Inspection System and Inspection Method for Secondary Battery

Abstract

To provide an inspection system and an inspection method capable of inspecting defects in an organic fiber layer at a manufacturing stage.SOLUTION: An inspection system of an embodiment has an image sensor and an inspection device. The image sensor captures an image of an electrode structure in a secondary battery in which a fiber layer is formed on a surface of an electrode that includes a current collector and an active material layer, from the fiber layer side. The inspection device inspects presence or absence of delamination of the fiber layer on the basis of color change in an image obtained from imaging data of the image sensor.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an inspection system and an inspection method for secondary batteries.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a secondary battery, the layer of organic fibers formed on the electrode may have various defects during manufacturing. It is desired to be able to inspect such defects in the layer of organic fibers at the manufacturing stage.

[0005] The embodiments provide an inspection system and an inspection method capable of inspecting defects in the layer of organic fibers at the manufacturing stage.

Means for Solving the Problems

[0006] The inspection system of the embodiment includes an image sensor and an inspection device. The image sensor images the electrode structure in a secondary battery in which a fiber layer is formed on the surface of an electrode including a current collector and an active material layer from the side of the fiber layer. The inspection device inspects the presence or absence of peeling of the fiber layer based on a color change in an image obtained from the imaging data of the image sensor.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 7

[0008] Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a diagram showing an example of an inspection system for a secondary battery according to an embodiment. The inspection system 1 is a system for inspecting defects in a fiber layer formed on an electrode sheet 10 manufactured in the manufacturing stage of a secondary battery. The electrode sheet 10 manufactured in the manufacturing stage is introduced into the inspection system 1 by a roller 10a and conveyed in the direction of arrow A by a roller 10b. The rollers 10a and 10b are configured to rotate, for example, by a motor. The electrode sheet 10 forms a battery in an electrode structure included in the secondary battery.

[0009]

[0010] The driving device 20 has a driving circuit for driving the rollers 10a and 10b. This driving circuit generates, for example, 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.The encoder 30 is installed near the roller 10b and detects the amount of rotation of the roller 10b. Then, the encoder 30 outputs the amount of rotation of the roller 10b as the conveyance amount of the electrode sheet 10 to the inspection device 50. The encoder 30 is, for example, an optical encoder that detects the amount of rotation of the roller 10b by counting an optical pattern attached to the roller 10b. The encoder 30 does not necessarily have to be an optical encoder. Also, the encoder 30 may be installed near the roller 10a instead of near the roller 10b.

[0011] The image sensor 40 is installed above the electrode sheet 10, images the electrode sheet 10, and generates imaging data related to the electrode sheet 10. The image sensor 40 may be a CMOS (Complementary Metal Oxide Semiconductor) type image sensor or a CCD (Charge Coupled Device) type image sensor. Then, the image sensor 40 outputs the generated imaging data to the inspection device 50. Here, the image sensor 40 is a line sensor in which pixels are arranged along the width direction of the electrode sheet 10 orthogonal to the conveyance direction of the electrode sheet 10. The number of lines of the image sensor 40 may be one line or a plurality of lines. On the other hand, it is desirable that the pixels in the width direction of the image sensor 40 are arranged with a width equal to or greater than the width of the electrode sheet 10. Also, each pixel of the image sensor 40 is composed of three sub-pixels of R (red), G (green), and B (blue). That is, the image sensor 40 is configured to be able to generate a color image. It is desirable that the imaging frame rate of the image sensor 40 is synchronized with the conveyance speed of the electrode sheet 10.

[0012] The inspection device 50 inspects the presence or absence of defects and their positions in the electrode sheet 10 based on the conveyance amount of the electrode sheet 10 input from the encoder 30 and the image of the electrode sheet 10 input from the image sensor 40. The inspection device 50 can be configured by a computer such as a personal computer.

[0013] Figure 2A is a cross-sectional view showing the configuration of the electrode sheet 10. The electrode sheet 10 is a sheet material including a positive electrode 11 and a negative electrode 12. Between the positive electrode 11 and the negative electrode 12, it is insulated by a fiber layer 13 including organic fibers as an insulator. The fiber layer 13 is not a self-supporting film but is supported by the negative electrode 12. The electrode sheet 10 can be cut to an appropriate length to form a battery in the electrode structure of the secondary battery.

[0014] The negative electrode 12 is configured 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 configured by providing a positive electrode active material layer 11b on the surface of a positive electrode current collector 11a. As the negative electrode current collector 12a and the positive electrode current collector 11a, a metal foil such as aluminum is used. 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, and 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.

[0015] As the negative electrode active material, for example, lithium titanate can be used. As the lithium titanate, for example, Li having a spinel structure 4+x Ti 5 O 12 (0 ≦ x ≦ 3), or Li having a lamstellarite structure 2+y Ti 3 O 7 (0 ≦ y ≦ 3) can be mentioned. The average particle diameter of the primary particles of the negative electrode active material is preferably in the range of 0.001 to 1 μm. The particle shape may be either granular or fibrous. In the case of fibrous, the fiber diameter is preferably 0.1 μm or less.

[0016] As the negative electrode conductive agent, for example, acetylene black, carbon black, graphite, etc. can be used. As the binder for binding the negative electrode active material and the negative electrode conductive agent, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber, etc. can be used.

[0017] As the positive electrode active material, a general lithium transition metal composite oxide can be used. For example, LiCoO 2 , LiNi 1-x Co x O 2 (0 < x < 0.3), LiMn x Ni y Co z O 2 (0 < x < 0.5, 0 < y < 0.5, 0 ≦ z < 0.5), LiMn 2-x M x O 4 (M is Li, Mg, Co, Al, Ni, 0 < x < 0.2), LiMPO 4 (M is Fe, Co, Ni), etc. can be used.

[0018] As the positive electrode conductive agent, for example, carbonaceous materials such as acetylene black, carbon black, and graphite can be used. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber can be used.

[0019] The fiber layer 13 acts as a separator that is lithium ion conductive and electrically insulating. The fiber layer 13 can be directly formed on the surface of the negative electrode 12 or the positive electrode 11 using, for example, an electrospinning method, an inkjet method, a jet dispenser method, or a spray coating method, with a solution of an organic material as the raw material. Here, 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 current collector 12a of the negative electrode 12 and the positive electrode current collector 11a of the positive electrode 11 are not covered by the fiber layer 13 and protrude from the fiber layer 13. By adopting such a configuration, misalignment of the electrode surfaces and the occurrence of short circuits due to burrs on the electrodes and current collectors are suppressed. Moreover, since the edges of the electrodes are covered with an insulator including the fiber layer 13, the occurrence of shorts at the edges is avoided, and the safety of the battery can be enhanced. Covering the edges of the electrodes with an insulator including the fiber layer 13 also leads to an improvement in the self-discharge characteristics.

[0020] 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, for example, polyamideimide, polyamide, polyolefin, polyether, polyimide, polyketone, polysulfone, cellulose, polyvinyl alcohol (PVA), and polyvinylidene fluoride (PVdF). Examples of polyolefins include polypropylene (PP) and polyethylene (PE).

[0021] FIG. 2B is a diagram showing the state of the electrode sheet 10 during the inspection of the fiber layer 13. FIG. 2B shows the state of viewing the electrode sheet 10 from the side of the image sensor 40 in FIG. 1. In FIG. 2B, it is assumed that the fiber layer 13 is formed on the negative electrode 12. In the embodiment, when the formation of the fiber layer 13 is completed at the manufacturing stage, before the positive electrode 11 is formed, the electrode sheet 10 is introduced into the inspection system 1 via the roller 10a. That is, the electrode sheet 10 is introduced so that the fiber layer 13 is exposed as viewed from the image sensor 40. The image sensor 40 captures an image of the electrode sheet 10 from the side of the fiber layer 13 at a frame rate synchronized with the conveyance speed of the electrode sheet 10. Then, the image sensor 40 outputs the captured image data to the inspection device 50. When the image sensor 40 is a one-line sensor, the captured image data is data for one line of the electrode sheet 10 in which each pixel has luminance values of R, G, and B.

[0022] FIG. 3 is a diagram showing the hardware configuration of the inspection device 50. The inspection device 50 can be various terminal devices such as a personal computer (PC) and a tablet terminal. As shown in FIG. 3, the inspection device 50 includes a processor 51, a ROM 52, a RAM 53, a storage 54, an input interface 55, a communication device 56, and a display device 57 as hardware.

[0023] The processor 51 is a processor that controls the overall operation of the inspection device 50. The processor 51 is, for example, 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), an FPGA (Field Programmable Gate Array), etc. The processor 51 may be a single CPU or the like, or may be a plurality of CPUs or the like.

[0024] The ROM (Read Only Memory) 52 is a non-volatile memory. The ROM 52 stores the startup program of the inspection device 50 and the like. The RAM (Random Access Memory) 53 is a volatile memory. The RAM 53 is used, for example, as a working memory during processing in the processor 51.

[0025] The storage 54 is a storage such as a hard disk drive or a solid state drive, for example. The storage 54 stores various programs executed by the processor 51 such as an inspection program.

[0026] 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 according to this signal.

[0027] 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 image sensor 40. The communication device 56 may be a communication device for wired communication or a communication device for wireless communication.

[0028] The display device 57 is a display device such as a liquid crystal display and an organic EL display. The display device 57 displays various images. The display device 57 may be provided separately from the inspection device 50.

[0029] Figure 4 is a flowchart showing the operation of the inspection device 50. The operation in Figure 4 is executed by the processor 51. During the operation in Figure 4, the electrode sheet 10 is conveyed by the rollers 10a and 10b. The encoder 30 detects the rotation amount of the roller 10b at a constant period and outputs the detected rotation amount to the inspection device 50 as the conveyance amount of the electrode sheet 10. Further, the image sensor 40 performs imaging in synchronization with the conveyance of the electrode sheet 10 and outputs the imaging data to the inspection device 50.

[0030] In step S1, the processor 51 calculates the imaging position of the image sensor 40 based on the conveyance amount of the electrode sheet 10 acquired from the encoder 30. The imaging position is the position of the electrode sheet 10 that the image sensor 40 is imaging. If the length of the manufactured electrode sheet 10 is determined and the conveyance speeds of the rollers 10a and 10b are constant, the imaging position of the image sensor 40 can be calculated from the conveyance amount. Further, the processor 51 acquires the imaging data from the image sensor 40 and associates the acquired imaging data with the calculated imaging position and stores it in, for example, the RAM 53.

[0031] In step S2, the processor 51 determines whether to generate an image from the imaging data. For example, it is determined to generate an image when the imaging data of the number of lines sufficient to form an image is stored in the RAM 53. The number of lines sufficient to form an image is determined according to, for example, the screen size of the display device 57. In step S2, when it is not determined to generate an image, the process returns to step S1. In this case, the processor 51 continues to acquire the imaging data and the imaging position. In step S2, when it is determined to generate an image, the process proceeds to step S3.

[0032] In step S3, the processor 51 generates an image by combining imaging data in line units. Then, the processor 51 stores the generated image in, for example, the storage 54.

[0033] In step S4, the processor 51 determines whether the imaging of the electrode sheet 10 is completed. For example, when the conveyance amount exceeds a threshold value, it is determined that the imaging of the electrode sheet 10 is completed. In step S4, when it is determined that the imaging of the electrode sheet 10 is not completed, the process returns to step S1. In step S4, when it is determined that the imaging of the electrode sheet 10 is completed, the process proceeds to step S5.

[0034] In step S5, the processor 51 performs a defect detection process. The defect detection process is a process of detecting a defect in the fiber layer 13 of the electrode sheet 10 from the image. After the defect detection process, the process proceeds to step S6. Details of the defect detection process will be described later.

[0035] In step S6, the processor 51 displays the result of the defect detection on the display device 57. Then, the processor 51 ends the process of FIG. 4. For example, the processor 51 causes the display device 57 to display an image in which a defect in the fiber layer 13 is detected. The processor 51 may emphasize the position of the defect or further display information related to the defect such as the number of defects.

[0036] FIG. 5 is a flowchart showing the defect detection process according to the embodiment. In the embodiment, peeling is detected as a defect in the fiber layer 13. Peeling is a defect in which a part of the fiber layer 13 has peeled off and remains on the negative current collector 12a.

[0037] In step S11, the processor 51 selects one image from the images stored in the storage 54. For example, the processor 51 selects the images in the order in which they are stored in the storage 54.

[0038] In step S12, the processor 51 sets an inspection area and detects a peeling start position in the inspection area.

[0039] The process of step S12 will be described. FIG. 6A is a diagram showing the inspection area. As shown in FIG. 6A, the inspection area DA is an area of the negative electrode current collector 12a excluding the fiber layer 13 in the image, and is set in the image in this embodiment. Assuming that the negative electrode current collector 12a and the fiber layer 13 are manufactured without error in the manufacturing stage of the electrode sheet 10, the start position in the width direction of the inspection area DA is the position of the end of the negative electrode current collector 12a, and the end position is the position of the end of the fiber layer 13. These positions can be obtained as design values, for example. In reality, considering the manufacturing errors of the negative electrode current collector 12a and the fiber layer 13, a certain margin may be included in the start position in the width direction of the inspection area DA.

[0040] In FIG. 6A, assume that there is peeling of the fiber layer 13 on the negative electrode current collector 12a. In this case, when looking at the negative electrode current collector 12a from above, the peeled fiber layer 13 can be seen on the negative electrode current collector 12a. FIG. 6B is a graph of the luminance values along the L line in FIG. 6A. The horizontal axis in FIG. 6B is the pixel position along the L line, and the vertical axis is the luminance value. Note that the origin on the horizontal axis in FIG. 6B is set at the position of the end of the negative electrode current collector 12a, that is, the start position of the inspection area DA. And the graph r is a graph of the luminance value of the R sub-pixel, the graph g is a graph of the luminance value of the G sub-pixel, and the graph b is a graph of the luminance value of the B sub-pixel.

[0041] In FIG. 6B, the pixel positions at the left end of the inspection area DA have low luminance values for all of the R pixel, G pixel, and B pixel. This represents the color of the negative electrode current collector 12a. On the other hand, at a certain pixel position in the inspection area DA, the luminance values of the R pixel and the G pixel increase rapidly compared to the luminance of the B pixel. That is, the color of this pixel represents a substantially yellow color. This is the color of the organic material used in the manufacture of the fiber layer 13.

[0042] Thus, when there is peeling of the fiber layer 13 from the negative electrode current collector 12a, a color change occurs in the image. Therefore, the processor 51 scans the values of the pixels in the inspection region DA line by line from the start position side of the inspection region, and detects the position of the pixel having the color of the organic material of the fiber layer 13 (in this embodiment, particularly the yellow color peculiar to the fiber layer 13 directly formed on the negative electrode 12 by the electrospinning method) first detected for each line as the peeling start position. In this embodiment, based on the luminance of the three sub-pixels of the R pixel, G pixel, and B pixel, the color of the organic material of the fiber layer 13 first detected for each line in the inspection region DA is detected, and the position is detected as the peeling start position.

[0043] In this embodiment, the color peculiar to the organic material of the fiber layer 13 is yellow. For example, the position of the yellow pixel in the inspection region DA is the position of the pixel where the luminance value of the R pixel and the luminance value of the G pixel are equal to or greater than the threshold value TH. In this case, the threshold values TH of the luminance value of the R pixel and the luminance value of the G pixel may be the same value or different values. Also, after the peeling start position is detected, the position of the pixel where the luminance value of the R pixel and the luminance value of the G pixel are less than the threshold value TH corresponds to the peeling end position. The processor 51 may also detect the peeling end position for each line. Also, depending on the way of peeling, there may be a case where there are a plurality of peeling start positions in one line. In this case, the processor 51 may detect only the first peeling start position or may detect all the peeling start positions.

[0044] Here, returning to the description of FIG. 5. In step S13, the processor 51 calculates the median value of the peeling start positions detected for each line for one image. That is, the processor 51 calculates the median value M of the peeling start positions for each line shown in FIG. 6B for one image.

[0045] In step S14, the processor 51 determines whether the condition that the median value M satisfies TH L <M<TH H is satisfied. The threshold value TH L and TH Hare the distances from the ends of the negative electrode current collector 12a, respectively, and are thresholds for determining the presence or absence of peeling. In step S14, when it is determined that the median value M does not satisfy the condition of TH L < M < TH H , the process proceeds to step S16. That the median value of the peeling start position is greater than the threshold TH H means that there is peeling only around the fiber layer 13. In the embodiment, when there is peeling only around the fiber layer 13, it is not regarded as a defect. Also, that the median value of the peeling start position is less than the threshold TL L means that there is peeling only at the ends of the negative electrode current collector 12a. In the embodiment, even when there is peeling only at the ends of the negative electrode current collector 12a, it is not regarded as a defect. In step S14, when it is determined that the median value M satisfies the condition of TH L < M < TH H , the process proceeds to step S15.

[0046] In step S15, the processor 51 associates the peeling start position of each line in the image with the position of the peeling defect and stores it, for example, in the storage 54 in association with the image. Then, the process proceeds to step S16. As described above, there may be a plurality of peeling start positions for each line. In this case, the processor 51 may store all the peeling start positions in association with the image in the storage 54. Also, the processor 51 may store the peeling end position in association with the image together with the peeling start position in the storage 54. In this case, the processor 51 may store all the peeling end positions in association with the image in the storage 54, or may store only the last detected peeling end position.

[0047] In step S16, the processor 51 determines whether the process of detecting peeling for all images has been completed. In step S16, when it is determined that the process of detecting peeling for all images has not been completed, the process returns to step S11. In step S16, when it is determined that the process of detecting peeling for all images has been completed, the processor 51 ends the process of FIG. 5.

[0048] FIG. 7 is a diagram showing an example of displaying a peeling defect. This display is performed, for example, in step S6 of FIG. 4. For example, when peeling is detected in the image shown in FIG. 7, the peeling start position is highlighted as shown in FIG. 7. In practice, it is cumbersome to display the peeling start positions of all lines, so the median value of the peeling start positions may be highlighted. Furthermore, in order to visually clarify the peeling distance, arrows from a predetermined reference position, for example, the threshold value TH L to the peeling start position of each line or the median value of the peeling start positions may be displayed. The reference position is not limited to the position of the threshold value TH L and may be, for example, a position on the current collector sufficiently away from the end of the fiber layer 13.

[0049] As described above, according to the embodiment, the presence or absence of a peeling defect in the fiber layer in the electrode sheet can be inspected by the color change in the image. That is, in the embodiment, the presence or absence of a peeling defect can be inspected with a simple configuration of only an image sensor. Further, in the embodiment, the inspection can be performed by putting the electrode sheet at the stage where the fiber layer is formed into the inspection sheet. That is, the inspection can be performed at the manufacturing stage.

[0050] [Modification Example] In the above-described embodiment, the presence or absence of peeling is determined by comparing the median value of the peeling start position with a threshold value. In contrast, the presence or absence of peeling may be determined by comparing various statistical values such as the average value and the minimum value of the peeling start position with a threshold value.

[0051] Further, in the above-described embodiment, the shape of the current collector is rectangular, that is, the distance from the end of the current collector to the end of the fiber layer is assumed to be constant. In contrast, various shapes such as a comb shape can be used for the shape of the current collector. When the distance from the end of the current collector to the end of the fiber layer is not constant, for example, a threshold value of the peeling start position may be set for each line. Then, the processor 51 may determine whether the peeling start position for each line is equal to or greater than the threshold value, and determine the presence or absence of peeling according to a majority decision or the like of the determination results.

[0052] In the above-described embodiment, the inspection region is set in the negative electrode current collector 12a. In contrast, the fiber layer 13 may also be formed on the positive electrode active material layer 11b of the positive electrode 11. In this case, the inspection region may be set in the positive electrode current collector 11a.

[0053] Further, in the above-described embodiment, the electrode sheet 10 conveyed by the rollers 10a and 10b is configured to be imaged by the image sensor 40 whose position is fixed. In contrast, conversely, the position of the electrode sheet 10 may be fixed, and the image sensor 40 may be configured to scan the electrode sheet 10.

[0054] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0055] 1 Inspection system, 10 Electrode sheet, 10a, 10b Roller, 11 Positive electrode, 11a Positive electrode current collector, 11b Positive electrode active material layer, 12 Negative electrode, 12a Negative electrode current collector, 12b Negative electrode active material layer, 13 Fiber layer, 20 Driving device, 30 Encoder, 40 Image sensor, 50 Inspection device, 51 Processor, 52 ROM, 53 RAM, 54 Storage, 55 Input interface, 56 Communication device, 57 Display device.

Claims

1. An image sensor that images an electrode structure in a secondary battery in which a fiber layer is formed on the surface of an electrode including a current collector and an active material layer from the side of the fiber layer, An inspection device that inspects the presence or absence of peeling of the fiber layer based on a color change in an image obtained from the imaging data of the image sensor, An inspection system for a secondary battery having the above.

2. The inspection device, Sets the region of the current collector as an inspection region, Scans the inspection region in the image from the side of the fiber layer and detects, as the start position of peeling of the fiber layer, the pixel at which the color of the fiber layer is first detected. The inspection system for a secondary battery according to Claim 1.

3. The inspection device, Performs detection of the color of the fiber layer based on the luminance of red, green, and blue sub-pixels constituting the pixels of the image. The inspection system for a secondary battery according to Claim 2.

4. The inspection device, Detects the start position of peeling of the fiber layer for each line of the image, Inspects the presence or absence of peeling of the fiber layer based on a comparison between a statistical value calculated from a plurality of start positions of peeling of the fiber layer detected for each line and a threshold value. The inspection system for a secondary battery according to Claim 2 or 3.

5. The image sensor is a line sensor in which pixels are arranged along the width direction of the electrode structure. The inspection system according to any one of Claims 1 to 4.

6. Imaging an electrode structure in a secondary battery in which a fiber layer is formed on the surface of an electrode including a current collector and an active material layer from the side of the fiber layer to obtain imaging data, Inspecting the presence or absence of peeling of the fiber layer based on a color change in an image obtained from the imaging data, An inspection method for a secondary battery having the above.

Images