Solid electrolytic capacitor and method for manufacturing solid electrolytic capacitor

Abstract

Provided is a solid electrolytic capacitor having a high withstand voltage. A solid electrolytic capacitor (1) is provided with: a porous anode body having a valve metal (11) and a dielectric oxide film layer (12) formed on the surface of the valve metal (11); and an electrolyte layer (20) formed on the surface of the dielectric oxide film layer (12). The electrolyte layer (20) is provided with: a first conductive polymer layer (21) that is formed by chemical polymerization and is in contact with the dielectric oxide film layer (12); a second conductive polymer layer (22) formed by electrolytic polymerization and formed on the opposite side of the dielectric oxide film layer (12) with respect to the first conductive polymer layer (21); and a conductive barrier layer (23) formed between the first conductive polymer layer (21) and the second conductive polymer layer (22). The barrier layer (23) prevents a conductive polymer layer from being formed by electrolytic polymerization in a region closer to the anode body (10) than the barrier layer (23).

Description

Technical Field

[0001] This disclosure relates to solid electrolytic capacitors and methods for manufacturing solid electrolytic capacitors. Background Technology

[0002] Solid electrolytic capacitors are used as small, high-capacitance capacitors for electronic devices and the like. Patent Document 1 describes a method for manufacturing a solid electrolytic capacitor in which a conductive polymer layer is formed by electrolytic polymerization, exhibiting excellent electrostatic capacitance (Cs) and equivalent series resistance (ESR).

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-89542 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] In recent years, in addition to small size and high capacitance, capacitors with high voltage resistance have also been desired.

[0008] The purpose of this disclosure is to provide a solid electrolytic capacitor with high voltage resistance.

[0009] Technical means for solving technical problems

[0010] A solid electrolytic capacitor according to one embodiment of the present disclosure.

[0011] The anode comprises a porous anode body and an electrolyte layer. The porous anode body has a valve metal and a dielectric oxide film layer formed on the surface of the valve metal. The electrolyte layer is formed on the surface of the dielectric oxide film layer.

[0012] The electrolyte layer comprises:

[0013] A first conductive polymer layer, formed by chemical polymerization, is in contact with the dielectric oxide film layer;

[0014] A second conductive polymer layer, formed by electrolytic polymerization, is formed on the opposite side of the dielectric oxide film layer relative to the first conductive polymer layer; and

[0015] A barrier layer, which is formed between the first conductive polymer layer and the second conductive polymer layer and is conductive,

[0016] The barrier layer prevents the formation of a conductive polymer layer by electrolytic polymerization in the region closer to the anode than the barrier layer.

[0017] A method for manufacturing a solid electrolytic capacitor according to one embodiment of this disclosure includes:

[0018] A process of forming a first conductive polymer layer on the surface of a porous anode body having a valve metal and a dielectric oxide film layer formed on the surface of the valve metal by chemical polymerization.

[0019] The process of forming a conductive barrier layer on the first conductive polymer layer; and

[0020] The process of forming a second conductive polymer layer on the barrier layer by electrolytic polymerization.

[0021] Invention Effects

[0022] According to this disclosure, it is possible to provide a solid electrolytic capacitor with high voltage resistance. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view showing a solid electrolytic capacitor according to one embodiment of the present disclosure.

[0024] Figure 2 This is a schematic cross-sectional view showing the electrolyte layer of a solid electrolytic capacitor according to an embodiment of the present disclosure.

[0025] Figure 3 This is a schematic cross-sectional view showing the electrolyte layer of a first existing example of a solid electrolytic capacitor.

[0026] Figure 4 This is a schematic cross-sectional view showing the electrolyte layer of a second existing example of a solid electrolytic capacitor. Detailed Implementation

[0027] Hereinafter, specific examples of the solid electrolytic capacitor and the method of manufacturing the solid electrolytic capacitor of the present disclosure will be described with reference to the accompanying drawings, but the present disclosure is not limited to these examples.

[0028] [The structure of a solid electrolytic capacitor]

[0029] Figure 1 This is a cross-sectional view showing a solid electrolytic capacitor 1 according to one embodiment of the present disclosure. Figure 1 As shown, the solid electrolytic capacitor 1 includes an anode body 10, an electrolyte layer 20, and a cathode layer 30. The solid electrolytic capacitor 1 of this embodiment can be formed by sequentially stacking the electrolyte layer 20 and the cathode layer 30 on the anode body 10.

[0030] The anode body 10 is porous and has a valve metal 11 and a dielectric oxide film layer 12 formed on the surface of the valve metal 11. The valve metal 11 is, for example, a sintered body containing valve metal particles or a porous metal body that has undergone surface roughening treatment. Examples of valve metals 11 include at least one selected from the group consisting of aluminum, tantalum, niobium, tungsten, titanium, and zirconium, or alloys of these valve metals. Preferably, at least one valve metal selected from the group consisting of aluminum, tantalum, and niobium is preferred.

[0031] The dielectric oxide film layer 12 is an oxide film formed by oxidizing the surface of the valve metal 11. Specifically, the dielectric oxide film layer 12 can be formed on the surface of the valve metal 11 by electrolytic oxidation in an aqueous solution containing oxalic acid, citric acid, phosphoric acid, or their salts. The dielectric oxide film layer 12 is also formed in the pores of the anode body 10 through electrolytic oxidation. The thickness of the dielectric oxide film layer 12 can be appropriately adjusted according to the voltage during electrolytic oxidation.

[0032] The electrolyte layer 20 is composed of a solid electrolyte such as a conductive polymer. In this embodiment, the electrolyte layer 20 includes a first conductive polymer layer 21, a second conductive polymer layer 22, and a barrier layer 23 (see reference). Figure 2 A first conductive polymer layer 21 is formed on the surface of the dielectric oxide film layer 12. A second conductive polymer layer 22 is formed on the opposite side of the dielectric oxide film layer 12 relative to the first conductive polymer layer 21.

[0033] Examples of conductive polymers constituting the first conductive polymer layer 21 or the second conductive polymer layer 22 include conductive polymers containing thiophene, aniline, pyrrole, or their derivatives as repeating units, and combinations of two or more of these. Additionally, the conductive polymer may be doped with a dopant having anionic groups or a salt thereof.

[0034] In the solid electrolytic capacitor 1 of this embodiment, the first conductive polymer layer 21 is formed by chemical polymerization. The second conductive polymer layer 22 is formed by electrolytic polymerization. The thickness of the first conductive polymer layer 21 is, for example, 1 nm or more and 300 μm or less. The thickness of the second conductive polymer layer 22 is, for example, 1 μm or more and 300 μm or less.

[0035] A barrier layer 23 is formed between the first conductive polymer layer 21 and the second conductive polymer layer 22. The barrier layer 23 is conductive and may also be composed of conductive polymers. The barrier layer 23 is formed by methods other than chemical polymerization and electrolytic polymerization, thereby distinguishing it from the first conductive polymer layer 21 and the second conductive polymer layer 22. The barrier layer 23 is formed, for example, by coating a conductive polymer dispersion or conductive polymer solution and drying it. For example, as a dopant, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS), i.e., a PEDOT / PSS dispersion, can be used. Alternatively, a self-doped soluble conductive polymer solution containing anionic groups with doping function in a π-conjugated polymer can also be used. The barrier layer 23 prevents the formation of a conductive polymer layer by electrolytic polymerization in the region closer to the anode body 10 than the barrier layer 23. Details of the electrolyte layer 20 in this embodiment will be described later.

[0036] The cathode layer 30 is disposed on the electrolyte layer 20. The cathode layer 30 may be composed, for example, of a carbon layer and a silver layer stacked on the carbon layer, but is not particularly limited. The cathode layer 30 is connected to the lead frame 60b. The cathode layer 30 is, for example, as shown in the diagram. Figure 1 As shown, it is connected to the cathode-side lead frame 60b via conductive adhesive 50.

[0037] The anode lead 40 is a lead used to ensure electrical connection between the anode body 10 and the outside. The anode lead 40 can be a metal wire embedded in the valve metal 11, for example, a metal wire of the same type as the valve metal. The anode lead 40 is connected to the lead frame 60a on the anode side. The anode lead 40 and the lead frame 60a are connected, for example, by welding.

[0038] After connecting the anode lead 40 and the cathode layer 30 to the lead frame 60a and 60b respectively, the outer resin 70 is formed using a molding machine or the like, thereby obtaining the solid electrolytic capacitor 1.

[0039] [Methods for forming the electrolyte layer]

[0040] Methods for forming the conductive polymer layer constituting the electrolyte layer 20 mainly include chemical polymerization, electrolytic polymerization, and coating and drying of conductive polymer dispersions or solutions. An overview of each method and the characteristics of the resulting electrolyte layer will be described. In the following description, the conductive polymer layer formed by chemical polymerization will sometimes be referred to as a "chemically polymerized layer," and the conductive polymer layer formed by electrolytic polymerization will sometimes be referred to as an "electrolytically polymerized layer." Furthermore, the method of coating and drying a conductive polymer dispersion or solution is sometimes referred to as "solution coating."

[0041] Chemical polymerization and electrolytic polymerization are methods that form conductive polymers by immersing an anode or other material in a monomer solution, allowing the monomers to polymerize on the surface of the material (in-situ polymerization). If a porous anode is immersed in a monomer solution, the monomers enter the pores (P) of the anode, thus forming an electrolyte layer inside the anode in both chemical and electrolytic polymerization. The formation of an electrolyte layer inside the anode increases the contact area between the dielectric oxide film and the electrolyte layer, resulting in a high-capacitance capacitor.

[0042] In chemical polymerization, oxidant crystals are formed by immersing an object such as an anode in an oxidant solution and then drying it. Next, the object with the oxidant crystals is immersed in a monomer solution, and polymerization of the monomers is induced by contact between the monomers and the oxidant crystals, thereby forming a conductive polymer layer. Chemically polymerized layers have low uniformity as films and tend to form three-dimensional shapes with many irregularities and low density.

[0043] In electrolytic polymerization, an electrochemical reaction is utilized to flow an electric current through a solution containing monomers and a supporting electrolyte, thereby polymerizing the monomers to obtain a conductive polymer layer. The electrolytically polymerized layer, as a film, exhibits high uniformity and density. Furthermore, the film obtained through electrolytic polymerization also demonstrates high dimensional stability, and an electrolyte layer can be uniformly formed even at the corners of the object. Therefore, electrolytic polymerization enables the manufacture of smaller capacitors. On the other hand, while an electric current needs to flow through the monomer solution for electrolytic polymerization, it is difficult to flow current through a dielectric oxide film layer, making it challenging to directly form an electrolytically polymerized layer on the dielectric oxide film layer. Therefore, a method is employed whereby a conductive polymer layer is formed on the dielectric oxide film layer through chemical polymerization or solution coating prior to electrolytic polymerization.

[0044] On the other hand, compared to monomer solutions, conductive polymer dispersions or solutions are less likely to penetrate the pores of the anode. Therefore, unlike chemical polymerization or electrolytic polymerization, it is difficult to form an electrolyte layer inside the anode when forming an electrolyte layer via solution coating. Furthermore, while solution coating can yield highly uniform films, unlike electrolytic polymerization, it is difficult to form an electrolyte layer at the corners of the object. Therefore, to reliably form an electrolyte layer at the corners, the thickness of the electrolyte layer needs to be increased, which is considered detrimental to the miniaturization of capacitors.

[0045] [Detailed Composition of the Electrolyte Layer]

[0046] Next, the structure of the electrolyte layer 20 in this embodiment will be compared with that of a conventional example and explained in more detail. Figure 2 This diagram shows the cross-sectional structure of the solid electrolytic capacitor 1 according to this embodiment. Figure 3The cross-sectional structure of the first existing example solid electrolytic capacitor 101 is shown. Figure 4 The cross-sectional structure of the solid electrolytic capacitor 201 of the second existing example is shown. Figures 2 to 4 A porous structure consisting of valve metal 11 and a dielectric oxide film layer 12 formed on the surface of valve metal 11 is commonly shown. Furthermore, as an electrolyte layer, in... Figure 2 Electrolyte layer 20 is shown in the figure. Figure 3 Electrolyte layer 120 is shown in the figure. Figure 4 Electrolyte layer 220 is shown in the figure. Figures 2 to 4 All are enlarged cross-sectional views near the boundary between the anode body 10 and the electrolyte layers 20, 120, and 220.

[0047] (First existing example)

[0048] First of all, Figure 3 The solid electrolytic capacitor 101 of the first existing example will be described. The electrolyte layer 120 of the solid electrolytic capacitor 101 is composed of a chemically polymerized layer 121 and an electrolytically polymerized layer 122.

[0049] As described above, according to chemical polymerization, a conductive polymer layer is formed not only on the surface of the anode body 10 but also inside. Therefore, in the first conventional example of a solid electrolytic capacitor 101, as... Figure 3 As shown, a chemically polymerized layer 121 is also formed in the pores P of the anode body 10. Furthermore, the chemically polymerized layer 121 exhibits low uniformity as a film. Therefore, as... Figure 3 As schematically shown, even if a chemically polymerized layer 121 is formed on the dielectric oxide film layer 12, the dielectric oxide film layer 12 cannot be completely covered by the chemically polymerized layer 121 alone, and becomes partially exposed.

[0050] In the first existing example, an electrolytic polymer layer 122 is formed after the chemically polymerized layer 121 is formed. The electrolytic polymerization process is the same as the chemical polymerization, with the electrolytic polymer layer 122 formed not only on the surface of the anode body 10 but also in the pores P. Therefore, the electrolytic polymer layer 122 partially overlaps the chemically polymerized layer 121, while in the portion where the chemically polymerized layer 121 is not formed, it is formed directly on the dielectric oxide film layer 12.

[0051] like Figure 3 As shown, a dielectric oxide film layer 12 is formed on the surface of the valve metal 11, but there are defects D where the dielectric oxide film layer 12 is absent and the valve metal 11 is exposed. In the first prior art example, when there are defects D such as... Figure 3The defect D of the hole P shown may also form a conductive polymer layer (chemically polymerized layer 121 or electrolytically polymerized layer 122). If a conductive polymer layer is formed in the defect D, the current can flow in that part without passing through the dielectric oxide film layer 12, and therefore the withstand voltage of the capacitor may be reduced.

[0052] However, in the case of chemical polymerization, the uniformity of the formed chemically polymerized layer 121 is not high. Therefore, even if a chemically polymerized layer 121 is formed at the defect portion D, it is possible to oxidize and insulate the chemically polymerized layer 121 formed at the defect portion D by performing a localized chemical conversion treatment afterwards (e.g., applying a weak current), thus preventing a decrease in withstand voltage. On the other hand, compared with the chemically polymerized layer 121, the electrolytic polymerized layer 122 has high uniformity. Therefore, when an electrolytic polymerized layer 122 is formed at the defect portion D, it is difficult to perform a treatment to locally insulate the electrolytic polymerized layer 122. As a result, as... Figure 3 As shown, in the defect portion D, the electrolytic polymer layer 122 is in direct contact with the valve metal 11, resulting in a decrease in withstand voltage. Therefore, in the configuration of the first prior art, which has a combination of chemically polymerized layer 121 and electrolytic polymerized layer 122, it is difficult to obtain a high withstand voltage.

[0053] (Second existing example)

[0054] Next, for Figure 4 The solid electrolytic capacitor 201 of the second existing example will be described. The solid electrolytic capacitor 201 has an electrolyte layer 220. First, a conductive polymer layer 223 is formed on the surface of the anode body 10 by solution coating, and then a chemical polymer layer 221 and an electrolytic polymer layer 222 are sequentially stacked to form the electrolyte layer 220.

[0055] In solution coating, because the conductive polymer dispersion or conductive polymer solution does not enter the pore P of the anode body 10, therefore... Figure 4 As shown, a conductive polymer layer 223 is formed only on the surface of the anode body 10. Next, a chemically polymerized layer 221 and an electrolytically polymerized layer 222 are formed sequentially. However, because the conductive polymer layer 223 has already been formed, the monomer solution cannot enter the interior of the pore P, therefore, the chemically polymerized layer 221 or the electrolytically polymerized layer 222 cannot be formed inside the pore P. Therefore, in Figure 4 In the capacitor with the configuration shown in the second conventional example, the contact area between the dielectric oxide film layer 12 and the electrolyte layer 220 is reduced, resulting in a decrease in capacitance and an increase in equivalent series resistance (ESR).

[0056] (This implementation method)

[0057] Next, for Figure 2A solid electrolytic capacitor 1 according to one embodiment of the present disclosure will be described. Figure 2 As shown, the solid electrolytic capacitor 1 includes an electrolyte layer 20, which is composed of a first conductive polymer layer 21 (hereinafter referred to as the chemically polymerized layer 21) formed by chemical polymerization, a second conductive polymer layer 22 (hereinafter referred to as the electrolytic polymerized layer 22) formed by electrolytic polymerization, and a barrier layer 23 formed by solution coating.

[0058] In this embodiment, the chemical polymerization layer 21 and Figure 3 The first existing example shown is similarly formed by entering the hole P of the anode body 10.

[0059] The solid electrolytic capacitor 1 in this embodiment and Figure 3 Unlike the first existing example shown, a barrier layer 23 is formed after the chemical polymerization layer 21 and before the electrolytic polymerization layer 22. As described above, since the conductive polymer dispersion or conductive polymer solution cannot enter the pore P, the barrier layer 23 formed by solution coating... Figure 2 The form shown is only formed on the surface of the anode body 10.

[0060] If the electrolytic polymer layer 22 is formed after the barrier layer 23 is formed, the presence of the barrier layer 23 prevents the formation of the electrolytic polymer layer 22 on the side closer to the anode body 10 than the barrier layer 23. Therefore, the electrolytic polymer layer 22 is not formed in the hole P of the anode body 10, and the formation of the electrolytic polymer layer in the defect portion D can be avoided.

[0061] According to the configuration of this embodiment, and Figure 3 Compared to the first existing example shown, the capacitor's withstand voltage is improved because the formation of the electrolytic polymer layer 22 in the defective portion D is prevented. Furthermore, compared to... Figure 4 Compared to the second existing example shown, the capacitance is larger because a chemically polymerized layer 21 is formed in the hole P. Furthermore, since the electrolytically polymerized layer 22 is formed on a relatively flat barrier layer 23 rather than on the more uneven chemically polymerized layer 21, a more uniform film with excellent dimensional accuracy can be obtained, making it suitable for capacitor miniaturization.

[0062] When the barrier layer 23 is formed by coating a conductive polymer dispersion, the particle size of the conductive polymer contained in the conductive polymer dispersion is preferably 5 nm or more. Here, the particle size of the conductive polymer refers to the d50 (median particle size) in the number distribution. The particle size of the conductive polymer can be determined based on dynamic light scattering. There is no particular upper limit to the particle size of the conductive polymer; for example, it can be below 100 nm. The particle size of the conductive polymer can be adjusted according to the polymerization rate, which varies, for example, depending on the intensity of the external force applied during the dispersion treatment of the conductive polymer dispersion, the polymerization temperature, the amount or rate of oxidant added, and the stirring conditions.

[0063] The barrier layer 23 preferably has a water absorption of 50% by mass or less over 24 hours in an atmosphere with a temperature of 85°C and a humidity of 85% RH. Because the barrier layer 23 has low water absorption, it is difficult for it to swell or peel off when immersed in the electrolytic polymerization solution, thus preventing ESR deterioration and size increase. Furthermore, the barrier layer 23 preferably has a contact angle with water of 10 degrees or more. A contact angle of 10 degrees or more with water provides sufficient hydrophobicity, preventing swelling and peeling of the barrier layer 23 when immersed in the electrolytic polymerization solution. Methods to reduce water absorption or increase the contact angle with water include, for example, using a layer of PSS (poly(4-styrene sulfonic acid)) doped with PEDOT (poly(3,4-ethylenedioxythiophene)) as the barrier layer 23, and reducing the proportion of PSS as a hydrophilic dopant; using anion with hydrophobicity having a long-chain alkyl or phenyl group as a dopant; or adding a hydrophobic binder resin to the dispersion. When adding an adhesive resin, examples of the added resin include: fluorinated resins, polyester resins, oxetane resins, polyurethane resins, polyimide resins, styrene-butadiene rubbers, melamine resins, silicone resins, alkyd resins, phenolic resins, epoxy resins, butyral resins, acrylic resins, and organosilicon resins. In this disclosure, any of the above-mentioned methods, or a combination of two or more methods, can be used to modify the properties of the barrier layer, such as water absorption and contact angle with water. Furthermore, the properties of the barrier layer 23, such as water absorption and contact angle with water, can be considered the same as the properties of a separate film formed from the same material as the barrier layer 23, and it is not necessary to directly measure the properties of the barrier layer 23 assembled in the capacitor.

[0064] The ratio of the area where the barrier layer 23 is formed to the surface of the anode body 10 where the electrolyte layer 20 is formed (hereinafter, sometimes referred to as "barrier layer coverage") is preferably 50% or more. Here, the surface area of ​​the anode body is not taking into account the actual surface area of ​​the pores, but rather the area of ​​the surface when viewed as a simple shape such as a cuboid, ignoring the pores. By increasing the barrier layer coverage, the formation of the electrolytic polymerization layer 22 at the anode body 10 can be more reliably prevented. The barrier layer coverage is more preferably 80% or more, and most preferably 100%.

[0065] Preferably, the first conductive polymer layer (chemically polymerized layer) 21 is primed. Primer treatment improves adhesion to the subsequently laminated barrier layer 23 and increases barrier layer coverage. The primer material is not particularly limited; for example, polyamines or their salts can be used. More specifically, examples include 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, and their derivatives. Primer treatment is performed, for example, by impregnating the chemically polymerized layer 21 in an aqueous amine solution as illustrated above and then drying it.

[0066] The barrier layer 23 preferably has a sufficiently low sheet resistance. Specifically, when the barrier layer 23 is formed by solution coating, the sheet resistance of the film obtained by coating and drying the conductive polymer dispersion or conductive polymer solution used to form the barrier layer 23 is preferably 100 Ω / □ or less. A sufficiently low sheet resistance of the barrier layer 23 helps to avoid poor formation of the electrolytic polymerization layer and an increase in ESR.

[0067] The thickness of the barrier layer 23 is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. By using the thickness of the barrier layer 23 within the above range, the increase of ESR can be avoided, and the formation of the electrolytic polymerization layer on the anode body 10 side can be effectively prevented. The lower limit of the thickness of the barrier layer 23 is not particularly limited, for example, it can be 0.1 μm or more, or 0.5 μm or more.

[0068] The solid electrolytic capacitor 1 includes a carbon layer formed on a second conductive polymer layer 22 and a silver layer formed on the carbon layer as a cathode layer 30. The surface line roughness Ra of the silver layer is preferably 3.0 μm or less. If the silver layer is flat, the dimensional stability is high, and the capacitor can be miniaturized easily. Since the flatter the surface of the electrolytic polymer layer 22 formed under the silver layer, the smaller the surface line roughness Ra of the silver layer, by adopting the electrolyte layer 20 configuration of this disclosure, it is easy to make the surface line roughness Ra of the silver layer within the above-mentioned range.

[0069] Whether the finished capacitor has the structure of the solid electrolytic capacitor disclosed herein can be confirmed by disassembling the capacitor and observing and evaluating it. The finished capacitor may also be, for example, a resin-molded capacitor.

[0070] [Example]

[0071] The following specific embodiments are given to further illustrate the solid electrolytic capacitor of this disclosure, but this disclosure is not limited to these embodiments.

[0072] [Fabrication of Polymer Membranes]

[0073] First, in order to evaluate the properties of the conductive polymer layer used as a barrier layer in a solid electrolytic capacitor, a polymer film was prepared separately using a conductive polymer dispersion for forming the barrier layer.

[0074] (Experimental Example 1)

[0075] As conductive polymer dispersion A, a dispersion was prepared in water by dispersing PEDOT / PSS (a conductive polymer doped with poly(4-styrene sulfonic acid) (PSS) in poly(3,4-ethylenedioxythiophene) (PEDOT), polyester resin (manufactured by Koyo Chemical Industry Co., Ltd., PLASCOAT (registered trademark) Z-687), and ethylene glycol. Based on JIS Z8828:2019, the particle size of the conductive polymer contained in the dispersion was determined by dynamic light scattering using a dynamic light scattering apparatus (manufactured by Otsuka Electronics Co., Ltd., ESLZ-1000ZS). Conductive polymer dispersion A was diluted with pure water to a weight ratio of 50 times, and the measurement was performed using a quartz cell at a wavelength of 660 nm, a scattering angle of 15°, and a temperature of 25°C. The particle size was calculated using the cumulative method (Lavange method). The particle size of the conductive polymer here is the d50 (median particle size) in the number distribution.

[0076] Next, 1 ml of conductive polymer dispersion A was dropped onto a glass plate and dried in a drying oven at 150°C for 30 minutes to obtain polymer film A.

[0077] <Water absorption>

[0078] The obtained polymer film A was cut and placed in a constant temperature and humidity bath at 85°C and 85% RH for 24 hours. After that, it was removed from the constant temperature and humidity bath and a test piece was scraped off with a scraper. The obtained test piece was placed in a thermogravimetric-differential thermal analysis device (Hitachi High Technology Co., Ltd., STA7200) and heated from 25°C to 150°C at a rate of 10°C / min. The weight change of the test piece was measured. Based on the weight of the test piece before heating and at 150°C, the water absorption (%) was calculated using the following formula (1).

[0079] Water absorption (%) = ((weight before heating) - (weight at 150℃)) / (weight at 150℃) × 100 Equation (1)

[0080] <Contact Angle>

[0081] 10 μL of pure water was dropped onto polymer membrane A, which was obtained by the same method as described above, and the contact angle θ relative to the water was measured. Specifically, assuming that the top view of the water droplet on polymer membrane A is a perfect circle, the contact angle θ was calculated using the formula θ = 2arctan(h / r) (θ / 2 method) based on the radius r of the perfect circle and the height h of the water droplet.

[0082] Thin-film resistors

[0083] 1 ml of a conductive polymer dispersion was coated onto a glass plate in a 2.0 × 2.0 cm area and dried in a drying oven at 150 °C for 30 minutes to obtain polymer film A. The film resistance (Ω / □) of the obtained polymer film A was measured using a resistivity meter (Mitsubishi Chemical Corporation, Loresta-GP MCP-T610) via the four-probe method.

[0084] The composition of conductive polymer dispersion A, and the results of the determination of the particle size, water absorption, contact angle with water, and thin-film resistance of the conductive polymer in polymer film A obtained from conductive polymer dispersion A are shown in Table 1.

[0085] (Experimental Examples 2-8)

[0086] Conductive polymer dispersions B to G, having compositions different from conductive polymer dispersion A, were prepared, and the same procedures and measurements were performed as in Experimental Example 1. Furthermore, as conductive polymer solution H, an aqueous solution containing self-doped PEDOT was prepared, and the water absorption, contact angle, and thin-film resistance were measured using the same method as in Example 1. The composition and evaluation results of each conductive polymer dispersion and conductive polymer solution are shown in Table 1.

[0087] [Table 1]

[0088]

[0089] [Manufacturing of Solid Electrolytic Capacitors] (Example 1)

[0090] The solid electrolytic capacitor of Example 1 is manufactured through the following steps 1 to 6.

[0091] (Step 1: Formation of capacitor elements)

[0092] First, tantalum micropowder with a specific charge of approximately 1,500,000 μFV / g was compressed using a powder compactor to obtain a roughly rectangular compact with a diameter of 0.19 mm, a length of 2.5 mm, a width of 1.5 mm, and a thickness of 0.6 mm. The direction along the length of the tantalum wire is the length direction of the compact. The length of the tantalum wire protruding from the surface of the compact is 5.0 mm. The resulting compact was sintered at 1300 °C in an inert gas atmosphere to obtain a porous sintered body of tantalum micropowder. Using the sintered body of tantalum micropowder as a valve metal, it was anodized at 15 V in an aqueous phosphoric acid solution at 85 °C to obtain a capacitor element (anode) with a dielectric oxide film layer composed of tantalum oxide integrally formed on the surface of the sintered body of tantalum micropowder. In the following description, the capacitor element with a certain layer or terminal formed on its surface is sometimes simply referred to as a "capacitor element".

[0093] (Process 2: Chemical Polymerization)

[0094] Next, the capacitor element obtained in step 1 is immersed in a methanol solution of ferric p-toluenesulfonate, which serves as both an oxidant and a dopant, for 10 minutes, then removed from the solution and dried at room temperature for 30 minutes (step 2-a). Then, the capacitor element is immersed in a thiophene derivative (3,4-ethylenedioxythiophene), which serves as a monomer, for 1 minute, then removed from the solution and kept at room temperature for 30 minutes to polymerize 3,4-ethylenedioxythiophene (step 2-b). Afterward, the capacitor element is immersed in ethanol to clean unreacted substances and oxidant residues (step 2-c). This series of polymerization operations, including step 2-a (oxidant filling), step 2-b (polymerization of 3,4-ethylenedioxythiophene), and step 2-c (cleaning), is repeated a total of 6 times to obtain a capacitor element with a first conductive polymer layer (chemically polymerized layer) formed on its surface. This first conductive polymer layer (chemically polymerized layer) is composed of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with p-toluenesulfonic acid.

[0095] (Step 3: Formation of the barrier layer)

[0096] The capacitor element obtained in step 2 is immersed in conductive polymer dispersion A for 1 minute, then lifted out and dried at 150°C for 30 minutes. This yields a capacitor element with a barrier layer formed on the first conductive polymer layer.

[0097] (Process 4: Electrolytic Polymerization)

[0098] The capacitor element obtained in step 3 is immersed in a solution containing 3,4-ethylenedioxythiophene and sodium organic sulfonate, and configured such that a stainless steel wire (Φ1.0mm) is in contact with the capacitor element from the outside as a power supply terminal. Using the power supply terminal side as the anode, a DC voltage of less than 3V is applied, and electrolytic polymerization is performed. This yields a capacitor element with a second conductive polymer layer (electrolytic polymerization layer) formed on the barrier layer.

[0099] (Step 5: Formation of the cathode layer)

[0100] The capacitor element obtained in step 4 is immersed in graphite paste for 1 minute, then removed and dried at 120°C for 1 hour to form a carbon layer on the second conductive polymer layer. Next, the capacitor element is immersed in silver paste for 1 minute, then removed and dried at 120°C for 1 hour to form a silver layer on the carbon layer. The stacked structure of the carbon layer and the silver layer constitutes a cathode layer.

[0101] (Process 6: Electrode installation and molding)

[0102] In the capacitor element obtained in step 5, the valve metal lead is connected to the anode electrode by welding. Furthermore, a conductive adhesive is used to connect the silver layer to the cathode electrode. Finally, an outer resin is formed on the capacitor element using a molding machine to obtain the solid electrolytic capacitor of Example 1.

[0103] (Examples 2~8)

[0104] In step 3, conductive polymer dispersions B to G and conductive polymer solution H are used to replace conductive polymer dispersion A when forming the barrier layer, otherwise the process is the same as in Example 1, and solid electrolytic capacitors of Examples 2 to 8 are obtained.

[0105] (Example 9)

[0106] In order to change the coverage of the barrier layer, only about half of the capacitor element was immersed in the conductive polymer dispersion A in step 3, otherwise the same as in Example 1, to obtain the solid electrolytic capacitor of Example 9.

[0107] (Example 10)

[0108] After step 2 and before step 3, the capacitor element is immersed in a primer solution (5% by mass of 1,10-decanediamine aqueous solution) for 1 minute and dried at 125°C for 30 minutes to perform primer treatment. Otherwise, it is the same as in Example 1, and the solid electrolytic capacitor of Example 10 is obtained.

[0109] (Examples 11~14)

[0110] In order to change the thickness of the barrier layer, in step 3, the number of repetitions of the step of immersing in the conductive polymer dispersion A for 1 minute and the step of drying for 30 minutes were changed to 3 times, 5 times, 10 times and 15 times respectively. Otherwise, it was the same as in Example 1, and solid electrolytic capacitors of Examples 11 to 14 were obtained.

[0111] (Example 15)

[0112] The barrier layer was not formed by performing step 3, but otherwise it was the same as in Example 1, resulting in the solid electrolytic capacitor of Example 15.

[0113] (Example 16)

[0114] In step 2, the number of repetitions of steps 2-a to 2-c is set to 10, and steps 3 to 4 are not performed so that the barrier layer and electrolytic polymerization layer are not formed. Otherwise, it is the same as in Example 1, and the solid electrolytic capacitor of Example 16 is obtained.

[0115] The solid electrolytic capacitors of Examples 1 to 16 were evaluated for coverage, withstand voltage, equivalent series resistance (ESR), and surface roughness of the capacitor elements.

[0116] Coverage

[0117] After the barrier layer formation in step 3 is completed and before step 4 is performed, the appearance of the barrier layer formation on the five surfaces of each capacitor element (excluding the surface with protruding tantalum wires) is photographed using an optical microscope (KEYENCE, VHX-5000). The photographs are saved as bitmaps. The saved photographs are imported into spreadsheet software (Microsoft Excel) as binary data, and the pixel information of the image is extracted from the binary data. The pixel information is converted to grayscale using a luminance method. A histogram is created based on the grayscale values, and a binarization threshold is determined using a pattern method. The image is binarized using the determined threshold, defining the covered portion of the barrier layer on the capacitor element as black and the uncovered portion as white. The coverage rate of the barrier layer is calculated based on the ratio of the pixels determined to be black to the outer surface area of ​​the capacitor element. Furthermore, the outer surface area of ​​the capacitor element here does not take into account the actual surface area of ​​the pores of the capacitor element as a porous body, but rather the surface area when the capacitor element is viewed as a cuboid without considering the pores.

[0118] <Voltage Withstand>

[0119] Each capacitor was placed in a constant temperature bath at 85°C, and the voltage was increased at a rate of 1V / second while the current value was measured when a DC voltage was applied. The voltage at which the current value exceeded 200mA was defined as the withstand voltage (V).

[0120] <Equivalent Series Resistance (ESR)>

[0121] For each capacitor, the equivalent series resistance (ESR) at 100 kHz was measured using an LCR meter (Hewlett Packard, 4263B LCR METER).

[0122] Surface roughness

[0123] After the silver layer is formed in step 6 and before step 7, the surface roughness of the capacitor element is measured. Specifically, a three-dimensional measuring machine (KEYENCE, VR-6100) is used to measure the line roughness at three different locations on the surface of the capacitor element where the silver layer has been formed, and the surface line roughness Ra (μm) is calculated based on the average of the three measurements.

[0124] The evaluation results of the solid electrolytic capacitors in Examples 1 to 16 are shown in Tables 2 and 3.

[0125] [Table 2]

[0126]

[0127] [Table 3]

[0128]

[0129] In Tables 2 and 3, Examples 1, 2, 5-13 are exemplary cases, and Examples 3, 4, 15, and 16 are comparative examples. Based on the comparison of Examples 1 and 15, it can be seen that the withstand voltage is improved by providing a barrier layer. Based on Examples 1-3 and Examples 9-12, it can be seen that the higher the coverage of the barrier layer, the higher the withstand voltage. Based on Examples 1 and 10-14, it can be seen that the smaller the thickness of the barrier layer, the smaller the equivalent series resistance.

[0130] Furthermore, in the case of forming a barrier layer with low hydrophobicity as in Examples 3 and 4, the barrier layer swells and the surface linear roughness Ra deteriorates. However, in barrier layers with improved hydrophobicity as in Examples 1, 2, 5, 6, and 7, swelling can be suppressed and the deterioration of surface roughness can be prevented. Here, as a method to improve the hydrophobicity of the barrier layer, examples include using anion with hydrophobicity having long-chain alkyl or phenyl groups as a dopant, adding a hydrophobic binder resin to the dispersion, etc., but are not limited to these methods.

[0131] Table 2

[0132] Table 3

[0133] Explanation of reference numerals in the attached figures

[0134] 1, 101, 201 solid electrolytic capacitors

[0135] 10 Anode Body

[0136] 11 valve metal

[0137] 12 Dielectric Oxide Film Layer

[0138] 20, 120, 220 electrolyte layers

[0139] 21, 121, 221 First conductive polymer layer (chemical polymerization layer)

[0140] 22, 122, 222 Second conductive polymer layer (electrolytic polymerization layer)

[0141] 23 Barrier Layers

[0142] 223 conductive polymer layer

[0143] 30 cathode layers

[0144] 40 anode lead

[0145] 50 conductive adhesive

[0146] 60a and 60b lead frames

[0147] 70 outer resin

Claims

1. A solid electrolytic capacitor comprising a porous anode body having a valve metal and a dielectric oxide film layer formed on a surface of the valve metal, and an electrolyte layer formed on a surface of the dielectric oxide film layer, the electrolyte layer comprising: a first conductive polymer layer formed by chemical polymerization, in contact with the dielectric oxide film layer; a second conductive polymer layer formed by electrolytic polymerization, formed on an opposite side of the dielectric oxide film layer from the first conductive polymer layer; and a barrier layer formed between the first conductive polymer layer and the second conductive polymer layer and having conductivity, the barrier layer preventing formation of a conductive polymer layer by electrolytic polymerization in a region on the anode body side of the barrier layer.

2. The solid electrolytic capacitor according to claim 1, the barrier layer being formed by applying and drying a conductive polymer dispersion liquid or a conductive polymer solution.

3. The solid electrolytic capacitor according to claim 2, a particle size d50 in a number distribution of the conductive polymer contained in the conductive polymer dispersion liquid being 5 nm or more.

4. The solid electrolytic capacitor according to claim 1 or 2, a water absorption amount of the barrier layer under an atmosphere of a temperature of 85°C and a humidity of 85% RH for 24 hours being 50% by mass or less.

5. The solid electrolytic capacitor according to claim 1 or 2, a proportion of an area in which the barrier layer is formed with respect to an area of a face of the anode body in which the electrolyte layer is formed being 50% or more.

6. The solid electrolytic capacitor according to claim 1 or 2, the first conductive polymer layer being subjected to primer treatment.

7. The solid electrolytic capacitor according to claim 2, a sheet resistance of a film obtained by applying and drying the conductive polymer dispersion liquid or the conductive polymer solution used to form the barrier layer being 100 Ω / D or less.

8. The solid electrolytic capacitor according to claim 1 or 2, a thickness of the barrier layer being 30 μm or less.

9. The solid electrolytic capacitor according to claim 1 or 2, further comprising a carbon layer formed on the second conductive polymer layer, and a silver layer formed on the carbon layer, a surface line roughness Ra of the silver layer being 3.0 μm or less.

10. A method of manufacturing a solid electrolytic capacitor, comprising: a step of forming a first conductive polymer layer by chemical polymerization on a surface of a porous anode body having a valve metal and a dielectric oxide film layer formed on a surface of the valve metal; a step of forming a barrier layer having conductivity on the first conductive polymer layer; and a step of forming a second conductive polymer layer by electrolytic polymerization on the barrier layer.

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