Steel foil for battery container, and pouch battery container manufactured with the same

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 a steel foil for battery containers suitable for use as battery containers for lithium ion secondary batteries and the like, and to a pouch-type battery container produced from the steel foil. [Background technology]

[0002] Lithium-ion secondary batteries (hereinafter also referred to as "LiBs") are widely known as high-power, long-life, and high-performance secondary batteries for use in portable electronic devices or vehicles. These lithium-ion secondary batteries are broadly divided into pouch-type and metal can-type. The exterior of pouch-type LiBs is generally made of a laminated material consisting of metal foil and resin film molded into a bag shape. Pouch-type LiBs have the advantages of being lightweight, having high heat dissipation properties due to the ability to reduce the battery thickness, and being able to freely design the battery shape to match the shape of the device.

[0003] In the laminated material used as the packaging material for the above-mentioned pouch-type LiB, aluminum foil is widely used as the metal foil because of its light weight. On the other hand, battery packaging materials using steel foil have also been known in the past because of their strength. For example, Patent Document 1 discloses a technology for housing electrodes and the like in a pouch using a laminated metal sheet, which is a thin metal sheet coated with a resin. Patent Document 1 also 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 by using a rolled metal sheet having a thickness of 200 μm or less, plating the rolled metal sheet with Ni, and then rolling and heat treating the rolled metal sheet. Polyolefin resins are sometimes formed on the rolled metal sheet to improve corrosion resistance to electrolytes, etc., and Patent Document 2 mentions that the use of the diffusion alloy layer improves adhesion between the rolled metal sheet and the polyolefin resin.

[0005] Patent Document 4 discloses a battery can in which the contents of carbon, manganese, phosphorus, etc. contained in a steel sheet are specified in order to manufacture a battery can having corrosion resistance to a strongly alkaline electrolyte, and 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 Application Laid-Open No. 2001-202932 [Patent Document 2] International Publication No. 2016 / 013572 [Patent Document 3] International Publication No. 2016 / 013575 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-078894 Summary of the Invention [Problem to be solved by the invention]

[0007] Secondary batteries that can be installed in the above-mentioned vehicles and electronic devices are required to have not only high output but also high capacity. Here, if simply increasing capacity is all that is required, it may be sufficient to accommodate an appropriate 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, weight increase must be minimized.

[0008] One method to achieve high capacity while minimizing weight increases is to increase the internal volume of the battery container by performing molding under more stringent conditions. In other words, if the exterior material for a pouch-type LiB can be manufactured by deep-drawing a thin laminated material, it will be possible to maximize the space for electrodes and increase battery capacity. However, the conventional techniques including those described in Patent Documents 1 to 4 above are not suitable for such molding processes, and there is much room for improvement.

[0009] Thus, excellent processability (formability) is extremely important for metal sheets used for battery containers in order to improve product competitiveness. The present invention aims to solve the above-mentioned problems, for example, by providing a steel foil for battery containers that can suppress cracking of the substrate even when forming a metal sheet for battery applications, and a pouch-shaped battery container manufactured using the same.

[0010] Furthermore, metal sheets for battery containers are required to have improved resistance to contents against non-aqueous electrolytes such as organic electrolytes prepared by dissolving lithium salts in organic solvents. The present disclosure also aims to solve this problem and to provide a steel foil for battery containers that has excellent resistance to contents against non-aqueous electrolytes filled inside the containers, and a pouch-type battery container manufactured using the same. [Means for solving the problem]

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

[0012] According to the present invention, it is possible to realize a steel foil for battery containers that can withstand rigorous forming processing even when it is thin, and that has excellent resistance to the contents of the nonaqueous electrolyte filled inside the container. [Brief explanation of the drawings]

[0013] [Figure 1(a)] 1 is a schematic diagram showing a steel foil 10 for battery containers according to the present embodiment. [Figure 1(b)] 1 is a schematic diagram showing a steel foil 10 for battery containers according to the present embodiment. [Figure 2(a)]1 is a schematic diagram showing the strain distribution of a steel foil 10 for battery containers according to this embodiment. [Figure 2(b)] 1 is a schematic diagram showing a forming limit line of a steel foil 10 for battery containers according to this embodiment. [Figure 3] 1A to 1C are diagrams showing an example of a manufacturing process for a steel foil 10 for battery containers according to this embodiment. [Figure 4] 3A and 3B are diagrams showing an example of the shape of a battery container according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the steel foil 10 for battery containers of this embodiment will be described with reference to Fig. 1. For convenience, in Fig. 1, the thickness direction of the steel foil 10 for battery containers is defined as the Z direction, and the rolling direction of the steel foil 10 for battery containers is defined as the X direction. However, the definition of these directions does not restrict the scope of the present invention.

[0015] <Steel foil for battery containers> As shown in FIG. 1, a steel foil 10 for battery containers according to this embodiment has a substrate 1 made of steel foil. Various steel foils that can be used as the substrate of a battery container can be exemplified as the substrate 1. For example, low-carbon aluminum-killed steel (carbon content: 0.01 to 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 as the carbon steel.

[0016] The steel foil 10 for battery containers 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. These characteristics will be described below.

[0017] An object of the present invention is to provide a steel foil that can be used to manufacture battery containers by deep drawing, etc. A further object is to provide a steel foil for battery containers that, when manufacturing a battery container having a recess by square cylinder drawing, can reduce the radius of curvature of both the Rc of the four corners of the recess and the Rp between the side wall and bottom of the recess as much as possible. This is based on the viewpoint of increasing the area in which the electrodes are arranged in the resulting battery container and further reducing the dead space in the battery.

[0018] As a result of intensive research by the present inventors to solve the above problems, it has been found that the above problems can be solved by specifying the strain in a steel foil for battery containers taking into consideration the deformation mode during forming. Specifically, it has been found that by specifying the maximum value of the maximum principal strain in uniaxial deformation and the maximum value of the maximum principal strain in plane strain deformation of a steel foil for battery containers, it is possible to suppress the occurrence of cracks and the like even when processing such as deep drawing is performed, thereby making it possible to produce suitable electrical containers.

[0019] In order to improve the formability of steel foil for battery containers, the present inventors have conducted a detailed study on square-cup drawing, which is typically used as an exterior material for pouch-type LiBs. As a result, it has been found that in this forming method, the deformation mode differs in each part during forming.

[0020] Specifically, 0.5 mm diameter dots were printed with a dot center-to-center distance of 1.0 mm on the steel foil for battery containers prior to square-tube drawing. After square-tube drawing, the spread between the dots on the resulting molded body was observed using a three-dimensional strain measurement system (ARGUS) manufactured by GOM Corporation to observe the deformation mode. Figure 2(a) shows an example of strain distribution plotting the strain in the resulting molded body. It has been shown that the square-tube drawn molded body has many plane strain deformation and uniaxial deformation regions. Based on these observation results, the inventors believed that deep drawability, such as square-tube drawing, could be improved by improving plane strain deformation and uniaxial deformability.

[0021] Furthermore, the inventors also observed changes in the forming limit line (Fig. 2(b)) due to differences in the steel type by repeating the above forming process while changing the steel type used for the substrate 1. As a result, it was confirmed that the forming limit line and formable region change depending on the carbon content in the steel and the heat treatment conditions after rolling the steel foil. The inventors have found that by setting the plane strain deformation and uniaxial deformation of the steel foil for battery containers to predetermined values, it is possible to achieve suitable formability when manufacturing the desired exterior material for a high-capacity pouch-type LiB.

[0022] In this embodiment, a known method can be used to measure strain. For example, in the strain distribution shown in Fig. 2, which is obtained by deforming a test piece and timing immediately before cracks (fissures) occur, the vertical axis represents the maximum principal strain (ε1), the horizontal axis represents the minimum principal strain (ε2), the in-plane strain ratio β is ε2 / ε1, and -0.5≦β<0 represents the uniaxial deformation region, β=0 represents the plane strain deformation region, and the region of 0<β≦1 represents the biaxial deformation region. This allows the maximum value of the maximum principal strain in uniaxial deformation and the maximum value of the maximum principal strain in plane strain deformation to be obtained. By setting the maximum value of the maximum principal strain in uniaxial deformation and the maximum value of the maximum principal strain in plane strain deformation of the steel foil for battery containers to the above values, when a steel foil having a thickness of 10 to 200 μm is drawn to produce a molded body having a rectangular recess, it is possible to form the body without cracking even if the radius of curvature Rc of the four corners, the radius of curvature Rp between the sidewalls and the bottom of the recess, and the depth D of the recess are each set to a certain value or higher. Note that the radius of curvature Rc of the four corners, the radius of curvature Rp between the sidewalls and the bottom of the recess, and the depth D of the recess will be described later. From the above viewpoint, it is more preferable that the steel foil for battery containers of this embodiment has a maximum value of the maximum principal strain in uniaxial deformation of 0.45 or more and a maximum value of the maximum principal strain in plane strain deformation of 0.2 or more.

[0023] In this embodiment, the thickness of the substrate 1 is preferably 10 to 200 μm, and more preferably 25 to 100 μm. If the thickness is less than 10 μm, pinholes may occur during the cold rolling process, or the thickness gradient may become unstable, resulting in unstable quality. Furthermore, cracks may occur during the molding process, which may prevent the intended effect of the present application from being achieved. 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] An example of the component composition of the substrate 1 is shown below. (C:0.0001~0.15% by weight) C is an element that increases the strength of the base material 1. If the C content is excessive, the strength increases too much and rollability decreases, so the upper limit of the C content is set to 0.15% by weight. On the other hand, there is no particular restriction on the lower limit of the C content, but in consideration of costs, 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 substrate 1. If the Si content is excessive, the strength increases too much and rollability decreases, so the upper limit of the Si content is set to 0.5 wt%. On the other hand, there is no particular restriction on the lower limit of the Si content, but in consideration of costs, the lower limit of the Si content is set to 0.001 wt%. The Si content is more preferably 0.001 to 0.02 wt%.

[0026] (Mn:0.01~1.0wt%) Mn is an element that increases the strength of the base material 1. If the Mn content is excessive, the strength increases too much and rollability decreases, so the upper limit of the Mn content is set to 1.0 wt%. On the other hand, there is no particular restriction on the lower limit of the Mn content, but in consideration of costs, the lower limit of the Mn content is set to 0.01 wt%. The Mn content is more preferably 0.01 to 0.5 wt%.

[0027] (P:0.001~0.05wt%) P is an element that increases the strength of the base material 1. If the P content is excessive, the strength increases too much and rollability decreases, so the upper limit of the P content is set to 0.05% by weight. On the other hand, there is no particular restriction on the lower limit of the P content, but in consideration of costs, 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 the substrate 1. Therefore, the lower the S content, the better. In particular, when the S content exceeds 0.02 wt%, the corrosion resistance decreases significantly, so the upper limit of the S content is set to 0.02 wt%. On the other hand, there is no particular restriction on the lower limit of the S content, but in consideration of costs, the lower limit of the S content is set to 0.0001 wt%. The S content is more preferably 0.001 to 0.01 wt%.

[0029] (Al:0.0005~0.20wt%) Al is added, for example, as a deoxidizing element to the base material 1. To obtain the deoxidizing effect, the Al content is preferably 0.0005% by weight or more. However, an excessive Al content reduces rollability, so the upper limit of the Al content is set to 0.20% by weight. On the other hand, there is no particular restriction on the lower limit of the Al content, but in consideration of costs, 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 workability of the base material 1. Therefore, the lower the N content, the better. In particular, if the N content exceeds 0.0040% by weight, the workability decreases significantly, so the upper limit of the N content is set to 0.0040% by weight. On the other hand, there is no particular restriction on the lower limit of the N content, but in consideration of costs, 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] (balance: Fe and unavoidable impurities) The main element of the remainder of the substrate 1 is Fe, and the rest are impurities that are inevitably mixed in during production.

[0032] Other additional elements may include Ti, Nb, B, Cu, Ni, Sn, and Cr. In particular, Ti and Nb have the effect of fixing C and N in the base material 1 as carbides and nitrides, thereby improving the workability of the base material 1. Therefore, when the C content is in the range of 0.001 to 0.01 wt %, one or both of Ti: 0.01 to 0.1 wt % and Nb: 0.001 to 0.05 wt % may be contained. Furthermore, the base material 1 according to this embodiment is preferably a steel plate having a Cr content of less than 10.5%.

[0033] Preferably, the substrate 1 according to this embodiment is annealed after cold rolling, so that it has at least one of the following properties. As shown in Table 1, the temperature and time required for annealing the substrate 1 according to this embodiment are 5 to 15 hours when annealing is performed at 500°C to less than 750°C, and 5 seconds to 30 minutes when annealing is performed at 750 to 900°C. More preferably, the annealing time is 6 to 10 hours when annealing is performed at 600°C to less than 750°C, and 10 seconds to 5 minutes when annealing is performed at 750 to 900°C.

[0034] [Table 1]

[0035] (tensile strength) The tensile strength of the substrate 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, cracks and holes may occur due to deformation caused by external forces, which may result in leakage of the electrolyte. Furthermore, if the tensile strength exceeds 700 MPa, the processability becomes poor. The tensile strength of the substrate 1 is more preferably 270 to 650 MPa. When better processability is required, it is even more preferably 280 to 450 MPa. In this embodiment, the tensile strength of the substrate 1 is a value obtained in accordance with the "Metallic Material Tensile Test Method" described in JIS standard Z2241.

[0036] (stretch) The elongation of the substrate 1 according to this embodiment is preferably 5 to 55%. If the elongation of the substrate 1 is less than 5%, workability at corners is poor, and cracks may occur during processing. On the other hand, if the elongation exceeds 55%, high temperatures and long times are required as annealing conditions to achieve these properties, which reduces productivity. The elongation of the substrate 1 is more preferably 15 to 55%, and even more preferably 20 to 50%. In this embodiment, the elongation of the substrate 1 is a value obtained in accordance with "20: Breaking elongation (%) A measurement formula (7)" in "Methods for tensile testing of metallic materials" described in JIS standard Z2241. As will be described later, from the viewpoint of preventing cracking of the substrate 1 and peeling of the resin film from the substrate 1 during molding, the elongation of the substrate 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 plated layer) is formed on at least one surface of the above-mentioned substrate 1. The surface on which the surface treatment layer 2 is formed is preferably the surface that will become the inner surface of the battery container. In addition, the surface of the steel foil 10 for battery containers that will be the outer surface of the battery container may also be formed with a surface treatment layer 2 that is the same as the surface that will be the inner surface described above, or at least one layer of the same. This is in order to prevent oxidation and ensure ease of manufacturing. The surface treatment layer 2 is preferably a plating layer formed by electroplating. Specific examples of the surface treatment layer 2 include a Cr plating layer, and Ni alloy plating, such as a Ni plating layer and an Fe-Ni alloy plating layer. Furthermore, a plurality of these plating layers may be provided. For example, a Ni plating layer may be formed on the base material 1, and then a Cr plating layer may be formed thereon.

[0038] Forming the above-described plating layer on at least one surface of the substrate 1 can improve adhesion to, for example, a resin film that is further formed on the plating layer. Furthermore, even if the resin film is damaged, corrosion resistance to the electrolyte can be ensured.

[0039] The surface treatment layer 2 of this embodiment may be formed, for example, after the substrate 1 is cold-rolled and then annealed, or it may be formed after the substrate 1 is cold-rolled but before annealing. When the substrate 1 is Ni-plated before being annealed, an Fe-Ni diffusion layer may be formed by heat treatment. In this case, an Fe-Ni diffusion layer may be formed between the Ni-plated layer and the substrate 1, or iron (Fe) of the substrate 1 may diffuse throughout the Ni-plated layer, forming an Fe-Ni diffusion layer directly on the substrate 1. The heat treatment conditions may be set to the same temperature and time ranges as those for the annealing of the substrate 1 described above.

[0040] In addition, in FIG. 1(b), the surface treatment layer 2 is formed on both sides of the substrate 1, but it may be formed at least on the surface that will become the inner surface of the battery container. Alternatively, different types of surface treatment layers 2 (electroplated layers) may be formed on both sides of the substrate 1. For example, an electroplated layer (first electroplated layer) containing at least one of a Ni plating layer and a Cr plating layer may be formed on the surface of the substrate 1 that will become the inner surface of the battery container, and an electroplated layer (second electroplated layer) containing a Zn plating layer or a 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 on the surface that will become the outer surface of the battery container. In this case, the electroplated layer containing the Zn plating layer or Zn alloy plating layer as a sacrificial corrosion protection layer may have a Zn content of, for example, 3 to 30 g / m 2 The plating amount is preferably 5 to 25 g / m 2 It is more preferable that the plating amount is 10 ...

[0041] When applying Ni plating to the substrate 1 as the surface treatment layer 2, the cold-rolled metal sheet can be electrolytically degreased and pickled in a conventional manner, and then the Ni plating bath shown below can be used, for example. The Ni plating bath is primarily a nickel sulfate bath known as a Watts bath, but other baths such as a sulfamic acid bath, a boron fluoride bath, and a chloride bath can also be used. (Example of Ni plating bath composition and conditions) Nickel sulfate: 200-350g / l Nickel chloride: 20-60g / l Boric acid: 10-50g / l pH: 1.5 to 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 base material 1 may be formed using not only pure Ni, but also an alloy containing Ni, such as a Ni-Co alloy or an Fe-Ni alloy. That is, in this specification, unless otherwise specified, the term "Ni plating layer" includes not only a "layer composed of Ni alone" but also a "layer composed of an alloy containing Ni." Furthermore, the "layer composed of an alloy containing Ni" may be a "diffusion layer in which Ni and a metal element other than Ni are mutually diffused," or an "alloy plating layer in which Ni and a metal element other than Ni are co-electrodeposited." Similarly, in this specification, unless otherwise specified, the term "Cr plating layer" includes not only a "layer composed of Cr alone" but also a "layer composed of an alloy containing Cr." Furthermore, the "layer composed of an alloy containing Cr" may be a "diffusion layer in which Cr and a metal element other than Cr are mutually diffused," or an "alloy plating layer in which Cr and a metal element other than Cr are co-electrodeposited." The "Cr plating layer" also includes so-called chromate treatment, in which a chromium hydrate oxide is formed on the surface to be treated. Furthermore, when the surface treatment layer contains metal elements other than Ni and Cr, the same can be understood as above.

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

[0044] In addition, the Ni plating as the surface treatment layer 2 of this embodiment has a plating amount of 0.5 to 50.0 g / m 2 The Ni plating is preferably 0.5 g / m 2If the Ni plating is less than 50.0 g / m, the surface coverage is insufficient, resulting in excessive exposure of the substrate and insufficient resistance to contents. 2 If the thickness exceeds this range, the thickness of the plating layer will increase, which will result in an increase in the thickness of the steel foil 10 for battery containers, leading to an increase in weight. In addition, an increase in the plating processing time and plating amount will cause problems such as a decrease in productivity and an increase in manufacturing costs. Furthermore, when a heat treatment is performed after forming Ni plating on the substrate 1 as the surface treatment layer 2, an Fe—Ni diffusion layer can be formed. From the viewpoint of improving workability, the thickness of this Fe—Ni diffusion layer is preferably 0.2 μm or more and 3.0 μm or less. The thickness of the Fe—Ni diffusion layer can be determined, for example, using a high-frequency glow discharge optical emission spectrometer, by calculating the measurement time from the point at which the Fe intensity reaches 10% of its saturated value until the Ni intensity reaches 10% of its maximum value after reaching its maximum value.

[0045] Furthermore, when applying Cr plating as the surface treatment layer 2 to the substrate 1, the cold-rolled metal sheet can be electrolytically degreased and pickled in a conventional manner, and then, for example, a Cr plating bath shown below can be used. (Example of Cr plating bath composition and conditions) CrO3: 30-200g / l NaF: 1-10g / l pH: 1.0 or less Bath temperature: 35~65℃ Current density: 5~50A / dm 2

[0046] In this case, the Cr plating as the surface treatment layer 2 has a plating amount of 0.05 to 10.0 g / m 2 The Cr plating is preferably 0.05 g / m. 2 If the plating thickness is less than 10.0 g / m, the surface coverage is insufficient, resulting in an extremely large amount of exposed substrate 1, which causes a problem of insufficient resistance to contents. 2If the thickness exceeds this limit, the same problems as above will arise, such as an increase in weight, a decrease in productivity, and an increase in manufacturing costs.

[0047] Furthermore, when Cr plating is applied as the surface treatment layer 2, it is even more preferable that the Cr plating layer have a higher proportion of metallic Cr than the proportion of Cr hydrated oxide (CrOx). Here, the metallic Cr and Cr hydrated oxide (CrOx) can be calculated, for example, as follows. First, in step 1, the total Cr amount in the Cr plating applied to the substrate is measured. Next, in step 2, the Cr-plated substrate is dissolved in high-temperature alkali to dissolve the Cr hydrated oxide, and the amount of Cr remaining in the substrate is measured as the metallic Cr amount. Finally, in step 3, the amount of Cr hydrated oxide is calculated (Cr hydroxide amount = total Cr amount - metallic Cr amount). All of the above measurements can be performed using a commercially available X-ray fluorescence spectrometer. In this embodiment, the values measured for the substrate on which the surface treatment layer is formed satisfy the following: 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-mentioned suitable ranges.

[0048] <Thermoplastic resin> At least one surface of the steel foil 10 for battery containers according to this embodiment may be coated with a thermoplastic resin layer 3, and it is preferable to provide the thermoplastic resin layer 3 at least on the surface that will become the inner surface of the battery container. In the steel foil 10 for battery containers according to this embodiment, the thermoplastic resin layer 3 may be formed on the above-mentioned surface treatment layer 2. In other words, the steel foil 10 for battery containers may be configured as a laminated plate in which the surface treatment layer 2 is coated with the thermoplastic resin layer 3 (FIG. 1(b)), or may be configured to only have the surface treatment layer 2 formed thereon, or may be configured to have neither the surface treatment layer 2 nor the thermoplastic resin layer 3. The substrate 1 may also be coated with the thermoplastic resin layer 3 without the surface treatment layer 2 interposed therebetween (FIG. 1(a)). The thickness of such a thermoplastic resin layer 3 is 10 to 100 μm, and more preferably 10 to 50 μm. In addition, examples of the material for the thermoplastic resin layer 3 in this embodiment include polyolefin resin, polyester resin, and polyamide resin. The polyolefin resin, polyester resin, or polyamide resin preferably coats both sides of the steel foil 10 for battery containers. In this case, one side of the steel foil 10 for battery containers (the side facing the inner surface of the battery can) is preferably coated with a polyolefin resin (particularly a polypropylene resin).

[0049] As such polypropylene resin, various polypropylene resins such as random propylene resin, homopropylene resin and block propylene resin may be used in a single layer or in a multi-layer structure by superposing these. In this embodiment, known additives may be added to the polypropylene resin. Examples of such additives include low-crystalline ethylene-butene copolymers, low-crystalline propylene-butene copolymers, terpolymers consisting of a three-component copolymer of ethylene, butene, and propylene, silica, zeolite, antiblocking agents such as acrylic resin beads, and fatty acid amide slip agents. Furthermore, slip agents (to improve the physical stability of the material) and antioxidants may also be added as the additives described above.

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

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

[0052] The thermoplastic resin layer 3 may be configured to cover the steel foil 10 for battery containers via a known adhesive. Examples of the known adhesive include acid-modified polyolefin resin, epoxy resin, acrylic resin, urethane resin, silicone resin, polyisobutylene resin, fluororesin, and inorganic adhesives such as water glass.

[0053] The thermoplastic resin layer 3 may be formed by laminating a film, or by extrusion lamination, in which a heated and melted resin material for the thermoplastic resin layer 3 is extruded into a film shape through a slit having an extrusion width 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 are no particular limitations on whether the film is stretched or not, and the film may be, for example, an unstretched film, a uniaxially stretched film, or a biaxially stretched film.

[0054] <Method of manufacturing steel foil for battery containers> Next, a method for producing the steel foil 10 for battery containers of this embodiment will be described with reference to FIG. First, a steel sheet is prepared and cold-rolled by feeding the steel sheet into a rolling mill (Step 1). This results in a cold-rolled steel foil (substrate 1) having a thickness of 10 to 200 μm. This cold-rolling may be performed in multiple stages as needed, with heat treatments being performed between stages.

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

[0056] After step 2, the substrate 1 is subjected to a surface treatment (plating treatment) to form a surface treatment layer 2 (electroplated layer) containing at least one of a Ni plating layer and a Cr plating layer on at least one surface of the substrate 1 (step 3). Note that 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. The surface treatment layer 2 (electroplated layer) formed in step 3 has a plating amount of 0.5 to 50.0 g / m for a Ni plating layer, for example. 2 For a Cr plating layer, the plating amount is 0.05 to 10.0 g / m 2 It is preferable that: The annealing in step 2 may be carried out after the surface treatment layer 2 is formed. Furthermore, after the annealing in step 2 and the formation of the surface treatment layer 2, a heat treatment (diffusion treatment) may be further performed, for example, to improve workability. The heat treatment conditions at this time can be the same as the annealing conditions described in step 2. Note that if the rolling step in step 1 is carried out after the plating treatment, cracks may occur on the surface of the plating film, which may reduce adhesion and corrosion resistance, and this is not preferable.

[0057] The substrate 1 after step 2, or the substrate 1 after steps 2 and 3, preferably has 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 has been formed is subjected to a process (resin coating process) in which the above-described thermoplastic resin layer 3 is coated to a thickness of about 10 to 50 μm. Note that step 4 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 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 side of the substrate 1 that will become the inner surface of the battery container, and may be formed by film lamination or extrusion lamination. The temperature of the substrate 1 when coating with the thermoplastic resin layer 3 is adjusted to, for example, room temperature to 280°C, preferably 250°C or less, depending on the type of lamination. After going through steps 1 to 4 as described above, the steel foil 10 for battery containers can be obtained.

[0060] <Battery container> Next, the battery container of this embodiment manufactured using the above-mentioned steel foil 10 for battery containers will be described. The battery container of this embodiment is manufactured by applying processes such as drawing and heat sealing to the above-mentioned steel foil 10 for battery containers. In particular, the battery container of this embodiment is preferably in the form of a pouch manufactured by square cylinder drawing. More specifically, a drawing process (deep drawing, etc.) is performed on the steel foil 10 for battery containers to form the steel foil 10 for battery containers into a container shape as shown in Fig. 4. More specifically, the container shape of this embodiment has a rectangular recess of depth D with corners of a curvature radius Rc (called Rc because they are circumferential corners) at its four corners so that a rectangular electrode plate can be accommodated. The sidewall of this recess is connected to its bottom surface by a curvature radius Rp (called Rp because it is determined by the radius of the punch). Note that, in the container of Fig. 4, the corner radii R of the recess are equal at all four corners, but Rc and Rp may each have a different value. Here, the reason why the steel foil 10 for battery containers of this embodiment is very effective for the shape of the battery container having such radii of curvature Rc and Rp and depth D will be described in detail below.

[0061] <Curvature radii Rc and Rp and depth D for high capacity> First, to achieve high capacity by using the steel foil 10 for battery containers as a battery container, the Rc of the four corners of the recesses described above during molding, the Rp between the side walls and bottom of the recesses, and the depth D are all important, but the balance between Rp and the depth D is particularly important. Achieving such a balance is particularly important for battery containers for automotive applications, because it would be ideal to enlarge individual batteries so that a single battery can achieve the battery characteristics of multiple conventional batteries. This is also important not only for single-cell batteries, but also when multiple batteries are aggregated and used as a module. It is desirable that the radius of curvature of both Rc and Rp be as small as possible from the viewpoint of increasing the area in which the electrodes are arranged and further reducing the dead space inside the battery. The value of the 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. The value of the radius of curvature Rc varies depending on the application and battery size, but 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, in order to increase the capacity when used as a battery container, increasing the number of electrodes stacked and housed increases the capacity of the entire battery, and therefore it is also effective to increase the depth D. The value of such depth D is preferably 5 mm or more, more preferably 6 mm or more, and even more preferably 10 mm or more. Against this background, the inventors have conducted extensive research into the relationship between the desirable radius of curvature Rp and depth D, and have concluded that when the steel foil 10 for battery containers is processed under the above-mentioned conditions to increase capacity, there are issues with formability and resistance to contents after forming (resistance to electrolyte).

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

[0064] The first problem is that cracks are likely to occur during molding. When steel foil is used as the substrate 1 as described in this embodiment, the specific gravity is greater than when conventional aluminum is used as the substrate, so the thickness of the substrate 1 needs to be reduced to prevent an increase in the battery weight. When the thickness of the steel foil used as the substrate 1 is reduced in this way, cracks and the like in the substrate 1 are likely to occur.

[0065] The second issue is the resistance to the contents (resistance to the electrolyte) after molding. When drawing is performed under the harsh processing conditions described above, cracks may occur in the resin film. Therefore, even if cracks do occur, it is necessary to make the surface of the substrate 1 resistant to leaching.

[0066] In response to the first problem described above, it has been discovered that in the battery container of this embodiment, by setting the maximum value of the maximum principal strain in uniaxial deformation of the steel foil for the battery container to 0.25 or more and the maximum value of the maximum principal strain in plane strain deformation to 0.1 or more, it is possible to suppress cracking even when drawing is performed under severe processing conditions as described above. Furthermore, in order to solve the second problem, it was found that by forming a surface treatment layer on at least one side of the steel foil for battery containers, it is possible to prevent the base material from leaching into the electrolyte even if a defect occurs in the resin film. 2 Ni plating layer of 0.05g / m or more 2 When the surface treatment layer (electroplated layer) contains at least one of the above Cr plating layers, sufficient resistance to contents can be obtained when used as a battery container, which is preferable.

[0067] The battery container is sealed after containing battery elements such as electrode plates and electrolyte, and the steel foil 10 for battery containers of this embodiment can also be used as a lid member for the battery container used for sealing. The lid member, which is a constituent member of such a battery container, may have a storage space similar to that of the battery container body shown in FIG. 4, or may be used as a flat plate. Furthermore, when sealing the battery container, it is preferable to heat-seal the lid member to the flange portion on the periphery of the battery container body, which has a drawn storage portion. In this case, it is preferable to configure the coating resins on the opposing surfaces of the battery container body and the lid member so that the same type of resin faces each other, such as polypropylene resin or polyester resin. The above-mentioned sealing method is merely an example and is not limiting; for example, a known adhesive may be used.

[0068] The battery container obtained in this embodiment is formed using the steel foil 10 for battery containers of this embodiment described above, and therefore 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, lithium-ion batteries, etc. In particular, since the battery container of this embodiment has excellent electrolyte resistance as described above, it can be suitably used for nonaqueous batteries containing an organic solvent electrolyte as the contents. [Example]

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

[0070] Example 1 First, a cold-rolled sheet (thickness: 50 μm) of low-carbon steel having the chemical composition shown below was prepared as a steel foil to be used as the substrate 1. C: 0.04 wt%, Mn: 0.22 wt%, Si: 0.001 wt%, P: 0.01 wt%, S: 0.01 wt%, balance: Fe and unavoidable impurities

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

[0072] (Measurement of principal strain) 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 method described above. These measurements were performed using a non-contact three-dimensional strain and displacement measurement system (ARAMIS) manufactured by GOM. A random pattern was applied to the sample in advance using a spray or other method. Triangulation was performed by continuously photographing the deformation with two cameras. The process of change in the random pattern was obtained as three-dimensional position information, and the maximum principal strain (ε1) in the plate plane just before fracture and the minimum principal strain (ε2) perpendicular to it were measured. Uniaxial deformation was performed using a tensile testing machine using a JIS No. 5 specimen. Equibiaxial deformation and plane strain deformation were measured using an Erichsen testing machine. A 150 mm diameter circular blank was used for equibiaxial deformation, and a blank with both ends cut to a width of approximately 65 mm was used for plane strain deformation. A 60mm diameter spherical punch was used, and Vaseline was applied to the tip of the punch to reduce friction between the punch and the blank. As a result of the measurement, the maximum value of the maximum principal strain in uniaxial deformation of the substrate 1 of this example was 0.40. Similarly, the maximum value of the maximum principal strain in plane strain deformation was 0.14.

[0073] (Formation of Thermoplastic Resin Layer 3) First, a polyethylene film (trade name "Daiwa Protack P-563B" manufactured by Daiwa Kasei Co., Ltd.) having a thickness of 50 μm was prepared as the thermoplastic resin layer 3. Next, the polyethylene film was attached to both sides of the substrate 1 to cover it.

[0074] (Evaluation of formability) After applying lubricating oil to the steel foil 10 for battery containers coated with the thermoplastic resin layer 3 as described above, deep drawing was performed using a 50 mm × 50 mm punch to form the above-mentioned recesses. In this deep drawing, the Rc of the four corners of the recess was set to 3.0 mm, and the Rp between the side wall and bottom of the recess was set to both 1.0 mm and 3.0 mm. Press forming was performed until abnormalities such as cracks or tears occurred in the steel foil 10 for battery containers, and the processing was stopped when the abnormalities occurred.

[0075] The formability of the steel foil 10 for battery containers after press molding was evaluated by visually observing cracks in the substrate 1 and lifting or cracks in the thermoplastic resin layer 3 at the four corners of the battery container, according to the following criteria. [Evaluation criteria] ⊚: When Rp was both 1.0 mm and 3.0 mm, the above-mentioned abnormalities in the substrate were not observed even when the molding depth exceeded 10 mm. ◯: The above-mentioned abnormality in the substrate was observed before the forming depth reached 5 mm when Rp was either 1.0 mm or 3.0 mm, but not when Rp was the other 1.0 mm or 3.0 mm. ×: In both cases where Rp was 1.0 mm and 3.0 mm, breakage or cracking was observed in the substrate before the molding depth reached 5 mm.

[0076] <Example 2> The procedures were the same as in Example 1 except for the matters described below. First, a cold-rolled sheet (thickness: 50 μm) of ultra-low carbon steel having the chemical composition shown below was prepared as a steel foil to be used as the substrate 1. 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 substrate 1 having the following properties. Tensile strength (TS): 340 MPa Elongation (EL): 23.7% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation of the substrate 1 obtained above were measured 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 the substrate 1 of this example was 0.27. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 was 0.23.

[0077] Example 3 The procedures were the same as in Example 1 except for the matters described below. First, a cold-rolled sheet (thickness: 80 μm) of ultra-low carbon steel having the chemical composition shown below was prepared as a steel foil to be used as the substrate 1. 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 substrate 1 having the following properties. Tensile strength (TS): 301 MPa Elongation (EL): 42.0%

[0079] The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation of the substrate 1 obtained above were measured 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 the substrate 1 of this example was 0.65. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 was 0.30.

[0080] Example 4 The same substrate as in Example 3 was used, and the same procedures as in Example 3 were carried out except for the matters described below. That is, the prepared steel foil was annealed at 640° C. for 8 hours to obtain a substrate 1 having the following properties. Tensile strength (TS): 332 MPa Elongation (EL): 39.0% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation of the substrate 1 obtained above were measured 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 the substrate 1 of this example was 0.62. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 was 0.30.

[0081] <Example 5> The same procedure as in Example 4 was carried out, except that the steel foil used as the substrate 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 of the obtained substrate 1 were measured 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 the substrate 1 of this example was 0.63. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 was 0.31.

[0082] Example 6 The same cold-rolled sheet of extra-low carbon steel as in Example 5 was used as the substrate 1, and a surface treatment layer 2 was formed in the following manner. (Formation of surface treatment layer 2) The substrate 1 was subjected to electrolytic degreasing and acid pickling by immersion in sulfuric acid, and then electroplated under the following conditions to obtain a Ni plating amount of 4.5 g / m 2 The conditions for forming the Ni plating layer were as follows: (Conditions for forming 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] Subsequently, a heat treatment was carried out at 800° C. for 10 seconds to obtain a substrate 1 on which a surface treatment layer 2 having the following properties was formed. Tensile strength (TS): 325 MPa Elongation (EL): 37.3%

[0084] The substrate 1 on which the surface treatment layer 2 obtained above was formed was measured for the maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation 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 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 having the surface treatment layer 2 formed thereon was coated on both sides with a thermoplastic resin layer 3 in the same manner as in Example 1, and then the moldability was evaluated.

[0085] Example 7 A substrate 1 having a surface treatment layer 2 formed thereon and having the following properties was obtained in the same manner as in Example 6, except that the heat treatment conditions were set to 800° C. for 30 seconds. Tensile strength (TS): 326 MPa Elongation (EL): 35.6% The substrate 1 on which the surface treatment layer 2 obtained above was formed was measured for the maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation 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 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 A substrate 1 having a surface treatment layer 2 formed thereon and having the following properties was obtained in the same manner as in Example 6, except that the heat treatment conditions were set to 820° C. for 10 seconds. Tensile strength (TS): 325 MPa Elongation (EL): 30.2% The substrate 1 on which the surface treatment layer 2 obtained above was formed was measured for the maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation 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 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 A substrate 1 having a surface treatment layer 2 formed thereon and having the following properties was obtained in the same manner as in Example 6, except that the heat treatment conditions were set to 850° C. for 10 seconds. Tensile strength (TS): 339 MPa Elongation (EL): 30.7% The substrate 1 on which the surface treatment layer 2 obtained above was formed was measured for the maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation 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 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 was used. The same procedures as in Example 2 were carried out except for the matters described below. That is, the prepared steel foil was annealed at 560° C. for 8 hours to obtain a substrate 1 having the following properties. Tensile strength (TS): 385MPa Elongation (EL): 20.6% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation of the substrate 1 obtained above were measured 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 the substrate 1 of this comparative example was 0.19. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 was 0.16.

[0089] <Comparative Example 2> The same substrate as in Example 2 was used. The same procedures as in Example 2 were carried out except for the matters described below. That is, the prepared steel foil was annealed at 640° C. for 8 hours to obtain a substrate 1 having the following properties. Tensile strength (TS): 373 MPa Elongation (EL): 16.8% The maximum principal strain in uniaxial deformation and the maximum principal strain in plane strain deformation of the substrate 1 obtained above were measured 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 the substrate 1 of this comparative example was 0.17. Similarly, the maximum value of the maximum principal strain in plane strain deformation of the substrate 1 was 0.13.

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

[0091] [Table 2]

[0092] In Examples 1 to 9, the steel foil 10 for battery containers coated with the thermoplastic resin layer 3 was subjected to severe drawing with a curvature radius of a predetermined value or less, and the results showed that the occurrence of cracks was suppressed when the battery container was manufactured. These results also showed that sufficient resistance to contents could be obtained when the battery container was used as a non-aqueous battery container. On the other hand, in Comparative Examples 1 and 2, when drawing with a small radius of curvature is performed in the manufacture of the battery container, cracks may occur, and sufficient resistance to contents may not 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 containers for non-aqueous batteries such as lithium ion secondary batteries, and can be applied to a wide range of industrial fields 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. A steel foil for battery containers used as battery containers, A steel foil for battery containers, characterized in that the maximum value of maximum principal strain in uniaxial deformation is 0.25 or more and the maximum value of maximum principal strain in plane strain deformation is 0.1 or more.

2. 2. The steel foil for battery containers according to claim 1, which has a surface treatment layer formed on at least one side.

3. 3. The steel foil for battery containers according to claim 1, 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. The steel foil for battery containers according to any one of claims 1 to 3, wherein the thickness of the substrate is 10 to 200 µm.

5. The steel foil for battery containers according to any one of claims 1 to 4, further comprising a maximum value of maximum principal strain in equibiaxial deformation of 0.2 or more.

6. 6. The steel foil for battery containers according to claim 4 or 5, wherein the substrate has a C content of 0.15% by weight or less, 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.

7. The steel foil for battery containers according to any one of claims 4 to 6, wherein the C content in the substrate is 0.05% by weight or less.

8. The steel foil for battery containers according to any one of claims 4 to 7, wherein the substrate has an Nb content of 0.05% by weight or less or a Ti content of 0.1% by weight or less.

9. The surface treatment layer has a thickness of 0.5 to 50.0 g / m ２ Ni plating layer of 0.05 to 10.0 g / m ２ The steel foil for battery containers according to any one of claims 1 to 8, wherein the Cr plating layer is any one of the above.

10. The steel foil for battery containers according to any one of claims 1 to 9, which has a thermoplastic resin layer formed on at least one side.

11. A pouch-shaped battery container obtained by heat-sealing the steel foil for battery containers according to any one of claims 1 to 10.

12. The pouch-shaped battery container according to claim 11, which is for a non-aqueous battery.

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