Aluminum foil and method of forming the same

Abstract

This disclosure provides aluminum foil and a method for forming the same. The method includes: performing a multi-stage formation process on the aluminum foil, the multi-stage formation process including three to eight stages; wherein, for aluminum foil with a target formation withstand voltage greater than or equal to 145V and less than or equal to 185V, a first mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the first stage of formation; for aluminum foil with a target formation withstand voltage greater than or equal to 105V and less than 145V, a second mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the second stage of formation; for aluminum foil with a target formation withstand voltage greater than or equal to 65V and less than 105V, a third mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the third stage of formation. By introducing ammonium dihydrogen phosphate in advance during the main formation stage for aluminum foils with different target formation withstand voltage ranges, and utilizing its electrochemical behavior at specific formation stages, the density and chemical stability of the oxide film are optimized, significantly improving the hydration resistance of the aluminum foil.

Description

Technical Field

[0001] This disclosure relates to the field of capacitors, and more particularly to aluminum foil and methods for forming the same. Background Technology

[0002] The formation process of aluminum foil for aluminum electrolytic capacitors is a key step in forming a high-quality oxide film. The traditional six-stage formation process uses a single ammonium adipate system, and a typical flow includes: primary formation, secondary formation, tertiary formation, quaternary formation, quinary formation, sixth formation, phosphoric acid passivation, first-stage repair formation, heat treatment, second-stage repair formation, and drying. The primary formation stages one through six typically use a 7wt% to 15wt% ammonium adipate solution. This process exhibits stable oxide film growth efficiency, but it is prone to hydration reactions under long-term high humidity conditions, leading to oxide film degradation, manifested as a significant extension of the voltage rise time.

[0003] Hydration resistance has become a bottleneck restricting the reliability of low-voltage aluminum foil, specifically manifested in the following ways: hydration degradation, where the oxide film reacts with water molecules to form hydrated alumina in boiling water tests, leading to a decrease in dielectric properties; voltage rise time drift, with the voltage rise time increasing by 80-120% after 6 hours of boiling, severely affecting the capacitor's fast response characteristics; and indiscriminate treatment across voltage ranges, as traditional processes do not consider the differentiated impact of different formation voltage ranges on the oxide film structure, employing a uniform bath solution formulation. Therefore, further improvements in this area are desired. Summary of the Invention

[0004] Embodiments of this disclosure provide a method for forming aluminum foil, comprising: performing a multi-stage formation process on the aluminum foil, the multi-stage formation process including three to eight stages of formation; wherein, for aluminum foil with a target formation withstand voltage greater than or equal to 145V and less than or equal to 185V, a first mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the first stage of formation; for aluminum foil with a target formation withstand voltage greater than or equal to 105V and less than 145V, a second mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the second stage of formation; and for aluminum foil with a target formation withstand voltage greater than or equal to 65V and less than 105V, a third mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the tertiary stage of formation.

[0005] In some embodiments, the mass concentration of ammonium adipate in the first mixture is 7% to 15%, and the mass concentration of ammonium dihydrogen phosphate is 0.1% to 1%.

[0006] In some embodiments, the mass concentration of ammonium adipate in the first mixture is 8% to 12%, and the mass concentration of ammonium dihydrogen phosphate is 0.3% to 0.8%.

[0007] In some embodiments, the mass concentration of ammonium adipate in the second mixture is 7% to 15%, and the mass concentration of ammonium dihydrogen phosphate is 0.1% to 1%.

[0008] In some embodiments, the mass concentration of ammonium adipate in the second mixture is 8% to 12%, and the mass concentration of ammonium dihydrogen phosphate is 0.3% to 0.8%.

[0009] In some embodiments, the mass concentration of ammonium adipate in the third mixture is 7% to 15%, and the mass concentration of ammonium dihydrogen phosphate is 0.1% to 1%.

[0010] In some embodiments, the mass concentration of ammonium adipate in the third mixture is 8% to 12%, and the mass concentration of ammonium dihydrogen phosphate is 0.3% to 0.8%.

[0011] In some embodiments, the multi-stage formation process includes a six-stage formation process, with each stage having a formation temperature of 75°C to 85°C and a formation time of 8 min to 12 min. The voltages used in the first to sixth stages of formation are 10% to 12%, 38% to 42%, 66% to 70%, 82% to 86%, 91% to 95%, and 95% to 99% of the target formation withstand voltage, respectively. For aluminum foil with a target formation withstand voltage greater than or equal to 145V and less than or equal to 185V, a first mixture of ammonium adipate and ammonium dihydrogen phosphate is used only in the first stage of formation. For aluminum foil with a target formation withstand voltage greater than or equal to 105V and less than 145V, a second mixture of ammonium adipate and ammonium dihydrogen phosphate is used only in the second stage of formation. For aluminum foil with a target formation withstand voltage greater than or equal to 65V and less than 105V, a third mixture of ammonium adipate and ammonium dihydrogen phosphate is used only in the third stage of formation.

[0012] In some embodiments, the method further includes: after a multi-stage formation process, performing phosphate passivation, primary repair formation, heat treatment, secondary repair formation, and drying on the aluminum foil.

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

[0014] This disclosure improves the hydration resistance of aluminum foil by introducing ammonium dihydrogen phosphate (NH4H2PO4) in advance during the main formation stage for aluminum foils with different target formation pressure resistance stages, and by utilizing its electrochemical behavior in specific formation stages to optimize the density and chemical stability of the oxide film. Attached Figure Description

[0015] Figure 1 A schematic flowchart of a method for forming aluminum foil according to some embodiments is shown. Detailed Implementation

[0016] 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.

[0017] 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.

[0018] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0019] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0020] 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.

[0021] 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.

[0022] This disclosure significantly improves the hydration resistance of aluminum foil by precisely controlling process parameters while maintaining the formation efficiency and electrical properties of the product, thereby reducing the pressure rise time after 6 hours of boiling in water by more than 50%.

[0023] like Figure 1 As shown, embodiments of this disclosure provide a method for forming aluminum foil, comprising: performing a multi-stage formation process on the aluminum foil, the multi-stage formation process including three to eight stages of formation. In some embodiments, the multi-stage formation process includes three, four, five, six, seven, or eight stages of formation. Figure 1 As shown, in some embodiments, for aluminum foil with a target forming withstand voltage greater than or equal to 145V and less than or equal to 185V, a first mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the primary forming process. For example... Figure 1 As shown, in some embodiments, for aluminum foil with a target forming withstand voltage greater than or equal to 105V and less than 145V, a second mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the secondary forming process. For example... Figure 1As shown, in some embodiments, for aluminum foil with a target forming withstand voltage greater than or equal to 65V and less than 105V, a third mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the three-stage forming process. That is, for aluminum foil or capacitors with different target withstand voltage ranges, ammonium dihydrogen phosphate is added to the bath solution at a specific forming level. The target forming withstand voltage of the aluminum foil corresponds to the DC withstand voltage value that the aluminum foil can withstand after the complete forming process (i.e., the breakdown voltage corresponding to the oxide film thickness). This voltage directly determines what rated voltage capacitor it can be used to manufacture.

[0024] Typically, the oxide film thickness of aluminum foil increases with the target formation withstand voltage, leading to more defects in the oxide film and consequently, poorer hydration resistance. Therefore, for aluminum foils with higher target formation withstand voltage, ammonium dihydrogen phosphate is introduced in the first-stage formation process to generate aluminum phosphate, hindering the migration of oxygen-containing substances into the oxide film, reducing the possibility of aluminum hydroxide formation, and decreasing internal defects, thereby improving the hydration resistance of the aluminum foil. For aluminum foils with relatively lower target formation withstand voltage, ammonium dihydrogen phosphate can be introduced in later formation stages (e.g., second- or third-stage formation). After the fourth-stage formation, when the oxide film is largely formed, introducing ammonium dihydrogen phosphate at this point only improves the surface layer with limited effect. By introducing ammonium dihydrogen phosphate earlier in the main formation stage for aluminum foils with different target formation withstand voltage ranges, its electrochemical behavior at specific formation stages can optimize the density and chemical stability of the oxide film, significantly improving the hydration resistance of the aluminum foil.

[0025] In some embodiments, the mass concentration of ammonium adipate in the first mixture is 7% to 15%, and the mass concentration of ammonium dihydrogen phosphate is 0.1% to 1%. In some embodiments, the mass concentration of ammonium adipate in the first mixture is 8% to 12%, and the mass concentration of ammonium dihydrogen phosphate is 0.3% to 0.8%. In some embodiments, the mass concentration of ammonium adipate in the first mixture can be 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any suitable value therebetween, and the mass concentration of ammonium dihydrogen phosphate can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any suitable value therebetween. If the concentration of ammonium adipate is too low, the conductivity of the first mixture will decrease, its buffering capacity will be weak, its pH will fluctuate easily, its oxygen evolution inhibition effect will be poor, and the membrane growth rate will be slow and uneven. If the concentration of ammonium adipate is too high, the viscosity of the first mixture will be too high, ion migration will be hindered, membrane growth will be too slow, production efficiency will decrease, and excessive organic residues may be formed, which will increase leakage current. If the concentration of ammonium dihydrogen phosphate is too low, its effect on optimizing the microstructure of the oxide film will be relatively limited. If the concentration of ammonium dihydrogen phosphate is too high, its effect on improving hydration resistance will no longer be improved, and it will instead lead to a decrease in membrane quality. This is because both adipic acid and phosphate ions are adsorbed on the aluminum surface. When the concentration of ammonium dihydrogen phosphate is too high, phosphate ions may excessively occupy reaction sites, inhibiting the beneficial effects of adipic acid ions (such as inhibiting oxygen evolution), which will lead to a decrease in membrane quality. Therefore, the concentration of ammonium dihydrogen phosphate is best kept below 0.8%.

[0026] In some embodiments, the mass concentration of ammonium adipate in the second mixture is 7% to 15%, and the mass concentration of ammonium dihydrogen phosphate is 0.1% to 1%. In some embodiments, the mass concentration of ammonium adipate in the second mixture is 8% to 12%, and the mass concentration of ammonium dihydrogen phosphate is 0.3% to 0.8%. In some embodiments, the mass concentration of ammonium adipate in the second mixture can be 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any suitable value therebetween, and the mass concentration of ammonium dihydrogen phosphate can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any suitable value therebetween. If the concentration of ammonium adipate is too low, the conductivity of the second mixture will decrease, its buffering capacity will be weak, its pH will fluctuate easily, its oxygen evolution inhibition effect will be poor, and the membrane growth rate will be slow and uneven. If the concentration of ammonium adipate is too high, the viscosity of the second mixture will be too high, ion migration will be hindered, membrane growth will be too slow, production efficiency will decrease, and excessive organic residues may be formed, which will increase leakage current. If the concentration of ammonium dihydrogen phosphate is too low, its effect of optimizing the microstructure of the oxide film will be relatively limited. If the concentration of ammonium dihydrogen phosphate is too high, its effect of improving hydration resistance will no longer be improved, and it will instead lead to a decrease in membrane quality. This is because both adipic acid and phosphate ions are adsorbed on the aluminum surface. When the concentration of ammonium dihydrogen phosphate is too high, phosphate ions may excessively occupy reaction sites, inhibiting the beneficial effects of adipic acid (such as inhibiting oxygen evolution), which will lead to a decrease in membrane quality. Therefore, the concentration of ammonium dihydrogen phosphate is best kept below 0.8%.

[0027] In some embodiments, in the third mixture, the mass concentration of ammonium adipate is 7% to 15%, and the mass concentration of ammonium dihydrogen phosphate is 0.1% to 1%. In some embodiments, in the third mixture, the mass concentration of ammonium adipate is 8% to 12%, and the mass concentration of ammonium dihydrogen phosphate is 0.3% to 0.8%. In some embodiments, in the third mixture, the mass concentration of ammonium adipate can be 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any suitable value therebetween, and the mass concentration of ammonium dihydrogen phosphate can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any suitable value therebetween. If the concentration of ammonium adipate is too low, the conductivity of the third mixture will decrease, its buffering capacity will be weak, its pH will fluctuate easily, its oxygen evolution inhibition effect will be poor, and the membrane growth rate will be slow and uneven. If the concentration of ammonium adipate is too high, the viscosity of the third mixture will be too high, ion migration will be hindered, membrane growth will be too slow, production efficiency will decrease, and excessive organic residues may be formed, which will increase leakage current. If the concentration of ammonium dihydrogen phosphate is too low, its effect on optimizing the microstructure of the oxide film will be relatively limited. If the concentration of ammonium dihydrogen phosphate is too high, its effect on improving hydration resistance will no longer be improved, and it will instead lead to a decrease in membrane quality. This is because both adipic acid and phosphate ions are adsorbed on the aluminum surface. When the concentration of ammonium dihydrogen phosphate is too high, phosphate ions may excessively occupy reaction sites, inhibiting the beneficial effects of adipic acid (such as inhibiting oxygen evolution), which will lead to a decrease in membrane quality. Therefore, the concentration of ammonium dihydrogen phosphate is best kept below 0.8%.

[0028] In some embodiments, the multi-stage formation process includes a six-stage formation process, with each stage having a formation temperature of 75°C to 85°C and a formation time of 8 min to 12 min. In some embodiments, the voltages used in the first to sixth stage formation processes are 10% to 12%, 38% to 42%, 66% to 70%, 82% to 86%, 91% to 95%, and 95% to 99% of the target formation withstand voltage, respectively. In some embodiments, for aluminum foil with a target formation withstand voltage greater than or equal to 145V and less than or equal to 185V, a first mixture of ammonium adipate and ammonium dihydrogen phosphate is used only in the first stage formation; for aluminum foil with a target formation withstand voltage greater than or equal to 105V and less than 145V, a second mixture of ammonium adipate and ammonium dihydrogen phosphate is used only in the second stage formation; and for aluminum foil with a target formation withstand voltage greater than or equal to 65V and less than 105V, a third mixture of ammonium adipate and ammonium dihydrogen phosphate is used only in the third stage formation. Adding ammonium dihydrogen phosphate in more (e.g., two, three, etc.) formation stages can easily cause a decrease in the specific capacitance of the formed capacitor.

[0029] In some embodiments, the method further includes: after a multi-stage formation process, subjecting the aluminum foil to phosphoric acid passivation, primary repair formation, heat treatment, secondary repair formation, and drying. In some embodiments, in phosphoric acid passivation, a 5wt% to 10wt% H3PO4 solution is used, the temperature is 45°C to 65°C, and the reaction time is 0.5 min to 5 min. In some embodiments, in primary repair formation, 0.5wt% to 1.5wt% ammonium dihydrogen phosphate is used, the temperature and voltage can be the same as the final stage formation, and the time can be 6 min to 10 min. In some embodiments, the heat treatment temperature is 350°C to 550°C, and the reaction time is 1 min to 5 min. In some embodiments, the parameters of secondary repair formation can be the same as those of primary repair formation. In some embodiments, the drying temperature can be 200°C to 260°C, and the time is 1 min to 3 min. It should be understood that the above-described processes of phosphoric acid passivation, primary repair formation, heat treatment, secondary repair formation, and drying are merely exemplary and are not intended to limit this disclosure.

[0030] To better understand this disclosure, specific embodiments are described below.

[0031] Example 1:

[0032] The target voltage is 160V.

[0033] Step 1: Primary formation bath solution: 10wt% ammonium adipate + 0.5wt% ammonium dihydrogen phosphate, temperature: 80℃, time: 10min, voltage: constant current boost to 19V, constant voltage maintenance;

[0034] Steps 2-6: Second to Sixth Stage Transformation

[0035] Bath solution: 10wt% ammonium adipate, temperature 80℃, time 10min

[0036] The voltages for levels 2 through 6 are 64V, 109V, 134V, 149V, and 155V, respectively.

[0037] Step 7: Phosphoric acid passivation

[0038] Bath solution: 6 wt% phosphoric acid, temperature 55℃, time 120 seconds;

[0039] Step 8: Repair and transform in one go

[0040] Bath solution: 0.8wt% ammonium dihydrogen phosphate, temperature 80℃, voltage 153V, time 8 minutes;

[0041] Step 9: Heat Treatment

[0042] Temperature: 450℃, nitrogen atmosphere, time: 2 minutes;

[0043] Step 10: Secondary Repair and Formation

[0044] Same parameters as in step 8;

[0045] Step 11: Drying

[0046] Temperature: 230℃, time: 1.5 minutes.

[0047] Comparative Example 1

[0048] The primary formation bath solution was 10 wt% ammonium adipate, and the other steps and parameters were the same as in Example 1.

[0049] Example 2

[0050] The target voltage is set to 118V.

[0051] Step 1: Primary formation bath solution: ammonium adipate 12wt%, temperature: 80℃, time: 8min, voltage: constant current boost to 14V, constant voltage maintenance;

[0052] Step 2: Secondary formation bath solution: 12wt% ammonium adipate + 0.8wt% ammonium dihydrogen phosphate, temperature: 80℃, time: 8min, voltage: 47V;

[0053] Steps 3-6: Level 3 to Level 6 transformation

[0054] Bath solution: 12wt% ammonium adipate, temperature 80℃, time 8min

[0055] The voltages for levels 3 through 6 are 80V, 99V, 110V, and 114V, respectively.

[0056] Step 7: Phosphoric acid passivation

[0057] Bath solution: 6 wt% phosphoric acid, temperature 55℃, time 120 seconds;

[0058] Step 8: Repair and transform in one go

[0059] Bath solution: 0.8wt% ammonium dihydrogen phosphate, temperature 80℃, voltage 153V, time 8 minutes;

[0060] Step 9: Heat Treatment

[0061] Temperature: 450℃, nitrogen atmosphere, time: 2 minutes;

[0062] Step 10: Secondary Repair and Formation

[0063] Same parameters as in step 8;

[0064] Step 11: Drying

[0065] Temperature: 230℃, time: 1.5 minutes.

[0066] Comparative Example 2

[0067] The secondary formation bath solution was 12 wt% ammonium adipate, and the other steps and parameters were the same as in Example 2.

[0068] Example 3

[0069] The target voltage is 92V.

[0070] Steps 1-2: Primary formation bath solution: ammonium adipate 8wt%, temperature: 80℃, time: 12min, voltage: constant current boost to 11V, constant voltage maintenance;

[0071] Step 2: Secondary formation bath solution: ammonium adipate 8wt%, temperature: 80℃, time: 12min, voltage: 37V;

[0072] Step 3: Tertiary formation bath solution: 8wt% ammonium adipate + 0.3wt% ammonium dihydrogen phosphate, temperature: 80℃, time: 12min, voltage: 63V;

[0073] Steps 4-6: Level 4 to 6 transformation

[0074] Bath solution: 8 wt% ammonium adipate, temperature 80℃, time 12 min

[0075] The voltages for levels 4 through 6 are 77V, 86V, and 89V, respectively.

[0076] Step 7: Phosphoric acid passivation

[0077] Bath solution: 6 wt% phosphoric acid, temperature 55℃, time 120 seconds;

[0078] Step 8: Repair and transform in one go

[0079] Bath solution: 0.8wt% ammonium dihydrogen phosphate, temperature 80℃, voltage 153V, time 8 minutes;

[0080] Step 9: Heat Treatment

[0081] Temperature: 450℃, nitrogen atmosphere, time: 2 minutes;

[0082] Step 10: Secondary Repair and Formation

[0083] Same parameters as in step 8;

[0084] Step 11: Drying

[0085] Temperature: 230℃, time: 1.5 minutes.

[0086] Comparative Example 3

[0087] The third-stage formation bath solution was 8 wt% ammonium adipate, and the other steps and parameters were the same as in Example 3.

[0088] In addition, parameters such as withstand voltage, boost time, and specific capacity were tested using methods commonly used in the art. Table 1 shows the test results for the comparative examples and embodiments.

[0089] Table 1

[0090]

[0091] As shown in Table 1, for the 160V product, the voltage rise time after boiling for 6 hours decreased from 85 seconds in the original process to 38 seconds, a reduction of 55.3%; for the 118V product, the voltage rise time decreased from 72 seconds to 34 seconds, a reduction of 52.8%; and for the 92V product, the voltage rise time decreased from 58 seconds to 27 seconds, a reduction of 53.4%. Furthermore, the withstand voltage and specific capacity remained stable after boiling for 6 hours, showing no significant changes.

[0092] The method disclosed herein can achieve the following benefits: (1) Improved hydration resistance: the pressure rise time after boiling in water (100°C) for 6 hours is reduced by more than 50%, which is better than the industry average; (2) Precise optimization of voltage range: the best modification time is selected according to the product characteristics of different voltage ranges to avoid over-processing; (3) Strong process compatibility: only the single formation tank formula needs to be adjusted, and there is no need to modify the production line, resulting in low cost.

[0093] 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 forming aluminum foil, characterized in that, include: A multi-stage formation process is performed on aluminum foil, the multi-stage formation process including three to eight stages of formation process; For aluminum foil with a target forming withstand voltage greater than or equal to 145V and less than or equal to 185V, only the first mixture of ammonium adipate and ammonium dihydrogen phosphate is used in the first forming stage.

2. The method according to claim 1, characterized in that, In the first mixture, the mass concentration of ammonium adipate is 7% to 15%, and the mass concentration of ammonium dihydrogen phosphate is 0.1% to 1%.

3. The method according to claim 2, characterized in that, In the first mixture, the mass concentration of ammonium adipate is 8% to 12%, and the mass concentration of ammonium dihydrogen phosphate is 0.3% to 0.8%.

4. The method according to claim 1, characterized in that, The multi-stage formation process includes a six-stage formation process. The formation temperature of each stage is 75°C to 85°C, and the formation time of each stage is 8 min to 12 min. The voltages used in the first to sixth stages of the formation process are 10% to 12%, 38% to 42%, 66% to 70%, 82% to 86%, 91% to 95%, and 95% to 99% of the target formation withstand voltage, respectively.

5. The method according to claim 1, characterized in that, Also includes: After the multi-stage formation process, the aluminum foil undergoes phosphate passivation, primary repair formation, heat treatment, secondary repair formation, and drying.

6. An aluminum foil, characterized in that, The aluminum foil is the aluminum foil obtained by the method according to any one of claims 1 to 5.

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