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

Abstract

This electrode foil for electrolytic capacitors comprises: an anode having a porous part and a core part continuous with the porous part; and a dielectric layer covering a surface of a metal skeleton that constitutes the porous part. An interface layer containing a first element is provided between the metal skeleton constituting the porous part and the dielectric layer. The first element is at least one element selected from the group consisting of sulfur, nitrogen, and phosphorus.

Description

[Technical Field]

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

[0002] The electrode foil of an electrolytic capacitor includes an anode body having a porous portion on its surface. The anode body is made of, for example, a metal foil containing a valve metal, and the porous portion is formed by etching the metal foil, thereby increasing the capacitance of the electrolytic capacitor. The electrode foil also includes a dielectric layer covering the porous portion. For example, Patent Document 1 proposes forming the dielectric layer by a vapor phase method. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 26247 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] In an electrolytic capacitor in which the surface of the dielectric layer is covered with a conductive polymer compound, if a defect occurs in the dielectric layer, leakage current is likely to increase. [Means for solving the problem]

[0005] One aspect of the present invention relates to an electrode foil for an electrolytic capacitor, comprising: an anode body having a porous portion and a core portion continuous with the porous portion; and a dielectric layer covering a surface of a metal skeleton constituting the porous portion, wherein an interfacial layer containing a first element is present between the metal skeleton and the dielectric layer, and the first element is at least one selected from the group consisting of sulfur, nitrogen, and phosphorus.

[0006] Another aspect of the present invention relates to an electrolytic capacitor including a capacitor element, the capacitor element including the above-described electrolytic capacitor electrode foil and a conductive polymer compound covering at least a portion of the dielectric layer.

[0007] Yet another aspect of the present invention relates to a method for producing an electrode foil for an electrolytic capacitor, comprising: a first step of preparing an anode body having a porous portion and a core portion continuous with the porous portion; a second step of forming an interface layer that covers a surface of a metal skeleton constituting the porous portion and contains a first element; and a third step of forming a dielectric layer that is continuous with the interface layer, wherein the first element is at least one element selected from the group consisting of sulfur, nitrogen, and phosphorus.

[0008] Yet another aspect of the present invention relates to a method for producing an electrolytic capacitor, including a step comprising the above-described method for producing an electrode foil for an electrolytic capacitor, and a fourth step of covering at least a portion of the dielectric layer with a conductive polymer compound. [Effects of the Invention]

[0009] According to the present invention, an increase in leakage current of an electrolytic capacitor can be suppressed. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a main part of an electrode foil according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of the part surrounded by the dashed line X in FIG. [Figure 3] FIG. 4 is a cross-sectional view schematically illustrating a main part of an electrode foil according to another embodiment of the present invention. [Figure 4] FIG. 3 is an enlarged view of a portion surrounded by a dashed line Y in FIG. 2. [Figure 5] FIG. 2 is a cross-sectional view showing an example of an anode body having tunnel-shaped pits. [Figure 6] FIG. 10 is a cross-sectional view showing another example of an anode body having tunnel-shaped pits. [Figure 7] FIG. 10 is a schematic cross-sectional view showing yet another example of an anode body having tunnel-shaped pits. [Figure 8] FIG. 2 is a cross-sectional view showing an example of an anode body including a porous portion having main pits and small pits. [Figure 9] FIG. 2 is a cross-sectional view showing an example of an anode body including a porous portion having a main pit and branch pits. [Figure 10] FIG. 1 is a cross-sectional view of an electrolytic capacitor. [Figure 11] FIG. 2 is a perspective view schematically illustrating the configuration of a wound body provided in the electrolytic capacitor. DETAILED DESCRIPTION OF THE INVENTION

[0011] An electrode foil for an electrolytic capacitor according to one embodiment of the present invention includes an anode body having a porous portion and a core portion continuous with the porous portion, and a dielectric layer covering the surface of a metal skeleton constituting the porous portion. Hereinafter, the anode body having a porous portion will also be referred to as a metal foil having a porous portion.

[0012] The porous portion has a metal skeleton and a dielectric layer, and the metal skeleton and the dielectric layer have an interface layer containing a first element, the first element being at least one element selected from the group consisting of sulfur, nitrogen, and phosphorus.

[0013] The provision of the interfacial layer described above can sufficiently reduce leakage current and improve the reliability of electrolytic capacitors. This is presumably because, when defects in the dielectric layer are repaired, the interfacial layer containing the first element forms a high-quality film that contains a large amount of amorphous components and is less likely to generate leakage current.

[0014] In medium- to high-voltage electrolytic capacitors, defects in the dielectric layer are particularly likely to increase leakage current, and therefore the provision of the interface layer significantly reduces leakage current. The withstand voltage of the electrode foil used in medium- to high-voltage electrolytic capacitors is, for example, 30 V or higher, preferably 120 V or higher, more preferably 160 V or higher, and even more preferably 200 V or higher.

[0015] The first elements sulfur and phosphorus are advantageous in that they easily form an amorphous phase, while nitrogen is advantageous in that it inhibits crystallization.

[0016] The thickness of the interface layer may be thin and does not need to have a clear layer structure. It is sufficient that a region where the first element is unevenly distributed can be confirmed between the dielectric layer and the metal skeleton. In other words, if the first element is detected in a microregion between the dielectric layer and the metal skeleton by analysis such as EDX, GD-OES, or FE-AES, which will be described later, it can be considered that an interface layer has been formed. The thickness of the interface layer is, for example, 10 nm or less, and may be 0.1 nm or more and 5 nm or less. The thickness of the interface layer is the average thickness of any 10 points on the interface layer in a cross-sectional image of the porous portion of the electrode foil in the thickness direction obtained by a scanning electron microscope (SEM).

[0017] From the viewpoint of easily sufficiently reducing leakage current, the content of the first element relative to all elements in the interface layer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more. From the viewpoint of easily ensuring that the dielectric layer and the interface layer have appropriate thicknesses, the content of the first element may be 0.01% by mass or more and 10% by mass or less, or may be 0.50% by mass or more and 5% by mass or less.

[0018] The distribution or concentration of each element in the interface layer and the dielectric layer can be analyzed by, for example, energy dispersive X-ray spectroscopy (EDX), glow discharge optical emission spectroscopy (GD-OES), field emission Auger electron spectroscopy (FE-AES), etc. For example, when GD-OES is performed on the interface layer from the surface on the first layer side along the depth direction, if a peak attributed to the first element is observed, it can be determined that the interface layer contains the first element corresponding to that peak.

[0019] The anode body includes a first metal, and the dielectric layer has a first layer including an oxide of a second metal. The second metal may be the same as or different from the first metal. An interface layer that is continuous with the first layer exists between the metal skeleton that constitutes the porous portion and the first layer. An interface layer may exist at the boundary between the first layer and the metal skeleton, or at the boundary between the first layer and another layer that covers the metal skeleton (e.g., part of the second layer described below).

[0020] The interface layer contains at least the first element and may further contain the first metal and / or the second metal as an oxide. The interface layer may be formed, for example, from an insulating compound (such as an oxide) containing the first element, or may be formed by functional groups that are bonded to the metal skeleton on the surface of the metal skeleton and contain the first element.

[0021] When the second metal is different from the first metal, a second metal with a high dielectric constant can be selected without being restricted by the first metal, making it easier to improve the capacitance of the electrolytic capacitor. Furthermore, the range of choices for the second metal is broadened, making it easier to impart various performance characteristics to the dielectric layer without being restricted by the first metal. The first metal may include Al. The second metal may include at least one selected from the group consisting of Ta, Nb, Ti, Si, Zr, and Hf.

[0022] When the first layer contains two or more oxides of the second metal, the two or more oxides may be mixed or may be arranged in layers. The first layer may contain a composite oxide containing two or more metals. From the viewpoint of increasing the capacitance of the electrolytic capacitor, it is preferable that the oxide of the second metal has a higher dielectric constant than the oxide of the first metal. Furthermore, from the viewpoint of increasing the withstand voltage of the electrolytic capacitor, it is preferable that the second metal is Ta, Ti, Si, or the like.

[0023] Here, Fig. 1 is a cross-sectional schematic diagram showing an example of an electrode foil, Fig. 1 shows a part of a porous portion having a dielectric layer, and Fig. 2 is an enlarged view of the part surrounded by the dashed line X in Fig. 1.

[0024] As shown in FIG. 1, the anode foil 10 includes an anode body 110, which is an integrated body of a core portion 111 and a porous portion 112, and a dielectric layer 120 (first layer 121) that covers the surface of the metal skeleton that constitutes the porous portion 112. The porous portion 112 has a large number of tunnel-shaped pits P surrounded by the metal skeleton. The dielectric layer 120 is provided so as to cover at least a portion of the surface of the metal skeleton. The first layer 121 contains an oxide of a second metal and has a thickness T1. An interface layer 130 is provided at the boundary between the first layer 121 and the metal skeleton. D in FIG. 1 indicates the thickness of the porous portion. In the case of a medium- to high-voltage electrolytic capacitor, the thickness T1 of the first layer 121 is, for example, 40 nm or more and 200 nm or less.

[0025] (2nd layer) The electrode foil may have a second layer containing the first metal between the metal skeleton and the first layer. In this case, the dielectric layer has the first and second layers. The second layer is formed by chemical conversion treatment of the anode body, and defects in the first layer can be repaired as a result. The second layer may contain an oxide of the first metal and an oxide of the second metal, or may contain a composite oxide of the first metal and the second metal.

[0026] The second layer formed by chemical conversion of an anode body having a first layer and an interface layer on its surface has a region (interface layer) containing the first element at least on the first layer side. If the second layer is thin, the entire second layer may be a region (interface layer) containing the first element. As a result of chemical conversion (formation of the second layer), a high-quality coating with low crystallinity and low defect density is likely to be formed in the region containing the first element. This further reduces leakage current. When forming the second layer by chemical conversion, it is preferable to use a valve metal suitable for chemical conversion as the first metal.

[0027] The thickness T2 of the second layer is not particularly limited, but may be smaller than the thickness T1 of the first layer. By making the thickness of the first layer relatively large, for example, when a second metal with a high dielectric constant is selected, the capacitance of the electrolytic capacitor can be significantly improved. The thickness T2 of the second layer is, for example, 0.5 nm or more and 200 nm or less, and may be 5 nm or more and 100 nm or less.

[0028] The ratio of the thickness T1 of the first layer to the thickness T2 of the second layer is not particularly limited and may be set appropriately depending on the application, desired effects, etc. For example, the thickness ratio: T1 / T2 may be 1 or more, 2 or more, or 5 or more.

[0029] Here, Fig. 3 is a cross-sectional schematic diagram showing another example of an electrode foil. Fig. 3 shows a part of a porous portion having a dielectric layer on the surface. Fig. 4 is an enlarged view of the part surrounded by dashed line Y in Fig. 3. In Fig. 3, components corresponding to those in Fig. 1 are given the same reference numerals as in Fig. 1, and descriptions of configurations that overlap with those in Fig. 1 will be omitted. In Fig. 4, components corresponding to those in Fig. 2 are given the same reference numerals as in Fig. 2, and descriptions of configurations that overlap with those in Fig. 2 will be omitted.

[0030] As shown in Fig. 3, the dielectric layer 120 has, in order from the metal skeleton side of the porous portion, a second layer 122 and a first layer 121. The first layer 121 has a thickness T1, and the second layer has a thickness T2. As shown in Fig. 4, the second layer 122 has a region (interface layer 130) containing the first element on the first layer 121 side. If the thickness of the second layer is very small, the entire second layer may be a region (interface layer) containing the first element.

[0031] (anode body) The anode body is, for example, an integrated body of a core portion and a porous portion. The anode body is obtained, for example, by etching a part of a metal foil containing a first metal. The porous portion is the outer part of the metal foil that has been made porous by etching, and the remaining part, which is the inner part of the metal foil, is the core portion.

[0032] The metal skeleton refers to a metal portion having a microstructure in the porous portion. The porous portion has pits or pores surrounded by the metal skeleton. The dielectric layer is provided so as to cover at least a portion of the surface of the metal skeleton surrounding the pits or pores.

[0033] The thickness 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, and the like. The thickness D of the porous portion is, for example, 10 μm or more and 160 μm or less, and may be 50 μm or more and 160 μm or less. The thickness D of the porous portion may be, for example, 1 / 10 or more and 5 / 10 or less of the thickness of the anode body per side. The thickness D of the porous portion is determined by obtaining an SEM image of a cross section of the porous portion of the anode body (electrode foil) in the thickness direction and calculating the average thickness value at any 10 points. Hereinafter, the thicknesses of the dielectric layers, i.e., the thickness T1 of the first layer and the thickness T2 of the second layer, are determined in the same manner.

[0034] The porous portion has multiple pits (pores). The pits may have a tunnel-like shape. Examples of the tunnel-like pits include columnar (e.g., cylindrical, rectangular, etc.), pyramidal (e.g., conical, rectangular, etc.), and frustum (e.g., truncated cone, rectangular, etc.). The multiple tunnel-like pits included in the porous portion may have the same or different shapes. The length direction of the tunnel-like pit is parallel to the axis of the cylinder if the pit is cylindrical, and parallel to a line passing through the centers of the top and bottom surfaces of the truncated cone if the pit is truncated cone. In the case of tunnel-like pits, an interfacial layer is easily formed on the wall surface of the pit. Furthermore, a large dielectric layer (first layer), for example, with a thickness of 20 nm or more and 300 nm or less, is easily formed from the surface side of the porous portion to the core side (deep part of the pit). ALD is easily used to form a film covering the wall surface of the pit. The pit walls can be easily covered with the conductive polymer or the conductive polymer and the liquid component to the depth of the pit. This makes it easy to obtain an electrode foil with low resistance, high heat dissipation, and high strength. The pits may also be shaped like a sponge.

[0035] From the viewpoint of increasing the surface area and forming the dielectric layer deep in the porous portions (pits), the average diameter (pore diameter) of the pits (pores) may be, for example, 50 nm or more and 2100 nm or less. When the average diameter of the pits is 200 nm or more, it is easy to attach the first treatment liquid containing the first element to the wall surfaces of the pits in the second step (a step of impregnating the anode body with the first treatment liquid containing the first element) described below. Furthermore, it is easy to cover the wall surfaces of the pits with the conductive polymer compound or the conductive polymer compound and a liquid component in the fourth step (a step of impregnating the electrode foil with the second treatment liquid containing the conductive polymer compound) described below.

[0036] The average diameter of the tunnel-shaped pits may be 170 nm to 2100 nm, 200 nm to 2100 nm, or 500 nm to 1500 nm. When the average diameter of the tunnel-shaped pits is within the above range, it is easy to form a relatively thick dielectric layer deep into the porous portion (pits), making it easy to obtain an electrode foil suitable for medium- to high-voltage electrolytic capacitors. Furthermore, the average diameter of the spongy pits may be 50 nm to 500 nm, or 80 nm to 300 nm.

[0037] The average pit diameter is the most frequent pore diameter in the volumetric pore diameter distribution measured with a mercury porosimeter. In the case of tunnel-shaped pits, the average pit diameter may be determined by measuring the diameters of 10 arbitrary pits on an SEM image of a cross section of the porous portion of the electrode foil (anode body) in the thickness direction and calculating the average value.

[0038] The tunnel-shaped pits include at least main pits extending from the surface side of the porous portion toward the core side. The main pits make it easy to form a dielectric layer up to the core side of the porous portion and to impregnate a conductive polymer compound or a liquid component. The main pits may extend in the thickness direction of the porous portion (a direction perpendicular to the surface of the porous portion) or may extend at an angle relative to the thickness direction of the porous portion. In a cross section of the porous portion of the anode body in the thickness direction, the angle (acute angle) formed between the length direction of the main pit and the thickness direction of the porous portion may be 80° or less, 45° or less, 30° or less, or 15° or less.

[0039] The diameter of the main pit may be larger or smaller on the core side of the porous portion than on the surface side. As a result, in a cross section of the porous portion of the anode body in the thickness direction, the wall surface of the main pit may be inclined with respect to the length direction of the main pit. In this case, the pit can be easily impregnated with a conductive polymer compound or a conductive polymer compound and a liquid component. In this case, the shape of the main pit is, for example, a pyramidal or frustum shape. Furthermore, in this case, the inclination angle of the main pit (length direction) with respect to the thickness direction of the porous portion is preferably 15° or less. When the length direction of the main pit approximately coincides with the thickness direction of the porous portion, the inclination angle of the wall surface of the main pit with respect to the length direction of the main pit approximately coincides with the inclination angle of the wall surface of the main pit with respect to the thickness direction of the porous portion. In the above case, the inclination angle (acute angle) of the wall surface of the main pit with respect to the length direction of the main pit is preferably 0.01° or more and 3° or less, more preferably 0.1° or more and 2.8° or less, even more preferably 0.1° or more and 2.5° or less, and particularly preferably 0.2° or more and 2.2° or less. The inclination angle of the wall surface of the main pit can be adjusted by, for example, the crystal orientation of the metal foil and etching conditions (for example, the type of etching solution (acid), current density, solution temperature, etching time, etc.).

[0040] The angle formed between the wall surface of the main pit and the length direction of the main pit can be determined by measuring the above angle for any 10 main pits using an SEM image of a cross section of the porous portion of the electrode foil (anode body) in the thickness direction and calculating the average value. The angle formed between the length direction of the main pit (the direction in which the main pit extends) and the thickness direction of the porous portion can be determined in a similar manner.

[0041] The anode body has a first main surface and a second main surface opposite the first main surface, the porous portion has a first porous portion provided on the first main surface side and a second porous portion provided on the second main surface side, and the main pit may have a first pit in the first porous portion and a second pit in the second porous portion. At least a portion of the first pit may further extend from the first porous portion toward the second porous portion. In this case, a dielectric layer is likely to be formed deep into the pit, which facilitates penetration of a conductive polymer compound or a liquid component and increases the surface area of ​​the anode body, which is advantageous in terms of improving capacitance.

[0042] Furthermore, at least some of the first pits may extend further from the first porous portion toward the second porous portion and connect to at least some of the second pits. The ratio (number ratio) of first pits connected to second pits to the total number of first pits is, for example, 5% or more, and may be 5% or more and 20% or less. When a source gas is supplied to the anode body (porous portion) by the ALD method, the source gas that has entered the pits from one side of the first main surface or the second main surface may migrate into the pits on the other side of the first main surface or the second main surface. This makes it easy for the source gas to diffuse deep into the first pits and the second pits. Furthermore, unnecessary components in the source gas that have entered the pits from one side of the first main surface or the second main surface are easily discharged from the pits on the other side of the first main surface or the second main surface to the outside. This makes it easy to form a uniform film on the surfaces of the first pits and the second pits in a short period of time. When the ALD method is used to supply source gases into the pits, the increase in pressure inside the pits is suppressed, allowing the source gases to be smoothly supplied into the pits, facilitating the formation of a dense film (dielectric layer), which is advantageous for reducing leakage current in electrolytic capacitors. Furthermore, when the ALD method is used to exhaust the source gases inside the pits, the source gases are smoothly exhausted, preventing excess source gas components from remaining in the dielectric layer. This shortens exhaust time and increases productivity. When a conductive polymer compound or liquid component is infiltrated into the pits during the manufacture of electrolytic capacitors, the increase in pressure inside the pits is suppressed, allowing the conductive polymer compound or liquid component to infiltrate into the pits smoothly, which is advantageous for reducing leakage current and ESR in electrolytic capacitors.

[0043] Here, Fig. 5 is a cross-sectional view showing an example of an anode body, in which the porous portion of the anode body is cut in the thickness direction.

[0044] 5, anode body 300 has porous portion 310 and core portion 320 continuous with porous portion 310. Anode body 300 has first main surface 301 and second main surface 302 opposite first main surface 301. Porous portion 310 has first porous portion 311 provided on the first main surface 301 side and second porous portion 312 provided on the second main surface 302 side. First porous portion 311 has tunnel-shaped first pit 331, and second porous portion 312 has tunnel-shaped second pit 332. First pit 331 and second pit 332 are main pits.

[0045] The diameter of the first pit 331 is smaller on the core portion 320 side than on the first main surface 301 side of the first porous portion 311. As a result, the wall surface of the first pit 331 is inclined with respect to the thickness direction of the first porous portion 311 (the direction perpendicular to the first main surface 301). The first pit 331 is frustum-shaped, and the length direction of the first pit 331 substantially coincides with the thickness direction of the first porous portion.

[0046] The diameter of the second pit 332 is smaller on the core portion 320 side than on the second main surface 302 side of the second porous portion 312. As a result, the wall surface of the second pit 332 is inclined with respect to the thickness direction of the second porous portion 312 (the direction perpendicular to the second main surface 302). The second pit 332 is frustum-shaped, and the length direction of the second pit 332 substantially coincides with the thickness direction of the second porous portion 312.

[0047] In a cross section of porous portion 310 of anode body 300 in the thickness direction, the angle formed by the wall surface of first pit 331 and the thickness direction of first porous portion 311 (angle θ 3A ) is, for example, 0.01° or more and 2.8° or less, and may be 0.1° or more and 2.8° or less. In a cross section of porous portion 310 of anode body 300 in the thickness direction, the angle formed by the wall surface of second pit 332 and the thickness direction of second porous portion 312 (angle θ3B ) is, for example, 0.01° or more and 2.8° or less, and may be 0.1° or more and 2.8° or less.

[0048] The anode body shown in Figure 5 is advantageous in terms of strength. In addition, because the pit diameter is large on the main surface side of the porous portion (the pit opening side), it is easy to infiltrate the conductive polymer compound or the conductive polymer compound and a liquid component into the porous portion, which is advantageous for reducing the ESR of the electrolytic capacitor.

[0049] The first pit and the second pit in Fig. 5 are truncated cones, but may be truncated pyramidal, conical, or pyramidal. The length direction of the first pit and the second pit in Fig. 5 roughly coincides with the thickness direction of the first porous portion and the second porous portion, respectively, but may be slightly inclined within a range of 15° or less with respect to the thickness direction of the first porous portion and the second porous portion, respectively. The first pit and the second pit may further have small pits and / or branch pits, as described below.

[0050] Here, Fig. 6 is a cross-sectional schematic diagram showing another example of an anode body. Fig. 6 shows a cross section in the thickness direction of the porous portion of the anode body. In Fig. 6, components corresponding to those in Fig. 5 are assigned the same reference numerals as in Fig. 5, and descriptions of configurations that overlap with Fig. 5 will be omitted.

[0051] In the anode body 400 shown in FIG. 6, the first porous portion 311 has a tunnel-shaped first pit 431, and the second porous portion 312 has a tunnel-shaped second pit 432. The first pit 431 and the second pit 432 are main pits. The diameter of the first pit 431 is larger on the core portion 320 side of the first porous portion 311 than on the first main surface 301 side. As a result, the wall surface of the first pit 431 is inclined with respect to the thickness direction of the first porous portion 311 (the direction perpendicular to the first main surface 301). The first pit 431 is shaped like a truncated cone, and the length direction of the first pit 431 approximately coincides with the thickness direction of the first porous portion 311.

[0052] The diameter of the second pit 432 is larger on the core portion 320 side than on the second main surface 302 side of the second porous portion 312. As a result, the wall surface of the second pit 432 is inclined with respect to the thickness direction of the second porous portion 312 (the direction perpendicular to the second main surface 302). The second pit 432 is frustum-shaped, and the length direction of the second pit 432 is approximately the same as the thickness direction of the second porous portion 312.

[0053] In a cross section of porous portion 310 of anode body 400 in the thickness direction, the angle formed by the wall surface of first pit 431 and the thickness direction of first porous portion 311 (angle θ 4A ) is, for example, 0.01° or more and 2.2° or less, and may be 0.1° or more and 2.2° or less. In a cross section of porous portion 310 of anode body 400 in the thickness direction, the angle formed by the wall surface of second pit 432 and the thickness direction of second porous portion 312 (angle θ 4B ) is, for example, 0.01° or more and 2.2° or less, and may be 0.1° or more and 2.2° or less.

[0054] The anode body of Figure 6 can be produced by etching the substrate while suppressing dissolution of the surface of the substrate, which is advantageous in that it increases the electrostatic capacitance of the electrode foil and increases the capacitance of the electrolytic capacitor.

[0055] The first pit and the second pit in Fig. 6 are truncated cones, but may be truncated pyramids. The length direction of the first pit and the second pit in Fig. 6 roughly coincides with the thickness direction of the first porous portion and the second porous portion, respectively, but may be slightly inclined within a range of 15° or less with respect to the thickness direction of the first porous portion and the second porous portion, respectively. The first pit and the second pit may further have small pits and / or branch pits, as described below.

[0056] Here, Fig. 7 is a cross-sectional schematic diagram showing yet another example of an anode body. Fig. 7 shows a cross section in the thickness direction of the porous portion of the anode body. In Fig. 7, components corresponding to those in Fig. 5 are assigned the same reference numerals as in Fig. 5, and descriptions of configurations that overlap with Fig. 5 will be omitted.

[0057] 7, some of first pits 331 extend further from first porous portion 311 toward second porous portion 412, have third pits 533 penetrating core portion 320, and are connected to some of second pits 332. The proportion (number ratio) of first pits having third pits 533 to all first pits may be, for example, 5% or more and 20% or less.

[0058] 5 to 7, the first pits and second pits have the same shape, but the shapes of the first pits and second pits may be different from each other. The first pits and second pits shown in Fig. 7 have the same shape as the first pits and second pits shown in Fig. 5, but the shapes are not limited to this.

[0059] The tunnel-shaped pits may further include small pits in the surface region of the porous portion. The small pits are shorter than the main pits, and the ratio of the length of the small pits to the length of the main pits is 0.7 or less, and may be 0.6 or less. The surface region of the porous portion refers to a region having a depth from the surface of the porous portion of 10 μm or less. The small pits are pits that exist only in a region having a depth from the surface of the porous portion of 10 μm or less. The surface region of the porous portion is, for example, a region having a thickness of 20% or less of the thickness of the porous portion, and the thickness of the porous portion is, for example, 50 μm or more. The small pits may be formed due to the influence of rolling processing of the metal foil. In this case, small pits may be formed with a relatively large inclination angle with respect to the thickness direction of the porous portion. The inclusion of small pits further increases the surface area of ​​the anode body, thereby further increasing the capacitance. The small pits may be connected to the main pits or may not be connected to the main pits. From the viewpoint of ensuring the strength of the anode body, it is preferable that the proportion of small pits present is small compared to the main pits, and the number of small pits is preferably, for example, 5% to 20% of the number of main pits.

[0060] The length of the main pits is the average length of 20 random main pits determined using an SEM image of a cross section in the thickness direction of the porous portion of the electrode foil (anode body).The length of the small pits is the average length of 10 random small pits present in a region 10 μm or less deep from the surface of the porous portion determined using an SEM image of a cross section in the thickness direction of the porous portion of the electrode foil (anode body).

[0061] The small pits may have a larger inclination angle with respect to the thickness direction of the porous portion than the main pits. If the inclination angle of the small pits is large, small pits with a relatively large length dimension may exist in the surface region of the porous portion, which tends to increase the surface area of ​​the anode body and further increase the capacitance. In a cross section of the porous portion of the anode body in the thickness direction, the angle (acute angle) formed by the length direction of the small pits and the thickness direction of the porous portion may be 5° or more and 88° or less, 10° or more and 85° or less, more than 45° and 85° or less, or 50° or more and 85° or less.

[0062] The angle (acute angle) formed by the length direction of the small pits and the thickness direction of the porous portion can be determined by measuring the above angle for any 10 small pits using an SEM image of a cross section of the porous portion of the electrode foil (anode body) in the thickness direction and calculating the average value.

[0063] The tunnel-shaped pit may further include a branch pit branching off from the main pit. The inclusion of the branch pit increases the surface area of ​​the anode body, further increasing the capacitance. From the viewpoint of ensuring the strength of the anode body, the angle formed between the length direction of the main pit and the length direction of the branch pit in a cross section of the porous portion of the anode body in the thickness direction may be 70° or more and 110° or less, or 80° or more and 100° or less. The branch pit has a length that is, for example, 5% or more and 25% or less of the length of the main pit.

[0064] The angle formed by the length direction of the main pit and the length direction of the branch pits can be determined by measuring the above angle for any 10 branch pits using an SEM image of a cross section in the thickness direction of the porous part of the electrode foil (anode body) and calculating the average value of these angles.

[0065] Here, Fig. 8 is a cross-sectional schematic diagram showing an example of an anode body including a porous portion having main pits and small pits. Fig. 8 shows a cross section in the thickness direction of the porous portion of the anode body.

[0066] Anode body 600 has a porous portion 610 and a core portion 620 continuous with porous portion 610. Anode body 600 has a first main surface 601 and a second main surface 602 opposite to first main surface 601. Porous portion 610 has a first porous portion 611 provided on the first main surface 601 side and a second porous portion 612 provided on the second main surface 602 side, with core portion 620 interposed therebetween. First porous portion 611 has a tunnel-shaped first pit 631, and second porous portion 612 has a tunnel-shaped second pit 632.

[0067] 8, the first pit 631 includes a main pit 631a and small pits 631b. The small pits 631b are present in the surface region of the first porous portion 611 (a region having a depth of 10 μm or less from the main surface 602 of the first porous portion 611) and have a length of 70% or less of the main pit 631a. The second pit 632 includes a main pit 632a and small pits 632b. The small pits 632b are present in the surface region of the second porous portion 612 (a region having a depth of 10 μm or less from the main surface 602 of the second porous portion 612) and have a length of 70% or less of the main pit 632a.

[0068] In a cross section of the porous portion 610 of the anode body 600 in the thickness direction, the angle formed by the length direction of the main pit 631a and the thickness direction of the first porous portion 611 (the direction perpendicular to the first main surface 601) (angle θ in FIG. 8) 6A) is, for example, 45° or less. In a cross section of porous portion 610 of anode body 600 in the thickness direction, the angle formed by the length direction of main pit 632a and the thickness direction of second porous portion 612 (direction perpendicular to second main surface 602) (angle θ 6B ) is, for example, 45° or less.

[0069] In a cross section of the porous portion 610 of the anode body 600 in the thickness direction, the angle formed by the length direction of the small pits 631b and the thickness direction of the first porous portion 611 (angle θ 6C ) may be 30° or more and 88° or less, or may be more than 45° and 85° or less. In a cross section of porous portion 610 of anode body 600 in the thickness direction, the angle formed by the length direction of small pits 632b and the thickness direction of second porous portion 612 (angle θ in FIG. 8 6D ) may be 30° or more and 88° or less, or may be more than 45° and 85° or less. Although the first pit and the second pit in FIG. 8 are cylindrical, the shape of the pit is not limited to this and may be a prism, etc.

[0070] Here, Fig. 9 is a cross-sectional schematic diagram showing an example of an anode body having main pits and branch pits. Fig. 9 shows a cross section in the thickness direction of the porous portion of the anode body. In Fig. 9, components corresponding to those in Fig. 8 are assigned the same reference numerals as in Fig. 8, and descriptions of configurations that overlap with Fig. 8 will be omitted.

[0071] 9, in anode body 700, first porous portion 611 has a tunnel-shaped first pit 731, and second porous portion 612 has a tunnel-shaped second pit 732. First pit 731 includes a main pit 731a and a branch pit 731b branching off and extending from main pit 731a. Second pit 732 includes a main pit 732a and a branch pit 731b branching off and extending from main pit 731a.

[0072] In a cross section of the porous portion 610 of the anode body 700 in the thickness direction, the length direction of the main pit 731a substantially coincides with the thickness direction of the first porous portion 611 (direction perpendicular to the first main surface 601). In a cross section of the porous portion 610 of the anode body 700 in the thickness direction, the length direction of the main pit 732a substantially coincides with the thickness direction of the second porous portion 612 (direction perpendicular to the second main surface 602). The main pit (length direction) may be slightly inclined within a range of 15° or less with respect to the thickness direction of the porous portion.

[0073] In a cross section of the porous portion 610 of the anode body 700 in the thickness direction, the angle formed by the length direction of the main pit 731a and the length direction of the branch pit 731b (angle θ 7A ) is, for example, 70° or more and 110° or less, and preferably 85° or more and 95° or less. In a cross section of porous portion 610 of anode body 700 in the thickness direction, the angle formed by the length direction of main pit 732a and the length direction of branch pit 732b (angle θ 7B ) is, for example, 70° or more and 110° or less, and preferably 85° or more and 95° or less. Although the first pit and the second pit in FIG. 9 are cylindrical, the shape of the pit is not limited to this and may be a prism or the like.

[0074] [Electrolytic capacitor] An electrolytic capacitor according to one embodiment of the present invention includes a capacitor element. The capacitor element includes the above-described electrode foil for electrolytic capacitors and a conductive polymer compound covering at least a portion of the dielectric layer. A cathode body may be further disposed so as to face the above-described electrode foil for electrolytic capacitors (porous portion). In this case, it is sufficient that the conductive polymer compound is interposed between the electrode foil (porous portion) and the cathode body. In this manner, the conductive polymer compound and the cathode body may form a cathode section.

[0075] (Conductive polymer compound) Examples of conductive polymer compounds include π-conjugated polymers. Examples of conductive polymer compounds include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. These may be used alone or in combination of two or more types, or may be copolymers of two or more types of monomers. The weight-average molecular weight of the conductive polymer compound is, for example, 1,000 to 100,000.

[0076] 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.

[0077] The conductive polymer compound may be doped with a dopant. The dopant may be a polyanion. Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used alone or in combination of two or more. Furthermore, these may be polymers of a single monomer or copolymers of two or more monomers. Among these, polyanions derived from polystyrene sulfonic acid are preferred.

[0078] For example, at least a portion of the surface of the dielectric layer is covered with a solid electrolyte layer containing at least a conductive polymer compound. The solid electrolyte layer may contain a dopant in addition to the conductive polymer compound. In an electrolytic capacitor, the conductive polymer compound (solid electrolyte layer) constitutes a part of the cathode part together with the cathode body. The solid electrolyte layer may further contain an additive, if necessary.

[0079] (liquid component) The electrolytic capacitor may include a capacitor element and a liquid component. The liquid component is in contact with the dielectric layer (first layer) directly or via a conductive polymer compound. The liquid component may be present, together with the conductive polymer compound, between the anode body (dielectric layer) and the cathode body.

[0080] The liquid component may be a non-aqueous solvent, or an electrolyte solution containing 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. When the porous portion is impregnated with the electrolyte solution, defects in the dielectric layer are repaired by the electrolyte solution. At this time, the presence of an interface layer containing the first element makes it easier to form a high-quality coating. This further reduces leakage current.

[0081] The non-aqueous solvent is preferably a high-boiling solvent, for example, a polyol compound, a cyclic sulfone compound such as sulfolane, a lactone compound such as γ-butyrolactone, an amide compound such as N-methylacetamide, N,N-dimethylformamide, or N-methyl-2-pyrrolidone, an ester compound such as methyl acetate, a carbonate compound such as propylene carbonate, an ether compound such as 1,4-dioxane, a ketone compound such as methyl ethyl ketone, or formaldehyde.

[0082] The liquid component preferably contains a polyol compound. The conductive polymer compound is easily dispersed in the polyol compound in a good state, and the conductive polymer compound easily penetrates into the pits and coats the walls of the pits. In this way, the contact between the dielectric layer and the conductive polymer compound is easily improved.

[0083] The polyol compound preferably contains at least one selected from the group consisting of glycol compounds and glycerin compounds (hereinafter also referred to as glycol compounds, etc.). When the liquid component contains glycol compounds, etc., the conductive polymer compound is more likely to swell, the orientation of the conductive polymer compound is improved, the conductivity of the conductive polymer compound (solid electrolyte layer) is improved, and the ESR is likely to be reduced. In addition, glycol compounds, etc., have a relatively high boiling point, which prevents permeation from the sealing part of the electrolytic capacitor to the outside, prevents a decrease in the film repair function due to a decrease in the solvent, and prevents a decrease in voltage resistance.

[0084] Glycol compounds include alkylene glycols, polyalkylene glycols, and the like. The weight-average molecular weight of the polyalkylene glycol is, for example, 100 to 3,000, or may be 100 to 2,000. The weight-average molecular weight of the polyethylene glycol is, for example, 100 to 600, or may be 100 to 400. Specific examples include ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, diethylene glycol, and triethylene glycol. Among glycol compounds, ethylene glycol is preferred because it has low viscosity and easily dissolves acid components and base components. Furthermore, ethylene glycol is preferred because it has high thermal conductivity and excellent heat dissipation properties, thereby improving heat resistance.

[0085] Glycerin compounds include glycerin, polyglycerin, and derivatives thereof. Examples of the derivatives of glycerin or polyglycerin include esters in which at least some of the hydroxy groups of glycerin or polyglycerin are esterified, and alkylene oxide adducts of glycerin or polyglycerin.

[0086] Polyglycerol contains a repeating structure of glycerol units. The number of repeating glycerol units contained in polyglycerol is, for example, 2 to 20, or may be 2 to 12, or may be 2 to 10, or may be 2 to 6. Examples of polyglycerol include diglycerol and triglycerol. The weight-average molecular weight of polyglycerol is, for example, preferably 200 to 3,000, and more preferably 300 to 800.

[0087] 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 inorganic acids include phosphoric acid, boric acid, and sulfuric acid.

[0088] The organic carboxylic acid compound may include at least one selected from the group consisting of aromatic carboxylic acid compounds and aliphatic carboxylic acid compounds.

[0089] Aliphatic carboxylic acid compounds include saturated aliphatic carboxylic acids and unsaturated aliphatic carboxylic acids. Examples of saturated aliphatic carboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, stearic acid, and behenic acid. Examples of unsaturated aliphatic carboxylic acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and oleic acid. One type of aliphatic carboxylic acid compound may be used alone, or two or more types may be used in combination.

[0090] Examples of aromatic carboxylic acid compounds include phthalic acid (ortho-isomer), isophthalic acid (meta-isomer), terephthalic acid (para-isomer), benzoic acid, salicylic acid, trimellitic acid, pyromellitic acid, etc. One type of aromatic carboxylic acid compound may be used alone, or two or more types may be used in combination.

[0091] In particular, from the viewpoint of improving the film repair function and thermal stability, it is preferable that the organic carboxylic acid compound contains at least one selected from the group consisting of benzoic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, and 1,7-octanedicarboxylic acid.

[0092] Examples of the base component include primary to tertiary amine compounds. Examples of the amine compound include monoalkylamines such as ethylamine, dialkylamines such as diethylamine, and trialkylamines such as triethylamine. In addition, compounds (including quaternary compounds) having an alkyl-substituted amidine group, such as imidazole compounds, may also be used as the base component.

[0093] 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.

[0094] The liquid component preferably contains more acid components than base components. The acid components lower the pH of the electrolyte from the beginning and suppress de-doping of the dopant from the conductive polymer. By containing more acid components than base components, de-doping of the dopant from the conductive polymer (deterioration of the solid electrolyte) can be suppressed. In addition, the acid components contribute to the film repair function of the liquid component, so it is preferable to contain more acid components than base components.

[0095] From the viewpoints of suppressing dedoping of the dopant from the conductive polymer (suppressing deterioration of the solid electrolyte layer) and improving the film repair function, the molar ratio of the acid component to the base component (acid component / base component) is, for example, 1.1 or more, preferably 1.5 or more, and more preferably 1.5 or more and 10 or less.

[0096] 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.

[0097] (cathode body) The cathode body may be made of a metal foil. The type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a non-metal different from the metal constituting the metal foil. Examples of dissimilar metals and non-metals include metals such as titanium and non-metals such as carbon.

[0098] (separator) When a metal foil is used for the cathode body, a separator may be disposed between the metal foil and the anode body. The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0099] (others) The electrolytic capacitor may have at least one capacitor element, or may have a plurality of capacitor elements, the number of capacitor elements included in the electrolytic capacitor being determined depending on the intended use.

[0100] [Method of manufacturing electrode foil for electrolytic capacitors] A method for manufacturing an electrode foil for an electrolytic capacitor includes a first step of preparing an anode body having a porous portion and a core portion continuous with the porous portion. The method also includes a second step of forming an interface layer covering the surface of a metal skeleton constituting the porous portion, and a third step of forming a dielectric layer continuous with the interface layer. The interface layer contains a first element, and the first element is at least one element selected from the group consisting of sulfur, nitrogen, and phosphorus.

[0101] (1st step) In the first step, for example, a metal foil containing a first metal is etched to roughen the surface of the metal foil. By roughening the surface, a plurality of pits or pores are formed on the surface of the metal foil. The etching is performed by immersing the metal foil in an etching solution (acid solution). The etching can be performed, for example, by direct current etching using a direct current or by alternating current etching using an alternating current.

[0102] The type of the first metal is not particularly limited, but valve metals such as aluminum (Al), tantalum (Ta), and niobium (Nb) or alloys containing valve metals can be used because they facilitate the formation of the second layer by chemical conversion. Furthermore, copper (Cu) may be contained in the metal foil to effectively form a porous portion. The thickness of the metal foil is not particularly limited, but is, for example, 15 μm or more and 300 μm or less.

[0103] (2nd process) In the second step, the anode body may be impregnated with a first treatment liquid containing the first element. For example, the anode body may be immersed in the first treatment liquid, or the anode body may be sprayed with the first treatment liquid. From the viewpoint of improving productivity, the second step may be performed during the first step.

[0104] The first treatment liquid may be, for example, an aqueous solution containing the first element. The aqueous solution may be an alkaline solution. However, from the viewpoint of suppressing damage to the metal skeleton, it is desirable that the alkaline solution has mild alkalinity. The pH of the alkaline solution is set to, for example, 8 to 13. The solvent of the alkaline solution desirably contains water as a main component, and 80 mass % or more of the solvent may be water. Furthermore, when the treatment time with the first treatment liquid is short, within 5 minutes, the aqueous solution containing the first element may be an acidic solution. In the case of an acidic solution, it is desirable that the acidic solution contains 0.2 mass % or more of aluminum ions from the viewpoint of suppressing damage to the metal skeleton.

[0105] The first treatment liquid may be, for example, an aqueous solution of a compound containing a first element. Examples of compounds containing sulfur include sulfuric acid. Examples of compounds containing nitrogen include nitric acid. Examples of compounds containing phosphorus include phosphoric acid, ammonium dihydrogen phosphate, phosphonic acid, and phosphinic acid.

[0106] From the viewpoint of improving the capacitance of the electrolytic capacitor, the content of the first element in the first treatment liquid is desirably a trace amount, and may be, for example, 0.01 ppm to 500 ppm, or 0.1 ppm to 100 ppm. Furthermore, when the first treatment liquid is an acidic aqueous solution and the step of impregnating the anode body with the first treatment liquid is performed in a short time, the content of the compound containing the first element in the first treatment liquid may be 0.1 mass % to 10 mass %, or 0.5 mass % to 5 mass %.

[0107] In the second step, the anode element to which the first treatment liquid is applied may be dried or heated. The temperature during the heat treatment is, for example, 200°C or higher and 550°C or lower, and preferably 250°C or higher and 500°C or lower. In this case, the heating atmosphere may be an oxidizing atmosphere, but a non-oxidizing atmosphere is preferable from the viewpoint of forming an interface layer that is as thin, uniform, and stable as possible. The non-oxidizing atmosphere may be an atmosphere in which the mole fraction of an inert gas (such as a rare gas such as Ar or He, or nitrogen) exceeds 90%, a reduced pressure atmosphere, or the like. The heat treatment hydrogenates unstable oxygen that is not bonded to the first metal, generating many surface hydroxyl groups and forming a stable interface layer.

[0108] (3rd step) In the third step, the dielectric layer may be formed by a gas phase method. When a thick dielectric layer is to be formed, the dielectric layer may be formed by a liquid phase method such as a sol-gel method. Examples of gas phase methods include vacuum deposition, chemical vapor deposition, mist deposition, sputtering, pulsed laser deposition, and atomic layer deposition (ALD). Among these, the ALD method is advantageous in that it can form a dense dielectric layer deep within the porous portion. The thickness of the first layer is not particularly limited, but may be, for example, 0.5 nm to 250 nm, or 5 nm to 100 nm.

[0109] The ALD method is a film formation method in which a source gas containing a second metal and an oxidant are alternately supplied to a reaction chamber in which a target object is placed, forming a dielectric layer (first layer) containing an oxide of the second metal on the surface of the target object. In the ALD method, a self-limiting mechanism functions, allowing the second metal to deposit on the surface of the target object in atomic layers. Therefore, the thickness of the first layer can be controlled by the number of cycles, with one cycle consisting of the supply of source gas → exhaust (purging) of the source gas → supply of oxidant → exhaust (purging) of the oxidant. In other words, the ALD method makes it easy to control the thickness of the dielectric layer formed.

[0110] While CVD is generally performed at temperatures of 400 to 900° C., the ALD method can be performed at temperatures of 100 to 400° C. In other words, the ALD method is superior in that it can suppress thermal damage to the metal foil.

[0111] Examples of the oxidizing agent used in the ALD method include water, oxygen, ozone, etc. The oxidizing agent may be supplied to the reaction chamber as plasma using the oxidizing agent as a raw material.

[0112] The second metal is supplied to the reaction chamber as a precursor gas containing the second metal. The precursor is, for example, an organometallic compound containing the second metal, which facilitates chemical adsorption of the second metal to the target material. Various organometallic compounds conventionally used in ALD methods can be used as the precursor.

[0113] An example of a precursor containing Al is trimethylaluminum ((CH3)3Al). Examples of precursors containing Zr include bis(methyl-η-cyclopentadienyl)methoxymethylzirconium (Zr(CH3C5H4)2CH3OCH3), tetrakis(dimethylamido)zirconium(IV) ([(CH3)2N]4Zr), tetrakis(ethylmethylamido)zirconium(IV) (Zr(NCH3C2H5)4), and zirconium(IV) t-butoxide (Zr[OC(CH3)3]4).

[0114] Examples of precursors containing Ta include (t-butylimido)tris(ethylmethylamino)tantalum(V) (C 13 H 33 N4Ta, TBTEMT), tantalum(V) pentaethoxide (Ta(OC2H5)5), (t-butylimido)tris(diethylamino)tantalum(V) ((CH3)3CNTa(N(C2H5)2)3), pentakis(dimethylamino)tantalum(V) (Ta(N(CH3)2)5).

[0115] Examples of precursors containing Nb include niobium(V) ethoxide (Nb(OCH2CH3)5, tris(diethylamido)(t-butylimido)niobium(V) (C 16 H 39 N4Nb) and others.

[0116] Examples of precursors containing Si include N-sec-butyl(trimethylsilyl)amine (CH 19 NSi), 1,3-diethyl-1,1,3,3-tetramethyldisilazane (CH 23NSi2), 2,4,6,8,10-pentamethylcyclopentasiloxane ((CH3SiHO)5), pentamethyldisilane ((CH3)3SiSi(CH3)2H), tris(isopropoxy)silanol ([(HC)2CHO]3SiOH), chloropentanemethyldisilane ((CH3)3SiSi(CH3)2Cl), dichlorosilane (SiH2Cl2), tridimethylaminosilane (Si[N(CH3)2]4), tetraethylsilane (Si(C2H5)4), tetramethylsilane (Si(CH3)4), tetraethoxysilane (Si(OC2H5)4), dodecamethylcyclohexasilane ((Si(CH3)2)6), silicon tetrachloride (SiCl4), silicon tetrabromide (SiBr4), etc.

[0117] Examples of precursors containing Ti include bis(t-butylcyclopentadienyl)titanium(IV) dichloride (C 18 H 26 C l2 Ti), tetrakis(dimethylamino)titanium(IV) ([(CH3)2N]4Ti, TDMAT), tetrakis(diethylamino)titanium(IV) ([(C2H5)2N]4Ti), tetrakis(ethylmethylamino)titanium(IV) (Ti[N(C2H 5) (CH3)]4), titanium(IV) (diisopropoxide-bis(2,2,6,6-tetramethyl-3,5-heptanedionate (Ti[OCC(CH3)3CHCOC(CH3)3]2(OC3H7)2), titanium tetrachloride (TiCl4), titanium(IV) isopropoxide (Ti[OCH(CH3)2]4), titanium(IV) ethoxide (Ti[O(C2H5)]4), etc.

[0118] Examples of precursors containing Hf include hafnium tetrachloride (HfCl4), tetrakisdimethylaminohafnium (Hf[N(CH3)2]4), tetrakisethylmethylaminohafnium (Hf[N(C2H5)(CH3)]4), tetrakisdiethylaminohafnium (Hf[N(C2H5)2]4), and hafnium-t-butoxide (Hf[OC(CH3)3]4).

[0119] (Step a) The third step may further include a step a of subjecting an anode body having an interface layer and a first layer on its surface to chemical conversion (anodization). This allows a second layer to be formed between the metal skeleton and the first layer. The thickness T2 of the second layer can be controlled by the voltage applied to the anode body during chemical conversion. The chemical conversion solution is not particularly limited, but an aqueous solution of diammonium adipate can be used, for example. In this case, a valve metal suitable for chemical conversion is preferably used as the first metal.

[0120] The ALD method can form a thin and uniform dielectric layer (first layer). However, in reality, the surface of the deep pits in the porous portion may have macro defects such as pinholes or micro defects such as lattice defects. When forming the second layer, the ionized first metal diffuses into the first layer, repairing the defects in the first layer. As a result, a dielectric layer with a uniform thickness and reduced defects such as pinholes is formed overall. This increases the capacitance of the electrolytic capacitor, increases the natural potential of the anode body, and improves voltage resistance.

[0121] [Manufacturing method of electrolytic capacitors] A method for manufacturing an electrolytic capacitor according to one embodiment of the present invention includes a method for manufacturing an electrode foil for an electrolytic capacitor (first to third steps) and a fourth step of covering at least a portion of the dielectric layer with a conductive polymer compound. The manufacturing method may further include a step of arranging a cathode body so as to face the electrode foil for an electrolytic capacitor. In this case, a conductive polymer compound may be interposed between the electrode foil and the cathode body. In this way, the conductive polymer compound and the cathode body may form a cathode part.

[0122] (4th step) In the fourth step, the electrode foil may be impregnated with a second treatment liquid containing a conductive polymer compound. The second treatment liquid may be applied to the dielectric layer to form a solid electrolyte layer. The second treatment liquid may be a solution of a conductive polymer compound or a dispersion of a conductive polymer compound. The second treatment liquid preferably contains a conductive polymer compound and the above-mentioned liquid component. In this case, the surface of the dielectric layer is covered with a solid electrolyte layer (conductive polymer compound), and the anode body (porous portion) can be impregnated with the liquid component. When the liquid component contains a polyol compound, the conductive polymer compound is dispersed in a good state in the second treatment liquid, which makes it easy for the conductive polymer compound to penetrate into the pits and coat the wall surfaces of the pits with the conductive polymer compound.

[0123] When the anode element having a dielectric layer is an anode foil as shown in Figures 1 and 3, before forming the cathode portion, a wound body 100 as shown in Figure 11 may be produced. Figure 11 is a development view for explaining the configuration of wound body 100.

[0124] When producing the wound body 100, a cathode foil 20 is prepared in addition to the anode foil 10. The cathode foil 20 can be made of a metal foil, similar to the anode foil 10. The type of metal constituting the cathode foil 20 is not particularly limited, but valve metals such as Al, Ta, and Nb, or alloys containing valve metals, can be used. If necessary, the surface of the cathode foil 20 may be roughened.

[0125] Next, the anode foil 10 and the cathode foil 20 are wound with the separator 30 interposed therebetween. One end of the lead tab 50A or 50B is connected to the anode foil 10 and the cathode foil 20, respectively, and the lead tabs 50A and 50B are wound to form the wound body 100. Lead wires 60A and 60B are connected to the other ends of the lead tabs 50A and 50B, respectively.

[0126] The separator 30 is not particularly limited, and for example, a nonwoven fabric containing cellulose, polyethylene terephthalate, vinylon, aramid fiber, or the like as a main component can be used.

[0127] Next, a stop tape 40 is placed on the outer surface of the cathode foil 20 located in the outermost layer of the wound body 100, and the end of the cathode foil 20 is fixed with the stop tape 40. If the anode foil 10 is prepared by cutting it from a large foil, the wound body 100 may be further subjected to a chemical conversion treatment to provide a dielectric layer on the cut surface. A second layer may also be formed at this time.

[0128] The wound body 100 is impregnated with the second treatment liquid. The method is not particularly limited, but may be, for example, a method of immersing the wound body 100 in the second treatment liquid contained in a container, or a method of dropping the second treatment liquid onto the wound body 100. The impregnation may be carried out under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa, preferably 40 kPa to 100 kPa.

[0129] Next, the wound body 100 is sealed to obtain the electrolytic capacitor 200 as shown in Fig. 10. To manufacture the electrolytic capacitor 200, first, 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.

[0130] Next, sealing member 212, which is formed so that lead wires 60A and 60B pass through it, is placed above wound body 100, and wound body 100 is sealed in bottomed case 211. Sealing member 212 may be made of any insulating material, and is preferably made of an elastic material. Among these, highly heat-resistant materials such as silicone rubber, fluororubber, ethylene propylene rubber, hypalon rubber, butyl rubber, and isoprene rubber are preferred.

[0131] Next, horizontal drawing is performed near the open end of bottomed case 211, and the open end is curled by crimping it to sealing member 212. Finally, seat plate 213 is placed on the curled portion to complete the sealing. Thereafter, an aging process may be performed while applying the rated voltage.

[0132] In the above embodiment, a wound-type electrolytic capacitor has been described, but the scope of application of the present invention is not limited to the above, and the present invention can also be applied to other electrolytic capacitors, for example, stacked-type electrolytic capacitors. [Industrial Applicability]

[0133] According to the present invention, an electrode foil for an electrolytic capacitor, an electrolytic capacitor, and a method for manufacturing the same that can sufficiently reduce leakage current can be obtained. 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. [Explanation of symbols]

[0134] 10: anode foil, 20: cathode foil, 30: separator, 40: stop tape, 50A, 50B: lead tab, 60A, 60B: lead wire, 100: wound body, 110: anode body, 111: core part, 112: porous part, 120: dielectric layer, 121: first layer, 122: second layer, 130: interface layer, 200: electrolytic capacitor, 211: bottomed case, 212: sealing member, 213: seat plate, 300, 400, 500, 600, 700: anode body, 3 01,601: first main surface, 302,602: second main surface, 310,610: porous portion, 311,611: first porous portion, 312,612: second porous portion, 320,620: core portion, 331,431,631,731: first pit, 332,432,632,732: second pit, 533: third pit, 631a,632a,731a,732a: main pit, 631b,632b: small pit, 731b,732b: branch pit

Claims

1. an anode body having a porous portion and a core portion continuous with the porous portion; a dielectric layer covering the surface of the metal skeleton constituting the porous portion; Equipped with the porous portion has a plurality of tunnel-shaped pits, an interface layer containing a first element is provided between the metal skeleton and the dielectric layer; when the interface layer is subjected to GD-OES analysis along a depth direction of the interface layer from a surface of the interface layer on the dielectric layer side, a peak attributed to the first element is observed; a content of the first element relative to all elements in the interface layer is 0.50 mass% or more and 5 mass% or less; an electrode foil for an electrolytic capacitor, wherein the first element is at least one element selected from the group consisting of sulfur, nitrogen, and phosphorus; a conductive polymer compound that covers at least a portion of the dielectric layer; An electrolytic capacitor comprising:

2. 2. The electrolytic capacitor according to claim 1, wherein the average diameter of the pits is 170 nm or more and 2100 nm or less.

3. 3. The electrolytic capacitor according to claim 1, wherein the pits include at least a main pit extending from the surface side of the porous portion toward the core portion.

4. 4. The electrolytic capacitor according to claim 3, wherein the diameter of the main pit is smaller on the core side of the porous portion than on the surface side of the porous portion.

5. 4. The electrolytic capacitor according to claim 3, wherein the diameter of the main pit is larger on the core side of the porous portion than on the surface side of the porous portion.

6. 6. The electrolytic capacitor according to claim 4, wherein in a cross section of the porous portion of the anode body in the thickness direction, a wall surface of the main pit is inclined with respect to a longitudinal direction of the main pit.

7. 7. The electrolytic capacitor according to claim 6, wherein the wall surface of the main pit is inclined at an angle of 0.01° to 3° with respect to the longitudinal direction of the main pit.

8. The anode body has a first main surface and a second main surface opposite to the first main surface, the porous portion has a first porous portion provided on the first main surface side and a second porous portion provided on the second main surface side, the main pit has a first pit in the first porous portion and a second pit in the second porous portion, 8. The electrolytic capacitor according to claim 3, wherein at least a portion of the first pit further extends from the first porous portion toward the second porous portion.

9. 9. The electrolytic capacitor according to claim 8, wherein at least a portion of the first pit is connected to at least a portion of the second pit.

10. 10. The electrolytic capacitor according to claim 3, wherein, in a cross section of the anode body taken in the thickness direction of the porous portion, an angle formed between a length direction of the main pit and a thickness direction of the porous portion is 45° or less.

11. 11. The electrolytic capacitor according to claim 3, wherein the pits include small pits in the surface region of the porous portion, each having a length of 70% or less of the length of the main pit.

12. 12. The electrolytic capacitor according to claim 11, wherein, in a cross section of the anode body taken in the thickness direction of the porous portion, an angle formed between a length direction of the small pits and a thickness direction of the porous portion is greater than 45° and equal to or less than 88°.

13. the pits include branch pits branching and extending from the main pit, 13. The electrolytic capacitor according to claim 3, wherein, in a cross section of the porous portion of the anode body in the thickness direction, an angle formed between a length direction of the main pit and a length direction of the branch pits is 70° or more and 110° or less.

14. the metal skeleton includes a first metal; the first metal includes Al; the dielectric layer comprises an oxide of a second metal; 14. The electrolytic capacitor according to claim 1, wherein the second metal comprises at least one selected from the group consisting of Ta, Nb, Ti, Si, Zr, and Hf.

15. An electrolytic capacitor described in any one of claims 1 to 14, further comprising a liquid component.

16. The electrolytic capacitor of claim 15 , wherein the liquid component comprises a polyol compound.

17. a first step of preparing an anode body having a porous portion and a core portion continuous with the porous portion; a second step of forming an interface layer that covers the surface of the metal skeleton constituting the porous portion and contains a first element; a third step of forming a dielectric layer continuous with the interface layer; a fourth step of covering at least a portion of the dielectric layer with a conductive polymer compound; Equipped with the porous portion has a plurality of tunnel-shaped pits, when the interface layer is subjected to GD-OES analysis along a depth direction of the interface layer from a surface of the interface layer on the dielectric layer side, a peak attributed to the first element is observed; a content of the first element relative to all elements in the interface layer is 0.50 mass% or more and 5 mass% or less; The method for manufacturing an electrolytic capacitor, wherein the first element is at least one element selected from the group consisting of sulfur, nitrogen, and phosphorus.

18. The method for manufacturing an electrolytic capacitor according to claim 17 , wherein in the second step, the anode body is impregnated with a first treatment liquid containing the first element.

19. 19. The method for manufacturing an electrolytic capacitor according to claim 17, wherein in the third step, the dielectric layer is formed by atomic layer deposition.

20. 20. The method for manufacturing an electrolytic capacitor according to claim 17, wherein in the fourth step, the electrode foil is impregnated with a second treatment liquid containing the conductive polymer compound.

21. The method for manufacturing an electrolytic capacitor according to claim 20 , wherein the second treatment liquid contains a polyol compound.

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