Inspection system and inspection method for secondary batteries

Abstract

An inspection system according to an embodiment includes an imaging sensor and an inspection device. The imaging sensor captures an image of an electrode structure in a secondary battery, including a current collector and an active material layer, from the fiber layer side. The inspection device inspects for peeling of the fiber layer based on color changes in an image obtained from the imaging sensor's image data.

Description

Technical Field

[0001] Embodiments relate to an inspection system and an inspection method for a secondary battery. Background Art

[0002] In secondary batteries such as lithium secondary batteries, porous separators are used to prevent contact between the positive electrode and the negative electrode. For example, a layer of nano-sized organic fibers is used as the separator.

[0003] In secondary batteries, the organic fiber layer formed on the electrode may have various defects during production. It is desirable to be able to detect defects in such an organic fiber layer during production. Summary of the Invention

[0004] An inspection system according to an embodiment includes an imaging sensor and an inspection device. The imaging sensor captures an image of an electrode structure in a secondary battery, including a current collector and an active material layer, from the fiber layer side. The inspection device detects the presence of peeling of the fiber layer based on color changes in an image obtained from the imaging sensor's image data. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 This is a diagram showing an example of an inspection system for a secondary battery according to an embodiment.

[0006] Figure 2A It is a cross-sectional view showing the structure of an electrode sheet.

[0007] Figure 2B This is a diagram showing the state of the electrode sheet during inspection of the fiber layer.

[0008] Figure 3 This is a diagram showing the hardware configuration of the inspection device.

[0009] Figure 4 This is a flowchart showing the operation of the inspection device.

[0010] Figure 5 Flowchart showing defect detection processing according to an embodiment.

[0011] Figure 6A It is a diagram showing the inspection area.

[0012] Figure 6B It is along Figure 6A A curve showing the brightness values ​​of the L line.

[0013] Figure 7 It is a diagram showing a display example of a peeling defect. DETAILED DESCRIPTION

[0014] Hereinafter, embodiments will be described with reference to the drawings. Figure 1This diagram illustrates an example of an inspection system for a secondary battery according to an embodiment. Inspection system 1 is used to inspect defects in the fiber layer formed in electrode sheets 10 produced during the manufacturing phase of a secondary battery. Electrode sheets 10 produced during the manufacturing phase are fed into inspection system 1 via rollers 10a and conveyed in the direction of arrow A by rollers 10b. Rollers 10a and 10b are configured to rotate, for example, via a motor. Electrode sheets 10 form the cells of the electrode structure included in a secondary battery.

[0015] The driving device 20 includes a driving circuit for driving the rollers 10a and 10b. The driving circuit generates a driving current for driving the motors of the rollers 10a and 10b, and supplies the generated driving current to the rollers 10a and 10b.

[0016] The encoder 30 is positioned near the roller 10b and detects the rotation of the roller 10b. The encoder 30 outputs the rotation of the roller 10b to the inspection device 50 as the feed rate of the electrode sheet 10. The encoder 30 is, for example, an optical encoder that counts optical patterns attached to the roller 10b to detect the rotation of the roller 10b. The encoder 30 is not necessarily an optical encoder. Alternatively, the encoder 30 may be positioned near the roller 10a rather than the roller 10b.

[0017] The imaging sensor 40 is disposed above the electrode sheet 10 and images the electrode sheet 10 to generate imaging data related to the electrode sheet 10. The imaging sensor 40 can be either a CMOS (Complementary Metal Oxide Semiconductor) imaging sensor or a CCD (Charge Coupled Device) imaging sensor, and the imaging sensor 40 outputs the generated imaging data to the inspection device 50. Here, the imaging sensor 40 is a line sensor having pixels arranged along the width direction of the electrode sheet 10, which is orthogonal to the conveying direction of the electrode sheet 10. The number of rows of the imaging sensor 40 can be either one or multiple rows. On the other hand, the pixels in the width direction of the imaging sensor 40 are preferably arranged with a width greater than the width of the electrode sheet 10. In addition, each pixel of the imaging sensor 40 is composed of three sub-pixels: R (red), G (green), and B (blue). That is, the imaging sensor 40 is configured to generate a color image. The imaging frame rate of the imaging sensor is preferably synchronized with the conveying speed of the electrode sheet 10.

[0018] The inspection device 50 inspects the presence and location of defects in the electrode sheet 10 based on the feed amount of the electrode sheet 10 input from the encoder 30 and the image of the electrode sheet 10 input from the imaging sensor 40. The inspection device 50 may be composed of a computer such as a personal computer.

[0019] Figure 2A This is a cross-sectional view showing the structure of an electrode sheet 10. The electrode sheet 10 is a sheet material comprising a positive electrode 11 and a negative electrode 12. The positive electrode 11 and the negative electrode 12 are insulated by a fiber layer 13 composed of organic fibers, which serves as an insulator. The fiber layer 13 is not a self-standing film but is supported by the negative electrode 12. The electrode sheet 10 can be cut into appropriate lengths to form a battery within the electrode structure of a secondary battery.

[0020] The negative electrode 12 is formed by providing a negative electrode active material layer 12b on the surface of a negative electrode current collector 12a. Similarly, the positive electrode 11 is formed by providing a positive electrode active material layer 11b on the surface of a positive electrode current collector 11a. Metal foils such as aluminum are used as the negative electrode current collectors 12a and 11a. The negative electrode active material layer 12b is formed using a slurry containing a negative electrode active material, a negative electrode conductive agent, and a binder. The positive electrode active material layer 11b is formed using a slurry containing a positive electrode active material, a positive electrode conductive agent, and a binder.

[0021] As the negative electrode active material, for example, lithium titanate can be used. Examples of lithium titanate include Li 4+x Ti5O 12 (0≤x≤3), Li with forsterite structure 2+y Ti3O7 (0≤y≤3). The average particle size of the primary particles of the negative electrode active material is preferably in the range of 0.001μm to 1μm. The particle shape may be either granular or fibrous. In the case of fibrous particles, the fiber diameter is preferably 0.1μm or less.

[0022] Examples of the negative electrode conductive agent include acetylene black, carbon black, and graphite. Examples of the binder for binding the negative electrode active material and the negative electrode conductive agent include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, and styrene butadiene rubber.

[0023] As the positive electrode active material, a general lithium transition metal composite oxide is used. For example, LiCoO2, LiNi 1-x Co x O2(0<x<0.3), LiMn x Ni y Co z O2(0<x<0.5, 0<y<0.5, 0≤z<0.5), LiMn 2-x M x O4 (M is Li, Mg, Co, Al, Ni, 0<x<0.2), LiMPO4 (M is Fe, Co, Ni), etc.

[0024] Examples of the positive electrode conductive agent include carbonaceous materials such as acetylene black, carbon black, and graphite, and examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.

[0025] The fiber layer 13 functions as a lithium-ion conductive and electrically insulating separator. The fiber layer 13 can be formed directly on the surface of the negative electrode 12 or positive electrode 11 using a solution of an organic material as a raw material, for example, using electrospinning, inkjet, jet dispenser, or spraying. The fiber layer 13 also covers the edges of the negative electrode active material layer 12b of the negative electrode 12 and the positive electrode active material layer 11b of the positive electrode 11. On the other hand, the edges of the negative electrode collector 12a of the negative electrode 12 and the positive electrode collector 11a of the positive electrode 11 are not covered by the fiber layer 13 but instead protrude from the fiber layer 13. This structure suppresses misalignment of the electrode surfaces and the occurrence of short circuits caused by shearing between the electrodes and the current collectors. Furthermore, since the edges of the electrodes are covered by the insulator comprising the fiber layer 13, short circuits at the edges are avoided, thereby improving battery safety. Covering the edges of the electrodes with the insulator comprising the fiber layer 13 also improves self-discharge characteristics.

[0026] For example, in electrospinning, a solution prepared by dissolving an organic material in a solvent is used. The organic material can be selected from the group consisting of polyamide-imide, polyamide, polyolefin, polyether, polyimide, polyketone, polysulfone, cellulose, polyvinyl alcohol (PVA), and polyvinylidene fluoride (PVdF). Examples of polyolefins include polypropylene (PP) and polyethylene (PE).

[0027] Figure 2B This is a diagram showing the state of the electrode sheet 10 when the fiber layer 13 is being inspected. Figure 2B is viewed from the imaging sensor 40 side Figure 1 The state of the electrode sheet 10. Figure 2B In the embodiment, the fiber layer 13 is formed on the negative electrode 12. In the case where the formation of the fiber layer 13 is completed at the manufacturing stage, the electrode sheet 10 is fed into the inspection system 1 via the roller 10a before the positive electrode 11 is formed. That is, the electrode sheet 10 is fed into the inspection system 1 in such a manner that the fiber layer 13 is exposed when viewed from the imaging sensor 40. The imaging sensor 40 captures the image of the electrode sheet 10 from the fiber layer 13 side at a frame rate synchronized with the conveying speed of the electrode sheet 10. The imaging sensor 40 then outputs the image data to the inspection device 50. When the imaging sensor 40 is a single-line sensor, the image data is data for one line of the electrode sheet 10, where each pixel has brightness values ​​of R, G, and B.

[0028] Figure 3: is a diagram showing the hardware structure of the inspection device 50. The inspection device 50 can be various terminal devices such as a personal computer (PC) and a tablet terminal. Figure 3 As shown, the inspection device 50 includes a processor 51 , a ROM 52 , a RAM 53 , a memory 54 , an input interface 55 , a communication device 56 , and a display device 57 as hardware.

[0029] The processor 51 controls the overall operation of the inspection device 50. For example, the processor 51 is a CPU (Central Processing Unit). The processor 51 may be an MPU (Micro-Processing Unit), a GPU (Graphics Processing Unit), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field Programmable Gate Array). The processor 51 may be a single CPU or multiple CPUs.

[0030] ROM (Read Only Memory) 52 is a nonvolatile memory. ROM 52 stores a startup program for the inspection device 50 , etc. RAM (Random Access Memory) 53 is a volatile memory. RAM 53 is used as a working memory during processing by the processor 51 , for example.

[0031] The memory 54 is, for example, a hard disk drive, a solid state drive, or the like. The memory 54 stores various programs executed by the processor 51, such as an inspection program.

[0032] The input interface 55 includes input devices such as a touch panel, a keyboard, and a mouse. When an input device of the input interface 55 is operated, a signal corresponding to the operation content is input to the processor 51. The processor 51 performs various processes based on the signal.

[0033] The communication device 56 is a communication device for the inspection device 50 to communicate with external devices such as the encoder 30 and the imaging sensor 40. The communication device 56 may be a communication device for wired communication or a communication device for wireless communication.

[0034] The display device 57 is a display device such as a liquid crystal display or an organic EL display. The display device 57 displays various images. The display device 57 may be provided separately from the inspection device 50.

[0035] Figure 4It is a flowchart showing the operation of the inspection device 50 . Figure 4 The action is executed by the processor 51. Figure 4 During this operation, the electrode sheet 10 is conveyed by rollers 10a and 10b. The encoder 30 detects the rotation amount of the roller 10b at a predetermined period and outputs the detected rotation amount as the conveyance amount of the electrode sheet 10 to the inspection device 50. Furthermore, the imaging sensor 40 captures images in synchronization with the conveyance of the electrode sheet 10 and outputs the captured image data to the inspection device 50.

[0036] In step S1, the processor 51 calculates the imaging position of the imaging sensor 40 based on the feed rate of the electrode sheet 10 obtained from the encoder 30. The imaging position is the position of the electrode sheet 10 captured by the imaging sensor 40. The length of the manufactured electrode sheet 10 is fixed, and if the feed speed of the rollers 10a and 10b is constant, the imaging position of the imaging sensor 40 can be calculated based on the feed rate. Furthermore, the processor 51 obtains imaging data from the imaging sensor 40 and associates the obtained imaging data with the calculated imaging position, storing the data in, for example, the RAM 53.

[0037] In step S2, processor 51 determines whether to generate an image from the image data. For example, if only enough lines of image data are stored in RAM 53 to form an image, it is determined that an image is being generated. The number of lines that can form an image is determined, for example, by the screen size of display device 57. If it is not determined in step S2 that an image is being generated, processing returns to step S1. In this case, processor 51 continues to acquire image data and image positions. If it is determined in step S2 that an image is being generated, processing transfers to step S3.

[0038] In step S3 , the processor 51 generates an image by combining the image data in line units and then stores the generated image in the memory 54 , for example.

[0039] In step S4, the processor 51 determines whether the imaging of the electrode sheet 10 is complete. For example, if the transport amount exceeds a threshold, the imaging of the electrode sheet 10 is determined to be complete. If the imaging of the electrode sheet 10 is not determined to be complete in step S4, the process returns to step S1. If the imaging of the electrode sheet 10 is determined to be complete in step S4, the process transfers to step S5.

[0040] In step S5, the processor 51 performs defect detection processing. The defect detection processing is a process for detecting defects in the fiber layer 13 of the electrode sheet 10 from the image. After the defect detection processing, the process transfers to step S6. The details of the defect detection processing will be described later.

[0041] In step S6, the processor 51 displays the result of the defect detection on the display device 57. Then, the processor 51 ends Figure 4 For example, the processor 51 causes the display device 57 to display an image showing defects in the fiber layer 13. The processor 51 may emphasize the position of the defect or further display information related to the defect, such as the number of defects.

[0042] Figure 5 This is a flowchart showing the defect detection process of the embodiment. In the embodiment, peeling is detected as a defect of the fiber layer 13. Peeling is a defect in which a portion of the fiber layer 13 peels off and remains on the negative electrode current collector 12a.

[0043] In step S11, the processor 51 selects one image from the images stored in the memory 54. For example, the processor 51 selects the images in the order in which they are stored in the memory 54.

[0044] In step S12 , the processor 51 sets an inspection area and detects a peeling start position in the inspection area.

[0045] The processing of step S12 will be described. Figure 6A is a diagram showing the inspection area. Figure 6A As shown, the inspection area DA is the area of ​​the negative electrode current collector 12a in the image, excluding the fiber layer 13. In this embodiment, it is defined in the image. Assuming that the negative electrode current collector 12a and the fiber layer 13 are manufactured without errors during the manufacturing stage of the electrode sheet 10, the widthwise start position of the inspection area DA is at the end of the negative electrode current collector 12a, and the end position is at the end of the fiber layer 13. These positions can be obtained as design values, for example. In practice, to account for manufacturing errors in the negative electrode current collector 12a and the fiber layer 13, a slight margin may be included in the widthwise start position of the inspection area DA.

[0046] exist Figure 6A In the figure, it is assumed that the fiber layer 13 is peeled off in the negative electrode current collector 12a. In this case, when the negative electrode current collector 12a is observed from above, the peeled fiber layer 13 can be observed on the negative electrode current collector 12a. Figure 6B It is along Figure 6A A curve showing the brightness values ​​of the L line. Figure 6B The horizontal axis is the pixel position along the L line, and the vertical axis is the brightness value. Figure 6B The origin on the horizontal axis is set at the end of the negative electrode current collector 12a, that is, the starting position of the inspection area DA. Curve r is a curve showing the luminance values ​​of the R sub-pixels, curve g is a curve showing the luminance values ​​of the G sub-pixels, and curve b is a curve showing the luminance values ​​of the B sub-pixels.

[0047] exist Figure 6BAt the left end of the inspection area DA, the brightness values ​​of the R, G, and B pixels are all low. This indicates the color of the negative electrode current collector 12a. Meanwhile, at a certain pixel position in the inspection area DA, the brightness values ​​of the R and G pixels are sharply higher than the brightness of the B pixel. In other words, the color of this pixel is generally yellow. This is the color of the organic material used in the manufacture of the fiber layer 13.

[0048] In this way, when the fiber layer 13 of the negative electrode current collector 12a is peeled off, a color change occurs in the image. Therefore, the processor 51 scans the pixel values ​​in the inspection area DA from the starting position side of the inspection area for each row, and detects the position of the pixel having the color of the organic material of the fiber layer 13 detected first for each row (in this embodiment, the yellow color unique to the fiber layer 13 formed directly on the negative electrode 12 by electrospinning) as the peeling start position. In this embodiment, the position having the color of the organic material of the fiber layer 13 detected first for each row in the inspection area DA is detected as the peeling start position based on the brightness of the three sub-pixels: R pixel, G pixel, and B pixel.

[0049] In the present embodiment, the color unique to the organic material of the fiber layer 13 is yellow, but for example, the position of the yellow pixel in the inspection area DA is the position of the pixel where the brightness value of the R pixel and the brightness value of the G pixel are greater than the threshold value TH. In addition, in this case, the threshold value TH of the brightness value of the R pixel and the brightness value of the G pixel can be the same value or different values. In addition, after the stripping start position is detected, the position of the pixel where the brightness value of the R pixel and the brightness value of the G pixel are less than the threshold value TH is equivalent to the stripping end position. The processor 51 can also detect the stripping end position of each row. In addition, depending on the stripping method, there are cases where multiple stripping start positions exist on one row. In this case, the processor 51 can detect only the initial stripping start position or all the stripping start positions.

[0050] Here, return Figure 5 In step S13, the processor 51 calculates the median value of one image of the peeling start position detected for each line. That is, the processor 51 calculates Figure 6B The median value M of one image at the peeling start position for each row is shown.

[0051] In step S14, the processor 51 determines whether the median value M satisfies TH L <M<TH H The threshold TH and TH H The distance from the end of the negative electrode current collector 12a is a threshold value for determining whether or not there is peeling. In step S14, it is determined that the median value M does not satisfy THL <M<TH H If the condition is met, the process transfers to step S16. The central value of the peeling start position is greater than the threshold value TH H This means that there is peeling only around the fiber layer 13. In the embodiment, if there is peeling only around the fiber layer 13, it is not considered a defect. In addition, the central value of the peeling start position is less than the threshold value TL L This means that there is peeling only at the end of the negative electrode current collector 12a. In the embodiment, even if there is peeling only at the end of the negative electrode current collector 12a, it is not considered a defect. In step S14, it is determined that the median value M satisfies TH L <M<TH H When the condition is met, the processing transfers to step S15.

[0052] In step S15, the processor 51 stores the peeling start position of each row in the image as the position of the peeling defect in association with the image in, for example, the memory 54. Thereafter, the processing transfers to step S16. As described above, there may be a case where there are multiple peeling start positions per row. In this case, the processor 51 may also store all the peeling start positions in association with the image in the memory 54. In addition, the processor 51 may also store the peeling end position in association with the image in the memory 54 together with the peeling start position. In this case, the processor 51 may store all the peeling end positions in association with the image in the memory 54, or may store only the last detected peeling end position.

[0053] In step S16, the processor 51 determines whether the process of detecting peeling of all images is completed. If it is determined in step S16 that the process of detecting peeling of all images is not completed, the process returns to step S11. If it is determined in step S16 that the process of detecting peeling of all images is completed, the processor 51 ends the process. Figure 5 processing.

[0054] Figure 7 This is a diagram showing an example of a display of a peeling defect. Figure 4 For example, in step S6 Figure 7 In the case where peeling is detected in the image shown, Figure 7 As shown, the peeling start position is highlighted. In fact, if the peeling start position of all rows is displayed, it will be complicated, so the center value of the peeling start position can also be highlighted. Furthermore, a predetermined reference position, such as a threshold value TH, can be displayed to visually indicate the peeling distance. L The reference position is not limited to the threshold value TH. LThe position may be, for example, a position on the current collector that is sufficiently away from the end of the fiber layer 13 .

[0055] As described above, according to the embodiments, it is possible to inspect the electrode sheet for peeling defects by observing color changes in an image. Specifically, according to the embodiments, inspection for peeling defects is possible using a simple configuration consisting solely of an imaging sensor. Furthermore, according to the embodiments, inspection can be performed by placing the electrode sheet, already having a fiber layer formed, onto an inspection sheet. In other words, inspection can be performed during the manufacturing process.

[0056] [Modification]

[0057] In the above embodiment, the presence of peeling is determined by comparing the median value of the peeling start position with a threshold value. In contrast, the presence of peeling can be determined by comparing various statistical values ​​such as the average value and minimum value of the peeling start position with a threshold value.

[0058] In the above-described embodiment, the current collector is rectangular in shape, meaning that the distance from the end of the current collector to the end of the fiber layer is constant. Alternatively, the current collector may have various shapes, such as a comb-like shape. If the distance from the end of the current collector to the end of the fiber layer is not constant, a threshold for the peeling start position may be set for each row, for example. Furthermore, the processor 51 may determine for each row whether the peeling start position is above the threshold and determine whether peeling has occurred based on the number of such determinations.

[0059] In the above embodiment, the inspection region is set in the negative electrode current collector 12a. However, the fiber layer 13 may be formed in the positive electrode active material layer 11b of the positive electrode 11. In this case, the inspection region can be set in the positive electrode current collector 11a.

[0060] In the above embodiment, the imaging sensor 40 is fixed in position to capture an image of the electrode sheet 10 conveyed by the rollers 10a and 10b. Conversely, the imaging sensor 40 may scan the electrode sheet 10 while keeping the position of the electrode sheet 10 fixed.

[0061] While several embodiments of the present invention have been described, these embodiments are provided as examples and are not intended to limit the scope of the invention. These novel embodiments may be implemented in various other ways, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are intended to be within the scope and spirit of the invention and are encompassed by the invention as set forth in the claims and their equivalents.

Claims

1. An inspection system for a secondary battery, comprising: An imaging sensor for capturing an image of an electrode structure in a secondary battery having a fiber layer formed on a surface of an electrode including a current collector and an active material layer, from the fiber layer side; as well as an inspection device for inspecting whether the fiber layer is peeled off based on color changes in an image obtained from the imaging data of the imaging sensor; The inspection device sets the region of the current collector as an inspection region, The inspection device scans the inspection area in the image from the fiber layer side, and detects the pixel where the color of the fiber layer is first detected as the starting position of the peeling of the fiber layer in each line of the image. The inspection device determines that the fiber layer has peeled off when the position statistic is greater than a first threshold value, which is the distance from the end of the collector, and less than a second threshold value, which is the distance from the end of the collector and is greater than the first threshold value. The position statistic is calculated based on the starting positions of the peeling of the multiple fiber layers detected for each row.

2. The inspection system for a secondary battery according to claim 1, wherein The inspection device detects the color of the fiber layer based on the brightness of red sub-pixels, green sub-pixels, and blue sub-pixels constituting pixels of the image.

3. The inspection system according to claim 1 or 2, wherein: The imaging sensor is a line sensor in which pixels are arranged along the width direction of the electrode structure.

4. A method for inspecting a secondary battery, comprising the following steps: capturing an image of an electrode structure in a secondary battery having a fiber layer formed on a surface of an electrode including a current collector and an active material layer, from the fiber layer side, and obtaining image data; and inspecting whether the fiber layer is peeled off based on color changes in an image obtained from the camera data; In the step of inspecting whether the fiber layer is peeled off: The region of the current collector is set as an inspection region, The inspection area in the image is scanned from the fiber layer side, and the pixel where the color of the fiber layer is first detected is detected as the starting position of the peeling of the fiber layer in each line of the image. When the position statistic is greater than a first threshold value which is the distance from the end of the collector and less than a second threshold value which is the distance from the end of the collector and is greater than the first threshold value, it is determined that the fiber layer has peeled off. The position statistic is calculated based on the starting positions of the peeling of the multiple fiber layers detected for each row.

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