Electrode foil for electrolytic capacitors and electrolytic capacitors

Abstract

This electrode foil for electrolytic capacitors comprises a metal foil that comprises a porous part and a core part that is continuous with the porous part. The metal foil has a main surface to which pores of the porous part open; and the porous part has a plurality of recesses that open to the main surface, while being dispersed in the form of dots in the surface direction of the metal foil. The opening diameters of the pores of the porous part are less than 2 μm, while the opening diameters of the recesses are not less than 2 μm.

Description

[Technical Field]

[0001] This invention relates to electrode foil for electrolytic capacitors and electrolytic capacitors. [Background technology]

[0002] The electrode foil of an electrolytic capacitor uses a metal foil that includes a porous portion and a core portion continuous with the porous portion. The porous portion is formed by etching the metal foil, and the formation of the porous portion increases the surface area of ​​the electrode foil, thereby increasing the capacitance of the electrolytic capacitor.

[0003] Patent Document 1 discloses a strip-shaped electrode foil comprising an expanded portion formed on the surface of the foil and a core portion which is the remaining portion after removing the expanded portion, wherein a plurality of dividing portions are provided that extend in the width direction of the electrode foil and divide the expanded portion. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-224844 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] By creating a segment, the indentation depth (Erichsen value) in the Erichsen test increases. However, the segment extends in the width direction of the electrode foil, resulting in low tensile strength in the length direction and low bending strength in the width direction of the electrode foil, making it prone to foil breakage during the manufacturing process. This foil breakage occurs when cracks form in the width direction of the electrode foil along the segment due to tension generated during transport by the transport rollers and bending stress generated during winding by the winding rollers.

[0006] Furthermore, during the manufacturing process of electrolytic capacitors using electrode foils with a divided section, the electrode foil may bend, and the bending stress resulting from this bending may cause the foil to break. The bending of the electrode foil can occur, for example, due to the winding of the electrode foil during the fabrication of the winding body, or due to slack during the transport of the electrode foil. In addition, if there is a process in the manufacturing process of electrolytic capacitors in which the electrode foil is twisted to change its orientation, the stress generated by the twisting of the electrode foil may concentrate at the divided section, causing the foil to break. [Means for solving the problem]

[0007] One aspect of the present invention relates to an electrode foil for an electrolytic capacitor, comprising a metal foil including a porous portion and a core portion continuous with the porous portion, wherein the metal foil has a main surface on which the pores of the porous portion open, and the porous portion has a plurality of recesses that open to the main surface and are dispersed in a dot-like manner in the planar direction of the metal foil, the pores of the porous portion are less than 2 μm, and the opening diameter of the recesses is 2 μm or more.

[0008] Another aspect of the present invention relates to an electrolytic capacitor comprising a wound body and an electrolyte, wherein the wound body is constructed by winding a strip-shaped anode foil, a strip-shaped cathode foil facing the anode foil, and a separator disposed between the anode foil and the cathode foil, and at least one of the anode foil and the cathode foil includes a metal foil having a porous portion and a core portion continuous with the porous portion, the metal foil having a main surface on which the pores of the porous portion open, the porous portion having a plurality of recesses that open to the main surface and are dispersed in a dot-like manner in the planar direction of the metal foil, the pores of the porous portion being less than 2 μm, and the opening diameter of the recesses being 2 μm or more. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress foil breakage of electrode foils for electrolytic capacitors. [Brief explanation of the drawing]

[0010] [Figure 1]It is a front view schematically showing an example of an electrode foil for an electrolytic capacitor according to an embodiment of the present invention. [Figure 2] It is a sectional view taken along line II-II of FIG. 1. [Figure 3] It is a view showing a modified example of the recess of FIG. 1. FIGS. 3(a) to 3(c) show cases where the opening shape of the recess is circular, square, and hexagonal, respectively. FIG. 3(d) shows a case where the opening shape of the recess is a square with all corners rounded. FIGS. 3(e) to 3(g) show cases where the opening shape of the recess is drop-shaped. FIG. 3(h) shows a case where the opening shape of the recess is hexagonal star-shaped. Note that the broken lines in FIGS. 3(b) to 3(h) indicate the maximum diameter of the opening, respectively. [Figure 4] It is a view schematically showing an example when the wound body A is viewed from the end face side. [Figure 5] It is a sectional view schematically showing an electrolytic capacitor according to an embodiment of the present invention. [Figure 6] It is a perspective view schematically showing the configuration of the wound body of FIG. 5. [Figure 7] It is a SEM image showing the state after applying tension to the electrode foil for an electrolytic capacitor according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0011] The novel features of the present invention are described in the appended claims. However, the present invention relates to both the configuration and the content, and will be better understood from the following detailed description in combination with other objects and features of the present invention and with reference to the drawings.

[0012] [Electrode Foil for Electrolytic Capacitor] The electrode foil for an electrolytic capacitor according to an embodiment of the present invention includes a metal foil including a porous portion and a core portion continuous with the porous portion. The metal foil has a main surface (hereinafter also referred to as the main surface S) where the pores of the porous portion open. The porous portion has a plurality of recesses that open to the main surface S. The plurality of recesses are dispersed and arranged in a dot shape in the plane direction of the metal foil (as viewed from the main surface S side). The opening diameter of the recess is larger than the opening diameter of the pores of the porous portion. That is, the pores of the porous portion are less than 2 μm, and the opening diameter of the recess is 2 μm or more. In the present specification, when simply described as "opening diameter", it means "the maximum diameter of the opening". That is, the opening diameter of the recess means the maximum diameter of the opening of the recess. The opening diameter of the pores of the porous portion means the maximum diameter of the opening of the pore. Hereinafter, the plurality of recesses having an opening diameter of 2 μm or more and dispersed and arranged in a dot shape in the plane direction of the metal foil as described above are also referred to as "recess groups". The plurality of recesses are provided spaced apart from each other in the porous portion.

[0013] Conventionally, in the manufacturing process of an electrode foil (electrolytic capacitor), due to the tension generated in the longitudinal direction of the strip-shaped electrode foil and the bending stress generated in the width direction, cracks may occur linearly along the width direction of the strip-shaped electrode foil, resulting in foil breakage. In a strip-shaped electrode foil provided with a slit portion elongated in the width direction, the tensile strength in the length direction of the electrode foil and the folding resistance in the width direction of the electrode foil are low, and the above-mentioned foil breakage is likely to occur.

[0014] On the other hand, in the electrode foil according to the present embodiment, since the porous portion has a recess group, a high tensile strength can be obtained. In a strip-shaped electrode foil, a high tensile strength can be obtained in both the length direction and the width direction. When stress is applied to the electrode foil by tension, fine cracks extending radially from the inner wall of the recess are formed as viewed from the main surface S side, and the stress is dispersed and relaxed. Therefore, foil breakage due to the tension generated during the conveyance of the electrode foil by the conveyance roller is suppressed. Here, FIG. 7 is a SEM image showing the state of the electrode foil for an electrolytic capacitor according to an embodiment of the present invention after tension is applied. FIG. 7 shows a state in which cracks are formed radially from the recesses by applying tension to the electrode foil.

[0015] Furthermore, in the electrode foil according to this embodiment, high bending strength is obtained because the porous portion has a group of recesses. In the strip-shaped electrode foil, high bending strength is obtained in both the length direction and the width direction. When the electrode foil is bent, fine cracks are formed that extend radially from the inner wall of the recesses when viewed from the main surface S side, and the bending stress generated in the electrode foil by the formation of these cracks is dispersed and relieved. Therefore, foil breakage caused by bending of the electrode foil (winding of the electrode foil during electrode foil manufacturing, winding of the electrode foil during winding body manufacturing, slack during electrode foil transport, etc.) and twisting of the electrode foil is suppressed.

[0016] However, even if the opening diameter of the recess is larger than the opening diameter of the pores in the porous section, if the opening diameter of the recess is less than 2 μm, radial fine cracks may not form easily, and the bending strength may decrease.

[0017] From the viewpoint of improving tensile strength and bending strength, the recess may extend at an angle with respect to the main surface S. From the viewpoint of ease of recess formation, the recess may extend approximately perpendicular to the main surface S. Note that "approximately perpendicular to the main surface S" means that the recess extends at an angle of 80° to 100° with respect to the main surface S.

[0018] When the maximum and minimum diameters of the opening of a recess are D1 and D2, respectively, the ratio of the minimum diameter D2 to the maximum diameter D1 of the recess opening, D2 / D1, may be, for example, 0.1 or more and 1 or less, 0.2 or more and 0.8 or less, or 0.4 or more and 0.75 or less.

[0019] Examples of concave shapes include columnar (e.g., cylindrical, rectangular prism, etc.), conical (e.g., conical, square pyramidal, etc.), and frustum (e.g., frustum of a cone, frustum of a square pyramidal, etc.).

[0020] From the viewpoint of increasing the bending strength of the electrode foil, the opening diameter of the recess (maximum diameter D1) is preferably 4 μm or more, and more preferably 8 μm or more. From the viewpoint of improving the bending strength of the electrode foil and ensuring tensile strength, the opening diameter of the recess is preferably 120 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less. The opening diameter of the recess may be within a range that is an arbitrary combination of the above upper and lower limits, for example, it may be 2 μm or more and 120 μm or less, 4 μm or more and 120 μm or less, or 8 μm or more and 100 μm or less.

[0021] From the perspective of increasing the bending strength of the electrode foil, the main surface S is 1 mm 2 The number of recesses present in the area may be 4 or more, 10 or more, or 30 or more. From the viewpoint of improving the bending strength and ensuring the tensile strength of the electrode foil, the main surface S is 1 mm 2 The number of recesses present in the area may be 62,500 or less, 40,000 or less, 20,000 or less, 7,000 or less, or 625 or less. (Main surface S, 1 mm) 2 The number of recesses present in a given area may be any combination of the above upper and lower limits, for example, it may be 4 or more and 40,000 or less, or 30 or more and 7,000 or less. Also, the 1 mm of the main surface S 2 The number of recesses present per unit area may be between 10 and 62,500. Many recesses with small opening diameters may be provided in the porous portion. For example, recesses with an opening diameter of 5 μm or less may be provided within 1 mm of the main surface S. 2 You may set aside 20,000 prizes.

[0022] The metal foil may be in the shape of a strip, with recesses arranged in both the longitudinal and widthwise directions of the metal foil. In this case, it is preferable that the number of recesses arranged in the longitudinal direction of the metal foil per 1 mm Nx and the number of recesses arranged in the widthwise direction of the metal foil per 1 mm Ny satisfy the relationship Nx / Ny < 1. More preferably, Nx / Ny < 0.9. When Nx / Ny is within the above range, it is advantageous in terms of improving the tensile strength in the longitudinal direction of the metal foil and improving the folding strength in the widthwise direction of the metal foil.

[0023] From the viewpoint of improving the bending strength and ensuring the tensile strength of the electrode foil, the spacing W between adjacent recesses may be 2 μm or more, 4 μm or more, or 6 μm or more. From the viewpoint of increasing the bending strength of the electrode foil, the spacing W between adjacent recesses may be 2400 μm or more, 1200 μm or less, or 800 μm or less. The spacing W between adjacent recesses may be within a range that is an arbitrary combination of the above upper and lower limits, for example, 2 μm or more and 2400 μm or less, or 6 μm or more and 1200 μm or less. Note that the above spacing W refers to the shortest distance between adjacent recesses.

[0024] From the viewpoint of the bending strength and tensile strength of the electrode foil, when adjacent recesses each have an opening diameter (maximum opening diameter) D1 and are provided with a gap W between them, it is preferable that the relationship between the opening diameter D1 and the gap W satisfies D1 / W ≤ 2. D1 / W is, for example, 0.005 or more and 2 or less, preferably 0.02 or more and 1 or less, and more preferably 0.1 or more and 1 or less.

[0025] It is preferable that the multiple recesses are regularly arranged in the planar direction of the metal foil. It is preferable that the multiple recesses are equally spaced in the planar direction of the metal foil. In the planar direction of the metal foil, the multiple recesses may be arranged in a staggered pattern or in a square grid pattern. If the electrode foil is in the shape of a strip, the spacing W of the recesses may be varied in the length direction. When two porous parts are arranged with a core in between, the two porous parts may have the same or different recess sizes (opening diameters), shapes, spacing W, and arrangement configurations.

[0026] The ratio of the average opening diameter Da of the recess to the average pore diameter Dp of the porous portion, Da / Dp, is preferably 20 or more, more preferably 67 or more, and even more preferably 67 or more and 800 or less.

[0027] The average pore diameter Dp of the porous section is determined by measuring the pore diameter distribution of the electrode foil (porous section) using a mercury porosimeter. Specifically, the average pore diameter Dp is determined by the pore diameter (mode diameter) corresponding to the peak (the largest peak if multiple peaks exist) that appears on the pore distribution curve obtained by the measurement (vertical axis: log differential pore volume, horizontal axis: pore diameter). For example, the AutoPore V series manufactured by Micromeristics is used as a measuring device for the average pore diameter Dp. The above pore distribution curve shows the pore distribution of the porous section in the range where the pore diameter is less than 2 μm. Typically, the diameter (opening diameter) of the recesses is much larger than that of the pores in the porous section, and under the same conditions as the measurement of the porous section, the diameter of the recesses is difficult to measure with a mercury porosimeter.

[0028] The average aperture diameter Da of the recesses is determined by using a scanning electron microscope (SEM) to obtain images of the main surface S of the electrode foil, arbitrarily selecting 20 apertures with a maximum diameter of 2 μm or more as recesses, measuring the maximum diameter D1 of these apertures, and calculating their average value.

[0029] Examples of the shapes of the recess openings include circular, elliptical, polygonal, star-shaped, and teardrop-shaped. It is preferable that at least some of the corners of the polygon are rounded, and it is more preferable that all of the corners of the polygon are rounded. The shapes of the openings of the multiple recesses provided in the porous portion may be the same or different from each other. Polygons include triangles, quadrilaterals, hexagons, etc. Star shapes include shapes with interior angles of 180 degrees or more, and typical shapes are multi-pointed stars such as pentagrams and hexagrams. The multiple sides constituting the star shape may be the same or different from each other.

[0030] In the case of a strip-shaped electrode foil, it is preferable that the openings of the multiple recesses have a shape such that the direction of the maximum diameter of the opening is approximately parallel to the length direction of the electrode foil. This is advantageous for improving the tensile strength in the length direction of the electrode foil. For example, if the recess has an elliptical opening shape, it is preferable that the elliptical opening is provided such that the major axis (maximum diameter D1) of the ellipse is approximately parallel to the length direction of the electrode foil. Note that the direction of the maximum diameter D1 of the recess opening being approximately parallel to the length direction of the electrode foil means that the angle formed between the direction of the maximum diameter D1 of the recess opening and the length direction of the electrode foil is within the range of -20° to 20°.

[0031] The porous portion may include a first porous portion and a second porous portion arranged on either side of the core portion. In this case, the metal foil has a first main surface on which the pores of the first porous portion are open, and a second main surface on which the pores of the second porous portion are open. At least one of the first porous portion and the second porous portion may have a group of recesses.

[0032] It is preferable that the first porous part and the second porous part each have a group of recesses. In this case, the first porous part has a plurality of first recesses that open to the first main surface and are dispersed and arranged in a dot shape in the plane direction of the metal foil, and the second porous part has a plurality of second recesses that open to the second main surface and are dispersed and arranged in a dot shape in the plane direction of the metal foil. The aperture diameters of the pores of the first porous part and the second porous part are each less than 2 μm, and the aperture diameters of the first recess and the second recess are each 2 μm or more. Hereinafter, an electrode foil in which the first porous part and the second porous part arranged with the core part interposed therebetween each have a group of recesses is also referred to as "electrode foil E".

[0033] The number of first recesses present per 1 mm of the first main surface 2 may be made larger than the number of second recesses present per 1 mm of the second main surface. In the case of a strip-shaped metal foil, in at least a partial region in the length direction of the metal foil, the number of first recesses present per 1 mm of the first main surface 2 may be made larger than the number of second recesses present per 1 mm of the second main surface. Thereby, when the electrode foil is wound with the first main surface facing outward, the bending stress can be effectively dispersed in the first porous part (first main surface side) where the bending stress increases. 2 The number of first recesses present per 1 mm of the first main surface 2 may be made larger than the number of second recesses present per 1 mm of the second main surface. Thereby, when the electrode foil is wound with the first main surface facing outward, the bending stress can be effectively dispersed in the first porous part (first main surface side) where the bending stress increases.

[0034] It is preferable that the depth H of the recess and the thickness T (thickness per side) of the porous part have a relationship of 0.067 ≦ H / T ≦ 1. H / T is more preferably 0.083 or more and 1 or less, and more preferably 0.16 or more and 0.67 or less. When H / T is 0.16 or more, the folding resistance of the electrode foil is likely to be increased. When H / T is 0.67 or less, the tensile strength of the electrode foil is likely to be ensured. When H / T is 1 or less, the strength of the electrode foil (core part) is likely to be ensured.

[0035] Within the range where the strength of the electrode foil (core part) is ensured, the recess may further extend from the porous part to the core part. In this case, the depth h of the recess in the core part is, for example, 7 μm or less, and may be 4 μm or less.

[0036] The depth H of the recess is determined by measuring the distance from the opening to the deepest point of 10 arbitrarily selected recesses using an SEM image of the electrode foil cross-section, and averaging these measurements. The thickness T of the porous portion is determined by measuring the thickness of 10 arbitrary points in the porous portion using an SEM image of the cross-section in the thickness direction of the electrode foil, and averaging these measurements.

[0037] (electrode foil) The metal foil used for the electrode foil contains, for example, a valve-acting metal such as aluminum (Al), tantalum (Ta), or niobium (Nb). The metal foil may also contain the valve-acting metal as an alloy or compound containing the valve-acting metal. The metal foil may be an integrated material consisting of a core and a porous portion. The porous portion is formed, for example, by etching the surface of the metal foil containing the valve-acting metal to roughen the surface of the metal foil. The porous portion is the outer part of the metal foil that has been porousized by etching, and the remaining part, which is the inner part of the metal foil, is the core. For example, a strip-shaped metal foil is used for the electrode foil, and its width is, for example, 1.5 mm or more and 520 mm or less.

[0038] The thickness T of the porous portion is not particularly limited and can be appropriately selected depending on the application of the electrolytic capacitor, the required voltage withstand voltage, etc. For example, the thickness T of the porous portion may be 1 / 10 or more and 5 / 10 or less of the thickness of the metal foil on each side. In the case of anode foil, the thickness D of the porous portion may be, for example, 10 μm or more and 160 μm or less, or 50 μm or more and 160 μm or less.

[0039] The metal foil includes a metal framework that constitutes the porous portion. The metal framework refers to the metal portion having a microstructure within the porous portion. The porous portion has multiple pores (pits) surrounded by the metal framework. From the viewpoint of increasing the surface area and forming the dielectric layer deep within the porous portion, the range of the pore diameter (aperture diameter) is less than 2000 nm, and may be between 100 nm and 1500 nm.

[0040] The shape of the pores (pits) may be spongy or tunnel-shaped. The tunnel-shaped pits include pits that extend from the surface side of the porous portion toward the core side. In the case of sponge-like pits, the range of pore diameter (aperture diameter) is, for example, 600 nm or less, but may be 50 nm or more and 500 nm or less. In the case of sponge-like pits, the average pore diameter Dp may be 80 nm or more and 400 nm or less, or 80 nm or more and 300 nm or less. Electrode foil having sponge-like pits is used, for example, in low-voltage electrolytic capacitors. Specifically, it is used in electrolytic capacitors using chemical foil of 200 V or less. In the case of tunnel-shaped pits, the range of pore diameter (aperture diameter) is, for example, 1900 nm or less, but may be 100 nm or more and 1800 nm or less. In the case of tunnel-shaped pits, the average pore diameter Dp may be 200 nm or more and 1700 nm, or 400 nm or more and 1400 nm or less. Electrode foil having tunnel-shaped pits is used, for example, in medium-high voltage electrolytic capacitors.

[0041] The electrode foil may include a dielectric layer covering the metal skeleton that constitutes the porous portion having a group of recesses. In this case, the electrode foil can be used as an anode foil. The dielectric layer covers at least a portion of the outer surface (main surface S) of the porous portion, the pores of the porous portion, and the inner wall surface of the recesses. That is, the dielectric layer is provided so as to cover at least a portion of the surface of the metal skeleton surrounding the pores and recesses.

[0042] The thickness of the metal foil may be 10 μm or more, 60 μm or more, or 90 μm or more. When the thickness of the metal foil is large, 100 μm or more, the bending stress applied to the electrode foil during winding is large, so the bending stress dispersion effect of the recesses is significantly obtained.

[0043] The thickness of the dielectric layer may be 2 nm or more, 4 nm or more, 12 nm or more, or 24 nm or more. Electrode foils having a dielectric layer with a thickness of 12 nm or more can be used as anode foils. Electrode foils having a dielectric layer with a thickness of 24 nm or more can be used as anode foils for electrolytic capacitors with a rated voltage of 20 V or more. When the dielectric layer thickness is large, 24 nm or more, the bending stress applied to the dielectric layer during the winding of the electrode foil is large, resulting in a significant dispersion effect of bending stress due to the group of recesses. The thickness of the dielectric layer is determined by measuring the thickness of 10 arbitrary points in the dielectric layer using SEM or transmission electron microscope (TEM) images of the cross-section in the thickness direction of the electrode foil, and averaging these measurements.

[0044] (Method of manufacturing electrode foil) The method for manufacturing electrode foil according to this embodiment includes, for example, a step of etching a metal foil and a step of forming a group of recesses in the etched foil.

[0045] In the etching process, the surface of the metal foil containing the valve metal is roughened by etching, forming a porous region continuous with the core. The etching process may be electrolytic etching or chemical etching. For example, a strip of metal foil (e.g., 500 mm wide) is used for the etching process.

[0046] For example, electrolytic etching can be used to mass-produce electrode foils having porous portions containing pores with a diameter (aperture diameter) of less than 2 μm. AC etching can produce electrode foils having porous portions containing sponge-like pits with a diameter of 1.5 μm or less. DC etching can produce electrode foils having porous portions containing tunnel-like pits with a diameter of 2 μm or less. AC etching is preferred because it makes it easier to increase the difference between the pore aperture diameter and the recess aperture diameter of the porous portion.

[0047] In the process of forming the recesses, the recesses may be formed by pressing a jig having multiple protrusions onto a metal foil with a roughened surface. Alternatively, the recesses may be formed on both roughened surfaces of the metal foil by conveying the metal foil between a pair of rollers having multiple protrusions and pressing the rollers. The recesses may also be formed by laser processing, blasting, etching, or the like.

[0048] The method for manufacturing electrode foil may include a step of slitting the etched foil. For example, a strip of etched foil with a width of 500 mm is slit to a width of 1.5 mm or more and 40 mm or less. The slitting may be performed before or after the recess formation step. In the slitting process, a roller for transporting the metal foil and a roller for winding the metal foil after slitting are used in the slitting apparatus. When the slit width is small, such as 10 mm or less, the metal foil may break due to tension or bending stress applied to the metal foil during transport and winding by the rollers. When slitting is performed after the recess formation step, the presence of the recesses suppresses foil breakage during slitting.

[0049] The method for manufacturing the electrode foil may include a step of forming a dielectric layer that covers the metal skeleton constituting the porous portion having a group of recesses. The dielectric layer formation step may be performed before or after the recess formation step. In the dielectric layer formation step, an oxide film containing a valve-acting metal may be formed on the surface of the metal foil having the porous portion (porous portion having a group of recesses) by anodic oxidation (chemical conversion treatment).

[0050] The above-described method for manufacturing electrode foil may include the steps of conveying and winding the metal foil using rollers. When the metal foil has a group of recesses, foil breakage due to tension and bending stress applied to the metal foil during conveying and winding by the rollers is suppressed. In this case, stress concentration on irregularities and scratches on the electrode foil caused by irregularities and scratches on the surface of the roller is suppressed, and foil breakage associated with such stress concentration is suppressed. Furthermore, stress concentration on irregularities and scratches on the electrode foil caused by particles or foreign matter that get trapped between the roller and the metal foil is suppressed, and foil breakage associated with such stress concentration is suppressed.

[0051] The electrode foil for electrolytic capacitors according to this embodiment may be used as at least one of the anode foil and cathode foil of a wound-type electrolytic capacitor, or as the anode body of a laminated-type electrolytic capacitor.

[0052] Here, Figure 1 is a schematic front view showing an example of an electrode foil for an electrolytic capacitor according to one embodiment of the present invention. The strip-shaped electrode foil 300 (metal foil) in Figure 1 has a first main surface S1 and a second main surface S2 opposite to the first main surface S1, and Figure 1 shows a part of the electrode foil 300 as viewed from the first main surface S1 side. In Figure 1, the X direction and Y direction indicate the length direction and width direction of the strip-shaped electrode foil, respectively. Figure 2 is a cross-sectional view taken along line II-II of Figure 1. Figure 2 is a schematic diagram showing a cross-section of the electrode foil 300 in the thickness direction and the Y direction of Figure 1. Note that the electrode foil for an electrolytic capacitor according to the present invention is not limited to the electrode foil shown in Figures 1 and 2. Each figure is schematic, and the ratio of the dimensions of each component (for example, the ratio of the size and spacing of recesses) etc. may differ from reality.

[0053] The strip-shaped electrode foil 300 (metal foil) has a first porous portion 310a and a core portion 320 continuous with the first porous portion 310a. The electrode foil 300 has a first main surface S1 on which the pores (not shown) of the first porous portion 310a open. The porous portion 310a has a plurality of elliptical columnar recesses 330a that open into the first main surface 310S. The plurality of first recesses 330a are spaced apart from each other and are dispersed in a dot-like manner in the planar direction (X direction and Y direction) of the electrode foil 300. The opening diameter of the pores of the first porous portion 310a is less than 2 μm, and the opening diameter of the first recesses 330a is 2 μm or more. The opening diameter of the recesses 330a may be, for example, 8 μm or more, or 10 μm or more.

[0054] As shown in Figure 1, the multiple first recesses 330a are arranged in a staggered pattern in the planar direction of the electrode foil 300. By arranging the multiple recesses 330a as shown in Figure 1, the bending strength (especially the bending strength in the Y direction) and tensile strength (especially the tensile strength in the X direction) of the electrode foil 300 are effectively increased.

[0055] The first recess 330a shown in Figure 1 has an elliptical opening, and the recess is provided such that the major axis of the ellipse (maximum diameter D1 of the opening) is approximately parallel to the X direction. Furthermore, the recess is provided such that the minor axis of the ellipse (minimum diameter D2 of the opening) is approximately parallel to the Y direction. In this case, the tensile strength in the X direction and the bending strength in the Y direction are particularly likely to be improved. The ratio of the minimum diameter D2 to the maximum diameter D1 of the opening of the recess 330a, D2 / D1, should be within the range exemplified above, for example, 0.1 or more and 0.8 or less.

[0056] Multiple first recesses 330a are arranged at equal intervals. The distance W between adjacent first recesses 330a may be within the range exemplified above, for example, preferably 12 μm or more and 2000 μm or less. The ratio of the maximum diameter D1 of the first recess to the distance W of the first recesses 330a: D1 / W may be within the range exemplified above, for example, preferably 0.02 or more and 1.0 or less. The ratio of the depth H of the first recess 330a to the thickness T of the first porous portion 310a: H / T may be within the range exemplified above, for example, preferably 0.16 or more and 1 or less.

[0057] The recess in Figure 1 has an elliptical opening shape, but the shape of the recess's opening is not limited to this. The shape of the recess's opening may be circular, square, or hexagonal, as shown in Figures 3(a) to (c). It may also be a square with all corners rounded, as shown in Figure 3(d), or a teardrop shape, as shown in Figures 3(e) to (g). It may also be a hexagram shape, as shown in Figure 3(h). It is preferable to provide a recess having the opening shapes shown in Figures 3(b) to (h) such that the direction of the maximum diameter, indicated by the dashed line in Figures 3(b) to (h), points in the X direction in Figure 1.

[0058] The first recess 330a is elliptical in shape, but the shape of the first recess is not limited to this and may be columnar or pyramidal in shape, etc. Multiple first recesses 330a are the same shape and size as each other, but multiple first recesses may be different in shape and / or size. The arrangement of the first recesses 330a is not limited to the arrangement of recesses 330a shown in Figure 1, but may be, for example, a square grid. The direction of the maximum diameter D1 of the recess 330a in Figure 1 is approximately parallel to the X direction, but the direction of the maximum diameter D1 of the first recess 330a does not have to be parallel to the X direction. The first recesses are arranged at a constant interval W, but the interval W of the first recesses may be changed, and may be changed in the X direction and / or Y direction.

[0059] As shown in Figure 2, the strip-shaped electrode foil 300 (metal foil) includes a second porous portion 310b and a core portion 320 continuous with the second porous portion 310b. That is, the first porous portion 310a and the second porous portion 310b are arranged so as to sandwich the core portion 320. The electrode foil 300 has a second main surface S2 through which the pores (not shown) of the second porous portion 310b are open.

[0060] The porous portion 310b has a plurality of second recesses 330b that open to the second main surface S2. The plurality of second recesses 330b are spaced apart from each other and are dispersed in a dot-like manner in the planar direction of the electrode foil 300. The opening diameter of the pores in the second porous portion 310b is less than 2 μm, and the opening diameter of the second recesses 330b is 2 μm or more. The second recesses are the same as the first recesses in terms of shape, size, spacing, and arrangement (hereinafter also referred to as shape, etc.).

[0061] The first recess 330a and the second recess 330b have the same shape, but the first recess and the second recess may have different shapes. For example, the spacing between the first recesses may be smaller than the spacing between the second recesses.

[0062] [Electrolytic capacitor] An electrolytic capacitor according to an embodiment of the present invention includes a winding body and an electrolyte. The winding body is constructed by winding a strip-shaped anode foil, a strip-shaped cathode foil facing the anode foil, and a separator disposed between the anode foil and the cathode foil. At least one of the anode foil and the cathode foil is an electrode foil for an electrolytic capacitor according to an embodiment of the present invention. That is, at least one of the anode foil and the cathode foil includes a metal foil including a porous portion and a core portion continuous with the porous portion. The metal foil has a main surface from which the pores of the porous portion open. The porous portion opens to the main surface and has a plurality of recesses that are dispersed in a dot-like manner in the plane direction of the metal foil. The opening diameter of the pores in the porous portion is less than 2 μm, and the opening diameter of the recesses is 2 μm or more.

[0063] The height Lc of the winding is, for example, 50 mm or less, but may also be 20 mm or less, or 15 mm or less. The height Lc of the winding is approximately equal to the width dimension of the electrode foil.

[0064] When the product size is large (for example, when the height Lc of the wound body is 30 mm or more), electrode foils with a large width dimension (for example, 30 mm or less) are used. With electrode foils with a large width dimension, foil breakage is likely to occur due to twisting of the electrode foil. Therefore, by providing a group of recesses in electrode foils with a large width dimension, foil breakage caused by twisting of the electrode foil is significantly suppressed, improving the reliability of large products (for example, large capacitors of the screw terminal type or lead terminal type).

[0065] On the other hand, when the product size is small (for example, when the height Lc of the winding is 20 mm or less), electrode foils with a small width (for example, 20 mm or less) are used. Electrode foils with a small width can be obtained by slitting electrode foils with a large width (for example, 125 mm or more and 500 mm or less) to the desired small width (20 mm or less). The presence of recesses distributes the stress applied to the electrode foil during slitting, suppressing the occurrence of cracks caused by this stress and the resulting foil breakage, significantly improving the quality of electrode foils with small width dimensions. Furthermore, in the capacitor manufacturing process, the presence of recesses significantly suppresses foil breakage caused by tension during transport of electrode foils with small width dimensions by rollers. As a result, aging (restorative chemical formation) during capacitor manufacturing is performed efficiently, stable characteristics such as capacitor leakage current are obtained, and the reliability of small-sized products is improved.

[0066] The ratio of the average opening diameter Da of the recess to the height Lc of the wound body, Da / Lc, is 0.5 × 10⁻⁶. -4 The above is 2.4 × 10 -4 The following is also acceptable: 1 × 10 -4 The above is 2 x 10 -4 The following is also acceptable.

[0067] When electrode foil E is used for at least one of the anode foil and cathode foil, the electrode foil E may be wound in the winding body such that its first main surface faces the outer circumference of the winding body. Hereinafter, a winding body comprising electrode foil E wound so that its first main surface faces the outer circumference of the winding body will also be referred to as "winding body A".

[0068] In the case of wound body A, 1 mm of the first main surface 2 The number of first recesses N1 present in the second main surface is 1 mm 2 The number of second recesses present in a given area may be greater than the number of second recesses present in a given area (N2). In the case of wound body A, the bending stress is greater in the first porous portion (first main surface side) of the electrode foil E than in the second porous portion (second main surface side). Therefore, by making the number of first recesses N1 greater than the number of second recesses N2, the effect of dispersing bending stress by the group of recesses can be efficiently obtained. The ratio of N1 / N2 may be 1.02 or more and 2.0 or less, or 1.05 or more and 1.8 or less.

[0069] In a portion of the inner circumference region P and / or a portion of the outer circumference region Q of the winding body A, the ratio of N1 / N2 may be 1.05 or greater and 1.8 or less. Here, Figure 4 is a schematic diagram showing an example of the winding body A as viewed from the end face side. The winding body A is a winding body 400 constructed by winding an anode foil and a cathode foil around a winding core 410 with a separator in between. When the radial thickness of the winding body 400 from the innermost circumference E1 to the outermost circumference E2 is t, region P refers to the region where the radial distance from the innermost circumference E1 of the winding body 400 is (1 / 4)t or less. Region Q refers to the region where the radial distance from the innermost circumference E1 of the winding body is (3 / 4)t or greater.

[0070] On the winding core side of winding body A, the first main surface is 1 mm 2 The number of first recesses present may be larger. The radius of curvature of the electrode foil E, when viewed from the end face side of the winding body A, is smaller on the core side of the winding body A than on the outer circumference side, and the bending stress on the first porous portion (first main surface side) of the electrode foil E is larger. Therefore, by increasing the number of first recesses on the core side of the winding body A than on the outer circumference side, the bending stress dispersion effect by the group of recesses can be efficiently obtained.

[0071] For example, in a portion of the inner circumference region P of the wound body A, the first main surface is 1 mm 2 The number of first recesses present in each region may be increased. In the case of wound body A, the bending stress applied to the first porous portion (first main surface side) of the electrode foil E is particularly large within region P. Therefore, by increasing the number of first recesses in region P, the effect of dispersing the bending stress by the group of recesses can be efficiently obtained.

[0072] On the outer side of the winding body A, rather than on the core side, the second main surface is 1 mm 2 The number of second recesses present may be larger. Since the degree of compression of the second porous portion (second main surface side) of the electrode foil E is smaller on the outer circumference side of the winding body A than on the core side (it is more susceptible to the effects of bending of the electrode foil E), increasing the number of second recesses on the outer circumference side of the winding body A than on the inner circumference side makes it easier to efficiently obtain the effect of distributing bending stress by the group of recesses.

[0073] (Anode foil) The anode foil comprises a metal foil having a porous portion and a core portion continuous with the porous portion, and a dielectric layer covering the porous portion. The porous portion is formed, for example, by etching a metal foil containing a valve-acting metal to roughen the surface of the metal foil. The dielectric layer is obtained, for example, by forming an oxide film containing a valve-acting metal on the roughened surface of the metal foil by anodic oxidation (chemical conversion). The valve-acting metal includes, for example, aluminum (Al), tantalum (Ta), niobium (Nb), etc. The metal foil may contain the valve-acting metal as an alloy or compound containing a valve-acting metal.

[0074] The thickness of the anode foil is, for example, 60 μm or more and 200 μm or less. Because the anode foil is relatively thick, when an electrode foil with a group of recesses is used for the anode foil, the effect of dispersing bending stress due to the recesses is easily obtained.

[0075] (Cathode foil) The cathode foil can be a metal foil containing valve-acting metals such as Al, Ta, and Nb. If necessary, the surface of the metal foil may be roughened by etching. That is, the cathode foil may be a metal foil having a porous portion and a core portion continuous with the porous portion.

[0076] The thickness of the cathode foil is, for example, 10 μm or more and 70 μm or less. Because the cathode foil is relatively thin, when an electrode foil with a group of recesses is used for the cathode foil, the improvement in tensile strength due to the recesses is easily obtained.

[0077] (Separator) The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamides, aromatic polyamides such as aramids) may be used.

[0078] (electrolyte) The electrolyte covers at least a portion of the anode foil (dielectric layer) and is interposed between the anode foil (dielectric layer) and the cathode foil. The electrolyte includes at least one of a solid electrolyte and a liquid electrolyte. If the electrolyte includes a solid electrolyte, the electrolytic capacitor may also include a solid electrolyte and a liquid electrolyte, or a solid electrolyte and a non-aqueous solvent. Hereinafter, the liquid electrolyte and non-aqueous solvent will be collectively referred to as the liquid component.

[0079] (solid electrolyte) The solid electrolyte contains a conductive polymer. Examples of conductive polymers include π-conjugated polymers. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, and polyaniline. The conductive polymer may be used alone, in combination of two or more types, or as a copolymer of two or more monomers. The weight-average molecular weight of the conductive polymer is, for example, 1,000 to 1,000,000.

[0080] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc., refer to polymers that have polypyrrole, polythiophene, polyfuran, polyaniline, etc., as their basic skeletons. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc., may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0081] Conductive polymers can be doped with dopants. Solid electrolytes may contain dopants together with the conductive polymer. Examples of dopants include polystyrene sulfonic acid. Solid electrolytes may further contain additives as needed.

[0082] The liquid component is in direct contact with the dielectric layer or via a conductive polymer. The liquid component may be a non-aqueous solvent or a liquid electrolyte. The electrolyte contains a non-aqueous solvent and an ionic substance (solute (e.g., an organic salt)) dissolved therein. The non-aqueous solvent may be an organic solvent or an ionic liquid.

[0083] As the non-aqueous solvent, a high-boiling point solvent is preferred. For example, polyol compounds such as ethylene glycol, sulfone compounds such as sulfolane, lactone compounds such as γ-butyrolactone, ester compounds such as methyl acetate, carbonate compounds such as propylene carbonate, ether compounds such as 1,4-dioxane, and ketone compounds such as methyl ethyl ketone can be used.

[0084] The liquid component may contain an acid component (anion) and a base component (cation). A salt (solute) may be formed by the acid component and the base component. The acid component contributes to the film repair function. Examples of acid components include organic carboxylic acids and inorganic acids. Examples of inorganic acids include phosphoric acid, boric acid, and sulfuric acid. Examples of base components include primary to tertiary amine compounds.

[0085] An organic salt is a salt in which at least one of the anion and cation is an organic substance. Examples of organic salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0086] From the viewpoint of suppressing dopant dedoping (degradation of solid electrolyte) from conductive polymers, it is preferable that the liquid component contains more acidic components than basic components. Furthermore, since the acidic components contribute to the film repair function of the liquid component, it is also preferable that the liquid component contains more acidic components than basic components. The molar ratio of acidic components to basic components (acidic component / basic component) is, for example, 1.1 or higher. From the viewpoint of suppressing dopant dedoping from conductive polymers, the pH of the liquid component may be 6 or less, or it may be 1 or more, or 5 or less.

[0087] Here, Figure 5 is a schematic cross-sectional view showing an electrolytic capacitor according to one embodiment of the present invention. Figure 6 is a schematic perspective view showing the configuration of the winding body of Figure 5. In Figure 6, the X direction indicates the length direction of the strip-shaped anode foil 10 and cathode foil 20, and the Y direction indicates the width direction of the anode foil 10 and cathode foil 20.

[0088] The electrolytic capacitor 200 comprises a winding body 100. The winding body 100 is constructed by winding an anode foil 10 and a cathode foil 20 with a separator 30 in between. At least one of the anode foil 10 and the cathode foil 20 is an electrode foil according to an embodiment of the present invention. The height Lc of the winding body 100 is approximately equal to the width (Y direction) dimension of the anode foil 10 and the cathode foil 20.

[0089] One end of lead tabs 50A and 50B are connected to the anode foil 10 and cathode foil 20, respectively, and the winding body 100 is formed by winding the lead tabs 50A and 50B. Lead wires 60A and 60B are connected to the other ends of lead tabs 50A and 50B, respectively.

[0090] A winding stopper tape 40 is placed on the outer surface of the cathode foil 20, which is located in the outermost layer of the winding body 100, and the end of the cathode foil 20 is fixed by the winding stopper tape 40. If the anode foil 10 is prepared by cutting from a large sheet of foil, the winding body 100 may be further treated with a chemical conversion process to provide a dielectric layer on the cut surface.

[0091] The winding body 100 contains an electrolyte, with the electrolyte interposed between the anode foil 10 (dielectric layer) and the cathode foil. The winding body 100 containing the electrolyte is prepared, for example, by impregnating the winding body 100 with a treatment solution containing the electrolyte. The impregnation may be carried out under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa. The treatment solution may contain a solid electrolyte and an electrolyte solution or a non-aqueous solvent.

[0092] The winding body 100 is housed in the closed-bottom case 211 such that the lead wires 60A and 60B are located on the opening side of the closed-bottom case 211. The material of the closed-bottom case 211 can be a metal such as aluminum, stainless steel, copper, iron, or brass, or an alloy thereof.

[0093] The winding body 100 is sealed inside the bottomed case 211 by placing a sealing member 212 at the opening of the bottomed case 211, crimping the open end of the bottomed case 211 to the sealing member 212 to create a curl, and placing a seat plate 213 on the curled portion.

[0094] The sealing member 212 is formed so that the lead wires 60A and 60B pass through it. The sealing member 212 can be made of any insulating material, and an elastic material is preferred. Among these, silicone rubber, fluororubber, ethylene propylene rubber, Hypalon rubber, butyl rubber, isoprene rubber, etc., which have high heat resistance are preferred.

[0095] [Examples] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0096] Examples 1-5 Electrode foils with the same structure as those in Figures 1 and 2 were obtained, except that the shape of the recesses was cylindrical. Specifically, a strip-shaped Al foil with a thickness of 120 μm (length direction: 80,000 mm, width direction: 500 mm) was etched on both sides to roughen the surface of the Al foil. This formed porous sections (thickness T: 45 μm) with sponge-like pits (average pore diameter Dp: 0.17 μm) on both sides of the Al foil. After slitting this electrode foil to a width of 10 mm, a plurality of cylindrical recesses (diameter (maximum opening diameter D1): 100 μm, depth H: 45 μm) were formed on both sides of the aluminum foil using a predetermined jig. In this way, electrode foils a1 to a5 having porous sections with groups of recesses on both sides were obtained. The plurality of recesses were arranged in a staggered pattern as in Figure 1, and the spacing W of the recesses in Figure 1 was changed to the values ​​shown in Table 1. a1 to a5 represent the electrode foils of Examples 1 to 5.

[0097] Comparative Example 1 Electrode foil b1 was obtained in the same manner as in Example 1, except that multiple recesses were not formed on both sides of the aluminum foil.

[0098] The following evaluations were performed on each electrode foil obtained in the above examples and comparative examples. [Evaluation: Folding strength] The bending strength in the width direction (Y direction in Figure 1) of the strip-shaped electrode foil was measured in accordance with the test method for electrode foils for aluminum electrolytic capacitors of the Japan Electronic Machinery Industry Standard (EIAJ RC-2364A). The bending strength was expressed as a relative value with the bending strength of electrode foil b1 of Comparative Example 1 set to 100. The evaluation results are shown in Table 1.

[0099] [Table 1]

[0100] Electrode foils a1 to a5 showed higher bending strength than electrode foil b1. In particular, electrode foil a5 showed a significant increase in bending strength.

[0101] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Industrial applicability]

[0102] The electrode foil according to the present invention is suitably used in electrolytic capacitors where high reliability is required. [Explanation of symbols]

[0103] 10: Anode foil, 20: Cathode foil, 30: Separator, 40: Winding stopper tape, 50A, 50B: Lead tab, 60A, 60B: Lead wire, 100, 400: Winding body, 200: Electrolytic capacitor, 211: Bottomed case, 212: Sealing member, 213: Base plate, 300: Electrode foil, 310a: First porous section, 310b: Second porous section, 320: Core section, 330a: First recess, 330b: Second recess

Claims

1. The metal foil includes a porous portion and a core portion continuous with the porous portion. The metal foil has a main surface on which the pores of the porous portion are open, The porous portion has an opening on the main surface and a plurality of recesses that are dispersed in a dot-like manner in the planar direction of the metal foil. The opening diameter of the pores in the porous portion is less than 2 μm. The electrode foil for electrolytic capacitors has an opening diameter of the recess in the range of 2 μm or more and 120 μm or less.

2. The aforementioned metal foil is in the shape of a strip, The recesses are arranged in the length direction of the metal foil and in the width direction of the metal foil. The electrode foil for an electrolytic capacitor according to claim 1, wherein the number of recesses arranged in the longitudinal direction of the metal foil per 1 mm in the longitudinal direction of the metal foil, Nx, and the number of recesses arranged in the width direction of the metal foil per 1 mm in the width direction of the metal foil, Ny, satisfy the relationship Nx / Ny < 1.

3. When adjacent recesses each have an opening diameter D1 and are provided with a gap W between them, The electrode foil for an electrolytic capacitor according to claim 1 or 2, wherein the aperture diameter D1 and the spacing W satisfy the relationship D1 / W ≤ 2.

4. The electrode foil for an electrolytic capacitor according to any one of claims 1 to 3, wherein the ratio of the average opening diameter Da of the recess to the average pore diameter Dp of the porous portion, Da / Dp, is 20 or more.

5. The electrode foil for an electrolytic capacitor according to any one of claims 1 to 4, wherein the depth H of the recess and the thickness T of the porous portion have a relationship of 0.067 ≤ H / T ≤ 1.

6. The electrode foil for an electrolytic capacitor according to any one of claims 1 to 5, wherein the shape of the opening of the recess is at least one selected from the group consisting of a circle, an ellipse, a star shape, and a polygon with at least some rounded corners.

7. The aforementioned metal foil is in the shape of a strip, The electrode foil for electrolytic capacitor according to any one of claims 1 to 6, wherein the width dimension of the metal foil is 1.5 mm or more and 520 mm or less.

8. The porous portion includes a first porous portion and a second porous portion arranged on either side of the core portion. The main surface has a first main surface through which the pores of the first porous portion are open, and a second main surface through which the pores of the second porous portion are open. The electrode foil for an electrolytic capacitor according to any one of claims 1 to 7, wherein the plurality of recesses include a plurality of first recesses arranged in the first porous portion and opening to the first main surface, and a plurality of second recesses arranged in the second porous portion and opening to the second main surface.

9. 1 mm of the first main surface ２ The number of the first recess present in each area is equal to the number of recesses in the second main surface per 1 mm. ２ The electrode foil for electrolytic capacitor according to claim 8, wherein the number of second recesses present in each area is greater than the number of second recesses present in each area.

10. The electrode foil for an electrolytic capacitor according to any one of claims 1 to 9, comprising a dielectric layer covering the metal skeleton constituting the porous portion having the plurality of recesses.

11. The electrode foil for electrolytic capacitor according to claim 10, wherein the thickness of the metal foil is 10 μm or more.

12. The electrode foil for an electrolytic capacitor according to claim 10 or 11, wherein the thickness of the dielectric layer is 2 nm or more.

13. A metal foil comprising a porous portion and a core portion continuous with the porous portion, The metal foil has a main surface on which the pores of the porous portion are open, The porous portion has an opening on the main surface and a plurality of recesses that are dispersed in a dot-like manner in the planar direction of the metal foil. The opening diameter of the pores in the porous portion is less than 2 μm. The opening diameter of the recess is 2 μm or more. The aforementioned recesses are present in a range of 4 to 40,000 per 1 mm² of the main surface, in an electrode foil for an electrolytic capacitor.

14. A metal foil comprising a porous portion and a core portion continuous with the porous portion, The metal foil has a main surface on which the pores of the porous portion are open, The porous portion has an opening on the main surface and a plurality of recesses that are dispersed in a dot-like manner in the planar direction of the metal foil. The opening diameter of the pores in the porous portion is less than 2 μm. The opening diameter of the recess is 2 μm or more. Electrode foil for electrolytic capacitors, wherein adjacent recesses are provided with a gap W of 2 μm or more and 2400 μm or less between them.

15. It comprises a coiled body and an electrolyte, The aforementioned wound body is constructed by winding together a strip-shaped anode foil, a strip-shaped cathode foil facing the anode foil, and a separator disposed between the anode foil and the cathode foil. At least one of the anode foil and the cathode foil includes a metal foil having a porous portion and a core portion continuous with the porous portion, The metal foil has a main surface on which the pores of the porous portion are open, The porous portion has an opening on the main surface and a plurality of recesses that are dispersed in a dot-like manner in the planar direction of the metal foil. The opening diameter of the pores in the porous portion is less than 2 μm. The opening diameter of the recess is 2 μm or more. The aforementioned recesses are present in an electrolytic capacitor in a range of 10 to 62,500 per 1 mm² of the main surface.

16. The electrolytic capacitor according to claim 15, wherein the opening diameter of the recess is in the range of 4 μm or more and 120 μm or less.

17. The electrolytic capacitor according to claim 15 or 16, wherein the height Lc of the winding body is 20 mm or less.

18. The electrolytic capacitor according to any one of claims 15 to 17, wherein the depth H of the recess and the thickness T of the porous portion have a relationship of 0.067 ≤ H / T ≤ 1.

19. The electrolytic capacitor according to any one of claims 15 to 18, wherein the shape of the opening of the recess is at least one selected from the group consisting of a circle, an ellipse, a star shape, and a polygon with at least some rounded corners.

20. comprising a coiled body and an electrolyte, The aforementioned wound body is constructed by winding together a strip-shaped anode foil, a strip-shaped cathode foil facing the anode foil, and a separator disposed between the anode foil and the cathode foil. At least one of the anode foil and the cathode foil includes a metal foil having a porous portion and a core portion continuous with the porous portion, The metal foil has a main surface on which the pores of the porous portion are open, The porous portion has an opening on the main surface and a plurality of recesses that are dispersed in a dot-like manner in the planar direction of the metal foil. The opening diameter of the pores in the porous portion is less than 2 μm. The opening diameter of the recess is 2 μm or more. An electrolytic capacitor in which adjacent recesses are provided with a gap W of 2 μm or more and 2400 μm or less between them.

21. comprising a coiled body and an electrolyte, The aforementioned wound body is constructed by winding together a strip-shaped anode foil, a strip-shaped cathode foil facing the anode foil, and a separator disposed between the anode foil and the cathode foil. At least one of the anode foil and the cathode foil includes a metal foil having a porous portion and a core portion continuous with the porous portion, The metal foil has a main surface on which the pores of the porous portion are open, The porous portion has an opening on the main surface and a plurality of recesses that are dispersed in a dot-like manner in the planar direction of the metal foil. The opening diameter of the pores in the porous portion is less than 2 μm. The opening diameter of the recess is 2 μm or more. An electrolytic capacitor in which the ratio of the average opening diameter Da of the recess to the height Lc of the winding body, Da / Lc, is 0.5 × 10⁻⁴ or more and 2.4 × 10⁻⁴ or less.

22. comprising a coiled body and an electrolyte, The aforementioned wound body is constructed by winding together a strip-shaped anode foil, a strip-shaped cathode foil facing the anode foil, and a separator disposed between the anode foil and the cathode foil. At least one of the anode foil and the cathode foil includes a metal foil having a porous portion and a core portion continuous with the porous portion, The metal foil has a main surface on which the pores of the porous portion are open, The porous portion has an opening on the main surface and a plurality of recesses that are dispersed in a dot-like manner in the planar direction of the metal foil. The opening diameter of the pores in the porous portion is less than 2 μm. The opening diameter of the recess is 2 μm or more. The porous portion includes a first porous portion and a second porous portion arranged on either side of the core portion. The main surface has a first main surface through which the pores of the first porous portion are open, and a second main surface through which the pores of the second porous portion are open. The plurality of recesses include a plurality of first recesses arranged in the first porous portion and opening to the first main surface, and a plurality of second recesses arranged in the second porous portion and opening to the second main surface, in an electrolytic capacitor.

23. In the aforementioned winding, the metal foil is wound such that the first main surface faces the outer circumference of the winding. 1 mm of the first main surface ２ The number of the first recess present in each area is equal to the number of recesses in the second main surface per 1 mm. ２ The electrolytic capacitor according to claim 22, wherein the number of second recesses present in a given area is greater than the number of recesses present in that area.

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