Thermochromic composite coating for lithium battery graphite negative electrode defect detection and preparation method and application thereof

Abstract

The invention discloses a thermochromic composite coating for lithium battery graphite negative electrode defect detection, the thermochromic composite coating comprises the following components by weight: 5-15% of a matrix, 20-40% of a functional material, 0.05-0.2% of a heat conduction material, 0.1-0.5% of a dispersant and the balance of a deionized water solvent, the matrix is a water-soluble polymer, the functional material is a thermochromic microcapsule, and the heat conduction material is a carbon nanotube. The method has the advantages that the detection of the graphite negative electrode of the curved-surface lithium battery is supported, the detection cost is relatively low, the detection resolution is higher, and the detection speed is higher.

Description

Technical Field

[0001] This invention relates to the field of lithium battery manufacturing technology, and in particular to a thermochromic composite coating for detecting defects in graphite anodes of lithium batteries, its preparation method, and its application. Background Technology

[0002] Interlayer defects (such as microcracks and abnormal porosity) in graphite anode materials for lithium batteries can lead to uneven lithium-ion intercalation, causing capacity decay. The industry requires the defect area ratio to be <0.5%. Traditional detection relies on scanning electron microscopy (SEM) or X-ray diffraction (XRD), which requires specialized equipment and the testing cost is >500 yuan per sample.

[0003] Existing technologies disclose conductive ink development and ultrasonic transmission methods for detecting interlayer defects in graphite anode materials for lithium batteries, wherein: Conductive ink method: ink containing silver nanowires is coated on the surface of the negative electrode and the defect area is identified by conductive zebra pattern. However, silver nanowires are expensive (>20 yuan / time) and cannot detect subsurface defects. The process is time-consuming: a single test takes more than 30 minutes and cannot provide real-time feedback on production quality.

[0004] Ultrasonic method: This method measures the change in the propagation speed of ultrasonic waves in a material to estimate the internal porosity. It requires precise probe positioning, takes more than 30 minutes per sample, and has an error rate of more than 15%. Summary of the Invention

[0005] The purpose of this invention is to provide a thermochromic composite coating for detecting defects in graphite anodes of lithium batteries, its preparation method and application, which supports the detection of curved graphite anodes of lithium batteries, while having relatively low detection cost, higher detection resolution and faster detection speed.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A thermochromic composite coating for detecting defects in graphite anodes of lithium batteries, characterized in that it comprises the following components by weight percentage: 5-15% matrix, 20-40% functional material, 0.05-0.2% thermally conductive material, 0.1-0.5% dispersant, and the balance being a deionized water solvent, wherein the matrix is ​​a water-soluble polymer, the functional material is thermochromic microcapsules, and the thermally conductive material is carbon nanotubes.

[0007] Preferably, the matrix is ​​a water-soluble polymer, namely polyvinyl alcohol, with a molecular weight range of 10~100kDa and a degree of alcoholysis of 88~99mol.

[0008] Preferably, the thermochromic microcapsule has a core-shell structure, comprising a core and a shell. The core comprises the following components by weight percentage: 0.5-2% leuco dye, 2-10% developer, and the balance being a mixed solvent. The shell is a mixture of gelatin and gum arabic in a 1:1 mass ratio, and the mass of the shell is 2-4 times the mass of the core. The thermochromic microcapsule is prepared by mixing the leuco dye, developer, and mixed solvent, and then stirring at 60-70°C for 15-20 minutes until completely dissolved. A homogeneous core material solution was prepared, and then a gelatin aqueous solution was added to the core material solution at a speed of 2000-3000 rpm. The mixture was emulsified for 5-10 minutes to form an oil-in-water emulsion. A gum arabic solution was then slowly added to the emulsion. The pH of the system was adjusted to 4.0-4.5 with dilute acetic acid. After cooling to below 10°C, 1% of glutaraldehyde by mass of the system was added as a crosslinking agent. The mixture was stirred for 1 hour, filtered, washed, and vacuum dried at 40°C to obtain black thermochromic microcapsule powder with a particle size distribution of 5-20 μm.

[0009] Preferably, the leuco dye is crystal violet lactone, the color developer is bisphenol A, and the mixed solvent is a mixture of tetradecyl alcohol and hexadecyl alcohol in a mass ratio of 1:1.

[0010] Preferably, the carbon nanotubes are single-walled or multi-walled CNTs with a length of 1~10 μm and a diameter of 1~10 nm.

[0011] Preferably, the critical temperature of the thermochromic composite coating is 43~47℃, and the color change range is from black to colorless.

[0012] Preferably, the dispersant is SDBS or Tween-80.

[0013] A method for preparing a thermochromic composite coating for detecting defects in graphite anodes of lithium batteries includes the following steps: S1. Add the matrix to deionized water and stir at 80-90℃ for 1-2 hours until completely dissolved, then cool to room temperature; S2, add dispersant to matrix solution and stir at room temperature for 10-15 minutes; S3, add thermally conductive material, and ultrasonically disperse using 300-500W power for 30-40 minutes; S4, add thermochromic microcapsules and stir at a low speed of 500-800 rpm for 20-30 minutes; S5 is filtered through a 0.22μm organic filter membrane to remove undispersed thermally conductive material agglomerates and microcapsule impurities, resulting in a thermochromic composite coating.

[0014] An application of a thermochromic composite coating for detecting defects in graphite anodes of lithium batteries involves coating the graphite anode of a lithium battery with the thermochromic composite coating, which changes color under thermal stimulation, thereby quickly identifying defects on the surface of the graphite anode of the lithium battery.

[0015] Preferably, the specific testing steps are as follows: Use compressed air to blow away dust from the surface of the graphite negative electrode of the lithium battery, then wipe the surface with anhydrous ethanol to remove oil stains, and let it air dry at room temperature for 5-10 minutes. The coating solution is loaded into the spray gun and sprayed 1-2 times at a uniform speed along the length of the graphite negative electrode of the lithium battery under the conditions of spraying pressure of 0.3-0.5MPa, spraying distance of 15-25cm and spraying speed of 5-10cm / s to form a composite coating with a dry film thickness of 10-12μm. Place the coated negative electrode sheet under an infrared lamp with a power of 30~80W, control the distance between the lamp and the negative electrode sheet to be 10~15cm, and irradiate it evenly for 20~40 seconds; High-definition cameras are used to capture images of the graphite anode surface of lithium batteries. Image analysis software is used to identify color differences. In normal areas, the local temperature is higher than the color change temperature due to heat conduction, and the coating is colorless. In defective areas, the temperature is lower than the color change temperature due to impaired heat conduction, and the coating remains black. The area and number of black areas are counted to complete defect detection.

[0016] In summary, the beneficial effects of this invention are: it can detect curved lithium battery graphite anodes, while the detection cost is relatively low, the detection resolution is higher, and the detection speed is faster. Detailed Implementation

[0017] The specific embodiments of the present invention will be further described below. These embodiments do not constitute a limitation on the present invention.

[0018] A thermochromic composite coating for detecting defects in graphite anodes of lithium batteries comprises the following components by weight percentage: 5-15% matrix, 20-40% functional material, 0.05-0.2% thermally conductive material, 0.1-0.5% dispersant, and the balance being a deionized water solvent. The matrix is ​​a water-soluble polymer, the functional material is thermochromic microcapsules, and the thermally conductive material is carbon nanotubes.

[0019] The matrix is ​​a water-soluble polymer, polyvinyl alcohol, with a molecular weight range of 10~100kDa and a degree of alcoholysis of 88~99mol.

[0020] The thermochromic microcapsules have a core-shell structure, comprising a core and a wall. The core consists of the following components by weight percentage: 0.5–2% leuco dye, 2–10% developer, and the balance being a mixed solvent. The wall is a mixture of gelatin and gum arabic in a 1:1 mass ratio, with the wall mass being 2–4 times the mass of the core. The thermochromic microcapsules are prepared by mixing the leuco dye, developer, and mixed solvent, and then stirring at 60–70°C for 15–20 minutes until completely dissolved, forming a homogeneous core material solution. Next, the core material solution is added to the gelatin aqueous solution at a speed of 2000-3000 rpm, and emulsified for 5-10 minutes to form an oil-in-water emulsion. Then, the gum arabic solution is slowly added to the above emulsion, and the pH value of the system is adjusted to 4.0-4.5 with dilute acetic acid. After cooling to below 10℃, 1% of the total mass of glutaraldehyde is added as a crosslinking agent, and the mixture is stirred for 1 hour. After filtration, washing, and vacuum drying at 40℃, black thermochromic microcapsule powder with a particle size distribution of 5-20 μm is obtained.

[0021] The leuco dye is crystal violet lactone, the color developer is bisphenol A, and the mixed solvent is a mixture of tetradecyl alcohol and hexadecyl alcohol in a mass ratio of 1:1.

[0022] Carbon nanotubes are single-walled or multi-walled CNTs, with a length of 1~10 μm and a diameter of 1~10 nm.

[0023] The critical temperature of the thermochromic composite coating is 43~47℃, and the color change range is from black to colorless.

[0024] The dispersant is SDBS or Tween-80.

[0025] A method for preparing a thermochromic composite coating for detecting defects in graphite anodes of lithium batteries includes the following steps: S1. Add the matrix to deionized water and stir at 80-90℃ for 1-2 hours until completely dissolved, then cool to room temperature; S2, add dispersant to matrix solution and stir at room temperature for 10-15 minutes; S3, add thermally conductive material, and ultrasonically disperse using 300-500W power for 30-40 minutes; S4, add thermochromic microcapsules and stir at a low speed of 500-800 rpm for 20-30 minutes; S5 is filtered through a 0.22μm organic filter membrane to remove undispersed thermally conductive material agglomerates and microcapsule impurities, resulting in a thermochromic composite coating.

[0026] An application of a thermochromic composite coating for detecting defects in graphite anodes of lithium batteries involves coating the graphite anode of a lithium battery with the thermochromic composite coating, which changes color under thermal stimulation, thereby quickly identifying defects on the surface of the graphite anode of the lithium battery.

[0027] An application of a thermochromic composite coating for defect detection in graphite anodes of lithium batteries, the specific detection steps are as follows: Use compressed air to blow away dust from the surface of the graphite negative electrode of the lithium battery, then wipe the surface with anhydrous ethanol to remove oil stains, and let it air dry at room temperature for 5-10 minutes. The coating solution is loaded into the spray gun and sprayed 1-2 times at a uniform speed along the length of the graphite negative electrode of the lithium battery under the conditions of spraying pressure of 0.3-0.5MPa, spraying distance of 15-25cm and spraying speed of 5-10cm / s to form a composite coating with a dry film thickness of 10-12μm. Place the coated negative electrode sheet under an infrared lamp with a power of 30~80W, control the distance between the lamp and the negative electrode sheet to be 10~15cm, and irradiate it evenly for 20~40 seconds; High-definition cameras are used to capture images of the graphite anode surface of lithium batteries. Image analysis software is used to identify color differences. In normal areas, the local temperature is higher than the color change temperature due to heat conduction, and the coating is colorless. In defective areas, the temperature is lower than the color change temperature due to impaired heat conduction, and the coating remains black. The area and number of black areas are counted to complete defect detection.

[0028] Example 1 A thermochromic composite coating for detecting defects in graphite anodes of lithium batteries: 5% polyvinyl alcohol, 40% thermochromic microcapsules, 0.2% carbon nanotubes, 0.1% SDBS, and the balance being a deionized water solvent.

[0029] Testing steps: Purge with 0.2MPa compressed air, wipe with anhydrous ethanol and air dry for 8 minutes; Spraying: Pressure 0.4MPa, distance 20cm, speed 8cm / s, one spray, dry film thickness 10μm; Infrared irradiation: 50W infrared lamp, distance 12cm, irradiation for 30 seconds (infrared thermal imager monitoring: normal area temperature 48℃, defect area temperature 42℃). Recognition: The camera captured images at a resolution of 1920×1080, analyzed using ImageJ.

[0030] Defect identification rate: 100% (all prefabricated defects were identified); Detection time: 38 seconds / piece; Coating residue: 0.3% residue after water washing.

[0031] Example 2 A thermochromic composite coating for detecting defects in graphite anodes of lithium batteries: 7% polyvinyl alcohol, 30% thermochromic microcapsules, 0.1% carbon nanotubes, 0.2% Tween-80 and the balance being deionized water solvent.

[0032] Testing steps: Purge with 0.2MPa compressed air, wipe with anhydrous ethanol and air dry for 8 minutes; Spraying: Pressure 0.4MPa, distance 20cm, speed 8cm / s, one spray, dry film thickness 10μm; Infrared irradiation: 50W infrared lamp, distance 12cm, irradiation for 30 seconds (infrared thermal imager monitoring: normal area temperature 48℃, defect area temperature 42℃). Recognition: The camera captured images at a resolution of 1920×1080, analyzed using ImageJ.

[0033] Defect identification rate: 98%; Detection time: 36 seconds / piece; Coating residue: 0.2% residue after water washing.

[0034] Example 3 A thermochromic composite coating for detecting defects in graphite anodes of lithium batteries: 15% polyvinyl alcohol, 20% thermochromic microcapsules, 0.05% carbon nanotubes, 0.5% Tween-80 and the balance being deionized water solvent.

[0035] Testing steps: Purge with 0.2MPa compressed air, wipe with anhydrous ethanol and air dry for 8 minutes; Spraying: Pressure 0.4MPa, distance 20cm, speed 8cm / s, one spray, dry film thickness 10μm; Infrared irradiation: 50W infrared lamp, distance 12cm, irradiation for 30 seconds (infrared thermal imager monitoring: normal area temperature 48℃, defect area temperature 42℃). Recognition: The camera captured images at a resolution of 1920×1080, analyzed using ImageJ.

[0036] Defect identification rate: 99%; Detection time: 39 seconds / piece; Coating residue: 0.1% residue rate after water washing.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the scope of its essence and protection. Such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A thermochromic composite coating for defect detection in lithium battery graphite anodes, characterized by, According to the weight percentage, the following components are included: 5-15% base, 20-40% functional material, 0.05-0.2% heat-conducting material, 0.1-0.5% dispersant, and the rest is deionized water solvent, the base is water-soluble polymer, the functional material is thermochromic microcapsule, and the heat-conducting material is carbon nanotube.

2. A thermochromic composite coating for defect detection of graphite anode of lithium battery according to claim 1, characterized in that: The base is water-soluble polymer, which is polyvinyl alcohol, the molecular weight of polyvinyl alcohol is in the range of 10-100 kDa, and the alcoholysis degree is 88-99 mol%.

3. A thermochromic composite coating for defect detection of graphite anode of lithium battery according to claim 1, characterized in that: The thermochromic microcapsule is a core-shell structure, including a capsule core and a capsule wall, the capsule core includes the following components by weight percentage: 0.5-2% leuco dye, 2-10% color developer, and the rest is mixed solvent, the capsule wall is a mixed material of gelatin and gum arabic with a mass ratio of 1:1, the mass of the capsule wall is 2-4 times the mass of the capsule core, and the preparation method of the thermochromic microcapsule is: mixing the leuco dye, color developer and mixed solvent, stirring at 60-70℃ for 15-20 minutes until completely dissolved to form a uniform core material solution, then adding the core material solution into the gelatin aqueous solution at a speed of 2000-3000 rpm, emulsifying for 5-10 minutes to form an oil-in-water emulsion, then slowly adding the gum arabic solution into the above emulsion, adjusting the pH value of the system to 4.0-4.5 with dilute acetic acid, cooling to below 10℃, then adding 1% glutaraldehyde as a crosslinking agent based on the total mass of the system, stirring for 1 hour, filtering, washing, and vacuum drying at 40℃ to obtain black thermochromic microcapsule powder with a particle size distribution of 5-20μm.

4. A thermochromic composite coating for defect detection of graphite anode of lithium battery according to claim 3, characterized in that: The leuco dye is crystal violet lactone, the color developer is bisphenol A, and the mixed solvent is a mixture of tetradecanol and hexadecanol with a mass ratio of 1:

1.

5. A thermochromic composite coating for defect detection of lithium battery graphite anodes according to claim 1, characterized in that: The carbon nanotube is single-walled or multi-walled CNT, with a length of 1-10μm and a diameter of 1-10nm.

6. A thermochromic composite coating for defect detection of lithium battery graphite anodes according to claim 1, characterized in that: The critical temperature of the thermochromic composite coating is 43-47℃, and the color changing interval is from black to colorless.

7. A thermochromic composite coating for defect detection of lithium battery graphite anodes according to claim 1, characterized in that: The dispersant is SDBS or Tween-80.

8. The method for preparing a thermochromic composite coating for defect detection of graphite anodes for lithium batteries according to any one of claims 1 to 7, characterized in that: The steps include: S1, add the base to deionized water, stir at 80-90℃ for 1-2 hours until completely dissolved, and cool to room temperature; S2, add the dispersant to the base solution, stir at room temperature for 10-15 minutes; S3, add the heat-conducting material, and use ultrasonic dispersion with a power of 300-500W for 30-40 minutes; S4, add the thermochromic microcapsule, and stir at a low speed of 500-800rpm for 20-30 minutes; S5, filter with a 0.22μm organic filter membrane to remove the agglomerates of the heat-conducting material and the impurities of the microcapsule, and obtain the thermochromic composite coating.

9. Use of a thermochromic composite coating for the detection of defects in graphite anodes for lithium batteries according to any one of claims 1 to 7, characterized in that, The thermochromic composite coating is coated on the graphite negative electrode of lithium battery, which changes color under thermal stimulation, and quickly identifies the defects on the surface of the graphite negative electrode of lithium battery.

10. Use of a thermochromic composite coating for the detection of defects in graphite anodes for lithium batteries according to claim 9, characterized in that: The specific detection steps are: Use compressed air to blow the surface of the graphite negative electrode of lithium battery to remove dust, then wipe the surface with anhydrous ethanol to remove oil stains, and air dry at room temperature for 5-10 minutes; The coating solution is loaded into a spray gun, and the coated negative electrode is sprayed at a spray pressure of 0.3-0.5 MPa, a spray distance of 15-25 cm, and a spray speed of 5-10 cm / s for 1-2 times along the length direction of the lithium battery graphite negative electrode to form a composite coating with a dry film thickness of 10-12 μm. The coated negative electrode is placed under an infrared lamp with a power of 30-80 W, the distance between the lamp and the negative electrode is controlled to be 10-15 cm, and the negative electrode is uniformly irradiated for 20-40 seconds. The surface image of the lithium battery graphite negative electrode is collected by a high-definition camera, and the color difference is identified by image analysis software. The normal area has a local temperature greater than the discoloration temperature due to heat conduction, and the coating is colorless. The temperature of the defect area is less than the discoloration temperature due to the obstruction of heat conduction, and the coating remains black. The area and number of black areas are counted to complete the defect detection.