Electrode foil for electrolytic capacitors, and electrolytic capacitor

Abstract

This electrode foil for electrolytic capacitors comprises a metal foil including: a porous part; and a core part that is continuous with the porous part. The metal foil has a main surface on which pores of the porous part open, and the porous part has a plurality of recesses that open in the main surface and that are disposed so as to be dispersed in the form of dots in the surface direction of the metal foil. The opening diameter of the pores of the porous part is less than 2 μm. The recesses that are adjacent to each other respectively have an opening diameter of D1 μm and an opening diameter of D2 μm, and are provided so as to have a gap of L μm therebetween. The opening diameter D1 and the gap L satisfy relationships of 2≤D1 and 2≤L / D1≤50. The opening diameter D2 and the gap L satisfy relationships of 2≤D2 and 2≤L / D2≤50.

Description

Electrode foil for electrolytic capacitors and electrolytic capacitors

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

[0002] The electrode foil of an electrolytic capacitor is made of a metal foil that includes a porous portion and a core portion that is 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 proposes an electrode foil made of a strip-shaped foil, which includes an expanded surface portion formed on the surface of the foil, a core portion which is the remaining portion of the foil excluding the expanded surface portion, and a plurality of dividing portions which extend in the expanded surface portion in the width direction of the strip and divide the expanded surface portion. The dividing portions have a groove width of 50 μm or less, including 0 μm, when the foil is flattened.

[0004] JP 2017-224844 A

[0005] By providing a dividing section, the indentation depth (Erichsen value) in the Erichsen test increases. However, the dividing section extends in the width direction of the electrode foil, and the folding endurance strength of the electrode foil in the width direction is low. Stress generated when the electrode foil is wound causes cracks to form in the width direction of the electrode foil along the dividing section, resulting in a crack that extends almost linearly from one end of the electrode foil to the other end in the width direction. This results in foil breakage. Prevention of foil breakage during electrode foil winding is still insufficient.

[0006] One aspect of the present disclosure includes a metal foil having a porous portion and a core portion continuous with the porous portion, the metal foil having a main surface to which pores of the porous portion open, the porous portion having a plurality of recesses that open to the main surface and are arranged in a dot-like dispersed manner in a direction of the main surface, the opening diameter of the pores of the porous portion being less than 2 μm, and the recesses adjacent to each other each having a diameter of D １ μm and D ２ The openings have a diameter of D １ The distance L is 2≦D １ , and 2≦L / D １ ≦50, and the opening diameter D ２The distance L is 2≦D ２ , and 2≦L / D ２ The present invention relates to an electrode foil for an electrolytic capacitor, which satisfies the relationship of ≦50.

[0007] Another aspect of the present disclosure relates to a battery including a wound body and an electrolyte, the wound body being configured by winding an anode foil, a 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 including 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 pores of the porous portion open, the porous portion having a plurality of recesses that open to the main surface and are arranged in a dot pattern in a direction of the main surface, the opening diameter of the pores in the porous portion being less than 2 μm, and the recesses adjacent to each other each having a diameter of D １ μm and D ２ The openings have a diameter of D １ The distance L is 2≦D １ , and 2≦L / D １ ≦50, and the opening diameter D ２ The distance L is 2≦D ２ , and 2≦L / D ２ ≦50.

[0008] Another aspect of the present disclosure relates to an electrolytic capacitor including: a wound body; and an electrolyte; the wound body is configured by winding an anode foil, a 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 pores of the porous portion open, the pores of the porous portion having an opening diameter of less than 2 μm; the porous portion has a plurality of recesses that open to the main surface and are arranged in a dot pattern dispersed in the direction of the main surface, the opening diameter of the recesses being 2 μm or more; and cracks exist between adjacent recesses.

[0009] According to the present disclosure, it is possible to prevent breakage of the electrode foil for an electrolytic capacitor when the electrode foil is wound.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] 6 is a front view of a main part schematically showing an example of an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure; FIG. 7 is a front view of a main part schematically showing another example of an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure; FIG. 8 is a cross-sectional view taken along III-III in FIG. 2; FIG. 9 is an SEM image showing a state after winding of an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure; FIG. 10 is a diagram schematically showing an example of a wound body as viewed from an end face side; FIG. 11 is a cross-sectional view schematically showing an electrolytic capacitor according to an embodiment of the present disclosure; FIG. 12 is a perspective view schematically showing the configuration of the wound body of FIG.

[0012] The following describes embodiments of the electrolytic capacitor according to the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be used as examples. However, other numerical values ​​and materials may be used as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be interpreted as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more materials may be used in combination.

[0013] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0014] In the following description, the terms "contain" or "comprise" encompass "contain (or include)," "consist essentially of," and "consist of."

[0015] "Electrolytic capacitor" may be read as "solid electrolytic capacitor", and "capacitor" may be read as "capacitor".

[0016] [Electrolytic Capacitor Electrode Foil] An electrolytic capacitor electrode foil according to an embodiment of the present disclosure 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) on which the pores of the porous portion are open. The porous portion has a plurality of recesses opening on the main surface S. The recesses are arranged in a dot-like pattern dispersed in the plane direction of the metal foil (as viewed from the main surface S). The opening diameter of the recesses is larger than the opening diameter of the pores in the porous portion. That is, the pores in the porous portion are less than 2 μm, and the opening diameter of the recesses is 2 μm or more. Note that, in this specification, the term "opening diameter" simply refers to the "maximum diameter of the opening." That is, the opening diameter of the recesses refers to the maximum diameter of the opening of the recess. The opening diameter of the pores in the porous portion refers to the maximum diameter of the opening of the pore. Hereinafter, the plurality of recesses having an opening diameter of 2 μm or more and arranged in a dot-like pattern dispersed in the plane direction of the metal foil will also be referred to as a "recess group." The recesses are spaced apart from one another in the porous portion.

[0017] Adjacent recesses are D １ (μm) and D ２ The aperture diameter D (μm) is provided at an interval L (μm). １ and the interval L is 2≦D １ , and 2≦L / D １ The relationship of ≦50 is satisfied. ２ and the interval L is 2≦D ２ , and 2≦L / D ２ The relationship of ≦50 is satisfied.

[0018] D １ and D ２ may be the same or different from each other. １ / D ２ is in the range of 6 / 10 or more and 10 / 6 or less. １ / D ２ may be 8 / 10 or more and 10 / 8 or less, or may be 1.

[0019] Hereinafter, “opening diameter D １ " and "Opening diameter D ２ " and " may be collectively referred to as "opening diameter D." L / D may be 2 or more and 30 or less, 2 or more and 20 or less, or 5 or more and 10 or less.

[0020] The term "adjacent recesses" refers to recesses that are located next to each other and are closest to each other. The term "distance L" refers to the length of a line segment that connects the adjacent recesses on the main surface S at the shortest distance.

[0021] The multiple recesses allow high-quality cracks, as described below, to be formed when the electrode foil is wound, and suppress the formation of cracks that extend linearly from one end of the foil to the other end in the width direction, which can cause the foil to break.

[0022] The winding of the electrode foil forms cracks between the recesses, which relieves the stress caused by the winding of the electrode foil and prevents the electrode foil from breaking during winding. The winding of the electrode foil is performed during the process of winding the electrode foil around a roll, the process of forming a wound body, etc. in the capacitor manufacturing process.

[0023] The cracks are formed so as to extend from the inner walls of the recesses when viewed from the main surface S, and so as to connect the cracks extending from the recesses. The length and shape of the cracks, as well as the direction in which the cracks extend, can be controlled by the recess group. Depending on the arrangement of the recess group, the cracks may be formed so as to curve slightly between the recesses on the main surface S.

[0024] If the recess groups were not provided, stress would be generated when the electrode foil is wound during the capacitor manufacturing process, causing cracks to rapidly progress across the foil width, potentially leading to foil breakage. In contrast, in a capacitor equipped with the electrode foil according to the present disclosure, cracks are formed between the recesses in the electrode foil in the wound capacitor element, preventing foil breakage. The formation of cracks between the recesses in the electrode foil in the wound capacitor element indicates that the stress generated when the electrode foil is wound during the capacitor manufacturing process is alleviated.

[0025] Furthermore, cracks and foil breakage may occur due to vibrations when the capacitor is in use by a user. In contrast, the electrode foil according to the present disclosure can suppress foil breakage and the like due to vibrations when the capacitor is in use, and is suitable for use in capacitors for vehicles and the like that require high reliability against vibrations.

[0026] During the manufacturing process of electrolytic capacitors, the metal foil (sheet) used as the raw material for the electrode foil comes into contact with processing liquids (e.g., etching solutions, chemical conversion solutions) and rollers, which can cause unevenness (or scratches). When the electrode foil is wound, stress concentrates on these unevennesses, which can lead to foil breakage during winding. Furthermore, rolled foil (original aluminum foil) is typically used for the metal foil, which has rolling marks created during the manufacturing process. The rolling marks can cause uneven etching pits, which can locally reduce folding strength and lead to foil breakage during winding. In contrast, the use of an electrode foil according to the present disclosure can prevent the above-mentioned foil breakage.

[0027] However, even if the opening diameter of the recesses is larger than the opening diameter of the pores of the porous portion, if the opening diameter D is less than 2 μm, the cracks are less likely to form and the folding strength tends to decrease. Also, if L / D is less than 2, the spacing between the recesses becomes small and the strength tends to decrease. If L / D is greater than 50, the spacing between the recesses becomes large, the number of recesses per unit area of ​​the main surface S decreases, and the effect of the recesses tends to be reduced.

[0028] The above D １ , D ２, and L are calculated as follows: An image of the main surface S of the electrode foil is obtained using a scanning electron microscope (SEM). Using this image, an opening with a maximum diameter of 2 μm or more is considered to be an opening of a recess, and two recesses that are adjacent to each other and closest to each other are considered to be adjacent recesses. The maximum diameter of each opening of the two recesses is calculated, and D １ and D ２ Line segments are drawn connecting the adjacent recesses, and the length of the shortest line segment among the line segments is determined and set as L.

[0029] In the direction perpendicular to the winding direction when the metal foil is wound, adjacent recesses may be provided with a distance L therebetween. Here, "a direction perpendicular to the winding direction" means a direction at an angle of 65° to 115° with respect to the winding direction. In the direction perpendicular to the winding direction, not all of the recesses may be aligned in a fixed direction, and recesses in different directions may be mixed within the above angle range.

[0030] The plurality of recesses may be arranged in a staggered pattern. In this case, the plurality of recesses are spaced apart by an interval L in the winding direction when the metal foil is wound. １ (μm) apart, and the spacing L ２ (μm) apart, and the spacing L ３ The spacing L may be 1 μm. １ ~L ３ The smallest interval among these may be the interval L.

[0031] The adjacent recesses have circular openings of the same size, and one of the adjacent recesses may be provided in the winding direction when the metal foil is wound relative to the other recess. In this case, the distance L may be 15 μm or more and 250 μm or less. Note that "provided in the winding direction" does not only include the case where the adjacent recesses are provided along the winding direction when the metal foil is wound, but also the case where one recess is provided shifted from the other recess in the direction perpendicular to the winding direction by a distance of no more than one recess from the winding direction. The above "same size" means that D １ / D ２is in the range of 6 / 10 or more and 10 / 6 or less. １ / D ２ may be 8 / 10 or more and 10 / 8 or less, or may be 1.

[0032] FIG. 1 is a front view of a main portion illustrating an example of an electrode foil according to an embodiment of the present disclosure. In FIG. 1, the X and Y directions respectively indicate the length direction (winding direction) and width direction of the strip-shaped electrode foil. Multiple recesses are distributed across the main surface S (X and Y directions) of the electrode foil 351, and FIG. 1 shows a partial region including recesses arranged in the X direction of the electrode foil 351. As shown in FIG. 1, adjacent recesses 381 and 382 are provided on the main surface S of the electrode foil 351 (porous portion 361), and have circular openings with the same opening diameter D. The opening diameter D is 2 μm or more. The adjacent recesses 381 and 382 are provided along the X direction. That is, one recess 381 is spaced apart from the other recess 382 by a distance L. １１ are provided in the X direction with a gap therebetween.

[0033] Furthermore, one recess 381 may be provided slightly offset in the Y direction (direction perpendicular to the winding direction) from the other recess 382 within a range of one recess 381 (opening diameter D or less) from the X direction. For example, one recess 381 may be provided at a distance L from the other recess 382. １２ Alternatively, the recess 381 may be provided at a position indicated by the broken circle from the X direction, shifted in the Y direction by the distance of one recess 381 .

[0034] L １１ / D (or L １２ / D) is 2 or more and 50 or less. １１ (or L １２ ) may be 15 μm or more and 250 μm or less. １１ (or L １２ When the thickness (mm) of the metal foil is 15 μm or more, if the metal foil is a rolled foil and the X direction is the rolling direction, strength in the rolling direction is ensured even if the recesses are arranged in the rolling direction. In this case, cracks are likely to be formed in the Y direction by winding, and the cracks formed in the Y direction can be appropriately distributed in the X direction.

[0035] The metal foil may be a rolled foil, and the winding direction of the metal foil may be parallel to the rolling direction of the rolled foil. In this case, the influence of rolling marks during winding can be reduced compared to when the metal foil is wound in a direction perpendicular to the rolling direction. Note that "the winding direction is parallel to the rolling direction of the rolled foil" means that the angle formed between the winding direction and the rolling direction is within the range of -20° to 20°.

[0036] The depth H (μm) of the recess and the thickness T (thickness per side) (μm) of the porous portion preferably satisfy the relationship 0.05≦H / T≦1.2. The "depth H of the recess" refers to the distance from the opening of the recess to its deepest portion. H / T may be 0.1 or more and 1.1 or less, 0.2 or more and 1.1 or less, or 0.5 or more and 1 or less. When H / T is 0.05 or more (or 0.2 or more), the folding strength of the electrode foil is easily ensured. When H / T is 1.2 or less (or 1.0 or less), the strength of the electrode foil (core portion) is easily ensured. Furthermore, H / T may be greater than 1 and less than 1.2. That is, the recess may extend further from the porous portion to the core portion within a range in which the strength of the electrode foil (core portion) is ensured. In this case, the depth h of the recess within the core portion may be, for example, 7 μm or less, or 4 μm or less.

[0037] The depth H of the recess is determined by measuring the distance from the opening to the deepest part of the recess using an SEM image of the cross section of the electrode foil, and the thickness T of the porous portion is determined by measuring the thickness at any 10 points of the porous portion using an SEM image of the cross section in the thickness direction of the electrode foil and averaging the measured values.

[0038] The diameter of the recess may be larger on the main surface side than on the core side. For example, when the opening diameter of the recess is D, the diameter of the recess in the same direction as the opening diameter D when moving a distance D from the opening of the recess in the depth direction may be 0.8D or less, or may be 0.05D or more and 0.8D or less.

[0039] From the viewpoint of improving the tensile strength and folding endurance, the recesses may extend at an angle with respect to the main surface S. From the viewpoint of easiness in forming the recesses, the recesses may extend perpendicular to the main surface S. Note that being perpendicular to the main surface S means that the recesses extend at an angle of 80° to 100° with respect to the main surface S.

[0040] The maximum and minimum diameters of the opening of one recess are D Ｌ and D Ｓ When the maximum diameter of the recessed portion opening is D Ｌ Minimum diameter D Ｓ Ratio of: D Ｓ / D Ｌ may be, for example, 0.05 or more and 1 or less, or 0.2 or more and 1 or less.

[0041] Examples of the shape of the recess include a columnar shape (for example, a cylindrical shape, an elliptical cylinder shape, a rectangular column shape, or the like), a pyramidal shape (for example, a conical shape, a rectangular pyramidal shape, or the like), and a truncated pyramidal shape (for example, a truncated conical shape, a rectangular pyramidal shape, or the like).

[0042] From the viewpoint of increasing the folding endurance of the electrode foil, the opening diameter D of the recess is preferably 4 μm or more, more preferably 8 μm or more. From the viewpoint of improving the folding endurance of the electrode foil and ensuring the 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 any combination of the above upper and lower limits, for example, 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. The opening diameter D (μm) of the recess and the thickness F (μm) of the electrode foil preferably satisfy the relationship D / F<0.5, and more preferably satisfy the relationship D / F<0.25 (or 0.2).

[0043] The recesses are preferably arranged regularly in the surface direction of the metal foil. The recesses are preferably arranged at equal intervals in the surface direction of the metal foil. In the surface direction of the metal foil, the recesses may be arranged in a staggered pattern or in a square lattice pattern. When two porous portions are arranged with a core portion between them, the opening diameter D, spacing L, shape, arrangement, etc. of the recesses may be the same or different from each other.

[0044] Examples of the shape of the opening of the recess include a circle, an ellipse, a polygon, a star, and a teardrop. 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. Polygons include triangles, rectangles, hexagons, etc. Star shapes include shapes with interior angles of 180 degrees or more, and typical shapes are polypointed stars such as pentagrams and hexagrams. The multiple sides that make up the star shape may be the same or different.

[0045] The porous portion may be formed on one surface of the metal foil or on both surfaces of the metal foil. When the porous portion is formed on both surfaces of the metal foil, the recessed portion group may be provided on one surface of the metal foil or on both surfaces of the metal foil.

[0046] (Electrode Foil) The metal foil used for the electrode foil contains, for example, a valve metal such as aluminum (Al), tantalum (Ta), or niobium (Nb). The metal foil may contain the valve metal as an alloy or compound containing the valve metal. The metal foil may be an integrated product of a core portion and a porous portion. The porous portion is formed, for example, by roughening the surface of a metal foil containing a valve metal by etching. The porous portion is the outer portion of the metal foil that has been made porous by etching, and the remaining portion, which is the inner portion of the metal foil, is the core portion. 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.

[0047] 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, etc. The thickness T of the porous portion may be, for example, 1 / 10 to 5 / 10 of the thickness of the metal foil per side. In the case of an anode foil, the thickness T of the porous portion is, for example, 10 μm to 160 μm, and may be 50 μm to 160 μm.

[0048] The metal foil includes a metal skeleton that constitutes the porous portion. The metal skeleton refers to a metal portion having a microstructure in the porous portion. The porous portion has a plurality of pores (pits) surrounded by the metal skeleton. From the viewpoint of increasing the surface area and forming the dielectric layer deep within the porous portion, the pore diameter (opening diameter) may be in the range of less than 2000 nm, and may be 100 nm or more and 1500 nm or less.

[0049] The shape of the pores (pits) may be sponge-like or tunnel-like. Tunnel-like pits include pits that extend from the surface side of the porous portion toward the core side.

[0050] In the case of spongy pits, the pore diameter (opening diameter) may be, for example, 600 nm or less, or may be 50 nm or more and 500 nm or less. In the case of spongy pits, the average pore diameter Dp may be 80 nm or more and 400 nm or less, or may be 100 nm or more and 300 nm or less. Electrode foils having spongy pits are used, for example, in low-voltage electrolytic capacitors. Specifically, they are used in electrolytic capacitors using chemically formed foils of 200 V or less. In the case of tunnel-shaped pits, the pore diameter (opening diameter) may be, for example, 1900 nm or less, or 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 may be 400 nm or more and 1400 nm or less. Electrode foils having tunnel-shaped pits are used, for example, in medium- to high-voltage electrolytic capacitors using chemically formed foils of 180 V or more.

[0051] The average pore diameter Dp of the porous portion is determined by measuring the pore diameter distribution of the electrode foil (porous portion) using a mercury porosimeter. Specifically, the pore diameter (mode diameter) corresponding to the apex of a peak (the largest peak if multiple peaks exist) that appears on the pore distribution curve (vertical axis: log differential pore volume, horizontal axis: pore diameter) obtained by the measurement is determined as the average pore diameter Dp. For example, an AutoPore V series manufactured by Micromeritics Corporation is used as the measurement device.

[0052] The pore distribution curve shows the distribution of pores in the porous portion in the range of pore diameters of less than 2 μm. Normally, the recesses have much larger diameters (opening diameters) than the pores in the porous portion, and it is difficult to measure the diameters of the recesses using a mercury porosimeter under the same conditions as those for measuring the porous portion.

[0053] The electrode foil may include a dielectric layer covering the metal skeleton that constitutes the porous portion having the recessed portion. In this case, the electrode foil can be used as an anode foil. The dielectric layer covers the outer surface (main surface S) of the porous portion and at least a portion of the inner wall surfaces of the pores and recessed portions of the porous portion. In other words, the dielectric layer is provided so as to cover at least a portion of the surface of the metal skeleton that surrounds the pores and recessed portions.

[0054] The thickness F of the metal foil (electrode foil) may be 10 μm or more, 60 μm or more, or 80 μm or more (or 100 μm or more). When the thickness F of the metal foil is 80 μm or more (or 100 μm or more), the stress generated during winding is large, and therefore, the stress is significantly alleviated by the formation of cracks between the recesses.

[0055] 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. An electrode foil having a dielectric layer with a thickness of 24 nm or more can be used as an anode foil for an electrolytic capacitor with a rated voltage of 20 V or more. Particularly when used in a hybrid capacitor, it is preferable to form a dielectric layer with a thickness of 50 nm or more, and the chemical conversion voltage during chemical conversion is preferably 30 V or more. When the chemical conversion voltage is 30 V or more, the dielectric layer also becomes thick, which is likely to cause issues with the strength of the electrode foil, and therefore the effect of stress relaxation due to crack formation between the recesses is significant. The thickness of the dielectric layer is determined by measuring the thickness at any 10 points on the dielectric layer using SEM or TEM images of a cross section of the electrode foil in the thickness direction and averaging these measurements.

[0056] (Method for manufacturing electrode foil) The method for manufacturing an 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. In the etching step, the surface of the metal foil containing a valve metal is etched to roughen the surface of the metal foil, thereby forming a porous portion continuous with the core. The etching may be electrolytic etching or chemical etching.

[0057] Electrolytic etching allows for the mass production of electrode foils having porous portions containing pores with diameters (opening diameters) of less than 2 μm. AC etching allows for the production of electrode foils having porous portions containing spongy pits with diameters of 1.5 μm or less. DC etching allows for the production of electrode foils having porous portions containing tunnel-shaped pits with diameters of less than 2 μm. AC etching is preferred because it is easy to increase the difference between the opening diameters of the pores in the porous portions and the opening diameters of the recesses.

[0058] In the recess group forming step, the recess group may be formed by pressing a jig having a plurality of protrusions against the metal foil having a roughened surface. The metal foil having roughened surfaces may be transported between a pair of rollers having a plurality of protrusions, and the recess group may be formed on both roughened surfaces of the metal foil by pressing the pair of rollers. The recess group may be formed by laser processing, blast processing, etching, or the like.

[0059] The method for manufacturing an electrode foil may include a step of slitting the etched foil. For example, a strip of etched foil having 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 the step of forming the recessed portion group, or after the step of forming the recessed portion group (or after the step of forming the dielectric layer). After the slitting, the metal foil may be wound around a roller. When the slit width is small, such as 10 mm or less, foil breakage may occur due to stress generated in the metal foil when the metal foil is wound around a roller. However, when the step of winding the metal foil around a roller is performed after the step of forming the recessed portion group, such foil breakage is suppressed.

[0060] The method for manufacturing an electrode foil may include a step of forming a dielectric layer covering the metal skeleton that constitutes the porous portion having the recessed portion group. The dielectric layer forming step may be performed before or after the recessed portion forming step. In the dielectric layer forming step, an oxide film containing a valve metal may be formed on the surface of the metal foil having the porous portion (porous portion having the recessed portion group) by anodization (chemical conversion treatment).

[0061] 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 electrolytic capacitor, or as the anode body of a laminated electrolytic capacitor.

[0062] FIG. 2 is a front view schematically illustrating another example of an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure. The strip-shaped electrode foil 350 (metal foil) in FIG. 2 has a first main surface S1 and a second main surface S2 opposite the first main surface S1. FIG. 2 illustrates a portion of the electrode foil 350 as viewed from the first main surface S1 side. In FIG. 2, the X and Y directions respectively indicate the length and width directions of the strip-shaped electrode foil. FIG. 3 is a cross-sectional view taken along III-III in FIG. 2. FIG. 3 is a schematic diagram illustrating a cross section of the electrode foil 350 in the thickness direction and the Y direction in FIG. 2. Note that the electrode foil for an electrolytic capacitor according to the present disclosure is not limited to the electrode foil illustrated in FIGS. 2 and 3. Each figure is a schematic illustration, and the dimensional ratios of the components (e.g., the ratio between the size of the recesses and the spacing) may differ from the actual ratios.

[0063] The strip-shaped electrode foil 350 (metal foil) has a first porous portion 360a and a core portion 370 continuous with the first porous portion 360a. The electrode foil 350 has a first main surface S1 on which the pores (not shown) of the first porous portion 360a open. The first porous portion 360a has a plurality of cylindrical recesses 380a opening on the first main surface S1. The plurality of first recesses 380a are spaced apart from one another and are arranged in a dot-like pattern in the surface directions (X direction and Y direction) of the electrode foil 350. The opening diameter of the pores in the first porous portion 360a is less than 2 μm. When the electrode foil 350 is a rolled foil, the X direction is preferably the rolling direction.

[0064] As shown in FIG. 2 , the multiple first recesses 380a are arranged at equal intervals in a staggered pattern. Adjacent first recesses 380a are arranged with a distance L between them. The multiple first recesses 380a have circular openings and have an opening diameter D (μm). The opening diameter D of the first recesses 380a is 2 μm or more. L / D is 2 or more and 50 or less. In this case, when the electrode foil is wound in the X direction, good quality cracks are formed between the first recesses 380a, which relieves stress caused by winding, increases folding strength in the Y direction, and suppresses foil breakage during winding.

[0065] The first recesses 380a are spaced apart from one another at intervals L in the winding direction (X direction) of the metal foil. １ (μm) apart, and the spacing L ２ (μm) apart, and the spacing L ３ They are arranged with a gap of L (μm). １ and L ３ are the same as each other, and L ２ is smaller than the distance L. That is, L １ / D and L ３ / D is 2 or more and 50 or less. １ and the interval L ２ That is, 2<L ２ / L １In this case, the folding endurance in the Y direction is significantly improved. In particular, when a large stress is generated in the Y direction, the effect of stress relaxation due to crack formation between the recesses is significantly obtained. Examples of such cases include when slitting the electrode foil, when curving the electrode foil and changing the angle of travel during the electrode foil transport process, when forming a wound body, and when placing a sealing member at the opening of a bottomed case that houses a wound body with attached leads and performing crimping.

[0066] In FIG. １ Is L ３ It has the same dimensions as L １ L ３ The arrangement of the recesses may be adjusted so that the thickness is smaller than L １ L ３ The arrangement of the recesses may be adjusted so that the recesses are smaller than L １ >L ３ A relationship like this is desirable.

[0067] By winding the metal foil in the X direction, the cracks are generated in the L direction of FIG. ２ The gap L is easily formed in the direction (Y direction). １ Depending on the size of the crack, the crack is mainly ２ While forming in the direction (Y direction), ３ In this way, the stress caused by the winding can be effectively alleviated. １ The crack may be, for example, 15 μm or more and 250 μm or less. The crack is formed so as to connect, for example, 50 to 500 of the first recesses 380a.

[0068] The electrode foil 350 has a thickness F (μm). F and D / F are, for example, within the ranges exemplified above. The first porous portion 360a has a thickness T (μm), and the first recess 380a has a depth H (μm). T and H / T are, for example, within the ranges exemplified above.

[0069] The opening shape of the first recess shown in FIG. 2 is circular, but is not limited to this. The opening shape of the recess may be elliptical, rectangular, hexagonal, etc. The shape of the first recess is cylindrical, but is not limited to this, and may be a columnar or cone shape other than cylindrical. The multiple first recesses have the same shape and size, but may be different in shape and / or size from each other. The arrangement of the first recesses is not limited to the arrangement shown in FIG. 2, and may be, for example, a square lattice shape. Furthermore, the X direction and Y direction may be the width direction and length direction of the strip-shaped electrode foil, respectively. In this case, in FIG. 2, L １ and L ２ are L respectively. ２ and L １ Even when the Y direction is the winding direction, good quality cracks are formed, the folding strength in the X direction is increased, and foil breakage during winding is suppressed.

[0070] 3, the strip-shaped electrode foil 350 (metal foil) includes a second porous portion 360b and a core portion 370 continuous with the second porous portion 360b. That is, the first porous portion 310a and the second porous portion 360b are arranged to sandwich the core portion 370. The electrode foil 350 has a second main surface S2 on which the pores (not shown) of the second porous portion 360b are open.

[0071] The porous portion 360b has a plurality of second recesses 380b that open to the second main surface S2. The second recesses 380b have the same shape, size, spacing, and arrangement as the first recesses 380a, but the first recesses and the second recesses may have different shapes, etc.

[0072] Here, Fig. 4 is an SEM image showing an example of an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure after winding. Fig. 4 shows a portion of the surface of the electrode foil. The vertical direction of the image is the longitudinal direction (winding direction) of the strip-shaped electrode foil and also the rolling direction of the electrode foil. The recess groups shown in Fig. 4 have the same arrangement as the recess groups shown in Fig. 2. As shown in Fig. 4, by winding the electrode foil, cracks are formed between the recess groups in a direction perpendicular to the winding direction (rolling direction).

[0073] [Electrolytic Capacitor] The electrolytic capacitor according to the present disclosure includes a wound body and an electrolyte. The wound body is formed by winding an anode foil, a cathode foil facing the anode foil, and a separator disposed between the anode foil and the cathode foil. The wound body and the electrolyte are collectively referred to as a capacitor element. 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 opening diameter of the pores of the porous portion is less than 2 μm. The porous portion is open to the main surface and has a plurality of recesses arranged in a dot pattern distributed along the main surface.

[0074] In the electrolytic capacitor according to the embodiment of the present disclosure, adjacent recesses are each D １ (μm) and D ２ The aperture diameter D (μm) is provided at an interval L (μm). １ and the interval L is 2≦D １ , and 2≦L / D １ The relationship of ≦50 is satisfied. ２ and the interval L is 2≦D ２ , and 2≦L / D ２ The relationship of ≦50 is satisfied.

[0075] In the electrolytic capacitor according to the embodiment of the present disclosure, cracks may exist between the recesses of the metal foil in the wound body, and the cracks are formed by winding the metal foil having the recesses and are formed to connect the recesses.

[0076] In addition, in the electrolytic capacitor according to another embodiment of the present disclosure, the opening diameter of the recesses is 2 μm or more, and cracks exist between the recesses. １ (μm) and D ２ (μm), and the interval L (μm) between the recesses is 2≦D １ , 2≦L / D １ ≦50, 2≦D ２ , and 2≦L / D ２ The relationship may be satisfied.

[0077] It is preferable that the cracks extend in a direction perpendicular to the winding direction of the metal foil (width direction) so as to connect at least two or more recesses. Such cracks can be formed by appropriately arranging the recesses (for example, in a staggered pattern as shown in FIG. 2) so that the L / D ratio falls within the range of 2 to 50. For example, a crack is formed so as to connect 2 to 100 recesses.

[0078] 5 is a diagram schematically illustrating an example of a wound body as viewed from an end face side. The wound body 400 is configured by winding an anode foil and a cathode foil around a winding core 410 with a separator interposed therebetween. When the radial thickness of the wound body 400 from the innermost periphery E1 to the outermost periphery E2 is t, the "region P" refers to a region of the wound body 400 whose radial distance from the innermost periphery E1 is equal to or less than (¼)t.

[0079] Cracks may be present at least in region P of the wound body. There may be more cracks in region P than in regions other than region P. Breakage of the electrode foil during winding tends to occur in region P, where the stress caused by winding is likely to be large. On the other hand, good quality cracks that relieve this stress are likely to be formed in region P due to the winding of the electrode foil. By having cracks present in region P, breakage of the electrode foil during winding can be efficiently suppressed.

[0080] The metal foil has a dimension L in the direction perpendicular to the winding direction of the wound body (width direction). Ｗ mm, and the area of ​​the main surface L Ｗ ２ mm ２ In this case, cracks are likely to form between the recesses when the metal foil is wound, and the cracks are likely to relieve the stress generated when the metal foil is wound. Ｗ is the height L of the wound body Ｃ It is almost equivalent to L Ｗ For example, L may be 30 mm or less, or 10 mm or less. Ｗ When the area of ​​the main surface is 30 mm or less, L Ｗ ２ mm ２ The number of recesses per hole may be 1850 or less. ＷWhen the area of ​​the main surface is 10 mm or less, L Ｗ ２ mm ２ The number of recesses per hole may be 625 or less.

[0081] At least one of the anode foil and the cathode foil may be made of a metal foil E. In the metal foil E, the porous portion includes a first porous portion and a second porous portion disposed on either side of a core portion, the main surfaces of which include a first main surface to which the pores of the first porous portion open and a second main surface to which the pores of the second porous portion open, and the plurality of recesses are disposed in the first porous portion and include a plurality of first recesses that open to the first main surface. In this case, cracks formed between the first recesses due to winding tend to relieve stress generated on the first main surface of the metal foil due to winding.

[0082] The plurality of recesses (recess group) of the metal foil E may further include a plurality of second recesses arranged in the second porous portion and opening onto the second main surface. In this case, cracks formed between the second recesses by winding tend to ease the stress generated on the second main surface side of the metal foil by winding.

[0083] From the viewpoint of improving folding endurance, it is preferable that the first recess and the second recess are provided at positions that do not face each other across the core portion.

[0084] In the wound body, the metal foil E may be wound so that the first main surface faces the outer periphery of the wound body. Hereinafter, a wound body including the metal foil E wound so that the first main surface faces the outer periphery of the wound body will be referred to as a "wound body A."

[0085] In the wound body A, the stress generated by winding of the metal foil E is likely to be greater on the first main surface (the outer peripheral side of the wound body) than on the second main surface (the inner peripheral side of the wound body), and the first recess provides a significant stress relief effect. If the stress generated by winding is also greater on the second main surface side, a second recess may be provided on the second main surface. In region P of the wound body A, the stress generated by winding is greater, and it is therefore desirable to provide the first recess and the second recess.

[0086] (Anode Foil) The anode foil includes 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 roughening the metal foil by etching the metal foil containing a valve metal. The valve metal includes, for example, aluminum (Al), tantalum (Ta), niobium (Nb), etc. The metal foil may contain the valve metal as an alloy or compound containing the valve metal.

[0087] The dielectric layer can be obtained by forming an oxide film containing a valve metal on the surface of a roughened metal foil by, for example, anodizing (chemical conversion treatment). The chemical conversion voltage when chemically treating the Al foil may be, for example, 4 V or more, or 40 V or more.

[0088] The thickness of the anode foil may be, for example, 60 μm or more and 200 μm or less, or 80 μm or more (or 100 μm or more) and 200 μm or less. The larger the capacity, the thicker the anode foil tends to be. For example, in the case of a high-capacity anode foil having a thickness of 100 μm or more, the effect of stress relaxation due to crack formation between recesses is significantly obtained.

[0089] (Cathode Foil) The cathode foil may be a metal foil containing a valve metal such as Al, Ta, or 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. The thickness of the cathode foil is, for example, 10 μm or more and 70 μm or less.

[0090] (Separator) The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (for example, aliphatic polyamide, aromatic polyamide such as aramid).

[0091] (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. When the electrolyte includes a solid electrolyte, the electrolytic capacitor may include a solid electrolyte and a liquid electrolyte, or a solid electrolyte and a non-aqueous solvent. Hereinafter, the liquid electrolyte and the non-aqueous solvent are collectively referred to as the liquid component.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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 a liquid electrolyte (electrolytic solution). The electrolytic 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] Here, Fig. 6 is a cross-sectional view schematically illustrating an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 7 is a perspective view schematically illustrating the configuration of the wound body of Fig. 6. In Fig. 7, 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.

[0101] Electrolytic capacitor 200 includes a wound body 100. Wound body 100 is configured by winding an anode foil 10 and a cathode foil 20 with separator 30 interposed therebetween. An electrode foil according to an embodiment of the present disclosure is used for at least one of anode foil 10 and cathode foil 20. Height Lc of wound body 100 is approximately equal to the dimension in the width direction (Y direction) of anode foil 10 and cathode foil 20.

[0102] 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.

[0103] 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.

[0104] 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 containing the electrolyte. The impregnation may be performed under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa. The treatment liquid may contain a solid electrolyte and an electrolytic solution or a non-aqueous solvent.

[0105] 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.

[0106] 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.

[0107] 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, silicone rubber, fluororubber, ethylene propylene rubber, hypalon rubber, butyl rubber, isoprene rubber, and the like, which have high heat resistance, are preferred.

[0108] [Examples] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the examples.

[0109] Examples 1 to 7, Comparative Examples 1 and 2 The strip-shaped electrode foil shown in FIG. 2 was produced by the following procedure. First, a strip-shaped Al foil with a thickness of 120 μm was prepared. A rolled foil with the rolling direction parallel to the length direction (X direction) was used for the Al foil. Both sides of the Al foil were subjected to an etching treatment to roughen the surface of the Al foil. As a result, porous portions (thickness T: 45 μm, average pore diameter Dp: 0.2 μm) with spongy pits were formed on both sides of the Al foil. A plurality of cylindrical recesses (depth H: 45 μm) were formed on both sides of the Al foil using a predetermined jig, providing a group of recesses arranged in a staggered pattern as shown in FIG. 2. The opening diameter D and spacing L of the recesses in FIG. 2 were set to the values ​​shown in Table 1. The main surface L of the metal foil Ｗ ２ (mm ２ The number of recesses present per electrode foil was the value shown in Table 1. In this manner, electrode foils a1 to a7 and b1 to b2 were obtained. a1 to a7 correspond to Examples 1 to 7, and b1 to b2 correspond to Comparative Examples 1 and 2.

[0110] Comparative Example 3 An electrode foil b3 was obtained in the same manner as in a1, except that the plurality of recesses was not formed on both sides of the aluminum foil.

[0111] The electrode foils of the examples and comparative examples obtained above were evaluated as follows.

[0112] [Evaluation: Folding endurance] The electrode foil was sampled along the X direction to obtain a strip-shaped sample piece (length: 100 mm, width: 10 mm). The folding endurance of the sample piece in the width direction (Y direction) was measured. The measurement was performed in accordance with the test method for electrode foils for aluminum electrolytic capacitors of the Electronic Industry Standards of Japan (EIAJ RC-2364A). The folding endurance was expressed as a relative value, with the folding endurance of electrode foil b3 of Comparative Example 3 being set at 100. The evaluation results are shown in Table 1.

[0113]

[0114] In a1 to a7, higher folding endurance strength was obtained than in b1 to b3.

[0115] Examples 8 to 15 Electrode foils a8 to a15 were produced and evaluated in the same manner as for a4, except that the depth H of the recesses was changed so that H / T would have the values ​​shown in Table 2. The evaluation results are shown in Table 2.

[0116]

[0117] In particular, a4 and a9 to a14, which have an H / T ratio of 0.05 or more and 1.2 or less, exhibited excellent folding strength.

[0118] Furthermore, electrode foil a4 was sampled along the Y direction to obtain a strip-shaped sample piece, and the folding endurance of the sample piece in the width direction (X direction) was also measured. The results are shown in Table 3. Table 3 also shows the measurement results when a4 in Table 1 was sampled along the X direction.

[0119]

[0120] Higher folding endurance was obtained in the Y direction than in the X direction.

[0121] The electrode foil according to the present disclosure is suitable for use in electrolytic capacitors that require high reliability.

[0122] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0123] 10: anode foil, 20: cathode foil, 30: separator, 40: winding stop tape, 50A, 50B: lead tabs, 60A, 60B: lead wires, 100, 400: wound body, 200: electrolytic capacitor, 211: bottomed case, 212: sealing member, 213: seat plate, 350, 351: electrode foil, 360a: first porous portion, 360b: second porous portion, 361: porous portion, 370: core portion, 380a: first recess portion, 380b: second recess portion, 381, 382: recess portion, 410: winding core

Claims

1. 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 a plurality of recesses that are open to the main surface and are arranged in a dot-like pattern in a direction toward the main surface, The opening diameter of the pores of the porous portion is less than 2 μm, The adjacent recesses are each D 1 μm and D 2 The apertures have an aperture diameter of 1 μm and are spaced apart by an interval of L μm. The opening diameter D 1 The distance L is 2≦D 1 , and 2≦L / D 1 The relationship is satisfied: ≦50; The opening diameter D 2 The distance L is 2≦D 2 , and 2≦L / D 2 Electrode foil for electrolytic capacitors, which satisfies the relationship:

2. 2 . The electrode foil for an electrolytic capacitor according to claim 1 , wherein adjacent recesses are provided at the interval L in a direction perpendicular to a winding direction when the metal foil is wound.

3. The plurality of recesses are arranged in a staggered pattern, The metal foil is wound with an interval L in the winding direction. 1 μm apart, The distance L in the direction perpendicular to the winding direction 2 μm apart, The distance L 3 μm apart, The distance L 1 ~L 3 2. The electrode foil for an electrolytic capacitor according to claim 1, wherein the distance L is the smallest distance among the distances.

4. The distance L 1 and the interval L 2 That is, 2<L 2 / L 1 Fulfilling the relationship, The distance L 1 and the interval L 3 4. The electrode foil for an electrolytic capacitor according to claim 3, wherein the distance L is the smallest distance among the distances.

5. The adjacent recesses have the same size and circular openings, one of the adjacent recesses is provided in a winding direction of the metal foil relative to the other recess, 2. The electrode foil for an electrolytic capacitor according to claim 1, wherein the distance L is 15 μm or more and 250 μm or less.

6. The metal foil is a rolled foil, 6. The electrode foil for electrolytic capacitors according to claim 2, wherein the winding direction is parallel to a rolling direction of the rolled foil.

7. 2 . The electrode foil for an electrolytic capacitor according to claim 1 , wherein a depth H μm of said recesses and a thickness T μm of said porous portion satisfy a relationship of 0.05≦H / T≦1.

2.

8. 2 . The electrode foil for an electrolytic capacitor according to claim 1 , wherein a diameter of the recess is larger on the main surface side than on the core side.

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

10. A wound body and an electrolyte, the wound body is configured by winding an anode foil, a 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 a plurality of recesses that are open to the main surface and are arranged in a dot-like pattern in a direction toward the main surface, The opening diameter of the pores of the porous portion is less than 2 μm, The adjacent recesses are each D 1 μm and D 2 The apertures have an aperture diameter of 1 μm and are spaced apart by an interval of L μm. The opening diameter D 1 The distance L is 2≦D 1 , and 2≦L / D 1 The relationship is satisfied: ≦50; The opening diameter D 2 The distance L is 2≦D 2 , and 2≦L / D 2 An electrolytic capacitor that satisfies the relationship:

11. The metal foil has a dimension L in a direction perpendicular to the winding direction of the wound body. W mm, The area L of the main surface W 2 mm 2 11. The electrolytic capacitor of claim 10, wherein there are 30 to 2660 of the recesses per unit area.

12. The electrolytic capacitor of claim 10 , wherein a crack exists between the recesses.

13. 13. The electrolytic capacitor according to claim 12, wherein the crack extends in a direction perpendicular to a winding direction of the metal foil so as to connect at least two of the recesses.

14. The crack exists at least in the region P of the winding body, 13. The electrolytic capacitor according to claim 12, wherein the region P is a region whose radial distance from the innermost circumference of the winding body is t / 4 or less, where t is a radial thickness from the innermost circumference to the outermost circumference of the winding body.

15. 15. The electrolytic capacitor of claim 14, wherein the cracks are more present in the region P than in regions other than the region P.

16. the porous portion includes a first porous portion and a second porous portion disposed on either side of the core portion, the main surface includes a first main surface to which the pores of the first porous portion are open and a second main surface to which the pores of the second porous portion are open, The electrolytic capacitor according to claim 10 , wherein the plurality of recesses include a plurality of first recesses disposed in the first porous portion and opening to the first main surface.

17. 17. The electrolytic capacitor according to claim 16, wherein the plurality of recesses include a plurality of second recesses disposed in the second porous portion and opening to the second main surface.

18. 18. The electrolytic capacitor according to claim 17, wherein the first recess and the second recess are provided at positions that do not face each other across the core portion.

19. 17. The electrolytic capacitor according to claim 16, wherein in the wound body, the metal foil is wound such that the first main surface faces an outer periphery of the wound body.

20. A wound body and an electrolyte, the wound body is configured by winding an anode foil, a 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 opening diameter of the pores of the porous portion is less than 2 μm, the porous portion has a plurality of recesses that are open to the main surface and are arranged in a dot-like pattern in a direction toward the main surface, The opening diameter of the recess is 2 μm or more, A crack exists between the recesses.

21. The adjacent recesses are each D 1 μm and D 2 The apertures have an aperture diameter of 1 μm and are spaced apart by an interval of L μm. The opening diameter D 1 The distance L is 2≦D 1 , and 2≦L / D 1 The relationship is satisfied: ≦50; The opening diameter D 2 The distance L is 2≦D 2 , and 2≦L / D 2 21. The electrolytic capacitor of claim 20, satisfying the relationship: ≦50.

22. The metal foil has a dimension L in a direction perpendicular to the winding direction of the wound body. W mm, The area L of the main surface W 2 mm 2 21. The electrolytic capacitor of claim 20, wherein there are 30 to 2660 of the recesses per unit area.

23. 21. The electrolytic capacitor according to claim 20, wherein the crack extends in a direction perpendicular to a winding direction of the metal foil so as to connect at least two or more of the recesses.

24. The crack exists at least in the region P of the winding body, 21. The electrolytic capacitor according to claim 20, wherein the region P is a region whose radial distance from the innermost circumference of the winding body is t / 4 or less, where t is a radial thickness from the innermost circumference to the outermost circumference of the winding body.

25. 25. The electrolytic capacitor of claim 24, wherein the cracks are more present in the region P than in regions other than the region P.

26. the porous portion includes a first porous portion and a second porous portion disposed on either side of the core portion, the main surface includes a first main surface to which the pores of the first porous portion are open and a second main surface to which the pores of the second porous portion are open, 21. The electrolytic capacitor according to claim 20, wherein the plurality of recesses include a plurality of first recesses disposed in the first porous portion and opening to the first main surface.

27. 27. The electrolytic capacitor of claim 26, wherein the plurality of recesses include a plurality of second recesses disposed in the second porous portion and opening to the second main surface.

28. 28. The electrolytic capacitor according to claim 27, wherein the first recess and the second recess are provided at positions that do not face each other across the core portion.

29. 27. The electrolytic capacitor according to claim 26, wherein in the wound body, the metal foil is wound such that the first main surface faces an outer periphery of the wound body.