Chemical conversion liquid, method for manufacturing electrolytic capacitor, and electrolytic capacitor

Abstract

Disclosed is a chemical conversion liquid which is used for repair of an aluminum oxide film that is formed on at least one of an anode foil and a cathode foil contained in an electrolytic capacitor element, and which is characterized by containing at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid, and a chelating agent that forms an aluminum complex which is bonded to the aluminum oxide film.　

Description

Chemical conversion solution, electrolytic capacitor manufacturing method, and electrolytic capacitor

[0001] The present invention relates to a chemical conversion solution, a method for manufacturing an electrolytic capacitor, and an electrolytic capacitor.

[0002] In a manufacturing process of an electrolytic capacitor, for example, an anode foil and a cathode foil are wound with a separator interposed therebetween, and an oxide film, which serves as a dielectric, is formed on the surface of the wound anode foil (see, for example, Patent Documents 1 and 2).

[0003] International Publication No. 2017 / 090241 Japanese Patent Application Laid-Open No. 2022-59471

[0004] Since minute defects occur in the oxide film during the winding process, etc., the oxide film is repaired by chemical conversion treatment. For example, in the case of solid electrolytic capacitors and hybrid capacitors, chemical conversion treatment is performed using an acidic chemical solution before the conductive polymer layer is formed.

[0005] If too much acid is supplied to the surface of the anode foil, the balance between repair and destruction of the oxide film may be disrupted, resulting in an increase in leakage current. Furthermore, aluminum ions eluted from the oxide film may react chemically with the acid to form insoluble aluminum compounds, which may block the conductive path between the oxide film and the conductive polymer layer and increase the ESR (equivalent series resistance). Increased leakage current and ESR degrade the characteristics of the electrolytic capacitor.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a chemical conversion solution that can improve the characteristics of an electrolytic capacitor, a method for manufacturing an electrolytic capacitor, and an electrolytic capacitor.

[0007] The chemical conversion solution of the present invention is used to repair an aluminum oxide film formed on at least one of an anode foil and a cathode foil included in an electrolytic capacitor element, and is characterized by containing at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid, and a chelating agent that forms an aluminum complex that bonds with the aluminum oxide film.

[0008] In the chemical conversion solution, the electrolytic capacitor element may have a separator sandwiched between the anode foil and the cathode foil, and the aluminum complex may be bonded to a conductive polymer layer formed on the separator.

[0009] The chemical conversion solution may contain aluminum or at least one aluminum compound selected from aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum acetate, aluminum silicate, aluminum lactate, and aluminum fluoride, and the chelating agent may bind to the at least one aluminum compound or aluminum ions ionized from the aluminum.

[0010] In the chemical conversion solution, the molar concentration of the at least one aluminum compound or the aluminum may be 0.000125 to 0.00075 mol / kg.

[0011] In the chemical conversion solution, the electrolytic capacitor element may be impregnated with the electrolytic solution.

[0012] In the chemical conversion solution, the chelating agent may have a molar concentration of 0.0000125 to 0.000125 mol / kg.

[0013] In the chemical conversion solution, the molar concentration of at least one of the phosphoric acid, phosphorous acid, and hypophosphorous acid may be 0.0025 to 0.025 mol / kg.

[0014] In the chemical conversion solution, the chelating agent may contain at least one of nitrilotriacetic acid, ethylenediaminetetraacetic acid, glycoletherdiaminetetraacetic acid, propaminediaminetetraacetic acid, cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid.

[0015] The method for manufacturing an electrolytic capacitor of the present invention includes the steps of forming an electrolytic capacitor element including an anode foil and a cathode foil having an aluminum oxide film formed on at least one of them, and a separator sandwiched between the anode foil and the cathode foil, and, after the step of forming the electrolytic capacitor element, repairing the aluminum oxide film using a chemical conversion solution, wherein the chemical conversion solution contains at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid, and a chelating agent that forms an aluminum complex that bonds with the aluminum oxide film.

[0016] The above manufacturing method may further include a step of forming a conductive polymer layer on the separator after the step of repairing the aluminum oxide film, and the aluminum complex may be bonded to the conductive polymer layer.

[0017] The above manufacturing method may further include a step of impregnating the electrolytic capacitor element with an electrolytic solution after the step of forming the conductive polymer layer.

[0018] The electrolytic capacitor of the present invention has an electrolytic capacitor element including an anode foil and a cathode foil, at least one of which has an aluminum oxide film formed on it, and a separator sandwiched between the anode foil and the cathode foil, and is characterized in that the anode foil, the cathode foil, and the separator are coated with at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid, and an aluminum complex containing a chelating agent and aluminum hydroxide ions in a molar ratio of 1:0.1 to 1:6.

[0019] In the electrolytic capacitor, the separator may include a conductive polymer layer, and the aluminum complex may be bonded to the aluminum oxide film and the conductive polymer layer.

[0020] In the electrolytic capacitor, the electrolytic capacitor element may be impregnated with an electrolyte solution containing the aluminum complex.

[0021] According to the present invention, the characteristics of an electrolytic capacitor can be improved.

[0022] FIG. 1 is a side view showing an example of an aluminum electrolytic capacitor. FIG. 2 is a perspective view showing an example of an electrolytic capacitor element. FIG. 3 is a cross-sectional view showing a portion of a cross section taken along line A-A in FIG. 2. FIG. 4 is a flowchart showing an example of a manufacturing process for an aluminum electrolytic capacitor. FIG. 5 is a diagram showing an example of a buffering effect against an acid in a chemical conversion solution. FIG. 6 is a diagram schematically showing a chemical reaction between a chelating agent, aluminum hydroxide, phosphoric acid, and water. FIG. 7a is a diagram schematically showing an example of bonding between an aluminum oxide film and a conductive polymer layer. FIG. 7b is a diagram schematically showing another example of bonding between an aluminum oxide film and a conductive polymer layer. FIG. 8 is a diagram schematically showing an example of forming an aluminum oxide film by supplying aluminum ions.

[0023] [Embodiment] (Configuration of Aluminum Electrolytic Capacitor) Fig. 1 is a side view showing an example of an aluminum electrolytic capacitor 1. In Fig. 1, a cross section of the interior of the aluminum electrolytic capacitor 1 is shown in the right half across the center line Lc of the aluminum electrolytic capacitor 1.

[0024] The aluminum electrolytic capacitor 1 is an example of an electrolytic capacitor. In this example, a conductive polymer hybrid aluminum electrolytic capacitor (hereinafter referred to as a hybrid capacitor) is used as the aluminum electrolytic capacitor 1, but a solid electrolytic capacitor may also be used. The aluminum electrolytic capacitor 1 is mounted on an electronic circuit board and is used for coupling, decoupling, smoothing, and the like, for example.

[0025] The aluminum electrolytic capacitor 1 has an electrolytic capacitor element 10, a case 11, a sealing body 12, a seat plate 13, a pair of battledore portions 112, a pair of round bar portions 111, and a pair of lead portions 110. The battledore portions 112, the round bar portions 111, and the lead portions 110 are extraction electrodes of the electrolytic capacitor element 10, with the round bar portions 111 extending from the tip of the battledore portion 112 and the lead portions 110 extending from the tip of the round bar portions 111. Note that while only one of the battledore portions 112 and round bar portions 111 is shown in Figure 1, the other battledore portion 112 and round bar portion 111 are provided symmetrically across the center line Lc.

[0026] Case 11 is made of aluminum and has a cylindrical shape with a closed upper opening. Case 11 covers electrolytic capacitor element 10 and sealing body 12 and functions as an exterior of aluminum electrolytic capacitor 1. The shape of case 11 is not limited to a cylindrical shape and may be a rectangular tube shape.

[0027] Sealing body 12 is a generally cylindrical member made of an elastic material such as butyl rubber, etc. Sealing body 12 is adjacent to electrolytic capacitor element 10 and seals the opening at the bottom of case 11.

[0028] As will be described later, the electrolytic capacitor element 10 has a configuration in which an anode foil, a cathode foil, and a separator (electrolytic paper) are stacked and wound together. A pair of battledore parts 112 are disposed inside the electrolytic capacitor element 10, and a pair of round rod parts 111 extend from the bottom of the electrolytic capacitor element 10.

[0029] The battledore portion 112, the round bar portion 111, and the lead portion 110 are made of aluminum or the like. The pair of battledore portions 112 are crimped to the anode foil and the cathode foil, respectively, and function as the anode terminal and the cathode terminal of the aluminum electrolytic capacitor 1. Each round bar portion 111 is inserted into a pair of through holes 120 formed in the sealing body 12. Note that while only one of the through holes 120 is shown in FIG. 1 , the other through hole 120 is provided at a symmetrical position across the center line L.

[0030] The lead portion 110 has a flat plate shape and is bent into an L shape, with its tip portion extending along the surface of the base plate 13. The portion of the lead portion 110 on the round bar portion 111 side is inserted into a through hole 130 in the base plate 13. The lead portion 110 is soldered to a pad on the electronic circuit board during the reflow process of the electronic circuit board.

[0031] The seat plate 13 is a plate-like member made of resin or the like, and is provided below the case 11 and the sealing member 12. The seat plate 13 supports the case 11 and the sealing member 12 relative to the electronic circuit board on which they are mounted. The seat plate 13 is provided with through holes 130 for the lead portions 110 and grooves 131 for accommodating the bent tip portions of the lead portions 110. The grooves 131 extend outward from near the center along the bottom surface of the seat plate 13. The bottom surface of the seat plate 13 serves as the mounting surface for the aluminum electrolytic capacitor 1 on the electronic circuit board, allowing the plate-like lead portions 110 to be soldered to pads on the electronic circuit board. Note that while this embodiment describes a surface-mount type aluminum electrolytic capacitor 1, the examples described below can also be applied to lead types that do not have the seat plate 13.

[0032] (Configuration of Electrolytic Capacitor Element) Fig. 2 is a perspective view showing an example of an electrolytic capacitor element 10. In Fig. 2, components common to those in Fig. 1 are assigned the same reference numerals, and their description will be omitted. Note that Fig. 2 shows a state before the lead portion 110 is bent. The electrolytic capacitor element 10 has a wound body 100 formed by winding an anode foil 101, a cathode foil 102, and separators 103 and 104, and a pair of lead electrodes 19a and 19b connected to the anode foil 101 and the cathode foil 102. The lead electrode 19a is an anode terminal, and the lead electrode 19b is a cathode terminal.

[0033] The anode foil 101 and the cathode foil 102 are formed, for example, from aluminum and its alloy foil, vapor-deposited foil, or the like. The surface of the anode foil 101 is etched to increase the electrode area. This ensures that the electrolytic capacitor element 10 has a predetermined capacitance. Furthermore, an extremely thin aluminum oxide film is formed on the surface of the anode foil 101 as an oxide coating. This insulates the anode foil 101 from other components. The aluminum oxide film functions as a dielectric, allowing the electrolytic capacitor element 10 to function as a capacitor. The thickness of the anode foil 101 is, for example, 5 to 200 μm. This thickness range is preferable because it achieves an appropriate balance between the strength of the anode foil 101 and the amount of capacitance it generates.

[0034] The surface of the cathode foil 102 may also be subjected to etching. An oxide film, an inorganic layer, or a carbon layer may be formed on the surface of the cathode foil 102.

[0035] The separators 103 and 104 are wound while being sandwiched between the anode foil 101 and the cathode foil 102. The wound body 100 is an example of a layered structure of the separators 103 and 104, the anode foil 101, and the cathode foil 102. The separators 103 and 104 are made of at least one material selected from cellulose, rayon, glass fiber, and the like. The wound body 100 is a substantially cylindrical element formed by winding the anode foil 101, the cathode foil 102, and the separators 103 and 104. In this embodiment, the height direction of the electrolytic capacitor element 10 is defined along the height of this substantially cylindrical shape. The pair of extraction electrodes 19a and 19b extend downward in the height direction of the wound body 100. The height direction substantially coincides with the direction in which the round bar portions 111 of each extraction electrode 19a and 19b extend.

[0036] During the manufacturing process of the aluminum electrolytic capacitor 1, the wound body 100 is immersed in a dispersion or solution of an electrolytic solution and a conductive polymer. This causes the separators 103, 104 to retain the electrolytic solution and the conductive polymer layer. In the case of a solid electrolytic capacitor, the electrolytic solution is not retained. The thickness of the separators 103, 104 is, for example, 1 to 100 μm. This thickness range is preferable because it maintains a good balance between the strength, insulating properties, porosity, and conductive material of the separators 103, 104.

[0037] The electrolyte solution may contain polyhydric alcohols, sulfone compounds, lactone compounds, carbonate compounds, diether compounds of polyhydric alcohols, monohydric alcohols, etc. These may be used alone or in combination of two or more.

[0038] The polyhydric alcohol preferably contains at least one of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, polyalkylene glycol, and glycerin. As the polyalkylene glycol, it is preferable to use polyethylene glycol having an average molecular weight of 200 to 1,000 or polypropylene glycol having an average molecular weight of 200 to 5,000.

[0039] Examples of lactone compounds that can be used include γ-butyrolactone and γ-valerolactone. Examples of carbonate compounds that can be used include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate as a solvent. It is particularly desirable to use ethylene glycol, polyalkylene glycol, γ-butyrolactone, and sulfolane.

[0040] The electrolyte may contain a solute, such as an acid component, a base component, a salt of an acid component and a base component, a nitro compound, or a phenol compound.

[0041] The acid component may be an organic acid, an inorganic acid, or a composite compound of an organic acid and an inorganic acid. Examples of the organic acid include carboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, maleic acid, succinic acid, glutaric acid, adipic acid, benzoic acid, 4-hydroxybenzoic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, and azelaic acid. Examples of the inorganic acid include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, phosphate esters, and phosphate diesters.

[0042] Examples of the composite compound of an organic acid and an inorganic acid that can be used include borodisalicylic acid, borodisalic acid, and borodiglycolic acid.

[0043] The base component may be a primary to tertiary amine, a quaternary ammonium, a quaternized amidinium, or the like. Examples of the primary to tertiary amine that may be used include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, N,N-diisopropylethylamine, tetramethylethylenediamine, hexamethylenediamine, and aniline. Examples of the quaternary ammonium that may be used include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of the quaternized amidinium that may be used include ethyldimethylimidazolinium and tetramethylimidazolinium.

[0044] Fig. 3 is a cross-sectional view showing a portion of a cross section taken along line A-A in Fig. 2. The separator 103 is sandwiched between the anode foil 101 and the cathode foil 102. The anode foil 101 has aluminum oxide films 31 adjacent to the separators 103 on both sides, and aluminum layers 30 between the aluminum oxide films 31.

[0045] The aluminum oxide film 31 functions as a dielectric and is formed on the surface of the etched anode foil 101. A large number of small holes, called pits, are formed in the aluminum oxide film 31 by etching. When the electrolytic capacitor element 10 is immersed in an electrolyte solution during the manufacturing process of the aluminum electrolytic capacitor 1, the electrolyte fills not only the separator 103 but also the pits.

[0046] Prior to the immersion in the electrolyte, a conductive polymer immersion process is performed. By immersing the electrolytic capacitor element 10 in the conductive polymer dispersion, a conductive polymer layer 40 is formed on the separator 103. In this embodiment, an example is given in which the aluminum oxide film 31 is formed on the anode foil 101, but an aluminum oxide film may be formed on the cathode foil 102 instead of the anode foil 101 or together with the anode foil 101.

[0047] 4 is a flowchart showing an example of a manufacturing process for the aluminum electrolytic capacitor 1. In manufacturing the aluminum electrolytic capacitor 1, an anode foil 101, a cathode foil 102, a separator 103, and the like are prepared (step St1). For example, the thickness of the anode foil 101 is 5 to 200 (μm), and the thickness of the separator is 1 to 100 (μm). Pits are formed on the surfaces of the anode foil 101 and the cathode foil 102 by etching.

[0048] A chemical conversion treatment is performed on the anode foil 101, and an aluminum oxide film 31 is formed on the etched surface. A pair of lead electrodes 19 a, 19 b are connected to the anode foil 101 and the cathode foil 102, respectively. The lead electrodes 19 a, 19 b can be connected by, for example, crimping, but the invention is not limited to this.

[0049] Next, the anode foil 101, separator 103, cathode foil 102, and separator 103 are stacked in this order and wound, and the outer surfaces are secured with a winding tape to produce a wound body 100 (step St2). This produces an electrolytic capacitor element 10 prior to immersion in a conductive polymer solution and an electrolyte solution. At this time, minute defects are generated in the aluminum oxide film 31 due to the attachment of the lead electrodes 19a, 19b to the anode foil 101 and the above-mentioned winding. Note that this step is an example of a process for forming an electrolytic capacitor element 10 including the anode foil 101 and the cathode foil 102, at least one of which has the aluminum oxide film 31 formed thereon, and the separator 103 sandwiched between the anode foil 101 and the cathode foil 102.

[0050] Next, the wound body 100 is immersed in a chemical conversion solution, and a predetermined voltage is applied to the anode foil 101 to perform a chemical conversion treatment again (step St3). This repairs minute defects in the aluminum oxide film 31. Furthermore, an aluminum oxide film is formed on the surfaces of the cut edges (ends) of the anode foil 101 in the vertical direction. The chemical conversion treatment again is an example of a process for repairing the aluminum oxide film 31.

[0051] The chemical conversion solution contains water as a solvent and at least the following components. The detailed effects of the chemical conversion solution will be described later. At least one of phosphoric acid, phosphorous acid, and hypophosphorous acid (hereinafter referred to as acid); A chelating agent that forms an aluminum complex that bonds with the aluminum oxide film 31; At least one aluminum compound selected from aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum acetate, aluminum silicate, aluminum lactate, and aluminum fluoride, or aluminum

[0052] Next, in a reduced pressure atmosphere, the wound body 100 is immersed in a dispersion liquid of a conductive polymer to impregnate the dispersion liquid into the wound body 100 (step St4). Note that instead of the dispersion liquid of a conductive polymer, the wound body 100 may be immersed in a solution containing a conductive polymer.

[0053] Next, the wound body 100 is dried (step St5). At this time, the water, which is the solvent of the conductive polymer liquid impregnated in the separator 103 inside the wound body 100, evaporates, and the nanoparticles form the conductive polymer layer 40. The processes of steps St4 and St5 are an example of a process of forming the conductive polymer layer 40 on the separators 103 and 104.

[0054] Next, electrolytic capacitor element 10 is impregnated with the electrolyte in a reduced pressure atmosphere (step St6). Next, electrolytic capacitor element 10 is housed in case 11 and sealed with sealing body 12 (step St7). At this time, extraction electrodes 19a, 19b extending from electrolytic capacitor element 10 are inserted into through-holes 120 in sealing body 12. Thereafter, aging treatment may be performed while applying a rated voltage to aluminum electrolytic capacitor 1. The manufacturing process for aluminum electrolytic capacitor 1 is performed in this manner. Note that the manufacturing process for aluminum electrolytic capacitor 1 is one example of a manufacturing method for aluminum electrolytic capacitor 1.

[0055] (Effects of Chemical Conversion Solution) Fig. 5 is a diagram showing an example of the buffering effect against the acid in the chemical conversion solution. Fig. 5 schematically shows the state of a chemical reaction near the surface of the anode foil 101 where there is no aluminum oxide film 31. Note that in this embodiment, an example is given in which the aluminum oxide film 31 formed on the anode foil 101 is repaired. However, the effects described below can also be obtained when repairing the aluminum oxide film formed on the cathode foil 102 instead of or together with the anode foil 101.

[0056] As shown by the symbol G1a, hydronium ions (H ３ O ＋ ) occurs, and when a voltage is applied in the re-chemical conversion treatment, the aluminum (element) of the anode foil 101 is positively charged. Therefore, the lone electron pair of the hydronium ion is attracted to the aluminum.

[0057] Next, as shown by symbol G1b, aluminum bonds with the hydronium ion, forming H ２ moves to the cathode foil 102 side, and aluminum hydroxide (Al(OH) ３ ) is generated. As a result, the outermost surface of the anode foil 101 is covered with OH groups.

[0058] Next, as shown by the symbol G1c, aluminum ions (Al ＋ ) on the outermost surface of the anode foil 101 is bonded to the OH group. ２ O ３ ) film 31 is formed. Note that hydrogen is generated by bonding of aluminum ions.

[0059] Next, as shown by the symbol G1d, the hydronium ions act on the aluminum oxide film 31, destroying the aluminum oxide film 31. As a result, the aluminum oxide film 31 returns to aluminum hydroxide.

[0060] In this way, the action of the acid repeatedly forms (i.e., repairs) and destroys the aluminum oxide film 31. If an excessive amount of acid is supplied to the surface of the anode foil 101 at this time, the balance between repair and destruction of the aluminum oxide film 31 may be lost, and leakage current may increase.

[0061] However, the chelating agent in the chemical conversion solution acts as a buffer against the acid because it forms an aluminum complex that bonds with the aluminum oxide film 31. In this embodiment, the chelating agent is triethylenetetramine hexaacetic acid (TTHA), but is not limited to this.

[0062] As indicated by the symbol G1e, the aluminum complex of TTHA binds to the aluminum oxide film 31. As a result, the surface of the aluminum oxide film 31 is covered with a coating 32 of the aluminum complex, which suppresses destruction of the aluminum oxide film 31 by hydronium ions. Furthermore, because TTHA absorbs and releases acid, it is possible to adjust the amount of acid on the surface of the anode foil 101 to an appropriate level. Therefore, the chelating agent can maintain a balance between repair and destruction of the aluminum oxide film 31, thereby reducing leakage current.

[0063] FIG. 6 is a diagram showing a chemical reaction between a chelating agent, aluminum hydroxide, phosphoric acid, and water. For example, if phosphoric acid (H ３ P.O. ４ When the aluminum hydroxide on the surface of the anode foil 101 is dissolved, the aluminum hydroxide dissolves and turns into poorly soluble aluminum phosphate (Al ３ P.O. ４ ) is generated, inhibiting the ionization of aluminum. Furthermore, aluminum phosphate crystallizes and prevents the conductive polymer layer 40 from adhering to the aluminum oxide film 31, suppressing the formation of a conductive path and increasing the ESR. This also applies when the chemical conversion solution contains phosphorous acid and hypophosphorous acid instead of or together with phosphoric acid.

[0064] However, TTHA chemically reacts with aluminum hydroxide, phosphoric acid, and water to form an aluminum complex, generating aluminum ions. This improves the reactivity of the chemical conversion solution and promotes the formation and repair of the aluminum oxide film 31. Furthermore, suppressing the generation of aluminum phosphate improves the adhesion of the conductive polymer layer 40, thereby reducing the ESR of the aluminum electrolytic capacitor 1.

[0065] 7a is a diagram schematically illustrating an example of the bonding state between an aluminum oxide film 31 and a conductive polymer layer 40. The conductive polymer layer 40 of this embodiment contains polyethylene sulfonic acid.

[0066] A conductive path is formed when OH groups in the aluminum oxide film 31 on the surface of the anode foil 101 separate and bond with sulfonate ions in the polyethylene sulfonic acid. However, because the surface of the anode foil 101 has a complex uneven shape due to the etching process, the conductive path is not necessarily stable. Furthermore, in the case of a hybrid capacitor, there is a risk that the aluminum oxide film 31 and the conductive polymer layer 40 may separate due to the electrolyte impregnated in the separators 103 and 104.

[0067] 7b is a diagram schematically illustrating another example of bonding between the aluminum oxide film 31 and the conductive polymer layer 40. TTHA forms an aluminum complex, and the COO group of the aluminum complex bonds strongly with the aluminum oxide film 31. This causes the aluminum complex to adhere to the surface of the anode foil 101. Meanwhile, the aluminum complex bonds with the sulfonate ion via the aluminum ion. This results in a strong bond between the aluminum oxide film 31 and the conductive polymer layer 40 via the aluminum complex. This improves the adhesion of the conductive polymer layer 40 and enhances the formation of a conductive path, thereby reducing the ESR of the aluminum electrolytic capacitor 1.

[0068] 8 is a diagram schematically illustrating an example of the formation of an aluminum oxide film 31 by supplying aluminum ions. Because the chemical conversion solution contains one type of aluminum compound or aluminum, TTHA bonds with the aluminum compound or aluminum ions ionized from aluminum to form an aluminum complex, as indicated by symbol G3a, even in the absence of aluminum ions eluted from the anode foil 101 by phosphoric acid.

[0069] Next, as shown by reference symbol G3b, aluminum ions are supplied to the OH groups of the aluminum hydroxide in the anode foil 101. This forms an aluminum oxide film 31 on the surface of the anode foil 101. Thereafter, as shown by reference symbol G3c, the aluminum complex returns to TTHA, leaving Al-OH on the surface of the anode foil 101, but it combines with the aluminum ions again to repeat the above reaction. Therefore, TTHA functions as a catalyst, allowing the aluminum oxide film 31 to be formed.

[0070] In this way, the aluminum ions in the chemical conversion solution actively promote the chemical reaction. As a result, the aluminum oxide film 31 is formed more densely than when the chemical conversion solution does not contain aluminum ions. This prevents the aluminum oxide film 31 and the conductive polymer layer 40 from peeling off together, thereby extending the life of the aluminum electrolytic capacitor 1. In this way, the chemical conversion solution of this embodiment improves the characteristics of the aluminum electrolytic capacitor 1.

[0071] In this embodiment, TTHA is used as the chelating agent, but the present invention is not limited thereto. The chelating agent may contain at least one of nitrilotriacetic acid, ethylenediaminetetraacetic acid, glycoletherdiaminetetraacetic acid, propaminediaminetetraacetic acid, cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid. This allows the formation of an aluminum complex that is more stable than a monodentate complex.

[0072] Furthermore, it is preferable that the molar concentration of the chelating agent in the chemical conversion solution be 0.00001 to 0.000125 mol / kg, as this favorably improves the characteristics of the aluminum electrolytic capacitor 1. It is also preferable that the molar concentration of the aluminum compound or aluminum in the chemical conversion solution be 0.0000125 to 0.00075 mol / kg, as this favorably improves the characteristics of the aluminum electrolytic capacitor 1. It is also preferable that the molar concentration of at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid in the chemical conversion solution be 0.0025 to 0.025 mol / kg, as this favorably improves the characteristics of the aluminum electrolytic capacitor 1.

[0073] The electrolytic capacitor element 10 of the aluminum electrolytic capacitor 1 contains residue of the chemical conversion solution. An aluminum complex containing at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid, and a chelating agent and aluminum hydroxide ions in a molar ratio of 1:0.1 to 1:6 is adhered to the anode foil 101, the cathode foil 102, and the separator 103. This molar ratio allows the balance between repair and destruction of the aluminum oxide film 31 to be metastable, thereby reducing the ESR and leakage current of the aluminum electrolytic capacitor 1.

[0074] Furthermore, separators 103 and 104 contain an aluminum complex bonded to aluminum oxide film 31. The aluminum complex is bonded to aluminum oxide film 31 and conductive polymer layer 40. As a result, as described above, aluminum oxide film 31 and conductive polymer layer 40 are firmly bonded together, and peeling due to the electrolytic solution is suppressed. Furthermore, in the case of a hybrid capacitor, the electrolytic solution impregnated into electrolytic capacitor element 10 contains an aluminum complex, which allows the aluminum complex to be suitably distributed throughout electrolytic capacitor element 10, and the above-described effects can improve the characteristics of aluminum electrolytic capacitor 1.

[0075] Samples 1 to 16 of the aluminum electrolytic capacitor 1 described above were fabricated. Samples 1 to 8 were solid electrolytic capacitors, and Samples 9 to 16 were hybrid capacitors. Samples 9 to 16 were fabricated according to the above manufacturing process, while Samples 1 to 8 were fabricated according to the above manufacturing process except for step St6. The diameter of the case 11 of Samples 1 to 16 was 10 mm, and the height of Samples 1 to 16 was 10 mm. The rated voltage and capacitance (nominal values) of Samples 1 to 16 were 80 V and 47 μF, respectively.

[0076] An aqueous dispersion of a composite product (PEDOT:PSS) made of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid was used as the polymer dispersion liquid for forming the conductive polymer layer 40. An ethylene glycol-based electrolyte was used.

[0077]

[0078] Table 1 shows the molar mass concentration (mol / kg), conductivity (μS / cm), and hydrogen ion exponent (pH) of each component for Samples No. 1 to 16. Samples No. 2, 4 to 8, 10, and 12 to 16 were treated with a chemical conversion solution containing phosphoric acid, TTHA, aluminum hydroxide, and ammonia, with water as the solvent. Samples No. 1 and 9 were treated with a comparative chemical conversion solution containing phosphoric acid and ammonia, with water as the solvent, but without TTHA or aluminum hydroxide. Samples No. 3 and 11 were treated with a chemical conversion solution containing TTHA, phosphoric acid, and ammonia, with water as the solvent, but without aluminum hydroxide. During the chemical conversion treatment, electrolytic capacitor element 10, consisting of anode foil 101 and cathode foil 102 wound with separators 103 and 104 interposed therebetween, was immersed in the chemical conversion solution.

[0079] The TTHA molar concentrations of Samples Nos. 2 and 10 were 0.00001 mol / kg, and the TTHA molar concentrations of Samples Nos. 3, 4, 11, and 12 were 0.0000125 mol / kg. The TTHA molar concentrations of Samples Nos. 5, 6, 13, and 14 were 0.000125 mol / kg, and the TTHA molar concentrations of Samples Nos. 7, 8, 15, and 16 were 0.00015 mol / kg.

[0080] The molar concentrations of phosphoric acid in Samples Nos. 1, 3, 4, 9, 11, and 12 were 0.0025 mol / kg, and the molar concentrations of phosphoric acid in Samples Nos. 2 and 10 were 0.002 mol / kg. The molar concentrations of phosphoric acid in Samples Nos. 5 to 7 and 13 to 15 were 0.025 mol / kg, and the molar concentrations of phosphoric acid in Samples Nos. 8 and 16 were 0.03 mol / kg.

[0081] The molar mass concentration of aluminum hydroxide in Samples No. 2 and 10 was 0.00001 mol / kg, and the molar mass concentration of aluminum hydroxide in Samples No. 4, 5, 12, and 13 was 0.0000125 mol / kg. The molar mass concentration of aluminum hydroxide in Samples No. 6 and 14 was 0.00075 mol / kg, and the molar mass concentration of aluminum hydroxide in Samples No. 7, 8, 15, and 16 was 0.0009 mol / kg.

[0082] The molar concentrations of ammonia in Samples Nos. 1, 3, 4, 9, 11, and 12 were 0.005 mol / kg, and the molar concentrations of ammonia in Samples Nos. 2 and 10 were 0.004 mol / kg. The molar concentrations of ammonia in Samples Nos. 5 to 7 and 13 to 15 were 0.05 mol / kg, and the molar concentrations of ammonia in Samples Nos. 8 and 16 were 0.06 mol / kg. In this way, the hydrogen ion exponent of each chemical conversion solution was adjusted to less than pH 7.

[0083] Regarding the electrical conductivity of the chemical conversion solution for the solid electrolytic capacitors, Sample No. 3 had the smallest conductivity, and Sample No. 1 had the second smallest. Sample No. 8 had the highest conductivity. Regarding the electrical conductivity of the chemical conversion solution for the hybrid capacitors, Sample No. 11 had the smallest conductivity, and Sample No. 9 had the second smallest. Sample No. 16 had the highest conductivity.

[0084]

[0085]

[0086] Table 2 shows the evaluation results for solid electrolytic capacitor samples 1 to 8, and Table 3 shows the evaluation results for hybrid capacitor samples 9 to 16. A load test was conducted at 150°C with an applied voltage of 80 V. The capacitance (μF), loss angle (tan δ), ESR (Ω), and leakage current (μA) of aluminum electrolytic capacitor 1 were measured in an initial state and 1000 hours after the start of voltage application in a 20°C environment. The capacitance, loss angle, and ESR were measured using an LCR meter. The leakage current was measured by connecting a resistor between the positive side of a DC power supply and the anode terminal of samples 1 to 16, measuring the voltage across the resistor for 1 minute with a data logger, and converting the measured voltage to an average current value. The capacitance ratio ΔC / Co (%) was calculated from the capacitance decrease ΔC (<0) after 1000 hours relative to the initial capacitance Co.

[0087] Samples No. 1 and 9 were used as comparative examples not containing TTHA and were compared with other samples No. 2 to 8 and 10 to 16. In Table 2, samples with ESR and leakage current lower than those of sample No. 1 were judged as "OK," and samples with ESR and leakage current equal to or higher than those of sample No. 1 were judged as "NG." Similarly, in Table 3, samples with ESR and leakage current lower than those of sample No. 9 were judged as "OK," and samples with ESR and leakage current equal to or higher than those of sample No. 9 were judged as "NG."

[0088] For the solid electrolytic capacitor, Sample No. 1 did not form sufficient conductive paths compared to Samples No. 2 to 8, which contained TTHA, and the aluminum oxide film 31 was not sufficiently repaired. On the other hand, Samples No. 2 to 8 formed sufficient conductive paths due to the action of TTHA, and the aluminum oxide film 31 was sufficiently repaired. Therefore, the ESR and leakage current of Samples No. 2 to 8 after 1000 hours were lower than those of Sample No. 1. Therefore, Samples No. 2 to 8 were rated "OK." The loss angles of Samples No. 2 to 8 were also lower than those of Sample No. 1. Furthermore, the capacitance ratio (absolute value) of Sample No. 1 was smaller than that of Samples No. 2 to 8 because a sufficient dielectric constant could not be obtained due to the absence of TTHA.

[0089] Furthermore, for the hybrid capacitors, the ESR and leakage current of Samples No. 10 to 16 after 1000 hours were lower than that of Sample No. 9 for the same reasons as above. Therefore, Samples No. 10 to 16 were judged to be "OK." The loss angles of Samples No. 10 to 16 were also lower than that of Sample No. 9. Furthermore, the capacitance ratio (absolute value) of Sample No. 9 was smaller than that of Samples No. 10 to 16 because a sufficient dielectric constant could not be obtained due to the absence of TTHA.

[0090] After 1000 hours, the ESR, leakage current, and loss angle of Samples No. 7 and 8 were larger than those of Samples No. 4 to 6, and the ESR, leakage current, and loss angle of Samples No. 15 and 16 were larger than those of Samples No. 12 to 14. This is thought to be because the molar concentrations of TTHA in Samples No. 7, 8, 15, and 16 were larger than those in Samples No. 4 to 6 and 12 to 14, and the large amounts of TTHA inhibited the formation of conductive paths.

[0091] Furthermore, the ESR, leakage current, and loss angle of Sample No. 2 after 1000 hours were greater than those of Sample Nos. 4 to 6, and the ESR, leakage current, and loss angle of Sample No. 10 after 1000 hours were greater than those of Sample Nos. 12 to 14. This is thought to be because the TTHA molar concentration of Sample Nos. 2 and 10 was lower than that of Sample Nos. 4 to 6 and 12 to 14, resulting in fewer conductive paths and, in addition, the conductive paths were cut off as breakdown of the aluminum oxide film 31 progressed. Therefore, the TTHA molar concentration is preferably 0.0000125 to 0.000125 mol / kg.

[0092] Furthermore, the ESR, leakage current, and loss angle of Sample No. 4 after 1000 hours were smaller than those of Sample No. 3, and the ESR, leakage current, and loss angle of Sample No. 12 after 1000 hours were smaller than those of Sample No. 11. Because the chemical conversion solution used for Samples No. 4 and 12 contained aluminum hydroxide, as described above, aluminum ions ionized from the aluminum hydroxide formed aluminum oxide film 31 more densely than those of Samples No. 3 and 11, resulting in reduced ESR and loss angle.

[0093] The ESR of Samples Nos. 7 and 8 increased significantly compared to that of Samples Nos. 4 to 6, and the ESR of Samples Nos. 15 and 16 increased significantly compared to that of Samples Nos. 12 to 14. This is because if there is too much aluminum hydroxide, the TTHA layer formed on the surface of aluminum oxide film 31 becomes thick, cutting off the conductive path.

[0094] Furthermore, the ESR of Sample No. 2 is significantly higher than that of Sample Nos. 4 to 6, and the ESR of Sample No. 10 is significantly higher than that of Sample Nos. 12 to 14. This is because if the amount of aluminum hydroxide is too small, the amount of conductive polymer attached to the aluminum complex becomes insufficient.

[0095] Therefore, the molar concentration of aluminum hydroxide is preferably 0.000125 to 0.00075 mol / kg. The molar ratio of soluble TTHA to aluminum hydroxide is 1:0.1 to 1:6, which makes it possible to achieve a quasi-stable balance between destruction and repair of the aluminum oxide film 31.

[0096] Furthermore, it is preferable that the molar concentration of at least one of the phosphoric acids is 0.0025 to 0.025 mol / kg, since this reduces the ESR, leakage current, and loss angle, as in Samples Nos. 4 to 6 and 12 to 14. If the molar concentration of the phosphoric acid is less than 0.0025 mol / kg, OH groups are less likely to be generated on the surface of the anode foil 101, while if the molar concentration of the phosphoric acid is greater than 0.025 mol / kg, the attack of the phosphoric acid on the aluminum oxide film 31 becomes too strong, reducing the pressure resistance of the chemical conversion solution.

[0097] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Claims

1. A chemical conversion solution used to repair an aluminum oxide film formed on at least one of an anode foil and a cathode foil included in an electrolytic capacitor element, the chemical conversion solution comprising at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid, and a chelating agent that forms an aluminum complex that bonds with the aluminum oxide film.

2. The chemical conversion solution according to claim 1, wherein the electrolytic capacitor element has a separator sandwiched between the anode foil and the cathode foil, and the aluminum complex bonds to a conductive polymer layer formed on the separator.

3. The chemical conversion solution according to claim 1 or 2, characterized in that it contains aluminum or at least one type of aluminum compound selected from the group consisting of aluminum oxide, aluminum hydroxide, aluminum carbonate, aluminum acetate, aluminum silicate, aluminum lactate, and aluminum fluoride, and the chelating agent bonds with the at least one type of aluminum compound or with aluminum ions ionized from the aluminum.

4. The chemical conversion solution according to claim 3, characterized in that the mass molar concentration of the at least one aluminum compound or the aluminum is 0.000125 to 0.00075 mol / kg.

5. The chemical conversion solution according to claim 1 or 2, wherein the electrolytic capacitor element is impregnated with an electrolyte.

6. The chemical conversion solution according to claim 4, characterized in that the chelating agent has a molar concentration of 0.0000125 to 0.000125 mol / kg.

7. The chemical conversion solution according to claim 4, characterized in that the molar concentration of at least one of the phosphoric acid, phosphorous acid, and hypophosphorous acid is 0.0025 to 0.025 mol / kg.

8. The chemical conversion solution according to claim 1 or 2, characterized in that the chelating agent contains at least one of nitrilotriacetic acid, ethylenediaminetetraacetic acid, glycol ether diaminetetraacetic acid, propaminediaminetetraacetic acid, cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid.

9. A method for manufacturing an electrolytic capacitor, comprising: a step of forming an electrolytic capacitor element including an anode foil and a cathode foil, at least one of which has an aluminum oxide film formed thereon, and a separator sandwiched between the anode foil and the cathode foil; and a step of repairing the aluminum oxide film using a chemical conversion solution after the step of forming the electrolytic capacitor element, wherein the chemical conversion solution contains at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid, and a chelating agent that forms an aluminum complex that bonds with the aluminum oxide film.

10. The method for producing an electrolytic capacitor according to claim 9, further comprising the step of forming a conductive polymer layer on the separator after the step of repairing the aluminum oxide film, wherein the aluminum complex bonds with the conductive polymer layer.

11. The method for producing an electrolytic capacitor according to claim 10, further comprising the step of impregnating the electrolytic capacitor element with an electrolyte after the step of forming the conductive polymer layer.

12. An electrolytic capacitor comprising an electrolytic capacitor element including an anode foil and a cathode foil, at least one of which has an aluminum oxide film formed on it, and a separator sandwiched between the anode foil and the cathode foil, wherein the anode foil, the cathode foil, and the separator are coated with at least one of phosphoric acid, phosphorous acid, and hypophosphorous acid, and an aluminum complex containing a chelating agent and aluminum hydroxide ions in a molar ratio of 1:0.1 to 1:

6.

13. The electrolytic capacitor according to claim 12, wherein the separator includes a conductive polymer layer, and the aluminum complex is bonded to the aluminum oxide film and the conductive polymer layer.

14. The electrolytic capacitor according to claim 12 or 13, wherein the electrolytic capacitor element is impregnated with an electrolyte solution containing the aluminum complex.

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