Electrode foil for electrolytic capacitor, electrolytic capacitor, method for producing electrode foil for electrolytic capacitor, and method for producing electrolytic capacitor

Abstract

This electrode foil for an electrolytic capacitor comprises: a metal foil having a first main surface and a second main surface opposite the first main surface, and including a first porous portion on the first main surface side and a second porous portion on the second main surface side; a first dielectric layer covering a surface of the first porous portion; and a second dielectric layer covering a surface of the second porous portion. The thickness F1 of the first dielectric layer and the thickness F2 of the second dielectric layer satisfy the relationship 0.75≤F1 / F2≤0.97.

Description

Electrode foil for electrolytic capacitors, electrolytic capacitor, method for manufacturing electrode foil for electrolytic capacitors, and system for manufacturing electrode foil for electrolytic capacitors

[0001] The present disclosure relates to an electrode foil for an electrolytic capacitor, an electrolytic capacitor, a method for manufacturing an electrode foil for an electrolytic capacitor, and a system for manufacturing an electrode foil for an electrolytic capacitor.

[0002] Electrolytic capacitor electrode foils consist of a metal foil (etched foil) with both surfaces roughened by etching, and a dielectric layer covering both surfaces of the etched foil. Forming the dielectric layer by chemical conversion treatment (anodic oxidation) of the etched foil is advantageous in terms of mass production. Meanwhile, technologies for forming the dielectric layer using atomic layer deposition and other methods have been investigated, but these methods present challenges in terms of mass production.

[0003] Patent Document 1 proposes a method for manufacturing an electrode, including: (i) a step of preparing a core material and a porous body formed of the first metal integrally with the core material; (ii) a step of chemically converting the porous body to form a first dielectric layer containing an oxide of the first metal so as to cover at least a portion of the porous body; and (iii) a step of forming a second dielectric layer containing an oxide of a second metal different from the first metal by atomic layer deposition so as to cover at least a portion of the first dielectric layer.

[0004] International Publication No. 2018 / 180029

[0005] During the manufacturing process of an electrolytic capacitor (or electrode foil), the electrode foil may be curved, for example, when the electrode foil is wound or transported by rollers.

[0006] When the electrode foil is bent, tensile stress occurs on one surface of the electrode foil that becomes convex, which easily causes cracks and damages the dielectric layer on that surface.Furthermore, the cracks (damaged areas of the dielectric layer) may cause foil breaks.

[0007] On the other hand, in recent years, there has been an increasing demand for higher capacity electrode foils. A method for forming a dielectric layer advantageous for achieving higher capacity is to form a high-dielectric-constant metal oxide layer on the surface of an etched foil by atomic layer deposition and then enhance the crystallinity of the layer by heat treatment. However, the dielectric layer formed by this method is more brittle and has poorer adhesion to the etched foil than a dielectric layer (chemical conversion coating) formed by chemical conversion treatment. Therefore, the dielectric layer is more susceptible to damage on the convex surface side of the electrode foil when the electrode foil is bent, which reduces the reliability of the electrode foil.

[0008] One aspect of the present disclosure relates to an electrode foil for an electrolytic capacitor (first electrode foil), comprising: a metal foil having a first main surface and a second main surface opposite the first main surface, the metal foil having a first porous portion on the first main surface side and a second porous portion on the second main surface side; a first dielectric layer covering a surface of the first porous portion; and a second dielectric layer covering a surface of the second porous portion, wherein a thickness F1 of the first dielectric layer and a thickness F2 of the second dielectric layer satisfy the relationship 0.75≦F1 / F2≦0.97.

[0009] Another aspect of the present disclosure relates to an electrode foil for an electrolytic capacitor (second electrode foil), comprising: a metal foil having a first main surface and a second main surface opposite to the first main surface, the metal foil having a first porous portion on the first main surface side and a second porous portion on the second main surface side; a first dielectric layer covering a surface of the first porous portion; and a second dielectric layer covering a surface of the second porous portion, wherein a capacitance C1 generated on the first main surface side having the first dielectric layer and a capacitance C2 generated on the second main surface side having the second dielectric layer satisfy the relationship 0.80≦C2 / C1≦0.99.

[0010] Yet another aspect of the present disclosure relates to an electrode foil for an electrolytic capacitor (third electrode foil), in which the metal foil of the above-mentioned first electrode foil or second electrode foil has an anode lead portion and a cathode forming portion, and in the cathode forming portion, surfaces of the first porous portion and the second porous portion are covered with the first dielectric layer and the second dielectric layer, respectively.

[0011] Yet another aspect of the present disclosure relates to an electrolytic capacitor including: a wound body; and an electrolyte; the wound body being configured by winding an anode foil, a cathode foil, and a separator disposed between the anode foil and the cathode foil; and the anode foil being the first electrode foil or the second electrode foil described above.

[0012] Yet another aspect of the present disclosure relates to an electrolytic capacitor comprising a laminate in which a plurality of capacitor elements are stacked, the capacitor elements including an anode body having an anode lead portion and a cathode forming portion, and a cathode portion covering the cathode forming portion, the laminate having an anode laminate portion in which a plurality of the anode lead portions are stacked, and a cathode laminate portion in which a plurality of the cathode forming portions covered by the cathode portions are stacked, and at least one of the anode bodies of the plurality of capacitor elements is the third electrode foil described above.

[0013] Yet another aspect of the present disclosure relates to a method for manufacturing an electrode foil for an electrolytic capacitor, including a first step of preparing a metal foil having a first main surface and a second main surface opposite the first main surface, the metal foil having a first porous portion on the first main surface side and a second porous portion on the second main surface side, and a second step of separately forming a first dielectric layer covering the surface of the first porous portion and a second dielectric layer covering the surface of the second porous portion.

[0014] Yet another aspect of the present disclosure relates to a manufacturing system for electrode foil for electrolytic capacitors, the system including a film formation unit that uses atomic layer deposition to individually form a first dielectric layer covering the surface of the first porous portion and a second dielectric layer covering the surface of the second porous portion on a metal foil having a first main surface and a second main surface opposite the first main surface, and a first porous portion on the first main surface side and a second porous portion on the second main surface side.

[0015] According to the present disclosure, an electrode foil for an electrolytic capacitor having a large capacity and excellent reliability can be provided.

[0016] The novel features of the present disclosure are set forth in the appended claims, but the present disclosure, both in terms of structure and content, together with other objects and features of the present disclosure, will be better understood from the following detailed description taken in conjunction with the drawings.

[0017] Fig. 4 is a cross-sectional schematic view of a metal foil prepared in a first step of a method for manufacturing an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 5 is a configuration diagram showing an example of a manufacturing system for an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 6 is a configuration diagram showing another example of a manufacturing system for an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 7 is a cross-sectional schematic view of an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 8 is a perspective view schematically showing the configuration of the wound body of Fig. 4.

[0018] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits are exemplified for numerical values ​​of specific physical properties or conditions, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more materials may be used in combination.

[0019] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0020] [Method for manufacturing electrode foil for electrolytic capacitor] A method for manufacturing electrode foil for electrolytic capacitor according to an embodiment of the present disclosure includes a first step of preparing a metal foil having a first main surface and a second main surface opposite to the first main surface, and having a first porous portion on the first main surface side and a second porous portion on the second main surface side, and a second step of separately forming a first dielectric layer covering the surface of the first porous portion and a second dielectric layer covering the surface of the second porous portion.

[0021] (First Step) The first porous portion and the second porous portion are simultaneously formed by roughening both surfaces of a substrate sheet containing a first metal by etching, and the unetched portion remains as a core portion. That is, the metal foil has the first porous portion, the second porous portion, and a core portion continuous with the first porous portion and the second porous portion. The metal foil is an integrated product of the first porous portion, the second porous portion, and the core portion. Both surfaces of the substrate sheet are simultaneously roughened by etching. The etching may be chemical etching or electrolytic etching. Hereinafter, the first porous portion and the second porous portion may be collectively referred to simply as the "porous portion."

[0022] The thickness T of the porous portion is not particularly limited and may be appropriately selected depending on the application of the electrolytic capacitor, the required withstand voltage, rated capacity, etc. The thickness T of the porous portion may be selected, for example, from the range of 10 μm or more and 160 μm or less. The thickness T of the porous portion may be, for example, 1 / 10 or more and 5 / 10 or less of the thickness of the metal foil. The thickness T of the porous portion may be determined by cutting the electrode foil (or metal foil) so as to obtain a cross section of the core portion and the porous portion in the thickness direction, taking an electron microscope photograph of the cross section, and averaging the thicknesses at any 10 points of the porous portion.

[0023] The porous portion has a large number of pits (or pores) surrounded by a metal portion. The pit diameter peak of the pits (or pore diameter peak of the pores) of the porous portion is not particularly limited, but may be, for example, 50 nm to 2000 nm, or may be 100 nm to 300 nm, from the viewpoint of increasing the surface area and forming the dielectric layer deep in the porous portion. The pit diameter (pore diameter) peak is the most frequent pore diameter of the volume-based pore diameter distribution measured, for example, with a mercury porosimeter.

[0024] 1 is a cross-sectional view schematically illustrating a metal foil prepared in a first step of a method for manufacturing an electrolytic capacitor electrode foil according to an embodiment of the present disclosure. The metal foil 300 has a first main surface S1 and a second main surface S2 opposite the first main surface. The metal foil 300 has a first porous portion 310a on the first main surface S1 side, a second porous portion 310b on the second main surface S2 side, and a core portion 320 continuous with the first porous portion 310a and the second porous portion 310b. The first porous portion 310a and the second porous portion 310b each have a number of pits (not shown) surrounded by a metal portion. The first porous portion 310a and the second porous portion 310b each have a thickness T.

[0025] (Second Process) In the second process, a first dielectric layer covering the surface of the first porous portion and a second dielectric layer covering the surface of the second porous portion are formed separately. That is, in the second process, the step of forming the second dielectric layer is provided separately from the step of forming the first dielectric layer, and the second dielectric layer is not formed in the step of forming the first dielectric layer, and the first dielectric layer is not formed in the step of forming the second dielectric layer. Hereinafter, the first dielectric layer and the second dielectric layer may be collectively referred to simply as "dielectric layer."

[0026] The dielectric layer is provided so as to cover at least a portion of the surface of the metal portion constituting the porous portion. The dielectric layer can be formed, for example, by atomic layer deposition (ALD). The dielectric layer may contain an oxide of a first metal contained in the metal portion constituting the porous portion (the substrate sheet of the first step). The dielectric layer may contain an oxide of a second metal different from the first metal. When forming the dielectric layer by ALD, the second metal can be appropriately selected without being limited by the first metal, and an oxide of the second metal having a higher dielectric constant than the oxide of the first metal can be formed, which is advantageous for increasing the capacity of the electrolytic capacitor. Furthermore, the wider range of second metals to choose from allows the dielectric layer to be imparted with various performance properties without being limited by the first metal.

[0027] The type of the first metal is not particularly limited, but the first metal may be a valve metal such as aluminum (Al), tantalum (Ta), or niobium (Nb), or an alloy containing a valve metal.

[0028] Examples of the second metal include Al, Ta, Nb, silicon (Si), titanium (Ti), zirconium (Zr), and hafnium (Hf). These may be used alone or in combination of two or more. That is, the dielectric layer may contain Al, Ta, Nb, silicon (Si), titanium (Ti), zirconium (Zr), and hafnium (Hf). ２ O ３ , Ta ２ O ５ , Nb ２ O ５ , SiO ２ , TiO ２ , ZrO ２ , HfO ２ The dielectric layer may contain one or more of the oxides of the second metal. When the dielectric layer contains two or more oxides of the second metal, the oxides of the second metal may be mixed or may be arranged in layers. From the viewpoint of increasing the capacitance of the electrolytic capacitor, it is preferable that the oxide of the second metal has a higher dielectric constant than the oxide of the first metal.

[0029] In the second step, a dielectric layer A advantageous for achieving high capacitance can be formed on one of the first and second dielectric layers, and a dielectric layer B excellent in resistance to tensile stress can be formed on the other of the first and second dielectric layers. In this case, the formation of the dielectric layer A can increase the capacitance of the electrode foil. Furthermore, by curving the electrode foil so that the main surface bearing the dielectric layer A is concave, damage to the dielectric layer during bending of the electrode foil can be suppressed. That is, when the electrode foil is bent, one surface of the electrode foil becomes convex, generating tensile stress. However, by designating this surface as the main surface bearing the dielectric layer B, damage to the dielectric layer due to tensile stress is suppressed. Meanwhile, the other surface of the electrode foil becomes concave, generating compressive stress. Therefore, even if the dielectric layer A has a relatively low strength and adhesion to the porous portion compared to the dielectric layer B, damage to the dielectric layer due to tensile stress can be avoided by designating this other surface as the main surface bearing the dielectric layer A. This improves the reliability of the electrode foil.

[0030] The second step of forming the first and second dielectric layers individually can be performed, for example, using a manufacturing system described below. If the dielectric layer is formed by chemical conversion treatment, a chemical conversion film is simultaneously formed on both sides of the metal foil in a chemical conversion solution. Generally, if the dielectric layer is formed by the ALD method, a film formation device is used to simultaneously form a metal oxide film on both sides of the metal foil contained in a reaction chamber. In these cases, the process of forming the dielectric layer on one surface of the metal foil also serves as the process of forming the dielectric layer on the other surface, making it difficult to form the first and second dielectric layers individually.

[0031] The second step may include a step 2A in which a first dielectric layer is formed by ALD at a first temperature TA1, and a step 2B in which a second dielectric layer is formed by ALD at a second temperature TA2. The first temperature TA1 may be the same as or different from the second temperature TA2. By appropriately adjusting the first temperature TA1 and the second temperature TA2, it is possible to control the film formation properties on the first and second main surfaces by ALD.

[0032] The metal M1 contained in the first dielectric layer may be the same as or different from the metal M2 contained in the second dielectric layer. The metal M1 and the metal M2 may be a second metal different from the first metal contained in the metal portion constituting the porous portion. From the viewpoint of increasing capacity, when the first metal is Al, the second metal is preferably Ti, Si, Hf, or Nb. The metal M2 may include Al and a metal other than Al.

[0033] Atomic layer deposition (ALD) is a film formation method in which a source gas containing a metal M and an oxidant are alternately supplied to a reaction chamber in which a target object is placed, to form a dielectric layer containing an oxide of the metal M on the surface of the target object. In the ALD method, a self-limiting action functions, so the metal M is deposited on the surface of the target object in atomic layers. Therefore, the thickness of the dielectric layer is controlled by the number of cycles, which is one cycle consisting of supply of source gas → exhaust (purging) of the source gas → supply of oxidant → exhaust (purging) of the oxidant. In other words, the ALD method makes it easy to control the thickness of the dielectric layer formed.

[0034] Examples of oxidizing agents used in the ALD method include water, oxygen, ozone, etc. The oxidizing agent may be supplied to the reaction chamber as plasma using the oxidizing agent as a raw material.

[0035] The metal M may include a first metal or a second metal. The metal M is supplied to the reaction chamber as a precursor gas (raw material gas) containing the metal M. The precursor is, for example, an organometallic compound containing the second metal, which makes it easier for the metal M to be chemically adsorbed to the target object. As the precursor, various organometallic compounds conventionally used in the ALD method can be used.

[0036] Examples of precursors containing Al include trimethylaluminum ((CH ３ ) ３ Examples of precursors containing Ta include (t-butylimido)tris(ethylmethylamino)tantalum(V) (C 13 H 33 N4Ta, TBTEMT), tantalum(V) pentaethoxide (Ta(OC2H5)5), etc.

[0037] Examples of precursors containing Nb include niobium(V) ethoxide (Nb(OCH2CH3)5, tris(diethylamido)(t-butylimido)niobium(V) (C 16 H 39 Examples of precursors containing Si include N-sec-butyl(trimethylsilyl)amine (CH 19 Examples include tetraethylsilane (Si(C2H5)4), tetraethoxysilane (Si(OC2H5)4), silicon tetrachloride (SiCl4), and the like.

[0038] Examples of precursors containing Ti include tetrakis(dimethylamino)titanium(IV) ([(CH3)2N]4Ti, TDMAT), titanium tetrachloride (TiCl4), titanium(IV) ethoxide (Ti[O(C2H5)]4), etc. Examples of precursors containing Zr include tetrakis(ethylmethylamido)zirconium(IV) (Zr(NCH3C2H5)4), zirconium(IV) t-butoxide (Zr[OC(CH3)3]4), etc.

[0039] Examples of precursors containing Hf include hafnium tetrachloride (HfCl4), tetrakisdimethylaminohafnium (Hf[N(CH3)2]4), and hafnium-t-butoxide (Hf[OC(CH3)3]4).

[0040] In the step 2A (step 2B), the thickness of the first dielectric layer (second dielectric layer) may be controlled by the first temperature TA1 (second temperature TA2). In addition to the first temperature TA1 (second temperature TA2), the thickness of the first dielectric layer (second dielectric layer) may be controlled by the deposition time, the purge time, the number of cycles, etc.

[0041] The film formation conditions, such as the temperature and pressure during film formation, the type of source gas (metal M), and the number of cycles, may be different between the second A step and the second B step.

[0042] Step 2B may be performed after Step 2A. In this case, Step 2A preferably doubles as a step of heat-treating the second main surface at a first temperature TA1. In this case, Step 2A heat-treats the second main surface using the heat generated during film formation on the first main surface. This heat treatment allows an oxide film of the metal portion constituting the second porous portion to be formed on the surface of the second porous portion. In this case, Step 2B forms a second dielectric layer on the surface of the second porous portion via the oxide film, which has excellent adhesion to the metal portion. In this case, the adhesion of the second dielectric layer to the metal portion is improved, and peeling of the second dielectric layer from the surface of the second porous portion is suppressed. Furthermore, while the formation of the oxide film reduces leakage current, it tends to reduce the capacitance on the second main surface. Therefore, the second dielectric layer can be formed on the second main surface as a dielectric layer B with excellent resistance to tensile stress. The thickness of the oxide film can be controlled by appropriately adjusting the first temperature TA1. The oxide film has a thickness that is, for example, 90% to 97% of the thickness F2 of the second dielectric layer. The oxide film functions as a dielectric together with the film formed by the ALD method.

[0043] In the case of electrode foils used in electrolytic capacitors with a low withstand voltage (e.g., less than 16 V), a dielectric layer with a small thickness (e.g., less than 16 nm) is formed, and therefore the oxide film has a large effect, and although the leakage current reduction effect is significant, the capacitance is likely to decrease. Therefore, the effect of forming the first dielectric layer and the second dielectric layer separately can be significantly achieved.

[0044] In the case of electrode foils used in electrolytic capacitors with a high withstand voltage (e.g., 16 V or higher), a thick dielectric layer (e.g., 16 nm or higher) is formed, which reduces the effect of the oxide film and relatively suppresses the decrease in capacitance. The effect is even greater in hybrid electrolytic capacitors with a high withstand voltage (e.g., 20 V or higher).

[0045] When step 2B is performed after step 2A, step 2B preferably also serves as a step of heat-treating the first main surface having the first dielectric layer at a second temperature TA2. In this case, in step 2B, the first main surface is heat-treated using the heat generated during film formation on the second main surface. This heat treatment can enhance the crystallinity of the first dielectric layer. Therefore, the first dielectric layer can be formed on the first main surface as dielectric layer A, which is advantageous for achieving high capacitance. By appropriately adjusting the second temperature TA2, the crystallinity of the first dielectric layer can be controlled. While the first dielectric layer, which is dielectric layer A, is more advantageous for achieving high capacitance than the second dielectric layer, which is dielectric layer B, it tends to be more brittle and have poor adhesion to the porous portion.

[0046] When the first dielectric layer is formed as the dielectric layer A, it is preferable that substantially no thin oxide film is formed between the first dielectric layer and the metal portion that constitutes the porous portion. A thin natural oxide film may exist between the first dielectric layer and the metal portion that constitutes the porous portion, but it is desirable that the thickness of the natural oxide film be much thinner than that of the oxide film on the second dielectric layer side.

[0047] Alternatively, the step 2A may be carried out after the step 2B, and the first dielectric layer and the second dielectric layer may be formed as the dielectric layer B and the dielectric layer A, respectively.

[0048] The first temperature TA1 and the second temperature TA2 preferably satisfy the relationships of the following formulas (i) to (iii), for example. Film formation by the ALD method and heat treatment utilizing the heat generated during film formation can be performed at a temperature of 90°C or higher and 400°C or lower, thereby suppressing thermal damage to the metal foil. (i) 0≦|TA1−TA2|≦50 (ii) 90≦TA1≦400 (iii) 90≦TA2≦400

[0049] [Manufacturing System for Electrolytic Capacitor Electrode Foil] A manufacturing system for electrolytic capacitor electrode foil according to an embodiment of the present disclosure includes a film formation unit configured to separately form a first dielectric layer covering the surface of the first porous portion and a second dielectric layer covering the surface of the second porous portion by atomic layer deposition on a metal foil having a first main surface and a second main surface opposite the first main surface, the first porous portion being located on the first main surface and a second porous portion being located on the second main surface. That is, in the film formation unit, the second film formation unit that forms the second dielectric layer covering the surface of the second porous portion is provided separately from the first film formation unit that forms the first dielectric layer covering the surface of the first porous portion. The first film formation unit does not form the second dielectric layer, and the second film formation unit does not form the first dielectric layer. The film formation unit can form one of the first dielectric layer and the second dielectric layer as dielectric layer A, and the other of the first dielectric layer and the second dielectric layer as dielectric layer B.

[0050] The film formation unit may include, in a first film formation region, a plurality of first nozzles facing the first main surface and supplying a first source gas to the first main surface, and, in a second film formation region isolated from the first film formation region, a plurality of second nozzles facing the second main surface and supplying a second source gas to the second main surface. In this case, the manufacturing system may include a first moving means that moves the plurality of first nozzles along the first main surface in the first film formation region, and a second moving means that moves the plurality of second nozzles along the second main surface in the second film formation region.

[0051] In the first film formation region, a first dielectric layer may be formed by moving a plurality of first nozzles (nozzles a to d described below) with a first moving means relative to the first main surface of the metal foil, thereby performing film formation for a predetermined number of cycles.In the second film formation region, a second dielectric layer may be formed by moving a plurality of second nozzles (nozzles a to d described below) with a second moving means relative to the second main surface of the metal foil, thereby performing film formation for a predetermined number of cycles.

[0052] The manufacturing system may include a conveying means for conveying the metal foil between the first film formation region and the second film formation region. In this case, the first moving means may move the plurality of first nozzles along the metal foil conveying path in the first film formation region, and the second moving means may move the plurality of second nozzles along the metal foil conveying path in the second film formation region. While the metal foil is conveyed by the conveying means, the moving means may move the plurality of nozzles to form a predetermined number of film cycles. The conveying means may include a conveying roller. In this case, a roll-to-roll method can be adopted, improving productivity.

[0053] The transport path of the metal foil may include a straight path and / or a curved path along which the metal foil is transported in a curved manner in each of the first and second film formation regions. In this case, the first moving means and the second moving means may move the plurality of first nozzles and the plurality of second nozzles, respectively, along the straight path and / or the curved path.

[0054] The first moving means may move the plurality of first nozzles in the first film formation region in the same direction as the metal foil transport direction or the opposite direction, or may move them back and forth on the transport path. The second moving means may move the plurality of second nozzles in the second film formation region in the same direction as the metal foil transport direction or the opposite direction, or may move them back and forth on the transport path.

[0055] When the conveying path of the metal foil includes a curved path along which the metal foil is conveyed while being curved, it is desirable to form a dielectric layer B on the main surface side where the curvature of the metal foil forms a convex portion, and a dielectric layer A on the main surface side where the curvature of the metal foil forms a concave portion. The formation of the dielectric layer B suppresses damage to the dielectric layer due to tensile stress.

[0056] The manufacturing system may also include a transport roller that transports the metal foil between the first film formation region and a second film formation region separated from the first film formation region. In this case, the film formation unit may include a first film formation device that supplies a first source gas to the first main surface in the first film formation region, and a second film formation device that supplies a second source gas to the second main surface in the second film formation region. The film formation device may include a moving means or may be configured to be movable by the moving means.

[0057] More specifically, the film formation section may include a plurality of nozzles in each of the first film formation region (first film formation device) and the second film formation region (second film formation device). The plurality of nozzles include a nozzle a that supplies a source gas to the main surface (porous portion) of the metal foil, a nozzle b that exhausts the source gas from the main surface (porous portion) of the metal foil, a nozzle c that supplies an oxidant (or plasma gas) to the main surface (porous portion) of the metal foil, and a nozzle d that exhausts the oxidant (or plasma gas) from the main surface (porous portion) of the metal foil. The first nozzle and the second nozzle are nozzle a.

[0058] The multiple nozzles are repeatedly arranged in the order of nozzles a to d in the longitudinal direction of the long metal foil (the direction in which the metal foil is transported). Each nozzle has an opening with a width corresponding to the width of the long metal foil. The distance between the nozzle opening and the main surface of the metal foil facing the nozzle opening is very short, allowing efficient supply or exhaust of source gas (oxidizer or plasma gas) in the area facing the nozzle opening. Within the film formation area, the nozzles a to d are moved sequentially over any point on the main surface of the metal foil by the movement or reciprocating motion of the multiple nozzles (film formation devices), and film formation is performed.

[0059] Film formation may be performed first in the first film formation region, followed by film formation in the second film formation region. In this case, heat generated during film formation on the first main surface by the first film formation device (multiple nozzles in the first film formation region) can be utilized for heat treatment of the second main surface. That is, the first film formation device (multiple nozzles in the first film formation region) can also serve as a first heat treatment device for heat treatment of the second main surface in the first film formation region. This heat treatment can form an oxide film (oxide of the first metal contained in the metal portion) of the metal portion constituting the second porous portion on the surface of the second porous portion on the second main surface side. In this case, the second film formation device (multiple nozzles in the second film formation region) forms a second dielectric layer on the surface of the second porous portion via the oxide film, which has excellent adhesion to the metal portion. In this case, peeling of the second dielectric layer from the surface of the second porous portion is suppressed. Furthermore, while the formation of this oxide film can reduce leakage current, it tends to reduce capacitance on the second main surface side. Therefore, the second dielectric layer is obtained on the second principal surface side as the dielectric layer B having excellent resistance to tensile stress.

[0060] Furthermore, when a film is formed in the second film formation region after a film is formed in the first film formation region, the heat generated during film formation on the second main surface by the second film formation device (multiple nozzles in the second film formation region) can be used for heat treatment of the first main surface. That is, the second film formation device (multiple nozzles in the second film formation region) can also serve as a second heat treatment device for heat treatment of the first main surface having the first dielectric layer in the second film formation region. This heat treatment can enhance the crystallinity of the first dielectric layer. As a result, the first dielectric layer is obtained on the first main surface as dielectric layer A, which is advantageous for achieving high capacitance. Compared to the second dielectric layer B, the first dielectric layer, which is dielectric layer A, is advantageous for achieving high capacitance, but tends to be brittle and have poor adhesion to the porous portion.

[0061] When the second film formation device (multiple nozzles in the second film formation region) also serves as the second heat treatment device, heat generated during film formation on the second main surface is conducted to the first main surface via the core, and the conducted heat can be used to heat-treat the first main surface. If the heat conducted to the first main surface is insufficient due to heat dissipation or thermal conductivity, a separate means for heating the first main surface from the first main surface side may be provided in addition to the heat source used during film formation on the second main surface. Furthermore, it is preferable to provide a means for measuring the temperature of the first main surface. It is even more preferable to provide a means for controlling the temperature of the first main surface by measuring the temperature of the first main surface using the means for measuring the temperature of the first main surface and feeding the measured temperature back to the means for heating the first main surface.

[0062] The first temperature TA1 during film formation by the first film formation device (multiple nozzles in the first film formation region) (or during heat treatment as the first heat treatment device) and the second temperature TA2 during film formation by the second film formation device (multiple nozzles in the second film formation region) (or during heat treatment as the second heat treatment device) may be the same or different from each other. TA1 and TA2 preferably satisfy the relationships of the above formulas (i) to (iii), for example.

[0063] The number X1 of the first nozzles may be the same as or different from the number X2 of the second nozzles. When the first dielectric layer is formed as the dielectric layer A, the number X1 of the first nozzles may be smaller than the number X2 of the second nozzles.

[0064] The number of cycles N1 for film formation by the first film formation device (plurality of nozzles in the first film formation region) may be the same as or different from the number of cycles N2 for film formation by the second film formation device (plurality of nozzles in the second film formation region). When the first dielectric layer is formed as the dielectric layer A, the number of cycles N1 may be smaller than the number of cycles N2. A smaller number of film formation cycles can reduce the thickness of the dielectric layer A, which is advantageous in terms of increasing capacity.

[0065] The metal M1 contained in the first source gas may be the same as or different from the metal M2 contained in the second source gas. The metal M1 and the metal M2 may be a second metal different from the first metal contained in the metal portion constituting the porous portion. From the viewpoint of increasing capacity, when the first metal is Al, the second metal may be at least one selected from the group consisting of Ti, Si, Hf, and Nb.

[0066] The metal foil may be transported by the transport rollers in the order of the first film-forming region and the second film-forming region, or in the order of the second film-forming region and the first film-forming region.

[0067] Here, FIG. 2 is a configuration diagram showing an example of a manufacturing system for an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure.

[0068] The manufacturing system 400 includes rollers 410a to 410c that transport the metal foil 300 from a first film deposition area 430a to a second film deposition area 430b that is separated from the first film deposition area 430a.

[0069] The manufacturing system 400 also includes a film formation unit including a first film formation device 420a that supplies a first source gas to the first main surface S1 of the metal foil 300 while oscillating a first film formation region 430a, and a second film formation device 420b that supplies a second source gas to the second main surface S2 of the metal foil 300 while oscillating a second film formation region 430b.

[0070] The film formation process (second process) performed by the manufacturing system 400 shown in FIG. 2 will be described in detail below. The metal foil 300 is transported to the first film formation zone 430a by rollers. While an arbitrary point P1 on the metal foil 300 passes through the first film formation zone 430a (the transport path of the metal foil 300 for a distance L1 within the first film formation zone 430a), the first film formation device 420a oscillates in the first film formation zone 430a. That is, the first film formation device 420a reciprocates for a distance L1 along the transport path of the metal foil 300 within the first film formation zone 430a. During this reciprocating motion, the first film formation device 420a forms a film on the first main surface S1 at the arbitrary point P1 on the metal foil 300 for a number of cycles N1. Depending on the desired number of cycles N1, the first film formation device 420a may form a film on both the forward and return paths, or on either the forward or return path.

[0071] The first film formation device 420a includes a plurality of first nozzles that supply a first source gas to the first main surface S1. Film formation with a cycle number N1 is typically performed by setting a speed V2a at which the first nozzles move along the transport path due to the reciprocating motion of the first film formation device 420a to be greater than a speed V1a at which an arbitrary point P1 on the metal foil 300 moves along the transport path. V1a and V2a may be appropriately set depending on the desired cycle number N1 and the number X1 of first nozzles. For 50 cycles or more, V2a / V1a≧2 is preferred. From the viewpoint of productivity, V2a / V1a≧5 is preferred.

[0072] After the first film formation device 420a forms a film on the first main surface S1, the metal foil 300 is transported to the second film formation zone 430b by rollers. While an arbitrary point P2 on the second main surface S2 of the metal foil 300 passes through the second film formation zone 430b (the transport path of the metal foil 300 for a distance L2 within the second film formation zone 430b), the second film formation device 420b oscillates in the second film formation zone 430b. That is, the second film formation device 420b reciprocates for a distance L2 along the transport path of the metal foil 300 within the second film formation zone 430b. During this reciprocating motion, the second film formation device 420b forms a film on the second main surface S2 of the metal foil 300 at the arbitrary point P2 on the second main surface S2 for a number of cycles N2. Depending on the desired number of cycles N2, the second film formation device 420b may perform film formation on both the forward and return paths, or on either the forward or return path.

[0073] The second film formation device 420b includes a plurality of second nozzles that supply the second source gas to the second main surface S2. Film formation with the number of cycles N2 is typically performed by setting the speed V2b at which the second nozzles move along the transport path due to the reciprocating motion of the second film formation device 420b to be greater than the speed V1b at which an arbitrary point P2 on the metal foil 300 moves along the transport path. V1b and V2b may be appropriately set depending on the desired number of cycles N2 and the number X2 of second nozzles. For 50 cycles or more, V2b / V1b≧2 is preferred. From the viewpoint of productivity, V2b / V1b≧5 is preferred.

[0074] More specifically, the film forming apparatus 420a (420b) includes the nozzles a to d. In the case of the manufacturing system shown in Fig. 2, while an arbitrary point on the main surface of the metal foil moves through the film forming region, the nozzles a to d are moved sequentially onto an arbitrary point P on the main surface of the metal foil by swinging (reciprocating motion) the film forming apparatus, thereby forming a film.

[0075] Here, FIG. 3 is a configuration diagram showing another example of a manufacturing system for an electrode foil for an electrolytic capacitor according to an embodiment of the present disclosure.

[0076] The manufacturing system 500 includes rollers 510a to 510c that transport the metal foil 300 from a first film deposition area 530a to a second film deposition area 530b isolated from the first film deposition area 530a and reciprocate the metal foil 300 in each of the first film deposition area 530a and the second film deposition area 530b.

[0077] The manufacturing system 500 also includes a film formation unit. The film formation unit includes a first film formation apparatus 520a that supplies a first source gas to the first main surface S1 of the metal foil 300 in a first film formation region 530a, and a second film formation apparatus 520b that supplies a second source gas to the second main surface S2 of the metal foil 300 in a second film formation region 400b. The first film formation apparatus 520a includes a plurality of first nozzles that supply the first source gas to the first main surface S1. The second film formation apparatus 520b includes a plurality of second nozzles that supply the second source gas to the second main surface S2.

[0078] 3, the film formation process (second process) performed by the manufacturing system 500 is described in detail below. The metal foil 300 is transported to the first film formation region 530a by the rollers 510a to 510c, and an arbitrary point P1 on the metal foil 300 travels back and forth along a transport path of a distance L3 within the first film formation region 530a. During this time, the first film formation device 520a forms a film on the first main surface S1 of the arbitrary point P1 on the metal foil 300 for a number of cycles N1.

[0079] After the first film formation device 520a forms a film on the first main surface S1, the metal foil 300 is transported to the second film formation region 530b by the rollers 510a to 510c, and an arbitrary point P2 of the metal foil 300 travels back and forth along a transport path of a distance L4 within the second film formation region 530b. During this time, the second film formation device 520b forms a film on the second main surface S2 of the arbitrary point P2 of the metal foil 300 by the number of cycles N2.

[0080] More specifically, the film forming apparatus 520a (520b) is equipped with the nozzles a to d. In the case of the manufacturing system shown in Fig. 3, an arbitrary point P on the main surface of the metal foil is moved sequentially to a position facing the nozzles a to d by a reciprocating motion within the film forming region of the metal foil, thereby forming a film.

[0081] In the manufacturing system shown in FIG. 2, stress on the metal foil and rollers is smaller than in the manufacturing system shown in FIG. 3. However, if the desired number of cycles N1 (N2) is large, it is necessary to increase the number of nozzles X1 (X2) of the film-forming device 420a (420b), lengthen the travel distance L1 (L2), or increase V2a / V1a (V2b / V1b). This may result in a larger device and higher equipment costs. On the other hand, compared to the manufacturing system shown in FIG. 2, the manufacturing system shown in FIG. 3 can reduce equipment costs by fixing the film-forming device. However, since the metal foil is moved back and forth by the rollers, stress on the metal foil may be greater. Furthermore, since the rotation direction of the rollers needs to be changed to move the metal foil back and forth, stress on the rollers may also be greater. The manufacturing system shown in FIG. 2 and the manufacturing system shown in FIG. 3 may be combined, and in some cases, this combination may be more effective.

[0082] Below, matters common to the manufacturing system 400 in FIG. 2 and the manufacturing system 500 in FIG. 3 will be described.

[0083] The first film formation device 420a (520a) is arranged in the first film formation region 430a (530a) on the first main surface S1 side of the metal foil 300 being transported by rollers. The second film formation device 420b (520b) is arranged in the second film formation region 430b (530b) on the second main surface S2 side of the metal foil 300 being transported by rollers.

[0084] Since the first film formation region 430a (530a) and the second film formation region 430b (530b) are isolated from each other, the first film formation apparatus 420a (520a) and the second film formation apparatus 420b (520b) are isolated from each other. Therefore, in the first film formation region 430a (530a), the second film formation apparatus 420b (520b) does not supply the second source gas to the first main surface S1 and the second main surface S2 of the metal foil 300. In the second film formation region 430b (530b), the first film formation apparatus 420a (520a) does not supply the first source gas to the first main surface S1 and the second main surface S2 of the metal foil 300.

[0085] In the first film formation region 430a (530a), the first film formation apparatus 420a (520a) supplies a first source gas to the first main surface S1 of the metal foil 300, but does not supply the first source gas to the second main surface S2 of the metal foil 300. In the second film formation region 430b (530b), the second film formation apparatus 420b (520b) supplies a second source gas to the second main surface S2 of the metal foil 300, but does not supply the second source gas to the first main surface S1 of the metal foil 300.

[0086] The transport rollers 410a to 410c (510a to 510c) shown in FIG. 2 (FIG. 3) transport the metal foil 300 to the first film formation region 430a (530a) and the second film formation region 430b (530b) in this order.

[0087] The first film formation device 420a (520a) can also serve as a first heat treatment device for heat-treating the second main surface S2 in the first film formation region 430a (530a). This heat treatment can form an oxide film (oxide of the first metal contained in the metal portion) of the metal portion constituting the second porous portion on the surface of the second porous portion on the side of the second main surface S2. In this case, the second film formation device 420b (520b) forms a second dielectric layer on the surface of the second porous portion via the oxide film, which has excellent adhesion to the metal portion. In this case, peeling of the second dielectric layer from the surface of the second porous portion is suppressed. Furthermore, while the formation of this oxide film can reduce leakage current, it tends to reduce capacitance on the second main surface side. Therefore, the second dielectric layer is obtained on the second main surface side as a dielectric layer B with excellent resistance to tensile stress.

[0088] Furthermore, the second film formation apparatus 420b (520b) can also serve as a second heat treatment apparatus for heat-treating the first main surface S1 having the first dielectric layer in the second film formation region 430b (530b). This heat treatment can enhance the crystallinity of the first dielectric layer. As a result, the first dielectric layer is obtained on the first main surface as dielectric layer A, which is advantageous for achieving high capacitance. While the first dielectric layer, which is dielectric layer A, is more advantageous for achieving high capacitance than the second dielectric layer, which is dielectric layer B, it tends to be more brittle and have poor adhesion to the porous portion.

[0089] The first temperature TA1 during film formation by the first film formation apparatus 420a (520a) (or during heat treatment as the first heat treatment apparatus) and the second temperature TA2 during film formation by the second film formation apparatus 420b (520b) (or during heat treatment as the second heat treatment apparatus) may be the same or different. TA1 and TA2 preferably satisfy the relationships of the above formulas (i) to (iii), for example.

[0090] The number X1 of the first nozzles may be the same as or different from the number X2 of the second nozzles. From the viewpoint of forming the first dielectric layer as the dielectric layer A, the number X1 of the first nozzles may be smaller than the number X2 of the second nozzles.

[0091] The number of cycles N1 for film formation by the first film formation apparatus 420a (520a) may be the same as or different from the number of cycles N2 for film formation by the second film formation apparatus 420b (520b). From the viewpoint of forming the first dielectric layer as the dielectric layer A, the number of cycles N1 may be smaller than the number of cycles N2. A smaller number of film formation cycles can reduce the thickness of the dielectric layer A, which is advantageous in terms of increasing capacity.

[0092] In the manufacturing system 400 (500), the roller 410c (510a, 510c) may curve the metal foil 300 during film formation. The metal foil 300 is curved so that the second main surface S2 side, on which the second dielectric layer as the dielectric layer B is formed, forms a convex portion, and the first main surface S1 side, on which the first dielectric layer as the dielectric layer A is formed, forms a concave portion, thereby suppressing damage to the dielectric layer due to tensile stress.

[0093] In the manufacturing system 400 (500), the metal foil 300 is transported in the order of the first film deposition area and the second film deposition area, but may be transported in the order of the second film deposition area and the first film deposition area. The first dielectric layer and the second dielectric layer may be formed as the dielectric layer B and the dielectric layer A, respectively.

[0094] In the above manufacturing method (or the above manufacturing system), in the second step (or film formation section), the first dielectric layer and the second dielectric layer may be formed as dielectric layer A and dielectric layer B, respectively. In this case, the first dielectric layer and the second dielectric layer can be formed so that the thickness F1 of the first dielectric layer and the thickness F2 of the second dielectric layer satisfy the relationship of the following formula (1).

[0095] 0.75≦F1 / F2≦0.97 (1)

[0096] Alternatively, in the above case, the first dielectric layer and the second dielectric layer can be formed so that the capacitance C1 generated on the first main surface side having the first dielectric layer and the capacitance C2 generated on the second main surface side having the second dielectric layer satisfy the relationship of the following formula (2).

[0097] 0.80≦C2 / C1≦0.99 (2)

[0098] [Electrode foil for electrolytic capacitors] The electrode foil for electrolytic capacitors comprises a metal foil having a first main surface and a second main surface opposite to the first main surface, with a first porous portion on the first main surface side and a second porous portion on the second main surface side, a first dielectric layer covering the surface of the first porous portion, and a second dielectric layer covering the surface of the second porous portion.

[0099] In an electrode foil for an electrolytic capacitor according to one embodiment of the present disclosure (hereinafter also referred to as a "first electrode foil"), the thickness F1 of the first dielectric layer and the thickness F2 of the second dielectric layer satisfy the relationship of the above formula (1). That is, F1 / F2 is 0.75 or more and 0.97 or less. F1 / F2 may also be 0.85 or more and 0.95 or less.

[0100] The dielectric layer thicknesses F1 and F2 refer to the thickness of the dielectric layer covering the outer surface of the porous portion (metal foil). The dielectric layer thicknesses F1 and F2 are determined by measuring the thickness of the dielectric layer at any 10 points using cross-sectional images of the electrode foil in the thickness direction taken by SEM or TEM and averaging the measured values.

[0101] In addition, in an electrode foil for an electrolytic capacitor according to another embodiment of the present disclosure (hereinafter also referred to as a "second electrode foil"), the capacitance C1 generated on the first main surface side having the first dielectric layer and the capacitance C2 generated on the second main surface side having the second dielectric layer satisfy the relationship of the above formula (2). That is, C2 / C1 is 0.8 or more and 0.99 or less. C2 / C1 may be 0.8 or more and 0.97 or less, or 0.8 or more and 0.95 or less.

[0102] The capacitances C1 and C2 can be determined by sealing (or coating) one of the first and second main surfaces of the electrode foil and measuring the other unsealed main surface in an electrolyte.

[0103] By using the above manufacturing method (manufacturing system), the first dielectric layer and the second dielectric layer can be individually formed as dielectric layer A and dielectric layer B, respectively, to obtain the above electrode foil.

[0104] The metal foil of the first electrode foil or the second electrode foil may have an anode lead portion and a cathode forming portion, and in the cathode forming portion, the surfaces of the first porous portion and the second porous portion may be covered with a first dielectric layer and a second dielectric layer, respectively. Hereinafter, such an electrode foil will also be referred to as a "third electrode foil."

[0105] [Electrolytic Capacitor] An electrolytic capacitor according to an embodiment of the present disclosure includes a wound body and an electrolyte. The wound body is formed by winding an anode foil, a cathode foil, and a separator disposed between the anode foil and the cathode foil. The anode foil is the first electrode foil or the second electrode foil described above. By using the first electrode foil or the second electrode foil, an electrolytic capacitor with high capacity and high reliability can be obtained.

[0106] The wound body is formed by winding strip-shaped anode foil and cathode foil around a winding core with a separator interposed therebetween, and winding the resulting foil into a columnar shape. In the wound body, the first electrode foil or the second electrode foil is preferably arranged so that its first main surface (the main surface facing the first dielectric layer formed as dielectric layer A) faces the axial center of the wound body (the winding core side).

[0107] The electrolytic capacitor may further include a lead member connected to the anode foil. In this case, the anode foil and the lead member are preferably connected by a crimping portion at the overlapping portion where the second main surface of the anode foil and the lead member overlap. The lead member is preferably disposed on the second main surface side of the anode foil at the overlapping portion (crimping portion). When the lead member is crimped to the anode foil, tensile stress tends to be generated on the side of the anode foil's main surface that overlaps the lead member. Therefore, from the perspective of suppressing damage to the dielectric layer, it is preferable to overlap the second main surface having the second dielectric layer formed as dielectric layer B with the lead member. Furthermore, the above method is preferable from the perspective of suppressing cracks originating from damaged portions of the dielectric layer and reducing contact resistance.

[0108] The crimped portion is formed as follows: The lead member is placed on one main surface of the anode foil, and a needle-shaped member is used to drill a predetermined position in the overlapping portion from the lead member side. At this time, a portion of the lead member is pulled out to the other surface of the anode foil. The pulled out portion is then tightly attached to the other main surface of the anode foil.

[0109] (Cathode foil) The cathode foil may be a metal foil containing a valve metal such as Al, Ta, or Nb. If necessary, the surface of the metal foil may be roughened by etching. That is, the cathode foil may be a metal foil having a porous portion and a core portion continuous with the porous portion.

[0110] (Separator) The separator 30 is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (for example, aliphatic polyamide, aromatic polyamide such as aramid).

[0111] (Electrolyte) The electrolyte includes at least one of a solid electrolyte and an electrolytic solution. The cathode portion may include a solid electrolyte and an electrolytic solution, or may include a solid electrolyte and a non-aqueous solvent. Hereinafter, the electrolytic solution and the non-aqueous solvent are collectively referred to as "liquid components." The dielectric layer is coated with a solid electrolyte (or electrolytic solution), for example, by impregnating the electrode foil (or wound body) with a treatment solution (or electrolytic solution) containing a conductive polymer. The treatment solution may include a non-aqueous solvent.

[0112] The solid electrolyte includes a conductive polymer. Examples of the conductive polymer include π-conjugated polymers. Examples of the conductive polymer include polypyrrole, polythiophene, polyfuran, and polyaniline. The conductive polymer may be used alone or in combination of two or more types, or may be a copolymer of two or more types of monomers. The weight-average molecular weight of the conductive polymer is, for example, 1,000 to 100,000.

[0113] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. refer to polymers having polypyrrole, polythiophene, polyfuran, polyaniline, etc. as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc. may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene), etc.

[0114] The conductive polymer may be doped with a dopant. The solid electrolyte may contain a dopant together with the conductive polymer. Examples of the dopant include polystyrene sulfonic acid. The solid electrolyte may further contain an additive, if necessary.

[0115] The liquid component is in contact with the dielectric layer directly or via a conductive polymer. The liquid component may be a non-aqueous solvent or an electrolyte solution. The electrolyte solution contains a non-aqueous solvent and an ionic substance (solute (e.g., organic salt)) dissolved therein. The non-aqueous solvent may be an organic solvent or an ionic liquid.

[0116] The non-aqueous solvent is preferably a high-boiling solvent, for example, a polyol compound such as ethylene glycol, a sulfone compound such as sulfolane, a lactone compound such as γ-butyrolactone, an ester compound such as methyl acetate, a carbonate compound such as propylene carbonate, an ether compound such as 1,4-dioxane, or a ketone compound such as methyl ethyl ketone.

[0117] The liquid component may contain an acid component (anion) and a base component (cation). The acid component and the base component may form a salt (solute). The acid component contributes to the film repair function. Examples of the acid component include organic carboxylic acids and inorganic acids. Examples of the inorganic acid include phosphoric acid, boric acid, and sulfuric acid. Examples of the base component include primary to tertiary amine compounds.

[0118] The organic salt is a salt in which at least one of the anion and cation contains an organic substance. Examples of the organic salt include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0119] From the viewpoint of suppressing dedoping of the dopant from the conductive polymer (deterioration of the solid electrolyte), the liquid component preferably contains more acid components than base components. Furthermore, since the acid components contribute to the film repair function of the liquid component, it is also preferable that the liquid component contains more acid components than base components. The molar ratio of the acid component to the base component (acid component / base component) is, for example, 1.1 or more. From the viewpoint of suppressing dedoping of the dopant from the conductive polymer, the pH of the liquid component may be 6 or less, or may be 1 or more and 5 or less.

[0120] Here, Fig. 4 is a cross-sectional view schematically illustrating an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 4 shows an example of an electrolytic capacitor including a wound capacitor element. Fig. 5 is a perspective view schematically illustrating the configuration of the wound body of Fig. 4.

[0121] Electrolytic capacitor 200 includes a wound body 100. Wound body 100 is formed by winding an anode foil 10 and a cathode foil 20 with a separator 30 interposed therebetween.

[0122] One end of each of lead tabs 50A and 50B is connected to anode foil 10 and cathode foil 20, respectively, and lead tabs 50A and 50B are wound to form wound body 100. Lead wires 60A and 60B are connected to the other ends of lead tabs 50A and 50B, respectively.

[0123] A stop tape 40 is disposed on the outer surface of the cathode foil 20 located at the outermost layer of the wound body 100, and the ends of the cathode foil 20 are fixed by the stop tape 40. When the anode foil 10 is prepared by cutting it from a large foil, the wound body 100 may further be subjected to a chemical conversion treatment in order to provide a dielectric layer on the cut surface.

[0124] The wound body 100 contains an electrolyte, and the electrolyte is interposed between the anode foil 10 (dielectric layer) and the cathode foil 20. The wound body 100 containing the electrolyte is formed, for example, by impregnating the wound body 100 with a treatment liquid (or electrolytic solution) containing a conductive polymer. The impregnation may be performed under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa.

[0125] The wound body 100 is housed in the bottomed case 211 so that the lead wires 60A and 60B are located on the opening side of the bottomed case 211. The bottomed case 211 can be made of a metal such as aluminum, stainless steel, copper, iron, brass, or an alloy of these metals.

[0126] A sealing member 212 is placed at the opening of a bottomed case 211 in which the wound body 100 is housed, the open end of the bottomed case 211 is crimped to the sealing member 212 and curled, and a seat plate 213 is placed at the curled portion, thereby sealing the wound body 100 within the bottomed case 211.

[0127] The sealing member 212 is formed so that the lead wires 60A and 60B pass through it. The sealing member 212 may be made of any insulating material, and is preferably made of an elastic material. Among these, silicone rubber, fluororubber, ethylene propylene rubber, hypalon rubber, butyl rubber, isoprene rubber, and the like, which have high heat resistance, are preferred.

[0128] An electrolytic capacitor according to another embodiment of the present disclosure includes a laminate including a plurality of capacitor elements stacked together, each of the capacitor elements including an anode body having an anode lead portion and a cathode forming portion, and a cathode portion covering the cathode forming portion. The laminate includes an anode laminate portion including a plurality of stacked anode lead portions, and a cathode laminate portion including a plurality of stacked cathode forming portions each covered by a cathode portion. At least one of the anode bodies of the plurality of capacitor elements is the third electrode foil described above. Use of the third electrode foil allows for a high-capacity, high-reliability electrolytic capacitor to be obtained.

[0129] When a laminate is formed, the thickness of the cathode laminate in the stacking direction tends to be greater at the center of the surface perpendicular to the stacking direction of the cathode laminate and smaller at the periphery, making the electrode foil more likely to bend. That is, the surface of the electrode foil closer to the center of the stacking direction of the laminate tends to have a concave shape. Therefore, in the laminate, it is preferable that the third electrode foil be arranged so that its first main surface (the main surface facing the first dielectric layer formed as dielectric layer A) faces the center of the stacking direction of the laminate.

[0130] A multilayer electrolytic capacitor includes, for example, the above-described laminate and a resin exterior body that seals the laminate. The cathode portion includes a solid electrolyte layer that covers at least a portion of the cathode forming portion, and a cathode extraction layer that covers at least a portion of the solid electrolyte layer. The cathode extraction layer includes, for example, a silver paste layer and a carbon layer. An anode lead is connected to the anode laminate portion. A cathode lead is connected to the cathode extraction layer at one end of the laminate in the stacking direction. Portions of the anode lead and the cathode lead are exposed from the exterior body.

[0131] The electrode foil for electrolytic capacitors according to the present disclosure is suitably used in electrolytic capacitors that require high capacity and high reliability.

[0132] While the present disclosure has been described with respect to presently preferred embodiments, such disclosure should not be interpreted as limiting. Various variations and modifications will no doubt become apparent to those skilled in the art to which the present disclosure pertains upon reading the above disclosure. Accordingly, the appended claims should be interpreted to cover all variations and modifications without departing from the true spirit and scope of the present disclosure.

[0133] 10: anode foil, 20: cathode foil, 30: separator, 40: stop tape, 60A, 60B: lead wire, 50A, 50B: lead tab, 100: wound body, 200: electrolytic capacitor, 211: bottomed case, 212: sealing member, 213: seat plate, 300: metal foil, S1: first main surface, S2: second main surface, 310a: first porous portion, 310b: second porous portion, 320: core, 400, 400: electrode foil manufacturing system, 410a to 410c, 510a to 510c: rollers, 420a, 520a: first film forming device, 420b, 520b: second film forming device, 430a, 530a: first film forming region, 430b, 530b: second film forming region

Claims

1. A metal foil having a first main surface and a second main surface opposite to the first main surface, the metal foil having a first porous portion on the first main surface side and a second porous portion on the second main surface side; a first dielectric layer covering a surface of the first porous portion; a second dielectric layer covering a surface of the second porous portion; Equipped with The thickness F1 of the first dielectric layer and the thickness F2 of the second dielectric layer are 0.75≦F1 / F2≦0.97 Electrode foil for electrolytic capacitors that satisfies the above requirements.

2. A metal foil having a first main surface and a second main surface opposite to the first main surface, the metal foil having a first porous portion on the first main surface side and a second porous portion on the second main surface side; a first dielectric layer covering a surface of the first porous portion; a second dielectric layer covering a surface of the second porous portion; Equipped with A capacitance C1 generated on the first main surface side having the first dielectric layer and a capacitance C2 generated on the second main surface side having the second dielectric layer are 0.80≦C2 / C1≦0.99 Electrode foil for electrolytic capacitors that satisfies the above requirements.

3. The metal foil has an anode extraction portion and a cathode formation portion, 3. The electrode foil for an electrolytic capacitor according to claim 1, wherein in the cathode formation portion, surfaces of the first porous portion and the second porous portion are covered with the first dielectric layer and the second dielectric layer, respectively.

4. A wound body and an electrolyte, the wound body is configured by winding an anode foil, a cathode foil, and a separator disposed between the anode foil and the cathode foil, 3. An electrolytic capacitor, wherein the anode foil is the electrode foil according to claim 1.

5. 5. The electrolytic capacitor according to claim 4, wherein in the wound body, the electrode foil is arranged such that the first main surface faces an axis of the wound body.

6. Further, a lead member connected to the anode foil is provided, 5 . The electrolytic capacitor according to claim 4 , wherein the anode foil and the lead member are connected by a crimping portion at an overlapping portion where the second main surface of the anode foil and the lead member overlap.

7. a laminate in which a plurality of capacitor elements are laminated, the capacitor elements including an anode body having an anode lead portion and a cathode forming portion, and a cathode portion covering the cathode forming portion; the laminate includes an anode laminate portion in which a plurality of the anode lead portions are laminated, and a cathode laminate portion in which a plurality of the cathode formation portions covered with the cathode portion are laminated, An electrolytic capacitor, wherein at least one of the anode bodies of the plurality of capacitor elements is the electrode foil according to claim 3 .

8. 8. The electrolytic capacitor according to claim 7, wherein in the laminate, the electrode foil is arranged such that the first main surface faces a center side in a lamination direction of the laminate.

9. A first step of preparing a metal foil having a first main surface and a second main surface opposite to the first main surface, the metal foil having a first porous portion on the first main surface side and a second porous portion on the second main surface side; a second step of separately forming a first dielectric layer covering a surface of the first porous portion and a second dielectric layer covering a surface of the second porous portion; The method for producing an electrode foil for an electrolytic capacitor includes the steps of:

10. The second step comprises: A step 2A of forming the first dielectric layer at a first temperature TA1° C. by atomic layer deposition; and a second B step of forming the second dielectric layer at a second temperature TA2° C. by atomic layer deposition.

11. After the step 2A, the step 2B is carried out; 11. The method for producing an electrode foil for an electrolytic capacitor according to claim 10, wherein the second B step also serves as a step of heat-treating the first surface having the first dielectric layer at the second temperature TA2 to enhance crystallinity of the first dielectric layer.

12. The second A step also includes a step of heat-treating the second main surface at the first temperature TA1 to form an oxide film of a metal portion constituting the second porous portion on a surface of the second porous portion, 12 . The method for producing an electrode foil for an electrolytic capacitor according to claim 11 , wherein in the second B step, the second dielectric layer is formed on a surface of the second porous portion via the oxide film.

13. The first temperature TA1 and the second temperature TA2 are The method for producing an electrode foil for electrolytic capacitors according to any one of claims 10 to 12, wherein the relationships 0≦|TA1-TA2|≦50, 90≦TA1≦400, and 90≦TA2≦400 are satisfied.

14. The thickness F1 of the first dielectric layer and the thickness F2 of the second dielectric layer are 0.75≦F1 / F2≦0.97 The method for producing an electrode foil for electrolytic capacitors according to any one of claims 9 to 12, which satisfies the following relationship:

15. a capacitance C1 generated on the first main surface side having the first dielectric layer, and a capacitance C2 generated on the second main surface side having the second dielectric layer, 0.80≦C2 / C1≦0.99 The method for producing an electrode foil for electrolytic capacitors according to any one of claims 9 to 12, which satisfies the following relationship:

16. A manufacturing system for electrode foil for electrolytic capacitors, comprising: a film formation unit that, on a metal foil having a first main surface and a second main surface opposite to the first main surface, and having a first porous portion on the first main surface side and a second porous portion on the second main surface side, forms a first dielectric layer covering a surface of the first porous portion and a second dielectric layer covering a surface of the second porous portion by atomic layer deposition.

17. The film forming unit includes: a plurality of first nozzles facing the first main surface in a first film formation region and configured to supply a first source gas to the first main surface; a plurality of second nozzles facing the second main surface in a second film formation region isolated from the first film formation region and supplying a second source gas to the second main surface; The manufacturing system for electrode foil for electrolytic capacitors comprises: a first moving means for moving the first nozzles along the first main surface in the first film formation region; 17. The system for producing an electrode foil for an electrolytic capacitor according to claim 16, further comprising: a second moving means for moving the plurality of second nozzles along the second main surface in the second film formation region.

18. a conveying means for conveying the metal foil in the first film-forming region and the second film-forming region, the first moving means moves the plurality of first nozzles along a transport path of the metal foil within the first film formation region; 18. The system for manufacturing an electrode foil for an electrolytic capacitor according to claim 17, wherein the second moving means moves the plurality of second nozzles along a transport path of the metal foil within the second film formation area.

19. a transport path of the metal foil includes a straight path and / or a curved path along which the metal foil is transported in a curved manner in each of the first film formation region and the second film formation region; 19. The system for manufacturing an electrode foil for an electrolytic capacitor according to claim 18, wherein the first moving means and the second moving means respectively move the plurality of first nozzles and the plurality of second nozzles along the linear path and / or the curved path.

20. 20. The system for manufacturing an electrode foil for an electrolytic capacitor according to claim 18 or 19, wherein the first moving means moves the plurality of first nozzles in the first film formation region in the same direction as or opposite to the transport direction of the metal foil, or reciprocates on the transport path.

21. 20. The system for manufacturing an electrode foil for an electrolytic capacitor according to claim 18 or 19, wherein the second moving means moves the plurality of second nozzles in the second film formation region in the same direction as or opposite to the transport direction of the metal foil, or reciprocates on the transport path.

22. a conveying roller that conveys the metal foil through a first film-forming region and a second film-forming region separated from the first film-forming region; The film forming unit includes: a first film formation device that supplies a first source gas to the first main surface in the first film formation region; a second film formation device that supplies a second source gas to the second main surface in the second film formation region; The system for manufacturing an electrode foil for an electrolytic capacitor according to claim 16 , comprising:

23. a conveying roller that conveys the metal foil in a first film-forming region and a second film-forming region separated from the first film-forming region; the first film formation apparatus supplies the first source gas to the first main surface while oscillating in the first film formation region; 23. The system for producing an electrode foil for an electrolytic capacitor according to claim 22, wherein the second film formation device supplies the second raw material gas to the second main surface while oscillating in the second film formation region.

24. a transport roller that transports the metal foil in a first film-forming region and a second film-forming region separated from the first film-forming region and reciprocates the metal foil in each of the first film-forming region and the second film-forming region; The film forming unit includes: a first film formation device that supplies a first source gas to the first main surface in the first film formation region; a second film formation device that supplies a second source gas to the second main surface in the second film formation region; The system for manufacturing an electrode foil for an electrolytic capacitor according to claim 16 , comprising:

25. the first film forming apparatus includes a plurality of first nozzles that supply the first source gas to the first main surface; the second film forming apparatus includes a plurality of second nozzles that supply the second source gas to the second main surface; The system for manufacturing an electrode foil for an electrolytic capacitor according to any one of claims 22 to 24, wherein the number of the first nozzles and the number of the second nozzles are different from each other.

26. the transport roller transports the metal foil through the first film-forming region and the second film-forming region in this order; the first film formation device also serves as a first heat treatment device that heat-treats the second main surface in the first film formation region to form an oxide film of a metal portion constituting the second porous portion on a surface of the second porous portion, The system for manufacturing an electrode foil for an electrolytic capacitor according to any one of claims 22 to 24, wherein the second film formation device also serves as a second heat treatment device that heat-treats the first main surface having the first dielectric layer in the second film formation region to enhance crystallinity of the first dielectric layer.

27. The thickness F1 of the first dielectric layer and the thickness F2 of the second dielectric layer are 0.75≦F1 / F2≦0.97 The system for producing an electrode foil for an electrolytic capacitor according to any one of claims 16 to 19 or any one of claims 22 to 24, wherein the above relationship is satisfied.

28. a capacitance C1 generated on the first main surface side having the first dielectric layer, and a capacitance C2 generated on the second main surface side having the second dielectric layer, 0.80≦C2 / C1≦0.99 The system for producing an electrode foil for an electrolytic capacitor according to any one of claims 16 to 19 or any one of claims 22 to 24, wherein the above relationship is satisfied.