Pretreatment method and production method of electrode foil for aluminum electrolytic capacitor, electrode foil, and capacitor

Abstract

The present disclosure provides a pretreatment method and preparation method of an electrode foil for an aluminum electrolytic capacitor, an electrode foil and a capacitor, the pretreatment method comprising the following steps: a cleaning step, alkali washing and acid washing of an aluminum light foil; a coating step, coating a polyvinylidene fluoride (PVDF) composite modification solution on the cleaned aluminum light foil; a phase inversion step, immersing the coated aluminum light foil into an anti-solvent bath to form a uniform porous PVDF composite interface layer on the surface of the aluminum foil; and an activation step, activating the aluminum light foil with an acid solution. In the present disclosure, the PVDF composite interface modification is introduced into the pretreatment of the electrode foil, a uniform porous PVDF interface layer is constructed through ultrathin coating and phase inversion, and beneficial effects such as uniform site induction, electric field homogenization, infiltration enhancement, mild activation, low residue, etc. are achieved, and the process is simple, suitable for a continuous production line, and has important industrial value.

Description

Technical Field

[0001] This disclosure relates to the technical field of electrode foil for aluminum electrolytic capacitors, and particularly to a pretreatment method for electrode foil for aluminum electrolytic capacitors, a method for preparing electrode foil, an electrode foil obtained by the preparation method, and a capacitor containing the electrode foil. Background Technology

[0002] With the rapid development of the electronic information industry, aluminum electrolytic capacitors have placed more stringent requirements on the performance of anodic corrosion foil. The manufacturing process of corrosion foil mainly includes pretreatment, electrochemical porosimetry, porosimetry, formation, and post-treatment. Among these processes, the pretreatment of the aluminum foil is a key step that determines the distribution of corrosion holes, specific capacitance stability, and uniformity of residual core.

[0003] Existing pretreatment processes mainly consist of alkaline washing for degreasing followed by acid washing for neutralization. The principle is to use strong alkali to remove rolling oil, natural oxide layers, and impurities from the aluminum foil surface; then, strong acid is used to remove alkaline residue and generate slight activation points, providing initial sites for subsequent electrochemical corrosion. However, existing pretreatment processes result in uneven activation of the aluminum foil surface, with randomly distributed pore sites. The low surface energy of the aluminum foil leads to strong hydrophobicity and poor wettability of the etching solution, making it impossible to precisely control the direction and morphology of pore growth, thus failing to meet the high consistency requirements of high-end medium- and high-voltage electrode foils.

[0004] Industry research has attempted to optimize pretreatment processes through additive modification, low-temperature pre-oxidation, laser pre-drilling, and metal ion induction, but significant shortcomings remain. Additives can leave residues, easily contaminate the etching solution, and have poor stability; low-temperature pre-oxidation requires high-temperature equipment, resulting in high energy consumption, high costs, and is unfavorable for high-speed production lines; laser pretreatment equipment is expensive, complex to maintain, and difficult to perform large-area uniform treatment; metal ion induction is prone to localized enrichment and still cannot fundamentally solve the problem of pore uniformity.

[0005] Therefore, there is an urgent need in the field for an electrode foil pretreatment process that can achieve uniform site induction and enhanced wetting. Summary of the Invention

[0006] This disclosure provides a pretreatment method for electrode foil used in aluminum electrolytic capacitors, comprising the following steps: The cleaning process involves alkaline washing and acid washing of the aluminum foil. The coating step involves coating the cleaned aluminum foil with a polyvinylidene fluoride (PVDF) composite modification solution. In the phase inversion step, the coated aluminum foil is immersed in a PVDF anti-solvent bath to form a uniformly porous PVDF composite interface layer on the aluminum foil surface; and The activation step involves activating the aluminum foil with an acid solution.

[0007] According to the pretreatment method for electrode foil for aluminum electrolytic capacitors described in this disclosure, the PVDF composite modification solution contains PVDF and a solvent, and PVDF accounts for 3 to 8 wt% of the total weight of the PVDF composite modification solution.

[0008] According to the pretreatment method for electrode foil for aluminum electrolytic capacitors described in this disclosure, the solvent in the PVDF composite modification solution is a polar solvent, preferably one or more of DMF, DMSO, and NMP.

[0009] According to the pretreatment method for electrode foil for aluminum electrolytic capacitors described in this disclosure, the coating step involves forming a liquid film of PVDF composite modification liquid by dip coating or roll coating.

[0010] According to the pretreatment method for electrode foil for aluminum electrolytic capacitors described in this disclosure, the thickness of the liquid film of the PVDF composite modification liquid formed in the coating step is 50-200 nm.

[0011] According to the pretreatment method for electrode foil for aluminum electrolytic capacitors described in this disclosure, the temperature of the PVDF antisolvent bath in the phase conversion step is 25-50℃, and the treatment time is 10-60 s.

[0012] According to the pretreatment method for electrode foil for aluminum electrolytic capacitors described in this disclosure, in the activation step, the aluminum foil is treated with an acid solution of pH 3.0-5.0 at 30-60°C for 10-60 s.

[0013] According to the pretreatment method for electrode foil for aluminum electrolytic capacitors described in this disclosure, the acid solution in the activation step is a phosphoric acid solution.

[0014] This disclosure also provides a method for preparing electrode foil for aluminum electrolytic capacitors, which includes the pretreatment method for the electrode foil described above.

[0015] This disclosure also provides an electrode foil for an aluminum electrolytic capacitor, the electrode foil being obtained by the preparation method described in this disclosure.

[0016] This disclosure also provides an aluminum electrolytic capacitor comprising an electrode foil prepared according to the preparation method described herein.

[0017] This disclosure introduces PVDF composite interface modification into the pretreatment of electrode foil. A uniform porous PVDF interface layer is constructed through ultra-thin coating and phase transformation, achieving beneficial effects such as uniform site induction, electric field homogenization, enhanced wetting, mild activation, and low residue. The process is simple, adaptable to continuous production lines, and has significant industrial value. Furthermore, this disclosure significantly improves the surface condition of aluminum foil through the synergistic effect of PVDF composite interface modification and mild activation, eliminating defects such as uneven activation, localized over-corrosion, and poor wettability inherent in traditional processes. Attached Figure Description

[0018] Figure 1 This is a flowchart of a pretreatment method for electrode foil for aluminum electrolytic capacitors according to the present disclosure.

[0019] Figure 2-4 These are SEM images of the residual core of the electrode foil for the aluminum electrolytic capacitor obtained in Embodiments 1-3 of this disclosure.

[0020] Figure 5-7 These are SEM images of the residual cores of the electrode foil for aluminum electrolytic capacitors obtained in Comparative Examples 1-3 of this disclosure. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0024] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0025] 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.

[0026] 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.

[0027] This disclosure provides a pretreatment method for electrode foil used in aluminum electrolytic capacitors, comprising the following steps: S1 - Cleaning step, alkaline washing and acid washing of aluminum foil; S2 - Coating step: Coating the cleaned aluminum foil with a polyvinylidene fluoride (PVDF) composite modification solution; In the S3 phase transformation step, the coated aluminum foil is immersed in a PVDF anti-solvent bath to form a PVDF composite interface layer with uniform pores on the aluminum foil surface. S4 - Activation step, using an acid solution to activate the aluminum foil.

[0028] In the cleaning process, the continuously conveyed aluminum foil undergoes sequential alkaline washing for degreasing, acid washing for neutralization, and pure water rinsing to remove surface oil, natural oxide film debris, and impurities, resulting in a clean aluminum foil surface. The alkaline washing can be performed using aqueous solutions of alkalis such as NaOH or KOH. For example, a 3-5 wt% NaOH or KOH aqueous solution can be used to treat the aluminum foil at 50-55°C for 12-20 seconds, with the pH controlled at 9-11. A pH above 11 can cause excessive etching of the aluminum foil substrate, while a pH below 9 will result in insufficient degreasing. Next, the acid washing can be performed using aqueous solutions of acids such as HNO3 or HCl, with the pH of the solution controlled within the range of 0.5-2.0. For example, an 8-12 wt% nitric acid solution can be used at room temperature for 8-10 seconds; alternatively, a 6-10 wt% hydrochloric acid solution can be used. A pH below 0.5 will prematurely corrode the aluminum foil, while a pH above 2.0 will fail to completely remove the loose oxide film.

[0029] In the coating step, the PVDF composite modification solution contains PVDF and a solvent, and the components are thoroughly mixed by stirring before use. The PVDF content in the PVDF composite modification solution is 3-8 wt%. When the PVDF content in the PVDF composite modification solution is less than 3 wt%, the solid content in the composite modification solution is too low, making it difficult to form a continuous and complete film after coating. This results in a large number of breaks or missing pores in the porous interface formed after phase transformation, making it impossible to uniformly induce corrosion sites, and localized pore defects and concentrated over-corrosion are likely to occur. Conversely, when the PVDF content in the PVDF composite modification solution is higher than 8 wt%, the viscosity of the composite modification solution will increase sharply, easily producing thick films, flow marks, and uneven film thickness after coating. This leads to a slower solvent extraction rate during phase transformation, reduced internal pores, and excessively high density in the film, which will significantly inhibit the penetration of the corrosion solution, resulting in insufficient overall corrosion and a decrease in specific volume. At the same time, the thick film is prone to localized detachment, disrupting the uniformity of the distribution of sites on the aluminum foil surface.

[0030] The solvent in the PVDF composite modification solution is a good solvent for PVDF, typically a polar solvent. Preferably, the polar solvent is one or more of DMF, DMSO, and NMP.

[0031] A liquid film of polyvinylidene fluoride (PVDF) composite modification solution can be formed by dip coating or roll coating. The coating thickness can be controlled to form a uniform, ultra-thin liquid film on the surface of the aluminum foil. The thickness of the liquid film can be 50-200 nm. If the liquid film thickness is less than 50 nm, the film is too thin and prone to local film fractures and pinhole defects, failing to completely cover the aluminum foil surface, making it difficult to form a continuous and uniform induced interface, resulting in a dispersed distribution of corrosion sites and a tendency for localized concentrated corrosion. If the liquid film thickness is greater than 200 nm, the film is too thick, making it difficult for the solvent to quickly dissipate during phase transformation. The film porosity decreases, and the excessive density hinders the penetration of the corrosion solution. Simultaneously, the high stress of the thick film easily causes local peeling and flaking, resulting in missing sites and significantly reducing pore uniformity. A liquid film with a thickness in the range of 50-200 nm can completely coat the aluminum foil surface, construct a continuous and uniform porous induction interface, stably provide uniform initial corrosion sites, and ensure rapid solvent extraction during the phase transformation process, forming a PVDF interface layer with suitable porosity. This balances the requirements for site induction and corrosion solution penetration, making it suitable for continuous pretreatment production of aluminum foil. Those skilled in the art can adjust the specific thickness based on the specific production conditions, balancing cost and output stability.

[0032] In the phase transformation step, the coated aluminum foil is immersed in a PVDF antisolvent bath, and a uniform porous PVDF composite interface layer is formed on the aluminum foil surface through solvent-antisolvent exchange, thereby achieving site induction, electric field homogenization and wetting enhancement.

[0033] The solvent-antisolvent exchange process essentially involves the diffusion of a polar solvent within the liquid film on the aluminum foil surface into the coagulation bath, while water from the coagulation bath permeates into the liquid film. This bidirectional diffusion triggers liquid-liquid phase separation of the PVDF molecular chains, leading to gel precipitation and solidification to form a thin film with interconnected micropores. The selection of the solvent in the antisolvent bath primarily considers the following four aspects: 1) It should be a poor solvent for PVDF, inducing liquid-liquid phase separation and rapid gel formation; 2) It should be completely miscible with the polar solvent in the PVDF composite modification solution; 3) It should be liquid at room temperature or low temperature, have low volatility, be non-corrosive, and not damage the aluminum foil matrix; 4) It should be completely removed by rinsing in subsequent washing steps, leaving no residual impurities to interfere with corrosion and pore formation. The antisolvent can be water, ethanol, isopropanol, ethylene glycol, or mixtures thereof. Preferably, the antisolvent bath can be a deionized water bath or an ethanol water bath, both of which are low-cost, readily available, suitable for continuous production lines, and will not contaminate the bath solution.

[0034] The temperature of the antisolvent bath can be 25-50℃, and the processing time can be 10-60 s. Below 25℃, the solvent diffusion rate is slow, the phase transformation is incomplete, and the film layer has few pores and insufficient induction sites. Above 50℃, the solvent is rapidly precipitated, easily leading to macroporous defects and poor interface integrity. A processing time shorter than 10 s results in insufficient exchange between the solvent and the antisolvent, causing the film layer to not fully solidify and easily detach. A processing time exceeding 60 s does not significantly improve performance and reduces production line operating efficiency.

[0035] In the activation step, free PVDF residue can be removed by washing with water first, and then a low-concentration weak acid system can be used for gentle surface activation without damaging the substrate or causing over-corrosion. Then, pure water is used to thoroughly remove the residual liquid, providing a clean, uniformly activated, and orderly surface for subsequent pore formation and enlargement corrosion.

[0036] Specifically, aluminum foil can be treated with a dilute acid solution with a pH of 3.0-5.0 at 30-60℃ for 10-60 seconds. The dilute acid solution is preferably a dilute phosphoric acid aqueous solution. When the pH is below 3.0, the acidity is too strong, and the hydrogen ion concentration is too high, which will cause severe etching of the aluminum foil substrate, resulting in excessive wear of the aluminum substrate, a significant reduction in the thickness of the residual core, and large differences in surface activation, easily leading to localized deep etching and an increase in co-occurrence. When the pH is above 5.0, the acidity is too weak, and the hydrogen ion content is insufficient to completely dissolve the dense natural oxide film on the aluminum foil surface. The residual oxide film area will inhibit the formation of corrosion sites, resulting in sparse and uneven distribution of etched holes and a decrease in specific volume. Maintaining the pH in the 3.0-5.0 range allows for gentle and uniform peeling of the surface oxide film, achieving balanced activation. This avoids excessive erosion of the aluminum substrate while ensuring consistent corrosion activity across the entire foil surface, guaranteeing uniform and stable subsequent pore formation.

[0037] This disclosure also provides a method for preparing electrode foil for aluminum electrolytic capacitors, including the pretreatment method of the electrode foil described above.

[0038] This disclosure also provides an electrode foil for an aluminum electrolytic capacitor, the electrode foil being obtained by the preparation method described in this disclosure.

[0039] This disclosure also provides an aluminum electrolytic capacitor comprising an electrode foil prepared according to the preparation method described herein.

[0040] Compared with the prior art, the technical solution disclosed herein has the following significant advantages: 1. Uniform interface induction significantly improves corrosion pore consistency and specific volume. The PVDF porous layer provides uniform pore-forming sites, and the PVDF porous interface provides uniform induction sites. The electric field distribution is uniform, the pore size consistency is significantly improved, and the porosity is greatly reduced.

[0041] 2. Significantly improves wettability and eliminates localized over-corrosion. The high polarity and porous structure of PVDF significantly improve the wetting and spreading of the etchant, eliminating dry areas / bubbles on high-speed production lines and significantly reducing over-etching and perforation defects.

[0042] 3. Gentle activation without damaging the substrate, resulting in more stable residual core. The modified + mild activation mode disclosed herein provides a PVDF porous interface layer that can provide uniform induction sites, homogenize the electric field distribution, and improve the wetting and spreading of the etching solution. The mild activation with dilute phosphoric acid avoids damage to the substrate. The two work together to achieve a high-quality and stable etching pore structure, and the product consistency, yield and overall performance are significantly improved, which can stably meet the requirements of industrial production of medium and high pressure etching foil.

[0043] 4. No harmful residues, green and stable The PVDF interface layer can be completely removed or controllably retained through phase inversion and water washing, leaving no organic surfactant residue, without contaminating the corrosion bath solution, and exhibiting stronger batch stability.

[0044] 5. Simple process, compatible with existing production lines No major equipment modifications are required; only dip coating / roller coating and water bath units need to be added. The investment is small, the results are quick, and it is easy to carry out continuous industrial production.

[0045] 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 through specific embodiments.

[0046] Example 1 Aluminum foil with a thickness of 130μm was selected and pretreated as follows: S1 - Basic Cleaning The aluminum foil was treated with a 5 wt% NaOH aqueous solution at 55℃ for 20 s, and then rinsed with pure water at room temperature for 15 s; then the aluminum foil was treated with a 10 wt% HNO3 aqueous solution at room temperature for 10 s, and then rinsed with pure water with a conductivity ≤1 μS / cm for 20 s.

[0047] S2 - Coating Step A polyvinylidene fluoride (PVDF) composite modification solution was coated onto a cleaned aluminum foil using a dip-coating method. The coating was then filtered for 10 seconds, and the liquid film thickness was controlled to be 100 nm. The PVDF composite modification solution contained 5 wt% PVDF, with the remainder being the solvent DMF.

[0048] S3 - Phase Transformation Steps The coated aluminum foil was treated in a 30°C deionized water bath for 30 seconds to form a PVDF composite interface layer with uniform pores on the aluminum foil surface. Then, excess PVDF was removed by rinsing with room temperature pure water.

[0049] S4 - Activation Step The aluminum foil was treated with a 0.5 wt% dilute phosphoric acid aqueous solution at 40°C for 30 s, and then rinsed with pure water with a conductivity ≤0.8 μS / cm for 60 s.

[0050] Example 2 Aluminum foil with a thickness of 130μm was selected and pretreated as follows: S1 - Basic Cleaning The aluminum foil was treated with a 5 wt% NaOH aqueous solution at 55℃ for 20 s, and then rinsed with pure water at room temperature for 15 s; then the aluminum foil was treated with a 10 wt% HNO3 aqueous solution at room temperature for 10 s, and then rinsed with pure water with a conductivity ≤1 μS / cm for 20 s.

[0051] S2 - Coating Step A polyvinylidene fluoride (PVDF) composite modification liquid was coated onto cleaned aluminum foil using a roller coating method at a pressure of 0.4 MPa and a liquid film thickness of 150 nm. The PVDF composite modification liquid contained 6 wt% PVDF, with the remainder being the solvent DMSO.

[0052] S3 - Phase Transformation Steps The coated aluminum foil was treated in a 40°C deionized water bath for 20 seconds to form a PVDF composite interface layer with uniform pores on the aluminum foil surface. Then, it was washed with room temperature pure water to remove excess PVDF.

[0053] S4 - Activation Step The aluminum foil was treated with a 0.6 wt% dilute phosphoric acid aqueous solution at 45°C for 20 s, and then rinsed with pure water with a conductivity ≤0.8 μS / cm for 50 s.

[0054] Example 3 Aluminum foil with a thickness of 130μm was selected and pretreated as follows: S1 - Basic Cleaning The aluminum foil was treated with a 5 wt% NaOH aqueous solution at 55℃ for 20 s, and then rinsed with pure water at room temperature for 15 s; then the aluminum foil was treated with a 10 wt% HNO3 aqueous solution at room temperature for 10 s, and then rinsed with pure water with a conductivity ≤1 μS / cm for 20 s.

[0055] S2 - Coating Step A polyvinylidene fluoride (PVDF) composite modification solution was coated onto cleaned aluminum foil using an dip-coating method, followed by leaching for 10 seconds and controlling the liquid film thickness to be 80 nm. The PVDF composite modification solution contained 4 wt% PVDF, with the remainder being a mixed solvent DMF:NMP (7:3).

[0056] S3 - Phase Transformation Steps The coated aluminum foil was treated in a 35°C deionized water bath for 40 seconds to form a PVDF composite interface layer with uniform pores on the aluminum foil surface. Then, excess PVDF was removed by rinsing with room temperature pure water.

[0057] S4 - Activation Step Aluminum foil was treated with a 0.3 wt% dilute phosphoric acid aqueous solution at 35°C for 30 s, and then rinsed with pure water with a conductivity ≤0.8 μS / cm for 60 s.

[0058] Comparative Example 1 Aluminum foil with a thickness of 130μm was selected and pretreated as follows: The aluminum foil was treated with a 5 wt% NaOH aqueous solution at 55℃ for 20 s, and then rinsed with pure water at room temperature for 15 s; then the aluminum foil was treated with a 10 wt% HNO3 aqueous solution at room temperature for 10 s, and then rinsed with pure water with a conductivity ≤1 μS / cm for 20 s.

[0059] Comparative Example 2 High-purity aluminum foil with a thickness of 130μm was selected and pretreated as follows: The cleaning solution was treated with 0.1 wt% sodium dodecylbenzenesulfonate, a conventional anionic surfactant. The solution was then soaked at 55°C for 20 seconds, rinsed with pure water for 15 seconds, activated with 0.5 wt% dilute phosphoric acid for 30 seconds, and rinsed with pure water for 60 seconds.

[0060] Comparative Example 3 High-purity aluminum foil with a thickness of 130μm was selected and pretreated as follows: The basic acid-base cleaning was the same as in Comparative Example 1. After rinsing, the sample was immersed in a dilute phosphoric acid solution containing 2 ppm bismuth chloride for 25 seconds. Corrosion was induced by the precipitation of trace metal particles on the surface, followed by routine water washing.

[0061] Appendix Figure 2-7 The following are SEM images of the residual cores of the above embodiments and comparative examples; and the electrode foils in the above embodiments and comparative examples were tested under the same electrochemical corrosion conditions, and the test results are shown in Table 1 below.

[0062] Table 1 - Composition of the forming solution and current density in the post-forming step, and related properties of the formed foil. From the appendix Figure 2-7As can be seen from the SEM images of the residual cores in Examples 1-3, the thickness of the residual core layer of the substrate is continuous and flat, with minimal fluctuation in thickness. The tunnel holes growing from the surface of the aluminum foil inward are vertical and regular, with uniform hole depth and parallel arrangement of channels. The spacing between adjacent holes is uniform, and there are no large areas of interconnected holes or local deep corrosion hollowing areas in the cross-section. In Comparative Example 1, the SEM of the cross-section shows that the thickness of the residual core varies greatly, and some areas are thinned by deep corrosion. Multiple channels are connected laterally to form large cavities. In some areas, corrosion penetrates to the vicinity. The tunnels are of varying lengths, and the cross-section is severely damaged. In Comparative Example 2, the cross-section shows that there are irregular concavities in some parts of the residual core. Some channels are distorted in the middle and have varying depths. Scattered holes are connected laterally. Due to the residue of additives, the local corrosion is weak and shallow blind holes appear. In Comparative Example 3, it can be observed that the holes in the area corresponding to the metal enrichment point are clustered and deeply excavated. Some residual cores are excessively corroded and thinned. The corrosion holes in other positions are shallow. The density of holes in the cross-section is obviously differentiated.

[0063] Regarding the residual core thickness, compared to the conventional process in Comparative Example 1, the residual core thicknesses in Examples 1, 2, and 3 were increased by 33.33%, 37.50%, and 30.21%, respectively; compared to the surfactant process in Comparative Example 2, the increases were 21.90%, 25.71%, and 19.05%, respectively; and compared to the metal ion process in Comparative Example 3, the increases were 14.29%, 17.86%, and 11.61%, respectively. In terms of specific volume, the products in the three examples showed an improvement of 4.8%-6.5% compared to the conventional process, 2.9%-4.7% compared to the surfactant process, and 1.9%-3.6% compared to the metal ion process.

[0064] Comparative Example 2 uses industry-standard organic surfactants in combination with weak acid cleaning. Although this alleviates over-corrosion compared to traditional strong acid processes, the organic additives are easily adsorbed and remain in the micro-crevices of the aluminum foil, making them impossible to rinse and remove completely. The residual impurities disrupt the corrosion initiation point, and problems such as pore size fluctuations, uneven local corrosion, and co-occurrence cannot be eradicated.

[0065] Comparative Example 3 uses a trace amount of bismuth salt metal ion-induced pretreatment, relying on surface-deposited metal particles to act as etching points. While this method achieves better uniformity than conventional surfactant processes, metal ions tend to accumulate locally at the grain boundaries of the aluminum foil, leading to localized deep etching and a lack of etching points in some areas, resulting in significant shortcomings in product performance. The electrode foil preparation method in this disclosure relies on the uniform distribution of PVDF porous interfaces and the homogenization of the electric field, combined with gentle activation using dilute phosphoric acid. This method avoids the risks of organic additives and heavy metal residues, and the porosity is generally below 3%. The PVDF porous membrane can accurately anchor the corrosion initiation point and optimize the wetting effect of the etching solution. Low-temperature activation with dilute phosphoric acid prevents excessive etching of the substrate. These multiple factors work synergistically to achieve a comprehensive upgrade in product quality.

[0066] 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 pretreatment method for electrode foil used in aluminum electrolytic capacitors, characterized in that, Includes the following steps: The cleaning process involves alkaline washing and acid washing of the aluminum foil. The coating step involves coating the cleaned aluminum foil with a polyvinylidene fluoride (PVDF) composite modification solution. In the phase transformation step, the coated aluminum foil is immersed in a PVDF anti-solvent bath to form a PVDF composite interface layer with uniform pores on the aluminum foil surface. as well as The activation step involves activating the aluminum foil with an acid solution.

2. The pretreatment method for electrode foil for aluminum electrolytic capacitors according to claim 1, wherein, The PVDF composite modification solution contains PVDF and a solvent, with PVDF accounting for 3 to 8 wt% of the total weight of the PVDF composite modification solution.

3. The pretreatment method for electrode foil for aluminum electrolytic capacitors according to claim 2, wherein, The solvent is a polar solvent, and the solvent includes one or more of DMF, DMSO, and NMP.

4. The pretreatment method for electrode foil for aluminum electrolytic capacitors according to claim 1, wherein, The coating step uses dip coating or roller coating to form a liquid film of PVDF composite modification liquid.

5. The pretreatment method for electrode foil for aluminum electrolytic capacitors according to claim 1, wherein, The thickness of the liquid film of the PVDF composite modification liquid formed in the coating step is 50-200 nm.

6. The pretreatment method for electrode foil for aluminum electrolytic capacitors according to claim 1, wherein, The temperature of the deionized water bath or ethanol water bath in the phase transformation step is 25-50℃, and the processing time is 10-60 s.

7. The pretreatment method for electrode foil for aluminum electrolytic capacitors according to claim 1, wherein, In the activation step, the aluminum foil is treated with an acidic solution with pH 3.0-5.0 at 30-60℃ for 10-60 seconds.

8. A method for preparing electrode foil for aluminum electrolytic capacitors, characterized in that, The method includes a pretreatment method for electrode foil for aluminum electrolytic capacitors according to any one of claims 1 to 7.

9. An electrode foil for an aluminum electrolytic capacitor, characterized in that, The electrode foil is obtained by the pretreatment method described in claim 1 or by the preparation method described in claim 8.

10. An aluminum electrolytic capacitor, characterized in that, The aluminum electrolytic capacitor comprises an electrode foil obtained by the preparation method described in claim 8.

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