A method for preparing low-voltage formed foil for solid-state aluminum electrolytic capacitors

Abstract

The present invention discloses a method for preparing low-voltage chemically formed foil for solid-state aluminum electrolytic capacitors. The preparation method comprises first immersing the low-voltage chemically formed foil in a liquid containing a hydroxylamine organic compound, then treating it under inert gas protection to increase its electrostatic capacitance by 2% to 8% compared to before treatment; then employing a three-stage electrochemical anodization process, with each stage of the anodization process employing a lower current density. The low-voltage chemically formed foil prepared by the improved process has higher electrostatic capacitance, more stable performance, and longer lifespan. Solid-state aluminum electrolytic capacitors prepared using the low-voltage chemically formed foil have improved electrostatic capacitance and lifespan (especially high-temperature lifespan), better meeting the requirements of solid-state aluminum electrolytic capacitors.

Description

Technical Field

[0001] The invention belongs to the field of chemically formed foil preparation, and in particular relates to a method for preparing a low-voltage chemically formed foil for a solid-state aluminum electrolytic capacitor. Background Art

[0002] Unlike liquid capacitors, which use electrolytes, solid aluminum electrolytic capacitors utilize polymer solid electrolytes. Due to the poor fluidity of solid electrolytes, solid aluminum electrolytic capacitors suffer from specific capacitance extraction issues. Therefore, anode foils with high electrostatic capacitance are required. Furthermore, since solid aluminum electrolytic capacitors cannot self-repair defects in the anode foil's oxide film, the oxide film must exhibit more stable performance.

[0003] In the prior art, chemical foil is commonly used as the anode foil of solid aluminum electrolytic capacitors. Chemical foil is made by electrochemically or chemically corroding a specially made high-purity aluminum foil to expand its surface area, and then forming a layer of oxide film (aluminum oxide) on the surface through electrochemical formation. In order to increase the electrostatic capacitance of chemical foil, the prior art uses a sol-gel method to make a uniformly dispersed colloid from elements such as titanium, strontium, and barium. The colloid is then applied to the surface of the electrode film and a high-dielectric thin film is generated through heat treatment. However, the foil after this treatment is prone to poor appearance. The prior art also uses a process based on this method to perform an annealing treatment, which improves the appearance quality of the resulting product. According to the voltage during the chemical formation process, chemical foil is generally divided into four types: ultra-low voltage (below 7V), low voltage (7-170V), medium-high voltage, and high voltage. For low-voltage formation, the current density is generally controlled to be between 0.1 and 0.8A / cm 2 However, the low-pressure chemically formed foils prepared by existing methods still have room for improvement in terms of electrostatic capacitance and oxide film stability. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art and provides a method for preparing a low-voltage chemically formed foil for solid-state aluminum electrolytic capacitors. The low-voltage chemically formed foil prepared using the method has a higher electrostatic capacitance and a longer lifespan, better meeting the requirements of solid-state aluminum electrolytic capacitors.

[0005] Another object of the present invention is to provide a low-voltage formed foil for solid aluminum electrolytic capacitors prepared by the preparation method.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for preparing a low-voltage formed foil for a solid aluminum electrolytic capacitor comprises the following steps:

[0008] S1. Immerse the low-voltage corrosion foil of aluminum electrolytic capacitors in a liquid containing hydroxylamine organic matter and then dry it under inert gas protection to increase its electrostatic capacitance by 2% to 8% compared with that before treatment;

[0009] S2. Perform the first stage of electrochemical anodization on the corroded foil after treatment in S1. The current density of the anodization is 0.01~0.05A / cm 2 ;

[0010] S3. Perform a second stage of electrochemical anodization on the corroded foil after treatment in S2. The current density used for anodization is 0.005 to 0.05 A / cm 2 ;

[0011] S4. Perform a third-stage electrochemical anodization on the corroded foil after treatment in S3. The current density used for anodization is 0.001 to 0.04 A / cm 2 ;

[0012] S5. The corroded foil treated in S4 is cleaned, depolarized, cleaned again, and then electrochemically repaired. The current density used for electrochemical repair is 0.001 to 0.005 A / cm 2 ;

[0013] S6. Cleaning, annealing, heat treating, chemically repairing, cleaning, and drying the corroded foil after the treatment in S5 to obtain the low-voltage chemical-formed foil for the solid aluminum electrolytic capacitor.

[0014] In the present invention, step S1 forms a dielectric layer with a higher dielectric constant on the surface of the low-voltage formed foil for aluminum electrolytic capacitors by immersing the foil in a liquid containing a hydroxylamine organic compound, thereby increasing the electrostatic capacitance of the foil. During the electrochemical oxidation and electrochemical repair processes, a lower current density is used to reduce capacitance decay during the oxidation process, while also improving the quality of the resulting oxide film. This results in a solid low-voltage formed foil for aluminum electrolytic capacitors with improved capacitance, more stable performance, and a longer lifespan.

[0015] Preferably, in S1., the immersion treatment comprises immersing the low-voltage etching foil for aluminum electrolytic capacitors in a liquid having a hydroxylamine organic compound concentration of 0.2 to 0.5%. When the liquid concentration of the hydroxylamine organic compound is too high, the dielectric constant of the dielectric layer formed on the surface of the low-voltage etching foil for aluminum electrolytic capacitors is not ideal, i.e., it is not ideal for improving the electrostatic capacitance of the etching foil. If the liquid concentration of the hydroxylamine organic compound is too low, no significant improvement is achieved.

[0016] Preferably, in S1., the soaking time is preferably 6 min to 10 min.

[0017] Preferably, in S1., the hydroxylamine organic compound is a hydroxyl substituted compound of an alkylamine.

[0018] More preferably, the hydroxyl-substituted product of the alkylamine is diethanolamine, triethanolamine or ethanolamine.

[0019] More preferably, S1. The low-voltage corrosion foil of the aluminum electrolytic capacitor is immersed in a liquid containing hydroxylamine organic matter, and then dried under the protection of an inert gas, so that the electrostatic capacitance thereof is increased by 4% to 8% compared with that before the treatment.

[0020] In the present invention, the electrostatic capacitance of the low-voltage corrosion foil is measured according to the Electronic Industries Association Japan (EIAJ RC-2364A) Electrode Foil Inspection Test Method 1999 Edition test (23V).

[0021] Preferably, in S1., the drying is performed at 400-520°C.

[0022] The voltages selected for the first-stage electrochemical anodization, the second-stage electrochemical anodization, and the third-stage electrochemical anodization are related to the rated withstand voltage Vf of the formed foil product.

[0023] Preferably, the voltage of the first stage electrochemical anodization is 25% to 35% of Vf.

[0024] Preferably, the voltage of the second stage electrochemical anodization is 55% to 65% of Vf.

[0025] Preferably, the voltage of the third stage electrochemical anodization is 100% Vf.

[0026] Preferably, the first stage electrochemical anodization, the second stage electrochemical anodization or the third stage electrochemical anodization is carried out in an aqueous ammonium adipate solution. The concentration of the aqueous ammonium adipate solution can refer to the prior art. Preferably, the mass concentration of the aqueous ammonium adipate solution is independently selected from 8 to 15%.

[0027] Preferably, the current density of the first stage electrochemical anodization, the second stage electrochemical anodization or the third stage electrochemical anodization is independently selected from 0.002 to 0.04 A / cm 2 More preferably, the current density of the first stage electrochemical anodization, the second stage electrochemical anodization or the third stage electrochemical anodization is independently selected from 0.002 to 0.03 A / cm 2 .

[0028] Preferably, the current density used in the first stage electrochemical anodization, the current density used in the second stage electrochemical anodization, and the current density used in the third stage electrochemical anodization decrease in sequence.

[0029] Preferably, the time of the first stage electrochemical anodization, the second stage electrochemical anodization or the third stage electrochemical anodization is independently selected from 300 to 600 seconds.

[0030] In S5., the depolarization operation can refer to the prior art. Preferably, in S5., the depolarization is performed in phosphoric acid.

[0031] Preferably, in S5., the electrochemical repair is performed in an aqueous solution of ammonium adipate. The concentration of the aqueous solution of ammonium adipate can refer to the prior art. Preferably, the mass concentration of the aqueous solution of ammonium adipate is selected from 10 to 15%.

[0032] Preferably, in S5., the voltage of the electrochemical repair is 100% Vf.

[0033] Preferably, the electrochemical repair time is selected from 400 to 800 seconds.

[0034] In S6., the annealing heat treatment is performed in accordance with existing techniques. Preferably, in S6., the annealing heat treatment is performed at 430-530°C. Preferably, the annealing heat treatment lasts for 80-240 seconds. Because annealing heat treatment affects the dielectric layer structure, existing techniques typically perform chemical repairs after annealing heat treatment.

[0035] In S6., chemical repair is performed according to existing techniques. Preferably, the chemical repair is performed by immersion in an aqueous solution of ammonium dihydrogen phosphate. Preferably, the mass concentration of the aqueous solution of ammonium dihydrogen phosphate is 0.1-0.5%. The immersion time for chemical repair depends on the size of the product and is generally between 180 and 500 seconds.

[0036] A low-voltage formed foil for solid aluminum electrolytic capacitors prepared by the preparation method.

[0037] A solid aluminum electrolytic capacitor uses a low-voltage formed foil for the solid aluminum electrolytic capacitor as a positive electrode foil.

[0038] A method for increasing the electrostatic capacitance and / or life of a solid-state aluminum electrolytic capacitor, comprising preparing a low-voltage formed foil constituting the solid-state aluminum electrolytic capacitor by the following method, comprising the following steps:

[0039] S1. Immerse the low-voltage corrosion foil of aluminum electrolytic capacitors in a liquid containing hydroxylamine organic matter and then dry it under inert gas protection to increase its electrostatic capacitance by 2% to 8% compared with that before treatment;

[0040] S2. Perform the first stage electrochemical anodization on the corroded foil after the treatment in S1. The current density of the first stage electrochemical anodization is 0.01~0.05A / cm 2 ;

[0041] S3. Perform a second electrochemical anodization on the corroded foil after treatment in S2. The current density used in the second electrochemical anodization is 0.005~0.05A / cm 2 ;

[0042] S4. Perform a third-stage electrochemical anodization on the corroded foil after treatment in S3. The current density used in the third-stage electrochemical anodization is 0.001 to 0.04 A / cm 2 ;

[0043] S5. The corroded foil treated in S4 is cleaned, depolarized, cleaned again, and then electrochemically repaired. The current density used for electrochemical repair is 0.001 to 0.005 A / cm 2 ;

[0044] S6. Cleaning, annealing, heat treating, chemically repairing, cleaning, and drying the corroded foil after the treatment in S5 to obtain the low-voltage chemical-formed foil for the solid aluminum electrolytic capacitor.

[0045] The lifespan is more preferably the high-temperature lifespan of the solid aluminum electrolytic capacitor. In the present invention, the high-temperature lifespan refers to the lifespan of the solid aluminum electrolytic capacitor at 105°C.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The present invention provides a method for preparing low-voltage chemically formed foil for solid-state aluminum electrolytic capacitors. Through an improved process, the low-voltage chemically formed foil for aluminum electrolytic capacitors is immersed in a liquid containing a hydroxylamine organic compound, thereby increasing its electrostatic capacitance by 2% to 8% compared to before treatment. Combined with subsequent processing techniques, the prepared low-voltage chemically formed foil has higher electrostatic capacitance, more stable performance, and longer life. Solid-state aluminum electrolytic capacitors prepared with the low-voltage chemically formed foil have improved electrostatic capacitance and life (especially high-temperature life), better meeting the requirements of solid-state aluminum electrolytic capacitors. DETAILED DESCRIPTION

[0048] The present invention is further described in detail below with reference to specific examples. The examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0049] Comparative Examples 1 to 2 and Examples 1 to 8

[0050] The rated withstand voltage Vf of the chemically formed foil product prepared in the embodiment is 23V, and the specific preparation operation is as follows.

[0051] S1. Treating the aluminum electrolytic capacitor with a low-voltage etching foil, specifically, soaking the low-voltage etching foil in an aqueous solution containing hydroxylamine organic matter with a mass concentration of 0.2-0.5%, and then drying it at 480° C. under the protection of an inert gas.

[0052] S2. The corroded foil treated in S1 is subjected to first-stage electrochemical anodization in an ammonium adipate solution at a current density of 0.01 to 0.05 A / cm 2 ; The first stage electrochemical anodic oxidation voltage is 7V;

[0053] S3. The corroded foil treated in S2 is subjected to a second-stage electrochemical anodization in an ammonium adipate solution. The current density used for the anodization is 0.005 to 0.05 A / cm 2 ; The second stage electrochemical anodic oxidation voltage is 15V;

[0054] S4. The corroded foil treated in S3 is subjected to a third-stage electrochemical anodization in an ammonium adipate solution. The current density used for the anodization is 0.001 to 0.04 A / cm 2 ; The third stage electrochemical anodic oxidation voltage is 23V;

[0055] S5. The corroded foil treated in S4 is sequentially cleaned with pure water, depolarized by immersion in a phosphoric acid solution, cleaned again with pure water, and then electrochemically repaired in an ammonium adipate aqueous solution at a current density of 0.001 to 0.005 A / cm 2 ;Electrochemical repair voltage is 23V;

[0056] S6. The corroded foil after the treatment in S5. is cleaned, annealed, and chemically repaired by immersing in a 0.5% aqueous solution of ammonium dihydrogen phosphate, cleaned, and dried to obtain the low-voltage chemically formed foil for the solid aluminum electrolytic capacitor.

[0057] The process parameters of Examples 1 to 10 are detailed in Table 1.

[0058]

[0059]

[0060] Comparative Example 3

[0061] The process steps are the same as those in Example 1, except that in S1., the mass concentration of the diethanolamine aqueous solution used for soaking is 1%, the soaking time is also 7 minutes, and the low-pressure corrosion foil EIAJ test specific capacitance (23V) after soaking is 111μF / cm 2This indicates that when the concentration of the diethanolamine aqueous solution is too high, the dielectric constant of the dielectric layer formed on the surface of the low-voltage etched foil for aluminum electrolytic capacitors is not ideal, which means that it is not ideal for improving the electrostatic capacitance of the etched foil. Subsequently, S2. to S6. were performed using the same process parameters as in Example 1 to obtain the low-voltage etched foil.

[0062] The performance of the low-pressure formed foils prepared in Comparative Examples 1 to 3 and Examples 1 to 8 was tested, and the electrostatic capacitance was tested in the following manner:

[0063] Use electrostatic capacitance tester: measurement accuracy ±2%, test frequency: 120±5HZ, measurement voltage ≤0.5Vrms.

[0064] Low-pressure chemically formed foils prepared in Comparative Examples 1-3 and Examples 1-8 served as anodes, and platinum mesh served as cathodes. Measurements were conducted in a solution consisting of 150 g of ammonium adipate and 1000 mL of pure water at 30°C. The measured portion of the test piece was 50 mm long and 10 mm wide.

[0065] High temperature resistance is tested in the following way:

[0066] The low-voltage chemically formed foils prepared in Comparative Examples 1-3 and Examples 1-8 were used as positive electrode foils, along with negative electrode foils and electrolytic paper to form solid-state aluminum electrolytic capacitors. The capacitors were sized 8 mm by 12 mm. The lifespan of these capacitors was tested in a constant-temperature oven at 105°C.

[0067] Table 2

[0068] <![CDATA[23Vf Capacitance (μF / cm 2 )]]> 105℃ high temperature life (h) Comparative Example 1 107 4700 Comparative Example 2 109 5000 Comparative Example 3 109.5 4750 Example 1 112 4950 Example 2 114 5300 Example 3 114 4950 Example 4 116 5350 Example 5 113 4950 Example 6 115 5350 Example 7 115 4950 Example 8 117 5400

[0069] From the comparison of Examples 1, 3, 5, and 7 with Comparative Example 1, and the comparison of Examples 2, 4, 6, and 8 with Example 2, it can be seen that after the corroded foil is pretreated and then prepared under the same conditions into a low-voltage formed foil for solid aluminum electrolytic capacitors, the electrostatic capacitance and high-temperature life of the low-voltage formed foil are improved.

[0070] From the comparison of Examples 1 and 2, Examples 3 and 4, Examples 5 and 6, and Examples 7 and 8, it can be seen that the electrostatic capacitance and high-temperature life of the low-pressure formed foil product are improved by carrying out anodization at a lower current density in each stage of anodization.

[0071] From the comparison between Example 2 and Example 3, it can be seen that the current density of the chemical formation process is too high, and the electrostatic capacitance loss is more serious, which to a certain extent offsets the effect of the electrostatic capacitance improvement brought about by the increase in dielectric constant by immersing the low-voltage corrosion foil in a liquid containing hydroxylamine organic matter.

[0072] It can be seen from Comparative Example 3 that when the mass concentration of the diethanolamine aqueous solution is too high, the dielectric constant of the dielectric layer formed on the surface of the low-voltage corrosion foil for aluminum electrolytic capacitors is not ideal, and the electrostatic capacitance and high-temperature life of the low-voltage corrosion foil product prepared therefrom are not significantly improved.

[0073] Although different customers have different requirements for the electrostatic capacitance of the electrostatic foil, the current market generally requires 23Vf electrostatic capacitance 106μF / cm 2 It can also meet the requirements, but as some high-end customers expect higher electrostatic capacitance, the low-voltage chemical foil product of the present invention can meet the requirements of customers with higher requirements for electrostatic capacitance.

[0074] The above-mentioned Example 8 is a preferred embodiment of the present invention, but the embodiments of the present invention are not limited to the above-mentioned examples. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a low-voltage chemical foil for a solid aluminum electrolytic capacitor, characterized in that: The steps include: S1. Immerse aluminum electrolytic capacitor foil in a solution containing hydroxylamine as the sole solute at a concentration of 0.2 to 0.5%, and then dry it under inert gas to increase its capacitance by 2 to 8% compared to before treatment. The drying is carried out at 400-520°C; S2. Perform the first stage electrochemical anodization on the corroded foil after the treatment in S1. The current density of the first stage electrochemical anodization is 0.01~0.05A / cm 2 ; S3. Perform a second electrochemical anodization on the corroded foil after treatment in S2. The current density used in the second electrochemical anodization is 0.005~0.05A / cm 2 ; S4. Perform a third-stage electrochemical anodization on the corroded foil after treatment in S3. The current density used in the third-stage electrochemical anodization is 0.001 to 0.04 A / cm 2 ; S5. The corroded foil treated in S4 is cleaned, depolarized, cleaned again, and then electrochemically repaired. The current density used for electrochemical repair is 0.001 to 0.005 A / cm 2 ; S6. Cleaning, annealing, heat treating, chemically repairing, cleaning, and drying the corroded foil after the treatment in S5 to obtain the low-voltage chemical-formed foil for the solid aluminum electrolytic capacitor.

2. The method for preparing a low-voltage chemically formed foil for a solid aluminum electrolytic capacitor according to claim 1, characterized in that: In S1., the hydroxylamine organic compound is a hydroxyl-substituted compound of alkylamine.

3. The method for preparing a low-voltage chemically formed foil for a solid aluminum electrolytic capacitor according to claim 2, characterized in that: The hydroxyl substituent of the alkylamine is diethanolamine, triethanolamine or ethanolamine.

4. The method for preparing a low-voltage chemically formed foil for a solid aluminum electrolytic capacitor according to claim 1, wherein: In S1., the drying is performed at 400-520°C.

5. The method for preparing a low-voltage chemically formed foil for a solid aluminum electrolytic capacitor according to claim 1, characterized in that: The current density used in the first stage electrochemical anodization, the current density used in the second stage electrochemical anodization, and the current density used in the third stage electrochemical anodization decrease in sequence.

6. The method for preparing a low-voltage chemically formed foil for a solid aluminum electrolytic capacitor according to claim 1, characterized in that: The time of the first stage electrochemical anodization, the second stage electrochemical anodization or the third stage electrochemical anodization is 300 to 600 seconds.

7. The method for preparing a low-voltage chemically formed foil for a solid aluminum electrolytic capacitor according to claim 1, characterized in that: The first-stage electrochemical anodization, the second-stage electrochemical anodization or the third-stage electrochemical anodization is carried out in an ammonium adipate aqueous solution, wherein the mass concentration of the ammonium adipate aqueous solution is 8-15%.

8. A low-voltage formed foil for solid aluminum electrolytic capacitors prepared by the preparation method according to any one of claims 1 to 7.

9. A solid aluminum electrolytic capacitor, using the low-voltage formed foil for solid aluminum electrolytic capacitors according to claim 8 as a positive electrode foil.

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