Manufacturing method of electrolytic capacitor

Abstract

To provide a method for manufacturing an electrolytic capacitor having small variation of characteristics.SOLUTION: A manufacturing method to be disclosed includes a process (iii) for oxidizing at least a portion of the surface of an anode body to form a dielectric layer by applying a direct current voltage between a first electrode 210 and a second electrode 220 in a state in which the anode body is immersed in a chemical conversion liquid 202. In the process (iii), at least one selected between a distance between first and second anode bodies 113a and 113b and the second electrode 220, and the area of the second electrode 220 facing the first and second anode bodies 113a and 113b is made different between the first anode body 113a and the second anode boy 113b so as to reduce difference between conversion current flowing to the first anode body 113a existing at an end and conversion current flowing to the second anode body 113b existing on an inner side of the first anode body 113a.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing an electrolytic capacitor. [Background technology]

[0002] An electrolytic capacitor includes an anode body and a dielectric layer formed on the surface of the anode body. In general, the dielectric layer is formed by anodizing the surface of the anode body (chemical conversion treatment).

[0003] Conventionally, various anodization methods have been proposed. For example, Patent Document 1 (JP Patent Publication 2005-327899A) discloses "an anodization apparatus for valve metal elements for solid electrolytic capacitors, which fixes a plurality of valve metal elements for solid electrolytic capacitors to a metal cross bar by the anode lead wires of the elements and applies a direct current between the cross bar and a cathode electrode to perform anodization, the cathode electrode being composed of an electrode parallel to the bottom surface of the elements and an electrode parallel to the side surface, and the cathode electrode being mesh-shaped." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-327899 A Summary of the Invention [Problem to be solved by the invention]

[0005] As a result of the investigation, the inventors of the present application have newly found that the thickness of the dielectric layer formed on each of the multiple anode bodies varies widely in the conventional method. One of the objectives of the present disclosure is to provide a method for manufacturing an electrolytic capacitor with reduced variation in the thickness of the dielectric layer and reduced variation in characteristics. [Means for solving the problem]

[0006] One aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor, the method including the steps of: (i) preparing a plurality of anode parts each including an anode body and an anode wire protruding from a first end face of the anode body; (ii) arranging the plurality of anode bodies at intervals along a predetermined direction to form an anode body group, and connecting the plurality of anode wires connected to the plurality of anode bodies to a first electrode for chemical conversion; and (iii) applying a direct current voltage between the first electrode and a second electrode while the plurality of anode bodies connected to the first electrode via the anode wires are immersed in a chemical conversion solution to oxidize at least a portion of the surface of the anode body to form a dielectric layer, wherein in the step (iii), The second electrode is in contact with the chemical conversion solution and is arranged along the anode body group, and when the anode bodies at the ends of the anode body group are defined as first anode bodies and the anode body located more inward than the first anode bodies is defined as a second anode body, in the step (iii), at least one selected from a distance between the first and second anode bodies and the second electrode and an area of ​​the second electrode facing the first and second anode bodies is made different between the first anode body and the second anode body so that a difference between a chemical conversion current flowing in the first anode body and a chemical conversion current flowing in the second anode body is reduced. Effect of the Invention

[0007] According to the present disclosure, electrolytic capacitors with small variation in characteristics can be manufactured. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view illustrating an example of an electrolytic capacitor manufactured by the manufacturing method of the present disclosure. [Diagram 2] FIG. 2 is a perspective view illustrating an example of an anode part used in the manufacturing method of the present disclosure. [Diagram 3] FIG. 2 is a diagram illustrating an example of a process of the manufacturing method according to the present disclosure. [Figure 4] FIG. 4 is a diagram illustrating an example of a step subsequent to the step in FIG. 3. [Diagram 5]4 is a diagram illustrating another example of a step subsequent to the step in FIG. 3. FIG. [Figure 6] 4 is a diagram illustrating another example of a step subsequent to the step in FIG. 3. FIG. [Figure 7] 4 is a diagram illustrating another example of a step subsequent to the step in FIG. 3. FIG. [Figure 8] 4 is a diagram illustrating another example of a step subsequent to the step in FIG. 3. FIG. [Figure 9] 4 is a diagram illustrating another example of a step subsequent to the step in FIG. 3. FIG. [Figure 10] FIG. 2 is a diagram illustrating another example of a step of the manufacturing method of the present disclosure. [Figure 11] 1 is a graph showing an example of evaluation results of an electrolytic capacitor manufactured by a method according to an embodiment of the present invention. [Figure 12] 1 is a graph showing an example of an evaluation result of an electrolytic capacitor manufactured by a method of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In the following, an embodiment of the manufacturing method according to the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure can be obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "numerical value A or more and numerical value B or less."

[0010] (Method of manufacturing electrolytic capacitor) The method for producing an electrolytic capacitor according to the present embodiment includes the following steps (i) to (iii) in this order. From another viewpoint, the following production method is a method for producing a member (anode body having a dielectric layer formed on the surface) of an electrolytic capacitor.

[0011] (Step (i)) Step (i) is a step of preparing a plurality of anode parts including an anode body and an anode wire protruding from a first end face of the anode body. There is no limitation on the anode body and the anode wire, and a known anode body and anode wire may be used. Alternatively, the anode part may be fabricated by a known method. Examples of the anode body and the anode wire, and examples of the method of forming them will be described later. (Step (ii)) Step (ii) is a step of connecting a plurality of anode wires connected to the plurality of anode bodies to a first electrode for chemical formation in a state where the plurality of anode bodies are arranged at intervals along a predetermined direction to form an anode body group. That is, in step (ii), a plurality of anode wires connected to the plurality of anode bodies are connected to a first electrode for chemical formation in a state where the plurality of anode parts are arranged at intervals along a predetermined direction. The plurality of anode bodies may be arranged in a line or in a matrix.

[0012] The shape of the first electrode is selected according to the arrangement of the anode body group. For example, when a plurality of anode bodies are arranged in a row, the first electrode may have a linear shape (e.g., rod-like or plate-like). When a plurality of anode bodies are arranged in a matrix, the first electrode may be composed of a plurality of linear electrodes or may be a lattice-like electrode. The first electrode and the anode wire are electrically connected. Usually, the anode wire is fixed to the first electrode by a method such as welding. There is no particular limitation on the material of the first electrode, and it may be a conductive metal (e.g., iron, iron alloy, copper, copper alloy, aluminum, etc.).

[0013] The number of anode bodies included in the anode body group is not limited, and may be in the range of 10 to 200 (for example, in the range of 40 to 100). The interval between adjacent anode bodies is also not particularly limited. The interval may be in the range of 1 to 20 mm (for example, in the range of 2 to 6 mm). Usually, the interval is constant, but the interval does not have to be constant.

[0014] (Step (iii)) In step (iii), a plurality of anode bodies connected to the first electrode via an anode wire are immersed in a chemical conversion solution, and a DC voltage is applied between the first electrode and the second electrode to oxidize (anodize) at least a portion of the surface of the anode body to form a dielectric layer. In step (iii), the second electrode is arranged so as to be in contact with the chemical conversion solution and to be along the anode body group. Here, among the anode body group, a plurality of anode bodies present at the end are defined as first anode bodies, and an anode body present on the inside of the first anode body is defined as a second anode body. In step (iii), at least one selected from the distance between the first and second anode bodies and the second electrode, and the area of ​​the second electrode facing the first and second anode bodies, is made different between the first anode body and the second anode body so that the difference between the chemical conversion current flowing through the first anode body and the chemical conversion current flowing through the second anode body is reduced.

[0015] According to the method of the present disclosure, as described in the examples, the difference between the formation current flowing through the first anode body and the formation current flowing through the second anode body can be reduced. As a result, the variation in thickness of the dielectric layer formed on the surface of the anode body can be reduced. Therefore, according to the method of the present disclosure, electrolytic capacitors with high reliability and characteristics can be manufactured with a high yield.

[0016] The first anode body may be composed of only the anode body located at the end, or may be composed of the anode body located at the end and a plurality of anode bodies in the vicinity thereof. For example, when a plurality of anode bodies are arranged in a line, the two anode bodies at both ends may be the first anode bodies. Alternatively, the anode bodies at both ends and the plurality of anode bodies in the vicinity thereof may be the first anode bodies. When a plurality of anode bodies are arranged in a matrix, the anode body located at the outermost edge may be the first anode body. Alternatively, the plurality of anode bodies at the outermost edge and the vicinity thereof may be the first anode bodies. The second anode body is an anode body other than the first anode body, and is arranged between the first anode bodies.

[0017] In step (iii), the surface of the anode body is oxidized and changed into a dielectric layer. For example, when the anode body is made of tantalum, a tantalum oxide layer is formed on the surface of the anode body. There is no particular limitation on the chemical conversion liquid, and a known chemical conversion liquid used in the chemical conversion treatment of the anode body of an electrolytic capacitor may be used. For example, the chemical conversion liquid may be any of an acidic aqueous solution, a neutral aqueous solution, and a basic aqueous solution. Examples of the acidic aqueous solution include an aqueous solution of phosphoric acid, an aqueous solution of nitric acid, an aqueous solution of acetic acid, and an aqueous solution of sulfuric acid. Other examples of the chemical conversion liquid include an aqueous solution of tartrate, an aqueous solution of oxalate, and an aqueous solution of tetraborate.

[0018] The second electrode is disposed so as to be in contact with the chemical conversion solution. For example, the second electrode may be immersed in the chemical conversion solution. Alternatively, at least a part of an electrolytic cell in which the chemical conversion solution is disposed may be used as the second electrode. It is preferable to use a metal that is stable during chemical conversion as the material of the second electrode. Examples of the material of the second electrode include iron alloy, nickel, chromium, gold, platinum, tantalum, titanium, and carbon. The second electrode may be in the form of a plate or a mesh.

[0019] The manufacturing method of this embodiment may satisfy the following condition (1). By satisfying condition (1), the difference between the formation current flowing through the first anode body and the formation current flowing through the second anode body can be reduced in the formation treatment of step (iii). An example of this configuration will be described later. (1) In the step (iii), the shortest distance between the first anode body and the second electrode is made longer than the shortest distance between the second anode body and the second electrode.

[0020] The shortest distance L1 between the first anode body and the second electrode may be greater than 1 time the shortest distance L2 between the second anode body and the second electrode, and may be greater than 1 time and up to 10 times (for example, in the range of 1.05 to 2.3 times). When the shortest distance L1 and / or the shortest distance L2 take multiple values, all of those values ​​satisfy the above relationship.

[0021] A first example (1a) and a second example (1b) that satisfy the condition (1) are described below. In the first example (1a), the second electrode is bent and / or curved so as to move away from the first anode body. In the second example (1b), the length De2 of the second electrode in the above-mentioned predetermined direction (the direction in which the anode bodies are arranged) is shorter than the length Dp of the anode body group in the predetermined direction. In the second example (1b), the length De2 (mm) is less than 1 time the length Dp (mm) and may be in the range of 0.85 to 0.97 times.

[0022] The manufacturing method of this embodiment may satisfy the following condition (2). By satisfying condition (2), the difference between the formation current flowing through the first anode body and the formation current flowing through the second anode body can be reduced in the formation treatment of step (iii). An example of this configuration will be described later. (2) In step (iii), the area of ​​the second electrode facing the first anode body is smaller than the area of ​​the second electrode facing the second anode body. For example, a through hole may be formed in the second electrode facing the first anode body.

[0023] When condition (2) is satisfied, the area S1 of the portion of the second electrode facing the first anode body is less than 1 time the area S2 of the portion of the second electrode facing the second anode body, and may be 0.01 times or more and less than 1 time the area S2, or may be in the range of 0.01 to 0.3 times the area S2 (for example, in the range of 0.03 to 0.15 times).

[0024] The manufacturing method of this embodiment may satisfy the following condition (3). (3) The second electrode is arranged to face at least one of the second end face opposite to the first end face of the anode body (the end face from which the anode wire protrudes) and the side face connecting the first end face and the second end face. For example, the second electrode may be arranged to face only the second end face of the anode body, may be arranged to face only the side face of the anode body, or may be arranged to face both the second end face and the side face of the anode body. When the second electrode is arranged to face the side face of the anode body, the second electrode may be arranged to face only one side face of the anode body group arranged side by side. Alternatively, two second electrodes may be arranged to sandwich the anode body group. When the electrode (counter electrode) that pairs with the first electrode is composed of two or more electrodes, at least one of the electrodes is a second electrode having the above-mentioned characteristics.

[0025] The manufacturing method of this embodiment may satisfy two selected from the above conditions (1) to (3). For example, the manufacturing method of this embodiment may satisfy conditions (1) and (2), or conditions (1) and (3), or conditions (2) and (3). Alternatively, the manufacturing method of this embodiment may satisfy all of the above conditions (1) to (3).

[0026] An anode part having a dielectric layer formed on its surface is obtained by a process including steps (i) to (iii). Therefore, in one aspect, the present disclosure provides a method for producing an anode part having a dielectric layer formed on its surface. The production method includes the above-mentioned steps (i) to (iii).

[0027] After steps (i) to (iii), a process for forming parts necessary for the electrolytic capacitor is carried out to obtain the electrolytic capacitor. There are no limitations on these processes, and known methods may be used.

[0028] In one example of a manufacturing method for an electrolytic capacitor in which the anode body is a sintered body, an electrolyte layer is formed on a dielectric layer, and a cathode extraction layer is formed on the electrolyte layer. In this manner, a capacitor element is produced. Next, an anode lead terminal is connected to the anode wire, and a cathode lead terminal is connected to the cathode extraction layer. Then, an exterior body is formed so as to cover the capacitor element, a portion of the anode lead terminal, and a portion of the cathode lead terminal. In this manner, an electrolytic capacitor is obtained.

[0029] In one example of a method for manufacturing an electrolytic capacitor in which the anode body is a wound body of metal foil, in step (i), a wound body is prepared by winding an anode body (metal foil), a separator, and a cathode foil. The wound body includes an anode part. The anode part includes an anode body (metal foil) and an anode wire protruding from a first end face of the anode body (a first end face of the wound anode body). Usually, a dielectric layer is formed on the surface of the anode body (metal foil), but the dielectric layer is not formed on at least a part of the end face of the anode body. Therefore, a dielectric layer is formed in the part where the dielectric layer is not formed by the above steps (ii) and (iii). After the dielectric layer is formed, an electrolyte layer is formed inside the wound body to prepare a capacitor element. The prepared capacitor element is enclosed in a case to obtain a wound electrolytic capacitor. The electrolyte layer may be a solid electrolyte layer or an electrolyte layer containing a liquid component. There is no particular limitation on the components and the forming method thereof, and known components and forming methods may be used.

[0030] As an example of the configuration and components of an electrolytic capacitor manufactured by the manufacturing method of the present disclosure, an example in which a sintered anode body is used will be described below. The example electrolytic capacitor described below includes a capacitor element, an exterior body, an anode lead terminal, and a cathode lead terminal. Note that the configuration and components of an electrolytic capacitor manufactured by the method of the present disclosure are not limited to the following example.

[0031] (Capacitor element) The capacitor element includes an anode portion, a dielectric layer, and a cathode portion. The capacitor element is not particularly limited, and a capacitor element used in a known solid electrolytic capacitor may be used.

[0032] The anode part includes an anode body and an anode wire. The anode body may be a porous sintered body or a metal foil with a porous surface. The dielectric layer is formed on the surface of the anode body. The cathode part includes an electrolyte layer and a cathode extraction layer. The electrolyte layer is disposed between the dielectric layer formed on the surface of the anode body and the cathode extraction layer. There are no particular limitations on these components, and components used in known solid electrolytic capacitors may be applied. Examples of these components are described below.

[0033] (Anode body) The anode body may be made of a valve metal. Examples of the valve metal include titanium (Ti), tantalum (Ta), niobium (Nb), aluminum (Al), and alloys containing these metals. The anode body may be formed by sintering particles of the material (e.g., particles of the valve metal) or by etching the metal material. The dielectric layer formed on the surface of the anode body is formed by the process described above.

[0034] (anode wire) The anode wire may be a wire made of a metal. Examples of materials for the anode wire include the valve metals mentioned above, copper, etc. A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes from the end face of the anode body.

[0035] (electrolyte layer) The electrolyte layer is not particularly limited, and an electrolyte layer used in a known solid electrolytic capacitor may be applied. In this specification, the electrolyte layer may be read as a solid electrolyte layer, and the electrolytic capacitor may be read as a solid electrolytic capacitor. The electrolyte layer may be a laminate of two or more different electrolyte layers.

[0036] The electrolyte layer is disposed so as to cover at least a part of the dielectric layer. The electrolyte layer may be formed using a manganese compound or a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. These may be used alone or in combination. The conductive polymer may be a copolymer of two or more monomers. The derivative of a conductive polymer means a polymer having a conductive polymer as a basic skeleton. For example, an example of a polythiophene derivative includes poly(3,4-ethylenedioxythiophene).

[0037] It is preferable that a dopant is added to the conductive polymer. The dopant can be selected according to the conductive polymer, and a known dopant may be used. Examples of the dopant include naphthalenesulfonic acid, p-toluenesulfonic acid, polystyrenesulfonic acid, and salts thereof. An example of the electrolyte layer is formed using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid (PSS).

[0038] The electrolyte layer containing the conductive polymer may be formed by polymerizing a raw material monomer on the dielectric layer, or by applying a liquid containing the conductive polymer (and a dopant, if necessary) to the dielectric layer and then drying it.

[0039] (Cathode extraction layer) The cathode extraction layer is a conductive layer and is disposed so as to cover at least a portion of the electrolyte layer. The cathode extraction layer may include a carbon layer formed on the 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, and may be formed, for example, of a known silver paste.

[0040] (Cathode lead terminal and anode lead terminal) The cathode lead terminal includes a cathode terminal portion exposed at the bottom surface of the electrolytic capacitor and a connection portion connected to the cathode terminal portion. The connection portion is electrically connected to the cathode portion. For example, the connection portion may be connected to the cathode lead layer by a conductive layer (e.g., a silver paste layer) or the like. The anode lead terminal includes an anode terminal portion exposed at the bottom surface of the electrolytic capacitor and a wire connection portion connected to the anode terminal portion. The wire connection portion is connected to an anode wire. The lead terminal may be formed by processing a metal sheet (including a metal plate and a metal foil) made of a metal (copper, copper alloy, etc.) by a known metal processing method.

[0041] (Exterior body) The exterior body is disposed around the capacitor element so that the capacitor element is not exposed on the surface of the electrolytic capacitor. Furthermore, the exterior body insulates the anode lead terminal and the cathode lead terminal. Therefore, the exterior body is made of an insulating material. There is no limitation on the method for forming the exterior body, and it may be formed by a known method. For example, the exterior body may be formed by disposing a material for the exterior body so as to cover a part of the lead terminal and the capacitor element, and then curing the material. In this manner, an electrolytic capacitor is obtained.

[0042] An example of a wound electrolytic capacitor includes a plate group, an electrolyte, and a case. The plate group includes a winding body, an anode wire, and a cathode wire. The winding body is formed by winding an anode body (metal foil), a separator, and a cathode foil. The anode wire is connected to the anode body (metal foil), and the cathode wire is connected to the cathode foil. The anode body is formed of a metal including the valve metal described above. The surface of the anode body is made porous, and a dielectric layer is formed on the surface. The separator is impregnated with an electrolyte. The electrolyte of the wound electrolytic capacitor may include a liquid component. There is no particular limitation on these components, and known components used in wound electrolytic capacitors may be used.

[0043] In one aspect, the present disclosure provides a chemical conversion treatment method and a chemical conversion treatment apparatus for forming a dielectric layer on a surface of an anode body. The chemical conversion treatment method includes the above-mentioned steps (i) to (iii). The chemical conversion treatment apparatus includes a tank in which a chemical conversion treatment liquid is placed, a first electrode, and a second electrode, and further includes a DC power source as necessary. There is no particular limitation on the tank, and a known tank used in chemical conversion treatment may be used. The first electrode and the second electrode have been described above, so a duplicated description will be omitted.

[0044] In the following, an example of the method of the present disclosure for manufacturing an electrolytic capacitor will be specifically described with reference to the drawings. The above-mentioned configurations can be applied to the example of the method described below. The example of the method described below can be modified based on the above description. The matters described below may be applied to the above embodiment. In the embodiment described below, components that are not essential to the method of the present disclosure may be omitted.

[0045] (Embodiment 1) In the first embodiment, an example of the manufacturing method according to the present disclosure will be described. FIG. 1 is a schematic cross-sectional view of an example of an electrolytic capacitor manufactured by the manufacturing method of the first embodiment. The electrolytic capacitor 100 shown in FIG. 1 includes a capacitor element 110, an anode lead terminal 120, a cathode lead terminal 130, an outer casing 101, and a conductive layer 141. The capacitor element 110 includes an anode part 111, a dielectric layer 114, and a cathode part 115. The anode part 111 includes an anode body 113 and an anode wire 112. The anode body 113 is a rectangular parallelepiped porous sintered body, and a dielectric layer 114 is formed on the surface. A part of the anode wire 112 protrudes from one end face of the anode body 113 toward the front face 100f of the electrolytic capacitor 100. The other part of the anode wire 112 is embedded in the anode body 113.

[0046] Cathode section 115 includes an electrolyte layer 116 arranged so as to cover at least a portion of dielectric layer 114, and a cathode extraction layer 117 formed on electrolyte layer 116. Cathode extraction layer 117 includes, for example, a carbon layer formed on electrolyte layer 116, and a metal particle layer formed on the carbon layer. The metal particle layer is, for example, a metal paste layer (for example, a silver paste layer) formed using a metal paste.

[0047] The anode lead terminal 120 includes an anode terminal portion 121 and a wire connection portion 122. The anode terminal portion 121 is exposed at the bottom surface 100b of the electrolytic capacitor 100. The wire connection portion 122 is connected to the anode wire 112. The cathode lead terminal 130 includes a cathode terminal portion 131 and a connection portion 132. The cathode terminal portion 131 is exposed at the bottom surface 100b of the electrolytic capacitor 100. The connection portion 132 is electrically connected to the cathode extraction layer 117 by a conductive layer 141.

[0048] In the manufacturing method of the first embodiment, first, a plurality of anode parts 111 are prepared. As shown in Fig. 2, the anode part 111 includes an anode body 113 and an anode wire 112 protruding from a first end face 113e1 of the anode body 113. The anode body 113 has a second end face on the side opposite to the first end face 113e1, and a side face 113s connecting the first end face 113e1 and the second end face 113e2. The anode body 113 of the example shown in Fig. 2 is substantially rectangular parallelepiped-shaped and has four side faces 113s.

[0049] Next, as shown in Fig. 3, in a state where the multiple anode bodies 113 are arranged at intervals along a predetermined direction D to form an anode body group 113G, the multiple anode wires 112 connected to the multiple anode bodies 113 are connected to a first electrode 210 for chemical conversion. In the first embodiment, the multiple anode bodies 113 are arranged in a line. The first electrode 210 is an elongated plate-like electrode that extends linearly. The anode wires 112 are fixed and electrically connected to the first electrode 210 by, for example, welding.

[0050] Next, as shown in FIG. 4, a DC voltage is applied between the first electrode 210 and the second electrode 220 while a plurality of anode bodies 113 connected to the first electrode 210 via the anode wire 112 are immersed in the chemical conversion solution 202. This oxidizes at least a portion of the surface of the anode body 113 to form a dielectric layer 114. At this time, a portion of the surface of the anode wire 112 may also be oxidized. FIG. 4 shows an example in which the second electrode 220 is formed only at a position facing the second end surface 113e2 of the anode body 113 (the first anode body 113a and the second anode body 113b). The chemical conversion solution 202 is placed in a tank 201. The second electrode 220 is also immersed in the chemical conversion solution 202.

[0051] In step (iii), the second electrode 220 is arranged in contact with the chemical conversion solution 202 and along the anode body group 113G. Here, among the anode body group 113G, the multiple anode bodies 113 present at the ends are defined as first anode bodies 113a, and the anode body 113 present on the inner side of the first anode body 113a is defined as second anode body 113b. Note that, although FIG. 4 shows an example in which the two anode bodies 113 at both ends are defined as first anode bodies 113a, the multiple anode bodies 113 at both ends and in their vicinity may be defined as first anode bodies 113a (this also applies to other embodiments).

[0052] Second electrode 220 is a long and thin plate-like electrode, but is bent at central bent portion 220a as shown in Fig. 4. In the example shown in Fig. 4, second electrode 220 is bent so that a portion of second electrode 220 facing first anode body 113a is moved away from the anode body group. Therefore, the shortest distance L1 between first anode body 113a and second electrode 220 is longer than the shortest distance L2 between second anode body 113b and second electrode 220. This configuration can reduce the difference between the formation current flowing through first anode body 113a and the formation current flowing through second anode body 113b in step (iii).

[0053] The second electrode 220 may be curved from the center outward so that the shortest distance L1 between the first anode body 113a and the second electrode is longer than the shortest distance L2 between the second anode body 113b and the second electrode 220. A diagram of such a second electrode 220 is shown in Fig. 5. The second electrode 220 is curved so as to move away from the anode body group 113G as it approaches the end.

[0054] The second electrode 220 may be bent at the end so that the shortest distance L1 between the first anode body 113a and the second electrode is longer than the shortest distance L2 between the second anode body 113b and the second electrode 220. A diagram of such a second electrode 220 is shown in FIG. 6. The second electrode 220 shown in FIG. 6 is bent at two bent portions 220a located at positions corresponding to between the first anode body 113a and the second anode body 113b. The second electrode 220 between the two bent portions 220a is a flat plate.

[0055] The length of the second electrode 220 in the direction D (the direction D in which the anode bodies 113 are arranged) may be shorter than the length of the anode body group 113G in the direction D. A cross-sectional view of such a second electrode 220 is shown in FIG. 7. In the example shown in FIG. 7, the length De2 of the second electrode 220 in the direction D is shorter than the length Dp of the anode body group 113G in the direction D. In addition, the second electrode 220 does not exist in a portion of the anode body group 113G facing the first anode body 113a at the end. As a result, the shortest distance L1 between the first anode body 113a and the second electrode 220 is longer than the shortest distance L2 between the second anode body 113b and the second electrode 220. The distance between the second electrode 220 and the anode body group 113G in the direction D is, for example, (Dp-De2) / 2.

[0056] From another point of view, the embodiment shown in FIG. 7 is an example in which the areas of the second electrode 220 are different in the portion facing the first anode body 113a and the second anode body 113b. Specifically, the area S1 (not shown) of the portion facing the first anode body 113a is smaller than the area S2 (not shown) of the portion facing the second anode body 113b. Here, the area of ​​the second electrode 220 in the portion facing the anode body 113 is the following area. First, the surface of the anode body 113 facing the second electrode 220 (the second end surface 113e2 of the anode body 113 in the example of FIG. 7) is projected in a direction perpendicular to the surface toward the second electrode 220. At this time, the area of ​​the portion where the projected plane and the surface of second electrode 220 overlap is the area of ​​second electrode 220 facing anode body 113. In the case of the example shown in Fig. 7, area S1 of second electrode 220 facing first anode body 113a is zero. Area S2 of second electrode 220 facing second anode body 113b is equal to the area of ​​second end face 113e2.

[0057] 8 is a schematic cross-sectional view showing an example of another method for making the areas of the second electrode 220, which face the first anode body 113a and the second anode body 113b, different from each other. In the example shown in FIG. 1 Anode body 113 a Through holes 220h are formed in a portion of second electrode 220 facing first anode body 113a. As a result, area S1 of second electrode 220 facing first anode body 113a is smaller than area S2 of second electrode 220 facing second anode body 113b. Second electrode 220 shown in FIG. 8 is plate-shaped, and shortest distance L1 and shortest distance L2 are equal, but they do not have to be equal.

[0058] When the second electrode is in a mesh shape, the surface density of the portion of second electrode 220 facing first anode body 113a may be smaller than the surface density of the portion of second electrode 220 facing second anode body 113b. In this case, too, the area of ​​second electrode 220 facing first anode body 113a can be smaller than the area of ​​second electrode 220 facing second anode body 113b.

[0059] In the above figure, an example in which the second electrode 220 is disposed only in a portion facing the second end surface 113e2 of the anode body 113 is shown. However, the second electrode 220 may be disposed in a portion facing the second end surface 113e2 of the anode body 113 and a portion facing the side surface 113s, as shown in FIG. 9. FIG. 9 is a schematic diagram of the arrangement of the electrodes viewed from the second end surface 113e2 side. In the example shown in FIG. 9, three second electrodes 220 are used as counter electrodes. FIG. 9 shows an example in which the second electrode 220 shown in FIG. 4 is used, but other second electrodes may be used. In addition, any one or two of the three second electrodes 220 shown in FIG. 9 may be omitted. For example, one or two second electrodes 220 disposed in a portion facing the second end surface 113e2 of the anode body 113 may be used as counter electrodes. Furthermore, only one of the multiple electrodes constituting the counter electrode may be the second electrode 220, and the other electrodes may be normal electrodes.

[0060] In the first embodiment, an example in which the anode body is a sintered body has been described. However, as described above, the anode body may be a metal foil. In this case, a perspective view of an example of an electrode plate assembly including an anode part prepared in step (i) is shown in FIG. 10. The electrode plate assembly 300 shown in FIG. 10 includes a wound body 310, an anode wire (anode lead) 322, and a cathode wire 323. The wound body 310 includes an anode body (metal foil), a cathode foil, and a separator. They are stacked and wound so that the separator is disposed between the anode body and the cathode foil. The surface of the metal foil that is the anode body is made porous. A dielectric layer is formed on at least a part of the porous surface. Usually, no dielectric layer is formed on the end face of the metal foil. The anode part of the example shown in FIG. 11 includes a wound anode body (metal foil) and an anode wire 322 protruding from a first end face 313e1 of the wound anode body. The anode wire 322 is connected to the anode body and the cathode wire 323 is connected to the cathode foil.

[0061] The wound anode body includes a first end face 313e1, a second end face 313e2 opposite to the first end face 313e1, and a side face 313s connecting them. By replacing the anode portion 111 in the above-described embodiment with the electrode plate group 300 (including the anode portion) shown in FIG. 10 and carrying out steps (ii) and (iii), it is possible to form a dielectric layer on at least a portion of the surface of the anode body included in the electrode plate group shown in FIG. 10. Specifically, the anode wires 3 of the multiple electrode plate groups 300 (multiple anode portions) are wound in a wire-like shape. 2 2 to the first electrode 210 and then perform step (iii). By performing step (iii), a dielectric layer can be formed on the end face of the anode body on which no dielectric layer has been formed. Even in this case, the variation in the thickness of the dielectric layer to be formed can be reduced.

[0062] Steps (i) to (iii) can be carried out as described above. Thereafter, an electrolytic capacitor can be manufactured by the above-mentioned steps. EXAMPLES

[0063] The present disclosure is further illustrated by the following examples.

[0064] In this example, the shape of the electrode (counter electrode) used in the chemical conversion treatment was changed, and the chemical conversion treatment was performed to form a dielectric layer. Then, an electrolytic capacitor was produced using the anode body on which the dielectric layer was formed.

[0065] Specifically, first, multiple anodes were fabricated, each consisting of an anode body (tantalum sintered body) and an anode wire embedded in it. 106 anodes were then lined up at regular intervals, and the anode wire was welded to a long, thin, plate-shaped first electrode.

[0066] Next, the anode body welded to the first electrode and the second electrode were immersed in a chemical conversion solution. A phosphoric acid aqueous solution was used as the chemical conversion solution. In the manufacture of electrolytic capacitor A1, a chemical conversion treatment was performed using an electrode having a shape similar to that of the second electrode 220 shown in FIG. 4. In the manufacture of electrolytic capacitor C1 of the comparative example, a chemical conversion treatment was performed using a straight plate-shaped electrode as in the conventional case.

[0067] Then, a DC voltage was applied between the first electrode and the second electrode to perform chemical conversion treatment, thereby forming a dielectric layer on the surface of 106 anode bodies. In this way, an anode part with a dielectric layer formed thereon was obtained. Using the obtained anode part, 106 electrolytic capacitors A1 and 106 electrolytic capacitors C1 were manufactured. For the electrolyte layer, a polymer electrolyte layer containing a dopant was used.

[0068] The electrolytic capacitor A1 produced using 53 anode parts whose positions fixed to the first electrode were on one side of the center was measured for capacitance.Similarly, the electrolytic capacitor C1 produced using 53 anode parts whose positions fixed to the first electrode were on one side of the center was measured for capacitance.

[0069] FIG. 11 shows the relationship between the position fixed to the first electrode and the capacitance for electrolytic capacitor A1. FIG. 12 shows the relationship between the position fixed to the first electrode and the capacitance for electrolytic capacitor C1. The numbers on the horizontal axis in FIG. 11 and FIG. 12 indicate the numbers given in the order of arrangement from the end of the first electrode. The number 1 on the horizontal axis is an electrolytic capacitor using an anode part arranged at the very end of the first electrode. The number 53 on the horizontal axis is an electrolytic capacitor using an anode part arranged at the position closest to the center of the first electrode. As shown in FIG. 11, in electrolytic capacitor A1, the capacitance was almost constant regardless of the position where the anode part was fixed to the first electrode. On the other hand, as shown in FIG. 12, in electrolytic capacitor C1, the capacitance of the electrolytic capacitor using the anode part fixed to the end of the first electrode was greatly reduced. This is considered to be due to the following reasons.

[0070] Consider the case where a plurality of anode bodies are arranged in a row to form an anode body group in the chemical conversion treatment. In this case, the first anode body present at the end of the anode body group mainly shares the current supplied from the second electrode with one adjacent anode body. On the other hand, the second anode body present inside the first anode body mainly shares the current supplied from the second electrode with two anode bodies present around it. Therefore, when a conventional counter electrode is used, the chemical conversion current flowing through the first anode body is greater than the chemical conversion current flowing through the second anode body. As a result, when a conventional counter electrode is used, the dielectric layer formed on the surface of the first anode body becomes thick, and the electrostatic capacitance of an electrolytic capacitor using the dielectric layer decreases. On the other hand, the manufacturing method according to the present disclosure can reduce the difference between the chemical conversion current flowing through the first anode body and the chemical conversion current flowing through the second anode body. As a result, an electrolytic capacitor with high characteristics and small variation in characteristics can be manufactured regardless of the position at which the anode body is fixed to the first electrode.

[0071] When a conventional counter electrode is used, the increase in formation current at the ends does not necessarily occur only in the anode body at the very end, but may also occur in anode bodies adjacent to that anode body. [Industrial Applicability]

[0072] The present disclosure can be used for a method for manufacturing an electrolytic capacitor. [Explanation of symbols]

[0073] 100: Electrolytic capacitor 110: Capacitor element 111: Anode part 112: Anode wire 113: Anode body 113a: first anode body 113b: second anode body 113e1: First end face 113e2: second end face 113G:Anode body group 113s :Side 114: Dielectric layer 202:Chemical liquid 210: First electrode 220: second electrode 220h: Through hole

Claims

1. (i) preparing a plurality of anode parts each including an anode body and an anode wire protruding from a first end surface of the anode body; (ii) connecting a plurality of the anode wires connected to the anode bodies to a first electrode for chemical conversion in a state in which the plurality of the anode bodies are arranged at intervals along a predetermined direction to form an anode body group; and (iii) applying a DC voltage between the first electrode and the second electrode while the plurality of anode bodies connected to the first electrode via the anode wire are immersed in a chemical conversion solution to oxidize at least a portion of a surface of the anode bodies to form a dielectric layer, In the step (iii), the second electrode is disposed so as to be in contact with the chemical conversion solution and along the anode body group, When the anode bodies at the ends of the anode body group are defined as first anode bodies and the anode body located more inward than the first anode bodies is defined as a second anode body, In the step (iii), at least one selected from a distance between the first and second anode bodies and the second electrode and an area of ​​the second electrode facing the first and second anode bodies is made different between the first anode body and the second anode body so that a difference between a chemical formation current flowing in the first anode body and a chemical formation current flowing in the second anode body is reduced; In the step (iii), an area of ​​the second electrode facing the first anode body is smaller than an area of ​​the second electrode facing the second anode body, a through hole is formed in the second electrode at a portion facing the first anode body.

2. 2. The manufacturing method according to claim 1, wherein in the step (iii), a shortest distance between the first anode body and the second electrode is longer than a shortest distance between the second anode body and the second electrode.

3. The method of claim 2 , wherein the second electrode is bent and / or curved away from the first anode body.

4. The manufacturing method according to claim 2 , wherein a length of the second electrode in the predetermined direction is shorter than a length of the anode body group in the predetermined direction.

5. The manufacturing method according to any one of claims 1 to 4, wherein the second electrode is disposed to face at least one surface selected from a second end surface of the anode body opposite to the first end surface and a side surface connecting the first end surface and the second end surface.

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