interior or part of the electrode assembly within 3 turns in the winding direction in which the electrode assembly is wound on the winding axis from the inner end of the first electrode. Claim 10 An electrode assembly according to claim 1, wherein the first electrode comprises a first surface facing the winding axis of the electrode assembly and a second surface opposite to the first surface, and a first extension line drawn by extending a straight line connecting two points where the direction of curvature changes within a distance of 5 mm from the inner end of the first electrode on the first surface of the first electrode; and a second extension line drawn by extending a straight line connecting two points at a distance of 5 mm from the inner end of the first electrode on the surface of the second electrode facing the first surface of the first electrode, wherein the two extension lines form an angle of 25° or less. Claim 11 An electrode assembly according to claim 1, wherein the first electrode does not contain cracks or wrinkles in the interior or part of the electrode assembly within 3 turns in the winding direction in which the electrode assembly is wound on a winding axis from the inner end of the first electrode. Claim 12 delete Claim 13 (a) a placement process for forming a laminate by arranging a first electrode, a separator, and a second electrode in sequence; and (b) a winding process for manufacturing an electrode assembly by winding the laminate around a winding axis using a winding core, wherein the winding core includes a first winding core portion and a second winding core portion, and the winding process includes inserting a separator between the first winding core portion and the second winding core portion, and an extension line connecting the winding axis and the inner end of the first electrode; A method for manufacturing an electrode assembly, wherein the angle formed by the extension line connecting the winding axis and the maximum curvature point of the first electrode is greater than 40° and less than or equal to 98°, and based on a cross-section perpendicular to the winding axis of the electrode assembly, the maximum curvature point of the first electrode is provided within or in a part of the electrode assembly within 3 turns in the winding direction in which the electrode assembly is wound on the winding axis from the inner end of the first electrode, and is a point where the curvature of the first electrode is maximum in an area with an azimuth angle greater than 0° and less than or equal to 180° in the direction opposite to the winding direction of the electrode assembly from the inner end of the first electrode, and the flatness fraction, which is the ratio of the area where the curvature of the first electrode is 1 or less in the interior or part of the core portion of the electrode assembly, is greater than 3% and less than or equal to 13.5%. Claim 14 A method for manufacturing an electrode assembly according to claim 13, wherein the first core and the second core are asymmetric with respect to a cross-section perpendicular to the winding axis of the electrode assembly. Claim 15 A method for manufacturing an electrode assembly according to claim 13, wherein, based on a cross-section perpendicular to the winding axis of the electrode assembly, the cross-sectional area of ​​the first core portion is smaller than the cross-sectional area of ​​the second core portion, and the placement process is performed such that the inner end of the first electrode is placed on the outer surface of the first core portion. Claim 16 A method for manufacturing an electrode assembly according to claim 13, wherein the winding process is performed while maintaining a tension of 400 gf or more. Claim 17 An electrode assembly manufactured by the manufacturing method according to Paragraph 13. Claim 18 A secondary battery comprising an electrode assembly according to any one of claims 1, 4 through 11 and 17.

Images