metal foil

Abstract

A metal foil comprising: a core portion having a first surface and a second surface on the opposite side thereof, and formed of a metal material; and a clad portion on at least one surface of the core portion, and using zinc as a base material, wherein, when X-ray diffraction measurement is performed on both surfaces of the metal foil, the intensity ratio of the peak intensity S of a peak derived from a (002) surface of zinc to the peak intensity S of a peak derived from a (101) surface of zinc in either surface is 1.01 or more. (002) (101) The intensity ratio of the peak intensity S of a peak derived from a (002) surface of zinc to the peak intensity S of a peak derived from a (101) surface of zinc in either surface is 1.01 or more.​

Description

Technical Field

[0001] The present invention relates to a metal foil having a core formed of a metallic material and a cladding portion with zinc as the base material. Background Technology

[0002] Previously, zinc-containing metal foils have been used in negative electrode active materials for batteries. For example, the applicant previously proposed a zinc foil and a negative electrode active material for primary batteries using the same, wherein the zinc foil contains bismuth, and the remainder consists of zinc and unavoidable impurities, with the average grain size of the zinc being 0.2 μm or more and 8 μm or less (see Patent Document 1). This zinc foil has the advantage that, when used as a negative electrode active material for a battery, the amount of gas generated during long-term storage of the battery is suppressed compared to the use of conventional rolled zinc foil.

[0003] In recent years, secondary batteries that use zinc as the negative electrode active material, such as air / zinc batteries and manganese / zinc batteries, have attracted much attention. These batteries effectively utilize the economic and safety advantages of zinc and are expected to serve as high-capacity next-generation batteries for use in mobile devices or drones.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: US2022 / 0037654A1 Summary of the Invention

[0007] When using zinc foil as the negative electrode active material in secondary batteries, shape stability during long-term storage is required.

[0008] However, the inventors conducted research and concluded that conventional zinc foil sometimes warped or elongated during long-term storage, indicating room for improvement in shape stability.

[0009] The objective of this invention is to provide a technique that eliminates the problems associated with the aforementioned conventional techniques.

[0010] The inventors conducted in-depth research and found that the above-mentioned problems can be solved by the following metal foil, in which a cladding portion with zinc as the base material is combined with a core portion formed of a metal material, and has a specific crystalline orientation of zinc on both sides.

[0011] Based on the above understanding, the present invention provides a metal foil having:

[0012] The core has a first surface and a second surface located on its opposite side, and is formed of a metallic material; and

[0013] The cladding portion is located on at least one side of the core portion, and zinc is used as the base material.

[0014] Among them, when X-ray diffraction measurements were performed on both sides of the above-mentioned metal foil, the peak intensity S of the peak originating from the (002) plane of zinc in any side was... (002) Peak intensity S relative to the peak from the (101) plane of zinc (101) The strength ratio (hereinafter, also known as "S") (002) / S (101) All of them are above 1.01. Attached Figure Description

[0015] Figure 1 This is a captured image from the software used to determine the size of zinc grains.

[0016] Figure 2 This is a schematic diagram showing the area between electrodes used to calculate the electrolyte circulation rate.

[0017] Figure 3 This is a schematic diagram illustrating the dimensions of the metal foil. (1) is a three-dimensional view of the metal foil, and (2) is a view of the metal foil viewed from the side.

[0018] Figure 4 The results are X-ray diffraction measurements of the metal foils in Examples 1-4.

[0019] Figure 5 The results are X-ray diffraction measurements of the metal foils in Comparative Examples 1 to 3. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below.

[0021] The metal foil of this embodiment has a core and a cladding portion located on at least one surface of the core. In this embodiment, the metal foil is obtained by electrolytic zinc plating. The core corresponds to a substrate disposed in an electrolyte as a cathode in an electrolytic plating process using an electrolyte containing zinc ions, and the cladding portion corresponds to an electrolytic layer deposited on the substrate using zinc as a base material. Hereinafter, the core and the cladding portion will be further described.

[0022] In this embodiment, the core has a first surface and a second surface located on its opposite side. The first surface and the second surface are preferably parallel to each other. The core of this embodiment is in the form of a foil, similar to a metal foil. This foil has a thickness direction in a direction orthogonal to the first and second surfaces. Thus, the shape of the core of this embodiment, having a first surface and a second surface located on its opposite side, can be exemplified by a flat shape that extends thinly. The shape of the core is sometimes referred to as film-like, sheet-like, or layered. The center position in the thickness direction of the metal foil in this embodiment can be located in the core or in the cladding portion.

[0023] The core is formed of a metallic material. The metallic material uses a metal as the base material. Considering factors such as dimensional and shape stability during long-term storage as a substrate, and ease of acquisition, copper, zinc, and aluminum can be listed as base metals constituting the core. Considering factors such as ease of formation of the cladding layer, tightness of adhesion to the cladding layer, and prevention of passivation, at least one selected from copper and zinc is particularly preferred. Therefore, the core is particularly preferably selected from at least one selected from copper foil and zinc foil.

[0024] The term "using metal as the base material" refers to a metal content of 80% or more by mass. The metal content in the core can be 90% or more by mass, 95% or more by mass, 99% or more by mass, or 99.5% or more by mass. Particularly when the metal is selected from at least one of copper and zinc, a content of the lower limit mentioned above is preferred. Therefore, when the base metal constituting the core is copper, the copper content in the core can be 90% or more by mass, 95% or more by mass, 99% or more by mass, or 99.5% or more by mass. Furthermore, when the base metal constituting the core is zinc, the zinc content in the core can be 90% or more by mass, 95% or more by mass, 99% or more by mass, or 99.5% or more by mass.

[0025] The metal foil of this embodiment exhibits a predetermined peak intensity ratio derived from zinc on both sides during X-ray diffraction measurements. That is, zinc is present on the surface of both sides of the metal foil. Therefore, when the core of the metal foil uses a metal other than zinc as the base material, cladding portions using zinc as the base material are formed on both sides of the core. On the other hand, when the core of the metal foil uses zinc as the base material, since zinc is present on the surface of the core itself, if the aforementioned peak intensity ratio is satisfied on one side of the core surface, the cladding portion can be formed on only one side of the core surface, or it can be formed on both sides.

[0026] Besides its shape stability after long-term storage, a metal foil with a copper core is also preferred in terms of reducing manufacturing costs. The copper foil can be either electrolytic copper foil or rolled copper foil. In the case of a copper core, a cladding layer with zinc as the base material is formed on both sides of the copper foil. In this cladding layer formed on both sides of the copper foil, the peak intensity S originating from the (002) plane of zinc is... (002) Peak intensity S relative to the peak from the (101) plane of zinc (101) The strength of S (002) / S (101) All values ​​are 1.01 or higher. It should be noted that, in this specification, the "electrode surface" of the electrolytic foil refers to the side that is in contact with the cathode during the fabrication of the electrolytic foil (e.g., electrolytic copper foil). Furthermore, in this specification, the "deposition surface" of the electrolytic foil refers to the side where the electrolytic metal (e.g., electrolytic copper) gradually deposits during the fabrication of the electrolytic foil, i.e., the side that is not in contact with the cathode.

[0027] When the core is made of copper foil, it is preferably composed of copper, additives and unavoidable impurities or copper and unavoidable impurities.

[0028] When the core is copper foil, the added element can 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.

[0029] Sulfur, phosphorus, and oxygen are examples of unavoidable impurities when the core is made of copper foil. The amount of each of these unavoidable impurities in the core, on a mass basis, is preferably 100 ppm or less, more preferably 10 ppm or less. It should be noted that the content of each of the various added elements listed above can also be in amounts below the same upper limit as the preferred upper limit for these unavoidable impurities. That is, for each metal selected from the group consisting of tin, zinc, aluminum, iron, nickel, manganese, beryllium, tungsten, titanium, boron, cerium, lanthanum, praseodymium, and neodymium, the amount in the core, on a mass basis, can also be 100 ppm or less, or 10 ppm or less.

[0030] The amounts of each added element and unavoidable impurity described in this specification can be used independently. For example, the amounts of the 14 elements from tin to neodymium mentioned above can be used individually or in any combination.

[0031] When the core is zinc foil, it exhibits particularly excellent suitability as a secondary battery, and is therefore preferred. The zinc foil can be either electrolytic zinc foil or rolled zinc foil. When the zinc foil is electrolytic zinc foil, by forming a cladding portion on at least one of the electrode surfaces and the deposition surface of the electrolytic zinc foil, it is easy to obtain an S-value on either side when X-ray diffraction measurements are performed on both sides of the metal foil.(002) / S (101) All are metal foils with a thickness of 1.01 or higher, therefore they are preferred.

[0032] Furthermore, when the core is rolled zinc foil, forming cladding portions on both sides of the core makes it easy to obtain S values ​​on either side when X-ray diffraction measurements are performed on both sides of the metal foil. (002) / S (101) All are metal foils with a thickness of 1.01 or higher, therefore they are preferred.

[0033] When the core is zinc foil, it is preferably composed of zinc, additives and unavoidable impurities or zinc and unavoidable impurities.

[0034] When the core is zinc foil, the added element can be at least one selected from the group consisting of bismuth, indium, magnesium, calcium, gallium, tin, barium, strontium, silver and manganese.

[0035] As unavoidable impurities when the core is zinc foil, iron, copper, lead, cadmium, nickel, chromium, sodium, and potassium can be listed. When the core is zinc foil, the amount of each of these unavoidable impurities in the core is preferably 100 ppm or less, more preferably 10 ppm or less. It should be noted that the content of each of the various added elements listed above can also be at or below the same upper limit as the preferred upper limit for these unavoidable impurities. That is, for each metal selected from the group consisting of bismuth, indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese, the amount in the core, on a mass basis, can also be 100 ppm or less, or 10 ppm or less.

[0036] The proportions of copper, zinc, the aforementioned added elements, and unavoidable impurities in the core are determined by sampling the core from zinc foil and performing ICP emission spectroscopy. After dissolving the sample in acidic solutions such as nitric acid or hydrochloric acid, the concentrations of metals other than zinc are determined by ICP emission spectroscopy. The solution concentration of all metals is set to 1, and the proportions of each metal element are converted to mass. As for sampling the core, after confirming its location through observation using a scanning electron microscope (described later), if the cladding is located on only one side of the core, sampling can be performed by simply removing the core's side surface using a milling cutter or file. Furthermore, if the cladding is located on both sides of the core, the cladding can be removed using a milling cutter or file to obtain a sample formed from the core.

[0037] From the viewpoint of achieving excellent shape and dimensional stability, the core thickness Wr is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. Furthermore, from the perspective of flexibility, the core thickness Wr is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. From these aspects, the core thickness Wr 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.

[0038] When the core is copper foil, from the viewpoint of improving the elongation of the zinc foil and enhancing its repeatability, the average size of the copper grains in the core is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 100 μm or less. Furthermore, from the viewpoint of further emphasizing the advantage of reducing gas generation, the average size of the zinc grains in the cladding is preferably 80 μm or less, more preferably 60 μm or less, and even more preferably 40 μm or less.

[0039] When the core is zinc foil, from the viewpoint of improving the elongation of the zinc foil and enhancing its repeatability, the average size of the zinc grains in the core is preferably 24 μm or more, more preferably 35 μm or more, and even more preferably 100 μm or less. Furthermore, from the viewpoint of further emphasizing the advantage of reducing gas generation, the average size of the zinc grains in the cladding is preferably less than 100 μm, more preferably 50 μm or less, and even more preferably 10 μm or less.

[0040] It should be noted that the core may or may not contain bismuth. Preferably, the core is essentially free of bismuth, meaning that the bismuth content in the core is below 90 ppm by mass.

[0041] The cladding portion is located on at least one surface of the core. The cladding portion can be formed on only one of the two surfaces of the core, or it can be formed on both surfaces; however, it is preferred that the cladding portion be formed on both surfaces of the core due to its excellent shape stability during long-term storage. In this embodiment, the cladding portion is a layer stacked with the core. Furthermore, in this embodiment, the cladding portion is formed in a manner that it is in direct contact with the core. On the surface of the core where the cladding portion is located, the cladding portion can completely cover that surface of the core, or it can only partially cover it.

[0042] The cladding layer uses zinc as the base material. The meaning of "using zinc as the base material" is the same as that of the core layer. The zinc content in the cladding layer can be above 90% by mass, above 95% by mass, above 99% by mass, or above 99.5% by mass.

[0043] The cladding may or may not contain bismuth. For example, the cladding may consist of zinc, bismuth, additive elements other than bismuth, and unavoidable impurities, or it may consist of zinc, bismuth, and unavoidable impurities. The cladding may or may not be an alloy.

[0044] When the cladding contains additive elements other than bismuth, it is advantageous to use a metal element with a higher hydrogen overpotential (also known as hydrogen overpotential) or a higher redox potential than zinc. Examples of 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 aforementioned additive elements in the cladding, in terms of the total proportion of indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese, is preferably 10,000 ppm or less by mass, more preferably 8,000 ppm or less. Furthermore, when the cladding contains additive elements selected from indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese, the total amount is preferably 10 ppm or more by mass.

[0045] Examples of unavoidable impurities in the cladding layer include iron, copper, aluminum, lead, cadmium, nickel, chromium, sodium, and potassium. The total mass percentage of these unavoidable impurities in the cladding layer, calculated based on the combined proportions of iron, copper, aluminum, lead, cadmium, nickel, chromium, sodium, and potassium, is preferably 100 ppm or less, more preferably 10 ppm or less. Furthermore, magnesium and calcium may also be unavoidable impurities. In this case, the total mass percentage 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.

[0046] When the cladding layer contains bismuth, gas generation during battery storage can be effectively suppressed. Regarding the content ratio of bismuth in the cladding layer, it is preferably 100 ppm or more by mass, more preferably 300 ppm or more, and even more preferably 400 ppm or more. Furthermore, a bismuth content ratio of 10,000 ppm or less by mass in the cladding layer has the advantage of uniform dispersion within the cladding layer; therefore, it is preferably 3,000 ppm or less, and even more preferably 1,200 ppm or less. On the other hand, from the viewpoint of further improving the shape stability of the metal foil of this embodiment, the cladding layer preferably does not contain bismuth substantially. "Substantially does not contain bismuth" preferably means that the bismuth content ratio in the cladding layer is 90 ppm or less.

[0047] When the cladding contains bismuth, the amount of deformation over time tends to increase. However, in the present invention, even in such cases, the amount of deformation over time can be reduced. Therefore, it is preferable from the perspective of obtaining the effect of reducing the amount of gas due to the bismuth content while reducing the amount of deformation over time.

[0048] Furthermore, in the case where the cladding portion does not contain bismuth, it is preferable from the perspective of being able to further reduce the amount of deformation over time.

[0049] The proportions of zinc, the additive elements listed above, and the unavoidable impurities listed above in the cladding are determined by sampling the cladding from the zinc foil and performing ICP emission spectroscopy. The method for performing ICP emission spectroscopy on the sample is the same as that for the core. As for sampling the cladding, after confirming the location of the cladding by observation in a scanning electron microscope (described later), the exposed surface of the cladding on the zinc foil is simply removed using a milling cutter, file, or similar tool, and then the sample is taken.

[0050] The average size of the zinc grains in the aforementioned cladding portion is 2 μm or more. Since the zinc foil is kept in a dense state, this is preferably 20 μm or more, and even more preferably 50 μm or less. Furthermore, from the viewpoint of further enhancing the advantage of reducing gas generation, the average size of the zinc grains in the aforementioned cladding portion is preferably less than 100 μm, more preferably 80 μm or less, and even more preferably 50 μm or less. To produce grains of this size in the cladding portion, it is suitable to manufacture the cladding portion by electrolysis.

[0051] When the cladding portion is formed on both sides of the core, it is sufficient to satisfy the above average size in one cladding portion.

[0052] The average grain size of zinc was determined using the following method. For the determination, a center-gun scanning electron microscope (SUPRA 55VP, Carl Zeiss Co., Ltd.) with a thickness direction of FE zinc foil equipped with an electron backscatter diffraction (EBSD) evaluation device (OIM Data Collection Ver. 7.2.0, manufactured by TSL Solutions Co., Ltd.) and an associated EBSD analysis device were used. Samples with cross-sections cut using an ultramicrotome were prepared. For these samples, grain size data were obtained from a cross-sectional view that allowed for the determination of the overall thickness of the sample using the EBSD method. Specifically, for the core grains, the average grain size was determined by observing the grains in the core of the overall zinc foil cross-section (along the thickness direction) with a field of view of "core thickness × 200 μm in the direction perpendicular to the core thickness direction". For the grains in the cladding section, the average size of the grains is determined by observing the grains in the cladding section of the entire cross-section of the zinc foil with a field of view of "the thickness of the cladding section × 200 μm in the direction perpendicular to the thickness direction of the cladding section".

[0053] For background processing of EBSD measurement data, the "Binning" setting should be set to 4x4 (160x120) when the "Background Subtraction," "Normalize Intensity Histgram," and "Dynamic Background Subtraction" options are unchecked in the "Image Processing" section of the aforementioned EBSD evaluation device. "Gain" and "Exposure" can also be applied according to the image within the "Camera" section, such as... Figure 1 As shown, the Kikuchi pattern is not observed in electron diffraction, and the conditions are appropriately changed to achieve 30±1fps. Under this condition, with the "Ave" value in the "Image Processing Function" set to 10, background information is obtained using "Capture Bkd".

[0054] When measuring grain size, the WD value is set to 15±1mm. With "Image Processing" selected and "Background Subtraction", "Normalize Intensity Histgram", and "Dynamic Background Subtraction" enabled, select "Zn" in "Phase" of "Capture Pattern" on the observation site of the EBSD evaluation device. Adjust the WD value under the condition that the "Fit" value of "Solutions" is within 1.5 and the "CI" value is higher than 0.1.

[0055] Grain size is determined by using "StartScan" to measure the cross-sectional image of the sample taken from "Capture SEM" within "Scan".

[0056] The measured data were analyzed using the "Grain Size Quick Chart" function in the EBSD analysis program (OIM Analysis Ver. 7.3.1, manufactured by TSLSolutions Co., Ltd.) to calculate the average grain size. This average grain size was used as the average grain size of zinc in this invention.

[0057] In this measurement, an orientation difference of 15° or more was considered a grain boundary. However, since zinc has a hexagonal close-packed crystal structure, twin grain boundaries were considered. The orientation difference at a certain grain boundary was represented by a rotation axis and a rotation angle. The cases where the rotation axis was represented by (1) below, and the rotation angles were 94.8±1° and 57±1°, and the cases where the rotation axis was represented by (2) below, and the rotation angles were 34.8±1° and 64.3±1°, were not considered grain boundaries. The conditions of the scanning electron microscope during observation were set as follows: accelerating voltage: 20kV, aperture: 60μm, high current mode, sample angle: 70°. The observation magnification, measurement area, and step size could also be appropriately changed according to the size of the grains.

[0058] [Mathematical Expression 1]

[0059]

[0060] It should be noted that the above describes the method for determining the average size of zinc grains. However, when determining the average size of copper grains, simply replace "Zn" with "Cu" in the "Phase" of the "Capture Pattern" of the EBSD evaluation device at the observation site in the above description of the determination method.

[0061] From the viewpoint of shape stability during long-term storage, the thickness Wd of the cladding portion is preferably 5 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more. From the perspective of manufacturing thin batteries, a cladding portion thickness Wd of less than 300 μm is preferred, more preferably 250 μm or less, and even more preferably 150 μm or less. From these aspects, the cladding portion thickness Wd is preferably 5 μm or more and less than 300 μm, more preferably 20 μm or more and less than 250 μm, and even more preferably 40 μm or more and less than 150 μm.

[0062] When a cladding portion is provided on both sides of the core, the thickness of the cladding portion is set to the average of the thicknesses of the two sides.

[0063] When the cladding portion has two sides, it is preferable that the thickness of each cladding portion falls within the aforementioned range. It should be noted that when the cladding portion has two sides, the thickness of each cladding portion may be equal or different, but from the viewpoint of suppressing warping of the metal foil, the thickness of the cladding portion on both sides is preferably equal. The difference in thickness between the cladding portions on both sides is preferably 50 μm or less, more preferably 20 μm or less.

[0064] The thickness of the core and cladding can be determined by observing the cross-section along the thickness direction of the metal foil using a scanning electron microscope (SEM), detecting the interface between the core and cladding, and measuring the thickness of the core and cladding separately.

[0065] However, during the manufacturing of metal foil, the thickness of the cladding portion can also be determined by subtracting the thickness of the manufactured metal foil from the thickness of the core portion, which is used as raw material.

[0066] When the thickness of the core is set to Wr and the thickness of the cladding portion is set to Wd, a Wd / Wr ratio of 4 or less is preferred from the perspective of ease of manufacturing. In particular, a Wd / Wr ratio of 0.99 or less is preferred from the perspective of further improving shape stability during long-term storage, more preferably 0.8 or less, and especially preferably 0.7 or less. From the viewpoint of forming the cladding portion in the same way, a Wd / Wr ratio of 0.1 or more is preferred, more preferably 0.2 or more, and especially preferably 0.3 or more. From these aspects, a Wd / Wr ratio of 0.1 or more and 4.0 or less is preferred, more preferably 0.1 or more and 0.99 or less, further preferably 0.2 or more and 0.8 or less, and especially preferably 0.3 or more and 0.7 or less is preferred.

[0067] For the metal foil of the present invention, when X-ray diffraction measurements were performed on both sides of the metal foil, a peak originating from the (002) plane of zinc was observed. More specifically, for the metal foil, when X-ray diffraction measurements were performed on both sides of the metal foil, in either side, S(002) / S (101) All are 1.01 or higher. In this way, by having a core formed of a metallic material and having the same zinc orientation on both sides, the metal foil of the present invention becomes a metal foil with good shape stability after long-term storage. Furthermore, the S in each of the two sides of the metal foil... (002) / S (101) A value of 1.01 or higher is preferred from the perspective of preventing dendrite formation.

[0068] In addition, as an easily measurable S (002) / S (101) The metal foil is preferably composed of two sides, with the side with zinc as the base material being the outermost layer.

[0069] For metal foil, when X-ray diffraction measurements are performed on both sides of the metal foil separately, S (002) / S (101) More preferably, it is 1.01 or higher, and even more preferably 1.10 or higher. The sulfur content in the metal foil... (002) / S (101) The value is possible (especially S). (101) The peak intensity ratio increases infinitely (when the intensity is low), therefore there is no upper limit. The peak intensity ratio mentioned in this specification refers to the peak height ratio.

[0070] The (002) facet of zinc originates from a hexagonal crystal. The sulfur content in each of the two sides of the metal foil... (002) / S (101) Metal foils exceeding the aforementioned lower limit can be obtained by forming an electrolytic layer with zinc as the base material on a substrate formed of metal material using an electrolytic zinc plating method, and by employing a suitable manufacturing method described later.

[0071] For the metal foil of the present invention, when X-ray diffraction measurements are performed on both sides of the metal foil, peaks originating from the (101) plane of zinc may or may not be observed. The (101) plane of zinc originates from a hexagonal crystal.

[0072] Peaks originating from the (002) plane of zinc are typically observed in the range of 2θ = 36.30 ± 0.3°. Furthermore, peaks originating from the (101) plane of zinc are typically observed in the range of 2θ = 43.24 ± 0.3°. Cu-Kα rays are used as the X-ray source in the X-ray diffraction measurement.

[0073] In X-ray diffraction measurements using Cu-Kα rays as the X-ray source, within the range of 2θ = 15 to 120°, the peak originating from the (002) plane of zinc is preferably the peak with the highest intensity among all planes of the metal foil.

[0074] In X-ray diffraction measurements using Cu-Kα rays as the X-ray source, peaks other than those originating from the (002) plane of zinc and the (101) plane of zinc (hereinafter also referred to as "other peaks") can be observed on each facet of the metal foil within the range of 2θ = 15 to 120°. However, from the perspective of achieving uniform crystal alignment, it is preferable that these peaks are not observed. In the case of observed other peaks, the ratio of their peak intensity to the peak intensity of the peak originating from the (002) plane of zinc is preferably 0.99 or less, more preferably 0.9 or less.

[0075] The metal foil of the present invention exhibits excellent shape stability after long-term storage. Specifically, when the metal foil is cut into pieces 190 mm long and 90 mm wide and sealed together with argon in a gas-tight container, and stored at a temperature of 80°C and a relative humidity of 50% for 96 hours, the deformation obtained by subtracting the original size from the size after storage is preferably less than 0.5 mm in the longitudinal direction, more preferably less than 0.3 mm, and even more preferably less than 0.1 mm.

[0076] Furthermore, when the metal foil is stored under the above conditions, the amount of deformation obtained by subtracting the size before storage from the size after storage is preferably 0.5 mm or less in the transverse direction, more preferably 0.3 mm or less, and even more preferably 0.1 mm or less. Moreover, the amount of deformation, i.e., warping, in the height direction of the metal foil is preferably 5 mm or less, more preferably 4 mm or less, and even more preferably 3 mm or less.

[0077] It should be noted that, for example, vertical and horizontal directions... Figure 3 As shown in (1), the directions are parallel to and orthogonal to the plane of the metal foil. The longitudinal dimension after storage is... Figure 3 The maximum length of the longitudinal W in the sample shown in (1) is the length of the part that is most elongated in the longitudinal W before preservation, provided that the longitudinal W dimension in the sample is uniform along the transverse V. The transverse dimension after preservation is also the maximum length of the transverse V (the length of the part that is most elongated in the transverse V after preservation, provided that the transverse V dimension in the sample is uniform along the longitudinal W before preservation).

[0078] In addition, warping Figure 3 (2) shows the deformation of the height H when the object is placed on a flat surface. It should be noted that this deformation is the difference between the height of the highest point relative to the flat surface and the height before preservation.

[0079] The parameters of the metal foil described above are as shown in the embodiments described later. The two sides of the metal foil of the present invention are formed by electrolytic plating using an electrolytic layer with zinc as the base material. This can be achieved by using a suitable manufacturing method described later, especially by adopting a suitable thickness in the core and cladding portions or adjusting the electrolytic concentration or current density and the immersion time in the electrolyte.

[0080] The core and cladding are preferably bonded in an inseparable manner. This inseparable bond means that when a cross-section along the thickness direction of the metal foil is observed using a scanning electron microscope, one or more grains with shapes spanning the interface between the core and cladding are observed. Such shapes result from grain growth in the cladding that aligns the orientation planes of the grains in the core. In detail, in a cross-section along the thickness direction of the metal foil in this embodiment, at the interface between the core and cladding, a row of holes formed by multiple small holes is observed, and the location of the interface can be determined through this row of holes. When the scanning electron microscope image is a reflective electron image, the different orientation planes of the grains are reflected in the image, resulting in varying shades of color for each zinc grain. Based on these shades, the shape of the zinc grains can be determined. When one or more grains with continuous shapes spanning the interface between the core and cladding are observed, it can be determined that the core and cladding are bonded in an inseparable manner; preferably, two or more are observed. It should be noted that the interface between the core and the cladding can also be identified by using EDS analysis (energy dispersive spectroscopy) to confirm the presence of metallic elements or additive elements that form the base material.

[0081] In order to bond the core and the cladding in an inseparable manner, the metal foil can be manufactured using a suitable manufacturing method described later.

[0082] From the perspective of reducing passivation in batteries such as secondary batteries, metal foils may also be aluminum-free. For example, the proportion of aluminum in the metal foil, based on the mass of the metal foil, may be less than 1%, less than 0.1%, or less than 0.05%.

[0083] From the viewpoint of reducing environmental impact, the metal foil is preferably lead-free. The lead content, based on the mass of the metal foil, is preferably 200 ppm or less, more preferably 100 ppm or less, and even more preferably 50 ppm or less. Furthermore, the metal foil may be cadmium-free or contain cadmium as an unavoidable impurity. The cadmium content in the metal foil is preferably as low as possible. In particular, the cadmium content, based on mass, is preferably 10 ppm or less.

[0084] The proportions of aluminum, lead, and cadmium in the metal foil were determined by ICP emission spectroscopy. For determinations using ICP emission spectroscopy, the same method as described above can be employed.

[0085] The metal foil of the present invention is preferably a thin metal foil with a thickness of 15 μm or more and 900 μm or less, more preferably 25 μm or more and 500 μm or less, and even more preferably 30 μm or more and 300 μm or less. The thickness of the metal foil is measured by the method described above. Such a thin metal foil is suitable as a negative electrode material for secondary batteries, especially for stacked secondary batteries such as bipolar batteries. In particular, the metal foil of the present invention is suitable for secondary batteries, especially stacked secondary batteries, due to its excellent shape stability during long-term storage.

[0086] Next, a preferred method for manufacturing the zinc foil of the present invention will be described.

[0087] The manufacturing method includes the following steps: using a substrate formed of a metal material having a first side and a second side located on the opposite side as a cathode, immersing the substrate in an electrolyte containing zinc ions at 10 to 90°C for 1 to 10 minutes; and after the immersion step, electroplating at least one side of the substrate with an electrolyte containing zinc ions to form an electrolytic layer with zinc as the base material.

[0088] However, at least one side of the aforementioned substrate, when subjected to X-ray diffraction measurements, S (002) / S (101) In cases where the value is less than 1.01, an electrolytic layer with zinc as the base material is formed at least on that surface by electrolytic plating.

[0089] The description of the core can be used as an example of the substrate.

[0090] Examples of electrolytes containing zinc ions include aqueous solutions of zinc sulfate, zinc nitrate, and zinc chloride. The concentration of zinc in the electrolyte is preferably 30 g / L or more and 100 g / L or less, more preferably 35 g / L or more and 90 g / L or less.

[0091] Furthermore, when the cladding contains bismuth, the electrolyte may contain bismuth ions in addition to zinc ions. Examples of bismuth ion sources include bismuth nitrate. When using bismuth ions in the electrolyte, the mass ratio of bismuth to the total mass of zinc and bismuth in the electrolyte is preferably 10 ppm or more and 10,000 ppm or less, more preferably 15 ppm or more and 8,000 ppm or less, further preferably 20 ppm or more and 7,000 ppm or less, and even more preferably 30 ppm or more and 6,500 ppm or less. When the electrolyte does not contain bismuth, the mass ratio of bismuth to the mass of zinc in the electrolyte is preferably less than 10 ppm, preferably 6 ppm or less, and further preferably 3 ppm or less.

[0092] 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 at the time of electrolysis can be 2 or less.

[0093] In this manufacturing method, before electroplating with an electrolyte, the substrate serving as the cathode is immersed in the electrolyte at 10–90°C for 1–10 minutes. This facilitates obtaining S-shaped deposits on the surface formed by subsequent electroplating. (002) / S (101) The metal foil has a thickness of 1.01 or higher. From this perspective, the temperature of the electrolyte is more preferably 10–80°C, and even more preferably 15–35°C. The immersion time before electroplating is more preferably 3–8 minutes. The inventors believe that this pre-immersion has the effect of smoothing the surface of the electrode (core), thereby facilitating the obtaining of the aforementioned S-type deposition surface. (002) / S (101) Metal foil with a thickness of 1.01 or higher.

[0094] In the electrolysis method, the anode and cathode are immersed in an electrolyte containing a zinc source, and the cathode is used as the substrate to deposit an electrolytic layer with zinc as the base material on its surface. The preferred method is one that allows for easy acquisition of a cladding portion with a small average grain size. As the anode used in the electrolysis, a known size-stabilized electrode (DSE) is preferably used. Examples of suitable DSEs include titanium electrodes coated with iridium oxide and titanium electrodes coated with ruthenium oxide.

[0095] From the viewpoint of successfully obtaining metal foils with good shape stability, it is advantageous to circulate the electrolyte during electrolysis. To circulate the electrolyte, an electrolysis apparatus can be used, for example, comprising a closed flow path, an electrolytic cell disposed within that flow path, and a pump disposed within that flow path. The pump is driven to direct the electrolyte in one direction through the electrolytic cell. The anode and cathode used in electrolysis only need to be immersed in the electrolytic cell in a relative position. Preferably, the anode and cathode are arranged in the electrolytic cell such that their opposing surfaces (or electrodeposition surfaces for the cathode) are parallel to the direction of electrolyte flow.

[0096] When electrolysis is performed while circulating the electrolyte, it is advantageous to adjust the electrolyte flow rate, i.e., the circulation speed, to smoothly obtain zinc foil that achieves the desired effect. Specifically, it is preferable to set the electrolyte circulation speed to 0.001 L / (min·mm). 2 ) or more and 1L / (min·mm 2 ) or less, preferably set to 0.002L / (min·mm 2 ) or more and 0.6 L / (min·mm 2 Below this, it is further preferred to set it to 0.003 L / (min·mm). 2 ) or more and 0.4 L / (min·mm 2 The following is a more preferred setting: 0.005 L / (min·mm) 2 ) or more and 0.04 L / (min·mm 2 The following is a calculation method: The circulation rate is calculated by dividing the electrolyte flow rate (L / min) by the inter-electrode area (mm²). 2 The area between the electrodes is calculated using... Figure 2 As shown, it is expressed as the product of the electrode spacing (mm) and the width of the electrodeposition electrode (mm). Figure 2 In this process, it is preferable that the electrolyte flows in a direction perpendicular to the paper surface. Furthermore, in... Figure 2 In the middle, the plate-shaped electrodes extend in a direction orthogonal to the paper surface.

[0097] The current density during electrolysis is one of the factors affecting the grain size of zinc in the resulting zinc foil. Specifically, by applying a current density higher than that under typical zinc electrolysis conditions, many fine crystals can be generated, thereby easily obtaining zinc foil with a small average grain size. From this perspective, it is preferable to set the current density to 1000 A / m. 2 Above and 10000A / m 2 Hereinafter, it is more preferable to set it to 1000A / m 2 Above and 6000A / m 2 Hereinafter, a further preferred setting is 1000A / m2 Above and 4000A / m 2 the following.

[0098] The electrolyte can be supplied for electrolysis in either a heated or unheated state. When electrolysis is performed with the electrolyte heated, the electrolyte temperature is preferably set to 10°C or higher and 90°C or lower. More preferably, the electrolyte temperature is 20°C or higher and 90°C or lower, even more preferably 30°C or higher and 80°C or lower, and still more preferably 30°C or higher and 70°C or lower. Electrolysis continues until the zinc foil thickness reaches the target value.

[0099] The above-mentioned electroplating is preferably performed in a single process. For example, when an electrolytic layer with zinc as the base material is formed on both sides of a substrate by electroplating, it is preferable to perform the electroplating while both sides of the substrate are in contact with the electrolyte, thereby forming an electrolytic layer with zinc as the base material on both sides in one step.

[0100] 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 is conductive, it also functions as a current collector. Therefore, the metal foil itself can be used as a negative electrode without using a current collector. It should also be noted that it can be used as a negative electrode active material for primary batteries.

[0101] As shown in the evaluation results of the embodiments described later, batteries incorporating the metal foil of the present invention can be used as electrode materials with good shape stability even when stored at high temperatures for extended periods. Therefore, they are suitable for use in rechargeable batteries.

[0102] Based on the above understanding, the present invention provides the following [1] to [8].

[0103] [1] A metal foil comprising:

[0104] The core has a first surface and a second surface located on its opposite side, and is formed of a metallic material; and

[0105] The cladding portion is located on at least one side of the core portion, and zinc is used as the base material.

[0106] When X-ray diffraction measurements were performed on both sides of the aforementioned metal foil, the peak intensity S of the peak originating from the (002) plane of zinc in either side was... (002) Peak intensity S relative to the peak from the (101) plane of zinc (101) The strength ratios are all above 1.01.

[0107] [2] According to the metal foil described in [1], when the metal foil is cut into 190 mm in length and 90 mm in width and sealed together with argon into a sealable container and stored at a temperature of 80°C and a relative humidity of 50% for 96 hours, the dimensional change after storage is less than 0.5 mm in length and less than 0.5 mm in width, and the warping is less than 5 mm.

[0108] [3] The metal foil according to [1] or [2], wherein the cladding portion is formed on both sides of the core portion.

[0109] [4] The metal foil according to any one of [1] or [3], wherein the core portion and the cladding portion are bonded together in a manner that they cannot be separated.

[0110] [5] The metal foil according to any one of [1] to [4], wherein the core is a copper foil or a zinc foil.

[0111] [6] The metal foil according to any one of [1] to [5], wherein the core is an electrolytic copper foil, a rolled zinc foil, an electrolytic zinc foil or a rolled zinc foil.

[0112] [7] The metal foil according to any one of [1] to [5], wherein the thickness of the core is 5 μm or more and 300 μm or less.

[0113] [8] The metal foil according to any one of [1] to [6], wherein the thickness of the cladding portion is 5 μm or more and 300 μm or less.

[0114] [9] The metal foil according to any one of [1] to [8], wherein, in the core, the metal as the base material is copper or the core is a rolled zinc foil and the cladding portion is formed on both sides of the core, or

[0115] The core is an electrolytic zinc foil and the aforementioned cladding is formed on at least the electrode surface thereon.

[0116]

[10] The metal foil according to any one of [1] to [9], wherein the cladding portion substantially does not contain bismuth.

[0117]

[11] An electrode material for a secondary battery, comprising the metal foil described in [1] or [2].

[0118] Example

[0119] The present invention will now be described in more detail through embodiments. However, the scope of the present invention is not limited to the embodiments described. Unless otherwise specified, "%" refers to "mass %".

[0120] [Example 1]

[0121] (1) Preparation of substrate

[0122] As a substrate, an electrolytic copper foil (99.9% purity, manufactured by Mitsui Metals Mining) with the thickness shown in Table 1 was prepared.

[0123] (2) Preparation of electrolyte

[0124] Zinc oxide was used as the zinc compound. It was dissolved in water along with sulfuric acid to prepare the electrolyte. The concentration of zinc in the electrolyte was set to 50 g / L. The concentration of sulfuric acid was set to 200 g / L, calculated by converting the total amount of sulfate ions to H₂SO₄. Bismuth nitrate was added to the electrolyte. The concentration of bismuth nitrate was adjusted to 700 ppm by mass relative to the total mass of zinc and bismuth. The aforementioned electrolytic copper foil was used as the cathode. The cathode was immersed in the electrolyte at 20°C for 5 minutes.

[0125] (3) Zinc reduction precipitation

[0126] As the anode, a DSE formed from a titanium electrode coated with iridium oxide is used.

[0127] A current is passed between the anode and cathode while the electrolyte is heated to 30°C. The current density is set to 2000 A / m. 2 The electrolyte circulation rate was set to 0.021 L / (min). · mm 2 The process involves immersing both sides of the electrolytic copper foil in an electrolyte solution for electrolysis, forming an electrolytic zinc layer with a thickness as shown in Table 1 on both sides of the copper foil, resulting in a copper-zinc composite foil where the electrolytic zinc layer and the electrolytic copper foil are integrated. In this composite foil, the electrolytic copper foil corresponds to the core, and the electrolytic zinc layer corresponds to the cladding. The resulting composite foil is washed with deionized water and dried with hot air.

[0128] [Example 2]

[0129] In steps (2) and (3) of Example 1, bismuth nitrate was not used. Apart from these points, copper-zinc composite foil was obtained in the same manner as in Example 1.

[0130] [Example 3]

[0131] In step (1) of Example 1, the substrate was changed from electrolytic copper foil to rolled zinc foil (99.99% purity, manufactured by Mitsui Sumitomo Metal Mining) of the thickness shown in Table 1. Apart from this, a composite foil, namely zinc foil, integrating the rolled zinc foil and the electrolytic zinc layer, was obtained in the same manner as in Example 1.

[0132] [Example 4]

[0133] (1) Manufacturing of electrolytic zinc foil as a substrate

[0134] Zinc oxide was used as the zinc compound. It was dissolved in water along with sulfuric acid to prepare the electrolyte. The concentration of zinc in the electrolyte was set to 50 g / L. The concentration of sulfuric acid was set to 200 g / L, calculated by converting the total amount of sulfate ions to H₂SO₄. An aluminum plate was used as the cathode. The cathode was immersed in the electrolyte at 30°C for 5 minutes.

[0135] As the anode, a DSE consisting of a titanium electrode coated with iridium oxide is used.

[0136] A current is passed between the anode and cathode while the electrolyte is heated to 30°C. The current density is set to 2000 A / m. 2 The electrolyte circulation rate was set to 0.021 L / (min). · mm 2 And make it cycle.

[0137] Electrolysis is performed under these conditions, forming an electrolytic zinc layer on one side of the aluminum plate. After electrolysis, the electrolytic zinc layer is peeled off from the aluminum plate at the cathode to obtain zinc foil. The obtained zinc foil is washed with deionized water and dried with hot air.

[0138] (2) Manufacturing of the cladding layer

[0139] (2-1) Zinc oxide was used as the zinc compound. It was dissolved in water along with sulfuric acid to prepare the electrolyte. The concentration of zinc in the electrolyte was set at 50 g / L. The concentration of sulfuric acid was set at 200 g / L, calculated by converting the total amount of sulfate ions to H₂SO₄.

[0140] (2-2) In Example 2, the deposition surface of the electrolytic zinc foil obtained in (1) was masked before use as the cathode. Furthermore, the electrolyte obtained in (2-1) was used as the electrolyte. The unmasked electrode surface of the electrolytic zinc foil (the aluminum plate side surface in process (1)) was immersed in the electrolyte for an immersion process and electroplating. Except for these points, the operation was the same as in Example 2, forming an electrolytic zinc layer with an electrolytic thickness of the value recorded in Table 1 on the electrode surface of the electrolytic zinc foil. Thus, a composite foil, i.e., a zinc foil, was obtained where the electrolytic zinc layer and the electrolytic zinc foil were integral.

[0141] [Comparative Example 1]

[0142] This example demonstrates the manufacture of electrolytic zinc foil identical to the embodiment in Patent Document 1.

[0143] Zinc oxide was used as the zinc compound. It was dissolved in water along with sulfuric acid to prepare the electrolyte. The concentration of zinc in the electrolyte was set to 50 g / L. The concentration of sulfuric acid was set to 200 g / L, calculated by converting the total amount of sulfate ions to H₂SO₄. Bismuth nitrate was added to the electrolyte. The concentration of bismuth nitrate was adjusted to 700 ppm by mass relative to the total mass of zinc and bismuth. An aluminum plate was used as the cathode. The cathode was immersed in the electrolyte at 30°C for 5 minutes.

[0144] As the anode, a DSE consisting of a titanium electrode coated with iridium oxide is used.

[0145] A current is passed between the anode and cathode while the electrolyte is heated to 30°C. The current density is set to 2000 A / m. 2 The electrolyte circulation rate was set to 0.021 L / (min). · mm 2 And make it cycle.

[0146] Electrolysis is performed under these conditions, forming an electrolytic zinc layer on one side of the aluminum plate. After electrolysis, the electrolytic zinc layer is peeled off from the aluminum plate at the cathode to obtain zinc foil. The obtained zinc foil is washed with deionized water and dried with hot air.

[0147] [Comparative Example 2]

[0148] In steps (2) and (3) of Example 1, one side of the electrolytic copper foil, which serves as the cathode, is masked, and an electrolytic zinc layer is deposited only on one side. Apart from this, the operation is the same as in Example 1, resulting in a copper-zinc composite foil in which an electrolytic zinc layer is formed on one side of the electrolytic copper foil and the electrolytic copper foil are integral.

[0149] [Comparative Example 3]

[0150] In steps (2) and (3) of Example 3, one side of the rolled zinc foil, which serves as the cathode, is masked, and an electrolytic zinc layer is deposited only on one side. Apart from this, the operation is the same as in Example 3, resulting in a composite foil, i.e., a zinc foil, in which the electrolytic zinc layer and the rolled zinc layer are integrally formed on one side of the rolled zinc foil.

[0151] The following measurements / evaluations were performed on the metal foils obtained in each embodiment and comparative example. The results are shown in Table 1.

[0152] The bismuth content in the cladding of these metal foils is also shown in Table 1. The bismuth content in the cladding is a value obtained by ICP emission spectroscopy analysis of the metal foils obtained in each example / comparative example. Specifically, it is determined as follows.

[0153] In Example 1 and Comparative Example 2, the metal foil was dissolved in an aqueous nitric acid solution, and the mass of Bi and Zn in the solution was determined. The ratio of "mass of Bi / (mass of Zn + mass of Bi)" was calculated.

[0154] In Example 3 and Comparative Example 3, the metal foil was dissolved in an aqueous nitric acid solution, and the Bi content in the solution was measured. Furthermore, the zinc mass of the electrolyte after electroplating during cladding formation was determined by ICP emission spectroscopy. The zinc mass of the cladding was obtained by subtracting the zinc mass from the zinc mass in the electrolyte before electroplating. From these values, "Bi mass / (Zn mass of the cladding + Bi mass)" was calculated.

[0155] Regarding the metal foil of Comparative Example 1, the metal foil was dissolved in an aqueous nitric acid solution, and the mass of Bi and Zn in the solution was determined. The ratio of "mass of Bi / (mass of Zn + mass of Bi)" was then calculated. However, since the metal foil of Comparative Example 1 did not have a cladding portion and only contained a core portion, the amount of bismuth in the core portion was recorded in Table 1.

[0156] [XRD Measurement Conditions]

[0157] An X-ray diffraction apparatus (Bruker, D8 ADVANCE) was used. The measurement conditions were as follows. The XRD results of the metal foils obtained in Examples 1-4 are shown in Table 1 and... Figure 4 In this paper, the XRD results of the metal foils obtained in Comparative Examples 1 to 3 are shown in Table 1 and Table 2. Figure 5 The XRD surfaces of the metal foils are as described in Table 1 (for the core, the electrolytic surface or deposition surface is recorded in the case of electrolytic foil, and the rolling surface is recorded in the case of rolled foil. In addition, the presence or absence of the cladding portion is recorded).

[0158] • Radiation source: Cu-Kα rays

[0159] • Tube voltage: 40kV

[0160] Tube current: 40mA

[0161] • Scanning speed: 10.5 deg / min

[0162] • Step size: 0.015 deg

[0163] • Scanning range: 2θ = 15 degrees to 120 degrees

[0164] [Evaluation (deformation after time)]

[0165] The metal foils obtained in the examples and comparative examples were cut into pieces 190 mm long and 90 mm wide, placed on a flat surface, and their dimensions (length, width, and height) were measured. Then, the metal foils were placed in a sealed container whose internal gas was replaced with argon gas and sealed in an airtight state. They were stored at 80°C and 50% relative humidity for 96 hours, and the dimensions were measured again. Dimensions were measured using a metal ruler. The deformation (mm) was calculated by subtracting the original dimension from the dimension after the time interval. The results are shown in Table 1.

[0166]

[0167] As shown in Table 1, in each embodiment, the amount of deformation after time was suppressed. In contrast, regarding the S of the electrode surface of the electrolytic zinc foil... (002) / S (101) For Comparative Example 1, which has a value lower than 1.01, the dimensional elongation over time is significant. Furthermore, the S-shaped surface lacks an electrolytic layer. (002) / S (101) For the metal foils of Comparative Examples 2 and 3, which have a value lower than 1.01, the warping is significant after long-term storage.

[0168] Industrial availability

[0169] According to the present invention, zinc-containing metal foil with excellent shape stability during long-term storage can be provided.

Claims

1. A metal foil having: a core portion having a first surface and a second surface on the opposite side thereof, and being a copper foil or a zinc foil; and a clad portion on at least one surface of the core portion, and being made of zinc as a base material, wherein the thickness of the clad portion is 5 μm or more and 300 μm or less.

2. A metal foil for use as an electrode material for a secondary battery, the metal foil having: a core portion having a first surface and a second surface on the opposite side thereof, and being a copper foil or a zinc foil; and a clad portion on at least one surface of the core portion, and being made of zinc as a base material.

3. A metal foil for use as an electrode material for a secondary battery, the metal foil having: a core portion having a first surface and a second surface on the opposite side thereof, and being a copper foil or a zinc foil; and a clad portion on at least one surface of the core portion, and being made of zinc as a base material, wherein the thickness of the clad portion is 5 μm or more and 300 μm or less. wherein In X-ray diffraction measurement of both faces of the metal foil, the intensity ratio of the peak intensity S of the peak derived from the (002) face of zinc to the peak intensity S of the peak derived from the (101) face of zinc in either face （002） was 1.01 or more （101） ​ When the metal foil is cut into 190 mm in the longitudinal direction and 90 mm in the lateral direction, and stored under conditions of a temperature of 80°C, a relative humidity of 50%, and for 96 hours, the change in the dimensions after storage is 0.5 mm or less in the longitudinal direction and 0.5 mm or less in the lateral direction, and the warpage is 5 mm or less. The clad portion is formed on both surfaces of the core portion. The core portion and the clad portion are combined in a non-separable manner. The thickness of the core portion is 5 μm or more and 300 μm or less. wherein In X-ray diffraction measurement of both faces of the metal foil, the intensity ratio of the peak intensity S of the peak derived from the (002) face of zinc to the peak intensity S of the peak derived from the (101) face of zinc in either face was 1.01 or more. （002） the intensity ratio of the peak intensity S of the peak derived from the (002) face of zinc to the peak intensity S of the peak derived from the (101) face of zinc in either face was 1.01 or more. （101） ​ 8. An electrode material for a secondary battery, comprising a metal foil having: a core portion having a first surface and a second surface on the opposite side thereof, and being a copper foil or a zinc foil; and a clad portion on at least one surface of the core portion, and being made of zinc as a base material.

9. The electrode material for a secondary battery according to claim 8, wherein the thickness of the clad portion is 5 μm or more and 300 μm or less. ​ wherein In X-ray diffraction measurement of both faces of the metal foil, the intensity ratio of the peak intensity S of the peak derived from the (002) face of zinc to the peak intensity S of the peak derived from the (101) face of zinc in either face （002） the intensity ratio of the peak intensity S of the peak derived from the (002) face of zinc to the peak intensity S of the peak derived from the (101) face of zinc （101） is 1.01 or more, ​ 4. The metal foil according to any one of claims 1 to 3, wherein ​ 5. The metal foil according to any one of claims 1 to 3, wherein ​ 6. The metal foil according to any one of claims 1 to 3, wherein ​ 7. The metal foil according to any one of claims 1 to 3, wherein ​ ​ ​ ​ wherein, In X-ray diffraction measurement of both faces of the metal foil, the intensity ratio of the peak intensity S of the peak derived from the (002) face of zinc to the peak intensity S of the peak derived from the (101) face of zinc in either face was 1.01 or more. （002） the intensity ratio of the peak intensity S of the peak derived from the (002) face of zinc to the peak intensity S of the peak derived from the (101) face of zinc in either face was 1.01 or more. （101） ​

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