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

Abstract

This electrode foil for electrolytic capacitors comprises a metal foil that has a porous part on a main surface thereof and a dielectric layer that covers the porous part. The metal foil contains a valve action metal. When the electrode foil has a withstand voltage of not more than 7 V, indentation depth H is not more than 17 μm. When the withstand voltage of the electrode foil is more than 7 V but not more than 22 V, the indentation depth H is not more than 13.5 μm. When the withstand voltage of the electrode foil is more than 22 V but not more than 160 V, the indentation depth H is not more than 10.5 μm.

Description

Electrode foil, electrolytic capacitor, and method for manufacturing electrode foil CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-123555, filed on July 30, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to an electrode foil, an electrolytic capacitor, and a method for manufacturing the electrode foil.

[0003] The electrode foil of an electrolytic capacitor includes a metal foil containing a valve metal and having a porous portion on a main surface thereof, and a dielectric layer covering the porous portion. The porous portion increases the surface area of ​​the electrode foil, thereby enabling a high capacitance.

[0004] Patent Document 1 proposes an electrode foil for an aluminum electrolytic capacitor, characterized in that aluminum foil that has been subjected to a surface expansion treatment by etching is compressed in the foil thickness direction, thereby increasing the surface area per unit volume compared to before compression.

[0005] Japanese Patent Application Publication No. 11-26320

[0006] There is a demand for improved reliability in electrolytic capacitors.

[0007] One aspect of the present disclosure relates to an electrode foil having a withstand voltage of 7 V or less, the electrode foil comprising: a metal foil having a porous portion on a main surface; and a dielectric layer covering the porous portion, the metal foil including a valve action metal; and an indentation depth H of 17 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portion covered with the dielectric layer, as measured by a nanoindentation method.

[0008] Another aspect of the present disclosure relates to an electrode foil having a withstand voltage of more than 7 V and not more than 22 V, the electrode foil comprising: a metal foil having a porous portion on a main surface; and a dielectric layer covering the porous portion, the metal foil including a valve action metal, wherein the indentation depth H measured by a nanoindentation method when a maximum indentation load of 500 mN is applied to the main surface having the porous portion covered with the dielectric layer is 13.5 μm or less.

[0009] Yet another aspect of the present disclosure relates to an electrode foil having a withstand voltage of more than 22 V and not more than 160 V, the electrode foil comprising: a metal foil having a porous portion on a main surface; and a dielectric layer covering the porous portion, the metal foil including a valve action metal; and an indentation depth H of 10.5 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portion covered with the dielectric layer, as measured by a nanoindentation method.

[0010] Yet another aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element, the capacitor element 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, the anode foil being the above-described electrode foil.

[0011] Yet another aspect of the present disclosure relates to a method for manufacturing an electrode foil used in an electrolytic capacitor having a withstand voltage of 7 V or less, the method including: an etching step of etching a sheet containing a valve action metal; a compression step of compressing the etched sheet in a thickness direction to form porous portions on a main surface of the sheet; and a step of forming a dielectric layer covering the porous portions by performing a chemical conversion treatment on the compressed sheet, wherein the method has an indentation depth H of 17 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portions covered with the dielectric layer, as measured by a nanoindentation method.

[0012] Yet another aspect of the present disclosure relates to a method for manufacturing an electrode foil having a withstand voltage of more than 7 V and not more than 22 V, the method including: an etching step of etching a sheet containing a valve action metal; a compression step of compressing the etched sheet in a thickness direction to form porous portions on a main surface of the sheet; and a step of forming a dielectric layer covering the porous portions by performing a chemical conversion treatment on the compressed sheet, wherein the method has an indentation depth H of 13.5 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portions covered with the dielectric layer, as measured by a nanoindentation method.

[0013] Yet another aspect of the present disclosure relates to a method for manufacturing an electrode foil having a withstand voltage of more than 22 V and not more than 160 V, the method including: an etching step of etching a sheet containing a valve action metal; a compression step of compressing the etched sheet in a thickness direction to form porous portions on a main surface of the sheet; and a step of forming a dielectric layer covering the porous portions by performing a chemical conversion treatment on the compressed sheet, wherein the method has an indentation depth H of 10.5 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portions covered with the dielectric layer, as measured by a nanoindentation method.

[0014] According to the present disclosure, the reliability of electrolytic capacitors can be improved.

[0015] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0016] 1 is a cross-sectional view schematically illustrating an example of an electrode foil according to an embodiment of the present disclosure; 2 is a cross-sectional view schematically illustrating an example of an electrolytic capacitor according to an embodiment of the present disclosure; 3 is a perspective view schematically illustrating a configuration of a wound body;

[0017] 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.

[0018] (Electrode Foil) An electrode foil according to an embodiment of the present disclosure includes a metal foil having a porous portion on a main surface thereof and a dielectric layer covering the porous portion. The metal foil includes a valve metal. The dielectric layer covers the surface of the metal skeleton that constitutes the porous portion. The electrode foil can be used in an electrolytic capacitor.

[0019] (Indentation Depth H) In the case of an electrode foil with a withstand voltage of 7 V or less (hereinafter also referred to as "electrode foil E1"), the indentation depth H is 17 μm or less. In the case of an electrode foil with a withstand voltage of more than 7 V and less than or equal to 22 V (hereinafter also referred to as "electrode foil E2"), the indentation depth H is 13.5 μm or less. In the case of an electrode foil with a withstand voltage of more than 22 V and less than or equal to 160 V (hereinafter also referred to as "electrode foil E3"), the indentation depth H is 10.5 μm or less.

[0020] The indentation depth H is the indentation depth measured by nanoindentation on the main surface of the electrode foil (the main surface of the metal foil having a porous portion covered with a dielectric layer) when the maximum indentation load is 500 mN. The withstand voltage is determined in accordance with the test method for electrode foil for aluminum electrolytic capacitors (EIAJ RC-2364A) of the Electronic Industries Association of Japan standard.

[0021] When the above-mentioned configuration is satisfied, an electrode foil having high tensile strength and high capacitance can be obtained, and the use of such an electrode foil can improve the reliability of electrolytic capacitors.

[0022] To increase capacitance, it is conceivable to increase the pit density or thickness of the porous portion to increase the surface area. However, increasing the pit density or thickness reduces the strength of the electrode foil, which can lead to cracks or foil breakage in the electrode foil during the manufacturing process of electrolytic capacitors. The reduction in electrode foil strength is due to a reduction in the strength of the surface layer of the porous portion covered by the dielectric layer, and this reduction in surface layer strength is particularly noticeable when the pit density or thickness of the porous portion is high.

[0023] The following factors (a) to (c) are presumed to be factors that reduce the strength of the surface layer of the porous portion covered with the dielectric layer: (a) The surface layer is likely to deteriorate when the etching solution comes into contact with the surface of the metal foil during electrolytic etching. (b) The stress generated when the electrode foil (chemically processed foil) is wound during the manufacturing process of the electrolytic capacitor is likely to be large in the surface layer. This stress is large, for example, when the diameter of the roller that winds the electrode foil (chemically processed foil) is small. Furthermore, this stress is larger on the outer periphery of the wound electrode foil (chemically processed foil) than on the inner periphery. (c) Rolled foil is usually used for raw material sheets containing valve metals (e.g., aluminum foil), and rolling marks are present, and rolling marks are likely to remain on the surface layer even in electrode foils (chemically processed foils).

[0024] In contrast, in the present disclosure, by setting the indentation depth H within the above range, the decrease in strength that accompanies an increase in the capacity of the electrode foil is suppressed, and both high capacity and improved tensile strength can be achieved. The indentation depth H can be adjusted by the thickness of the compressed porous portion, the thickness of the dielectric layer covering the porous portion, etc. It can be adjusted by the conditions of the etching step (such as the amount of dissolution of the sheet surface), the conditions of the compression step (such as the compression ratio), and the conditions of the anodization step (such as the anodization voltage), etc., which will be described later. The indentation depth H can be adjusted to some extent by the etching conditions, but it is difficult to adjust it to the above range by the etching conditions alone for high-capacity electrode foils with thick porous layers.

[0025] To improve the reliability of electrolytic capacitors, the strength of electrode foils (chemically formed foils) in which a dielectric layer is formed on the surface of a metal foil (porous portion) is important. Electrode foils with a dielectric layer of a predetermined thickness are used depending on the electrode foil's withstand voltage (the rated voltage of the electrolytic capacitor). For example, electrode foils with a thicker dielectric layer are used for high withstand voltages (rated voltages). The indentation depth H, etc., also varies depending on the thickness of the dielectric layer (chemically formed film). Electrode foils (chemically formed foils) with high withstand voltages (chemically formed voltages) have a thicker dielectric layer (chemically formed film) and a higher proportion of dielectric (e.g., aluminum oxide). Furthermore, the pit diameter of the porous portion may be large. These factors can increase the brittleness of the foil. Embrittlement increases hardness, but on the other hand, the foil becomes brittle, which may result in a decrease in bending strength, making it necessary to increase the strength level of the electrode foil. Based on the above findings, the inventors conducted extensive research and discovered that by setting the indentation depth H within a specific range depending on the withstand voltage (rated voltage), it is possible to achieve both suppression of strength reduction and high capacity.

[0026] The dielectric layer may be a chemical conversion coating formed by chemical conversion treatment. The chemical conversion coating may be formed to a predetermined thickness depending on the withstand voltage (rated voltage). When the same metal foil is used for chemical conversion treatment, the thicker the chemical conversion coating formed, the smaller the indentation depth H tends to be.

[0027] The withstand voltage (film withstand voltage) of the electrode foil E1 is 7 V or less. The dielectric layer may be a chemical conversion film formed by chemical conversion treatment. In the case of the electrode foil E1, the chemical conversion voltage may be, for example, 7 V or less. The thickness of the chemical conversion film of the electrode foil E1 is, for example, 5 nm or more and 15 nm or less. The electrode foil E1 is used, for example, in an electrolytic capacitor having a rated voltage of 6 V or less (or 5 V or less).

[0028] The withstand voltage (film withstand voltage) of the electrode foil E2 is greater than 7 V and equal to or less than 22 V, or may be greater than 7 V and equal to or less than 20 V. The dielectric layer may be a chemical conversion film formed by chemical conversion treatment. In the case of the electrode foil E2, the chemical conversion voltage may be, for example, greater than 7 V and equal to or less than 22 V (or equal to or less than 20 V). The thickness of the chemical conversion film of the electrode foil E2 is, for example, greater than 15 nm and equal to or less than 32 nm. The electrode foil E2 is used, for example, in an electrolytic capacitor having a rated voltage of greater than 5 V and equal to or less than 19 V (or equal to or less than 16 V).

[0029] The withstand voltage (film withstand voltage) of the electrode foil E3 is greater than 22 V and less than 160 V, and may be greater than 70 V and less than 160 V. The dielectric layer may be a chemical conversion film formed by chemical conversion treatment. In the case of the electrode foil E3, the chemical conversion voltage may be, for example, greater than 22 V (or greater than 70 V) and less than 160 V. The thickness of the chemical conversion film of the electrode foil E3 is, for example, greater than 32 nm and less than 220 nm. The electrode foil E3 is used, for example, in an electrolytic capacitor having a rated voltage of greater than 16 V and less than 130 V.

[0030] From the viewpoint of improving the tensile strength and capacity of the electrode foil, the indentation depth H of the electrode foil E1 is preferably 15 μm or less, more preferably 14 μm or less, and even more preferably 12 μm or less. From the viewpoint of ensuring capacity, the indentation depth H of the electrode foil E1 may be 6 μm or more, or may be 8 μm or more.

[0031] From the viewpoint of improving the tensile strength and capacity of the electrode foil, the indentation depth H of the electrode foil E2 is preferably 12.5 μm or less, more preferably 11.5 μm or less, and even more preferably 10 μm or less. From the viewpoint of ensuring capacity, the indentation depth H of the electrode foil E2 may be 5 μm or more, or may be 6 μm or more.

[0032] From the viewpoint of improving the tensile strength and capacity of the electrode foil, the indentation depth H of the electrode foil E3 is preferably 9.5 μm or less, more preferably 8 μm or less, and even more preferably 7 μm or less. From the viewpoint of ensuring capacity, the indentation depth H of the electrode foil E3 may be 4 μm or more, or may be 5 μm or more.

[0033] (Hardness X) From the viewpoint of improving the tensile strength and capacity of the electrode foil, the hardness X of the electrode foil E1 is preferably 67 mN / mm ２ More preferably, 90 mN / mm ２ More preferably, it is 110 mN / mm ２ From the viewpoint of ensuring capacitance, the hardness X of the electrode foil E1 is, for example, 200 mN / mm ２ or less, and ２ It may be the following:

[0034] From the viewpoint of improving the tensile strength and capacity of the electrode foil, the hardness X of the electrode foil E2 is preferably 110 mN / mm ２ More preferably, 125 mN / mm ２ More preferably, it is 150 mN / mm ２ More preferably, it is 190 mN / mm ２ From the viewpoint of ensuring capacity, the hardness X of the electrode foil E2 is, for example, 360 mN / mm ２ or less, and ２ It may be the following:

[0035] From the viewpoint of improving the tensile strength and capacity of the electrode foil, the hardness X of the electrode foil E3 is preferably 180 mN / mm ２ More preferably, 225 mN / mm ２ More preferably, it is 250 mN / mm ２ More preferably, it is 350 mN / mm ２ In order to ensure the capacity, the hardness X of the electrode foil E3 is set to, for example, 750 mN / mm ２ or less, and ２ It may be the following:

[0036] The hardness X is the hardness measured by nanoindentation when the maximum indentation load on the main surface of the electrode foil (the main surface of the metal foil having the porous portion covered with the dielectric layer) is 500 mN.

[0037] (Elastic Modulus Y) The elastic modulus Y of the electrode foil E1 is 6000 mN / mm ２or more, and 7000 mN / mm ２ or more, and ２ The elastic modulus Y of the electrode foil E2 may be 7000 mN / mm ２ or more, and 9000 mN / mm ２ or more, 12500 mN / mm ２ The elastic modulus Y of the electrode foil E3 may be 12000 mN / mm ２ or more, 15,000 mN / mm ２ or more, 17000 mN / mm ２ It may be more than that.

[0038] The elastic modulus Y is the elastic modulus measured by nanoindentation when the maximum indentation load on the main surface of the electrode foil (the main surface of the metal foil having a porous portion covered with a dielectric layer) is 500 mN.

[0039] The elastic modulus Y (Young's modulus) indicates the ease of deformation of a material. Within the elastic deformation range, the stress and strain applied to the material are generally proportional, with the elastic modulus serving as a proportionality constant (Hooke's Law). The higher the hardness X, the higher the elastic modulus Y tends to be. In particular, as the hardness X of the porous portion increases, the tensile strength also increases. Similar to hardness X, elastic modulus Y is also an important parameter from the perspective of increasing the strength of electrode foil for electrolytic capacitors. For example, by appropriately adjusting the thickness of the etched foil (porous portion), the thickness of the dielectric layer, the compressibility, etc., the hardness X and elastic modulus Y can be increased within the above ranges.

[0040] The indentation depth H, hardness X, and elastic modulus Y are determined by nanoindentation in accordance with ISO 14577-1 (2014). An indenter is pressed into the main surface of the electrode foil (the main surface of the metal foil having a porous portion covered with a dielectric layer), and an indentation load is applied up to 500 mN. The indentation depth when the maximum load of 500 mN is reached and held for 5 seconds is determined as the indentation depth H.

[0041] The measurement conditions are as follows: (Measurement conditions) Measuring device: Ultra-microindentation hardness tester "ENT-5" manufactured by Elionix Co., Ltd. Ambient temperature: 30°C Indenter: Berkovich-type diamond indenter Test load (maximum indentation load): 500 mN Measurement points: Average of three points During measurement, the electrode foil sample is fixed to the sample stage using STE TAPE manufactured by SHINTO PAINT.

[0042] In the pore distribution of the porous portion measured by mercury intrusion porosimetry, the cumulative pore volume V0 (cm ３ / g) and cumulative pore volume V1 (cm ３ / g) and cumulative pore volume V2 (cm ３ / g), it is preferable that the relationships V1 / V0≦0.76 and V2 / V0≦0.94 are satisfied. ３ / g) is the cumulative pore volume (cm) of pores with diameters of 0.01 μm or more and 10 μm or less. ３ / g). The cumulative pore volume V1 is the cumulative pore volume (cm ３ / g). The cumulative pore volume V2 is the cumulative pore volume (cm ３ The pore size distribution is measured using, for example, an AutoPore V series manufactured by Micromeritics.

[0043] When V1 / V0 and V2 / V0 satisfy the above relationships, it is easy to obtain an indentation depth H within the above range. The smaller V1 / V0 and V2 / V0, the greater the proportion of small-diameter pores, making it easier to use the electrode foil as a low-voltage electrode foil. In low-voltage electrode foils, the thickness of the chemical conversion coating is small, and clogging of small-diameter pores by the chemical conversion coating is easily suppressed.

[0044] V1 / V0 is more preferably 0.69 or less, and even more preferably 0.68 or less. V2 / V0 is more preferably 0.92 or less, and even more preferably 0.91 or less.

[0045] From the viewpoint of improving strength and capacity, the thickness TA of the metal foil may be, for example, 90 μm or more, 100 μm or more, 105 μm or more, or 120 μm or more. Furthermore, the thickness TA of the metal foil may be 200 μm or less, 150 μm or less, or less than 125 μm. The thickness of the metal foil may be, for example, 100 μm or more and less than 125 μm.

[0046] From the viewpoint of improving capacity, the thickness T of the porous portion (thickness per side) may be 25 μm or more and 90 μm or less, 35 μm or more and 80 μm or less, or 35 μm or more and less than 50 μm.

[0047] When the thickness TA of the metal foil is within the above range, the thickness T of the porous portion can be increased within the above range while ensuring a sufficient thickness of the core portion. The thickness of the core portion may be, for example, 20 μm or more, or 25 μm or more. The thickness of the core portion may also be, for example, 28 μm or less.

[0048] When the thickness TA of the metal foil is large (for example, when it is 100 μm or more or 105 μm or more), the stress generated in the metal foil (surface layer) during winding becomes large, and therefore, when the indentation depth H is within the above range, the effect of improving the tensile strength is significantly obtained.

[0049] The ratio (thickness per side of the porous portion / thickness of the core portion) may be 1.5 or more, or 1.7 or more, and the ratio (thickness per side of the porous portion / thickness of the core portion) may be 2.1 or less, or 2.0 or less.

[0050] The surface roughness Ra of the metal foil (roughness of the outer surface of the porous portion) is preferably 1.5 μm or less, more preferably 0.1 μm or more and 1.5 μm or less, and may be 0.5 μm or more and 1.5 μm or less. The surface roughness Ra of the metal foil means the arithmetic mean roughness, and the arithmetic mean roughness Ra is determined in accordance with JIS B 0601:2001.

[0051] When the surface roughness Ra of the metal foil is reduced to 1.5 μm or less by the compression process described below, the influence of rolling marks can be sufficiently reduced. The surface roughness of the metal foil can be made smaller than the surface roughness due to the rolling marks of the original foil, and unnecessary oxides along the rolling marks can be removed. Furthermore, when the surface roughness Ra of the metal foil is 0.1 μm or more, the surface area of ​​the metal foil is sufficiently secured, making it easy to increase the capacity.

[0052] The metal foil contains a valve metal. Examples of the valve metal include Al, Ta, and Nb. The metal foil may be a foil of a valve metal (e.g., Al), or may be a foil containing an alloy or compound containing the valve metal (e.g., Al). The dielectric layer is formed by anodization (chemical conversion treatment). The dielectric layer is, for example, a layer containing an oxide of a valve metal (e.g., aluminum oxide).

[0053] The porous portion has an inner layer region on the core portion side and a surface layer region on the opposite side of the core portion. When the thickness (thickness per side) of the porous portion is T, the surface layer region is a region that is a distance of T / 4 or less from the outer surface of the porous portion (the main surface of the metal foil having the porous portion). The inner layer region is a region that is a distance of T / 4 or less from the boundary between the porous portion and the core portion.

[0054] The average diameter D1 of the pores in the surface layer region is preferably smaller than the average diameter D2 of the pores in the inner layer region. In this case, the retention of the electrolyte in the pores of the porous portion is enhanced, improving contact between the dielectric layer and the electrolyte. The compression process described below facilitates the formation of a porous portion in which D1 / D2 is less than 1. Note that, in this specification, the term "diameter" simply refers to "diameter." D1 / D2 is preferably 0.98 or less, and may be 0.95 or less, or may be 0.9 or less. From the viewpoint of improving capacitance, the ratio of D1 to D2 (D1 / D2) is preferably 0.5 or more, more preferably 0.55 or more, and may be 0.6 or more, or may be 0.7 or more. The range of D1 / D2 may be, for example, 0.5 or more and 0.98 or less, or 0.55 or more and 0.95 or less.

[0055] The porosity P1 of the surface layer region is preferably smaller than the porosity P2 of the inner layer region. In this case, the retention of the electrolyte in the pores of the porous portion is enhanced, improving contact between the dielectric layer and the electrolyte. The compression process described below makes it easy to form a porous portion in which P1 / P2 is less than 1. P1 / P2 may be 0.95 or less, 0.92 or less, or 0.85 or less. From the viewpoint of improving capacitance, the ratio of P1 to P2 (P1 / P2) is preferably 0.5 or more, more preferably 0.55 or more, and may be 0.6 or more, or 0.7 or more. The range of P1 / P2 may be, for example, 0.5 or more and 0.95 or less, or 0.55 or more and 0.92 or less.

[0056] The average diameters D1 and D2 can be determined as follows: (i) A cross-sectional image of the electrode foil is obtained using a scanning electron microscope (SEM). Using this image, the thickness of the porous portion is measured at 10 arbitrary points, and the average value is calculated to define the thickness T of the porous portion. (ii) The region at a distance of T / 4 or less from the outer surface of the porous portion (surface S1 in Figure 1) is defined as the surface region. (iii) A cross-sectional image of the surface region is obtained, and the image is subjected to a binarization process to distinguish between the metal skeleton region that constitutes the surface region and the pore (pit) region outside the metal skeleton region. (iv) A point within the pore region of the surface region is arbitrarily selected, and a line segment that passes through the point and crosses the pore region is drawn, and the length of the line segment at its shortest length is measured. This measurement is performed at 20 arbitrary points within the pore region of the surface region, and the average of the obtained measurements is determined to define the average diameter D1 of the pores in the surface region. (v) The region of the porous portion at a distance of T / 4 or less from the boundary with the core portion (surface B in FIG. 1) is defined as the inner layer region. The average pore diameter D2 of the inner layer region is also determined in the same manner as in (iii) and (iv) above.

[0057] The porosity P1 is determined by measuring the area S0 of the entire surface region after the binarization process in (iii) above and the area S1 of the region occupied by pores in the image, and then calculating (S1 / S0) × 100. The porosity P2 is determined in the same manner as above.

[0058] The main surfaces of the electrode foil (metal foil) include a first main surface and a second main surface opposite the first main surface. The porous portion may include, via a core portion, a first porous portion having the first main surface and a second porous portion having the second main surface. The dielectric layer may include a first dielectric layer covering the first porous portion and a second dielectric layer covering the second porous portion. In this case, it is sufficient that at least one of the first indentation depth H1 and the second indentation depth H2 is within the above-mentioned range of indentation depth H. It is preferable that both the first indentation depth H1 and the second indentation depth H2 are within the above-mentioned range of indentation depth H.

[0059] Furthermore, the first indentation depth H1 may be smaller than the second indentation depth H2. In this case, it is preferable that the anode foil is wound in the wound body so that the first main surface faces the outer periphery of the wound body. Since the outer periphery of the wound body experiences a larger tensile stress during winding, making the first indentation depth H1 smaller than the second indentation depth H2 significantly suppresses cracks during winding.

[0060] 1 is a cross-sectional view schematically illustrating an example of an electrode foil according to an embodiment of the present disclosure. Fig. 1 shows a cross section of the electrode foil in the thickness direction. It should be noted that the electrode foil according to the present disclosure is not limited to this.

[0061] The electrode foil includes a metal foil 300 having a porous portion on a main surface thereof and a dielectric layer (not shown) covering the porous portion. The metal foil 300 includes a valve metal. The main surfaces of the metal foil 300 include a first main surface S1 and a second main surface S2 opposite the first main surface S1. The porous portion includes a first porous portion 310 on the first main surface S1 and a second porous portion 320 on the second main surface S2. The metal foil 300 includes a core portion 330 and the first porous portion 310 and the second porous portion 320 connected to the core portion 330. The core portion 330 is formed between the first porous portion 310 and the second porous portion 320. The dielectric layer includes a first dielectric layer (not shown) covering the metal skeleton constituting the first porous portion 310 and a second dielectric layer (not shown) covering the metal skeleton constituting the second porous portion 320.

[0062] At least one of the first indentation depth H1 and the second indentation depth H2 is within the above-mentioned range. The first indentation depth H1 is the indentation depth measured by nanoindentation when the maximum indentation load on the first main surface S1 having the first porous portion 310 covered with the first dielectric layer is 500 mN. The second indentation depth H2 is the indentation depth measured by nanoindentation when the maximum indentation load on the second main surface S2 having the second porous portion 320 covered with the second dielectric layer is 500 mN. It is preferable that both the first indentation depth H1 and the second indentation depth H2 are within the above-mentioned range. The first indentation depth H1 may be approximately the same as or different from the second indentation depth H2.

[0063] The porous portion 310 has a thickness T (μm) and includes an inner layer region 312 on the core portion 330 side and a surface layer region 311 on the opposite side of the core portion 330. The surface layer region 311 is a region that is a distance of T / 4 or less from the outer surface S of the porous portion 310. The inner layer region 312 is a region that is a distance of T / 4 or less from the boundary B between the porous portion 310 and the core portion 330. The same can be said for the porous portion 320 (surface layer region 321 and inner layer region 322).

[0064] (Method for manufacturing electrode foil) The method for manufacturing electrode foil according to an embodiment of the present disclosure includes an etching step, a compression step, and a chemical conversion step. In the etching step, a sheet containing a valve metal is etched. This forms a porous portion on the main surface of the sheet. In the compression step, the etched sheet is compressed in the thickness direction to form a porous portion (a moderately compressed porous portion) on the main surface of the sheet. In the chemical conversion step, the compressed sheet is subjected to a chemical conversion treatment to form a dielectric layer that covers the porous portion. In the case of electrode foil E1, the indentation depth H is 17 μm or less. In the case of electrode foil E2, the indentation depth H is 13.5 μm or less. In the case of electrode foil E3, the indentation depth H is 10.5 μm or less.

[0065] (Etching Process) The sheet used in the etching process (hereinafter also referred to as "raw material sheet") contains a valve metal. Examples of the valve metal include Al, Ta, and Nb. The raw material sheet may be a sheet of a valve metal (e.g., Al), or may be a sheet containing an alloy or compound containing a valve metal (e.g., Al). A long or strip-shaped rolled sheet (rolled foil) is usually used as the raw material sheet.

[0066] In the etching process, the surface of a sheet containing a valve metal is roughened by etching. The etching process forms porous portions on the main surface of the sheet, and the remaining portion remains as a core. That is, after the etching process, the sheet has a core and a porous portion continuous with the core, and the porous portion occupies the main surface of the sheet. The porous portions are usually formed on both main surfaces of the sheet, sandwiching the core.

[0067] The etching treatment may be electrolytic etching or chemical etching, and can be carried out using a known technique. ２ It may be performed at a current density of 1.5 A / cm ２ It may be performed at a current density of 1.2 A / cm ２ The etching may be performed at the following current density: The current density may be changed during the etching.

[0068] The electrolytic etching is preferably AC etching, but DC etching is also acceptable. AC etching is likely to form porous portions containing sponge-like pits with relatively small diameters. DC etching is likely to form porous portions containing tunnel-like pits with relatively large diameters. Larger pit diameters in the porous portions make it easier to form thicker dielectric layers, which is advantageous in terms of higher voltages.

[0069] When the etching time is TE, the temperature of the etching solution may be set to 10°C or more and 60°C or less between 0 and 0.7TE, and may be set to 5°C or more and 40°C or less between 0.7TE and TE. In this case, the variation in pit diameter in the thickness direction of the porous portion can be reduced. The etching time TE is, for example, 15 minutes or more and 30 minutes or less.

[0070] (Compression Process) In the compression process, the etched sheet is compressed. In the compression process, the etched sheet may be compressed by conveying it between a pair of rollers. The porous portion (particularly the surface layer) formed by the etching process has low strength and is easily compressed in the compression process. The thickness of the porous portion (particularly the surface layer) is reduced by compression. The thickness of the core portion may be slightly reduced before and after compression, but it is desirable that it remains almost unchanged.

[0071] During the manufacturing process of electrolytic capacitors, the sheet may come into contact with processing liquids (e.g., etching liquids, chemical conversion liquids) or rollers, resulting in unevenness (or scratches). During this manufacturing process, stress may concentrate on these unevennesses, causing the sheet to break (or crack). Furthermore, the aluminum foil used for the sheet may have rolling marks created during the manufacturing process, and etching pits may be formed unevenly along the rolling marks, i.e., along the length of the long sheet (rolling direction). The rolling marks may cause the sheet to break (or crack). To address this issue, as described above, by appropriately compressing the etched sheet, the effects of the unevenness and rolling marks are reduced, the strength of the surface layer of the sheet is increased, and the sheet breakage or other problems are suppressed.

[0072] The thickness TA of the compressed sheet may be 90 μm or more and 200 μm or less, or 120 μm or more and 200 μm or less. The thickness T of the porous portion per side after compression may be 25 μm or more and {(TA / 2)-10} μm or less. When the thickness T is within the above range, the core portion can be secured with a sufficient thickness. Furthermore, the thickness T may be 25 μm or more and 90 μm or less, or 35 μm or more (or 40 μm or more) and 80 μm or less. In high-capacity foils, the thickness T of the porous portion is large, and the effect of improving the surface layer strength by compression is significantly obtained. In particular, in capacitors containing a solid electrolyte and a liquid component (such as an electrolytic solution), high-capacity foils are used, and the thickness TA of the sheet (electrode foil) is preferably 100 μm or more (or 105 μm or more) or 120 μm or more, and the thickness T of the porous portion per side is preferably 25 μm or more or 35 μm or more (or 40 μm or more).

[0073] The compression ratio (thickness reduction ratio) of the sheet in the compression step may be 4% or more and 40% or less, 8% or more and 30% or less, or 10% or more and 25% or less. The compression ratio of the sheet is calculated by ((TB-TA) / TB) x 100, where TA is the thickness of the sheet after compression and TB is the thickness of the sheet before compression.

[0074] The compression rate (thickness reduction rate) of the porous portion in the compression step may be 5% or more and 40% or less, 9% or more and 30% or less, or 14% or more and 25% or less. The thickness reduction rate of the porous portion is calculated by ((T0-T) / T0) x 100, where T is the thickness per side of the porous portion after compression, and T0 is the thickness per side of the porous portion before compression. The core may be compressed so that the thickness remains almost the same before and after compression.

[0075] (Chemical Conversion Process) In the chemical conversion process, the compressed sheet is subjected to a chemical conversion treatment to form a dielectric layer (chemical conversion film) that covers the porous portion. In the case of an aluminum sheet, an aluminum oxide layer is formed as a chemical conversion film by the chemical conversion treatment. A chemical conversion film of a predetermined thickness can be formed by adjusting the chemical conversion voltage etc. according to the withstand voltage (rated voltage of the electrolytic capacitor). The withstand voltage can be approximately the same as the chemical conversion voltage or slightly lower than the chemical conversion voltage.

[0076] (Electrolytic Capacitor) An electrolytic capacitor according to an embodiment of the present disclosure includes a wound capacitor element, and the wound capacitor element includes 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. The anode foil is an electrode foil according to an embodiment of the present disclosure. Because the electrode foil according to the present disclosure has high strength, the occurrence of cracks or foil breakage in the electrode foil included in the wound body is suppressed.

[0077] In electrolytic capacitors with a rated voltage of 20 V or higher, for example, an Al foil chemically treated at a chemical conversion voltage of 30 V or higher is often used as the anode foil. Furthermore, in electrolytic capacitors containing a conductive polymer and a liquid component, for example, an Al foil chemically treated at a chemical conversion voltage of 40 V or higher is often used as the anode foil. In such anode foils, an electrode foil with a relatively large pit diameter is used, forming a dielectric layer with a relatively large thickness (e.g., a thickness of 45 nm or higher), which tends to reduce the strength of the surface layer. Therefore, the use of an electrode foil according to an embodiment of the present disclosure significantly improves reliability. At chemical conversion voltages of 30 V or higher (or 40 V or higher), the resulting chemical conversion film becomes thick. Therefore, using an electrode foil with a large pit diameter prevents pit blockage due to a thick chemical conversion film, thereby efficiently achieving high capacity.

[0078] (Anode Foil) The thickness of the anode foil may be 90 μm or more and 200 μm or less, or may be 120 μm or more and 200 μm or less. The thickness of the dielectric layer is, for example, 45 nm or more.

[0079] (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. The electrode foil according to the present disclosure or a compressed, unformed, etched foil obtained during the manufacturing process of the electrode foil according to the present disclosure may be used as the cathode foil. The thickness of the cathode foil is, for example, 70 μm or more and 100 μm or less.

[0080] (Separator) The separator 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).

[0081] (Electrolyte) The electrolyte covers at least a portion of the anode foil (dielectric layer) and is interposed between the anode foil (dielectric layer) and the cathode foil. The electrolyte includes at least one of a solid electrolyte and an electrolytic solution. The capacitor element may include a solid electrolyte, or may include a solid electrolyte and a liquid component (electrolytic solution or a non-aqueous solvent).

[0082] The dielectric layer is coated with an electrolyte by, for example, impregnating the anode foil (or wound body) with a treatment solution (or electrolyte solution) containing a conductive polymer. In the above-described electrode foil, D1 is smaller than D2 (and P1 is smaller than P2), so that the treatment solution impregnated in the porous portion tends to remain in the pores, and the inner walls of the pores tend to be covered with electrolyte, improving contact between the anode foil (dielectric layer) and the electrolyte.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] The liquid component may be an electrolytic solution or a non-aqueous solvent. The electrolytic solution includes 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 2 is a cross-sectional view schematically illustrating an example of an electrolytic capacitor according to an embodiment of the present disclosure, and FIG. 3 is a perspective view schematically illustrating the configuration of the wound body of FIG.

[0092] Electrolytic capacitor 200 includes a capacitor element, and the capacitor element includes wound body 100 and an electrolyte (not shown). Wound body 100 is formed by winding anode foil 10 and cathode foil 20 with separator 30 interposed therebetween.

[0093] 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.

[0094] 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.

[0095] An electrolyte is interposed between the anode foil 10 (dielectric layer) and the cathode foil 20 in the wound body 100. The capacitor element is obtained, for example, by impregnating the wound body 100 with a treatment liquid containing an electrolyte. The impregnation may be performed under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa.

[0096] 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.

[0097] A sealing member 212 is placed at the opening of a bottomed case 211 that contains the wound body 100 and the electrolyte, the open end of the bottomed case 211 is crimped to the sealing member 212 and curled, and a seat plate 213 is placed on the curled portion, thereby sealing the wound body 100 inside the bottomed case 211.

[0098] 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.

[0099] The electrode foil according to the embodiment of the present disclosure can be used in an electrolytic capacitor including the above-described wound capacitor element, but may also be used in an electrolytic capacitor including a laminated capacitor element. In this case, the porous portion is formed on at least a portion of the surface of the metal foil. The laminated capacitor element includes, for example, an anode body, a solid electrolyte layer covering the dielectric layer of the anode body, and a cathode extraction layer covering the solid electrolyte layer. The anode body is the electrode foil according to the embodiment of the present disclosure. The cathode extraction layer includes, for example, a carbon layer and a silver paste layer. An anode lead is connected to the portion of the anode body not covered by the dielectric layer, and a cathode lead is connected to the cathode extraction layer.

[0100] One or more laminated capacitor elements may be used. A laminate may be formed by stacking a plurality of laminated capacitor elements. Stress is likely to occur in the anode bodies (connection sides with the anode leads) located at both ends of the laminate. However, the electrode foil of the present disclosure has high strength, so that cracks caused by such stress are suppressed.

[0101] The anode body is produced, for example, by cutting (or punching) a predetermined shape from a large sheet after chemical conversion treatment. The sheet that has undergone the etching step, compression step, and chemical conversion step of the present disclosure has high strength, so the occurrence of cracks or defects due to cutting or the like is suppressed.

[0102] <<Appendix>> The above embodiments disclose the following techniques. (Technology 1) An electrode foil having a withstand voltage of 7 V or less, the electrode foil comprising a metal foil having a porous portion on a main surface thereof and a dielectric layer covering the porous portion, the metal foil containing a valve metal, and an indentation depth H of 17 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portion covered with the dielectric layer, as measured by nanoindentation. (Technology 2) The electrode foil according to Technology 1, wherein the dielectric layer is a chemical conversion coating. (Technology 3) The electrode foil according to Technology 1 or 2, used in an electrolytic capacitor having a rated voltage of 6 V or less. (Technology 4) The electrode foil according to Technology 1, wherein a hardness of 67 mN / mm2 when a maximum indentation load of 500 mN is applied to the main surface having the porous portion covered with the dielectric layer, as measured by nanoindentation. ２ The electrode foil according to any one of the above techniques 1 to 3, wherein the elastic modulus measured by a nanoindentation method when a maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 7000 mN / mm ２ The electrode foil according to any one of Techniques 1 to 4, wherein the withstand voltage is greater than 7 V and less than or equal to 22 V, and the electrode foil comprises a metal foil having a porous portion on a main surface thereof and a dielectric layer covering the porous portion, the metal foil containing a valve metal, and the indentation depth H of the main surface having the porous portion covered with the dielectric layer when a maximum indentation load of 500 mN is measured by nanoindentation is 13.5 μm or less. (Technology 7) The electrode foil according to Technique 6, wherein the dielectric layer is a chemical conversion coating. (Technology 8) The electrode foil according to Technique 6 or 7, which is used in an electrolytic capacitor having a rated voltage of greater than 5 V and less than or equal to 19 V. (Technology 9) The electrode foil according to Technique 9, wherein the hardness of the main surface having the porous portion covered with the dielectric layer when a maximum indentation load of 500 mN is measured by nanoindentation is 110 mN / mm ２The electrode foil according to any one of techniques 6 to 8, wherein the elastic modulus measured by a nanoindentation method when a maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 9000 mN / mm ２ The electrode foil according to any one of Techniques 6 to 9, wherein the withstand voltage is greater than 22 V and less than or equal to 160 V, and the electrode foil comprises a metal foil having a porous portion on a main surface thereof and a dielectric layer covering the porous portion, the metal foil containing a valve metal, and wherein the indentation depth H measured by nanoindentation on the main surface having the porous portion covered with the dielectric layer at a maximum indentation load of 500 mN is 10.5 μm or less. (Technology 12) The electrode foil according to Technique 11, wherein the dielectric layer is a chemical conversion coating. (Technology 13) The electrode foil according to Technique 11 or 12, which is used in an electrolytic capacitor having a rated voltage of greater than 16 V and less than or equal to 130 V. (Technology 14) The electrode foil according to Technique 11 or 12, wherein the hardness measured by nanoindentation on the main surface having the porous portion covered with the dielectric layer at a maximum indentation load of 500 mN is 180 mN / mm ２ The electrode foil according to any one of techniques 11 to 13, wherein the elastic modulus measured by a nanoindentation method when a maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 15,000 mN / mm ２ The electrode foil according to any one of techniques 11 to 14, wherein the pore distribution of the porous portion measured by mercury intrusion porosimetry is: ３ / g) and the cumulative pore volume V1 (cm ３ / g) and the cumulative pore volume V2 (cm ３ / g) satisfies the relationships V1 / V0≦0.76 and V2 / V0≦0.94. (Technology 17) The electrode foil according to any one of Technologies 1 to 16, wherein the thickness of the metal foil is 100 μm or more and less than 125 μm. (Technology 18) The electrode foil according to any one of Technologies 1 to 17, wherein the thickness of the porous portion is 35 μm or more and less than 50 μm. (Technology 19) An electrolytic capacitor comprising: a capacitor element, the capacitor element comprising a wound body and an electrolyte, the wound body being formed by winding an anode foil and a cathode foil with a separator disposed between the anode foil and the cathode foil, and the anode foil being the electrode foil according to any one of Technologies 1 to 18. (Technology 20) The main surface of the metal foil of the anode foil includes a first main surface and a second main surface opposite to the first main surface, the porous portion includes a first porous portion on the first main surface and a second porous portion on the second main surface, the dielectric layer includes a first dielectric layer covering the first porous portion and a second dielectric layer covering the second porous portion, a first indentation depth H1 measured by nanoindentation at a maximum indentation load of 500 mN on the first main surface having the first porous portion covered with the first dielectric layer is smaller than a second indentation depth H2 measured by nanoindentation at a maximum indentation load of 500 mN on the second main surface having the second porous portion covered with the second dielectric layer, and at least the first indentation depth H1 is the indentation depth H, 20. The electrolytic capacitor according to claim 19, wherein the anode foil is wound in the wound body such that the first main surface faces an outer periphery of the wound body.(Technology 21) A method for manufacturing an electrode foil having a withstand voltage of 7 V or less, comprising: an etching step of etching a sheet containing a valve metal; a compression step of compressing the etched sheet in a thickness direction to form porous portions on a main surface of the sheet; and a chemical conversion step of forming a dielectric layer covering the porous portions on the compressed sheet, wherein the indentation depth H measured by a nanoindentation method at a maximum indentation load of 500 mN on the main surface having the porous portions covered with the dielectric layer is 17 μm or less. (Technology 22) A method for manufacturing an electrode foil for an electrolytic capacitor according to Technology 21, wherein a chemical conversion voltage for the chemical conversion treatment is 7 V or less. (Technology 23) The hardness measured by a nanoindentation method at a maximum indentation load of 500 mN on the main surface having the porous portions covered with the dielectric layer is 67 mN / mm. ２ The method for producing an electrode foil according to Technology 21 or 22, wherein the elastic modulus measured by a nanoindentation method when a maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 7000 mN / mm ２The method for manufacturing an electrode foil according to any one of Techniques 21 to 23, wherein the withstand voltage is higher than 7 V and lower than 22 V, and the method comprises: an etching step of etching a sheet containing a valve metal; a compression step of compressing the etched sheet in a thickness direction to form porous portions on a main surface of the sheet; and a chemical conversion step of forming a dielectric layer covering the porous portions on the compressed sheet, wherein the indentation depth H measured by nanoindentation at a maximum indentation load of 500 mN on the main surface having the porous portions covered with the dielectric layer is 13.5 μm or less. (Technology 26) The method for manufacturing an electrode foil according to Technique 25, wherein the chemical conversion voltage is higher than 7 V and lower than 22 V. (Technology 27) The hardness measured by nanoindentation at a maximum indentation load of 500 mN on the main surface having the porous portions covered with the dielectric layer is 110 mN / mm ２ (Technology 28) The method for producing an electrode foil according to Technology 25 or 26, wherein the elastic modulus measured by a nanoindentation method when a maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 9000 mN / mm ２The method for manufacturing an electrode foil according to any one of Techniques 25 to 27, wherein: (Technology 29) A method for manufacturing an electrode foil having a withstand voltage of more than 22 V and not more than 160 V, comprising: an etching step of etching a sheet containing a valve metal; a compression step of compressing the etched sheet in a thickness direction to form porous portions on a main surface of the sheet; and a chemical conversion step of forming a dielectric layer covering the porous portions on the compressed sheet, wherein an indentation depth H measured by a nanoindentation method at a maximum indentation load of 500 mN on the main surface having the porous portions covered with the dielectric layer is 10.5 μm or less. (Technology 30) A method for manufacturing an electrode foil according to Technique 29, wherein a chemical conversion voltage for the chemical conversion treatment is more than 22 V and not more than 160 V. (Technology 31) The hardness measured by a nanoindentation method when the maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 180 mN / mm ２ (Technology 32) The method for producing an electrode foil according to Technology 29 or 30, wherein the elastic modulus measured by a nanoindentation method when a maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 15,000 mN / mm ２ The method for producing an electrode foil according to any one of techniques 29 to 31, wherein the pore distribution of the porous portion measured by mercury intrusion porosimetry is: ３ / g) and the cumulative pore volume V1 (cm ３ / g) and the cumulative pore volume V2 (cm ３ / g) satisfies the relationships V1 / V0≦0.76 and V2 / V0≦0.94.

[0103] [Examples] Hereinafter, the present disclosure will be described in more detail based on examples, but the present disclosure is not limited to the examples.

[0104] <Electrode Foils A1 to A4, A11 to A14, A21 to A24> (Etching Step) Metal foils (thickness TB: 125 μm) were etched to obtain metal foils (etched foils) having a core and a porous portion. Al foils were used as the metal foils. Porous portions (thickness T0 per side: 50 μm) were formed on both sides of the metal foil, and the thickness of the core was 25 μm. In the etching step, AC etching was performed at a current density of 1.5 A / cm. ２ The etching time was also adjusted appropriately to obtain the desired amount of dissolution.

[0105] (Compression step) The etched metal foil was compressed in the thickness direction. At this time, the compression ratio was changed to obtain metal foils a1 to a4 with thicknesses TA (total thickness) shown in Table 1. The thickness T (μm) of each side of the compressed porous portion was calculated by (metal foil thickness TA - core thickness) / 2. Compression was performed by conveying the etched foil between a pair of rollers.

[0106]

[0107] (Formation of Dielectric Layer) Metal foils a1 to a4 were subjected to a chemical conversion treatment to form a dielectric layer covering the porous portion. The chemical conversion treatment and withstand voltage measurement were performed in accordance with the Electronic Industries Association of Japan standard, Test Method for Electrode Foils for Aluminum Electrolytic Capacitors (EIAJ RC-2364A). The chemical conversion voltage was 5 V, 20 V, or 70 V. In this manner, electrode foils A1 to A4 (electrode foil E1, chemical conversion voltage 5 V), electrode foils A11 to A14 (electrode foil E2, chemical conversion voltage 20 V), and electrode foils A21 to A24 (electrode foil E3, chemical conversion voltage 70 V) were produced. The withstand voltage was approximately the same as or slightly lower than the chemical conversion voltage.

[0108] Electrode foils B1, B11, and B21 were prepared in the same manner as electrode foils A1, A11, and A21, except that metal foil b1 was used instead of metal foil a1, and metal foil b1 was prepared as the etched metal foil without being compressed.

[0109] (Indentation depth H, hardness X, elastic modulus Y) The indentation depth H, hardness X, and elastic modulus Y were determined by the methods described above. Note that in each table, the indentation depth H and other values ​​are shown as measured values ​​for one main surface of the electrode foil, but almost the same measured values ​​were also obtained for the other main surface of the electrode foil.

[0110] (V1 / V0, V2 / V0) Using the method described above, the V1 / V0 and V2 / V0 of the porous portion of each metal foil before chemical conversion treatment were determined. As a result, for metal foils a1 to a4, V1 / V0 was within a range of 0.76 or less, and V2 / V0 was within a range of 0.94 or less. For metal foil b1, V1 / V0 was greater than 0.76, and V2 / V0 was greater than 0.94. Note that V1 / V0 and V2 / V0 indicate measured values ​​for one main surface of the metal foil, but approximately similar measured values ​​were obtained for the other main surface of the metal foil.

[0111] (Tensile strength) For each metal foil before chemical conversion treatment, a strip-shaped sample (70 mm in length, 10 mm in width) was prepared, and the tensile strength of the sample in the length direction was measured in accordance with the test method for electrode foil for aluminum electrolytic capacitors (EIAJ RC-2364A) of the Electronic Industries Association of Japan standard. The measurement results are shown in Table 1. In Table 1, the tensile strength is shown as a relative value when the tensile strength of metal foil b1 is set to 100.

[0112] (Capacitance / Thickness) For each electrode foil, the electrostatic capacitance per unit thickness of the electrode foil (capacitance / thickness) was measured in accordance with the test method for electrode foil for aluminum electrolytic capacitors of the Electronic Industrial Standards of Japan (EIAJ RC-2364A).

[0113] The measurement results are shown in Tables 2 to 4. In Table 2, the capacitance / thickness indicates a relative value when the capacitance / thickness of anode foil B1 is set to 100. In Table 3, the capacitance / thickness indicates a relative value when the capacitance / thickness of anode foil B11 is set to 100. In Table 4, the capacitance / thickness indicates a relative value when the capacitance / thickness of anode foil B21 is set to 100.

[0114]

[0115]

[0116]

[0117] Metal foils a1 to a4 had a higher tensile strength than metal foil b1. Electrode foils A1 to A4 had a higher (capacity / thickness) than electrode foil B1. Electrode foils A11 to A14 had a higher (capacity / thickness) than electrode foil B11. Electrode foils A21 to A24 had a higher (capacity / thickness) than electrode foil B21.

[0118] The electrode foils A1 to A4 had a smaller indentation depth H and a larger hardness X and elastic modulus Y than the electrode foil B1, resulting in a higher tensile strength. The electrode foils A11 to A14 had a smaller indentation depth H and a larger hardness X and elastic modulus Y than the electrode foil B11, resulting in a higher tensile strength. The electrode foils A21 to A24 had a smaller indentation depth H and a larger hardness X and elastic modulus Y than the electrode foil B21, resulting in a higher tensile strength.

[0119] <Electrode Foils A5 to A8, A15 to 18, A25 to A28> (Etching Step) Metal foils (thickness TB: 125 μm) were subjected to an etching process to obtain metal foils (etched foils) having a core portion and a porous portion. Al foils were used as the metal foils. Porous portions (thickness per side T0: 51 μm) were formed on both sides of the metal foil, and the thickness of the core portion was set to 23 μm. In the etching process, AC etching was performed at a current density of 1.5 A / cm ２ The etching time was also adjusted appropriately to obtain the desired amount of dissolution.

[0120] (Compression step) The etched metal foil was compressed in the thickness direction. At this time, the compression ratio was changed to obtain metal foils a5 to a8 with thicknesses TA (total thickness) shown in Table 5. The thickness T (μm) of each compressed porous portion per side was calculated by (metal foil thickness TA - core thickness) / 2. Compression was performed by conveying the etched foil between a pair of rollers.

[0121]

[0122] (Formation of Dielectric Layer) Metal foils a5 to a8 were subjected to chemical conversion treatment to form a dielectric layer covering the porous portion. The chemical conversion treatment and measurement of withstand voltage were performed in the same manner as described above. The chemical conversion voltage was 5 V, 20 V, or 70 V. In this manner, electrode foils A5 to A8 (electrode foil E1, chemical conversion voltage 5 V), electrode foils A15 to A18 (electrode foil E2, chemical conversion voltage 20 V), and electrode foils A25 to A28 (electrode foil E3, chemical conversion voltage 70 V) were produced. The withstand voltage was approximately the same as or slightly lower than the chemical conversion voltage.

[0123] Electrode foils B2, B12, and B22 were prepared as metal foil b2 using the etched metal foil without compression. Electrode foils B2, B12, and B22 were prepared in the same manner as electrode foils A5, A15, and A25, except that metal foil b2 was used instead of metal foil a5.

[0124] (Indentation depth H, hardness X, elastic modulus Y) The indentation depth H, hardness X, and elastic modulus Y were determined by the methods described above. Note that in each table, the indentation depth H and other values ​​are shown as measured values ​​for one main surface of the electrode foil, but almost the same measured values ​​were also obtained for the other main surface of the electrode foil.

[0125] (V1 / V0, V2 / V0) Using the method described above, the V1 / V0 and V2 / V0 of the porous portion of each metal foil before chemical conversion treatment were determined. As a result, for metal foils a5 to a8, V1 / V0 was within a range of 0.76 or less, and V2 / V0 was within a range of 0.94 or less. For metal foil b2, V1 / V0 was greater than 0.76, and V2 / V0 was greater than 0.94. Note that V1 / V0 and V2 / V0 indicate measured values ​​for one main surface of the metal foil, but approximately similar measured values ​​were obtained for the other main surface of the metal foil.

[0126] (Tensile strength) The tensile strength of each metal foil before chemical conversion treatment was measured in the same manner as above. The measurement results are shown in Table 5. In Table 5, the tensile strength is shown as a relative value when the tensile strength of metal foil b2 is set to 100.

[0127] (Capacitance / Thickness) For each electrode foil, the electrostatic capacitance per unit thickness of the electrode foil (capacitance / thickness) was measured in the same manner as above.

[0128] The measurement results are shown in Tables 6 to 8. In Table 6, the capacitance / thickness indicates a relative value when the capacitance / thickness of anode foil B2 is set to 100. In Table 7, the capacitance / thickness indicates a relative value when the capacitance / thickness of anode foil B12 is set to 100. In Table 8, the capacitance / thickness indicates a relative value when the capacitance / thickness of anode foil B22 is set to 100.

[0129]

[0130]

[0131]

[0132] Metal foils a5 to a8 had a higher tensile strength than metal foil b2. Electrode foils A5 to A8 had a higher (capacity / thickness) than electrode foil B2. Electrode foils A15 to A18 had a higher (capacity / thickness) than electrode foil B12. Electrode foils A25 to A28 had a higher (capacity / thickness) than electrode foil B22.

[0133] Electrode foils A5 to A8 had a smaller indentation depth H and a larger hardness X and elastic modulus Y than electrode foil B2, resulting in a higher tensile strength. Electrode foils A15 to A18 had a smaller indentation depth H and a larger hardness X and elastic modulus Y than electrode foil B12, resulting in a higher tensile strength. Electrode foils A25 to A28 had a smaller indentation depth H and a larger hardness X and elastic modulus Y than electrode foil B22, resulting in a higher tensile strength.

[0134] The electrode foil according to the present disclosure is suitable for use in electrolytic capacitors that require high reliability.

[0135] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0136] 10: Anode foil, 20: Cathode foil, 30: Separator, 40: Winding tape, 50A, 50B: Lead tabs, 60A, 60B: Lead wires, 100, 400: Wound body, 200: Electrolytic capacitor, 211: Bottomed case, 212: Sealing member, 213: Seat plate, 300: Electrode foil, 310, 320: Porous portion, 311: Surface region, 312: Inner region, 330: Core portion

Claims

1. An electrode foil having a withstand voltage of 7 V or less, the electrode foil comprising a metal foil having a porous portion on a main surface thereof and a dielectric layer covering the porous portion, the metal foil including a valve metal, and an indentation depth H of 17 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portion covered with the dielectric layer, as measured by a nanoindentation method.

2. The electrode foil according to claim 1, wherein the dielectric layer is a chemical conversion coating.

3. The electrode foil according to claim 1, which is used in an electrolytic capacitor having a rated voltage of 6 V or less.

4. The hardness measured by a nanoindentation method when the maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 67 mN / mm ２ The electrode foil according to claim 1 .

5. The modulus of elasticity measured by a nanoindentation method when the maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 7000 mN / mm ２ The electrode foil according to claim 1 .

6. An electrode foil with a withstand voltage of more than 7V and not more than 22V, comprising a metal foil having a porous portion on a main surface thereof and a dielectric layer covering the porous portion, the metal foil containing a valve metal, and an indentation depth H of 13.5μm or less when a maximum indentation load of 500mN is applied to the main surface having the porous portion covered with the dielectric layer, as measured by a nanoindentation method.

7. The electrode foil according to claim 6, wherein the dielectric layer is a conversion coating.

8. The electrode foil according to claim 6, which is used in an electrolytic capacitor having a rated voltage of more than 5 V and not more than 19 V.

9. The hardness measured by a nanoindentation method when the maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 500 mN is 110 mN / mm ２ The electrode foil according to claim 6 .

10. The modulus of elasticity measured by a nanoindentation method when the maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 9000 mN / mm ２ The electrode foil according to claim 6 .

11. An electrode foil with a withstand voltage of more than 22 V and not more than 160 V, comprising a metal foil having a porous portion on a main surface thereof and a dielectric layer covering the porous portion, the metal foil containing a valve metal, and an indentation depth H of 10.5 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portion covered with the dielectric layer, as measured by a nanoindentation method.

12. The electrode foil according to claim 11, wherein the dielectric layer is a conversion coating.

13. The electrode foil according to claim 11, which is used in an electrolytic capacitor having a rated voltage of more than 16 V and not more than 130 V.

14. The hardness measured by a nanoindentation method when the maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 180 mN / mm ２ The electrode foil according to claim 11 .

15. The modulus of elasticity measured by a nanoindentation method when the maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 15,000 mN / mm ２ The electrode foil according to claim 11 .

16. In the pore distribution of the porous portion measured by mercury intrusion porosimetry, the cumulative pore volume V0 (cm ３ / g) and the cumulative pore volume V1 (cm ３ / g) and the cumulative pore volume V2 (cm ３ 12. The electrode foil according to claim 1, wherein V1 / V0 and V2 / V0 (g) satisfy the relationships V1 / V0≦0.76 and V2 / V0≦0.

94.

17. The electrode foil according to any one of claims 1, 6, and 11, wherein the thickness of the metal foil is 100 μm or more.

18. The electrode foil according to any one of claims 1, 6, and 11, wherein the thickness of the porous portion is 35 μm or more and less than 50 μm.

19. An electrolytic capacitor comprising a capacitor element, the capacitor element comprising a wound body and an electrolyte, the wound body being formed by winding an anode foil, a cathode foil, and a separator disposed between the anode foil and the cathode foil, the anode foil being an electrode foil as defined in any one of claims 1, 6, and 11.

20. The main surfaces of the metal foil of the anode foil include a first main surface and a second main surface opposite to the first main surface, the porous portion includes a first porous portion on the first main surface and a second porous portion on the second main surface, the dielectric layer includes a first dielectric layer covering the first porous portion and a second dielectric layer covering the second porous portion, a first indentation depth H1 measured by nanoindentation at a maximum indentation load of 500 mN on the first main surface having the first porous portion covered with the first dielectric layer is smaller than a second indentation depth H2 measured by nanoindentation at a maximum indentation load of 500 mN on the second main surface having the second porous portion covered with the second dielectric layer, and at least the first indentation depth H1 is the indentation depth H, 20. The electrolytic capacitor according to claim 19, wherein the anode foil is wound in the wound body such that the first main surface faces an outer periphery of the wound body.

21. A method for manufacturing an electrode foil having a withstand voltage of 7 V or less, comprising: an etching step of etching a sheet containing a valve metal; a compression step of compressing the etched sheet in the thickness direction to form porous portions on a main surface of the sheet; and a step of forming a dielectric layer that covers the porous portions by performing a chemical conversion treatment on the compressed sheet, wherein the indentation depth H measured by a nanoindentation method when a maximum indentation load of 500 mN is applied to the main surface having the porous portions covered with the dielectric layer is 17 μm or less.

22. The method for producing an electrode foil for an electrolytic capacitor according to claim 21, wherein the chemical conversion treatment is carried out at a chemical conversion voltage of 7 V or less.

23. The hardness measured by a nanoindentation method when the maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 67 mN / mm ２ The method for producing an electrode foil according to claim 21 , wherein the electrode foil is made of a material selected from the group consisting of ethylenediaminetetraacetic acid and propylene glycol.

24. The elastic modulus measured by a nanoindentation method when the maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 7000 mN / mm ２ The method for producing an electrode foil according to claim 21 , wherein the electrode foil is made of a material selected from the group consisting of ethylenediaminetetraacetic acid and propylene glycol.

25. A method for manufacturing an electrode foil having a withstand voltage of more than 7 V and not more than 22 V, comprising: an etching step of etching a sheet containing a valve metal; a compression step of compressing the etched sheet in the thickness direction to form porous portions on a main surface of the sheet; and a step of forming a dielectric layer covering the porous portions by performing a chemical conversion treatment on the compressed sheet, wherein the indentation depth H measured by nanoindentation is 13.5 μm or less when a maximum indentation load of 500 mN is applied to the main surface having the porous portions covered with the dielectric layer.

26. The method for producing an electrode foil according to claim 25, wherein the chemical conversion treatment is carried out at a chemical conversion voltage of more than 7 V and not more than 22 V.

27. The hardness measured by a nanoindentation method when the maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 110 mN / mm ２ The method for producing an electrode foil according to claim 25, wherein the method is as described above.

28. The elastic modulus measured by a nanoindentation method when the maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 9000 mN / mm ２ The method for producing an electrode foil according to claim 25, wherein the method is as described above.

29. A method for manufacturing an electrode foil having a withstand voltage of more than 22 V and not more than 160 V, comprising: an etching step of etching a sheet containing a valve metal; a compression step of compressing the etched sheet in the thickness direction to form porous portions on a main surface of the sheet; and a chemical conversion step of forming a dielectric layer that covers the porous portions on the compressed sheet, wherein the indentation depth H measured by nanoindentation is 10.5 μm or less when the maximum indentation load on the main surface having the porous portions covered with the dielectric layer is 500 mN.

30. The method for producing an electrode foil according to claim 29, wherein the chemical conversion treatment is carried out at a chemical conversion voltage of more than 22 V and not more than 160 V.

31. The hardness measured by a nanoindentation method when the maximum indentation load applied to the main surface having the porous portion covered with the dielectric layer is 180 mN / mm ２ The method for producing an electrode foil according to claim 29, wherein the method is as described above.

32. The elastic modulus measured by a nanoindentation method when the maximum indentation load on the main surface having the porous portion covered with the dielectric layer is 500 mN is 15,000 mN / mm ２ The method for producing an electrode foil according to claim 29, wherein the method is as described above.

33. In the pore distribution of the porous portion measured by mercury intrusion porosimetry, the cumulative pore volume V0 (cm ３ / g) and the cumulative pore volume V1 (cm ３ / g) and the cumulative pore volume V2 (cm ３ 30. The method for producing an electrode foil according to claim 21, 25, or 29, wherein V1 / V0≦0.76 and V2 / V0≦0.94 are satisfied.

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