Electrolytic capacitor

Abstract

To provide an electrolytic capacitor having good capacitance and low ESR.SOLUTION: A electrolytic capacitor has a porous anode body, an anode wire, a dielectric layer formed on the surface of the anode body, and a capacitor element having a conductive polymer. In a volume-based Log differential pore diameter distribution of a void of the anode body having the dielectric layer measured in an element cross section intersecting the anode wire of the capacitor element, a first peak having a peak top at a first pore diameter D1 and a second peak having a peak top at a second pore diameter D2 (D1<D2) are observed. The D2 / D1 ratio is 2.7 or more, and the Log differential pore diameter distribution is measured in an intermediate region of the element cross section. The intermediate region includes an intermediate point between a center of the anode wire in the element cross section and a point farthest from the center on an outer surface of the capacitor element. A ratio (Rpm) of an area of the conductive polymer in the intermediate region to the area of the intermediate region is 10% or more.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an electrolytic capacitor. [Background technology]

[0002] Patent Document 1 proposes "a solid electrolytic capacitor comprising an anode body formed of a sintered body of metal particles, a dielectric layer provided on the surface of the anode body, and a conductive polymer layer provided on the surface of the dielectric layer, wherein the anode body includes a first anode portion and a second anode portion provided so as to cover the first anode portion, and the particle size of the metal particles of the second anode portion is smaller than the particle size of the metal particles of the first anode portion." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-244184 Summary of the Invention [Problem to be solved by the invention]

[0004] Progress is being made in developing high-performance electrolytic capacitors with reduced equivalent series resistance (ESR), leakage current (LC), and capacitance degradation rate, but there is still room for improvement. [Means for solving the problem]

[0005] One aspect of the present invention provides a capacitor element including a porous anode body, an anode wire partially embedded in the anode body, a dielectric layer formed on a surface of the anode body, and a conductive polymer covering at least a portion of the dielectric layer, wherein a volume-based Log differential pore size distribution of voids in the anode body having the dielectric layer measured in a cross section of the capacitor element intersecting the anode wire includes a first peak having a peak top at a first pore diameter D1 and a second peak having a peak top at a second pore diameter D2 larger than the first pore diameter D1. a second peak having a peak top is observed, a ratio (D2 / D1) of the second pore diameter D2 to the first pore diameter D1 is 2.7 or more, the Log differential pore size distribution is measured in a middle region of the element cross section, the middle region includes a middle point between the center of the anode wire in the element cross section and a point on the outer surface of the capacitor element farthest from the center, and a ratio (Rpm) of the area of ​​the conductive polymer in the middle region to the area of ​​the middle region is 10% or more. [Effects of the Invention]

[0006] According to the present disclosure, a high-performance electrolytic capacitor can be provided. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a diagram showing the position of a cross section of an element. [Figure 2] FIG. 10 is a diagram showing an example of an intermediate region in a cross section of an element. [Figure 3] FIG. 1 is a schematic cross-sectional view of an example of an electrolytic capacitor according to an embodiment of the present disclosure. [Figure 4] FIG. 10 is a diagram showing image data of an intermediate region in an embodiment. [Figure 5] FIG. 1 is a diagram showing the volume-based Log differential pore size distribution of pores in an anode body having a dielectric layer, determined from the element cross section of a capacitor element of an example. DETAILED DESCRIPTION OF THE INVENTION

[0008] 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 used as examples, but other numerical values ​​and materials may be used as long as the effects of the present disclosure are obtained. Note that components other than those characteristic of the present disclosure may be those of known electrolytic capacitors. In this specification, when a "range between numerical value A and numerical value B" is mentioned, the range includes numerical value A and numerical value B.

[0009] [Electrolytic capacitor] An electrolytic capacitor according to one embodiment of the present disclosure (hereinafter also referred to as "capacitor (C)") includes a porous anode body, an anode wire partially embedded in the anode body, a dielectric layer formed on the surface of the anode body, and a conductive polymer covering at least a portion of the dielectric layer. The smallest unit of an electrolytic capacitor including the anode body, anode wire, dielectric layer, and conductive polymer is also referred to as a "capacitor element." The capacitor (C) is a concept that encompasses both electrolytic capacitors and capacitor elements.

[0010] The capacitor element is divided into an anode portion and a cathode portion. The anode portion and the cathode portion are insulated by a dielectric layer. The anode body and the anode wire constitute the anode portion. The cathode portion includes at least a solid electrolyte layer and may also include a cathode extraction layer.

[0011] The solid electrolyte layer contains at least a conductive polymer. An electrolytic capacitor having a solid electrolyte layer (or a conductive polymer) is also called a "solid electrolytic capacitor." Note that "capacitor" may be read as "capacitor."

[0012] The cathode extraction layer may include, for example, 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.

[0013] The anode wire is made of metal. A part of the anode wire is embedded in the anode body, and the other part protrudes from the anode body. That is, the anode wire has an embedded part that is embedded in the anode body and a protruding part that protrudes outside the anode body.

[0014] The dielectric layer is formed on at least a portion of the surface of the anode body. The dielectric layer is formed, for example, by subjecting the anode body to a chemical conversion treatment and growing an oxide film on the surface of the anode body. In the chemical conversion treatment, the surface of the anode body may be anodized by immersing the anode body in a chemical conversion solution. The oxide film may also be formed using a gas phase method such as atomic layer deposition (ALD). The surface of the anode body may also be oxidized by heating the anode body in an oxygen-containing atmosphere.

[0015] Since the anode body is porous, the anode body having the dielectric layer has voids, and the pore size distribution or pore volume distribution of the voids in the anode body significantly affects the performance of the electrolytic capacitor.

[0016] In the present disclosure, the volume-based Log differential pore size distribution of voids in an anode body having a dielectric layer is controlled. However, the volume-based Log differential pore size distribution of voids in an anode body having a dielectric layer is a local distribution inside the anode body measured from a cross section of the element intersecting with an anode wire of a capacitor element. The cross section of the element may be a cross section that intersects with the anode wire and is parallel to an end face of the anode body from which a portion of the anode wire protrudes. The cross section of the element may be a cross section that is perpendicular to the anode wire.

[0017] The volume-based Log differential pore size distribution of voids measured from the element cross section of a capacitor element is measured in a middle region of the element cross section. The middle region is defined to include the midpoint (hereinafter also referred to as "midpoint (M)") between the center of the anode wire in the element cross section (hereinafter also referred to as "center (C)") and the point on the outer surface of the capacitor element farthest from the center (C) (hereinafter also referred to as "point (O)"). Hereinafter, the volume-based Log differential pore size distribution of voids measured in a local middle region inside the anode body will also be referred to as "Log differential pore size distribution (D)."

[0018] When the cross section of the element is rectangular, point (O) is located at the tip of a corner of the rectangle. The center (C) of the anode wire may be identified as the area centroid of the cross section of the anode wire. The midpoint (M) is on the line segment connecting the center (C) and point (O), and the distance between the midpoint (M) and the center (C) is equal to the distance between the midpoint (M) and point (O). The intermediate region includes the midpoint (M) and has an area of, for example, 2500 μm 2 ~7500μm 2 The intermediate region may be a region that includes the midpoint (M) as the area center of gravity.

[0019] In the log differential pore size distribution (D), a first peak having a peak top at a first pore diameter D1 is observed, and a second peak having a peak top at a second pore diameter D2 larger than the first pore diameter D1 is observed. Hereinafter, the region where pores constituting the first peak exist will also be referred to as the first region (R1), and the region where pores constituting the second peak exist will also be referred to as the second region (R2).

[0020] The metal for forming the anode body is a valve metal such as aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), or hafnium (Hf). These metals may be used alone or in combination of two or more. Among these, it is preferable to use at least one of Ta and Nb.

[0021] The porous anode body may be a sintered body of a compact of metal particles. In this case, the anode body is formed by forming material particles and sintering the compact. Examples of material particles include metal particles, alloy particles, and metal compound particles. These particles may be used alone or in combination of two or more types.

[0022] The first region (R1) may be a region where first particles, which are material particles, are sintered together, and the second region (R2) may be a region where second particles, which are material particles, are sintered together. By making the average particle diameter d1 of the first particles smaller than the average particle diameter d2 of the second particles, a Log differential pore size distribution (D) may be achieved in which a first peak having a peak top at the first pore diameter D1 is observed and a second peak having a peak top at the second pore diameter D2 is observed.

[0023] The average particle diameter d1 of the first particles, which are material particles, may be, for example, 1 μm or less, or 0.3 μm or less. The average particle diameter d2 of the second particles, which are material particles, may be, for example, 3 μm or more, or 5 μm or more. By using such first particles and second particles, it becomes easier to achieve a Log differential pore size distribution (D) having a sharp first peak and a clear second peak. The average particle diameter d1 of the first particles and the average particle diameter d2 of the second particles are each a median diameter in a volume-based particle size distribution determined by a laser diffraction / scattering particle size distribution measuring device.

[0024] The first region is necessary to provide the anode body with a sufficiently large specific surface area, which contributes to an increase in capacitance. On the other hand, the second region has low bulk resistance and is easy for the conductive polymer to penetrate to extract electricity. Therefore, a thick conductive path is formed in the second region.

[0025] Here, the ratio (D2 / D1) of the second pore diameter D2 to the first pore diameter D1 is controlled to 2.7 or more. By setting the D2 / D1 ratio to 2.7 or more, the filling rate of the conductive polymer in the voids can be increased. The pores that form the second peak play an important role as migration paths for the conductive polymer filled in the voids. When the D2 / D1 ratio of the Log differential pore size distribution (D) in the intermediate region has a large value of 2.7 or more, the penetration of the conductive polymer from the pores that form the second peak into the pores that form the first peak is improved, which tends to increase the filling rate of the conductive polymer inside the anode body having a dielectric layer.

[0026] The D2 / D1 ratio may be 2.7 or more, but may also be 2.8 or more, 2.9 or more, or 3.0 or more. When the D2 / D1 ratio is controlled in this manner, the penetration of the conductive polymer from the pores constituting the second peak into the pores constituting the first peak is improved. The upper limit of the D2 / D1 ratio is, for example, 4.0 or less, or may be 3.5 or less, or 3.4 or less. The intermediate region having such a Log differential pore size distribution (D) has voids that are more suitable for filling with the conductive polymer.

[0027] The Log differential pore size distribution (D) in the "intermediate region" is a Log differential pore size distribution at a localized location inside the capacitor element, and therefore cannot be measured by conventional general pore size distribution measurement methods such as mercury intrusion porosimetry (a measurement method using a mercury porosimeter).

[0028] The ratio (Rpm) of the area of ​​the conductive polymer (solid electrolyte layer) in the intermediate region to the area of ​​the intermediate region is controlled to 10% or more. That is, in the capacitor (C) according to the present disclosure, the conductive polymer fills the voids in the intermediate region at a high rate, and a large area of ​​the dielectric layer is covered with a thick conductive polymer. Therefore, inside the anode body having the dielectric layer, peeling of the conductive polymer from the dielectric layer is suppressed, and heat generation is suppressed due to the large conductive path and low resistance, and even if oxidative degradation occurs, the reduction in effective area is limited. This makes it possible to obtain a high-performance electrolytic capacitor with suppressed ESR, leakage current, and capacity degradation rate.

[0029] The rate (Rpm) is preferably 10.5% or more, and more preferably 11% or more. The rate (Rpm) can be controlled by the D2 / D1 ratio. In addition to the D2 / D1 ratio, the rate (Rpm) can be more effectively controlled by appropriately selecting at least one parameter described below.

[0030] The difference (D2-D1) between the first pore diameter D1 and the second pore diameter D2 may be 1.2 μm or more, 1.5 μm or more, or 2.0 μm or more. In this case, in the intermediate region, the penetration of the conductive polymer from the pores constituting the second peak to the pores constituting the first peak is further improved, and a thicker conductive path is formed.

[0031] A difference (D2-D1) of 1.2 μm or more means that multiple conductive paths with different functions can be formed in the intermediate region deep within the anode body. The larger the second pore diameter D2, the thicker the conductive paths formed by the conductive polymer in the second region, which is advantageous for reducing ESR. On the other hand, the smaller the first pore diameter D1, the larger the specific surface area of ​​the first region, and the greater the capacitance. The fine conductive paths formed by the conductive polymer in the first region function as tributaries connecting to the thick conductive paths in the second region. As a result, a conductive path with excellent current collection performance is formed overall.

[0032] The second pore diameter D2 is, for example, 2.0 μm or more, and may be 2.5 μm or more. When the second pore diameter D2 is 2.0 μm or more, the bulk resistance of the second region is lowered and a thicker conductive path can be formed in the capacitor (C). In other words, making the second pore diameter D2 sufficiently large is advantageous for reducing the ESR.

[0033] The second pore diameter D2 is 5 μm or less, and may be 3 μm or less. When the second pore diameter D2 is 5 μm or less, the specific surface area of ​​the second region increases, and the capacitance further increases.

[0034] The first pore diameter D1 is, for example, 0.7 μm or more, and may be 0.8 μm or more. When the first pore diameter D1 is 0.7 μm or more, the intrusion of the conductive polymer into the pores in the first region is further improved, and a thicker conductive path is formed.

[0035] The first pore diameter D1 is 2.0 μm or less, and may be 1.5 μm or less. When the first pore diameter D1 is 2.0 μm or less, the specific surface area of ​​the first region is significantly increased, and the capacitance is further increased.

[0036] To obtain a high-performance electrolytic capacitor in which ESR, leakage current, and capacity degradation rate are all suppressed, it is desirable to provide pores of sufficient volume in the intermediate region of the anode body having the dielectric layer and to form the first and second regions in a well-balanced manner. From the viewpoint of the balance between the first and second regions, the ratio (V1 / V2) of the volume V1 of the pores constituting the first peak to the volume V2 of the pores constituting the second peak is, for example, from 0.4 to 0.62, and preferably 0.5 to 0.6.

[0037] The ratio (Rvd) of the remaining area, obtained by subtracting the area of ​​the anode body having the dielectric layer in the intermediate region from the area of ​​the intermediate region, to the area of ​​the intermediate region is, for example, 30% or more, or may be 31% or more, or may be 33% or more. The ratio (Rvd) corresponds to the "porosity" of the intermediate region of the anode body having the dielectric layer. The ratio (Rvd) (porosity) may be, for example, 40% or less. This makes it easier to fill a large amount of conductive polymer deep into the anode body.

[0038] (Method for measuring Log differential pore size distribution (D)) An example of a method for measuring the Log differential pore size distribution (D) will now be described with reference to the drawings. First, a cross section of a capacitor (C) is formed so as to intersect with the anode wire of the capacitor element.

[0039] FIG. 1 shows an example of the position at which the element cross sections are formed, with the anode body 1 divided into four quarters by three element cross sections L1, L2, and L3 that intersect with the anode wire 2. The element cross sections L1, L2, and L3 are all parallel to the end face S1 of the anode body 1 from which a portion of the anode wire 2 protrudes. If the distance from the end face S1 of the anode body to the back face S2 opposite the end face S1 is H, then L1 is located 0.12H away from the end face S1. L2 is located 0.5H away from the end face S1. L3 is located 0.88H away from the end face S1.

[0040] Each element cross section is polished and processed by a cross-section polisher (CP). After that, the area is 2500 μm 2 ~7500μm 2 defines an intermediate region.

[0041] FIG. 2 is a diagram showing an example of a middle region MR defined in the element cross section L2. The middle region MR is defined to include a midpoint (M) between the center (C) of the anode wire 2 in the element cross section L2 and the point (O) on the outer surface of the capacitor element that is farthest from the center (C). The midpoint (M) is located on the line segment connecting the center (C) and point (O), and the distance between the midpoint (M) and the center (C) is equal to the distance between the midpoint (M) and point (O). Because the element cross section L2 is rectangular, point (O) is located at the tip of a corner of the rectangle. The center (C) of the anode wire is the area center of gravity of the cross section of the anode wire 2. The midpoint (M) is the area center of gravity of the middle region (MR). In the illustrated example, the middle region (MR) is rectangular, but the shape of the middle region (MR) is not limited.

[0042] Next, backscattered electron and secondary electron images of the defined intermediate region are taken using a scanning electron microscope (SEM). By converting the captured backscattered electron and secondary electron images into multi-values ​​using discriminant analysis and combining them, it is possible to identify the metal parts of the anode body, the dielectric layer, the conductive polymer, voids, etc., and measure the distribution of the metal parts, dielectric layer, conductive polymer, and voids.

[0043] For example, when the image of the intermediate region is divided into a first image portion of the anode body having a dielectric layer and a second image portion other than the first image portion, the second image portion shows the distribution of pores in the anode body having a dielectric layer. In other words, by analyzing the second image portion, the volume-based Log differential pore size distribution (Log differential pore size distribution (D)) of the pores in the anode body having a dielectric layer can be obtained. Furthermore, the second image portion can also be divided into a filled portion filled with a conductive polymer and an unfilled portion not filled with a conductive polymer.

[0044] The second image portion is acquired as a set of multiple (at least 1000) voids. Each of the multiple voids forming the set has a variety of shapes, but all of the voids are converted into circles. Specifically, each void is considered to be a circle (equivalent circle) having the same area as the area of ​​the void. Then, the diameter of the equivalent circle (circle equivalent diameter) is calculated. The area of ​​a certain void is defined as S (μm 2 ), the equivalent circle diameter of the pores is calculated as 2√S / √π. Then, the pores are considered as cylinders with a thickness of 1 μm, and the cumulative pore volume distribution is obtained. The cumulative pore volume distribution is approximated as the sum of two cumulative distribution functions. The Log differential pore size distribution (D) is calculated by differentiating the approximate equation with respect to the minute region of pore size on a logarithmic scale.

[0045] The log differential pore size distribution (D) may be calculated using image analysis type particle size distribution measurement software (for example, MAC-View (Mountec Co., Ltd.)).

[0046] The Log differential pore size distribution (D) is calculated for one or more intermediate regions in each of the three element cross sections L1, L2, and L3, and the average of all the measured Log differential pore size distributions (D) is calculated.

[0047] By approximating the log differential pore size distribution (D) to the sum of two normal distributions, it is possible to separate the distribution into a first peak having a peak top at a first pore diameter D1 and a second peak having a peak top at a second pore diameter D2. The volume of the pores that make up the first peak is V1, and the volume of the pores that make up the second peak is V2. V1 and V2 are calculated by converting the log differential pore size distribution (D) separated into the first and second peaks into a pore volume distribution.

[0048] When the log differential pore size distribution (D) is approximated by the sum of the normal distribution AD1 corresponding to the first peak and the normal distribution AD2 corresponding to the second peak, the approximation formula is B((1-P2)AD1+P2 AD2), where B is a constant and P2 is the ratio of the volume V2 of the pores that make up the second peak to the total pore volume (V1+V2) in the pore volume distribution.

[0049] (Method for measuring the area ratio (Rpm) of conductive polymers) As mentioned above, by analyzing the multi-valued electron image of the intermediate region, it is possible to identify the metal part of the anode body, the dielectric layer, the conductive polymer, voids, etc. Therefore, it is possible to measure the ratio of the area of ​​the conductive polymer image part to the area of ​​the intermediate region as a ratio (Rpm).

[0050] 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 the 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).

[0051] It is preferable that a dopant be added to the conductive polymer. The dopant can be selected depending on the conductive polymer, and known dopants may be used. Examples of the dopant include low-molecular-weight dopants such as alkylbenzenesulfonic acids such as benzenesulfonic acid and p-toluenesulfonic acid, naphthalenesulfonic acid, and anthraquinonesulfonic acid, and polymer dopants such as polystyrenesulfonic acid, polyestersulfonic acid, and phenolsulfonic acid novolac resin.

[0052] An example of a solid electrolyte layer is formed using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS).

[0053] The solid electrolyte layer containing a conductive polymer is formed on at least a part of the dielectric layer by a method of impregnating the dielectric layer with a monomer or oligomer and then polymerizing the monomer or oligomer by chemical polymerization or electrolytic polymerization, or by impregnating the anode body on which the dielectric layer has been formed with a solution or dispersion of the conductive polymer (and a dopant as necessary) and drying it.

[0054] (Method for measuring the remaining area ratio (Rvd (void ratio))) As mentioned above, image analysis of the multi-valued electron image of the intermediate region makes it possible to identify the metal portion of the anode body, the dielectric layer, the conductive polymer, voids, etc. Therefore, it is possible to measure the ratio (Rvd) of the remaining area (void ratio) obtained by subtracting the area of ​​the image portion of the anode body with the dielectric layer from the area of ​​the intermediate region. When the image of the intermediate region is divided into a first image portion of the anode body with the dielectric layer and a second image portion other than the first image portion, the ratio (Rvd) can also be said to be the ratio of the area of ​​the second image portion to the area of ​​the intermediate region.

[0055] [Manufacturing method of electrolytic capacitors] An example of a method for manufacturing an electrolytic capacitor will be described. First, an anode body is prepared. The anode body may be a sintered body of a compact of a secondary particle mixture. The secondary particle mixture is a mixture of first secondary particles formed by agglomeration of first particles and second secondary particles formed by agglomeration of second particles. The first secondary particles are obtained by heating the first particles to agglomerate them. The second secondary particles are obtained by heating the second particles to agglomerate them. In other words, the first particles and the second particles are mixed in a pre-agglomerated state.

[0056] A secondary particle mixture in which the first particles and the second particles are mixed in a pre-agglomerated state may be molded and sintered, so that a first peak having a peak top at the first pore diameter D1 and a second peak having a peak top at the second pore diameter D2 are observed in the Log differential pore diameter distribution (D) of the anode body having a dielectric layer.

[0057] In this case, the ratio (D2 / D1) of the second pore diameter D2 to the first pore diameter D1 may be controlled to 2.7 or more by controlling the average particle diameter d1 of the first particles, which are material particles, the average particle diameter d2 of the second particles, the size of the first secondary particles, the size of the second secondary particles, etc.

[0058] In the step of obtaining a secondary particle mixture, the proportion of the second secondary particles in the total of the first secondary particles and the second secondary particles may be, for example, 5% by mass or more and 40% by mass or less, 5% by mass or more and 20% by mass or less, or 10% by mass or more and 20% by mass or less. When the proportion of the second secondary particles is 40% by mass or less, the second secondary particles are easily surrounded by the first secondary particles and undergo thermal shrinkage, and sintering between the first secondary particles and the second secondary particles and between the second secondary particles themselves easily proceeds.

[0059] Next, the secondary particle mixture is molded into a predetermined shape to obtain a molded body. The shape of the molded body is selected depending on the shape of the anode body. The shape of the anode body is not particularly limited, but for example, it has a pair of opposing main surfaces and side surfaces that intersect with each of the pair of main surfaces. For example, a portion of the anode wire is embedded in the secondary particle mixture, and the secondary particle mixture is pressure-molded into a rectangular parallelepiped shape. The obtained molded body is then sintered to form an anode body in which a portion of the anode wire is embedded.

[0060] As described above, by sintering the compact, it is possible to obtain an anode body having a first region where the first particles are sintered together and a second region where the second particles are sintered together.

[0061] Next, a dielectric layer is formed on the surface of the anode body by performing chemical conversion or the like on the anode body, and then a cathode portion is formed to cover at least a part of the dielectric layer.

[0062] Next, the present invention will be described in more detail with reference to the drawings, but the following examples are not intended to limit the present invention. The drawings shown below are schematic and do not accurately reflect the shapes, dimensions, number, etc. of actual components.

[0063] 3 is a schematic cross-sectional view of an example of an electrolytic capacitor according to an embodiment of the present disclosure. Electrolytic capacitor 20 includes capacitor element 10 having an anode portion 6 and a cathode portion 7, exterior resin 11 that seals capacitor element 10, a first terminal (anode lead terminal) 13 electrically connected to anode portion 6 and partially exposed from exterior resin 11, and a second terminal (cathode lead terminal) 14 electrically connected to cathode portion 7 and partially exposed from exterior resin 11. Anode portion 6 includes an anode body 1 and an anode wire 2. First terminal 13 is bonded to anode wire 2. Connection surface 14a of second terminal 14, which is disposed inside exterior resin 11, is bonded to cathode extraction layer 5 via conductive member 8.

[0064] A dielectric layer 3 is formed on the surface of the anode body 1. The cathode section 7 has a solid electrolyte layer 4 covering at least a portion of the dielectric layer 3, and a cathode extraction layer 5 covering the surface of the solid electrolyte layer 4. The solid electrolyte layer 4 contains a conductive polymer. The cathode extraction layer 5 has a carbon layer formed to cover the solid electrolyte layer 4 and a metal paste layer formed on the surface of the carbon layer. The carbon layer contains a conductive carbon material such as graphite and a resin. The metal paste layer contains, for example, metal particles (e.g., silver) and a resin. The configuration of the cathode extraction layer 5 is not limited to this configuration. The configuration of the cathode extraction layer 5 may be any configuration that has a current collecting function.

[0065] 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 first terminal from the second 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.

[0066] The first terminal is an anode terminal electrically connected to the anode portion of the capacitor element (specifically, the anode wire), and the second terminal is a cathode terminal electrically connected to the cathode portion of the capacitor element.

[0067] (Addendum) The above description discloses the following techniques. (Technology 1) a porous anode body; an anode wire partially embedded in the anode body; a dielectric layer formed on the surface of the anode body; a conductive polymer covering at least a portion of the dielectric layer; a capacitor element comprising: In a volume-based Log differential pore size distribution of voids contained in the anode body having the dielectric layer measured in a cross section of the capacitor element intersecting the anode wire, a first peak having a peak top at a first pore diameter D1; a second peak having a peak top at a second pore diameter D2 larger than the first pore diameter D1 is observed; a ratio (D2 / D1) of the second pore diameter D2 to the first pore diameter D1 is 2.7 or more; The Log differential pore size distribution is measured in a middle region of the cross section of the element, the intermediate region includes a midpoint between a center of the anode wire in the cross section of the element and a point on the outer surface of the capacitor element farthest from the center, An electrolytic capacitor, wherein the ratio (Rpm) of the area of ​​the conductive polymer in the intermediate region to the area of ​​the intermediate region is 10% or more. (Technology 2) The electrolytic capacitor according to technique 1, wherein the difference (D2-D1) between the first pore diameter D1 and the second pore diameter D2 is 1.2 μm or more. (Technology 3) The second pore diameter D2 is 2.0 μm or more, 3. The electrolytic capacitor according to claim 1, wherein the first pore diameter D1 is 0.7 μm or more. (Technology 4) The second pore diameter D2 is 5 μm or less, 4. The electrolytic capacitor according to claim 3, wherein the first pore diameter D1 is 2 μm or less. (Technology 5) 5. The electrolytic capacitor according to any one of techniques 1 to 4, wherein the ratio (V1 / V2) of the volume V1 of the pores constituting the first peak to the volume V2 of the pores constituting the second peak is 0.4 or more and 0.62 or less. (Technology 6) 6. The electrolytic capacitor according to any one of techniques 1 to 5, wherein a ratio (Rvd) of a remaining area obtained by subtracting an area of ​​the anode body having the dielectric layer in the intermediate region from the area of ​​the intermediate region to an area of ​​the intermediate region is 30% or more.

[0068] Hereinafter, experimental examples and examples of the present invention will be described, but the present invention is not limited to the following.

[0069] Examples 1 and 2, Comparative Example 1 Using the procedure below, 1000 electrolytic capacitors (rated voltage 35V, capacitance 47μF) as shown in Figure 1 were fabricated.

[0070] (i) Fabrication of capacitor elements (ii) Preparation of the anode body Ta was used as the anode material. Ta wire was used as the anode wire. One end of the Ta wire was embedded in the secondary particle mixture, and the secondary particle mixture was molded into a rectangular parallelepiped. The molded body was then sintered in a vacuum. This resulted in an anode (i.e., anode part) consisting of a porous sintered Ta body with part of the Ta wire embedded.

[0071] The sizes of the first and second secondary particles that make up the secondary particle mixture, the mass ratio of the first and second secondary particles in the secondary particle mixture, the average particle diameter of the first particles that make up the first secondary particles, and the average particle diameter of the second particles that make up the second secondary particles were appropriately selected so that the Log differential pore size distribution (D) in the intermediate region of the capacitor element would be obtained with the physical properties shown in Table 1 (D1, D2, D2 / D1 ratio, difference (D2-D1), V1, V2, V1 / V2 ratio). The physical properties in Table 1 are for an area of ​​5000 μm 2 The backscattered electron image and secondary electron image of the rectangular central region were taken with an SEM at a magnification of 1500. In Table 1, the values ​​of V1 and V2 are relative values ​​when the value of V1 in electrolytic capacitor B1 of Comparative Example 1 is set to 1.00.

[0072] [Table 1]

[0073] (i-ii) Formation of dielectric layer The anode body and part of the wire were immersed in an anodizing bath filled with an electrolytic solution of phosphoric acid, and a uniform oxide film was formed as a dielectric layer on the surface of the anode body and part of the surface of the wire by anodizing. The anodization was performed in a 0.1 mass % phosphoric acid solution at an anodizing voltage of 10 V.

[0074] (i-iii) Formation of solid electrolyte layer Next, 3,4-ethylenedioxythiophene (monomer), iron(III) p-toluenesulfonate, and 1-butanol were mixed to prepare a polymerization solution. The anode body with the dielectric layer was then immersed in this polymerization solution, then removed from the polymerization solution and heat-treated in air. In this case, iron(III) p-toluenesulfonate served as both an oxidant and a dopant. In this way, the monomer was polymerized on the dielectric layer, producing a first conductive polymer containing poly(3,4-ethylenedioxythiophene) (PEDOT) through chemical polymerization.

[0075] Next, the anode body with the conductive polymer formed thereon was washed, and then the anode body with the conductive polymer attached was immersed in an aqueous dispersion containing PEDOT as a conjugated polymer and polystyrene sulfonate (PSS) as a polymer dopant. After immersion, the anode body was removed and dried under atmospheric pressure. In this way, a conductive polymer containing PEDOT and PSS was formed so as to cover the first conductive polymer. In this way, an anode body with a solid electrolyte layer containing the first and second conductive polymers was obtained.

[0076] (i-iv) Formation of carbon layer A dispersion of carbon particles (carbon paste) was applied to the solid electrolyte layer, and then heated at 200° C. to form a carbon layer (thickness: approximately 3 μm) on the surface of the solid electrolyte layer.

[0077] (iv) Formation of a metal paste layer A metal paste containing silver particles, a binder resin, and a solvent was applied to the surface of the carbon layer, and then heated at 200° C. to form a metal paste layer (thickness: 10 μm), thereby obtaining a capacitor element.

[0078] (ii) Fabrication of electrolytic capacitors A conductive adhesive was applied to the metal paste layer to form a conductive member, and the cathode lead terminal and the metal paste layer were joined. The anode wire and the anode lead terminal were joined by resistance welding. Next, the capacitor elements with the joined lead terminals were sealed with an exterior resin using a transfer molding method to produce electrolytic capacitors A1 and A2 of Examples 1 and 2 and electrolytic capacitor B1 of Comparative Example 1.

[0079] [evaluation] (1) Initial ESR, initial capacitance For the electrolytic capacitors A1, A2, and B1 fabricated above, the initial capacitance Cap(0) (μF) and the initial ESR (mΩ) at a frequency of 100 kHz were measured using a four-terminal LCR meter at 20°C, and the average values ​​were calculated. The ESR results are shown in Table 1.

[0080] (2) Leakage current (LC) For the electrolytic capacitors A1, A2, and B1 fabricated above, a 1 kΩ resistor was connected in series and the rated voltage was applied for 1 minute from a DC power supply in an environment of 20°C, after which the leakage current was measured and the average value was calculated. The results are shown in Table 1.

[0081] (3) Capacitance change rate (ΔCap) After measuring Cap(0), ESR, and LC, a high-temperature load test (accelerated test) was conducted. That is, the rated voltage was applied to the electrolytic capacitor at a temperature of 145°C for 250 hours. After the accelerated test, the electrostatic capacitance (Cap(X)) of the electrolytic capacitor was calculated. The capacitance change (ΔCap) was calculated using the following formula. The results are shown in Table 1.

[0082] ΔCap(%)=100×(Cap(0)-Cap(X)) / Cap(0)

[0083] Using the methods described above, the proportion of the area of ​​the conductive polymer (Rpm), Rvd (porosity), and the proportion of the area of ​​the anode body having a dielectric layer to the area of ​​the intermediate region (Rt(%)=100-Rvd) were determined. The results are shown in Table 1. FIG. 4 shows image data of the intermediate region of the example. FIG. 5 shows the volume-based Log differential pore size distribution of the voids in the anode body having a dielectric layer determined from the element cross-section of the capacitor element of the example. The D2 / D1 ratios of electrolytic capacitors A1 and A2 exceeded 2.7, indicating that the Rpm of electrolytic capacitors A1 and A2 was much higher than that of electrolytic capacitor B1. [Industrial Applicability]

[0084] The present disclosure can be used in electrolytic capacitors that include porous anode bodies. [Explanation of symbols]

[0085] 20: Electrolytic capacitor 10: Capacitor element 1: Anode body 2: Anode wire 2a: Buried part 2b:Protrusion 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode extraction layer 6: Anode part 7: Cathode 8: Conductive material 11: Exterior resin 13: 1st terminal 14: 2nd terminal 14a: Connection surface

Claims

1. a porous anode body; an anode wire partially embedded in the anode body; a dielectric layer formed on the surface of the anode body; a conductive polymer covering at least a portion of the dielectric layer; a capacitor element comprising: In a volume-based Log differential pore size distribution of voids contained in the anode body having the dielectric layer measured in a cross section of the capacitor element intersecting the anode wire, a first peak having a peak top at a first pore diameter D1; A second peak having a peak top at a second pore diameter D2 larger than the first pore diameter D1 is observed, The ratio (D2 / D1) of the second pore diameter D2 to the first pore diameter D1 is 2.7 or more, The Log differential pore size distribution is measured in a middle region of the cross section of the element, the intermediate region includes a midpoint between a center of the anode wire in the cross section of the element and a point on the outer surface of the capacitor element farthest from the center, An electrolytic capacitor, wherein the ratio (Rpm) of the area of ​​the conductive polymer in the intermediate region to the area of ​​the intermediate region is 10% or more.

2. 2. The electrolytic capacitor according to claim 1, wherein the difference (D2-D1) between the first pore diameter D1 and the second pore diameter D2 is 1.2 μm or more.

3. The second pore diameter D2 is 2.0 μm or more, 2. The electrolytic capacitor according to claim 1, wherein the first pore diameter D1 is 0.7 μm or more.

4. The second pore diameter D2 is 5 μm or less, 4. The electrolytic capacitor according to claim 3, wherein the first pore diameter D1 is 2 μm or less.

5. 2. The electrolytic capacitor according to claim 1, wherein a ratio (V1 / V2) of a volume V1 of the pores constituting the first peak to a volume V2 of the pores constituting the second peak is 0.4 or more and 0.62 or less.

6. 2. The electrolytic capacitor according to claim 1, wherein a ratio (Rvd) of a remaining area obtained by subtracting an area of ​​the anode body having the dielectric layer in the intermediate region from an area of ​​the intermediate region to an area of ​​the intermediate region is 30% or more.

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