Solid electrolytic capacitor and method for producing solid electrolytic capacitor

Abstract

A solid electrolytic capacitor according to an embodiment of the present disclosure comprises a capacitor element including a porous anode body containing tantalum, a dielectric layer formed on at least a part of the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer. The dielectric layer contains tantalum as a main component metallic element and at least one of an alkali metal and an alkaline earth metal as a secondary component metallic element. By adding ammonia water to 0.1 g of the anode body provided with the dielectric layer, a first dissolution liquid in which the dielectric layer is dissolved in ammonia water is obtained. After volatilizing a liquid from the first dissolution liquid to obtain a solid, the solid is dissolved in 20 mL of pure water to obtain a second dissolution liquid, which contains 0.23 mg / L or more of at least one of the alkali metal and the alkaline earth metal.

Description

Solid electrolytic capacitor and method for manufacturing solid electrolytic capacitor

[0001] The present invention relates to a solid electrolytic capacitor and a method for manufacturing a solid electrolytic capacitor.

[0002] A solid electrolytic capacitor includes a capacitor element including, for example, an anode body, a dielectric layer formed on at least part of a surface of the anode body, and a solid electrolyte layer covering at least part of the dielectric layer. It is known to use a porous anode body containing metal in a capacitor element. The porous body containing metal is generally configured as a sintered body obtained by sintering metal-containing powder.

[0003] Patent Document 1 discloses a method for manufacturing a capacitor element in which after a chemical conversion step of forming a dielectric layer on a surface layer portion of an anode body obtained by molding and then sintering powder containing tungsten as a main component, a semiconductor layer and a conductor layer are sequentially formed on the dielectric layer, wherein before forming the dielectric layer, there is an etching step of removing a natural oxide film formed on an outer surface of the anode body and a surface layer portion of an inner pore surface such that the thickness thereof falls within a range of 0.5 to 5.0 nm, and the chemical conversion step is performed at a temperature of -4 to 18° C. for 7 to 110 minutes after reaching a predetermined voltage. Patent Document 1 also discloses that the etching step is performed by bringing an alkaline solution into contact with the anode body, and that sodium hydroxide or potassium hydroxide is used as the alkali.

[0004] Furthermore, in addition to disclosing that the capacitor element manufactured by the above manufacturing method can suppress occurrence of cracks in the dielectric layer on the outer surface of the anode body, Patent Document 1 also discloses that impregnation of a cathode (organic semiconductor layer) in pores of the anode body is improved. Patent Document 1 also discloses that a tungsten electrolytic capacitor including the above capacitor element has improved capacitance and improved LC characteristics.

[0005] Japanese Patent No. 5798279

[0006] Incidentally, in recent years, there has been a demand for further reduction of leakage current (LC) in solid electrolytic capacitors that use a porous material containing metal as the anode. While this further reduction of leakage current is particularly desired in solid electrolytic capacitors that use a porous material containing tantalum as the metal (a porous anode), sufficient research has not yet been conducted on this. Furthermore, sufficient research has also not yet been conducted on the manufacturing methods of such solid electrolytic capacitors.

[0007] Therefore, the object of this disclosure is to provide a solid electrolytic capacitor comprising a porous anode body containing tantalum and capable of further reducing leakage current, and a method for manufacturing the solid electrolytic capacitor.

[0008] One aspect of the present invention relates to a solid electrolytic capacitor comprising a capacitor element including a porous anode body containing tantalum, a dielectric layer formed on at least a portion of the surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the dielectric layer contains tantalum as the main component metal element and at least one of an alkali metal and an alkaline earth metal as a secondary component metal element, and a first solution is obtained by adding ammonia water to 0.1 g of the anode body having the dielectric layer to dissolve the dielectric layer in the ammonia water, and after volatilizing the liquid from the first solution to obtain a solid component, the second solution obtained by dissolving the solid component in 20 mL of pure water contains at least 0.23 mg / L or more of the alkali metal and the alkaline earth metal.

[0009] Another aspect of the present invention relates to a method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing a porous anode body containing tantalum; a second step of bringing an alkaline solution containing at least one of an alkali metal and an alkaline earth metal into contact with the surface of the anode body; a third step of forming a dielectric layer on at least a portion of the surface of the anode body after the second step; and a fourth step of forming a solid electrolyte layer covering at least a portion of the dielectric layer.

[0010] According to this disclosure, it is possible to provide a solid electrolytic capacitor comprising a porous anode body containing tantalum and capable of further reducing leakage current, and a method for manufacturing the solid electrolytic capacitor.

[0011] This is a side cross-sectional view showing the configuration of a solid electrolytic capacitor according to one embodiment of the present disclosure. This is a side view showing the configuration of the cathode lead frame before it is connected to the capacitor element.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] A solid electrolytic capacitor according to an embodiment of the present disclosure comprises a capacitor element including a porous anode body containing tantalum, a dielectric layer formed on at least a portion of the surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer.

[0016] In the solid electrolytic capacitor according to the embodiment of this disclosure, the dielectric layer includes tantalum as the main component metal and at least one of an alkali metal and an alkaline earth metal as the secondary component metal.

[0017] In the solid electrolytic capacitor according to the embodiment of this disclosure, a first solution is obtained by adding ammonia water to 0.1 g of an anode body having a dielectric layer to dissolve the dielectric layer in ammonia water. After volatilizing the liquid from the first solution to obtain a solid, the solid is dissolved in 20 mL of pure water to obtain a second solution containing at least 0.23 mg / L or more of an alkali metal and an alkaline earth metal. Pure water means water with an electrical resistivity of 0.1 MΩ·cm or more and 1.5 MΩ·cm or less. Pure water includes, for example, water obtained by at least one treatment selected from the group consisting of ion exchange, distillation, and reverse osmosis membrane filtration.

[0018] In the solid electrolytic capacitor according to the embodiment of this disclosure, it is important that (i) the dielectric layer contains tantalum as the main component metal element and at least one of an alkali metal and an alkaline earth metal as a secondary component metal element, and (ii) a first solution is obtained by adding ammonia water to 0.1 g of an anode body equipped with the dielectric layer to dissolve the dielectric layer in ammonia water, the liquid component is evaporated from the first solution to obtain a solid component, and the second solution obtained by dissolving the solid component in 20 mL of pure water contains at least 0.23 mg / L of at least one of an alkali metal and an alkaline earth metal. The reasons for this will be explained below.

[0019] In a solid electrolytic capacitor equipped with a porous anode containing tantalum, a dielectric layer is formed on the surface of the porous anode containing tantalum, as described above. The porous anode containing tantalum is usually obtained by sintering tantalum particles. Therefore, in such an anode, voids are formed between the tantalum particles, and these voids connect from the outer surface of the anode to the interior, forming pores. Consequently, in such a solid electrolytic capacitor, the dielectric layer is formed not only on the outer surface of the anode but also on the inner wall surface of the pores formed from the outer surface to the interior.

[0020] In solid electrolytic capacitors equipped with a porous anode containing tantalum as described above, leakage current may increase due to defect formation in the dielectric layer. Defect formation in the dielectric layer can occur, for example, due to damage to the dielectric layer itself, or due to gaps (voids) formed between the surface of the anode (outer surface and inner wall surface of the pores) and the dielectric layer. Gaps between the surface of the anode and the dielectric layer occur due to insufficient adhesion of the dielectric layer to the surface of the anode.

[0021] In porous anodes containing tantalum, the dielectric layer is typically formed as a tantalum oxide film. Since tantalum is a hard metal, this property is thought to result in a hard tantalum oxide film. While this hardness is useful for densely covering the outer surface of the anode, it is also thought to make it prone to the formation of minute defects. For example, inside the anode, pores are formed in a complex and interwoven manner, and the hard tantalum oxide film is thought to be unable to adequately conform to the inner walls of these pores. Therefore, there is a concern that dielectric layers formed from tantalum oxide films may develop a relatively large number of minute defects on the inner walls of pores formed inside the anode.

[0022] However, the solid electrolytic capacitor according to the embodiment of this disclosure satisfies conditions (i) and (ii) as described above. That is, the dielectric layer contains tantalum as the main component metal element and contains at least one of alkali metals and alkaline earth metals in predetermined amounts or more as minor component metal elements. Both alkali metals and alkaline earth metals are soft metals. Therefore, by including at least one of alkali metals and alkaline earth metals in predetermined amounts or more in the dielectric layer, the soft properties of alkali metals and alkaline earth metals can be expressed in the dielectric layer. Consequently, it is considered that such a dielectric layer can adequately follow the inner wall surface of the intricately formed pores inside the anode body, and that the occurrence of defects can be suppressed. As a result, it is considered that the dielectric layer according to the embodiment of this disclosure can suppress the occurrence of defects more effectively than conventional dielectric layers (more specifically, dielectric layers that do not contain at least one of alkali metals and alkaline earth metals in predetermined amounts or more as minor component metal elements), which is expected to lead to a reduction in leakage current in the solid electrolytic capacitor.

[0023] In the following, a solid electrolytic capacitor according to one embodiment of the present disclosure will be described with reference to the drawings. The solid electrolytic capacitor according to one embodiment of the present disclosure only needs to have at least one capacitor element. That is, the solid electrolytic capacitor according to one embodiment of the present disclosure may have one capacitor element or may have multiple capacitor elements. In the following, an example in which the solid electrolytic capacitor has one capacitor element will be described.

[0024] [Solid Electrolytic Capacitor] As shown in Figure 1, a solid electrolytic capacitor 100 according to one embodiment of the present disclosure includes a capacitor element 10 having an anode portion 6 and a cathode portion 7, a cathode lead frame 14 electrically connected to the cathode portion 7, and an outer casing 11 covering the capacitor element 10. The solid electrolytic capacitor 100 according to one embodiment of the present disclosure further includes an anode lead frame 13 electrically connected to the anode portion 6.

[0025] <Capacitor Element> The capacitor element 10 has a bottom surface B, an upper surface U opposite to the bottom surface B, and two side surfaces connecting the bottom surface B and the upper surface U. Note that Figure 1 is a cross-sectional view, so the side surfaces are not shown.

[0026] (Anode section) The anode section 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 one embodiment of the present disclosure, as shown in Figure 1, the anode section 6 is electrically connected to the anode lead frame 13.

[0027] In a solid electrolytic capacitor 100 according to one embodiment of the present disclosure, the anode body 1 extends in a first direction D1, as shown in Figure 1. Also, as shown in Figure 1, the anode wire 2 also extends in the first direction D1, so the anode portion 6 (anode body 1 + anode wire 2) also extends in the first direction D1.

[0028] The anode body 1 is, for example, a porous sintered body obtained by sintering metal particles. The anode body 1 has, for example, a rectangular parallelepiped shape. In a solid electrolytic capacitor 100 according to one embodiment of the present disclosure, particles containing tantalum (Ta) are used as the metal particles. Tantalum is a valve metal. The particles containing tantalum may be tantalum particles or particles of an alloy containing tantalum. As particles of an alloy containing tantalum, for example, particles of an alloy containing tantalum and at least one element selected from the group consisting of silicon, vanadium, and boron can be used. Alternatively, as particles of an alloy containing tantalum, particles of an alloy containing tantalum and a typical element (such as nitrogen) can also be used. Particles of an alloy containing tantalum usually contain tantalum as the main component. Particles of an alloy containing tantalum, for example, contain 50 atomic percent or more of tantalum.

[0029] The anode wire 2 is made of a conductive material. The material used to form the anode wire 2 is not particularly limited, and valve metals such as titanium (Ti), tantalum (Ta), and niobium (Nb) can be used. Copper, aluminum, and aluminum alloys can also be used as the material used to form the anode wire 2. The material used to form the anode body and the material used to form the anode wire 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.

[0030] 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.

[0031] 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 anode body 1 is a porous sintered body obtained by sintering particles containing tantalum (Ta). Therefore, in the anode body 1, the dielectric layer 3 is formed on the outer surface of the anode body 1 and on the inner wall surface of pores formed inside the anode body 1. The pores are formed by gaps formed between tantalum-containing particles that are connected from the outer surface to the interior of the anode body 1. In a solid electrolytic capacitor 100 according to one embodiment of the present disclosure, the dielectric layer 3 is formed on at least a part of the surface 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 solution to anodize the surface of the anode body 1, and heating the anode body 1 in an oxygen-containing atmosphere.

[0032] In a solid electrolytic capacitor 100 according to one embodiment of the present disclosure, the dielectric layer 3 contains tantalum as the main component metal and at least one of an alkali metal and an alkaline earth metal as a secondary component metal element. In a solid electrolytic capacitor 100 according to one embodiment of the present disclosure, a first solution is obtained by adding ammonia water to 0.1 g of an anode body 1 equipped with the dielectric layer 3 to dissolve the dielectric layer 3 in ammonia water. After volatilizing the liquid from the first solution to obtain a solid, the second solution is obtained by dissolving this solid in 20 mL of pure water, and the second solution contains at least 0.23 mg / L or more of an alkali metal and an alkaline earth metal. This is thought to allow the dielectric layer 3 to sufficiently conform to the inner wall surface of the pores in the porous anode body 1 containing tantalum. Furthermore, since tantalum is included as the main component metal, it is thought that the outer surface of the porous anode body 1 containing tantalum can be covered relatively densely. Therefore, in a solid electrolytic capacitor 100 according to one embodiment of the present disclosure, it is thought that defect formation in the dielectric layer 3 is suppressed, and thus leakage current can be further reduced.

[0033] The content of alkali metals and alkaline earth metals in the second solution is preferably 0.25 mg / L or more, and more preferably 0.30 mg / L or more. The content of alkali metals and alkaline earth metals in the second solution may be 2.00 mg / L or less, 1.00 mg / L or less, 0.50 mg / L or less, or 0.40 mg / L or less. It is believed that by having the content of alkali metals and alkaline earth metals in the second solution within the above range, it is possible to achieve an even better balance between the conformability of the dielectric layer placed in the pores and the density of the dielectric layer placed on the outer surface. Therefore, leakage current can be further sufficiently reduced in the solid electrolytic capacitor 100.

[0034] The alkali metal and alkaline earth metal content in the second solution can be measured, for example, by following the procedure below. Procedure (1) A solid electrolytic capacitor is treated with fuming nitric acid to obtain an anode body with a dielectric layer formed on it. The fuming nitric acid dissolves the outer casing (resin casing) covering the capacitor element and the solid electrolyte layer (conductive polymer layer) contained in the capacitor element. (2) 0.1 g of the sample for analysis is cut out from the anode body with the dielectric layer formed on it. (3) 28% by mass of ammonia water is added to the sample for analysis to dissolve the dielectric layer contained in the sample for analysis and obtain the first solution. The portion of the sample corresponding to the anode remains undissolved in the ammonia water. (4) After the liquid is evaporated from the first solution to obtain the solid, 20 mL of pure water is added to this solid and sonicated for 30 minutes. (5) The concentration of at least one of the alkali metal and alkaline earth metal contained in the second solution is measured using a multi-type ICP emission spectrometer (for example, ICPE-9800 manufactured by Shimadzu Corporation).

[0035] Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Ce), and francium (Fr). Examples of alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0036] At least one of the alkali metal and alkaline earth metal may be present throughout the entire dielectric layer 3, or mainly in the region on the anode 1 side. The region on the anode 1 side means the region up to 10% of the total thickness of the dielectric layer, with respect to the outer surface of the anode 1. At least one of the alkali metal and alkaline earth metal may form a composite oxide with tantalum in the dielectric layer 3. For example, if at least one of the alkali metal and alkaline earth metal is sodium, then in the dielectric layer 3, sodium is NaTaO ３ It may exist as Na ２ Ta ４ O １１ It may exist as Na２ Ta ２ O ６ It may exist as such.

[0037] The method for incorporating at least one of the alkali metal and alkaline earth metal into the dielectric layer 3 is not particularly limited. For example, as will be described later, first, an alkaline solution containing at least one of the alkali metal and alkaline earth metal is brought into contact with at least a portion of the surface of the anode body 1 (the outer surface and the inner wall surface of the pores) to deposit at least one of the alkali metal and alkaline earth metal onto at least a portion of the surface of the anode body 1. Next, with at least a portion of the surface of the anode body 1 having at least one of the alkali metal and alkaline earth metal deposited on it, at least a portion of the surface of the anode body 1 is anodized. This makes it possible to obtain a dielectric layer 3 that contains tantalum as the main component metal element and at least one of the alkali metal and alkaline earth metal as a secondary component metal element. In the dielectric layer 3 obtained in this way, at least one of the alkali metal and alkaline earth metal is mainly present in the region on the anode body 1 side.

[0038] The dielectric layer 3 preferably contains an alkali metal as a minor metallic element, and more preferably contains sodium as the alkali metal. Since alkali metals are softer than alkaline earth metals, the conformability of the dielectric layer placed in the pores of the anode body 1 can be further improved. Furthermore, because the alkali metal is sodium, a suitable composite oxide can be formed in the dielectric layer 3.

[0039] (Cathode section) The cathode section 7 has a solid electrolyte layer 4 formed on the dielectric layer 3 and a cathode layer 5 covering the solid electrolyte layer 4. In the solid electrolytic capacitor 100 according to one embodiment of the present disclosure, the solid electrolyte layer 4 is formed to cover at least a part of the dielectric layer 3. In the example of Figure 1, the solid electrolyte layer 4 is formed to cover the entire surface of the dielectric layer 3. For example, a manganese compound and a conductive polymer can be used for the solid electrolyte layer 4.

[0040] Examples of the conductive polymer include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyparaphenylene vinylene, polyacene, polythiophene vinylene, polyfluorene, polyvinylcarbazole, polyvinylphenol, polypyridine, and derivatives of these polymers. These polymers may be used singly or in combination of two or more. The conductive polymer may be a copolymer of two or more monomers. In consideration of excellent conductivity, polythiophene, polyaniline, or polypyrrole is preferably used as the conductive polymer. In consideration of excellent water repellency in addition to conductivity, polypyrrole is preferably used as the conductive polymer.

[0041] The solid electrolyte layer 4 containing the conductive polymer may be formed, for example, by polymerizing raw material monomers on the dielectric layer 3, or may be formed by applying a liquid containing the conductive polymer onto the dielectric layer 3. The solid electrolyte layer 4 may be composed of one layer, or may be composed of two or more layers. When the solid electrolyte layer 4 is composed of two or more layers, the composition of the conductive polymer contained in each layer may be different, and the formation method (for example, polymerization method) of each layer may be different.

[0042] In the present specification, polypyrrole, polythiophene, polyfuran, polyaniline, and the like mean polymers having polypyrrole, polythiophene, polyfuran, polyaniline, and the like as basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, and the like also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) (PEDOT) and the like. Further, when synthesizing poly(3,4-ethylenedioxythiophene), 3,4-ethylenedioxythiophene (EDOT) is used as a monomer.

[0043] To the polymerization liquid for forming a conductive polymer, or to the solution or dispersion liquid of a conductive polymer, various known dopants may be added in order to improve the conductivity of the conductive polymer. The dopant is not particularly limited, and examples 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, hydroxybenzenesulfonic acid, butylnaphthalenesulfonic acid, benzenesulfonic acid, polystyrenesulfonic acid (PSS), polyvinylsulfonic acid, methanesulfonic acid, and derivatives thereof, etc. Examples of the derivatives include metal salts such as lithium salts, potassium salts and sodium salts; ammonium salts such as methylammonium salts, dimethylammonium salts and trimethylammonium salts; piperidinium salts, pyrrolidinium salts, pyrrolinium salts, and the like.

[0044] When the conductive polymer is dispersed in a dispersion medium in the form of particles, the average particle diameter D50 of the particles is, for example, 0.01 µm or more and 0.5 µm or less. When the average particle diameter D50 falls within the above range, the conductive polymer particles easily penetrate into the inside of the anode body 1.

[0045] The cathode layer 5 includes, for example, a carbon layer 5a formed so as to cover the solid electrolyte layer 4, and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a contains, for example, a conductive carbon material such as graphite and a resin. The metal paste layer 5b contains, 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 having a current collecting function is acceptable.

[0046] <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.

[0047] 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.

[0048] <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.

[0049] 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.

[0050] <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.

[0051] 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).

[0052] 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.

[0053] [Method for Manufacturing a Solid Electrolytic Capacitor] A method for manufacturing a solid electrolytic capacitor according to one embodiment of the present disclosure comprises a first step (S1), a second step (S2), a third step (S3), and a fourth step (S4). The first step (S1) to the fourth step (S4) will be described below.

[0054] (1) First Step (S1) In the first step (S1), a porous anode body containing tantalum is prepared. For example, particles containing tantalum (e.g., tantalum particles) and an anode wire are placed in a mold and pressure-molded so that a part of the anode wire (first part) is embedded in the tantalum particles, and then the tantalum particles are sintered in a vacuum. This creates an anode portion in which 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. In this anode portion, the porous sintered body corresponds to the anode body. Therefore, by creating the anode portion as described above, a porous anode body containing tantalum can be prepared. The pressure for pressure molding is not particularly limited, and is, for example, about 10 N to 100 N. A binder such as polyacrylic carbonate may be mixed with the tantalum particles as needed. Another example of the first step is to purchase a commercially available anode section from which a portion of the anode wire is drawn out from one end face of a tantalum sintered body, and prepare a porous anode body containing tantalum.

[0055] (2) Second step (S2) In the second step (S2), an alkaline solution containing at least one of an alkali metal and an alkaline earth metal is brought into contact with the surface of the anode (a porous anode containing tantalum). By bringing the alkaline solution into contact with the surface of the anode, the natural oxide film formed on the surface of the anode can be removed, and the irregularities originating from the tantalum particle gaps can be reduced. The surface of the anode refers to both the outer surface of the anode and the inner wall surface of the pores formed inside the anode. By performing the second step (S2), the surface of the anode, in particular the inner wall surface of the pores formed inside the anode can be sufficiently exposed. In addition, in the second step (S2), washing with water may be performed after washing with the alkaline solution.

[0056] In the second step (S2), the pH of the alkaline solution is preferably 9 or higher. The pH of the alkaline solution may be 10 or higher, or 11 or higher. By having the pH of the alkaline solution within the above range, the native oxide film formed on the surface of the anode can be removed more effectively.

[0057] In the second step (S2), the alkaline solution preferably contains at least one of the alkali metal and the alkaline earth metal in a concentration of 1.0 g / L or more. The alkaline solution may contain at least one of the alkali metal and the alkaline earth metal in a concentration of 1.5 g / L or more. The alkaline solution may contain at least one of the alkali metal and the alkaline earth metal in a concentration of 5.0 g / L or less, 3.0 g / L or less, or 2.0 g / L or less. By having the concentration of at least one of the alkali metal and the alkaline earth metal within the above range, the native oxide film formed on the surface of the anode can be removed more thoroughly, and at least one of the alkali metal and the alkaline earth metal can be deposited on the surface of the anode in a suitable amount.

[0058] The alkaline solution preferably contains an alkali metal, and more preferably contains sodium as the alkali metal. Since alkali metals are softer than alkaline earth metals, a dielectric layer that can conform even more sufficiently to the inner wall surface of the pores can be formed in the third step described later. Furthermore, the use of sodium as the alkali metal allows for the formation of a suitable composite oxide in the dielectric layer.

[0059] The alkaline solution preferably contains a salt comprising at least one of an alkali metal salt and an alkaline earth metal salt. Both the alkali metal salt and the alkaline earth metal salt may be hydroxides, phosphates, carbonates, or hydrogen phosphates. In this case, in the alkaline solution, the alkali metal is derived from the alkali metal salt, and the alkaline earth metal is derived from the alkaline earth metal salt. Furthermore, if the alkaline solution contains sodium, the sodium is preferably derived from at least one selected from the group consisting of sodium hydroxide, trisodium phosphate, sodium carbonate, and disodium hydrogen phosphate. By using such salts, it becomes easier to adjust the pH of the alkaline solution to a level suitable for removing the native oxide film from the surface of the anode.

[0060] Step 2 (S2) is preferably carried out using an alkaline solution at 30°C or higher, more preferably using an alkaline solution at 40°C or higher, more preferably using an alkaline solution at 50°C or higher, and preferably using an alkaline solution at 60°C or higher. The temperature of the alkaline solution should be within a range in which the liquid component does not easily volatilize. Therefore, the temperature of the alkaline solution may be less than 100°C, 90°C or lower, 80°C or lower, or 70°C or lower. By setting the temperature of the alkaline solution within the above range, the native oxide film can be efficiently removed from the surface of the anode. Note that the temperature of the alkaline solution refers to the liquid temperature of the alkaline solution.

[0061] (3) Third step (S3) In the third step (S3), after the second step (S2), a dielectric layer is formed on the surface of at least a portion of the 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 portion of the porous sintered body (anode) is connected to the 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.

[0062] As described above, in the second step (S2), a dielectric layer is formed by attaching at least one of an alkali metal and an alkaline earth metal to the surface of the anode (outer surface and inner wall surface of the pores). As a result, the formed dielectric layer contains tantalum as the main component metal element and at least one of an alkali metal and an alkaline earth metal as a secondary component metal element. Since such a dielectric layer contains tantalum as the main component metal element, it can cover the outer surface of the anode relatively densely. Furthermore, since such a dielectric layer contains at least one of an alkali metal and an alkaline earth metal as a secondary component metal element, it can adequately conform to the inner wall surface of the pores formed inside the dielectric layer.

[0063] (4) Fourth step (S4) In the fourth step (S4), a solid electrolyte layer is formed that covers at least a portion of the dielectric layer. In one embodiment of the present disclosure, an example of forming a solid electrolyte layer containing a conductive polymer will be described. The solid electrolyte layer containing a conductive polymer can be formed, for example, by impregnating an anode body on which the dielectric layer is formed with at least one of a monomer and an oligomer, and then polymerizing at least one of the monomer and the oligomer by chemical polymerization or electrolytic polymerization, or by impregnating an anode body on which the dielectric layer is formed with a solution or dispersion of a conductive polymer, and then drying it. The solid electrolyte layer is formed on at least a portion of the dielectric layer.

[0064] Next, a carbon layer is formed by applying carbon paste onto the solid electrolyte layer and drying it, and then a metal paste layer is formed by applying metal paste onto the carbon layer and drying it. This forms a cathode layer on the solid electrolyte layer, which is composed 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 collection function is acceptable. Thus, a capacitor element for a solid electrolytic capacitor according to one embodiment of the present disclosure is manufactured.

[0065] A method for manufacturing a solid electrolytic capacitor according to one embodiment of the present disclosure may further include the following fifth step (S5) to seventh step (S7) in addition to the first step (S1) to fourth step (S4) as described above.

[0066] (5) Fifth step (S5) In the fifth step (S5), the anode lead frame and the cathode lead frame are prepared. For the anode lead frame, for example, a single flat conductor (conductor plate) is prepared. For the cathode lead frame, for example, a single flat conductor (conductor plate) is bent into a stepped shape and prepared (see Figure 2). 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 2. 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. In Figure 2, the boundary between the cathode lead embedding portion 141 and the cathode lead exposed portion 142 is shown by a dashed line.

[0067] (6) Sixth step (S6) In the sixth step (S6), first, a conductive adhesive is applied to a predetermined location on the lower surface of the capacitor element, and then a part 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.

[0068] 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.

[0069] (7) Step 7 (S7) In Step 7 (S7), 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 anode lead frame and the cathode lead frame is exposed from the mold. For the cathode lead frame 14, the cathode lead exposed portion 142 (see Figure 2) is exposed from the mold. In the case of 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 adjusted as appropriate, taking into consideration the thermosetting temperature of the thermosetting resin used.

[0070] As described above, by carrying out up to step 7 (S7), 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.

[0071] 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.

[0072] As described above, by carrying out the first step (S1) to the seventh step (S7), a solid electrolytic capacitor according to one embodiment of the present disclosure (for example, a solid electrolytic capacitor as shown in Figure 1) can be manufactured.

[0073] 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.

[0074] (Note) The following technologies are disclosed by the above description. (Technology 1) A capacitor element comprising: a porous anode body containing tantalum; a dielectric layer formed on at least a part of the surface of the anode body; and a solid electrolyte layer covering at least a part of the dielectric layer, wherein the dielectric layer contains tantalum as a main component metal element and at least one of an alkali metal and an alkaline earth metal as a secondary component metal element, and a first solution is obtained by adding ammonia water to 0.1 g of the anode body having the dielectric layer to dissolve the dielectric layer in the ammonia water, and after volatilizing the liquid from the first solution to obtain a solid, the second solution obtained by dissolving the solid in 20 mL of pure water contains at least 0.23 mg / L or more of the alkali metal and the alkaline earth metal. (Technology 2) The solid electrolytic capacitor according to Technology 1, wherein the dielectric layer contains the alkali metal as the secondary component metal. (Technology 3) The solid electrolytic capacitor according to Technology 2, wherein the alkali metal contains sodium. (Technical 4) A method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing a porous anode body containing tantalum; a second step of bringing an alkaline solution containing at least one of an alkali metal and an alkaline earth metal into contact with the surface of the anode body; a third step of forming a dielectric layer on at least a portion of the surface of the anode body after the second step; and a fourth step of forming a solid electrolyte layer covering at least a portion of the dielectric layer. (Technical 5) The method for manufacturing a solid electrolytic capacitor according to Technical 4, wherein the pH of the alkaline solution is 9 or higher. (Technical 6) The method for manufacturing a solid electrolytic capacitor according to Technical 4 or 5, wherein the alkaline solution contains at least one of the alkali metal and the alkaline earth metal in an amount of 0.1 g / L or more. (Technical 7) The method for manufacturing a solid electrolytic capacitor according to any one of Technical 4 to 6, wherein the second step is carried out using the alkaline solution at a temperature of 30°C or higher. (Technical 8) The method for manufacturing a solid electrolytic capacitor according to any one of Technical 4 to 7, wherein the alkaline solution contains an alkali metal.(Technical 9) The method for manufacturing a solid electrolytic capacitor according to Technical 8, wherein the alkaline solution contains sodium as the alkali metal. (Technical 10) The method for manufacturing a solid electrolytic capacitor according to Technical 9, wherein the sodium is derived from at least one selected from the group consisting of sodium hydroxide, trisodium phosphate, sodium carbonate, and disodium phosphate.

[0075] 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.

[0076] [Example 1] <Capacitor element> (Anode part) Tantalum (Ta) particles and an anode wire were placed in a mold and pressure-molded so that the first part was embedded in valve-acting metal particles, and then the valve-acting 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. Camphor was mixed with the tantalum (Ta) particles as a binder. Furthermore, in the anode part produced as described above, the porous sintered body corresponds to the anode body.

[0077] The anode body of the anode section prepared as described above was immersed in a sodium hydroxide aqueous solution at a temperature (liquid temperature) of 65°C for 45 minutes to clean the surface of the anode body (outer surface and inner walls of the pores). The sodium hydroxide concentration in the sodium hydroxide aqueous solution was 0.069 mol / L (equivalent to 1.6 g / L of sodium). The pH of the sodium hydroxide aqueous solution was 12.8. After washing with the sodium hydroxide aqueous solution, the anode body of the anode section was immersed in pure water for 15 minutes to perform water washing.

[0078] (Dielectric layer) A porous sintered body (anode) was immersed in a chemical conversion tank filled with an aqueous phosphoric acid solution (phosphoric acid concentration of 0.02% by mass), and a second portion of the porous sintered body (anode) was connected to the anode provided in the chemical conversion tank to perform anodic oxidation, thereby forming a dielectric layer on the surface of the porous sintered body (anode) consisting of an oxide film of valve-acting metal (an oxide film containing Ta and Na). The anodic oxidation was carried out under the condition of applying a DC voltage of 80 V for 40 hours.

[0079] (Cathode) First, a reaction solution was prepared by mixing ethanol (liquid medium), iron(III) p-toluenesulfonate (oxidizing agent), and EDOT (3,4-ethylenedioxythiophene) monomer. A porous sintered body (anode) with a dielectric layer formed on it was immersed in the reaction solution for about 3 to 10 seconds. Next, after removing the anode from the reaction solution, the EDOT monomer was polymerized by heating at 210°C for 3 minutes in the air. In this way, the polymerization reaction proceeded on the dielectric layer to form a first conductive polymer layer containing poly(3,4-ethylenedioxythiophene) (PEDOT).

[0080] Next, the anode body, on which the first conductive polymer layer was formed, was immersed for about 3 to 10 seconds in an aqueous dispersion containing the second conductive polymer at a concentration of 1% to 4% by mass. Then, after removing the anode body from the aqueous dispersion, it was heated in air at a temperature of 60°C to 200°C for 20 minutes to form the second conductive polymer layer on the first conductive polymer layer. This resulted in obtaining a solid electrolyte layer in which the second conductive polymer layer was arranged on the first conductive polymer layer. The second conductive polymer used was poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS).

[0081] A dispersion of graphite particles in water was applied to a solid electrolyte layer, and then dried to form a carbon layer on the solid electrolyte 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 solid electrolyte 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.

[0082] [Comparative Example 1] A capacitor element according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the anode body of the anode portion was washed with pure water instead of washing with an aqueous sodium hydroxide solution.

[0083] [Comparative Example 2] A capacitor element according to Comparative Example 2 was obtained in the same manner as in Example 1, except that neither cleaning with an aqueous sodium hydroxide solution nor water cleaning with pure water was performed on the anode body of the anode portion.

[0084] ≪Evaluation≫ ・Sodium content The sodium content of the dielectric layer of the capacitor elements in each example (Example 1, and Comparative Examples 1 and 2) was investigated. The sodium content was determined by adding ammonia water to 0.1 g of an anode body equipped with a dielectric layer to obtain a first solution in which the dielectric layer was dissolved in ammonia water. After volatilizing the liquid from the first solution to obtain a solid, the sodium content of the second solution obtained by dissolving this solid in 20 mL of pure water was measured. The sodium content in the second solution was measured according to the procedure described in the above Embodiment section. ・Leakage current A 1 kΩ resistor was connected in series with the solid electrolytic capacitors in each example, and the leakage current (μA) was measured after applying a rated voltage of 10 V from a DC power supply for 40 seconds. For each example of solid electrolytic capacitor, the leakage current was calculated as the arithmetic mean of 20 solid electrolytic capacitors.

[0085] The results of evaluating the sodium content and leakage current of the solid electrolytic capacitors in each example are shown in Table 1 below.

[0086]

[0087] Table 1 shows that in Example 1, the sodium content in the second solution was 0.39 mg / L, and the leakage current was a low value of 0.92 μA. In contrast, in Comparative Example 1, the sodium content in the second solution was 0.22 mg / L, and the leakage current was a high value of 1.49 μA. In Comparative Example 2, the sodium content in the second solution was 0.22 mg / L, and the leakage current was an even higher value of 6.42 μA. From this, it can be seen that the leakage current of the solid electrolytic capacitor can be further reduced by cleaning the surface of the anode with sodium hydroxide and then incorporating a predetermined amount or more of sodium into the dielectric layer. It is presumed that in Comparative Examples 1 and 2, the sodium contained in trace amounts in the tantalum particles was incorporated into the dielectric layer, and this was detected.

[0088] 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.

[0089] The solid electrolytic capacitor and the method for manufacturing the solid electrolytic capacitor described herein can be used in applications where further reduction of leakage current is required.

[0090] 1: Anode body, 2: Anode wire, 2a: First part, 2b: Second part, 3: Dielectric layer, 4: Solid electrolyte 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. A capacitor element comprising: a porous anode body containing tantalum; a dielectric layer formed on at least a portion of the surface of the anode body; and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the dielectric layer contains tantalum as the main component metal element and at least one of an alkali metal and an alkaline earth metal as a secondary component metal element, and a first solution is obtained by adding ammonia water to 0.1 g of the anode body having the dielectric layer to dissolve the dielectric layer in the ammonia water, the liquid component is evaporated from the first solution to obtain a solid component, and the second solution obtained by dissolving the solid component in 20 mL of pure water contains at least 0.23 mg / L or more of the alkali metal and the alkaline earth metal.

2. The solid electrolytic capacitor according to claim 1, wherein the dielectric layer contains the alkali metal as the minor component metal element.

3. The solid electrolytic capacitor according to claim 2, wherein the alkali metal comprises sodium.

4. A method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing a porous anode body containing tantalum; a second step of bringing an alkaline solution containing at least one of an alkali metal and an alkaline earth metal into contact with the surface of the anode body; a third step of forming a dielectric layer on at least a portion of the surface of the anode body after the second step; and a fourth step of forming a solid electrolyte layer covering at least a portion of the dielectric layer.

5. The method for manufacturing a solid electrolytic capacitor according to claim 4, wherein the pH of the alkaline solution is 9 or higher.

6. The method for manufacturing a solid electrolytic capacitor according to claim 4 or 5, wherein the alkaline solution contains at least one of the alkali metal and the alkaline earth metal in a concentration of 0.1 g / L or more.

7. The method for manufacturing a solid electrolytic capacitor according to claim 4 or 5, wherein the second step is carried out using the alkaline solution at a temperature of 30°C or higher.

8. The method for manufacturing a solid electrolytic capacitor according to claim 4, wherein the alkaline solution contains an alkali metal.

9. The method for manufacturing a solid electrolytic capacitor according to claim 8, wherein the alkaline solution contains sodium as the alkali metal.

10. The method for manufacturing a solid electrolytic capacitor according to claim 9, wherein the sodium is derived from at least one selected from the group consisting of sodium hydroxide, trisodium phosphate, sodium carbonate, and disodium hydrogen phosphate.

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