Solid electrolytic capacitor and method for manufacturing same

Abstract

This solid electrolytic capacitor includes: a porous body made of a valve metal; a dielectric layer formed on a surface of the porous body; a first conductive layer covering the dielectric layer; a second conductive layer laid on the first conductive layer; a carbon layer laid on the second conductive layer; and a silver layer laid on the carbon layer. The first conductive layer contains one or more selected from the group consisting of polyaniline, a polyaniline derivative, polythiophene, a polythiophene derivative, polypyrrole, and a polypyrrole derivative. The second conductive layer contains polyaniline or a polyaniline derivative.

Description

Solid electrolytic capacitor and its manufacturing method

[0001] The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

[0002] In solid electrolytic capacitors such as aluminum electrolytic capacitors and tantalum capacitors, conductive polymers are used as the material for the solid electrolyte layer. The outer layer of a solid electrolytic capacitor generally has a laminated structure of three layers: a conductive polymer layer, a carbon layer, and a silver paste layer. The charge stored inside the capacitor element is extracted to the outside through each of these layers. Patent Document 1 discloses a tantalum capacitor in which a conductive polymer layer, a carbon layer, and a silver layer are formed in this order on a tantalum sintered body having a dielectric oxide layer (Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2023-99299

[0004] However, in the conventional configuration disclosed in Patent Document 1, the interface resistance between each layer is large, which results in a large equivalent series resistance (ESR) of the capacitor, resulting in a large loss in the amount of current extracted.

[0005] Therefore, after extensive research, the inventors discovered that by adopting a specific configuration for each layer of a solid electrolytic capacitor, it is possible to reduce the interfacial resistance between each layer and obtain a solid electrolytic capacitor with low equivalent series resistance, and thus completed the present invention.

[0006] An object of the present invention is to provide a solid electrolytic capacitor with a low equivalent series resistance and a method for manufacturing the same.

[0007] According to the present invention, the following solid electrolytic capacitors and the like are provided. 1. A solid electrolytic capacitor comprising: a porous body made of a valve metal, a dielectric layer formed on the surface of the porous body, a first conductive layer covering the dielectric layer, a second conductive layer laminated on the first conductive layer, a carbon layer laminated on the second conductive layer, and a silver layer laminated on the carbon layer, wherein the first conductive layer comprises one or more selected from the group consisting of polyaniline, polyaniline derivatives, polythiophene, polythiophene derivatives, polypyrrole, and polypyrrole derivatives, and the second conductive layer comprises polyaniline or a polyaniline derivative. 2. The solid electrolytic capacitor according to item 1 above, wherein the dielectric layer comprises an oxide of the valve metal. 3. The solid electrolytic capacitor according to item 1 or 2 above, wherein the first conductive layer comprises a polyaniline composite in which polyaniline is doped with a proton donor. 4. 4. The solid electrolytic capacitor according to any one of 1 to 3 above, wherein the second conductive layer comprises a polyaniline composite in which polyaniline is doped with a proton donor. 5. The solid electrolytic capacitor according to 3 or 4 above, wherein the polyaniline composite is a polyaniline composite doped with sulfosuccinic acid. 6. The solid electrolytic capacitor according to any one of 1 to 5 above, wherein the carbon layer is a layer formed using an organic solvent-based carbon paste. 7. The solid electrolytic capacitor according to any one of 1 to 6 above, wherein the silver layer comprises granular silver. 8. The solid electrolytic capacitor according to any one of 1 to 7 above, wherein the valve metal is selected from the group consisting of aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. 9. A method for producing a solid electrolytic capacitor, comprising the following steps (A-1) or (A-2) and steps (B) to (E):(A-1) A step of immersing a part or the whole of a porous body having a valve metal oxide in a first conductive polymer composition containing a conductive polymer and a solvent; (A-2) A step of immersing a part or the whole of a porous body having a valve metal oxide in a first conductive polymer composition containing a conductive polymer, a solvent, and a phenolic compound; (B) A step of removing the porous body from the first conductive polymer composition used in the step (A-1) or (A-2) and holding it at a temperature equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition; (C) A step of immersing a part or the whole of the porous body after the step (B) in a second conductive polymer composition containing a conductive polymer and a solvent that are the same as or different from the first conductive polymer composition, and drying; (D) A step of immersing a part or the whole of the porous body after the step (C) in a liquid containing an organic solvent-based carbon paste, and drying; (E) A step of immersing a part or the whole of the porous body after the step (D) in a liquid containing a silver paste, and drying. 10. The method for producing a solid electrolytic capacitor according to 9 above, wherein the first conductive polymer composition comprises a polyaniline composite in which polyaniline is doped with a proton donor. 11. The method for producing a solid electrolytic capacitor according to 9 or 10 above, wherein the second conductive polymer composition comprises a polyaniline composite in which polyaniline is doped with a proton donor. 12. The method for producing a solid electrolytic capacitor according to 10 or 11 above, wherein the polyaniline composite is a polyaniline composite doped with sulfosuccinic acid. 13. A solid electrolytic capacitor obtained by the method for producing a solid electrolytic capacitor according to any one of 9 to 12 above.

[0008] According to the present invention, a solid electrolytic capacitor having a low equivalent series resistance and a method for manufacturing the same can be provided.

[0009] Fig. 1 is a schematic diagram of a solid electrolytic capacitor according to one embodiment of the present invention, and Fig. 2 is an enlarged schematic diagram of a cross section of the solid electrolytic capacitor according to one embodiment of the present invention.

[0010] The solid electrolytic capacitor and the method for manufacturing the same of the present invention are described in detail below. In this specification, "x to y" represents a numerical range of "x or more and y or less." The upper and lower limits of the numerical ranges can be combined in any combination.

[0011] [Solid Electrolytic Capacitor] A solid electrolytic capacitor according to one aspect of the present invention includes a porous body made of a valve metal, a dielectric layer formed on the surface of the porous body, a first conductive layer covering the dielectric layer, a second conductive layer laminated on the first conductive layer, a carbon layer laminated on the second conductive layer, and a silver layer laminated on the carbon layer, wherein the first conductive layer contains one or more selected from the group consisting of polyaniline, polyaniline derivatives, polythiophene, polythiophene derivatives, polypyrrole, and polypyrrole derivatives, and the second conductive layer contains polyaniline or a polyaniline derivative.

[0012] The solid electrolytic capacitor according to one embodiment of the present invention has the above-described structure, which allows for a reduction in equivalent series resistance. It is believed that the use of highly hydrophobic polyaniline in the second conductive layer improves interfacial adhesion with the carbon layer containing a carbon material, which is also a hydrophobic material, thereby reducing interfacial resistance.

[0013] Fig. 1 is a schematic diagram of a solid electrolytic capacitor according to one embodiment of the present invention, and Fig. 2 is an enlarged schematic diagram of a cross section of the solid electrolytic capacitor. The solid electrolytic capacitor 100 according to one embodiment of the present invention includes an anode body 110 composed of a porous body 111 made of a valve metal and a dielectric layer 112 formed on the surface of the porous body, a first conductive layer 120 covering the dielectric layer, a second conductive layer 130 laminated on the first conductive layer, a carbon layer 140 laminated on the second conductive layer, and a silver layer 150 laminated on the carbon layer. The solid electrolytic capacitor 100 according to one embodiment of the present invention may also include a wire 160 containing a valve metal. The wire 160 penetrates at least a portion of the porous body 111.

[0014] The first conductive layer 120 is also called an internal solid electrolyte layer, an internal coating layer, an inner layer, etc. The second conductive layer 130 is also called an external coating layer, an outer layer, etc. Each component constituting the solid electrolytic capacitor according to one embodiment of the present invention will be described below.

[0015] [Porous Body] The porous body is made of a valve metal. The porous body is a material that has pores, preferably with a large number of pores with diameters of about 1 nm to 10 μm. By using a porous body, the surface area of ​​the valve metal can be increased. As a result, the capacitance of the capacitor can be increased, making it possible to realize a small, large-capacity capacitor.

[0016] The shape of the porous body is not particularly limited, and may be, for example, a molded body or a film (foil) having a certain thickness. The length, width, and thickness of the molded porous body are not particularly limited, and for example, each is independently 15 μm or more and 5 mm or less. The thickness of the film (foil) of the porous body is not particularly limited, and for example, is 15 μm or more and 300 μm or less.

[0017] Pore ​​structures include, but are not limited to, tunnel-like pits, spongy pits, voids between densely packed powder particles, etc. The porous body may contain only one type of these structures, or two or more types.

[0018] The method for producing the porous body is not particularly limited, but for example, a porous body may be formed by sintering metal powder made of a valve metal, or a film (foil) made of a valve metal may be etched to form a large number of holes.

[0019] In one embodiment, the porous body is a sintered body of valve metal obtained by sintering a compact containing valve metal powder and a binder. The sintered body of valve metal can be produced by mixing and stirring valve metal powder, a binder, and a solvent in a certain ratio, compressing the mixed powder into a rectangular parallelepiped, and then sintering the resultant at high temperature and under high vibration.

[0020] Examples of the valve metal include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony, and aluminum or tantalum is preferred. These metals may be used alone or in combination of two or more.

[0021] Examples of binders include cellulose-based binders, such as one or more binders selected from the group consisting of nitrocellulose, methylcellulose, ethylcellulose, and hydroxypropylcellulose. One binder may be used alone, or two or more binders may be used in combination.

[0022] [Dielectric Layer] The dielectric layer is formed on the surface of the porous body. In one embodiment, the dielectric layer is made of an oxide of a valve metal contained in the porous body.

[0023] The method for producing the dielectric layer is not particularly limited, but examples thereof include anodic oxidation, in which an oxide film grows on the surface layer by passing a current through a porous body as an anode in an electrolytic solution. Examples of the electrolytic solution include phosphates, borates, citrates, adipates, etc. One type of electrolytic solution may be used alone, or two or more types may be used in combination.

[0024] The thickness of the dielectric layer is designed according to the required withstand voltage, capacitance, etc., and is preferably, for example, 1 nm or more and 500 nm or less, and more preferably 10 nm or more and 100 nm or less.

[0025] [Anode Body] In this specification, the porous body made of a valve metal and the dielectric layer formed on the surface of the porous body are collectively referred to as the anode body. The submerged capacity of the anode body is, for example, preferably 100 μF or more and 2000 μF or less, and more preferably 500 μF or more and 1500 μF or less. The submerged capacity of the anode body can be measured by the method described in the Examples.

[0026] [First Conductive Layer] The first conductive layer (hereinafter also referred to as "internal solid electrolyte layer") covers the dielectric layer and contains one or more selected from the group consisting of polyaniline, polyaniline derivatives, polythiophene, polythiophene derivatives, polypyrrole, and polypyrrole derivatives. Here, the polythiophene may be polythiophene doped with a polyanion such as polystyrene sulfonic acid, or a self-doped polythiophene.

[0027] These conductive polymers may be polymerized after the monomer is impregnated into the anode body, or the polymer may be impregnated into the anode body.

[0028] These conductive polymers may be used alone or in combination of two or more.

[0029] In one embodiment, the first conductive layer contains polyaniline or a polyaniline derivative having a weight average molecular weight of preferably 10,000 or more, more preferably 20,000 or more, even more preferably 30,000 or more and 1,000,000 or less, still more preferably 40,000 or more and 1,000,000 or less, and particularly preferably 52,000 or more and 1,000,000 or less.

[0030] For example, when used in a solid electrolyte layer of a solid electrolytic capacitor, a conductive polymer with a larger molecular weight is generally preferable from the viewpoint of increasing the strength of the resulting electrolyte layer. On the other hand, a larger molecular weight increases the viscosity, which may make it difficult to impregnate the pores of a porous body. The weight-average molecular weight of polyaniline is measured by the method described in the Examples.

[0031] From the viewpoints of versatility and economy, the polyaniline is preferably unsubstituted. When the polyaniline has a substituent, examples of the substituent include linear or branched hydrocarbon groups such as methyl, ethyl, hexyl, and octyl groups; alkoxy groups such as methoxy and ethoxy groups; aryloxy groups such as phenoxy groups; and trifluoromethyl groups (-CF ３ Examples of halogenated hydrocarbons include halogenated hydrocarbons such as aryl groups.

[0032] In one embodiment, the first conductive layer includes a polyaniline composite in which polyaniline is doped with a proton donor. The use of a polyaniline composite tends to improve solubility in a solvent. The doping of polyaniline with a proton donor can be confirmed by ultraviolet, visible, or near-infrared spectroscopy or X-ray photoelectron spectroscopy. Any proton donor can be used without particular limitations, as long as it has sufficient acidity to generate carriers in the polyaniline.

[0033] Examples of the proton donor include Bronsted acids and salts thereof. Preferred are organic acids and salts thereof, and more preferred are proton donors represented by the following formula (I): M(XARn)m (I)

[0034] M in formula (I) is a hydrogen atom, an organic free radical, or an inorganic free radical. Examples of organic free radicals include a pyridinium group, an imidazolium group, and an anilinium group. Examples of inorganic free radicals include lithium, sodium, potassium, cesium, ammonium, calcium, magnesium, and iron. X in formula (I) is an anionic group, such as —SO ３ － Group, -PO ３ ２－ Group, -PO ４ (OH) － group, -OPO ３ ２－ group, -OPO ２ (OH) － Group, -COO － groups, and preferably —SO ３ － It is the base.

[0035] A in formula (I) is a substituted or unsubstituted hydrocarbon group (e.g., having 1 to 20 carbon atoms). The hydrocarbon group may be a linear or cyclic saturated aliphatic hydrocarbon group, a linear or cyclic unsaturated aliphatic hydrocarbon group, or an aromatic hydrocarbon group. Examples of linear saturated aliphatic hydrocarbon groups include linear or branched alkyl groups (e.g., having 1 to 20 carbon atoms). Examples of cyclic saturated aliphatic hydrocarbon groups include cycloalkyl groups (e.g., having 3 to 20 carbon atoms) such as cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. The cyclic saturated aliphatic hydrocarbon group may be formed by condensing multiple cyclic saturated aliphatic hydrocarbon groups. Examples include norbornyl, adamantyl, and condensed adamantyl groups. Examples of linear unsaturated aliphatic hydrocarbon groups (e.g., having 2 to 20 carbon atoms) include linear or branched alkenyl groups. Examples of cyclic unsaturated aliphatic hydrocarbon groups (e.g., having 3 to 20 carbon atoms) include cyclic alkenyl groups. Examples of aromatic hydrocarbon groups (having, for example, 6 to 20 carbon atoms) include phenyl groups, naphthyl groups, and anthracenyl groups.

[0036] When A is a substituted hydrocarbon group, the substituent is an alkyl group (having, for example, 1 to 20 carbon atoms), a cycloalkyl group (having, for example, 3 to 20 carbon atoms), a vinyl group, an allyl group, an aryl group (having, for example, 6 to 20 carbon atoms), an alkoxy group (having, for example, 1 to 20 carbon atoms), a halogen atom, a hydroxy group, an amino group, an imino group, a nitro group, a silyl group, or an ester bond-containing group.

[0037] R in formula (I) is bonded to A and is -H, -R １ , -OR １ , -COR １ , -COOR １ , -(C=O)-(COR １ ), or -(C=O)-(COOR １ ) is a substituent represented by the formula: R １ represents a hydrocarbon group which may have a substituent, a silyl group, an alkylsilyl group, -(R ２ O) x-R ３ group, or -(OSiR ３ ２ ) x-OR３ R is a group. ２ is an alkylene group, R ３ is a hydrocarbon group, and x is an integer of 1 or more. When x is 2 or more, multiple R ２ may be the same or different, and multiple R ３ may be the same or different from each other.

[0038] R １ Examples of the hydrocarbon group (having, for example, 1 to 20 carbon atoms) include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, a pentadecyl group, and an eicosanyl group. The hydrocarbon group may be linear or branched. The substituent of the hydrocarbon group is an alkyl group (having, for example, 1 to 20 carbon atoms), a cycloalkyl group (having, for example, 3 to 20 carbon atoms), a vinyl group, an allyl group, an aryl group (having, for example, 6 to 20 carbon atoms), an alkoxy group (having, for example, 1 to 20 carbon atoms), a halogen atom, a hydroxy group, an amino group, an imino group, a nitro group, or an ester bond-containing group. R ３ The hydrocarbon group of R １ is the same as:

[0039] R ２ Examples of the alkylene group (having, for example, 1 to 20 carbon atoms) include a methylene group, an ethylene group, and a propylene group. In formula (I), n is an integer of 1 or more. When n is 2 or more, multiple Rs may be the same or different. In formula (I), m is the valence of M / the valence of X.

[0040] The compound represented by formula (I) is preferably a dialkylbenzenesulfonic acid, a dialkylnaphthalenesulfonic acid, or a compound containing two or more ester bonds. The compound containing two or more ester bonds is more preferably a sulfophthalic acid ester or a compound represented by the following formula (II):

[0041]

[0042] In formula (II), M and X are the same as in formula (I). X is -SO ３ － The group R is preferred. ４, R ５ , and R ６ are each independently a hydrogen atom, a hydrocarbon group, or R ９ ３ Si-groups. Three R ９ are each independently a hydrocarbon group. ４ , R ５ , and R ６ When R is a hydrocarbon group, examples of the hydrocarbon group include a linear or branched alkyl group having 1 to 24 carbon atoms, an aryl group containing an aromatic ring (having, for example, 6 to 20 carbon atoms), and an alkylaryl group (having, for example, 7 to 20 carbon atoms). ９ As the hydrocarbon group of R ４ , R ５ , and R ６ This is the same as in the case of

[0043] R in formula (II) ７ and R ８ are each independently a hydrocarbon group or -(R １０ O) ｑ -R １１ R is a group. １０ is a hydrocarbon group or a silylene group. １１ is a hydrogen atom, a hydrocarbon group, or R １２ ３ Si-. q is an integer of 1 or more. Three R １２ are each independently a hydrocarbon group.

[0044] R ７ and R ８ When is a hydrocarbon group, examples of the hydrocarbon group include linear or branched alkyl groups having 1 to 24 carbon atoms, preferably 4 or more carbon atoms, aryl groups containing an aromatic ring (having, for example, 6 to 20 carbon atoms), and alkylaryl groups (having, for example, 7 to 20 carbon atoms). Specific examples include linear or branched butyl groups, pentyl groups, hexyl groups, octyl groups, and decyl groups.

[0045] R ７ and R ８ In R １０When R is a hydrocarbon group, examples of the hydrocarbon group include a linear or branched alkylene group having 1 to 24 carbon atoms, an arylene group containing an aromatic ring (having, for example, 6 to 20 carbon atoms), an alkylarylene group (having, for example, 7 to 20 carbon atoms), or an arylalkylene group (having, for example, 7 to 20 carbon atoms). ７ and R ８ In R １１ and R １２ When R is a hydrocarbon group, the hydrocarbon group may be ４ , R ５ , and R ６ As in the case of (1), q is preferably 1 to 10.

[0046] R ７ and R ８ Ga-(R １０ O) ｑ -R １１ Specific examples of the compound represented by formula (II) when it is a group include the two compounds represented by the following formulae: (In the formula, X is the same as in formula (I).)

[0047] The compound represented by the above formula (II) is more preferably a sulfosuccinic acid derivative represented by the following formula (III).

[0048] In formula (III), M is the same as in formula (I). m' is the valence of M. １３ and R １４ are each independently a hydrocarbon group or -(R １５ O) ｒ -R １６ R is a group. １５ is a hydrocarbon group or a silylene group, and R １６ is a hydrogen atom, a hydrocarbon group, or R １７ ３ Si-group, and r is an integer of 1 or more. １７ are each independently a hydrocarbon group. When r is 2 or more, multiple R １５ may be the same or different from each other.

[0049] R １３ and R １４When R is a hydrocarbon group, the hydrocarbon group may be ７ and R ８ It is the same as R １３ and R １４ In this case, R １５ When R is a hydrocarbon group, the hydrocarbon group may be any of the above-mentioned R １０ It is the same as R １３ and R １４ In this case, R １６ and R １７ When R is a hydrocarbon group, the hydrocarbon group may be any of the above-mentioned R ４ , R ５ , and R ６ It is preferable that r is 1 to 10.

[0050] R １３ and R １４ Ga-(R １５ O) ｒ -R １６ Specific examples of the group include R ７ and R ８ In -(R １０ O) ｑ -R １１ It is the same as R １３ and R １４ As the hydrocarbon group of R ７ and R ８ The same applies to the above, and a butyl group, a hexyl group, a 2-ethylhexyl group, and a decyl group are preferred.

[0051] The compound represented by formula (I) is preferably di(2-ethylhexyl)sulfosuccinic acid or sodium di(2-ethylhexyl)sulfosuccinate.

[0052] It is known that the conductivity and solubility in a solvent of a polyaniline composite can be controlled by changing the structure of the proton donor (Japanese Patent No. 3384566). In this embodiment, an optimal proton donor can be selected depending on the required properties for each application.

[0053] The doping ratio of the proton donor to the polyaniline is preferably 0.30 or more and 0.65 or less, more preferably 0.32 or more and 0.60 or less, even more preferably 0.33 or more and 0.57 or less, and particularly preferably 0.34 or more and 0.55 or less. Typically, a doping ratio of 0.30 or more ensures sufficient solubility of the polyaniline composite in an organic solvent. The doping ratio is defined as (the number of moles of the proton donor doped into the polyaniline) / (the number of moles of the polyaniline monomer unit). For example, a doping ratio of 0.5 for a polyaniline composite containing unsubstituted polyaniline and a proton donor means that one proton donor is doped for every two polyaniline monomer unit molecules. The doping ratio can be calculated if the number of moles of the proton donor and the polyaniline monomer unit in the polyaniline composite can be measured. For example, when the proton donor is an organic sulfonic acid, the number of moles of sulfur atoms derived from the proton donor and the number of moles of nitrogen atoms derived from the monomer unit of polyaniline are quantified by organic elemental analysis, and the doping ratio can be calculated by taking the ratio of these values.

[0054] The polyaniline composite preferably contains unsubstituted polyaniline and sulfonic acid as a proton donor, and satisfies the following formula (1): 0.32≦S ５ / N ５ ≦0.60 (1) (wherein, S ５ is the total number of moles of sulfur atoms contained in the polyaniline composite, and N ５ is the total number of moles of nitrogen atoms contained in the polyaniline composite. The number of moles of nitrogen atoms and sulfur atoms is a value measured by, for example, organic elemental analysis.

[0055] The method for producing the polyaniline composite is not particularly limited, and it can be produced, for example, by the production method described below. For example, the proton donor described above, aniline corresponding to the polyaniline described above, and optionally a surfactant (e.g., a nonionic emulsifier) ​​are dissolved in a water-immiscible organic solvent (e.g., a hydrocarbon solvent (preferably toluene or xylene)), and an acidic aqueous solution (e.g., an aqueous phosphoric acid solution) is added thereto. The reaction solution, which has two liquid phases, the water-immiscible organic solvent and the water, is stirred, and a polymerization initiator (e.g., ammonium persulfate) is added to carry out polymerization. After polymerization, the water-immiscible organic solvent phase is separated by allowing the solution to stand, thereby obtaining a polyaniline composite water-immiscible organic solvent solution. This solution is transferred to an evaporator, and the volatiles are evaporated and distilled off to obtain a polyaniline composite (protonated polyaniline).

[0056] [Second Conductive Layer] The second conductive layer (hereinafter also referred to as "external coating layer") is laminated on the first conductive layer. As shown in FIG. 1 , the first conductive layer impregnates the inside of the pores of the anode body, while the second conductive layer further coats the anode body and the first conductive layer from the outside.

[0057] The second conductive layer contains polyaniline or a polyaniline derivative. These may be used alone or in combination of two or more. The same description of the first conductive layer can be applied to the polyaniline and polyaniline derivative.

[0058] In one embodiment, the second conductive layer comprises a polyaniline composite in which the polyaniline is doped with a proton donor, hi one embodiment, the second conductive layer comprises a polyaniline composite in which the polyaniline is doped with sulfosuccinic acid.

[0059] [Carbon Layer] The carbon layer is laminated on the second conductive layer. The carbon layer contains a carbon material as a main component. The content of the carbon material in the carbon layer is, for example, 60% by mass or more, preferably 70% by mass or more. When the content of the carbon material is within this range, high adhesion between the second conductive layer and the silver layer can be easily ensured.

[0060] Examples of carbon materials include activated carbon, carbon black, carbon nanohorns, graphene, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, carbon nanotubes, carbon nanofibers, etc. These carbon materials may be used alone or in combination of two or more.

[0061] The carbon layer may contain other components such as known binders, additives, etc. The upper limit of the content of the carbon material in the carbon layer can be determined depending on the content of other components and is not particularly limited, but is, for example, 99 mass% or less.

[0062] The carbon layer is formed, for example, by a method of applying a carbon paste to the surface of the second conductive layer and drying it, etc. The carbon paste can be applied by, for example, a dipping method, sponge transfer, screen printing, spray application, a dispenser, inkjet printing, etc.

[0063] The carbon paste contains a carbon material and a dispersion medium. Examples of the dispersion medium include water, an organic medium, and a mixture thereof. The carbon paste may also contain other components such as known binders and additives.

[0064] In one embodiment, the carbon layer is a layer prepared using an organic solvent-based carbon paste, which refers to a form in which a carbon material is dispersed in an organic solvent.

[0065] Examples of the organic solvent include aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, ketones, ethers, esters, etc. Specific examples of the solvent (b) described below can also be used.

[0066] The organic solvent-based carbon paste has good compatibility with highly hydrophobic polyaniline, and is expected to provide excellent interfacial adhesion between the second conductive layer and the formed carbon layer, thereby reducing interfacial resistance.

[0067] In one embodiment, the carbon layer is laminated by impregnating the anode element having the first conductive layer and the second conductive layer described above with an organic solvent (organic solvent-based carbon paste) in which the carbon material described above is dispersed, and then drying the resulting mixture at a predetermined temperature to volatilize the organic solvent.

[0068] [Silver Layer] A silver (Ag) layer is laminated on the carbon layer. The silver layer preferably contains plate-like silver or granular silver, and particularly preferably contains granular silver. The silver layer may contain both plate-like silver and granular silver. When the silver layer contains granular silver, the dispersibility of silver is improved at the interface between the carbon layer and the silver layer, and it is expected that the interface resistance will be reduced.

[0069] The silver layer contains silver as a main component. The silver content in the silver layer is, for example, 60 mass % or more, preferably 70 mass % or more. When the silver content is in this range, sufficient conductivity is likely to be obtained.

[0070] The silver layer may contain other components such as known binders, additives, etc. The upper limit of the silver content in the silver layer can be determined depending on the contents of other components and is not particularly limited, but is, for example, 99 mass% or less.

[0071] The silver layer is laminated, for example, by a method of applying a silver paste to the surface of the carbon layer and drying it. The silver paste may be in the form of silver dispersed in a solvent.

[0072] The shape of the silver is not limited as long as it can be dispersed in the solvent, and examples include plate-like silver and granular silver. The solvent is not particularly limited as long as it can disperse silver, and known solvents can be used. Examples include aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, ketones, ethers, and esters. Specific examples of the solvent (b) described below can also be used. The silver paste can be applied by, for example, immersion, sponge transfer, screen printing, spray application, dispenser, inkjet printing, etc.

[0073] In one embodiment, the silver layer is laminated by impregnating the anode element having the above-described first conductive layer, second conductive layer, and carbon layer into an organic solvent in which silver is dispersed, and then drying the anode element at a predetermined temperature to volatilize the organic solvent.

[0074] The solid electrolytic capacitor according to this embodiment can be manufactured, for example, by the manufacturing method of the present invention described below.

[0075] [Method for Manufacturing a Solid Electrolytic Capacitor] A method for manufacturing a solid electrolytic capacitor according to one aspect of the present invention includes the following step (A-1) or (A-2) and steps (B) to (E). (A-1) A step of immersing a part or the whole of a porous body having a valve metal oxide in a first conductive polymer composition containing a conductive polymer and a solvent. (A-2) A step of immersing a part or the whole of a porous body having a valve metal oxide in a first conductive polymer composition containing a conductive polymer, a solvent, and a phenolic compound. (B) A step of removing the porous body from the first conductive polymer composition used in step (A-1) or (A-2) and holding it at a temperature below the boiling point of the solvent contained in the first conductive polymer composition. (C) A step of immersing a part or the whole of the porous body after step (B) in a second conductive polymer composition containing a conductive polymer and a solvent that are the same as or different from the first conductive polymer composition, and drying it. (D) A step of immersing a part or the whole of the porous body after step (C) in a liquid containing an organic solvent-based carbon paste, and drying it. (E) A step of immersing a part or the whole of the porous body after step (D) in a liquid containing a silver paste, and drying it.

[0076] The above steps (A-1) or (A-2) and (B) are steps of forming a first conductive layer on the surface of the anode body. The above step (C) is a step of forming a second conductive layer, the above step (D) is a step of forming a carbon layer, and the above step (E) is a step of forming a silver layer. In one embodiment, a method for producing a solid electrolytic capacitor according to one aspect of the present invention includes steps (A-1), (B), (C), (D), and (E). In one embodiment, a method for producing a solid electrolytic capacitor according to one aspect of the present invention includes steps (A-2), (B), (C), (D), and (E).

[0077] [Step of Forming First Layer] <Steps (A-1) and (A-2)> The step of forming the first layer includes either step (A-1) or (A-2). In step (A-1), a porous body having an oxide of a valve metal is partially or entirely immersed in a first conductive polymer composition containing a conductive polymer and a solvent. In step (A-2), a porous body having an oxide of a valve metal is partially or entirely immersed in a first conductive polymer composition containing a conductive polymer, a solvent, and a phenolic compound.

[0078] The porous body and the valve metal can be the same as those described in the solid electrolytic capacitor according to one aspect of the present invention. The first conductive polymer composition in step (A-1) contains a conductive polymer and a solvent. The first conductive polymer composition in step (A-2) contains a conductive polymer, a solvent, and a phenolic compound.

[0079] [(a) Conductive Polymer] Examples of the conductive polymer (hereinafter also referred to as "component (a)") include polyaniline, polyaniline derivatives, polythiophene, polythiophene derivatives, polypyrrole, polypyrrole derivatives, etc. These may be used alone or in combination of two or more.

[0080] The polyaniline, polyaniline derivatives, polythiophene, polythiophene derivatives, polypyrrole, and polypyrrole derivatives can be those described in the solid electrolytic capacitor according to one aspect of the present invention.

[0081] In one embodiment, the first conductive polymer composition contains polyaniline or a polyaniline derivative. Since the first conductive polymer composition is impregnated into the pores of the anode body and the first conductive layer is coated on the surface of the dielectric layer, the weight-average molecular weight of the polyaniline and polyaniline derivative used in the first conductive polymer composition is preferably smaller than the weight-average molecular weight of the polyaniline and polyaniline derivative used in the second conductive polymer composition described below. For example, the weight-average molecular weight of the polyaniline and polyaniline derivative used in the first conductive polymer composition is preferably 100,000 or less.

[0082] In one embodiment, the first conductive polymer composition comprises a polyaniline composite in which the polyaniline is doped with a proton donor, hi one embodiment, the first conductive polymer composition comprises a polyaniline composite in which the polyaniline is doped with sulfosuccinic acid.

[0083] [(b) Solvent] The solvent (hereinafter also referred to as "component (b)") is not particularly limited as long as it dissolves or disperses the conductive polymer. It is particularly preferable that the solvent (component (b)) dissolves the conductive polymer. However, this does not include the component (c) described below.

[0084] The solvent is preferably an organic solvent. Examples thereof include aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, ketones, ethers, and esters. These may be used alone or in combination of two or more.

[0085] The organic solvent may be a water-soluble organic solvent, or may be an organic solvent that is substantially immiscible with water (a water-immiscible organic solvent). A highly polar organic solvent can be used as the water-soluble organic solvent, and may be a protic polar solvent or an aprotic polar solvent. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 1-ethoxy-2-propanol, 2-ethoxy-1-propanol, 1-butanol, 2-butanol, 2-pentanol, benzyl alcohol, and alkoxy alcohols (e.g., 1-methoxy-2-propanol, 3-methoxy-1-butanol, and 3-methoxy-3-methylbutanol); ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethers such as tetrahydrofuran, 4-methyltetrahydropyran, dioxane, diethyl ether, and ethylene glycol mono-tert-butyl ether; and aprotic polar solvents such as N-methylpyrrolidone.

[0086] Examples of the water-immiscible organic solvent that can be used include hydrocarbon solvents such as hexane, benzene, toluene, xylene, ethylbenzene, and tetralin; halogen-containing solvents such as methylene chloride, chloroform, carbon tetrachloride, dichloroethane, and tetrachloroethane; ester solvents such as ethyl acetate, isobutyl acetate, n-butyl acetate, ethyl lactate, and methyl lactate; ketone solvents such as methyl isobutyl ketone (MIBK), methyl ethyl ketone, cyclopentanone, and cyclohexanone; and ether solvents such as cyclopentyl methyl ether. Furthermore, an isoparaffin solvent containing one or more isoparaffins may be used as the hydrocarbon solvent.

[0087] Alternatively, a commercially available solvent such as "Kyowasol C900" (manufactured by KH Neochem Co., Ltd.) can also be used.

[0088] Among these, toluene, xylene, methyl isobutyl ketone, chloroform, trichloroethane, and ethyl acetate are preferred in terms of excellent solubility of the conductive polymer.

[0089] In the case of a polyaniline composite, the composite can be dissolved even in an alcoholic solvent such as isopropyl alcohol, 1-butanol, 2-butanol, 2-pentanol, benzyl alcohol, alkoxy alcohol, etc. Alcohols are preferable to aromatic solvents such as toluene from the viewpoint of reducing environmental impact.

[0090] When an organic solvent is used as the solvent, it is preferable to use a mixed organic solvent in which a water-immiscible organic solvent and a water-soluble organic solvent are mixed in a mass ratio of 99 to 1:1 to 99, since this prevents the generation of gels during storage and enables long-term storage. The mixed organic solvent may contain one or more water-immiscible organic solvents and one or more water-soluble organic solvents.

[0091] The concentration of component (a) relative to the total amount of the solvent (component (b)) [component (a) × 100 / (component (a) + component (b))] may be 0.01% by mass or more, 0.03% by mass or more, 0.05% by mass or more, or 2.0% by mass or more. It is usually 15.0% by mass or less, 13.0% by mass or less, 12.0% by mass or less, 10.0% by mass or less, 9.0% by mass or less, or 8.0% by mass or less.

[0092] When the conductive polymer composition further contains a component (c) described below, the concentration of the component (a) is usually 0.3 to 20 mass %, preferably 0.5 to 20 mass %, more preferably 1 to 15 mass %, even more preferably 1 to 10 mass %, and still more preferably 1 to 7 mass %, relative to the conductive polymer composition.

[0093] The content of component (b) can be adjusted appropriately depending on the amounts of other components and is not limited, but can be, for example, 200 to 20,000 parts by mass, 300 to 17,000 parts by mass, 500 to 12,000 parts by mass, 500 to 5,000 parts by mass, or 500 to 1,500 parts by mass per 100 parts by mass of component (a).

[0094] [(c) Phenolic Compound] The phenolic compound (component (c)) is not particularly limited and is a compound represented by ArOH (where Ar is an aryl group or a substituted aryl group). Note that component (c) is a component different from component (b).

[0095] Specific examples of the phenolic compound include substituted phenols such as phenol, o-, m-, or p-cresol, o-, m-, or p-ethylphenol, o-, m-, or p-propylphenol, o-, m-, or p-butylphenol, o-, m-, or p-chlorophenol, salicylic acid, hydroxybenzoic acid, and hydroxynaphthalene; polyhydric phenolic compounds such as catechol and resorcinol; and polymeric compounds such as phenolic resins, polyphenols, and poly(hydroxystyrene).

[0096] Furthermore, a phenolic compound represented by the following formula (C1) can be used. (wherein n is an integer of 1 to 5. When n is 2 or more, a plurality of R ２１ may be the same or different. ２１ is an alkyl group having 2 to 10 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkylthio group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkylaryl group having 7 to 20 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms.

[0097] The above R ２１ Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl, and tertiary amyl. Examples of the alkenyl group include the above-mentioned alkyl group with an unsaturated bond in the molecule. Examples of the cycloalkyl group include cyclopentane and cyclohexane. Examples of the alkylthio group include methylthio and ethylthio. Examples of the aryl group include phenyl and naphthyl. Examples of the alkylaryl group and the arylalkyl group include the above-mentioned substituents obtained by combining the alkyl group and the aryl group. Among these groups, R ２１ As the alkyl group, a methyl group or an ethyl group is preferred.

[0098] Specific examples of the phenolic compound represented by formula (C1) include 4-tert-amylphenol, 2-isopropylphenol, 4-isopropyl-3-methylphenol, 2-isopropyl-5-methylphenol (thymol), 5-isopropyl-2-methylphenol (carvacrol), and 4-(1,1,3,3-tetramethylbutyl)phenol.

[0099] The content of component (c) is preferably 10 to 5,000 parts by mass, more preferably 10 to 2,000 parts by mass, and more preferably 10 to 1,000 parts by mass, per 100 parts by mass of component (a). The content of component (c) may be 100 to 10,000 parts by mass per 100 parts by mass of component (a). Use of such a phenolic compound is preferred because it improves electrical conductivity and solubility in alcohol.

[0100] The content of component (c) in the conductive polymer composition is 1 to 80% by mass, more preferably 5 to 60% by mass, and even more preferably 10 to 40% by mass. The use of such a phenolic compound is preferable because it improves the conductivity and improves the solubility in alcohol. Component (c) may also be mixed with component (b) and used as a mixed solvent. In this case, the concentration of component (a) in the solvent is calculated based on the combined mass of components (b) and (c).

[0101] [(d) Heat Stabilizer] The conductive polymer composition may further contain (d) a heat stabilizer (hereinafter also referred to as "component (d)").

[0102] The heat resistance stabilizer (component (d)) may be an acidic substance or a salt of an acidic substance, provided that component (d) does not include component (c).

[0103] The acidic substance may be either an organic acid, which is an acid of an organic compound, or an inorganic acid, which is an acid of an inorganic compound, and is preferably an organic acid. The acidic substance is preferably an organic acid containing one or more sulfonic acid groups.

[0104] The organic acid having a sulfonic acid group is preferably a cyclic, linear, or branched alkylsulfonic acid, a substituted or unsubstituted aromatic sulfonic acid, or a polysulfonic acid having one or more sulfonic acid groups. Examples of the alkylsulfonic acid include methanesulfonic acid, ethanesulfonic acid, and di(2-ethylhexyl)sulfosuccinic acid. Here, the alkyl group is preferably a linear or branched alkyl group having 1 to 18 carbon atoms. Examples of the aromatic sulfonic acid include those having 6 to 20 carbon atoms, such as sulfonic acids having a benzene ring, sulfonic acids having a naphthalene skeleton, and sulfonic acids having an anthracene skeleton. Examples of the aromatic sulfonic acid include substituted or unsubstituted benzenesulfonic acid, substituted or unsubstituted naphthalenesulfonic acid, and substituted or unsubstituted anthracenesulfonic acid.

[0105] The substituent is, for example, a substituent selected from the group consisting of an alkyl group (e.g., one having 1 to 20 carbon atoms), an alkoxy group (e.g., one having 1 to 20 carbon atoms), a hydroxy group, a nitro group, a carboxy group, and an acyl group, and one or more of these may be substituted.

[0106] Specific examples of aromatic sulfonic acids include compounds represented by the following formula (D1) or (D2). (In formula (D1), l is 1 or more, m is an integer of 0 or more and 5 or less, and n is an integer of 0 or more and 5 or less. When one of m and n is 0, the other is 1 or more.) (In formula (D2), q is 1 or more, p is an integer of 0 to 7, and each R is independently an alkyl group having 1 to 20 carbon atoms, a carboxy group, a hydroxyl group, a nitro group, a cyano group, or an amino group.)

[0107] l is preferably 1 to 3. m is preferably 1 to 3. n is preferably 0 to 3. q is preferably 1 to 3. p is preferably 0 to 3. R is preferably an alkyl group having 1 to 20 carbon atoms, a carboxy group, or a hydroxyl group.

[0108] Examples of aromatic sulfonic acids include 4-sulfophthalic acid, 5-sulfoisophthalic acid, 5-sulfosalicylic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 2-hydroxy-6-naphthalenesulfonic acid, 1,5-naphthalenedisulfonic acid, 2,6-naphthalenedisulfonic acid, p-phenolsulfonic acid, toluenesulfonic acid, p-xylene-2-sulfonic acid, 4,4'-biphenyldisulfonic acid, dibenzofuran-2-sulfonic acid, flavianic acid, (+)-10-camphorsulfonic acid, monoisopropylnaphthalenesulfonic acid, 1-pyrenesulfonic acid, etc. Among these, from the viewpoint of improving heat resistance, 4-sulfophthalic acid, 5-sulfosalicylic acid, 5-sulfoisophthalic acid, 2-naphthalenesulfonic acid, dibenzofuran-2-sulfonic acid, flavianic acid, 2-hydroxy-6-naphthalenesulfonic acid, and 1-pyrenesulfonic acid are preferred.

[0109] Examples of salts of acidic substances include salts of the compounds listed above. Counter ions of the salts include sodium, lithium, potassium, cesium, ammonium, calcium, barium, etc. Component (d) may be a hydrate.

[0110] The content of component (d) is preferably 0.1 to 1000 parts by mass, more preferably 1 to 100 parts by mass, even more preferably 1 to 30 parts by mass, and still more preferably 2 to 8 parts by mass, per 100 parts by mass of component (a).

[0111] [(e) Additives] In addition to the above components, the conductive polymer composition may contain an additive (hereinafter also referred to as "component (e)"), if necessary. However, component (e) does not include any of the above components (a) to (d). Examples of additives include adhesion promoters, fillers, thixotropy-imparting agents, rheology control agents, and binder resins.

[0112] Examples of adhesion promoters include silane coupling agents such as isocyanate silane and glycidyl silane, and polymer coupling agents such as acidic polyester. Examples of commercially available adhesion promoters include "BYK-4510" (manufactured by BYK Additives & Instruments). Examples of fillers include alumina, silica, titania, and zirconia.

[0113] The conductive polymer composition may consist essentially of components (a) and (b) and, optionally, components (c), (d), and (e). In this case, unavoidable impurities may be contained. For example, 70% by mass or more, 80% by mass or more, 90% by mass or more, 98% by mass or more, 99% by mass or more, or 99.5% by mass or more of the conductive polymer composition may be components (a) and (b) and, optionally, components (c), (d), and (e). Alternatively, the conductive polymer composition may consist only of components (a) and (b) and, optionally, components (c), (d), and (e).

[0114] The method for immersing the porous body containing a valve metal oxide in the first conductive polymer composition is not particularly limited. The entire porous body may be immersed in the conductive polymer composition in a single operation, or the porous body may be immersed in the conductive polymer composition stepwise or continuously. "Stepwise immersion" means that the porous body is moved in multiple steps and immersed stepwise in the conductive polymer composition. In other words, "stepwise immersion" means that the immersion operation is performed stepwise, and the porous body is removed from the conductive polymer composition in step (B) after a series of stepwise immersion operations. "Continuous immersion" means that the porous body is moved continuously at a predetermined speed and gradually immersed in the conductive polymer composition. By stepwise or continuously immersing the porous body in the conductive polymer composition, the conductive polymer can be smoothly impregnated into the pores of the porous body.

[0115] When the porous body is entirely immersed in the conductive polymer composition by a single pouring operation, the time for which the porous body is held in the conductive polymer composition (hereinafter simply referred to as the immersion time) is usually 1 to 30 minutes, and preferably 1 to 10 minutes.

[0116] When the porous body is moved in multiple steps and immersed in the conductive polymer composition stepwise, first, a portion of the porous body from the bottom to a predetermined height is immersed in the conductive polymer composition and maintained in the immersed state for, for example, 1 to 30 minutes, preferably 1 to 10 minutes, and then the porous body is moved so that a portion of the non-immersed portion is further immersed in the conductive polymer composition and maintained in the immersed state for, for example, 1 to 20 minutes, preferably 1 to 10 minutes.

[0117] The temperature of the conductive polymer composition into which the porous body is immersed is not particularly limited, and is usually room temperature (for example, 15 to 30° C., or 25° C.).

[0118] <Step (B)> Step (B) is a step in which the porous body is removed from the first conductive polymer composition used in step (A-1) or (A-2) and is maintained at a temperature equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition. This causes the liquid film formed at the openings of the pores of the porous body to disappear, thereby eliminating the liquid-sealed state. Therefore, the amount of conductive polymer composition filled into the pores can be increased.

[0119] In step (B), the holding temperature is a temperature not higher than the boiling point of the solvent contained in the first conductive polymer composition, and may be appropriately selected depending on the type of solvent, for example, room temperature. The holding time is usually 30 seconds to 5 minutes, and preferably 1 minute to 2 minutes.

[0120] In one embodiment, a cycle of steps (A) and (B) may be repeated multiple times before step (C). When a cycle of steps (A) and (B) is repeated multiple times before step (C), the multiple layers formed in the series of cycles are collectively referred to as an internal solid electrolyte layer (first conductive layer).

[0121] In one embodiment, a drying step (B1) may be performed after the step (B) and before the step (C). The temperature in the drying step does not need to be equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition. The drying temperature is usually 30 to 200°C, and preferably 100 to 180°C. The drying time is usually 10 to 120 minutes, and preferably 30 to 90 minutes. Before the drying step (B1), a cycle of steps (A) and (B) may be repeated multiple times.

[0122] [Step of Forming Second Conductive Layer] <Step (C)> Step (C) is a step of immersing a part or the whole of the porous body after step (B) in a second conductive polymer composition containing a conductive polymer that is the same as or different from the first conductive polymer composition and a solvent, and drying the second conductive polymer composition, thereby forming a second conductive layer.

[0123] The conductive polymer, solvent, and immersion are the same as those described in step (A). In one embodiment, the second conductive polymer composition contains polyaniline or a polyaniline derivative. Because the second conductive polymer composition does not need to be impregnated into the pores of the anode body, the weight-average molecular weight of the polyaniline and polyaniline derivative used in the second conductive polymer composition can be greater than the weight-average molecular weight of the polyaniline and polyaniline derivative used in the first conductive polymer composition. This allows the coating layer to be provided with the strength, heat resistance, and other properties required for its function. For example, the weight-average molecular weight of the polyaniline and polyaniline derivative used in the second conductive polymer composition is preferably 100,000 or more.

[0124] In one embodiment, the second conductive polymer composition comprises a polyaniline composite in which the polyaniline is doped with a proton donor, hi one embodiment, the second conductive polymer composition comprises a polyaniline composite in which the polyaniline is doped with sulfosuccinic acid.

[0125] In step (C), the drying temperature is not particularly limited and may be appropriately selected depending on the type of solvent. The drying temperature is usually 30 to 200° C., preferably 100 to 180° C. The drying time is usually 10 to 120 minutes, preferably 30 to 90 minutes.

[0126] In one embodiment, step (C) may be repeated multiple times before step (D). In this case, the multiple layers formed in a series of cycles are collectively referred to as an outer coating layer (second conductive layer).

[0127] [Carbon Layer Formation Step] In step (D), the porous body obtained after step (C) is partially or entirely immersed in a liquid containing an organic solvent-based carbon paste, followed by drying. The organic solvent-based carbon paste may be any of the organic solvent-based carbon pastes described above in connection with the solid electrolytic capacitor according to one aspect of the present invention.

[0128] In the carbon layer forming step, the immersion time is usually 5 seconds to 1 minute, and preferably 10 to 30 seconds. The drying temperature is usually 30 to 200° C., and preferably 100 to 180° C. The drying time is usually 10 to 120 minutes, and preferably 30 to 90 minutes.

[0129] [Silver Layer Formation Step] In step (E), the porous body obtained after step (D) is partially or entirely immersed in a solution containing a silver paste, followed by drying. The silver paste may be any of those described in connection with the solid electrolytic capacitor according to one aspect of the present invention.

[0130] In the silver layer forming step, the immersion time is usually 5 seconds to 1 minute, and preferably 10 to 30 seconds. The drying temperature is usually 30 to 200°C, and preferably 100 to 180°C. The drying time is usually 10 to 720 minutes, and preferably 30 to 360 minutes. As long as the desired silver layer is formed, the drying time may be 10 to 120 minutes, 30 to 90 minutes, or the like.

[0131] A solid electrolytic capacitor according to an aspect of the present invention can be used as a circuit element mounted on an electric / electronic circuit board, particularly as a circuit element mounted on an automobile or the like.

[0132] Production Example 1 (Production of Polyaniline Composite 1) 32.4 g of "Neocol SWC" (di-2-ethylhexyl sodium sulfosuccinate, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 13.3 g of aniline, and 0.9 g of "Sorbon T-20" (nonionic emulsifier having a polyoxyethylene sorbitan fatty acid ester structure, manufactured by Toho Chemical Industry Co., Ltd.) were placed in a 1,000 mL separable flask and dissolved in 320.4 g of toluene. 450 g of an 8.5 mass % aqueous phosphoric acid solution was added thereto, and the reaction liquid having two liquid phases, toluene and water, was stirred and cooled to an internal temperature of 5°C.

[0133] When the internal temperature of the reaction solution reached 5°C, a solution of 39.3 g of APS (ammonium persulfate) dissolved in 90.2 g of 8.5 wt% aqueous phosphoric acid solution was added using a dropping funnel while stirring the reaction solution, and the solution was stirred for 4 hours while maintaining the internal temperature at 5°C. After stirring was stopped, the contents were transferred to a separatory funnel, and the aqueous phase and toluene phase (organic phase) were allowed to stand and separated. After separation, the toluene phase (organic phase) was washed once with 180.3 g of 8.5 wt% aqueous phosphoric acid solution and five times with 328.0 g of ion-exchanged water to obtain a polyaniline complex toluene solution.

[0134] The solution was transferred to an evaporator, heated in a water bath at 60°C, and reduced pressure to evaporate and remove the volatile components, thereby obtaining Polyaniline Composite 1 (protonated polyaniline). The weight-average molecular weight (Mw) of the polyaniline in Polyaniline Composite 1 was 73,000.

[0135] The weight-average molecular weights of polyaniline in Polyaniline Composite 1 and Polyaniline Composite 2 (described later) were measured as follows. 1.65 to 1.85 g of lithium bromide was dissolved in 2000 mL of NMP (N-methyl-2-pyrrolidone) to prepare a 0.01 M lithium bromide NMP solution. 14 μL of triethylamine was added to 10 mL of this 0.01 M lithium bromide NMP solution, and the mixture was stirred to dissolve the mixture and obtain a homogeneous solution. 50 μL of the polyaniline composite toluene solution was then added dropwise, stirred, and mixed. The mixture was then passed through a 0.45 μM filter to prepare a sample for gel permeation chromatography (GPC) measurement.

[0136] Using a GPC measurement sample, GPC measurement was performed using a GPC column (Shodex KF-806M manufactured by Showa Denko K.K., two columns connected together) under the following measurement conditions: Solvent: NMP containing 0.01 M LiBr Flow rate: 0.70 mL / min Column temperature: 60°C Injection volume: 100 μL UV detection wavelength: 270 nM

[0137] The weight average molecular weight obtained by the above method is a value converted into polystyrene (PS). The doping ratio of the proton donor (sodium di-2-ethylhexyl sulfosuccinate) to polyaniline was 0.36.

[0138] Production Example 2 (Production of Polyaniline Composite 2) 10.13 g of "Neocol SWC" (di-2-ethylhexyl sodium sulfosuccinate, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 4.17 g of aniline, and 0.32 g of "Sorbon T-20" (nonionic emulsifier having a polyoxyethylene sorbitan fatty acid ester structure, manufactured by Toho Chemical Industry Co., Ltd.) were placed in a 1,000 mL separable flask and dissolved in 238.37 g of toluene. 353.70 g of a 17% by mass aqueous phosphoric acid solution was added thereto, and the reaction liquid having two liquid phases, toluene and water, was stirred and cooled until the internal temperature of the reaction liquid was −2° C.

[0139] When the internal temperature of the reaction solution reached -2°C, a solution of 12.3 g of APS (ammonium persulfate) dissolved in 48 g of 17% by mass aqueous phosphoric acid solution was added using a dropping funnel while stirring the reaction solution, and the solution was stirred for 18 hours while maintaining the internal temperature at -2°C. After stirring was stopped, the contents were transferred to a separatory funnel, and the aqueous phase and toluene phase (organic phase) were allowed to stand and separated. After separation, the toluene phase (organic phase) was washed once with 59.4 g of 8.5% by mass aqueous phosphoric acid solution and three times with 108.14 g of ion-exchanged water to obtain a polyaniline complex toluene solution.

[0140] This solution was transferred to an evaporator, heated in a water bath at 60°C, and reduced pressure to evaporate and remove the volatile components, thereby obtaining Polyaniline Composite 2 (protonated polyaniline). The weight-average molecular weight (Mw) of the polyaniline in Polyaniline Composite 2 was 112,000. The doping ratio of the proton donor (sodium di-2-ethylhexyl sulfosuccinate) to the polyaniline was 0.36.

[0141] Production Example 3 (Anode Body) Twenty pellet-shaped tantalum powder sintered compacts (1.71 mm x 3.01 mm x 2.89 mm porous bodies) made from tantalum powder having a specific capacity of 250,000 μFV / g were anodized by applying a voltage of up to 8.8 V in a 0.5% phosphoric acid electrolyte, forming a dielectric (tantalum oxide) on the surface of the tantalum powder sintered compact (porous body), thereby obtaining an anode body for a tantalum capacitor. The submerged capacitance of the anode body was measured using 10% by mass phosphoric acid as the electrolyte and a platinum black electrode as the counter electrode. The submerged capacitance of the anode body was 961 μF.

[0142] Example 1 (1) Preparation of Conductive Polymer Composition D (First Conductive Polymer Composition) for Forming First Conductive Layer 49 g of 1-propanol (component (b), boiling point 97°C, manufactured by Tokyo Chemical Industry Co., Ltd.), 49 g of p-tert-amylphenol (component (c), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 42 g of Kyowazole C900 (component (b), manufactured by KH Neochem Co., Ltd.) were mixed with stirring until homogeneous, to prepare mixed solvent α. 7 g of polyaniline composite 1 (component (a)) obtained in Production Example 1 was dissolved in 133 g of mixed solvent α, to obtain polyaniline composite solution A (polyaniline composite concentration: 5 mass %).

[0143] 10 g of 2-naphthalenesulfonic acid hydrate (component (d), manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 90 g of 1-propanol (component (b), boiling point 97°C, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to prepare a heat resistance stabilizer solution B. 20 g of BYK-4510 (component (e), manufactured by BYK Additives & Instruments) was dissolved in 100 g of mixed solvent α to prepare an adhesion-imparting solution C.

[0144] To 21 g of the polyaniline composite solution A (polyaniline composite concentration: 5% by mass), 0.237 g of the heat resistance stabilizer solution B and 0.105 g of the adhesion-imparting solution C were added and mixed with stirring, thereby obtaining a conductive polymer composition D (first conductive polymer composition) for forming a first conductive layer.

[0145] (2) Formation of Internal Solid Electrolyte Layer (First Conductive Layer) [First Immersion] The anode body obtained in Production Example 3 was fixed to a metal bar and hung, and the anode body was immersed in conductive polymer composition D up to one-third of its height from the bottom end and held for two minutes. Next, the anode body was immersed in conductive polymer composition D up to two-thirds of its height from the bottom end and held for two minutes. Next, the entire anode body was immersed in conductive polymer composition D and held for one minute. In this way, the first immersion of the anode body was completed. Next, the anode body was pulled out of conductive polymer composition D, and the entire anode body was held at room temperature for one minute while exposed to air.

[0146] [Second Immersion] Next, the anode body was immersed in conductive polymer composition D up to one-third of the height from the bottom end, and held for two minutes. Next, the anode body was immersed in conductive polymer composition D up to two-thirds of the height from the bottom end, and held for two minutes. Next, the entire anode body was immersed in conductive polymer composition D, and held for one minute. In this manner, the second immersion of the anode body was performed. Next, the anode body was pulled out of conductive polymer composition D, dried at 40°C for seven minutes, and then further dried at 140°C for five minutes, to form an internal solid electrolyte layer (first conductive layer).

[0147] (3) Preparation of Conductive Polymer Composition G (Second Conductive Polymer Composition) for Forming Second Conductive Layer 30 g of 1-ethoxy-2-propanol (component (b), manufactured by Tokyo Chemical Industry Co., Ltd.), 30 g of 1-propanol, and 40 g of p-tert-amylphenol were mixed with stirring until homogeneous, to prepare mixed solvent ε. 10 g of polyaniline composite 2 (component (a)) obtained in Production Example 2 was dissolved in 90 g of mixed solvent ε to obtain polyaniline composite solution E (polyaniline composite concentration: 10 mass %).

[0148] 20 g of BYK-4510 (component (e), manufactured by BYK Additives & Instruments) was dissolved in 100 g of mixed solvent ε to prepare an adhesion-imparting solution F. 0.564 g of heat resistance stabilizer solution B and 0.075 g of adhesion-imparting solution F were added to 7.5 g of polyaniline complex solution E (polyaniline complex concentration: 10 mass %) and mixed with stirring to obtain a conductive polymer composition G (second conductive polymer composition) for forming a second conductive layer.

[0149] (4) Formation of Outer Coating Layer (Second Conductive Layer) First, the anode body obtained in (3) above was immersed in a 4-sulfophthalic acid solution (4-sulfophthalic acid concentration: 1% by mass) prepared by dissolving 4-sulfophthalic acid (component (d), manufactured by Tokyo Chemical Industry Co., Ltd.) in isopropyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd.) and held for 10 minutes. Next, the anode body was pulled out of the 4-sulfophthalic acid solution and dried at 150°C for 60 minutes. Next, the anode body was immersed in a conductive polymer composition G for forming a second conductive layer and held for 5 minutes.

[0150] Next, the anode body was pulled out of the conductive polymer composition G and dried at 100° C. for a predetermined time of 30 to 60 minutes, and then further dried at 150° C. for a predetermined time of 30 to 60 minutes, thereby coating the exterior of the anode body. This step of immersing the anode body in the conductive polymer composition for forming the second conductive layer and drying it is called dipping, and dipping was performed once.

[0151] Next, the entire anode body was immersed in a 4-sulfophthalic acid solution (4-sulfophthalic acid concentration: 1% by mass) prepared by dissolving 4-sulfophthalic acid (component (d), manufactured by Tokyo Chemical Industry Co., Ltd.) in isopropyl alcohol, and held for 10 minutes. Next, the anode body was pulled out of the 4-sulfophthalic acid solution and dried at 150°C for 60 minutes to obtain an anode body having an inner solid electrolyte layer (first conductive layer) and an outer coating layer (second conductive layer).

[0152] (5) Formation of Carbon Layer The anode body (having the first conductive layer and the second conductive layer) obtained in (4) above was immersed in an undiluted carbon paste: FUAE (solvent: ketone-based, manufactured by Nippon Graphite Industries Co., Ltd.) for 10 seconds, and then dried at 150°C for 30 minutes.

[0153] (6) Formation of Silver Layer Next, a silver paste: H9113-6 (granular, manufactured by Namics Corporation) was diluted 1.2 times with a dilution solvent: diethylene glycol monobutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.), and the diluted solution was stirred and mixed to obtain a silver paste solution. In this solution, the anode element obtained in (5) above was immersed for 10 seconds, and then dried at 100°C for 30 minutes and further dried at 150°C for 30 minutes to obtain a capacitor.

[0154] <Evaluation of Electrical Properties> For the capacitors obtained above, the capacitance (Cap) and dielectric loss (tan δ) at a frequency of 120 Hz, as well as the equivalent series resistance (ESR) at a frequency of 100 kHz were measured before and after the heat treatment using an LCR meter "Precision LCR Meter E4980A" (manufactured by Agilent Technologies Japan, Ltd.). The evaluation results are shown in Table 1.

[0155] Example 2 A capacitor was manufactured and evaluated in the same manner as in Example 1, except that a carbon paste: TU10S (solvent: alcohol-based, manufactured by Asahi Chemical Research Institute Co., Ltd.) diluted 40 times with diethylene glycol monoethyl ether was used to form the carbon layer, and a silver paste: H9113-6 (granular, manufactured by Namics Corporation) diluted 1.2 times with a dilution solvent: diethylene glycol monobutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) was used to form the silver layer. The evaluation results are shown in Table 1.

[0156] A capacitor was manufactured and evaluated in the same manner as in Example 2, except that the silver layer was formed using silver paste H9480S (plate-shaped, manufactured by Namics Corporation) diluted 1.2 times with diethylene glycol monobutyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) as a dilution solvent. The evaluation results are shown in Table 1.

[0157] Example 4 A capacitor was manufactured and evaluated in the same manner as in Example 2, except that the silver layer was formed by diluting silver paste 4922N (plate-shaped, manufactured by DuPont) 1.5 times with a dilution solvent butyl acetate (manufactured by Tokyo Chemical Industry Co., Ltd.). The evaluation results are shown in Table 1.

[0158] Example 5 A capacitor was manufactured and evaluated in the same manner as in Example 1, except that the silver paste EC209A (granular and plate-shaped, manufactured by Mitsuboshi Belting Co., Ltd.) was diluted 1.1 times with a dilution solvent N-methylpyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd.) to form the silver layer. The evaluation results are shown in Table 1.

[0159] Comparative Example 1 A capacitor was produced and evaluated in the same manner as in Example 1, except that PEDOT / PSS (ethylene glycol-added product, manufactured by Sigma-Aldrich) was used without dilution as the second conductive polymer composition. The evaluation results are shown in Table 1.

[0160] Comparative Example 2 A capacitor was produced and evaluated in the same manner as in Example 3, except that PEDOT / PSS (ethylene glycol-added product, manufactured by Sigma-Aldrich) was used without dilution as the second conductive polymer composition. The evaluation results are shown in Table 1.

[0161]

[0162] The capacitors of Examples 1 to 5, which used a conductive polymer composition containing a polyaniline complex in the formation of the outer coating layer (second conductive layer), had superior dielectric loss (tan δ) and equivalent series resistance (ESR) compared to the capacitors of Comparative Examples 1 and 2, which used PEDOT / PSS.

[0163] The capacitors of Examples 1 and 2, which used granular silver paste to form the silver layer, had particularly excellent dielectric loss (tan δ) and equivalent series resistance (ESR) compared to the capacitors of Examples 3 and 4, which used plate-shaped silver paste.

[0164] The capacitor of Example 5, which used a combination of granular and plate-shaped silver pastes to form the silver layer, had particularly excellent dielectric loss (tan δ) and equivalent series resistance (ESR) compared to the capacitors of Examples 3 and 4, which used plate-shaped silver pastes.

[0165] The capacitor of Example 1, which used a carbon paste with a ketone-based solvent in forming the carbon paste layer, had better dielectric loss (tan δ) and equivalent series resistance (ESR) than the capacitors of Examples 2 to 4, which used carbon paste with an alcohol-based solvent.

[0166] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention. Accordingly, these numerous modifications are within the scope of the present invention. The contents of all documents cited in this specification and of the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims

1. A solid electrolytic capacitor comprising: a porous body made of a valve metal; a dielectric layer formed on the surface of the porous body; a first conductive layer covering the dielectric layer; a second conductive layer laminated on the first conductive layer; a carbon layer laminated on the second conductive layer; and a silver layer laminated on the carbon layer, wherein the first conductive layer comprises one or more selected from the group consisting of polyaniline, polyaniline derivatives, polythiophene, polythiophene derivatives, polypyrrole, and polypyrrole derivatives, and the second conductive layer comprises polyaniline or a polyaniline derivative.

2. The solid electrolytic capacitor according to claim 1, wherein said dielectric layer comprises an oxide of said valve metal.

3. The solid electrolytic capacitor of claim 1 or 2, wherein the first conductive layer comprises a polyaniline composite in which the polyaniline is doped with a proton donor.

4. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the second conductive layer comprises a polyaniline composite in which polyaniline is doped with a proton donor.

5. The solid electrolytic capacitor according to claim 3 or 4, wherein the polyaniline complex is a polyaniline complex doped with sulfosuccinic acid.

6. The solid electrolytic capacitor according to any one of claims 1 to 5, wherein the carbon layer is a layer formed using an organic solvent-based carbon paste.

7. The solid electrolytic capacitor according to claim 1, wherein the silver layer contains granular silver.

8. The solid electrolytic capacitor according to claim 1, wherein the valve metal is selected from the group consisting of aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony.

9. A method for producing a solid electrolytic capacitor, comprising the following steps (A-1) or (A-2) and (B) to (E): (A-1) A step of immersing a part or the whole of a porous body having an oxide of a valve metal in a first conductive polymer composition containing a conductive polymer and a solvent. (A-2) A step of immersing a part or the whole of a porous body having an oxide of a valve metal in a first conductive polymer composition containing a conductive polymer, a solvent, and a phenolic compound. (B) A step of removing the porous body from the first conductive polymer composition used in the step (A-1) or (A-2) and holding it at a temperature equal to or lower than the boiling point of the solvent contained in the first conductive polymer composition. (C) A step of immersing a part or the whole of the porous body after the step (B) in a second conductive polymer composition containing a conductive polymer and a solvent that are the same as or different from the first conductive polymer composition, and drying the second conductive polymer composition. (D) A step of immersing a part or the whole of the porous body after the step (C) in a liquid containing an organic solvent-based carbon paste, and drying the second conductive polymer composition. (E) A step of immersing a part or the whole of the porous body after the step (D) in a liquid containing a silver paste, and drying the second conductive polymer composition.

10. The method of making a solid electrolytic capacitor according to claim 9, wherein the first conductive polymer composition comprises a polyaniline composite in which polyaniline is doped with a proton donor.

11. The method for producing a solid electrolytic capacitor according to claim 9 or 10, wherein the second conductive polymer composition comprises a polyaniline complex in which polyaniline is doped with a proton donor.

12. The method for producing a solid electrolytic capacitor according to claim 10 or 11, wherein the polyaniline composite is a polyaniline composite doped with sulfosuccinic acid.

13. A solid electrolytic capacitor obtained by the method for producing a solid electrolytic capacitor according to any one of claims 9 to 12.

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