Electrolytic Iron Foil

Abstract

[Subject] The purpose of the present invention is to provide an electrolytic foil and a collector for a battery, which can suppress the cracking and breaking during manufacturing that are worried about with thin filming, and further have sufficient strength and elongation during repeated charge and discharge in a secondary battery. [Solution] An electrolytic iron foil characterized by having a thickness of less than 20 μm, having a first surface and a second surface, and in both the first surface and the second surface, the value obtained by dividing the three-dimensional surface property parameter Sv by the thickness is less than 0.27.

Description

Technical Field

[0001] The present invention relates to an electrolytic foil particularly suitable for use as a current collector for a secondary battery or the like, and more particularly to an electrolytic iron foil. Background Art

[0002] Thinning the current collector is effective for increasing the capacity of conventionally used lithium ion secondary batteries, nickel hydrogen batteries, and the like. Electrolytic copper foil and the like are widely known as electrolytic foils for secondary batteries.

[0003] For example, Patent Document 1 discloses an electrolytic copper foil for use as a negative electrode for lithium ion secondary batteries, the purpose of which is to prevent foil breakage, wrinkles, and the like from occurring.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-014608 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, when copper foil is used for a battery collector, the possibility of strength reduction depending on the heating temperature during manufacture is considered a problem. In view of the above-mentioned issues, the inventors have studied metal materials that can suppress strength reduction even when heating during electrode manufacturing, and the results focus on iron (Fe) which has little strength reduction in the heating temperature region during collector manufacturing and is originally known as a material with excellent strength and elongation. In addition, iron is abundant in resources and also has advantages in terms of cost.

[0009] When iron or a metal material with a high iron content is used as a current collector material, the following material properties should be considered.

[0010] That is, when a metal with a high iron content is used as a current collector material, it may react with the electrolyte for aqueous battery applications. However, if it is a non-aqueous battery application, a current collector material with a high iron content can be used.

[0011] When manufacturing an iron foil having a thickness suitable for use as a current collector, a method of manufacturing by rolling and a method of manufacturing by electroplating can be considered.

[0012] Among them, when rolling is used to manufacture iron foil with a thickness less than 20 μm, continuous production is difficult and foreign matter and impurities are easily involved during rolling, resulting in many quality problems. In addition, the elongation of the iron foil obtained by work hardening may not be obtained. On the other hand, it is considered to use electroplating to manufacture iron foil, thereby manufacturing iron foil with strength, elongation, and thickness suitable for collectors.

[0013] The present inventors have conducted intensive studies in view of the above characteristics, and have completed the present invention. That is, an object of the present invention is to provide an electrolytic iron foil which can suppress cracking and breaking during handling, etc. and has strength and elongation.

[0014] Means for solving problems

[0015] Specifically, the electrolytic iron foil of the present invention is characterized in that (1) the foil has a thickness of less than 20 μm, has a first surface and a second surface, and a value obtained by dividing the three-dimensional surface texture parameter Sv by the thickness of the first surface and the second surface is 0.27 or less.

[0016] In the electrolytic iron foil of (1) above, preferably (2) on at least one of the first surface and the second surface, the value obtained by dividing the three-dimensional surface texture parameter Sv by the thickness is 0.24 or less.

[0017] In the electrolytic iron foil of (1) or (2) above, (3) preferably, on at least one of the first surface and the second surface, a three-dimensional surface texture parameter Sdq (root mean square slope) is 0.06 or more.

[0018] In the electrolytic iron foil according to any one of (1) to (3) above, (4) the iron content in the foil is preferably 80% by weight or more.

[0019] In the electrolytic iron foil according to any one of (1) to (4) above, (5) the elongation is preferably 1.2% or more.

[0020] In the electrolytic iron foil according to any one of (1) to (5) above, preferably (6) on at least one of the first surface and the second surface, a three-dimensional surface texture parameter Sdr is 0.2% or more.

[0021] In addition, the electrolytic iron foil for a battery current collector in the present invention preferably comprises (7) the electrolytic iron foil according to any one of (1) to (6).

[0022] Furthermore, the electrolytic iron foil for a non-aqueous battery current collector in the present invention (8) preferably comprises the electrolytic iron foil according to any one of (1) to (7).

[0023] Effects of the Invention

[0024] According to the present invention, it is possible to provide an electrolytic iron foil which can suppress cracking and breaking during handling, and to provide an electrolytic iron foil which has sufficient strength and elongation to withstand repeated charge and discharge even when used as a current collector of a secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram showing a cross-sectional view of the electrolytic iron foil 10 in this embodiment.

[0026] Figure 2 This is a schematic diagram of a test piece for measuring the tensile strength, maximum load, and elongation of the electrolytic iron foil 10 in this embodiment. DETAILED DESCRIPTION

[0027] 《Electrolytic Iron Foil 10》

[0028] Hereinafter, embodiments of the electrolytic foil for carrying out the present invention will be described.

[0029] Figure 1 This is a diagram schematically showing an electrolytic iron foil according to one embodiment of the present invention. The electrolytic iron foil according to this embodiment can be used as a current collector for a battery positive electrode in addition to a current collector for a battery negative electrode.

[0030] The battery may be a secondary battery or a primary battery. In particular, a non-aqueous secondary battery such as a lithium secondary battery, a sodium secondary battery, a magnesium secondary battery, or an all-solid battery can be applied.

[0031] like Figure 1 As shown, the electrolytic iron foil 10 of the present embodiment has a first surface 10a and a second surface 10b. The electrolytic iron foil 10 of the present embodiment can be pure iron, and as long as the subject of the present invention can be solved, it can contain one or more metals other than iron as secondary components, and can also contain inevitable impurities. Here, pure iron refers to the content of metal elements other than iron being less than 0.1% by weight. By making the content of metal elements other than iron less than 0.1% by weight, the generation of rust is reduced compared with the rolled iron foil (also called rolled steel foil) in normal circulation. Therefore, it has the advantages of excellent corrosion resistance and rust resistance during transportation and storage.

[0032] In addition, the iron foil in the present invention is defined as a foil having an iron content of 80% by weight or more. It is preferable to set the iron content to 80% by weight or more and contain metals other than iron as secondary components, thereby having the properties of iron (strength, elongation) and taking into account both the improvement of strength and the cost.

[0033] In the present embodiment, when the electrolytic iron foil 10 contains a metal other than iron, examples of the metal other than iron include nickel, cobalt, molybdenum, phosphorus, boron, etc. From the viewpoint of having the characteristics (strength, elongation) of iron and further seeking to improve the strength, the metal other than iron preferably contains nickel. In this case, the content of nickel in the foil is preferably 3% by weight or more and less than 20% by weight, more preferably 3% by weight or more and less than 18% by weight, and further preferably 5% by weight or more and less than 16% by weight.

[0034] In addition, in this embodiment, when all metals contained in the electrolytic iron foil 10 are set to 100 weight %, the content rate of metals other than iron and nickel is preferably 0.1 weight % or less.

[0035] In the present embodiment, as a method for obtaining the contents of iron and metals other than iron contained in the electrolytic iron foil, for example, inductively coupled plasma (ICP) emission spectrometry can be cited, etc. In addition, the metal content can be calculated from the obtained contents of each metal.

[0036] The electrolytic iron foil 10 of the present embodiment is formed by electroplating. Specifically, the electrolytic iron foil 10 can be formed using an electroplating bath containing iron ions.

[0037] It is to be noted that the electrolytic iron foil 10 of the present embodiment has a first surface and a second surface. For the convenience of the following description, when manufacturing the electrolytic iron foil 10, the surface (substrate surface) in contact with the support (substrate) supporting the electrolytic foil is set as the first surface 10a, and the other surface (electrolysis surface) is set as the second surface 10b. It is to be noted that, hereinafter, the first surface (10a) is referred to as the substrate surface, and the second surface 10b is referred to as the electrolysis surface.

[0038] The electrolytic iron foil 10 of this embodiment may be a coating without adding a brightener to the above-mentioned electroplating bath (also referred to as "non-bright iron coating" for convenience), or a "bright iron coating" with adding a brightener (including a brightener for semi-brightness).

[0039] It should be noted that the above-mentioned "brightness" or "non-brightness" is difficult to distinguish with strict numerical values ​​based on visual evaluation of appearance. Furthermore, the degree of brightness may also vary depending on other parameters such as the bath temperature described later. Therefore, the "brightness" and "non-brightness" used in this embodiment are only definitions focusing on the presence or absence of a brightener.

[0040] The electrolytic iron foil 10 of the present embodiment is characterized in that it has a first surface 10a (base material surface) and a second surface 10b (electrolysis surface), and the value obtained by dividing the three-dimensional surface property parameter Sv by the thickness of the electrolytic iron foil 10 on both the first surface 10a (base material surface) and the second surface 10b (electrolysis surface) is 0.27 or less. In addition, it is preferred that the value obtained by dividing the three-dimensional surface property parameter Sv by the thickness of the electrolytic iron foil 10 on at least one of the first surface 10a and the second surface 10b is 0.24 or less. The reason is as follows.

[0041] That is, regarding the electrolytic iron foil 10 of the present embodiment, as the capacity of secondary batteries increases, there is a demand for thinner electrolytic foils used in current collectors. As a result, in order to meet these demands, high-strength metal foils are manufactured by electroplating.

[0042] The present inventors have repeatedly conducted in-depth studies to produce an electrolytic foil that can suppress cracking and breaking during manufacturing and handling (including battery assembly) that are concerns associated with thinning, and can also suppress wrinkling and breaking when using active materials that have a large volume change during repeated charge and discharge in secondary batteries.

[0043] As a result, the inventors found that when electrolytic iron foil is used as a high-strength electrolytic foil, the above-mentioned effects can be obtained by controlling the surface shape, and thus conceived the present invention.

[0044] Specifically, as a parameter representing the surface shape of the electrolytic iron foil of the present embodiment, the “maximum valley depth” (three-dimensional surface texture parameter Sv) in the surface roughness specified in ISO 25178-2:2012 is applied.

[0045] That is, the tensile strength of a metal foil is theoretically a value that is not affected by thickness. However, according to the research of the present inventors, in fact, when the thickness of the electrolytic iron foil becomes thinner (specifically, less than 20 μm), the tensile strength is sometimes extremely reduced compared to the expected value. For example, when making multiple 6 μm electrolytic iron foils made under the same bath conditions, sometimes a significant reduction in strength occurs due to manufacturing conditions, etc. In other words, it has been confirmed that even when making electrolytic iron foils of the same thickness, the tensile strength and maximum load are sometimes significantly reduced. As one of the reasons, the present inventors believe that the reason is that it is easily affected by the unevenness of the metal foil surface.

[0046] In particular, it was found that due to the generation of significantly deep concave and trough portions, the original strength (tensile strength or maximum load, etc.) of the electrolytic iron foil may not be obtained. Figure 1In the case of a portion where the distance t between the first surface 10a and the second surface 10b shown in (b) is particularly short, the stress concentrates on this portion and the cracks generated become cracks that propagate to the entire electrolytic iron foil starting from this portion. As a result, it is believed that the foil is easily broken and shattered, and only a strength lower than the original strength can be obtained.

[0047] It is to be noted that in electrolytic iron foil, although it also depends on the plating conditions, when the foil is formed after plating without grinding, the electrolytic surface is prone to show the unevenness of the plating particles precipitated due to iron plating, that is, unevenness with a small spacing, and the unevenness is easy to become larger than the plating composed of extremely fine grains (plating with a strong leveling effect). In addition, on the contrary, the substrate surface side does not reflect the unevenness of the substrate as in the case of extremely fine grains, but is easy to reflect the large unevenness existing on the surface of the support. In other words, in the iron foil where the unevenness of the plating particles is easy to appear, it is necessary to control so that the unevenness of the electrolytic surface side does not become too large, and since the unevenness of the electrolytic surface side is easy to appear, the unevenness control of the substrate surface side also becomes important.

[0048] As a result of repeated studies based on the above assumptions, in the surface of the electrolytic iron foil of the present embodiment, the relationship between Sv (maximum valley depth) and the thickness of the electrolytic iron foil is set to a predetermined value, thereby obtaining an electrolytic iron foil that has not been available in the past.

[0049] The electrolytic iron foil 10 of the present embodiment based on the above-mentioned subject matter is characterized in that the value of "Sv (maximum valley depth) [μm] / thickness of the electrolytic iron foil 10 [μm]" on both sides (either the first side 10a or the second side 10b) is 0.27 or less. In addition, the thickness of the electrolytic iron foil 10 is referred to as "thickness".

[0050] When the value of Sv (maximum valley depth) / thickness of the electrolytic iron foil 10 exceeds 0.27 on any surface, it is possible that the required value of the original strength (tensile strength or maximum load) of the electrolytic iron foil cannot be obtained, so it is not preferred. In other words, it is characterized in that it does not exceed 0.27 on any surface. From the perspective of further stabilizing the strength (easy to maintain the original strength), it is preferably 0.24 or less, and more preferably 0.22 or less on at least one of the first surface 10a and the second surface 10b. Furthermore, from the perspective of further stabilizing the strength, the value of Sv / thickness on both surfaces of the electrolytic iron foil 10 (either the first surface 10a or the second surface 10b) is further preferably 0.24 or less, and particularly preferably 0.22 or less. In addition, there is no particular restriction on the lower limit value of Sv (maximum valley depth) / thickness of the electrolytic iron foil 10, and it is preferably 0.01 or more.

[0051] It should be noted that the three-dimensional surface property parameter Sv of the electrolytic iron foil 10 of the present embodiment can be obtained using a known non-contact three-dimensional surface roughness measuring device or the like.

[0052] It is noted that, from the viewpoint of further suppressing cracking and breaking during manufacturing and handling (including battery assembly), in the electrolytic iron foil 10 of the present embodiment, the values ​​of Sv [μm] (maximum valley depth), Sz [μm] (maximum height), and Sa [μm] (arithmetic mean height) on the first surface 10a and the second surface 10b preferably have the following values. It is noted that the three-dimensional surface texture parameters in the present embodiment refer to the values ​​measured in accordance with ISO-25178-2: 2012 (corresponding to JIS B 0681-2: 2018).

[0053] Sv···less than 5.0 μm, more preferably less than 4.0 μm

[0054] Sz···less than 10.0 μm, more preferably less than 8.0 μm

[0055] Sa···less than 1.0 μm, more preferably less than 0.6 μm

[0056] Here, the lower limits of Sv, Sz, and Sa are not particularly limited, but usually, Sv is preferably 0.2 μm or more, Sz is preferably 0.8 μm or more, and Sa is preferably 0.03 μm or more.

[0057] In addition, from the viewpoint of active material adhesion, in the electrolytic iron foil 10 of the present embodiment, each value of Sdq (root mean square slope), Sdr (developed interface area ratio), and Sal (autocorrelation length) of at least one of the first surface 10a and the second surface 10b preferably has the following values. It should be noted that the three-dimensional surface property parameters in the present embodiment refer to the values ​​measured in accordance with ISO-25178-2:2012 (corresponding to JIS B 0681-2:2018).

[0058] Sdq···0.06% or more, more preferably 0.10% or more, further preferably 0.20% or more Sdr···0.20% or more, more preferably 0.50% or more, further preferably 1.00% or more

[0059] Sal···less than 50 μm, more preferably 30 μm or less, further preferably 20 μm or less

[0060] When used as a current collector, from the viewpoint of close adhesion of the active material, an electrolytic iron foil having finely spaced concavities and convexities formed by plated crystal grains is preferred. In particular, by setting the values ​​of Sdq and Sdr to the above ranges, the concavities and convexities of the plated crystal grains can be made into a suitable shape. In particular, by setting the Sdr of at least any one surface to 1.00% or more, it is expected that the close adhesion of the active material will be further improved.

[0061] The upper limit of Sdq is not particularly limited, but is less than 1. The upper limit of Sdr is not particularly limited, but when it is extremely large, the unevenness may be too high, so it is usually less than 50%.

[0062] Regarding the lower limit of Sdq, from the viewpoint of improving the adhesion of the active material on both sides, the Sdq of both the first side and the second side is preferably 0.06 or more, more preferably 0.1 or more, and further preferably 0.2 or more. In addition, regarding the lower limit of Sdr, from the viewpoint of improving the adhesion of the active material on both sides, the Sdr of both the first side and the second side is 0.20% or more, more preferably 0.5% or more, and further preferably 1.0% or more. The lower limit of Sal is not particularly limited, and is usually preferably 1 μm or more.

[0063] It should be noted that in order to control the three-dimensional surface property parameters Sv, Sz, Sa, Sdq, Sdr, and Sal in the electrolytic iron foil 10 of the present embodiment within the range of the above values, as described later, methods such as controlling plating conditions, grinding the surface of the support body, and controlling the unevenness of the surface of the electrolytic iron foil obtained by etching treatment, electrolytic grinding, etc. can be listed.

[0064] Next, the thickness of the electrolytic iron foil 10 in the present embodiment will be described.

[0065] The thickness of the electrolytic iron foil 10 in this embodiment is characterized by being less than 20 μm. This is because a thickness of more than 20 μm is inconsistent with the design concept, since the original goal is to achieve high capacity by thinning the foil, and the cost advantage over the known rolled foil is reduced.

[0066] In addition, the upper limit of the thickness of the electrolytic iron foil 10 in the present embodiment is preferably 18 μm or less, more preferably 15 μm or less, and further preferably 12 μm or less.

[0067] The lower limit of the thickness of the electrolytic iron foil 10 in this embodiment is not particularly limited, but is preferably 1.5 μm, for example. The reasons include strength against the effects of charge and discharge, and cracks, breakage, and wrinkles that may occur during battery manufacturing and handling.

[0068] In addition, the lower limit of the thickness of the electrolytic iron foil 10 in the present embodiment is more preferably 5 μm or more.

[0069] In addition, the "thickness of the electrolytic iron foil 10" in this embodiment can be obtained by thickness measurement using a micrometer or thickness measurement based on a weight method.

[0070] The tensile strength of the electrolytic iron foil 10 of the present embodiment is preferably 130 MPa or more. A tensile strength of less than 130 MPa is not preferred because cracks may occur due to repeated charge and discharge when used as a current collector of a secondary battery.

[0071] The lower limit of the tensile strength of the electrolytic iron foil 10 in this embodiment is more preferably 180 MPa or more, and more preferably 350 MPa or more. On the other hand, the upper limit of the tensile strength of the electrolytic iron foil 10 in this embodiment is more preferably 800 MPa or less, and more preferably 700 MPa or less.

[0072] The maximum load of the electrolytic iron foil 10 of the present embodiment is preferably 12.0 N or more, and more preferably 15.0 N or more. If the maximum load is less than 12.0 N, the foil may be broken or cracked when manufacturing the electrolytic iron foil 10 and manufacturing the battery, which reduces the handling property (operability), so it is not preferred.

[0073] In this embodiment, the tensile strength and maximum load of the electrolytic iron foil 10 can be measured, for example, as follows. The SD-type bar sample cutter (model: SDL-200) manufactured by Dunbel Co., Ltd. is used, and a cutter (model: SDK-400) in accordance with JIS K6251 is used. Figure 2 The metal piece is punched out in the shape of a dumbbell No. 4 of JIS K6251 as shown. Then, the tensile test can be carried out using the test piece in accordance with the tensile test method of JIS Z 2241, which is the JIS standard for metal test pieces.

[0074] The elongation of the electrolytic iron foil 10 of the present embodiment is preferably 1.2% to 15%, more preferably 1.5% to 15%, and further preferably 2.0% to 15%. When the elongation is less than 1.2%, when the obtained electrolytic iron foil is used as a current collector of a secondary battery, it may not be able to cope with repeated charge and discharge, so it is not preferred. It should be noted that the elongation of the electrolytic iron foil in the present embodiment refers to the value measured according to the tensile test method of JIS Z 2241, similar to the above-mentioned tensile strength and maximum load.

[0075] Since the electrolytic iron foil 10 of the present embodiment has the above-described configuration, the following effects are achieved.

[0076] That is, in the process of manufacturing a metal foil as a current collector, the drying temperature may reach 200° C. or higher (400° C. or lower), and the copper foil used as a conventional current collector material may have its strength reduced by the drying temperature.

[0077] Since the material property of iron is that the strength reduction in the above-mentioned heating temperature band is low, when the electrolytic iron foil of this embodiment is used as a current collector, the strength reduction during heating during the above-mentioned manufacturing and handling (when assembling a battery, when used as a current collector) can be suppressed.

[0078] Furthermore, in the electrolytic iron foil of the present embodiment, by controlling Sv (maximum valley depth) [μm] / thickness [μm] of the electrolytic iron foil 10, even in the case of a thin foil, the decrease in strength and elongation due to the influence of the unevenness of the foil surface can be suppressed. Therefore, it is possible to provide an electrolytic iron foil that can suppress the cracking and breaking of the foil during manufacturing and handling (when assembling a battery, when using it as a current collector) when the electrolytic iron foil is used as a current collector, and the electrolytic iron foil has strength and elongation.

[0079] [Method for Manufacturing Electrolytic Iron Foil 10]

[0080] When producing the electrolytic iron foil 10 of the present embodiment, electrolytic iron is formed on a support body composed of a titanium plate, a stainless steel plate, or the like, and then the plating layer is peeled off from the support body by a known method, thereby obtaining the electrolytic iron foil 10 .

[0081] The specific material of the support body is not limited to the titanium plate or the stainless steel plate described above, and other known metal materials can be applied within the scope of the present invention.

[0082] In addition, hereinafter, the titanium plate is also referred to as a Ti base material.

[0083] The conditions of the electrolytic iron plating bath are as follows.

[0084] [High concentration iron plating conditions]

[0085] Bath composition

[0086] Ferric chloride tetrahydrate: 500~1000g / L

[0087] Temperature: 60~110℃

[0088] pH: below 3.0

[0089] ·Stirring: air stirring or jet stirring

[0090] Current density: 3~100A / dm 2

[0091] In addition, hydrochloric acid, sulfuric acid, etc. can be used for the adjustment of the said pH.

[0092] It should be noted that, regarding the temperature of the bath of the above-mentioned high-concentration iron plating, when it is lower than 60°C, the three-dimensional surface property parameter Sv tends to become high, and in addition, the layer may not be precipitated, and it may be peeled off from the support body with the increase of stress during plating, so it is not preferred. From the viewpoint of improving manufacturing efficiency, it is more preferably 85°C or higher. On the other hand, the upper limit of the bath temperature is not particularly limited, but when it exceeds 110°C, the evaporation of the plating bath becomes violent, and the productivity is poor, so it is not preferred.

[0093] It should be noted that regarding the pH of the bath of the high-concentration iron plating, when the pH exceeds 3.0, the three-dimensional surface property parameter Sv tends to become high, so it is not preferred. From the viewpoint of controlling the three-dimensional surface property parameter Sv to a preferred value, the pH is more preferably below 1.0. Regarding the current density, when the pH is set to below 1.0, it is preferred to set the current density to 5 A / dm based on the relationship between the dissolution rate of iron and the precipitation rate of iron. 2 above.

[0094] [Low concentration iron plating conditions]

[0095] Bath composition

[0096] Ferric chloride tetrahydrate: 200~500g / L

[0097] Total amount of any one or more of aluminum chloride, calcium chloride, beryllium chloride, manganese chloride, potassium chloride, chromium chloride, lithium chloride, sodium chloride, magnesium chloride, and titanium chloride: 20-300 g / L

[0098] Temperature: 25~110℃

[0099] pH: below 5.0

[0100] ·Stirring: air stirring or jet stirring

[0101] Current density: 3~100A / dm 2

[0102] Regarding the current density of the low-concentration iron plating, the current density is less than 3A / dm 2 In the case of 10A / dm, the three-dimensional surface texture parameter Sv tends to become high, and it may be impossible to produce foil, and the production efficiency may be reduced, so it is not preferred. From the viewpoint of improving the production efficiency, it is more preferable to set it to 10A / dm 2 On the other hand, when the current exceeds 100A / dm 2In the case of 80A / dm, plating burn may occur, or the stress during plating may increase and the plating may peel off from the support body, so it is not preferred. From the perspective of suppressing plating burn and improving production efficiency, it is more preferably set to 80A / dm 2 In addition, an appropriate amount of an anti-dent agent may be added.

[0103] Regarding the bath composition of the low-concentration iron plating, any one of aluminum chloride, calcium chloride, beryllium chloride, manganese chloride, potassium chloride, chromium chloride, lithium chloride, sodium chloride, magnesium chloride, and titanium chloride may be added alone or in combination of a plurality of them.

[0104] The plating bath when forming the electrolytic iron foil 10 of the present embodiment may also contain nickel as described above. By adding nickel to the bath, the three-dimensional surface property parameter Sv tends to be lowered, and the strength and corrosion resistance of the foil can be improved. In addition, by adding nickel to the bath, the current density under the plating conditions can be increased, which also has the advantage of improving productivity.

[0105] As the plating bath containing nickel, the following conditions can be mentioned.

[0106] Bath composition

[0107] Ferric chloride tetrahydrate: 500~1000g / L

[0108] Nickel chloride hexahydrate or nickel sulfate hexahydrate: 10~400g / L

[0109] Temperature: 60~110℃

[0110] pH: below 3.0

[0111] ·Stirring: air stirring or jet stirring

[0112] Current density: 3~100A / dm 2

[0113] As a method for producing the electrolytic iron foil 10 according to the present embodiment, the following steps can be roughly listed.

[0114] First, the support body on which the plated layer is formed is subjected to pretreatment such as grinding, cleaning, wiping, water washing, pickling, etc., and then immersed in the above-mentioned plating bath to form an electrolytic iron plated layer on the support body. The formed plated layer is dried and then peeled off to obtain an electrolytic iron foil 10.

[0115] In the above process, the grinding in the pretreatment of the support is described. When the electrolytic iron foil 10 of the present embodiment is manufactured, the surface shape of the support for forming the plating layer is substantially transferred to the plating layer and becomes one surface (substrate surface) of the electrolytic iron foil 10. In addition, the thinner the thickness of the electrolytic iron foil 10, the thinner the shape of the surface (electrolysis surface) of the electrolytic iron foil 10, and the higher the possibility of being affected by the surface shape of the support.

[0116] In other words, in the electrolytic iron foil of this embodiment, although it also depends on the plating conditions, the electrolytic surface is prone to unevenness of the plating particles precipitated by the iron plating. In addition, the substrate surface side is prone to reflect the large unevenness existing on the support surface.

[0117] Therefore, in the present embodiment, in order to set the value of the three-dimensional surface texture parameter Sv of each surface of the electrolytic iron foil 10 to the above range, it is preferable to control the surface shape of the support, for example, the surface roughness Sa of the support.

[0118] Specifically, the surface roughness Sa of the support is preferably 0.25 μm or less, more preferably 0.20 μm or less, and further preferably 0.18 μm or less. In addition, when nickel is contained in the plating bath when forming the electrolytic iron foil, the surface roughness Sa of the support is particularly preferably 0.16 μm or less. In addition, there is no particular restriction on the lower limit of the surface roughness Sa of the support, but it is preferably 0.01 μm or more.

[0119] In order to set the surface roughness Sa of the support body to the above value, for example, the surface of the support body can be ground by using known means. Here, the grinding direction is not particularly limited, and grinding can be performed in a specific direction such as the width direction or the length direction of the support body, or it can be performed randomly.

[0120] Before or after the electrolytic iron foil 10 is peeled off from the support, the outermost surface of the electrolytic iron foil 10 may be subjected to roughening treatment, rust prevention treatment, etc. within the range that can solve the problem of the present invention. In addition, a known treatment for imparting conductivity such as carbon coating may be applied.

[0121] For example, by providing a nickel roughening layer and a copper roughening layer on both sides of the electrolytic iron foil 10, the adhesion performance of the active material when used as a current collector can be improved, so it is preferred. It should be noted that the roughening layer is disclosed in, for example, International Publication WO2020 / 017655, so a detailed description is omitted here.

[0122] It should be noted that in this embodiment, as a method for controlling the surface roughness (three-dimensional surface properties) of the electrolytic iron foil 10, a method of controlling the plating conditions as described above and a method of grinding the surface of the support body are listed and described, but are not limited to these. For example, by using etching treatment, electrolytic grinding, etc. to smooth the surface of the electrolytic iron foil 10 itself, the desired three-dimensional surface properties can also be obtained.

[0123] In this embodiment, an example of manufacturing electrolytic iron foil by a continuous manufacturing method (e.g., drum method, roll-to-roll method) using a support is described, but the present invention is not limited to this method, and for example, batch manufacturing using a cut plate is also possible.

[0124] The electrolytic iron foil 10 in the present embodiment may be a laminated electrolytic foil having at least one metal layer on at least one of the first surface 10a and the second surface 10b. In this case, the metal layer may include Cu, Ni, Co, Zn, Sn, Cr, and alloys thereof. In particular, the metal layer may be a nickel-iron alloy layer, or a laminated electrolytic foil of the electrolytic iron foil 10 in the present embodiment and a nickel-iron alloy layer.

[0125] Example

[0126] The present invention will be described in more detail below with reference to Examples. First, the measurement methods in the Examples will be described.

[0127] [Determination of tensile strength, maximum load and elongation]

[0128] The tensile strength, maximum load and elongation of the obtained electrolytic foil were measured as follows. First, a metal sheet was punched out using an SD-type rod-type sample cutter (model: SDL-200) manufactured by Danbel Co., Ltd. and a cutter (model: SDK-400) in accordance with JIS K 6251-4. Next, the test piece was subjected to a tensile test in accordance with the tensile test method of JIS Z 2241, a JIS standard for metal test pieces. A schematic diagram of the test piece is shown in FIG. Figure 2 .

[0129] In addition, as the apparatus of the tensile test, a tensile testing machine (Tensilon RTC-1350A, a universal material testing machine manufactured by ORIENTEC) was used. Moreover, as the measurement conditions, the test was performed at room temperature and a tensile speed of 10 mm / min.

[0130] The elongation was calculated using the following formula.

[0131] (Travel distance (stroke) of the testing machine) / (distance between original marking points)×100

[0132] In addition, the maximum test force in the above tensile test is shown in the table as the maximum load [N].

[0133] [Measurement of thickness]

[0134] The thickness of the obtained electrolytic foil was measured using a micrometer. The obtained value is shown in the column "Measured Thickness" in Table 1.

[0135] [Measurement of surface shape]

[0136] In the obtained electrolytic foil, the surface in contact with the support (substrate surface) is set as the first surface, and the other surface (electrolytic surface) is set as the second surface, and the surface shape of each surface is measured. Specifically, using the laser microscope OLS5000 manufactured by Olympus Corporation, the values ​​of the three-dimensional surface property parameters Sv [μm] (maximum valley depth), Sz [μm] (maximum height), Sa [μm] (arithmetic mean height), Sdq (root mean square slope), Sdr (developed interface area ratio), and Sal (autocorrelation length) are calculated and measured. On this basis, Sv [μm] / measured thickness [μm] is calculated. It should be noted that the above-mentioned three-dimensional surface property parameters in this embodiment refer to the values ​​measured in accordance with ISO-25178-2: 2012 (corresponding to JIS B 0681-2: 2018).

[0137] As a measurement method, three fields of view (1 field of view 258μm×258μm) are scanned under the condition of 50 times the objective lens (lens name: MPLAPON50XLEXT) to obtain analysis data. Next, for the obtained analysis data, an analysis application is used to perform automatic correction processing, namely noise removal and tilt correction. Then, click the icon for surface roughness calculation measurement for analysis to obtain various parameters of surface roughness. It should be noted that the filtering conditions (F operation, S filtering, L filtering) in the analysis were not set at all, and the analysis was performed under no conditions. The results are shown in Table 2 (the parameter values ​​are set to the average values ​​in the three fields of view).

[0138] [Manufacturing of negative electrode plates and evaluation of active material adhesion]

[0139] Artificial graphite (particle size: about 10 μm) is used as the negative electrode active material and polyvinylidene fluoride (PVDF) is used as the binder. N-methylpyrrolidone (NMP) is added in an appropriate amount to a mixture of 96% by weight of the negative electrode active material and 4% by weight of the binder, respectively, to prepare a negative electrode mixture paste with adjusted viscosity. The negative electrode mixture paste is applied to the electrolytic surface side of the electrolytic foil and dried to prepare a negative electrode plate. At this time, the total mass of the negative electrode active material and the binder becomes 5 mg / cm after drying. 2 The coating is carried out in a manner of

[0140] For evaluation of the adhesion of the active material, a 180° bending test was performed on the negative electrode plate with the coated surface facing outward to confirm whether the negative electrode active material was peeled off. The results are shown in Table 3.

[0141] A case where there is no peeling of the active material in the bent portion is defined as A.

[0142] The case where the exposure of the base material could not be confirmed visually at the bent portion and only a portion of it was peeled off was designated as B.

[0143] The case where the base material is partially peeled off while the base material can be visually confirmed to be exposed at the bent portion is defined as C.

[0144] The case where the active material peeled off at the bent portion and its periphery and the exposure of the substrate was visually confirmed was defined as D.

[0145] <Example 1>

[0146] Electrolytic iron is formed on a support. Specifically, first, a Ti substrate is used as a support on the upper surface of which an electrolytic iron foil is formed, and the surface of the Ti substrate is ground so that the surface roughness Sa of the Ti substrate becomes the value in Table 1. The grinding direction is roughly parallel to the length direction of the Ti substrate (the traveling direction, longitudinal direction during continuous manufacturing). The Ti substrate is subjected to known pretreatments such as pickling and water washing using 7wt% sulfuric acid. Next, the pretreated Ti substrate is impregnated and electrolyzed in the iron plating bath shown below, and an electrolytic iron plating layer of the thickness shown in Table 1 is formed on the Ti substrate as an electrolytic foil.

[0147] [Iron plating conditions]

[0148] Bath composition

[0149] Ferric chloride tetrahydrate: 725g / L

[0150] Temperature: 90℃

[0151] pH: 1.0

[0152] ·Stirring: Air stirring

[0153] Current density: 10A / dm 2

[0154] After the plated layer formed as described above was fully dried, the plated layer was peeled off from the Ti substrate to obtain an electrolytic iron foil. The thickness of the obtained electrolytic iron foil was the value shown in "actually measured thickness" in Table 1.

[0155] The obtained electrolytic iron foil was subjected to measurement of tensile strength, maximum load, elongation, thickness, surface shape of the electrolytic surface and the substrate surface, and evaluation of adhesion with the active material.

[0156] It is to be noted that the content of Fe and Mn in the electrolytic iron foil is Fe: 99.9wt% or more, Mn: less than 0.01wt% of pure iron. It can be confirmed that the obtained foil is not a rolled iron foil based on the Mn content (refer to the discrimination method A described later). The Fe and Mn contents are numerical values ​​obtained by calculation. When calculating, first, the electrolytic iron foil of Example 1 is dissolved, and the Mn content is measured by ICP emission analysis (measuring device: manufactured by Shimadzu Corporation, inductively coupled plasma emission spectrometer ICPE-9000). At this time, the remaining part other than Mn is set to Fe, and the Fe content is calculated. The content of each metal is calculated based on the Fe and Mn contents.

[0157] <Example 2>

[0158] The same procedure as in Example 1 was carried out except that the thickness was set as shown in Table 1. The results are shown in Tables 1 to 3.

[0159] <Examples 3 and 4>

[0160] The same procedure as in Example 1 was carried out except that the iron plating conditions were as follows and the thickness was as shown in Table 1. The results are shown in Tables 1 to 3.

[0161] Bath composition

[0162] Ferric chloride tetrahydrate: 725g / L

[0163] Nickel chloride hexahydrate: 75g / L

[0164] Temperature: 90℃

[0165] pH: 1.0

[0166] ·Stirring: Air stirring

[0167] Current density: 20A / dm 2

[0168] It should be noted that in Example 3, the iron foil is as follows: the contents of Fe, Ni and Mn in the electrolytic iron plating layer are Fe: 93.1wt%, Ni: 6.9wt%, Mn: less than 0.01wt%, and nickel is contained as a secondary component. It can be confirmed that the obtained foil is not a rolled foil based on the Mn content (refer to the discrimination method A described later). The contents of Fe, Ni and Mn are numerical values ​​obtained by calculation. When calculating, first, the electrolytic iron plating layer of Example 3 is dissolved, and the contents of Ni and Mn are measured by ICP emission analysis (measuring device: manufactured by Shimadzu Corporation, inductively coupled plasma emission spectrometry device ICPE-9000). At this time, the remaining part other than Ni and Mn is set to Fe, and the Fe content is calculated. The contents of each metal are calculated based on the contents of Fe, Ni and Mn.

[0169] <Examples 5 to 10>

[0170] The iron plating conditions were set as follows. In addition to the current density (A / dm 2 ), thickness, and surface roughness Sa of the Ti substrate were set as shown in Table 1. The same procedure as in Example 1 was performed. The results are shown in Tables 1 to 3.

[0171] Bath composition

[0172] Ferric chloride tetrahydrate: 300g / L

[0173] Aluminum chloride hexahydrate: 180g / L

[0174] Temperature: 90℃

[0175] pH: 1.0

[0176] ·Stirring: Air stirring

[0177] <Examples 11 to 13>

[0178] The iron plating conditions were set as follows. In addition to the current density (A / dm 2 ), thickness, and surface roughness Sa of the Ti substrate were set as shown in Table 1. The same procedure as in Example 1 was performed. The results are shown in Tables 1 to 3.

[0179] Bath composition

[0180] Ferric chloride tetrahydrate: 400g / L

[0181] Calcium chloride: 180g / L

[0182] Saccharin sodium: 3g / L

[0183] Sodium dodecyl sulfate: 0.1g / L

[0184] Sodium gluconate: 2g / L

[0185] Temperature: 90℃

[0186] pH: 1.5

[0187] ·Stirring: Air stirring

[0188] <Examples 14 to 18, 25 to 27>

[0189] The iron plating conditions were set as follows. In addition to the current density (A / dm 2 ), thickness, and surface roughness Sa of the Ti substrate were set as shown in Table 1. The same procedure as in Example 1 was performed. The results are shown in Tables 1 to 3.

[0190] Bath composition

[0191] Ferric chloride tetrahydrate: 1000g / L

[0192] Temperature: 90℃

[0193] pH: below 1.0

[0194] ·Stirring: Air stirring

[0195] <Example 19>

[0196] In the electroplating, the current density was changed as shown in Table 1 to continuously deposit. That is, as shown in "lower 5 / upper 15" in Table 1, the current density was changed as shown in Table 1 to continuously deposit. 2 After forming the target lower layer with a thickness of 1 μm, the 2 The upper layer was formed to have a thickness as shown in Table 1. Except for this, the same procedure as in Example 14 was carried out. The results are shown in Tables 1 to 3.

[0197] <Example 20>

[0198] In the electroplating, as shown in Table 1, the current density was changed in the same manner as in Example 19, and the deposition was continued. That is, as shown in "lower 5 / upper 15" in Table 1, the current density was changed at 5 A / dm 2 After forming the target lower layer with a thickness of 5 μm, the 2 The upper layer was formed to have a thickness as shown in Table 1. Except for this, the same procedure as in Example 14 was carried out. The results are shown in Tables 1 to 3.

[0199] <Example 21>

[0200] In the electroplating, the current density was changed as shown in Table 1 to continuously deposit. That is, as shown in "lower 15 / upper 5" in Table 1, the current density was changed as shown in Table 1 to continuously deposit. 2 After forming the target lower layer of 10 μm thickness, the 2The upper layer was formed to have a thickness as shown in Table 1. Except for this, the same procedure as in Example 14 was carried out. The results are shown in Tables 1 to 3.

[0201] <Examples 22 to 24>

[0202] The same procedure as in Example 14 was performed except that the thickness was set as shown in Table 1. The obtained electrolytic iron foil was annealed by box annealing at the temperature and time shown in Table 1. The results are shown in Tables 1 to 3.

[0203] <Example 28>

[0204] The Ti substrate pretreated in the same manner as in Example 1 was impregnated and electrolytically plated in the iron plating bath shown below to form an electrolytic iron plating layer having a thickness shown in Table 1 on the Ti substrate as an electrolytic foil. The surface roughness Sa of the Ti substrate was the value shown in Table 1. The results are shown in Tables 1 to 3.

[0205] Bath composition

[0206] Ferric chloride tetrahydrate: 1000g / L

[0207] Temperature: 105℃

[0208] pH: 1.0

[0209] ·Stirring: Air stirring

[0210] Current density: 50A / dm 2

[0211] The results are shown in Tables 1-2.

[0212] <Examples 29 to 30>

[0213] The same procedure as in Example 28 was carried out except that the thickness was set to the value shown in Table 1. The results are shown in Tables 1 to 3.

[0214] <Example 31>

[0215] The same procedure as in Example 1 was carried out except that the iron plating conditions were as follows and the thickness was as shown in Table 1. The results are shown in Tables 1 to 3.

[0216] Bath composition

[0217] Ferric chloride tetrahydrate: 500g / L

[0218] Nickel chloride hexahydrate: 200g / L

[0219] Temperature: 100℃

[0220] pH: 1.0

[0221] ·Stirring: Air stirring

[0222] Current density: 20A / dm 2

[0223] It should be noted that in Example 31, the contents of Fe, Ni and Mn in the electrolytic iron plating are Fe: 86.0wt%, Ni: 14.0wt%, and Mn: less than 0.01wt%. The contents of Fe, Ni and Mn are numerical values ​​obtained by calculation. When calculating, first, the electrolytic iron plating of Example 31 is dissolved, and the contents of Ni and Mn are measured by ICP emission analysis (measuring device: manufactured by Shimadzu Corporation, inductively coupled plasma emission spectrometry ICPE-9000). At this time, the remaining part other than Ni and Mn is set to Fe, and the Fe content is calculated. The contents of each metal are calculated based on the contents of Fe, Ni and Mn.

[0224] <Example 32>

[0225] The electrolytic iron foil obtained in the same manner as in Example 31 was annealed by box annealing at the temperature and time shown in Table 1. The results are shown in Tables 1 to 3.

[0226] <Comparative Example 1>

[0227] The same procedure as in Example 1 was carried out except that the surface roughness Sa of the Ti substrate was set as shown in Table 1. The results are shown in Tables 1 to 3.

[0228] <Comparative Example 2>

[0229] The same procedure as in Example 3 was carried out except that the surface roughness Sa of the Ti substrate was set as shown in Table 1. The results are shown in Tables 1 to 3.

[0230] <Comparative Example 3>

[0231] A rolled iron foil (manufactured by Niraco Co., Ltd., model number: FE-223171) having a thickness shown in Table 1 was used. The results are shown in Tables 1 to 3.

[0232] It should be noted that the contents of Fe and Mn in the rolled iron foil are Fe: 99.67wt% and Mn: 0.33wt% or more. The contents of Fe and Mn are numerical values ​​obtained by calculation. When calculating, first, the rolled iron foil of Comparative Example 3 is dissolved, and the Mn content is measured by ICP emission analysis (measuring device: inductively coupled plasma emission spectrometer ICPE-9000 manufactured by Shimadzu Corporation). At this time, the remaining part other than Mn is set to Fe, and the Fe content is calculated. The contents of each metal are calculated based on the contents of Fe and Mn.

[0233] <Comparative Example 4>

[0234] Electrolytic copper foil was formed on a Ti substrate under the following plating conditions. The thickness and substrate surface roughness were as shown in Table 1. The results are shown in Tables 1 to 3.

[0235] Bath composition

[0236] Copper sulfate pentahydrate: 200g / L

[0237] Sulfuric acid: 45g / L

[0238] Temperature: 35℃

[0239] pH: below 1.0

[0240] ·Stirring: Air stirring

[0241] Current density: 10A / dm 2

[0242] <Comparative Example 5>

[0243] The electrolytic copper foil obtained in the same manner as in Comparative Example 4 was annealed by box annealing at the temperature and time shown in Table 1. The results are shown in Tables 1 to 3.

[0244] [Table 1]

[0245]

[0246] [Table 2]

[0247]

[0248] [Table 3]

[0249]

[0250] It was confirmed that each of the Examples had preferred properties such as tensile strength, maximum load, and elongation. On the other hand, it was confirmed that the Comparative Examples could not achieve the desired properties from the perspective of tensile strength or elongation.

[0251] More specifically, in Example 1, since Sv / thickness of both sides is less than 0.27, it has preferred characteristics such as tensile strength, maximum load, and elongation. On the other hand, in Comparative Example 1 produced under the same conditions, since Sv / thickness of one side exceeds 0.27, it is believed that there is a local weak part, so it can be seen that the original characteristics, namely tensile strength and maximum load, are not fully manifested. It can be seen that when comparing Example 3 and Comparative Example 2, among the electrolytic iron foils produced under the same conditions, in Comparative Example 2 where Sv / thickness exceeds 0.27, the various characteristics are inferior to those of Example 3, and the original characteristics are not manifested.

[0252] It can be further seen that, for Example 22, in which the electrolytic iron foil produced under the same conditions as Example 17 was annealed at 350°C for 4 hours, although the tensile strength decreased by about 24%, it was still able to maintain a state of sufficient tensile strength and maximum load, and even if it was heated in the battery manufacturing process, the decrease in tensile strength could be suppressed. On the other hand, it can be seen that when comparing Comparative Examples 4 and 5, which are samples of copper foil, the tensile strength and maximum load decreased by about 60% and softened significantly when the copper foil was subjected to 350°C heat. When used as a collector, the foil may be cracked or broken during manufacturing and handling. In addition, in each of the other embodiments, by setting Sv / thickness to less than 0.27 on both sides, each characteristic can be within a preferred range.

[0253] In addition, each of the examples was confirmed to have close adhesion with the active material on at least one surface (the first surface or the second surface). On the other hand, the rolled iron foil of Comparative Example 2 was confirmed to not have the above-mentioned characteristics.

[0254] In more detail, it was confirmed that in Examples 1 to 32, when the value of Sdq (root mean square slope) or Sdr (developed interface area ratio) on at least any one surface is large or the value of Sal (autocorrelation length) is small, the effect of the binder is fully exerted and the adhesion with the active material is excellent.

[0255] In Examples 1 to 4 and 7 to 32, it was confirmed that the values ​​of Sdq or Sdr on the first and second surfaces were controlled to be large and the value of Sal was small, and both surfaces had excellent adhesion to the active material.

[0256] On the other hand, in Examples 5 and 6, it was confirmed that although the Sdq or Sdr value in at least one surface (the first surface or the second surface) was controlled to be large and the Sal value was small, the adhesion with the active material was excellent, but the Sdq or Sdr value in the other surface was small and the Sal value was large, so the effect of the binder was difficult to take effect, and the adhesion with the active material was poor. In addition, in Comparative Example 3, it was confirmed that the Sdq or Sdr value of the first surface and the second surface was small and the Sal value was large, so the adhesion with the active material was poor.

[0257] In addition, there are various methods for distinguishing the electrolytic iron foil shown in the example and the rolled iron foil shown in the comparative example 3, and the main distinguishing methods are described below.

[0258] <Judgment method A>

[0259] As a method of distinguishing between electrolytic iron foil and rolled iron foil from the perspective of the chemical composition, quantitative analysis using ICP emission analysis can be cited. That is, when rolled iron foil is manufactured using a blast furnace or an electric furnace, it is difficult to keep the mixing of manganese (Mn) below a certain level. Therefore, when the total element composition contains more than 0.3wt% Mn, it can be judged as rolled iron foil. On the other hand, when Mn is less than 0.05wt%, it can be judged as electrolytic iron foil. It should be noted that quantitative analysis using this ICP emission analysis is an effective means of distinguishing between foils before and after annealing.

[0260] <Judgment method B>

[0261] As a method for distinguishing between electrolytic iron foil and rolled iron foil from the perspective of the crystal orientation index, the confirmation of the diffraction peak using X-ray diffraction can be cited. That is, when the crystal orientation index is calculated based on the intensity ratio of the diffraction peak using X-ray diffraction, the rolled iron foil tends to have a stronger orientation on the (211) plane. In addition, compared with the electrolytic iron foil, the influence of the (211) plane remains strongly in the rolled iron foil even after annealing. On the other hand, in the case of the electrolytic iron foil, the orientation of the (110) plane is relatively strong, so the orientation of the (211) plane tends to be weak, and the electrolytic iron foil and the rolled iron foil can be distinguished based on the orientation of the (211) plane.

[0262] In order to more accurately distinguish between the electrolytic iron foil and the rolled iron foil after the heat treatment, it is preferable to use the above-mentioned distinguishing method A in combination.

[0263] <Judgment method C>

[0264] Electrolytic iron foil and rolled iron foil can also be distinguished from the perspective of crystal structure. That is, when observing the crystal structure of rolled iron foil before annealing, the surface becomes grains extending in the rolling direction, and when observing the cross section, it is composed of multiple grains in the plate thickness direction and becomes grains extending in the rolling direction. On the other hand, in the case of electrolytic iron foil, the surface does not become grains extending in the rolling direction, and in the cross section, it becomes a structure that grows from the substrate surface side to the electrolysis surface side.

[0265] It should be noted that the above-mentioned crystal structure changes according to heat treatment, so the above-mentioned identification method can also be applied to the material after heat treatment according to the heat treatment conditions, but basically, in the identification of electrolytic iron foil and rolled iron foil after heat treatment, it is preferred to use the above-mentioned identification methods A and B in combination.

[0266] <Judgment method D>

[0267] In addition, electrolytic iron foil and rolled iron foil can also be distinguished from the viewpoint of surface roughness. That is, when measuring the three-dimensional surface property parameters (Sdq, Sdr, Sal, etc.) obtained by using a laser microscope, rolling stripes unique to the rolling process are formed on both sides of the rolled iron foil, so Sdq, Sdr, and Sal are mostly outside the range of numerical values ​​represented as preferred values ​​in this embodiment. On the other hand, in the case of electrolytic iron foil, since the roughness of the substrate is easily transferred to the substrate surface, the surface roughness is mostly similar to that of the rolled iron foil, but the electrolytic surface has surface unevenness accompanied by the unique crystal growth precipitated by electrolysis, and Sdq, Sdr, and Sal are within the range of numerical values ​​represented as preferred values ​​in this embodiment.

[0268] In addition, since the surface roughness value described above changes when the material surface is etched or polished, it is preferable to use the above-mentioned determination method B or C in addition to the above-mentioned determination method A.

[0269] It should be noted that the above-described embodiment and examples can be modified in various ways without departing from the spirit and scope of the present invention.

[0270] Furthermore, the electrolytic iron foil in the above-described embodiments and examples is mainly used as a battery current collector, but is not limited thereto and can be applied to other uses such as a heat dissipation material and an electromagnetic wave shielding material.

[0271] Possibility of industrial application

[0272] As described above, the electrolytic iron foil, battery current collector, and battery of the present invention can be applied to industries in a wide range of fields such as automobiles and electronic devices.

[0273] Explanation of symbols

[0274] 10 Electrolytic Iron Foil

[0275] 10a Side 1

[0276] 10b Side 2

Claims

1. Electrolytic iron foil, It is characterized in that The thickness is less than 20 μm, and the first surface and the second surface have a first surface and a second surface, and the value obtained by dividing the three-dimensional surface texture parameter Sv by the thickness is 0.27 or less. In at least one of the first surface and the second surface, the three-dimensional surface texture parameter Sdq is greater than or equal to 0.06, The Sv is a maximum valley depth, and the Sdq is a root mean square slope. The Sv and Sdq are values ​​measured according to ISO-25178-2:2012.

2. The electrolytic iron foil according to claim 1, in, In at least one of the first surface and the second surface, the value obtained by dividing the three-dimensional surface texture parameter Sv by the thickness is 0.24 or less.

3. The electrolytic iron foil according to claim 1 or 2, in, The iron content in the foil is 80% by weight or more.

4. The electrolytic iron foil according to claim 1 or 2, in, The elongation is 1.2% or more.

5. The electrolytic iron foil according to claim 1 or 2, in, In at least one of the first surface and the second surface, a three-dimensional surface texture parameter Sdr is 0.2% or more, The Sdr is a developed interface area ratio, and the Sdr is a value measured in accordance with ISO-25178-2:2012.

6. A battery current collector comprising the electrolytic iron foil according to any one of claims 1 to 5.

7. A non-aqueous battery current collector comprising the electrolytic iron foil according to any one of claims 1 to 5.

8. Use of the electrolytic iron foil according to any one of claims 1 to 5 as a battery current collector.

9. Use of the electrolytic iron foil according to any one of claims 1 to 5 as a current collector for a non-aqueous battery.

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