Metal layer coated zinc foil and its manufacturing method

Abstract

The metal layer-coated zinc foil according to the present invention has: a foil body comprising zinc as a base material; and a metal layer disposed on a surface of the foil body. A metal element contained in a coating metal layer is at least one selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese. The coating metal layer has a thickness of preferably 5.0×10-1-3.0×103 nm. The coating metal layer is preferably disposed on one surface or both surfaces of the foil body. The foil body is preferably an electrolytic foil.

Description

[Technical Field]

[0001] The present invention relates to a metal layer-coated zinc foil and a method for producing the same, and more particularly to a metal layer-coated zinc foil that can be suitably used as a negative electrode active material for primary or secondary batteries, and a method for producing the same. [Background technology]

[0002] The present applicant previously proposed a zinc foil containing bismuth and zinc as a base material, and a negative electrode active material for primary batteries using the zinc foil (see Patent Document 1). In this zinc foil, the bismuth content is 100 ppm or more and 10,000 ppm or less by mass, and the zinc crystal grain size is 0.2 μm or more and 8 μm or less. Use of this zinc foil as a negative electrode active material has the advantage of suppressing the amount of gas generated during long-term storage of the battery compared to conventional methods. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. WO2020 / 071350 Brochure Summary of the Invention

[0004] The zinc foil described in Patent Document 1 can reduce the amount of gas generated during long-term storage of a battery to a practical level. However, in the case of a thin battery, for example, with a thickness of only a few millimeters, even a small amount of gas generation significantly increases the thickness of the battery. Since thin batteries are often used as power sources for portable electronic devices, an increase in battery thickness affects the reliability of the portable electronic devices. Therefore, the requirements for gas generation in thin batteries are much stricter than those for conventional batteries. Therefore, an object of the present invention is to provide a zinc foil for use as a negative electrode active material, which, when used as a negative electrode active material in a thin battery in particular, produces less gas than ever before in the battery.

[0005] The present invention solves the above-mentioned problems by providing a metal layer-coated zinc foil having a foil body made of zinc as a base material and a metal layer disposed on the surface of the foil body, wherein the metal element contained in the metal layer is at least one selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram showing the inter-electrode area used to calculate the circulation rate of the electrolyte. [Figure 2] Figure 2 is a screenshot of the software used to determine the size of zinc crystal grains. DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention will be described below based on preferred embodiments. The metal layer-coated zinc foil of the present invention has a foil body made of zinc as a base material and a metal layer disposed on the surface (one or both sides) of the foil body. 1. Zinc-based foil body First, a preferred embodiment of a foil body having zinc as a base material (hereinafter also referred to as "zinc foil") will be described. The term "based on zinc" means that the zinc content of the foil body is preferably 80 mass % or more. The zinc content can be measured by ICP atomic emission spectroscopy.

[0008] 1-1. Zinc foil grain size One of the features of the foil body used in the present invention is that the zinc crystal grain size is smaller than that of conventional zinc foils. This suppresses gas generation during battery storage compared to conventional zinc foils. While the reason for this is not entirely clear, the inventors believe that the distribution of small zinc crystal grains and the presence of numerous grain boundaries may be responsible for the change in hydrogen overvoltage. To further enhance this advantage, the zinc crystal grain size is preferably 0.2 μm to 50.0 μm, more preferably 0.5 μm to 50.0 μm, even more preferably 1.0 μm to 30.0 μm, even more preferably 2.0 μm to 26.0 μm, and particularly preferably 3.0 μm to 26.0 μm. A suitable method for producing crystal grains of this size in the foil body will be described later. It should be noted that crystal grain size is a different concept from the crystallite size determined from an XRD pattern.

[0009] 1-2.Method for measuring grain size of zinc foil The size of the zinc crystal grains in the foil body used in the present invention is measured by the following method. For the measurement, an FE gun-type 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 are used. A cross-section of a sample is cut out using an ultramicrotome, and data on the crystal grain size in a cross-sectional view of this sample is obtained according to the EBSD method, allowing the thickness of the entire sample to be measured. Background processing of EBSD measurement data is performed under the following conditions: "Background Subtraction," "Normalize Intensity Histogram," and "Dynamic Background Subtraction" are unchecked in the "Image Processing" of the EBSD evaluation device, and "Binning" is set to 4x4 (160x120). "Gain" and "Exposure" may be adjusted as appropriate so that the image in "Camera" is such that no Kikuchi pattern is observed in electron diffraction, as shown in Figure 2, and the frame rate is 30±1 fps. Under these conditions, background information is obtained using "Capture Bkd" with the "Ave" value in the "Image Processing Function" set to 10. The WD value when measuring the crystal grain size is 15±1 mm. 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 within 1.5 and the "CI" value is higher than 0.1. The crystal grain size is measured by "Start Scan" on a photograph of the cross section of the sample taken with "Capture SEM" in "Scan." The measured data is used to determine the average grain size (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 average grain size is the size of the zinc grains in the present invention. 1-3. Crystal structure of zinc foil In this measurement, a misorientation of 15° or more is considered a grain boundary. However, because the crystalline structure of zinc is a hexagonal close-packed structure, twin grain boundaries are taken into consideration. The misorientation at a grain boundary is expressed in terms of the rotation axis and rotation angle. When the rotation axis is expressed by (1) below and the rotation angle is 94.8±1° and 57±1°, or when the rotation axis is expressed by (2) below and the rotation angle is 34.8±1° and 64.3±1°, it is not considered a grain boundary. The conditions for the scanning electron microscope during observation are an acceleration voltage of 20 kV, an aperture diameter of 60 μm, 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.

[0010]

number

[0011] 1-4. Metal elements contained in zinc foil As described above, the foil body used in the present invention is made of zinc as a base material. It may be 100% zinc by mass, but preferably contains a small amount of another metal element other than zinc. This effectively suppresses gas generation during battery storage. From this perspective, it is advantageous to use a metal element having a higher hydrogen overvoltage than zinc or a more noble oxidation-reduction potential than zinc. Examples of such metal elements include at least one selected from the group consisting of bismuth, indium, aluminum, magnesium, calcium, gallium, tin, barium, strontium, silver, and manganese. Among these metal elements, the use of at least one selected from the group consisting of bismuth, indium, aluminum, tin, silver, and gallium is preferred in terms of further suppressing gas generation, and the use of at least one selected from the group consisting of bismuth, indium, tin, and silver is even more preferred in terms of further suppressing gas generation. In particular, the use of bismuth is even more preferred.

[0012] 1-5. Metal element content of zinc foil From the viewpoint of effectively suppressing gas generation during battery storage, the content of metal elements in the foil body, expressed as the total amount of metal elements, is preferably 10 ppm to 10,000 ppm by mass, more preferably 15 ppm to 8,000 ppm, even more preferably 20 ppm to 7,000 ppm, even more preferably 30 ppm to 6,500 ppm, and particularly preferably 40 ppm to 6,000 ppm. The content of metal elements in the foil body can be measured by ICP atomic emission spectroscopy. For ICP atomic emission spectroscopy, a method conforming to JIS H1111 can be used. Specifically, after dissolving the foil body in an acidic aqueous solution such as hydrochloric acid, the concentration of contained metals other than zinc is measured by ICP atomic emission spectroscopy, and the content of each metal element is converted by mass, assuming the solution concentration of all metals is 1.

[0013] 1-6. Zinc foil containing metal element bismuth Among the above metal elements, it is preferable to include bismuth in the foil body, since this more effectively suppresses gas generation during battery storage. To further suppress gas generation during battery storage, the bismuth content in the foil body is preferably 10 ppm to 10,000 ppm by mass, more preferably 15 ppm to 8,000 ppm, even more preferably 20 ppm to 6,000 ppm, even more preferably 30 ppm to 3,000 ppm, and even more preferably 40 ppm to 1,200 ppm.

[0014] 1-7. Lead and cadmium contained in zinc foil The foil body used in the present invention may contain lead or cadmium as unavoidable impurities. However, from the viewpoint of reducing environmental impact, it is desirable that the foil body is lead-free. Even if the foil body contains lead, it is desirable that the content be as low as possible. Specifically, the lead content is preferably 60 ppm or less by mass, more preferably 50 ppm or less, and even more preferably 40 ppm or less. The lead content in the foil body is measured by ICP atomic emission spectroscopy. Similarly, it is desirable that the foil body is free of cadmium, or if it contains cadmium, its content be as low as possible. In particular, it is desirable that the cadmium content be 10 ppm or less by mass.

[0015] 1-8. State of metallic elements contained in zinc foil The state of existence of the above-mentioned metal elements in the foil itself is unclear, but at least they are not in a solid solution with zinc. A solid solution state is a state in which the crystal structure of zinc changes when a metal element is added. When element mapping is performed on a cross section of the foil itself containing metal elements using energy dispersive X-ray spectroscopy (characteristic X-ray detection method) with a scanning electron microscope, mapping images of the state of existence of zinc and mapping images of the state of existence of the metal elements are obtained.

[0016] It is preferable that the metal elements in the foil body are present as uniformly as possible. Whether the presence is uniform or not can be confirmed by observing the mapping image of the metal elements described below. This further suppresses gas generation during battery storage compared to conventional zinc foils containing metal elements. To achieve such a presence of the metal elements, it is advantageous to reduce the size of the zinc crystal grains in the foil body as described above. In particular, if the metal element and zinc are not compatible, the metal element is likely to segregate near the grain boundaries of the zinc crystal grains. In this case, if the zinc crystal grain size is large, the presence of the metal elements will be nonuniform when observed macroscopically so that the presence of the grain boundaries can be seen. Conversely, if the zinc crystal grain size is small, the presence of the metal elements will be uniform when observed macroscopically so that the presence of the grain boundaries can be seen. For this reason, it is advantageous to reduce the size of the zinc crystal grains in the foil body.

[0017] Conventionally, zinc foil containing metal elements has been produced by rolling a casting of zinc containing metal elements. When zinc containing metal elements is produced by casting, the growth of zinc crystal grains progresses due to the cooling conditions, making it difficult to produce small crystal grains. As a result, metal elements precipitate near the grain boundaries of large zinc crystal grains, and when observed under magnification large enough to see the presence of the grain boundaries, the metal elements are present in a non-uniform state. In contrast, in the present invention, the foil body is preferably produced by the electrolytic method described below. This makes it possible for the first time to easily produce small zinc crystal grains and achieve as uniform a presence state of metal elements as possible.

[0018] The state of existence of metal elements in the foil body used in the present invention can be determined based on a mapping image of the metal elements obtained by energy dispersive X-ray spectroscopy (hereinafter also referred to as "EDS") using a scanning electron microscope (hereinafter also referred to as "SEM"). Specifically, when a plurality of squares each 300 nm on a side are hypothetically set in the mapping image, the state of existence of the metal elements is uniform to the extent that metal elements are observed in preferably 2% by number or more, more preferably 5% by number or more, and even more preferably 10% by number or more of the total number of the squares. The number of squares is 48 or more.

[0019] 1-9. Apparent density of zinc foil The foil body used in the present invention is characterized by a lower apparent density than conventional zinc foils, such as those manufactured by rolling, which also reduces gas generation during battery storage compared to conventional zinc foils.

[0020] The apparent density of the foil itself is specifically 3.0 g / cm 3 More than 7.0g / cm 3 Preferably, it is 4.0 g / cm or less. 3 More than 7.0g / cm 3 More preferably, it is 5.0 g / cm or less. 3 More than 7.0g / cm 3 It is more preferable that the apparent density of the foil body is within this range. By setting the apparent density of the foil body within this range, gas generation during storage of the battery can be effectively suppressed. A suitable method for producing a foil body having such an apparent density will be described later.

[0021] The apparent density is a value calculated from the volume determined by measuring the external dimensions of the foil body and the mass of the foil body. The method for calculating the volume by measuring the external dimensions of the foil body is as follows: The area of ​​the foil body in a plan view is calculated from the vertical and horizontal dimensions of the foil body. The thickness of the foil body is measured using a micrometer. The thickness is taken as the arithmetic mean of the measurement results at 15 points. The mass of the sample whose volume is determined from the area and thickness is measured, and the apparent density is calculated from the volume and mass. The apparent density calculated in this way is also called the apparent density by external measurement. Note that although the apparent density of zinc foil and the apparent density of the foil body are strictly different, the apparent density of zinc foil and the apparent density of the foil body can be considered to be essentially the same because the metal layer provided on the surface of the foil body is extremely thin.

[0022] 1-10. Density other than the apparent density of zinc foil Densities other than apparent density are also thought to affect gas generation. Other density measurement methods include, for example, the Archimedes method and other measurement methods conforming to JIS Z8807:2012. Further measurement methods include the density and specific gravity measurement method using a pycnometer, the density and specific gravity measurement method using a Le Chatelier pycnometer, the density and specific gravity measurement method using the submerged weighing method, the density and specific gravity measurement method using the acoustic method, and the density and specific gravity measurement method using the gas displacement method.

[0023] 1-11.Thickness of zinc foil In relation to the apparent density of the foil body described above, the foil body is thin, preferably having a thickness of 10 μm or more and 500 μm or less, more preferably 15 μm or more and 400 μm or less, even more preferably 20 μm or more and 400 μm or less, and particularly preferably 20 μm or more and 300 μm or less. The thickness of the foil body is measured with a micrometer as described above.

[0024] 2. Manufacturing method of the foil body Next, a preferred method for manufacturing the foil body will be described. The foil body can be manufactured by the rolling method described above, but is preferably manufactured by an electrolytic method.

[0025] 2-1. Electrolytic method In the electrolysis method, an anode and a cathode are immersed in an electrolyte containing a zinc source, and zinc foil is deposited on the cathode. The foil obtained by the electrolysis method is also called "electrolytic foil." Examples of electrolytes containing a zinc source include aqueous zinc sulfate, aqueous zinc nitrate, and aqueous zinc chloride solutions. The zinc concentration in the electrolyte is preferably 30 g / L or more and 100 g / L or less, since this facilitates the production of a foil with small crystal grain size. A known dimensionally stabilized electrode (DSE) is preferably used as the anode used in the electrolysis. Suitable examples of DSE include titanium electrodes coated with iridium oxide and titanium electrodes coated with ruthenium oxide. On the other hand, there are no particular limitations on the type of cathode, and any material that does not affect the reduction of zinc can be selected. For example, aluminum can be used.

[0026] 2-2. Electrolyte for electrolysis The electrolytic solution may contain, as necessary, the above-mentioned metal element source in addition to the zinc source. The concentration of the metal element source contained in the electrolytic solution is, in terms of the mass ratio of the metal element to the total mass of zinc and the metal element in the electrolytic solution, preferably 10 ppm to 10,000 ppm, more preferably 15 ppm to 8,000 ppm, even more preferably 20 ppm to 7,000 ppm, still more preferably 30 ppm to 6,500 ppm, particularly preferably 30 ppm to 6,000 ppm, and particularly preferably 400 ppm to 6,000 ppm.

[0027] The electrolyte may further contain other compounds, such as sulfuric acid, for the purpose of adjusting the pH of the electrolyte.

[0028] 2-3. Electrolyzer From the viewpoint of successfully obtaining a foil body having the desired apparent density, the inventors have found that it is advantageous to circulate the electrolyte during electrolysis. To circulate the electrolyte, for example, an electrolysis device including 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 in a state where they face each other. The anode and cathode are preferably disposed in the electrolytic cell so that their facing surfaces (the electrodeposited surface of the cathode) are parallel to the flow direction of the electrolyte.

[0029] 2-4.Circulation speed 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 foil body having the desired apparent density. 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 it is preferable to set it to 0.002L / (min·mm 2 ) or more than 0.6L / (min·mm 2 ) or less, and it is more preferable to set it to 0.003 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 1 / 2 of the flow rate (L / min) of the electrolyte relative to the inter-electrode area (mm 2 ) The inter-electrode area is calculated by dividing the inter-electrode distance (mm) by the electrodeposition electrode length (mm), as shown in FIG. 1. In FIG. 1, it is preferable to circulate the electrolyte in a direction perpendicular to the paper surface.

[0030] 2-5.Current density The current density during electrolysis is one of the factors that affect the size of zinc crystal grains in the resulting foil body and the apparent density of the foil body. Specifically, by increasing the current density above the conditions for normal zinc electrolysis, a large number of fine crystals can be generated, which makes it easy to obtain a foil body with small crystal grains. 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 1000A / 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 the current density to 500 A / m or less. 2 It is of a low level.

[0031] 2-6. Electrolysis conditions The electrolysis can be performed with the electrolytic solution in an unheated or heated state. When electrolysis is performed with the electrolytic solution in a heated state, the temperature of the electrolytic solution is preferably set to 10°C or higher and 90°C or lower. The temperature of the electrolytic solution is more preferably 20°C or higher and 90°C or lower, even more preferably 30°C or higher and 80°C or lower, and even more preferably 30°C or higher and 70°C or lower. This process is continued until the thickness of the foil body reaches the desired value. Electrolysis is carried out under the above conditions, and zinc is reduced and deposited on the cathode immersed in the electrolytic solution, to obtain the desired foil body.

[0032] 3.Coating metal layer Next, the coating metal layer (hereinafter simply referred to as "metal layer") disposed on the surface of the foil body will be described. This metal layer is disposed on one or both surfaces of the foil body by a coating forming means described below.

[0033] 3-1. Metal elements contained in the coated metal layer The metal element contained in the metal layer may be at least one selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese. Among these metal elements, it is preferable to use at least one of bismuth and indium, particularly from the viewpoint of further suppressing gas generation.

[0034] 3-2. Thickness of the metal coating layer The thickness of the metal layer is 5.0×10 -1 nm or more 3.0×10 3 nm or less is preferable, and more preferably 1.0 nm or more and 1.0 × 10 3 nm or less, more preferably 1.0 × 10 1 nm or more 5.0×10 2 The thickness of the metal layer is measured by an optical emission surface analyzer, which will be described later.

[0035] The metal layer is disposed on one or both surfaces of the foil body. When the metal layer is disposed on both sides of the foil body, the thickness of the metal layer differs between one side and the other side of the foil body, and the thickness of one side (T C ) than the thickness of the other surface (T S ) is preferably larger than the thickness ratio (T S / T C ) is preferably 2 or more, more preferably 2.3 or more. S / T C The upper limit of is preferably 5.0, which has the advantageous effect of achieving both good discharge characteristics and suppression of gas generation. When the foil body is made of, for example, an electrolytic foil, one side is the electrode side of the foil body (hereinafter also referred to as "C side"), and the other side is the deposition side (hereinafter also referred to as "S side") that comes into contact with the electrolyte. In this case, the thickness of the metal layer is the thickness of the C side (T C ) than the thickness of the S surface (T S ) is preferably larger, since the above-mentioned effect becomes more pronounced. It is possible to determine which of the foil's surfaces is the C-face and which is the S-face by observing the surface. Specifically, the C-face is smoother and has a smaller specific surface area than the S-face. Additionally, the crystal grain size is smaller on the C-face than on the S-face.

[0036] 3-3.Thickness of metal layer coated zinc foil The metal layer-coated zinc foil having the coating metal layer and the foil body is thin, preferably having a thickness of 1 μm or more and 1000 μm or less, more preferably 3 μm or more and 800 μm or less, and even more preferably 10 μm or more and 500 μm or less. The thickness of the metal layer-coated zinc foil is measured by the same method as that for the foil body. Such thin metal layer-coated zinc foil is particularly suitable as a negative electrode material for thin primary batteries and secondary batteries.

[0037] 4.Method for manufacturing coated metal layer Next, a method for producing a metal coating layer, that is, a method for forming a metal layer coating on a foil body, will be described. The coating may be formed by sputtering, PVD, CVD, reduction plating, electroplating, or displacement plating. Of these coating methods, displacement plating is preferred from the viewpoint of process continuity when the foil body is produced by an electrolytic method.

[0038] 4-1. Substitution plating method The displacement plating method is a plating method that utilizes the difference in ionization tendency, and is an excellent method for forming a metal layer. A preferred embodiment of the displacement plating method will be described below. As a displacement plating solution for displacement plating, an aqueous solution of nitric acid or other acidic solution of a metal element having a desired concentration is prepared and dissolved in ion-exchanged water. As described above, the metal element may be at least one selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese. Among these metal elements, it is preferable to use at least one of bismuth and indium, particularly from the viewpoint of further suppressing gas generation. The concentration of the metal element in the displacement plating solution can be appropriately selected depending on the type of the target metal element, the thickness of the coating metal layer, and other conditions. When bismuth is used as the metal element, the bismuth concentration in the displacement plating solution is preferably adjusted to 0.1 mg / L or more and 100,000.0 mg / L or less. In this case, bismuth nitrate can be used as the bismuth compound. When indium is used as the metal element, the indium concentration in the displacement plating solution is preferably adjusted to 0.1 mg / L or more and 100,000.0 mg / L or less. If necessary, various complexing agents, including chelating agents such as ethylenediaminetetraacetic acid, may be added to the displacement plating solution. The pH of the displacement plating solution may be adjusted to a predetermined range by adding an alkaline solution, such as aqueous ammonia or a sodium hydroxide solution, to the displacement plating solution. The foil body is immersed in the displacement plating solution prepared in this manner to obtain a foil body coated with a metal layer. The immersion temperature and immersion time may be appropriately adjusted depending on the thickness of the metal layer.

[0039] 4-2. Electroplating method Electroplating is a plating method that uses an electric current and is an excellent method for forming a metal layer. A preferred embodiment of the electroplating method will be described below. As an electroplating solution for the electroplating method, an aqueous solution of nitric acid or other acidic solution of metal elements having a desired concentration is prepared. As described above, the metal element may be at least one selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese. Among these metal elements, it is preferable to use at least one of bismuth, indium, and tin, particularly from the viewpoint of further suppressing gas generation. The concentration of the metal element in the electroplating solution can be appropriately selected depending on the type of the target metal element, the thickness of the coated metal layer, and other conditions. When tin is used as the metal element, the tin concentration in the electroplating solution is preferably adjusted to 1.0 g / L or more and 100.0 g / L or less. In this case, tin nitrate can be used as the tin compound. When indium is used as the metal element, the indium concentration in the electroplating solution is preferably adjusted to 1.0 g / L or more and 100.0 g / L or less. If necessary, various complexing agents, including chelating agents such as ethylenediaminetetraacetic acid, may be added to the electroplating solution. In addition, the pH of the electroplating solution may be adjusted to a predetermined range by adding an alkaline solution, such as aqueous ammonia or a sodium hydroxide solution, to the electroplating solution. The foil body is immersed in the plating solution prepared in this manner and a current is passed through it to obtain a foil body coated with a metal layer. The current density, immersion temperature, and immersion time during the current passage can be appropriately adjusted depending on the surface condition and thickness of the desired metal layer. When applying current, the foil body immersed in the electroplating solution is used as the cathode, and the counter electrode is used as the anode. When forming a metal layer on each surface of the foil body, it is preferable to arrange a pair of counter electrodes facing each surface of the foil body. The counter electrode is preferably a flat plate made of the same metal as the metal layer that coats the foil body, which allows the concentration of the metal element during electroplating to be constant during current flow.

[0040] 5.Negative electrode active material for batteries The metal layer-coated zinc foil obtained as described above is suitable for use as a negative electrode active material for primary and secondary batteries. Examples of such primary batteries include manganese-zinc batteries and air-zinc batteries. Examples of secondary batteries include nickel-zinc batteries and air-zinc batteries. The metal layer-coated zinc foil of the present invention is particularly suitable for use as a negative electrode active material for thin batteries. Furthermore, since the metal layer-coated zinc foil itself is conductive, the zinc foil also functions as a current collector. This allows the metal layer-coated zinc foil itself to be used as a negative electrode without using a current collector.

[0041] A thin battery is one whose thickness is, for example, at most a few millimeters. The exterior cases of many thin batteries are made of a softer material than conventional batteries (e.g., cylindrical nickel-plated iron exterior cases), such as resins such as metal-laminated resin films or heat-resistant resin films. An example of a thin battery is a battery whose constituent elements are a power generating element, which is a unit consisting of a positive electrode, an electrolyte, and a negative electrode, and a resin exterior body that houses the power generating element. While such batteries are prone to battery expansion due to gas generation, gas generation can be effectively suppressed by using the metal layer-coated zinc foil of the present invention. In a thin battery, the thickness of the structure of one unit consisting of a positive electrode, an electrolyte, and a negative electrode is generally as thin as 5 mm or less. In a thin battery, it is preferable to use a single unit. [Example]

[0042] 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, "%" or "ppm" means "% by mass" or "ppm by mass" expressed on a mass basis.

[0043] Example 1 (1) 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 200 g / L, calculated as the total amount of sulfate ions as H2SO4. Bismuth nitrate was added to this. The bismuth concentration was adjusted so that the bismuth content in the target zinc foil was 750 ppm. (2) Reductive deposition of zinc The anode was a DSE consisting of a titanium electrode coated with iridium oxide. The cathode was an aluminum plate. Electric current was applied between the anode and cathode while the electrolyte was heated to 35°C. The electrolyte circulation rate was 0.029 L / (min·mm 2 ) and the current density was 2000A / m 2 Electrolysis was carried out under these conditions to obtain a foil body made of electrolytic foil with a thickness of 50 μm. (3) Preparation of displacement plating solution Bismuth nitrate was dissolved in ion-exchanged water to adjust the bismuth concentration to 36 mg / L, and ammonia water was added to adjust the pH to 6 to prepare a displacement plating solution. (4) Surface treatment of the foil itself The foil body obtained in (2) above was immersed for 5 minutes in the displacement plating solution obtained in (3) above at 25° C. to obtain a metal bismuth layer-coated zinc foil.

[0044] Example 2 A displacement plating solution was prepared in the same manner as in Example 1, except that the bismuth concentration in the surface treatment solution was set to 50 mg / L and ethylenediaminetetraacetic acid was added in an amount equimolar to the bismuth nitrate. Furthermore, a metal bismuth layer-coated zinc foil was obtained in the same manner as in Example 1, except that the immersion time of the foil body was set to 10 minutes.

[0045] Example 3 A displacement plating solution was prepared in the same manner as in Example 1, except that indium nitrate was used instead of bismuth nitrate, the indium concentration was adjusted to 960 mg / L, and sodium hydroxide was added to adjust the pH to 6.5. Furthermore, a metal indium layer-coated zinc foil was obtained in the same manner as in Example 1, except that the immersion time of the foil body was set to 30 seconds.

[0046] Example 4 The electroplating solution used was DAIN IN-161 (manufactured by Daiwa Kasei Co., Ltd.), an indium electroplating solution adjusted to an indium concentration of 30,000 mg / L. An indium plate (manufactured by Nilaco Corporation) was used as the anode. The foil body obtained in (2) above was used as the cathode. The cathode was placed between two anodes. With the electroplating solution maintained at 30°C, electricity was passed between the anode and cathode so that a metal layer of a predetermined thickness was formed on the surface of the foil body, and a zinc foil coated with a metal indium layer was obtained. The current density was 1 A / cm. 2 It was decided.

[0047] Example 5 The electroplating solution used was DAIN TINGOOD 101 (manufactured by Daiwa Chemical Industry Co., Ltd.), which was adjusted to a tin concentration of 20,000 mg / L. A tin plate (manufactured by Nilaco Corporation) was used as the anode. The electroplating solution was maintained at 25°C, and the current density was set to 2 A / cm. 2 A metal tin layer-coated zinc foil was obtained in the same manner as in Example 4, except for the above.

[0048] Comparative Example 1 The foil body having a thickness of 50 μm obtained in (2) of Example 1 was used as it was without being subjected to the metal layer coating treatments of (3) and (4) above.

[0049] 〔evaluation〕 For the zinc foils obtained in the examples and comparative examples, the content ratio of each element, the size of zinc crystal grains, and the apparent density of the zinc foil were measured by the methods described above. The amount of gas generated from the zinc foil was also measured by the following method. The results are shown in Table 1.

[0050] [Measurement of gas generation rate] A 20% aqueous solution of ammonium chloride was used as the electrolyte. Zinc foil was immersed in this electrolyte and left to stand at 60°C for one week. The amount of hydrogen gas generated during this time was measured using a glass cell. The measurement results were converted into the amount of gas generated per unit area and per day.

[0051] [Identification of metal elements contained in the coated metal layer and measurement of the thickness of the coated metal layer] The metal elements contained in the coating metal layer on the coated surface of the zinc foil were identified and the thickness of the coating metal layer was measured using a Marcus-type high-frequency glow discharge optical emission surface analyzer (GD-OES, manufactured by Horiba, Ltd., JY-5000RF). The discrimination and measurement (power = 30 W) were performed by digging into the zinc foil from its surface using argon sputtering, while measuring the intensity of each detected metal element. Sputtering was performed in pulse mode, with a sputtering rate of 14.5 nm / s (Cu equivalent), and the sputtering time was converted into the digging depth. Specifically, seven metal elements were measured: bismuth, indium, aluminum, gallium, tin, silver, and manganese. From the depth profile obtained for each element, elements with an intensity of 0.2 Volt or higher and a peak top were identified as metal elements contained in the coating metal layer. The thickness of the metal layer was calculated based on the depth profile of the identified metal element, starting from the outermost surface, and based on the time it took for the intensity to decrease to 1 / 5 of the maximum intensity, using the sputtering rate. In addition, when peak tops of multiple metal species exist, the peak top position is not necessarily located only on the outermost surface of the metal layer-coated zinc foil, but may be located between the outermost surface and the zinc layer. When peak tops of multiple metal species are observed, the thickness of the metal layer can be calculated by starting from the outermost surface and selecting the time closest to the zinc layer as the end point from among multiple times at which the intensity of the metal element becomes 1 / 5 of the peak top, and using the sputtering rate mentioned above based on that time.

[0052] [Table 1]

[0053] As is clear from the results shown in Table 1, the metal layer-coated zinc foils obtained in the examples produced less gas than the zinc foils of the comparative examples. [Industrial Applicability]

[0054] According to the present invention, there is provided a zinc foil for use as an anode active material, which, when used as an anode active material in a thin battery in particular, generates less gas than ever before in the battery.

Claims

1. A metal layer-coated zinc foil having a foil body made of zinc as a base material and a metal layer disposed on the surface of the foil body, the metal element contained in the metal layer is at least one selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese; A metal layer-coated zinc foil, wherein the metal layer is disposed on both sides of the foil body, and the thickness of the metal layer differs between one side and the other side.

2. The metal layer-coated zinc foil according to claim 1 , wherein the metal element contained in the metal layer is at least one of bismuth, indium, and tin.

3. The metal layer-coated zinc foil according to claim 1 or 2, wherein the metal element contained in the metal layer is at least one of bismuth and indium.

4. The thickness of the metal layer is 5.0 × 10 －１ nm or more 3.0×10 ３ The metal layer-coated zinc foil according to claim 1 , wherein the surface roughness is 0.05 nm or less.

5. The metal layer-coated zinc foil according to claim 1 , wherein the foil body is an electrolytic foil.

6. The thickness of one surface of the metal layer (T Ｃ ) to the thickness of the other surface (T Ｓ ) ratio (T Ｓ / T Ｃ 6. The metal layer-coated zinc foil according to claim 1, wherein the number of carbon atoms is 2 or more.

7. The metal layer-coated zinc foil according to claim 1 , wherein the foil body has zinc as a base material and contains a metal element other than zinc.

8. 8. The metal layer coated zinc foil according to claim 7, wherein the metal element contained in the foil body is at least one selected from the group consisting of bismuth, indium, aluminum, magnesium, calcium, gallium, tin, barium, strontium, silver and manganese.

9. The metal layer-coated zinc foil according to claim 7 or 8, wherein the metal element contained in the foil body is bismuth.

10. 10. The metal layer coated zinc foil according to claim 7, wherein the content of the metal element contained in the foil body is 10 ppm or more and 10,000 ppm or less by mass with respect to the foil body.

11. 11. A method for producing a metal layer-coated zinc foil according to claim 1, wherein a metal layer containing at least one metal element selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese is formed on the surface of a foil body having zinc as a base material by a coating forming means.

12. The method according to claim 11, wherein the coating formation method is displacement plating.

13. The method according to claim 11 or 12, wherein the foil body is immersed in a displacement plating solution containing ions of at least one metal element selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese.

14. The method according to claim 13, wherein the metal element that becomes ions contained in the displacement plating solution is at least one of bismuth and indium.

15. The method according to claim 11, wherein the coating forming means is an electroplating method.

16. 16. The manufacturing method according to claim 15, wherein the foil body is immersed in an electroplating solution containing ions of at least one metal element selected from the group consisting of bismuth, indium, aluminum, gallium, tin, silver, and manganese, and an electric current is passed through the electroplating solution so that a layer containing the metal element having a predetermined thickness is formed.

17. The method according to claim 16, wherein the metal element that becomes ions contained in the electroplating solution is at least one of bismuth and indium.

18. A negative electrode active material for a battery, which uses the metal layer-coated zinc foil according to any one of claims 1 to 10.

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