Metal foil

Abstract

A metal foil having a first surface and a second surface located opposite thereto, a core portion made of a metal material, and a clad portion located on at least one surface of the core portion and made of zinc as a base material, wherein when both surfaces of the metal foil are subjected to X-ray diffraction measurement, the peak intensity S of a peak derived from the (101) plane of zinc is greater than or equal to 100 nm on both surfaces. (101) The peak intensity S of the peak originating from the (002) plane of zinc (002) The intensity ratio is 1.01 or more.

Description

[Technical field]

[0001] The present invention relates to a metal foil having a core made of a metallic material and a clad made of zinc. [Background technology]

[0002] Conventionally, metal foils containing zinc have been used as negative electrode active materials for batteries. For example, the present applicant previously proposed a zinc foil containing bismuth, the balance being zinc and unavoidable impurities, and having an average size of zinc crystal grains of 0.2 μm to 8 μm, and a primary battery negative electrode active material using the same (see Patent Document 1). When the zinc foil is used as a negative electrode active material for a battery, the amount of gas generated during long-term storage of the battery is advantageously suppressed compared to the case of using a conventional rolled zinc foil.

[0003] In recent years, secondary batteries that use zinc as the negative electrode active material, such as air-zinc secondary batteries and manganese-zinc secondary batteries, have been attracting attention. Taking advantage of the economical and safe properties of zinc, these secondary batteries are expected to be used in mobile devices, drones, and other devices as large-capacity next-generation storage batteries. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US2022 / 0037654A1 Summary of the Invention

[0005] When zinc foil is used as the negative electrode active material of a secondary battery, shape stability is required during long-term storage. However, the inventors have found through their investigations that conventional zinc foils may warp or stretch when stored for a long period of time, and that there is room for improvement in terms of shape stability.

[0006] An object of the present invention is to provide a technique capable of solving the problems associated with the above-mentioned conventional techniques.

[0007] As a result of extensive research, the inventors have discovered that the above-mentioned problems can be solved by combining a core made of a metal material with a cladding made of zinc as a base material, thereby creating a metal foil having a specific zinc crystal orientation on both sides. The present invention is based on the above findings, and provides a core portion having a first surface and a second surface opposite thereto, the core portion being made of a metal material; A metal foil having a clad portion located on at least one surface of the core portion and having a zinc base material, When both sides of the metal foil were subjected to X-ray diffraction measurement, the peak intensity S (101) The peak intensity S of the peak originating from the (002) plane of zinc (002) The intensity ratio (hereinafter referred to as "S (002) / S (101) ") is 1.01 or more. [Brief description of the drawings]

[0008] [Figure 1] Figure 1 is a screenshot of the software used to determine zinc grain size. [Diagram 2] FIG. 2 is a schematic diagram showing the inter-electrode area used for calculating the circulation speed of the electrolyte. [Diagram 3] 3 is a schematic diagram for explaining the dimensions of the metal foil, where (1) is a perspective view of the metal foil and (2) is a view of the metal foil as seen from the side. [Figure 4] FIG. 4 shows the results of X-ray diffraction measurement of the metal foils of Examples 1 to 4. [Diagram 5] FIG. 5 shows the results of X-ray diffraction measurement of the metal foils of Comparative Examples 1 to 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Preferred embodiments of the present invention will now be described. The metal foil of this embodiment has a core portion and a clad portion located on at least one surface of the core portion. In this embodiment, the metal foil is obtained by electrolytic zinc plating. The core portion corresponds to a substrate placed as a cathode in an electrolytic solution containing zinc ions in electrolytic plating, and the clad portion corresponds to an electrolytic layer having zinc as a base material deposited on the substrate. The core portion and the clad portion will be further described below.

[0010] In this embodiment, the core part has a first surface and a second surface located opposite thereto. The first surface and the second surface are preferably parallel to each other. The core part of this embodiment has a foil form, similar to the metal foil. This foil has a thickness direction perpendicular to the first surface and the second surface. Thus, the shape of the core part of this embodiment having the first surface and the second surface located opposite thereto may be a thin and flat shape. The shape of the core part may be called a film, a sheet, or a layer. The center position in the thickness direction of the metal foil of this embodiment may be located in the core part or in the clad part.

[0011] The core part is made of a metal material. The metal material has a metal as a base material. In terms of the stability of dimensions and shape during long-term storage as a substrate, ease of availability, etc., examples of base metals constituting the core part include copper, zinc, aluminum, etc., and in terms of ease of forming the clad part, adhesion with the clad part, and prevention of passivation, at least one selected from copper and zinc is particularly preferred. For this reason, it is particularly preferred that the core part is at least one selected from copper foil and zinc foil.

[0012] The term "base metal" means that the metal occupies a content of 80% by mass or more. The content of the metal in the core part may be 90% by mass or more, 95% by mass or more, 99% by mass or more, or 99.5% by mass or more. In particular, when the metal is at least one selected from copper and zinc, the content is preferably equal to or more than the lower limit. Therefore, when the base metal constituting the core part is copper, the content of copper in the core part may be 90% by mass or more, 95% by mass or more, 99% by mass or more, or 99.5% by mass or more. When the base metal constituting the core part is zinc, the content of zinc constituting the core part may be 90% by mass or more, 95% by mass or more, 99% by mass or more, or 99.5% by mass or more.

[0013] The metal foil of this embodiment has a predetermined peak intensity ratio derived from zinc on both sides when measured by X-ray diffraction. That is, zinc is present on both sides of the metal foil. Therefore, when the core part of the metal foil is made of a metal other than zinc as a base material, clad parts having zinc as a base material are formed on both sides of the core part. On the other hand, when the core part of the metal foil is made of zinc as a base material, zinc is present on the surface of the core part itself, so that when one side of the surface of the core part satisfies the above-mentioned peak intensity ratio, the clad part may be formed on only one side of the surface of the core part, or may be formed on both sides.

[0014] A metal foil having a copper foil core is preferred not only for its shape stability after long-term storage, but also for its ability to reduce manufacturing costs. The copper foil may be either an electrolytic copper foil or a rolled copper foil. When the core is copper foil, clad portions made of zinc as a base material are formed on both sides of the copper foil. The clad portions formed on both sides of the copper foil each have a peak intensity S (101) The peak intensity S of the peak originating from the (002) plane of zinc (002) Intensity ratio S (002) / S (101)is 1.01 or more. In this specification, the "electrode surface" of the electrolytic foil refers to the surface that was in contact with the cathode when the electrolytic foil (e.g., electrolytic copper foil) was produced. In addition, in this specification, the "deposition surface" of the electrolytic foil refers to the surface on which the electrolytic metal (e.g., electrolytic copper) is deposited when the electrolytic foil is produced, that is, the surface that is not in contact with the cathode.

[0015] When the core portion is a copper foil, it is preferable that the core portion is made of copper, an additive element, and unavoidable impurities, or made of copper and unavoidable impurities.

[0016] When the core portion is a copper foil, the additive element may be at least one selected from the group consisting of tin, zinc, aluminum, iron, nickel, manganese, beryllium, tungsten, titanium, boron, cerium, lanthanum, praseodymium, and neodymium.

[0017] In the case where the core part is a copper foil, examples of the inevitable impurities include sulfur, phosphorus, and oxygen. The amount of each of the above-mentioned inevitable impurities is preferably 100 ppm or less, more preferably 10 ppm or less, by mass in the core part. The content of each of the above-mentioned various additive elements may be equal to or less than the upper limit of the preferable upper limit of these inevitable impurities. That is, each of the metals selected from the group consisting of tin, zinc, aluminum, iron, nickel, manganese, beryllium, tungsten, titanium, boron, cerium, lanthanum, praseodymium, and neodymium may be 100 ppm or less, or 10 ppm or less, by mass in the core part. The amounts of each additive element and inevitable impurities described in this specification can be used independently. For example, the amounts of each of the 14 elements from tin to neodymium can be used alone or in any combination.

[0018] When the core part is a zinc foil, it is preferable because it is particularly suitable for a secondary battery. The zinc foil may be either an electrolytic zinc foil or a rolled zinc foil. When the zinc foil is an electrolytic zinc foil, a clad part is formed on at least the electrode surface of the electrode surface and the deposition surface of the electrolytic zinc foil, so that when both surfaces of the metal foil are subjected to X-ray diffraction measurement, S is formed on both surfaces. (002) / S (101) It is preferable that the elongation ratio is 1.01 or more, since the metal foil can be easily obtained. In addition, when the core is made of rolled zinc foil, the clad is formed on both sides of the core when both sides of the metal foil are subjected to X-ray diffraction analysis and found to have S (002) / S (101) It is preferable that the elongation ratio is 1.01 or more, since the metal foil can be easily obtained.

[0019] When the core portion is a zinc foil, it is preferable that the core portion is made of zinc, an additive element, and unavoidable impurities, or made of zinc and unavoidable impurities.

[0020] When the core portion is a zinc foil, the additive element may be at least one selected from the group consisting of bismuth, indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese.

[0021] Examples of the inevitable impurities when the core part is a zinc foil include iron, copper, lead, cadmium, nickel, chromium, sodium, and potassium. When the core part is a zinc foil, the amount of the inevitable impurities described above is preferably 100 ppm or less, more preferably 10 ppm or less, for each of them alone in the core part. The content of the various additive elements listed above may be equal to or less than the upper limit of the preferable upper limit of these inevitable impurities. That is, the metals selected from the group consisting of bismuth, indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese described above may be 100 ppm or less, or 10 ppm or less, for each of them alone, on a mass basis, in the core part.

[0022] The content ratios of copper, zinc, each of the above-mentioned additive elements, and each of the unavoidable impurities in the core part are measured by sampling the core part from the zinc foil and subjecting it to ICP emission spectrometry. After dissolving the sample in an acidic solution such as nitric acid or hydrochloric acid, the concentration of the contained metals other than zinc is measured by ICP emission spectrometry, and the content ratios of each metal element are converted into mass with the solution concentration of all metals being 1. As a method for sampling the core part, the position of the core part is confirmed by observation with a scanning electron microscope described later, and if the clad part is located only on one side of the core part, the surface on the core part side may be scraped off with a cutter, file, etc., and sampled. Also, if the clad part is located on both sides of the core part, the clad part may be removed using a cutter, file, etc., to obtain a sample consisting of the core part.

[0023] From the viewpoint of achieving excellent stability of shape and size, the thickness Wr of the core portion is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. From the viewpoint of flexibility, the thickness Wr of the core portion is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. From these viewpoints, the range of the thickness Wr of the core portion is preferably 5 μm or more and 300 μm or less, more preferably 10 μm or more and 200 μm or less, and even more preferably 15 μm or more and 150 μm or less.

[0024] When the core part is a copper foil, the average size of the copper crystal grains in the core part is preferably 5 μm or more from the viewpoint of making the zinc foil excellent in elongation and improving flexibility during repeated use, more preferably 10 μm or more, and even more preferably 100 μm or less. The average size of the zinc crystal grains in the cladding part is preferably 80 μm or less, more preferably 60 μm or less, and even more preferably 40 μm or less, from the viewpoint of making the advantage of reducing the amount of gas generated more prominent.

[0025] When the core part is a zinc foil, the average size of the zinc crystal grains in the core part is preferably 24 μm or more from the viewpoint of making the zinc foil excellent in elongation and improving the flexibility of repeated use, more preferably 35 μm or more, and even more preferably 100 μm or less. The average size of the zinc crystal grains in the cladding part is preferably less than 100 μm, more preferably 50 μm or less, and even more preferably 10 μm or less, from the viewpoint of making the advantage of reducing the amount of gas generated more prominent.

[0026] The core part may or may not contain bismuth. The core part being substantially free of bismuth preferably means that the bismuth content of the core part is 90 ppm by mass or less.

[0027] The cladding portion is located on at least one surface of the core portion. The cladding portion may be formed on only one surface of the core portion or on both surfaces, but it is preferable that the cladding portion is formed on both surfaces of the core portion, since this provides excellent shape stability during long-term storage. In this embodiment, the cladding portion is a layer laminated with the core portion. In this embodiment, the cladding portion is formed so as to be in direct contact with the core portion. On the surface of the core portion where the cladding portion is located, the cladding portion may cover the entire surface of the core portion or may cover only a part of the surface.

[0028] The cladding portion is made of zinc as a base material. The meaning of "made of zinc as a base material" is the same as that of the core portion. The zinc content in the cladding portion may be 90 mass% or more, 95 mass% or more, 99 mass% or more, or 99.5 mass% or more.

[0029] The cladding portion may contain bismuth or may not contain bismuth. For example, the composition of the cladding portion may be composed of zinc, bismuth, an additive element other than bismuth and inevitable impurities, zinc, bismuth and inevitable impurities, zinc, an additive element other than bismuth and inevitable impurities, or zinc and inevitable impurities. The cladding portion may be an alloy or may not be an alloy.

[0030] When the clad portion contains an additive element other than bismuth, it is advantageous to use one having a hydrogen overvoltage higher than that of zinc or a redox potential higher than that of zinc. Such metal elements include at least one selected from the group consisting of indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese. The amount of the additive element described above is preferably 10000 ppm or less, more preferably 8000 ppm or less, based on the total ratio of indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese in the clad portion. In addition, when the clad portion contains an additive element selected from indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese, the total amount is preferably 10 ppm or more based on the mass.

[0031] Examples of the inevitable impurities in the cladding include iron, copper, aluminum, lead, cadmium, nickel, chromium, sodium, and potassium. The above-mentioned inevitable impurities are preferably 100 ppm or less, more preferably 10 ppm or less, based on the total mass ratio of iron, copper, aluminum, lead, cadmium, nickel, chromium, sodium, and potassium in the cladding. There are also cases where magnesium and calcium are inevitable impurities. In this case, the total of iron, copper, aluminum, lead, cadmium, nickel, chromium, sodium, potassium, magnesium, and calcium is preferably 100 ppm or less, more preferably 10 ppm or less.

[0032] When the clad portion contains bismuth, gas generation during storage of the battery is effectively suppressed. When the clad portion contains bismuth, the content ratio of bismuth in the clad portion is preferably 100 ppm or more by mass, more preferably 300 ppm or more, and even more preferably 400 ppm or more. In addition, the content ratio of bismuth in the clad portion is preferably 10000 ppm or less by mass, since this has the advantage of uniform dispersion in the clad portion, more preferably 3000 ppm or less, and even more preferably 1200 ppm or less. On the other hand, from the viewpoint of further improving the shape stability of the metal foil of this embodiment, it is preferable that the clad portion does not substantially contain bismuth. When the clad portion does not substantially contain bismuth, it is preferable that the content ratio of bismuth in the clad portion is 90 ppm or less. When the cladding portion contains bismuth, the amount of deformation over time is likely to be large; however, in the present invention, even in such a case, the amount of deformation over time can be reduced, which is preferable in that it reduces the amount of deformation over time while obtaining the effect of reducing the amount of gas due to the bismuth content. Moreover, it is preferable that the cladding does not contain bismuth, since the amount of deformation over time can be further reduced.

[0033] The content ratio of zinc, each of the additive elements listed above, and each of the inevitable impurities listed above in the clad part is measured by sampling the clad part from the zinc foil and subjecting it to ICP optical emission spectroscopy. The method of subjecting the sample to ICP optical emission spectroscopy is the same as that of the core part. The clad part can be sampled by confirming the position of the clad part by observation with a scanning electron microscope described later, and then scraping off the surface of the zinc foil where the clad part is exposed with a cutter, file, etc., and sampling it.

[0034] The average size of the zinc crystal grains in the cladding is preferably 2 μm or more in order to keep the zinc foil in a dense state, more preferably 20 μm or more, and even more preferably 50 μm or less. The average size of the zinc crystal grains in the cladding is preferably less than 100 μm in order to make the advantage of reducing the amount of gas generated more prominent, more preferably 80 μm or less, and even more preferably 50 μm or less. In order to produce crystal grains of such a size in the cladding, it is suitable to manufacture the cladding by an electrolytic method. When the cladding is formed on both sides of the core, it is sufficient that the average size is satisfied in one of the claddings.

[0035] The average size of zinc crystal grains is measured by the following method. For the measurement, a scanning electron microscope (SUPRA 55VP, manufactured by Carl Zeiss Co., Ltd.) with a center gun type in the thickness direction of the FE zinc foil equipped with an electron backscatter diffraction (hereinafter also referred to as "EBSD") evaluation device (OIM Data Collection Ver. 7.2.0, manufactured by TSL Solutions Co., Ltd.) and an attached EBSD analysis device are used. A sample with a cross section cut out using an ultramicrotome is prepared, and data on the crystal grain size in a cross-sectional view that allows the thickness of the entire sample to be measured is obtained for this sample according to the EBSD method. Specifically, for the crystal grains in the core part, the crystal grains are observed in a field of view of "core part thickness x 200 μm in a direction perpendicular to the thickness direction of the core part" in the core part of the cross section (cross section along the thickness direction) of the entire zinc foil, and the average size of the crystal grains is obtained. For the crystal grains in the clad part, the crystal grains are observed in a field of view of "clad part thickness x 200 μm in a direction perpendicular to the thickness direction of the clad part" in the cross section of the entire zinc foil, and the average size of the crystal grains is obtained.

[0036] Background processing of EBSD measurement data is performed with "Binning" set to 4x4 (160x120) with "Background Subtraction", "Normalize Intensity Histgram", and "Dynamic Background Subtraction" unchecked in "Image Processing" of the EBSD evaluation device. "Gain" and "Exposure" may be appropriately changed so that the image in "Camera" is in a state where no Kikuchi pattern is observed in electron diffraction as shown in Figure 1, and the fps is 30±1. Under these conditions, background information is obtained by "Capture Bkd" with the "Ave" value in "Image Processing Function" set to 10.

[0037] The WD value when measuring the crystal grain size is 15±1 mm. With "Background Subtraction," "Normalize Intensity Histgram," and "Dynamic Background Subtraction" checked in "Image Processing," "Zn" is selected from "Phase" in "Capture Pattern" of the EBSD evaluation device at the observation point, and the WD value is adjusted under the following conditions: the "Fit" value in "Solutions" is within 1.5 and the "CI" value is higher than 0.1.

[0038] The crystal grain size is measured by "Start Scan" on a photograph of the cross section of the sample taken with "Capture SEM" in "Scan." The measured data is used to determine the grain size (average) by selecting "All data" from the "Grain Size Quick Chart" in the analysis menu of the EBSD analysis program (OIM Analysis Ver. 7.3.1, manufactured by TSL Solutions Co., Ltd.). This grain size (average) is the average size of zinc grains in the present invention.

[0039] In this measurement, a misorientation of 15° or more is regarded as a grain boundary. However, since the crystal structure of zinc is a hexagonal close-packed structure, the misorientation at a grain boundary is expressed by the rotation axis and rotation angle, taking into consideration twin grain boundaries, and is not regarded as a grain boundary when the rotation axis is expressed by the following (1) and the rotation angle is 94.8±1° and 57±1°, or when the rotation axis is expressed by the following (2) and the rotation angle is 34.8±1° and 64.3±1°. The conditions of the scanning electron microscope during observation are accelerating voltage: 20 kV, aperture diameter: 60 μm, High Current mode, and sample angle: 70°. The observation magnification, measurement area, and step size may be changed as appropriate depending on the size of the crystal grain.

[0040]

number

[0041] The above is an explanation of how to determine the average crystal grain size of zinc. When measuring the average crystal grain size of copper, in the above explanation of the measurement method, instead of selecting "Zn" from "Phase" in "Capture Pattern" of the EBSD evaluation device at the observation point, select "Cu."

[0042] From the viewpoint of shape stability during long-term storage, the clad portion has a thickness Wd of preferably 5 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more. From the viewpoint of producing a thin battery, the clad portion has a thickness Wd of preferably less than 300 μm, more preferably 250 μm or less, and even more preferably 150 μm or less. From these viewpoints, the clad portion has a thickness Wd of preferably 5 μm or more and less than 300 μm, more preferably 20 μm or more and 250 μm or less, and even more preferably 40 μm or more and 150 μm or less. When clad portions are disposed on both sides of the core portion, the thickness of the clad portion is defined as the average thickness of the clad portions on both sides. When the clad portion is on both sides, it is preferable that the thickness of each clad portion is within the above range. When the clad portion is on both sides, the thickness of each clad portion may be the same or different, but from the viewpoint of suppressing warping of the metal foil, it is preferable that the thickness of the clad portion on both sides is the same. The difference in thickness between the clad portions on both sides is preferably 50 μm or less, more preferably 20 μm or less. The thicknesses of the core and clad portions can be determined by observing a cross section of the metal foil along the thickness direction with a scanning electron microscope (SEM), detecting the interface between the core and clad portions, and measuring the thicknesses of the core and clad portions, respectively. However, the thickness of the cladding portion can also be obtained by using the thickness of the core portion as the raw material when manufacturing the metal foil and subtracting this from the thickness of the metal foil after manufacturing.

[0043] When the thickness of the core portion is Wr and the thickness of the clad portion is Wd, Wd / Wr is preferably 4 or less in terms of ease of production. In particular, Wd / Wr is preferably 0.99 or less in terms of better shape stability effect during long-term storage, more preferably 0.8 or less, and particularly preferably 0.7 or less. From the viewpoint of uniformly forming the clad portion, Wd / Wr is preferably 0.1 or more, more preferably 0.2 or more, and particularly preferably 0.3 or more. From these points of view, Wd / Wr is preferably 0.1 or more and 4.0 or less, more preferably 0.1 or more and 0.99 or less, even more preferably 0.2 or more and 0.8 or less, and particularly preferably 0.3 or more and 0.7 or less.

[0044] In the metal foil of the present invention, when both sides of the metal foil are subjected to X-ray diffraction measurement, a peak derived from the (002) plane of zinc is observed. More specifically, when both sides of the metal foil are subjected to X-ray diffraction measurement, a peak derived from the (002) plane of zinc is observed on both sides. (002) / S (101)In this way, the metal foil of the present invention has a core made of a metal material and has the same zinc orientation on both sides, so that the metal foil has good shape stability even after long-term storage. (002) / S (101) It is also preferable for preventing the generation of dendrites that the ratio is 1.01 or more. Also, S (002) / S (101) In order to facilitate measurement of the above, it is preferable that the metal foil has a zinc-based surface as the outermost layer on both sides thereof.

[0045] When both sides of the metal foil were subjected to X-ray diffraction measurement, (002) / S (101) is more preferably 1.01 or more, and even more preferably 1.10 or more. (002) / S (101) The value of (especially S (101) The upper limit is not limited because the peak intensity ratio may be infinitely large if the intensity of the peak is small. The peak intensity ratio in this specification is the peak height ratio.

[0046] The (002) plane of zinc originates from a hexagonal crystal. (002) / S (101) The metal foil having a Zn content of 0.1 to 1.0% by weight or more can be obtained by forming an electrolytic layer having zinc as a base material on a substrate made of a metal material by electrolytic zinc plating and employing a suitable manufacturing method described later.

[0047] In the metal foil of the present invention, when both sides of the metal foil are subjected to X-ray diffraction measurement, a peak derived from the (101) plane of zinc may or may not be observed. The (101) plane of zinc is derived from a hexagonal crystal.

[0048] The peak originating from the zinc (002) plane on each side of the metal foil is usually observed in the range of 2θ=36.30±0.3°. Also, the peak originating from the zinc (101) plane on each side of the metal foil is usually observed in the range of 2θ=43.24±0.3°. Here, Cu-kα radiation is used as the X-ray source in the X-ray diffraction measurement.

[0049] In X-ray diffraction measurement using Cu-kα radiation as an X-ray source, it is preferred that the peak derived from the zinc (002) plane is the peak of maximum intensity on each surface of the metal foil within the range of 2θ=15 to 120°. In an X-ray diffraction measurement using Cu-kα radiation as an X-ray source, peaks other than the peak derived from the zinc (002) plane and the peak derived from the zinc (101) plane (hereinafter also referred to as "other peaks") may be observed on each surface of the metal foil within the range of 2θ=15 to 120°, but it is preferable that they are not observed in terms of uniform crystal arrangement. When other peaks are observed, the peak intensity ratio of the peak derived from the zinc (002) plane is preferably 0.99 or less, more preferably 0.9 or less.

[0050] The metal foil of the present invention has excellent shape stability even after long-term storage. Specifically, when the metal foil is cut into a size of 190 mm length and 90 mm width, sealed together with argon in an airtight container, and stored under conditions of a temperature of 80° C. and a relative humidity of 50% for 96 hours, the deformation amount obtained by subtracting the dimension before storage from the dimension after storage is preferably 0.5 mm or less in the vertical direction, more preferably 0.3 mm or less, and even more preferably 0.1 mm or less. When the metal foil is stored under the above conditions, the deformation amount obtained by subtracting the dimension before storage from the dimension after storage is preferably 0.5 mm or less in the horizontal direction, more preferably 0.3 mm or less, and even more preferably 0.1 mm or less. Furthermore, the warpage of the metal foil, which is the deformation amount in the height direction, is preferably 5 mm or less, more preferably 4 mm or less, and even more preferably 3 mm or less. The vertical and horizontal directions are parallel to the plane of the metal foil and perpendicular to each other, as shown in Fig. 3(1), for example. The vertical dimension after storage is the maximum length in the vertical direction W of the sample shown in Fig. 3(1) (if the dimension of the vertical direction W of the sample is uniform along the horizontal direction V before storage, it is the length of the part that has stretched the most in the vertical direction W due to storage). The horizontal dimension after storage is also the maximum length in the horizontal direction V (if the dimension of the horizontal direction V of the sample is uniform along the vertical direction W before storage, it is the length of the part that has stretched the most in the horizontal direction V due to storage). The warpage is the amount of deformation at height H when the product is placed on a flat surface, as shown in Fig. 3(2). The amount of deformation is the difference between the height of the highest point relative to the flat surface and the height before storage.

[0051] As shown in the examples described below, each of the parameters of the metal foil described above can be obtained by forming both sides of the metal foil of the present invention with an electrolytic layer using zinc as a base material by an electrolytic plating method, and employing a suitable manufacturing method described below, particularly by selecting appropriate thicknesses for the core and clad parts in the suitable manufacturing method, and adjusting the electrolytic concentration, current density, and immersion time in the electrolyte.

[0052] It is preferable that the core portion is inseparably bonded to the clad portion. The core portion is inseparably bonded to the clad portion when the cross section of the metal foil along the thickness direction is observed with a scanning electron microscope, and one or more crystal grains are observed that straddle the interface between the core portion and the clad portion. Such a shape is caused by the grain growth of the crystal grains in the clad portion so as to align the orientation planes of the crystal grains in the core portion. In detail, in the cross section of the metal foil along the thickness direction of the present embodiment, a row of holes consisting of a plurality of small holes is observed at the interface between the core portion and the clad portion, and the position of the interface can be identified by this row of holes. When the scanning electron microscope image is a backscattered electron image, the color shade of each zinc crystal grain is different in the microscope image, reflecting the difference in the orientation planes of the crystal grains. The shape of the zinc crystal grains can be identified by this difference in shade. When one or more crystal grains that are continuous across the interface between the core portion and the clad portion are observed, it can be determined that the core portion and the clad portion are inseparably bonded, and it is preferable that two or more are observed. The interface between the core and cladding can also be identified by EDS analysis (energy dispersive spectroscopy) to confirm the locations of the metallic elements and additive elements that form the base material. In order to bond the core and clad portions inseparably, the metal foil may be produced by a suitable production method described below.

[0053] The metal foil may not contain aluminum from the viewpoint of reducing passivation in batteries such as secondary batteries. For example, the aluminum content of the metal foil may be 1% or less, 0.1% or less, or 0.05% or less, based on the mass of the metal foil.

[0054] From the viewpoint of reducing the environmental load, it is desirable that the metal foil does not contain lead. The lead content is preferably 200 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less, based on the mass of the metal foil. The metal foil may contain no cadmium or may contain cadmium as an inevitable impurity. It is desirable that the cadmium content in the metal foil is as low as possible. In particular, the cadmium content is desirably 10 ppm or less based on the mass.

[0055] The content ratios of aluminum, lead, and cadmium in the metal foil are measured by ICP atomic emission spectrometry. The same method as above can be used for the measurement by ICP atomic emission spectrometry.

[0056] The metal foil of the present invention is thin, preferably having a thickness of 15 μm to 900 μm, more preferably 25 μm to 500 μm, and even more preferably 30 μm to 300 μm. The thickness of the metal foil is measured by the above-mentioned method. Such a thin metal foil is suitable for use as a negative electrode material for secondary batteries, particularly for stacked secondary batteries such as bipolar batteries. In particular, the metal foil of the present invention has excellent shape stability during long-term storage, making it suitable for secondary batteries, particularly stacked secondary batteries.

[0057] Next, a preferred method for producing the zinc foil of the present invention will be described. This manufacturing method includes a step of using a substrate having a first surface made of a metal material and a second surface opposite the first surface as a cathode, immersing the substrate in an electrolytic solution containing zinc ions at 10 to 90°C for 1 to 10 minutes, and a step of performing electrolytic plating on at least one surface of the substrate after the immersion step, using the electrolytic solution containing zinc ions to form an electrolytic layer containing zinc as a base material.

[0058] However, when at least one surface of the substrate is measured by X-ray diffraction, (002) / S (101) When the ratio is less than 1.01, an electrolytic layer containing zinc as a base material is formed on at least that surface by electrolytic plating. The description of the base material can be the same as that of the core portion described above.

[0059] Examples of the electrolyte containing zinc ions include an aqueous zinc sulfate solution, an aqueous zinc nitrate solution, an aqueous zinc chloride solution, etc. The concentration of zinc contained in the electrolyte is preferably 30 g / L or more and 100 g / L or less, and more preferably 35 g / L or more and 90 g / L or less.

[0060] In addition, when bismuth is contained in the clad portion, the electrolyte may contain bismuth ions in addition to zinc ions. Examples of bismuth ion sources include bismuth nitrate. When using bismuth ions contained in the electrolyte, the concentration is preferably 10 ppm or more and 10000 ppm or less of the mass of bismuth relative to the total mass of zinc and bismuth in the electrolyte from the viewpoint of suppressing gas generation, more preferably 15 ppm or more and 8000 ppm or less, even more preferably 20 ppm or more and 7000 ppm or less, and even more preferably 30 ppm or more and 6500 ppm or less. When the electrolyte does not contain bismuth, the ratio of the mass of bismuth to the mass of zinc in the electrolyte is preferably less than 10 ppm, preferably 6 ppm or less, and even more preferably 3 ppm or less.

[0061] The electrolyte may further contain other compounds. For example, sulfuric acid may be added to adjust the pH of the electrolyte. The pH of the electrolyte may be 2 or less at the time of electrolysis.

[0062] In this manufacturing method, prior to electrolytic plating using an electrolytic solution, the substrate, which is a cathode, is immersed in the electrolytic solution at 10 to 90° C. for 1 to 10 minutes. (002) / S (101)From this viewpoint, the temperature of the electrolytic solution is more preferably 10 to 80°C, and even more preferably 15 to 35°C. The immersion time before electrolytic plating is more preferably 3 to 8 minutes. The inventors believe that the pre-immersion has the effect of smoothing the surface of the electrode (core portion), thereby improving the S of the deposition surface. (002) / S (101) It is believed that it is easy to obtain a metal foil with a refractive index of 1.01 or more.

[0063] In the electrolysis method, an anode and a cathode are immersed in an electrolytic solution containing a zinc source, and an electrolytic layer made of zinc as a base material is deposited on the surface of the cathode as the base material. This is preferred because it is easy to obtain a clad portion with a small average crystal grain size. As the anode used for electrolysis, it is preferred to use a known dimensionally stabilized electrode (DSE). As the DSE, for example, a titanium electrode coated with iridium oxide, a titanium electrode coated with ruthenium oxide, etc. are preferably used. From the viewpoint of successfully obtaining a metal foil with good shape stability, it is advantageous to circulate the electrolyte during electrolysis. In order to circulate the electrolyte, for example, an electrolysis device equipped with a closed flow path, an electrolytic cell arranged in the flow path, and a pump arranged in the flow path may be used, and the pump may be driven to circulate the electrolyte in one direction through the electrolytic cell. The anode and cathode used for electrolysis may be immersed in the electrolytic cell in a state where they face each other. The anode and cathode are preferably placed in the electrolytic cell so that their facing surfaces (electrodeposition surfaces in the case of the cathode) are parallel to the flow direction of the electrolyte.

[0064] When electrolysis is performed while circulating the electrolyte, it is advantageous to adjust the flow rate of the electrolyte, i.e., the circulation rate, from the viewpoint of successfully obtaining zinc foil having the desired effect. In detail, the circulation rate of the electrolyte is adjusted to 0.001 L / (min mm 2 ) or more 1L / (min mm 2 ) or less, and it is preferable to set it to 0.002L / (min mm 2 ) or more than 0.6L / (min mm 2) or less, and it is more preferable to set it to 0.003L / (min mm 2 ) or more 0.4L / (min mm 2 ) or less, and it is more preferable to set it to 0.005 L / (min mm 2 ) or more than 0.04L / (min mm 2 It is even more preferable to set the circulation speed to be equal to or less than 1 / 2 the flow rate of the electrolyte (L / min) relative to the inter-electrode area (mm 2 ) The inter-electrode area is expressed as the product of the inter-electrode distance (mm) and the electrodeposition electrode width (mm), as shown in FIG. 2. In FIG. 2, it is preferable to flow the electrolyte in a direction perpendicular to the paper. In FIG. 2, the plate-shaped electrodes extend in a direction perpendicular to the paper.

[0065] The current density during electrolysis is one of the factors that affect the size of zinc crystal grains in the resulting zinc foil. In detail, by increasing the current density above the conditions for normal zinc electrolysis, a large number of fine crystals can be generated, and thus zinc foil with a small average grain size can be easily obtained. From this perspective, the current density is set to 1000 A / m 2 More than 10000A / m 2 It is preferable to set it to less than 1000A / m 2 More than 6000A / m 2 It is more preferable to set it to 1000 A / m or less. 2 More than 4000A / m 2 It is more preferable to set it as follows:

[0066] The electrolytic solution can be subjected to electrolysis in a non-heated or heated state. When electrolysis is performed in a heated state, the temperature of the electrolytic solution is preferably set to 10°C or higher and 90°C or lower. The temperature of the electrolytic solution is more preferably 20°C or higher and 90°C or lower, even more preferably 30°C or higher and 80°C or lower, and even more preferably 30°C or higher and 70°C or lower. This is continued until the thickness of the zinc foil reaches the desired value.

[0067] The electrolytic plating is preferably a one-time process. For example, when forming an electrolytic layer having zinc as a base material as a cladding portion on both sides of a substrate by electrolytic plating, it is preferable to perform electrolytic plating in a state where both sides of the substrate are in contact with an electrolytic solution, thereby forming an electrolytic layer having zinc as a base material on both sides at once.

[0068] The metal foil of the present invention obtained as described above is suitable for use as a negative electrode active material for secondary batteries. Examples of secondary batteries include nickel-zinc batteries, air-zinc batteries, and manganese-zinc batteries. Furthermore, since the metal foil itself has electrical conductivity, the metal foil also functions as a current collector. This makes it possible to use the metal foil itself as a negative electrode without using a current collector. It can also be used as a negative electrode active material for primary batteries. As shown in the evaluation results of the examples described later, the battery including the metal foil of the present invention can be used as an electrode material with good shape stability even when stored at high temperatures for a long period of time. Therefore, it can be suitably used for secondary batteries.

[0069] The present invention is based on the above findings and provides the following [1] to [8]. [1] A core portion having a first surface and a second surface opposite thereto, and made of a metal material; A metal foil having a clad portion located on at least one surface of the core portion and having a zinc base material, When both sides of the metal foil were subjected to X-ray diffraction measurement, the peak intensity S (101) The peak intensity S of the peak originating from the (002) plane of zinc (002) The metal foil has an intensity ratio of 1.01 or more. [2] The metal foil according to [1], wherein when the metal foil is cut to a size of 190 mm in length and 90 mm in width, sealed in a sealable container together with argon, and stored at a temperature of 80°C and a relative humidity of 50% for 96 hours, the change in dimensions after storage is 0.5 mm or less in the lengthwise direction and 0.5 mm or less in the widthwise direction, and the warpage is 5 mm or less. [3] The metal foil according to [1] or [2], wherein the clad portion is formed on both sides of the core portion. [4] The metal foil according to any one of [1] to [3], wherein the core portion and the clad portion are inseparably bonded to each other. [5] The metal foil according to any one of [1] to [4], wherein the core part is a copper foil or a zinc foil. [6] The core part is made of electrolytic copper foil, rolled copper The metal foil according to any one of [1] to [5], which is a zinc foil, an electrolytic zinc foil, or a rolled zinc foil. [7] The metal foil according to any one of [1] to [5], wherein the thickness of the core portion is 5 μm or more and 300 μm or less. [8] The metal foil according to any one of [1] to [6], wherein the clad portion has a thickness of 5 μm or more and 300 μm or less. [9] In the core portion, the base metal is copper, or the core portion is a rolled zinc foil and the clad portion is formed on both sides of the core portion, or The metal foil according to any one of [1] to [8], wherein the core portion is an electrolytic zinc foil, and the clad portion is formed on at least an electrode surface thereof.

[10] The metal foil according to any one of [1] to [9], wherein the clad portion is substantially free of bismuth.

[11] An electrode material for a secondary battery, comprising the metal foil according to [1] or [2]. EXAMPLES

[0070] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass".

[0071] Example 1 (1) Preparation of the substrate As a substrate, electrolytic copper foil (purity 99.9%, manufactured by Mitsui Mining & Smelting) having the thickness shown in Table 1 was prepared. (2) Preparation of electrolyte Zinc oxide was used as the zinc compound. It was dissolved in water together with sulfuric acid to prepare an electrolyte. The zinc concentration in the electrolyte was 50 g / L. The sulfuric acid concentration was adjusted so that the total amount of sulfate ions was H 2 SO 4 The calculated value was 200 g / L. Bismuth nitrate was added to the electrolytic solution. The concentration of bismuth nitrate was adjusted so that the ratio of bismuth to the total mass of zinc and bismuth was 700 ppm by mass. The above electrolytic copper foil was used as the cathode. The cathode was immersed in the electrolytic solution at 20° C. for 5 minutes.

[0072] (3) Reduction and precipitation of zinc The anode used was a DSE consisting of an iridium oxide coated titanium electrode. A current was passed between the anode and the cathode while the electrolyte was heated to 30°C. The current density was 2000A / m 2 The electrolyte was circulated at a rate of 0.021 L / (min mm 2 ) and circulation was performed. Both sides of the electrolytic copper foil were immersed in the electrolyte to perform electrolysis, and electrolytic zinc layers with electrolytic thicknesses shown in Table 1 were formed on both sides of the electrolytic copper foil, to obtain a copper-zinc composite foil in which the electrolytic zinc layer and the electrolytic copper foil were integrated. In this composite foil, the electrolytic copper foil corresponds to the core, and the electrolytic zinc layer corresponds to the clad. The obtained composite foil was washed with ion-exchanged water and dried with hot air.

[0073] Example 2 Bismuth nitrate was not used in steps (2) and (3) of Example 1. A copper-zinc composite foil was obtained in the same manner as in Example 1 except for these points.

[0074] Example 3 In step (1) of Example 1, the substrate was changed from electrolytic copper foil to rolled zinc foil (purity 99.99%, manufactured by Mitsui Sumitomo Metal Mining Co., Ltd.) having the thickness shown in Table 1. Other than this, a zinc foil was obtained as in Example 1, which was a composite foil in which the rolled zinc foil and the electrolytic zinc layer were integrated.

[0075] Example 4 (1) Manufacturing of electrolytic zinc foil as a base material Zinc oxide was used as the zinc compound. It was dissolved in water together with sulfuric acid to prepare an electrolyte. The zinc concentration in the electrolyte was 50 g / L. The sulfuric acid concentration was adjusted so that the total amount of sulfate ions was H 2 SO 4 The calculated value was 200 g / L. An aluminum plate was used as the cathode. The cathode was immersed in the electrolyte at 30° C. for 5 minutes. The anode used was a DSE consisting of an iridium oxide coated titanium electrode. A current was passed between the anode and the cathode while the electrolyte was heated to 30°C. The current density was 2000A / m 2 The electrolyte was circulated at a rate of 0.021 L / (min mm 2 ) and cycled it. Electrolysis was performed in this state to form an electrolytic zinc layer on one side of the aluminum plate. After electrolysis, the electrolytic zinc layer was peeled off from the cathode aluminum plate to obtain zinc foil. The obtained zinc foil was washed with ion-exchanged water and dried with hot air. (2) Manufacturing of clad parts (2-1) Zinc oxide was used as the zinc compound. This was dissolved in water together with sulfuric acid to prepare an electrolyte. The zinc concentration in the electrolyte was 50 g / L. The sulfuric acid concentration was adjusted so that the total amount of sulfate ions was H 2 SO 4 The converted value was set at 200 g / L. (2-2) In Example 2, the electrolytic zinc foil obtained in (1) was used as the cathode with the deposition surface masked. The electrolytic solution obtained in (2-1) was used as the electrolytic solution. The unmasked electrode surface of the electrolytic zinc foil (the surface on the aluminum plate side in the step (1)) was immersed in the electrolytic solution to perform the immersion process and electrolytic plating. Except for these points, an electrolytic zinc layer having an electrolytic thickness of the value shown in Table 1 was formed on the electrode surface of the electrolytic zinc foil in the same manner as in Example 2. As a result, a zinc foil was obtained that is a composite foil in which the electrolytic zinc layer and the electrolytic zinc foil are integrated.

[0076] Comparative Example 1 This example is an example in which an electrolytic zinc foil similar to that in the example of Patent Document 1 was produced. Zinc oxide was used as the zinc compound. It was dissolved in water together with sulfuric acid to prepare an electrolyte. The zinc concentration in the electrolyte was 50 g / L. The sulfuric acid concentration was adjusted so that the total amount of sulfate ions was H 2 SO 4 The calculated value was 200 g / L. Bismuth nitrate was added to the electrolyte. The concentration of bismuth nitrate was adjusted so that the ratio of bismuth to the total mass of zinc and bismuth was 700 ppm by mass. An aluminum plate was used as the cathode. The cathode was immersed in the electrolyte at 30° C. for 5 minutes. The anode used was a DSE consisting of an iridium oxide coated titanium electrode. A current was passed between the anode and the cathode while the electrolyte was heated to 30°C. The current density was 2000A / m 2 The electrolyte was circulated at a rate of 0.021 L / (min mm 2 ) and cycled it. Electrolysis was performed in this state to form an electrolytic zinc layer on one side of the aluminum plate. After electrolysis, the electrolytic zinc layer was peeled off from the cathode aluminum plate to obtain zinc foil. The obtained zinc foil was washed with ion-exchanged water and dried with hot air.

[0077] Comparative Example 2 In steps (2) and (3) of Example 1, one side of the electrolytic copper foil used as the cathode was masked, and an electrolytic zinc layer was deposited only on one side. Except for this, a copper-zinc composite foil was obtained in the same manner as in Example 1, in which an electrolytic zinc layer was formed on one side of the electrolytic copper foil and the electrolytic copper foil were integrated.

[0078] Comparative Example 3 In steps (2) and (3) of Example 3, one side of the rolled zinc foil used as the cathode was masked, and an electrolytic zinc layer was deposited only on that side. Except for this, a zinc foil was obtained in the same manner as in Example 3, which was a composite foil in which an electrolytic zinc layer was formed on one side of the rolled zinc foil and the electrolytic zinc layer was integrated with the rolled zinc layer.

[0079] The metal foils obtained in the respective Examples and Comparative Examples were subjected to the following measurements and evaluations. The results are shown in Table 1. The amount of bismuth in the clad of these metal foils is also shown in Table 1. The bismuth content in the clad was measured by ICP atomic emission spectrometry for the metal foils obtained in each Example and Comparative Example. Specifically, it was determined as follows. In Example 1 and Comparative Example 2, the metal foil was dissolved in an aqueous nitric acid solution, and the masses of Bi and Zn in the solution were determined, and "mass of Bi / (mass of Zn+mass of Bi)" was calculated. In Example 3 and Comparative Example 3, the metal foil was dissolved in a nitric acid aqueous solution to measure the Bi content in the solution. The zinc mass of the electrolytic solution after electrolytic plating when forming the clad portion was measured by ICP atomic emission spectrometry. The zinc mass of the clad portion was determined by subtracting this mass from the zinc mass of the electrolytic solution before electrolytic plating. From these, "Bi mass / (Zn mass of clad portion+Bi mass)" was calculated. For the metal foil of Comparative Example 1, the metal foil was dissolved in a nitric acid aqueous solution, and the Bi mass and Zn mass in the solution were determined, and "Bi mass / (Zn mass+Bi mass)" was calculated. However, since the metal foil of Comparative Example 1 did not have a clad portion and consisted only of a core portion, Table 1 lists the bismuth amount in the core portion.

[0080] [XRD measurement conditions] An X-ray diffractometer (D8ADVANCE, manufactured by Bruker) was used. The measurement conditions were as follows. Table 1 and FIG. 4 show the results of XRD measurement of both sides of the metal foils obtained in Examples 1 to 4, and Table 1 and FIG. 5 show the results of XRD measurement of both sides of the metal foils obtained in Comparative Examples 1 to 3. The surfaces of the metal foils subjected to XRD measurement are as shown in Table 1 (for the core portion, the electrolytic surface or deposition surface is shown in the case of electrolytic foils, and the rolled surface is shown in the case of rolled foils. Also, the presence or absence of a clad portion is shown). ·Radiation source: Cu-kα radiation Tube voltage: 40kV ·Tube current: 40mA Scan speed: 10.5deg / min Step: 0.015deg Scan range: 2θ=15 degrees to 120 degrees

[0081] [Evaluation (deformation over time)] Each metal foil obtained in the examples and comparative examples was cut to a length of 190 mm and a width of 90 mm, placed on a flat surface, and the length, width, and height dimensions were measured. The metal foil was then placed in an airtight container in which the gas inside had been replaced with argon gas, sealed in an airtight state, and stored under conditions of a temperature of 80°C and a relative humidity of 50% for 96 hours, and each dimension was measured again. The dimensions were measured using a metal ruler. The deformation amount (mm) was calculated by subtracting the dimension before aging from the dimension after aging. The results are shown in Table 1.

[0082] [Table 1]

[0083] As shown in Table 1, in each example, the amount of deformation after aging was suppressed. (002) / S (101) In Comparative Example 1, where the value of S was less than 1.01, the dimensional elongation over time was large. (002) / S (101) The metal foils of Comparative Examples 2 and 3, in which the value was less than 1.01, showed large warpage after long-term storage. [Industrial Applicability]

[0084] According to the present invention, there is provided a zinc-containing metal foil which has excellent shape stability when stored for a long period of time.

Claims

1. a core portion having a first surface and a second surface opposite thereto, the core portion being made of a metal material; A metal foil having a clad portion located on at least one surface of the core portion and having a zinc base material, When both sides of the metal foil were subjected to X-ray diffraction measurement, the peak intensity S （１０１） The peak intensity S of the peak originating from the (002) plane of zinc （００２） is 1.01 or more, The metal foil has a thickness of 5 μm or more and 300 μm or less.

2. For use as an electrode material for a secondary battery, a core portion having a first surface and a second surface opposite thereto, the core portion being made of a metal material; A metal foil having a clad portion located on at least one surface of the core portion and having a zinc base material, When both surfaces of the metal foil are subjected to X-ray diffraction measurement, the intensity ratio of the peak intensity S(002) of the peak originating from the (002) plane of zinc to the peak intensity S(101) of the peak originating from the (101) plane of zinc is 1.01 or more on both surfaces.

3. For use as an electrode material for a secondary battery, a core portion having a first surface and a second surface opposite thereto, the core portion being made of a metal material; A metal foil having a clad portion located on at least one surface of the core portion and having a zinc base material, When both surfaces of the metal foil are subjected to X-ray diffraction measurement, the intensity ratio of the peak intensity S(002) of the peak originating from the zinc (002) plane to the peak intensity S(101) of the peak originating from the zinc (101) plane is 1.01 or more on both surfaces; The metal foil has a thickness of 5 μm or more and 300 μm or less.

4. 4. The metal foil according to claim 1, wherein when the metal foil is cut to a size of 190 mm in length and 90 mm in width and stored under conditions of a temperature of 80° C. and a relative humidity of 50% for 96 hours, the change in dimensions after storage is 0.5 mm or less in the length direction and 0.5 mm or less in the width direction, and the warpage is 5 mm or less.

5. The metal foil according to claim 1 , wherein the clad portion is formed on both sides of the core portion.

6. The metal foil according to claim 1 , wherein the core portion and the clad portion are inseparably bonded to each other.

7. The metal foil according to claim 1 , wherein the core portion is a copper foil or a zinc foil.

8. The metal foil according to claim 1 , wherein the core portion has a thickness of 5 μm or more and 300 μm or less.

9. A core portion having a first surface and a second surface opposite thereto, and made of a metal material; A metal foil having a clad portion located on at least one surface of the core portion and having a zinc base material, An electrode material for a secondary battery comprising a metal foil, wherein when both surfaces of the metal foil are subjected to X-ray diffraction measurement, the intensity ratio of a peak intensity S(002) derived from a zinc (002) plane to a peak intensity S(101) derived from a zinc (101) plane is 1.01 or more on both surfaces.

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