Aluminum foil and method for producing the same

Abstract

This invention relates to the field of aluminum processing technology, and provides an aluminum foil and its preparation method. The preparation method includes the following steps: S1, unwinding an aluminum foil roll to obtain aluminum foil; S2, performing a cleaning pretreatment on the aluminum foil; S3, coating the surface of the pre-treated aluminum foil with a cleaning solution; S4, drying and curing the aluminum foil coated with the cleaning solution at a temperature of 80~125°C to form a solid cleaning layer; S5, performing a physical field-assisted surface activation treatment on the solid cleaning layer to obtain a preliminary aluminum foil sample; S6, winding the preliminary aluminum foil sample to obtain the aluminum foil roll. The aluminum foil of this invention exhibits a stable surface expansion dyne value of over 50 and a stable water contact angle of less than 15°, while achieving high-speed production of over 120 m / min, greatly improving coating uniformity and adhesion.

Description

Technical Field

[0001] This invention relates to the field of aluminum processing technology, and in particular to an aluminum foil used as a current collector in power batteries and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles, portable electronic devices, and large-scale energy storage systems, the market is placing ever-increasing demands on the energy density of lithium-ion batteries. In lithium-ion batteries and related fields, aluminum foil is a core material for the positive electrode current collector, and its surface properties directly determine the coating quality of the electrode slurry, thus having a crucial impact on the electrochemical performance of lithium-ion batteries. Therefore, improving the surface tension of aluminum foil to optimize its coating adaptability has become one of the urgent technical problems to be solved in the fields of non-ferrous metal processing and lithium-ion battery manufacturing.

[0003] With the rapid development of new energy vehicles, portable electronic devices and large-scale energy storage systems, the demand for lithium-ion batteries and sodium-ion batteries continues to rise and gradually enters the international market. However, due to increasingly stringent green and environmental protection regulations, positive and negative electrode materials are gradually shifting from traditional oil-based formulations to more environmentally friendly water-based formulations, which in turn puts forward higher requirements on the surface tension of the current collectors that support the positive and negative electrode materials.

[0004] In related technologies, the industry commonly uses coating cleaning processes to improve the surface tension of aluminum foil. However, existing methods face several insurmountable technical bottlenecks, specifically: First, the surface tension improvement effect is limited. Aluminum foil treated with existing coating cleaning processes typically only achieves an expansion dyne value of 36-42, corresponding to a water contact angle generally above 40°, which is insufficient to meet the high surface tension requirements of aluminum foil used in lithium-ion batteries, safety coating current collectors, sodium-ion batteries, and other fields. Secondly, the surface coating performance is unsatisfactory. Due to the low surface tension of aluminum foil after processing by existing processes, the microscopic surface coating layer is uneven, which easily leads to uneven coating and high leakage rate when coating materials such as electrode paste are applied to its surface. In addition, the adhesion between the coating layer and the aluminum foil substrate is weak. These defects will further increase the resistance of lithium-ion battery electrodes, seriously affecting the battery's charge-discharge performance, cycle life and other core electrochemical indicators. Thirdly, production efficiency is limited. Traditional coating cleaning processes mostly use wet cleaning methods such as alkaline washing or acid washing. In order to ensure the cleaning and surface activation effect, aluminum foil requires a long immersion treatment time. This directly limits the production line speed to 60~80m / min, making it difficult to break through the threshold of 100m / min, which has become a key bottleneck restricting the capacity improvement of related industries.

[0005] Therefore, the aluminum foil prepared in the above manner has a low expansion dyne value, a small surface water contact angle, and poor coating performance, or the production speed is limited, resulting in low production capacity. Summary of the Invention

[0006] The purpose of this invention is to provide an aluminum foil and its efficient preparation method, in order to solve the problems of low expansion dyne value, small surface water contact angle and poor coating performance of existing aluminum foils.

[0007] To address the aforementioned technical problems, in a first aspect, embodiments of the present invention provide a method for preparing aluminum foil, the method comprising the following steps:

[0008] S1. Unwind the aluminum foil roll to obtain aluminum foil; S2. Perform a cleaning pretreatment on the aluminum foil; S3. Coat the surface of the aluminum foil after cleaning pretreatment with a cleaning solution; The cleaning solution comprises the following components and mass percentages: 20-40% alcohol ether, 3-5% polymeric organic acid, 1-3% polyacrylic acid, 0.1-1% adhesion promoter, and the remainder is deionized water. S4. The aluminum foil coated with the cleaning solution is dried and cured at a temperature of 80~125°C to form a solid cleaning layer; S5. Perform physical field-assisted surface activation treatment on the solid cleaning layer to obtain the initial aluminum foil sample; S6. The initial aluminum foil is wound up to obtain the aluminum foil roll.

[0009] Preferably, the aluminum foil is subjected to degreasing and oil removal treatment; wherein, during the degreasing process, the ambient temperature is maintained at 20~35℃ and the ambient humidity is maintained at 25%~39%.

[0010] Preferably, the ambient temperature is 25°C and the ambient humidity is 35%.

[0011] Preferably, the ambient temperature is 30°C and the ambient humidity is 30%.

[0012] Preferably, in step S3, the working environment temperature for coating the cleaning solution is 20~40℃, and the humidity of the coating operation environment is less than 40%.

[0013] Preferably, in step S5, the physical field-assisted surface activation treatment is any one of low-temperature plasma treatment at 20~40°C, ultraviolet light irradiation, and corona treatment.

[0014] Preferably, the corona treatment is a surface activation treatment of the solid cleaning layer by using a corona treatment device; wherein the corona power of the corona treatment device is 10~20kW and the corona gap is 1~2mm.

[0015] Preferably, in step S6, the winding speed is 120~160m / min.

[0016] Secondly, embodiments of the present invention provide an aluminum foil, which is made by the above-described method for preparing aluminum foil, and is used as a positive current collector for lithium or sodium-ion batteries, or as a negative current collector for sodium-ion batteries; wherein the surface extension dyne value of the aluminum foil is ≥50 and the water contact angle is ≤15°.

[0017] Compared with the prior art, the aluminum foil in this invention is obtained by unwinding an aluminum foil roll; the aluminum foil is pre-treated with a cleaning solution; the surface of the pre-treated aluminum foil is coated with a cleaning solution; the aluminum foil coated with the cleaning solution is dried and cured at a temperature of 80~125°C to form a solid cleaning layer; the solid cleaning layer is subjected to a physical field-assisted surface activation treatment to obtain a preliminary aluminum foil; the preliminary aluminum foil is then wound up to obtain the final aluminum foil. The resulting aluminum foil has a high surface expansion factor, a small surface water contact angle, a cleaner, more uniform, and smoother microstructure, excellent coating performance, and is suitable for high-speed production. Attached Figure Description

[0018] 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 This is a flowchart of the method for preparing aluminum foil provided in Embodiment 1 of the present invention; Figure 2 This is a diagram illustrating the outward expansion effect of the aluminum foil provided in Embodiment 1 of the present invention. Figure 3 This is a test diagram of aluminum foil with a water contact angle ≤35° provided in an embodiment of the present invention; Figure 4 This is a test diagram of the aluminum foil with a water contact angle of <10° provided in Embodiment 2 of the present invention; Figure 5 This is a test diagram of the water contact angle of the aluminum foil provided in Embodiment 3 of the present invention, which is 10°~20°. Figure 6 This is a test diagram of the water contact angle of the aluminum foil provided in Comparative Example 1 of the present invention, which is 40°~50°. Figure 7 This is a schematic diagram of the microstructure under traditional cleaning processes. Figure 8 This is a schematic diagram of the microstructure under the cleaning process of the present invention. Detailed Implementation

[0019] 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.

[0020] Example 1 Please see the appendix Figures 1-2 As shown in the figure, this invention provides a method for preparing aluminum foil, the method comprising the following steps: Step S1: Unwind the aluminum foil roll to obtain aluminum foil. Unwinding the aluminum foil roll using an unwinding machine ensures a smooth release of the aluminum foil, preventing stretching deformation, wrinkles, or surface scratches caused by tension fluctuations. This provides a dimensionally stable and surface-intact substrate for subsequent processes, ensuring overall process consistency.

[0021] Step S2: Perform a pre-cleaning treatment on the aluminum foil. This involves using corona discharge, baking, or a combination of both to initially remove residual rolling oil from the aluminum foil surface. Simultaneously, an electric spark breaks down oxygen molecules in the air, generating ozone that reacts with residual rolling oil molecules on the substrate surface. This introduces preliminary polar groups and moderately roughens the surface, providing a highly active substrate surface for the gravure coating process. This is a crucial pre-treatment step for improving coating adhesion and surface tension.

[0022] Among them, baking is beneficial to improve the volatilization efficiency of residual small molecule hydrocarbons on the substrate surface, while corona treatment can promote the oxidative decomposition of esters that are difficult to volatilize on the substrate surface, thereby increasing the number of hydroxyl and carboxyl groups on the substrate surface. Therefore, the cleaning pretreatment method can be determined by freely combining and matching based on the residual oil situation on the aluminum foil surface in S1.

[0023] Step S3: Coat the surface of the aluminum foil after cleaning pretreatment with a cleaning solution.

[0024] The cleaning solution comprises the following components and mass percentages: 20-40% alcohol ether, 3-5% polymeric organic acid, 1-3% polyacrylic acid, 0.1-1% adhesion promoter, and the remainder is deionized water.

[0025] Step S4: The aluminum foil coated with the cleaning solution is dried and cured at a temperature of 80~125°C to form a solid cleaning layer. This process converts the wet film coated by the gravure printing plate into a dry film. Through solvent evaporation and resin cross-linking curing, the cleaning layer forms a stable physicochemical structure, preventing coating peeling and component migration during subsequent physical field activation, while ensuring a tight bond between the coating and the aluminum foil substrate.

[0026] Step S5: Perform physical field-assisted surface activation treatment on the solid cleaning layer to obtain the initial aluminum foil sample. In this way, through the synergistic effect of "forming a solid layer with a specific cleaning solution" and "physical field-assisted activation", the limits of traditional chemical cleaning are broken, and the outward expansion dyne value is stably reached above 50, with a maximum of 66, which further leads to a revolutionary improvement in surface tension.

[0027] Step S6: The initial aluminum foil is wound up to obtain the aluminum foil roll.

[0028] In practical implementation, the aluminum foil produced through steps S1-S6 exhibits superior coating performance: extremely high surface tension ensures excellent wettability of the electrode paste, reducing the coating failure rate to below 0.5%, and the adhesion of the primer to over 1200 N / m. The electrode resistivity is also lower compared to conventionally cleaned coating foils. By replacing "wetting" with "coating," combined with efficient physical field activation, the production line speed can be increased to 120-180 m / min, doubling capacity and significantly improving production efficiency. The process is carried out at room temperature or low temperature, avoiding the high energy consumption and environmental pollution problems of traditional acid-alkali high-temperature cleaning, further improving environmental protection and energy-saving effects. The resulting aluminum foil has a high surface expansion yoke value, a small surface water contact angle, excellent coating performance, and is suitable for high-speed production.

[0029] In this embodiment, step S2 specifically includes the following steps: The aluminum foil undergoes a pre-treatment cleaning process. This can be achieved by using corona discharge to generate a high concentration of ozone molecules at a specific temperature. The strong oxidizing properties of ozone remove residual non-volatile rolling oils and esters from the substrate surface. Simultaneously, baking can be used to accelerate the volatilization of residual small-molecule hydrocarbons on the substrate surface. This initial removal of surface oil contaminants prevents them from hindering the bonding between the coating and the substrate.

[0030] In this embodiment, the ambient temperature is 25°C and the ambient humidity is 35%. The cleaning effect is good.

[0031] In this embodiment, the ambient temperature is 30°C and the ambient humidity is 30%. The cleaning effect is good.

[0032] In this embodiment, in step S3, the working environment temperature for applying the cleaning solution is 20~40℃, and the humidity of the coating environment is less than 40%. The coating effect is good, and cleaning is convenient.

[0033] In this embodiment, in step S5, the physical field-assisted surface activation treatment is any one of low-temperature plasma treatment at 20~40℃, ultraviolet light irradiation, and corona treatment.

[0034] Low-temperature plasma treatment involves ionizing the working gas into low-temperature plasma containing high-energy electrons, ions, free radicals, and excited-state molecules at 20-40°C under normal pressure or low vacuum using radio frequency, microwave, or DC discharge. These high-energy particles bombard the aluminum foil surface (including the gravure-coated cleaning layer) non-thermally, achieving surface activation through a dual action of "physical bombardment + chemical modification." It exhibits strong synergy with the gravure-coated cleaning layer, allowing for the targeted introduction of polar groups suitable for subsequent applications (e.g., oxygen plasma for improving hydrophilicity in the battery field, and nitrogen plasma for improving the compatibility of conductive pastes in the electronics field). The treatment time is short (5-15 seconds), making it suitable for high-speed production lines of 50-200 m / min.

[0035] like Figure 3 As shown, ultraviolet light irradiation treatment, applied to the cleaning layer on the aluminum foil surface at 20~40℃, activates the surface through a photochemical reaction. This rapidly increases the surface tension of the aluminum foil to 55~60mN / m, with a water contact angle ≤35°. The activation process only acts on the coating surface (depth ≤1μm), without damaging the internal structure of the cleaning layer. The coating hardness retention rate is ≥90%, making it suitable for scenarios requiring high coating integrity.

[0036] Corona treatment uses high-voltage, high-frequency discharge at 20-40°C to ionize the air between the electrode and the aluminum foil surface (grounded), forming low-temperature plasma and achieving surface activation. The high-energy electrons and ions generated by the high-voltage electric field bombard the aluminum foil surface, breaking the surface molecular chains and simultaneously cleaning surface oil and dust.

[0037] In this embodiment, the corona treatment is a surface activation treatment of the solid cleaning layer using a corona treatment device; wherein the corona power of the corona treatment device is 10~20kW, and the corona gap is 1~2mm. In the corona treatment device, the corona gap refers to the vertical distance between the high-voltage discharge electrode and the ground electrode (or the surface of the substrate being treated) during corona treatment, and is one of the core process parameters of corona treatment, directly determining the ionization effect, energy transfer efficiency, and the surface activation quality of the aluminum foil. Optionally, the corona power of the corona treatment device is 15kW, and the corona gap is 1.5mm.

[0038] In this embodiment, in step S6, the winding speed is 120~160m / min. This results in a fast winding speed and high winding efficiency.

[0039] Example 2 like Figure 4 As shown, this embodiment of the invention provides a method for preparing aluminum foil by preparing a cleaning solution: take 30% alcohol ether, 4% polymeric organic acid, 2% polyacrylic acid, 0.5% adhesion promoter, and add deionized water to 100%.

[0040] Under conditions of 25℃ and 35% humidity, 1100-H18 alloy aluminum foil underwent unwinding and degreasing pretreatment. A cleaning solution was applied to the aluminum foil surface using a gravure roller coater. The foil was then dried and cured in hot air at 110℃ to form a solid cleaning layer. The solid cleaning layer was then surface-activated using a corona treatment device with a corona power of 15kW and a corona gap of 1.5mm. Finally, the foil was wound up at a speed of 120 m / min using a rewinder.

[0041] The aluminum foil prepared in this way has an expansion dyne value of 58 and a water contact angle of <10°. When used as a primer for positive electrode safety coating slurry, the undercoating rate is 0.2%, and the primer adhesion is 1400 N / m.

[0042] Example 3 like Figure 5 As shown, this embodiment of the invention provides a method for preparing aluminum foil. A cleaning solution is prepared by adding deionized water to a mixture of 35% alcohol ether, 4.5% polymeric organic acid, 1.5% polyacrylic acid, and 0.3% adhesion promoter. The solution is then applied to the surface of the 1060-H18 aluminum foil under conditions of 30°C and 30% humidity, followed by unwinding and degreasing pretreatment. The cleaning solution is then applied to the aluminum foil surface using a slot transfer coating machine. The foil is dried and cured at 100°C to form a solid cleaning layer. The solid cleaning layer is then surface-activated using a low-temperature plasma treatment device. Finally, the foil is wound up at a speed of 150 m / min using a winding machine.

[0043] The resulting aluminum foil has an expansion factor of 52 and a water contact angle between 10° and 20°. When used for coating lithium iron phosphate cathode slurry, it exhibits a missing coating rate of 0.8% and an adhesion strength of 500 N / m.

[0044] Comparative Example 1 like Figure 6 As shown, this embodiment of the invention provides a method for preparing aluminum foil by preparing a cleaning solution: take 30% alcohol ether, 4% polymeric organic acid, 2% polyacrylic acid, 0.5% adhesion promoter, and add deionized water to 100%.

[0045] Under conditions of 25℃ and 35% humidity, 1100-H18 alloy aluminum foil was unwound and pre-treated by degreasing. A cleaning solution was applied to the surface of the aluminum foil using a gravure roller coater. The foil was then dried and cured in hot air at 110℃ to form a solid cleaning layer. Finally, the foil was wound up at a speed of 120 m / min using a rewinder.

[0046] The resulting aluminum foil has an expansion dyne value of 42 and a water contact angle between 40° and 50°. When used with the same slurry, the undercoating rate is 3.0%, and the primer adhesion is 600 N / m.

[0047] As can be seen from Examples 2 and 3 and the comparative examples, the present invention, through the synergistic effect of the cleaning solution formulation and physical field activation treatment, enables the aluminum foil surface to achieve a stable expansion dyne value of over 50 and a stable water contact angle of less than 15°, while achieving high-speed production of over 120 m / min, greatly improving coating uniformity and adhesion, and is particularly suitable for the preparation of lithium-ion battery electrodes with extremely high coating performance requirements.

[0048] In this embodiment, as Figure 7-8 The comparison of microstructures under different cleaning processes of the present invention and the traditional method shows that the cleaning effect of the present invention is better.

[0049] Example 4 This invention provides an aluminum foil, which is made by the above-described method for preparing aluminum foil, and is used as a positive electrode current collector in a lithium-ion battery.

[0050] The aluminum foil has a surface extension dyne value ≥ 50 and a water contact angle ≤ 15°. Specifically, it has a surface extension dyne value not less than 50, a water contact angle not greater than 15°, and its surface exhibits micro / nano-scale activated structures formed by physical field-assisted surface activation treatment. This high surface tension aluminum foil is used in the fabrication of lithium-ion battery electrodes.

[0051] The application of the aforementioned high surface tension aluminum foil in the preparation of lithium-ion battery electrodes. Since the aluminum foil in this embodiment is prepared using the method described in the above embodiments, it also achieves the technical effects achieved by the preparation method described in the above embodiments, and will not be elaborated further here.

[0052] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0053] 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 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 aluminum foil, characterized in that, The preparation method includes the following steps: S1. Unwind the aluminum foil roll to obtain aluminum foil; S2. Perform a cleaning pretreatment on the aluminum foil; S3. Coat the surface of the aluminum foil after cleaning pretreatment with a cleaning solution; The cleaning solution comprises the following components and mass percentages: 20-40% alcohol ether, 3-5% polymeric organic acid, 1-3% polyacrylic acid, 0.1-1% adhesion promoter, and the remainder is deionized water. S4. The aluminum foil coated with the cleaning solution is dried and cured at a temperature of 80~125°C to form a solid cleaning layer; S5. Perform physical field-assisted surface activation treatment on the solid cleaning layer to obtain the initial aluminum foil sample; S6. The initial aluminum foil is wound up to obtain the aluminum foil roll.

2. The method for preparing aluminum foil according to claim 1, characterized in that, Step S2 specifically includes the following steps: The aluminum foil strip is subjected to degreasing and oil removal treatment; wherein, during the degreasing process, the ambient temperature is maintained at 20~35℃ and the ambient humidity is maintained at 25%~39%.

3. The method for preparing aluminum foil according to claim 2, characterized in that, The ambient temperature is 25°C and the ambient humidity is 35%.

4. The method for preparing aluminum foil according to claim 2, characterized in that, The ambient temperature is 30°C and the ambient humidity is 30%.

5. The method for preparing aluminum foil according to claim 1, characterized in that, In step S3, the working environment temperature for applying the cleaning solution is 20~40℃, and the humidity of the coating operation environment is less than 40%.

6. The method for preparing aluminum foil according to claim 1, characterized in that, In step S5, the physical field-assisted surface activation treatment can be performed using any one of the following: low-temperature plasma treatment at 20-40°C, ultraviolet light irradiation, and corona treatment.

7. The method for preparing aluminum foil according to claim 6, characterized in that, The corona treatment is a surface activation treatment performed on the solid cleaning layer using a corona treatment device; wherein the corona power of the corona treatment device is 10~20kW and the corona gap is 1~2mm.

8. The method for preparing aluminum foil according to claim 1, characterized in that, In step S6, the winding speed is 120~160m / min.

9. An aluminum foil, characterized in that, The aluminum foil is made by the method for preparing aluminum foil according to any one of claims 1-8, and the aluminum foil is used as a positive current collector for lithium or sodium-ion batteries, or as a positive or negative current collector for sodium-ion batteries; wherein the surface extension dyne value of the aluminum foil is ≥50 and the water contact angle is ≤15°.

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