electrolytic capacitor

Abstract

The invention includes a capacitor element comprising a positive electrode body, a dielectric layer covering at least a portion of the positive electrode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a negative electrode extraction layer covering at least a portion of the solid electrolyte layer. The negative electrode extraction layer comprises a carbon material and a first polymer having an acid group. The acid group contains at least one selected from the group consisting of sulfone groups, carboxyl groups, and derivatives thereof, thereby suppressing a rise in ESR as an electrolytic capacitor.

Description

[Technical Field]

[0001] The present invention relates to an electrolytic capacitor. [Background technology]

[0002] An electrolytic capacitor includes a capacitor element and an exterior body that covers the capacitor element. An example of an electrolytic capacitor is a solid electrolytic capacitor that uses a conductive polymer or the like as a solid electrolyte. In this case, the capacitor element includes an anode body, a dielectric layer formed on the anode body, a solid electrolyte layer formed on the dielectric layer, and a cathode extraction layer formed on the solid electrolyte layer. The cathode extraction layer is electrically connected to a cathode lead terminal.

[0003] As a configuration of the cathode extraction layer, for example, Patent Document 1 proposes adding an aromatic compound having a sulfonic acid group to the carbon layer to improve the adhesion between the carbon layer and a solid electrolyte layer containing a conductive polymer, thereby reducing the equivalent series resistance (ESR) of the electrolytic capacitor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-27998 Summary of the Invention

[0005] However, the electrolytic capacitor of Patent Document 1 does not provide a sufficient effect of improving ESR (particularly, the effect of suppressing the increase in ESR in a high-temperature environment), and further improvement is desired.

[0006] One aspect of the present invention relates to an electrolytic capacitor including a capacitor element including an anode body, a dielectric layer covering at least a portion of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode extraction layer covering at least a portion of the solid electrolyte layer, wherein the cathode extraction layer includes a carbon material and a first polymer having an acid group, and the acid group includes at least one selected from the group consisting of a sulfonic group, a carboxyl group, and derivatives thereof.

[0007] This can suppress the increase in ESR of electrolytic capacitors equipped with solid electrolyte layers. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an electrolytic capacitor according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Electrolytic capacitor] An electrolytic capacitor according to one embodiment of the present invention includes a capacitor element including an anode body, a dielectric layer covering at least a portion of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode extraction layer covering at least a portion of the solid electrolyte layer. The cathode extraction layer includes a carbon material and a first polymer having an acid group. The acid group includes at least one selected from the group consisting of a sulfonic group, a carboxyl group, and derivatives thereof.

[0010] In electrolytic capacitors with a solid electrolyte layer, the capacitor element is usually covered with a resin exterior body, but air (particularly oxygen, or oxygen and moisture) can easily permeate the exterior body and enter the interior. If air that has entered the electrolytic capacitor comes into contact with the solid electrolyte layer, the conductive polymer contained in the solid electrolyte layer may deteriorate.

[0011] In a capacitor element, at least a portion of the solid electrolyte layer is covered with a cathode extraction layer. The cathode extraction layer typically includes a carbon layer. However, the carbon layer is typically an aggregate of particulate carbon material, and therefore is not dense. Therefore, when air enters an electrolytic capacitor, it easily permeates the carbon layer. The air that permeates the carbon layer may come into contact with the solid electrolyte layer and degrade the conductive polymer contained in the solid electrolyte layer. This degradation of the conductive polymer is particularly pronounced under high temperatures and / or high humidity. Degradation of the conductive polymer increases the resistance of the solid electrolyte layer, thereby increasing the ESR of the electrolytic capacitor.

[0012] In the electrolytic capacitor of this embodiment, the capacitor element includes a carbon layer included in a cathode extraction layer that covers at least a portion of the solid electrolyte layer, and the carbon layer contains a first polymer having an acid group in addition to a carbon material. The conductive polymer has a functional group that is easily positively charged (e.g., an -S- group or an -NH- group), First polymer The acid groups can bond with these functional groups of the conductive polymer. Meanwhile, the polymer chains of the first polymer can entangle the carbon particles, allowing the first polymer to adhere firmly to the carbon material. This enhances the adhesion between the carbon material and the conductive polymer through the first polymer. This improves the gas barrier properties of the carbon layer and reduces air permeation. This suppresses an increase in the resistance of the solid electrolyte layer and an increase in the ESR of the electrolytic capacitor.

[0013] Furthermore, because the first polymer is more thermally stable than its monomer, it is easier to maintain high adhesion between the carbon material and the conductive polymer even in high-temperature environments. Therefore, by including the first polymer, it is possible to suppress a high increase in ESR even at high temperatures.

[0014] The acid group is, for example, a sulfonic acid group (-SO3H) or a carboxyl group (-COOH), and is introduced into a monomer corresponding to the repeating unit of the first polymer. The acid group may be a derivative of the sulfonic acid group and / or the carboxyl group. The derivative of the sulfonic acid group and / or the carboxyl group includes an anionic group formed by dissociating a proton from the sulfonic acid group and / or the carboxyl group, and a salt of the anionic group with a cation (e.g., sodium salt). The derivative may also be an ester of the acid group with an alcohol.

[0015] In addition to the first polymer, a second polymer may be included in the cathode extraction layer. The second polymer can synergistically enhance the effect of suppressing the ESR increase, or can impart other functions to the second polymer. The second polymer, like the first polymer, may or may not have acid groups. The second polymer may be, for example, water-soluble. Water-soluble polymers generally have polar groups and can be tightly oriented by hydrogen bonding. This leaves little space for gases such as oxygen to diffuse within the polymer, making it difficult for gases to permeate through the polymer. Therefore, the second polymer can improve oxygen barrier properties. This suppresses oxidative degradation of the conductive polymer, further suppressing the increase in ESR.

[0016] Among water-soluble polymers, cellulose-based polymers and polyvinyl alcohol are preferred for use as the second polymer due to their high oxygen barrier properties. Cellulose-based polymers include cellulose ethers and cellulose esters, and may include derivatives in which the hydroxyl groups of glucose, a monomer that constitutes cellulose, are chemically modified, such as carboxymethyl cellulose or hydroxyethyl cellulose. The derivatives of cellulose-based polymers may also have a higher-order structure, particularly a fibril structure.

[0017] The cathode extraction layer may have a two-layer structure consisting of a first conductive layer covering at least a portion of the solid electrolyte layer and a second conductive layer covering at least a portion of the first conductive layer. In this case, the first polymer may be contained in at least the first conductive layer. This improves adhesion between the solid electrolyte layer and the first conductive layer, thereby suppressing an increase in ESR. For example, the first conductive layer may be a carbon layer and the second conductive layer may be a silver paste layer.

[0018] The structure of the electrolytic capacitor will be described in more detail below, with reference to the drawings as appropriate. Fig. 1 is a cross-sectional view that schematically shows the structure of an electrolytic capacitor according to one embodiment of the present invention. In the illustrated example, electrolytic capacitor 1 includes a capacitor element 2, a resin exterior body 3 that seals capacitor element 2, and an anode lead terminal 4 and a cathode lead terminal 5, at least a portion of which is exposed to the outside of exterior body 3. Exterior body 3 has a substantially rectangular parallelepiped outer shape, and electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape.

[0019] Capacitor element 2 includes an anode body 6 constituting an anode portion, a dielectric layer 7 covering anode body 6, and a cathode portion 8 covering dielectric layer 7.

[0020] The anode body 6 includes a region facing the cathode portion 8 and a region not facing the cathode portion 8. Of the region of the anode body 6 not facing the cathode portion 8, an insulating separation layer 13 is formed in a portion adjacent to the cathode portion 8, thereby restricting contact between the cathode portion 8 and the anode body 6. The insulating separation layer 13 covers the surface of the anode body 6 in a strip shape, for example. Of the region of the anode body 6 not facing the cathode portion 8, another part is electrically connected to the anode lead terminal 4 by welding. The cathode lead terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0021] The cathode section 8 includes a solid electrolyte layer 9 covering the dielectric layer 7, and a cathode extraction layer 10 covering the solid electrolyte layer 9. The cathode extraction layer 10 includes a carbon layer 11 (first conductive layer) and a silver paste layer 12 (second conductive layer). The carbon layer 11 includes a carbon material and a first polymer. The inclusion of the first polymer in the carbon layer 11 increases the adhesion between the carbon layer 11 and the solid electrolyte layer 9, so that even if air enters the interior of the exterior body 3, contact between the solid electrolyte layer 9 and the air can be suppressed. This suppresses deterioration of the conductive polymer included in the solid electrolyte layer 9.

[0022] The structure of the electrolytic capacitor will be described in more detail below. (Capacitor element 2) Capacitor element 2 includes an anode body 6 constituting an anode portion, a dielectric layer 7, and a cathode portion 8 including a solid electrolyte layer 9. Cathode portion 8 includes solid electrolyte layer 9 and a cathode extraction layer 10 covering solid electrolyte layer 9.

[0023] The electrolytic capacitor is required to have at least one capacitor element 2, and may have one or more capacitor elements 2. The number of capacitor elements included in the electrolytic capacitor may be determined depending on the application.

[0024] (Anode body 6) The anode body 6 may contain a valve metal, an alloy containing a valve metal, or a compound containing a valve metal. These materials may be used alone or in combination. Examples of preferred valve metals include aluminum, tantalum, niobium, and titanium. Anode body 6 having a porous surface can be obtained by roughening the surface of a substrate (such as a foil- or plate-shaped substrate) containing a valve metal by etching or other methods. The anode body 6 may also be a compact or sintered body of particles containing a valve metal. Note that sintered bodies have a porous structure. In other words, when the anode body 6 is a sintered body, the entire anode body 6 may be porous.

[0025] (Dielectric layer 7) The dielectric layer 7 is formed by anodizing the valve metal on the surface of the anode body 6 by chemical conversion treatment or the like. The dielectric layer 7 may be formed so as to cover at least a portion of the anode body 6. The dielectric layer 7 is usually formed on the surface of the anode body 6. Since the dielectric layer 7 is formed on the porous surface of the anode body 6, it is formed along the inner wall surfaces of holes and depressions (pits) on the surface of the anode body 6.

[0026] Dielectric layer 7 contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer 7 is not limited to this, and may be any material that functions as a dielectric. When the surface of anode body 6 is porous, dielectric layer 7 is formed along the surface of anode body 6 (including the inner wall surfaces of the pores).

[0027] (Cathode part 8) (Solid electrolyte layer 9) The solid electrolyte layer 9 constituting the cathode section 8 contains a conductive polymer and may further contain a dopant or additive, as necessary. Examples of conductive polymers that can be used include polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and / or polythiophene vinylene, and derivatives thereof. The solid electrolyte layer 9 can be formed, for example, by chemically polymerizing and / or electrolytically polymerizing raw material monomers on the dielectric layer 7. Alternatively, the solid electrolyte layer 9 can be formed by contacting the dielectric layer 7 with a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed. The solid electrolyte layer 9 may be formed so as to cover at least a portion of the dielectric layer 7.

[0028] (Cathode extraction layer 10) Cathode extraction layer 10 constituting cathode part 8 includes carbon layer 11 and silver paste layer 12. Cathode extraction layer 10 is formed so as to cover at least a portion of solid electrolyte layer 9.

[0029] (Carbon layer 11) The carbon layer 11 (first conductive layer) contains a carbon material and a first polymer, and has electrical conductivity. The carbon layer 11 may contain a binder and / or an additive, etc., as necessary.

[0030] The carbon material is preferably conductive carbon particles. Examples of carbon particles include graphite, graphene, carbon black, soft carbon, and hard carbon. As the graphite, a material having a graphite-type crystal structure is used, and either artificial graphite or natural graphite may be used. As the carbon particles, carbon nanotubes, carbon fibers, and the like may be used. The carbon particles may be carbon nanotubes, carbon fibers, and other fibrous carbon materials cut to an appropriate length (including pulverized products). These carbon particles may be used alone or in combination of two or more.

[0031] The carbon particles preferably include scaly particles. In this case, it is easy to fill the carbon layer 11 with the carbon particles overlapping in layers. A first polymer may be interposed between the overlapping scaly particles. As a result, the carbon layer 11 and the solid electrolyte layer 9 are closely attached to each other, making it difficult for air to penetrate. This suppresses deterioration of the conductive polymer contained in the solid electrolyte layer 9. There are no particular restrictions on the type of carbon material that makes up the particles as long as they are in a scaly form, but graphite, graphene, and the like tend to have a scaly form, and scaly particles are easily available.

[0032] The average aspect ratio of the carbon particles is, for example, 1.5 or more, preferably 2 or more. When the average aspect ratio of the carbon particles is in this range, many flat particles such as scaly particles are contained. This makes it easier to pack the carbon particles in a stacked state in the carbon layer 11. Therefore, a densely formed carbon layer can further enhance the air permeation suppression effect of the carbon layer 11.

[0033] The average aspect ratio of the carbon particles is determined from an electron microscope photograph of the cross section of the carbon layer 11 as follows: First, a number of (e.g., 10) carbon particles are selected, and the maximum diameter D1 and the maximum diameter D2 in the direction perpendicular to the maximum diameter D1 are measured for each carbon particle. Then, the aspect ratio of each particle is determined by dividing D1 by D2, and these are then averaged to calculate the average aspect ratio.

[0034] The average particle size of the carbon particles is, for example, 0.05 μm or more, preferably 0.1 μm or more. When the average particle size is in this range, the carbon particles can be easily packed densely in the carbon layer 11, making it easy to ensure high conductivity. The average particle size of the carbon particles is preferably 10 μm or less, more preferably 5 μm or less. In this case, the gaps between the carbon particles can be easily filled with silver, further enhancing the effect of suppressing air permeation in the carbon layer 11.

[0035] The average particle size of the carbon particles can be determined by selecting any number of carbon particles (for example, 10 particles) in an electron microscope photograph of the cross section of the carbon layer 11, measuring the particle size of each carbon particle, and averaging the measured values. The particle size of the carbon particles is defined as the diameter of a circle having the same area as the cross section of the carbon particles observed in the electron microscope photograph.

[0036] The carbon layer 11 contains a first polymer having an acid group in addition to a carbon material. The conductive polymer contained in the solid electrolyte layer 9 is easily positively charged by hole doping. Specifically, for example, the -NH- group or -N= group contained in polypyrrole or polyaniline, or the -S- group contained in polythiophene, are respectively -NH2 + -group, -NH + = group or -S += group and easily exists. The acid groups of the first polymer bond with these positively charged functional groups, which allows the first polymer to adhere to the conductive polymer. Meanwhile, the polymer chains of the first polymer attach to the surface of the carbon particles in an entangled manner, which allows the first polymer to adhere to the carbon particles. As a result, the adhesion between the carbon particles and the conductive polymer is improved through the first polymer. This reduces the permeation of air from the carbon layer 11 to the solid electrolyte layer 9, and suppresses the increase in resistance due to deterioration of the conductive polymer (i.e., the increase in ESR of the electrolytic capacitor).

[0037] In the first polymer, the acid group may be a sulfonic acid group (-SO3H), a carboxyl group (-COOH), or a derivative thereof. Derivatives include anionic groups formed by dissociating a proton from the acid group, salts of anionic groups with cations, and esters formed by reacting an acid group with an alcohol. The acid group is introduced into a monomer corresponding to the repeating unit of the first polymer. The number of acid groups contained in the first polymer may be 50 or more, or 85 or more, per 100 monomers.

[0038] The content of the first polymer may be 1 part by mass or more, 2 parts by mass or more, 5 parts by mass or more, or 10 parts by mass or more per 100 parts by mass of the carbon material. When the first polymer is contained in an amount of 1 part by mass or more per 100 parts by mass of the carbon material, the adhesion between the cathode extraction layer (carbon layer) and the solid electrolyte layer is improved, and an increase in the ESR of the electrolytic capacitor can be suppressed. On the other hand, if the content of the first polymer is too large, the viscosity of the carbon paste used to form the carbon layer increases. Furthermore, the resistance of the carbon layer increases, which may cancel out the effect of suppressing the increase in ESR. Therefore, the workability of applying the carbon paste is impaired. This offsets the effect of suppressing the increase in ESR. To avoid this, the content of the first polymer is preferably 5000 parts by mass or less relative to 100 parts by mass of the carbon material. The content of the first polymer may be 1000 parts by mass or less, or may be 100 parts by mass or less relative to 100 parts by mass of the carbon material.

[0039] The content of the first polymer may be 1 to 5000 parts by mass, 2 to 1000 parts by mass, 5 to 100 parts by mass, or 10 to 100 parts by mass relative to 100 parts by mass of the carbon material.

[0040] The weight average molecular weight of the first polymer is, for example, within the range of 2,000 to 1,000,000. weight average By using a first polymer having a molecular weight within this range, the carbon layer 11 and the solid electrolyte layer 9 are closely attached to each other, the permeation of air from the carbon layer 11 to the solid electrolyte layer 9 is reduced, and an increase in ESR can be suppressed.

[0041] The first polymer may be a resin material.

[0042] As the first polymer, for example, examples having a sulfonic group include a polymer having an aromatic sulfonic acid in its monomer structure and a polymer having an aliphatic sulfonic acid in its monomer structure. Examples of polymers having an aromatic sulfonic acid in their monomer structure include polystyrene sulfonic acid and phenolsulfonic acid novolac resin. Examples of polymers having an aliphatic sulfonic acid in their monomer structure include polyvinyl sulfonic acid and polyallyl sulfonic acid. Examples of the first polymer having a carboxyl group (or a derivative thereof) include acrylic resins such as polyacrylic acid, polymethacrylic acid, polymethyl acrylate, and polymethyl methacrylate, as well as polyethylene terephthalate. Furthermore, the first polymer may be polyacrylethylsulfonic acid, polyacrylbutylsulfonic acid, polymethacryl sulfonic acid, poly-2-acrylamido-2-methylpropanesulfonic acid, or the like.

[0043] In addition to the first polymer, a second polymer may be included in the carbon layer. The second polymer may be water-soluble. A water-soluble second polymer is likely to bond with another second polymer or the first polymer through hydrogen bonding, and the hydrogen bonding within the molecular chain tends to form a dense structure. This leaves little space for gases such as oxygen to diffuse within the polymer, making it difficult for gases to permeate through the polymer. Therefore, the second polymer can improve oxygen barrier properties. This suppresses oxidative degradation of the conductive polymer, further suppressing an increase in the ESR of the electrolytic capacitor.

[0044] Examples of the second polymer having excellent oxygen barrier properties include a cellulose-based polymer and / or polyvinyl alcohol. The cellulose-based polymer derivatives include those with a higher structure, particularly a fibril structure. The use of fibrillated cellulose is preferred because it not only enhances the oxygen barrier property but also imparts thixotropy and stabilizes the carbon paste when it forms a carbon layer after application.

[0045] The weight-average molecular weight of the second polymer is, for example, in the range of 2,000 to 1,000,000. The content of the second polymer is not limited, but may be, for example, 10 parts by mass or less per 100 parts by mass of the carbon material in consideration of workability. Like the first polymer, the second polymer may have an acid group. The content of the second polymer may be 5 to 50 parts by mass, 5 to 35 parts by mass, 8 to 35 parts by mass, or 8 to 32 parts by mass per 100 parts by mass of the first polymer.

[0046] Known components used in carbon layers of electrolytic capacitors can be used without any particular limitation as the binder and additive contained in the carbon layer 11. The carbon layer 11 may also contain a metal element such as silver.

[0047] The average thickness of the carbon layer 11 is, for example, 0.01 μm or more and 50 μm or less. The average thickness can be determined, for example, by measuring the thickness of the carbon layer 11 at multiple points (for example, 10 points) in an electron microscope photograph of the cross section of the carbon layer 11 and averaging the measured values.

[0048] (Silver paste layer 12) The silver paste layer 12 (second conductive layer) contains, for example, silver particles and a binder. The silver paste layer 12 may contain additives, etc., as necessary. Examples of additives include known additives used in silver paste layers.

[0049] The silver particles may contain other metal elements, and the content of other metal elements in the silver particles is preferably 0.1 mass % or less.

[0050] The silver content in the silver paste layer 12 is, for example, more than 50 mass % and preferably 70 mass % or more. When the silver content is in this range, high conductivity of the silver paste layer 12 is ensured, thereby improving the current collection from the capacitor element 2.

[0051] The silver paste layer 12 may contain the above-mentioned first polymer and / or second polymer.

[0052] Although there are no particular limitations on the binder contained in the silver paste layer 12, a cured product of a curable resin is preferred. Examples of the curable resin include thermosetting resins such as epoxy resins.

[0053] (Exterior body 3) The exterior housing 3 covers the capacitor element 2. Typically, the lead terminals 4 and 5 are also partially covered by the exterior housing 3. The exterior housing 3 is formed by sealing the capacitor element 2 and portions of the lead terminals 4 and 5 with a resin material.

[0054] The exterior body 3 preferably contains a cured product of a curable resin composition, and may contain a thermoplastic resin or a composition containing the same. As the curable resin composition or thermoplastic resin (composition), those exemplified below can be used.

[0055] In an exterior body 3 made of a resin material, the resin material is prone to deterioration and damage due to mechanical impact, and external air is prone to permeate the exterior body 3 and enter the interior. According to the present embodiment, the inclusion of the first polymer improves the adhesion of the cathode extraction layer (carbon layer), thereby improving the gas barrier properties of the cathode extraction layer. Therefore, even when an exterior body 3 made of a resin material is used, contact of the solid electrolyte layer 9 with air can be suppressed (or reduced).

[0056] (Lead terminals 4 and 5) One end of each of the lead terminals 4 and 5 is electrically connected to the capacitor element 2, and the other end is extended to the outside of the exterior housing 3. In the electrolytic capacitor 1, one end of each of the lead terminals 4 and 5 is covered by the exterior housing 3 together with the capacitor element 2. As the lead terminals 4 and 5, any lead terminal used in electrolytic capacitors can be used without any particular limitation, and for example, what is called a lead frame may be used. Examples of materials for the lead terminals 4 and 5 include metals such as copper or alloys thereof.

[0057] [Manufacturing method of electrolytic capacitors] The electrolytic capacitor is manufactured by a manufacturing method including the steps of forming a dielectric layer to cover at least a portion of the anode body, forming a solid electrolyte layer to cover at least a portion of the dielectric layer, and forming a cathode extraction layer on at least a portion of the solid electrolyte layer. The step of forming the cathode extraction layer may include, for example, the steps of forming a carbon layer and forming a silver paste layer on at least a portion of the carbon layer. The manufacturing method of the electrolytic capacitor may further include the step of preparing the anode body prior to the step of forming the dielectric layer. The manufacturing method of the electrolytic capacitor may also further include the steps of electrically connecting lead terminals to the capacitor element and covering the capacitor element and portions of the lead terminals with an exterior body (sealing step). Each step will be described in more detail below.

[0058] (Step of Preparing Anode Body 6) In this step, the anode body 6 that constitutes the anode part is formed by a known method depending on the type of the anode body 6. Anode body 6 can be prepared, for example, by roughening the surface of a foil- or plate-shaped substrate containing a valve metal. The roughening may be performed by etching (e.g., electrolytic etching) the substrate surface as long as it can form irregularities on the substrate surface. Alternatively, the valve metal powder may be molded into a desired shape (for example, a block) to obtain a compact, which may then be sintered to form anode body 6 having a porous structure.

[0059] (Step of forming dielectric layer 7) In this step, a dielectric layer 7 is formed on the anode body 6. The dielectric layer 7 is formed by anodizing the anode body 6. The anodization can be performed by a known method, such as chemical conversion treatment. The chemical conversion treatment can be performed, for example, by immersing the anode body 6 in a chemical conversion solution to impregnate the surface of the anode body 6 with the chemical conversion solution, and applying a voltage between the anode body 6 as an anode and a cathode immersed in the chemical conversion solution. As the chemical conversion solution, for example, an aqueous solution of phosphoric acid or the like is preferably used.

[0060] (Step of forming solid electrolyte layer 9) In this step, a solid electrolyte layer 9 is formed on the dielectric layer 7. For example, a treatment liquid containing a conductive polymer is applied to the anode body 6 on which the dielectric layer 7 has been formed, and then dried to form the solid electrolyte layer 9. The treatment liquid may further contain other components such as a dopant. For example, poly(3,4-ethylenedioxythiophene) (PEDOT) is used as the conductive polymer. For example, polystyrene sulfonic acid (PSS) is used as the dopant. The treatment liquid is, for example, a dispersion or solution of the conductive polymer. Examples of the dispersion medium (solvent) include water, an organic solvent, or a mixture thereof. The solid electrolyte layer 9 may be formed by chemically polymerizing and / or electrolytically polymerizing raw material monomers of the conductive polymer on the dielectric layer 7.

[0061] (Step of forming cathode extraction layer 10) In this step, cathode extraction layer 10 is formed by sequentially laminating carbon layer 11 and silver paste layer 12 on solid electrolyte layer 9.

[0062] (Formation process of carbon layer 11) In this step, carbon paste is applied to at least a portion of the solid electrolyte layer 9 to form the carbon layer 11. The carbon paste coating formed on at least a portion of the solid electrolyte layer 9 may be further heated to form the carbon layer 11.

[0063] The carbon paste contains a carbon material, a first polymer, and a dispersion medium. The dispersion medium may be water, an organic medium, or a mixture thereof. The carbon paste may contain a binder and / or an additive, as needed. The carbon paste may further contain a second polymer.

[0064] Examples of the carbon material contained in the carbon paste include those described for the carbon layer 11. The carbon material preferably contains scaly carbon particles. The average aspect ratio and average particle size of the carbon particles can be selected from the ranges described for the carbon layer 11. Similarly, examples of the first and second polymers include those described for the carbon layer 11.

[0065] The average aspect ratio and average particle size of the carbon particles are measured for the carbon particles used in the carbon paste. The average aspect ratio of the carbon particles can be calculated in the same manner as the average aspect ratio of the carbon particles contained in the carbon layer 11, except that it is determined from an electron microscope photograph of the carbon particles. The average particle size of the carbon particles is the 50% particle size D50 (i.e., median size) in the volume-based particle size distribution determined using a laser diffraction / scattering particle size distribution analyzer.

[0066] The binder contained in the carbon paste is not particularly limited, and may be any known binder used in producing a carbon layer. Preferred binders include polymer binders such as thermoplastic resins (such as polyester resins) and thermosetting resins (such as polyimide resins and epoxy resins).

[0067] The additives are not particularly limited and may include known additives used in producing carbon layers, such as dispersants, surfactants, antioxidants, preservatives, bases, and / or acids.

[0068] The carbon layer 11 may be formed by applying a carbon paste to at least a part of the solid electrolyte layer 9 to form a coating film, and then drying the coating film. After the coating film is formed, the coating film may be further heated.

[0069] The carbon paste may be brought into contact with the solid electrolyte layer 9. For example, the anode body 6 including the solid electrolyte layer 9 may be immersed in the carbon paste, or the carbon paste may be applied to the surface of the solid electrolyte layer 9 using a known coater or the like.

[0070] The temperature at which the carbon paste coating is heated is, for example, 150°C or higher and 300°C or lower.

[0071] (Step of forming silver paste layer 12) In this step, a silver paste layer 12 is formed on at least a portion of the carbon layer 11. The silver paste layer 12 can be formed by applying silver paste to at least a portion of the carbon layer 11. The silver paste can contain silver particles, a binder, a dispersion medium, and, if necessary, additives. For the silver particles, binder, and additives, see the description of the silver paste layer 12. The silver paste may contain a first polymer and / or a second polymer. Examples of dispersion mediums include water, an organic medium, and mixtures thereof.

[0072] The silver paste layer 12 can be formed by drying and / or heating a coating of silver paste formed on at least a part of the carbon layer 11. For example, when a thermosetting resin is used as the binder, the silver paste layer 12 is formed by heating the coating of silver paste to harden the binder.

[0073] (Lead terminal connection process) In this step, the anode lead terminal 4 and the cathode lead terminal 5 are electrically connected to the capacitor element 2. The connection of each lead terminal may be performed after the capacitor element 2 is fabricated. The cathode lead terminal 5 is connected to the capacitor element 2 after the capacitor element 2 is fabricated, but the anode lead terminal 4 may be connected to the anode body 6 at an appropriate stage in the process of fabricating the capacitor element 2. For example, when forming a porous anode body by sintering, a compact formed into the desired shape is obtained with one end of a rod-shaped anode lead terminal embedded in valve metal powder. Then, this compact may be sintered to form a porous anode body in which one end of the anode lead terminal is embedded.

[0074] When a laminate of multiple capacitor elements is used, the anode lead terminal 4 can be connected to the anode body 6 in the same manner as above. The cathode lead terminal 5 may be connected to a capacitor element in the same manner as above, or one end of the cathode lead terminal 5 may be connected to a laminate of multiple capacitor elements in which the cathode portions 8 are electrically connected to each other.

[0075] (Sealing process) In this step, the capacitor element 2 and portions of the lead terminals 4 and 5 are covered with the exterior housing 3, thereby sealing the capacitor element 2 with the exterior housing 3. More specifically, after the capacitor element 2 and the lead terminals 4 and 5 are electrically connected, the capacitor element 2 and portions of the lead terminals 4 and 5 can be sealed by covering them with the resin that constitutes the resin exterior housing.

[0076] The exterior housing 3 can be formed using molding techniques such as injection molding, insert molding, and compression molding. The exterior housing 3 can be formed, for example, by using a predetermined mold to fill predetermined locations with a curable resin composition or a thermoplastic resin (composition) so as to cover the capacitor element 2 and one end of the lead terminals 4 and 5. When a laminate of multiple capacitor elements is used, the resin exterior housing can be formed so as to cover the laminate and part of the lead terminals.

[0077] The curable resin composition may contain, in addition to the curable resin, a filler, a curing agent, a polymerization initiator, and / or a catalyst. Examples of the curable resin include epoxy resin, phenolic resin, urea resin, polyimide, polyamideimide, polyurethane, diallyl phthalate, and unsaturated polyester. The curable resin composition may contain multiple curable resins.

[0078] The filler is preferably, for example, insulating particles (inorganic or organic) and / or fibers. Examples of insulating materials constituting the filler include insulating compounds (oxides, etc.) such as silica and alumina, glass, and mineral materials (talc, mica, clay, etc.). The resin outer packaging may contain one type of these fillers or a combination of two or more types. The filler content in the resin outer packaging is, for example, 10 to 90% by mass.

[0079] Examples of the thermoplastic resin that can be used include polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), etc. The composition containing the thermoplastic resin may contain the above-mentioned filler in addition to the thermoplastic resin.

[0080] [Example] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0081] Examples 1 to 12 An electrolytic capacitor 1 shown in FIG. 1 was fabricated in the following manner, and its characteristics were evaluated. (1) Fabrication of capacitor elements An aluminum foil (thickness: 100 μm) was prepared as a substrate, and the surface of the aluminum foil was etched to obtain an anode body 6. The anode body 6 was immersed in a 0.3 mass % phosphoric acid solution (liquid temperature: 70°C) and a direct current voltage of 70 V was applied for 20 minutes to form a dielectric layer 7 containing aluminum oxide (Al2O3) on the surface of the anode body 6. Thereafter, an insulating resist tape (separation layer 13) was attached to a predetermined location on the anode body 6.

[0082] An aqueous solution containing pyrrole monomer and p-toluenesulfonic acid was prepared. The monomer concentration in this aqueous solution was 0.5 mol / L, and the p-toluenesulfonic acid concentration was 0.3 mol / L. The anode body 6 on which the dielectric layer 7 had been formed and the counter electrode were immersed in the resulting aqueous solution, and electrolytic polymerization was carried out at 25°C and a polymerization voltage of 3 V to form a solid electrolyte layer 9.

[0083] A dispersion (carbon paste) of flake natural graphite and a first polymer shown in Table 1 dispersed in water was applied to the solid electrolyte layer 9, and then heated at 200° C. to form a carbon layer 11 on the surface of the solid electrolyte layer. The proportion of graphite particles in the carbon paste was 5 mass %.

[0084] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of carbon layer 11, and then heated to harden the binder resin, thereby forming silver paste layer 12. In this way, cathode extraction layer 10 composed of carbon layer 11 and silver paste layer 12 was formed.

[0085] In this manner, a plurality of capacitor elements 2 having carbon layers with different compositions were obtained.

[0086] (2) Assembly of electrolytic capacitors An anode lead terminal 4, a cathode lead terminal 5, and an adhesive layer 14 were further arranged on the capacitor element 2, and an exterior body 3 was formed using a resin containing silica particles as a filler, thereby producing an electrolytic capacitor.

[0087] Examples 13 to 19 In preparing the carbon paste, in addition to the first polymer shown in Table 1, 6 parts by mass of the second polymer shown in Table 1 was added to 100 parts by mass of the carbon material to obtain a carbon paste. Except for this, electrolytic capacitors were produced in the same manner as in Examples 1 to 12.

[0088] Examples 20 to 22 In preparing the carbon paste, in addition to the first polymer shown in Table 1, the second polymer was added in an amount of parts by mass shown in Table 1 per 100 parts by mass of the carbon material to obtain a carbon paste. Except for this, an electrolytic capacitor was produced in the same manner as in Example 13.

[0089] Comparative Examples 1 and 2 In the preparation of the carbon paste, p-phenolsulfonic acid or p-toluenesulfonic acid was added as a low molecular weight additive instead of the first polymer, and the carbon paste was obtained. Except for this, an electrolytic capacitor was fabricated in the same manner as in Example 1.

[0090] Comparative Examples 3 and 4 In preparing the carbon paste, carboxymethyl cellulose (weight average molecular weight 100,000) was added in place of the first polymer in the proportion shown in Table 1. Except for this, electrolytic capacitors were produced in the same manner as in Examples 1 to 12.

[0091] Table 1 shows the content of additives (first and second polymers, or low-molecular-weight additives) in the carbon paste for each of the electrolytic capacitors of Examples 1 to 22 and Comparative Examples 1 and 2. Table 1 shows the content of the first and second polymers in parts by mass relative to 100 parts by mass of the carbon material. Table 1 also shows the molecular weights (weight-average molecular weights) of the first and second polymers, and the introduction amount of acid groups contained in the first and second polymers ( corresponding to the repeating units of the first and second polymers Monoma -1 The number of acid groups (carboxy groups per 100 monomers) is also shown. In Table 1, the electrolytic capacitors of Examples 1 to 22 are designated A1 to A22, respectively. The electrolytic capacitors of Comparative Examples 1 and 2 are designated B1 and B2, respectively. In Examples 13 to 18, 20 to 22 and Comparative Examples 3 and 4, an ammonium salt of carboxymethyl cellulose was used, and one having 30 acid groups (carboxy groups) per 100 monomers was used.

[0092] The electrolytic capacitors of the examples and comparative examples prepared above were evaluated as follows. [Evaluation] In an environment of 20°C, the ESR value (mΩ) of the electrolytic capacitor at a frequency of 100 kHz was measured using an LCR meter for four-terminal measurement, and the initial ESR value (X0) (mΩ) was taken as the ESR value.

[0093] Next, the electrolytic capacitor was placed in a 125°C environment for 1000 hours. After 1000 hours, the ESR value (X1) (mΩ) of the electrolytic capacitor was measured using the same method as above. The ESR change rate was calculated using the following formula. ESR change rate = X1 / X0

[0094] The evaluation results are shown in Table 2. In Table 2, the initial ESR is shown as a relative value, with the initial ESR of electrolytic capacitor B1 of Comparative Example 1 taken as 100.

[0095] [Table 1]

[0096] [Table 2] [Industrial Applicability]

[0097] The electrolytic capacitor of the present invention can suppress deterioration of the conductive polymer contained in the solid electrolyte layer and suppress an increase in ESR even when exposed to a high-temperature or high-humidity atmosphere, and therefore can be used in a variety of applications where a low ESR is required. [Explanation of symbols]

[0098] 1: electrolytic capacitor, 2: capacitor element, 3: exterior body, 4: anode lead terminal, 5: cathode lead terminal, 6: anode body, 7: dielectric layer, 8: cathode part, 9: solid electrolyte layer, 10: cathode lead layer, 11: carbon layer, 12: silver paste layer, 13: separation layer, 14: adhesive layer

Claims

1. a capacitor element including an anode body, a dielectric layer covering at least a portion of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode extraction layer covering at least a portion of the solid electrolyte layer, the cathode extraction layer includes a carbon material and a first polymer having an acid group, the acid group includes at least one selected from the group consisting of a sulfone group and a derivative thereof; a portion of the capacitor element is covered with an exterior body; the outer casing includes a curable resin and a filler, The content of the filler in the outer casing is 10 to 90 mass %, the weight average molecular weight of the first polymer is 30,000 or more and 1,000,000 or less; the cathode extraction layer further includes a second polymer different from the first polymer and having a weight-average molecular weight of 100,000 or more and 1,000,000 or less, The content of the second polymer is 10 parts by mass or less per 100 parts by mass of the carbon material, and 5 to 50 parts by mass per 100 parts by mass of the first polymer.

2. 2. The electrolytic capacitor according to claim 1, wherein the first polymer includes a polymer having an aromatic sulfonic acid in its monomer structure.

3. the acid group is introduced into a monomer corresponding to a repeating unit of the first polymer; 3. The electrolytic capacitor according to claim 1, wherein the number of the acid groups is 50 or more per 100 of the monomers.

4. 4. The electrolytic capacitor according to claim 1, wherein the content of the first polymer is 1 part by mass or more and 5000 parts by mass or less with respect to 100 parts by mass of the carbon material.

5. 5. The electrolytic capacitor according to claim 1, wherein the second polymer is water-soluble.

6. The electrolytic capacitor of claim 5 , wherein the second polymer comprises a cellulosic polymer.

7. The electrolytic capacitor of claim 5 , wherein the second polymer comprises polyvinyl alcohol.

8. the cathode extraction layer includes a first conductive layer covering at least a portion of the solid electrolyte layer and a second conductive layer covering at least a portion of the first conductive layer, The electrolytic capacitor according to any one of claims 1 to 7, wherein the first conductive layer comprises the first polymer.

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