Battery case

Abstract

To provide a battery case for a secondary battery, which can suppress corrosion of a steel plate in a processed portion when it comes into contact with an electrolyte for the secondary battery. [Solution] The present invention relates to a battery case for a pouch-type secondary battery made of a surface-treated steel sheet, and the surface of the surface-treated steel sheet that will become the inner surface of the battery case has an Sn-based alloy plating layer located on the surface of a base steel sheet, a chemical conversion coating layer located on the Sn-based alloy plating layer and containing at least Zr, and a resin layer located on the chemical conversion coating layer and containing a polyolefin-based resin, and the Sn-based alloy plating layer has islands of Sn formed on an Fe-Ni-Sn alloy layer, and the amount of Sn in metal equivalent is 0.10 to 10.00 g / m 2 Sn in the range of 2 to 200 mg / m as metal Ni equivalent 2 The mass of Zr per unit area in the chemical conversion coating layer is 1.0 to 100.0 mg / m 2 The thickness of the resin layer is in the range of 10 to 100 μm.

Description

[Technical Field]

[0001] The present invention relates to a battery case for a secondary battery. [Background technology]

[0002] Secondary batteries such as nickel-cadmium batteries, nickel-metal hydride batteries, and lithium-ion batteries are widely used as power sources for electronic devices or electronic components, such as mobile phones, smartphones, notebook personal computers, portable tablet devices, video cameras, electric vehicles, satellites, and social infrastructure components. Lithium-ion secondary batteries, in particular, have excellent energy density and output characteristics, and are therefore widely used in mobile devices, such as mobile phones, smartphones, and portable tablet devices, which require small size and light weight. Traditionally, aluminum alloys have been used as packaging materials for these small batteries from the viewpoints of light weight, formability, and cost.

[0003] In recent years, secondary batteries have also been adopted as power sources in large devices such as electric vehicles, hybrid vehicles, and solar battery storage batteries. To improve output capacity, batteries for these large devices require an increased amount of electrolyte, which results in larger battery sizes. Packaging materials for such large batteries are required to be safer (e.g., more robust and durable) than packaging materials for small batteries.

[0004] Aluminum alloys, which have traditionally been used as battery packaging materials, are metal materials with low rigidity. Therefore, in order to increase the pressure resistance against increased pressure inside the battery, it was necessary to increase the thickness of the aluminum alloy. Furthermore, aluminum alloys are metal materials with poor buckling resistance. Therefore, when using flanges around the case to bundle and secure battery cells together, auxiliary bundling materials were required. Therefore, when using aluminum alloys as battery packaging materials, there were limitations to the space-saving and cost-reduction potential of the battery. Furthermore, aluminum alloys are metal materials with a high thermal expansion coefficient. Therefore, there was also the problem of significant thermal shock being applied to the packaging material due to heat generated during charging and discharging of secondary batteries.

[0005] As a means for solving the above problems, the following Patent Document 1 proposes using stainless steel sheet as a packaging member for so-called pouch-type batteries. More specifically, Patent Document 1 discloses a technology for manufacturing a battery by accommodating battery components (positive electrode, negative electrode, separator, electrolyte, etc.) in the internal space of a case member obtained by forming an austenitic stainless steel sheet, and joining the case members together by seam welding.

[0006] The battery exterior material made of stainless steel plate disclosed in Patent Document 1 has high strength and a small thermal expansion coefficient, and therefore can solve the above problems. However, when manufacturing a battery using the battery exterior material disclosed in Patent Document 1, the battery components are welded while housed in a case, which may cause deterioration of the battery components (especially the resin separator) due to welding heat. Furthermore, not only the battery of Patent Document 1, but also batteries using cases made of metal materials such as stainless steel plate may experience an excessive increase in internal pressure of the container during use, which may lead to the container bursting. To prevent such an excessive increase in internal pressure of the container, a safety valve may be provided; however, safety valves have a complex structure, which increases manufacturing costs.

[0007] As a means of solving the above-mentioned problems of welding heat and manufacturing costs, it has been proposed to use a laminate of a stainless steel plate and a heat-sealable resin film as a battery packaging material (see, for example, Patent Document 2 below). A battery is manufactured by housing battery components (positive and negative electrodes, separators, electrolyte, etc.) inside a case member made of this resin-coated stainless steel plate and joining the case members together by heat fusion. The technology disclosed in Patent Document 2 joins the case members by heat fusion rather than welding, so deterioration of the battery members due to welding heat does not occur. Furthermore, the bond strength achieved by heat fusion is significantly weaker than that achieved by welding. Therefore, such a battery case using heat fusion has the advantage of not requiring a safety valve, because the case members separate at the heat-sealed surface even if the internal pressure of the container rises excessively. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-52100 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-164565 Summary of the Invention [Problem to be solved by the invention]

[0009] However, while the present inventors were studying the case of manufacturing a secondary battery case by deep drawing using the steel sheet described in Patent Document 2, they recognized that if the deep drawing depth is large, the steel sheet will corrode at the processed portion when it comes into contact with an electrolyte for a secondary battery. Such corrosion at the processed portion may affect battery characteristics such as charge / discharge characteristics.

[0010] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a battery case for a secondary battery that can suppress corrosion of the steel plate in the processed portion when it comes into contact with the battery electrolyte. [Means for solving the problem]

[0011] In order to solve the above problems, the present inventors have conducted extensive research and have found that by using a surface-treated steel sheet as the material for a battery case for a secondary battery, in which a chemical conversion coating layer containing Zr is formed on an Sn-based alloy-plated steel sheet, and further a resin containing a polyolefin-based resin as a main component is formed on the chemical conversion coating layer, it is possible to suppress the lifting of the resin or peeling of the resin in the processed area when the case is brought into contact with an electrolyte for a secondary battery. The gist of the present invention, which was completed based on these findings, is as follows.

[0012] (1) A battery case for a pouch-type secondary battery made of a surface-treated steel sheet, wherein the surface of the surface-treated steel sheet that will become the inner surface of the battery case has: a Sn-based alloy plating layer located on the surface of a steel sheet that serves as a base material; a chemical conversion treatment layer that is located on the Sn-based alloy plating layer and contains at least Zr; and a resin layer that is located on the chemical conversion treatment layer and contains a polyolefin-based resin, wherein the Sn-based alloy plating layer is a plating layer in which islands of Sn are formed on an Fe-Ni-Sn alloy layer, and the amount of Sn in metal equivalent is 0.10 to 10.00 g / m 2 Sn in the range of 2 to 200 mg / m as metal Ni equivalent. 2 and Zr mass per unit area in the chemical conversion treatment layer is 1.0 to 100.0 mg / m 2 and the thickness of the resin layer is within a range of 10 to 100 μm. (2) The battery case according to (1), wherein the chemical conversion layer further contains P, and the ratio of the mass of Zr per unit area to the mass of P per unit area, Zr / P, is within the range of 1.0 to 3.0. (3) The battery case according to (1) or (2), wherein the surface of the surface-treated steel sheet that will become the outer surface of the battery case has the Sn-based alloy plating layer located on the surface of the steel sheet that serves as the base material, the chemical conversion treatment layer located on the Sn-based alloy plating layer, and a second resin layer containing a polyolefin-based resin located on the chemical conversion treatment layer, and wherein the melting point of the polyolefin resin contained in the resin layer is lower than the melting point of the polyolefin-based resin contained in the second resin layer. (4) The battery case according to (3), wherein the polyolefin resin contained in the second resin layer is a polyethylene terephthalate resin. [Effects of the Invention]

[0013] As described above, according to the present invention, it is possible to provide a battery case for a secondary battery that can suppress corrosion of the steel plate in the processed portion when it comes into contact with the battery electrolyte. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an explanatory diagram showing an example of a secondary battery according to an embodiment of the present invention; [Figure 2A] 2 is a cross-sectional view showing an example of a cross section of the secondary battery shown in FIG. 1 taken along the AA cutting line. [Figure 2B] 2 is a cross-sectional view showing another example of a cross section of the secondary battery shown in FIG. 1 taken along the AA cutting line. [Figure 3] FIG. 2 is an explanatory diagram schematically illustrating an example of a laminate structure of the surface-treated steel sheet according to the embodiment. [Figure 4] FIG. 1 is an explanatory diagram schematically illustrating a battery case member produced in a test example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted.

[0016] (Regarding secondary batteries) First, an example of a secondary battery that is the focus of attention in the embodiment of the present invention will be described below with reference to FIGS. 1 to 2B. Fig. 1 is an explanatory diagram showing an example of a secondary battery according to the present embodiment. Fig. 2A is a cross-sectional view showing an example of a cross section of the secondary battery shown in Fig. 1 taken along the AA cutting line, and Fig. 2B is a cross-sectional view showing another example of a cross section of the secondary battery shown in Fig. 1 taken along the AA cutting line.

[0017] As shown schematically in Fig. 1, this embodiment focuses on a so-called pouch-type secondary battery 1. The secondary battery 1 according to this embodiment has a battery case 10, and the inside of this battery case 10 contains a battery unit (not shown in Fig. 1) having a positive electrode, a negative electrode, a separator, etc., and an electrolyte (not shown in Fig. 1). Although not shown in Fig. 1, the battery case 10 is provided with a positive electrode terminal, a negative electrode terminal, etc. for mounting the secondary battery 1 in an electronic device, etc.

[0018] The battery case 10 according to this embodiment is made of a surface-treated steel sheet, as described in detail below. A processed portion 11 is formed on a part of the surface-treated steel sheet by performing various forming processes such as deep drawing.

[0019] As illustrated in FIG. 2A , a battery case 10 according to this embodiment is composed of, for example, two surface-treated steel plates 100A and 100B. In the example illustrated in FIG. 2A , a processed portion 11 is formed in a portion of the surface-treated steel plate 100A by deep drawing or the like, and a convex portion as the processed portion 11 and a flange portion as the non-processed portion are present. The battery case 10 illustrated in FIG. 2A is a so-called pouch-type battery case in which the flange portion of the surface-treated steel plate 100A and the surface-treated steel plate 100B are integrated by thermal fusion. Furthermore, the presence of the convex portion as the processed portion 11 creates an internal space between the surface-treated steel plate 100A and the surface-treated steel plate 100B. This internal space holds a battery unit 3 that functions as a secondary battery and an electrolyte 5.

[0020] In the battery case 10 according to this embodiment, for example, as shown in Fig. 2B, the processed portion 11 may be formed on both the surface-treated steel plates 100A and 100B. Even in this case, the flange portion of the surface-treated steel plate 100A and the flange portion of the surface-treated steel plate 100B are integrated by thermal fusion to form a so-called pouch-type battery case. The internal space of such a battery case holds a battery unit 3 and an electrolyte 5 that function as a secondary battery.

[0021] Here, the shape of the battery case 10 of the secondary battery according to this embodiment is not limited to the shapes shown in FIGS. 1 to 2B, and various shapes such as a rectangular parallelepiped tubular shape or a cylindrical shape can be applied.

[0022] The type of secondary battery is not particularly limited, and examples include various secondary batteries such as lithium ion batteries, lithium polymer batteries, nickel-metal hydride batteries, nickel-cadmium batteries, etc. Inside the battery case 10 according to this embodiment, a battery unit 3 and an electrolyte 5 corresponding to such various secondary batteries are appropriately selected and held.

[0023] (About Surface-Treated Steel Sheet 100) Next, the surface-treated steel sheet 100 used as the material for the battery case 10 according to this embodiment will be described in detail with reference to Fig. 3. Fig. 3 is an explanatory diagram that schematically shows an example of a layered structure of the surface-treated steel sheet according to this embodiment.

[0024] <Configuration of the surface-treated steel sheet 100 on the inner surface of the case> As shown schematically in Figure 3, the surface of the surface-treated steel sheet 100 according to this embodiment on the inner surface side of the battery case 10 (the side on which the battery unit 3 and the electrolyte 4 are present) has an Sn-based alloy plating layer 103 located on the surface of the base steel sheet 101, a chemical conversion treatment layer 105 located on the Sn-based alloy plating layer 103, and a resin layer 107 located on the chemical conversion treatment layer 105.

[0025] <About Base Steel Sheet 101> The base steel plate 101 serves as the housing of the battery case 10 according to this embodiment. Furthermore, the base steel plate 101 has a higher melting point than conventionally used Al plates, and therefore has excellent heat resistance and safety. The base steel plate 101 according to this embodiment is not particularly specified, and any steel plate used for general Sn-based alloy plated steel plates can be used.

[0026] Examples of such steel sheets include low-carbon steel and extra-low-carbon steel. Specific examples include those described in JIS G3303:2022, JIS G3315:2022, JIS Z1602:2003, and those described in ASTM A624, ASTM A625, ASTM A626, ASTM A650, ASTM A657A, etc. can be used. Also, the manufacturing methods and materials of the known steel sheets as described above are not particularly limited, and they may be manufactured through known processes such as hot rolling, pickling, cold rolling, annealing, temper rolling, etc. from the normal steel slab manufacturing process.

[0027] Here, the thickness of the base steel sheet 101 (thickness d0 in FIG. 3) can be appropriately set according to the required mass, required strength, required processing depth, etc. as a battery exterior material. From the perspective of reducing the mass of the battery case, the thinner the thickness d0, the better. However, the thinner the thickness d0, the lower the strength and workability, and the manufacturing cost increases. From the perspective of ensuring the strength of the battery case 10, the thickness d0 is preferably 100 μm or more. Also, even when performing deep drawing processing of about 50 mm, if the thickness d0 is 100 μm, it can sufficiently withstand the deep drawing processing. Considering such points and the generally required strength and processing depth of the battery case, the thickness d0 of the base steel sheet 101 is preferably, for example, within the range of 130 to 180 μm.

[0028] <Regarding the Sn-based alloy plating layer 103> In the battery case 10 according to the present embodiment, the Sn-based alloy plating layer 103 contributes to improving the corrosion resistance of the battery case 10. The Sn-based alloy plating layer 103 according to the present embodiment is a plating layer in which island-like Sn is formed on the Fe-Ni-Sn alloy layer, and as the amount of metallic Sn in terms of mass, it contains Sn within the range of 0.10 to 10.00 g / m 2 and, as the amount of metallic Ni in terms of mass, it contains Ni within the range of 2.0 to 200.0 mg / m 2 of the range. [[ID=IS]]

[0029] <About the Fe-Ni-Sn alloy layer> In the Sn-based alloy plating layer 103 according to this embodiment, the Fe-Ni-Sn alloy layer has the effect of improving the corrosion resistance of the plated steel sheet. As will be described in detail below, the Sn-based alloy plating layer 103 according to this embodiment is formed by forming a Ni-based plating (more specifically, a Ni plating or an Fe-Ni plating) as an undercoat plating and a Sn plating on the base steel sheet 101, and then alloying part or all of the Ni with part of the Sn by a fusion heat treatment.

[0030] The Fe-Ni-Sn alloy layer contains Ni and Sn, which are electrochemically nobler metals than iron, thereby reducing pinholes and improving the corrosion resistance of Fe itself, thereby improving the corrosion resistance of the Sn-based alloy plating layer 103 according to this embodiment to the battery electrolyte (hereinafter also referred to as electrolyte resistance).

[0031] The effect of Ni on improving corrosion resistance is determined by the amount of Ni in the Ni plating layer or Fe-Ni plating layer formed as an undercoat on the steel sheet. 2 If the amount is equal to or greater than this, the effect of improving the corrosion resistance is exhibited. Therefore, in this embodiment, the amount of Ni per side is set to 2 mg / m in terms of metallic Ni. 2 The amount of Ni per side is preferably 10 mg / m2 in terms of metallic Ni. 2 More preferably, the amount of Ni metal is 20 mg / m 2 That's all.

[0032] Here, the greater the amount of Ni, the greater the effect of improving corrosion resistance. However, if the amount of Ni per side is 200 mg / m2 in terms of metallic Ni, 2 When the amount of Ni exceeds 200 mg / m, the effect of improving corrosion resistance is saturated, and further increase in the amount of Ni is not economically preferable. Therefore, in this embodiment, the amount of Ni per side is set to 200 mg / m in terms of metallic Ni. 2The amount of Ni per side is preferably 150 mg / m2 in terms of metallic Ni. 2 More preferably, it is 100 mg / m in terms of metallic Ni. 2 The following is the result.

[0033] <About island Sn> The Sn islands formed on the Fe-Ni-Sn alloy layer have the effect of improving corrosion resistance. Sn acts as a barrier film to prevent corrosion of Fe, while also forming stable compounds in battery electrolyte, improving corrosion resistance. Furthermore, the presence of Sn islands on the Fe-Ni-Sn alloy layer has a synergistic effect with the chemical conversion treatment layer 105, which is located on the Sn-based alloy plating layer 103 and has a fine surface unevenness, improving adhesion to the resin layer 107, which will be described later, and further improving the corrosion resistance of the plated steel sheet.

[0034] The effect of improving corrosion resistance due to the island-like Sn is such that the amount of Sn per side of the Sn-based alloy plating layer 103 (i.e., the total amount of Sn present as island-like Sn and the amount of Sn contained in the Fe-Ni-Sn alloy layer) is 0.10 g / m2 in terms of metallic Sn. 2 Therefore, in this embodiment, the amount of Sn per side is 0.10 g / m in terms of metallic Sn. 2 The amount of Sn per side is preferably 0.50 g / m in terms of metallic Sn. 2 More preferably, the amount of Sn metal is 1.00 g / m or more. 2 That's all.

[0035] Here, the greater the amount of Sn, the greater the effect of improving corrosion resistance. However, if the amount of Sn per side is 10.00 g / m2 in terms of metallic Sn, 2 If the amount of Sn exceeds 10.00 g / m, the effect of improving corrosion resistance is saturated, and any further increase in the amount of Sn is not economically preferable. Therefore, in this embodiment, the amount of Sn per side is set to 10.00 g / m in terms of metallic Sn. 2The amount of Sn per side is preferably 8.00 g / m2 in terms of metallic Sn. 2 More preferably, the amount of Sn metal is 5.00 g / m or less. 2 The following is the result.

[0036] Here, in order to confirm the distribution state of the Fe-Ni-Sn alloy layer and the island-like Sn as described above in the state of the manufactured battery case 10, a cross-sectional sample is obtained by cutting the surface-treated steel sheet 100, which is the raw material, in the thickness direction from approximately the center of the processed portion 11 of the manufactured battery case 10 (for example, approximately the center of the top surface of the processed portion 11 as shown in Figure 1), and the cross-sectional sample is observed using a scanning electron microscope (SEM).

[0037] Furthermore, when determining the amount of Ni and the amount of Sn in the Sn-based alloy plating layer 103 from the state of the manufactured battery case 10, measurement can be performed using inductively coupled plasma (ICP) emission spectroscopy.

[0038] In this case, a measurement sample of 30 mm × 30 mm is taken from approximately the center of the processed portion 11 of the manufactured battery case 10 (for example, approximately the center of the top surface of the processed portion 11 as shown in FIG. 1 ). The obtained measurement sample is stripped of the chemical conversion layer 105 and resin layer 107 using commercially available hydrogen peroxide (35% by mass), and the exposed Sn-based alloy plating layer 103 is then analyzed using a commercially available ICP optical emission spectrometer (for example, 799ce manufactured by Agilent Technologies).

[0039] <Regarding chemical conversion treatment layer 105> In the battery case 10 according to this embodiment, the chemical conversion layer 105 is a layer containing at least Zr. In the battery case 10 according to this embodiment, the chemical conversion layer 105 improves the electrolyte resistance of the battery case 10 and also improves adhesion between the chemical conversion layer 105 and the resin layer 107 located above the chemical conversion layer 105. This improvement in electrolyte resistance is due to the excellent chemical stability of the Zr component contained in the chemical conversion layer 105. Furthermore, the above-described improvement in adhesion is achieved because the surface of the chemical conversion layer 105 has fine irregularities, which has a synergistic effect with the anchoring effect of the Sn-based alloy plating layer 103 due to the island-like Sn, resulting in an even more excellent anchoring effect. As a result, good adhesion is achieved between the chemical conversion layer 105 and the resin layer 107 formed above it.

[0040] In the chemical conversion treatment layer 105 according to this embodiment, the Zr component is thought to exist in the form of various ionic compounds containing Zr, such as zirconium oxide, zirconium phosphate, zirconium hydroxide, zirconium fluoride, etc. As will be described in detail below, the chemical conversion treatment layer 105 according to this embodiment is formed using an electrolyte solution containing Zr ions, and the components corresponding to the anions in the ionic compounds described above are derived from various anions that may be present in the electrolyte solution used during formation.

[0041] In addition, various compounds are added to the above-mentioned electrolytic solution to achieve an electrolytic solution with desired chemical components. Therefore, the chemical conversion treatment layer 105 according to this embodiment may contain components derived from water, various compounds, and impurities that may be present in such an electrolytic solution. Examples of components derived from compounds that may be present in such an electrolytic solution include F, Ca, Ti, Mn, etc.

[0042] In the chemical conversion treatment layer 105 according to this embodiment, the mass of Zr per unit area (which can also be regarded as the amount of Zr attached) is 1.0 to 100.0 mg / m per side in terms of metallic Zr. 2The mass of Zr per unit area in the chemical conversion treatment layer 105 is within the range of 1 mg / m 2 If the coating weight of the chemical conversion treatment layer 105 is less than 1.0 mg / m, the barrier properties derived from the Zr element will be insufficient, and the effect of improving corrosion resistance will be insufficient. 2 By satisfying the above, it is possible to improve corrosion resistance by the barrier properties exhibited by the Zr element. The mass of Zr per unit area in the chemical conversion treatment layer 105 is preferably 10.0 mg / m 2 or more, more preferably 30.0 mg / m 2 That's all.

[0043] On the other hand, the mass of Zr per unit area in the chemical conversion treatment layer 105 is 100.0 mg / m 2 If the coating mass of the chemical conversion layer 105 is more than 100.0 mg / m, the chemical conversion layer 105 itself becomes susceptible to brittle fracture, and the corrosion resistance of the chemical conversion layer 105 decreases. 2 By satisfying the above condition, it is possible to improve corrosion resistance while preventing brittle fracture of the chemical conversion coating layer 105 itself. The mass of Zr per unit area in the chemical conversion coating layer 105 is preferably 80.0 mg / m 2 or less, more preferably 50.0 mg / m 2 The following is the result.

[0044] Here, when determining the mass of Zr per unit area as described above from the state of the manufactured battery case 10, measurement using fluorescent X-ray analysis may be carried out.

[0045] In this case, a calibration curve for the mass of Zr per unit area of ​​metal is first determined in advance using a Zr sample with a known Zr mass per unit area. Then, a measurement sample measuring 30 mm × 30 mm is taken from approximately the center of the processed portion 11 of a manufactured battery case 10 (for example, approximately the center of the top surface of the processed portion 11 as shown in FIG. 1 ). The resin layer 107 of the obtained measurement sample is peeled off using commercially available hydrogen peroxide (35% by mass). The exposed chemical conversion layer 105 is analyzed using a commercially available X-ray fluorescence analyzer (for example, a ZSX Primus manufactured by Rigaku Corporation) to measure the fluorescent X-ray intensity. The obtained fluorescent X-ray intensity and the previously prepared calibration curve can be used to determine the Zr mass per unit area.

[0046] Furthermore, by including a P component in the chemical conversion treatment layer 105 according to this embodiment in addition to the Zr component, it is possible to further improve adhesion between the chemical conversion treatment layer 105 and the resin layer 107. Examples of such P components include various phosphoric acids and phosphates. The P component can be incorporated into the chemical conversion treatment layer 105 by adding a P-containing compound such as phosphoric acid or phosphate to the electrolyte used in forming the chemical conversion treatment layer 105.

[0047] Although it is not clear why the inclusion of the P component in the chemical conversion treatment layer 105 further improves adhesion, it is presumed that the inclusion of the P component results in the formation of a compound of P and Zr (e.g., zirconium phosphate), making the chemical conversion treatment layer 105 more stable, preventing deterioration when the chemical conversion treatment layer 105 comes into contact with the electrolyte, and further improving adhesion between the chemical conversion treatment layer 105 and the resin layer 107.

[0048] Furthermore, when the chemical conversion treatment layer 105 according to this embodiment further contains a P component, the P component may react with components derived from the base steel sheet 101, the Sn-based alloy plating layer 103, or the resin layer 107 to form phosphate compounds such as iron phosphate, nickel phosphate, tin phosphate, and zirconium phosphate. It is presumed that the corrosion resistance of the chemical conversion treatment layer 105 is further improved by the generation of such various phosphate compounds.

[0049] The effect of the P component in further improving adhesion as described above can be achieved by setting the ratio Zr / P, the mass of Zr per unit area (mass per unit area in terms of metallic Zr) to the mass of P per unit area (mass per unit area in terms of P amount), within the range of 1.0 to 3.0. The ratio Zr / P, the mass of Zr per unit area to the mass of P per unit area, is more preferably 1.4 or more, and even more preferably 1.8 or more. Furthermore, the ratio Zr / P, the mass of Zr per unit area to the mass of P per unit area, is more preferably 2.6 or less, and even more preferably 2.3 or less.

[0050] The ratio Zr / P can be calculated by measuring the mass of P per unit area in the same manner as for the mass of the Zr component, and then dividing the separately measured mass of Zr by the mass of P.

[0051] <Regarding the resin layer 107> The resin layer 107 in the battery case 10 according to this embodiment is located on the chemical conversion treatment layer 105 and contains a polyolefin resin as a main component.

[0052] One type of secondary battery that is of interest in this embodiment is a lithium ion battery. In a lithium ion battery, a lithium salt containing highly reactive fluoride ions (e.g., lithium hexafluorophosphate (LiPF6)) is used as one of the components of the electrolyte solution 5. When such an electrolyte deteriorates or is hydrolyzed, hydrofluoric acid is generated, which affects various battery components including the battery case 10.

[0053] Here, the presence of the resin layer 107 according to this embodiment on the surface of the battery case 10 that can come into contact with the electrolyte (i.e., the surface on the inner surface of the case) can improve corrosion resistance while preventing corrosion due to the generated hydrofluoric acid. To achieve this effect, the resin layer 107 according to this embodiment uses a polyolefin resin as the main film-forming component.

[0054] Furthermore, the resin layer 107 according to this embodiment has the function of isolating the interior of the secondary battery 1 from the outside air and creating a sealed system. That is, when the secondary battery 1 using the battery case 10 according to this embodiment is sealed by heat fusion, the resin layer 107 of one of the surface-treated steel plates 100 is heat-fused to the other surface-treated steel plate 100 or the metal electrode. This makes it possible to isolate the interior of the secondary battery 1 from the outside air and prevent leakage of the electrolyte solution 5.

[0055] In particular, when water vapor gas from the outside air penetrates into the interior of the secondary battery 1, the electrolyte in the electrolytic solution undergoes hydrolysis. When a fluorine-containing compound is present as a component of the electrolytic solution, as in a lithium-ion battery, hydrofluoric acid is produced by this hydrolysis. In this case, not only does the hydrofluoric acid deteriorate the performance of the secondary battery itself, but if the Sn-based alloy plating layer 103 has structural defects such as pinholes, it may also corrode the steel sheet. From this perspective, the resin layer 107 according to this embodiment also functions as a barrier to prevent the electrolytic solution 5 from penetrating into the surface of the base steel sheet 101.

[0056] In the resin layer 107 according to this embodiment, the type of polyolefin resin is not particularly limited, and various known polyolefin resins can be appropriately selected. Examples of such polyolefin resins include low-density polyethylene resin, medium-density polyethylene resin, high-density polyethylene resin, linear low-density polyethylene resin, ethylene-α-olefin copolymer resin, ethylene-acrylic acid copolymer resin, ethylene-methacrylic acid copolymer resin, ethylene-acrylic acid ester copolymer resin, ethylene-methacrylic acid ester copolymer resin, ethylene-vinyl acetate copolymer resin, ionomer resin, polypropylene resin, ethylene-propylene copolymer resin, acid-modified polyolefin resin (olefin resin graft-modified with unsaturated carboxylic acid, copolymer resin of ethylene or propylene with acrylic acid or methacrylic acid, metal-crosslinked olefin resin), etc.

[0057] In the resin layer 107 according to this embodiment, it is particularly preferable to use a polypropylene resin among the various polyolefin resins mentioned above.

[0058] In resin layer 107 according to this embodiment, the content of the polyolefin resin is preferably 50.0% by mass or more, and more preferably 80.0% by mass or more, relative to the total mass of resin layer 107. The higher the content of the polyolefin resin, the better, and it may be 100% by mass.

[0059] Furthermore, the resin layer 107 according to this embodiment may further contain additives such as anti-rust pigments, dispersants, leveling agents, waxes, aggregates, diluting solvents, etc., as needed, within the range that does not impair the effects described above. However, even when various additives such as those described above are added, the total content thereof is preferably 5 mass % or less with respect to the total mass of the resin layer 107.

[0060] The thickness of the resin layer 107 according to this embodiment (thickness d1 in FIG. 3) is in the range of 10 to 100 μm. If the thickness of the resin layer 107 is less than 10 μm, the electrolyte resistance will be insufficient, and the adhesion of the resin layer 107 will also be insufficient. When the thickness d1 of the resin layer 107 is 10 μm or more, the above-described electrolyte resistance and adhesion can be achieved. The thickness d1 of the resin layer 107 is preferably 20 μm or more, and more preferably 30 μm or more.

[0061] On the other hand, if the thickness d1 of the resin layer 107 exceeds 100 μm, the adhesiveness of the resin layer 107 will decrease due to residual stress in the resin layer 107. By setting the thickness d1 of the resin layer 107 to 100 μm or less, it is possible to improve the electrolyte resistance while preventing the adhesiveness from decreasing due to the residual stress. The thickness d1 of the resin layer 107 is preferably 80 μm or less, and more preferably 60 μm or less.

[0062] Here, the thickness d1 of the resin layer 107 according to this embodiment can be measured by taking a cross-sectional sample from the battery case 10 of interest by cutting the surface-treated steel sheet 100, which is the material, in the thickness direction and observing the cross-section of the cross-sectional sample using a scanning electron microscope (SEM). Those skilled in the art can easily determine the position of the interface between the resin layer 107 and the chemical conversion layer 105. Using a length measurement function or the like implemented in the SEM, the thickness of the portion corresponding to the resin layer 107 is measured at any three locations. The measured values ​​obtained are averaged over the number of observation locations, and the resulting value can be used as the thickness of the resin layer 107.

[0063] In addition, Figure 3 illustrates the case where the resin layer 107 of this embodiment is located directly above the chemical conversion treatment layer 105, but an adhesive layer (not shown) may be present between the resin layer 107 of this embodiment and the chemical conversion treatment layer 105.

[0064] The configuration of the surface-treated steel sheet 100 on the surface on the inner surface side of the case has been described in detail above with reference to FIG.

[0065] <Configuration of the surface-treated steel sheet 100 on the outer surface of the case> In the surface-treated steel sheet 100 according to this embodiment, the configuration of the surface on the outer side (the side in contact with the outside air) of the battery case 10 is not particularly specified. However, it is preferable that a Sn-based alloy plating layer 103 is present on the surface on the outer side of the case of the surface-treated steel sheet 100 according to this embodiment, as illustrated in Fig. 3, in order to ensure the corrosion resistance of the surface-treated steel sheet 100.

[0066] Furthermore, even on the outer surface of the case, there is a possibility that the electrolyte solution 5 may adhere to the outer surface of the case, for example, when the electrolyte solution 5 is sealed in. Therefore, in order to ensure resistance to the electrolyte solution, it is preferable that the outer surface of the case has a chemical conversion treatment layer 105 similar to that described above, as exemplified in FIG.

[0067] The presence of the Sn-based alloy plating layer 103 and chemical conversion treatment layer 105 on the outer surface of the case also makes it possible to ensure various properties of the battery case 10, such as corrosion resistance, insulation, and processability.

[0068] In addition, it is preferable that a second resin layer 111 made of an organic resin is present on the surface of the outer surface of the case in order to ensure the various properties required of the material of the battery case 10, such as processability, design, puncture resistance, insulation, etc.

[0069] The organic resin contained in the second resin layer 111 is not particularly limited, and various known organic resins can be used depending on the desired properties. Furthermore, as such an organic resin, a polyolefin resin similar to that of the resin layer 107 according to this embodiment can also be used.

[0070] However, considering that the secondary battery 1 having the battery case 10 according to this embodiment is manufactured by heat fusion, it is preferable that the melting point of the organic resin contained in the second resin layer 111 is higher than the melting point of the polyolefin resin contained in the resin layer 107 (in other words, the melting point of the polyolefin resin contained in the resin layer 107 is lower than the melting point of the organic resin contained in the second resin layer 111). This prevents the second resin layer 111 from melting before the resin layer 107 is heat fused, and enables the battery case 10 to be reliably sealed.

[0071] Taking the above situation into consideration, and further taking into consideration the impact resistance and manufacturing cost of the second resin layer 111, the organic resin contained in the second resin layer 111 is , Po It is preferably a polyethylene terephthalate resin.

[0072] The thickness of the second resin layer 111 (thickness d2 in FIG. 3) is not particularly limited either, and can be set appropriately depending on the desired properties, and may have the same thickness as the resin layer 107. Furthermore, although FIG. 3 illustrates the case where the second resin layer 111 has a single-layer structure, the second resin layer 111 may be composed of multiple layers.

[0073] The surface-treated steel sheet 100 used as the material for the battery case 10 according to this embodiment has been described in detail above with reference to FIG.

[0074] (Regarding manufacturing methods for battery cases for secondary batteries) Next, a method for manufacturing the battery case 10 for a secondary battery according to this embodiment will be described in detail.

[0075] <<About the manufacturing method of surface-treated steel sheet 100>> First, an example of a method for manufacturing the surface-treated steel sheet 100 that is the material for the battery case 10 according to this embodiment will be described in detail.

[0076] First, a steel plate is prepared as the base material of the surface-treated steel plate 100. Here, the method for manufacturing the base steel plate is not particularly limited, and a cast slab that has undergone a general steelmaking process may be processed into a steel plate of a predetermined size through processes such as hot rolling, pickling, cold rolling, annealing, pickling, and temper rolling.

[0077] The surface-treated steel sheet 100 according to this embodiment can be manufactured by sequentially carrying out the following steps on the base steel sheet obtained as described above: cleaning at least one surface of the steel sheet; forming an Sn-based alloy plating layer; forming a chemical conversion treatment layer; and forming a resin layer.

[0078] (Regarding the process of cleaning the base steel sheet) In the process of cleaning at least one surface of the base steel sheet, oils, oxides, and other foreign matter that may be present on the surface of the base steel sheet are removed from the surface of the base steel sheet. This allows the surface of the base steel sheet to be cleaned. This treatment may be performed on at least the surface on which the Sn-based alloy plating layer 103, the chemical conversion coating layer 105, and the resin layer 107 are to be formed, but it is preferable to perform this treatment on both surfaces of the base steel sheet.

[0079] Various known treatment methods can be used to remove the above-mentioned oils, oxides, foreign matter, etc. Examples of such treatment methods include chemical treatments such as degreasing treatment followed by pickling treatment, and mechanical treatments such as shot blasting, sand blasting, grit blasting, and dry ice blasting. The above-mentioned chemical treatments and mechanical treatments may also be combined.

[0080] When the surface of the base steel sheet is cleaned by chemical treatment, the degreasing treatment is carried out, for example, in a sodium hydroxide aqueous solution with a concentration of 10 to 50 g / L, at a liquid temperature of 20 to 80°C, and a current density of 5 to 40 A / dm 2 Then, cathodic electrolytic degreasing treatment or anodic electrolytic degreasing treatment can be carried out for 0.2 to 5 seconds.

[0081] In addition to pickling treatments in which the base steel sheet is simply immersed in electroless pickling, anodic electrolytic pickling, which has a significant effect of cleaning the surface of the base steel sheet, can also be applied. The above-mentioned electroless pickling treatment may be combined with electrolytic pickling treatment using anodic electrolysis. These pickling treatments may also be combined with cathodic electrolytic pickling. The number of pickling treatments may be one or more. The order in which the various pickling treatments are performed is not particularly limited.

[0082] (Regarding the process of forming the Sn-based alloy plating layer) As explained above, the Sn-based alloy plating layer in which island-like Sn is formed on an Fe-Ni-Sn alloy layer is formed by forming an Ni plating layer or an Fe-Ni plating layer as an undercoat on a base steel sheet, and then forming an Sn plating layer on the Ni plating layer or the Fe-Ni plating layer, followed by a heat-melting treatment. That is, the melting heat treatment alloys the Fe of the steel sheet, the Ni of the Ni plating layer, and part of the Sn of the Sn plating layer to form an Fe-Ni-Sn alloy layer, and the remaining Sn plating layer becomes island-like Sn.

[0083] <Ni-based plating> The method of Ni plating and Fe-Ni plating is not particularly limited, and various known electroplating methods can be used. Examples of such electroplating methods include electrolytic Ni plating and electroless Ni plating, but the detailed manufacturing method is not particularly specified.

[0084] Examples of electrolytic Ni plating methods include electrolysis using conventionally well-known sulfuric acid baths, chloride baths, sulfamic acid baths, citric acid baths, acetic acid baths, and aqueous solutions containing a mixture of these. These electrolytic solutions may contain pH buffers or additives such as boric acid, sodium sulfate, polyethylene glycol (PEG), butynediol, coumarin, sodium benzenesulfonate, and saccharin. These electrolytic solutions may also contain various elements such as Fe, Co, Na, K, Cu, Mg, Ca, Zn, Pb, Mn, Si, S, F, and C.

[0085] The electrolysis conditions when using the electrolytic Ni plating method are not particularly specified. For example, in a Ni plating bath mainly containing 20 to 400 g / L of nickel sulfate, 20 to 400 g / L of nickel chloride, or both, and 20 to 50 g / L of boric acid, the plating bath temperature is 10 to 80°C, the pH is 2.0 to 6.0, and the current density is 0.5 to 100 A / dm 2 Applicable electrolysis conditions include a plating bath temperature of 20 to 70°C, a pH of 3.0 to 5.0, and a treatment time of 0.3 to 5 seconds. This electrolysis treatment may be carried out not only once but also multiple times. Cathodic electrolysis, in which the base steel sheet is the cathode, may also be performed, and a combination of cathodic electrolysis and anodic electrolysis may be used. More preferred electrolysis conditions include a plating bath temperature of 20 to 70°C, a pH of 3.0 to 5.0, and a treatment time of 0.3 to 5 seconds. Within these conditions, a uniform Ni plating layer can be efficiently formed.

[0086] In this embodiment, "Ni plating" refers not only to metallic Ni plating, but also to metallic Ni containing impurities and metallic Ni to which trace elements such as W, Mo, B, Co, etc. have been added.

[0087] <Sn plating> The method for plating Sn on the formed Ni or Fe-Ni plating layer is not particularly limited, and various known plating methods can be used, such as a hot-dip method in which the steel sheet is immersed in molten Sn for plating, various electroplating methods, etc. However, it is preferable to use an electroplating method. The details of the electroplating method are not particularly specified, and for example, an electrolytic method using a well-known ferrostane bath, halogen bath, alkaline bath, etc. may be used.

[0088] There are no particular restrictions on the electrolytic conditions when using electroplating. For example, in a ferrostane bath, the plating bath temperature is 35 to 60°C, and the current density is 10 to 100 A / dm 2 Applicable conditions include a plating bath temperature of 20 to 70°C, a pH of 3.0 to 5.0, and a treatment time of 0.3 to 5.0 seconds. This range allows for efficient formation of a uniform Sn plating layer.

[0089] In this embodiment, "Sn plating" refers not only to plating with metallic tin, but also to plating with metallic tin mixed with impurities and plating with metallic tin added with trace elements.

[0090] <Heat melting treatment> After the Sn plating as described above, the Sn-plated steel sheet is subjected to a heat-melting treatment (also called a reflow treatment), in which the steel sheet is heated to a temperature equal to or higher than 231.9°C, which is the melting point of Sn. This heat-melting treatment melts the Sn plating and alloys it with the underlying Ni plating layer or Fe-Ni plating layer to form an Fe-Ni-Sn alloy layer, and further forms island-shaped Sn layers, resulting in a Sn-based alloy plating layer with excellent electrolyte resistance.

[0091] (Regarding the process of forming the chemical conversion coating layer) In the step of forming a chemical conversion layer, the chemical conversion layer is formed on the Sn-based alloy plating layer formed, for example, as described above. The method for forming the chemical conversion layer may be any of various known treatment methods, and is not particularly limited. For example, a treatment method may be used in which the base steel sheet on which the Sn-based alloy plating layer has been formed (i.e., the Sn-based alloy-plated steel sheet) is immersed in a bath containing Zr ions, or the Sn-based alloy-plated steel sheet is subjected to cathodic electrolysis in a catholyte solution containing Zr ions.

[0092] In the above-mentioned immersion treatment, the surface of the Sn-based alloy plating layer as the base is etched, forming a chemical conversion coating layer containing Zr. As a result, the amount of Zr deposited tends to be non-uniform and the treatment time is long.

[0093] On the other hand, cathodic electrolysis can produce a uniform coating by surface cleaning due to forced charge transfer and hydrogen generation at the steel sheet interface, combined with the adhesion-promoting effect of an increased pH. Furthermore, cathodic electrolysis can be completed in a short time of several seconds to several tens of seconds due to the coexistence of nitrate ions and ammonium ions in the catholyte. Therefore, cathodic electrolysis is extremely advantageous from an industrial perspective.

[0094] Therefore, it is preferable to use a method based on cathodic electrolysis to form a chemical conversion coating layer containing Zr. In addition to the above methods, coating and spraying can also be used. Furthermore, phosphoric acid-based treatment solutions, sulfuric acid-based treatment solutions, etc. can also be used as treatment solutions (electrolytes).

[0095] When the P component is contained in the chemical conversion coating layer so that the Zr / P mass ratio is within the range of 1.0 to 3.0, various phosphorus-containing compounds may be contained in the Zr-containing electrolyte so that the P concentration is 1 / 3 to 1 times the Zr concentration. Furthermore, such a treatment solution may contain F, Ca, Ti, Mn, etc.

[0096] (Regarding the process of forming the resin layer) In the step of forming a resin layer, a resin layer is formed on the chemical conversion treatment layer formed as described above. Here, the method for forming the resin layer is not particularly limited and can be appropriately selected from various known methods.

[0097] For example, a polyolefin resin film may be laminated on the chemical conversion treatment layer (lamination method). Here, the lamination method includes a thermal lamination method, a sand lamination method, etc. The polyolefin resin film may be a commercially available one, or may be produced using a T-die extruder, etc. The polyolefin resin film may be unstretched, uniaxially stretched, or biaxially stretched.

[0098] Alternatively, a polyolefin resin composition may be applied onto the chemical conversion treatment layer (coating method). Here, the coating method includes a method of melting the resin composition and applying it with a bar coater, a roll coater, or the like, a method of immersing the chemically treated Sn-based alloy plated steel sheet in the melted resin composition, and a method of dissolving the resin composition in a solvent and applying it with a bar coater, a roll coater, a spin coater, or the like.

[0099] Furthermore, when forming a second resin layer on the chemical conversion treatment layer, the same method as above can be used, using a resin film or resin composition using a desired organic resin.

[0100] Through the steps described above, the surface-treated steel sheet 100 that will be the material for the battery case 10 according to this embodiment can be manufactured.

[0101] <<Regarding the manufacturing method of the battery case 10>> The method for manufacturing a battery case 10 from the surface-treated steel sheet 100 obtained as described above involves using a plurality of the surface-treated steel sheets 100 as the raw material to manufacture battery case members by a known processing method so as to realize the desired shape of the battery case 10. The obtained battery case members are then joined together to realize the desired shape of the battery case 10.

[0102] The following description will be given taking as an example the case of manufacturing a battery case 10 having the shape shown in FIGS. 1 to 2B. In this case, as shown in Figures 2A and 2B, various processing methods such as deep drawing are applied to at least one of the two surface-treated steel sheets 100 to form a tray-shaped battery case member with flanges. At this time, it is important to perform the forming process so that a convex portion protrudes from the surface on the side on which the resin layer 107 is formed. Thereafter, it is preferable to overlap the flanges with the protruding portion facing outward and then seal the flanges by bonding them together.

[0103] A preferred method for bonding the surface-treated steel sheets 100 together is to bond the surfaces on which the resin layers 107 are present by thermal fusion bonding, as described above. In this case, as shown schematically in Fig. 2B, the surface-treated steel sheets 100 that have been shaped may be bonded together, or as shown schematically in Fig. 2A, only one of the surface-treated steel sheets 100 may be shaped.

[0104] Here, the forming method for obtaining the desired battery case component from the surface-treated steel sheet 100 is not particularly limited, and can be appropriately selected from various known processing methods such as pressing, ironing, drawing, etc.

[0105] The method for manufacturing the battery case 10 for a secondary battery according to this embodiment has been described in detail above.

[0106] (Regarding the manufacturing method of the secondary battery 1) The method for manufacturing various types of secondary batteries 1 using the battery case 10 obtained as described above is not particularly limited, and various methods capable of manufacturing pouch-type secondary batteries can be appropriately selected.

[0107] For example, the battery unit 3 having the positive electrode, negative electrode, separator, etc., and the battery internal parts such as the electrolyte 5 may be housed in the battery case 10 manufactured as described above, and then bonded by heat fusion.

[0108] The method for manufacturing the secondary battery 1 has been briefly described above. [Example]

[0109] The battery case for the secondary battery according to the present embodiment will be specifically described below with reference to test examples. Note that the test example shown below is merely one example of the battery case for the secondary battery according to the present embodiment, and the battery case for the secondary battery according to the present embodiment is not limited to the following example.

[0110] First, a base steel sheet to be used in the test was prepared. The base steel sheet used was a steel sheet (low-carbon cold-rolled steel sheet manufactured by Nippon Steel Corporation) that is commonly used for containers. The thickness of the steel sheet used was 0.17 mm. Next, an Sn-based alloy plating layer, a chemical conversion coating layer, and a resin layer were formed on the surface of the prepared base steel sheet by the following methods, and then a battery case for a secondary battery was produced.

[0111] (Formation of Sn-based alloy plating layer) The above-mentioned base steel sheet was subjected to pretreatments of electrolytic alkaline degreasing, water washing, pickling with dilute sulfuric acid, and water washing, and then nickel plating was performed in a sulfuric acid bath. The amount of nickel deposited was 1 to 300 mg / m2 in terms of metallic nickel. 2 The Ni plating was then electroplated with Sn using a phenolsulfonic acid bath. The Sn deposition amount was 0.05 to 15.00 g / m2 in terms of metallic Sn. 2The steel sheets having the Ni and Sn plating layers thus prepared were subjected to a heat-melting treatment at a sheet temperature of 245°C, followed by water cooling to form Sn-based alloy plating layers. The amounts of Ni and Sn in the Sn-based alloy plating layer were determined by immersing the steel sheets after the Sn-based alloy plating layer formation in 10% nitric acid to dissolve the Sn-based alloy plating layer containing Ni and Sn, and analyzing the Ni and Sn in the resulting solution using an ICP optical emission spectrometer (799ce manufactured by Agilent Technologies).

[0112] (Formation of chemical conversion coating layer) A chemical conversion coating layer containing Zr was formed on the surface of the obtained Sn-based alloy plated steel sheet by electrolysis. The chemical conversion coating layer containing Zr was formed by immersing the steel sheet on which the Sn-based alloy plated layer had been formed in an aqueous solution containing zirconium fluoride with a Zr ion concentration of 1500 ppm at a bath temperature of 50°C and a current density of 5 A / dm 2 The Zr deposition amount was adjusted to 0.5 to 110.0 mg / m by adjusting the electrolysis time. 2 A chemical conversion coating layer containing Zr within the range of 0.01 to 0.01 was formed. In some test examples, P, Ti, or Mn was added to the aqueous solution. Phosphoric acid was used as the P source, titanium fluoride was used as the Ti source, and manganese fluoride was used as the Mn source. In some test examples, the aqueous solution for electrolysis was prepared using water containing Ca as a mineral.

[0113] The mass of Zr per unit area (Zr deposition amount) was determined by X-ray fluorescence spectroscopy (Rigaku ZSX Primus). After the chemical conversion coating layer was formed by electrolysis, the Sn-based alloy plated steel sheet on which the chemical conversion coating layer was formed was washed with water and dried. This process was performed on both sides of the Sn-based alloy plated steel sheet.

[0114] (Formation of resin layer) A resin layer was formed on the chemical conversion layer by thermal lamination so that the thickness was within the range of 5 to 120 μm. Specifically, a polypropylene resin film (melting point: 165°C) was thermocompressed with a roll onto the chemical conversion treated Ni-plated steel sheet heated to 260°C in an oven. The roll temperature was 60°C, and the nip thickness was 20 kgf / cm. 2 A polypropylene resin film was thermocompressed onto one side of a chemically treated Sn-based alloy plated steel sheet, and a polyethylene terephthalate resin film (melting point: 265°C) with a thickness of 5 to 100 μm was thermocompressed onto the other side at a pressure of 1 kgf (approximately 9.8 N) for a bonding time of 1 second to produce a surface-treated steel sheet that would become the material for the battery case. Note that for some samples, an acid-modified polypropylene resin film (melting point: 160°C) was also laminated as a resin other than polypropylene.

[0115] (Production of battery case components) Each of the surface-treated steel sheets prepared as described above was pressed to produce a tray-shaped battery case member with a 10 mm wide flange around the periphery, as shown in Figure 4. The depth of the tray-shaped recess was 35 mm.

[0116] (Corrosion resistance evaluation method) Each of the manufactured battery case members was evaluated from the viewpoint of corrosion resistance (ie, electrolyte resistance) of the processed portion. Test pieces (10 mm × 120 mm) were cut from the vertical wall of a battery case member having the shape shown in Figure 4 and immersed in a battery electrolyte at 85°C for 28 days in a sealable Teflon (registered trademark) container, then washed with ethanol and dried. The battery electrolyte used was lithium hexafluorophosphate (LiPF6) diluted to a concentration of 1 mol / L with a 1:1 mixture of ethylene carbonate and diethyl carbonate. A peel test (23°C, 180°C, tensile speed 20 mm / min) in accordance with JIS K 6854-2:1999 was then performed, and the peeled surface of the resin layer was observed using a 20x magnifying glass to evaluate the corrosion condition.

[0117] Those in which no corrosion was observed were given a rating of "EX", those in which the corrosion area ratio to the peeling surface was less than 10% were given a rating of "VG", those in which the corrosion area ratio to the peeling surface was more than 10% but less than 30% were given a rating of "G", and those in which the corrosion area ratio to the peeling surface was more than 30% were given a rating of "B".

[0118] The test results when the Sn-based alloy plating weight, Zr coating weight, and resin layer thickness were changed are summarized in Table 1 below, and the test results when the P ratio in the Zr coating layer was changed are summarized in Table 2 below.

[0119] [Table 1]

[0120] [Table 2]

[0121] In the test results shown in Table 1, A1 to A34, in which the Sn-based alloy plating weight, Zr coating weight, and resin layer thickness were all within the range of the present invention, had good corrosion resistance. On the other hand, B1 to B8, in which any of the Sn-based alloy plating weight, Zr coating weight, and resin layer thickness was outside the range of the present invention, had poor corrosion resistance.

[0122] Furthermore, in the test results shown in Table 2, A33 to A38, which have a Zr / P ratio in the range of 1.0 to 3.0, exhibited particularly good corrosion resistance.

[0123] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

[0124] The embodiments disclosed herein are illustrative in all respects and are not limiting. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope of the appended claims, the technical scope of the present invention as described below, and the spirit thereof. For example, the components of the above-described embodiments may be arbitrarily combined within the scope that does not impair the effects of the components. Furthermore, such an arbitrary combination naturally provides the functions and effects of each of the components involved in the combination, and also provides other functions and effects that are apparent to those skilled in the art from the description of this specification.

[0125] Furthermore, the effects described in this specification are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present invention may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects. [Explanation of symbols]

[0126] 1 Secondary battery 3 Battery Unit 5 Electrolyte 10 Battery case 11 Processing Department 100 Surface-treated steel sheet 101 Base steel plate 103 Sn-based alloy plating layer 105 Chemical conversion coating layer 107 Resin layer 111 Second resin layer

Claims

1. A battery case for a pouch-type secondary battery made of a surface-treated steel plate, The surface of the surface-treated steel sheet that will become the inner surface of the battery case is a Sn-based alloy plating layer located on the surface of a steel sheet serving as a substrate; a chemical conversion coating layer located on the Sn-based alloy plating layer and containing at least Zr; a resin layer located on the chemical conversion treatment layer and containing a polyolefin-based resin; It has The Sn-based alloy plating layer is The plating layer is an Fe—Ni—Sn alloy layer on which island-shaped Sn is formed, 0.10 to 10.00 g / m in terms of metal Sn ２ and 2 to 200 mg / m in terms of metal Ni. ２ and Ni in the range The mass of Zr per unit area in the chemical conversion treatment layer is 25.0 to 80.0 mg / m ２ is within the range of The battery case, wherein the resin layer has a thickness in the range of 10 to 100 μm.

2. The chemical conversion treatment layer further contains P, 2. The battery case according to claim 1, wherein a ratio of the mass of Zr per unit area to the mass of P per unit area, Zr / P, is within a range of 1.0 to 3.

0.

3. The surface of the surface-treated steel sheet that will become the outer surface of the battery case is the Sn-based alloy plating layer located on the surface of a steel sheet serving as a substrate; the chemical conversion treatment layer located on the Sn-based alloy plating layer; a second resin layer containing an organic resin and located on the chemical conversion treatment layer; It has The battery case according to claim 1 , wherein the melting point of the polyolefin resin contained in the resin layer is lower than the melting point of the organic resin contained in the second resin layer.

4. The battery case according to claim 3 , wherein the organic resin contained in the second resin layer is a polyethylene terephthalate resin.

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