Electrolytic capacitor

Abstract

An electrolytic capacitor according to an embodiment of the present disclosure comprises a capacitor element including: an anode body that extends in a first direction; a dielectric layer that covers at least a portion of the anode body; and a conductive polymer layer that includes a conductive polymer and that covers at least a portion of the dielectric layer. The conductive polymer layer includes a monovalent cation, and the content of the element constituting the monovalent cation in the conductive polymer layer is less than 23,000 ppm.

Description

Electrolytic capacitors

[0001] This invention relates to an electrolytic capacitor.

[0002] An electrolytic capacitor comprises, for example, a capacitor element including an anode extending in a first direction, a dielectric layer covering at least a portion of the anode, and a solid electrolyte layer covering at least a portion of the dielectric layer. In such an electrolytic capacitor, the solid electrolyte layer may be configured as a conductive polymer layer containing a conductive polymer. Various studies have been conducted on conductive polymers.

[0003] Patent Document 1 discloses a method for producing a conductive composition by chemical oxidative polymerization, in which a conductive composition is obtained by repeating units of a thiophene derivative having a specific structure containing organic acid ions and inorganic acid ions of anionic surfactants as dopants. In other words, Patent Document 1 discloses a conductive composition containing a conductive polymer having conjugated double bonds with repeating units of thiophene having a specific structure, obtained by chemical oxidative polymerization. Furthermore, Patent Document 1 discloses that the conductive composition containing the conductive polymer obtained as described above exhibits high conductivity and high thermal stability.

[0004] Patent Document 2 discloses a dispersant and dopant for the synthesis of conductive polymers, characterized by comprising polystyrene sulfonic acid having a number average molecular weight of 50,000 to 1,000,000, a total residual amount of bromine and chlorine of 100 ppm or less, and a residual amount of styrene sulfonic acid monomer of 1% by mass or less. Patent Document 2 also discloses a conductive polymer composition obtained by chemical oxidative polymerization using the above-mentioned dispersant and dopant for the synthesis of conductive polymers, a polymerizable monomer, and an oxidizing agent consisting of a persulfate and a ferric salt. Furthermore, Patent Document 2 discloses a solid electrolytic capacitor characterized by having an anode made of a porous valve metal selected from tantalum, niobium, and aluminum, a dielectric layer made of an oxide film of the valve metal, and a solid electrolyte layer made of the above-mentioned conductive polymer composition. Patent Document 2 also discloses that a solid electrolytic capacitor including a solid electrolyte layer made of the above-mentioned conductive polymer composition can reduce the ESR (equivalent series resistance) and increase the capacitance.

[0005] Patent No. 3451177 Patent No. 5191171

[0006] Incidentally, in recent years, there has been a demand for further reduction in the equivalent series resistance (ESR) of electrolytic capacitors equipped with a conductive polymer layer. To achieve further reduction in equivalent series resistance (ESR), it is necessary to further improve the conductivity of the conductive polymer layer. However, it is still difficult to say that sufficient research has been conducted on this matter.

[0007] Therefore, the object of this disclosure is to provide an electrolytic capacitor that can improve the conductivity of a conductive polymer layer.

[0008] One aspect of the present invention relates to an electrolytic capacitor comprising a capacitor element including an anode extending in a first direction, a dielectric layer covering at least a portion of the anode, and a conductive polymer layer containing a conductive polymer and covering at least a portion of the dielectric layer, wherein the conductive polymer layer contains a monovalent cation, and the content of the elements constituting the monovalent cation in the conductive polymer layer is less than 23,000 ppm.

[0009] According to this disclosure, it is possible to provide an electrolytic capacitor that can improve the conductivity of a conductive polymer layer.

[0010] This is a side cross-sectional view showing the configuration of a solid electrolytic capacitor according to one embodiment of this disclosure. This is a flowchart for explaining the manufacturing method of a solid electrolytic capacitor according to one embodiment of this disclosure. This is a side view showing the configuration of the cathode lead frame before it is connected to the capacitor element.

[0011] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. Notwithstanding, known components may be applied to components of parts that are characteristic of this disclosure. In this specification, when "the range of numerical values ​​A to numerical values ​​B" is used, that range includes numerical values ​​A and B.

[0012] In the following explanation, when examples are given for the lower and upper limits of numerical values ​​related to specific physical properties or conditions, any combination of either of the given lower limits and any of the given upper limits is permitted, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, unless otherwise specified, one type may be selected and used alone, or two or more types may be used in combination.

[0013] This disclosure includes any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims. In other words, any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims is possible, as long as it does not result in a technical inconsistency.

[0014] [Electrolytic Capacitor] An electrolytic capacitor according to an embodiment of the present disclosure comprises a capacitor element including an anode body extending in a first direction, a dielectric layer covering at least a portion of the anode body, and a conductive polymer layer containing a conductive polymer and covering at least a portion of the dielectric layer. The electrolytic capacitor of the present disclosure may be a solid electrolytic capacitor containing only a conductive polymer as the electrolyte, or a solid-liquid hybrid electrolytic capacitor containing a conductive polymer and a liquid component (e.g., an electrolyte) as the electrolyte. In short, the electrolytic capacitor of the present disclosure only needs to contain a conductive polymer as the electrolyte.

[0015] In the electrolytic capacitor according to the embodiments of this disclosure, the conductive polymer layer contains a monovalent cation. In the electrolytic capacitor according to the embodiments of this disclosure, the content of the elements constituting the monovalent cation in the conductive polymer layer is less than 23,000 ppm.

[0016] In the electrolytic capacitor according to the embodiment of this disclosure, it is important that the content of elements constituting monovalent cations in the conductive polymer layer is less than 23,000 ppm. In short, it is important that the conductive polymer layer contains monovalent cations in a specific range of amounts. The reasons for this are explained below.

[0017] Conductive polymers contained in conductive polymer layers are typically doped to improve their conductivity. Doped conductive polymers are classified into self-doped conductive polymers and non-self-doped conductive polymers.

[0018] Self-doped conductive polymers have a conjugated polymer skeleton and functional groups (such as anionic groups) that are directly or indirectly bonded to this skeleton by covalent bonds and function as dopants. An anionic group is a group that acquires a negative charge when a cation dissociates. Non-self-doped conductive polymers have a non-self-doped conjugated polymer and a dopant (for example, an external dopant such as an anionic dopant). A non-self-doped conjugated polymer is a conjugated polymer that does not contain functional groups that function as dopants.

[0019] Self-doped conductive polymers are synthesized by chemically oxidative polymerization or electrolytic polymerization of a first monomer having a functional group that functions as a dopant (e.g., an anionic group). Further, non-self-doped conductive polymers are synthesized by chemically oxidative polymerization or electrolytic polymerization of a second monomer having no functional group that functions as a dopant in the presence of a dopant (e.g., an anionic dopant).

[0020] When synthesizing a self-doped conductive polymer by chemically oxidative polymerization, an oxidizing agent is used in addition to the first monomer, and when synthesizing a self-doped conductive polymer by electrolytic polymerization, a supporting electrolyte is used in addition to the first monomer. Further, when synthesizing a non-self-doped conductive polymer by chemically oxidative polymerization, an oxidizing agent is used in addition to the second monomer and the dopant, and when synthesizing a non-self-doped conductive polymer by electrolytic polymerization, a supporting electrolyte is used as necessary in addition to the second monomer and the dopant.

[0021] Therefore, monovalent cations derived from the oxidizing agent may remain in the self-doped conductive polymer synthesized by chemically oxidative polymerization, and monovalent cations derived from the supporting electrolyte may remain in the self-doped conductive polymer synthesized by electrolytic polymerization. Further, in the non-self-doped conductive polymer synthesized by chemically oxidative polymerization, monovalent cations that are counter cations of the anionic dopant and monovalent cations derived from the oxidizing agent remain, and in the non-self-doped conductive polymer synthesized by electrolytic polymerization, monovalent cations that are counter cations of the anionic dopant and monovalent cations derived from the supporting electrolyte may remain.

[0022] In the chemical oxidation polymerization of non-self-doped conductive polymers, if the amount of monovalent cations is high, dopants such as anionic dopants may not be able to fit regularly into the structure of the conductive polymer, which raises concerns that the regularity of the crystal structure of the resulting conductive polymer will be disrupted. In this case, there is a concern that the conductivity of the conductive polymer with disrupted crystal structure will decrease. Similarly, in the electrolytic polymerization of non-self-doped conductive polymers, if the amount of monovalent cations is high, there is a concern that the regularity of the crystal structure of the resulting conductive polymer will be disrupted, which raises concerns that the conductivity of the conductive polymer will decrease. Furthermore, even in the chemical oxidation polymerization and electrolytic polymerization of self-doped conductive polymers, if the amount of monovalent cations is high as described above, there is a concern that the regularity of the crystal structure of the resulting conductive polymer will be disrupted due to the effects of the monovalent cations on functional groups such as anionic groups, which raises concerns that the conductivity of the conductive polymer will decrease. Furthermore, there are concerns that the breakdown of the crystal structure of the conductive polymer as described above may lead to a decrease in the ratio of functional groups such as anionic groups that contribute to conductivity, or a decrease in the ratio of dopants such as anionic dopants that contribute to conductivity, resulting in a decrease in the conductivity of the conductive polymer.

[0023] In short, in conductive polymers obtained by either chemical oxidation polymerization or electrolytic polymerization, there is a concern that the conductivity of the conductive polymer will decrease if a large amount of monovalent cations remain in the conductive polymer.

[0024] However, in the electrolytic capacitor according to the embodiment of this disclosure, the content of elements constituting monovalent cations in the conductive polymer layer is low, less than 23,000 ppm. Therefore, it is thought that a decrease in the conductivity of the conductive polymer can be suppressed, as a result of a large amount of residual monovalent cations in the conductive polymer layer causing a disruption in the regularity of the crystal structure of the conductive polymer. Furthermore, it is thought that a decrease in the conductivity of the conductive polymer can also be suppressed, as a disruption in the crystal structure of the conductive polymer can cause a decrease in the ratio of functional groups such as anionic groups that contribute to conductivity, or a decrease in the ratio of dopants such as anionic dopants that contribute to conductivity.

[0025] Hereinafter, a solid electrolytic capacitor according to an embodiment of the present disclosure will be described with reference to the drawings. A solid electrolytic capacitor according to an embodiment of the present disclosure only needs to include at least one capacitor element. That is, a solid electrolytic capacitor according to an embodiment of the present disclosure may include one capacitor element, or may include a plurality of capacitor elements. Hereinafter, an example in which the solid electrolytic capacitor includes one capacitor element will be described.

[0026] 《Solid Electrolytic Capacitor》 As shown in FIG. 1, a solid electrolytic capacitor 100 according to an embodiment of the present disclosure includes a capacitor element 10 having an anode part 6 and a cathode part 7, a cathode lead frame 14 electrically connected to the cathode part 7, and an outer package 11 covering the capacitor element 10. The solid electrolytic capacitor 100 according to an embodiment of the present disclosure further includes an anode lead frame 13 electrically connected to the anode part 6.

[0027] <Capacitor Element> The capacitor element 10 has a lower surface B, an upper surface U opposite to the lower surface B, and two side surfaces connecting the lower surface B and the upper surface U. Note that, since FIG. 1 is a cross-sectional view, the side surfaces are not shown therein.

[0028] (Anode Part) The anode part 6 includes an anode body 1, an anode wire 2 extending from one end face E1 of the anode body 1, and a dielectric layer 3. In the solid electrolytic capacitor 100 according to an embodiment of the present disclosure, as shown in FIG. 1, the anode part 6 is electrically connected to the anode lead frame 13.

[0029] In the solid electrolytic capacitor 100 according to an embodiment of the present disclosure, the anode body 1 extends in a first direction D1 as shown in FIG. 1. Furthermore, as shown in FIG. 1, the anode wire 2 also extends in the first direction D1, and therefore the anode part 6 (the anode body 1 + the anode wire 2) also extends in the first direction D1.

[0030] The anode 1 is, for example, a porous sintered body obtained by sintering metal particles. The anode 1 has, for example, a rectangular parallelepiped shape. As the metal particles, valve metal particles such as titanium (Ti), tantalum (Ta), and niobium (Nb) can be used. The anode 1 may be obtained by sintering one type of metal particle, or by sintering two or more types of metal particles. The metal particles may be alloy particles composed of two or more types of metals. As the alloy particles, for example, alloy particles containing a valve metal and at least one element selected from the group consisting of silicon, vanadium, and boron can be used. Alternatively, alloy particles containing a valve metal and a typical element (such as nitrogen) can also be used. The above alloy particles usually contain a valve metal as the main component. The above alloy particles, for example, contain 50 atomic percent or more of the valve metal.

[0031] The anode wire 2 is made of a conductive material. The material used to form the anode wire 2 is not particularly limited and can be, for example, a valve metal as described above, as well as copper, aluminum, and aluminum alloys. The material used to form the anode body 1 and the material used to form the anode wire 2 may be the same or different. The cross-sectional shape of the anode wire 2 is not particularly limited and can be circular, track-shaped, elliptical, rectangular, or polygonal. A track-shaped cross-section is a shape consisting of parallel straight lines and two curves connecting the ends of these lines.

[0032] The anode portion 6 can be manufactured, for example, by embedding the first portion 2a of the anode wire 2 in the metal particle powder, press-molding it into a rectangular parallelepiped shape, and then sintering it. As a result, the second portion 2b of the anode wire 2 is drawn out (extended) from one end face E1 of the anode body 1. In the anode wire 2, the second portion 2b is in contact with the anode lead frame 13 and electrically connected. The second portion 2b may be welded to the anode lead frame 13. The welding method is not particularly limited and examples include resistance welding and laser welding.

[0033] As described above, the anode portion 6 has a dielectric layer 3. The dielectric layer 3 is formed on the surface of the anode body 1. In a solid electrolytic capacitor 100 according to one embodiment of the present disclosure, the dielectric layer 3 covers at least a part of the anode body 1. The dielectric layer 3 is composed of, for example, a metal oxide. Methods for forming a layer containing a metal oxide on the surface of the anode body 1 include, for example, immersing the anode body 1 in a chemical conversion solution to anodize the surface of the anode body 1, and heating the anode body 1 in an oxygen-containing atmosphere. The dielectric layer 3 is not limited to a layer containing a metal oxide as described above, and only needs to have insulating properties.

[0034] (Cathode section) The cathode section 7 has a conductive polymer layer 4 formed on the dielectric layer 3 and a cathode layer 5 covering the conductive polymer layer 4. In the solid electrolytic capacitor 100 according to one embodiment of the present disclosure, the conductive polymer layer 4 contains a conductive polymer and covers at least a part of the dielectric layer 3. In the example of Figure 1, the conductive polymer layer 4 is formed to cover the entire surface of the dielectric layer 3.

[0035] To improve conductivity, conductive polymers are typically doped. Doped conductive polymers are classified into self-doped and non-self-doped conductive polymers.

[0036] Self-doped conductive polymers have a conjugated polymer skeleton and functional groups (such as anionic groups) that are directly or indirectly bonded to this skeleton by covalent bonds and function as dopants. An anionic group is a group that acquires a negative charge when a cation dissociates.

[0037] Examples of anionic groups include sulfo groups, carboxyl groups, phosphate groups, and phosphone groups. Self-doped conductive polymers may contain one or more anionic groups, or two or more. From the viewpoint of enhancing conductivity, it is preferable that self-doped conductive polymers have at least a sulfo group as anionic groups.

[0038] The anionic group may be present in any form, such as free, ester, or salt. Alternatively, the anionic group may be present in a form that interacts with or is complexed with components contained in the conductive polymer layer 4. In this specification, all of these forms are simply referred to as anionic groups.

[0039] Examples of conjugated polymers that constitute the backbone of self-doped conductive polymers include polymers that have a π-conjugated polymer as their basic backbone. Examples of π-conjugated polymers include polypyrrole, polythiophene, polyaniline, polyfuran, polyimidazole, polypyrazole, polyoxazole, polyisoxazole, polythiazole, polyisothiazole, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene. The above polymers only need to contain at least one monomer unit that constitutes the basic backbone. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituents). For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0040] Self-doped conductive polymers have anionic groups in the backbone of these conjugated polymers. The anionic groups may be introduced directly into the backbone of the conjugated polymer or via linking groups. Preferred linking groups include polyvalent groups (e.g., divalent groups) containing alkylene groups. For example, aliphatic polyvalent groups (e.g., divalent groups) such as alkylene groups, -R １ -X-R ２ - group (X is an oxygen or sulfur element, R １ and R ２These are alkylene groups that may be the same or different. The number of carbon atoms in each alkylene group included in the linking group is, for example, 1 to 10. The number of carbon atoms may be 1 to 6. The alkylene group may be linear or branched. The linking group may, for example, contain at least one alkylene group with 2 or more carbon atoms. The number of carbon atoms in such an alkylene group may be 2 to 10 (or 3 to 10), or 2 to 6 (or 3 to 6). For example, R １ is an alkylene group having 1 to 6 carbon atoms, R ２ The linking group may be an alkylene group having 2 or more (or 3 or more) and 10 or fewer carbon atoms. On the other hand, the linking group is not limited to the above.

[0041] Non-self-doped conductive polymers consist of a non-self-doped conjugated polymer and a dopant (external dopant). A non-self-doped conjugated polymer is a conjugated polymer that does not contain functional groups that function as dopants.

[0042] Examples of conjugated polymers include those exemplified as conjugated polymers constituting the backbone of self-doped conductive polymers (e.g., π-conjugated polymers). Conjugated polymers may be used individually or in combination of two or more types.

[0043] The dopant may be a single-molecule anion or a polymer anion.

[0044] A monomolecule anion is an anion derived from a monomolecule compound. Examples of monomolecule compounds include 1,5-naphthalenedisulfonic acid, 1,6-naphthalenedisulfonic acid, 1-octanesulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 2,6-naphthalenedisulfonic acid, 2,7-naphthalenedisulfonic acid, 2-methyl-5-isopropylbenzenesulfonic acid, 4-octylbenzenesulfonic acid, 4-nitrotoluene-2-sulfonic acid, m-nitrobenzenesulfonic acid, n-octylsulfonic acid, n-butanesulfonic acid, n-hexanesulfonic acid, o-nitrobenzenesulfonic acid, p-ethylbenzenesulfonic acid, trifluoromethanesulfonic acid, hydrooxybenzenesulfonic acid, butylnaphthalenesulfonic acid, benzenesulfonic acid, and methanesulfonic acid. Monomolecule compounds may also be derivatives. Examples of derivatives include metal salts such as lithium salts, potassium salts, and sodium salts; ammonium salts such as methylammonium salts, dimethylammonium salts, and trimethylammonium salts; piperidium salts, pyrrolidium salts, and pyrrolinium salts. The monomolecule compound may also be an anionic surfactant. In this case, the monomolecule anion may be an anion derived from the anionic surfactant. An example of an anionic surfactant is sodium dodecyl sulfate (SDS).

[0045] Polymeric anions are anions derived from polymeric compounds. Examples of polymeric compounds include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacrylate sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. Polymeric compounds may also be derivatives. Examples of derivatives include metal salts such as lithium salts, potassium salts, and sodium salts, ammonium salts such as methylammonium salts, dimethylammonium salts, and trimethylammonium salts, piperidium salts, pyrrolidium salts, and pyrrolinium salts. Polymeric compounds may be polymers of a single monomer or copolymers of two or more monomers.

[0046] One dopant may be used alone, or two or more dopants may be used in combination. For example, a monomolecular anion and a polymer anion may each be used alone, two or more monomolecular anions may be used in combination, two or more polymer anions may be used in combination, or one or more monomolecular anions and one or more polymer anions may be used in combination.

[0047] As will be described later, when a non-self-doped conductive polymer is obtained by electrolytic polymerization, the aforementioned monomolecular compound and polymer compound may act as a supporting electrolyte in the polymerization solution. Therefore, dopants such as a monomolecular anion derived from a monomolecular compound and a polymer anion derived from a polymer compound act to improve the conductivity of the conductive polymer in the conductive polymer, and may act to ensure the conductivity of the polymerization solution during electrolytic polymerization. In addition, as will be described later, although the polymerization solution for electrolytic polymerization contains an inorganic chlorine compound (for example, potassium perchlorate (KClO ４ )) as a supporting electrolyte, an anion derived from the inorganic chlorine compound (for example, a perchlorate ion (ClO ４ － )) may act to improve the conductivity of the conductive polymer in the conductive polymer.

[0048] The dopant is preferably a monomolecule anion, and among monomolecule anions, it is preferable that it is an anion derived from an anionic surfactant. By using an anion derived from an anionic surfactant as the dopant, the solubility of the monomer in water can be increased by emulsification when the polymerization solution contains water as a solvent. This increases the monomer concentration in the polymerization solution, making it possible to obtain a conductive polymer with excellent conductivity. The anionic surfactant preferably contains a sulfonate or a sulfate ester salt. An example of such an anionic surfactant is sodium dodecyl sulfate (SDS). That is, when the conductive polymer layer 4 contains a non-self-doped conductive polymer as the conductive polymer, it is preferable that the conductive polymer layer 4 contains an anion derived from an anionic surfactant as the dopant.

[0049] When the conductive polymer layer 4 contains a sulfonate or sulfate ester as an anionic surfactant, the conductive polymer preferably contains a conjugated polymer made of a thiophene derivative. In this case, the ratio of the sulfur (S) element content C2 derived from the dopant to the sulfur (S) element content C1 derived from the conjugated polymer made of the thiophene derivative (C2 / C1) is preferably 0.45 or less. C2 / C1 may be 0.2 or more. In this case, the conductive polymer will contain a sufficient amount of dopant that does not disrupt the crystal structure of the conductive polymer. Therefore, the conductive polymer can exhibit even higher conductivity. The content C1 and C2 can be measured according to the following procedure.

[0050] Measurement Procedure (1) The sulfur (S) content in the conductive polymer layer is measured by ICP-AES analysis. The ICP-AES analysis will be described later. (2) A sample separate from the sample used for ICP-AES analysis is taken from the conductive polymer layer. (3) X-ray photoelectron spectroscopy (XPS) is performed on the taken sample to obtain an XPS spectrum with binding energy (in eV) on the x-axis and intensity (in a.u.) on the y-axis. Peak separation (fitting) is performed on this XPS spectrum to determine the first peak attributed to the monomer and the second peak attributed to the dopant. (4) The peak area S1 of the first peak and the peak area S2 of the second peak are determined. (5) The ratio R1 (S1 / (S1+S2)) of S1 to the sum of S1 and S2, and the ratio R2 (S2 / (S1+S2)) of S2 to the sum of S1 and S2 are calculated. Then, the sulfur (S) content is multiplied by R1 to calculate the sulfur (S) content derived from the conductive polymer, and the sulfur (S) content is multiplied by R2 to calculate the sulfur (S) content derived from the dopant.

[0051] XPS can be performed under the following conditions: • X-ray photoelectron spectroscopy system: VersaProbe (ULVAC-PHI) • X-ray source: monochromated-Al-Kα • Measurement diameter: 100 μm • Photoelectron extraction angle: 90°

[0052] Both the self-doped conductive polymer and the non-self-doped conductive polymer are preferably conjugated polymers composed of heterocyclic compounds having a five-membered ring structure. In other words, the conjugated polymer is preferably composed of heterocyclic compounds having a five-membered ring structure as monomers, which are polymerized. The heterocyclic compounds having a five-membered ring structure preferably include at least one selected from the group consisting of pyrrole, furan, thiophene, imidazole, pyrazole, oxazole, isoxazole, thiazole, and isothiazole. The heterocyclic compounds having a five-membered ring structure also include derivatives thereof. For example, thiophene includes 3,4-ethylenedioxythiophene (EDOT). The conjugated polymer composed of heterocyclic compounds having a five-membered ring structure preferably includes a conjugated polymer composed of a thiophene derivative. In other words, the conjugated polymer preferably contains a thiophene derivative as a monomer. The thiophene derivative is preferably 3,4-ethylenedioxythiophene (EDOT).

[0053] Conductive polymers can be obtained by chemical oxidation polymerization or electrolytic polymerization of monomers (hereinafter also simply referred to as monomers) that constitute the conductive polymer.

[0054] Chemical oxidation polymerization can be carried out by chemically oxidizing a monomer using a solvent, an oxidizing agent, a monomer, and, if necessary, a dopant. Note that dopants are used when synthesizing non-self-doped conductive polymers, but not when synthesizing self-doped conductive polymers. Suitable solvents include, for example, water, sulfuric acid, methanol, ethanol, propanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, chloroform, dichloromethane, carbon tetrachloride, benzene, toluene, xylene, tetrahydrofuran, N-methyl-2-pyrrolidone, and propylene carbonate. The monomer and dopant should be appropriately selected depending on the desired conductive polymer. For example, when using a thiophene derivative (e.g., EDOT) as the monomer, it is preferable to use an anion derived from an anionic surfactant as the dopant. In this case, sodium dodecyl sulfate (SDS) is preferred as the anionic surfactant. Suitable oxidizing agents include ferric chloride, iron(III) tri(p-toluenesulfonate), sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide, and potassium permanganate. The polymerization conditions for chemical oxidation polymerization can be selected according to the solvent, oxidizing agent, monomer, and, if necessary, the type of dopant compound used.

[0055] In electropolymerization, a conductive polymer is obtained by polymerizing monomers in a solvent. Dopants may be used in electropolymerization as needed. In electropolymerization, dopants are used when synthesizing non-self-doped conductive polymers, but not when synthesizing self-doped conductive polymers. The solvents exemplified above can be used. Monomers and dopants should be appropriately selected depending on the desired conductive polymer.

[0056] Examples of electrolytic polymerization include a method in which monomers are polymerized by applying a potential sweep method or a constant voltage method using a potentiostat to a polymerization solution obtained by dissolving or suspending monomers and, optionally, dopants in a solvent, and a method in which monomers are polymerized by applying a constant current method using a galvanostat to the polymerization solution. The dopant functions as a supporting electrolyte in the polymerization solution. The conditions for the potential sweep method, constant voltage method, and constant current method can be appropriately selected depending on the type of solvent, monomer, and, if necessary, dopant used.

[0057] The polymerization solution may contain supporting electrolytes other than dopants. Examples of supporting electrolytes include inorganic chlorine compounds. Preferably, the inorganic chlorine compound contains a chlorine-containing anion as anion. Examples of chlorine-containing anions include chloride ions (Cl － ), and perchlorate ions (ClO ４ － Examples include the perchlorate ion (ClO). ４ － It is preferable that the chlorine-containing anion acts as a dopant in addition to acting as a supporting electrolyte. It is preferable that the inorganic chlorine compound contains a monovalent cation. Examples of monovalent cations include alkali metal ions. Examples of alkali metal ions include lithium ions (Li ＋ ), sodium ions (Na ＋ ), potassium ions (K ＋ ), rubidium ion (Rb ＋ ), cesium ions (Cs ＋ ), and francium ions (Fr ＋ ) are some examples.

[0058] Electropolymerization can be carried out with an anode body having a dielectric layer formed on it immersed in a polymerization solution for electropolymerization. Electropolymerization may be carried out using a two-electrode system or a three-electrode system. A two-electrode system uses two electrodes: an anode body and a counter electrode, while a three-electrode system uses three electrodes: an anode body, a counter electrode, and a reference electrode. When electropolymerization is carried out using a three-electrode system, the polymerization reaction can be controlled more precisely than when electropolymerization is carried out using a two-electrode system. Therefore, an electropolymerized film with superior film quality can be obtained. In addition, although fine depressions are usually formed on the surface of the anode body, by carrying out electropolymerization using a three-electrode system, the packing density of the conductive polymer in these fine depressions can be increased.

[0059] The conductive polymer layer 4 may be formed, for example, by chemical oxidation polymerization or electrolytic polymerization of monomers on the dielectric layer 3 to obtain a conductive polymer, as described above, or by coating the dielectric layer 3 with a liquid containing the conductive polymer. The conductive polymer layer 4 may consist of one layer or two or more layers. If the conductive polymer layer 4 consists of two or more layers, the composition of the conductive polymer contained in each layer may be different, and the method of forming each layer (e.g., polymerization method) may be different.

[0060] When conductive polymers are dispersed in a dispersion medium in the form of particles, the average particle size D50 is, for example, 0.01 μm or more and 0.5 μm or less. Having an average particle size D50 within this range makes it easier for the conductive polymer particles to penetrate into the interior of the anode 1.

[0061] It is preferable that the conductive polymer layer 4 is a layer formed by electrolytic polymerization. Whether or not the conductive polymer layer 4 is a layer formed by electrolytic polymerization can be determined, for example, by observing a scanning electron microscope (SEM) image (cross-sectional SEM image) of the cross-section in the thickness direction of the capacitor element. For example, if the cross-sectional SEM image shows that the conductive polymer layer is filled relatively densely and uniformly inside the pores of the anode body, it can be determined that the conductive polymer layer is formed by electrolytic polymerization. It should be noted that whether or not the conductive polymer layer is filled relatively densely and uniformly can be determined by common technical knowledge. Furthermore, if a portion of the conductive polymer layer is taken and, for example, an ICP-AES analysis is performed as described later, and no metal elements (e.g., Fe) contained in the oxidizing agent of chemical oxidation polymerization are detected, it can be determined that the conductive polymer layer is formed by electrolytic polymerization.

[0062] The conductive polymer layer 4 contains monovalent cations. These monovalent cations may originate from, for example, an oxidizing agent and a supporting electrolyte. The content of the elements constituting the monovalent cations in the conductive polymer layer is less than 23,000 ppm. ppm refers to the mass content (mg / kg) of the elements constituting the monovalent cations per 1 kg of the conductive polymer layer. Examples of monovalent cations include alkali metal ions. Examples of alkali metal ions include lithium ions (Li ＋ ), sodium ions (Na ＋ ), potassium ions (K ＋ ), rubidium ion (Rb ＋ ), cesium ions (Cs ＋ ), and francium ions (Fr ＋ ) are some examples.

[0063] The content of elements constituting monovalent cations in a conductive polymer layer is measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Specifically, the measurement is performed according to the following procedure: Measurement procedure (1) A portion of the conductive polymer layer is taken as a sample, and the mass of the sample is measured. (2) The sample after mass measurement is completely dissolved in a heated acid solution (for example, a mixed acid of hydrofluoric acid and nitric acid) to obtain an analytical sample solution. The volume of the analytical sample solution is measured. (3) The concentration C0 of the sample in the analytical sample solution is determined by dividing the mass of the sample by the volume of the analytical sample solution. (4) The obtained analytical sample solution is analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to determine the concentration Ci of each element constituting monovalent cations in the analytical sample solution. Here, i is the element species constituting the monovalent cation contained in the analytical sample solution. For example, Li is present as a monovalent cation in the analytical sample solution. ＋ and Na ＋ If present, determine the concentrations of lithium and sodium elements as Ci. (5) Divide the concentration Ci of each element by the concentration C0 of the sample to calculate the content of each element (ppm (mg / kg)) in the conductive polymer layer. For example, if lithium and sodium elements are present, calculate the content of lithium and sodium elements in the conductive polymer layer.

[0064] The conductive polymer layer 4 preferably contains sodium ions and lithium ions as monovalent cations. The sodium element content in the conductive polymer layer is preferably less than 22,000 ppm. Furthermore, the sodium element content in the conductive polymer layer is more preferably 10,000 ppm or more and 21,000 ppm or less. The lithium element content in the conductive polymer layer is preferably 20 ppm or more and 400 ppm or less. The total sodium and lithium element content in the conductive polymer layer is preferably 13,000 ppm or more and 21,000 ppm or less. By having the sodium and lithium element content in the conductive polymer layer within the above ranges, the conductivity of the conductive polymer can be further increased.

[0065] The conductive polymer layer 4 preferably contains a chlorine-containing anion as anion. Examples of chlorine-containing anions include chloride ions (Cl － ), and perchlorate ions (ClO ４ － Examples include the perchlorate ion (ClO). ４ － It is preferable that the conductive polymer layer contains less than 20,000 ppm of chlorine. It is even more preferable that the conductive polymer layer contains 900 ppm or more and 5,000 ppm or less of chlorine. The conductive polymer layer may contain 3,000 ppm or less of chlorine. By having the chlorine content in the conductive polymer layer within the above range, the conductivity of the conductive polymer can be further increased. The chlorine content in the conductive polymer layer is measured by analysis using inductively coupled plasma atomic emission spectroscopy (ICP-AES) according to the procedure described above. It is preferable that the conductive polymer layer contains a chlorine-containing anion as a dopant or supporting electrolyte. In this case, it is preferable that the chlorine-containing anion is an anion derived from an inorganic chlorine compound.

[0066] The cathode layer 5 includes, for example, a carbon layer 5a formed to cover the conductive polymer layer 4, and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a includes, for example, a conductive carbon material such as graphite and a resin. The metal paste layer 5b includes, for example, metal particles such as silver and a resin. The configuration of the cathode layer 5 is not limited to the above, and any configuration that has a current collection function is acceptable.

[0067] <Cathode Lead Frame> The cathode lead frame 14 is electrically connected to the cathode portion 7. As shown in Figure 1, the cathode lead frame 14 is connected to the cathode layer 5 in the cathode portion 7, for example, via a conductive adhesive 8. The cathode lead frame 14 has a cathode lead embedded portion 141 which is embedded inside the outer casing 11 and electrically connected to the cathode portion 7, and a cathode lead exposed portion 142 which is exposed to the outside from one end face E2 of the outer casing 11.

[0068] The material used to form the cathode lead frame 14 is not particularly limited as long as it is electrochemically and chemically stable and conductive. The material used to form the cathode lead frame 14 may be a metal such as copper, or a nonmetal. The cathode lead frame 14 can be formed by bending a flat conductor (conductor plate). From the viewpoint of reducing the height, the thickness of the conductor plate (length between the two main surfaces of the conductor plate) may be 25 μm or more and 200 μm or 25 μm or more and 100 μm or less.

[0069] <Anode Lead Frame> The anode lead frame 13 is electrically connected to the anode portion 6, as shown in Figure 1. The anode lead frame 13 has an anode lead embedding portion 131 embedded inside the outer casing 11, and an anode lead exposed portion 132 exposed to the outside from the other end face E3 opposite to one end face E2 of the outer casing. The anode lead embedding portion 131 has an anode lead portion 131a that is electrically connected to the anode wire 2. The anode lead portion 131a and the anode wire 2 are joined by welding.

[0070] The material used to form the anode lead frame 13 is not particularly limited as long as it is electrochemically and chemically stable and electrically conductive. The material used to form the anode lead frame 13 may be a metal such as copper, or a nonmetal. The anode lead frame 13 can be formed by bending a flat conductor (conductor plate). From the viewpoint of reducing the height, the thickness of the conductor plate (length between the two main surfaces of the conductor plate) may be 25 μm or more and 200 μm or 25 μm or more and 100 μm or less.

[0071] <Outer Covering> The outer covering 11 covers the capacitor element 10. The outer covering 11 is configured to cover the entire capacitor element 10. The outer covering 11 is provided to electrically insulate the anode lead frame 13 and the cathode lead frame 14, and is made of an insulating material (outer covering material). The outer covering 11 also protects the capacitor element 10 from impact and moisture. The outer covering material includes, for example, a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane resin, polyimide resin, and unsaturated polyester resin.

[0072] If the outer casing 11 is made of an outer casing material containing a thermosetting resin, an inorganic filler may be included in the outer casing 11. This can increase the strength of the outer casing 11. Examples of inorganic fillers that can be used include silicon dioxide (silica), aluminum oxide (alumina), zirconium oxide (zirconia), titanium oxide (titania), and magnesium oxide (magnesia).

[0073] The average particle size of inorganic fillers is, for example, 60 μm to 80 μm. The average particle size of inorganic fillers can be determined in the same way as the average particle sizes of conductive and insulating particles.

[0074] [Method for Manufacturing a Solid Electrolytic Capacitor] A method for manufacturing a solid electrolytic capacitor according to one embodiment of the present disclosure, as shown in Figure 2, comprises the steps of: preparing a capacitor element (capacitor element preparation step (S1)); preparing an anode lead frame and a cathode lead frame (lead frame preparation step (S2)); electrically connecting the anode lead frame and the cathode lead frame to the capacitor element (connection step (S3)); and sealing the capacitor element, a part of the anode lead frame, and a part of the cathode lead frame (sealing step (S4)).

[0075] (1) Preparation step of capacitor element (S1) Valve metal particles and anode wire are placed in a mold and pressure-molded so that a part of the anode wire (first part) is embedded in the valve metal particles, and then the valve metal particles are sintered in a vacuum. As a result, the first part of the anode wire is embedded inside the porous sintered body, and the second part of the anode wire is drawn out (extended) from one end face of the porous sintered body to create an anode portion. In this anode portion, the porous sintered body corresponds to the anode body. The pressure for pressure molding is not particularly limited, for example, it is about 10 N to 100 N. A binder such as polyacrylic carbonate may be mixed with the valve metal particles as needed.

[0076] Next, a dielectric layer is formed on the porous sintered body (anode). Specifically, the porous sintered body (anode) is immersed in a chemical tank filled with an electrolytic aqueous solution (for example, an aqueous phosphoric acid solution), and the second part of the porous sintered body (anode) is connected to an anode provided in the chemical tank to perform anodic oxidation, thereby forming a dielectric layer consisting of an oxide film of a valve-acting metal on the surface of the porous sintered body (anode). The electrolytic aqueous solution is not limited to an aqueous phosphoric acid solution, but can also be nitric acid, acetic acid, sulfuric acid, etc.

[0077] Next, a conductive polymer layer is formed on the dielectric layer. The conductive polymer layer can be formed, for example, by impregnating the anode body on which the dielectric layer is formed with a polymerization solution containing monomers, and then polymerizing the monomers by chemical oxidation polymerization or electrolytic polymerization, or by impregnating the anode body on which the dielectric layer is formed with a solution or dispersion of conductive polymers, and then drying it. The conductive polymer layer is formed on at least a portion of the dielectric layer.

[0078] The conductive polymer layer is preferably formed by electrolytic polymerization. Electrolytic polymerization can be carried out with the anode body, on which the dielectric layer is formed, immersed in a polymerization solution for electrolytic polymerization. Electrolytic polymerization may be carried out using a two-electrode system or a three-electrode system. When electrolytic polymerization is carried out using a three-electrode system, the polymerization reaction can be controlled more precisely than when electrolytic polymerization is carried out using a two-electrode system. Therefore, an electrolytic polymerized film with excellent film quality can be obtained. In addition, although fine depressions are usually formed on the surface of the anode body, the packing rate of the conductive polymer in these fine depressions can be increased by carrying out electrolytic polymerization using a three-electrode system.

[0079] The polymerization solution contains monomers. Preferably, the monomer is a heterocyclic compound having a five-membered ring structure. The monomer preferably contains at least one selected from the group consisting of pyrrole, furan, thiophene, imidazole, pyrazole, oxazole, isoxazole, thiazole, and isothiazole, as a heterocyclic compound having a five-membered ring structure. Note that derivatives of heterocyclic compounds having a five-membered ring structure are also included as heterocyclic compounds having a five-membered ring structure. For example, thiophene includes 3,4-ethylenedioxythiophene (EDOT). Preferably, the heterocyclic compound having a five-membered ring structure is 3,4-ethylenedioxythiophene (EDOT).

[0080] The polymerization solution preferably contains a dopant in addition to the monomer. The dopant preferably contains an anion derived from an anionic surfactant. The anionic surfactant preferably contains a sulfonate or a sulfate ester salt. The anionic surfactant preferably contains sodium dodecyl sulfate (SDS).

[0081] Polymerization solutions typically contain a solvent. Examples of solvents include water and organic solvents. Water and organic solvents may be used in combination. The polymerization solution may also contain an oxidizing agent as needed. An example of an oxidizing agent is Fe. ３＋ Examples of compounds capable of generating oxidizing agents include ferric sulfate, persulfates (such as sodium persulfate and ammonium persulfate), and hydrogen peroxide. The oxidizing agent may be used alone or in combination of two or more.

[0082] For example, a Ti electrode can be used as the counter electrode, and for example, a silver / silver chloride electrode (Ag / Ag) can be used as the reference electrode. ＋ ) can be used.

[0083] In electropolymerization, the voltage applied to the anode (polymerization voltage) is, for example, 0.6V to 1.5V. By applying a voltage within this range and performing electropolymerization using a three-electrode system, the packing density of the conductive polymer in the fine depressions formed on the surface of the anode can be further increased. Note that the polymerization voltage in three-electrode electropolymerization is calculated as follows: Reference electrode (silver / silver chloride (Ag / Ag) ＋ This refers to the potential of the anode relative to the )). The electrolytic polymerization temperature may be 5°C to 60°C or 15°C to 35°C. Note that the electrolytic polymerization temperature refers to the temperature of the polymerization solution.

[0084] Next, a carbon layer is formed by applying carbon paste to the conductive polymer layer and drying it, and then a metal paste layer is formed by applying metal paste to the carbon layer and drying it. This creates a cathode layer on the conductive polymer layer, consisting of the carbon layer and the metal paste layer. The configuration of the cathode layer is not limited to the above, and any configuration that has a current-collecting function is acceptable. A capacitor element is then fabricated.

[0085] (2) Lead frame preparation process (S2) In the lead frame preparation process, the anode lead frame and the cathode lead frame are prepared. For example, a single flat conductor (conductor plate) is prepared as the anode lead frame. For example, a single flat conductor (conductor plate) is bent into a stepped shape to prepare as the cathode lead frame (see Figure 3). The cathode lead frame 14 prepared in this way has a cathode lead embedding portion 141 and a cathode lead exposed portion 142, as shown in Figure 3. The cathode lead embedding portion 141 is the part that will be covered by the outer casing material in the sealing process described later, and the cathode lead exposed portion 142 is the part that will not be covered by the outer casing material in the sealing process described later. Note that in Figure 3, the boundary between the cathode lead embedding portion 141 and the cathode lead exposed portion 142 is shown by a dashed line.

[0086] (3) Connection process (S3) First, a conductive adhesive is applied to a predetermined location on the lower surface of the capacitor element, and then a portion of the cathode lead embedding portion 141 is connected to the lower surface of the capacitor element via the conductive adhesive. This electrically connects the cathode lead frame 14 to the capacitor element.

[0087] Next, the second portion of the anode wire is brought into contact with a portion of the anode lead frame. Then, the second portion of the anode wire is welded to the portion of the anode lead frame. This electrically connects the anode lead frame to the capacitor element. Laser welding or resistance welding can be used for the welding described above. As a result, a capacitor element in which the anode lead frame and cathode lead frame are electrically connected can be obtained.

[0088] (4) Sealing process (S4) After placing the capacitor element and the outer casing material (for example, uncured thermosetting resin and inorganic filler) into the mold, the capacitor element is sealed by a transfer molding method or a compression molding method. At this time, a portion of the flat anode lead frame and cathode lead frame is exposed from the mold. As shown in Figure 3, for the cathode lead frame 14, the cathode lead exposed portion 142 is exposed. Also, for the anode lead frame, the portion exposed from the mold becomes the anode lead exposed portion. The molding conditions are not particularly limited, and the molding time and molding temperature can be set appropriately considering the thermosetting temperature of the thermosetting resin used.

[0089] As described above, an intermediate solid electrolytic capacitor can be obtained in which the entire capacitor element and a portion of the anode lead frame and cathode lead frame are covered by an outer casing. In the intermediate solid electrolytic capacitor obtained as described above, the cathode lead exposed portion extends from one end face of the outer casing, and the anode lead exposed portion extends from the other end face of the outer casing (the face opposite to the one end face). At this stage, the anode lead frame is flat, and the cathode lead frame is stepped.

[0090] Next, for the intermediate solid electrolytic capacitor product, the exposed cathode leads of the cathode lead frame are bent along one end face and the bottom surface of the casing, and the exposed anode leads of the anode lead frame are bent along the other end face and the bottom surface of the casing.

[0091] As described above, by performing the capacitor element preparation step (S1), the lead frame preparation step (S2), the connection step (S3), and the sealing step (S4), a solid electrolytic capacitor according to one embodiment of this disclosure (for example, a solid electrolytic capacitor as shown in Figure 1) can be manufactured.

[0092] In this specification, an example has been described in which the solid electrolytic capacitor 100 comprises one capacitor element 10, but the number of capacitor elements 10 in the solid electrolytic capacitor 100 may be multiple.

[0093] Furthermore, although this specification describes a solid electrolytic capacitor as an example of an electrolytic capacitor, electrolytic capacitors are not limited to solid electrolytic capacitors. An electrolytic capacitor may also be a solid-liquid hybrid type electrolytic capacitor containing a conductive polymer and a liquid component (e.g., electrolyte) as the electrolyte.

[0094] (Note) The following technologies are disclosed by the above description. (Technology 1) An electrolytic capacitor comprising a capacitor element including an anode body extending in a first direction, a dielectric layer covering at least a part of the anode body, and a conductive polymer layer containing a conductive polymer and covering at least a part of the dielectric layer, wherein the conductive polymer layer contains a monovalent cation, and the content of the elements constituting the monovalent cation in the conductive polymer layer is less than 23,000 ppm. (Technology 2) The electrolytic capacitor according to Technology 1, wherein the conductive polymer layer contains sodium ions and lithium ions as the monovalent cation. (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the content of the sodium element in the conductive polymer layer is less than 22,000 ppm. (Technology 4) The electrolytic capacitor according to Technology 3, wherein the content of the sodium element in the conductive polymer layer is 10,000 ppm or more and 21,000 ppm or less. (Technology 5) An electrolytic capacitor according to any one of Technologies 1 to 4, wherein the content of lithium element in the conductive polymer layer is 20 ppm or more and 400 ppm or less. (Technology 6) An electrolytic capacitor according to Technology 2, wherein the total content of sodium element and lithium element in the conductive polymer layer is 13,000 ppm or more and 21,000 ppm or less. (Technology 7) An electrolytic capacitor according to any one of Technologies 1 to 6, wherein the conductive polymer layer contains a chlorine-containing anion as anion, and the content of chlorine element in the conductive polymer layer is less than 20,000 ppm. (Technology 8) An electrolytic capacitor according to Technology 7, wherein the content of chlorine element in the conductive polymer layer is 900 ppm or more and 5,000 ppm or less. (Technology 9) An electrolytic capacitor according to any one of Technologies 1 to 8, wherein the conductive polymer layer is a layer formed by electrolytic polymerization. (Technical 10) The electrolytic capacitor according to Technical 7 or 8, wherein the conductive polymer layer contains the chlorine-containing anion as a dopant or supporting electrolyte, and the chlorine-containing anion is an anion derived from an inorganic chlorine compound. (Technical 11) The electrolytic capacitor according to Technical 10, wherein the anion derived from the inorganic chlorine compound is a perchlorate ion.(Technology 12) The electrolytic capacitor according to any one of Technologies 1 to 11, wherein the conductive polymer layer comprises a conjugated polymer consisting of a heterocyclic compound having a five-membered ring structure as the conductive polymer. (Technology 13) The electrolytic capacitor according to Technology 12, wherein the conjugated polymer consisting of a heterocyclic compound having a five-membered ring structure comprises a conjugated polymer consisting of a thiophene derivative. (Technology 14) The electrolytic capacitor according to any one of Technologies 1 to 13, wherein the conductive polymer layer comprises an anion derived from an anionic surfactant as a dopant. (Technology 15) The electrolytic capacitor according to Technology 14, wherein the anionic surfactant comprises a sulfonate or a sulfate ester salt. (Technology 16) The electrolytic capacitor according to Technology 15, wherein the conductive polymer layer comprises a conjugated polymer consisting of a thiophene derivative, and the ratio of the sulfur content C2 derived from the dopant to the sulfur content C1 derived from the conjugated polymer consisting of the thiophene derivative (C2 / C1) is 0.45 or less.

[0095] The present disclosure will be described below in detail based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0096] [Example 1] <Capacitor element> (Anode part) Valve metal particles (Ta particles) and an anode wire were placed in a mold and pressure molded so that the first part was embedded in the valve metal particles, and then the valve metal particles were sintered in a vacuum. As a result, an anode part was produced in which the first part of the anode wire was embedded inside the porous sintered body, and the second part of the anode wire was drawn out (extended) from one end face of the porous sintered body. Polyacrylic carbonate was mixed with the valve metal particles as a binder. Furthermore, in the anode part produced as described above, the porous sintered body corresponds to the anode body.

[0097] (Dielectric layer) A porous sintered body (anode) is immersed in a chemical conversion tank filled with an aqueous phosphoric acid solution (phosphoric acid concentration of 0.010 mass%), and a second part of the porous sintered body (anode) is connected to the anode provided in the chemical conversion tank to perform anodizing, thereby forming an oxide film of valve metal (Ta) on the surface of the porous sintered body (anode). ２ O ５A dielectric layer consisting of a coating was formed. Anodizing was carried out under the condition of applying a DC voltage of 10V.

[0098] (Cathode section) A mixed solution was prepared by dissolving or suspending 3,4-ethylenedioxythiophene (EDOT, monomer) and sodium dodecyl sulfate (SDS, dopant) in deionized water. While stirring the mixed solution, lithium perchlorate (LiClO2) dissolved in deionized water was added. ４ The polymerization solution according to Example 1 was prepared by adding ). The polymerization solution according to Example 1 contained EDOT at a concentration of 300 mmol / L, SDS at a concentration of 600 mmol / L, and LiClO ４ It contained at a concentration of 2.5 mmol / L. The composition of the polymerization solution according to Example 1 is shown in Table 1 below. Electrolytic polymerization was carried out using the polymerization solution according to Example 1 in a three-electrode system. More specifically, electrolytic polymerization was carried out as follows. First, a porous sintered body (anode) with a dielectric layer formed thereon, a counter electrode, and a reference electrode (silver / silver chloride reference electrode) were immersed in the polymerization solution according to Example 1. Next, at a liquid temperature of 25°C, a voltage was applied to the porous sintered body so that the potential of the porous sintered body relative to the reference electrode was 1.1V, and electrolytic polymerization was carried out. This formed a conductive polymer layer on the dielectric layer of the porous sintered body. That is, a conductive polymer layer according to Example 1 was formed on the dielectric layer of the porous sintered body.

[0099] A dispersion of graphite particles in water was applied to a conductive polymer layer, and then dried to form a carbon layer on the conductive polymer layer. Drying was carried out at 130 to 180°C for 10 to 30 minutes. Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the carbon layer, and then the binder resin was heat-cured to form a silver paste layer on the carbon layer. The binder resin was heat-cured at 150 to 200°C for 10 to 60 minutes. This formed a cathode layer on the conductive polymer layer consisting of the carbon layer and the silver paste layer. As a result, a cathode portion having a solid electrolyte layer and a cathode layer covering the solid electrolyte layer was fabricated, and a capacitor element according to Example 1 was obtained.

[0100] [Example 2] In the formation of the cathode, LiClO in the polymerization solution ４A capacitor element according to Example 2 was fabricated in the same manner as in Example 1, except that the concentration was changed to 5.0 mmol / L. The composition of the polymerization solution according to Example 2 is shown in Table 1 below.

[0101] [Example 3] In the formation of the cathode, LiClO in the polymerization solution ４ A capacitor element according to Example 3 was fabricated in the same manner as in Example 1, except that the concentration was changed to 10.0 mmol / L. The composition of the polymerization solution according to Example 3 is shown in Table 1 below.

[0102] [Example 4] In the formation of the cathode, LiClO in the polymerization solution ４ A capacitor element according to Example 4 was fabricated in the same manner as in Example 1, except that the concentration was changed to 30.0 mmol / L. The composition of the polymerization solution according to Example 4 is shown in Table 1 below.

[0103] [Example 5] In the formation of the cathode, LiClO in the polymerization solution ４ A capacitor element according to Example 5 was fabricated in the same manner as in Example 1, except that the concentration was changed to 60.0 mmol / L. The composition of the polymerization solution according to Example 5 is shown in Table 1 below.

[0104] [Comparative Example 1] In the formation of the cathode, LiClO in the polymerization solution ４ Except for changing the concentration to 0.0 mmol / L, that is, LiClO in the polymerization solution ４ A capacitor element according to Comparative Example 1 was fabricated in the same manner as in Example 1, except that it did not contain [a specific compound]. The composition of the polymerization solution according to Comparative Example 1 is shown in Table 1 below.

[0105] [Comparative Example 2] In the formation of the cathode, LiClO in the polymerization solution ４ A capacitor element according to Comparative Example 2 was fabricated in the same manner as in Example 1, except that the concentration was changed to 100.0 mmol / L. The composition of the polymerization solution according to Comparative Example 2 is shown in Table 1 below.

[0106]

[0107] Furthermore, the content of each element (chlorine (Cl), lithium (Li), sodium (Na), and sulfur (S)) in the conductive polymer layer was measured using the capacitor elements of each example (Examples 1 to 5, Comparative Example 1, and Comparative Example 2). The content of each element was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), as described in the Embodiments section above. In addition, the content of sulfur (S) derived from PEDOT and sulfur (S) derived from SDS was also measured. The content of sulfur (S) derived from PEDOT and sulfur (S) derived from SDS was measured by a combination of analysis by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and analysis by X-ray photoelectron spectroscopy (XPS), as described in the Embodiments section above. The results of measuring the content of each element (Cl, Li, Na, and S) in the conductive polymer layer for each example are shown in Table 2 below. Furthermore, Table 2 below shows the results of measurements of the sulfur content derived from PEDOT and the sulfur content derived from SDS.

[0108]

[0109] ≪Evaluation≫ ・Conductivity of the conductive polymer layer The conductivity of the conductive polymer layer was measured using capacitor elements related to each example (Examples 1 to 5, Comparative Example 1, and Comparative Example 2). Specifically, first, the conductivity of five arbitrary locations in the conductive polymer layer of the capacitor element related to each example was measured using a Lorestar-GP (MCP-T610 series 4 probe) manufactured by Nitto Seikou Analytech Co., Ltd. Next, the arithmetic mean of the conductivity values ​​at the five locations was taken, and the resulting arithmetic mean was taken as the conductivity of the conductive polymer of the capacitor element related to each example. ・ESR The ESR value (mΩ) of the capacitor element related to each example at a frequency of 100 kHz was measured using an LCR meter for 4-terminal measurement. The ESR measurement was performed in an environment of 20°C. The ESR value of the capacitor element related to each example was taken as the arithmetic mean of the ESR values ​​of 40 capacitor elements.

[0110] The results of evaluating the conductivity and ESR of the conductive polymer layer for each example of capacitor element are shown in Table 3 below. Note that the conductivity and ESR of the conductive polymer layer were evaluated using a different capacitor element than the one used to analyze the content of each element in the conductive polymer layer.

[0111]

[0112] Table 3 shows that the conductivity of the conductive polymer layer in the capacitor elements of Examples 1 to 5 is high, at 250 S / cm or more, whereas the conductivity of the conductive polymer layer in the capacitor elements of Comparative Examples 1 and 2 is low, at less than 250 S / cm. Consequently, the ESR of the capacitor elements of Examples 1 to 5 is low, at 4.6 mΩ or less, while the ESR of the capacitor elements of Comparative Examples 1 and 2 is high, exceeding 4.6 mΩ.

[0113] Furthermore, referring to Table 2, it can be seen that in the capacitor elements of Examples 1 to 5, the content of elements constituting monovalent cations in the conductive polymer layer (sum of Na content and Li content) is less than 23,000 ppm, whereas in the capacitor elements of Comparative Examples 1 and 2, the content of elements constituting monovalent cations in the conductive polymer layer (sum of Na content and Li content) is 23,000 ppm or more.

[0114] These findings demonstrate that by reducing the content of elements constituting monovalent cations in the conductive polymer layer to less than 23,000 ppm, the conductivity of the conductive polymer layer in a solid electrolytic capacitor can be sufficiently increased, and the ESR can be sufficiently reduced.

[0115] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0116] The electrolytic capacitors relating to this disclosure can be used in applications where it is required to improve the conductivity of the conductive polymer layer.

[0117] 1: Anode body, 2: Anode wire, 2a: First part, 2b: Second part, 3: Dielectric layer, 4: Conductive polymer layer, 5: Cathode layer, 5a: Carbon layer, 5b: Metal paste layer, 6: Anode part, 7: Cathode part, 8: Conductive adhesive, 10: Capacitor element, 11: Outer casing, 13: Anode lead frame, 14: Cathode lead frame, 100: Solid electrolytic capacitor, 131: Anode lead embedded part, 132: Anode lead exposed part, 141: Cathode lead embedded part, B: Bottom surface, D1: First direction, E1: One end face of the anode body, E2: One end face of the outer casing, E3: Other end face of the outer casing, U: Top surface

Claims

1. An electrolytic capacitor comprising a capacitor element including an anode body extending in a first direction, a dielectric layer covering at least a portion of the anode body, and a conductive polymer layer containing a conductive polymer and covering at least a portion of the dielectric layer, wherein the conductive polymer layer contains a monovalent cation, and the content of the elements constituting the monovalent cation in the conductive polymer layer is less than 23,000 ppm.

2. The electrolytic capacitor according to claim 1, wherein the conductive polymer layer contains sodium ions and lithium ions as the monovalent cations.

3. The electrolytic capacitor according to claim 1 or 2, wherein the sodium element content in the conductive polymer layer is less than 22,000 ppm.

4. The electrolytic capacitor according to claim 3, wherein the content of the sodium element in the conductive polymer layer is 10,000 ppm or more and 21,000 ppm or less.

5. The electrolytic capacitor according to claim 1 or 2, wherein the lithium element content in the conductive polymer layer is 20 ppm or more and 400 ppm or less.

6. The electrolytic capacitor according to claim 2, wherein the total content of sodium and lithium elements in the conductive polymer layer is 13,000 ppm or more and 21,000 ppm or less.

7. The electrolytic capacitor according to claim 1 or 2, wherein the conductive polymer layer contains a chlorine-containing anion as anion, and the content of chlorine element in the conductive polymer layer is less than 20,000 ppm.

8. The electrolytic capacitor according to claim 7, wherein the content of the chlorine element in the conductive polymer layer is 900 ppm or more and 5000 ppm or less.

9. The electrolytic capacitor according to claim 1 or 2, wherein the conductive polymer layer is a layer formed by electrolytic polymerization.

10. The electrolytic capacitor according to claim 7, wherein the conductive polymer layer contains the chlorine-containing anion as a dopant or supporting electrolyte, and the chlorine-containing anion is an anion derived from an inorganic chlorine compound.

11. The electrolytic capacitor according to claim 10, wherein the anion derived from the inorganic chlorine compound is a perchlorate ion.

12. The electrolytic capacitor according to claim 1 or 2, wherein the conductive polymer layer comprises a conjugated polymer consisting of a heterocyclic compound having a five-membered ring structure as the conductive polymer.

13. The electrolytic capacitor according to claim 12, wherein the conjugated polymer comprising the heterocyclic compound having a five-membered ring structure includes a conjugated polymer comprising a thiophene derivative.

14. The electrolytic capacitor according to claim 1 or 2, wherein the conductive polymer layer contains anions derived from an anionic surfactant as a dopant.

15. The electrolytic capacitor according to claim 14, wherein the anionic surfactant comprises a sulfonate or a sulfate ester salt.

16. The electrolytic capacitor according to claim 15, wherein the conductive polymer comprises a conjugated polymer made of a thiophene derivative, and the ratio of the sulfur content C2 derived from the dopant to the sulfur content C1 derived from the conjugated polymer made of the thiophene derivative (C2 / C1) is 0.45 or less.

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