A foamed aluminum electrode foil for an aluminum electrolytic capacitor and a method of manufacturing the same
By constructing a dense aluminum reinforcing layer on a foamed aluminum matrix through a coating-sintering method, the mechanical strength and conductivity issues of foamed aluminum electrode foil were solved, resulting in aluminum electrolytic capacitor electrode foil with high specific surface area and low resistance, suitable for the manufacture of aluminum electrolytic capacitors.
Patent Information
- Application Number
- CN202610375716.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-25
- Publication Date
- 2026-06-30
AI Technical Summary
In existing technologies, the increase in specific surface area of traditional etched aluminum foil is limited, and aluminum foam as electrode foil suffers from poor mechanical strength, poor conductivity, and difficulty in forming a high-quality oxide film.
A dense aluminum reinforcement layer is constructed on a foamed aluminum matrix using a coating-sintering process. Metallurgical bonding is formed through slurry coating and multi-stage sintering, thus constructing a highly efficient three-dimensional conductive network.
A foamed aluminum electrode foil with high specific surface area, excellent mechanical strength and low resistance has been developed, which is suitable for use in aluminum electrolytic capacitors, compatible with traditional manufacturing processes and suitable for mass production.
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Figure CN122314657A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of aluminum electrolytic capacitor technology, specifically relating to a foamed aluminum electrode foil for aluminum electrolytic capacitors and its preparation method. Background Technology
[0002] The core component of an aluminum electrolytic capacitor is an aluminum foil electrode with a high specific surface area, which has undergone etching treatment. Its capacitance is directly proportional to the effective surface area of the electrode foil. Traditional processes increase the surface area by electrochemically etching nano- to micron-sized pits into the foil. However, this method has limitations: the etching depth is limited, further miniaturization leads to a sharp decrease in the mechanical strength of the foil, the pit structure is prone to collapse in subsequent processes, and the inherent two-dimensional planar expansion pattern restricts further increases in specific surface area.
[0003] Aluminum foam is a porous metal material with a three-dimensional interconnected pore structure and a porosity of up to 90%. Theoretically, it can provide a specific surface area far exceeding that of corrosion foil, making it an ideal substrate for preparing ultra-high specific capacitance electrodes. However, direct application has serious problems: (1) The pore walls of aluminum foam are sharp and fragile, and are easily powdered and detached during formation, cutting, and winding processes, resulting in short circuit risks; (2) Its porous structure has a large volume resistance, which leads to an increase in the equivalent series resistance (ESR) of the electrode; (3) It has high surface activity, making it difficult to form a uniform and dense dielectric oxide film.
[0004] Existing technologies attempt to deposit conductive layers on the surface of aluminum foam using physical vapor deposition (PVD) or chemical vapor deposition (CVD), but these methods suffer from problems such as expensive equipment, weak coating adhesion, and difficulty in achieving uniform coverage of three-dimensional deep pores. Therefore, developing a surface modification method that can strengthen the structure of aluminum foam while constructing an efficient three-dimensional conductive network is crucial for its application as an electrode foil in aluminum electrolytic capacitors. Summary of the Invention
[0005] In view of the above-mentioned prior art, the present invention provides a foamed aluminum electrode foil for aluminum electrolytic capacitors and a method for preparing the same, which overcomes the limitations of traditional corrosion aluminum foil in increasing specific surface area, as well as the problems of poor mechanical strength, poor conductivity, and difficulty in forming a high-quality oxide film when foamed aluminum is directly used as electrode foil. The present invention provides a foamed aluminum-based composite foil with high mechanical strength, excellent conductive network, and suitable for use as an electrode of aluminum electrolytic capacitors.
[0006] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors, characterized by comprising the following steps: (1) Matrix pretreatment: Aluminum foam is used as the matrix. The aluminum foam is soaked in hydrochloric acid solution, washed, soaked in acetone and then dried. (2) Slurry preparation: Weigh 80-95 parts of aluminum powder, 5-10 parts of organic binder, 5-10 parts of pore-forming agent, 1-2 parts of dispersant and organic solvent by mass and mix them to prepare a slurry with a viscosity of 4000-7000 mPa.s; (3) Coating: Apply the slurry evenly to both sides of the aluminum foam; (4) Drying: The coated aluminum foam is dried at 100~120℃; (5) Roll pressing: The dried aluminum foam is subjected to roll pressing treatment; (6) Sintering: The rolled aluminum foam is sintered under a protective atmosphere or vacuum. First, the temperature is raised to 300~450℃ at a rate of 5℃ / min and held for 120~150min; then the temperature is raised to 550℃ at a rate of 5℃ / min and held for 360~400min; then the temperature is raised to 610~650℃ at a rate of 5℃ / min and held for 120~240min; finally, the temperature is lowered to 100℃ at a rate of 10℃ / min and cooled with the furnace to obtain the final product.
[0007] The beneficial effects of the above-mentioned technical solution of this invention are as follows: The core of this invention is to use a three-dimensional interconnected foam aluminum foil with high porosity as a skeleton, and to construct a thin, dense, and firmly bonded aluminum reinforcement layer on its huge inner surface through a coating-sintering process. Aluminum powder, organic binder, and solvent are formulated into a slurry with appropriate viscosity and rheological properties. The purity and fineness of the aluminum powder directly affect the density and conductivity of the conductive layer after sintering. Through dip coating, spraying, and other methods, the slurry not only covers the surface of the foam aluminum, but also fully penetrates into the surface pores using capillary action, covering the internal pore walls. Roll pressing enhances the contact between the aluminum powder and the matrix, which helps to form a strong metallurgical bond in subsequent sintering. A three-stage sintering process is carried out under a protective atmosphere with precise control: the first stage removes organic matter, the second stage removes carbon, and the third stage involves long-term solid-state sintering at a temperature close to but slightly below the melting point of aluminum. During this process, micro-melting diffusion on the surface of aluminum powder particles forms neck connections and densifies the particles, while interdiffusion occurs with the foam aluminum matrix, forming a strong metallurgical bonding interface. Therefore, through the preparation method of the present invention, the porous aluminum foam matrix and the dense aluminum reinforcement layer covering its surface by metallurgical bonding together constitute a highly efficient three-dimensional continuous conductive network.
[0008] Based on the above technical solution, the present invention can be further improved as follows.
[0009] Furthermore, the aluminum foam has a thickness of 0.3~1.0 mm, a porosity of 90~98%, and an average pore size of 0.1~2 mm.
[0010] Furthermore, the concentration of the hydrochloric acid solution was 0.05M, and the soaking time for both the hydrochloric acid solution and acetone was 10 minutes.
[0011] Furthermore, the aluminum powder has a particle size of 3~5μm and a purity of not less than 99.98%.
[0012] Furthermore, the organic binder is at least one of polyvinyl butyral, ethyl cellulose, and acrylic resin; the pore-forming agent is starch; the dispersant is phenolic resin; and the organic solvent is at least one of anhydrous ethanol, terpineol, and ethylene glycol.
[0013] Furthermore, the slurry is uniformly coated onto the surface of the aluminum foam by dip coating, doctor blade coating, spraying, or roller coating processes, and the wet film thickness after coating is 0.5~1.3mm.
[0014] Furthermore, the dip coating method is as follows: the pretreated foam aluminum foil is completely immersed in the slurry, and after 30 seconds it is pulled out of the liquid surface at a constant speed of 2 cm / min to obtain a uniform coating.
[0015] Furthermore, the drying time in step (4) is 60 min.
[0016] Furthermore, the thickness of the rolled aluminum foam is 120~150μm.
[0017] Furthermore, the foamed aluminum electrode foil for aluminum electrolytic capacitors prepared by the above preparation method.
[0018] The beneficial effects of this invention are: (1) Ultra-high specific surface area and high specific capacitance potential: The foamed aluminum matrix provides a three-dimensional high specific surface area that traditional etched foils cannot achieve, laying the foundation for manufacturing micro or high voltage large-capacity capacitors with ultra-high specific capacitance.
[0019] (2) Excellent mechanical strength and structural stability: The dense aluminum reinforcement layer on the surface wraps around and strengthens the fragile aluminum foam pore walls like an armor, enabling it to withstand the stress of subsequent formation, cutting, winding and other processing, and preventing pulverization.
[0020] (3) Excellent three-dimensional conductive network: The dense aluminum layer formed by sintering forms a continuous, low-resistance conductive path on the surface and internal pore walls of the aluminum foam skeleton, which greatly reduces the bulk resistance and contact resistance of the electrode, and is beneficial to reducing the ESR of the capacitor.
[0021] (4) Good process compatibility: The modified electrode foil has a dense aluminum layer on its surface, which is similar to the surface properties of traditional foil. It can be directly anodized to form a dielectric oxide film (formation), and has good compatibility with traditional capacitor manufacturing processes.
[0022] (5) The method is simple and the cost is controllable: the process equipment requirements are low and it is suitable for large-scale production. Attached Figure Description
[0023] Figure 1A schematic diagram of an aluminum powder-foamed aluminum three-dimensional electrode foil; Figure 2 The images shown are SEM images of the foamed aluminum electrode foil for aluminum electrolytic capacitors prepared in Example 1, where (a) is at magnification of 80 and (b) is at magnification of 30000. Detailed Implementation
[0024] The specific embodiments of the present invention will be described in detail below with reference to examples.
[0025] Example 1: A foamed aluminum electrode foil for aluminum electrolytic capacitors, a schematic diagram of the aluminum powder-foamed aluminum three-dimensional electrode foil is shown below. Figure 1 As shown, its preparation method is as follows: (1) Substrate pretreatment: Select aluminum foam foil with a thickness of 0.5 mm, a porosity of 90%, and an average pore diameter of 0.5 mm. Soak it in dilute hydrochloric acid with a concentration of 0.05 M for 10 min to roughen the pore wall surface, then rinse it with ultrapure water, and then soak it in acetone for 10 min to ensure that the aluminum foam surface is clean and free of impurities, and finally dry it.
[0026] (2) Slurry preparation: Weigh 85 parts of high-purity aluminum powder (99.98%) with a particle size of 3~5μm, 7 parts of ethyl cellulose, 1 part of phenolic resin, 7 parts of starch and ethylene glycol by mass and mix them in a planetary mixer for 3 hours. Control the amount of organic solvent (ethylene glycol) to make the viscosity of the slurry 5000 mPa·s. After mixing, put it in a vacuum box to defoam and obtain a uniform slurry.
[0027] (3) Coating: The pretreated aluminum foam is completely immersed in the slurry, held for 30 seconds, and then pulled out of the liquid surface at a constant speed (2 cm / min) to obtain a uniform coating with a wet film thickness of about 0.6 mm.
[0028] (4) Drying: Place the aluminum foam obtained in step (3) in a 120℃ oven and dry for 60 min.
[0029] (5) Rolling: The gap of the roller press is adjusted to 130μm to roll the aluminum foam.
[0030] (6) Sintering: The rolled aluminum foam is placed in a tube furnace with high-purity argon gas (flow rate of 200 sccm) and heated to 300°C at a rate of 5°C / min, held for 120 min to completely remove the binder; then heated to 550°C at a rate of 5°C / min, held for 360 min to remove excess carbon; then heated to 650°C at a rate of 5°C / min, held for 120 min; finally cooled to 500°C at a rate of 10°C / min (protected tube furnace program), and cooled with the furnace to obtain the final product.
[0031] The SEM image of the foamed aluminum electrode foil prepared for aluminum electrolytic capacitors in this embodiment is shown below. Figure 2 As shown. At lower magnification ( Figure 2 (a) The three-dimensional, continuous, porous network framework structure of the aluminum foam matrix can be observed; the framework itself is porous, forming a large number of interconnected pores. At higher magnification ( Figure 2 (b) It can be clearly seen that a dense reinforcing layer formed by sintered aluminum powder is uniformly covered and tightly bonded to the surface and internal pore walls of the aluminum foam skeleton. The interface between the aluminum reinforcing layer and the underlying aluminum foam matrix is clear, but the bond is tight, with no obvious gaps or signs of peeling.
[0032] Example 2: A foamed aluminum electrode foil for aluminum electrolytic capacitors, the preparation method of which is as follows: (1) Substrate preparation: Select aluminum foam foil with a thickness of 0.5 mm, a porosity of 90%, and an average pore diameter of 0.5 mm. Soak it in dilute hydrochloric acid with a concentration of 0.05 M for 10 min to roughen the pore wall surface, then rinse it with ultrapure water, and then soak it in acetone for 10 min to ensure that the aluminum foam surface is clean and free of impurities, and finally dry it.
[0033] (2) Slurry preparation: Compared with step (2) of Example 1, the amount of ethylene glycol is reduced to prepare a slurry with a viscosity of 7000 mPa.s.
[0034] (3) Coating: The coating is applied to both sides of the foam aluminum foil using a doctor blade coating method, and the thickness of the wet film on one side is controlled to be about 200 μm. Then, it is pre-dried in an oven at 120°C for 60 min.
[0035] (4) Roller pressing: Two-stage roller pressing is adopted. The first stage has a linear pressure of 15 kN / m to make the slurry smoothly embedded in the matrix. The second stage increases the linear pressure to 45 kN / m for final compaction, resulting in aluminum foam with a thickness of about 130 μm.
[0036] (5) Sintering: The rolled aluminum foam is placed in a tube furnace with high-purity argon gas (flow rate of 200 sccm), heated to 300°C at a rate of 5°C / min, held for 120 min to completely remove the binder; then heated to 550°C at a rate of 5°C / min, held for 360 min to remove excess carbon; then heated to 650°C at a rate of 5°C / min, held for 120 min; finally cooled to 500°C at a rate of 10°C / min (protected tube furnace program), and cooled with the furnace to obtain the final product.
[0037] Example 3: A foamed aluminum electrode foil for aluminum electrolytic capacitors, the preparation method of which is as follows: (1) Substrate pretreatment: Select aluminum foam foil with a thickness of 1 mm, a porosity of 95%, and an average pore diameter of 2 mm. Soak it in dilute hydrochloric acid with a concentration of 0.05 M for 10 min to roughen the pore wall surface, then rinse it with ultrapure water, and then soak it in acetone for 10 min to ensure that the aluminum foam surface is clean and free of impurities, and finally dry it.
[0038] (2) Slurry preparation: Weigh 95 parts of high-purity aluminum powder (99.98%) with a particle size of 3~5μm, 10 parts of polyvinyl butyral, 2 parts of phenolic resin, 10 parts of starch and terpineol by mass. Mix them in a planetary mixer for 3 hours. Control the amount of terpineol to make the viscosity of the slurry 7000 mPa·s. After mixing, put it in a vacuum box to defoam and obtain a uniform slurry.
[0039] (3) Dip coating: The slurry is evenly applied to both sides of the aluminum foam by spraying, and the wet film thickness is about 1.3 mm.
[0040] (4) Drying: Place the aluminum foam obtained in step (3) in a 120℃ oven and dry for 60 min.
[0041] (5) Roller pressing: The gap of the roller press is adjusted to 150μm, and the aluminum foam is rolled.
[0042] (6) Sintering: The rolled aluminum foam is placed in a tube furnace with high-purity argon gas (flow rate of 200 sccm) and heated to 450°C at a rate of 5°C / min, held for 120 min to completely remove the binder; then heated to 550°C at a rate of 5°C / min, held for 360 min to remove excess carbon; then heated to 650°C at a rate of 5°C / min, held for 120 min; finally cooled to 500°C at a rate of 10°C / min (protected tube furnace program), and cooled with the furnace to obtain the final product.
[0043] Example 4: A foamed aluminum electrode foil for aluminum electrolytic capacitors, the preparation method of which is as follows: (1) Substrate pretreatment: Select aluminum foam foil with a thickness of 1 mm, a porosity of 98%, and an average pore size of 1 mm. Soak it in dilute hydrochloric acid with a concentration of 0.05 M for 10 min to roughen the pore wall surface, then rinse it with ultrapure water, and then soak it in acetone for 10 min to ensure that the aluminum foam surface is clean and free of impurities, and finally dry it.
[0044] (2) Slurry preparation: Weigh 80 parts of high-purity aluminum powder (99.98%) with a particle size of 3~5μm, 5 parts of acrylic resin, 1 part of phenolic resin, 8 parts of starch and anhydrous ethanol by mass. Mix and stir in a planetary mixer for 3 hours. Control the amount of anhydrous ethanol to make the viscosity of the slurry 6000 mPa·s. After stirring, put it in a vacuum box to defoam and obtain a uniform slurry.
[0045] (3) Coating: The pretreated aluminum foam is completely immersed in the slurry, held for 30 seconds, and then pulled out of the liquid surface at a constant speed (2 cm / min) to obtain a uniform coating with a wet film thickness of about 0.6 mm.
[0046] (4) Drying: Place the aluminum foam obtained in step (3) in a 120℃ oven and dry for 60 min.
[0047] (5) Roller pressing: The gap of the roller press is adjusted to 150μm, and the aluminum foam is rolled.
[0048] (6) Sintering: The rolled aluminum foam is placed in a tube furnace with high-purity argon gas (flow rate of 200 sccm), heated to 300°C at a rate of 5°C / min, held for 150 min to completely remove the binder; then heated to 550°C at a rate of 5°C / min, held for 400 min to remove excess carbon; then heated to 610°C at a rate of 5°C / min, held for 240 min; finally cooled to 500°C at a rate of 10°C / min (protected tube furnace program), and cooled with the furnace to obtain the final product.
[0049] Comparative Example 1: An aluminum electrolytic capacitor electrode foil, the preparation method of which is as follows: (1) Substrate preparation: Select double-sided aluminum foil with a thickness of 30μm; (2) Slurry preparation: Same as step (2) in Example 2; (3) Double-sided coating: The aluminum foil is coated on both sides by a doctor blade coating method, and the wet film thickness on one side is controlled to be about 200 μm. Then it is pre-dried in an oven at 120℃ for 60 min. After drying, the aluminum foil thickness is about 130 μm. (4) Sintering: Same as step (5) in Example 2.
[0050] Comparative Example 2: A method using commercially etched foil Commercially available high-pressure anodic corrosion foil with a thickness of 130μm and a rated formation voltage of 500V was used as a comparison sample.
[0051] Experimental Example: Performance Testing 1. Anodizing (conversion) treatment: The electrode foil samples obtained in Examples 1, 2, and Comparative Example 1 were placed in a 50 g / L boric acid aqueous solution (temperature 85°C), and firstly, at a concentration of 50 mA / cm²... 2 Anodizing was performed at a current density of 30 min, followed by increasing the voltage to 52V to form an initial dielectric oxide layer. Subsequently, annealing was carried out in air at 500℃ for 3-5 min. Finally, a second formation was performed in the same solution at a current density of 20 mA / cm². 2The time is 5 minutes to ensure the integrity of the dielectric membrane.
[0052] The commercially etched foil in Comparative Example 2 already has a dielectric layer, requiring no additional formation, and can be tested directly.
[0053] 2. Test Results: Key performance tests were performed on the electrode foils prepared in all the above embodiments and comparative examples, and the results are shown in Table 1.
[0054] Table 1 Performance test results of the electrode foils prepared in the examples and comparative examples
[0055] Note: The bending performance test involves repeatedly bending the electrode foil 180° until cracks or breaks appear, in order to evaluate mechanical strength and flexibility.
[0056] 3. Results Analysis: (1) Specific volume performance: The aluminum foam electrode foils prepared in Examples 1 and 2 of this invention have significantly higher surface area specific volumes than those in Comparative Example 1 (optical foil matrix composite foil) and Comparative Example 2 (traditional commercial etched foil). This fully demonstrates the great advantage of the three-dimensional porous structure of aluminum foam in increasing the effective surface area of the electrode, and the composite coating process did not significantly block its high specific surface area characteristics.
[0057] (2) Withstand voltage performance: All samples reached a withstand voltage level of over 500V, and the difference was within the error range, indicating that the surface dense aluminum reinforcement layer formed by the method of the present invention can effectively support and form a uniform and dense dielectric alumina layer, which meets the insulation requirements of high voltage capacitors.
[0058] (3) Mechanical properties: The bending properties of Examples 1 and 2 are better than those of the commercial etched foil in Comparative Example 2, indicating that the dense aluminum layer on the surface significantly enhances the originally fragile aluminum foam structure. Although slightly lower than that of the optical foil substrate in Comparative Example 1 (because its substrate itself is a dense foil), it fully meets the mechanical strength requirements of the electrode foil in subsequent processing such as cutting and winding.
[0059] In summary, this invention, through an innovative composite structure design of "aluminum foam matrix + dense aluminum reinforcement layer" and a corresponding coating-rolling-sintering preparation method, has successfully prepared a novel electrode foil for aluminum electrolytic capacitors that combines high specific capacitance, good voltage resistance, and excellent mechanical strength. Its comprehensive performance is powerful, effectively solving the bottleneck problem of direct application of aluminum foam, and it demonstrates significant progress and promising application prospects.
[0060] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.
Claims
1. A method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors, characterized in that, Includes the following steps: (1) Matrix pretreatment: Aluminum foam is used as the matrix. The aluminum foam is soaked in hydrochloric acid solution, washed, soaked in acetone and then dried. (2) Slurry preparation: Weigh 80-95 parts of aluminum powder, 5-10 parts of organic binder, 5-10 parts of pore-forming agent, 1-2 parts of dispersant and organic solvent by mass and mix them to prepare a slurry with a viscosity of 4000-7000 mPa.s; (3) Coating: The slurry is uniformly coated on both sides of the aluminum foam; (4) Drying: The coated aluminum foam is dried at 100~120℃; (5) Roll pressing: The dried aluminum foam is subjected to roll pressing treatment; (6) Sintering: The rolled aluminum foam is sintered under a protective atmosphere or vacuum. First, the temperature is raised to 300~450℃ at a rate of 5℃ / min and held for 120~150min; then the temperature is raised to 550℃ at a rate of 5℃ / min and held for 360~400min; then the temperature is raised to 610~650℃ at a rate of 5℃ / min and held for 120~240min; finally, the temperature is lowered to 100℃ at a rate of 10℃ / min and cooled with the furnace to obtain the final product.
2. The method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The aluminum foam has a thickness of 0.3~1.0 mm, a porosity of 90~98%, and an average pore size of 0.1~2 mm.
3. The method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The concentration of the hydrochloric acid solution was 0.05M, and the soaking time for both the hydrochloric acid solution and acetone was 10 minutes.
4. The method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The aluminum powder has a particle size of 3~5μm and a purity of not less than 99.98%.
5. The method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The organic binder is at least one of polyvinyl butyral, ethyl cellulose, and acrylic resin; the pore-forming agent is starch; the dispersant is phenolic resin; and the organic solvent is at least one of anhydrous ethanol, terpineol, and ethylene glycol.
6. The method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The slurry is uniformly coated onto the surface of the aluminum foam by dip coating, blade coating, spraying or roller coating processes, and the wet film thickness after coating is 0.5~1.3mm.
7. The method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors according to claim 6, characterized in that, The dip coating method is as follows: the pretreated foam aluminum foil is completely immersed in the slurry, and after 30 seconds it is pulled out of the liquid surface at a constant speed of 2 cm / min to obtain a uniform coating.
8. The method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The drying time in step (4) is 60 minutes.
9. The method for preparing foamed aluminum electrode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The thickness of the rolled aluminum foam is 120~150μm.
10. A foamed aluminum electrode foil for an aluminum electrolytic capacitor prepared by the preparation method according to any one of claims 1 to 9.