Cathode foil for electrolytic capacitors, electrolytic capacitors, and methods for manufacturing the same.

Abstract

A cathode foil for electrolytic capacitors comprises a metal porous part, a metal core part which is contiguous with the metal porous part, a first main surface on which pores of the metal porous part open, and a coating film which covers the metal porous part. The coating film is formed to a depth of 10% or more of the thickness of the metal porous part as observed in the direction of the thickness of the metal porous part. The coating film may contain a first layer which contains a first element and is electrically conductive and / or a second layer which is an oxide layer containing a second element. According to this configuration, a cathode foil for electrolytic capacitors can be provided, which can exhibit excellent properties.

Description

[Technical Field]

[0001] The present invention relates to cathode foil for electrolytic capacitors, electrolytic capacitors, and methods for manufacturing the same. [Background technology]

[0002] The anode of an electrolytic capacitor uses a metal foil containing a valve-acting metal. To increase capacitance, at least a portion of the main surface of the metal material is subjected to treatment such as etching to form a porous body. Subsequently, the porous body is subjected to a chemical conversion treatment to form a layer of metal oxide (dielectric) on the surface of the pores or irregularities of the porous body.

[0003] On the other hand, the cathode body is constructed using various materials depending on the application, including roughened metal foil, chemically converted foil obtained by further chemical conversion of roughened metal foil, or a non-valve metal such as titanium formed on the surface of the metal foil.

[0004] Patent Document 1 describes a cathode foil for a solid electrolytic capacitor, in which a first conductive layer, a mixed layer comprising the material constituting the first conductive layer and carbon, and a second conductive layer substantially composed of carbon are formed on an electrode substrate that is not roughened. Here, the component concentration of the mixed layer is changed from a component composition substantially containing only the material constituting the first conductive layer to a component composition substantially containing only carbon, as one moves from the first conductive layer to the second conductive layer, thereby achieving high capacitance and improving the characteristics of the electrolytic capacitor, such as low ESR. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-174865 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Provided are a cathode foil for an electrolytic capacitor capable of realizing excellent characteristics and a method for manufacturing the same.

Means for Solving the Problems

[0007] One aspect of the present invention Cathode foil for electrolytic capacitors related to this product. has a metal porous part, a metal core part continuous with the metal porous part, ,before and a film covering the metal porous part. The pores in the porous metal portion open up on the first main surface of the cathode foil for the electrolytic capacitor. The film is formed to a depth of 10% or more of the thickness of the metal porous part in the thickness direction of the metal porous part. From the first main surface ru.

[0008] Another aspect of the present invention Electrolytic capacitors related to is The above shadow provided with a cathode foil, an anode body having a dielectric layer formed on the surface, and an electrolyte. ru.

[0009] Another aspect of the present invention Method for manufacturing cathode foil for electrolytic capacitors related to this method includes a step of preparing a metal substrate having a metal porous part and a metal core part continuous with the metal porous part, and a step of forming a film on the surface of the metal part constituting the metal porous part of the metal substrate. ru. The film is formed by product( ALD law (atomic layer deposition). ru.

[0010] Another aspect of the present invention Method for manufacturing electrolytic capacitors related to this method is The above shadow to obtain a cathode foil using a method for manufacturing a cathode foil, prepare an anode body having a dielectric layer on the surface, and form a capacitor element using the anode body and the cathode foil for an electrolytic capacitor. ,shadow nothing.

Advantages of the Invention

[0011] By using the cathode foil of the present invention, the characteristics of an electrolytic capacitor can be improved.

Brief Description of the Drawings

[0012] [Figure 1] ​​It is a cross-sectional view schematically showing the configuration of a cathode foil for an electrolytic capacitor according to an embodiment of the present invention. [Figure 2] It is a cross-sectional schematic view showing an enlarged part of the metal porous part of the cathode foil for the electrolytic capacitor. [Figure 3] It is a cross-sectional schematic view showing another example of the cathode foil for the electrolytic capacitor shown in FIG. 2. [Figure 4] It is a cross-sectional schematic view showing still another example of the cathode foil for the electrolytic capacitor shown in FIG. 2. [Figure 5] It is a cross-sectional view schematically showing an electrolytic capacitor according to an embodiment of the present invention. [Figure 6] It is a schematic view of a part of a wound body included in the electrolytic capacitor developed.

Embodiments for Carrying Out the Invention

[0013] [Cathode Foil for Electrolytic Capacitor] The cathode foil for an electrolytic capacitor according to an embodiment of the present invention has a metal porous part, a metal core part continuous with the metal porous part, a first main surface where the pores of the metal porous part open, and a film covering the metal porous part. More specifically, the film covers the surface of the metal skeleton constituting the metal porous part. The film may include a conductive first layer containing a first element and / or a second layer that is an oxide film containing a second element. The film may include both the first layer and the second layer. In that case, the first layer covers at least a part of the second layer.

[0014] In the present embodiment, at least one main surface (the first main surface) of the cathode foil is roughened, and pores are formed in the first main surface of the cathode foil in so as to open. The part where the pores are formed on the first main surface side of the cathode foil is the metal porous part, and the inside of the foil where the pores are not formed cathode is the metal core part.

[0015] The main surfaces of the cathode foil (cathode body) and anode foil (anode body) are the two surfaces that occupy the largest area macroscopically (visually) among the surfaces of these electrode foils. The end surfaces of the cathode foil and anode foil are the surfaces at the ends other than the main surfaces of these electrode foils, and in the case of large electrode foils that have been cut, the cut surface is also included. In a wound body, the surfaces of the electrode foils that are located on the top and bottom surfaces other than the circumferential surfaces are the end surfaces.

[0016] Typically, a native oxide film is formed on the surface of the cathode foil. This native oxide film is... cathode It has the effect of protecting the metal portion of the foil from the electrolyte. However, the thickness of the native oxide film may not be sufficient to protect the metal portion from the electrolyte, and the reaction between the metal portion and the electrolyte proceeds easily when voltage is applied. Furthermore, the reaction between the metal portion and the electrolyte proceeds easily through the thinner parts of the native oxide film. As a result, gas generation and degradation due to oxidation of the cathode foil may increase. In addition, native acid film In some cases, sufficient water resistance may not be achieved, and if the electrolyte contains moisture, the foil is more likely to deteriorate due to hydration reactions. As a result, the ESR tends to be high.

[0017] To suppress the degradation of the cathode foil, it is conceivable to perform a chemical conversion treatment on the cathode foil to form a thick oxide film. In this case, capacitance may also be generated on the cathode side. If capacitance is generated on the cathode side in addition to the anode side, the overall capacitance (composite capacitance) of the electrolytic capacitor will decrease. However, by forming an oxide film of appropriate thickness (corresponding to the second layer described later) on the roughened cathode foil and deliberately increasing the capacitance on the cathode side, it is possible to suppress the decrease in the overall capacitance of the electrolytic capacitor.

[0018] Using a roughened cathode foil increases the contact area between the electrolyte and the cathode foil, making it easier to lower the ESR. It also allows for an increase in the capacitance on the cathode side. On the other hand, cathode When the surface area of ​​the foil increases, cathode Reactions with electrolytes become more likely to occur on the surface of the foil. cathode The foil is prone to deterioration.

[0019] Therefore, in the electrode foil for the electrolytic capacitor according to this embodiment, in one embodiment, the surface of the cathode foil may be covered with a conductive first layer. This can suppress the development of capacitance on the cathode side. By electrically connecting the conductive first layer to the metal core, the cathode foil substantially functions as a conductor, and the decrease in capacitance of the electrolytic capacitor can be suppressed. In addition, in the case of an electrolytic capacitor using a solid electrolyte such as a conductive polymer, the conductive polymer is formed to fill the pores deep inside the metal porous part. In this case, since the inner walls of the pores are covered with the first layer, the adhesion between the solid electrolyte and the cathode foil is improved, and the ESR can be reduced. The first layer contains a first element. The first element may be at least one element selected from the group consisting of carbon, nickel, silver, and gold.

[0020] Furthermore, in one embodiment, the electrode foil for the electrolytic capacitor according to this embodiment may have the surface of the cathode foil coated with a second layer, which is an oxide film. This can moderately increase the capacitance generated on the cathode side and suppress a decrease in the overall capacitance of the electrolytic capacitor. In addition, the second layer suppresses the reaction between the metal part and the electrolyte, thereby suppressing the degradation of the cathode foil and maintaining a low ESR. Furthermore, an electrolytic capacitor with excellent voltage resistance can be obtained. The second layer contains a second element. The second element may be at least one selected from the group consisting of aluminum, titanium, silicon, tantalum, niobium, hafnium, and zirconium.

[0021] The thickness of the second layer is set to a desired thickness according to the characteristics of the electrolytic capacitor. From the viewpoint of maintaining capacitance, the thickness of the second layer is obtained by chemically forming a metal containing a second element at 4V. Oxide film The thickness should be less than or equal to the specified thickness. For example, if the second element is aluminum, the thickness of the second layer should be 5 nm or less. On the other hand, from the viewpoint of increasing the pressure resistance, the thickness of the second layer can be obtained by chemically converting a metal containing the second element at 4V. Oxide film It may be made thicker than the initial thickness. Note that the above description does not necessarily mean that the second layer is formed by chemical conversion treatment; for example, it includes cases where the second layer is formed by deposition to a thickness that would be obtained if chemical conversion were performed with 4V.

[0022] Furthermore, when the second element is aluminum, titanium, silicon, tantalum, niobium, hafnium, or zirconium, the thickness obtained by chemical conversion of the metal containing the second element with 4V is given below. In the following, the thickness in the case of silicon corresponds to the thickness of a silicon oxide film that yields the same pressure resistance as an aluminum oxide film formed by 4V conversion. Aluminum: 5nm Titanium: 12nm Silicon: 2nm Tantalum: 6nm Niobium: 9nm Hafnium: 11nm Zirconium: 8nm

[0023] The coating, including the first and / or second layer, has the following characteristics in the thickness direction of the porous metal portion: From the first main surface of the porous metal part, Up to a depth of 10% or more, 20% or more, 30% or more, or 50% or more of the thickness of the porous metal portion. In the area It's sufficient if it's formed.

[0024] The first and / or second layer can be formed by ALD (Atomic Layer Deposition). According to the ALD method, the raw material gas (precursor material) diffuses through the voids formed by the pores of the porous metal, penetrating deep into the winding pores. As a result, the first and / or second layer can adhere to the inner walls of pores that are not exposed from the first main surface through which the pores of the porous metal are open, and are shielded by the metal framework of the porous metal. Therefore, using the ALD method, the first and / or second layer can be deposited in the region extending from the first main surface to the depths of the porous metal. However, in the ALD method, while the raw material gas (precursor material) can reach deep into the porous metal away from the outer surface (first main surface) through the pores, it becomes more difficult for the precursor material to reach further away from the first main surface. Consequently, the thickness of the film is determined by the distance from the first main surface (more precisely, the diffusion distance of the raw material gas supplied through the pores from the first main surface). The shorter ) It may have a distribution that is thicker and thinner as it moves away from the first main surface (closer to the metal core).

[0025] A second layer may be formed by chemical conversion treatment. However, when forming a second layer by chemical conversion treatment, applying a conversion voltage of 4V or less does not stabilize the conversion state, making it difficult to form a thin conversion film with a uniform thickness, few defects, and a dense structure. In some cases, parts of the metal skeleton surface of the porous metal portion may not have a second layer or the second layer may be thin. As a result, the foil is prone to deterioration due to reaction with the electrolyte. In contrast, when forming a second layer by the ALD method, the thickness of the second layer may depend on the distance from the first main surface if the thickness of the cathode foil exceeds, for example, 50 μm, but a uniform and dense film with few defects can be formed. Therefore, it becomes easy to cover the surface of the metal skeleton with a dense and defect-free second layer using the ALD method.

[0026] In the thickness direction of the porous metal portion, a third layer containing at least one of phosphorus and nitrogen may be attached to regions exceeding 10% of the thickness of the porous metal portion. The third layer may also be attached to the deeper parts of the porous metal portion on the metal core side where the film including the first and / or second layers is not formed. The inclusion of phosphorus and / or nitrogen gives the third layer high solvent resistance to various solvents (especially water) that constitute the liquid component (e.g., electrolyte). Furthermore, when the first and / or second layers are formed using the ALD method, the adhesion between the first and / or second layers and the metal framework, and the coverage of the first and / or second layers are improved.

[0027] In particular, when the pH of the liquid component is less than 7 and acidic, if the acidic liquid component comes into contact with the metal skeleton or metal core of the porous metal part, the cathode foil is prone to corrosion and degradation. However, by providing a third layer, the degradation of the cathode foil can be suppressed. By providing a third layer, an excellent degradation suppression effect on the cathode body can be obtained even when the pH of the liquid component is less than 5. Furthermore, even when used in a high-temperature, high-humidity environment, for example, at 85°C or higher and 85% or higher humidity, moisture resistance can be improved.

[0028] Furthermore, even if the liquid component contains water, the hydration reaction of the metal skeleton or metal core can be suppressed. For example, the liquid component may contain water in the range of 3 to 15% by mass. Even in that case, the hydration reaction is suppressed because the third layer contains phosphorus and / or nitrogen. Therefore, by providing the third layer, the deterioration of the cathode foil can be suppressed even when the liquid component contains water.

[0029] The third layer may also be interposed between the film, which includes the first and / or second layers, and the porous metal portion. Even if cracks occur in the film, the surface of the porous metal portion is covered by the third layer, so the metal skeleton of the porous metal portion is not exposed and contact with the liquid component is suppressed. Therefore, deterioration of the cathode foil can be suppressed and the increase in ESR can be suppressed.

[0030] If the coating includes a second layer, the second layer may also contain phosphorus and / or nitrogen. If a third layer is interposed between the coating and the porous metal portion, the third layer may constitute part or all of the second layer in the coating.

[0031] The third layer can be attached to the inner walls of the pores, for example, by impregnating a roughened cathode foil with a solution containing a phosphorus and / or nitrogen compound (e.g., ammonium phosphate solution), and then drying it by heat treatment. The impregnation with the solution may be carried out simultaneously with or in parallel with the chemical conversion treatment if the conversion solution contains a phosphorus compound and / or a nitrogen compound. The chemical conversion treatment may be carried out before the formation of the first and / or second layer, or after the formation of the first and / or second layer.

[0032] Figure 1 shows a schematic cross-sectional view of a cathode foil according to one embodiment of the present invention. The cathode foil 22 is an integrated material of a metal core 31 and a metal porous portion 32, with pores in the metal porous portion 32 opening at the first main surface S1. The metal porous portion 32 has a second main surface S2 at the boundary with the metal core 31. thickness difference( From the first main surface S1The depth (i.e., the distance between the first principal surface S1 and the second principal surface S2) is denoted by T0.

[0033] The porous metal portion 32 has pits or pores surrounded by a metal skeleton. A coating 33 is formed on the porous metal portion 32 in a region of a predetermined thickness (depth) from the first main surface S1, so as to cover the surface of the metal skeleton of the porous metal portion 32 (see Figures 2 to 4). The coating 33 may include a first layer 35 and / or a second layer 36. The thickness T1 of the region of the porous metal portion 32 on which the coating 33 is formed is 10% or more of the thickness T0 of the porous metal portion 32 (T1 ≥ 0.1T0). The thickness T1 may be 30% or more of the thickness T0.

[0034] In this embodiment, both the first layer 35 and the second layer 36 may be formed from the first main surface S1 to a depth exceeding 10% or more of the thickness T0 of the metal porous portion 32. However, it is sufficient if at least one of the first layer 35 and the second layer 36 is formed from the first main surface S1 to a depth exceeding 10% or more of the thickness T0 of the metal porous portion 32. Preferably, at least the first layer 35 is formed from the first main surface S1 to a depth exceeding 10% or more of the thickness T0 of the metal porous portion 32.

[0035] The thickness of the porous metal portion is not particularly limited and can be appropriately selected depending on the application of the electrolytic capacitor, the required voltage withstand voltage, etc. The thickness of the porous metal portion may be, for example, 1 μm to 60 μm. Furthermore, the thickness T0 of the porous metal portion may be, for example, 1 / 10 or more and less than 5 / 10 of the thickness of the cathode foil. The thickness T0 of the porous metal portion can be determined by cutting the cathode foil so that a cross-section in the thickness direction of the metal core and the porous metal portion is obtained, taking an electron microscope image of the cross-section, and taking the average value of the thickness at any 10 points in the porous metal portion. The thickness T1 is determined as the average value of the thickness at any 10 points in the region of the porous metal portion where a film 33 with a thickness of 1 nm or more can be confirmed in the above electron microscope image.

[0036] Figure 2 shows a schematic cross-sectional view of the region near the first main surface S1 of the porous metal portion 32 in the cathode foil 22. Note that in Figure 2, the pores of the porous metal portion and the first layer 35 and third layer 37 are highlighted for illustrative purposes. The scale of each component in the figure (especially the film thickness of the first layer 35 and third layer 37) does not correspond to the actual scale. This is also true for Figures 3 and 4 shown later.

[0037] As shown in Figure 2, the cathode foil 22 has a first main surface S1 that is roughened, and pores 38 are formed on the roughened main surface. The pores 38 are winding and branching, extending from the first main surface S1 towards the interior of the porous metal portion 32. The inner walls of the pores 38 are covered with a film 33 that includes the first layer 35.

[0038] The thickness of the first layer 35 is approximately constant, but it can become thicker closer to the first main surface S1 (more precisely, the shorter the shortest distance to the first main surface S1 via the pores 38). The first layer 35 also adheres to areas (regions X1 and Y1 in Figure 2) that are not exposed from the first main surface S1 and are shielded from the outside by the metal framework of the porous metal portion 32. Such a film 33 can be obtained by depositing the first layer 35 using the ALD method.

[0039] A third layer 37 is formed between the coating 33 and the metal framework of the porous metal portion 32. The third layer 37 contains phosphorus and / or nitrogen and is water-resistant. The third layer 37 may also be formed in the deeper parts of the porous metal portion 32 where the coating 33 is not formed (regions where the depth from the first main surface S1 exceeds T1), although this is not shown.

[0040] Figure 3 shows another example of a cathode foil according to one embodiment of the present invention. Similar to Figure 2, Figure 3 is an enlarged schematic cross-sectional view of the region near the first main surface S1 of the porous metal portion 32. In Figure 3, for illustrative purposes, the pores of the porous metal portion and the second layer 36 and third layer 37 are highlighted. The scale of each component in the figure (especially the film thickness of the second layer 36 and third layer 37) does not correspond to the actual scale. This is also true for Figure 4, which will be shown later.

[0041] Similar to Figure 2, the cathode foil 22A shown in Figure 3 has a roughened first main surface S1, and pores 38 are formed on the roughened main surface. The inner walls of the pores 38 are covered with a film 33 including a second layer 36.

[0042] The thickness of the second layer 36 is approximately constant, but it can become thicker closer to the first main surface S1 (more precisely, the shorter the shortest distance to the first main surface S1 via the pores 38). The second layer 36 also adheres to areas (regions X2 and Y2 in Figure 3) that are not exposed from the first main surface S1 and are shielded from the outside by the metal skeleton of the porous metal portion 32. Such a film 33 is obtained by depositing the second layer 36 by the ALD method. Similar to Figure 2, a third layer 37 is formed between the film 33 and the metal skeleton of the porous metal portion 32. The third layer 37 can also be formed in the deeper parts of the porous metal portion 32 where the film 33 is not formed (regions where the depth from the first main surface S1 exceeds T1), although this is not shown.

[0043] Figure 4 shows yet another example of a cathode foil according to one embodiment of the present invention. Figure 4, like Figures 2 and 3, is an enlarged schematic cross-sectional view of the region near the first main surface S1 of the porous metal portion 32. In the cathode foil 22B shown in Figure 4, the inner walls of the pores 38 are covered with a film 33 including a first layer 35 and a second layer 36. The first layer 35 covers the second layer 36.

[0044] The thickness of the first layer 35 and the second layer 36 is formed to be thicker on the side closer to the first main surface S1 (more precisely, the shorter the shortest distance to the first main surface S1 via the pores 38). In addition, the first layer 35 and the second layer 36 are attached to areas that are not exposed from the first main surface S1 and are shielded from the outside by the metal skeleton of the porous metal portion 32 (areas X3 and Y3 in Figure 4). Similar to Figures 2 and 3, a third layer 37 is formed between the film 33 and the metal skeleton of the porous metal portion 32. The third layer 37 may also be formed in the deeper parts of the porous metal portion 32 where the film 33 is not formed (areas where the depth from the first main surface S1 exceeds T1), although this is not shown.

[0045] The film thickness of the first layer 35 is, for example, 1 nm to 50 nm, or it may be 1 nm to 30 nm. The film thickness of the second layer 36 is, for example, 1 nm to 10 nm. The film thickness of the coating 33 (the sum of the film thicknesses of the first and second layers) is, for example, 2 nm to 60 nm. These film thicknesses are determined as the average value of the film thickness at any 10 points in the surface region where the depth from the first main surface S1 is 100 nm or less, in an electron microscope image of the cross-section in the thickness direction of the porous metal portion 32.

[0046] The thickness of the third layer 37 is, for example, 2 nm or less, and may be between 0.08 nm and 2 nm. The thickness of the third layer 37 is determined as the average value of the thickness at any 10 points in an electron microscope image of the cross-section in the thickness direction of the porous metal portion 32.

[0047] From the viewpoint of suppressing the degradation of the cathode foil, the concentration of phosphorus or nitrogen contained in the third layer is preferably, for example, 0.5 at% to 7.0 at%, and more preferably 1.0 at% to 5.0 at%. The concentration of phosphorus or nitrogen in the third layer is determined by observing a cross-section of the cathode foil cut in the thickness direction using a transmission electron microscope (TEM), and performing a compositional analysis of a desired region of the cathode foil using an X-ray microanalyzer (XMA). The concentration of phosphorus or nitrogen is determined by taking the average of the measurements at any 10 points.

[0048] The type of metal that constitutes the metal core and the metal porous part is not particularly limited, but metals that have a valve function, such as aluminum, tantalum, and niobium, are preferred.

[0049] The roughening of the cathode foil (formation of a porous metal portion) is preferably carried out by etching the metal foil. Alternatively, if necessary, an oxide film (second layer) may be formed on the surface of the cathode foil by chemical conversion treatment.

[0050] The pore diameter peak of the pits or pores in the porous metal portion is not particularly limited, but from the viewpoint of increasing the surface area and forming the first or second layer deep into the porous metal portion, it may be set to, for example, 50 nm to 2000 nm, or it may be set to 100 nm to 300 nm. The pore diameter peak is the most frequent pore diameter in the volume-based pore diameter distribution measured, for example, with a mercury porosimeter.

[0051] Examples of conductive materials for forming the first layer include amorphous carbon, metals, or conductive metal compounds, which can be deposited by the ALD method. Preferably, the metals and metal compounds are those that do not easily form a passivation film due to contact with air. Examples of metals include silver, gold, titanium, titanium alloys, nickel, and nickel alloys. Examples of metal compounds include nitrides and carbides, with nitrides being preferred. Examples of metals constituting the metal compound include titanium and / or nickel. The first layer may contain one of these materials, or two or more.

[0052] When forming the first and second layers, the thickness of the region where the second layer is formed is the thickness of the porous metal portion. 3 If the thickness T0 of layer 2 is 10% or more, the first layer may be formed in a shallow region near the first main surface S1. In this case, the method for depositing the first layer is not limited to the ALD method, but may also be a vapor phase method such as chemical vapor deposition, vacuum deposition, sputtering, or ion plating.

[0053] The elements other than oxygen contained in the oxide film that constitutes the second layer (the second element) may be the same as or different from the metal elements that constitute the porous metal portion.

[0054] When forming a coating including a first layer and a second layer, the thickness (depth) of the region where the first layer is formed within the porous metal portion may be greater than the thickness (depth) of the region where the second layer is formed. In this case, it is also possible to electrically connect the first layer to the metal skeleton portion on the metal core side of the porous metal portion. This makes it easy to prevent the cathode side capacitance caused by the second layer from occurring.

[0055] [Electrolytic capacitor] The electrolytic capacitor according to this embodiment comprises a cathode foil for electrolytic capacitors, an anode body with a dielectric layer formed on its surface, and an electrolyte. The components of the electrolytic capacitor other than the cathode foil will be described in detail below.

[0056] (Anode) The anode can be a metal foil. The type of metal contained in the metal foil is not particularly limited, but it is preferable to include a metal with valve properties such as aluminum, tantalum, niobium, or titanium, as this facilitates the formation of a dielectric layer. Among these, those containing a secondary metal as the main component, such as elemental metals like aluminum or alloys like aluminum alloys, are preferred. The surface of the anode is roughened, and a dielectric layer is formed on the roughened surface of the metal foil.

[0057] (Separator) In electrolytic capacitors that use an electrolyte solution, a separator may be used to separate the anode and the cathode foil. The separator material can be a nonwoven fabric or film mainly composed of cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, or glass.

[0058] (electrolyte) The electrolyte may include a liquid component and / or a solid electrolyte. If the electrolyte does not include a solid electrolyte, the liquid component is an electrolyte solution. If the electrolyte includes a solid electrolyte, the liquid component may or may not be an electrolyte solution. The liquid component may have the effect of improving the repairability of the dielectric layer formed on the surface of the anode body on the anode side of the electrolytic capacitor. A conductive polymer can be used as the solid electrolyte.

[0059] (conductive polymer) Preferred conductive polymers include polypyrrole, polythiophene, and polyaniline. These may be used individually, in combination of two or more, or as copolymers of two or more monomers. The weight-average molecular weight of the conductive polymer is not particularly limited, but is, for example, 1,000 to 1,000,000.

[0060] In this specification, polypyrrole, polythiophene, and polyaniline, etc., refer to polymers that have polypyrrole, polythiophene, and polyaniline, respectively, as their basic skeletons. Therefore, polypyrrole, polythiophene, and polyaniline, etc., may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) (PEDOT), etc.

[0061] Dopants may be added to conductive polymers. From the viewpoint of suppressing dedoping from conductive polymers, it is desirable to use polymer dopants. Examples of polymer dopants include anions such as polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used individually or in combination of two or more. Furthermore, these may be homopolymers or copolymers of two or more monomers. Among these, polystyrene sulfonic acid (PSS) is preferred.

[0062] The weight-average molecular weight of the dopant is not particularly limited, but is preferably, for example, 1,000 to 1,000,000, as it facilitates the formation of a homogeneous solid electrolyte layer.

[0063] (Liquid component) The liquid component may be a non-aqueous solvent, or a mixture of a non-aqueous solvent and an ionic substance (solute, e.g., an organic salt) dissolved therein (i.e., an electrolyte). The non-aqueous solvent may be an organic solvent or an ionic liquid. A high-boiling point solvent is preferred as the non-aqueous solvent. For example, polyhydric alcohols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (GBL), amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate (PC), ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde can be used. Polymeric solvents may also be used as the high-boiling point solvent.

[0064] Examples of polymeric solvents include polyalkylene glycols, derivatives of polyalkylene glycols, and compounds in which at least one hydroxyl group of a polyhydric alcohol is substituted with polyalkylene glycol (including derivatives). Specifically, examples include polyethylene glycol (PEG), polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, and polybutylene glycol. These may be used individually or in mixtures of two or more. The polymeric solvent may also be, for example, an ethylene glycol-propylene glycol copolymer, an ethylene glycol-butylene glycol copolymer, or a propylene glycol-butylene glycol copolymer. The copolymer may be a random copolymer.

[0065] The liquid component may contain acidic and basic components. Polycarboxylic acids and monocarboxylic acids can be used as the acidic component. Examples of the polycarboxylic acids mentioned above include aliphatic polycarboxylic acids ([saturated polycarboxylic acids, e.g., oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebatic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid]; [unsaturated polycarboxylic acids, e.g., maleic acid, fumaric acid, eicotanoic acid]), aromatic polycarboxylic acids (e.g., phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid), and alicyclic polycarboxylic acids (e.g., cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, etc.). Examples of the above monocarboxylic acids include aliphatic monocarboxylic acids (1 to 30 carbon atoms) ([saturated monocarboxylic acids, e.g., formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, stearic acid, behenic acid]; [unsaturated monocarboxylic acids, e.g., acrylic acid, methacrylic acid, oleic acid]), aromatic monocarboxylic acids (e.g., benzoic acid, cinnamic acid, naphthoic acid), and oxycarboxylic acids (e.g., salicylic acid, mandelic acid, resorcinic acid). Among these, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcinic acid are preferred because they have high conductivity and are thermally stable.

[0066] Inorganic acids include carbon compounds, hydrogen compounds, boron compounds, sulfur compounds, nitrogen compounds, and phosphorus compounds. Representative examples of inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl phosphate esters, boric acid, borofluoric acid, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, and naphthalenesulfonic acid. Furthermore, composite compounds of organic and inorganic acids can be used as the acid component. Examples include borodiglycolic acid, borodisalicylic acid, and borodisalicylic acid.

[0067] The basic component is a compound having an alkyl-substituted amidine group, such as imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds). Specifically, 1,8-diazabicyclo[5,4,0]undecene-7, 1,5-diazabicyclo[4,3,0]nonene-5, 1,2-dimethylimidazolinium, 1,2,4-trimethylimidazoline, 1-methyl-2-ethylimidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptylimidazoline, 1-methyl-2-(3'heptyl)imidazoline, 1-methyl-2-dodecylimidazoline, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1-methylimidazole, and 1-methylbenzimidazole are preferred as they can provide capacitors with high conductivity and excellent impedance performance.

[0068] Quaternary salts of compounds having an alkyl-substituted amidine group can also be used as the base component, including imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) that have been quaternized with an alkyl or arylalkyl group having 1 to 11 carbon atoms. Specifically, these can provide capacitors with high conductivity and excellent impedance performance, such as 1-methyl-1,8-diazabicyclo[5,4,0]undecene-7, 1-methyl-1,5-diazabicyclo[4,3,0]nonene-5, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium, 1,2-dimethyl-3-ethyl-imidazolinium, and 1,3,4-trimethyl-2 -Ethylimidazolinium, 1,3-dimethyl-2-heptylimidazolinium, 1,3-dimethyl-2-(3'heptyl)imidazolinium, 1,3-dimethyl-2-dodecylimidazolinium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium, 1,3-dimethylimidazolium, 1-methyl-3-ethylimidazolium, and 1,3-dimethylbenzimidazolium are preferred.

[0069] Furthermore, tertiary amines can also be used as the base component, including trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl n-propylamine, dimethylisopropylamine, methylethyl n-propylamine, methylethylisopropylamine, diethyl n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, etc.) and phenyl group-containing amines (dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.). Among these, trialkylamines are preferred due to their high conductivity, and it is more preferable to include at least one selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. In addition, secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia may also be used as the base component.

[0070] The liquid component may contain an acidic component, a basic component, and / or a salt of the acidic component and the basic component. The salt may be an inorganic salt or an organic salt. An organic salt is a salt in which at least one of the anion and cation is an organic substance. Examples of organic salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0071] The pH of the liquid component may be less than 7, or 5 or less. By setting the pH of the liquid component within the above range, dedoping of the conductive polymer dopant can be suppressed. On the other hand, if the pH of the liquid component is less than 7, the cathode foil becomes more susceptible to degradation. In this case, it is advisable to form the aforementioned third layer on the surface of the porous metal portion of the cathode foil. The inclusion of phosphorus and / or nitrogen in the third layer can suppress the degradation of the cathode foil. Furthermore, even when borodioxalic acid, borodiglycolic acid, or borodisalicylic acid, which are corrosive to metals such as aluminum in the cathode foil, are added to the liquid component, the degradation of the cathode foil can be suppressed.

[0072] Figure 5 is a schematic cross-sectional view of an electrolytic capacitor according to this embodiment, and Figure 6 is a schematic diagram showing a portion of the windings included in the electrolytic capacitor unfolded. However, the following embodiments do not limit the present invention.

[0073] As shown in Figure 5, the electrolytic capacitor comprises, for example, a capacitor element 10, a bottomed case 11 housing the capacitor element 10, a sealing member 12 closing the opening of the bottomed case 11, a base plate 13 covering the sealing member 12, lead wires 14A and 14B extending from the sealing member 12 and passing through the base plate 13, lead tabs 15A and 15B connecting the lead wires to the electrodes of the capacitor element 10, and a liquid component (not shown). The capacitor element 10 is housed in the outer case together with the liquid component. The area near the opening end of the bottomed case 11 is tapered inward, and the opening end is curled so as to be crimped to the sealing member 12.

[0074] The capacitor element 10 is manufactured, for example, by attaching a conductive polymer to a wound body as shown in Figure 6. The wound body comprises an anode 21 having a dielectric layer, a cathode (cathode foil) 22 containing a first metal having a valve function, and a separator 23 interposed between them. The conductive polymer is attached so as to cover at least a portion of the surface of the dielectric layer of the anode 21. The capacitor element 10 further comprises a lead tab 15A connected to the anode 21 and a lead tab 15B connected to the cathode 22.

[0075] The anode 21 and cathode 22 are wound around a separator 23. The outermost circumference of the winding is secured by a winding stopper tape 24. Figure 6 shows the state in which a portion of the winding is unfolded before securing the outermost circumference. The anode 21 comprises a metal foil with a roughened surface that has irregularities, and a dielectric layer is formed on the main surface of the metal foil with irregularities.

[0076] Although the above embodiments described wound electrolytic capacitors, the scope of application of the present invention is not limited to those described above. It can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a sintered metal body as the anode, and multilayer electrolytic capacitors that use a metal plate as the anode.

[0077] [Manufacturing method for cathode foil for electrolytic capacitors and electrolytic capacitors] In the following, an example of a manufacturing method for the cathode foil for electrolytic capacitors and the electrolytic capacitors described above will be explained step by step.

[0078] A method for manufacturing cathode foil for electrolytic capacitors according to this embodiment includes, for example, the steps of (i) preparing a metal substrate having a metal porous portion and a metal core portion continuous with the metal porous portion, and (ii) forming a film on the surface of the metal portion constituting the metal porous portion of the metal substrate. In step (ii), the film is formed by atomic layer deposition (ALD). The manufacturing method may further include the step of (iii) depositing at least one of phosphorus and nitrogen in a region in the thickness direction of the metal porous portion to a depth exceeding 10% of the thickness of the metal porous portion.

[0079] An electrolytic capacitor can be manufactured by a method that includes the steps of: (iv) obtaining a cathode foil for an electrolytic capacitor using the above steps; (v) preparing an anode having a dielectric layer on its surface; and (v) forming a capacitor element using the anode and the cathode foil for an electrolytic capacitor.

[0080] Process (i) Step (i) of preparing the metal substrate may be, for example, a step of roughening the surface of a metal foil. Roughening creates a porous metal portion having a plurality of pits or pores on the surface side of the metal foil. At the same time, a metal core portion integrated with the porous metal portion is formed on the inner part of the metal foil. Roughening can be carried out by known methods, for example, by etching. Etching can be carried out, for example, by DC etching with a DC current or AC etching with an AC current.

[0081] The type of metal that makes up the metal foil is not particularly limited, but valve metals such as aluminum (Al), tantalum (Ta), and niobium (Nb), or alloys containing valve metals, can be used. The thickness of the metal foil is not particularly limited, but for example, it is 15 μm or more and 100 μm or less.

[0082] Process (ii) The step of forming a film (ii) may include the step of forming a conductive first layer containing a first element, and / or the step of forming a second layer which is an oxide film containing a second element. The first element may be at least one selected from the group consisting of carbon, nickel, silver, and gold. The second element may be at least one selected from the group consisting of aluminum, titanium, silicon, tantalum, niobium, hafnium, and zirconium. Both the first and second layers may be formed. In this case, the first layer is formed after the second layer.

[0083] The first and second layers can be formed, for example, by atomic layer deposition (ALD). Using the ALD method, a dense film with few defects can be formed even in the deepest parts of the porous metal, including the innermost parts of the winding pores. Furthermore, the first and second layers can adhere to the inner walls of pores that are not exposed from the outer surface of the foil (i.e., shielded from the outside by the metal framework of the porous metal). In contrast, when a film including the first and / or second layers is formed using vapor phase methods such as vacuum deposition or sputtering, the film can be formed to cover the inner walls of pores in shallow regions near the outer surface of the foil, but it is difficult to form in the deep parts of the porous metal that are not exposed from the outer surface of the porous metal.

[0084] In the ALD method, the precursor material for forming the film can reach regions somewhat away from the outer surface by passing through the pores of the porous metal. However, the further away from the outer surface of the foil, the more difficult it becomes for the precursor material to reach. Therefore, the film thickness formed on the porous metal may have a distribution where it is thicker on the outer surface side of the foil and thinner as it moves away from the outer surface. The film thickness at any point in the porous metal (the thickness of the first and / or second layers) depends on the length of the shortest path to the outer surface through the pores of the porous metal, and does not necessarily depend on the shortest distance to the outer surface, but generally, foil The closer the layer is to the outer surface, the thicker it forms.

[0085] According to the ALD method, a raw material gas containing a first or second element is supplied to a reaction chamber where the object is placed, allowing for the formation of a conductive first layer containing the first element, or a second layer which is an oxide film of the second element, on the surface of the object. In the ALD method, a self-limiting mechanism is in operation, so the first or second element forms on the surface of the object at an atomic layer level. It deposits there. Therefore, the thickness of the first and second layers can be controlled by the number of cycles, which include the supply of raw material gas and the exhaust (purging) of raw material gas in one cycle. In other words, the thickness of the first and / or second layers can be easily controlled using the ALD method.

[0086] The first or second element is supplied to the reaction chamber as a precursor gas containing either the first or second element. The precursor is, for example, an organometallic compound containing the first or second element, which facilitates the chemical adsorption of each element to the target material. Various organometallic compounds conventionally used in ALD (Advanced Liquid Processing) can be used as precursors.

[0087] When forming the second layer by the ALD method, a raw material gas containing the second element and an oxidizer are alternately supplied to the reaction chamber. The thickness of the second layer is controlled by the number of cycles, where one cycle consists of supplying the raw material gas, purging the raw material gas, supplying the oxidizer, and purging the oxidizer. Examples of oxidizers include water, oxygen, and ozone. The oxidizer may also be supplied to the reaction chamber as a plasma using the oxidizer as a raw material.

[0088] Furthermore, while CVD is generally performed at temperatures of 400-900°C, the ALD method can be carried out at temperatures of 100-400°C. In other words, the ALD method is superior in that it can suppress thermal damage to the metal foil.

[0089] Examples of carbon-containing precursors that can be used to form the first layer include alkanes with 5 to 11 carbon atoms, such as hexane.

[0090] Examples of Ni-containing precursors include bis(cyclopentadiniel)nickel (Ni(C5H5)2), bis(isopropylcyclopentadiniel)nickel (Ni(i-C3H7C4H5)2), bis(ethylcyclopentadiniel)nickel (Ni(C2H5C4H5)2), and tetrakis(trifluorophosphine)nickel (Ni(PF3)4).

[0091] Furthermore, examples of precursors containing Ag include 2,2,6,6-tetramethylheptane-3,5-dione silver(I)(Ag(C) 11 H 19 Examples of precursors containing Au, such as O2, include dimethyl(acetylacetonate) gold(III) (Au((CH3)2)C5H7O2).

[0092] Examples of aluminum-containing precursors that can be used to form the second layer include trimethylaluminum ((CH3)3Al).

[0093] In addition, examples of the precursor containing Ti include bis(t-butylcyclopentadienyl)titanium(IV) dichloride (C 18 H 26 C l2 Ti), tetrakis(dimethylamino)titanium(IV) ([(CH3)2N]4Ti, TDMAT), tetrakis(diethylamino)titanium(IV) ([(C2H5)2N]4Ti), tetrakis(ethylmethylamino)titanium(IV) (Ti[N(C2H5)(CH3)]4), titanium(IV) diisopropoxide-bis(2,2,6,6-tetramethyl-3,5-heptanedionate) (Ti[OCC(CH3)3CHCOC(CH3)3]2(OC3H7)2), titanium tetrachloride (TiCl4), titanium(IV) isopropoxide (Ti[OCH(CH3)2]4), titanium(IV) ethoxide (Ti[O(C2H5)]4), and the like.

[0094] In addition, examples of the precursor containing Si include N-sec-butyl(trimethylsilyl)amine (C7H 19 NSi), 1,3-diethyl-1,1,3,3-tetramethyldisilazane (C8H 23 NSi2), 2,4,6,8,10-pentamethylcyclopentasiloxane ((CH3SiHO)5), pentamethyldisilane ((CH3)3SiSi(CH3)2H), tris(isopropoxy)silanol ([(H3C)2CHO]3SiOH), chloropentamethyldisilane ((CH3)3SiSi(CH3)2Cl), dichlorosilane (SiH2Cl2), tris(dimethylamino)silane (Si[N(CH3)2]4), tetraethylsilane (Si(C2H5)4), tetramethylsilane (Si(CH3)4), tetraethoxysilane (Si(OC2H5)4), dodecamethylcyclohexasilane ((Si(CH3)2)6), silicon tetrachloride (SiCl4), silicon tetrabromide (SiBr4), and the like.

[0095] In addition, examples of the precursor containing Ta include (t-butylimido)tris(ethylmethylamino)tantalum(V) (C 13 H 33Examples include N4Ta (TBTEMT), tantalum(V) pentaethoxide (Ta(OC2H5)5), (t-butylimide)tris(diethylamino)tantalum(V)((CH3)3CNTa(N(C2H5)2)3), and pentakis(dimethylamino)tantalum(V)(Ta(N(CH3)2)5).

[0096] Furthermore, precursors containing Nb include, for example, niobium(V) ethoxide (Nb(OCH2CH3)5, tris(diethylamide)(t-butylimide)niobium(V)(C 16 H 39 Examples include N4Nb).

[0097] Examples of Hf-containing precursors include hafnium tetrachloride (HfCl4), tetrakisdimethylaminohafnium (Hf[N(CH3)2]4), tetrakisethylmethylaminohafnium (Hf[N(C2H5)(CH3)]4), tetrakisdiethylaminohafnium (Hf[N(C2H5)2]4), and hafnium-t-butoxide (Hf[OC(CH3)3]4).

[0098] Furthermore, examples of precursors containing Zr include bis(methyl-η) 5 Cyclopentadienyl)methoxymethylzirconium (Zr(CH3C5H4)2CH3OCH3), tetrakis(dimethylamide)zirconium(IV)([(CH3)2N]4Zr), tetrakis(eth Zirconium(IV)(Zr(NCH3C2H5)4) 、 Examples include zirconium(IV)t-butoxide (Zr[OC(CH3)3]4).

[0099] Using the ALD method, a coating including the first and / or second layer can be formed to a depth of 10% or more of the thickness of the porous metal portion in the thickness direction of the porous metal portion.

[0100] When the first layer is formed by the ALD method, the second layer may be formed by a chemical conversion treatment of the cathode foil. Details of the chemical conversion treatment will be described later.

[0101] Process (iii) Step (iii) of depositing at least one of phosphorus and nitrogen onto the surface of the porous metal is carried out, for example, by impregnating the porous metal with a solution containing at least one of phosphorus and nitrogen. Subsequent heat treatment causes the phosphorus and / or nitrogen deposited on the inner walls of the pores to diffuse into the porous metal, and a layer (third layer) containing at least one of phosphorus and nitrogen may be formed on the surface of the porous metal. The third layer can improve the water resistance of the electrolytic capacitor.

[0102] Impregnation with a solution containing at least one of phosphorus and nitrogen may be carried out during the conversion process of the cathode foil. If the conversion solution contains phosphorus or nitrogen, the solution containing the phosphorus compound or nitrogen compound can be impregnated into the pores in parallel with the growth of the oxide film on the inner walls of the pores. In this case, as the oxide film grows on the inner walls of the pores, phosphorus and / or nitrogen diffuse into the oxide film, and an oxide film containing phosphorus and / or nitrogen grows.

[0103] Alternatively, a third layer may be formed by impregnating the converted cathode foil with a solution containing at least one of phosphorus and nitrogen. Subsequent heat treatment causes the phosphorus and / or nitrogen adhering to the inner walls of the pores to diffuse into the interior of the converted oxide film, and a third layer containing phosphorus and / or nitrogen grows on at least the surface of the oxide film.

[0104] The converted cathode foil may be subjected to a second conversion using a conversion solution containing at least one of phosphorus and nitrogen. In this case, the voltage applied to the cathode during the second conversion may be higher or lower than the voltage applied during the previous conversion treatment. If the second conversion is performed at a voltage lower than that applied during the previous conversion treatment, the oxide film will not grow further, but the diffusion of phosphorus and / or nitrogen into the oxide film will be promoted. This will allow for the formation of a thicker third layer. Furthermore, the phosphorus and / or nitrogen content in the third layer can be increased.

[0105] The chemical conversion treatment can be carried out, for example, by applying a positive voltage to the metal foil while the cathode foil is immersed in the chemical conversion solution. If necessary, the chemical conversion treatment may be performed at a temperature of, for example, 50 to 85°C.

[0106] Examples of chemical conversion solutions include aqueous solutions containing phosphoric acid, adipic acid, boric acid, oxalic acid, sulfuric acid, and / or salts thereof. Of these, phosphates contain phosphorus, and therefore a phosphorus-containing third layer can be grown through chemical conversion treatment. Examples of phosphates include ammonium phosphate, potassium phosphate, and sodium phosphate.

[0107] Examples of nitrogen-containing chemical solutions include aqueous solutions containing ammonium salts. The ammonium salt may be a primary, secondary, tertiary, or quaternary ammonium salt in which one or more hydrogen atoms of the ammonium cation are substituted with an organic functional group. In particular, ammonium phosphate salts are preferred because they contain both phosphorus and nitrogen, thus easily forming a third layer containing phosphorus and nitrogen. Examples of ammonium phosphate salts include diammonium monohydrogen phosphate and monoammonium dihydrogen phosphate.

[0108] The chemical solution may contain one or more salts containing phosphorus and / or nitrogen. The chemical solution may also contain salts that do not contain phosphorus or nitrogen, such as adipicates, borates, potassium salts, or sodium salts. From the viewpoint of workability, it is preferable to use aqueous solutions of ammonium phosphate, such as an aqueous solution of monoammonium dihydrogen phosphate, or an aqueous solution of ammonium adipate.

[0109] The formation of the third layer (impregnation with a solution containing phosphorus and / or nitrogen) may be performed before the formation of the first layer (and / or the second layer) by the ALD method, or after the formation of the first layer (and / or the second layer) by the ALD method. In the former case, the third layer is formed throughout the entire depth of the porous metal portion, and the third layer may be interposed between the first and second layers and the porous metal portion. In the latter case, phosphorus or nitrogen is less likely to diffuse into the porous metal portion from the outer surface of the porous metal portion where the first layer has already been formed. For this reason, the third layer may be formed exclusively in the deeper part of the porous metal portion on the metal core side where the first layer has not been formed. In either case, the third layer may adhere to a region in the thickness direction of the porous metal portion that is deeper than 10% of the thickness of the porous metal portion.

[0110] The cathode foil after chemical treatment may be washed and dried as needed.

[0111] Phosphorus compounds (e.g., PO4) adhering to the cathode foil 3- The content can be analyzed by ion chromatography. Cathode foil The amount of phosphorus compounds attached to it is, for example, 3 mg / m². 2 More than 300mg / m 2 The following is the case: 5 mg / m² 2 More than 100mg / m 2 The following are preferable.

[0112] From a mass production standpoint, large sheets of metal foil are typically subjected to surface roughening or chemical conversion treatments. In this case, the treated metal foil is cut to the desired size to prepare the cathode foil.

[0113] Process (iv) In step (iv) of preparing an anode having a dielectric layer on its surface, a metal foil containing the valve metal, which is the raw material for the anode, is prepared, and the surface of the metal foil is roughened. Roughening creates multiple irregularities on the surface of the metal foil. Roughening is preferably performed by etching the metal foil. The etching can be performed, for example, by a DC electrolytic method or an AC electrolytic method.

[0114] Next, a dielectric layer is formed on the surface of the roughened metal foil. The formation method is not particularly limited, but it can be formed by chemical conversion treatment of the metal foil. Through chemical conversion treatment of the metal foil, the surface of the metal foil is oxidized, and a dielectric layer, which is an oxide film, is formed.

[0115] The chemical conversion treatment can be carried out, for example, using a chemical conversion solution. The chemical conversion treatment can be performed by immersing the metal foil in the chemical conversion solution and then heat-treating it. The temperature at this time is, for example, 50-80°C. Alternatively, the chemical conversion treatment may be carried out by immersing the metal foil in the chemical conversion solution and applying a voltage. Both heat treatment and voltage application may be performed during the chemical conversion treatment. The chemical conversion solution can be appropriately determined from those described for the chemical conversion of cathode materials. The anode body after chemical conversion treatment may be washed and dried as needed.

[0116] Typically, for mass production purposes, large sheets of metal foil undergo surface roughening and chemical conversion treatments. In this case, the anode is prepared by cutting the treated metal foil to the desired size. The cut anode has a dielectric layer on its main surface.

[0117] Process (v) Next, a capacitor element is formed using the anode and cathode foil for electrolytic capacitors (step (v)).

[0118] First, a wound body is fabricated using the cathode foil obtained in steps (i) to (iii) and the anode prepared in step (iv). The anode body 21 and the cathode foil are wound together via a separator 23. At this time, by winding while incorporating the lead tabs 15A and 15B, the lead tabs 15A and 15B can be raised from the wound body, as shown in Figure 6.

[0119] The materials of the lead tabs 15A and 15B are not particularly limited, and any conductive material will suffice. Similarly, the materials of the lead wires 14A and 14B connected to the respective lead tabs 15A and 15B are not particularly limited, and any conductive material will suffice.

[0120] Next, among the wound anode body 21, cathode foil and separator 23, the resealing tape 24 is placed on the outer surface of the cathode foil, which is the outermost layer, and the cathode foil Secure the end with tape 24.

[0121] The third layer may be formed on the cathode foil after the winding body has been constructed. In this case, for example, the winding body is impregnated with a solution containing at least one of phosphorus and nitrogen to deposit at least one of phosphorus and nitrogen on the surface of the porous metal portion of the cathode foil. Subsequent heat treatment causes the phosphorus and / or nitrogen deposited on the inner walls of the pores to diffuse into the porous metal portion, and the third layer can be formed on the surface of the porous metal portion. When chemical conversion treatment is performed, the chemical conversion treatment may be carried out by heat treatment while the winding body is immersed in the chemical conversion solution. Alternatively, the treatment may be carried out by immersing the third electrode together with the winding body in the chemical conversion solution and applying a positive voltage to the anode of the winding body with the third electrode as the counter electrode. Both heat treatment and voltage application may be performed. The temperature conditions for the chemical conversion solution and the chemical conversion treatment can be appropriately determined from those described in step (iii). The chemical conversion treatment may be carried out with the entire winding body immersed in the chemical conversion solution, or with at least the top and bottom surfaces of the winding body immersed in the chemical conversion solution. Furthermore, the wound bodies after chemical treatment are washed and dried as needed.

[0122] When a third layer is formed on the wound material, phosphorus and / or nitrogen may also adhere to the surface of the first or second layer. As a result, any cracks that may exist on the surface of the first or second layer may be covered with the phosphorus and / or nitrogen-containing layer.

[0123] If cracks occur in the first or second layer, liquid components can penetrate the metal core through the cracks, easily degrading the cathode foil. As a result, the ESR may increase. However, by forming a third layer containing phosphorus and / or nitrogen after the formation of the first or second layer, the inner walls of the pores in the deeper parts of the porous metal can be covered with the third layer, and cracks that have formed in the first or second layer can also be covered with the third layer. This suppresses the increase in ESR due to foil degradation and allows the ESR to be kept low. In this case, the third layer can be formed to fill any cracks that may exist in the first and / or second layer.

[0124] In particular, when manufacturing electrolytic capacitors, if the anode and cathode foil are laminated with a separator in between to form a winding, cracks are prone to occur in the first layer after the winding is formed. By performing a process to form a third layer after the winding is formed, the cracks that occur in the first layer are filled in by the third layer, and the deterioration of the cathode foil and the increase in ESR can be suppressed.

[0125] In the case of an electrolytic capacitor containing a solid electrolyte such as a conductive polymer, a step of attaching the conductive polymer to the winding may be performed. The conductive polymer is attached so as to cover at least a portion of the dielectric layer of the anode 21. Between the anode 21 and the cathode (cathode foil) 22, the conductive polymer may, but is not limited to, be attached in a layer to the surface of the dielectric layer of the anode 21 to form a conductive polymer layer (or solid electrolyte layer). The conductive polymer may also cover at least a portion of the surface of the separator 23. Furthermore, the conductive polymer may be formed to fill the pores of the cathode. The conductive polymers described above can be used.

[0126] The conductive polymer may be attached to the winding by applying a solution containing monomers, dopants, and oxidizing agents to the capacitor element and then chemically or electrolytically polymerizing it in place. Alternatively, the conductive polymer may be attached to the winding by applying a processing solution containing the conductive polymer (hereinafter simply referred to as a polymer dispersion) to the winding. The polymer dispersion can be rapidly impregnated by forming an oxide film on the main surface of the cathode or a dielectric layer on the anode.

[0127] The concentration of the conductive polymer in the polymer dispersion is preferably 0.5 to 10% by mass. Furthermore, the average particle size D50 of the conductive polymer is preferably, for example, 0.01 to 0.5 μm. Here, the average particle size D50 is the median diameter in the volume particle size distribution determined by a particle size distribution analyzer using dynamic light scattering.

[0128] The polymer dispersion comprises a liquid dispersion medium and a conductive polymer dispersed in the liquid dispersion medium. The polymer dispersion may be a solution in which the conductive polymer is dissolved in the liquid dispersion medium, or a dispersion in which particles of the conductive polymer are dispersed in the liquid dispersion medium. After impregnating the wound body with the processing liquid, it is usually dried to volatilize at least a portion of the liquid dispersion medium.

[0129] To suppress the dedoping of conductive polymers, an acid may be dissolved in the liquid dispersion medium. Preferred acids include phosphoric acid, sulfuric acid, phthalic acid, benzoic acid, nitrobenzoic acid, salicylic acid, trimellitic acid, and pyromellitic acid.

[0130] Polymer dispersions can be obtained, for example, by dispersing a conductive polymer in a liquid dispersion medium, or by polymerizing a precursor monomer in a liquid dispersion medium to produce conductive polymer particles. Preferred polymer dispersions include, for example, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS), i.e., PEDOT / PSS. Antioxidants for conductive polymers may be added, but since PEDOT / PSS hardly oxidizes, it is not necessary to use antioxidants.

[0131] The liquid dispersion medium may be water, a mixture of water and a non-aqueous solvent, or a non-aqueous solvent. The non-aqueous solvent is not particularly limited, but for example, protic solvents and aprotic solvents can be used. Examples of protic solvents include alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, and propylene glycol, and ethers such as formaldehyde and 1,4-dioxane. Examples of aprotic solvents include amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, and ketones such as methyl ethyl ketone.

[0132] A simple and preferred method for applying (impregnating) the polymer dispersion to the wound material is, for example, immersing the wound material in a polymer dispersion contained in a container. Alternatively, ultrasonic vibration may be applied to the wound material or polymer dispersion while it is immersed in the polymer dispersion. Drying after removing the wound material from the polymer dispersion is preferably carried out at, for example, 50 to 300°C. The steps of applying the polymer dispersion to the wound material and drying the wound material may be repeated two or more times. By performing these steps multiple times, the coverage rate of the conductive polymer on the wound material can be increased.

[0133] As a result, a capacitor element 10 is obtained in which a conductive polymer is attached so as to cover at least a portion of the dielectric layer. The conductive polymer formed on the surface of the dielectric layer functions as a de facto cathode material.

[0134] Next, by further impregnating the capacitor element 10 with a liquid component (electrolyte), an electrolytic capacitor with excellent dielectric layer repair capabilities can be obtained.

[0135] The method for impregnating the capacitor element 10 with the liquid component is not particularly limited. For example, a simple and preferred method is to immerse the capacitor element 10 in the liquid component contained in a container. Impregnation is preferably carried out under reduced pressure, for example, in an atmosphere of 10 to 100 kPa. Examples of the liquid component include the materials mentioned above.

[0136] Next, the capacitor element 10 is sealed. Specifically, the capacitor element 10 is first placed in the closed-bottom case 11 so that the lead wires 14A and 14B are located on the opening at the top of the closed-bottom case 11. The material of the closed-bottom case 11 can be a metal such as aluminum, stainless steel, copper, iron, or brass, or an alloy thereof.

[0137] Next, a sealing member 12, formed so that the lead wires 14A and 14B pass through it, is placed above the capacitor element 10, sealing the capacitor element 10 inside the bottomed case 11. Then, a lateral drawing process is performed near the open end of the bottomed case 11, and the open end is crimped to the sealing member 12 and curled. Finally, a base plate 13 is placed on the curled portion to complete the electrolytic capacitor as shown in Figure 5. After that, an aging process may be performed while applying the rated voltage.

[0138] The sealing member 12 is formed of an elastic material containing a rubber component. Examples of rubber components that can be used include butyl rubber (IIR), nitrile rubber (NBR), ethylene propylene rubber, ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), isoprene rubber (IR), Hypalon rubber, silicone rubber, and fluororubber. The sealing member 12 may also contain fillers such as carbon black and silica.

[0139] Furthermore, after sealing the capacitor element 10, a chemical conversion treatment may be performed as needed to form a dielectric layer on the anode or an oxide film on the cathode. This chemical conversion treatment can be carried out using an electrolyte. For example, the chemical conversion treatment can be performed by applying a positive voltage to the anode and cathode while the capacitor element 10 is immersed in the electrolyte. At this time, a heat treatment is usually also performed. The temperature for the heat treatment is, for example, 80 to 150°C. [Industrial applicability]

[0140] This invention can be used in electrolytic capacitors. [Explanation of Symbols]

[0141] 10: Capacitor element 11: Case with bottom 12: Sealing member 13: Seat board 14A, 14B: Lead wires 15A, 15B: Lead tabs 21: Anode 22,22A,22B: Cathode foil 31: Metal core 32: Metal porous part 33: Coating 35: 1st layer 36:Second layer 37:Third layer 38: Pores 23: Separator 24: Retaining tape

Claims

1. A porous metal portion, A metal core portion continuous with the aforementioned porous metal portion, A method for manufacturing cathode foil for an electrolytic capacitor, comprising a coating that covers the aforementioned porous metal portion, On the first main surface of the cathode foil, the pores within the porous metal portion are open. A step of preparing a metal substrate having the metal porous portion having a thickness of 1 μm or more and 60 μm or less, and the metal core portion, The process includes forming the film on the surface of the metal portion constituting the porous metal portion of the metal substrate, The step of forming the aforementioned film includes the steps of forming a conductive first layer containing a first element selected from the group consisting of carbon, nickel, silver, and gold, and forming a second layer which is an oxide film containing a second element not included in the porous metal portion. In the step of forming the first layer, the first layer having a thickness of 1 nm to 30 nm is formed by atomic layer deposition (ALD) in a region to a depth of 50% or more of the thickness of the metal porous portion, and is also attached to the inner walls of the pores that are not exposed from the first main surface from which the pores of the metal porous portion open, and that are shielded by a metal skeleton having pores that curve toward the depth of the metal porous portion. In the process of forming the second layer, the second layer, having a thickness of 1 nm to 10 nm, is deposited by atomic layer deposition (ALD) onto the inner walls of the pores that are not exposed from the first main surface through which the pores of the metal porous portion are open, and which are shielded by the metal framework of the metal porous portion. A method for manufacturing cathode foil for electrolytic capacitors.

2. A method for manufacturing cathode foil for an electrolytic capacitor according to claim 1, wherein the step of forming the first layer is performed after the step of forming the second layer.

3. The method for manufacturing cathode foil for electrolytic capacitors according to claim 1 or 2, wherein the second element is at least one selected from the group consisting of aluminum, titanium, silicon, tantalum, niobium, hafnium, and zirconium.

4. A method for manufacturing cathode foil for electrolytic capacitors according to any one of claims 1 to 3, further comprising the step of depositing at least one of phosphorus and nitrogen in a region exceeding 10% of the thickness of the metal porous portion in the thickness direction of the metal porous portion.

5. A step of obtaining cathode foil for an electrolytic capacitor using a method for manufacturing cathode foil for an electrolytic capacitor described in any one of claims 1 to 4, A step of preparing an anode having a dielectric layer on its surface, A method for manufacturing an electrolytic capacitor, comprising the step of forming a capacitor element using the anode and the cathode foil for the electrolytic capacitor.

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