Rapid detection method for bonding effect of battery pole piece

Abstract

The invention discloses a rapid detection method for the bonding effect of a battery pole piece, and relates to the field of detection of battery pole pieces. The detection method comprises the following steps: S1, fixing a cut electrode plate to be detected; s2, acquiring an image of the section of the electrode piece to be tested by using an image tester; s3, amplifying the section image of the electrode pole piece obtained in the step S2 by adopting a CCD (Charge Coupled Device) image sensor to obtain an amplified image picture; s4, analyzing the amplified image picture, and judging the bonding effect of the section of the electrode piece to be detected; according to the method, an image tester is adopted to obtain an image picture of the section of the pole piece, and rapid and accurate judgment on the bonding effect of the pole piece of the electrode is realized through targeted recognition processing on the image picture of the section of the pole piece; the detection method is simple, reliable in result, small in detection equipment investment, convenient to operate and suitable for rapid detection of the pole piece bonding effect in the pole piece large-scale production process.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, specifically to the field of detection of battery electrode sheets, and particularly to a rapid detection method for the bonding effect of battery electrode sheets. Background Art

[0002] The preparation processes of battery electrode sheets are mainly divided into two types: dry process and wet process. Among them, the dry process preparation is to first prepare a self-supporting film, and then thermocompression bond the film with the current collector to prepare the electrode sheet. The dry process for preparing electrode sheets does not use solvents, which can eliminate processes such as coating, drying, and solvent recovery, thereby reducing manufacturing costs and improving production efficiency; the electrodes prepared by the dry process can have a higher tap density, thus accommodating more active substances (adhesive materials) and improving the energy density of the battery. Therefore, the dry electrode process has natural advantages in the preparation of electrode sheets and electrolyte membranes for all-solid-state batteries, showing broad applicability and future potential in the field of advanced battery manufacturing.

[0003] However, the dry process for preparing electrode sheets is a composite bonding method between surfaces through the lamination of the film and the current collector. This composite bonding method is very likely to have internal non-bonding situations. At the same time, after long-term cycling of all electrodes, the adhesive material may fall off from the current collector. Both non-bonding and detachment can be considered as insufficient bonding between the adhesive material and the current collector, which not only affects the cycle life and energy density of the battery, but may also cause excessive local current in the battery, generating heat and increasing the risk of thermal runaway. It can be seen that the bonding effect of battery electrode sheets directly affects battery performance and safety.

[0004] It is difficult to judge the bonding effect of battery electrode sheets by the naked eye, and it can only be detected by testing means. Currently, the main method for detecting non-bonding of electrode sheets is to judge through SEM images of the electrode sheet cross-section. Although this method has high accuracy, during the detection process, it is necessary to first perform argon ion polishing on the electrode sheet cross-section and then observe the cross-section through SEM. It has the defects of long detection time and high cost, which is obviously extremely unfavorable for the rapid production and popularization and application of battery electrode sheets. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the existing detection methods for the bonding effect of battery electrode sheets, which have long detection time and high cost, and propose a rapid detection method for the bonding effect of battery electrode sheets.

[0006] To achieve the above-mentioned invention purpose, the present invention provides a rapid detection method for the bonding effect of battery electrode sheets, including the following steps: S1. Fix the cut electrode sheet to be tested; S2. Use an image measuring instrument to obtain the image of the cross-section of the electrode sheet to be tested; S3. Use a CCD image sensor to magnify the cross-sectional image of the electrode plate obtained in step S3 to obtain a magnified image picture. S4. Analyze the magnified image picture to judge the bonding effect of the cross-section of the electrode plate to be measured.

[0007] A rapid detection method for the bonding effect of a battery electrode plate provided by the present invention utilizes the principle that different substances have different characteristics of light reflection, transmission and absorption, resulting in different optical images of the two bonding substances on the cross-section of the electrode plate. An image tester is used to obtain the image picture of the cross-section of the electrode plate, and through targeted recognition and processing of the image picture of the cross-section of the electrode plate, rapid and accurate judgment of the bonding effect of the electrode plate is realized. This detection method can rapidly and accurately judge the bonding effect of the electrode plate, and the method is simple, the result is reliable, the investment in detection equipment is small, the operation is convenient, and it is suitable for the rapid detection of the bonding effect of the electrode plate during the large-scale production process of the electrode plate.

[0008] Among them, before step S1, there is also step S0: cut the electrode plate to be measured to expose the cross-section of the electrode plate, and clean the cross-section of the electrode plate. Through cleaning, it can be ensured as much as possible that there is no obvious dust and foreign matter on the cross-section of the electrode plate.

[0009] Preferably, when cutting the electrode plate to be measured, cut it along the thickness direction of the electrode plate. In the preferred cutting method, the cross-section after cutting can more accurately reflect the bonding effect between the current collector and the diaphragm.

[0010] Preferably, the cross-section is cleaned by blowing to remove dust and foreign matter. While having a good cleaning effect on dust and foreign matter, it can also avoid affecting the cross-section morphology, thus ensuring the accuracy of the detection result.

[0011] Among them, in step S1, preferably, a fixture is used to fix the electrode plate to be measured, and after fixing, the upper surface of the fixture is lower than the cross-section of the electrode plate. More preferably, after fixing, the upper surface of the fixture is more than 1 mm lower than the cross-section of the electrode plate, which can reduce the influence of the image of the upper surface of the fixture on the cross-section analysis result during cross-section observation.

[0012] Among them, in step S2, preferably, the light intensity of the image tester is 3500 - 4000 lux.

[0013] Preferably, an imaging tester with a 2X - 7X magnifying lens is used to obtain the image of the cross-section of the electrode sheet to be tested; more preferably, when using the imaging tester to obtain the image of the cross-section of the electrode sheet to be tested, first use a magnifying lens less than 2X to focus on the electrode sheet (select an appropriate light source and magnifying lens, and cooperate with the use of the lens lifting button to make the image contour of the electrode sheet to be tested clear in the lens), and then use a 2X - 7X magnifying lens to collect the image of the cross-section of the electrode sheet; it can quickly focus, shorten the image acquisition time, and better obtain a complete cross-section image.

[0014] Among them, in step S3, preferably, the method of analyzing the image picture includes: obtaining the RGB gray value of the pixel points in the image picture; judging whether the pixel points belong to black pixel points according to the RGB gray value of the pixel points; if there are black pixel points on the bonding interface between the current collector and the bonding material, then connect the black pixel points adjacent to the non-black pixel points on the bonding interface to obtain the black area on the bonding interface in the image picture; calculate the projection length of the black area on the current collector of the electrode sheet and mark it.

[0015] Preferably, the method of judging whether a pixel point belongs to a black pixel point is: when the RGB gray value of the pixel point is lower than 50, the pixel point is a black pixel point, and when the RGB gray value of the pixel point is not lower than 50, the pixel point is a non-black pixel point.

[0016] Among them, in step S4, preferably, the method of judging the bonding effect of the cross-section of the electrode sheet to be tested is: when the maximum projection length of the black area on the bonding interface between the current collector and the bonding material is less than 10 μm (including the case where there is no black area), the bonding effect of the cross-section of the electrode sheet to be tested is excellent; when the maximum projection length of the black area on the bonding interface between the current collector and the bonding material is 10 - 20 μm, the bonding effect of the cross-section of the electrode sheet to be tested is qualified; when there is a black area with a projection length greater than 20 μm on the bonding interface between the current collector and the bonding material, the bonding effect of the cross-section of the electrode sheet to be tested is unqualified; this judgment method is obtained according to the influence degree of the bonding effect on the performance of the electrode sheet, and can quickly, efficiently and accurately judge and classify the bonding effect of the electrode sheet.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. A rapid detection method for the bonding effect of a battery electrode sheet provided by the present invention utilizes the principle that different substances have different light reflection, transmission and absorption characteristics, resulting in different optical images of the two bonding substances on the cross-section of the electrode sheet. An imaging tester is used to obtain the image picture of the cross-section of the electrode sheet, and through the targeted recognition and processing of the image picture of the cross-section of the electrode sheet, the rapid and accurate judgment of the bonding effect of the electrode sheet is realized.

[0018] 2. A rapid detection method for the bonding effect of battery electrode sheets provided by the present invention can quickly and accurately judge the bonding effect of electrode sheets, with simple method, reliable results, small investment in detection equipment and convenient operation, and is applicable to the rapid detection of the bonding effect of electrode sheets during large-scale production of electrode sheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flowchart of the rapid detection method for the bonding effect of battery electrode sheets in Embodiment 1 of the present invention; Figure 2 is an image picture of the current collector observed by using the rapid detection method for the bonding effect of battery electrode sheets in Embodiment 1 of the present invention; Figure 3 is an image picture of electrode sheet sample 1 observed by using the rapid detection method for the bonding effect of battery electrode sheets in Embodiment 1 of the present invention; Figure 4 is an image picture of electrode sheet sample 2 observed by using the rapid detection method for the bonding effect of battery electrode sheets in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The present invention will be further described in detail below in combination with test examples and specific embodiments. However, it should not be understood that the scope of the above-mentioned subject matter of the present invention is limited to the following embodiments. All technologies implemented based on the content of the present invention belong to the scope of the present invention.

[0021] Embodiment 1 A rapid detection method for the bonding effect of battery electrode sheets (the flowchart is as Figure 1 shown) includes the following steps: S1. Fix the electrode sheet to be tested by using a fixture, and the upper surface of the fixture is 1 mm lower than the cross-section of the electrode sheet; S2. Set the parameters of the image tester (LED lamp with a light source intensity of 4000 lux). First, focus on the electrode sheet with a 0.7-fold lens, and then use a 4.5-fold lens to collect images of the cross-section of the electrode sheet. Magnify the cross-section image of the electrode sheet to 200 times through a CCD image sensor to obtain an image picture of the cross-section of the electrode sheet to be tested; S3. Use image processing software to obtain the RGB gray values of the pixel points in the image picture; according to the RGB gray values, judge whether the pixel points belong to black pixel points (pixel points with RGB gray values lower than 50); if there are black pixel points, connect the continuous black pixel points to obtain the black area in the image picture, use a computer to calculate the projection length of the black area on the current collector of the electrode sheet, and mark it; S4. When the maximum projected length of the black area on the bonding interface between the current collector and the bonding material is less than 10 μm, the bonding effect of the cross-section of the electrode sheet to be tested is excellent; when the maximum projected length of the black area on the bonding interface between the current collector and the bonding material is 10 - 20 μm, the bonding effect of the cross-section of the electrode sheet to be tested is qualified; when there is a black area with a projected length greater than 20 μm on the bonding interface between the current collector and the bonding material, the bonding effect of the cross-section of the electrode sheet to be tested is unqualified.

[0022] Example 2 A rapid detection method for the bonding effect of battery electrode sheets includes the following steps: S1. Cut the electrode sheet to be tested along the thickness direction of the sheet to expose the cross-section of the sheet; clean the cross-section of the sheet by blowing air with a rubber pipette bulb to ensure that there is no obvious dust and foreign matter on the cross-section of the sheet. S2. Fix the electrode sheet to be tested with a fixture, and the upper surface of the fixture is 2 mm lower than the cross-section of the sheet. S3. Set the parameters of the image tester (LED lamp with a light source intensity of 3500 lux), first focus on the electrode sheet with a 1.2x lens, then use a 7x lens to collect images of the cross-section of the electrode sheet, and magnify the cross-section image of the sheet to 200 times through a CCD image sensor to obtain an image picture of the cross-section of the electrode sheet to be tested. S4. Use image processing software to obtain the RGB gray values of the pixel points in the image picture; according to the RGB gray values, determine whether the pixel points belong to black pixel points (pixel points with an RGB gray value lower than 50); if there are black pixel points, connect the continuous black pixel points to obtain the black area in the image picture, use a computer to calculate the projected length of the black area on the current collector of the electrode sheet, and mark it. S5. When the maximum projected length of the black area on the bonding interface between the current collector and the bonding material is less than 10 μm, the bonding effect of the cross-section of the electrode sheet to be tested is excellent; when the maximum projected length of the black area on the bonding interface between the current collector and the bonding material is 10 - 20 μm, the bonding effect of the cross-section of the electrode sheet to be tested is qualified; when there is a black area with a projected length greater than 20 μm on the bonding interface between the current collector and the bonding material, the bonding effect of the cross-section of the electrode sheet to be tested is unqualified.

[0023] Example 3 A rapid detection method for the bonding effect of battery electrode sheets includes the following steps: S1. Cut the electrode sheet to be tested along the thickness direction of the sheet to expose the cross-section of the sheet; clean the cross-section of the sheet by blowing air with a rubber pipette bulb to ensure that there is no obvious dust and foreign matter on the cross-section of the sheet. S2. Fix the electrode sheet to be tested with a fixture, and the upper surface of the fixture is 1 mm lower than the cross-section of the sheet. S3. Set the parameters of the image tester (LED lamp with a light source intensity of 4000 lux). First, use a 0.7x lens to focus on the pole piece, and then use a 2x lens to collect images of the cross-section of the electrode pole piece. Magnify the cross-section image of the pole piece to 300 times through a CCD image sensor to obtain an image of the cross-section of the electrode pole piece to be tested; S4. Use image processing software to obtain the RGB grayscale values of the pixel points in the image; according to the RGB grayscale values, determine whether the pixel points belong to black pixel points (pixel points with RGB grayscale values lower than 50); if there are black pixel points, connect the continuous black pixel points to obtain the black area in the image, and use a computer to calculate the projected length of the black area on the current collector of the pole piece and mark it; S5. When the maximum projected length of the black area on the bonding interface between the current collector and the bonding material is less than 10 μm, the bonding effect of the cross-section of the electrode pole piece to be tested is excellent; when the maximum projected length of the black area on the bonding interface between the current collector and the bonding material is 10 - 20 μm, the bonding effect of the cross-section of the electrode pole piece to be tested is qualified; when there is a black area with a projected length greater than 20 μm on the bonding interface between the current collector and the bonding material, the bonding effect of the cross-section of the electrode pole piece to be tested is unqualified.

[0024] Comparative Example 1 Use SEM to detect the bonding property of the cross-section of the pole piece. The specific method includes: S1. Use argon ion polishing technology to prepare the electrode pole piece to be tested and expose the cross-section of the pole piece; S2. Use conductive glue to paste the pole piece on a 90° cross-section internal thread sample stage with the cross-section facing up; S3. Put the sample stage with the sample into a sputtering coater for sputtering; S4. Set the acceleration voltage of the SEM to 15 KV and the magnification to 200 times, and observe whether there is an unbonded area between the bonding material and the current collector.

[0025] Experimental Example: Preparation of pole piece samples: Mix graphite, PTFE binder, and conductive agent evenly in a mass ratio of 95:5:3 and then fibrillate. The thickness of the fibrillated powder after thinning into a film is 100 - 110 μm. The film is thermally flat-pressed and compounded with a coated carbon current collector to prepare a dry electrode pole piece. By adjusting the temperature, time, and pressure during the rolling and compounding process, a compaction density of 1.5 g / cm 3The pole pieces, among which, the hot flat pressing parameters of pole piece sample 1 (with diaphragms hot-pressed on both sides of the current collector) are 100°C, 4t, 1 min; the hot flat pressing parameters of pole piece sample 2 (with a diaphragm hot-pressed on one side of the current collector) are 100°C, 6t, 1 min. Cut sample 1 and sample 2 into small strips of 2 cm * 5 cm, and use the detection methods in Examples 1-3 and Comparative Example 1 to detect the composite (bonding) situation of the detection section, and record the detection time, cost and results as shown in Table 1; among them, the image pictures of the current collector, pole piece sample 1, and pole piece sample 2 observed by using the detection method of Example 1 are respectively as Figure 2 , Figure 3 , Figure 4 shown.

[0026] Table 1 Statistical results of the detection methods in Examples 1-3 and Comparative Example 1

[0027] Analyzing the above statistical results, it can be seen that although the prior art in the comparative example can also accurately judge the bonding situation of the paste interface, it has the defects of long detection time and high cost. The detection method of the present invention utilizes the different characteristics of different substances in light reflection, transmission and absorption, resulting in different optical images of the two bonding substances at the pole piece section. An image tester is used to obtain the image pictures of the pole piece section, and through the targeted recognition and processing of the image pictures of the pole piece section, it can not only quickly and accurately judge the bonding interface situation of the electrode pole piece, but also has the advantages of simple method, reliable results, small investment in detection equipment, and convenient operation, and is suitable for the rapid detection of the bonding effect of pole pieces in the large-scale production process of pole pieces.

Claims

1. A rapid detection method for the bonding effect of battery pole pieces, characterized in that: The following steps are involved: S1, fixing the cut electrode piece to be tested; S2, using an image tester to obtain an image of a cross section of the electrode to be tested; S3, using a CCD image sensor to amplify the electrode cross-section image obtained in step S2 to obtain an amplified image; S4. Analyze the enlarged image to determine the bonding effect of the electrode section to be tested.

2. The rapid detection method according to claim 1, characterized in that: Before step S1, the method further includes step S0: cutting the electrode piece to be tested to expose the cross section of the electrode piece, and cleaning the cross section of the electrode piece.

3. The rapid detection method according to claim 2, characterized in that: In step S0, when cutting the electrode sheet to be tested, the cutting is performed along the thickness direction of the electrode sheet; the cross section is cleaned by blowing to remove dust and foreign matter.

4. The rapid detection method according to claim 1, characterized in that: In step S1, a fixture is used to fix the electrode piece to be tested, and after fixation, the upper surface of the fixture is lower than the cross section of the electrode piece.

5. The rapid detection method according to claim 4, characterized in that: After fixation, the upper surface of the fixture is more than 1 mm lower than the cross section of the electrode piece.

6. The rapid detection method according to claim 1, characterized in that: In step S2, the light intensity of the image tester is 3500-4000 lux.

7. The rapid detection method according to claim 1, characterized in that: In step S2, an image tester with a 2X-7X magnification microscope is used to obtain an image of the cross section of the electrode to be tested.

8. The rapid detection method according to claim 1, characterized in that: In step S3, the method for analyzing the image includes: obtaining the RGB grayscale value of the pixel in the image; judging whether the pixel is a black pixel according to the RGB grayscale value of the pixel; if there is a black pixel on the bonding interface between the current collector and the adhesive material, connecting the black pixel adjacent to the non-black pixel on the bonding interface to obtain the black area on the bonding interface in the image; calculating the projection length of the black area on the electrode plate current collector and marking it.

9. The rapid detection method according to claim 8, characterized in that: The method for judging whether a pixel is a black pixel is as follows: when the RGB grayscale value of a pixel is less than 50, the pixel is a black pixel; and when the RGB grayscale value of a pixel is not less than 50, the pixel is a non-black pixel.

10. The rapid detection method according to any one of claims 1 to 9, characterized in that: In step S4, the method for judging the bonding effect of the electrode section to be tested is: when the maximum projection length of the black area on the bonding interface between the current collector and the adhesive material is less than 10 μm, the bonding effect of the electrode section to be tested is excellent; When the maximum projection length of the black area on the bonding interface between the current collector and the bonding material is 10-20 μm, the bonding effect of the electrode section to be tested is qualified; When a black area with a projection length greater than 20 μm exists on the bonding interface between the current collector and the adhesive material, the bonding effect of the electrode section to be tested is unqualified.

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