Method and device for evaluating core deformation degree of cylindrical battery cell

Abstract

The present invention relates to a method for evaluating the degree of core deformation of a cylindrical battery cell, comprising the steps of: preparing a cylindrical battery cell having a structure in which a jelly-roll shaped electrode assembly is housed within a cylindrical can; CT scanning the cylindrical battery cell to obtain an image of a cross-section perpendicular to the winding axis of the electrode assembly; and measuring the degree of deformation of the electrode assembly core portion shown in the image.

Description

Technology Field

[0001] The present invention relates to a method and apparatus for evaluating the degree of core deformation of a cylindrical battery cell. Background Technology

[0003] Recently, rechargeable secondary batteries are being widely used as an energy source for wireless mobile devices. Furthermore, secondary batteries are attracting attention as an energy source for electric vehicles and hybrid electric vehicles, which are being proposed as solutions to address air pollution caused by conventional gasoline and diesel vehicles that use fossil fuels. Consequently, the types of applications utilizing secondary batteries are becoming highly diversified due to their advantages, and it is expected that secondary batteries will be applied to a wider range of fields and products in the future than they are today.

[0004] These secondary batteries are classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium-polymer batteries depending on the composition of the electrodes and electrolytes; among these, the use of lithium-ion polymer batteries is increasing due to their low risk of electrolyte leakage and ease of manufacturing. Generally, secondary batteries are classified according to the shape of the battery case into cylindrical and prismatic batteries, in which the electrode assembly is housed in a cylindrical or prismatic metal can, and pouch-type batteries, in which the electrode assembly is housed in a pouch-type case made of an aluminum laminate sheet. The electrode assembly housed in the battery case is a power generation element capable of charging and discharging, consisting of a positive electrode, a negative electrode, and a separator structure interposed between the positive and negative electrodes. It is further classified into a jelly-roll type, which is wound with a separator interposed between long sheet-type positive and negative electrodes coated with active material, and a stack type, in which multiple positive and negative electrodes of a predetermined size are sequentially stacked with a separator interposed between them.

[0005] Among these, the cylindrical battery cell is manufactured by housing an electrode assembly wound in a jelly-roll form into a cylindrical can.

[0006] Figure 1 is a photograph showing the core shape of a cylindrical battery cell with a collapsed core.

[0007] Generally, in a cylindrical battery cell, a core is formed in the center of the electrode assembly, which is a hollow space formed along the winding axis. Immediately after the battery cell is manufactured, the cross-section of the core is nearly circular; however, as the battery cell undergoes repeated charging and discharging, the electrodes within the electrode assembly degenerate, causing the core to collapse. When the core collapses, the core portion changes into a distorted shape, as shown in Figures 1 (a) and (b). When the core takes on such a distorted shape, there is a problem in that the end of the positive or negative electrode located in the core portion may penetrate the separator and come into contact with the negative or positive electrode, thereby causing a short circuit.

[0008] Conventionally, in order to verify the shape of such a core, it was necessary to directly disassemble the battery cell to directly verify the shape of the core as shown in FIG. 1 (a) or (b), and there was no technology available to quantitatively measure the degree of deformation of the core. Furthermore, when evaluating the degree of deformation of the core by disassembling the battery cell in this manner, there was a problem in that it was difficult to determine the degree of deformation of the core according to the charge-discharge cycle of the battery cell. Prior art literature

[0010] Korean Patent Publication No. 10-2015-0091288 The problem to be solved

[0011] The present invention aims to provide a method for evaluating the degree of deformation of a core in a cylindrical battery cell, which can inspect for battery cell lifespan degradation and safety issues in advance by quantitatively evaluating the degree of deformation of the core within the cylindrical battery cell using a non-destructive method. means of solving the problem

[0013] A method for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention comprises: a step of preparing a cylindrical battery cell having a structure in which a jelly-roll shaped electrode assembly is housed within a cylindrical can; a step of CT scanning the cylindrical battery cell to obtain an image of a cross-section perpendicular to the winding axis of the electrode assembly; and a step of measuring the degree of deformation of the electrode assembly core portion shown on the image.

[0014] Specifically, the step of measuring the degree of deformation of the core portion may be to measure the circularity of the electrode assembly core portion shown in the image.

[0015] In a specific example, the above circularity may be the ratio of the length of the minimum diameter to the maximum diameter of the electrode assembly core.

[0016] In a specific example, the step of measuring the circularity may include: drawing a first reference line of a regular polygonal shape; adjusting the size, position, and angle of the image so that a cylindrical can in the image touches the first reference line; and drawing a plurality of second reference lines passing through the center point of the first reference line and measuring the length of the portion where each second reference line overlaps with the core.

[0017] At this time, a process of adjusting the size of the image can be performed so that the outermost surface of the cylindrical can contacts the first reference line on the inner side of the area formed by the first reference line.

[0018] In a specific example, during the process of adjusting the size, position, and angle of the above image,

[0019] The image can be rotated so that the cathode tab located at the outermost edge of the electrode assembly touches the first reference line.

[0020] In a specific example, the angle formed by the adjacent second reference line may be 5 to 30°.

[0021] In a specific example, the above circular shape is the value obtained by dividing the minimum value of the length of the part where the second baseline and the core overlap by the maximum value.

[0022] In addition, the method for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention may further include the step of repeatedly charging and discharging the battery cell and measuring the degree of deformation of the core according to the charge-discharge cycle.

[0023] At this time, if the circularity is less than a preset value or the amount of change in circularity is greater than or equal to a preset value, the battery cell can be determined to be defective.

[0024] In addition, the present invention provides a device for evaluating the degree of core deformation of a cylindrical battery cell.

[0025] The device for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention comprises: a shooting unit that obtains an image of a cross-section perpendicular to the winding axis of an electrode assembly by CT scanning a cylindrical battery cell having a structure in which a jelly-roll shaped electrode assembly is housed in a cylindrical can; and a measuring unit that measures the degree of deformation of the electrode assembly core portion shown on the image.

[0026] At this time, the above measuring unit can measure the circularity of the electrode assembly core portion shown on the image.

[0027] In a specific example, the measuring unit can adjust the size, position, and angle of an image so that a first reference line of a regular polygonal shape contacts a cylindrical can, and measure the length of the portion where a plurality of second reference lines passing through the center point of the first reference line overlap with the core.

[0028] In a specific example, the above circular shape may be the value obtained by dividing the minimum value of the length of the part where the second baseline and the core overlap by the maximum value.

[0029] In addition, the core deformation degree evaluation device of a cylindrical battery cell according to the present invention may further include a judgment unit for determining whether the battery cell is defective and a charging / discharging unit for charging and discharging the battery cell.

[0030] In another example, the charging / discharging unit repeatedly charges and discharges the battery cell, and the measuring unit can measure the degree of deformation of the core according to the charging / discharging cycle.

[0031] In a specific example, the above-mentioned judgment unit may determine that the battery cell is defective if the circularity is less than a preset value or if the amount of change in circularity is greater than or equal to a preset value. Effects of the invention

[0033] The present invention allows for the quantitative evaluation of the degree of deformation of the core within a cylindrical battery cell using a non-destructive method, utilizing images obtained by CT scanning of the cylindrical battery cell. Furthermore, based on this, it is possible to evaluate the degradation of battery cell lifespan and safety issues in advance. Brief explanation of the drawing

[0035] Figure 1 is a photograph showing the core shape of a cylindrical battery cell with a collapsed core. FIG. 2 is a flowchart showing the sequence of a method for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention. Figure 3 is a schematic diagram showing the structure of a cylindrical battery cell. Figure 4 is a schematic diagram showing a cross-section of a cylindrical battery cell. Figure 5 is a schematic diagram showing the shape of a reference line for measuring the circularity of the core of a cylindrical battery cell. Figures 6 to 8 are schematic diagrams illustrating the process of measuring the circularity of a core using a reference line. FIG. 9 is a block diagram showing the configuration of a device for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention. Figures 10 and 11 are photographs showing the core shape and circularity of a cylindrical battery cell measured in different battery cells. Figure 12 is a photograph showing the change in core shape and circularity as the cycle progresses of the cylindrical battery cell in Example 2. Specific details for implementing the invention

[0036] The present invention will be described in detail below. Prior to this, terms or words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe their invention, they must be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0037] In this application, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof. Furthermore, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "immediately above" the other part, but also cases where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only cases where it is "immediately below" the other part, but also cases where there is another part in between. Additionally, in this application, being "placed on" may include cases where it is placed on the lower part as well as on the upper part.

[0039] The present invention will be described in detail below.

[0040] FIG. 2 is a flowchart showing the sequence of a method for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention.

[0041] Referring to FIG. 2, the method for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention comprises: a step (S10) of preparing a cylindrical battery cell having a structure in which a jelly-roll shaped electrode assembly is housed within a cylindrical can; a step (S20) of CT scanning the cylindrical battery cell to obtain an image of a cross-section perpendicular to the winding axis of the electrode assembly; and a step (S30) of measuring the degree of deformation of the electrode assembly core portion shown on the image.

[0042] As previously explained, as the battery cell undergoes repeated charging and discharging, the electrodes within the electrode assembly degrade, causing the core to collapse. When the core collapses, the core portion deforms into a distorted shape. In such a distorted state, the tip of the positive or negative electrode located in the core portion may penetrate the separator and come into contact with the negative or positive electrode, potentially causing a short circuit.

[0043] The present invention allows for the quantitative evaluation of the degree of deformation of the core within a cylindrical battery cell using a non-destructive method, utilizing images obtained by CT scanning of the cylindrical battery cell. Furthermore, based on this, it is possible to evaluate the degradation of battery cell lifespan and safety issues in advance.

[0044] Each step of the method for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention will be described in detail below.

[0046] Preparation of cylindrical battery cells

[0047] First, prepare a cylindrical battery cell having a structure in which a jelly-roll shaped electrode assembly is housed inside a cylindrical can.

[0048] Figure 3 is a schematic diagram showing the structure of a cylindrical battery cell, and Figure 4 is a schematic diagram showing a cross-sectional image of a cylindrical battery cell.

[0049] Referring to FIG. 3, a cylindrical battery cell (1) is manufactured by housing a jelly-roll type electrode assembly (30) in a cylindrical can (10), injecting an electrolyte so that the electrode assembly (30) is immersed in the cylindrical can (10), and then mounting a cap assembly (20) on the open top of the cylindrical can (10). Meanwhile, the electrode assembly (30) is a jelly-roll type manufactured by stacking a positive electrode (31) and a negative electrode (32) with a separator (33) interposed therein and then winding it in one direction. Since the details regarding the positive electrode, negative electrode, separator, and electrolyte are known to a person skilled in the art, a detailed explanation is omitted.

[0050] The cylindrical can (10) may be made of metal, preferably stainless steel. Additionally, the cylindrical can may include a storage portion in which an electrode assembly can be housed, and may have an open top portion. The open top portion of the cylindrical can (10) may be bent to form a beading portion so that it can be sealed after the cap assembly (20) is mounted, and the top portion may be bent to form a crimping portion to secure the cap assembly (20). The beading portion is formed at the contact point between the cap assembly and the cylindrical can and may have a shape that is indented toward the inside of the cylindrical can. Additionally, the bottom portion of the cylindrical can may serve as a negative terminal for connection with an external circuit.

[0051] Additionally, the cylindrical can (10) may be made of metal, preferably stainless steel. Additionally, the cylindrical can (10) may include a storage portion in which an electrode assembly (30) can be stored, and may have an open top portion.

[0052] Meanwhile, the cap assembly (20) is structured such that a cap and a safety vent are in close contact inside a sealing gasket that is mounted in a space formed on the upper inner surface of the clamping and beading portions of the cylindrical can (10). The central part of the cap protrudes upward, so it can function as a positive terminal for connection with an external circuit.

[0053] Furthermore, an insulating plate is mounted on the upper surface of the electrode assembly (30) to prevent contact with the electrode lead, thereby preventing a short circuit caused by contact between the electrode assembly and the electrode lead.

[0054] Meanwhile, referring to FIGS. 3 and 4, a core (34) in the form of a hollow space is formed in the center of the electrode assembly (30) wound in the shape of a jelly roll. A center pin (not shown), which is a cylindrical metal material, may be inserted into the core (34) to provide a certain strength to the electrode assembly, and in some cases, the center pin may be removed after welding the electrode to a cylindrical can or cap assembly. The negative electrode tab (35) protrudes from the bottom of the jelly roll and extends along the inner wall of the cylindrical can, and is welded to the inner wall of the cylindrical can. That is, the negative electrode tab (35) is located in the space between the inner wall of the cylindrical can (10) and the electrode assembly (30) as shown in FIG. 4.

[0056] <CT 촬영>

[0057] When a cylindrical battery cell is prepared, the cylindrical battery cell is CT-photographed to obtain a cross-sectional image perpendicular to the winding axis of the electrode assembly. In this case, a cross-sectional image in the shape of Fig. 4 can be obtained. Multiple images can be obtained for each battery cell.

[0058] The above CT imaging can be performed by a conventional CT measuring device. For example, the CT measuring device may be equipped with a table that rotates while carrying a battery, an X-ray generator for generating X-rays to be transmitted through the battery, an X-ray detector for detecting X-rays transmitted through the battery, and a computer capable of obtaining an image of a predetermined area of ​​the battery cross-section from the transmitted X-rays and storing it.

[0060] <Measurement of Core Deformation Degree>

[0061] When an image is obtained through CT scanning, the degree of deformation of the electrode assembly core portion shown in the image is measured. The core portion of the electrode assembly is a circular portion located at the center of the electrode assembly in the image. In addition, the degree of deformation of the core portion refers to the degree to which the core is compressed.

[0062] Specifically, the step of measuring the degree of deformation of the core portion may be to measure the circularity of the electrode assembly core portion shown in the image. Since the core of a jelly-roll type electrode assembly is generally circular, when a core collapse phenomenon occurs, the circular shape of the core portion is deformed into an elliptical or distorted shape, and the present invention can quantitatively measure the degree of deformation of the core by measuring the circularity of the core portion.

[0063] The above circularity is the ratio of the length of the minimum diameter to the maximum diameter of the electrode assembly core. Here, the maximum diameter refers to the length of the part of the line passing through the center of the core that overlaps with the core, where the length of the part of the line passing through the center of the core that overlaps with the core is maximum, and the minimum diameter refers to the length of the part of the line passing through the center of the core that overlaps with the core, where the length of the part of the line passing through the center of the core that overlaps with the core is minimum. The present invention has the advantage of easily identifying whether there is a defect or the degree of deterioration of a cylindrical battery cell by quantitatively evaluating the degree of deformation of the core of a cylindrical battery cell using circularity.

[0064] In the present invention, the circularity can be measured using reference lines drawn in two types.

[0065] FIG. 5 is a schematic diagram showing the shape of a reference line for measuring the circularity of a core of a cylindrical battery cell, and FIG. 6 to 8 are schematic diagrams showing the process of measuring the circularity of a core using a reference line.

[0066] Referring to FIG. 5, the reference line includes a first reference line (11) in the shape of a regular polygon and a plurality of second reference lines (12) passing through the center point of the first reference line.

[0067] In addition, in the present invention, the circularity is measured after overlapping the first reference line (11) and the second reference line (12) with the cross-sectional image of the cylindrical battery cell.

[0068] First, a first reference line is constructed. The first reference line is in the form of a regular polygon, such as an equilateral triangle, square, regular pentagon, regular hexagon, and regular octagon, and there are no specific restrictions on its shape; however, a first reference line in the form of a simple square can be constructed and used.

[0069] Referring to FIGS. 4 and 6, the first reference line (11) can be drawn on a cross-sectional image of a cylindrical battery cell obtained earlier. For example, the first reference line (11) can be drawn using separate image software, and the cross-sectional image can be superimposed thereon. Subsequently, in the cross-sectional image of the cylindrical battery cell, the size, position, and angle of the image can be adjusted so that the cylindrical can (10) comes into contact with the first reference line (11).

[0070] At this time, the size of the image is adjusted so that the outermost surface of the cylindrical can (10) comes into contact with the first reference line (11) on the inner side of the area formed by the first reference line (11). Through this, the center of the cross-sectional image of the cylindrical battery cell, that is, the center point of the cylindrical battery cell (or cylindrical can) on the image, can be made to coincide with the center point of the first reference line in the shape of a regular polygon.

[0071] In addition, during the process of adjusting the size, position, and angle of the above image, the image can be rotated so that the negative tab (35) located at the outermost edge of the electrode assembly (30) comes into contact with the first reference line (11). This is to fix the position of the image consistently, and through this process, multiple images can be compared at the same position, and as described later, it is possible to easily observe the degree of deformation when checking core deformation during cycle progression. Here, the fact that the negative tab (35) comes into contact with the first reference line (11) means that the cylindrical can (10) in contact with the negative tab (35) from the outside of the negative tab (35) comes into contact with the first reference line. More specifically, as shown in FIG. 6, the image can be rotated so that one end of the negative tab (35) is adjacent to the first reference line, and in this case, the part of the cylindrical can (10) in contact with one end of the negative tab (35) can come into contact with the first reference line (11).

[0072] After drawing the first reference line (11) and completing the alignment of the image, a plurality of second reference lines (12) are drawn on the image. The second reference lines (12) are drawn in the shape of straight lines passing through the center point of the first reference line (11). As previously explained, since the center point of the first reference line (11) coincides with the center point of the cylindrical battery cell, the second reference lines (12) pass through the center point of the cylindrical battery cell.

[0073] At this time, the second reference lines (12) are arranged at predetermined intervals around the center point of the cylindrical battery cell. Specifically, the angle formed by adjacent second reference lines may be 5 to 30°, more specifically 10 to 25°, and more specifically 15 to 20°. As described below, the length of the portion where the second reference lines overlap with the core is measured and the circularity is calculated from it. If the angle between the second reference lines is excessively large, an error occurs in the circularity. On the other hand, if the angle between the second reference lines is excessively small, the number of second reference lines whose lengths need to be measured increases excessively, thereby reducing the inspection speed.

[0074] In addition, there is no special limitation on the length of the second reference lines (12), and for example, as shown in FIG. 6, the length of the second reference lines can be made to match the diameter of the cylindrical can, or the two ends of the second reference lines can be made to touch the first reference line.

[0075] When the first reference line and the second reference line are drawn on the cross-sectional image of the cylindrical battery cell in this manner, a shape as shown in FIG. 6 is obtained. Subsequently, the circularity of the cylindrical battery cell is measured. Referring to FIG. 6, in the present invention, the circularity is the length of the portion where each second reference line overlaps with the core ( l It includes the process of measuring ).

[0076] Figures 7 and 8 illustrate a specific process for measuring circularity. In Figures 7 and 8, the core portion of the electrode assembly is shown in enlarged form for convenience of explanation, and the core of the electrode assembly is shown deformed into an elliptical shape.

[0077] In FIG. 7, multiple second reference lines are drawn to pass through the center point of a cylindrical battery cell, and the angle formed by adjacent second reference lines is 15°. At this time, as shown in FIG. 6, the length of the portion where each second reference line overlaps with the core is measured. The circularity is the value obtained by dividing the minimum value of the length of the portion where the second reference line overlaps with the core by the maximum value. Specifically, the two lines indicated by thick lines in FIG. 7 are the second reference lines where the length of the portion where the second reference line overlaps with the core is the maximum and minimum, respectively. At this time, as shown in FIG. 8, if the maximum value of the length where the second reference line overlaps with the core is 'a' and the minimum value of the length where the second reference line overlaps with the core is 'b', the circularity can be calculated as b / a.

[0079] When the degree of deformation of the core of the cylindrical battery cell is measured in the manner described above, a process of evaluating the battery cell is performed.

[0080] Specifically, if the circularity is less than a preset value, the battery cell can be determined to be defective. The preset value can be set through a database obtained in advance. Specifically, a reference value is set from values ​​extracted from the database, and this is compared with the measured circularity value, and the defect status of the battery cell is determined based on the result of the comparison. Furthermore, as described below, if the amount of change in circularity is greater than or equal to the preset value, the battery cell can be determined to be defective.

[0081] In addition, the present invention can evaluate the effect of the progress of charge-discharge cycles on the battery cell.

[0082] Specifically, the method for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention may further include the step of repeatedly charging and discharging the battery cell and measuring the degree of deformation of the core according to the charge-discharge cycle. As previously explained, as the electrode assembly of a cylindrical battery cell deteriorates as the charge-discharge cycle progresses, a core collapse phenomenon occurs in which the core becomes distorted. By measuring the change in the circularity of the cylindrical battery cell core, the present invention makes it easy to determine the degree of deformation of the core due to the repetition of charge-discharge cycles in a single battery cell. In this case, for a single cylindrical battery cell, the circularity in the initial state before proceeding with the charge-discharge cycle can be measured, and the circularity can be measured at regular intervals while proceeding with the cycle, and the results can be compared and evaluated.

[0083] In the present invention, as the charge / discharge cycle of the battery cell progresses, the circularity of the core gradually decreases, so if the amount of change in circularity according to the charge / discharge cycle is greater than a preset value, the battery cell can be determined to be defective.

[0084] As explained above, the method for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention can pre-evaluate the lifespan degradation and safety issues of the battery cell by quantitatively evaluating the degree of deformation of the core within the cylindrical battery cell using a non-destructive method.

[0086] In addition, the present invention provides an apparatus for evaluating the degree of core deformation of a cylindrical battery cell. The apparatus for evaluating the degree of core deformation of a cylindrical battery cell can be used to perform a method for evaluating the degree of core deformation of a cylindrical battery cell as described above.

[0087] FIG. 9 is a block diagram showing the configuration of a device for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention.

[0088] Referring to FIG. 9, the device (100) for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention comprises: a shooting unit (110) that obtains an image of a cross-section perpendicular to the winding axis of the electrode assembly by CT scanning a cylindrical battery cell having a structure in which a jelly-roll shaped electrode assembly is housed in a cylindrical can; and a measuring unit (120) that measures the degree of deformation of the electrode assembly core portion shown on the image.

[0089] At this time, the measuring unit (120) can measure the circularity of the electrode assembly core portion shown on the image.

[0090] Specifically, the measuring unit (120) can draw a first reference line in the shape of a regular polygon and adjust the size, position, and angle of the image so that the center point of the first reference line and the center point of the cylindrical battery cell coincide with each other by drawing a first reference line in the shape of a regular polygon and adjusting the size, position, and angle of the image so that the first reference line and the cylindrical can come into contact.

[0091] Subsequently, the measuring unit (120) draws a plurality of second reference lines passing through the center point of the first reference line and measures the length of the portion where the second reference line overlaps with the core. At this time, the circularity is the value obtained by dividing the minimum value of the length of the portion where the second reference line overlaps with the core by the maximum value. The detailed method of drawing the first reference line and the second reference line and measuring the circularity by combining them with a cross-sectional image of a cylindrical battery cell is the same as described above.

[0092] In this way, when the circularity of the core portion of the cylindrical battery cell is measured, the determination unit (130) determines whether the battery cell is defective. The determination unit (130) determines the battery cell to be defective if the circularity is less than a preset value or if the amount of change in circularity is greater than or equal to a preset value.

[0093] Meanwhile, the device for evaluating the degree of core deformation of a cylindrical battery cell according to the present invention further includes a charging / discharging unit (140) for charging and discharging the battery cell. The charging / discharging unit (140) repeatedly charges and discharges the battery cell to proceed with a cycle, thereby degrading the cylindrical battery cell.

[0094] When the circularity is measured by the imaging and measuring units while the charge-discharge cycle is in progress, the measuring unit measures the degree of core deformation according to the charge-discharge cycle. Specifically, the measuring unit measures the change in the circularity of the core according to the charge-discharge cycle. If the amount of change in circularity according to the charge-discharge cycle is greater than or equal to a preset value, the judgment unit determines the battery cell to be defective.

[0096] The present invention will be described in detail below with reference to examples to aid in understanding. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the following embodiments. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0098] Preparation Example

[0099] Manufacture of battery cells

[0100] Li[Ni] functioning as a positive electrode active material 0.6 Mn 0.2 Co 0.2 An anode composite was prepared by mixing 6.7 parts by weight of ]O29, 1.3 parts by weight of graphite functioning as a conductive material, and 2.0 parts by weight of polyvinylidene fluoride (PVdF) functioning as a binder. An anode composite slurry was prepared by dispersing the obtained anode composite in 1-methyl-2-pyrrolidone functioning as a solvent. An anode was manufactured by coating, drying, and pressing this slurry onto both sides of an aluminum foil with a thickness of 20 μm.

[0101] A cathode composite was prepared by mixing 97.6 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) functioning as cathode active materials, 1.2 parts by weight of styrene-butadiene rubber (SBR) functioning as a binder, and 1.2 parts by weight of carboxymethyl cellulose (CMC). A cathode composite slurry was prepared by dispersing this cathode composite in ion-exchanged water functioning as a solvent. A cathode was manufactured by coating, drying, and pressing this slurry onto both sides of a copper foil with a thickness of 20 μm.

[0102] A non-aqueous electrolyte was prepared by dissolving LiPF6 to a concentration of 1.0 M in an organic solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a composition of 3:3:4 (volume ratio).

[0103] A jelly-roll type electrode assembly was manufactured by laminating and winding the anode and cathode prepared above with a porous polyethylene separator interposed between them.

[0104] The above electrode assembly was housed in a cylindrical can made of metal material, and a cap assembly was mounted on the open top of the cylindrical can to manufacture a cylindrical battery cell with a structure as shown in Fig. 4.

[0106] Example 1

[0107] <CT 촬영>

[0108] Two battery cells manufactured according to the above manufacturing example were each X-ray CT scanned to obtain cross-sectional images of the cylindrical battery cells. The cross-sectional images of the battery cells are shown in FIG. 10 (a) and FIG. 11 (a), respectively. Commercially available conventional CT equipment can be used.

[0110] Circularity Measurement

[0111] The above cross-sectional image was uploaded to image software. Separately, a square-shaped first reference line was drawn, and the image size was adjusted so that the cylindrical can in the cross-sectional image contacts the first reference line from the inside. In addition, the image was rotated and aligned so that one end of the cathode tab contacts the first reference line.

[0112] Subsequently, multiple second reference lines passing through the center point of the first reference line were drawn at 15° angle intervals. The length of the portion where the second reference lines overlapped with the core shown in the cross-sectional image was measured, and the circularity was calculated by dividing the minimum value by the maximum value. More specifically, the circularity was expressed as a percentage of the minimum value relative to the maximum value.

[0113] At this time, FIG. 10(b) shows an image for calculating the circularity of the core portion in the cross-sectional image according to FIG. 10(a), and FIG. 11(b) shows an image for calculating the circularity of the core portion in the cross-sectional image according to FIG. 11(a). In FIG. 10(b) and FIG. 11(b), the white line in the left image represents the second reference line where the length of the portion overlapping with the core is maximum, and the white line in the right image represents the second reference line where the length of the portion overlapping with the core is minimum. As a result of calculating the circularity in this manner, the circularity of the cylindrical battery cell in the image shown in FIG. 10 was 86.6%, and the circularity of the image shown in FIG. 11 was 95.0%.

[0114] As a result of the measurement, it was quantitatively confirmed that the circularity of the core of the cylindrical battery cell shown in Fig. 11 was greater than that of the cylindrical battery cell shown in Fig. 10.

[0116] Example 2

[0117] A cylindrical battery cell was manufactured according to the manufacturing example. At this time, the circularity of the core portion was measured after CT scanning of the cylindrical battery cell in the initial cycle stage (one charge / discharge cycle) using the same method as in Example 1. The results are shown in FIG. 12 (cycle initial). In FIG. 12, the white line in the upper left image represents the second reference line where the length of the portion overlapping with the core is maximum, and the white line in the upper right represents the second reference line where the length of the portion overlapping with the core is minimum.

[0118] In addition, the battery cell was charged and discharged 500 times, and then the circularity was measured in the same way. In Fig. 12, the white line in the lower left image represents the second reference line where the length of the part overlapping with the core is maximum, and the white line in the lower right represents the second reference line where the length of the part overlapping with the core is minimum.

[0119] As a result of measuring the circularity, the circularity of the core portion of the battery cell was calculated to be 91% during the initial cycle stage, and the circularity of the core portion of the battery cell was calculated to be 77% after 500 cycles. In other words, it was confirmed that the core deforms as the cycle progresses, and the present invention can quantitatively determine the degree of deformation of the core as the cycle progresses.

[0121] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the drawings disclosed in this invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by these drawings. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

[0123] Meanwhile, although terms indicating directions such as up, down, left, right, front, and back have been used in this specification, these terms are used merely for convenience of explanation, and it is obvious that they may vary depending on the location of the object or the position of the observer. Explanation of the symbols

[0125] 1: Cylindrical battery cell 10: Cylindrical can 11: First baseline 12: Second baseline 20: Cap Assembly 30: Electrode assembly 31: Bipolar 32: Cathode 33: Separator 34: Core 35: Cathode tab 100: Device for evaluating the degree of core deformation of a cylindrical battery cell 110: Filming Department 120: Measurement section 130: Judgment panel 140: Charging / Discharging Section

Claims

Claim 1 A method for evaluating the degree of deformation of a core of a cylindrical battery cell, comprising: a step of preparing a cylindrical battery cell having a structure in which a jelly-roll shaped electrode assembly is housed within a cylindrical can; a step of CT scanning the cylindrical battery cell to obtain an image of a cross-section perpendicular to the winding axis of the electrode assembly; and a step of measuring the degree of deformation of the core portion of the electrode assembly shown in the image; wherein the step of measuring the degree of deformation of the core portion is to measure the circularity of the electrode assembly core portion shown in the image, and the circularity is the ratio of the length of the minimum diameter to the maximum diameter of the electrode assembly core. Claim 2 delete Claim 3 delete Claim 4 A method for evaluating the degree of deformation of a core of a cylindrical battery cell according to claim 1, wherein the step of measuring the degree of deformation of the core portion comprises: a process of drawing a first reference line of a regular polygonal shape; a process of adjusting the size, position, and angle of an image so that a cylindrical can in the image contacts the first reference line; and a process of drawing a plurality of second reference lines passing through the center point of the first reference line and measuring the length of the portion where each second reference line overlaps with the core. Claim 5 A method for evaluating the degree of core deformation of a cylindrical battery cell according to claim 4, further comprising the process of adjusting the size of an image so that the outermost surface of the cylindrical can contacts the first reference line on the inner side of the area formed by the first reference line. Claim 6 A method for evaluating the degree of core deformation of a cylindrical battery cell, wherein, in the process of adjusting the size, position, and angle of the image, the image is rotated so that a negative tab located at the outermost edge of the electrode assembly comes into contact with a first reference line. Claim 7 A method for evaluating the degree of core deformation of a cylindrical battery cell, wherein, in paragraph 4, the angle formed by adjacent second reference lines is 5 to 30°. Claim 8 A method for evaluating the degree of deformation of a core of a cylindrical battery cell, wherein the circular shape is the value obtained by dividing the minimum value of the length of the part where the second reference line and the core overlap by the maximum value. Claim 9 A method for evaluating the degree of deformation of a core of a cylindrical battery cell according to claim 1, further comprising the step of repeatedly charging and discharging the battery cell and measuring the degree of deformation of the core according to the charge-discharge cycle. Claim 10 A method for evaluating the degree of core deformation of a cylindrical battery cell according to claim 1, wherein the battery cell is determined to be defective if the degree of circularity is less than a preset value or if the amount of change in the degree of circularity is greater than or equal to a preset value. Claim 11 An apparatus for evaluating the degree of deformation of a core of a cylindrical battery cell, comprising: a scanning unit that obtains an image of a cross-section perpendicular to the winding axis of the electrode assembly by CT scanning a cylindrical battery cell having a structure in which a jelly-roll shaped electrode assembly is housed inside a cylindrical can; and a measuring unit that measures the degree of deformation of the electrode assembly core portion shown on the image; wherein the measuring unit measures the circularity of the electrode assembly core portion shown on the image, and the measuring unit adjusts the size, position, and angle of the image so that a first reference line of a regular polygon shape contacts the cylindrical can, and measures the length of the portion where a plurality of second reference lines passing through the center point of the first reference line overlap with the core. Claim 12 delete Claim 13 delete Claim 14 In claim 11, the above-mentioned circular shape is a value obtained by dividing the minimum value of the length of the portion where the second reference line and the core overlap by the maximum value, in an evaluation device for the degree of core deformation of a cylindrical battery cell. Claim 15 A device for evaluating the degree of core deformation of a cylindrical battery cell, further comprising a judgment unit for determining whether the battery cell is defective and a charge / discharge unit for charging and discharging the battery cell, in claim 11. Claim 16 In claim 15, the charging / discharging unit repeatedly charges and discharges the battery cell, and the measuring unit measures the degree of deformation of the core of a cylindrical battery cell according to the charging / discharging cycle. Claim 17 In item 15, the above-mentioned judgment unit determines the battery cell as defective when the circularity is less than a preset value or when the change in circularity is greater than or equal to a preset value. This is an evaluation device for the degree of core deformation of a cylindrical battery cell.

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