Corrosion process for anode aluminum foil of electrolytic capacitor

Abstract

The invention discloses an electrolytic capacitor anode aluminum foil corrosion process, and belongs to the technical field of electrolytic capacitor anode aluminum foil corrosion processes. The method is used for solving the technical problems of poor hydration resistance and acid corrosion resistance of an aluminum oxide film of the anode aluminum foil of the electrolytic capacitor in the prior art, and how to increase the hole depth of the anode aluminum foil and improve the surface expansion effect of the anode aluminum foil of the electrolytic capacitor. A corrosion process of an electrolytic capacitor anode aluminum foil comprises the following steps: performing alkaline washing on the anode aluminum foil, and performing acid washing by adopting a phosphoric acid solution to obtain the pretreated anode aluminum foil; nano tin is deposited on the surface of the pretreated anode aluminum foil in a pulse mode, then primary corrosion and secondary corrosion are conducted in sequence, and the anode aluminum foil with holes formed is obtained; immersing the anode aluminum foil subjected to hole forming into corrosion expansion liquid to corrode and broach, and finally obtaining the electrolytic capacitor anode aluminum foil subjected to the corrosion process. The electrolytic capacitor anode aluminum foil prepared by the invention has the advantages of large hole depth, good corrosion expansion effect and large specific volume.

Description

Technical Field

[0001] This invention belongs to the technical field of corrosion process technology for anode aluminum foil of electrolytic capacitors, specifically a corrosion process for anode aluminum foil of electrolytic capacitors. Background Technology

[0002] With the rapid development of technologies such as rail transit, flat panel displays, electric vehicles, solar energy, wind power generation, and medium- and high-voltage frequency converters, there is an urgent need for wide-temperature-range, ultra-high-voltage-resistant, long-life, and highly stable aluminum electrolytic capacitors in their control circuits. An aluminum electrolytic capacitor is a type of capacitor consisting of an anode aluminum foil, an Al2O3 dielectric layer formed on the aluminum foil, and a cathode electrolyte. It plays a crucial role in electronic circuits due to its small size, high specific capacitance, and low cost. The anode foil is the key material in the manufacture of aluminum electrolytic capacitors, determining their specific capacitance and other electrical properties.

[0003] The production process of anode aluminum foil for electrolytic capacitors involves multiple precision steps. The basic process of etching and forming the foil includes: etching pretreatment, hole formation, hole enlargement, post-treatment, and the formation process. Etching is the preceding step in foil manufacturing and is crucial for improving the performance of electrolytic capacitors. Patent application CN103187176A discloses an etching process for anode aluminum foil of electrolytic capacitors. The steps for preparing the anode aluminum foil in this invention include five steps: pretreatment, AC pre-etching, intermediate chemical treatment, subsequent AC etching, and post-treatment. Existing technologies employ ultrasonic assistance in the AC pre-etching and subsequent AC etching processes to ensure uniform etching of the prepared anode aluminum foil. However, how to increase the hole depth of the anode foil and improve the etching expansion effect remains a pressing technical problem to be solved.

[0004] Furthermore, the traditional manufacturing process for solid-state aluminum electrolytic capacitors involves directly impregnating the core with a conductive polymer, or impregnating monomers and oxidants to form a conductive polymer, which is then cured into the dielectric material of the solid-state capacitor. During this process, the impregnation solution has a pH value close to 2-3, which corrodes the alumina film. Therefore, further improving the hydration resistance and acid corrosion resistance of the alumina film used for the anode aluminum foil during the etching process is a pressing technical problem that needs to be solved.

[0005] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a corrosion process for the anode aluminum foil of electrolytic capacitors, which solves the technical problems of poor hydration resistance and acid corrosion resistance of the anode aluminum foil in the prior art, as well as how to increase the hole depth of the anode aluminum foil and improve the surface expansion effect of the anode aluminum foil of electrolytic capacitors.

[0007] The objective of this invention can be achieved through the following technical solutions: A etching process for the anode aluminum foil of an electrolytic capacitor includes the following steps: S1. Alkaline washing of anode aluminum foil, acid washing with phosphoric acid solution, washing and drying to obtain pretreated anode aluminum foil; S2. Pulse deposition of nano-tin on the surface of the pretreated anode aluminum foil to obtain anode aluminum foil with deposited tin; S3. The tin-deposited anode aluminum foil is placed in a primary etching solution for primary etching, and then placed in a secondary etching solution for secondary etching to obtain the anode aluminum foil with perforated holes. S4. The anode aluminum foil with enlarged holes is immersed in an etching and expanding solution to etch and expand the holes, thus obtaining the anode aluminum foil with expanded holes. S5. After the anode aluminum foil is expanded, it is pickled, washed with water, and dried to prepare the electrolytic capacitor anode aluminum foil that has completed the corrosion process.

[0008] Furthermore, in step S1, the concentration of the phosphoric acid solution is 3-5 wt%, the pickling time is 80-100 s, and the pickling temperature is 20-25℃.

[0009] Furthermore, in step S2, the current density for pulse deposition of nano-tin is 80-100 mA / cm². 2 The pulse duration is 1 second, the pulse interval is 1 second, and the total deposition time is 20-25 seconds.

[0010] Further, in step S3, the primary etching solution is obtained by mixing equal volumes of 1-1.5 mol / L hydrochloric acid solution and 3-3.5 mol / L sulfuric acid solution; the ultrasonic etching frequency is 30-40 kHz, the ultrasonic etching temperature is 45-55℃, and the ultrasonic etching time is 3-5 min; the secondary etching solution is obtained by uniformly mixing 0.5-1 mol / L hydrochloric acid solution, 3-3.5 mol / L sulfuric acid solution, and oxalic acid in a mass ratio of 50:50:0.5-1; the ultrasonic etching frequency is 20-30 kHz, the ultrasonic etching temperature is 25-35℃, and the ultrasonic etching time is 3-5 min.

[0011] Further, in step S4, the method for preparing the corrosion expansion fluid includes the following steps: A1. Concentrated sulfuric acid is added to phenol and stirred at 95-100℃ for 4-4.5 hours to obtain a mixture; NaOH solution is added dropwise to the mixture to adjust its pH to 7-8, and then formaldehyde solution is added to obtain the reactants; Sulfuric acid reacts with phenol to produce phenolsulfonic acid; phenolsulfonic acid and formaldehyde undergo condensation polymerization to obtain a condensation-type sulfonic acid-based ion exchange resin, which is the reactant prepared.

[0012]

[0013] A2. Add itaconic acid and deionized water to the reactants, stir well to obtain the reaction system; adjust the pH of the reaction system to 3-4, and then carry out the esterification reaction at 115-125℃ for 3-6 hours. Remove the deionized water by rotary evaporation to obtain the unsaturated alcohol ester. Under acid catalysis, itaconic acid reacts with acidic polymers to form unsaturated alcohol esters. The reaction formula for the esterification reaction of itaconic acid with acidic polymers to obtain unsaturated alcohol esters is as follows:

[0014] A3. Mix unsaturated alcohol ester, methyl methacrylate, ethyl acetate, initiator and deionized water to obtain reactants; suspend the reactants at 40-50℃ for 3.5-6.5h, then filter to obtain resin; wash the resin with alcohol and dry to obtain a strongly acidic adsorption resin; add deionized water to the strongly acidic adsorption resin and mix to prepare a corrosion expansion solution.

[0015] Further, in step A1, the mass ratio of concentrated sulfuric acid to phenol is 1:1.2-1.3, and the volume ratio of the mixture to formaldehyde solution is 100mL:20-30mL; in step A2, the weight ratio of reactants, itaconic acid, and deionized water is 100:13-26:150-250.

[0016] Further, in step A3, the ratio of unsaturated alcohol ester, methyl methacrylate, ethyl acetate, initiator and deionized water is 80-90g:10-20g:0.1-0.3g:0.2-0.5g:200mL; the ratio of strong acid adsorption resin and deionized water is 3-5g:100mL.

[0017] Furthermore, in step S4, the corrosion expansion frequency is 20-30KHz, the corrosion expansion temperature is 25-35℃, and the corrosion expansion time is 8-12min.

[0018] Furthermore, in step S5, the pickling uses a nitric acid solution with a concentration of 20-30 wt% and a pickling time of 25-35 seconds; the drying temperature is 50-55℃.

[0019] The present invention has the following beneficial effects: 1. In this invention, the surface of the anode aluminum foil of the electrolytic capacitor is a composite alumina film. After alkaline washing, the oil, natural oxide layer, and microscopic scratches on the surface of the anode aluminum foil can be removed, exposing active sites and providing a uniform surface for subsequent acid treatment and electrochemical corrosion. The alkaline-washed anode aluminum foil naturally cures at room temperature, forming a dense alumina structure on the surface. Subsequently, phosphoric acid washing is used, and the phosphate groups combine with the aluminum film on the outer layer of the alumina to form a water-repellent layer of aluminum phosphate. Utilizing the alumina film and the aluminum phosphate water-repellent layer on the anode foil surface improves the hydration resistance and acid corrosion resistance of the alumina film on the anode foil, thereby mitigating the corrosive effect of directly impregnated conductive polymers on the alumina film of the solid aluminum electrolytic capacitor core.

[0020] 2. A trace amount of nano-tin is deposited on the surface of the pretreated anode aluminum foil using pulsed laser deposition equipment, forming Cu-Al micro-cells that improve and promote corrosion. The deposited tin on the aluminum foil surface can form numerous micro-cell units with the aluminum, generating a galvanic effect that increases the corrosion efficiency of the aluminum foil in the mixed acid system, and increases the density and depth of the pits. Because the anode aluminum foil forms a corrosion galvanic couple, it can achieve excellent corrosion results even without applying an external current. Furthermore, since the surface of the pretreated anode aluminum foil is passivated, the uneven adsorption of chloride ions on the metal surface can easily damage the deposited tin, leading to uneven corrosion and the formation of small-diameter, deep pits extending into the substrate. Ultrasonic etching further enhances the corrosion process.

[0021] 3. In this invention, the anode aluminum foil with formed pores is immersed in an etching and expanding solution for etching and expanding the pores, resulting in an expanded anode aluminum foil. Phenol sulfonic acid and formaldehyde are condensed, then esterified with itaconic acid, and then polymerized with methyl methacrylate to prepare a resin polymer with strong acidity and adsorption properties. The above resin polymer is mixed with deionized water to obtain the prepared etching and expanding solution. The etching and expanding solution can effectively adsorb chloride ions inside the anode aluminum foil with formed pores and can further accelerate the expansion of pores. Secondary etching is used to expand the pores, while cleaning the chloride ions remaining from the primary and secondary etching processes. Under these etching conditions, the corrosion pores on the aluminum foil surface are evenly distributed, the etching and expanding effect is good, and the tunnel pore density, length, and specific capacitance are relatively high. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] The nano-tin used in Examples 4-6 of this invention was purchased from Pioneer Nano, with item number XFJ175 and a diameter of 50nm. Example 1

[0024] This embodiment provides a method for preparing an etching and pore-expanding solution for the etching process of aluminum foil anodes in electrolytic capacitors, including the following steps: A1. Add 95wt% concentrated sulfuric acid to phenol at a mass ratio of 1:1.2 and stir at 95℃ for 4 hours to obtain a mixture. Adjust the pH to 7 by adding 1mol / L NaOH solution to 100mL of the mixture, and then add 20mL of 30wt% formaldehyde solution to obtain the reactants.

[0025] A2. According to the weight percentage, add 100 parts of the reactants to the reaction vessel, then add 13 parts of itaconic acid and 150 parts of deionized water to the reaction vessel, stir well to obtain the reaction system. Add 0.1 mol / L concentrated sulfuric acid dropwise to the reaction system to adjust its pH to 3, and then carry out the esterification reaction at 115℃ for 3 hours. Remove the deionized water by rotary evaporation to obtain the unsaturated alcohol ester.

[0026] A3. According to parts by weight, add 80g of unsaturated alcohol ester, 10g of methyl methacrylate, 0.1g of ethyl acetate, 0.2g of benzoyl peroxide, and 200mL of deionized water to the reactor, mix well, and obtain the reactant. The reactant is suspended and polymerized at 40℃ for 3.5h, then filtered to obtain the resin. The resin is washed with ethanol and then dried to constant weight to obtain a strongly acidic adsorption resin. 3g of the strongly acidic adsorption resin is added to 100mL of deionized water and mixed well to obtain the prepared corrosion and pore-expanding solution. Example 2

[0027] This embodiment provides a method for preparing an etching and pore-expanding solution for the etching process of aluminum foil anodes in electrolytic capacitors, including the following steps: A1. Add 96wt% concentrated sulfuric acid to phenol at a mass ratio of 1:1.3 and stir at 98℃ for 4.2 h to obtain a mixture. Adjust the pH to 8 by adding 1mol / L NaOH solution dropwise to 100mL of the mixture, and then add 25mL of 32wt% formaldehyde solution to obtain the reactants.

[0028] A2. According to the weight percentage, add 100 parts of the reactants to the reaction vessel, then add 15 parts of itaconic acid and 200 mL of deionized water to the reaction vessel, stir well to obtain the reaction system. Add 0.15 mol / L concentrated sulfuric acid dropwise to the reaction system to adjust its pH to 3.5, and then carry out the esterification reaction at 120℃ for 5 h. Remove the deionized water by rotary evaporation to obtain the unsaturated alcohol ester.

[0029] A3. According to parts by weight, add 85g of unsaturated alcohol ester, 15g of methyl methacrylate, 0.2g of ethyl acetate, 0.3g of benzoyl peroxide, and 200mL of deionized water to the reactor, mix well, and obtain the reactant. The reactant is suspended and polymerized at 45℃ for 5.5h, then filtered to obtain the resin. The resin is washed with ethanol and then dried to constant weight to obtain a strongly acidic adsorption resin. 4g of the strongly acidic adsorption resin is added to 100mL of deionized water and mixed well to obtain the prepared corrosion and pore-expanding solution. Example 3

[0030] This embodiment provides a method for preparing an etching and pore-expanding solution for the etching process of aluminum foil anodes in electrolytic capacitors, including the following steps: A1. Add 98wt% concentrated sulfuric acid to phenol at a mass ratio of 1:1.3 and stir at 100℃ for 4.5 h to obtain a mixture. Adjust the pH to 8 by adding 2mol / L NaOH solution dropwise to 100mL of the mixture, and then add 30mL of 35wt% formaldehyde solution to obtain the reactants.

[0031] A2. According to the weight percentage, add 100 parts of the reactants to the reaction vessel, then add 26 parts of itaconic acid and 250 mL of deionized water to the reaction vessel, stir well to obtain the reaction system. Add 0.2 mol / L concentrated sulfuric acid dropwise to the reaction system to adjust its pH to 4, and then carry out the esterification reaction at 125℃ for 3-6 hours. Remove the deionized water by rotary evaporation to obtain the unsaturated alcohol ester.

[0032] A3. According to parts by weight, add 90g of unsaturated alcohol ester, 20g of methyl methacrylate, 0.3g of ethyl acetate, 0.5g of benzoyl peroxide, and 200mL of deionized water to the reactor, mix well, and obtain the reactant. The reactant is suspended and polymerized at 50℃ for 6.5h, then filtered to obtain the resin. The resin is washed with ethanol and then dried to constant weight to obtain a strongly acidic adsorption resin. 5g of the strongly acidic adsorption resin is added to 100mL of deionized water and mixed well to obtain the prepared corrosion and pore-expanding solution. Example 4

[0033] This embodiment provides a etching process for the anode aluminum foil of an electrolytic capacitor, including the following steps: S1. Select aluminum foil with a purity of 99.99%, a thickness of 100 μm, and a cubic texture as the anode aluminum foil. Heat a 0.3 mol / L NaOH solution to 40℃, and immerse the anode aluminum foil in the NaOH solution for 100s at a solid-liquid ratio of 1:3. Then remove it and wash it with deionized water to remove the alkaline solution from the surface of the anode aluminum foil, obtaining the alkaline-washed anode aluminum foil. Let the alkaline-washed anode aluminum foil stand at 20℃ for 5 minutes, and then immerse it in a 3wt% phosphoric acid solution at 20℃ for 80s at a solid-liquid ratio of 1:3. Then remove it, wash it with deionized water, and dry it at 40℃ to constant weight, which is the prepared pretreated anode aluminum foil.

[0034] S2. Nano-tin was deposited on the surface of pretreated anode aluminum foil using a pulsed laser deposition system. The electrolyte was a mixture of 0.5 mol / L sodium stannate trihydrate, 1 mol / L sodium hydroxide solution, and 0.2 mol / L potassium sodium tartrate. The pulse deposition current density was 80 mA / cm². 2 The pulse duration was 1s, the pulse interval was 1s, and the total deposition time was 20s, ultimately producing a tin-deposited anode aluminum foil.

[0035] S3. Mix equal volumes of 1 mol / L hydrochloric acid solution and 3 mol / L sulfuric acid solution to obtain a primary etching solution. Place the tin-deposited anode aluminum foil in the primary etching solution for primary etching at a solid-liquid ratio of 1:3, aided by ultrasonication. The primary etching frequency is 30 kHz, the temperature is 45 °C, and the etching time is 3 min, resulting in a primary etched anode aluminum foil. Mix 0.5 mol / L hydrochloric acid solution, 3 mol / L sulfuric acid solution, and oxalic acid uniformly at a mass ratio of 50:50:0.5 to obtain a secondary etching solution. Place the primary etched anode aluminum foil in the secondary etching solution for secondary etching at a solid-liquid ratio of 1:3, aided by ultrasonication. The secondary etching frequency is 20 kHz, the temperature is 25 °C, and the etching time is 3 min, resulting in a perforated anode aluminum foil.

[0036] S4. Immerse the anode aluminum foil after drilling into the etching and drilling solution prepared in Example 1 for etching and drilling, and assist with ultrasonication. The etching and drilling frequency is 20KHz, the etching and drilling temperature is 25℃, and the etching and drilling time is 8min to obtain the anode aluminum foil after drilling.

[0037] S5. The anode aluminum foil after the hole expansion is immersed in a 20wt% nitric acid solution for 25s, then washed with pure water 3 times, and dried at 50℃ to obtain the electrolytic capacitor anode aluminum foil with the corrosion process completed. Example 5

[0038] This embodiment provides a etching process for the anode aluminum foil of an electrolytic capacitor, including the following steps: S1. Pretreatment: Aluminum foil with a purity of 99.99%, a thickness of 100 μm, and a cubic texture was selected as the anode foil. A 0.4 mol / L NaOH solution was heated to 45°C. The anode foil was immersed in the NaOH solution for 130 seconds at a solid-liquid ratio of 1:4, then removed and washed with deionized water to remove the alkaline solution from the surface, resulting in an alkaline-washed anode foil. The alkaline-washed anode foil was allowed to stand at 23°C for 6 minutes, then immersed in a 4 wt% phosphoric acid solution for 90 seconds at a solid-liquid ratio of 1:4. It was then removed, washed with deionized water, and dried at 46°C to constant weight, yielding the pretreated anode foil.

[0039] S2. Nano-tin was deposited on the surface of the pretreated anode aluminum foil using pulse deposition technology. The electrolyte was a mixture of 0.06 mol / L sodium stannate trihydrate, 1.2 mol / L sodium hydroxide solution, and 0.25 mol / L potassium sodium tartrate. The pulse deposition current density was 80 mA / cm². 2 The pulse duration was 1s, the pulse interval was 1s, and the total deposition time was 25s, ultimately producing a tin-deposited anode aluminum foil.

[0040] S3. Mix equal volumes of 1.2 mol / L hydrochloric acid solution and 3.2 mol / L sulfuric acid solution to obtain a primary etching solution. Place the tin-deposited anode aluminum foil in this primary etching solution for primary etching, aided by ultrasonication. The primary etching process involved etching at a frequency of 35 kHz, a temperature of 50 °C, and a duration of 4 min, yielding a primary etched anode aluminum foil. A secondary etching solution was prepared by uniformly mixing 0.8 mol / L hydrochloric acid, 3.2 mol / L sulfuric acid, and oxalic acid in a mass ratio of 50:50:0.8. The primary etched anode aluminum foil was then subjected to ultrasonic etching in the secondary etching solution at a frequency of 25 kHz, a temperature of 30 °C, and a duration of 5 min, resulting in a perforated anode aluminum foil.

[0041] S4. Immerse the anode aluminum foil after hole enlargement in the etching and hole-enlarging solution to enlarge the hole, and assist with ultrasonic etching. The etching frequency is 25KHz, the etching temperature is 30℃, and the etching time is 10min to obtain the anode aluminum foil after hole enlargement.

[0042] S5. The anode aluminum foil after the hole expansion is immersed in a 25wt% nitric acid solution for 30s, then washed with pure water 4 times, and dried to obtain the electrolytic capacitor anode aluminum foil with the corrosion process completed. Example 6

[0043] This embodiment provides a etching process for the anode aluminum foil of an electrolytic capacitor, including the following steps: S1. Pretreatment: Aluminum foil with a purity of 99.99%, a thickness of 100 μm, and a cubic texture was selected as the anode foil. A 0.5 mol / L NaOH solution was heated to 50°C. The anode foil was immersed in the NaOH solution for 160 seconds at a solid-liquid ratio of 1:5, then removed and washed with deionized water to remove the alkaline solution from the surface, resulting in an alkaline-washed anode foil. The alkaline-washed anode foil was allowed to stand at 25°C for 10 minutes, then immersed in a 5 wt% phosphoric acid solution for 100 seconds at a solid-liquid ratio of 1:5. It was then removed, washed with deionized water, and dried at 50°C to constant weight, yielding the pretreated anode foil.

[0044] S2. Nano-tin was deposited on the surface of the pretreated anode aluminum foil using pulse deposition technology. The electrolyte was a mixture of 0.1 mol / L sodium stannate trihydrate, 1.5 mol / L sodium hydroxide solution, and 0.3 mol / L potassium sodium tartrate. The pulse deposition current density was 100 mA / cm². 2 The pulse duration was 1s, the pulse interval was 1s, and the total deposition time was 30s, ultimately producing a tin-deposited anode aluminum foil.

[0045] S3. Mix equal volumes of 1.5 mol / L hydrochloric acid solution and 3.5 mol / L sulfuric acid solution to obtain a primary etching solution. Place the tin-deposited anode aluminum foil in the primary etching solution for primary etching, assisted by ultrasound. The primary etching frequency is 40 kHz, the primary etching temperature is 55℃, and the primary etching time is 5 min, resulting in a primary etched anode aluminum foil. Mix 1 mol / L hydrochloric acid solution, 3.5 mol / L sulfuric acid solution, and oxalic acid in a mass ratio of 50:50:1 to obtain a secondary etching solution. Place the primary etched anode aluminum foil in the secondary etching solution for secondary etching. The secondary etching frequency is 30 kHz, the secondary etching temperature is 35℃, and the secondary etching time is 5 min, resulting in a perforated anode aluminum foil.

[0046] S4. Immerse the anode aluminum foil after hole enlargement in the etching and hole-enlarging solution to enlarge the hole, and assist with ultrasonic etching. The etching frequency is 30KHz, the etching temperature is 35℃, and the etching time is 12min to obtain the anode aluminum foil after hole enlargement.

[0047] S5. The anode aluminum foil after the hole expansion is immersed in a 30wt% nitric acid solution for 235s, then washed with pure water 5 times, and dried to obtain the electrolytic capacitor anode aluminum foil with the corrosion process completed.

[0048] Comparative Example 1 The difference between this comparative example and Example 6 is that the prepared corrosion and pore-expanding fluid is replaced with an equal mass of 15wt% nitric acid solution.

[0049] Comparative Example 2 The difference between this comparative example and Example 6 is that in step S1, the alkali-washed anode aluminum foil is directly immersed in a phosphoric acid solution for acid washing, then washed with deionized water and dried at 50°C to constant weight, which is the pretreated anode aluminum foil.

[0050] Comparative Example 3 The difference between this comparative example and Example 6 is that step S2 is omitted, and nano-tin is not deposited on the surface of the pretreated anode aluminum foil.

[0051] Performance testing: 1. The thickness of the aluminum foil prepared in Examples 4-6 before and after etching was measured using a micrometer. The thickness of the aluminum foil before etching was marked as D1 (nm), and the thickness of the aluminum foil after etching was measured as D2 (nm). The thinning rate of the aluminum foil was: Thinning rate ℘=D1-D2 / D1 2. Weigh the aluminum foil before corrosion (W1, g) and after corrosion (W2, g) using an electronic analytical balance, and calculate the weight loss rate (Ω) of the aluminum foil.

[0052] Weight loss rate Ω = W1 - W2 / W1 3. The anode aluminum foils prepared in Examples 4-6 were sequentially formed at 21V according to the EIAJ standard procedure, and their specific capacitance was tested. The specific test results are shown in Table 1.

[0053] Table 1. Sample Performance Test Data Data Analysis: Thinning rate refers to the reduction in aluminum foil thickness caused by surface corrosion; surface corrosion of the anode aluminum foil leads to pinholes and collapse, which is detrimental to corrosion expansion. Weight loss rate is the weight lost by the anode aluminum foil due to corrosion, including vertical corrosion and surface corrosion; vertical corrosion forms tunnels, which is beneficial for corrosion expansion of the aluminum foil. The aluminum foils prepared in Examples 4-6 have high surface corrosion and can form significant vertical corrosion. Among them, Example 6 still has a high weight loss rate with the least thinning rate. In Comparative Example 2, the anode aluminum foil after alkaline washing did not naturally oxidize at room temperature to form an alumina film, but was directly acid-washed. The alumina film layer after acid washing is uneven in thickness, and the uneven corrosion during the two corrosion processes helps to deepen the corrosion. Therefore, the anode aluminum foil prepared in Comparative Example 2 has a high weight loss rate and a low thinning rate. In Comparative Example 3, the pretreated anode aluminum foil did not deposit nano-tin on its surface. Nano-tin and anode aluminum can form a large number of micro-battery units, which can still have good corrosion effects without applying an external current. Therefore, the anodic aluminum foil prepared in Comparative Example 3 had poor corrosion effect, and the thinning rate and weight loss rate were both reduced, while the thinning rate / weight loss rate ratio was relatively high.

[0054] The anode aluminum foils of the electrolytic capacitors prepared in Examples 4-6 of this invention all exhibited large specific capacitance values ​​and good electrochemical performance upon testing. However, in Comparative Example 1, nitric acid solution was used instead of the prepared etching and pore-expanding solution. The anode aluminum foil after pore formation had pores of varying depths, with chloride ions adsorbed on both the inner and outer surfaces of the pores. The strongly acidic adsorption resin contained in the etching and pore-expanding solution had a high adsorption rate for chloride ions, thus the prepared anode aluminum foils all had large specific capacitance values. The anode aluminum foil prepared in Comparative Example 1 had a higher residual chloride ion concentration and a lower specific capacitance value.

[0055] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0056] In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A etching process for the anode aluminum foil of an electrolytic capacitor, characterized in that, Includes the following steps: S1. Alkaline washing of anode aluminum foil, acid washing with phosphoric acid solution, washing and drying to obtain pretreated anode aluminum foil; S2. Pulse deposition of nano-tin on the surface of the pretreated anode aluminum foil to obtain anode aluminum foil with deposited tin; S3. The tin-deposited anode aluminum foil is placed in a primary etching solution for primary etching, and then placed in a secondary etching solution for secondary etching to obtain the anode aluminum foil with perforated holes. S4. The anode aluminum foil with enlarged holes is immersed in an etching and expanding solution to etch and expand the holes, thus obtaining the anode aluminum foil with expanded holes. S5. After the anode aluminum foil is expanded, it is pickled, washed with water, and dried to prepare the electrolytic capacitor anode aluminum foil that has completed the corrosion process.

2. The etching process for the anode aluminum foil of an electrolytic capacitor according to claim 1, characterized in that, In step S1, the concentration of the phosphoric acid solution is 3-5 wt%, the pickling time is 80-100 s, and the pickling temperature is 20-25℃.

3. The etching process for the anode aluminum foil of an electrolytic capacitor according to claim 1, characterized in that, In step S2, the pulse deposition current density of nano-tin is 80-100 mA / cm². 2 The pulse duration is 1 second, the pulse interval is 1 second, and the total deposition time is 20-25 seconds.

4. The etching process for the anode aluminum foil of an electrolytic capacitor according to claim 1, characterized in that, In step S3, the primary etching solution is obtained by mixing equal volumes of 1-1.5 mol / L hydrochloric acid solution and 3-3.5 mol / L sulfuric acid solution; the ultrasonic etching frequency is 30-40 kHz, the ultrasonic etching temperature is 45-55℃, and the ultrasonic etching time is 3-5 min; the secondary etching solution is obtained by uniformly mixing 0.5-1 mol / L hydrochloric acid solution, 3-3.5 mol / L sulfuric acid solution, and oxalic acid in a mass ratio of 50:50:0.5-1; the ultrasonic etching frequency is 20-30 kHz, the ultrasonic etching temperature is 25-35℃, and the ultrasonic etching time is 3-5 min.

5. The etching process for the anode aluminum foil of an electrolytic capacitor according to claim 1, characterized in that, In step S4, the method for preparing the corrosion expansion fluid includes the following steps: A1. Concentrated sulfuric acid is added to phenol and stirred at 95-100℃ for 4-4.5 hours to obtain a mixture; alkaline solution is added dropwise to the mixture to adjust its pH to 7-8, and then formaldehyde solution is added to obtain the reactants; A2. Add itaconic acid and deionized water to the reactants, stir well to obtain the reaction system; adjust the pH of the reaction system to 3-4, and then carry out the esterification reaction at 115-125℃ for 3-6 hours. Remove the deionized water by rotary evaporation to obtain the unsaturated alcohol ester. A3. Mix unsaturated alcohol ester, methyl methacrylate, ethyl acetate, initiator and deionized water to obtain reactants; suspend the reactants at 40-50℃ for 3.5-6.5h, then filter to obtain resin; wash the resin with alcohol and dry to obtain a strongly acidic adsorption resin; add deionized water to the strongly acidic adsorption resin and mix to prepare a corrosion expansion solution.

6. The etching process for the anode aluminum foil of an electrolytic capacitor according to claim 5, characterized in that, In step A1, the mass ratio of concentrated sulfuric acid to phenol is 1:1.2-1.3, and the volume ratio of the mixture to formaldehyde solution is 100mL:20-30mL; in step A2, the weight ratio of reactants, itaconic acid, and deionized water is 100:13-26:150-250.

7. The etching process for the anode aluminum foil of an electrolytic capacitor according to claim 5, characterized in that, In step A3, the weight ratio of unsaturated alcohol ester, methyl methacrylate, ethyl acetate, initiator and deionized water is 80-90g:10-20g:0.1-0.3g:0.2-0.5g:200mL; the volume ratio of strong acid adsorption resin and deionized water is 3-5g:100mL.

8. The etching process for the anode aluminum foil of an electrolytic capacitor according to claim 1, characterized in that, In step S4, the corrosion expansion frequency is 20-30KHz, the corrosion expansion temperature is 25-35℃, and the corrosion expansion time is 8-12min.

9. The etching process for the anode aluminum foil of an electrolytic capacitor according to claim 1, characterized in that, In step S5, the pickling uses a nitric acid solution with a concentration of 20-30 wt% and a pickling time of 25-35 seconds; the drying temperature is 50-55℃.

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