Electrolytic capacitor and method for manufacturing the same

Abstract

The disclosed electrolytic capacitor (100) includes a capacitor element (10). The capacitor element (10) includes: an anode body having a dielectric layer formed on the surface, and an electrolyte layer arranged adjacent to the dielectric layer. The electrolyte layer includes: a conductive polymer doped with a dopant, conductive particles, and a non-aqueous solvent.

Description

Technical Field

[0001] The present invention relates to electrolytic capacitors and methods for manufacturing the same. Background Art

[0002] Capacitors used in electronic devices are required to have large capacity and low equivalent series resistance (ESR) values ​​in high-frequency regions. As large-capacity and low-ESR capacitors, electrolytic capacitors using conductive polymers such as polypyrrole, polythiophene, polyfuran, and polyaniline are promising. Patent document 1 (International Publication No. 2012 / 117994) discloses "a conductive polymer solution containing: a conductive polymer, a polysulfonic acid or its salt that functions as a dopant for the conductive polymer, a mixture of a polyacid and a carbon material, and a solvent" (claim 1 of patent document 1) as a conductive polymer solution for forming a solid electrolyte layer. In addition, patent document 1 discloses a solid electrolytic capacitor manufactured using the conductive polymer solution.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2012 / 117994 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] Currently, an electrolytic capacitor having a low rate of increase in ESR over a long period of time is required. Under such circumstances, one of the objects of the present application is to provide an electrolytic capacitor having a low rate of increase in ESR over a long period of time.

[0008] Solutions for solving problems

[0009] One aspect of the present application relates to an electrolytic capacitor including a capacitor element including an anode body having a dielectric layer formed on a surface thereof and an electrolyte layer disposed adjacent to the dielectric layer, the electrolyte layer including a conductive polymer doped with a dopant, conductive particles, and a non-aqueous solvent.

[0010] Another aspect of the present application relates to a method for manufacturing an electrolytic capacitor. The method comprises: step (i) of preparing a capacitor element precursor, the capacitor element precursor comprising an anode body having a dielectric layer formed on the surface; step (ii) of forming a polymer layer adjacent to the dielectric layer by an impregnation treatment, the polymer layer comprising a conductive polymer doped with a dopant and conductive particles; and step (iii) of impregnating the polymer layer with a non-aqueous solvent.

[0011] Effects of the Invention

[0012] According to the present application, an electrolytic capacitor having a low rate of increase in ESR over a long period of time can be obtained.

[0013] The novel features of the present invention are described in the appended claims, but the present invention, both as to the structure and content, together with other objects and features of the present invention, can be better understood through the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a cross-sectional view schematically showing an example of the electrolytic capacitor of the present application.

[0015] Figure 2 To schematically illustrate Figure 1 A diagram of a portion of an electrolytic capacitor is shown. DETAILED DESCRIPTION

[0016] Hereinafter, the embodiments of the present application will be described by way of example, but the present application is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes illustrated, but other numerical values ​​and materials may also be applied as long as the effects of the present application can be obtained.

[0017] (Electrolytic Capacitors)

[0018] The electrolytic capacitor of the present application includes a capacitor element. The capacitor element includes: an anode body having a dielectric layer formed on the surface, and an electrolyte layer disposed adjacent to the dielectric layer. The electrolyte layer includes: a conductive polymer doped with a dopant, conductive particles, and a non-aqueous solvent.

[0019] The capacitor element may include: a foil-shaped anode body having a dielectric layer formed on the surface, a foil-shaped cathode body, a separator arranged between the anode body and the cathode body, and an electrolyte layer arranged between the anode body and the cathode body. Hereinafter, such a capacitor element is sometimes referred to as a "first capacitor element". The first capacitor element may be a winding type or a stacked type. In one example of a winding type capacitor element, a foil-shaped anode body, a foil-shaped cathode body and a separator are wound in a manner that a separator is arranged between the anode body and the cathode body. In one example of a stacked type capacitor element, a foil-shaped anode body, a foil-shaped cathode body and a separator are folded into a zigzag shape in a manner that a separator is arranged between the anode body and the cathode body.

[0020] Alternatively, the capacitor element may include: a porous anode body having a dielectric layer formed on the surface, a cathode layer, and an electrolyte layer disposed between the anode body and the cathode layer. Hereinafter, such a capacitor element is sometimes referred to as a "second capacitor element". In the first and second capacitor elements, the electrolyte layer is adjacent to the dielectric layer formed on the surface of the anode body.

[0021] (Conductive polymer)

[0022] The conductive polymer contained in the electrolyte layer is described below.

[0023] Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and their derivatives. The derivatives include polymers with polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene as basic skeletons. For example, derivatives of polythiophene include poly(3,4-ethylenedioxythiophene) and the like. These conductive polymers can be used alone or in combination. In addition, the conductive polymer can be a copolymer of two or more monomers. The weight average molecular weight of the conductive polymer is not particularly limited, for example, it can be in the range of 1000 to 100000. A preferred example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0024] A dopant is doped in the conductive polymer. From the viewpoint of suppressing dedoping from the conductive polymer, a polymer dopant is preferably used as the dopant. Examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic acid sulfonic acid, polymethacrylic acid sulfonic acid, poly (2-acrylamide-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, etc. They can be used alone or in combination of two or more. A part of them can be included in the electrolyte layer in the form of a salt. A preferred example of a dopant is polystyrene sulfonic acid (PSS).

[0025] The weight average molecular weight of the dopant is not particularly limited, but can be in the range of 1,000 to 100,000 from the viewpoint of easily forming a homogeneous electrolyte layer.

[0026] In the electrolytic capacitor of the present application, the dopant may be polystyrene sulfonic acid, and the conductive polymer may be poly(3,4-ethylenedioxythiophene). That is, the electrolyte layer may include poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0027] (Liquid ingredients)

[0028] The electrolyte layer of the electrolytic capacitor of the present application contains a non-aqueous solvent. The electrolyte layer may contain an electrolyte (non-aqueous electrolyte), and the electrolyte (non-aqueous electrolyte) contains a non-aqueous solvent and an alkaline component dissolved in the non-aqueous solvent. That is, the electrolyte layer of the electrolytic capacitor of the present application may contain a liquid component. Hereinafter, the liquid component (non-aqueous solvent or electrolyte) contained in the electrolyte layer is sometimes referred to as "liquid component (L)". It should be noted that in this specification, the liquid component (L) may be a component that is liquid at room temperature (25°C) or a component that is liquid at the temperature when the electrolytic capacitor is in use. An electrolytic capacitor having an electrolyte layer containing a liquid component (L) is sometimes referred to as a hybrid capacitor.

[0029] The non-aqueous solvent contained in the electrolyte layer may be an organic solvent or an ionic liquid. Examples of the non-aqueous solvent include polyols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (γBL), amides such as N-methylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, formaldehyde, etc.

[0030] In addition, as a non-aqueous solvent, a polymer solvent can be used. Examples of polymer solvents include compounds in which at least one hydroxyl group in polyalkylene glycol, a derivative of polyalkylene glycol, or a polyol is substituted with polyalkylene glycol (including derivatives), etc. Specifically, examples of polymer solvents include polyethylene glycol (PEG), polyethylene glycol glycerol ether, polyethylene glycol diglycerol ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glycerol ether, polypropylene glycol diglycerol ether, polypropylene glycol sorbitol ether, polybutylene glycol, etc. Examples of polymer solvents also include copolymers of ethylene glycol-propylene glycol, copolymers of ethylene glycol-butylene glycol, copolymers of propylene glycol-butylene glycol, etc. A non-aqueous solvent can be used alone or in combination of two or more.

[0031] As described above, the electrolyte layer may contain a nonaqueous solvent and an alkali component (base) dissolved in the nonaqueous solvent. Alternatively, the electrolyte layer may contain a nonaqueous solvent and an alkali component and / or an acid component (acid) dissolved in the nonaqueous solvent.

[0032] As the acid component, polycarboxylic acids and monocarboxylic acids can be used. Examples of the polycarboxylic acids include aliphatic polycarboxylic acids ([saturated polycarboxylic acids, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid]; [unsaturated polycarboxylic acids, such as maleic acid, fumaric acid, itaconic acid]), aromatic polycarboxylic acids (such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid), and alicyclic polycarboxylic acids (such as cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, etc.).

[0033] Examples of the monocarboxylic acids include aliphatic monocarboxylic acids (having 1 to 30 carbon atoms) ([saturated monocarboxylic acids, such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid, lauric acid, myristic acid, stearic acid, behenic acid]; [unsaturated monocarboxylic acids, such as acrylic acid, methacrylic acid, oleic acid]), aromatic monocarboxylic acids (such as benzoic acid, cinnamic acid, naphthoic acid), and hydroxycarboxylic acids (such as salicylic acid, mandelic acid, and dihydroxybenzoic acid).

[0034] Among these, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and dihydroxybenzoic acid are thermally stable and can be preferably used.

[0035] As the acid component, an inorganic acid can be used. Representative examples of inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl phosphates, boric acid, fluoroboric acid, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, naphthalenesulfonic acid, etc. In addition, as the acid component, a composite compound of an organic acid and an inorganic acid can be used. Examples of such composite compounds include boron diglycolic acid, boron dioxalic acid, boron disalicylic acid, etc.

[0036] The base component may be a compound having an alkyl-substituted amidine group, for example, an imidazole compound, a benzimidazole compound, an alicyclic amidine compound (pyrimidine compound, imidazoline compound), etc. Specifically, 1,8-diazabicyclo[5,4,0]undecene-7, 1,5-diazabicyclo[4,3,0]nonene-5, 1,2-dimethylimidazolinium, 1,2,4-trimethylimidazoline, 1-methyl-2-ethyl-imidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptylimidazoline, 1-methyl-2-(3'heptyl)imidazoline, 1-methyl-2-dodecylimidazoline, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1-methylimidazole, 1-methylbenzimidazole are preferred. By using these, a capacitor having excellent impedance performance can be obtained.

[0037] As the base component, a quaternary salt of a compound having an alkyl-substituted amidine group can be used. Examples of such a base component include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) quaternized with an alkyl group having 1 to 11 carbon atoms or an arylalkyl group. Specifically, 1-methyl-1,8-diazabicyclo[5,4,0]undecene-7, 1-methyl-1,5-diazabicyclo[4,3,0]nonene-5, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium, 1,2-dimethyl-3-ethylimidazolinium, 1,3,4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2-heptylimidazolinium, 1,3-dimethyl-2-(3'heptyl)imidazolinium, 1,3-dimethyl-2-dodecylimidazolinium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidinium, 1,3-dimethylimidazolium, 1-methyl-3-ethylimidazolium, and 1,3-dimethylbenzimidazolium are preferred. By using these, a capacitor having excellent impedance performance can be obtained.

[0038] In addition, as the base component, a tertiary amine can be used. Examples of tertiary amines include trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyln-propylamine, dimethylisopropylamine, methylethyln-propylamine, methylethylisopropylamine, diethyln-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, etc.), and phenyl-containing amines (dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.). Among them, from the perspective of high conductivity of the electrolyte layer, trialkylamines are preferred, and more preferably at least one selected from trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine is included. In addition, as the base component, secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia can be used.

[0039] The liquid component (L) may contain a salt of an acid component and an alkali component. The salt may be an inorganic salt and / or an organic salt. An organic salt is a salt in which at least one of an anion and a cation contains an organic substance. As an organic salt, for example, trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, 1,2,3,4-tetramethylimidazolinium phthalate, 1,3-dimethyl-2-ethylimidazolinium phthalate, etc. may be used. In the case where the liquid component (L) contains a salt of an acid component and an alkali component, dedoping may also occur easily due to the alkali component contained in the salt, so the composition of the present application is particularly effective.

[0040] In order to suppress dedoping of the dopant, the pH of the liquid component (L) may be set to less than 7, or may be set to 5 or less (for example, in the range of 2 to 4.5).

[0041] For electrolytic capacitors, it is important that the ESR is low. By using an electrolyte layer comprising a conductive polymer doped with a dopant, a low ESR can be achieved. However, the inventors of the present application have found that when using an electrolyte layer comprising a conductive polymer doped with a dopant and a liquid component (L), although the initial ESR is low, the deterioration phenomenon of the ESR increasing over time is large. The cause was studied, and it was found that in the electrolyte layer comprising a liquid component (L), there is a situation where the dopant is easily dedoped. It is believed that due to this dedoping, the ESR increases over time. Therefore, compared with a solid electrolytic capacitor comprising a solid electrolyte without a liquid component (L), it is important for an electrolytic capacitor comprising a liquid component (L) to suppress the increase of the ESR over time.

[0042] The conductivity of the conductive polymer is high, so it is effective for reducing ESR. However, the conductivity of the conductive polymer decreases due to time degradation, so the ESR increases. In particular, when the electrolyte layer contains a liquid component (L), the increase in ESR becomes larger. On the other hand, it is believed that the conductivity of the conductive particles will hardly deteriorate over time. Therefore, by adding conductive particles, the increase in ESR over time can be suppressed.

[0043] In the electrolytic capacitor of the present application, the dopant may be a dopant containing an acidic group or a polymer dopant containing an acidic group. Through research, the inventors of the present application have newly discovered that when a dopant containing an acidic group is used, dedoping may occur significantly as the pH rises. Therefore, when a dopant containing an acidic group is used, it is particularly important to suppress the increase in ESR over time.

[0044] In the electrolytic capacitor of the present application, the dopant may be a polymer dopant containing an acidic group, and the electrolyte layer may include an electrolyte containing a non-aqueous solvent and an alkaline component dissolved in the non-aqueous solvent. In this case, dedoping is easily caused by the alkaline component, so it is particularly important to suppress the increase of ESR over time. As described above, the electrolytic capacitor of the present application includes conductive particles, so it is possible to suppress the increase of ESR over time.

[0045] Examples of the acidic group include a sulfonic acid group, a carboxyl group, etc. The polymer dopant containing an acidic group is a polymer (polymer) in which at least a part of the structural units contains an acidic group. Examples of such a polymer dopant include the above-mentioned polymer dopant.

[0046] In the electrolytic capacitor of the present application, the content of the alkali component in the electrolyte can be 0.1% by mass or more and 20% by mass or less. When the amount of the alkali component is 0.1% by mass or more, it is particularly important to use conductive particles. In addition, by setting the amount of the alkali component to 20% by mass or less, it is easy to dissolve the alkali component in the electrolyte. It should be noted that in the case where the electrolyte contains a salt of an acid component and an alkali component (for example, the electrolyte contains the salt as a solute), the content of the alkali component in the electrolyte is calculated based on the mass of the electrolyte and the mass of the alkali component in the salt.

[0047] The content of the liquid component (L) in the electrolyte layer may be in the range of 50 to 99.5% by mass. The total content of the conductive polymer and the dopant in the electrolyte layer may be in the range of 0.5 to 10% by mass. The content of the conductive particles in the electrolyte layer may be in the range of 0.025 to 5% by mass. The total mass Wm (g) of the conductive polymer and the dopant contained in the electrolyte layer and the mass Wp (g) of the conductive particles contained in the electrolyte layer may satisfy 1 < Wm / Wp, for example, 2 ≤ Wm / Wp ≤ 20. Alternatively, the ratio Wp / Wm may be greater than 0.05, greater than 0.15, greater than 0.35, greater than 0.50, or greater than 1.0. The ratio Wp / Wm may be less than 10, less than 5.0, or less than 2.0. These lower limits and upper limits may be combined arbitrarily. For example, the ratio Wp / Wm can be in the range of 0.05 to 10, the range of 0.15 to 10, the range of 0.35 to 10, the range of 0.50 to 10, or the range of 1.0 to 10. The upper limit of any of these ranges can be replaced by 5.0 or 2.0. By setting the ratio Wp / Wm to be greater than 0.05 (for example, greater than 0.15, greater than 0.35, or greater than 1.0), an electrolytic capacitor having a particularly low rate of increase in ESR can be obtained. By setting the ratio Wp / Wm to be less than 10 (for example, less than 5.0 or less than 2.0), in particular, the ESR can be reduced and the reduction in electrostatic capacitance can be suppressed. It should be noted that the ratio Wp / Wm is equal to (the content of conductive particles in the electrolyte layer) / (the total content of conductive polymers and dopants in the electrolyte layer).

[0048] (Conductive particles)

[0049] The conductive particles contained in the electrolyte layer are described below. The conductive particles are particles formed of a conductive material. It should be noted that the conductive particles are different from the conductive polymers described above. The conductive particles are typically formed of a material that is not a polymer.

[0050] The conductive particles contained in the electrolyte layer may be only one kind of conductive particles, or may contain multiple conductive particles. The conductive particles may be particles of conductive carbon materials, or may be particles containing materials other than conductive carbon materials. Examples of materials other than conductive carbon materials include conductive nickel-phosphorus (Ni-P) materials, conductive indium-tin (In-Sn) materials, conductive tin oxide, conductive tin-silver (Sn-Ag), etc. The conductive particles may be metal particles (e.g., particles of nickel or other metals).

[0051] In the electrolytic capacitor of the present application, the conductive particles may include at least one particle selected from particles of carbon black, particles of carbon nanotubes, particles of graphite, and particles of graphene. These particles are preferred in that the average particle size, the structure of the particles, and the surface properties can be variously controlled. The conductive particles may be composed of only one of these particles, or may be composed of a plurality of these particles.

[0052] In the electrolytic capacitor of the present application, the total mass of the conductive polymer and the dopant contained in the electrolyte layer can be greater than the mass of the conductive particles contained in the electrolyte layer. That is, the total content (mass %) of the conductive polymer and the dopant in the electrolyte layer can be greater than the content (mass %) of the conductive particles in the electrolyte layer. The above-mentioned conductive polymer is generally more conductive than the above-mentioned conductive particles. Therefore, increasing the content of the conductive polymer is effective for reducing the initial ESR.

[0053] The electrolytic capacitor of the present application can satisfy the following conditions (1) and (2).

[0054] (1) The anode body has a porous portion on its surface (the surface where the dielectric layer is formed), and the average particle size of the conductive particles is larger than the average pore size of the porous portion on the surface of the anode body.

[0055] (2) The conductive polymer is in the form of particles, and the average particle size of the conductive polymer is smaller than the average pore size of the porous portion of the surface of the anode body.

[0056] As described above, the above-mentioned conductive polymer is generally more conductive than the above-mentioned conductive particles. Therefore, by arranging the conductive polymer near the surface of the anode body, the initial ESR can be reduced. When the above-mentioned conditions (1) and (2) are met, it is easy to arrange the conductive polymer in the gaps (pores) of the porous part of the anode body. That is, the conductive polymer is easily arranged in the part of the dielectric layer close to the surface of the anode body. As a result, the initial ESR can be reduced.

[0057] In this specification, the average particle size of particles is the median particle size (D 50). The median particle size is determined, for example, using a laser diffraction / scattering particle size distribution measuring apparatus.

[0058] In this specification, the average pore size of the porous portion of the surface of the anode body is the median diameter (D) at which the cumulative volume is 50% in the volume-based pore distribution. 50 ). The median particle size can be determined, for example, by gas adsorption pore distribution measurement.

[0059] The electrolytic capacitor of the present application can satisfy the following condition (3).

[0060] (3) The electrolyte layer includes a polymer layer containing a conductive polymer (conductive polymer layer), the polymer layer including: a first polymer layer formed on the dielectric layer on the surface of the anode body, and a second polymer layer formed on the first polymer layer. That is, the first polymer layer is arranged between the dielectric layer on the surface of the anode body and the second polymer layer.

[0061] When the electrolyte layer includes the first polymer layer and the second polymer layer, the conductive polymer included in the first polymer layer and the conductive polymer included in the second polymer layer may be the same or different. The conductive particles may be included in both the first polymer layer and the second polymer layer, or only in one of them. When both the first polymer layer and the second polymer layer include conductive particles, the conductive particles included in the first polymer layer and the conductive particles included in the second polymer layer may be the same or different.

[0062] The electrolytic capacitor of the present application can satisfy the conditions of (3) above and (4) below.

[0063] (4) The content (mass %) of the conductive particles in the second polymer layer is greater than the content (mass %) of the conductive particles in the first polymer layer. The conductive particles may be contained in both the first polymer layer and the second polymer layer, or only in the second polymer layer.

[0064] The above condition (4) can be replaced by the following condition: (4') The content rate (mass %) of the conductive polymer in the first polymer layer is greater than the content rate (mass %) of the conductive polymer in the second polymer layer. By reducing the content rate of conductive particles in the first polymer layer and increasing the content rate of conductive polymer, the proportion of conductive polymer in the portion of the dielectric layer close to the surface of the anode body can be increased. As a result, the initial ESR can be reduced.

[0065] The electrolytic capacitor of the present application can satisfy the following conditions (A) and (B), and can further satisfy condition (C). By satisfying these conditions, an electrolytic capacitor with high characteristics and reliability can be obtained.

[0066] (A) The conductive polymer is poly(3,4-ethylenedioxythiophene) and the dopant is polystyrene sulfonic acid.

[0067] (B) The conductive particles are particles of a conductive carbon material, for example, at least one selected from particles of carbon black, particles of carbon nanotubes, particles of graphite, and particles of graphene. Alternatively, the conductive particles may be at least one selected from particles of metal particles and particles of a conductive carbon material.

[0068] (C) The total mass Wm (g) of the conductive polymer and the dopant contained in the electrolyte layer and the mass Wp (g) of the conductive particles contained in the electrolyte layer satisfy 1 < Wm / Wp, for example, 2 ≤ Wm / Wp ≤ 20. Alternatively, the ratio Wp / Wm may be within the above range.

[0069] The components of the capacitor element other than the electrolyte (anode body, cathode body, separator, etc.) are not particularly limited, and known components can be used. Examples of these components of the first capacitor element will be described below.

[0070] (Anode)

[0071] The anode body can use a metal foil having a dielectric layer formed on the surface. The type of metal constituting the metal foil is not particularly limited. From the aspect of easy formation of the dielectric layer, examples of metals constituting the metal foil include metals having valve functions such as aluminum, tantalum, niobium, titanium, and alloys of metals having valve functions. A preferred example is aluminum and aluminum alloys. Usually, the surface of the anode body is roughened (made porous). The dielectric layer of the anode body is formed in the porous portion (roughened surface). The electrolyte layer is in contact with the dielectric layer of the anode body.

[0072] (Cathode)

[0073] A metal foil can be used as the cathode body. The type of metal constituting the metal foil is not particularly limited. Examples of metals constituting the metal foil include valve metals such as aluminum, tantalum, niobium, titanium, and alloys of valve metals. A preferred example is aluminum and aluminum alloys. A chemical conversion coating may be provided on the surface of the cathode body, and a coating of a metal (dissimilar metal) or a non-metallic film different from the metal constituting the cathode body may also be provided. As dissimilar metals and non-metals, for example, metals such as titanium and non-metals such as carbon can be cited.

[0074] (Spacer)

[0075] The separator can be a sheet-like object that can be impregnated with an electrolyte, for example, a sheet-like object that has insulation and can be impregnated with an electrolyte can be used. The separator can be a woven fabric, a non-woven fabric, or a porous film. Examples of materials for the separator include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamide-imide, polyetherimide, rayon, and glass.

[0076] The components of the second capacitor element other than the electrolyte layer are described below by way of example. The second capacitor element includes a porous anode body having a dielectric layer formed on the surface, a cathode layer, and an electrolyte layer disposed between the anode body and the cathode layer.

[0077] The porous anode body may be, for example, a porous sintered body obtained by sintering material particles containing a valve metal. The anode body may be in the shape of a rectangular parallelepiped. Examples of valve metals include titanium (Ti), tantalum (Ta), niobium (Nb), and the like. The material particles may be formed of an alloy containing a valve metal. For example, an alloy containing a valve metal, and silicon, vanadium, boron, and the like may be used. The alloy of the valve metal contains the valve metal as a main component, for example, containing more than 50 atomic % of the valve metal. In addition, material particles formed of a compound containing a valve metal and a typical element such as nitrogen may be used. The material particles may be used alone or in combination of two or more.

[0078] The anode body of the second capacitor element is porous, and thus has a porous portion on the surface, and the dielectric layer is formed in the porous portion. The electrolyte layer is in contact with the dielectric layer of the anode body. The dielectric layer is formed, for example, by subjecting a sintered body serving as the anode body to a chemical conversion treatment and growing an oxide film on the surface of the sintered body.

[0079] The cathode layer has a current collecting function. The cathode layer is formed, for example, of a conductive material. The cathode layer may be a conductive layer formed in a manner covering the electrolyte layer. The cathode layer may include: a carbon layer formed in a manner covering the electrolyte layer, and a metal paste layer formed on the carbon layer. The carbon layer may include conductive carbon materials such as graphite and a resin. The metal paste layer may include metal particles (e.g., silver particles) and a resin. The cathode layer can be formed by applying the above-mentioned materials, etc.

[0080] (Method for manufacturing electrolytic capacitor)

[0081] The following describes the method of the present application for manufacturing an electrolytic capacitor. According to the manufacturing method, the electrolytic capacitor of the present application can be manufactured. It should be noted that the matters described in the electrolytic capacitor of the present application can be applied to the following manufacturing method, so repeated descriptions are sometimes omitted. For example, the constituent elements of the capacitor element are described above, so repeated descriptions are sometimes omitted. In addition, the matters described in the following manufacturing method can be applied to the above-mentioned electrolytic capacitor.

[0082] The production method according to the present application includes step (i), step (ii), and step (iii), which are described below.

[0083] (Process (i))

[0084] Step (i) is a step of preparing a capacitor element precursor including an anode body having a dielectric layer formed on the surface. Step (i) may be a step of forming the capacitor element precursor by a known method.

[0085] In the case of manufacturing an electrolytic capacitor including a first capacitor element, step (i) may be a step of forming a capacitor element precursor, wherein the capacitor element precursor includes: a foil-shaped anode body having a dielectric layer formed on the surface, a foil-shaped cathode body, and a separator disposed between the anode body and the cathode body. In this case, as described above, the capacitor element precursor may be a wound type or a stacked type. In the case of manufacturing an electrolytic capacitor including a second capacitor element, the capacitor element precursor may be composed of an anode body (porous anode body) having a dielectric layer formed on the surface, and an anode wire partially buried in the anode body.

[0086] (Step (ii))

[0087] Step (ii) is a step of forming a polymer layer including a conductive polymer doped with a dopant and conductive particles so as to be adjacent to the dielectric layer by an impregnation treatment.

[0088] The infiltration treatment of step (ii) can be an infiltration treatment (x) in which a dispersion is infiltrated into a capacitor element precursor, wherein the dispersion comprises a conductive polymer and conductive particles doped with a dopant. For example, the dispersion can be infiltrated by immersing the capacitor element precursor in the dispersion. By removing (drying) the dispersion medium of the dispersion infiltrated into the capacitor element precursor, a polymer layer comprising a conductive polymer and conductive particles doped with a dopant can be configured adjacent to the dielectric layer. It should be noted that the infiltration treatment (x) can be performed multiple times. In this case, a drying process for removing the dispersion medium of the infiltrated dispersion can be performed before performing the infiltration treatment (x) after the second time.

[0089] The dispersion medium of the dispersion liquid is not particularly limited, and a known dispersion medium can be used. For example, an aqueous liquid containing water can be used as the dispersion medium, or water can be used.

[0090] The content of the conductive polymer and conductive particles in the dispersion is not particularly limited as long as it is a content that can achieve the impregnation treatment. The content of the conductive polymer in the dispersion can be, for example, in the range of 0.1 mass % to 10 mass %. The content of the conductive particles in the dispersion can be adjusted according to the content of the conductive polymer.

[0091] By adjusting the mass (content) of the conductive polymer in the dispersion and the mass (content) of the conductive particles, the ratio of these in the formed electrolyte layer can be adjusted. For example, by making the mass (content) of the conductive polymer in the dispersion greater than the mass (content) of the conductive particles in the dispersion, the mass of the conductive polymer contained in the electrolyte layer can be greater than the mass of the conductive particles contained in the electrolyte layer.

[0092] The impregnation treatment of step (ii) may include an impregnation treatment (y) and an impregnation treatment (z). For the impregnation treatment (y) and the impregnation treatment (z), the impregnation treatment (y) may be performed first, the impregnation treatment (z) may be performed first, or both may be performed simultaneously. In a preferred example, the impregnation treatment (z) is performed after the impregnation treatment (y). It should be noted that the impregnation treatment (y) and the impregnation treatment (z) may be performed multiple times independently of each other. In addition, a drying process for removing the dispersion medium of the infiltrated dispersion may be performed after the impregnation treatment (y) and the impregnation treatment (z).

[0093] The impregnation treatment (y) is an impregnation treatment in which the first dispersion containing the conductive polymer doped with the dopant is impregnated into the capacitor element precursor. The impregnation treatment (z) is an impregnation treatment in which the second dispersion containing the conductive particles is impregnated into the capacitor element precursor. Regarding the dispersion medium of the first dispersion and the second dispersion, and the impregnation method, the dispersion medium and the impregnation method described in the impregnation treatment (x) can be applied.

[0094] In one example, the first dispersion does not contain conductive particles, and the second dispersion does not contain conductive polymer doped with a dopant. However, the first dispersion may contain conductive particles, and the second dispersion may contain conductive polymer doped with a dopant.

[0095] The case where both the first dispersion and the second dispersion contain a conductive polymer doped with a dopant is described. In this case, drying can be performed after performing any of the impregnation treatments (y) and (z), and then the other impregnation treatment can be performed. By operating in this way, a polymer layer including the first polymer layer and the second polymer layer can be formed. In addition, by adjusting the content of conductive particles in the first dispersion and the content of conductive particles in the second dispersion, the content of conductive particles in the first polymer layer and the content of conductive particles in the second polymer layer can be adjusted.

[0096] (Process (iii))

[0097] Step (iii) is a step of impregnating the polymer layer formed in step (ii) with a non-aqueous solvent. Thus, an electrolyte layer comprising a conductive polymer doped with a dopant, conductive particles and a non-aqueous solvent is formed. Step (iii) may be a step of impregnating the polymer layer formed in step (ii) with an electrolyte solution comprising a non-aqueous solvent. That is, step (iii) may be a step of impregnating the polymer layer formed in step (ii) with a liquid component (L).

[0098] The impregnation method in step (iii) is not particularly limited, and a known method can be used. For example, the capacitor element precursor after step (ii) can be immersed in a non-aqueous solvent (or electrolyte). The non-aqueous solvent (or electrolyte) used in step (iii) can be the substances described above.

[0099] In the production method of the present application, the dopant may be a polymer dopant containing an acidic group, and the step (iii) may be a step of impregnating the polymer layer with an electrolyte solution containing a non-aqueous solvent and an alkali component dissolved in the non-aqueous solvent.

[0100] Through step (iii), a first capacitor element can be obtained. Alternatively, through step (iii), an anode body and an electrolyte layer of a second capacitor element can be obtained. After step (iii), an electrolytic capacitor can be produced using the constituent elements obtained in step (iii). The steps are not particularly limited, and known methods can be used.

[0101] Hereinafter, examples of electrolytic capacitors involved in the present application will be described in detail with reference to the accompanying drawings, but the electrolytic capacitors of the present application are not limited to the following figures. The above-mentioned constituent elements can be applied to the constituent elements of an electrolytic capacitor of an example described below. In addition, the constituent elements of an electrolytic capacitor of an example described below can be changed based on the above description. In addition, the matters described below can be applied to the above-mentioned embodiments. It should be noted that sometimes the same symbols are marked on the same parts and repeated descriptions are omitted.

[0102] (Implementation Method 1)

[0103] In Embodiment 1, an example of an electrolytic capacitor according to the present application is described. This electrolytic capacitor is an electrolytic capacitor including a first capacitor element. Figure 1 A cross section of an example of electrolytic capacitor 100 according to Embodiment 1 is schematically shown. Figure 2 Show that Figure 1 FIG. 1 is a schematic diagram showing a portion of capacitor element 10 included in electrolytic capacitor 100 .

[0104] like Figure 1 As shown, the electrolytic capacitor 100 includes: a capacitor element 10, a bottomed case 11 for accommodating the capacitor element 10, a sealing member 12 for blocking the opening of the bottomed case 11, a seat plate 13 covering the sealing member 12, leads 14A and 14B extending from the sealing member 12 and penetrating the seat plate 13, and lead tabs 15A and 15B for connecting the leads 14A and 14B to electrodes of the capacitor element 10. The capacitor element 10 is accommodated in the bottomed case 11. The opening end of the bottomed case 11 is necked inwardly, and the opening end of the bottomed case 11 is crimped in such a way that the sealing member 12 is riveted.

[0105] Reference Figure 2 The capacitor element 10 includes: a foil-shaped anode body 21 with a dielectric layer formed on the surface, a foil-shaped cathode body 22, and a separator 23 and an electrolyte layer (not shown) arranged therebetween. The anode body 21 and the cathode body 22 are wound with the separator 23 arranged therebetween. The outermost periphery of the wound body is fixed by a stop tape 24. The lead connector 15A is connected to the anode body 21, and the lead connector 15B is connected to the cathode body 22. It should be noted that Figure 2 The partially unfolded state is shown before the outermost periphery of the wound body is fixed.

[0106] Example

[0107] Hereinafter, the embodiments of the present application will be described in more detail through examples.

[0108] (Example)

[0109] [Fabrication of capacitor A1]

[0110] Capacitor A1 is a winding type electrolytic capacitor having a rated voltage of 35 V and a rated electrostatic capacity of 270 μF. Capacitor A1 was manufactured in the following steps.

[0111] (Preparation of cathode and anode bodies)

[0112] The cathode body uses Al foil (aluminum foil) with a thickness of 70μm. An anode body with a dielectric layer formed on the surface is made according to the following steps. First, prepare an Al foil with a thickness of 120μm. The Al foil is subjected to a DC etching treatment to roughen the surface. Next, the Al foil is subjected to a chemical conversion treatment. Specifically, the Al foil is immersed in an aqueous solution of ammonium adipate, and a voltage of 50V is applied to the Al foil while a chemical conversion treatment is performed at 70°C for 30 minutes, thereby forming a dielectric layer (thickness: about 70nm) on the surface of the Al foil. In this way, an anode body with a dielectric layer formed on the surface is obtained. Thereafter, the anode body is cut into a specified size, thereby preparing the anode body of capacitor A1.

[0113] (Preparation of PEDOT:PSS dispersion)

[0114] A dispersion of a second conductive polymer doped with a dopant is prepared by the following method. First, 3,4-ethylenedioxythiophene and polystyrene sulfonic acid (dopant) are dissolved in ion exchange water to prepare a mixed solution thereof. While stirring the obtained mixed solution, iron (III) sulfate (oxidant) dissolved in ion exchange water is added to carry out a polymerization reaction. After the reaction, the obtained reaction solution is dialyzed to remove unreacted monomers and excess oxidant. In this way, a dispersion of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (about 5% by mass relative to poly(3,4-ethylenedioxythiophene)) is obtained. Hereinafter, poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid is sometimes referred to as "PEDOT:PSS".

[0115] (Adding conductive particles to PEDOT:PSS dispersion)

[0116] Nickel metal particles (spherical, average particle size: 2 μm) were added to the PEDOT:PSS dispersion to prepare a treatment solution A containing PEDOT:PSS and conductive particles.

[0117] (Production of wound body)

[0118] The anode lead connector and cathode lead connector connected with the lead wire are connected to the above-mentioned anode body and cathode body respectively. Then, the anode body and the cathode body are wound in a manner of sandwiching a spacer in the middle, and the outer surface is fixed with a stop tape. The spacer uses a non-woven fabric formed of cellulose. The wound body (capacitor element precursor) is made in this way. The prepared wound body is immersed in an ammonium adipate solution, and a voltage of 50V is applied to the anode body while a chemical conversion treatment is performed again at 70°C for 60 minutes. Through this chemical conversion treatment, a dielectric layer is formed mainly on the end face of the anode body.

[0119] (Formation of Conductive Polymer Layer)

[0120] First, the treatment liquid A is placed in a container. Next, the wound body is immersed in the treatment liquid A in the container for 15 minutes in a reduced pressure atmosphere (40 kPa) at room temperature, and then the wound body is lifted from the treatment liquid A. In this way, the treatment liquid A is impregnated into the wound body. Next, in a drying furnace, the wound body is dried at 60°C for 30 minutes, and then at 150°C for 30 minutes. Thus, the solvent contained in the treatment liquid A is dried. In this way, a conductive polymer layer containing conductive particles is formed.

[0121] (Impermeation of electrolyte)

[0122] The wound body having a conductive polymer layer is impregnated with an electrolyte at room temperature and atmospheric pressure. As the electrolyte, a solution is used in which polyethylene glycol, γ-butyrolactone, cyclopentane sulfone and mono(ethyldimethylamine)phthalate (solute) are mixed in a mass ratio of polyethylene glycol: γ-butyrolactone: cyclopentane sulfone: mono(ethyldimethylamine)phthalate = 30:30:20:20. In this way, a capacitor element including an electrolyte layer is obtained. The capacitor element is sealed to complete the electrolytic capacitor. Thereafter, an aging treatment is performed at 130°C for 2 hours while applying the rated voltage. In this way, capacitor A1 is obtained.

[0123] [Fabrication of capacitors A2 and A3]

[0124] The capacitors A2 and A3 were produced using the same materials and conditions as the capacitor A1 except that the content of the conductive particles in the processing liquid A was different.

[0125] [Fabrication of capacitors B1 to B3]

[0126] Capacitors B1 to B3 were produced using the same materials and conditions as capacitor A1, except for the type and content of conductive particles contained in treatment liquid A. In the production of capacitors B1 to B3, graphene (scaly, average particle size 0.4 μm) was used as conductive particles.

[0127] [Fabrication of capacitor C1 (comparative example)]

[0128] The capacitor C1 was produced using the same materials and conditions as the capacitor A1 except that the conductive particles were not used. Therefore, the conductive polymer layer of the capacitor C1 contained PEDOT:PSS but did not contain conductive particles.

[0129] (ESR measurement)

[0130] The equivalent series resistance (ESR) of the electrolytic capacitor produced by the above operation is measured. ESR is measured at 20°C using a 4-terminal LCR meter. For ESR, the initial value after the electrolytic capacitor is produced and the value after the electrolytic capacitor is placed at high temperature (placed at 145°C for 150 hours and 500 hours) are measured. Then, as an indicator of long-term characteristics, the ESR change rate is calculated by the following formula.

[0131] ESR change rate (%) = {100 × (ESR value after high temperature storage) / (initial ESR value)} - 100

[0132] The conditions for forming part of the electrolyte layer of the above-mentioned electrolytic capacitor are shown in Table 1. It should be noted that the mass ratio (or content ratio) of the conductive particles and PEDOT:PSS in the formed electrolyte layer is considered to be equal to the ratio of their content in the treatment liquid. Therefore, their mass ratio in the electrolyte layer is calculated based on their content in the treatment liquid. In addition, the evaluation results of the ESR of the above-mentioned electrolytic capacitor are shown in Table 2.

[0133] [Table 1]

[0134]

[0135] [Table 2]

[0136]

[0137] The ESR change rate is preferably low. As shown in Table 2, for the electrolytic capacitor C1 of the comparative example, the ESR increases significantly due to high temperature storage. In contrast, the ESR change rates of the electrolytic capacitors A1 to A3 and B1 to B3 are sufficiently low. The mass ratio of conductive particles / (PEDOT:PSS) is preferably 0.15 or more, more preferably 0.35 or more or 1.0 or more.

[0138] Industrial Applicability

[0139] The present application can be applied to electrolytic capacitors and methods for manufacturing the same.

[0140] Although the present invention has been described with respect to the present preferred embodiments, such disclosure is not to be construed in a limiting sense. Various modifications and variations will undoubtedly be apparent to those skilled in the art of the present invention upon reading the above disclosure. Therefore, the appended claims should be interpreted as including all modifications and variations without departing from the true spirit and scope of the present invention.

[0141] Description of Reference Numerals

[0142] 10 Capacitor elements

[0143] 21 Anode

[0144] 22 Cathode

[0145] 23 Spacer

[0146] 100 Electrolytic Capacitors

Claims

1. An electrolytic capacitor comprising a capacitor element, The capacitor element includes: an anode body having a dielectric layer formed on a surface thereof, and an electrolyte layer disposed adjacent to the dielectric layer. The electrolyte layer comprises: a conductive polymer doped with a dopant, conductive particles and a non-aqueous solvent. The anode body has a porous portion on the surface, The average particle size of the conductive particles is larger than the average pore size of the porous portion. The conductive polymer is in particle form. The average particle size of the conductive polymer is smaller than the average pore size of the porous portion.

2. The electrolytic capacitor according to claim 1, wherein: The dopant is a polymer dopant containing an acidic group. The electrolyte layer includes an electrolytic solution, and the electrolytic solution includes the nonaqueous solvent and an alkali component dissolved in the nonaqueous solvent.

3. The electrolytic capacitor according to claim 2, wherein: The content of the alkaline component in the electrolytic solution is 0.1 mass % or more and 20 mass % or less.

4. The electrolytic capacitor according to claim 1 or 2, wherein: The total mass of the conductive polymer and the dopant contained in the electrolyte layer is greater than the mass of the conductive particles contained in the electrolyte layer.

5. The electrolytic capacitor according to claim 1 or 2, wherein: The conductive particles are particles of a conductive carbon material.

6. The electrolytic capacitor according to claim 1 or 2, wherein: The conductive particles include at least one type of particles selected from the group consisting of carbon black particles, carbon nanotube particles, graphite particles, and graphene particles.

7. The electrolytic capacitor according to claim 1 or 2, wherein: The electrolyte layer includes a polymer layer containing the conductive polymer. The polymer layer includes: a first polymer layer formed on the dielectric layer, and a second polymer layer formed on the first polymer layer. The content of the conductive particles in the second polymer layer is greater than the content of the conductive particles in the first polymer layer. The content of the conductive particles is expressed in mass %.

8. The electrolytic capacitor according to claim 1 or 2, wherein: The dopant is polystyrene sulfonic acid, The conductive polymer is poly (3,4-ethylenedioxythiophene).

9. A method for manufacturing an electrolytic capacitor, comprising: Step i, preparing a capacitor element precursor, wherein the capacitor element precursor includes an anode body having a dielectric layer formed on the surface; Step ii, forming a polymer layer adjacent to the dielectric layer by an impregnation treatment, the polymer layer comprising a conductive polymer doped with a dopant and conductive particles; and Step iii, impregnating the polymer layer with a non-aqueous solvent, The anode body has a porous portion on the surface, The average particle size of the conductive particles is larger than the average pore size of the porous portion. The conductive polymer is in particle form. The average particle size of the conductive polymer is smaller than the average pore size of the porous portion.

10. The manufacturing method according to claim 9, wherein: The dopant is a polymer dopant containing an acidic group. The step iii is a step of impregnating the polymer layer with an electrolyte solution, wherein the electrolyte solution includes the non-aqueous solvent and an alkali component dissolved in the non-aqueous solvent.

11. The manufacturing method according to claim 9 or 10, wherein: The impregnation treatment in the step ii is an impregnation treatment x of impregnating the capacitor element precursor with a dispersion containing the conductive polymer doped with the dopant and the conductive particles.

12. The manufacturing method according to claim 9 or 10, wherein: The impregnation treatment in step ii includes: an impregnation treatment y of impregnating the capacitor element precursor with a first dispersion liquid containing the conductive polymer doped with the dopant; and The impregnation treatment z is to impregnate the capacitor element precursor with the second dispersion liquid containing the conductive particles.

13. The manufacturing method according to claim 9 or 10, wherein: The dopant is polystyrene sulfonic acid, The conductive polymer is poly (3,4-ethylenedioxythiophene).

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