Electrode foil for electrolytic capacitor, electrolytic capacitor and method for producing same

Abstract

To provide an electrode foil for a capacitor in which a good dielectric layer is formed deep into a metal porous part by etching, and a method for manufacturing the same.SOLUTION: An electrode foil for an electrolytic capacitor includes a metal porous portion 112, and a metal core portion 111 continuous to the metal porous portion, and when the porous metal portion is divided into three equal parts of a first region R1, a second region R2, and a third region R3 in the thickness direction of the porous metal portion in order from the metal core side, and the porosity P1, P2, and P3 of the first, second, and third regions satisfy P1<P2<P3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrode foil for an electrolytic capacitor, an electrolytic capacitor, and a method for producing the same. [Background technology]

[0002] For example, a metal foil containing a valve metal is used for the anode of an electrolytic capacitor. In order to increase the capacitance of the electrolytic capacitor, the main surface of the metal foil is etched to form a metal porous portion. The metal foil is then subjected to a chemical conversion treatment to form a metal oxide (dielectric) layer on the surface of the metal skeleton (metal portion) that constitutes the metal porous portion.

[0003] Patent Document 1 teaches a method for manufacturing an electrode foil in which aluminum is etched by applying an alternating current in an aqueous solution containing hydrochloric acid as the main component with at least one of sulfuric acid, oxalic acid, and phosphoric acid added thereto, and teaches a method in which the current density step for applying the alternating current is set to a maximum value at the start of the etching process and gradually decreased from that maximum value, until the current density reaches zero at an intermediate stage before it reaches zero.

[0004] On the other hand, US Pat. No. 5,399,633 teaches forming a dielectric layer by atomic layer deposition. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-203529 A [Patent Document 2] International Publication No. 2017 / 26247 Brochure Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 aims to efficiently increase the surface area of an aluminum foil and enhance the capacitance of an electrode foil for an aluminum electrolytic capacitor. However, there are limitations to increasing the capacitance by expanding the surface area using the above method.

[0007] Further, when forming a dielectric layer by atomic layer deposition, for example, the source gas of the dielectric layer may not reach the deep part of the etching pit, making it difficult to form a dielectric layer in the deep part of the metal porous part. In particular, when the porosity of the surface layer of the etching pit, especially the region from the surface to 1 / 3, is smaller than the porosity of the deeper part, it becomes very difficult for the source gas to reach the deep part, and it may not be possible to form a sufficient dielectric layer in the deep part.

Means for Solving the Problem

[0008] One aspect of the present invention relates to an electrode foil for an electrolytic capacitor, which includes a metal porous part and a metal core part continuous with the metal porous part, and when the metal porous part is equally divided into a first region, a second region, and a third region in order from the metal core part side in the thickness direction of the metal porous part, the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3.

[0009] Another aspect of the present invention has a step of preparing a metal foil and a roughening step of forming a metal porous part by roughening the metal foil. The roughening step includes an etching step of applying a current to the metal foil. The etching step includes a first electrolysis step of applying a current with a first current density to the metal foil in a first treatment liquid to obtain a first etched foil, a second electrolysis step of applying a current with a second current density to the first etched foil in a second treatment liquid after the first electrolysis step to obtain a second etched foil, a third electrolysis step of applying a current with a third current density to the second etched foil in a third treatment liquid after the second electrolysis step to obtain a third etched foil, a first washing step of washing the first etched foil after the first electrolysis step and before the second electrolysis step, and a second washing step of washing the etched foil after the second electrolysis step and before the third electrolysis step. The present invention relates to a method for manufacturing an electrode foil for an electrolytic capacitor that satisfies the relationship of first current density > second current density > third current density.

[0010] Yet another aspect of the present invention includes an anode body having a metal porous part and a metal core part continuous with the metal porous part, and a dielectric layer covering the surface of the metal skeleton constituting the metal porous part. The dielectric layer has a first layer with a thickness T1 containing an oxide of a second metal different from the first metal contained in the metal part. When the metal porous part is equally divided into a first region, a second region, and a third region in the thickness direction of the metal porous part in order from the metal core part side, the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3. The present invention relates to an electrode foil for an electrolytic capacitor.

[0011] Still another aspect of the present invention relates to an electrode foil for an electrolytic capacitor, comprising: an anode body having a porous metal portion and a metal core portion continuous with the porous metal portion; and a dielectric layer covering at least a part of the surface of the metal portion constituting the porous metal portion, wherein when the porous metal portion having the dielectric layer is divided into three equal regions in the thickness direction thereof in order from the metal core portion side, i.e., a first region, a second region, and a third region, the porosity Q1 of the first region, the porosity Q2 of the second region, and the porosity Q3 of the third region satisfy Q1 < Q2 < Q3.

[0012] Still another aspect of the present invention relates to a method for manufacturing an electrode foil for an electrolytic capacitor, comprising: preparing an anode body having a porous metal portion and a metal core portion continuous with the porous metal portion; and forming a dielectric layer covering the surface of the metal portion constituting the porous metal portion, wherein when the porous metal portion is divided into three equal regions in the thickness direction thereof in order from the metal core portion side, i.e., a first region, a second region, and a third region, the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3, and the step of forming the dielectric layer includes depositing an oxide of a second metal different from a first metal contained in the metal portion on the surface of the porous metal portion by a vapor phase method to form a first layer having a thickness T1.

[0013] Still another aspect of the present invention relates to an electrolytic capacitor, comprising: the above-described electrode foil for an electrolytic capacitor; and a cathode portion covering at least a part of the dielectric layer.

[0014] Still another aspect of the present invention relates to a method for manufacturing an electrolytic capacitor, comprising: the steps included in the method for manufacturing the above-described electrode foil for an electrolytic capacitor; and forming a cathode portion covering at least a part of the dielectric layer.

Advantages of the Invention

[0015] According to the present invention, when forming the dielectric layer, a good dielectric layer can be formed even in the deep part of the porous metal portion, so that a high-performance electrode foil for an electrolytic capacitor can be obtained.

[0016] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view of an anode body according to one embodiment of the present invention. [Diagram 2] 2 is a schematic cross-sectional view showing an enlarged portion of a porous portion having a dielectric layer according to an embodiment of the present invention. FIG. [Diagram 3] 4 is a schematic cross-sectional view showing an enlarged portion of a porous portion having a dielectric layer according to another embodiment of the present invention. FIG. [Figure 4] FIG. 2 is a schematic cross-sectional view of an electrolytic capacitor. [Diagram 5] FIG. 2 is a perspective view showing a schematic configuration of a wound body provided in the electrolytic capacitor. [Figure 6] FIG. 2 is an explanatory diagram showing a schematic view of a part of an etching device used in a surface roughening step according to an embodiment of the present invention. [Figure 7] 1 is a graph showing the relationship between the distance from the surface of the anode body and the porosity (Al residual rate) in the metal porous portion according to Example 1A of the present invention. [Figure 8] 10 is a graph showing the relationship between the distance from the surface of the anode body and the porosity (Al residual rate) in the metal porous portion according to Example 2 of the present invention. [Figure 9] 1 is a graph showing the relationship between the distance from the surface of the anode body and the porosity (Al residual rate) in a metal porous portion according to Comparative Example 2 of the present invention. [Figure 10] FIG. 4 is a diagram showing the change in current density during an etching process according to one embodiment of the present invention. [Figure 11] FIG. 4 is a diagram showing the variation of current density during an etching process according to another embodiment of the present invention. [Figure 12] FIG. 13 is a diagram showing the change in current density during an etching process according to yet another embodiment of the present invention. [Figure 13] FIG. 13 is a diagram showing the change in current density during an etching process according to yet another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, the electrode foil for electrolytic capacitors before the formation of the dielectric layer is also referred to as the "first electrode foil" or "anode body," and the electrode foil for electrolytic capacitors with the dielectric layer is also referred to as the "second electrode foil." In addition, below, the first etching foil, the second etching foil, and the third etching foil are not particularly distinguished from the metal foil, and may all be simply referred to as the metal foil.

[0019] The electrode foil for electrolytic capacitor (first electrode foil) according to this embodiment includes a metal porous portion and a metal core portion continuous with the metal porous portion. That is, the first electrode foil is an integrated body of the metal core portion and the metal porous portion. The first electrode foil can be used as an anode body of an electrolytic capacitor.

[0020] The second electrode foil has a first electrode foil (or an anode body) and a dielectric layer covering at least a part of the surface of the metal part constituting the metal porous part of the first electrode foil. That is, the second electrode foil has a metal porous part, a metal core part continuous with the metal porous part, and a dielectric layer covering the surface of the metal part (metal skeleton) constituting the metal porous part. The dielectric layer covers the surface of the metal part (metal skeleton) constituting the metal porous part. The configuration of the dielectric layer is not particularly limited.

[0021] The first electrode foil (or anode body) is obtained, for example, by roughening a part of a metal foil made of a first metal contained in the metal part constituting the porous part by etching, etc. The metal porous part is the surface side (outer side) part of the metal foil that has been made porous by etching, and the remaining part, which is the inner part of the metal foil, is the metal core part.

[0022] When the metal porous portion of the first electrode foil is equally divided into three regions, namely a first region, a second region, and a third region in order from the metal core portion side in the thickness direction of the metal porous portion, the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3.

[0023] Also, when the metal porous portion of the second electrode foil is equally divided into three regions, namely a first region, a second region, and a third region in order from the metal core portion side in the thickness direction of the metal porous portion, the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3.

[0024] In the second electrode foil, the thickness of the dielectric layer varies depending on the rated voltage of the electrolytic capacitor, but it has a thickness of 4 nm to 300 nm and is formed relatively thinly along the shape of the surface of the metal portion. Therefore, the porosities Q1 to Q3 of the first to third regions of the second electrode foil on which the dielectric layer is formed are smaller by the thickness of the dielectric layer than P1 to P3 of the first electrode foil before the dielectric layer is formed.

[0025] When P1 < P2 < P3 is satisfied, the porosity of the second electrode foil also satisfies Q1 < Q2 < Q3. That is, when the metal porous portion having the dielectric layer is equally divided into three regions, namely a first region, a second region, and a third region in order from the metal core portion side in the thickness direction of the metal porous portion of the second electrode foil, the porosity Q1 of the first region, the porosity Q2 of the second region, and the porosity Q3 of the third region satisfy Q1 < Q2 < Q3.

[0026] Conversely, when Q1 < Q2 < Q3 is satisfied, it can be said that the porosity of the metal porous portion also satisfies P1 < P2 < P3.

[0027] In the first electrode foil, the porosity of the metal porous part increases as it approaches the surface side of the first electrode foil. Therefore, a good dielectric layer can be formed even in the deep part of the metal porous part, and a high-performance electrode foil for electrolytic capacitors can be obtained. Further, in an electrolytic capacitor using an electrolytic solution, a solid electrolyte, etc. as a cathode material, the permeability of the electrolytic solution into the metal porous part and the fillability of the solid electrolyte (for example, a conductive polymer) are improved, the capacitance achievement rate of the electrolytic capacitor also increases, and it is also advantageous for reducing ESR and suppressing leakage current.

[0028] Next, the electrolytic capacitor according to this embodiment includes a second electrode foil and a cathode part that covers at least a part of the dielectric layer.

[0029] Also in the second electrode foil having a dielectric layer, the porosity of the metal porous part having the dielectric layer increases as it approaches the surface side of the second electrode foil. Therefore, in an electrolytic capacitor using an electrolytic solution, a solid electrolyte, etc. as a cathode material, the permeability of the electrolytic solution into the metal porous part and the fillability of the solid electrolyte are improved. Therefore, the capacitance achievement rate of the electrolytic capacitor also increases, and it is also advantageous for reducing ESR and suppressing leakage current.

[0030] The cathode part may contain a conductive polymer as a solid electrolyte. When P1 < P2 < P3 or Q1 < Q2 < Q3 is satisfied, it becomes easy to impregnate the conductive polymer up to the first region.

[0031] The cathode part may contain an electrolytic solution. When P1 < P2 < P3 or Q1 < Q2 < Q3 is satisfied, it becomes easy to impregnate the electrolytic solution up to the first region.

[0032] Hereinafter, an example of the dielectric layer will be described in more detail.

[0033] The metal porous part has pits or pores surrounded by a metal part containing a first metal. The dielectric layer is provided so as to cover at least a part of the surface of the metal part surrounding the pits or pores.

[0034] The dielectric layer may contain an oxide of the first metal included in the metal portion. Further, the dielectric layer may have a first layer with a thickness T1 containing an oxide of a second metal different from the first metal included in the metal portion. When an oxide of a second metal different from the first metal is included in the dielectric layer, for example, a second metal with a high dielectric constant can be selected without being restricted by the first metal. Therefore, it becomes easier to improve the capacitance of the electrolytic capacitor. Also, since the range of selection of the second metal expands, various performances can be imparted to the dielectric layer without being restricted by the first metal.

[0035] Here, when the metal porous portion is equally divided into three regions, namely a first region, a second region, and a third region in order from the metal core portion side in the thickness direction of the metal porous portion of the first metal foil, the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3. That is, the porosity of the metal porous portion increases as it approaches the surface side of the anode body. Therefore, when forming a dielectric layer by a vapor phase method such as atomic layer deposition, the raw material gas of the dielectric layer easily diffuses to the deep part of the metal porous portion, and a good dielectric layer can be formed up to the deep part of the metal porous portion. For example, even when an oxide of the second metal is preferentially deposited on the surface layer portion (i.e., the third region) of the metal porous portion at the initial stage of the film formation of the dielectric layer, if P1 < P2 < P3 is satisfied, since the porosity P3 of the surface layer portion is large, the entrance of the pit is less likely to be blocked by the dielectric layer. Therefore, the film formation of the dielectric layer proceeds well. As a result, the high capacitance of the electrode foil is achieved, and the permeability of the electrolytic solution to the metal porous portion and the filling property of the solid electrolyte (e.g., conductive polymer) are improved, the capacitance achievement rate of the electrolytic capacitor also increases, which is also advantageous for reducing ESR and suppressing leakage current.

[0036] Furthermore, in the gas phase method, the source gas is consumed first in the surface layer (third region) of the etching pit, so the amount of source gas that reaches the deepest part (first region) is small. On the other hand, if the porosity P3 of the third region is larger than the porosities P1 and P2 of the deeper parts, the source gas easily penetrates into the etching pit. Also, if the porosity P1 of the deepest part (first region) is small, the surface area of ​​the deepest part is also small, so the amount of source gas required to form the dielectric layer may be small. Therefore, a good dielectric layer can be efficiently formed up to the deepest part of the etching pit. For example, even if the etching pit is sponge-like with a specific surface area of ​​50 times or more, the dielectric layer can be easily formed up to the deepest part.

[0037] In addition, in the deep part of the metal porous part (e.g., the first region), the porosity is relatively small, and the pit diameter (or pore diameter) of the etching pit is relatively small. In other words, in the deep part of the metal porous part, many fine pores exist, and a considerable surface area is secured. Therefore, even if the surface area near the surface of the anode body (e.g., the third region) is relatively small, it is easy to secure a sufficiently large capacitance.

[0038] The porosity of the metal porous portion may be measured by the following method. First, the anode body (first electrode foil) is cut so that a cross section of the metal core and metal porous parts in the thickness direction of the anode body is obtained, and an electron microscope photograph of the cross section is taken. Next, the image of the cross section is binarized to distinguish the metal part from the voids. Next, the image is divided into a plurality of parts (for example, at intervals of 0.1 μm) along a path parallel to the thickness direction of the anode body from the surface side of the anode body toward the metal core side, and the average value of the porosity of each part after division is calculated as the porosity. By using the calculated value, a graph showing the relationship between the distance from the surface of the anode body and the porosity can be drawn (see Figures 7 to 9). In the first region, the second region, and the third region, a plurality of porosities at arbitrary positions at equal intervals are extracted, and the average value of the plurality of porosities is calculated to obtain the porosity P1, the porosity P2, and the porosity P3. The porosity Q1, the porosity Q2, and the porosity Q3 of the second electrode foil having a dielectric layer can also be measured in the same manner.

[0039] P2 and P3 may satisfy P2 × 1.1 ≤ P3, or may satisfy P2 × 1.2 ≤ P3. Also, P1 and P2 may satisfy P1 × 1.05 ≤ P2, or may satisfy P1 × 1.1 ≤ P2.

[0040] Also, Q2 and Q3 vary depending on the thickness of the dielectric layer or the rated voltage of the electrolytic capacitor. For example, Q2 × 1.1 ≤ Q3 may be satisfied, or Q2 × 1.2 ≤ Q3 may be satisfied. Also, Q1 and Q2 may satisfy Q1 × 1.05 ≤ Q2, or may satisfy Q1 × 1.1 ≤ Q2.

[0041] FIG. 1 shows a cross-sectional schematic view of an anode body (first electrode foil) according to an embodiment of the present invention. The anode body 110 is an integrated body of a metal core part 111 and a metal porous part 112, and the thickness of the metal porous part 112 is indicated by T. The metal porous part 112 can be divided into three equal parts, namely, a first region R1, a second region R2, and a third region R3, each having a thickness of T / 3, in order from the metal core part 111 side as shown in the illustrated example. When calculating the porosity P1 to P3, as described above, the cross-sectional image of each region is divided into a plurality (for example, at intervals of 0.1 μm) along a path parallel to the thickness direction of the anode body from the surface side of the anode body toward the metal core part side, and the average value of the porosity of each divided part may be calculated as the porosity P1 to P3. Note that the cross-sectional schematic view of the second electrode foil having a dielectric layer is the same as that of FIG. 1, and the procedure for calculating the porosity Q1 to Q3 is also the same.

[0042] The porosity P1, P2, and P3 of the first region R1, the second region R2, and the third region R3 may further satisfy P1 / P2 < P3 / P2. Similarly, in the second electrode foil having a dielectric layer, Q1 / Q2 < Q3 / Q2 may be satisfied. In this case, the porosity does not increase at a constant rate from the metal core part toward the surface of the anode body, but the rate of increase in porosity is higher on the surface side of the anode body than in the deep part. Therefore, while the action of promoting the diffusion of the raw material gas of the dielectric layer by the first region R1 is strengthened, a surface area sufficient to sufficiently increase the capacitance is ensured in the third region R3.

[0043] P1 to P3 may satisfy P2 / P1 < P3 / P2, may satisfy 1.05 × P2 / P1 < P3 / P2, or may satisfy 1.3 × P2 / P1 < P3 / P2. Similarly, Q1 to Q3 may satisfy Q2 / Q1 < Q3 / Q2, may satisfy 1.05 × Q2 / Q1 < Q3 / Q2, or may satisfy 1.3 × Q2 / Q1 < Q3 / Q2.

[0044] P1 may be, for example, 30% or more. P2 may be, for example, 40% or more, and may be 50% or more. Also, P3 may be 60% or more. However, from the viewpoint of ensuring sufficient strength of the first electrode foil (anode body), it is preferable that P3 is 80% or less, P2 is preferably 70% or less, and P1 is preferably 60% or less. Similarly, Q1 may be, for example, 30% or more. Q2 may be, for example, 40% or more, and may be 50% or more. Also, Q3 may be 60% or more. However, from the viewpoint of ensuring sufficient strength of the second electrode foil, it is preferable that Q3 is 80% or less, Q2 is preferably 70% or less, and Q1 is preferably 60% or less.

[0045] When P1 to P3 are within the above ranges, when forming a dielectric layer in a liquid phase such as formation (anodic oxidation), the formation liquid easily penetrates to the deep part of the metal porous part. Also, when forming a dielectric layer by a vapor phase method such as atomic layer deposition, the diffusibility of the raw material gas of the dielectric layer into the deep part of the metal porous part is further improved. However, from the viewpoint of ensuring sufficient strength of the first electrode foil and the second electrode foil, it is preferable that P3 or Q3 is 80% or less, P2 or Q2 is preferably 70% or less, and P1 or Q1 is preferably 60% or less.

[0046] The thickness of the metal porous portion is not particularly limited and may be appropriately selected depending on the application of the electrolytic capacitor, the required withstand voltage, and the like. The thickness of the metal porous portion may be selected, for example, from the range of 10 μm to 160 μm. The thickness of the metal porous portion may be, for example, 1 / 10 or more and 5 / 10 or less of the thickness of the first electrode foil or the second electrode foil. The thickness T of the metal porous portion may be determined by cutting the first electrode foil or the second electrode foil so as to obtain a cross section in the thickness direction of the metal core portion and the metal porous portion, taking an electron microscope photograph of the cross section, and averaging the thicknesses of any 10 points of the metal porous portion.

[0047] The pore diameter peak of the pits or pores in the metal porous portion is not particularly limited, but may be, for example, 50 nm to 2000 nm, or may be 100 nm to 300 nm, from the viewpoint of increasing the surface area and forming the dielectric layer deep in the metal porous portion. The pore diameter peak is, for example, the most frequent pore diameter of the volume-based pore diameter distribution measured by a mercury porosimeter.

[0048] The withstand voltage of the electrolytic capacitor is not particularly limited, and may be, for example, a relatively small withstand voltage of 1 V or more and less than 4 V, or may be a relatively large withstand voltage of 4 V or more, 15 V or more, or 100 V or more. When obtaining an electrolytic capacitor having a withstand voltage of 4 V or more, it is preferable that the thickness of the dielectric layer is 4 nm or more. When obtaining an electrolytic capacitor having a withstand voltage of 15 V or more, it is preferable that the thickness of the dielectric layer is 21 nm or more.

[0049] More specifically, when obtaining an electrolytic capacitor having a large withstand voltage of, for example, 60 V or more, the pore diameter peak of the metal porous portion may be, for example, 50 to 300 nm, the thickness of the metal porous portion may be, for example, 30 to 160 μm, and the thickness of the dielectric layer may be, for example, 30 to 100 nm.

[0050] In the case of an electrolytic capacitor with a withstand voltage of, for example, 100 V or more, the shape of the etching pits may be a generally columnar, conical, or truncated conical shape in which the pit diameter is larger on the surface side of the anode body and smaller on the metal core side, and which extends in a tunnel shape from the surface side of the anode body toward the metal core side.

[0051] When obtaining an electrolytic capacitor having a relatively low withstand voltage, for example, a withstand voltage of 10 V or less, the pore diameter peak of the metal porous portion may be, for example, 20 to 200 nm, the thickness of the metal porous portion may be, for example, 30 to 160 μm, and the thickness of the dielectric layer may be, for example, 4 to 30 nm.

[0052] The first metal may include, for example, Al, and the second metal may include, for example, at least one selected from the group consisting of Ta, Nb, Ti, Si, Zr, and Hf.

[0053] In the dielectric layer, an oxide of the first metal may be provided between a metal portion containing the first metal and an oxide of the second metal. Hereinafter, in the dielectric layer, a portion formed by the oxide containing the second metal is also referred to as a first layer, and a portion formed by the oxide containing the first metal is also referred to as a second layer.

[0054] For example, an oxide (first layer) containing a second metal may be formed on a natural oxide film of a first metal formed on the surface of a metal part. After the first layer is formed on the natural oxide film, the metal part may be anodized to form an oxide (second layer) of the first metal of any thickness between the metal part and the oxide (first layer) containing the second metal.

[0055] The second layer may include a composite oxide of an oxide of the first metal and an oxide of the second metal. By forming the second layer, even if a defect exists in the first layer, the defect can be repaired. Thus, the performance of the dielectric layer is further improved.

[0056] The thickness T1 of the first layer and the thickness T2 of the second layer may satisfy T1≧2×T2 or T1≧3×T2 at least in the third region. By making the thickness of the first layer relatively large in this way, for example, when a second metal with a high dielectric constant is selected, the capacitance of the electrolytic capacitor can be significantly improved. Note that, according to the configuration of the metal porous portion, it becomes easier for the raw material gas to reach a deeper portion, so that T1>T2 can be satisfied even in the first region.

[0057] The thicknesses of the first and second layers can be determined by cutting the anode body so as to obtain a cross-section of the metal porous portion in the thickness direction, taking an electron microscope photograph of the cross-section, and calculating the average thickness value at any ten points in the first or second layer.

[0058] The first layer preferably contains at least one additive element selected from the group consisting of C, P, B, and N. The additive element is preferably distributed from the surface of the first layer to a depth of at least 0.05×T1 (the thickness of the first layer). This makes it possible to impart sufficient acid resistance to the dielectric layer and to sufficiently reduce leakage current. The first layer is formed of a dielectric containing an oxide of a second metal different from the first metal. The second metal can form a dielectric with a high dielectric constant, but in the process of forming the second metal, defects in the dielectric layer that cause an increase in leakage current are likely to occur. The additive element penetrates into the defects to impart acid resistance to the dielectric layer and suppress an increase in leakage current. In the electrolytic capacitor according to this embodiment, the above elements can be efficiently added to the dielectric layer.

[0059] The method for producing the first electrode foil will be further described below.

[0060] The first electrode foil is manufactured by a method having, for example, a step of preparing a metal foil and a roughening step of forming a metal porous portion by roughening the metal foil. The roughening step includes an etching step of etching the metal foil. By roughening, a metal porous portion having a plurality of pits or pores is formed on the surface side of the metal foil. At the same time, a metal core portion integrated with the metal porous portion is formed in the inner portion of the metal foil. The etching can be performed, for example, by direct current etching using a direct current or alternating current etching using an alternating current.

[0061] The etching conditions are set such that when the metal porous portion is equally divided into a first region, a second region, and a third region in the thickness direction from the metal core portion side in order, the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3. Specifically, for example, in an etching solution mainly composed of hydrochloric acid, by applying a predetermined alternating current to an aluminum foil or an aluminum alloy foil, the porosities P1, P2, and P3 can be arbitrarily set.

[0062] The roughening step may include an etching step of applying a current to the metal foil to etch the metal foil. At this time, for example, a current is applied to the metal foil such that the current density gradually and on average becomes smaller. The actual change in the current density may be continuous or stepwise. As the etching step progresses, a metal porous portion is gradually formed on the metal foil.

[0063] Here, "the current density gradually and on average becomes smaller" means that when the relationship between the time when a current is applied to the metal foil and the current density is represented by an approximate curve or an approximate straight line, the approximate curve or the approximate straight line has a negative slope (the change rate of the current density is negative). The approximate formula corresponding to the approximate curve or the approximate straight line may be a linear function or a function of the second degree or higher. However, when the correlation coefficient of the approximate formula is R, the coefficient of determination R 2is preferably in the range of 0.75 to 0.99, more preferably 0.82 to 0.99, or even 0.85 to 0.99. The approximation curve is preferably a downward convex curve.

[0064] After the first electrode foil is obtained, if the chemical voltage used to form the dielectric layer on the first electrode foil is relatively high (for example, if the chemical voltage is 60 V or more (or even 100 V or more)), it is desirable to gradually decrease the current density used to obtain the first metal foil in a linear manner. In this case, relatively large pores can be formed in the metal porous portion. On the other hand, if the chemical voltage used to form the dielectric layer on the first electrode foil is relatively low (for example, if the chemical voltage is less than 60 V (or even 10 V or less)), it is desirable to gradually decrease the current density used to obtain the first metal foil in a quadratic manner or along a downwardly convex curve. In this case, relatively small pores can be formed in the metal porous portion.

[0065] In the etching process, it is desirable to apply a current to the metal foil intermittently. Specifically, in the etching process, it is desirable to repeat at least two periods each of a period during which a current is applied to the metal foil (hereinafter also referred to as an electrolysis period) and a period during which no current is applied (hereinafter also referred to as an electrolysis period). Note that a slight current (for example, 1% or less of the first current density described below or 0.001 A / cm) is preferably applied. 2 The period during which the electric current (hereinafter referred to as "electrolysis") flows through the metal foil may be included in the electroless period during which no electric current is applied. For example, in the case of a roll-to-roll etching process using a production line with multiple etching tanks, rollers for transporting the metal foil are installed below the etching tanks. The current flowing through the metal foil decreases during and before and after contact with the rollers. This period may be included in the electroless period.

[0066] During the electrolysis period, the ionic species of the metal element constituting the metal foil tend to be concentrated in the pits or pores being formed in the metal foil. For efficient etching, it is more effective to temporarily stop the application of electric current and promote the diffusion of the ionic species than to constantly apply electric current to the metal foil to generate the ionic species of the metal element. It is believed that by providing intermittent electroless periods, the diffusion of the ionic species of the metal element is promoted and the concentration of the ionic species in the pits or pores is reduced, enabling more efficient etching.

[0067] When the period from the start to the end of the etching process (the end of the last electrolysis period) is T0, the total electrolysis period during which a current is applied to the metal foil is T1, and the total non-electrolysis period during which a current is not applied to the metal foil is T2, then T0=T1+T2 holds. The total electrolysis period T1 may be, for example, 10-70% or 30-70% of T0. The non-electrolysis period may be used for a process such as cleaning the metal foil. That is, the non-electrolysis period may be a cleaning step for cleaning the metal foil. During the cleaning period, the metal foil may be introduced into a cleaning solution in a cleaning tank, or the metal foil may be washed with a shower of cleaning solution or running water.

[0068] The period T0 from the start to the end of the etching process and the total electrolysis period T1 during which a current is applied to the metal foil are not particularly limited, and may be set appropriately depending on the thickness of the first electrode foil, the desired depth of the etching pit, etc. The period T0 may be, for example, 16 minutes or more and 70 minutes or less. The electrolysis period T1 may be, for example, 7 minutes or more and 50 minutes or less.

[0069] The method of providing the electroless period is not particularly limited. For example, during the electroless period, the metal foil may be immersed in any of the treatment liquids (etching liquid, cleaning liquid, etc.), or may not be immersed in the treatment liquid. For example, in one etching tank, when an opposing region between the metal foil and the anode electrode is intermittently provided, and etching is performed while the metal foil and the anode electrode are facing each other, the period during which the metal foil and the anode electrode are not facing each other is the electroless period. In this case, the metal foil is present in the treatment liquid even during at least a part of the electroless period.

[0070] On the other hand, when the etching process is performed by a roll-to-roll method using a production line having a plurality of etching tanks, a path outside the etching tanks along which a predetermined length of metal foil is transported can be provided between a pair of adjacent etching tanks. In this case, the period during which the metal foil is transported through the path outside the etching tanks is an electroless period, and the metal foil passes through an external path without a processing liquid during at least a part of the electroless period.

[0071] Treatment liquids include treatment liquids for various purposes, but the main treatment liquids are etching liquids for applying an electric current to metal foils to roughen the surface, cleaning liquids for cleaning metal foils, etc. Among them, when cleaning metal foils, the effect of promoting the diffusion of ionic species of metal elements that are dissolved by electrolytic etching is large.

[0072] As the etching solution, for example, a hydrochloric acid aqueous solution is preferable, and an aqueous solution containing sulfuric acid, nitric acid, phosphoric acid, oxalic acid, etc. in addition to hydrochloric acid may also be used. The aqueous solution may contain various additives such as a chelating agent. The concentration of hydrochloric acid, the concentration of other acids, and the temperature of the etching solution are not particularly limited, and may be appropriately set according to the desired shape of the etching pit and the performance of the capacitor. The concentration of hydrochloric acid in the etching solution is, for example, 1 mol / L or more and 10 mol / L or less. The concentration of other acids in the etching solution is, for example, 0.01 mol / L or more and 1 mol / L or less. The temperature of the etching solution during the electrolytic etching process is not particularly limited, and is, for example, 15°C or more and 60°C or less.

[0073] The cleaning liquid may be water (ion-exchanged water), but when cleaning is the main purpose, it is preferable to wash for a short time with an aqueous solution containing a soluble acid such as hydrochloric acid, phosphoric acid, dilute sulfuric acid, or oxalic acid. When water is used to wash the metal foil, impurities are easily removed and ionic species are easily diffused. In this case, a washing step for 10 seconds or more, 20 seconds or more, or even 60 seconds or more may be performed. By protecting the surface of the metal foil, etching in the depths of the metal foil is more likely to proceed effectively.

[0074] The etching process may include, for example, a first electrolysis step of impregnating a metal foil with a first treatment liquid and applying a current of a first current density to the metal foil, a second electrolysis step of impregnating a metal foil (first etching foil) with a second treatment liquid after the first electrolysis step and applying a current of a second current density to the metal foil, and a third step of impregnating a metal foil (second etching foil) with a third treatment liquid after the second electrolysis step and applying a current of a third current density to the metal foil. In this case, the relationship of first current density>second current density>third current density may be satisfied. However, the first current density, second current density, and third current density mean the average current density in the electrolysis period of the first electrolysis step, the second electrolysis step, and the third electrolysis step, respectively. The average current density can be calculated using the integrated value of the current applied to the metal foil during each electrolysis period and each electrolysis period.

[0075] Of the period T0 from the start to the end of the etching process, the first electrolysis step may occupy 0.2×T0 to 0.4×T0, the second electrolysis step may occupy 0.2×T0 to 0.4×T0, and the third electrolysis step may occupy 0.2×T0 to 0.4×T0. The total of the first electrolysis step, the second electrolysis step, and the third electrolysis step may occupy 0.7×T0 or more. In each electrolysis step, the electrolysis period may be intermittent and may include a non-electrolysis period.

[0076] After the first electrolysis step and before the second electrolysis step, a first cleaning step for cleaning the metal foil (first etching foil) may be performed. After the second electrolysis step and before the third electrolysis step, a second cleaning step for cleaning the metal foil (second etching foil) may be performed. Here, the first electrolysis step and the second electrolysis step are each terminated with an electrolysis period and then transitioned to the first cleaning step or the second cleaning step, which is an electroless period. As already mentioned, the first electrolysis step and the second electrolysis step may further include an electroless period in the process. The electroless period may include another cleaning step other than the first cleaning step and the second cleaning step. However, the first cleaning step and the second cleaning step are steps different from the first to third electrolysis steps.

[0077] The treatment liquid (that is, the cleaning liquid) used in the first and second cleaning steps may be a dilute acid aqueous solution as already described, or may be a solution containing hydrochloric acid, phosphoric acid, dilute sulfuric acid, oxalic acid, or the like.

[0078] The first treatment liquid may contain, for example, hydrochloric acid as a main component and may also contain aluminum, sulfuric acid, phosphoric acid, and / or nitric acid. The first current density is, for example, 0.20 to 0.25 A / cm 2 The total electrolysis period in the first electrolysis step may be, for example, 1 to 10 minutes, and the total non-electrolysis period may be, for example, 1 to 10 minutes. After the first electrolysis step and before the second electrolysis step, the metal foil (first etching foil) may be taken out of the first treatment solution and washed with a washing solution.

[0079] The second treatment liquid may contain, for example, hydrochloric acid as a main component and may also contain aluminum, sulfuric acid, phosphoric acid, and / or nitric acid. The second current density is, for example, 0.19 to 0.24 A / cm 2 The total electrolysis period in the second electrolysis step may be, for example, 1 to 10 minutes, and the total non-electrolysis period may be, for example, 1 to 10 minutes. After the second electrolysis step and before the third electrolysis step, the metal foil (second etching foil) may be taken out of the first treatment solution and washed with a washing solution.

[0080] The third treatment liquid may contain, for example, hydrochloric acid as a main component and may contain aluminum, sulfuric acid, phosphoric acid, and / or nitric acid. The third current density may be, for example, 0.18 to 0.23 A / cm 2 and the total electrolysis period in the third electrolysis step may be, for example, 1 to 10 minutes, and the total electroless period may be, for example, 1 to 10 minutes. After the third electrolysis step, the metal foil (the third etching foil or the first electrode foil) may be taken out from the third treatment liquid and further washed with a cleaning liquid.

[0081] In the above example, the hydrochloric acid concentrations of the main components of the first treatment liquid, the second treatment liquid, and the third treatment liquid may be the same or may be different.

[0082] According to the method as described above, when the metal porous part is equally divided into three regions, namely, a first region, a second region, and a third region in order from the metal core part side in the thickness direction of the metal porous part, it is possible to easily obtain a first electrode foil in which the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3.

[0083] Next, the manufacturing method of the second electrode foil and the electrolytic capacitor will be further described.

[0084] The second electrode foil is manufactured, for example, by a method including: (i) a step of preparing an anode body (the first electrode foil) having a metal porous part and a metal core part continuous with the metal porous part; and (ii) a step of forming a dielectric layer covering the surface of the metal part constituting the metal porous part. The electrolytic capacitor is manufactured by a method including, in addition to the above steps (i) and (ii), (iii) a step of forming a cathode part covering the dielectric layer.

[0085] Step (i) The step (i) of preparing the anode body (first electrode foil) is, for example, a step of roughening a metal foil containing a first metal by etching, and a first electrode foil is prepared in which the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region satisfy P1 < P2 < P3. When P1 < P2 < P3 is satisfied, when forming a dielectric layer by chemical conversion (anodic oxidation), the chemical conversion solution easily penetrates deep into the metal porous part, and when forming a dielectric layer by a vapor phase method, the source gas or the like easily penetrates deep into the metal porous part. Therefore, a good dielectric layer can be formed deep into the metal porous part.

[0086] The type of the first metal is not particularly limited, but a valve metal such as aluminum (Al), tantalum (Ta), niobium (Nb) or an alloy containing a valve metal can be used from the viewpoint that it is easy to form a dielectric layer or a second layer by chemical conversion. The thickness of the metal foil is not particularly limited, but is, for example, 15 μm or more and 300 μm or less.

[0087] Step (ii) The step (ii) of forming the dielectric layer may be, for example, a step of chemically converting (anodizing) the anode body (first electrode foil). For example, by immersing the first electrode foil in a chemical conversion solution such as an ammonium adipate solution, an ammonium phosphate solution, or an ammonium borate solution and applying a voltage to the first electrode foil, a second electrode foil having a dielectric layer formed on the surface of the metal portion can be obtained.

[0088] Further, the step (ii) of forming the dielectric layer may be, for example, a step of depositing an oxide of a second metal different from the first metal contained in the metal portion on the surface of the metal portion by a vapor phase method to form a first layer having a thickness T1. Thereby, a second electrode foil having a dielectric layer formed on the surface of the metal portion can be obtained.

[0089] Examples of the second metal include Al, Ta, Nb, silicon (Si), titanium (Ti), zirconium (Zr), hafnium (Hf), etc. These may be used alone or in combination of two or more. That is, the first layer contains Al 2 O 3, Ta 2 O 5 , Nb 2 O 5 , SiO 2 , TiO 2 , ZrO 2 , HfO 2 The second metal oxide may be contained alone or in combination of two or more kinds. When the first layer contains two or more kinds of oxides of the second metal, the two or more kinds of oxides may be mixed, or each may be arranged in a layer. From the viewpoint of increasing the capacitance of the electrolytic capacitor, it is preferable that the oxide of the second metal has a higher relative dielectric constant than the oxide of the first metal. Also, from the viewpoint of improving the withstand voltage of the electrolytic capacitor, the second metal is preferably Ta 、 Ti, Si, etc. are preferred.

[0090] Examples of the gas phase method include vacuum deposition, chemical vapor deposition, mist deposition, sputtering, pulsed laser deposition, and atomic layer deposition (ALD). Among them, the ALD method is superior in that it can form a dense dielectric layer deep inside the metal porous portion. The thickness of the first layer is not particularly limited, but may be, for example, 0.5 nm or more and 200 nm or less, or 5 nm or more and 200 nm or less.

[0091] Fig. 2 shows an example of an anode foil 10 including an anode body 110 which is an integrated body of a metal core portion 111 and a metal porous portion 112, and a dielectric layer 120 which covers the surface of the metal portion which constitutes the metal porous portion 112. Fig. 2 is a schematic cross-sectional view showing an enlarged view of a part of the metal porous portion 112 which has only a first layer 121 as the dielectric layer 120.

[0092] The metal porous portion 112 has a large number of pits (or pores) P surrounded by a metal portion. The dielectric layer 120 (first layer 121) is provided so as to cover at least a part of the surface of the metal portion. The first layer 121 contains an oxide of a second metal different from the first metal contained in the metal portion, and its thickness is indicated as T1.

[0093] The ALD method is a film formation method in which a source gas containing a second metal and an oxidant are alternately supplied to a reaction chamber in which a target object is placed, to form a dielectric layer (first layer) containing an oxide of the second metal on the surface of the target object. In the ALD method, a self-limiting effect works, so the second metal is deposited on the surface of the target object in atomic layers. Therefore, the thickness of the first layer is controlled by the number of cycles, which is one cycle consisting of supply of source gas → exhaust (purging) of source gas → supply of oxidant → exhaust (purging) of oxidant. In other words, the ALD method can easily control the thickness of the dielectric layer to be formed.

[0094] In addition, while CVD is generally performed at temperatures of 400 to 900° C., the ALD method can be performed at temperatures of 100 to 400° C. In other words, the ALD method is superior in that it can suppress thermal damage to the metal foil.

[0095] Examples of the oxidizing agent used in the ALD method include water, oxygen, ozone, etc. The oxidizing agent may be supplied to the reaction chamber as plasma using the oxidizing agent as a raw material.

[0096] The second metal is supplied to the reaction chamber as a precursor gas containing the second metal. The precursor is, for example, an organometallic compound containing the second metal, which makes the second metal more likely to be chemically adsorbed to the target object. As the precursor, various organometallic compounds that have been conventionally used in the ALD method can be used.

[0097] An example of a precursor containing Al is trimethylaluminum ((CH 3 ) 3 Examples of precursors containing Zr include bis(methyl-η5-cyclopentadienyl)methoxymethylzirconium (Zr(CH 3 C 5 H 4 ) 2 CH 3 OCH 3 ), tetrakis(dimethylamido)zirconium(IV) ([(CH 3 ) 2 N] 4Zr), tetrakis(ethylmethylamido)zirconium(IV) (Zr(NCH 3 C 2 H 5 ) 4 ) 、 Zirconium(IV) t-butoxide (Zr[OC(CH 3 ) 3 ] 4 ) and the like. Examples of precursors containing Nb include niobium (V) ethoxide (Nb(OCH 2 CH 3 ) 5 , tris(diethylamido)(t-butylimido)niobium(V)(C 16 H 39 N 4 Nb) etc.

[0098] An example of a precursor containing Ta is (t-butylimido)tris(ethylmethylamino)tantalum(V) (C 13 H 33 N 4 Ta, TBTEMT), Tantalum(V) Pentaethoxide (Ta(OC 2 H 5 ) 5 ), (t-butylimido)tris(diethylamino)tantalum(V)((CH 3 ) 3 CNTa(N(C 2 H 5 ) 2 ) 3 ), pentakis(dimethylamino)tantalum(V) (Ta(N(CH 3 ) 2 ) 5 ) etc.

[0099] Examples of precursors containing Nb include niobium(V) ethoxide (Nb(OCH 2 CH 3 ) 5 , tris(diethylamido)(t-butylimido)niobium(V)(C 16 H 39 N 4 Nb) etc.

[0100] Examples of precursors containing Si include N-sec-butyl(trimethylsilyl)amine (C 7 H 19 NSi), 1,3-diethyl-1,1,3,3-tetramethyldisilazane (C 8 H 23 NSi 2 ), 2,4,6,8,10-pentamethylcyclopentasiloxane ((CH 3 SiHO) 5 ), pentamethyldisilane ((CH 3 ) 3 SiSi(CH 3 ) 2 H), tris(isopropoxy)silanol ([(H 3 C) 2 CH] 3 SiOH), chloropentanemethyldisilane ((CH 3 ) 3 SiSi(CH 3 ) 2 Cl), dichlorosilane (SiH 2 Cl 2 ), tridimethylaminosilane (Si[N(CH 3 ) 2 ] 4 ), tetraethylsilane (Si(C 2 H 5 ) 4 ), tetramethylsilane (Si(CH 3 ) 4 ), tetraethoxysilane (Si(OC 2 H 5 ) 4 ), dodecamethylcyclohexasilane ((Si(CH 3 ) 2 ) 6 ), silicon tetrachloride (SiCl 4 ) Silicon tetrabromide (SiBr 4 ) etc.

[0101] An example of a precursor containing Ti is bis(t-butylcyclopentadienyl)titanium(IV) dichloride (C 18 H 26 C l2 Ti), tetrakis(dimethylamino)titanium(IV) ([(CH3 ) 2 N] 4 Ti, TDMAT), tetrakis(diethylamino)titanium(IV) ([(C 2 H 5 ) 2 N] 4 Ti), tetrakis(ethylmethylamino)titanium(IV) (Ti[N(C 2 H 5 )(CH 3 )] 4 ), titanium(IV) (diisopropoxide-bis(2,2,6,6-tetramethyl-3,5-heptanedionate (Ti[OCC(CH 3 ) 3 CHCOC(CH 3 ) 3 ] 2 (OC 3 H 7 ) 2 ), titanium tetrachloride (TiCl 4 ), titanium(IV) isopropoxide (Ti[OCH(CH 3 ) 2 ] 4 ), titanium(IV) ethoxide (Ti[O(C 2 H 5 )] 4 ) etc.

[0102] Zr-containing precursors include, for example, bis(methyl-η 5 Cyclopentadienyl)methoxymethylzirconium (Zr(CH 3 C 5 H 4 ) 2 CH 3 OCH 3 ), tetrakis(dimethylamido)zirconium(IV) ([(CH 3 ) 2 N] 4 Zr), tetrakis(ethylmethylamido)zirconium(IV) (Zr(NCH 3 C 2 H 5 ) 4 ) 、 Zirconium(IV) t-butoxide (Zr[OC(CH 3 ) 3 ]4 ) etc.

[0103] Examples of precursors containing Hf include hafnium tetrachloride (HfCl 4 ), tetrakisdimethylaminohafnium (Hf[N(CH 3 ) 2 ] 4 ), tetrakisethylmethylaminohafnium (Hf[N(C 2 H 5 )(CH 3 )] 4 ), tetrakisdiethylaminohafnium (Hf[N(C 2 H 5 ) 2 ] 4 ), hafnium t-butoxide (Hf[OC(CH 3 ) 3 ] 4 ) etc.

[0104] The method for producing the second electrode foil may further include a step of forming (anodizing) the anode body on which the oxide of the second metal has been deposited (i.e., the anode body having the first layer). This allows a second layer containing the oxide of the first metal and having a thickness T2 to be formed between the metal portion containing the first metal and the oxide of the second metal (the first layer). The thickness T2 can be controlled by the voltage applied to the anode body during the forming process.

[0105] As described above, when the porosity P1 of the deepest part (first region) of the etching pit is small, a good dielectric layer can be efficiently formed up to the deepest part. Also, when the porosity P3 of the surface part (third region) of the etching pit is large, the source gas can easily penetrate and reach the deepest part. As a result, it becomes easy to control the ratio of the first layer to the second layer to be high even in the first region, and it becomes possible to form a dielectric layer with a high dielectric constant over the entire metal porous part.

[0106] Furthermore, when the first layer contains at least one additive element selected from the group consisting of C, P, B, and N, for example, the anode body having the dielectric layer may be immersed in an aqueous solution containing the additive element, and then heat-treated (for example, heated to 180° C. or higher). The additive element may be attached to the anode body having the dielectric layer by a gas phase method such as deposition. To further diffuse the additive element, the heating temperature of the heat treatment may be set to 250° C. or higher.

[0107] The aqueous solution containing the additive element may be an aqueous solution of a compound containing the additive element, and examples of such compounds that can be used include carboxylic acids containing C (carbon), such as oxalic acid, malonic acid, adipic acid, succinic acid, glutaric acid, sebacic acid, and tartaric acid; compounds containing N (nitrogen), such as ammonium salts, such as diammonium adipate; compounds containing P (phosphorus), such as phosphoric acid, ammonium phosphate, phosphonic acid, and phosphinic acid; and compounds containing B (boron), such as boric acid and ammonium borate.

[0108] 3 is an enlarged schematic cross-sectional view of a portion of the metal porous portion 112 having a first layer 121 and a second layer 122 as the dielectric layer 120. The dielectric layer 120 has, in order from the metal portion side, the second layer 122 and the first layer 121. The thickness of the first layer 121 is indicated as T1, and the thickness of the second layer is indicated as T2.

[0109] According to the ALD method, a thin and uniform dielectric layer (first layer) can be formed. However, in reality, the surface of the deep pits in the metal porous portion may have defects such as pinholes. When forming the second layer, the ionized first metal diffuses into the first layer, and has the effect of repairing the defects in the first layer. As a result, a dielectric layer with a uniform thickness and no pinholes is formed as a whole. Therefore, the capacitance of the electrolytic capacitor is increased, the voltage resistance is improved, and the leakage current is reduced.

[0110] The thickness T2 of the second layer is not particularly limited, but may be smaller than the thickness T1 of the first layer. The thickness T2 of the second layer is, for example, 0.5 nm or more and 200 nm or less, and may be 5 nm or more and 200 nm or less.

[0111] The ratio of the thickness T1 of the first layer to the thickness T2 of the second layer is not particularly limited and may be appropriately set depending on the application, the desired effect, etc. For example, the thickness ratio: T1 / T2 may be 2 or more, 3 or more, or 5 or more in at least the third region.

[0112] Process (iii) In the step (iii) of forming the cathode portion covering the dielectric layer, for example, an anode body having a dielectric layer may be impregnated with an electrolytic solution and / or a solid electrolyte layer may be formed on the surface of the dielectric layer. When both the formation of the solid electrolyte layer and the impregnation with the electrolytic solution are performed, the solid electrolyte layer may be formed on the dielectric layer, and then the impregnation with the electrolytic solution may be performed.

[0113] The electrolyte may be a non-aqueous solvent or a mixture of a non-aqueous solvent and an ionic substance (solute (e.g., organic salt)) dissolved therein. The non-aqueous solvent may be an organic solvent or an ionic liquid.

[0114] The non-aqueous solvent is preferably a high boiling point solvent, for example, polyhydric alcohols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane, lactones such as γ-butyrolactone, amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde can be used.

[0115] An organic salt is a salt in which at least one of the anion and the cation contains an organic substance. For example, trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, mono-1,3-dimethyl-2-ethylimidazolinium phthalate, etc. may be used as the organic salt.

[0116] The solid electrolyte layer includes, for example, a manganese compound, a conductive polymer, and the like. As the conductive polymer, polypyrrole, polythiophene, polyaniline, and derivatives thereof can be used. The solid electrolyte layer including the conductive polymer can be formed, for example, by chemical polymerization and / or electrolytic polymerization of a raw material monomer on the dielectric layer. The solid electrolyte layer may be formed by attaching a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed to the dielectric layer.

[0117] When the anode element having a dielectric layer is an anode foil as shown in Figures 1 to 3, a wound body 100 as shown in Figure 5 may be produced before forming the cathode part. Figure 5 is a development view for explaining the configuration of wound body 100.

[0118] When preparing the wound body 100, in addition to the anode foil 10, the cathode foil 20 is prepared. The cathode foil 20 may be a metal foil, similar to the anode foil 10. The type of metal constituting the cathode foil 20 is not particularly limited, but a valve metal such as Al, Ta, or Nb, or an alloy containing a valve metal, may be used. If necessary, the surface of the cathode foil 20 may be roughened.

[0119] Next, the anode foil 10 and the cathode foil 20 are wound with the separator 30 interposed therebetween. One end of the lead tab 50A or 50B is connected to the anode foil 10 and the cathode foil 20, respectively, and the lead tabs 50A and 50B are wound to form the wound body 100. The other ends of the lead tabs 50A and 50B are connected to lead wires 60A and 60B, respectively.

[0120] The separator 30 is not particularly limited, and for example, a nonwoven fabric containing cellulose, polyethylene terephthalate, vinylon, aramid fiber, or the like as a main component can be used.

[0121] Next, a winding tape 40 is disposed on the outer surface of the cathode foil 20 positioned at the outermost layer of the wound body 100, and the end portion of the cathode foil 20 is fixed with the winding tape 40. When the anode foil 10 is prepared by cutting a large-sized foil, further formation treatment may be performed on the wound body 100 in order to provide a dielectric layer on the cut surface.

[0122] The method of impregnating the wound body 100 with a liquid for forming an electrolyte such as an electrolytic solution, a solution in which a conductive polymer is dissolved, and / or a dispersion in which a conductive polymer is dispersed is not particularly limited. For example, a method of immersing the wound body 100 in an electrolytic solution, a solution or a dispersion contained in a container, a method of dropping an electrolytic solution, a solution or a dispersion onto the wound body 100, or the like can be used. The impregnation may be performed under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa, preferably 40 kPa to 100 kPa. When P1 < P2 < P3 or Q1 < Q2 < Q3 is satisfied, even when the viscosity of the liquid for forming the electrolyte is 10 mPa·s or more, particularly 50 mPa·s or more, and further 100 mPa·s or more, the permeability of the liquid for forming the electrolyte into the metal porous portion can be increased, the capacitance achievement rate of the electrolytic capacitor is also increased, and it is also advantageous for reducing ESR and suppressing leakage current.

[0123] Next, by sealing the wound body 100, an electrolytic capacitor 200 as shown in FIG. 4 is obtained. To manufacture the electrolytic capacitor 200, first, the wound body 100 is housed in a bottomed case 211 so that the lead wires 60A and 60B are positioned on the opening side of the bottomed case 211. As the material of the bottomed case 211, metals such as aluminum, stainless steel, copper, iron, brass, or alloys thereof can be used.

[0124] Next, a sealing member 212 formed so as to penetrate the lead wires 60A and 60B is disposed above the wound body 100, and the wound body 100 is sealed in the bottomed case 211. The sealing member 212 may be an insulating material, and an elastic body is preferable. Among them, silicone rubber, fluororubber, ethylene propylene rubber, hypalon rubber, butyl rubber, isoprene rubber, etc. having high heat resistance are preferable.

[0125] Next, a horizontal drawing process is performed near the open end of bottomed case 211, and the open end is curled by crimping it to sealing member 212. Finally, sealing is completed by placing seat plate 213 on the curled portion. Thereafter, an aging process may be performed while applying a rated voltage.

[0126] FIG. 6 is an explanatory diagram showing a schematic diagram of an etching apparatus used in the roll-to-roll etching process. The etching apparatus 300 includes an etching tank 310 for holding an etching solution, a plurality of transport rolls 320 for transporting a metal foil 301, a pair of electrodes 330 facing the metal foil 301, and an AC power source 340 for applying a current to the electrodes 330. The metal foil 301 moves in the etching tank 310 while being transported via the plurality of transport rolls 320. The metal foil 301 is etched while facing the electrodes 330 in the etching tank 310 (during electrolysis). As a result, a metal foil (etched foil) 302 that is at least partially etched is obtained.

[0127] FIG. 6 shows a case where etching is performed on a long metal foil 301, but the present invention is not limited to this. For example, etching may be performed on a metal foil having a certain area that is placed stationary. Also, in FIG. 6, a pair of electrodes is used, but the present invention is not limited to this. For example, etching may be performed by placing a metal foil opposite one electrode and connecting the electrode and the metal foil to an AC power source. Furthermore, there may be multiple etching tanks. One etching tank may have two or more pairs of electrodes.

[0128] In the above embodiment, a wound-type electrolytic capacitor has been described, but the scope of application of the present invention is not limited to the above, and the present invention can also be applied to other electrolytic capacitors, for example, stacked-type electrolytic capacitors.

[0129] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0130] Example 1A In this example, after forming the first layer as a dielectric layer by ALD method, formation was carried out at a formation voltage of 65 V to produce a second electrode foil (formed foil). Hereinafter, a specific manufacturing method will be described.

[0131] (Fabrication of Anode Body (First Electrode Foil)) An Al foil with a thickness of 150 μm was prepared as a metal foil. The Al foil was pretreated with an aqueous hydrochloric acid solution, and then an etching process was performed by applying an alternating current in an etching solution mainly composed of hydrochloric acid. The etching current (current density, frequency), etching time, and etching solution temperature were appropriately adjusted to obtain an etched foil (first electrode foil) having a metal porous part with a thickness of 55 μm and the following porosity on both surfaces of the Al foil.

[0132] The peak pore diameter of the metal porous part was 170 nm. The porosity P1 of the first region R1, the porosity P2 of the second region R2, and the porosity P3 of the third region R3 were 55%, 62%, and 75% respectively, and P1 < P2 < P3. Also, P2 / P1 = 1.13 and P3 / P2 = 1.21, satisfying P2 / P1 < P3 / P2.

[0133] Fig. 7 shows the relationship between the distance from the surface of the anode body in the metal porous part and the porosity (Al remaining ratio).

[0134] (Fabrication of Second Electrode Foil) Next, by ALD method (temperature: 200 °C, precursor: (t-butylimide)tris(ethylmethylamino)tantalum(V) (C 13 H 33 N 4 Ta, TBTEMT), oxidant: H 2 O, pressure: 10 Pa, 3000 cycles), an oxide containing Ta was formed as a dielectric layer (first layer) on the surface of the Al skeleton (metal part) constituting the porous part.

[0135] Subsequently, the Al foil (the first electrode foil having the first layer) was subjected to a forming treatment to form a second layer containing an oxide of Al between the Al skeleton and the first layer, thereby obtaining a second electrode foil. In the forming treatment, the Al foil having the first layer was immersed in an aqueous solution of diammonium adipate (adipic acid ammonium concentration: 10% by mass), a direct current was applied, and after reaching a forming voltage of about 65 V, it was held for about 10 minutes. After washing with water, it was heated in air at 300 °C for 5 minutes, and then the obtained second electrode foil was cut into a predetermined shape.

[0136] As a result of elemental analysis, the first layer (thickness: about 80 nm) contained Ta 2 O 5 and the second layer (thickness: about 10 nm) contained Al 2 O 3 (T1 = 8×T2).

[0137] <<Comparative Example 1A>> Using an Al foil with a thickness of 150 μm, an etched foil (the first electrode foil) having a metal porous part with a thickness of 55 μm and the following porosity on both surfaces of the Al foil was obtained by appropriately adjusting the etching current (current density, frequency), etching time, and etching solution temperature. The peak pore diameter of the metal porous part was 165 nm. The porosity P1 of the first region R1, the porosity P2 of the second region R2, and the porosity P3 of the third region R3 were 51%, 49%, and 52% respectively, and P1 < P2 < P3 was not satisfied. A second electrode foil was produced and evaluated in the same manner as in Example 1A, except that this anode body (the first electrode foil) was used.

[0138] [Evaluation] For the obtained second electrode foil, the capacitance and leakage current were measured. The leakage current was measured as the integrated value of the leakage current flowing until 60 V while applying a voltage while increasing the voltage at a rate of 0.2 V / second after immersing in an acidic aqueous solution at 35 °C for 60 minutes. Table 1 shows the relative values of Example 1A when the result of Comparative Example 1A is taken as 100.

[0139] <<Example 1B>> For the etched foil (the first electrode foil) obtained in Example 1A, the first layer was not formed by the ALD method, and forming at a forming voltage of 65 V was performed. Al2 O 3 A second electrode foil (formed foil) having a dielectric layer containing O was produced and evaluated in the same manner.

[0140] For the formation treatment, the first electrode foil was immersed in an aqueous solution of diammonium adipate (adipic acid ammonium concentration: 10% by mass), a direct current was applied, and after reaching a formation voltage of about 65 V, it was held for about 10 minutes. After washing with water, it was heated in air at 300 °C for 5 minutes, and then the obtained second electrode foil was cut into a predetermined shape.

[0141] 《Comparative Example 1B》 For the etching foil (first electrode foil) obtained in Comparative Example 1A, the first layer was not formed by the ALD method, and formation was performed at a formation voltage of 65 V similar to Example 1B, and Al 2 O 3 A second electrode foil (formed foil) having a dielectric layer containing O was produced and evaluated in the same manner.

[0142] Table 1 shows the relative values of Example 1B when the result of Comparative Example 1B is taken as 100.

[0143] 《Example 2》 Using an Al foil with a thickness of 120 μm, an etching foil (first electrode foil) having a metal porous part with a thickness of 40 μm and the following porosity on both surfaces of the Al foil was obtained by appropriately adjusting the etching current (current density, frequency), etching time, and etching solution temperature. The porosity P1 in the first region R1, the porosity P2 in the second region R2, and the porosity P3 in the third region R3 were 50%, 55%, and 70% respectively, satisfying P1 < P2 < P3. Also, P2 / P1 = 1.10 and P3 / P2 = 1.27, satisfying P2 / P1 < P3 / P2. A second electrode foil was produced and evaluated in the same manner as in Example 1A, except that this anode body (first electrode foil) was used.

[0144] Fig. 8 shows the relationship between the distance from the surface of the anode body in the metal porous part of Example 2 and the porosity (Al remaining ratio).

[0145] 《Example 3》 For the etching foil (first electrode foil) obtained in Example 2, without forming the first layer by ALD method, formation was carried out at the same formation voltage of 65 V as in Example 1B, and Al 2 O 3 A second electrode foil (formed foil) having a dielectric layer containing was produced and evaluated in the same manner.

[0146] <<Comparative Example 2>> Using an Al foil with a thickness of 120 μm, the etching current (current density, frequency), etching time, and etching solution temperature were appropriately adjusted to obtain an etching foil (first electrode foil) having a metal porous part with a thickness of 40 μm and the following porosity on both surfaces of the Al foil. The porosity P1 in the first region R1, the porosity P2 in the second region R2, and the porosity P3 in the third region R3 were 55%, 50%, and 52% respectively, and did not satisfy P1 < P2 < P3. Except for using this anode body (first electrode foil), in the same manner as in Example 3, the first layer was not formed by ALD method, and only the formation treatment was performed on the first electrode foil to produce a second electrode foil and evaluated in the same manner.

[0147] Fig. 9 shows the relationship between the distance from the surface of the anode body in the metal porous part of Comparative Example 2 and the porosity (Al remaining ratio).

[0148] Table 1 shows the relative values of Examples 2 and 3 when the result of Comparative Example 2 was taken as 100.

[0149]

Table 1

[0150] In Examples 1A and 1B, compared with Comparative Examples 1A and 1B, the capacitance was improved and the leakage current was reduced. Also, in Examples 2 and 3, compared with Example 2, the capacitance was improved and the leakage current was reduced.

[0151] <<Example 4>> An Al foil with a thickness of 150 μm was prepared as a metal foil, and the following etching process was carried out. The current density is shown as a relative value when the first current density in the first electrolysis step is 100%.

[0152] <First electrolysis step> The Al foil was pretreated with an aqueous hydrochloric acid solution, and then an AC current with the following profile was applied to it in an etching solution whose main component was hydrochloric acid.

[0153] Electrolysis duration: current density 100%, 5 min (step 1 in Figure 10)

[0154] <First cleaning step> Electroless period: 8 minutes of pure water cleaning

[0155] <Second electrolysis step> An alternating current with the following profile was applied to the Al foil (etched foil) after the first step in an etching solution mainly containing hydrochloric acid.

[0156] Electrolysis period: current density 93%, 5 min (step 2 in Figure 10)

[0157] <Second cleaning step> Electroless period: 8 minutes of pure water cleaning

[0158] <Third electrolysis step> An alternating current with the following profile was applied to the Al foil (second etching foil) after the second step in an etching solution (electrolyte) containing hydrochloric acid as the main component.

[0159] Electrolysis duration: current density 90.7%, 5 min (step 3 in Figure 10)

[0160] <Third washing step> Electroless period: 8 minutes of pure water cleaning T1=15 minutes T2=16 minutes T0=T1+T2=31 minutes

[0161] As a result of the above, a first electrode foil having a metal porous portion with a thickness of 40 μm and the following porosity was obtained on both surfaces of the Al foil. The peak pore diameter of the metal porous portion was 170 nm. The porosity P1 of the first region R1, the porosity P2 of the second region R2, and the porosity P3 of the third region R3 satisfied P1 < P2 < P3 and P2 / P1 < P3 / P2.

[0162] Figure 10 shows a plot of the change in current density in the etching process and its approximate straight line. The coefficient of determination R 2 is 0.92.

[0163] 《Example 5》 An Al foil with a thickness of 120 μm was prepared as the metal foil, and the following etching process was performed. The current density is shown as a relative value when the first current density in the first sub-step of the first electrolysis step is 100%.

[0164] <First electrolysis step> The Al foil was pretreated with an aqueous hydrochloric acid solution, and then an alternating current with the following profile was applied in an etching solution mainly composed of hydrochloric acid.

[0165] (i) First sub-step (step 1 in Figure 11) Electrolysis period: current density 100%, 3 minutes Non-electrolysis period: washing with pure water for 8 minutes

[0166] (ii) Second sub-step (step 2 in Figure 11) Electrolysis period: current density 94.8%, 3 minutes

[0167] <First washing step> Non-electrolysis period: washing with pure water for 8 minutes

[0168] <Second electrolysis step> An alternating current with the following profile was applied to the Al foil (first etched foil) after the first electrolysis step in an etching solution (electrolyte) mainly composed of hydrochloric acid.

[0169] (i) First sub-step (Step 3 in Figure 11) Electrolysis period: Current density 95.4%, 3 minutes Non-electrolysis period: Cleaning with pure water for 8 minutes

[0170] (ii) Second sub-step (Step 4 in Figure 11) Electrolysis period: Current density 92.3%, 3 minutes

[0171] <Second cleaning step> Non-electrolysis period: Cleaning with pure water for 8 minutes

[0172] <Third electrolysis step> An alternating current with the following profile was applied to the Al foil (second etching foil) after the second electrolysis step in an etching solution mainly composed of hydrochloric acid.

[0173] (i) First sub-step (Step 5 in Figure 11) Electrolysis period: Current density 93.1%, 3 minutes Non-electrolysis period: Cleaning with pure water for 8 minutes

[0174] (ii) Second sub-step (Step 6 in Figure 11) Electrolysis period: Current density 90.5%, 3 minutes

[0175] <Third cleaning step> Non-electrolysis period: Cleaning with pure water for 8 minutes T1 = 18 minutes T2 = 40 minutes T0 = T1 + T2 = 58 minutes

[0176] As a result of the above, a first electrode foil having a metal porous portion with a thickness of 40 μm and the following porosity on both surfaces of the Al foil was obtained. The peak pore diameter of the metal porous portion was 170 nm. The porosity P1 of the first region R1, the porosity P2 of the second region R2, and the porosity P3 of the third region R3 were 50%, 55%, and 70% respectively, and P1 < P2 < P3. Also, P2 / P1 = 1.10, P3 / P2 = 1.27, and P2 / P1 < P3 / P2 was satisfied.

[0177] FIG. 11 shows a plot of the current density during the etching process and its approximation line. The coefficient of determination R 2 is 0.82.

[0178] Example 6 An Al foil having a thickness of 150 μm was prepared as the metal foil, and the following etching process was carried out. The current density is shown as a relative value when the first current density in the first sub-step of the first step is set as 100%.

[0179] <First electrolysis step> The Al foil was pretreated with an aqueous hydrochloric acid solution, and then an AC current with the following profile was applied to it in an etching solution whose main component was hydrochloric acid.

[0180] (i) First substep (Step 1 in Figure 12) Electrolysis period: 100% current density, 3 minutes Electroless period: 8 minutes of pure water cleaning

[0181] (ii) Second sub-step (step 2 in Figure 12) Electrolysis period: current density 94.8%, 3 minutes

[0182] <First cleaning step> Electroless period: 8 minutes of pure water cleaning

[0183] <Second electrolysis step> An alternating current having the following profile was applied to the Al foil after the first electrolysis step (first etching foil) in an etching solution containing hydrochloric acid as a main component.

[0184] (i) First substep (step 3 in Figure 12) Electrolysis period: current density 95.4%, 3 minutes Electroless period: 8 minutes of pure water cleaning

[0185] (ii) Second sub-step (step 4 in Figure 12) Electrolysis period: current density 92.3%, 3 minutes

[0186] <Second Washing Step> Electrolysis-free period: Washing with pure water for 8 minutes

[0187] <Third Electrolysis Step> An alternating current with the following profile was applied to the Al foil (second etching foil) after the second electrolysis step in an etching solution (electrolyte) mainly composed of hydrochloric acid.

[0188] (i) First sub-step (step 5 in FIG. 12) Electrolysis period: Current density 93.1%, 3 minutes Electrolysis-free period: Washing with pure water for 8 minutes

[0189] (ii) Second sub-step (step 6 in FIG. 12) Electrolysis period: Current density 90.5%, 3 minutes

[0190] <Third Washing Step> Electrolysis-free period: Washing with pure water for 8 minutes T1 = 18 minutes T2 = 40 minutes T0 = T1 + T2 = 58 minutes

[0191] As a result, a first electrode foil having a metal porous portion with a thickness of 55 μm and the following porosity on both surfaces of the Al foil was obtained. The peak pore diameter of the metal porous portion was 170 nm. The porosity P1 of the first region R1, the porosity P2 of the second region R2, and the porosity P3 of the third region R3 were 55%, 62%, and 75% respectively, and P1 < P2 < P3. Also, P2 / P1 = 1.13 and P3 / P2 = 1.21, satisfying P2 / P1 < P3 / P2.

[0192] FIG. 12 shows a plot of the transition of the current density in the etching process and its approximate curve. The coefficient of determination R 2 is 0.96.

[0193] <<Example 7>> An Al foil with a thickness of 150 μm was prepared, and an etching process having the following 9 sub-steps was carried out in one electrolytic cell. The current density is shown as a relative value when the first current density in the first sub-step is 100%.

[0194] The Al foil was pretreated with an aqueous hydrochloric acid solution, and then an alternating current with the following profile was applied in an etching solution (electrolyte) mainly composed of hydrochloric acid.

[0195] (i) First sub-step (step 1 in FIG. 13) Electrolysis period: Current density 100%, 3 minutes Non-electrolysis period: 8 minutes

[0196] (ii) Second sub-step (step 2 in FIG. 13) Electrolysis period: Current density 93.4%, 3 minutes Non-electrolysis period: 8 minutes

[0197] (iii) Third sub-step (step 3 in FIG. 13) Electrolysis period: Current density 95.8%, 3 minutes Non-electrolysis period: 8 minutes

[0198] (iv) Fourth sub-step (step 4 in FIG. 13) Electrolysis period: Current density 88.2%, 3 minutes Non-electrolysis period: 8 minutes

[0199] (v) Fifth sub-step (step 5 in FIG. 13) Electrolysis period: Current density 87.2%, 3 minutes T1 = 15 minutes T2 = 32 minutes T0 = T1 + T2 = 47 minutes

[0200] As a result of the above, a first electrode foil having a metal porous portion with a thickness of 40 μm and the following porosity on both surfaces of the Al foil was obtained. The peak pore diameter of the metal porous portion was 170 nm. The porosity P1 of the first region R1, the porosity P2 of the second region R2, and the porosity P3 of the third region R3 satisfied P1 < P2 < P3 and P2 / P1 < P3 / P2.

[0201] FIG. 13 shows a plot of the current density during the etching process and its approximation line. The coefficient of determination R 2 is 0.83. [Industrial Applicability]

[0202] According to the present invention, for example, since a dielectric layer can be formed deep inside a metal porous portion, the performance of an electrolytic capacitor can be improved.

[0203] Although the present invention has been described with respect to the presently preferred embodiments, such disclosure should not be interpreted as limiting. Various variations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be interpreted to cover all variations and modifications without departing from the true spirit and scope of the present invention. [Explanation of symbols]

[0204] 10: anode foil, 20: cathode foil, 30: separator, 40: stop tape, 50A, 50B: lead tabs, 60A, 60B: lead wires, 100: wound body, 110: anode body, 111: metal core, 112: metal porous portion, 120: dielectric layer, 121: first layer, 122: second layer, 200: electrolytic capacitor, 211: bottomed case, 212: sealing member, 213: seat plate

Claims

1. Providing a metal foil; A roughening step of forming a metal porous portion by roughening the metal foil, The roughening step includes an etching step of applying a current to the metal foil, The etching step includes: a first electrolysis step of applying a current of a first current density to the metal foil in a first treatment solution to obtain a first etched foil; a second electrolysis step of applying a current having a second current density smaller than the first current density to the first etched foil in a second treatment solution after the first electrolysis step to obtain a second etched foil; a third electrolysis step of applying a current having a third current density smaller than the first current density to the second etched foil in a third treatment solution after the second electrolysis step to obtain a third etched foil; having The method further includes a step of forming a dielectric layer covering a surface of a metal portion constituting the metal porous portion after the surface roughening step, When the metal porous portion is divided into three equal regions, a first region, a second region and a third region, in that order from the metal core portion side, in the thickness direction of the metal porous portion, a porosity P1 of the first region, a porosity P2 of the second region, and a porosity P3 of the third region after the step of forming the dielectric layer satisfy P1<P2<P3, The P1, the P2, and the P3 satisfy P2 / P1<P3 / P2. A method for manufacturing electrode foil for electrolytic capacitors.

2. A method of manufacturing a semiconductor device, comprising the steps of: preparing a metal foil; A roughening step of forming a metal porous portion by roughening the metal foil, The roughening step includes an etching step of applying a current to the metal foil, The etching step includes: a first electrolysis step of applying a current of a first current density to the metal foil in a first treatment solution to obtain a first etched foil; a second electrolysis step of applying a current having a second current density smaller than the first current density to the first etched foil in a second treatment solution after the first electrolysis step to obtain a second etched foil; a third electrolysis step of applying a current having a third current density smaller than the first current density to the second etched foil in a third treatment solution after the second electrolysis step to obtain a third etched foil; having The method further includes a step of forming a dielectric layer covering a surface of a metal portion constituting the metal porous portion after the surface roughening step, When the metal porous portion having the dielectric layer is divided into three equal regions, a first region, a second region and a third region, in that order from the metal core portion side, in a thickness direction of the metal porous portion, a porosity Q1 of the first region, a porosity Q2 of the second region, and a porosity Q3 of the third region after the step of forming the dielectric layer satisfy Q1<Q2<Q3; The Q1, the Q2, and the Q3 satisfy Q2 / Q1<Q3 / Q2. A method for manufacturing electrode foil for electrolytic capacitors.

3. When the metal porous portion having the dielectric layer is divided into three equal regions, a first region, a second region and a third region, in the thickness direction of the metal porous portion, in that order from the metal core portion side, a porosity Q1 of the first region, a porosity Q2 of the second region, and a porosity Q3 of the third region after the step of forming the dielectric layer satisfy Q1<Q2<Q3; The Q1, the Q2, and the Q3 satisfy Q2 / Q1<Q3 / Q2. A method for producing the electrode foil for electrolytic capacitors according to claim 1.

4. A method comprising the steps of: preparing a metal foil; A roughening step of forming a metal porous portion by roughening the metal foil, The roughening step includes an etching step of applying a current to the metal foil, The etching step includes: a first electrolysis step of applying a current of a first current density to the metal foil in a first treatment solution to obtain a first etched foil; a second electrolysis step of applying a current having a second current density smaller than the first current density to the first etched foil in a second treatment solution after the first electrolysis step to obtain a second etched foil; a third electrolysis step of applying a current having a third current density smaller than the first current density to the second etched foil in a third treatment solution after the second electrolysis step to obtain a third etched foil; having The method further includes a step of forming a dielectric layer covering a surface of a metal portion constituting the metal porous portion after the surface roughening step, The step of forming the dielectric layer includes: forming a first layer having a thickness T1 by depositing an oxide of a second metal different from the first metal contained in the metal portion on a surface of the metal porous portion by a vapor phase method; and forming a second layer having a thickness T2 and including an oxide of the first metal between the metal portion and the oxide of the second metal by chemically converting the anode body having the first layer. A method for manufacturing electrode foil for electrolytic capacitors.

5. The step of forming the dielectric layer includes: forming a first layer having a thickness T1 by depositing an oxide of a second metal different from the first metal contained in the metal portion on a surface of the metal porous portion by a vapor phase method; and forming a second layer having a thickness T2 and including an oxide of the first metal between the metal portion and the oxide of the second metal by chemically converting the anode body having the first layer. The method for producing the electrode foil for electrolytic capacitors according to any one of claims 1 to 3.

6. The first metal includes Al, and the second metal includes at least one selected from the group consisting of Ta, Nb, Ti, Si, Zr, and Hf. The method for producing the electrode foil for electrolytic capacitors according to claim 4 or 5.

7. The etching step includes: a first cleaning step of cleaning the first etching foil after the first electrolysis step and before the second electrolysis step; A second cleaning step of cleaning the second etching foil after the second electrolysis step and before the third electrolysis step. The method for producing the electrode foil for electrolytic capacitors according to any one of claims 1 to 6.

8. A method for producing an electrode foil for electrolytic capacitors according to any one of claims 1 to 7, comprising the steps of: and forming a cathode portion covering at least a portion of the dielectric layer. A method for manufacturing electrolytic capacitors.

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