Steel foil for battery containers and pouch-type battery containers manufactured therefrom

Abstract

To provide a steel foil for a battery container capable of suppressing cracks of a base material in molding.SOLUTION: In a steel foil for a battery container, the maximum value of the maximum main strain for uniaxial deformation is equal to or more than 0.25, and the maximum value of the maximum main strain for plane strain deformation is equal to or more than 0.1.SELECTED DRAWING: Figure 1(a)

Description

[Technical Field]

[0001] The present invention relates to steel foil suitable for use as a battery container, such as a lithium-ion secondary battery, and to a pouch-type battery container manufactured therefrom. [Background technology]

[0002] Lithium-ion rechargeable batteries (hereinafter also referred to as "LiB") are widely known as high-performance batteries with high output and long lifespan, used as secondary batteries in portable electronic devices or vehicles. Such lithium-ion rechargeable batteries are mainly classified into pouch type and metal can type. For pouch-type LiBs, a laminated material consisting of metal foil and resin film is generally used as the outer casing material, which is formed into a bag shape. Pouch-type LiBs have advantages such as being lightweight, having high heat dissipation due to the ability to make the battery thickness thin, and being able to freely design the battery shape to match the shape of the device.

[0003] In the laminated materials used as the outer casing for the pouch-type LiBs described above, aluminum foil is widely used as the metal foil due to its light weight. On the other hand, battery casing materials using steel foil are also known from the standpoint of strength. For example, Patent Document 1 discloses a technology in which electrodes and the like are housed in a pouch using a laminated metal plate made by coating a thin metal plate with resin. Furthermore, Patent Document 1 mentions the use of iron or an iron alloy as the metal foil core material.

[0004] Furthermore, Patent Documents 2 and 3 disclose a technique for forming a diffusion alloy layer containing Ni and Fe on the surface of a rolled metal sheet with a thickness of 200 μm or less by applying Ni plating to the rolled metal sheet, followed by rolling and heat treatment. Polyolefin resins are sometimes formed on rolled metal sheets to improve corrosion resistance to electrolytes, etc., and Patent Document 2 mentions that using the above-mentioned diffusion alloy layer improves the adhesion between the rolled metal sheet and the polyolefin resin.

[0005] Patent Document 4 discloses a battery can that has corrosion resistance to strongly alkaline electrolytes, which specifies the content of carbon, manganese, phosphorus, etc., contained in the steel plate, and also discloses a battery can in which a bright nickel layer is formed on the inner surface via a nickel-iron alloy layer and a matte or semi-bright nickel layer. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-202932 [Patent Document 2] International Publication No. 2016 / 013572 [Patent Document 3] International Publication No. 2016 / 013575 [Patent Document 4] Japanese Patent Publication No. 2005-078894 [Overview of the project] [Problems that the invention aims to solve]

[0007] The secondary batteries that can be installed in the vehicles and electronic devices mentioned above are required to have not only high output but also high capacity. If simply increasing capacity were sufficient, it might suffice to house a corresponding amount of electrode active material in a relatively large container. However, especially for secondary batteries installed in vehicles, an increase in the weight of the battery itself immediately leads to a decrease in fuel efficiency, so even to achieve high capacity, the increase in weight must be kept to a minimum.

[0008] As a method to achieve high capacity while avoiding weight increase as much as possible, it is conceivable that the internal volume of the battery container will be increased by performing molding under more stringent conditions. In other words, if the outer material of a pouch-type LiB can be manufactured by applying deep drawing or similar processes to thin laminated material, it will be possible to maximize the space for housing electrodes and improve battery capacity. However, the conventional technologies, including those described in Patent Documents 1 to 4 above, are not suitable for such molding processes, and there is considerable room for improvement.

[0009] Thus, metal sheets for battery containers have excellent processability (formability). teeth This is extremely important for improving product competitiveness. The present invention aims to solve the above-mentioned problems as an example, and aims to provide a steel foil for battery containers that can suppress cracking of the base material even when forming it using a metal sheet for battery applications, and a pouch-type battery container manufactured using the same.

[0010] Furthermore, metal plates for battery containers require improved resistance to non-aqueous electrolytes, such as organic electrolytes in which lithium salts are dissolved in organic solvents. This disclosure aims to solve this problem and provides a steel foil for battery containers that has excellent resistance to non-aqueous electrolytes filled inside the container, and a pouch-type battery container manufactured using the same. [Means for solving the problem]

[0011] To solve the above-mentioned problems, the steel foil for a battery container in one embodiment of the present invention is characterized in that (1) the maximum value of the maximum principal strain in uniaxial deformation is 0.25 or more and the maximum value of the maximum principal strain in plane strain deformation is 0.1 or more. Furthermore, in (1) above, it is preferable to have (2) a surface treatment layer formed on at least one side. Furthermore, in (1) or (2) above, it is preferable that (3) the maximum value of the maximum principal strain of the uniaxial deformation is 0.45 or more and the maximum value of the maximum principal strain of the plane strain deformation is 0.2 or more. Furthermore, in any of the above (1) to (3), it is preferable that (4) the thickness of the substrate is 10 to 200 μm. Furthermore, in any of the above (1) to (4), it is preferable that the maximum value of the maximum principal strain of the biaxial deformation, such as (5), is 0.2 or more. In the above (4) or (5), (6) it is preferable that in the base material, the C content is 0.15 wt% or less, the Si content is 0.5 wt% or less, the Mn content is 1.0 wt% or less, the P content is 0.05 wt% or less, and the S content is 0.02 wt% or less. In any one of the above (4) to (6), (7) it is preferable that in the base material, the C content is 0.05 wt% or less. In any one of the above (4) to (7), (8) it is preferable that in the base material, the Nb content is 0.05 wt% or less or the Ti content is 0.1 wt% or less. In any one of the above (1) to (8), (9) the surface treatment layer is a Ni plating layer of 0.5 to 50.0 g / m 2 or a Cr plating layer of 0.05 to 10.0 g / m 2 is preferably any one of them. In any one of the above (1) to (9), (10) it is preferable to have a thermoplastic resin layer formed on at least one side. In order to solve the above problems, a pouch-type battery container in one embodiment of the present invention is (11) characterized by being obtained by heat-sealing the steel foil for battery containers according to any one of the above (1) to (10). Further, in the above (11), (12) the pouch-type battery container is preferably for non-aqueous batteries.

Effects of the Invention

[0012] According to the present invention, it is possible to realize a steel foil for battery containers that can withstand at least severe forming processes as a material for battery containers, and further has excellent resistance to the content of the non-aqueous electrolyte filled inside the container.

Brief Description of the Drawings

[0013] [Figure 1(a)] It is a schematic diagram showing the steel foil 10 for battery containers according to this embodiment. [Figure 1(b)] It is a schematic diagram showing the steel foil 10 for battery containers according to this embodiment. [Figure 2(a)]This is a schematic diagram showing the strain distribution of the steel foil 10 for the battery container according to this embodiment. [Figure 2(b)] This is a schematic diagram showing the forming limit line of the steel foil 10 for the battery container according to this embodiment. [Figure 3] This figure shows an example of the manufacturing process for the steel foil 10 for battery containers according to this embodiment. [Figure 4] This figure shows an example of the shape of the battery container according to this embodiment. [Modes for carrying out the invention]

[0014] The steel foil 10 for the battery container of this embodiment will be described below with reference to Figure 1. In Figure 1, for convenience, the thickness direction of the steel foil 10 for the battery container will be described as the Z direction, and the rolling direction of the steel foil 10 for the battery container will be described as the X direction. However, these definitions of directions do not reduce the scope of the rights of the present invention.

[0015] <Steel foil for battery containers> As shown in Figure 1, the steel foil 10 for the battery container according to this embodiment is located on a base material 1 made of steel foil. Examples of base material 1 include various steel foils that can be used as base materials for battery containers. For example, as carbon steel, low-carbon aluminum-killed steel (carbon content 0.01-0.15 wt%), ultra-low carbon steel with a carbon content of 0.003 wt% or less, or non-aging ultra-low carbon steel obtained by further adding Ti or Nb to ultra-low carbon steel can be used.

[0016] The steel foil 10 for the battery container according to this embodiment is characterized in that the maximum value of the maximum principal strain in uniaxial deformation is 0.25 or more, and the maximum value of the maximum principal strain in plane strain deformation is 0.1 or more. The above features will be described below.

[0017] The present invention aims to provide steel foil that can be used to manufacture battery containers by processing such as deep drawing. Furthermore, when manufacturing a battery container having a recess by rectangular tube drawing, the present invention aims to provide steel foil for battery containers that can minimize the radius of curvature of both the Rc at the four corners of the recess and the Rp between the side wall and the bottom surface of the recess as much as possible. This is based on the idea of ​​increasing the area where electrodes are placed in the resulting battery container, and also reducing dead space within the battery.

[0018] In order to solve the above problems, the inventors conducted intensive research and found that the above problems can be solved by defining the strain in the steel foil for battery containers, taking into account the deformation mode during molding. Specifically, by defining the maximum value of the maximum principal strain for uniaxial deformation and the maximum principal strain for plane strain deformation of the steel foil for battery containers, it is possible to manufacture suitable electrical containers by suppressing the occurrence of cracks and other defects even when subjected to processing such as deep drawing.

[0019] The inventors of this invention conducted a detailed study on rectangular tube drawing, a method typically used as an outer casing for pouch-type lithium-ion batteries, in order to improve the formability of steel foil for battery containers. As a result, they found that in this molding method, the deformation mode differs in each part during molding.

[0020] Specifically, 0.5 mm diameter dots were printed on steel foil for battery containers before rectangular tube drawing, with a dot center point spacing of 1.0 mm. After rectangular tube drawing, the deformation mode was observed by observing the spread between dots on the resulting molded body using a GOM 3D strain measurement system (ARGUS). Figure 2(a) shows an example of strain distribution plotted in the resulting molded body. It is shown that the rectangular tube drawn molded body has a large amount of plane strain deformation and uniaxial deformation regions. From these observations, the inventors believe that deep drawing formability, such as rectangular tube drawing, can be improved by improving plane strain deformation and uniaxial deformation capabilities.

[0021] Furthermore, the inventors repeated the forming process by changing the type of steel used for the base material 1 in various ways, and observed the changes in the forming limit line (Figure 2(b)) due to differences in steel type. As a result, they confirmed that the forming limit line and the formable region change depending on the carbon content in the steel and the heat treatment conditions after steel foil rolling. Furthermore, we found that by setting the planar strain deformation and uniaxial deformation of the steel foil for the battery container to predetermined values, it is possible to achieve suitable moldability when manufacturing the outer casing material for the target high-capacity pouch-type LiB.

[0022] In this embodiment, known methods can be applied as the method for measuring strain. For example, in the strain distribution shown in Figure 2, obtained just before cracking occurs after deformation is applied to the test piece, the vertical axis represents the maximum principal strain (ε1), the horizontal axis represents the minimum principal strain (ε2), and the in-plane strain ratio β is ε2 / ε1. By defining -0.5≦β<0 as the uniaxial deformation region, β=0 as the plane strain deformation region, and 0<β≦1 as the biaxial deformation region, the maximum value of the maximum principal strain for uniaxial deformation and the maximum value of the maximum principal strain for plane strain deformation can be obtained. By setting the maximum value of the maximum principal strain of uniaxial deformation and the maximum principal strain of plane strain deformation of the steel foil for battery containers to the above values, it is preferable that when manufacturing a molded body with a rectangular recess by drawing a steel foil with a thickness of 10 to 200 μm, the molding can be performed without cracking even if the radius of curvature Rc of the four corners, the radius of curvature Rp between the side wall of the recess and the bottom surface of the recess, and the depth D of the recess are set to a certain level or higher. The radii of curvature Rc of the four corners, the radius of curvature Rp between the side wall of the recess and the bottom surface of the recess, and the depth D of the recess will be described later. In the steel foil for battery containers of this embodiment, it is even more preferable from the above viewpoint that the maximum value of the maximum principal strain in uniaxial deformation is 0.45 or more, and the maximum value of the maximum principal strain in plane strain deformation is 0.2 or more.

[0023] In this embodiment, the thickness of the base material 1 is preferably 10 to 200 μm, and more preferably 25 to 100 μm. If the thickness is less than 10 μm, the quality tends to be unstable, such as the occurrence of pinholes in the cold rolling process or instability in the thickness difference. In addition, cracks may occur in the molding process, and the effects intended for this application may not be obtained. On the other hand, if the thickness exceeds 200 μm, the objective of reducing the weight of the battery container may not be achieved.

[0024] Here is an example of the component composition of base material 1. (C:0.0001~0.15% by weight) Carbon (C) is an element that increases the strength of the base material 1. If the C content is excessive, the strength will increase too much and the rollability will decrease, so the upper limit of the C content is set to 0.15% by weight. On the other hand, there is no particular lower limit for the C content, but considering the cost, the lower limit of the C content is set to 0.0001% by weight. The C content is more preferably 0.0005 to 0.05% by weight, and even more preferably 0.001 to 0.01% by weight.

[0025] (Si:0.001~0.5wt%) Si is an element that increases the strength of the base material 1. If the Si content is too high, the strength will increase too much and the rollability will decrease, so the upper limit of the Si content is set to 0.5% by weight. On the other hand, there is no particular lower limit for the Si content, but considering the cost, the lower limit of the Si content is set to 0.001% by weight. The Si content is more preferably 0.001 to 0.02% by weight.

[0026] (Mn:0.01~1.0wt%) Mn is an element that increases the strength of the base material 1. If the Mn content is too high, the strength will increase too much and the rollability will decrease, so the upper limit of the Mn content is set to 1.0% by weight. On the other hand, there is no particular lower limit for the Mn content, but considering the cost, the lower limit of the Mn content is set to 0.01% by weight. The Mn content is more preferably 0.01 to 0.5% by weight.

[0027] (P:0.001~0.05wt%) P is an element that increases the strength of base material 1. If the P content is too high, the strength will increase too much and the rollability will decrease, so the upper limit of the P content is set to 0.05% by weight. On the other hand, there is no particular lower limit for the P content, but considering the cost, the lower limit of the P content is set to 0.001% by weight. The P content is more preferably 0.001 to 0.02% by weight.

[0028] (S:0.0001~0.02% by weight) S is an element that reduces the corrosion resistance of base material 1. Therefore, a lower S content is preferable. In particular, since the reduction in corrosion resistance becomes significant when the S content exceeds 0.02% by weight, the upper limit of the S content is set to 0.02% by weight. On the other hand, there is no particular lower limit for the S content, but considering the cost, the lower limit of the S content is set to 0.0001% by weight. The S content is more preferably 0.001 to 0.01% by weight.

[0029] (Al:0.0005~0.20wt%) Al is added, for example, as a deoxidizing element to base material 1. To obtain the deoxidizing effect, it is preferable that the Al content be 0.0005% by weight or more. However, since excessive Al content reduces rollability, the upper limit of the Al content is set to 0.20% by weight. On the other hand, there is no particular lower limit for the Al content, but considering the cost, the lower limit of the Al content is set to 0.0005% by weight. The Al content is more preferably 0.001 to 0.10%.

[0030] (N:0.0001~0.0040wt%) N is an element that reduces the processability of base material 1. Therefore, a lower N content is preferable. In particular, since the reduction in processability becomes significant when the N content exceeds 0.0040% by weight, the upper limit of the N content is set to 0.0040% by weight. On the other hand, there is no particular lower limit for the N content, but considering the cost, the lower limit of the N content is set to 0.0001% by weight. The N content is more preferably 0.001 to 0.0040% by weight.

[0031] (Remainder: Fe and unavoidable impurities) The main element in the remainder of base material 1 is Fe, and the others are impurities that inevitably get mixed in during manufacturing.

[0032] In addition, Ti, Nb, B, Cu, Ni, Sn, and Cr may be included as additional components. Ti and Nb, in particular, have the effect of fixing C and N in the base material 1 as carbides and nitrides, respectively, thereby improving the processability of the base material 1. For this reason, when the C content is in the range of 0.001 to 0.01% by weight, one or two types of Ti may be included in the range of 0.01 to 0.1% by weight and Nb in the range of 0.001 to 0.05% by weight. Furthermore, in this embodiment, a steel sheet with a Cr content of less than 10.5% is more preferable for the base material 1.

[0033] In this embodiment, the base material 1 is preferably cold-rolled and then annealed to possess at least one of the following characteristics. In this embodiment, the temperature and time required for annealing the base material 1 are as shown in Table 1: 5 to 15 hours when performed at 500°C to less than 750°C, and 5 seconds to 30 minutes when performed at 750°C to 900°C. More preferably, 6 to 10 hours when performed at 600°C to less than 750°C, and 10 seconds to 5 minutes when performed at 750°C to 900°C.

[0034] [Table 1]

[0035] (Tensile strength) The tensile strength of the base material 1 according to this embodiment is preferably 260 to 700 MPa. If the tensile strength is less than 260 MPa, when used as a battery container, it will deform under external force, causing cracks and holes, which can lead to problems such as electrolyte leakage. Also, if the tensile strength exceeds 700 MPa, the processability becomes poor. The tensile strength of the base material 1 is more preferably 270 to 650 MPa. If even better processability is required, it is even more preferably 280 to 450 MPa. In this embodiment, the tensile strength of the base material 1 is determined by the value obtained in accordance with the "Tensile Test Method for Metallic Materials" described in JIS standard Z2241.

[0036] (stretch) The elongation of the base material 1 according to this embodiment is preferably 5 to 55%. If the elongation of the base material 1 is less than 5%, the workability at the corners will be poor, and cracking may occur during processing. If the elongation exceeds 55%, high temperatures and long annealing times will be required to achieve such characteristics, resulting in poor productivity. The elongation of the base material 1 is more preferably 15 to 55%, and even more preferably 20 to 50%. In this embodiment, the elongation of the base material 1 is a value obtained in accordance with "20: Formula (7) for measuring elongation at break (%) A" of the "Tensile testing method for metallic materials" described in JIS standard Z2241. As will be described later, from the viewpoint of suppressing cracking of the base material 1 during molding and peeling of the resin film from the base material 1, the elongation of the base material 1 is preferably 20% or more, and more preferably 30% or more.

[0037] <Surface treatment layer> In the steel foil 10 for battery containers according to this embodiment, it is preferable that a surface treatment layer 2 (hereinafter also referred to as a plating layer) is formed on at least one side of the base material 1 described above. The surface on which this surface treatment layer 2 is formed is preferably the inner surface of the battery container. Furthermore, the outer surface of the battery container steel foil 10 may also have a surface treatment layer 2 formed on it, which is the same as, or at least one layer the same as, the inner surface described above, from the viewpoint of preventing oxidation and ensuring ease of manufacture. The surface treatment layer 2 is preferably a plating layer formed by electroplating. Specifically, the surface treatment layer 2 includes a Cr plating layer, and Ni alloy plating as exemplified by a Ni plating layer and an Fe-Ni alloy plating layer. Furthermore, there may be multiple such plating layers; for example, a Ni plating layer may be formed on the substrate 1, followed by a Cr plating layer.

[0038] By forming the above-described plating layer on at least one surface of the substrate 1, for example, the adhesion to a resin film further formed on the plating layer can be improved. Furthermore, even if defects occur in the resin film, corrosion resistance to the electrolyte can be ensured.

[0039] The surface treatment layer 2 of this embodiment may be formed, for example, after the base material 1 has been cold-rolled and then annealed, or it may be formed after the base material 1 has been cold-rolled but before it has been annealed. In the case where the base material 1 is Ni-plated before it is annealed, an Fe-Ni diffusion layer may be formed by heat treatment. In this case, the Fe-Ni diffusion layer may be formed between the Ni-plating layer and the base material 1, or the iron (Fe) of the base material 1 may diffuse throughout the Ni-plating layer, and the Fe-Ni diffusion layer may be formed directly on the base material 1. The heat treatment conditions can be within a suitable range of temperature and time, similar to those for the annealing of the base material 1 described above.

[0040] Furthermore, although the surface treatment layer 2 is formed on both sides of the substrate 1 in Figure 1(b), the surface treatment layer 2 may also be formed on at least the side that faces the inner surface of the battery container. Alternatively, different types of surface treatment layers 2 (electroplating layers) may be formed on both sides of the substrate 1. For example, on the side of the substrate 1 that will be the inner surface of the battery container, an electroplating layer (first electroplating layer) containing at least one of a Ni plating layer and a Cr plating layer may be formed, while on the side that will be the outer surface of the battery container, an electroplating layer (second electroplating layer) containing a Zn plating layer or Zn alloy layer (e.g., Zn-Ni, Zn-Co, Zn-Co-Mo, Zn-Fe, Zn-Sn, etc.) with a different corrosion resistance mechanism (as a sacrificial corrosion protection layer) may be formed. In this case, the electroplating layer containing the Zn plating layer or Zn alloy plating layer as a sacrificial corrosion protection layer may contain, for example, Zn at a concentration of 3 to 30 g / m². 2 The plating amount is preferably 5 to 25 g / m². 2 It is even more preferable that the plating amount be as specified. Since Zn plating dissolves in the electrolyte, it cannot be used on the inner surface which is in constant contact, but by using it on the outer surface of the battery container, it is effective in sacrificial corrosion protection when a small amount of electrolyte adheres to it. In particular, when a small amount of electrolyte adheres to the end face, if one side (the outer surface) is plated with Zn as described above, the Zn will dissolve preferentially at the end face, which can suppress the corrosion of the base material (iron) and thus prevent leakage of the electrolyte, making it effective.

[0041] When applying Ni plating as a surface treatment layer 2 on the substrate 1, the cold-rolled metal sheet is electrolytically degreased and pickled using the usual method, and then, for example, the Ni plating bath shown below can be used. The main Ni plating bath used is a nickel sulfate bath called a Watt bath, but other baths such as sulfamic acid baths, borofluoride baths, and chloride baths may also be used. (Example of Ni plating bath composition and conditions) Nickel sulfate: 200-350 g / l Nickel chloride: 20-60 g / l Boric acid: 10-50 g / l pH: 1.5~5.0 Bath temperature: 40~70℃ Current density: 1~40A / dm 2

[0042] Furthermore, the Ni plating as the surface treatment layer 2 formed on the substrate 1 may be formed not only with pure Ni, but also with an alloy containing Ni, such as a Ni-Co alloy or an Fe-Ni alloy. In other words, in this specification, unless otherwise specified, the "Ni plating layer" includes not only "a layer composed solely of Ni" but also "a layer composed of an alloy containing Ni." Furthermore, the "layer composed of an alloy containing Ni" may be either "a diffusion layer in which Ni and other metal elements are mutually diffused" or "an alloy plating layer in which Ni and other metal elements are electrodeposited together." Similarly, in this specification, unless otherwise specified, "Cr plating layer" includes not only "layers composed solely of Cr" but also "layers composed of alloys containing Cr." Furthermore, "layers composed of alloys containing Cr" may be "diffusion layers in which Cr and other metallic elements are mutually diffused" or "alloy plating layers in which Cr and other metallic elements are electrodeposited together." The "Cr plating layer" also includes so-called chromate treatment, which forms chromium hydrated oxide on the surface to be treated. Furthermore, the same understanding applies when the surface treatment layer contains metallic elements other than Ni and Cr.

[0043] In other words, surface treatment layer 2 may include any of the following: a Ni plating layer composed solely of Ni, an Fe-Ni diffusion layer in which Fe is diffused, or an Fe-Ni alloy plating layer in which both Fe and Ni are electrodeposited. In this specification, "composed solely of Ni" means that Ni is the only metallic element, and it is permissible to include impurities such as less than 0.1% carbon and less than 0.05% sulfur, which are derived from plating bath additives or are inevitably mixed in during the plating formation process.

[0044] Furthermore, the Ni plating used as the surface treatment layer 2 in this embodiment has a plating amount of 0.5 to 50.0 g / m². 2 Ni plating is preferred. The amount of Ni plating is 0.5 g / m 2If it is less than that, there will be a problem that the surface coating is insufficient, the exposure of the base material increases extremely, and the resistance to the content physical properties is insufficient. On the other hand, when the plating amount of Ni plating exceeds 50.0 g / m 2 2 , the thickness of the plating layer becomes thick, which leads to an increase in the thickness of the steel foil 10 for battery containers and an increase in weight. In addition, an increase in the plating treatment time and the plating amount causes problems such as deterioration of productivity and an increase in manufacturing cost. In addition, when Ni plating is formed on the base material 1 as the surface treatment layer 2 and then heat treatment is performed, an Fe-Ni diffusion layer can be formed. From the viewpoint of improving workability, the Fe-Ni diffusion layer preferably has a thickness of 0.2 μm or more and 3.0 μm or less. The thickness of the Fe-Ni diffusion layer can be obtained, for example, using a high-frequency glow discharge optical emission spectrometer, starting from the point when the Fe intensity reaches 10% of its saturation value, after the Ni intensity shows its maximum value, until the Ni intensity reaches 10% of its maximum value. The measurement time can be calculated, and it can be determined based on the calculated measurement time.

[0045] When Cr plating is applied as the surface treatment layer 2 on the base material 1, after degreasing and pickling the cold-rolled metal sheet by an ordinary method, for example, the following Cr plating bath can be used as an example. (Example of Cr plating bath composition and conditions) CrO3: 30~200 g / l NaF: 1~10 g / l pH: 1.0 or less Bath temperature: 35~65 °C Current density: 5~50 A / dm 2

[0046] In this case, the Cr plating as the surface treatment layer 2 is preferably Cr plating with a plating amount of 0.05~10.0 g / m 2 If the plating amount of Cr plating is less than 0.05 g / m 2 2 , there will be a problem that the surface coating is insufficient, the exposure of the base material 1 increases extremely, and the resistance to the content physical properties is insufficient. On the other hand, when the plating amount of Cr plating is 10.0 g / m 2This is because exceeding this limit leads to problems such as increased weight, decreased productivity, and higher manufacturing costs, similar to those mentioned above.

[0047] Furthermore, when applying Cr plating as the surface treatment layer 2, it is even more preferable that the proportion of metallic Cr is greater than the proportion of Cr hydrated oxide (CrOx) in the Cr plating layer. Here, the calculation of metallic Cr and Cr hydrated oxide (CrOx) can be carried out by the following method, for example. First, in step 1, the total amount of Cr in the Cr plating applied to the substrate is measured. Next, in step 2, the substrate with this Cr plating is dissolved with a high-temperature alkali to dissolve the Cr hydrated oxide, and the amount of Cr remaining in the substrate is measured as the amount of metallic Cr. Finally, in step 3, the amount of Cr hydrated oxide is calculated (amount of Cr hydroxide = total amount of Cr - amount of metallic Cr). All of the above measurements can be carried out using a commercially available X-ray fluorescence detector. In this embodiment, the values ​​measured on the substrate on which the surface treatment layer is formed satisfy the following conditions: the maximum value of the maximum principal strain in uniaxial deformation is 0.25 or more, and the maximum value of the maximum principal strain in plane strain deformation is 0.1 or more. Similarly, it is preferable that the tensile strength and elongation of the substrate on which the surface treatment layer is formed also satisfy the above preferred range.

[0048] <Thermoplastic resin> In this embodiment, the steel foil 10 for the battery container may have at least one surface covered with a thermoplastic resin layer 3, and it is preferable that at least one surface is covered with the thermoplastic resin layer 3, which is on the inner surface side of the battery container. In this embodiment, the steel foil 10 for the battery container may have the thermoplastic resin layer 3 formed on the surface treatment layer 2 described above. In other words, the steel foil 10 for the battery container may be configured as a laminate board in which the surface treatment layer 2 is covered with a thermoplastic resin layer 3 (Figure 1(b)), or it may be configured in which only the surface treatment layer 2 is formed, or it may even be configured without the surface treatment layer 2 and the thermoplastic resin layer 3. Furthermore, the substrate 1 may be covered with a thermoplastic resin layer 3 without the surface treatment layer 2 (Figure 1(a)). The thickness of such thermoplastic resin layer 3 is 10 to 100 μm, and more preferably 10 to 50 μm. Furthermore, examples of materials for the thermoplastic resin layer 3 in this embodiment include polyolefin resins, polyester resins, or polyamide resins. It is preferable that the polyolefin resin, polyester resin, or polyamide resin covers both sides of the steel foil 10 for the battery container. In this case, it is preferable that one side of the steel foil 10 for the battery container (the inner surface side of the battery can) is covered with a polyolefin resin (particularly polypropylene resin).

[0049] Such polypropylene resins may be various types of polypropylene resins, such as random propylene resin, homopropylene resin, and blocked propylene resin, used as single layers, or they may be layered to form multiple layers. In addition, in this embodiment, known additives may be added to the polypropylene resin. Examples of such additives include low-crystallinity ethylene-butene copolymers, low-crystallinity propylene-butene copolymers, terpolymers consisting of a three-component copolymer of ethylene, butene, and propylene, antiblocking agents such as silica, zeolite, and acrylic resin beads, and fatty acid amide-based slip agents. Furthermore, slip agents (to improve the physical stability of the material) and antioxidants may also be added as additives as described above.

[0050] On the other hand, the other side of the steel foil 10 for the battery container (the outer surface of the battery can) is preferably coated with one of the following: polyester resin, polyamide resin, or polyolefin resin. Of these, polyethylene terephthalate is preferred as the polyester resin. In addition to polyethylene terephthalate, other polyester resins such as polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate can be used. Furthermore, modified resins such as urethane-modified polyester resin, acrylic-modified polyester resin, and epoxy-modified polyester resin may also be used.

[0051] Furthermore, the thickness of the resin covering one side of the battery container steel foil 10 (for example, the inner surface of the battery can) and the thickness of the resin covering the other side (for example, the outer surface of the battery can) can be appropriately adjusted within the above thickness range depending on the required corrosion resistance and processability, and the thicknesses of both sides may be the same or different. Furthermore, when using polyester resin, it is preferable that this polyester resin is non-oriented. Furthermore, the other side of the battery container steel foil 10 (the outer side of the battery can) is not limited to the polyester resin (polyethylene terephthalate) described above, and both sides of the battery container steel foil 10 may be coated with polypropylene resin. Alternatively, both sides of the battery container steel foil 10 may be coated with polyester resin.

[0052] Furthermore, the thermoplastic resin layer 3 may be in a form in which the steel foil 10 for the battery container is coated via a known adhesive. Examples of known adhesives include acid-modified polyolefin resins, epoxy resins, acrylic resins, urethane resins, silicone resins, polyisobutylene resins, fluororesins, or inorganic adhesives such as water glass.

[0053] The method for forming the thermoplastic resin layer 3 may be by laminating a film, or by an extrusion lamination method in which the heated and melted material resin of the thermoplastic resin layer 3 is extruded into a film shape through a slit of an extrusion molding machine and directly laminated onto the substrate 1 or the surface treatment layer 2. When laminating after forming the film, there is no particular limit to whether or not the film is stretched; for example, it may be an unstretched film, a uniaxially oriented film, or a biaxially oriented film.

[0054] <Method for manufacturing steel foil for battery containers> Next, the manufacturing method of the steel foil 10 for the battery container of this embodiment will be described with reference to Figure 3. First, a steel sheet is prepared and cold-rolled by feeding it into a rolling mill (Step 1). This forms a cold-rolled steel foil (base material 1) with a thickness of 10 to 200 μm. This cold rolling may be carried out in multiple stages as needed, and heat treatment may be performed in between.

[0055] Next, the obtained substrate 1 is subjected to annealing treatment (Step 2). At this time, the temperature and time of the substrate 1 in the annealing treatment are 5 to 15 hours if performed at 500°C to less than 750°C, and 5 seconds to 30 minutes if performed at 750°C to 900°C. More preferably, it is 6 to 10 hours if performed at 600°C to less than 750°C, and 10 seconds to 5 minutes if performed at 750°C to 900°C.

[0056] After step 2, the substrate 1 is subjected to surface treatment (plating) to form a surface treatment layer 2 (electroplating layer) containing at least one Ni plating layer and a Cr plating layer on at least one surface of the substrate 1 (step 3). Note that this step 3 is not an essential step in the manufacturing method of the steel foil 10 for battery containers of this embodiment and may be omitted as appropriate. For the surface treatment layer 2 (electroplating layer) formed in step 3, for example, if it is a Ni plating layer, the plating amount should be 0.5 to 50.0 g / m². 2 For a Cr plating layer, the plating amount should be 0.05 to 10.0 g / m². 2 It is preferable that this be the case. Note that the annealing in step 2 may be performed after the surface treatment layer 2 has been formed. Furthermore, after performing the annealing in step 2 and forming the surface treatment layer 2, a heat treatment (diffusion treatment) may be further applied, for example, to improve workability. The heat treatment conditions at this time can be the same as the annealing conditions described in step 2. Furthermore, performing the rolling process in Step 1 after the plating treatment is undesirable because it may cause cracks to form on the surface of the plating film, reducing adhesion and corrosion resistance.

[0057] Furthermore, it is preferable that the base material 1 after step 2, or the base material 1 after both steps 2 and 3, has either a tensile strength of 260 to 700 MPa or an elongation of 5 to 55%.

[0058] Next, in step 4, the substrate 1 on which the surface treatment layer 2 is formed is coated with the thermoplastic resin layer 3 described above to a thickness of about 10 to 50 μm (resin coating treatment). Note that this step 4 is not an essential step in the manufacturing method of the battery container steel foil 10 of this embodiment, and may be omitted as appropriate unless it is configured as a laminate plate (surface-treated steel foil).

[0059] The thermoplastic resin layer 3 is preferably formed on at least the inner surface of the battery container on the substrate 1, and can be formed by film lamination or extrusion lamination. The temperature of the substrate 1 when coating with this thermoplastic resin layer 3 is adjusted to, for example, room temperature to 280°C, preferably 250°C or lower, depending on the lamination method. As described above, the steel foil 10 for the battery container can be obtained after going through steps 1 to 4.

[0060] <Battery container> Next, the battery container of this embodiment, manufactured using the steel foil 10 for battery containers described above, will be explained. The battery container of this embodiment is manufactured by applying processes such as deep drawing and heat sealing to the steel foil 10 for the battery container described above. In particular, the battery container of this embodiment is preferably in a so-called pouch shape, manufactured by deep drawing of a rectangular tube. More specifically, the steel foil 10 for the battery container is subjected to a drawing process (such as deep drawing) to form the steel foil 10 for the battery container into the container shape shown in Figure 4. More specifically, the container shape of this embodiment has rectangular recesses with a depth D, where corners with a radius of curvature Rc (referred to as Rc because they are circumferential corners) are formed at the four corners, so as to be able to accommodate rectangular electrode plates. Furthermore, the side walls of these recesses and the bottom surface of the recesses are connected by a radius of curvature Rp (referred to as Rp because it is defined by the R of the punch). In the container of Figure 4, the corner radii of the four corners of the recess described above are equal, but Rc and Rp may be different values. The reasons why the steel foil 10 for battery containers of this embodiment is very effective for battery containers with such radii of curvature Rc and Rp and depth D will be explained in detail below.

[0061] <Radius of curvature Rc and Rp and depth D for increasing capacity> First, in order to increase capacity by using the steel foil 10 for battery containers as a battery container, the Rc of the four corners of the recess during the molding process, the Rp between the side wall and the bottom surface of the recess, and the depth D are all important, but the balance between Rp and depth D is particularly important. Establishing such a balance is especially important for battery containers used in automobiles, as it allows for the enlargement of individual batteries, enabling a single battery to provide the battery characteristics of multiple conventional batteries. This is also important not only for single-cell batteries, but also when multiple batteries are assembled and used as modules. Furthermore, it is desirable to minimize the radius of curvature of both Rc and Rp as much as possible, from the perspective of increasing the area on which the electrodes are placed and reducing dead space within the battery. The value of such a radius of curvature Rp is preferably 3 mm or less, more preferably 1.5 mm or less, and even more preferably 1.0 mm or less. Furthermore, the value of such a radius of curvature Rc varies depending on the application and battery size, but it is preferably less than 10 mm, more preferably 8 mm or less, and even more preferably 3 mm or less.

[0062] On the other hand, to increase the capacity when used as a battery container, increasing the number of electrodes that are stacked and housed increases the overall capacity of the battery, and therefore increasing the depth D is also effective. The value of such a depth D is preferably 5 mm or more, more preferably 6 mm or more, and 10 mm or more. Against this backdrop, the inventors diligently investigated the relationship between the desirable radius of curvature Rp and depth D, and concluded that when processing the steel foil 10 for battery containers under the above conditions in order to increase capacity, there are problems with formability and the resistance of the contents after molding (resistance to electrolyte).

[0063] In other words, firstly, the smaller the radius of curvature Rp, the more difficult the forming process becomes, and the difficulty increases dramatically when the radius of curvature Rp is 1.0 mm or less. Furthermore, regarding the depth D, the deeper the forming process, the stricter the processing conditions become for the steel foil 10 material for the battery container. In particular, when a specific radius of curvature Rp condition and depth D condition are combined for steel foil with a thickness of 10 μm to 200 μm, as used in this embodiment, the following two problems arise.

[0064] The first challenge is that cracks are more likely to occur during the molding process. In the case of using steel foil as the base material 1, as explained in this embodiment, the specific gravity is higher than when using aluminum as the base material, so it is necessary to reduce the thickness of the base material 1 in order to suppress the increase in battery weight. When the thickness of the steel foil used as the base material 1 is reduced in this way, cracks and other problems are more likely to occur in the base material 1.

[0065] The second challenge is the resistance to internal materials (resistance to electrolytes) after molding. When deep drawing is performed under the harsh processing conditions described above, cracks may occur in the resin film. Therefore, even if cracks occur, it is necessary to ensure that the surface of the base material 1 does not easily dissolve.

[0066] In response to the first problem described in detail above, we found that in the battery container of this embodiment, by setting the maximum value of the maximum principal strain of uniaxial deformation of the steel foil for the battery container to 0.25 or more, and the maximum value of the maximum principal strain of plane strain deformation to 0.1 or more, it is possible to suppress cracking even when deep drawing is performed under the severe processing conditions described above. Furthermore, to address the second problem mentioned above, we found that by forming a surface treatment layer on at least one side of the steel foil for the battery container, it is possible to suppress the dissolution of the substrate into the electrolyte even if a defect occurs in the resin film. In this case, the surface treatment layer was 0.5 g / m 2 The above Ni plating layer and 0.05 g / m 2 A surface treatment layer (electroplating layer) containing at least one of the above-mentioned Cr plating layers is preferable because it provides sufficient resistance to the contents when used as a battery container.

[0067] The battery container is sealed after housing battery elements such as electrode plates and electrolyte, and the steel foil 10 for the battery container in this embodiment can also be used as a lid member for the battery container used for sealing. The lid member, which is a component of such a battery container, may have a housing space similar to that of the battery container body shown in Figure 4, or it may be used as a flat plate. Furthermore, when sealing the battery container, it is preferable to heat-seal the lid member with the flange portion at the periphery of the battery container body, which has a drawn housing portion. In this case, it is preferable that the coating resins on the opposing surfaces of the battery container body and the lid member be of the same type, such as polypropylene resins facing each other or polyester resins facing each other. The sealing method described above is just an example and is not limited thereto; for example, a known adhesive may be used.

[0068] Since the battery container obtained in this embodiment is formed using the steel foil 10 for battery containers of this embodiment described above, it can be suitably used as a battery container for various primary or secondary batteries such as alkaline batteries, nickel-metal hydride batteries, nickel-cadmium batteries, and lithium-ion batteries. In particular, since the battery container of this embodiment has excellent electrolyte resistance as described above, it can be suitably used for non-aqueous batteries that contain an organic solvent electrolyte as its contents. [Examples]

[0069] Next, the present invention will be described in more detail with reference to examples.

[0070] <Example 1> First, as the base material 1, a cold-rolled sheet (50 μm thick) of low-carbon steel having the chemical composition shown below was prepared. C: 0.04 wt%, Mn: 0.22 wt%, Si: 0.001 wt%, P: 0.01 wt%, S: 0.01 wt%, remainder: Fe and unavoidable impurities

[0071] Next, the prepared steel foil was annealed at 750°C for 10 seconds to obtain a base material 1 having the following characteristics. • Tensile strength (TS): 364 MPa • Elevation (EL): 28.6%

[0072] (Measurement of principal strain) For the substrate 1 obtained above, the maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured using the method described above. These maximum principal strains were measured using a non-contact three-dimensional strain and displacement measurement system (ARAMIS) manufactured by GOM. Using a sample that had been pre-coated with a random pattern using spray, etc., triangulation was performed by continuously photographing the deformation with two cameras, and the process of change in the random pattern was acquired as three-dimensional position information, thereby measuring the maximum principal strain (ε1) in the plate surface just before fracture and the minimum principal strain (ε2) orthogonal to it. Uniaxial deformation was measured using a tensile testing machine and a tensile test using a JIS No. 5 piece. Equibiaxial deformation and plane strain deformation were measured using an Erichsen testing machine. For equibiaxial deformation, a 150 mmφ circular blank was used, and for plane strain deformation, a blank was used in which both ends of a circular blank were cut so that the width was approximately 65 mm. A 60mm diameter ball-head punch was used, and petroleum jelly was applied to the tip of the punch to reduce friction between the punch and the blank before molding. The measurement results showed that the maximum principal strain value in uniaxial deformation of base material 1 in this embodiment was 0.40. Similarly, the maximum principal strain value in plane strain deformation was 0.14.

[0073] (Formation of thermoplastic resin layer 3) First, a 50 μm thick polyethylene film (product name "Daiwa Protac P-563B," manufactured by Daiwa Chemical Co., Ltd.) was prepared as the thermoplastic resin layer 3. Next, the polyethylene film was attached to both sides of the base material 1 to cover it.

[0074] (Evaluation of moldability) As described above, lubricating oil was applied to the steel foil 10 for the battery container, which was coated with a thermoplastic resin layer 3, and then deep drawing was performed using a 50 mm x 50 mm punch to form the recess described above. In this deep drawing process, the Rc of the four corners of the recess was set to 3.0 mm, and the Rp between the side wall and the bottom surface of the recess was set to both 1.0 mm and 3.0 mm. Press molding was performed until abnormalities such as cracks or tears occurred in the steel foil 10 for the battery container, and the process was stopped when such abnormalities occurred.

[0075] Furthermore, the moldability of the steel foil 10 for the battery container after press molding was evaluated by visually observing cracks in the base material 1 and lifting or cracking of the thermoplastic resin layer 3 at the four corners of the battery container, according to the following criteria. [Evaluation Criteria] ◎: No abnormalities were observed in the substrate even when the molding depth exceeded 10 mm, at both Rp values ​​of 1.0 mm and 3.0 mm. ○: The above abnormality in the substrate was observed before the molding depth reached 5 mm in either Rp 1.0 mm or 3.0 mm, but not in the other case. ×: In both Rp values ​​of 1.0 mm and 3.0 mm, tears and cracks were observed in the substrate before the molding depth reached 5 mm.

[0076] <Example 2> Except for the matters described below, the procedure was the same as in Example 1. First, as the base material 1, a cold-rolled sheet (thickness 50 μm) of ultra-low carbon steel having the chemical composition shown below was prepared. C: 0.001% by weight, Mn: 0.30% by weight, Si: 0.01% by weight, P: 0.01% by weight, S: 0.01% by weight, Nb: 0.02% by weight, balance: Fe and inevitable impurities. Next, the prepared steel foil was annealed at 670°C for 8 hours to obtain a base material 1 having the following characteristics. • Tensile strength (TS): 340 MPa • Growth (EL): 23.7% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured for the substrate 1 obtained above using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal strain in uniaxial deformation of substrate 1 in this example was 0.27. Similarly, the maximum value of the maximum principal strain in plane strain deformation of substrate 1 was 0.23.

[0077] <Example 3> Except for the matters described below, the procedure was the same as in Example 1. First, as the base material 1, a cold-rolled sheet (80 μm thick) of ultra-low carbon steel having the chemical composition shown below was prepared. C: 0.001% by weight, Mn: 0.15% by weight, Si: 0.01% by weight, P: 0.01% by weight, S: 0.01% by weight, Ti: 0.03% by weight, Nb: 0.004% by weight, balance: Fe and inevitable impurities.

[0078] Next, the prepared steel foil was annealed at 820°C for 20 seconds to obtain a base material 1 having the following characteristics. • Tensile strength (TS): 301 MPa • Elevation (EL): 42.0%

[0079] The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured for the substrate 1 obtained above using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal strain in uniaxial deformation of substrate 1 in this example was 0.65. Similarly, the maximum value of the maximum principal strain in plane strain deformation of substrate 1 was 0.30.

[0080] <Example 4> Using the same substrate as in Example 3 described above, the procedure was carried out in the same manner as in Example 3, except for the matters described below. Specifically, by annealing the prepared steel foil at 640°C for 8 hours, a base material 1 having the following characteristics was obtained. • Tensile strength (TS): 332 MPa • Growth (EL): 39.0% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured for the substrate 1 obtained above using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal strain in uniaxial deformation of substrate 1 in this example was 0.62. Similarly, the maximum value of the maximum principal strain in plane strain deformation of substrate 1 was 0.30.

[0081] <Example 5> The procedure was the same as in Example 4, except that the steel foil used as the base material 1 was a cold-rolled sheet of ultra-low carbon steel with a thickness of 50 μm. The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured for the obtained base material 1 using the same method as in Example 1. As a result of the measurements, the maximum value of the maximum principal strain in uniaxial deformation of base material 1 in this example was 0.63. Similarly, the maximum value of the maximum principal strain in plane strain deformation of base material 1 was 0.31.

[0082] <Example 6> Using the same extremely low-carbon steel cold-rolled sheet as in Example 5 as the base material 1, a surface treatment layer 2 was formed according to the following procedure. (Formation of surface treatment layer 2) After electrolytic degreasing and pickling by sulfuric acid immersion on substrate 1, electroplating was performed under the following conditions, resulting in a Ni plating amount of 4.5 g / m². 2 A surface treatment layer 2 (electroplated nickel layer) was formed. The conditions for forming the above nickel plating layer were as follows. (Conditions for forming the Ni plating layer) Bath composition: Nickel sulfate, nickel chloride, boric acid, pit inhibitor pH: 4.3 Bath temperature: 55℃ Current density: 10A / dm 2

[0083] Next, by performing a heat treatment at 800°C for 10 seconds, a substrate 1 was obtained on which a surface treatment layer 2 having the following characteristics was formed. • Tensile strength (TS): 325 MPa • Growth (EL): 37.3%

[0084] The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured on the substrate 1 on which the surface treatment layer 2 obtained above was formed, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal strain in uniaxial deformation of the substrate 1 on which the surface treatment layer 2 of this example was formed was 0.62. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 on which the surface treatment layer 2 was formed was 0.30. The substrate 1 on which this surface treatment layer 2 was formed was then coated on both sides with a thermoplastic resin layer 3, similar to the method used in Example 1, and the moldability was evaluated.

[0085] <Example 7> Except for the heat treatment conditions being 800°C for 30 seconds, the same procedure as in Example 6 was followed to obtain a substrate 1 on which a surface treatment layer 2 having the following characteristics was formed. • Tensile strength (TS): 326 MPa • Growth (EL): 35.6% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured on the substrate 1 on which the surface treatment layer 2 obtained above was formed, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal strain in uniaxial deformation of the substrate 1 on which the surface treatment layer 2 of this example was formed was 0.62. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 on which the surface treatment layer 2 was formed was 0.31.

[0086] <Example 8> Except for the heat treatment conditions being 820°C for 10 seconds, the same procedure as in Example 6 was followed to obtain a substrate 1 on which a surface treatment layer 2 having the following characteristics was formed. • Tensile strength (TS): 325 MPa • Elevation (EL): 30.2% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured on the substrate 1 on which the surface treatment layer 2 obtained above was formed, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal strain in uniaxial deformation of the substrate 1 on which the surface treatment layer 2 of this example was formed was 0.52. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 on which the surface treatment layer 2 was formed was 0.26.

[0087] <Example 9> Except for the heat treatment conditions being 850°C for 10 seconds, the same procedure as in Example 6 was followed to obtain a substrate 1 on which a surface treatment layer 2 having the following characteristics was formed. • Tensile strength (TS): 339 MPa • Elevation (EL): 30.7% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured on the substrate 1 on which the surface treatment layer 2 obtained above was formed, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal strain in uniaxial deformation of the substrate 1 on which the surface treatment layer 2 of this example was formed was 0.54. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 on which the surface treatment layer 2 was formed was 0.28.

[0088] <Comparative Example 1> The same substrate as in Example 2 described above was used. Except for the matters described below, the procedure was the same as in Example 2. Specifically, by annealing the prepared steel foil at 560°C for 8 hours, a base material 1 having the following characteristics was obtained. • Tensile strength (TS): 385 MPa • Elevation (EL): 20.6% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured for the substrate 1 obtained above using the same method as in Example 1. The measurement results showed that, This comparative example The maximum principal strain value for uniaxial deformation of base material 1 was 0.19. Similarly, the maximum principal strain value for plane strain deformation of base material 1 was 0.16.

[0089] <Comparative Example 1> The same substrate as in Example 2 described above was used. Except for the matters described below, the procedure was the same as in Example 2. Specifically, by annealing the prepared steel foil at 560°C for 8 hours, a base material 1 having the following characteristics was obtained. • Tensile strength (TS): 385 MPa • Elevation (EL): 20.6% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation were measured for the substrate 1 obtained above using the same method as in Example 1. The measurement results showed that, This comparative example The maximum principal strain value for uniaxial deformation of base material 1 was 0.19. Similarly, the maximum principal strain value for plane strain deformation of base material 1 was 0.16.

[0090] Table 2 shows the material specifications and moldability evaluation of each sample used in Examples 1-9 and Comparative Examples 1-2 described above.

[0091] [Table 2]

[0092] In Examples 1 to 9, when steel foil 10 for battery containers coated with a thermoplastic resin layer 3 was subjected to a tight drawing process with a radius of curvature below a predetermined level, it was found that the occurrence of cracks during the manufacturing of the battery container was suppressed. Furthermore, these results indicate that sufficient resistance to the contents can be obtained when used as a non-aqueous battery container. On the other hand, in Comparative Examples 1 and 2, when deep drawing with a small radius of curvature was performed during the manufacturing of the battery container, cracks occurred, and there is a possibility that sufficient resistance to the contents cannot be obtained when used as a non-aqueous battery container. [Industrial applicability]

[0093] The steel foil for battery containers of the present invention exhibits sufficient formability and resistance to contents for use as a container for non-aqueous batteries such as lithium-ion secondary batteries, and can be applied to a wide range of industries that use batteries. [Explanation of symbols]

[0094] 1 Base material 2. Surface treatment layer 3 Thermoplastic resin layer 10 Steel foil for battery containers

Claims

1. Steel foil for battery containers, used as a battery container, The thickness of the steel foil used as the base material is 10 to 200 μm. In the aforementioned substrate, the C content is 0.001 to 0.01% by weight, Ti is 0.01 to 0.1% by weight, and the Nb content is 0.001 to 0.05% by weight. A steel foil for battery containers, characterized in that the maximum value of the maximum principal strain in uniaxial deformation is 0.25 or more, and the maximum value of the maximum principal strain in plane strain deformation is 0.1 or more.

2. Having a surface treatment layer formed on at least one side, The surface treatment layer is 0.5 to 50.0 g / m² ２ Ni plating layer, or 0.05 to 10.0 g / m ２ The steel foil for a battery container according to claim 1, which is any of the Cr plating layers.

3. The steel foil for a battery container according to claim 1 or 2, wherein the maximum value of the maximum principal strain in the uniaxial deformation is 0.45 or more and the maximum value of the maximum principal strain in the plane strain deformation is 0.2 or more.

4. Furthermore, the steel foil for a battery container according to any one of claims 1 to 3, wherein the maximum value of the maximum principal strain of equibiaxial deformation is 0.2 or more.

5. The steel foil for a battery container according to any one of claims 1 to 4, wherein the substrate has a Si content of 0.5% by weight or less, a Mn content of 1.0% by weight or less, a P content of 0.05% by weight or less, and a S content of 0.02% by weight or less.

6. A steel foil for a battery container according to any one of claims 1 to 5, having a thermoplastic resin layer formed on at least one side.

7. A pouch-type battery container obtained by heat-sealing the steel foil for battery containers described in any one of claims 1 to 6.

8. A pouch-type battery container according to claim 7, for use with non-aqueous batteries.

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