Electrode foil, method for manufacturing same, and electrolytic capacitor

Abstract

The present disclosure addresses the problem of improving the durability of an electrode foil for an electrolytic capacitor. An electrode foil (1) is for an electrolytic capacitor. The electrode foil (1) comprises a strip-shaped foil body (8), a porous layer (2), a groove portion (4), and a dense layer (5). The foil body (8) contains a valve metal. The porous layer (2) is provided on a surface of the foil body (8). The groove portion (4) is provided in the porous layer (2) and extends linearly along the short direction of the surface of the foil body (8). The dense layer (5) is provided on a surface of the groove portion (4) and contains a valve metal (51) and / or a valve metal oxide (52).

Description

Electrode foil, method for producing the same, and electrolytic capacitor

[0001] The present disclosure relates to an electrode foil, a method for producing the same, and an electrolytic capacitor. More specifically, the present disclosure relates to an electrode foil for an electrolytic capacitor, a method for producing the same, and an electrolytic capacitor.

[0002] The electrode foil of the electrolytic capacitor disclosed in Patent Document 1 and Patent Document 2 is formed of a strip-shaped foil, and includes an expanded surface portion, a core portion, and a plurality of divided portions. The expanded surface portion is formed on the surface of the foil. The core portion is the remaining part of the foil excluding the expanded surface portion. The divided portions extend in the width direction of the strip in the expanded surface portion and divide the expanded surface portion. The plurality of divided portions disperse bending stress when the electrode foil is wound, thereby preventing stress concentration. In the electrode foil of the electrolytic capacitor disclosed in Patent Document 1, the divided portions are provided at intervals with an average pitch of 2.1 mm or less. In the electrode foil of the electrolytic capacitor disclosed in Patent Document 2, when the divided portion is in a flattened state, the groove width thereof is 50 µm or less including 0.

[0003] Since the electrode foils of the electrolytic capacitors disclosed in Patent Document 1 and Patent Document 2 include the divided portions, the foil is likely to break due to insufficient strength. Further, since the electrode foil includes the divided portions, the cross-sectional area in the width direction is reduced, which causes a problem that the durability of the electrode foil itself tends to decrease.

[0004] Japanese Patent Application Laid-Open No. 2017-224843Japanese Patent Application Laid-Open No. 2017-224844

[0005] An object of the present disclosure is to provide an electrode foil capable of improving durability, a method for producing the same, and an electrolytic capacitor.

[0006] An electrode foil according to one aspect of the present disclosure includes a strip-shaped foil body, a porous layer, a groove portion, and a dense layer. The foil body contains a valve metal. The porous layer is provided on a surface of the foil body. The groove portion is provided in the porous layer and extends linearly along the lateral direction of the surface of the foil body. The dense layer is provided on a surface of the groove portion and contains at least one of the valve metal and a valve metal oxide.

[0007] An electrolytic capacitor according to another aspect of the present disclosure includes a capacitor element having an anode foil that is the electrode foil described above, and a cathode foil.

[0008] A method for manufacturing an electrode foil according to yet another aspect of the present disclosure includes a first step, a second step, a third step, and a fourth step. In the first step, a strip-shaped foil body containing a valve metal is prepared. In the second step, the surface of the foil body is etched. In the third step, the surface of the etched foil body is chemically converted. In the fourth step, grooves are formed and a dense layer is formed on the surface of the grooves. The grooves extend linearly along the short direction of the surface of the foil body. The dense layer contains at least one of the valve metal and a valve metal oxide.

[0009] According to this disclosure, it is possible to provide electrode foils that can improve durability, a method for manufacturing the same, and electrolytic capacitors.

[0010] Figure 1 is a cross-sectional view of an electrolytic capacitor equipped with an electrode foil according to one embodiment of the present disclosure. Figure 2 is a partially unfolded perspective view of the capacitor element of the electrolytic capacitor. Figure 3 is a plan view of the electrode foil. Figure 4 is a cross-sectional view of the electrode foil of Figure 3 taken along line IV-IV. Figure 5 is an enlarged cross-sectional view of the dense layer of Figure 4. Figure 6 is a cross-sectional photograph of the dense layer. Figure 7 is an explanatory diagram of a method for measuring the thickness of the porous layer. Figure 8 is a plan view showing a crack occurring in the electrode foil. Figure 9 is a plan view of an electrode foil according to another embodiment. Figure 10 is a plan view of an electrode foil according to another embodiment. Figure 11 is a plan view of an electrode foil according to another embodiment. Figure 12 is a plan view of an electrode foil according to another embodiment. Figure 13 is a plan view of an electrode foil according to another embodiment. Figure 14 is a plan view of an electrode foil according to another embodiment.

[0011] Hereinafter, electrode foils, their manufacturing methods, and electrolytic capacitors according to the embodiments will be described in detail with reference to the drawings. However, the figures described in the following embodiments are schematic diagrams, and the dimensional ratios of the sizes of each component do not necessarily reflect the actual dimensional ratios. Furthermore, the configurations described in the following embodiments are merely examples of the present disclosure. The present disclosure is not limited to the following embodiments, and various modifications are possible depending on the design, etc., as long as the effects of the present disclosure can be achieved.

[0012] (Embodiment) (Summary) The electrode foil 1 according to this embodiment is an electrode foil for an electrolytic capacitor. The electrode foil 1 comprises a strip-shaped foil body 8, a porous layer 2, grooves 4, and a dense layer 5 (see Figures 3 and 4). The foil body 8 contains a valve-acting metal 51. The porous layer 2 is provided on the surface of the foil body 8. The grooves 4 are provided in the porous layer 2 and extend linearly along the short-side direction DR1 of the surface of the foil body 8. The dense layer 5 is provided on the surface of the grooves 4 and contains at least one of the valve-acting metal 51 and a valve-acting metal oxide 52 (see Figure 5).

[0013] In the following, the short-side direction DR1 of the surface of the foil body 8 may be referred to as the width direction of the electrode foil 1 (foil body 8). Also, during the manufacturing of the electrode foil 1, the strip-shaped foil body 8 is transported along the long-side direction DR2 of the surface of the foil body 8 while various processes such as etching are performed. For this reason, the long-side direction DR2 of the surface of the foil body 8 may be referred to as the transport direction of the electrode foil 1 (foil body 8). The manufacturing method of the electrode foil 1 will be explained in more detail in "(2) Method for manufacturing electrode foil".

[0014] In this case, the dense layer 5 has at least one of the valve-acting metal 51 and the valve-acting metal oxide 52 present more densely than the porous layer 2. "Present densely" here can be rephrased as the porosity of the dense layer 5 being smaller than that of the porous layer 2. In the porous layer 2, the porosity may be, for example, 30% or more and 90% or less by volume, or 50% or more and 80% or less by volume. In contrast, the porosity of the dense layer 5 is 15% or less or 10% or less. Therefore, by setting the porosity threshold to, for example, 40%, it becomes possible to distinguish between the dense layer 5 and the porous layer 2 based on the measured porosity. The porosity can be measured using known methods.

[0015] Furthermore, the electrolytic capacitor 100 according to this embodiment includes a capacitor element 10 (see Figure 1). As shown in Figure 2, the capacitor element 10 has an electrode foil 1 which is an anode foil and a cathode foil 22. The capacitor element 10 further has a separator 23 provided between the anode foil (electrode foil 1) and the cathode foil 22. The electrode foil 1 is used as the anode foil of the electrolytic capacitor 100. When the electrolytic capacitor 100 is in use, cracks may occur in the internal electrode foil 1 due to external stress, and the electrode foil 1 may break.

[0016] Therefore, the electrode foil 1 according to this embodiment includes grooves 4 that extend linearly along the short direction DR1 on the surface of the foil body 8, and a dense layer 5 on the surface of the grooves 4 containing at least one of a valve-acting metal 51 and a valve-acting metal oxide 52. This relieves stress caused by bending and twisting of the electrode foil 1, suppresses the occurrence or propagation of cracks, and improves the bending strength of the electrode foil 1 itself. This improves the durability of the electrode foil 1.

[0017] Furthermore, since the electrolytic capacitor 100 according to this embodiment uses a highly durable electrode foil 1 as the anode foil of the capacitor element 10, reliability can be improved.

[0018] (Details) The electrode foil 1, its manufacturing method, and the electrolytic capacitor 100 according to this embodiment will be described in detail below with reference to Figures 1 to 8.

[0019] (1) Electrode foil As described above, the electrode foil 1 comprises a foil body 8, a porous layer 2, a groove portion 4, and a dense layer 5. The electrode foil 1 further comprises a core portion 3.

[0020] The foil body 8 is a strip-shaped metal foil in plan view (see Figure 3). The foil body 8 contains aluminum, which is the valve metal 51. The valve metal 51 contains 98% by weight or more of aluminum. In this embodiment, the valve metal 51 is aluminum, but it may also be titanium, tantalum, niobium, etc.

[0021] The porous layer 2 is provided on the surface of the foil body 8 (see Figure 4). The porous layer 2 is formed on both sides of the foil body 8 in the thickness direction, leaving the central core portion 3 intact, by an etching process described later. A dielectric layer is formed on the surface of the metal that has been roughened by the etching process. The dielectric is an oxide film (aluminum oxide) formed on the surface of the metal by a chemical conversion process described later. Therefore, the porous layer 2 includes the roughened metal and the dielectric formed on the surface of the roughened metal. The dielectric may also be formed on the surface of the metal that forms the dense layer 5.

[0022] The core portion 3 is the remaining part of the foil body 8 after removing the porous layer 2 (see Figure 4). In other words, the core portion 3 is the central part of the foil body 8 in the thickness direction.

[0023] The grooves 4 extend linearly along the short-side direction DR1 of the surface of the foil body 8 (porous layer 2) (see Figure 3). The grooves 4 are rectangular in shape when viewed from above. In this embodiment, the foil body 8 is provided with a plurality of grooves 4. That is, the plurality of grooves 4 extend parallel to the short-side direction DR1 of the foil body 8. The plurality of grooves 4 are arranged in the longitudinal direction DR2 of the foil body 8 at predetermined intervals. Of the plurality of grooves 4, the distance L5 between the centers of two adjacent grooves 4 in the longitudinal direction DR2 of the foil body 8 (see Figure 3) is 270% or less of the thickness d1 of the porous layer 2 (see Figures 4 and 5). Note that the distance L5 between the centers of two adjacent grooves 4 does not include cases where the two grooves 4 are touching in the longitudinal direction DR2 of the foil body 8. That is, the distance L5 is greater than the width of the grooves 4 in the longitudinal direction DR2 of the foil body 8. The thickness d1 of the porous layer 2 is defined as the distance from the surface of the foil 8 to the core 3. In the following, the distance L5 between the centers of two adjacent grooves 4 in the longitudinal direction DR2 of the foil 8 may be simply referred to as "the distance L5 between the centers of the grooves 4".

[0024] The grooves 4 are provided in the porous layers 2 on both sides in the thickness direction of the foil body 8 (see Figure 4). In this embodiment, the grooves 4 are V-shaped in cross-section, but they may be U-shaped. The depth L1 of the grooves 4 (see Figure 5) is 30% or more and 80% or less of the thickness d1 of the porous layer 2.

[0025] Furthermore, the width L3 of the groove 4 (see Figure 3) is 75% or more and 100% or less of the thickness d1 of the porous layer 2. The width L3 of the groove 4 is the dimension of the groove 4 in the longitudinal direction DR2 of the foil body 8.

[0026] The distance L4 (see Figure 3) from the edge of the foil body 8 to the groove 4 in the short-side direction DR1 of the foil body 8 is 20% or less of the width dimension W1 in the short-side direction DR1 of the foil body 8. In the following, the edge of the foil body 8 in the short-side direction DR1 may simply be referred to as the "edge of the electrode foil 1".

[0027] The dense layer 5 is provided on the surface of the groove 4 and contains at least one of a valve-acting metal 51 and a valve-acting metal oxide 52 (see Figure 5). In this embodiment, the valve-acting metal 51 of the dense layer 5 is aluminum. The valve-acting metal oxide 52 of the dense layer 5 is aluminum oxide. In other words, the dense layer 5 contains at least one of aluminum and aluminum oxide. Here, at least one of the valve-acting metal 51 and the valve-acting metal oxide 52 is denser in the dense layer 5 compared to the porous layer 2. Therefore, in this embodiment, at least one of aluminum and aluminum oxide is denser in the dense layer 5 compared to the porous layer 2.

[0028] In this embodiment, the dense layer 5 is provided in a V-shape in cross-section along the surface of the V-shaped groove 4. The maximum thickness L2 of the dense layer 5 (see Figure 5) is 5% or more and 20% or less of the thickness d1 of the porous layer 2.

[0029] In this embodiment, the dense layer 5 is provided in a V-shape in cross-section along the surface of the V-shaped groove 4. However, the dense layer 5 may be provided so as to fill most of the depth of the groove 4. In such a case, for example, the maximum thickness L2 of the dense layer 5 may be defined as half the width L3 of the groove 4 (see Figure 3).

[0030] (2) Method for manufacturing electrode foil Hereinafter, an example of the method for manufacturing electrode foil 1 of this embodiment will be described step by step. The method for manufacturing electrode foil 1 of this embodiment includes a first step, a second step, a third step, and a fourth step.

[0031] (2.1) First Step In the first step, a foil body 8 containing the valve metal 51 is prepared. Specifically, a strip-shaped sheet is used for the foil body 8. The foil body 8 contains 98% by weight or more of aluminum as the valve metal 51. In other words, the foil body 8 may contain less than 2% of impurities (excluding the valve metal 51). That is, the foil body 8 may be a sheet of the valve metal 51, or a sheet of an alloy or compound containing the valve metal 51.

[0032] (2.2) Second Step In the second step, the surface of the foil body 8 is etched. In the second step, the surface of the foil body 8 is etched while the foil body 8 is transported by a plurality of rollers (not shown) to form a porous layer 2. The etching process forms a porous layer 2 on both sides of the foil body 8, leaving the core portion 3 in the thickness direction of the foil body 8. The etching process may be electrolytic etching or chemical etching. The etching process increases the surface area of ​​the electrode foil 1, thereby increasing the capacitance of the electrolytic capacitor 100.

[0033] (2.3) Third Step In the third step, the surface of the etched foil 8 is subjected to a chemical conversion treatment. In the third step, the surface of the etched foil 8 is subjected to a chemical conversion treatment while the foil 8 is transported by a plurality of rollers (not shown). The chemical conversion treatment forms an oxide film on the roughened metal surface, and this oxide film becomes a dielectric layer. The chemical conversion treatment can be carried out by, for example, applying a voltage to the foil 8 while it is immersed in a treatment solution. The treatment solution is not particularly limited, but for example, an ammonium adipate solution may be used. Since a dielectric layer is formed by the chemical conversion treatment, the withstand voltage of the electrolytic capacitor 100 can be increased.

[0034] (2.4) Fourth Step In the fourth step, grooves 4 are formed that extend linearly along the short direction DR1 on the surface of the foil body 8. Furthermore, a dense layer 5 containing at least one of valve-acting metal 51 and valve-acting metal oxide 52 is formed on the surface of the grooves 4. In the fourth step, the dense layer 5 is formed by selectively melting the surface of the foil body 8. In this embodiment, the dense layer 5 is formed by selectively melting the surface of the foil body 8 by laser processing. More specifically, grooves 4 extending along the short direction DR1 are formed on the surface of the foil body 8 by laser processing, and the dense layer 5 is formed on the surface of the grooves 4. Laser processing allows for more precise control of the dimensions of the dense layer 5, such as the amount, width, and length. This further enhances the effect of suppressing foil breakage of the electrode foil 1.

[0035] In the above manufacturing process, cracks may develop or propagate in the foil body 8 due to stresses such as tension during transport, bending that occurs when passing through rollers, and twisting that occurs during transport.

[0036] In the manufacturing method of the electrode foil 1 according to this embodiment, a groove 4 is formed linearly along the short direction DR1 on the surface of the foil body 8, and a dense layer 5 containing at least one of a valve-acting metal 51 and a valve-acting metal oxide 52 is formed on the surface of the groove 4. As a result, stress caused by bending and twisting of the electrode foil 1 is relieved, the occurrence or propagation of cracks can be suppressed, and the bending strength of the electrode foil 1 itself can be improved. This improves the durability of the electrode foil 1.

[0037] (3) Electrolytic capacitor The configuration of the electrolytic capacitor 100 according to this embodiment will be described in detail below.

[0038] The electrolytic capacitor 100 according to this embodiment is a wound-type solid electrolytic capacitor in which the electrolyte is solid and an oxide film, which is a dielectric layer, is formed on the electrode foil 1, which is the anode foil.

[0039] The electrolytic capacitor 100 according to this embodiment includes a capacitor element 10 (see Figure 1). As shown in Figure 2, the capacitor element 10 has an electrode foil 1 which is an anode foil and a cathode foil 22. The capacitor element 10 further includes a separator 23 provided between the anode foil (electrode foil 1) and the cathode foil 22.

[0040] As described above, the electrolytic capacitor 100 includes a capacitor element 10. As shown in Figure 1, the electrolytic capacitor 100 includes a bottomed case 11, a sealing member 12, a base plate 13, electrode terminals 14A, 14B, lead tabs 15A, 15B, and a capacitor element 10.

[0041] (3.1) Bottomed Case The bottomed case 11 is configured to accommodate the capacitor element 10. Specifically, the bottomed case 11 is a cylindrical member with a closed bottom and an open top. Therefore, the capacitor element 10 can be inserted into the bottomed case 11 through the opening. The bottomed case 11 is made of one or more materials selected from the group consisting of, for example, aluminum, stainless steel, copper, iron, brass and alloys thereof.

[0042] (3.2) The opening of the sealed case 11 is sealed by a sealing member 12. The sealing member 12 is made of a rubber material such as EPT (ethylene-propylene terpolymer) or IIR (isobutylene-isoprene rubber), or a resin material such as epoxy resin. The sealing member 12 has a pair of through holes. The bottomed case 11 is drawn inward near its opening end, and the opening end is curled, thereby crimping the sealing member 12. Furthermore, this sealing member 12 is covered by a base plate 13. The base plate 13 is made of an electrically insulating resin material, for example.

[0043] (3.3) Electrode Terminals and Lead Tabs A pair of electrode terminals 14A and 14B are led out from the through-hole of the sealing member 12 and penetrate through the seat plate 13. A pair of lead tabs 15A and 15B are embedded in the sealing member 12. The lead tab 15A electrically connects the electrode terminal 14A and the electrode of the capacitor element 10 (the electrode foil 1, which is an anode foil). The lead tab 15B electrically connects the electrode terminal 14B and the electrode of the capacitor element 10 (the cathode foil 22).

[0044] (3.4) Capacitor Element Hereinafter, the capacitor element 10 housed in the bottomed case 11 will be described in detail.

[0045] As shown in FIG. 2, the capacitor element 10 of the present embodiment is a wound body. The wound body shown in FIG. 2 shows a state where the capacitor element 10 is taken out from the electrolytic capacitor 100 shown in FIG. 1 and partially developed.

[0046] As described above, the capacitor element 10 includes the electrode foil 1 of the present embodiment which is an anode foil, the cathode foil 22, and the separator 23. As shown in FIG. 2, the anode foil (electrode foil) 1 is electrically connected with the lead tab 15A, and the cathode foil 22 is electrically connected with the lead tab 15B. Therefore, the anode foil (electrode foil) 1 is electrically connected to the electrode terminal 14A via the lead tab 15A, and the cathode foil 22 is electrically connected to the electrode terminal 14B via the lead tab 15B.

[0047] As shown in FIG. 5, the electrode foil 1 which is an anode foil includes a foil body 8 and a dielectric layer formed on the surface of a metal foil. That is, the capacitor element 10 includes an anode foil with a dielectric layer formed on the surface thereof.

[0048] The surface of the foil body 8 is roughened. Thereby, the surface area of the foil body 8 can be increased, and the area of the dielectric layer formed on the surface of the foil body 8 can also be increased. The roughening method is not particularly limited, for example, an etching method can be employed.

[0049] The dielectric layer is formed by chemical conversion treatment of the surface of the metal foil. This chemical conversion treatment creates an oxide film on the surface of the metal foil, and this oxide film becomes the dielectric layer. The chemical conversion treatment can be carried out, for example, by applying a voltage to the metal foil while it is immersed in a treatment solution. The treatment solution is not particularly limited, but for example, an ammonium adipate solution can be used.

[0050] The cathode foil 22 can be a metal foil similar to the metal foil (electrode foil 1) used in the manufacture of the anode foil. The surface of the cathode foil 22 may be roughened. The surface of the cathode foil 22 may have a layer formed on it, for example, containing titanium or carbon.

[0051] The separator 23 is provided between the electrode foil 1, which is the anode foil, and the cathode foil 22. The electrode foil 1, which is the anode foil, the cathode foil 22, and the separator 23 are wound together in an overlapping state, as shown in Figure 2. The separator 23 is a nonwoven fabric containing, for example, cellulose fibers, kraft, polyethylene terephthalate, polyphenylene sulfide, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, glass, vinylon, or aramid fibers. In this embodiment, it is preferable that the separator 23 contains cellulose fibers. The outermost periphery of the capacitor element 10 is secured and fixed with a winding tape 24.

[0052] In the capacitor element 10, a solid electrolyte (not shown) is formed between the electrode foil 1, which is the anode foil, and the cathode foil 22. The solid electrolyte (not shown) is held in place by a separator 23.

[0053] The separator 23 is overlapped so that one end of it protrudes beyond one end of the electrode foil 1, which is the anode foil, and the cathode foil 22. Then, the protruding separator 23 is wound first to create a winding core (not shown), and then the layers of the electrode foil 1, which is the anode foil, the cathode foil 22, and the separator 23 are wound around this winding core (not shown) as the winding axis.

[0054] The capacitor element 10 created in this way is subjected to an aging process, after which an electrolyte is formed, and it is housed in a bottomed case 11. The electrode terminals 14A and 14B are pulled out, and the opening of the bottomed case 11 is sealed with a sealing member 12, thus taking the form of a wound-type solid electrolytic capacitor.

[0055] (3.5) Applications of Electrolytic Capacitors The applications of electrolytic capacitors 100 are not particularly limited. For example, electrolytic capacitors 100 can be mounted on the circuit board of an ECU (Engine Control Unit) in an automobile, or used in switching power supplies, etc. As for this type of automobile, electric vehicles or hybrid vehicles are mainly envisioned, but gasoline engine vehicles or diesel engine vehicles may also be used. Electrolytic capacitors 100 may also be used in motorcycles (including electric motorcycles), aircraft, ships, drones, etc. Electrolytic capacitors 100 may also be used in power supplies for CPUs (Central Processing Units) in server equipment, computer equipment, and home game consoles, etc. In addition, electrolytic capacitors 100 may be used in power supplies for FPGAs (Field-Programmable Gate Arrays) in communication equipment and industrial equipment, and power supplies for GPUs (Graphics Processing Units) in graphics boards, etc. The applications of electrolytic capacitors 100 are not limited to these, and they can be used in a wide range of fields.

[0056] When using the electrolytic capacitor 100, stress generated by external vibrations may cause cracks to form in the internal electrode foil 1, potentially leading to fracture of the electrode foil 1. Figure 8 is a plan view showing the appearance of a crack in the electrode foil 1. As shown in Figure 8, stress caused by bending and twisting of the electrode foil 1 causes a crack CK1 to form along the width direction DR1 of the electrode foil 1. In the electrode foil 1 of this embodiment, linear grooves 4 and dense layers 5 are formed along the width direction DR1 of the electrode foil 1. In other words, in the electrode foil 1 of this embodiment, the linear grooves 4 and dense layers 5 extend along the direction of the crack CK1. This reduces the stress generated by bending and twisting of the electrode foil 1, and suppresses the propagation of the crack CK1. The bending strength of the electrode foil 1 itself can be improved. In this embodiment, since a highly durable electrode foil 1 is used in the capacitor element 10, the reliability of the electrolytic capacitor 100 can be increased.

[0057] [Examples] The structure and manufacturing method of the electrode foil 1 of this embodiment will be described in more detail below based on the examples, however, the structure and manufacturing method of the electrode foil 1 are not limited to the contents of the following examples.

[0058] [Electrode Foil Preparation] (Step 1) A strip of raw material foil with a thickness of 130 μm was prepared. The raw material foil was aluminum foil with an aluminum content of 99.98% by weight. The silicon content was 40 ppm by mass (parts per million), the iron content was 40 ppm by weight, and the copper content was 30 ppm by weight.

[0059] (Second step) The aluminum foil was etched. This formed a porous layer with sponge-like pits on both surfaces of the aluminum foil.

[0060] (Third step) The etched aluminum foil (hereinafter also referred to as etched foil) was subjected to a chemical conversion treatment to form a dielectric layer with a dielectric strength equivalent to 60V on the surface of the metal portion constituting the porous layer.

[0061] (Fourth step) Linear grooves and a dense layer were formed along the width direction of the surface of the chemically treated etched foil. To form the grooves and dense layer, the porous portion treated with chemical conversion was selectively removed and melted by irradiating the surface of the etched foil with a laser. A laser with a wavelength of 1064 nm, an output of 15 W, and a continuous oscillation type was used. The processing speed was set to 3000 mm / sec.

[0062] [Evaluation] (Folding Strength) The folding strength of the electrode foil 1 prepared as described above in the transport direction (longitudinal direction) was measured. The measurement was carried out in accordance with the test method for electrode foils for aluminum electrolytic capacitors of the Japan Electronic Machinery Industry Standard (EIAJ RC-2364A). Folding strength was measured by fixing the electrode foil 1 to a clamp with an R3.5 mm radius while a load of 550 g was applied to it, and repeatedly bending loads were applied, and the number of times until the electrode foil 1 broke (hereinafter referred to as "number of folding cycles") was measured. The measurement was carried out using test pieces obtained by cutting the electrode foil 1 to dimensions of 100 mm in the length direction and 10 mm in the width direction.

[0063] Furthermore, the depth L1 of the groove 4, the maximum thickness L2 of the dense layer 5, and the width L3 of the groove 4 were measured using a scanning electron microscope (SEM) after preparing cross-sectional processed samples of the groove 4. The distance L4 from the edge of the electrode foil 1 to the groove 4, and the distance L5 between the centers of the grooves 4, were measured using the set values ​​for the laser processing conditions of the grooves.

[0064] Furthermore, the ratio of the groove depth L1, the maximum thickness L2 of the dense layer 5, the width L3 of the groove 4, and the distance L5 between the centers of the grooves 4 to the thickness d1 (50 μm) of the porous layer was calculated. The thickness d1 of the porous layer 2 was measured as follows. First, as shown in Figure 7, the electrode foil 1 is placed on a measurement table 200 with a flat surface. In the thickness direction of the electrode foil 1 placed on the measurement table 200, the boundary between the porous layer 2 and the core 3, and the surface of the porous layer 2 are uneven. A cross-sectional photograph (500x magnification with a scanning electron microscope) of an arbitrary part of the electrode foil 1 is taken. Figure 6 is an enlarged view of a part of the cross-sectional photograph. As shown in Figure 7, in the captured cross-sectional image, the vertex P1 of the core 3 is identified at the boundary between the porous layer 2 and the core 3. A parallel line is drawn passing through the vertex P1 and parallel to the surface of the measurement table 200. Then, the vertex P2 of the porous layer 2 is identified on the surface of the porous layer 2. Draw parallel lines passing through vertex P2 and parallel to the surface of the measurement table 200. The shortest distance between the two parallel lines corresponds to the distance from the surface of the foil 8 to the core 3 in Figures 4 and 5. Therefore, the thickness d1 of the porous layer 2 can be measured by measuring the shortest distance between the two parallel lines.

[0065] Furthermore, the ratio of the distance L4 from the edge of the electrode foil 1 to the groove 4 to the width dimension W1 in the short direction DR1 of the foil body 8 was calculated. The thickness D1 of the electrode foil 1 is measured by measuring the shortest distance from the surface of the measurement table 200, passing through the apex P2 of the porous layer 2, to a parallel line parallel to the surface of the measurement table 200. This allows the thickness D1 of the electrode foil 1 to be measured.

[0066] Tables 1 to 5 show the results of evaluating the folding strength of electrode foil 1 of the example in comparison with the electrode foil of the comparative example. The electrode foil of the comparative example is an electrode foil that does not have grooves and a dense layer. Specifically, the electrode foil of the comparative example was manufactured using the same raw material foil as the example, and by etching and chemical conversion treatment under the same conditions as the example. The improvement rate (%) of folding strength in Tables 1 to 5 shows the ratio of the number of folding cycles of each example to the number of folding cycles of the comparative example (undisclosed). The inventors used 50% as the baseline value and evaluated the improvement rate (%) of folding strength in three stages (△, ○, ◎). An improvement rate of 0 or more and less than 50% is △ (somewhat good), an improvement rate of 50% or more and less than 100% is ○ (quite good), and an improvement rate of 100% or more is ◎ (very good).

[0067] (Evaluation of folding strength at groove depth L1) The evaluation results of the folding strength at groove depth L1 are shown in Table 1. Although omitted here, in each of Examples 1 to 8 in Table 1, the distance L4 from the edge of the electrode foil 1 to the groove 4 was set to 0 (μm), and the distance L5 between the centers of the grooves 4 was set to 100 (μm).

[0068]

[0069] The electrode foils 1 of Examples 1 to 8 showed a higher rate of improvement in bending strength compared to the electrode foil of the comparative example. This is thought to be because the dense layer 5 formed in the groove 4 relieved the stress caused by bending and twisting of the electrode foil 1, thereby suppressing the occurrence or propagation of cracks.

[0070] In particular, the electrode foil 1 of Examples 3 to 7 showed an improvement of 50% or more in bending strength. In the electrode foil 1 of Examples 3 to 7, the depth L1 of the groove was in the range of 15 μm or more and 45 μm or less. In other words, the ratio of the depth L1 of the groove 4 to the thickness d1 (50 μm) of the porous layer 2 was in the range of 30% or more and 80% or less. It is thought that by setting the depth L1 of the groove 4 within the above range, the stress caused by bending and twisting of the electrode foil 1 is more easily relieved, and the occurrence or propagation of cracks is more easily suppressed. As a result, the bending strength of the electrode foil 1 can be further improved.

[0071] In contrast, the electrode foils 1 of Examples 1, 2, and 8 showed a higher rate of improvement in folding strength compared to the electrode foil of the comparative example, but still fell below the standard value of 50%. Specifically, the depth L1 of the groove 4 in Example 1 was 6.1 μm, and the depth L1 of the groove 4 in Example 2 was 10.4 μm. The depth L1 of the groove 4 in both Examples 1 and 2 fell below the lower limit of the above range. On the other hand, the depth L1 of the groove 4 in Example 8 was 51.5 μm, exceeding the upper limit of the above range. In other words, although the dense layer 5 formed in the groove 4 improves the folding strength of the electrode foil 1, it is thought that if the depth L1 of the groove 4 is too small or too large, it becomes difficult to relieve the stress caused by bending and twisting of the electrode foil 1.

[0072] (Evaluation of folding strength at the maximum thickness L2 of the dense layer 5) The evaluation results of the folding strength at the maximum thickness L2 of the dense layer 5 are shown in Table 2. Although omitted here, in each of Examples 9 to 16 in Table 2, the distance L4 from the edge of the electrode foil 1 to the groove 4 was set to 0 (μm), and the distance L5 between the centers of the grooves 4 was set to 100 (μm).

[0073]

[0074] The electrode foils 1 of Examples 9 to 16 showed a higher rate of improvement in bending strength compared to the electrode foil of the comparative example. This is thought to be because the dense layer 5 formed in the groove 4 relieved the stress caused by bending and twisting of the electrode foil 1, thereby suppressing the occurrence or propagation of cracks.

[0075] In particular, in the electrode foil 1 of Examples 9 to 15, the improvement rate of the bending strength increased by more than 50%. In the electrode foil 1 of Examples 9 to 15, the maximum thickness L2 of the dense layer 5 was in the range of 3 μm or more and 11 μm or less. In other words, the ratio of the maximum thickness L2 of the dense layer 5 to the thickness d1 (50 μm) of the porous layer 2 was in the range of 5% or more and 20% or less. It is thought that by setting the maximum thickness L2 of the dense layer 5 within the above range, it became easier to relieve the stress caused by bending and twisting of the electrode foil 1, and it became easier to suppress the occurrence or propagation of cracks. As a result, the bending strength of the electrode foil 1 can be further improved.

[0076] In contrast, the electrode foil 1 of Example 16 showed a higher rate of improvement in folding strength compared to the electrode foil of the comparative example, but it still fell below the standard value of 50%. Specifically, in the electrode foil 1 of Example 16, the maximum thickness L2 of the dense layer 5 was 12.3 μm, which exceeded the upper limit of the above range (11 μm). Although the dense layer 5 formed in the groove 4 improves the folding strength of the electrode foil 1, if the dense layer 5 is too thick, it is thought that not only will the increase in folding strength be suppressed, but the thermal effects on the foil due to melting will be greater, making manufacturing difficult. Conversely, if the dense layer 5 is too thin, it is thought that the increase in folding strength will be suppressed.

[0077] (Evaluation of folding strength at groove width L3) The evaluation results of the folding strength at groove width L3 are shown in Table 3. Although omitted here, in each of Examples 17 to 24 in Table 3, the distance L4 from the end of the electrode foil 1 to the groove 4 was set to 0 (μm), and the distance L5 between the centers of the grooves 4 was set to 100 (μm).

[0078]

[0079] The electrode foils 1 of Examples 17 to 24 showed a higher rate of improvement in bending strength compared to the electrode foils of the comparative examples. This is thought to be because the dense layer 5 formed in the grooves 4 alleviated the stress caused by bending and twisting of the electrode foil 1, thereby suppressing the occurrence or propagation of cracks.

[0080] In particular, in the electrode foil 1 of Examples 19 to 23, the improvement rate of the bending strength increased by more than 50%. In the electrode foil 1 of Examples 19 to 23, the width L3 of the groove 4 was in the range of 40 μm or more and 55 μm or less. In other words, the ratio of the width L3 of the groove 4 to the thickness d1 (50 μm) of the porous layer 2 was in the range of 75% or more and 100% or less. It is thought that by setting the width L3 of the groove 4 within the above range, the stress caused by bending and twisting of the electrode foil 1 is more easily relieved, and the occurrence or propagation of cracks is more easily suppressed. As a result, the bending strength of the electrode foil 1 can be further improved.

[0081] In contrast, the electrode foils 1 of Examples 17, 18, and 24 showed a higher rate of improvement in folding strength compared to the electrode foil of the comparative example, but still fell below the standard value of 50%. Specifically, the width L3 of the groove 4 in Example 17 was 26.8 μm, and the width L3 of the groove 4 in Example 18 was 37.6 μm, both of which were below the lower limit of the above range (40 μm). On the other hand, the width L3 of the groove 4 in Example 24 was 66 μm, which exceeded the upper limit of the above range (55 μm). Although the dense layer 5 formed in the groove 4 improves the folding strength of the electrode foil 1, if the width L3 of the groove 4 is too small, the increase in folding strength is suppressed, and it becomes difficult to manufacture the electrolytic capacitor 100. Also, if the width L3 of the groove 4 is too large, the capacitance of the electrolytic capacitor 100 tends to decrease as a result.

[0082] (Evaluation of folding strength at the distance L4 from the edge of electrode foil 1 to the groove 4) The evaluation results of the folding strength at the distance L4 from the edge of electrode foil 1 to the groove 4 are shown in Table 4. Although omitted here, the distance L5 between the centers of the grooves 4 was set to 100 (μm) for each of the electrode foils 1 in Examples 25 to 32 in Table 4.

[0083]

[0084] The electrode foils 1 of Examples 25 to 32 showed a higher rate of improvement in bending strength compared to the electrode foils of the comparative examples. This is thought to be because the dense layer 5 formed in the grooves 4 alleviated the stress caused by bending and twisting of the electrode foil 1, thereby suppressing the occurrence or propagation of cracks.

[0085] In particular, in the electrode foil 1 of Examples 25 to 30, the improvement rate of the bending strength increased by more than 50%. In the electrode foil 1 of Examples 25 to 30, the distance L4 from the edge of the electrode foil 1 to the groove 4 was in the range of 2000 μm or less. In other words, the ratio of the distance L4 from the edge of the electrode foil 1 to the groove 4 to the width dimension W1 in the short direction DR1 of the electrode foil 1 was in the range of 20% or less. It is thought that by setting the distance L4 from the edge of the electrode foil 1 to the groove 4 within the above range, it becomes easier to relieve the stress caused by bending and twisting of the electrode foil 1, and it becomes easier to suppress the occurrence or propagation of cracks. As a result, the bending strength of the electrode foil 1 can be further improved.

[0086] In contrast, the electrode foils 1 of Examples 31 and 32 showed a higher rate of improvement in folding strength compared to the electrode foil of the comparative example, but still fell below the standard value of 50%. Specifically, the distance L4 from the edge of the electrode foil 1 to the groove 4 of Example 31 was 3000 μm, and the distance L4 from the edge of the electrode foil 1 to the groove 4 of Example 32 was 4000 μm, both exceeding the upper limit of the above range (2000 μm). Although the dense layer 5 formed in the groove 4 improves the folding strength of the electrode foil 1, the increase in folding strength is suppressed when the distance L4 from the edge of the electrode foil 1 to the groove 4 is large.

[0087] (Evaluation of folding strength at the distance L5 between the centers of the grooves 4) The evaluation results of the folding strength at the distance L5 between the centers of the grooves 4 are shown in Table 5. Although omitted here, in each of Examples 33 to 40 in Table 5, the distance L4 from the edge of the electrode foil 1 to the groove 4 was set to 0 (μm).

[0088]

[0089] The electrode foils 1 of Examples 33 to 38 and Example 40 showed a higher rate of improvement in bending strength compared to the electrode foils of the comparative examples. This is thought to be because the dense layer 5 formed in the grooves 4 alleviated the stress caused by bending and twisting of the electrode foil 1, thereby suppressing the occurrence or propagation of cracks. Note that the electrode foil 1 of Example 39 was excluded from the evaluation.

[0090] In particular, the electrode foil 1 of Examples 33 to 38 showed an improvement of 50% or more in bending strength. The distance L5 between the centers of the grooves 4 in Examples 33 to 38 was in the range of 150 μm or less in all cases. In other words, the ratio of the distance L5 between the centers of the grooves 4 to the thickness d1 (50 μm) of the porous layer 2 was in the range of 270% or less. It is thought that by setting the distance L4 from the edge of the electrode foil 1 to the grooves 4 within the above range, it becomes easier to relieve the stress caused by bending and twisting of the electrode foil 1, and thus easier to suppress the occurrence or propagation of cracks. As a result, the bending strength of the electrode foil 1 can be further improved.

[0091] In contrast, the electrode foil 1 of Example 40 showed a higher rate of improvement in folding strength compared to the electrode foil of the comparative example, but it still fell below the standard value of 50%. Specifically, the distance L5 between the centers of the grooves 4 in Example 40 was 300 μm, which exceeded the upper limit of the above range (150 μm). Although the dense layer 5 formed in the grooves 4 improves the folding strength of the electrode foil 1, the increase in folding strength is suppressed when the distance L5 between the centers of the grooves 4 is large. It is thought that the increase in folding strength is suppressed if the distance L5 between the centers of the grooves 4 is too small or too large.

[0092] In the above embodiments and each embodiment, where "greater than or equal to" is used in the comparison of two values, it may also be used as "greater than." In other words, whether or not the case where the two values ​​are equal is included in the comparison of two values ​​can be arbitrarily changed depending on the setting of the reference value, etc., so there is no technical difference between "greater than" and "greater than or equal to." Similarly, where "less than or equal to" is used, it may also be used as "less than."

[0093] (4) Other Embodiments The above embodiments and each embodiment are merely one of many embodiments of the present disclosure. The above embodiments can be modified in various ways depending on the design, etc., as long as the objectives of the present disclosure are achieved. Other embodiments of the above embodiments are listed below. The embodiments described below can be combined and applied as appropriate.

[0094] (4.1) Example 1-1 In the electrode foil 1 of the above embodiment, as shown in Figure 3, a plurality of grooves 4 extending linearly along the short direction DR1 of the foil body 8 are formed at predetermined intervals over the entire area of ​​the longitudinal direction DR2 of the foil body 8, but they may also be formed in a part of the longitudinal direction DR2 of the foil body 8.

[0095] Figure 9 is a plan view of the electrode foil 1A according to Embodiment 1-1. As shown in Figure 9, the electrode foil 1A is similar to the above embodiment in that multiple grooves 4 are formed at predetermined intervals, but it differs from the above embodiment in that they are densely formed in areas with high bending stress.

[0096] In the modified example 1, the electrode foil 1A is wound together with the separator 23 and cathode foil 22 to produce a capacitor element 10, as shown in Figure 2, similar to the embodiment described above. However, the diameter of the circle is small near the center of the capacitor element 10, but gradually increases towards the outside. In the embodiment described above, the electrode foil 1 is prone to distortion near the center of the capacitor element 10 (near the lead tabs 15A and 15B in Figure 2). As a result, bending stress concentrates near the center of the capacitor element 10, making the electrode foil 1 prone to breaking. Note that the area with high bending stress can be described as the area with a small bending radius.

[0097] As shown in Figure 9, in the electrode foil 1A according to Example 1-1, a plurality of grooves 4 are formed in a portion of the longitudinal direction DR2 of the foil body 8. The portion of the longitudinal direction DR2 of the foil body 8 corresponds to the portion of the winding capacitor element 10 where the bending stress is large. According to the electrode foil 1A of Modified Example 1, for example, during use of a wound electrolytic capacitor 100, the bending stress applied to the electrode foil 1A can be effectively reduced, making it less likely for cracks to occur.

[0098] (4.2) Example 1-2 In the electrode foil 1 of the above embodiment, as shown in Figure 3, a plurality of grooves 4 extending linearly along the short direction DR1 of the foil body 8 are formed in the longitudinal direction DR2 of the foil body 8 at predetermined intervals, but two adjacent grooves 4 in the longitudinal direction DR2 of the foil body 8 may be connected.

[0099] Figure 10 is a plan view of the electrode foil 1B according to Embodiment 1-2. As shown in Figure 10, the groove 4 of the electrode foil 1B is a first groove 41, and the electrode foil 1B is further provided with a second groove 42. More specifically, the second groove 42 extends linearly along the longitudinal direction DR2 of the foil body 8 and connects two adjacent first grooves 41 in the longitudinal direction DR2 of the foil body 8. In other words, the groove 4 of the electrode foil 1B differs from the above embodiment (see Figure 3) in that it includes a second groove 42.

[0100] According to the electrode foil 1B of Example 1-2, the effect of suppressing the propagation of cracks that may occur due to stress can be further enhanced compared to the electrode foil 1 of the above embodiment. As a result, the durability of electrode foil 1B can be further improved.

[0101] (4.3) Example 1-3 In the electrode foil 1 of the above embodiment, as shown in Figure 3, a plurality of grooves 4 extending linearly along the short direction DR1 of the foil body 8 are formed in the longitudinal direction DR2 of the foil body 8 at predetermined intervals. However, a plurality of grooves that intersect diagonally with the plurality of grooves 4 may be further formed.

[0102] Figure 11 is a plan view of the electrode foil 1C according to Example 1-3. As shown in Figure 11, the groove 4 of the electrode foil 1C is a first groove 41, and the electrode foil 1C is further provided with a second groove 42.

[0103] More specifically, the multiple second grooves 42 extend linearly along a direction inclined with respect to the longitudinal direction DR2 of the foil body 8, and are formed intersecting with the multiple first grooves 41. In other words, the electrode foil 1C according to Examples 1-3 differs from the above embodiment (see Figure 3) in that it has multiple second grooves 42.

[0104] According to the electrode foil 1C of Examples 1-3, the effect of suppressing the propagation of cracks that may occur due to stress can be further enhanced compared to the electrode foil 1 of the above embodiment. As a result, the durability of electrode foil 1C can be further improved.

[0105] (4.4) Example 1-4 In the electrode foil 1 of the above embodiment, as shown in Figure 3, the plurality of grooves 4 extend parallel to the short direction DR1 of the foil body 8, but they may be inclined with respect to the short direction DR1.

[0106] Figure 12 is a plan view of the electrode foil 1D according to Embodiments 1-4. As shown in Figure 12, the direction in which the multiple grooves 4 extend is inclined at an angle of several degrees with respect to the short direction DR1. In other words, the phrase "the grooves 4 are aligned with the short direction DR1 of the foil body 8" as used in this disclosure may include a state in which the longitudinal direction of the linear grooves 4 is perfectly parallel to the short direction DR1 of the foil body 8, and a state in which the longitudinal direction of the grooves 4 is inclined at an angle of several degrees with respect to the short direction DR1. Here, an inclination at an angle of several degrees means, for example, an inclination at an angle of plus or minus 10 degrees or less. The electrode foil 1D according to Embodiments 1-4 can also be made to have the same effects as in the above embodiments.

[0107] Furthermore, the phrase "the linear groove 4 extends along the short-side direction DR1 of the foil 8" as used in this disclosure may include both a state in which the linear groove 4 extends continuously along the short-side direction DR1 of the foil 8 and a state in which the linear groove 4 is partially interrupted along the short-side direction DR1 of the foil 8. The partially interrupted portion of the linear groove 4 may be referred to as the gap between the grooves 4. The gap between the grooves 4 is permitted to be within 10% of the total length of the longitudinal direction (the direction of DR1 in Figure 12, etc.). In other words, the same effects as in the above embodiments can be obtained even with the electrode foil 1D according to Examples 1-4.

[0108] (4.5) Example 1-5 In the electrode foil 1 of the above embodiment, as shown in Figure 3, the plurality of grooves 4 extend parallel to the short direction DR1 of the foil body 8, but may also include a plurality of inclined portions with respect to the short direction DR1.

[0109] Figure 13 is a plan view of the electrode foil 1E according to Embodiments 1-5. As shown in Figure 13, each of the multiple grooves 4 is V-shaped in plan view in the short-side direction DR1 of the foil body 8. That is, the linear groove 4 is composed of a linear first part and a linear second part. The first part is inclined at an angle of several degrees with respect to the short-side direction DR1 of the foil body 8. The second part is inclined at an angle of several degrees with respect to the short-side direction DR1 of the foil body 8. Here, the state of being inclined at an angle of several degrees includes, for example, a state of being inclined at an angle of within plus or minus 10 degrees. The first part and the second part are connected at the central part of the groove 4. The electrode foil 1E according to Embodiments 1-5 can also be obtained in the same way as in the above embodiments.

[0110] (4.6) Example 1-6 In the electrode foil 1 of the above embodiment, as shown in Figure 3, a plurality of grooves 4 extending linearly along the short direction DR1 of the foil body 8 are formed in the longitudinal direction DR2 of the foil body 8 at predetermined intervals. However, a plurality of grooves intersecting in a direction perpendicular to the plurality of grooves 4 may be further formed.

[0111] Figure 14 is a plan view of the electrode foil 1F according to Embodiments 1-6. As shown in Figure 14, the groove 4 of the electrode foil 1F is a first groove 41, and the electrode foil 1F is further provided with a second groove 42. More specifically, the plurality of second grooves 42 extend linearly along the longitudinal direction DR2 of the foil body 8. The plurality of second grooves 42 are formed in the short direction DR1 of the foil body 8 at predetermined intervals. The plurality of second grooves 42 are formed intersecting the plurality of first grooves 41 in a direction perpendicular to it (DR2 in the figure).

[0112] The electrode foil 1F of Examples 1-6 can enhance the effect of suppressing the propagation of cracks that may occur due to stress compared to the electrode foil 1 of the above embodiment. This makes it possible to further improve the durability of the electrode foil 1F.

[0113] (4.7) Example 1-7 In the manufacturing method of the electrode foil 1 of the above embodiment, in the fourth step, the dense layer 5 is formed by selectively melting the surface of the foil body 8 by laser processing. Alternatively, the dense layer 5 may be formed by selectively melting the surface of the foil body 8 by one of the following methods: resistance heating, arc heating, plasma heating, and gas flame heating.

[0114] The dense layer 5 may also be formed by methods other than melting. For example, the grooves 4 and the dense layer 5 may be formed by compressing the porous layer 2 from above along the short direction DR1 of the foil body 8 using an elongated jig.

[0115] Furthermore, in the manufacturing method of the electrode foil 1 according to the above embodiment, the formation of the grooves 4 and the dense layer 5 is performed in the final fourth step. However, the formation of the grooves 4 and the dense layer 5 may be performed in separate steps. That is, the manufacturing method of the electrode foil 1 may include a fourth step for forming the grooves 4 and a fifth step for forming the dense layer 5. In the fourth step for forming the grooves 4, grooves 4 extending linearly along the short direction of the surface of the foil body 8 are formed by cutting. Specifically, the grooves 4 are formed by machining or laser. Note that the laser used here is a pulsed laser, unlike the continuous-wave laser used in the manufacturing method of the electrode foil 1 according to the above embodiment. This reduces the amount of molten material in the foil body 8, making it easier to form only the grooves 4. Subsequently, in the fifth step for forming the dense layer 5, a dense layer 5 containing at least one of valve-acting metal 51 and valve-acting metal oxide 52 is formed on the surface of the grooves 4 by vapor deposition or plating.

[0116] In the manufacturing method of the electrode foil 1 of the above embodiment, the electrode foil 1 is manufactured by carrying out each step in the order of the first, second, third, and fourth steps, but the order of the fourth and third steps may be reversed. That is, after etching is performed on the surface of the foil body 8, grooves 4 extending along the short direction DR1 are formed on the surface of the foil body 8 by laser processing, and a dense layer 5 is formed on the surface of the grooves 4. Finally, a chemical conversion treatment is performed on the surface of the foil body 8 (including the dense layer 5). In this case, the dielectric can be formed not only on the surface of the metal roughened by the etching treatment, but also on the surface of the metal forming the dense layer 5.

[0117] (5) Modified Examples In the above embodiment, the electrolytic capacitor 100 is a wound-type solid electrolytic capacitor in which the electrolyte is solid and a dielectric layer is formed on the electrode foil 1 which is the anode foil. In contrast, it may also be a non-solid electrolytic capacitor in which the electrolyte is liquid and a dielectric layer is formed on the electrode foil 1 which is the anode foil. Alternatively, it may be a hybrid electrolytic capacitor that has both liquid and solid electrolytes. It may also be a bipolar electrolytic capacitor in which dielectric layers are formed on both the electrode foil 1 which is the anode foil and the cathode foil.

[0118] In the above embodiment, the electrode foil 1, which is the anode foil, is applied to a wound-type electrolytic capacitor, but it may also be applied to a multilayer electrolytic capacitor or other forms. In other words, in the above embodiment, the electrolytic capacitor 100 is a wound-type electrolytic capacitor, but it may also be a multilayer electrolytic capacitor.

[0119] (Summary) Based on the embodiments described above, the following embodiments are disclosed.

[0120] The electrode foil (1, 1A to 1F) of the first embodiment is an electrode foil for an electrolytic capacitor. The electrode foil (1, 1A to 1F) comprises a foil body (8), a porous layer (2), grooves (4), and a dense layer (5). The foil body (8) is strip-shaped and contains a valve-acting metal. The porous layer (2) is provided on the surface of the foil body (8). The grooves (4) are provided in the porous layer (2) and extend linearly along the short direction (DR1) of the surface of the foil body (8). The dense layer (5) is provided on the surface of the grooves (4) and contains at least one of a valve-acting metal (51) and a valve-acting metal oxide (52).

[0121] According to this embodiment, since a dense layer (5) is provided in the groove (4) of the electrode foil (1, 1A to 1F), the stress caused by bending and twisting of the electrode foil (1, 1A to 1F) is relieved, suppressing the occurrence or propagation of cracks, and improving the bending strength of the electrode foil (1, 1A to 1F) itself. As a result, the durability of the electrode foil (1, 1A to 1F) can be improved. Ultimately, a highly reliable electrolytic capacitor (100) can be provided.

[0122] In the second embodiment, the electrode foils (1, 1A to 1F) have, in the first embodiment, a groove (4) depth (L1) that is 30% or more and 80% or less of the thickness (d1) of the porous layer (2).

[0123] According to this embodiment, by setting the depth of the groove (4) within the above range, the bending strength of the electrode foil (1, 1A to 1F) can be further improved.

[0124] In the third embodiment, the electrode foils (1, 1A to 1F) have a maximum thickness (L2) of the dense layer (5) that is 5% or more and 20% or less of the thickness (d1) of the porous layer (2), in the first or second embodiment.

[0125] According to this embodiment, by setting the maximum thickness (L2) of the dense layer (5) within the above range, the bending strength of the electrode foils (1, 1A to 1F) can be further improved.

[0126] In the fourth embodiment, the electrode foil (1, 1A to 1F) has a groove width (L3) of 4 that is 75% or more and 100% or less of the thickness (d1) of the porous layer (2) in any one of the first to third embodiments.

[0127] According to this embodiment, by setting the width (L3) of the groove (4) within the above range, the bending strength of the electrode foil (1, 1A to 1F) can be further improved.

[0128] In the fifth embodiment, the electrode foils (1, 1A to 1F) are such that, in any one of the first to fourth embodiments, the distance (L4) from at least one end of the foil body (8) in the short direction (DR1) to the groove (4) is 20% or less of the dimension of the foil body (8) in the short direction (DR1).

[0129] According to this embodiment, by setting the distance (L4) from the edge of the electrode foil (1, 1A to 1F) within the above range, the bending strength of the electrode foil (1, 1A to 1F) can be further improved.

[0130] In the sixth embodiment, the electrode foil (1, 1A to 1F) is provided with a plurality of grooves (4) in any one of the first to fifth embodiments. The plurality of grooves (4) are arranged in the longitudinal direction (DR2) of the foil (8). The distance (L4) between the centers of two adjacent grooves (4) in the longitudinal direction (DR2) is 270% or less of the thickness (d1) of the porous layer (2).

[0131] According to this embodiment, by setting the distance (L4) between the centers of two adjacent grooves (4) within the above range, the bending strength of the electrode foils (1, 1A to 1F) can be further improved.

[0132] In the seventh embodiment, the electrode foil (1, 1A to 1F) is such that, in any one of the first to sixth embodiments, the valve metal (51) contains 98% by weight or more of aluminum.

[0133] According to this embodiment, by using aluminum for the electrode foil (1, 1A to 1F), the surface area can be increased by etching. Furthermore, aluminum oxide formed by chemical conversion treatment (anodic oxidation) can be used as the dielectric layer. Aluminum oxide has high breakdown voltage, allowing for a reduction in its effective thickness. This makes it easier to increase the capacitance of the electrode foil (1, 1A to 1F).

[0134] The electrode foil (1, 1A to 1F) of the eighth embodiment is such that, in any one of the first to seventh embodiments, the dense layer (5) includes at least one of aluminum and aluminum oxide.

[0135] According to this embodiment, by including highly ductile aluminum in the dense layer (5), the stress on the electrode foils (1, 1A to 1F) against bending and twisting is made easier to relieve. Furthermore, by including highly hard aluminum oxide in the dense layer (5), the bending strength of the electrode foils (1, 1A to 1F) can be improved.

[0136] In the ninth embodiment, the electrode foil (1, 1A to 1F) is such that in any one of the first to eighth embodiments, the groove (4) is a first groove (41). The foil body (8) is further provided with a second groove (42). The second groove (42) extends linearly along the longitudinal direction (DR2) of the foil body (8).

[0137] According to this embodiment, the bending strength of the electrode foils (1, 1A to 1F) can be further improved.

[0138] The configurations relating to the second to ninth aspects are not essential to the electrode foils (1, 1A to 1F) and can be omitted as appropriate.

[0139] The electrolytic capacitor (100) of the tenth embodiment comprises a capacitor element (10). The capacitor element (10) has an anode foil which is an electrode foil (1, 1A to 1F) of any one embodiment of the first to ninth embodiments, and a cathode foil (22).

[0140] According to this embodiment, a highly durable electrode foil (1, 1A to 1F) can be used as the anode foil of the capacitor element (10), thereby providing a highly reliable electrolytic capacitor (100).

[0141] A method for manufacturing electrode foils (1, 1A to 1F) according to the eleventh embodiment includes a first step, a second step, a third step, and a fourth step. In the first step, a strip-shaped foil body (8) containing a valve metal (51) is prepared. In the second step, the surface of the foil body (8) is etched. In the third step, the surface of the etched foil body (8) is chemically converted. In the fourth step, grooves (4) are formed and a dense layer (5) is formed on the surface of the grooves (4). The grooves (4) extend linearly along the short direction (DR1) of the surface of the foil body (8). The dense layer (5) contains at least one of the valve metal (51) and a valve metal oxide (52).

[0142] According to this embodiment, by forming a dense layer (5) in the groove (4) of the electrode foil (1, 1A to 1F), stress caused by bending and twisting of the electrode foil (1, 1A to 1F) can be relieved, and the bending strength of the electrode foil (1, 1A to 1F) itself can be improved. As a result, the durability of the electrode foil (1, 1A to 1F) can be improved.

[0143] The method for manufacturing electrode foils (1, 1A to 1F) according to the twelfth embodiment is as follows: In the eleventh embodiment, in the fourth step, a dense layer (5) is formed by selectively melting the surface of the foil body (8).

[0144] According to this embodiment, grooves (4) and a dense layer (5) can be selectively formed on the surface of the foil body (8) by melting, so the dimensions such as the amount, width, and length of the dense layer (5) can be controlled. The bending strength of the electrode foils (1, 1A to 1F) can be improved.

[0145] The manufacturing method for electrode foils (1, 1A to 1F) according to the 13th embodiment is as follows: In the 11th or 12th embodiment, in the fourth step, a dense layer (5) is formed by selectively melting the surface of the foil body (8) by laser processing.

[0146] According to this embodiment, since grooves (4) and dense layers (5) can be formed simultaneously by laser processing, the dimensions of the dense layer (5), such as the amount, width, and length, can be controlled more precisely. The bending strength of the electrode foils (1, 1A to 1F) can be improved.

[0147] The configurations relating to the 12th or 13th embodiment are not essential to the manufacturing method of the electrode foil (1, 1A to 1F) and can be omitted as appropriate.

[0148] 1 Electrode foil (anodic foil) 2 Porous layer 3 Core 4 Groove 5 Dense layer 8 Foil body 10 Capacitor element 11 Case 12 Sealing member 13 Base plate 14 Electrode terminal 15 Lead tab 22 Cathode foil 23 Separator 41 First groove 42 Second groove 51 Aluminum (valve metal) 52 Aluminum oxide (valve metal oxide) 100 Electrolytic capacitor L1 Depth of groove L2 Maximum thickness of dense layer L3 Width of groove L4 Distance from edge of electrode foil to groove L5 Distance between centers of grooves d1 Thickness of porous layer W1 Width dimension of electrode foil D1 Thickness of electrode foil DR1 Width direction of foil body (short side) DR2 Transport direction of foil body (long side) CK1 Crack

Claims

1. An electrode foil comprising: a strip-shaped foil containing a valve-acting metal; a porous layer provided on the surface of the foil; grooves provided in the porous layer and extending linearly along the short-side direction of the surface of the foil; and a dense layer provided on the surface of the grooves containing at least one of the valve-acting metal and a valve-acting metal oxide.

2. The electrode foil according to claim 1, wherein the depth of the groove is 30% or more and 80% or less of the thickness of the porous layer.

3. The electrode foil according to claim 1, wherein the maximum thickness of the dense layer is 5% or more and 20% or less of the thickness of the porous layer.

4. The electrode foil according to claim 1, wherein the width of the groove is 75% or more and 100% or less of the thickness of the porous layer.

5. The electrode foil according to claim 1, wherein the distance from at least one end of the foil body in the short direction to the groove is 20% or less of the dimension of the foil body in the short direction.

6. The electrode foil according to claim 1, wherein the foil body is provided with a plurality of grooves, the plurality of grooves are arranged in the longitudinal direction of the foil body, and the distance between the centers of two adjacent grooves in the longitudinal direction is 270% or less of the thickness of the porous layer.

7. The electrode foil according to claim 1, wherein the valve-acting metal contains 98% by weight or more of aluminum.

8. The electrode foil according to claim 1, wherein the dense layer comprises at least one of aluminum and aluminum oxide.

9. The electrode foil according to claim 1, wherein the front groove is a first groove, and the foil body is further provided with a second groove that extends linearly along the longitudinal direction of the foil body.

10. An electrolytic capacitor comprising a capacitor element having an anode foil which is an electrode foil according to any one of claims 1 to 9, and a cathode foil.

11. A method for manufacturing an electrode foil, comprising: a first step of preparing a strip-shaped foil containing a valve-acting metal; a second step of etching the surface of the foil; a third step of chemically converting the etched surface of the foil; and a fourth step of forming linear grooves along the short-side direction of the surface of the foil, and forming a dense layer on the surface of the grooves containing at least one of the valve-acting metal and a valve-acting metal oxide.

12. The method for manufacturing an electrode foil according to claim 11, wherein in the fourth step, the dense layer is formed by selectively melting the surface of the foil body.

13. The method for manufacturing an electrode foil according to claim 11 or 12, wherein in the fourth step, the dense layer is formed by selectively melting the surface of the foil body by laser processing.

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