Electrolytic capacitor

Abstract

This electrolytic capacitor comprises: a porous positive electrode body; a positive electrode lead partially embedded in the positive electrode body; a dielectric layer formed on the surface of the positive electrode body; and a negative electrode part covering at least a part of the dielectric layer. The positive electrode body is a sintered body of particles containing a valve action metal element, and the particles include first particles and second particles. The particle diameter of the first particles is less than 150 μm, and the particle diameter of the second particles is at least 150 μm. The average circularity C2 of the second particles is greater than the average circularity C1 of the first particles, and the difference C2-C1 between the average circularity C1 of the first particles and the average circularity C2 of the second particles is at least 0.05.

Description

Electrolytic capacitor Cross-reference to Related Applications

[0001] The present application claims the benefit of priority from Japanese Patent Application No. 2025-054924 filed with the Japan Patent Office on March 28, 2025, the entire content of which is incorporated herein by reference.

[0002] The present disclosure relates to an electrolytic capacitor.

[0003] In recent years, development of electrolytic capacitors having low equivalent series resistance (ESR) and excellent frequency characteristics has been progressing. An electrolytic capacitor includes a porous anode body, a dielectric layer formed on a surface of the anode body, and a cathode portion covering at least a part of the dielectric layer.

[0004] As the anode body, a sintered compact of a molded body of metal particles is used. The molded body is generally manufactured by arranging an anode lead at a predetermined position in a mold, charging metal particles into the mold, and performing pressure molding.

[0005] Patent Document 1 proposes "an anode body for a solid electrolytic capacitor obtained by pressure-molding valve-action metal powder, implanting an anode lead wire to form a molded body, and sintering the molded body at high temperature in vacuum, wherein the valve-action metal powder is obtained by adding and mixing a first valve-action metal powder and a second valve-action metal powder made of the same metal as the first valve-action metal powder and having the same powder CV as the first valve-action metal powder".

[0006] Japanese Unexamined Patent Publication No. 2007-88144

[0007] In recent years, there has been a demand for electrolytic capacitors having good capacitance and low ESR (equivalent series resistance).

[0008] One aspect of the present disclosure relates to an electrolytic capacitor comprising a porous anode body, an anode lead partially embedded in the anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer, wherein the anode body is a sintered body of particles containing a valve-acting metal element, the particles comprising first particles and second particles, the particle diameter of the first particles being less than 150 μm, the particle diameter of the second particles being 150 μm or more, the average circularity C2 of the second particles being greater than the average circularity C1 of the first particles, and the difference between the average circularity C1 of the first particles and the average circularity C2 of the second particles: C2-C1 being 0.05 or more.

[0009] According to this disclosure, it is possible to provide an electrolytic capacitor that has good capacitance and low ESR.

[0010] Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0011] This is a flowchart illustrating a method for preparing a particle mixture. This is a schematic cross-sectional view of an example of an electrolytic capacitor according to an embodiment of this disclosure. This is a diagram showing the volume-based pore size distribution of the anode. X1 is the anode of the example, and Y1 is the anode of the comparative example.

[0012] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit.

[0013] This disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0014] An electrolytic capacitor according to one embodiment of the present disclosure comprises a porous anode body, anode leads partially embedded in the anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer.

[0015] Hereinafter, the anode body, anode lead, dielectric layer, and cathode portion may be collectively referred to as a "capacitor element." The anode body and anode lead may be collectively referred to as the "anode portion." There are no particular limitations on the configuration of the cathode portion; it may be a known cathode portion or a cathode portion having a similar configuration.

[0016] The anode body is a sintered body of particles containing valve-acting metal elements (hereinafter also referred to as "valve-acting metal particles"). The valve-acting metal particles consist of first particles and second particles. The particle diameter of the first particle is less than 150 μm, and the particle diameter of the second particle is 150 μm or more. The average circularity C2 of the second particle is greater than the average circularity C1 of the first particle. The difference between the average circularity C1 of the first particle and the average circularity C2 of the second particle, C2-C1, is 0.05 or more. Here, particle diameter refers to the diameter of a circle having the same area as the projected area of ​​the particle (equivalent circle diameter). The circularity of the particle is 4πS / L. ２ It can be calculated using the following formula. In the formula, S represents the area of ​​the projected image of the particle, and L represents the perimeter of the projected image.

[0017] Hereinafter, a first particle with a particle diameter of less than 150 μm and an average circularity C1 that is 0.05 or more smaller than the average circularity C2 of the second particle may be referred to as a "small particle." A second particle with a particle diameter of 150 μm or more and an average circularity C2 that is 0.05 or more larger than the average circularity C1 of the first particle may be referred to as a "large particle."

[0018] The porous anode body is a sintered body containing the large and small particles described above, and is formed by molding a particle mixture containing the large and small particles and sintering the molded body. The large particles are highly circular and relatively uniform in shape. In the anode body containing the large particles described above, the large particles are densely arranged, and relatively large pores formed by the large particles are uniformly distributed within the anode body. In such an anode body, the cathode (conductive polymer) can easily penetrate deep into the anode body, and the cathode (conductive polymer) can easily fill the pores throughout the anode body uniformly. Therefore, the ESR of the electrolytic capacitor can be sufficiently reduced, and the draw capacitance to the formed dielectric layer can be maximized.

[0019] Furthermore, because small particles have a lower degree of circularity and a smaller particle size than large particles, they can contribute to increasing the specific surface area of ​​the anode. As a result, the capacitance of the electrolytic capacitor can be sufficiently increased.

[0020] The volume-based pore size distribution (Log differential pore volume) of the anode body described above has a first peak and a second peak. The pore size of the second peak is larger than the pore size of the first peak. Two distinct peaks are formed in the above pore size distribution (Log differential pore volume). The first peak may be formed, for example, in the range where the pore size is 1 μm or less (or 0.5 μm or less). The above pore size distribution may have, for example, a first peak in the range where the pore size is 0.5 μm or less, and a second peak in the range where the pore size is greater than 0.5 μm.

[0021] The first peak is mainly due to small particles, while the second peak is due to pores (gaps) formed between particles by increasing the circularity of the large particles compared to the small particle size. From the viewpoint of ensuring a sufficiently large capacitance, it is desirable for the first peak to be sufficiently large. On the other hand, the presence of the second peak means that relatively large pores, which are advantageous for reducing ESR, are sufficiently formed inside the anode. From the viewpoint of achieving a sufficiently small ESR, it is desirable for the second peak to be sufficiently large.

[0022] The volume-based pore size distribution of an anode with a dielectric layer shifts toward smaller pore sizes compared to the volume-based pore size distribution of the anode before the dielectric layer is formed. However, since the thickness of the dielectric layer is on the order of nanometers, the amount of shift is small. Therefore, the volume-based pore size distribution of the anode does not change significantly before and after the formation of the dielectric layer. Thus, if the volume-based pore size distribution of an anode with a dielectric layer has a first peak in the range of small pore sizes and a second peak in the range of pore sizes larger than the first peak, then the volume-based pore size distribution of the anode before the dielectric layer is formed also has a first peak in the range of small pore sizes and a second peak in the range of pore sizes larger than the first peak. Conversely, if the volume-based pore size distribution of the anode body before the dielectric layer is formed has a first peak in the range of small pore sizes and a second peak in the range of pore sizes larger than the first peak, then the volume-based pore size distribution of the anode body with the dielectric layer will also have a first peak in the range of small pore sizes and a second peak in the range of pore sizes larger than the first peak. The range of small pore sizes mentioned above is, for example, the range where the pore size is 5 μm or less. The range where the pore size is larger than the first peak mentioned above is, for example, the range where the pore size is greater than 5 μm.

[0023] From the viewpoint of ensuring a sufficiently large capacitance, it is desirable that the height of the first peak be greater than the height of the second peak. By ensuring that the height of the first peak is sufficiently larger than the height of the second peak, it becomes possible to achieve a sufficiently small ESR while ensuring a sufficiently large capacitance. The height of the first peak may be, for example, 1.5 times or more, or 1.8 times or more, the height of the second peak.

[0024] The particle size D1 of the first particle may be, for example, 30 μm or more and less than 150 μm, or 50 μm or more and less than 150 μm. The particle size D2 of the second particle may be, for example, 150 μm or more and 250 μm or less, or 150 μm or more and 200 μm or less.

[0025] When the difference between the average circularity C1 of the first particle and the average circularity C2 of the second particle, C2-C1, is 0.05 or greater, the effects of both the first and second particles are sufficiently obtained. From the viewpoint of easily forming the first and second peaks, C2-C1 may be 0.1 or greater, or 0.2 or greater. From a similar viewpoint, the ratio of the average circularity C2 of the second particle to the average circularity C1 of the first particle, C2 / C1, may be, for example, 1.1 or greater, 1.2 or greater, or 1.5 or greater.

[0026] From the viewpoint of easily forming relatively large pores uniformly inside the anode and easily forming a second peak in the pore size distribution, the average circularity C2 of the second particle is preferably 0.4 or higher, more preferably 0.45 or higher or 0.5 or higher. Furthermore, the average circularity C2 of the second particle may be less than 1, or 0.9 or lower or 0.8 or lower.

[0027] The average circularity C1 of the first particle is smaller than the average circularity C2 of the second particle. The average circularity C1 of the first particle may be, for example, 0.4 or less, or 0.35 or less. Also, the average circularity C1 of the first particle may be 0.3 or more.

[0028] By using the first and second particles described above, a sharp first peak is easily formed in the volume-based pore size distribution of the anode body in the range where the pore size is 0.5 μm or less, and a clear second peak is easily formed in the range where the pore size is greater than 0.5 μm.

[0029] The average circularity C1 of the first particle and the average circularity C2 of the second particle can be determined by the following method. First, a cross-section of the anode body is formed before or after the formation of the dielectric layer, and the cross-section is treated with polishing and a cross polisher. Then, the treated cross-section is observed with a scanning electron microscope (SEM) and a cross-sectional image of the anode body is taken. The cross-sectional image is analyzed using image analysis type particle size distribution measurement software (for example, MAC-View from Mountec Co., Ltd.), the contours of 150 to 200 particles are identified, the area enclosed by the contours is determined as the area of ​​the particle, and the length of the contours is determined as the perimeter of the particle.

[0030] The particle diameter is determined by finding the diameter of a circle with the same area as the particle (equivalent diameter). The circularity of the particle is then calculated using the area and perimeter of the particle according to the following formula. A circularity of 1 indicates a perfect circle.

[0031] Circularity = (4π × area of ​​particle) / (perimeter of particle) ２

[0032] Particles with a diameter of 150 μm or more are designated as the first particle, and the average value C1 of the circularity of the first particle is calculated. Particles with a diameter of less than 150 μm are designated as the second particle, and the average value C2 of the circularity of the second particle is calculated.

[0033] The volume-based pore size distribution (Log differential pore volume) of the anode body before or after the formation of the dielectric layer can be measured, if necessary, by separating the cathode portion from the anode body and using, for example, a mercury intrusion porosimeter (e.g., AutoPore V from Micromeritics). The method for separating the cathode portion from the anode body is not particularly limited, but for example, the cathode portion (e.g., a solid electrolyte layer) can be removed from the anode body using fuming nitric acid.

[0034] In the volume-based pore size distribution of the anode (Log differential pore volume), the pore size d1 corresponding to the first peak is smaller than the pore size d2 corresponding to the second peak. The difference between the pore size d1 corresponding to the first peak and the pore size d2 corresponding to the second peak may be, for example, 0.45 μm or more, or 0.5 μm or more. The pore size d1 may be 0.45 μm or less, or 0.4 μm or less. The pore size d2 may be 0.7 μm or more, or 0.8 μm or more.

[0035] To achieve high capacitance and low ESR by giving the anode body having a dielectric layer sufficient height first and second peaks, it is desirable to include first and second particles in a balanced manner. Specifically, in the cross-section of the anode body, it is preferable that the total area S2 of the second particles is larger than the total area S1 of the first particles. That is, it is preferable that the total area S1 of the first particles is smaller than the total area S2 of the second particles. In the cross-section of the anode body, the ratio of the total area S1 of the first particles to the total area (S1 + S2) of the first and second particles may be, for example, 15% or more, or 20% or more. Also, the ratio of the total area S1 of the first particles may be, for example, 40% or less, or 30% or less. When the ratio of the total area S1 of the first particles is 15% or more (or 20% or more), it is easier to secure a sufficient specific surface area of ​​the anode body. When the proportion of the total area S1 of the first particles is 40% or less (or 30% or less), the presence of a sufficient number of second particles with a greater average circularity than the first particles makes it easier for relatively large pores to be uniformly formed throughout the anode body.

[0036] The ratio of the total area of ​​the first particle to the total area of ​​the second particle can be determined, for example, by the following method: First, the first and second particles are identified within the observation field to be measured using the method described above. Next, the total area of ​​the first particle, S1, is determined, and the total area of ​​the second particle, S2, is determined. The ratio of the total area of ​​the first particle is then calculated by S1 / (S1+S2) × 100. The number of observation fields to be measured should be five or more. The size of each observation field should be 0.01 mm. ２ This concludes the process. Calculate the average value of the proportion of the total area of ​​the first particle obtained in all observation fields.

[0037] (Anode) A porous anode is a sintered body of particles containing valve-acting metal elements and is made of metal. The anode is formed by shaping particles containing valve-acting metal elements into a predetermined shape (e.g., a rectangular parallelepiped) and sintering the shaped body. Examples of material particles include metal particles, alloy particles, and metal compound particles. These particles may be used individually or as a mixture of two or more types. The particles containing valve-acting metal elements (first particles, second particles) usually form secondary particles. The formation of secondary particles can increase the specific surface area of ​​the anode.

[0038] Examples of valve-acting metallic elements include aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), and hafnium (Hf). These may be used individually or in combination of two or more. In particular, it is desirable to use at least one of Ta and Nb.

[0039] The particles containing the valve-acting metal element include first particles and second particles. The first and second particles may contain different valve-acting metal elements, but from the viewpoint of stable characteristics of the electrolytic capacitor, production process, and production management, it is preferable that the first and second particles contain a common valve-acting metal element.

[0040] (Method for manufacturing an anode) An anode is obtained by molding a particle mixture containing first particles and second particles into a predetermined shape and sintering the molded body. That is, the method for manufacturing an anode includes a particle mixture preparation step, a molding step, and a sintering step.

[0041] (Process for preparing particle mixtures) Particle mixtures can be prepared, for example, by the following method. Here, Figure 1 is a flowchart illustrating the process for preparing mixed powders. In Figure 1, a1 shows the particles that passed through the sieve in the first classification process. a2 shows the particles that passed through the sieve in the second classification process. b1 shows the particles that remained on the sieve in the first classification process. b2 shows the particles that remained on the sieve in the second classification process.

[0042] Raw material particles of a valve-action metal element are prepared (S1). The average circularity of the raw material particles is, for example, in the range of 0.2 or more and 0.4 or less. The raw material particles are usually secondary particles. The secondary particles may be formed, for example, by heating and agglomerating primary particles. First, a first classification process is performed on the raw material particles using a sieve with a predetermined opening (S2). The size of the sieve opening may be appropriately determined, for example, from the range of 100 µm or more and 160 µm or less. It is preferable to use a sieve with an opening of 150 µm because it facilitates adjusting the balance between first particles and second particles. When the opening is 150 µm, particles having a particle diameter of less than 150 µm pass through the sieve.

[0043] Next, for particles b1 remaining on the sieve, a second classification process is performed while applying vibration using a sieve shaker (S3). For the sieve shaker, for example, AS200 manufactured by Retsch can be used. The sieve used in the second classification process may have the same opening size as the sieve used in the first classification process, or may have a slightly smaller opening size than the sieve used in the first classification process.

[0044] Through the second classification process (processing by a vibrating sieve), the particles b1 remaining on the sieve gradually have their corners removed and become rounded, resulting in particles b2 with high circularity. A particle mixture is obtained by mixing the particles b2, particles a1 that passed through the sieve in the first classification process, and particles a2 that passed through the sieve in the second classification process (S4).

[0045] When the opening of the sieve used in the first classification process and the second classification process is 150 µm, substantially all of the particles b2 can be obtained as second particles, making it easy to adjust the average circularity C2 of the second particles. Further, in this case, substantially all of the particles a1 and a2 can be obtained as first particles, making it easy to adjust the average circularity C1 of the first particles.

[0046] For example, in the second classification process using a sieve shaker, the circularity of the particles b2 (the average circularity C2 of the second particles) can be adjusted by the shaking width, shaking time, and the like.

[0047] The proportion of the second particle in the particle mixture may be, for example, 30% by mass or more, or 40% by mass or more. Alternatively, the proportion of the second particle in the particle mixture may be 50% by mass or less. When the proportion of the second particle is 30% by mass or more (or 40% by mass or more), the second particle is sufficiently present, making it easier for relatively large pores to be uniformly formed throughout the anode and for a clear peak to be formed. When the proportion of the second particle is 50% by mass or less, the first particle is sufficiently present, making it easier for a sharp first peak to be formed and for a sufficient specific surface area of ​​the anode to be secured.

[0048] (Molding and Sintering Process) Next, the particle mixture is molded into a predetermined shape to obtain a molded body. The shape of the molded body is selected according to the shape of the anode. For example, the molded body may be produced by filling a predetermined mold with the particle mixture and press-molding it. In this case, other components (such as binders) may be added to the particle mixture to improve the packability of the particle mixture into the mold. The shape of the anode is not particularly limited, but for example, it may have a pair of opposing main surfaces and sides that intersect the pair of main surfaces. For example, a portion of the anode lead is embedded in the particle mixture, and the particle mixture is press-molded into a columnar or rectangular parallelepiped shape. Then, the obtained molded body is sintered to form an anode body in which a portion of the anode lead is embedded.

[0049] (Anode Lead) The anode lead is made of metal. A portion of the anode lead is embedded in the anode body, and the remaining portion protrudes from the anode body. In other words, the anode lead has an embedded portion that is embedded in the anode body and a protruding portion that extends to the outside of the anode body.

[0050] (Dielectric layer) The dielectric layer formed on the surface of the anode is not particularly limited and may be formed by known methods. For example, the dielectric layer is formed by subjecting the anode to a chemical conversion (anodic oxidation) treatment and growing an oxide film on the surface of the anode. The chemical conversion treatment may be performed by immersing the anode in a chemical conversion solution and anodizing the surface of the anode. Alternatively, a vapor phase method such as atomic layer deposition (ALD) may be used, or the surface of the anode may be oxidized by heating it in an oxygen-containing atmosphere.

[0051] (Cathode portion) The cathode portion covers at least a part of the dielectric layer. A capacitor element can be obtained by forming the cathode portion. The cathode portion includes, for example, an electrolyte in contact with the dielectric layer. The electrolyte may be a solid electrolyte or a liquid electrolyte. The cathode portion may include, for example, a solid electrolyte layer covering at least a part of the dielectric layer, or a cathode layer covering at least a part of the solid electrolyte layer.

[0052] There are no particular limitations on the solid electrolyte layer, and solid electrolytes used in known electrolytic capacitors may be applied. The solid electrolyte layer may be a laminate of two or more different solid electrolyte layers. The solid electrolyte layer is arranged to cover at least a portion of the dielectric layer. The solid electrolyte layer may be formed using manganese compounds or conductive polymers.

[0053] Conductive polymers may be π-conjugated polymers, and examples of conductive polymers include polypyrrole, polythiophene, polyaniline, and their derivatives. These may be used individually or in combination. Conductive polymers may also be copolymers of two or more monomers. A derivative of a conductive polymer refers to a polymer that uses a conductive polymer as its basic skeleton. For example, an example of a derivative of polythiophene is poly(3,4-ethylenedioxythiophene).

[0054] It is preferable that a dopant is added to the conductive polymer. The dopant can be selected according to the conductive polymer, and known dopants may be used. Examples of dopants include naphthalene sulfonic acid, p-toluenesulfonic acid, polystyrene sulfonic acid, and salts thereof. An example of a solid electrolyte layer is formed using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS).

[0055] A solid electrolyte layer containing a conductive polymer is formed on at least a portion of the dielectric layer by impregnating the dielectric layer with monomers or oligomers, and then polymerizing the monomers or oligomers by chemical polymerization or electrolytic polymerization, or by impregnating the anode body on which the dielectric layer is formed with a solution or dispersion of a conductive polymer (and dopant if necessary) and drying it.

[0056] The cathode layer may be a conductive layer formed on a solid electrolyte layer, for example, a conductive layer formed to cover the solid electrolyte 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.

[0057] (Other) An electrolytic capacitor may have a first terminal (anode terminal) electrically connected to the anode portion (specifically, the anode lead) of the capacitor element, and a second terminal (cathode terminal) electrically connected to the cathode portion. The electrolytic capacitor may include an outer resin enclosure arranged around the capacitor element. Parts of the first and second terminals extend outside the outer resin enclosure. The second terminal has a connection surface with the cathode portion. The connection surface is connected to the cathode portion, for example, via a conductive member.

[0058] There are no particular limitations on the shape, size, etc., of the capacitor element; it may be a known capacitor element or a capacitor element having a similar configuration.

[0059] Next, we will explain in more detail with reference to the drawings, but the following examples are not limiting to the present invention. The diagrams shown below are schematic and do not accurately reflect the actual shape, dimensions, number, etc. of the components.

[0060] Figure 2 is a schematic cross-sectional view of an example of an electrolytic capacitor according to the present disclosure. The electrolytic capacitor 20 includes a capacitor element 10 having an anode portion 6 and a cathode portion 7, an outer resin 11 that seals the capacitor element 10, a first terminal 13 electrically connected to the anode portion 6 and partially exposed from the outer resin 11, and a second terminal 14 electrically connected to the cathode portion 7 and partially exposed from the outer resin 11. The anode portion 6 has an anode body 1 and an anode lead 2. The anode lead 2 has an embedded portion 2a embedded in the anode body 1 and a protruding portion 2b that protrudes to the outside of the anode body 1. The first terminal 13 is joined to the protruding portion 2b of the anode lead 2. The connection surface 14a of the second terminal 14, which is located inside the outer resin 11, is joined to the cathode layer 5 via a conductive member 8.

[0061] A dielectric layer 3 is formed on the surface of the anode 1. The cathode 7 has a solid electrolyte layer 4 that covers at least a part of the dielectric layer 3, and a cathode layer 5 that covers the surface of the solid electrolyte layer 4. The cathode layer 5 has a carbon layer 5a formed to cover the solid electrolyte layer 4, and a metal paste layer 5b formed on the surface of the carbon layer 5a. The carbon layer 5a contains a conductive carbon material such as graphite and a resin. The metal paste layer 5b contains, for example, metal particles (e.g., silver) and a resin. However, the configuration of the cathode layer 5 is not limited to this configuration. The configuration of the cathode layer 5 is acceptable as long as it has a current collection function.

[0062] The outer resin is positioned around the capacitor element so that the capacitor element is not exposed on the surface of the electrolytic capacitor. Furthermore, the outer resin insulates the first terminal and the second terminal. A known outer resin used for electrolytic capacitors may be used for the outer resin. For example, the outer resin may be formed using an insulating resin material used for sealing capacitor elements. The outer resin may also be formed by housing the capacitor element in a mold and introducing an uncured thermosetting resin and filler into the mold by a transfer molding method, compression molding method, or the like, and then curing it.

[0063] The first terminal is an anode terminal electrically connected to the anode portion (specifically, the anode lead) of the capacitor element. A portion of the first terminal is exposed from the outer resin and used as an external anode terminal. The first terminal may be formed, for example, by processing a metal sheet (including metal plates and metal foils) made of a metal (copper, copper alloy, etc.) using a known metalworking method.

[0064] The second terminal is a cathode terminal electrically connected to the cathode portion of the capacitor element. A portion of the second terminal is exposed from the outer resin and used as an external cathode terminal. The second terminal may be formed, for example, by processing a metal sheet (including metal plates and metal foils) made of a metal (copper, copper alloy, etc.) using a known metalworking method.

[0065] (Note) The following technologies are disclosed by the above description. (Technology 1) An electrolytic capacitor comprising: a porous anode body; an anode lead partially embedded in the anode body; a dielectric layer formed on the surface of the anode body; and a cathode portion covering at least a part of the dielectric layer, wherein the anode body is a sintered body of particles containing a valve-acting metal element, the valve-acting metal particles include first particles and second particles, the particle diameter of the first particles is less than 150 μm, the particle diameter of the second particles is 150 μm or more, the average circularity C2 of the second particles is greater than the average circularity C1 of the first particles, and the difference between the average circularity C1 of the first particles and the average circularity C2 of the second particles: C2-C1 is 0.05 or more. (Technology 2) The electrolytic capacitor according to Technology 1, wherein the difference between the average circularity C1 of the first particles and the average circularity C2 of the second particles: C2-C1 is 0.1 or more. (Technology 3) An electrolytic capacitor according to Technology 1 or 2, wherein the average circularity C2 of the second particle is 0.4 or greater. (Technology 4) An electrolytic capacitor according to any one of Technology 1 to 3, wherein the volume-based pore size distribution of the anode body having the dielectric layer has a first peak and a second peak, and the pore size of the second peak is greater than the pore size of the first peak. (Technology 5) An electrolytic capacitor according to Technology 4, wherein the pore size distribution has the first peak in the range where the pore size is 0.5 μm or less, and the second peak in the range where the pore size is greater than 0.5 μm. (Technology 6) An electrolytic capacitor according to any one of Technology 1 to 5, wherein the first particle and the second particle contain a common valve-acting metal element. (Technology 7) An electrolytic capacitor according to any one of Technology 1 to 6, wherein in the cross-section of the anode body, the total area of ​​the first particle is smaller than the total area of ​​the second particle.

[0066] The present disclosure will be described in detail below based on examples, but the present disclosure is not limited to the following examples.

[0067] 《Electrolytic Capacitor X1》 An electrolytic capacitor as shown in Figure 2 was fabricated according to the following procedure.

[0068] (Preparation of particle mixture) Ta particles were prepared as raw material particles. The raw material particles were subjected to a first classification treatment using a sieve (mesh size: 150 μm) to separate them into particles a1 with a particle diameter of less than 150 μm and particles b1 with a particle diameter of 150 μm or more. The particles b1 were subjected to a second classification treatment using a sieve shaker (mesh size: 150 μm) to separate them into particles a2 with a particle diameter of less than 150 μm and particles b2 with a particle diameter of 150 μm or more. Due to the shaking treatment, the average circularity of particles b2 was greater than that of particles b1.

[0069] In this way, particle b2 was obtained as the second particle. Particles a1 and a2 were recovered to obtain the first particle. Particles a1 and a2 (first particles) and particle b2 (second particle) were mixed to obtain a particle mixture. The average circularity C1 of the first particle was 0.35, and the average circularity C2 of the second particle was 0.50. C2 / C1 was 1.42, and C2-C1 was 0.15. The proportion of the second particle (particle b2) in the particle mixture was 42% by mass.

[0070] (Fabrication of the anode) A Ta wire was used as the anode wire. The particle mixture was formed into a rectangular parallelepiped with one end of the Ta wire embedded in it, and then the molded body was sintered in a vacuum to obtain a sintered Ta body (anode). In this way, a porous anode body X1 (anode portion) in which a portion of the Ta wire was embedded was obtained.

[0071] In the cross-section of the anode X1, the total area S1 of the first particles was smaller than the total area S2 of the second particles. The ratio of the total area S1 of the first particles to the total area (S1 + S2) of the first and second particles was 40% or less.

[0072] (Formation of Dielectric Layer) The anode and a portion of the wire were immersed in a conversion tank filled with an electrolytic aqueous solution of phosphoric acid, and anodizing was performed to form a uniform oxide film as a dielectric layer on the surface of the anode and the surface of a portion of the wire. Anodizing was performed in a 0.1 mass% phosphoric acid aqueous solution at a conversion voltage of 10 V.

[0073] (Formation of Solid Electrolyte Layer) Next, a polymerization solution was prepared by mixing 3,4-ethylenedioxythiophene (monomer), p-iron(III) toluenesulfonate, and 1-butanol. An anode having a dielectric layer was immersed in this polymerization solution, and then the anode was removed from the polymerization solution and heat-treated in the air. In this case, p-iron(III) toluenesulfonate functions as an oxidizing agent and a dopant. In this way, the monomer was polymerized on the dielectric layer, and a first conductive polymer containing poly(3,4-ethylenedioxythiophene) (PEDOT) was produced by chemical polymerization.

[0074] Next, the anode body on which the conductive polymer was formed 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 sulfonic acid (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 having a solid electrolyte layer containing the first and second conductive polymers was obtained.

[0075] (Formation of carbon layer) After applying a dispersion of carbon particles (carbon paste) to the solid electrolyte layer, a carbon layer (approximately 3 μm thick) was formed on the surface of the solid electrolyte layer by heating at 200°C.

[0076] (Formation of metal paste layer) A metal paste containing silver particles, binder resin, and solvent was applied to the surface of the carbon layer. Then, it was heated at 200°C to form a metal paste layer (10 μm thick) and obtain a capacitor element.

[0077] (Fabrication of electrolytic capacitors) A conductive adhesive, which will serve as a conductive component, was applied to a metal paste layer, and the cathode lead terminals were joined to the metal paste layer. The anode wire and anode lead terminals were joined by resistance welding. Next, the capacitor elements with each lead terminal joined were sealed with an outer resin using a transfer molding method to fabricate an electrolytic capacitor.

[0078] 《Electrolytic Capacitor Y1》 Anode Y1 was obtained in the same manner as anode X1, except that the raw material particles were used as they were without classification treatment instead of a particle mixture. Electrolytic capacitor Y1 was manufactured in the same manner as electrolytic capacitor X1, except that anode Y1 was used instead of anode X1.

[0079] When the raw material particles were subjected to a first-stage classification process using a sieve (mesh opening: 150 μm), they were separated into particles a1 with a particle diameter of less than 150 μm and particles b1 with a particle diameter of 150 μm or more. The average circularity of particles a1 was 0.35, and the average circularity of particles b1 was 0.38.

[0080] [Evaluation: Initial ESR] For each electrolytic capacitor fabricated as described above, the initial capacitance and the initial ESR (mΩ) at a frequency of 100 kHz were measured using a four-terminal LCR meter in an environment of 20°C.

[0081] The evaluation results are shown in Table 1. In the table, the electrolytic capacitor X1 equipped with anode X1 is an example, and the electrolytic capacitor Y1 equipped with anode Y1 is a comparative example. The ESR in the table is a relative value when the ESR of electrolytic capacitor Y1 is set to 100. The capacitance in the table is a relative value when the capacitance of electrolytic capacitor Y1 is set to 100.

[0082]

[0083] Here, Figure 3 shows the volume-based pore size distribution (Log differential pore volume) of anodes X1 and Y1. It was confirmed that anode X1 has a sharp first peak P1 in the range of pore size 0.5 μm or less, and a clear second peak P2 in the range of pore size greater than 0.5 μm. The pore size d1 of the first peak P1 was 0.37 μm, and the pore size d2 of the second peak P2 was 1.45 μm, and the height of the first peak P1 was 1.4 times the height of the second peak P2.

[0084] In anode X1, the second peak P2 was observed in the pore size distribution shown in Figure 3, and the ESR was significantly reduced in electrolytic capacitor X1 compared to electrolytic capacitor Y1. Furthermore, in anode X1, the first peak P1 was observed in the pore size distribution shown in Figure 3, and good capacitance was obtained in electrolytic capacitor X1.

[0085] This disclosure can be used in electrolytic capacitors that have a porous anode.

[0086] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0087] 20: Electrolytic capacitor, 10: Capacitor element, 1: Anode body, 2: Anode wire, 2a: Embedded part, 2b: Protruding part, 3: Dielectric layer, 4: Solid electrolyte layer, 5: Cathode layer, 6: Anode part, 7: Cathode part, 8: Conductive member, 11: Outer resin, 13: First terminal, 14: Second terminal, 14a: Connection surface

Claims

1. An electrolytic capacitor comprising: a porous anode body; an anode lead partially embedded in the anode body; a dielectric layer formed on the surface of the anode body; and a cathode portion covering at least a portion of the dielectric layer, wherein the anode body is a sintered body of particles containing a valve-acting metal element, the particles include first particles and second particles, the particle diameter of the first particles is less than 150 μm, the particle diameter of the second particles is 150 μm or more, the average circularity C2 of the second particles is greater than the average circularity C1 of the first particles, and the difference between the average circularity C1 of the first particles and the average circularity C2 of the second particles: C2 - C1 is 0.05 or more.

2. The difference between the average circularity C1 of the first particle and the average circularity C2 of the second particle: C2-C1 is 0.1 or greater, the electrolytic capacitor according to claim 1.

3. The electrolytic capacitor according to claim 1, wherein the average circularity C2 of the second particle is 0.4 or greater.

4. The electrolytic capacitor according to claim 1, wherein the volume-based pore size distribution of the anode body having the dielectric layer has a first peak and a second peak, and the pore size of the second peak is larger than the pore size of the first peak.

5. The electrolytic capacitor according to claim 4, wherein the pore size distribution has the first peak in the range where the pore size is 0.5 μm or less, and the second peak in the range where the pore size is greater than 0.5 μm.

6. The electrolytic capacitor according to claim 1, wherein the first particle and the second particle contain a common valve-acting metal element.

7. The electrolytic capacitor according to claim 1, wherein in the cross-section of the anode, the total area of ​​the first particles is smaller than the total area of ​​the second particles.

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