A method for producing a composite anode foil having a gradient porosity and an aluminum electrolytic capacitor

Abstract

A method for preparing a composite anode foil with gradient porosity includes the following steps: 1) pretreating a etched foil as a base foil; 2) forming an additive porous layer on the base foil using 3D printing to form an anode foil precursor; 3) vacuum annealing the anode foil precursor formed in step 2) at a temperature of 380-480°C for 1-5 hours; hydrogen is added to the inert gas stream during annealing. In this invention, during annealing, hydrogen is added to the inert protective gas. The hydrogen can capture trace amounts of oxygen in the furnace and desorbed water vapor in the pores, inhibiting secondary oxidation of the aluminum interface inside the obtained composite anode foil; and promoting slight interfacial diffusion and widening of the original metallurgical bonding area between the aluminum powder or aluminum alloy powder and the base foil.

Description

Technical Field

[0001] This invention relates to an anode foil for aluminum electrolytic capacitors, and more particularly to a method for preparing a composite anode foil with gradient porosity. Background Technology

[0002] Currently, the anode foils used in aluminum electrolytic capacitors are mainly etched foils and multilayer foils. Electrochemically etched foils rely solely on tunnel corrosion of the aluminum foil substrate to increase the specific surface area, but the increase in specific capacitance is nearing its theoretical limit; furthermore, the etching process generates a large amount of acidic waste liquid, resulting in high environmental treatment costs. To further increase the specific capacitance of the anode foil, multilayer foils are now available on the market.

[0003] Laminated foil is made by coating a 3-8μm aluminum powder slurry onto a light foil on one or both sides, and then sintering it at a high temperature above 600℃. The slurry contains an organic binder. During sintering, the decomposition of the organic binder produces oxidizing gases such as water vapor and carbon dioxide. These gases remain in the gaps between the aluminum powder particles and react directly with the active aluminum at the sintering temperature to form alumina. At the same time, the residual carbon from the cracking will destroy the original oxide passivation film on the aluminum surface, exposing fresh metallic aluminum to be continuously oxidized, thereby inhibiting the formation of sintering necks. It is difficult to form an effective metallurgical bond between the particles. The porous layer is maintained only by physical stacking, resulting in low cohesive strength and easy powdering and peeling from the aluminum foil substrate interface. In addition, the thermal expansion coefficients of aluminum and alumina are significantly different, resulting in residual stress at the interface, generating a large number of microcracks, which reduces the bending performance and thermal cycling stability of the material.

[0004] To address this issue, as disclosed in patents CN115064387A and CN 111146005A, a reducing gas is added to the protective gas flow during the sintering process. The reducing gas can inhibit the oxidation of aluminum powder and the base foil to some extent. However, the slurry sintering process relies on an organic carrier, which is prone to drawbacks such as poor pore uniformity, softening and warping of the aluminum foil substrate at high temperatures, and difficulty in controlling batch consistency. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a composite anode foil with gradient porosity and an aluminum electrolytic capacitor.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is: a method for preparing a composite anode foil with gradient porosity, comprising the following steps:

[0007] 1) Pre-treat the etched foil used as the base foil;

[0008] 2) An additive porous layer is formed on the base foil using 3D printing to create an anode foil precursor;

[0009] 3) The anode foil precursor formed in step 2) is vacuum annealed at 380-480℃ for 1-5 hours; hydrogen is added to the inert gas stream during annealing.

[0010] In the above-described method for preparing composite anode foil with gradient pores, preferably, the volume ratio of hydrogen to inert gas flow is 1:10 to 1:20; the inert gas flow includes nitrogen or argon.

[0011] The above-mentioned method for preparing composite anode foil with gradient porosity, preferably, includes step 2) specifically comprising the following steps:

[0012] 2.1) Preheat the base foil to 120-160℃ in the 3D cold spray oxygen-free chamber;

[0013] 2.2) Using a 3D additive cold spray gun in an inert gas atmosphere, aluminum powder or aluminum alloy powder with a diameter of 1-10 μm is sprayed onto the base foil to achieve mechanical interlocking and / or metallurgical bonding to form an additive porous layer, thus obtaining the anode foil precursor. The driving gas of the 3D additive cold spray gun includes high-purity industrial N2, the spraying pressure is between 2.6-3.2 MPa, the temperature of the driving gas in the 3D additive cold spray gun is between 420-500℃, the spraying distance between the 3D additive cold spray gun and the base foil is between 15-22 mm, and the powder feeding rate of the 3D additive cold spray gun is between 15-50 g / min.

[0014] In the above-described method for preparing composite anode foil with gradient pores, preferably, steps 2.1) and 2.2) use a vacuum or inert gas protection, and hydrogen is added under a vacuum or inert gas atmosphere; the volume ratio of hydrogen to inert gas is 1:10-1:20; the inert gas includes nitrogen or argon.

[0015] An aluminum electrolytic capacitor includes an anode foil prepared by the above-described method for preparing high-specific-capacitance composite anode foil.

[0016] Compared with the prior art, the advantages of the present invention are as follows: In the present invention, during annealing, hydrogen is added to the inert protective gas. The hydrogen can capture trace amounts of oxygen in the furnace and desorbed water vapor in the pores, inhibiting secondary oxidation of the aluminum interface inside the obtained composite anode foil; and promoting slight interfacial diffusion and widening of the original metallurgical bonding area between the aluminum powder or aluminum alloy powder and the base foil. Detailed Implementation

[0017] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0018] It should be noted that when a component is described as being "fixed to, attached to, connected to or connected to" another component, it can be directly fixed to, attached to, connected to or connected to the other component, or it can be indirectly fixed to, attached to, connected to or connected to the other component through other intermediate connectors.

[0019] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0020] Example 1

[0021] This embodiment provides a method for preparing a composite anode foil with gradient porosity, including the following steps:

[0022] 1) Pre-treat the etched foil used as the base foil; the pre-treatment includes the following steps:

[0023] 1.1) Immerse the base foil in an organic solvent and ultrasonically clean for at least 15 minutes;

[0024] 1.2) Immerse the base foil treated in step 1.1) in a 1-10 g / L NaOH solution for 5-20 seconds, then rinse it with deionized water.

[0025] 1.3) Plasma treatment: After step 1.2) is completed on the base foil, plasma treatment is performed; argon or argon-hydrogen mixture is used as the working gas source, the vacuum degree is controlled at 0.5-5Pa, the radio frequency power is 100-300W, and the treatment time is 60-180s.

[0026] 2) An additive porous layer is formed on the base foil using 3D printing to form an anode foil precursor.

[0027] 2.1) Preheat the base foil to 120-160℃ in the oxygen-free cavity of 3D cold spraying.

[0028] 2.2) Using a 3D additive cold spray gun in an inert gas atmosphere, aluminum powder or aluminum alloy powder with a diameter of 1-10 μm is sprayed onto the base foil to achieve mechanical interlocking and / or metallurgical bonding to form an additive porous layer, thus obtaining the anode foil precursor. The driving gas of the 3D additive cold spray gun includes high-purity industrial N2, the spraying pressure is between 2.6-3.2 MPa, the temperature of the driving gas in the 3D additive cold spray gun is between 420-500℃, the spraying distance between the 3D additive cold spray gun and the base foil is between 15-22 mm, and the powder feeding rate of the 3D additive cold spray gun is between 15-50 g / min.

[0029] In steps 2.1) and 2.2), a vacuum or inert gas is used for protection, and hydrogen is added in a vacuum or inert gas atmosphere; the volume ratio of hydrogen to inert gas is 1:10-1:20; the inert gas includes nitrogen or argon.

[0030] 3) The anode foil precursor formed in step 2) is vacuum annealed at 380-480℃ for 1-5 hours; hydrogen is added to the inert gas stream during annealing; the volume ratio of hydrogen to inert gas stream is 1:10-1:20; the inert gas stream includes nitrogen or argon.

[0031] In this embodiment, whether it is hydrogen in step 2) or hydrogen in step 3), it is necessary to ensure that the oxygen-free cavity of 3D cold spraying and the annealing furnace are inert gas atmospheres.

[0032] In this embodiment, the base foil is an etched foil, on which many 0.8-1.2μm tunnel blind holes are etched. After pretreatment, trace amounts of water vapor and oxygen remain in the tunnel blind holes. These trace amounts of water vapor react with the exposed aluminum in the additive porous layer during annealing to form an alumina insulating barrier, weakening the metallurgical bond between particles, increasing the resistance of the additive porous layer, and inducing micro-defects at the interface.

[0033] In this embodiment, because the 3D additive cold spray gun rapidly sprays aluminum powder or aluminum alloy powder onto the etched foil to form an additive porous layer, the water vapor and oxygen escaping from the blind holes of the etched foil tunnels and reacting with the aluminum powder or aluminum alloy powder particles, as well as with the bonding surfaces between the particles and the etched foil, mainly occur during the annealing and heat preservation stage. Therefore, how to reduce the impact of residual water vapor and oxygen in the pre-treated blind holes on the additive porous layer during the annealing stage has become a critical technical challenge to be solved in the process of 3D printing to form composite anode foils with gradient porosity.

[0034] In this embodiment, hydrogen is added to an inert atmosphere during annealing at 380-480℃ for 1-5 hours. Within this annealing temperature range, hydrogen cannot reduce the native dense alumina on the surface of aluminum particles; however, hydrogen can capture trace amounts of oxygen in the furnace and desorb water vapor from the pores, continuously reducing the partial pressure of oxidizing components in the environment. This inhibits the oxidation of the 3D-printed porous additive layer and reduces the blockage of the metal conductive pathways at the metallurgical interface of aluminum powder or aluminum alloy powder. Simultaneously, the penetrating power of hydrogen molecules accelerates the removal of blind holes in the corrosion foil and the removal of water vapor and surface hydroxyl oxides adsorbed on the pores of the porous additive layer. Although hydrogen cannot reduce the existing oxide film, it ensures the smooth release of residual stress generated by impact during annealing, stabilizing the conductivity of the porous additive layer and the interfacial bonding strength between the porous additive layer and the electrode foil.

[0035] In this embodiment, the added hydrogen gas can continuously remove trace amounts of oxygen and water vapor in the annealing environment, inhibiting the formation of new alumina at the interface of aluminum foil, aluminum powder particles, or aluminum alloy particles, and preventing the new oxide film from blocking the migration of metal interface atoms. Under the temperature conditions of 380-480℃, since there is no new oxide layer to continuously shield, aluminum atoms obtain sufficient diffusion channels at the clean metallurgical bonding interface of aluminum powder or aluminum alloy powder, thereby promoting slight solid-state interdiffusion at the interface, gradually widening the metallurgical bonding area already formed in the 3D spraying stage, and strengthening the interface connection between the porous layer and the base foil.

[0036] In this embodiment, the annealing temperature should not exceed 480 °C. Although higher temperatures significantly accelerate the atomic diffusion rate of the aluminum matrix, they also cause noticeable grain coarsening and matrix softening deformation in the aluminum foil, easily leading to warping and wrinkling. Furthermore, higher temperatures significantly increase the rate of oxidation induced by trace amounts of water vapor and oxygen within the system. Even if the mixed gas contains hydrogen, it is difficult to completely suppress the continuous formation of new alumina at the activated aluminum interface. Therefore, the annealing temperature is generally controlled below 480 °C.

[0037] The anode foil obtained by forming the anode foil precursor obtained in step 3) can be used to manufacture aluminum electrolytic capacitors.

[0038] In this embodiment, during annealing, hydrogen is added to the inert protective gas. The hydrogen can capture trace amounts of oxygen and desorbed water vapor in the pores of the furnace, inhibiting secondary oxidation of the aluminum interface inside the obtained composite anode foil; and promoting slight interfacial diffusion and widening of the original metallurgical bonding area between the aluminum powder or aluminum alloy powder and the base foil.

Claims

1. A method for preparing a composite anode foil with gradient porosity, characterized in that, Includes the following steps: 1) Pre-treat the etched foil used as the base foil; 2) An additive porous layer is formed on the base foil using 3D printing to create an anode foil precursor; 3) The anode foil precursor formed in step 2) is vacuum annealed at 380-480℃ for 1-5 hours; hydrogen is added to the inert gas stream during annealing.

2. The method for preparing the composite anode foil with gradient porosity according to claim 1, characterized in that: The volume ratio of hydrogen to inert gas is between 1:10 and 1:20; the inert gas stream includes nitrogen or argon.

3. The method for preparing the composite anode foil with gradient porosity according to claim 1, characterized in that: Step 2) specifically includes the following steps: 2.1) Preheat the base foil to 120-160℃ in the 3D cold spray oxygen-free chamber; 2.2) Using a 3D additive cold spray gun in an inert gas atmosphere, aluminum powder or aluminum alloy powder with a diameter of 1-10 μm is sprayed onto the base foil to achieve mechanical interlocking and / or metallurgical bonding to form an additive porous layer, thus obtaining the anode foil precursor. The driving gas of the 3D additive cold spray gun includes high-purity industrial N2, the spraying pressure is between 2.6-3.2 MPa, the temperature of the driving gas in the 3D additive cold spray gun is between 420-500℃, the spraying distance between the 3D additive cold spray gun and the base foil is between 15-22 mm, and the powder feeding rate of the 3D additive cold spray gun is between 15-50 g / min.

4. The method for preparing the composite anode foil with gradient porosity according to claim 3, characterized in that: In steps 2.1) and 2.2), a vacuum or inert gas protection is used, and hydrogen is added in a vacuum or inert gas atmosphere; the volume ratio of hydrogen to inert gas is 1:10-1:20; the inert gas includes nitrogen or argon.

5. An aluminum electrolytic capacitor, characterized in that: The anode foil prepared by the method for preparing high specific capacity composite anode foil according to any one of claims 1-4.