Corrosion foil and preparation method thereof

Abstract

The invention provides a corrosion foil and a preparation method thereof. The preparation method comprises the following steps: carrying out first treatment on an aluminum foil in a first alkaline solution containing zinc ions; after the first treatment, performing first etching on the aluminum foil to form a main tunnel; and performing second etching on the aluminum foil in an etching solution containing copper ions to form a branch tunnel on the main tunnel. By adopting a multi-section hole forming mode of adding zinc ions and copper ions, longitudinal main tunnel holes and transverse branch tunnel holes which are uniform in length and do not interfere with each other can be effectively formed in the etched foil, so that the limitation of a theoretical specific surface area is broken through, and the product capacity is further improved.

Description

Technical Field

[0001] This disclosure relates to the field of capacitors, and in particular to etched foils and methods for their preparation. Background Technology

[0002] Aluminum electrolytic capacitors are widely used in electronic products due to their advantages such as high specific capacitance, small size, good voltage withstand capability, self-healing ability, and low cost. The capacitance performance of the anode foil plays a crucial role in the overall performance of the capacitor, and the key to improving the capacitance of the anode foil lies in increasing its surface area. Although various pretreatment methods have been used to optimize the etching structure, some problems still exist, limiting further improvement in the specific surface area of ​​the aluminum foil. Therefore, further improvements in this area are desired. Summary of the Invention

[0003] Embodiments of this disclosure provide a method for preparing an etched foil, comprising: performing a first treatment on an aluminum foil in a first alkaline solution containing zinc ions; performing a first etching on the aluminum foil after the first treatment to form a main tunnel; and performing a second etching on the aluminum foil in an etching solution containing copper ions to form branch tunnels on the main tunnel.

[0004] In some embodiments, the thickness of the aluminum foil is 140 μm to 150 μm.

[0005] In some embodiments, the first treatment of aluminum foil in a first alkaline solution containing zinc ions includes: treating at a temperature of 40°C to 55°C for 0.5 min to 3 min, wherein the concentration of zinc ions in the first alkaline solution is 0.05 mol / L to 0.1 mol / L.

[0006] In some embodiments, the alkali in the first alkali solution includes sodium hydroxide and / or potassium hydroxide, and the concentration of the alkali in the first alkali solution is from 0.5 mol / L to 1 mol / L.

[0007] In some embodiments, the first etching of the aluminum foil includes: performing pulsed DC etching in a mixed acid solution, and repeating it three to five times; wherein, in the pulsed DC etching, an initial current, a middle current and an end current are used sequentially, the current density of the initial current is greater than the current density of the middle current, and the current density of the middle current is greater than the current density of the end current.

[0008] In some embodiments, the initial current density is 1 A / cm². 2 Up to 3A / cm 2 The current density in the middle section is 0.5 A / cm², lasting from 0.5 s to 1 s. 2 Up to 1A / cm 2 The duration was 8 to 11 seconds, and the current density at the end was 0.12 A / cm². 2 Up to 0.5A / cm2 The duration is 5 to 7 seconds; the mixed acid solution includes HCl and H2SO4, with the concentration of HCl in the mixed acid solution being 0.5 mol / L to 1 mol / L and the concentration of H2SO4 in the mixed acid solution being 3 mol / L to 3.3 mol / L.

[0009] In some embodiments, the second etching of aluminum foil in an etching solution containing copper ions includes: immersing the aluminum foil in the etching solution containing copper ions for a first time; performing DC etching in the etching solution at a preset current density for a second time, repeating this process one to three times.

[0010] In some embodiments, the etching solution is a sodium chloride solution containing oxalic acid and copper nitrate, wherein the mass concentration of oxalic acid in the etching solution is 0.5% to 1%, the mass concentration of copper nitrate in the etching solution is 0.01% to 0.2%, the mass concentration of sodium chloride in the etching solution is 5% to 10%, the temperature of the etching solution is 70°C to 80°C, the first time is 60s to 120s, and the preset current density is 50mA / cm². 2 Up to 2.5A / cm 2 The second time is 1 to 5 seconds.

[0011] In some embodiments, the preparation method further includes: performing a second treatment on the aluminum foil in a second alkaline solution before performing a first treatment on the aluminum foil in a first alkaline solution containing zinc ions; placing the aluminum foil in an acid solution for DC hole expansion operation after performing a second etching on the aluminum foil; and cleaning and drying the aluminum foil.

[0012] In some embodiments, the second treatment of the aluminum foil in the second alkaline solution includes: immersing the aluminum foil in a 0.05 mol / L to 0.2 mol / L sodium hydroxide solution at 60°C to 80°C for 1 min to 3 min, followed by washing with water; in the DC aperture widening operation, the acid solution includes a nitric acid solution at a temperature of 70°C to 75°C and a concentration of 1 mol / L to 1.5 mol / L, and the current density in the DC aperture widening operation is 0.1 A / cm². 2 Up to 0.2A / cm 2 The cleaning of the aluminum foil includes: cleaning in a 0.1 mol / L to 0.15 mol / L dilute hydrochloric acid solution at a temperature of 45°C to 50°C for 1 to 2 minutes, then cleaning in a 0.1 mol / L to 0.2 mol / L dilute nitric acid solution at a temperature of 60°C to 70°C for 1 to 2 minutes, followed by rinsing with water for 5 to 8 minutes; drying includes drying at a temperature of 300°C to 400°C.

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

[0014] This disclosure utilizes a multi-segment perforation mode with added zinc and copper ions to effectively generate longitudinal main tunnel holes and transverse branch tunnel holes of uniform length that do not interfere with each other on the etched foil, thereby breaking through the limitation of theoretical specific surface area and further improving product capacity. Attached Figure Description

[0015] Figure 1 A schematic flowchart of a method for preparing an etched foil according to some embodiments is shown.

[0016] Figure 2 A scanning electron microscope image of the etched foil obtained in Comparative Example 1 is shown.

[0017] Figure 3 A scanning electron microscope image of the etched foil obtained in Example 1 is shown.

[0018] Figure 4 A scanning electron microscope image of the etched foil obtained in Example 2 is shown.

[0019] Figure 5 A scanning electron microscope image of the etched foil obtained in Example 3 is shown. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0023] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0024] 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.

[0025] 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.

[0026] This disclosure effectively improves the capacity and corrosion uniformity of aluminum foil by adding zinc and copper ions. Before electrolytic etching, the aluminum foil is immersed in a solution containing trace amounts of Zn. 2+ The aluminum foil is treated in an alkaline solution (e.g., NaOH solution) at a certain temperature. This step utilizes an immersion reduction reaction to chemically plate zinc onto the aluminum foil surface, forming a micro (Zn-Al) galvanic cell. This dissolves the oxide film on the aluminum foil surface, making the aluminum foil more susceptible to chloride ion corrosion, reducing charge transfer resistance, thereby increasing pitting density and improving the density and distribution of pits and tunnels.

[0027] Subsequently, the aluminum foil is subjected to DC etching in a mixed acid solution (e.g., HCl and H₂SO₄) to form main tunnels perpendicular to the aluminum foil surface. The uniformity of the tunnel holes is significantly improved with the participation of zinc ions. Following this, in the copper ion treatment step, the etched aluminum foil is immersed in a neutral etching solution containing oxalic acid and copper salts (e.g., Cu(NO₃)₂). Utilizing the natural blocking corrosion cell effect, copper nuclei are chemically deposited on the inner surface of the main tunnels, forming micro (Cu-Al) galvanic cells. Subsequently, DC etching with a weak current is performed in this solution, prompting the formation of branch tunnels on the main tunnels.

[0028] To meet the requirements of high-voltage applications, the formed etched tunnels undergo further DC etching to widen them. This DC widening operation is performed in an acid solution (e.g., HNO3 solution). The aluminum foil with widened tunnels is then anodized to formation voltages of 100V and 520V to obtain the finished electrode foil.

[0029] Although the branch tunnels formed by the preparation method disclosed herein reduce the bending strength of the etched aluminum foil, the high-thickness etched aluminum foil itself has excellent metal ductility and strength, so sacrificing some strength in exchange for a significant increase in capacity is a feasible solution.

[0030] like Figure 1 As shown, the preparation method of this disclosure includes step S101, in which aluminum foil is subjected to a first treatment in a first alkaline solution containing zinc ions. In some embodiments, this step involves chemically plating zinc on the surface of the aluminum foil to form a micro (Zn-Al) galvanic cell, dissolving the oxide film on the surface of the aluminum foil, making the aluminum foil more susceptible to corrosion, reducing charge transfer resistance, thereby increasing pitting density and improving the density and distribution of pits and tunnels.

[0031] In some embodiments, the preparation method of this disclosure includes step S102, in which, after the first treatment, the aluminum foil is first etched to form a main tunnel. In some embodiments, the first etching forms a main tunnel perpendicular to the surface of the aluminum foil, and with the participation of zinc ions, the uniformity of the tunnel holes is significantly improved.

[0032] In some embodiments, the preparation method of this disclosure includes step S103, which involves a second etching of an aluminum foil in an etching solution containing copper ions to form branch tunnels on the main tunnel. This step utilizes the natural occlusion corrosion cell effect to chemically deposit copper nuclei on the inner surface of the main tunnel, forming micro (Cu-Al) galvanic cells. A second etching is then performed in this solution, prompting the formation of branch tunnels on the main tunnel, i.e., inducing the growth of branch tunnels (lateral branch holes) from the sidewalls of the main tunnel, thus constructing a tree-like structure.

[0033] By employing a multi-segment pore formation mode with added zinc and copper ions, the etched foil can effectively produce longitudinal main tunnel holes and transverse branch tunnel holes of uniform length that do not interfere with each other, thereby overcoming the limitations of theoretical specific surface area and further improving product capacity. In some related schemes, electrodeposition of single Cu or Zn ions can reduce corrosion resistance and improve corrosion uniformity in direct current pore formation, thereby increasing the density and length of tunnel holes. However, the capacity improvement effect of this scheme is still limited, and if the tunnel holes are too long, it will cause a significant reduction in the mechanical strength of the aluminum foil. This disclosure, after etching uniform tunnel holes in the presence of Zn ions, further utilizes Cu ions to promote the formation of branch tunnel holes, rather than simply increasing the tunnel hole length as in some existing technologies. This branch tunnel hole formation scheme of this disclosure avoids the adverse consequences of excessively long tunnel holes causing core penetration and a significant decrease in mechanical strength. Due to the formation of branch tunnels or branch tunnel holes, a significant increase in capacity is achieved, and compared to the reduction in mechanical strength of aluminum foil caused by excessively long tunnel holes, the mechanical strength of the aluminum foil of this disclosure is reduced.

[0034] In some embodiments, the thickness of the aluminum foil is 140 μm to 150 μm. Aluminum foils within this thickness range exhibit excellent ductility and strength, and are advantageous for increasing the surface area of ​​the aluminum foil, thereby increasing capacity while reducing the number of aluminum foil layers required for aluminum electrolytic capacitors.

[0035] In some embodiments, the first treatment of aluminum foil in a first alkaline solution containing zinc ions includes: treating at a temperature of 40°C to 55°C for 0.5 min to 3 min, wherein the concentration of zinc ions in the first alkaline solution is 0.05 mol / L to 0.1 mol / L. In some embodiments, the temperature of the first treatment can be 40°C, 45°C, 50°C, 55°C, or other suitable values ​​between them. If the temperature is too low, insufficient reaction is likely to occur; if the temperature is too high, over-corrosion is likely to occur. In some embodiments, the treatment time is 0.5 min, 1 min, 2 min, 3 min, or other suitable values ​​between them. If the time is too short, insufficient reaction is likely to occur; if the time is too long, over-corrosion is likely to occur. In some embodiments, the concentration of zinc ions in the first alkaline solution is 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, or other suitable values ​​between them. If the concentration of zinc ions is too low, its effect is relatively limited; if the concentration of zinc ions is too high, over-corrosion is likely to occur.

[0036] In some embodiments, the alkali in the first alkali solution includes sodium hydroxide and / or potassium hydroxide, and the alkali concentration in the first alkali solution is from 0.5 mol / L to 1 mol / L. In some embodiments, the alkali concentration in the first alkali solution is 0.5 mol / L, 0.8 mol / L, 1 mol / L, or other suitable values ​​between them. If the alkali concentration in the first alkali solution is too low, its effect is relatively limited; if the alkali concentration in the first alkali solution is too high, excessive corrosion is likely to occur.

[0037] In some embodiments, the first etching of the aluminum foil includes: pulsed DC etching in a mixed acid solution, repeated three to five times; wherein, in the pulsed DC etching, an initial current, a mid-section current, and a final current are used sequentially, with the initial current density being greater than the mid-section current density, and the mid-section current density being greater than the final current density. In some embodiments, pulsed DC etching in the mixed acid solution can generate deep and straight main tunnel holes perpendicular to the aluminum foil surface; repeating the process three to five times can increase the tunnel length. In some embodiments, using a larger initial current in the initial stage can break down the residual oxide film, quickly initiate corrosion, and form initial holes; using a moderate mid-section current in the mid-section stage can maintain the longitudinal growth of existing holes, suppress the formation of new holes, and ensure stable hole distribution; using a smaller final current in the final stage can smooth the channels, prevent local over-etching, and optimize the morphology.

[0038] In some embodiments, the initial current density is 1 A / cm². 2 Up to 3A / cm 2 The current density in the middle section is 0.5 A / cm², lasting from 0.5 s to 1 s.2 Up to 1A / cm 2 The duration was 8 to 11 seconds, and the current density at the end was 0.12 A / cm². 2 Up to 0.5A / cm 2 The current is controlled for 5 to 7 seconds. This stepped current control enables "precise hole opening and directional growth," improving the neatness and depth consistency of the holes.

[0039] In some embodiments, the mixed acid solution comprises HCl and H₂SO₄, wherein the concentration of HCl in the mixed acid solution is 0.5 mol / L to 1 mol / L, and the concentration of H₂SO₄ in the mixed acid solution is 3 mol / L to 3.3 mol / L. In some embodiments, HCl provides Cl₂. － Ions play a role in activating corrosion, promoting pitting nucleation and pore growth; Cl － It has strong penetrating power, capable of destroying the Al2O3 oxide film and inducing localized corrosion (pitting corrosion), which is conducive to the formation of deep and straight longitudinal tunnels. If the concentration of HCl is too low, Cl... － Insufficient HCl concentration makes it difficult to effectively break through the oxide film, thus limiting the overall increase in specific surface area; if the HCl concentration is too high, the corrosion is too severe, easily leading to over-corrosion. In some embodiments, H2SO4 provides SO4²⁻. － H₂SO₄ ions act as corrosion inhibitors and stabilizers; they can form a partial passivation layer on the pore wall, inhibiting lateral expansion and concentrating corrosion development in the vertical direction, thus helping to improve the verticality and uniformity of the pores. If the concentration of H₂SO₄ is too low, its corrosion inhibition ability is insufficient, and its effect on inhibiting lateral corrosion is relatively limited; if the concentration of H₂SO₄ is too high, it can easily cause excessive passivation, inhibiting the dissolution reaction of aluminum.

[0040] In some embodiments, the second etching of the aluminum foil in an etching solution containing copper ions includes: immersing the aluminum foil in the etching solution containing copper ions for a first time, during which Cu particles are preferentially deposited in the narrow region of the main tunnel using the "natural occlusion cell effect" as catalytic sites for subsequent corrosion; and performing DC etching in the etching solution at a preset current density for a second time, repeating this process one to three times. Cu and Al form a (Cu-Al) galvanic cell, with Al acting as the anode and being corroded and dissolved, forming transverse branch holes on the sidewall of the main tunnel.

[0041] In some embodiments, the etching solution is a sodium chloride solution containing oxalic acid and copper nitrate, wherein the mass concentration of oxalic acid in the etching solution is 0.5% to 1%. In some embodiments, the mass concentration of oxalic acid in the etching solution is 0.5%, 0.8%, 1%, or other suitable values ​​between them. If the mass concentration of oxalic acid is too low, the corrosion effect is relatively limited; if the mass concentration of oxalic acid is too high, the corrosion morphology deteriorates. In some embodiments, the mass concentration of copper nitrate in the etching solution is 0.01% to 2%. In some embodiments, the mass concentration of copper nitrate in the etching solution is 0.01%, 0.1%, 0.2%, or other suitable values ​​between them. If the mass concentration of copper nitrate is too low, it is difficult to form Al-Cu microcells; if the mass concentration of copper nitrate is too high, over-corrosion can easily affect the morphology. In some embodiments, the mass concentration of sodium chloride in the etching solution is 5% to 10%. In some embodiments, the mass concentration of sodium chloride in the etching solution is 5%, 6%, 7%, 8%, 9%, 10%, or other suitable values ​​between them. If the mass concentration of sodium chloride is too low, Cl － Insufficient concentration makes it difficult to effectively activate the aluminum surface; excessive concentration of sodium chloride can easily lead to over-corrosion. In some embodiments, the temperature of the etching solution is 70°C to 80°C. In some embodiments, the temperature of the etching solution is 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, or other suitable values ​​between them. If the temperature is too low, the reaction efficiency is low; if the temperature is too high, over-corrosion is likely to occur. In some embodiments, the first time is 60s to 120s. In some embodiments, the first time is 60s, 70s, 80s, 90s, 100s, 110s, 120s, or other suitable values ​​between them. If the first time is too short, the reaction is insufficient; if the first time is too long, over-corrosion is likely to occur. In some embodiments, the preset current density is 50mA / cm. 2 Up to 2.5A / cm 2 In some embodiments, the preset current density is 50 mA / cm². 2 0.1A / cm 2 0.5A / cm 2 1A / cm 2 1.5A / cm 2 2A / cm 2 2.5A / cm 2 Or other suitable values ​​between them. If the preset current density is too low, the reaction efficiency is low; if the preset current density is too high, over-corrosion is likely to occur. In some embodiments, the second time is 1 s to 5 s, for example, 2 s, 3 s, or 4 s. If the second time is too short, the reaction is insufficient; if the second time is too long, over-corrosion is likely to occur.

[0042] In some embodiments, the preparation method further includes: before performing a first treatment on the aluminum foil in a first alkaline solution containing zinc ions, performing a second treatment on the aluminum foil in a second alkaline solution to remove oil stains and natural oxide film from the aluminum foil surface and clean the surface; after performing a second etching on the aluminum foil, placing the aluminum foil in an acid solution for DC hole expansion operation to enlarge the diameter of the main tunnel and branch tunnel, further increase the surface area, and improve the subsequent formation efficiency; and cleaning and drying the aluminum foil.

[0043] In some embodiments, the second treatment of the aluminum foil in the second alkaline solution comprises: immersing the aluminum foil in a 0.05 mol / L to 0.2 mol / L sodium hydroxide solution at 60°C to 80°C for 1 min to 3 min, followed by washing with water. In some embodiments, during the DC aperture widening operation, the acid solution comprises a nitric acid solution at a temperature of 70°C to 75°C and a concentration of 1 mol / L to 1.5 mol / L, and the current density during the DC aperture widening operation is 0.1 A / cm². 2 Up to 0.2A / cm 2 By employing the above parameters in the DC aperture enlargement operation, the pore size can be appropriately widened, balancing capacity and strength. In some embodiments, cleaning the aluminum foil includes: cleaning in a 0.1 mol / L to 0.15 mol / L dilute hydrochloric acid solution at a temperature of 45°C to 50°C for 1 to 2 minutes to remove residual metal ions, followed by cleaning in a 0.1 mol / L to 0.2 mol / L dilute nitric acid solution at a temperature of 60°C to 70°C for 1 to 2 minutes to passivate the surface and improve stability, and then rinsing with water for 5 to 8 minutes. In some embodiments, drying includes drying at a temperature of 300°C to 400°C to prepare for formation.

[0044] To better understand this disclosure, specific embodiments are described below.

[0045] Example 1 S1. Select 150μm thick aluminum foil, soak it in 70℃ sodium hydroxide (0.1mol / L) solution for 2min, and then wash it with pure water.

[0046] S2. Immerse the product obtained in S1 in an immersion solution containing trace amounts of Zn. 2+ The sample was treated in a 0.5 mol / L (NaOH) solution (0.05 mol / L) at 40 °C for 1.5 minutes.

[0047] S3. The product obtained in S2 was subjected to pulsed DC etching in a mixed acid solution of HCl (0.9 mol / L) and H2SO4 (3.2 mol / L) (initial current density 3 A / cm). 2 The duration is 0.5s, and the mid-section current is 1A / cm.2 The duration is 10 seconds, and the terminal current is 0.12 A / cm. 2 Repeat five times (lasting 5 seconds) to form the main tunnel perpendicular to the aluminum foil surface.

[0048] S4. The product obtained in S3 was immersed in a neutral etching solution containing 0.75 wt% oxalic acid and 0.15 wt.% Cu(NO3)2 at 75°C and 5 wt% NaCl for 70 s, followed by etching at 90 mA / cm in this solution. 2 The current density is used for DC etching for 4.5 seconds, and this process is repeated once to induce the formation of branch tunnels on the main tunnel.

[0049] S5. The product obtained in S4 was placed in a 1.2 mol / L HNO3 solution at 70°C with a flow rate of 0.14 A / cm. 2 DC borehole expansion operation.

[0050] S6. Wash the product obtained in S5 in dilute hydrochloric acid solution (0.1 mol / L) at 45°C for 1 min, then wash it in dilute nitric acid solution (0.2 mol / L) at 60°C for 2 min, and finally rinse it with pure water for 8 min. Dry it at 400°C.

[0051] S7. The product obtained in S6 is subjected to a formation process to obtain the finished etched foil.

[0052] Example 2 S1. Select 150μm thick aluminum foil, soak it in 70℃ sodium hydroxide (0.1mol / L) solution for 2min, and then wash it with pure water.

[0053] S2. Immerse the product obtained in S1 in an immersion solution containing trace amounts of Zn. 2+ The sample was treated in a 0.7 mol / L (NaOH) solution (0.05 mol / L) at 45 °C for 1 minute.

[0054] S3. The product obtained in S2 was subjected to pulsed DC etching in a mixed acid solution of HCl (0.9 mol / L) and H2SO4 (3.2 mol / L) (initial current density 2.5 A / cm). 2 The duration is 0.5s, and the mid-section current is 0.75A / cm. 2 The duration is 10 seconds, and the terminal current is 0.15 A / cm. 2 Repeat five times (lasting 5 seconds) to form the main tunnel perpendicular to the aluminum foil surface.

[0055] S4. The product obtained in S3 was immersed in a neutral etching solution containing 0.5 wt% oxalic acid and 0.1 wt% Cu(NO3)2 at 77°C for 70 s, followed by etching at 1 A / cm in this solution. 2Perform DC etching for 3 seconds, repeat twice, to induce the formation of branch tunnels on the main tunnel.

[0056] S5. The product obtained in S4 was placed in a 1.2 mol / L HNO3 solution at 70°C with a flow rate of 0.14 A / cm. 2 DC borehole expansion operation.

[0057] S6. The product obtained in S5 was washed in dilute hydrochloric acid solution (0.1 mol / L) at 45°C for 1 min, then washed in dilute nitric acid solution (0.2 mol / L) at 60°C for 2 min, and finally rinsed with pure water for 8 min. It was then dried at 400°C.

[0058] S7. The product obtained in S6 is subjected to a formation process to obtain the finished etched foil.

[0059] Example 3 S1. Select 150μm thick aluminum foil, soak it in 70℃ sodium hydroxide (0.1mol / L) solution for 2min, and then wash it with pure water.

[0060] S2. Immerse the product obtained in S1 in an immersion solution containing trace amounts of Zn. 2+ The sample was treated in a 1 mol / L (NaOH) solution (0.05 mol / L) at 50 °C for 0.5 minutes.

[0061] S3. The product obtained in S2 was subjected to pulsed DC etching in a mixed acid solution of HCl (0.9 mol / L) and H2SO4 (3.2 mol / L) (initial current density 2.5 A / cm). 2 The duration is 0.5s, and the mid-section current is 0.75A / cm. 2 The duration is 10 seconds, and the terminal current is 0.15 A / cm. 2 Repeat five times (lasting 5 seconds) to form the main tunnel perpendicular to the aluminum foil surface.

[0062] S4. The product obtained in S3 was immersed in a neutral etching solution containing 0.5 wt% oxalic acid and 0.15 wt% Cu(NO3)2 at 80 °C for 70 s, followed by etching at 1.5 A / cm in this solution. 2 Perform DC etching for 2 seconds, repeat twice, to induce the formation of branch tunnels on the main tunnel.

[0063] S5. The product obtained in S4 was placed in a 1.2 mol / L HNO3 solution at 70°C with a flow rate of 0.14 A / cm. 2 DC borehole expansion operation.

[0064] S6. The product obtained in S5 was washed in dilute hydrochloric acid solution (0.1 mol / L) at 45°C for 1 min, then washed in dilute nitric acid solution (0.2 mol / L) at 60°C for 2 min, and finally rinsed with pure water for 8 min. It was then dried at 400°C.

[0065] S7. The product obtained in S6 is subjected to a formation process to obtain the finished etched foil.

[0066] Comparative Example 1 S1. Select 150μm thick aluminum foil, soak it in 70℃ sodium hydroxide (0.1 mol / L) solution for 2 min, and then wash it with pure water.

[0067] S2. The product obtained in S1 was subjected to pulsed DC etching in a mixed acid solution of HCl (0.9 mol / L) and H2SO4 (3.2 mol / L) (initial current density 3 A / cm). 2 The duration is 0.5s, and the mid-section current is 1A / cm. 2 The duration is 10 seconds, and the terminal current is 0.12 A / cm. 2 Repeat five times (lasting 5 seconds) to form the main tunnel perpendicular to the aluminum foil surface.

[0068] S3. The product obtained in S2 was placed in a 1.2 mol / L HNO3 solution at 70℃ with a flow rate of 0.14 A / cm. 2 DC borehole expansion operation.

[0069] S4. The product obtained in S3 was washed in dilute hydrochloric acid solution (0.1 mol / L) at 45°C for 1 min, then washed in dilute nitric acid solution (0.2 mol / L) at 60°C for 2 min, and finally rinsed with pure water for 8 min. It was then dried at 400°C.

[0070] S5. The product obtained in S4 is subjected to a formation process to obtain the finished etched foil.

[0071] Figures 2 to 5 Scanning electron microscope (SEM) images of the etched foils obtained in Comparative Examples 1 to 3 are shown respectively. It can be seen from the figures that the proportion of branch tunnel holes in the etched foils in Examples 1-3 is significantly increased.

[0072] In addition, the withstand voltage and specific capacitance of the aluminum foil samples were tested: voltage, specific capacitance, and number of bends were tested using methods commonly used in the art. The number of bends refers to the number of times the foil was repeatedly bent until it broke. Table 1 shows the test results for Comparative Example 1 and Examples 1-3.

[0073] Table 1 As can be seen from the above, Zn is used in Examples 1-3. 2+ With Cu2+ Alternating the treatment of aluminum foil can effectively increase the proportion of branch tunnel holes, thereby increasing the surface area of ​​the aluminum foil and thus increasing its capacity. Although it will reduce the strength to some extent, the increase in capacity is huge, providing a feasible solution for the corrosion production of high-thickness electrode foil.

[0074] 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 an etched foil, characterized in that, include: The aluminum foil is first treated in a first alkaline solution containing zinc ions; After the first process, the aluminum foil is first etched to form the main tunnel; The aluminum foil is then subjected to a second etching in an etching solution containing copper ions to form branch tunnels on the main tunnel.

2. The preparation method according to claim 1, characterized in that, The thickness of the aluminum foil is 140 μm to 150 μm.

3. The preparation method according to claim 1, characterized in that, The first treatment of aluminum foil in a first alkaline solution containing zinc ions includes: The solution is treated at a temperature of 40°C to 55°C for 0.5 min to 3 min, wherein the concentration of zinc ions in the first alkaline solution is 0.05 mol / L to 0.1 mol / L.

4. The preparation method according to claim 3, characterized in that, The alkali in the first alkaline solution includes sodium hydroxide and / or potassium hydroxide, and the concentration of the alkali in the first alkaline solution is from 0.5 mol / L to 1 mol / L.

5. The preparation method according to claim 1, characterized in that, The first etching of the aluminum foil includes: Pulsed DC etching is performed in a mixed acid solution and repeated three to five times; In the pulsed DC etching process, an initial current, a middle current, and an end current are used sequentially. The current density of the initial current is greater than that of the middle current, and the current density of the middle current is greater than that of the end current.

6. The preparation method according to claim 5, characterized in that, The initial current density is 1 A / cm². 2 Up to 3A / cm 2 The current density of the intermediate current is 0.5 A / cm², lasting from 0.5 s to 1 s. 2 Up to 1A / cm 2 The current density of the terminal current is 0.12 A / cm², lasting from 8 to 11 seconds. 2 Up to 0.5A / cm 2 Lasts 5 to 7 seconds; The mixed acid solution includes HCl and H2SO4, wherein the concentration of HCl in the mixed acid solution is from 0.5 mol / L to 1 mol / L, and the concentration of H2SO4 in the mixed acid solution is from 3 mol / L to 3.3 mol / L.

7. The preparation method according to claim 1, characterized in that, The second etching of the aluminum foil in an etching solution containing copper ions includes: The aluminum foil is immersed in an etching solution containing copper ions for a first time; DC etching is performed in the etching solution at a preset current density for a second time, and this process is repeated one to three times.

8. The preparation method according to claim 7, characterized in that, The etching solution is a sodium chloride solution containing oxalic acid and copper nitrate. The mass concentration of oxalic acid in the etching solution is 0.5% to 1%, the mass concentration of copper nitrate in the etching solution is 0.01% to 0.2%, the mass concentration of sodium chloride in the etching solution is 5% to 10%, the temperature of the etching solution is 70°C to 80°C, and the first time is 60s to 120s. The preset current density is 50 mA / cm². 2 Up to 2.5A / cm 2 The second time is from 1 second to 5 seconds.

9. The preparation method according to claim 1, characterized in that, Also includes: Before the aluminum foil is subjected to a first treatment in a first alkaline solution containing zinc ions, the aluminum foil is subjected to a second treatment in a second alkaline solution; After the aluminum foil is etched a second time, the aluminum foil is placed in an acid solution for DC hole expansion operation; The aluminum foil is then cleaned and dried.

10. The preparation method according to claim 9, characterized in that, The second treatment of the aluminum foil in the second alkaline solution includes: immersing the aluminum foil in a 0.05 mol / L to 0.2 mol / L sodium hydroxide solution at 60°C to 80°C for 1 min to 3 min, and then washing it with water; In the DC borehole enlargement operation, the acid solution includes a nitric acid solution, the temperature of which is 70°C to 75°C, the concentration of which is 1 mol / L to 1.5 mol / L, and the current density in the DC borehole enlargement operation is 0.1 A / cm². 2 Up to 0.2A / cm 2 ; The cleaning of the aluminum foil includes: cleaning in a 0.1 mol / L to 0.15 mol / L dilute hydrochloric acid solution at a temperature of 45°C to 50°C for 1 to 2 minutes, then cleaning in a 0.1 mol / L to 0.2 mol / L dilute nitric acid solution at a temperature of 60°C to 70°C for 1 to 2 minutes, and then rinsing with water for 5 to 8 minutes. The drying process includes drying at a temperature of 300°C to 400°C.

11. A corrosion foil, characterized in that, The etched foil is the etched foil obtained by the preparation method according to any one of claims 1 to 10.

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