A cord for battery containers and a pouch-type battery container manufactured therefrom

Abstract

The present invention is a steel foil for a battery container characterized by having a maximum principal distortion value of uniaxial deformation of 0.25 or more and a maximum principal distortion value of planar deformation of 0.1 or more. According to the present invention, a steel foil for a battery container can be provided that suppresses breakage of the substrate when performing strict molding processing for a battery container.

Description

Technology Field

[0001] The present invention relates to a steel foil for a battery container that is desirable as a battery container such as a lithium-ion secondary battery, and a pouch-type battery container manufactured by the same. 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, which are installed in portable electronic devices or vehicles. Such lithium-ion rechargeable batteries are broadly classified into pouch type and metal can type. As the outer casing for pouch-type LiBs, a laminated material consisting of a metal foil and a resin film, formed into a pouch shape, is generally used. Pouch-type LiBs have advantages such as being lightweight, having high heat dissipation due to the ability to make the battery thin, and the ability to freely design the battery shape to match the device shape.

[0003] In the laminated material used as the outer casing for the aforementioned pouch-type LiB, aluminum foil is widely used as the metal foil due to its lightweight nature. On the other hand, from the perspective of strength, battery outer casings using steel foil are also conventionally known. For example, Patent Document 1 discloses a technology for housing electrodes, etc., within a pouch using a laminated metal plate coated with resin on a thin metal plate. Furthermore, according to this Patent Document 1, the intent is to use iron or an iron alloy as the metal foil core material.

[0004] In addition, Patent Document 2 and Patent Document 3 disclose a technique for forming a diffusion alloy layer containing Ni and Fe on the surface of a rolled metal plate by using a rolled metal plate with a thickness of 200 μm or less, and then performing rolling and heat treatment after Ni plating on the rolled metal plate. In order to improve corrosion resistance to electrolytes, a polyolefin-based resin is formed on the rolled metal plate, and according to this Patent Document 2, the purpose is to improve the adhesion between the rolled metal plate and the polyolefin-based resin by using the diffusion alloy layer.

[0005] Patent Document 4 discloses a battery can having corrosion resistance to a strong alkaline electrolyte, wherein the content of carbon, manganese, phosphorus, etc. contained in the steel plate is specified, and a glossy nickel layer is formed on the inner surface through a nickel-iron alloy layer and a matte or semi-glossy nickel layer. Prior art literature

[0006] Japanese Patent Publication No. 2001-202932, International Publication No. 2016 / 013572, International Publication No. 2016 / 013575, Japanese Patent Publication No. 2005-078894 The problem to be solved

[0007] Secondary batteries capable of being installed in the aforementioned vehicles or electronic devices are required to have high capacity in addition to high output. In cases where simply increasing capacity is sufficient, it may be enough to accommodate electrode active material in a relatively large container. However, particularly for secondary batteries installed in vehicles, an increase in the weight of the battery itself immediately leads to a deterioration in fuel efficiency; therefore, weight increase must be suppressed as much as possible to achieve high capacity.

[0008] As a method to achieve high capacity while avoiding weight increase as much as possible, it is assumed that the internal capacity of the battery container is increased by performing molding processing under stricter conditions. That is, if the outer material of a pouch-type LiB can be manufactured by performing deep drawing molding, etc. on a thin laminated material, it becomes possible to maximize the space for accommodating the electrode and improve the battery capacity.

[0009] However, the prior art including the aforementioned patent documents 1 to 4 is not suitable for such molding processing and there is a great deal of room for improvement.

[0010] As such, for metal plates used as battery containers, excellent processability (formability) becomes very important for improving product competitiveness. The present invention aims to solve the above-mentioned problem as an example, and aims to provide a steel foil for a battery container capable of suppressing breakage of the substrate even when forming processing is performed using a metal plate for battery applications, for example, and a pouch-type battery container manufactured using the same.

[0011] In addition, regarding metal plates for battery containers, it is required to improve their dissolution properties with respect to non-aqueous electrolytes, such as organic electrolytes in which a lithium salt is dissolved in an organic solvent. The present disclosure aims to solve this problem and aims to provide a steel foil for a battery container having excellent dissolution properties with respect to a non-aqueous electrolyte filled inside the container, and a pouch-type battery container manufactured using the same. means of solving the problem

[0012] In order to solve the above problem, the steel for a battery container in one embodiment of the present invention is characterized by (1) having a maximum principal distortion value of uniaxial deformation of 0.25 or more and a maximum principal distortion value of planar deformation of 0.1 or more.

[0013] In addition, in the above (1), (2) it is preferable to have a surface treatment layer formed on at least one side.

[0014] In addition, in (1) or (2) above, (3) it is preferable that the maximum value of the maximum principal distortion of the uniaxial deformation is 0.45 or higher, and the maximum value of the maximum principal distortion of the planar distortion deformation is 0.2 or higher.

[0015] In addition, in any one of the above (1) to (3), it is preferable that the thickness of the (4) substrate be 10 to 200 μm.

[0016] In addition, in any one of the above (1) to (4), it is preferable that the maximum value of the maximum principal distortion of (5) is 0.2 or higher.

[0017] In the above (4) or (5), (6) it is preferable that 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.

[0018] In any one of the above (4) to (6), (7) it is preferable that the C content in the above description be 0.05 weight% or less.

[0019] In any one of the above (4) to (7), (8) it is preferable that the Nb content in the above description be 0.05 weight% or less or the Ti content be 0.1 weight% or less.

[0020] In any one of the above (1) to (8), (9) it is preferable that the surface treatment layer is one of a Ni plating layer of 0.5 to 50.0 g / m² or a Cr plating layer of 0.05 to 10.0 g / m².

[0021] 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.

[0022] In addition, to solve the above-mentioned problem, a pouch-type battery container in one embodiment of the present invention is characterized by (11) being obtained by heat sealing a steel foil for a battery container described in any one of claims (1) to (10). In addition, in (11), (12) it is preferable that the pouch-type battery container is for a non-aqueous battery. Effects of the invention

[0023] According to the present invention, it is possible to realize a thin film for a battery container that can withstand strict molding processing even when thin, and also has excellent dissolution properties against a non-aqueous electrolyte filled inside the container. Brief explanation of the drawing

[0024] FIG. 1a is a schematic diagram showing a steel foil (10) for a battery container according to the present embodiment. FIG. 1b is a schematic diagram showing a steel foil (10) for a battery container according to the present embodiment. FIG. 2a is a schematic diagram showing the distortion distribution of the steel foil (10) for the battery container according to the present embodiment. FIG. 2b is a schematic diagram showing the molding limit line of the steel foil (10) for the battery container according to the present embodiment. FIG. 3 is a drawing showing an example of the manufacturing process of a steel foil (10) for a battery container according to the present embodiment. FIG. 4 is a drawing showing an example of the shape of a battery container according to the present embodiment. Specific details for implementing the invention

[0025] Hereinafter, the battery container foil (10) of the present embodiment will be described using FIG. 1. Also, in FIG. 1, for convenience, the thickness direction of the battery container foil (10) will be described as the Z direction, and the rolling direction of the battery container foil (10) will be described as the X direction. However, the definition of these directions does not reduce the scope of the present invention.

[0026] Compulsion for battery containers

[0027] The battery container (10) according to the present embodiment has a substrate (1) made of a steel plate as shown in FIG. 1.

[0028] As for the substrate (1), various types of steel that can be applied as a substrate for a battery container may be exemplified. For example, as carbon steel, 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 formed by adding Ti or Nb to ultra-low carbon steel may be applied.

[0029] The steel foil (10) for a battery container according to the present embodiment is characterized in that the maximum value of the maximum principal distortion of the uniaxial deformation is 0.25 or higher, and the maximum value of the maximum principal distortion of the planar distortion deformation is 0.1 or higher. The above characteristics will be explained below.

[0030] The present invention aims to provide a steel sheet capable of manufacturing a battery container by performing processing such as deep drawing. In addition, when manufacturing a battery container having a concave portion by square drawing, the invention aims to provide a steel sheet for a battery container that enables reducing the radius of curvature of both Rc at the four corners of the concave portion and Rp between the side wall and the bottom surface of the concave portion as much as possible.

[0031] This is based on the perspective of increasing the area where the electrodes are placed in the battery container obtained, and also reducing the dead space within the battery.

[0032] In order to solve the above problem, the inventors carefully examined the matter and discovered that the problem can be solved by defining a distortion that takes into account the deformation mode during molding in a steel foil for a battery container. Specifically, by defining the maximum value of the maximum principal distortion of the uniaxial deformation and the maximum value of the maximum principal distortion of the planar distortion deformation of the steel foil for a battery container, it was discovered that it is possible to manufacture a desirable electrical container by suppressing the occurrence of cracking, etc., even when processing such as deep drawing molding is performed.

[0033] In order to improve the formability of steel foil for battery containers, the inventors examined in detail the square tube drawing molding, which is typically used as an outer material for pouch-type LiBs. As a result, it was found that in this molding method, the deformation mode differs in each part during molding.

[0034] Specifically, 0.5 mm diameter dots were printed on a steel foil for a battery container prior to rectangular drawing molding, with a dot center point spacing of 1.0 mm. After performing rectangular drawing molding, the deformation mode was observed by observing the widening between dots on the obtained molded body using a GOM 3D distortion measurement system (ARGUS). FIG. 2a is a diagram showing an example of a distortion distribution plotting the distortion in the obtained molded body. It is shown that the rectangular drawing molded body has many regions of planar distortion deformation and uniaxial deformation. Based on these observation results, the inventors believed that deep drawing formability, such as that of rectangular drawing molding, could be improved by enhancing the planar distortion deformation and uniaxial deformation capabilities.

[0035] In addition, the inventors observed changes in the forming limit line (Fig. 2b) due to differences in steel grades by repeating the forming process while varying the steel grade of the substrate (1) used. As a result, it was confirmed that the forming limit line and the forming area change due to differences in the carbon content in the steel and the heat treatment conditions after steel rolling.

[0036] In addition, it was discovered that desirable moldability can be realized when manufacturing the outer material of a high-capacity pouch-type LiB by setting the planar distortion deformation and uniaxial deformation of the steel for the battery container to a predetermined value.

[0037] In addition, in this embodiment, a known method can be applied as a method for measuring distortion. For example, in the distortion distribution shown in FIG. 2 obtained at the timing immediately before fracture (cracking) occurs after applying deformation to a test specimen, the vertical axis is set to maximum principal distortion (ε1), the horizontal axis to minimum principal distortion (ε2), and the in-plane distortion ratio (β) to ε2 / ε1. By setting -0.5≤β<0 as the uniaxial deformation region, β=0 as the plane distortion deformation region, and the region 0<β≤1 as the biaxial deformation region, the maximum value of the maximum principal distortion of uniaxial deformation and the maximum value of the maximum principal distortion of plane distortion deformation can be obtained.

[0038] By setting the maximum value of the maximum principal distortion of the uniaxial deformation and the maximum principal distortion of the planar deformation of the steel for the battery container to the above values, when manufacturing a molded body having a rectangular concave portion by drawing forming a steel with a thickness of 10 to 200 μm, it is desirable that the molding can be performed without causing cracking even if the radius of curvature of the four corners (Rc), the radius of curvature between the side wall of the concave portion and the bottom surface of the concave portion (Rp), and the depth of the concave portion (D) each exceed a certain condition. In addition, the radius of curvature of the four corners (Rc), the radius of curvature between the side wall of the concave portion and the bottom surface of the concave portion (Rp), and the depth of the concave portion (D) described above will be described later.

[0039] In the present embodiment, it is more preferable that the maximum value of the maximum principal distortion of the uniaxial deformation is 0.45 or higher, and the maximum value of the maximum principal distortion of the planar distortion deformation is 0.2 or higher.

[0040] 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, the quality is prone to instability, such as when a pinhole occurs during the cold rolling process or when the difference in plate thickness gradient becomes unstable. In addition, there is a risk that cracking may occur during the forming process, and the effect intended for the present invention may not be obtained. On the other hand, if the thickness exceeds 200 μm, there is a possibility that the purpose of making the battery container lighter cannot be achieved.

[0041] Here, an example of the composition of the component of the material (1) is shown below.

[0042] (C: 0.0001–0.15 wt%)

[0043] C is an element that increases the strength of the substrate (1). Since an excessive amount of C leads to an excessive increase in strength and a decrease in rolling performance, the upper limit of the C content is set to 0.15 wt%. On the other hand, there is no particular limit on the lower limit of the C content, but considering the cost, the lower limit of the C content is set to 0.0001 wt%. In addition, the C content is more preferably 0.0005 to 0.05 wt%, and even more preferably 0.001 to 0.01 wt%.

[0044] (Si: 0.001–0.5 wt%)

[0045] Si is an element that increases the strength of the substrate (1). If the Si content is excessive, the strength increases excessively and rolling performance decreases, so the upper limit of the Si content is set to 0.5 wt%. On the other hand, there is no particular limit on the lower limit of the Si content, but considering the cost, the lower limit of the Si content is set to 0.001 wt%. In addition, the Si content is more preferably 0.001 to 0.02 wt%.

[0046] (Mn: 0.01–1.0 wt%)

[0047] Mn is an element that increases the strength of the substrate (1). Since an excessive amount of Mn increases the strength excessively and reduces rolling performance, the upper limit of the Mn content is set to 1.0 wt%. On the other hand, there is no particular limit on the lower limit of the Mn content, but considering the cost, the lower limit of the Mn content is set to 0.01 wt%. In addition, the Mn content is more preferably 0.01 to 0.5 wt%.

[0048] (P: 0.001–0.05 wt%)

[0049] P is an element that increases the strength of the substrate (1). Since an excessive amount of P leads to an excessive increase in strength and a decrease in rolling performance, the upper limit of the P content is set to 0.05 weight%. Meanwhile, there is no particular limit on the lower limit of the P content, but considering the cost, the lower limit of the P content is set to 0.001 weight%. In addition, the P content is more preferably 0.001 to 0.02 weight%.

[0050] (S: 0.0001–0.02 wt%)

[0051] S is an element that reduces the corrosion resistance of the substrate (1). Therefore, it is desirable for the S content to be as low as possible. In particular, since the corrosion resistance decreases significantly when the S content exceeds 0.02 weight%, the upper limit of the S content is set to 0.02 weight%. On the other hand, there is no particular limit on the lower limit of the S content, but considering the cost, the lower limit of the S content is set to 0.0001 weight%. In addition, the S content is more preferably 0.001 to 0.01 weight%.

[0052] (Al: 0.0005–0.20 wt%)

[0053] Al is added as a deoxidizing element, for example, of the substrate (1). To obtain the effect of deoxidation, it is desirable to have an Al content of 0.0005 wt% or more. However, since rolling performance decreases when the Al content is excessive, the upper limit of the Al content is set to 0.20 wt%. On the other hand, there is no particular limit on the lower limit of the Al content, but considering the cost, the lower limit of the Al content is set to 0.0005 wt%. In addition, the Al content is more preferably 0.001 to 0.10%.

[0054] (N: 0.0001–0.0040 wt%)

[0055] N is an element that lowers the processability of the substrate (1). Therefore, it is desirable for the N content to be as low as possible. In particular, since the decrease in processability becomes significant when the N content exceeds 0.0040 wt%, the upper limit of the N content is set to 0.0040 wt%. On the other hand, there is no particular limit on the lower limit of the N content, but considering the cost, the lower limit of the N content is set to 0.0001 wt%. In addition, the N content is more preferably 0.001 to 0.0040 wt%.

[0056] (Remainder: Fe and unavoidable impurities)

[0057] The main element among the remainder of the material (1) is Fe, and the rest are impurities that are inevitably mixed in during manufacturing.

[0058] In addition, Ti, Nb, B, Cu, Ni, Sn, and Cr may be included as additional components. In particular, Ti and Nb have the effect of improving the processability of the substrate (1) by fixing C and N in the substrate (1) as carbides and nitrides. Therefore, in the range of C content to 0.001 to 0.01 weight%, one or two types may be included in the range of Ti: 0.01 to 0.1 weight% and Nb: 0.001 to 0.05 weight%. Furthermore, the substrate (1) according to the present embodiment is more preferably a steel plate with less than 10.5% Cr.

[0059] In addition, the substrate (1) according to the present embodiment is preferably annealed after cold rolling to possess at least one of the following characteristics. In addition, the temperature and time required for annealing the substrate (1) in the present embodiment 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.

[0060]

[0061] (tensile strength)

[0062] The tensile strength of the substrate (1) according to the present embodiment is preferably 260 to 700 MPa. If the tensile strength is less than 260 MPa, when used as a battery container, it is deformed by external forces, causing cracking and holes, which leads to leakage of the electrolyte. In addition, if the tensile strength exceeds 700 MPa, the processability becomes insufficient. Furthermore, the tensile strength of the substrate (1) is more preferably 270 to 650 MPa. If greater processability is required, it is more preferably 280 to 450 MPa.

[0063] In addition, in this embodiment, the tensile strength of the material (1) is a value obtained in accordance with the “Method for Tensile Testing of Metal Materials” described in JIS Standard Z2241.

[0064] (height)

[0065] It is preferable that the elongation of the substrate (1) according to the present embodiment be 5 to 55%. This is because if the elongation of the substrate (1) is less than 5%, workability at the corners becomes insufficient, and there is a risk of breakage occurring during processing. In addition, if the elongation exceeds 55%, high temperature and a long time are required as an annealing conditions to exhibit such characteristics, which leads to poor productivity. Furthermore, the elongation of the substrate (1) is more preferably 15 to 55%, and even more preferably 20 to 50%.

[0066] In addition, in this embodiment, the elongation of the material (1) is a value obtained in accordance with “20: Elongation at Break (%) A (7) of the “Method for Tensile Testing of Metal Materials” described in JIS Standard Z2241.

[0067] In addition, as described below, from the perspective of suppressing cracking of the substrate (1) or peeling of the resin film from the substrate (1) during molding processing, the elongation of the substrate (1) is preferably 20% or more, and more preferably 30% or more.

[0068] Surface treatment layer

[0069] In the steel foil (10) for a battery container according to the present 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 above-described substrate (1).

[0070] The surface on which this surface treatment layer (2) is formed is preferably the inner side of the battery container.

[0071] In addition, regarding the outer side of the battery container of the battery container (10), from the perspective of establishing oxidation prevention and ease of manufacturing, it may be the same as the inner side mentioned above, or at least one layer may be formed with the same surface treatment layer (2).

[0072] As for this surface treatment layer (2), it is preferable that it be a plating layer formed by electroplating. Specifically, the surface treatment layer (2) may be a Cr plating layer, and an alloy plating of Ni, such as a Ni plating layer and an Fe-Ni alloy plating layer. In addition, there may be multiple of these plating layers, and for example, a Cr plating layer may be formed after a Ni plating layer is formed on the substrate (1).

[0073] By forming a plating layer as described above on at least one side of the substrate (1), the adhesion to a resin film additionally formed on the plating layer, for example, can be improved. In addition, even if a defect occurs in the resin film, corrosion resistance to the electrolyte can be ensured.

[0074] In addition, the surface treatment layer (2) of the present embodiment may be formed, for example, after the substrate (1) has been cold-rolled and annealed, or it may be formed after the substrate (1) has been cold-rolled and before annealing. Among these, when Ni plating is performed on the substrate (1) before annealing, an Fe-Ni diffusion layer may be formed by heat treatment. At this time, an Fe-Ni diffusion layer may be formed between the Ni plating layer and the substrate (1), or the iron (Fe) of the substrate (1) may diffuse throughout the Ni plating layer, so that an Fe-Ni diffusion layer is formed directly on the substrate (1). As for the conditions for heat treatment, the temperature and time may be within a preferred range, similar to the annealing of the substrate (1) described above.

[0075] In addition, in FIG. 1b, a surface treatment layer (2) is formed on both sides of the substrate (1), and at least the surface treatment layer (2) may be formed on the side that becomes the inner surface of the battery container.

[0076] Alternatively, different types of surface treatment layers (2) (electroplating layers) may be formed on each side of the substrate (1). For example, on the side of the substrate (1) that becomes the inner side 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, and on the side of the substrate (1) that becomes the outer side of the battery container, an electroplating layer (second electroplating 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.) having a different corrosion resistance mechanism (as a sacrificial protection layer) may be formed. In this case, the electroplating layer containing the Zn plating layer or Zn alloy plating layer as a sacrificial protection layer preferably has a plating amount of Zn of 3 to 30 g / m², and more preferably has a plating amount of 5 to 25 g / m². Since Zn plating dissolves in the electrolyte, it cannot be used on the inner side that is in constant contact; however, by using it on the outer side of the battery container, it is effective for sacrificial protection when a small amount of electrolyte adheres. In particular, when a small amount of electrolyte adheres to the end surface, if the outer side is Zn-plated as described above, the Zn melts preferentially on the end surface, thereby suppressing corrosion of the base iron and preventing electrolyte leakage, making it effective.

[0077] In addition, when performing Ni plating as a surface treatment layer (2) on a substrate (1), a cold-rolled metal plate may be electrolytically degreased and pickled in a conventional manner, and then, for example, the Ni plating bath shown below may be used. In addition, a nickel sulfate bath called a Watt bath is mainly used as the Ni plating bath, but other baths such as a sulfamic acid bath, boron fluoride bath, and chloride bath may also be used.

[0078] (Example of Ni plating bath composition and conditions)

[0079] Nickel sulfate: 200–350 g / ℓ

[0080] Nickel chloride: 20–60 g / ℓ

[0081] Boric acid: 10–50 g / ℓ

[0082] pH: 1.5–5.0

[0083] Bath temperature: 40–70°C

[0084] Current density: 1–40 A / d m²

[0085] In addition, the Ni plating formed as a surface treatment layer (2) on the substrate (1) may be formed using not only pure Ni, but also alloys containing Ni, such as Ni-Co alloy or Fe-Ni alloy.

[0086] That is, in this specification, the "Ni plating layer" includes, in addition to the "layer composed solely of Ni," a "layer composed of an alloy containing Ni" unless specifically stated otherwise. Furthermore, the "layer composed of an alloy containing Ni" may be a "diffusion layer in which Ni and metal elements other than Ni are mutually diffused," or an "alloy plating layer in which both Ni and metal elements other than Ni are deposited."

[0087] Likewise, in this specification, the “Cr plating layer” includes, in addition to the “layer composed solely of Cr,” a “layer composed of an alloy containing Cr” unless specifically stated otherwise. Furthermore, the “layer composed of an alloy containing Cr” may be a “diffusion layer in which Cr and metal elements other than Cr are mutually diffused,” or an “alloy plating layer in which both Cr and metal elements other than Cr are deposited.” The “Cr plating layer” also includes a so-called chromate treatment that forms chromium hydrate oxide on the surface to be treated.

[0088] In addition, even if the surface treatment layer contains metal elements other than Ni and Cr, it can be understood in the same way as above.

[0089] In other words, the surface treatment layer (2) may include any one 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 both Fe and Ni are deposited. In addition, the phrase “composed only of Ni” in this specification means having only Ni as the metal element, and allows for the inclusion of impurities such as less than 0.1% carbon or less than 0.05% sulfur that are inevitably mixed in during the plating process or materials derived from plating bath additives.

[0090] In addition, the Ni plating as the surface treatment layer (2) of the present embodiment is preferably a Ni plating with a plating amount of 0.5 to 50.0 g / m². If the amount of Ni plating is less than 0.5 g / m², the surface coating is insufficient, and the exposure of the substrate increases drastically, resulting in a problem of insufficient heat dissolution properties. On the other hand, if the amount of Ni plating exceeds 50.0 g / m², the thickness of the plating layer increases, and the thickness of the steel foil (10) for the battery container also increases, leading to an increase in weight. Furthermore, this is because an increase in the plating processing time or the amount of plating causes problems such as a deterioration in productivity or an increase in manufacturing costs.

[0091] In addition, when a Ni plating is formed on the substrate (1) as a surface treatment layer (2) and then heat treatment is performed, an Fe-Ni diffusion layer can be formed. For the sake of improved processability, it is preferable that the Fe-Ni diffusion layer has a thickness of 0.2 μm or more and 3.0 μm or less.

[0092] In addition, the thickness of the Fe-Ni diffusion layer can be determined by using, for example, a high-frequency glow discharge emission spectroscopic analysis device to calculate the measurement time from the point where the Fe intensity reaches 10% of its saturation value, to the point where the Ni intensity reaches 10% of its maximum value, and then to the point where the Ni intensity reaches 10% of its maximum value, and based on the calculated measurement time.

[0093] In addition, when performing Cr plating as a surface treatment layer (2) on the substrate (1), after electrolytically degreasing and pickling the cold-rolled metal plate in a conventional manner, for example, the Cr plating bath shown below can be used.

[0094] (Example of Cr plating bath composition and conditions)

[0095] CrO3: 30–200 g / ℓ

[0096] NaF: 1–10 g / ℓ

[0097] pH: 1.0 or lower

[0098] Bath temperature: 35–65°C

[0099] Current density: 5–50 A / d m²

[0100] In this case, the Cr plating as the surface treatment layer (2) is preferably a Cr plating with a plating amount of 0.05 to 10.0 g / m². If the amount of Cr plating is less than 0.05 g / m², the surface coating is insufficient, and the exposure of the substrate (1) increases drastically, resulting in a problem of insufficient heat dissolution properties. On the other hand, if the amount of Cr plating exceeds 10.0 g / m², problems such as increased weight, reduced productivity, and increased manufacturing costs occur, as described above.

[0101] In addition, when performing Cr plating as a surface treatment layer (2), it is more preferable to have a Cr plating layer in which the proportion of metallic Cr is greater than the proportion of Cr hydrated oxide (CrOx). Here, the method for calculating metallic Cr and Cr hydrated oxide (CrOx) can be carried out, for example, by the method shown below. First, as Step 1, the total amount of Cr in the Cr plating performed on the substrate is measured. Next, as Step 2, the Cr hydrated oxide is dissolved by treating the substrate on which the Cr plating was performed with a high-temperature alkali, and the amount of Cr remaining on the substrate is measured as the amount of metallic Cr. Finally, as Step 3, the amount of Cr hydrated oxide is calculated (amount of Cr hydrated oxide = total amount of Cr - amount of metallic Cr). In addition, all of the above measurements can be performed using a commercially available fluorescence X-ray detector.

[0102] In addition, in this embodiment, the measured value for a substrate on which a surface treatment layer is formed satisfies that the maximum value of the maximum principal distortion of uniaxial deformation is 0.25 or higher, and the maximum value of the maximum principal distortion of planar distortion deformation is 0.1 or higher.

[0103] In addition, it is desirable that the tensile strength and elongation also satisfy the above-mentioned preferred ranges as a substrate with a surface treatment layer formed thereon.

[0104] Thermoplastic resin

[0105] In the present embodiment, the steel foil (10) for a battery container may have at least one surface covered with a thermoplastic resin layer (3), and it is preferable to form it on at least the surface that becomes the inner side of the battery container. In addition, in the steel foil (10) for a battery container in the present embodiment, the thermoplastic resin layer (3) may be formed on the surface treatment layer (2) described above.

[0106] In other words, the steel plate (10) for the battery container may be composed of a laminate plate in which the surface treatment layer (2) is coated with a thermoplastic resin layer (3) (Fig. 1b), or it may be composed only of having a surface treatment layer (2), or it may be composed without a surface treatment layer (2) and a thermoplastic resin layer (3). In addition, the substrate (1) may be coated with a thermoplastic resin layer (3) without interposing a surface treatment layer (2) (Fig. 1a).

[0107] The thickness of such a thermoplastic resin layer (3) is 10 to 100 μm, and more preferably 10 to 50 μm.

[0108] In addition, polyolefin resin, polyester resin, or polyamide resin are exemplified as materials for the thermoplastic resin layer (3) of the present embodiment. 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 side of the battery can) is covered with a polyolefin resin (particularly polypropylene resin).

[0109] As such polypropylene resin, various polypropylene resins such as random propylene resin, homopropylene resin, and block propylene resin may be used as a single layer, or they may be polymerized to form a multilayer structure.

[0110] In addition, in the present embodiment, known additives may be added to the polypropylene resin. Examples of such additives include, for instance, low-crystallinity ethylene-butene copolymers, low-crystallinity propylene-butene copolymers, terpolymers composed of ethylene, butene, and propylene ternary copolymers, antiblocking agents such as silica, zeolites, and acrylic resin beads, and fatty acid amide-based slip agents. Furthermore, for instance, slip agents (to improve the physical stability of the material) or antioxidants may also be added as the above-mentioned additives.

[0111] On the other hand, the other side (the outer side of the battery can) of the steel foil (10) for the battery container is preferably coated with one of a polyester resin, a polyamide resin, or a polyolefin resin. Among these, as the polyester resin, it is preferable to coat it with polyethylene terephthalate. In addition, as the polyester resin, in addition to polyethylene terephthalate, examples such as polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate may be used. Furthermore, modified resins such as urethane-modified polyester resin, acrylic-modified polyester resin, and epoxy-modified polyester resin may also be used.

[0112] In addition, the thickness of the resin covering one side (e.g., the inner side of the battery can) and the thickness of the resin covering the other side (e.g., the outer side of the battery can) of the steel foil (10) for the battery container can be appropriately adjusted within the thickness range according to the required corrosion resistance and processability, and the thicknesses of both sides may be the same or different.

[0113] In addition, when using a polyester resin, it is preferable that the polyester resin be non-oriented.

[0114] In addition, the other side (outer side of the battery can) of the battery container foil (10) is not limited to the polyester resin (polyethylene terephthalate) mentioned above, and both sides of the battery container foil (10) may be coated with polypropylene resin. Alternatively, both sides of the battery container foil (10) may be coated with polyester resin.

[0115] In addition, the thermoplastic resin layer (3) may be in the form of covering the battery container foil (10) through a known adhesive. In addition, as a known adhesive, for example, acid-modified polyolefin resin, epoxy resin, acrylic resin, urethane resin, silicone resin, polyisobutylene-based resin, fluoropolymer resin, or inorganic adhesive such as water glass may be used.

[0116] As a method for forming the above thermoplastic resin layer (3), it may be formed by laminating a film, or by an extrusion lamination method in which the heated and melted material resin of the above thermoplastic resin layer (3) is extruded into a film shape through a slit of the extrusion width of an extrusion molding machine and directly laminated onto a substrate (1) or a surface treatment layer (2). When laminating after forming the above film, the presence or absence of stretching of the above film is not particularly limited, and for example, it may be an unstretched film, a uniaxially stretched film, or a biaxially stretched film.

[0117] Method for manufacturing a battery container

[0118] Next, with reference to FIG. 3, a method for manufacturing the steel foil (10) for the battery container of the present embodiment will be described.

[0119] First, a steel plate is prepared, and cold rolling is performed by feeding the steel plate into a rolling mill (Step 1). By this, a cold-rolled steel sheet (substrate (1)) with a thickness of 10 to 200 μm is formed. This cold rolling may be performed in multiple stages as needed, and heat treatment may be performed in between.

[0120] Next, an annealing treatment is performed on the obtained substrate (1) (Step 2). At this time, the temperature and time of the substrate (1) during the annealing treatment are 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.

[0121] After Step 2, a surface treatment (plating treatment) is performed on the substrate (1) to form a surface treatment layer (2) (electroplating layer) containing at least one of a Ni plating layer and a Cr plating layer on at least one side of the substrate (1) (Step 3). In addition, this Step 3 is not an essential process in the method for manufacturing the steel foil (10) for a battery container of the present embodiment and may be omitted as appropriate.

[0122] As for the surface treatment layer (2) (electroplating layer) formed in Step 3, for example, if it is a Ni plating layer, the plating amount is 0.5 to 50.0 g / m², and if it is a Cr plating layer, the plating amount is 0.05 to 10.0 g / m².

[0123] In addition, the annealing of Step 2 may be performed after forming the surface treatment layer (2).

[0124] In addition, after forming the surface treatment layer (2) after performing the annealing of Step 2, further heat treatment (diffusion treatment) may be performed, for example, with the aim of improving processability. At this time, the heat treatment conditions can be performed under conditions similar to the annealing conditions described in Step 2.

[0125] In addition, if the rolling process of Step 1 is performed after the plating process, cracks may occur on the surface of the plating film, potentially reducing adhesion and corrosion resistance, which is undesirable.

[0126] In addition, the substrate (1) after step 2, or the substrate (1) after step 2 and step 3, preferably has one of the characteristics of having a tensile strength of 260 to 700 MPa or an elongation of 5 to 55%.

[0127] Next, in Step 4, a treatment (resin coating treatment) is performed on the substrate (1) on which the surface treatment layer (2) is formed, by coating the thermoplastic resin layer (3) described above with a thickness of about 10 to 50 μm. In addition, this Step 4 is not an essential process in the method for manufacturing the steel foil (10) for a battery container of the present embodiment, and may be omitted as long as it is not configured as a laminate plate (surface-treated steel foil).

[0128] As a method for forming the thermoplastic resin layer (3), it is preferable to form it on at least the side of the substrate (1) that becomes the inner surface of the battery container, and it may be a film laminate or an extrusion laminate. In addition, the temperature of the substrate (1) when coating with the thermoplastic resin layer (3) is adjusted to room temperature to 280°C, preferably 250°C or lower, depending on the type of laminate.

[0129] As described above, a steel plate (10) for a battery container can be obtained after going through steps 1 to 4.

[0130] Battery container

[0131] Next, the battery container of the present embodiment manufactured by the above-mentioned battery container steel (10) will be described.

[0132] The battery container of the present embodiment is manufactured by performing processing such as drawing molding or heat sealing on the aforementioned battery container foil (10). In addition, the battery container of the present embodiment is particularly preferably a so-called pouch shape manufactured by square tube drawing molding.

[0133] More specifically, a drawing process (deep drawing process, etc.) is performed on the thin sheet (10) for the battery container to form the thin sheet (10) for the battery container into a container shape as shown in FIG. 4. More specifically, the container shape of the present embodiment has a rectangular concave portion of depth (D) in which corner portions with a radius of curvature (Rc) (referred to as Rc because they are corners in the circumferential direction) are formed at the four corners so as to accommodate a rectangular electrode plate. In addition, the side wall of the concave portion and the bottom surface of the concave portion are connected by a radius of curvature (Rp) (referred to as Rp because it is defined as the R of the punch). In addition, in the container of FIG. 4, the corners (R) of the four corners of the aforementioned concave portion are identical, but these Rc and Rp may each have different values.

[0134] Hereinafter, the reason why the steel foil (10) for the battery container of this embodiment is very effective for the shape of the battery container having such a radius of curvature (Rc and Rp) and depth (D) is described in detail below.

[0135] Radius of curvature (Rc and Rp) and depth (D) for high-capacity scaling

[0136] First, in order to increase the capacity of the battery container using the steel foil (10) as a battery container, the Rc of the four corners in the aforementioned concave portion during molding processing, the Rp between the side wall and the bottom surface of the concave portion, and the depth (D) are all important, but the balance between Rp and the depth (D) is particularly important. Furthermore, establishing such a balance is particularly important for battery containers for automotive applications because it is ideal to enlarge individual batteries and ensure that the characteristics of multiple batteries are guaranteed in a single battery. It is also important when not limited to single-cell batteries, but when multiple batteries are assembled and used as a module.

[0137] Furthermore, regarding the aforementioned Rc and Rp, it is desirable to make the radius of curvature of both as small as possible from the perspective of increasing the area where the electrodes are placed and reducing dead space within the battery.

[0138] The value of such 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.

[0139] In addition, the value of such radius of curvature (Rc) varies depending on the application and battery size, but preferably it is less than 10 mm, more preferably 8 mm or less, and even more preferably 3 mm or less.

[0140] On the other hand, in order to increase capacity by using it as a battery container, increasing the number of electrodes stacked and accommodated can increase the overall capacity of the battery, so it is also effective to increase the depth (D). As for the value of such depth (D), 5 mm or more is preferable, more preferably 6 mm or more, and 10 mm or more.

[0141] Under this background, the inventors carefully examined the relationship between the radius of curvature (Rp) and the depth (D) and concluded that when the steel foil (10) for the battery container is processed under the above conditions to increase capacity, there are problems with moldability and resistance to electrolyte after molding.

[0142] In other words, first of all, as the radius of curvature (Rp) becomes smaller, the difficulty of the forming process increases, and especially if the radius of curvature (Rp) is 1.0 mm or less, the difficulty increases dramatically. Also, regarding the depth (D), the deeper the forming process is attempted, the stricter the processing conditions for the material of the steel foil (10) for the battery container become. In particular, when a specific radius of curvature (Rp) condition and a depth (D) condition are combined in the steel foil with a thickness of 10 μm to 200 μm used in this embodiment, the following two problems arise.

[0143] First of all, the first problem is that breakage is likely to occur during the forming process. As explained in the first embodiment, when using a steel foil as the substrate (1), the specific gravity is higher compared to when using conventional aluminum as the substrate, so it is necessary to thin the thickness of the substrate (1) to suppress the increase in battery weight. When the thickness of the steel foil as the substrate (1) is thinned in this way, breakage of the substrate (1) is likely to occur.

[0144] Next, the second challenge is the non-dissolution properties (resistance to electrolyte) after molding. When drawing molding is performed under strict processing conditions as described above, there is a possibility that cracking of the resin film may occur. Therefore, even if cracking occurs, it is necessary to make the surface of the substrate (1) difficult to dissolve.

[0145] Regarding the first problem described in detail above, in the battery container of the present embodiment, it was discovered that by setting the maximum value of the maximum principal distortion of the uniaxial deformation of the battery container as described above to 0.25 or higher, and the maximum value of the maximum principal distortion of the planar distortion deformation to 0.1 or higher, it is possible to suppress breakage even when drawing forming is performed under strict processing conditions as described above.

[0146] In addition, regarding the second problem mentioned above, it was discovered 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 leaching of the substrate into the electrolyte even if a defect occurs in the resin film. At this time, it is preferable that the surface treatment layer be a surface treatment layer (electroplating layer) containing at least one of a Ni plating layer of 0.5 g / m² or more and a Cr plating layer of 0.05 g / m² or more, as sufficient non-dissolution properties are obtained when used as a battery container.

[0147] In addition, the battery container is sealed after accommodating battery elements such as electrode plates or electrolytes, and the steel foil (10) for the battery container in this embodiment can also be applied as a lid member of the battery container used for sealing. The lid member, which is a component of such a battery container, may have a receiving space formed similar to that of the battery container body shown in FIG. 4, or it may be used in a flat state. Furthermore, when sealing the battery container, it is preferable to heat seal the lid member at the flange portion of the perimeter edge of the battery container body having a drawing-processed receiving portion. In this case, it is preferable to configure the coating resins on the surfaces facing the battery container body and the lid member so that resins of the same type face each other, such as polypropylene resins or polyester resins. In addition, the above sealing method is an example and is not limited thereto, and for example, a known adhesive may be used.

[0148] Since the battery container obtained in this embodiment is formed using the steel foil (10) for the battery container of this embodiment described above, it can be preferably used as a battery container for various primary or secondary batteries, such as alkaline batteries, nickel-hydrogen batteries, nickel-cadmium batteries, and lithium-ion batteries. In particular, since the battery container of this embodiment has excellent resistance to electrolyte as described above, it can be preferably used for non-aqueous batteries that contain an organic solvent electrolyte as a content.

[0149] Examples

[0150] Next, the present invention will be explained in more detail with reference to examples.

[0151] <Example 1>

[0152] First, as a steel plate to be used as the material (1), a cold-rolled plate of low-carbon steel (thickness 50 μm) having the chemical composition shown below was prepared.

[0153] 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

[0154] Next, by performing annealing at 750°C for 10 seconds on the prepared steel, a substrate (1) having the following characteristics was obtained.

[0155] · Tensile strength (TS): 364 MPa

[0156] · Height (EL): 28.6%

[0157] (Measurement of principal distortion)

[0158] Regarding the material (1) obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar distortion deformation were measured using the method described above. In addition, the measurement of these maximum principal distortions was performed using a non-contact three-dimensional distortion and displacement measurement system (ARAMIS) manufactured by GOM. Using a sample that had a random pattern applied in advance with a spray or the like, triangulation was performed by continuously photographing the deformation state with two cameras, and the process of change of the random shape was acquired as three-dimensional position information, thereby measuring the maximum principal distortion (ε1) within the plate surface immediately before fracture and the minimum principal distortion (ε2) orthogonal to it. Uniaxial deformation was performed by tensile testing using a tensile testing machine and a tensile test according to JIS No. 5. Ecclesson testing machines were used for equiaxial deformation and planar distortion deformation. For equiaxial deformation, a circular blank of 150 mmφ was used, and for planar distortion deformation, a blank with both ends of the circular blank cut to a width of approximately 65 mm was used. A 60 mmφ round head punch was used, and to reduce friction between the punch and the blank, petroleum jelly was applied to the tip of the punch and formed.

[0159] As a result of the measurement, the maximum value of the maximum principal distortion in the uniaxial deformation of the material (1) of the present embodiment was 0.40. Likewise, the maximum value of the maximum principal distortion in the planar distortion deformation was 0.14.

[0160] (Formation of the thermoplastic resin layer (3))

[0161] First, as a thermoplastic resin layer (3), a polyethylene film with a thickness of 50 μm (product name "Daiwa Protech P-563B" manufactured by Daiwa Kasei Co., Ltd.) was prepared. Next, the polyethylene film was adhered to and coated on both sides of the substrate (1).

[0162] (Evaluation of plasticity)

[0163] After applying lubricant to the steel foil (10) for a battery container coated with a thermoplastic resin layer (3) as described above, deep drawing was performed using a 50 mm × 50 mm punch to form the aforementioned concave portion. In addition, in this deep drawing process, the Rc of the four corners in the concave portion was set to 3.0 mm, and the Rp between the side wall and the bottom surface of the concave portion was set to both 1.0 mm and 3.0 mm. Press forming was performed until an abnormality such as cracking or tearing occurred in the steel foil (10) for the battery container, and processing was stopped at the point when the abnormality occurred.

[0164] In addition, the moldability of the steel foil (10) for the battery container after press molding was evaluated by visually observing the cracking of the substrate (1) or the lifting or cracking of the thermoplastic resin layer (3) at the four corners of the battery container, and was performed according to the following criteria.

[0165] [metewand]

[0166] ◎: At Rp of 1.0 mm and 3.0 mm, the above abnormalities of the description were not confirmed even when the molding depth exceeded 10 mm.

[0167] ○: The above abnormality of the description was confirmed before the molding depth reached 5 mm in either Rp of 1.0 mm or 3.0 mm, but the other was not confirmed.

[0168] ×: At Rp of 1.0 mm and 3.0 mm, tearing or cracking was observed in the substrate before the molding depth reached 5 mm.

[0169] <Example 2>

[0170] Except for the matters described below, the procedure was carried out in the same manner as Example 1.

[0171] First, as a steel plate to be used as the material (1), a cold-rolled plate of ultra-low carbon steel (thickness 50 μm) having the chemical composition shown below was prepared.

[0172] C: 0.001 wt%, Mn: 0.30 wt%, Si: 0.01 wt%, P: 0.01 wt%, S: 0.01 wt%, Nb: 0.02 wt%, remainder: Fe and unavoidable impurities

[0173] Next, by performing annealing on the prepared steel at 670°C for 8 hours, a substrate (1) having the following characteristics was obtained.

[0174] · Tensile Strength (TS): 340 MPa

[0175] · Height (EL): 23.7%

[0176] With respect to the substrate (1) obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar distortion deformation were measured, respectively, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) of this example was 0.27. Likewise, the maximum value of the maximum principal distortion in planar distortion deformation of the substrate (1) was 0.23.

[0177] <Example 3>

[0178] Except for the matters described below, the procedure was carried out in the same manner as Example 1.

[0179] First, as a steel plate to be used as the material (1), a cold-rolled plate of ultra-low carbon steel (thickness 80 μm) having the chemical composition shown below was prepared.

[0180] C: 0.001 wt%, Mn: 0.15 wt%, Si: 0.01 wt%, P: 0.01 wt%, S: 0.01 wt%, Ti: 0.03 wt%, Nb: 0.004 wt%, remainder: Fe and unavoidable impurities

[0181] Next, by performing annealing at 820°C for 20 seconds on the prepared steel, a substrate (1) having the following characteristics was obtained.

[0182] · Tensile Strength (TS): 301 MPa

[0183] · Height (EL): 42.0%

[0184] With respect to the substrate (1) obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar deformation were measured, respectively, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) of this example was 0.65. Likewise, the maximum value of the maximum principal distortion in planar deformation of the substrate (1) was 0.30.

[0185] <Example 4>

[0186] Using the same description as in Example 3 above, matters other than those described below were carried out in the same manner as in Example 3.

[0187] That is, by performing annealing at 640°C for 8 hours on the prepared steel, a substrate (1) having the following characteristics was obtained.

[0188] · Tensile strength (TS): 332 MPa

[0189] · Height (EL): 39.0%

[0190] With respect to the substrate (1) obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar deformation were measured, respectively, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) of this example was 0.62. Likewise, the maximum value of the maximum principal distortion in planar deformation of the substrate (1) was 0.30.

[0191] <Example 5>

[0192] As for the steel plate serving as the substrate (1), the procedure was carried out in the same manner as Example 4, except that the thickness of the cold-rolled plate of ultra-low carbon steel was set to 50 μm. For the obtained substrate (1), the maximum principal distortion in uniaxial deformation and the maximum principal distortion in plane distortion deformation were measured, respectively, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) of this example was 0.63. Likewise, the maximum value of the maximum principal distortion in plane distortion deformation of the substrate (1) was 0.31.

[0193] <Example 6>

[0194] A cold-rolled plate of ultra-low carbon steel, such as in Example 5, was used as the substrate (1), and a surface treatment layer (2) was formed in the following order.

[0195] (Formation of surface treatment layer (2))

[0196] With respect to the substrate (1), electrolytic degreasing and acid immersion in sulfuric acid were performed, and then electroplating was performed under the following conditions to form a surface treatment layer (2) (electro-Ni plating layer) with a Ni plating amount of 4.5 g / m². In addition, the conditions for forming the Ni plating layer were as follows.

[0197] (Conditions for the formation of the Ni plating layer)

[0198] Bath composition: Nickel sulfate, nickel chloride, boric acid, peat inhibitor

[0199] pH: 4.3

[0200] Bath temperature: 55℃

[0201] Current density: 10A / dm²

[0202] By continuously performing heat treatment at 800°C for 10 seconds, a substrate (1) having a surface treatment layer (2) having the following characteristics was obtained.

[0203] · Tensile Strength (TS): 325 MPa

[0204] · Height (EL): 37.3%

[0205] With respect to the substrate (1) on which the surface treatment layer (2) obtained above is formed, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar deformation were each measured using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) on which the surface treatment layer (2) of this example is formed was 0.62. Likewise, the maximum value of the maximum principal distortion in planar deformation of the substrate (1) on which the surface treatment layer (2) is formed was 0.30.

[0206] With respect to the substrate (1) on which the surface treatment layer (2) is formed, both sides of the substrate (1) were coated with a thermoplastic resin layer (3) as in Example 1, and then an evaluation of moldability was performed.

[0207] <Example 7>

[0208] A substrate (1) having a surface treatment layer (2) having the following characteristics was obtained by performing the same as in Example 6, except that the heat treatment conditions were set to 800°C for 30 seconds.

[0209] · Tensile strength (TS): 326 MPa

[0210] · Height (EL): 35.6%

[0211] With respect to the substrate (1) having the surface treatment layer (2) formed thereon obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar deformation were each measured using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) having the surface treatment layer (2) formed thereon in this example was 0.62. Likewise, the maximum value of the maximum principal distortion in planar deformation of the substrate (1) having the surface treatment layer (2) formed thereon was 0.31.

[0212] <Example 8>

[0213] A substrate (1) having a surface treatment layer (2) having the following characteristics was obtained by performing the same as in Example 6, except that the heat treatment conditions were set to 820°C for 10 seconds.

[0214] · Tensile Strength (TS): 325 MPa

[0215] · Height (EL): 30.2%

[0216] With respect to the substrate (1) having the surface treatment layer (2) formed thereon obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar deformation were measured, respectively, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) having the surface treatment layer (2) formed thereon in this example was 0.52. Likewise, the maximum value of the maximum principal distortion in planar deformation of the substrate (1) having the surface treatment layer (2) formed thereon was 0.26.

[0217] <Example 9>

[0218] A substrate (1) having a surface treatment layer (2) having the following characteristics was obtained by performing the same as in Example 6, except that the heat treatment conditions were set to 850°C for 10 seconds.

[0219] · Tensile Strength (TS): 339 MPa

[0220] · Height (EL): 30.7%

[0221] With respect to the substrate (1) having the surface treatment layer (2) formed thereon obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar deformation were each measured using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) having the surface treatment layer (2) formed thereon in this example was 0.54. Likewise, the maximum value of the maximum principal distortion in planar deformation of the substrate (1) having the surface treatment layer (2) formed thereon was 0.28.

[0222] <Comparative Example 1>

[0223] The same material as in Example 2 described above was used. Except for the matters described below, the procedure was carried out in the same manner as in Example 2.

[0224] That is, by performing annealing at 560°C for 8 hours on the prepared steel, a substrate (1) having the following characteristics was obtained.

[0225] · Tensile Strength (TS): 385 MPa

[0226] · Height (EL): 20.6%

[0227] With respect to the substrate (1) obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar deformation were measured, respectively, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) of this example was 0.19. Likewise, the maximum value of the maximum principal distortion in planar deformation of the substrate (1) was 0.16.

[0228] <Comparative Example 2>

[0229] The same material as in Example 2 described above was used. Except for the matters described below, the procedure was carried out in the same manner as in Example 2.

[0230] That is, by performing annealing at 640°C for 8 hours on the prepared steel, a substrate (1) having the following characteristics was obtained.

[0231] · Tensile Strength (TS): 373 MPa

[0232] · Height (EL): 16.8%

[0233] With respect to the substrate (1) obtained above, the maximum principal distortion in uniaxial deformation and the maximum principal distortion in planar deformation were measured, respectively, using the same method as in Example 1. As a result of the measurement, the maximum value of the maximum principal distortion in uniaxial deformation of the substrate (1) of this example was 0.17. Likewise, the maximum value of the maximum principal distortion in planar deformation of the substrate (1) was 0.13.

[0234] The material specifications and moldability evaluations of each sample used in the above-mentioned Examples 1 to 9 and Comparative Examples 1 to 2 are shown in Table 2.

[0235]

[0236] In Examples 1 to 9, when a rigid drawing molding process was performed using a steel foil (10) for a battery container coated with a thermoplastic resin layer (3) with a radius of curvature less than or equal to a predetermined value, it was found that the occurrence of breakage was suppressed when manufacturing it as a battery container. Furthermore, these results showed that sufficient non-water-based properties were obtained when using it as a non-water-based battery container.

[0237] On the other hand, in Comparative Examples 1 and 2, when drawing molding with a small radius of curvature is performed in the manufacture of battery containers, cracking may occur, and there is a possibility that sufficient internal dissolution properties may not be obtained when used as a non-aqueous battery container.

[0238] (Industrial Applicability)

[0239] The steel foil for battery containers according to the present invention can exhibit sufficient moldability and non-dissolvability for use in containers for non-aqueous batteries, such as lithium-ion secondary batteries, and thus can be applied to a wide range of industries utilizing batteries. Explanation of the symbols

[0240] 1: Entry 2: Surface treatment layer 3: Thermoplastic resin layer 10: Compulsion for battery containers

Claims

Claim 1 A battery container steel foil used as a battery container, wherein the thickness of the steel foil to be used as a battery container is 10 to 200 μm, the carbon content in the said steel foil is 0.0001 to 0.15 wt%, and the maximum value of the maximum principal distortion of uniaxial deformation is 0.25 or higher and the maximum value of the maximum principal distortion of planar deformation is 0.1 or higher by performing an annealing treatment in the said steel foil at a temperature greater than 640°C and less than 750°C for 6 to 10 hours, or at a temperature of 750°C and 900°C for 5 seconds to 30 minutes. Claim 2 A battery container die used as a battery container, characterized in that the thickness of the die used as a base is 10 to 200 μm, and in the above base, the C content is 0.001 to 0.01 wt%, the Ti content is 0.01 to 0.1 wt% or the Nb content is 0.001 to 0.05 wt%, and the maximum value of the maximum principal distortion of uniaxial strain is 0.25 or higher and the maximum value of the maximum principal distortion of planar strain is 0.1 or higher. Claim 3 A steel foil for a battery container having a surface treatment layer formed on at least one side, in accordance with claim 1 or 2. Claim 4 A steel wire for a battery container according to claim 1 or 2, wherein the maximum value of the maximum principal distortion of the uniaxial deformation is 0.45 or higher and the maximum value of the maximum principal distortion of the planar distortion deformation is 0.2 or higher. Claim 5 A steel for a battery container according to claim 1 or 2, wherein the maximum value of the maximum principal distortion of the equiaxial deformation is 0.2 or greater. Claim 6 A steel foil for a battery container according to claim 1 or 2, wherein 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. Claim 7 In claim 1, a steel foil for a battery container having a C content of 0.05 weight% or less in the above description. Claim 8 A steel foil for a battery container according to claim 1, wherein the Nb content is 0.05 wt% or less or the Ti content is 0.1 wt% or less in the above description. Claim 9 A steel foil for a battery container according to claim 3, wherein the surface treatment layer is either a Ni plating layer of 0.5 to 50.0 g / m² or a Cr plating layer of 0.05 to 10.0 g / m². Claim 10 A steel foil for a battery container having a thermoplastic resin layer formed on at least one side, according to claim 1 or 2. Claim 11 A pouch-type battery container obtained by heat-sealing a battery container die described in claim 1 or 2. Claim 12 In claim 11, a pouch-type battery container for non-aqueous batteries.

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