阅读说明：本技术 化成箔的制备方法及其应用 (Preparation method and application of formed foil ) 是由 余英凤 邓利松 李刚 何凤荣 于 2019-09-26 设计创作，主要内容包括：本发明涉及化成箔的制备方法及其应用,具体提出了化成箔的制备方法,该方法包括：将腐蚀箔在己二酸铵水溶液中进行三级化成处理；将三级化成处理后的腐蚀箔在磷酸水溶液中进行浸渍处理；将浸渍处理后的腐蚀箔在己二酸铵水溶液中进行第四级化成处理；将第四级化成处理后的腐蚀箔进行第一热处理；将第一热处理后的腐蚀箔进行第五级化成处理,以便获得所述化成箔,所述第五级化成处理是在有机膦酸和离子液体的醇类溶液中进行的。相比现有技术中的化成箔,该方法制备的化成箔在到达电压基本一致的情况下,比容没有衰减,同时耐水性显著增强。(The invention relates to a preparation method and application of a formed foil, and particularly provides a preparation method of a formed foil, which comprises the following steps: carrying out three-stage chemical conversion treatment on the etched foil in an ammonium adipate water solution; dipping the etched foil after the three-stage formation treatment in a phosphoric acid aqueous solution; carrying out fourth-stage formation treatment on the etched foil after the dipping treatment in an ammonium adipate water solution; carrying out first heat treatment on the etched foil subjected to the fourth-stage chemical conversion treatment; and carrying out fifth-stage formation treatment on the etched foil after the first heat treatment so as to obtain the formed foil, wherein the fifth-stage formation treatment is carried out in an alcohol solution of organic phosphonic acid and ionic liquid. Compared with the formed foil in the prior art, the formed foil prepared by the method has the advantages that the specific volume is not attenuated under the condition that the reaching voltage is basically consistent, and meanwhile, the water resistance is obviously enhanced.)

1. A method for preparing a formed foil is characterized by comprising the following steps:

carrying out three-stage chemical conversion treatment on the etched foil in an ammonium adipate water solution;

dipping the etched foil after the three-stage formation treatment in a phosphoric acid aqueous solution;

carrying out fourth-stage formation treatment on the etched foil after the dipping treatment in an ammonium adipate water solution;

carrying out first heat treatment on the etched foil subjected to the fourth-stage chemical conversion treatment;

and carrying out fifth-stage chemical conversion treatment on the etched foil after the first heat treatment, wherein the fifth-stage chemical conversion treatment is carried out in an alcohol solution of organic phosphonic acid and ionic liquid.

2. The method of claim 1, wherein the ionic liquid is a carboxyl-functionalized ionic liquid;

optionally, in the carboxyl functionalized ionic liquid, the cation is 1-carboxymethyl-3-methylimidazole cation or 1-carboxyethyl-3-methylimidazole cation, and the anion is nitrate ion, bis (trifluoromethanesulfonyl) imide ion or hydrogen sulfate ion;

preferably, the ionic liquid comprises at least one selected from the group consisting of 1-carboxyethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt, 1-carboxyethyl-3-methylimidazolium nitrate, 1-carboxyethyl-3-methylimidazolium hydrogen sulfate, 1-carboxymethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt, 1-carboxymethyl-3-methylimidazolium nitrate, or 1-carboxymethyl-3-methylimidazolium hydrogen sulfate;

optionally, the organophosphonic acid comprises at least one member selected from nitrilotrimethylene triphosphonic acid, hydroxyethylidene diphosphonic acid, or diethylenetriamine pentamethylene phosphonic acid;

optionally, the alcohol comprises at least one selected from the group consisting of ethylene glycol, glycerol, 1, 2-propanediol, 1, 3-propanediol, benzyl alcohol, or cyclohexanol.

3. The method of claim 1, wherein the organophosphonic acid: the ionic liquid is as follows: the mass ratio of the alcohols is 1-3:5-8:89 to 94.

4. The method of claim 1, wherein the first heat treatment is a vacuum heat treatment;

optionally, in the first heat treatment, the degree of vacuum is not higher than 200 Pa;

optionally, the first heat treatment is carried out at a temperature of 400 to 550 ℃;

optionally, the time of the first heat treatment is 5-10 min.

5. The method of claim 1, further comprising: and carrying out second heat treatment on the etched foil after the fifth-level chemical conversion treatment.

6. The method according to claim 5, wherein the second heat treatment is performed under an argon atmosphere;

optionally, the second heat treatment is carried out at a temperature of 200-300 ℃;

optionally, the time of the second heat treatment is 5-10 min.

7. The method according to claim 1, wherein in the three-stage formation treatment, the first-stage formation treatment is carried out under the condition that the voltage is 8-12V,

optionally, the second-stage chemical conversion treatment is carried out under the condition that the voltage is 18-25V,

optionally, the third-stage chemical conversion treatment is carried out under the condition that the voltage is 32-36V;

optionally, the fourth formation treatment is carried out under the condition that the voltage is 32-36V;

optionally, the fifth-stage chemical treatment is carried out under the condition that the voltage is 32-36V;

optionally, the first stage of formation treatment, the second stage of formation treatment, the third stage of formation treatment and the fourth stage of formation treatment are carried out at the temperature of 70-80 ℃;

optionally, the fifth-stage chemical conversion treatment is carried out at the temperature of 50-70 ℃;

optionally, the time of the first-stage formation treatment, the second-stage formation treatment, the third-stage formation treatment and the fourth-stage formation treatment is 5-10 min;

optionally, the time of the fifth-stage chemical conversion treatment is 4-8 min;

optionally, the dipping treatment is carried out at the temperature of 30-50 ℃;

optionally, the time of the dipping treatment is 4-8 min.

8. The method according to claim 1, wherein in the ammonium adipate water solution, the mass fraction of ammonium adipate is 5-10%;

optionally, in the phosphoric acid aqueous solution, the mass fraction of phosphoric acid is 1-3%.

9. A chemical foil produced by the method according to any one of claims 1 to 8.

10. An electrolytic capacitor, comprising: the formed foil of claim 9.

Technical Field

The invention relates to the field of anode corrosion formed foil for an aluminum electrolytic capacitor, in particular to a preparation method and application of the formed foil.

Background

Along with the development of miniaturization of the whole electronic equipment, urgent needs are brought to the volume reduction and specific volume improvement of the aluminum electrolytic capacitor, and the anodic formed foil is used as a core material in the aluminum electrolytic capacitor and plays a decisive role in various characteristics of the capacitor. The existing low-voltage anode foil formation process generally comprises three-stage formation, high-temperature heat treatment and four-stage formation in a solution of boric acid and borax and an adipate water solution, and finally dipping treatment in an ammonium dihydrogen phosphate solution. In the low-voltage aluminum electrolytic capacitor, the moisture content of the electrolyte is high, and an oxide film on the surface of the electrode foil and water undergo a hydration reaction to produce hydrated alumina or aluminum hydroxide, so that the withstand voltage of the electrode foil is reduced, and the leakage current is increased. Hydrogen is generated during hydration reaction, so that the internal pressure of a capacitor shell rises, the capacitor expands, leaks and even explodes, the service lives of the capacitor and an electronic product are influenced, and safety problems are caused.

Chinese patent CN201811533670.4 discloses a process method for improving the water resistance of formed foil, which is characterized by comprising the following steps: 1. soaking the formed foil into a phosphoric acid aqueous solution, and then washing with ionized water; 2. carrying out high-temperature heat treatment on the formed foil washed in the step 1; 3. soaking the formed foil subjected to high-temperature heat treatment in the step 2 into a mixed solution of ammonium adipate and ammonium dihydrogen phosphate, and cleaning with ionized water; 4. soaking the washed formed foil into sodium polyacrylate, and then washing with ionized water; 5. carrying out normal-temperature heat treatment on the formed foil washed in the step 4; 6. and (5) taking out the treated formed foil after the temperature of the formed foil subjected to the heat treatment in the step (5) is reduced.

Chinese patent CN 201711084924.4 discloses a treatment method and application for improving water resistance of a low-voltage electrode foil, which is characterized by comprising the following steps: placing the aluminum foil after corrosion treatment in an aqueous solution of azelaic acid and azelaic acid salt, soaking the aluminum foil in an aqueous solution of propyl titanate after formation and washing, then placing the aluminum foil in an aqueous solution of azelaic acid and azelaic acid salt, placing the aluminum foil in an aqueous solution of phosphoric acid after formation and washing, passivating at the temperature of 30-45 ℃, then performing heat treatment at the temperature of 400-600 ℃, placing the aluminum foil after washing in an aqueous solution of titanium phosphate, washing with formation water, and drying to obtain the low-voltage electrode foil.

The low-pressure formed foil obtained by the preparation method disclosed by the prior art has poor water resistance, and further improvement space exists.

Disclosure of Invention

The present application is based on the discovery and recognition by the inventors of the following facts and problems:

the conventional method for improving the water resistance of the low-pressure formed foil is to use a phosphorus-containing substance in pretreatment or formation to react with hydrated alumina or aluminum hydroxide on the surface of the formed foil to generate aluminum phosphate, so as to play a role in enhancing the water resistance. Since the formation reaction is generally carried out in an aqueous solution system, a large amount of hydrated alumina or aluminum hydroxide is inevitably produced on the surface of the oxide film, and these substances are poor in water resistance. On one hand, the crystal form alumina film with better water resistance can be converted into a crystal form alumina film with better water resistance by partial dehydration through heat treatment; on the other hand, by reacting with phosphoric acid or a phosphate substance, a part of the aluminum hydroxide is dissolved or converted into a phosphate film, but only a small amount of hydrated alumina or aluminum hydroxide is converted or dissolved by both of these effects, and a large amount of hydrated alumina or aluminum hydroxide is still present, resulting in poor water resistance of the formed foil. Based on the above problems, the present inventors propose a novel method for producing a formed foil, which significantly increases the water resistance of the formed foil produced by the method compared to conventional formed foils.

To this end, in a first aspect of the invention, the invention proposes a method for producing a chemical foil. According to an embodiment of the invention, the method comprises: carrying out three-stage chemical conversion treatment on the etched foil in an ammonium adipate water solution; dipping the etched foil after the three-stage formation treatment in a phosphoric acid aqueous solution; carrying out fourth-stage formation treatment on the etched foil after the dipping treatment in an ammonium adipate water solution; carrying out first heat treatment on the etched foil subjected to the fourth-stage chemical conversion treatment; and carrying out fifth-stage formation treatment on the etched foil after the first heat treatment so as to obtain the formed foil, wherein the fifth-stage formation treatment is carried out in an alcohol solution of organic phosphonic acid and ionic liquid. The inventors have found that the re-generation of hydrated alumina or aluminum hydroxide during the remedial formation can be avoided by using a non-aqueous formation liquid instead of an aqueous formation liquid in the fifth-stage formation treatment. However, in organic solvent systems, the solubility of common inorganic salts is poor, and the conductivity of the liquid is insufficient, and thus the inorganic salts cannot be used in chemical conversion. The ionic liquid is in a liquid state while having high conductivity, and can be mutually soluble with an organic solvent in any proportion, so that the ionic liquid can be used for replacing the traditional inorganic salt. However, since the ionic liquid has the characteristics of high conductivity and high oxidation efficiency, under the condition of formation and electrification, the ionic liquid is decomposed and consumed preferentially, so that the formed liquid is unstable, and the performance uniformity of the formed foil is poor; meanwhile, under high voltage, the ionic liquid is easy to decompose, and the application range of the ionic liquid is further limited. The inventor of the application discovers through a large number of experiments that the organic phosphonic acid has good chelating and low-limit inhibition capability, and can form strong complexing action with the ionic liquid, so that on one hand, the ionic liquid can be stabilized, the decomposition voltage of the ionic liquid can be improved, and meanwhile, the consumption rate of the ionic liquid can be regulated and controlled by controlling the addition amount of the organic phosphonic acid, so that the composition of the formed liquid is in a controllable range, and the uniformity of the performance of the formed foil is further ensured. On the other hand, due to the synergistic effect of the ionic liquid and the organic phosphonic acid, a compact and wide phosphating film layer can be rapidly formed on the surface of the oxide film after the oxide film is generated, the competition of a phosphating reaction and a hydration degradation reaction in water system formation is effectively avoided, and the water resistance of the formed foil is further improved. In addition, the alcohol organic solvent contains a large amount of hydroxyl, and can be complexed with organic phosphonic acid and the ionic liquid to form a hydrogen bond, so that the dissolving amount and stability of the ionic liquid and the organic phosphonic acid are further enhanced. Therefore, the formed foil prepared by the method according to the embodiment of the invention can have no attenuation of specific volume and remarkably enhanced water resistance compared with the formed foil in the prior art under the condition of basically consistent arrival voltage through the mutual synergistic cooperation of the ionic liquid, the organic phosphoric acid and the alcohol solvent in the fifth-level formation treatment.

According to an embodiment of the present invention, the method may further include at least one of the following additional technical features:

according to an embodiment of the present invention, the ionic liquid is a carboxyl functionalized ionic liquid. The inventor finds that the carboxyl functionalized ionic liquid has strong acidity, strong oxidation capacity and metal complexing capacity relative to other ionic liquids, and has good performance on dissolving metal oxides and metal compounds. In the formation process, on one hand, hydrated alumina and aluminum hydroxide generated on the surface of the formed foil in the water-based formation liquid can be dissolved to the maximum extent, and on the other hand, due to the strong oxidizing capability of the hydrated alumina and the aluminum hydroxide, the hydrated alumina and the aluminum hydroxide can be rapidly promoted to be converted into crystal form alumina, so that the proportion of the crystal form alumina in the oxide film layer is increased. Thus, the formed foil prepared according to the method of the embodiment of the present invention is better in water resistance.

According to an embodiment of the present invention, in the carboxyl functional ionic liquid, the cation is 1-carboxymethyl-3-methylimidazole cation or 1-carboxyethyl-3-methylimidazole cation, and the anion is nitrate ion, bis (trifluoromethanesulfonyl) imide ion or hydrogen sulfate ion. In some embodiments, the ionic liquid comprises at least one selected from the group consisting of 1-carboxyethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt, 1-carboxyethyl-3-methylimidazolium nitrate, 1-carboxyethyl-3-methylimidazolium hydrogen sulfate, 1-carboxymethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt, 1-carboxymethyl-3-methylimidazolium nitrate, and 1-carboxymethyl-3-methylimidazolium hydrogen sulfate. Thus, the formed foil prepared according to the method of the embodiment of the present invention is better in water resistance.

According to an embodiment of the invention, the organophosphonic acid comprises at least one selected from nitrilotrimethylene triphosphonic acid, hydroxyethylidene diphosphonic acid, diethylenetriamine pentamethylene phosphonic acid. Thus, the formed foil prepared according to the method of the embodiment of the present invention is better in water resistance.

According to an embodiment of the present invention, the alcohol includes at least one selected from the group consisting of ethylene glycol, glycerol, 1, 2-propanediol, 1, 3-propanediol, benzyl alcohol, and cyclohexanol. The inventor finds that a large amount of hydroxyl groups in the alcohol solvent can be complexed with the ionic liquid to further stabilize the finished liquid. Thus, the formed foil prepared according to the method of the embodiment of the present invention has higher voltage and better water resistance.

According to an embodiment of the present invention, the organophosphonic acid: the ionic liquid is as follows: the mass ratio of the alcohols is (1-3): (5-8): (89-94), such as 1: (5-8): (89-94), 2: (5-8): (89-94), 3: (5-8): (89-94), (1-3): 5: (89-94), (1-3): 6: (89-94), (1-3): 7: (89-94), (1-3): 8: (89-94), (1-3): (5-8): 89. (1-3): (5-8): 90. (1-3): (5-8): 91. (1-3): (5-8): 92. (1-3): (5-8): 93 or (1-3): (5-8): 94. specifically, the organic phosphonic acid: the ionic liquid is as follows: the mass ratio of the alcohols is 1:5: 94. 3:8:89 or 2:6: 92. the inventor finds that the amounts of the ionic liquid, the organic phosphonic acid and the alcohol solvent are required to be kept in a proper proportion range, when the content of the ionic liquid is too high, the amount of the organic phosphonic acid is not enough to perform complete complexation, so that part of the ionic liquid is rapidly consumed, the formed liquid is unstable, the ionic liquid is greatly consumed at the formation starting stage, the conductivity of the formed bath is rapidly reduced, the bath pressure is higher, and the finally obtained formed foil voltage is lower. Meanwhile, when the content of the ionic liquid is too high, the formed liquid is sticky and difficult to enter holes of the formed foil, so that the formed effect is poor. When the content of organic phosphonic acid is higher, the free organic phosphonic acid will corrode the formed foil, so that the capacity of the formed foil is reduced. Thus, the organic phosphonic acid: the ionic liquid is as follows: when the mass ratio of the alcohol solvent is within the range, the formed foil prepared by the method of the embodiment of the invention has higher voltage, higher capacity and better water resistance.

According to an embodiment of the invention, the first heat treatment is a vacuum heat treatment. The first heat treatment can promote the conversion of hydrated alumina and aluminum hydroxide to crystal form alumina, the crystal shrinkage is accompanied while the crystal form conversion, so that the oxide film layer has defects or an unformed part is exposed, and chemical liquid enters the defects or the unformed part for repairing and forming during later formation to improve the quality of the oxide film. The inventors have found that the first heat treatment carried out in a vacuum environment promotes, on the one hand, the evaporation of the residual water in the pores of the formed foil; on the other hand, the conversion of hydrated alumina and aluminum hydroxide to crystalline alumina can be further promoted. Thus, the water resistance of the formed foil prepared according to the method of the embodiment of the present invention is further improved.

According to an embodiment of the present invention, in the first heat treatment, the degree of vacuum is not higher than 200 Pa. Specifically, the degree of vacuum is 100Pa, 120Pa, 150Pa, 160Pa, 180Pa, or 200 Pa. The inventors found that if the degree of vacuum is too high, the water resistance of the resultant foil is significantly reduced. Thus, in the first heat treatment, when the degree of vacuum is not higher than 200Pa, the water resistance of the formed foil produced by the method according to the embodiment of the present invention is further improved.

According to an embodiment of the present invention, the first heat treatment is performed at a temperature of 400 to 550 ℃, such as 420, 440, 460, 480, 500, 520 or 540 ℃. Therefore, evaporation of residual water in pores of the formed foil can be further promoted, conversion of hydrated alumina and aluminum hydroxide to crystal form alumina can be further promoted, and the prepared formed foil is better in water resistance.

According to an embodiment of the present invention, the time of the first heat treatment is 5 to 10min, such as 6, 7, 8 or 9 min.

According to an embodiment of the invention, the method further comprises: and carrying out second heat treatment on the etched foil after the fifth-level chemical conversion treatment. The inventors have found that by adding the secondary high-temperature treatment, the formation liquid (water, ionic liquid, ammonium adipate, organic phosphonic acid, etc.) remaining in the pores of the formation foil can be volatilized or decomposed, thereby reducing dissolution or corrosion of the formation liquid on the oxide film. Thus, the water resistance of the formed foil prepared according to the method of the embodiment of the present invention is further improved.

According to an embodiment of the invention, the second heat treatment is performed under an argon atmosphere. According to an embodiment of the present invention, the purity of the argon gas is not less than 99.99%. The inventors have found that when the second heat treatment is carried out in air, oxygen in the air reacts with the phosphate film on the surface of the oxide film to break the phosphate film, resulting in deterioration of the water resistance of the formed foil. When the secondary high-temperature treatment is carried out in the argon atmosphere, the phosphating film can be effectively prevented from being damaged in the high-temperature aerobic atmosphere; meanwhile, the argon can be adsorbed in the loose hydrated oxide film layer to play a role in protecting the loose hydrated oxide film layer. Thus, when the second heat treatment is performed under an argon atmosphere, the water resistance of the formed foil produced by the method according to the embodiment of the present invention is further improved.

According to an embodiment of the present invention, the second heat treatment is performed at a temperature of 200 to 300 ℃, such as 220, 240, 250, 260 or 280 ℃. The inventor finds that the temperature of the secondary heat treatment cannot be too high, crystal form conversion can occur due to the too high temperature, defects are generated, and the leakage current of the formed foil is increased. Therefore, when the temperature of the second heat treatment is 200-300 ℃, the formed foil prepared by the method provided by the embodiment of the invention has better water resistance.

According to an embodiment of the present invention, the time of the second heat treatment is 5 to 10min, such as 6, 7, 8 or 9 min.

According to an embodiment of the invention, in the three-stage formation treatment, the first-stage formation treatment is performed at a voltage of 8-12V, such as 9, 10 or 11V. According to an embodiment of the present invention, in the three-stage formation process, the second-stage formation process is performed at a voltage of 18-25V, such as 19, 20, 21, 22, 23 or 24V. According to an embodiment of the present invention, in the three-stage formation process, the third-stage formation process is performed at a voltage of 32-36V, such as 33, 34 or 35V. According to an embodiment of the present invention, the fourth formation treatment is performed at a voltage of 32 to 36V, such as 33, 34 or 35V. According to an embodiment of the present invention, the fifth-stage formation treatment is performed at a voltage of 32 to 36V, such as 33, 34 or 35V. Thus, the formed foil prepared according to the method of the embodiment of the present invention is better in water resistance.

According to an embodiment of the invention, the first, second, third and fourth formation treatments are carried out at a temperature of 70 to 80 ℃, such as 72, 74, 76 or 78 ℃. The temperatures of the first formation treatment, the second formation treatment, the third formation treatment and the fourth formation treatment may be the same or different. According to an embodiment of the invention, the fifth-stage chemical treatment is performed at a temperature of 50-70 ℃, such as 52, 54, 56, 58, 60, 62, 64, 66 or 68 ℃. Thus, the formed foil prepared according to the method of the embodiment of the present invention is better in water resistance.

According to the embodiment of the invention, the time of the first stage formation treatment, the second stage formation treatment, the third stage formation treatment and the fourth stage formation treatment is 5-10min, such as 6, 7, 8 or 9 min. It should be noted that the time of the first-stage formation processing, the second-stage formation processing, the third-stage formation processing, and the fourth-stage formation processing may be the same or different. According to the embodiment of the invention, the time of the fifth-stage formation treatment is 4-8min, such as 5, 6 or 7 min.

According to an embodiment of the invention, the impregnation is carried out at a temperature of 30 to 50 ℃, such as 32, 34, 36, 38, 40, 42, 44, 46 or 48 ℃. According to an embodiment of the invention, the time of the impregnation treatment is 4-8min, such as 5, 6 or 7 min. Thus, the formed foil prepared according to the method of the embodiment of the present invention is better in water resistance.

According to the embodiment of the invention, the mass fraction of the ammonium adipate in the ammonium adipate water solution is 5-10%, such as 6%, 7%, 8% or 9%. According to the embodiment of the invention, the phosphoric acid in the phosphoric acid aqueous solution has a mass fraction of 1-3%, such as 1.5%, 2% or 2.5%. Thus, the formed foil prepared according to the method of the embodiment of the present invention is better in water resistance.

In a second aspect of the invention, the invention proposes a formed foil, which is prepared by a method according to any one of the preceding claims, according to an embodiment of the invention. The inventor finds that compared with the formed foil in the prior art, the formed foil according to the embodiment of the invention can achieve no attenuation of specific volume and simultaneously remarkably enhance water resistance under the condition of basically consistent arrival voltage.

In a third aspect of the present invention, an electrolytic capacitor is provided. According to an embodiment of the invention, the electrolytic capacitor comprises a formed foil prepared by the method described above.

Detailed Description

The following detailed description of embodiments of the invention is intended to be illustrative, and not to be construed as limiting the invention.

The purpose of the invention is realized by the following technical scheme:

the water-resistant low-pressure formed foil and the preparation method thereof comprise the following steps:

A. and (3) placing the low-pressure corrosion foil in 5-10% by mass of ammonium adipate water solution, applying 8-12V voltage at 70-80 ℃, and performing first-stage formation for 5-10 min.

B. And (3) placing the foil subjected to the first-stage formation in 5-10% by mass of ammonium adipate water solution, applying a voltage of 18-25V at 70-80 ℃, and performing second-stage formation for 5-10 min.

C. And (3) placing the foil subjected to the second-stage formation in 5-10% by mass of ammonium adipate water solution, applying a voltage of 32-36V at 70-80 ℃, and performing third-stage formation for 5-10 min.

D. And (3) soaking the foil subjected to the third-stage formation in 1-3% phosphoric acid water solution at the temperature of 30-50 ℃ for 4-8 min.

E. And (3) placing the foil subjected to the phosphoric acid dipping treatment in an ammonium adipate water solution with the mass fraction of 5-10%, applying a voltage of 32-36V at 70-80 ℃, and performing fourth-stage formation for 5-10 min.

F. And (3) placing the foil subjected to the fourth-stage formation at the temperature of 400-550 ℃ for first heat treatment, wherein the vacuum degree is below 200Pa, and the treatment time is 5-10 min.

G. And (3) placing the foil subjected to the first heat treatment in an alcohol solution of organic phosphonic acid and ionic liquid, applying a voltage of 32-36V at 50-70 ℃, and performing fifth-stage formation for 4-8 min. The fifth-grade formed liquid comprises organic phosphonic acid in a mass ratio: ionic liquid: the alcohol solvent is 1-3:5-8: 89-94.

H. And carrying out second heat treatment on the foil subjected to the fifth-stage treatment. The mixture is placed at the temperature of 200 ℃ and 300 ℃ under the argon atmosphere, the treatment time is 5-10min, and the argon purity is 99.99%.

In some embodiments, the organophosphonic acid comprises at least one member selected from the group consisting of nitrilotrimethylene triphosphonic acid, hydroxyethylidene diphosphonic acid, diethylenetriamine pentamethylene phosphonic acid.

In some embodiments, the ionic liquid comprises at least one selected from the group consisting of 1-carboxyethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt, 1-carboxyethyl-3-methylimidazolium nitrate, 1-carboxyethyl-3-methylimidazolium hydrogen sulfate, 1-carboxymethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt, 1-carboxymethyl-3-methylimidazolium nitrate, and 1-carboxymethyl-3-methylimidazolium hydrogen sulfate. In some embodiments, the ionic liquid comprises at least one selected from the group consisting of 1-carboxyethyl-3-methylimidazole nitrate, 1-carboxyethyl-3-methylimidazole hydrogensulfate, 1-carboxyethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt.

In some embodiments, the alcoholic solvent includes at least one selected from the group consisting of ethylene glycol, glycerol, 1, 2-propanediol, 1, 3-propanediol, benzyl alcohol, cyclohexanol.

The technical effects are as follows:

the method of the invention can reduce the generation of hydrated alumina and aluminum hydroxide on one hand, promote the conversion of the hydrated alumina and the aluminum hydroxide to crystal form alumina on the other hand, simultaneously generate compact and more widely covered phosphating films on the surface and enhance the water resistance of low-pressure formed foil.

The present invention will be further described with reference to specific embodiments, but the present invention is not limited to the examples in any way.