A method for manufacturing a high specific capacity anode foil having improved pore uniformity

Abstract

This invention relates to a method for manufacturing a high-capacity anode foil with improved porosity uniformity in aluminum electro-etching foil. The method comprises pretreatment, multi-V porosimetry etching, multi-V enlargement etching, and post-treatment steps. The invention primarily relates to the porosimetry etching process, which involves adding a metal surface cleaning agent to the porosimetry solution to more effectively reduce the formation of the Al2(SO4)3 film on the foil surface during the multi-V porosimetry process, exposing more Al substrate. This particularly improves the surface condition of areas where porosimetry is difficult, resulting in more opportunities for porosimetry and thus producing a high-capacity anode foil with more and more uniform pores.

Description

Technical Field

[0001] This invention relates to the field of anode foil for aluminum electrolytic capacitors, and in particular to a method for manufacturing a high-specific-capacitance anode foil that improves the uniformity of pore formation in aluminum electrolytic capacitor foil. Background Technology

[0002] Electrode foil is the core raw material of aluminum electrolytic capacitors and is widely used in industrial frequency conversion, consumer electronics and other complete machine markets. With the rapid development of electronic technology and the further increase in the assembly density and integration of electronic complete machines, products such as smart homes, 5G, AI, wind and solar power generation and new energy vehicles have a growing demand for miniaturization of capacitors, which puts forward higher requirements for the specific capacitance of anode foil.

[0003] In actual production, manufacturers employ various methods to improve the specific capacitance per unit area of ​​aluminum foil, such as enhancing the uniformity of pore formation, increasing the original foil thickness, and maintaining the residual thickness after etching. Under normal circumstances, during electrolytic pore formation, pores are more likely to germinate at grain boundaries, while pore formation on crystal surfaces is more difficult, easily leading to pore inhomogeneity. This manifests as more pores at grain boundaries that tend to coalesce, fewer pores on crystal surfaces, and more shallow pores. Increasing the pore formation charge further exacerbates these inhomogeneities. This industry demands new materials and functions in the manufacture of traditional aluminum electrolytic capacitors. As the requirement for high specific capacitance of anode foil continues to increase, most domestic and international etching foil manufacturers currently improve specific capacitance by increasing the thickness of the raw foil or maintaining a certain level of residual etching thickness. However, this also increases the volume of the winding during capacitor winding, affecting the capacitor's case size and ultimately impacting its performance. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a method for manufacturing a high-capacity anode foil that improves the uniformity of hole formation in aluminum electrolytic etching foil. The manufacturing method of the present invention starts from the perspective of hole uniformity and hole growth consistency. By adding metal surface cleaning agents such as phosphate esters or silicates to the multi-stage hole formation process formula, it is beneficial to increase the initiation of initial holes at the crystal plane and increase the pitting potential at the grain boundary to weaken its hole formation ability, thereby achieving a more uniform hole formation effect.

[0005] A method for manufacturing a high-specific-capacity anode foil to improve the uniformity of pore formation in aluminum electro-etched foil includes the following steps:

[0006] S1, Pretreatment: Take aluminum foil and immerse it in phosphoric acid at a temperature of 60-90℃ for 40-100 seconds;

[0007] S2, Multi-V Pore Corrosion: The aluminum foil treated with S1 is immersed in a pore-forming solution, which is a mixture containing 3-4% aluminum ions, 30-35% sulfuric acid, 4-5% hydrochloric acid, and 0.02-0.5% metal surface cleaner by mass; and an average current density of 0.5-0.6 A / cm is applied at 70-75°C. 2 The variable current was used to create an electro-erosion hole for 15-25 seconds, and this process was repeated multiple times to obtain a first-level foil.

[0008] S3, Multi-V Pore Enlargement Etching: The primary foil obtained in S2 is washed with water and then placed in a pore enlargement solution; etching is performed at 60-75℃ and a current density of 0.15-0.2 A / cm². 2 Under electrolytic conditions, multi-V electrolytic hole expansion corrosion is performed, with a total time of 450-550s, to obtain a secondary foil;

[0009] S4, Post-processing: The secondary foil obtained in S3 is washed with water, then placed in nitric acid and chemically cleaned at 60-70℃ for 60-120s; then washed with water and dried to obtain high specific capacity anode foil.

[0010] The manufacturing method of high-capacitance anode foil for improving the uniformity of pitting in aluminum electro-etching foil according to the present invention includes four major steps: pretreatment, pitting etching, pit enlargement etching, and post-treatment. From the perspective of pitting uniformity and consistent pore growth, the present invention, in the pretreatment step S1, firstly, immerses the aluminum foil in phosphoric acid at a temperature of 60-90℃ for 40-70 seconds. This removes oil stains from the aluminum foil surface and forms a dense oxide film on the aluminum foil surface. In the multi-stage pitting etching process of step S2, by adding a metal surface cleaning agent to the pitting solution formulation, it is beneficial to increase the initiation of initial pits at the crystal planes and increase the pitting potential at the grain boundaries to weaken their pitting ability, thereby achieving a more uniform pitting effect. In the multi-stage pitting corrosion process of step S3, the pitting corrosion process involves the continuous formation and dissolution of an oxide film on the aluminum foil surface. By adjusting the degree of oxide film formation and dissolution, the ultimate goal is to enlarge the pore size and depth, thereby increasing the specific volume. Step S3 further enlarges the pores obtained in step S2, achieving a high specific volume. Post-treatment removes metallic impurity ions, foil ash, and other impurities from the aluminum foil surface and the pits.

[0011] This invention reduces the formation of Al2(SO4)3 film on the foil surface more effectively during the multi-V pore formation process by adding a metal surface cleaning agent to the pore formation liquid, exposing more Al substrate, especially improving the surface condition of areas where pore formation is difficult, and obtaining more opportunities for pore formation, thereby producing a high specific capacity anode foil with more and more uniform pores.

[0012] Furthermore, the aluminum foil used in step S1 is a soft electronic aluminum foil with a purity greater than or equal to 99.985%.

[0013] Furthermore, the metal surface cleaning agent is a phosphate ester or silicate-based agent. Phosphate ester or silicate-based metal surface cleaning agents can strengthen the Al2O3 film on the aluminum foil surface and, to a certain extent, slow down the formation of the Al2(SO4)3 film.

[0014] Furthermore, in step S2, the current change of the variable current conforms to i = x t The mode is defined as follows: 0 < x < 1, and t is the energizing time. By performing electrochemical corrosion using this variable current mode, larger pore sizes can be obtained, which facilitates subsequent pore-enlarging corrosion and avoids clogging.

[0015] Furthermore, in step S2, the number of surface pores is ≥10. 7 / cm 2 The first-stage aluminum foil. Through the multi-stage porosimetry etching of this invention, the number of porosities on the aluminum foil surface is ≥10. 7 / cm 2 The pores are more even.

[0016] Further, in step S2, the mass percentage content of the metal surface cleaning agent in the pore-forming liquid is 0.05-0.5%. Adding 0.05-0.5% of the metal surface cleaning agent can increase both the specific volume and the flexural strength. More preferably, the mass percentage content of the metal surface cleaning agent in the pore-forming liquid is 0.01-0.5%.

[0017] Further, in step S3, a secondary foil with a surface pore size of 0.8-1.3 μm is obtained. Through the multi-V pore-expanding etching of this invention, etched holes with larger pore sizes and higher specific volumes are obtained.

[0018] Further, in step S3, the expanding solution is a mixture containing 1-2% aluminum ions, ≤1% phosphoric acid, and 5-8% nitric acid. During the expanding corrosion process, high-concentration nitric acid is used to deeply corrode the pores. The concentration of nitric acid affects the degree of expanding the pores; a low concentration results in weak corrosion, small pores, and low specific volume, while a high concentration results in strong corrosion but easily dissolves the aluminum foil, affecting quality. In this invention, the concentration of nitric acid is controlled at 5-8%, combined with 1-2% aluminum ions and ≤1% phosphoric acid, to obtain pores with larger pore size and higher specific volume.

[0019] Further, in step S4, the nitric acid is 5% by mass. This facilitates the removal of surface metal impurity ions, foil ash, and chloride ions and other impurities within the etched pits.

[0020] Furthermore, in step S4, drying is carried out at 120-200°C.

[0021] The advantages of this invention compared to existing technologies are as follows: It utilizes a metal surface cleaning agent to strengthen the Al2O3 film on the surface of the electronic aluminum foil and, to a certain extent, slows down the formation of the aluminum sulfate film. On the one hand, this allows for the formation of more exposed aluminum substrates on the crystal plane, reducing its pitting potential and resulting in more uniform pore formation points. On the other hand, the slowing down of the aluminum sulfate film formation facilitates the depth and expansion of pores, reducing the proportion of shallow and ineffective pores. This invention significantly improves the electrostatic specific capacitance of the etched foil by enhancing the uniformity of pore distribution and the regularity of pore depth.

[0022] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0023] Figure 1 Here is a SEM image of the high specific capacitance anode foil from Example 1;

[0024] Figure 2 Here is a SEM image of the high specific capacitance anode foil from Example 2;

[0025] Figure 3 Here is a SEM image of the high specific capacitance anode foil from Example 3;

[0026] Figure 4 Here is a SEM image of the high specific capacitance anode foil from Example 4;

[0027] Figure 5 SEM image of the high specific capacity anode foil in Comparative Example 1;

[0028] Figure 6 This is a SEM image of the high specific capacity anode foil from Comparative Example 2. Detailed Implementation

[0029] Example 1

[0030] This embodiment provides a method for manufacturing a high-capacity anode foil that improves the uniformity of aperture formation in aluminum electro-etching foil, comprising the following steps:

[0031] S1, Preprocessing:

[0032] Take a 125μm thick soft electronic aluminum foil with a purity greater than or equal to 99.985% and immerse it in phosphoric acid at 65℃ for 75s;

[0033] S2, multi-V porosiform corrosion:

[0034] The S1-treated aluminum foil was immersed in a foaming solution at 73°C. In this embodiment, the foaming solution was a mixture containing 3.5% aluminum ions, 33% sulfuric acid, 4.5% hydrochloric acid, and 0.05% sodium metasilicate by mass. An average current density of 0.5 A / cm² was applied. 2The current density i = 0.7 is consistent with the given current density. t A variable current (t is the energizing time) was used to create surface pores for 22 seconds, repeated 5 times, resulting in a surface pore count ≥10. 7 / cm 2 First-grade foil;

[0035] S3, Multi-V Pore Enlargement Etching: The primary foil obtained in S2 is washed with water and then placed in a pore enlargement solution. In this embodiment, the pore enlargement solution is a mixture containing 2% aluminum ions, 0.8% phosphoric acid, and 7% nitric acid by mass. The etching is carried out at 70°C and a current density of 0.15 A / cm². 2 Under these conditions, multiple electro-corrosion processes were performed for a total of 520 seconds to obtain a secondary foil with a surface pore size of 0.8-1.3 μm.

[0036] S4, Post-processing: The secondary foil obtained in S3 is washed with water, and then placed in 1% aluminum ions and 5% nitric acid by mass percentage for chemical cleaning at 60°C for 80s; then it is taken out, washed with water, and dried at 150°C to obtain the high specific capacity anode foil (etched foil) of this embodiment.

[0037] Example 2

[0038] This embodiment provides a method for manufacturing a high-capacity anode foil that improves the uniformity of aperture formation in aluminum electro-etching foil, comprising the following steps:

[0039] S1, Preprocessing:

[0040] Take a 125μm thick soft electronic aluminum foil with a purity greater than or equal to 99.985% and immerse it in phosphoric acid at 65℃ for 75s;

[0041] S2, multi-V porosiform corrosion:

[0042] The S1-treated aluminum foil was immersed in a foaming solution at 75°C. In this embodiment, the foaming solution was a mixture containing 3.5% aluminum ions, 31% sulfuric acid, 5% hydrochloric acid, and 0.1% sodium metasilicate by mass. An average current density of 0.5 A / cm² was applied. 2 The current density i = 0.7 is consistent with the given current density. t A variable current (t is the energizing time) was used to create surface pores for 22 seconds, repeated 5 times, resulting in a surface pore count ≥10. 7 / cm 2 First-grade foil;

[0043] S3, Multi-V Pore Enlargement Etching: The primary foil obtained in S2 is washed with water and then placed in a pore enlargement solution. In this embodiment, the pore enlargement solution is a mixture containing 2% aluminum ions, 0.7% phosphoric acid, and 7% nitric acid by mass. The etching is carried out at 70°C and a current density of 0.2 A / cm². 2Under these conditions, multiple electro-corrosion processes were performed for a total of 460 seconds to obtain a secondary foil with a surface pore size of 0.8-1.3 μm.

[0044] S4, Post-processing: The secondary foil obtained in S3 is washed with water, and then placed in 1% aluminum ions and 5% nitric acid by mass percentage for chemical cleaning at 65°C for 80s; then it is taken out, washed with water, and dried at 150°C to obtain the high specific capacity anode foil (etched foil) of this embodiment.

[0045] Example 3

[0046] This embodiment provides a method for manufacturing a high-capacity anode foil that improves the uniformity of aperture formation in aluminum electro-etching foil, comprising the following steps:

[0047] S1, Preprocessing:

[0048] Take a 125μm thick soft electronic aluminum foil with a purity greater than or equal to 99.985% and immerse it in phosphoric acid at 65℃ for 75s;

[0049] S2, multi-V porosiform corrosion:

[0050] The S1-treated aluminum foil was immersed in a foaming solution at 75°C. In this embodiment, the foaming solution was a mixture containing 3.5% aluminum ions, 33% sulfuric acid, 4.5% hydrochloric acid, and 0.02% alkylolamide phosphate by mass. An average current density of 0.5 A / cm² was applied. 2 The current density i = 0.7 is consistent with the given current density. t A variable current (t is the energizing time) was used to create surface pores for 22 seconds, repeated 5 times, resulting in a surface pore count ≥10. 7 / cm 2 First-grade foil;

[0051] S3, Multi-V Pore Enlargement Etching: The primary foil obtained in S2 is washed with water and then placed in a pore enlargement solution. In this embodiment, the pore enlargement solution is a mixture containing 2% aluminum ions, 0.8% phosphoric acid, and 7% nitric acid by mass. The etching is carried out at 70°C and a current density of 0.15 A / cm². 2 Under these conditions, multiple electro-corrosion processes were performed for a total of 520 seconds to obtain a secondary foil with a surface pore size of 0.8-1.3 μm.

[0052] S4, Post-processing: The secondary foil obtained in S3 is washed with water, then placed in 1% aluminum ions and 5% nitric acid, and chemically cleaned at 65°C for 80 seconds; then taken out, washed with water, and dried at 150°C to obtain the high specific capacity anode foil (corrosion foil) of this embodiment.

[0053] Example 4

[0054] This embodiment provides a method for manufacturing a high-capacity anode foil that improves the uniformity of aperture formation in aluminum electro-etching foil, comprising the following steps:

[0055] S1, Preprocessing:

[0056] Take a 125μm thick soft electronic aluminum foil with a purity greater than or equal to 99.985% and immerse it in phosphoric acid at 65℃ for 75s;

[0057] S2, multi-V porosiform corrosion:

[0058] The S1-treated aluminum foil was immersed in a foaming solution at 75°C. In this embodiment, the foaming solution was a mixture containing 3.5% aluminum ions, 31% sulfuric acid, 5% hydrochloric acid, and 0.05% alkylolamide phosphate by mass. An average current density of 0.5 A / cm² was applied. 2 The current density i = 0.7 is consistent with the given current density. t A variable current (t is the energizing time) was used to create surface pores for 22 seconds, repeated 5 times, resulting in a surface pore count ≥10. 7 / cm 2 First-grade foil;

[0059] S3, Multi-V Pore Enlargement Etching: The primary foil obtained in S2 is washed with water and then placed in a pore enlargement solution. In this embodiment, the pore enlargement solution is a mixture containing 2% aluminum ions, 0.7% phosphoric acid, and 7% nitric acid by mass. The etching is carried out at 70°C and a current density of 0.2 A / cm². 2 Under these conditions, multiple electro-corrosion processes were performed for a total of 460 seconds to obtain a secondary foil with a surface pore size of 0.8-1.3 μm.

[0060] S4, Post-processing: The secondary foil obtained in S3 is washed with water, and then placed in 1% aluminum ions and 5% nitric acid by mass percentage for chemical cleaning at 65°C for 80s; then it is taken out, washed with water, and dried at 150°C to obtain the high specific capacity anode foil (etched foil) of this embodiment.

[0061] Comparative Example 1

[0062] This comparative example provides a method for manufacturing a high-specific-capacity anode foil that improves the uniformity of pore formation in aluminum electro-etching foil, comprising the following steps:

[0063] S1, Preprocessing:

[0064] Take a 125μm thick soft electronic aluminum foil with a purity greater than or equal to 99.985% and immerse it in phosphoric acid at 65℃ for 75s;

[0065] S2, multi-V porosiform corrosion:

[0066] The S1-treated aluminum foil was immersed in a foaming solution at 75°C. The foaming solution in this comparative example was a mixture containing 3.5% aluminum ions, 33% sulfuric acid, and 5% hydrochloric acid by mass. An average current density of 0.5 A / cm² was applied. 2 The current density i = 0.7 is consistent with the given current density. t A variable current (t is the energizing time) was used to create an electro-erosion hole for 22 seconds, repeated 5 times, to obtain a first-level foil;

[0067] S3, Multi-V Pore Enlargement Etching: The primary foil obtained in S2 is washed with water and then placed in a pore enlargement solution. The pore enlargement solution in this comparative example is a mixture containing 2% aluminum ions, 0.8% phosphoric acid, and 7% nitric acid by mass. The etching is carried out at 70°C and a current density of 0.15 A / cm². 2 Under these conditions, multiple electro-corrosion processes were performed for a total of 500 seconds to obtain a secondary foil;

[0068] S4, Post-processing: The secondary foil obtained in S3 is washed with water, then placed in 1% aluminum ions and 5% nitric acid by mass, and chemically cleaned at 65°C for 80s; then taken out, washed with water, and dried at 150°C to obtain the high specific capacity anode foil (etched foil) of this comparative example.

[0069] Comparative Example 2

[0070] This comparative example provides a method for manufacturing a high-specific-capacity anode foil that improves the uniformity of pore formation in aluminum electro-etching foil, comprising the following steps:

[0071] S1, Preprocessing:

[0072] Take a 125μm thick soft electronic aluminum foil with a purity greater than or equal to 99.985% and immerse it in phosphoric acid at 65℃ for 75s;

[0073] S2, Pore corrosion:

[0074] The S1-treated aluminum foil was immersed in a foaming solution at 75°C. The foaming solution in this comparative example was a mixture containing 3.5% aluminum ions, 31% sulfuric acid, and 5% hydrochloric acid by mass. An average current density of 0.5 A / cm² was applied. 2 The current density i = 0.7 is consistent with the given current density. t A variable current (t is the energizing time) was used to create an electro-erosion hole for 22 seconds, repeated 5 times, to obtain a first-level foil;

[0075] S3, Pitting and Etching: The primary foil obtained in S2 is washed with water and then placed in a pitting solution. The pitting solution in this comparative example is a mixture containing 2% aluminum ions, 0.7% phosphoric acid, and 7% nitric acid by mass. The etching process is carried out at 70°C and a current density of 0.2 A / cm². 2Under these conditions, multiple electro-corrosion processes were performed for a total of 460 seconds to obtain a secondary foil;

[0076] S4, Post-processing: The secondary foil obtained in S3 is washed with water, then placed in 1% aluminum ions and 5% nitric acid by mass, and chemically cleaned at 65°C for 80s; then taken out, washed with water, and dried at 150°C to obtain the high specific capacity anode foil (etched foil) of this comparative example.

[0077] test

[0078] The high specific capacitance anode foils (etched foils) prepared in Examples 1-4 and Comparative Examples 1-2 were tested respectively. The tests included flexural strength, tensile strength, capacitance, and etched foil thickness. The test results are shown in Table 1.

[0079] Table 1 - Test results of high specific capacity anodic foil (corrosion foil) in Examples 1-4 and Comparative Examples 1-2

[0080]

[0081] As shown in Table 1, the electrostatic capacitance of the high specific capacity anode foils in Examples 1-4 is higher than that of Comparative Examples 1 and 2 without the addition of metal surface cleaning agent. This shows that by adding phosphate ester or silicate metal surface cleaning agent to the pore formation solution, this application can improve the pore formation uniformity, thereby increasing the specific capacity of the corrosion foil and thus meeting the requirements of high specific capacity anode foil.

[0082] In addition, SEM tests were performed on the high specific capacity anode foils prepared in Examples 1-4 and Comparative Examples 1-2, respectively. The main test item was the distribution of pores at a depth of 10 μm on the surface. The test results can be found in [link to relevant documentation]. Figures 1-6 The high specific capacity anode foils prepared in Examples 1-4 of this application have more uniform pore size, which can improve the pore size uniformity compared with Comparative Examples 1 and 2.

[0083] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A method for manufacturing a high-specific-capacity anode foil to improve the uniformity of aperture formation in aluminum electro-etching foil, characterized in that: Includes the following steps: S1, Pretreatment: Take aluminum foil and immerse it in phosphoric acid at a temperature of 60-90℃ for 40-100 seconds; S2, Multi-V Pore Corrosion: The aluminum foil treated with S1 is immersed in a pore-forming solution, which is a mixture containing 3-4% aluminum ions, 30-35% sulfuric acid, 4-5% hydrochloric acid, and 0.02-0.5% metal surface cleaning agent by mass; and an average current density of 0.5-0.6 A / cm is applied at 70-75°C. 2 The variable current was used to create an electro-erosion hole for 15-25 seconds, and this process was repeated multiple times to obtain a first-level foil. The metal surface cleaning agent is either a phosphate ester or a silicate; the current change of the variable current conforms to i=x. t The mode, where 0 < x < 1, and t is the power-on time; S3, Multi-V Pore Enlargement Etching: The primary foil obtained in S2 is washed with water and then placed in a pore-enlargement solution, which is a mixture containing 1-2% aluminum ions, ≤1% phosphoric acid, and 5-8% nitric acid by mass; at 60-75℃ and a current density of 0.15-0.2 A / cm². 2 Under electrolytic conditions, multi-V electrolytic hole expansion corrosion is performed, with a total time of 450-550s, to obtain a secondary foil; S4, Post-processing: The secondary foil obtained in S3 is washed with water, then placed in nitric acid and chemically cleaned at 60-70℃ for 60-120s; then washed with water and dried to obtain high specific capacity anode foil.

2. The method for manufacturing a high specific capacitance anode foil with improved porosity of aluminum electro-etched foil according to claim 1, characterized in that: The aluminum foil used in step S1 is a soft electronic aluminum foil with a purity greater than or equal to 99.985%.

3. The method for manufacturing a high specific capacitance anode foil with improved porosity of aluminum electro-etched foil according to claim 1, characterized in that: In step S2, the number of surface pores is ≥10. 7 / cm 2 The first-level foil.

4. The method for manufacturing a high specific capacitance anode foil with improved porosity of aluminum electro-etched foil according to claim 1, characterized in that: In step S2, the mass percentage content of the metal surface cleaning agent in the pore-forming liquid is 0.1-0.5%.

5. The method for manufacturing a high-specific-capacity anode foil with improved porosity of aluminum electro-etched foil according to claim 1, characterized in that: In step S3, a secondary foil with a surface pore size of 0.8-1.3 μm is obtained.

6. The method for manufacturing a high specific capacitance anode foil with improved porosity of aluminum electro-etched foil according to claim 1, characterized in that: Step S4, the nitric acid is 5% by mass.

7. The method for manufacturing a high specific capacitance anode foil with improved porosity of aluminum electro-etched foil according to claim 1, characterized in that: In step S4, drying is carried out at 120-200℃.

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