Metal foil

Abstract

This metal foil has a core portion that has a first surface and a second surface positioned on the opposite side from the first surface and is made of a metal material, and a cladding portion that is positioned on at least one surface of the core portion and in which zinc is used as a base material, wherein, when both surfaces of the metal foil are respectively subjected to X-ray diffraction measurement, the intensity ratio of the peak intensity S(002) of the peak derived from the (002) plane of the zinc to the peak intensity S(101) of the peak derived from the (101) plane of the zinc is 1.01 or more on either surface.

Description

Metal foil

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

[0002] Conventionally, zinc-containing metal foils have been used as negative electrode active materials in batteries. For example, the present applicant previously proposed a zinc foil containing bismuth, the remainder being zinc and unavoidable impurities, in which the average size of the zinc crystal grains is 0.2 μm to 8 μm, and a primary battery negative electrode active material using the same (see Patent Document 1). This zinc foil has the advantage that, when used as a negative electrode active material in a battery, the amount of gas generated during long-term storage of the battery is reduced compared to when conventional rolled zinc foil is used.

[0003] In recent years, secondary batteries using zinc as the negative electrode active material, such as air-zinc secondary batteries and manganese-zinc secondary batteries, have attracted attention. Taking advantage of the economical and safe properties of zinc, these secondary batteries are expected to be used as next-generation high-capacity storage batteries in mobile devices, drones, and other devices.

[0004] US2022 / 0037654A1

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

[0006] An object of the present invention is to provide a technique that can solve the problems of the conventional techniques described above.

[0007] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by a metal foil in which a core made of a metal material is combined with a cladding made of zinc as a base material, and both surfaces of the metal foil have a specific crystal orientation of zinc. The present invention is based on the above-mentioned findings and provides a metal foil having a core having a first surface and a second surface located opposite the first surface and made of a metal material, and a cladding located on at least one surface of the core 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 the peak derived from the (101) plane of zinc is 0.01 or more on both surfaces. （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.

[0008] FIG. 1 is a captured image of software used to determine the size of zinc crystal grains. FIG. 2 is a schematic diagram showing the inter-electrode area used to calculate the circulation rate of the electrolyte. FIG. 3 is a schematic diagram explaining the dimensions of the metal foil. (1) is a perspective view of the metal foil, and (2) is a view of the metal foil from the side. FIG. 4 shows the results of X-ray diffraction measurement of the metal foils of Examples 1 to 4. FIG. 5 shows the results of X-ray diffraction measurement of the metal foils of Comparative Examples 1 to 3.

[0009] A preferred embodiment of the present invention will be described below. 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 containing zinc as a base material deposited on the substrate. The core portion and the clad portion will be described in further detail below.

[0010] In this embodiment, the core portion 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 portion of this embodiment is in the form of a foil, similar to a metal foil. This foil has a thickness direction perpendicular to the first surface and the second surface. As such, the shape of the core portion of this embodiment, which has a first surface and a second surface located opposite thereto, can be a thin, wide, flat shape. The shape of the core portion may be called a film, sheet, or layer. The center position in the thickness direction of the metal foil of this embodiment may be located in the core portion or in the clad portion.

[0011] The core portion is made of a metal material. The metal material has a metal as its base material. From the viewpoints of dimensional and shape stability during long-term storage as a substrate, ease of availability, etc., examples of base metals constituting the core portion include copper, zinc, aluminum, etc., and from the viewpoints of ease of forming the clad portion, adhesion to the clad portion, 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 portion be at least one selected from copper foil and zinc foil.

[0012] The term "metal-based" means that the metal accounts for 80% by mass or more. The metal content in the core portion 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 greater than the above lower limit. Therefore, when the base metal constituting the core portion is copper, the copper content in the core portion may be 90% by mass or more, 95% by mass or more, 99% by mass or more, or 99.5% by mass or more. Furthermore, when the base metal constituting the core portion is zinc, the zinc content constituting the core portion 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] In the metal foil of this embodiment, both surfaces have a predetermined peak intensity ratio derived from zinc when measured by X-ray diffraction. That is, zinc is present on both surfaces of the metal foil. Therefore, when the core portion of the metal foil is made of a metal other than zinc as a base material, clad portions made of zinc as a base material are formed on both surfaces of the core portion. On the other hand, when the core portion of the metal foil is made of zinc as a base material, zinc is present on the surface of the core portion itself. Therefore, when one surface of the core portion satisfies the above-mentioned peak intensity ratio, clad portions may be formed on only one surface of the core portion, or on both surfaces.

[0014] A metal foil having a copper foil core is preferred in that it not only has shape stability after long-term storage but also can 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 having 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 an electrolytic foil refers to the surface that was in contact with the cathode during the preparation of the electrolytic foil (e.g., electrolytic copper foil). In addition, in this specification, the "deposition surface" of an electrolytic foil refers to the surface on which the electrolytic metal (e.g., electrolytic copper) is deposited during the preparation of the electrolytic foil, i.e., the surface that is not in contact with the cathode.

[0015] When the core portion is a copper foil, it is preferable that it is made of copper, an additive element and inevitable impurities, or copper and inevitable 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] When the core portion is a copper foil, examples of inevitable impurities include sulfur, phosphorus, and oxygen. The amount of each of the aforementioned inevitable impurities in the core portion is preferably 100 ppm or less, more preferably 10 ppm or less, by mass. The content of the various additive elements listed above may be equal to or less than the preferred upper limits of these inevitable impurities. That is, the content of 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 in the core portion may be 100 ppm or less, or 10 ppm or less, by mass. The amounts of each additive element and inevitable impurity described in this specification can be used independently. For example, the amounts 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 measured by X-ray diffraction, S is found on both surfaces. （００２） / S （１０１） In addition, when the core portion is a rolled zinc foil, clad portions are formed on both sides of the core portion, and when both sides of the metal foil are subjected to X-ray diffraction analysis, the clad portions are formed on both sides of the core portion, and when both sides of the metal foil are subjected to X-ray diffraction analysis, the clad portions are formed on both sides of the core portion, and the clad portions are formed on both sides of the core portion. （００２） / S （１０１） It is preferable that the value 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 inevitable impurities, or made of zinc and inevitable 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] When the core part is a zinc foil, examples of inevitable impurities include iron, copper, lead, cadmium, nickel, chromium, sodium, and potassium. When the core part is a zinc foil, the amount of each of the above-mentioned inevitable impurities in the core part is preferably 100 ppm or less, more preferably 10 ppm or less, for each element. The content of the various additive elements listed above may be equal to or less than the preferred upper limit of each of these inevitable impurities. That is, each of the metals selected from the group consisting of bismuth, indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese may be 100 ppm or less, or 10 ppm or less, for each element, for each element, by mass, in the core part.

[0022] The content ratios of copper, zinc, the above-mentioned additive elements, and the inevitable impurities in the core portion are measured by sampling the core portion from the zinc foil and subjecting it to ICP atomic emission spectroscopy. After dissolving the sample in an acidic solution such as nitric acid or hydrochloric acid, the concentration of contained metals other than zinc is measured using ICP atomic emission spectroscopy, and the content ratios of various metal elements are converted by mass, assuming the solution concentration of all metals is 1. The core portion can be sampled by confirming the position of the core portion through observation with a scanning electron microscope (described below). If the clad portion is located on only one side of the core portion, the surface on the core portion side can be scraped off with a cutter, file, or the like and sampled. Furthermore, if the clad portion is located on both sides of the core portion, the clad portion can be removed using a cutter, file, or the like to obtain a sample consisting of the core portion.

[0023] From the viewpoint of achieving excellent stability of shape and dimensions, 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. Furthermore, 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, more preferably 10 μm or more, and even more preferably 100 μm or less, from the viewpoint of making the zinc foil excellent in elongation and improving flexibility during repeated use. The average size of the zinc crystal grains in the clad 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 generation more pronounced.

[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 flexibility during 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 clad 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 pronounced.

[0026] The core may or may not contain bismuth. The core being substantially free of bismuth preferably means that the bismuth content of the core 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 of the two surfaces of the core portion, or on both surfaces; however, it is preferable that the cladding portion is formed on both surfaces of the core portion, as this provides excellent shape stability during long-term storage. In this embodiment, the cladding portion is a layer laminated with the core portion. Furthermore, 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 portion 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% by mass or more, 95% by mass or more, 99% by mass or more, or 99.5% by 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 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 or may not be an alloy.

[0030] When the cladding 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 more noble than that of 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 additive element described above is preferably 10,000 ppm or less, more preferably 8,000 ppm or less, by mass, in terms of the total ratio of indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese in the cladding portion. Furthermore, when an additive element selected from indium, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese is contained, the total amount is preferably 10 ppm or more, by mass.

[0031] Examples of unavoidable impurities in the cladding portion include iron, copper, aluminum, lead, cadmium, nickel, chromium, sodium, and potassium. The total amount of the above-mentioned unavoidable impurities in the cladding portion is preferably 100 ppm or less, more preferably 10 ppm or less, on a mass basis. Magnesium and calcium may also be unavoidable impurities. In this case, the total amount 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 bismuth content 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. Furthermore, the bismuth content in the clad portion is preferably 10,000 ppm or less by mass, since this has the advantage of uniform dispersion within the clad portion, more 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, it is preferable that the clad portion is substantially free of bismuth. By substantially free of bismuth, it is preferable that the bismuth content in the clad portion is 90 ppm or less. When the cladding contains bismuth, the amount of deformation over time tends to increase, but in the present invention, even in such a case, the amount of deformation over time can be reduced, which is preferable in that the amount of deformation over time can be reduced while obtaining the effect of reducing the amount of gas due to the bismuth content.Furthermore, when the cladding does not contain bismuth, the amount of deformation over time can be further reduced.

[0033] The content ratios of zinc, the above-listed additive elements, and the above-listed inevitable impurities in the clad portion are measured by sampling the clad portion from the zinc foil and subjecting it to ICP optical emission spectroscopy. The method for subjecting the sample to ICP optical emission spectroscopy is the same as for the core portion. The clad portion can be sampled by first confirming the position of the clad portion by observation with a scanning electron microscope (described later), and then scraping off the exposed surface of the clad portion of the zinc foil with a cutter, file, or the like, and sampling it.

[0034] The average size of the zinc crystal grains in the clad portion is preferably 2 μm or more in order to maintain the zinc foil in a dense state, more preferably 20 μm or more, and even more preferably 50 μm or less. Furthermore, the average size of the zinc crystal grains in the clad portion is preferably less than 100 μm, more preferably 80 μm or less, and even more preferably 50 μm or less, from the viewpoint of further enhancing the advantage of reducing the amount of gas generated. To produce crystal grains of such a size in the clad portion, it is preferable to manufacture the clad portion by an electrolytic method. When the clad portion is formed on both sides of the core portion, it is sufficient that the average size is satisfied in one of the clad portions.

[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 K.K.) 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 analyzer is used to measure the thickness direction of the FE zinc foil. A cross-section is cut out using an ultramicrotome to prepare a sample, and data on the crystal grain size in a cross-sectional view of this sample, from which the thickness of the entire sample can be measured, is obtained according to the EBSD method. Specifically, for the crystal grains in the core portion, the crystal grains are observed in a field of view of "thickness of the core portion × 200 μm in a direction perpendicular to the thickness direction of the core portion" in the core portion of the cross-section (cross-section along the thickness direction) of the entire zinc foil, and the average size of the crystal grains is determined. Regarding the crystal grains in the clad portion, the crystal grains are observed in a field of view of "thickness of the clad portion x 200 μm in a direction perpendicular to the thickness direction of the clad portion" in the clad portion of the cross section of the entire zinc foil, and the average size of the crystal grains is determined.

[0036] Background processing of EBSD measurement data is performed under the following conditions: "Background Subtraction," "Normalize Intensity Histogram," and "Dynamic Background Subtraction" in "Image Processing" of the EBSD evaluation device are unchecked, and "Binning" is set to 4x4 (160x120). "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 FIG. 1 and at 30±1 fps. Under these conditions, background information is acquired by "Capture Bkd" under the condition that the "Ave" value in "Image Processing Function" is 10.

[0037] The WD value when measuring the crystal grain size is 15±1 mm, and with "Background Subtraction," "Normalize Intensity Histogram," 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 conditions that the "Fit" value in "Solutions" is 1.5 or less and the "CI" value is higher than 0.1.

[0038] The grain size is measured by "Start Scan" on a photograph of the cross section of the sample taken by "Capture SEM" in "Scan." This measurement data is used to determine the grain size (average) using "All data" in the "Grain Size Quick Chart" 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 the zinc grains in the present invention.

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

[0040]

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

[0042] From the viewpoint of shape stability during long-term storage, the clad portion preferably has a thickness Wd of 5 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more. In terms of producing a thin battery, the clad portion preferably has a thickness Wd of less than 300 μm, more preferably 250 μm or less, and even more preferably 150 μm or less. From these viewpoints, the clad portion thickness Wd is 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 respective sides. When clad portions are disposed on both sides, it is preferable that the thickness of each clad portion is within the above range. Note that when clad portions are disposed on both sides, the thicknesses of the clad portions may be equal to or different from each other, but from the viewpoint of suppressing warping of the metal foil, it is preferable that the thicknesses of the clad portions on both sides are equal to each other. 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 portion and the clad portion 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 portion and the clad portion, and measuring the thickness of the core portion and the clad portion, respectively. However, the thickness of the clad portion can also be determined by using the thickness of the core portion as a raw material during the production of the metal foil and subtracting this from the thickness value of the metal foil after production.

[0043] When the thickness of the core portion is Wr and the thickness of the clad portion is Wd, it is preferable that Wd / Wr is 4 or less from the viewpoint of ease of production. In particular, Wd / Wr is preferably 0.99 or less from the viewpoint of even 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 forming a uniform 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 viewpoints, 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] When both surfaces of the metal foil of the present invention are subjected to X-ray diffraction analysis, a peak derived from the (002) plane of zinc is observed. More specifically, when both surfaces of the metal foil are subjected to X-ray diffraction analysis, a peak derived from the (002) plane of zinc is observed on both surfaces. （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 thereof, so that the metal foil has good shape stability even after long-term storage. （００２） / S （１０１） It is also preferable that S is 1.01 or more in terms of preventing the generation of dendrites. （００２） / S （１０１） In order to facilitate measurement of the above, it is preferable that the surface of the metal foil having zinc as the base material be the outermost surface.

[0045] When both surfaces of the metal foil were subjected to X-ray diffraction analysis, S （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 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） A metal foil having a Zn content of at least the above lower limit can be obtained by forming an electrolytic layer containing zinc as a base material on a substrate made of a metal material using an electrolytic zinc plating method, and employing a suitable manufacturing method described below.

[0047] When both surfaces of the metal foil of the present invention are subjected to X-ray diffraction analysis, 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 derived from the zinc (002) plane on each surface of the metal foil is usually observed in the range of 2θ = 36.30 ± 0.3°. The peak derived from the zinc (101) plane on each surface 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 for the X-ray diffraction measurement.

[0049] In X-ray diffraction measurements using Cu-kα radiation as an X-ray source, it is preferable that the peak derived from the zinc (002) plane be the peak of greatest intensity on each side of the metal foil within the range of 2θ = 15 to 120°. In X-ray diffraction measurements 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 side 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. If 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 length of 190 mm and a width of 90 mm, sealed in an airtight container with argon, and stored at a temperature of 80°C and a relative humidity of 50% for 96 hours, the deformation amount obtained by subtracting the dimensions before storage from the dimensions after storage is preferably 0.5 mm or less in the lengthwise direction, more preferably 0.3 mm or less, and even more preferably 0.1 mm or less. Furthermore, when the metal foil is stored under the above conditions, the deformation amount obtained by subtracting the dimensions before storage from the dimensions after storage is preferably 0.5 mm or less in the widthwise 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 lengthwise and widthwise directions are parallel to the plane of the metal foil and perpendicular to each other, as shown in FIG. 3 (1), for example. The longitudinal dimension after storage is the maximum length in the longitudinal direction W of the sample shown in Figure 3 (1) (if the longitudinal dimension W of the sample was uniform along the transverse direction V before storage, this is the length of the portion that stretched the most in the longitudinal direction W due to storage). The transverse dimension after storage is also the maximum length in the transverse direction V (if the transverse dimension V of the sample was uniform along the longitudinal direction W before storage, this is the length of the portion that stretched the most in the transverse direction V due to storage). Furthermore, warpage is the amount of deformation of the height H when the sample is placed on a flat surface, as shown in Figure 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 below, each parameter of the metal foil described above can be obtained by forming an electrolytic layer using zinc as a base material on both sides of the metal foil of the present invention by electrolytic plating, and by employing a suitable manufacturing method described below, particularly by selecting appropriate thicknesses for the core and clad portions in the suitable manufacturing method, and by adjusting the electrolytic concentration, current density, and immersion time in the electrolyte.

[0052] The core portion is preferably inseparably bonded to the clad portion. The inseparable bond between the core portion and the clad portion refers to the observation of one or more crystal grains straddling the interface between the core portion and the clad portion when a cross section of the metal foil taken along the thickness direction is observed with a scanning electron microscope. This shape results from the growth of crystal grains in the clad portion such that the orientation planes of the crystal grains in the core portion are aligned. More specifically, in a cross section of the metal foil taken along the thickness direction of this embodiment, a row of small holes is observed at the interface between the core portion and the clad portion, and this row of holes allows the position of the interface to be identified. When the scanning electron microscope image is a backscattered electron image, the color shade of each zinc crystal grain varies, reflecting the differences in the orientation planes of the crystal grains. The shape of the zinc crystal grains can be identified from this difference in shade. When one or more crystal grains are observed that are continuous across the interface between the core portion and the clad portion, 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 clad portions can also be confirmed by EDS analysis (energy dispersive spectroscopy) to confirm the locations of the metal elements and additive elements that make up the base material. In order to inseparably bond the core and clad portions, the metal foil may be manufactured by a suitable manufacturing method described below.

[0053] The metal foil may be aluminum-free 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. Furthermore, the metal foil may be free of cadmium or may contain it as an inevitable impurity. It is desirable that the cadmium content in the metal foil be 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 spectroscopy. The same method as described above can be used for the measurement by ICP atomic emission spectroscopy.

[0056] The metal foil of the present invention is thin, preferably having 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 thin metal foils are suitable as negative electrode materials 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 method comprises the steps of: immersing a substrate having a first surface made of a metal material and a second surface opposite the first surface as a cathode in an electrolytic solution containing zinc ions at 10 to 90°C for 1 to 10 minutes; and, after the immersion step, electroplating at least one surface of the substrate 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 above-mentioned description of the core portion can be used to describe the substrate.

[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] Furthermore, 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 10,000 ppm or less, more preferably 15 ppm or more and 8,000 ppm or less, even more 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, relative to the total mass of zinc and bismuth in the electrolyte, from the viewpoint of suppressing gas generation. 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 even more preferably 3 ppm or less.

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

[0062] In this manufacturing method, prior to electroplating using an electrolytic solution, the substrate, which is the 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 electroplating is more preferably 3 to 8 minutes. The inventors have found 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 having a value of 1.01 or more.

[0063] In the electrolysis method, an anode and a cathode are immersed in an electrolyte containing a zinc source, and an electrolytic layer containing zinc as the base material is deposited on the surface of the cathode, which serves as the substrate. This is preferred because it allows for easy production of a clad portion with a small average crystal grain size. A known dimensionally stabilized electrode (DSE) is preferably used as the anode used in the electrolysis. Examples of suitable DSEs include titanium electrodes coated with iridium oxide and titanium electrodes coated with ruthenium oxide. From the perspective of successfully obtaining a metal foil with good shape stability, it is advantageous to circulate the electrolyte during electrolysis. To circulate the electrolyte, for example, an electrolysis device equipped with a closed flow path, an electrolytic cell disposed in the flow path, and a pump disposed 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 in the electrolysis may be immersed in the electrolytic cell, facing each other. The anode and cathode are preferably placed in the electrolytic cell so that their opposing surfaces (electrodeposition surfaces of the cathode) are parallel to the direction of flow 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 a zinc foil having the desired effect. Specifically, the circulation rate of the electrolyte is adjusted to 0.001 L / (min.mm ２ ) or more 1L / (min・mm ２ ) or less, and ２ ) or more than 0.6L / (min.mm ２ ) or less, and it is more preferable to set it to 0.003 L / (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 the flow rate (L / min) of the electrolyte and the area between the electrodes (mm ２) is calculated. As shown in FIG. 2, the inter-electrode area is expressed as the product of the inter-electrode distance (mm) and the electrodeposition electrode width (mm). In FIG. 2, it is preferable to circulate the electrolyte in a direction perpendicular to the paper surface. In FIG. 2, the plate-shaped electrodes extend in a direction perpendicular to the paper surface.

[0065] The current density during electrolysis is one of the factors that affect the size of zinc crystal grains in the resulting zinc foil. Specifically, by increasing the current density above that of normal zinc electrolysis, a large number of fine crystals can be generated, thereby making it easy to obtain zinc foil with a small average crystal grain size. 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 1000 A / m or less. 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 an unheated state or in a heated state. When electrolysis is performed with the electrolytic solution heated, 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 process 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 electrolytic layers containing zinc as a base material as cladding portions on both sides of a substrate by electrolytic plating, it is preferable to perform electrolytic plating while keeping both sides of the substrate in contact with an electrolytic solution, thereby forming electrolytic layers containing 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 is conductive, 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 below, batteries equipped with 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 long periods of time. This makes it suitable for use in secondary batteries.

[0069] The present invention is based on the above findings and provides the following [1] to [8]. [1] A metal foil having a core portion made of a metal material, which has a first surface and a second surface located opposite the first surface, and a clad portion located on at least one surface of the core portion and made of zinc, 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 0.015 μm on both surfaces. （１０１） The peak intensity S of the peak originating from the (002) plane of zinc （００２）

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[0106] [ [6] The metal foil according to any one of [1] to [5], wherein the core portion is an electrolytic copper foil, a rolled 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 thickness of the clad portion is 5 μm or more and 300 μm or less. [9] The metal foil according to any one of [1] to [8], wherein the base metal of the core portion is copper, or the core portion is a rolled zinc foil with the clad portion formed on both sides of the core portion, or the core portion is an electrolytic zinc foil with the clad portion formed on at least the 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].

[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 substrate: Electrolytic copper foil (purity 99.9%, manufactured by Mitsui Mining & Smelting Co., Ltd.) having the thickness shown in Table 1 was prepared as the substrate. (2) Preparation of electrolyte: 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 ４The 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) Reductive Deposition of Zinc A DSE consisting of a titanium electrode coated with iridium oxide was used as the anode. A current was passed between the anode and cathode while the electrolyte was heated to 30°C. The current density was 2000 A / 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, resulting in 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 A copper-zinc composite foil was obtained in the same manner as in Example 1, except that bismuth nitrate was not used in steps (2) and (3) of Example 1.

[0074] 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. A zinc foil was obtained as a composite foil in which the rolled zinc foil and the electrolytic zinc layer were integrated in the same manner as in Example 1, except for this point.

[0075] [Example 4] (1) Production of electrolytic zinc foil as a substrate Zinc oxide was used as the zinc compound. This was dissolved in water together with sulfuric acid to prepare an electrolytic solution. The zinc concentration in the electrolytic solution was 50 g / L. The sulfuric acid concentration was adjusted so that the total amount of sulfate ions was H ２ SO ４The 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. A DSE consisting of a titanium electrode coated with iridium oxide was used as the anode. A current was passed between the anode and cathode while the electrolyte was heated to 30°C. The current density was 2000 A / m ２ The electrolyte was circulated at a rate of 0.021 L / (min.mm ２ ) and circulated. Electrolysis was carried out in this state, forming 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) Production of clad part (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 set to 50 g / L. The sulfuric acid concentration was set to H ２ SO ４ The value calculated as 200 g / L was used as a cathode. (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 facing the aluminum plate in step (1)) was immersed in the electrolytic solution to perform the immersion step and electroplating. Except for these points, an electrolytic zinc layer having an electrolytic thickness shown in Table 1 was formed on the electrode surface of the electrolytic zinc foil in the same manner as in Example 2. This resulted in a zinc foil that was a composite foil in which the electrolytic zinc layer and the electrolytic zinc foil were integrated.

[0076] Comparative Example 1 This example is an example of producing an electrolytic zinc foil similar to the example in Patent Document 1. Zinc oxide was used as the zinc compound. This was dissolved in water together with sulfuric acid to prepare an electrolytic solution. The zinc concentration in the electrolytic solution was 50 g / L. The sulfuric acid concentration was adjusted so that the total amount of sulfate ions was H ２ SO ４The 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. A DSE consisting of a titanium electrode coated with iridium oxide was used as the anode. A current was passed between the anode and cathode while the electrolyte was heated to 30°C. The current density was 2000 A / m ２ The electrolyte was circulated at a rate of 0.021 L / (min.mm ２ ) and circulated. Electrolysis was performed in this state, and an electrolytic zinc layer was formed 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 electrodeposited copper foil used as the cathode was masked, and an electrolytic zinc layer was deposited only on that side. Except for this, a copper-zinc composite foil was obtained in the same manner as in Example 1, in which the electrolytic zinc layer was formed on one side of the electrodeposited 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, the same procedure as in Example 3 was repeated to obtain a zinc foil that was a composite foil in which the electrolytic zinc layer was formed on one side of the rolled zinc foil and the rolled zinc layer were integrated.

[0079] The metal foils obtained in each Example and Comparative Example were subjected to the following measurements and evaluations. The results are shown in Table 1. The amount of bismuth in the clad portion of these metal foils is also shown in Table 1. The bismuth content in the clad portion was measured by ICP atomic emission spectroscopy on 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 a nitric acid aqueous solution, and the Bi and Zn masses in the solution were determined, and the "Bi mass / (Zn mass + Bi mass)" was calculated. In Example 3 and Comparative Example 3, the metal foil was dissolved in a nitric acid aqueous solution, and the Bi content in the solution was measured. In addition, the zinc mass in the electrolyte after electroplating during clad formation was measured by ICP atomic emission spectroscopy. The zinc mass of the clad portion was determined by subtracting this mass from the zinc mass in the electrolyte before electroplating. From these values, the "Bi mass / (Zn mass + Bi mass of the clad portion)" was calculated. For the metal foil of Comparative Example 1, the metal foil was dissolved in a nitric acid solution, and the Bi mass and Zn mass in the solution were determined, and the "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 amount of bismuth in the core portion.

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

[0081] [Evaluation (deformation amount after aging)] 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 whose internal gas had been replaced with argon gas, sealed in an airtight state, and stored at a temperature of 80°C and a relative humidity of 50% for 96 hours, after which 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]

[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.

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

Claims

1. A metal foil having a first surface and a second surface 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 metal foil has an intensity ratio of 1.01 or more.

2. The metal foil according to claim 1, wherein when the metal foil is cut to a size of 190 mm length and 90 mm width 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 length direction and 0.5 mm or less in the width direction, and the warpage is 5 mm or less.

3. The metal foil according to claim 1 or 2, wherein the clad portion is formed on both sides of the core portion.

4. The metal foil according to claim 1 or 2, wherein the core portion and the clad portion are inseparably bonded to each other.

5. The metal foil according to claim 1 or 2, wherein the core portion is a copper foil or a zinc foil.

6. The metal foil according to claim 1 or 2, wherein the thickness of the core portion is 5 μm or more and 300 μm or less.

7. The metal foil according to claim 1 or 2, wherein the thickness of the clad portion is 5 μm or more and 300 μm or less.

8. An electrode material for a secondary battery comprising the metal foil according to claim 1 or 2.

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