Electrolytic capacitor

Abstract

The disclosed electrolytic capacitor comprises a layered element. The layered element includes: a plurality of positive electrode foils 23, each of which includes a metal portion 25 and an oxide film 26 that is formed on the surface of the metal portion 25; a plurality of negative electrode foils; and a separator that is interposed between the positive electrode foil 23 and the negative electrode foil. A portion of each positive electrode foil 23 is a joint portion 24a, the joint portions 24a being joined to each other by joining the metal portions 25 to each other. The ratio of the oxide film 26 to the metal portion 25 is lower in the joint portions 24a of the positive electrode foils 23 than in the remaining portions of the positive electrode foils 23. This makes it possible to reduce ESR.

Description

electrolytic capacitor

[0001] The present disclosure relates to electrolytic capacitors.

[0002] Conventionally, there has been known a multilayer electrolytic capacitor having a multilayer element formed by stacking a plurality of electrode foils (for example, see Patent Document 1). The method of manufacturing an electrolytic capacitor in Patent Document 1 includes the steps of placing metal foils for electrical connection on the multilayer element, piercing the metal foils with needles so as to penetrate the metal foils, and placing lead frames at the positions of the through holes formed thereby and performing resistance welding to connect the electrode foils to the lead frames.

[0003] Patent No. 5854510

[0004] In recent years, there has been a demand for further reduction in equivalent series resistance (ESR) in multilayer electrolytic capacitors. In this situation, one of the objects of the present disclosure is to reduce ESR.

[0005] One aspect of the present disclosure relates to an electrolytic capacitor including a laminated element having a plurality of anode foils, each of which includes a metal portion and an oxide film formed on a surface of the metal portion, a plurality of cathode foils, and a separator interposed between the anode foils, wherein a portion of each anode foil is a joint portion where the metal portions are joined together, and the ratio of the oxide film to the metal portion at the joint portion of the anode foil is smaller than that at the remainder of the anode foil.

[0006] Another aspect of the present disclosure relates to an electrolytic capacitor including an anode foil including a metal portion and an oxide film formed on a surface of the metal portion, and an anode lead connected to the anode foil, wherein a portion of the anode foil is a joint portion that is joined to the anode lead via the metal portion, and the joint portion of the anode foil has a smaller ratio of the oxide film to the metal portion than the remainder of the anode foil.

[0007] According to the present disclosure, the ESR can be reduced.

[0008] 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 application, will be better understood from the following detailed description taken in conjunction with the drawings.

[0009] Fig. 2 is a cross-sectional view conceptually showing an example of the configuration of a multilayer element according to the present disclosure. Fig. 3 is a plan view of the multilayer element of Fig. 1. Fig. 4 is a plan view of an electrolytic capacitor including the multilayer element of Fig. 2. Fig. 5 is a cross-sectional view conceptually showing a first anodic bonding portion and its periphery, with an anode shared lead omitted. Fig. 6 is an enlarged cross-sectional view schematically showing the first anodic bonding portion.

[0010] The following describes an example of an embodiment of an electrolytic capacitor according to the present disclosure. However, the present disclosure is not limited to the example described below. While the following description may use specific numerical values ​​and materials, other numerical values ​​and materials may be used as long as the effects of the present disclosure are obtained.

[0011] An electrolytic capacitor according to one embodiment of the present disclosure (hereinafter also referred to as electrolytic capacitor A) includes a laminate. The laminate has a plurality of anode foils, a plurality of cathode foils, and a separator. The anode foils and the cathode foils may be alternately laminated with separators sandwiched between them. Note that "electrolytic capacitor" may be read as "solid electrolytic capacitor" or "solid-liquid hybrid electrolytic capacitor," and "capacitor" may be read as "capacitor."

[0012] Each of the anode foils includes a metal portion and an oxide film formed on the surface of the metal portion. The anode foil may be formed in a sheet shape. The oxide film may be composed of an oxide of a metal that constitutes the metal portion. The oxide film may constitute a dielectric layer. At least a portion of the oxide film (dielectric layer) may be covered with a solid electrolyte.

[0013] The material of the metal portion may be, for example, a valve metal, or an alloy or compound containing a valve metal, such as aluminum, tantalum, or niobium.

[0014] The oxide film (dielectric layer) may be formed, for example, by immersing a foil made of a metal portion in a chemical conversion solution such as an ammonium adipate solution and subjecting the foil to a chemical conversion treatment while applying a voltage as necessary.

[0015] The solid electrolyte includes, for example, a manganese compound or a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. A solid electrolyte containing a conductive polymer can be formed, for example, by chemical polymerization and / or electrolytic polymerization of raw material monomers on a dielectric layer. Alternatively, the solid electrolyte can be formed, for example, by applying a solution in which a conductive polymer is dissolved or a dispersion in which a conductive polymer is dispersed to the dielectric layer.

[0016] Each of the plurality of cathode foils may be made of a metal foil. The metal foil may be made of the valve metal described above. The surface of the cathode foil may be roughened. An oxide film may be formed on the surface of the cathode foil as needed. A conductive layer such as a carbon layer may be formed on the surface of the cathode foil as needed.

[0017] The separator is interposed between the anode foil and the cathode foil. The separator may electrically insulate the anode foil and the cathode foil. The separator may be a nonwoven fabric. The nonwoven fabric may be made of fibers such as cellulose, polyethylene terephthalate, vinylon, and polyamide (aliphatic polyamide, aromatic polyamide, etc.). The separator may be impregnated with a solid electrolyte.

[0018] A part of each anode foil is a joint portion where the metal portions are joined together. The joint portion may be provided in a region of each anode foil that does not overlap with the cathode foil or the separator in the stacking direction of the laminate. The joint portion may be formed by overlapping the regions of each anode foil that do not overlap with the cathode foil or the separator, and joining the regions by, for example, ultrasonic welding or laser welding.

[0019] The ratio of the oxide film to the metal portion at the joint of the anode foil is smaller than that at the remainder of the anode foil. Here, the ratio of the oxide film to the metal portion may be determined directly as the ratio of the area of ​​the oxide film to the area of ​​the metal portion in a cross section of the anode foil passing through the joint, or may be determined indirectly as the content of oxygen atoms per unit volume.

[0020] Such a joint has very low connection resistance because the metal parts are joined together. Furthermore, the ratio of oxide film to metal part at the joint is low, which also contributes to reducing the connection resistance at the joint. Reducing the connection resistance at the joint, i.e., reducing the connection resistance between multiple anode foils, leads to a reduction in the ESR of electrolytic capacitor A.

[0021] At least a portion of the joint may have a layered mixture of metal and oxide films. In this case, the oxide film creates an anchoring effect, which can increase the joint strength between the metal parts. Furthermore, the presence of an oxide film that is weaker than the metal film allows the oxide film to absorb or mitigate vibrations that may be transmitted to the joint. As a result, this configuration can prevent damage to the joint at the joint and ultimately increase the reliability of the electrolytic capacitor A.

[0022] The joint does not need to have a through hole along the stacking direction of the laminated elements. In this case, the strength of the joint can be sufficiently ensured and the metal resistance of the joint can be reduced. Furthermore, while forming a through hole may cause cracks in the anode foil around the through hole, this configuration does not form a through hole, making it less likely for cracks to occur in the anode foil.

[0023] The ratio of the oxide film to the metal portion at the thinnest portion of the joint may be 0% or more and 50% or less. By keeping this ratio within this range, the ESR of electrolytic capacitor A can be sufficiently reduced and sufficient joint strength at the joint can be ensured. This ratio may be 0% or more and 20% or less. The ratio of the oxide film to the metal portion may be a ratio related to the area of ​​each portion in a cross section passing through the joint. This ratio may be calculated, for example, as an average value over the entire bottom of the joint.

[0024] When viewed from the stacking direction of the stacked element, the area of ​​the bottom of the joint is 0.2 mm 2 More than 20 mm 2 By setting the area of ​​the bottom of the joint within this range, the ESR of the electrolytic capacitor A can be sufficiently reduced and the joint strength at the joint can be sufficiently ensured. 2 More than 5 mm 2 The bottom of the joint refers to a region of the joint that is 10 μm or less from the thinnest part toward the opening of the joint in the depth direction of the joint (or the stacking direction of the stacked elements).

[0025] The ratio of the thickness of the thinnest part of the joint to the thickness of the other parts of the anode foil may be 20% or more and 60% or less. The former thickness may be the sum of the thickness of the metal part and the thickness of the oxide film, or may be calculated as, for example, the average thickness of any five points on the other parts of the anode foil. By keeping this ratio within this range, the connection resistance between multiple anode foils can be further reduced.

[0026] An electrolytic capacitor according to another embodiment of the present disclosure (hereinafter also referred to as electrolytic capacitor B) includes an anode foil and an anode lead.

[0027] The anode foil may be the same as the anode foil of electrolytic capacitor A.

[0028] The anode lead is connected to the anode foil. The anode lead may be electrically and mechanically connected to the anode foil. The anode lead may be made of a metal (e.g., copper or a copper alloy). The anode lead may serve as an external terminal of the electrolytic capacitor B.

[0029] A part of the anode foil is a joint portion that is joined to the anode lead via a metal portion. The joint portion may be formed by overlapping a predetermined region of the anode foil with the anode lead and joining the region by, for example, ultrasonic welding or laser welding.

[0030] The ratio of oxide film to metal at the joint of the anode foil is smaller than that at the rest of the anode foil. Because this joint is connected to the anode lead via the metal, the connection resistance is very low. Furthermore, the ratio of oxide film to metal at the joint is small, which also contributes to reducing the connection resistance at the joint. Reducing the connection resistance at the joint, i.e., reducing the connection resistance between multiple anode foils, leads to a reduction in the ESR of electrolytic capacitor B.

[0031] An oxide film may be formed on the surface of the anode lead. When ultrasonic bonding is used to form the joint, the oxide film on the surface of the anode lead can be removed efficiently. That is, if an oxide film is formed on the surface of the anode lead, the connection resistance between the anode lead and the anode foil tends to be high. However, in the joint according to the present disclosure, the proportion of the oxide film is reduced, and therefore the connection resistance between the anode lead and the anode foil can be sufficiently reduced.

[0032] The thickness of the oxide film on the surface of the anode lead may be 1 nm or more, or may be 10 nm or more. Even when the thickness of the oxide film on the surface of the anode lead is 10 nm or more, the proportion of the oxide film is small in the joint according to the present disclosure, so that the connection resistance between the anode lead and the anode foil can be sufficiently reduced.

[0033] At least a portion of the joint may have a layered mixture of the metal portion and the oxide film. In this case, the oxide film provides an anchoring effect, which can increase the bond strength between the anode foil and the anode lead. Furthermore, the presence of the oxide film, which is weaker than the metal portion, allows the oxide film to absorb or mitigate any vibrations that may be transmitted to the joint. As a result, this configuration can prevent damage to the joint at the joint and ultimately increase the reliability of the electrolytic capacitor B.

[0034] The ratio of the oxide film to the metal portion at the thinnest portion of the joint may be 0% or more and 50% or less. By keeping this ratio within this range, the ESR of electrolytic capacitor B can be sufficiently reduced and sufficient joint strength at the joint can be ensured. This ratio may be 0% or more and 20% or less. Note that the ratio of the oxide film to the metal portion may be a ratio related to the respective areas in a cross section passing through the joint.

[0035] As described above, according to the present disclosure, at the joints that join multiple anode foils together, the ESR of the electrolytic capacitor can be reduced by joining metal portions together and reducing the amount of oxide film.

[0036] An example of an electrolytic capacitor according to the present disclosure will be described in detail below with reference to the drawings. The components described above can be applied to the components of the example electrolytic capacitor described below. The components of the example electrolytic capacitor described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above-described embodiment. Of the components of the example electrolytic capacitor described below, components that are not essential to the electrolytic capacitor according to the present disclosure may be omitted. Note that the diagrams shown below are schematic and do not accurately reflect the shapes and numbers of actual components.

[0037] As shown in FIGS. 1 to 3, the electrolytic capacitor 10 of this embodiment includes a multilayer element 20 and a case 40.

[0038] 1, the multilayer element 20 includes a plurality of units 21 connected in parallel to one another. Each unit 21 has a plurality of capacitor elements 22 connected in parallel to one another.

[0039] Each capacitor element 22 includes an anode foil 23, a cathode foil 27, and a separator 29 interposed therebetween. The anode foil 23 and the cathode foil 27 are made of a valve metal or an alloy or compound containing a valve metal. The separator 29 is made of, for example, a nonwoven fabric. The separator 29 is impregnated with a liquid component or an electrolyte solution.

[0040] The anode foil 23 is in the form of a foil or sheet and has a rectangular outer shape. An anode lead portion 24 is provided at one end of the anode foil 23 in the longitudinal direction (the left-right direction in FIG. 1 ). The anode foil 23 has a metal portion 25 (see FIG. 4 ), and the surface of the metal portion 25 is roughened to form a porous portion. An oxide film (dielectric layer) 26 (see FIG. 4 ) is formed on the surface of the porous portion (the surface of the metal portion 25). At least a portion of the oxide film 26 is covered with a solid electrolyte.

[0041] Cathode foil 27 is in the form of a foil or sheet and has a rectangular outer shape. A cathode lead portion 28 is provided at one end of anode foil 23 in the longitudinal direction (the left-right direction in FIG. 1 ). The rest of cathode foil 27, excluding cathode lead portion 28, is in contact with the solid electrolyte.

[0042] In this embodiment, three anode foils 23 and four cathode foils 27 are stacked with separators 29 interposed between them to form one unit 21. Two units 21 are stacked together to form a laminated element 20. Based on the number of anode foils 23, one unit 21 is made up of three capacitor elements 22, and the laminated element 20 is made up of six capacitor elements 22.

[0043] The laminated element 20 further includes a metal anode shared lead 31. In this embodiment, two anode shared leads 31 are provided. The anode extraction portions 24 of the three capacitor elements 22 constituting each unit 21 are stacked and joined together with the anode shared lead 31. This joining can be performed, for example, by ultrasonic bonding. By using ultrasonic bonding, the oxide film 26 can be removed and the metal portions 25 can be joined together at the same time. The joined portions of each anode foil 23 are joint portions 24a joined together by the joining of the metal portions 25. The joint portions 24a and the anode shared lead 31 are joined together to form a first anode joint portion 32. An oxide film (not shown) having a thickness of 10 nm or more may be formed on the surface of the anode shared lead 31. The anode shared lead 31 is an example of an anode lead.

[0044] The ratio of the oxide film 26 to the metal portion 25 in the joint portion 24a of the anode foil 23 is smaller than that in the remainder of the anode foil 23. The ratio of the oxide film 26 to the metal portion 25 in the thinnest part of the joint portion 24a is preferably 0% or more and 50% or less, more preferably 0% or more and 20% or less, and even more preferably 0% or more and 10% or less. When viewed from the stacking direction of the laminated element 20 (the vertical direction in FIG. 1 ), the area of ​​the bottom of the joint portion 24a is 0.2 mm 2 More than 20 mm 2 Preferably, it is 0.7 mm or less. 2 More than 1.7 mm 2 It is more preferable that the ratio of the thickness of the thinnest portion of the joint portion 24a to the thickness of the portions of the anode foil 23 other than the joint portion 24a is 20% or more and 60% or less. The joint portion 24a does not have a through hole along the stacking direction of the laminated element 20.

[0045] As shown in FIG. 5, preferably, at least a portion of the bonded portion 24a (or at least a portion of the first anodic bonded portion 32) includes a mixture of the metal portion 25 and the oxide film 26 in a layered form.

[0046] 1 , the two anode shared leads 31 are overlapped and joined to each other to form a second anode bonding portion 33. When the anode shared lead 31 is in a sheet shape, the second anode bonding portion 33 has a generally flat shape. In addition, the second anode bonding portion 33 is disposed so as not to overlap with the first anode bonding portion 32 in the stacking direction of the multilayer element 20.

[0047] The laminated element 20 further includes a metallic shared cathode lead 34. In this embodiment, two shared cathode leads 34 are provided. The cathode lead portions 28 of the three capacitor elements 22 constituting each unit 21 are stacked and joined together with the shared cathode lead 34. For this joining, ultrasonic joining may be used, for example. The joined portions of each cathode foil 27 and the shared cathode lead 34 constitute a first cathode joining portion 35.

[0048] The two cathode shared leads 34 are overlapped and joined to each other to form a second cathode joint portion 36. When the cathode shared lead 34 is sheet-shaped, the second cathode joint portion 36 has a generally flat shape. In addition, the second cathode joint portion 36 is arranged so as not to overlap with the first cathode joint portion 35 in the stacking direction of the stacked element 20.

[0049] As shown in FIG. 3 , the case 40 houses the multilayer element 20. An anode shared lead 31 extends from one side of the case 40 (the left side in FIG. 3 ). A cathode shared lead 34 extends from another side of the case 40 (the right side in FIG. 3 ). The multilayer element 20 may be housed in the case 40 together with a liquid component or an electrolyte solution. The case 40 may be made of a laminate sheet having a metal barrier layer, but is not limited to this. For example, the case 40 may be made of a metal such as aluminum, stainless steel, copper, iron, or brass, or an alloy thereof.

[0050] <<Supplementary Notes>> The above embodiments disclose the following technologies. (Technology 1) An electrolytic capacitor comprising a laminated element, wherein the laminated element comprises: a plurality of anode foils each including a metal portion and an oxide film formed on the surface of the metal portion; a plurality of cathode foils; and a separator interposed between the anode foil and the cathode foil, wherein a portion of each anode foil is a joint portion where the metal portions are joined to each other by joining the metal portions, and the joint portion of the anode foil has a smaller ratio of the oxide film to the metal portion than the remainder of the anode foil. (Technology 2) An electrolytic capacitor according to Technology 1, wherein the metal portion and the oxide film are mixed in a layered manner in at least a portion of the joint portion. (Technology 3) An electrolytic capacitor according to Technology 1 or 2, wherein the joint portion does not have a through-hole along the stacking direction of the laminated element. (Technology 4) The electrolytic capacitor according to any one of Technologies 1 to 3, wherein the ratio of the oxide film to the metal portion at the thinnest portion of the joint is 0% or more and 50% or less. (Technology 5) The area of ​​the bottom of the joint, as viewed from the stacking direction of the multilayer element, is 0.2 mm 2 More than 20 mm 2The electrolytic capacitor according to any one of Techniques 1 to 4, which is as follows: (Technology 6) The electrolytic capacitor according to any one of Techniques 1 to 5, in which the ratio of the thickness of the thinnest part of the joint to the thickness of the part of the anode foil other than the joint is 20% or more and 60% or less. (Technology 7) An electrolytic capacitor comprising: an anode foil including a metal portion and an oxide film formed on the surface of the metal portion; and an anode lead connected to the anode foil, wherein a part of the anode foil is a joint portion joined to the anode lead via the metal portion, and the joint portion of the anode foil has a smaller ratio of the oxide film to the metal portion than the remainder of the anode foil. (Technology 8) The electrolytic capacitor according to Technique 7, in which an oxide film is formed on the surface of the anode lead. (Technology 9) The electrolytic capacitor according to Technique 8, in which the oxide film on the surface of the anode lead has a thickness of 10 nm or more. (Technology 10) The electrolytic capacitor according to any one of Technologies 7 to 9, wherein the metal portion and the oxide film are mixed in layers in at least a part of the joint. (Technology 11) The electrolytic capacitor according to any one of Technologies 7 to 10, wherein the ratio of the oxide film to the metal portion in the thinnest part of the joint is 0% or more and 50% or less.

[0051] 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.

[0052] The present disclosure can be used for electrolytic capacitors.

[0053] 10: Electrolytic capacitor 20: Laminated element 21: Unit 22: Capacitor element 23: Anode foil 24: Anode lead portion 24a: Joint portion 25: Metal portion 26: Oxide coating 27: Cathode foil 28: Cathode lead portion 29: Separator 31: Anode shared lead (anode lead) 32: First anode bonding portion 33: Second anode bonding portion 34: Cathode shared lead 35: First cathode bonding portion 36: Second cathode bonding portion 40: Case

Claims

1. An electrolytic capacitor comprising: a laminated element comprising: a plurality of anode foils, each of which includes a metal portion and an oxide film formed on a surface of the metal portion; a plurality of cathode foils; and a separator interposed between the anode foils and the cathode foils, wherein a portion of each of the anode foils is a joint portion that is joined to each other by bonding the metal portions, and the joint portion of the anode foil has a smaller ratio of the oxide film to the metal portion than a remainder of the anode foil.

2. The electrolytic capacitor according to claim 1, wherein in at least a portion of the joint, the metal portion and the oxide film are mixed in a layered manner.

3. The electrolytic capacitor according to claim 1 or 2, wherein the joint portion does not have a through hole extending along the stacking direction of the multilayer element.

4. The electrolytic capacitor according to claim 1 or 2, wherein the ratio of said oxide film to said metal portion at the thinnest portion of said joint is 0% or more and 50% or less.

5. When viewed from the stacking direction of the laminated element, the area of ​​the bottom of the joint is 0.2 mm 2 More than 20 mm 2 3. The electrolytic capacitor according to claim 1, wherein:

6. The electrolytic capacitor according to claim 1 or 2, wherein the ratio of the thickness of the thinnest portion of the joint to the thickness of the portion of the anode foil other than the joint is 20% or more and 60% or less.

7. An electrolytic capacitor comprising: an anode foil including a metal portion and an oxide film formed on a surface of the metal portion; and an anode lead connected to the anode foil, wherein a part of the anode foil is a junction that is joined to the anode lead via the metal portion, and the junction of the anode foil has a smaller ratio of the oxide film to the metal portion than a remainder of the anode foil.

8. The electrolytic capacitor according to claim 7, wherein an oxide film is formed on the surface of the anode lead.

9. The electrolytic capacitor according to claim 8, wherein the thickness of the oxide film on the surface of the anode lead is 10 nm or more.

10. The electrolytic capacitor according to any one of claims 7 to 9, wherein in at least a portion of the joint, the metal portion and the oxide film are mixed in a layered manner.

11. The electrolytic capacitor according to any one of claims 7 to 9, wherein the ratio of said oxide film to said metal portion at the thinnest portion of said joint is not less than 0% and not more than 50%.

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