A formed foil for aluminum electrolytic capacitors and its preparation method

Abstract

This invention discloses a formed foil for aluminum electrolytic capacitors and its preparation method. The preparation method includes: ultrasonically cleaning a base sintered foil in a first treatment solution, followed by calcination at 550-580°C; boiling the calcined foil in a second treatment solution to obtain a second treated foil, which is then subjected to a formation treatment to obtain a formed foil. The first treatment solution comprises citric acid, polyepoxysuccinic acid, and adipic acid at concentrations of 1-5 g / L, 0.2-0.4 g / L, and 0.3-0.8 g / L, respectively; the second treatment solution comprises phosphate and borate at concentrations of 0.05-0.5 g / L and 0.1-1.0 g / L, respectively. This invention solves the problem of carbide residue in the wet coating process for preparing sintered foil, and the resulting formed foil can be further used to obtain anode foil for aluminum electrolytic capacitors with high specific capacitance and low leakage current.

Description

Technical Field

[0001] This invention relates to the technical field of aluminum electrolytic capacitors, and more specifically to the technical field of sintered foil for aluminum electrolytic capacitors. Background Technology

[0002] Aluminum electrolytic capacitors are widely used in communication equipment, consumer electronics, instrumentation, energy-saving lighting, and other fields. The anode foil is a key material in aluminum electrolytic capacitor products, significantly impacting capacitor performance. Currently, the market uses sintered anode foil. Its preparation process includes: preparing a slurry from metal powder, binder, dispersant, and solvent, coating it onto the surface of aluminum foil, followed by drying, degreasing, sintering, and formation to obtain a high-capacity anode foil. The metal powder primarily consists of valve metals such as aluminum, titanium, niobium, and tantalum, with aluminum and titanium being the most common. In the sintered foil preparation process, the oxides formed from the valve metals act as a dielectric, limiting the anode foil's performance. Simultaneously, the dispersant and binder dissolved in the solvent form residual carbides after sintering, adhering to the valve metal surface and even filling the gaps between metal particles, significantly reducing the anode foil's surface area. Furthermore, these carbides hinder the formation of an oxide dielectric layer in subsequent formation steps, resulting in a series of problems such as high formation energy consumption, increased oxide film defects, high leakage current, and long voltage boosting time.

[0003] To address the above issues, some existing technologies have adopted improved solutions. For example, patent document CN108461294B discloses a method that uses anodizing bath as a carbon layer source, and forms fibrous metal carbon filaments through high-temperature carbonization of the tunnel pores and surface of the etched foil, which are then coated with nanoparticles to obtain a sintered foil. Patent document CN 110648849B discloses a process of sintering valve metal powder at 620°C for 40 hours under an alkane-nitrogen mixed gas, or sintering a slurry made of valve metal powder, solvent, and organic resin of different contents. Patent document CN111463016B discloses a process of adding specific valve metal particles to sinter aluminum powder at a higher temperature. However, although the above technologies reduce the content of residual carbides to some extent by modifying the morphology of carbides, rationally structuring the powder, and sintering at high temperatures, a considerable amount of carbides still remain on the surface of the valve metal, preventing further improvement in the performance of the sintered foil. Summary of the Invention

[0004] To address the shortcomings of the existing technology, the present invention aims to provide a new sintered foil for aluminum electrolytic capacitors and its preparation method. The preparation method effectively solves the problem of residual carbides in the wet coating preparation of sintered foil by adding a pre-treatment process between the sintering and formation processes, reducing energy consumption in the preparation process, and producing anode foil with high capacity, low leakage current, and short boost time.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing electrolytic foil for aluminum electrolytic capacitors, comprising:

[0007] The basic sintered foil obtained after the sintering process is placed in a first treatment solution with a pH value controlled at 4-6 and ultrasonically cleaned at 60-80℃ to obtain the first treated foil.

[0008] The first processed foil is cleaned and then calcined at 550-580°C for 1.5-2.5 minutes to obtain the first calcined foil;

[0009] The first calcined foil was boiled in a second treatment solution with a pH value controlled at 5-6 to obtain the second treated foil.

[0010] The second processed foil is subjected to a formation process to obtain a formed foil;

[0011] The first treatment solution comprises: citric acid at a concentration of 1-5 g / L, polyepoxysuccinic acid at a concentration of 0.2-0.4 g / L, and adipic acid at a concentration of 0.3-0.8 g / L; the second treatment solution comprises: phosphate at a concentration of 0.05-0.5 g / L and borate at a concentration of 0.1-1.0 g / L.

[0012] According to some preferred embodiments of the present invention, the ultrasonic cleaning time is 1-3 minutes.

[0013] According to some preferred embodiments of the present invention, the roasting time is 1.5-2.5 min.

[0014] According to some preferred embodiments of the present invention, the boiling time is 5-8 minutes.

[0015] According to some preferred embodiments of the present invention, the phosphate includes a first phosphate and a second phosphate, wherein the first phosphate is ammonium dihydrogen phosphate, and its concentration in the second treatment solution is 0.05-0.15 g / L; and in the second treatment solution, the concentration of the second phosphate is 0.1-0.3 g / L, and the concentration of the borate is 0.1-0.8 g / L.

[0016] According to some preferred embodiments of the present invention, the phosphate includes a first phosphate and a second phosphate, wherein the first phosphate is ammonium dihydrogen phosphate, and the second phosphate is selected from one or more of sodium phosphate, potassium phosphate, sodium pyrophosphate, and ammonium dihydrogen phosphate; the borate is selected from ammonium pentaborate and / or sodium tetraborate.

[0017] According to some preferred embodiments of the present invention, the borate is selected from ammonium pentaborate and / or sodium tetraborate.

[0018] According to some preferred embodiments of the present invention, the formation process includes: placing the second treated foil in a boric acid solution with a mass percentage of 15% and forming it at a voltage of 500-540V.

[0019] According to some preferred embodiments of the present invention, the formation process includes: placing the second treated foil in a mixed solution of boric acid with a mass percentage of 10% and ammonium pentaborate with a mass percentage of 5% and performing formation at a voltage of 500-540V.

[0020] According to some preferred embodiments of the present invention, the formation process is a four-stage formation process.

[0021] According to some preferred embodiments of the present invention, the basic sintered foil is obtained by the following preparation process:

[0022] Titanium powder, binder, dispersant, and organic solvent are mixed to obtain a mixed slurry;

[0023] The mixed slurry is coated onto the surface of the first aluminum foil after degreasing and drying, and then the second aluminum foil after degreasing and drying is placed on top of the mixed slurry. After the two foils are bonded together, they are dried and degreased at 150°C for 1 to 2 hours to obtain a pre-sintered foil.

[0024] The pre-sintered foil is heat-treated at 500–580°C for 10–24 hours in an inert atmosphere to obtain the basic sintered foil.

[0025] According to some preferred embodiments of the present invention, the adhesive is selected from one or more of epoxy resin, phenolic resin, polyurethane, and polyacrylate.

[0026] According to some preferred embodiments of the present invention, the dispersant is selected from one or more of polyacrylic acid, fatty acids, and polyacrylamide.

[0027] According to some preferred embodiments of the present invention, the organic solvent is selected from alcohols and / or lipid organic solvents.

[0028] The present invention further provides a chemically formed foil prepared according to the above preparation method, which does not contain residual carbides adhering to the pores after sintering, and has high capacity, high power-on efficiency and low leakage current.

[0029] In the preparation method of the present invention, the first treatment liquid and the second treatment liquid can fully clean and expand the pores of the residual carbides after sintering, and make the oxide film formed thereafter have a compact structure and excellent performance, thereby improving the capacity and electro-energizing efficiency of the electroformed foil.

[0030] This invention addresses the problems in existing technologies where valve metal wet coating on aluminum foil results in residual carbides adhering to the valve metal surface after the dispersant and binder in the solvent sinter, leading to slow oxide film formation time, high energy consumption, and numerous defects in the formed oxide film during subsequent formation processes. By designing a special pre-formation treatment process, this invention reduces residual carbides on the valve metal surface, fully utilizes the potential of the high dielectric layer of the valve metal oxide, and obtains anode foil with high specific capacitance. Detailed Implementation

[0031] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the embodiments are only used to illustrate the present invention and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the scope of the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0032] The base sintered foils used in the following examples were all obtained through the following process:

[0033] (1) The aluminum foil is degreased by alkaline washing and acid washing, and then dried;

[0034] (2) Titanium powder, adhesive, dispersant polyacrylic acid and solvent ethylene glycol methyl ether are mixed and stirred evenly to obtain a viscous slurry. The adhesive is a mixture of tetrabutyl titanate and polyacrylate with a volume ratio of 1:2.5.

[0035] (3) Coat one side of the dried aluminum foil with slurry, smooth it out, and then cover it with another aluminum foil so that the slurry adheres to the surface of the aluminum foil from top to bottom. After completion, put the sample into a drying oven and dry and degrease it at 150°C for 1 to 2 hours to obtain a pre-sintered foil.

[0036] (4) The pre-sintered foil is heat-treated at 500-580℃ for 10-24h under inert gas protection to obtain the basic sintered foil.

[0037] Example 1

[0038] The following steps are used to prepare the electrolytic foil for aluminum electrolytic capacitors:

[0039] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH value controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 1 g / L citric acid, 0.2 g / L polyepoxysuccinic acid and 0.3 g / L adipic acid.

[0040] (2) After rinsing the foil obtained in step (1) with running water, bake it at 580°C for 2.5 min.

[0041] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.15 g / L ammonium dihydrogen phosphate, 0.2 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0042] (4) Perform a four-stage formation process on the foil obtained in step (3) to obtain a formed foil; the four-stage formation process specifically includes:

[0043] Primary formation: The foil treated in step (3) is placed in the primary formation solution for formation treatment. The primary formation solution includes 1-2.5 g / L triethanolamine, 1-3 g / L metaboric acid, 1.5-5 g / L ammonium pentaborate, 4-6 g / L ammonium hydrogen azelaate, and 6-8 g / L fumaric acid. The bath temperature is controlled at 80-90℃, the voltage is 150-200V, and the current density is 0.3-0.5A / cm. 2 The time is 5-10 minutes;

[0044] Secondary formation: The foil after primary formation is placed in a secondary formation solution for further formation treatment. The secondary formation solution includes 0.5-2 g / L triethanolamine, 5-10 g / L ammonium pentaborate, 3-5 g / L ammonium hydrogen azelaate, 3-6 g / L fumaric acid, and 10-25 g / L metaboric acid. The bath temperature is controlled at 80-90℃, the voltage is 300-350V, and the current density is 0.3-0.5 A / cm². 2 The time is 5-10 minutes;

[0045] Cleaning: The foil after secondary formation treatment is placed into a cleaning tank for cleaning;

[0046] Three-stage formation: The cleaned foil is placed in a three-stage formation solution for formation treatment. The three-stage formation solution includes 30-50 g / L metaboric acid, 1-5 g / L fumaric acid, and 2-4 g / L ammonium azelaate. The bath temperature is controlled at 80-90℃, the voltage is 400-450V, and the current density is 0.3-0.5A / cm². 2 The time is 5-10 minutes;

[0047] Fourth-stage formation: The foil after the third-stage formation treatment is placed in the fourth-stage formation solution for further formation treatment. The fourth-stage formation solution includes 50-60 g / L metaboric acid and 2-4 g / L ammonium azelaate. The bath temperature is controlled at 80-90℃, the voltage is 530V, and the current density is 0.3-0.5A / cm². 2 The time is 10-15 minutes;

[0048] (5) After cleaning the obtained electrolytic foil, place it in a baking furnace and bake it at 520-550℃ for 2 minutes to obtain the first baked foil;

[0049] (6) The first calcined foil is placed in the fourth-stage forming solution for repair treatment to obtain the first repaired foil. During the repair treatment, the temperature of the forming solution is controlled at 80-90℃, the voltage is 530V, and the current density is 0.3-0.5A / cm. 2 The time is 5-10 minutes;

[0050] (7) Place the first repair foil in phosphoric acid with a mass percentage of 10%, soak for 150-180 seconds, and then rinse it clean.

[0051] (8) The cleaned foil obtained in step (7) is placed in a four-stage forming solution for repair treatment to obtain a second repaired foil. During the repair treatment, the temperature of the forming solution is controlled at 80-90℃, the voltage is 530V, and the current density is 0.3-0.5A / cm². 2 The time is 5-10 minutes;

[0052] (9) After cleaning the second repair foil, place it in a baking furnace and bake it at 430-500℃ for 2 minutes to obtain the second baked foil;

[0053] (10) The second calcined foil is placed in the fourth-stage forming solution for repair treatment to obtain the third repaired foil. During the repair treatment, the temperature of the forming solution is controlled at 80-90℃, the voltage is 530V, and the current density is 0.3-0.5A / cm². 2 The time is 5-10 minutes;

[0054] (11) The third repair foil was added to a post-treatment solution of ammonium dihydrogen phosphate with a concentration of 0.5 g / L and immersed at 50-60℃ for 6 min to obtain the post-treatment foil;

[0055] (12) Place the post-processed foil into a drying oven and dry it at 200°C to obtain chemically formed foil.

[0056] Tests showed that the capacity of the resulting electroformed foil was 20% higher than that of electroformed foil obtained by conventional processes.

[0057] Example 2

[0058] The electroformed foil is prepared by the following steps:

[0059] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 3 g / L citric acid, 0.3 g / L polyepoxysuccinic acid and 0.5 g / L adipic acid.

[0060] (2) After rinsing the foil obtained in step (1) with running water, bake it at 580°C for 2.5 min.

[0061] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.15 g / L ammonium dihydrogen phosphate, 0.2 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0062] (4) The foil obtained in step (3) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0063] Example 3

[0064] The electroformed foil is prepared by the following steps:

[0065] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 5 g / L citric acid, 0.4 g / L polyepoxysuccinic acid and 0.7 g / L adipic acid.

[0066] (2) After rinsing the foil obtained in step (1) with running water, bake it at 580°C for 2.5 min.

[0067] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.15 g / L ammonium dihydrogen phosphate, 0.2 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0068] (4) The foil obtained in step (3) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0069] Example 4

[0070] The electroformed foil is prepared by the following steps:

[0071] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 3 g / L citric acid, 0.3 g / L polyepoxysuccinic acid and 0.5 g / L adipic acid.

[0072] (2) After rinsing the foil obtained in step (1) with running water, bake it at 580°C for 2.5 min.

[0073] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.1 g / L ammonium dihydrogen phosphate, 0.1 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0074] (4) The foil obtained in step (3) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0075] Example 5

[0076] The electroformed foil is prepared by the following steps:

[0077] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 3 g / L citric acid, 0.3 g / L polyepoxysuccinic acid and 0.5 g / L adipic acid.

[0078] (2) After rinsing the foil obtained in step (1) with running water, bake it at 580°C for 2.5 min.

[0079] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.2 g / L ammonium dihydrogen phosphate, 0.3 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0080] (4) The foil obtained in step (3) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0081] Example 6

[0082] The electroformed foil is prepared by the following steps:

[0083] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 3 g / L citric acid, 0.3 g / L polyepoxysuccinic acid and 0.5 g / L adipic acid.

[0084] (2) After rinsing the foil obtained in step (1) with running water, bake it at 580°C for 2.5 min.

[0085] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.15 g / L ammonium dihydrogen phosphate, 0.2 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0086] (4) The foil obtained in step (3) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0087] Example 7

[0088] The electroformed foil is prepared by the following steps:

[0089] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH value controlled at 4-6 and ultrasonically cleaned at 60°C for 3 min. The first treatment solution contains 3 g / L citric acid, 0.3 g / L polyepoxysuccinic acid and 0.5 g / L adipic acid.

[0090] (2) After rinsing the foil obtained in step (1) with running water, bake it at 550°C for 2.5 min.

[0091] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 6 minutes. The second treatment solution contains 0.15 g / L ammonium dihydrogen phosphate, 0.2 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0092] (4) The foil obtained in step (3) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0093] Example 8

[0094] The electroformed foil is prepared by the following steps:

[0095] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 3 g / L citric acid, 0.3 g / L polyepoxysuccinic acid and 0.5 g / L adipic acid.

[0096] (2) After rinsing the foil obtained in step (1) with running water, bake it at 550°C for 2.5 min.

[0097] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.15 g / L ammonium dihydrogen phosphate, 0.2 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0098] (4) The processed foil obtained in step (3) is placed in a boric acid solution with a mass percentage of 15% and subjected to formation treatment at a voltage of 520V to obtain a formed foil.

[0099] Example 9

[0100] The electroformed foil is prepared by the following steps:

[0101] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 3 g / L citric acid, 0.3 g / L polyepoxysuccinic acid and 0.5 g / L adipic acid.

[0102] (2) After rinsing the foil obtained in step (1) with running water, bake it at 580°C for 2.5 min.

[0103] (3) The calcined foil obtained in step (2) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.15 g / L ammonium dihydrogen phosphate, 0.2 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0104] (4) The processed foil obtained in step (3) is placed in a mixed solution of boric acid with a mass percentage of 10% and ammonium pentaborate with a mass percentage of 5%, and the foil is formed by voltage of 520V to obtain the formed foil.

[0105] Comparative Example 1

[0106] The electroformed foil is prepared by the following steps:

[0107] (1) Boil the basic sintered foil obtained after the sintering process in pure water for 10 minutes.

[0108] (2) The foil obtained in step (1) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0109] Comparative Example 2

[0110] The electroformed foil is prepared by the following steps:

[0111] (1) Boil the basic sintered foil obtained after the sintering process in pure water for 10 minutes.

[0112] (2) The foil obtained in step (1) is placed in a boric acid solution with a mass percentage of 15% and subjected to formation treatment at a voltage of 520V to obtain a formed foil.

[0113] Comparative Example 3

[0114] The electroformed foil is prepared by the following steps:

[0115] (1) Boil the basic sintered foil obtained after the sintering process in pure water for 10 minutes.

[0116] (2) The processed foil obtained in step (1) is placed in a mixed solution of boric acid with a mass percentage of 10% and ammonium pentaborate with a mass percentage of 5%, and the foil is formed by voltage of 520V to obtain the formed foil.

[0117] Comparative Example 4

[0118] The electroformed foil is prepared by the following steps:

[0119] (1) The basic sintered foil obtained after the sintering process is placed in the first treatment solution with pH value controlled at 4-6 and ultrasonically cleaned at 85°C for 3 min. The first treatment solution contains 1 g / L citric acid, 0.2 g / L polyepoxysuccinic acid and 0.3 g / L adipic acid.

[0120] (2) After rinsing the foil obtained in step (1) with running water, bake it at 580°C for 2.5 min.

[0121] (3) The calcined foil obtained in step (2) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0122] Comparative Example 5

[0123] The electroformed foil is prepared by the following steps:

[0124] (1) The basic sintered foil obtained after the sintering process is rinsed with running water and then baked at 580℃ for 2.5min.

[0125] (2) The calcined foil obtained in step (1) is placed in a second treatment solution with a pH value controlled at 5-6 and boiled for 8 minutes. The second treatment solution contains 0.15 g / L ammonium dihydrogen phosphate, 0.2 g / L sodium phosphate and 0.5 g / L sodium tetraborate.

[0126] (3) The foil obtained in step (2) is subjected to formation treatment according to the process (4)-(12) in Example 1 to obtain the formed foil.

[0127] The foils obtained in Examples 1-9 and Comparative Examples 1-5 were tested. The testing equipment included: a TV characteristic tester for formed foil, an LCR tester for formed foil, a bending tester, and a measuring tank with a capacity of 1000 ml.

[0128] The leakage current, withstand voltage, and withstand voltage rise time were tested using a TV characteristic tester at a temperature of 85℃. The test solution was 1000ml containing 70g of boric acid with a resistivity of 7.5±0.3KΩ·cm and a pH of 3.2. The test current was 2.0±0.2mA. During the test, the time it took for the rated diaphragm withstand voltage (Vf) to reach 90% of the voltage (Vr) from the start of power-on was recorded as the rise time. After 3 minutes of testing, the withstand voltage, withstand voltage rise time, and leakage current were read.

[0129] The capacity was tested using an LCR meter. The test solution was 1000ml of pure water containing 80g of ammonium pentaborate, with a resistivity of 30±5Ω·cm, a pH of 7.4, and a test temperature of 30℃.

[0130] Bending data was tested using a bending machine.

[0131] The results are as follows:

[0132] Table 1. Comparison of foil performance in examples and comparative models.

[0133]

[0134]

[0135] It can be seen that the foils prepared by the pretreatment and formation processes of the present invention in Examples 1-9 have higher capacity than foils prepared by conventional methods. Furthermore, after removing carbides and forming an oxide film, they exhibit advantages such as shorter voltage rise time and lower leakage current. Examples 1 and 2 show even better results. It can also be seen that the product performance after co-treatment with the two treatment solutions is significantly better than the product performance obtained by treating with either treatment solution alone.

[0136] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing electrolytic foil for aluminum electrolytic capacitors, characterized in that, It includes: The basic sintered foil obtained after the sintering process is placed in a first treatment solution with a pH value controlled at 4-6 and ultrasonically cleaned at 60-80℃ to obtain the first treated foil. The first processed foil is cleaned and then calcined at 550-580°C for 1.5-2.5 minutes to obtain the first calcined foil; The first calcined foil was boiled in a second treatment solution with a pH value controlled at 5-6 to obtain the second treated foil. The second processed foil is subjected to a formation process to obtain a formed foil; The first treatment solution comprises: citric acid at a concentration of 1-5 g / L, polyepoxysuccinic acid at a concentration of 0.2-0.4 g / L, and adipic acid at a concentration of 0.3-0.8 g / L; the second treatment solution comprises: phosphate at a concentration of 0.05-0.5 g / L and borate at a concentration of 0.1-1.0 g / L.

2. The preparation method according to claim 1, characterized in that, in, The ultrasonic cleaning time is 1-3 min; and / or the calcination time is 1.5-2.5 min; and / or the boiling time is 5-8 min.

3. The preparation method according to claim 1, characterized in that, The phosphates include a first phosphate and a second phosphate. The first phosphate is ammonium dihydrogen phosphate, and its concentration in the second treatment solution is 0.05-0.15 g / L. The concentration of the second phosphate in the second treatment solution is 0.1-0.3 g / L, and the concentration of the borate is 0.1-0.8 g / L.

4. The preparation method according to claim 1, characterized in that, The phosphate includes a first phosphate and a second phosphate, wherein the first phosphate is ammonium dihydrogen phosphate and the second phosphate is selected from one or more of sodium phosphate, potassium phosphate, sodium pyrophosphate, and ammonium dihydrogen phosphate; the borate is selected from ammonium pentaborate and / or sodium tetraborate.

5. The preparation method according to claim 1, characterized in that, The formation process includes: placing the second processed foil in a boric acid solution with a mass percentage of 15% and forming it at a voltage of 500-540V.

6. The preparation method according to claim 1, characterized in that, The formation process includes: placing the second processed foil into a mixed solution of boric acid with a mass percentage of 10% and ammonium pentaborate with a mass percentage of 5%, and performing formation at a voltage of 500-540V.

7. The preparation method according to claim 1, characterized in that, The formation process is a four-stage formation process.

8. The preparation method according to claim 1, characterized in that, The basic sintered foil is obtained through the following preparation process: Titanium powder, binder, dispersant, and organic solvent are mixed to obtain a mixed slurry; The mixed slurry is coated onto the surface of the first aluminum foil after degreasing and drying, and then the second aluminum foil after degreasing and drying is placed on top of the mixed slurry. After the two foils are bonded together, they are dried and degreased at 150°C for 1 to 2 hours to obtain a pre-sintered foil. The pre-sintered foil is heat-treated at 500~580℃ for 10~24h in an inert atmosphere to obtain the basic sintered foil.

9. The preparation method according to claim 8, characterized in that, The adhesive is a mixture of tetrabutyl titanate and polyacrylate in a volume ratio of 1:2.5; the dispersant is selected from one or more of polyacrylic acid, fatty acids, and polyacrylamide; and the organic solvent is ethylene glycol methyl ether.

10. The electroformed foil obtained by the preparation method according to any one of claims 1-9.

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