Electrolytic capacitor

Abstract

An electrolytic capacitor comprises: an anode body having a porous body containing a valve-acting metal and a dielectric layer covering the porous body; and a solid electrolyte layer filling the pores of the porous body and covering the dielectric layer. The porous body has a first region on the outer surface side of the porous body and a second region other than the first region. When the shortest distance from the outer surface of the porous body to its center is defined as D, the first region is the region closest to the outer surface of the porous body to a distance less than 0.5D. The filling ratio R2 of the solid electrolyte layer in the second region is smaller than the filling ratio R1 of the solid electrolyte layer in the first region. The ratio of filling ratio R2 to filling ratio R1, R2 / R1, is 1 / 10 or less.

Description

Technical Field

[0001] This invention relates to an electrolytic capacitor. Background Technology

[0002] In recent years, the development of electrolytic capacitors with low equivalent series resistance (ESR) and excellent frequency characteristics has been underway. An electrolytic capacitor comprises: an anode body having a porous body containing a valve-acting metal and a dielectric layer covering the porous body; and a solid electrolyte layer filling the pores of the porous body and covering the dielectric layer.

[0003] Patent Document 1 discloses a solid electrolytic capacitor in which the thickness of the conductive polymer compound layer at the center of the capacitor element is at least 0.02 μm and less than 0.14 μm. Furthermore, Patent Document 1 proposes that, in the aforementioned solid electrolytic capacitor, the difference between the thickness of the conductive polymer compound layer at the center of the capacitor element and the thickness of the conductive polymer compound layer near the outer surface of the capacitor element is within 0.08 μm.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 11-87177 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In recent years, there has been a demand to reduce the ESR of electrolytic capacitors. Regarding the electrolytic capacitor described in Patent Document 1, although the ESR increase at high temperatures has been suppressed, the reduction in ESR of the electrolytic capacitor is still insufficient.

[0009] Solution for solving the problem

[0010] One aspect of the present invention relates to an electrolytic capacitor comprising: an anode body having a porous body containing a valve-acting metal and a dielectric layer covering the porous body; and a solid electrolyte layer filling the pores of the porous body and covering the dielectric layer, the porous body having a first region on the outer surface side of the porous body and a second region other than the first region, wherein when the shortest distance from the outer surface of the porous body to the center is defined as D, the first region is a region closer to the outer surface of the porous body than 0.5D, the filling rate R2 of the solid electrolyte layer in the second region is smaller than the filling rate R1 of the solid electrolyte layer in the first region, and the ratio of the filling rate R2 to the filling rate R1, R2 / R1, is 1 / 10 or less.

[0011] The effects of the invention

[0012] According to the present invention, it is possible to provide electrolytic capacitors with low ESR.

[0013] Although novel features of the invention are described in the appended claims, the invention can be better understood through the following detailed description, which relates to both structure and content, and in conjunction with other objects and features of the invention and with reference to the accompanying drawings. Attached Figure Description

[0014] Figure 1 A cross-sectional view is shown to illustrate an example of an electrolytic capacitor according to one embodiment of the present invention.

[0015] Figure 2 A cross-sectional view of an anode with a solid electrolyte layer formed on its surface is shown schematically.

[0016] Figure 3 This is a cross-sectional view showing the first and second regions of the porous material.

[0017] Figure 4 for Figure 3 Sectional view of line IV-IV. Detailed Implementation

[0018] The following examples illustrate embodiments of the electrolytic capacitors disclosed herein, but the disclosure is not limited to the examples described below. In the following description, specific values ​​and materials are sometimes shown, but other values ​​and materials may be used as long as the effects of the disclosure are achieved. In this specification, the phrase "value A to value B" includes both value A and value B, and can be read as "value A or higher and value B or lower." In the following description, when lower and upper limits of values ​​related to specific physical properties, conditions, etc., are shown, any combination of any of the shown lower limits and any of the shown upper limits may be used, as long as the lower limit is not higher than the upper limit. When multiple materials are shown, one may be selected for use alone, or two or more may be combined.

[0019] Furthermore, this disclosure includes a combination of the contents of any two or more claims selected from the plurality of claims recited in the appended claims. In other words, the contents of any two or more claims selected from the plurality of claims recited in the appended claims can be combined, provided that no technical contradiction arises.

[0020] "Electrolytic capacitor" can also be read as "solid electrolytic capacitor", and "capacitor" can also be read as "capacitor".

[0021] One embodiment of the present invention relates to an electrolytic capacitor comprising: an anode body having a porous body containing a valve-acting metal and a dielectric layer covering the porous body; and a solid electrolyte layer filling the pores of the porous body and covering the dielectric layer. Hereinafter, the combination of the anode body and the solid electrolyte layer (or the combination of the anode body, the solid electrolyte layer, and the cathode layer described later) will also be referred to as a capacitor element. The porous body has a first region on the outer surface side of the porous body and a second region other than the first region. When the shortest distance from the outer surface of the porous body to its center is defined as D, the first region is the region closer to the outer surface of the porous body than 0.5D.

[0022] The fill rate R2 of the solid electrolyte layer in the second region is smaller than the fill rate R1 of the solid electrolyte layer in the first region, and the ratio R2 / R1 is less than 1 / 10. In this case, a low ESR in the electrolytic capacitor can be achieved.

[0023] In the first region (the outer surface of the porous body) where a large amount of current flows, a larger amount of solid electrolyte layer is filled, increasing conductivity. This creates numerous conductive pathways through the solid electrolyte layer filling the pores of the porous body, allowing current to flow efficiently between the metal framework and the pores of the porous body via the solid electrolyte layer. Conversely, in the second region (the central side of the porous body), the amount of solid electrolyte layer is controlled to ensure sufficient capacity. This allows current to flow easily through the low-resistivity metal framework constituting the porous body, suppressing the increase in resistance caused by current flowing through the solid electrolyte layer. When R2 / R1 is 1 / 10 or less, the effects of the first and second regions complement each other, effectively reducing ESR.

[0024] From the perspective of easily reducing ESR, R2 / R1 is preferably 3 / 100 or less, more preferably 1 / 100 or less. From the perspective of easily ensuring capacity, R2 / R1 is preferably 1 / 1000 or more, more preferably 3 / 1000 or more. From the perspective of reducing ESR and ensuring capacity, the range of R2 / R1 can be 1 / 1000 or more and 1 / 10 or less, 1 / 1000 or more and 3 / 100 or less, or 1 / 1000 or more and 1 / 100 or less.

[0025] From the perspective of easily reducing ESR, R1 is preferably 80% or more. Similarly, R2 is preferably 9% or less, more preferably 2.5% or less. From the perspective of ensuring capacity, R2 can be 0.08% or more, or 0.25% or more.

[0026] The solid electrolyte layer filling rate R (%) refers to the ratio of the area occupied by the solid electrolyte layer to the area occupied by the pores (pores of the anode body) in a cross-section of the anode body observed through an electron microscope (containing the line segment of the specified shortest distance D). The area occupied by the pores in the cross-section is the value obtained by subtracting the area occupied by the anode body (the sum of the porous material and the dielectric layer) in the cross-section from the total area of ​​the cross-section. Scanning electron microscopes (SEM) or transmission electron microscopes (TEM) can be used as electron microscopes.

[0027] R1 and R2 can be obtained using the following method.

[0028] The capacitor element removed from the disassembled electrolytic capacitor is processed using a cross-section polisher (CP) to obtain a sample cross-section for SEM observation. The sample cross-section (the cross-section of the anode) is observed using SEM to obtain an image (e.g., magnification: 100x to 100,000x). Based on the SEM image, the overall area S0 of the image is calculated (e.g., 0.9 μm). 2 ~1000μm 2 The area S1 occupied by the anode (the sum of the porous body and the dielectric layer) and the area S2 occupied by the solid electrolyte layer are calculated. The fill rate R (%) is calculated as {S2 / (S0-S1)}×100. It should be noted that the value obtained by subtracting S1 from S0 is the area occupied by the pores.

[0029] The filling rate R1 of the solid electrolyte layer in Region 1 is obtained by calculating the filling rate R of any number of regions (e.g., 3 to 5 regions) at any depth from the outer surface of the porous material in Region 1 using SEM images, and then finding the maximum value among them. At least one of these regions is located near the outer surface of the porous material. It should be noted that "near the outer surface of the porous material" refers to a region closer to the outer surface of the porous material than 0.2D. The filling rate of the solid electrolyte layer near the outer surface of the porous material can be R1. For example, when 0.5D is 225 μm to 410 μm, with respect to the center of the aforementioned 3 regions, it can be near the outer surface of the porous material (near 0 μm), at a depth of 50 μm from the outer surface, and at a depth of 100 μm from the outer surface.

[0030] The filling rate R2 of the solid electrolyte layer in the second region is obtained by calculating the filling rate R of any number of regions (e.g., 3 to 5 regions) at any depth from the boundary between the second and first regions using SEM images, and then averaging these values. At least one of these regions is located near the center of the porous material. It should be noted that "near the center of the porous material" refers to a region closer to the center of the porous material than 0.2D. In the case where an anode lead (described later) is present at the center of the porous material, "near the center of the porous material" refers to the vicinity of the anode lead. The filling rate of the solid electrolyte layer near the center of the porous material can be R2. In the above, the observation of the sample cross-section is performed using SEM, but it can also be performed using TEM.

[0031] The fill rate R is calculated based on any number of regions at any depth in regions 1 and 2. It can be confirmed that the fill rate R is smaller in region 2 than in region 1.

[0032] From the perspective of easily achieving the effect of low ESR by setting R2 / R1 to 1 / 10 or less, the conductivity of the solid electrolyte layer is preferably 15 S / cm or more (or 20 S / cm or more) and 500 S / cm or less, more preferably 15 S / cm or more (or 20 S / cm or more) and 300 S / cm or less. Similarly, the conductivity of the solid electrolyte layer is more preferably 15 S / cm or more (or 20 S / cm or more) and 200 S / cm or less, particularly preferably 15 S / cm or more (or 20 S / cm or more) and 150 S / cm or less.

[0033] From the perspective of reducing ESR and ensuring capacity, when the conductivity of the solid electrolyte layer is 15 S / cm or more (or 20 S / cm or more) and 150 S / cm or less, R1 can be 80% or more, and R2 / R1 can be 1 / 1000 or more and 1 / 10 or less (preferably 1 / 100 or more and 1 / 10 or less).

[0034] Similarly, when the conductivity of the solid electrolyte layer is greater than 150 S / cm and less than 200 S / cm, R1 can be 80% or more, and R2 / R1 can be 1 / 1000 or more and less than 1 / 10 (preferably 1 / 100 or more and less than 1 / 10).

[0035] Similarly, when the conductivity of the solid electrolyte layer is greater than 200 S / cm and less than 300 S / cm, R1 can be 80% or more, and R2 / R1 can be 1 / 1000 or more and less than 3 / 100 (preferably 1 / 100 or more and less than 3 / 100).

[0036] Similarly, when the conductivity of the solid electrolyte layer is greater than 300 S / cm and less than 500 S / cm, R1 can be greater than 80%, and R2 / R1 can be greater than 1 / 1000 and less than 1 / 100.

[0037] The conductivity of the solid electrolyte layer can be determined by the following method.

[0038] The electrolytic capacitor is disassembled, the capacitor element is removed, and the composition of the solid electrolyte layer is analyzed. When using either the first or second processing solution to form the solid electrolyte layer, the composition of the first or second processing solution can also be analyzed. Analytical methods include TEM (transmission electron microscopy)-EELS (electron energy loss spectroscopy), NMR (nuclear magnetic resonance spectroscopy), and Raman spectroscopy.

[0039] Based on the analytical results, a sample film containing the same composition as the solid electrolyte layer (e.g., thickness 20 μm to 40 μm) is formed, and the conductivity of this sample film is determined as the conductivity of the solid electrolyte layer. The Loresta-GX and PSP probes manufactured by Nitto Seiko Analytical Technology Co., Ltd. can be used as the conductivity measuring apparatus.

[0040] When forming the solid electrolyte layer using either the first or second processing solution described later, the sample film can also be formed using either the first or second processing solution described later. When the solid electrolyte layer consists of the first and second layers described later, a sample film with the same stacked structure of the first and second layers as the solid electrolyte layer can also be formed. The thickness ratio of the first to the second layer in the sample film can be appropriately determined based on the thickness ratio T2 / T1 described later. This thickness T1 can be considered as the total thickness of the first and second layers. This thickness T2 can be considered as the thickness of the first layer.

[0041] The ratio of the thickness T2 of the solid electrolyte layer near the center of the porous body (the region closer to the center than 0.2D) to the thickness T1 of the solid electrolyte layer near the outer surface of the porous body (the region closer to the outer surface than 0.2D): T2 / T1 is, for example, 0.1 or less, or it may be more than 0.01 and less than 0.1. The thickness T2 of the solid electrolyte layer near the center of the porous body is, for example, less than 0.02 μm (or less than 0.017 μm). The solid electrolyte layer of thickness T1 may, for example, be formed by the first layer and the second layer described later. The solid electrolyte layer of thickness T2 may, for example, be formed by the first layer described later.

[0042] It should be noted that the thickness T1 of the aforementioned solid electrolyte layer was obtained by taking an SEM image of the sample cross-section in the same manner as R1 and R2, measuring the thickness at any 10 points near the outer surface of the porous material using this image, and calculating their average value. The thickness T2 of the aforementioned solid electrolyte layer was obtained by measuring the thickness at any 10 points near the center of the porous material and calculating their average value.

[0043] (porous body)

[0044] Porous materials contain valve-acting metals. Suitable valve-acting metals include aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), and hafnium (Hf).

[0045] As a porous body, for example, a sintered body using a molded body containing raw material particles (raw material powder) that contain a valve-acting metal. These particles can be particles of the valve-acting metal, particles of an alloy containing the valve-acting metal, or particles of a compound containing the valve-acting metal. Only one type of particle can be used, or a mixture of two or more types can be used.

[0046] Porous bodies can be obtained, for example, by pressing raw material particles into a predetermined shape to form a molded body, and then sintering the molded body. Alternatively, an anode lead can be positioned at a predetermined location in a mold, raw material particles can be fed into the mold, and then pressed to form a molded body. The molded body can also be sintered to obtain a porous body with a portion of the anode lead embedded within it. Porous bodies are typically cuboids.

[0047] (Anode lead)

[0048] The anode body may also have a rod-shaped anode lead partially embedded in the porous material. A portion of the anode lead may be embedded in the porous material by passing through its center. If the porous material is cuboid, the anode lead is embedded from one end face of the cuboid. The anode lead may contain valve-acting metal. A portion of the anode lead is embedded in the porous material, with the remainder protruding from it. This remainder is connected to the anode lead terminal by welding or the like.

[0049] (Dielectric layer)

[0050] The dielectric layer is formed in the form of covering the outer surface of the porous material and the inner walls of the pores of the porous material. The dielectric layer is formed, for example, by subjecting the porous material to a chemical conversion treatment and growing an oxide coating on the surface of the porous material. The chemical conversion treatment can also be carried out by immersing the porous material in a chemical conversion solution and anodizing the surface of the porous material. Alternatively, the porous material can be heated in an oxygen-containing atmosphere to oxidize the surface of the porous material.

[0051] (Solid electrolyte layer)

[0052] The solid electrolyte layer is configured to cover at least a portion of the dielectric layer. The solid electrolyte layer may fill the pores of the porous material through the dielectric layer and may be formed on the outer surface of the porous material. The solid electrolyte layer may be a stack of two or more different solid electrolyte layers.

[0053] The solid electrolyte layer may contain, for example, a conductive polymer. The conductive polymer can be a π-conjugated polymer, and examples include polypyrrole, polythiophene, polyaniline, and their derivatives. These can be used alone or in combination. Furthermore, the conductive polymer can be a copolymer of two or more monomers. It should be noted that derivatives of conductive polymers refer to polymers with conductive polymers as their basic backbone. For example, examples of polythiophene derivatives include poly(3,4-ethylenedioxythiophene) (PEDOT).

[0054] Dopants can also be added to conductive polymers. That is, the solid electrolyte layer can contain both a conductive polymer and a dopant. The conductive polymer can be contained in the solid electrolyte layer in a dopant-doped state. The dopant can be selected based on the conductive polymer, or well-known dopants can be used. Examples of dopants include benzenesulfonic acid, alkylbenzenesulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, polystyrene sulfonic acid (PSS), and their salts. The solid electrolyte layer may, for example, contain PEDOT doped with PSS.

[0055] A solid electrolyte layer containing conductive polymers can be formed, for example, by impregnating a first processing solution containing monomers (or oligomers) onto a surface to form a porous body (anolyte) with a dielectric layer, followed by polymerization of the monomers (or oligomers) via chemical polymerization or electrolytic polymerization. In the case of chemical polymerization, the first processing solution contains, for example, monomers (or oligomers), an oxidant, and a solvent (or dispersion medium). Examples of monomers include 3,4-ethylenedioxythiophene (EDOT) and pyrrole. The first processing solution may contain dopants.

[0056] Alternatively, a solid electrolyte layer can also be formed by impregnating a porous body (anode) with a dielectric layer on its surface with a second processing solution containing a conductive polymer, followed by drying. The second processing solution may contain, for example, a conductive polymer, a solvent (or dispersion medium), and, if necessary, a dopant.

[0057] The conductivity of a solid electrolyte layer can be adjusted, for example, by changing the conductive polymer, dopants, polymerization conditions (polymerization method, oxidants, etc.).

[0058] The solid electrolyte layer formation process may include: a first step, forming a thin solid electrolyte layer (hereinafter also referred to as layer 1) in regions 1 and 2; and a second step, after the first step, forming a thick solid electrolyte layer (hereinafter also referred to as layer 2) in region 1 (particularly near the outer surface of the porous body). In this case, it is easy to control R2 / R1 to be less than 1 / 10. It is easy to control R1 as the filling rate based on the sum of layers 1 and 2. It is easy to control R2 as the filling rate based on layer 1. The components (conductive polymer, dopant, etc.) contained in layers 1 and 2 may be the same or different from each other.

[0059] In the first step, chemical polymerization can be carried out at a low temperature (e.g., within the temperature range where chemical polymerization can be carried out below 10°C). In this case, the diffusion of the first processing liquid (polymerization liquid) is suppressed, and a thin solid electrolyte layer is easily formed in the first and second regions.

[0060] In the second step, electrolytic polymerization can also be performed in a manner that forms a thick second layer in the first region. For example, the current value can be changed, and electrolytic polymerization can be performed in multiple steps. For example, a step (2a) of electrolytic polymerization with a large current can be performed, followed by a step (2b) of electrolytic polymerization with a small current for a longer time. In step (2a), a thick second layer can be formed to a certain extent to block the pores of the porous material in the first region. Therefore, the formation of the second layer in step (2b) occurs in the first region and is suppressed in the second region. Thus, by performing electrolytic polymerization with a small current for a longer time in step (2b), the filling rate of the solid electrolyte layer in the first region can be sufficiently increased, so that R2 / R1 is less than 1 / 10.

[0061] (other)

[0062] The capacitor element may have a cathode layer covering at least a portion of the solid electrolyte layer. The electrolytic capacitor may also have anode and cathode leads electrically connected to the capacitor element, and an outer resin casing disposed around the capacitor element. The cathode leads are connected to the cathode portion via conductive components. The anode leads are connected to the ends of the anode leads protruding from the porous material. There are no particular limitations on the shape, size, etc., of the capacitor element; it may be a known capacitor element or a capacitor element with the same structure.

[0063] (Cathode layer)

[0064] The cathode layer may comprise a carbon layer formed on a solid electrolyte layer and a metal paste layer formed on the carbon layer. The carbon layer may be formed from a conductive carbon material such as graphite and a resin. The metal paste layer may be formed from metal particles (e.g., silver particles) and a resin, or, for example, from a known silver paste.

[0065] (Conductive components)

[0066] The cathode layer is connected to the cathode lead terminal via a conductive component. That is, the cathode layer (cathode portion) is electrically connected to the cathode lead terminal. The conductive component is made of a conductive material. The conductive component can be formed using a material containing metal particles (e.g., silver particles) and resin, or, for example, using a known metal paste (e.g., silver paste). The conductive component is formed by heating the metal paste. It should be noted that the conductive component can also be composed of multiple conductive layers of different types.

[0067] (Outer resin)

[0068] The outer resin is disposed around the capacitor element in a manner that prevents the capacitor element from being exposed on the surface of the electrolytic capacitor. Furthermore, the outer resin insulates the anode lead terminals from the cathode lead terminals. Known outer resins used in electrolytic capacitors can be used as the outer resin. For example, the outer resin can also be formed using an insulating resin material used in sealing the capacitor element. The outer resin can also be formed by housing the capacitor element in a mold, introducing uncured thermosetting resin and filler into the mold using transfer molding, compression molding, or similar methods, and then allowing it to cure.

[0069] Examples of outer resins include epoxy resins, phenolic resins, silicone resins, melamine resins, urea resins, alkyd resins, polyurethanes, polyimides, and unsaturated polyesters. Outer resins may contain substances other than resin (inorganic fillers, etc.).

[0070] (Cathode lead terminal)

[0071] A portion of the cathode lead terminals protrudes from the outer resin and serves as external cathode terminals. The material of the cathode lead terminals can be any material suitable for use as cathode lead terminals in electrolytic capacitors. For example, known materials for cathode lead terminals used in electrolytic capacitors can be used. Cathode lead terminals can be formed by processing metal sheets (including metal plates and metal foils) made of metal (copper, copper alloys, etc.) using known metalworking methods.

[0072] (Anode lead terminal)

[0073] A portion of the anode lead terminals protrudes from the outer resin and serves as external anode terminals. The material of the anode lead terminals can be any material suitable for use as anode lead terminals in electrolytic capacitors. For example, known materials for anode lead terminals used in electrolytic capacitors can be used. The anode lead terminals can be formed by processing metal sheets (including metal plates and metal foils) made of metal (copper, copper alloys, etc.) using known metalworking methods.

[0074] Figure 1 A cross-sectional view is shown schematically as an example of an electrolytic capacitor according to this embodiment. Figure 2 A cross-sectional view of an anode with a solid electrolyte layer formed on its surface is shown schematically. Figure 3 This is a cross-sectional view showing the first and second regions of the porous material. Figure 4 for Figure 3 Sectional view of line IV-IV. Figure 3 and 4 This is a cross-sectional view of the center C containing the porous material. It should be noted that all figures are schematic and the proportions of the dimensions (length, width, thickness, etc.) of the constituent elements may not be the same as the actual dimensions.

[0075] The electrolytic capacitor 20 includes: a capacitor element 10, an outer casing resin 11 sealing the capacitor element 10, and an anode lead terminal 12 and a cathode lead terminal 13 electrically connected to the capacitor element 10. A portion of the anode lead terminal 12 and the cathode lead terminal 13 are exposed from the outer casing resin 11. A portion of the anode lead terminal 12 and the cathode lead terminal 13 are covered by the outer casing resin 11 together with the capacitor element 10.

[0076] The capacitor element 10 includes: an anode body 1, a solid electrolyte layer 2 formed on the anode body 1, and a cathode layer 3 formed on the solid electrolyte layer 2. The anode body 1 includes: a porous body 4 containing a valve-acting metal, and a dielectric layer 5 covering the porous body 4. The dielectric layer 5 is formed in such a way that it covers the outer surface S and the inner wall surface of the pores 7 of the porous body 4. The anode body 1 has a porous shape that is substantially the same as that of the porous body 4.

[0077] The porous body 4 has a generally cuboid shape and six sides. A portion of the anode lead 6 extends from one side of the porous body 4. That is, the anode lead 6 has a first portion 6a embedded in the interior of the porous body 4 from one side and a second portion 6b extending from one side of the porous body 4. The second portion 6b is joined to the anode lead terminal 12 by welding or the like. In this embodiment, although the first portion 6a is embedded in the porous body 4 through the center C of the porous body 4, it may also be embedded in the porous body 4 without passing through the center C of the porous body 4.

[0078] The solid electrolyte layer 2 is formed in such a way that it covers at least a portion of the dielectric layer 5. The solid electrolyte layer 2 fills the pores 7 of the porous body 4 (anode body 1). The solid electrolyte layer 2 is formed in such a way that it covers the outer surface S of the porous body 4 and the inner wall surface of the pores 7 through the dielectric layer 5.

[0079] like Figure 3 and Figure 4 As shown, the porous body 4 has a first region 4a on the outer surface side of the porous body 4 and a second region 4b outside the first region 4a. When the shortest distance from the outer surface S of the porous body 4 to the center C is set as D, the first region 4a is the region whose distance from the outer surface S of the porous body 4 is closer than 0.5D. Figure 3 and Figure 4 (Cross-section section). The filling rate of the solid electrolyte layer 2 in the porous body 4 is smaller in the second region 4b than in the first region 4a. The ratio of the filling rate R2 of the solid electrolyte layer 2 in the second region 4b to the filling rate R1 of the solid electrolyte layer 2 in the first region 4a is less than 1 / 10.

[0080] The cathode layer 3 is formed to cover the surface of the solid electrolyte layer 2. The cathode layer 3 comprises a carbon layer 3a formed to cover the solid electrolyte layer 2, and a metal paste layer 3b formed on the surface of the carbon layer 3a. The cathode lead terminal 13 is bonded to the cathode layer 3 (metal paste layer 3b) via a conductive member 8. The carbon layer 3a comprises a conductive carbon material such as graphite and resin. The metal paste layer 3b comprises, for example, metal particles (e.g., silver) and resin. It should be noted that the structure of the cathode layer 3 is not limited to this structure. The cathode layer 3 can be any structure that has a current-collecting function.

[0081] [Example]

[0082] The present invention will now be described in detail based on embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0083] Examples 1-6

[0084] (Preparation of porous materials)

[0085] One end of the anode lead is embedded in Ta particles, which are then shaped into cuboids and sintered in a vacuum. This yields a porous body (Ta sintered body) with a portion of the anode lead embedded within it. The shortest distance D from the outer surface to the center of the porous body is 450 μm. A Ta lead is used as the anode lead.

[0086] (Formation of the dielectric layer)

[0087] A porous material with a portion of the anode leads embedded is immersed in a chemical conversion tank filled with an aqueous solution of phosphoric acid, which serves as the electrolytic solution, for anodizing. This forms an oxide coating (dielectric layer) on the surface of the porous material. It should be noted that during anodizing, the concentration of phosphoric acid, the chemical conversion voltage, and the temperature can be appropriately selected within the ranges of 0.01–5% by mass, 2–100 V, and 20–80 °C.

[0088] (Formation of a solid electrolyte layer)

[0089] (Step 1)

[0090] First, a thin first layer (conductivity 21 S / cm) containing polypyrrole and a dopant is formed in regions 1 and 2 of a porous body having a dielectric layer on its surface (step 1). A sulfonate with a naphthalene framework is used as the dopant. The first layer is formed by chemical polymerization. The chemical polymerization is carried out using a treatment solution containing pyrrole, the dopant, an oxidant, and water. By performing chemical polymerization at a low temperature (within the temperature range where chemical polymerization can be carried out below 10°C), a relatively thin first layer is formed in regions 1 and 2, and the thickness T2 of the solid electrolyte layer near the center of the porous body is set to the values ​​shown in Table 1.

[0091] (Step 2)

[0092] Next, a thick second layer containing polypyrrole and a dopant (conductivity 21 S / cm) is formed in the first region of the porous body having a dielectric layer on its surface (step 2). The same dopant used to form the first layer is used. The second layer is formed by electrolytic polymerization. Electrolytic polymerization is performed using a treatment solution containing pyrrole, the dopant, and water. Step (2a) of electrolytic polymerization with a high current is performed at 25°C, followed by step (2b) of electrolytic polymerization with a low current for a longer time. Thus, a thick second layer is formed in the first region, and the thickness T1 of the solid electrolyte layer near the outer surface of the porous body is set to the values ​​shown in Table 1.

[0093] Therefore, in the second region, a solid electrolyte layer is formed approximately from the first layer. In the first region (particularly on the outer surface side of the porous body), a solid electrolyte layer is formed from the first and second layers. Thus, the solid electrolyte layer is formed in such a way that the filling rate of the solid electrolyte layer in the porous body is smaller in the second region than in the first region. The conductivity of the solid electrolyte layer is 21 S / cm.

[0094] In the above, the temperature during chemical polymerization in the first step (the first layer formation step) is adjusted, and the filling rate R2 of the solid electrolyte layer in the second region is set to the value shown in Table 1. The magnitude of the current and the duration of current flow during electrolytic polymerization in the second step (the second layer formation step) are adjusted, and the filling rate R1 of the solid electrolyte layer in the first region is set to the value shown in Table 1.

[0095] It should be noted that the filling rates R1 of the solid electrolyte layer in region 1 and R2 of the solid electrolyte layer in region 2 were determined using the aforementioned method during the formation of the solid electrolyte layer. Furthermore, the thickness T1 of the solid electrolyte layer near the outer surface of the porous body and the thickness T2 of the solid electrolyte layer near the center of the porous body were also determined using the aforementioned method. The determined values ​​of T1 and T2 are shown in Table 1.

[0096] (Formation of the cathode layer)

[0097] A dispersion of carbon particles (carbon paste) is coated onto a solid electrolyte layer and heated to form a carbon layer on the surface of the solid electrolyte layer. A metal paste containing silver particles, binder resin, and solvent is then coated onto the surface of the carbon layer and heated to form a metal paste layer, resulting in a cathode layer composed of the carbon layer and the metal paste layer. This yields a capacitor element.

[0098] (The fabrication of electrolytic capacitors)

[0099] A conductive adhesive material, serving as a conductive component, is applied to a metal paste layer, and the cathode lead terminal and the metal paste layer are bonded together. The anode lead is bonded to the anode lead terminal by resistance welding. Next, the capacitor element with each lead terminal bonded is sealed with an external resin. Thus, an electrolytic capacitor is obtained. In Table 1, X1 to X6 represent the electrolytic capacitors of Examples 1 to 6, respectively.

[0100] Comparative Example 1

[0101] In the second step of the solid electrolyte layer formation process, electrolytic polymerization is carried out at 25°C with a small current for a relatively long time (step (2a) is not performed), thereby forming a second layer to a certain extent in the second region (near the center of the porous body). The thickness T2 of the solid electrolyte layer near the center of the porous body is set to the value shown in Table 1. The filling rate R2 of the solid electrolyte layer in the second region is set to the value shown in Table 1, and R2 / R1 is set to 3 / 10.

[0102] Except as described above, the electrolytic capacitor Y1 is manufactured in the same manner as the electrolytic capacitor X1 in Example 1.

[0103] [Rating 1]

[0104] For each electrolytic capacitor obtained above, the capacitance (μF) at 120Hz and the ESR (mΩ) at 100kHz were measured using a four-terminal LCR meter at 20°C. The capacitance is expressed as a relative value with Y1's capacitance set to 100. A capacitance of 75 or higher is considered good. The evaluation results are shown in Table 1.

[0105] [Table 1]

[0106]

[0107] Among electrolytic capacitors X1 to X6, a lower ESR was obtained than that of electrolytic capacitor Y1. Among electrolytic capacitors X1 to X5, good capacitance was obtained.

[0108] Examples 7-9

[0109] The conductivity of the solid electrolyte layer was set to the values ​​shown in Table 2. The conductivity of the solid electrolyte layer was adjusted by changing the types of dopants used to form the first and second layers. Except as described above, electrolytic capacitors X7 to X9 of Examples 7 to 9 were fabricated in the same manner as the electrolytic capacitor X1 of Example 1.

[0110] Comparative Examples 2-4

[0111] The conductivity of the solid electrolyte layer was set to the values ​​shown in Table 2. The conductivity of the solid electrolyte layer was adjusted by changing the types of dopants used to form the first and second layers. In addition to the above, electrolytic capacitors Y7 to Y9 of Comparative Examples 2 to 4 were fabricated in the same manner as the electrolytic capacitor Y1 of Comparative Example 1.

[0112] Examples 10-13

[0113] The solid electrolyte layer is formed as follows.

[0114] (Step 1)

[0115] First, a thin first layer containing PEDOT and a dopant is formed in the first and second regions of a porous body having a dielectric layer on its surface (first step). The formation of the first layer is carried out by chemical polymerization. The chemical polymerization is carried out using a treatment solution containing EDOT, a dopant, an oxidant, and water. The thin first layer is formed in the first and second regions by carrying out chemical polymerization at a low temperature (within the temperature range where chemical polymerization can be carried out below 10°C).

[0116] (Step 2)

[0117] Next, a thick second layer containing PEDOT and a dopant is formed in the first region of the porous body having a dielectric layer on its surface (second step). The same dopant used to form the first layer is used. The second layer is formed by electrolytic polymerization. Electrolytic polymerization is performed using a treatment solution containing PEDOT, the dopant, and water. A step (2a) of electrolytic polymerization with a high current is performed at 25°C. After step (2a), a step (2b) of electrolytic polymerization with a low current for a longer time is performed, thereby forming a thick second layer in the first region.

[0118] The conductivity of the solid electrolyte layer was set to the values ​​shown in Table 2. The conductivity of the solid electrolyte layer was adjusted by changing the types of dopants used to form the first and second layers.

[0119] Therefore, in the second region, a solid electrolyte layer is formed approximately from the first layer. In the first region (particularly on the outer surface side of the porous body), a solid electrolyte layer is formed from the first and second layers. Thus, a solid electrolyte layer is formed in the second region such that the filling rate of the solid electrolyte layer in the porous body is smaller than that in the first region.

[0120] In the above, the temperature during chemical polymerization in the first step (the step of forming the first layer) is adjusted so that the filling rate R2 of the solid electrolyte layer in the second region is 0.25%. The magnitude of the current and the duration of current flow during electrolytic polymerization in the second step (the step of forming the second layer) are adjusted so that the filling rate R1 of the solid electrolyte layer in the first region is set to 84%. R2 / R1 is 3 / 1000. The thickness T1 of the solid electrolyte layer near the outer surface of the porous body is 170 nm. The thickness T2 of the solid electrolyte layer near the center of the porous body is 0.51 nm.

[0121] In addition to the above, electrolytic capacitors X10 to X13 of Examples 10 to 13 were manufactured in the same manner as the electrolytic capacitor X1 of Example 1.

[0122] Comparative Examples 5-8

[0123] In the second step of the solid electrolyte layer formation process, a second layer of a certain degree is also formed in the second region (near the center of the porous body) by electrolytic polymerization at 25°C with a small current for a relatively long time (step (2a) is not performed). The thickness T2 of the solid electrolyte layer near the center of the porous body is set to 51 nm, the filling rate R2 of the solid electrolyte layer in the second region is set to 25%, and R2 / R1 is set to 3 / 10.

[0124] In addition to the above, electrolytic capacitors Y10 to Y13 of Comparative Examples 5 to 8 were manufactured in the same manner as the electrolytic capacitors X10 to X13 of Examples 10 to 13.

[0125] [Rating 2]

[0126] The ESR of each electrolytic capacitor was measured using the same method as in Evaluation 1. Furthermore, based on the measurement results, the degree of ESR reduction resulting from R2 / R1 ratios of 3 / 10 to 3 / 1000 was investigated by keeping the conductivity of the solid electrolyte layer constant. Specifically, when the ESRs of electrolytic capacitors with the same solid electrolyte layer conductivity (R2 / R1 = 3 / 1000) and electrolytic capacitors with R2 / R1 = 3 / 10 were x and y respectively, x / y was calculated as the ESR ratio. For example, the ESR ratio for electrolytic capacitor X1 is the ratio of the ESR value of electrolytic capacitor X1 to the ESR value of electrolytic capacitor Y1. The smaller the ESR ratio, the greater the ESR reduction effect. The ESR ratios were calculated for electrolytic capacitors X1, X7 to X13. The evaluation results are shown in Table 2.

[0127] [Table 2]

[0128]

[0129] Electrolytic capacitors X1 and X7 to X13 exhibited lower ESRs than electrolytic capacitors Y1 and Y7 to Y13, respectively. Among them, electrolytic capacitors X1 and X7 to X12, with a solid electrolyte layer conductivity of 15 to 500 S / cm, showed an ESR ratio of 0.95 or less, demonstrating an excellent low ESR effect resulting from an R2 / R1 ratio of 1 / 10 or less. In particular, electrolytic capacitors X1 and X7 to X10, with a solid electrolyte layer conductivity of 15 to 200 S / cm, showed an ESR ratio of 0.87 or less, demonstrating a significant low ESR effect resulting from an R2 / R1 ratio of 1 / 10 or less.

[0130] Industrial availability

[0131] This invention can be used in electrolytic capacitors having a porous anode body and a portion of the anode leads embedded in the anode body. The electrolytic capacitors of this invention can be used in various applications requiring low ESR.

[0132] Although the invention has been described in conjunction with presently preferred embodiments, this disclosure should not be interpreted as limiting. Various modifications and alterations will be readily apparent to those skilled in the art upon reading the foregoing disclosure. Therefore, the appended claims should be construed as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0133] Explanation of reference numerals in the attached figures

[0134] 1: Anode body; 2: Solid electrolyte layer; 3: Cathode layer; 3a: Carbon layer; 3b: Metal paste layer; 4: Porous body; 4a: Region 1; 4b: Region 2; 5: Dielectric layer; 6: Anode lead; 6a: Part 1; 6b: Part 2; 7: Hole; 8: Conductive component; 10: Capacitor element; 11: Outer resin; 12: Anode lead terminal; 13: Cathode lead terminal; 20: Electrolytic capacitor.

Claims

1. An electrolytic capacitor comprising: An anode body having a porous body comprising a valve-acting metal and a dielectric layer covering the porous body; and A solid electrolyte layer fills the pores of the porous body and covers the dielectric layer. The porous material has a first region on the outer surface side of the porous material and a second region outside the first region. When the shortest distance from the outer surface of the porous material to its center is defined as D, the first region is the region whose distance from the outer surface of the porous material is closer than 0.5D. The filling rate R2 of the solid electrolyte layer in the second region is smaller than the filling rate R1 of the solid electrolyte layer in the first region. The ratio of the fill rate R2 to the fill rate R1, R2 / R1, is less than 1 / 10.

2. The electrolytic capacitor according to claim 1, wherein, The ratio R2 / R1 is greater than 1 / 1000 and less than 1 / 10.

3. The electrolytic capacitor according to claim 2, wherein, The ratio R2 / R1 is greater than 1 / 1000 and less than 3 / 100.

4. The electrolytic capacitor according to any one of claims 1 to 3, wherein, The fill rate R1 is above 80%.

5. The electrolytic capacitor according to any one of claims 1 to 3, wherein, The fill rate R2 is below 9%.

6. The electrolytic capacitor according to any one of claims 1 to 3, wherein, The conductivity of the solid electrolyte layer is above 15 S / cm and below 500 S / cm.

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