Carbon paste for solid electrolytic capacitor, solid electrolytic capacitor element, and solid electrolytic capacitor

Abstract

The invention provides a carbon paste for a solid electrolytic capacitor, a solid electrolytic capacitor element, and a solid electrolytic capacitor. A carbon paste for a solid electrolytic capacitor includes first carbon particles having an average primary particle diameter of 40 nm or more and 100 nm or less. The ratio of the first carbon particles in the dry solid content is from 25% by volume to 75% by volume (inclusive).

Description

[0001] This application is a divisional application of National Application No. 202180072892.4 (International Application No. PCT / JP2021 / 039263), which entered the Chinese national phase on April 25, 2023, and is entitled "Carbon paste for solid electrolytic capacitors, solid electrolytic capacitor elements and solid electrolytic capacitors". Technical Field

[0002] This application relates to carbon paste for solid electrolytic capacitors, solid electrolytic capacitor elements, and solid electrolytic capacitors. Background Technology

[0003] A solid electrolytic capacitor comprises a solid electrolytic capacitor element and a resin outer casing or shell that seals the solid electrolytic capacitor element. The solid electrolytic capacitor element comprises a capacitor base element including an anode and a solid electrolyte layer, and a cathode. More specifically, the capacitor base element comprises at least an anode, a dielectric layer formed on the surface of the anode, and a solid electrolyte layer containing conductive polymer components covering at least a portion of the dielectric layer. The capacitor base element may also include a carbon layer covering at least a portion of the solid electrolyte layer.

[0004] Patent Document 1 discloses a solid electrolytic capacitor, characterized in that it comprises a plurality of stacked units, each unit having a valve-acting metal substrate having a porous layer on its surface, a dielectric layer formed on the surface of the porous layer, and a solid electrolyte layer disposed on the dielectric layer. A conductive layer exists between the stacked units, at least one of the conductive layers comprising a metal foil. The units and the conductive layers are sealed by an outer packaging resin. The anode side end face of the valve-acting metal substrate is directly connected to an external anode electrode formed on the surface of the outer packaging resin at one end face of the solid electrolytic capacitor. The metal foil is directly connected to an external cathode electrode formed on the surface of the outer packaging resin at the other end face of the solid electrolytic capacitor.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2018 / 074408 Summary of the Invention

[0008] The electrical connection state between the cathode and the basic elements of a solid electrolytic capacitor affects capacitor performance, such as the equivalent series resistance (ESR). Further improvements in capacitor performance are required.

[0009] The carbon paste for the solid electrolytic capacitor of the first aspect of this application comprises first carbon particles with an average particle size of 40 nm or more and 100 nm or less, and the first carbon particles account for 25% or more and 75% or less of the dry solid composition.

[0010] The solid electrolytic capacitor element of the second aspect of this application comprises a capacitor base element, a cathode, and a first carbon layer disposed between the capacitor base element and the cathode. The capacitor base element comprises an anode, a dielectric layer formed on the surface of the anode, and a solid electrolyte layer covering at least a portion of the dielectric layer. The first carbon layer comprises first carbon particles with an average primary particle size of 40 nm or more and 100 nm or less, and the proportion of the first carbon particles in the first carbon layer is 25% by volume or more and 75% by volume or less.

[0011] The solid electrolytic capacitor of the third aspect of this application comprises at least one of the above-mentioned solid electrolytic capacitor elements.

[0012] Carbon paste and solid electrolytic capacitor elements, as well as solid electrolytic capacitors, can be provided to suppress ESR in solid electrolytic capacitors. Attached Figure Description

[0013] Figure 1 This is a cross-sectional schematic diagram of the solid electrolytic capacitor according to the first embodiment of this application.

[0014] Figure 2 This is a cross-sectional schematic diagram of a solid electrolytic capacitor according to the second embodiment of this application.

[0015] Figure 3 This is a cross-sectional schematic diagram of the solid electrolytic capacitor according to the third embodiment of this application.

[0016] Figure 4A This is a cross-sectional schematic diagram of the solid electrolytic capacitor of the fourth embodiment of this application when cut with a plane parallel to the length direction of the anode body and the stacking direction of the solid electrolytic capacitor elements.

[0017] Figure 4B This is a cross-sectional schematic diagram of the solid electrolytic capacitor of the fourth embodiment when cut with a plane parallel to the length direction of the cathode body and the stacking direction of the solid electrolytic capacitor elements. Detailed Implementation

[0018] In solid electrolytic capacitors, the capacitor base element, including the anode and solid electrolyte layer, is typically in simple contact with the cathode, or bonded together with a conductive adhesive layer. In this simple contact, the contact resistance between the capacitor base element and the cathode increases, and the adhesive strength is low. This makes it easy for misalignment between the capacitor base element and the cathode to occur when sealing the solid electrolytic capacitor element containing the capacitor base element and cathode. In this specification, this misalignment is sometimes referred to as lamination misalignment.

[0019] When lamination misalignment occurs, the conductivity between the capacitor's basic elements and the cathode decreases, leading to reduced capacitor performance such as increased ESR. Furthermore, lamination misalignment makes it difficult to house the solid electrolytic capacitor elements within the desired space in the mold when sealing them with the resin outer casing. This results in a larger variation in the thickness of the resin outer casing formed on the outside of the solid electrolytic capacitor elements, reducing the performance and strength of the solid electrolytic capacitor. In areas where the resin outer casing is thinner, air can easily penetrate. Once air penetrates the interior of the solid electrolytic capacitor, the solid electrolyte layer deteriorates due to the moisture or oxygen present in the air, or the metal parts in the cathode and anode corrode, further reducing capacitor performance. Consequently, the product lifespan is shortened. Even a small degree of lamination misalignment in a single solid electrolytic capacitor element becomes significant over the entire stack. Therefore, in stacks of multiple solid electrolytic capacitor elements, variations in the thickness of the resin outer casing are prone to occur.

[0020] Furthermore, conductive adhesive layers have traditionally been formed using conductive adhesives such as pastes containing silver particles. However, pastes containing silver particles are expensive, and depending on the type of cathode, the contact resistance can increase. Using conductive carbon (e.g., carbon black) as a substitute for silver particles can also be considered. However, while general carbon black has a relatively well-developed structure, its primary particles have a small average particle size and a large specific surface area. To ensure sufficient adhesive strength of the conductive adhesive layer and to keep the viscosity of the paste used to form the conductive adhesive layer low, a large amount of binder is required, thus reducing the conductivity of the conductive adhesive layer. On the other hand, if the binder ratio in the paste is reduced and the conductive carbon ratio is increased, the paste viscosity becomes too high, reducing coatability, and even if the conductivity of the conductive adhesive layer can be improved, the adhesive strength decreases. Therefore, it is difficult to ensure both high adhesive strength and high conductivity for conductive adhesive layers containing conductive carbon.

[0021] In view of the above, the carbon paste of the first aspect of this application contains carbon particles (sometimes referred to as first carbon particles) with an average particle size of 40 nm or more and 100 nm or less in a ratio of 25% to 75% by volume of the dry solids content. The solid electrolytic capacitor element of the second aspect includes a carbon layer (sometimes referred to as a first carbon layer) disposed between the capacitor base element and the cathode body, containing primary particles at a ratio of 25% to 75% by volume. The first carbon particles have high conductivity and a larger average particle size of primary particles compared to ordinary carbon black. Therefore, if carbon paste is used in the bonding of the capacitor base element and the cathode body, sufficient adhesive strength can be ensured in the formed first carbon layer even with a small amount of adhesive. Since the first carbon particles can be densely filled in the first carbon layer, high conductivity of the first carbon layer can be ensured. In addition, by obtaining sufficient adhesive strength between the capacitor base element and the cathode body, the contact resistance between the capacitor base element and the cathode body can be suppressed to be low, and the lamination misalignment of the capacitor base element and the cathode body can be suppressed. Therefore, the ESR of solid electrolytic capacitors can be kept low. Furthermore, high electrostatic capacitance of solid electrolytic capacitors can be ensured. By suppressing lamination misalignment, the intrusion of air into the solid electrolytic capacitor element is reduced, thereby suppressing degradation of the solid electrolyte layer. Therefore, the degradation of capacitor performance is suppressed, thereby increasing product lifespan. By using the aforementioned carbon paste, high conductivity and adhesive strength can be obtained even without using pastes containing expensive silver particles, thus offering a cost advantage.

[0022] Hereinafter, the carbon paste, solid electrolytic capacitor and solid electrolytic capacitor element (hereinafter sometimes simply referred to as capacitor element) of this application will be described in more detail with reference to the accompanying drawings as needed.

[0023] [Carbon paste]

[0024] (The first carbon particle)

[0025] The average particle size of the primary carbon particles is 40 nm or more and 100 nm or less, or 50 nm or more and 80 nm or less. In contrast, the average particle size of carbon black used in general conductive materials is less than 40 nm. In addition, the average particle size of graphite particles used in the constituent components of solid electrolytic capacitors is typically 500 nm or more and 1 μm or less.

[0026] By using first carbon particles, high adhesive strength can be achieved even with a small amount of binder compared to using conventional carbon black, thus enabling high-density filling of the first carbon particles in the carbon paste or first carbon layer. Furthermore, by ensuring the average particle size of the first carbon particles is within the aforementioned range, viscosity can be kept relatively low even with high-density filling in the carbon paste. Additionally, by giving the first carbon particles a certain specific surface area, high adhesive strength can be achieved while ensuring high conductivity of the first carbon layer, compared to the case of graphite particles.

[0027] In this specification, the term "average particle size" refers to the cumulative 50% particle size (median diameter) in the particle size distribution of a volume-based sample measured using a particle size distribution measuring device based on dynamic light scattering. For example, the DLS-8000 light scattering photometer manufactured by Otsuka Electronics Co., Ltd. can be used as a particle size distribution measuring device based on dynamic light scattering.

[0028] It should be noted that, when determining the average particle size of carbonaceous material collected from carbon paste, a dispersion containing sample D, obtained according to the following steps, can be used as the sample for determining the average particle size. A specified amount of carbon paste is collected and dried under reduced pressure. An appropriate amount of water is added to the resulting dried product (sample A), and the resulting mixture (sample B) is centrifuged to separate it into a solid (sample C) and a liquid (liquid I). The solid sample C is washed with water, cleaned with an organic solvent, and dried to obtain the carbonaceous material (sample D). The liquid (liquid II) obtained by washing with water and organic solvent is then recovered separately. Sample D is dispersed in a liquid dispersion medium using a surfactant to prepare the dispersion for determination.

[0029] In addition, when determining the average particle size of carbonaceous material collected from the first carbon layer of a solid electrolytic capacitor element, a dispersion containing sample H, obtained according to the following steps, is used as the sample for determining the average particle size. First, a sample is prepared by embedding a solid electrolytic capacitor into a curable resin and curing the resin. The sample is then subjected to grinding, milling, or other treatments to expose the first carbon layer on the capacitor element. The exposed first carbon particles are scraped off, and a specified amount of sample (sample E) is collected. Sample E is mixed with a 1.0% by mass aqueous solution of nitric acid and left at room temperature (above 20°C and below 35°C) for 1 day. The resulting mixture (sample F) is centrifuged to separate it into a solid (sample G) and a liquid (liquid III). The solid sample G is washed with water, cleaned with an organic solvent, and dried to obtain carbonaceous material (sample H). At this time, the liquid obtained from the water washing and organic solvent cleaning is separately recovered (liquid IV). Sample H is dispersed in a liquid dispersion medium using a surfactant to prepare the dispersion for determination.

[0030] The organic solvent used as the cleaning agent for sample C or G, such as those exemplified in the preparation of the carbon paste described later, should be an organic solvent capable of dissolving polymeric components that cannot be removed by water washing. For example, pure water or an organic medium that is liquid at room temperature (e.g., 20°C–35°C) can be used as the dispersion medium for preparing the dispersion. The type and concentration of the surfactant, the type of dispersion medium, and the concentration of sample D or sample H in the dispersion should each be selected within a range suitable for preparing a dispersion suitable for determining the average particle size.

[0031] The oil absorption of dibutyl phthalate (DBP) in the first carbon particle is preferably 75 mL / 100g or less, and can also be 60 mL / 100g or less. When the DBP oil absorption of the first carbon particle is within this range, higher adhesive strength is easily obtained even when the first carbon particle is densely packed in the carbon paste or first carbon layer. There is no particular limitation on the lower limit of the DBP oil absorption of the first carbon particle, for example, it is 55 mL / 100g or more. For general carbon black, the DBP oil absorption is greater than 80 mL / 100g. The DBP oil absorption can be determined using the aforementioned sample D or sample H.

[0032] The preferred BET specific surface area of ​​the first carbon particle is 42 m². 2 / g or less, or 35m 2 / g or less. With a BET specific surface area in this range, even with high-density packing of first carbon particles in the carbon paste or first carbon layer, higher bond strength is easily achieved. There is no particular limitation on the lower limit of the BET specific surface area of ​​the first carbon particles, for example, 23m². 2 / g or more. It should be noted that for graphite particles, the BET specific surface area is typically 10m². 2 / g or less. For general carbon black, the BET specific surface area is greater than 35m². 2 / g, usually 60m 2 / g or more.

[0033] The BET specific surface area is calculated using the Brunauer-Emmett-Teller equation (BET equation) via nitrogen gas adsorption. The BET specific surface area can be determined using either sample D or sample H as described above.

[0034] In carbonaceous materials, the size Lc of the crystallites along the c-axis is a parameter representing the crystallinity of the graphite structure. Graphite forms a structure in which hexagonal grid layers containing carbon atoms are regularly stacked. The larger the Lc, the higher the crystallinity in the stacking direction of the hexagonal grid layers, meaning that the more hexagonal grid layers are stacked regularly. The size Lc of the crystallites along the c-axis of the first carbon particle is preferably 1.5 nm or more, but it can also be 3 nm or more, 4 nm or more, or 5 nm or more. The size Lc of the crystallites along the c-axis of the first carbon particle can be, for example, less than 100 nm, but it can also be less than 50 nm or less than 10 nm, or less than 7 nm or less than 6 nm. When Lc is in this range, the conductivity of the first carbon layer can be further improved because the high crystallinity of the first carbon particle can be ensured. The lower and upper limits of Lc can be combined arbitrarily.

[0035] It should be noted that for general graphite particles, Lc is determined by the particle size after crushing, and is approximately 3 μm to 10 μm. For carbon black, a common conductive carbon, the Lc is less than 1.5 nm, typically below 1.3 nm. For example, Ketjen black has an Lc of 0.87 nm, acetylene black has an Lc of 1.3 nm, and carbonaceous materials that serve as the raw material for the first carbon particle have an Lc of less than 1.2 nm.

[0036] The size Lc of the crystallites along the c-axis of the first carbon particle is determined by analyzing the X-ray diffraction (XRD) pattern of the first carbon particle using the Halder-Wagner formula. The XRD pattern of the first carbon particle can be determined using either sample D or sample H under the conditions described below. More specifically, firstly, the sample is placed on a glass plate of uniform thickness and positioned in an XRD apparatus, allowing a beam of light radiated from an X-ray tube to enter the sample, and the diffracted X-ray pattern is detected. The intensity data of the obtained X-ray pattern is analyzed using integrated powder X-ray analysis software with the Halder-Wagner formula, thereby determining Lc.

[0037] Measurement Apparatus: X-ray diffraction measuring apparatus (model RINT-TTR II) manufactured by Rigaku Corporation.

[0038] For cathode: Cu-Kα

[0039] Tube voltage: 40kV

[0040] Tube current: 30mA and above

[0041] Measurement range (2θ): 10°~90°

[0042] Measurement interval: 0.04° / second

[0043] Analysis software: Integrated powder X-ray analysis software (using the Halder-Wagner method)

[0044] It should be noted that the crystallite size Lc is calculated using the Halder-Wagner formula below.

[0045] [Number 1]

[0046]

[0047] (β is the integral width (minus the contribution from the diffraction line spread from the measuring device), θ is the Bragg angle, κ is the shape factor, λ is the wavelength, D is the crystallite size, and ε is the microstrain).

[0048] The proportion of the first carbon particles in the dry solids component of the carbon paste is 25% by volume or more, and preferably 35% by volume or more or 45% by volume or more, or possibly 50% by volume or more, from the viewpoint of ensuring higher conductivity of the first carbon layer. The proportion of the first carbon particles in the dry solids component of the carbon paste is 75% by volume or less, and preferably 70% by volume or less or 60% by volume or less, from the viewpoint of ensuring higher adhesion strength between the capacitor's basic components and the cathode and the first carbon layer. These lower and upper limits can be combined arbitrarily.

[0049] To determine the proportion of the first carbon particles from the carbon paste, firstly, the mass of the aforementioned sample D is measured, and the type of the first carbon particles is identified using known analytical methods based on sample D. The volume of the first carbon particles is determined based on the identified specific gravity of the first carbon particles obtained from literature values, etc., and the mass of sample D. The binder is separated from liquids I and II recovered when obtaining the aforementioned samples C and D using known separation methods, and the mass of the binder is measured. The type of binder is identified using known analytical methods. The volume of the binder is determined based on the identified specific gravity of the binder obtained from literature values, etc., and the measured mass of the binder. The proportion of the first carbon particles (volume %) is determined by dividing the volume of the first carbon particles by the sum of the volumes of the first carbon particles and the binder, and converting the result to a percentage. When the ratio of the first carbon particles is determined from the first carbon layer, the ratio (volume %) of the first carbon particles can be determined in the same way as when it is determined from the carbon paste, except that sample H is used instead of sample D, and liquids III and IV are used instead of liquids I and II.

[0050] First carbon particles can be obtained, for example, by high-temperature calcination of furnace black. Since furnace black is inexpensive, using carbon paste containing first carbon particles significantly reduces the cost of solid electrolytic capacitors compared to using pastes containing silver. However, because furnace black has a larger average particle size than other carbon blacks, graphitization is difficult to achieve during manufacturing. Furthermore, furnace black contains a large amount of impurities such as alkali metals, alkaline earth metals, and sulfur, which can easily reduce reliability when used in solid electrolytic capacitors. Therefore, first carbon particles can be obtained, for example, by calcining furnace black in an active gas atmosphere at high temperatures (e.g., above 1800°C). This reduces the impurity content and promotes graphitization, resulting in first carbon particles with high conductivity. Hydrogen can be used as an example of an active gas. The calcination temperature is, for example, between 1800°C and 2500°C. On the other hand, acetylene black or Ketjen black have a high degree of graphitization among carbon blacks, resulting in high conductivity of the particles themselves. However, because these carbons have small average particle size and large specific surface area, they require a large amount of binder, making it difficult to ensure the high conductivity of conductive adhesive layers formed using these carbons.

[0051] Carbon paste typically contains carbon particles, as well as binders and organic solvents. Additives may also be included as needed. There are no particular limitations on additives; examples of well-known additives used in carbon paste can be cited. Water may also be included as needed.

[0052] There are no particular limitations on the type of binder; for example, organic polymers can be used. The organic polymer can be either a curable resin or a thermoplastic resin. Alternatively, a curable resin and a thermoplastic resin can be mixed. The curable resin can be a thermosetting resin. A curable resin composition comprising a curable resin and at least one selected from polymerization initiators, curing agents, curing accelerators, and curing catalysts can be used as a binder.

[0053] Examples of organic polymers include epoxy resins, acrylic resins, polyimide resins, polyamide resins, polyurethane resins, polyester resins, fluoropolymers, polyurethane resins, vinyl resins, polyolefin resins, phenoxy resins, and rubber-like materials. One type of organic polymer can be used, or two or more can be used in combination. Bisphenol F type epoxy resins, bisphenol A type epoxy resins, or mixtures thereof can be used as epoxy resins. Furthermore, epoxy resins can include multifunctional epoxy resins. Tetra(hydroxyphenyl)ethane type resins can be used as multifunctional epoxy resins.

[0054] In particular, by including polyester resin in the adhesive, the viscosity of the adhesive can be reduced, and the coatability of the carbon paste can be improved. The number-average molecular weight (Mn) of the polyester resin is preferably 10,000 or more and 25,000 or less. By setting the number-average molecular weight of the polyester resin within the above range, the viscosity of the adhesive can be appropriately reduced. It should be noted that multiple polyester resins with different number-average molecular weights can be mixed and used. Furthermore, when the adhesive contains polyester resin, the percentage of polyester resin in the adhesive is preferably 60% by mass or less.

[0055] The choice of organic solvent should only consider factors such as volatility during the formation of the first carbon layer and the type of binder. There are no particular limitations on organic solvents; examples include alcohols (including terpenoids), ketones, esters, ethers, amides, nitriles, sulfoxides, and hydrocarbons (including terpenes). Specifically, α-terpineol, cyclopentanone, ethyl carbitol, and cyclohexanone can be used as organic solvents. The carbon paste can contain one or more organic solvents.

[0056] When the adhesive contains a curable resin as described above, a curing agent may also be incorporated. Imidazole-based curing agents such as 2-phenyl-4-methyl-hydroxymethylimidazolium and 2-phenyl-4,5-dihydroxymethylimidazolium can be used as curing agents. Furthermore, the reaction start temperature of the curing agent is preferably 130°C or higher and 155°C or lower, and preferably higher than the evaporation temperature of the organic solvent. If curing of the curable resin in the adhesive begins at a temperature lower than the evaporation temperature of the organic solvent, more organic solvent will remain in the cured adhesive without evaporation. Therefore, when the finished solid electrolytic capacitor is brought to a high temperature during reflow processes, the remaining organic solvent evaporates, which can cause cracks in the conductive adhesive layer formed from carbon paste and the outer packaging, potentially leading to a decrease in reliability.

[0057] Carbon paste can be obtained by mixing the constituent components. Mixing can be carried out using known methods, such as using a mixer, kneader, homogenizer, etc. Degassing treatment can be performed as needed during the preparation of the carbon paste.

[0058] Because the primary carbon particles have a larger average particle size and a more developed structure, even when used at a high volume ratio, the carbon paste can achieve a lower viscosity compared to using ordinary carbon black. The viscosity of the carbon paste at 25°C is, for example, 400 Pa·s or less, preferably 350 Pa·s or less. The viscosity of the carbon paste can be measured using a Type B viscometer at a rotation speed of 10 rpm.

[0059] [Solid electrolytic capacitors]

[0060] (Solid electrolytic capacitor element)

[0061] A solid electrolytic capacitor comprises a basic capacitor element, a cathode, and a first carbon layer disposed between the basic capacitor element and the cathode.

[0062] (First carbon layer)

[0063] The first carbon layer contains first carbon particles at a ratio of 25% to 75% by volume. The first carbon layer can be formed by applying the aforementioned carbon paste to the surface of at least one of the capacitor's basic element and the cathode, laminating the other on the surface of the carbon paste coating, and typically allowing it to dry. The application of the carbon paste is not limited to known coating methods (e.g., dip coating, spray coating), and can be performed using printing methods, or combinations thereof. For the composition of the first carbon layer, please refer to the description of the carbon paste.

[0064] The thickness of the first carbon layer can be, for example, 1 μm or more and 10 μm or less, or 5 μm or more and 10 μm or less.

[0065] (Basic components of a capacitor)

[0066] The capacitor basic element includes an anode, a dielectric layer formed on the surface of the anode, and a solid electrolyte layer covering at least a portion of the dielectric layer. The capacitor basic element may further include a second carbon layer disposed between the solid electrolyte layer and the first carbon layer.

[0067] (Anode)

[0068] The anode body can contain valve-acting metal, alloys containing valve-acting metal, and compounds containing valve-acting metal. These materials can be used alone or in combination of two or more. For example, aluminum, tantalum, niobium, and titanium are preferred as valve-acting metals. A porous anode body can be obtained, for example, by roughening the surface of a substrate (foil-like or plate-like substrate, etc.) containing the valve-acting metal using etching or similar methods. Roughening can be performed, for example, using etching. Furthermore, the anode body can be a shaped body or a sintered body of particles containing valve-acting metal. It should be noted that the shaped body and the sintered body have a porous structure overall.

[0069] (Dielectric layer)

[0070] The dielectric layer is an insulating layer that functions as a dielectric, formed in a manner that covers at least a portion of the surface of the anode body. The dielectric layer can be formed by anodizing the valve-acting metal on the surface of the anode body using a chemical forming process. The dielectric layer only needs to be formed in a manner that covers at least a portion of the anode body. The dielectric layer is typically formed on the surface of the anode body. Because the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner wall of the pits in the anode body.

[0071] The dielectric layer contains an oxide of the valve-acting metal. For example, when tantalum is used as the valve-acting metal, the dielectric layer contains Ta₂O₅; when aluminum is used as the valve-acting metal, the dielectric layer contains Al₂O₃. It should be noted that the dielectric layer is not limited to these; any material that functions as a dielectric can be used.

[0072] (Solid electrolyte layer)

[0073] A solid electrolyte layer is formed on the surface of the anode body, sandwiched between and covering the dielectric layer. The solid electrolyte layer does not necessarily need to cover the entire dielectric layer (the entire surface); it only needs to cover at least a portion of the dielectric layer. The solid electrolyte layer constitutes at least a portion of the cathode of the solid electrolytic capacitor.

[0074] The solid electrolyte layer contains a conductive polymer. The solid electrolyte layer may also contain at least one of a dopant or an additive, depending on the requirements.

[0075] Known conductive polymers used in solid electrolytic capacitors, such as π-conjugated conductive polymers, can be used as conductive polymers. Examples of conductive polymers include those with polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylidene, polyphenylene oxide, and polythiophene vinylidene as their basic backbone. Among these, polymers with polypyrrole, polythiophene, or polyaniline as their basic backbone are preferred. The aforementioned polymers also include homopolymers, copolymers of two or more monomers, and their derivatives (substitutes with substituents, etc.). For example, polythiophene may include poly(3,4-ethylidene dioxythiophene).

[0076] Conductive polymers can be used alone or in combination of two or more.

[0077] The solid electrolyte layer may also contain dopants. For example, at least one selected from anionic and polyanionic dopants may be used.

[0078] Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions; there are no particular limitations. Examples of dopants that generate sulfonate ions include benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid.

[0079] Examples of polyanionic polymers include high-molecular-weight polysulfonic acids and high-molecular-weight polycarboxylic acids. Examples of high-molecular-weight polysulfonic acids include polyvinylsulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic acid sulfonic acids, and polymethacrylic acid sulfonic acids. Examples of high-molecular-weight polycarboxylic acids include polyacrylic acid and polymethacrylic acid. Polyanionic polymers also include polyester sulfonic acid and phenolic resins with phenolic sulfonic acid. However, polyanionic polymers are not limited to these examples.

[0080] Dopants can be contained in the solid electrolyte layer in the form of free form, anionic form, or salt form, or in the form of binding or interacting with conductive polymers.

[0081] The amount of dopant contained in the solid electrolyte layer is, for example, 10 parts by mass or more and 1000 parts by mass or more and 500 parts by mass or more and 50 parts by mass or less and 200 parts by mass relative to 100 parts by mass of the conductive polymer.

[0082] The solid electrolyte layer can be a single layer or multiple layers. In the case of a multi-layer solid electrolyte layer, the conductive polymers contained in each layer can be the same or different. Furthermore, the dopants contained in each layer can be the same or different.

[0083] The solid electrolyte layer may, as needed, also contain known additives and known conductive materials other than conductive polymers. Examples of such conductive materials include at least one selected from conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0084] It should be noted that a layer to improve adhesion can be sandwiched between the dielectric layer and the solid electrolyte layer.

[0085] A solid electrolyte layer can be formed, for example, by polymerizing a precursor containing a conductive polymer onto a dielectric layer using a treatment solution. Polymerization can be performed using at least one of chemical polymerization and electrolytic polymerization. Examples of precursors for the conductive polymer include monomers, oligomers, or prepolymers. A solid electrolyte layer can also be formed by attaching a treatment solution (e.g., a dispersion or solution) containing a conductive polymer to a dielectric layer and then drying it. Examples of dispersion media (or solvents) include water, organic solvents, or mixtures thereof. The treatment solution may also contain other components (selected from at least one of dopants and additives).

[0086] When using a treatment solution containing a precursor of a conductive polymer, an oxidizing agent is used to polymerize the precursor. The oxidizing agent can be included in the treatment solution as an additive. Alternatively, the oxidizing agent can be coated onto the anode body before or after the treatment solution is brought into contact with the anode body to which a dielectric layer is formed. Examples of such oxidizing agents include sulfates, sulfonic acids, or salts thereof. One oxidizing agent can be used alone, or two or more can be used in combination.

[0087] The process of forming a solid electrolyte layer by impregnation and polymerization (or drying) in a treatment solution can be performed once or repeatedly. In each iteration, the composition and viscosity of the treatment solution can be kept the same, or at least one condition can be changed.

[0088] (Second carbon layer)

[0089] The second carbon layer contains carbon particles (called second carbon particles). The second carbon particles are distinguished from the first carbon particles by the average particle size of their primary particles. The average particle size of the primary particles in the second carbon particles is typically greater than 100 nm, but can also be greater than 500 nm. For example, the average particle size of the primary particles in the second carbon particles is less than 1 μm. The average particle size of the second carbon particles can be determined based on the characteristics of the first carbon particles.

[0090] Examples of second carbon particles include graphite (man-made graphite, natural graphite, etc.).

[0091] The second carbon layer, in addition to containing the second carbon particles, typically also contains a binder. The second carbon layer may also contain additives as needed. Examples of binders include organic polymers (organic polymers exemplified as binders for carbon pastes, as well as cellulose-based resins such as carboxymethyl cellulose or its salts, cellulose ethers, cellulose esters, etc.). As organic polymers, either hydrophilic or hydrophobic organic polymers can be used, or a combination of these organic polymers can be used. The binder may contain one or more organic polymers. The binder can be either a curable resin (or a curable resin composition) or a thermoplastic resin.

[0092] The proportion of the second carbon particle in the second carbon layer is, for example, greater than 70% by volume, greater than 71% by volume, or greater than 71% by volume, or greater than 80% by volume. The proportion of the second carbon particle in the second carbon layer is, for example, less than 95% by volume. The proportion of the second carbon particle in the second carbon layer can be determined based on the proportion of the first carbon particle.

[0093] The thickness of the second carbon layer is, for example, 0.1 μm or more and 100 μm or less, or 0.5 μm or more and 50 μm or less.

[0094] The second carbon layer can be formed, for example, by coating a dispersion containing the components of the second carbon layer and a liquid medium to cover at least a portion of the surface of the solid electrolyte layer, followed by drying. The dispersion is generally prepared by mixing the components of the second carbon layer and the liquid medium. The liquid medium can be selected based on the type of binder, and can be either water or an organic liquid medium. The organic liquid medium can be selected from the organic solvents exemplified for carbon paste.

[0095] (Layer containing metal particles)

[0096] The basic elements of a capacitor may include a layer containing metal particles disposed between the first carbon layer and the second carbon layer, but it is not necessary to have a layer containing metal particles.

[0097] A layer containing metal particles can be formed, for example, by laminating a composition containing metal particles onto the surface of a second carbon layer. Examples of metal particle-containing layers include metal paste layers formed using a composition containing metal powder such as silver particles and a binder (organic polymer, etc.). Thermoplastic resins can be used as binders; however, curable resins (thermosetting resins, etc.) such as polyimide resins and epoxy resins are preferred.

[0098] (Cathode)

[0099] The cathode may contain, for example, at least a metal foil. There are no particular restrictions on the type of metal constituting the foil; examples include aluminum, aluminum alloys, copper, or copper alloys. The metal foil may use valve-acting metals such as aluminum, tantalum, or niobium, or alloys containing valve-acting metals.

[0100] The first carbon layer preferably contacts the cathode. By fixing the first carbon layer in contact with the cathode, the capacitor base element can be reliably fixed to the cathode. Furthermore, it is preferable not to sandwich a layer containing metal particles between the capacitor base element and the cathode. For example, even if the capacitor base element has a layer containing metal particles on its surface, reducing manufacturing costs can be achieved by not sandwiching other layers containing metal particles (e.g., a silver paste layer) between the capacitor base element and the cathode.

[0101] The surface of the metal foil can be porous as needed. A porous metal foil can be obtained by roughening the metal foil (e.g., etching). An oxide film can be formed on the surface of the metal foil.

[0102] The cathode may comprise a metal foil and a surface layer formed on the surface of the metal foil. In this case, the capacitor element is configured such that the surface layer of the metal foil is in contact with the first carbon layer. The surface layer may contain, for example, a material different from the metal foil (metal, metal compound, nonmetal, etc.). Examples of such materials include conductive materials. Examples of conductive materials constituting the surface layer include metals (titanium, nickel, etc.), metal compounds such as titanium compounds (nitrides, carbides, carbonitrides, oxides, etc.), and carbonaceous materials. The surface layer may contain one or more of these materials.

[0103] The surface layer is preferably formed using vapor phase methods, sintering methods, etc. This is because high conductivity can be obtained by directly fixing the conductive material to the metal foil. Examples of vapor phase methods include vapor deposition (vacuum deposition, electron beam deposition, arc plasma deposition, etc.), sputtering, CVD, etc. The surface layer can be formed on one surface of the metal foil or on two surfaces. The surface layer can be a single-layer structure or a multi-layer structure. In a multi-layer surface layer, each layer can, for example, have at least one different composition and structure (density, etc.).

[0104] The thickness of the metal foil can be, for example, 0.1 μm or more and 100 μm or less, or 1 μm or more and 50 μm or less.

[0105] The thickness of the surface layer can be, for example, greater than 0.5 μm and less than 10 μm on each side of the metal foil, or greater than 1 μm and less than 5 μm.

[0106] (other)

[0107] Solid electrolytic capacitors may have a substrate supporting the solid electrolytic capacitor element, as needed. Examples of substrates include insulating substrates, metal substrates, or printed circuit boards.

[0108] The capacitor element is sealed using an outer packaging (such as a resin outer packaging) or a housing. For example, the capacitor element and the resin material of the outer packaging (such as uncured thermosetting resin and fillers) can be contained in a mold, and the capacitor element can be sealed with a resin outer packaging using transfer molding, compression molding, or other methods.

[0109] Solid electrolytic capacitors can be wound, chip-type, or multilayer. A solid electrolytic capacitor requires at least one capacitor element, or it can have two or more capacitor elements stacked together. The configuration of the capacitor elements depends on the type of solid electrolytic capacitor.

[0110] If at least one of the capacitor elements in a solid electrolytic capacitor has a first carbon layer containing first carbon particles at a ratio of 25% to 75% by volume, the conductivity improvement effect brought about by the first carbon layer can be obtained. From the viewpoint of improving the effect of reducing stacking misalignment and easily obtaining the conductivity improvement effect of the entire solid electrolytic capacitor, it is preferable that at least 50% (more preferably at least 75%) of the capacitor elements in the solid electrolytic capacitor have the first carbon layer, and more preferably all capacitor elements have the first carbon layer.

[0111] Furthermore, the volatile organic components remaining in the solid electrolytic capacitor (residual volatile organic compounds) are preferably below 2000 μg / g per unit mass of the solid electrolytic capacitor. It can be considered that the residual volatile organic compounds in solid electrolytic capacitors are mainly organic solvents contained in carbon paste, etc. If the residual organic solvents in the solid electrolytic capacitor volatilize when high temperatures are reached during processes such as reflow, they can become a cause of cracks in the conductive adhesive layer and outer packaging, potentially leading to a decrease in reliability.

[0112] For residual volatile organic compounds, the sample (solid electrolytic capacitor) is placed in a stainless steel tube and analyzed by TD-GC / MS (Thermal Desorption-Gas Chromatograph / Mass spectrometry). Specifically, the components volatilized from the sample are detected and their amounts are determined using the following apparatus and measurement conditions.

[0113] Measurement apparatus: TurboMatrixATD / Clarus SQ8T / Clarus680

[0114] (PerkinElmer)

[0115] Column: SPB-5 (60m × 0.25mm × 0.25μm)

[0116] Column temperature conditions: 35℃·5min~(10℃ / min)~100℃

[0117] ~(20℃ / min)~290℃·19min

[0118] Sample heating conditions: 260℃·1min

[0119] Carrier gas: Helium (1 mL / min)

[0120] Injection volume: 0.2%

[0121] Measurement mode: Scan (m / z = 24–500)

[0122] Alternatively, as a method for evaluating the amount of residual volatile components in a solid electrolytic capacitor, the method of measuring the weight loss caused by the residual volatile components (including all residual volatile components, including residual organic volatile components) can also be used. The weight loss caused by the residual volatile components is preferably 1.0% by weight or less. To measure the weight loss caused by the residual volatile components, the sample (solid electrolytic capacitor) is cut with pliers and subjected to TG-DTA (Thermogravimetry-Differential Thermal Analysis). Specifically, the components volatilized from the sample are detected using the following apparatus and measurement conditions, and their amount is determined.

[0123] Measurement apparatus: TA6000 (manufactured by Hitachi High-tech Science Co., Ltd.)

[0124] Baking treatment: 85℃ for 12 hours (under N2 atmosphere)

[0125] Spectrum measurement: 25–300℃

[0126] Heating conditions: 10℃ / min

[0127] Carrier gas: N2 atmosphere

[0128] In solid electrolytic capacitors, leads such as lead frames are used to draw current from the capacitor element. More specifically, one end of the anode lead is electrically connected to the anode body, and the other end of the anode lead is led outward from the outer casing or housing. Similarly, one end of the cathode lead is electrically connected to the cathode body, and the other end of the cathode lead is led outward from the outer casing or housing. The other ends of each lead exposed from the outer casing or housing are used for welding to the substrate on which the solid electrolytic capacitor is to be mounted. The connection between the leads and the anode or cathode body can be made by welding or by using a conductive adhesive. The aforementioned carbon paste can be used as a conductive adhesive. For example, metals such as copper or copper alloys can be used to construct the leads.

[0129] Solid electrolytic capacitors can have external electrodes. Sometimes the external electrode on the anode side is referred to as the first external electrode, and the external electrode on the cathode side as the second external electrode. The anode and cathode can be connected to the external electrodes using leads. Alternatively, the ends of the anode and cathode can be exposed from the outer casing or housing, and the exposed ends can be electrically connected to the external electrodes. The connection between the exposed ends of the anode and cathode and the external electrodes can be performed using at least one method selected from bonding, plating, vapor phase coating, cold spraying, firing, and electrolytic deposition. The exposed ends of the anode and cathode can be connected to the external electrodes using a conductive contact layer. An intermediate electrode layer can be provided between the external electrodes and the outer casing or housing, covering the exposed ends of the anode and cathode and, if necessary, the contact layer.

[0130] In a solid electrolytic capacitor with a laminated structure, the ends of the anode and cathode of each capacitor element can be exposed from the outer casing and electrically connected to external electrodes, allowing current to be drawn from the ends of the anode and cathode. In this case, the end of the anode of each capacitor element can be exposed on one main surface of the outer casing, or on two or more main surfaces. Similarly, the end of the cathode of each capacitor element can be exposed on one main surface of the outer casing, or on two or more main surfaces. From the viewpoint of suppressing short circuits, it is preferable that the ends of the cathode and anode are typically exposed on their respective main surfaces.

[0131] For example, the anode body has a pair of opposing ends (referred to as first ends), and the cathode body has a pair of opposing ends (referred to as second ends). Furthermore, the outer casing has a first main surface, a second main surface opposite to the first main surface, a third main surface intersecting the first and second main surfaces, and a fourth main surface opposite to the third main surface. It should be noted that the fourth main surface intersects the first and second main surfaces. In this case, it can be configured such that one first end of the anode body protrudes from the outer casing in the first main surface and is electrically connected to an external electrode on the anode side (referred to as the first external electrode), and one second end of the cathode body protrudes from the outer casing in any one of the second to fourth main surfaces and is electrically connected to an external electrode on the cathode side (referred to as the second external electrode). Furthermore, if the other first end of the anode body protrudes in the second main surface and is electrically connected to the first external electrode, from the viewpoint of suppressing short circuits, it is preferable that the pair of second ends of the cathode body do not protrude from the outer casing in the second main surface. The direction in which the pair of first ends of the anode body face each other is designated as the first direction, and the direction in which the pair of second ends of the cathode body face each other is designated as the second direction. In this case, the first direction and the second direction can be parallel or intersecting. For example, if one second end of the cathode body protrudes from the outer packaging in the second main surface, the first direction and the second direction are parallel. If one second end of the cathode body protrudes from the outer packaging in the third or fourth main surface, the first direction and the second direction intersect.

[0132] Figure 1 This is a cross-sectional schematic diagram of a solid electrolytic capacitor according to the first embodiment of this application. The solid electrolytic capacitor 1 includes a capacitor element 2, a substrate S supporting the capacitor element 2, a resin outer casing 3 sealing the capacitor element 2, an external electrode (first external electrode) 4a on the anode side, and an external electrode (second external electrode) 5a on the cathode side. The resin outer casing 3 has a generally cuboid shape, and the solid electrolytic capacitor 1 also has a generally cuboid shape.

[0133] The capacitor element 2 includes a capacitor base element E comprising an anode body 6, a cathode body 9 comprising a metal foil, and a first carbon layer C1 bonding the capacitor base element E to the cathode body 9. The capacitor base element E includes an anode body 6, a dielectric layer 7 covering the anode body 6, a solid electrolyte layer 8 covering the dielectric layer 7, and a second carbon layer C2 covering the solid electrolyte layer 8. The anode body 6 has a pair of opposing first ends e1, and the cathode body 9 has a pair of opposing second ends e2. Furthermore, the anode body 6 includes a region opposing the cathode body 9 and a region not opposing it. In the region of the anode body 6 not opposing the cathode body 9, adjacent to the cathode body 9, an insulating separation layer 13 is formed in a strip-like manner covering the surface of the anode body 6, restricting contact between the cathode body 9 and the anode body 6. It should be noted that the insulating separation layer 13 is not necessarily required; if the separation layer 13 is not provided, this portion is filled with a resin outer casing 3.

[0134] One of the pair of first ends e1 of the anode body 6 protrudes from the first main surface m1 of the resin outer packaging 3 and is electrically connected to the first external electrode 4a. An intermediate electrode layer 4b is provided between the first external electrode 4a and the first main surface m1 of the resin outer packaging 3. A contact layer 4c is provided between the intermediate electrode layer 4b and the first end e1 of the anode body 6 protruding from the first main surface m1. The first end e1 of the anode body 6 protruding from the resin outer packaging 3 is electrically connected to the first external electrode 4a via the contact layer 4c and the intermediate electrode layer 4b.

[0135] One of the pair of second ends e2 of the cathode body 9 protrudes from the second main surface m2 of the resin outer packaging 3, opposite to the first main surface m1, and is electrically connected to the second external electrode 5a. An intermediate electrode layer 5b is provided between the second external electrode 5a and the second main surface m2 of the resin outer packaging. The second end e2 of the cathode body 9 protruding from the resin outer packaging 3 is electrically connected to the second external electrode 5a via the intermediate electrode layer 5b. In the example shown, the first direction (the length direction of the anode body 6) in which the pair of first ends e1 of the anode body 6 face each other is parallel to the second direction (the length direction of the cathode body 9) in which the pair of second ends e2 of the cathode body 9 face each other.

[0136] In the case of a solid electrolytic capacitor having a stack of multiple capacitor elements, if we consider two adjacent capacitor elements of the stack, it is preferable that a cathode is sandwiched between the capacitor basic elements contained in each capacitor element, and a first carbon layer is disposed between the cathode and each capacitor basic element.

[0137] In solid electrolytic capacitors with multiple capacitor elements stacked together, stacking misalignment can easily become significant. By using the carbon paste described above, even in solid electrolytic capacitors with stacked elements, stacking misalignment can be reduced, and the degradation of capacitor performance, such as an increase in ESR, can be suppressed.

[0138] Figure 2 This is a cross-sectional schematic diagram of a solid electrolytic capacitor according to the second embodiment of this application. The solid electrolytic capacitor 11 includes a laminate L of multiple capacitor elements 2, a substrate S supporting the laminate L, a resin outer casing 3 sealing the laminate L, a first external electrode 4a, and a second external electrode 5a. The laminate L includes multiple stacked capacitor base elements E and a cathode body 9 containing metal foil disposed between adjacent capacitor base elements E. A first carbon layer C1 is disposed between the capacitor base elements E and the cathode body 9 to bond them together. It should be noted that... Figure 2 It is parallel to the first direction opposite to the pair of first ends e1 of the anode body 6 and to the stacking direction D of the capacitor element 2. L A schematic diagram of the cross-section when a solid electrolytic capacitor 11 is cut with a plane in a parallel direction. For anything else... Figure 2 The composition can be referred to Figure 1 Explanation.

[0139] In the case of a solid electrolytic capacitor having a laminate of capacitor elements, carbon paste can be used to bond the cathode body of the capacitor element located on the outermost side of the laminate to the cathode lead (lead frame, etc.).

[0140] Figure 3 This is a cross-sectional schematic diagram of a solid electrolytic capacitor according to the third embodiment of this application. The solid electrolytic capacitor 21 includes a laminate L of multiple capacitor elements 22, a resin outer casing 3 sealing the laminate L, and anode leads 14 and cathode leads 15, each with at least a portion exposed outside the resin outer casing 3. It should be noted that... Figure 3 It is parallel to the first direction opposite to the pair of first ends e1 of the anode body 6 and to the stacking direction D of the capacitor element 22. L A schematic diagram of the cross-section of a solid electrolytic capacitor 21 cut by a plane in a parallel direction.

[0141] In the laminate L, the first end e1 of the anode body 6 of the basic capacitor element E contained in each capacitor element 22 is electrically connected to one end of the anode lead 14 by welding in a bundled state. One end of the cathode lead 15 is electrically connected to the cathode body 9 by means of the first carbon layer C1 formed using the aforementioned carbon paste. A portion of the other end of the anode lead 14 is led outward from the first main surface m1 of the resin outer packaging 3. A portion of the other end of the cathode lead 15 is led outward from the second main surface m2 of the resin outer packaging 3. For other... Figure 3 The composition can be referred to Figure 1 and Figure 2 Explanation.

[0142] It should be noted that, Figure 2 and Figure 3 The composition of the basic capacitor element E is omitted in the text.

[0143] In the case of a solid electrolytic capacitor having a stack of multiple capacitor elements, a first end of the anode body of each capacitor element may be alternately exposed from the outer packaging or shell in the first main surface and the second main surface in the stacking direction of the stack, and electrically connected to the first external electrode.

[0144] Figure 4A The solid electrolytic capacitor of the fourth embodiment of this application is used in the first direction D1 and the stacking direction D. L A schematic diagram of the cross-section when cutting with a plane in a parallel direction. Figure 4B The solid electrolytic capacitor of the fourth embodiment is used in the second direction D2 and the stacking direction D. L A schematic diagram of the cross-section when cutting with a plane in a parallel direction.

[0145] The solid electrolytic capacitor 31 includes a laminate L of multiple capacitor elements 32, a substrate S supporting the laminate L, a resin outer casing 3 sealing the laminate L, a first external electrode 4a, and a second external electrode 5a. The laminate L includes multiple stacked capacitor base elements E and a cathode body 9 containing metal foil disposed between adjacent capacitor base elements E. A first carbon layer C1 is disposed between the capacitor base elements E and the cathode body 9 to bond them together.

[0146] In the anode body 6 of each basic capacitor element E, one of the first ends is in the stacking direction D. LThe cathode body 9 of each capacitor element 32 alternately exposes from the first main surface m1 and the second main surface m2 opposite to the first main surface m1, and is electrically connected to the first external electrode 4a. Additionally, in each capacitor element 32, the second end e2 of the cathode body 9 exposes from the third main surface m3 of the resin outer packaging 3 and is electrically connected to the second external electrode 5a. Furthermore, the other second end e2 exposes from the fourth main surface m4 opposite to the third main surface m3 of the resin outer packaging and is electrically connected to the second external electrode 5a. In this case, the first direction D1 and the second direction D2 intersect. For any other... Figure 4A and Figure 4B The composition can be referred to Figure 1 and Figure 2 The explanation is as follows. It should be noted that... Figure 4A and Figure 4B The composition of a portion of the basic capacitor element E is omitted in the text.

[0147] [Example]

[0148] The present application will now be described in detail based on the embodiments and comparative examples; however, the present application is not limited to the following embodiments.

[0149] Solid electrolytic capacitors EA1 to EA8

[0150] Make according to the following guidelines Figure 1 Solid electrolytic capacitors 1 (solid electrolytic capacitors EA1 to EA8) are shown, and their characteristics are evaluated.

[0151] (1) Preparation of anode body 6

[0152] The two surfaces of the aluminum foil (thickness: 100 μm) used as the substrate were roughened by etching, thereby creating the anode body 6.

[0153] (2) Formation of dielectric layer 7

[0154] The other end of the anode body 6 is immersed in the formation solution, and a DC voltage of 10V is applied for 20 minutes to form a dielectric layer 7 containing aluminum oxide.

[0155] (3) Formation of solid electrolyte layer 8

[0156] An aqueous solution containing pyrrole monomer and p-toluenesulfonic acid was prepared. The monomer concentration in the aqueous solution was 0.5 mol / L, and the p-toluenesulfonic acid concentration was 0.3 mol / L.

[0157] In the obtained aqueous solution, the anode 6 and the counter electrode, on which the dielectric layer 7 is formed in (2) above, are immersed, and electrolytic polymerization is carried out at 25°C with a polymerization voltage of 3V (relative to the polymerization potential of the silver reference electrode) to form a solid electrolyte layer 8.

[0158] (4) Formation of the second carbon layer C2

[0159] A liquid dispersion was prepared by wet pulverizing graphite particles (the second carbon particle) and dispersing materials (such as cellulose derivatives) together with water. The volume ratio of graphite particles to dispersing materials (graphite particles:dispersing materials) was set to 50:20. The average particle size of the primary particles of the second carbon particle, determined using the steps described above, was 0.7 μm.

[0160] The anode body 6, with the solid electrolyte layer 8 formed in step (3) above, is impregnated in a liquid dispersion. After being removed from the dispersion, it is dried, thereby forming a second carbon layer C2 on the surface of the solid electrolyte layer 8. The drying is carried out at 150–200°C for 10–30 minutes. The thickness of the second carbon layer C2 is 0.5 μm. By operating in this manner, a total of 20 capacitor basic elements E are formed.

[0161] (5) Formation of capacitor element 2

[0162] (a) Preparation of carbon paste

[0163] Carbon particles (average primary particle size 65 nm, Lc = 1.15 nm) were calcined at 2500 °C for 9 hours in a gaseous atmosphere, and the resulting graphitized carbon was used as the first carbon particle. The first carbon particle, determined using the previously described steps, had an average primary particle size of 65 nm, an Lc of 5.2 nm, a DBP oil absorption of 60 mL / 100 g, and a BET specific surface area of ​​27 m². 2 / g.

[0164] The first carbon particles, epoxy resin (bisphenol F type epoxy resin and imidazole-based curing agent) as a binder, and α-terpineol as an organic solvent were stirred in a mixing and degassing machine and further mixed in a three-roll mill to prepare a carbon paste. The viscosity of the carbon paste at 25°C, determined using the steps described above, was 330 Pa·s.

[0165] (b) Bonding of the capacitor's basic element E to the cathode 9

[0166] A carbon paste is applied to the surface of the second carbon layer C2 or the cathode 9 by sandwiching a carbon paste film between the second carbon layer C2 and the metal foil shown in Table 1, thereby alternately overlapping the capacitor basic element E and the cathode 9. When using a metal foil with a surface layer, the metal foil is overlapped such that the surface layer contacts the carbon paste. The binder in the carbon paste film is then cured, thereby producing the capacitor element. The binder is cured by heating at 150–200°C for 10–60 minutes. Furthermore, the volume ratio of the first carbon particles in the first carbon layer C1 (or the dry solid component in the carbon paste) is set to the values ​​shown in Table 1.

[0167] It should be noted that the following metal foil is used as the cathode body 9.

[0168] (c1) C-fired Al foil: aluminum foil with a surface layer of fired carbonaceous material (surface layer thickness: 3μm, aluminum foil thickness: 20μm)

[0169] (c2) Ti-coated Al foil: Aluminum foil with a surface layer containing titanium metal (surface layer thickness: 3 μm, aluminum foil thickness: 20 μm)

[0170] (c3) Ni vapor-deposited Al foil: Aluminum foil with nickel metal vapor-deposited on its surface (surface layer thickness: 3μm, aluminum foil thickness: 20μm)

[0171] (c4) C vapor-deposited Al foil: Aluminum foil with carbonaceous material vapor-deposited on its surface (surface layer thickness: 3μm, aluminum foil thickness: 20μm)

[0172] (c5) Cu foil: Copper foil thickness: 20μm

[0173] (c6) Al foil: Aluminum foil thickness: 20μm

[0174] (6) Assembly of solid electrolytic capacitor 11

[0175] With the first end e1 of the anode body 6 and the second end e2 of the cathode body 9 of each capacitor element 2 of the laminated body L obtained in (5) above led out, a mold is formed to form a resin outer packaging body 3 made of insulating resin around the capacitor element 2. At this time, it is set that the first end e1 of the anode body 6 and the second end e2 of the cathode body 9 are led out from the first main surface m1 and the second main surface m2 opposite to the first main surface m1 of the resin outer packaging body 3, respectively. The part of the anode body 6 exposed from the resin outer packaging body 3 is connected to the first external electrode 4a on the anode side with the contact layer 4c and the intermediate electrode layer 4b sandwiched in between. The part of the cathode body 9 exposed from the resin outer packaging body 3 is electrically connected to the second external electrode 5a on the cathode side with the intermediate electrode layer 5b sandwiched in between. By operating in this way, the solid electrolytic capacitor 11 is completed. The contact layer 4c, the intermediate electrode layer 4b and 5b are each formed by coating a silver paste containing silver particles and epoxy resin and firing. In the same manner as above, a total of 20 solid electrolytic capacitors were manufactured.

[0176] (7) Evaluation

[0177] The following evaluation was conducted using solid electrolytic capacitors.

[0178] (a) Determination of ESR

[0179] The ESR of a solid electrolytic capacitor is determined using the following steps.

[0180] At 20°C, the capacitance (μF) of each solid electrolytic capacitor at 120 Hz was measured using a 4-terminal LCR meter, and the ESR (mΩ) at 100 kHz was also measured. The average values ​​of the capacitance and ESR for the 20 solid electrolytic capacitors were then calculated.

[0181] Solid Electrolytic Capacitor C1

[0182] The capacitor element E and the cathode body 9 are laminated without using carbon paste, thereby creating a laminate of capacitor elements. In addition, a total of 20 solid electrolytic capacitors C1 are manufactured and evaluated in the same manner as the solid electrolytic capacitor E1.

[0183] Solid Electrolytic Capacitor C2

[0184] Instead of carbon paste, silver paste was used to laminate the capacitor base element E with the cathode body 9, thereby creating a laminate of the capacitor element. A paste containing silver particles and epoxy resin as a binder was used as the silver paste. Heating at 150–200°C for 10–60 minutes cured the binder contained in the silver paste coating, thus forming a layer containing silver particles. In addition, a total of 20 solid electrolytic capacitors C2 were manufactured and evaluated in the same manner as the solid electrolytic capacitor E1.

[0185] The evaluation results are shown in Table 1. In Table 1, C1 and C2 are comparative examples. Table 1 also shows the type of paste used in the bonding of the capacitor's basic components to the cathode, and the volume ratio of conductive particles (first carbon particles or silver particles) in the dry solids component of the paste.

[0186] [Table 1]

[0187]

[0188] As shown in Table 1, it can be seen that the solid electrolytic capacitors EA1 to EA8 using carbon paste in this embodiment achieve the same electrostatic capacitance and lower ESR compared to the solid electrolytic capacitor C2 using silver paste. Even with the use of carbon paste, which is less expensive than silver paste, sufficient performance can be obtained. Furthermore, compared to the solid electrolytic capacitor C1, which simply stacks the capacitor base element E with the cathode body 9 without using carbon paste, the ESR of the solid electrolytic capacitors EA1 to EA8 using carbon paste in this embodiment is suppressed to an extremely low level. Moreover, when comparing the solid electrolytic capacitors EA1, EA7, and EA8 using C-fired Al foil as the cathode body, the ESR of the solid electrolytic capacitor EA1, with a conductive particle ratio of 50% by volume, is suppressed even lower than that of the solid electrolytic capacitors EA7 and EA8, with conductive particle ratios of 25% and 75% by volume, respectively.

[0189] Solid Electrolytic Capacitors EB1-EB10

[0190] Following the same principles as solid electrolytic capacitors EA1 to EA8, the composition of the carbon paste was changed to produce a product that... Figure 2 Solid electrolytic capacitors 11 shown are solid electrolytic capacitors (solid electrolytic capacitors EB1 to EB10) with seven basic capacitor elements stacked on top of each other, and their characteristics are evaluated. The composition of the carbon paste and the evaluation results of electrostatic capacitance and ESR are shown in Table 2. In addition, the reaction start temperature of the curing agent and the evaporation temperature of the solvent used in solid electrolytic capacitors EB1 to EB10 are shown in Tables 3 and 4, respectively.

[0191] [Table 2]

[0192]

[0193] [Table 3]

[0194]

[0195] [Table 4]

[0196]

[0197] In addition, for the solid electrolytic capacitor EB7, the residual volatile components were determined by compositional mass analysis and gravimetric analysis using the method described above. The results showed that the residual organic volatile components per unit mass were 1157 μg / g, and the weight reduction due to the residual volatile components was 0.6 wt%.

[0198] Industrial availability

[0199] According to this application, the initial ESR of a solid electrolytic capacitor can be suppressed to a low level. Therefore, the solid electrolytic capacitor element and the solid electrolytic capacitor can be used in various applications requiring high reliability.

[0200] Explanation of reference numerals in the attached figures

[0201] 1, 11, 21, 31: Solid electrolytic capacitor; 2, 22, 32: Solid electrolytic capacitor element; 3: Resin outer casing; 4a: First external electrode; 4b: Intermediate electrode layer; 4c: Contact layer; 5a: Second external electrode; 5b: Intermediate electrode layer; 6: Anode; 7: Dielectric layer; 8: Solid electrolyte layer; 9: Cathode; 13: Separation layer; 14: Anode lead; 15: Cathode lead; C1: First carbon layer; C2: Second carbon layer; E: Basic capacitor element; L: Laminated structure; S: Substrate; e1: First end of anode 6; e2: Second end of cathode 9; m1: First main surface of resin outer casing 3; m2: Second main surface of resin outer casing 3; m3: Third main surface of resin outer casing 3; m4: Fourth main surface of resin outer casing 3; D L : Stacking direction, D1: first direction, D2: second direction

Claims

1. A carbon paste for solid electrolytic capacitors, comprising primary carbon particles with an average particle size of 40 nm or more and 100 nm or less. The first carbon particle accounts for more than 25% by volume and less than 75% by volume in the dry solids composition.

2. The carbon paste for solid electrolytic capacitors according to claim 1, wherein, The oil absorption of the first carbon particle containing dibutyl phthalate is less than 80 mL / 100 g.

3. The carbon paste for a solid electrolytic capacitor according to claim 1 or 2, wherein, The BET specific surface area of ​​the first carbon particle is 35 m². 2 / g or less.

4. The carbon paste for solid electrolytic capacitors according to any one of claims 1 to 3, wherein, The size of the microcrystals along the c-axis of the first carbon particle is greater than 1.5 nm.

5. The carbon paste for solid electrolytic capacitors according to any one of claims 1 to 4, further comprising a binder. The adhesive comprises at least one of thermoplastic resin and curable resin.

6. The carbon paste for a solid electrolytic capacitor according to claim 5, wherein, The adhesive comprises the curable resin.

7. The carbon paste for a solid electrolytic capacitor according to claim 6, wherein, The curable resin includes epoxy resin.

8. The carbon paste for a solid electrolytic capacitor according to claim 7, wherein, The epoxy resin includes multifunctional epoxy resins.

9. The carbon paste for a solid electrolytic capacitor according to claim 8, wherein, The multifunctional epoxy resin is a tetra(hydroxyphenyl)ethane type resin.

10. The carbon paste for a solid electrolytic capacitor according to claim 7, wherein, The epoxy resin comprises at least one of bisphenol F type epoxy resin and bisphenol A type epoxy resin.

11. The carbon paste for a solid electrolytic capacitor according to any one of claims 5 to 10, wherein, The adhesive also contains polyester resin.

12. The carbon paste for a solid electrolytic capacitor according to claim 11, wherein, The polyester resin accounts for less than 60% by mass in the adhesive.

13. The carbon paste for a solid electrolytic capacitor according to any one of claims 6 to 12, wherein, The adhesive also includes a curing agent. The reaction start temperature of the curing agent is above 130°C and below 155°C.

14. The carbon paste for a solid electrolytic capacitor according to claim 13, wherein, The adhesive also contains a solvent. The reaction start temperature of the curing agent is higher than the evaporation temperature of the solvent.

15. A solid electrolytic capacitor element, comprising: A basic capacitor element comprising an anode body, a dielectric layer formed on the surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer; cathode body; and A first carbon layer disposed between the capacitor base element and the cathode body. The first carbon layer comprises first carbon particles with an average particle size of 40 nm or more and 100 nm or less. The proportion of the first carbon particles in the first carbon layer is more than 25% by volume and less than 75% by volume.

16. The solid electrolytic capacitor element according to claim 15, wherein, The first carbon layer is in contact with the cathode body. No layer containing metal particles is sandwiched between the basic capacitor element and the cathode.

17. The solid electrolytic capacitor element according to claim 15 or 16, wherein, The cathode body comprises at least a metal foil.

18. The solid electrolytic capacitor element according to claim 17, wherein, The metal foil comprises aluminum, aluminum alloy, copper, or copper alloy.

19. The solid electrolytic capacitor element according to claim 17 or 18, wherein, The cathode body includes the metal foil and a surface layer formed on the surface of the metal foil. The surface layer comprises at least one selected from nickel, titanium, titanium compounds, and carbonaceous materials.

20. A solid electrolytic capacitor comprising at least one solid electrolytic capacitor element according to any one of claims 15 to 19.

21. The solid electrolytic capacitor according to claim 20, wherein, The residual volatile organic compounds per unit mass are less than 2000 μg / g.

22. The solid electrolytic capacitor according to claim 20, wherein, The weight loss due to residual volatile components is less than 1.0% by weight.

23. The solid electrolytic capacitor according to claim 20, comprising a laminate having a plurality of solid electrolytic capacitor elements including the solid electrolytic capacitor element.

24. The solid electrolytic capacitor according to claim 23, further comprising an outer packaging body sealing the laminate, a first external electrode, and a second external electrode. In each of the plurality of solid electrolytic capacitor elements, the anode body has a pair of first ends facing each other, and the cathode body has a pair of second ends facing each other. The outer packaging body has a first main surface, a second main surface opposite to the first main surface, a third main surface intersecting the first main surface and the second main surface, and a fourth main surface opposite to the third main surface. One of the pair of first ends of the respective anode bodies of the plurality of solid electrolytic capacitor elements protrudes from the first main surface of the outer casing and is electrically connected to the first external electrode. One of the pair of second ends of the respective cathodes of the plurality of solid electrolytic capacitor elements protrudes from any one of the second, third, and fourth main surfaces of the outer casing and is electrically connected to the second external electrode.

25. The solid electrolytic capacitor according to claim 24, wherein, The other of the pair of first ends of the respective anode bodies of the plurality of solid electrolytic capacitor elements protrudes from the second main surface of the outer casing and is electrically connected to the first external electrode. The pair of second ends of the cathode body are not exposed from the second main surface of the outer packaging body.

26. The solid electrolytic capacitor according to claim 25, wherein, One of the pair of second ends of the respective cathodes of the plurality of solid electrolytic capacitor elements protrudes from the third main surface of the outer casing and is electrically connected to the second external electrode. The other of the pair of second ends of the respective cathodes of the plurality of solid electrolytic capacitor elements is exposed from the fourth main surface of the outer casing and electrically connected to the second external electrode.

27. The solid electrolytic capacitor according to claim 23, further comprising an outer casing sealing the laminate, a first external electrode, and a second external electrode. In each of the plurality of solid electrolytic capacitor elements, the anode body has a pair of first ends facing each other, and the cathode body has a pair of second ends facing each other. The outer packaging body has a first main surface, a second main surface intersecting the first main surface, a third main surface opposite to the first main surface, and a fourth main surface opposite to the second main surface. The anode bodies of the plurality of solid electrolytic capacitor elements are stacked such that one of the pair of first ends is alternately exposed from the first main surface and the second main surface of the outer packaging body, and the one of the pair of first ends is electrically connected to the first external electrode.

28. The solid electrolytic capacitor according to claim 27, wherein, One of the pair of second ends of the respective cathodes of the plurality of solid electrolytic capacitor elements protrudes from the third main surface of the outer casing and is electrically connected to the second external electrode. The other of the pair of second ends of the respective cathodes of the plurality of solid electrolytic capacitor elements is exposed from the fourth main surface of the outer casing and electrically connected to the second external electrode.

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