Aluminum-based composite anode foil and its preparation method

Abstract

This invention relates to the field of anode foil preparation technology, specifically to a composite anode foil based on an aluminum substrate and its preparation method, comprising the following steps: S1. Aluminum foil pretreatment; S2. Corrosion modification; S3. Medium-temperature thermal curing. This invention provides a chemical basis for the high-concentration, stable existence and uniform transport of titanium ions in the etching solution through a modified complexing agent; the modified etching solution enables the expansion and pore formation of the aluminum foil and the in-situ uniform anchoring of the TiO2 precursor on the inner wall of the pores; the modified formation solution achieves in-situ defect repair, effectively reducing leakage current and improving withstand voltage stability. The synergistic effect of the modified complexing agent, modified etching solution, and modified formation solution achieves a synergistic optimization between a significant increase in the specific capacitance of the composite anode foil and effective suppression of leakage current, significantly improving the overall electrical performance of the product while simplifying the process, and has good prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of anode foil preparation technology, specifically to composite anode foil based on an aluminum substrate and its preparation method. Background Technology

[0002] Aluminum electrolytic capacitors are widely used in electronic devices such as household appliances, industrial power supplies, new energy power generation, new energy vehicles, and 5G communication systems due to their advantages such as large capacitance per unit volume and low cost. The anode foil, as the core component of aluminum electrolytic capacitors, directly determines key technical indicators such as capacitance, leakage current, losses, lifespan, and reliability. With the continuous development of electronic devices towards miniaturization, lightweighting, and high frequency operation, the demand for improving the specific capacitance of the anode foil is becoming increasingly urgent.

[0003] Currently, the overall technical level of domestic electrode foil products still lags behind international advanced levels. The specific capacitance of domestically produced electrode foil is about 30% lower than the world's advanced level. Specifically, there are significant gaps in terms of pit density, uniformity of pit distribution, and dielectric properties of oxide film. Every year, a large amount of high-end electrode foil needs to be imported from countries such as Japan and South Korea to meet the domestic market's production demand for high-capacity, miniaturized aluminum electrolytic capacitors.

[0004] The main approaches to improving the specific capacitance of anodic foil can be categorized into three types: increasing the specific surface area of ​​the anodic oxide film; increasing the relative permittivity of the oxide film; and reducing the thickness of the oxide film. In traditional industrial processes, electrochemical corrosion is commonly used to create and expand pores in high-purity aluminum foil. This increases the specific surface area by generating numerous sponge-like or tunnel-like micropores on and inside the foil. Then, anodizing is performed to form an Al2O3 dielectric film on the pore walls, resulting in an etched foil. However, Al2O3 has a relatively low permittivity, typically around 8-10, and after years of electrochemical surface-expanding corrosion, the specific surface area of ​​the aluminum alloy foil has reached its limit. Relying solely on a pure Al2O3 dielectric film or simply increasing the corrosion expansion ratio is insufficient to meet the ever-growing demand for high specific capacitance.

[0005] Therefore, the efficient integration of corrosion-induced pore formation and surface expansion with the introduction of high dielectric constant materials, and the effective repair of micro-defects in composite dielectric films through formation processes, has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a composite anode foil based on an aluminum substrate and a method for preparing the same.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The method for preparing composite anode foil based on an aluminum substrate includes the following preparation steps: S1. Aluminum foil pretreatment: Immerse high-purity aluminum foil in sodium hydroxide solution at 50-80℃ for 30-120s, and rinse with deionized water to obtain pretreated high-purity aluminum foil; S2. Corrosion modification: Immerse the pretreated high-purity aluminum foil obtained in step S1 into the modified etching solution and soak it at 50-80℃ for 10-30 minutes, accompanied by ultrasonic waves during the etching process; S3. Medium-temperature heat curing: Take out the aluminum foil after corrosion modification in step S2, clean it with deionized water, dry it and then perform medium-temperature heat curing treatment. S4. Anodizing: The aluminum foil cured in step S3 is anodized in a modified forming solution using a stepped pressure increase method. After being cleaned with deionized water and dried, a composite anode foil based on an aluminum substrate is finally obtained. The preparation of the modified etchant includes the following steps: S21. By mass, 100-110 parts of acid mixture and 500-600 parts of deionized water are stirred and mixed at 5-10℃ and 100-200 r / min to obtain a primary mixture; S22. Maintaining the stirring speed in step S21, slowly add 20-30 parts of titanium tetrachloride, 10-15 parts of tetrabutyl titanate and 3-8 parts of modified complexing agent to the primary mixture, and completely dissolve to obtain the secondary mixture; S23. Add 0.5-1 parts sodium dodecylbenzenesulfonate, 3-5 parts PEG-400, 8-12 parts hydrogen peroxide and 150-200 parts deionized water to the secondary mixture obtained in step S22, and stir evenly to obtain the modified corrosion solution.

[0008] Preferably, the preparation of the modified complexing agent includes the following steps: S221. Dissolve 2-5 parts of citric acid in 10-20 parts of deionized water by weight, and stir at 100-150 r / min at 25-30℃ until completely dissolved to obtain an aqueous solution of citric acid. S222. Dissolve 5-10 parts of acetylacetone in 20-40 parts of anhydrous ethanol, and stir until completely dissolved to obtain an acetylacetone-ethanol mixture. S223. The citric acid aqueous solution obtained in step S221 is slowly added dropwise to the acetylacetone-ethanol mixture at a speed of 150-200 r / min. After the addition is complete, the mixture is stirred for 8-10 min and then aged at 2-8℃ for 2-3 h to finally obtain the modified complexing agent.

[0009] Preferably, the preparation of the modified formation liquid includes the following steps: S41. By mass, mix 40-60 parts ammonium adipate, 8-12 parts ammonium borate, 1-3 parts ammonium pentaborate with 700-800 parts deionized water and stir at 40-50℃ for 10-15 minutes. S42. Add 0.5-1 part of citric acid to the solution obtained in step S41, control the pH at 6-7 using dilute ammonia, add 0.1-0.3 parts of PEG-6000, and stir until completely dissolved; S43. Add 2-4 parts of nano silica hydrosol (particle size 10-20nm, solid content 30%) dropwise to the solution obtained in step S42, and then ultrasonically disperse at a frequency of 40kHz for 3-5 minutes to obtain the modified solution.

[0010] Preferably, the curing temperature for the medium-temperature heat curing treatment is 300-500℃, the heating rate is 5-10℃ / min, and the holding time is 15-60min.

[0011] Preferably, the constant current density of the stepped voltage boost method is 0.5-2 mA / cm². 2 The temperature is 30-50℃, and the voltage is increased to the rated voltage of 50-250V and then cooled to 15-25℃, and maintained for 10-20 minutes.

[0012] Preferably, the acid mixture is composed of hydrochloric acid, sulfuric acid, and phosphoric acid in a mass ratio of 10:1:0.8.

[0013] Preferably, the concentration of the sodium hydroxide solution in step S1 is 0.5-2 mol / L.

[0014] Preferably, the frequency of the ultrasonic wave in step S2 is 30-40kHz.

[0015] Preferably, the stirring speed in step S41 is 100-200 r / min.

[0016] The composite anode foil based on an aluminum substrate was prepared by the above-described method.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a chemical basis for the stable high-concentration and uniform transport of titanium ions in the etching solution through a modified complexing agent; the modified etching solution enables the expansion and pore formation of aluminum foil and the in-situ uniform anchoring of TiO2 precursors on the inner wall of the pores; the modified formation solution enables in-situ defect repair, effectively reducing leakage current and improving withstand voltage stability. The synergistic effect of the modified complexing agent, modified etching solution, and modified formation solution achieves a synergistic optimization between a significant increase in the specific capacitance of the composite anode foil and effective suppression of leakage current, significantly improving the overall electrical performance of the product while simplifying the process, and has good prospects for industrial application. Attached Figure Description

[0018] Figure 1 This is a process flow diagram for the preparation of the composite anode foil based on an aluminum substrate according to the present invention; Figure 2 This is a flow chart of the preparation process of the modified corrosive liquid of the present invention; Figure 3 This is a flow chart of the preparation process of the modified chemical solution of the present invention; Figure 4 This is a process flow diagram for preparing the modified complexing agent of the present invention. Detailed Implementation

[0019] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Please see Figures 1-4 The present invention provides a technical solution: Example 1 Preparation method of composite anode foil based on aluminum substrate: Before preparing the composite anode foil based on the aluminum substrate, the modified complexing agent, modified etching solution, and modified formation solution are prepared first: The preparation of the modified complexing agent includes the following steps: S221. Dissolve 2g of citric acid in 10g of deionized water and stir at 100r / min at 25℃ until completely dissolved to obtain an aqueous solution of citric acid; S222. Dissolve 5g of acetylacetone in 20g of anhydrous ethanol and stir until completely dissolved to obtain an acetylacetone-ethanol mixture. S223. The citric acid aqueous solution obtained in step S221 is slowly added dropwise to the acetylacetone-ethanol mixture at a speed of 150 r / min. After the addition is complete, the mixture is stirred for 8 min and then aged at 2℃ for 2 h to finally obtain the modified complexing agent.

[0021] The preparation of the modified etchant includes the following steps: S21. Mix 100g of acid mixture (hydrochloric acid, sulfuric acid, and phosphoric acid in a mass ratio of 10:1:0.8) with 500g of deionized water at 5℃ and a speed of 100r / min to obtain a primary mixture; S22. Maintaining the stirring speed in step S21, slowly add 20g titanium tetrachloride, 10g tetrabutyl titanate and 3g modified complexing agent dropwise to the primary mixture until completely dissolved to obtain the secondary mixture; S23. Add 0.5g sodium dodecylbenzenesulfonate, 3g PEG-400, 8g hydrogen peroxide and 150g deionized water to the secondary mixture obtained in step S22, and stir evenly to obtain the modified corrosion solution.

[0022] The preparation of the modified chemical solution includes the following steps: S41. Mix 40g ammonium adipate, 8g ammonium borate, 1g ammonium pentaborate with 700g deionized water and stir at 100r / min for 10min at 40℃. S42. Add 0.5g of citric acid to the solution obtained in step S41, control the pH at 6 using dilute ammonia, add 0.1g of PEG-6000, and stir until completely dissolved; S43. Add 2g of nano-silica hydrosol dropwise to the solution obtained in step S42, and then ultrasonically disperse it at a frequency of 40kHz for 3min to obtain the modified formation solution.

[0023] S1. Aluminum foil pretreatment: High-purity aluminum foil is immersed in a 0.5 mol / L sodium hydroxide solution at 50℃ for 30 seconds, and then rinsed with deionized water to obtain pretreated high-purity aluminum foil; S2. Corrosion modification: The pretreated high-purity aluminum foil obtained in step S1 is immersed in the modified corrosion solution and soaked at 50°C for 10 min. During the corrosion process, ultrasonic waves with a frequency of 30 kHz are used. S3. Medium-temperature heat curing: Take out the aluminum foil modified by corrosion in step S2, clean it with deionized water, dry it and then carry out medium-temperature heat curing treatment. The curing temperature is 300℃, the heating rate is 5℃ / min and the holding time is 15min. S4. Anodizing: The aluminum foil cured in step S3 is anodized in a modified forming solution using a stepped voltage increase method, with a constant current density of 0.5 mA / cm². 2 The temperature is 30℃, the voltage is increased to the rated voltage of 50V and then cooled to 15℃, maintained for 10 minutes, and finally a composite anode foil based on an aluminum substrate is obtained after cleaning with deionized water and drying.

[0024] Example 2 Preparation method of composite anode foil based on aluminum substrate: Before preparing the composite anode foil based on the aluminum substrate, the modified complexing agent, modified etching solution, and modified formation solution are prepared first: The preparation of the modified complexing agent includes the following steps: S221. Dissolve 5g of citric acid in 20g of deionized water and stir at 150r / min at 30℃ until completely dissolved to obtain an aqueous solution of citric acid; S222. Dissolve 10g of acetylacetone in 40g of anhydrous ethanol and stir until completely dissolved to obtain an acetylacetone-ethanol mixture. S223. The citric acid aqueous solution obtained in step S221 is slowly added dropwise to the acetylacetone-ethanol mixture at a speed of 200 r / min. After the addition is complete, the mixture is stirred for 10 min and then aged at 8℃ for 3 h to finally obtain the modified complexing agent.

[0025] The preparation of the modified etchant includes the following steps: S21. Mix 110g of acid mixture (hydrochloric acid, sulfuric acid, and phosphoric acid in a mass ratio of 10:1:0.8) with 600g of deionized water at 10℃ and a speed of 200r / min to obtain a primary mixture; S22. While maintaining the stirring speed in step S21, slowly add 30g titanium tetrachloride, 15g tetrabutyl titanate and 8g modified complexing agent dropwise to the primary mixture until completely dissolved to obtain the secondary mixture; S23. Add 1g sodium dodecylbenzenesulfonate, 5g PEG-400, 12g hydrogen peroxide and 200g deionized water to the secondary mixture obtained in step S22, and stir evenly to obtain the modified corrosion solution.

[0026] The preparation of the modified chemical solution includes the following steps: S41. Mix 60g ammonium adipate, 12g ammonium borate, 3g ammonium pentaborate with 800g deionized water and stir at 200r / min for 15min at 50℃. S42. Add 1g of citric acid to the solution obtained in step S41, control the pH at 7 using dilute ammonia, add 0.3g of PEG-6000, and stir until completely dissolved; S43. Add 4g of nano-silica hydrosol dropwise to the solution obtained in step S42, and then ultrasonically disperse it at a frequency of 40kHz for 5min to obtain the modified formation solution.

[0027] S1. Aluminum foil pretreatment: High-purity aluminum foil is immersed in a 2 mol / L sodium hydroxide solution at 80℃ for 120s, and then rinsed with deionized water to obtain pretreated high-purity aluminum foil; S2. Corrosion modification: The pretreated high-purity aluminum foil obtained in step S1 is immersed in the modified corrosion solution and soaked at 80°C for 30 min. During the corrosion process, ultrasonic waves with a frequency of 40 kHz are used. S3. Medium-temperature heat curing: Take out the aluminum foil modified by corrosion in step S2, clean it with deionized water, dry it and then carry out medium-temperature heat curing treatment. The curing temperature is 500℃, the heating rate is 10℃ / min, and the holding time is 60min. S4. Anodizing: The aluminum foil cured in step S3 is anodized in a modified forming solution using a stepped voltage increase method, with a constant current density of 2 mA / cm². 2 The temperature is 50℃, the voltage is increased to the rated voltage of 250V and then cooled to 25℃, maintained for 20 minutes, and finally a composite anode foil based on an aluminum substrate is obtained after cleaning with deionized water and drying.

[0028] Example 3 Preparation method of composite anode foil based on aluminum substrate: Before preparing the composite anode foil based on the aluminum substrate, the modified complexing agent, modified etching solution, and modified formation solution are prepared first: The preparation of the modified complexing agent includes the following steps: S221. Dissolve 3g of citric acid in 12g of deionized water and stir at 120r / min at 26℃ until completely dissolved to obtain an aqueous solution of citric acid; S222. Dissolve 7g of acetylacetone in 25g of anhydrous ethanol and stir until completely dissolved to obtain an acetylacetone-ethanol mixture. S223. The citric acid aqueous solution obtained in step S221 is slowly added dropwise to the acetylacetone-ethanol mixture at a speed of 160 r / min. After the addition is complete, the mixture is stirred for 9 min and then aged at 4℃ for 2.5 h to finally obtain the modified complexing agent.

[0029] The preparation of the modified etchant includes the following steps: S21. Mix 105g of acid mixture (hydrochloric acid, sulfuric acid, and phosphoric acid in a mass ratio of 10:1:0.8) with 550g of deionized water at 7℃ and a speed of 150r / min to obtain a primary mixture; S22. Maintaining the stirring speed in step S21, slowly add 22g titanium tetrachloride, 12g tetrabutyl titanate and 5g modified complexing agent dropwise to the primary mixture until completely dissolved to obtain the secondary mixture; S23. Add 0.7g sodium dodecylbenzenesulfonate, 4g PEG-400, 10g hydrogen peroxide and 160g deionized water to the secondary mixture obtained in step S22, and stir evenly to obtain the modified corrosion solution.

[0030] The preparation of the modified chemical solution includes the following steps: S41. Mix 50g ammonium adipate, 10g ammonium borate, 2g ammonium pentaborate with 750g deionized water and stir at 150r / min for 12min at 45℃. S42. Add 0.7g of citric acid to the solution obtained in step S41, control the pH at 6.5 using dilute ammonia, add 0.2g of PEG-6000, and stir until completely dissolved; S43. Add 3g of nano-silica hydrosol dropwise to the solution obtained in step S42, and then ultrasonically disperse it at a frequency of 40kHz for 4min to obtain the modified formation solution.

[0031] S1. Aluminum foil pretreatment: High-purity aluminum foil is immersed in a 1mol / L sodium hydroxide solution at 60℃ for 60s, and then rinsed with deionized water to obtain pretreated high-purity aluminum foil; S2. Corrosion modification: The pretreated high-purity aluminum foil obtained in step S1 is immersed in the modified etching solution and soaked at 60°C for 20 minutes. During the etching process, ultrasonic waves with a frequency of 35kHz are used. S3. Medium-temperature heat curing: Take out the aluminum foil modified by corrosion in step S2, clean it with deionized water, dry it and then carry out medium-temperature heat curing treatment. The curing temperature is 400℃, the heating rate is 7℃ / min and the holding time is 30min. S4. Anodizing: The aluminum foil cured in step S3 is anodized in a modified forming solution using a stepped voltage increase method, with a constant current density of 1 mA / cm². 2 The temperature is 40℃, the voltage is increased to the rated voltage of 100V and then cooled to 20℃, maintained for 15 minutes, and finally obtained as a composite anode foil based on an aluminum substrate after being cleaned with deionized water and dried.

[0032] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no modified complexing agent was added in this comparative example; the remaining steps are exactly the same in Comparative Example 1 and Example 1.

[0033] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the modified etching solution in this comparative example is replaced with an acid mixture of hydrochloric acid, sulfuric acid and phosphoric acid in a mass ratio of 10:1:0.8. The other steps are exactly the same in Comparative Example 2 and Example 1.

[0034] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the modified formation liquid is replaced with a mixture of phosphoric acid solution and ammonium pentaborate in a mass ratio of 1:1. The remaining steps are exactly the same in Comparative Example 3 and Example 1.

[0035] Performance testing: The performance of the aluminum-based composite anode foils obtained in Examples 1-3 and Comparative Examples 1-3 was tested in accordance with SJ / T 11140-2022 "Electrode Foil for Aluminum Electrolytic Capacitors", GB / T 3615-2016 "Aluminum Foil for Electrolytic Capacitors" and SJ / T 10557.1-2022 "Technical Conditions for Aluminum Foil for Electrolytic Capacitors".

[0036] Samples of 50 mm × 30 mm were cut from the aluminum-based composite anode foils obtained in Examples 1-3 and Comparative Examples 1-3. These samples were ultrasonically cleaned with anhydrous ethanol for 10 min, dried at 50°C for 10 min, and cooled to room temperature. The electrolyte was a 3% ammonium borate aqueous solution (pH 6.5-7.0); the test temperature was 30°C; the test frequency was 120 Hz; and the AC signal voltage was 0.5 V (RMS). The samples were fully immersed in a constant-temperature electrolytic cell containing a 3% ammonium borate aqueous solution (the liquid level ≥ 10 mm above the upper edge of the sample). The sample was used as the working anode, and a large-area graphite plate as the cathode. An LCR digital bridge was used at 0.9 kV·cm⁻¹. -1 The capacitance of the sample was measured under weak field conditions, and the specific capacitance was obtained by reading the capacitance value.

[0037] A 50mm × 30mm sample was cut from the aluminum-based composite anode foil obtained in Examples 1-3 and Comparative Examples 1-3, connected to a leakage current tester, and a graphite plate was used as the cathode. The constant current was boosted to the rated voltage (the boosting mode was consistent with the formation conditions of each example / comparative example). The voltage was then maintained at this rated voltage for 60s, and the leakage current value I after relative stability was recorded. The leakage current was calculated from the effective area of ​​the sample.

[0038] Samples of 50mm × 30mm were cut from the aluminum-based composite anode foils obtained in Examples 1-3 and Comparative Examples 1-3, and connected to a leakage current tester at 1.0mA / cm. 2 A constant current density voltage rise was applied, and the time taken for the voltage to rise to 90% of the rated voltage was recorded. The voltage value (the withstand voltage) was recorded after another 180 seconds of continuous voltage rise, and the withstand voltage retention rate was calculated. The final results are shown in Table 1 below: Table 1 Performance Test Results As shown in Table 1, the composite anode foil based on an aluminum substrate obtained in the examples outperforms the comparative examples in all aspects. The difference in specific capacitance between Example 3 and Comparative Example 3 is not significant. Although Comparative Example 3 used a conventional formation solution (ammonium pentaborate mixture), its pre-process still retained the TiO2 pre-deposition effect brought about by the modified etching solution and modified complexing agent of this invention, thus maintaining a high specific capacitance. The data demonstrate that the synergistic effect of the modified complexing agent, modified etching solution, and modified formation solution achieves a synergistic optimization between a significant increase in the specific capacitance of the composite anode foil and effective suppression of leakage current. This simplifies the process while significantly improving the overall electrical performance of the product, showing promising prospects for industrial applications.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite anode foil based on an aluminum substrate, characterized in that, The preparation steps include the following: S1. Aluminum foil pretreatment: Immerse high-purity aluminum foil in sodium hydroxide solution at 50-80℃ for 30-120s, and rinse with deionized water to obtain pretreated high-purity aluminum foil; S2. Corrosion modification: Immerse the pretreated high-purity aluminum foil obtained in step S1 into the modified corrosion solution and soak it at 50-80℃ for 10-30 minutes, accompanied by ultrasonic waves during the corrosion process; S3. Medium-temperature heat curing: Take out the aluminum foil after corrosion modification in step S2, clean it with deionized water, dry it and then perform medium-temperature heat curing treatment. S4. Anodizing: The aluminum foil cured in step S3 is anodized in a modified forming solution using a stepped pressure increase method. After being cleaned with deionized water and dried, a composite anode foil based on an aluminum substrate is finally obtained. The preparation of the modified corrosive liquid includes the following steps: S21. By mass, 100-110 parts of acid mixture and 500-600 parts of deionized water are stirred and mixed at 5-10℃ and 100-200 r / min to obtain a primary mixture; S22. Maintaining the stirring speed in step S21, slowly add 20-30 parts of titanium tetrachloride, 10-15 parts of tetrabutyl titanate and 3-8 parts of modified complexing agent to the primary mixture, and completely dissolve to obtain the secondary mixture; S23. Add 0.5-1 parts sodium dodecylbenzenesulfonate, 3-5 parts PEG-400, 8-12 parts hydrogen peroxide and 150-200 parts deionized water to the secondary mixture obtained in step S22, and stir evenly to obtain the modified corrosion solution. The preparation of the modified complexing agent includes the following steps: S221. Dissolve 2-5 parts of citric acid in 10-20 parts of deionized water by weight, and stir at 100-150 r / min at 25-30℃ until completely dissolved to obtain an aqueous solution of citric acid; S222. Dissolve 5-10 parts of acetylacetone in 20-40 parts of anhydrous ethanol, and stir until completely dissolved to obtain an acetylacetone-ethanol mixture. S223. The citric acid aqueous solution obtained in step S221 is slowly added dropwise to the acetylacetone-ethanol mixture at a speed of 150-200 r / min. After the addition is complete, the mixture is stirred for 8-10 min and then aged at 2-8℃ for 2-3 h to finally obtain the modified complexing agent. The preparation of the modified chemical solution includes the following steps: S41. By mass, mix 40-60 parts ammonium adipate, 8-12 parts ammonium borate, 1-3 parts ammonium pentaborate with 700-800 parts deionized water and stir at 40-50℃ for 10-15 minutes. S42. Add 0.5-1 part of citric acid to the solution obtained in step S41, control the pH at 6-7 using dilute ammonia, add 0.1-0.3 parts of PEG-6000, and stir until completely dissolved; S43. Add 2-4 parts of nano-silica hydrosol dropwise to the solution obtained in step S42, and then ultrasonically disperse at a frequency of 40kHz for 3-5 minutes to obtain the modified solution.

2. The method for preparing the composite anode foil based on an aluminum substrate according to claim 1, characterized in that, The curing temperature of the medium-temperature heat curing treatment is 300-500℃, the heating rate is 5-10℃ / min, and the holding time is 15-60min.

3. The method for preparing the composite anode foil based on an aluminum substrate according to claim 1, characterized in that, The constant current density of the stepped voltage boost method is 0.5-2 mA / cm². 2 The temperature is 30-50℃, and the voltage is increased to the rated voltage of 50-250V and then cooled to 15-25℃, and maintained for 10-20 minutes.

4. The method for preparing the composite anode foil based on an aluminum substrate according to claim 1, characterized in that, The acid mixture is composed of hydrochloric acid, sulfuric acid, and phosphoric acid in a mass ratio of 10: 1：0.8。 5. The method for preparing the composite anode foil based on an aluminum substrate according to claim 1, characterized in that, In step S1, the concentration of the sodium hydroxide solution is 0.5-2 mol / L.

6. The method for preparing the composite anode foil based on an aluminum substrate according to claim 1, characterized in that, In step S2, the frequency of the ultrasound is 30-40kHz.

7. The method for preparing the composite anode foil based on an aluminum substrate according to claim 1, characterized in that, The stirring speed in step S41 is 100-200 r / min.

8. A composite anode foil based on an aluminum substrate, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

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