Electrolytic capacitor electrode foil, electrolytic capacitor, and method for manufacturing electrolytic capacitor

Abstract

An electrode foil for an electrolytic capacitor includes: an anode body containing a first metal; a first dielectric layer covering at least a part of the anode body and containing an oxide of the first metal; and a second dielectric layer covering at least a part of the first dielectric layer and containing an oxide of a second metal. The first metal includes at least one selected from titanium, tantalum, niobium, and aluminum, and the second metal includes at least one selected from silicon, zirconium, hafnium, and tantalum. The thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

Description

Technical Field

[0001] The present invention relates to an electrode foil for an electrolytic capacitor, an electrolytic capacitor, and a method for manufacturing an electrolytic capacitor. Background Art

[0002] Conventionally, in an electrolytic capacitor, a dielectric layer containing an oxide of a valve metal is formed on the surface of minute irregularities of a substrate containing a valve metal whose surface has been roughened by chemical conversion (anodic oxidation).

[0003] However, in Patent Document 1, for the purpose of increasing the capacitance and reducing the leakage current, another dielectric layer containing an oxide of a valve metal different from the valve metal contained in the above dielectric layer and additives such as carbon is proposed to be formed on the above dielectric layer.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-115475 Summary of the Invention

[0007] However, in the method of Patent Document 1, it is sometimes impossible to simultaneously increase the capacitance and improve the withstand voltage.

[0008] That is, the electrode foil for an electrolytic capacitor according to the first aspect of the present invention includes: an anode body containing a first metal; a first dielectric layer covering at least a part of the anode body and containing an oxide of the first metal; and a second dielectric layer covering at least a part of the first dielectric layer and containing an oxide of a second metal different from the first metal, the first metal including at least one selected from titanium, tantalum, niobium, and aluminum, and the second metal including at least one selected from silicon, zirconium, hafnium, and tantalum. Moreover, the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

[0009] The electrolytic capacitor according to the second aspect of the present invention includes: the electrode foil of the first aspect, and a solid electrolyte layer covering at least a part of the second dielectric layer of the electrode foil. The solid electrolyte layer contains a conductive polymer.

[0010] The manufacturing method of the electrolytic capacitor according to the third aspect of the present invention includes the following first process and second process. In the first process, a substrate containing a first metal is chemically converted to form a first dielectric layer containing an oxide of the first metal so as to cover at least a part of the substrate. In the second process, a second dielectric layer containing an oxide of a second metal different from the first metal and having a thickness T2 smaller than the thickness T1 of the first dielectric layer is formed so as to cover at least a part of the first dielectric layer, and an electrode foil is obtained. The first metal contains at least one selected from titanium, tantalum, niobium, and aluminum, and the second metal contains at least one selected from silicon, zirconium, hafnium, and tantalum.

[0011] According to the present invention, an electrolytic capacitor with a large capacitance and excellent withstand voltage can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a cross-sectional view schematically showing a surface portion of an electrode foil according to an embodiment of the present invention.

[0013] Figure 2 is a perspective view schematically showing the configuration of a wound body included in an electrolytic capacitor according to an embodiment of the present invention.

[0014] Figure 3 is a cross-sectional view schematically showing an electrolytic capacitor according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] [Electrode Foil for Electrolytic Capacitor]

[0016] The electrode foil for an electrolytic capacitor according to an embodiment of the present invention includes: an anode body containing a first metal; a first dielectric layer covering at least a part of the anode body and containing an oxide of the first metal; and a second dielectric layer covering at least a part of the first dielectric layer and containing an oxide of a second metal different from the first metal. The first metal contains at least one selected from titanium (Ti), tantalum (Ta), niobium (Nb), and aluminum (Al). The second metal contains at least one selected from silicon (Si), zirconium (Zr), hafnium (Hf), and tantalum (Ta). The thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

[0017] By covering at least a part of the first dielectric layer with the second dielectric layer, the withstand voltage of the electrolytic capacitor is improved. In addition, by making the thickness T2 of the second dielectric layer smaller than the thickness T1 of the first dielectric layer, an electrolytic capacitor with a large capacitance can be obtained at low cost regardless of the dielectric constant of the second dielectric layer. By making the thickness T2 of the second dielectric layer smaller than the thickness T1 of the first dielectric layer, excellent withstand voltage and high capacitance can be obtained with good balance, and an electrolytic capacitor with a large CV value described later can be obtained.

[0018] When the first metal contains at least one selected from Ti, Ta, Nb, and Al, it is easy to form the first dielectric layer by chemical conversion. From the viewpoint of being more advantageous in terms of cost, the first metal preferably contains Al. The oxide of the first metal (the first dielectric layer) contains at least one selected from TiO2, Ta2O5, Nb2O5, and Al2O3. Forming such a first dielectric layer thickly is advantageous for reducing the cost of the process.

[0019] The second metal contains at least one selected from Si, Zr, Hf, and Ta. In this case, it is easy to form a dense and uniform-thickness second dielectric layer by the Atomic Layer Deposition (ALD) method. From the viewpoint of easily forming a second dielectric layer with high breakdown voltage and small thickness, the second metal preferably contains Si. From the viewpoint of increasing the capacitance, the second metal preferably contains Hf. The oxide of the second metal (the second dielectric layer) contains at least one selected from SiO2, ZrO2, HfO2, and Ta2O5. When the second dielectric layer contains two or more oxides of the second metal, the respective oxides may be mixed or may be arranged in layers separately. By forming a thin film of the oxide of the second metal on the first dielectric layer, the breakdown voltage of the electrolytic capacitor can be increased at low cost. From the aspect that is advantageous for increasing the capacitance of the electrolytic capacitor, the oxide of the second metal preferably has a relative dielectric constant higher than that of the oxide of the first metal.

[0020] The ratio of the thickness T1 of the first dielectric layer to the thickness T2 of the second dielectric layer: T1 / T2 preferably exceeds 1 and is 20 or less. When T1 / T2 is 20 or less, it is easy to increase the breakdown voltage at low cost. From the viewpoint of the balance among cost reduction, capacitance increase, and breakdown voltage, T1 / T2 is more preferably 1.25 or more and 10 or less, and further preferably 1.5 or more and 5 or less.

[0021] The total thickness of the thickness T1 of the first dielectric layer and the thickness T2 of the second dielectric layer is, for example, 7 nm or more and 500 nm or less. From the viewpoint of increasing the capacitance, it is preferable that the total thickness of T1 and T2 is small. For example, it may be 7 nm or more and 12.5 nm or less, or may be 7 nm or more and 10.5 nm or less. When the dielectric layer is composed of the first dielectric layer and the second dielectric layer, compared with the case where the dielectric layer is composed only of the first dielectric layer, the thickness of the dielectric layer can be reduced and the breakdown voltage can be increased. The thickness T2 of the second dielectric layer is, for example, 0.5 nm or more and 250 nm or less.

[0022] The composition of the oxide of the first metal contained in the first dielectric layer and the oxide of the second metal contained in the second dielectric layer can be determined by performing elemental analysis based on energy dispersive X-ray spectroscopy (EDX) using the cross-section of the electrode foil.

[0023] The thickness T1 of the first dielectric layer and the thickness T2 of the second dielectric layer are determined by observing the cross-section of the electrode foil using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Specifically, using the cross-sectional image of the electrode foil obtained by SEM or TEM, the thickness is measured at any 10 positions of the first dielectric layer, and their average value is obtained as the thickness T1. For the thickness of the second dielectric layer, it is also measured at any 10 positions, and their average value is obtained as the thickness T2.

[0024] Hereinafter, with reference to Figure 1 An example of the electrode foil according to an embodiment of the present invention will be described. Figure 1 It is a cross-sectional view schematically showing the surface portion of the electrode foil according to an embodiment of the present invention.

[0025] The electrode foil includes: an anode body 110 containing a first metal, and an anode foil 10 having a dielectric layer 120 covering at least a part of the anode body 110. The dielectric layer 120 includes: a first dielectric layer 121 covering at least a part of the anode body 110, and a second dielectric layer 122 covering at least a part of the first dielectric layer 121. The first dielectric layer 121 contains an oxide of the first metal. The second dielectric layer 122 contains an oxide of a second metal different from the first metal. The thickness T2 of the second dielectric layer 122 is smaller than the thickness T1 of the first dielectric layer 121.

[0026] The anode body 110 is a metal foil having a roughened surface by etching or the like and containing a first metal, and has a core portion 111 and a porous portion 112. The porous portion 112 has a plurality of pits P. The first dielectric layer 121 is formed by chemical conversion of the metal foil up to the surface of the deepest part of the pits P. The second dielectric layer 122 is formed by ALD method up to the surface of the deepest part of the pits P.

[0027] [Electrolytic capacitor]

[0028] The electrolytic capacitor according to an embodiment of the present invention includes: the above-mentioned electrode foil, and a solid electrolyte layer covering at least a part of the second dielectric layer of the above-mentioned electrode foil. The solid electrolyte layer contains a conductive polymer (π-conjugated polymer). The conductive polymer includes polypyrrole, polythiophene, polyaniline, and their derivatives, etc.

[0029] The electrolytic capacitor may also include a solvent. The solvent preferably contains a glycol compound and / or a glycerol compound (hereinafter also referred to as a glycol compound, etc.). The glycol compound, etc. may be included in the electrolytic solution described later. By making the solvent contain a glycol compound, etc., the orientation or crystallinity of the π-conjugated polymer contained in the solid electrolyte layer can be improved. Thereby, the conductivity of the solid electrolyte layer is increased, and the equivalent series resistance (ESR) of the electrolytic capacitor becomes low. In addition, the contact property between the solid electrolyte layer and the second dielectric layer is improved, and the withstand voltage characteristic is improved.

[0030] The glycol compound includes ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyalkylene glycol with a molecular weight of about 190 to 400, etc. The glycerol compound includes glycerol, polyglycerol, etc. The degree of polymerization of polyglycerol is preferably 2 or more and 20 or less. The glycol compound, etc. may be used alone or in combination of two or more.

[0031] The electrolytic capacitor may also include an electrolytic solution. By using the electrolytic solution, an electrolytic capacitor with excellent repair function of the dielectric layer can be obtained. The electrolytic solution includes, for example: a solvent, and an ionic substance (solute, such as an organic salt) dissolved in the solvent.

[0032] The solvent may be an organic solvent or an ionic liquid. As the solvent, a high-boiling solvent is preferred. For example, carbonate compounds such as propylene carbonate, cyclic sulfones such as sulfolane, lactones such as γ-butyrolactone, amides such as N-methylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, esters such as methyl acetate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, formaldehyde, etc. may be used. The solvent may be used alone or in combination of two or more.

[0033] An organic salt means a salt in which at least one of the anion and the cation contains an organic substance. As the organic salt, for example, trimethylamine maleate, triethylamine borodisalicylate, ethyl dimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, mono-1,3-dimethyl-2-ethylimidazolinium phthalate, etc. may be used. The organic salt may be used alone or in combination of two or more.

[0034] The first dielectric layer is a chemical conversion film. From the perspective of forming the second dielectric layer, the ratio of the thickness T1 (nm) of the first dielectric layer to the chemical conversion rate R (nm / V) of the chemical conversion film formation: T1 / R, and the rated voltage Vw (V) of the electrolytic capacitor preferably satisfy the relationship of (T1 / R) / Vw ≤ 3. (T1 / R) / Vw is more preferably 2.5 or less, further preferably 2.0 or less, and particularly preferably 1.5 or less. In this case, it is easy to adjust the thickness balance of the first dielectric layer and the second dielectric layer so that T1 / T2 exceeds 1 and is 20 or less, and it is easy to achieve high withstand voltage, high capacitance, and cost reduction with good balance. It should be noted that the chemical conversion rate R refers to the thickness (nm) of the chemical conversion film (the layer of the oxide of the first metal) formed per 1 volt of the chemical conversion voltage Vf on average.

[0035] The chemical conversion rate R changes according to the metal type of the first metal. For example, when the first metal is Al, the chemical conversion rate R is 1.4 nm / V (for products above a certain level) or 2.0 nm / V (for products below a certain level). It should be noted that electrolytic capacitors with a rated voltage Vw of 10 V or less are regarded as products below a certain level, and electrolytic capacitors with a rated voltage Vw exceeding 10 V are regarded as products above a certain level. When the first metal is Ta, the chemical conversion rate R is 2 nm / V.

[0036] [Manufacturing method of electrolytic capacitor]

[0037] The manufacturing method of the electrolytic capacitor according to the embodiment of the present invention includes: a first step of chemically converting a substrate containing a first metal to form a first dielectric layer containing an oxide of the first metal so as to cover at least a part of the substrate; a second step of forming a second dielectric layer containing an oxide of a second metal different from the first metal and having a thickness T2 smaller than the thickness T1 of the first dielectric layer so as to cover at least a part of the first dielectric layer, thereby obtaining an electrode foil. The first metal contains at least one selected from Ti, Ta, Nb, and Al. The second metal contains at least one selected from Si, Zr, Hf, and Ta. Through the first step and the second step, the above-mentioned electrode foil can be obtained.

[0038] Hereinafter, each step will be described in detail.

[0039] (First step)

[0040] The substrate containing the first metal is chemically converted to form a first dielectric layer containing an oxide of the first metal in such a way as to cover at least a part of the substrate. A metal foil having a roughened surface can generally be used for the substrate. The metal foil can be a foil of the first metal or an alloy foil containing the first metal. The thickness of the metal foil is not particularly limited, for example, it is 15 μm or more and 300 μm or less. The roughening is carried out by an etching process or the like. By roughening, a plurality of pits are formed on the surface of the metal foil. The first dielectric layer can be formed by chemical conversion of the metal foil up to the surface of the deepest part of the pits.

[0041] In the first step, a chemical conversion voltage Vf is applied to the substrate. The thickness T1 of the first dielectric layer varies according to the chemical conversion voltage Vf. From the viewpoint of forming the second dielectric layer, the ratio of the chemical conversion voltage Vf to the rated voltage Vw of the electrolytic capacitor: Vf / Vw is preferably 3.0 or less, more preferably 2.5 or less, further preferably 2.0 or less, and particularly preferably 1.5 or less. In this case, it is easy to adjust the thickness balance of the first dielectric layer and the second dielectric layer so that T1 / T2 exceeds 1 and is 20 or less, and it is easy to achieve high withstand voltage, high capacitance, and cost reduction with good balance.

[0042] The method for chemically converting the substrate is not particularly limited. For example, it is carried out by immersing the substrate in a chemical conversion solution such as an ammonium adipate solution and applying a prescribed voltage Vf (anodic oxidation).

[0043] The pore diameter of the pits formed on the surface of the metal foil is not particularly limited. From the aspects of being able to increase the surface area and the second dielectric layer being easily formed up to the deep part of the pits, it is preferably 50 to 2000 nm. The pore diameter of the pits refers to, for example, the pore size at the highest frequency in the pore size distribution measured by a mercury porosimeter. The depth of the pits is also not particularly limited and can be appropriately set according to the thickness of the metal foil. Among them, from the aspects of being able to increase the surface area and maintaining the strength of the electrode foil, the depth of the pits (the thickness D of the etching region where the pits are formed) is preferably 1 / 10 or more and 4 / 10 or less of the thickness of the metal foil before etching. The thickness D of the etching region is the average value of any 10 points in the cross-sectional image of the metal foil obtained by SEM or TEM.

[0044] (Second step)

[0045] In the second step, a second dielectric layer containing an oxide of a second metal different from the first metal and having a thickness T2 smaller than the thickness T1 of the first dielectric layer is formed in such a way as to cover at least a part of the first dielectric layer. In the second step, it is preferable to form the second dielectric layer so that the ratio of the thickness T1 of the first dielectric layer to the thickness T2 of the second dielectric layer: T1 / T2 exceeds 1 and is 20 or less.

[0046] In the second process, it is preferable to form the second dielectric layer by atomic layer deposition (ALD method). In the case of using the ALD method, a second dielectric layer with a small thickness and uniform thickness can be formed. In the case of using the ALD method, the deviation of the thickness values of the second dielectric layer at 10 positions measured when obtaining the thickness T2 is small, and the standard deviation is, for example, 0.5 nm or less.

[0047] The ALD method is a film-forming method in which a raw material gas containing a second metal and an oxidizing agent are alternately supplied to a reaction chamber in which an object is disposed, and a layer containing an oxide of the second metal (second dielectric layer) is formed on the surface of the object. In the ALD method, a self-limiting action functions, and thus the second metal accumulates on the surface of the object in atomic layer units. Therefore, the thickness of the second dielectric layer is controlled by the number of cycles in which the supply of the raw material gas → the exhaust (purge) of the raw material gas → the supply of the oxidizing agent → the exhaust (purge) of the oxidizing agent is one cycle. That is, the ALD method is a preferable method in terms of easily controlling the thickness of the formed layer. In addition, compared with chemical vapor deposition (CVD) performed under temperature conditions of 400 to 900 °C, the ALD method can be performed under temperature conditions of 100 to 400 °C. That is, the ALD method is excellent in terms of being able to suppress thermal damage to the metal foil.

[0048] In the ALD method, if the pore diameter of the pit is about 10 nm, for example, a thin film can be formed on the surface of the deep part of the pit. As described above, the pits formed on the surface of the metal foil usually have a pore diameter of 50 nm or more. Therefore, according to the ALD method, a second dielectric layer can also be formed on the surface of the deep part of a pit with a small pore diameter and a large depth, that is, a pit with a large aspect ratio.

[0049] As the oxidizing agent, an oxidizing agent conventionally used in the ALD method can be used. Examples of the oxidizing agent include water, oxygen, ozone, etc. The oxidizing agent can be supplied to the reaction chamber in the form of a plasma using the oxidizing agent as a raw material.

[0050] For the second metal, a precursor (precursor) gas containing the second metal is gasified and supplied to the reaction chamber. The precursor is an organometallic compound containing the second metal, and thus the second metal is easily chemisorbed on the object. As the precursor, various organometallic compounds conventionally used in the ALD method can be used.

[0051] Examples of the precursor containing Si include N-sec-butyl(trimethylsilyl)amine (C7H 19NSi), 1,3 - diethyl - 1,1,3,3 - tetramethyldisilazane (C8H23NSi2), 2,4,6,8,10 - pentamethylcyclopentasiloxane ((CH3SiHO)5), pentamethyldisilane ((CH3)3SiSi(CH3)2H), tris(dimethylamino)silane ([(CH3)2N]3SiH), tris(isopropoxy)silanol ([(H3C)2CHO]3SiOH), monochloropentamethyldisilane ((CH3)3SiSi(CH3)2Cl), dichlorosilane (SiH2Cl2), tris(dimethylamino)silane (Si[N(CH3)2]4), tetraethylsilane (Si(C2H5)4), tetramethylsilane (Si(CH3)4), tetraethoxysilane (Si(OC2H5)4), dodecamethylcyclohexasilane ((Si(CH3)2)6), silicon tetrachloride (SiCl4), silicon tetrabromide (SiBr4), bis(ethylmethylamino)silane (H2Si[N(C2H5)(CH3)]2), bis(diethylamino)silane (H2Si[N(C2H5)2]2), bis(tert - butylamino)silane (H2Si[NH(C4H9)]2), etc.

[0052] As a precursor containing Zr, examples include: bis(methyl - η 5 cyclopentadienyl)methoxymethylzirconium (Zr(CH3C5H4)2CH3OCH3), tetra(dimethylamino)zirconium(IV) ([(CH3)2N]4Zr), tetra(ethylmethylamino)zirconium(IV) (Zr(NCH3C2H5)4), zirconium(IV) tert - butoxide (Zr[OC(CH3)3]4), etc.

[0053] As a precursor containing Hf, examples include: hafnium tetrachloride (HfCl4), tetra(dimethylamino)hafnium (Hf[N(CH3)2]4), tetra(ethylmethylamino)hafnium (Hf[N(C2H5)(CH3)]4), tetra(diethylamino)hafnium (Hf[N(C2H5)2]4), hafnium(IV) tert - butoxide (Hf[OC(CH3)3]4), etc.

[0054] As a precursor containing Ta, examples include: tris(ethylmethylamide)(tert - butylimide)tantalum(V) (Ta(N - t - C4H9[N(C2H5)CH3]3), tantalum(V) ethoxide (Ta(OC2H5)5), tris(diethylamide)(tert - butylimide)tantalum(V) ((CH3)3CNTa(N(C2H5)2)3), penta(dimethylamino)tantalum(V) (Ta(N(CH3)2)5), etc.

[0055] (Third process)

[0056] The manufacturing method of the electrolytic capacitor described above may include a third process of forming a solid electrolyte layer containing a conductive polymer in such a manner as to cover at least a part of the second dielectric layer of the electrode foil. The solid electrolyte layer can be formed, for example, by chemically polymerizing and / or electrolytically polymerizing a raw material monomer on the second dielectric layer of the electrode foil. Alternatively, the solid electrolyte layer can be formed by coating a solution in which a conductive polymer is dissolved or a dispersion in which a conductive polymer is dispersed on the second dielectric layer of the electrode foil. After the third process (after forming the solid electrolyte layer), a solvent or an electrolytic solution can be further infiltrated into the electrode foil.

[0057] In the case where the anode body having a dielectric layer is an electrode foil (anode foil) as shown in Figure 1 a winding body 100 as shown in Figure 2 can be fabricated before the third process. Figure 2 is an exploded view for explaining the constitution of the winding body 100.

[0058] When fabricating the winding body 100, in addition to the anode foil 10, a cathode foil 20 is also prepared. The cathode foil 20 can also use a metal foil in the same manner as the anode foil 10. The type of the metal constituting the cathode foil 20 is not particularly limited, and valve action metals such as Al, Ta, Nb, etc. or alloys containing valve action metals can be used. If necessary, the surface of the cathode foil 20 can be roughened.

[0059] Next, the anode foil 10 and the cathode foil 20 are wound with a spacer 30 interposed therebetween. One end of a lead terminal 50A or 50B is connected to each of the anode foil 10 and the cathode foil 20, and the winding body 100 is formed while winding the lead terminals 50A and 50B. Leads 60A and 60B are connected to the other ends of the lead terminals 50A and 50B, respectively.

[0060] The spacer 30 is not particularly limited, and for example, a non-woven fabric mainly composed of cellulose, polyethylene terephthalate, vinylon, aromatic polyamide fiber, etc. can be used.

[0061] Next, a stop tape 40 is disposed on the outer surface of the cathode foil 20 located on the outermost layer of the winding body 100, and the end of the cathode foil 20 is fixed with the stop tape 40. It should be noted that in the case where the anode foil 10 is prepared by cutting from a large sheet of foil, in order to provide a dielectric layer on the cut surface, the winding body 100 can be further subjected to a chemical conversion treatment.

[0062] A solution in which a conductive polymer is dissolved or a dispersion in which a conductive polymer is dispersed is infiltrated into the wound body 100 to form a solid electrolyte layer between the anode foil 10 and the cathode foil 20. The wound body 100 after forming the solid electrolyte layer can be further infiltrated with a solvent or an electrolytic solution. As a method for infiltrating the solution or the like, for example, a method of immersing the wound body 100 in a solution or the like accommodated in a container, a method of dropping a solution or the like onto the wound body 100 can be cited. The infiltration can be carried out under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa, preferably 40 kPa to 100 kPa.

[0063] Next, by sealing the wound body 100, an electrolytic capacitor 200 as shown in Figure 3 can be obtained. In order to manufacture the electrolytic capacitor 200, first, the wound body 100 is accommodated in the bottomed case 211 such that the lead wires 60A and 60B are located on the opening side of the bottomed case 211. As the material of the bottomed case 211, metals such as aluminum, stainless steel, copper, iron, brass, or their alloys can be used.

[0064] Next, a sealing member 212 formed so as to penetrate the lead wires 60A and 60B is disposed above the wound body 100, and the wound body 100 is sealed in the bottomed case 211. The sealing member 212 only needs to be an insulating substance, and an elastomer is preferred. Among them, silicone rubber, fluororubber, ethylene-propylene rubber, Hypalon (trademark) rubber, butyl rubber, isoprene rubber, etc. with high heat resistance are preferred.

[0065] Next, a necking process is performed on the vicinity of the open end of the bottomed case 211, and the open end is riveted to the sealing member 212 for curling. Finally, the sealing is completed by disposing a seat plate 213 at the curled portion. Then, the aging treatment can be performed while applying the rated voltage.

[0066] In the above-described embodiment, the wound type electrolytic capacitor has been described, but the application range of the present invention is not limited to the above, and it can also be applied to other electrolytic capacitors, for example, a stacked type electrolytic capacitor.

[0067] Examples

[0068] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the examples.

[0069] <<Example 1>>

[0070] A wound type electrolytic capacitor (Φ (diameter) 6.3 mm × L (length) 9.9 mm) with a rated voltage Vw of 2.0 V was manufactured. Hereinafter, a specific manufacturing method of the electrolytic capacitor will be described.

[0071] (Manufacture of Anode Foil)

[0072] Prepare an Al foil with a thickness of 120 μm. Perform DC etching on the Al foil to roughen the surface. An etched area with a thickness of 40 μm is formed on the surface of the Al foil, and the pore diameter of the pits is 100 - 200 nm.

[0073] Perform a chemical conversion treatment on the Al foil with a roughened surface to form a first dielectric layer so as to cover the fine uneven surface of the Al foil. The chemical conversion treatment is carried out by immersing the Al foil in an ammonium adipate solution and applying a chemical conversion voltage Vf to the Al foil. Set the chemical conversion voltage Vf to 5.0 V and Vf / Vw to 2.5.

[0074] Next, form a second dielectric layer by ALD method (temperature: 300 °C, precursor: tris(dimethylamino)silane, oxidant: O3, pressure: 1 Pa, 30 cycles) so as to cover the first dielectric layer. In this way, an anode body (anode foil) having a first dielectric layer and a second dielectric layer successively on the surface is obtained. Then, cut the anode foil into a specified size.

[0075] Through EDX analysis, it was confirmed that the second dielectric layer is a SiO2 layer and the first dielectric layer is an Al2O3 layer. The thickness T1 of the first dielectric layer and the thickness T2 of the second dielectric layer obtained by the above method are 10 nm and 3 nm respectively, and T1 / T2 is 3.3. Since the second dielectric layer is formed by ALD method, the deviation of the measured values of the thickness of the second dielectric layer at 10 positions is small, and the standard deviation is 0.2 nm. The first metal is Al, the chemical conversion rate R is 2.0 nm / V (the following product), and (T1 / R) / Vw is 2.5.

[0076] (Fabrication of the cathode foil)

[0077] Perform an etching treatment on an Al foil with a thickness of 50 μm to roughen the surface of the Al foil, and a cathode foil is obtained. Then, cut the cathode foil into a specified size.

[0078] (Fabrication of the wound body)

[0079] Connect the anode lead joint and the cathode lead joint to the anode foil and the cathode foil, and wind the anode foil and the cathode foil with a spacer while winding the lead joints. Connect the anode lead and the cathode lead to the end portions of the respective lead joints protruding from the wound body. Then, perform a chemical conversion treatment on the fabricated wound body again to form a dielectric layer at the cut end of the anode foil. Next, fix the end portion of the outer surface of the wound body with a stop tape.

[0080] (Preparation of the conductive polymer dispersion)

[0081] A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene and polystyrenesulfonic acid as a dopant in ion-exchanged water. While stirring the obtained mixed solution, iron(III) sulfate (oxidizing agent) dissolved in ion-exchanged water was added to carry out a polymerization reaction. After the reaction, the obtained reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, and a conductive polymer dispersion containing about 5% by mass of polystyrenesulfonic acid-doped polyethylenedioxythiophene was obtained.

[0082] (Formation of solid electrolyte layer)

[0083] In a reduced-pressure atmosphere (40 kPa), the wound body was immersed in the conductive polymer dispersion contained in a specified container for 5 minutes, and then the wound body was lifted from the conductive polymer dispersion. Next, the wound body impregnated with the conductive polymer dispersion was dried in a drying furnace at 150 °C for 20 minutes, and a solid electrolyte layer containing a conductive polymer was formed between the anode foil and the cathode foil.

[0084] (Sealing of wound body)

[0085] The wound body having the solid electrolyte layer was sealed, and the Figure 3 electrolytic capacitor shown was completed. Then, while applying the rated voltage Vw, an aging treatment was carried out at 130 °C for 2 hours.

[0086] [Evaluation]

[0087] For the obtained electrolytic capacitor, the capacitance was measured. In addition, while increasing the voltage at a rate of 1.0 V / second, the breakdown voltage at which an overcurrent of 0.5 A flows was measured. The capacitance was expressed in the form of an index (capacitance index C) with the capacitance of the electrolytic capacitor of Comparative Example 3 set to 100. The breakdown voltage was expressed in the form of an index (breakdown voltage index V) with the breakdown voltage of the electrolytic capacitor of Comparative Example 3 set to 100.

[0088] 《Examples 2 to 4 and Comparative Examples 1 to 2》

[0089] The thickness T2 of the second dielectric layer was set to the value shown in Table 1, and an electrolytic capacitor was produced by the same method as in Example 1 except for this, and evaluation was carried out. The thickness T2 of the second dielectric layer was controlled by changing the number of cycles of the ALD method.

[0090] 《Comparative Example 3》

[0091] The second dielectric layer was not formed, and an electrolytic capacitor was produced by the same method as in Example 1 except for this, and evaluation was carried out.

[0092] 《Examples 5 to 6》

[0093] The thickness T1 of the first dielectric layer and the thickness T2 of the second dielectric layer were set to the values shown in Table 1, respectively. Except for this, an electrolytic capacitor was fabricated by the same method as in Example 1 and evaluated. The thickness T1 of the first dielectric layer was controlled by changing the chemical conversion voltage Vf. The thickness T2 of the second dielectric layer was controlled by changing the number of cycles of the ALD method.

[0094] The evaluation results of the electrolytic capacitors of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1. It should be noted that the CV value is also shown in Table 1. The CV value is obtained by multiplying the capacitance by the breakdown voltage and represents the amount of electric charge that the electrolytic capacitor can store. In Table 1, the CV value is expressed in the form of an index (CV index) with the CV value of Comparative Example 3 set to 100.

[0095] [Table 1]

[0096]

[0097] In the electrolytic capacitors of Examples 1 to 6 in which the second dielectric layer was formed, the breakdown voltage resistance was improved compared to the electrolytic capacitor of Comparative Example 3 in which the second dielectric layer was not formed. In the electrolytic capacitors of Examples 1 to 6 where T1 / T2 exceeds 1, excellent breakdown voltage resistance and good capacitance were well balanced, and the CV value increased compared to the electrolytic capacitor of Comparative Example 3.

[0098] In the electrolytic capacitors of Examples 1 to 3 and 5 to 6 where T1 / T2 exceeds 1 and is 20 or less, the breakdown voltage resistance was further improved and a larger CV value was obtained. Among them, in the electrolytic capacitors of Examples 5 to 6 where the total thickness of T1 and T2 is small, a larger capacitance was obtained and the CV value further increased.

[0099] In the electrolytic capacitors of Comparative Examples 1 to 2 where T1 / T2 is 1 or less, the capacitance decreased and the CV value decreased compared to the electrolytic capacitor of Comparative Example 3.

[0100] 《Example 7》

[0101] The thickness T1 of the first dielectric layer was set to 5 nm. Except for this, an electrolytic capacitor was fabricated by the same method as in Example 1 and evaluated. The thickness T1 of the first dielectric layer was controlled by changing the chemical conversion voltage Vf. By EDX analysis, it was confirmed that the second dielectric layer was a SiO2 layer.

[0102] 《Example 8》

[0103] In the production of the electrode foil, tetra(dimethylamino)zirconium(IV) was used as the precursor in the ALD method. Other than that, an electrolytic capacitor was produced in the same manner as in Example 1 and evaluated. Through EDX analysis, it was confirmed that the second dielectric layer was a ZrO2 layer.

[0104] 《Example 9》

[0105] In the production of the electrode foil, tetra(dimethylamino)hafnium was used as the precursor in the ALD method. Other than that, an electrolytic capacitor was produced in the same manner as in Example 1 and evaluated. Through EDX analysis, it was confirmed that the second dielectric layer was a HfO2 layer.

[0106] 《Example 10》

[0107] In the production of the electrode foil, penta(dimethylamino)tantalum(V) was used as the precursor in the ALD method. Other than that, an electrolytic capacitor was produced in the same manner as in Example 1 and evaluated. Through EDX analysis, it was confirmed that the second dielectric layer was a Ta2O5 layer.

[0108] The evaluation results of the electrolytic capacitors of Examples 7 to 10 are shown in Table 2.

[0109] [Table 2]

[0110]

[0111] In any of the examples, an electrolytic capacitor having a large capacitance and excellent withstand voltage characteristics was obtained. When the second metal oxide was SiO2, a thin and dense second dielectric layer was formed, and the withstand voltage characteristics were further improved. When the second metal oxide was HfO2, the capacitance was further increased.

[0112] Industrial Applicability

[0113] Since the electrode foil of the present invention has an increased capacitance and withstand voltage characteristics, it can be used for capacitors for various applications.

[0114] Explanation of Reference Numerals

[0115] 10: Anode foil, 110: Anode body, 111: Core part, 112: Porous part, 120: Dielectric layer, 121: First dielectric layer, 122: Second dielectric layer, P: Pit, 20: Cathode foil, 30: Spacer, 40: Anti-unwinding tape, 60A, 60B: Leads, 50A, 50B: Lead connectors, 100: Wound body, 200: Electrolytic capacitor, 211: Bottomed case, 212: Sealing member, 213: Base plate

Claims

1. An electrode foil for an electrolytic capacitor, comprising: An anode body containing aluminum, A first dielectric layer covering at least a part of the anode body and containing Al2O3, and A second dielectric layer covering at least a part of the first dielectric layer and containing SiO2, The thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer, and the ratio T1 / T2 of the thickness T1 of the first dielectric layer to the thickness T2 of the second dielectric layer is 1.3 or more and 20 or less, The total thickness of the thickness T1 of the first dielectric layer and the thickness T2 of the second dielectric layer is 7 nm or more and 12.5 nm or less.

2. The electrode foil for an electrolytic capacitor according to claim 1, wherein The thickness T1 of the first dielectric layer is 4 nm or more and 10 nm or less, The thickness T2 of the second dielectric layer is 0.5 nm or more and 9.1 nm or less.

3. An electrolytic capacitor, comprising: The electrode foil according to claim 1 or 2, and A solid electrolyte layer covering at least a part of the second dielectric layer of the electrode foil, The solid electrolyte layer contains a conductive polymer.

4. The electrolytic capacitor according to claim 3, wherein, It further comprises a solvent or an electrolyte solution.

5. The electrolytic capacitor according to claim 3 or 4, wherein The first dielectric layer is a chemical conversion film, The ratio T1 / R of the thickness T1 of the first dielectric layer to the chemical conversion rate R at which the chemical conversion film is formed, and the rated voltage Vw of the electrolytic capacitor satisfy the relationship (T1 / R) / Vw ≤ 3, Wherein, the unit of the thickness T1 of the first dielectric layer is nm, the unit of the chemical conversion rate R at which the chemical conversion film is formed is nm / V, and the unit of the rated voltage Vw of the electrolytic capacitor is V.

6. A method for manufacturing an electrolytic capacitor, comprising: A first step of chemically converting a substrate containing aluminum to form a first dielectric layer containing Al2O3 in a manner covering at least a part of the substrate; A second step of forming a second dielectric layer containing SiO2 and having a thickness T2 smaller than the thickness T1 of the first dielectric layer in a manner covering at least a part of the first dielectric layer to obtain an electrode foil, The ratio T1 / T2 of the thickness T1 of the first dielectric layer to the thickness T2 of the second dielectric layer is 1.3 or more and 20 or less, The total thickness of the thickness T1 of the first dielectric layer and the thickness T2 of the second dielectric layer is 7 nm or more and 12.5 nm or less.

7. The method for manufacturing an electrolytic capacitor according to claim 6, wherein The thickness T1 of the first dielectric layer is 4 nm or more and 10 nm or less, The thickness T2 of the second dielectric layer is 0.5 nm or more and 9.1 nm or less.

8. The method for manufacturing an electrolytic capacitor according to claim 6, wherein In the second step, the second dielectric layer is formed by atomic layer deposition.

9. The method for manufacturing an electrolytic capacitor according to any one of claims 6 to 8, wherein In the first step, a chemical conversion voltage Vf is applied to the substrate, The ratio of the chemical conversion voltage Vf to the rated voltage Vw of the electrolytic capacitor: Vf / Vw is 3 or less.

10. The manufacturing method of the electrolytic capacitor according to any one of claims 6 to 8, wherein, It further includes a third process of forming a solid electrolyte layer containing a conductive polymer so as to cover at least a part of the second dielectric layer of the electrode foil.

11. The method for manufacturing an electrolytic capacitor according to claim 10, wherein after the third process, it further includes a process of impregnating the electrode foil with a solvent or an electrolytic solution.

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