Anodized aluminum foil, method for producing the same, and aluminum electrolytic capacitor

Abstract

The present disclosure provides an anodically etched aluminum foil, a preparation method thereof and an aluminum electrolytic capacitor. The preparation method of the anodically etched aluminum foil comprises: etching an aluminum foil with an etching solution containing hydrochloric acid to obtain an etched aluminum foil; performing a first spray water washing on the etched aluminum foil; cleaning the etched aluminum foil in an ammonium salt solution, wherein the content of phosphate ions, fluoride ions and carbonate ions in the ammonium salt solution is 0.01% or less; and performing a second spray water washing on the etched aluminum foil. The method of the present disclosure can effectively clean the residual chloride ions of the etched aluminum foil without obvious damage to the pore structure, so that the specific capacity of the aluminum foil can be maintained.

Description

Technical Field

[0001] This disclosure relates to the field of capacitors, and in particular to anodic etched aluminum foil, its preparation method, and aluminum electrolytic capacitors. Background Technology

[0002] Low-voltage sponge-pore etching of aluminum foil for aluminum electrolytic capacitors involves a core manufacturing process that utilizes a high-concentration hydrochloric acid system combined with electro-etching to create a sponge-like microporous structure, providing a foundation for high specific capacitance energy storage. Currently, in industrial production, aluminum foil reacts in a strongly acidic etching system to generate aluminum chloride active deposits. These deposits cannot hydrolyze into a film under strong acid conditions. However, after the aluminum foil is removed from the etching solution and comes into contact with a water washing medium, the aluminum chloride adhering to the surface and deep within the sponge micropores undergoes rapid hydrolysis, generating an in-situ hydrated aluminum hydroxide gel film encapsulating bound chloride ions. This gel film is highly dense and has high adsorption stability, effectively trapping a large number of chloride ions within the sponge micropore walls and the film layer, forming stubborn residual chlorine contamination that is difficult to remove with conventional water washing. If the residual chloride ion content exceeds the standard, subsequent formation processes will disrupt the uniformity of oxide film growth, leading to increased leakage current, decreased withstand voltage stability, and a significant shortening of capacitor service life. This is a core industry pain point restricting the consistency of quality and performance improvement of low-voltage sponge-pore aluminum foil products.

[0003] Currently, the industry mainstream only adopts two types of treatment schemes for dechlorination cleaning of sponge-pore aluminum foil after hydrochloric acid perforation, but both have inherent technical defects. One type is the strong acid chemical cleaning process, which mainly uses high-concentration sulfuric acid, nitric acid and other strong acids for single etching and cleaning. Although this scheme can forcibly dissolve the surface hydrated aluminum hydroxide gel film and remove some free chloride ions, the strong acid medium has no selective corrosion characteristics and will simultaneously erode the thin-walled sponge microporous structure of low-pressure aluminum foil, causing problems such as micropore wall dissolution, pore shape collapse and pore size distortion, which directly leads to a significant decrease in the effective specific volume of aluminum foil. Another type is the strong acid cleaning coupled with DC electric adsorption for synergistic dechlorination. This process adds DC electric field cleaning to the strong acid cleaning and etching process, relying on the electric field to drive the migration and desorption of chloride ions. Although the dechlorination effect is improved compared to strong acid cleaning alone, there is an electric field attenuation effect in the deep micropores, blind holes and narrow neck areas of the sponge. The electric field force cannot effectively cover the entire micropore area, and the chloride ions trapped inside the deep holes are still difficult to remove completely. The dechlorination uniformity is poor and the batch stability is insufficient. At the same time, the DC electric adsorption process is prone to defects such as hydrogen evolution on the aluminum foil surface, local electrolytic arcing, and local over-etching of the foil surface. This increases the additional equipment investment, power consumption and operation and maintenance costs. The process is cumbersome and complicated, and the adaptability to production lines and mass production economy are poor.

[0004] In addition, existing conventional pure water rinsing processes can only remove free chloride ions from the surface of aluminum foil, failing to destroy the hydrated aluminum hydroxide coating structure generated by hydrolysis. They have no effect on removing chloride ions trapped in the film layer or deep within the micropores, exhibiting extremely poor dechlorination performance. They can only be used as an auxiliary pre-cleaning process and cannot meet the industrial standards for controlling residual chloride in high-quality aluminum foil. Therefore, the industry urgently needs to develop a method for cleaning residual chloride ions in aluminum foil that requires no strong acid or etching, no DC-assisted treatment, and achieves efficient deep dechlorination, intact protection of the sponge-like pore structure, simplified process flow, and strong mass production stability. Summary of the Invention

[0005] The present disclosure provides a method for preparing anodized aluminum foil, comprising: using an etching solution containing hydrochloric acid to etch aluminum foil to obtain etched aluminum foil; subjecting the etched aluminum foil to a first spray water wash; cleaning the etched aluminum foil in an ammonium salt solution, wherein the contents of phosphate ions, fluoride ions and carbonate ions in the ammonium salt solution are less than 0.01%; and subjecting the etched aluminum foil to a second spray water wash.

[0006] In some embodiments, the ammonium salt solution does not contain phosphate ions, fluoride ions, and carbonate ions, and the ammonium salt solution includes one or more of ammonium bisulfate, ammonium nitrate, ammonium sulfate, ammonium formate, ammonium acetate, ammonium lactate, ammonium succinate, and ammonium maleate, and the mass concentration of the ammonium salt solution is 12% to 20%.

[0007] In some embodiments, the first spray wash and the second spray wash each independently include: spray washing performed at a temperature of 20°C to 30°C using a double-sided countercurrent spray method.

[0008] In some embodiments, in the first spray washing, the nozzle outlet velocity is 5 m / s to 20 m / s, the flow rate per unit width is 5 L / min·m to 25 L / min·m, and the angle between the spray jet and the aluminum foil surface is 30° to 60°; in the second spray washing, the nozzle outlet velocity is 5 m / s to 20 m / s, the flow rate per unit width is 5 L / min·m to 25 L / min·m, and the angle between the spray jet and the aluminum foil surface is 30° to 60°.

[0009] In some embodiments, cleaning the etched aluminum foil in an ammonium salt solution includes isothermal cleaning at 50°C to 70°C for 60 to 150 seconds.

[0010] In some embodiments, a reverse spraying assembly is provided in an immersion tank containing an ammonium salt solution, the angle between the spray jet and the aluminum foil surface is 30° to 60°, and the spray flow rate is 1.5 m / s to 4 m / s.

[0011] In some embodiments, the preparation method further includes: pretreating the aluminum foil before etching it; performing a water washing and stabilization treatment on the etched aluminum foil; and performing a thermal stabilization treatment on the etched aluminum foil after the water washing and stabilization treatment.

[0012] In some embodiments, the pretreatment uses an acid or alkali solution with a mass concentration of 5% to 15%, a temperature of 50°C to 80°C, and a treatment time of 60s to 180s. The acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and the alkali solution includes one or more of sodium hydroxide, potassium hydroxide, and ammonia. Etching the aluminum foil with an etching solution containing hydrochloric acid includes using a mixture of hydrochloric acid with a mass concentration of 5% to 15% and one or more of sulfuric acid, oxalic acid, succinic acid, maleic acid, and citric acid with a mass concentration of 0.05% to 0.2%, a temperature of 15°C to 40°C, a current density of 0.1 A / cm² to 0.3 A / cm², and a hole-forming time of 12 to 15 min. The water washing stabilization treatment is performed at a temperature of 30°C to 60°C for 60s to 180s. The thermal stabilization treatment includes heat treatment at a temperature of 350°C to 450°C in an air atmosphere for 60s to 120s.

[0013] Another embodiment of this disclosure provides an anodized aluminum foil, which is an anodized aluminum foil obtained according to any of the above pretreatment methods.

[0014] Another embodiment of this disclosure provides an aluminum electrolytic capacitor comprising the aforementioned anodicly etched aluminum foil.

[0015] This disclosure removes excess corrosion solution by spraying water, then cleans the aluminum foil in an ammonium salt cleaning solution, followed by spraying water to remove excess cleaning solution, thus completing the removal of residual chloride ions. This method effectively removes residual chloride ions from corroded aluminum foil without significantly damaging the pore structure, thereby maintaining a high specific volume of the aluminum foil. Attached Figure Description

[0016] Figure 1 A schematic flowchart illustrating a method for preparing anodized aluminum foil according to an embodiment of the present disclosure is shown.

[0017] Figure 2 A schematic diagram of the cleaning process for anodized aluminum foil according to an embodiment of the present disclosure is shown.

[0018] Figure 3 Scanning electron microscope (SEM) images of anodic etched aluminum foil prepared according to embodiments and comparative examples of this disclosure are shown. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of this disclosure will be described in detail below with reference to the accompanying drawings.

[0020] Exemplary embodiments will be described more fully below with reference to the accompanying drawings; however, these exemplary embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will enable those skilled in the art to fully understand the scope of this disclosure.

[0021] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0022] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded.

[0024] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted as having an idealized or overly formal meaning unless expressly so defined herein. Unless otherwise stated, percentage concentrations herein are mass percentage concentrations.

[0025] This disclosure aims to overcome numerous technical defects in existing sponge-pore aluminum foil cleaning processes after high-concentration hydrochloric acid AC etching to create pores, particularly regarding residual chloride ion removal. Existing strong acid cleaning methods tend to over-etch the microporous structure, leading to a decrease in the aluminum foil's specific volume. Strong acid combined with DC adsorption for chloride removal suffers from problems such as deep-pore electric field attenuation, uneven chloride removal, easy electrolytic defects on the foil surface, high equipment investment, complex processes, and high production costs. Conventional pure water rinsing can only remove surface free chloride and cannot break the hydrated aluminum hydroxide coating generated by hydrolysis, making it difficult to remove bound chloride ions inside the micropores, thus failing to meet the mass production requirements of low residual chloride and high stability for high-end aluminum foil. Therefore, this disclosure provides an anodic etching aluminum foil preparation method that eliminates the need for strong acid etching and DC electric field-assisted chloride removal. It effectively removes bound chloride ions from the micropores while fully preserving the sponge-pore microstructure and the aluminum foil's specific volume properties, simplifying production processes, reducing equipment and operating costs, and improving batch consistency and subsequent formation compatibility.

[0026] like Figure 1 As shown, embodiments of this disclosure provide a method for preparing anodized aluminum foil, including step S101, using an etching solution containing hydrochloric acid to etch the aluminum foil to obtain etched aluminum foil. In some embodiments, to increase the specific volume of the aluminum foil, it is necessary to increase the specific volume of the aluminum foil by etching, and hydrochloric acid is a commonly used etching solution. After etching with hydrochloric acid, chloride ions are easily left in the pores of the etched aluminum foil.

[0027] In some embodiments, the preparation method of this disclosure further includes step S102, which involves a first spray water wash on the etched aluminum foil. In some embodiments, deionized water with a conductivity ≤1 μS / cm is used for the first spray water wash to remove residual etching solution adhering to the surface of the aluminum foil.

[0028] In some embodiments, the preparation method of this disclosure further includes step S103, cleaning the corroded aluminum foil in an ammonium salt solution, wherein the content of phosphate ions, fluoride ions, and carbonate ions in the ammonium salt solution is less than 0.01%. The weak acid anions formed by the dissociation of ammonium salt provide a mild, weakly acidic environment, selectively loosening and dissociating the hydrated aluminum hydroxide gel membrane coated with chloride ions, clearing the microporous channels of the sponge, and not corroding the aluminum substrate and the microporous thin-walled structure. Ammonium ions replace the bound chloride ions in the membrane layer and inside the micropores with free chloride ions through ion replacement and ion exchange. Combining the first spray water wash and the subsequent second spray water wash, the forced replacement of old and new cleaning solutions inside the micropores is accelerated, promoting the rapid outward discharge of dissociated chloride ions and thoroughly removing stubborn residual chloride in deep pores and blind pores. Phosphate ions, fluoride ions, carbonate ions, etc., are prone to forming insoluble aluminum salt precipitates. By ensuring that the content of phosphate ions, fluoride ions, and carbonate ions in the ammonium salt solution is less than 0.01%, the formation of insoluble aluminum salt precipitates during the cleaning process can be avoided. In some embodiments, the content of phosphate ions, fluoride ions and carbonate ions in the ammonium salt solution is less than 0.001%.

[0029] In some embodiments, the preparation method disclosed herein further includes step S104, which involves a second spray water wash of the etched aluminum foil to remove residual cleaning solution and dissociated free chloride ions from the surface and micropores.

[0030] This disclosed method effectively removes chloride ions coated in micropores while fully preserving the microstructure of the sponge pores and the specific volume properties of the aluminum foil. It simplifies production processes, reduces equipment and operating costs, and improves batch consistency and compatibility with subsequent formation processes. This method can effectively clean residual chloride ions from aluminum foil with complex sponge pore structures, achieving a residual chloride ion concentration of 0.1~0.5 mg / m³ after cleaning. 2 Furthermore, it does not cause significant damage to the sponge's pore structure, thus maintaining a high specific volume of the aluminum foil.

[0031] In some embodiments, ideally, the ammonium salt solution is free of phosphate, fluoride, and carbonate ions. In some embodiments, the ammonium salt solution includes one or more of ammonium bisulfate, ammonium nitrate, ammonium sulfate, ammonium formate, ammonium acetate, ammonium lactate, ammonium succinate, and ammonium maleate. These ammonium salts can dissociate to form weak acid anions, providing a mildly acidic environment, selectively loosening and dissociating the chloride-coated hydrated aluminum hydroxide gel membrane, clearing the microporous channels of the sponge, and not corroding the aluminum substrate and microporous thin-walled structure. In some embodiments, the mass concentration of the ammonium salt solution is 12% to 20%. In some embodiments, the mass concentration of the ammonium salt solution is 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any suitable value between them. If the mass concentration of the ammonium salt solution is too low, its effect on dissociating the chloride-coated hydrated aluminum hydroxide gel membrane is relatively limited; if the mass concentration of the ammonium salt solution is too high, it can easily lead to excessive acidity and waste of raw materials.

[0032] In some embodiments, the first spray wash and the second spray wash each independently include: spray washing using a double-sided countercurrent spray method at a temperature of 20°C to 30°C. If the temperature is too low, the washing efficiency will be reduced; if the temperature is too high, watermarks are likely to occur.

[0033] In some embodiments, in the first spray wash, the nozzle outlet velocity is 5 m / s to 20 m / s, the flow rate per unit width is 5 L / min·m to 25 L / min·m, and the angle between the spray jet and the aluminum foil surface is 30° to 60°. In the second spray wash, the nozzle outlet velocity is 5 m / s to 20 m / s, the flow rate per unit width is 5 L / min·m to 25 L / min·m, and the angle between the spray jet and the aluminum foil surface is 30° to 60°. In some embodiments, such as Figure 2 As shown, the first and second spray water washes employ 1 to 3 levels of double-sided countercurrent spraying, with the aluminum foil flowing horizontally and spray pipes set on both the upper and lower sides. The upper and lower nozzles are symmetrically inclined to form opposing shear flows, thereby enhancing the displacement and scouring of the channels.

[0034] In some embodiments, cleaning the etched aluminum foil in an ammonium salt solution includes isothermal cleaning at 50°C to 70°C for 60 to 150 seconds. If the temperature is too low, the ion exchange reaction rate of ammonium salt replacing chloride ions will decrease; if the temperature is too high, excessively high temperatures may cause some components in the ammonium salt solution to decompose or accelerate volatilization, affecting the stability of the cleaning solution. If the cleaning time is too short, the cleaning may not be sufficient; if the cleaning time is too long, the cleaning efficiency will be affected.

[0035] In some embodiments, such as Figure 2As shown, a reverse spray assembly is installed in the immersion tank containing the ammonium salt solution. During cleaning, the cleaning solution flows against the direction of aluminum foil travel, with the spray jet forming an angle of 30° to 60° with the aluminum foil surface, and the spray velocity being 1.5 m / s to 4 m / s. In some embodiments, the etched aluminum foil travels through the immersion tank containing the ammonium salt solution, and a reverse spray assembly is installed inside the immersion tank in the opposite direction of aluminum foil travel, with the spray nozzles tilted towards the aluminum foil surface. This achieves forced convection displacement dechlorination deep within the micropores, improving dechlorination efficiency.

[0036] In some embodiments, the preparation method further includes: pretreating the aluminum foil before etching to remove oil and impurities and form a micro-etched surface; performing a water washing and stabilization treatment on the etched aluminum foil; and performing a thermal stabilization treatment on the etched aluminum foil after the water washing and stabilization treatment. In some embodiments, the pretreatment uses an acid solution or alkaline solution with a mass concentration of 5% to 15%, a temperature of 50°C to 80°C, and a treatment time of 60s to 180s. The acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and the alkaline solution includes one or more of sodium hydroxide, potassium hydroxide, and ammonia. In some embodiments, etching the aluminum foil using an etching solution containing hydrochloric acid includes using a mixed solution of hydrochloric acid with a mass concentration of 5% to 15% and one or more of sulfuric acid, oxalic acid, succinic acid, maleic acid, and citric acid with a mass concentration of 0.05% to 0.2%, a temperature of 15°C to 40°C, a current density of 0.1 A / cm² to 0.3 A / cm², and a hole formation time of 12 to 15 min. In some embodiments, the water washing stabilization treatment is carried out at a temperature of 30°C to 60°C for a duration of 60s to 180s. In some embodiments, the water washing stabilization treatment uses a deionized water solution, optionally compounded with one or more of a weakly basic buffer salt, a weakly chelating stabilizer, and a weakly basic alkanolamine. In some embodiments, the heat stabilization treatment includes heat treatment at a temperature of 350°C to 450°C in air for 60s to 120s.

[0037] This disclosure employs an ammonium salt solution in conjunction with multi-stage countercurrent spraying for chlorination removal. The weak acid anions formed by the dissociation of ammonium salts provide a mild, weakly acidic environment, selectively loosening and dissociating the hydrated aluminum hydroxide gel membrane coated with chloride ions, thus clearing the microporous channels without corroding the aluminum substrate and the thin-walled microporous structure. Ammonium ions, through ion replacement and ion exchange, convert bound chloride ions in the membrane layer and within the micropores into free chloride ions. Combined with multi-stage double-sided countercurrent spraying of pure water and reverse shearing scouring within the tank, the forced replacement of old and new cleaning solutions within the micropores is accelerated, promoting the rapid outward discharge of dissociated chloride ions and thoroughly removing stubborn residual chlorine from deep pores and blind pores. Subsequent water stabilization treatment neutralizes trace residual acid on the surface, complexes trace impurity ions, and inhibits secondary hydrolysis and regeneration of the hydrated membrane on the aluminum foil surface. Thermal stabilization calcination achieves dehydration and densification of the microporous interface and solidification and shaping of the surface adsorption layer, stabilizing the porous interface structure and ensuring the uniformity of subsequent oxide film growth.

[0038] This disclosure abandons the traditional strong acid etching and DC electro-adsorption dechlorination process, and adopts a mild ammonium salt buffered pure chemical cleaning system. It targets and breaks down the film to remove chlorine without damaging the microstructure of the sponge pores, effectively preserving the porous structure and specific capacitance of the aluminum foil, reducing product performance loss, and improving production yield. This disclosure relies on chemical displacement combined with reverse forced convection flushing for dechlorination, eliminating dead zones caused by electric field attenuation. It ensures good uniformity of chloride ion removal inside micropores and blind holes, resulting in high batch stability, effectively reducing aluminum foil leakage current, and improving withstand voltage performance and capacitor lifespan. The method of this disclosure does not require the configuration of DC power supplies, conductive rollers, electrodes, or other electrochemical equipment. The process flow is simple, equipment investment is low, energy consumption and maintenance costs are low, and it has strong applicability to mass production. Furthermore, the overall process parameter window of this disclosure is wide, operation is simple, and controllability is strong, making it suitable for continuous large-scale industrial production, with good application prospects and economic benefits.

[0039] The following description, in conjunction with specific embodiments, will provide a better understanding of this disclosure.

[0040] Example 1 A method for preparing sponge-pore anodic etching aluminum foil, the specific steps of which are as follows: S21. Chemical pretreatment of aluminum foil: Degreasing and micro-corrosion treatment is carried out using an 8% sulfuric acid solution at a temperature of 65℃ for 120 seconds to remove oil and oxide impurities from the aluminum foil surface and build a uniform micro-corrosion substrate surface. S22. Alternating current etching to create porosity: A composite etching solution of 10% hydrochloric acid and 0.1% succinic acid is used as the main etching solution. The etching solution temperature is 25℃, the alternating current etching time is 13min, and the current density is controlled at 0.2A / cm². A low-pressure special sponge-like microporous structure is stably formed on the aluminum foil surface. S23. Residual Chlorine Special Cleaning Treatment: S11. Use pure water with a conductivity ≤1μS / cm to perform a two-stage (i.e., set up two water washing spray devices) double-sided countercurrent pre-spray water wash on the aluminum foil after perforation. The water washing temperature is 25℃, the outlet flow velocity of the spray nozzle is 10m / s, the flow rate per unit width is 15L / min·m, and the angle between the spray jet and the aluminum foil surface is 45° to remove most of the residual composite corrosion liquid adhering to the aluminum foil surface; S12. Send the pre-cleaned aluminum foil into the ammonium salt buffer cleaning tank. The cleaning solution is a 15% mass fraction ammonium bisulfate and ammonium nitrate compound system (mass ratio of 1:1). The cleaning temperature is 60℃, and the constant temperature immersion cleaning is performed for 100s; the cleaning tank is equipped with a counter-current spray component, the spray tilt angle is 45°, the spray flow velocity is 2.5m / s, and the cleaning solution flows against the direction of aluminum foil movement to rinse; S13. After cleaning, use pure water with a conductivity ≤1μS / cm to perform a double-sided countercurrent pre-spray water wash on the aluminum foil surface. The aluminum foil is subjected to a two-stage double-sided countercurrent final spray water wash with μS / cm pure water. The water washing process parameters are consistent with the pre-spray water wash to thoroughly remove residual ammonium salt cleaning solution and dissociated free chloride ions from the surface and micropores of the aluminum foil. S24. Water-based stabilization treatment: Pure deionized water is used as the stabilization treatment solution. The treatment temperature is 45℃, and the immersion stabilization treatment is carried out for 120 seconds to neutralize the trace residual acid on the aluminum foil surface, complex the trace impurity ions in the micropores, and inhibit the abnormal regeneration of the hydrated aluminum hydroxide film. S25. Thermal stabilization and calcination treatment: The stabilized aluminum foil is placed in an air atmosphere muffle furnace and calcined at 400℃ for 90s. This completes the dehydration and densification of the microporous interface and the curing and shaping of the surface adsorption layer, resulting in the finished sponge-pore anodic corrosion aluminum foil.

[0041] In this embodiment, the residual chloride ion content of the prepared aluminum foil was 0.22 mg / m², the specific volume retention rate (specific volume retention rate (%) = (specific volume value of aluminum foil after cleaning C1 / reference specific volume value of aluminum foil before cleaning C0) × 100%. The measurement method was electrochemical method (JIS C5141 and GB / T 3615 standards)) was 98.7%, the leakage current value was stable, and the microporous structure was intact without collapse or distortion.

[0042] Example 2 A method for preparing sponge-pore anodic etching aluminum foil, the specific steps of which are as follows: S21. Chemical pretreatment of aluminum foil: A compound acid solution of 5% hydrochloric acid and 0.1% sulfuric acid is used for degreasing and micro-corrosion treatment at a temperature of 50℃ and a treatment time of 180s to remove surface impurities and build a uniform pretreated surface. S22. Alternating current corrosion porosimetry: A composite system of 0.05% maleic acid and citric acid (0.03% maleic acid and 0.02% citric acid) was prepared using a 5% hydrochloric acid solution. The corrosion solution temperature was 15℃, the alternating current corrosion porosimetry time was 15min, and the current density was 0.1A / cm², forming a uniform and dense sponge microporous structure. S23. Residual Chlorine Special Cleaning Treatment: S11. Use pure water with conductivity ≤1 μS / cm for a first-stage (i.e., one water spray device) double-sided countercurrent pre-spray water wash, with a water wash temperature of 20℃, a spray nozzle outlet flow velocity of 5m / s, a unit width flow rate of 5L / min·m, and a spray angle of 30° to remove free corrosion residues from the surface; S12. Use ammonium salt buffer cleaning solution, which is a compound system of 12% ammonium sulfate and ammonium acetate (mass ratio of 1:1), with a cleaning temperature of 50℃ and constant temperature cleaning for 150s; the countercurrent spray angle in the tank is 30°, the spray flow velocity is 1.5m / s, and the cleaning solution flows countercurrently to remove chlorine; S13. Use pure water with the same parameters for a first-stage double-sided countercurrent final spray water wash to thoroughly remove residual cleaning agents and free chloride ions; S24. Water system stabilization treatment: Deionized water is mixed with trace amounts of ammonium bicarbonate (to make the pH of the buffer salt 7.5) to form a weakly alkaline buffer salt. The treatment temperature is 30℃ and the treatment time is 180s to achieve surface acid-base neutralization and complexation and stabilization of trace impurities. S25. Heat stabilization baking treatment: Heat treatment at 350℃ for 120s in air atmosphere to complete the heat curing and shaping of the microporous structure, and obtain the finished etched aluminum foil.

[0043] In this embodiment, the aluminum foil prepared had a chloride ion residue of 0.41 mg / m², a specific volume retention rate of 98.2%, excellent batch-to-batch consistency, and no micropore over-etching damage.

[0044] Example 3 A method for preparing sponge-pore anodic etching aluminum foil, the specific steps of which are as follows: S21. Chemical pretreatment of aluminum foil: Degreasing and micro-corrosion treatment with 15% sodium hydroxide alkaline solution at 80℃ for 60 seconds to quickly remove surface oil and oxide layer. S23. Alternating current corrosion porosimetry: A composite system of 0.2% oxalic acid and succinic acid (0.15% oxalic acid + 0.05% succinic acid) is used with a 15% hydrochloric acid solution as the main concentration. The corrosion solution temperature is 40℃, the alternating current corrosion porosimetry time is 12min, and the current density is 0.3A / cm², which efficiently forms a sponge pore structure. S23. Residual Chlorine Special Cleaning Treatment: S11. Use pure water with conductivity ≤1 μS / cm for a 3-stage (i.e., three water spray devices) double-sided countercurrent pre-spray water wash, with a water wash temperature of 30℃, a spray nozzle outlet flow velocity of 20m / s, a unit width flow rate of 25L / min·m, and a spray angle of 60° to enhance the removal of residual liquid in the early stage; S12. The ammonium salt buffer cleaning solution uses a compound system of 20% by mass ammonium lactate and ammonium maleate (mass ratio of 1:1), a cleaning temperature of 70℃, and constant temperature cleaning for 60s; the countercurrent spray in the tank is tilted at an angle of 60°, and the spray flow velocity is 4m / s, to remove the chlorine trapped in the deep pores through high-intensity convection displacement; S13. Perform a 3-stage double-sided countercurrent final spray water wash with the same parameters to thoroughly purify the micropores and residual components on the foil surface. S24. Water-based stabilization treatment: Deionized water is mixed with a trace amount of weakly basic alkaline amine stabilizer (to make the pH of the solution 7.5), the treatment temperature is 60℃, and the treatment time is 60s to achieve rapid surface stabilization and passivation. S25. Heat stabilization baking treatment: Heat treatment at 450℃ for 60s in air atmosphere, rapid baking and solidification to obtain finished sponge-pore anodic corrosion aluminum foil.

[0045] In this embodiment, the aluminum foil has a chloride ion residue of 0.38 mg / m², a specific volume retention rate of 98.1%, and high chloride removal efficiency, making it suitable for high-speed mass production line needs.

[0046] Examples 4-7 The parameters of Examples 4-7 are the same as those of Example 1, except that the total concentration of the ammonium salt solution is different: 10% for Example 4, 12% for Example 5, 20% for Example 6, and 22% for Example 7.

[0047] Comparative Example 1 (Traditional strong acid + DC adsorption cleaning process) The aluminum foil pretreatment and hydrochloric acid composite system AC etching process were exactly the same as in Example 1. After the holes were formed, the traditional cleaning process was used: immersion in 10% nitric acid strong acid for 90 seconds for etching and cleaning, followed by DC adsorption treatment with a current density of 0.08 A / cm² and an electro-cleaning time of 20 seconds. The subsequent pure water rinsing for 30 seconds, conventional stabilization and calcination processes were all consistent with those in Example 1.

[0048] The aluminum foil prepared in the comparative example had a chloride ion residue of 1.25 mg / m², a specific volume retention rate of only 92.3%, obvious micropore dissolution and collapse, pore size distortion, high leakage current, large batch performance fluctuations, and a mass production yield significantly lower than that of the product in the embodiments of this disclosure.

[0049] The performance parameters of the finished sponge-hole anodic etched aluminum foil of the examples and comparative examples are shown in Table 1.

[0050] The measurement methods for each parameter are as follows: The method for measuring boost time is based on SJ / T 11140-2022.

[0051] The voltage measurement method is in accordance with SJ / T 11140-2022.

[0052] The specific volume measurement method is based on SJ / T 11140-2022 and GB / T 3615-2016.

[0053] The CV product is the product of voltage and specific capacitance.

[0054] The method for measuring leakage current is based on SJ / T 11140-2022, IEC 60384-4 and GB / T 7332-2011.

[0055] Hydration treatment: The aluminum foil is immersed in pure water at 95°C or above for 60 minutes to simulate the hydration aging under the service environment of the capacitor. The performance measurement methods are the same as above.

[0056] Impedance measurement methods are based on ISO 17475 and GB / T 20042.4.

[0057] The bending measurement method is based on GB / T 22314-2023 (MIT method) and SJ / T 11140-2022.

[0058] The method for measuring chloride ion residue is based on SJ / T 11140-2022 and GB / T 3615-2016.

[0059] Table 1 shows the performance parameters of the finished sponge-hole anodic corrosion aluminum foil of each embodiment and comparative example. Figure 3 SEM images of the etched aluminum foils prepared in Examples 1-3 and Comparative Example 1 are shown.

[0060] Table 1 As shown in Table 1, the method disclosed herein produces a significantly lower chloride ion residue and a higher specific volume in the etched aluminum foil. Furthermore, a comparison of Examples 1 and 4 to 7 reveals that when the concentration of the ammonium salt solution is below 12%, the chloride ion residue is relatively high (Example 4), and when the concentration of the ammonium salt solution is above 20%, the capacity loss is severe (Example 7).

[0061] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A method for preparing anodized aluminum foil, characterized in that, include: Aluminum foil is etched using an etching solution containing hydrochloric acid to obtain etched aluminum foil; The corroded aluminum foil is subjected to a first spray water wash; The corroded aluminum foil was cleaned in an ammonium salt solution; The corroded aluminum foil is then subjected to a second spray water wash; The ammonium salt solution does not contain phosphate ions, fluoride ions, or carbonate ions. The ammonium salt solution includes one or more of ammonium bisulfate, ammonium nitrate, ammonium sulfate, ammonium formate, ammonium acetate, ammonium lactate, ammonium succinate, and ammonium maleate. The mass concentration of the ammonium salt solution is 12% to 20%.

2. The preparation method according to claim 1, characterized in that, The first spray washing and the second spray washing each independently include: spray washing performed at a temperature of 20°C to 30°C using a double-sided countercurrent spray method.

3. The preparation method according to claim 2, characterized in that, In the first spray washing, the nozzle outlet flow velocity is 5 m / s to 20 m / s, the unit width flow rate is 5 L / min·m to 25 L / min·m, and the angle between the spray jet and the aluminum foil surface is 30° to 60°. In the second spray washing, the nozzle outlet flow velocity is 5 m / s to 20 m / s, the flow rate per unit width is 5 L / min·m to 25 L / min·m, and the angle between the spray jet and the aluminum foil surface is 30° to 60°.

4. The preparation method according to claim 1, characterized in that, The etching of the aluminum foil is cleaned in an ammonium salt solution by constant temperature cleaning at 50°C to 70°C for 60 to 150 seconds.

5. The preparation method according to claim 4, characterized in that, A reverse spraying assembly is provided in the immersion tank containing the ammonium salt solution. The angle between the spray jet and the surface of the aluminum foil is 30° to 60°, and the spray flow rate is 1.5 m / s to 4 m / s.

6. The preparation method according to any one of claims 1 to 5, characterized in that, Also includes: The aluminum foil is pretreated before it is etched. The corroded aluminum foil is subjected to water washing and stabilization treatment; The corroded aluminum foil after water washing and stabilization treatment was subjected to thermal stabilization treatment.

7. The preparation method according to claim 6, characterized in that, The pretreatment uses an acid or alkali solution with a mass concentration of 5% to 15%, a temperature of 50°C to 80°C, and a treatment time of 60s to 180s. The acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and the alkali solution includes one or more of sodium hydroxide, potassium hydroxide, and ammonia water. The etching of aluminum foil using an etching solution containing hydrochloric acid includes using a hydrochloric acid solution with a mass concentration of 5% to 15% and a mixed solution of one or more of sulfuric acid, oxalic acid, succinic acid, maleic acid, and citric acid with a mass concentration of 0.05% to 0.2%, at a temperature of 15°C to 40°C, a current density of 0.1 A / cm² to 0.3 A / cm², and a hole formation time of 12 to 15 min. The water washing and stabilization treatment is carried out at a temperature of 30°C to 60°C for a duration of 60 seconds to 180 seconds. The heat stabilization treatment includes heat treatment at a temperature of 350°C to 450°C for 60 to 120 seconds in an air atmosphere.

8. An anodized aluminum foil, characterized in that, The anodic etched aluminum foil is an anodic etched aluminum foil obtained by the preparation method according to any one of claims 1 to 7.

9. An aluminum electrolytic capacitor, characterized in that, The aluminum electrolytic capacitor includes the anolyzed aluminum foil as described in claim 8.

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