Composite oxide film for aluminum electrolytic capacitor for hydrogen fuel cell and method for manufacturing the same

Abstract

This invention discloses a composite oxide film for aluminum electrolytic capacitors used in hydrogen fuel cells and its preparation method, belonging to the technical field of aluminum electrolytic capacitors. The preparation method includes: sequentially performing surface cleaning, neutralization, formation, and activation pretreatment on high-purity aluminum foil to prepare a surface-activated Al2O3 base film; selecting tetrabutyl titanate as the titanium source, mixing solvent, chelating agent, and hydrolyzing agent in a preset molar ratio, and preparing TiO2 sol through stirring, coupling agent modification, and ultrasonic dispersion; coating the TiO2 sol onto the surface of the Al2O3 base film using a dip-coating process to form a wet film; and transforming the wet film into anatase TiO2 coating through segmented sintering to obtain an Al2O3-TiO2 composite oxide film. The composite oxide film comprises a sequentially composited Al2O3 base film and anatase TiO2 coating, with a tight, gapless interface. This invention, through material composite and process optimization, enables the composite oxide film to possess low dielectric loss, high breakdown voltage, high humidity resistance, and vibration resistance, making it suitable for the harsh operating conditions of hydrogen fuel cells and improving the capacitor's service life and stability.

Description

Technical Field

[0001] This invention relates to the field of aluminum electrolytic capacitor technology, and more specifically to a composite oxide film for aluminum electrolytic capacitors used in hydrogen fuel cells and its preparation method. Background Technology

[0002] Hydrogen fuel cells, as efficient and clean energy conversion devices, are increasingly widely used in new energy vehicles, distributed power generation, and other fields. Their operating environment is characterized by harsh features such as high humidity, strong vibration, frequent start-stop shocks, and high-frequency electrical signal transmission. Aluminum electrolytic capacitors, as core energy storage and filtering components in hydrogen fuel cell systems, directly affect the system's stability and lifespan. The oxide film dielectric layer is a key component of aluminum electrolytic capacitors, undertaking the core functions of insulation, energy storage, and charge transfer, and must simultaneously meet multiple requirements such as low dielectric loss, high breakdown voltage, low interfacial impedance, and resistance to harsh environments. However, traditional single Al2O3 oxide films have drawbacks such as limited dielectric constant, large dielectric loss drift under high humidity conditions, and insufficient corrosion resistance, making them unsuitable for the complex operating conditions of hydrogen fuel cells. This leads to problems such as rapid performance degradation and short lifespan, becoming a key bottleneck restricting the improvement of the reliability of hydrogen fuel cell systems.

[0003] To address the performance shortcomings of traditional oxide films, the industry is gradually exploring composite oxide film structural designs, achieving synergistic performance optimization through the combination of multiple materials. Currently, existing composite oxide film technologies mostly focus on general electronic device applications, employing processes such as physical deposition and chemical vapor deposition to prepare multi-component coatings. However, these processes suffer from high equipment costs, low coating-base film bonding strength, and difficulties in large-scale production. Some technologies attempt to improve capacitor performance through electrolyte formulation optimization and electrode structure improvements, but these do not address the fundamental structure of the oxide film dielectric layer, making it difficult to simultaneously achieve synergistic improvements in low dielectric loss, high breakdown voltage, and resistance to harsh environments. Furthermore, existing composite oxide film technologies are not specifically designed for the special operating conditions of hydrogen fuel cells, such as high humidity and vibration. Coatings are prone to peeling and cracking under long-term harsh environments, failing to meet the long-life and high-reliability requirements of hydrogen fuel cell systems.

[0004] Chinese patent (CN117954230A) discloses a method for preparing medium- and high-voltage composite electrochemical foil. Its advantage lies in using atomic layer deposition (ALD) to deposit metal oxides (such as TiO2) to form a high-dielectric film, and then opening Al³⁺ channels through a mid-processing step to form an alumina-MOx-alumina composite structure. This effectively improves the specific capacity and hydration resistance of the electrochemical foil and is suitable for medium- and high-voltage applications. However, this method has significant drawbacks: the ALD process requires a vacuum environment and precision equipment, resulting in high production costs and difficulty in large-scale production. Furthermore, the mid-processing steps of hydration, freezing, and high-temperature heating are complex and may affect the structural stability of the composite membrane, making it unsuitable for the harsh operating conditions such as high humidity and vibration required by hydrogen fuel cells.

[0005] Chinese patent (CN115116752A) describes a method for preparing a slurry containing high-dielectric-voltage valve metal oxides using a sol-gel method. After coating, the slurry undergoes degreasing, sintering, and chemical formation to form a composite oxide film. Its advantages include solving the problems of complex and costly processes mentioned above. The sol-gel method allows the high-dielectric-voltage oxides to be firmly loaded onto aluminum particles, improving the specific capacity of the electrode foil. However, this method still has drawbacks: the sol preparation does not specifically control particle size and dispersibility, resulting in insufficient coating uniformity; the interface design between the base film and the coating is not optimized, and the sintering temperature is too high (560-650℃), easily leading to film cracking; furthermore, it does not consider the moisture resistance and vibration resistance requirements under special operating conditions, making it difficult to meet the requirements for use in harsh environments.

[0006] The sol-gel method has attracted widespread attention in the field of oxide film preparation due to its advantages such as simple process, low cost, good coating uniformity, and precise control of component ratios. This method can achieve uniform dispersion of different components through molecular-level raw material mixing, which is beneficial to improving the structural density and performance stability of composite oxide films. However, when applying the sol-gel method to the preparation of composite oxide films for aluminum electrolytic capacitors in hydrogen fuel cells, several technical challenges remain: first, how to achieve a tight bond between TiO2 and Al2O3 substrate films and avoid interfacial delamination through raw material ratio and process parameter control; second, how to control the particle size and crystal transformation of TiO2 to ensure that the composite oxide film has both low dielectric loss and high dielectric constant; and third, how to improve the moisture resistance and vibration resistance of the composite oxide film to adapt to the harsh operating conditions of hydrogen fuel cells.

[0007] Therefore, developing a dedicated composite oxide film preparation technology based on the sol-gel method to solve the above-mentioned technical pain points is of great practical significance and application value for promoting the performance upgrade of aluminum electrolytic capacitors for hydrogen fuel cells and ensuring the stable operation of hydrogen fuel cell systems. Summary of the Invention

[0008] Based on the above-mentioned technical problems, this application discloses a composite oxide film suitable for aluminum electrolytic capacitors used in hydrogen fuel cells and its preparation method. The method for preparing the composite oxide film specifically includes:

[0009] A surface-activated Al2O3 base film is prepared by pretreating high-purity aluminum foil. The pretreatment includes sequential surface cleaning, neutralization, formation and activation treatments.

[0010] Titanium source, solvent, chelating agent and hydrolyzing agent are selected and mixed in a preset molar ratio. After stirring, an initial sol is formed. A coupling agent is added to the initial sol and the mixture is dispersed and modified to obtain TiO2 sol.

[0011] The TiO2 sol was coated onto the surface of the Al2O3 base film using a dip-coating process to form a continuous wet film.

[0012] The aluminum foil coated with the wet film is subjected to segmented sintering treatment to transform the wet film into anatase TiO2 coating, thereby obtaining an Al2O3-TiO2 composite oxide film.

[0013] Preferably, the step of pretreating the high-purity aluminum foil includes:

[0014] High-purity aluminum foil with a purity of ≥99.5% and a thickness of 8-18μm is selected, and after being successively treated with alkali washing and nitric acid neutralization, it is mainly formed in a composite electrolyte containing boric acid and adipic acid to generate a dense Al2O3 base film with a thickness of 120-180nm.

[0015] The Al2O3 substrate film was surface activated by immersing it in a dilute hydrochloric acid solution, rinsed with deionized water until the pH reached 6.8-7.2, and then vacuum dried.

[0016] Preferably, the alkaline washing process parameters are: using 4%-6% NaOH solution, treating at 35-45℃ for 8-12 min; the nitric acid neutralization process parameters are: using 8%-12% nitric acid solution, treating at 20-30℃ for 4-6 min; the main formation process parameters are: boric acid mass fraction of 0.6%-1.0%, adipic acid mass fraction of 0.1%-0.3%, current density of 5-7 mA / cm², temperature of 60-70℃, and the dielectric loss tanδ of the Al₂O₃ base film at 1 kHz ≤ 0.025.

[0017] Preferably, the process parameters for surface activation are: dilute hydrochloric acid solution concentration of 0.08%-0.12%, temperature of 25-35℃, and treatment time of 2-4 min, so that nanoscale micropores with a pore size of 3-12 nm are formed on the surface of the Al2O3 base film; the process parameters for vacuum drying are: temperature of 75-85℃ and time of 1.5-2.5 h.

[0018] Preferably, the titanium source is tetrabutyl titanate, the solvent is anhydrous ethanol, the chelating agent is glacial acetic acid, and the hydrolyzing agent is deionized water;

[0019] The steps for preparing TiO2 sol include: slowly adding tetrabutyl titanate dropwise into anhydrous ethanol, stirring until clear in the first stage, then adding glacial acetic acid and deionized water in sequence for the second stage of stirring to form a transparent initial sol.

[0020] Add 0.4%-0.6% by mass of a silane coupling agent, selected from KH-550 or KH-560, to the initial sol. After ultrasonic dispersion, the TiO2 sol is obtained, and the TiO2 particle size in the TiO2 sol satisfies the formula: ,in The particle size of TiO2 is... For correction factor, For ultrasonic dispersion power, The time is for ultrasonic dispersion, and the particle size of the TiO2 particles is controlled between 15-35 nm.

[0021] Preferably, the process parameters for the first stage of stirring are: stirring rate 280-320 r / min, stirring time 18-22 min; the process parameters for the second stage of stirring are: stirring rate 480-520 r / min, stirring time 55-65 min; and the process parameters for the ultrasonic dispersion are: power 280-320 W, time 12-18 min.

[0022] Preferably, the process parameters for the dip-coating method are as follows: the activated aluminum foil is vertically immersed into the TiO2 sol, pulled up at a uniform speed of 4-6 mm / s, and left to stand at room temperature for 8-12 minutes. The dip-coating-standing step is repeated to control the dry film thickness of the TiO2 coating to be 12-18 nm, and the dry film thickness satisfies the formula: ,in The dry film thickness of the TiO2 coating. For the lifting rate, This is the sol concentration coefficient. This represents the number of dip-coating cycles.

[0023] Preferably, the segmented sintering process includes:

[0024] First stage of adhesive removal: The aluminum foil coated with the wet film is heated from room temperature to 180-220℃ at a heating rate of 4-6℃ / min and held at that temperature for 25-35min.

[0025] The second stage of crystallization involves heating from 180-220℃ to 480-520℃ at a rate of 1.5-2.5℃ / min and holding at that temperature for 55-65min, to transform amorphous TiO2 into anatase, with an anatase phase purity ≥92%.

[0026] Preferably, the modification treatment includes adding 0.1%-0.3% by mass of graphene oxide to the initial sol, wherein the mass ratio of graphene oxide to silane coupling agent is 1:(1.5-2.5), followed by ultrasonic dispersion and magnetic stirring composite treatment for 20-40 min at a stirring rate of 350-450 r / min, thereby improving the density and corrosion resistance of the TiO2 coating.

[0027] One of the composite oxide films for aluminum electrolytic capacitors used in hydrogen fuel cells includes an Al2O3 base film and an anatase TiO2 coating sequentially laminated together.

[0028] The Al2O3 base film has a dense oxide film structure with a thickness of 120-180nm. Its surface is distributed with nanoscale micropores with a pore size of 3-12nm. The Al2O3 base film is made of high-purity alumina and is formed by chemical conversion treatment of high-purity aluminum foil.

[0029] The anatase TiO2 coating is a continuous and dense capping layer with a thickness of 12-18 nm, which is tightly attached to the inner wall and outer surface of the micropores of the Al2O3 base film. The anatase TiO2 coating contains an organic-inorganic combined phase derived from a silane coupling agent, and optionally contains a graphene oxide dispersed phase. The purity of the anatase phase in the anatase TiO2 coating is ≥92%.

[0030] The Al2O3 base film and the anatase TiO2 coating form a composite structure with a tight interface. The interface of the composite structure has no obvious gaps, and the anatase TiO2 coating completely covers the surface and microporous area of ​​the Al2O3 base film.

[0031] Compared with the prior art, the technical solution of this application has the following technical effects:

[0032] This invention prepares Al2O3-TiO2 composite oxide films through sol-gel method and segmented sintering process. The low impedance characteristics of Al2O3 base film are combined with the high dielectric constant and corrosion resistance of anatase TiO2, so that the composite oxide film can maintain low dielectric loss under high frequency conditions, while also having excellent insulation performance. It can effectively meet the high frequency electrical signal transmission requirements of hydrogen fuel cells and solve the shortcomings of single oxide film performance.

[0033] This invention improves the interfacial bonding strength of the composite oxide film by optimizing the pretreatment process of aluminum foil and modifying the sol-gel. The nanoscale micropores on the surface of the base film provide sufficient adhesion sites for the TiO2 coating. The introduction of silane coupling agent further strengthens the interfacial interaction, making the coating less prone to peeling and cracking. The structural design allows the composite oxide film to withstand the harsh mechanical environment of hydrogen fuel cell system vibration, start-stop impact, etc., ensuring the structural stability of the capacitor.

[0034] The composite oxide film structure and preparation process of this invention are highly compatible. The dense structure of the TiO2 coating can effectively isolate water vapor and corrosive substances, preventing the base film from being eroded. At the same time, the precise control of process parameters ensures the structural uniformity and density of the composite oxide film, enabling it to maintain stable performance in high humidity environments and avoid problems such as dielectric loss drift. This extends the service life of aluminum electrolytic capacitors in hydrogen fuel cell systems and improves reliability.

[0035] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings.

[0036] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0038] Based on the description of the figures and their corresponding technical content in the document, the titles of the figures are as follows:

[0039] Figure 1 The graph shows the trend of dielectric loss tanδ as a function of aging time in different embodiments;

[0040] Figure 2 This is a schematic diagram of the composite oxide film structure of aluminum electrolytic capacitors used in hydrogen fuel cells. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. In the following description, specific details such as specific configurations and components are provided merely to help fully understand the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. In addition, for clarity and brevity, descriptions of known functions and structures are omitted in the embodiments.

[0042] It should be understood that the phrase "an embodiment" or "this embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "an embodiment" or "this embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0043] Furthermore, reference numerals and / or letters may be repeated in different examples within this application. Such repetition is for the purpose of simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or settings discussed.

[0044] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. The term " / and" in this article describes another type of relationship between related objects, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the related objects before and after it are in an "or" relationship.

[0045] In this article, the term "at least one" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, "at least one of A and B" can mean: A exists alone, A and B exist simultaneously, or B exists alone.

[0046] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion.

[0047] This embodiment provides a method for preparing a composite oxide film for an aluminum electrolytic capacitor used in hydrogen fuel cells. The preparation method includes the following steps:

[0048] High-purity aluminum foil was pretreated by sequentially undergoing surface cleaning, neutralization, formation and activation treatments to prepare a surface-activated Al2O3 base film.

[0049] Titanium source, solvent, chelating agent and hydrolyzing agent are selected, mixed and stirred according to a preset molar ratio to form an initial sol, and a coupling agent is added to the initial sol and dispersed and modified to prepare TiO2 sol;

[0050] The TiO2 sol was coated onto the surface of the Al2O3 base film using a dip-coating process to form a continuous wet film.

[0051] The aluminum foil coated with the wet film is subjected to segmented sintering treatment to transform the wet film into anatase TiO2 coating, thereby obtaining an Al2O3-TiO2 composite oxide film.

[0052] Example 1 illustrates in detail the specific implementation of the above preparation method:

[0053] The experimental materials included: high-purity aluminum foil: purity ≥99.5%, thicknesses of 8μm, 12μm, and 18μm; titanium source: tetrabutyl titanate (analytical grade); solvent: anhydrous ethanol (analytical grade); chelating agent: glacial acetic acid (analytical grade); hydrolyzing agent: deionized water; silane coupling agents: KH-550 and KH-560 (industrial grade); graphene oxide: 5-10 layers, sheet diameter 1-5μm (industrial grade); sodium hydroxide, nitric acid, hydrochloric acid, boric acid, and adipic acid (all analytical grade).

[0054] The experimental equipment includes: a magnetic stirrer (speed range 0-1000 r / min); an ultrasonic disperser (power range 0-500 W); a vacuum drying oven (temperature range room temperature-200℃, vacuum degree ≤-0.095 MPa); a muffle furnace (temperature range room temperature-1000℃, heating rate 0-10℃ / min); a dip-coating device (adjustable pull-out rate 0-10 mm / s); an X-ray diffractometer (XRD) for detecting TiO2 crystal form; a dielectric property tester (test frequency range 1 kHz-1 MHz); a cross-cut tester (cross-cut spacing 1 mm); a constant temperature and humidity chamber (temperature range 0-100℃, relative humidity range 30%-98%); and a vibration test bench (frequency range 10-2200 Hz, acceleration range 0-25 g).

[0055] Example 1: This example provides a method for preparing a composite oxide film for an aluminum electrolytic capacitor used in hydrogen fuel cells. The specific steps are as follows:

[0056] Pretreatment of Al2O3 base film: High-purity aluminum foil with a purity of 99.5% and a thickness of 12μm was placed in a 4% NaOH solution and washed at 35℃ for 12min to remove surface oil and oxide layer; then it was placed in an 8% nitric acid solution and neutralized at 20℃ for 6min; the treated aluminum foil was placed in a composite electrolyte containing 0.6% boric acid and 0.1% adipic acid by mass, and the main formation was carried out at a current density of 5mA / cm² and 60℃ to generate an Al2O3 base film with a thickness of 120nm; the Al2O3 base film was immersed in a 0.08% dilute hydrochloric acid solution and activated at 25℃ for 4min to form nanoscale micropores with a pore size of 3-8nm; it was rinsed with deionized water until pH=6.8 and dried in a vacuum drying oven at 75℃ for 2.5h.

[0057] Preparation of TiO2 sol: The raw materials were prepared by molar ratio n[tetrabutyl titanate]∶n[anhydrous ethanol]∶n[glacial acetic acid]∶n[deionized water]=1∶8∶1.5∶1.2. Tetrabutyl titanate was slowly added dropwise to anhydrous ethanol and stirred at 280 r / min for 22 min until clear. Glacial acetic acid and deionized water were added in sequence and stirred at 480 r / min for 65 min to form the initial sol.

[0058] Add 0.4% by mass of silane coupling agent KH-550 to the initial sol, and ultrasonically disperse at 280W for 18 min to obtain TiO2 sol, wherein the TiO2 particle size is controlled at 15-25nm.

[0059] The coating was applied using an dip-coating method, in which the activated aluminum foil was vertically immersed into the TiO2 sol and pulled up at a uniform speed of 4 mm / s. The foil was then left to stand at room temperature for 12 min. This dip-coating-standing process was repeated once to control the dry film thickness of the TiO2 coating to be 12 nm.

[0060] Segmented sintering, including the first stage of debinding and the second stage of crystallization;

[0061] In the first stage of adhesive removal, the aluminum foil coated with wet film is placed in a muffle furnace and heated from room temperature to 180°C at a heating rate of 4°C / min, and held at that temperature for 35min.

[0062] The second stage of crystallization involves heating from 180℃ to 480℃ at a rate of 1.5℃ / min and holding at that temperature for 65min, which transforms amorphous TiO2 into anatase. The purity of the anatase phase is ≥92%, resulting in an Al2O3-TiO2 composite oxide film.

[0063] Example 2, the difference between this example and Example 1 is:

[0064] In the pretreatment step, alkaline washing was performed using 5% NaOH solution at 40℃ for 10 min; nitric acid neutralization was performed using 10% nitric acid solution at 25℃ for 5 min; the composite electrolyte contained 0.8% boric acid and 0.2% adipic acid, with a current density of 6 mA / cm², a temperature of 65℃, and an Al₂O₃ base film thickness of 150 nm.

[0065] Surface activation was performed using a 0.1% dilute hydrochloric acid solution at 30°C for 3 minutes, resulting in micropores with a diameter of 5-10 nm; vacuum drying was then carried out at 80°C for 2 hours.

[0066] The molar ratio of TiO2 sol raw materials is 1:10:2:1.5. The stirring speed in the first stage is 300 r / min and the time is 20 min. The stirring speed in the second stage is 500 r / min and the time is 60 min. The amount of silane coupling agent added is 0.5%. The ultrasonic dispersion power is 300 W and the time is 15 min. The particle size of TiO2 particles is 20-30 nm.

[0067] Dip-coating pull-up rate 5 mm / s, stand at room temperature for 10 min, repeat dip-coating twice, TiO2 coating dry film thickness 15 nm;

[0068] Segmented sintering: debinding temperature 200℃, heating rate 5℃ / min, holding time 30min; crystallization temperature 500℃, heating rate 2℃ / min, holding time 60min, anatase phase purity ≥95%.

[0069] Example 3, the difference between this example and Example 1 is:

[0070] High-purity aluminum foil with a purity of 99.8% and a thickness of 8μm was selected; alkaline washing was performed using 6% NaOH solution at 45℃ for 8 minutes; nitric acid neutralization was performed using 12% nitric acid solution at 30℃ for 4 minutes.

[0071] The composite electrolyte contains 1.0% boric acid and 0.3% adipic acid, with a current density of 7 mA / cm², a temperature of 70℃, and an Al₂O₃ substrate film thickness of 180 nm.

[0072] Surface activation was performed using a 0.12% dilute hydrochloric acid solution at 35°C for 2 minutes, resulting in micropores with a diameter of 8-12 nm. Vacuum drying was then carried out at 85°C for 1.5 hours.

[0073] The molar ratio of TiO2 sol raw materials is 1:12:2.5:1.8. The stirring rate in the first stage is 320 r / min and the time is 18 min. The stirring rate in the second stage is 520 r / min and the time is 55 min.

[0074] The silane coupling agent used was KH-560, with an addition amount of 0.6%. The ultrasonic dispersion power was 320W and the time was 12min. The TiO2 particle size was 25-35nm.

[0075] Dip-coating pull-up rate 6 mm / s, stand at room temperature for 8 min, repeat dip-coating 3 times, TiO2 coating dry film thickness 18 nm.

[0076] Segmented sintering: debinding temperature 220℃, heating rate 6℃ / min, holding time 25min; crystallization temperature 520℃, heating rate 2.5℃ / min, holding time 55min, anatase phase purity ≥94%.

[0077] Example 4 differs from Example 2 in that, in the modification treatment step of TiO2 sol preparation, in addition to adding 0.5% silane coupling agent KH-550, 0.1% graphene oxide by mass fraction is also added. The mass ratio of graphene oxide to silane coupling agent is 1:1.5. After ultrasonic dispersion at 300W for 15 minutes, it is then magnetically stirred at 350r / min for 40 minutes. All other steps and parameters are the same as in Example 2.

[0078] Example 5 differs from Example 2 in that: the amount of graphene oxide added is 0.2% by mass, the mass ratio of graphene oxide to silane coupling agent is 1:2.0, the composite treatment time is 30 min, the stirring rate is 400 r / min, and other steps and parameters are the same as in Example 2.

[0079] Example 6 differs from Example 2 in that: the amount of graphene oxide added is 0.3% by mass, the mass ratio of graphene oxide to silane coupling agent is 1:2.5, the composite treatment time is 20 min, the stirring rate is 450 r / min, and other steps and parameters are the same as in Example 2.

[0080] Comparative Example 1 differs from Example 2 in that: the surface activation treatment of the Al2O3 base film was not performed, and the Al2O3 base film after formation was directly vacuum dried before subsequent coating. All other steps and parameters are the same as in Example 2.

[0081] Comparative Example 2 differs from Example 2 in that no silane coupling agent was added during the preparation of the TiO2 sol, while the other steps and parameters were the same as in Example 2.

[0082] Comparative Example 3 differs from Example 2 in that the molar ratio of the raw materials for the TiO2 sol is n[tetrabutyl titanate]∶n[anhydrous ethanol]∶n[glacial acetic acid]∶n[deionized water]=1∶5∶1∶1, while the other steps and parameters are the same as in Example 2.

[0083] Comparative Example 4 differs from Example 2 in that: the segmented sintering adopts a single temperature sintering, directly raising the temperature from room temperature to 500°C at a rate of 5°C / min, and holding for 90min. All other steps and parameters are the same as in Example 2.

[0084] Comparative Example 5 differs from Example 5 in that the mass ratio of graphene oxide to silane coupling agent is 1:1, while the other steps and parameters are the same as in Example 5.

[0085] Comparative Example 6: This comparative example is a single Al2O3 base film. Only the pretreatment steps of the Al2O3 base film in Example 2 were performed, without TiO2 sol coating and sintering treatment.

[0086] Performance tests were conducted based on Examples 1-6 and Comparative Examples 1-6, including: dielectric properties, weather resistance, bonding strength, vibration resistance, and crystal purity.

[0087] Dielectric properties were measured using a dielectric performance tester at a test frequency of 8kHz, which was used to detect dielectric loss tanδ and breakdown voltage.

[0088] Weather resistance was assessed by placing the sample in a constant temperature and humidity chamber at 40℃ and 95% relative humidity for 1000 hours and then measuring the change rate of dielectric loss.

[0089] The adhesion strength of the coating is tested using the cross-cut test (1mm spacing between cuts), and grades 1-2 are considered acceptable.

[0090] To assess vibration resistance, the sample was fixed on a vibration test bench and vibrated at a frequency of 10-2200Hz and an acceleration of 20g for 24 hours. The coating was then observed to see if it peeled off.

[0091] The crystal purity was determined using X-ray diffraction to detect the anatase phase purity of the TiO2 coating.

[0092] The improvement effect of the technical solution of this application on the comprehensive performance of the composite oxide film is shown in Table 1. The test data of the core indicators such as dielectric properties, weather resistance, bonding strength, vibration resistance and crystal purity of Examples 1-6 and Comparative Examples 1-6 are shown in Table 1. All tests were strictly performed in accordance with the standard procedures set above.

[0093] Table 1 Core Performance Test Results

[0094] Group Dielectric loss tanδ (8kHz) Breakdown voltage (V) Weather resistance dielectric loss change rate (%) Adhesion rating Post-vibration coating condition Anatase phase purity Example 1 0.017 175 11 Level 2 No shedding 92 Example 2 0.015 185 8 Level 1 No shedding 95 Example 3 0.016 182 9 Level 1 No shedding 94 Example 4 0.014 190 7 Level 1 No shedding 95 Example 5 0.013 195 6 Level 1 No shedding 95 Example 6 0.014 192 7 Level 1 No shedding 95 Comparative Example 1 0.020 165 18 Level 3 Localized detachment 93 Comparative Example 2 0.022 160 22 Level 3 Partial detachment 94 Comparative Example 3 0.025 155 25 Level 2 No obvious shedding 88 Comparative Example 4 0.023 158 23 Level 2 No obvious shedding 85 Comparative Example 5 0.018 178 13 Level 1 No shedding 95 Comparative Example 6 0.028 150 35 - - -

[0095] As can be clearly seen from the data in Table 1, the core performance of all embodiments is significantly better than that of the comparative examples. Among them, Example 2, as the baseline optimization scheme, has a dielectric loss as low as 0.015, a breakdown voltage of 185V, a weather resistance dielectric loss change rate of only 8%, and an adhesion level of 1, which fully meets the demanding operating conditions of hydrogen fuel cells. The performance of Examples 4-6 with the addition of graphene oxide is further improved, especially Example 5, which has the best overall performance, proving that the synergistic modification effect of graphene oxide and silane coupling agent is significant. In contrast, the comparative examples, due to the lack of key process steps or parameters deviating from the optimization range, all showed problems such as increased dielectric loss, decreased breakdown voltage, and worsened weather resistance. Among them, Comparative Example 6 with a single Al2O3 base film had the worst performance, which fully demonstrates the technical advantages of the composite oxide film structure and preparation method of this application.

[0096] like Figure 1 As shown in the figure, the dynamic change trend of dielectric loss tanδ with aging time under the harsh operating conditions of hydrogen fuel cells in different embodiments is clearly seen from the figure. The dielectric loss curves corresponding to Embodiments 1, 2, and 5 provided in this application are always in the low range and the growth rate is slow. Among them, Embodiment 1, as the basic scheme, has an initial dielectric loss of 0.017 at 0h and only increases to 0.0207 after 1000h aging, with an increase of less than 22%. The initial dielectric loss of Embodiment 2 (optimized baseline scheme) is 0.015 and the dielectric loss after 1000h is 0.0178, with an increase of about 18.7%, which reflects the improvement in weather resistance after the optimization of process parameters. The performance of Embodiment 5 (optimal scheme) is the most outstanding. Its initial dielectric loss is only 0.013 and the dielectric loss after 1000h aging only increases slightly to 0.0143, with an increase of less than 10%, which fully meets the excellent index of weather resistance dielectric loss change rate ≤10% in Table 1.

[0097] The dielectric loss curve of Comparative Example 6 (single Al2O3 base film) showed that the initial dielectric loss reached 0.028, far exceeding all examples, and increased sharply with aging time. At 1000h, the dielectric loss exceeded 0.06, an increase of more than 114% compared with the initial value. This corresponds to the result in Table 1 that the change rate of dielectric loss in weather resistance of Comparative Example 6 reached 35%, revealing the performance shortcomings of traditional single oxide films under long-term high humidity and vibration conditions.

[0098] Table 2. Correlation Analysis of Process Parameters

[0099] Group Key process differences <![CDATA[TiO2 particle size]]> Coating thickness Interface Combination Status Core performance advantages Example 1 Low concentration of coupling agent, low ultrasonic power 15-25 12 Closely integrated Basic performance meets standards, and cost is low. Example 2 Optimize raw material ratio and sintering parameters 20-30 15 Closely integrated Low dielectric loss and high breakdown voltage Example 3 High-purity aluminum foil, high-concentration coupling agent 25-35 18 Closely integrated Excellent weather resistance and vibration resistance Example 4 Low content graphene oxide modification 20-30 15 Extremely tight integration Dielectric loss further reduced Example 5 Optimize the ratio of graphene oxide to coupling agent 20-30 15 Extremely tight integration Best overall performance Example 6 High-content graphene oxide modification 20-30 15 Extremely tight integration Breakdown voltage protrusion Comparative Example 1 No surface activation treatment 20-30 15 Combined loose All performance aspects declined Comparative Example 2 Coupling agent-free modification 30-45 15 Combined loose Poor dielectric loss and weather resistance Comparative Example 3 Raw material ratio deviates from the optimized range 40-55 15 Combining general Low crystal purity, high dielectric loss Comparative Example 4 Single temperature sintering 20-30 15 Combining general Low crystal purity, low breakdown voltage Comparative Example 5 Imbalance in the ratio of graphene oxide to coupling agent 20-30 15 Closely integrated Slightly poor weather resistance Comparative Example 6 <![CDATA[Single Al2O3-based membrane]]> - - - Worst overall performance

[0100] The correlation analysis results in Table 2 show that the precise control of process parameters plays a decisive role in product performance: the surface activation treatment of Al2O3 base film and the modification of silane coupling agent are the key to ensuring tight interfacial bonding. The absence of either step will lead to a deterioration in bonding state and a decrease in performance; the raw material ratio and the segmented sintering process directly affect the particle size and crystal purity of TiO2 particles. Deviation from the optimized range will cause an increase in dielectric loss; the ratio of graphene oxide to silane coupling agent needs to be strictly controlled at 1:(1.5-2.5). An imbalance in the ratio will weaken the modification effect.

[0101] As can be seen from Tables 1 and 2, the performance of Examples 1-6 is better than that of Comparative Examples 1-6, especially Examples 2, 4, and 5, which show outstanding performance. This proves that the preparation method of this application can effectively improve the dielectric properties, weather resistance, bonding strength and vibration resistance of the composite oxide film.

[0102] Comparing Example 2 with Comparative Examples 1-4, it can be seen that surface activation of Al2O3 base film, modification with silane coupling agent, optimized raw material ratio and segmented sintering process are the key to ensuring the performance of composite oxide film. The absence of any one of these steps will lead to a significant decrease in performance.

[0103] Comparing Examples 2, 4, 5, and 6, it can be seen that adding graphene oxide and optimizing its ratio with silane coupling agent can further improve the density and corrosion resistance of the composite oxide film, thereby reducing dielectric loss and increasing breakdown voltage.

[0104] Example 7: This application provides a composite oxide film for an aluminum electrolytic capacitor used in a hydrogen fuel cell. The composite oxide film is prepared using the preparation method described in any of the above embodiments, or using the preparation method of Example 2. Figure 2 As shown, the specific structure is as follows:

[0105] The composite oxide film consists of an Al2O3 base film and anatase TiO2 coating sequentially laminated together;

[0106] The Al2O3 base film has a dense oxide film structure with a thickness of 150nm and nanoscale micropores with a pore size of 5-10nm distributed on the surface. It is made of high-purity alumina and is formed by alkaline washing, neutralization, main formation and surface activation treatment of 99.5% pure aluminum foil.

[0107] The anatase TiO2 coating is a continuous and dense capping layer with a thickness of 15 nm, which is tightly attached to the inner wall and outer surface of the micropores of the Al2O3 base film. The coating contains an organic-inorganic combined phase derived from the silane coupling agent KH-550, and the purity of the anatase phase is ≥95%.

[0108] The Al2O3 base film and the anatase TiO2 coating form a tightly bonded composite structure with no obvious gaps at the interface. The TiO2 coating completely covers the surface and microporous area of ​​the Al2O3 base film.

[0109] In another aspect of this application, an aluminum electrolytic capacitor for a hydrogen fuel cell is provided, comprising the composite oxide film described in any of the above embodiments or the composite oxide film prepared by the preparation method described in any of the above embodiments;

[0110] The aluminum electrolytic capacitor, by using the composite oxide film of this application as the dielectric layer, has characteristics such as low dielectric loss, high breakdown voltage, high humidity resistance, and vibration resistance. It can be adapted to the harsh operating conditions of high humidity, vibration, and high frequency of hydrogen fuel cells, significantly improving the service life and stability of the capacitor, thereby ensuring the reliable operation of the hydrogen fuel cell system.

[0111] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter changes made to these embodiments within the spirit and principles of the present invention, without departing from the principles and spirit of the present invention, through conventional substitutions or to achieve the same function, fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite oxide film for an aluminum electrolytic capacitor for a hydrogen fuel cell, characterized by, include: A surface-activated Al2O3 base film is prepared by pretreating high-purity aluminum foil. The pretreatment includes sequential surface cleaning, neutralization, formation and activation treatments. Titanium source, solvent, chelating agent and hydrolyzing agent are selected and mixed in a preset molar ratio. After stirring, an initial sol is formed. A coupling agent is added to the initial sol and the mixture is dispersed and modified to obtain TiO2 sol. The TiO2 sol was coated onto the surface of the Al2O3 base film using a dip-coating process to form a continuous wet film. The aluminum foil coated with the wet film is subjected to segmented sintering treatment to transform the wet film into anatase TiO2 coating, thereby obtaining Al2O3-TiO2 composite oxidation. The titanium source is tetrabutyl titanate, the solvent is anhydrous ethanol, the chelating agent is glacial acetic acid, and the hydrolyzing agent is deionized water; The steps for preparing TiO2 sol include: slowly adding tetrabutyl titanate dropwise into anhydrous ethanol, stirring until clear in the first stage, then adding glacial acetic acid and deionized water in sequence for the second stage of stirring to form a transparent initial sol; Add 0.4%-0.6% by mass of a silane coupling agent, selected from KH-550 or KH-560, to the initial sol. After ultrasonic dispersion, the TiO2 sol is obtained, and the TiO2 particle size in the TiO2 sol satisfies the formula: ,in The particle size of TiO2 is... For correction factor, For ultrasonic dispersion power, The time is for ultrasonic dispersion, and the particle size of the TiO2 particles is controlled between 15-35 nm.

2. The preparation method according to claim 1, characterized in that, The pretreatment steps for the high-purity aluminum foil include: High-purity aluminum foil with a purity of ≥99.5% and a thickness of 8-18μm is selected, and after being successively treated with alkali washing and nitric acid neutralization, it is mainly formed in a composite electrolyte containing boric acid and adipic acid to generate a dense Al2O3 base film with a thickness of 120-180nm. The Al2O3 substrate film was surface activated by immersing it in a dilute hydrochloric acid solution, rinsed with deionized water until the pH reached 6.8-7.2, and then vacuum dried.

3. The preparation method according to claim 2, characterized in that, The alkaline washing process parameters are: using 4%-6% NaOH solution, treating at 35-45℃ for 8-12 minutes; the nitric acid neutralization process parameters are: using 8%-12% nitric acid solution, treating at 20-30℃ for 4-6 minutes; the main formation process parameters are: boric acid mass fraction of 0.6%-1.0%, adipic acid mass fraction of 0.1%-0.3%, current density of 5-7 mA / cm², temperature of 60-70℃, and the dielectric loss tanδ of the Al₂O₃ base film at 1 kHz ≤ 0.

025.

4. The preparation method according to claim 2, characterized in that, The surface activation process parameters are: dilute hydrochloric acid solution concentration 0.08%-0.12%, temperature 25-35℃, and treatment time 2-4 min, so that nanoscale micropores with a pore size of 3-12 nm are formed on the surface of the Al2O3 base film; the vacuum drying process parameters are: temperature 75-85℃ and time 1.5-2.5 h.

5. The preparation method according to claim 1, characterized in that, The process parameters for the first stage of stirring are: stirring rate 280-320 r / min, stirring time 18-22 min; the process parameters for the second stage of stirring are: stirring rate 480-520 r / min, stirring time 55-65 min; the process parameters for ultrasonic dispersion are: power 280-320 W, time 12-18 min.

6. The preparation method according to claim 1, characterized in that, The process parameters for the dip-coating method are as follows: the activated aluminum foil is vertically immersed into the TiO2 sol, pulled up at a uniform speed of 4-6 mm / s, and left to stand at room temperature for 8-12 minutes. The dip-coating-standing step is repeated to control the dry film thickness of the TiO2 coating to be 12-18 nm, and the dry film thickness satisfies the formula: ,in The dry film thickness of the TiO2 coating. For the lifting rate, This is the sol concentration coefficient. This represents the number of dip-coating cycles.

7. The preparation method according to claim 1, characterized in that, The segmented sintering process includes: First stage of adhesive removal: The aluminum foil coated with the wet film is heated from room temperature to 180-220℃ at a heating rate of 4-6℃ / min and held at that temperature for 25-35min. The second stage of crystallization involves heating from 180-220℃ to 480-520℃ at a rate of 1.5-2.5℃ / min and holding at that temperature for 55-65min, to transform amorphous TiO2 into anatase, with an anatase phase purity ≥92%.

8. The preparation method according to claim 1, characterized in that, The modification treatment includes adding 0.1%-0.3% by mass of graphene oxide to the initial sol, wherein the mass ratio of graphene oxide to silane coupling agent is 1:(1.5-2.5), followed by ultrasonic dispersion and magnetic stirring composite treatment for 20-40 min at a stirring rate of 350-450 r / min, thereby improving the density and corrosion resistance of the TiO2 coating.

9. A composite oxide membrane for an aluminum electrolytic capacitor used in a hydrogen fuel cell, characterized in that, It includes an Al2O3 base film and anatase TiO2 coating that are sequentially composited; The Al2O3 base film has a dense oxide film structure with a thickness of 120-180nm. Its surface is distributed with nanoscale micropores with a pore size of 3-12nm. The Al2O3 base film is made of high-purity alumina and is formed by chemical conversion treatment of high-purity aluminum foil. The anatase TiO2 coating is a continuous and dense capping layer with a thickness of 12-18 nm, which is tightly attached to the inner wall and outer surface of the micropores of the Al2O3 base film. The anatase TiO2 coating contains an organic-inorganic combined phase derived from a silane coupling agent and a graphene oxide dispersed phase. The purity of the anatase phase in the anatase TiO2 coating is ≥92%. The Al2O3 base film and the anatase TiO2 coating form a composite structure with a tight interface. The interface of the composite structure has no obvious gaps, and the anatase TiO2 coating completely covers the surface and microporous area of ​​the Al2O3 base film.

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