Conductive coating with improved gray value, battery aluminum foil and preparation method of conductive coating

Abstract

The invention discloses a conductive coating with an improved gray value, a battery aluminum foil and a preparation method thereof, and the preparation method of the battery aluminum foil with the improved gray value comprises the following steps: S1, mixing a raw material formula with a solvent, and preparing conductive slurry through a grinding and dispersing technology; and S2, uniformly coating at least one side surface of an aluminum foil base material with the conductive slurry, and drying the aluminum foil base material coated with the conductive slurry until the solvent in the conductive slurry is completely removed to form a conductive coating, thereby obtaining the battery aluminum foil with the increased gray value. According to the preparation method, the high gray value and small resistance of the battery aluminum foil can be kept at the same time, so that the battery aluminum foil has high visual recognition degree, and the conductivity of the battery aluminum foil can be kept.

Description

Technical Field

[0001] This invention relates to the field of aluminum processing technology, and in particular to a conductive coating with improved grayscale value, battery aluminum foil, and a method for preparing the same. Background Technology

[0002] With the development of industries such as new energy vehicles, energy storage systems and electronic equipment, the demand for lithium-ion batteries, which are the core power source for these devices, is continuously increasing.

[0003] Battery aluminum foil is an aluminum foil substrate used as a current collector in lithium-ion batteries. It possesses characteristics such as high conductivity and high tensile strength. Furthermore, by coating the surface of the aluminum foil substrate with a conductive coating composed of conductive agents and binders, the conductivity and adhesion between the current collector and the electrode active material can be effectively improved, thereby enhancing the rate performance and cycle life of lithium-ion batteries. The aluminum foil substrate coated with the conductive coating is hereinafter referred to as battery aluminum foil.

[0004] Due to the large demand for lithium-ion batteries, they need to be produced through automated machinery. The automated machinery production process for lithium-ion batteries requires positioning, defect detection, and dimensional measurement of the battery aluminum foil, which serves as the current collector.

[0005] However, because the conductive coating of battery aluminum foil is mainly composed of dark black conductive carbon black, its surface color is dark and its gray value is low. This results in low recognition of battery aluminum foil, which can easily lead to misjudgment, inaccurate positioning, or missed defects by the vision system of automated machinery, seriously affecting the production qualification rate and efficiency of lithium-ion batteries.

[0006] To improve the grayscale value of battery aluminum foil, the existing technology uses a method of reducing the amount of conductive agent in the conductive coating. While this can improve the grayscale value of the battery aluminum foil, it also increases the resistance of the battery aluminum foil, resulting in relatively weak electrical performance of the finished lithium-ion battery.

[0007] Therefore, there is an urgent need for a battery aluminum foil with high grayscale value and low resistance to solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a conductive coating with improved grayscale value, a battery aluminum foil, and a method for preparing the same, in order to solve the problem that the battery aluminum foil used in lithium-ion batteries in the prior art cannot simultaneously maintain its high grayscale value and low resistance.

[0009] In a first aspect, embodiments of the present invention provide a method for preparing battery aluminum foil with enhanced grayscale value, comprising the following steps: Step S1: Mix the raw material formula and solvent, and prepare a conductive paste by grinding and dispersing process; The components and mass percentages of the raw material formulation are as follows: conductive carbon black = 5~15%, flake graphite = 5~15%, graphene = 1~5%, and the remainder is binder; Step S2: The conductive paste is uniformly coated on at least one side of the aluminum foil substrate, and the aluminum foil substrate coated with the conductive paste is dried until the solvent in the conductive paste is completely removed to form a conductive coating, thereby obtaining the battery aluminum foil with improved gray value.

[0010] Preferably, in step S1, the particle size distribution of the conductive paste is controlled to meet the following conditions: D10 is 0.10~0.15μm, D50 is 0.50~0.60μm, and D90 is less than or equal to 3.00μm; the flake graphite is flake graphite with mirror reflection effect, and its D50 particle size is 0.30~1.50μm.

[0011] Preferably, step S1 further includes: grinding and dispersing the conductive slurry and then subjecting the conductive slurry to ultrasonic treatment; wherein the power of the ultrasonic treatment is 500~1000W and the ultrasonic treatment time is 20~40min.

[0012] Preferably, in step S2, the coating method is gravure coating or microgravure coating.

[0013] Preferably, in step S2, the density of the conductive coating on the battery aluminum foil with increased grayscale value is 0.3~0.7 g / m³. 2 .

[0014] Secondly, embodiments of the present invention provide a conductive coating with enhanced grayscale value, wherein the components and mass percentages of the conductive coating with enhanced grayscale value are: conductive carbon black = 5~15%, flake graphite = 5~15%, graphene = 1~5%, and the balance is binder.

[0015] Preferably, the flake graphite is a scaly graphite with a mirror-reflective effect and has a D50 particle size of 0.30~1.50μm.

[0016] Preferably, the conductive coating that enhances grayscale value is in CIE L a The grayscale value in the b color space is greater than 32.

[0017] Thirdly, embodiments of the present invention provide a battery aluminum foil with enhanced grayscale value, comprising an aluminum foil substrate and a conductive coating coated on the surface of the aluminum foil substrate; wherein the battery aluminum foil is prepared by the preparation method of the battery aluminum foil with enhanced grayscale value as described above.

[0018] Compared with existing technologies, the method for preparing battery aluminum foil with improved grayscale value in this invention limits the composition and mass percentage of the raw material formula of the conductive paste. This allows for a reduction in the amount of conductive agent used, while the stable three-dimensional conductive network of conductive carbon black and graphene components compensates for the high resistance caused by point-to-point contact of sheet graphite. This ensures a low sheet resistance of the conductive coating, thus maintaining a low resistance while improving the grayscale value of the conductive coating. In other words, it maintains both high grayscale value and low resistance of the battery aluminum foil, giving it high visual recognition while preserving its conductivity. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 A schematic flowchart illustrating the steps of a method for preparing battery aluminum foil with enhanced grayscale value according to an embodiment of the present invention; Figure 2 The images show a comparison of the actual surface of the battery aluminum foil provided in Comparative Example 1 and the actual surface of the battery aluminum foil provided in Specific Example 1 of the present invention. In the images, (a) is a view of the actual surface of the battery aluminum foil provided in Comparative Example 1, and (b) is a view of the actual surface of the battery aluminum foil provided in Specific Example 1. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 This invention provides a conductive coating with improved grayscale value, the composition and mass percentage of which are: conductive carbon black = 5~15%, flake graphite = 5~15%, graphene = 1~5%, and the balance is binder.

[0022] Among them, a conductive coating with enhanced grayscale value is applied to an aluminum foil substrate to form a battery aluminum foil that serves as a current collector in a lithium-ion battery.

[0023] The flake graphite has a mirror-reflective effect, which can improve the gloss and grayscale value of the conductive coating, thus solving the problem of the conductive coating being too dark in the prior art.

[0024] The flake graphite can be selected from flaky graphite. Preferably, the flake graphite is KS-6 graphite. Since KS-6 graphite is mass-produced graphite, its cost is lower than that of other light-colored conductive agents such as silver powder, and it can significantly improve the gray value and brightness of the conductive coating, making it suitable for large-scale production.

[0025] The particle size (D50 particle size) corresponding to the cumulative particle size distribution of the flake graphite reaching 50% is 0.30~1.50μm.

[0026] The conductive coating that enhances grayscale value in CIE L a The grayscale value in the b color space is greater than 32. Preferably, the conductive coating with the enhanced grayscale value is in CIE L... a The grayscale value in the b color space is greater than 35.

[0027] Compared with existing technologies, the conductive coating with enhanced grayscale value in this invention improves the gloss and grayscale value of the conductive coating by limiting its composition and mass percentage and by ensuring that the flake graphite has a specular reflection effect. In addition, by reducing the amount of conductive agent, a stable three-dimensional conductive network can be constructed by conductive carbon black and graphene to compensate for the high resistance caused by point-to-point contact of flake graphite, thus ensuring the low sheet resistance of the conductive coating. In this way, the grayscale value of the conductive coating can be improved while maintaining its low resistance. Ultimately, after the conductive coating is applied to the aluminum foil substrate to form the battery aluminum foil, the battery aluminum foil can maintain a high grayscale value and low resistance, thus achieving high visual recognition and maintaining the conductivity of the battery aluminum foil.

[0028] Example 2 This invention provides a method for preparing battery aluminum foil with improved grayscale value, combined with... Figure 1 As shown, it includes the following steps: S1. Mix the raw material formula and solvent, and prepare a conductive slurry through a grinding and dispersion process.

[0029] The raw material formulation comprises the following components and mass percentages: conductive carbon black = 5~15%, flake graphite = 5~15%, graphene = 1~5%, with the remainder being a binder; the flake graphite is a scaly graphite with a mirror-reflective effect and has a D50 particle size of 0.30~1.50μm.

[0030] In this embodiment, the components, mass percentages, particle size, and material parameters of the raw material formulation are the same as those of the conductive coating with improved grayscale value in Example 1, and will not be repeated here.

[0031] Solvents can be deionized water, N-methylpyrrolidone, or other solutions that can mix all the components in the raw material formulation together.

[0032] The particle size distribution of the conductive paste is controlled to meet the following conditions: The particle size (D10 particle size) corresponding to a cumulative particle size distribution of 10% is 0.10~0.15μm, the particle size corresponding to a cumulative particle size distribution of 50% is 0.50~0.60μm, and the particle size (D90 particle size) corresponding to a cumulative particle size distribution of 90% is less than or equal to 30μm.

[0033] Step S1 further includes: ultrasonic treatment of the conductive paste; wherein the ultrasonic treatment power is 500~1000W and the ultrasonic treatment time is 20~40min.

[0034] S2. The conductive paste is uniformly coated on at least one side of the aluminum foil substrate, and the aluminum foil substrate coated with the conductive paste is dried until the solvent in the conductive paste is completely removed to form a conductive coating, thereby obtaining the battery aluminum foil with improved gray value.

[0035] In this embodiment, all sides of the aluminum foil substrate are coated with the conductive paste.

[0036] The coating method is gravure coating or micro-gravure coating.

[0037] The density of the conductive coating on any side of the battery aluminum foil with improved grayscale value is 0.3~0.7 g / m³. 2 .

[0038] The conductive coating in this embodiment is the same as the conductive coating with grayscale value enhancement in Embodiment 1. Therefore, it can also achieve the technical effect of the conductive coating with grayscale value enhancement in Embodiment 1, which will not be elaborated here.

[0039] The obtained battery aluminum foil is used as a current collector in a lithium-ion battery.

[0040] This embodiment controls the particle size corresponding to the cumulative distribution of conductive slurry reaching 10%, 50%, and 90%, respectively, and combines this with ultrasonic treatment to ensure that each component in the raw material formulation can be uniformly dispersed in the conductive slurry. This avoids the situation where the conductive coating is rough or has uneven gloss due to agglomeration, thereby obtaining a conductive coating with high gray value and uniform surface.

[0041] Due to the conductive coating in CIE L a The grayscale value in the b color space is greater than 32, and it can form a sufficient color contrast with the electrode active material layer. Therefore, when the battery aluminum foil is used as a current collector for lithium-ion batteries and produced by automated machinery, it can improve the recognition and accuracy of the vision system during inspection, thereby improving the production qualification rate and efficiency of lithium-ion batteries.

[0042] To better demonstrate the technical effects of the battery aluminum foil preparation method that improves grayscale value in this embodiment, the following analysis will be conducted through two specific examples and two comparative examples.

[0043] Specific example one Step 1: Mix the following raw material formula and solvent, and prepare conductive paste by grinding and dispersing process.

[0044] The components and mass percentages of the raw material formulation are as follows: conductive carbon black = 10%, KS-6 graphite = 10%, graphene = 3%, acrylate binder = 77%; the solvent in the conductive slurry accounts for approximately 25% by mass.

[0045] The particle size corresponding to a cumulative particle size distribution of the conductive slurry reaching 10% is 0.12 μm, the particle size corresponding to a cumulative particle size distribution of the conductive slurry reaching 50% is 0.55 μm, and the particle size corresponding to a cumulative particle size distribution of the conductive slurry reaching 90% is 2.80 μm.

[0046] Step 2: The conductive paste is subjected to ultrasonic treatment; the ultrasonic treatment power is 800W and the ultrasonic treatment time is 30min.

[0047] Step 3: Using a micro-gravure coating machine, the ultrasonically treated conductive paste is evenly coated onto all sides of the aluminum foil substrate, and the aluminum foil substrate coated with the conductive paste is dried until the solvent in the conductive paste is completely removed, resulting in a battery aluminum foil with improved grayscale value containing the aluminum foil substrate and the conductive coating.

[0048] The conductive coating on any one side of the battery aluminum foil has a thickness of 1.50 μm and a surface density of 0.5 g / m². 2 .

[0049] Step 4: Use a colorimeter to measure the grayscale value of the conductive coating in the battery aluminum foil with improved grayscale value, and use a four-probe resistor to measure the sheet resistance of the conductive coating in the battery aluminum foil with improved grayscale value. Finally, the grayscale value of the conductive coating in the battery aluminum foil with improved grayscale value is 36.8, and the sheet resistance of the conductive coating in the battery aluminum foil with improved grayscale value is 45mΩ / □.

[0050] Specific example two Step 1: Mix the following raw material formula and solvent, and prepare conductive paste by grinding and dispersing process.

[0051] The components and mass percentages of the raw material formulation are as follows: conductive carbon black = 12%, KS-6 graphite = 7%, graphene = 3%, acrylate binder = 78%; the solvent in the conductive slurry accounts for approximately 25% by mass.

[0052] The particle size corresponding to a cumulative particle size distribution of the conductive slurry reaching 10% is 0.12 μm, the particle size corresponding to a cumulative particle size distribution of the conductive slurry reaching 50% is 0.55 μm, and the particle size corresponding to a cumulative particle size distribution of the conductive slurry reaching 90% is 2.80 μm.

[0053] Step 2: The conductive paste is subjected to ultrasonic treatment; the ultrasonic treatment power is 800W and the ultrasonic treatment time is 30min.

[0054] Step 3: Using a micro-gravure coating machine, the ultrasonically treated conductive paste is evenly coated onto all sides of the aluminum foil substrate, and the aluminum foil substrate coated with the conductive paste is dried until the solvent in the conductive paste is completely removed, resulting in a battery aluminum foil with improved grayscale value containing the aluminum foil substrate and the conductive coating.

[0055] The conductive coating on any one side of the battery aluminum foil has a thickness of 1.50 μm and a surface density of 0.5 g / m². 2 .

[0056] Step 4: Use a colorimeter to measure the grayscale value of the conductive coating in the battery aluminum foil with improved grayscale value, and use a four-probe resistor to measure the sheet resistance of the conductive coating in the battery aluminum foil with improved grayscale value. Finally, the grayscale value of the conductive coating in the battery aluminum foil with improved grayscale value is 34.2, and the sheet resistance of the conductive coating in the battery aluminum foil with improved grayscale value is 42mΩ / □.

[0057] Comparative Example 1 Step 1: Mix the following raw material formula and solvent, and prepare conductive paste by grinding and dispersing process.

[0058] The components and mass percentages of the raw material formulation are as follows: conductive carbon black = 20%, acrylate binder = 80%; the solvent in the conductive slurry has a mass percentage of 25%.

[0059] Step 2: The conductive paste is subjected to ultrasonic treatment; the ultrasonic treatment power is 800W and the ultrasonic treatment time is 30min.

[0060] Step 3: Use a coating machine to evenly coat the ultrasonically treated conductive paste onto all sides of the aluminum foil substrate, and dry the aluminum foil substrate coated with conductive paste until the solvent in the conductive paste is completely removed, to obtain the battery aluminum foil containing the aluminum foil substrate and the conductive coating.

[0061] Step 4: Use a colorimeter to measure the gray value of the conductive coating in the battery aluminum foil, and use a four-probe resistor to measure the sheet resistance of the conductive coating in the battery aluminum foil. Finally, the gray value of the conductive coating in the battery aluminum foil is 27.5, and the sheet resistance of the conductive coating in the battery aluminum foil is 38mΩ / □.

[0062] like Figure 2 As shown, by comparing Specific Example 1 and Specific Example 2 with Comparative Example 1, it can be seen that this embodiment, by adding flake graphite with a specific proportion, morphology, and properties, and controlling the particle size corresponding to the cumulative distribution of conductive paste reaching 10%, 50%, and 90%, can improve the grayscale value of the conductive coating in the battery aluminum foil while slightly increasing its sheet resistance, so that the battery aluminum foil can meet the recognition requirements of the vision system during detection.

[0063] Comparative Example 2 Step 1: Mix the following raw materials and solvent evenly to obtain a conductive paste.

[0064] The components and mass percentages of the raw material formulation are as follows: conductive carbon black = 10%, KS-6 graphite = 10%, graphene = 3%, acrylate binder = 77%; the mass percentage of the solvent in the conductive slurry is 25%.

[0065] The particle size corresponding to the cumulative particle size distribution of the conductive paste reaching 90% is greater than 4.00 μm.

[0066] Step 2: Use a coating machine to evenly coat the conductive paste onto all sides of the aluminum foil substrate, and dry the aluminum foil substrate coated with the conductive paste until the solvent in the conductive paste is completely removed, to obtain the battery aluminum foil containing the aluminum foil substrate and the conductive coating.

[0067] Step 3: Use a colorimeter to measure the gray value of the conductive coating in the battery aluminum foil, and use a four-probe resistor to measure the sheet resistance of the conductive coating in the battery aluminum foil. Finally, the gray value of the conductive coating in the battery aluminum foil is 31.0, and the sheet resistance of the conductive coating in the battery aluminum foil is 65mΩ / □.

[0068] By comparing Specific Example 1 and Specific Example 2 with Comparative Example 2, it can be seen that this embodiment, through thorough grinding and ultrasonic treatment, and by controlling the particle size corresponding to the cumulative distribution of conductive slurry reaching 10%, 50%, and 90%, can reduce the sheet resistance of the conductive coating in the battery aluminum foil while increasing the gray value of the conductive coating. This allows the battery aluminum foil to meet the recognition requirements of the vision system and ensure better conductivity.

[0069] Example 3 This embodiment provides a battery aluminum foil with enhanced grayscale value, comprising an aluminum foil substrate and a conductive coating applied to the surface of the aluminum foil substrate; wherein, the battery aluminum foil with enhanced grayscale value is prepared by the preparation method of battery aluminum foil with enhanced grayscale value in Embodiment 2. Since the battery aluminum foil in this embodiment is prepared by the preparation method of battery aluminum foil with enhanced grayscale value in Embodiment 2, it can also achieve the technical effect achieved by the preparation method of battery aluminum foil with enhanced grayscale value in Embodiment 2, and will not be elaborated here.

[0070] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing battery aluminum foil with improved grayscale value, characterized in that, The method for preparing the battery aluminum foil with improved grayscale value includes the following steps: Step S1: Mix the raw material formula and solvent, and prepare a conductive paste by grinding and dispersing process; The components and mass percentages of the raw material formulation are as follows: conductive carbon black = 5~15%, flake graphite = 5~15%, graphene = 1~5%, and the remainder is binder; Step S2: The conductive paste is uniformly coated on at least one side of the aluminum foil substrate, and the aluminum foil substrate coated with the conductive paste is dried until the solvent in the conductive paste is completely removed to form a conductive coating, thereby obtaining the battery aluminum foil with improved gray value.

2. The method for preparing battery aluminum foil with improved grayscale value as described in claim 1, characterized in that, In step S1, the particle size distribution of the conductive paste is controlled to meet the following conditions: D10 is 0.10~0.15μm, D50 is 0.50~0.60μm, and D90 is less than or equal to 3.00μm; the flake graphite is flake graphite with mirror reflection effect, and its D50 particle size is 0.30~1.50μm.

3. The method for preparing battery aluminum foil with improved grayscale value as described in claim 2, characterized in that, Step S1 further includes: grinding and dispersing the conductive slurry and then subjecting the conductive slurry to ultrasonic treatment; wherein the power of the ultrasonic treatment is 500~1000W and the ultrasonic treatment time is 20~40min.

4. The method for preparing battery aluminum foil with improved grayscale value as described in claim 1, characterized in that, In step S2, the coating method is gravure coating or micro-gravure coating.

5. The method for preparing battery aluminum foil with improved grayscale value as described in claim 1, characterized in that, In step S2, the density of the conductive coating on the battery aluminum foil with improved grayscale value is 0.3~0.7 g / m³. 2 .

6. A conductive coating that enhances grayscale value, characterized in that, The composition and mass percentage of the conductive coating that enhances grayscale value are: conductive carbon black = 5~15%, flake graphite = 5~15%, graphene = 1~5%, and the remainder is binder.

7. The conductive coating for improving grayscale value as described in claim 6, characterized in that, The flake graphite is a scaly graphite with a mirror-reflective effect and has a D50 particle size of 0.30~1.50μm.

8. The conductive coating for improving grayscale value as described in claim 6, characterized in that, The conductive coating that enhances grayscale value in CIE L a The grayscale value in the b color space is greater than 32.

9. A battery aluminum foil with improved grayscale value, characterized in that, The grayscale-enhanced battery aluminum foil includes an aluminum foil substrate and a conductive coating applied to the surface of the aluminum foil substrate; wherein the grayscale-enhanced battery aluminum foil is prepared by the method for preparing grayscale-enhanced battery aluminum foil according to any one of claims 1-5.

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