阅读说明：本技术 电解电容器用电极箔、电解电容器及它们的制造方法 (Electrode foil for electrolytic capacitor, and method for producing same ) 是由 吉村满久 中野翔介 吉田宽 椿真佐美 栗原直美 小川美和 于 2019-10-30 设计创作，主要内容包括：一种电解电容器用电极箔,其具备金属多孔部和与金属多孔部连续的金属芯部,在金属多孔部的厚度方向上将金属多孔部从金属芯部侧起依次三等分为第一区域、第二区域和第三区域时,第一区域的空隙率P1、第二区域的空隙率p2和第三区域的空隙率p3满足P1＜P2＜P3。(An electrode foil for electrolytic capacitors, comprising a metal porous portion and a metal core portion continuous with the metal porous portion, wherein when the metal porous portion is divided into a first region, a second region and a third region in the thickness direction of the metal porous portion in three equal parts in order from the metal core portion 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.)

1. An electrode foil for electrolytic capacitors, comprising a metal porous portion and a metal core portion continuous with the metal porous portion,

when the metal porous portion is equally divided into 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, a porosity P1 of the first region, a porosity P2 of the second region, and a porosity P3 of the third region satisfy P1 < P2 < P3.

2. The electrode foil for electrolytic capacitors as claimed in claim 1, which further satisfies P2/P1 < P3/P2.

3. The electrode foil for electrolytic capacitors as claimed in claim 1 or 2, wherein P1 is 60% or less.

4. The electrode foil for electrolytic capacitors as claimed in any one of claims 1 to 3, wherein P2 is 70% or less.

5. The electrode foil for electrolytic capacitors as claimed in any one of claims 1 to 4, wherein P3 is 80% or less.

6. The electrode foil for electrolytic capacitors as claimed in any one of claims 1 to 5, further comprising a dielectric layer covering at least a part of the surface of the metal portion constituting the metal porous portion.

7. An electrolytic capacitor, comprising:

an electrode foil for electrolytic capacitors according to claim 6; and

a cathode portion covering at least a portion of the dielectric layer.

8. The electrolytic capacitor according to claim 7,

the cathode portion includes a conductive polymer,

the conductive polymer is impregnated into the first region.

9. The electrolytic capacitor according to claim 7 or 8,

the cathode portion contains an electrolyte solution,

the electrolyte solution is impregnated into the first region.

10. A method for manufacturing an electrode foil for an electrolytic capacitor, comprising:

a step of preparing a metal foil, and

a roughening step of forming metal porous portions by roughening the metal foil,

the roughening process includes an etching process of applying a current to the metal foil,

the etching process comprises:

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 of a second 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 of a third current density to the second etched foil in a third treatment solution after the second electrolysis step to obtain a third etched foil;

a first cleaning step of cleaning the first etched foil after the first electrolysis step and before the second electrolysis step; and

a second cleaning step of cleaning the second etched foil after the second electrolysis step and before the third electrolysis step,

the method for manufacturing the electrode foil for the electrolytic capacitor satisfies the relation of first current density > second current density > third current density.

11. The method of manufacturing an electrode foil for electrolytic capacitors as claimed in claim 10, wherein, when the metal porous portion is divided into a first region, a second region and a third region in the order of three equal divisions 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.

12. An electrode foil for an electrolytic capacitor, comprising:

an anode body having a metal porous portion and a metal core portion continuous with the metal porous portion; and

a dielectric layer covering at least a part of a surface of the metal portion constituting the metal porous portion,

the dielectric layer has a first layer of thickness T1, the first layer comprising an oxide of a second metal different from the first metal contained in the metal portion,

when the metal porous portion is equally divided into 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, a porosity P1 of the first region, a porosity P2 of the second region, and a porosity P3 of the third region satisfy P1 < P2 < P3.

13. The electrode foil for electrolytic capacitors as claimed in claim 12, which further satisfies P2/P1 < P3/P2.

14. The electrode foil for electrolytic capacitors as claimed in claim 12 or 13, wherein P1 is 60% or less.

15. The electrode foil for electrolytic capacitors as claimed in any one of claims 12 to 14, wherein P2 is 70% or less.

16. The electrode foil for electrolytic capacitors as claimed in any one of claims 12 to 15, wherein P3 is 80% or less.

17. The electrode foil for electrolytic capacitors as claimed in any one of claims 12 to 16, wherein the first metal contains Al and the second metal contains at least 1 selected from Ta, Nb, Ti, Si, Zr and Hf.

18. The electrode foil for electrolytic capacitors as claimed in any one of claims 12 to 17, wherein a second layer having a thickness T2 comprising an oxide of the first metal is provided between the metal part and the first layer.

19. The electrode foil for electrolytic capacitors as claimed in claim 18, wherein, in the first region, T1 > T2.

20. The electrode foil for electrolytic capacitors as claimed in any one of claims 12 to 19, wherein when the metal porous portion having the dielectric layer is equally divided into a first region, a second region and a third region in order from the metal core portion side, 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.

21. An electrode foil for an electrolytic capacitor, comprising:

an anode body having a metal porous portion and a metal core portion continuous with the metal porous portion; and

a dielectric layer covering at least a part of a surface of the metal portion constituting the metal porous portion,

when the metal porous portion having the dielectric layer is divided into a first region, a second region, and a third region in order from the metal core portion side, 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.

22. An electrolytic capacitor, comprising:

an electrode foil for electrolytic capacitors as claimed in any one of claims 12 to 21; and

a cathode portion covering at least a portion of the dielectric layer.

23. A method for manufacturing an electrode foil for an electrolytic capacitor, comprising:

preparing an anode body having a metal porous portion and a metal core portion continuous with the metal porous portion; and

a step of forming a dielectric layer covering the surface of the metal portion constituting the metal porous portion,

when the metal porous portion is equally divided into a first region, a second region, and a third region in the 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 satisfy P1 < P2 < P3,

the step of forming the dielectric layer includes: a first layer of a thickness T1 is formed by depositing an oxide of a second metal different from the first metal contained in the metal portion on the surface of the metal porous portion by a vapor phase method.

24. The method of manufacturing an electrode foil for an electrolytic capacitor according to claim 23, wherein the step of forming the dielectric layer further comprises the steps of: and a step of forming a second layer having a thickness T2 including an oxide of the first metal between the metal portion and an oxide of the second metal by chemically converting the anode body having the first layer.

25. A method for manufacturing an electrolytic capacitor, comprising:

the step of providing the method for producing an electrode foil for electrolytic capacitors according to claim 10, 11, 23 or 24; and

and forming a cathode portion covering at least a part of the dielectric layer.

Technical Field

The present invention relates to an electrode foil for an electrolytic capacitor, and methods for manufacturing the same.

Background

As the anode body of the electrolytic capacitor, for example, a metal foil containing a valve metal can be used. In order to increase the capacity of the electrolytic capacitor, the main surface of the metal foil is etched to form a metal porous portion. Then, the metal foil is subjected to chemical conversion treatment to form a layer of metal oxide (dielectric) on the surface of the metal skeleton (metal portion) constituting the metal porous portion.

Patent document 1 teaches a method for manufacturing an electrode foil, in which an alternating current is applied to an aqueous solution containing hydrochloric acid as a main component and at least 1 of sulfuric acid, oxalic acid, and phosphoric acid, thereby etching aluminum, the step of the current density of the applied alternating current is such that the etching starts at a maximum value and gradually decreases from the maximum value, and the current density is set to 0 in a middle stage before the current density reaches 0.

On the other hand, patent document 2 teaches forming a dielectric layer by an atomic layer deposition method.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2005-203529

Patent document 2: international publication No. 2017/26247 pamphlet

Disclosure of Invention

Problems to be solved by the invention

Patent document 1 aims to effectively increase the surface area of an aluminum foil and to improve the electrostatic capacity of an electrode foil for an aluminum electrolytic capacitor. However, the above method has a limit in increasing the surface area and increasing the capacitance.

In addition, when the dielectric layer is formed by the atomic layer deposition method, for example, a raw material gas of the dielectric layer may not reach a deep portion of the etching pit, and it may be difficult to form the dielectric layer in a deep portion of the metal porous portion. However, when the porosity of the surface layer of the etching pit, particularly the region distant from the surface 1/3, is smaller than the porosity of the deeper part thereof, the raw material gas is very difficult to reach the deeper part, and a sufficient dielectric layer may not be formed in the deeper part.

Means for solving the problems

One aspect of the present invention relates to an electrode foil for an electrolytic capacitor, including a metal porous portion and a metal core portion continuous to the metal porous portion, wherein when the metal porous portion is divided into a first region, a second region, and a third region in the thickness direction of the metal porous portion in three equal parts in order from the metal core portion side, a porosity P1 of the first region, a porosity P2 of the second region, and a porosity P3 of the third region satisfy P1 < P2 < P3.

Another aspect of the present invention relates to a method for manufacturing an electrode foil for an electrolytic capacitor, including: preparing a metal foil; and a roughening step of roughening the metal foil to form a metal porous portion, the roughening step including an etching step of applying a current to the metal foil, the etching step including: 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 of a second 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 of a third current density to the second etched foil in a third treatment solution after the second electrolysis step to obtain a third etched foil; a first cleaning step of cleaning the first etched foil after the first electrolysis step and before the second electrolysis step; and a second cleaning step of cleaning the second etched foil after the second electrolysis step and before the third electrolysis step, wherein the method for manufacturing an electrode foil for an electrolytic capacitor satisfies a relationship of first current density > second current density > third current density.

Still another aspect of the present invention relates to an electrode foil for an electrolytic capacitor, including: an anode body having a metal porous portion and a metal core portion continuous with the metal porous portion; and a dielectric layer covering a surface of a metal skeleton constituting the metal porous portion, the dielectric layer having a first layer having a thickness T1, the first layer including an oxide of a second metal different from the first metal contained in the metal portion, and when the metal porous portion is divided into a first region, a second region, and a third region in the order of three times in the thickness direction of the metal porous portion from the metal core portion side, a porosity P1 of the first region, a porosity P2 of the second region, and a porosity P3 of the third region satisfy P1 < P2 < P3.

Still another aspect of the present invention relates to an electrode foil for an electrolytic capacitor, including: an anode body having a metal porous portion and a metal core portion continuous with the metal porous portion; and a dielectric layer covering at least a part of a surface of the metal portion constituting the metal porous portion, wherein when the metal porous portion having the dielectric layer is divided into a first region, a second region, and a third region in the thickness direction of the metal porous portion in three parts in 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 satisfy Q1 < Q2 < Q3.

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

Another aspect of the present invention relates to an electrolytic capacitor including: an electrode foil for the electrolytic capacitor; and a cathode portion covering at least a part of the dielectric layer.

Another aspect of the present invention relates to a method for manufacturing an electrolytic capacitor, including: a step of providing the method for manufacturing an electrode foil for an electrolytic capacitor; and forming a cathode portion covering at least a part of the dielectric layer.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, when the dielectric layer is formed, a favorable dielectric layer can be formed to the deep portion of the metal porous portion, and thus a high-performance electrode foil for an electrolytic capacitor can be obtained.

While the novel features of the present invention are set forth in the appended claims, the present invention is directed to both the structure and the content thereof, and other objects and features thereof will be better understood from the following detailed description taken in conjunction with the accompanying drawings.

Drawings

Fig. 1 is a schematic cross-sectional view of an anode body according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view showing a part of a porous portion having a dielectric layer in an enlarged manner according to an embodiment of the present invention.

Fig. 3 is a schematic cross-sectional view showing a part of a porous portion having a dielectric layer in another embodiment of the present invention in an enlarged manner.

FIG. 4 is a schematic cross-sectional view of an electrolytic capacitor.

Fig. 5 is a perspective view schematically showing a structure of a wound body provided in an electrolytic capacitor.

Fig. 6 is an explanatory view schematically showing a part of an etching apparatus used in the roughening step according to one embodiment of the present invention.

Fig. 7 is a graph showing the relationship between the distance from the surface of the anode body and the porosity (Al remaining percentage) in the porous metal portion in example 1A of the present invention.

Fig. 8 is a graph showing the relationship between the distance from the surface of the anode body and the porosity (Al remaining percentage) in the porous metal portion in example 2 of the present invention.

Fig. 9 is a graph showing the relationship between the distance from the surface of the anode body and the porosity (Al remaining percentage) in the porous metal portion of comparative example 2 of the present invention.

Fig. 10 is a diagram showing a change in current density in the etching step according to the embodiment of the present invention.

Fig. 11 is a diagram showing a change in current density in an etching step according to another embodiment of the present invention.

Fig. 12 is a diagram showing a change in current density in an etching step according to still another embodiment of the present invention.

Fig. 13 is a diagram showing a change in current density in an etching step according to still another embodiment of the present invention.

Detailed Description

Hereinafter, the electrode foil for electrolytic capacitors before the dielectric layer is formed is referred to as "first electrode foil" or "anode body", and the electrode foil for electrolytic capacitors having the dielectric layer is referred to as "second electrode foil". In the following description, the first etched foil, the second etched foil, the third etched foil, and the metal foil may be simply referred to as metal foils without particularly distinguishing them from each other.

The electrode foil for electrolytic capacitors (first electrode foil) of the present 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 product of the metal core portion and the metal porous portion. The first electrode foil may be used as an anode body of an electrolytic capacitor.

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

The first electrode foil (or anode body) is obtained by roughening a metal foil formed of a first metal contained in a metal portion constituting the porous portion by etching or the like, for example. The metal porous portion is a surface side (outer side) portion of the metal foil that is made porous by etching, and the remaining portion that is an inner portion of the metal foil is a metal core portion.

When the metal porous portion is equally divided into a first region, a second region, and a third region in the order from the metal core portion side in the thickness direction of the metal porous portion of the first electrode 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.

When the metal porous portion of the second electrode foil is divided into a first region, a second region, and a third region in the order of three equal divisions 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.

The thickness of the dielectric layer in the second electrode foil varies depending on the rated voltage of the electrolytic capacitor, and has a thickness of 4nm to 300nm, and is formed relatively thin along the shape of the surface of the metal portion. Therefore, the void ratios Q1 to Q3 in the first to third regions of the second electrode foil on which the dielectric layer is formed are smaller than those in the first electrode foil before the dielectric layer is formed, by the thickness of the dielectric layer, P1 to P3.

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 divided into the first region, the second region, and the third region in the order of three in the thickness direction of the metal porous portion of the second electrode foil from the metal core portion side, 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.

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

In the first electrode foil, the closer to the surface side of the first electrode foil, the higher the porosity of the metal porous portion. Therefore, a favorable dielectric layer can be formed to the deep part of the metal porous portion, and a high-performance electrode foil for an electrolytic capacitor can be obtained. In an electrolytic capacitor using an electrolytic solution, a solid electrolyte, or the like as a cathode material, the permeability of the electrolytic solution into the metal porous portion and the filling property of the solid electrolyte (for example, a conductive polymer) become good, the capacity realization rate of the electrolytic capacitor also becomes high, and the electrolytic capacitor is advantageous for the reduction of ESR and the suppression of leakage current.

Next, the electrolytic capacitor of the present embodiment includes a second electrode foil and a cathode portion covering at least a part of the dielectric layer.

In the second electrode foil having the dielectric layer, the porosity of the metal porous portion having the dielectric layer is increased as the surface side of the second electrode foil is closer to the second electrode foil. Therefore, in an electrolytic capacitor using an electrolytic solution, a solid electrolyte, or the like as a cathode material, the permeability of the electrolytic solution into the metal porous portion and the filling property of the solid electrolyte become good. Therefore, the electrolytic capacitor has a high capacity realization rate, and is advantageous for reducing ESR and suppressing leakage current.

The cathode portion may contain a conductive polymer as a solid electrolyte. When P1 < P2 < P3 or Q1 < Q2 < Q3 is satisfied, the conductive polymer can be easily impregnated into the first region.

The cathode portion may contain an electrolyte. When P1 < P2 < P3 or Q1 < Q2 < Q3 is satisfied, the first region is easily impregnated with the electrolytic solution.

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

The metal porous portion has a pit or a pore surrounded by a metal portion containing the first metal. The dielectric layer is provided so as to cover at least a part of the surface of the metal portion surrounding the recess or the pore.

The dielectric layer may include an oxide of the first metal contained in the metal portion. In addition, the dielectric layer may have a first layer of thickness T1 that includes an oxide of a second metal different from the first metal contained in the metal portion. In the case where the dielectric layer contains an oxide of a second metal different from the first metal, the second metal having a high dielectric constant can be selected without being limited to the first metal, for example. Therefore, the capacity of the electrolytic capacitor can be easily increased. Further, since the selection range of the second metal is expanded, various properties can be imparted to the dielectric layer without being restricted by the first metal.

Here, when the metal porous portion of the first metal foil is divided into a first region, a second region, and a third region in the order of trisection 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. That is, the closer to the surface side of the anode body, the higher the porosity of the metal porous portion. Therefore, when the dielectric layer is formed by a vapor phase method such as an atomic layer deposition method, the raw material gas of the dielectric layer is easily diffused to the deep portion of the metal porous portion, and a favorable dielectric layer can be formed to the deep portion of the metal porous portion. For example, even when the oxide of the second metal is preferentially deposited on the surface layer portion (i.e., the third region) of the metal porous portion in the initial stage of the formation of the dielectric layer, if P1 < P2 < P3 is satisfied, the porosity P3 of the surface layer portion is large, and therefore the entrance of the pit is not easily blocked by the dielectric layer. Therefore, the dielectric layer can be formed satisfactorily. This realizes an increase in capacity of the electrode foil, and also improves the permeability of the electrolytic solution into the metal porous portion and the filling property of the solid electrolyte (for example, a conductive polymer), and the capacity realization rate of the electrolytic capacitor is increased, which is also advantageous for reducing ESR and suppressing leakage current.

In the vapor phase method, the source gas is consumed first in the surface layer portion (third region) of the pit, and therefore the amount of the source gas reaching the deepest portion (first region) is reduced. On the other hand, when the porosity P3 of the third region is larger than the porosities P1 and P2 in the deeper portion, the raw material gas can easily enter the etching pits. When the porosity P1 of the deepest portion (first region) is small, the surface area of the deepest portion is also small, and therefore the amount of the raw material gas required to form the dielectric layer can be small. Therefore, a favorable dielectric layer can be formed efficiently up to the deepest portion of the etching pits. For example, even a sponge-like etching pit having a specific surface area of 50 times or more can be easily formed up to the deepest portion of the dielectric layer.

In the deep portion (for example, the first region) of the metal porous portion, the porosity is relatively small, and the pit diameter (or the pore diameter) of the etching pit is relatively small. In other words, a large number of fine pores are present in the deep part of the metal porous part, and a considerable surface area is secured. Therefore, even when the surface area in the vicinity of the surface of the anode body (for example, the third region) is relatively small, it is easy to secure a sufficiently large capacitance.

The porosity of the metal porous portion may be measured by the following method.

First, the anode body (first electrode foil) was cut so as to obtain a cross section in the thickness direction of the metal core portion and the metal porous portion of the anode body, and an electron micrograph of the cross section was taken. Next, the image of the cross section is binarized to distinguish between metal portions and voids. Next, the image was divided into a plurality of pieces (for example, 0.1 μm intervals) along a path parallel to the thickness direction of the anode body from the surface side of the anode body toward the metal core portion, and the average value of the void ratios of the divided pieces was calculated as the void ratio. Using the calculated values, a graph showing the relationship between the distance from the surface of the anode body and the porosity can be drawn (see fig. 7 to 9). In the first region, the second region, and the third region, the void ratios at a plurality of arbitrary positions are extracted at equal intervals, and the average value of the plurality of void ratios may be calculated as the void ratio P1, the void ratio P2, and the void ratio P3. The porosity Q1, the porosity Q2, and the porosity Q3 of the second electrode foil having the dielectric layer were also measured in the same manner.

P2 and P3 can satisfy P2X 1.1. ltoreq.P 3, and also satisfy P2X 1.2. ltoreq.P 3. In addition, P1 and P2 may satisfy P1X 1.05. ltoreq.P 2, and may also satisfy P1X 1.1. ltoreq.P 2.

Q2 and Q3 may be different depending on the thickness of the dielectric layer or the rated voltage of the electrolytic capacitor, and may satisfy, for example, Q2X 1.1. ltoreq. Q3 or Q2X 1.2. ltoreq. Q3. In addition, Q1 and Q2 may satisfy Q1X 1.05. ltoreq.Q 2, and may also satisfy Q1X 1.1. ltoreq.Q 2.

Fig. 1 shows a schematic cross-sectional view of an anode body (first electrode foil) according to an embodiment of the present invention. Anode element 110 is an integral part of metal core portion 111 and metal porous portion 112, and the thickness of metal porous portion 112 is represented by T. As shown in the illustrated example, the metal porous portion 112 may be trisected in order from the metal core portion 111 side into a first region R1, a second region R2, and a third region R3 of respective thicknesses T/3. When calculating the porosity P1 to P3, the sectional images of the respective regions are divided into a plurality of sections (for example, 0.1 μm intervals) along a path parallel to the thickness direction of the anode body from the surface side of the anode body toward the metal core portion, and the average value of the porosities of the respective sections after the division is calculated as the porosity P1 to P3, as described above. The schematic cross-sectional view of the second electrode foil having the dielectric layer is also the same as that in fig. 1, and the procedure for calculating the void ratios Q1 to Q3 is also the same.

The void ratios 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. Likewise, in the second electrode foil having the dielectric layer, Q1/Q2 < Q3/Q2 can also be satisfied. In this case, the porosity is not increased from the metal core portion to the surface of the anode body at a constant increase rate, but the increase rate of the porosity is increased in the surface side of the anode body as compared with the deep portion. Therefore, the first region R1 has an enhanced effect of promoting diffusion of the raw material gas of the dielectric layer, while a surface area capable of sufficiently increasing the capacitance is secured in the third region R3.

P1-P3 can satisfy P2/P1 < P3/P2, can satisfy 1.05 XP 2/P1 < P3/P2, and can satisfy 1.3 XP 2/P1 < P3/P2. Similarly, Q1 to Q3 may satisfy Q2/Q1 < Q3/Q2, 1.05 XQ 2/Q1 < Q3/Q2, or 1.3 XQ 2/Q1 < Q3/Q2.

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

When P1 to P3 are in the above range, when the dielectric layer is formed in a liquid phase such as chemical conversion (anodic oxidation), the chemical conversion liquid easily penetrates into the deep portion of the metal porous portion. In addition, when the dielectric layer is formed by a vapor phase method such as an atomic layer deposition method, the diffusion of the raw material gas of the dielectric layer into the deep portion of the metal porous portion is further improved. However, from the viewpoint of ensuring sufficient strength of the first electrode foil and the second electrode foil, P3 or Q3 is preferably 80% or less, P2 or Q2 is preferably 70% or less, and P1 or Q1 is preferably 60% or less.

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 from the range of 10 μm to 160 μm, for example. 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 as an average value of thicknesses at arbitrary 10 points of the metal porous portion 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, and taking an electron micrograph of the cross section.

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

The withstand voltage of the electrolytic capacitor is not particularly limited, and may be, for example, a relatively small withstand voltage of 1V or more and less than 4V, or a relatively large withstand voltage of 4V or more, 15V or more, or 100V or more. In the case of obtaining an electrolytic capacitor having a withstand voltage of 4V or more, the thickness of the dielectric layer is preferably 4nm or more. In the case of obtaining an electrolytic capacitor having a withstand voltage of 15V or more, the thickness of the dielectric layer is preferably 21nm or more.

More specifically, for example, in the case of obtaining an electrolytic capacitor having a large withstand voltage of 60V or more, the peak of the pore diameter of the metal porous portion may be, for example, 50 to 300nm, 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.

In the case of an electrolytic capacitor having a withstand voltage of, for example, 100V or more, the etching pit may have a substantially columnar, conical or truncated conical shape extending from the surface side of the anode body to the metal core side in a tunnel shape, with a large pit diameter on the surface side of the anode body and a small pit diameter on the metal core side.

In the case of obtaining an electrolytic capacitor having a low withstand voltage, for example, a withstand voltage of 10V or less, the peak of the pore diameter of the metal porous portion may be, for example, 20 to 200nm, 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.

The first metal may comprise Al, for example. At this time, the second metal may contain, for example, at least 1 selected from Ta, Nb, Ti, Si, Zr, and Hf.

In the dielectric layer, an oxide of the first metal may be provided between the metal portion containing the first metal and the oxide of the second metal. Hereinafter, a portion of the dielectric layer including an oxide of the second metal is also referred to as a first layer, and a portion including an oxide of the first metal is also referred to as a second layer.

For example, an oxide (first layer) containing the second metal may be formed on the natural oxide film of the first metal formed on the surface of the metal portion. In addition, after the first layer is formed on the natural oxide film, the metal portion may be subjected to anodic chemical conversion to form an oxide of the first metal (second layer) in an arbitrary thickness between the metal portion and the oxide containing the second metal (first layer).

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 in the case where the first layer has a defect, the defect can be repaired. Therefore, the performance of the dielectric layer is further improved.

The thickness T1 of the first layer and the thickness T2 of the second layer may satisfy T1. gtoreq.2XT 2, or T1. gtoreq.3XT 2 at least in the third region. By relatively increasing the thickness of the first layer in this way, for example, in the case of selecting a second metal having a high dielectric constant, the capacity of the electrolytic capacitor can be significantly improved. In addition, according to the configuration of the metal porous portion, the raw material gas can easily reach a deeper portion, and therefore, T1 > T2 may be set in the first region.

The thicknesses of the first layer and the second layer may 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 micrograph of the cross section, and averaging the thicknesses of any 10 points of the first layer or the second layer.

The first layer preferably comprises at least 1 additional element selected from C, P, B and N. The additive elements are preferably distributed at least to a depth of 0.05 × T1 (thickness of the first layer) from the surface of the first layer. This can provide the dielectric layer with sufficient acid resistance, and can sufficiently reduce leakage current. The first layer is formed of a dielectric comprising an oxide of a second metal different from the first metal. The second metal may form a dielectric having a high dielectric constant, but defects in the dielectric layer, which may cause an increase in leakage current, are likely to occur during the formation of the second metal. By adding an element into the defect to impart acid resistance to the dielectric layer, increase in leakage current can be suppressed. In the electrolytic capacitor of the present embodiment, the above-described elements can be efficiently added to the dielectric layer.

Hereinafter, a method for manufacturing the first electrode foil will be further described.

The first electrode foil is manufactured, for example, by the following method: the method comprises the following steps: preparing a metal foil; and a roughening step of roughening the metal foil to form metal porous portions. The roughening process includes an etching process 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. Meanwhile, a metal core portion integrated with the metal porous portion is formed at an inner portion of the metal foil. The etching may be performed by, for example, direct current etching based on direct current or alternating current etching based on alternating current.

Regarding the conditions for etching, when the metal porous portion is divided into the first region, the second region, and the third region in the order of trisection from the metal core portion side in the thickness direction thereof, the porosity P1 of the first region, the porosity P2 of the second region, and the porosity P3 of the third region are set to satisfy P1 < P2 < P3. Specifically, for example, in an etching solution containing hydrochloric acid as a main component, the porosity P1, P2, and P3 can be arbitrarily set by applying a predetermined alternating current to an aluminum foil or an aluminum alloy foil, for example.

The roughening process may include an etching process 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 so that the current density gradually and evenly decreases. The current density may be varied continuously or in stages. As the etching process proceeds, a metal porous portion is gradually formed on the metal foil.

Here, "the current density gradually decreases on average" means that when the relationship between the time when the current is applied to the metal foil and the current density is expressed by an approximate curve or an approximate straight line, the approximate curve or the approximate straight line has a negative slope (the current density is gradually decreased on average)Is negative). The approximation formula corresponding to the approximation curve or the approximation straight line may be a linear function or a function having a quadratic or higher order. Wherein, when the correlation coefficient of the approximate expression is R, the coefficient R is determined²Preferably 0.75 or more and 0.99 or less, more preferably 0.82 or more and 0.99 or less, or 0.85 or more and 0.99 or less. In addition, the approximate curve is preferably a curve that is convex downward.

After the first electrode foil is obtained, when the chemical conversion voltage at the time of forming the dielectric layer on the first electrode foil is relatively large (for example, when the chemical conversion voltage is 60V or more (further, 100V or more)), it is preferable that the current density at the time of obtaining the first metal foil is gradually decreased as a linear function. In this case, large pores can be formed in the metal porous portion. On the other hand, when the chemical conversion voltage at the time of forming the dielectric layer on the first electrode foil is relatively small (for example, when the chemical conversion voltage is less than 60V (further, 10V or less)), the current density at the time of obtaining the first metal foil preferably decreases gradually as a quadratic function or along a curve that is convex downward. In this case, relatively small pores can be formed in the metal porous portion.

In the etching step, it is preferable that the current is intermittently applied to the metal foil. Specifically, in the etching step, a period in which current is applied to the metal foil (hereinafter, also referred to as an electrolysis period) and a period in which current is not applied (hereinafter, also referred to as an electroless period) are preferably repeated 2 times or more. The minute current (for example, 1% or less or 0.001A/cm of the first current density described later)²Below) the period of flow through the metal foil may be included in an electroless period in which no current is applied. For example, in the case of a roll-to-roll etching process using a production line having a plurality of etching baths, a roll for conveying a metal foil is provided below the etching bath. The current flowing in the metal foil decreases during and before and after contact with the roller. This period may be included in the electroless period.

During the electrolysis, ion species of the metal element constituting the metal foil tend to be concentrated in the pits or pores formed in the metal foil. In order to perform effective etching, it is effective to temporarily substantially stop the application of current and promote the diffusion of ion species, as compared with the case where ion species of a metal element are generated by stably applying current to a metal foil. It is considered that by intermittently providing the electroless period, diffusion of the ion species of the metal element is promoted, and the concentration of the ion species in the pit or the pore is reduced, whereby more effective etching can be performed.

When a period from the start to the end of the etching step (when the last electrolysis period ends) is T0, a total electrolysis period in which current is applied to the metal foil is T1, and a total non-electrolysis period in which current is not applied to the metal foil is T2, T0 is T1+ T2. The total electrolysis period T1 may be, for example, 10 to 70% of T0, or 30 to 70%. The electroless plating solution can also be used for cleaning and the like of the metal foil. That is, there may be a cleaning step of cleaning the metal foil during electroless plating. During the cleaning period, the metal foil may be introduced into the cleaning liquid in the cleaning tank, or may be cleaned by spraying or running water of the cleaning liquid.

The period T0 from the start to the end of the etching process and the total electrolysis period T1 during which current is applied to the metal foil are not particularly limited, and may be appropriately set according to the thickness of the first electrode foil, the desired depth of the etching pits, and the like. The period T0 may be, for example, 16 minutes to 70 minutes. The electrolysis period T1 may be, for example, 7 minutes to 50 minutes.

The arrangement scheme during electroless plating is not particularly limited. For example, the metal foil may be impregnated with any treatment liquid (etching liquid, cleaning liquid, etc.) or may not be impregnated with the treatment liquid during the electroless plating. For example, when an opposing region between the metal foil and the anode electrode is intermittently provided in one etching chamber and etching is performed while the metal foil and the anode electrode are opposing each other, a period in which the metal foil and the anode electrode do not oppose each other is an electroless period. In this case, the metal foil is also present in the processing liquid in at least a part during the electroless plating.

On the other hand, when the etching step is performed by a roll-to-roll method using a production line having a plurality of etching chambers, an etching chamber external path for conveying a metal foil of a predetermined length can be provided between a pair of adjacent etching chambers. In this case, the period during which the metal foil is conveyed through the etching bath external path is the electroless period, and at least a part of the metal foil during the electroless period passes through the external path without the processing liquid.

The treatment liquid includes various treatment liquids for various purposes, and the main treatment liquids include an etching liquid for applying a current to the metal foil for roughening, a cleaning liquid for cleaning the metal foil, and the like. Among these, in the case of cleaning the metal foil, the effect of promoting diffusion of ion species of the metal element dissolved by etching by electrolysis is large.

As the etching liquid, for example, a hydrochloric acid aqueous solution is preferable, and an aqueous solution containing sulfuric acid, nitric acid, phosphoric acid, oxalic acid, and the like in addition to hydrochloric acid may be used. The aqueous solution may contain various additives such as a chelating agent. The concentration of the hydrochloric acid in the etching solution, the concentration of the other acids, and the temperature 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 to 10 mol/L. The concentration of the other acid 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 in the electrolytic etching step is not particularly limited, and is, for example, 15 ℃ to 60 ℃.

The cleaning liquid may be water (ion-exchanged water), but when the main purpose is cleaning, it is preferable to perform cleaning 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 for cleaning the metal foil, impurities are easily removed and ion species are easily diffused. In this case, the cleaning step may be performed for 10 seconds or more, 20 seconds or more, and further 60 seconds or more. By protecting the surface of the metal foil, etching of the deep portion of the metal foil is easily and efficiently performed.

The etching process may include, for example: a first electrolysis step of immersing the metal foil in a first treatment solution and applying a current having a first current density to the metal foil; a second electrolysis step of immersing the metal foil (first etched foil) in a second treatment solution after the first electrolysis step, and applying a current having a second current density to the metal foil; and a third step of immersing the metal foil (second etched foil) in a third treatment solution after the second electrolysis step, and applying a current having a third current density to the metal foil. At this time, the relationship of the first current density > the second current density > the third current density can be satisfied. However, the first current density, the second current density and the third current density refer to average current densities during electrolysis in 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 in each electrolysis period and each electrolysis period.

In a period T0 from the start to the end of the etching process, the first electrolysis step may be 0.2 XT 0-0.4 XT 0, the second electrolysis step may be 0.2 XT 0-0.4 XT 0, and the third electrolysis step may be 0.2 XT 0-0.4 XT 0. The total of the first electrolysis step, the second electrolysis step and the third electrolysis step may be 0.7 × T0 or more. In each electrolysis step, the electrolysis period may be intermittent, and may include an electroless period.

A first cleaning step of cleaning the metal foil first etched foil) may be performed after the first electrolysis step and before the second electrolysis step. In addition, after the second electrolysis step and before the third electrolysis step, a second cleaning step of cleaning the metal foil (second etched foil) may be further performed. Here, the first electrolysis step and the second electrolysis step are transferred to the first cleaning step or the second cleaning step, respectively, during the non-electrolysis period after the electrolysis period ends. As described above, the first electrolysis step and the second electrolysis step may further include an electroless period within the process. The electroless process may also include additional cleaning steps beyond the first cleaning step and the second cleaning step. However, the first cleaning step and the second cleaning step are different steps from the first electrolysis step to the third electrolysis step.

The treatment liquid (i.e., the cleaning liquid) used in the first cleaning step and the second cleaning step may be a dilute aqueous acid solution as described above, or may be a solution containing hydrochloric acid, phosphoric acid, dilute sulfuric acid, oxalic acid, or the like.

The first treatment liquid contains, for example, hydrochloric acid as a main component, and may contain aluminum, sulfuric acid, phosphoric acid and/or aluminumNitric acid. The first current density is, for example, 0.20 to 0.25A/cm²In other words, the total time of the electrolysis period in the first electrolysis step may be, for example, 1 to 10 minutes, and the total time of the 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 etched foil) may be taken out from the first treatment liquid and washed with a washing liquid.

The second treatment liquid contains, for example, hydrochloric acid as a main component, and may contain aluminum, sulfuric acid, phosphoric acid, and/or nitric acid. The second current density is, for example, 0.19 to 0.24A/cm²In other words, the total time of the electrolysis period in the second electrolysis step may be, for example, 1 to 10 minutes, and the total time of the 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 etched foil) may be taken out from the first treatment liquid and washed with a washing liquid.

The third treatment liquid contains, for example, hydrochloric acid as a main component, and may contain aluminum, sulfuric acid, phosphoric acid, and/or nitric acid. The third current density is, for example, 0.18 to 0.23A/cm²In other words, the total time of the electrolysis period in the third electrolysis step may be, for example, 1 to 10 minutes, and the total time of the non-electrolysis period may be, for example, 1 to 10 minutes. After the third electrolysis step, the metal foil (third etched foil or first electrode foil) may be taken out from the third treatment liquid and further washed with a washing liquid.

In the above examples, the concentrations of the hydrochloric acid in the main components of the first, second, and third treatment liquids may be the same or different.

According to the method described above, when the metal porous portion is divided into the first region, the second region, and the third region in the order of trisection from the metal core portion side in the thickness direction of the metal porous portion, the 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 can be easily obtained.

Next, a method for manufacturing the second electrode foil and the electrolytic capacitor will be further described.

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

Step (i)

The step (i) of preparing the anode body (first electrode foil) is, for example, a step of etching a metal foil containing a first metal to roughen the metal foil, 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, the chemical conversion solution easily penetrates into the deep portion of the metal porous portion when the dielectric layer is formed by chemical conversion (anodic oxidation), and the raw gas or the like easily penetrates into the deep portion of the metal porous portion when the dielectric layer is formed by a gas phase method. Therefore, a favorable dielectric layer can be formed to the deep portion of the metal porous portion.

The type of the first metal is not particularly limited, and a valve metal such as aluminum (Al), tantalum (Ta), or niobium (Nb), or an alloy containing a valve metal can be used in order to facilitate formation of the dielectric layer or the second layer by chemical conversion. The thickness of the metal foil is not particularly limited, and is, for example, 15 μm or more and 300 μm or less.

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, a voltage is applied to the first electrode foil in a state where the first electrode foil is immersed in a chemical conversion solution such as an ammonium adipate solution, an ammonium phosphate solution, or an ammonium borate solution, thereby obtaining a second electrode foil in which a dielectric layer is formed on the surface of the metal portion.

The step (ii) of forming the dielectric layer may be a step of 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 the surface of the metal portion by a vapor phase method, for example. Thereby, the second electrode foil having the dielectric layer formed on the surface of the metal portion was obtained.

Examples of the second metal include Al, Ta, Nb, silicon (Si), titanium (Ti), zirconium (Zr), hafnium (Hf), and the like. These may be used alone or in combination of 2 or more. That is, the first layer may contain Al₂O₃、Ta₂O₅、Nb₂O₅、SiO₂、TiO₂、ZrO₂、HfO₂Etc. or 2 or more. When the first layer contains 2 or more oxides of the second metal, the 2 or more oxides may be present in a mixture or may be arranged in a layered form. From the viewpoint of increasing the capacity of the electrolytic capacitor, the oxide of the second metal preferably has a higher relative permittivity than the oxide of the first metal. In addition, from the viewpoint of improving the withstand voltage of the electrolytic capacitor, the second metal is preferably Ta, Ti, Si, or the like.

Examples of the vapor phase method include a vacuum evaporation method, a chemical evaporation method, a mist evaporation method, a sputtering method, a pulse laser Deposition method, and an Atomic Layer Deposition method (ALD method). Among them, the ALD method is excellent in that a dense dielectric layer can be formed to a deep portion of the metal porous portion. The thickness of the first layer is not particularly limited, and may be, for example, 0.5nm or more and 200nm or less, or 5nm or more and 200nm or less.

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

Metal porous portion 112 has a plurality 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 represented by T1.

The ALD method is a film formation method in which a raw material gas containing a second metal and an oxidizing agent are alternately supplied to a reaction chamber in which an object is placed, thereby forming a dielectric layer (first layer) containing an oxide of the second metal on the surface of the object. In the ALD method, since Self-stopping (Self-limiting) is performed, the second metal is deposited on the surface of the object in units of atomic layers. Therefore, the thickness of the first layer is controlled by setting the number of cycles of 1 cycle to supply of the raw material gas → exhaust (purge) of the raw material gas → supply of the oxidizing agent → exhaust (purge) of the oxidizing agent. That is, the ALD method can easily control the thickness of the formed dielectric layer.

The ALD method can be performed at a temperature of 100 to 400 ℃ as compared with CVD performed at a temperature of 400 to 900 ℃. That is, the ALD method is excellent in that thermal damage to the metal foil can be suppressed.

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

The second metal is supplied to the reaction chamber in the form of a gas containing a precursor (precursor) of the second metal. The precursor is, for example, an organometallic compound containing a second metal, and thus the second metal is easily chemisorbed to the target. As the precursor, various organometallic compounds conventionally used in the ALD method can be used.

Examples of the precursor containing Al include trimethylaluminum ((CH)₃)₃Al), and the like. Examples of the Zr-containing precursor include bis (. eta.5-cyclopentadienyl) methoxymethylzirconium (Zr (CH)₃C₅H₄)₂CH₃OCH₃) Tetrakis (dimethylamido) zirconium (IV) ([ (CH)₃)₂N]₄Zr), tetrakis (methylethylamido) zirconium (IV) (Zr (NCH)₃C₂H₅)₄) Zirconium (IV) tert-butoxide (Zr [ OC (CH)₃)₃]₄) And the like. Examples of the Nb-containing precursor include niobium (V) ethoxide (Nb (OCH)₂CH₃)₅Tris (diethylamido) (tert-butyl)Imide group) niobium (V) (C)₁₆H₃₉N₄Nb), and the like.

Examples of the precursor containing Ta include (tert-butylimidoyl) tris (methylethylamino) tantalum (V) (C)₁₃H₃₃N₄Ta, TBTEMT), tantalum (V) pentaethanolate (Ta (OC)₂H₅)₅) And (tert-butylimidoyl) tris (diethylamino) tantalum (V) ((CH)₃)₃CNTa(N(C₂H₅)₂)₃) Pentakis (dimethylamino) tantalum (V) (Ta (N (CH))₃)₂)₅) And the like.

Examples of the Nb-containing precursor include niobium (V) ethoxide (Nb (OCH)₂CH₃)₅Tris (diethylamido) (tert-butylimido) niobium (V) (C)₁₆H₃₉N₄Nb), and the like.

Examples of the precursor containing Si include N-sec-butyl (trimethylsilyl) amine (C)₇H₁₉NSi), 1, 3-diethyl-1, 1, 3, 3-tetramethyldisilazane (C)₈H₂₃NSi₂) 2, 4, 6, 8, 10-pentamethylcyclopentasiloxane ((CH)₃SiHO)₅) Pentamethyldisilane ((CH)₃)₃SiSi(CH₃)₂H) Tris (isopropoxy) silanol ([ (H)₃C)₂CHO]₃SiOH), chloropentane methyldisilane ((CH)₃)₃SiSi(CH₃)₂Cl), dichlorosilane (SiH)₂Cl₂) Tris (dimethylamino) silane (Si [ N (CH) ]₃)₂]₄) Tetraethyl silane (Si (C)₂H₅)₄) Tetramethylsilane (Si (CH)₃)₄) Tetraethoxysilane (Si (OC)₂H₅)₄) Dodecamethylcyclohexasilane ((Si (CH))₃)₂)₆) Silicon tetrachloride (SiCl)₄) Silicon tetrabromide (SiBr)₄) And the like.

Examples of the precursor containing Ti include bis (tert-butylcyclopentadienyl) titanium (IV) dichloride (C)₁₈H₂₆C₁₂Ti), tetrakis (dimethylamino) titanium (IV) ([ (CH)₃)₂N]₄TiTDMAT), tetrakis (diethylamino) titanium (IV) ([ (C)₂H₅)₂N]₄Ti, tetra (methylethylamino) titanium (IV) (Ti [ N (C) ]₂H₅)(CH₃)]₄) And (diisopropoxy-bis (2, 2, 6, 6-tetramethyl-3, 5-heptanedionato titanium (IV) (Ti [ OCC (CH))₃)₃CHCOC(CH₃)₃]₂(OC₃H₇)₂) Titanium tetrachloride (TiCl)₄) Titanium (IV) isopropoxide (Ti [ OCH (CH) ]₃)₂]₄) Titanium (IV) ethoxide (Ti [ O (C) ]₂H₅)]₄) And the like.

Examples of the Zr-containing precursor include bis (methyl-. eta.)⁵Cyclopentadienyl) methoxymethylzirconium (Zr (CH)₃C₅H₄)₂CH₃OCH₃) Tetrakis (dimethylamido) zirconium (IV) ([ (CH)₃)₂N]₄Zr), tetrakis (methylethylamido) zirconium (IV) (Zr (NCH)₃C₂H₅)₄) Zirconium (IV) tert-butoxide (Zr [ OC (CH)₃)₃]₄) And the like.

As the Hf-containing precursor, for example, hafnium tetrachloride (HfCl) is exemplified₄) Tetra (dimethylamino) hafnium (Hf [ N (CH) ]₃)₂]₄) Tetra (methylethylamino) hafnium (Hf [ N (C) ]₂H₅)(CH₃)]₄) Tetra (diethylamino) hafnium (Hf [ N (C) ]₂H₅)₂]₄) Hafnium tert-butoxide (Hf [ OC (CH))₃)₃]₄) And the like.

The method of manufacturing the second electrode foil may further include a step of chemically converting (anodizing) the anode body formed by depositing the oxide of the second metal (i.e., the anode body having the first layer). Thereby, the second layer including the oxide of the first metal and having the thickness T2 may be formed between the metal portion including 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 at the time of chemical conversion.

As described above, when the porosity P1 of the deepest portion (first region) of the etching pit is small, a favorable dielectric layer can be formed efficiently up to the deepest portion. In addition, when the porosity P3 of the surface layer portion (third region) of the etching pit is large, the raw material gas can easily enter, and the raw material gas can easily reach the deepest portion. As a result, even in the first region, the ratio of the first layer to the second layer can be easily controlled to be high, and a dielectric layer having a high dielectric constant can be formed over the entire metal porous portion.

In the case where at least 1 additive element selected from C, P, B and N is contained in the first layer, for example, the anode body having the dielectric layer may be immersed in an aqueous solution containing the additive element and then subjected to heat treatment (for example, heated to 180 ℃. The additive element can be attached to the anode body having the dielectric layer by a vapor phase method such as vapor deposition. The heating temperature of the heat treatment may be 250 ℃ or higher in order to further diffuse the additive element.

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

In fig. 3, a portion of the metal porous portion 112 having the first layer 121 and the second layer 122 as the dielectric layer 120 is enlarged and shown in the form of a schematic cross-sectional view. The dielectric layer 120 has a second layer 122 and a first layer 121 in this order from the metal portion side. The thickness of the first layer 121 is indicated by T1 and the thickness of the second layer is indicated by T2.

According to the ALD method, a thin and uniform dielectric layer (first layer) can be formed. However, in practice, there are cases where defects such as pinholes are present on the surface of the deep portion of the recess in the metal porous portion. When the second layer is formed, the ionized first metal diffuses into the first layer, and has the function of repairing the defects of the first layer. As a result, a dielectric layer having a uniform thickness without pinholes is formed as a whole. Therefore, the capacity of the electrolytic capacitor is increased, the voltage resistance is improved, and the leakage current is reduced.

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

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 according to the application, the desired effect, and the like. For example, the ratio of the thicknesses: T1/T2 may be 2 or more, 3 or more, or 5 or more in at least the third region.

Procedure (iii)

In the step (iii) of forming the cathode portion covering the dielectric layer, for example, the anode element having the 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. In the case where both the formation of the solid electrolyte layer and the impregnation of the electrolytic solution are performed, the impregnation of the electrolytic solution may be performed after the formation of the solid electrolyte layer on the dielectric layer.

The electrolyte solution may be a nonaqueous solvent or a mixture of a nonaqueous solvent and an ionic substance (solute (e.g., organic salt)) dissolved therein. The nonaqueous solvent may be an organic solvent or an ionic liquid.

As the nonaqueous solvent, a high boiling point solvent is preferable. 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-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.

The organic salt is a salt in which at least one of an anion and a cation contains an organic substance. Examples of the organic salt include trimethylamine maleate, triethylamine bissalicylate, ethyldimethylamine phthalate, mono 1, 2, 3, 4-tetramethylimidazolinium phthalate, and mono 1, 3-dimethyl-2-ethylimidazolium phthalate.

The solid electrolyte layer contains, for example, a manganese compound, a conductive polymer, and the like. As the conductive polymer, polypyrrole, polythiophene, polyaniline, a derivative thereof, and the like can be used. The solid electrolyte layer containing a conductive polymer can be formed by, for example, chemically polymerizing and/or electrolytically polymerizing a raw material monomer on the dielectric layer. The solid electrolyte layer can be formed by adhering a solution in which a conductive polymer is dissolved or a dispersion in which a conductive polymer is dispersed to the dielectric layer.

In the case where the anode body having the dielectric layer is the anode foil shown in fig. 1 to 3, a roll body 100 as shown in fig. 5 may be produced before the cathode portion is formed. Fig. 5 is a developed view for explaining the structure of the roll body 100.

When wound body 100 is produced, cathode foil 20 is prepared in addition to anode foil 10. As the cathode foil 20, a metal foil can be used as the anode foil 10. The type of metal constituting cathode foil 20 is not particularly limited, and valve metal such as Al, Ta, and Nb, or an alloy containing valve metal may be used. The surface of the cathode foil 20 may be roughened as necessary.

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

The spacer 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.

Next, a tape stopper 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 of the cathode foil 20 is fixed by the tape stopper 40. When anode foil 10 is prepared by cutting a large piece of foil, wound body 100 may be further subjected to a chemical conversion treatment in order to provide a dielectric layer on the cut surface.

A method of impregnating the roll 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 liquid in which a conductive polymer is dispersed, is not particularly limited. For example, a method of immersing the roll body 100 in an electrolytic solution, a solution, or a dispersion contained in a container, a method of dropping the electrolytic solution, the solution, or the dispersion into the roll body 100, or the like may be used. The impregnation may be carried out under reduced pressure, for example, in an atmosphere of 10kPa to 100kPa, preferably 40kPa 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 10mPa · s or more, particularly 50mPa · s or more, or even 100mPa · s or more, the permeability of the liquid for forming the electrolyte into the metal porous portion can be increased, the capacity realization rate of the electrolytic capacitor becomes high, and reduction of ESR and suppression of leak current are also advantageous.

Next, the roll 100 is sealed to obtain an electrolytic capacitor 200 as shown in fig. 4. To manufacture the electrolytic capacitor 200, first, the wound body 100 is housed in the bottomed case 211 such that the leads 60A, 60B are positioned on the opening side of the bottomed case 211. As a material of the bottomed case 211, a metal such as aluminum, stainless steel, copper, iron, brass, or an alloy thereof can be used.

Next, the sealing member 212 formed so that the leads 60A and 60B penetrate therethrough 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 is preferably an elastomer. Among them, silicone rubber, fluororubber, ethylene-propylene rubber, hypalon rubber, butyl rubber, isoprene rubber, and the like having high heat resistance are preferable.

Next, the vicinity of the open end of the bottomed case 211 is subjected to lateral drawing, and the open end is crimped to the sealing member 212 to perform crimping. Finally, sealing is completed by disposing a seat plate 213 at the curled portion. Then, the aging treatment may be performed while applying a rated voltage.

Fig. 6 is an explanatory view schematically showing an etching apparatus used in the roll-to-roll etching step. The etching apparatus 300 includes: an etching bath 310 for holding an etching solution; a plurality of conveying rollers 320 that convey the metal foil 301; a pair of electrodes 330 facing the metal foil 301; and an ac power source 340 for supplying current to the electrode 330. The metal foil 301 moves in the etching chamber 310 while being conveyed by a plurality of conveying rollers 320. The metal foil 301 is etched in the etching bath 310 while facing the electrode 330 (during the electrolysis period). Thereby, an at least partially etched metal foil (etched foil) 302 is obtained.

Fig. 6 shows a case where the long metal foil 301 is etched, but the present invention is not limited to this. For example, a metal foil having a certain area may be left standing to be etched. In fig. 6, a pair of electrodes is used, but the present invention is not limited thereto. For example, the metal foil may be opposed to 1 electrode, and the electrode and the metal foil may be connected to an ac power supply to perform etching. In addition, the number of etching grooves may be plural. There may be more than 2 pairs of electrodes in 1 etch bath.

In the above embodiment, the winding type electrolytic capacitor was explained, but the application range of the present invention is not limited to the above, and the present invention can be applied to other electrolytic capacitors, for example, a laminated type electrolytic capacitor.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples.

EXAMPLE 1A

In this example, a first layer was formed as a dielectric layer by ALD, and then chemical conversion was performed at a chemical conversion voltage of 65V to produce a second electrode foil (chemical conversion foil). Hereinafter, a specific production method will be described.

(production of Anode body (first electrode foil))

An Al foil having a thickness of 150 μm was prepared as a metal foil. The Al foil is pretreated with an aqueous hydrochloric acid solution, and then an etching step is performed by applying an alternating current to an etching solution containing hydrochloric acid as a main component. By appropriately adjusting the etching current (current density, frequency), etching time, and etching solution temperature, an etched foil (first electrode foil) having metal porous portions 55 μm thick on both surfaces of the Al foil, the metal porous portions having the following porosity, was obtained.

The peak of the 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. In addition, P2/P1 is 1.13, P3/P2 is 1.21, and P2/P1 < P3/P2 are satisfied.

Fig. 7 shows the relationship between the distance from the surface of the anode body in the metal porous portion and the porosity (Al remaining percentage).

(production of second electrode foil)

Next, tantalum (V) (C) (tert-butylamido) tris (methylethylamino) tris (methyl-ethyl-amino) precursor was formed by ALD method (temperature: 200 ℃ C.)₁₃H₃₃N₄Ta, TBTEMT), oxidizing agent: h₂O, pressure: 10Pa, 3000 cycles), an oxide containing Ta was formed as a dielectric layer (first layer) on the surface of the Al skeleton (metal portion) constituting the porous portion.

Next, the Al foil (first electrode foil having the first layer) was subjected to chemical conversion treatment, and a second layer containing an oxide of Al was formed between the Al skeleton and the first layer, thereby obtaining a second electrode foil. In the chemical conversion treatment, the Al foil having the first layer was immersed in an aqueous diammonium adipate solution (ammonium adipate concentration of 10 mass%), a direct current was applied thereto, a chemical conversion voltage was increased to about 65V, the resultant was held for about 10 minutes, and after washing with water, the resultant second electrode foil was heated in air at 300 ℃ for 5 minutes, and then cut into a predetermined shape.

As a result of the elemental analysis, the first layer (thickness: about 80nm) contained Ta₂O₅The second layer (thickness: about 10nm) contains Al₂O₃(T1＝8×T2)。

Comparative example 1A

Using an Al foil having a thickness of 150 μm, an etching current (current density, frequency), etching time, and etching solution temperature were appropriately adjusted to obtain an etched foil (first electrode foil) having metal porous portions having a thickness of 55 μm on both surfaces of the Al foil, the metal porous portions having the following porosity. The peak of the pore diameter of the metal porous portion 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 in the same manner as in example 1A, except that this anode body (first electrode foil) was used, and evaluation was performed in the same manner.

[ evaluation ]

The electrostatic capacity and the leakage current were measured for the obtained second electrode foil. The leakage current was measured by immersing the sample in an acidic aqueous solution at 35 ℃ for 60 minutes, applying a voltage while increasing the voltage at a rate of 0.2V/sec, and measuring the integrated value of the leakage current flowing up to 60V. Table 1 shows the relative values of example 1A when the results of comparative example 1A are set to 100.

EXAMPLE 1B

The etched foil (first electrode foil) obtained in example 1A was chemically converted at a chemical conversion voltage of 65V without forming the first layer by the ALD method, to produce a foil containing Al₂O₃The second electrode foil (chemical conversion foil) of the dielectric layer(s) of (1) was evaluated in the same manner as above.

The chemical conversion treatment was carried out by immersing the first electrode foil in an aqueous diammonium adipate solution (ammonium adipate concentration: 10% by mass), applying a direct current to the solution to bring the chemical conversion voltage to about 65V, holding the solution for about 10 minutes, washing the film with water, heating the film in air at 300 ℃ for 5 minutes, and then cutting the obtained second electrode foil into a predetermined shape.

Comparative example 1B

The etched foil (first electrode foil) obtained in comparative example 1A was subjected to chemical conversion at a chemical conversion voltage of 65V, which was the same as that of example 1B, without forming the first layer by the ALD method, to produce a foil containing Al₂O₃The second electrode foil (chemical conversion foil) of the dielectric layer(s) of (1) was evaluated in the same manner as above.

Table 1 shows the relative values of example 1B when the results of comparative example 1B were set to 100.

EXAMPLE 2

Using an Al foil having a thickness of 120 μm, an etching current (current density, frequency), etching time, and etching solution temperature were appropriately adjusted to obtain an etched foil (first electrode foil) having metal porous portions having a thickness of 40 μm on both surfaces of the Al foil, the metal porous portions having the following porosity. 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 was satisfied. In addition, P2/P1 is 1.10, P3/P2 is 1.27, and P2/P1 < P3/P2 are satisfied. A second electrode foil was produced in the same manner as in example 1A, except that this anode body (first electrode foil) was used, and evaluation was performed in the same manner.

Fig. 8 shows the relationship between the distance from the surface of the anode body and the porosity (Al remaining ratio) in the metal porous portion of example 2.

EXAMPLE 3

The etched foil (first electrode foil) obtained in example 2 was subjected to chemical conversion at a chemical conversion voltage of 65V in the same manner as in example 1B, without forming the first layer by the ALD method, to thereby prepare a foil having Al content₂O₃The second electrode foil (chemical conversion foil) of the dielectric layer(s) of (1) was evaluated in the same manner as above.

Comparative example 2

Using an Al foil having a thickness of 120 μm, an etching current (current density, frequency), etching time, and etching solution temperature were appropriately adjusted to obtain an etched foil (first electrode foil) having metal porous portions having a thickness of 40 μm on both surfaces of the Al foil, the metal porous portions having the following porosity. 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%, 50%, and 52%, respectively, and P1 < P2 < P3 was not satisfied. Except for using the anode body (first electrode foil), the first electrode foil was subjected to only chemical conversion treatment without forming the first layer by the ALD method to prepare a second electrode foil, and the evaluation was performed in the same manner as in example 3.

Fig. 9 shows the relationship between the distance from the surface of the anode body and the porosity (Al remaining percentage) in the porous metal portion of comparative example 2.

Table 1 shows relative values of examples 2 and 3 when the result of comparative example 2 is 100.

[ Table 1]

	Electrostatic capacity	Leakage current
			Example 1A	115％	83％
Comparative example 1A	100％	100％
			Example 1B	109％	93％
Comparative example 1B	100％	100％
			Example 2	119％	74％
Example 3	108％	93％
			Comparative example 2	100％	100％

In examples 1A and 1B, the capacitance was improved and the leakage current was reduced as compared with comparative examples 1A and 1B. In examples 2 and 3, the capacitance was improved and the leakage current was reduced as compared with example 2.

EXAMPLE 4

An Al foil having a thickness of 150 μm was prepared as a metal foil, and the following etching step was performed. The current density is represented as a relative value when the first current density in the first electrolysis step is set to 100%.

< first electrolytic step >

After the Al foil was pretreated with a hydrochloric acid aqueous solution, an alternating current having the following curve was applied to an etching solution containing hydrochloric acid as a main component.

During the electrolysis: current Density 100%, 5 minutes (step 1 of FIG. 10)

< first cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

< second electrolytic step >

In an etching solution containing hydrochloric acid as a main component, an alternating current having the following curve was applied to the Al foil (second etched foil) after the first step.

During the electrolysis: current Density 93%, 5 minutes (step 2 of FIG. 10)

< second cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

< third electrolytic step >

In an etching solution (electrolytic solution) containing hydrochloric acid as a main component, an alternating current having the following curve was applied to the Al foil (second etched foil) after the second step.

During the electrolysis: current Density 90.7%, 5 minutes (step 3 of FIG. 10)

< third cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

T1 ═ 15 minutes

T2 ═ 16 minutes

T0-T1 + T2-31 min

As a result, a first electrode foil having metal porous portions of 40 μm in thickness on both surfaces of the Al foil was obtained, the metal porous portions having the following porosity. The peak of the 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 satisfy P1 < P2 < P3, P2/P1 < P3/P2.

Fig. 10 shows a graph showing the transition of the current density in the etching step and an approximate straight line thereof. Coefficient of determination R of approximate straight line²Is 0.92.

EXAMPLE 5

An Al foil having a thickness of 120 μm was prepared as a metal foil, and the following etching step was performed. The current density is represented as a relative value when the first current density in the first sub-step of the first electrolysis step is set to 100%.

< first electrolytic step >

After the Al foil was pretreated with a hydrochloric acid aqueous solution, an alternating current having the following curve was applied to an etching solution containing hydrochloric acid as a main component.

(i) First substep (step 1 of FIG. 11)

During the electrolysis: current density 100%, 3 min

During the non-electrolysis period: washing with pure water for 8 minutes

(ii) Second substep (step 2 of FIG. 11)

During the electrolysis: current density 94.8%, 3 min

< first cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

< second electrolytic step >

In an etching solution (electrolytic solution) containing hydrochloric acid as a main component, an alternating current having the following curve was applied to the Al foil (first etched foil) after the first electrolysis step.

(i) First substep (step 3 of FIG. 11)

During the electrolysis: current density 95.4%, 3 min

During the non-electrolysis period: washing with pure water for 8 minutes

(ii) Second substep (step 4 of FIG. 11)

During the electrolysis: current density 92.3%, 3 min

< second cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

< third electrolytic step >

In an etching solution containing hydrochloric acid as a main component, an alternating current having the following curve was applied to the Al foil (second etched foil) after the second electrolysis step.

(i) First substep (step 5 of FIG. 11)

During the electrolysis: current density 93.1%, 3 min

During the non-electrolysis period: washing with pure water for 8 minutes

(ii) Second substep (step 6 of FIG. 11)

During the electrolysis: current density 90.5%, 3 min

< third cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

T1 ═ 18 minutes

T2 ═ 40 minutes

T0-T1 + T2-58 min

As a result, a first electrode foil having metal porous portions of 40 μm in thickness on both surfaces of the Al foil was obtained, the metal porous portions having the following porosity. The peak of the 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. In addition, P2/P1 is 1.10, P3/P2 is 1.27, and P2/P1 < P3/P2 are satisfied.

Fig. 11 shows a graph showing the transition of the current density in the etching step and an approximate straight line thereof. Coefficient of determination R of approximate straight line²Is 0.82.

EXAMPLE 6

An Al foil having a thickness of 150 μm was prepared as a metal foil, and the following etching step was performed. The current density is represented as a relative value when the first current density in the first sub-step of the first step is set to 100%.

< first electrolytic step >

After the Al foil was pretreated with a hydrochloric acid aqueous solution, an alternating current having the following curve was applied to an etching solution containing hydrochloric acid as a main component.

(i) First substep (step 1 of FIG. 12)

During the electrolysis: current density 100%, 3 min

During the non-electrolysis period: washing with pure water for 8 minutes

(ii) Second substep (step 2 of FIG. 12)

During the electrolysis: current density 94.8%, 3 min

< first cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

< second electrolytic step >

In an etching solution containing hydrochloric acid as a main component, an alternating current having the following curve was applied to the Al foil (first etched foil) after the first electrolysis step.

(i) First substep (step 3 of FIG. 12)

During the electrolysis: current density 95.4%, 3 min

During the non-electrolysis period: washing with pure water for 8 minutes

(ii) Second substep (step 4 of FIG. 12)

During the electrolysis: current density 92.3%, 3 min

< second cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

< third electrolytic step >

In an etching solution (electrolytic solution) containing hydrochloric acid as a main component, an alternating current having the following curve was applied to the Al foil (second etched foil) after the second electrolysis step.

(i) First substep (step 5 of FIG. 12)

During the electrolysis: current density 93.1%, 3 min

During the non-electrolysis period: washing with pure water for 8 minutes

(ii) Second substep (step 6 of FIG. 12)

During the electrolysis: current density 90.5%, 3 min

< third cleaning step >

During the non-electrolysis period: washing with pure water for 8 minutes

T1 ═ 18 minutes

T2 ═ 40 minutes

T0-T1 + T2-58 min

As a result, a first electrode foil having metal porous portions with a thickness of 55 μm on both surfaces of the Al foil, which had the following porosity, was obtained. The peak of the 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. In addition, P2/P1 is 1.13, P3/P2 is 1.21, and P2/P1 < P3/P2 are satisfied.

Fig. 12 shows a graph showing the transition of the current density in the etching process and an approximate curve thereof. Coefficient of determination R of approximation curve²Is 0.96.

EXAMPLE 7

An Al foil having a thickness of 150 μm was prepared, and an etching process having the following 9 sub-steps was performed in 1 electrolytic bath. The current density is represented as a relative value when the first current density in the first substep is set to 100%.

After the Al foil was pretreated with a hydrochloric acid aqueous solution, an alternating current having the following curve was applied to an etching solution (electrolytic solution) containing hydrochloric acid as a main component.

(i) First substep (step 1 of FIG. 13)

During the electrolysis: current density 100%, 3 min

During the non-electrolysis period: 8 minutes

(ii) Second substep (step 2 of FIG. 13)

During the electrolysis: current density 93.4%, 3 min

During the non-electrolysis period: 8 minutes

(iii) Third substep (step 3 of FIG. 13)

During the electrolysis: current density 95.8%, 3 min

During the non-electrolysis period: 8 minutes

(iv) Substep 4 (step 4 of FIG. 13)

During the electrolysis: current density 88.2%, 3 min

During the non-electrolysis period: 8 minutes

(v) Substep 5 (step 5 of FIG. 13)

During the electrolysis: current density 87.2%, 3 min

T1 ═ 15 minutes

T2 ═ 32 minutes

T0-T1 + T2-47 min

As a result, a first electrode foil having metal-porous portions of 40 μm thickness on both surfaces of the Al foil was obtained, the metal-porous portions having the following porosity. The peak of the 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 satisfy P1 < P2 < P3, P2/P1 < P3/P2.

Fig. 13 shows a graph showing the transition of the current density in the etching step and an approximate straight line thereof. Coefficient of determination R of approximate straight line²Is 0.83.

Industrial applicability

According to the present invention, for example, the dielectric layer can be formed to the deep portion of the metal porous portion, and therefore, the performance of the electrolytic capacitor can be improved.

The present invention has been described with respect to the presently preferred embodiments, but such disclosure should not be construed in a limiting sense. Various modifications and alterations will no doubt become apparent to those skilled in the art to which this invention pertains from a reading of the above disclosure. Therefore, it is intended that the appended claims be interpreted as including all such alterations and modifications as fall within the true spirit and scope of the invention.

Description of the reference numerals

10: anode foil, 20: cathode foil, 30: spacer, 40: tape stop, 50A, 50B: lead tab, 60A, 60B: lead, 100: roll, 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: a seat board.