A method for preparing a porous anode aluminum foil for an electrolytic capacitor based on laser additive manufacturing

Abstract

This invention provides a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, comprising the following steps: selecting aluminum foil with a thickness of 30 μm and aluminum powder particles with an average particle size of 5-6 μm as raw materials; adding the aluminum powder particles to the aluminum foil through a feeding hopper, and controlling the thickness of the aluminum powder particles using a vibrating scraper below the feeding hopper, so that the aluminum powder is basically spread in a single layer on the aluminum foil to ensure the single-layer distribution of aluminum spheres; adding a dispersant to the raw materials to prevent the spheres from clumping; and adding high-frequency vibration with an amplitude of micrometers to the scraper at the outlet of the feeding hopper to facilitate the single-layer spread of spheres and to cover the entire plane; using a linear laser to weld the aluminum powder particles, completely welding the covered aluminum metal particles. After one side of the aluminum foil is completely welded with the aluminum powder particles, the aluminum foil is flipped over by a flipping device, and then the other side of the aluminum foil is covered and welded with the aluminum powder particles. The preparation method provided by this invention solves the problems of decreased specific surface area and decreased porosity or capacitance of electrode foil in the electrode foil manufacturing process.

Description

Technical Field

[0001] This invention relates to the field of capacitor technology, and in particular to a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing. Background Technology

[0002] Capacitors include film capacitors, ceramic capacitors, and electrolytic capacitors. Among these, tantalum electrolytic capacitors and aluminum electrolytic capacitors are the most commonly used; aluminum electrolytic capacitors are widely used due to their large volumetric capacitance and low cost per unit capacitance. The aluminum foil electrodes of aluminum electrolytic capacitors are typically prepared using electrochemical etching to obtain a porous structure, followed by anodic oxidation to grow an aluminum oxide film on the etched foil surface, thus achieving its dielectric properties. The degree of etching of the aluminum foil varies depending on the operating voltage, employing different etching conditions. Specifically, in medium- and high-voltage capacitors, where the oxide film is thicker, direct current etching is often used to form tunnel pores; in low-voltage capacitors, to obtain a high specific surface area, alternating current etching is often used to form sponge pores.

[0003] However, regardless of whether DC or AC corrosion is used, corrosion solutions containing hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, etc., must be used, which places a huge burden on the environment. Post-treatment of the corrosion solution also imposes a significant burden on the process and economy.

[0004] According to literature review, patent document CN103563028A proposes an electrode foil for electrolytic capacitors, which has a single-sided or double-sided sintered aluminum powder body on an aluminum substrate without requiring electrochemical corrosion treatment. Patent document CN104620342A proposes an electrode foil characterized by forming a porous layer composed of sintered aluminum powder on the surface of the aluminum material. Patent document CN105874549A proposes an electrode foil for aluminum electrolytic capacitors, comprising a porous sintered body composed of aluminum and aluminum alloy powders maintaining inter-pores and a supporting substrate. Patent document CN103688327A proposes an electrode material for electrolytic capacitors, characterized by having an aluminum substrate and a powder sintered body, the sintered body being obtained by pressing and sintering a film composed of aluminum or aluminum alloy powder. Patent document CN104919552A proposes a method of attaching a paste containing aluminum powder to an aluminum substrate, and then sintering this paste to obtain a porous aluminum foil for electrolytic capacitors. Patent document CN104094370A proposes a method for preparing an electrode material, characterized by forming a mold on an aluminum substrate and clamping the substrate from both sides to form a stack, and then attaching aluminum powder to the aluminum substrate and sintering it.

[0005] In the methods described above, the porous structure is achieved solely by altering the composition of aluminum or aluminum alloy powder. However, whether through direct aluminum powder sintering or pre-forming a film before sintering, the specific surface area of ​​the sintered aluminum foil is limited due to the excessively fine aluminum powder particles. This is because finer aluminum powder has a higher surface energy, leading to powder fusion during sintering, filling the gaps between powder particles, reducing the specific surface area, and resulting in limited or even decreased improvement in electrostatic capacitance. The electrode foils obtained in the aforementioned literature are suitable for high-voltage foils where high porosity is not required.

[0006] Patent document CN105393320A discloses a method for improving the electrode material of aluminum electrolytic capacitors. This method involves sintering aluminum and aluminum alloy powders together with electrically insulating particles to create a sintered layer that maintains high capacitance even when used in low-voltage electrolytic capacitors. However, the addition of insulating particles makes it difficult to sinter the electrode foil. Furthermore, the insulating particles reduce conductivity, thus affecting the efficiency of subsequent anodizing processes.

[0007] In summary, in the process of sintering aluminum powder to obtain electrode foil, finer aluminum powder needs to be used to obtain electrode foil with high specific capacitance. However, using fine-particle aluminum powder to prepare electrode foil will face the following problems:

[0008] (1) Fine aluminum powder has a larger surface energy, which makes it easier to fuse and sinter, resulting in a decrease in the specific surface area of ​​the electrode foil;

[0009] (2) When using fine aluminum powder, the sintering temperature will be limited, which will lead to a decrease in the porosity or capacitance of the electrode foil. That is, the sintering temperature of aluminum powder cannot be too high. If the sintering temperature is too high, the aluminum powder will melt, which will lead to a decrease in the porosity of the electrode foil. However, if the sintering temperature is too low, the aluminum powder will not melt sufficiently and the aluminum powder particles will not be tightly connected, which will cause the sintering neck to break in subsequent processing, thus failing to exert dielectric properties, and ultimately causing a decrease in capacitance or even powder loss.

[0010] In addition, sintering needs to be carried out at 250-650℃ for 1-100 hours under vacuum or inert atmosphere. The sintering process is time-consuming, energy-intensive, requires large equipment, and occupies a large area.

[0011] Therefore, it is necessary to provide a new method for preparing high specific volume porous anode aluminum foil to overcome the problems existing in the prior art. Summary of the Invention

[0012] This invention provides a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, which solves the problems of decreased specific surface area and decreased porosity or capacitance of electrode foil in the electrode foil process.

[0013] To address the aforementioned technical problems, this invention provides a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, comprising the following steps:

[0014] Aluminum foil with a thickness of 30μm and aluminum powder particles with an average particle size of 5-6μm are selected as raw materials. The aluminum powder particles are added to the aluminum foil through a feeding hopper, and the thickness of the aluminum powder particles is controlled by a vibrating scraper below the feeding hopper, so that the aluminum powder is basically spread in a single layer on the aluminum foil; in order to ensure the single-layer distribution of aluminum balls.

[0015] A dispersant is added to the raw material to prevent the spheres from clumping together. A high-frequency vibration with an amplitude of micrometers is added to the scraper at the outlet of the feeding hopper to facilitate the single-layer flat laying of the spheres and to cover the entire plane.

[0016] The aluminum powder particles are fused together using a linear laser to completely fuse the covered aluminum metal particles.

[0017] To ensure good welding between aluminum balls and foil, and between aluminum balls themselves, semiconductor lasers with high aluminum absorption efficiency (880, 915, or 976 nm) are selected as the welding heat source. The ultraviolet band, which has even higher absorption efficiency, was not chosen because ultraviolet lasers have low photoelectric conversion efficiency and are expensive, making them less cost-effective for welding aluminum balls compared to infrared semiconductor lasers.

[0018] The key to welding is matching the output of laser energy with the moving speed of the aluminum foil strip. At this point, the aluminum sphere and the aluminum foil surface, which are irradiated by the laser, liquefy within a few nanometers and fuse together.

[0019] Specifically, the specific heat of aluminum is 0.88 kJ / kg / ℃; the melting point of aluminum is 660℃; assuming a room temperature of 20℃; 0.88 × (660 - 20) = 563.2 kJ / kg; therefore, the heat required to raise the temperature from 20℃ to the melting point is 563.2 kJ / kg. The latent heat of fusion of pure aluminum is 393 kJ / kg; therefore, the total heat consumed to melt 1 kg of aluminum is 563.2 + 393 = 956.2 kJ. We precisely control the energy output of the laser so that the aluminum sphere is in a molten state with a surface thickness of just a few nanometers, enabling welding with minimal contact area.

[0020] Then, the aluminum foil passes through the next feeding chamber, where aluminum metal particles continue to be covered on top and laser-welded. This process is repeated until aluminum metal particles with a total height of 50μm are welded on top of the aluminum foil.

[0021] Subsequently, the aluminum foil is flipped over using a flipping device consisting of guide rollers. Aluminum powder particles are then covered and welded on the side where the aluminum metal particles have not been fused. The welding height is also 50μm, ultimately forming a 130μm thick anode aluminum foil for aluminum electrolytic capacitors.

[0022] This invention also provides a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, comprising the following steps:

[0023] Aluminum foil with a thickness of 30μm and aluminum powder particles with an average particle size of 5-6μm are selected as raw materials. The aluminum powder particles are uniformly sprayed onto the aluminum foil through an aluminum powder nozzle. A linear laser is used to fuse the aluminum powder particles, ensuring complete fusion. The aluminum foil is then passed through another aluminum powder nozzle, where aluminum powder particles are sprayed onto it again and laser fusion is performed. This process is repeated until a total of 50μm high aluminum powder particles are fused onto the aluminum foil. The device is then used to reverse the aluminum foil, and aluminum powder particles are sprayed and fused on the other side, with the same fusion height of 50μm, ultimately forming a 130μm thick anode aluminum foil for aluminum electrolytic capacitors.

[0024] Another method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing provided by the present invention includes the following steps:

[0025] Aluminum foil with a thickness of 30μm and aluminum powder particles with an average particle size of 5-6μm are selected as raw materials. The aluminum powder particles are evenly sprayed onto the aluminum foil through an aluminum powder nozzle. A linear laser is used to fuse the aluminum powder particles, ensuring complete fusion. The aluminum foil then passes through the next aluminum powder nozzle, where aluminum powder particles are sprayed onto it again and laser fusion is performed. This process is repeated until a total of 50μm high aluminum powder particles are fused onto the aluminum foil. Subsequently, a flipping device consisting of guide rollers is used to flip the aluminum foil, and aluminum powder particles are sprayed and fused onto the side where aluminum powder particles were not fused, with a fusion height of 50μm, ultimately forming a 130μm thick anode aluminum foil for aluminum electrolytic capacitors.

[0026] Compared with related technologies, the method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing provided by the present invention has the following beneficial effects:

[0027] Overcome the following problems:

[0028] (1) Fine aluminum powder has a larger surface energy, which makes it easier to fuse and sinter, resulting in a decrease in the specific surface area of ​​the electrode foil;

[0029] (2) When using fine aluminum powder, the sintering temperature will be limited, which will lead to a decrease in the porosity or capacitance of the electrode foil. That is, the sintering temperature of aluminum powder cannot be too high. If the sintering temperature is too high, the aluminum powder will melt, which will lead to a decrease in the porosity of the electrode foil. However, if the sintering temperature is too low, the aluminum powder will not melt sufficiently and the aluminum powder particles will not be tightly connected, which will cause the sintering neck to break in subsequent processing, thus failing to exert dielectric properties, and ultimately causing a decrease in capacitance or even powder loss. Attached Figure Description

[0030] Figure 1 A flowchart illustrating a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, provided by the present invention.

[0031] Figure 2 Another flowchart of a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing provided by the present invention.

[0032] Figure 3 This is a schematic diagram of a flipping device for a method of preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, provided by the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] First Embodiment

[0035] Please see Figure 1 The present invention provides a flowchart of a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing.

[0036] The present invention provides a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, comprising the following steps:

[0037] Aluminum foil with a thickness of 30μm and aluminum powder particles with an average particle size of 5-6μm are selected as raw materials. The aluminum powder particles are added to the aluminum foil through a feeding hopper, and the thickness of the aluminum powder particles is controlled by a vibrating scraper below the feeding hopper, so that the aluminum powder is basically spread in a single layer on the aluminum foil; in order to ensure the single-layer distribution of aluminum balls.

[0038] A dispersant is added to the raw material to prevent the spheres from clumping together. A high-frequency vibration with an amplitude of micrometers is added to the scraper at the outlet of the feeding hopper to facilitate the single-layer flat laying of the spheres and to cover the entire plane.

[0039] The aluminum powder particles are fused together using a linear laser to completely fuse the covered aluminum metal particles.

[0040] To ensure good welding between aluminum balls and foil, and between aluminum balls themselves, semiconductor lasers with high aluminum absorption efficiency (880, 915, or 976 nm) are selected as the welding heat source. The ultraviolet band, which has even higher absorption efficiency, was not chosen because ultraviolet lasers have low photoelectric conversion efficiency and are expensive, making them less cost-effective for welding aluminum balls compared to infrared semiconductor lasers.

[0041] The key to welding is matching the output of laser energy with the moving speed of the aluminum foil strip. At this point, the aluminum sphere and the aluminum foil surface, which are irradiated by the laser, liquefy within a few nanometers and fuse together.

[0042] Specifically, the specific heat of aluminum is 0.88 kJ / kg / ℃; the melting point of aluminum is 660℃; the room temperature is assumed to be 20℃; 0.88 × (660 - 20) = 563.2 kJ / kg; therefore, the heat required to raise the temperature from 20℃ to the melting point is 563.2 kJ / kg. The latent heat of fusion of pure aluminum is 393 kJ / kg; therefore, the total heat consumed to melt 1 kg of aluminum is 563.2 + 393 = 956.2 kJ.

[0043] Then, the aluminum foil passes through the next feeding chamber, where aluminum metal particles continue to be covered on top and laser-welded. This process is repeated until aluminum metal particles with a total height of 50μm are welded on top of the aluminum foil.

[0044] Subsequently, the aluminum foil enters the flipping device, with the side having fused aluminum particles on top and the side not having fused aluminum particles on the bottom. The aluminum foil passes over three guide rollers from top to bottom, with the side having fused aluminum particles on the bottom and the side not having fused aluminum particles on top, thus achieving the flipping. Afterwards, aluminum powder particles are covered and fused onto the side not having fused aluminum particles, with a fusion height of 50μm, ultimately forming a 130μm thick anode aluminum foil for aluminum electrolytic capacitors.

[0045] Second Embodiment

[0046] Please see Figure 2 The diagram shows another workflow for a method of preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, provided by the present invention.

[0047] This invention also provides a method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, comprising the following steps:

[0048] Aluminum foil with a thickness of 30μm and aluminum powder particles with an average particle size of 5-6μm are selected as raw materials. The aluminum powder particles are evenly sprayed onto the aluminum foil through an aluminum powder nozzle. A linear laser is used to fuse the aluminum powder particles, ensuring complete fusion. The aluminum foil then passes through the next aluminum powder nozzle, where aluminum powder particles are sprayed onto it again, and laser fusion is performed. This process is repeated until a total of 50μm high aluminum powder particles are fused onto the aluminum foil. The aluminum foil then enters a flipping device, with the side with fused aluminum powder particles on top and the side without fused particles on the bottom. The foil passes over three guide rollers from top to bottom, with the side with fused aluminum powder particles on the bottom and the side without fused particles on top, thus achieving the flipping. Afterwards, aluminum powder particles are sprayed and fused onto the side without fused aluminum powder particles, with the fusion height also reaching 50μm, ultimately forming a 130μm thick anode aluminum foil for aluminum electrolytic capacitors.

[0049] Compared with related technologies, the method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing provided by the present invention has the following beneficial effects:

[0050] Overcome the following problems:

[0051] (1) Fine aluminum powder has a larger surface energy, which makes it easier to fuse and sinter, resulting in a decrease in the specific surface area of ​​the electrode foil;

[0052] (2) When using fine aluminum powder, the sintering temperature will be limited, which will lead to a decrease in the porosity or capacitance of the electrode foil. That is, the sintering temperature of aluminum powder cannot be too high. If the sintering temperature is too high, the aluminum powder will melt, which will lead to a decrease in the porosity of the electrode foil. However, if the sintering temperature is too low, the aluminum powder will not melt sufficiently and the aluminum powder particles will not be tightly connected, which will cause the sintering neck to break in subsequent processing, thus failing to exert dielectric properties, and ultimately causing a decrease in capacitance or even powder loss.

[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 porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing, characterized in that, The process includes the following steps: (1) Aluminum foil is laid flat on the conveying device. When passing through the first feeding hopper, aluminum powder particles are added to the aluminum foil through the feeding hopper. Then, a linear laser is used to weld the aluminum powder particles, completely fusing the single layer of aluminum metal particles onto the aluminum foil; (2) As the aluminum foil moves with the conveying device, it passes through the next feeding hopper, and a single layer of aluminum powder particles continues to be covered on top, and the aluminum powder particles are welded using a linear laser; this process is repeated until a total of 50 μm thick aluminum metal particles are welded onto one side of the aluminum foil; 3) The aluminum foil is flipped so that the side that has not been fused with aluminum powder particles is on top. Steps (1) and (2) are repeated to finally obtain porous anode aluminum foil for electrolytic capacitors. Aluminum foil with a thickness of 30μm and aluminum powder particles with an average particle size of 5-6μm are selected as raw materials. The aluminum powder particles are added to the aluminum foil through the feeding bin, and the thickness of the aluminum powder particles is controlled by the scraper vibrating below the feeding bin, so that the aluminum powder is basically spread in a single layer on the aluminum foil to ensure the single-layer distribution of the aluminum powder particles.

2. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: The aluminum foil thickness in step (1) is 30 μm, the average particle size of the aluminum powder particles is 5-6 μm, and a dispersant is added to the aluminum powder particles to prevent the spheres from clumping.

3. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: The types of conveying devices in step (1) are belt conveyors, roller conveyors, and plate chain conveyors.

4. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: The feed hopper outlet in step (1) is equipped with a scraper and subjected to high-frequency vibration with an amplitude of micrometers.

5. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: The flipping device in step (2) mainly consists of three guide rollers. After the aluminum foil passes around the three guide rollers from top to bottom, the side of the fused aluminum metal particles that was originally at the top is now at the bottom, and the side of the unfused aluminum metal particles that was originally at the bottom is now at the top, thus achieving the flipping.

6. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: The final electrolytic capacitor formed in step (3) has an anode aluminum foil thickness of 130 μm.

7. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: The laser type of the linear laser in step (1) is a semiconductor laser.

8. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: The wavelength of the laser in step (1) is 880 nanometers.

9. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: In step (1), the wavelength of the linear laser is 915 nanometers.

10. The method for preparing porous anode aluminum foil for electrolytic capacitors based on laser additive manufacturing according to claim 1, characterized in that: In step (1), the wavelength of the linear laser is 976 nanometers.

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