Solid electrolytic capacitor and method for manufacturing same

Abstract

Provided are: a solid electrolytic capacitor having improved capacitance while maintaining good short-circuiting resistance; and a method for manufacturing the same. This solid electrolytic capacitor is provided with a laminate, a conductive polymer, and a tape. The laminate is formed by disposing an anode foil and a cathode foil so as to overlap each other with a separator containing at least fibrillated fibers interposed therebetween. The conductive polymer is formed through attachment of a conductive polymer liquid, and at least the separator is impregnated with the same. The tape is wound on and fixed to the peripheral surface of the laminate, and has a contact angle of less than 50° with respect to the conductive polymer liquid. This method for manufacturing a solid electrolytic capacitor comprises: a winding-fixing step for winding the tape having a contact angle of less than 50° with respect to the conductive polymer liquid on the peripheral surface of the laminate to be fixed thereto; and a solid electrolyte formation step for immersing the laminate having the tape wound thereon and fixed thereto in the conductive polymer liquid to attach the conductive polymer to the inside of the laminate.

Description

Solid electrolytic capacitor and manufacturing method

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

[0002] Electrolytic capacitors have anode and cathode foils made of valve metals such as tantalum or aluminum. The anode foil is enlarged by shaping the valve metal into a sintered or etched foil, and the enlarged surface is coated with a dielectric film. An electrolyte is interposed between the anode and cathode foils. The electrolyte is in close contact with the uneven surface of the anode foil and functions as the true cathode.

[0003] Solid electrolytic capacitors filled with conductive polymers as electrolytes are rapidly becoming popular. Conductive polymers are derived from monomers with π-conjugated double bonds. An example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT), which has excellent adhesion to dielectric films. Conductive polymers exhibit high conductivity when polyanions such as organic sulfonic acids are used as dopants during chemical oxidative polymerization or electrolytic oxidative polymerization.

[0004] In addition to low equivalent series resistance, solid electrolytic capacitors have the advantage of being long-lasting, as they are not susceptible to drying-up due to evaporation of the electrolyte over time. However, so-called hybrid-type solid electrolytic capacitors, which use both a conductive polymer and an electrolyte to repair defects in the dielectric film and reduce leakage current in solid electrolytic capacitors, are also becoming popular.

[0005] A wound type solid electrolytic capacitor is known. A wound type solid electrolytic capacitor includes a laminate consisting of an anode foil, a cathode foil, and a separator. The anode foil and the cathode foil are strip-shaped foils. The cathode foil and the anode foil are arranged opposite each other with the separator interposed between them. The strip is then wound so that the short side of the strip is aligned with the winding axis and the long side of the strip is curved. A strip-shaped tape is wrapped around the outer periphery of the laminate to prevent it from unraveling (see, for example, Patent Document 1).

[0006] In such solid electrolytic capacitors, natural fiber separators such as cellulose are one option for the separator. However, natural fiber separators have a coarse mesh and may not be able to capture minute metallic foreign particles of a few micrometers in size. Therefore, for solid electrolytic capacitors using natural fiber separators, measures are required to prevent short-circuiting between the anode foil and the cathode foil due to metallic foreign particles.

[0007] In contrast to this natural fiber separator, a separator containing at least fibrillated fibers, which are fibers that have been fluffed, is sometimes used (see, for example, Patent Document 2). Fibrillated fibers have a denser structure than natural fibers. Therefore, separators containing at least fibrillated fibers can capture minute metallic foreign matter of about several μm in size, compared to natural fiber separators. This ability to easily capture minute metallic foreign matter of about several μm in size is referred to as excellent short-circuit resistance.

[0008] Japanese Patent Laid-Open No. 1-201911 Japanese Patent Laid-Open No. 2008-166308

[0009] Furthermore, separators containing at least fibrillated fibers are thinner than natural fiber separators. Therefore, the volume of the anode foil per unit volume of the element housing can be increased. Therefore, separators containing at least fibrillated fibers are expected to improve the capacitance of solid electrolytic capacitors due to their thin thickness. However, solid electrolytic capacitors using fibrillated fibers for the separator often have lower capacitance than solid electrolytic capacitors using natural fiber separators.

[0010] When manufacturing a solid electrolytic capacitor, a portion of a separator is immersed in a conductive polymer liquid, allowing the separator to absorb the conductive polymer liquid. The conductive polymer liquid is a dispersion or solution in which a conductive polymer is dispersed or dissolved. This manufacturing method allows the separator to be impregnated with the conductive polymer liquid. However, separators containing at least fibrillated fibers with a dense structure have a high air resistance and therefore a lower ability to absorb the conductive polymer liquid than natural fiber separators. Therefore, separators containing at least fibrillated fibers are prone to have areas that are not impregnated with the conductive polymer liquid, resulting in a lower capacitance of the solid electrolytic capacitor.

[0011] The present invention has been proposed to solve the above-mentioned problems, and its object is to provide a solid electrolytic capacitor having improved capacitance while maintaining good short-circuit resistance, and a method for manufacturing the same.

[0012] In order to solve the above problems, the solid electrolytic capacitor of this embodiment includes an anode foil having a dielectric coating formed thereon, a cathode foil facing the anode foil, a separator containing at least fibrillated fibers, a laminate in which the anode foil and the cathode foil are stacked with the separator interposed therebetween, a conductive polymer formed by adhering a conductive polymer liquid and impregnating at least the separator, and a tape wound around the periphery of the laminate and having a contact angle of less than 50° with the conductive polymer liquid.

[0013] The tape may cover an area of ​​40% to 63% of the periphery of the laminate.

[0014] The separator may have an air resistance of 1.7 [s / 100 mL] or more.

[0015] The separator may have an air resistance of 5.4 [s / 100 mL] or more.

[0016] The tape may have a base material and an adhesive layer, and the base material may be made of resin.

[0017] In order to solve the above-mentioned problems, the method for manufacturing a solid electrolytic capacitor of this embodiment includes a laminate-forming step of forming a laminate by stacking an anode foil having a dielectric coating formed thereon, a separator containing at least fibrillated fibers, and a cathode foil; a winding-up step of winding up the circumferential surface of the laminate with tape having a contact angle with the conductive polymer liquid of less than 50°; and a solid electrolyte-forming step of immersing the laminate wound up with the tape in a conductive polymer liquid to adhere a conductive polymer to the interior of the laminate.

[0018] According to the present invention, it is possible to improve the capacitance of a solid electrolytic capacitor using a separator that contains at least fibrillated fibers.

[0019] 1 is a graph showing the relationship between the contact angle of the tape and the capacitance appearance rate of the solid electrolytic capacitor, and a graph showing the relationship between the contact angle of the tape and the capacitance increase rate of the solid electrolytic capacitor.

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

[0021] (Overall Structure and Manufacturing Method) A solid electrolytic capacitor is a passive device that obtains capacitance through the dielectric polarization of a dielectric film and stores and discharges electric charge. This solid electrolytic capacitor includes an anode foil and a cathode foil with a dielectric film formed on the surface. The anode foil and the cathode foil are arranged opposite each other. A separator is interposed between the anode foil and the cathode foil to prevent short-circuiting between the anode foil and the cathode foil.

[0022] A conductive polymer is attached to the dielectric film on the anode foil. The conductive polymer is the electrolyte of the solid electrolytic capacitor. The conductive polymer is held in place by a fibrous separator and adheres to the dielectric film on the anode foil, connecting it to the dielectric film and the cathode foil to create a conductive path, making it the true cathode. A liquid electrolyte can also be used in solid electrolytic capacitors. The liquid electrolyte fills the gaps between the dielectric film and the conductive polymer.

[0023] This solid electrolytic capacitor includes a laminate formation process. The laminate may be formed by stacking an anode foil and a cathode foil with a separator interposed therebetween, and the wound body formed by winding the laminate is also one type of laminate.

[0024] A strip of tape is wrapped around the outer periphery of the laminate to prevent the laminate from unraveling. The process of winding the laminate with this tape is specifically called the winding process. This tape has a base material and an adhesive layer, and is wrapped around the entire periphery of the laminate, covering the entire periphery of the laminate.

[0025] Prior to the laminate formation step, lead terminals may be connected to the anode foil and the cathode foil, respectively. The lead terminals are electrically and mechanically connected to the anode foil and the cathode foil by stitching, cold welding, ultrasonic welding, laser welding, or the like. The lead terminals are conductors that electrically connect the solid electrolytic capacitor to a mounting substrate.

[0026] After the element formation process, the process proceeds to the solid electrolyte formation process. After the element formation process, the process may not immediately proceed to the solid electrolyte formation process, but may instead include, for example, a re-chemical conversion treatment to repair damage to the dielectric film caused by element formation, a cleaning treatment to remove the chemical conversion solution, a drying treatment to evaporate the chemical conversion solution and cleaning solution, and other treatments. In the solid electrolyte formation process, a conductive polymer is attached to the inside of the laminate. The conductive polymer is formed in the separator and is in close contact with at least a portion of the dielectric film.

[0027] The conductive polymer is formed in the laminate using a conductive polymer liquid. The conductive polymer liquid is a dispersion or solution in which a conductive polymer is dispersed or dissolved. A portion of the laminate is immersed in the conductive polymer liquid. Then, the separator absorbs the conductive polymer liquid. In this way, the entire laminate, including the separator, is impregnated with the conductive polymer liquid. The laminate may be immersed in the conductive polymer liquid once or multiple times. Alternatively, the laminate may be impregnated with the conductive polymer liquid in a reduced pressure environment.

[0028] After the laminate is impregnated with the conductive polymer liquid, the solvent in the conductive polymer liquid is removed by drying. The temperature environment is, for example, 40°C or higher and 200°C or lower, and the drying time is, for example, in the range of 3 minutes to 180 minutes. The drying process may be repeated multiple times. Drying may also be performed in a reduced pressure environment, for example, by reducing the pressure to 5 kPa to 100 kPa.

[0029] Here, the separator contains at least fibrillated fibers. A separator containing at least fibrillated fibers has superior short-circuit resistance compared to natural fibers. Fibrillated fibers are fibers in which thin fibers are generated by branching from the surface of the original fibers, and can be formed, for example, by beating. A separator containing at least this fibrillated fiber is made up of entangled thin fibers, and is therefore likely to capture minute metallic foreign matter of about several μm in size. Therefore, even if the separator is thin, it has excellent short-circuit resistance.

[0030] The separator may be dried at a temperature of 120° C. or higher in at least one of the separator manufacturing process and the solid electrolytic capacitor manufacturing process. Drying the separator at a temperature of 120° C. or higher facilitates the formation of a conductive polymer in the laminate in the solid electrolyte forming process.

[0031] The tape used has a contact angle, which is related to wettability with the conductive polymer liquid, of less than 50°. When a tape having a contact angle, which is related to wettability with the conductive polymer liquid, of less than 50° is combined with a separator containing at least fibrillated fibers, the capacitance appearance rate of the solid electrolytic capacitor tends to increase as the contact angle decreases.

[0032] The contact angle relating to the wettability with the conductive polymer liquid was determined by the θ / 2 method using the conductive polymer liquid that was actually impregnated into the laminate. The angle between the tape surface and a line connecting the left and right endpoints of the droplet of conductive polymer liquid formed by dropping the droplet on the tape surface and the vertex was determined, and this angle was doubled to obtain the contact angle relating to the wettability between the tape and the conductive polymer liquid. Specifically, a 10 μL droplet of conductive polymer liquid was placed on the surface of a horizontally stretched tape, and the contact angle between the tape surface and the droplet of conductive polymer liquid 1,000 ms after dropping was determined by the θ / 2 method. The average of five measurements was taken as the contact angle.

[0033] The capacitance appearance ratio is the ratio of the capacitance of a solid electrolytic capacitor to the capacitance of the anode side. That is, the capacitance appearance ratio is a percentage obtained by dividing the capacitance of a solid electrolytic capacitor by the total capacitance when the solid electrolytic capacitor is regarded as a capacitor with the anode side and the cathode side connected in series. The total capacitance is obtained by multiplying the anode side capacitance and the cathode side capacitance and dividing the result by the sum of the anode side capacitance and the cathode side capacitance.

[0034] A separator containing at least fibrillated fibers refers to a separator containing at least fibrillated fibers in which thin fibers are generated so as to branch from the surface of the original fibers. Furthermore, in order to ensure short-circuit resistance, the separator preferably has an air resistance of 0.2 [s / 100 mL] or more, more preferably 1.7 [s / 100 mL] or more, and most preferably 5.4 [s / 100 mL] or more. A separator containing at least fibrillated fibers with an air resistance of 1.7 or more is less likely to absorb a conductive polymer liquid, and exhibits improved capacitance when combined with a tape having a contact angle of less than 50°. When the fibrillated fibers have an air resistance of 5.4 [s / 100 mL], the separator exhibits a particularly significant improvement in capacitance when combined with a tape having a contact angle of less than 50°.

[0035] Preferably, a separator containing at least fibrillated fibers with an air resistance of less than 5.5 s / 100 mL is used. This separator has dense interstices between the fibers, making it difficult for the conductive polymer liquid to diffuse within the separator. Therefore, even when combined with a tape with a contact angle of less than 50°, a separator containing at least fibrillated fibers with an air resistance of 5.5 s / 100 mL or more will have a reduced efficiency in achieving an improved capacitance.

[0036] The air permeability resistance is also called the Gurley value, and is the time required for 100 mL of air to permeate the separator. The air permeability resistance is measured by the Gurley method in accordance with JIS P8117:2009. A gasket with an inner diameter of 28.6 mm is used for the measurement. However, for those with an air permeability resistance of 1 s / 100 mL or less, the measurement is performed using a gasket with an inner diameter of 6 mm and converted to a value measured with an inner diameter of 28.6 mm. Specifically, the value obtained with an inner diameter of 6 mm is multiplied by 6. ２ / 28.6 ２ Use the conversion formula to multiply by.

[0037] The type of tape is not particularly limited, except for paper, as long as the contact angle, which is related to wettability with the conductive polymer liquid, is less than 50°. Resin is preferred as the substrate for such tapes, and examples of resin include polyester, polyphenylene sulfide, polyvinyl chloride, polyimide polyethylene, polypropylene, and polyethylene terephthalate. The contact angle, which is related to wettability with the conductive polymer liquid, may be reduced to less than 50° by surface-treating the tape substrate. Examples of surface treatment methods include corona treatment, plasma treatment, chemical treatment, and matte treatment. Paper tapes are weak against circumferential tension and are prone to breakage during the reflow process of solid electrolytic capacitors. Therefore, the capacitance of solid electrolytic capacitors decreases when paper tapes are used.

[0038] If the contact angle, which is related to the wettability between the tape and the conductive polymer liquid, is 50° or more, the tape that fastens the laminate will repel the conductive polymer liquid, preventing the conductive polymer liquid from penetrating from the circumferential surface of the laminate. This occurs because the force of the tape repelling the conductive polymer liquid is greater than the force that absorbs the conductive polymer liquid from the circumferential surface of the laminate. A solid electrolytic capacitor having a separator that contains at least fibrillated fibers has a low ability to absorb the conductive polymer liquid due to the high air resistance of the separator, and is prone to producing areas that are not impregnated with the conductive polymer, resulting in a low capacitance of the solid electrolytic capacitor.

[0039] On the other hand, if the contact angle relating to the wettability between the tape and the conductive polymer liquid is less than 50°, the force with which the conductive polymer is sucked up from the peripheral surface of the laminate becomes greater than the force with which the tape repels the conductive polymer. As a result, the conductive polymer liquid creeps up the tape, and the peripheral surface of the laminate is also impregnated with the conductive polymer, reducing the area on the separator that is not impregnated with the conductive polymer, thereby achieving the effect of increasing the capacitance of the solid electrolytic capacitor. In order for the conductive polymer to creep up the tape, the contact angle relating to the wettability between the tape and the conductive polymer liquid is preferably less than 50°, more preferably less than 45°, and most preferably less than 42°.

[0040] Furthermore, the coverage area of ​​the peripheral surface of the laminate with the tape is preferably 40% to 63%. That is, when comparing the lengths of the laminate along the cylindrical axis, the widthwise length of the tape is preferably 40% to 63% of the height of the laminate. If the coverage area exceeds 63%, the area exposed from the tape becomes small, making it difficult to impregnate the laminate with the conductive polymer liquid in the solid electrolyte layer formation process. On the other hand, if the coverage area falls below 40% to 32%, the area exposed by the tape becomes even larger, increasing the capacitance appearance rate, but causing breakage during the reflow process of the solid electrolytic capacitor, resulting in a decrease in the electrostatic capacitance of the solid electrolytic capacitor.

[0041] The conductive polymer in the conductive polymer solution is a self-doped conjugated polymer doped with an intramolecular dopant, or a conjugated polymer doped with an external dopant molecule. Conjugated polymers are obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of monomers or their derivatives having π-conjugated double bonds. The dopant or external dopant molecule acts as an acceptor that readily accepts electrons into the conjugated polymer, or as a donor that readily donates electrons, which allows the conductive polymer to exhibit high conductivity.

[0042] As the conjugated polymer, any known polymer can be used without any particular limitation. Examples include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, etc. These conjugated polymers may be used alone or in combination of two or more types, or may even be a copolymer of two or more types of monomers.

[0043] Among the above conjugated polymers, preferred are conjugated polymers obtained by polymerizing thiophene or a derivative thereof, and preferred are conjugated polymers obtained by polymerizing 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothieno[3,4-b][1,4]dioxin), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, or derivatives thereof. The thiophene derivative is preferably a compound selected from thiophenes having substituents at the 3rd and 4th positions, and the substituents at the 3rd and 4th positions of the thiophene ring may form a ring together with the carbon atoms at the 3rd and 4th positions. The alkyl group or alkoxy group preferably has 1 to 16 carbon atoms.

[0044] In particular, a polymer of 3,4-ethylenedioxythiophene, known as EDOT, i.e., poly(3,4-ethylenedioxythiophene), known as PEDOT, is preferred. Furthermore, a substituent may be added to 3,4-ethylenedioxythiophene. For example, an alkylated ethylenedioxythiophene having an alkyl group having 1 to 5 carbon atoms added as a substituent may be used. Examples of alkylated ethylenedioxythiophenes include methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), butylated ethylenedioxythiophene (i.e., 2-butyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), and 2-alkyl-3,4-ethylenedioxythiophene.

[0045] Any known dopant can be used without any particular limitation. A single dopant may be used, or two or more dopants may be used in combination. Furthermore, a polymer or a monomer may be used. Examples of dopants include inorganic acids such as polyanions, boric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, oxalic acid, citric 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.

[0046] Examples of the polyanion include a substituted or unsubstituted polyalkylene, a substituted or unsubstituted polyalkenylene, a substituted or unsubstituted polyimide, a substituted or unsubstituted polyamide, and a substituted or unsubstituted polyester, and include a polymer consisting only of a structural unit having an anionic group, and a polymer consisting of a structural unit having an anionic group and a structural unit not having an anionic group. Specific examples of the polyanion include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0047] An example of such a conductive polymer is poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, and hereinafter this conductive polymer will be referred to as PEDOT / PSS.

[0048] The main solvent of the conductive polymer liquid is water. The solvent for the conductive polymer liquid may be a mixture of water and an organic solvent, as long as the conductive polymer particles or powder can be dispersed or dissolved therein. However, depending on the compatibility with the tape, it is preferable that 65 wt % or more of the solvent be water. Furthermore, organic solvents and various additives may be added as necessary. Suitable examples of organic solvents in the solvent include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, and nitrile compounds.

[0049] Examples of polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. Examples of alcohols include methanol, ethanol, propanol, and butanol. Examples of esters include ethyl acetate, propyl acetate, and butyl acetate. Examples of hydrocarbons include hexane, heptane, benzene, toluene, and xylene. Examples of carbonate compounds include ethylene carbonate and propylene carbonate. Examples of ether compounds include dioxane and diethyl ether. Examples of linear ethers include ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, and polypropylene glycol dialkyl ether. Examples of heterocyclic compounds include 3-methyl-2-oxazolidinone. Examples of nitrile compounds include acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile.

[0050] The pH of the conductive polymer liquid may be adjusted, and polyhydric alcohols and various additives may be added as needed. Examples of pH adjusters include aqueous ammonia, sodium hydroxide, primary amines, secondary amines, and tertiary amines. Examples of polyhydric alcohols include sorbitol, ethylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, polyoxypropylene glycol, glycerin, polyglycerin, polyoxyethyleneglycerin, xylitol, erythritol, mannitol, dipentaerythritol, pentaerythritol, and combinations of two or more of these. Polyhydric alcohols are high-boiling point solvents, and at least a portion of them remains in the solid electrolytic capacitor. Furthermore, polyhydric alcohols are effective in reducing the ESR and improving the withstand voltage of solid electrolytic capacitors. Examples of additives include organic binders, surfactants, dispersants, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers.

[0051] The anode foil and cathode foil of the solid electrolytic capacitor are not particularly limited. The anode foil and cathode foil are long 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 99% or higher, but may also contain silicon, iron, copper, magnesium, zinc, and the like.

[0052] The long foil may be formed by stretching a valve metal or the like, or by sintering a valve metal powder. A surface-expanding layer is formed on one or both sides of the anode foil. The surface-expanding layer may be an etched layer formed by etching the foil, a sintered layer formed by sintering valve metal powder, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto the foil. That is, the surface-expanding layer has a porous structure consisting of tunnel-like pits, spongy pits, or voids between densely packed powder or particles.

[0053] The tunnel-shaped etching pits are holes dug in the foil thickness direction. These tunnel-shaped etching pits are typically formed by passing a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current in an acidic aqueous solution, such as nitric acid. The spongy etching pits turn the surface-expanding layer into a sponge-like layer with fine, interconnected voids. These spongy etching pits are formed by passing an alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0054] The sintered layer is produced by obtaining a powder of a valve action metal of the same or different type as the foil body by a milling method, atomization method, melt spinning method, rotating disk method, rotating electrode method, etc., forming a paste with a binder or solvent, applying it to the foil body, drying it, and heating and sintering it in a vacuum or reducing atmosphere, etc. The atomization method may be any of water atomization method, gas atomization method, and water gas atomization method. The vapor deposition layer is produced by, for example, resistance heating vapor deposition method or electron beam heating vapor deposition method. This vapor deposition layer is formed by heating and vaporizing a valve action metal of the same or different type as the foil body by resistance heat or electron beam energy, and depositing the vapor of valve action metal particles on the surface of the foil body.

[0055] The dielectric coating is formed on the uneven surface of the surface-expanding layer. The dielectric coating is typically an oxide coating formed on the uneven surface of the surface-expanding layer. If the anode foil is made of aluminum, it is an aluminum oxide layer formed by oxidizing the uneven surface of the surface-expanding layer. In the chemical conversion treatment to form the dielectric coating, a voltage is applied to the anode foil in a chemical conversion solution until the desired withstand voltage is achieved. The chemical conversion solution is a solution that does not contain halogen ions, and examples of such solutions include phosphoric acid-based chemical conversion solutions such as ammonium dihydrogen phosphate, boric acid-based chemical conversion solutions such as ammonium borate, and adipic acid-based chemical conversion solutions such as ammonium adipate.

[0056] A surface-expanding layer may be formed on the cathode foil as needed, just like on the anode foil. Plain foil without a surface-expanding layer may also be used as the cathode foil. The cathode foil may also have a dielectric coating, just like the anode foil. The dielectric coating may be a natural oxide coating or a thin oxide coating (about 1 to 10 V) formed by chemical conversion treatment. The natural oxide coating is formed when the cathode body reacts with oxygen in the air.

[0057] The cathode foil may have a conductive layer laminated on its surface. The conductive layer may be a layer containing, for example, a metal nitride such as titanium, zirconium, tantalum, or niobium, a metal carbide, a metal carbonitride, or carbon. The metal nitride, metal carbide, metal carbonitride, and carbon are formed by vapor deposition, slurry coating, or the like.

[0058] When an electrolyte solution is used in a solid electrolytic capacitor, the solid electrolyte formation process is followed by the electrolyte impregnation process. The electrolyte solution is a mixed solution in which a solute is dissolved in a solvent and, if necessary, an additive is added. The electrolyte solution does not need to dissolve a solute, and may be a solvent only, or may contain a solvent and an additive. Examples of the solvent for the electrolyte solution include protic organic polar solvents and aprotic organic polar solvents, which may be used alone or in combination of two or more. The solute for the electrolyte solution includes an anion component and a cation component. The solute is typically a salt of an organic acid, a salt of an inorganic acid, or a salt of a complex compound of an organic acid and an inorganic acid, which may be used alone or in combination of two or more. An acid that becomes an anion and a base that becomes a cation may be added separately to the solvent.

[0059] Examples of protic organic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, polyglycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, and alkylene oxide adducts of polyhydric alcohols such as polyethylene glycol and polyoxyethylene glycerin. Among these, polyhydric alcohols are preferred as solvents, with ethylene glycol and glycerin being particularly preferred. Ethylene glycol and glycerin cause changes in the higher-order structure of the conductive polymer, resulting in improved initial ESR characteristics and also improved high-temperature characteristics. It is even better if the ethylene glycol content in the solvent is 30 wt % or more.

[0060] Representative examples of aprotic organic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, and hexamethylphosphoric amide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, glutaronitrile, etc. Examples of sulfoxides include dimethyl sulfoxide, etc.

[0061] Examples of organic acids that serve as anionic components as solutes include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedioic acid, azelaic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, t-butyl adipic acid, 11-vinyl-8-octadecenedioic acid, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, as well as phenols and sulfonic acids.

[0062] Furthermore, examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, silicic acid, etc. Examples of composite compounds of organic acids and inorganic acids include borodisalicylic acid, borodioxalic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcylic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid, etc.

[0063] Furthermore, examples of at least one salt of an organic acid, an inorganic acid, or a complex compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, and potassium salts. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of quaternized amidinium salts include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0064] Other additives may also be added to the electrolyte. Examples of additives include complex compounds of boric acid and polysaccharides (e.g., mannitol, sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds (e.g., o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol), and phosphate esters. These may be used alone or in combination of two or more. The amount of additive added is not particularly limited, but it is preferable to add it to an amount that does not deteriorate the characteristics of the solid electrolytic capacitor, for example, 60 wt % or less of the electrolyte.

[0065] The solid electrolytic capacitor and the manufacturing method 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.

[0066] Example 1 A solid electrolytic capacitor of Example 1 was fabricated as follows. First, anode foil and cathode foil were strip-shaped aluminum foils stretched to a long length. The anode foil and cathode foil were subjected to AC etching to enlarge the surface area. After enlarging the surface area, the anode foil was subjected to a chemical conversion treatment to form a dielectric film.

[0067] A fibrillated cellulose separator with an air resistance of 5.48 [s / 100 mL] was placed between the anode foil and the cathode foil, and the foil was wound in a longitudinal direction to form a laminate. A tape with a width of 79% of the total axial length of the laminate and a contact angle of 41.3°, which indicates wettability with the conductive polymer solution, was prepared and used to secure the outer periphery of the wound foil.

[0068] After the element formation process, a chemical conversion treatment was performed again to repair damage to the dielectric film of the laminate. The chemical conversion solution used in the chemical conversion treatment was an aqueous solution of ammonium dihydrogen phosphate dissolved in water. The applied voltage was 1.1 to 1.2 times the chemical conversion treatment voltage of the anode foil, and was applied for 20 minutes. After that, a cleaning treatment was performed using a chemical conversion solution cleaning solution made of pure water to remove the chemical conversion solution from the laminate. After the cleaning treatment, the laminate was left to stand in a temperature environment of 150°C for 30 minutes, whereby a drying treatment was performed to evaporate the chemical conversion solution remaining in the laminate.

[0069] The laminate was impregnated with a conductive polymer dispersion. The conductive polymer dispersion was a water-dispersed poly(3,4-ethylenedioxythiophene) (PEDOT / PSS) doped with polystyrene sulfonic acid (PSS). PEDOT / PSS was added at a ratio of 1.2 wt% to the total conductive polymer solution. Ethylene glycol was also added to the conductive polymer solution at a ratio of 10 wt% to the conductive polymer solution. In the solid electrolytic capacitor of Example 1, the viscosity of the conductive polymer solution was adjusted to 30 mPa·s by dispersion treatment using an ultrasonic homogenizer. The contact angle of the tape wound around the wound body with droplets of the conductive polymer solution was 41.3°.

[0070] The laminate was impregnated with the conductive polymer solution for 10 minutes at room temperature and in a reduced pressure environment of 80 kPa or less. After the impregnation step, the laminate was left to stand at room temperature for 10 minutes and then in a temperature environment of 110°C for 30 minutes to dry the laminate.

[0071] After impregnating with the conductive polymer liquid and drying, the laminate was housed in an outer case, and the outer case was sealed with a sealing material. The sealing material and the outer case were tightly attached by crimping. The resulting solid electrolytic capacitor was subjected to an aging treatment in which a voltage of 40 V was applied for 1 hour. As a result, an electrolytic capacitor of Example 1 was produced, having a diameter of 10 mm, a height of 10 mm, a rated voltage of 35 WV, and a rated capacitance of 270 μF.

[0072] (Examples 2 and 3) Solid electrolytic capacitors of Examples 2 and 3 were also produced. For the solid electrolytic capacitor of Example 2, a tape having a width of 79% of the total axial length of the laminate and a contact angle of 34.9° related to wettability with the conductive polymer liquid was prepared, and the outer periphery of the laminate was wound and secured with this tape. For the solid electrolytic capacitor of Example 3, a tape having a width of 79% of the total axial length of the laminate and a contact angle of 32.8° related to wettability with the conductive polymer liquid was prepared, and the outer periphery of the laminate was wound and secured with this tape. The solid electrolytic capacitors of Examples 2 and 3 were produced with the same configuration, composition, manufacturing method, and manufacturing conditions as Example 1, except for the contact angle of the tape.

[0073] (Comparative Examples 1 and 2) Solid electrolytic capacitors of Comparative Examples 1 and 2 were fabricated. For the solid electrolytic capacitor of Comparative Example 1, a tape having a width of 79% of the total axial length of the laminate and a contact angle of 63.7° related to wettability with the conductive polymer liquid was prepared, and the outer periphery of the laminate was wound and secured with this tape. For the solid electrolytic capacitor of Comparative Example 2, a tape having a width of 79% of the total axial length of the laminate and a contact angle of 50.0° related to wettability with the conductive polymer liquid was prepared, and the outer periphery of the laminate was wound and secured with this tape. The solid electrolytic capacitors of Comparative Examples 1 and 2 were fabricated with the same configuration, composition, manufacturing method, and manufacturing conditions as Example 1, except for the contact angle of the tape.

[0074] (Reference Examples 1 and 2) Solid electrolytic capacitors were produced in Reference Examples 1 and 2. In the solid electrolytic capacitors in Reference Examples 1 and 2, a natural fiber separator having an air resistance of 0.03 [s / 100 mL] was interposed between the anode foil and the cathode foil, and the foil was wound so that the strip was curled in the longitudinal direction to form a laminate.

[0075] For the solid electrolytic capacitor of Reference Example 1, a tape having a width of 79% of the total axial length of the laminate and a contact angle of 63.7° related to wettability with the conductive polymer liquid was prepared, and the outer periphery of the laminate was wound and secured with this tape.For the solid electrolytic capacitor of Reference Example 2, a tape having a width of 79% of the total axial length of the laminate and a contact angle of 34.9° related to wettability with the conductive polymer liquid was prepared, and the outer periphery of the laminate was wound and secured with this tape.

[0076] The solid electrolytic capacitors of Reference Examples 1 and 2 were fabricated using the same configuration, composition, manufacturing method and conditions as Example 1, except for the type of separator and the contact angle of the tape.

[0077] (Capacitance Appearance Rate) The capacitance appearance rate and capacitance increase rate of the solid electrolytic capacitors of Examples 1 and 2, Comparative Examples 1 and 2, and Reference Examples 1 and 2 were measured. First, the solid electrolytic capacitors were disassembled, and test pieces of specified areas were cut out from the anode foil and cathode foil. The anode foil test pieces were immersed in a capacitance measurement solution in a glass measurement tank using a platinum plate as the counter electrode, and the anode-side capacitance was measured using a capacitance meter. Furthermore, the cathode foil test pieces were immersed in a capacitance measurement solution in a glass measurement tank using a platinum plate as the counter electrode, and the cathode-side capacitance was measured using a capacitance meter.

[0078] The cut-out area is 1 cm ２ The capacitance measurement liquid was an aqueous solution of ammonium adipate at 30°C, the capacitance meter was a potentiostat and frequency response analyzer, an electrochemical impedance analyzer, an LCR meter, or the like, and the measurement conditions were a DC bias voltage of 0 V to 1.5 V and an AC amplitude of 0.1 V to 1 V.

[0079] The capacitance appearance rate was calculated by dividing the product of the anode-side capacitance and the cathode-side capacitance by the sum of the anode-side capacitance and the cathode-side capacitance. Furthermore, the capacitance increase rate of Reference Example 2 was calculated based on Reference Example 1, which used a tape with a contact angle of 63.7°. Furthermore, the capacitance increase rates of Comparative Example 2 and Examples 1 to 3 were calculated based on Comparative Example 1, which used a tape with a contact angle of 63.7°.

[0080] The calculation results are shown in Table 1 below. The graphs shown in Figures 1 and 2 were also created based on Table 1 below. Figure 1 is a graph showing the relationship between the contact angle of the tape and the capacitance appearance rate of the solid electrolytic capacitor. Figure 2 is a graph showing the relationship between the contact angle of the tape and the capacitance increase rate of the solid electrolytic capacitor.

[0081] (Table 1)

[0082] As shown in Table 1 and Reference Examples 1 and 2 in Figures 1 and 2, when natural fibers are used as the separator, there is no significant change in the capacitance appearance rate of the solid electrolytic capacitor even if the laminate is wound and fastened with a tape having a low contact angle related to the wettability with the conductive polymer liquid.

[0083] Furthermore, comparing Comparative Examples 1 and 2, there is no significant change in the capacitance appearance rate of the solid electrolytic capacitor even when the laminate is wound with a tape having a low contact angle, which is related to wettability with the conductive polymer liquid. On the other hand, as in Examples 1 to 3, when a separator containing at least fibrillated fibers is used and the laminate is wound with a tape having a contact angle of less than 50°, which is related to wettability with the conductive polymer liquid, the capacitance appearance rate of the solid electrolytic capacitor is improved by 10% or more compared to when the contact angle is 50° or more.

[0084] That is, it was confirmed that the capacitance appearance rate of a solid electrolytic capacitor can be significantly improved by using a separator containing at least fibrillated fibers, which provides high short-circuit resistance, and by using a tape with a contact angle of less than 50°, which is related to wettability with the conductive polymer liquid.

[0085] (Example 4) A solid electrolytic capacitor of Example 4 was fabricated. The solid electrolytic capacitor of Example 4 was the same as Example 2 in that a tape with a contact angle of 34.9°, which is related to wettability with the conductive polymer liquid, was prepared. However, the width of the tape in Example 4 was reduced to 63% of the total axial length of the laminate. In Example 4, this tape was used to wrap around the outer periphery of the laminate. The solid electrolytic capacitor of Example 4 was fabricated with the same configuration, composition, manufacturing method, and manufacturing conditions as Example 2, except for the contact angle of this tape.

[0086] (Example 5) A solid electrolytic capacitor of Example 5 was fabricated. The solid electrolytic capacitor of Example 5 was the same as Example 2 in that a tape with a contact angle of 34.9°, which is related to wettability with the conductive polymer liquid, was prepared. However, the width of the tape in Example 5 was further reduced to 48% of the total axial length of the laminate. In Example 5, this tape was used to wrap around the outer periphery of the laminate. The solid electrolytic capacitor of Example 5 was fabricated with the same configuration, composition, manufacturing method, and manufacturing conditions as Example 2, except for the contact angle of this tape.

[0087] (Reference Examples 3 and 4) Solid electrolytic capacitors of Reference Examples 3 and 4 were fabricated. The solid electrolytic capacitor of Reference Example 3 was identical to Example 2 in that a tape with a contact angle of 34.9°, which is related to wettability with the conductive polymer liquid, was prepared. However, the width of the tape in Reference Example 3 was further reduced to 63% of the total axial length of the laminate. The solid electrolytic capacitor of Reference Example 4 was identical to Example 2 in that a tape with a contact angle of 34.9°, which is related to wettability with the conductive polymer liquid, was prepared. However, the width of the tape in Reference Example 3 was further reduced to 48% of the total axial length of the laminate. In Reference Examples 3 and 4, these tapes were wound around the outer periphery of the laminate. The solid electrolytic capacitors of Reference Examples 3 and 4 were fabricated with the same configuration, composition, manufacturing method, and manufacturing conditions as Reference Example 2, except for the contact angle of the tape.

[0088] (Capacitance Appearance Rate) The capacitance appearance rate and capacitance increase rate were measured for the solid electrolytic capacitors of Examples 4 and 5, and Reference Examples 3 and 4. The measurement method and conditions for the capacitance appearance rate were the same as those for Example 1. The capacitance appearance rate and capacitance increase rate for the solid electrolytic capacitors of Examples 4 and 5, and Reference Examples 3 and 4 are shown in Table 2 below, together with those for Comparative Example 1, Example 2, Reference Example 1, and Reference Example 2.

[0089] (Table 2)

[0090] As shown in Table 2 above, there is no significant change in the capacitance appearance rate in Reference Examples 3 and 4 compared to Reference Examples 1 and 2. On the other hand, it can be seen that Examples 4 and 5 show a clear improvement in the capacitance appearance rate compared to Example 2. In Examples 4 and 5, the width of the tape is 48% or more and 63% or less of the total axial length of the laminate.

[0091] (Examples 6 to 8) Solid electrolytic capacitors of Examples 6 to 8 were fabricated. The solid electrolytic capacitor of Example 6 was the same as Example 4, except that it contained a conductive polymer and an electrolyte solution. The solid electrolytic capacitor of Example 6 had a separator made of fibrillated cellulose with an air resistance of 5.48 [s / 100 mL], and a tape with a contact angle of 34.9° relating to wettability with the conductive polymer solution and a width of 63% of the total axial length of the laminate.

[0092] The electrolyte impregnated in the wound body of Example 6 was prepared by adding ammonium azelaate to ethylene glycol as a solvent. The ammonium azelaate was added to the solvent so that the concentration of azelaic acid was 0.2 mol / kg and the concentration of ammonium ions was 0.2 mol / kg. Furthermore, as additives, phosphate ester and p-nitrobenzoic acid were added so that their total amount was 2 wt % relative to the total amount of the electrolyte. After a conductive polymer was attached between the anode foil and the cathode foil, the laminate was immersed in the electrolyte, and the laminate was impregnated with the electrolyte.

[0093] The solid electrolytic capacitor of Example 7 is the same as Example 5, except that it contains a conductive polymer and an electrolyte solution. The solid electrolytic capacitor of Example 5 has a separator made of fibrillated cellulose with an air resistance of 5.48 [s / 100 mL], a tape with a contact angle indicating wettability with the conductive polymer solution of 34.9°, and a width of 48% of the total axial length of the laminate. The composition of the electrolyte solution and the method and conditions for impregnation of the electrolyte solution are the same as those of Example 6.

[0094] In the solid electrolytic capacitor of Example 8, the width of the tape is 40% of the total axial length of the laminate. Other than that, it is the same as Examples 6 and 7, including the inclusion of a conductive polymer and an electrolyte solution.

[0095] (Reference Examples 5 to 7) Solid electrolytic capacitors of Reference Examples 5 to 7 were fabricated. The solid electrolytic capacitor of Reference Example 5 was the same as Reference Example 1, except that it contained a conductive polymer and an electrolyte solution. The solid electrolytic capacitor of Reference Example 5 had a natural fiber separator with an air resistance of 0.03 [s / 100 mL], a tape with a contact angle of 63.7° indicating wettability with the conductive polymer solution, and a width of 79% of the total axial length of the laminate. The composition of the electrolyte solution and the method and conditions for impregnating the electrolyte solution were the same as those of Example 6.

[0096] The solid electrolytic capacitor of Reference Example 6 is the same as Reference Example 3, except that it contains a conductive polymer and an electrolyte solution. The solid electrolytic capacitor of Reference Example 6 has a natural fiber separator with an air resistance of 0.03 [s / 100 mL], a tape with a contact angle of 63.7° (relative to wettability with the conductive polymer solution) and a width of 79% of the total axial length of the laminate. The composition of the electrolyte solution and the method and conditions for impregnation of the electrolyte solution are the same as those of Example 6.

[0097] The solid electrolytic capacitor of Reference Example 7 is the same as Reference Example 8, except that it contains a conductive polymer and an electrolyte solution. The solid electrolytic capacitor of Reference Example 7 has a natural fiber separator with an air resistance of 0.03 [s / 100 mL], a tape with a contact angle of 63.7° (relative to wettability with the conductive polymer solution) and a width of 48% of the total axial length of the laminate. The composition of the electrolyte solution and the method and conditions for impregnation of the electrolyte solution are the same as those of Example 6.

[0098] (Comparative Example 3) A solid electrolytic capacitor of Comparative Example 3 was fabricated. The solid electrolytic capacitor of Comparative Example 3 was identical to Comparative Example 1, except that it contained a conductive polymer and an electrolyte solution. The solid electrolytic capacitor of Comparative Example 3 had a fibrillated fiber separator with an air resistance of 5.48 [s / 100 mL], a tape with a contact angle of 63.7° indicating wettability with the conductive polymer solution, and a width of 79% of the total axial length of the laminate. The composition of the electrolyte solution and the method and conditions for impregnating the electrolyte solution were the same as those of Example 6.

[0099] (Capacitance Appearance Rate) The capacitance appearance rate and capacitance increase rate were measured for the solid electrolytic capacitors of Examples 6 to 8, Comparative Example 3, and Reference Examples 5 and 7. The measurement method and conditions for the capacitance appearance rate were the same as those in Example 1. The capacitance appearance rate and capacitance increase rate for the solid electrolytic capacitors of Examples 6 to 8, Comparative Example 3, and Reference Examples 5 and 7 are shown in Table 3 below.

[0100] (Table 3)

[0101] As shown in Table 3 above, there is no significant change in the capacitance appearance rate in Reference Examples 6 and 7 compared to Reference Example 1. On the other hand, it can be seen that Examples 6 to 8 have a clearly improved capacitance appearance rate compared to Comparative Example 3. In Examples 6 and 8, the width of the tape is in the range of 40% to 63% of the total axial length of the laminate.

[0102] Taking Tables 2 and 3 together, it was confirmed that the capacitance appearance rate of the solid electrolytic capacitor can be further improved by using a tape having a width of 40% to 63% of the total axial length of the laminate, in other words, by covering 40% to 63% of the area of ​​the circumferential surface of the laminate with tape.

[0103] Example 9 A solid electrolytic capacitor of Example 9 was also fabricated. The solid electrolytic capacitor of Example 9 had a fibrillated cellulose separator with an air resistance of 1.77 [s / 100 mL] between the anode foil and the cathode foil. As in Example 2, a tape with a width of 79% of the total axial length of the laminate and a contact angle of 34.9°, which indicates wettability with the conductive polymer solution, was prepared and used to wrap the outer periphery of the laminate. Thus, the solid electrolytic capacitor of Example 9 was fabricated with the same configuration, composition, manufacturing method, and manufacturing conditions as Example 2, except for the air resistance of the fibrillated cellulose separator.

[0104] Example 10 A solid electrolytic capacitor of Example 10 was also fabricated. The solid electrolytic capacitor of Example 10 had a fibrillated cellulose separator with an air resistance of 5.93 [s / 100 mL] between the anode foil and the cathode foil. As in Example 2, a tape with a width of 79% of the total axial length of the laminate and a contact angle of 34.9°, which indicates wettability with the conductive polymer solution, was prepared and used to wrap the outer periphery of the laminate. Thus, the solid electrolytic capacitor of Example 10 was fabricated with the same configuration, composition, manufacturing method, and manufacturing conditions as Example 2, except for the air resistance of the fibrillated cellulose separator.

[0105] Comparative Example 4 A solid electrolytic capacitor of Comparative Example 4 was fabricated. The solid electrolytic capacitor of Comparative Example 4, like Example 9, had a fibrillated cellulose separator with an air resistance of 1.77 [s / 100 mL] between the anode foil and the cathode foil. However, a tape with a width of 79% of the total axial length of the laminate and a contact angle of 63.7°, which indicates wettability with the conductive polymer solution, was prepared and used to wrap around the outer periphery of the laminate. The solid electrolytic capacitor of Comparative Example 4 was fabricated with the same configuration, composition, and manufacturing method and conditions as Example 9, except for the contact angle of the tape.

[0106] Comparative Example 5 A solid electrolytic capacitor of Comparative Example 5 was fabricated. The solid electrolytic capacitor of Comparative Example 5, like Example 10, had a fibrillated cellulose separator with an air resistance of 5.93 [s / 100 mL] between the anode foil and the cathode foil. However, a tape with a width of 79% of the total axial length of the laminate and a contact angle of 63.7°, which indicates wettability with the conductive polymer solution, was prepared and used to wrap around the outer periphery of the laminate. The solid electrolytic capacitor of Comparative Example 5 was fabricated with the same configuration, composition, and manufacturing method and conditions as Example 9, except for the contact angle of the tape.

[0107] (Capacitance Appearance Rate) The capacitance appearance rate and capacitance increase rate were measured for the solid electrolytic capacitors of Examples 9 and 10, Comparative Examples 4 and 5, as well as Reference Examples 1 and 2, Comparative Example 1, and Example 2. The measurement method and conditions for the capacitance appearance rate were the same as those in Example 1. The measurement results are shown in Table 4 below.

[0108] (Table 4)

[0109] As shown in Example 9 in Table 4, the air resistance of the separator containing at least fibrillated fibers is 1.77 [s / 100 mL], and by winding and fastening the laminate with tape having a contact angle of less than 50°, which is related to wettability with the conductive polymer liquid, the capacitance appearance rate of the solid electrolytic capacitor is improved by nearly 10% compared to Comparative Example 4, which has a contact angle of 50° or more.

[0110] That is, it was confirmed that the use of a separator containing at least fibrillated fibers with an air resistance of 1.77 [s / 100 mL] or more provides high short-circuit resistance, while the use of a tape with a contact angle of less than 50°, which is related to wettability with the conductive polymer liquid, further significantly improves the capacitance appearance rate of the solid electrolytic capacitor.

[0111] Furthermore, as shown in Table 4, when the air resistance of the separator containing at least fibrillated fibers is 5.93 [s / 100 mL], even if the laminate is wound with tape having a contact angle of less than 50°, which is related to the wettability with the conductive polymer liquid, the effect of improving the capacitance reaches its upper limit, and no difference in the capacity increase rate is observed between Comparative Example 5 and Example 10.

[0112] Therefore, it was confirmed that the capacitance appearance rate of a solid electrolytic capacitor can be improved more efficiently by using a separator containing at least fibrillated fibers with an air resistance of 5.5 [s / 100 mL] or less, which provides high short-circuit resistance, and by using a tape with a contact angle of less than 50°, which indicates wettability with the conductive polymer liquid.

Claims

1. A solid electrolytic capacitor comprising: an anode foil having a dielectric coating formed thereon; a cathode foil facing the anode foil; a separator including at least fibrillated fibers; a laminate formed by stacking the anode foil and the cathode foil with the separator interposed therebetween; a conductive polymer formed by applying a conductive polymer liquid and impregnating at least the separator; and a tape wound around the periphery of the laminate, the tape having a contact angle of less than 50° with the conductive polymer liquid.

2. The solid electrolytic capacitor according to claim 1, wherein the tape covers an area of ​​40% to 63% of the periphery of the laminate.

3. The solid electrolytic capacitor according to claim 1, wherein the separator has an air resistance of 1.7 [s / 100 mL] or more.

4. The solid electrolytic capacitor according to claim 1, wherein the separator has an air resistance of 5.4 [s / 100 mL] or more.

5. The solid electrolytic capacitor according to claim 1, wherein the tape has a base material and an adhesive layer, and the base material is made of resin.

6. A method for manufacturing a solid electrolytic capacitor, comprising: a laminate-forming step of stacking an anode foil having a dielectric film formed thereon, a separator containing at least fibrillated fibers, and a cathode foil to form a laminate; a winding-up step of winding up the periphery of the laminate with tape having a contact angle with a conductive polymer liquid of less than 50°; and a solid electrolyte-forming step of immersing the laminate wound up with the tape in the conductive polymer liquid to adhere the conductive polymer to the interior of the laminate.

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