Method for producing electrolytic iron foil

Abstract

To provide a method for producing electrolytic iron foil having high purity and excellent in smoothness and flexibility.SOLUTION: The method for producing an electrolytic iron foil includes a step of forming an electrolytic iron foil F on the surface of a cathode drum 1 by using the cathode drum 1 rotating in a state of being at least partially immersed in an electrolytic solution 3 and an anode 2 arranged so as to face the cathode drum 1 in the electrolytic solution 3 and passing an electric current through the cathode drum 1 and the anode 2. The temperature of the electrolytic solution 3 is 50 to 90 °C, the content of Fe2 + in the electrolytic solution 3 is 40 to 200g / L, the pH of the electrolytic solution 3 is 2.0 to 4.0, and the density of the current is 50 to 500A / m2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing electrolytic iron foil, and more particularly to a method for producing electrolytic iron foil using a cathode drum as a cathode. [Background technology]

[0002] Electrolytic iron foil not only has excellent mechanical properties such as strength and elongation, but also has cost advantages because it is made from iron, which is a plentiful resource. Therefore, electrolytic iron foil has a wide range of applications, including battery current collectors, battery exterior materials, and laminated core materials, and various research and development efforts have been conducted to date.

[0003] For example, Patent Document 1 proposes a method for producing electrolytic iron foil by using an insoluble anode to electrodeposit iron onto an electroforming substrate and then peeling off the electrodeposited iron layer, in which the ferrous ions, free iron acid, and temperature in the electrolyte are adjusted. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 58-73786 Summary of the Invention [Problem to be solved by the invention]

[0005] Although Patent Document 1 discloses a method using an insoluble anode, the present inventors attempted to produce an electrolytic iron foil with extremely high purity by a method using a soluble anode. The electrolytic iron foil is required to have not only high iron purity but also smoothness such as being free of pinholes, distortion, and irregularities. In addition, since the present inventors are considering a manufacturing method using a cathode drum, the electrolytic iron foil is also required to have flexibility so that it can be appropriately peeled from the cathode drum.

[0006] From this perspective, an object of the present invention is to provide a method for producing an electrolytic iron foil that is high in purity and has excellent smoothness and flexibility. [Means for solving the problem]

[0007] As a result of numerous experiments and studies on electrolytic iron foil, the inventors discovered that in order to achieve high levels of purity, smoothness, and flexibility, it is necessary to specify the manufacturing conditions very precisely, and thus created the present invention.

[0008] The above problems can be solved by the following means. The method for producing electrolytic iron foil according to the present invention includes a step of forming electrolytic iron foil on a surface of a cathode drum by passing a current through the cathode drum and the anode, the anode comprising an insoluble anode case and a soluble raw iron introduced into the anode case, the temperature of the electrolytic solution being 50 to 90°C, and the Fe content of the electrolytic solution being 100% or less. 2+ The content of the electrolyte is 40 to 200 g / L, the pH of the electrolyte is 2.0 to 4.0, and the current density of the current is 50 to 500 A / m 2 is. The method for producing electrolytic iron foil according to the present invention is characterized by the temperature of the electrolyte, the Fe content of the electrolyte, and the 2+ By precisely specifying the content of the compound, the pH of the electrolyte, and the current density, it is possible to continuously produce electrolytic iron foil that is high in purity and has excellent smoothness and flexibility. In the method for producing an electrolytic iron foil according to the present invention, the total content of C, P, S, Si, Co, Cu, Mn, and Ni in the electrolytic iron foil is preferably 38 ppm or less. The method for producing electrolytic iron foil according to the present invention specifies the total content of impurities to be equal to or less than a predetermined value, thereby more reliably achieving high purity in the produced electrolytic iron foil. The method for producing an electrolytic iron foil according to the present invention is characterized in that the temperature of the electrolytic solution is [A] °C, the pH of the electrolytic solution is [B], and the current density of the current is [C] A / m 2and the Fe in the electrolyte 2+ When the content of is [D] g / L, it is preferable that the value calculated by 2.5A + 30B - 0.1C + 0.05D - 190 is 0 or more. The method for producing electrolytic iron foil according to the present invention can more reliably produce high-purity electrolytic iron foil with excellent smoothness and flexibility, since the value calculated by the predetermined formula is 0 or more. [Effects of the Invention]

[0009] According to the method for producing electrolytic iron foil of the present invention, it is possible to produce electrolytic iron foil that is high in purity and has excellent smoothness and flexibility. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram for explaining a method for producing an electrolytic iron foil according to the present embodiment. [Figure 2] FIG. 1 is a schematic diagram of an anode used when producing an electrolytic iron foil according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] First, the "electrolytic iron foil" manufactured by the method for manufacturing electrolytic iron foil according to this embodiment will be described.

[0012] [Electrolytic iron foil] The electrolytic iron foil is an iron foil obtained through an electrolytic iron foil forming process described below, and the iron foil contains impurities other than iron. The electrolytic iron foil can be used for, but not limited to, battery current collectors, battery exterior materials, and laminated core materials (for power electronics).

[0013] (impurities) The impurities contained in the electrolytic iron foil are impurities that are inevitably mixed in during production, and specific examples thereof include C, P, S, Si, Co, Cu, Mn, and Ni. The total content of these impurities is preferably 38 ppm or less, more preferably 35 ppm or less. When the total content of impurities in the electrolytic iron foil is below a predetermined value, in other words, when the iron purity of the electrolytic iron foil is high, not only do various properties (mechanical properties and magnetic properties) become excellent, but the movement of dislocations is less likely to be hindered by impurities, resulting in excellent processability and suppressed rust generation. Furthermore, the content of each of the components listed as impurities is not particularly limited, but it is preferable that C is 20 ppm or less, and each of the other components is 5 ppm or less. In this specification, 1 ppm is synonymous with 0.0001 wt% (mass%).

[0014] (Thickness) The thickness of the electrolytic iron foil can be, for example, 20 to 200 μm. From the viewpoint of strength and ease of handling during processing, the thickness of the electrolytic iron foil is preferably 50 μm or more. However, it is possible to reduce the thickness of the electrolytic iron foil to 10 μm or less by processing such as rolling.

[0015] [Method of manufacturing electrolytic iron foil according to this embodiment] Next, a method for producing an electrolytic iron foil according to this embodiment will be described with reference to FIGS. The method for producing an electrolytic iron foil according to this embodiment includes an electrolytic iron foil forming step, and may include other steps as appropriate. Each step will be described in detail below.

[0016] (Electrolytic iron foil forming process) As shown in FIG. 1, in the electrolytic iron foil forming process, an electric current is passed through a cathode drum 1 and an anode 2 to form an electrolytic iron foil F on the surface of the cathode drum 1. In detail, in the electrolytic iron foil forming process, a constant current is applied to the cathode drum 1 and the anode 2, and Fe is discharged from the anode 2. 2+ The ions are dissolved into electrolyte 3, and the Fe 2+ The ions are deposited (electrodeposited) on the surface of the cathode drum 1 as electrolytic iron foil F. In addition, Fe from anode 2 2+ When ions are eluted, elements with a lower ionization tendency (higher equilibrium potential) than Fe are less likely to be eluted, and when electrolytic iron foil F is deposited on the cathode drum 1, elements with a higher ionization tendency (lower equilibrium potential) than Fe are less likely to be deposited, thereby achieving high purity of the electrolytic iron foil F that is formed.

[0017] (cathode) As shown in FIG. 1, the cathode 1 used in the electrolytic iron foil forming process is a cathode drum 1 having a drum shape (cylindrical shape). If the cathode drum 1 is made of stainless steel, corrosion may progress due to components in the electrolyte 3 during long-term use, which may make it difficult to peel the electrolytic iron foil F from the cathode drum 1. Furthermore, if the cathode drum 1 is made of stainless steel, components of the stainless steel may dissolve into the electrolyte 3, increasing the amount of impurities in the electrolytic iron foil F. Therefore, the cathode drum 1 is preferably made of pure titanium or a titanium alloy, which does not present such concerns. The width and outer diameter of the cathode drum 1 are not particularly limited, and may be set appropriately depending on the required size of the electrolytic iron foil F. 1, the cathode drum 1 is partially immersed in the electrolytic solution, but the entire drum may be immersed as long as at least the surface on which the electrolytic iron foil F is to be formed is immersed. Also, while FIG. 1 shows the cathode drum 1 rotating clockwise, it may also rotate counterclockwise and the electrolytic iron foil F may be pulled out from the right side of the drum.

[0018] (anode) As shown in FIG. 1, an anode 2 used in the electrolytic iron foil forming process is placed in an electrolytic solution 3 so as to face a cathode drum 1 . 2, the anode 2 is configured to include an insoluble anode case 21 and soluble raw iron 22 placed inside the case 21. The anode case 21 has a surface facing the cathode drum 1, which is provided with a soluble iron source 22 inside the case 21, and the soluble iron source 22 is appropriately transferred to the electrolyte 3. 2+The anode 2 (anode case 21) has a mesh-like surface 21a through which ions can elute. The mesh-like surface 21a of the anode 2 facing the cathode drum 1 is curved to fit along the lower surface of the cathode drum 1, and the anode 2 (anode case 21) is installed such that the mesh-like surface 21a is spaced a predetermined distance (for example, 10 to 100 mm) from the lower surface of the cathode drum 1. The raw material iron-22 acts as a soluble anode, and Fe 2+ The iron raw material from which ions are eluted can be pure iron, iron scrap, etc. On the other hand, the material of the anode case 21 may be any insoluble material, but for the same reasons as those for the cathode drum 1, pure titanium or a titanium alloy is preferred. 1 and 2, the anode case 21 is composed of two members, but it may be composed of one member or three or more members. However, the anode case 21 is preferably configured to have an inlet 21b that is open at the top so that raw iron 22 consumed during the electrolytic iron foil formation process can be easily added.

[0019] (electrolyte) The electrolytic solution 3 used in the electrolytic iron foil forming step is a liquid for electrolytic deposition stored in an electrolytic cell 4 . The electrolyte 3 is Fe 2+ Although the liquid composition is not particularly limited as long as it satisfies the above content, it contains an anionic surfactant such as sodium dodecyl sulfate, linear alkylbenzene sulfonate, linear alkylnaphthalene sulfonate, etc. The content of the anionic surfactant in the electrolytic solution 3 is preferably 0.1 to 10 g / L, and more preferably 0.5 to 5 g / L. In the electrolytic iron foil formation process, hydrogen generation occurs as a competitive reaction with iron electrodeposition on the cathode. If hydrogen accumulates on the electrodeposited iron and creates insulation due to hydrogen bubbles, iron cannot be electrodeposited at that location, leaving traces of the bubbles. To avoid this situation, the content of the anionic surfactant is preferably equal to or greater than the predetermined value described above.

[0020] (Electrolyte: Temperature) The temperature of the electrolytic solution 3 is preferably 50 to 90°C, more preferably 50 to 70°C. If the temperature of the electrolyte 3 is less than 50°C, the electrolytic iron foil F formed may become brittle and lose its flexibility. On the other hand, if the temperature of the electrolyte 3 exceeds 90°C, water will evaporate rapidly, which may cause the balance of iron concentration and pH to be easily lost. In addition, the high temperature of the electrolyte 3 makes it more susceptible to oxidation, and the Fe ions in the electrolyte may be easily dissolved. 2+ Fe 3+ This turns into iron(III) hydroxide particles, which physically become mixed into the electrolytic iron foil and are prone to causing poor electrodeposition.

[0021] (Electrolyte:Fe 2+ (content of Electrolyte 3 Fe 2+ The content is preferably 40 to 200 g / L. Electrolyte 3 Fe 2+ If the content of Fe in the electrolyte 3 is less than 40 g / L, the amount of impurities in the formed electrolytic iron foil F may increase, and pinholes may occur. 2+ If the content exceeds 200 g / L, the amount of impurities in the formed electrolytic iron foil F may increase, and distortion may occur.

[0022] (Electrolyte: pH) The pH of the electrolytic solution 3 is preferably 2.0 to 4.0. If the pH of the electrolytic solution 3 is less than 2.0, the resulting electrolytic iron foil F may contain a large amount of impurities and may have pinholes or distortion. On the other hand, if the pH of the electrolytic solution 3 is more than 4.0, the resulting electrolytic iron foil F may be brittle and prone to cracking. The pH may be adjusted by adding hydrochloric acid, sulfuric acid, or the like.

[0023] (current density) The current density of the current flowing through the cathode drum 1 and the anode 2 in the electrolytic iron foil forming process is 50 to 500 A / m 2 is preferred. Current density is 50A / m 2On the other hand, if the current density is less than 500 A / m, productivity will decrease. 2 If the temperature exceeds this range, the resulting electrolytic iron foil F may contain a large amount of impurities, distortion may occur, and the resulting electrolytic iron foil F may become brittle and lose its flexibility.

[0024] (Regarding the prescribed formula for manufacturing conditions) As described above, the method for producing the electrolytic iron foil according to this embodiment is carried out by adjusting the "temperature of the electrolytic solution," "pH of the electrolytic solution," "current density of the electric current," and "Fe content of the electrolytic solution." 2+ The four manufacturing conditions, "content of" and "content of" are very important and need to be precisely controlled. The inventors have found the following by examining the results of numerous experiments. Specifically, when the temperature of the electrolyte is [A] °C, the pH of the electrolyte is [B], and the current density is [C] A / m 2 The electrolyte Fe 2+ When the content of [A] is [D] g / L, it has been confirmed that when the value calculated by "150{(A-60) / 60}+90{(B-3) / 3}-30{(C-300) / 300}+5{(D-100) / 100}+25", i.e., "2.5A+30B-0.1C+0.05D-190", is 0 or greater, it is possible to more reliably produce electrolytic iron foil with high purity and excellent smoothness and flexibility. The value calculated by the above-mentioned predetermined formula is more preferably 0 or more and 100 or less, and even more preferably 0 or more and 80 or less. The constants in the above formulas have been determined based on the results of numerous experiments.

[0025] (Other processes) The method for producing an electrolytic iron foil according to this embodiment may include, after the electrolytic iron foil formation step, a washing step for removing surface dirt and the like, a drying step for drying off moisture after washing, a heat treatment step for removing residual stress and adjusting the crystalline structure, a slitting step for cutting to a desired width, and a winding step for recovering the electrolytic iron foil in the form of a roll as a product.

[0026] As described above, in the method for producing an electrolytic iron foil according to the present embodiment, the temperature of the electrolyte, the Fe content of the electrolyte, 2+ By precisely specifying the content of , the pH of the electrolyte, and the current density, it is possible to produce high-purity electrolytic iron foil with excellent smoothness and flexibility. Furthermore, because the produced electrolytic iron foil is high in purity, it not only has excellent properties (mechanical properties and magnetic properties), but also excellent processability and rust prevention. Furthermore, according to the manufacturing method of the electrolytic iron foil of this embodiment, since the foil is manufactured by an electrolytic method using a cathode drum and soluble raw iron charged into an anode case, it is possible to realize continuous manufacturing of high-purity electrolytic iron foil and also to avoid the increase in cost due to rolling compared to rolled iron foil manufactured by rolling. [Example]

[0027] Next, the present invention will be described by way of examples that satisfy the requirements of the present invention and comparative examples that do not.

[0028] [Sample production] A sample (electrolytic iron foil F) having a thickness of approximately 100 μm was produced using a cathode drum 1, an anode 2, and an electrolytic solution 3 configured as shown in FIGS. The temperature, pH, and iron concentration (Fe 2+ The content of the cathode drum 1 and the current density of the current applied to the anode 2 were as shown in Table 1. During production, the conditions shown in Table 1 were maintained approximately constant. The temperature and pH of the electrolyte 3 were measured using a commercially available thermometer and pH meter, and the iron concentration was measured by redox titration using potassium permanganate. The pH of the electrolyte 3 was adjusted by adding hydrochloric acid. The "value calculated by the specified formula" shown in Table 1 refers to "150{(A-60) / 60}+90{(B-3) / 3}-30{(C-300) / 300}+5{(D-100) / 100}+25, i.e., 2.5A+30B-0.1C+0.05D-190" (A: temperature of the electrolyte (°C), B: pH of the electrolyte, C: current density (A / m 2), D: Fe in the electrolyte 2+ The content of α-glucan was 100% (g / L).

[0029] The conditions other than those shown in Table 1 were as follows, and were the same for each sample. (Cathode drum 1) Material: Pure titanium Outer diameter: 300cm Width: 200cm Rotation speed: Controlled so that the sample thickness is approximately 100 μm (Anode 2) Anode case 21 material: Pure titanium Distance between anode case 21 and cathode drum 1: 5 cm Total circumferential length of anode case 21 (mesh surface 21a): 60 cm (= 30 cm × 2) Width of anode case 21 (mesh surface 21a): 180 cm Raw iron 22: Pure iron Amount of raw material iron 22 added: 10 kg (Electrolyte 3) Solution composition: 40-200 g / L of ferrous chloride, 1 g / L of anionic surfactant, and the remainder of the solution was water to achieve the iron concentration shown in Table 1. Agitation: Pump agitation (Electrolytic cell 4) Material: Fiber reinforced plastic (FRP)

[0030] (Measurement method) The content of each impurity element in each sample produced by the above method was measured using an EMIA-920V manufactured by Horiba, Ltd., a UV-1900i manufactured by Shimadzu Corporation, and an ICPE-9820 manufactured by Shimadzu Corporation. Table 2 shows the measurement results.

[0031] (For each evaluation) Regarding "high purity," if the total content of each element in the measurement results was 38 ppm or less, it was evaluated as "Good (high purity)," and if it exceeded 38 ppm, it was evaluated as "Poor (not high purity)." Regarding "smoothness," the surface of the sample (5 cm x 5 cm) was visually inspected, and if no pinholes, distortions, or irregularities were found, it was rated as "Good (excellent smoothness)," whereas if pinholes or distortions were found, it was rated as "Pinholes (poor smoothness)" or "Distortion (poor smoothness)," respectively. Regarding "flexibility," when a sample (length 10 cm, width 19 cm) was peeled off from cathode drum 1, if it could be peeled off properly, it was evaluated as "Good (excellent flexibility)," and if cracks or other damage occurred and it was not possible to recover it as foil, it was evaluated as "Poor flexibility (poor flexibility)." Table 3 shows the evaluation results.

[0032] [Table 1]

[0033] [Table 2]

[0034] [Table 3]

[0035] (Review of results) Samples 1 to 7 satisfied all of the manufacturing conditions specified in the present invention, and were therefore found to be "highly pure" and to have excellent "smoothness" and "flexibility." The details are as follows: Since Sample 1 was produced under the conditions shown in Table 1, it was free from nodular electrodeposits caused by impurities and was a smooth electrolytic iron foil. In Sample 2, the temperature of the electrolyte was set lower than in Sample 1, resulting in an electrolytic iron foil that was slightly harder, but it was smooth and the amount of impurities was not significantly different. For Sample 3, the current density was set higher and the iron concentration in the electrolyte lower than for Sample 1, creating conditions that would allow hydrogen generation to occur in competition with iron electrodeposition. However, the resulting electrolytic iron foil was smooth and pinhole-free, and the amount of impurities was also kept low. For Sample 4, iron was electrodeposited slowly by setting the electrolyte pH higher and the current density significantly lower than for Sample 3, but the resulting electrolytic iron foil had excellent flexibility and relatively few impurities. However, since Sample 4 has a low current density and a slow production speed, it is not suitable for mass production, but it was confirmed that it is effective for small-scale production. For Sample 5, the electrolyte temperature was set high, the pH of the electrolyte was set low, and the current density was set high, creating conditions that favored hydrogen generation, which occurs in competition with iron electrodeposition. However, because the electrolyte temperature was maintained at 70°C or higher (and did not fall below 70°C), a smooth electrolytic iron foil with few impurities was obtained. For Sample 6, iron was electrodeposited slowly by setting the pH of the electrolyte higher than for Sample 5, the current density significantly lower, and the iron concentration in the electrolyte higher, but the resulting electrolytic iron foil had fewer impurities (particularly less C) than Sample 4. Like Sample 4, Sample 6 was confirmed to be effective for small-scale production. For sample 7, the pH of the electrolyte was higher than for samples 5 and 6, the current density was intermediate between the two samples, and the iron concentration in the electrolyte was set lower, but the resulting electrolytic iron foil was smooth and had fewer impurities. Note that the temperature and pH of the electrolyte were higher, so the divalent iron ions (Fe 2+ ) is a trivalent iron ion (Fe 3+ ) and is easily generated in the electrolyte as iron hydroxide. Therefore, care must be taken to manage the flow rate (stirring speed) of the electrolyte, as there is a risk of iron hydroxide being physically mixed into the electrolytic iron foil.

[0036] On the other hand, Samples 8 to 12 did not satisfy at least one of the manufacturing conditions specified in the present invention, and therefore did not provide favorable results. The details are as follows. In Sample 8, the temperature and pH of the electrolyte were set lower than in Sample 1, and in particular the pH was below the specified value, so hydrogen generation, which occurred in competition with iron electrodeposition, became dominant, and many pinholes due to hydrogen generation were observed on the surface of the electrolytic iron foil. In addition, Sample 8 contained a large amount of impurities, and was evaluated as not being of high purity. For Sample 9, the current density was set higher than for Sample 1, and because the current density exceeded the specified value, the production speed was faster, but the electrolytic iron foil was warped toward the anode at the end of the cathode drum, resulting in distorted electrolytic iron foil. In addition, Sample 9 contained a large amount of impurities, and was evaluated as not being of high purity. For Sample 10, the current density and iron concentration of the electrolyte were set significantly lower than for Sample 8, and both were below the specified values, resulting in numerous pinholes. In addition, Sample 10 contained a large amount of impurities, and was therefore evaluated as not being of high purity. In Sample 11, the temperature of the electrolyte was set lower than in Sample 3, and the pH and iron concentration of the electrolyte were set higher. Because the temperature of the electrolyte was below the predetermined value, the electrolytic iron foil was quite brittle and immediately cracked when attempting to peel it off from the cathode drum, making it impossible to recover the foil. Sample 12 had the same electrolyte pH as Sample 8, but the iron concentration of the electrolyte was set higher. However, as with Sample 9, the electrolytic iron foil was found to be warped toward the anode at the edge of the cathode drum, resulting in a distorted electrolytic iron foil. In addition, Sample 12 contained a large amount of impurities and was evaluated as not being highly pure. Combining the results of Sample 12 and Sample 8, it was confirmed that the pH of the electrolyte has a significant impact on each effect.

[0037] Furthermore, as shown in Table 1, Samples 1 to 7, which were able to exhibit the effects of the present invention (high purity, smoothness, and flexibility), had values ​​calculated by the predetermined formula of 0 or more. On the other hand, Samples 8 to 12, which were unable to exhibit one or more of the effects of the present invention, had values ​​calculated by the predetermined formula of less than 0. From the above, it has been found that the specified formula proposed by the inventors provides a clear indicator as to whether or not each effect of the present invention is exhibited, and it has been confirmed that each effect of the present invention is exhibited more reliably when the value calculated by the specified formula is 0 or greater. [Explanation of symbols]

[0038] 1 cathode drum 2 Anode 21 Anode case 21a Mesh surface 21b Inlet 22 Raw Iron 3 Electrolyte 4 Electrolytic cell F Electrolytic iron foil

Claims

1. The method includes a step of using a cathode drum that rotates while at least a portion of the cathode drum is immersed in an electrolytic solution, and an anode that is disposed in the electrolytic solution so as to face the cathode drum, and passing a current through the cathode drum and the anode to form an electrolytic iron foil on a surface of the cathode drum, the anode comprises an insoluble anode case and soluble raw iron introduced into the anode case; The temperature of the electrolyte is 50 to 90°C, Fe in the electrolyte ２＋ The content is 40 to 200 g / L, The pH of the electrolyte is 2.0 to 4.0, The current density of the current is 50 to 500 A / m ２ A method for manufacturing electrolytic iron foil.

2. 2. The method for producing an electrolytic iron foil according to claim 1, wherein the total content of C, P, S, Si, Co, Cu, Mn, and Ni in the electrolytic iron foil is 38 ppm or less.

3. The temperature of the electrolytic solution is [A] °C, the pH of the electrolytic solution is [B], and the current density of the current is [C] A / m ２ and the Fe of the electrolyte ２＋ 3. The method for producing an electrolytic iron foil according to claim 1, wherein the value calculated by 2.5A + 30B - 0.1C + 0.05D - 190 is 0 or more, when the content of [D] g / L is [D] g / L.

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