Electrolytic capacitor and method of manufacturing the same

Abstract

An electrolytic capacitor has a capacitor element including: a porous anode body including an anode base and a dielectric layer formed on a surface of the anode base; and a solid electrolyte layer covering at least a portion of the dielectric layer. The anode body has a plurality of main surfaces, and at least a portion of a first surface layer of at least one of the plurality of main surfaces of the anode body is denser than an inside of the anode body.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrolytic capacitor and a manufacturing method thereof. BACKGROUND

[0002] An electrolytic capacitor is mounted on various electronic devices because of small equivalent series resistance (ESR) and excellent frequency characteristics. The electrolytic capacitor generally has a capacitor element having an anode portion and a cathode portion. The anode portion includes a porous anode body, and a dielectric layer is formed on the surface of the anode body. The dielectric layer is in contact with an electrolyte. There is an electrolytic capacitor using a solid electrolyte such as a conductive polymer as an electrolyte (for example, Patent Literature 1).

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Laid-Open No. 2009-182157 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] Improving the reliability of an electrolytic capacitor using a solid electrolyte.

[0008] MEANS FOR SOLVING THE PROBLEMS

[0009] An electrolytic capacitor of one aspect of the present disclosure has a capacitor element including: a porous anode body including an anode base and a dielectric layer formed on the surface of the anode base; and a solid electrolyte layer covering at least a part of the dielectric layer. The anode body has a plurality of main surfaces, and at least a part of a first surface layer of at least one of the main surfaces of the anode body is denser than the inside of the anode body.

[0010] Another aspect of the present disclosure is a manufacturing method of an electrolytic capacitor having a capacitor element including: a porous anode body including an anode base and a dielectric layer formed on the surface of the anode base; and a solid electrolyte layer covering at least a part of the dielectric layer. The method of the present disclosure includes: a step of preparing an anode base material including a binder body of metal powder; a step of sintering the anode base material; a step of obtaining the anode body including the anode base and the dielectric layer by performing chemical conversion treatment on the sintered anode base material; and a step of covering at least a part of the dielectric layer with the solid electrolyte layer.

[0011] In the method of the present disclosure, the anode substrate has a plurality of main surfaces, and the method further has a densification step that increases the density of at least a portion of at least one of the main surfaces of the anode substrate.

[0012] Effects of Invention

[0013] With the electrolytic capacitor or the manufacturing method of an electrolytic capacitor of the present disclosure, the reliability of the electrolytic capacitor can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a perspective view schematically showing the shape of an anode body used in an electrolytic capacitor of one embodiment of the present application.

[0015] Figure 2 is a cross-sectional view schematically showing an electrolytic capacitor of one embodiment of the present application.

[0016] Figure 3A is an electron microscope photograph of the surface of a main surface of an anode substrate before densification of the main surface of the anode substrate.

[0017] Figure 3B is an electron microscope photograph of the surface of a main surface of an anode substrate after densification of the main surface of the anode substrate.

[0018] Figure 4A is an electron microscope photograph of the cross section of a surface layer of a main surface of an anode substrate after densification of the main surface of the anode substrate.

[0019] Figure 4B is an electron microscope photograph of the cross section of the inside of an anode substrate after densification of a main surface of the anode substrate. DETAILED DESCRIPTION

[0020] [Electrolytic Capacitor]

[0021] The electrolytic capacitor of one embodiment of the present application includes a capacitor element including a porous anode body including an anode base and a dielectric layer formed on the surface of the anode base, and a solid electrolyte layer covering at least a portion of the dielectric layer. The anode body has a plurality of main surfaces, and at least a portion of a surface layer X of a main surface of the anode body is denser than the inside Y of the anode body.

[0022] The anode body typically has the shape of a rectangular solid. In this case, the plurality of main surfaces refer to the respective surfaces of the rectangular solid. The surface layer of the anode body refers to a region within 3 μm in depth from the surface of the anode body. The inside of the anode body refers to a region 20 μm or more in depth from the surface of each main surface of the anode body.

[0023] In the case where the anode body has a plurality of main surfaces, an edge portion connecting two of the plurality of main surfaces to each other and / or a vertex portion connecting three or more of the plurality of main surfaces to each other can be formed. The edge portion refers to an area of an edge at which two main surfaces of the anode body intersect and a vicinity thereof. The vertex portion refers to an area of a vertex at which three main surfaces of the anode body intersect and a vicinity thereof. Here, the edge portion and the vertex portion are collectively referred to as a "corner portion".

[0024] The dielectric layer is generally formed by oxidizing the surface of the anode substrate through chemical conversion treatment on the anode substrate. Therefore, the properties of the dielectric layer formed through chemical conversion are affected by the surface state of the anode substrate before the chemical conversion treatment.

[0025] The anode substrate before the chemical conversion treatment can be manufactured, for example, by compacting, sintering metal powder in a mold. In this case, the particles of the metal are exposed on the main surfaces of the anode substrate, and the surface is not flat, has a large surface roughness, and easily has a shape having unevenness when observed microscopically. In particular, in the edge portion connecting two main surfaces of the anode substrate to each other and the vertex portion connecting three or more main surfaces to each other, the surface of the anode substrate is not flat, has a large surface roughness, and easily has a shape having unevenness when observed microscopically. If the dielectric layer is grown through chemical conversion treatment in this state, the dielectric layer is likely to have defects at the uneven portions. If the dielectric layer has defects, a path through which current flows between the solid electrolyte and the valve-acting metal via the defective portions is sometimes generated, and the leakage current increases.

[0026] In addition, the anode body after the chemical conversion treatment, which has an outer shape reflecting the outer shape of the anode substrate before the chemical conversion treatment, is porous, and thus is fragile and easily damaged. In particular, the corner portion of the anode body has a low mechanical strength compared to other portions except the corner portion, and thermal stress is likely to concentrate. Damage to the porous portion sometimes leads to damage to the dielectric layer covering the porous portion. Damage to the dielectric layer sometimes leads to an increase in the leakage current.

[0027] In the electrolytic capacitor of the present embodiment, by densely forming the surface layer of the main surface of the anode substrate before the chemical conversion treatment, defects in the dielectric layer at the time of chemical conversion when the dielectric layer is formed through chemical conversion treatment can be reduced. As a result, the leakage current can be reduced. In addition, the mechanical strength of the dielectric layer can be improved. Thus, damage to the dielectric layer after the chemical conversion can be suppressed. As a result, the increase in the leakage current is suppressed.

[0028] Regarding the density of the surface layer of the main surface of the anode body, the porosity P1 of the surface layer X of the main surface of the anode body is preferably 0.02 times or more and 0.7 times or less than the porosity P2 of the interior Y of the anode body. If the porosity P1 is 0.7 times or less than the porosity P2, the surface layer X is sufficiently dense relative to the interior Y, damage to the dielectric layer after chemical conversion is suppressed, and the increase in leakage current is suppressed. The porosity P1 is more preferably 0.5 times or less than the porosity P2, and may be even more preferably 0.3 times or less. On the other hand, if the porosity P1 is 0.02 times or more than the porosity P2, a solid electrolyte layer covering the dielectric layer is easily formed in the fine pores of the anode body. The porosity P1 is more preferably 0.05 times or more than the porosity P2, and may be even more preferably 0.1 times or more.

[0029] Electrolytic capacitors may contain trace amounts of aluminum due to manufacturing processes near the surface of the dielectric layer or the anode. It should be noted that "trace amount" means that in the region within 1 μm of the anode surface, the aluminum content in the dielectric layer is 0.001% by weight or more and 10% by weight or less. The aluminum content in the dielectric layer can also be 0.01% by weight or more and 10% by weight or less.

[0030] At least a portion of the corner portion of the anode body can have a curved or chamfered shape. By having a curved surface or chamfering at least a portion of the corner portion, damage to the dielectric layer in the corner portion is suppressed, enabling the realization of an electrolytic capacitor with low leakage current. Therefore, the reliability of the electrolytic capacitor can be improved. Preferably, in addition to the surface layer of the main surface of the anode body, the corner portion is also densified.

[0031] At least a portion of the corner portion has a curved shape, not limited to cases where the cross-sectional shape of the corner portion is curved. For example, the cross-sectional shape of the corner portion can also be a broken line with multiple obtuse angles. When the cross-sectional shape is convex, and the straight line corresponding to one principal face and the straight line corresponding to the adjacent principal face are connected by at least one straight line and / or curve, it can be said that the corner portion has a curved shape or a chamfered shape. In other words, having a curved shape or a chamfered shape also means that the cross-sectional shape of the corner portion in a section perpendicular to the two adjacent principal faces does not have any areas with sharp angles below 90°.

[0032] A solid electrolyte layer is formed by covering the dielectric layer. When the corners of the anode body do not have curved surfaces, the thickness of the solid electrolyte layer at the corners tends to be thin. This is especially true when the solid electrolyte layer contains conductive polymers, formed through chemical polymerization; the thickness of the solid electrolyte layer at the corners is prone to be thin. However, by forming at least a portion of the corners as curved surfaces, the thinning of the solid electrolyte layer at the corners can be suppressed, allowing the solid electrolyte layer to be formed with a uniform thickness. As a result, the electrolytic capacitor is more resistant to external stress, suppressing the increase in leakage current and the occurrence of short-circuit failures. Furthermore, the withstand voltage is improved.

[0033] The surface layer Z of the corner portion adjacent to surface layer X can be denser than surface layer X and interior layer Y. By densely forming the surface layer Z of the corner portion, the mechanical strength of the corner portion can be further improved. Therefore, the suppression effect of increasing leakage current through the corner portion can be improved.

[0034] Even when the corner portion is not curved and is not chamfered, sufficient mechanical strength can be obtained by densely forming the surface layer Z. Therefore, the increase in leakage current through the corner portion can be suppressed. However, it is preferable that if at least a portion of the portion containing the surface layer Z is curved or chamfered, leakage current can be further suppressed.

[0035] The surface layer Z is denser than the surface layer X and the interior layer Y because the porosity P3 in the surface layer Z is smaller than the porosity P1 in the surface layer X and the porosity P2 in the interior layer Y. The surface layer Z can have a portion where the ratio of porosity P3 to porosity P1, P3 / P1, is less than 1. P3 / P1 can be less than 0.8 or less than 0.5. Alternatively, P3 / P1 can be less than 1 in any part of the surface layer Z.

[0036] Furthermore, when at least a portion of the corner portion has a curved surface, the curvature of the curved surface can be, for example, 0.002 (1 / μm) to 0.05 (1 / μm), more preferably 0.005 (1 / μm) to 0.02 (1 / μm).

[0037] It should be noted that the curvature and porosity are determined through image analysis of cross-sectional photographs of the anode body in a specified region. The cross-section is photographed using a scanning electron microscope (SEM), and image processing, such as binarization of the photographed image in a 5μm × 10μm field of view, is performed to distinguish the pore portion from the rest. Porosity can be determined as the proportion of the area occupied by the pore portion in the total area of ​​the pore portion and the rest of the body. Preferably, the images are taken at 10 arbitrary locations, and the porosity is determined as the average of the area proportions of the pore portion obtained at those 10 locations. Porosity P1 (porosity P3) is determined based on the area proportion of the pore portion in region A within surface layer X (surface layer Z). Similarly, porosity P2 is determined based on the area proportion of the pore portion in region B within interior layer Y. The curvature of the corner portion is also calculated by taking photographs of the anode body from a certain main surface side and performing image analysis on the resulting contour shape near the corner (vertex).

[0038] Densification of the surface layer of the anode body, as described later, can be achieved by placing the anode substrate (before sintering, or after sintering but before the formation of the dielectric layer) together with a vibrating member such as dielectric particles in a container and vibrating the container. Through vibration, the main surface of the anode substrate collides with the vibrating member, and through this collision, the surface layer of the main surface becomes denser than the interior due to compression. Here, the forming process of pressing and shaping the anode substrate into a cuboid shape by embedding powdered valve-acting metal particles in a pressure forming machine using a mold to obtain the anode substrate before the formation of the dielectric layer is called primary forming, and the aforementioned densification forming process is called secondary forming.

[0039] At this point, the vibrating component collides not only with the main surface of the anode substrate but also with the corner portions. Due to their low mechanical strength, the corner portions are easily compressed by the impact. Therefore, while being compressed by the impact, the corner portions can be formed into curved shapes. The density of the surface layer Z of the corner portions is higher than that of the surface layer X and the interior Y of the main surface (lower porosity).

[0040] On the other hand, when the anode substrates collide directly with each other without a vibrating component, the corners of the anode substrates primarily collide with the main surfaces of other anode substrates. As a result, cracks sometimes occur due to the impact. Furthermore, densification of the main surfaces takes a long time, leading to greater deviations in densification and increased characteristic deviations in the electrolytic capacitor. Additionally, the anode substrates are more prone to breakage. In contrast, by colliding the anode substrates with a vibrating component, breakage can be suppressed, and the main surfaces of the anode substrates can be uniformly densified in a shorter time.

[0041] Figure 1 This is a schematic perspective view showing an example of the anode body (or anode substrate) used in the electrolytic capacitor of this embodiment. Figure 1As shown, the anode body 1 has a roughly rectangular shape, with six main faces 101A to 101F exposed. It should be noted that 101D to 101F are hidden from view and therefore not shown.

[0042] In principal faces 101A to 101F, near the edges where two adjacent principal faces intersect, connecting surfaces can be formed by taking the corners of the edge portions. Figure 1 In the example, connecting surface 102C lies between principal surfaces 101A and 101B, connecting surface 102A lies between principal surfaces 101B and 101C, and connecting surface 102B lies between principal surfaces 101A and 101C. Additionally, a second connecting surface is formed near the vertices where the three principal surfaces intersect by taking the corners of the vertices. Figure 1 In the example, a second connecting surface 103A is present at the vertex where the main surfaces 101A to 101C intersect. The second connecting surface 103A connects the connecting surfaces 102A to 102C to each other. The connecting surfaces 102A to 102C and the second connecting surface 103A are machined into curved surfaces with rounded corners. The connecting surfaces 102A to 102C and the second connecting surface 103A can be curved surfaces, or they can be composed of one or more planes (e.g., the corners are chamfered).

[0043] It should be noted that, Figure 1 An example of the shape of the anode body is shown. For the anode substrate before chemical conversion treatment, it also has a roughly cuboid shape with 6 main faces 101A to 101F exposed. The corners of the edges and vertices connecting the main faces are removed and processed into a rounded shape.

[0044] At least a portion of the surface layer of the main surfaces 101A to 101F is formed to be denser than the interior. As a result, the surface of the main surfaces 101A to 101F has fewer irregularities, and the mechanical strength of the anode substrate and the anode body is improved. Consequently, a dielectric layer with fewer defects is formed on the surface of the anode body 1. As a result, leakage current can be reduced. Furthermore, damage to the dielectric layer can be suppressed, and the increase in leakage current caused by damage to the dielectric layer can be suppressed, thus maintaining a low leakage current.

[0045] Furthermore, by having the anode substrate with chamfered or curved corners, a dielectric layer with fewer defects can be formed at the corners, thereby improving the reduction of leakage current. Additionally, by increasing the mechanical strength of the brittle and easily damaged corners of the anode body, the concentration of thermal stress is mitigated, thus improving the suppression of leakage current increases caused by damage to the dielectric layer and maintaining a lower leakage current.

[0046] The surface layer of the connecting surfaces 102A-102C and / or the second connecting surface 103A can be formed to be denser than the surface layer of the porous main surfaces 101A-101F. That is, the porosity P3 of the surface layer of the connecting surfaces 102A-102C and / or the second connecting surface 103A can be less than the internal porosity P2 of the anode body 1 and less than the porosity P1 of the surface layer of the main surfaces 101A-101F.

[0047] The anode conductor 2 extends from the main surface 101B of the anode body 1. The anode body 1 and the anode conductor 2 constitute the anode section 6.

[0048] The configuration of the electrolytic capacitor according to this embodiment will be described below with appropriate reference to the accompanying drawings. However, the present invention is not limited thereto. Figure 2 This is a cross-sectional schematic diagram of the electrolytic capacitor according to this embodiment.

[0049] The electrolytic capacitor 20 includes: a capacitor element 10 having an anode portion 6 and a cathode portion 7; an outer casing 11 sealing the capacitor element 10; an anode lead terminal 13 electrically connected to the anode portion 6 and partially exposed from the outer casing 11; and a cathode lead terminal 14 electrically connected to the cathode portion 7 and partially exposed from the outer casing 11. The anode portion 6 has an anode body 1 and an anode wire 2. The anode body 1 includes a dielectric layer 3 formed on its surface. The cathode portion 7 has a solid electrolyte layer 4 covering at least a portion of the dielectric layer 3 and a cathode layer 5 covering the surface of the solid electrolyte layer 4.

[0050] <Capacitor Components>

[0051] The capacitor element 10 will be described in detail below using the case where a solid electrolyte layer is used as the electrolyte as an example.

[0052] The anode section 6 has an anode body 1 and an anode wire 2 extending from one side of the anode body 1 and electrically connected to the anode lead terminal 13.

[0053] The anode body 1 is, for example, a rectangular porous sintered body obtained by sintering metal particles. As the aforementioned metal particles, particles of valve-acting metals such as titanium (Ti), tantalum (Ta), and niobium (Nb) can be used. The anode body 1 can use one or more types of metal particles. The metal particles can also be alloys containing two or more metals. For example, alloys containing valve-acting metals, silicon, vanadium, boron, etc., can be used. Alternatively, compounds containing valve-acting metals and typical elements such as nitrogen can also be used. The valve-acting metal alloy is predominantly composed of the valve-acting metal, for example, containing 50 atomic percent or more of the valve-acting metal.

[0054] The anode wire 2 is made of a conductive material. The material of the anode wire 2 is not particularly limited; for example, in addition to the valve-acting metal mentioned above, copper, aluminum, and aluminum alloys can also be used. The materials constituting the anode body 1 and the anode wire 2 can be the same or different. The anode wire 2 has a first portion 2a embedded inside the anode body 1 from one side of the anode body 1, and a second portion 2b extending from the aforementioned side of the anode body 1. The cross-sectional shape of the anode wire 2 is not particularly limited; examples include circular, orbital (a shape formed by parallel straight lines and two curves connecting the ends of these lines), elliptical, rectangular, and polygonal shapes.

[0055] The anode portion 6 is manufactured, for example, by pressing and shaping it into a cuboid while embedding the first portion 2a within the aforementioned metal particle powder, and then sintering it. Consequently, the second portion 2b of the anode wire 2 is led out vertically from one side of the anode body 1. The second portion 2b is joined to the anode lead terminal 13 by welding or the like, thus electrically connecting the anode wire 2 to the anode lead terminal 13. The welding method is not particularly limited; resistance welding, laser welding, etc., are examples. Then, a process can be performed to form curved surfaces at the corners of the cuboid.

[0056] A dielectric layer 3 is formed on the surface of the anode body 1. The dielectric layer 3 is, for example, composed of a metal oxide. Methods for forming a layer containing a metal oxide on the surface of the anode body 1 include, for example, anodic oxidation of the surface of the anode body 1 by immersing the anode body 1 in a chemical conversion solution, and heating the anode body 1 in an oxygen-containing atmosphere. The dielectric layer 3 is not limited to a layer containing the aforementioned metal oxide; it can be any layer that has insulating properties.

[0057] (Cathode section)

[0058] The cathode portion 7 has a solid electrolyte layer 4 and a cathode layer 5 covering the solid electrolyte layer 4. The solid electrolyte layer 4 is formed in such a way that it covers at least a portion of the dielectric layer 3.

[0059] The solid electrolyte layer 4 can be made of, for example, manganese compounds or conductive polymers. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene. These can be used alone or in combination. Furthermore, the conductive polymer can also be a copolymer of two or more monomers. From the perspective of excellent conductivity, polythiophene, polyaniline, and polypyrrole can be used. In particular, from the perspective of excellent water resistance, polypyrrole can be used.

[0060] The solid electrolyte layer 4, containing the aforementioned conductive polymer, is formed, for example, by polymerizing the raw material monomers on the dielectric layer 3. Alternatively, it is formed by coating the dielectric layer 3 with a liquid containing the aforementioned conductive polymer. The solid electrolyte layer 4 consists of one or more solid electrolyte layers. When the solid electrolyte layer 4 consists of two or more layers, the composition of the conductive polymer used in each layer, the formation method (polymerization method), etc., can be different.

[0061] It should be noted that in this specification, polypyrrole, polythiophene, polyfuran, and polyaniline refer to polymers with polypyrrole, polythiophene, polyfuran, and polyaniline as their basic backbones, respectively. Therefore, polypyrrole, polythiophene, polyfuran, and polyaniline may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0062] To improve the conductivity of conductive polymers, various dopants can be added to the polymerization liquid, solution, or dispersion used to form the conductive polymer. There are no particular limitations on the dopants; examples include naphthalenesulfonic acid, p-toluenesulfonic acid, and polystyrenesulfonic acid.

[0063] When the conductive polymer is dispersed in the dispersion medium as particles, the average particle size D50 is, for example, 0.01 μm or more and 0.5 μm or less. If the average particle size D50 is within this range, the particles can easily penetrate into the interior of the anode body 1.

[0064] The cathode layer 5 may have, for example, a carbon layer 5a formed to cover the solid electrolyte layer 4 and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a comprises a conductive carbon material such as graphite and a resin. The metal paste layer 5b comprises, for example, metal particles (e.g., silver) and a resin. It should be noted that the configuration of the cathode layer 5 is not limited to this configuration. The cathode layer 5 may be configured to have a current-collecting function.

[0065] <Anode Lead Terminal>

[0066] The anode lead terminal 13 is electrically connected to the anode body 1 via the second portion 2b of the anode wire 2. The material of the anode lead terminal 13 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The anode lead terminal 13 can be, for example, a metal such as copper, or a non-metal. Its shape is not particularly limited as long as it is flat. From the viewpoint of minimizing height, the thickness of the anode lead terminal 13 (the distance between the main surfaces of the anode lead terminal 13) can be 25 μm or more and 200 μm or less, or 25 μm or more and 100 μm or less.

[0067] One end of the anode lead terminal 13 can be joined to the anode wire 2 by means of conductive adhesive material, solder, resistance welding, or laser welding. The other end of the anode lead terminal 13 extends outward from the outer casing 11 and protrudes from the outer casing 11. The conductive adhesive material is, for example, a mixture of thermosetting resin and carbon particles and metal particles, as described later.

[0068] <Cathode lead terminal>

[0069] The cathode lead terminal 14 is electrically connected to the cathode portion 7 at the junction 14a. When the cathode layer 5 and the cathode lead terminal 14 connected to the cathode layer 5 are viewed from the normal direction of the cathode layer 5, the junction 14a is the portion of the cathode lead terminal 14 that overlaps with the cathode layer 5.

[0070] The cathode lead terminal 14 is bonded to the cathode layer 5, for example, via a conductive adhesive material 8. One end of the cathode lead terminal 14 forms part of the joint 14a and is disposed inside the outer casing 11. The other end of the cathode lead terminal 14 extends outward. Therefore, a portion of the cathode lead terminal 14 including the other end is exposed from the outer casing 11.

[0071] The material of the cathode lead terminal 14 is not particularly limited, as long as it is electrochemically and chemically stable and conductive. The cathode lead terminal 14 can be a metal such as copper, or a non-metal. Its shape is also not particularly limited; for example, it can be a long strip or a flat plate. From the viewpoint of minimizing height, the thickness of the cathode lead terminal 14 can be 25 μm or more and 200 μm or less, or 25 μm or more and 100 μm or less.

[0072] <Exterior body>

[0073] The outer casing 11 is provided to electrically insulate the anode lead terminal 13 from the cathode lead terminal 14, and is made of an insulating material (outer casing material). The outer casing material may include, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, and unsaturated polyester.

[0074] Manufacturing Methods of Electrolytic Capacitors

[0075] Hereinafter, an example of a method for manufacturing an electrolytic capacitor according to this embodiment will be described.

[0076] A method for manufacturing an electrolytic capacitor is a method for manufacturing a solid electrolytic capacitor having a capacitor element comprising: a porous anode body comprising an anode substrate and a dielectric layer formed on the surface of the anode substrate; and a solid electrolyte layer covering at least a portion of the dielectric layer. The manufacturing method includes: a step of preparing an anode substrate comprising a binder of metal powder; a step of sintering the anode substrate; a step of obtaining an anode body comprising an anode substrate and a dielectric layer by subjecting the sintered anode substrate to a chemical conversion treatment; and a step of covering at least a portion of the dielectric layer with the solid electrolyte layer. The anode substrate has multiple main surfaces. The manufacturing method further includes a densification step that increases the density of at least a portion of at least one of the multiple main surfaces of the anode substrate.

[0077] (1) Preparation process of anode substrate

[0078] First, an anode substrate is prepared to serve as the substrate for manufacturing the anode body 1. A porous material can be used as the anode substrate. In this case, valve-acting metal particles and anode wire 2 are placed into a mold with the first part 2a embedded in the valve-acting metal particles, and pressure molding is performed to obtain an anode substrate containing a binder of valve-acting metal particles. The pressure during pressure molding is not particularly limited. A binder such as polyacrylate carbonate can be mixed into the valve-acting metal particles as needed.

[0079] Valve-acting metal particles are typically formed and sintered (secondary forming) using a mold with a cuboid internal space under pressure. In this case, the anode substrate before sintering has multiple main faces corresponding to the cuboid. Furthermore, the sintered anode substrate is also cuboid in shape, with multiple main faces. In this case, the multiple main faces are directly connected to each other to form edges and vertices. Typically, the corners of the edges and / or vertices connecting the multiple main faces are sharp at the front, resulting in a shape without curved surfaces.

[0080] The main surface of the press-formed anode substrate can be densified (high-densityed). In the densification process, densification (high-densitying) is achieved, for example, by causing dielectric particles to collide with the main surface of the anode substrate. Preferably, densification can be performed by vibrating the anode substrate and dielectric particles together. More specifically, densification can be achieved by placing the anode substrate and dielectric particles together on a container or base, and vibrating the container or base in the vertical and / or horizontal directions. Along with the vibration of the container or base, the anode substrate and dielectric particles vibrate, promoting collisions between them. Through the collisions between the dielectric particles and the main surface of the anode substrate, the surface layer of the main surface of the anode substrate is compressed, resulting in high density.

[0081] In addition to colliding with the main surface of the anode substrate, the dielectric particles can also collide with the corner portions (edge ​​portions and vertex portions) that connect the main surfaces of the anode substrate to each other. As a result, in addition to the main surface of the anode substrate, the corner portions are compressed to form curved surfaces, and at least a portion of the corner portions can be formed to a higher density than the denser regions of the main surface.

[0082] The base (or the bottom of the container) can be a sieve. A moderately low coefficient of static friction facilitates the movement of media particles and their collisions with the anode substrate. Through these collisions, a large portion of the anode substrate's surface is compressed. If the base is a sieve, direct collisions between the anode wire and the base are reduced, thus lowering the risk of bending. The mesh size of the sieve only needs to be smaller than the minimum external dimensions of the anode substrate to prevent it from falling through the sieve openings. The mesh size can be 1mm or larger, or 2mm or larger but less than 3.4mm. If the mesh size is 1mm or larger, it is easier to reduce the curvature deviation at the corners to a certain value.

[0083] Alternatively, with the anode substrate placed on top of the dielectric particles, an external force can be applied to the dielectric particles to cause the anode body and dielectric particles to vibrate together. More specifically, for example, the anode substrate and dielectric particles can be mixed and then fed together into a vibratory mill, which is then operated. The vibratory mill is preferably one capable of applying vertical vibration in addition to the horizontal direction. In contrast, even when the anode substrate and dielectric particles are fed into a rotating barrel, they are not subjected to vibration, making it difficult to achieve a densification effect on the main surface of the anode substrate. While the rotation of the anode substrate and dielectric particles may cause collisions between the dielectric particles and the anode substrate, densification of the main surface requires a long time, making it difficult to achieve uniform densification. Furthermore, the anode substrate and dielectric particles are pushed upwards with the rotation of the drum, resulting in a large impact when they fall, which can easily cause cracks and defects in the anode substrate.

[0084] The density of the dielectric particles can be 0.15 to 0.4 times the density (true density) of the anode substrate. When the density of the dielectric particles is within the above range, the energy generated by the collision of the dielectric particles can be effectively used for the compressive deformation of the anode substrate.

[0085] The dielectric particles can be alumina particles, zirconia particles, etc. The particle size (average particle size) of the dielectric particles can be less than 1 / 3 or less than 1 / 5 of the maximum size of the anode body. In this case, the dielectric particles are more likely to collide with the main surface compared to the corners of the anode substrate, and the main surface of the anode substrate is easily compressed uniformly due to the collision. It should be noted that the maximum size of the anode body refers to the maximum Ferete diameter of the anode body excluding the anode wire; in the case of a cuboid anode body, it refers to the length of the longest side. The particle size (average particle size) of the dielectric particles can be, for example, 0.1 mm to 3 mm, or 0.5 mm to 2 mm.

[0086] When using alumina particles as dielectric particles, if the anode substrate is made of a valve-acting metal other than aluminum (e.g., tantalum), trace amounts of alumina from the dielectric particles may adhere to the anode substrate due to collisions between the dielectric particles and the substrate. By chemically converting the anode substrate with the attached alumina, the anode body can contain a dielectric layer containing alumina. If the amount of alumina in the dielectric layer is trace, it improves the insulation of the dielectric layer, increases the withstand voltage, and reduces leakage current. However, if the amount of alumina in the dielectric layer is too large, the dielectric layer contains multiple materials with different dielectric constants, which may sometimes lead to a decrease in capacitance. The amount of alumina adhering to the anode substrate can be controlled appropriately by factors such as the vibration frequency, the particle size of the dielectric particles, the mixing ratio of the anode substrate and dielectric particles in the container, and the collision time of the dielectric particles.

[0087] The dielectric particles can have at least a portion of their surface pre-coated with a metal identical to the constituent metal of the metal powder in the anode substrate. Here, the constituent metal refers to the main component, not an impurity contained in the anode substrate. This prevents the adhesion of metals (or metal compounds) other than the valve-acting metal constituting the anode body to the anode substrate when the dielectric particles collide with it. For example, when using alumina particles as dielectric particles, the adhesion of alumina to the surface of the anode substrate is suppressed. The coating of the dielectric particle surface can be performed using known methods. However, if the dielectric particles (e.g., alumina particles) collide with the anode substrate, the alumina from the dielectric particles adheres to the anode substrate, while the constituent metal of the anode substrate adheres to the surface of the dielectric particles. As a result, the surface of the dielectric particles can be coated with a metal identical to the constituent metal of the anode substrate. Thus, dielectric particles with surfaces coated with the same metal as the constituent metal of the anode substrate can also be used.

[0088] In this way, in the method of causing the anode substrate and the dielectric particles to vibrate together and collide, the surface layer of the main surface of the anode substrate can be compressed efficiently, thereby making the main surface denser.

[0089] In contrast, when anode substrates collide directly with each other without the use of dielectric particles, the main impact occurs at the corners of the anode substrates against the main surfaces of other anode substrates. As a result, breakage due to impact is likely. In particular, the anode substrate located at the bottom of the container is subjected to the weight of other anode substrates, making it prone to cracking or breakage. Furthermore, there are instances where anode wires disposed on the anode substrates bend due to collisions with other anode substrates. Additionally, since densification of the main surfaces takes a long time, the density variation within the main surfaces becomes larger, making it difficult to compress the main surfaces of the anode substrates with uniform density. Therefore, it is evident that the productivity of the anode body tends to decrease without the use of dielectric particles.

[0090] However, by colliding the dielectric particles with the anode substrate, it is easy to achieve a dense structure by compressing the surface layer of the anode substrate through the dielectric particles, thus enabling the anode body to be densified at a uniform density in a short time. Furthermore, it also suppresses the bending of the anode wire.

[0091] (2) Sintering process

[0092] The anode substrate is then sintered. Sintering is preferably carried out under reduced pressure. The first portion 2a of the anode wire is embedded inside the porous sintered body from one side.

[0093] Densification can also be performed on the porous sintered body after sintering. However, since the bonding between metal particles is not strong and they are easily compressed, the densification process is preferably performed on the anode substrate after pressure forming before sintering. When densifying the anode substrate, which is the porous sintered body after sintering, the densification can be performed in the same way as the densification of the anode substrate before sintering.

[0094] When an anode substrate is obtained by pressurizing metal powder, metal particles are attached to the main surface of the anode substrate both before and after sintering. Microscopically, these particles are mostly uneven, exhibiting a bumpy shape. However, the dielectric layer is formed by covering the entire surface of the particles during formation; therefore, the metal particles attached to the main surface do not contribute to capacitance. During the densification process, by compressing the surface layer of the anode substrate together with the metal particles, the dielectric layer formed on the particle surface can also contribute to capacitance, thus increasing capacitance.

[0095] (3) Process for obtaining the anode (chemical conversion treatment process)

[0096] Next, the sintered anode substrate is subjected to chemical conversion treatment to obtain a porous anode body 1 comprising an anode substrate and a dielectric layer formed on the surface of the anode substrate. Specifically, the anode substrate is immersed in a chemical conversion tank filled with an electrolytic aqueous solution (e.g., an aqueous phosphoric acid solution), and the second portion 2b of the anode wire 2 is connected to the anode body of the chemical conversion tank for anodizing. This allows an dielectric layer 3 comprising an oxide film containing a valve-acting metal to be formed on the surface of the porous portion. The electrolytic aqueous solution is not limited to an aqueous phosphoric acid solution; nitric acid, acetic acid, sulfuric acid, etc., can also be used. The unanodized core portion of the anode body 1 constitutes the anode substrate.

[0097] Furthermore, the formal chemical conversion process preferably includes a first chemical conversion step and a second chemical conversion step. The first chemical conversion step uniformly forms a dielectric layer on the surface and inside of the porous anode substrate. The second chemical conversion step forms a dielectric layer thicker than the dielectric layer formed in the first chemical conversion step on the surface and near the surface of the porous anode. The second chemical conversion step is preferably performed after the first chemical conversion step. It should be noted that the series of chemical conversion processes including the first and second chemical conversion steps is referred to as a dual chemical conversion.

[0098] In the first chemical conversion process, for example by immersing the anode substrate in an aqueous solution (e.g., an aqueous solution of phosphoric acid) and performing anodizing, a dielectric layer 3 containing an oxide film of a valve-acting metal can be formed on the surface of the porous portion.

[0099] In the second chemical conversion step, for example, by immersing the anode substrate in an electrolytic aqueous solution (e.g., sodium tetraborate) and performing anodizing, a dielectric layer 3 comprising an oxide film containing a valve-acting metal can be formed on the surface of the porous portion. The applied voltage for anodizing in the second chemical conversion step is preferably higher than the applied voltage for anodizing in the first chemical conversion step. The anodizing time in the second chemical conversion step is preferably shorter than the anodizing time in the first chemical conversion step.

[0100] Furthermore, from the viewpoint of reducing leakage current of electrolytic capacitor 20, suppressing the occurrence of short circuit failure, and improving voltage withstand characteristics, it is preferable that the thickness of the surface portion and the area near the surface portion of the anode body 1, where the dielectric layer 3 is formed thicker through the second chemical conversion process, is thicker than the thickness of the area densified through secondary forming.

[0101] By performing the first and second chemical conversion processes described above, the density and mechanical strength of the surface layer and surrounding area of ​​the anode body 1 can be increased, thus increasing the stress from the outside. As a result, the leakage current of the electrolytic capacitor 20 is suppressed, and the occurrence of short circuit failure is suppressed, thereby improving the withstand voltage characteristics.

[0102] The surface density and mechanical strength of the anode body 1 can be evaluated, for example, by comparing Vickers hardness. Table 1 compares the Vickers hardness of the anode body 1 with and without secondary forming and dual chemical conversion. Vickers hardness is the average of the measurements taken at any eight points on the main surface of the anode body 1. As a result, the Vickers hardness is the highest in the anode body 1 that has undergone secondary forming and dual chemical conversion. That is, by implementing secondary forming and dual chemical conversion, the electrolytic capacitor 20 becomes stronger relative to external stress, which can suppress the increase of leakage current and the occurrence of short circuit failure, and improve the withstand voltage.

[0103] [Table 1]

[0104] Vickers hardness [HV] 35.2 41.2 44.4 51.2 Secondary forming Not performed Not performed Performed Performed Double chemical conversion Not performed Performed Not performed Performed

[0105] (4) Solid electrolyte layer formation process

[0106] Next, at least a portion of the dielectric layer 3 is covered with a solid electrolyte layer 4. This yields the capacitor element 10.

[0107] The solid electrolyte layer 4 containing conductive polymers is formed, for example, by impregnating monomers or oligomers into the anode body 1 on which the dielectric layer 3 is formed, and then polymerizing the monomers or oligomers by chemical polymerization or electrolytic polymerization, or by impregnating a solution or dispersion of conductive polymers into the anode body 1 on which the dielectric layer 3 is formed and then drying it, thereby forming at least a portion of the dielectric layer 3.

[0108] The solid electrolyte layer 4 can be formed, for example, by immersing the anode body 1, on which the dielectric layer 3 is formed, in a dispersion containing a conductive polymer, a binder, and a dispersion medium, removing it, and drying it. The dispersion may also contain a binder and / or conductive inorganic particles (e.g., conductive carbon materials such as carbon black). Additionally, the conductive polymer may contain a dopant. The conductive polymer and dopant can be selected from the substances exemplified for the solid electrolyte layer 4, respectively. A known binder can be used. The dispersion may contain known additives used in forming the solid electrolyte layer.

[0109] Next, a cathode layer 5 is formed by sequentially coating a carbon paste and a metal paste onto the surface of the solid electrolyte layer 4, thereby forming a cathode layer 5 consisting of a carbon layer 5a and a metal paste layer 5b. The configuration of the cathode layer 5 is not limited to this; any configuration that has a current collection function is acceptable.

[0110] Next, the anode lead terminal 13 and the cathode lead terminal 14 are prepared. The second part 2b of the anode wire 2 erected from the anode body 1 is joined to the anode lead terminal 13 by laser welding, resistance welding, or the like. In addition, after applying the conductive adhesive material 8 to the cathode layer 5, the cathode lead terminal 14 is joined to the cathode portion 7 via the conductive adhesive material 8.

[0111] Next, the materials of the capacitor element 10 and the outer casing 11 (e.g., uncured thermosetting resin and filler) are contained in a mold, and the capacitor element 10 is sealed by transfer molding, compression molding, or the like. At this time, a portion of the anode lead terminal 13 and the cathode lead terminal 14 are exposed from the mold. The molding conditions are not particularly limited; the time and temperature conditions can be appropriately set, taking into account the curing temperature of the thermosetting resin used.

[0112] Finally, the exposed portions of the anode lead terminal 13 and the cathode lead terminal 14 are bent along the outer casing 11 to form a bent portion. Thus, a portion of the anode lead terminal 13 and the cathode lead terminal 14 are disposed on the mounting surface of the outer casing 11.

[0113] Electrolytic capacitor 20 is manufactured using the methods described above.

[0114] exist Figure 3A and Figure 3B The image shows an electron microscope photograph of the surface of the main face of the anode substrate in the manufacturing method of this embodiment. Valve-acting metal (Ta) is present in the white areas, and voids (pores) are present in the black areas. Figure 3A This is a photo taken before the densification process. Figure 3B This is a photo after the densification process. It should be noted that... Figure 3A and Figure 3B These are electron microscope images taken at the same magnification. Figure 3B This result was obtained during the densification process when a pre-sintered anode substrate (0.8mm × 3.7mm × 5.2mm) with embedded anode wires and a roughly rectangular shape was fed into a vibratory mill along with alumina particles with an average particle size of 1mm and the vibratory mill was run. No cracks or defects were observed in any of the anode substrates, nor was any bending of the anode wires observed.

[0115] exist Figure 4A and Figure 4B The image shows an electron microscope photograph of the cross-section of the anode substrate after the densification process. Figure 4A This is a cross-sectional photograph of the surface layer X of the main surface of the anode substrate. Figure 4B This is a cross-sectional photograph of the internal Y-section of the anode substrate. It should be noted that... Figure 4A and Figure 4B These are electron microscope images taken at the same magnification. For example... Figure 4A As shown, the surface layer X has fewer voids compared to the interior layer Y, indicating densification. Figure 4A In the middle, the porosity P1 of the surface layer X was calculated to be 0.016. Figure 4B In the middle, the porosity P2 of the internal Y is calculated to be 0.057.

[0116] To address this, unsintered anode substrates were placed in a φ55mm×55mm stainless steel container and rotated at 150 rpm for 5 minutes using a ball mill rotary table. In this case, surface layer X was not densified, cracks or defects were observed in 20% of the total anode substrate, and significant bending of the anode wires was confirmed in 0.7% of the total anode substrate. It should be noted that if the rotation speed is less than 150 rpm, the anode substrate slides on the container wall, making uniform treatment impossible.

[0117] Additionally, sintered anode substrate and φ1mm alumina particles were placed in a φ55mm×55mm stainless steel container and subjected to rotation at 80 rpm for 5 minutes using a ball mill rotary table. In this case, cracks or defects were observed in 5% of the total anode substrate.

[0118] As mentioned above, it is believed that when the pre-sintering components are rotated inside the container, a large force is applied locally between the corner of the anode substrate and the container wall, which can cause cracking or damage, or bending of the anode wire.

[0119] Industrial availability

[0120] This invention can be used in electrolytic capacitors and is suitable for use in electrolytic capacitors in which a porous body is used as the anode.

[0121] Explanation of reference numerals in the attached figures

[0122] 20: Electrolytic capacitors

[0123] 10: Capacitor Components

[0124] 1: Anode body

[0125] 2: Anode wire

[0126] 2a: Part One

[0127] 2b: Part Two

[0128] 3: Dielectric layer

[0129] 4: Solid electrolyte layer

[0130] 5: Cathode layer

[0131] 5a: Carbon layer

[0132] 5b: Metal paste layer

[0133] 6: Anode section

[0134] 7: Cathode section

[0135] 8: Conductive adhesive materials

[0136] 11: Exterior body

[0137] 13: Anode lead terminal

[0138] 14: Cathode lead terminal

[0139] 14a: Joint

[0140] 101A~101C: Main surfaces of the anode body

[0141] 102A~102C: Connecting surfaces

[0142] 103A: Second connecting surface.

Claims

1. An electrolytic capacitor comprising a capacitor element, said capacitor element comprising: A porous anode body comprising an anode substrate and a dielectric layer formed on the surface of the anode substrate; and A solid electrolyte layer that covers at least a portion of the dielectric layer. The anode body has multiple main faces. At least a portion of the first surface layer of at least one of the plurality of main surfaces of the anode body is denser than the interior of the anode body. In a region with a depth of less than 1 μm extending from at least one of the plurality of main surfaces of the anode body, the dielectric layer comprises aluminum. The aluminum content in the dielectric layer within the region is in the range of 0.001% by weight or more and 10% by weight or less.

2. An electrolytic capacitor comprising a capacitor element, said capacitor element comprising: A porous anode body comprising an anode substrate and a dielectric layer formed on the surface of the anode substrate; and A solid electrolyte layer that covers at least a portion of the dielectric layer. The anode body has multiple main faces. The anode body has a corner portion, which comprises multiple vertex portions and multiple edge portions. The plurality of edge portions are each connected to two of the plurality of principal faces, and the plurality of vertex portions are each connected to three or more of the plurality of principal faces. The first surface layer of at least one of the plurality of main surfaces of the anode body is adjacent to at least a portion of the second surface layer of the corner portion. At least a portion of the first surface layer of at least one of the plurality of main surfaces of the anode body is denser than the interior of the anode body. At least a portion of the second surface layer of the corner portion is denser than the first surface layer and the interior of the anode body.

3. The electrolytic capacitor according to claim 1 or 2, wherein, At least a portion of the first surface layer of each of the plurality of main surfaces is denser than the interior of the anode body.

4. The electrolytic capacitor according to claim 1 or 2, wherein, The porosity of at least a portion of the first surface layer is more than 0.02 times and less than 0.7 times that of the interior.

5. The electrolytic capacitor according to claim 1 or 2, wherein, The solid electrolyte layer contains conductive polymers.

6. The electrolytic capacitor according to claim 1 or 2, wherein, The anode substrate is a sintered body of valve-acting metal particles.

7. A method for manufacturing an electrolytic capacitor, comprising the method for manufacturing an electrolytic capacitor according to any one of claims 1 to 6, wherein, The electrolytic capacitor includes a capacitor element, which comprises: A porous anode body comprising an anode substrate and a dielectric layer formed on the surface of the anode substrate; as well as A solid electrolyte layer that covers at least a portion of the dielectric layer. The method for manufacturing the electrolytic capacitor includes: The process of preparing an anode substrate containing a binder of metal powder; The process of sintering the anode substrate; The process of obtaining the anode body comprising the anode substrate and the dielectric layer by performing a chemical conversion treatment on the sintered anode substrate; and The process of covering at least a portion of the dielectric layer with the solid electrolyte layer. The anode substrate has multiple main surfaces. The method for manufacturing the electrolytic capacitor further includes a densification step, which increases the density of at least a portion of at least one of the plurality of main surfaces of the anode substrate. In the densification process, the anode substrate is vibrated together with the dielectric particles, thereby causing the dielectric particles to collide with at least one of the plurality of main surfaces of the anode substrate.

8. The method for manufacturing an electrolytic capacitor according to claim 7, wherein, The average particle size of the medium particles is less than 1 / 3 of the maximum size of the anode body.

9. The method for manufacturing an electrolytic capacitor according to claim 7, wherein, The medium particles comprise aluminum oxide particles.

10. The method for manufacturing an electrolytic capacitor according to claim 7, wherein, At least a portion of the surface of the medium particles is coated with the same metal as the constituent metal of the metal powder.

11. A method for manufacturing an electrolytic capacitor according to any one of claims 7 to 10, wherein, The densification process is performed on the anode substrate before sintering.

12. The method for manufacturing an electrolytic capacitor according to any one of claims 7 to 10, wherein, The densification process is performed on the anode substrate after sintering and before the chemical conversion treatment.

13. The method for manufacturing an electrolytic capacitor according to any one of claims 7 to 10, wherein, The anode substrate has an edge portion connecting two of the plurality of main surfaces and a vertex portion connecting three or more of the plurality of main surfaces. The anode substrate further has a corner portion, the corner portion comprising the vertex portion and a plurality of side portions, which are respectively the side portions. In the densification process, the corner portion is formed to have a higher density than at least a portion of the region of at least one of the plurality of main surfaces.

14. A method for manufacturing an electrolytic capacitor according to any one of claims 7 to 10, wherein, The chemical transformation treatment includes a first chemical transformation step and a second chemical transformation step. The thickness of the dielectric layer formed in the second chemical conversion process is greater than the thickness of the dielectric layer formed in the first chemical conversion process.

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