Electrode foil, preparation method thereof and aluminum electrolytic capacitor

Abstract

The invention provides an electrode foil, a preparation method thereof and an aluminum electrolytic capacitor, and the method comprises the steps: placing a corrosion foil in an electrolyte containing sulfuric acid and organic carboxylic acid, and carrying out the pre-formation treatment, thereby obtaining a pre-formation product; the pre-formed product is placed in a phosphoric acid solution to be etched, and an etched product is obtained; and carrying out re-formation treatment on the etching product to obtain the electrode foil. By adopting the preparation method provided by the invention, the uniformity of an oxide film of the electrode foil can be effectively improved, impurities are deeply removed, and the interface performance is optimized, so that the specific capacitance is remarkably improved, the hydration resistance and the corrosion resistance are enhanced, and the service life of the electrode foil is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials. Specifically, the present application relates to an electrode foil and a method for preparing the same and an aluminum electrolytic capacitor. BACKGROUND

[0002] The electrode foil is the core of the aluminum electrolytic capacitor, and its quality determines the specific capacitance and working voltage of the aluminum electrolytic capacitor, and directly affects the service life of the capacitor. The current development trend of the electronic industry is miniaturization of the whole machine, and the capacitor occupies a large proportion of space in electronic products, so reducing the volume of the aluminum electrolytic capacitor is the key to the miniaturization of the whole machine, which puts higher requirements on the capacity of the electrode foil.

[0003] In the field of preparing the electrode foil of the aluminum electrolytic capacitor, the existing formation process has many technical bottlenecks: (1) Poor quality of the oxide layer: the core role of the formation process is to form an aluminum oxide dielectric layer on the surface of the aluminum foil through electrochemical oxidation, and the uniformity of the coverage is directly related to the utilization efficiency of the effective specific surface area. If the oxide layer is unevenly distributed or has defects in the pores, it will cause two main problems: first, the defect area of the oxide layer may not be able to store charge stably, and the effective area actually participating in charging and discharging is less than the geometric surface area theoretically formed by corrosion; second, uneven oxide layer will lead to local electric field concentration, thus aggravating the risk of leakage current and dielectric breakdown, further reducing the reliability of the capacitor. The existing direct current formation process has deficiencies in controlling the quality and uniformity of the oxide layer in the corrosion pores, and it is difficult to indirectly improve the effective specific surface area. Under the condition of a single sulfuric acid system, the porous oxide film formed has low dielectric strength, and due to the high reaction rate, concentration polarization phenomenon is easy to occur, resulting in differences in the oxide film at the pore opening and the pore bottom; in addition, local overheating may cause the oxide film to crack and dissolve, leading to an increase in leakage current; the single carboxylic acid system is weakly acidic, and it is difficult to effectively dissolve Al 3+ hydrolysis products, resulting in residual unreacted aluminum powder at the bottom of the pores, and the residual aluminum forms a local conductive channel, reducing the effective dielectric layer thickness; at the same time, the strong adsorption of carboxylate ions on the surface of the aluminum oxide prematurely passivates the reaction interface, resulting in termination of the oxidation reaction in the deep pores, incomplete oxidation of the deep pores, and thus limiting the potential for improving the specific capacitance.

[0004] (2) Incomplete removal of pollutants: The anode foil etching process of aluminum electrolytic capacitor is a key technology to improve its specific surface area. The porous structure is formed by electrochemical etching, and the nanoscale and microscale etching holes distributed on the surface can effectively improve the specific surface area, thereby significantly improving the capacity of the capacitor. However, about 60% to 70% of the aluminum powder generated in the aluminum foil etching process is embedded in the deep layer of the etching hole. The existing spray cleaning has a removal rate of less than 40% for the aluminum powder in the hole and the sub-surface aluminum powder with weak bonding force, resulting in an increase in electrode contact resistance, easy short circuit between electrodes during the winding process of the capacitor, and an increase in risk. In addition, the residual Cl - Easily embedded into the lattice of the oxide film, forming ion migration channels, accelerating the hydration failure process, and destroying the structure of the oxide film.

[0005] (3) Insufficient interface treatment precision: The traditional chemical dissolution method has obvious limitations, resulting in deviation in etching depth. Excessive etching will reduce the number of effective holes, reduce the specific capacity, and increase the roughness of the aluminum matrix and the interface defect density, which seriously interferes with the uniformity and stability of the dielectric layer.

[0006] (4) Weak hydration resistance: The hydration resistance is a key factor that restricts the service life and reliability of aluminum electrolytic capacitors. The oxide film on the surface of the electrode foil is the working medium of the aluminum electrolytic capacitor, which directly contacts with the aqueous electrolyte during work. The adsorption of water molecules will form amorphous hydrated aluminum oxide, which will destroy the structure of the insulating layer, leading to a decrease in the dielectric properties of the electrode foil and an increase in the leakage current, ultimately resulting in the failure of the aluminum electrolytic capacitor, which cannot meet the market demand for high-performance electrode foil. In addition, the traditional phosphoric acid treatment method results in low coverage of AlPO4, single crystal structure and lack of gradient distribution, which makes it easy to occur crystal phase transition in the hydration environment. In order to improve the hydration stability, multiple phosphating treatments are required, which will result in a decrease in the surface hole density and specific capacity, making it difficult to meet the market demand for high-performance electrode foil.

[0007] The comprehensive analysis shows that the existing technology has obvious shortcomings in pore structure regulation, pollutant removal, interface optimization, and hydration resistance enhancement. These defects limit the specific capacity, reliability, and service life of the electrode foil, making it difficult to meet the application requirements of high-end capacitors. Therefore, it is urgent to realize the optimization of performance through the coordinated innovation of multi-scale structure design and process. SUMMARY

[0008] The present application aims to at least partially solve the technical problems existing in the prior art. To this end, the present application proposes an electrode foil and its preparation method and an aluminum electrolytic capacitor. By using the preparation method proposed in the present application, the uniformity of the oxide film of the electrode foil can be effectively improved, impurities can be removed deeply, and the interface performance can be optimized, thereby significantly improving the specific capacity, enhancing the hydration resistance and corrosion resistance, and prolonging the service life of the electrode foil.

[0009] In a first aspect, this application provides a method for preparing electrode foil. According to an embodiment of this application, the method includes: placing an etched foil in an electrolyte containing sulfuric acid and an organic carboxylic acid for pre-formation treatment to obtain a pre-formation product; placing the pre-formation product in a phosphoric acid solution for etching treatment to obtain an etched product; and subjecting the etched product to a re-formation treatment to obtain the electrode foil.

[0010] According to the preparation method of this application, a high-density, high-quality barrier layer is successfully constructed on the surface of an aluminum substrate by pre-forming with sulfuric acid and organic carboxylic acid. This barrier layer significantly improves the ability to block water molecule penetration, effectively reduces the destructive effect of hydration reaction on the oxide film structure, and thus enhances the uniformity of the oxide film coverage, thereby indirectly improving the specific capacitance of the electrode foil. Furthermore, the organic carboxylic acid reacts with the alumina on the surface of the etched foil to form a soluble aluminum carboxylate complex. This reaction continuously dissolves the loose oxide layer on the aluminum foil surface and the metal particles attached thereto, avoiding the particle accumulation phenomenon caused by localized over-corrosion in traditional single-acid systems. During the anodic oxidation process, its strong oxidizing properties preferentially corrode the grain boundary defect regions of the aluminum substrate, promoting the formation of main channels and converting the deep-seated residual metallic aluminum into soluble Al. 3+ This reduces the amount of unreacted metal powder residue. Therefore, sulfuric acid and organic carboxylic acids work together in the pre-cleaning stage to reduce unreacted metal powder residue.

[0011] In the pre-forming stage, in addition to forming a barrier layer, one or more layers of low-dielectric-constant oxide films are also formed. These oxide films are usually located outside the barrier layer, exhibiting a porous structure and a high specific surface area. Due to the relatively poor dielectric properties of the low-dielectric-constant oxide films, their insulation performance is inferior to that of the barrier layer. Phosphoric acid can effectively dissolve the low-dielectric-constant oxide films on the surface of the pre-formed product while preserving the functional underlying film. Through phosphoric acid etching, the gradient structure of the oxide film can be reconstructed, generating a composite crystalline layer with an outer layer of AlPO4·2H2O and an inner layer of AlPO4. The outer hydrated layer acts as a dynamic barrier, inhibiting the penetration of water molecules, while the anhydrous inner phase ensures dielectric properties, thereby improving hydration resistance. Furthermore, PO4… 3- Preferentially adsorbed at the active sites on the aluminum matrix, via PO4 3- Competitive adsorption displacement Cl - It enhances the capillary force of corrosion pores, promotes the penetration of acid into the depth of micropores, dissolves submicron-sized metal particles and aluminum foil ash remaining in the pores, and achieves deep removal of impurities.

[0012] By repairing and optimizing the defects of the oxide film through a re-reconstitution stage electrochemical method, its uniformity and density are enhanced, thereby improving the specific capacitance, withstand voltage and electrochemical stability of the electrode foil.

[0013] Therefore, by adopting the preparation method, the electrode foil oxidation film uniformity can be effectively improved, impurities can be effectively removed, and the interface performance can be optimized, so that the specific capacitance is significantly improved, the hydration resistance and corrosion resistance are enhanced, and the service life of the electrode foil is prolonged.

[0014] According to the embodiments of the present application, the above method for preparing an electrode foil can further have the following additional technical features: According to the embodiments of the present application, the concentration of sulfuric acid in the electrolyte is 0.01wt%-2wt%, and the concentration of organic carboxylic acid is 1wt%-10wt%.

[0015] According to the embodiments of the present application, the organic carboxylic acid includes one or more of oxalic acid, citric acid, tartaric acid, malic acid, malonic acid, and adipic acid.

[0016] According to the embodiments of the present application, the temperature of the pre-formation treatment is 15°C-50°C, and the time is 0.5 min-10 min.

[0017] According to the embodiments of the present application, the current of the pre-formation treatment is direct current and / or pulse direct current.

[0018] According to the embodiments of the present application, the current density of the pre-formation treatment is 10 mA / cm 2 -500 mA / cm 2 .

[0019] According to the embodiments of the present application, the duty cycle of the pulse direct current of the pre-formation treatment is 10%-80%.

[0020] According to the embodiments of the present application, the frequency of the pulse direct current of the pre-formation treatment is 10 Hz-800 Hz.

[0021] According to the embodiments of the present application, the voltage of the pre-formation treatment is a constant voltage and / or a step-varying voltage; when the voltage is a constant voltage, the constant voltage is 3 V-50 V; when the voltage is a step-varying voltage, the initial stage voltage is 3 V-10 V, and the time is 0.5 min-5 min; the main stage voltage is 3 V-50 V, and the time is 0.5 min-5 min.

[0022] According to the embodiments of the present application, the concentration of phosphoric acid in the phosphoric acid solution is 0.4 wt%-15 wt%.

[0023] According to the embodiments of the present application, the temperature of the etching treatment is 20°C-50°C, and the time is 0.5 min-10 min.

[0024] According to embodiments of the present application, the current density of the etching treatment is 5 mA / cm 2 300 mA / cm 2 .

[0025] According to embodiments of the present application, the current of the etching treatment is pulse direct current, the frequency of the pulse direct current is 10 Hz-500 Hz, and the duty cycle is 10%-80%.

[0026] According to embodiments of the present application, the voltage of the etching treatment is 3 V-50 V.

[0027] According to embodiments of the present application, after the reformation treatment, further comprising a post-treatment, the post-treatment comprising a phosphoric acid treatment, a heat treatment and a supplement formation treatment; wherein the phosphoric acid treatment, the heat treatment and the supplement formation treatment are independently performed at least once.

[0028] In the second aspect of the present application, an electrode foil is provided. According to embodiments of the present application, the electrode foil is prepared by the method of the first aspect.

[0029] In the third aspect of the present application, an application of the aforementioned electrode foil is provided. According to embodiments of the present application, the application is the electrode foil prepared by the preparation method of the first aspect or the electrode foil of the second aspect as an electrode foil of an aluminum electrolytic capacitor.

[0030] The fourth aspect of the present application provides an aluminum electrolytic capacitor. According to embodiments of the present application, the aluminum electrolytic capacitor comprises the electrode foil prepared by the preparation method of the first aspect or the electrode foil of the second aspect.

[0031] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION

[0032] Embodiments of the present application are described in detail below. The embodiments described below are exemplary only and are not intended to limit the present application, which can be embodied in various forms.

[0033] It should be noted that the terms "first", "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or a specific number of the technical features indicated. Thus, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. Further, in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more, and similarly, the meaning of "a plurality of kinds" is two or more kinds.

[0034] The term "wt%" means weight percent.

[0035] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the application. Any numerical values are approximations only. Numerical ranges include all values from and including the lower and the upper values, in increments of one unit used in the respective lowering and upper values. The endpoints of the ranges are not included. Any numerical value, however, can be expressed as approximately using the "about" term, as in the approximately x.y.z. Any numerical value, range or weight percentage can be approximated as a value, range or percentage by adding the term "about" before the respective value, range or percentage.

[0036] In this document, the terms "comprising" or "including" or "having" are intended to be open-ended terms that specifically permit the inclusion of one or more of the indicated steps, features, elements, components, or the like.

[0037] The following problems exist for the existing electrode foil manufacturing technology: (1) In a single acidizing system (such as using only sulfuric acid or using only a certain carboxylic acid), the barrier type oxide layer formed at the junction of the aluminum base and the oxide film is usually of poor quality (such as insufficient density, uniformity, and insulation), which limits the maximum voltage that can be applied in the chemical conversion process, thereby hindering the sufficient growth of the porous oxide layer required for high specific capacitance, and ultimately resulting in limited improvement of the specific capacitance of the aluminum electrode foil; (2) Residual chloride ions and foil ash are difficult to remove in depth, resulting in increased leakage current and shortened service life; (3) The direct current chemical conversion has significant thermal effects, and the oxide film is prone to cracking or dissolution; (4) The oxide film has poor hydration resistance and is prone to hydrolytic degradation.

[0038] The present application proposes an electrode foil and a preparation method thereof and an aluminum electrolytic capacitor, which will be described in detail below.

[0039] Method for preparing electrode foil In a first aspect, the present application proposes a method for preparing an electrode foil. According to an embodiment of the present application, the method comprises: placing a corrosion foil in an electrolyte containing sulfuric acid and an organic carboxylic acid for pre-chemical conversion treatment to obtain a pre-chemical conversion product; placing the pre-chemical conversion product in a phosphoric acid solution for etching treatment to obtain an etching product; and performing re-chemical conversion treatment on the etching product to obtain an electrode foil.

[0040] Thus, by using the preparation method proposed in the present application, the uniformity of the oxide film of the electrode foil can be effectively improved, impurities can be removed in depth, and the interface performance can be optimized, thereby significantly improving the specific capacitance, enhancing the hydration resistance and corrosion resistance, and prolonging the service life of the electrode foil.

[0041] According to an embodiment of the present application, the concentration of sulfuric acid in the electrolyte is 0.01 wt% to 2 wt%, for example, 0.01 wt%, 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2 wt%, etc. Thus, the sulfuric acid is beneficial to play the following roles: assisting in adjusting the oxidation reaction; on the basis of the carboxylic acid system, the addition of sulfuric acid helps to optimize the density and uniformity of the barrier type aluminum oxide layer; mild modification of the pore structure has a moderate dissolution adjustment effect on the porous aluminum oxide layer, which is beneficial to improve the pore connectivity or pore wall stability; promoting impurity dissolution, which helps to dissolve the residual trace amounts of metal aluminum or impurities during the dissolution treatment process, reducing their adverse effects on electrical properties; balancing film formation and dissolution, and the dissolution effect of sulfuric acid at this concentration is relatively controllable, which helps to inhibit the risk of excessive local corrosion caused by high sulfuric acid concentration, leading to pore wall collapse and abnormal increase in surface roughness.

[0042] According to an embodiment of the present application, the concentration of organic carboxylic acid in the electrolyte is 1 wt% to 10 wt%, for example, 1 wt%, 2 wt%, 4 wt%, 5 wt%, 6 wt%, 8 wt%, 10 wt%, etc. Thus, the organic carboxylic acid can complex Al 3+ , refine the subsurface branch holes, dissolve the loose oxide layer on the surface of the aluminum foil and the metal particles attached thereto, and inhibit local over-corrosion. In addition, using the above concentration of organic carboxylic acid can also avoid the appearance of sparse branch hole network and the generation of excessive aluminum carboxylate precipitates to block the pore channels.

[0043] According to an embodiment of the present application, the organic carboxylic acid includes one or more of oxalic acid, citric acid, tartaric acid, malic acid, malonic acid, and adipic acid.

[0044] According to an embodiment of the present application, the electrolyte is an aqueous solution containing sulfuric acid and organic carboxylic acid.

[0045] According to an embodiment of the present application, the temperature of the pre-formation treatment is 15°C to 50°C, for example, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, etc. Thus, the reaction rate is suitable, which is beneficial to form a complete and relatively dense pore oxidation film, the acid solution is not easy to evaporate, and the resulting electrode foil has better hydration resistance and corrosion resistance.

[0046] According to an embodiment of the present application, the time of the pre-formation treatment is 0.5 min to 10 min, for example, 0.5 min, 1 min, 2 min, 4 min, 5 min, 6 min, 8 min, 10 min, etc. Thus, it is beneficial to fully branch the pores, the growth rate of the porous layer is optimal, a complete and relatively dense porous structure is formed, and thus the specific surface area of the electrode foil is effectively improved.

[0047] According to an embodiment of the present application, the current of the pre-formation treatment is direct current and / or pulse direct current. With pulse direct current, the pulse-off time allows electrolyte cooling and ion diffusion, avoiding local overheating leading to oxide film cracking and dissolution, reducing thermal effects; the instantaneous high current density of the pulse can promote uniform growth of the oxide film, forming a dense oxide film, reducing concentration polarization.

[0048] According to an embodiment of the present application, the current density of the pre-formation treatment is 10 mA / cm 2 500 mA / cm 2 , for example, 10 mA / cm 2 , 50 mA / cm 2 , 100 mA / cm 2 , 150 mA / cm 2 , 200 mA / cm 2 , 250 mA / cm 2 , 300 mA / cm 2 , 350 mA / cm 2 , 400 mA / cm 2 , 450 mA / cm 2 , 500 mA / cm 2 , etc. Thus, it is beneficial to quickly form a film, obtain a sufficient depth of the pore, and avoid the increase of film defects caused by Joule heating effect.

[0049] According to an embodiment of the present application, the duty cycle of the pulse direct current of the pre-formation treatment is 10% to 80%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc. Thus, the chemical reaction can occur sufficiently, the specific surface area is improved, the film layer density is enhanced to improve hydration resistance, and the increase of film layer brittleness caused by significant thermal effect is avoided, and cracks are easily generated during subsequent peeling. Dynamic adjustment technology can be used, such as using a high duty cycle (e.g., 80%) for the first n1 minutes and switching to a low duty cycle (e.g., 30%) for the last n2 minutes.

[0050] According to an embodiment of the present application, the frequency of the pulse direct current of the pre-formation treatment is 10 Hz to 800 Hz, for example, 10 Hz, 50 Hz, 100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, 600 Hz, 700 Hz, 800 Hz, etc. Thus, high-frequency current can effectively suppress concentration polarization and optimize the off period. And by suppressing concentration polarization, the cracking or dissolution of the oxide film caused by Joule heating can be avoided; at the same time, by controlling the off period, the release of aluminum oxide volume shrinkage stress can be promoted, avoiding stress accumulation.

[0051] According to the embodiments of the present application, the current of the pre-formation treatment can be a superimposed current of direct current and pulse direct current, can be direct current first and then pulse direct current, can be pulse direct current first and then direct current, and can be only pulse direct current.

[0052] The sulfuric acid / organic carboxylic acid double acid electrolyte synergistic effect is adopted, the frequency and duty cycle of the pulse direct current are combined for regulation, the dynamic balance of the current density-temperature-concentration field is established, a high-quality barrier layer is formed at the junction of the aluminum base and the oxide film, the uniformity of the barrier layer oxide film coverage is improved, and the specific capacitance of the electrode foil is indirectly improved.

[0053] In order to further enhance the performance, the duty cycle and the frequency of the pulse direct current can be synergistically optimized. High frequency is combined with low duty cycle, short-time strong field breaks through the double-layer barrier, suppresses side reactions, and reduces leakage current; low frequency is combined with high duty cycle, continuous ion injection compensates for lattice defects, forms a gradient oxygen vacancy concentration distribution, and improves hydration stability.

[0054] According to the embodiments of the present application, the voltage of the pre-formation treatment is a constant voltage and / or a step-varying voltage.

[0055] In some embodiments, when the voltage is a constant voltage, the constant voltage is 3 V to 50 V, for example, can be 3 V, 5 V, 10 V, 15 V, 20 V, 25 V, 30 V, 35 V, 40 V, 45 V, 50 V, etc. The formation voltage can be adjusted according to the required voltage of the product.

[0056] In some embodiments, when the voltage is a step-varying voltage, the initial stage voltage is 3 V to 10 V, and the time is 0.5 min to 5 min, which induces uniform nucleation of the aluminum oxide film; the main stage voltage is 3 V to 50 V, and the time is 0.5 min to 5 min, which promotes further growth of the oxide film.

[0057] According to the embodiments of the present application, the concentration of phosphoric acid in the phosphoric acid solution is 0.4 wt% to 15 wt%, for example, can be 0.4 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, etc. In this way, the poor quality film layer formed by pre-formation can be quickly etched, the gradient structure of the oxide film is reconstructed, and the outer layer AlPO4·2H2O / inner layer AlPO4 composite crystal layer is generated. The outer layer hydration layer acts as a dynamic barrier to inhibit water molecule penetration, and the inner layer anhydrous phase guarantees dielectric performance, and the hydration resistance is improved. Over-etching is avoided to cause pore wall collapse and increase roughness.

[0058] According to the embodiments of the present application, the etching treatment has a temperature of 20-50°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C. In this way, the poor-quality film layer formed by pre-formation can be etched quickly, the gradient structure of the oxide film is restructured, and the outer layer AlPO4·2H2O / inner layer AlPO4 composite crystal layer is generated, the outer layer hydrated layer acts as a dynamic barrier to inhibit water molecule penetration, and the inner layer anhydrous phase guarantees the dielectric property, and the hydration resistance is improved. The acid solution is not easy to volatilize, avoiding damage to the oxide film due to excessively high temperature, and even corrosion of the aluminum substrate.

[0059] According to the embodiments of the present application, the etching treatment has a time of 0.5-10 min, for example, 0.5 min, 1 min, 2 min, 4 min, 5 min, 6 min, 8 min or 10 min. In this way, the acid solution can act on the film layer sufficiently, the poor-quality film layer formed by pre-formation is removed, the gradient structure of the oxide film is restructured, and the outer layer AlPO4·2H2O / inner layer AlPO4 composite crystal layer is generated, the outer layer hydrated layer acts as a dynamic barrier to inhibit water molecule penetration, and the inner layer anhydrous phase guarantees the dielectric property, and the hydration resistance is improved. In addition, the oxide film has an appropriate thickness, reducing the difficulty of subsequent stripping.

[0060] According to the embodiments of the present application, the etching treatment has a current density of 5 mA / cm 2 ~300 mA / cm 2 , for example, 5 mA / cm 2 , 10 mA / cm 2 , 50 mA / cm 2 , 100 mA / cm 2 , 150 mA / cm 2 , 200 mA / cm 2 , 250 mA / cm 2 , 300 mA / cm 2 , etc. In this way, the current density range is conducive to rapid etching, while avoiding excessive stripping to cause damage to the oxide film or corrosion of the aluminum substrate. In addition, when a sufficiently high current density pulse (e.g., ≥100 mA / cm 2 ) is used, the generated Joule heat can increase the temperature of the inner layer, inhibit water molecules from being embedded, and maintain the anhydrous AlPO4 structure; the anhydrous layer has higher density and dielectric constant, which can further guarantee the insulation property of the dielectric layer.

[0061] According to the embodiments of the present application, the current of the etching treatment is pulse direct current, the frequency of the pulse direct current is 10 Hz-500 Hz, for example, can be 10 Hz, 50 Hz, 100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, etc.; the duty cycle of the pulse direct current is 10%-80%, for example, can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc. Thus, the depolarization effect is achieved.

[0062] According to the embodiments of the present application, the voltage of the etching treatment is 3 V-50 V, for example, can be 3 V, 5 V, 10 V, 15 V, 20 V, 25 V, 30 V, 35 V, 40 V, 45 V, 50 V, etc. The formation voltage can be adjusted according to the required voltage of the product.

[0063] According to the embodiments of the present application, the phosphoric acid solution is an aqueous solution of phosphoric acid.

[0064] According to the embodiments of the present application, before the re-formation treatment, the etching foil is subjected to a boiling water treatment.

[0065] In some embodiments, the boiling water treatment includes boiling the etching foil in boiling water for 5-20 min, for example, can be 5 min, 10 min, 15 min, 20 min, etc. In some embodiments, the boiling water treatment can be optionally omitted.

[0066] According to the embodiments of the present application, after the re-formation treatment, further includes a post-treatment, the post-treatment includes a phosphoric acid treatment, a heat treatment and a supplement formation treatment, wherein the phosphoric acid treatment, the heat treatment and the supplement formation treatment are each independently performed at least once.

[0067] According to the embodiments of the present application, the sequence of the re-formation treatment and the at least one phosphoric acid treatment, heat treatment and supplement formation treatment can be adjusted as needed, and does not have to be performed in a certain order.

[0068] In some embodiments, the re-formation treatment adopts a multi-stage formation method, for example, the formation stages are 2, 3, 4 or 5 stages.

[0069] In some embodiments, the formation stages are 2 stages, that is, the re-formation includes a first-stage formation and a second-stage formation.

[0070] In some embodiments, the formation stages are 3 stages, that is, the re-formation includes a first-stage formation, a second-stage formation and a third-stage formation.

[0071] In some embodiments, the number of formation stages is 4, i.e., the re-formation includes a first formation, a second formation, a third formation, and a fourth formation.

[0072] In some embodiments, the number of formation stages is 5, i.e., the re-formation includes a first formation, a second formation, a third formation, a fourth formation, and a fifth formation.

[0073] In some embodiments, each of the formation solutions in the re-formation process independently comprises at least one of ammonium adipate, ammonium dihydrogen phosphate, boric acid, and ammonium pentaborate.

[0074] In some embodiments, the concentration of the solute in the formation solution is 0.1-25 wt%, for example, it can be 0.1 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, etc.

[0075] In some embodiments, the temperature of each of the formation stages in the re-formation process is independently 50-90°C, for example, it can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.

[0076] In some embodiments, the time of each of the formation stages in the re-formation process is independently 1-10 min, for example, it can be 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.

[0077] In some embodiments, the voltage of each of the formation stages in the re-formation process is independently 10-100% of the rated voltage, for example, it can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% of the rated voltage, etc., wherein the fifth formation voltage > fourth formation voltage > third formation voltage > second formation voltage > first formation voltage.

[0078] In some embodiments, the current density of each of the formation stages in the re-formation process is independently 10-600 mA / cm 2 , for example, it can be 10 mA / cm 2 , 100 mA / cm 2 , 200 mA / cm 2 , 300 mA / cm 2 , 400 mA / cm 2 , 500 mA / cm 2 , 600 mA / cm 2 , etc.

[0079] In some embodiments, the temperature of each of the heat treatments is independently 300-700°C, for example, 300°C, 400°C, 500°C, 600°C, 700°C, etc., and the time is independently 1-10 min, for example, 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.

[0080] In some embodiments, the phosphoric acid treatment comprises soaking the etched foil in a phosphoric acid solution having a concentration of 1.5 wt% to 10 wt% phosphoric acid, and the temperature of the phosphoric acid treatment is 45°C to 75°C and the time is 2 to 6 min. In some embodiments, the phosphoric acid solution used in the phosphoric acid treatment is an aqueous solution of phosphoric acid.

[0081] In some embodiments, each of the supplemental formation treatments independently comprises placing the etched foil in an ammonium dihydrogen phosphate solution (having a concentration of 5 wt% to 15 wt% ammonium dihydrogen phosphate), and the temperature of each of the supplemental formation treatments is independently 75°C to 85°C, the time of each of the supplemental formation treatments is independently 2 to 3 min, the voltage of each of the supplemental formation treatments is independently 33 to 520 V, and the current density of each of the supplemental formation treatments is independently 100 to 600 mA / cm 2 .

[0082] In some embodiments, the etched foil can be subjected to a water washing treatment with clean water before any of the post-treatments to remove surface residual impurities.

[0083] In summary, the technology integration of sulfuric acid / organic carboxylic acid double acid synergistic pre-formation, phosphoric acid interface strengthening, and impurity synergistic removal breaks through the bottleneck of traditional process single-aperture regulation and impurity residue, and for the first time realizes the synergistic optimization of electrode foil micro-nano composite structure and phosphoric acid aluminum enhanced interface, providing an innovative solution for high specific capacitance and long-life aluminum electrolytic capacitors.

[0084] Advantages: 1. The present application improves the quality and uniformity of the barrier-type oxide layer at the junction of the electrode foil aluminum base and the oxide film, indirectly improves the specific capacitance, uses a sulfuric acid / organic carboxylic acid double acid electrolyte, effectively controls the reaction rate, reduces the cracking and dissolution of the oxide film, and forms a high-quality, uniform barrier-type oxide layer in the etched hole.

[0085] 2. The present application optimizes the microstructure of the electrode foil by increasing the effective specific surface area, thereby improving the specific capacitance, which is derived from the core determination formula of specific capacitance: C S = εS / 4πkd (where C SFor specific capacitance, ε is the dielectric constant, S is the effective specific surface area, k is the vacuum dielectric constant, d is the oxide film thickness), under the premise of maintaining the compactness of the oxide film, increasing the effective specific surface area can directly improve the specific capacitance.

[0086] 3. The application can deeply clean the electrode foil by chemical dissolution and ion replacement method, effectively remove the deeply residual foil ash, chloride ions, other metal impurities, etc. of the corrosion foil, reduce the discharge effect of the aluminum foil tip, reduce the defect density of the dielectric layer, reduce the leakage current, improve the overall quality of the electrode foil, and thus prolong the service life of the prepared capacitor.

[0087] 4. The method of the application adopts pulse direct current for pre-formation, and the pulse power-off time allows electrolyte cooling and ion diffusion, avoiding local overheating leading to oxide film cracking and dissolution, reducing thermal effects; the instantaneous high current density of the pulse can promote the uniform growth of the oxide film, form a dense oxide film, and reduce concentration polarization; by adjusting the pulse parameters (such as duty cycle, frequency), the quality of the oxide film can be further improved.

[0088] 5. The application establishes an in-situ growth model of aluminum phosphate to increase the effective initial contact area between phosphate and aluminum matrix, improve the amount of aluminum phosphate generated, form a composite crystal structure of AlPO4·2H2O (outer layer) and AlPO4 (inner layer) in the dielectric layer, and improve the hydration resistance and corrosion resistance of the oxide film.

[0089] 6. The application introduces an oxide film dynamic stripping technique, uses a current method to achieve precise removal of the interface oxide film, controls the stripping depth of the oxide film by adjusting the pulse frequency and current density, ensures that only the loose layer containing impurities on the surface is removed, and the functional medium film at the bottom is retained.

[0090] 7. The electrode foil prepared by the application has a simple preparation process, can be compatible with existing processes, and reduces production costs.

[0091] 8. Through the synergistic effect of sulfuric acid and organic carboxylic acid, a high-quality barrier layer is formed at the junction between the aluminum base and the oxide film, the coverage uniformity of the barrier layer is improved, and the specific capacitance of the electrode foil is indirectly improved. At the same time, the organic carboxylic acid complex removes surface metal particles, and the sulfuric acid oxidizes the deep residual aluminum powder into soluble Al 3+ , and the sulfuric acid and organic carboxylic acid play a pre-cleaning role in the pre-formation stage. Therefore, the hydration resistance and insulation of the electrode foil as a whole are improved.

[0092] Electrode foil In the second aspect of the application, an electrode foil is provided. According to embodiments of the application, the electrode foil is prepared by the method of the first aspect. Therefore, the electrode foil of the application has uniform oxide film quality and strong interface performance, and has excellent specific capacitance, hydration resistance, corrosion resistance, insulation and service life.

[0093] In a third aspect of the present application, an application of the electrode foil is provided. According to embodiments of the present application, the application is the electrode foil prepared by the preparation method of the first aspect of the present application or the electrode foil of the second aspect of the present application.

[0094] Aluminum electrolytic capacitor In a fourth aspect of the present application, the fourth aspect of the present application provides an aluminum electrolytic capacitor. According to embodiments of the present application, the aluminum electrolytic capacitor comprises the electrode foil prepared by the preparation method of the first aspect of the present application or the electrode foil of the second aspect of the present application. Thus, the aluminum electrolytic capacitor of the present application has excellent electrochemical performance and service life.

[0095] It should be noted that the features and advantages described above for the preparation of the electrode foil also apply to the electrode foil and the aluminum electrolytic capacitor, and will not be repeated here.

[0096] The solutions of the present application will be explained below in conjunction with examples. Those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. If the specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or according to the product instructions are used. If the reagents or instruments are not specified by the manufacturer, they are all conventional products that can be obtained by purchase.

[0097] Example 1 In this example, a 33Vf electrode foil was prepared according to the following method: S01: Pre-formation treatment An etching foil with a thickness of 120 μm was placed in an electrolyte (the electrolyte was an aqueous solution of sulfuric acid and oxalic acid, the concentration of sulfuric acid in the electrolyte was 0.01 wt%, and the concentration of oxalic acid was 4 wt%) for pre-formation treatment according to the following pre-formation treatment parameters, and the temperature was 20°C.

[0098] Pre-formation treatment parameters: the current mode was first pulse direct current and then direct current, the first 0.5 min was pulse direct current, the duty cycle was 60%, the frequency was 50 Hz, the current density was 25 mA / cm 2 , and the voltage was 3V; the last 2 min was direct current, the current density was 25 mA / cm 2 , and the voltage was 5V.

[0099] S02: Selective chemical etching treatment The etching foil treated by S01 is placed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, and the concentration of phosphoric acid in the phosphoric acid solution is 2 wt%) for selective chemical etching treatment, the temperature is 20°C, and the electric parameters of the selective chemical etching treatment are as follows: the pulse direct current density is 15 mA / cm 2 , the frequency is 100 Hz, the duty cycle is 30%, the voltage is 3V, and the time is 0.5 min.

[0100] S03: Reformation and post-treatment The etching foil treated by S02 is placed in an ammonium adipate solution (the ammonium adipate solution is an aqueous solution of ammonium adipate, and the concentration of ammonium adipate in the solution is 15 wt%) for five-stage reformation, and the temperature of each stage is independently 75°C, the voltage of each stage is independently 20%, 40%, 60%, 80%, and 100% of the rated formation voltage, and the current density of each stage is independently 100 mA / cm 2 , and the constant voltage time of each stage is independently 3 min.

[0101] First heat treatment: After water washing, the etching foil is subjected to first heat treatment, and the temperature of the first heat treatment is 480°C, and the time is 2 min.

[0102] First reformation treatment: The etching foil after the first heat treatment is placed in an ammonium dihydrogen phosphate solution (the ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, and the concentration of ammonium dihydrogen phosphate in the solution is 15 wt%) for first reformation treatment, the temperature of the first reformation treatment is 75°C, the time is 2 min, the voltage is 33 V, and the current density is 100 mA / cm 2 .

[0103] First phosphoric acid treatment: The etching foil after the first reformation treatment is immersed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, and the concentration of phosphoric acid in the solution is 1.5 wt%) for treatment, the temperature is 45°C, and the time is 2 min.

[0104] Second heat treatment: After water washing, the etching foil after the phosphoric acid treatment is subjected to second heat treatment, and the temperature of the second heat treatment is 480°C, and the time is 2 min.

[0105] Second reformation treatment: The etching foil after the second heat treatment is placed in an ammonium dihydrogen phosphate solution (the ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, and the concentration of ammonium dihydrogen phosphate in the solution is 15 wt%) for second reformation treatment, the temperature of the second reformation treatment is 75°C, the time is 2 min, the voltage is 33 V, and the current density is 100 mA / cm 2 , and the electrode foil is obtained after water washing and drying.

[0106] Example 2 In this example, the 33Vf electrode foil was prepared according to the following method: S01: Pre-formation treatment The etching foil with a thickness of 120 pm was placed in an electrolyte (the electrolyte was an aqueous solution of sulfuric acid and citric acid, the concentration of sulfuric acid in the electrolyte was 0.01 wt%, and the concentration of citric acid was 10 wt%) for pre-formation treatment according to the following pre-formation treatment electrical parameters, and the temperature was 50°C.

[0107] Pre-formation treatment electrical parameters: the current mode was superimposed direct current and pulse direct current, wherein the direct current density was 5 mA / cm 2 ; the pulse direct current, the duty ratio was dynamically adjusted, the duty ratio was 70% for the first 0.5 min, the frequency was 10 Hz, the current density was 50 mA / cm 2 , the voltage was 3V, the duty ratio was 30% for the last 5 min, the frequency was 500 Hz, the current density was 100 mA / cm 2 , and the voltage was 5V.

[0108] S02: Selective chemical etching treatment The etching foil treated by S01 was placed in a phosphoric acid solution (the phosphoric acid solution was an aqueous solution of phosphoric acid, and the concentration of phosphoric acid in the phosphoric acid solution was 15 wt%) for selective chemical etching treatment, and the temperature was 20°C, wherein the electrical parameters of the selective chemical etching treatment were as follows: the pulse direct current density was 5 mA / cm 2 , the frequency was 100 Hz, the duty ratio was 30%, the voltage was 3V, and the time was 1 min.

[0109] S03: Re-formation and post-treatment The etching foil treated by S02 was placed in an ammonium adipate solution (the ammonium adipate solution was an aqueous solution of ammonium adipate, and the concentration of ammonium adipate in the solution was 15 wt%) for five-stage formation in sequence, and the temperature of each stage was independently 75°C, the voltage of each stage was independently 20%, 40%, 60%, 80%, and 100% of the rated formation voltage, the current density of each stage was independently 100 mA / cm 2 , and the constant voltage time of each stage was independently 3 min.

[0110] First heat treatment: after washing with water, the etching foil was subjected to a first heat treatment, and the temperature of the first heat treatment was 500°C, and the time was 2 min.

[0111] First-time compensatory formation treatment: the etching foil after the first-time heat treatment was placed in an ammonium dihydrogen phosphate solution (ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, the concentration of ammonium dihydrogen phosphate in the solution is 15 wt%) for the first-time compensatory formation treatment, the temperature of the first-time compensatory formation treatment was 75°C, the time was 2 min, the voltage was 33 V, and the current density was 100 mA / cm 2 .

[0112] First-time phosphoric acid treatment: the etching foil after the first-time compensatory formation treatment was immersed in a phosphoric acid solution (phosphoric acid solution is an aqueous solution of phosphoric acid, the concentration of phosphoric acid in the solution is 1.5 wt%) for treatment, the temperature was 45°C, and the time was 2 min.

[0113] Second-time heat treatment: the etching foil after the phosphoric acid treatment was washed with water and then subjected to a second-time heat treatment, the temperature of the second-time heat treatment was 480°C, and the time was 2 min.

[0114] Second-time compensatory formation treatment: the etching foil after the second-time heat treatment was placed in an ammonium dihydrogen phosphate solution (ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, the concentration of ammonium dihydrogen phosphate in the solution is 15 wt%) for the second-time compensatory formation treatment, the temperature of the second-time compensatory formation treatment was 75°C, the time was 2 min, the voltage was 33 V, and the current density was 100 mA / cm 2 , and then dried to obtain an electrode foil.

[0115] Example 3 In this example, a 105Vf electrode foil was prepared according to the following method: S01: Pre-formation treatment An etching foil with a thickness of 120 μm was placed in an electrolyte (electrolyte is an aqueous solution of sulfuric acid and tartaric acid, the concentration of sulfuric acid in the electrolyte is 0.05 wt%, and the concentration of tartaric acid is 10 wt%) for pre-formation treatment according to the following pre-formation treatment electrical parameters, and the temperature was 35°C.

[0116] Pre-formation treatment electrical parameters: the current mode was pulse direct current, the duty ratio was dynamically adjusted, the duty ratio was 80% for the first 2 min, the frequency was 85 Hz, the current density was 50 mA / cm 2 , the voltage was 5 V, the duty ratio was 50% for the last 3 min, the frequency was 500 Hz, the current density was 20 mA / cm 2 , and the voltage was 30 V.

[0117] S02: Selective chemical etching treatment The etching foil treated by S01 is placed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, the concentration of phosphoric acid in the phosphoric acid solution is 6 wt%) for selective chemical etching treatment, the temperature is 40°C, and the electric parameters of the selective chemical etching treatment are as follows: the pulse direct current density is 30 mA / cm 2 , the frequency is 100 Hz, the duty cycle is 30%, the voltage is 15 V, and the time is 5 min.

[0118] S03: Reformation and post-treatment The etching foil treated by S02 is placed in a mixed solution of ammonium adipate and boric acid (the mixed solution is an aqueous solution of ammonium adipate and boric acid, the concentration of ammonium adipate in the mixed solution is 15 wt%, and the concentration of boric acid is 1 wt%) for first-stage, second-stage and third-stage reformation in sequence, the temperature of each stage is independently 75°C, the voltage of each stage is independently 30%, 60% and 100% of the rated formation voltage, the current density of each stage is independently 100 mA / cm 2 , and the constant voltage time of each stage is independently 5 min.

[0119] First phosphoric acid treatment: after washing with water, the etching foil is immersed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, the concentration of phosphoric acid in the solution is 1.5 wt%) for treatment, the temperature is 75°C, and the time is 3 min.

[0120] First heat treatment: after washing with water, the etching foil after the phosphoric acid treatment is subjected to the first heat treatment, the temperature of the first heat treatment is 500°C, and the time is 3 min.

[0121] First reformation treatment: the etching foil after the first heat treatment is placed in an ammonium dihydrogen phosphate solution (the ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, the concentration of ammonium dihydrogen phosphate in the solution is 5 wt%) for the first reformation treatment, the temperature of the first reformation treatment is 85°C, the time is 2 min, the voltage is 105 V, and the current density is 100 mA / cm 2 , and the electrode foil is obtained after drying after washing with water.

[0122] Example 4 In this example, a 105 Vf electrode foil is prepared according to the following method: S01: Pre-reformation treatment An etching foil with a thickness of 120 μm is placed in an electrolyte (the electrolyte is an aqueous solution of sulfuric acid, tartaric acid and malonic acid, the concentration of sulfuric acid in the electrolyte is 0.05 wt%, the concentration of tartaric acid is 1.5 wt%, and the concentration of malonic acid is 7 wt%) for pre-reformation treatment according to the following pre-reformation treatment electric parameters, and the temperature is 15°C.

[0123] Pre-formation treatment: current mode is pulse direct current, duty cycle is dynamically adjusted, duty cycle is 65% in the first 2 min, frequency is 120 Hz, current density is 100 mA / cm 2 , voltage is 10 V, duty cycle is 20% in the last 3 min, frequency is 240 Hz, current density is 50 mA / cm 2 , voltage is 30 V.

[0124] S02: Selective chemical etching treatment The etching foil treated by S01 is placed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, and the concentration of phosphoric acid in the phosphoric acid solution is 0.4 wt%) for selective chemical etching treatment, and the temperature is 50°C, wherein the electrical parameters of the selective chemical etching treatment are: pulse direct current density is 300 mA / cm 2 , frequency is 50 Hz, duty cycle is 40%, voltage is 15 V, and time is 5 min.

[0125] S03: Re-formation and post-treatment The etching foil treated by S02 is placed in a mixed solution of ammonium adipate and boric acid (the mixed solution is an aqueous solution of ammonium adipate and boric acid, the concentration of ammonium adipate in the mixed solution is 15 wt%, and the concentration of boric acid is 1 wt%) for three-stage formation in turn, and the temperature of each stage is independently 75°C, the voltage of each stage is independently 30%, 60%, and 100% of the rated formation voltage, and the current density of each stage is independently 100 mA / cm 2 , and the constant voltage time of each stage is independently 5 min.

[0126] First phosphoric acid treatment: after washing with water, the etching foil is immersed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, and the concentration of phosphoric acid in the solution is 1.5 wt%) for treatment, the temperature is 75°C, and the time is 3 min.

[0127] First heat treatment: after washing with water, the etching foil after the phosphoric acid treatment is subjected to a first heat treatment, and the temperature of the first heat treatment is 570°C, and the time is 2 min.

[0128] First supplementary formation treatment: the etching foil after the first heat treatment is placed in an ammonium dihydrogen phosphate solution (the ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, and the concentration of ammonium dihydrogen phosphate in the solution is 5 wt%) for first supplementary formation treatment, the temperature is 85°C, the time is 2 min, the voltage is 105 V, and the current density is 100 mA / cm 2 , and the electrode foil is obtained after drying after washing with water.

[0129] Example 5 In this embodiment, the 520Vf electrode foil was prepared according to the following method: S01: pre-formation treatment The etching foil with a thickness of 120 μm was subjected to pre-formation treatment in an electrolyte (the electrolyte was an aqueous solution of sulfuric acid and oxalic acid, the concentration of sulfuric acid in the electrolyte was 2 wt%, and the concentration of oxalic acid was 8 wt%) according to the following pre-formation treatment electrical parameters, and the temperature was 30°C.

[0130] Pre-formation treatment electrical parameters: pulse direct current mode, dynamic duty cycle adjustment, the duty cycle was 80% for the first 2.5 min, the frequency was 40 Hz, the current density was 400 mA / cm 2 , the voltage was 10V, the duty cycle was 35% for the next 2.5 min, the frequency was 100 Hz, and the current density was 500 mA / cm 2 , the voltage was 50V.

[0131] S02: selective chemical etching treatment The etching foil treated by S01 was subjected to selective chemical etching treatment in a phosphoric acid solution (the phosphoric acid solution was an aqueous solution of phosphoric acid, and the concentration of phosphoric acid in the phosphoric acid solution was 12 wt%), and the temperature was 45°C, wherein the electrical parameters of the selective chemical etching treatment were as follows: pulse direct current density was 200 mA / cm 2 , the frequency was 50 Hz, the duty cycle was 40%, the voltage was 40V, and the time was 4 min.

[0132] S03: re-formation and post-treatment After being boiled in boiling water for 15 min, the etching foil treated by S02 was subjected to primary formation and secondary formation in an aqueous ammonium dihydrogen phosphate solution (the concentration of ammonium dihydrogen phosphate was 0.14 wt%), and the temperature of each formation was independently 85°C, the voltage of each formation was independently 20% and 40% of the rated formation voltage, and the current density of each formation was independently 400 mA / cm 2 , and the constant voltage time of each formation was independently 7 min; after washing with water, the etching foil was subjected to tertiary formation, quaternary formation, and quinary formation in a mixed solution of boric acid and ammonium pentaborate (the mixed solution was an aqueous solution of boric acid and ammonium pentaborate, the concentration of boric acid in the mixed solution was 10 wt%, and the concentration of ammonium pentaborate was 0.1 wt%), and the temperature of each formation was independently 90°C, the voltage of each formation was independently 60%, 80%, and 100% of the rated formation voltage, and the current density of each formation was independently 600 mA / cm 2 , and the constant voltage time of each formation was independently 7 min.

[0133] First phosphoric acid treatment: after water washing, the etching foil is immersed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, and the concentration of phosphoric acid in the solution is 10 wt%) for treatment, the temperature is 65°C, and the time is 6 min.

[0134] First heat treatment: after water washing of the etching foil after the phosphoric acid treatment, the first heat treatment is performed, the temperature of the first heat treatment is 550°C, and the time is 4 min.

[0135] First complementary formation treatment: the etching foil after the first heat treatment is placed in an ammonium dihydrogen phosphate solution (the ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, and the concentration of ammonium dihydrogen phosphate in the solution is 5 wt%) for the first complementary formation treatment, the temperature of the first complementary formation treatment is 85°C, the time is 3 min, the voltage is 520 V, and the current density is 600 mA / cm 2 , the second phosphoric acid treatment, the second complementary formation treatment, the second heat treatment, and the third complementary formation treatment are performed according to the above conditions, and the electrode foil is obtained after water washing and drying.

[0136] Example 6 In this example, a 520Vf electrode foil is prepared according to the following method: S01: Pre-formation treatment An etching foil with a thickness of 120 μm is placed in an electrolyte (the electrolyte is an aqueous solution of sulfuric acid and adipic acid, the concentration of sulfuric acid in the electrolyte is 1.5 wt%, and the concentration of adipic acid is 5 wt%) for pre-formation treatment according to the following pre-formation treatment electrical parameters, and the temperature is 40°C.

[0137] Pre-formation treatment electrical parameters: the current mode is pulse direct current, the duty ratio is dynamically adjusted, the duty ratio is 76% for the first 1 min, the frequency is 500 Hz, the current density is 400 mA / cm 2 , the voltage is 10 V, the duty ratio is 20% for the last 3 min, the frequency is 800 Hz, and the current density is 10 mA / cm 2 , and the voltage is 45 V.

[0138] S02: Selective chemical etching treatment The etching foil after S01 treatment is placed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, and the concentration of phosphoric acid in the solution is 6 wt%) for selective chemical etching treatment, the temperature is 20°C, and the electrical parameters of the selective chemical etching treatment are as follows: the pulse direct current density is 45 mA / cm 2 , the frequency is 60 Hz, the duty ratio is 50%, the voltage is 35 V, and the time is 10 min.

[0139] S03: Re-formation and post-treatment The etching foil subjected to S02 treatment is boiled in boiling water for 15 min, then subjected to primary and secondary chemical conversion in an aqueous ammonium dihydrogen phosphate solution (the concentration of ammonium dihydrogen phosphate is 0.14 wt%), each independently at a temperature of 85℃, and each at a voltage of 20% and 40% of the rated forming voltage, respectively, and each independently at a current density of 400 mA / cm 2 , respectively; after washing with water, subjected to tertiary, quaternary and quinary chemical conversion in a mixed solution of boric acid and ammonium pentaborate (the mixed solution is an aqueous solution of boric acid and ammonium pentaborate, the concentration of boric acid in the mixed solution is 10 wt%, and the concentration of ammonium pentaborate is 0.1 wt%), each independently at a temperature of 90℃, and each at a voltage of 60%, 80% and 100% of the rated forming voltage, respectively, and each independently at a current density of 600 mA / cm 2 , respectively; and each independently for a constant voltage time of 7 min.

[0140] First phosphoric acid treatment: after washing with water, the etching foil is immersed in a phosphoric acid solution (the phosphoric acid solution is an aqueous solution of phosphoric acid, the concentration of phosphoric acid in the solution is 10 wt%) at a temperature of 65℃ for 6 min.

[0141] First heat treatment: after washing with water, the etching foil subjected to the phosphoric acid treatment is subjected to a first heat treatment at a temperature of 550℃ for 4 min.

[0142] First supplementary formation treatment: the etching foil subjected to the first heat treatment is subjected to a first supplementary formation treatment in an ammonium dihydrogen phosphate solution (the ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, the concentration of ammonium dihydrogen phosphate in the solution is 5 wt%) at a temperature of 85℃ for 3 min, a voltage of 520 V and a current density of 600 mA / cm 2 , and the second supplementary formation treatment, the second heat treatment and the third supplementary formation treatment are performed according to the above conditions, and the electrode foil is obtained after washing with water and drying.

[0143] Comparative Example 1 In comparison with Example 3, the S01 and S02 steps are deleted, and only the S03 step is included, as follows: The etching foil with a thickness of 120 μm was sequentially subjected to first-stage plating, second-stage plating and third-stage plating in a mixed solution of ammonium adipate and boric acid (the mixed solution was an aqueous solution of ammonium adipate and boric acid, the concentration of ammonium adipate in the mixed solution was 15 wt%, and the concentration of boric acid was 1 wt%), each of the plating temperatures was independently 75°C, each of the plating voltages was 30%, 60%, and 100% of the rated plating voltage, and each of the plating current densities was independently 100 mA / cm 2 , and each of the constant voltage times of the plating was independently 5 min.

[0144] First phosphoric acid treatment: after water washing, the etching foil was immersed in a phosphoric acid solution (the phosphoric acid solution was an aqueous solution of phosphoric acid, the concentration of phosphoric acid in the solution was 1.5 wt%) for treatment, the temperature was 75°C, and the time was 3 min.

[0145] First heat treatment: after water washing of the etching foil after the phosphoric acid treatment, the first heat treatment was performed, the temperature of the first heat treatment was 500°C, and the time was 3 min.

[0146] First supplementary plating treatment: the etching foil after the first heat treatment was placed in an ammonium dihydrogen phosphate solution (the ammonium dihydrogen phosphate solution was an aqueous solution of ammonium dihydrogen phosphate, the concentration of ammonium dihydrogen phosphate in the solution was 5 wt%) for the first supplementary plating treatment, the temperature of the first supplementary plating treatment was 85°C, the time was 2 min, the voltage was 105 V, and the current density was 100 mA / cm 2 , and the electrode foil was obtained after water washing and drying.

[0147] Comparative Example 2 In comparison with Example 3, the steps S01 and S02 were deleted, and the step S03 was modified, and the details were as follows: The etching foil with a thickness of 120 μm was sequentially subjected to first-stage plating, second-stage plating, third-stage plating, fourth-stage plating and fifth-stage plating in a mixed solution of ammonium adipate and boric acid (the mixed solution was an aqueous solution of ammonium adipate and boric acid, the concentration of ammonium adipate in the mixed solution was 15 wt%, and the concentration of boric acid was 1 wt%), each of the plating temperatures was independently 75°C, each of the plating voltages was 20%, 40%, 60%, 80%, and 100% of the rated plating voltage, and each of the plating current densities was independently 100 mA / cm 2 , and each of the constant voltage times of the plating was independently 5 min.

[0148] First phosphoric acid treatment: after water washing, the etching foil was immersed in a phosphoric acid solution (the phosphoric acid solution was an aqueous solution of phosphoric acid, the concentration of phosphoric acid in the solution was 1.5 wt%) for treatment, the temperature was 75°C, and the time was 3 min.

[0149] First-time compensatory formation treatment: the etching foil after phosphoric acid treatment was placed in an ammonium dihydrogen phosphate solution (ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, the concentration of ammonium dihydrogen phosphate in the solution is 5 wt%) for first-time compensatory formation treatment, the temperature of first-time compensatory formation treatment was 85°C, the time was 2 min, the voltage was 105 V, and the current density was 100 mA / cm 2 .

[0150] First-time heat treatment: the etching foil after first-time compensatory formation treatment was washed with water and then subjected to first-time heat treatment, the temperature of first-time heat treatment was 500°C, and the time was 3 min.

[0151] Second-time compensatory formation treatment: the etching foil after first-time heat treatment was placed in an ammonium dihydrogen phosphate solution (ammonium dihydrogen phosphate solution is an aqueous solution of ammonium dihydrogen phosphate, the concentration of ammonium dihydrogen phosphate in the solution is 5 wt%) for second-time compensatory formation treatment, the temperature of second-time compensatory formation treatment was 85°C, the time was 2 min, the voltage was 105 V, and the current density was 100 mA / cm 2 .

[0152] The electrode foil was obtained after the second-time phosphoric acid treatment, third-time compensatory formation treatment, second-time heat treatment, and fourth-time compensatory formation treatment, and then washing and drying.

[0153] Comparative Example 3 Compared with Example 3, the steps of S01 and S03 were unchanged, and the step of S02 was modified as follows: S02: selective chemical etching treatment The etching foil after S01 treatment was immersed in a phosphoric acid solution (phosphoric acid solution is an aqueous solution of phosphoric acid, the concentration of phosphoric acid in the solution is 6 wt%) for immersion corrosion, the temperature was 40°C, and the time was 5 min.

[0154] Comparative Example 4 Compared with Example 3, the steps of S02 and S03 were unchanged, and the step of S01 was modified to contain only a sulfuric acid solution, as follows: S01: pre-formation treatment The etching foil with a thickness of 120 μm was placed in a sulfuric acid aqueous solution with a sulfuric acid concentration of 0.05 wt% for pre-formation treatment, and the temperature was 35°C.

[0155] Current: the current mode was pulse direct current, the duty ratio was dynamically adjusted, the duty ratio was 80% for the first 2 min, the frequency was 85 Hz, the current density was 50 mA / cm 2 , the voltage was 5 V, the duty ratio was 50% for the last 3 min, the frequency was 500 Hz, the current density was 20 mA / cm 2 , and the voltage was 30 V.

[0156] Comparative Example 5 In comparison with Example 3, the S02 and S03 steps remain unchanged, and the S01 step is modified to contain only a tartaric acid solution, as follows: S01: Pre-formation treatment A 120-μm-thick etching foil was subjected to pre-formation treatment in a tartaric acid aqueous solution with a tartaric acid concentration of 10 wt%, at a temperature of 35°C.

[0157] Current: The current mode was pulsed direct current, with dynamic duty cycle adjustment. The duty cycle was 80% for the first 2 min, the frequency was 85 Hz, and the current density was 50 mA / cm 2 , the voltage was 5 V. The duty cycle was 50% for the last 3 min, the frequency was 500 Hz, and the current density was 20 mA / cm 2 , and the voltage was 30 V.

[0158] Test Example The electrode foils prepared in Examples 1-6 and Comparative Examples 1-5 were tested, and the specific capacitance and Tr60, etc. were tested according to the standard test method in the national standard SJ / T 11140-2022 for electrode foils for aluminum electrolytic capacitors. Specifically: Oxidation film voltage resistance and voltage rise time test method for high-voltage electrode foils (Example 5 and Example 6): The test solution was boric acid aqueous solution (concentration controlled according to rated voltage grading, such as 70 g / L for 170-700 V), the temperature was 85°C, and the projected area of the sample was 5 cm 2 . The sample was immersed in the test solution to a depth of 6-8 mm, and the sample was raised in voltage at a constant current of 2 mA. The time taken for the voltage to rise to 90% Vf from the start of power supply was recorded as the voltage rise time Tr. Timing started when the voltage rose to 90% of the rated formation voltage Vf, and the voltage value reached after 180 s of continuous power supply was the oxidation film voltage resistance V t . Oxidation film voltage resistance and voltage rise time test method for low-voltage electrode foils (Examples 1-4 and Comparative Examples 1-5): The test solution was ammonium adipate aqueous solution (concentration 150 g / L), the temperature was 85°C, and the projected area of the sample was 5 cm 2 . The sample was immersed in the test solution to a depth of 6-8 mm, and the sample was raised in voltage at a constant current of 1 mA. The time taken for the voltage to rise to 90% Vf from the start of power supply was recorded as the voltage rise time T r . Timing started when the voltage rose to 90% of the rated formation voltage Vf, and the voltage value reached after 180 s of continuous power supply was the oxidation film voltage resistance V t .

[0159] Hydrated resistance Tr60 test method: The sample that has been measured by the oxidation film pressure resistance test is placed in boiling water at ≥95℃ for 1 h, then the sample is immersed in the test solution (the type and concentration of the test solution is the same as that used in the oxidation film pressure resistance test), and the time from the start of power supply until the voltage rises to 90% Vf is recorded as the pressure rise time Tr60 after hydration treatment.

[0160] Specific capacitance test method: The projection area of the sample is 5 cm 2 After the pressure resistance test is completed and the sample is washed with pure water, the sample is immersed in a 30℃ test solution (80 g / L ammonium pentaborate aqueous solution for high-voltage electrode foil test solution, and 150 g / L ammonium adipate aqueous solution for low-voltage electrode foil test solution), and the test frequency is 120 Hz. The upper end of the measured part of the sample should be tangent to the liquid surface. The electrostatic capacity C is measured by an electrostatic capacity tester. m Divided by the area 5 cm 2 The obtained value is the specific capacitance.

[0161] Leakage current test method: The sample that has been measured by the oxidation film pressure resistance test is immersed in a 85℃ test solution (the type and concentration of the test solution is the same as that used in the oxidation film pressure resistance test), and a 90% Vf voltage is applied. The current value measured after 1 h of continuous power supply is the leakage current.

[0162] As can be seen from the data in Table 1, the preparation method of the electrode foil of the present application can improve the specific capacitance and enhance the hydration resistance.

[0163] As can be seen from Example 3, Comparative Example 1 and Comparative Example 2, without using double acid pre-formation and phosphoric acid etching before formation, the specific capacitance of the electrode foil is significantly reduced, and the hydration resistance and insulation are poor. Even if the formation conditions are adjusted, it is difficult to obtain better results.

[0164] As can be seen from Example 3 and Comparative Example 3, using phosphoric acid to electrochemically etch the pre-formation product can retain the functional bottom layer film and realize the reconstruction of the gradient structure of the oxidation film, generating an outer layer of AlPO4·2H2O / inner layer of AlPO4 composite crystal layer. The outer layer of the hydration layer acts as a dynamic barrier to inhibit the penetration of water molecules, and the inner layer of the anhydrous phase guarantees the dielectric performance, and the hydration resistance is improved.

[0165] As can be seen from Example 3, Comparative Example 4 and Comparative Example 5, through the synergistic effect of sulfuric acid and organic carboxylic acid, a high-quality barrier layer is formed at the junction of the aluminum base and the oxidation film, the uniformity of the barrier oxidation layer is improved, and the specific capacitance of the electrode foil is indirectly improved. At the same time, the organic carboxylic acid complex removes surface metal particles, and the sulfuric acid oxidizes the residual aluminum powder in the deep layer into soluble Al 3+ The sulfuric acid and organic carboxylic acid play a pre-cleaning role in the pre-formation stage. As a result, the hydration resistance and insulation of the electrode foil as a whole are improved.

[0166] Table 1 Summary of performance test results of electrode foils prepared in Examples and Comparative Examples

[0167] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those skilled in the art can make changes, modifications, substitutions and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method of producing an electrode foil, characterized by, The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil.

2. The method of claim 1, wherein, The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil.

3. The method of claim 1, wherein, The application relates to a preparation method of an electrode foil.

4. The method of claim 1, wherein, The application relates to a preparation method of an electrode foil. Optionally, the current density of the pre-formation treatment is 10 mA / cm 2 500 mA / cm 2 ; The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil.

5. The method of claim 1, wherein, The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil.

6. The method of claim 1, wherein, The application relates to a preparation method of an electrode foil. Optionally, the etching process has a current density of 5 mA / cm 2 300 mA / cm 2 ; The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil.

7. The method of claim 1, wherein, The application relates to a preparation method of an electrode foil.

8. An electrode foil, characterized by The application relates to a preparation method of an electrode foil. The application relates to a preparation method of an electrode foil.

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