solid electrolytic capacitor

Abstract

To provide an electrolytic capacitor for suppressing the rise of an ESR even in a high temperature environment.SOLUTION: An electrolytic capacitor includes an anode foil, a cathode body, a separator, and a solid electrolyte layer. The anode foil is made of valve metal and has a dielectric oxide film formed on a foil surface. The cathode body has a cathode foil of valve metal and a carbon layer laminated on the cathode foil. The solid electrolyte layer contains a conductive polymer held in the separator and doped with an acid component. The separator contains a fiber having hydroxyl group, intermolecularly bonded by 1,4-glycosidic bond, and alkali-treated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid electrolytic capacitor having a solid electrolyte. [Background technology]

[0002] Electrolytic capacitors that use valve metals such as tantalum or aluminum can achieve a small size and large capacitance by enlarging the surface area of ​​the valve metal serving as the anode-side counter electrode by forming it into a sintered body or etched foil, etc. In particular, solid electrolytic capacitors, in which a dielectric oxide film is covered with a solid electrolyte, are small in size, have large capacitance, and low equivalent series resistance. In addition, they are easy to fabricate into chips and are suitable for surface mounting, making them essential for the miniaturization, high functionality, and cost reduction of electronic devices.

[0003] Known solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes. In recent years, conductive polymers derived from monomers with π-conjugated double bonds have rapidly become popular as solid electrolytes. An example of such a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT). Conductive polymers exhibit high conductivity when polymerized by chemical oxidation or electrochemical oxidation using acidic dopants such as polyanions, typically organosulfonic acid (PSS). They also exhibit excellent adhesion to dielectric oxide films.

[0004] The conductive polymer is supported on a separator that prevents short circuits between the anode and cathode, and is connected between the surface of the dielectric oxide film on the anode side and the surface of the cathode, forming a conductive path connecting the surface of the dielectric oxide film and the surface of the cathode. Cellulose fibers such as kraft, Manila hemp, esparto, hemp, and rayon are often used as separators.

[0005] In order to reduce the equivalent series resistance (ESR), a solid electrolytic capacitor has been proposed in which a metal carbide with low specific electrical resistance, such as TiC, WC, or ZrC, is formed on the surface of the cathode foil (see, for example, Patent Document 1). According to this proposal, the ESR of the solid electrolytic capacitor can be reduced because the adhesion between the metal carbide on the cathode side and the conductive polymer is improved.

[0006] When metal carbide is formed on the surface of a cathode foil, there is a problem that an oxide film gradually grows on the surface of the metal carbide. To address this problem, a solid electrolytic capacitor has been proposed in which carbon is formed on the surface of the cathode foil using a dry plating method such as ion plating (see, for example, Patent Document 2). By forming a carbon layer on the surface of the cathode foil, it is possible to prevent the formation of an oxide film on the cathode side. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-109272 [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-190878 Summary of the Invention [Problem to be solved by the invention]

[0008] However, it was confirmed that when exposed to a high temperature environment of 150°C or higher, the ESR increases significantly even if a carbon layer is formed on the surface of the cathode foil. The reasons for this are thought to be as follows.

[0009] That is, the carbon material that makes up the carbon layer has surface functional groups such as hydroxyl groups on its surface. The β-glucose that makes up the cellulose fibers used in the separator also has hydroxyl groups in its molecules. In high-temperature environments above 150°C, hydrogen bonds between the hydroxyl groups of the cellulose fibers facilitate adhesion to the carbon layer. Second, the conductive polymer supported on the cellulose may be doped with an acid component as a dopant. Cellulose fibers are constructed by bonds between β-glucose molecules, i.e., 1,4-glycosidic bonds. When these 1,4-glycosidic bonds react with the acid component doped into the conductive polymer, the bonds between the cellulose fibers are broken as a result of the hydrolysis reaction.

[0010] As the bonds between the cellulose fibers break, they are separated into cellulose fibers that are attached to the carbon layer and those that are not. As the cellulose fibers are separated, the conductive polymers supported on the separator are also separated. This in turn breaks the conductive paths made up of connected conductive polymers. If the conductive paths are severed frequently, the ESR reduction effect of the solid electrolytic capacitor, which is based on the adhesion between the conductive polymer and the carbon layer, is lost.

[0011] At temperatures below 150°C, there is little reaction between the acid component doped into the conductive polymer and the 1,4-glycoside bond portion of the cellulose fiber. However, when a solid electrolytic capacitor is exposed to a temperature environment of 150°C or higher, the reaction between the acid component doped into the conductive polymer and the 1,4-glycoside bond portion of the cellulose fiber is accelerated. Therefore, when a solid electrolytic capacitor is exposed to a high-temperature environment of 150°C or higher, it is thought that the ESR will increase significantly even if a carbon layer is formed on the surface of the cathode foil.

[0012] The present invention has been proposed to solve the above problems, and an object of the present invention is to provide an electrolytic capacitor in which the increase in ESR is suppressed even in a high-temperature environment. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, the solid electrolytic capacitor of the present invention is characterized by comprising: an anode foil made of a valve metal and having a dielectric oxide film formed on the foil surface; a cathode body having a valve metal cathode foil and a carbon layer laminated on the cathode foil; a separator interposed between the anode foil and the cathode body, the separator including alkali-treated fibers having hydroxyl groups and bonded by 1,4-glycosidic bonds between molecules; and a solid electrolyte layer held by the separator and including a conductive polymer doped with an acid component.

[0014] According to this invention, the use of alkali-treated fibers reduces the amount of hydroxyl groups in the fibers, making it difficult for the separator to adhere to the carbon layer. Therefore, even if the 1,4-glycosidic bonds in the separator fibers are cleaved by the acid component doped in the conductive polymer, the separator is less likely to tear into the carbon layer side and the side away from the carbon layer. Furthermore, the conductive path formed by the conductive polymer held in the separator is not severed. Therefore, the increase in ESR of the solid electrolytic capacitor is suppressed even in high-temperature environments.

[0015] Therefore, if the separator is made of fibers having hydroxyl groups and intermolecular bonds formed by 1,4-glycosidic bonds, the present invention can provide an effect of suppressing an increase in ESR in a high-temperature environment. Typically, such fibers may be alkali-treated cellulose fibers. The acid component may be polystyrene sulfonic acid.

[0016] The fibers may be fibrillated. The fibers are entangled with each other through the fibrils, improving the bonding strength between the fibers of the separator. This makes the separator less likely to tear even if part of the separator is attached to the carbon layer. Therefore, the increase in ESR of this solid electrolytic capacitor can be further suppressed even in high-temperature environments.

[0017] An electrolyte may also be provided. [Effects of the Invention]

[0018] According to the present invention, an increase in ESR can be suppressed even when the electrolytic capacitor is exposed to a high-temperature environment. [Brief explanation of the drawings]

[0019] [Figure 1] 1 shows the ESR of the solid electrolytic capacitors of Example 1, Comparative Example 1, and Comparative Example 2, which do not contain an electrolytic solution. [Figure 2] 1 shows the rate of increase of the ESR of the solid electrolytic capacitors of Example 1, Comparative Example 1, and Comparative Example 2, which do not contain an electrolytic solution, with time 0 as the reference. [Figure 3] 1 shows the ESR of the solid electrolytic capacitors of Example 1, Comparative Example 1, and Comparative Example 2, each containing an electrolytic solution. [Figure 4] 1 shows the rate of increase of ESR of the solid electrolytic capacitors of Example 1, Comparative Example 1, and Comparative Example 2 containing an electrolytic solution, with time 0 as the reference. [Figure 5] 1 shows photographs of the surfaces of cathode bodies of Examples 1 and 2 and Comparative Examples 1, 3, and 4. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE INVENTION An electrolytic capacitor and a manufacturing method thereof according to an embodiment of the present invention will be described below. However, the present invention is not limited to the following embodiment.

[0021] (Overall composition) An electrolytic capacitor is a passive element that obtains capacitance through the dielectric polarization of a dielectric oxide film and stores and discharges electric charge through the capacitance. This electrolytic capacitor includes an anode foil with a dielectric oxide film formed on its surface, a cathode body, a solid electrolyte layer, and a separator. The anode foil and the cathode body are arranged opposite each other, and the separator and solid electrolyte layer are interposed between the anode foil and the cathode body. The anode foil and the cathode body are arranged in a stacked configuration, where they are alternately stacked with the separator sandwiched between them, or in a wound configuration, where they are wound with the separator sandwiched between them.

[0022] The solid electrolyte layer contains a conductive polymer. The conductive polymer is supported on a separator and arranged so as to connect between the dielectric oxide film formed on the surface of the anode foil and the cathode body, forming a conductive path and serving as the true cathode. Electrolytic capacitors can use both a solid electrolyte layer and an electrolyte solution, which fills the voids in the capacitor element. The capacitor element is formed by an anode foil with a dielectric oxide film formed thereon and a cathode body facing each other via a separator, with the conductive polymer attached.

[0023] (electrode foil) The cathode body includes a cathode foil. The anode foil and the cathode foil of the cathode body are foil bodies made of valve metals. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode foil is preferably 99.9% or higher, and that of the cathode foil is preferably about 99% or higher, but impurities such as silicon, iron, copper, magnesium, and zinc may be contained.

[0024] Anode and cathode foils have a surface-expanding layer formed on one or both surfaces of the foil. The surface-expanding layer is formed by electrolytic etching, chemical etching, sandblasting, or by vapor-depositing or sintering metal particles onto the foil. That is, the surface-expanding layer consists of tunnel-shaped pits, spongy pits, or voids between densely packed powder particles. Examples of electrolytic etching include DC etching and AC etching, in which DC or AC is applied in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. Chemical etching involves immersing the metal foil in an acid or alkaline solution. The tunnel-shaped pits may be formed long enough to penetrate the foil or may not reach the center of the foil.

[0025] The dielectric oxide film of the anode foil is typically an oxide film formed on the surface layer of the anode foil. For example, if the anode foil is an aluminum foil, this dielectric oxide film is aluminum oxide formed by oxidizing the surface layer of the surface-expanding layer. The dielectric oxide film is intentionally formed by a chemical conversion treatment in which a voltage is applied in a solution free of halogen ions, such as an aqueous solution of adipic acid, boric acid, or phosphoric acid. The surface layer of the cathode foil may also be intentionally formed by this chemical conversion treatment, or may be naturally formed. The natural oxide film that naturally forms on the surface layer of the cathode foil is formed by the cathode foil reacting with oxygen in the air.

[0026] (cathode body) The cathode body includes a carbon layer in addition to a cathode foil. The carbon layer is laminated on the cathode foil. The carbon layer is a layer containing a carbon material. The carbon material is fibrous carbon, carbon powder, or a mixture thereof. The fibrous carbon or carbon powder is preferably subjected to a porosity treatment such as an activation treatment or an opening treatment to form pores.

[0027] Examples of carbon powders include natural plant tissues such as coconut husks, synthetic resins such as phenols, activated carbon derived from fossil fuels such as coal, coke, and pitch, carbon blacks such as ketjen black, acetylene black, channel black, and thermal black, carbon nanohorns, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, and mesoporous carbon. Examples of fibrous carbon include carbon nanotubes and carbon nanofibers. Carbon nanotubes may be single-walled carbon nanotubes, which have a single graphene sheet, or multi-walled carbon nanotubes (MWCNTs), which have two or more graphene sheets rolled coaxially to form multiple tube walls.

[0028] This carbon layer is formed on the cathode foil by vacuum deposition, sputtering, ion plating, CVD, coating, electrolytic plating, electroless plating, or the like. In the coating method, a carbon material is dispersed in a dispersion solvent to prepare a slurry, which is then coated on the cathode foil by a slurry casting method, doctor blade method, spray atomization, or the like, and dried. In the vapor deposition method, the carbon material is evaporated by heating with electrical current in a vacuum, or by irradiating the carbon material with an electron beam in a vacuum, forming a film of the carbon material on the cathode foil. In the sputtering method, a target made of a carbon material and the cathode foil are placed in a vacuum chamber, and an inert gas is introduced into the vacuum chamber and a voltage is applied, causing the plasmatized inert gas to collide with the target, and carbon material particles knocked out from the target are deposited on the cathode foil.

[0029] The carbon layer is preferably formed on the surface-expanding layer of the cathode foil. It is also preferable to apply a press process to press the carbon layer against the cathode foil. In the press process, the laminate of the carbon layer and the cathode foil is sandwiched between press rollers and a linear press pressure is applied. The linear press pressure is preferably about 0.01 to 100 t / cm. By applying a press process to the carbon layer formed on the surface-expanding layer of the cathode foil, the carbon layer adheres to the cathode foil, reducing the ESR of the solid electrolytic capacitor.

[0030] The carbon material contained in the carbon layer may also be a mixture of flake or scaly graphite and carbon black, which is spherical carbon. The flake or scaly graphite preferably has an aspect ratio of minor axis to major axis in the range of 1:5 to 1:100. When a carbon layer containing this combination of carbon materials is laminated on a cathode foil, compressed, and pressed against the surface-expanding layer, the carbon black is easily rubbed into the surface-expanding layer by the graphite. The graphite easily deforms along the uneven surface of the surface-expanding layer, and easily accumulates on the uneven surface. The graphite then acts as a pressing lid to hold the spherical carbon inside the surface-expanding layer.

[0031] (Solid electrolyte layer) The solid electrolyte layer contains a conductive polymer. The conductive polymer is a conjugated polymer doped with an acid component as a dopant. The conjugated polymer is obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of a monomer or its derivative having a π-conjugated double bond. By performing a doping reaction on the conjugated polymer, the conductive polymer exhibits high conductivity. Any known conjugated polymer can be used without particular limitation. Examples of conjugated polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. These conjugated polymers may be used alone, in combination with two or more types, or as a copolymer of two or more monomers. A representative conductive polymer is poly(3,4-ethylenedioxythiophene), also known as PEDOT, doped with polystyrene sulfonic acid (PSS).

[0032] Known acid dopants can be used without any particular limitation. Examples include inorganic acids such as boric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, oxalic acid, citric acid, ascot acid, tartaric acid, squaric acid, rhodizonic acid, croconic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, borodisalicylic acid, bisoxalateborate acid, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid. Polyanions can also be used as dopants, including polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid. The dopant may be used alone or in combination of two or more kinds. Also, a polymer or a monomer may be used.

[0033] The conductive polymer is held by the separator and adheres to the dielectric oxide film of the anode foil and the cathode body by impregnating a capacitor element consisting of an anode foil with a dielectric oxide film and a cathode body facing each other through a separator with a dispersion liquid containing the conductive polymer. The solvent for the dispersion liquid can be any solvent that disperses conductive polymer particles or powder, and is typically water. Ethylene glycol may be used as the dispersion liquid solvent if necessary. It has been found that using ethylene glycol as the dispersion liquid solvent can reduce the electrical properties of the product, particularly the ESR characteristics. To improve the impregnation and electrical conductivity of the dispersion liquid, various additives may be used in the dispersion liquid or neutralization by adding cations may be performed.

[0034] The method of impregnating the conductive polymer dispersion liquid may involve immersing the capacitor element in the dispersion liquid, or applying it by dripping or spraying. Furthermore, the dispersion liquid may be impregnated not only into the entire capacitor element, but also into the anode foil or cathode body, and then the capacitor element may be assembled. To promote the impregnation of the dispersion liquid into the cathode foil or cathode body, a decompression treatment or a pressurization treatment may be performed as necessary. This application process may be repeated multiple times.

[0035] (electrolyte) When an electrolyte solution is used in combination, the solvent for the electrolyte solution is not particularly limited, and a protic organic polar solvent or an aprotic organic polar solvent can be used. Typical examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, oxyalcohol compounds, and water, such as ethylene glycol or propylene glycol. Typical examples of aprotic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides, such as sulfolane, γ-butyrolactone, ethylene carbonate, and propylene carbonate.

[0036] The solute contained in the electrolyte solution includes anionic and cationic components, typically organic acids such as adipic acid and benzoic acid or their salts, inorganic acids such as boric acid and phosphoric acid or their salts, or composite compounds of organic acids and inorganic acids such as borodisalicylic acid or their ionically dissociable salts, which may be used alone or in combination of two or more. Examples of these salts of organic acids, salts of inorganic acids, and at least one salt of a composite compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, potassium salts, etc. Anionic acids and cationic bases may be added separately to the electrolyte solution as solute components.

[0037] Furthermore, other additives can be added to the electrolyte. Examples of additives include polyethylene glycol, complex compounds of boric acid and polysaccharides (e.g., mannitol, sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds, phosphate esters, and colloidal silica. These may be used alone or in combination of two or more. Nitro compounds suppress the generation of hydrogen gas in electrolytic capacitors. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, and p-nitrophenol.

[0038] After preparation, the electrolyte solution is impregnated into the capacitor element on which the solid electrolyte layer has been formed. When the capacitor element is impregnated with the electrolyte solution, a reduced pressure treatment or a pressurized treatment may be performed as necessary to promote the impregnation. The impregnation process may be repeated multiple times.

[0039] (separator) The separator is a fiber that has hydroxyl groups and intermolecular bonds formed by 1,4-glycosidic bonds, and that has been pre-treated with alkali. An example of such a fiber is alkali-treated cellulose fiber. The alkali treatment reduces the number of hydroxyl groups in the fiber. The reduction in the number of hydroxyl groups in the fiber reduces the proportion of fibers that form hydrogen bonds with the hydroxyl groups in the carbon layer. This makes it difficult for the separator to adhere to the carbon layer.

[0040] If the separator were not attached to the carbon layer, the 1,4-glycosidic bonds present between the fiber molecules would react with the acid component doped into the conductive polymer. As the hydrolysis reaction progressed, the bonds between the fibers would break, but the fibers would be less likely to break. If the fibers were less likely to break, the conductive paths formed by the interconnected conductive polymers would not be disrupted. Therefore, the ESR reduction effect of the solid electrolytic capacitor, based on the adhesion between the conductive polymer and the carbon layer, would be maintained. In other words, the ESR of the solid electrolytic capacitor would be kept low even if it was exposed to a high-temperature environment of 150°C or higher.

[0041] The separator can retain moisture through hydrogen bonding between hydroxyl groups and water (HO). Therefore, it can be said that the water absorbency, which is the ability to retain moisture, correlates with the number of hydroxyl groups. The fibers used in the separator are preferably subjected to an alkali treatment until the water absorbency of the separator decreases to more than 26 mm / 10 min and less than 77 mm / 10 min.

[0042] By setting the separator's water absorbency to less than 77 mm / 10 min, this solid electrolytic capacitor can significantly suppress an increase in ESR, even in high-temperature environments. If the separator's water absorbency is 26 mm / 10 min or less, the hydroxyl groups in the fibers are excessively reduced by the alkali treatment, making the fibers themselves less able to absorb water. Therefore, when using a dispersion of a conductive polymer in water in the solid electrolyte layer formation process, for example, it becomes difficult to impregnate the separator with the conductive polymer, making it difficult to form a conductive path in the separator. Furthermore, if the separator's water absorbency is 77 mm / 10 min or more, the number of remaining hydroxyl groups in the fibers increases, resulting in a high adhesion between the separator and the carbon layer. Therefore, the separator is easily separated into fibers attached to the carbon layer and fibers not attached to the carbon layer by the acid component doped in the conductive polymer.

[0043] The water absorption was measured according to the Klemm method. Each separator was cut to a width of 15 mm and a length of 200 mm, and the bottom 30 mm was immersed in ultrapure water. After 10 minutes, the absorbency was measured by measuring the height of the absorbed material above the liquid surface, i.e., the length of the absorbed material. The presence or absence of separator adhesion to the carbon layer can be determined by, for example, leaving the solid electrolytic capacitor at a temperature of 170°C for 200 hours, disassembling the capacitor element, and checking for the presence or absence of fibers adhering to the carbon layer.

[0044] Furthermore, the separator fibers are preferably fibrillated by generating thin fibers that branch off from the surface of the original fibers. Fibrils can be formed by beating. The fibrillated fibers are entangled with each other using the fibrillated thin fibers, improving the separator's strength. Therefore, even if a portion of the separator adheres to the carbon layer, the separator is less likely to tear. Therefore, even in high-temperature environments, this solid electrolytic capacitor further suppresses the increase in ESR.

[0045] (Manufacturing method) Such an electrolytic capacitor is produced through an anode production process in which an anode foil is produced, a cathode production process in which a cathode body is produced, an element production process in which a capacitor element is produced in which an anode foil and a cathode foil are arranged opposite each other, a solid electrolyte layer formation process in which a solid electrolyte layer is formed on the capacitor element, and an electrolyte impregnation process in which an electrolyte is impregnated into the capacitor element with the solid electrolyte layer formed thereon.

[0046] In the anode fabrication process, a valve metal is stretched to form an anode foil, a surface-expanding layer is formed on the anode foil, and a dielectric oxide film is then formed on the surface of the surface-expanding layer. In the cathode fabrication process, a valve metal is stretched to form a cathode foil, a surface-expanding layer is then formed on the anode foil, and a carbon layer is then formed on the cathode foil by pressing.

[0047] Fibers having hydroxyl groups, such as cellulose fibers, are pre-treated with alkali and used as a separator. An anode foil with a dielectric oxide film formed thereon and a cathode body are then stacked together with the separator interposed between them. In the case of a laminated type, the anode foil, cathode body, and separator are alternately stacked in multiple layers. In the case of a wound type, the anode foil and cathode body stacked together with the separator interposed between them are wound together. In the solid electrolyte layer forming process, a dispersion liquid in which a conductive polymer is dispersed is impregnated into the capacitor element. In the electrolyte solution impregnation process, the capacitor element, which has a solid electrolyte layer formed through the solid electrolyte layer forming process, is impregnated with the electrolyte solution.

[0048] As a result, even if this solid electrolytic capacitor does not have a separator attached to the carbon layer and is exposed to a high-temperature environment of 150°C or higher, and the acid component doped into the conductive polymer promotes the hydrolysis reaction of the 1,4-glycoside bonds connecting the separator fibers, the conductive path through the conductive polymer will not be ruptured, and an increase in ESR can be suppressed. [Example]

[0049] The electrolytic capacitor of the present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0050] The solid electrolytic capacitor of Example 1 was fabricated as follows. First, the anode foil and cathode foil were aluminum foils with their surfaces enlarged. The surfaces were enlarged by AC etching. In the AC etching, the cathode foil was immersed in an acidic aqueous solution containing approximately 8% by weight of hydrochloric acid as the main electrolyte at a liquid temperature of 25°C, and an AC current of 10 Hz and a current density of 0.14 A / cm was applied. 2 A current of 1000kJ / min was applied to the aluminum foil for about 5 minutes.

[0051] To clarify the effects of the carbon layer and separator, a carbon layer was formed on both the anode and cathode foils. Carbon black was selected as the carbon material for the carbon layer. Carbon black powder, styrene butadiene rubber (SBR) as a binder, and a carboxymethyl cellulose sodium (CMC-Na) aqueous solution as a dispersant were mixed and kneaded to prepare a slurry, which was then uniformly applied to the anode and cathode foils. The slurry was then heated and dried to volatilize the solvent.

[0052] After the carbon layer was formed, a pressing process was carried out in which the carbon layer was pressed against the enlarged anode foil and cathode foil. In the pressing process, the laminate of the anode foil and the carbon layer and the laminate of the cathode foil and the carbon layer were sandwiched between press rollers and pressed with a pressure of 5.38 kNcm. -1 A linear press pressure of 1000 kJ / min was applied. The linear press pressure was applied using a press machine manufactured by Takumi Giken Co., Ltd. The diameter of the press roller was 180 mm, the press width was 130 mm, and the cathode body was transported once at 3 m / min. Aluminum tab-shaped lead terminals were stitch-connected to the anode foil and cathode foil, respectively.

[0053] A separator was sandwiched between anode foil and cathode foil with carbon layers formed thereon, and the resulting mixture was rolled up to produce a capacitor element. Here, the solid electrolytic capacitor of Example 1 used a separator made of rayon paper, a cellulose fiber that had been alkali-treated. Measurements showed that the alkali treatment of this rayon paper increased its water absorbency to 15 mm / 10 min or more.

[0054] Next, a conductive polymer dispersion was prepared. This dispersion consisted of a powder of polyethylenedioxythiophene (PEDOT), a conductive polymer doped with polystyrene sulfonate (PSS), dispersed in water. The capacitor element was immersed in this dispersion. While immersed, it was exposed to a pressure environment of 30 kPa for 5 minutes. After this, the capacitor element was removed and dried at 150°C for 30 minutes. As a result, the separator carried polyethylenedioxythiophene (PEDOT) doped with polystyrene sulfonate (PSS), and an electron path consisting of a conductive polymer was formed between the anode foil and the cathode foil.

[0055] The capacitor element was inserted into a cylindrical outer case with a bottom, and a sealing rubber was attached to the open end, and the case was sealed by crimping. The solid electrolytic capacitor of Example 1 thus fabricated had a diameter of 10 mm and a height of 8 mm.

[0056] Furthermore, solid electrolytic capacitors of Example 2 and Comparative Examples 1 to 4 were also fabricated. As shown in Table 1 below, the solid electrolytic capacitors of Example 2 and Comparative Examples 1 to 4 differ in whether or not they were impregnated with an electrolyte solution and in the type of separator. Furthermore, Example 2 and Comparative Examples 3 and 4, which include an electrolyte solution impregnation step, were fabricated through an electrolyte solution impregnation step in which a capacitor element impregnated with a conductive polymer dispersion was impregnated with an electrolyte solution. Other manufacturing methods, manufacturing conditions, and capacitor configurations for the solid electrolytic capacitors of Example 2 and Comparative Examples 1 to 4 were the same as those for Example 1.

[0057] (Table 1) TIFF0007786135000001.tif71161

[0058] As shown in Table 1, the separator of Example 2 is the same as that of Example 1, which is rayon paper that has been alkali-treated and has a water absorbency of 31 mm / 10 min. The solid electrolytic capacitor of Example 2 differs from Example 1 in that an electrolyte solution is used in addition to the conductive polymer. The electrolyte solution of Example 2 was prepared by using ethylene glycol as a solvent and adding ammonium azelaate as a solute.

[0059] The separator of Comparative Example 1 was manila paper, a cellulose fiber that had not been alkali-treated, and had a water absorbency of 77 mm / 10 min or more. The solid electrolytic capacitor of Comparative Example 1, like Example 1, did not use an electrolyte. The separator of Comparative Example 2 was chemical fiber paper that combined primarily nylon fiber with fibrillated acrylic fiber, and had a water absorbency of 26 mm / 10 min or more. The solid electrolytic capacitor of Comparative Example 2, like Example 1, did not use an electrolyte. The solid electrolytic capacitor of Comparative Example 3 had the same separator as Comparative Example 1 and also used the same electrolyte as Example 2. The solid electrolytic capacitor of Comparative Example 4 had the same separator as Comparative Example 2 and also used the same electrolyte as Example 2.

[0060] The solid electrolytic capacitors of Examples 1 and 2 and Comparative Examples 1 to 4 were exposed to a temperature environment of 170°C, and the ESR was measured after 0 hours, 160 hours, and 325 hours. "0 hours" refers to before exposure to a temperature environment of 170°C. The ESR measurement results are shown in graphs in Figures 1 to 4. Figure 1 shows the ESR of each of the solid electrolytic capacitors of Example 1, Comparative Example 1, and Comparative Example 2, which do not contain an electrolyte. Figure 2 shows the increase in ESR of each of the solid electrolytic capacitors of Example 1, Comparative Example 1, and Comparative Example 2, which do not contain an electrolyte, based on time 0. Figure 3 shows the ESR of each of the solid electrolytic capacitors of Example 2, Comparative Example 3, and Comparative Example 4, which contain an electrolyte. Figure 4 shows the increase in ESR of each of the solid electrolytic capacitors of Example 2, Comparative Example 3, and Comparative Example 4, which contain an electrolyte, based on time 0.

[0061] 1 to 4, the ESR of the solid electrolytic capacitors of Examples 1 and 2 and Comparative Examples 1 to 4 was almost the same at 0 hours. In contrast, after 160 hours and 325 hours, the ESR of all the solid electrolytic capacitors increased, but it was confirmed that the ESR of Examples 1 and 2 remained lower than that of the corresponding Comparative Examples 1 to 4. Furthermore, the ESR of Comparative Examples 2 and 4 became 1000 mΩ or higher or 2300 mΩ or higher after 160 hours.

[0062] The solid electrolytic capacitors of Examples 1 and 2 and Comparative Examples 1, 3, and 4 were exposed to a temperature environment of 170°C and then disassembled, and the surfaces of the cathode bodies were photographed. All but Comparative Example 4 were exposed to a temperature environment of 170°C for 513 hours, and Comparative Example 4 was exposed to a temperature environment of 170°C for 250 hours. The results are shown in FIG. 5. (a) in FIG. 5 is the cathode body of Example 1, (b) in FIG. 5 is the cathode body of Example 2, (c) in FIG. 5 is the cathode body of Comparative Example 1, (d) in FIG. 5 is the cathode body of Comparative Example 3, and (e) in FIG. 5 is the cathode body of Comparative Example 4.

[0063] As shown in Figure 5(e), it can be seen that a very large amount of nylon fibers adhere to the cathode body of Comparative Example 4, which used a separator made of nylon that was not alkali-treated. As shown in Figures 5(c) and 5(d), it can be seen that manila paper fibers adhere to the cathode bodies of Comparative Examples 1 and 3, which used a separator made of manila paper that was not alkali-treated, although not as much as in Comparative Example 4. On the other hand, as shown in Figures 5(a) and 5(b), no rayon paper fibers are observed to adhere to the cathode bodies of Examples 1 and 2, which used a separator made of alkali-treated rayon paper.

[0064] That is, when non-alkali-treated fibers are used as a separator, the bonds between the fibers are broken and the fibers are separated into fibers that are attached to the carbon layer and fibers that are not attached to the carbon layer. On the other hand, when alkali-treated fibers are used as a separator, even if the bonds between the fibers are broken, the fibers are less likely to attach to the carbon layer, which confirms that the fibers are not separated.

[0065] In general, as shown in Figures 1 to 5, when non-alkali-treated fibers are used as separators, the fibers are separated into those that adhere to the carbon layer and those that do not, the conductive paths formed by the connected conductive polymers are also cut, and the ESR reduction effect of the solid electrolytic capacitor is lost. On the other hand, as shown in Figures 1 to 5, when alkali-treated fibers are used as separators, the fibers are less likely to adhere to the carbon layer, so the fibers are not separated, the conductive paths formed by the connected conductive polymers are not cut, and the ESR reduction effect of the solid electrolytic capacitor is maintained.

Claims

1. an anode foil made of a valve metal and having a dielectric oxide film formed on the foil surface; a cathode body including a valve metal cathode foil and a carbon layer laminated on the cathode foil and having hydroxyl groups on its surface; a separator interposed between the anode foil and the cathode body, the separator including alkali-treated fibers having hydroxyl groups and intermolecular bonds formed by 1,4-glycosidic bonds; a solid electrolyte layer held by the separator and including a conductive polymer doped with an acid component; To have A solid electrolytic capacitor characterized by:

2. the fibers are alkali-treated cellulose fibers; 2. The solid electrolytic capacitor according to claim 1,

3. the fibers are fibrillated; 3. The solid electrolytic capacitor according to claim 1, wherein:

4. the acid component is polystyrene sulfonic acid; 4. The solid electrolytic capacitor according to claim 1, wherein:

5. Further comprising an electrolyte; 5. The solid electrolytic capacitor according to claim 1, wherein:

6. The separator has a water absorption rate of more than 26 mm / 10 min and less than 77 mm / 10 min, 6. The solid electrolytic capacitor according to claim 1, wherein:

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