Anode foil of aluminum electrolytic capacitor and preparation method of anode foil

Abstract

The invention relates to the technical field of thick film materials special for electronic components, and particularly discloses an aluminum electrolytic capacitor anode foil and a preparation method thereof. The aluminum electrolytic capacitor anode foil is composed of an aluminum foil substrate and an aluminum powder sintering layer formed on the surface of the aluminum foil substrate. A porous framework-conductive bridge composite structure is arranged in the aluminum powder sintering layer; the porous framework is composed of porous aluminum balls and common aluminum powder, the porous aluminum balls are spherical aluminum powder with three-dimensional through pores inside, and the conductive bridge is an aluminum metal sintering neck which is formed by sintering in a hydrogen atmosphere and is connected with the aluminum particles. The preparation method comprises the steps of preparation of aluminum-pore forming agent composite powder, preparation of slurry, coating, drying, presintering, salt leaching, final sintering and the like. The aluminum electrolytic capacitor anode foil with high specific capacitance, low impedance and high reliability can be prepared, the conductive network of the aluminum electrolytic capacitor anode foil is composed of the aluminum metal sintering neck, the resistance is low, the mechanical strength is high, the electrical performance of a capacitor is improved, and the service life of the capacitor is prolonged.

Description

Technical Field

[0001] This invention relates to the field of thick and thin film materials for electronic components, and more specifically to an aluminum electrolytic capacitor anode foil and its preparation method. Background Technology

[0002] Aluminum electrolytic capacitors are widely used in power supply circuits, consumer electronics, and other fields due to their large capacity, low cost, and high reliability. The anode foil, as its core energy storage component, depends on its specific surface area (affecting energy storage capacity) and conductivity (affecting charge and discharge efficiency). Traditional anode foils form a porous layer through electrochemical corrosion, but the corrosion channels are easily blocked, and the increase in specific surface area is limited. Existing coated anode foils mostly use a single aluminum powder sintered layer, which improves the specific surface area, but the contact resistance between aluminum particles is high, and pore collapse easily occurs after sintering, leading to a decrease in capacitance performance and cycle stability.

[0003] To address the aforementioned issues, there is an urgent need to develop an anode foil structure that balances high specific surface area with low contact resistance, while also providing a stable and scalable preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide an aluminum electrolytic capacitor anode foil and its preparation method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, on the one hand, the present invention provides an aluminum electrolytic capacitor anode foil, which is composed of an aluminum foil substrate and an aluminum powder sintered layer formed on its surface. The aluminum powder sintered layer has a porous skeleton-conductive bridge composite structure inside. The porous skeleton is composed of aluminum-pore-forming agent composite powder and ordinary aluminum powder. The aluminum-pore-forming agent composite powder is a spherical aluminum powder with three-dimensional through pores inside. The conductive bridge is an aluminum metal sintered neck formed by sintering in a hydrogen atmosphere and connecting aluminum particles.

[0006] Preferably, the aluminum-pore-forming agent composite powder has a particle size D90 of 5-50 μm and a porosity of 40-70%, and the pore-forming agent is at least one of sodium chloride, potassium chloride, or a soluble inorganic salt. Specifying the type of pore-forming agent (inorganic or soluble) ensures that the pore-forming process is residue-free and the pore structure is controllable.

[0007] Preferably, the particle size D90 of the ordinary aluminum powder is 1-20 μm, and the mass ratio of the aluminum-pore-forming agent composite powder to the ordinary aluminum powder is (30:70)-(60:40). This addresses the defect of easy pore collapse in the skeleton of a single aluminum-pore-forming agent composite powder: the 1-20 μm particle size of the ordinary aluminum powder can accurately fill the gaps between the 5-50 μm aluminum-pore-forming agent composite powder, and the mass ratio of 30:70-60:40 ensures a balance between pore retention rate and skeleton density. If the proportion of aluminum-pore-forming agent composite powder is too low (<30%), the specific surface area is insufficient; if it is too high (>60%), the ordinary aluminum powder will not fill the gaps sufficiently, and the pore collapse rate will rise to over 30% after sintering.

[0008] Preferably, the aluminum metal sintered neck is formed by sintering in a mixed atmosphere of hydrogen and nitrogen at 500-650℃, and its microstructure is a metallurgical bonding interface formed between aluminum particles through atomic diffusion. This clarifies that the conductive bridge is a pure aluminum-aluminum metallurgical bond with excellent conductivity. Simultaneously, an optimal temperature window (550-580℃) is defined for forming this high-quality conductive bridge; too low a temperature will result in insufficient sintering, while too high a temperature may lead to the collapse of the porous structure.

[0009] Preferably, the amount of pore-forming agent added to the molten aluminum is 10%-15% of the mass of the molten aluminum. Precise control of the number of pores in the porous aluminum spheres is crucial: <10% pore-forming agent results in a porosity below 40% (insufficient specific surface area), while >15% results in excessively thin aluminum sphere walls (prone to breakage during sintering); an addition of 10%-15% can stably achieve a porosity of 40-70%, ensuring a balance between the structural strength and specific surface area requirements of the porous aluminum spheres. The particle size of the pore-forming agent (D90 of 5-30 μm) directly determines the final pore size and distribution of the porous aluminum spheres, and is a key factor in controlling etching behavior.

[0010] On the other hand, the present invention also provides a method for preparing the anode foil of an aluminum electrolytic capacitor, comprising the following steps: Ordinary aluminum powder and pore-forming agent are mixed in a specified ratio and placed in a ball mill. Under the protection of inert nitrogen gas, the mixture is ball-milled at 200-300 rpm for 1-2 hours to obtain aluminum powder-pore-forming agent composite powder. A slurry is prepared by mixing aluminum-pore-forming agent composite powder, ordinary aluminum powder, binder and solvent, which is then coated onto an aluminum foil substrate and dried to form a blank. The preform is pre-sintered in a mixed atmosphere of hydrogen and nitrogen. The pre-sintered embryo is washed with salt and dried. The dried preform was sintered in a mixed atmosphere of hydrogen and nitrogen to obtain the anode foil for an aluminum electrolytic capacitor.

[0011] Preferably, the pre-sintering includes heating to 400-550°C at a rate of 3-10°C / min and holding for 30-90 min. The purpose of this stage is to decompose and remove the organic binder and initially establish the bonding strength between aluminum particles, making the blank sufficient for subsequent processing. The final sintering includes heating to 550-580°C at a rate of 2-8°C / min and holding for 60-150 min. In this stage, under the action of hydrogen reduction, a strong aluminum metal sintering neck is formed between the aluminum particles, ultimately obtaining an anode foil with a three-dimensional through-porous structure.

[0012] Salt washing involves immersing the pre-sintered green body in deionized water and performing ultrasonic-assisted cleaning at a power density of 0.3-0.8 W / cm² for 60-120 minutes, until the filtrate shows no chloride ion response when tested with a conductivity meter or silver nitrate solution. At this point, the green body is an open-pore, not fully dense structure, and the pore-forming agent particles come into contact with the external solvent through an interconnected pore network, thus being effectively dissolved and washed out.

[0013] Preferably, the hydrogen volume concentration in the mixed atmosphere is 3%-15%, with the balance being nitrogen. The hydrogen concentration (3%-15%) is a critical value for achieving effective reduction and promoting sintering. If the concentration is too low, the reduction effect is insufficient, and the oxide film hinders sintering; if the concentration is too high, costs increase and safety requirements become more stringent. This range represents the optimal choice for balancing technical effectiveness and cost control.

[0014] Preferably, the binder is at least one of polyvinyl alcohol, hydroxypropyl methylcellulose, or polyacrylate, and the slurry has a solid content of 50%-75% and a viscosity of 2000-6000 cP. To ensure the uniformity of slurry coating and the strength of the green body: water-soluble binders (such as PVA) are easy to clean and leave no residue; a solid content of 50%-75% avoids the slurry being too thin (<50% is prone to sagging) or too thick (>75% is difficult to coat); and a viscosity of 2000-6000 cP is suitable for the doctor blade coating process, avoiding porosity defects after sintering due to uneven green body.

[0015] Preferably, after coating and before sintering, the process further includes a rolling step of the billet, with a rolling pressure of 10-20 MPa and 1-2 rolling passes. This improves the density of the billet and the contact between aluminum particles: a rolling pressure of 10-20 MPa can increase the contact area between aluminum particles by more than 30% (avoiding insufficient contact when the pressure is <10% and compaction of pores when the pressure is >40%), and 1-2 rolling passes can balance "density" and "porosity retention", enhancing the structural stability and cycle life of the anode foil.

[0016] The core mechanism of this scheme is as follows: Mechanical ball milling uses mechanical force to deform ductile aluminum powder, cold-welding and encapsulating brittle pore-forming agent particles to form a highly uniform aluminum-pore-forming agent composite powder at the microscale. During rolling, ordinary aluminum powder with excellent plasticity deforms and flows, filling the gaps between rigid aluminum-pore-forming agent composite powder particles to form a prefabricated structure of "matrix-reinforcing phase". After salt washing treatment, the pore-forming agent inside the composite powder is dissolved and transformed in situ into porous aluminum spheres with three-dimensional interconnected pores, while the ordinary aluminum powder matrix forms a continuous conductive network. Finally, in hydrogen atmosphere sintering, hydrogen effectively removes the insulating oxide film on the surface of aluminum particles, causing aluminum atoms to diffuse at high temperature at the contact points to form a strong "aluminum metal sintering neck". These sintering necks act like high-speed conductive circuits, tightly connecting the porous aluminum spheres and ordinary aluminum powder into an integral network skeleton with both high conductivity and high mechanical strength.

[0017] The beneficial effects of this invention are as follows: (1) Significantly improve specific surface area and energy storage capacity: The scheme uses a porous aluminum sphere + ordinary aluminum powder composite porous skeleton design. The three-dimensional through pores of the porous aluminum sphere provide sufficient sites for charge storage, enabling the anode foil to obtain excellent specific surface area, which in turn significantly improves the specific capacitance. This effectively solves the problems of insufficient specific surface area and low energy storage capacity of traditional single aluminum powder skeleton.

[0018] (2) Establishing an efficient conductive network and optimizing charge transport performance: The aluminum metal sintering neck formed by sintering in a hydrogen atmosphere creates a stable conductive channel at the contact point of aluminum particles, which makes the anode foil have a low volume resistivity and significantly improves the charge transport efficiency, breaking through the technical bottleneck that high specific surface area is inevitably accompanied by high resistance.

[0019] (3) Enhance the stability of the skeleton structure and ensure long-term performance: The optimized ratio design of ordinary aluminum powder and porous aluminum balls ensures the density of the structure while retaining sufficient porosity. After sintering, the pore structure remains intact, effectively suppressing the performance degradation caused by pore collapse and ensuring the structural stability of the anode foil for long-term use.

[0020] (4) Improved cycle life and operational reliability: The synergistic effect of the composite porous skeleton and the aluminum metal sintered neck significantly enhances the structural integrity of the electrode material, exhibits excellent interface stability during long-term charge and discharge, significantly improves the specific capacitance retention rate, and extends the service life of the anode foil.

[0021] (5) The process is stable and controllable, which is conducive to industrialization: The preparation process adopts mature technologies such as "mechanical ball milling", "slurry coating" and "hydrogen atmosphere sintering". The key process parameters are clearly defined and easy to control. No special equipment investment is required. It has good production line compatibility and provides a reliable guarantee for large-scale production. Detailed Implementation

[0022] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0023] It should be noted that all reagents and raw materials used in this invention are commercially available, and the reagents are of analytical grade.

[0024] The polyacrylate is sourced from Dow Chemical Company, USA, and is designated as RHOPLEX™ HG-95P.

[0025] Hydroxypropyl methylcellulose is sourced from Shanxi Jinyang Pharmaceutical Excipients Co., Ltd., with CAS number 9004-65-3.

[0026] Raw material preparation: Aluminum foil substrate: 1060 pure aluminum foil, 100μm thick; Pore-forming agents: NaCl powder (average particle size 8μm), KCl powder (average particle size 5μm); Ordinary aluminum powder: 99.9% pure aluminum powder, particle size D90=1μm, 10μm, 20μm, 35μm, 50μm; Binders: Polyvinyl alcohol (PVA, degree of polymerization 1700), hydroxypropyl methylcellulose, polyacrylate; Carbon sources: methane, acetylene, ethylene; Inert gas: 99.99% argon, nitrogen: 99.99% high-purity nitrogen. Example 1

[0027] A method for preparing the anode foil of an aluminum electrolytic capacitor includes the following steps: Preparation of porous aluminum balls from aluminum-NaCl composite powder: Ordinary aluminum powder and NaCl powder were mixed in a volume ratio of 45:55 with a porosity of 55% and placed in a ball mill. Under the protection of inert nitrogen gas, the mixture was ball milled at 250 rpm for 1.5 h to obtain aluminum-NaCl composite powder (D90=25μm, porosity 55%). Slurry preparation: A porous framework (aluminum-NaCl composite powder: ordinary aluminum powder (D90=10μm) = 30:70 (mass ratio)), polyvinyl alcohol (accounting for 10% of the slurry mass) and deionized water were mixed to prepare a slurry with a solid content of 60% and a viscosity of 4000cP. Coating and drying: The slurry is coated on the aluminum foil substrate to a thickness of 50 μm, and dried at 100°C for 45 min to form a blank. Then the blank is rolled twice at 20 MPa. Pre-sintering: The rolled billet is heated to 400℃ in a mixed atmosphere (5% hydrogen + 95% nitrogen, V / V) at a rate of 3℃ / min and held for 120min. Salt washing: The pre-sintered green body is immersed in deionized water at a power density of 0.3 W / cm³. 2 The product was cleaned with ultrasonic assistance for 120 minutes and then dried to obtain the crude product.

[0028] Final sintering: The crude product is heated to 550°C at a rate of 2°C / min in a mixed atmosphere (5% hydrogen + 95% nitrogen, V / V) and held for 150 min to obtain the anode foil of aluminum electrolytic capacitor. Example 2

[0029] A method for preparing the anode foil of an aluminum electrolytic capacitor includes the following steps: Preparation of aluminum-KCl composite powder: Ordinary aluminum powder and KCl powder were mixed in a ratio of 60:40 with a porosity of 40% and placed in a ball mill. Under the protection of inert nitrogen gas, the mixture was ball milled at 300 rpm for 1 h to obtain aluminum-KCl composite powder (D90=5μm, porosity 40%). Slurry preparation: A porous framework (aluminum-KCl composite powder: ordinary aluminum powder (D90=1μm) = 20:80 (mass ratio)), hydroxypropyl methylcellulose (8% of slurry mass) and deionized water were mixed to prepare a slurry with a solid content of 50% and a viscosity of 2000 cP. Coating and drying: The slurry is coated on the aluminum foil substrate to a thickness of 40 μm, and dried at 80°C for 60 min to form a blank. Then the blank is rolled once at 10 MPa. Pre-sintering: The rolled billet is heated to 500℃ in a mixed atmosphere (3% hydrogen + 97% nitrogen, V / V) at a rate of 5℃ / min and held for 60min. Salt washing: The pre-sintered green body is immersed in deionized water at a power density of 0.5 W / cm³. 2 The product was cleaned with ultrasonic assistance for 100 minutes and then dried to obtain the crude product.

[0030] Final sintering: The crude product is heated to 570°C at a rate of 5°C / min in a mixed atmosphere (3% hydrogen + 97% nitrogen, V / V) and held for 120 min to obtain the anode foil of aluminum electrolytic capacitor. Example 3

[0031] A method for preparing the anode foil of an aluminum electrolytic capacitor includes the following steps: Preparation of aluminum-NaCl composite powder: Ordinary aluminum powder and NaCl powder were mixed in a ratio of 30:70 (porosity 70%) and placed in a ball mill. Under the protection of inert nitrogen gas, the mixture was ball milled at 300 rpm for 2 hours to obtain aluminum-NaCl composite powder (D90=50μm, porosity 70%). Slurry preparation: A porous framework (aluminum-NaCl composite powder: ordinary aluminum powder (D90=20μm) = 60:40 (mass ratio)), polyacrylate (accounting for 12% of the slurry mass) and deionized water were mixed to prepare a slurry with a solid content of 75% and a viscosity of 6000cP. Coating and drying: The slurry is coated on the aluminum foil substrate to a thickness of 60 μm, and dried at 120°C for 30 min to form a preform. The preform is then rolled twice at 15 MPa. Pre-sintering: The rolled billet is heated to 550°C at a rate of 10°C / min in a mixed atmosphere (15% hydrogen + 85% nitrogen, V / V) and held for 30 min. Salt washing: The pre-sintered green body is immersed in deionized water at a power density of 0.8 W / cm³. 2 The product was cleaned with ultrasonic assistance for 60 minutes and then dried to obtain the crude product.

[0032] Final sintering: The crude product is heated to 580°C at 8°C / min in a mixed atmosphere (15% hydrogen + 85% nitrogen, V / V) and held for 60 min to obtain the anode foil of aluminum electrolytic capacitor. Example 4

[0033] A method for preparing the anode foil of an aluminum electrolytic capacitor includes the following steps: Preparation of aluminum-KCl composite powder: Ordinary aluminum powder and KCl powder were mixed in a ratio of 40:60 with a porosity of 60% and placed in a ball mill. Under the protection of inert nitrogen gas, the mixture was ball milled at 240 rpm for 1.6 h to obtain aluminum-KCl composite powder (D90=35μm, porosity 60%). Slurry preparation: A porous framework (aluminum-KCl composite powder: ordinary aluminum powder (D90=15μm) = 45:55 (mass ratio)), polyacrylate + PVA (9% of slurry mass, mass ratio 1:1) and deionized water were mixed to prepare a slurry with a solid content of 65% and a viscosity of 5000cP. Coating and drying: The slurry is coated on the aluminum foil substrate to a thickness of 55 μm, and dried at 110℃ for 40 min to form a blank. Then the blank is rolled twice at 12 MPa. Pre-sintering: The rolled billet is heated to 450°C in a mixed atmosphere (8% hydrogen + 92% nitrogen, V / V) at a rate of 8°C / min and held for 50 min. Salt washing: The pre-sintered green body is immersed in deionized water at a power density of 0.6 W / cm³. 2 The product was cleaned with ultrasonic assistance for 80 minutes and then dried to obtain the crude product.

[0034] Final sintering: The crude product is heated to 560°C at a rate of 6°C / min in a mixed atmosphere (8% hydrogen + 92% nitrogen, V / V) and held for 80 min to obtain the anode foil of aluminum electrolytic capacitor.

[0035] Comparative Example 1 The aluminum-NaCl composite powder in Example 1 was replaced with an equal amount of ordinary aluminum powder, and the remaining components, steps and parameters were completely consistent with those in Example 1.

[0036] Comparative Example 2 The ordinary aluminum powder in Example 1 was replaced with an equal amount of aluminum-NaCl composite powder, and the remaining components, steps and parameters were completely consistent with those in Example 1.

[0037] Comparative Example 3 In the in-situ sintering step, the sintering atmosphere is pure nitrogen, with no hydrogen. The remaining components, steps, and parameters are completely consistent with those in Example 1.

[0038] The anode foils prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to relevant performance tests. The test standards and methods are as follows, and the test results are recorded in Table 1.

[0039] 1. BET specific surface area: According to GB / T 19587-2017, the liquid nitrogen adsorption method is adopted. After drying and removing impurities, the anode foil sample is placed in a liquid nitrogen environment at -196℃. The amount of nitrogen adsorption is measured in the relative pressure range of 0.05-0.3. The specific surface area is calculated by the BET two-parameter equation, which reflects the degree of development of the porous structure of the anode foil and provides a basis for the number of charge storage sites.

[0040] 2. Volume resistivity: According to GB / T 351-2021, the room temperature four-probe method is adopted. The four probes are pressed vertically on the surface of the pretreated anode foil sample (avoiding the edges), a stable current is passed through and the voltage of the inner probe is measured. Combined with the sintered layer thickness (total thickness minus aluminum foil substrate thickness), the resistivity is calculated according to the four-probe formula for thin samples to evaluate the conductivity of the anode foil.

[0041] 3. Specific capacitance: The CV method was used with 30wt% sulfuric acid as electrolyte to construct a three-electrode system (anode foil as working electrode, saturated calomel electrode as reference electrode, and platinum sheet as counter electrode). Cyclic voltammetry scans were performed at a scan rate of 10mV / s and a voltage range of 0-1V. The energy storage capacity of the anode foil was directly reflected by integrating the area of ​​the CV curve and calculating it according to the specific capacitance formula.

[0042] 4. Cyclic stability: The specific capacitance was measured after 1000 constant current charge-discharge tests (0-1V voltage range, 1mA / cm² current density). The retention rate was calculated as "specific capacitance of the 1000th cycle / specific capacitance of the 1st cycle × 100%" to evaluate the performance degradation trend of the anode foil during long-term charge-discharge.

[0043] 5. Pore collapse rate: Referring to GB / T 23561.1-2009, the porosity of the pre-sintered green body and the anode foil after sintering was determined by the impregnation method (calculated by dry weight, mass after saturated impregnation and aluminum density). The collapse rate was calculated as "(porosity before sintering - porosity after sintering) / porosity before sintering × 100%" to reflect the structural stability of the porous skeleton.

[0044] 6. Conductive bridge bonding strength: A custom ultrasonic oscillation test was used. The initial resistivity of the anode foil sample was measured first, and then ultrasonically oscillated at 300W power for 5 minutes. After drying, the resistivity after oscillation was measured. The change rate was calculated according to "(resistivity after oscillation - resistivity before oscillation) / resistivity before oscillation × 100%" to evaluate the interfacial bonding strength between the in-situ conductive bridge and the aluminum particles.

[0045] Table 1 Performance Test Results sample BET specific surface area (m² / g) Volume resistivity (μΩ・cm) Specific capacitance (μF / cm²) Retention rate after 1000 cycles (%) Pore ​​collapse rate (%) Conductive bridge bond strength (resistivity change rate, %) Example 1 32.5 8.2 720 90.5 8.3 5.2 Example 2 22.8 14.5 615 86.4 10.1 7.8 Example 3 43.1 6.1 834 92.8 6.4 4.1 Example 4 38.7 7.3 786 91.3 7.4 4.9 Comparative Example 1 15.2 25.6 480 75.3 15.7 - Comparative Example 2 38.9 19.8 592 78.5 32.6 - Comparative Example 3 31.6 42.3 516 72.1 9.2 - As shown in the table above, Comparative Example 1, lacking aluminum-NaCl composite powder, had a specific surface area of ​​only 46.8% of that of Example 1 (15.2 vs 32.5 m² / g). Due to the absence of three-dimensional interconnected pores and insufficient charge storage sites, the specific capacitance decreased by 33.3% (480 vs 720 μF / cm²). At the same time, ordinary aluminum powder had poor packing density, and the pore collapse rate increased to 15.7% (compared to only 8.3% in Example 1). This demonstrates that aluminum-NaCl composite powder is the core element for improving specific surface area and framework stability.

[0046] Although the specific surface area of ​​the single aluminum-NaCl composite powder in Comparative Example 2 was slightly higher (38.9 vs 32.5 m² / g), the pore collapse rate during sintering increased dramatically to 32.6% (compared to only 8.3% in Example 1) due to the lack of ordinary aluminum powder filling the gaps. This resulted in a decrease in specific capacitance of 18.1% (590 vs 720 μF / cm²), and insufficient contact between aluminum particles, leading to an increase in resistivity to 19.8 μΩ・cm (compared to only 8.2 μΩ・cm in Example 1). This demonstrates that the "composite skeleton" design of ordinary aluminum powder and aluminum-NaCl composite powder has a synergistic effect, which can avoid the collapse defects of a single porous structure.

[0047] Comparative Example 3 exhibited a surge in resistivity to 42.3 μΩ·cm (compared to only 8.2 μΩ·cm in Example 1), a 29.2% decrease in specific capacitance (510 vs 720 μF / cm²), and a cycling stability reduced to 72.1% due to resistive heating. Its volume resistivity was significantly higher than that of Example 1, and its mechanical strength was also poor. The lack of hydrogen's cleaning effect on the oxide film prevented the formation of effective metallurgical bonds between aluminum particles, demonstrating that the addition of hydrogen is crucial for reducing contact resistance and improving cycling stability.

[0048] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

[0049] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. An anode foil for an aluminum electrolytic capacitor, characterized in that, It consists of an aluminum foil substrate and an aluminum powder sintered layer formed on its surface. The aluminum powder sintered layer has a porous skeleton-conductive bridge composite structure. The porous skeleton is composed of aluminum-pore-forming agent composite powder and ordinary aluminum powder. The aluminum-pore-forming agent composite powder is a spherical aluminum powder with three-dimensional through pores. The conductive bridge is an aluminum metal sintered neck formed by sintering in a hydrogen atmosphere to connect aluminum particles.

2. The anode foil of the aluminum electrolytic capacitor according to claim 1, characterized in that, The aluminum-pore-forming agent composite powder has a particle size D90 of 5-50 μm and a porosity of 40-70%, and the pore-forming agent is at least one of sodium chloride, potassium chloride, or a soluble inorganic salt.

3. The anode foil of the aluminum electrolytic capacitor according to claim 2, characterized in that, The particle size D90 of the ordinary aluminum powder is 1-20μm, and the mass ratio of the aluminum-pore-forming agent composite powder to the ordinary aluminum powder is (30:70)-(60:40).

4. The anode foil of the aluminum electrolytic capacitor according to claim 1, characterized in that, The aluminum metal sintered neck is formed by sintering in a mixed atmosphere of hydrogen and nitrogen at 500-650℃, and its microstructure is a metallurgical bonding interface formed between aluminum particles through atomic diffusion.

5. The anode foil of the aluminum electrolytic capacitor according to claim 2, characterized in that, The amount of the pore-forming agent added to the molten aluminum is 10%-15% of the mass of the molten aluminum.

6. A method for preparing the anode foil of an aluminum electrolytic capacitor according to any one of claims 1-5, characterized in that, Includes the following steps: Ordinary aluminum powder and pore-forming agent are mixed in a specified ratio and placed in a ball mill. Under the protection of inert nitrogen gas, the mixture is ball-milled at 200-300 rpm for 1-2 hours to obtain aluminum-pore-forming agent composite powder. A slurry is prepared by mixing aluminum-pore-forming agent composite powder, ordinary aluminum powder, binder and solvent, which is then coated onto an aluminum foil substrate and dried to form a blank. The preform is pre-sintered in a mixed atmosphere of hydrogen and nitrogen. The pre-sintered embryo is washed with salt and dried. The dried preform was sintered in a mixed atmosphere of hydrogen and nitrogen to obtain the anode foil for an aluminum electrolytic capacitor.

7. The method for preparing the anode foil of an aluminum electrolytic capacitor according to claim 6, characterized in that, The pre-sintering includes heating to 400-550℃ at a rate of 3-10℃ / min and holding at that temperature for 30-90min; the final sintering includes heating to 550-580℃ at a rate of 2-8℃ / min and holding at that temperature for 60-150min.

8. The method for preparing the anode foil of an aluminum electrolytic capacitor according to claim 6, characterized in that, The volume concentration of hydrogen in the mixed atmosphere is 3%-15%, with the remainder being nitrogen.

9. The method for preparing the anode foil of an aluminum electrolytic capacitor according to claim 6, characterized in that, The binder is at least one of polyvinyl alcohol, hydroxypropyl methylcellulose or polyacrylate, and the slurry has a solid content of 50%-75% and a viscosity of 2000-6000 cP.

10. The method for preparing the anode foil of an aluminum electrolytic capacitor according to claim 6, characterized in that, After coating and before sintering, the process also includes rolling the billet at a pressure of 10-20 MPa and 1-2 rolling passes.