electrolytic capacitor

Abstract

This electrolytic capacitor comprises: an anode body that has a porous body containing a valve metal and a dielectric layer covering the porous body; and a solid electrolyte layer that fills the holes of the porous body and covers the dielectric layer. The fill ratio R of the solid electrolyte layer in the porous body decreases in a direction from the outer surface of the porous body toward the center thereof. The shortest distance D from the outer surface of the porous body to the center thereof and the distance X50 from the outer surface of the porous body when the fill ratio R of the solid electrolyte layer is 50% satisfy a specific relationship. In other words, if the CV value of the porous body is less than 100,000 μF·V / g, the relationship 0.1D≤X50<0.7D is satisfied. If the CV value of the porous body is at least 100,000 μF·V / g but less than 150,000 μF·V / g, the relationship 0.05D≤X50<0.3D is satisfied. If the CV value of the porous body is at least 150,000 μF·V / g, the relationship 0.03D≤X50<0.2D is satisfied.

Description

[Technical Field]

[0001] The present disclosure relates to electrolytic capacitors. [Background technology]

[0002] In recent years, progress has been made in the development of electrolytic capacitors with low equivalent series resistance (ESR) and excellent frequency characteristics. Electrolytic capacitors include a porous body containing a valve metal, a dielectric layer covering the porous body, and a solid electrolyte layer that fills the pores of the porous body and covers the dielectric layer.

[0003] Patent Document 1 proposes a solid electrolytic capacitor in which the thickness of the conductive polymer compound layer at the center of the capacitor element is at least 0.02 μm or more and 0.14 μm or less. Patent Document 1 also proposes that in the solid electrolytic capacitor, the difference in thickness between the conductive polymer compound layer at the center of the capacitor element and the conductive polymer compound layer near the outer surface of the capacitor element be within 0.08 μm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-87177 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a demand for a reduction in the ESR of electrolytic capacitors. Although the electrolytic capacitor described in Patent Document 1 suppresses an increase in ESR in a high-temperature environment, the reduction in ESR of electrolytic capacitors is still insufficient. [Means for solving the problem]

[0006] One aspect of the present disclosure relates to an electrolytic capacitor including: an anode body having a porous body containing a valve action metal and a dielectric layer covering the porous body; and a solid electrolyte layer filled in the pores of the porous body and covering the dielectric layer, wherein the CV value of the porous body is less than 100,000 μF V / g, a packing fraction R of the solid electrolyte layer in the porous body decreases from the outer surface to the center of the porous body, and a shortest distance D from the outer surface to the center of the porous body and a distance X from the outer surface of the porous body at which the packing fraction R of the solid electrolyte layer is 50% satisfy the relationship 0.1D≦X<0.7D.

[0007] Another aspect of the present disclosure relates to an electrolytic capacitor including an anode body having a porous body containing a valve action metal and a dielectric layer covering the porous body, and a solid electrolyte layer filled in the pores of the porous body and covering the dielectric layer, wherein the CV value of the porous body is equal to or greater than 100,000 μF V / g and less than 150,000 μF V / g, a packing fraction R of the solid electrolyte layer in the porous body decreases from the outer surface to the center of the porous body, and a shortest distance D from the outer surface to the center of the porous body and a distance X from the outer surface of the porous body at which the packing fraction R of the solid electrolyte layer is 50% satisfy the relationship 0.05D≦X<0.3D.

[0008] Yet another aspect of the present disclosure relates to an electrolytic capacitor including: an anode body having a porous body containing a valve action metal and a dielectric layer covering the porous body; and a solid electrolyte layer filled in the pores of the porous body and covering the dielectric layer, wherein the CV value of the porous body is 150,000 μF V / g or more, a filling rate R of the solid electrolyte layer in the porous body decreases from the outer surface to the center of the porous body, and a shortest distance D from the outer surface to the center of the porous body and a distance X from the outer surface of the porous body at which the filling rate of the solid electrolyte layer is 50% satisfy the relationship 0.03D≦X<0.2D. [Effects of the Invention]

[0009] According to the present disclosure, an electrolytic capacitor with low ESR can be provided.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an electrolytic capacitor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an anode body having a solid electrolyte layer formed on the surface thereof. [Figure 3] FIG. 1 is a cross-sectional view schematically showing an example of a porous body. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be interpreted as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more of the materials may be used in combination.

[0013] An electrolytic capacitor includes an anode body having a porous body containing a valve metal and a dielectric layer covering the porous body, and a solid electrolyte layer filling the pores of the porous body and covering the dielectric layer. Hereinafter, the anode body and solid electrolyte layer (or the anode body, solid electrolyte layer, and cathode layer described below) are collectively referred to as the "capacitor element." The packing ratio R of the solid electrolyte layer in the porous body typically decreases from the outer surface toward the center of the porous body. That is, the packing ratio R decreases as the distance X from the outer surface of the porous body increases.

[0014] The present inventors investigated the relationship between the packing fraction R in the depth direction of a porous body and the ESR, and obtained the following findings.

[0015] The degree to which the filling rate R on the surface side of the porous body affects the ESR varies depending on the CV value of the porous body. The larger the CV value, the smaller the effect of the filling rate R on the ESR deep inside the porous body, and the larger the effect of the filling rate R on the ESR at the surface of the porous body. Also, the higher the measurement frequency, the smaller the effect of the filling rate R on the ESR deep inside the porous body, and the larger the effect of the filling rate R on the ESR at the surface.

[0016] Furthermore, when the polymerization reaction rate is slowed down to slowly form the solid electrolyte layer, particularly when electrolytic polymerization is performed, which is suitable for precise control of the polymerization rate, the filling factor R can be increased from the surface to the depth of the porous body, but the polymerization time becomes longer. When the polymerization time is longer, the polymerization solution deteriorates due to the formation of oligomers, etc., and the conductivity of the formed solid electrolyte decreases, increasing the ESR.

[0017] The inventors of the present invention have conducted extensive research based on the findings obtained. As a result, it was found that the shortest distance D from the outer surface to the center of the porous body and the distance X 50 It has been found that when the following relationship (i), (ii), or (iii) is satisfied, the solid electrolyte layer is efficiently filled into the pores of the porous body, and the ESR can be reduced in both the low frequency region and the high frequency region. 50is the distance X from the outer surface of the porous body when the packing rate R of the solid electrolyte layer is 50%.

[0018] (i) If the CV value of the porous body is less than 100,000 μF·V / g, 0.1D≦X 50 <0.7D (ii) If the CV value of the porous body is 100,000 μF·V / g or more and less than 150,000 μF·V / g, 0.05D≦X 50 <0.3D (iii) When the CV value of the porous body is 150,000 μF·V / g or more, 0.03D≦X 50 <0.2D

[0019] Hereinafter, the distance X from the outer surface of the porous body is X 50 The region where the distance X from the outer surface of the porous body is less than or equal to X (the region where the filling rate R is 50% or more) is also referred to as the "first region." 50 (areas where the filling rate R is less than 50%) are also referred to as "second regions."

[0020] When the CV value is high, the effect of the filling rate (R) deep in the porous body on the ESR is small, and even if the first region is small, it tends to be easier to suppress the increase in ESR. By appropriately forming the first region according to the CV value, the formation time of the solid electrolyte layer containing the conductive polymer is shortened, and the decrease in conductivity of the solid electrolyte layer due to the increase in the formation time is suppressed. Therefore, electrolytic capacitors with low ESR and high capacitance can be realized at low cost.

[0021] When the measurement frequency is high (e.g., 500 kHz), the effect of the filling rate R deep in the porous body on the ESR is smaller than when the measurement frequency is low (e.g., 100 kHz), and the ESR is less likely to increase even when the first region is small. Therefore, by shortening the formation time of the solid electrolyte layer, it is easier to suppress the increase in ESR and the high cost that would otherwise occur due to long formation times.

[0022] (i) X 50When X is 0.1D or more, the first region is formed appropriately, a conductive path is formed efficiently by the solid electrolyte layer, and the ESR is significantly reduced. 50 is 0.05D or more, and (iii) X 50 Similarly, when the dielectric constant is 0.03D or more, the ESR is significantly reduced.

[0023] (i) X 50 When X is less than 0.7D, the polymerization time for forming the solid electrolyte layer can be shortened, and deterioration of the polymerization solution due to an increase in the polymerization time is suppressed. This suppresses a decrease in the electrical conductivity of the solid electrolyte due to deterioration of the polymerization solution and an increase in ESR resulting therefrom. 50 is less than 0.3D, and (iii) X 50 Similarly, when is less than 0.2D, the increase in ESR is suppressed.

[0024] In the case of (i) above, the CV value of the porous body may be 70,000 μF·V / g or more and less than 100,000 μF·V / g. In this case, the packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.1D may be 50% or more and 80% or less. In this case, the packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.7D may be more than 16% and 48% or less.

[0025] In the case of (ii) above, the packing ratio R of the solid electrolyte layer may be 50% or more and 83% or less when the distance X from the outer surface of the porous body is 0.05D. In this case, the packing ratio R of the solid electrolyte layer may be more than 13% and 44% or less when the distance X from the outer surface of the porous body is 0.3D.

[0026] In the case of (iii) above, the packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.03D may be 56% or more and 83% or less. In this case, the packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.2D may be 14% or more and 41% or less. In the case of (iii) above, the CV value may be, for example, 150,000 μF·V / g or more and 350,000 μF·V / g or less, or 150,000 μF·V / g or more and 200,000 μF·V / g or less.

[0027] From the viewpoint of facilitating a reduction in the time required for forming the solid electrolyte layer and a reduction in ESR, if the CV value of the porous body is less than 100,000 μF·V / g, the distance X 50 may be 0.1D or more and 0.69D or less, 0.1D or more and less than 0.5D, or 0.1D or more and less than 0.4D. From the same viewpoint, when the CV value of the porous body is 100,000 μF V / g or more and less than 150,000 μF V / g, the distance X 50 From the same viewpoint, when the CV value of the porous body is 150,000 μF·V / g or more, the distance X 50 may be 0.03D or more and 0.19D or less, or may be 0.03D or more and less than 0.1D.

[0028] The filling rate R (%) of the solid electrolyte layer is determined by the area (for example, an area of ​​5 μm ) of the cross section of the anode body (a cross section including the length direction of the shortest distance D) observed by an electron microscope. 2 ~30μm 2In a region (region (a)), the ratio of the area of ​​the solid electrolyte layer to the area of ​​the voids (pores in the anode body) in that region. The area of ​​the voids in that region is the value obtained by subtracting the area of ​​the anode body (the total area of ​​the porous body and the dielectric layer) in that region from the area of ​​the entire region. A scanning electron microscope (SEM) or a transmission electron microscope (TEM) can be used as the electron microscope. The filling ratio R of the solid electrolyte layer at a distance X from the outer surface of the porous body means the filling ratio R in a region where the depth of the distance X is located near the center.

[0029] The packing ratio R (%) of the solid electrolyte layer can be determined by the following method. The electrolytic capacitor is disassembled, and the capacitor element is taken out and processed with a cross-section polisher (CP) to obtain a sample cross section (cross section of the anode body). The sample cross section is observed by SEM or TEM, and an image (for example, magnification: 20,000 to 40,000 times) showing one region of the cross section (hereinafter referred to as the measurement region) is obtained. Using this image, the area S0 (for example, 5 μm 2 ~30μm 2 ), the area S1 of the anode body (total of the porous body and dielectric layer) in the measurement area, and the area S2 of the solid electrolyte layer in the measurement area are calculated.

[0030] Using the S0, S1, and S2 calculated above, the filling rate (%) is calculated using the following formula: The value obtained by subtracting S1 from S0 is the area of ​​voids in the measurement region.

[0031] Filling rate R={S2 / (S0-S1)}×100

[0032] distance 50 can be determined by the following method. The filling factor R is determined at measurement points where the distance X from the outer surface of the porous body is 0.01D, 0.03D, 0.05D, 0.1D, 0.2D, 0.3D, 0.4D, 0.5D, 0.7D, and 0.9D. The filling factor R at a distance X of 0.01D is determined by arbitrarily selecting several points (e.g., 3 to 5 points) in a measurement region at distance X = 0.01D, measuring the filling factor R at each point, and calculating the average value. Note that in the measurement region at distance X = 0.01D, a depth of distance X = 0.01D is included near the center of the measurement region. The filling factor R is determined in the same manner for distances other than 0.01D. The measurement regions at X = 0.01D, 0.03D, 0.05D, 0.1D, 0.2D, 0.3D, 0.4D, 0.5D, 0.7D, and 0.9D are set so that they do not overlap with each other.

[0033] The filling rate R is calculated for each measurement point of the distance X, and it is confirmed that the filling rate R decreases as the distance X increases. The maximum value M1 of the measurement points of the distance X where the filling rate R is 50% or more and the minimum value M2 of the measurement points of the distance X where the filling rate R is less than 50% are calculated. This determines the distance X (X 50 ) is greater than or equal to M1 and less than M2.

[0034] The electrical conductivity of the solid electrolyte layer may be, for example, 50 S / cm or more and 300 S / cm or less, or 60 S / cm or more and 200 S / cm or less.

[0035] The conductivity of the solid electrolyte layer can be determined by the following method. The electrolytic capacitor is disassembled, the capacitor element is removed, and the components of the solid electrolyte layer are analyzed. If the solid electrolyte layer is formed using a treatment liquid, the components of the treatment liquid may also be analyzed. Examples of analytical methods that can be used include TEM (transmission electron microscope)-EELS (electron energy loss spectroscopy), NMR (nuclear magnetic resonance spectroscopy), and Raman spectroscopy.

[0036] Based on the analysis results, a sample film (e.g., 20 μm to 40 μm thick) containing the same components as the solid electrolyte layer is formed, and the conductivity of the sample film is determined as the conductivity of the solid electrolyte layer. The Loresta-GX and PSP probe manufactured by Nitto Seiko Analytech Co., Ltd. can be used as the conductivity measurement device.

[0037] (porous body) The porous body contains a valve metal, such as aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), or hafnium (Hf).

[0038] The porous body may be, for example, a sintered compact of raw material particles (raw material powder) containing a valve metal. The particles may be particles of a valve metal, particles of an alloy containing a valve metal, or particles of a compound containing a valve metal. Only one type of particles may be used, or two or more types may be mixed and used.

[0039] The porous body can be obtained, for example, by press-molding raw material particles into a predetermined shape to obtain a molded body, and then sintering the molded body. For example, an anode wire may be placed in a predetermined position in a mold, raw material particles may be introduced into the mold, and the molded body may be press-molded to obtain a molded body. The molded body may be sintered to obtain a porous body in which a portion of the anode wire is embedded. The porous body is usually a rectangular parallelepiped.

[0040] The average particle size of the raw material particles is preferably, for example, 0.05 μm or more and 0.5 μm or less. The average particle size here refers to the median diameter (D50) in the volume particle size distribution determined by a laser diffraction particle size distribution analyzer.

[0041] The CV value of a porous body is expressed as the product of the formation voltage and the measured capacitance (capacity per unit mass excluding the anode wire) measured when the porous body is subjected to formation in an aqueous phosphoric acid solution (concentration: 0.02% by mass) at a formation voltage of 10 V and a temperature of 60°C for 2 hours and then the capacitance is measured at a frequency of 120 Hz.

[0042] The raw material particles used to form the porous body themselves have many fine irregularities, and if the surface area of ​​the raw material particles themselves is large, a porous body with a small pore size and a large surface area is likely to be obtained, and such a porous body is likely to have a large CV value.

[0043] The most frequent pore size of a porous body having a CV value of 70,000 μF·V / g or more but less than 100,000 μF·V / g is, for example, 0.24 μm or more but 0.37 μm or less. The most frequent pore size of a porous body having a CV value of 100,000 μF·V / g or more but less than 150,000 μF·V / g is, for example, 0.17 μm or more but 0.26 μm or less. The most frequent pore size of a porous body having a CV value of 150,000 μF·V / g or more is, for example, 0.10 μm or more but 0.21 μm or less. The most frequent pore size here refers to the most frequent pore size in a volumetric pore size distribution measured with a mercury porosimeter. Anode bodies are obtained by forming a thin oxide film on the surface of a porous body by chemical conversion treatment or the like, and the most frequent pore size of the anode body can be said to be approximately the same value as the most frequent pore size of the porous body.

[0044] The anode body may include a rod-shaped anode wire partially embedded in the porous body. A portion of the anode wire may be embedded in the porous body so as to pass through the center of the porous body. When the porous body is a rectangular parallelepiped, the anode wire is embedded in one end face of the rectangular parallelepiped. The anode wire may include a valve metal. A portion of the anode wire is embedded in the porous body, and the remainder protrudes from the porous body. The remainder is connected to an anode lead terminal by welding or the like.

[0045] (dielectric layer) The dielectric layer is formed so as to cover the outer surface of the porous body and the inner wall surfaces of the pores of the porous body. The dielectric layer is formed, for example, by subjecting the porous body to a chemical conversion treatment to grow an oxide film on the surface of the porous body. The chemical conversion treatment may be performed by immersing the porous body in a chemical conversion solution to anodize the surface of the porous body. Alternatively, the surface of the porous body may be oxidized by heating the porous body in an oxygen-containing atmosphere.

[0046] (Solid electrolyte layer) The solid electrolyte layer is disposed so as to cover at least a portion of the dielectric layer. The solid electrolyte layer may be filled in the pores of the porous body via the dielectric layer and formed on the outer surface of the porous body. The solid electrolyte layer may be a laminate of two or more different solid electrolyte layers.

[0047] The solid electrolyte layer includes a conductive polymer. The conductive polymer may be a π-conjugated polymer, and examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. These may be used alone or in combination. The conductive polymer may also be a copolymer of two or more monomers. Note that a derivative of a conductive polymer refers to a polymer having a conductive polymer as its basic skeleton. For example, an example of a polythiophene derivative is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0048] A dopant may be added to the conductive polymer. That is, the solid electrolyte layer may include a conductive polymer and a dopant. The conductive polymer may be contained in the solid electrolyte layer in a doped state with the dopant. The dopant can be selected depending on the conductive polymer, and known dopants may be used. Examples of dopants include benzenesulfonic acid, alkylbenzenesulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, polystyrenesulfonic acid (PSS), and salts thereof. The solid electrolyte layer may include, for example, PEDOT doped with PSS.

[0049] A solid electrolyte layer containing a conductive polymer can be formed, for example, by impregnating a porous body (anode body) having a dielectric layer formed on its surface with a first treatment liquid containing a monomer (or oligomer), and then polymerizing the monomer (or oligomer) by electrolytic polymerization or chemical polymerization. In the case of chemical polymerization, the first treatment liquid contains, for example, a monomer (or oligomer), an oxidizing agent, and a solvent (or dispersion medium). Examples of the monomer include 3,4-ethylenedioxythiophene (EDOT) and pyrrole. The first treatment liquid may also contain a dopant.

[0050] Alternatively, the solid electrolyte layer may be formed by impregnating a porous body (anode body) having a dielectric layer formed on its surface with a second treatment liquid containing a conductive polymer, followed by drying. The second treatment liquid contains, for example, a conductive polymer, a solvent (or a dispersion medium), and, if necessary, a dopant.

[0051] The filling rate R of the solid electrolyte layer in the depth direction of the porous body can be adjusted, for example, by changing the electrolytic polymerization conditions (current value, polymerization time, composition of the electrolyte solution, temperature, etc.), the chemical polymerization conditions (composition of the first treatment solution, polymerization time, temperature, etc.), etc. In electrolytic polymerization, the reaction rate can be easily controlled by the current value, and the filling rate can also be easily controlled.

[0052] The packing ratio R of the solid electrolyte layer in the depth direction of the porous body may be adjusted by combining the formation of the solid electrolyte layer by electrolytic polymerization and the formation of the solid electrolyte layer by chemical polymerization. Also, the packing ratio R of the solid electrolyte layer in the depth direction of the porous body may be adjusted by combining the formation of the solid electrolyte layer by the first treatment liquid and the formation of the solid electrolyte layer by the second treatment liquid.

[0053] (others) The capacitor element may include a cathode layer covering at least a portion of the solid electrolyte layer. The electrolytic capacitor may include an anode lead terminal and a cathode lead terminal electrically connected to the capacitor element, and an exterior resin disposed around the capacitor element. The cathode lead terminal is connected to the cathode part via a conductive member. The anode lead terminal is connected to an end of the anode wire protruding from the porous body. The shape, size, etc. of the capacitor element are not particularly limited, and may be a known capacitor element or a capacitor element having a similar configuration.

[0054] (cathode layer) The cathode layer may include a carbon layer formed on the solid electrolyte layer and a metal paste layer formed on the carbon layer. The carbon layer may be formed of a conductive carbon material such as graphite and a resin. The metal paste layer may be formed of metal particles (e.g., silver particles) and a resin, for example, a known silver paste.

[0055] (Conductive material) The cathode layer is connected to the connection portion of the cathode lead terminal by a conductive member. That is, the cathode layer (cathode portion) is electrically connected to the cathode lead terminal. The conductive member is made of a conductive material. The conductive member may be formed using a material containing metal particles (e.g., silver particles) and a resin, or may be formed using, for example, a known metal paste (e.g., silver paste). The conductive member is formed by heating the metal paste. The conductive member may be made of a plurality of conductive layers of different types.

[0056] (exterior resin) The exterior resin is disposed around the capacitor element so that the capacitor element is not exposed on the surface of the electrolytic capacitor. Furthermore, the exterior resin insulates the anode lead terminal from the cathode lead terminal. The exterior resin may be a known exterior resin used for electrolytic capacitors. For example, the exterior resin may be formed using an insulating resin material used to seal the capacitor element. The exterior resin may be formed by placing the capacitor element in a mold, introducing an uncured thermosetting resin and a filler into the mold by transfer molding, compression molding, or the like, and curing the resin.

[0057] Examples of the exterior resin include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane, polyimide, unsaturated polyester, etc. The exterior resin may contain substances other than resin (such as inorganic fillers).

[0058] (cathode lead terminal) A portion of the cathode lead terminal is exposed from the exterior resin and is used as a cathode external terminal. The material of the cathode lead terminal may be any material that can be used as a cathode lead terminal of an electrolytic capacitor. For example, a known cathode lead terminal material used in electrolytic capacitors may be used. The cathode lead terminal may be formed by processing a metal sheet (including a metal plate and a metal foil) made of a metal (copper, copper alloy, etc.) using a known metal processing method.

[0059] (Anode lead terminal) A portion of the anode lead terminal is exposed from the exterior resin and is used as an external anode terminal. The material of the anode lead terminal may be any material that can be used as a material for an anode lead terminal of an electrolytic capacitor. For example, a known anode lead terminal material used in electrolytic capacitors may be used. The anode lead terminal may be formed by processing a metal sheet (including a metal plate and a metal foil) made of a metal (copper, copper alloy, etc.) using a known metal processing method.

[0060] FIG. 1 is a cross-sectional view schematically showing an example of an electrolytic capacitor according to this embodiment. FIG. 2 is a cross-sectional view schematically showing an anode body having a solid electrolyte layer formed on the surface. FIG. 3 is a cross-sectional view schematically showing a porous body. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. FIGS. 3 and 4 are cross-sectional views including the center C of the porous body. In FIGS. 3 and 4, X is shown as an example. 50 = 0.5D, the electrolytic capacitor according to this embodiment is not limited to this. Note that each figure is a schematic illustration, and the ratios of the dimensions (length, width, thickness, etc.) of each component element may not be the same as those in reality.

[0061] Electrolytic capacitor 20 includes capacitor element 10, exterior resin 11 that seals capacitor element 10, and anode lead terminal 12 and cathode lead terminal 13 that are electrically connected to capacitor element 10. A portion of anode lead terminal 12 and cathode lead terminal 13 are each exposed from exterior resin 11. A portion of anode lead terminal 12 and cathode lead terminal 13 are covered by exterior resin 11 together with capacitor element 10.

[0062] Capacitor element 10 includes an anode body 1, a solid electrolyte layer 2 formed on anode body 1, and a cathode layer 3 formed on solid electrolyte layer 2. Anode body 1 includes a porous body 4 containing a valve metal and a dielectric layer 5 covering porous body 4. Dielectric layer 5 is formed so as to cover outer surface S of porous body 4 and the inner wall surfaces of holes 7. Anode body 1 has substantially the same porous shape as porous body 4.

[0063] The porous body 4 has a substantially rectangular parallelepiped shape and six side surfaces. A portion of the anode wire 6 extends from one side surface of the porous body 4. That is, the anode wire 6 has a first portion 6a that is embedded in the porous body 4 from one side surface of the porous body 4, and a second portion 6b that extends from the one side surface of the porous body 4. The second portion 6b is joined to the anode lead terminal 12 by welding or the like. In this embodiment, the first portion 6a is embedded in the porous body 4 so as to pass through the center C of the porous body 4; however, the first portion 6a may be embedded in the porous body 4 so as not to pass through the center C of the porous body 4.

[0064] The solid electrolyte layer 2 is formed so as to cover at least a portion of the dielectric layer 5. The solid electrolyte layer 2 fills the pores 7 of the porous body 4 (anode body 1). The solid electrolyte layer 2 is formed so as to cover the outer surface S of the porous body 4 and the inner wall surfaces of the pores 7 with the dielectric layer 5 interposed therebetween.

[0065] The packing rate R of the solid electrolyte layer 2 in the porous body decreases from the outer surface S of the porous body 4 toward the center C. That is, the packing rate R decreases as the distance X from the outer surface S of the porous body 4 increases. The shortest distance from the outer surface S of the porous body 4 to the center C is defined as D. The distance X (X 50 ) is 0.5D. As shown in Figures 3 and 4, the porous body 4 has a first region 4a on the outer surface side of the porous body 4 and a second region 4b other than the first region 4a. The first region 4a is a region (the shaded area in Figures 3 and 4) where the distance X from the outer surface S of the porous body 4 is 0.5D or less and where the filling rate R is 50% or more.

[0066] The cathode layer 3 is formed to cover the surface of the solid electrolyte layer 2. The cathode layer 3 has a carbon layer 3a formed to cover the solid electrolyte layer 2 and a metal paste layer 3b formed on the surface of the carbon layer 3a. The cathode lead terminal 13 is joined to the cathode layer 3 (metal paste layer 3b) via a conductive member 8. The carbon layer 3a contains a conductive carbon material such as graphite and a resin. The metal paste layer 3b contains, for example, metal particles (e.g., silver) and a resin. The configuration of the cathode layer 3 is not limited to this configuration. The cathode layer 3 may have any configuration as long as it has a current collecting function.

[0067] [Example] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0068] Examples 1 to 5, Comparative Examples 1 and 2 (Preparation of porous bodies) One end of the anode wire was embedded in the Ta particles, and the Ta particles were formed into a rectangular parallelepiped. The formed body was then sintered in a vacuum. In this way, a porous body (Ta sintered body) with a portion of the anode wire embedded was obtained. The shortest distance D from the outer surface to the center of the porous body was 450 μm. Ta wire was used as the anode wire.

[0069] (Formation of dielectric layer) The porous body with a portion of the anode wire embedded in it was subjected to chemical conversion treatment (anodic oxidation) to form a dielectric layer (22 nm thick) on the surface of the porous body, resulting in the anode body. The dielectric layer was a tantalum oxide (Ta2O5) layer. The chemical conversion treatment was performed by immersing the porous body in a 0.02 mass% phosphoric acid aqueous solution at a chemical conversion voltage of 10 V and a temperature of 60°C for 2 hours. The CV value of the porous body was 70,000 μF·V / g. The CV value was adjusted by adjusting the Ta particles (surface area, etc.) used in the porous body production process.

[0070] (Formation of solid electrolyte layer) A solid electrolyte layer (conductivity 80 S / cm) containing polypyrrole and a dopant was formed in the pores of a porous anode with a dielectric layer on its surface. The dopant was a sulfonate with a naphthalene skeleton. The solid electrolyte layer was formed by electrolytic polymerization. The electrolytic polymerization was carried out at 20°C using a treatment solution containing pyrrole, a dopant, and water. In the electrolytic polymerization, the current value and polymerization time were appropriately adjusted to set the packing ratio R of the solid electrolyte layer at the distance X from the outer surface of the porous body to the values ​​shown in Table 1.

[0071] [Table 1]

[0072] The packing ratio R of the solid electrolyte layer at the distance X from the outer surface of the porous body was determined by the method described above.

[0073] (Cathode layer formation) A dispersion of carbon particles (carbon paste) was applied to the solid electrolyte layer and heated to form a carbon layer on the surface of the solid electrolyte layer. A metal paste containing silver particles, a binder resin, and a solvent was applied to the surface of the carbon layer and heated to form a metal paste layer, resulting in a cathode layer composed of the carbon layer and the metal paste layer. In this way, a capacitor element was obtained.

[0074] (Fabrication of electrolytic capacitors) A conductive adhesive that serves as a conductive member was applied to the metal paste layer, and the cathode lead terminal and the metal paste layer were bonded. The anode wire and the anode lead terminal were bonded by resistance welding. Next, the capacitor element with each lead terminal bonded was sealed with an exterior resin. In this way, an electrolytic capacitor was obtained. In Table 1, A1-1 to A1-5 represent the electrolytic capacitors of Examples 1 to 5, respectively. B1-1 and B1-2 represent the electrolytic capacitors of Comparative Examples 1 and 2, respectively.

[0075] [evaluation] For each of the electrolytic capacitors obtained above, the ESR at a frequency of 100 kHz (hereinafter also referred to as ESR1) and the ESR at a frequency of 500 kHz (hereinafter also referred to as ESR2) were measured in an environment of 20°C using a four-terminal LCR meter.

[0076] The evaluation results are shown in Table 2. ESR1 is expressed as a relative value when the ESR1 value of electrolytic capacitor B1-1 of Comparative Example 2 is set to 100. ESR2 is expressed as a relative value when the ESR2 value of electrolytic capacitor B1-2 of Comparative Example 2 is set to 100. Table 2 also shows the formation time of the solid electrolyte layer. This formation time is the polymerization time in electrolytic polymerization. This formation time is expressed as a relative value when the formation time in Comparative Example 2 is set to 100.

[0077] [Table 2]

[0078] In the electrolytic capacitors A1-1 to A1-5, the time required to form the solid electrolyte layer was short, and both ESR1 and ESR2 were reduced. 50 In the electrolytic capacitor B1-1, where X is less than 0.1D, the ESR1 increased significantly. 50 In the electrolytic capacitor B1-2, where ESR2 is 0.7 or more, the time required for forming the solid electrolyte layer is long, and ESR2 increases significantly.

[0079] Examples 6 to 8, Comparative Examples 3 and 4 In the dielectric formation process, the porous body with a portion of the anode wire embedded was subjected to chemical conversion treatment (anodic oxidation), forming a dielectric layer (22 nm thick) on the surface of the porous body to obtain the anode body. The dielectric layer was a layer of tantalum oxide (Ta2O5). The chemical conversion treatment was performed by immersing the porous body in a 0.02 mass% phosphoric acid aqueous solution at a chemical conversion voltage of 10 V and a temperature of 60°C for 2 hours. The CV value of the porous body was 100,000 μF·V / g.

[0080] In the electrolytic polymerization in the solid electrolyte layer formation step, the current value and polymerization time were appropriately adjusted to set the packing ratio R of the solid electrolyte layer at the distance X from the outer surface of the porous body to the values ​​shown in Table 3.

[0081] [Table 3]

[0082] Except for the above, electrolytic capacitors A2-1 to A2-3 of Examples 6 to 8 and electrolytic capacitors B2-1 and B2-2 of Comparative Examples 3 and 4 were fabricated in the same manner as electrolytic capacitor A1-1 of Example 1 and evaluated.

[0083] The evaluation results are shown in Table 4. In Table 4, ESR1 is expressed as a relative value when the ESR1 value of electrolytic capacitor B2-1 of Comparative Example 3 is set to 100. ESR2 is expressed as a relative value when the ESR2 value of electrolytic capacitor B2-2 of Comparative Example 4 is set to 100. Table 4 also shows the formation time of the solid electrolyte layer. This formation time is the polymerization time in electrolytic polymerization. This formation time is expressed as a relative value when the formation time in Comparative Example 4 is set to 100.

[0084] [Table 4]

[0085] In the electrolytic capacitors A2-1 to A2-3, the time required to form the solid electrolyte layer was short, and both ESR1 and ESR2 were reduced. 50 In electrolytic capacitor B2-1, where X is less than 0.05D, ESR1 increased significantly. 50 In the electrolytic capacitor B2-2, where ESR2 is 0.3 or more, the time required for forming the solid electrolyte layer is long, and ESR2 increases.

[0086] Examples 9 to 11 and Comparative Examples 5 to 6 In the dielectric formation process, the porous body with a portion of the anode wire embedded was subjected to chemical conversion treatment (anodic oxidation), forming a dielectric layer (22 nm thick) on the surface of the porous body to obtain the anode body. The dielectric layer was a layer of tantalum oxide (Ta2O5). The chemical conversion treatment was performed by immersing the porous body in a 0.02 mass% phosphoric acid aqueous solution at a chemical conversion voltage of 10 V and a temperature of 60°C for 2 hours. The CV value of the porous body was 150,000 μF·V / g.

[0087] In the electrolytic polymerization in the solid electrolyte layer formation step, the current value and polymerization time were appropriately adjusted to set the packing ratio R of the solid electrolyte layer at the distance X from the outer surface of the porous body to the values ​​shown in Table 5.

[0088] [Table 5]

[0089] Except for the above, electrolytic capacitors A3-1 to A3-3 of Examples 9 to 11 and electrolytic capacitors B3-1 to B3-2 of Comparative Examples 5 and 6 were fabricated in the same manner as electrolytic capacitor A1-1 of Example 1 and evaluated.

[0090] The evaluation results are shown in Table 6. In Table 6, ESR1 is expressed as a relative value when the ESR1 value of electrolytic capacitor B3-1 of Comparative Example 5 is set to 100. ESR2 is expressed as a relative value when the ESR2 value of electrolytic capacitor B3-2 of Comparative Example 6 is set to 100. Table 6 also shows the formation time of the solid electrolyte layer. This formation time is the polymerization time in electrolytic polymerization. This formation time is expressed as a relative value when the formation time in Comparative Example 6 is set to 100.

[0091] [Table 6]

[0092] In the electrolytic capacitors A3-1 to A3-3, the time required to form the solid electrolyte layer was short, and both ESR1 and ESR2 were reduced. 50 In electrolytic capacitor B3-1, where X is less than 0.03D, ESR1 increased significantly. 50 In electrolytic capacitor B3-2, where D is 0.2D or more, the time required for forming the solid electrolyte layer is long, and ESR2 increases significantly. [Industrial Applicability]

[0093] The electrolytic capacitor according to the present disclosure can be used in a variety of applications where low ESR is required.

[0094] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention. [Explanation of symbols]

[0095] 1: anode body, 2: solid electrolyte layer, 3: cathode layer, 3a: carbon layer, 3b: metal paste layer, 4: porous body, 4a: first region, 4b: second region, 5: dielectric layer, 6: anode wire, 6a: first portion, 6b: second portion, 7: hole, 8: conductive member, 10: capacitor element, 11: exterior resin, 12: anode lead terminal, 13: cathode lead terminal, 20: electrolytic capacitor

Claims

1. an anode body having a porous body containing a valve metal and a dielectric layer covering the porous body; a solid electrolyte layer that fills the pores of the porous body and covers the dielectric layer; Equipped with The CV value of the porous body is less than 100,000 μF V / g, a packing ratio R of the solid electrolyte layer in the porous body decreases from the outer surface toward the center of the porous body, an electrolytic capacitor, wherein a shortest distance D from the outer surface to the center of the porous body and a distance X from the outer surface of the porous body when a filling rate R of the solid electrolyte layer is 50% satisfy the relationship 0.1D≦X<0.7D.

2. The CV value of the porous body is 70,000 μF V / g or more and less than 100,000 μF V / g, 2. The electrolytic capacitor according to claim 1, wherein a packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.1D is 50% or more and 80% or less.

3. The CV value of the porous body is 70,000 μF V / g or more and less than 100,000 μF V / g, 3. The electrolytic capacitor according to claim 1, wherein a packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.7D is greater than 16% and not greater than 48%.

4. an anode body having a porous body containing a valve metal and a dielectric layer covering the porous body; a solid electrolyte layer that fills the pores of the porous body and covers the dielectric layer; Equipped with The CV value of the porous body is 100,000 μF V / g or more and less than 150,000 μF V / g, a packing ratio R of the solid electrolyte layer in the porous body decreases from the outer surface toward the center of the porous body, an electrolytic capacitor, wherein a shortest distance D from the outer surface to the center of the porous body and a distance X from the outer surface of the porous body when a filling rate R of the solid electrolyte layer is 50% satisfy the relationship 0.05D≦X<0.3D.

5. 5. The electrolytic capacitor according to claim 4, wherein a packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.05D is 50% or more and 83% or less.

6. 6. The electrolytic capacitor according to claim 4, wherein a packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.3D is greater than 13% and not greater than 44%.

7. an anode body having a porous body containing a valve metal and a dielectric layer covering the porous body; a solid electrolyte layer that fills the pores of the porous body and covers the dielectric layer; Equipped with The CV value of the porous body is 150,000 μF V / g or more, a packing ratio R of the solid electrolyte layer in the porous body decreases from the outer surface toward the center of the porous body, an electrolytic capacitor, wherein a shortest distance D from the outer surface to the center of the porous body and a distance X from the outer surface of the porous body when a filling rate of the solid electrolyte layer is 50% satisfy the relationship 0.03D≦X<0.2D.

8. The CV value of the porous body is 150,000 μF V / g or more, 8. The electrolytic capacitor according to claim 7, wherein a packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.03D is 56% or more and 83% or less.

9. The CV value of the porous body is 150,000 μF V / g or more, 9. The electrolytic capacitor according to claim 7, wherein a packing ratio R of the solid electrolyte layer when the distance X from the outer surface of the porous body is 0.2D is 14% or more and 41% or less.

Images