Patent Application
20250149647
This application claims the benefit of Korean Patent Application Nos. 10-2023-0149964 filed Nov. 2, 2023 and 10-2024-0110579 filed Aug. 19, 2024, the disclosures of which are hereby incorporated herein by reference.
The present disclosure relates to an electrode assembly, a method for manufacturing an electrode assembly, and a secondary battery including the electrode assembly, and specifically, to an electrode assembly in which core deformation is improved by changing a design of the electrode assembly, a method for manufacturing an electrode assembly, and a cylindrical secondary battery including the electrode assembly.
For a cylindrical battery, a jelly-roll type electrode assembly is manufactured by rolling a long electrode having a predetermined width into a roll form. The cylindrical battery manufactured by inserting such an electrode assembly into a battery case undergoes repeated contraction/expansion of an electrode during charging and discharging. In particular, when a tab (in tab) is located in a core of the electrode assembly or a degree of contraction/expansion of the electrode assembly increases due to a silicon-based active material added in a negative electrode, a pressure acting on a core part of the electrode assembly greatly increases.
The core part of the cylindrical battery is a space where a winding core (mandrel) used for winding the electrode assembly is located, and there is an empty space, that is, a core cavity, used in a cylindrical battery assembly process, such as an insertion process of the electrode assembly into the battery case and a welding process.
Recently, as low-resistance/high-capacity designs are increasing, cases where the electrode assembly includes multiple tabs or a silicon-based active material is added are increasing. Accordingly, a possibility of core deformation of the electrode assembly due to the contraction/expansion of the electrode assembly increases. In particular, there are problems that the battery life is deteriorated due to a phenomenon (core collapse) in which the core cavity fails to maintain a circular shape and collapses, and that a negative electrode and a positive electrode come into direct contact to cause an internal short-circuit, leading to heat generation and ignition, due to a phenomenon (core impingement) in which an end portion of the positive electrode located at the core part and the negative electrode adjacent thereto are deformed beyond a certain level, causing damage to a separator between the positive electrode and the negative electrode.
In order to solve the problems of the deterioration in battery life, the damage to the separator and the internal short-circuit due to the deformation of the electrode assembly, it is necessary to develop a technology capable of addressing the phenomenon that the core cavity in the corresponding region fails to maintain a circular shape and collapses, and suppressing the occurrence of internal short-circuit due to the damage to the separator.
The present disclosure provides, among other things, an electrode assembly whose design improves core deformation, a method for manufacturing an electrode assembly, and a secondary battery including the electrode assembly.
However, the problem to be solved by the present disclosure is not limited to the above-described problem, and other problems not described will be apparenty understood by one skilled in the art from the following description.
The present disclosure is defined by the subject matter of the appended independent claims. Particular examples of the present disclosure are given by the additional features of the dependent claims.
An electrode assembly comprises a first electrode, a separator, and a second electrode. The first electrode, the separator and the second electrode are stacked and wound around a winding axis. An angle formed between a line extending from the winding axis through an inner end of the first electrode and a line extending from the winding axis through a curvature maximum point of the first electrode is greater than 40° and 98° or less. The angle may be determined in a plane perpendicular to the winding axis.
The terms first electrode and second electrode are used herein in accordance with the relevant technical field of battery designing and manufacturing, in particular in terms of a secondary battery. 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). The first electrode and the second electrode may have polarities opposite to each other so that they may receive and release the charge carriers, respectively, during a charging process of the electrode assembly, and vice versa in a discharging process of the electrode assembly. The materials and functionality of the first electrode and the second electrode may be as known in the art unless indicated otherwise herein.
For example, the first electrode may be a positive electrode and the second electrode may be a negative electrode. In other examples, the first electrode may be a negative electrode and the second electrode may be a positive electrode. Generally, a positive electrode may comprise a current collector, which may be provided as a plate, a sheet, or a film, on which a positive active material is deposited. For example, the positive active material may comprise a lithium metal oxide such as lithium cobalt oxide or lithium iron phosphate or any other proper material. The current collector of the positive electrode may be made of an electrically conductive material, for example aluminum. Generally, a negative electrode may comprise a current collector, which may be provided as a plate, a sheet, or a film, on which a negative active material is deposited. For example, the negative active material may comprise a carbon-based material, such as graphite. The current collector of the negative electrode may be made of an electrically conductive material, for example copper.
The term separator is used herein in accordance with the relevant technical field of battery designing and manufacturing, particularly in terms of a secondary battery. In particular, the separator may be a porous membrane configured to allow charge carriers (e.g., ions, lithium ions and/or electrons) to pass through while being generally impermeable for solid materials. The separator may be provided between the first electrode and the second electrode so as to prevent a short circuit therebetween.
The transfer of charge carriers between the first and second electrode may be enabled by an electrolyte which may be at least partially present between the first electrode and the second electrode. The electrolyte may be added to the electrode assembly after being arranged in a battery case. In specific examples, the electrode assembly may be considered to comprise an electrolyte so as to be present between the first electrode and the second electrode.
The first electrode, the separator and the second electrode may be provided as layers (or sheets). The first electrode, the separator and the second electrode may be laid upon one another in a specific sequence. In specific examples, the second electrode, the separator, the first electrode and another separator are laid upon one another in that order to form a so called mono-cell. In other examples, one or more mono-cells may be placed (repeatedly) on top of the mono-cell in said order to form a multi-cell.
The electrode assembly may comprise the mono-cell (or the multi-cell) wound to a roll. Such a roll-shaped electrode assembly may also be referred to as a jellyroll. Specifically, in the mono-cell, the first electrode, the separator and the second electrode, and optionally another separator, may be wound together around the winding axis. Accordingly, the electrode assembly may have a cylindrical shape, and particularly a cylindrical shape with a spiral (helical) cross-section. Further, the first electrode, the separator and the second electrode of the electrode assembly may be wound together (i.e., wound in a state of being stacked upon one other in said order) around the winding axis so for the electrode assembly to have a (general) cylindrical symmetry with respect to the winding axis. In the cylindrical symmetry, an axial direction may be parallel to the winding axis of the electrode assembly; a radial direction may be perpendicular to the winding axis and (approximately) perpendicular to an outer circumferential surface of the electrode assembly; and a circumferential direction may be perpendicular to the axial direction and the radial direction and go circularly around the winding axis. In addition, a winding direction of the electrode assembly may indicate a direction along one or each of the first electrode, the separator and the second electrode in a plan view. The winding direction may thus run along a spiral path around the winding axis. Depending on the context, the winding direction may be approximated to be circular around the winding axis, like the circumferential direction, in terms of a turning direction.
Unless indicated otherwise, an azimuth angle as used herein may indicate an angle between two lines in a plane perpendicular to the winding axis. The two lines forming the azimuth angle may intersect at the winding axis.
Generally, unless indicated otherwise, geometric features concerning a line, an angle, a curvature etc. as used herein refer to a plan view that is a cross-sectional view of the electrode assembly when viewed parallel to the winding axis. Accordingly, such geometric features may refer to the (approximate) cylindrical geometry of the electrode assembly in a wound state around the winding axis unless indicated otherwise. Furthermore, unless indicated otherwise, any line as used herein may indicate a straight line.
Here, the cylindrical symmetry as referred to herein may be an approximation in that a spiral plan view and/or a spiral cross-section of the electrode assembly is considered as an approximately circular plan view and/or a circular cross-section, respectively. The plan view of the electrode assembly may refer to a cross-sectional view parallel to the winding axis. The electrode assembly may have a spiral end face around the winding axis, as the first electrode, the separator and the second electrode are wound around the winding axis. The cross-section of the electrode assembly may refer to one perpendicular to the winding axis. The cross-section of the electrode assembly may be spiral around the winding axis, as the first electrode, the separator and the second electrode being wound around the winding axis.
At least one of the first electrode, the separator and the second electrode may have a rectangular shape in a plan view before winding. The winding axis may be parallel to (at least) one of the edges of the first electrode, the separator and the second electrode. In specific examples, the first electrode, the separator and the second electrode may each have a respective rectangular shape in a plan view, and arranged so that the corresponding edges of the first electrode, the separator and the second electrode are aligned parallel to each other.
Generally, the term curvature may be used herein as generally used in mathematics. In particular, the curvature may indicate a measure by which a curve deviates from being a straight line. Alternatively or additionally, the curvature may indicate a measure by which a surface deviates from being a plane. The curvature as used herein may indicate for any part of a curve how much a direction of the curve changes over a small distance travelled (e.g., in angle per distance). The curvature may be a measure of change of direction of a point along the curve. Particularly, the curvature may be a measure for a (instantaneous) change rate of unit tangent vector to the curve at point P, as the point P moves along the curve at unit speed. In a specific example, a position of point P(s) may be a function of the parameter s, which may be, for example, time or an arc length from a given origin; and T(s) may be a unit tangent vector of the curve at P(s), which is also the derivative of P(s) with respect to s. In such an example, the derivative of T(s) with respect to s may be a vector that is normal to the curve, and its length may be the curvature.
The curve as referred to herein may be a profile (and/or a contour, an outline, or the like) of the first electrode in the plan view (i.e., in a view parallel to the winding axis). Particularly, the first electrode may be provided as a sheet or a layer, so that the first electrode is perceived as a thick curve in the plan view. Alternatively or additionally, the same may apply to the second electrode and/or to the separator. The curve may be continuously differentiable near P, so that a tangent may vary continuously along the curve. The curve may be twice differentiable at any P so that a curvature exists along the curve, for example as a derivative of T(s) with respect to s as defined above.
Alternatively or additionally, the curvature as used herein may be determined in terms of an osculating circle at the curve. An osculating circle at point P of a curve may be a circle that has the same tangent as well as the same curvature as the curve. A tangent line may be an approximation of a curve at a point P of the curve. The osculating circle may be an approximation of the curve at the point P. The curvature of a straight line may be zero. If the curvature at a point is not equal to zero, then the reciprocal of the curvature is considered as a radius of curvature, i.e., the radius of an osculating circle. The center of the osculating circle is considered as the center of curvature and can be constructed by plotting the radius of curvature perpendicular to the tangent of the curve, in the direction in which the curve bends.
Further, the curvature as used herein may be determined as a derivative (or differential quotient) of a central angle at the center of the osculating circle with respect to a circular arc at the osculating circle.
In any of the above options for determining the curvature of the first electrode, the curvature may be determined in a plan view image or a cross-sectional image of the electrode assembly taken under a view angle parallel to the winding axis. In particular, the curve may be determined as the profile of the first electrode when visually determined in an image taken under a view angle of the electrode assembly parallel to the winding axis. The curvature may be determined from the curve.
The curvature maximum point as used herein may indicate a point at (or of or in) the first electrode (or the second electrode) at which a curvature of the first electrode (or the second electrode) is the greatest (i.e., at maximum) in a plan view of the electrode assembly. Accordingly, the curvature maximum point may be a point at the first electrode at which the first electrode exhibits the greatest curvature in the plan view of the electrode assembly. Alternatively or additionally, the curvature maximum point may be a point at the first electrode at which the osculating circle at the first electrode is the smallest. Additionally or alternatively, the same may apply to the second electrode and/or the separator.
In specific examples, the curvature of the first electrode may generally decrease as the first electrode extends from the winding axis toward an outer circumference of the electrode assembly. In other words, the curvature of the first electrode may generally decrease in a radial outward direction thereof or in an outward (winding) direction along the spiral of the first electrode. The general decrease of the curvature of the first electrode in an outward radial (or winding) direction may be due to the winding of the first electrode, the separator and the second electrode together around the winding axis. Additionally or alternatively, the curvature of the second electrode and/or the separator may generally decrease in a radial outward direction.
At the same time, the curvature maximum point may occur in a portion that is closer to the winding axis than to the outer circumference of the electrode assembly. A part of the electrode assembly that is closer to the winding axis than to the outer circumference of the electrode assembly in a plan view of the electrode assembly may be referred to as a core part. The core part may be further specified as detailed below. The curvature maximum point may occur, or may be located, in the core part of the electrode assembly (in a plan view). This may apply to the first electrode. Additionally or alternatively, this may also apply to the second electrode and/or the separator.
As the first electrode is wound around the winding axis, the first electrode extends, in a plan view, between an inner end of the first electrode and an outer end the first electrode in the winding direction. The inner end of the first electrode may be located at a radial inner position, for example near or close to the winding axis. The outer end of the first electrode may be located at a radial outward position, for example at or near the outer circumference of the electrode assembly. Similar may apply, alternatively or additionally, to the second electrode.
According to the present disclosure, a straight line (a first line) may be drawn that connects the winding axis with an inner end of the first electrode in a plane perpendicular to the winding axis. For example, the first line extends from the winding axis through the inner end of the first electrode in a plane perpendicular to the winding axis of the electrode assembly. The first line may be imaginary and constructed specifically for determining an angle between it (i.e., the first line) and another line (i.e., the second line as detailed below) that goes through the winding axis and the curvature maximum point.
According to the present disclosure, a straight line (a second line) may be drawn that connects the winding axis with the curvature maximum point of the first electrode in a plane perpendicular to the winding axis of the electrode assembly. For example, such a line extends from the winding axis through the curvature maximum point of the first electrode in a plane perpendicular to the winding axis of the electrode assembly. The second line may be imaginary and constructed specifically for determining the angle between it (i.e., the second line) and the line extending through the winding axis and the inner end of the first electrode (i.e., the first line).
In the present disclosure, said angle between the line extending from the winding axis through an inner end of the first electrode and the line extending from the winding axis through the curvature maximum point (i.e., between the first line and the second line), in a view parallel to the winding axis, may be greater than 40° and 98° or smaller. Alternatively, the angle may be in any of the value range as disclosed herein. As mentioned above, the view parallel to the winding axis may also mean a viewing angle in the axial direction of a cylindrical symmetry of the electrode assembly.
Alternatively or additionally, an electrode assembly may be provided in which a first electrode, a separator, and a second electrode are stacked and wound. At a core part of the electrode assembly, an angle may be formed between an inner end of the first electrode and a point at which a curvature of the first electrode is greatest is greater than 40° and 98° or less around a winding axis.
The core part may be as specified above and/or as detailed below. The longitudinal end portion of the first electrode may correspond to the inner end of the first electrode. The point at which a curvature of the first electrode is greatest may correspond to the curvature maximum point. The angle may be determined in the plan view of the electrode assembly or in a cross-section of the electrode assembly perpendicular to the winding axis of the electrode assembly, and may correspond to an azimuth angle with the vertex being in, or coinciding with, the winding axis.
Such an electrode assembly with the features as described above may be capable of achieving any of the technical effects as mentioned herein. Specifically, one, some or all of the electrodes of the electrode assembly may be subject to contraction and/or expansion in response to charging and discharging processes, which may lead to a deformation of the electrode assembly. The deformation may result in a winding core of the electrode assembly failing to maintain a cylindrical shape and collapsing thereby.
The electrode assembly as disclosed herein may exhibit an angle between the inner end of the first electrode and the curvature maximum point of the first electrode so as to suppress such problematic phenomenon of the winding core of the electrode assembly failing to maintain a cylindrical shape and thus collapsing due to deformation of the electrode assembly.
Consequently, the electrode assembly as disclosed herein may contribute to preventing damages to the first electrode, the second electrode and the separator. The electrode assembly as disclosed herein may also contribute to preventing an internal short-circuit between the first electrode and the second electrode. By this, the claimed subject matter may contribute to increasing the stability and overall lifetime of a battery.
The present disclosure may further refer to a manufacturing method of an electrode assembly. The method may implement an angle between the inner end of the first electrode and the curvature maximum point of the first electrode in the mentioned manner, thereby enabling a continuous manufacturing process, for example, using a conventional roll-to-roll process equipment, and thus increasing productivity and economic efficiency. The method may further achieve any of the technical effects as mentioned above and/or detailed below.
In an exemplary aspect, the curvature maximum point of the first electrode may be a point at which the curvature of the first electrode is maximum in a region in a cross-section of the electrode assembly perpendicular to the winding axis of the electrode assembly, the region extending from the inner end of the first electrode over an azimuth angle of 0° and 180° in a direction opposite to a winding direction in which the electrode assembly is wound around the winding axis.
As specified above, the winding direction as used herein may follow the winding of the first electrode (and/or the second electrode and the separator), which may be a spiral path around the winding axis. Accordingly, the winding direction of the first electrode may start at the inner end of the first electrode and follow the winding of the first electrode to its outer circumferential end in the plan view (and/or in a cross-section perpendicular to the winding axis). In the context of determining the azimuth angle, however, the winding direction may be a circular direction around the winding axis in the direction of the winding of the first electrode (i.e., directional in terms of a turning direction).
The azimuth angle may be determined in the cross-section of the electrode assembly perpendicular to the winding axis of the electrode assembly (or in the plan view of the electrode assembly), wherein the vertex of the azimuth angle coincides with the winding axis. In the context of the above-mentioned region in the cross-section of the electrode assembly, one of the sides of the azimuth angle may be given by a straight line that extends from the winding axis to the inner end of the first electrode (i.e., the first line). The other side of the azimuth angle may be given by a straight line that extends from the winding axis to the boundary of the above-mentioned region in the cross-section of the electrode assembly perpendicular to the winding axis of the electrode assembly.
Said region extends over (or spans over, or covers) an azimuth angle of 0° to 180°. In other word, said region covers an entire area between one boundary corresponding to an azimuth angle of 0° and another boundary corresponding to an azimuth angle of 180°. The boundaries meet at the winding axis and a further boundary is given by the outer circumference of the electrode assembly. A straight line extending from the winding axis through the inner end of the first electrode, i.e., the first line as indicated above, may correspond to an azimuth angle of 0°. The region extends opposite to the winding direction, i.e., covers an area opposite to an initial portion of the first electrode that extends from its inner end in the winding direction. With said region extending over an azimuth angle range of 0° to 180°, the region may cover half of the cross-section of the electrode assembly perpendicular to the winding axis of the electrode assembly (and/or half of the plan view of the electrode assembly), bounded by a straight line that extends through the winding axis and the inner end of the first electrode. In view of this, the region as mentioned above may have a shape of a semicircle or have a semicircular shape.
Alternatively or additionally, the point at which the curvature is greatest may be a point at which the curvature is greatest in a region above 0° and 180° or less in an opposite direction to a direction in which the electrode assembly is wound, based on the inner end of the first electrode.
In an exemplary aspect, the curvature maximum point of the first electrode may be formed in or at a part of the electrode assembly within 3 turns of the first electrode from the inner end thereof.
The part of the electrode assembly which is encircled by a third turn of the first electrode from the inner end thereof may be referred to as the core part. The core part may correspond to the core part as mentioned above. The core part may be implemented with any, some or all of the features described below.
Alternatively or additionally, the core part may be an electrode assembly that is a region within 3 turns from one end portion, in a longitudinal direction, of the first electrode. The longitudinal direction may refer to a state of the electrode assembly before winding and may correspond to the winding direction as used herein after winding. The one end may refer to the inner end of the first electrode.
In an exemplary aspect, 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 such that the first electrode active material layer extends to an inner end of the first electrode current collector, and the inner end of the first current collector . . . corresponds to the inner end of the first electrode.
In other words, the first electrode may comprise the first current collector and the first active material layer applied thereon. In the direction opposite to the winding direction, the first electrode terminates (at the inner end thereof) where the first current collector terminates. That is, the first electrode may not extend further than the first current collector in the direction opposite to the winding direction.
The active material layer may indicate a layer containing, or made of, an electrode active material as specified above. For example, the first electrode may be a positive electrode, and the active material layer may be a layer of a positive active material.
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, and wherein the first electrode current collector and the first electrode active material layer have longitudinal end portions at the same position.
In an exemplary aspect, the first electrode may comprise a first electrode uncoated portion in which the first electrode active material layer is not provided. The electrode assembly further comprises a first electrode tab physically connected to, or formed on, the first electrode uncoated portion.
The first electrode uncoated portion may indicate a portion of the first electrode, in particular of the first current collector, that is free of the first active material layer (i.e., free of the active material of the first electrode).
At least one electrode tab may be formed from, on or at the first electrode uncoated portion. The first electrode uncoated portion may be cut or notched (e.g., by forming one or more slits, notches or cuts or the like from an edge of the first electrode uncoated portion into the first electrode uncoated portion) so as to form one or more first electrode tabs. Alternatively or additionally, at least one electrode tab may be provided separately and attached to the first current collector or to the first electrode uncoated portion.
In an exemplary aspect, an angle formed between the line extending from the winding axis through the inner end of the first electrode (i.e., the first line, see above) and a line extending from the winding axis through a point at which the curvature of the first electrode is 1 or less may be greater than 0°. A mathematical value of the curvature may be determined as detailed above and/or specified below. In particular, the point at which the curvature of the first electrode is 1 or less may be within three turns from the inner end of the first electrode, i.e., in the core part of the electrode assembly. The angle as mentioned may refer to an azimuth angle as specified above, with the vertex being in (coinciding with) the winding axis.
In an exemplary aspect, the angle formed between the line extending from the winding axis through the inner end of the first electrode (i.e., the first line) and the line extending from the winding axis through the curvature maximum point of the first electrode (i.e., the second line) may be determined after activation of the electrode assembly.
Activation as used herein may refer to a process in which specific temperature(s) and charging and discharging conditions are applied to the electrode assembly (or a battery cell containing the same) to prepare the electrode assembly for use in a secondary battery. The activation may be also referred to as formation. The activation may include an aging process, a charging process and a discharging process, which may be performed in a specific order and, optionally, repeated in a specific order. The aging process may be configured for an electrolyte to permeate into the first electrode and the second electrode. For example, the aging process may be performed by storing the electrode assembly at a specific temperature (e.g. at 30° C.) for a specific duration (e.g., 30 minutes, 1 hour, 2 hours or 3 hours). The charging process may be configured for forming a layer of SEI, solid electrolyte interphase, from a decomposition of the electrolyte on the surface of the negative electrode. The charging process may include charging the electrode assembly to a certain charge level. After the charging process, optionally, another aging process may be performed at a raised temperature (e.g., 40° C., 50° C., 60° C. or 70° C.). Then the electrode assembly may be discharged at a specific C-rate (e.g., 0.1 C, 0.2 C, 0.5 C or 1.0 C). Optionally, a degassing process may be performed to remove a gas formed during the above processes of activation.
The first electrode and/or the second electrode may contract and/or expand during the activation. Hence, the technical effect achieved by the present disclosure may be particularly beneficial for an electrode assembly after undergoing (at least part of) the activation process.
Alternatively or additionally, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may be measured after activation.
In an exemplary aspect, the angle formed between the line extending from the winding axis through the inner end of the first electrode and the line extending from the winding axis through the curvature maximum point of the first electrode is determined after charging and discharging 50 times under conditions of 25° C., 1 C charge, and 1 C discharge.
Accordingly, said angle between the first line and the second line as referred to herein may be determined after at least 50 times of charge and discharge cycles (repetition) of the electrode assembly. Hence, a state or a quality of the electrode assembly may be determined with an increased accuracy.
Alternatively or additionally, the angle formed between the inner end of the first electrode and the point at which the curvature of the first electrode is greatest may be measured after charging and discharging 50 times under conditions of 25° C., 1 C charge, and 1 C discharge.
In an exemplary aspect, a circularity of the first electrode may be 89% or greater in or at a part of the electrode assembly within 3 turns of the first electrode from the inner end thereof. As mentioned above, the part of the electrode assembly within 3 turns of the first electrode from the inner end thereof may be referred to as the core part of the electrode assembly.
Alternatively or additionally, at the core part of the electrode assembly, a circularity of the first electrode may be 89% or greater.
The circularity as used herein may refer to a roundness in accordance with the teachings of the mathematical geometry. In particular, the circularity may be determined according to ISO 1101. The circularity as used herein may be determined as a two-dimensional parameter in a plan view of the electrode assembly. Additionally or alternatively, the circularity may be determined as detailed below.
In an exemplary aspect, the first electrode may have a first surface that faces the winding axis of the electrode assembly and a second surface opposite to the first surface. A first extension line may be drawn by extending a straight line connecting two points where a 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. A second extension line may be drawn by extending a straight line connecting two points within a distance of 5 mm from the inner end of the first electrode on a surface of the second electrode facing the first surface 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 inside the core part, i.e., within three winding turns of the first electrode from the inner end.
Alternatively or additionally, the first electrode may have a first surface in a direction of the winding axis of the electrode assembly and a second surface opposite to the first surface. A first extension line may be drawn by extending a straight line connecting two points where a direction of curvature changes at a (spaced) distance of 5 mm from the longitudinal end portion of the first electrode on the first surface of the first electrode. A second extension line may be drawn by extending a straight line connecting two points at a (spaced) distance of 5 mm from the longitudinal end portion of the first electrode on a surface of the second electrode facing the first surface of the first electrode form an angle of 25° or less with the first extension line.
In an exemplary aspect, the first electrode does not comprise a crack or a wrinkle. In particular, the first electrode does not comprise a crack or a wrinkle in or at a part of the electrode assembly within 3 turns of the first electrode from the inner end thereof, i.e., within the core part.
In an exemplary aspect, a flatness fraction of the first electrode may be greater than 3% and 13.5% or less in or at a part of the electrode assembly within 3 turns of the first electrode from the inner end thereof, i.e., within the core part.
The flatness as used herein may be determined in accordance with the definition as in the field of manufacturing and mechanical engineering. The flatness may be determined in accordance with ISO 12781-1. The flatness fraction as used herein may be determined as detailed below.
The present disclosure may further provide a method for manufacturing an electrode assembly. The method may comprise: arranging a first electrode, a separator and a second electrode upon each other in that order to form a stack; and winding the stack around a winding axis using a winding core. The winding core may comprise a first winding core part and a second winding core part. During the winding, the separator may be held between the first winding core part and the second winding core part. The arranging may be performed so that an angle formed between a line extending from the winding axis through an inner end of the first electrode and a line extending from the winding axis through a curvature maximum point of the first electrode is greater than 40° and 98° or less.
Such a method may be suitable to provide the electrode assembly as disclosed herein. Accordingly, the method as disclosed herein may be also suited to achieve the technical effects as mentioned above and detailed below.
Alternatively or additionally, a method for manufacturing an electrode assembly, wherein a first electrode, a separator, and a second electrode may be stacked and wound in the electrode assembly. The method may comprise: (a) supplying the first electrode, the separator, and the second electrode in a roll-to-roll manner; (b) sequentially arranging the supplied first electrode, separator, and second electrode to form a stack; and (c) winding the stack.
The winding may be performed using a winding core comprising a spacing part into which the separator is inserted; a first winding core part provided on one side of the spacing part with respect to the spacing part; and a second winding core part provided on the other side of the spacing part and having a different cross-sectional area from that of the first winding core part.
The arranging may be performed so that an angle formed between a longitudinal end portion of the first electrode and a point at which a curvature of the first electrode is greatest is greater than 40° and 98° or less around a winding axis.
The roll-to-roll manner, or a roll-to-roll process, may be used herein in accordance with the understanding in the field of manufacturing and industrial processing. In particular, the roll-to-roll manner may include performing one or more processes starting with a roll of a flexible material and re-reeling after the process(es) to create an output roll.
Specifically, the first electrode, the separator and the second electrode may be each provided in a continuous manner, particularly in a roll-to-roll manner, to be stacked upon one another in said order.
Here, the spacing part is used to hold the first electrode, the second electrode and the separator and wind them together. A hollow is formed at the center of the electrode assembly after winding, particularly after removing a winding core.
The cross-sectional areas of the first winding core part and the second winding core part may be determined in a plan view (i.e., in a view parallel to the winding axis) and/or in a cross-section perpendicular to the winding axis.
In an exemplary aspect, the first winding core part and the second winding core part may be not symmetrical to each other in a cross-section perpendicular to the winding axis of the electrode assembly. In particular, the first winding core part and the second winding core part may have different shapes and/or different sizes in a cross-section perpendicular to the winding axis of the electrode assembly.
In an exemplary aspect, in a cross-section perpendicular to the winding axis of the electrode assembly, an area of the first winding core part may be smaller than an area of the second winding core part. The arranging of the first electrode, the separator and the second electrode may be performed so that the inner end of the first electrode is arranged on an outer peripheral surface of the first winding core part.
Alternatively or additionally, the cross-sectional area of the first winding core part may be smaller than the cross-sectional area of the second winding core part. The arranging of the first electrode, the separator and the second electrode may be performed so that the longitudinal end portion of the first electrode is arranged on an outer peripheral surface of the first winding core part.
Alternatively or additionally, the winding is performed while keeping a tension of 3.92 N (or 400 gram-force (gf)) or higher.
Moreover, the present disclosure provides an electrode assembly that is manufactured by the method as disclosed herein.
A secondary battery may comprise the electrode assembly as disclosed herein. In an exemplary aspect, the secondary battery may comprise a battery case, particularly a cylindrical battery case, in which the electrode assembly is accommodated.
As a further example, an electrode assembly is provided in which a first electrode, a separator, and a second electrode are stacked and wound, wherein at a core part of the electrode assembly, an angle formed between a longitudinal end portion of the first electrode and a point at which a curvature of the first electrode is greater than 40° and 98° or less around a winding axis.
Another exemplary aspect of the present disclosure provides a method for manufacturing an electrode assembly in which a first electrode, a separator, and a second electrode are stacked and wound, the method including: (a) a supply process of supplying the first electrode, the separator, and the second electrode in a roll-to-roll manner; (b) an arranging process of sequentially arranging the supplied first electrode, separator, and second electrode to form a stack; and (c) a winding process of winding the stack, wherein the winding is performed using a winding core including a spacing part into which the separator is inserted, a first winding core part provided on one side of the spacing part with respect to the spacing part, and a second winding core part provided on the other side of the spacing part and having a different cross-sectional area from that of the first winding core part, and wherein the arranging process is performed so that an angle formed between a longitudinal end portion of the first electrode and a point at which a curvature of the first electrode is greatest is greater than 40° and 98° or less around a winding axis, and an electrode assembly manufactured by the method.
Still another exemplary aspect of the present disclosure provides a secondary battery including the electrode assembly described above; and a battery case for accommodating the electrode assembly.
The electrode assembly according to an exemplary aspect of the present disclosure satisfies a particular range of angles between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest, making it possible to address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of an electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, to prevent damage to the second electrode and the separator, and to prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
The method for manufacturing an electrode assembly according to an exemplary aspect of the present disclosure enables an electrode assembly, whose angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest has been set within a particular range of angles, to be manufactured in a simpler manner and is suitable for a continuous process using roll to roll process equipment of the related art, ensuring productivity and economic efficiency.
In addition, the secondary battery according to the present disclosure can address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of an electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, prevent damage to the second electrode and the separator, and prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
The effects of the present disclosure are not limited to the foregoing effects, and effects not described will be apparent and understood by one skilled in the art from the present specification and accompanying drawings.
Reference characters used in the present disclosure are as follows:
When one part “includes”, “comprises” or “has” one constituent element throughout the present specification, unless otherwise specifically described, this does not mean that another constituent element is excluded, but means that another constituent element may be further included.
Throughout the present specification, when a member is referred to as being “on” another member, the member can be in direct contact with another member or an intervening member may also be present.
An exemplary aspect of the present disclosure provides an electrode assembly in which a first electrode, a separator, and a second electrode are stacked and wound, wherein at a core part of the electrode assembly, an angle formed between a longitudinal end portion of the first electrode and a point at which a curvature of the first electrode is greatest is 52° or greater and 68° or less around a winding axis.
Here, the first electrode may include a first surface in a direction of a winding axis of the electrode assembly, and a second surface opposite to the first surface.
Additionally, the curvature may be calculated from a plurality of measurement points located on the first surface of the first electrode extracted from a computed tomography (CT) image, as described below.
The electrode assembly according to an exemplary aspect of the present disclosure satisfies a range of angles between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest, making it possible to address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of an electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, to prevent damage to the second electrode and the separator, and to prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
Specifically, when charging and discharging a battery, the electrodes included in the electrode assembly undergo repeated contraction/expansion, but outward expansion is limited due to the rigidity of a battery case surrounding an outer peripheral surface of the electrode assembly, so stress may be concentrated in a direction of a cavity that is an empty space located at the core part. Accordingly, a possibility of core deformation of the electrode assembly may increase.
The core deformation may be classified into a phenomenon that the core cavity of the electrode assembly fails to maintain a circular shape and collapses when internal stress reaches a certain level or higher, i.e., core collapse, and a phenomenon that an end portion of a first electrode located at the core part and a second electrode adjacent thereto are deformed beyond a certain level, causing damage to a separator between the first electrode and the second electrode and bringing the first electrode and the second electrode into direct contact with each other, i.e., core impingement.
In particular, the core collapse may be concentrated in a region vulnerable to the internal stress of the electrode assembly. Specifically, the core collapse may be concentrated in a region where the curvature of the first electrode is a specific value or smaller, i.e., a flat region. That is, at the core part of the electrode assembly, deformation due to internal stress may begin to occur from a region where the curvature of the first electrode is a specific value or smaller, and after a certain point in time, the core cavity no longer maintains a circular shape and may completely collapse. In an electrode assembly in which the core collapse has occurred, lithium ions can no longer be smoothly transferred between the first electrode and the second electrode, so the battery life may deteriorate.
Here, the curvature of the first electrode may be affected by a step due to a thickness of an electrode, the presence of a tab (or the like), a shape of the winding core, the tension acting on the electrode assembly upon winding, and the like. For example, the winding core may include a pair of winding core parts separated around the spacing part into which a separator is inserted, and when a certain level of tension is applied, the winding core is distorted, which may inevitably generate a region where the curvature of the first electrode is a specific value or smaller, that is, a flat region, and the core collapse may occur in the region where the curvature of the first electrode is the specific value or smaller.
In this case, when the angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest is set within a particular range, the phenomenon that the core cavity fails to maintain a circular shape and collapses, that is, the core collapse, can be improved. With this, damage to the second electrode and the separator can be prevented and an internal short-circuit between the first electrode and the second electrode can be prevented, so the stability and life characteristics of the battery can be improved.
According to an exemplary aspect of the present disclosure, at a core part of the electrode assembly, an angle formed between a longitudinal end portion of the first electrode and a point at which a curvature of the first electrode is greatest may be greater than 40° and 98° or less around a winding axis. The curvature maximum point may be in a region extending from the inner end of the first electrode over an azimuth angle of 0° and 180° in a direction opposite to a winding direction, in which the electrode assembly is wound around the winding axis. Specifically, at the core part of the electrode assembly, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may be greater than 40° and 98° or less, 45° or greater and 95° or less, 45° and greater and 90° or less, 45° and greater and 80° or less, 45° or greater and 70° or less, 45° or greater and 65° or less, 50° or greater and 95° or less, 50° or greater and 90° or less, 50° or greater and 80° or less, 50° or greater and 70° or less, 50° or greater and 65° or less, 60° or greater and 95° or less, 60° or greater and 90° or less, 60° or greater and 80° or less, 60° or greater and 70° or less, or 60° or greater and 65° or less around the winding axis.
When the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest satisfies the above-described range, it is possible to address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of the electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, to prevent damage to the second electrode and the separator, and to prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
In the below, as regards the angle formed between the longitudinal end portion of the first electrode of the present disclosure and the point at which the curvature of the first electrode is greatest, a curvature measurement target, a curvature measurement method, and a curvature measurement time point will be described in more detail.
According to an exemplary aspect of the present disclosure, the curvature may be measured for the first electrode, at the core part of the electrode assembly.
Here, the ‘core part’ may be a region including a core cavity located on a winding axis of the electrode assembly and a part of a stack structure of the wound separator/second electrode/separator/first electrode.
In other words, the core part may include a core cavity located on the winding axis of the electrode assembly, and a region up to one end portion, in a longitudinal direction, of the first electrode located on the innermost side where winding of the electrode assembly begins, that is, a region not including the first electrode. In addition, the core part may further include a region of a predetermined length including the first electrode from one end portion, in the longitudinal direction, of the first electrode, in a direction in which the first electrode is wound.
According to an exemplary aspect of the present disclosure, the core part may be a region within 3 turns from one end portion, in the longitudinal direction, of the first electrode. Specifically, the core part may be a region within 1 turn to 2.5 turns or within 1.5 turns to 2 turns from one end portion, in the longitudinal direction, of the first electrode.
Here, 1 turn may refer to a length required to wind an electrode or separator included in an electrode assembly by 360° from a reference point, and the length may be determined depending on an outer diameter of a winding core used for winding the electrode assembly, thicknesses of the separator and the electrode, and the number of windings of the separator and electrode positioned on an inner side of the reference point. For example, 1 turn of the first electrode may refer to a length required to wind the first electrode by 360° from the longitudinal end portion of the first electrode, in a direction in which the electrode assembly is wound.
In other words, the core part may refer to a region up to a point spaced 3 or less turns from one end portion, in the longitudinal direction, of the first electrode, a region up to a point spaced within 1 turn to 2.5 turns from one end portion, in the longitudinal direction, of the first electrode, or a region up to a point spaced within 1.5 turns to 2.5 turns from one end portion, in the longitudinal direction of the first electrode.
Since the point at which the curvature of the first electrode is greatest may be determined depending on the range of the core part, when the above-described range of the core part is satisfied, the point at which the curvature of the first electrode is greatest can be determined more efficiently, and the reliability of the determined point at which the curvature of the first electrode is greatest may be higher.
According to an exemplary aspect of the present disclosure, the curvature may be measured at the core part of the electrode assembly, may be measured for the first electrode, at the core part of the electrode assembly, and may be measured by extracting the first electrode from a CT image of the core part of the electrode assembly.
When a curvature measurement target is the first electrode located at the core part of the electrode assembly, the reliability of the curvature measurement may be higher, and by adjusting a position of the longitudinal end portion of the first electrode during assembly, the angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest can be more easily adjusted. With this, the deformation of the end portion of the first electrode located at the core part and the second electrode adjacent thereto is reduced, making it possible to address a phenomenon that the separator located between the first electrode and the second electrode is damaged, that is, core impingement.
According to an exemplary aspect of the present disclosure, the curvature may be calculated from 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 the first surface of an extracted first electrode, which is a direction of the winding axis of the electrode assembly, after extracting the first electrode from a CT image of the electrode assembly. More specifically, the curvature may be calculated from a plurality of measurement points located at regular intervals 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 around the winding axis.
According to an exemplary aspect of the present disclosure, 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.
When the above-described range of the number of measurement points is satisfied, the point at which the curvature of the first electrode is greatest can be determined more efficiently, and the reliability of the determined point at which the curvature of the first electrode is greatest may be higher.
According to an exemplary aspect of the present disclosure, the curvature may be measured at separate measurement points within the above-described range of the number of measurement points located at regular intervals or arbitrarily selected, at the core part, and the point at which the curvature is greatest may be determined.
According to an exemplary aspect of the present disclosure, the curvature may be a curvature in accordance with Formula 1 below. Specifically, the curvature calculated at the measurement point can be calculated according to Formula 1 below using coordinate values, that is, x-coordinate and y-coordinate, obtained from a plurality of measurement points located on the first surface of the first electrode extracted from the CT image.
In Formula 1 above, k is a curvature of the first electrode, x is an x-coordinate of the measurement point, y is a y-coordinate of the measurement point, x′ is a first derivative value of x, and y′ is a first derivative value of y, x″ is a second derivative value of x, and y″ is a second derivative value of y.
In other words, the calculation of the curvature may mean measuring x-coordinate and y-coordinate values at a plurality of measurement points at regular intervals located on the first surface of the first electrode, and calculating curvature values using the measured x-coordinates, y-coordinates and Formula 1. Specifically, the curvature may be calculated as a parametric expression of a plane curve, and the curvature, that is, a degree of bending, increases as the k value according to Formula 1 increases. More specifically, the curvature may be calculated using the above Formula through a Python program, and the x and y coordinate values may range from −3 to +3. Note that x′ and y′ may mean the slope of a tangent at each coordinate, and x″ and y″ may mean a rate of change of the slope.
If necessary, for the curvature value, one normalized using a radius of curvature of the electrode assembly for each measurement point may be used.
According to an exemplary aspect of the present disclosure, at the core part of the electrode assembly, the angle formed between the longitudinal end portion of the first electrode and a point at which the curvature of the first electrode is 1 or less may be greater than 0° around the winding axis.
Specifically, at the core part of the electrode assembly, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is 1 or less may be greater than 0° and less than 50° around the winding axis.
More specifically, at the core part of the electrode assembly, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is 1 or less may be 5° or greater and less than 50°, 10° or greater and 45° or less, or 15° or greater and 40° or less around the winding axis.
In other words, a region where the curvature of the first electrode is 1 or less, that is, a flat region, may be located between the point at which the curvature of the first electrode is greatest and the longitudinal end portion of the first electrode, and may not overlap the longitudinal end portion of the first electrode.
According to an exemplary aspect of the present disclosure, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may be measured in a region above 0° and 180° or less in an opposite direction to the direction in which the electrode assembly is wound, based on the longitudinal end portion of the first electrode. That is, the point at which the curvature is greatest may be a point at which the curvature is greatest in the region above 0° and 180° or less in the opposite direction to the direction in which the electrode assembly is wound, based on the longitudinal end portion of the first electrode.
In other words, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may be measured in the region above 0° and 180° or less in the opposite direction to the direction W in which the electrode assembly is wound, i.e., in a rotational direction R of the winding core used for winding the electrode assembly, based on the longitudinal end portion of the first electrode.
Specifically, stress generated as the cycle progresses is concentrated in a direction of the core cavity due to the rigidity of the battery case, so core deformation may occur in a flat region that is relatively vulnerable to the stress. In this case, in the region above 0° and 180° or less in the opposite direction to the direction W in which the electrode assembly is wound, i.e., in the rotational direction R of the winding core, based on the longitudinal end portion of the first electrode, the number of turns of the first electrode up to the outermost layer is relatively smaller and a distance from the longitudinal end portion of the first electrode that can slide is relatively longer, as compared to a region above 180° and 360° or less, so the concentrated stress is not relieved. Therefore, a possibility of deformation in the direction of the core cavity at the corresponding location may be higher.
In addition, as described below, the tension applied to the electrode assembly during winding causes distortion of the winding core. Therefore, when the winding core includes a spacing part, the point at which the curvature of the first electrode is greatest and the flat region may occur symmetrically at the spacing part. However, the flat region located in the region above 0° and 180° or less in the rotational direction R of the winding core, based on the longitudinal end portion of the first electrode is more vulnerable to the core deformation, and the possibility of core deformation may be higher in the flat region even after acceleration cycles.
Therefore, when the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest is measured in the region above 0° and 180° or less in the opposite direction to the direction in which the electrode assembly is wound based on the longitudinal end portion of the first electrode, the point at which the curvature of the first electrode is greatest can be determined more efficiently, and the effect of reducing the core deformation by the angle adjustment may be improved.
According to an exemplary aspect of the present disclosure, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may be measured after activation. Specifically, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may have been measured, after activation, in a state of standby for normal use and in a normally used state, that is, prior to the occurrence of core deformation. For example, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may be measured after charging and discharging 50 times under conditions of 25° C., 1 C charge, and 1 C discharge.
Here, the term ‘after activation’ may mean after a predetermined number of cycles for manufacturing a secondary battery and finishing a product. Specifically, the ‘after activation’ may include a storage state before start of active use including multiple cycles for power supply purposes, that is, before and after sale, and a state in which self-discharge during storage has been made.
The activation may refer to a step of checking the stability of a battery by repeating aging and charging/discharging after assembly of an electrode assembly and a battery case, and a ‘state before the occurrence of core deformation after activation’ can be achieved in a simple manner by performing a predetermined number of cycles, for example, 50 cycles under conditions of 1 C/1 C @25° C. for an obtained battery at any time point after assembly. However, the activation conditions are not limited to the above as long as they are within the range used in the art for achieving the same purpose.
The point at which the curvature of the first electrode is greatest may be determined depending on the curvature measurement time point. Therefore, when the above-described curvature measurement time point is satisfied, the point at which the curvature of the first electrode is greatest can be determined more efficiently, and the reliability of the determined point at which the curvature of the first electrode is greatest may be higher.
Specifically, referring to
Note that, as an additional influencing factor related to the occurrence of core deformation, when a first electrode tab is positioned at the 12 o'clock position (labeled as 180° in the figures), a second electrode tab located at the outermost part is preferably located between 5 o'clock (330°) and 8 o'clock (60°) or between 6 o'clock (0°) and 7 o'clock (30°), the longitudinal end portion of the first electrode located at the core part is preferably located between 5 o'clock (330°) and 9 o'clock (90°) or between 6.5 o'clock (15°) and 8 o'clock (60°), and the longitudinal end portion of the first electrode located at the outermost part is preferably located between 4 o'clock (300°) and 6 o'clock (60°) or between 4.5 (315°) o'clock and 5.5 o'clock (345°). Note that, an area of the core cavity is preferably 5 mm2 or greater and 15 mm2 or less, or 7 mm2 or greater and 13 mm2 or less. When the above-described additional influencing factors satisfy the above-described ranges, respectively, the effect of reducing the core deformation may be improved. Note that, the unit ‘o'clock’ indicates the relative position of each factor in a clockwise direction when the first electrode tab is positioned at 12 o'clock (180°) on the CT image, and may be measured in the opposite direction to the direction W in which the electrode assembly is wound, that is, in the rotational direction R of the winding core used for winding the electrode assembly. For example, 6 o'clock means forming an angle of 180° with the first electrode tab positioned at 12 o'clock, and 6 o'clock falls at the 0° position in the figures.
According to an exemplary aspect of the present disclosure, the first electrode may not include a crack or wrinkle at the core part of the electrode assembly. Here, the crack may refer to a crack that is visually recognized with the naked eye on the surface of the first electrode, and the wrinkle may refer to a case where a wrinkle or fold visually recognized with the naked eye has occurred on the surface of the first electrode.
When an electrode assembly including the first electrode with cracks is inserted into a battery case, the possibility of occurrence of low voltage and short-circuit due to foreign matters greatly increases. On the other hand, since the electrode assembly according to an exemplary aspect of the present disclosure does not include a first electrode with cracks or wrinkles at the core part, the battery stability can be improved.
According to an exemplary aspect of the present disclosure, at the core part of the electrode assembly, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may have a positive correlation with the flatness fraction of the first electrode. Specifically, referring to
Here, the flatness fraction (%) may refer to a fraction of the flat region of the first electrode in the first electrode, and the flat region may refer to a region with a curvature equal to or smaller than a reference value.
That is, the flatness fraction may refer to a fraction of a region with a curvature value equal to or smaller than a reference curvature value in the first electrode that is a measurement target. For example, the flatness fraction may be a fraction (%) of the number of measurement points with a curvature of 1 or less, based on 100% of the number of measurement points.
Since the flatness fraction of the first electrode may be determined depending on the reference curvature value, when the range of the above-described reference curvature value is satisfied, the flatness fraction of the first electrode can be determined more efficiently, and the reliability of the determined flatness fraction of the first electrode may be higher.
According to an exemplary aspect of the present disclosure, the flatness fraction of the first electrode may be greater than 3% and 13.5% or less at the core part of the electrode assembly. Specifically, at the core part of the electrode assembly, the flatness fraction of the first electrode may be greater than 3% and 13.5% or less, 5% or greater and 13% or less, 5% or greater and 10% or less, 7% or greater and 10% or less, or 7.5% or greater and 10% or less.
When the above-described flatness fraction range of the first electrode is satisfied, it is possible to address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of the electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, to prevent damage to the second electrode and the separator, and to prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
According to an exemplary aspect of the present disclosure, a roundness (circularity) of the first electrode may be 89% or greater at the core part of the electrode assembly. Specifically, at the core part of the electrode assembly, the circularity of the first electrode may be 89% or greater or 90% or greater, and may be 89% or greater and 99% or less, or 90% or greater and 98% or less.
Here, the circularity (%) may be a ratio of the minimum spaced distance between the winding axis and the first electrode based on 100% of the maximum spaced distance between the winding axis and the first electrode. Specifically, the circularity may refer to a ratio (%) of the minimum spaced distance between the winding axis and the first electrode to the maximum spaced distance between the winding axis and the first electrode.
When the above-described circularity range is satisfied, a shape of the electrode assembly can be closer to a circular shape, and resistance to stress acting on the core part may be excellent. Accordingly, it is possible to address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of an electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, to prevent damage to the second electrode and the separator, and to prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
However, the circularity may be different from the flatness fraction, which refers to the fraction of a region that is a measurement target where a curvature is equal to or smaller than the reference value. For example, there are cases where the circularity satisfies the above-described range but the flatness fraction does not satisfy the above-described range, depending on the shape of the electrode assembly. In this case, by adjusting the flatness fraction, in addition to the circularity, to within the above-described range, a case where the shape of the electrode assembly deviates from the circular shape at a specific position can be excluded. Accordingly, compared to the case of simply adjusting the circularity, it may be easier to control the shape of the electrode assembly, and the effect of reducing the core deformation may be improved. That is, the flatness fraction may be a more accurate reference for a degree to which the shape of the electrode assembly is ‘close to a circular shape’.
According to an exemplary aspect of the present disclosure, the first electrode may include 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 end portions at the same position. In other words, one end portion, in the longitudinal direction, of the first electrode may be of a free-edge shape.
With this, an area of an unnecessary uncoated portion on the first electrode current collector can be reduced to secure economic efficiency, and a slitting process can be performed after forming an active material layer on an electrode, so that the slitting process and a roll-to-roll process including a winding process can be performed more efficiently.
Here, the description ‘same position’ means that the end portions in the longitudinal direction are the same, and may include a case where the end portions are formed at substantially the same positions due to a process error that may occur in the slitting process or the like.
According to an exemplary aspect of the present disclosure, the first electrode may include a first electrode uncoated portion not provided with a first electrode active material layer, and may further include a first electrode tab provided on the first electrode uncoated portion.
In other words, the first electrode current collector may include a first electrode coated portion where the first electrode active material is coated and a first electrode uncoated portion where the first electrode active material is not coated, and may include a tab on the first electrode uncoated portion. Specifically, the first electrode current collector may include a first electrode uncoated portion and a first electrode tab provided on the first electrode uncoated portion.
That is, one end portion, in the longitudinal direction, of the first electrode may have a free-edge shape, and the first electrode uncoated portion may be located between both longitudinal end portions of the first electrode, and the first electrode tab provided on the first electrode uncoated portion may be a middle tab located between both longitudinal end portions of the first electrode. The uncoated portion may be formed at a location other than the longitudinal end portion of the electrode, that is, other than the core or outermost portion of the electrode assembly. In this case, the tab formed on the uncoated portion is called a middle tab. In other words, the middle tab may refer to a tab that is not located at the core or outermost portion of the electrode assembly. In some examples, the uncoated portion may be positioned along a top or bottom side of the first electrode along the winding axis.
According to an exemplary aspect of the present disclosure, the first electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. Specifically, for the first electrode current collector, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel each surface-treated with carbon, nickel, titanium, silver, or the like, or the like may be used. That is, the first electrode current collector may be provided in the form of surface-treated stainless steel, an aluminum foil, or the like.
In addition, the first electrode current collector may typically have a thickness of 3 to 50 μm, and a surface of the current collector may be formed with microscopic irregularities to enhance adhesive force of the first electrode active material. For example, the first electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foamed body, and a non-woven fabric body.
According to an exemplary aspect of the present disclosure, the first electrode active material may be a first electrode active material that is typically used. Specifically, the first electrode active material may be a layered compound such as a lithium cobalt oxide (LiCoO2) and a lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; a lithium manganese oxide such as chemical formula Li1+xMn2-xO4 (0≤x≤0.33), LiMnO3, LiMn2O3 and LiMnO2; a lithium copper oxide (Li2CuO2); a vanadium oxide such as LiV3O8, V2O5 and Cu2V2O7; Ni-site type lithium nickel oxide represented by chemical formula LiNi1-yMyO2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤y≤0.3); a lithium manganese composite oxide represented by chemical formula LiMn2-zM2O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and satisfies 0.01≤z≤0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn.); LiMn2O4 in which a part of Li of the chemical formula is substituted with an alkaline earth metal ion, or the like, but is not limited thereto. The first electrode may be Li metal.
According to an exemplary aspect of the present disclosure, 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 particular limitation as long as it does not cause a chemical change and has electronic conductivity in a battery to be configured. Specific examples of the first electrode conductive material may include graphite such as natural graphite or artificial graphite; a carbon-based material such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum and silver; a conductive whisker such as zinc oxide and potassium titanate; a conductive metal oxide such as titanium oxide; or a conductive polymer such as polyphenylene derivative, and the like, and any one thereof or a mixture of two or more thereof may be used.
Additionally, the first electrode binder serves to improve adhesion force between particles of the first electrode active material and adhesive force between the first electrode active material and the first electrode current collector. Specific examples may 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), fluoro rubber, or various copolymers thereof, and the like, and any one thereof or a mixture of two or more thereof may be used.
According to an exemplary aspect of the present disclosure, the second electrode may include a second electrode current collector and a second electrode active material layer provided on the second electrode current collector. Specifically, the second electrode may include a second electrode current collector and a second electrode active material layer formed on one surface or both surfaces of the second electrode current collector and including a second electrode active material. In other words, the second electrode active material layer may be formed on a second electrode coated portion of the second electrode current collector, and a surface not provided with the second electrode active material layer may be expressed as a second electrode uncoated portion.
According to an exemplary aspect of the present disclosure, the second electrode current collector may include a second electrode coated portion where the second electrode active material layer is formed and a second electrode uncoated portion where the second electrode active material layer is not formed, and may include a tab on the second electrode uncoated portion. Specifically, the second electrode current collector may include a second electrode uncoated portion and a second electrode tab formed on the second electrode uncoated portion. Accordingly, the manufactured electrode assembly may include one or more second electrode tabs.
According to an exemplary aspect of the present disclosure, the second electrode active material layer may include a second electrode active material including one or more selected from the group consisting of a silicon-based material and a carbon-based material. In addition, the second electrode active material layer may further include a second electrode conductive material and a second electrode binder, and for the second electrode active material, the second electrode conductive material, and the second electrode binder, materials that are used in the art may be used without limitation.
According to an exemplary aspect of the present disclosure, the second electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, for the second electrode current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel each surface-treated with carbon, nickel, titanium, silver, or the like, or the like may be used. Specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used for the second electrode current collector. A thickness of the second electrode current collector may be 5 μm or greater and 30 μm or less. However, the thickness of the second electrode current collector is not limited thereto.
According to an exemplary aspect of the present disclosure, the second electrode binder may include at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, 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), fluoro rubber, poly acrylic acid, and the above-described materials in which a hydrogen is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.
According to an exemplary aspect of the present disclosure, the second electrode conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; a conductive fiber such as a carbon fiber and a metal fiber; a conductive tube such as a carbon nanotube; metal powders such as fluorocarbon, aluminum, and nickel powder; a conductive whisker such as zinc oxide and potassium titanate; a conductive metal oxide such as titanium oxide; a conductive material such as polyphenylene derivative, and the like may be used.
According to an exemplary aspect of the present disclosure, the electrode assembly may include a plurality of separators. For example, the electrode assembly may have a structure where a separator/a second electrode/a separator/a first electrode are sequentially stacked. The separator serves to separate the first electrode and the second electrode and to provide a migration path of lithium ions, and any separator may be used without particular limitation as long as it is usually used as a separator in a secondary battery, and particularly, a separator having high moisture-retention ability for an electrolyte as well as a low resistance to migration of electrolyte ions may be preferably used. Specifically, a porous polymer film, for example, a porous polymer film manufactured from a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or a stacked structure having two or more layers thereof may be used. In addition, a usual porous non-woven fabric, for example, a non-woven fabric formed of high melting point glass fibers, polyethylene terephthalate fibers, or the like may be used. In addition, as the separator, a separator in which the above-described separator material is used as a base layer and a slurry containing a ceramic component or a polymer material in order to secure heat resistance or mechanical strength is coated on the base layer may be used. The separator having a single layer or multilayer structure may be selectively used. A thickness of the separator may be 5 μm or greater and 20 μm or less. However, the thickness of the separator is not limited thereto.
According to an exemplary aspect of the present disclosure, the angle formed between the first electrode and the second electrode may be 25° or less. Specifically, the first electrode may include a first surface in a direction of the winding axis of the electrode assembly and a second surface opposite to the first surface. With reference to
When the above-described angle range is satisfied, the end portion of the first electrode located at the core part and the second electrode adjacent thereto are not deformed beyond a certain level, so a phenomenon that 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 with each other, that is, core impingement, can be suppressed. With this, damage to the second electrode and the separator can be prevented and an internal short-circuit between the first electrode and the second electrode can be prevented, so the stability and life characteristics of the battery can be improved.
According to an exemplary aspect of the present disclosure, the first electrode and second electrode may be a positive electrode and a negative electrode, respectively. Specifically, the first electrode may be a positive electrode, and the second electrode may be a negative electrode.
Another exemplary aspect of the present disclosure provides a method for manufacturing an electrode assembly in which a first electrode, a separator, and a second electrode are stacked and wound, the method including: (a) a supply process of supplying the first electrode, the separator, and the second electrode in a roll-to-roll manner; (b) an arranging process of sequentially arranging the supplied first electrode, separator, and second electrode to form a stack; and (c) a winding process of winding the stack, The winding may be performed using a winding core including a spacing part into which the separator is inserted, a first winding core part provided on one side of the spacing part with respect to the spacing part, and a second winding core part provided on the other side of the spacing part and having a different cross-sectional area from that of the first winding core part. The arranging process may be performed so that an angle formed between a longitudinal end portion of the first electrode and a point at which a curvature of the first electrode is greatest is greater than 40° and is 98° or less around a winding axis. An electrode assembly manufactured by such method may be further provided.
The method for manufacturing an electrode assembly according to such exemplary aspect of the present disclosure simplifies the manufacture of an electrode assembly whose angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest to be within the ranges of angles disclosed herein. Such manufacturing method is also suitable for a continuous process using roll to roll process equipment of the related art, ensuring productivity and economic efficiency.
In addition, the secondary battery according to an exemplary aspect of the present disclosure can address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of an electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, prevent damage to the second electrode and the separator, and prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
Here, the core part, the longitudinal end portion of the first electrode, and the curvature, specifically, a curvature measurement target, a curvature measurement method, and a curvature measurement time point may be the same as those described above for the electrode assembly.
According to an exemplary aspect of the present disclosure, the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may be greater than 40° and 98° or less, 45° or greater and 95° or less, 45° and greater and 90° or less, 45° and greater and 80° or less, 45° or greater and 70° or less, 45° or greater and 65° or less, 50° or greater and 95° or less, 50° or greater and 90° or less, 50° or greater and 80° or less, 50° or greater and 70° or less, 50° or greater and 65° or less, 60° or greater and 95° or less, 60° or greater and 90° or less, 60° or greater and 80° or less, 60° or greater and 70° or less, or 60° or greater and 65° or less around the winding axis.
When the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest satisfies the above-described range, it is possible to address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of the electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, to prevent damage to the second electrode and the separator, and to prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
According to an exemplary aspect of the present disclosure, the method for manufacturing an electrode assembly may be performed in a roll-to-roll manner. Specifically, the steps (a) to (c) may be performed in a roll-to-roll manner in which a plurality of bendable metal foils and the like are processed while moving between rollers. Here, the roll-to-roll manner may refer to a manner of supplying an electrode current collector by unwinding a roll on which a flexible, thin metal sheet-like electrode current collector is wound, forming an electrode mixture layer by applying an electrode slurry including an electrode active material onto at least one surface of the electrode current collector and drying the electrode slurry, and then rewinding and collecting an electrode current collector processed from another roll.
The method for manufacturing an electrode assembly according to an exemplary aspect of the present disclosure enables an electrode assembly to be produced in a continuous process using roll to roll process equipment used in the art, while achieving a range of angles disclosed herein between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest.
That is, the method for manufacturing an electrode assembly according to an exemplary aspect of the present disclosure enables an electrode assembly whose angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest to be set within the ranges of angles disclosed herein while producing the electrode assembly in a continuous process using roll to roll process equipment of the related art, ensuring productivity and economic efficiency.
Specifically,
According to an exemplary aspect of the present disclosure, the winding may be performed using a winding core including a spacing part into which the separator is inserted, a first winding core part provided on one side of the spacing part with respect to the spacing part, and a second winding core part provided on the other side of the spacing part and having a different cross-sectional area from that of the first winding core part.
Specifically, the winding core may include a spacing part S into which the separator is inserted, a first winding core part A provided on one side with respect to the spacing part S, and a second winding core part B provided on the other side and having a different cross-sectional area from that of the first winding core part A. Since the winding core has the spacing part, a stack, such as a separator inserted into the spacing part, may be wound in a direction opposite to a rotational direction R of the winding core by rotation of the winding core.
If the winding core includes a first winding core part and a second winding core part having the same cross-sectional area as that of the first winding core part, distortion of the winding core may occur due to tension during winding, and the circularity of a core part of the manufactured electrode assembly may decrease. That is, the core part may be deformed into an oval shape due to tension during winding, which may be disadvantageous in terms of processability, outer diameter, and circularity.
On the other hand, when the winding core includes a first winding core part and a second winding core part having a different cross-sectional area from that of the first winding core part, the distortion and asymmetry of the winding core due to tension during winding are minimized and the average circularity of the core part is increased, minimizing the occurrence of core collapse.
Specifically, since the winding core includes a first winding core part and a second winding core part having a different cross-sectional area from that of the first winding core part, when the high tension is applied to the winding core, distortion may occur in a relatively small winding core part. Accordingly, with the spacing part as a center, the point at which the curvature of the first electrode is greatest may be located at a position adjacent to the relatively large winding core, and the flat region of the first electrode may be located at the position adjacent to a relatively small winding core.
In addition, in the region above 0° and 180° or less in the opposite direction to the direction W in which the electrode assembly is wound, i.e., in the rotational direction R of the winding core, based on the longitudinal end portion of the first electrode, the number of turns of the first electrode up to the outermost layer is relatively smaller and a distance from the longitudinal end portion of the first electrode that can slide is relatively longer, as compared to a region above 180° and 360° or less, so the concentrated stress is not relieved. Therefore, a possibility of deformation in the direction of the core cavity at the corresponding location may be higher.
That is, the winding core may include a pair of winding core parts separated around the spacing part into which a separator is inserted, and when a certain level of tension is applied, the winding core is distorted, which inevitably generates a region where the curvature of the first electrode is a specific value or smaller, that is, a flat region, and the core collapse may occur in the region where the curvature of the first electrode is the specific value or smaller.
In this case, in the region above 0° and 180° or less in the opposite direction to the direction W in which the electrode assembly is wound, i.e., in the rotational direction R of the winding core, based on the longitudinal end portion of the first electrode, when the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest is adjusted, the phenomenon of the core collapse can be addressed.
According to an exemplary aspect of the present disclosure, the cross-sectional area of the first winding core part may be smaller than the cross-sectional area of the second winding core part, and the arranging process may be performed so that the longitudinal end portion of the first electrode is arranged on an outer peripheral surface of the first winding core part.
Specifically, referring to
According to an exemplary aspect of the present disclosure, the arranging process may be performed so that the longitudinal end portion of the first electrode is arranged at a location 40% or more and 60% or less spaced apart from the spacing part based on 100% of a length of the outer peripheral surface of the first winding core part. Specifically, the arranging process may be performed so that the longitudinal end portion of the first electrode is arranged at a location 40% to 50% or 50% to 60%, for example, 50% spaced apart from the spacing part based on 100% of the length of the outer peripheral surface of the first winding core part. In other words, the longitudinal end portion of the first electrode may be arranged at a ½ location of the outer peripheral surface of the first winding core part, which is the location furthest from the spacing part of the winding core, on the outer peripheral surface of the first winding core part. Referring, for example, to
When the arranging process is performed so that the longitudinal end portion of the first electrode is arranged on the outer peripheral surface of the first winding core part, the angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest may be adjusted within a certain range. Referring, for example, to
According to an exemplary aspect of the present disclosure, the winding process may be performed while keeping tension of 400 gram-force (gf) or higher. Specifically, the tension may be 400 gf or higher and 500 gf or less. More specifically, the tension may be 410 gf or higher, 420 gf or higher, 430 gf or higher, 440 gf or higher, or 450 gf or higher, and may be 590 gf or less, 580 gf or less, 570 gf or less, 560 gf or less, or 550 gf or less.
When the tension satisfies the above-described range, due to the high tension in the winding process, with the spacing part as a center, the point at which the curvature of the first electrode is greatest may be located at a position adjacent to a relatively large winding core, the flat region of the first electrode may be located at a position adjacent to a relatively small winding core, and positions of the point at which the curvature of the first electrode is greatest and the flat region of the first electrode may be formed constant.
An exemplary aspect of the present disclosure provides an electrode assembly manufactured by the above-described method for manufacturing an electrode assembly.
The electrode assembly according to an exemplary aspect of the present disclosure adjusts the angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest, making it possible to address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of an electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, to prevent damage to the second electrode and the separator, and to prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
An exemplary aspect of the present disclosure provides a secondary battery including the electrode assembly described above, and a battery case for accommodating the electrode assembly. Specifically, the secondary battery may include the electrode assembly according to an exemplary aspect described above and a battery case for accommodating the electrode assembly.
The secondary battery according to the present disclosure can address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of an electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, prevent damage to the second electrode and the separator, and prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
According to an exemplary aspect of the present disclosure, the battery case may have a cylindrical shape. Specifically, the battery case may have a cylindrical shape, a square shape, a pouch shaped or the like depending on uses, but is not limited thereto.
According to an exemplary aspect of the present disclosure, the battery case may include an electrolyte therein. Specifically, the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte that may be used in the manufacturing of the lithium secondary battery, but is not limited thereto. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.
According to an exemplary aspect of the present disclosure, as the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dimetoxy ethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, or ethyl propionate may be used.
According to an exemplary aspect of the present disclosure, a lithium salt may be used as the metal salt, and the lithium salt is a material that is readily soluble in the non-aqueous electrolyte solution, in which, for example, one or more species selected from the group consisting of 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− may be used as an anion of the lithium salt.
According to an exemplary aspect of the present disclosure, one or more additives, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride, may be further included in the electrolyte for the purpose of improving the lifetime characteristic of the battery, suppressing a decrease in battery capacity, improving discharge capacity of the battery, and the like, in addition to the above-described electrolyte components.
An exemplary aspect of the present disclosure provides a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. Since the battery module and the battery pack include the secondary battery with high capacity, high battery stability and high life characteristics, the battery module and the battery pack may be used as a power source of a medium and large sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.
Below, Examples will be described in detail to specifically describe the present disclosure. However, the Examples according to the present disclosure may be modified in other forms, and the scope of the present disclosure is not construed as being limited to the following Examples. The Examples of the present specification are provided to more completely explain the present disclosure to one skilled in the art.
A first electrode active material slurry was prepared by adding Li(Ni0.89Co0.07Mn0.04)O2 as a first electrode active material, CNT as a first electrode conductive material, and polyvinylidene fluoride (PVdF) as a first electrode binder to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.92:0.5:1.58. The first electrode active material slurry was coated on an aluminum current collector with a thickness of 15 μm and a length of 63.9 mm in a width direction, followed by drying and rolling to form a first electrode active material layer, whereby a first electrode with a thickness of 135 μm was prepared.
Next, a second electrode active material composition was prepared by preparing natural graphite (C, average particle diameter: 17 μm) as a second electrode active material, and mixing the second electrode active material, carbon black as a second electrode conductive material, and styrene-butadiene rubber (SBR) as a second electrode binder at a weight ratio of 97.7:1.3:1.0. Then, 7.8 g of distilled water was added to 5 g of the second electrode active material composition, followed by stirring to prepare a second electrode active material slurry. The second electrode active material slurry was coated on a copper (Cu) metal thin film as a second electrode current collector with a thickness of 8 μm and a length of 65.2 mm in a width direction, followed by drying (drying temperature 120° C., 1 minute) to form a second electrode with an average thickness of 166 μm. In this case, the temperature of the circulating air was 60° C.
Thereafter, two separators were sequentially arranged and wound using a winding core with a diameter of 3.2 mm, and then the second electrode was input between the two separators, which was then additionally wound. In this case, the winding core including a spacing part where a separator is inserted, a first winding core part, and a second winding core part having a cross-sectional area different from that of the first winding core part was used, and the cross-sectional areas of the first and second winding core parts were 5.4 mm2 and 2.7 mm2, respectively. Advantageously, when using an asymmetrical winding core (i.e., a core in which the two winding core parts have different cross-sectional areas), it is possible to minimize the asymmetry that normally occurs during winding, in which the two winding core parts become at least slightly offset due to the winding tension. As a result, using an asymmetrical winding core can increase the average core circularity of the electrode assembly, and thereby minimize collapse.
After the separators and the second electrode were wound about three turns, the first electrode was input and wound, and a seal tape made of PET was attached and finished to wrap around the upper and lower outer peripheral surfaces of the electrode assembly at the end portion where the winding was completed.
In this case, based on the first winding core part located at a 6 o'clock direction and the second winding core part located at a 12 o'clock direction of the electrode assembly, the positions of the longitudinal end portions located at the core part and outermost portion of the first electrode and the position of the tab 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 end portions at the same position, and the unit ‘o'clock’ means that when the first electrode tab is located at 12 o'clock on the CT image, the relative position of each factor is shown clockwise. It is noted that, since the tab of the outermost second electrode is positioned at the radially outermost part of the electrode assembly (along its outer periphery), such second electrode tab is not shown in the figures herein, which are focused on the core of the electrode assembly.
The area and circularity of the core cavity measured from computed tomography (CT) images,
In this case, as regards the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest, the curvatures measured at each measurement point on the CT image were compared, the measurement point, at which the curvature has the greatest value in the region above 0° and 180° or less in the opposite direction to the direction in which the electrode assembly is wound, based on the longitudinal end portion of the first electrode, was determined as the point (curvature Max.) at which the curvature of the first electrode is greatest, and the angle formed between the point at which the curvature of the first electrode is greatest and the longitudinal end portion of the first electrode was measured around the winding axis and shown in Table 2 below. In the following Examples, Comparative Examples, and Experimental Examples, the point (curvature Max.) at which the curvature of the first electrode is greatest was measured using the same method.
A secondary battery was prepared by inserting the electrode assembly into a cylindrical battery case, injecting an electrolyte solution in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 20:5:75 and LiPF6 was dissolved therein to be 1.4 M, and sealing the cylindrical battery case with a cap assembly.
An electrode assembly and a secondary battery were prepared in the same manner as in Example 1, except that after 50 cycles under conditions of 4.25 V-2.5 V 1 C/1 C @25° C., the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was instead set to be 65° around the winding axis at the core part of the electrode assembly. By adjusting the longitudinal end during winding, the curvature of the manufactured electrode assembly is set, and accordingly, when the curvature of the manufactured electrode assembly is set, the curvature can be maintained within the corresponding condition even after 50 cycles
An electrode assembly and a secondary battery were prepared in the same manner as in Example 1, except that after 50 cycles under conditions of 4.25 V-2.5 V 1 C/1 C @25° C., the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was set to be 98.9° around the winding axis at the core part of the electrode assembly. Setting adjustments are made during the manufacturing process. By adjusting the longitudinal end during winding, the curvature of the manufactured electrode assembly is set, and accordingly, when the curvature of the manufactured electrode assembly is set, the curvature can be maintained within the corresponding condition even after 50 cycles.
An electrode assembly and a secondary battery were prepared in the same manner as in Example 1, except that after 50 cycles under conditions of 4.25 V-2.5 V 1 C/1 C @25° C., the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was set to be 112.4° around the winding axis at the core part of the electrode assembly. As in Comparative Example 1, the setting adjustments are made during the manufacturing process.
An electrode assembly and a secondary battery were prepared in the same manner as in Example 1, except that after 50 cycles under conditions of 4.25 V-2.5 V 1 C/1 C @25° C., the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was set to be 129.3° around the winding axis at the core part of the electrode assembly.
An electrode assembly and a secondary battery were prepared in the same manner as in Example 1, except that after 50 cycles under conditions of 4.25 V-2.5 V 1 C/1 C @25° C., the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was set to be 40° around the winding axis at the core part of the electrode assembly.
An electrode assembly and a secondary battery were prepared in the same manner as in Example 1, except that after 50 cycles under conditions of 4.25 V-2.5 V 1 C/1 C @25° C., the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was set to be 20° around the winding axis at the core part of the electrode assembly.
The flatness fractions of the secondary batteries of Example 1, Example 2 and Comparative Examples 1 to 3 were evaluated by the following method, and the results are shown in Table 2 below and
1) The first electrode is extracted from the CT image of the electrode assembly.
2) On the first surface of the first electrode, measurement points are set at 2° intervals from one end portion, in the longitudinal direction, of the first electrode, and the x-coordinates and y-coordinates of the measurement points are measured.
3) The curvature (k) for each measurement point is calculated according to Formula 1 below using the x-coordinate and y-coordinate of the measurement point.
In Formula 1 above, k is a curvature of the first electrode, x is an x-coordinate of the measurement point, y is a y-coordinate of the measurement point, x′ is a first derivative value of x, and y′ is a first derivative value of y, x″ is a second derivative value of x, and y″ is a second derivative value of y.
4) When the curvature value calculated at each measurement point is 1 or less, the corresponding measurement point is evaluated as a flat region, and a ratio of the number of measurement points evaluated as a flat region based on 100% of the total number of measurement points was evaluated as flatness fraction (%).
The occurrence or not of core collapse in the secondary batteries of Examples 1 and 2, and Comparative Examples 1 to 5 was evaluated by the following method, and the occurrence or not of core impingement was re-evaluated every 200 cycles. The results are shown in Table 2 below and
1) The first electrode is extracted from the CT image of the electrode assembly.
2-1) An area of the core cavity surrounded by the first electrode from one end portion, in the longitudinal direction, of the first electrode to a point corresponding to one turn in the longitudinal direction of the first electrode is measured.
2-2) When the area of the core cavity is less than 100% based on 100% of a sum of the cross-sectional areas of the spacing part, first winding core part, and second winding core part of the winding core used for winding the electrode assembly, the core collapse was evaluated as having occurred.
3-1) On the first surface of the first electrode, an extension line of the straight line corresponding to the minimum value and maximum value of the diameter of the core cavity of the extracted first electrode is drawn, and a concentric circle is drawn using the intersection of each straight line as the central axis, that is, the winding axis.
3-2) The maximum spaced distance between the winding axis and the first electrode and the minimum spaced distance between the winding axis and the first electrode from one end portion, in the longitudinal direction, of the first electrode to a point corresponding to one turn in the longitudinal direction of the first electrode are measured, respectively.
3-3) A ratio (%) of the minimum spaced distance between the winding axis and the first electrode to the maximum spaced distance between the winding axis and the first electrode, that is, the circularity of the core cavity, is calculated. When the calculated circularity of the core cavity was less than 89%, the core collapse was evaluated as having occurred.
On the other hand, in the case where an unknown secondary battery (unknown cell) is acquired, the above method for evaluating whether the core collapse has occurred may be applied in a manner of evaluating whether the core collapse has occurred at the time of initial acquisition, re-evaluating whether the core collapse has occurred every 200 cycles, and comparing and analyzing the result with the core collapse conditions of the secondary battery of the exemplary aspect according to the present disclosure.
The occurrence or not of core impingement in the secondary batteries of Examples 1 and 2, and Comparative Examples 1 to 5 was evaluated by the following method, and the occurrence or not of core impingement was re-evaluated every 200 cycles, and the results are shown in Table 2 below and
1) On a first surface of a first electrode 300, a first extension line E1 is drawn by extending a straight line connecting a longitudinal end portion 310 of the first electrode and a point 5 mm spaced apart from the end portion.
2-1) when the Second Electrode is Deformed
At the core part of the electrode assembly, on a surface of a second electrode 100 facing the first surface of the first electrode, a second extension line E2 is drawn by extending a straight line connecting two points where a direction of curvature changes within a spaced distance of 5 mm from the longitudinal end portion 310 of the first electrode.
2-2) when there is No Deformation in the Second Electrode
At the core part of the electrode assembly, on the surface of the second electrode 100 facing the first surface of the first electrode, a second extension line E2 is drawn by extending a straight line connecting two points 5 mm spaced apart from the longitudinal end portion 310 of the first electrode.
3) When an angle from the first extension line E1 to the second extension line E2 in a counterclockwise direction with respect to the intersection of the first extension line E1 and the second extension line E2 exceeded 25°, it was evaluated that the core impingement occurred.
On the other hand, in the case where an unknown secondary battery (unknown cell) is acquired, the above method for evaluating whether the core impingement has occurred may be applied in a manner of evaluating whether the core impingement has occurred at the time of initial acquisition, reevaluating whether the core impingement has occurred every 200 cycles, and comparing and analyzing the result with the core impingement conditions of the secondary battery of the exemplary aspect according to the present disclosure.
The occurrence or not of core crack was evaluated for the electrode assemblies of Example 1, Example 2, and Comparative Examples 1 to 5 by using the following method, and the results are shown in Table 2 below and
Specifically, the electrode assemblies of Examples 1 and 2, and Comparative Examples 1 to 5 were prepared, and the manufactured electrode assemblies were disassembled to visually check whether cracks or wrinkles occurred at the core part. In this case, when cracks or wrinkles were included at the core part, the core crack was evaluated as having occurred.
Specifically, part (a) of
Referring to Table 2 and FIGS. part (b) of
If cracks and resulting foreign matters occur in the first electrode at the core part of the electrode assembly during the winding process, the defect rate may increase and the processability may deteriorate. Accordingly, by satisfying the electrode assembly manufacturing process of this disclosure, the possibility of including a first electrode in which a core crack has occurred in the completed electrode assembly is reduced. That is, the input of first electrodes where cracks are expected to occur are excluded from the manufacturing process. As a result it is possible to prevent a decrease in productivity of the electrode assembly and secondary battery.
Specifically, when a cracked electrode assembly is inserted into the battery case, the possibility of occurrence of low voltage and short-circuit due to foreign matters in the first electrode greatly increases in the battery case. Accordingly, the possibility of occurrence of cracks in the first electrode can be reduced by adjusting the range of the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest, in the winding process. That is, it can be seen that the electrode assembly and the method for manufacturing an electrode assembly according to an exemplary aspect of the present disclosure are suitable for a continuous process using roll-to-roll process equipment in the related art, ensuring productivity and economic efficiency of the electrode assembly including the first electrode and the secondary battery.
The secondary battery of Example 1 was prepared, and charged and discharged 50 times under conditions of 25° C., 1 C charge and 1 C discharge.
While performing 200 cycles from SOC of 0% to SOC of 100% under conditions of 4.25 V-2.5 V 1 C/1 C @25° C., the position of the longitudinal end portion of the first electrode at SOC of 0% and SOC of 100% was extracted from the CT image and recorded, and a sliding range of the longitudinal end portion of the first electrode was measured. Thereafter, the sliding range of the longitudinal end portion of the first electrode was evaluated from CT images before activation and at SOC of 100%, and is shown in
The sliding range of the longitudinal end portion of the first electrode was measured in the same manner as in Reference Experimental Example 1, except that the secondary battery of Example 2 was used. Thereafter, the sliding range of the longitudinal end portion of the first electrode was evaluated from CT images before activation and at SOC of 100%, and is shown in
Referring to
With this, it can be seen that in the secondary batteries according to Examples 1 and 2, sliding of the first electrode may occur due to contraction/expansion of the electrode before activation and at SOC 100%, but the sliding occurs within a specific range (1° to 3°).
That is, the winding process is performed while maintaining tension of a specific value or higher, so the position of the point at which the curvature of the first electrode is greatest is maintained constant. Therefore, it can be seen that, even when the cycle progresses, the range of the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest is maintained within the sliding range (1° to) 3° of the longitudinal end portion of the first electrode.
Specifically,
More specifically, in
Referring to Table 2,
On the other hand, as in Comparative Examples 1 to 3, when the angle between the longitudinal end portion of the first electrode extracted from the CT image of the core part and the point at which the curvature of the first electrode is greatest was greater than 98°, or as in Comparative Examples 4 and 5, when the angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was 40° or less, i.e., when the above-described angle range was not satisfied, it was confirmed that the angle formed between the first extension line and the second extension line was 25° or greater and the core impingement occurred, or even when the core impingement did not occur, the core collapse occurred because the area of the core cavity was less than 100% based on 100% of the sum of the cross-sectional areas of the winding core used for winding or the circularity of the core cavity was less than 89%.
With this, it can be seen that the electrode assembly and the secondary battery including the same according to an exemplary aspect of the present disclosure adjust the angle between the longitudinal end portion of the first electrode extracted from the CT image of the core part and the point at which the curvature of the first electrode is greatest to a specific range, making it possible to address the phenomenon that the core cavity fails to maintain a circular shape and collapses due to deformation of an electrode assembly resulting from contraction/expansion of an electrode during charging and discharging of the battery, to prevent damage to the second electrode and the separator, and to prevent an internal short-circuit between the first electrode and the second electrode, so the stability and life characteristics of the battery can be improved.
Referring to Table 2 and
On the other hand, as in Comparative Example 2, when the angle formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was greater than 98° around the winding axis, that is, when the angle range formed between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest was not satisfied, it was confirmed that the angle formed between the first extension line and the second extension line was 25° or greater and the core impingement occurred, or even when the core impingement did not occur, the core collapse occurred because the area of the core cavity was less than 100% based on 100% of the sum of the cross-sectional areas of the winding core used for winding or the calculated circularity of the core cavity was less than 89%.
With this, it can be seen that the method for manufacturing an electrode assembly according to an exemplary aspect of the present disclosure enables an electrode assembly whose angle between the longitudinal end portion of the first electrode and the point at which the curvature of the first electrode is greatest has been adjusted as disclosed herein to be manufactured in a simpler manner and is suitable for a continuous process using roll to roll process equipment of the related art, ensuring productivity and economic efficiency.
The foregoing detailed description is intended to illustrate and explain the present disclosure. In addition, the foregoing description is only to show and describe the preferred aspect of the present disclosure, and as described above, the present disclosure can be used in various other combinations, changes and environments, and can be changed and modified within the scope of the concept of the disclosure disclosed in the present specification, within the scope equivalent to the above disclosure and/or within the scope of skill or knowledge in the art. Accordingly, the foregoing detailed description of the disclosure is not intended to limit the disclosure to the disclosed aspects. Furthermore, the appended claims should be construed to include other aspects as well.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2023-0149964 | Nov 2023 | KR | national |
| 10-2024-0110579 | Aug 2024 | KR | national |
