Solid aluminum electrolytic capacitor and method for preparing composite anode foil thereof

Abstract

This invention discloses a solid aluminum electrolytic capacitor and a method for preparing its composite anode foil. The method includes: adding dipropylene glycol monopropyl ether to a conductive polymer dispersion to prepare a working solution; subjecting an anode aluminum foil with an alumina dielectric layer on its surface to plasma treatment; coating the treated anode aluminum foil with the working solution, and after pre-drying, sequentially performing a first-stage and a second-stage heat treatment to form a conductive polymer film. This invention also discloses a solid aluminum electrolytic capacitor prepared using the composite anode foil. In this invention, plasma treatment cleans and activates the outer surface of the alumina dielectric layer, improving the wetting state of the anode aluminum foil; dipropylene glycol monopropyl ether and staged heat treatment are used to regulate the spreading and drying film-forming process of the working solution, which is beneficial for the formation of a conductive polymer film on the porous alumina dielectric layer surface.

Description

Technical Field

[0001] This invention belongs to the field of solid aluminum electrolytic capacitor manufacturing technology, and particularly relates to a solid aluminum electrolytic capacitor and a method for preparing its composite anode foil. Background Technology

[0002] With the development of applications such as data center power supplies, new energy vehicle electronics, and fast charging power supplies, power systems are placing higher demands on the low loss, high frequency ripple carrying capacity, and long-term reliability of solid aluminum electrolytic capacitors. Solid aluminum electrolytic capacitors typically use etched and formed aluminum anode foil as the anode structure, and a conductive polymer layer is set on the outside of the alumina dielectric layer formed by the formation.

[0003] After etching, the anode aluminum foil forms numerous micropores, which are then chemically treated to form an alumina dielectric layer on the pore wall surface. To utilize the effective area provided by the porous structure, the conductive polymer working fluid needs to enter the pores, spread sufficiently on the alumina dielectric layer surface, and form a continuous solid conductive layer after the dispersion medium is removed. Conductive polymer dispersions, such as PEDOT:PSS aqueous dispersion, possess characteristics such as coatability and film-forming conductivity, and can be used to form the aforementioned conductive polymer layer.

[0004] Existing technologies have disclosed methods for impregnating conductive polymers with a dielectric oxide film formed on the surface of a porous valve metal anode, followed by drying. For example, CN115223798B discloses a method for manufacturing an axially led-out organic polymer tantalum fixed capacitor, which involves electrochemically energizing a porous tantalum anode to form a tantalum pentoxide dielectric film, followed by impregnation with a PEDOT polymer solution under negative pressure, and then drying at room temperature and undergoing staged heating to form a polymer layer. This technology mainly promotes the penetration and film formation of conductive polymers in the porous tantalum anode through negative pressure impregnation and temperature control.

[0005] To improve the interfacial state between the inorganic dielectric layer and the conductive polymer layer, some processes also incorporate a silane-based connecting layer on the surface of the dielectric layer. This type of process requires controlling the hydrolysis, condensation, coating uniformity of the silane, as well as its compatibility with the subsequent conductive polymer working fluid, thus increasing the steps involved in connecting layer preparation and quality control.

[0006] However, formed aluminum anode foil exhibits different corrosion channels and alumina dielectric layer surface conditions compared to sintered tantalum anode bodies. For conductive polymer dispersions, such as PEDOT:PSS aqueous dispersions, the wetting state of the alumina dielectric layer affects the contact and spreading of the working fluid with the pore walls; the evaporation rate of water and other components in the wet film further affects the film's leveling, shrinkage, and continuity. Existing technologies have failed to simultaneously address the issues of surface activation of formed aluminum anode foil and control of the drying and film formation of the conductive polymer working fluid. Therefore, it is necessary to provide a composite anode foil preparation method that combines anode foil surface treatment and working fluid film formation control. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing composite anode foil for solid aluminum electrolytic capacitors, aiming to solve the technical problem in the prior art that it cannot simultaneously solve the surface activation of the aluminum anode foil and the control of the drying and film formation of the conductive polymer working fluid. This invention improves the wetting state of the anode aluminum foil surface through plasma treatment, and regulates the spreading and drying film formation process of the conductive polymer working fluid through dipropylene glycol monopropyl ether and staged heat treatment.

[0008] In a first aspect, the present invention provides a method for preparing composite anode foil for solid aluminum electrolytic capacitors, comprising: Dipropylene glycol monopropyl ether was added to the conductive polymer dispersion and mixed to obtain the working solution; An anode aluminum foil with an alumina dielectric layer formed on its surface is obtained, and the anode aluminum foil is subjected to plasma treatment. The working fluid is coated onto the surface of the plasma-treated anode aluminum foil to obtain a coated semi-finished product; The coated semi-finished product is pre-dried; The pre-dried coated semi-finished product is heat-treated sequentially at a first temperature and a second temperature higher than the first temperature, so that the conductive polymer in the conductive polymer dispersion forms a conductive polymer film layer, thereby obtaining a composite anode foil.

[0009] In one embodiment, the conductive polymer dispersion is a PEDOT:PSS aqueous dispersion, wherein PEDOT:PSS is a composite conductive polymer formed by poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate, and the solid content of the PEDOT:PSS aqueous dispersion is less than 1%.

[0010] In one embodiment, the mass of the dipropylene glycol monopropyl ether is 1% to 5% of the mass of the conductive polymer dispersion.

[0011] In one embodiment, the step of adding dipropylene glycol monopropyl ether to a conductive polymer dispersion and mixing to obtain a working solution includes: The dipropylene glycol monopropyl ether was slowly added to the PEDOT:PSS aqueous dispersion under stirring conditions of 200–400 rpm, and stirring was continued for at least 30 min to obtain the working solution.

[0012] In one embodiment, the plasma treatment is carried out in a process gas atmosphere, the process gas comprising at least one of oxygen, nitrogen, and argon.

[0013] In one embodiment, the step of plasma treating the anode aluminum foil includes: The anode aluminum foil is placed in a plasma treatment chamber, and the plasma treatment chamber is evacuated to a pressure not exceeding 10 Pa; the process gas is introduced to stabilize the working pressure at 50–200 Pa. The plasma is excited by a radio frequency power supply and processed for 30 s to 5 min. The frequency of the radio frequency power supply is 13.56 MHz.

[0014] In one embodiment, the step of coating the working fluid onto the plasma-treated anode aluminum foil surface to obtain a coated semi-finished product can be replaced by: The working solution is coated onto the plasma-treated anode aluminum foil using an immersion method to obtain a coated semi-finished product. The immersion time is 10–30 s and the lifting speed is 10–50 mm / min.

[0015] In one embodiment, the pre-drying temperature is room temperature to 60°C for 3 to 10 minutes; the first temperature is 80 to 120°C for 10 to 30 minutes; and the second temperature is 130 to 200°C for 20 to 60 minutes.

[0016] In a second aspect, the present invention provides a solid aluminum electrolytic capacitor, the solid aluminum electrolytic capacitor comprising a composite anode foil for a solid aluminum electrolytic capacitor, the composite anode foil for a solid aluminum electrolytic capacitor being manufactured by any one of the preparation methods described in the first aspect.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) Plasma acts on the outer surface of the formed alumina dielectric layer, which can remove some weakly attached contaminants and change the surface wetting state. In the experiment using pure oxygen as the process gas, the water contact angle of the untreated anode aluminum foil was 96.3°±0.3°; after plasma treatment and placement in air for 12 h, the water contact angle was 33.0°±0.2°, indicating that the wettability of the treated anode aluminum foil to water was significantly improved, and this improvement effect still existed 12 h after treatment.

[0018] (2) The evaporation rate of DPnP is lower than that of water, which can regulate the flow and spread of the wet film during the gradual evaporation of water; the pre-drying and two-stage heat treatment form a drying path with gradual temperature increase, which helps to reduce the risk of local shrinkage and uneven film formation caused by rapid evaporation of the wet film.

[0019] (3) The present invention combines the surface activation of the anode foil with the film formation control of the conductive polymer working fluid, eliminating the need for an additional independent coupling layer between the alumina dielectric layer and the conductive polymer film layer, resulting in a simpler process chain. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the composite anode foil preparation method of the present invention; Figure 2 A schematic diagram showing the surface state of the anodic aluminum foil before and after plasma treatment; Figure 3 Water contact angle diagrams for untreated anodic aluminum foil and anodic aluminum foil treated with plasma and left for 12 h. Figure 4 This is a cross-sectional scanning electron microscope image of a composite anode foil sample. Detailed Implementation

[0021] The present invention will now be described in conjunction with specific embodiments and accompanying drawings. These specific embodiments are used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, percentages are mass percentages relative to the mass of the conductive polymer dispersion.

[0022] In a first aspect, the present invention provides a method for preparing composite anode foil for solid aluminum electrolytic capacitors, comprising: S110, add dipropylene glycol monopropyl ether to the conductive polymer dispersion and mix to obtain the working solution; In this step, the conductive polymer dispersion is a dispersion system containing conductive polymers that can be coated and dried to form a solid conductive film. In a preferred embodiment, the conductive polymer dispersion is a PEDOT:PSS aqueous dispersion, wherein PEDOT:PSS is a composite conductive polymer formed from poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate, wherein PEDOT provides the conductive framework, and PSS is used for charge balance and to ensure stable dispersion of PEDOT in the aqueous phase. The solid content of the PEDOT:PSS aqueous dispersion is less than 1%, and Heraeus CLEVIOS K SN or Bailey Chemicals PES.51H.Z products can be used, or other PEDOT:PSS aqueous dispersions with similar composition and processing properties can also be used. The film-forming aid is dipropylene glycol monopropyl ether (DPnP), which has a high boiling point and slow evaporation at room temperature. The mass of the dipropylene glycol monopropyl ether is 1% to 5% of the mass of the conductive polymer dispersion, preferably 1% to 5%, and more preferably 3%.

[0023] This step includes: slowly adding the dipropylene glycol monopropyl ether to the PEDOT:PSS aqueous dispersion under stirring conditions of 200-400 rpm, and continuing to stir for at least 30 min to obtain the working solution.

[0024] S120, Obtain an anode aluminum foil with an alumina dielectric layer formed on its surface, and perform plasma treatment on the anode aluminum foil; In this step, plasma treatment primarily acts on the outer surface of the already formed alumina dielectric layer, and does not replace the formation step of the anode aluminum foil. The plasma removes some surface organic contaminants through particle bombardment and the action of active particles, and increases the number of surface polar sites, thereby improving the wetting and spreading conditions of the working fluid. The anode foil used is aluminum anode foil with an alumina dielectric layer formed on its surface, preferably pre-etched and formed aluminum anode foil, such as 115LHT16B85VF. Figure 2 As shown, before plasma treatment, there may be weakly attached contaminants on the outer surface of the alumina dielectric layer, and relatively few surface polar sites; after pure oxygen plasma treatment, some contaminants are removed, and the surface polarity and surface energy are improved. Figure 2 This is a schematic diagram of surface state changes, and does not represent actual dimensions or limit the specific types of functional groups formed after the treatment.

[0025] Furthermore, the plasma treatment is carried out in a low-pressure process gas atmosphere, which contains at least one of oxygen, nitrogen and argon, preferably pure oxygen; wherein the plasma can be excited by a radio frequency power supply or a microwave power supply; when a radio frequency power supply is used, the frequency can be 13.56 MHz.

[0026] The step of plasma treatment of the anode aluminum foil includes: The anode aluminum foil is placed in a plasma treatment chamber, and the plasma treatment chamber is evacuated to a pressure not exceeding 10 Pa; the process gas is introduced to stabilize the working pressure at 50–200 Pa. The plasma is excited by a radio frequency power supply and processed for 30 s to 5 min. The frequency of the radio frequency power supply is 13.56 MHz.

[0027] S130, the working fluid is coated onto the surface of the plasma-treated anode aluminum foil to obtain a coated semi-finished product; In this step, the working fluid can be applied by immersion or roller coating. When using immersion, the immersion time is preferably 10–30 s, and the lifting speed is preferably 10–50 mm / min.

[0028] This step can be replaced by: applying the working solution to the plasma-treated anode aluminum foil surface using an immersion method to obtain a coated semi-finished product, with an immersion time of 10-30 s and a lifting speed of 10-50 mm / min.

[0029] S140, the coated semi-finished product is pre-dried; In this step, the pre-drying temperature is preferably room temperature to 60 °C, and the time is preferably 3 to 10 min. After the working solution is coated, the more volatile components in the dispersion medium escape first. The slower-evaporating DPnP can be temporarily retained in the wet film for a certain period of time, so that the wet film can maintain a certain flow and leveling time, providing conditions for the contact and adjustment of conductive polymer particles or chain segments.

[0030] Here, room temperature refers to ambient temperature, which is 20°C to 30°C. For example, the pre-drying temperature can be 20°C to 60°C or 25°C to 60°C.

[0031] It should be noted that, in order to reduce the impact of surface recontamination and changes in surface condition during the placement process, it is preferable to apply the working solution within 4 hours after the plasma treatment is completed, and more preferably within 1 hour.

[0032] S150, the pre-dried coated semi-finished product is heat-treated sequentially at a first temperature and a second temperature higher than the first temperature, so that the conductive polymer in the conductive polymer dispersion forms a conductive polymer film layer, thereby obtaining a composite anode foil.

[0033] In this step, the first temperature is preferably 80-120 ℃, and the holding time at the first temperature is preferably 10-30 min; the second temperature is preferably 130-200 ℃, and the holding time at the second temperature is 20-60 min.

[0034] In steps S140 and S150, pre-drying, the first-stage heat treatment, and the second-stage heat treatment constitute a process of gradually removing volatile components, allowing the film layer to gradually take shape and stabilize from a wet film. This process mainly involves drying to form a film, adjusting particles or chain segments, and stabilizing the film layer structure, without requiring chemical cross-linking as a necessary condition.

[0035] In this embodiment, the surface activation of the substrate (anode aluminum foil) and the film-forming regulation of the working solution are respectively set before and after the coating of the working solution: the former improves the initial contact between the conductive polymer working solution and the alumina dielectric layer, while the latter regulates the spreading, evaporation, and setting processes of the wet film. The two measures are interconnected in the process sequence, together forming the preparation path of the composite anode foil.

[0036] In one embodiment, the preparation method further includes: repeating steps S130, S140 and S150 on the composite anode foil according to the target coverage amount until a composite anode foil that achieves the target coverage amount is obtained.

[0037] The number of repetitions in this step needs to be determined based on the anode foil pore structure, working fluid solid content, and target coverage.

[0038] As a complete embodiment of S110-S150, the specific steps are as follows: to prepare the working solution, weigh 100 parts by mass of PEDOT:PSS aqueous dispersion and place it in a stirring container, slowly add 3 parts by mass of DPnP under stirring at 300 rpm, and continue stirring for 30 min to make DPnP uniformly dispersed in PEDOT:PSS aqueous dispersion to obtain a working solution with uniform state. The formed anode aluminum foil (model 115LHT16B85VF) was cut to a suitable size for processing and evenly laid or suspended on the carrier of a Diener electronic ZEPTO low-pressure plasma treatment device, leaving gaps between adjacent foils to avoid mutual obstruction. Before processing, the cleanliness of the chamber and carrier was checked, and the chamber was closed and evacuated. Once the chamber pressure was no higher than 10 Pa, pure oxygen was introduced to stabilize the working pressure at 50 Pa. Oxygen plasma was then excited using a 13.56 MHz radio frequency power supply and treated on the anode aluminum foil for 2 minutes. The output of the plasma treatment device was set to a working state capable of forming and maintaining a stable oxygen plasma at the above pressure. The processing conditions should balance surface cleaning and activation effects with the integrity of the alumina dielectric layer. After plasma treatment, the anode aluminum foil is removed and immersed in the working solution for 20 seconds within 1 hour. It is then pulled up at a constant speed of 30 mm / min to allow the working solution to cover the surface of the anode aluminum foil and penetrate its corrosion channels, resulting in a coated semi-finished product. The speed is kept stable during the pulling process to reduce uneven liquid film thickness and flow marks, thus obtaining the coated semi-finished product. Place the coated semi-finished product in a clean, level environment and pre-dry it at 40 ℃ for 5 min to allow some of the moisture in the wet film to gradually escape and to prevent the wet film from flowing significantly during handling. Then, a two-stage heat treatment can be carried out using an oven or tunnel furnace: first, heat treatment at 100 °C for 20 min to further remove moisture and more volatile components; then heat treatment at 160 °C for 30 min to further reduce residual volatile components and allow PEDOT:PSS particles or segments to gradually contact, adjust and shape, forming a conductive polymer film layer to obtain a composite anode foil.

[0039] Depending on the target film coverage and thickness, the above coating, pre-drying, and two-stage heat treatment steps can be repeated after the previous heat treatment is completed and cooled. The number of repetitions is determined based on the anode foil pore structure, working liquid solid content, and target coverage state.

[0040] In this embodiment, the CLEVIOS K SN type PEDOT:PSS aqueous dispersion can be replaced by the PES.51H.Z type PEDOT:PSS aqueous dispersion. For different conductive polymer dispersions, the solid content, viscosity, or anode foil pore structure can be adjusted within the scope defined in the claims, including the DPNP addition amount, plasma treatment conditions, immersion time, pulling speed, and heat treatment conditions.

[0041] The contact angle of untreated anode aluminum foil and anode aluminum foil treated with pure oxygen plasma and then placed in air for 12 hours was tested using the water droplet method. The test images are shown below. Figure 3 As shown, the water contact angle of the untreated sample was 96.3°±0.3°; the water contact angle of the sample after plasma treatment and 12 h of storage was 33.0°±0.2°. The spread of water droplets on the treated sample significantly increased, indicating that pure oxygen plasma treatment can improve the wettability of the anode aluminum foil surface, and this improvement in wettability persisted even after 12 h of storage. Since the working solution in this embodiment is an aqueous PEDOT:PSS dispersion system, the improved wettability of the anode aluminum foil facilitates the contact and spread of the working solution on the alumina dielectric layer surface.

[0042] The cross-sectional morphology of the composite anode foil sample was observed using an electron microscope, and the results are as follows: Figure 4 As shown. Figure 4 The magnification is 200x, and the scale bar is 200 μm. The figure shows the porous cross-sectional structure of the anode aluminum foil and the coating layer on its surface, demonstrating that the method can be used for chemically formed anode aluminum foil with corrosion-resistant pore structures. This figure is used to illustrate the overall cross-sectional morphology of the composite anode foil and is not intended for quantitative evaluation of the number of film defects, adhesion, or electrical properties.

[0043] In a second aspect, the present invention discloses a solid aluminum electrolytic capacitor, the solid aluminum electrolytic capacitor comprising a composite anode foil for solid aluminum electrolytic capacitors, the composite anode foil for solid aluminum electrolytic capacitors being manufactured by any one of the preparation methods described in the first aspect.

[0044] The composite anode foil for solid aluminum electrolytic capacitors described in this aspect is as described in the first aspect and will not be repeated here.

[0045] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0046] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0047] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0048] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing composite anode foil for solid aluminum electrolytic capacitors, characterized in that, include: Dipropylene glycol monopropyl ether was added to the conductive polymer dispersion and mixed to obtain the working solution; An anode aluminum foil with an alumina dielectric layer formed on its surface is obtained, and the anode aluminum foil is subjected to plasma treatment. The working fluid is coated onto the surface of the plasma-treated anode aluminum foil to obtain a coated semi-finished product; The coated semi-finished product is pre-dried; The pre-dried coated semi-finished product is heat-treated sequentially at a first temperature and a second temperature higher than the first temperature, so that the conductive polymer in the conductive polymer dispersion forms a conductive polymer film layer, thereby obtaining a composite anode foil.

2. The preparation method according to claim 1, characterized in that, The conductive polymer dispersion is a PEDOT:PSS aqueous dispersion, wherein PEDOT:PSS is a composite conductive polymer formed by poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate, and the solid content of the PEDOT:PSS aqueous dispersion is less than 1%.

3. The preparation method according to claim 1, characterized in that, The mass of the dipropylene glycol monopropyl ether is 1% to 5% of the mass of the conductive polymer dispersion.

4. The preparation method according to claim 2, characterized in that, The step of adding dipropylene glycol monopropyl ether to a conductive polymer dispersion and mixing to obtain a working solution includes: The dipropylene glycol monopropyl ether was slowly added to the PEDOT:PSS aqueous dispersion under stirring conditions of 200–400 rpm, and stirring was continued for at least 30 min to obtain the working solution.

5. The preparation method according to claim 1, characterized in that, The plasma treatment is carried out in a process gas atmosphere, which contains at least one of oxygen, nitrogen, and argon.

6. The preparation method according to claim 5, characterized in that, The step of plasma treatment of the anode aluminum foil includes: The anode aluminum foil is placed in the plasma treatment chamber, the plasma treatment chamber is evacuated to no more than 10 Pa, and the process gas is introduced to stabilize the working pressure at 50-200 Pa. The plasma is excited by a radio frequency power supply and processed for 30 s to 5 min. The frequency of the radio frequency power supply is 13.56 MHz.

7. The preparation method according to claim 1, characterized in that, The step of coating the working fluid onto the plasma-treated anode aluminum foil surface to obtain a coated semi-finished product can be replaced by: The working solution is coated onto the plasma-treated anode aluminum foil using an immersion method to obtain a coated semi-finished product. The immersion time is 10–30 s and the lifting speed is 10–50 mm / min.

8. The preparation method according to claim 1, characterized in that, The pre-drying temperature is from room temperature to 60°C for 3 to 10 minutes; the first temperature is 80 to 120°C for 10 to 30 minutes; and the second temperature is 130 to 200°C for 20 to 60 minutes.

9. A solid aluminum electrolytic capacitor, characterized in that, The solid aluminum electrolytic capacitor includes a composite anode foil for solid aluminum electrolytic capacitors, which is manufactured by the preparation method described in any one of claims 1-8.

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