Modified polyacrylic acid binder, carbon-coated aluminum foil and preparation methods of modified polyacrylic acid binder and carbon-coated aluminum foil

Abstract

The invention relates to the technical field of batteries, and particularly discloses a modified polyacrylic acid binder as well as a preparation method and application thereof. The modified polyacrylic acid binder is formed by polymerizing polymeric monomers, the polymeric monomers comprise acrylic acid monomers and functional monomers, and the functional monomers are glycidyl methacrylate. According to the invention, the polyacrylic resin is subjected to epoxy group modification, so that the polyacrylic resin is subjected to self-crosslinking reaction in the heating and curing process to form a compact three-dimensional network structure, thereby obviously improving the water resistance, adhesive force and electrochemical stability of the carbon coating.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a modified polyacrylic acid binder and carbon-coated aluminum foil and a preparation method thereof. BACKGROUND

[0002] Carbon-coated aluminum foil is a composite material formed by uniformly coating a conductive paste on the surface of an aluminum foil and drying and curing it. It is used as a positive electrode current collector in lithium batteries, which can effectively reduce the internal resistance of the battery, improve the rate performance, enhance the adhesion strength and prolong the cycle life of the battery.

[0003] Currently, most of the carbon-coated aluminum foils on the market use a water-based system, and the binder is mainly SBR (styrene-butadiene rubber) or polyacrylate emulsion. However, these binders have obvious shortcomings in water resistance: SBR system: poor resistance to electrolyte and water, long-term immersion or in a high-humidity environment, the coating is easy to swell and fall off, resulting in battery performance degradation.

[0004] Conventional polyacrylate: although it has good adhesion, it contains a large number of hydrophilic carboxyl groups (-COOH) in its molecular chain, resulting in strong water absorption and poor stability of the volume resistivity of the coating in a humid environment.

[0005] In order to improve water resistance, the existing technology usually uses a method of adding a crosslinking agent (such as aziridine, carbodiimide, etc.). However, these crosslinking agents often have problems such as high toxicity, poor storage stability, or harsh crosslinking reaction conditions, which limit their widespread application.

[0006] Therefore, it is of great industrial application value to develop a new method that is environmentally friendly, has good storage stability, and can give the carbon-coated coating excellent water resistance and adhesion. SUMMARY

[0007] Therefore, the purpose of the present application is to provide a modified polyacrylic acid binder and carbon-coated aluminum foil and a preparation method thereof. The present application modifies the polyacrylic acid resin with an epoxy group, which undergoes a self-crosslinking reaction during the heating and curing process, forming a dense three-dimensional network structure, thereby significantly improving the water resistance, adhesion, and electrochemical stability of the carbon-coated coating.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: The present application provides a modified polyacrylic acid binder, which is polymerized from polymerized monomers, the polymerized monomers including an acrylic monomer and a functional monomer, the functional monomer being glycidyl methacrylate.

[0009] As a further improvement of the above-mentioned scheme of the present application, the acrylic monomer includes at least one of acrylic acid, butyl acrylate, and methyl methacrylate.

[0010] As a further improvement to the above-mentioned scheme of the present invention, the acrylic monomers include acrylic acid, butyl acrylate, and methyl methacrylate, and the mass ratio of acrylic acid, butyl acrylate, methyl methacrylate, and glycidyl methacrylate is 3-8:20-40:10-25:2-6.

[0011] As a further improvement to the above-mentioned solution of the present invention, the solid content of the modified polyacrylic acid adhesive is 40%-45%.

[0012] The present invention also provides a method for preparing the modified polyacrylic acid adhesive as described above, comprising the following steps: mixing an emulsifier, a molecular weight regulator and deionized water and heating to a first predetermined temperature; then simultaneously adding a polymerizable monomer and an initiator, with the adding time controlled at 2-4 hours; after the addition is completed, maintaining the temperature at the first predetermined temperature for 1-2 hours; cooling to below 40°C, adjusting the pH, filtering, and obtaining the modified polyacrylic acid resin adhesive.

[0013] As a further improvement to the above-described solution of the present invention, the first predetermined temperature is 75-85°C.

[0014] As a further improvement to the above-mentioned solution of the present invention, the first predetermined temperature is 80-85°C.

[0015] As a further improvement to the above-mentioned solution of the present invention, the pH adjustment is performed by using ammonia water to adjust the pH to 7.5-8.5.

[0016] The present invention also provides a carbon-coated aluminum foil, comprising an aluminum foil and a coating applied to the aluminum foil; the coating comprises a conductive agent, a binder, and a dispersant; based on the total weight of the solid components of the coating, the conductive agent accounts for 5-15 parts by weight, the binder accounts for 15-25 parts by weight, and the dispersant accounts for 0.5-2 parts by weight; wherein the binder is a modified polyacrylic acid binder as described in any one of claims 1-4.

[0017] As a further improvement to the above-mentioned solution of the present invention, the conductive agent is at least one of conductive carbon black, Ketjen black, carbon nanotubes, and graphene.

[0018] The present invention also provides a method for preparing carbon-coated aluminum foil as described above, which includes the following steps: The conductive agent, binder, solvent, and dispersant are added to a high-speed dispersant in proportion and dispersed at 2000-4000 rpm for 30-60 minutes to obtain a uniform and stable conductive paste. The conductive paste is then uniformly coated onto the surface of aluminum foil using a micro-gravure roller coating method, and the coated aluminum foil is then sent to an oven for segmented curing. First stage: Dry at 80-110℃ for 1-3 minutes to remove most of the free water; The second stage involves curing at 130-160℃ for 1-3 minutes. During this stage, the epoxy groups on the modified polyacrylic acid resin molecular chain undergo ring-opening esterification with the carboxyl groups to form a cross-linked network structure. After curing, the carbon-coated aluminum foil is obtained by winding, rewinding, and slitting.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly Improved Electrolyte Resistance and Stability: Due to the introduction of glycidyl methacrylate (GMA) containing epoxy groups into the polymer monomer, during the high-temperature curing process of carbon-coated aluminum foil, the epoxy groups of GMA can undergo efficient intramolecular and intermolecular cross-linking reactions with the carboxyl groups on the polyacrylic acid chain. This reaction forms a dense, three-dimensional hydrophobic network structure that significantly blocks the penetration of electrolytes and moisture, thereby significantly reducing the water absorption rate of the coating. This allows the coating to maintain excellent chemical and dimensional stability under long-term immersion or high-temperature and high-humidity environments, effectively alleviating problems such as coating swelling and peeling.

[0020] 2. Simultaneous Enhancement of Coating Adhesion and Cohesion: While retaining its inherent high adhesion to aluminum foil substrates and carbonaceous conductive agents, the modified polyacrylic resin significantly enhances the coating's cohesion through the aforementioned cross-linking network. This synergistic effect of "high adhesion + high cohesion" substantially improves the peel strength between the coating and the aluminum foil, effectively preventing coating detachment during battery manufacturing processes (such as rolling and slitting) or recycling.

[0021] 3. Stable and durable conductivity: Thanks to the dense hydrophobic coating formed by cross-linking, which effectively resists electrolyte corrosion, the interfacial contact resistance of the carbon-coated aluminum foil remains stable in the electrolyte. Even under harsh environments, its volume resistivity does not increase significantly, which helps the lithium-ion battery maintain a low internal resistance, thereby ensuring the battery's durability and reliability, especially its high-rate charge and discharge performance.

[0022] 4. Outstanding environmental friendliness and process safety: This invention uses an all-water-based system to prepare the binder and conductive paste, completely avoiding the use of traditional solvent-based processes or toxic crosslinking agents (such as aziridine), thus reducing VOC emissions at the source and making it environmentally friendly. Furthermore, the epoxy groups in this system only activate crosslinking during the later high-temperature curing stage, ensuring the long-term stability of the emulsion during storage, eliminating the risk of premature gelation, and providing a wide process window suitable for industrial production.

[0023] 5. Excellent overall performance and broad application prospects: In summary, the carbon-coated aluminum foil prepared by the modified polyacrylic acid binder of this invention has high peel strength, low and stable volume resistivity, excellent resistance to electrolyte corrosion and good environmental compatibility, and is particularly suitable for the field of high-performance lithium-ion batteries where the requirements for performance, life and safety are increasing. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of the carbon-coated aluminum foil provided by the present invention; Figure 2 This is a SEM image of the carbon-coated aluminum foil coating prepared in Example 1 of the present invention. Detailed Implementation

[0025] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] Example 1 This embodiment proposes a carbon-coated aluminum foil, the preparation of which includes the following steps: (1) Preparation of modified polyacrylic acid adhesive Mix 5 parts acrylic acid, 30 parts butyl acrylate, 15 parts methyl methacrylate and 4 parts glycidyl methacrylate evenly to prepare a monomer preemulsion, and dissolve 0.5 parts ammonium persulfate in 10 parts deionized water to prepare an initiator solution. Add 60 parts deionized water, 1.5 parts sodium dodecyl sulfate (emulsifier), and 0.2 parts dodecyl mercaptan (molecular weight adjuster) to a four-necked flask equipped with a stirrer, condenser, and constant-pressure dropping funnel, and heat to 80°C. At 80°C, simultaneously add monomer pre-emulsion and initiator solution, controlling the adding time to 3 hours. After the addition is complete, keep at 82°C for 1.5 hours. Cool to 35°C, adjust the pH to 8.0 with ammonia, filter, and obtain a modified polyacrylic acid resin emulsion with a solid content of approximately 42%.

[0028] (2) Preparation of conductive paste Prepare the raw materials according to the following weight ratio: 8 parts conductive carbon black SP, 2 parts graphite, 15 parts modified polyacrylic acid binder (solids), 74 parts solvent (deionized water and isopropanol mixed at a volume ratio of 2:1), and 1 part polycarboxylate dispersant. Put the above materials into a mixing tank, mix them evenly with low speed, and then transfer them to a high-speed disperser. Disperse them at 3000 rpm for 45 minutes. The slurry D50 is measured to be 4.9 μm, and a conductive slurry is obtained.

[0029] (3) Coating and curing A 12μm thick aluminum foil for lithium batteries was selected, and conductive paste was applied to its surface using a microgravure coating machine (220 mesh roller). It was then placed in a 10-meter-long tunnel oven, first dried at 100°C for 2 minutes, and then cured at 150°C for 2 minutes. After winding, it was slit to obtain the finished water-resistant carbon-coated aluminum foil. A cross-sectional view of the water-resistant carbon-coated aluminum foil in this embodiment is shown below. Figure 1 As shown, coating 1 is formed on both sides of the aluminum foil substrate 2.

[0030] Figure 2 Here is a SEM image of the carbon-coated aluminum foil coating prepared in this embodiment, from... Figure 2 As can be seen, the coating surface is uniform, the conductive particles are well dispersed, and there are no obvious cracks. The coating preparation process is generally successful, forming a continuous and dense conductive network.

[0031] Example 2 The difference between this embodiment and Embodiment 1 is as follows: In the step of preparing the modified polyacrylic acid adhesive, the amount of glycidyl methacrylate is 2 parts; In the step of preparing the conductive slurry, only a single conductive agent is used: 8 parts of conductive carbon black SP; In the curing step, the material is first dried at 100°C for 2 minutes, and then cured at 140°C for 2 minutes.

[0032] Example 3 The difference between this embodiment and Example 1 is that in the preparation step of the modified polyacrylic acid adhesive, the amount of each raw material is as follows: 3 parts acrylic acid, 40 parts butyl acrylate, 10 parts methyl methacrylate, and 5 parts glycidyl methacrylate are mixed evenly as a monomer pre-emulsion; in the curing step, the material is first dried at 80°C for 3 minutes and then cured at 150°C for 1.5 minutes.

[0033] Example 4 The difference between this embodiment and Embodiment 1 is that in the step of preparing the modified polyacrylic acid adhesive, 8 parts of acrylic acid, 20 parts of butyl acrylate, 25 parts of methyl methacrylate, and 6 parts of glycidyl methacrylate are mixed evenly as a monomer pre-emulsion; in the curing step, the product is first dried at 110°C for 1 minute and then cured at 160°C for 1 minute.

[0034] Example 5 The difference between this embodiment and Embodiment 1 is as follows: In the preparation step of the conductive paste in this embodiment, the raw materials are prepared according to the following weight ratio: 10 parts of conductive carbon black SP, 5 parts of graphite, 25 parts of modified polyacrylic acid binder (solid part), 58 parts of solvent, and 2 parts of polycarboxylate dispersant; In the curing step of this embodiment, the material is first dried at 100°C for 3 minutes, and then cured at 130°C for 2.5 minutes.

[0035] Example 6 The difference between this embodiment and Embodiment 1 is that in the step of preparing the conductive paste, the raw materials are prepared according to the following weight ratio: 5 parts conductive carbon black SP, 20 parts modified polyacrylic acid binder (solid part), 74.5 parts solvent, and 0.5 parts polycarboxylate dispersant.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example did not involve the step of modifying the polyacrylic acid binder. In the preparation of the conductive paste, commercially available ordinary polyacrylic acid was used as the binder.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that in the preparation of the conductive paste in this comparative example, the raw materials are prepared according to the following weight ratio: 8 parts conductive carbon black SP, 2 parts graphite, 12 parts modified polyacrylic acid binder (solid part), 77 parts solvent, and 1 part polycarboxylate dispersant.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that in the preparation of the conductive paste in this comparative example, the raw materials are prepared according to the following weight ratio: 8 parts conductive carbon black SP, 2 parts graphite, 30 parts modified polyacrylic acid binder (solid part), 59 parts solvent, and 1 part polycarboxylate dispersant.

[0039] Comparative Example 4 The difference between this comparative example and Example 1 is that in the curing step, this comparative example is first dried at 80°C for 3 minutes, and then cured at 100°C for 3 minutes.

[0040] Test case The carbon-coated aluminum foils prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to performance tests, and the test results are shown in the table below.

[0041]

[0042] According to the results in the table above: Comparison of Example 1 with Comparative Examples 2 and 3: When the amount of adhesive used is lower than the range of the present invention (Comparative Example 2: 12 parts), the coating adhesion (298 mN / mm), conductivity (6.2 mΩ), and electrolyte resistance all decrease significantly, while the water absorption rate (3.2%) increases, indicating that insufficient adhesion leads to a loose coating structure. When the amount of adhesive used is higher than the range of the present invention (Comparative Example 3: 30 parts), although the adhesion (411 mN / mm) and water resistance (14 times) are excellent, the film resistance increases sharply to 18.3 mΩ, seriously damaging the core conductive function of the carbon-coated aluminum foil, and significantly increasing the cost. Examples 1, 5, and 6 (with adhesive amounts of 15, 25, and 20 parts, respectively) achieve the best balance in adhesion, conductivity, and environmental resistance, proving the rationality of the adhesive amount range (15-25 parts) of the present invention.

[0043] Comparison of Example 1 and Comparative Example 4: Comparative Example 4 was cured at 100°C, which failed to trigger effective cross-linking between epoxy groups and carboxyl groups. Its coating had extremely low adhesion (185mN / mm), high resistance (12.7mΩ), poor resistance to electrolyte (overall swelling and peeling), and abnormally high water absorption (15.3%), resulting in severely deteriorated overall performance.

[0044] All embodiments of the present invention (curing temperature ≥130℃) exhibited excellent performance, demonstrating the necessity of the high-temperature curing stage for forming a dense cross-linked network and achieving the objectives of the present invention (high water resistance, high adhesion, and stable conductivity).

[0045] Comparison of Example 1 and Comparative Example 1: The coating prepared using unmodified ordinary polyacrylic acid adhesive (Comparative Example 1) exhibited the worst performance in all aspects, especially in terms of electrolyte resistance, water resistance, and water absorption, which contrasts sharply with the embodiments of the present invention. This fully demonstrates that the key inventive point for achieving a leap in performance is the introduction of glycidyl methacrylate (GMA) for epoxy modification and the formation of a self-crosslinking network through high-temperature curing.

[0046] The carbon-coated aluminum foil prepared by this invention achieves an optimal balance between conventional adhesion, water resistance, electrolyte resistance, low water absorption, and high conductivity by using a specific ratio of GMA-modified polyacrylic acid adhesive and under preferred dosage (15-25 parts) and specific curing process (130-160℃). Its comprehensive performance is significantly better than that of the unmodified system, the comparative ratio with suboptimal ratio and improper curing conditions, and fully meets the requirements of high-end lithium batteries for current collectors.

[0047] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0048] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A modified polyacrylic acid adhesive, characterized in that, It is polymerized from monomers, which include acrylic monomers and functional monomers, wherein the functional monomer is glycidyl methacrylate.

2. The modified polyacrylic acid adhesive according to claim 1, characterized in that, The acrylic monomers include at least one of acrylic acid, butyl acrylate, and methyl methacrylate.

3. The modified polyacrylic acid adhesive according to claim 2, characterized in that, The acrylic monomers include acrylic acid, butyl acrylate, and methyl methacrylate, with the mass ratio of acrylic acid, butyl acrylate, methyl methacrylate, and glycidyl methacrylate being 3-8:20-40:10-25:2-6.

4. The modified polyacrylic acid adhesive according to claim 2, characterized in that, The modified polyacrylic acid adhesive has a solid content of 40%-45%.

5. A method for preparing a modified polyacrylic acid adhesive as described in any one of claims 1-4, characterized in that, It includes the following steps: Emulsifier, molecular weight regulator and deionized water are mixed and heated to a first predetermined temperature; then polymerizable monomer and initiator are added dropwise simultaneously, with the addition time controlled at 2-4 hours; after the addition is completed, the mixture is kept at the first predetermined temperature for 1-2 hours; cooled to below 40°C, pH is adjusted, and the mixture is filtered to obtain modified polyacrylic acid resin adhesive.

6. The method for preparing the modified polyacrylic acid adhesive according to claim 5, characterized in that, The first predetermined temperature is 75-85℃.

7. The method for preparing the modified polyacrylic acid adhesive according to claim 5, characterized in that, The first predetermined temperature is 80-85℃.

8. The method for preparing the modified polyacrylic acid adhesive according to claim 5, characterized in that, The pH is adjusted to 7.5-8.5 using ammonia.

9. A carbon-coated aluminum foil, characterized in that, The coating comprises an aluminum foil and a coating applied to the aluminum foil; the coating comprises a conductive agent, a binder, and a dispersant; based on the total weight of the solid components of the coating, the conductive agent accounts for 5-15 parts by weight, the binder accounts for 15-25 parts by weight, and the dispersant accounts for 0.5-2 parts by weight; wherein the binder is a modified polyacrylic acid binder as described in any one of claims 1-4.

10. A method for preparing carbon-coated aluminum foil as described in claim 9, characterized in that, It includes the following steps: The conductive agent, binder, solvent and dispersant are added to the high-speed dispersant in proportion and dispersed at 2000-4000 rpm for 30-60 minutes to obtain a conductive slurry. The conductive slurry is coated on the surface of aluminum foil, and then the coated aluminum foil is sent to an oven for segmented curing: dried at 80-110℃ for 1-3 minutes, and then cured at 130-160℃ for 1-3 minutes to obtain carbon-coated aluminum foil.

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