Electrode foil for electrolytic capacitor, electrolytic capacitor, and method for manufacturing electrode foil for electrolytic capacitor

Abstract

This electrode foil for an electrolytic capacitor comprises a porous portion and a core portion continuous with the porous portion. The porous portion is divided in the thickness direction thereof into ten equal portions of a first region to a tenth region in order from an outer surface side of the porous portion, the first region to the tenth region respectively having around-pit lengths A1 to A10 μm / μm2. Specifically, among A1 to A10, a maximum value Amax of the around-pit length, an Nthmax region showing Amax, a minimum value Amin of the around-pit length in a region closer to the outer surface of the porous portion than the Nthmax region, and an Nthmin region showing Amin satisfy relationships \{(Amax / Amin-1)×100\} / (Nmax-Nmin) ≤ 6, 85 ≤ Amax, and 2 ≤ Nmax. By using such electrode foil, a high-capacity electrolytic capacitor can be provided.

Description

Electrode foil for electrolytic capacitor, electrolytic capacitor, and method for manufacturing electrode foil for electrolytic capacitor

[0001] The present disclosure relates to an electrode foil for an electrolytic capacitor, an electrolytic capacitor, and a method for manufacturing an electrode foil for an electrolytic capacitor.

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

[0003] Patent Document 1 proposes an electrolytic capacitor that contains, in a capacitor element having an anode foil made of etched foil with a porosity of 51% or less, a binder in which phosphate ions are bound to a water-soluble metal complex, and a solvent whose main component is water.

[0004] Japanese Patent Application Laid-Open No. 2002-359165

[0005] An electrode foil for an electrolytic capacitor according to one aspect of the present disclosure includes a porous portion and a core portion continuous with the porous portion, the porous portion being equally divided into ten regions, first to ten regions, in order from the outer surface side of the porous portion, in a thickness direction of the porous portion, and pit perimeters of the first to tenth regions are set to A1 to A10 μm / μm, respectively. ２ When A1 to A10 are set as the pit perimeter length, the maximum value A ｍａｘ And, A ｍａｘ Nth indicating ｍａｘ region and the Nth ｍａｘ The minimum value A of the pit perimeter length in the region on the outer surface side of the porous portion ｍｉｎ And, A ｍｉｎ Nth indicating ｍｉｎ The region is {(A ｍａｘ / A ｍｉｎ -1)×100} / (N ｍａｘ -N ｍｉｎ ) ≦6, 85 ≦A ｍａｘ , and 2≦N ｍａｘ Satisfy the relationship.

[0006] An electrolytic capacitor according to another aspect of the present disclosure includes the above-described electrode foil for an electrolytic capacitor, which has a dielectric layer covering at least a portion of a surface of a metal skeleton constituting the porous portion, and a cathode portion covering at least a portion of the dielectric layer.

[0007] A method for manufacturing an electrode foil for an electrolytic capacitor according to yet another aspect of the present disclosure includes a first step of preparing a metal foil and a second step of roughening the metal foil to form a porous portion, the second step including an etching step of etching the metal foil and an intermediate treatment step performed during the etching step, in which a protective film is formed on a portion of the surface of the metal foil by a vapor phase method.

[0008] According to the present disclosure, a high-capacity electrolytic capacitor can be obtained.

[0009] Fig. 1 is a cross-sectional schematic view of an electrode foil (anode body) according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional schematic view of an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 3 is a perspective view schematically illustrating the configuration of the wound body of Fig. 2.

[0010] Prior to describing the embodiments, the problems of the prior art will be briefly described below. Etching progresses from the surface to the interior of the metal foil, and dissolution tends to occur at the surface of the metal foil. This tends to reduce the surface area (perimeter of the pits) of the porous portion, and increasing the surface area of ​​the electrode foil is still insufficient to increase the capacitance. In view of the above problems, the present disclosure provides an electrode foil for an electrolytic capacitor, an electrolytic capacitor, and a method for manufacturing an electrode foil for an electrolytic capacitor, all of which are intended to provide a high-capacity electrolytic capacitor.

[0011] Hereinafter, the electrode foil for an electrolytic capacitor before the dielectric layer is formed will also be referred to as the "first electrode foil" or "anode body," and the electrode foil for an electrolytic capacitor with the dielectric layer will also be referred to as the "second electrode foil."

[0012] (First Electrode Foil) The electrode foil for an electrolytic capacitor (first electrode foil) according to this embodiment comprises a porous portion and a core portion continuous with the porous portion. That is, the first electrode foil is an integrated body of the core portion and the porous portion. The first electrode foil is used as an anode body of an electrolytic capacitor. The metal portion constituting the porous portion and the core portion contain a first metal.

[0013] The first electrode foil can be obtained, for example, by roughening a portion of a metal foil made of a first metal contained in the metal portion constituting the porous portion by etching the metal foil. The porous portion is the surface side (outer side) of the metal foil that has been made porous by etching, and the remaining portion, which is the inner part of the metal foil, is the core portion. The porous portion has pits (or pores) surrounded by the metal portion containing the first metal.

[0014] In the thickness direction of the porous portion, the porous portion is divided into ten equal parts, a first region to a tenth region, in order from the outer surface side (opposite to the core portion) of the porous portion (first electrode foil), and the pit perimeter lengths of the first region to the tenth region are respectively defined as A1 to A10 (μm / μm ２ ) In this case, the maximum value A of the pit perimeter lengths among A1 to A10 is ｍａｘ And, A ｍａｘ Nth indicating ｍａｘ region and the Nth ｍａｘ The minimum value A of the pit perimeter in the region on the outer surface side of the porous portion ｍｉｎ And, A ｍｉｎ Nth indicating ｍｉｎ The region satisfies the following relationships (i) to (iii).

[0015] (i) {(A ｍａｘ / A ｍｉｎ -1)×100} / (N ｍａｘ -N ｍｉｎ )≦6 (ii) 85≦A ｍａｘ , and (iii) 2≦N ｍａｘ

[0016] The maximum value A of the pit perimeter length among A1 to A10 ｍａｘ If there are multiple regions showing this, the region closest to the core among the multiple regions is designated as N ｍａｘ The Nth ｍａｘ The minimum value A of the pit perimeter in the region on the outer surface side of the porous portion ｍｉｎ When there are multiple regions showing this, the region closest to the outer surface of the porous portion among the multiple regions is designated as N ｍｉｎ For example, the pit perimeter lengths A1 to An of the first to n-th regions (n ​​is 2 or more) are all equal to the maximum value A ｍａｘWhen the nth region is N ｍａｘ The first region is N ｍｉｎ Then, A ｍｉｎ =A ｍａｘ In this case, the left side of equation (i) becomes 0.

[0017] A1 to A10 are A ｍｉｎ The pit perimeter length indexes L1 to L10 may be expressed as relative values ​​(hereinafter also referred to as pit perimeter length indexes L1 to L10) when the pit perimeter length index L1 is set to 100. In this case, for (i) above, the maximum pit perimeter length index L1 ｍａｘ And L ｍａｘ Nth indicating ｍａｘ region and the Nth ｍａｘ The minimum value L of the pit perimeter length index in the region on the outer surface side of the porous portion ｍｉｎ And L ｍｉｎ Nth indicating ｍｉｎ The area is (L ｍａｘ -L ｍｉｎ ) / (N ｍａｘ -N ｍｉｎ )≦6. ｍｉｎ =100.

[0018] No. N ｍａｘ The region is any one of the second region to the tenth region. ｍａｘ If the region is the second region, the Nth ｍｉｎ The region is the first region. ｍａｘ If the area is one of the third to tenth areas, the Nth ｍｉｎ The regions are the first region to the (Nth region ｍａｘ -1) It is in one of the areas.

[0019] The "pit perimeter" refers to the length of the contour of the area occupied by the pit in the cross section of the electrode foil (porous portion) in the thickness direction, and is expressed as the total length of the contour contained within a unit area of ​​the cross section. The larger the pit perimeter, the larger the surface area of ​​the electrode foil surface. The pit perimeter can be increased by forming many pits with small diameters.

[0020] When the above relationships (i) to (iii) are satisfied, A ｍａｘ is large, A ｍａｘ and Aｍｉｎ The difference (L ｍａｘ and L ｍｉｎ The difference between ｍａｘ A larger surface area per unit volume can be secured in the region on the outer surface side of the porous portion (surface layer of the porous portion) than in the region on the outer surface side of the porous portion. As a result, a higher capacity can be achieved. ｍａｘ -L ｍｉｎ ) / (N ｍａｘ -N ｍｉｎ ) is preferably 3 or less.

[0021] The thickness T of the porous portion may be 25 μm or more, 40 μm or more, or 25 μm or more and 160 μm or less. By increasing the thickness of the porous portion while increasing the surface area per unit volume, it is possible to further increase the surface area (increase capacity).

[0022] Generally, when the thickness T of the porous portion is increased within the above range, the dissolution reaction tends to progress in the surface layer of the porous portion as the etching progresses, and the pit diameter tends to increase (the pit perimeter tends to decrease). In particular, the larger the thickness T of the porous portion, the more difficult it becomes to achieve a high capacity. To address this, for example, by performing an intermediate treatment step (forming a protective film by atomic layer deposition) during the etching process, as will be described later, it is possible to effectively suppress the decrease in the pit perimeter in the surface layer of the porous portion, even when a porous portion with a large thickness T is formed. Even in a porous portion with a large thickness T, (L ｍａｘ -L ｍｉｎ ) / (N ｍａｘ -N ｍｉｎ ) can be reduced to 6 or less (or 3 or less), and the effect of increasing capacity can be significantly obtained.

[0023] The pit perimeter lengths A1 to A10 of the first to tenth regions can be determined as follows.

[0024] (a) An image of a cross section in the thickness direction of the first electrode foil (anode body) is obtained using an electron microscope. The electron microscope may be a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0025] (b) Image processing is performed. First, a filtering process is performed to remove noise. Next, a binarization process is performed to distinguish between pits (voids) and the metal skeleton that constitutes the porous portion, and the edges of the metal skeleton (the outline of the area occupied by the pits) are extracted.

[0026] (c) In the cross section of a porous portion having a thickness of T (μm), a region of width T / 10 extending in the thickness direction of the porous portion is arbitrarily selected. This region is divided into 10 equal parts in the thickness direction of the porous portion, and these are designated as the first region to the tenth region in order from the outer surface side of the porous portion (first electrode foil). That is, T / 10 × T / 10 square sections (for example, area: 9 μm) are arranged in a line in the thickness direction of the porous portion. ２ ~64μm ２ ) are set as the first region to the tenth region in order from the outer surface side of the porous portion.

[0027] (d) The total length of the outline of the area occupied by the pits contained in the first area (a section of T / 10 x T / 10 squares) is calculated, and the value obtained by dividing this length by the area of ​​the section is calculated as the pit perimeter length A1 of the first area. The pit perimeter lengths A2 to A10 of the second to tenth sections are also calculated in the same manner as A1. Furthermore, A1 to A10 are calculated by dividing A ｍｉｎ The pit perimeter length indices L1 to L10 of the first to tenth regions may be calculated as relative values ​​when A2 / A ｍｉｎ ) x 100.

[0028] From the viewpoint of increasing capacity, A ｍａｘ / A ｍｉｎ (L ｍａｘ / L ｍｉｎ ) may be 1 or more and 1.25 or less, and is preferably closer to 1 within the above range. For example, it is preferably 1 or more and 1.10 or less, and more preferably 1. From the viewpoint of increasing capacity, A ｍａｘ is 85 μm / μm ２ or more, 100 μm / μm ２ From the viewpoint of the formation of the dielectric layer and the impregnation of the electrolyte, ｍａｘ is, for example, 160 μm / μm ２ It may be 150 μm / μm or less, ２ It may be the following:

[0029] No. N ｍｉｎ The region is the Nth ｍａｘ The area is closer to the outer surface of the porous portion than the N ｍｉｎ <N ｍａｘ It is. ｍｉｎ may be 1 or more and 3 or less, or may be 1. That is, any one of L1 to L3 (or L1) is ｍｉｎ It may be N ｍａｘ may be 4 or more, or may be 4 or more and 6 or less. That is, any of L4 to L10 (or L4 to L6) is ｍａｘ It may be N ｍａｘ When the value is within the above range, a region with a large surface area is easily formed in the surface layer portion to the center portion of the porous portion, and it is easy to achieve a high capacity.

[0030] 1 shows a cross-sectional schematic diagram of an anode body (first electrode foil) according to one embodiment of the present disclosure. The anode body 110 is an integrated body of a core portion 111 and a porous portion 112, and the porous portion 112 has a thickness T. The porous portion 112 can be equally divided into ten regions, first to tenth, each having a thickness of T / 10, in order from the outer surface S side of the porous portion 112 (the side opposite the core portion 111). The porous portion 112 is formed on both sides of the anode body 110.

[0031] (Second Electrode Foil) The electrode foil for an electrolytic capacitor according to this embodiment may be a second electrode foil having a first electrode foil (or anode body) and a dielectric layer covering at least a part of the surface of the metal portion (metal skeleton) that constitutes the porous portion of the first electrode foil. The configuration of the dielectric layer is not particularly limited.

[0032] In the second electrode foil, the thickness of the dielectric layer varies depending on the rated voltage of the electrolytic capacitor, but is 4 nm to 300 nm, and is formed relatively thin to conform to the shape of the surface of the metal portion. Therefore, in the thickness direction of the porous portion of the second electrode foil, the porous portion is divided into 10 equal regions, 1st to 10th, in order from the outer surface side (opposite to the core) of the porous portion (second electrode foil), and the pit perimeter length indexes of the 1st to 10th regions are defined as LD1 to LD10 (μm / μm ２ ) and the maximum value of the pit perimeter length index among LD1 to LD10 is LD ｍａｘ And LDｍａｘ The area showing ｍａｘ The ND region ｍａｘ The minimum value of the pit perimeter length index in the region on the outer surface side of the porous portion is LD ｍｉｎ And LD ｍｉｎ The area showing ｍｉｎ When the area is ND ｍａｘ = N ｍａｘ , N.D. ｍｉｎ = N ｍｉｎ and (LD ｍａｘ -LD ｍｉｎ ) is (L ｍａｘ -L ｍｉｎ ) is almost equivalent to 2≦N. ｍａｘ , and (L ｍａｘ -L ｍｉｎ ) / (N ｍａｘ -N ｍｉｎ ) ≦6, then 2 ≦ LD ｍａｘ , and (LD ｍａｘ -LD ｍｉｎ ) / (ND ｍａｘ -ND ｍｉｎ )≦6. The above LD1 to LD10 can be determined in the same manner as the above L1 to L10.

[0033] The thickness T of the porous portion is not particularly limited and may be appropriately selected depending on the application of the electrolytic capacitor, the required withstand voltage, rated capacity, etc. The thickness T of the porous portion may be selected, for example, from the range of 10 μm to 160 μm. The thickness T of the 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 porous portion may be determined by cutting the first electrode foil or the second electrode foil so as to obtain a cross section of the core portion and the porous portion in the thickness direction, taking an electron microscope photograph of the cross section, and averaging the thicknesses of any 10 points in the porous portion.

[0034] The pit diameter peak of the pits (or pore diameter peak of the pores) in the porous portion is not particularly limited, but from the viewpoint of increasing the surface area and forming the dielectric layer deep in the porous portion, it may be, for example, 50 nm to 2000 nm, or may be 100 nm to 300 nm. The pit diameter (pore diameter) peak is the most frequent pore diameter in the volume-based pore diameter distribution measured, for example, with a mercury porosimeter.

[0035] (Dielectric Layer) The dielectric layer is provided so as to cover at least a portion of the surface of the metal portion surrounding the pit (or pore). The dielectric layer may contain an oxide of a first metal contained in the metal portion. The dielectric layer may also have a first layer with a thickness T1 containing an oxide of a second metal different from the first metal contained in the metal portion. When the dielectric layer contains an oxide of a second metal different from the first metal, for example, it is possible to select a second metal with a high dielectric constant without being restricted by the first metal. This makes it easier to improve the capacitance of the electrolytic capacitor. Furthermore, the wider range of choices for the second metal allows the dielectric layer to have a variety of performance characteristics without being restricted by the first metal.

[0036] The withstand voltage of the electrolytic capacitor is not particularly limited, and may be, for example, a relatively low withstand voltage of 1 V or more but less than 4 V, or may be a relatively high withstand voltage of 4 V or more, 15 V or more, or 100 V or more. To obtain an electrolytic capacitor with a withstand voltage of 4 V or more, it is preferable that the thickness of the dielectric layer be 4 nm or more. Furthermore, to obtain an electrolytic capacitor with a withstand voltage of 15 V or more, it is preferable that the thickness of the dielectric layer be 21 nm or more.

[0037] More specifically, when obtaining an electrolytic capacitor having a large withstand voltage of, for example, 60 V or more, the pore diameter peak of the porous portion may be, for example, 50 to 300 nm, the thickness of the 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.

[0038] When obtaining an electrolytic capacitor having a relatively low withstand voltage, for example, a withstand voltage of 10 V or less, the pore diameter peak of the porous portion may be, for example, 20 to 200 nm, the thickness of the 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.

[0039] (Method for manufacturing electrode foil) The method for manufacturing an electrode foil for an electrolytic capacitor according to this embodiment includes, for example, a first step of preparing a metal foil and a second step of roughening the metal foil to form a porous portion. The second step produces a first electrode foil.

[0040] (First Step) The metal foil prepared in the first step contains a first metal. The type of the first metal is not particularly limited, but valve metals such as aluminum (Al), tantalum (Ta), and niobium (Nb) or alloys containing valve metals can be used because they facilitate the formation of a dielectric layer or a second layer by chemical conversion. The thickness of the metal foil is not particularly limited, but is, for example, 15 μm or more and 300 μm or less.

[0041] (Second Step) (Etching Step) The second step includes an etching step in which the metal foil is etched. By roughening the surface through etching, a porous portion having a plurality of pits (or pores) is formed on the surface side of the metal foil. At the same time, a core portion integral with the porous portion is formed in the inner portion of the metal foil. The etching is performed, for example, by DC etching using a direct current or AC etching using an alternating current.

[0042] The etching process may be performed in multiple steps, or multiple etching tanks containing an etching solution may be arranged. The etching solution contains, for example, hydrochloric acid as a main component. The pit perimeter can be controlled, for example, by appropriately adjusting the etching current (current density, frequency), etching solution (concentration, temperature), etching time, etc. The etching current, etc. may be changed depending on the step. The etching current, etc. may be changed continuously or in stages. For example, the smaller the frequency, the more likely the starting point of pit formation is to move deeper into the electrode foil. The smaller the current density and the lower the etching solution temperature, the more likely the pit shape is to become finer. In addition, the number of steps (the number of etching tanks arranged) may be adjusted appropriately.

[0043] (Intermediate Treatment Step) The second step further includes an intermediate treatment step performed during the etching step. The intermediate treatment step is performed by temporarily interrupting the etching during the etching step. In the intermediate treatment step, a protective film is formed on a portion of the surface of the metal foil during etching. Specifically, the pit walls are covered with the protective film up to a predetermined depth in the porous region of the metal foil surface during etching, while the pit walls deep in the porous region are not covered with the protective film. This makes it possible to suppress pit growth (expansion of pit diameter) in the portion covered with the protective film, and to allow pits to extend and grow from that portion in the portion deep in the porous region that is not covered with the protective film.

[0044] By appropriately performing an intermediate treatment step during the etching step, the pits can be grown while adjusting the pit diameter. This allows the pit perimeter to be effectively controlled, and the enlargement of the pit diameter (decrease in the pit perimeter) due to the progress of the dissolution reaction in the surface layer of the porous portion as the etching proceeds can be effectively suppressed. That is, A ｍａｘ and A ｍｉｎ The difference can be reduced.

[0045] The thickness T of the porous portion may be 25 μm or more, or may be 40 μm or more. In this case, as etching progresses, a dissolution reaction occurs in the surface layer of the porous portion, which tends to increase the pit diameter. Therefore, by employing an intermediate treatment step (particularly, the step of forming a protective film by a vapor phase method described below), the effect of suppressing the increase in pit diameter (reduction in pit perimeter) in the surface layer can be significantly achieved. By employing an intermediate treatment step (particularly, the step of forming a protective film by a vapor phase method described below), the first electrode foil according to the present disclosure can be easily obtained.

[0046] The intermediate treatment step may be performed multiple times at a predetermined timing during the etching step. The protective film may be formed in stages while expanding the porous region in the depth direction as the etching progresses. The number of times and timing of the intermediate treatment step may be appropriately adjusted to adjust the pit perimeter. When forming a protective film by a gas phase method described below, the pit perimeter may be adjusted by appropriately adjusting the amount of source gas (oxidizing gas) supplied into the reaction chamber, the temperature within the reaction chamber, and the diffusion time of the source gas (oxidizing gas) within the reaction chamber. Furthermore, when forming a protective film by immersion in an acid treatment solution described below, the pit perimeter may be adjusted by appropriately adjusting the acid treatment solution (temperature, concentration) and the immersion time.

[0047] The intermediate treatment step may be a step of forming a protective film on a portion of the surface of the metal foil during etching by a vapor phase method. Examples of vapor phase methods include vacuum deposition, chemical vapor deposition, mist deposition, sputtering, pulsed laser deposition, and atomic layer deposition (ALD). Among these, ALD is preferred. Compared to the method of immersion in an acid treatment solution described below, vapor phase methods (particularly ALD) can stably form a protective film and easily control the thickness of the protective film and the film formation depth in the porous region (the region deep in the porous region where no film is formed). The thickness of the protective film can be adjusted to the degree of pit growth suppression. The film formation depth in the porous region can be adjusted to the region where pit growth is suppressed. The method of forming a protective film by immersion in an acid treatment solution described below makes it difficult to control the thickness and film formation depth of the protective film, making it difficult to stably form a protective film.

[0048] For example, in a film formation process using the ALD method, the thickness of the protective film can be easily controlled by the number of cycles. Furthermore, in this film formation process, the film formation depth in the porous region of the metal foil during etching can be controlled by the diffusion time and partial pressure of the source gas and oxidant in the reaction chamber. The diffusion time of the source gas (oxidant) in the reaction chamber is the time from when the source gas (oxidant) is supplied into the reaction chamber to when it is exhausted out of the reaction chamber in one cycle, as described below. The partial pressure is the pressure of the source gas (oxidant) in the reaction chamber.

[0049] The ALD method is a film formation method in which a source gas and an oxidant are alternately supplied to a reaction chamber in which the target object is placed, to form a predetermined film on the surface of the target object. In the ALD method, a self-limiting mechanism functions, so that metals contained in the source gas are deposited on the surface of the target object in atomic layers. Therefore, the thickness of the film can be easily controlled by the number of cycles, with one cycle consisting of supply of source gas → exhaust (purging) of source gas → supply of oxidant → exhaust (purging) of oxidant.

[0050] The source gas is supplied to the reaction chamber as a precursor gas. The precursor may contain a first metal. When the first metal contained in the metal foil prepared in the first step is Al, a precursor containing Al may be selected, for example, trimethylaluminum ((CH ３ ) ３ Examples of the oxidizing agent include water, oxygen, ozone, etc. The oxidizing agent may be supplied to the reaction chamber as plasma using the oxidizing agent as a raw material.

[0051] Alternatively, the intermediate treatment step may be a step of immersing the metal foil during etching in an acid treatment solution containing a phosphorus compound (e.g., an aqueous solution of sodium phosphate). For example, the depth of film formation in the porous region of the metal foil during etching can be controlled by adjusting the acid treatment solution (temperature, concentration) and immersion time.

[0052] In the second step, for example, a porous portion is formed by electrolytic etching using a plurality of etching tanks, and a protective film is formed using a film-forming device using a gas-phase method (such as an ALD method). In this case, from the viewpoint of improving productivity, the second step may be performed using a roll-to-roll method. In this case, the ALD process may be performed in a vacuum, or may be performed under atmospheric pressure or in an inert gas atmosphere. Alternatively, the metal foil after the intermediate treatment may be temporarily wound up, and then the etching process may be performed again. Alternatively, the metal foil may be temporarily wound up during etching, and then the intermediate treatment may be performed, wound up, and then the etching process may be performed again. Furthermore, the protective film may be formed using an immersion tank that holds an acid treatment solution.

[0053] The method for producing an electrode foil for an electrolytic capacitor according to this embodiment may further include a third step of forming a dielectric layer that covers at least a portion of the surface of the metal skeleton that constitutes the porous portion of the first electrode foil.

[0054] The step of forming the dielectric layer may be, for example, a step of subjecting the anode body (first electrode foil) to chemical conversion treatment (anodization). For example, 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, and a voltage is applied to the first electrode foil to obtain a second electrode foil having a dielectric layer formed on the surface of the metal portion.

[0055] Alternatively, the step of forming the dielectric layer may be a step of depositing an oxide of a second metal, different from the first metal contained in the metal portion, on the surface of the metal portion by a vapor deposition method to form a first layer having a thickness of T1, thereby obtaining a second electrode foil having a dielectric layer formed on the surface of the metal portion.

[0056] (Electrolytic Capacitor) The electrolytic capacitor according to this embodiment includes a second electrode foil and a cathode part covering at least a portion of the dielectric layer of the second electrode foil. The cathode part may include an electrolyte. The electrolyte covers at least a portion of the dielectric layer.

[0057] The electrolyte includes at least one of a solid electrolyte and an electrolytic solution. The cathode portion may include a solid electrolyte and an electrolytic solution, or may include a solid electrolyte and a non-aqueous solvent. Hereinafter, the electrolytic solution and the non-aqueous solvent are collectively referred to as "liquid components." The dielectric layer is coated with a solid electrolyte (or an electrolytic solution), for example, by impregnating the second electrode foil (or wound body) with a treatment solution (or an electrolytic solution) containing a conductive polymer. The treatment solution may include a non-aqueous solvent.

[0058] The solid electrolyte includes a conductive polymer. Examples of the conductive polymer include π-conjugated polymers. Examples of the conductive polymer include polypyrrole, polythiophene, polyfuran, and polyaniline. The conductive polymer may be used alone or in combination of two or more types, or may be a copolymer of two or more types of monomers. The weight-average molecular weight of the conductive polymer is, for example, 1,000 to 100,000.

[0059] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. refer to polymers having polypyrrole, polythiophene, polyfuran, polyaniline, etc. as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc. may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0060] The conductive polymer may be doped with a dopant. The solid electrolyte may contain a dopant together with the conductive polymer. Examples of the dopant include polystyrene sulfonic acid. The solid electrolyte may further contain an additive, if necessary.

[0061] The liquid component is in contact with the dielectric layer directly or via a conductive polymer. The liquid component may be a non-aqueous solvent or an electrolyte solution. The electrolyte solution contains a non-aqueous solvent and an ionic substance (solute (e.g., organic salt)) dissolved therein. The non-aqueous solvent may be an organic solvent or an ionic liquid.

[0062] The non-aqueous solvent is preferably a high-boiling solvent, for example, a polyol compound such as ethylene glycol, a sulfone compound such as sulfolane, a lactone compound such as γ-butyrolactone, an ester compound such as methyl acetate, a carbonate compound such as propylene carbonate, an ether compound such as 1,4-dioxane, or a ketone compound such as methyl ethyl ketone.

[0063] The liquid component may contain an acid component (anion) and a base component (cation). The acid component and the base component may form a salt (solute). The acid component contributes to the film repair function. Examples of the acid component include organic carboxylic acids and inorganic acids. Examples of the inorganic acid include phosphoric acid, boric acid, and sulfuric acid. Examples of the base component include primary to tertiary amine compounds.

[0064] The organic salt is a salt in which at least one of the anion and cation contains an organic substance. Examples of the organic salt include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0065] From the viewpoint of suppressing dedoping of the dopant from the conductive polymer (deterioration of the solid electrolyte), the liquid component preferably contains more acid components than base components. Furthermore, since the acid components contribute to the film repair function of the liquid component, it is also preferable that the liquid component contains more acid components than base components. The molar ratio of the acid component to the base component (acid component / base component) is, for example, 1.1 or more. From the viewpoint of suppressing dedoping of the dopant from the conductive polymer, the pH of the liquid component may be 6 or less, or may be 1 or more and 5 or less.

[0066] Here, Fig. 2 is a cross-sectional view schematically showing an electrolytic capacitor according to one embodiment of the present invention. Fig. 2 shows an example of an electrolytic capacitor including a wound capacitor element. Fig. 3 is a perspective view schematically showing the configuration of the wound body of Fig. 2.

[0067] Electrolytic capacitor 200 includes a wound body 100. Wound body 100 is formed by winding an anode foil 10 and a cathode foil 20 with a separator 30 interposed therebetween. Separator 30 is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0068] One end of each of lead tabs 50A and 50B is connected to anode foil 10 and cathode foil 20, respectively, and lead tabs 50A and 50B are wound to form wound body 100. Lead wires 60A and 60B are connected to the other ends of lead tabs 50A and 50B, respectively.

[0069] A stop tape 40 is disposed on the outer surface of the cathode foil 20 located at the outermost layer of the wound body 100, and the ends of the cathode foil 20 are fixed by the stop tape 40. When the anode foil 10 is prepared by cutting it from a large foil, the wound body 100 may further be subjected to a chemical conversion treatment in order to provide a dielectric layer on the cut surface.

[0070] The wound body 100 contains an electrolyte, and the electrolyte is interposed between the anode foil 10 (dielectric layer) and the cathode foil. The wound body 100 containing the electrolyte is formed, for example, by impregnating the wound body 100 with a treatment liquid (or electrolytic solution) containing a conductive polymer. The impregnation may be performed under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa.

[0071] The wound body 100 is housed in the bottomed case 211 so that the lead wires 60A and 60B are located on the opening side of the bottomed case 211. The bottomed case 211 can be made of a metal such as aluminum, stainless steel, copper, iron, brass, or an alloy of these metals.

[0072] A sealing member 212 is placed at the opening of a bottomed case 211 in which the wound body 100 is housed, the open end of the bottomed case 211 is crimped to the sealing member 212 and curled, and a seat plate 213 is placed at the curled portion, thereby sealing the wound body 100 within the bottomed case 211.

[0073] The sealing member 212 is formed so that the lead wires 60A and 60B pass through it. The sealing member 212 may be made of any insulating material, and is preferably made of an elastic material. Among these, highly heat-resistant materials such as silicone rubber, fluororubber, ethylene propylene rubber, hypalon rubber, butyl rubber, and isoprene rubber are preferred.

[0074] In the above embodiment, a wound electrolytic capacitor has been described. However, the scope of application of the present invention is not limited to this and can also be applied to other electrolytic capacitors, such as stacked electrolytic capacitors. A stacked electrolytic capacitor includes, for example, a stacked capacitor element and an exterior housing that seals the capacitor element. The stacked capacitor element includes an anode body, a solid electrolyte layer, and a cathode extraction layer that covers the solid electrolyte layer. The anode body includes the electrode foil (first electrode foil) having a porous portion formed on a portion of its surface, and a dielectric layer that covers the metal skeleton that constitutes the porous portion of the electrode foil. The solid electrolyte layer is formed to cover the dielectric layer. The cathode extraction layer includes, for example, a silver paste layer and a carbon layer. An anode lead is connected to a region of the anode body that is not covered by the dielectric layer, and a cathode lead is connected to the cathode extraction layer. Portions of the anode lead and cathode lead are exposed from the exterior housing. A stacked body may be formed by stacking multiple capacitor elements.

[0075] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples.

[0076] Examples 1 to 3, Comparative Example 1 (Preparation of First Electrode Foil) An Al foil (thickness: 100 μm) was prepared as a metal foil (Step 1). An etching step was performed on the Al foil, and an intermediate treatment step was further performed during the etching step to obtain a first electrode foil having porous portions on both surfaces of the Al foil (Step 2).

[0077] The etching process was performed as follows. The Al foil was pretreated with a hydrochloric acid solution, and then electrolytic etching was performed by applying an alternating current in an etching solution containing hydrochloric acid as the main component. In the etching process, the number of steps (number of etching tanks), etching current (current density, frequency), etching solution temperature, and etching time were appropriately adjusted. In Example 1 and Comparative Example 1, the etching current (current density, frequency) and etching solution (temperature, concentration) were appropriately changed in three stages depending on the progress of etching. In Examples 2 and 3, the etching current (current density, frequency) and etching solution (temperature, concentration) were appropriately changed in six stages depending on the progress of etching.

[0078] The intermediate treatment step was carried out as follows. In Example 1, a protective film was formed on a part of the surface of the Al foil by a vapor phase method as the intermediate treatment step. Specifically, the ALD method (temperature: 200°C, precursor: trimethylaluminum (Al(CH ３ ) ３ , TMA), oxidant: H ２ O, pressure: 10 Pa, 20 cycles) to form an oxide containing Al as a protective film. The number and timing of the intermediate treatment steps were adjusted appropriately. In one cycle, the diffusion time of the precursor (raw material gas) and the oxidizing agent in the reaction chamber was adjusted appropriately.

[0079] In Examples 2 and 3 and Comparative Example 1, as an intermediate treatment step, the Al foil was immersed in an aqueous sodium phosphate solution (temperature 70°C, concentration 15% by mass) to form a protective film on a part of the surface of the Al foil. The immersion time was adjusted appropriately. The number of times and timing of the intermediate treatment step were also adjusted appropriately. In Example 2, the immersion conditions were changed appropriately for each intermediate treatment step. In Example 3 and Comparative Example 1, the immersion conditions were kept constant for each intermediate treatment step.

[0080] In this way, porous portions having pit perimeter lengths A1 to A10 shown in Table 1 were formed on both surfaces of the Al foil to obtain first electrode foils. The pit perimeter lengths A1 to A10 shown in Table 1 were determined by the method described above. In X1-1 to X1-3, A1 is A ｍｉｎ and 100 μm / μm ２ Table 2 shows the pit perimeter length indices L1 to L10 calculated from A1 to A10. ｍａｘ , N ｍａｘ , L ｍｉｎ , N ｍｉｎ , and (L ｍａｘ -L ｍｉｎ ) / (N ｍａｘ -N ｍｉｎ In Tables 1 to 3, X1-1 to X3-1 represent the first electrode foils of Examples 1 to 3, and Y1-1 represents the first electrode foil of Comparative Example 1.

[0081]

[0082]

[0083]

[0084] (Preparation of Second Electrode Foil) The first electrode foil was subjected to a chemical conversion treatment to obtain a second electrode foil. Specifically, the first electrode foil was immersed in an aqueous solution of diammonium adipate (ammonium adipate concentration: 10% by mass), and a direct current was applied. After a conversion voltage of approximately 35 V was reached, the foil was held for approximately 10 minutes. After rinsing with water, the foil was heated in air at 300°C for 5 minutes. The resulting second electrode foil was then cut into a predetermined shape. Note that X1-2 to X3-2 represent the second electrode foils of Examples 1 to 3, and Y1-2 represents the second electrode foil of Comparative Example 1.

[0085] The capacitance (frequency: 120 Hz) of the second electrode foil obtained above was measured in an aqueous ammonium adipate solution (concentration: 15% by mass) at 30°C. The evaluation results are shown in Table 4. The capacitances in Table 4 are expressed as relative values, with the measured value for Y1-2 (second electrode foil) of Comparative Example 1 set to 100.

[0086]

[0087] As shown in Table 4, X1-2 to X3-2 provided higher capacities than Y1-2.

[0088] The electrode foil for electrolytic capacitors according to the present disclosure is suitably used in electrolytic capacitors that require large capacitance.

[0089] 10: Anode foil, 20: Cathode foil, 30: Separator, 40: Winding stop tape, 50A, 50B: Lead tabs, 60A, 60B: Lead wires, 100: Wound body, 110: Anode body, 111: Core portion, 112: Porous portion, 200: Electrolytic capacitor, 211: Bottomed case, 212: Sealing member, 213: Seat plate

Claims

1. A porous portion and a core portion continuous with the porous portion, In a thickness direction of the porous portion, the porous portion is equally divided into 10 regions, a first region to a tenth region, in order from an outer surface side of the porous portion; The pit perimeters in the first to tenth regions are A1 to A10 μm / μm, respectively. ２ When The maximum pit perimeter length Amax among A1 to A10, an Nmax region showing Amax; A minimum value Amin of the pit perimeter length in a region on the outer surface side of the porous portion from the Nmax region; The Nmin region indicating Amin is An electrode foil for an electrolytic capacitor, which satisfies the relationships {(Amax / Amin-1) x 100} / (Nmax-Nmin) ≤ 6, 85 ≤ Amax, and 2 ≤ Nmax.

2. 2. The electrode foil for electrolytic capacitors according to claim 1, which satisfies {(Amax / Amin-1) x 100} / (Nmax-Nmin) ≦ 3.

3. 3. The electrode foil for electrolytic capacitors according to claim 1, wherein Nmax satisfies 4≦Nmax.

4. 3. The electrode foil for an electrolytic capacitor according to claim 1, wherein the thickness T of the porous portion is 25 μm or more.

5. 3. The electrode foil for an electrolytic capacitor according to claim 1, further comprising a dielectric layer covering at least a part of a surface of the metal skeleton constituting the porous portion.

6. An electrolytic capacitor comprising: the electrode foil for an electrolytic capacitor according to claim 5; and a cathode part covering at least a part of the dielectric layer.

7. The electrolytic capacitor of claim 6 , wherein the cathode portion includes an electrolyte.

8. The electrolytic capacitor according to claim 6 , wherein the cathode portion includes a solid electrolyte.

9. A first step of preparing a metal foil; A second step of roughening the metal foil to form a porous portion; Including, The second step comprises: an etching step of etching the metal foil; an intermediate treatment step performed during the etching step; Including, In the intermediate treatment step, a protective film is formed on a part of the surface of the metal foil by a vapor phase method.

10. The method for producing an electrode foil for an electrolytic capacitor according to claim 9 , wherein in the intermediate treatment step, the protective film is formed by atomic layer deposition.