KR20230161702A - Method and system for detecting impurities in secondary battery based on optical coherence tomography - Google Patents

Abstract

According to an embodiment of the present invention, a secondary battery impurity inspection method performed by an OCT device includes (a) irradiating the light of the OCT device toward one side of the secondary battery on which electrode plate formation has been completed, and then detecting the light reflected from the secondary battery; Obtaining a tomographic image of the inside of the secondary battery by performing an OCT scan that collects light; and (b) analyzing the tomographic image and determining, based on the contrast of the tomographic image, whether impurities exist and whether the impurities are metals.

Description

Optical coherence tomography-based secondary battery impurity inspection method and system {METHOD AND SYSTEM FOR DETECTING IMPURITIES IN SECONDARY BATTERY BASED ON OPTICAL COHERENCE TOMOGRAPHY}

The present invention discloses an optical coherence tomography (OCT) device and relates to a method and system for examining impurities in a secondary battery using the same.

With the advent of the 4th Industrial Revolution, the importance of batteries is emerging. In particular, lithium secondary batteries, which have high energy density, low self-discharge rate, and guaranteed long lifespan, have been commercialized, leading to technological innovation in various fields.

For example, it stands out as a key element in the automotive market, including mobile IT devices, energy storage systems (ESS), and electric vehicles, contributing to improving the quality of life of modern people.

However, lithium is highly reactive and has an intense autocatalytic reaction, which raises the risk of exposure to fire.

This may cause an explosive reaction due to the user's carelessness, such as overcharging, but electrical defects due to structural defects or internal short circuits in the cell also act as important causes of fire accidents.

In particular, metal molecules or impurities in electrodes generated during the production of secondary batteries can cause internal electrical short-circuits during battery use, causing bigger problems as they are difficult to recognize in advance.

Specifically, the conductive material used to form the electrode generally contains a metal element that can freely participate in an electrochemical reaction, which may precipitate as a metal foreign material during the electrode process and form on the surface of the electrode plate.

These metal contaminants degrade battery performance and increase the cell defect rate. In addition, vibration or external pressure breaks through the separator, causing an internal short circuit, raising the risk of fire and reducing the stability of the cell.

Conventional techniques for testing impurities generally involved testing for damage to the internal separator at the stage of a finished secondary battery or estimating it through low-voltage defect inspection. Therefore, it was inevitable that it would be accompanied by enormous manufacturing losses.

Another prior art discloses a process of suctioning and removing foreign substances during the winding process of the separator, but it is difficult to remove metal foreign substances smaller than a certain size and has limitations in detecting them.

One technical problem to be solved by the present invention is to provide a method and system for inspecting impurities in a secondary battery using an optical coherence tomography (OCT) device.

However, the technical challenges that this embodiment aims to achieve are not limited to the technical challenges described above, and other technical challenges may exist.

According to an embodiment of the present invention, a secondary battery impurity inspection method performed by an OCT device includes (a) irradiating the light of the OCT device toward one side of the secondary battery on which electrode plate formation has been completed, and then detecting the light reflected from the secondary battery; Obtaining a tomographic image of the inside of the secondary battery by performing an OCT scan that collects light; and (b) analyzing the tomographic image and determining, based on the contrast of the tomographic image, whether impurities exist and whether the impurities are metals.

According to one embodiment of the present invention, step (a) includes sequentially scanning the secondary battery in one direction from one end to the other end.

According to one embodiment of the present invention, in step (a), the OCT device is pre-installed on one side of the conveyor belt, and the secondary battery is transported by the conveyor belt and sequentially passes through the OCT device. It is scanned as .

According to one embodiment of the present invention, step (a) combines the 2D tomography image obtained by scanning one cross-section of the secondary battery to obtain a 3D tomography image of the entire area of the secondary battery. Includes ;

According to one embodiment of the present invention, in step (b), if the tomographic image includes a part where the contrast or brightness of the border is different compared to other areas, it is derived that the part corresponds to an impurity.

According to one embodiment of the present invention, in step (b), when the inner region of the portion identified as the impurity in the tomography image is displayed in black differently from other regions, the impurity is determined to be a metal.

According to one embodiment of the present invention, in step (b), the top and bottom of the tomographic image for the derived impurity are specified, the pixel value between the top and bottom is calculated, and the pixel value is calculated. It includes the step of estimating the thickness of the impurity by converting it based on the optical path.

According to one embodiment of the present invention, step (b) includes, when the component of the impurity is identified, calculating the actual thickness of the impurity by applying a preset refractive index according to the component to the estimated thickness; Includes.

According to one embodiment of the present invention, in step (b), when the secondary battery is wrapped by a film and a part with a protruding shape is identified among the areas marked by the film in the tomographic image, the part is It is determined that impurities exist.

According to one embodiment of the present invention, the step (a) includes obtaining a tomographic image of the inside of the film by OCT scanning the secondary battery that is wrapped with a film and the wrapping process has been completed, and the step (b) It includes analyzing a tomographic image of the inside of the film to determine whether impurities exist in the film and whether the impurities are metals.

According to one embodiment of the present invention, in step (b), the tolerance area between the secondary battery and the film or between the films is displayed in black in the tomographic image.

According to one embodiment of the present invention, in step (b), a bright component is displayed in the tolerance area and the secondary battery area located inside the portion where the bright component is displayed is displayed in black unlike other secondary battery areas. In this case, it is assumed that metal impurities exist in the above portion.

According to one embodiment of the present invention, before step (a), a preset mark that can be identified only by infrared lighting is displayed on the film at a location where impurities in the secondary battery are presumed to be present.

According to one embodiment of the present invention, in step (a), the OCT device automatically identifies the mark and performs a scan at the position where the mark is displayed.

According to an embodiment of the present invention, an OCT-based secondary battery impurity inspection system includes a conveyor belt for transporting secondary batteries; and an OCT device disposed on one side of the conveyor belt to inspect the secondary battery for impurities, wherein the OCT device irradiates light toward one side of the secondary battery on which electrode plate formation is completed and then reflects the light from the secondary battery. An OCT scan that collects light is performed to obtain a tomographic image of the inside of the secondary battery, and the OCT device analyzes the tomographic image to determine whether impurities exist and whether the impurities are determined based on the contrast of the tomographic image. The goal is to determine whether it is a metal or not.

According to an embodiment of the present invention, an OCT-based secondary battery impurity inspection system includes a marking device that displays a preset mark that is identified only by infrared light on a film at a location pre-estimated to have impurities in the secondary battery. Including, the secondary battery is wrapped with a film and the wrapping process is completed.

According to one embodiment of the present invention, impurities present in a secondary battery can be detected using an OCT device.

According to one embodiment of the present invention, the size and material of the detected impurities can be determined using an OCT device.

According to one embodiment of the present invention, it is possible to quickly determine whether metal impurities that cause a risk of fire are present in a secondary battery through optical characteristics.

According to one embodiment of the present invention, even minute metal contaminants can be detected regardless of whether the separator is damaged.

According to an embodiment of the present invention, unlike the prior art, an inspection step can be inserted during the manufacturing process, thereby minimizing manufacturing losses.

According to one embodiment of the present invention, no separate inspection space is required. For example, impurity testing can be performed automatically by simply placing an OCT device near the conveyor that transports secondary batteries that have completed the assembly process to the next step. Therefore, efficiency of space utilization and speed of inspection are guaranteed. In addition, since it is OCT-based, it is harmless to the human body and is economical because the inspection system can be implemented compactly.

1 is a structural diagram of a secondary battery impurity inspection system according to an embodiment of the present invention.
Figure 2 is a block diagram showing the structure of an OCT device according to an embodiment of the present invention.
Figure 3 is a flowchart of a secondary battery impurity testing method according to an embodiment of the present invention.
Figures 4a to 4e are examples of tomographic images showing experimental data for explaining an embodiment of the present invention.
Figure 5 is a structural diagram showing another embodiment of a secondary battery impurity inspection system.

Below, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

Throughout the specification, when a part is said to be "connected" to another part, this includes not only the case where it is "directly connected," but also the case where it is "electrically connected" with another element in between. . Additionally, when a part "includes" a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

In this specification, 'part' includes a unit realized by hardware, a unit realized by software, and a unit realized using both. Additionally, one unit may be realized using two or more pieces of hardware, and two or more units may be realized using one piece of hardware. Meanwhile, '~ part' is not limited to software or hardware, and '~ part' may be configured to reside in an addressable storage medium or may be configured to reproduce one or more processors. Therefore, as an example, '~ part' refers to components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, and procedures. , subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and 'parts' may be combined into a smaller number of components and 'parts' or may be further separated into additional components and 'parts'. Additionally, components and 'parts' may be implemented to regenerate one or more CPUs within a device or a secure multimedia card.

Hereinafter, an embodiment of the present invention will be described in detail using the attached drawings.

1 is a structural diagram of a secondary battery impurity inspection system according to an embodiment of the present invention.

Referring to FIG. 1, a secondary battery impurity inspection system 1 according to an embodiment of the present invention may include an OCT device 100 and a conveyor belt 200.

The conveyor belt 200 according to one embodiment is a device that supports and transports the secondary battery 10 from the bottom, and is preferably included as one component in the manufacturing process of the secondary battery 10.

For example, the conveyor belt 200 transports the secondary batteries 10 on which each process has been completed in the order of electrode process, assembly process, formation process, and other additional processes. It can refer to the overall frame of the production line.

Alternatively, the conveyor belt 200 may be at least one conveyor belt among conveyor belts configured for a process after the formation of the electrode plate is completed.

Meanwhile, the conveyor belt 200 is illustrated as a device for transporting the secondary battery 10, but a person skilled in the art will easily understand that it can be easily modified into other types of transport devices, including chain-type conveyors. You will find out. In other words, the “conveyor belt” disclosed in the present invention should be interpreted as encompassing any transport device used in the production field of secondary batteries.

According to one embodiment, it does not matter whether the secondary battery 10 has been manufactured or not, but in order to minimize production loss, it is preferable to inspect secondary batteries in the manufacturing process including electrode plates.

According to one embodiment, the secondary battery 10 may have a plurality of electrode plates and a separator assembled and then have a circumference wrapped with a predetermined film. In this case, the presence of impurities can be estimated based on the shape of the film captured in the tomographic image and the brightness and darkness inside the film.

However, it is not limited to these embodiments, and the secondary battery 10 may be included in the scope of the present invention as long as the secondary battery 10 can be tested for impurities.

Additionally, the shape of the secondary battery 10 does not limit the present invention. For example, an embodiment of the present invention can be applied to cylindrical, prismatic, and pouch-shaped secondary batteries.

However, hereinafter, an embodiment of the present invention will be described using a representative rectangular shape for easy explanation.

The OCT (Optical Coherence Tomography) device 100 according to one embodiment irradiates light toward the secondary battery 10 and then performs an impurity test on the secondary battery 10 based on the reflected light.

Figure 2 is a block diagram showing the structure of an OCT device according to an embodiment of the present invention.

Referring to FIG. 3, the OCT device 100 according to an embodiment of the present invention may include a light source unit 110, an optical unit 120, and a control unit 130.

The light source unit 110 according to one embodiment includes a light source that generates light radiating toward the secondary battery 10. Here, the light source may output light of a preset wavelength or light whose wavelength varies with time under the control of the control unit 130, and light capable of multicolor dispersion, such as white light, may be preferable. Since the light irradiated by the light source unit 110 reaches the secondary battery through the optical unit 120, the light source unit 110 can be installed in the OCT device 100 at a preset angle with the optical unit 120. there is.

According to one embodiment, the light source unit 110 may radiate light in a straight line, and accordingly, a sequential OCT scan is performed in one direction from one end of the secondary battery 10 to the other end. For example, as shown in Figure 1, when the secondary battery 100 passes through the OCT device 100 through the conveyor belt 200, the light is irradiated sequentially from the front end to the back end according to the transfer direction. It is scanned.

The optical unit 120 according to one embodiment may include an optical splitter configured in an area within the path irradiated from the light source unit 110 to the secondary battery 10, and the optical splitter may be a type of beam splitter. You can.

According to one embodiment, the light splitter may split light generated from a light source into at least two paths. In addition, rotatable mirrors are included so that each divided light can be irradiated evenly to the secondary battery 10, and convex lenses are included to focus each light on one point of the secondary battery 10 and irradiate it. It can complement the depth. Here, one point may be an example of the location of an impurity estimated in advance.

Each light divided in this way passes through different optical path systems according to a preset reflection angle, and its travel path and length vary, and the same applies to the process of returning the scattered light after passing through the secondary battery 10. These are combined in the detection unit (not shown) within the optical unit 120 to cause interference, and the resulting interference signal is transmitted to the control unit 130.

The control unit 130 according to one embodiment may be connected to or include components related to driving control and data analysis of the OCT device 100, such as a CPU, power supply circuit, calculation circuit, database, etc.

In particular, as shown in FIG. 2, the control unit 130 according to one embodiment may include a tomography image acquisition unit 131 and a tomography image analysis unit 132.

The tomographic image acquisition unit 131 according to one embodiment converts the detected optical interference signal into an electrical signal and generates a tomographic image of the secondary battery 10 through this. That is, the tomography image acquisition unit 131 can acquire an optical coherence tomography image showing the interior of one side of the secondary battery 10, based on the spectrum of each light obtained from the optical unit 120.

According to one embodiment, the tomographic image acquisition unit 131 may acquire a 2D tomographic image by scanning one cross-section of the secondary battery 10. Additionally, 2D tomography images can be combined to generate a 3D tomography image of the entire area of the secondary battery 10.

According to one embodiment, the tomographic image acquisition unit 131 may acquire a tomographic image of the inside of the film when the secondary battery 10 is wrapped by a film.

The tomographic image analysis unit 132 according to one embodiment can detect the internal state and defects of the secondary battery 10 by analyzing the tomographic image acquired by the tomographic image acquisition unit 131.

In particular, it is possible to determine whether impurities exist based on the contrast or protruding shape displayed on the tomographic image.

According to one embodiment, the tomographic image analysis unit 132 may check whether the tomographic image includes a portion where the edge contrast or brightness is different compared to other regions, and determine that the portion corresponds to an impurity.

According to one embodiment, the tomographic image analysis unit 132 determines the brightness and darkness of the tomographic image of the inside of the impurity, starting from the position of the determined impurity, and determines whether the impurity is a metal or non-metal based on this.

According to one embodiment, the tomography image analysis unit 132 may specify a portion derived from an impurity in the tomography image and determine the thickness of the impurity based on the pixel value thereof.

According to one embodiment, the tomographic image analysis unit 132 may calculate the actual thickness of the impurity by applying the refractive index of the impurity to the estimated thickness of the impurity.

According to one embodiment, the tomographic image analysis unit 132 can measure the overall size, including the cross-sectional area, of impurities through 3D tomographic images, and can determine the overall location of each impurity scattered in the secondary battery 10. .

According to one embodiment, when the secondary battery 10 is wrapped with a film, the tomographic image analysis unit 132 may determine whether impurities exist in the film by analyzing the tomographic image of the inside of the film.

According to one embodiment, when the secondary battery 10 is wrapped with a film, the tomographic image analysis unit 132 determines that a portion having a protruding shape among the areas marked with a film in the tomographic image is identified, and impurities are present in the corresponding portion. It can be judged that

According to one embodiment, when the secondary battery 10 is wrapped with a film, the tomographic image analysis unit 132 displays a bright component between the films in the tomographic image or between the film and the secondary battery 10, and the bright component is displayed. If the inside of is displayed in black, it can be assumed that metallic impurities exist in the portion where the bright components are displayed.

According to one embodiment, the control unit 130 may refer to an MCU (micro controller unit) installed inside the main body of the OCT device 100, and may be included in a control device connected to the main body and configured outside the main body.

Meanwhile, the OCT device 100 according to one embodiment is installed on one side of the conveyor belt 200 and inspects the secondary battery 10 passing through the OCT device 100 through the conveyor belt 200 for impurities. Perform.

Referring to FIG. 1, the OCT device 100 can irradiate light in a direction perpendicular to the transport direction of the secondary battery 10 at the installed location. When the secondary battery 10 is transported by the conveyor belt 200 and faces the OCT device 100, an OCT scan is performed in which light is transmitted into the interior of the secondary battery 10 and then reflected or scattered.

As described above, the OCT scan may be performed in a straight line, and accordingly, the scan may be sequentially performed from the front end to the rear end of the secondary battery 10 according to the transfer direction.

Therefore, 2D tomographic images are sequentially acquired for each line forming the cross section of the secondary battery according to the scanning order. In addition, when the rear end of the secondary battery 10 passes through the OCT device 100, a 3D tomography image combining the 2D tomography image is generated, enabling overall observation of the interior of the cross section.

According to one embodiment, the OCT devices 100 may be arranged in directions facing each other toward the secondary battery 10. That is, at least two OCT devices 100 may be arranged on both sides of the conveyor belt 200 with their respective light sources facing each other. In this case, when one OCT device 100 performs an impurity test on one side of the secondary battery 10, the opposite OCT device 100 simultaneously performs an impurity test on the opposite side, thereby inspecting the entire secondary battery 10. Testing for impurities can be carried out quickly.

According to one embodiment, the system 1 may control the OCT device 100 to operate when the secondary battery 10 reaches a position corresponding to the OCT device 100. For example, the system 1 may maintain the OCT device 100 in an idle state and operate the OCT device 100 at the moment when one end of the secondary battery 10 faces the OCT device 100. Additionally, the moment the other end of the secondary battery 10 passes through the OCT device 100, the OCT device 100 can be controlled back to the idle state. In this way, since the power used for impurity testing is saved, an economic effect is created by reducing the capital and energy required to operate the system.

As described above, the secondary battery impurity test disclosed in the present invention may be performed during the secondary battery manufacturing process. Therefore, unlike in the past, it is not limited to the finished product stage, so manufacturing losses due to impurities can be minimized. In addition, by simply arranging an additional OCT device on the existing manufacturing line, it can be performed compactly without requiring a separate inspection space, contributing to improving the productivity of secondary batteries.

Hereinafter, an embodiment of the secondary battery impurity inspection method disclosed by the present invention will be described with reference to FIG. 3. In addition, an embodiment of the present invention is supported through the experimental data shown in FIGS. 4A to 4B. Overlapping explanations shall be replaced with the above-mentioned content.

Figure 3 is a flowchart of a secondary battery impurity testing method according to an embodiment of the present invention.

In step S310, the secondary battery 10 is transferred to the OCT device 100 by the conveyor belt 200. The OCT device 100 radiates light toward the conveyor belt 200, and the front end of the secondary battery 10 enters a state facing the OCT device 100 or enters a preset distance from the OCT device 100. You can control the light source to operate when

In step S320, the OCT device 100 performs an OCT scan on the secondary battery 10. At this time, as the secondary battery 10 passes through the OCT device 100, an OCT scan can be sequentially performed on the facing areas from one end to the other end of the secondary battery 10.

Specifically, the OCT device 100 irradiates the light of the OCT device 100 toward one side of the secondary battery 10 and collects the light reflected from the secondary battery 10. That is, the light generated from the light source unit 110 passes through the facing cross section of the secondary battery 10 and passes through the interior, and the reflected or scattered light is collected through the optical unit 120, and then the interference phenomenon progresses. do.

For example, the light generated from the light source unit 110 may be separated into a secondary battery optical path system and a reference optical path system through an optical separator and then scanned. In the case of the secondary battery light path system, light incident on the secondary battery 10 and reflected or scattered is returned, and in the case of the reference light path system, light coming out of the optical separator at a different angle is reflected by the mirror and returned. Each returning light is combined to cause interference, and the resulting interference signal is transmitted to the tomographic image acquisition unit 131.

In the case of a secondary battery optical path system, the irradiated light is reflected or scattered by the electrode plate or separator included in the secondary battery 10. Additionally, if impurities exist on the cross section of the secondary battery, some or all of the irradiated light may be absorbed or scattered on the surface of the impurities. In addition, when a film is wrapped around the secondary battery 10, the irradiated light is reflected or scattered from the film, and this can be implemented as many layers as the film wrapped around the secondary battery 10 (i.e., as many times as the number of times it is wrapped around the perimeter). there is.

Afterwards, in step S320, the OCT device 100 acquires a tomographic image based on the light collected by the OCT scan.

For example, the tomographic image acquisition unit 131 extracts the spectrum for each light collected according to the received interference signal. Afterwards, the extracted spectrum is expanded and concentrated on a line-shaped detector array such as a line scan camera, thereby converting optical signals for each wavelength into electrical signals. The tomographic image acquisition unit 131 may acquire a tomographic image of the secondary battery 10 based on pixels set in proportion to the wavelength component of the collected light and the voltage value of the electrical signal calculated according to a preset calculation equation.

In the tomographic image obtained in this way, an area representing the secondary battery 10 including the electrode plate is displayed. In particular, since the light is first reflected from the cross section where the light is irradiated, the cross section has high brightness and is displayed brightly, and as it goes inside, the amount of light transmitted decreases and the display gradually becomes darker.

Additionally, in the case of the secondary battery 10 being wrapped with a film and completing the wrapping process, light reflected from the film is also collected in the optical unit 120. Accordingly, in the tomographic image, in addition to the secondary battery 10, an area representing a film outside the secondary battery 10 is additionally displayed. Of course, the film layer displayed in the tomographic image may be composed of the number of times the film is wound around the secondary battery 10.

In addition, if there is another foreign matter in addition to the secondary battery 10 and the film, the tomographic image may include a portion where there is a difference in light and dark, and depending on the size, shape, and arrangement of the foreign material, the secondary battery 10 may have a cross section or Protruding shapes may additionally be displayed on the film.

In step S330, the OCT device 100 analyzes the tomographic image acquired in step S320 and determines whether impurities are present and whether the impurities are metals based on the contrast.

According to one embodiment, a tomography image analysis program is pre-stored in the OCT device 100. The tomographic image analysis unit 132 executes this and analyzes the tomographic image to determine the presence, size, and nature of impurities.

According to one embodiment, the tomographic image analysis program has a built-in algorithm that determines the presence, nature, and size of impurities through the tomographic image. This algorithm can be designed based on experimental data to be introduced below. Meanwhile, in this specification, representative experimental data is disclosed for explanation purposes, and actual experiments are not limited to this.

Figures 4a to 4e are examples of tomographic images showing experimental data for explaining an embodiment of the present invention.

The experimental data is a tomographic image obtained by performing an OCT scan on the cross section of the secondary battery 10 in which impurities are previously recognized. That is, it is a tomographic image of a cross section of the secondary battery 10 containing impurities, cutting through the center of the impurities.

In addition, the secondary battery 10 that was the subject of the experiment was wrapped with a film, and the tolerance area between the film and the secondary battery or between the films was displayed in black on the tomography image because there was no material.

Here, “black” is not limited to a term that simply represents a specific color, but is defined to include a state close to zero where the brightness is below a preset value.

Figure 4a shows experimental data of a tomographic image obtained by performing an OCT scan on a cross section of the secondary battery 10 containing spatter, which is a metal foreign substance. Here, the secondary battery 10 was wrapped with a film, and spatter under the film was photographed. Meanwhile, in the process of moving the focus to make the internal structure appear clearer, the image at the top of the film was weakened, and for this purpose, a line was marked on the right tomographic image to clearly identify the film.

Referring to FIG. 4A, light is scattered on the surface of the spatter formed between the second and third films from the top, and a border of bright components displayed in contrast to black can be found. In other words, if the edges of bright components other than the secondary battery and film are displayed in the tomographic image, it can be seen that the light was reflected or scattered there before reaching the secondary battery, and accordingly, it is clear that any foreign substances are present in the corresponding area. It can be judged that

In conclusion, when impurities exist in the secondary battery 10, the tomographic image may include a portion representing the border of the impurities outside (at the top) of the area where the secondary battery 10 is displayed. This part is realized as the irradiated light is reflected from the surface of the impurity, resulting in a difference in the contrast or brightness of the border compared to other areas.

That is, according to one embodiment of the present invention, when the tomography image analysis unit 100 detects a part in the tomography image where there is a difference in the contrast or brightness of the border compared to other areas, it is determined that the part corresponds to an impurity. You can.

Additionally, referring to Figure 4a, it can be seen that the area extending in a straight line at the bottom of the border is displayed in black. It is understood that most of the light irradiated by the secondary battery 10 is absorbed or scattered by impurities, so the structure beneath it is not captured.

In other words, through this experiment, it can be seen that when a metal impurity with high light reflectivity is composed in the secondary battery 10, the internal area at the location of the impurity is displayed in black on the tomographic image and is clearly distinguished from other areas of the secondary battery. there is.

On the other hand, Figure 4b is a tomographic image taken of the cross section of the secondary battery 10 made of non-metallic material. Referring to Figure 4b, like metal, a border of light and dark contrasting with other areas between the film and the secondary battery is found, but unlike metal, the area extending below it is confirmed to contain some bright components. This means that non-metallic materials such as plastic have a lower reflectivity of light compared to metals, so a predetermined amount of light appears to be transmitted below the impurity, and accordingly, the internal area of the impurity location is implemented with a brightness value higher than the preset value.

In conclusion, according to one embodiment of the present invention, the tomography image analysis unit 100 displays the inner region of the portion derived as an impurity in the tomography image as black (less than a preset brightness value) differently from other regions, The impurity can be judged to be a metal.

Meanwhile, the non-metallic material in FIG. 4B was identified as a foreign material in the form of a black wide dot as a result of visual inspection of the secondary battery 10. Therefore, Figure 4b confirms that when the foreign matter contained in the secondary battery 10 is larger than a certain area, the 3D tomographic shape of the surrounding area can be secured and the area of the foreign matter can be derived through this.

In an additional embodiment, the secondary battery impurity inspection system 1 or the OCT device 100 may provide a preset warning message or notification when metal impurities are detected. If metal impurities are included, there is a high risk of fire, so promptly notify the manager to minimize damage.

FIG. 4C is a tomographic image of a cross section of the secondary battery 10 with another spatter. Here, the spatter is formed below the film and has a sharp upper part, causing the film surrounding it to bend. Meanwhile, as in Figure 4a, the image at the top of the film was weakened in the process of moving the focus to make the internal structure appear clearer, and for this purpose, a line clearly identifying the film was displayed on the right tomographic image.

Referring to Figure 4c, a bright component border is displayed between the second and third films in contrast to black. In addition, unlike the film below, the second film and the first film are not parallel to the secondary battery 10 but are found to have a protruding shape. This indicates that light is scattered on the surface of the spatter and the film is deformed according to its shape, taking on a curved shape. In other words, Figure 4c supports the fact that when a protruding shape of the film is found in a tomography image, it can be more clearly determined that impurities exist in that area.

In conclusion, according to one embodiment of the present invention, the tomographic image analysis unit 132 detects that the secondary battery 10 is wrapped by a film and a portion with a protruding shape among the areas marked by the film in the tomographic image is identified. , it can be determined that impurities exist in that part.

Figure 4d is a tomographic image taken of a cross section of the secondary battery 10 composed of burrs, which are metal foreign substances. Referring to this, unlike in the case of spatter, the border representing the structure is not clearly displayed, but a portion containing a component that is particularly brighter than the surrounding area is observed between the films. Additionally, it is observed that the area extending downward from the bright component is displayed in black. This was an experiment targeting a burr, and it can be assumed that most of the light is absorbed or scattered due to the presence of metal impurities in that area.

Figure 4e is a tomographic image of a cross-section of the secondary battery 10 in which another burr is formed. Looking at this, you can see that the third film is slightly floating on the secondary incisor (10). This can be seen as being caused by a burr located between the film and the secondary battery 10, and as in Figure 4d, a component that is particularly brighter than the surrounding area is observed in the corresponding area. In addition, the area extending below the bright component is displayed in black, supporting the phenomenon that most of the light is scattered by the burr and the scan signal is not captured.

In conclusion, according to one embodiment of the present invention, the tomographic image analysis unit 132 displays a bright component rather than black in the tolerance area, and the secondary battery area located inside the area where the bright component is displayed is a different secondary battery area. If it is displayed in black differently from , it can be assumed that metal impurities exist in that part.

Meanwhile, the interior of the position derived from the impurity is displayed in black in the remaining experimental data except for Figure 4b, which corresponds to a non-metallic material, and the experimental data indicates that the internal area of the portion where the metal impurity is located is not represented in the tomography image. clearly supports.

According to one embodiment, the OCT device 100 can estimate the thickness of the derived impurities. Specifically, the tomography image analysis unit 132 specifies the top and bottom of the impurity in the tomography image, calculates the pixel value between the top and bottom, and then converts the calculated pixel value into an optical path to determine the thickness of the impurity. can be estimated.

For example, in the experiment in which Figure 4a was obtained, the top of the spatter in contact with the second film and the bottom in contact with the third film were specified through the border representing the spatter. Afterwards, the pixel value in the vertical direction between the top and bottom was measured to be 85 pixels, and as a result of converting this to an optical path through a preset algorithm, the thickness (h) of the spatter was estimated to be 149 um.

According to one embodiment, the tomographic image analysis unit 132 may calculate the actual thickness (h_actual) of the impurity by applying the refractive index (n) of the impurity to the estimated thickness (h_meas) as described above.

[Equation 1]

According to one embodiment, the thickness (height) of the impurity may be calculated through at least one 2D tomography image containing the impurity. However, the OCT device 100 can extract 2D tomographic images containing the impurity and generate a 3D tomographic image by combining them, and through this, the accurate height of the impurity can be calculated. Additionally, the area of the impurity can be calculated based on this by measuring the length of the impurity extending horizontally in the 3D tomographic image. In this way, the OCT device 100 can derive the overall shape and size of impurities.

Meanwhile, according to one embodiment of the present invention, when an impurity and its location are estimated in advance through the naked eye or other process equipment, an OCT scan is performed immediately at the location, thereby saving time and capital required for inspection of the impurity. .

In this regard, the secondary battery impurity inspection system according to an embodiment of the present invention may further include a marking device (not shown).

The marking device according to one embodiment may display a preset mark that can be identified only by infrared light on the film at a location in the secondary battery 10 where impurities are presumed to be present. For example, the marking device may be operated manually by an administrator, or may be placed on one side of the conveyor belt 200 and operated automatically under system control.

In this case, in step S320, the OCT device 100 can automatically identify the mark and perform an OCT scan at the location where the mark is displayed.

According to one embodiment, unlike the system 1 shown in FIG. 1, impurity testing may be possible by deploying only one OCT device 100, and an example of such system 1 is shown in FIG. 5. .

Referring to FIG. 5, the OCT device 100 may be located on top of the secondary battery 10 on which the mark 50 is displayed. For example, it may be installed at the top of the conveyor belt 200 in a direction facing the top of the secondary battery 10.

Afterwards, when the secondary battery 10 reaches below the OCT device 100, the OCT device 100 can determine the location of the mark and perform an OCT scan only at that location.

The OCT device 100 according to one embodiment may be designed so that the light source unit 110 can move to the position of the mark under the control of the control unit 130 that identifies the position of the mark. Alternatively, a guide member (not shown) that guides the OCT device 100 itself or the light source unit 110 to move to the position of the mark may be included in the system 1 while being connected to the OCT device 100. In this case, more rapid impurity testing can be performed, contributing to improved productivity.

The description of the present invention described above is for illustrative purposes, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical idea or essential features of the present invention. will be. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive. For example, each component described as unitary may be implemented in a distributed manner, and similarly, components described as distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. do.

10: Secondary battery
100: OCT device
200: conveyor belt
50: mark

Claims (16)

In a secondary battery impurity inspection method performed by an optical coherence tomography (OCT) device,
(a) irradiating light from an OCT device toward one side of a secondary battery on which electrode plate formation has been completed and then performing an OCT scan to collect light reflected from the secondary battery, thereby obtaining a tomographic image of the inside of the secondary battery; and
(b) analyzing the tomographic image and determining, based on the contrast of the tomographic image, whether impurities exist and whether the impurities are metals;
Secondary battery impurity testing method. According to clause 1,
The step (a) includes sequentially scanning the secondary battery in one direction from one end to the other. According to clause 2,
In step (a), the OCT device is pre-installed on one side of the conveyor belt, and the secondary battery is sequentially scanned as it is transported by the conveyor belt and passes through the OCT device. method of inspection. According to clause 2,
The step (a) includes combining 2D tomography images obtained by scanning one cross-section of the secondary battery to obtain a 3D tomography image of the entire area of the secondary battery. Inspecting secondary battery impurities. method. According to clause 1,
In step (b), if the tomographic image includes a part where the contrast or brightness of the border is different compared to other areas, it is derived that the part corresponds to an impurity. According to clause 5,
In step (b), when the inner region of the portion identified as the impurity in the tomographic image is displayed in black differently from other regions, the impurity is determined to be a metal. According to clause 1,
In step (b), the top and bottom of the tomographic image for the derived impurity are specified, the pixel value between the top and bottom is calculated, and the pixel value is converted based on the optical path to A secondary battery impurity testing method comprising: estimating the thickness of the impurity. According to clause 7,
The step (b) includes, when the component of the impurity is identified, calculating the actual thickness of the impurity by applying a preset refractive index according to the component to the estimated thickness. According to clause 1,
In step (b), when the secondary battery is wrapped by a film and a part with a protruding shape is identified among the areas marked by the film in the tomographic image, it is determined that impurities exist in the part. , Secondary battery impurity testing method. According to clause 1,
The step (a) includes obtaining a tomographic image of the inside of the film by OCT scanning the secondary battery that is wrapped with a film and the wrapping process has been completed,
The step (b) includes analyzing a tomographic image of the inside of the film to determine whether impurities exist in the film and whether the impurities are metals. According to clause 10,
In step (b), the tolerance area between the secondary battery and the film or between the films is displayed in black on the tomographic image. According to clause 11,
In step (b), when a bright component other than black is displayed in the tolerance area and the secondary battery area located inside the portion where the bright component is displayed is displayed in black unlike other secondary battery areas, the portion is A secondary battery impurity testing method that estimates the presence of metal impurities. According to clause 10,
Before step (a), a preset mark that can be identified only by infrared lighting is displayed on the film at a location pre-estimated to have impurities in the secondary battery. According to clause 13,
In step (a), the OCT device automatically identifies the mark and performs a scan at the location where the mark is displayed. In the OCT-based secondary battery impurity inspection system,
Conveyor belt transporting secondary batteries; And an OCT device disposed on one side of the conveyor belt to inspect the secondary battery for impurities,
After the OCT device irradiates light toward one side of the secondary battery on which electrode plate formation has been completed, performs an OCT scan to collect light reflected from the secondary battery to obtain a tomographic image of the inside of the secondary battery,
An OCT-based secondary battery impurity inspection system in which the OCT device analyzes the tomographic image and determines whether impurities exist and whether the impurity is a metal based on the contrast of the tomographic image. According to clause 15,
It further includes a marking device that displays a preset mark that can be identified only by infrared light on the film at a location presumed to contain impurities in the secondary battery,
An OCT-based secondary battery impurity inspection system in which the secondary battery is wrapped with a film and the wrapping process is completed.

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