Electrolytic Iron Foil

Abstract

Topic: 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 elongation, strength and thinness during repeated charge and discharge in a secondary battery. Solution: Electrolytic iron foil, characterized in that, in at least any one surface, the crystallite diameter of the iron (110) plane is 45nm or more and the thickness is less than 20μm.

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] When the copper foil described in Patent Document 1 is used for a battery current collector, the possibility of strength reduction depending on the heating temperature during manufacturing 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 current 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 elongation, strength, and thickness suitable for collectors.

[0013] For example, Japanese Patent Publication No. 58-73787 and Japanese Patent Publication No. 8-60392 disclose electrolytic iron foils that are not used as current collectors for batteries. However, these electrolytic iron foils do not have a thickness suitable for current collectors for high-capacity batteries, and are not protected against cracking and breaking during handling. In addition, they do not have the elongation and strength expected by the inventors.

[0014] The present inventors have conducted intensive studies in view of the above problems and have completed the present invention. That is, an object of the present invention is to provide an electrolytic iron foil which is thin and has elongation and strength and can suppress cracking and breaking during handling.

[0015] Means for solving problems

[0016] That is, the electrolytic iron foil of the present invention is characterized in that (1) on at least one surface, the crystallite diameter of the iron (110) plane is 45 nm or more and the thickness is less than 20 μm.

[0017] In the electrolytic iron foil of (1) above, it is preferred that (2) the crystal orientation index of the (110) plane on both surfaces is 0.2 or more.

[0018] In the electrolytic iron foil of (1) or (2) above, (3) preferably, in at least one surface, the average crystal grain size of crystal grains on the surface is 0.66 μm or more.

[0019] In the electrolytic iron foil according to any one of (1) to (3) above, preferably (4) the elongation is 1.6% or more.

[0020] In the electrolytic iron foil according to any one of (1) to (4) above, (5) the tensile strength is preferably 130 MPa or more.

[0021] In addition, the electrolytic iron foil for a battery current collector in the present invention preferably (6) comprises the electrolytic iron foil according to any one of (1) to (5) above.

[0022] Furthermore, the electrolytic iron foil for a nonaqueous battery current collector in the present invention (7) preferably comprises the electrolytic iron foil according to any one of (1) to (6).

[0023] Effects of the Invention

[0024] According to the present invention, it is possible to provide an electrolytic iron foil which is thin and can suppress cracking and breaking during handling. It is also possible to provide an electrolytic iron foil which has sufficient elongation and strength 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 used to measure the tensile strength and elongation of the electrolytic iron foil 10 in the present embodiment.

[0027] Figure 3 This is a diagram showing a method for measuring the crystal grain size on the surface using a focused ion beam machining observation apparatus (FIB) in the examples. DETAILED DESCRIPTION

[0028] Electrolytic Iron Foil

[0029] Hereinafter, embodiments of the electrolytic iron foil for carrying out the present invention will be described.

[0030] The electrolytic iron foil 10 of this embodiment can be applied to the collector of the positive electrode of the battery in addition to the collector of the negative electrode of the battery. As the type of battery, it can be a secondary battery or a primary battery. As non-aqueous secondary batteries, for example, lithium secondary batteries, sodium secondary batteries, magnesium secondary batteries, all-solid batteries, etc. can be listed.

[0031] The electrolytic iron foil 10 of the present embodiment is characterized in that, in at least one surface, the crystallite diameter of the iron (110) plane measured by X-ray diffraction is 45 nm ( ) or more. Generally, one iron grain is an aggregate of multiple crystallites. Crystallites refer to the largest aggregate of single crystals that can be regarded as crystallites.

[0032] The inventors of the present invention have repeatedly conducted tests by variously changing the electroplating conditions and the subsequent heat treatment conditions when manufacturing the electrolytic iron foil in the electrolytic iron foil 10 of the present embodiment. As a result, it has been found that, when the crystallite diameter is set to a predetermined size, an electrolytic iron foil having a sufficient elongation to withstand repeated charge and discharge can be obtained even when it is applied to a current collector of a secondary battery.

[0033] In the present embodiment, the reason why the crystallite diameter of the (110) plane of the contained iron is set to 45 nm or more is as follows.

[0034] That is, in this embodiment, an object is to provide an iron foil having a thickness suitable for use as a current collector and having elongation and strength.

[0035] Here, if the iron foil is manufactured by rolling, the crystallite diameter becomes small due to the processing strain, and it is difficult to obtain an iron foil having elongation.

[0036] Meanwhile, the electrolytic iron foil 10 can have the target elongation and strength by controlling the crystallite diameter of the iron (110) plane in at least any one plane to be 45 nm or more. Therefore, in the present embodiment, the crystallite diameter of the electrolytic iron foil 10 is set to be 45 nm or more.

[0037] The upper limit of the crystallite diameter is preferably 160 nm or less, more preferably 150 nm or less, and further preferably 120 nm or less.

[0038] It should be noted that in terms of further improving the elongation, the crystallite diameter is preferably 50 nm or more, more preferably 58 nm or more, more preferably 60 nm or more, and more preferably 80 nm or more. On the other hand, in the case of attaching importance to strength, the crystallite diameter is preferably less than 60 nm, more preferably less than 58 nm. In addition, in the case of wanting to balance both strength and elongation, the crystallite diameter is preferably 50 nm to 80 nm, more preferably 58 nm to 75 nm.

[0039] The electrolytic iron foil 10 of this embodiment specifies the crystallite diameter of the (110) plane of iron. The reason for this is that iron has a body-centered cubic structure, and by controlling the crystallite diameter of the (110) plane, which is the main sliding surface, the elongation of the electrolytic iron foil as a whole can be accurately controlled.

[0040] In the electrolytic iron foil 10 of the present embodiment, the crystallite diameter of the iron (110) plane is calculated from the half-peak width based on X-ray diffraction using the following formula. The X-ray diffraction measurement is performed using, for example, a known X-ray diffraction device. The crystallite diameter is calculated using the peak of the iron (110) plane appearing at 2θ=43 to 46 degrees.

[0041] D=K×λ / (β×cosθ)

[0042] D: Crystallite diameter

[0043] K: Scherrer constant (use K = 0.94)

[0044] λ: wavelength of the X-ray used

[0045] β: Half-height width of diffracted X-rays of the crystallite

[0046] θ: Bragg angle

[0047] In the electrolytic iron foil 10 of the present embodiment, the crystal orientation index of the (110) plane of iron is controlled, thereby making it possible to obtain an electrolytic iron foil having high elongation and strength.

[0048] That is, as the crystal orientation index, from the viewpoint of obtaining sufficient elongation, the crystal orientation index of the sliding surface of the BCC structure, i.e., the (110) surface, on both sides of the electrolytic iron foil is preferably 0.2 or more. It should be noted that in terms of improving the elongation, the crystal orientation index of the (110) surface on at least one of the surfaces is more preferably 0.4 or more, and further preferably 0.7 or more. It should be noted that there is no particular upper limit on the crystal orientation index of the (110) surface, and it is usually 3.0 or less.

[0049] In addition, from the viewpoint of further improving the elongation, the crystal orientation index of the (220) plane in at least any one of the planes is preferably 0.5 or more, more preferably 1.0 or more, more preferably 1.3 or more, and even more preferably 1.5 or more. In the case of further attaching importance to the elongation, it is particularly preferred that the crystal orientation index of the (220) plane in both planes is 1.3 or more. It should be noted that there is no particular restriction on the upper limit of the crystal orientation index of the (220) plane, which is usually 4.0 or less.

[0050] The crystal orientation index of the iron foil can be calculated as follows by measuring the diffraction intensity of each crystal plane on the surface with an X-ray diffractometer, and then using the diffraction peaks of the obtained iron film and the diffraction peaks of the standard powder using the method of Wilson and Rogers "KS Wilson and JA Rogers; Tech. Proceeding Amer. Electroplaters Soc., 51, 92 (1964)".

[0051] As the diffraction intensity data, when the X-ray source bulb is Cu(Kα), data of the (110), (200), (211) and (220) planes appearing in the diffraction angle (2θ) range of 20 to 100° are used.

[0052] Crystal orientation index of (110) plane = IF(110) / IFR(110)

[0053] In the above formula, IF(110) is the X-ray diffraction intensity ratio from the (110) plane, and IFR(110) is the theoretical X-ray diffraction intensity ratio of standard iron (powdered iron).

[0054] IF(110)=I(110) / [I(110)+I(200)+I(211)+I(220)]

[0055] IFR(110)=IR(110) / [IR(110)+IR(200)+IR(211)+IR(220)]

[0056] In the above formula, I(hkl) is the X-ray diffraction intensity from the (hkl) plane, and IR(hkl) is the X-ray diffraction intensity from the (hkl) plane described in 01-080-3816 of the ICDD PDF-2 2014 database of standard iron powder.

[0057] The crystal orientation indices of the (200) plane, (211) plane, and (220) plane can also be calculated in the same manner.

[0058] Crystal orientation index of (200) plane = IF(200) / IFR(200)

[0059] IF(200)=I(200) / [I(110)+I(200)+I(211)+I(220)]

[0060] IFR(200)=IR(200) / [IR(110)+IR(200)+IR(211)+IR(220)]

[0061] Crystal orientation index of (211) plane = IF(211) / IFR(211)

[0062] IF(211)=I(211) / [I(110)+I(200)+I(211)+I(220)]

[0063] IFR(211)=IR(211) / [IR(110)+IR(200)+IR(211)+IR(220)]

[0064] Crystal orientation index of (220) plane = IF(220) / IFR(220)

[0065] IF(220)=I(220) / [I(110)+I(200)+I(211)+I(220)]

[0066] IFR(220)=IR(220) / [IR(110)+IR(200)+IR(211)+IR(220)]

[0067] It should be noted that the X-ray diffraction intensity with the maximum diffraction intensity among the obtained X-ray diffraction intensities of the (110) plane, (200) plane, (211) plane, and (220) plane is set to 100, and the relative intensity obtained by dividing the diffraction intensity of other planes by their diffraction intensity values ​​can also be calculated based on the same data.

[0068] It is to be noted that in the present embodiment, as long as the crystallite diameter of the (110) surface of iron measured by X-ray diffraction on at least any one side is 45 nm or more, it is sufficient. It is known that in the electrolytic iron foil, there is a substrate surface side and an electrolysis surface side during manufacturing, and the substrate surface side is affected by the start of electrolysis, and the crystallite becomes slightly smaller. However, it is confirmed that if a sufficient crystallite diameter of 45 nm or more can be obtained on the electrolysis surface side, even if the crystallite diameter on the other side, i.e., the substrate surface, is less than 45 nm, the elongation is excellent.

[0069] It should be noted that when the crystallite diameter of the (110) surface of iron is 45nm or more when measured by X-ray diffraction in at least any one surface, from the viewpoint of further improving the elongation, the crystallite diameter of the (110) surface of iron measured from the other side is preferably 25nm or more, more preferably 35nm or more, more preferably 38nm or more, further more preferably 45nm or more, and particularly preferably 70nm or more. On the other hand, in the case of further emphasizing strength, it is preferably less than 60nm, more preferably less than 45nm. In addition, in the case of further wanting to take into account both elongation and strength, the above-mentioned crystallite diameter is preferably 35nm to 70nm, more preferably 38nm to 70nm, and further more preferably 35nm to 1nm.

[0070] The upper limit of the crystallite diameter is preferably 160 nm or less, more preferably 150 nm or less, and further preferably 120 nm or less.

[0071] In the electrolytic iron foil 10 of the present embodiment, as a method for controlling the size of the crystallite diameter, specifically, a method of controlling the plating conditions when manufacturing the electrolytic iron foil can be cited. In addition, when the obtained electrolytic iron foil is heat-treated, the size of the crystallite diameter can also be controlled by using a method of controlling the heat treatment conditions. The detailed methods for these will be described later.

[0072] like Figure 1 As shown, the electrolytic iron foil 10 of this embodiment has a first surface 10a and a second surface 10b. It is noted that, 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 for description. It is 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.

[0073] The electrolytic iron foil 10 of this embodiment can be pure iron. As long as the problem of the present invention can be solved, it can contain one or more metals other than iron as secondary components, and it can also contain inevitable impurities. Here, pure iron refers to the content of metal elements other than iron is 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 general circulation. Therefore, it has the advantages of excellent corrosion resistance and rust resistance during transportation and storage.

[0074] In the present invention, iron foil is defined as an iron foil having an iron content of 80% by weight or more in the foil. 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 the improvement of strength and cost.

[0075] 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.

[0076] In addition, in this embodiment, when all metals contained in the electrolytic iron foil are set to 100 weight %, the content rate of metals other than iron and nickel is preferably 0.1 weight % or less.

[0077] In the present embodiment, the content of iron and metals other than iron contained in the electrolytic iron foil may be obtained by, for example, inductively coupled plasma (ICP) emission spectrometry, etc. The metal content can be calculated from the obtained content of each metal.

[0078] The electrolytic iron foil 10 of the present embodiment is formed by electroplating. Specifically, the electrolytic iron foil can be formed using an electroplating bath containing iron ions.

[0079] In the production of the electrolytic iron foil of the present embodiment, the surface in contact with the support (substrate) supporting the electrolytic foil is referred to as the substrate surface, and the other surface is referred to as the electrolytic surface in the following description.

[0080] 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).

[0081] It should be noted that the above-mentioned "brightness" or "non-brightness" is difficult to distinguish with strict numerical values ​​based on the visual evaluation of the 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.

[0082] In the electrolytic iron foil 10 of the present embodiment, the value of the three-dimensional surface texture parameter Sa on at least one of the substrate surface and the electrolysis surface is preferably less than 1.0 μm, more preferably less than 0.6 μm, and further preferably 0.45 μm or less.

[0083] The present inventors have conducted research and found that in order to produce an electrolytic foil that can suppress cracking and breakage during manufacturing and handling (including battery assembly) that are concerned about thinning, and further suppress wrinkling and breakage when using active materials that have a large volume change during repeated charge and discharge in secondary batteries, in addition to setting the crystallite diameter that is a feature of the present invention to a specified size, it is also preferred to set the value of the above-mentioned three-dimensional surface texture parameter Sa to below a specified value.

[0084] The reason is considered to be as follows. That is, if the surface of the metal foil has too large unevenness, a thin portion may be formed locally due to the combination of the unevenness on the surface and the back, and the entire foil may be easily broken or cracked. Therefore, in order to obtain the original strength and elongation of the foil obtained by controlling the crystallite diameter, it is preferable to set the value of Sa to a specified value.

[0085] It should be noted that the three-dimensional surface property parameter Sa 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.

[0086] It should be noted that in the electrolytic iron foil 10 of the present embodiment, the values ​​of Sa [μm] (arithmetic mean height) and Sz [μm] (maximum height) on the substrate surface and the electrolytic surface preferably have the following values. It should be noted that the three-dimensional surface property parameters in the present embodiment refer to the values ​​measured according to ISO-25178-2: 2012 (corresponding to JIS B 0681-2: 2018).

[0087] Sa···less than 1.0 μm, more preferably less than 0.6 μm

[0088] Sz···less than 10.0 μm, more preferably less than 8.0 μm

[0089] Here, although the lower limits of Sa and Sz are not particularly limited, Sa is preferably 0.1 μm or more, and Sz is preferably 0.8 μm or more.

[0090] In addition, from the viewpoint of active material adhesion, in the electrolytic iron foil 10 of the present embodiment, the values ​​of Sdq (root mean square slope) and Sdr (developed interface area ratio) of at least one of the substrate surface and the electrolytic surface preferably have 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 JISB 0681-2:2018).

[0091] 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

[0092] 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 adhesion will be further improved.

[0093] 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%.

[0094] It should be noted that in order to control the three-dimensional surface property parameters Sa, Sz, Sdq, and Sdr in the electrolytic iron foil 10 of the present embodiment within the range of the above-mentioned values, as described later, methods of 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 or electrolytic grinding, etc. can be listed.

[0095] Next, the thickness of the electrolytic iron foil 10 in the present embodiment will be described.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] In addition, the "thickness of the electrolytic iron foil" in this embodiment can be obtained by thickness measurement using a micrometer or thickness measurement based on a weight method.

[0101] It should be noted that the tensile strength of the electrolytic iron foil 10 of the present embodiment is preferably 130 MPa or more. When the tensile strength is less than 130 MPa, the foil may be broken or ruptured during battery manufacturing, and the operability (handling property) is reduced, so it is not preferred. In addition, when applied to the collector of a secondary battery, it may not be able to withstand the volume change caused by repeated charging and discharging and cause rupture, so it is not preferred.

[0102] It is explained that, in terms of further emphasizing strength, the lower limit of tensile strength is more preferably 180MPa or more, and more preferably 350MPa or more. On the other hand, in the case of emphasizing elongation, the tensile strength is preferably 550MPa or less, and more preferably 450MPa or less. As the upper limit of tensile strength, it is preferably 800MPa or less, and more preferably 700MPa or less.

[0103] In the present embodiment, the tensile strength of the electrolytic iron foil 10 can be measured, for example, as follows. The sample is cut using an SD-type bar sample cutter (model: SDL-200) manufactured by Dunbel Co., Ltd. and a cutter (model: SDK-400) in accordance with JIS K 6251. Figure 2 The metal piece is punched out in the shape of a dumbbell No. 4 of JIS K 6251. The test piece can be used to perform a tensile test in accordance with the tensile test method of JIS Z 2241 as a JIS standard for metal test pieces.

[0104] The elongation of the electrolytic iron foil 10 of the present embodiment is preferably 1.6% to 15%, more preferably 1.8% to 15%, and further preferably 2.0% to 15%. When the elongation is less than 1.6%, 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 10 in the present embodiment refers to the value measured in accordance with JIS Z 2241 (Metallic Material Tensile Test Method).

[0105] Since the electrolytic iron foil 10 of the present embodiment has the above-described configuration, the following effects are achieved.

[0106] 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 strength of the copper foil used as a conventional current collector material may be reduced due to the drying temperature.

[0107] As a material property of iron, the strength reduction in the above heating temperature range is low, so when the electrolytic iron foil 10 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 using it as a current collector) can be suppressed.

[0108] It should be noted that in the electrolytic iron foil 10 of the present embodiment, from the viewpoint of further softening and improving the adhesion with the active material, the size of the surface grains in at least any one of the electrolysis surface or the substrate surface (the average crystal grain size on the surface) is preferably 0.66 μm or more. In particular, when strong adhesion is required, it is more preferably 3.20 μm or more. On the other hand, when having adhesion with the active material and further emphasizing strength, it is preferably less than 1.50 μm, and more preferably less than 1.30 μm. In addition, when having adhesion with the active material and wanting to balance both strength and elongation well, it is preferably 0.80 μm to 3.20 μm, more preferably 1.00 μm to 3.20 μm, and further preferably 1.30 μm to 3.20 μm.

[0109] In addition, when the average crystal grain size of the surface in at least any one of the electrolytic surface or the substrate surface is 0.66 μm or more, on the other hand, from the viewpoint of softening and fully having close adhesion with the active material, the average crystal grain size of the surface in the other surface is preferably 0.45 μm or more, more preferably 0.50 μm or more, further preferably 0.70 μm or more, further more preferably 1.00 μm or more, and particularly preferably 2.00 μm or more. On the other hand, in the case of having close adhesion with the active material and further emphasizing strength, it is preferably less than 1.00 μm, more preferably less than 0.70 μm. In addition, in the case of having close adhesion with the active material and wanting to take into account higher elongation and strength, it is preferably 0.50 μm to 2.00 μm, more preferably 0.70 μm to 2.00 μm, and further preferably 1.00 μm to 2.00 μm.

[0110] It should be noted that in this embodiment, the "average crystal grain size on the surface" refers to the average crystal grain size calculated from the grains at a position of 0.5 μm in the thickness direction from the surface side (electrolysis surface side or substrate surface side), which is equivalent to the average line segment length calculated according to JIS G 0551.

[0111] In the electrolytic iron foil 10 of the present embodiment, it is preferable to control the value of the crystal grain size to a predetermined value in order to improve the adhesion with the active material when used as a current collector.

[0112] 《Method for producing electrolytic iron foil》

[0113] When producing the electrolytic iron foil 10 of the present embodiment, electrolytic iron is formed on a support body including a titanium plate (Ti substrate) or a stainless steel plate, and then the plating layer is peeled off from the support body by a known method to obtain the electrolytic iron foil.

[0114] In addition, the specific material of the support body is not limited to the above-mentioned titanium plate or stainless steel plate, and other well-known metal materials can be applied within the limit not departing from the gist of the present invention.

[0115] In addition, hereinafter, the titanium plate is also referred to as a Ti base material.

[0116] The conditions of the iron electroplating bath are as follows.

[0117] [High concentration iron plating conditions]

[0118] Bath composition

[0119] Ferric chloride tetrahydrate: 500~1000g / L

[0120] Temperature: 60~110℃

[0121] pH: below 3.0

[0122] ·Stirring: air stirring or jet stirring

[0123] Current density: 3~100A / dm 2

[0124] In addition, hydrochloric acid, sulfuric acid, etc. can be used for the adjustment of the said pH.

[0125] It should be noted that when the temperature of the bath for the above-mentioned high-concentration iron plating is lower than 60°C, precipitation of the layer may occur, and the stress during plating may increase and the layer may be peeled off from the support body, and the crystallite diameter becomes smaller, so it is not preferred. From the viewpoint of improving production efficiency and stably obtaining a crystallite diameter of a specified size, it is more preferably set to 85°C or above. 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.

[0126] In addition, regarding the current density of the high-concentration iron plating bath, when the pH is 1.0 or less, the current density is more preferably 5 A / dm 2 above.

[0127] [Low concentration iron plating conditions]

[0128] Bath composition

[0129] Ferric chloride tetrahydrate: 200~500g / L

[0130] 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

[0131] Temperature: 25~110℃

[0132] pH: below 5.0

[0133] ·Stirring: air stirring or jet stirring

[0134] Current density: 3~100A / dm 2

[0135] Regarding the current density of the low-concentration iron plating, the current density is less than 3A / dm 2 When the A / dm is less than 10A / dm, the foil may not be produced and the production efficiency may be reduced, so it is not preferred. From the viewpoint of improving production efficiency, it is more preferred to set it to 10A / dm 2 On the other hand, when the current exceeds 100A / dm 2When the A / dm is 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 anti-dent agent may be added in an appropriate amount.

[0136] In addition, 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 a plurality of them may be added in combination.

[0137] As described above, the plating bath when forming the electrolytic iron foil 10 of this embodiment may also contain nickel. By adding nickel to the bath, 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.

[0138] As the plating bath containing nickel, the following conditions can be mentioned.

[0139] Bath composition

[0140] Ferric chloride tetrahydrate: 500~1000g / L

[0141] Nickel chloride hexahydrate or nickel sulfate hexahydrate: 10~400g / L

[0142] Temperature: 60~110℃

[0143] pH: below 3.0

[0144] ·Stirring: air stirring or jet stirring

[0145] Current density: 3~100A / dm 2

[0146] As a method for producing the electrolytic iron foil 10 according to the present embodiment, the following steps can be roughly listed.

[0147] 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.

[0148] 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. In addition, the thinner the thickness of the electrolytic iron foil, the thinner the shape of the surface (electrolysis surface) of the electrolytic iron foil, and the higher the possibility of being affected by the surface shape of the support.

[0149] Specifically, from the viewpoint of preventing the difficulty in peeling off the support during manufacturing or causing pinholes during foil manufacturing, 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.

[0150] 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 a known method. 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.

[0151] When the electrolytic iron foil is subjected to heat treatment before or after being peeled off from the support, it is preferred that the heat treatment conditions be within the range that can solve the problem of the present invention. For example, when the electrolytic iron foil 10 is pure iron, as a heat treatment condition, the temperature is preferably 150°C to 850°C, more preferably 200°C to 700°C, and further preferably 250°C to 600°C. In addition, when the electrolytic iron foil 10 contains one or more metals other than iron (nickel, etc.) as a secondary component, as a heat treatment condition, the temperature is preferably 150°C to 600°C, more preferably 200°C to 500°C, and further preferably 250°C to 400°C. It should be noted that when heat treatment is performed within the above-mentioned temperature range, there is no particular limitation on the time of heat treatment, but it is preferred that the soaking time be within the range of 1.5 hours to 20 hours (the total time of heating, soaking and cooling time is within the range of 4 hours to 80 hours). The above-mentioned heat treatment range is preferred from the viewpoint of the crystallite diameter in the (110) plane of iron, which is a feature of the present disclosure, and from the viewpoint of achieving both thinness, elongation, and strength, which are the issues.

[0152] Before or after the electrolytic iron foil is peeled off from the support, the outermost surface of the electrolytic iron foil 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.

[0153] For example, by providing a nickel roughening layer or a copper roughening layer on both sides of the electrolytic iron foil, 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 No. WO2020 / 017655, so a detailed description is omitted here.

[0154] In this embodiment, as a method for controlling the surface roughness (three-dimensional surface properties) of the electrolytic iron foil, a method of controlling the plating conditions as described above and a method of grinding the surface of the support are listed and described, but are not limited to these. For example, by smoothing the surface of the electrolytic iron foil itself by etching, electrolytic grinding, etc., the desired three-dimensional surface properties can also be obtained.

[0155] In this embodiment, an example of manufacturing electrolytic iron foil by continuous manufacturing using a support (e.g., drum type, roll-to-roll type) is described, but the present invention is not limited to this method, and for example, batch manufacturing using a cut plate is also possible.

[0156] The electrolytic iron foil 10 in this embodiment may also be a laminated electrolytic foil having at least one metal layer on at least one of the substrate surface and the electrolytic surface. 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 of this embodiment and a nickel-iron alloy layer.

[0157] 《Implementation Examples》

[0158] The present invention will be described in more detail below with reference to Examples. First, the measurement methods in the Examples will be described.

[0159] [Determination of crystallite diameter]

[0160] In order to measure the crystallite diameter, X-ray diffraction was performed using an X-ray diffractometer (SmartLab, a fully automatic multi-purpose horizontal X-ray diffractometer manufactured by Rigaku Corporation).

[0161] <Device Structure>

[0162] X-ray source: CuKα

[0163] Goniometer radius: 300nm

[0164] Optical system: Concentration method

[0165] (Incident side slit system)

[0166] Soller slit: 5°

[0167] Length limit slit: 5mm

[0168] Divergence slit: 2 / 3°

[0169] (Light-receiving side slit system)

[0170] Scattering slit: 2 / 3°

[0171] Soller slit: 5°

[0172] · Light receiving slit: 0.3mm

[0173] ·Monochromatization method: Counter monochromator method

[0174] Detector: Scintillation counter

[0175] <Measurement parameters>

[0176] Tube voltage-tube current: 45Kv 200mA

[0177] Scanning axis: 2θ / θ

[0178] Scan mode: continuous

[0179] ·Measurement range: 2θ20~100°

[0180] Scanning speed: 10° / min

[0181] Stride: 0.05°

[0182] A test piece was cut out from the obtained electrolytic iron foil and placed on a sample stand for measurement. X-ray diffraction measurement was performed on each of the electrolytic surface and the substrate surface using a reflection method in the range of X-ray diffraction angle 2θ = 20 to 100°. Then, the background was removed for the obtained measured value using the integrated powder X-ray analysis software PDXL manufactured by Rigaku Co., Ltd., and the crystallite diameter was calculated based on the following formula.

[0183] In addition, as the peak of the (110) plane of iron, the peak appearing between 2θ=43 and 46 degrees was used.

[0184] D=K×λ / (β×cosθ)

[0185] D: Crystallite diameter

[0186] K: Scherrer constant (use K = 0.94)

[0187] λ: wavelength of the X-ray used

[0188] β: Half-height width of diffracted X-rays of the crystallite

[0189] θ: Bragg angle

[0190] [Determination of crystal orientation index]

[0191] The crystal orientation index of the electrolytic iron foil was calculated using the method of Willson and Rogers from the measured value obtained by an X-ray diffractometer. The results are shown in Tables 2 and 3.

[0192] [Determination of tensile strength and elongation]

[0193] The tensile strength 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 Z2241, which is a JIS standard for metal test pieces. A schematic diagram of the test piece is shown in FIG. Figure 2 .

[0194] It should be noted that as a device for the tensile test, a tensile testing machine (Tensilon RTC-1350A, a universal material testing machine manufactured by ORIENTEC) was used. In addition, as measurement conditions, the test was performed at a tensile speed of 10 mm / min at room temperature.

[0195] The elongation was calculated using the following formula.

[0196] (Travel distance (stroke) of the testing machine) / (distance between original marking points)×100

[0197] [Measurement of thickness]

[0198] 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.

[0199] [Measurement of surface shape]

[0200] In the obtained electrolytic foil, the surface in contact with the support is set as the substrate surface, and the other surface is set as the electrolytic surface, and the surface shape of each surface is measured. Specifically, the value of the three-dimensional surface property parameter Sa [μm] (arithmetic mean height) is calculated and measured using a laser microscope OLS5000 manufactured by Olympus Corporation. It should be noted that the above-mentioned three-dimensional surface property parameter in this embodiment refers to the value measured in accordance with ISO-25178-2: 2012 (corresponding to JIS B 0681-2: 2018).

[0201] As a measurement method, three fields of view (1 field of view 258μm×258μm) were 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 was used to perform automatic correction processing, i.e., noise removal and tilt correction. Then, the icon of surface roughness measurement was clicked for analysis to obtain various parameters of surface roughness (the value of Sa recorded in Table 2 is the average value of the three fields of view). 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.

[0202] [Measurement of surface crystal grain size]

[0203] The surface crystal grain size was measured using the following apparatus and conditions.

[0204] FIB device: Made by JEOL Ltd., focused ion beam processing observation device (FIB)

[0205] Ion beam acceleration voltage: 30kV

[0206] Emission current: 2.0μA

[0207] As a FIB operation method, a test piece is cut out from the electrolytic iron foil and placed on a measuring sample stand with the electrolytic surface side at the top. The processing magnification is set to 2000, and the sample surface is carbon-coated by deposition processing. Then, the above-mentioned processing conditions are used to process the sample into a rectangular shape. After processing, the sample stand is tilted 30 degrees to obtain a cross-sectional image of the electrolytic iron foil (magnification 3000-10000).

[0208] As for the calculation of the average crystal grain size on the surface, the method of finding the average line segment length of each crystal grain of the test line crossing the crystal grain according to the cutting method described in JIS G 0551 is used. First, a straight test line of length L (10.0 μm to 40.0 μm) crossing the crystal grain on the cross-sectional image of the electrolytic iron foil obtained by cross-sectional processing by FIB is drawn from the surface layer on the electrolysis surface side and the substrate surface side to a position of 0.5 μm in the plane direction, and the number of crystal grains nL crossed by the straight test line is counted. It should be noted that at the end of the above-mentioned test line, when the above-mentioned test line ends in the crystal grain, the crystal grain is counted as 1 / 2. Furthermore, the average crystal grain size is calculated using the following formula.

[0209]

[0210] However, twin crystals are ignored and counted as one grain.

[0211] To explain, Figure 3The figure showing the method of obtaining the average crystal grain size in Example 1 is shown in FIG. In Example 1, the length L = 12.9 μm, the number of crystal grains in the electrolysis surface nL = 15, and the number of crystal grains on the substrate surface nL = 21. Therefore, the crystal grain size on the electrolysis surface side and the crystal grain size on the substrate surface side are calculated by the following formula to be 0.86 μm and 0.61 μm, respectively. The results are shown in Table 5.

[0212] [Number 1]

[0213]

[0214] [Manufacturing of negative electrode plates and evaluation of active material adhesion]

[0215] Artificial graphite (particle size: about 10 μm) was used as the negative electrode active material and polyvinylidene fluoride (PVDF) was used as the binder. N-methylpyrrolidone (NMP) was added in an appropriate amount to a mixture of 97 wt% and 3 wt% of the negative electrode active material and the binder, respectively, to prepare a negative electrode mixture paste with adjusted viscosity. The negative electrode mixture paste was applied to the electrolytic surface side of the electrolytic foil and dried. At this time, the total mass of the negative electrode active material and the binder after drying was 5 mg / cm 2 Then, a manual hydraulic pump (model: P-1B-041) manufactured by Riken Seiki Co., Ltd. was used to apply the coating at 1000 kg / cm 2 The negative electrode plate is manufactured by pressing.

[0216] For evaluation of active material adhesion, the negative electrode plate prepared as described above was subjected to a 180° bending test with the coated surface facing outward to confirm whether the negative electrode active material was peeled off. The results are shown in Table 5.

[0217] The case where there is no peeling of the active material in the bent portion is designated as A+.

[0218] A case where the base material could not be visually exposed at the bent portion and only part of the base material was peeled off was designated as A.

[0219] 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 designated as B.

[0220] The case where the active material was peeled off at the bent portion and its periphery and the exposure of the substrate was visually confirmed was designated as C.

[0221] <Example 1>

[0222] Electrolytic iron is formed on a support. Specifically, first, a Ti substrate is used as a support on 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 shown in the table. The grinding direction is roughly parallel to the length direction of the Ti substrate (the direction of travel, 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.

[0223] [Iron plating conditions]

[0224] Bath composition

[0225] Ferric chloride tetrahydrate: 725g / L

[0226] Temperature: 90℃

[0227] pH: 1.0

[0228] ·Stirring: Air stirring

[0229] Current density: 10A / dm 2

[0230] After the plated layer formed as described above is fully dried, the plated layer is peeled off from the Ti substrate to obtain an electrolytic iron foil.

[0231] The obtained electrolytic iron foil was subjected to measurement of crystallite diameter, measurement of crystal orientation index, calculation of relative strength between the electrolytic surface and the substrate surface, measurement of tensile strength and elongation, measurement of thickness, measurement of surface shape (Sa) between the electrolytic surface and the substrate surface, measurement of crystal grain size, and evaluation of adhesion with active material.

[0232] It should 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. Based on the Mn content, it was confirmed that the obtained foil was not a rolled iron foil (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.

[0233] In addition, the observation magnification when measuring the surface crystal grain size was set to 10000 times. The results are shown in Tables 1 to 5.

[0234] <Example 2>

[0235] The same procedure as in Example 1 was carried out except that the thickness was set as shown in Table 1. In addition, the observation magnification when measuring the crystal grain size on the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0236] <Example 3>

[0237] Electrolytic iron foil was obtained in the same manner as in Example 1 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 observation magnification for measuring the surface crystal grain size was set to 10000 times. The results are shown in Tables 1 to 5.

[0238] <Example 4>

[0239] Electrolytic iron foil was obtained in the same manner as in Example 1 except that the thickness was set as shown in Table 1 and the surface roughness Sa of the Ti substrate as a support was set to the value in Table 1. The obtained electrolytic iron foil was annealed by box annealing at the temperature and time shown in Table 1. In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0240] <Example 5>

[0241] The electrolytic iron foil obtained in the same manner as in Example 2 was annealed by box annealing at the temperature and time shown in Table 1. The observation magnification for measuring the surface crystal grain size was 2000 times. The results are shown in Tables 1 to 5.

[0242] <Example 6>

[0243] 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 to form an electrolytic foil.

[0244] Bath composition

[0245] Ferric chloride tetrahydrate: 725g / L

[0246] Nickel chloride hexahydrate: 75g / L

[0247] Temperature: 90℃

[0248] pH: 1.0

[0249] ·Stirring: Air stirring

[0250] Current density: 20A / dm 2

[0251] It is explained that the following iron foil is used: the content of Fe, Ni and Mn in the electrolytic iron foil is Fe: 93.1wt%, Ni: 6.9wt%, Mn: less than 0.01wt%, and nickel is contained as a secondary component. Based on the Mn content, it is confirmed that the obtained foil is not a rolled foil (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 foil of Example 6 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 spectrometer 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.

[0252] In addition, the observation magnification when measuring the surface crystal grain size was set to 10000 times. The results are shown in Tables 1 to 5.

[0253] <Example 7>

[0254] An electrolytic iron foil was obtained in the same manner as in Example 6 except that the surface roughness Sa of the Ti substrate as a support was set to the value shown in Table 1.

[0255] In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0256] <Example 8>

[0257] The same procedure as in Example 6 was carried out except that the thickness was set as shown in Table 1. In addition, the observation magnification when measuring the crystal grain size on the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0258] <Example 9>

[0259] The electrolytic iron foil obtained in the same manner as in Example 8 was annealed at the temperature and time shown in Table 1 by box annealing.

[0260] In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0261] <Example 10>

[0262] 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.

[0263] Bath composition

[0264] Ferric chloride tetrahydrate: 300g / L

[0265] Aluminum chloride hexahydrate: 180g / L

[0266] Temperature: 90℃

[0267] pH: 1.0

[0268] ·Stirring: Air stirring

[0269] Current density: 3A / dm 2

[0270] In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0271] <Example 11>

[0272] The same procedure as in Example 10 was carried out except that the current density was set to the value shown in Table 1. In addition, the observation magnification in measuring the surface crystal grain size was set to 10000 times. The results are shown in Tables 1 to 5.

[0273] <Example 12>

[0274] The same procedure as in Example 10 was performed except that the surface roughness Sa of the Ti substrate as the support was set to the value shown in Table 1. The observation magnification for measuring the surface crystal grain size was 10000 times. The results are shown in Tables 1 to 5.

[0275] <Example 13>

[0276] The same procedure as in Example 10 was performed except that the current density and the surface roughness Sa of the Ti substrate as the support were set to the values ​​shown in Table 1. The results are shown in Table 1. The observation magnification for measuring the surface crystal grain size was 10000 times. The results are shown in Tables 1 to 5.

[0277] <Example 14>

[0278] The same procedure as in Example 10 was performed except that the thickness and the current density were set to the values ​​shown in Table 1. The results are shown in Table 1. In addition, the observation magnification for measuring the surface crystal grain size was set to 7000 times. The results are shown in Tables 1 to 5.

[0279] <Example 15>

[0280] The same procedure as in Example 10 was performed except that the current density, thickness, and surface roughness Sa of the Ti substrate as a support were set to the values ​​shown in Table 1. The results are shown in Table 1. The observation magnification for measuring the surface crystal grain size was 7000 times. The results are shown in Tables 1 to 5.

[0281] <Example 16>

[0282] 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.

[0283] Bath composition

[0284] Ferric chloride tetrahydrate: 400g / L

[0285] Calcium chloride: 180g / L

[0286] Saccharin sodium: 3g / L

[0287] Sodium dodecyl sulfate: 0.1g / L

[0288] Sodium gluconate: 2g / L

[0289] Temperature: 90℃

[0290] pH: 1.5

[0291] ·Stirring: Air stirring

[0292] Current density: 5A / dm 2

[0293] In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0294] <Example 17>

[0295] The same procedure as in Example 16 was performed except that the current density and the surface roughness Sa of the Ti substrate as the support were set to the values ​​shown in Table 1. The results are shown in Table 1. The observation magnification for measuring the surface crystal grain size was 10000 times. The results are shown in Tables 1 to 5.

[0296] <Example 18>

[0297] The same procedure as in Example 16 was performed except that the surface roughness Sa of the Ti substrate as the support was set to the value shown in Table 1. The results are shown in Table 1. The observation magnification for measuring the surface crystal grain size was 10000 times. The results are shown in Tables 1 to 5.

[0298] <Example 19>

[0299] The same procedure as in Example 16 was performed except that the current density and the surface roughness Sa of the Ti substrate as the support were set to the values ​​shown in Table 1. The results are shown in Table 1. The observation magnification for measuring the surface crystal grain size was 10000 times. The results are shown in Tables 1 to 5.

[0300] <Example 20>

[0301] 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 to form an electrolytic foil.

[0302] Bath composition

[0303] Ferric chloride tetrahydrate: 1000g / L

[0304] Temperature: 90℃

[0305] pH: below 1.0

[0306] ·Stirring: Air stirring

[0307] Current density: 10A / dm 2

[0308] In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0309] <Example 21>

[0310] The same procedure as in Example 20 was carried out except that the current density and the thickness were set to the values ​​shown in Table 1. In addition, the observation magnification for measuring the surface crystal grain size was set to 6000 times. The results are shown in Tables 1 to 5.

[0311] <Example 22>

[0312] The same procedure as in Example 20 was carried out except that the thickness was set to the value shown in Table 1. In addition, the observation magnification for measuring the crystal grain size on the surface was set to 7000 times. The results are shown in Tables 1 to 5.

[0313] <Example 23>

[0314] The same procedure as in Example 20 was carried out except that the current density and the thickness were set to the values ​​shown in Table 1. In addition, the observation magnification for measuring the surface crystal grain size was set to 7000 times. The results are shown in Tables 1 to 5.

[0315] <Example 24>

[0316] 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. The same procedure as in Example 20 was carried out except for the above. The observation magnification for measuring the crystal grain size on the surface was 8000 times. The results are shown in Tables 1 to 5.

[0317] <Example 25>

[0318] In the electroplating, as shown in Table 1, the current density was changed in the same manner as in Example 24, 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. The same procedure as in Example 20 was carried out except for the above. The observation magnification for measuring the crystal grain size on the surface was 7000 times. The results are shown in Tables 1 to 5.

[0319] <Example 26>

[0320] 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 2 The upper layer was formed to have a thickness as shown in Table 1. The same procedure as in Example 20 was carried out except for the above. The observation magnification for measuring the crystal grain size on the surface was 7000 times. The results are shown in Tables 1 to 5.

[0321] <Example 27>

[0322] The electrolytic iron foil obtained in the same manner as in Example 20 was annealed by box annealing at the temperature and time shown in Table 1. The observation magnification for measuring the surface crystal grain size was set to 3000 times. The results are shown in Tables 1 to 5.

[0323] <Example 28>

[0324] The electrolytic iron foil obtained in the same manner as in Example 22 was annealed by box annealing at the temperature and time shown in Table 1. The observation magnification for measuring the surface crystal grain size was 7000 times. The results are shown in Tables 1 to 5.

[0325] <Example 29>

[0326] The electrolytic iron foil obtained in the same manner as in Example 22 was annealed by box annealing at the temperature and time shown in Table 1. The observation magnification for measuring the surface crystal grain size was 7000 times. The results are shown in Tables 1 to 5.

[0327] <Example 30>

[0328] The electrolytic iron foil obtained in the same manner as in Example 22 was annealed by box annealing at the temperature and time shown in Table 1. The observation magnification for measuring the surface crystal grain size was 3000 times. The results are shown in Tables 1 to 5.

[0329] <Example 31>

[0330] 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.

[0331] Bath composition

[0332] Ferric chloride tetrahydrate: 1000g / L

[0333] Temperature: 105℃

[0334] pH: 1.0

[0335] ·Stirring: Air stirring

[0336] Current density: 50A / dm 2

[0337] In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0338] <Examples 32-33>

[0339] The same procedure as in Example 31 was carried out except that the thickness was set to the value shown in Table 1. In addition, the observation magnification for measuring the crystal grain size on the surface was set to 7000 times. The results are shown in Tables 1 to 5.

[0340] <Example 34>

[0341] 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 to form an electrolytic foil.

[0342] Bath composition

[0343] Ferric chloride tetrahydrate: 500g / L

[0344] Nickel chloride hexahydrate: 200g / L

[0345] Temperature: 100℃

[0346] pH: 1.0

[0347] ·Stirring: Air stirring

[0348] Current density: 20A / dm 2

[0349] It should be noted that the contents of Fe, Ni and Mn in the electrolytic iron foil 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 foil of Example 34 is dissolved, and the contents of Ni and Mn are measured by ICP emission analysis (measuring device: inductively coupled plasma emission spectrophotometer ICPE-9000 manufactured by Shimadzu Corporation). 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.

[0350] In addition, the observation magnification when measuring the surface crystal grain size was set to 10000 times. The results are shown in Tables 1 to 5.

[0351] <Example 35>

[0352] The electrolytic iron foil obtained in the same manner as in Example 34 was annealed by box annealing at the temperature and time shown in Table 1.

[0353] In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0354] <Comparative Example 1>

[0355] The same procedure as in Example 1 was performed except that the surface roughness Sa of the Ti substrate as the support was set to the value shown in Table 1. The observation magnification for measuring the surface crystal grain size was 10000 times. The results are shown in Tables 1 to 5.

[0356] <Comparative Example 2>

[0357] A rolled iron foil having a thickness shown in Table 1 (manufactured by Niraco Co., Ltd., model number: FE-223171) was used.

[0358] It should be noted that the contents of Fe and Mn in the rolled iron foil are Fe: 99.67wt%, 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 2 is dissolved, and the Mn content is measured by ICP emission analysis (measurement device: Shimadzu Corporation, inductively coupled plasma emission spectrometry ICPE-9000). At this time, the balance 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.

[0359] In addition, the observation magnification when measuring the surface crystal grain size was set to 10000 times. The results are shown in Tables 1 to 5.

[0360] <Comparative Example 3>

[0361] An electrolytic copper foil was formed on a Ti substrate under the following plating conditions. The thickness and the surface roughness Sa of the Ti substrate were set as shown in Table 1.

[0362] Bath composition

[0363] Copper sulfate pentahydrate: 200g / L

[0364] Sulfuric acid: 45g / L

[0365] Temperature: 35℃

[0366] pH: below 1.0

[0367] ·Stirring: Air stirring

[0368] Current density: 10A / dm 2

[0369] In addition, the observation magnification when measuring the crystal grain size of the surface was set to 10000 times. The results are shown in Tables 1 to 5.

[0370] <Comparative Example 4>

[0371] 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 observation magnification for measuring the surface crystal grain size was 10,000 times. The results are shown in Tables 1 to 5.

[0372] [Table 1]

[0373]

[0374] [Table 2]

[0375]

[0376] [Table 3]

[0377]

[0378] [Table 4]

[0379]

[0380] [Table 5]

[0381]

[0382] It was confirmed that each of the Examples had preferred properties such as tensile strength and elongation, while it was confirmed that the Comparative Examples could not achieve the desired properties from the perspective of tensile strength or elongation.

[0383] In more detail, in Example 1, since the crystallite diameter of the iron (110) plane is greater than 45 nm on one side, it has preferred properties such as tensile strength and elongation. On the other hand, it can be seen that on both sides of Comparative Example 1, since the crystallite diameter of the iron (110) plane is less than 45 nm, the original property of iron, namely elongation, cannot be fully exhibited.

[0384] In the case of comparing Example 3 in which the electrolytic iron foil produced under the same conditions as Example 1 was annealed at 600°C, the tensile strength decreased due to annealing, but the foil had a certain strength (tensile strength of 130 MPa or more), and the elongation was significantly improved, so it can be said that the foil was able to be suppressed from cracking and breaking. It should be noted that Example 3 annealed at 600°C was annealed at a high temperature, so it is believed that the tensile strength was hardly reduced even if it was heated in the battery manufacturing process.

[0385] If we examine Comparative Example 2, which is a rolled iron foil, although it has the preferred tensile strength for iron, it cannot fully exhibit elongation because the crystallite diameter is less than 45 nm. It can be said that when used as a current collector, it may not be able to withstand the volume change caused by repeated charge and discharge and may break.

[0386] It can be seen that when the electrolytic iron foil produced under the same conditions as in Example 22 was annealed at 350°C for 4 hours (Example 28), although the tensile strength slightly decreased, sufficient tensile strength was maintained and the elongation was improved by about 24%.

[0387] On the other hand, a comparison between Comparative Examples 3 and 4, which are copper foil samples, shows that the copper foil softened significantly when heated to 350° C., and the tensile strength decreased to 119 MPa. Therefore, the tensile strength decreased during heating in the battery manufacturing process, and the strength may be insufficient.

[0388] In addition, in each of the other examples, by setting the crystallite diameter of the iron (110) plane on at least one surface to 45 nm or more, it is possible to set each characteristic to a preferred range.

[0389] In addition, each of the examples was confirmed to have adhesion with the active material on at least one surface (the first surface or the second surface). On the other hand, the iron foil shown in the comparative example was confirmed to not have the above-mentioned characteristics.

[0390] In more detail, in Examples 1 to 35, it was confirmed that the crystal grain size of at least any one surface was 0.66 μm or more, which was sufficient, and the adhesion with the active material was excellent. In addition, in Examples 2, 3, 5, 10 to 33, and 35, it was confirmed that the crystal grain size of at least any one surface was 1.00 μm or more, and the adhesion with the active material was more excellent. It should be noted that in Examples 1 to 6 and 8 to 34, it was confirmed that the crystal grain size of both surfaces was 0.45 μm or more, and both surfaces had sufficient adhesion with the active material.

[0391] On the other hand, in Examples 7 and 35, and Comparative Examples 1 and 3, it was confirmed that the crystal grain size on at least any one surface was 0.45 μm or more and had close adhesion with the active material, but when the crystal grain size on the other surface was less than 0.45 μm, no improvement in close adhesion with the active material was observed. In addition, in Comparative Example 2, it was confirmed that a rolled texture was formed, and no close adhesion with the active material was found.

[0392] 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 2, and the main distinguishing methods are described below.

[0393] <Judgment method A>

[0394] 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 by 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.

[0395] <Judgment method B>

[0396] 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 based on 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 also remains strongly in the rolled iron foil after annealing. On the other hand, in the case of 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.

[0397] 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.

[0398] <Judgment method C>

[0399] 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.

[0400] 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.

[0401] <Judgment method D>

[0402] 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 in the electrolytic surface, there are surface irregularities 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.

[0403] 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.

[0404] 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.

[0405] 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.

[0406] Possibility of industrial application

[0407] 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.

[0408] Explanation of symbols

[0409] 10 Electrolytic Iron Foil

[0410] 10a Side 1

[0411] 10b Side 2.

Claims

1. Electrolytic iron foil, characterized in that In at least any one of the planes, the crystallite diameter of the iron (110) plane is 45 nm or more, and the crystallite diameter is calculated using the peak of the iron (110) plane appearing at 2θ=43 to 46 degrees, The elongation is more than 1.6%, Thickness less than 20μm, The iron content in the electrolytic iron foil is 80% by weight or more.

2. The electrolytic iron foil according to claim 1, wherein: The crystal orientation index of the (110) plane of the two planes is 0.2 or more.

3. The electrolytic iron foil according to claim 1 or 2, wherein: In at least any one surface, the average crystal grain size of the crystal grains on the surface is 0.66 μm or more.

4. The electrolytic iron foil according to claim 1 or 2, wherein: The tensile strength is 130 MPa or more. 5 . A battery current collector comprising the electrolytic iron foil according to claim 1 . 6 . A non-aqueous battery current collector comprising the electrolytic iron foil according to claim 1 .

Images