Etching foil and method for producing the same

Abstract

The present disclosure provides a corrosion foil and a preparation method thereof, the preparation method comprising: subjecting an aluminum foil to a first treatment in a first alkaline solution containing zinc ions; after the first treatment, subjecting the aluminum foil to a first etching to form main tunnels; and subjecting the aluminum foil to a second etching in an etching solution containing copper ions to form branch tunnels on the main tunnels. By adopting a multi-stage pore-forming mode with the addition of zinc ions and copper ions, the aluminum foil can effectively form longitudinal main tunnel pores and transverse branch tunnel pores that are uniform in length and do not interfere with each other, thereby breaking through the limit of the theoretical specific surface area and further improving the product capacity.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of capacitors, and in particular to etching foil and a method for preparing the same. BACKGROUND

[0002] Aluminum electrolytic capacitors are widely used in electronic products due to their high specific capacitance, small size, good voltage resistance, self-healing ability, and low cost. The capacitance performance of the anode foil plays a key 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 a variety of pretreatment methods have been used to optimize the etching structure, there are still some problems that restrict the further improvement of the specific surface area of the aluminum foil. Therefore, further improvement in this regard is desired. SUMMARY

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

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

[0005] In some embodiments, the first treatment of the aluminum foil in the first alkaline solution containing zinc ions comprises: 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 alkaline solution comprises sodium hydroxide and / or potassium hydroxide, and the concentration of the alkali in the first alkaline solution is 0.5 mol / L to 1 mol / L.

[0007] In some embodiments, the first etching of the aluminum foil comprises: performing pulse direct current etching in a mixed acid solution, and repeating three to five times; wherein in the pulse direct current etching, an initial current, a middle current and a terminal current are used in sequence, 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 terminal current.

[0008] In some embodiments, the current density of the initial current is 1 A / cm 2 to 3 A / cm 2 , the current density of the middle current is 0.5 A / cm 2 to 1 A / cm 2 , and the current density of the terminal current is 0.12 A / cm 2 to 0.5 A / cm2 The mixed acid solution comprises HCl and H2SO4, 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.

[0009] In some embodiments, the second etching of the aluminum foil in the etching solution containing copper ions comprises: immersing the aluminum foil in the etching solution containing copper ions for a first time; and performing direct current etching in the etching solution at a preset current density for a second time, repeated one to three times.

[0010] In some embodiments, 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 50mA / cm 2 to 2.5A / cm 2 , and the second time is 1s to 5s.

[0011] In some embodiments, the preparation method further comprises: before the first treatment of the aluminum foil in the first alkali solution containing zinc ions, second treatment of the aluminum foil in a second alkali solution; after the second etching of the aluminum foil, placing the aluminum foil in an acid solution for a direct current hole expansion operation; and cleaning and drying the aluminum foil.

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

[0013] Another embodiment of the present disclosure provides a corrosion foil, which is obtained by any of the above preparation methods.

[0014] The present disclosure can effectively make the corrosion foil have longitudinal main tunnel holes and transverse branch tunnel holes of uniform length and not interfering with each other by adopting a multi-stage pore-forming mode of adding zinc ions and copper ions, thereby breaking through the limit of the theoretical specific surface area and further improving the product capacity. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A schematic flowchart of a preparation method of a corrosion foil according to some embodiments is shown.

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

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

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

[0019] Figure 5 A scanning electron microscope image of the corrosion foil obtained in Example 3 is shown. DETAILED DESCRIPTION

[0020] To make the skilled in the art better understand the technical solutions of the present disclosure, the technical solutions of the present disclosure are described in detail below in combination with the drawings.

[0021] In the following, example embodiments will be described more fully with reference to the accompanying drawings, in which example embodiments can be embodied in different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0022] In the case of no conflict, each embodiment of the present disclosure and each feature in the embodiments can be combined with each other.

[0023] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0024] The terms used herein are only used to describe specific embodiments and are not intended to limit the present disclosure. As used herein, the singular forms "a" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the terms "comprise" and / or "consist of, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0025] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an overly literal or overly formal sense unless expressly so defined herein.

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

[0027] After that, the aluminum foil is subjected to direct current etching in a mixed acid solution (e.g., HCl and H2SO4) to form main tunnels perpendicular to the surface of the aluminum foil. With the participation of zinc ions, the uniformity of the tunnel holes is significantly improved. Then, in the copper ion treatment step, the etched aluminum foil is immersed in a neutral etching solution containing oxalic acid and copper salt (e.g., Cu(NO3)2), and a copper nucleus is electrolessly deposited on the inner surface of the main tunnel by using the natural occlusion corrosion cell effect, forming a micro (Cu - Al) galvanic cell. Subsequently, direct current etching is performed in this solution with a weak current to form branch tunnels on the main tunnels.

[0028] To meet the needs of high-pressure applications, the formed etched tunnels are further subjected to direct current etching widening treatment, and direct current hole expansion is performed in an acid solution (e.g., HNO3 solution). After the aluminum foil with widened tunnels is anodized to a forming voltage of 100V and 520V, a finished electrode foil is obtained.

[0029] The branch hole tunnels formed by the preparation method of the present disclosure may reduce the bending strength of the etched aluminum foil, but since the high-thickness etched aluminum foil itself has excellent metal ductility and strength, it is a feasible solution to sacrifice part of the strength to greatly improve the capacity.

[0030] As shown in Figure 1 , the preparation method of the present disclosure includes a step S101 of treating the aluminum foil in a first alkaline solution containing zinc ions. In some embodiments, this step electrolessly plates zinc on the surface of the aluminum foil, forms a micro (Zn - Al) galvanic cell, dissolves the oxide film on the surface of the aluminum foil, makes the aluminum foil more susceptible to corrosion, reduces the charge transfer resistance, thereby increasing the pitting density, and improving the density and distribution of pits and tunnels.

[0031] In some embodiments, the preparation method of the present disclosure comprises step S102, after the first treatment, the aluminum foil is subjected to a first etching to form a main tunnel. In some embodiments, through the first etching, the main tunnel is formed perpendicular to the surface of the aluminum foil, and the tunnel hole uniformity is obviously improved with the participation of zinc ions.

[0032] In some embodiments, the preparation method of the present disclosure comprises step S103, the aluminum foil is subjected to a second etching in an etching solution containing copper ions to form branch tunnels on the main tunnel. This step utilizes the natural occlusion corrosion battery effect to chemically deposit copper nuclei on the inner surface of the main tunnel, forming a micro (Cu - Al) galvanic cell. Subsequent second etching in this solution promotes the formation of branch tunnels on the main tunnel, i.e. induces the growth of branch tunnels from the sidewall of the main tunnel (lateral branch holes), constructing a tree structure.

[0033] By adopting the multi-stage pore-forming mode with the addition of zinc ions and copper ions, the corrosion foil can effectively form longitudinal main tunnel holes and lateral branch tunnel holes that are uniform in length and do not interfere with each other, thereby breaking through the limit of the theoretical specific surface area and further improving the product capacity. In some related schemes, the corrosion resistance on the direct current pore-forming can be reduced and the corrosion uniformity can be improved by electrodeposition of single Cu ions or Zn ions, thereby further improving the density and length of the tunnel holes. However, the effect of this scheme on capacity improvement 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. After etching to obtain uniform tunnel holes in the presence of Zn ions, the present disclosure further utilizes Cu ions to promote the formation of branch holes of the tunnel holes, instead of simply increasing the length of the tunnel holes as in some prior art. The scheme of the present disclosure for forming branch tunnel holes avoids the adverse consequences of a significant reduction in mechanical strength caused by residual core penetration due to excessively long tunnel holes. Due to the formation of branch tunnels or branch tunnel holes, a significant improvement in capacity is achieved, and the reduction in the mechanical strength of the aluminum foil of the present disclosure is reduced compared to the residual core penetration caused by excessively long tunnel holes.

[0034] In some embodiments, the thickness of the aluminum foil is 140 μm to 150 μm. The aluminum foil in this thickness range has excellent metal ductility and strength, and is beneficial to increasing the surface area of the aluminum foil, which can reduce the number of layers of aluminum foil required for the aluminum electrolytic capacitor while improving the capacity.

[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 to 1 A / cm 2 for 8 s to 11 s, and the current density of the end current is 0.12 A / cm 2 to 0.5 A / cm 2 for 5 s to 7 s. Through this step current control, “precise hole starting and directional growth” can be achieved, and the uniformity and depth consistency of the holes are improved.

[0039] In some embodiments, the mixed acid solution includes HCl and H2SO4, 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 Cl － ions, which play a role in activating corrosion and promoting pitting nucleation and hole growth; Cl － has strong penetration ability, can damage the Al2O3 oxide film, induce local corrosion (pitting), and is conducive to the formation of deep and straight longitudinal tunnels. If the concentration of HCl is too low, the Cl － concentration is insufficient, and it is difficult to effectively break through the oxide film, and the overall specific surface area is relatively limited; if the concentration of HCl is too high, the corrosion is too severe, which can easily lead to over-corrosion. In some embodiments, H2SO4 provides SO4² － ions, which play a role in corrosion inhibition and stabilization; it can form a partial passivation layer on the hole wall, inhibit lateral expansion, and make corrosion more concentrated in the longitudinal direction, which helps to improve the verticality and uniformity of the holes. If the concentration of H2SO4 is too low, its corrosion inhibition ability is insufficient, and the effect of inhibiting lateral corrosion is relatively limited; if the concentration of H2SO4 is too high, it can easily cause excessive passivation and inhibit the dissolution reaction of aluminum.

[0040] In some embodiments, the second etching of the aluminum foil in the etching solution containing copper ions includes: immersing the aluminum foil in the etching solution containing copper ions for a first time, at which time, by using the “natural occluded cell effect”, Cu particles are preferentially deposited in the narrow region of the main tunnel as catalytic sites for subsequent corrosion; direct current etching in the etching solution at a preset current density for a second time, repeated one to three times. Cu and Al form a (Cu-Al) primary cell, Al is the anode and is corroded and dissolved, and lateral branch holes are formed on the side wall of the main tunnel.

[0041] In some embodiments, the etching solution is a sodium chloride solution containing oxalic acid and copper nitrate, the mass concentration of the oxalic acid in the etching solution is 0.5% to 1%. In some embodiments, the mass concentration of the oxalic acid in the etching solution is 0.5%, 0.8%, 1%, or other suitable values therebetween. If the mass concentration of the oxalic acid is too low, the corrosion effect is relatively limited; if the mass concentration of the oxalic acid is too high, the corrosion morphology is poor. In some embodiments, the mass concentration of the copper nitrate in the etching solution is 0.01% to 2%. In some embodiments, the mass concentration of the copper nitrate in the etching solution is 0.01%, 0.1%, 0.2%, or other suitable values therebetween. If the mass concentration of the copper nitrate is too low, it is relatively difficult to form Al-Cu micro-batteries; if the mass concentration of the copper nitrate is too high, it is easy to over-corrode and affect the morphology. In some embodiments, the mass concentration of the sodium chloride in the etching solution is 5% to 10%. In some embodiments, the mass concentration of the sodium chloride in the etching solution is 5%, 6%, 7%, 8%, 9%, 10%, or other suitable values therebetween. If the mass concentration of the sodium chloride is too low, the Cl － concentration is insufficient, and it is difficult to effectively activate the aluminum surface; if the mass concentration of the sodium chloride is too high, it is easy to over-corrode. 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 therebetween. If the temperature is too low, the reaction efficiency is relatively low; if the temperature is too high, it is easy to over-corrode. 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 therebetween. If the first time is too short, the reaction is not sufficient; if the first time is too long, it is easy to over-corrode. In some embodiments, the preset current density is 50mA / cm 2 to 2.5A / cm 2 . In some embodiments, the preset current density is 50mA / cm 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 therebetween. If the preset current density is too low, the reaction efficiency is relatively low; if the preset current density is too high, it is easy to over-corrode. In some embodiments, the second time is 1s to 5s, for example, 2s, 3s, or 4s. If the second time is too short, the reaction is not sufficient; if the second time is too long, it is easy to over-corrode.

[0042] In some embodiments, the preparation method further comprises: before the first treatment of the aluminum foil in the first alkaline solution containing zinc ions, a second treatment of the aluminum foil in a second alkaline solution to remove surface grease and natural oxide film of the aluminum foil, clean the surface; after the second etching of the aluminum foil, placing the aluminum foil in an acid solution for direct current hole expansion operation to expand the diameters of the main tunnel and branch tunnel, further increase the surface area, and improve the subsequent formation efficiency; 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, and then washing with water. In some embodiments, in the direct current hole expansion operation, the acid solution comprises a nitric acid solution, the temperature of the nitric acid solution is 70°C to 75°C, the concentration of the nitric acid solution is 1 mol / L to 1.5 mol / L, and the current density in the direct current hole expansion operation is 0.1 A / cm 2 to 0.2 A / cm 2 . By using the above parameters in the direct current hole expansion operation, the hole can be moderately widened, and the capacity and strength can be balanced. In some embodiments, the cleaning of the aluminum foil comprises: 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 min to 2 min to remove residual metal ions, 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 min to 2 min to passivate the surface and improve stability, and then rinsing with water for 5 min to 8 min. In some embodiments, the drying comprises baking at a temperature of 300°C to 400°C to prepare for formation.

[0044] In order to better understand the present disclosure, the following will be described in conjunction with specific embodiments.

[0045] Embodiment 1

[0046] S1. Select a 150 μm thick aluminum foil, immerse it in a 0.1 mol / L sodium hydroxide solution at 70°C for 2 min, and then wash it with pure water.

[0047] S2. Immerse the product obtained in S1 in a 0.5 mol / L (NaOH) solution containing a trace amount of Zn 2+ (0.05 mol / L) at 40°C for 1.5 min.

[0048] S3. Perform pulse direct current etching on the product obtained in S2 in a mixed acid solution of HCl (0.9 mol / L) and H2SO4 (3.2 mol / L) (initial current density 3 A / cm 2for 0.5 s, mid-portion current 1 A / cm 2 for 10 s, end-portion current 0.12 A / cm 2 for 5 s) repeated five times to form main tunnels perpendicular to the surface of the aluminum foil.

[0049] S4. The product obtained in S3 was immersed in a 75°C neutral etching solution of 5wt% NaCl containing 0.75wt% oxalic acid and Cu(NO3)2(0.15wt.%), for 70 s, followed by direct current etching in this solution at 90 mA / cm 2 for 4.5 s, repeated once to form branch tunnels on the main tunnels.

[0050] S5. The product obtained in S4 was subjected to direct current hole expansion at 70°C in a 1.2 mol / L HNO3 solution at 0.14 A / cm 2 for 5 s) repeated five times to form main tunnels perpendicular to the surface of the aluminum foil.

[0051] S6. The product obtained in S5 was cleaned in a dilute hydrochloric acid solution (0.1 mol / L) at 45°C for 1 min, in a dilute nitric acid solution (0.2 mol / L) at 60°C for 2 min, and then washed with pure water for 8 min. Drying was carried out at 400°C.

[0052] S7. The product obtained in S6 was subjected to chemical conversion treatment to obtain a finished etching foil.

[0053] Example 2

[0054] S1. A 150 μm thick aluminum foil was selected and immersed in a 70°C sodium hydroxide (0.1 mol / L) solution for 2 min, followed by pure water washing.

[0055] S2. The product obtained in S1 was immersed in a 0.7 mol / L (NaOH) solution containing a trace amount of Zn 2+ (0.05 mol / L) at 45°C for 1 min.

[0056] S3. The product obtained in S2 was subjected to pulse direct current 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 for 0.5 s, mid-portion current 0.75 A / cm 2 for 10 s, end-portion current 0.15 A / cm 2 for 5 s) repeated five times to form main tunnels perpendicular to the surface of the aluminum foil.

[0057] S4. The product obtained in S3 was immersed in a 70°C neutral etching solution containing 0.5wt% oxalic acid and Cu(N03)2(0.1wt%) for 70s, followed by a 1 A / cm 2 DC etching was performed for 3s, repeated twice, to form branch tunnels on the main tunnels.

[0058] S5. The product obtained in S4 was placed in a 70°C 1.2mol / L HN03 solution at 0.14 A / cm 2 DC hole expansion was performed.

[0059] S6. The product obtained in S5 was cleaned in a dilute HCl solution (0.1 mol / L) at 45°C for 1 min, in a dilute HN03 solution (0.2 mol / L) at 60°C for 2 min, and then in pure water for 8 min. Drying was performed at 400°C.

[0060] S7. The product obtained in S6 was subjected to chemical conversion treatment to obtain a finished etching foil.

[0061] Example 3

[0062] S1. A 150μm thick aluminum foil was selected and immersed in a 70°C NaOH (0.1mol / L) solution for 2 min, followed by pure water washing.

[0063] S2. The product obtained in S1 was immersed in a 1mol / L (NaOH) solution containing a trace amount of Zn 2+ (0.05mol / L) at 50°C for 0.5 min.

[0064] S3. The product obtained in S2 was subjected to pulsed DC etching (initial current density 2.5A / cm 2 for 0.5s, middle-stage current 0.75A / cm 2 for 10s, terminal current 0.15A / cm 2 for 5s) repeated five times in a mixed acid solution of HC1 (0.9 mol / L) and H2S04(3.2mol / L) to form main tunnels perpendicular to the surface of the aluminum foil.

[0065] S4. The product obtained in S3 was immersed in a 70°C neutral etching solution containing 0.5wt% oxalic acid and Cu(N03)2(0.15wt%) for 70s, followed by a 1.5A / cm 2 DC etching was performed for 2s, repeated twice, to form branch tunnels on the main tunnels.

[0066] S5. The product obtained in S4 was placed in 70°C, 1.2 mol / L HNO3 solution at 0.14 A / cm 2 Direct current reaming was performed.

[0067] S6. The product obtained in S5 was cleaned in dilute hydrochloric acid solution (0.1 mol / L) at 45°C for 1 min, then in dilute nitric acid solution (0.2 mol / L) at 60°C for 2 min, and then washed with pure water for 8 min. Drying was performed at 400°C.

[0068] S7. The product obtained in S6 was subjected to chemical conversion treatment to obtain a finished etching foil.

[0069] Comparative Example 1

[0070] S1. A 150 μm thick aluminum foil was selected and immersed in 70°C sodium hydroxide (0.1 mol / L) solution for 2 min, and then washed with pure water.

[0071] S2. The product obtained in S1 was subjected to pulse direct current 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 for 0.5 s, middle section current 1 A / cm 2 for 10 s, end current 0.12 A / cm 2 for 5 s) for five times to form main tunnels perpendicular to the surface of the aluminum foil.

[0072] S3. The product obtained in S2 was placed in 70°C, 1.2 mol / L HNO3 solution at 0.14 A / cm 2 Direct current reaming was performed.

[0073] S4. The product obtained in S3 was cleaned in dilute hydrochloric acid solution (0.1 mol / L) at 45°C for 1 min, then in dilute nitric acid solution (0.2 mol / L) at 60°C for 2 min, and then washed with pure water for 8 min. Drying was performed at 400°C.

[0074] S5. The product obtained in S4 was subjected to chemical conversion treatment to obtain a finished etching foil.

[0075] Figures 2 to 5 Scanning electron microscope images of the etching foils obtained in Comparative Example 1 to Example 3 are shown, respectively. As can be seen from the images, the proportion of branched tunnel holes in the etching foils of Examples 1-3 is significantly increased.

[0076] In addition, the pressure resistance and specific capacity of the aluminum foil samples were tested. The voltage, specific capacity and bending times were tested by using the method commonly used in the art, and the bending times refer to the number of times of repeated bending until the rupture. Table 1 shows the test results of Comparative Example 1 and Examples 1-3.

[0077] Table 1

[0078]

[0079] As can be seen from the above, the aluminum foil in Examples 1-3 is treated with Zn 2+ and Cu 2+ alternately, which can effectively increase the proportion of branched tunnel holes, thereby increasing the surface area of the aluminum foil, and further increasing the capacity, although the strength is reduced to some extent, but the capacity is greatly improved, which provides a feasible solution for the corrosion production of high-thickness electrode foil.

[0080] Example embodiments have been disclosed herein and, although the use of specific terms is exemplified throughout this specification, they are used in this context only and should not be construed as limiting unless otherwise explicitly stated. In some instances, it will be apparent to those skilled in the art that features, characteristics or / and elements described in connection with a particular embodiment can be used in conjunction with other embodiments unless otherwise explicitly stated. As such, various changes and modifications can be made to the described embodiments without departing from the scope of the disclosure as set forth in 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; 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 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. 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; performing DC etching in the etching solution at a preset current density for a second time, repeating this process one to three times.

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 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.

6. The preparation method according to claim 1, 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.

7. 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.

8. The preparation method according to claim 7, 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 orifice expansion operation, the acid solution includes a nitric acid solution, the temperature of which is 70°C to 75°C, and the concentration of which is 1 mol / L to 1.5 mol / L. The current density in the DC orifice expansion 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.

9. A type of etched foil, characterized in that, The etched foil is the etched foil obtained by the preparation method according to any one of claims 1 to 8.

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