Solid electrolytic capacitor element and solid electrolytic capacitor

Abstract

A solid electrolytic capacitor comprising: an anode body; a dielectric layer formed on a surface of the anode body; a solid electrolyte layer covering at least a portion of the dielectric layer; and a cathode lead layer covering at least a portion of the solid electrolyte layer. The cathode lead layer comprises a carbon layer that contacts and covers at least a portion of the solid electrolyte layer. The carbon layer contains a carbonaceous material and a transition metal ion component. The content of the transition metal ion component in the carbon layer is 17,000 ppm by mass or less.

Description

Technical Field

[0001] The present invention relates to a solid electrolytic capacitor element and a solid electrolytic capacitor. Background Art

[0002] A solid electrolytic capacitor comprises a solid electrolytic capacitor element, a resin exterior or housing that seals the solid electrolytic capacitor element, and external electrodes electrically connected to the solid electrolytic capacitor element. The solid electrolytic capacitor element comprises an anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion that covers at least a portion of the dielectric layer. The cathode portion comprises a solid electrolyte layer comprising a conductive polymer that covers at least a portion of the dielectric layer, and a cathode lead layer that covers at least a portion of the solid electrolyte layer. The cathode lead layer comprises, for example, a carbon layer and a silver paste layer.

[0003] Patent Document 1 proposes a solid electrolytic capacitor including a carbon layer containing carbon particles and silicic acid and / or silicate.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-258526 Summary of the Invention

[0007] A solid electrolytic capacitor element according to one aspect of the present invention includes:

[0008] Anode,

[0009] a dielectric layer formed on the surface of the anode body,

[0010] a solid electrolyte layer covering at least a portion of the dielectric layer, and

[0011] a cathode lead layer covering at least a portion of the solid electrolyte layer,

[0012] The cathode lead layer includes a carbon layer that contacts the solid electrolyte layer and covers at least a portion of the solid electrolyte layer.

[0013] The carbon layer includes a carbonaceous material and a transition metal ion component, and a content of the transition metal ion component in the carbon layer is 17000 ppm by mass or less.

[0014] A solid electrolytic capacitor according to another aspect of the present invention includes at least one solid electrolytic capacitor element described above.

[0015] According to the present invention, the initial equivalent series resistance (ESR) of a solid electrolytic capacitor can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to one embodiment of the present invention. DETAILED DESCRIPTION

[0017] Before describing the embodiments, problems in the conventional technology will be briefly described below.

[0018] In a solid electrolytic capacitor, if air invades the interior, due to the action of moisture or oxygen contained in the air, the conductive polymer may be oxidatively degraded, or the dopant contained in the solid electrolyte layer may be decomposed, causing the solid electrolyte layer to degrade and the conductivity of the solid electrolyte layer to decrease. When the conductivity of the solid electrolyte layer is low, the initial performance of the solid electrolytic capacitor decreases (for example, ESR increases or electrostatic capacitance decreases). In addition, during the use of the solid electrolytic capacitor, the conductivity of the solid electrolyte layer decreases, resulting in an increase in ESR or a decrease in electrostatic capacitance, etc., which reduces the performance of the solid electrolytic capacitor. The deterioration of the solid electrolyte layer is particularly significant in a high-temperature environment. Solid electrolytic capacitors are sometimes used in a high-temperature environment depending on their use. In addition, solid electrolytic capacitors are generally soldered to the substrate through a reflow process exposed to high temperature. If the solid electrolytic capacitor is exposed to high temperature, the degradation of the solid electrolyte layer becomes significant, the reduction in conductivity becomes significant, and therefore, the reduction in capacitor performance easily becomes apparent.

[0019] In a solid electrolytic capacitor, a carbon layer is provided in a manner covering at least a portion of a solid electrolyte layer. The carbon layer is formed, for example, by applying a liquid or pasty dispersion obtained by dispersing a carbonaceous material in a liquid medium to the surface of the solid electrolyte layer and drying it. In order to obtain a dispersion in which the carbonaceous material is dispersed with high dispersibility, the dispersion is usually prepared by wet-pulverizing the carbonaceous material using a liquid medium and finely dispersing it in the liquid medium. Wet pulverization is generally performed using a bead mill using stainless steel beads. However, it has been shown that if stainless steel beads are used for wet pulverization, a large amount of transition metal ions are mixed into the dispersion and the formed carbon layer. Transition metal ions sometimes act as oxidants. It has been shown that the presence of transition metal ions contained in the dispersion and the carbon layer is a cause of oxidative degradation of the conductive polymer as described above.

[0020] In view of the above situation, for the solid electrolytic capacitor element in one aspect of the present invention, in the carbon layer comprising a carbonaceous material and a transition metal ion component, the content of the transition metal ion component in the carbon layer is controlled to be less than 17000 ppm on a mass basis. As a result, the initial ESR of the solid electrolytic capacitor can be suppressed to a lower level. In addition, even when a solid electrolytic capacitor is used and when the solid electrolytic capacitor is exposed to high temperature, the increase in ESR can be suppressed to a lower level. Thus, a solid electrolytic capacitor element and a solid electrolytic capacitor with excellent time stability and thermal stability are obtained. By improving their stability, the reliability of the solid electrolytic capacitor element and the solid electrolytic capacitor can be improved. It can be considered that the ability to suppress the ESR to a lower level is due to the fact that by reducing the oxidation reaction of the conductive polymer, the degradation of the solid electrolyte layer is reduced, and the high conductivity of the solid electrolyte layer can be ensured and maintained.

[0021] Hereinafter, the solid electrolytic capacitor and the solid electrolytic capacitor element (hereinafter sometimes simply referred to as a capacitor element) of the present invention will be described in more detail with reference to the drawings as needed.

[0022] [Solid electrolytic capacitors]

[0023] A solid electrolytic capacitor comprises one or more capacitor elements. It suffices that at least one of the capacitor elements in the solid electrolytic capacitor contain a carbon layer having a transition metal ion content within the aforementioned range. Preferably, at least 50% of the capacitor elements in the solid electrolytic capacitor contain carbon layers having a transition metal ion content within the aforementioned range, more preferably at least 75%, and even more preferably, all of the capacitor elements contain carbon layers having a transition metal ion content within the aforementioned range.

[0024] (Capacitor element)

[0025] (Anode)

[0026] The anode body may include: valve metal, alloy containing valve metal, and compound containing valve metal. These materials may be used alone or in combination of two or more. As valve metal, for example, aluminum, tantalum, niobium, and titanium are preferably used. The anode body having a porous surface is obtained, for example, by roughening the surface of a substrate (foil-shaped or plate-shaped substrate, etc.) containing valve metal by etching. Roughening can be performed, for example, by etching treatment. In addition, the anode body may be a molded body containing particles of valve metal or a sintered body thereof. It should be noted that the molded body and the sintered body have a porous structure as a whole.

[0027] (Dielectric layer)

[0028] The dielectric layer is an insulating layer formed to cover at least a portion of the surface of the anode body, functioning as a dielectric. The dielectric layer is formed by anodic oxidation of the valve-action metal on the surface of the anode body, using a chemical conversion process or the like. The dielectric layer can be formed so as to cover at least a portion of the anode body. The dielectric layer is typically formed on the surface of the anode body. Since the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner walls of the pores and pits on the surface of the anode body.

[0029] The dielectric layer contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. It should be noted that the dielectric layer is not limited to this, and any dielectric layer may function as a dielectric.

[0030] (Cathode)

[0031] The cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer. The cathode portion is typically formed on at least a portion of the surface of the anode body, with the dielectric layer interposed therebetween. The solid electrolyte layer and cathode extraction layer are described below.

[0032] (Solid electrolyte layer)

[0033] The solid electrolyte layer is formed on the surface of the anode body, covering the dielectric layer via the dielectric layer. The solid electrolyte layer does not necessarily cover the entire dielectric layer (the entire surface); it can be formed to cover at least a portion of the dielectric layer. The solid electrolyte layer constitutes at least a portion of the cathode portion of the solid electrolytic capacitor.

[0034] The solid electrolyte layer contains a conductive polymer and may further contain at least one of a dopant and an additive as needed.

[0035] As the conductive polymer, known conductive polymers used for solid electrolytic capacitors, such as π-conjugated conductive polymers, can be used. As conductive polymers, for example, polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene can be mentioned. Among these, polymers with a basic skeleton of polypyrrole, polythiophene, or polyaniline are preferred. The above-mentioned polymers also include homopolymers, copolymers of two or more monomers, and their derivatives (substituents with substituents, etc.). For example, polythiophene includes poly(3,4-ethylenedioxythiophene) and the like.

[0036] The conductive polymer may be used alone or in combination of two or more.

[0037] The weight average molecular weight (Mw) of the conductive polymer is not particularly limited, but is, for example, 1,000 or more and 1,000,000 or less.

[0038] In this specification, the weight average molecular weight (Mw) is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). GPC is generally measured using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as a mobile phase.

[0039] The solid electrolyte layer may further contain a dopant. As the dopant, for example, at least one selected from anions and polyanions is used.

[0040] Examples of anions include, but are not limited to, sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that generate sulfonate ions include benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid.

[0041] Examples of polyanions include polymeric polysulfonic acids and polymeric polycarboxylic acids. Examples of polymeric polysulfonic acids include polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylic acidsulfonic acid, and polymethacrylic acidsulfonic acid. Examples of polymeric polycarboxylic acids include polyacrylic acid and polymethacrylic acid. Polyanions also include polyestersulfonic acid and phenolsulfonic acid novolac resins. However, the polyanions are not limited thereto.

[0042] The dopant may be contained in the solid electrolyte layer in a free form, an anion form, or a salt form, or may be contained in a form bonded to or interacting with the conductive polymer.

[0043] The amount of the dopant contained in the solid electrolyte layer is, for example, 10 to 1000 parts by mass, or 20 to 500 parts by mass or 50 to 200 parts by mass relative to 100 parts by mass of the conductive polymer.

[0044] The solid electrolyte layer may be a single layer or may be composed of multiple layers. In the case of a multi-layered solid electrolyte layer, the conductive polymer contained in each layer may be the same or different. Furthermore, the dopant contained in each layer may be the same or different.

[0045] The solid electrolyte layer may further contain known additives and known conductive materials other than the conductive polymer as needed. Examples of such conductive materials include at least one selected from conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0046] Note that a layer for improving adhesion may be interposed between the dielectric layer and the solid electrolyte layer.

[0047] The solid electrolyte layer is formed, for example, by polymerizing the precursor on the dielectric layer using a treatment solution containing a precursor of a conductive polymer. The polymerization can be carried out by at least any method of chemical polymerization and electrolytic polymerization. As precursors of the conductive polymer, monomers, oligomers or prepolymers can be mentioned. The solid electrolyte layer can be formed by attaching a treatment solution (such as a dispersion or solution) containing a conductive polymer to the dielectric layer and drying it. As a dispersion medium (or solvent), for example, water, an organic solvent, or a mixture thereof can be mentioned. The treatment solution may also contain other components (selected from at least one of a dopant and an additive, etc.).

[0048] When a treatment liquid containing a precursor of a conductive polymer is used, an oxidant is used to polymerize the precursor. The oxidant can be contained in the treatment liquid in the form of an additive. In addition, the oxidant can be applied to the anode body before or after the treatment liquid is brought into contact with the anode body on which the dielectric layer is formed. As such an oxidant, sulfates, sulfonic acids or their salts can be exemplified. The oxidant can be used alone or in combination of two or more. As sulfates, for example, sulfuric acid such as ferric sulfate, sodium persulfate, and salts of sulfuric acids and metals such as persulfate can be cited. As metals constituting the salt, for example, alkali metals (sodium, potassium, etc.), iron, copper, chromium, zinc, etc. can be cited. In addition to the function as an oxidant, sulfonic acid or its salt also has the function as a dopant. As sulfonic acid or its salt, the low molecular weight sulfonic acid or its salt exemplified for the dopant is used.

[0049] The process of forming the solid electrolyte layer by immersing in the treatment solution and polymerizing (or drying) can be performed once or repeatedly. In each case, the composition and viscosity of the treatment solution can be kept the same, or at least one of the conditions can be changed.

[0050] (Cathode extraction layer)

[0051] The cathode extraction layer may comprise at least a carbon layer that contacts the solid electrolyte layer and covers at least a portion of the solid electrolyte layer. Alternatively, the cathode extraction layer may comprise a carbon layer and a metal-containing layer covering the carbon layer. Examples of the metal-containing layer include at least one selected from a layer containing metal powder and a metal foil. The provision of the metal-containing layer facilitates charge extraction from the solid electrolytic capacitor element.

[0052] (Carbon layer)

[0053] The carbon layer comprises a carbonaceous material and a transition metal ion component. The carbon layer may also contain conductive particles other than the carbonaceous material (e.g., metal powder). The content of the transition metal ion component in the carbon layer is less than 17000 ppm by mass. By controlling the content of the transition metal ion component to a low level in this way, the high conductivity of the solid electrolyte layer can be ensured, and the initial ESR of the solid electrolytic capacitor can be suppressed to a low level. As needed, the carbon layer may, for example, contain at least one selected from a polymer component and an additive.

[0054] The carbon layer is formed, for example, by coating a dispersion comprising the constituents of the carbon layer and a liquid medium in a manner that covers at least a portion of the surface of the solid electrolyte layer and drying it. Generally speaking, the dispersion is prepared by wet-grinding the constituents of the carbon layer (specifically, one selected from carbonaceous materials, adhesives used as needed, and additives, etc.) and the liquid medium using a bead mill. It is believed that during the wet grinding, the metal components (mainly transition metal components) contained in the constituent components of the bead mill (for example, containers, plates, beads) are mixed into the dispersion in the form of ions. The transition metal ion components contained in the carbon layer are mainly mixed in during the wet grinding. For the dispersion used for the formation of the carbon layer, for example, by using ceramic beads comprising zirconia beads as beads for wet grinding, or by removing the transition metal ion components from the dispersion obtained by wet grinding, the content of the transition metal ion components can be reduced. These methods can also be combined. The removal of the transition metal ion components can be carried out, for example, by contacting an ion exchanger with the dispersion.

[0055] As the transition metal ion component, for example, ions of metals belonging to Groups 3 to 11 of the periodic table can be cited. Specific examples of the transition metal ions contained in the transition metal ion component include: Group 4 metal ions (titanium ions, zirconium ions, etc.), Group 5 metal ions (vanadium ions, niobium ions, etc.), Group 6 metal ions (chromium ions, molybdenum ions, etc.), Group 7 metal ions (manganese ions, etc.), Group 8 metal ions (iron ions, etc.), Group 9 metal ions (cobalt ions, etc.), Group 10 metal ions (nickel ions, etc.), Group 11 metal ions (copper ions, etc.), etc. The transition metal ion component may also contain metal ions from Periods 4 to 6 of the periodic table, may contain metal ions from Periods 4 and 5, or may contain metal ions from Period 4. The transition metal ion component may contain one type of transition metal ion, but more often contains two or more types.

[0056] The valence of each ion of the transition metal ion component contained in the carbon layer is not particularly limited. The valence of each transition metal ion may be monovalent or divalent or higher.

[0057] The transition metal ion component may include at least one selected from iron ions, nickel ions, and copper ions. These ions easily act as oxidants and easily cause oxidative degradation of the conductive polymer. Therefore, when the transition metal ion component includes such ions, the effect of controlling the content of the transition metal ion component can be more significantly exerted.

[0058] The content of the transition metal ion component in the carbon layer can be 17000ppm or less on a mass basis, preferably 15000ppm or less, or 10000ppm or less, or 5000ppm or less. When the content of the transition metal ion component is within this range, the initial ESR of the solid electrolytic capacitor can be suppressed to a relatively low level. In addition, even when the solid electrolytic capacitor is used for a long time or is exposed to high temperatures, the increase in ESR can be greatly reduced. The lower the content of the transition metal ion component in the carbon layer, the better, but it is difficult to set it to 0ppm. Therefore, the content of the transition metal ion component in the carbon layer is usually more than 0ppm on a mass basis.

[0059] From the perspective of suppressing the initial ESR and the increase in ESR to a low level, the iron ion content in the carbon layer is more preferably 5000 ppm or less, and even more preferably 4000 ppm or less, on a mass basis. In addition, if the iron ion content in the carbon layer (mass basis) is set to 1500 ppm or less or 1000 ppm or less (preferably 800 ppm or less), the initial ESR can be suppressed to a lower level, and even when the solid electrolytic capacitor is used for a long time or exposed to high temperatures, the increase in ESR can be further reduced.

[0060] From the perspective of suppressing the initial ESR and ESR increase to a low level, the nickel ion content in the carbon layer is more preferably 5000 ppm by mass or less, and even more preferably 4500 ppm or less. If the nickel ion content (by mass) in the carbon layer is 2500 ppm or less or 2000 ppm or less, the initial ESR can be suppressed to a lower level, and even when the solid electrolytic capacitor is used for a long time or exposed to high temperatures, the increase in ESR can be further reduced.

[0061] From the perspective of suppressing the initial ESR and the increase in ESR to a low level, the copper ion content in the carbon layer is more preferably 150 ppm or less, and even more preferably 100 ppm or less, on a mass basis. Furthermore, if the copper ion content (mass basis) in the carbon layer is 30 ppm or less or 15 ppm or less (preferably 10 ppm or less), the initial ESR can be suppressed to a lower level, and even when the solid electrolytic capacitor is used for a long time or exposed to high temperatures, the increase in ESR can be further reduced.

[0062] Typical metal ions are sometimes mixed into the carbon layer. Among the typical metal ions, there are also ions that promote the conduction of side reactions in the carbon layer and its vicinity (solid electrolyte layer, etc.). Therefore, from the perspective of maintaining high conductivity of the solid electrolyte layer, carbon layer, etc., it is preferred that the content of typical metal ions in the carbon layer is also small. Examples of such typical metal ions include ions of metals of Group 12 of the periodic table (zinc ions, etc.). The carbon layer may contain one such metal ion, or may contain two or more.

[0063] The total content of typical metal ions (such as metal ions of Group 12 of the periodic table) such as zinc ions in the carbon layer is preferably less than 15 ppm by mass, preferably less than 14 ppm, and may be less than 12 ppm. When the content of typical metal ions is within this range, it is easy to maintain higher conductivity of the solid electrolyte layer, carbon layer, etc. The content of such typical metal ions is usually more than 0 ppm by mass.

[0064] When determining the content of metal ions in the carbon layer of the solid electrolytic capacitor element, the content can be determined by the following method.

[0065] A solid electrolytic capacitor is embedded in a curable resin to produce a sample by curing the curable resin. The sample is subjected to grinding, milling, and other treatments to expose the carbon layer on the capacitor element. The surface of the exposed carbon layer is analyzed by energy dispersive X-ray spectroscopy (EDX) and qualitative analysis to confirm the presence of transition metal ions. If the carbon layer is confirmed to contain transition metal ions, the carbon layer is scraped off, a predetermined amount of sample (sample A) is taken, and the mass (m0) is measured. Sample A is mixed with a 1.0% by mass aqueous nitric acid solution and left at room temperature (20°C to 35°C) for one day. The resulting mixture (sample B) is centrifuged to separate into a solid (sample C) and a liquid (sample D). Using the separated liquid, sample D, high-frequency inductively coupled plasma (ICP) emission spectroscopy is used to determine the concentration of metal ions contained in sample B. The content of each metal ion in the carbon layer is determined based on this concentration and the mass m0. For ICP emission spectrometry, for example, Optima 5300DV manufactured by Perkin Elmer is used.

[0066] It should be noted that sample A is obtained by removing the metal-containing layer to expose the carbon layer, but in order to eliminate the influence of the metal contained in the metal-containing layer, when calculating the content of metal ions in the carbon layer, the concentration can also be calculated based on the ions of metal species other than the metal contained in the metal-containing layer (for example, silver).

[0067] As the carbonaceous material, a conductive carbonaceous material can generally be used. Examples of the carbonaceous material include graphite (artificial graphite, natural graphite, vapor-grown carbon, etc.), carbon black, and amorphous carbon. The carbon layer may comprise one carbonaceous material or two or more. The carbonaceous material may be in the form of particles or fibers, but preferably comprises at least particles.

[0068] The dispersion used to form the carbon layer is prepared by wet grinding using a bead mill. Therefore, the carbon layer contains a ground carbonaceous material. Such a carbonaceous material includes, for example, ground particles having a relatively small average particle size. The average particle size of such particles is, for example, less than 10 μm, or less than 5 μm, or less than 1.5 μm or less than 1 μm. When the carbonaceous material of the carbon layer contains particles having such an average particle size, conductive paths are easily formed between the particles, and high conductivity of the carbon layer can be obtained, thereby suppressing the initial ESR to a lower level. In addition, even if the solid electrolytic capacitor is used for a long time or exposed to high temperatures, the high conductivity of the carbon layer can be maintained, thereby easily ensuring the high reliability of the solid electrolytic capacitor element and the solid electrolytic capacitor. The lower limit of the average particle size of the above-mentioned particles is not particularly limited, and can be determined so that the volume resistance value of the carbon layer is, for example, less than 1.0 Ω·cm.

[0069] It should be noted that the above-mentioned average particle size refers to the 50% particle size (median diameter) accumulated in the volume-based particle size distribution measured by a particle size distribution measuring device using a dynamic light scattering method or a laser diffraction / scattering method. For example, when the average particle size is less than 10 μm, a particle size distribution measuring device using a dynamic light scattering method is used, and when the average particle size exceeds 10 μm, a particle size distribution measuring device using a laser diffraction / scattering method is used. As a particle size distribution measuring device based on a dynamic light scattering method, for example, a light scattering photometer DLS-8000 manufactured by Otsuka Electronics Co., Ltd. is used. As a particle size distribution measuring device using a laser diffraction / scattering method, for example, MT3200II manufactured by Microtrac is used.

[0070] When the above-mentioned average particle size is determined for a carbonaceous material taken from the carbon layer of a solid electrolytic capacitor element, a dispersion containing a sample E obtained by the following method is used as a sample for measuring the average particle size. First, the above-mentioned solid sample C is washed with water, cleaned with an organic solvent and dried to obtain a carbonaceous material (sample E). As an organic solvent, for example, an organic solvent that can dissolve high molecular components that cannot be removed by water washing can be selected from the organic solvents exemplified as organic liquid media for wet pulverization described later. The sample E is dispersed in a liquid dispersion medium using a surfactant to prepare a dispersion for measurement. As a dispersion medium, for example, pure water or an organic medium that is liquid at room temperature (for example, 20°C to 35°C) is used. The type and concentration of the surfactant, the type of the dispersion medium, and the concentration of the sample E in the dispersion can be selected within the range that can prepare a dispersion suitable for the measurement of the average particle size.

[0071] The polymer component contained in the carbon layer may be hydrophilic (for example, water-soluble or water-dispersible) or hydrophobic. The polymer component may include one type of polymer or two or more types of polymers.

[0072] As the hydrophilic polymer component, for example, there can be mentioned: a polymer containing at least one hydrophilic group selected from an acid group and a hydroxyl group (hereinafter sometimes referred to as the first polymer). Among them, the first polymer having an anionic group such as an acid group and a phenolic hydroxyl group is preferred. As the acid group, a sulfonic group, a carboxyl group, etc. can be mentioned. In the case of using an aqueous dispersion to form the carbon layer, from the viewpoint of easily ensuring high dispersibility, the first polymer preferably has a plurality of hydrophilic groups (particularly a plurality of anionic groups). As the hydrophilic polymer component, it is preferred to use a first polymer having at least an acid group, and it is also possible to use a first polymer having an acid group and a hydroxyl group.

[0073] It should be noted that, in the carbon layer, the acid groups of the polymer may be contained in a free form, in an anionic form, in a salt form, or in a state of interacting or bonding with the components contained in the carbon layer or the solid electrolyte layer. In this specification, all of the above-mentioned acid groups are sometimes included and simply referred to as "acid groups". In addition, in the carbon layer, the hydroxyl groups of the polymer may be contained in a free form, in an anionic form, or in a state of interacting or bonding with the components contained in the carbon layer or the solid electrolyte layer. In this specification, all of the above-mentioned hydroxyl groups are included and simply referred to as "hydroxyl groups". In addition, the same is true for anionic groups. In some cases, all of the anionic groups in the free form, the anionic form, the salt form, and the state of interacting or bonding with the components contained in the carbon layer or the solid electrolyte layer are included and simply referred to as "anionic groups".

[0074] The carbon layer may contain one type of first polymer, or may contain two or more types.

[0075] If a polymer anion comprising a monomer unit having an anionic group is used as the first polymer, the effect of suppressing dedoping from the solid electrolyte layer is improved. Therefore, even when the solid electrolytic capacitor is used for a long time or the solid electrolytic capacitor is exposed to high temperature, the high conductivity of the solid electrolyte layer can be maintained, and the increase in ESR can be suppressed to a lower level. Such a polymer anion is sometimes referred to as polymer 1A. As polymer 1A, a homopolymer having a monomer unit having an anionic group, a copolymer comprising two or more monomer units having anionic groups, a copolymer of a monomer unit having anionic groups and other copolymerizable monomers, etc. can be cited. The monomer unit with anionic groups can be aliphatic, or it can have at least one ring selected from aliphatic rings, aromatic rings, and heterocycles. The polymer component can include one polymer 1A or two or more.

[0076] Examples of polymer anions having a sulfonic group include polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylic acidsulfonic acid, polymethacrylic acidsulfonic acid, poly(2-acrylamide-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyestersulfonic acid, and phenolsulfonic acid novolac resins. Examples of polymer anions having a carboxyl group include copolymers using polyacrylic acid, polymethacrylic acid, and at least one of acrylic acid and methacrylic acid. Copolymers also include copolymers of at least one of acrylic acid and methacrylic acid with at least one of an acrylic acid ester and a methacrylic acid ester (such as methyl acrylate and methyl methacrylate). However, the polymer anions are not limited to these. These polymer anions are generally water-soluble.

[0077] As the first polymer, water-soluble cellulose derivatives, saponified products of polyvinyl acetate (partially saponified products, polyvinyl alcohol, etc.) are also preferred. Examples of water-soluble cellulose derivatives include cellulose ether compounds. Examples of cellulose ether compounds include carboxymethyl cellulose salts (sodium salts, potassium salts, and other alkali metal salts, ammonium salts, etc.), hydroxyethyl cellulose, and hydroxypropyl methyl cellulose. These first polymers are sometimes referred to as polymer 1B. Polymer 1B easily forms hydrogen bonds with organic molecules (specifically, polymers) contained in the carbon layer, making it easy to adopt a compact structure. Therefore, since there is little space for gases such as oxygen to diffuse within the polymer component, gases are not easy to penetrate. Therefore, when the polymer component contains polymer 1B, the oxygen barrier properties of the carbon layer can be improved, and the adhesion between the solid electrolyte layer and the carbon layer and the adhesion between the carbonaceous materials can be improved. As a result, oxidative degradation of the conductive polymer can be reduced, making it easy to maintain the conductivity of the solid electrolyte layer. In addition, if polymer 1B is used, a moderate thickening effect can be obtained, thereby easily improving the dispersibility of the constituent components in the dispersion. The polymer component may include one type of polymer 1B or two or more types. The polymer component may include polymer 1A and polymer 1B.

[0078] The weight average molecular weight Mw of the first polymer is, for example, 2,000 or more and 1,000,000 or less.

[0079] As polymers other than the first polymer, for example, fluororesins, acrylic resins (polyacrylates, etc.), polyester resins, polyurethane resins, vinyl resins (polyvinyl acetate, etc.), polyolefin resins, rubber-like materials (for example, styrene-butadiene copolymer rubber (SBR)), epoxy resins. As fluororesins, for example, vinylidene fluoride resins (polyvinylidene fluoride, vinylidene fluoride copolymers, etc.), fluorinated olefin resins (polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-ethylene copolymers, etc.) are mentioned. Such polymers are sometimes referred to as second polymers. The polymer component may include one second polymer or two or more. As needed, the polymer component may include the first polymer and the second polymer. The second polymer acts as a binder. In the second polymer, if a fluororesin is used, the adhesion of the dispersion to the solid electrolyte layer can be improved, and therefore, the adhesion of the solid electrolyte layer to the carbon layer can be improved. In addition, if a fluororesin is used, the dispersibility of the constituents in the dispersion is easily improved.

[0080] The second macromolecule is not easily soluble in water, usually with organic liquid medium combination and prepare dispersion.But, be not limited to this situation, as required, in the preparation of the dispersion comprising the second macromolecule, also can use the mixed medium of water or water and organic liquid medium.The second macromolecule can be thermoplastic resin, also can be curable resin (thermosetting resin, light-curable resin etc.).For curable resin, monomer component can be used as liquid medium.Polymer component can comprise a kind of second macromolecule, also can comprise two or more.

[0081] The content of the polymer component in the carbon layer can be selected from a wide range of, for example, 0.1 to 5000 parts by mass, or 0.5 to 1000 parts by mass, relative to 100 parts by mass of the carbonaceous material.

[0082] Relative to carbonaceous material 100 mass parts, the amount of the first macromolecular is, for example, more than 1 mass part and less than 5000 mass parts, can also be more than 2 mass parts and less than 1000 mass parts, can also be more than 10 mass parts and less than 100 mass parts.From the viewpoint of easily ensuring operability, relative to carbonaceous material 100 mass parts, the amount of macromolecular 1B is preferably less than 10 mass parts. In addition, when macromolecular component includes macromolecular 1A and macromolecular 1B, relative to macromolecular 1A 100 mass parts, the amount of macromolecular 1B is, for example, more than 5 mass parts and less than 50 mass parts, can also be more than 5 mass parts and less than 35 mass parts.

[0083] The content of the second polymer in the carbon layer relative to 100 parts by mass of the carbonaceous material is, for example, 10 parts by mass or less, 0.1 parts by mass to 10 parts by mass or less, or 0.5 parts by mass to 5 parts by mass or less.

[0084] Examples of additives included in the carbon layer include, but are not limited to, at least one selected from an aromatic compound having a sulfonic acid group, a thickener, a surface conditioner, and a surfactant. It should be noted that when the carbon layer includes an aromatic compound having a sulfonic acid group, the adhesion between the solid electrolyte layer and the carbon layer can be further improved, and dedoping in the solid electrolyte layer can be reduced.

[0085] Examples of aromatic compounds having sulfonic acid groups include aromatic sulfonic acids. In addition to the sulfonic acid group, the aromatic sulfonic acid may have at least one selected from a hydroxyl group and a carboxyl group. In the carbon layer, the sulfonic acid group, carboxyl group, and hydroxyl group of the aromatic compound may be present in any of the forms described for the polymer component.

[0086] As aromatic sulfonic acids, for example, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, butylnaphthalenesulfonic acid, phenolsulfonic acid, sulfosalicylic acid, hydroquinonesulfonic acid, hydroquinonedisulfonic acid, catecholsulfonic acid, catecholdisulfonic acid, pyrogallolsulfonic acid, pyrogalloldisulfonic acid, or salts thereof (for example, alkali metal salts (sodium salts, potassium salts, etc.)). Aromatic compounds having sulfonic acid groups also include condensates formed from aldehyde compounds of aromatic sulfonic acids (formaldehyde or its polymers (trioxane, etc.)). Specific examples of condensates include phenolsulfonic acid formaldehyde condensates, naphthalenesulfonic acid formaldehyde condensates, arylphenolsulfonic acid formaldehyde condensates, anthraquinonesulfonic acid formaldehyde condensates, or salts thereof (for example, alkali metal salts (sodium salts, potassium salts, etc.)). However, aromatic compounds having sulfonic acid groups are not limited to these.

[0087] The carbon layer may contain one type of aromatic compound having a sulfonic acid group, or may contain two or more types.

[0088] In the carbon layer, the amount of the aromatic compound having a sulfonic acid group is, for example, 4 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the carbonaceous material.

[0089] The thickness of the carbon layer may be, for example, 0.1 μm to 100 μm, 0.5 μm to 50 μm, or 1 μm to 20 μm.

[0090] As the ceramic bead for wet grinding during the preparation dispersion, zirconium oxide beads, zirconium oxide / silicon dioxide-based ceramic beads, titanium dioxide beads, aluminum oxide beads, sialon beads, silicon nitride beads etc. can be enumerated. The surface of the ceramic bead is smooth, and is not easy to damage the container, the dish etc. of mill, and is favourable for reducing the metal ion composition to be mixed into the dispersion. It should be noted that, sometimes in the ceramic bead, comprise the metal components such as transition metal, even if the constituent components of the ceramic bead are mixed into dispersion, in terms of the content of metal ion composition, compared with the situation of using stainless steel bead, also very few.

[0091] As an ion exchanger for removing ions from the dispersion, for example, an inorganic exchanger can be used, but by using an ion exchange resin (cation exchange resin, etc.), the content of the transition metal ion component can be easily reduced. If necessary, an inorganic ion exchanger and an ion exchange resin can be used in combination.

[0092] Wet grinding uses a liquid medium. Examples of the liquid medium include water, an organic liquid medium, a mixture of water and an organic liquid medium (a water-soluble organic liquid medium, etc.). It should be noted that the liquid medium only needs to have fluidity at room temperature (a temperature of 20°C or more and 35°C or less). Examples of the organic liquid medium include alcohols (e.g., ethanol, 2-propanol), ethers (e.g., diethyl ether, tetrahydrofuran), ketones (acetone, etc.), nitriles (acetonitrile, etc.), sulfoxides (dimethyl sulfoxide, etc.), and N-methyl-2-pyrrolidone. One organic liquid medium may be used alone, or two or more may be used in combination.

[0093] The carbon layer can be formed by immersing the anode body having the dielectric layer formed with the solid electrolyte layer in a liquid dispersion, or by applying a paste-like dispersion on the surface of the solid electrolyte layer and drying it.

[0094] (including metal layer)

[0095] Among the metal-containing layers, a layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the carbon layer. Such a metal-containing layer can be formed, for example, by using a metal paste layer formed using a composition containing metal powder such as silver particles and a resin (binder resin). The resin can be a thermoplastic resin, but preferably a thermosetting resin such as an imide resin or an epoxy resin is used.

[0096] In the metal-containing layer, the type of metal constituting the metal foil is not particularly limited, but valve metals such as aluminum, tantalum, and niobium, or alloys containing valve metals, are preferably used. The surface of the metal foil can be roughened by etching or the like as needed. A chemical conversion film can be provided on the surface of the metal foil, and a film of a metal different from the metal constituting the metal foil (dissimilar metal) or a non-metallic film can be provided. Examples of dissimilar metals include metals such as titanium. Examples of non-metallic materials include carbon (conductive carbonaceous materials, etc.).

[0097] The thickness of the metal-containing layer is, for example, 0.1 μm to 100 μm, may be 0.5 μm to 50 μm, or may be 1 μm to 20 μm.

[0098] (other)

[0099] Solid electrolytic capacitors can be wound, sheet, or laminated. For example, a solid electrolytic capacitor can include a laminate of two or more capacitor elements. The configuration of the capacitor elements can be selected based on the type of solid electrolytic capacitor.

[0100] In the capacitor element, one end of the cathode terminal is electrically connected to the cathode lead layer. For example, the cathode terminal is coated with a conductive adhesive on the cathode layer and bonded to the cathode layer via the conductive adhesive. One end of the anode terminal is electrically connected to the anode body. The other end of the anode terminal and the other end of the cathode terminal are each drawn out from the resin outer casing or housing. The other end of each terminal exposed from the resin outer casing or housing is used for connection to solder, etc., on the substrate to be mounted on the solid electrolytic capacitor.

[0101] The capacitor element is sealed using a resin outer body or a housing. For example, the material resin of the capacitor element and the outer body (for example, an uncured thermosetting resin and a filler) can be housed in a mold, and the capacitor element can be sealed with a resin outer body by transfer molding, compression molding, etc. At this time, the portion of the other end side of the anode terminal and the cathode terminal connected to the anode lead drawn out from the capacitor element is exposed from the mold. In addition, by housing the capacitor element in a bottomed housing in a manner such that the portion of the other end side of the anode terminal and the cathode terminal is located on the opening side of the bottomed housing, the opening of the bottomed housing is sealed with a sealant, thereby forming a solid electrolytic capacitor.

[0102] Figure 1 1 is a cross-sectional view schematically showing the structure of a solid electrolytic capacitor according to one embodiment of the present invention. Figure 1 As shown, solid electrolytic capacitor 1 includes capacitor element 2, resin outer casing 3 that seals capacitor element 2, and anode terminal 4 and cathode terminal 5, at least a portion of each of which is exposed outside resin outer casing 3. Anode terminal 4 and cathode terminal 5 can be made of metal such as copper or a copper alloy. Resin outer casing 3 has a generally rectangular parallelepiped shape, and solid electrolytic capacitor 1 also has a generally rectangular parallelepiped shape.

[0103] Capacitor element 2 includes an anode body 6, a dielectric layer 7 covering anode body 6, and a cathode body 8 covering dielectric layer 7. Cathode body 8 includes a solid electrolyte layer 9 covering dielectric layer 7 and a cathode lead layer 10 covering solid electrolyte layer 9, constituting the aforementioned cathode portion. In the illustrated example, cathode lead layer 10 includes a carbon layer 11 and a metal paste layer 12 serving as a metal-containing layer. According to the present invention, the content of transition metal ion components in carbon layer 11 is low. This suppresses oxidative degradation of the conductive polymer, thereby suppressing a decrease in the conductivity of the solid electrolyte layer. Consequently, the initial ESR of the solid electrolytic capacitor can be kept low.

[0104] Anode body 6 includes a region facing cathode body 8 and a region not facing cathode body 8. In the region not facing cathode body 8, an insulating separator layer 13 is formed adjacent to cathode body 8, covering the surface of anode body 6 in a stripe shape, thereby limiting contact between cathode bodies 8. In the region not facing cathode body 8, a portion of anode body 6 is electrically connected to anode terminal 4 by welding. Cathode terminal 5 is electrically connected to cathode body 8 via adhesive layer 14 formed of a conductive adhesive.

[0105] Example

[0106] Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0107] Solid Electrolytic Capacitor E1

[0108] According to the following points, make Figure 1 The solid electrolytic capacitor 1 (solid electrolytic capacitor E1) shown in FIG.

[0109] (1) Preparation of anode body 6

[0110] Anode body 6 was produced by roughening the surfaces of both sides of an aluminum foil (thickness: 100 μm) serving as a base material by etching.

[0111] (2) Formation of dielectric layer 7

[0112] The other end portion of anode body 6 was immersed in a chemical conversion solution, and a DC voltage of 70 V was applied for 20 minutes to form dielectric layer 7 containing aluminum oxide.

[0113] (3) Formation of Solid Electrolyte Layer 9

[0114] An aqueous solution containing a pyrrole monomer and p-toluenesulfonic acid was prepared. The monomer concentration in the aqueous solution was set to 0.5 mol / L, and the p-toluenesulfonic acid concentration was set to 0.3 mol / L.

[0115] Anode body 6 having dielectric layer 7 formed in (2) above and counter electrode were immersed in the obtained aqueous solution, and electrolytic polymerization was performed at 25° C. at a polymerization voltage of 3 V (polymerization potential relative to a silver reference electrode) to form solid electrolyte layer 9 .

[0116] (4) Formation of cathode body 8

[0117] A liquid dispersion was prepared by wet-milling graphite particles (a carbonaceous material) and a dispersant (e.g., a cellulose derivative) with water using a bead mill (manufactured by Nippon Coke & Engineering Co., Ltd., SC Mill). Zirconia beads were used as the beads. The mass ratio of graphite particles to dispersant was set at 100:50.

[0118] The anode body 6 having the solid electrolyte layer 9 formed thereon obtained in (3) is immersed in the liquid dispersion, removed from the dispersion, and then dried to form a carbon layer 11 at least on the surface of the solid electrolyte layer 9. Drying is performed at 150-200°C for 10-30 minutes.

[0119] Next, a silver paste containing silver particles and a binder resin (epoxy resin) is applied to the surface of the carbon layer 11 and heated at 150 to 200° C. for 10 to 60 minutes to cure the binder resin, thereby forming a metal paste layer 12. In this manner, a cathode body 8 including the carbon layer 11 and the metal paste layer 12 is formed.

[0120] Capacitor element 2 is produced as described above.

[0121] (5) Assembly of Solid Electrolytic Capacitor 1

[0122] Cathode body 8 of capacitor element 2 obtained in (4) above is joined to one end of cathode terminal 5 via conductive adhesive layer 14. One end of anode body 6 protruding from capacitor element 2 is joined to one end of anode terminal 4 by laser welding.

[0123] Next, resin sheath 3 made of insulating resin is formed by die molding around capacitor element 2 . The other end of anode terminal 4 and the other end of cathode terminal 5 are drawn out of resin sheath 3 .

[0124] In this way, a solid electrolytic capacitor was completed. A total of 20 solid electrolytic capacitors were produced in the same manner as above.

[0125] (6) Evaluation

[0126] The following evaluations were performed using a solid electrolytic capacitor.

[0127] (a) Determination of metal ion content in the carbon layer

[0128] The metal ion content in the carbon layer was measured by the above-mentioned method.

[0129] (b) ESR measurement

[0130] The ESR of the solid electrolytic capacitor was measured by the following method.

[0131] The initial ESR (mΩ) of each solid electrolytic capacitor was measured at a frequency of 100 kHz using a four-terminal LCR meter at 20° C. The average value (initial ESR) of the 20 solid electrolytic capacitors was calculated.

[0132] Next, an accelerated test was performed on the solid electrolytic capacitors by applying the rated voltage for 500 hours at 145°C. The ESR was then measured at 20°C using the same procedure as for the initial ESR, and the average value of 20 solid electrolytic capacitors (ESR after the accelerated test) was calculated.

[0133] Solid Electrolytic Capacitor E2

[0134] In the formation (4) of the cathode body 8 of the solid electrolytic capacitor E1, a strip of cation exchange resin was added to the obtained liquid dispersion, mixed for 1 hour, and then the cation exchange resin was removed. In this way, a liquid dispersion was prepared. A solid electrolytic capacitor 1 (solid electrolytic capacitor E2) was produced in the same manner as in the case of the solid electrolytic capacitor E1, except that the obtained liquid dispersion was used, and evaluation was performed.

[0135] 《Solid Electrolytic Capacitor C1》

[0136] In the formation (4) of the cathode body 8 of the solid electrolytic capacitor E1, stainless steel beads were used as beads. A solid electrolytic capacitor C1 was produced and evaluated in the same manner as in the case of the solid electrolytic capacitor E1 except for this.

[0137] The results of the initial ESR and the ESR after the 500-hour accelerated test of the produced solid electrolytic capacitor are shown in Table 1. The ESR is expressed as a relative value when the initial ESR of the solid electrolytic capacitor E1 is set to 1.

[0138] [Table 1]

[0139]

[0140] Industrial applicability

[0141] According to the present invention, the initial ESR of a solid electrolytic capacitor can be suppressed to a low level. Furthermore, the increase in ESR during long-term use or when the solid electrolytic capacitor is exposed to high temperatures can be suppressed to a low level. Consequently, solid electrolytic capacitor elements and solid electrolytic capacitors can be used in a variety of applications requiring high reliability.

[0142] Description of Reference Numerals

[0143] 1: Solid electrolytic capacitor, 2: Capacitor element, 3: Resin housing, 4: Anode terminal, 5: Cathode terminal, 6: Anode body, 7: Dielectric layer, 8: Cathode body, 9: Solid electrolyte layer, 10: Cathode lead layer, 11: Carbon layer, 12: Metal paste layer, 13: Separator layer, 14: Adhesive layer.

Claims

1. A solid electrolytic capacitor element comprising: Anode, a dielectric layer formed on the surface of the anode body, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode lead layer covering at least a portion of the solid electrolyte layer, The cathode lead layer includes a carbon layer, the carbon layer is in contact with the solid electrolyte layer and covers at least a portion of the solid electrolyte layer. The carbon layer comprises carbonaceous material and transition metal ion components, The content of the transition metal ion component in the carbon layer is 17000 ppm by mass or less.

2. The solid electrolytic capacitor element according to claim 1, wherein The transition metal ion component comprises iron ions, The content of the iron ions in the carbon layer is 5000 ppm by mass or less.

3. The solid electrolytic capacitor element according to claim 1 or 2, wherein: The transition metal ion component comprises nickel ions, The content of the nickel ions in the carbon layer is 5000 ppm by mass or less.

4. The solid electrolytic capacitor element according to claim 1 or 2, wherein: The transition metal ion component comprises copper ions, The content of the copper ions in the carbon layer is 150 ppm by mass or less.

5. The solid electrolytic capacitor element according to claim 1 or 2, wherein The carbonaceous material includes particles having an average particle size of 10 μm or less.

6. The solid electrolytic capacitor element according to claim 1 or 2, wherein: The carbon layer includes a polymer having at least one selected from an acid group and a hydroxyl group.

7. The solid electrolytic capacitor element according to claim 1 or 2, wherein: The carbon layer contains a fluororesin. 8 . A solid electrolytic capacitor comprising at least one solid electrolytic capacitor element according to claim 1 .

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