Method for repairing a conversion foil, conversion foil, aluminum electrolytic capacitor

Abstract

This disclosure provides a method for repairing electrolytic capacitor foil, electrolytic capacitor foil, and aluminum electrolytic capacitor, including a step of post-electrolytic treatment of the electrode foil using a constant current in a pure ammonium dihydrogen phosphate electrolytic solution, wherein the pure ammonium dihydrogen phosphate electrolytic solution contains only ammonium dihydrogen phosphate as an effective component. The repair method for electrolytic capacitor foil disclosed herein, by using a high concentration of pure ammonium dihydrogen phosphate and constant current post-electrolytic treatment, can effectively control the rate of the repair reaction and ensure the basic quantity of phosphate ions, thereby forming an effective repair material, aluminum phosphate, on the surface of the electrode foil, thus improving the water resistance of the low-voltage electrolytic capacitor foil.

Description

Technical Field

[0001] This disclosure relates to the technical field of electrode foil for capacitors, and particularly to a method for repairing formed foil, a formed foil, and an aluminum electrolytic capacitor. Background Technology

[0002] Low-voltage aluminum electrolytic capacitors use the oxide film on the surface of the electrode foil as the working medium. When in contact with the electrolyte, water molecules in the electrolyte easily react with the oxide film layer of the electrode foil, damaging the insulating structure of the oxide film. This leads to deterioration of the capacitor's performance and shortens its lifespan. Therefore, the hydration resistance of the electrode foil is crucial for its application in aluminum electrolytic capacitors, directly affecting the capacitor's lifespan, stability, and compatibility with electrolytes.

[0003] The oxide film on the surface of electrode foil is usually a coating of metal compounds formed on the electrode foil surface using a chemical formation process. Currently, there are two common techniques for improving the hydration resistance of formed foil: one is to treat the formed foil with phosphoric acid, transforming the ordinary oxide film on the surface, which lacks water resistance, into a poorly soluble, water-resistant aluminum phosphate anti-hydration film; the other is to use pure ammonium dihydrogen phosphate as the formation solution or add ammonium dihydrogen phosphate to the formation solution to directly grow an aluminum phosphate-containing oxide film on the oxide film surface, thereby improving the water resistance of the oxide film. Both techniques share the same drawback: only a small portion of the electrode foil surface forms an aluminum phosphate anti-hydration layer, while the majority is deposited as an ordinary oxide film. These ordinary oxide films are easily dissolved during subsequent water resistance tests or use in water-containing capacitors, leading to performance degradation.

[0004] Therefore, there is an urgent need in the field for a process that can effectively repair the surface coating of chemically formed foil to make it highly water resistant. Summary of the Invention

[0005] This disclosure provides a method for repairing electrolytic foil, including a step of performing post-electrolytic treatment on the electrode foil using a constant current in a pure ammonium dihydrogen phosphate electrolytic solution, wherein the pure ammonium dihydrogen phosphate electrolytic solution is an electrolytic solution containing only ammonium dihydrogen phosphate as an effective component.

[0006] According to the repair method of the formed foil disclosed herein, the post-formation treatment includes two or more post-formation treatments, wherein at least one post-formation treatment step is performed on the electrode foil in a pure ammonium dihydrogen phosphate forming solution using a constant current.

[0007] According to the repair method for the formed foil disclosed herein, the concentration range of ammonium dihydrogen phosphate in the pure ammonium dihydrogen phosphate forming solution is 0.5-5 wt%.

[0008] According to the repair method for electrolytic foil disclosed herein, the current density of the constant current is 2-100 mA / cm². 2 .

[0009] According to the repair method of the formed foil disclosed herein, the electrode foil is acid-treated between the second or more post-formation treatment steps.

[0010] According to the repair method of the electrode foil disclosed herein, the acid treatment step involves treating the electrode foil with a phosphoric acid solution of 1-10 wt%.

[0011] According to the repair method of the formed foil disclosed herein, the electrode foil is heat-treated between the second or more post-formation processing steps.

[0012] According to the repair method of the electroformed foil disclosed herein, the electrode foil is treated in the heat treatment step within a temperature range of 400 to 550°C.

[0013] According to the repair method of the electrode foil disclosed herein, before performing post-forming treatment on the electrode foil using a constant current in a pure ammonium dihydrogen phosphate forming solution, the method further includes: performing an anti-hydration treatment on the electrode foil using phosphoric acid or ammonium dihydrogen phosphate.

[0014] This disclosure provides a chemically formed foil, which is prepared according to any of the above-described methods for repairing chemically formed foils.

[0015] This disclosure provides an aluminum electrolytic capacitor comprising the above-described formed foil.

[0016] The repair method for the electrode foil disclosed herein, by employing a combination of high-concentration pure ammonium dihydrogen phosphate and constant-current post-forming, can reasonably control the rate of the repair reaction and ensure the basic quantity of phosphate ions, thereby forming an effective repair material, aluminum phosphate, on the electrode foil surface, thus improving the water resistance of the low-voltage electrode foil. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a foil repair method according to an embodiment of the present disclosure.

[0018] Figure 2 The surface state of the electrode foil obtained by conventional process is shown before and after hydration.

[0019] Figure 3 The state of the oxide film on the surface of the electrolytic foil after phosphoric acid treatment is shown, as well as the surface state of the electrolytic foil before and after hydration.

[0020] Figure 4 The voltage rise curve is for the formed foil that has been treated with phosphoric acid but has not undergone post-formation repair.

[0021] Figure 5This is a comparison graph showing the pressure rise curves of the electroformed foil obtained in the embodiments and comparative examples of this disclosure after hydration. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of this disclosure will be described in detail below with reference to the accompanying drawings.

[0023] Exemplary embodiments will be described more fully below with reference to the accompanying drawings; however, these exemplary embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will enable those skilled in the art to fully understand the scope of this disclosure.

[0024] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0025] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0026] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded.

[0027] Unless otherwise stated, the concentrations mentioned in this disclosure generally refer to the weight percentage of the solute in the solution, i.e., wt%.

[0028] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0029] As mentioned earlier, the most widely used technology in the industry to improve the hydration performance of formed electrode foil is to treat the formed foil with phosphoric acid or ammonium dihydrogen phosphate. The actual reaction that occurs in this process is a chemical reaction between phosphate ions and aluminum ions in the oxide film, forming a water-resistant aluminum phosphate anti-hydration film on the surface of the formed foil, thereby improving the water resistance of the formed foil.

[0030] However, the inventors discovered in their research that phosphoric acid, as a tribasic weak acid, ionizes in three steps, removing one hydrogen ion at a time, with the removal capacity decreasing rapidly with each step. This results in a hydrogen ion to phosphate ion concentration ratio of approximately 10 in the phosphoric acid treatment solution. 17 :1; In other words, the proportion of phosphate ions that can be effectively converted into an aluminum phosphate anti-hydration layer in the phosphoric acid treatment solution is very low. This leads to a situation where the rate at which a large number of hydrogen ions break down the oxide film and dissolve aluminum ions is much faster than the rate at which phosphate ions combine with aluminum ions to form an aluminum phosphate anti-hydration layer, causing additional damage to the oxide film. Therefore, it is usually necessary to repair the oxide film after phosphoric acid treatment to ensure its integrity and water resistance. Similarly, the dihydrogen phosphate ions in ammonium dihydrogen phosphate also have similar properties to phosphoric acid, with a very low content of ionized phosphate ions, resulting in only a small portion forming an aluminum phosphate anti-hydration layer, while the majority is deposited in the form of a regular oxide film.

[0031] Furthermore, for phosphoric acid-treated formed foils, the oxide film is severely corroded down to the metal layer by the phosphoric acid. For defective areas on the surface of the formed foil, the voltage applied by existing repair methods is far higher than the withstand voltage of the oxide film in that area, leading to a violent reaction and the dissolution of a large number of aluminum ions in the defective area. However, the rate at which ammonium dihydrogen phosphate used for repair dissociates into phosphate ions is far slower, resulting in the repair material mainly being a common oxide film without water resistance. These common oxide films are easily dissolved in subsequent water resistance tests or when used in water-containing capacitors, leading to performance degradation.

[0032] Figure 1 This is a schematic flowchart of a foil repair method according to an embodiment of the present disclosure.

[0033] After further research, referring to Figure 1 The inventors hereby provide a method for repairing electrolytic foil, comprising S1, a step of performing post-electrolytic treatment on the electrode foil in a pure ammonium dihydrogen phosphate electrolytic solution using a constant current, wherein the pure ammonium dihydrogen phosphate electrolytic solution is an electrolytic solution containing only ammonium dihydrogen phosphate as an effective component.

[0034] In this repair method, by limiting the precipitation rate of aluminum ions and increasing the dissociation rate of phosphate ions, the two are brought into balance as much as possible, thereby ensuring that the material being repaired is water-resistant aluminum phosphate, thus improving the water resistance of the foil.

[0035] In the repair method for the formed foil disclosed herein, the post-formation treatment may include two or more post-formation treatments, wherein at least one post-formation treatment step involves treating the electrode foil with a constant current in a pure ammonium dihydrogen phosphate forming solution. The treatment conditions for each post-formation step may be the same or different, as long as the integrity and effectiveness of the formed foil repair can be guaranteed.

[0036] The concentration of ammonium dihydrogen phosphate in the pure ammonium dihydrogen phosphate forming solution ranges from 0.5 to 5 wt%. Using a high concentration of pure ammonium dihydrogen phosphate as the forming solution ensures the basic quantity of phosphate ions and guarantees the effective follow-up of subsequent phosphate ions during the repair process.

[0037] In the repair method for electroformed foil disclosed herein, the current density of the constant current is 2-100 mA / cm². 2 Replacing the conventional constant-pressure repair method with a constant-current condition can effectively control the repair reaction rate, that is, control the rate of aluminum ion precipitation, slow down the repair process as much as possible, and make the reaction occur uniformly and gently to ensure the integrity of the repair.

[0038] In the repair method of the formed foil disclosed herein, the electrode foil is acid-treated between the plurality of post-formation processes, wherein the electrode foil is treated with a phosphoric acid solution with a concentration of 1-10 wt% in the acid treatment step.

[0039] The purpose of phosphoric acid treatment is to react phosphoric acid with the oxide film on the electrode foil surface to form insoluble aluminum phosphate that covers the oxide film surface, preventing the oxide film from contacting the aqueous electrolyte, thereby protecting the oxide film from water damage and improving the water resistance of the electrode foil.

[0040] In the repair method for the formed electrode foil disclosed herein, the electrode foil is heat-treated between the two or more post-formation processes. The heat treatment step involves processing the electrode foil at a temperature range of 400–550°C. The purpose of the heat treatment is to transform the hydrated oxide film, which has not fully converted into a crystalline oxide film, into a crystalline oxide film with better dielectric properties through high temperature.

[0041] The repair method for formed foil disclosed herein can be applied not only to the repair process of low-voltage formed foil after phosphoric acid treatment, but also to the repair process of medium- and high-voltage formed foil or laminated foil after phosphoric acid treatment, and is not limited by voltage.

[0042] The repair method for the electrode foil disclosed herein further includes: applying phosphoric acid or ammonium dihydrogen phosphate to the electrode foil for anti-hydration treatment before performing post-forming treatment on the electrode foil using a constant current in a pure ammonium dihydrogen phosphate forming solution.

[0043] This disclosure provides a chemically formed foil, which is prepared according to the above-described method for repairing chemically formed foil.

[0044] In addition, this disclosure also provides an aluminum electrolytic capacitor comprising the above-described formed foil.

[0045] According to a specific embodiment of this disclosure, the repair method includes: The subsequent transformation is as follows: temperature 65–85℃, time 3–6 min, voltage 95–99% Vf, current density 50–150 mA / cm². 2 The composition of the chemical solution is: 0.3-1 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Acid treatment: Immerse in a 4-7% phosphoric acid solution for 2-3 minutes at a temperature of 40-70°C, then rinse with water. The subsequent formation of the second phase involves the following steps: temperature 65–85℃, time 3–6 min, voltage 92–96% Vf, and current density 1–15 mA / cm². 2 The composition of the chemical solution is: 0.3-6 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Heat treatment: Heat treatment temperature 450~550℃, time 1~2min.

[0046] According to another specific embodiment of this disclosure, the repair method includes: The subsequent transformation is as follows: temperature 65–85℃, time 3–6 min, voltage 95–99% Vf, current density 50–150 mA / cm². 2 The composition of the chemical solution is: 0.3-1 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Acid treatment: Immerse in a 4-7% phosphoric acid solution for 2-3 minutes at a temperature of 40-70°C, then rinse with water. The subsequent formation of the second phase involves the following steps: temperature 65–85℃, time 3–6 min, voltage 92–96% Vf, and current density 1–15 mA / cm². 2 The composition of the chemical solution is: 0.3-6 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Heat treatment: Heat treatment temperature 450~550℃, time 1~2min; The subsequent transformation into three phases: temperature 65–85℃, time 3–6 min, voltage 92–96% Vf, current density 50–150 mA / cm². 2 The composition of the chemical solution is: 0.3-1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water and dried.

[0047] According to yet another embodiment of this disclosure, the remediation method includes: Multi-stage formation process: temperature 65–85℃, time 3–6 min, voltage gradually increased, current density 50–150 mA / cm² 2 The composition of the chemical solution is ammonium adipate and / or ammonium dihydrogen phosphate.

[0048] The subsequent transformation is as follows: temperature 65–85℃, time 3–6 min, voltage 95–99% Vf, current density 50–150 mA / cm². 2The composition of the chemical solution is: 0.3-1 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Acid treatment: Immerse in a 4-7% phosphoric acid solution for 2-3 minutes at a temperature of 40-70°C, then rinse with water. The subsequent formation of the second phase involves the following steps: temperature 65–85℃, time 3–6 min, voltage 92–96% Vf, and current density 1–15 mA / cm². 2 The composition of the chemical solution is: 0.3-6 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Heat treatment: Heat treatment temperature 450~550℃, time 1~2min.

[0049] According to yet another embodiment of this disclosure, the remediation method includes: Primary formation: Temperature 65–85℃, time 3–6 min, voltage 10–20% Vf, current density 50–150 mA / cm² 2 The primary formation solution consists of 4-6 wt% ammonium adipate, which is then washed with water. Secondary formation: Temperature 65–85℃, time 3–6 min, voltage 20–30% Vf, current density 50–150 mA / cm² 2 The primary formation solution consists of 4-6 wt% ammonium adipate, which is then washed with water. Three-stage formation: temperature 65–85℃, time 3–6 min, voltage 30–50% Vf, current density 50–150 mA / cm² 2 The primary formation solution consists of 4-6 wt% ammonium adipate, which is then washed with water. Fourth-stage formation: Temperature 65–85℃, Time 3–6 min, Voltage 50–70% Vf, Current density 50–150 mA / cm² 2 The primary formation solution consists of 4-6 wt% ammonium adipate, which is then washed with water. Five-stage formation: temperature 65–85℃, time 3–6 min, voltage 70–95% Vf, current density 50–150 mA / cm² 2 The primary formation solution consists of 4-6 wt% ammonium adipate, which is then washed with water. Sixth-stage formation: temperature 65–85℃, time 3–6 min, voltage 90–98% Vf, current density 50–150 mA / cm² 2 The primary formation solution consists of: 1-3 wt% ammonium adipate and 0.3-1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water. The subsequent transformation is as follows: temperature 65–85℃, time 3–6 min, voltage 95–99% Vf, current density 50–150 mA / cm². 2The composition of the chemical solution is: 0.3-1 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Acid treatment: Immerse in a 4-7% phosphoric acid solution for 2-3 minutes at a temperature of 40-70°C, then rinse with water. The subsequent formation of the second phase involves the following steps: temperature 65–85℃, time 3–6 min, voltage 92–96% Vf, and current density 1–15 mA / cm². 2 The composition of the chemical solution is: 0.3-6 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Heat treatment: Heat treatment temperature 450~550℃, time 1~2min; The subsequent transformation into three phases: temperature 65–85℃, time 3–6 min, voltage 92–96% Vf, current density 50–150 mA / cm². 2 The composition of the chemical solution is: 0.3-1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water and dried.

[0050] The repair method for electrolytic capacitor foil disclosed herein employs high-concentration pure ammonium dihydrogen phosphate and constant-current post-electrolytic formation. This effectively controls the rate of the repair reaction and ensures the basic quantity of phosphate ions, resulting in the complete and uniform formation of highly water-resistant aluminum phosphate on the electrode foil surface, thereby effectively improving the water resistance of the low-voltage electrolytic capacitor foil.

[0051] Furthermore, the repair method disclosed herein requires no modification to the production equipment, is easy to implement and does not increase costs; at the same time, it does not introduce additional chemical materials, and production management is simple and easy.

[0052] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of this disclosure will be described in detail below through specific embodiments.

[0053] Example 1 Primary formation: temperature 80℃, time 4 min, voltage 12%Vf, current density 100mA / cm² 2 The primary formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Secondary formation: temperature 80℃, time 4 min, voltage 28%Vf, current density 100mA / cm² 2 The secondary formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Third-stage formation: temperature 80℃, time 4 min, voltage 46%Vf, current density 100mA / cm² 2 The composition of the tertiary formation solution is: 5 wt% ammonium adipate, which is washed with water after removal. Fourth-stage formation: temperature 80℃, time 4 min, voltage 68%Vf, current density 100mA / cm² 2The composition of the fourth-stage formation solution is: 5 wt% ammonium adipate, which is washed with water after removal. Five-stage formation: temperature 80℃, time 4 min, voltage 82%Vf, current density 100mA / cm² 2 The fifth-stage formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Sixth-stage formation: temperature 80℃, time 6 min, voltage 98% Vf, current density 100 mA / cm² 2 The composition of the sixth-stage formation solution is: 4 wt% ammonium adipate and 1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water. The reaction was carried out at the following conditions: temperature 80℃, time 6 min, voltage 98% Vf, and current density 100 mA / cm². 2 The composition of the subsequent reaction solution is: 1 wt% ammonium dihydrogen phosphate, which is then removed and washed with water. Acid treatment: Immerse in a 7% phosphoric acid solution for 3 minutes at 60°C, then rinse with water. The subsequent formation of form II: temperature 85℃, time 5 min, voltage 93% Vf, current density 8 mA / cm² 2 The composition of the subsequent formation solution is: 1 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Heat treatment: 500℃ for 2 minutes; The subsequent transformation into three phases was carried out at the following conditions: temperature 85℃, time 4 min, voltage 93% Vf, and current density 100 mA / cm². 2 The composition of the subsequent tri-chemical solution is: 1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water and dried.

[0054] Example 2 Primary formation: temperature 80℃, time 4 min, voltage 12%Vf, current density 100mA / cm² 2 The primary formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Secondary formation: temperature 80℃, time 4 min, voltage 28%Vf, current density 100mA / cm² 2 The secondary formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Third-stage formation: temperature 80℃, time 4 min, voltage 46%Vf, current density 100mA / cm² 2 The composition of the tertiary formation solution is: 5 wt% ammonium adipate, which is washed with water after removal. Fourth-stage formation: temperature 80℃, time 4 min, voltage 68%Vf, current density 100mA / cm² 2 The composition of the fourth-stage formation solution is: 5 wt% ammonium adipate, which is washed with water after removal. Five-stage formation: temperature 80℃, time 4 min, voltage 82%Vf, current density 100mA / cm² 2 The fifth-stage formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Sixth-stage formation: temperature 80℃, time 6 min, voltage 98% Vf, current density 100 mA / cm² 2 The composition of the sixth-stage formation solution is: 4 wt% ammonium adipate and 1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water. The reaction was carried out at the following conditions: temperature 80℃, time 6 min, voltage 98% Vf, and current density 100 mA / cm². 2 The composition of the subsequent reaction solution is: 1 wt% ammonium dihydrogen phosphate, which is then removed and washed with water. Acid treatment: Immerse in a 7% phosphoric acid solution for 3 minutes at 60°C, then rinse with water. The subsequent formation of form II: temperature 85℃, time 5 min, voltage 93% Vf, current density 8 mA / cm² 2 The composition of the subsequent formation solution is: 2 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Heat treatment: 500℃ for 2 minutes; The subsequent transformation into three phases was carried out at the following conditions: temperature 85℃, time 4 min, voltage 93% Vf, and current density 100 mA / cm². 2 The composition of the subsequent tri-chemical solution is: 1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water and dried.

[0055] Example 3 Primary formation: temperature 80℃, time 4 min, voltage 12%Vf, current density 100mA / cm² 2 The primary formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Secondary formation: temperature 80℃, time 4 min, voltage 28%Vf, current density 100mA / cm² 2 The secondary formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Third-stage formation: temperature 80℃, time 4 min, voltage 46%Vf, current density 100mA / cm² 2 The composition of the tertiary formation solution is: 5 wt% ammonium adipate, which is washed with water after removal. Fourth-stage formation: temperature 80℃, time 4 min, voltage 68%Vf, current density 100mA / cm² 2 The composition of the fourth-stage formation solution is: 5 wt% ammonium adipate, which is washed with water after removal. Five-stage formation: temperature 80℃, time 4 min, voltage 82%Vf, current density 100mA / cm²2 The fifth-stage formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Sixth-stage formation: temperature 80℃, time 6 min, voltage 98% Vf, current density 100 mA / cm² 2 The composition of the sixth-stage formation solution is: 4 wt% ammonium adipate and 1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water. The reaction was carried out at the following conditions: temperature 80℃, time 6 min, voltage 98% Vf, and current density 100 mA / cm². 2 The composition of the subsequent reaction solution is: 1 wt% ammonium dihydrogen phosphate, which is then removed and washed with water. Acid treatment: Immerse in a 7% phosphoric acid solution for 3 minutes at 60°C, then rinse with water. The subsequent formation of form II: temperature 85℃, time 5 min, voltage 93% Vf, current density 5 mA / cm² 2 The composition of the subsequent formation solution is: 2 wt% ammonium dihydrogen phosphate, which is then washed with water after removal. Heat treatment: 500℃ for 2 minutes; The subsequent transformation into three phases was carried out at the following conditions: temperature 85℃, time 4 min, voltage 93% Vf, and current density 100 mA / cm². 2 The composition of the subsequent tri-chemical solution is: 1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water and dried.

[0056] Comparative Example 1 Primary formation: temperature 80℃, time 4 min, voltage 12%Vf, current density 100mA / cm² 2 The primary formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Secondary formation: temperature 80℃, time 4 min, voltage 28%Vf, current density 100mA / cm² 2 The secondary formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Third-stage formation: temperature 80℃, time 4 min, voltage 46%Vf, current density 100mA / cm² 2 The composition of the tertiary formation solution is: 5 wt% ammonium adipate, which is washed with water after removal. Fourth-stage formation: temperature 80℃, time 4 min, voltage 68%Vf, current density 100mA / cm² 2 The composition of the fourth-stage formation solution is: 5 wt% ammonium adipate, which is washed with water after removal. Five-stage formation: temperature 80℃, time 4 min, voltage 82%Vf, current density 100mA / cm² 2 The fifth-stage formation solution consists of 5 wt% ammonium adipate, which is then washed with water after removal. Sixth-stage formation: temperature 80℃, time 6 min, voltage 98% Vf, current density 100 mA / cm² 2 The composition of the sixth-stage formation solution is: 4 wt% ammonium adipate and 1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water. The reaction was carried out at the following conditions: temperature 80℃, time 6 min, voltage 98% Vf, and current density 100 mA / cm². 2 The composition of the subsequent reaction solution is: 1 wt% ammonium dihydrogen phosphate, which is then removed and washed with water. Acid treatment: Immerse in a 7% phosphoric acid solution for 3 minutes at 60°C, then rinse with water. The subsequent formation of form II: temperature 85℃, time 5 min, voltage 93% Vf, current density 100 mA / cm² 2 The composition of the subsequent formation solution is: ammonium adipate 4wt%, ammonium dihydrogen phosphate 1wt%, which is then washed with water. Heat treatment: 500℃ for 2 minutes; The subsequent transformation into three phases was carried out at a temperature of 85℃ for 4 minutes, with a voltage of 93% Vf and a current density of 100 mA / cm². 2 The composition of the subsequent tri-chemical solution is: 1 wt% ammonium dihydrogen phosphate. After removal, it is washed with water and dried.

[0057] The performance of the electroformed foils in the above embodiments and comparative examples was tested, and the results are shown in Table 1 and Appendix 1 below. Figure 2-5 .

[0058] Table 1 - Composition of the forming solution and current density in the post-forming step, and relevant performance parameters of the resulting formed foil. Note: Vt-oxide film has high pressure resistance. C - Capacitance Tr-boost time Lc - Leakage Current Vt720-hydration-treated oxide film is pressure resistant Tr720 - Pressurization time after hydration treatment As can be seen from the data in Table 1, the electroformed foil obtained by the repair method described in this disclosure has significantly reduced leakage current and greatly shortened boost time after hydration treatment, while maintaining other comparable properties.

[0059] Figure 2The diagram shows the change in the state of the oxide film on the electrode foil surface before and after conventional hydration treatment (Comparative Example 1). Hydration is a water-boiling operation performed on the electrode foil during the testing of its water resistance. Specifically, the electrode foil sample is placed in hot pure water at 95-100 degrees Celsius and kept at that temperature for a specific time. In this paper, Vt720 and Tr720 represent 720 minutes, or 12 hours, of hot pure water treatment. Figure 2 As shown, because ordinary oxide films dissolve upon contact with hot water, the repaired area formed by conventional repair methods is a mixture of ordinary oxide film (corresponding to the gray part in the figure) and water-resistant oxide film (corresponding to the orange part in the figure) (corresponding to the mixed gray and orange striped area in the figure). After hydration, the gray part dissolves, leaving empty spaces (white stripes), while the orange part remains, thus leaving a mixed stripe of orange and white.

[0060] Figure 3 The diagram shows the state of the oxide film on the surface of the phosphoric acid-treated foil and the state of the foil before and after hydration. The phosphoric acid-treated foil shows partial loss of the oxide film on its surface. Figure 3 The white portion in the middle. The chemically formed foil obtained by the repair method of this disclosure can form a water-resistant substance to fill the gap after phosphoric acid treatment, and hydration will not dissolve the filling material in this part, so it exhibits the same state before and after hydration.

[0061] Figure 4 This is the voltage rise curve of the formed foil after phosphoric acid treatment without post-forming repair. During the phosphoric acid treatment process, the corrosive H₂... + Excessive quantity will lead to over-corrosion of the oxide film, increasing its defects and causing an inflection point in the voltage rise curve at 40V. At this point, the oxide film exhibits certain defects, such as… Figure 3 As shown in the left figure. According to Figure 4 It can be seen that all samples show an inflection point at the same voltage (40V), indicating that the oxide film has a similar defect shape.

[0062] Figure 5 This is a comparison graph showing the pressure rise curves of the electroformed foil obtained in the embodiments and comparative examples of this disclosure after hydration. The red line is the pressure rise curve of the electroformed foil after hydration in Comparative Example 1, and the green and blue lines are the pressure rise curves of the electroformed foil after hydration in Examples 1 and 2, respectively. Figure 5It can be seen that the time for the pressure rise curve of the electrolytic foil prepared according to the repair method of this disclosure to become horizontal (approximately 60-70 s) is significantly shorter than that of Comparative Example 1 (approximately 160 s). The short pressure rise time in each embodiment of this disclosure indicates good water resistance, meaning that less oxide film is dissolved during the hydration treatment, thus requiring only a shorter time for complete repair. In contrast, the corresponding red line of Comparative Example 1 shows that the pressure rise time is almost more than three times that of the embodiments of this disclosure, indicating poor water resistance. A large amount of oxide film is dissolved during the hydration treatment, requiring a longer repair time. This suggests that when using the method of Comparative Example 1 to repair the oxide film after phosphoric acid treatment, the water resistance of the repaired portion is limited, which is related to... Figure 2 The defects on the surface of the foil shown are consistent.

[0063] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A method for repairing foil, characterized in that, include: The step of performing post-forming treatment on electrode foil using a constant current in a pure ammonium dihydrogen phosphate forming solution, wherein the pure ammonium dihydrogen phosphate forming solution contains only ammonium dihydrogen phosphate as an effective component.

2. The repair method for electroplated foil according to claim 1, characterized in that, The post-formation treatment includes two or more post-formation treatments, wherein at least one post-formation treatment step is performed on the electrode foil in a pure ammonium dihydrogen phosphate forming solution using a constant current.

3. The repair method for electroplated foil according to claim 1, characterized in that, The concentration range of ammonium dihydrogen phosphate in the pure ammonium dihydrogen phosphate formation solution is 0.5-5 wt%.

4. The repair method for electroplated foil according to claim 1, characterized in that, The current density of the constant current is 2-100 mA / cm². 2 .

5. The repair method for electroplated foil according to claim 2, characterized in that, The electrode foil is subjected to acid treatment and heat treatment between the second or more post-formation processing steps.

6. The repair method for electroplated foil according to claim 5, characterized in that, In the acid treatment step, a phosphoric acid solution with a concentration of 1-10 wt% is used to treat the electrode foil.

7. The repair method for electrolytic foil according to claim 5, characterized in that, In the heat treatment step, the electrode foil is treated at a temperature range of 400 to 550°C.

8. The method for repairing electroplated foil according to any one of claims 1 to 7, characterized in that, Before performing post-forming treatment of the electrode foil using a constant current in a pure ammonium dihydrogen phosphate forming solution, the process also includes: The electrode foil is treated with phosphoric acid or ammonium dihydrogen phosphate to resist hydration.

9. A type of electrolytic foil, characterized in that, The formed foil is prepared by the repair method of the formed foil according to any one of claims 1 to 8.

10. An aluminum electrolytic capacitor, characterized in that, Includes the chemically formed foil according to claim 9.

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