Electrolytic capacitor and method for manufacturing the same

Abstract

To provide an electrolytic capacitor with reduced leakage current and a manufacturing method thereof.SOLUTION: An electrolytic capacitor includes an etching layer provided on the surface of an electrode foil made of a valve metal, a dielectric oxide film layer formed on the surface of the etching layer, and a solid electrolyte layer containing thiophene or a derivative thereof formed by electrolytic polymerization on the dielectric oxide film layer, and the solid electrolyte layer contains a fibrous polymer formed in a network. Thiophene or a derivative thereof is 3,4-ethylenedioxythiophene or a derivative thereof.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrolytic capacitor and a method for manufacturing the same. [Background technology]

[0002] An electrolytic capacitor is constructed by forming a dielectric oxide film layer on the surface of an anode electrode made of a valve metal such as tantalum or aluminum and having micropores and etching pits, and then drawing out an electrode from the dielectric oxide film layer. The electrode is drawn out from the dielectric oxide film layer through a conductive electrolyte layer.

[0003] The electrolyte layer is required to have adhesion to the dielectric oxide film layer, density, uniformity, etc. In particular, adhesion inside the micropores and etching pits of the anode electrode has a large effect on the electrical properties, and so many electrolyte layers have been proposed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 173313 / 1983 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, conductive polymers such as polypyrrole are mainly produced by chemical oxidation polymerization (chemical polymerization) or electrolytic oxidation polymerization (electrolytic polymerization), but it is difficult to produce a strong and dense film by chemical polymerization. On the other hand, when a solid electrolyte layer is formed by electrolytic polymerization, it is desirable to improve the electrochemical properties of the capacitor.

[0006] The present invention has been proposed to solve the above problems, and has an object to provide an electrolytic capacitor with reduced leakage current and a method for manufacturing the same. [Means for solving the problem]

[0007] (1) The electrolytic capacitor of the present invention comprises an etching layer provided on a surface of an electrode foil made of a valve metal, a dielectric oxide film layer formed on the surface of the etching layer, and a solid electrolyte layer containing thiophene or a derivative thereof formed by electrolytic polymerization on the dielectric oxide film layer, the solid electrolyte layer containing a fibrous polymer formed in a mesh pattern.

[0008] (2) The fibrous polymer may be formed in a region within one-third of the surface of the etching layer.

[0009] (3) The thiophene or its derivative may be 3,4-ethylenedioxythiophene or its derivative.

[0010] A method for producing the electrolytic capacitor as described above is also an aspect of the present invention. Effect of the Invention

[0011] According to the present invention, it is possible to provide an electrolytic capacitor with reduced leakage current and a method for manufacturing the same. [Brief description of the drawings]

[0012] [Figure 1] 1A and 1B are views showing SEM images of electrode foils, where (a) shows an SEM image of an example, and (b) shows an SEM image of a comparative example. [Diagram 2] FIG. 2 shows SEM images of electrode foils, where (a) shows an SEM image of an example, and (b) to (d) show SEM images of comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] [1. Configuration] The electrolytic capacitor of this embodiment includes an electrode foil. The electrode foil can be used as the anode foil or cathode foil of the electrolytic capacitor, or may be used as both the anode foil and the cathode foil. The electrolytic capacitor can be a solid electrolytic capacitor in which the electrolyte is solid, or a hybrid electrolytic capacitor in which the electrolyte is a liquid and a solid. In addition to a laminated capacitor, the electrolytic capacitor can be a wound capacitor including a capacitor element in which an anode foil and a cathode foil are laminated with a separator interposed therebetween and wound.

[0014] The electrode foil is a foil made of a valve metal, such as aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode foil is preferably 99.9% or more, and that of the cathode foil is preferably 99% or more, but impurities such as silicon, iron, copper, magnesium, and zinc may be included.

[0015] The electrode foil has both sides enlarged by etching. That is, an etching layer with an enlarged surface area is formed on the surface of the electrode foil by performing electrochemical etching in an aqueous solution containing chloride to roughen the surface. The etching layer includes tunnel-like pits and spongy pits, and these pits can be considered to form voids within the layer. The electrode foil has a residual core portion that is not reached by the etching process. Furthermore, a dielectric oxide film layer is formed on the surface of the etching layer of the electrode foil by chemical conversion treatment depending on the application. The dielectric oxide film is formed by oxidizing the surface of the electrode foil, including the inner wall surface of the etching layer.

[0016] A solid electrolyte layer is formed on the electrode foil. The solid electrolyte layer of this embodiment is formed uniformly on the dielectric oxide film layer of the etching layer by electrolytic polymerization using thiophene or a derivative thereof. That is, the solid electrolyte layer contains thiophene or a derivative thereof. However, the solid electrolyte layer does not fill all of the voids present in the etching layer of the electrode foil, but is formed along the inner wall surface of the etching layer, so that voids remain in the etching layer.

[0017] Furthermore, in the gaps left in the etching layer, the solid electrolyte layer contains a fibrous polymer formed in a mesh-like shape. Specifically, the fibrous polymer is formed inside the etching layer so as to connect the solid electrolyte layer formed on the surface of the etching layer. Therefore, the fibrous polymer is spread in a mesh-like shape in the gaps in the etching layer. The fibrous polymer is preferably formed in a region within 1 / 3 of the surface side of the etching layer. As described above, the presence of the fibrous polymer in the etching layer means that there are gaps in the solid electrolyte layer.

[0018] The electrode foil on which the solid electrolyte layer is formed may be subjected to a repair chemical formation. There may be defects in the dielectric oxide film layer, but this repair chemical formation forms a dielectric oxide film at the defective portion, thereby repairing the defective portion. As described above, if there are voids in the solid electrolyte layer, the repair chemical formation liquid can easily penetrate into the defective portion of the film, accelerating the repair of the defective portion. This reduces the leakage current of the electrolytic capacitor.

[0019] A laminated capacitor element or a wound capacitor element is formed using the electrode foil as described above. The capacitor element is housed in a metal exterior case and sealed with a sealing body. The material of the exterior case can be aluminum, an aluminum alloy containing aluminum and manganese, or stainless steel. The sealing body can be rubber or a hard substrate. The sealing can be performed by covering the capacitor element with a laminate film. The capacitor element can also be sealed by molding it with a resin such as a heat-resistant resin or an insulating resin, or by forming the resin into a thin film on the capacitor element using a method such as dip coating or printing. The electrode foil has leads formed thereon for connecting each electrode to the outside. The leads are electrode extraction means for electrically connecting the electrode foil to the outside. The shape and formation method of these leads can be appropriately designed depending on the electrolytic capacitor. After that, an aging process is performed, and the production of the electrolytic capacitor is completed.

[0020] [2. Manufacturing method of electrolytic capacitors] The method for manufacturing the electrolytic capacitor of this embodiment as described above includes the following steps. (1) Pretreatment of electrode foil with warm water (2) A chemical conversion treatment process in which a dielectric oxide film layer is formed on the pretreated electrode foil. (3) Heat treatment of the electrode foil that has been chemically treated (4) An electrolytic polymerization step of forming a solid electrolyte layer containing thiophene or its derivative on the heat-treated electrode foil.

[0021] Each step will now be described in detail. (1) Pretreatment of electrode foil with warm water In the manufacture of an electrolytic capacitor, first, a flat valve metal foil such as aluminum is etched, and then a chemical conversion treatment is performed to form a dielectric oxide film layer. The dielectric oxide film layer is typically formed by performing a chemical conversion treatment in which an electrode foil is used as an anode in a chemical conversion solution that does not contain halogen ions, and a voltage is applied. As the chemical conversion solution, a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, or an adipic acid-based chemical conversion solution such as ammonium adipate can be used. The temperature of the chemical conversion solution in the chemical conversion treatment is preferably 10 to 95°C.

[0022] Then, the electrode foil is cut into a predetermined shape with a laser to obtain an electrode foil. The electrode foil is pretreated by immersing it in hot water. The temperature of the hot water is preferably 80 to 100°C. The time for immersing the electrode foil in the hot water is preferably 10 to 600 seconds. It is believed that this pretreatment using hot water forms a hydrated oxide layer in the form of scales on the cut surface of the electrode foil. The formation of hydrated oxide on the cut surface of the electrode foil in the hot water treatment allows a uniform dielectric oxide film layer to be formed by the subsequent end surface conversion treatment, which in turn contributes to the formation of a uniform solid electrolyte layer.

[0023] (2) A process in which a dielectric oxide film layer is formed by performing a chemical conversion treatment on the pretreated electrode foil. Next, the cut surface of the pretreated electrode foil is subjected to an end surface chemical conversion treatment to form a dielectric oxide film layer on the cut surface of the electrode foil. The dielectric oxide film layer can be formed under the same conditions as the chemical conversion treatment. For the electrode foil after the end surface chemical conversion treatment, an insulating resist may be printed and then dried to form a resist layer, if necessary. The insulating resist layer may be formed before the end surface chemical conversion treatment. In the above description, the electrode foil is cut after the dielectric oxide film layer is formed, pretreated with hot water, and then a dielectric oxide film layer is further formed on the cut surface of the electrode foil. However, the electrode foil that has been cut in advance may be pretreated with hot water, and then chemical conversion treatment may be performed once, including the end surface of the electrode foil, to form a dielectric oxide film.

[0024] (3) Heat treatment of the electrode foil that has been chemically treated The electrode foil after the chemical conversion treatment is placed in an electric furnace and heat-treated. The temperature of the heat treatment is preferably 250 to 500°C. The treatment time is preferably 1 to 60 minutes. This heat treatment makes the state of the dielectric oxide film on the surface of the electrode foil uniform, which contributes to the formation of a uniform solid electrolyte layer.

[0025] (4) A process of forming a solid electrolyte layer on the heat-treated electrode foil by electrolytic polymerization. The heat-treated electrode foil is electrolytically polymerized to form a solid electrolyte layer. The solid electrolyte layer can be formed by immersing the electrode foil in a polymerization solution and then electrolytically polymerizing the foil at a predetermined temperature. If necessary, the immersion in the polymerization solution and electrolytic polymerization may be repeated several times. The polymerization solution is a solution containing at least a monomer, a supporting electrolyte, and a solvent. Thiophene or its derivatives may be used as the monomer.

[0026] Examples of thiophene or its derivatives include 3,4-ethylenedioxythiophene (EDOT), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, and 3,4-alkoxythiophene. The number of carbon atoms of the alkyl group or alkoxy group is preferably 1 to 16. Among these, it is preferable to use 3,4-ethylenedioxythiophene, since it is possible to form a solid electrolyte layer with excellent thermal stability. In addition, thiophene or its derivatives may be a compound in which a side chain having an alkyl group is bonded to the ethylene group of EDOT. Examples include 2-ethyl-3,4-ethylenedioxythiophene (Et-EDOT), 2-butyl-3,4-ethylenedioxythiophene, and the like. Among these, the use of Et-EDOT may further improve leakage current characteristics.

[0027] The solvent of the polymerization solution is a non-aqueous solvent, and an organic solvent can be used. In particular, when acetonitrile is used as the solvent, the solid electrolyte layer may be formed uniformly. Since acetonitrile has low solubility of the oligomer of the monomer formed during electrolytic polymerization, it is considered that the solid electrolyte layer is formed uniformly on the electrode foil because the oligomer is prevented from diffusing into the solvent and the oligomer can be efficiently used for forming the solid electrolyte layer.

[0028] The polymerization liquid further contains a supporting electrolyte. The supporting electrolyte includes at least one compound selected from the group consisting of borodisalicylic acid and borodisalicylic acid salts. Examples of the salt include alkali metal salts such as lithium salts, sodium salts, and potassium salts, alkyl ammonium salts such as ammonium salts, ethyl ammonium salts, and butyl ammonium salts, dialkyl ammonium salts such as diethyl ammonium salts and dibutyl ammonium salts, trialkyl ammonium salts such as triethyl ammonium salts and tributyl ammonium salts, and tetraalkyl ammonium salts such as tetraethyl ammonium salts and tetrabutyl ammonium salts. The supporting electrolyte is preferably a quaternary ammonium salt. Quaternary ammonium salts have high electrical conductivity, and the current distribution to the electrode foil during electrolytic polymerization becomes uniform, so that the solid electrolyte layer is formed more uniformly, which leads to a reduction in leakage current. Examples of the quaternary ammonium ions of the quaternary ammonium salt include tetramethyl ammonium, triethyl methyl ammonium, and tetraethyl ammonium. For example, tetraethyl ammonium borodisalicylate (TeEA-BS), tetramethyl ammonium borodisalicylate (TeMA-BS), and the like can be used as the supporting electrolyte.

[0029] The polymerization temperature in the electrolytic polymerization is preferably -32°C or lower. By setting the polymerization temperature to -32°C or lower, leakage current of the electrolytic capacitor is reduced. The lower limit of the polymerization temperature may be determined based on the freezing point of the solvent. For example, when acetonitrile is used as the solvent, acetonitrile freezes at -45°C, so that current cannot be passed and a solid electrolyte layer cannot be formed. Therefore, when acetonitrile is used as the solvent, the polymerization temperature is preferably -32 to -44°C. The current conditions in the electrolytic polymerization vary depending on the shape of the electrode foil, but when electrolytic polymerization is performed on a flat electrode foil of, for example, 4 x 5 mm, the current is 5 to 10 mAcm. -2 It can be said that:

[0030] The electrode foil on which the solid electrolyte layer is formed may be subjected to a repair chemical formation. This repair chemical formation is a process for forming a dielectric oxide film on defective parts of the dielectric oxide film layer. As the chemical formation liquid, a phosphoric acid-based chemical formation liquid such as ammonium dihydrogen phosphate, a boric acid-based chemical formation liquid such as ammonium borate, an adipic acid-based chemical formation liquid such as ammonium adipate, or a chemical formation liquid in which boric acid and dicarboxylic acid such as citric acid are mixed can be used. The repair chemical formation treatment is performed by immersing the electrode foil on which the solid electrolyte layer is formed in the chemical formation liquid and applying a constant voltage. The applied voltage in the repair chemical formation treatment is appropriately set according to the chemical formation voltage of the electrode foil, and it is preferable to set the applied voltage during the repair chemical formation to, for example, 0.1 to 1.2 times the chemical formation voltage. The temperature of the chemical formation liquid in the repair chemical formation treatment is preferably 10 to 95°C. The treatment time is preferably 1 to 60 minutes.

[0031] The electrode foil obtained as described above can be appropriately treated in accordance with the design of the electrolytic capacitor, such as by forming leads for connecting each electrode to the outside. In addition, the obtained electrolytic capacitor may be further subjected to an aging treatment by applying a voltage.

[0032] [3. Effects] (1) The electrolytic capacitor of this embodiment includes an etching layer provided on a surface of an electrode foil made of a valve metal, a dielectric oxide film layer formed on the surface of the etching layer, and a solid electrolyte layer containing thiophene or a derivative thereof formed by electrolytic polymerization on the dielectric oxide film layer, wherein the solid electrolyte layer contains a fibrous polymer formed in a mesh pattern.

[0033] By forming a solid electrolyte layer containing thiophene or its derivatives by electrolytic polymerization, a mesh-like fibrous polymer can be formed, so that the solid electrolyte layer can be formed while leaving voids in the etching layer. As described above, the presence of a fibrous polymer in the solid electrolyte layer means that there are voids in the solid electrolyte layer. If there are voids in the solid electrolyte layer, the repair chemical solution can easily penetrate into the defective parts of the dielectric oxide film layer, and the repair of the defective parts is promoted. Therefore, the leakage current of the electrolytic capacitor can be reduced.

[0034] (2) The fibrous polymer is formed in a region within one-third of the surface of the etching layer.

[0035] Since the fibrous polymer is formed so as to reach the depth of the etching layer, many voids are left in the solid electrolyte layer. Therefore, the repair chemical solution can easily penetrate into the defects in the dielectric oxide film layer, accelerating the repair of the defects. This further reduces the leakage current of the electrolytic capacitor.

[0036] (3) The thiophene or its derivative is 3,4-ethylenedioxythiophene or its derivative.

[0037] By using 3,4-ethylenedioxythiophene or a derivative thereof as thiophene or a derivative thereof, it is possible to significantly reduce leakage current.

[0038] (4) The method for producing an electrolytic capacitor of the present embodiment includes a chemical conversion treatment step of forming a dielectric oxide film layer on an electrode foil made of a valve metal having an etching layer on its surface, and an electrolytic polymerization step of forming a solid electrolyte layer containing thiophene or a derivative thereof on the electrode foil on which the dielectric oxide film layer has been formed. In the electrolytic polymerization step, the electrode foil is immersed in a polymerization solution containing thiophene or a derivative thereof and a non-aqueous solvent, and electrolytic polymerization is performed at −32° C. or lower.

[0039] The above-mentioned manufacturing method makes it possible to form a solid electrolyte layer containing a fibrous polymer formed in a mesh shape. In particular, by using a polymerization solution containing thiophene or its derivative and a non-aqueous solvent and setting the polymerization temperature to -32°C or lower, it becomes possible to form a solid electrolyte layer containing a fibrous polymer. In the electrolytic capacitor manufactured in this way, the leakage current is reduced, and therefore the performance of the electrolytic capacitor can be improved.

[0040] (5) The non-aqueous solvent is acetonitrile.

[0041] Since acetonitrile has low solubility for the oligomers of the monomers formed during electrolytic polymerization, it is believed that the oligomers are prevented from diffusing into the solvent, and the oligomers can be efficiently used to form the solid electrolyte layer, leading to the formation of a uniform solid electrolyte layer on the electrode foil, thereby ensuring a reduction in leakage current.

[0042] (6) The polymerization liquid further contains a supporting electrolyte, and the supporting electrolyte is a quaternary ammonium salt.

[0043] For example, when the supporting electrolyte is a tertiary amine salt, it is possible to form a solid electrolyte layer, but due to its low electrical conductivity, the solid electrolyte layer may be concentrated in areas of the surface of the electrode foil where current is likely to concentrate during electrolytic polymerization, which may lead to an increase in leakage current. On the other hand, by using a quaternary ammonium salt with high electrical conductivity, current concentration on the surface of the electrode foil is alleviated, and a solid electrolyte layer is formed uniformly on the electrode foil, improving the leakage current characteristics of the electrolytic capacitor.

[0044] (7) The method further includes a step of pretreating the electrode foil with hot water prior to the chemical conversion treatment step.

[0045] It is believed that a hydrated oxide layer is formed in a scale-like shape on the cut surface of the electrode foil by performing a pretreatment using hot water before the chemical conversion treatment process on the cut surface of the electrode foil. The formation of a hydrated oxide on the cut surface of the electrode foil in the pretreatment using hot water allows a uniform dielectric oxide film layer to be formed in the subsequent chemical conversion treatment. Therefore, it becomes possible to form a uniform solid electrolyte layer.

[0046] (8) The method further includes a step of heat treating the electrode foil in an electric furnace after the chemical conversion treatment step.

[0047] By carrying out a heat treatment in an electric furnace after the chemical conversion treatment, the state of the dielectric oxide film layer on the electrode foil surface can be made uniform. Therefore, a uniform solid electrolyte layer can be formed. Furthermore, the capacitance of the electrolytic capacitor can be improved.

[0048] (9) The method further includes a repair chemical conversion step of forming a dielectric oxide film on a defect generated in the dielectric oxide film layer after the electrolytic polymerization step.

[0049] When the dielectric oxide film is repaired by chemical conversion after the electrolytic polymerization process, the chemical conversion solution can easily penetrate into the defective parts of the film through the voids in the solid electrolyte layer where the fibrous polymer is formed, and the repair of the defective parts is promoted, thereby reducing the leakage current of the electrolytic capacitor. EXAMPLES

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0051] Example 1 An electrode foil (nominal chemical conversion voltage: 8V) made of aluminum that had been etched and chemically treated was cut into a specified shape by a laser and then subjected to a pretreatment process in which it was immersed in pure water at 95°C for 120 seconds. After this pretreatment process, a chemical conversion process was performed to form a dielectric oxide film layer on the laser cut surface of the electrode foil. Specifically, a 90°C aqueous solution of ammonium dihydrogen phosphate was used, and a current density of 200 μA cm was applied. -2 A current was applied for 600 seconds at 100°C. After that, an insulating resist layer was printed and dried at 150°C for 20 minutes.

[0052] After the insulating resist layer was formed, the electrode foil was placed in an electric furnace at 300°C for 20 minutes for heat treatment. The electrode foil after heat treatment was immersed in a polymerization solution, and a solid electrolyte layer was formed by electrolytic polymerization. The polymerization solution contained 480 mM Et-EDOT and acetonitrile, and 260 mM tetraethylammonium borodisalicylate (TeEA-BS) as a supporting electrolyte. After immersing the electrode foil in this polymerization solution, it was heated at -44°C with 5 mAcm -2 A current of 10 ...

[0053] The electrode foil obtained in this manner was printed with carbon paste and dried at 120°C for 10 minutes, then printed with silver paste and dried at 150°C for 30 minutes to form a cathode terminal. The insulating resist layer and the dielectric oxide film layer were peeled off at predetermined locations using a laser to expose the electrode foil, and an anode terminal was formed on this exposed portion. The formation of the anode terminal includes pre-plating treatment and plating treatment. In addition to the laser method, the insulating resist layer and the dielectric oxide film layer can also be peeled off mechanically by pressing a jig against them.

[0054] The pre-plating treatments were as follows: Alkaline etching as smut treatment (treatment solution: K-130 aqueous solution (Kanigen Japan Co., Ltd.), treatment temperature: 55°C, treatment time: 60 seconds) Desmutting (treatment solution: 30% nitric acid aqueous solution, treatment temperature: room temperature, treatment time: 60 seconds) First Zn replacement treatment (treatment solution: K-102 aqueous solution (Kanigen Japan Co., Ltd.), treatment temperature: room temperature, treatment time: 20 seconds) Zn stripping treatment (treatment solution: 30% nitric acid aqueous solution, treatment temperature: room temperature, treatment time: 30 seconds) Second Zn replacement treatment (treatment solution: K-102 aqueous solution (Kanigen Japan Co., Ltd.), treatment temperature: room temperature, treatment time: 30 seconds)

[0055] The plating process was carried out in the following order: Electrolytic Ni plating (treatment solution: watt bath, treatment temperature: 50°C, current density: -100mAcm -2 , Processing time: 10 minutes) Electrolytic Sn / Ag plating (treatment solution: neutral Sn plating bath, treatment temperature: 50°C, current density: -10mAcm -2 , Processing time: 10 minutes) The Watt bath contains 300 g / L nickel sulfate hexahydrate, 50 g / L nickel chloride hexahydrate, and 40 g / L boric acid, and the neutral Sn plating bath contains 0.1 M tin sulfate, 0.01 M silver nitrate, and 0.2 M sodium pyrophosphate.

[0056] The cathode terminal and the anode terminal were formed as capacitor elements in the above manner, and the elements were divided into individual pieces by a laser to obtain electrolytic capacitors. The rated voltage of the electrolytic capacitor was 4 V. The obtained electrolytic capacitor was subjected to an aging treatment at 125° C. with a current density of 1 mA / element and a voltage of 4.6 V applied for 60 minutes.

[0057] Example 2 The electrochemical polymerization was carried out in the same manner as in Example 1, except that the electrochemical polymerization temperature was -40°C. Example 3 The electrochemical polymerization was carried out in the same manner as in Example 1, except that the electrochemical polymerization temperature was -35°C.

[0058] Example 4 The electrochemical synthesis was carried out in the same manner as in Example 1, except that the monomer was EDOT, the supporting electrolyte was 400 mM tetraethylammonium borodisalicylate, and the electropolymerization temperature was -42°C. Example 5 The electrochemical polymerization was carried out in the same manner as in Example 4, except that the electrochemical polymerization temperature was -35°C. Example 6 The electrochemical polymerization was carried out in the same manner as in Example 4, except that the electrochemical polymerization temperature was -32°C.

[0059] Comparative Example 1 The electrochemical polymerization was carried out in the same manner as in Example 1, except that the electrochemical polymerization temperature was -30°C. Comparative Example 2 The electrochemical polymerization was carried out in the same manner as in Example 1, except that the electrochemical polymerization temperature was -20°C. Comparative Example 3 The electrochemical polymerization was carried out in the same manner as in Example 1, except that the electrochemical polymerization temperature was -10°C.

[0060] Comparative Example 4 The preparation was carried out in the same manner as in Comparative Example 1, except that the monomer was EDOT and the supporting electrolyte was 400 mM tetraethylammonium borodisalicylate. Comparative Example 5 The preparation was carried out in the same manner as in Comparative Example 2, except that the monomer was EDOT and the supporting electrolyte was 400 mM tetraethylammonium borodisalicylate.

[0061] Comparative Example 6 The preparation was carried out in the same manner as in Example 1, except that the monomer was pyrrole. Comparative Example 7 The preparation was carried out in the same manner as in Example 2, except that the monomer was pyrrole. Comparative Example 8 The preparation was carried out in the same manner as in Example 3, except that the monomer was pyrrole. Comparative Example 9 It was produced in the same manner as in Comparative Example 1, except that the monomer was pyrrole. Comparative Example 10 It was produced in the same manner as in Comparative Example 2, except that the monomer was pyrrole. Comparative Example 11 It was produced in the same manner as in Comparative Example 3, except that the monomer was pyrrole.

[0062] Comparative Example 12 The preparation was carried out in the same manner as in Example 1, except that the solvent was water. Comparative Example 13 The preparation was carried out in the same manner as in Example 3, except that the solvent was γ-butyrolactone (GBL). Comparative Example 14 The preparation was carried out in the same manner as in Example 3, except that the solvent was propylene carbonate (PC). ( Working Example 15) The preparation was carried out in the same manner as in Example 3, except that the supporting electrolyte was triethylamine borodisalicylate (TEA-BS).

[0063] ( Working Example 16) The electrode foil was produced in the same manner as in Example 5, except that the step of pretreating the electrode foil with hot water prior to the chemical conversion treatment step on the cut surfaces of the electrode foil was not carried out. ( Working Example 17) Except for not carrying out the process of pretreating the electrode foil with hot water prior to the chemical conversion treatment process on the cut surface of the electrode foil, Working Example It was created in the same manner as 15. ( Working Example 18) The electrode foil was produced in the same manner as in Example 5, except that the step of heat treating the electrode foil in an electric furnace after the chemical conversion treatment step was not carried out.

[0064] <SEM image of electrode foil> Among the above examples and comparative examples, SEM images (25,000 times magnification) were taken and observed for Example 3, Comparative Examples 1 to 3, and 9. First, the SEM image of Example 3 is shown in FIG. 1(a), and the SEM image of Comparative Example 9 is shown in FIG. 1(b). In Example 3, in which Et-EDOT was used as a conductive polymer and electrolytic polymerization was performed at −35° C., it was confirmed that a fibrous polymer was formed in the voids of the solid electrolyte layer in a network shape, as surrounded by a solid line circle in the figure. That is, when thiophene or a derivative thereof is used as a conductive polymer under the above-mentioned temperature conditions, the diffusibility of the monomer and the oligomer generated by electrolytic polymerization is low, so that the formation of a solid electrolyte layer during electrolytic polymerization is restricted in the etching layer. Therefore, in the etching layer, a solid electrolyte layer is formed near the surface of the dielectric oxide film layer, while a solid electrolyte layer is difficult to form in the voids of the etching layer. Furthermore, by maintaining the voids of the etching layer, a polymerized film is formed in a fibrous shape from the solid electrolyte layer formed on the dielectric oxide film layer in the etching layer.

[0065] On the other hand, in Comparative Example 9, in which pyrrole was used as a monomer and electrolytic polymerization was performed at -35°C, a solid electrolyte layer was formed to fill the voids in the etching layer, as shown by the dotted circle in the figure, and no voids were present in the solid electrolyte layer. Therefore, the presence of a fibrous polymer could not be confirmed in Comparative Example 9. It was revealed that when pyrrole was used as a monomer, the diffusibility of the monomer was high, and a polymer film was densely formed in the etching layer, so that no voids were present.

[0066] Next, SEM images (25,000 times) of Example 3 and Comparative Examples 1 to 3 using Et-EDOT as a monomer are shown in Fig. 2(a) to (d), respectively. The electrolytic polymerization temperature of Example 3 shown in Fig. 2(a) is -35°C, and as described above, a fibrous polymer is formed in a mesh shape. On the other hand, the electrolytic polymerization temperature of Comparative Examples 1 to 3 shown in Fig. 2(b) to (d) exceeds -32°C. In such Comparative Examples 1 to 3, although a solid electrolyte layer is formed, it is formed so as to fill the voids in the etching layer. Therefore, the presence of the fibrous polymer could not be confirmed. When the electrolytic polymerization temperature exceeds -32°C, the diffusibility of the monomer and the oligomer generated by electrolytic polymerization is improved, and the formation rate of the solid electrolyte layer in the vicinity of the dielectric oxide film layer during electrolytic polymerization is improved. Then, the generation of polymerization reaction points is promoted, and a polymer film is formed so as to fill the voids in the etching layer.

[0067] <Measurement of electrochemical properties> The leakage current, capacitance, and ESR were measured for the above-mentioned Examples 1 to 6 and Comparative Examples 1 to 18. The capacitance was measured by applying an AC of 120 Hz, and the ESR was measured by applying an AC of 100 Hz. The measurement results are shown in the following table.

[0068] [Table 1]

[0069] First, in Comparative Example 12, since water was used as the solvent, a solid electrolyte layer was not formed. Therefore, it was impossible to measure the electrical properties. When water is contained in the solvent, for example, the chemical reaction of aluminum used in the electrode foil becomes dominant, and as a result, it is considered that the electrical oxidation of the monomer becomes inferior, and the formation of the solid electrolyte layer is inhibited. In Examples 1 to 6 and Comparative Examples 1 to 11 and 15 to 18, in which a non-aqueous solvent was used as the solvent for the polymerization liquid, a solid electrolyte layer was formed, and therefore it was found that the solvent should be a non-aqueous solvent.

[0070] Next, Comparative Example 13, in which γ-butyrolactone was used as the solvent, and Comparative Example 14, in which propylene carbonate was used as the solvent, will be examined. In Comparative Examples 13 and 14, in which a solvent other than acetonitrile was used, a solid electrolyte layer was not formed, and it was impossible to measure the electrical characteristics. On the other hand, in Examples 1 to 6 and Comparative Examples 1 to 11 and 15 to 18, in which a non-aqueous solvent using acetonitrile as the solvent for the polymerization solution was used, a solid electrolyte layer was formed. Since acetonitrile has low solubility of the oligomer body of the monomer formed during electrolytic polymerization, the oligomer body generated during electrolytic polymerization can be efficiently used to form a solid electrolyte layer. Therefore, it is considered that the solid electrolyte layer was formed uniformly on the electrode foil. When γ-butyrolactone or propylene carbonate was used as the solvent for the polymerization solution, it is presumed that the solubility of the oligomer body generated during electrolytic polymerization is high, so that the oligomer body generated during the electrolytic polymerization reaction is difficult to precipitate as a solid electrolyte layer on the electrode foil, and therefore the solid electrolyte layer was not formed.

[0071] Next, Examples 1 to 6 and Comparative Examples 1 to 11 and 15 to 18 in which a solid electrolyte layer was formed will be examined. First, Examples 1 to 3 and Comparative Examples 1 to 3 were prepared using Et-EDOT as a monomer. Here, the electrolytic polymerization temperature in Examples 1 to 3 was -35°C or lower, and the electrolytic polymerization temperature in Comparative Examples 1 to 3 was higher than -35°C. Comparing Examples 1 to 3 and Comparative Examples 1 to 3, in Examples 1 to 3 in which Et-EDOT was used as a monomer and the electrolytic polymerization temperature was -35°C or lower, a mesh-like fibrous polymer was formed in the solid electrolyte layer, so that the repair chemical solution easily penetrates into the defective parts of the dielectric oxide film layer, and repair of the defective parts is considered to be promoted. Therefore, it was found that the leakage current of the electrolytic capacitor was reduced.

[0072] In addition, Examples 4 to 6 and Comparative Examples 4 and 5 were prepared using EDOT as a monomer. Here, the electrolytic polymerization temperature in Examples 4 to 6 was -32°C or lower, and the electrolytic polymerization temperature in Comparative Examples 4 and 5 was higher than -32°C. Comparing Examples 4 to 6 with Comparative Examples 4 and 5, in Examples 4 to 6 in which the electrolytic polymerization temperature was -32°C or lower, a mesh-like fibrous polymer was formed in the solid electrolyte layer, so that the repair chemical solution easily penetrated into the defective parts of the dielectric oxide film layer, and repair of the defective parts was promoted. Therefore, it was revealed that the leakage current was significantly reduced.

[0073] It was found that the leakage current characteristics were significantly improved in all of Examples 1 to 3 and Examples 4 to 6. Here, when Example 3 and Example 5 were compared, it was found that, when the electrolytic polymerization temperature was the same at -35°C, Example 3, which used Et-EDOT as a monomer, had a reduced leakage current compared to Example 5, which used EDOT as a monomer. In other words, it was found that the leakage current characteristics were further improved when Et-EDOT was used as a monomer.

[0074] As is clear from Comparative Examples 6 to 11, when pyrrole was used as a monomer, a solid electrolyte layer was formed, but no significant effect was observed in each characteristic. Comparing Examples 3 and 5 with Comparative Example 8, it was found that, when the electrolytic polymerization temperature was the same at -35°C, Examples 3 and 5, which used thiophene or its derivative as a monomer, showed significantly improved leakage current characteristics and ESR characteristics.

[0075] Furthermore, the supporting electrolyte was 260 mM of a tertiary amine salt, triethylamine borodisalicylate (TEA-BS). Working Example Example 3 in which the supporting electrolyte was tetraethylammonium borodisalicylate (TeEA-BS) and Example 15 were examined. Working Example 15, even though the polymerization temperature was the same at -35°C, Working ExampleIt was revealed that the leakage current increased in Example 15. This is believed to be because the solid electrolyte layer was formed more uniformly in Example 3 because a quaternary ammonium salt with high conductivity was used.

[0076] In addition to the above, the manufacturing method was different from that of Example 5. Working Example 16 was created. Specifically, Working Example In No. 16, the step of immersing the electrode foil in pure water at 95° C. for 120 seconds was not performed. Working Example In Example 16, the leakage current was increased by about two times compared to Example 5. Working Example The manufacturing method is different from 15. Working Example 17 was produced. Specifically, Working Example In No. 17, the step of immersing the electrode foil in pure water at 95° C. for 120 seconds was not performed. Working Example In 17, Working Example The leakage current was about three times higher than in Example 15. From the above results, it became clear that the leakage current characteristics could be significantly improved by pretreating the electrode foil with warm water before the chemical conversion treatment process for the cut surfaces of the electrode foil.

[0077] In addition, Comparative Example 18 was produced using a manufacturing method different from that of Example 5. Specifically, in Comparative Example 18, the electrode foil was not subjected to heat treatment in an electric furnace at 300°C for 20 minutes, but was immersed in a polymerization solution to form a solid electrolyte by electrolytic polymerization. In Comparative Example 18, the leakage current was increased by about three times compared to Example 5. From the above results, it was revealed that the leakage current characteristics can be significantly improved by performing a process of heat treating the electrode foil in an electric furnace after the chemical conversion treatment process.

Claims

1. an etching layer provided on a surface of an electrode foil made of a valve metal; a dielectric oxide film layer formed on a surface of the etching layer; a solid electrolyte layer containing thiophene or a derivative thereof formed by electrolytic polymerization on the dielectric oxide film layer; the etching layer has voids; the solid electrolyte layer includes a fibrous polymer; an electrolytic capacitor, wherein the fibrous polymer is spread in a mesh-like pattern in the gaps of the etching layer so as to connect the solid electrolyte layer formed on the inner surfaces of the gaps;

2. 2. The electrolytic capacitor according to claim 1, wherein the fibrous polymer is formed in an area within one-third of the surface of the etching layer.

3. 3. The electrolytic capacitor according to claim 1, wherein the thiophene or a derivative thereof is 3,4-ethylenedioxythiophene or a derivative thereof.

4. a chemical conversion treatment step of forming a dielectric oxide film layer on an electrode foil made of a valve metal having an etching layer on its surface; and an electrolytic polymerization step of forming a solid electrolyte layer containing thiophene or a derivative thereof on the electrode foil on which the dielectric oxide film layer is formed, In the electrolytic polymerization step, the electrode foil is immersed in a polymerization solution containing thiophene or a derivative thereof, acetonitrile, and a quaternary ammonium salt as a supporting electrolyte, and electrolytic polymerization is performed at −32° C. or lower; The method further includes a repair chemical conversion step of forming a dielectric oxide film on a defect portion generated in the dielectric oxide film layer after the electrolytic polymerization step, A method for manufacturing an electrolytic capacitor, comprising: leaving voids in the etching layer; and spreading a fibrous polymer in a mesh pattern in the voids of the etching layer so as to connect a solid electrolyte layer formed on the inner surface of the voids.

5. 5. The method for producing an electrolytic capacitor according to claim 4, wherein the thiophene or a derivative thereof is 3,4-ethylenedioxythiophene or a derivative thereof.

6. 6. The method for producing an electrolytic capacitor according to claim 4, further comprising a step of pretreating the electrode foil with hot water before the chemical conversion treatment step.

7. The method for producing an electrolytic capacitor according to claim 4, further comprising the step of heat treating the electrode foil in an electric furnace after the chemical conversion treatment step.

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