Battery case for lithium-ion battery and lithium-ion battery

Abstract

The present invention relates to a battery case for a lithium-ion battery that is manufactured by welding a Ni-plated steel plate and suppresses elution of Fe from a cross section or a welded portion when the steel plate is cut in a plate thickness direction. The battery case for a lithium-ion battery is provided with a lid part, and a case body portion connected to the lid part via a weld metal. The lid part and the case body portion are respectively formed from a Ni-plated steel plate having a steel plate as a base material, and a Ni-based plating layer located on two surfaces facing each other in the plate thickness direction of the steel plate. The Ni content of the steel plate is 0.1 mass% or more. The adhesion amount of the Ni-based plating layer is 7.0 g / m2 or more per one side of the Ni-plated steel plate in terms of metallic Ni. The Ni concentration in the weld metal is 1.0% by mass or more. The lid part, the weld metal, and the case body portion are arranged in this order in the plate thickness direction of the lid part.

Description

Lithium-ion battery case and lithium-ion battery

[0001] This invention relates to a battery case for lithium-ion batteries and a lithium-ion battery.

[0002] The use of lithium-ion batteries as power sources for electric vehicles (EVs), plug-in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs) is expanding. To increase driving range and energy efficiency, there is a demand for larger battery capacity and higher volumetric energy density. Lithium-ion batteries come in various shapes, such as prismatic cases, cylindrical cases, and laminated pouch cases. However, from the perspective of energy density, prismatic cases are advantageous due to their superior space efficiency, and the size of prismatic cases is increasing.

[0003] Currently, aluminum plates are mainly used as the material for rectangular battery cases, although stainless steel plates (SUS) are sometimes used. One reason for selecting these materials is that the materials themselves have corrosion resistance to both the internal and external environments of the battery. Maintaining corrosion resistance to the electrolyte on the inside of the battery is particularly important. Over the long term, moisture from the atmosphere may enter the battery through gaskets at electrode penetrations, etc. Moisture that enters the battery and lithium hexafluoride phosphate (LiPF) contained in the electrolyte of lithium-ion batteries can cause corrosion. ６ ) reacts with the metal to produce hydrofluoric acid (HF). If metals inside the battery dissolve due to hydrofluoric acid, it can lead to a decrease in battery performance. However, since Al and SUS have corrosion resistance to hydrofluoric acid, there is no metal dissolution at a level that affects battery performance.

[0004] In the manufacturing method of a rectangular battery, first, a material such as an aluminum plate or stainless steel plate is subjected to deep drawing or bending to create the desired shape, and then, if necessary, welding is performed to form the battery case. Next, the battery contents, such as electrodes and electrolyte, are loaded into the battery case. Then, a lid made of the same material as the battery case is used to seal the opening of the battery case by laser welding or the like, thus completing the rectangular battery.

[0005] Japanese Patent Publication No. 2020-149790, Japanese Patent Publication No. Hei 1-115052, Japanese Patent Publication No. 2017-174698, Japanese Patent Publication No. 2006-324055

[0006] Ni (nitrile) has corrosion resistance to hydrofluoric acid. Therefore, Ni-plated steel sheets are used alongside aluminum (A) and stainless steel (SUS) as materials for cylindrical lithium-ion battery cases. Furthermore, Ni-plated steel sheets are used as materials for rectangular battery cases, specifically for alkaline and nickel-metal hydride batteries.

[0007] When welding Ni-plated steel sheets to obtain a rectangular battery case for lithium-ion batteries similar to those made of Al or SUS, there are concerns about the corrosion resistance of the welded parts of the container and lid. The edge surfaces of the Ni-plated steel sheets constituting the welded parts (the exposed cut edges when the Ni-plated steel sheet, which will be the material for the battery case, is cut in the thickness direction) and the weld metal surface do not have Ni-based plating. Therefore, the electrolyte used in lithium-ion batteries (e.g., LiPF) ６ In the case of (etc.), there are concerns about the leaching of Fe. The leaching of Fe could not only create holes in the battery case, but the leached Fe ions could also be reduced by the negative electrode and precipitate on the negative electrode, potentially causing a short circuit in the battery.

[0008] An example of a rectangular case for lithium-ion batteries made by welding is shown in Patent Document 1. Patent Document 1 describes a structure realized by welding a container and a lid, and a manufacturing method for realizing such a structure. Patent Document 1 also lists aluminum, aluminum alloy, stainless steel, iron, plated steel sheet, etc., as materials for the battery case. When Ni-plated steel sheet is applied to the structure disclosed in Patent Document 1, the weld metal and the cut edges of the steel sheet are exposed to the internal battery environment, raising concerns about Fe leaching. However, Patent Document 1 does not mention such Fe leaching.

[0009] Furthermore, an example of a rectangular battery case for alkaline batteries manufactured by welding Ni-plated steel sheets is shown in Patent Document 2. In Patent Document 2, regarding the weld metal, the lower limit of the Ni plating thickness near the weld is set to 2 μm in order to ensure corrosion resistance in the external environment of the battery. However, the method proposed in Patent Document 2 involves covering the entire surface of the container and lid, including the edges, with Ni plating before welding. Therefore, it is necessary to cover the edges with Ni plating after the container and lid are formed, which leads to increased costs. Also, since Patent Document 2 is a rectangular battery case for alkaline batteries, it does not mention corrosion resistance in the electrolyte environment of lithium-ion batteries. In alkaline batteries, unlike lithium-ion batteries, the electrolyte is strongly alkaline, so a passivation state is formed on the surface of the steel sheet. Therefore, corrosion resistance of the weld is not an issue on the inside of the battery.

[0010] Considering the manufacturing cost of lithium-ion batteries, it is preferable that the edges of the Ni-plated steel sheet be welded in their as-cut state (with the base steel sheet exposed). However, during such welding, depending on the penetration depth of the weld metal, the as-cut edges may remain exposed on the inner surface of the battery. In this case, if the edges of the steel sheet come into contact with the electrolyte held inside the battery, Fe will leach out from these edges. Furthermore, even if the weld metal is completely penetrated and covers the entire cut edge of the Ni-plated steel sheet that forms the battery case, the weld metal will still be exposed on the inner surface of the battery. In this case, if the weld metal comes into contact with the electrolyte, Fe, one of the components of the weld metal, will leach out. Thus, when manufacturing battery cases by welding, it is important to suppress the leaching of Fe from the weld.

[0011] Furthermore, in cylindrical batteries, as shown in Patent Document 3 above, a crimped joint with a gasket in between can be used to prevent contact between the cut end surface of the Ni-plated steel sheet and the electrolyte. Therefore, cylindrical batteries avoid the Fe elution problem described above.

[0012] In rectangular battery cases, one method of mechanically joining the container and lid instead of welding is the crimping joint shown in Patent Document 4. By using such a crimping joint, it is possible to prevent the cut edges of the steel plate from being exposed inside the battery case. However, when crimping, the radius of the crimped corner needs to be about 5 mm. Therefore, battery cases using crimping joints have a reduced internal volume compared to deep-drawn cases where the corner radius can be 1 mm. For this reason, the crimping joint used in Patent Document 4 is worth considering for the purpose of increasing volumetric energy density. In addition, the thickness of the crimped part needs to be about three times the thickness of the plate, resulting in a structure where the crimped part protrudes from the outer circumference of the battery case. As a result, the gap between adjacent cells becomes larger, which is something that needs to be considered from the perspective of saving space in the battery.

[0013] Based on the above circumstances, if the elution of Fe in the welded area can be suppressed when manufacturing lithium-ion battery cases using Ni-plated steel sheets by welding, it is thought that Ni-plated steel sheets can be applied to prismatic battery cases, which would contribute to increasing the size of the battery.

[0014] Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to provide a battery case for a lithium-ion battery and a lithium-ion battery that can suppress the elution of Fe from the welded part in a battery case for a lithium-ion battery manufactured by welding Ni-plated steel sheets.

[0015] While manufacturing battery cases for lithium-ion batteries by welding using Ni-plated steel sheets, the inventors investigated the corrosion resistance of the welded areas and discovered, as detailed below, that the elution of Fe into the electrolyte decreases as the Ni concentration in the weld metal increases. Based on this finding, the inventors conceived the idea that by adjusting the Ni concentration in the weld metal generated by welding, it would be possible to suppress the elution of Fe from the welded area, i.e., the weld metal and the edge of the Ni-plated steel sheet, and thus completed the present invention as detailed below. The gist of the present invention, completed based on this idea, is as follows.

[0016] (1) A battery case for a lithium-ion battery comprising a lid and a case body connected to the lid via a weld metal, wherein each of the lid and the case body is made of a Ni-plated steel sheet having a steel sheet as a base material and Ni-based plating layers located on two surfaces facing each other in the thickness direction of the steel sheet, the Ni content of the steel sheet is 0.1% by mass or more, and the amount of Ni-based plating layer attached is 7.0 g / m² in terms of metallic Ni per side of the Ni-plated steel sheet. ２(1) A battery case for a lithium-ion battery, wherein the Ni concentration in the weld metal is 1.0% by mass or more, and the lid, the weld metal, and the case body are arranged in order in the thickness direction of the lid. (2) The battery case for a lithium-ion battery according to (1), wherein the weld metal is a fully fused weld metal that extends over the entire thickness of the case body. (3) The Ni content of the steel plate is 5.0% by mass or less, and the amount of Ni-based plating layer attached is 30.0 g / m² in terms of metallic Ni per side of the Ni-plated steel plate. ２A battery case for a lithium-ion battery according to (1) or (2), wherein the Ni concentration in the weld metal is 8.0% by mass or less. (4) A battery case for a lithium-ion battery according to any one of (1) to (3), wherein the thickness of the steel plate is in the range of 0.10 to 1.00 mm. (5) A battery case for a lithium-ion battery according to any one of (1) to (4), wherein the battery case has an Fe-Ni alloy oxide film disposed on the base material of the case body at a position adjacent to the weld metal on the inner surface of the battery case, and the thickness of the oxide film is in the range of 10 to 50 nm. (6) A battery case for a lithium-ion battery according to any one of (1) to (5), wherein the Fe-Ni alloy oxide film is disposed on the surface of the weld metal on the inner surface of the battery case, and the thickness of the oxide film is in the range of 10 to 50 nm. (7) A battery case for a lithium-ion battery according to any one of (1) to (6), wherein the steel sheet has a chemical composition in mass%, containing C: 0.001 to 0.250%, Si: 0.002 to 0.100%, Mn: 0.05 to 0.80%, Ni: 0.1 to 5.0%, Al: 0.005 to 0.050%, P: 0.001 to 0.020%, S: 0.0001 to 0.2500%, N: 0.001 to 0.040%, with the remainder being Fe and impurities. (8) A battery case for a lithium-ion battery according to any one of (1) to (6), wherein the steel sheet has a chemical composition in mass%, containing C: 0.001 to 0.250%, Si: 0.002 to 0.100%, Mn: 0.05 to 0.80%, Ni: 0.1 to 5.0%, Al: 0.005 to 0.050%, P: 0.001 to 0.020%, S: 0.0001 to 0.2500%, and N: 0.001 to 0.040%, and further containing one or more elements selected from the group consisting of element groups A to E below, with the remainder being Fe and impurities.[Element group A]: One or more elements selected from the group consisting of Sn: 2.0% or less, Ti: 1.0% or less, and Cu: 1.50% or less [Element group B]: Nb: 0.200% or less [Element group C]: Mo: 3.0% or less [Element group D]: One or more elements selected from the group consisting of V: ​​0.10% or less, As: 0.10% or less, Sb: 0.50% or less, Ca: 0.050% or less, and Mg: 0.0500% or less [Element group E]: B: 0.0030% or less (9) The battery case for a lithium-ion battery according to (8), wherein the steel sheet has a chemical composition containing element group A. (10) The battery case for a lithium-ion battery according to (8), wherein the steel sheet has a chemical composition containing element group B. (11) The battery case for a lithium-ion battery according to (8), wherein the steel plate has a chemical composition containing the element group C. (12) The battery case for a lithium-ion battery according to (8), wherein the steel plate has a chemical composition containing the element group D. (13) The battery case for a lithium-ion battery according to (8), wherein the steel plate has a chemical composition containing the element group E. (14) The battery case for a lithium-ion battery according to any one of (1) to (13), wherein the Ni-based plating layer is a Ni plating layer. (15) The battery case for a lithium-ion battery according to any one of (1) to (13), wherein the Ni-based plating layer is a plating layer having a chemical composition in mass% of Fe: 1.0 to 20.0%, with the remainder being Ni and impurities. (16) A battery case for a lithium-ion battery according to any one of (1) to (13), wherein the Ni-based plating layer contains Fe: 1.0 to 20.0% by mass, and further contains one or more elements selected from the group consisting of element group F to element group H, with the remainder being Ni and impurities. [Element group F]: One or more elements selected from the group consisting of W: 50.0% or less, Co: 5.0% or less, and Mo: 30.0% or less [Element group G]: One or two elements selected from the group consisting of Sn: 0.1000% or less and Zn: 0.1000% or less [Element group H]: One or two elements selected from the group consisting of C: 0.01% or less and S: 0.01% or less (17) The Ni-based plating layer has a chemical composition containing element group F, the battery case for lithium-ion batteries according to (16).(18) The battery case for a lithium-ion battery according to (16), wherein the Ni-based plating layer has a chemical composition containing the element group G. (19) The battery case for a lithium-ion battery according to (16), wherein the Ni-based plating layer has a chemical composition containing the element group H. (20) The battery case for a lithium-ion battery according to any one of (1) to (19), wherein the welded part is a laser-welded part. (21) A lithium-ion battery having the battery case for a lithium-ion battery according to any one of (1) to (20).

[0017] As described above, according to the present invention, in a battery case for a lithium-ion battery manufactured by welding Ni-plated steel sheets, it is possible to suppress the elution of Fe from the cross-section and welded parts when the steel sheet is cut in the thickness direction.

[0018] This is a graph showing the relationship between the Ni concentration in the weld metal and the amount of Fe leached into the electrolyte. This is a graph showing the distribution of elements in the depth direction in Ni-containing weld metal. This is a schematic explanatory diagram showing a battery case for a lithium-ion battery according to an embodiment of the present invention and a lithium-ion battery using such a battery case. This is a schematic explanatory diagram showing a battery case for a lithium-ion battery according to the same embodiment and a lithium-ion battery using such a battery case. This is a schematic explanatory diagram showing a Ni-plated steel sheet used as the material for the battery case for a lithium-ion battery according to the same embodiment. This is a schematic diagram for explaining the structure near the weld of the battery case for a lithium-ion battery according to the same embodiment. This is a schematic diagram for explaining the structure near the weld of the battery case for a lithium-ion battery according to the same embodiment. This is a schematic diagram for explaining the structure near the weld of the battery case for a lithium-ion battery according to the same embodiment. This is a schematic diagram for explaining the structure near the weld of the battery case for a lithium-ion battery according to the same embodiment. This is a schematic diagram for explaining the structure near the weld of the battery case for a lithium-ion battery according to the same embodiment. This is a schematic explanatory diagram showing the structure near the weld of the battery case for a lithium-ion battery according to the same embodiment. This is a schematic explanatory diagram showing the structure of the evaluation material prepared in Test Example 1. This is a schematic diagram illustrating the structure of the evaluation material prepared in Test Example 2.

[0019] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In this specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant explanations are omitted. In the embodiments shown below, the notation "numerical value A to numerical value B" indicates that it is between "numerical value A" and "numerical value B".

[0020] (Relationship between Ni concentration in weld metal and amount of Fe leached into electrolyte) Before describing the lithium-ion battery case and lithium-ion battery according to the present invention, the relationship between Ni concentration in weld metal and amount of Fe leached into electrolyte, as discovered by the inventors, will be explained in detail below.

[0021] The inventors investigated the corrosion resistance of welded joints when manufacturing battery cases for lithium-ion batteries by welding using Ni-plated steel sheets. In this investigation, the inventors found that as the Ni concentration in the weld metal formed in the weld increased, the amount of Fe leached into the electrolyte decreased. Therefore, the inventors conducted the following verification to quantify the amount of Fe leached in this phenomenon.

[0022] The inventors prepared Ni-plated steel sheets (with the cross-section in the thickness direction of the steel sheet in its as-cut state, without Ni-based plating) using steel materials (manufactured by Nippon Steel Corporation) in which the amount of Ni in the steel was controlled to various values ​​as a base material, and used these Ni-plated steel sheets to fabricate multiple battery cases by laser welding. The welded joint of each battery case was measured in plan view at 1 cm ２ The sample was cut to a size suitable for measurement. The Ni concentration of the weld metal in the cut sample was measured using an electron probe microanalyzer (EPMA) mounted on a scanning electron microscope (SEM) (for example, a JXA-8230 manufactured by JEOL Corporation). The cut sample was also subjected to a lithium-ion battery electrolyte (1 mol / L LiPF). ６EC:DEC (1:1 v / v%) 1 mL (80 °C) was immersed for 500 hours, and the Fe concentration in the electrolytic solution was measured by inductively coupled plasma mass spectrometry (ICP-MS). The Fe concentration in the electrolytic solution identified by measurement with ICP-MS was taken as the amount of Fe eluted into the electrolytic solution.

[0023] The obtained results are shown in Fig. 1. Fig. 1 is a graph showing the relationship between the Ni concentration in the weld metal and the amount of Fe eluted into the electrolytic solution. In Fig. 1, the horizontal axis is the Ni concentration in the weld metal (unit: mass %), and the vertical axis is the amount of Fe eluted into the electrolytic solution (unit: μg / cm ２ )

[0024] As is clear from Fig. 1, when Ni is not contained in the weld metal, the amount of Fe elution was 90 μg / cm ２ . Also, it can be seen that the amount of Fe elution rapidly decreases as Ni is contained in the weld metal. Further, it can be seen that when the Ni concentration in the weld metal becomes 1 mass % or more, the amount of Fe elution is suppressed to a value of 20 μg / cm ２ or less.

[0025] Next, the present inventors measured the distribution state of elements in the depth direction for a weld metal having a Ni concentration of 1.0 mass % using X-ray photoelectron spectroscopy (XPS). The obtained results are shown in Fig. 2. Fig. 2 is a graph showing the distribution state of elements in the depth direction in a weld metal containing Ni. In Fig. 2, the horizontal axis is the sputter depth from the surface of the weld metal (SiO ２ conversion value, unit: nm), and the vertical axis is the concentration (unit: atomic %).

[0026] As is clear from FIG. 2, elements O and Fe are present near the surface of the weld metal. Also, it can be seen that as the sputter depth increases, the concentration of element O decreases while the concentration of Fe increases. Further, as the sputter depth increases, element Ni begins to be observed. From such analysis results, it is understood that an oxide film of Fe and Ni exists on the surface of the weld metal, and the film thickness is about several tens of nm. From such findings, it was presumed that not only the Ni concentration in the weld metal but also such an Fe—Ni alloy-based oxide film contributes to the effect of suppressing the elution of Fe.

[0027] In view of the above findings, the inventors adjusted the thickness of the Ni-based plating layer and the welding range of the steel sheet so that the Ni concentration in the weld metal would be 1.0% or more in a battery case for a lithium ion battery manufactured by welding the cross section when a Ni-plated steel sheet was cut in the plate thickness direction, and obtained the idea of covering the cut end face of the steel sheet with such weld metal. Hereinafter, the battery case for a lithium ion battery and the lithium ion battery according to an embodiment of the present invention, which were completed based on such an idea, will be described in detail.

[0028] (Regarding the lithium ion battery) <Regarding the overall configuration of the lithium ion battery> First, the overall configuration of the lithium ion battery according to an embodiment of the present invention will be described with reference to FIGS. 3 to 4B. FIGS. 3 to 4B are explanatory views schematically showing a battery case for a lithium ion battery according to the present embodiment and a lithium ion battery using such a battery case. Hereinafter, for convenience, the description may be made using the coordinate system shown in FIG. 3.

[0029] As schematically shown in FIG. 3, a lithium ion battery 1 according to the present embodiment includes a battery unit 3 having a positive electrode, a negative electrode, and a separator, and an electrolytic solution 5 containing a lithium salt, which are housed in a battery case 10 for a lithium ion battery according to the present embodiment (hereinafter simply abbreviated as “battery case 10”). Here, the battery case 10 according to the present embodiment has a case main body portion 11 and a lid portion 13.

[0030] [Regarding the battery unit 3 and the electrolyte 5] Here, the positive electrode (not shown), negative electrode (not shown), separator (not shown), and various active materials (not shown) provided on the positive and negative electrodes that constitute the battery unit 3 are not particularly limited. For each of these members that constitute the battery unit 3, various ones used in lithium-ion batteries can be appropriately used. Also, the specific structure of the battery unit 3 is not particularly limited, and various structures can be adopted.

[0031] Also, the specific shape and size of the battery unit 3 are not particularly limited. In FIG. 3, for the sake of convenience, the battery unit 3 having a rectangular shape is shown, but the shape of the battery unit 3 may be a cylindrical shape or other shapes.

[0032] Also, regarding the electrolyte 5, it only needs to contain a lithium salt that can generate lithium ions, and electrolytes containing various lithium salts (especially lithium salts containing fluorine) can be appropriately used. Examples of such lithium salts include LiPF ６ , LiBF ４ , LiN(SO ２ CF ３ ) ２ (Also called LiTFSI).

[0033] [Regarding the battery case 10] As shown in FIG. 3, the battery case 10 in the lithium-ion battery 1 according to the present embodiment houses the above-described battery unit 3 and electrolyte 5 inside. Such a battery case 10 is composed of a case main body portion 11 and a lid portion 13.

[0034] The case body 11 of the battery case 10 is a hollow member having an internal space capable of housing the battery unit 3 and the electrolyte 5. The case body 11 is composed of a bottom portion (not shown) and side portions. In Figure 1, the case body 11 has a rectangular bottom portion (not shown) and four side portions that create an internal space for housing the battery unit 3 and the electrolyte 5. After the battery unit 3 and the electrolyte 5 are housed in the internal space of the case body 11, the opening of the case body 11 is closed by the lid portion 13, as shown in Figure 3.

[0035] In Figure 3, the case body 11 of the battery case 10 is shown to have a rectangular shape. However, the specific shape of the case body 11 is not particularly defined. The case body 11 can have any shape as long as it is capable of accommodating the battery unit 3 and the electrolyte 5. A case body 11 having such a shape can be manufactured, for example, by deep drawing of the steel material.

[0036] Furthermore, the lid portion 13 is provided with an injection port 15, which is an opening for injecting the electrolyte into the storage case, and after the electrolyte is injected, the injection port 15 is closed with the injection port cover 17.

[0037] In the battery case 10 shown in Figure 3, after the battery unit 3 is housed in the internal space of the case body 11, the opening of the case body 11 is closed by the lid 13 and sealed by welding. As a result, a welded portion 21 is formed at the welded joint between the body 11 and the lid 13, as schematically shown in Figure 4A.

[0038] Subsequently, electrolyte 5 is injected into the battery case 10 through the injection port 15 provided in the lid 13. After the electrolyte 5 is injected, the injection port 15 on the lid 13 is closed by the injection port cover 17, and various joining processes such as welding or sealing with blind rivets are performed. As a result, the case body 11 and the lid 13 of the battery case 10 are integrated. Consequently, as schematically shown in Figure 4A, a joining processing section 23 is formed at the joint between the lid 13 and the injection port cover 17.

[0039] Here, various known welding methods can be used for welding the case body portion 11 and the lid portion 13 of the battery case 10. One such welding method is laser welding.

[0040] Furthermore, in Figures 3 to 4A, for illustrative purposes, the case body 11 of the battery case 10 is depicted as being composed of a single component. However, the case body 11 may be composed of a single component, or it may be composed of multiple components joined together by various welding methods (for example, seam welding or laser welding).

[0041] For example, when forming the side surface of a case body 11 having a rectangular shape as shown in Figure 3, two members are prepared by bending a steel plate, which will be the material for the battery case 10, into a roughly U-shape. These roughly U-shaped members are then butted together, overlapping some of their ends as needed, to form the shape of the side surface of the case body 11. The butt joints are then welded together by overlap seam welding or laser welding to form a joint. Alternatively, the steel plate that will be the material for the battery case is processed into a roughly cylindrical shape by bending it four times. The ends of the steel plates are then butted together, overlapping some of them as needed, to form the shape of the side surface of the case body 11. The butt joints are then welded together by overlap seam welding or laser welding to form a joint. After that, a steel plate that will form the bottom surface can be welded to the side surface of the case body 11 obtained as described above by laser welding or the like. In this case, the steel plate that will form the bottom surface should be shaped to match the shape of the body that will form the side surface of the case body 11. When the case body 11 is manufactured in this manner, the resulting battery case 10 will have welded joints 21 formed on the sides and bottom of the case body 11, as schematically shown in Figure 4B.

[0042] <Regarding the steel material used for the case body 11 and lid 13> Next, the steel material used for the case body 11 and lid 13 in the battery case 10 according to this embodiment will be described in detail with reference to Figure 5. Figure 5 is a schematic explanatory diagram showing a Ni-plated steel sheet used as the material for the battery case for a lithium-ion battery according to this embodiment.

[0043] As schematically shown in Figure 5, the Ni-plated steel sheet 100 used in this embodiment has a base steel sheet 101 and a Ni-based plating layer 103 located on both surfaces of the base steel sheet 101.

[0044] As explained earlier, in the battery case 10 according to this embodiment, the manufacturing process is controlled so that the Ni concentration in the weld metal at the welded joint is 1.0 mass% or more. In order to achieve a Ni concentration of 1.0 mass% or more in the weld metal, the battery case 10 according to this embodiment uses a specific Ni-plated steel sheet as the material for the case body 11 and the lid 13. This Ni-plated steel sheet is made by using a Ni-containing steel material with a specific Ni content as the base steel sheet, and providing a Ni-based plating layer on its surface to achieve a specific amount of Ni adhesion.

[0045] ◇Regarding the base steel sheet 101, the base steel sheet 101, which is the base material for the Ni-plated steel sheet 100, will be explained in detail below.

[0046] ≪Regarding the chemical composition of the base steel sheet 101≫ In order to achieve a Ni concentration of 1.0% or more in the weld metal as described above, the Ni content of the base steel sheet 101 according to this embodiment is 0.1% by mass or more. Furthermore, it is preferable that the Ni content of the steel sheet is 5.0% by mass or less. More specifically, according to one embodiment, the chemical composition of the base steel sheet 101 according to this embodiment is, in mass%, C: 0.001 to 0.250%, Si: 0.002 to 0.100%, Mn: 0.05 to 0.80%, Ni: 0.1 to 5.0%, Al: 0.005 to 0.050%, P: 0.001 to 0.020%, S: 0.0001 to 0.2500%, N: 0.001 to 0.040%, with the remainder being Fe and impurities.

[0047] Furthermore, according to another embodiment, the chemical composition of the base steel sheet 101 according to this embodiment contains, by mass%, C: 0.001 to 0.250%, Si: 0.002 to 0.100%, Mn: 0.05 to 0.80%, Ni: 0.1 to 5.0%, Al: 0.005 to 0.050%, P: 0.001 to 0.020%, S: 0.0001 to 0.2500%, and N: 0.001 to 0.040%, and further contains one or more elements selected from the group consisting of the following element groups A to E, with the remainder being Fe and impurities. The above-mentioned element groups A to E, as mentioned in another embodiment of the chemical composition of the base steel sheet 101 according to this embodiment, can be said to be elements that can be arbitrarily included in the chemical composition of the base steel sheet 101 according to this embodiment.

[0048] [Element Group A]: One or more elements selected from the group consisting of Sn: 2.0% or less, Ti: 1.0% or less, and Cu: 1.50% or less. [Element Group B]: Nb: 0.200% or less. [Element Group C]: Mo: 3.0% or less. [Element Group D]: One or more elements selected from the group consisting of V: ​​0.10% or less, As: 0.10% or less, Sb: 0.50% or less, Ca: 0.050% or less, and Mg: 0.0500% or less. [Element Group E]: B: 0.0030% or less.

[0049] [C: 0.001 to 0.250 mass%] Since carbon is an element that dissolves in steel and improves its strength, it is included in a predetermined amount or more. If the carbon content in the base steel sheet 101 is less than 0.001 mass%, the above-mentioned strength improvement effect cannot be achieved. For this reason, the carbon content in the base steel sheet 101 is 0.001 mass% or more. Furthermore, in order to achieve both the strength of the steel and the assurance of workability, it is preferable that the carbon content in the base steel sheet 101 be 0.005 mass% or more. By having a carbon content of 0.005 mass% or more, it is possible to suppress the coarsening of ferrite crystal grains and suppress surface roughness of the steel sheet that may occur during processing. The carbon content in the base steel sheet 101 is more preferably 0.015 mass% or more, and even more preferably 0.020 mass% or more.

[0050] On the other hand, if the carbon content in the base steel sheet 101 exceeds 0.250 mass%, the coarsening of the ferrite crystal grains becomes significant, and the strength as steel increases too much, which reduces workability (especially deep drawing workability), and is therefore undesirable. For this reason, the carbon content in the base steel sheet 101 should be 0.250 mass% or less. Preferably, the carbon content in the base steel sheet 101 is 0.200 mass% or less, more preferably 0.100 mass% or less, even more preferably 0.065 mass% or less, and even more preferably 0.050 mass% or less.

[0051] [Si: 0.002 to 0.100 mass%] Since Si is an element that improves the strength of steel, it is included in a predetermined amount or more. If the Si content in the base steel sheet 101 is less than 0.002 mass%, the strength improvement effect described above cannot be achieved. For this reason, the Si content in the base steel sheet 101 is set to 0.002 mass% or more. Furthermore, in order to achieve both the strength of the steel and the assurance of workability, the Si content in the base steel sheet 101 is preferably 0.005 mass% or more, and more preferably 0.010 mass% or more.

[0052] On the other hand, if the Si content in the base steel sheet 101 is excessive, it reduces the surface treatability of the steel sheet. This reduction in surface treatability becomes significant when the Si content exceeds 0.100 mass%. Therefore, the Si content in the base steel sheet 101 should be 0.100 mass% or less. Preferably, the Si content in the base steel sheet 101 is 0.050 mass% or less, and more preferably 0.020 mass% or less.

[0053] [Mn: 0.05 to 0.80 mass%] Mn is an effective element in preventing red-hot brittleness during hot rolling, which is caused by S inevitably present in the base steel sheet 101. This effect of preventing red-hot brittleness can be achieved by setting the Mn content in the base steel sheet 101 to 0.05 mass% or more. For this reason, the Mn content in the base steel sheet 101 is set to 0.05 mass% or more. Preferably, the Mn content in the base steel sheet 101 is 0.10 mass% or more, and more preferably 0.15 mass% or more.

[0054] On the other hand, if the Mn content in the base steel sheet 101 becomes excessive, the steel sheet hardens, and its workability (especially deep-drawing workability) decreases. Deep-drawing workability also decreases with increasing the C content in the base steel sheet 101, so when deep-drawing workability is important, it is preferable to avoid increasing both the Mn content and the C content. The hardening of the steel sheet due to Mn as described above becomes noticeable when the Mn content in the base steel sheet 101 exceeds 0.80 mass%. Therefore, the Mn content in the base steel sheet 101 should be 0.80 mass% or less. Preferably, the Mn content in the base steel sheet 101 is 0.40 mass% or less, and more preferably 0.25 mass% or less.

[0055] [Ni: 0.1% by mass or more] Ni is an element that generally improves the corrosion resistance of steel. Furthermore, by having the base steel plate 101 itself contain Ni, it becomes easier to make the Ni concentration in the weld metal generated during welding 1.0% by mass or more, thereby improving the corrosion resistance of the welded part of the battery case 10. The above-mentioned effect of improving the corrosion resistance of the welded part can be achieved by making the Ni content of the base steel plate 101 0.10% by mass or more. For this reason, the Ni content of the base steel plate 101 is set to 0.1% by mass or more.

[0056] Furthermore, Ni is an element that suppresses the elution of Fe into the electrolyte of a lithium-ion battery by forming an Fe-Ni alloy oxide film on the surface of the steel plate when the steel plate is heated. In the welded portion of the battery case 10 according to this embodiment, even if there is a portion of the cut end face of the Ni-plated steel plate 100 that is not covered by the weld metal, such an Fe-Ni alloy oxide film is formed on the surface of the cut end face (end face 31 in Figure 6A, which will be described in detail below) that is not covered by the weld metal, thereby suppressing the elution of Fe from the end face 31. This oxide film formation effect can be achieved by setting the Ni content of the base steel plate 101 to 0.5% by mass or more. Therefore, it is preferable that the Ni content of the base steel plate 101 be 0.5% by mass or more.

[0057] The Ni content in the base steel sheet 101 is more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more.

[0058] On the other hand, if the Ni content in the base steel sheet 101 exceeds 5.0% by mass, the effects of improving the corrosion resistance of the welded joint and forming an oxide film approach saturation, and the manufacturing cost to achieve the desired Ni content may increase. Therefore, it is preferable that the Ni content in the base steel sheet 101 be 5.0% by mass or less. More preferably, the Ni content in the base steel sheet 101 is 4.0% by mass or less, and even more preferably 3.5% by mass or less.

[0059] [Al: 0.005 to 0.050 mass%] Al is an element that deoxidizes steel. In addition, Al forms AlN with solid-solution N in the steel, fixing the solid-solution N. As a result, Al suppresses age hardening. This age hardening suppression effect can be achieved by setting the Al content in the base steel sheet 101 to 0.005 mass% or more. Therefore, the Al content in the base steel sheet 101 is set to 0.005 mass% or more. The Al content is preferably 0.008 mass% or more, more preferably 0.010 mass% or more, and even more preferably 0.015 mass% or more.

[0060] On the other hand, if the Al content of the base steel sheet 101 exceeds 0.050 mass%, not only will the manufacturing cost of the battery case 10 increase, but alumina clusters will be formed in the base steel sheet 101, causing scratches on the surface of the base steel sheet 101. From this viewpoint, the Al content of the base steel sheet 101 should be 0.050 mass% or less. Preferably, the Al content of the base steel sheet 101 is 0.023 mass% or less, more preferably 0.020 mass% or less, and even more preferably 0.018 mass% or less.

[0061] [P: 0.001 to 0.020 mass%] P is an element that is inevitably contained in steel. It is possible to reduce the P content in steel by dephosphorization treatment in the steelmaking process. However, reducing the P content to less than 0.001 mass% is undesirable because it excessively increases the manufacturing cost of the steel. From this viewpoint, the P content in the base steel sheet 101 is set to 0.001 mass% or more. Considering the manufacturing cost, the P content in the base steel sheet 101 may be 0.002 mass% or more, or 0.005 mass% or more.

[0062] On the other hand, since P is an element that improves the strength of steel, it may be included in the base steel sheet 101 up to a maximum of 0.020 mass%. However, P is also an element that embrittles steel and reduces its workability. Therefore, if the intention is not to ensure strength with P, it is preferable that the P content be 0.012 mass% or less. Furthermore, from the viewpoint of toughness and workability, it is preferable that the P content be even lower.

[0063] [S: 0.0001 to 0.0250 mass%] S is an element that is inevitably contained in steel. It is possible to reduce the S content in steel by desulfurization treatment in the steelmaking process. However, reducing the S content to less than 0.001 mass% is undesirable because it excessively increases the manufacturing cost of the steel. Therefore, the S content in the base steel sheet 101 is set to 0.0001 mass% or more. Considering the manufacturing cost, the S content in the base steel sheet 101 may be 0.0002 mass% or more, 0.0005 mass% or more, 0.0010 mass% or more, 0.0020 mass% or more, or 0.0050 mass% or more.

[0064] On the other hand, if the sulfur content of the base steel sheet 101 exceeds 0.0250 mass%, it can cause red-hot brittleness during hot rolling or MnS precipitation during continuous casting, leading to hot brittleness and slab cracking. Therefore, the sulfur content of the base steel sheet 101 should be 0.0250 mass% or less. Furthermore, the lower the sulfur content of the base steel sheet 101, the better.

[0065] [N: 0.001 to 0.040 mass%] N is an element that is inevitably contained in steel. Reducing the N content to less than 0.001 mass% is undesirable because it excessively increases the manufacturing cost of the steel. Therefore, the N content in the base steel sheet 101 is set to 0.001 mass% or more. The N content of the base steel sheet 101 is preferably 0.002 mass% or more, and more preferably 0.003 mass% or more.

[0066] On the other hand, if the N content of the base steel sheet 101 exceeds 0.040 mass%, nitrides and carbonitrides are formed in the steel, which degrades the material properties of the steel sheet and is therefore undesirable. For this reason, the N content of the base steel sheet 101 should be 0.040 mass% or less. Preferably, the N content of the base steel sheet 101 is 0.020 mass% or less, more preferably 0.010 mass% or less, and even more preferably 0.005 mass% or less.

[0067] In the base steel sheet 101 according to this embodiment, the remainder of the above C, Si, Mn, Ni, Al, P, S, and N is Fe and impurities. Here, "impurities" refers to components that are mixed into the steel sheet during the industrial manufacture of the steel sheet due to raw materials such as ore and scrap, or due to various factors in the manufacturing process.

[0068] Because the base steel sheet 101 according to this embodiment has the above-described chemical composition, the Ni-plated steel sheet 100 according to this embodiment can exhibit even better corrosion resistance.

[0069] Next, in a different embodiment of this invention, the element groups A to E that may be present in the chemical composition of the base steel sheet 101 will be described in detail.

[0070] In addition, in the base steel sheet 101 according to another embodiment of this embodiment, if at least one of the elements belonging to element groups A to E below is included, it is preferable that at least one of the elements belonging to element groups A to E below is included within the following content range, and the total content is 8.503% by mass or less.

[0071] By keeping the total content of elements belonging to element groups A to E to 8.503% by mass or less, it becomes possible to enjoy the effects exhibited by the addition of each element, as detailed below, without impairing each other. The total content of elements belonging to element groups A to E is preferably 5.000% by mass or less, and more preferably 4.000% by mass or less.

[0072] ◇Element Group A In another embodiment of the base steel sheet 101 according to this embodiment, element group A that the base steel sheet 101 may contain will be described. At least one of the elements of element group A shown below may be contained in the base steel sheet 101 in place of a portion of the remaining Fe. [Element Group A]: One or more elements selected from the group consisting of Sn: 2.0% or less, Ti: 1.0% or less, and Cu: 1.50% or less.

[0073] [Sn: 0 to 2.0 mass%] In the base steel sheet 101 according to this embodiment, it is possible to use it as a steel sheet even without containing Sn, so the lower limit of its content is 0 mass%. On the other hand, Sn is an element that can improve the corrosion resistance (especially the external corrosion resistance) of the base steel sheet 101 under various corrosive environments. For this reason, the Sn content can be greater than 0 mass%. This effect of improving corrosion resistance is manifested when the Sn content in the base steel sheet 101 is 0.1 mass% or more. For this reason, when Sn is included in the base steel sheet 101, it is preferable that the Sn content be 0.1 mass% or more. More preferably, the Sn content in the base steel sheet 101 is 0.2 mass% or more.

[0074] On the other hand, if the Sn content in the base steel sheet 101 exceeds 2.0% by mass, the above-mentioned effect of improving corrosion resistance will saturate, and the manufacturing cost of the steel will increase. Therefore, when Sn is included in the base steel sheet 101, it is preferable that the Sn content be 2.0% by mass or less. More preferably, the Sn content in the base steel sheet 101 is 1.0% by mass or less.

[0075] [Ti: 0 to 1.0 mass%] In the base steel sheet 101 according to this embodiment, it is possible that Ti may not be contained, so the lower limit of its content is 0 mass%. On the other hand, Ti is an element that improves the strength of the steel sheet and prevents a decrease in the corrosion resistance (especially the outer corrosion resistance) of the base steel sheet 101 by forming carbides with C in the base steel sheet 101. For this reason, the Ti content may be greater than 0 mass%. This effect is manifested when the Ti content in the base steel sheet 101 is 0.1 mass% or more. For this reason, when Ti is included in the base steel sheet 101, it is preferable that the Ti content be 0.1 mass% or more. More preferably, the Ti content in the base steel sheet 101 is 0.3 mass% or more.

[0076] On the other hand, if the Ti content in the base steel sheet 101 exceeds 1.0% by mass, the above effects become saturated and manufacturing costs increase. Therefore, when Ti is included in the base steel sheet 101, it is preferable that the Ti content be 1.0% by mass or less. More preferably, the Ti content in the base steel sheet 101 is 0.7% by mass or less.

[0077] [Cu: 0 to 1.50 mass%] In the base steel sheet 101 according to this embodiment, it is possible that it does not contain Cu, so the lower limit of its content is 0 mass%. On the other hand, Cu is an element that improves the corrosion resistance of steel (especially external corrosion resistance). For this reason, the Cu content can be greater than 0 mass%. This effect of improving corrosion resistance is exhibited when the Cu content in the base steel sheet 101 is 0.01 mass% or more. For this reason, when Cu is included in the base steel sheet 101, it is preferable that the Cu content be 0.01 mass% or more. More preferably, the Cu content in the base steel sheet 101 is 0.02 mass% or more.

[0078] On the other hand, if the Cu content in the base steel sheet 101 exceeds 1.50% by mass, the above-mentioned effect of improving corrosion resistance saturates, and manufacturing costs increase. Therefore, when Cu is included in the base steel sheet 101, it is preferable that the Cu content be 1.50% by mass or less. More preferably, the Cu content in the base steel sheet 101 is 1.00% by mass or less.

[0079] ◇Element Group B In another embodiment of the base steel sheet 101 according to this embodiment, element group B that the base steel sheet 101 may contain will be described. The elements of element group B shown below are elements that may be contained in the base steel sheet 101 in place of a portion of the remaining Fe. [Element Group B]: Nb: 0.200% or less

[0080] [Nb: 0 to 0.200 mass%] In the base steel sheet 101 according to this embodiment, it is possible that it does not contain Nb, so the lower limit of its content is 0 mass%. On the other hand, Nb is an element that forms fine carbides in steel and improves the toughness of steel through its grain-refining effect. For this reason, the Nb content can be greater than 0 mass%. This toughness improvement effect is manifested when the Nb content in the base steel sheet 101 is 0.050 mass% or more. For this reason, when Nb is included in the base steel sheet 101, it is preferable that the Nb content be 0.050 mass% or more. More preferably, the Nb content in the base steel sheet 101 is 0.070 mass% or more.

[0081] On the other hand, if the Nb content in the base steel sheet 101 exceeds 0.200 mass%, the carbides that are formed become coarser, and the toughness of the steel decreases. Therefore, when Nb is included in the base steel sheet 101, it is preferable that the Nb content be 0.200 mass% or less. More preferably, the Nb content in the base steel sheet 101 is 0.080 mass% or less.

[0082] ◇Element Group C In another embodiment of the base steel sheet 101 according to this embodiment, element group C that the base steel sheet 101 may contain will be described. The elements of element group C shown below are elements that may be contained in the base steel sheet 101 in place of a portion of the remaining Fe. [Element Group C]: Mo: 3.0% or less

[0083] [Mo: 0 to 3.0 mass%] In the base steel sheet 101 according to this embodiment, it is possible that Mo may not be contained, so the lower limit of its content is 0 mass%. On the other hand, Mo is an element that improves the electrolyte resistance of the base steel sheet 101. For this reason, the Mo content may be greater than 0 mass%. This effect of improving electrolyte resistance is manifested when the Mo content in the base steel sheet 101 is 0.2 mass% or more. For this reason, when Mo is included in the base steel sheet 101, it is preferable that the Mo content be 0.2 mass% or more. More preferably, the Mo content in the base steel sheet 101 is 0.5 mass% or more.

[0084] On the other hand, if the Mo content in the base steel sheet 101 exceeds 3.0% by mass, the above-mentioned effect of improving electrolyte resistance becomes saturated, and manufacturing costs increase. Therefore, when Mo is included in the base steel sheet 101, it is preferable that the Mo content be 3.0% by mass or less. More preferably, the Mo content in the base steel sheet 101 is 2.0% by mass or less.

[0085] ◇Element Group D In another embodiment of the base steel sheet 101 according to this embodiment, element group D that the base steel sheet 101 may contain will be described. At least one of the elements of element group D shown below may be contained in the base steel sheet 101 in place of a portion of the remaining Fe. [Element Group D]: One or more elements selected from the group consisting of V: ​​0.10% or less, As: 0.10% or less, Sb: 0.50% or less, Ca: 0.050% or less, and Mg: 0.0500% or less.

[0086] [V: 0 to 0.10 mass%] In the base steel sheet 101 according to this embodiment, it is possible that V may not be contained, so the lower limit of its content is 0 mass%. On the other hand, V is an element that improves the corrosion resistance of the processed part (processed part) in a member obtained by processing the base steel sheet 101. For this reason, the content of V may be greater than 0 mass%. This effect of improving the corrosion resistance of the processed part is manifested when the V content in the base steel sheet 101 is 0.01 mass% or more. For this reason, when V is included in the base steel sheet 101, it is preferable that the V content be 0.01 mass% or more. The V content in the base steel sheet 101 is more preferably 0.04 mass% or more.

[0087] On the other hand, if the V content in the base steel sheet 101 exceeds 0.10% by mass, the above-mentioned effect of improving the corrosion resistance of the processed part saturates, and the manufacturing cost increases. Therefore, when V is included in the base steel sheet 101, it is preferable that the V content be 0.10% by mass or less. More preferably, the V content in the base steel sheet 101 is 0.08% by mass or less.

[0088] [As: 0 to 0.10 mass%] In the base steel sheet 101 according to this embodiment, it is possible that it does not contain As, so the lower limit of its content is 0 mass%. On the other hand, As is an element that improves the corrosion resistance of the processed part in a member obtained by processing the base steel sheet 101. For this reason, the As content may be greater than 0 mass%. This effect of improving the corrosion resistance of the processed part is manifested when the As content in the base steel sheet 101 is 0.01 mass% or more. For this reason, when As is included in the base steel sheet 101, it is preferable that the As content be 0.01 mass% or more. The As content in the base steel sheet 101 is more preferably 0.02 mass% or more.

[0089] On the other hand, if the As content in the base steel sheet 101 exceeds 0.10% by mass, the above-mentioned effect of improving the corrosion resistance of the processed part will saturate, and the manufacturing cost will increase. For this reason, when As is included in the base steel sheet 101, it is preferable that the As content be 0.10% by mass or less. More preferably, the As content in the base steel sheet 101 is 0.06% by mass or less.

[0090] [Sb: 0 to 0.50 mass%] In the base steel sheet 101 according to this embodiment, it is possible that it does not contain Sb, so the lower limit of its content is 0 mass%. On the other hand, Sb is an element that improves the corrosion resistance of the processed part in a member obtained by processing the base steel sheet 101. For this reason, the content of Sb can be greater than 0 mass%. This effect of improving the corrosion resistance of the processed part is exhibited when the Sb content in the base steel sheet 101 is 0.01 mass% or more. For this reason, when Sb is included in the base steel sheet 101, it is preferable that the Sb content be 0.01 mass% or more. More preferably, the Sb content in the base steel sheet 101 is 0.02 mass% or more.

[0091] On the other hand, if the Sb content in the base steel sheet 101 exceeds 0.50% by mass, the above-mentioned effect of improving the corrosion resistance of the processed part will saturate, and the manufacturing cost will increase. For this reason, when Sb is included in the base steel sheet 101, it is preferable that the Sb content be 0.50% by mass or less. More preferably, the Sb content in the base steel sheet 101 is 0.30% by mass or less.

[0092] [Ca: 0 to 0.050 mass%] In the base steel sheet 101 according to this embodiment, it is possible that it does not contain Ca, so the lower limit of its content is 0 mass%. On the other hand, Ca is an element that improves the corrosion resistance of the processed part in a member obtained by processing the base steel sheet 101. For this reason, the Ca content may be greater than 0 mass%. This effect of improving the corrosion resistance of the processed part is manifested when the Ca content in the base steel sheet 101 is 0.001 mass% or more. For this reason, when Ca is included in the base steel sheet 101, it is preferable that the Ca content be 0.001 mass% or more. More preferably, the Ca content in the base steel sheet 101 is 0.005 mass% or more.

[0093] On the other hand, if the Ca content in the base steel sheet 101 exceeds 0.050 mass%, the above-mentioned effect of improving the corrosion resistance of the processed part will saturate, and the manufacturing cost of the steel will increase. For this reason, when Ca is included in the base steel sheet 101, it is preferable that the Ca content be 0.050 mass% or less. More preferably, the Ca content in the base steel sheet 101 is 0.010 mass% or less.

[0094] [Mg: 0 to 0.0500 mass%] In the base steel sheet 101 according to this embodiment, it is possible that it does not contain Mg, so the lower limit of its content is 0 mass%. On the other hand, Mg is an element that improves the corrosion resistance of the processed part in a component obtained by processing the base steel sheet 101. For this reason, the content of such Mg may be greater than 0 mass%. This effect of improving the corrosion resistance of the processed part is manifested when the Mg content in the base steel sheet 101 is 0.0001 mass% or more. For this reason, when Mg is included in the base steel sheet 101, it is preferable that the Mg content be 0.0001 mass% or more. The Mg content in the base steel sheet 101 is more preferably 0.0010 mass% or more.

[0095] On the other hand, if the Mg content in the base steel sheet 101 exceeds 0.0500 mass%, the above-mentioned effect of improving the corrosion resistance of the processed part will saturate, and the manufacturing cost of the steel will increase. For this reason, when Mg is included in the base steel sheet 101, it is preferable that the Mg content be 0.0500 mass% or less. More preferably, the Mg content in the base steel sheet 101 is 0.0100 mass% or less.

[0096] ◇Element Group E In another embodiment of the base steel sheet 101 according to this embodiment, the element group E that the base steel sheet 101 may contain will be described. The elements of element group E shown below are elements that may be contained in the base steel sheet 101 in place of a portion of the remaining Fe. [Element Group E]: B: 0.0030% or less

[0097] [B: 0 to 0.0030 mass%] In the base steel sheet 101 according to this embodiment, it is possible that B may not be contained, so the lower limit of its content is 0 mass%. On the other hand, B is an element that refines the recrystallized grains during annealing when manufacturing steel sheets. By refining the recrystallized grains, the rollability when cold rolling the steel sheet is improved, thus improving the productivity of the base steel sheet 101. For this reason, the content of B may be greater than 0 mass%. This recrystallized grain refinement effect becomes significant when the B content of the base steel sheet 101 is 0.0001 mass% or more. For this reason, when B is included in the base steel sheet 101, it is preferable that the B content of the base steel sheet 101 be 0.0001 mass% or more. The B content of the base steel sheet 101 is more preferably 0.0005 mass% or more, and even more preferably 0.0010 mass% or more.

[0098] On the other hand, if the B content of the base steel sheet 101 exceeds 0.0030% by mass, the optimal rolling rate due to refinement decreases, and the productivity of the base steel sheet 101 decreases. Therefore, when B is included in the base steel sheet 101, it is preferable that the B content of the base steel sheet 101 be 0.0030% by mass or less. More preferably, the B content of the base steel sheet 101 is 0.0025% by mass or less, and even more preferably 0.0020% by mass or less.

[0099] [Method for measuring chemical composition] The chemical composition of the base steel sheet 101 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry). For the Ni-plated steel sheet 100 having the base steel sheet 101 of interest, polishing is performed from the surface of the Ni-plated steel sheet 100 along the thickness direction to remove the Ni-based plating layer 103, and then polishing is performed further to a position corresponding to 1 / 4 of the thickness d of the base steel sheet 101. This removes the Ni-based plating layer 103 from the Ni-plated steel sheet 100 of interest, exposing the base steel sheet 101. A measurement sample is taken from this position. When taking a measurement sample, make sure to take the sample from a location sufficiently far from the weld (for example, at least 10 mm away from the edge of the weld). By performing measurements on the acquired measurement samples in accordance with JIS G 1258-1:2014, etc., it is possible to determine the content of elements other than C, N, and O in the chemical composition of the base steel sheet 101.

[0100] The carbon content of the base steel sheet 101 of interest can be determined by measuring a sample obtained in the same manner using the so-called combustion-infrared absorption method. The nitrogen content of the base steel sheet 101 of interest can be determined by measuring a sample obtained in the same manner using the so-called inert gas fusion-thermal conductivity method. The oxygen content of the base steel sheet 101 of interest can be determined by measuring a sample obtained in the same manner using the so-called inert gas fusion-non-dispersive infrared absorption method.

[0101] The chemical composition of the base steel sheet 101 according to this embodiment has been described in detail above.

[0102] ≪Regarding the thickness of the base steel plate 101≫ In the battery case 10 according to this embodiment, a Ni-plated steel plate having the above-mentioned chemical composition is used as the material for the case body 11 and the lid 13. Therefore, the battery case 10 according to this embodiment has superior mechanical strength compared to aluminum materials conventionally used for lithium-ion battery cases. As a result, even if the base steel plate 101 is thin, it is possible to satisfy the strength required for the battery case 10. Consequently, it becomes possible to miniaturize (thinner) lithium-ion batteries and reduce manufacturing costs.

[0103] More specifically, in the battery case 10 according to this embodiment, the thickness (thickness d in Figure 5) of the base steel plate 101 having the above-mentioned chemical composition is preferably in the range of 0.10 to 1.00 mm. The thickness of the base steel plate 101 is more preferably 0.25 mm or more, and even more preferably 0.30 mm or more. Furthermore, the thickness of the base steel plate 101 is more preferably 0.80 mm or less, and even more preferably 0.60 mm or less.

[0104] The thickness of the base steel plate 101 can be measured as follows. First, a measurement sample measuring 10 mm x 20 mm in size is obtained in a plan view from approximately the center of the case body 11 and lid 13, avoiding the location of the welded part of the battery case 10. Then, the obtained measurement sample is embedded in resin, polished, and a cross-sectional observation is performed.

[0105] ◇Regarding the Ni-based plating layer 103 ≪Regarding the amount of Ni-based plating layer 103 attached≫ As explained above, in the battery case 10 according to this embodiment, in order to ensure that the Ni concentration in the weld metal at the welded part is 1.0 mass% or more, a Ni-based plating layer 103 is provided on the surface of the base steel plate 101, as described above, as the material for the case body 11 and the lid 13, so as to result in a specific amount of Ni attached. More specifically, in the Ni-plated steel sheet 100 according to this embodiment, the amount of Ni-based plating layer 103 attached is 7.0 g / m² per side of the Ni-plated steel sheet 100, in terms of metallic Ni. ２The above is true. Furthermore, in the Ni-plated steel sheet 100 according to this embodiment, the amount of Ni-based plating layer 103 attached is 30.0 g / m² per side of the Ni-plated steel sheet 100, in terms of metallic Ni. ２ The following is preferable:

[0106] The amount of Ni-based plating layer 103 deposited on one side is 7.0 g / m² in terms of metallic Ni. ２ If the amount is less than this, the effect of coating the base steel plate 101 with Ni will be insufficient, and the possibility of Fe leaching will increase, which is undesirable. Therefore, in the battery case 10 according to this embodiment, the amount of Ni-based plating layer 103 attached to one side is 7.0 g / m² in terms of metallic Ni. ２ The above is complete. The amount of Ni-based plating layer 103 deposited on one side is preferably 8.0 g / m² in terms of metallic Ni. ２ The above is preferable, and more preferably 10.0 g / m ２ That's all.

[0107] On the other hand, the amount of Ni-based plating layer 103 deposited on one side is 30.0 g / m² in terms of metallic Ni. ２ If it exceeds this value, the effect of suppressing Fe elution from the weld metal as described above will saturate, while manufacturing costs may increase. Therefore, in the battery case 10 according to this embodiment, the amount of Ni-based plating layer 103 deposited on one side is 30.0 g / m² in terms of metallic Ni. ２ The following is preferable: The amount of Ni-based plating layer 103 deposited on one side is more preferably 25.0 g / m² in terms of metallic Ni. ２ The following, and more preferably 20.0 g / m² ２ The following applies:

[0108] The amount of Ni-based plating layer 103 can be measured as follows. First, a sample measuring 30 mm x 30 mm in plan view is cut from a location sufficiently far from the end of the weld (for example, a location 10 mm or more away). Then, the Ni-based plating layer 103 present in the obtained sample is dissolved with acid (for example, concentrated hydrochloric acid). Next, the Ni content in the obtained solution is measured by ICP-MS. The total amount of dissolved Ni can be determined by this measurement. By dividing the obtained total amount of Ni by twice the area, the amount of Ni-based plating layer 103 per side can be calculated.

[0109] ≪Regarding the chemical composition of the Ni-based plating layer 103≫ In the battery case 10 and Ni-plated steel sheet 100 according to this embodiment, the chemical composition of the Ni-based plating layer 103 is not particularly limited as long as it is capable of achieving the above-mentioned adhesion amount. For example, the Ni plating contained in the Ni-based plating layer 103 may be a general Ni plating composed of pure Ni, or it may be a Ni-based alloy plating containing various alloying metals.

[0110] In other words, the chemical composition of the Ni-based plating layer 103 according to this embodiment may, in some embodiment, be a Ni plating having a chemical composition consisting of Ni and impurities.

[0111] Furthermore, according to another embodiment, the chemical composition of the Ni-based plating layer 103 in this embodiment may be a plating layer having a chemical composition in which, by mass%, Fe: 1.0 to 20.0%, with the remainder being Ni and impurities.

[0112] Furthermore, according to yet another embodiment, the chemical composition of the Ni-based plating layer 103 in this embodiment may be a plating layer having a chemical composition in which, by mass%, Fe: 1.0 to 20.0%, and further, one or more elements selected from the group consisting of element groups F to H described below, with the remainder being Ni and impurities. The element groups F to H mentioned above, as referred to in another embodiment of the chemical composition of the Ni-based plating layer 103 in this embodiment, can be said to be elements that can be optionally included in the chemical composition of the Ni-based plating layer 103 in this embodiment.

[0113] [Element Group F]: One or more elements selected from the group consisting of W: 50.0% or less, Co: 5.0% or less, and Mo: 30.0% or less. [Element Group G]: One or two elements selected from the group consisting of Sn: 0.1000% or less and Zn: 0.1000% or less. [Element Group H]: One or two elements selected from the group consisting of C: 0.01% or less and S: 0.01% or less.

[0114] [Fe: 1.0 to 20.0 mass%] Fe is an element that diffuses from the base steel sheet 101 when alloying the Ni-based plating layer 103 according to this embodiment, and is also an element that suppresses the elution of metal ions from the Ni-based plating layer 103 into the electrolyte. This effect of resistance to metal ion elution is manifested when the Fe content in the Ni-based plating layer 103 is 1.0 mass% or more. Therefore, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, it is preferable that the Fe content be 1.0 mass% or more. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, it is more preferable that the Fe content be 5.0 mass% or more. Furthermore, Fe may be added to the plating bath used when manufacturing the Ni-based plating layer 103, within a range that does not impair the effects of the present invention.

[0115] On the other hand, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if the Fe content exceeds 20.0% by mass, the elution of metal ions from the Ni-based plating layer 103 into the electrolyte may actually increase. Therefore, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, it is preferable that the Fe content be 20.0% by mass or less. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, the Fe content is more preferably 15.0% by mass or less.

[0116] In the Ni-based plating layer 103 according to this embodiment, the remainder of the Fe is Ni and impurities. Here, "impurities" refers to components that are mixed into the plating layer due to raw materials such as ore and scrap, or various factors in the manufacturing process, when the Ni-based plating layer is manufactured industrially.

[0117] Next, in a Ni-based plating layer 103 according to another embodiment of this embodiment, the element groups F to H that may be present in the chemical composition of such Ni-based plating layer 103 will be described in detail.

[0118] In addition, in the Ni-based plating layer 103 according to another embodiment of this embodiment, if at least one of the elements belonging to the element groups F to H below is included, it is preferable that at least one of the elements belonging to the element groups F to H below is included within the following content range, and the total content is 50.0% by mass or less.

[0119] By keeping the total content of elements belonging to element groups F to H to 50.0% by mass or less, it becomes possible to enjoy the effects exhibited by the addition of each element, as detailed below, without impairing each other. The total content of elements belonging to element groups F to H is preferably 30.0% by mass or less, and more preferably 20.0% by mass or less.

[0120] ◇Element Group F In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, the element group F that the Ni-based plating layer 103 may contain will be described. At least one of the elements of the element group F shown below may be contained in the Ni-based plating layer 103 in place of a portion of the remaining Ni. [Element Group F]: One or more elements selected from the group consisting of W: 50.0% or less, Co: 5.0% or less, and Mo: 30.0% or less.

[0121] [W: 0 to 50.0 mass%] In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, it is possible that W may not be contained, so the lower limit of its content is 0 mass%. On the other hand, W is an element that, when contained in the Ni-based plating layer 103, suppresses the elution of metal ions from the Ni-based plating layer 103 into the electrolyte. For this reason, the content of W may be greater than 0 mass%. This effect of resistance to metal ion elution is manifested when the W content in the Ni-based plating layer 103 is 5.0 mass% or more. Furthermore, when the Ni-based plating layer 103 contains W, when the potential of the lithium-ion battery rises, the Ni-based plating layer 103 reacts with the electrolyte to form a protective film that exhibits a stable protective effect. From this viewpoint as well, it is preferable to include W when forming a Ni-based alloy plating layer as the Ni-based plating layer 103. From the above viewpoint, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if W is included in the plating layer, the W content is preferably 5.0% by mass or more. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if W is included in the plating layer, the W content is more preferably 10.0% by mass or more.

[0122] On the other hand, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if W is included in the plating layer, and the W content exceeds 50.0% by mass, the elution of metal ions from the Ni-based plating layer 103 into the electrolyte may actually increase. Therefore, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if W is included in the plating layer, it is preferable that the W content be 50.0% by mass or less. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if W is included in the plating layer, the W content is more preferably 40.0% by mass or less.

[0123] [Co: 0 to 5.0 mass%] In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, it is possible that it does not contain Co, so the lower limit of its content is 0 mass%. On the other hand, Co is an element that, when contained in the Ni-based plating layer 103, reduces the contact resistance of the Ni-based plating layer 103 and suppresses the elution of metal ions from the Ni-based plating layer 103 into the electrolyte. For this reason, the Co content can be greater than 0 mass%. This effect is achieved when the Co content in the Ni-based plating layer 103 is 0.0005 mass% or more. For this reason, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Co is included in the plating layer, it is preferable that the Co content be 0.0005 mass% or more. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Co is included in the plating layer, the Co content is more preferably 0.0100% by mass or more.

[0124] On the other hand, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Co is included in the plating layer, and the Co content exceeds 5.0% by mass, the elution of metal ions from the Ni-based plating layer 103 into the electrolyte may actually increase. Therefore, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Co is included in the plating layer, it is preferable that the Co content be 5.0% by mass or less. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Co is included in the plating layer, the Co content is more preferably 3.0% by mass or less.

[0125] [Mo: 0 to 30.0 mass%] In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, it is possible that Mo is not contained, so the lower limit of its content is 0 mass%. On the other hand, Mo is an element that, when contained in the Ni-based plating layer 103, reduces the contact resistance of the Ni-based plating layer 103 and suppresses the elution of metal ions from the Ni-based plating layer 103 into the electrolyte. For this reason, the content of such Mo can be greater than 0 mass%. This effect is manifested when the Mo content in the Ni-based plating layer 103 is 0.5 mass% or more. For this reason, when Mo is included in the plating layer when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, it is preferable that the Mo content be 0.5 mass% or more. When Mo is included in the plating layer when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, the Mo content is more preferably 1.0 mass% or more.

[0126] On the other hand, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Mo is included in the plating layer, and the Mo content exceeds 30.0% by mass, the contact resistance of the Ni-based plating layer 103 may increase. Therefore, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Mo is included in the plating layer, it is preferable that the Mo content be 30.0% by mass or less. Furthermore, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Mo is included in the plating layer, setting the Mo content to 5.0% by mass or less makes it possible to reduce the contact resistance of the Ni-based plating layer 103 while suppressing the elution of metal ions from the Ni-based plating layer 103 into the electrolyte. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Mo is included in the plating layer, the Mo content is more preferably 3.0% by mass or less.

[0127] ◇Element Group G In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, the element group G that the Ni-based plating layer 103 may contain will be described. At least one of the elements in the element group G shown below may be contained in the Ni-based plating layer 103 in place of a portion of the remaining Ni. [Element Group G]: One or two elements selected from the group consisting of Sn: 0.1000% or less and Zn: 0.1000% or less

[0128] [Sn: 0 to 0.1000 mass%] In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, it is possible that it does not contain Sn, so the lower limit of its content is 0 mass%. On the other hand, Sn is an element that, when contained in the Ni-based plating layer 103, suppresses the elution of metal ions from the Ni-based plating layer 103 into the electrolyte. For this reason, the content of Sn can be greater than 0 mass%. This effect is achieved when the Sn content in the Ni-based plating layer 103 is 0.0005 mass% or more. For this reason, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103 and including Sn in the plating layer, it is preferable that the Sn content be 0.0005 mass% or more. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103 and including Sn in the plating layer, the Sn content is more preferably 0.0050 mass% or more.

[0129] On the other hand, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Sn is included in the plating layer, and the Sn content exceeds 0.1000 mass%, a brittle Ni-Sn intermetallic compound may be formed, potentially reducing the workability of the Ni-plated steel sheet. Therefore, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Sn is included in the plating layer, it is preferable that the Sn content be 0.1000 mass% or less. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Sn is included in the plating layer, the Sn content is more preferably 0.0500 mass% or less.

[0130] [Zn: 0 to 0.1000 mass%] In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, it is possible that it does not contain Zn, so the lower limit of its content is 0 mass%. On the other hand, Zn is an element that, when contained in the Ni-based plating layer 103, improves the corrosion resistance (particularly electrolyte resistance) of the Ni-based plating layer 103. For this reason, the Zn content can be greater than 0 mass%. This effect is achieved when the Zn content in the Ni-based plating layer 103 is 0.0005 mass% or more. For this reason, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103 and including Zn in the plating layer, it is preferable that the Zn content be 0.0005 mass% or more. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103 and including Zn in the plating layer, the Zn content is more preferably 0.0050 mass% or more.

[0131] On the other hand, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Zn is included in the plating layer, and the Zn content exceeds 0.1000% by mass, the corrosion resistance improvement effect described above becomes saturated. Therefore, when forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Zn is included in the plating layer, it is preferable that the Zn content be 0.1000% by mass or less. When forming a Ni-based alloy plating layer as the Ni-based plating layer 103, if Zn is included in the plating layer, the Zn content is more preferably 0.0500% by mass or less.

[0132] ◇Element Group H In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, element group H that the Ni-based plating layer 103 may contain will be described. At least one of the elements of element group H shown below may be contained in the Ni-based plating layer 103 in place of a portion of the remaining Ni. [Element Group H]: One or two elements selected from the group consisting of C: 0.01% or less and S: 0.01% or less

[0133] [C: 0 to 0.01% by mass] In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, it is possible that it does not contain carbon, so the lower limit of its content is 0% by mass. On the other hand, since carbon is an element that may inevitably be mixed in with the additives added to the plating bath for manufacturing the Ni-based plating layer 103, the Ni-based plating layer 103 may contain carbon. That is, the content of such carbon may be greater than 0% by mass. On the other hand, if the carbon content in the plating bath for manufacturing the Ni-based plating layer 103 is too high, the Ni-based plating layer 103 may become brittle, and the corrosion resistance of the Ni-plated steel sheet may decrease, so the carbon content in the plating bath is adjusted. From the viewpoint of corrosion resistance as described above, it is preferable that the carbon content in the Ni-based plating layer 103 is 0.01% by mass or less.

[0134] [S: 0 to 0.01% by mass] In yet another embodiment of the Ni-based plating layer 103 according to this embodiment, it is possible that it does not contain sulfur, so the lower limit of its content is 0% by mass. On the other hand, sulfur is an element that may inevitably be mixed in with the additives added to the plating bath for manufacturing the Ni-based plating layer 103, so the Ni-based plating layer 103 may contain sulfur. That is, the content of such sulfur may be greater than 0% by mass. On the other hand, if the sulfur content in the plating bath for manufacturing the Ni-based plating layer 103 is too high, the Ni-based plating layer 103 may become brittle, and the corrosion resistance of the Ni-plated steel sheet may decrease, so the sulfur content in the plating bath is adjusted. From the viewpoint of corrosion resistance as described above, it is preferable that the sulfur content in the Ni-based plating layer 103 is 0.01% by mass or less.

[0135] The chemical composition of the Ni-based plating layer 103 according to this embodiment has been described in detail above. The chemical composition of the Ni-based plating layer 103 can be measured in the same manner as the chemical composition of the base steel sheet 101.

[0136] <Structure near the weld in the battery case 10> Next, with reference to Figures 6A to 7B, the structure near the weld in the lithium-ion battery case 10 and lithium-ion battery 1 according to this embodiment will be described in detail.

[0137] Figures 6A to 7B are schematic diagrams illustrating the structure near the weld of a battery case for a lithium-ion battery according to this embodiment. In Figures 6A to 7B, the focus is on the cross-section when the battery case 10 is cut in the height direction of the battery case. Note that in Figures 6A to 7B, the mechanism for preventing the lid 13 from falling into the internal space of the case body 11 is not shown. Also, in Figures 6A to 7B, the end face of the Ni-plated steel sheet that will be used as the material is shown as the end face 32 before welding with a dashed line.

[0138] As mentioned earlier, in the lithium-ion battery 1, after the battery unit 3 is housed in the internal space of the case body 11 of the battery case 10, the lid 13 is positioned to seal the opening of the case body 11, and the case body 11 and the lid 13 are welded together. As a result, a welded portion 21 is formed in the battery case 10 of the lithium-ion battery 1. Subsequently, electrolyte 5 is injected through the injection port 15 provided in the lid 13, and the injection port 15 is closed by the injection port cover 17.

[0139] The position at which the welded portion 21 is formed in the battery case 10 is not particularly limited, as it depends on the structure of the case body 11 and the lid 13. However, depending on the structure of the case body 11 and the lid 13, as shown in Figures 6A and 6B, the weld metal 201 is often formed to cover at least a portion of the end face 32 of the case body 11 before welding and the end face 33 of the lid 13 before welding. Here, the end face 32 of the case body 11 before welding and the end face 33 of the lid 13 before welding are the end faces of the Ni-plated steel sheet 100, which is the raw material. Such end faces are often not covered with the Ni-based plating layer 103. Such end faces are not particularly limited, but may be the cut end faces when the Ni-plated steel sheet 100 is cut in the thickness direction. Therefore, it can be said that the battery case 10 according to this embodiment has a welded portion formed by welding the end face of the Ni-plated steel sheet 100 before welding, or the cut end face when the Ni-plated steel sheet 100 is cut in the thickness direction.

[0140] Here, when welding the end face of the case body 11 and the end face of the lid 13 using laser welding or the like, depending on the welding conditions, a state of partial penetration welding may occur, as shown in Figure 6A. A state of partial penetration welding is a state in which a part of the end face of the case body 11 is covered with weld metal 201, and a part of the end face (end face 32 before welding) of the Ni-plated steel sheet 100, which is the material, remains. In other words, as a result of a part of the end face 32 before welding remaining, an end face 31 exists on the case body 11. Note that "at least a part of the end face or cut end face is covered with weld metal" means that at least a part of the end face 32 before welding on the Ni-plated steel sheet 100, which is the material, is incorporated into the weld metal after the welding process, and at least a part of the base steel sheet 101 of the Ni-plated steel sheet 100 is not exposed to the outside.

[0141] Furthermore, it is more preferable that the shape of the weld metal 201 be in a state of complete penetration welding (full penetration type), as shown in Figure 6B. A fully penetration type weld metal that extends across the entire thickness of the case body means that the weld metal 201 covers the entire surface of the end face 32 of the Ni-plated steel sheet 100, which is the material for the case body 11, before welding, so that the end face 32 is not exposed before welding. In other words, it means that the end face 32 of the Ni-plated steel sheet 100, which is the material, before welding is incorporated into the weld metal after the welding process, so that the base steel sheet 101 of the Ni-plated steel sheet 100 is not exposed to the outside. In this embodiment, partial penetration welding and full penetration welding also include the case in which the case body 11 and the lid 13 are connected at approximately a right angle, as illustrated in Figures 6A and 6B. By using a fully penetration type weld metal, the Fe elution behavior in the welded part 21 can be concentrated on the weld metal side, making it possible to stabilize the corrosion resistance design.

[0142] In the battery case 10 having the welded portion 21 as described above, the lid portion 13, the weld metal 201, and the case body portion 11 are arranged in order in the thickness direction of the lid portion 13 (which can also be considered as the normal direction of the planar portion of the lid portion 13; for example, the Z-axis direction in Figure 3).

[0143] [Regarding the weld metal 201] As schematically shown in Figures 6A and 6B, the welded portion 21 according to this embodiment has a weld metal 201. In addition, a heat-affected zone (HAZ) (not shown) may exist on the weld metal 201 side of the case body 11 and the weld metal 201 side of the lid 13 due to the heat generated during welding of the case body 11 and the lid 13. Such weld metal 201 and heat-affected zones can be easily distinguished by the difference in their appearance when observing a cross-section of the battery case 10 including the welded portion 21 as schematically shown in Figures 6A and 6B using a SEM (for example, JSM-7000F manufactured by JEOL Corporation). Note that the welded portion 21 according to this embodiment includes the weld metal 201, or the weld metal 201 and the end face 31, and the above-mentioned HAZ is not included in the welded portion 21.

[0144] Here, the weld metal 201 is the metal formed when the Ni-plated steel sheet 100, which is the material for the case body 11 and lid 13, melts during welding and then solidifies again. Therefore, the weld metal 201 is composed of various alloys of chemical components derived from the Ni-plated steel sheet 100. In addition, the weld metal 201 may contain impurities other than the above-mentioned components.

[0145] In the battery case 10 according to this embodiment, the Ni-plated steel sheet 100 used as the material for the case body 11 and the lid 13 has a base steel sheet 101 having a specific Ni content, and a Ni-based plating layer 103 having a specific amount of adhesion is provided on the surface of the base steel sheet 101. As a result, the weld metal 201 according to this embodiment has a Ni concentration of 1.0 mass% or more. Consequently, as explained earlier with reference to Figure 1, in the battery case 10 according to this embodiment, the elution of Fe from the welded part 21 (more specifically, the weld metal 201) is suppressed.

[0146] Here, the Ni concentration in the weld metal 201 is preferably 1.5% by mass or more, and more preferably 2.0% by mass or more. On the other hand, the higher the Ni concentration in the weld metal 201, the better, and there is no particular upper limit. However, if the Ni concentration in the weld metal 201 exceeds 8.0% by mass, the effect of suppressing the elution of Fe as described above gradually approaches saturation, and the manufacturing cost to make the Ni concentration in the weld metal 201 exceed 8.0% by mass may increase. Therefore, the Ni concentration in the weld metal 201 may be 8.0% by mass or less.

[0147] Furthermore, the chemical components constituting the weld metal 201 can be identified by observing the cross-section obtained by cutting the portion corresponding to the weld metal 201 using a SEM-EPMA (for example, JXA-8230 manufactured by JEOL Corporation).

[0148] More specifically, a sample for cross-sectional observation, including the welded portion 21 of the battery case 10, is cut from the center of the battery case 10 in the depth direction (Y-axis direction in Figure 3). The cutting direction for obtaining the cross-section is the thickness direction of the lid portion 13 (the longitudinal direction of the battery case 10, i.e., the Z-axis direction in Figure 3). After embedding the obtained cross-sectional observation sample in resin, it is polished appropriately, and the obtained cross-section is observed using SEM-EPMA. In this case, the acceleration voltage is set to 15 kV and the irradiation current to 0.05 μA. Furthermore, during observation, a 0.1 mm × 0.1 mm area of ​​the above cross-section is quantitatively analyzed, and the average value of 10 points is taken as the chemical composition of the weld metal.

[0149] [Regarding the oxide films 203 and 301] As schematically shown in Figures 7A and 7B, an oxide film 203 is formed on the surface of the weld metal 201 according to this embodiment (i.e., on the weld metal 201), in particular on the weld metal 201 on the inner surface side of the battery case 10. Here, the inner surface side of the battery case 10 refers to the side that comes into contact with the electrolyte. Also, as shown in Figure 7A, when the weld metal 201 is in a state of partial penetration welding, an oxide film 301 is formed on the surface of the remaining end face 31 (i.e., on the end face 31). These oxide films 203 and 301 are Fe-Ni alloy oxide films because the base steel sheet 101 in the Ni-plated steel sheet 100, which is the material of the battery case 10, contains a specific amount of Ni, and the amount of Ni-based plating layer 103 attached is within a specific range. Furthermore, the oxide films 203 and 301 may contain, in addition to the Fe-Ni alloy-based oxides described above, various oxides derived from the chemical components of the Ni-plated steel sheet 100, as well as impurities.

[0150] In the battery case 10 according to this embodiment, the surface of the weld metal 201 and the surface of the end face 31 are covered with the oxide film described above, which further suppresses the elution of Fe from the weld metal 201 and the base steel plate 101. As a result, the welded portion 21 of the battery case 10 according to this embodiment exhibits excellent corrosion resistance (electrolyte resistance). Furthermore, in the battery case 10 according to this embodiment, Fe ions that have eluted are reduced by the negative electrode, preventing Fe from precipitation on the negative electrode and thus preventing a short circuit, thus maintaining battery performance.

[0151] Here, the thickness of the oxide films 203 and 301 according to this embodiment, as shown in Figures 7A and 7B, is preferably in the range of 10 to 50 nm. By making the thickness of the oxide films 203 and 301 10 nm or more, it is possible to further improve the electrolyte resistance of the welded part 21. The thickness of the oxide films 203 and 301 is more preferably 15 nm or more.

[0152] On the other hand, by making the thickness of the oxide films 203 and 301 50 nm or less, it becomes possible to further improve the electrolyte resistance of the welded part 21 while preventing the peeling of the oxide films. More preferably, the thickness of the oxide films 203 and 301 is 45 nm or less.

[0153] The thickness of the oxide films 203 and 301 described above can be controlled to a desired state by controlling welding conditions such as the welding speed when welding the case body 11 and the lid 13, whether or not to use shielding gas, and the flow rate of the shielding gas.

[0154] Here, the thickness of the oxide films 203 and 301 described above can be measured by observing the cross-section using a transmission electron microscope (TEM), as detailed below.

[0155] First, a sample for cross-sectional observation, including the welded portion 21 of the battery case 10, is cut from the center of the battery case 10 in the depth direction (Y-axis direction in Figure 3). The cutting direction for obtaining the cross-section is the thickness direction of the lid portion 13, i.e., the longitudinal direction of the battery case 10 (Z-axis direction in Figure 3). A thin film sample of the cross-section near the surface of the welded portion 21 is prepared from the obtained cross-sectional observation sample using a Focused Ion Beam (FIB) device, and the thickness of the oxide film can be observed by TEM observation. Here, the size of the observation field is 200 nm × 200 nm. The thickness of the oxide films 203 and 301 is measured at three arbitrary locations within the observation field, and this measurement is performed in five arbitrary fields. The measured values ​​obtained in each observation field (15 values ​​each) are averaged over the number of measurement locations (i.e., 15 locations). The average value obtained in this way can be taken as the thickness of the oxide films 203 and 301.

[0156] Furthermore, by performing electron diffraction in addition to the TEM observation described above, it is possible to determine the crystal structure of oxide films 203 and 301 and to determine whether or not oxide films 203 and 301 are Fe-Ni alloy-based oxide films.

[0157] The battery case 10 for the lithium-ion battery 1 according to this embodiment and the configuration of the lithium-ion battery 1 using the battery case 10 have been described in detail above with reference to Figures 3 to 7B.

[0158] (Regarding the battery case for lithium-ion batteries and the method for manufacturing lithium-ion batteries) Next, an example of a battery case for lithium-ion batteries according to this embodiment and a method for manufacturing lithium-ion batteries using such a battery case will be described. In the following, the explanation will focus on the battery case 10 shown in Figure 4A.

[0159] <Regarding the manufacturing method of the Ni-plated steel sheet 100> The Ni-plated steel sheet 100, which is the material for the battery case 10 according to this embodiment, is manufactured by first producing a base steel sheet 101 using molten steel whose chemical composition has been adjusted to have the steel components described above, by various known methods, and then forming a Ni-based plating layer 103 on the surface of the manufactured base steel sheet 101.

[0160] The specific method for manufacturing the base steel sheet 101 is not particularly limited. A base steel sheet 101 of the desired thickness can be manufactured using molten steel whose chemical composition has been adjusted to have the steel composition described above, in accordance with various known methods.

[0161] Furthermore, in addition to electroplating and electroless plating, methods such as thermal spraying, cold spraying, sputtering, and vapor deposition can be applied to form the Ni-based plating layer 103. However, from a cost perspective, it is preferable to use electroplating or electroless plating.

[0162] For example, when forming a Ni plating layer as the Ni-based plating layer 103, known Ni plating methods such as electroplating can be used. In this case, if electroplating is used, various plating baths such as chloride baths, sulfuric acid baths, and watt baths can be used.

[0163] Here, after obtaining a predetermined Ni plating thickness, the formed Ni plating layer and the base steel sheet 101 may be alloyed by heating and annealing in a non-oxidizing atmosphere. By annealing, an Fe-Ni alloy layer is formed at the interface between the base steel sheet 101 and the Ni-based plating layer 103, thereby further improving plating adhesion. In addition, the electrodeposition structure of the Ni-based plating layer 103 softens due to recrystallization, preventing cracking and peeling of the Ni-based plating layer 103 due to processing. Furthermore, although slight pinholes may occur in Ni plating, annealing causes the portion of the base steel sheet that was exposed at the bottom of the pinhole to become an Fe-Ni alloy, resulting in an effect of suppressing Fe elution.

[0164] Here, the above annealing conditions are not specifically defined. For example, N ２ -4%H ２ After heating to a temperature of 700-850°C in an ambient atmosphere and the Ni plating layer has softened, the heating time should be appropriately selected to obtain the desired thickness of the Fe-Ni diffusion layer.

[0165] Furthermore, when forming a Ni-based alloy plating layer using various metal elements, the manufacturing method is not particularly limited. The Ni-based alloy plating layer can be formed using a plating bath adjusted to have the desired plating components, and by various known manufacturing methods.

[0166] <Regarding the manufacturing method of the battery case 10 and lithium-ion battery 1> Using the Ni-plated steel sheet 100 obtained as described above as a material, the case body 11 and lid 13 can be obtained by performing various processes such as deep drawing and bending to form a case body 11 and lid 13 having the desired shape.

[0167] In this case, the case body portion 11 may be formed so that there are no joints by using a processing method such as drawing. Alternatively, the case body portion 11 may be formed by preparing parts for forming the case body portion 11 (for example, multiple parts for forming the sides of the case body portion 11, or parts for forming the bottom surface of the case body portion 11) using a processing method such as bending, and then laser welding these parts together.

[0168] In the manufacturing method of the lithium-ion battery 1 using the lithium-ion battery case 10 described above, first, the battery unit 3 is placed inside the battery case 10, and then the case body 11 and the lid 13 of the battery case 10 are welded together using various welding methods, including laser welding. Finally, electrolyte 5 is injected into the battery case 10 through the liquid injection port 15 provided in the lid 13 and the port is closed by the liquid injection port cover 17.

[0169] Here, the process of storing the battery unit 3 and electrolyte 5 as described above is carried out using, for example, Ar or N ２ It is preferable to carry out the process under an inert gas atmosphere, or under an atmosphere where moisture is kept to a minimum (for example, an atmosphere with a dew point of -75°C or lower). Regarding the detailed method of housing the battery unit 3 in the battery case 10 and the detailed method of injecting the electrolyte 5 into the battery case 10, various known methods may be used as appropriate.

[0170] Furthermore, the welding work between the case body 11 and the lid 13 of the battery case 10 is carried out under an inert gas atmosphere, or under an atmosphere that minimizes moisture (for example, an atmosphere with a dew point of -75°C or lower) after the internal space of the battery case 10 has been replaced with an inert gas. Here, the inert gas is Ar gas, N ２ Examples include gas, carbon dioxide, helium, or a mixture of at least two of these gases.

[0171] More specifically, for example, the inert gas is blown into the internal space of the battery case 10 immediately before welding. Then, during welding, the inert gas is blown from above the battery case 10 while the welding is being performed. In this case, it is preferable that the amount of inert gas blown in is 0.5 L / min or more, and the amount blown from above is 20.0 L / min or more. This ensures that the inert gas is present in the internal space of the battery case 10, and the formation state of the oxide films 203 and 301 can be controlled. The upper limit of the amount of gas blown in is not specifically defined, but in practice it is around 1.0 L / min. The upper limit of the amount blown from above is not specifically defined, but in practice it is around 50.0 L / min.

[0172] Furthermore, the method for filling the internal space of the battery case 10 with an inert gas is not limited to blowing in an inert gas as described above.

[0173] By performing the work in an inert gas atmosphere as described above, the presence of oxygen can be sufficiently eliminated, and the thickness of the formed oxide films 203 and 301 can be controlled to a desired state.

[0174] Furthermore, there are no specific limitations on the welding conditions; the conditions should be adjusted as appropriate according to the material being used.

[0175] The battery case for a lithium-ion battery according to this embodiment and a method for manufacturing a lithium-ion battery using such a battery case have been described above.

[0176] The following describes in detail the battery case for lithium-ion batteries according to this embodiment, with reference to examples and comparative examples. Note that the following examples are merely examples of the battery case for lithium-ion batteries according to this embodiment, and the battery case for lithium-ion batteries according to this embodiment is not limited to the examples below.

[0177] (Test Example 1: In the case of partial penetration welding) A verification was conducted to simulate a situation in which the cut end surface is not completely covered by the weld metal inside the battery case, and a part of the cut end surface is exposed (i.e., in the case of partial penetration welding).

[0178] Base steel sheets (manufactured by Nippon Steel Corporation) with Ni content varied within the range of 0 to 5.0 mass% were used. These base steel sheets were plated with a Ni-based coating using a Watt bath to achieve the desired amount of Ni adhesion, and then annealed to produce Ni-plated steel sheets that would serve as the material for the battery case.

[0179] The content (mass%) of each component other than Ni in the above-mentioned base steel sheet is as follows: C: 0.100 mass%, Si: 0.100 mass%, Mn: 0.50 mass%, Al: 0.005 mass%, P: 0.007 mass%, S: 0.2500 mass%, N: 0.020 mass%

[0180] Furthermore, in the description of the alloy components of the plating in Table 1-1 below, the notation "≤0.01" indicates that the content was "greater than 0% by mass and 0.01% by mass or less".

[0181] The Ni-plated steel sheet manufactured as described above was cut to a size of 10 mm x 66 mm. The two 66 mm edges of these sheets were butted together on a flat surface, and a welded material measuring (sheet thickness) x 20 mm x 66 mm was formed by laser welding. The average penetration depth of the weld was set to 0.3 mm or 0.5 mm, resulting in a partial penetration weld in which a portion of the cut edge of the base steel sheet was exposed. The gap at the butt joint was approximately 50 μm.

[0182] The resulting weld material was examined using SEM-EPMA to observe the cross-section of the weld and determine the Ni concentration in the weld metal. The thickness of the oxide film was measured using the TEM method described earlier. The results are summarized in Table 1-2 below.

[0183] Next, these welded materials were electroplated with 5 μm-thick nickel, except for a 2 mm x 50 mm area around the butt joint of the steel plates on the opposite side of the laser irradiation surface, to act as a mask for the electrolyte. The unmasked areas simulate the state in which the cut edge of the base steel plate is exposed inside the battery case. The structure of the evaluation material obtained in this way is schematically shown in Figure 8.

[0184] As part of the elution investigation into the electrolyte, each prepared evaluation material was subjected to an electrolyte (1 mol / L LiPF manufactured by Kishida Chemical Co., Ltd.) in an Ar atmosphere glove box. ６ The material was sealed in an aluminum laminate pouch with 1 mL of EC:DEC (1:1 v / v%). As an accelerated test for Fe elution into the electrolyte, it was kept at 80°C for 500 hours. After that, the pouch was opened in the glove box mentioned above, the electrolyte was collected, the welding material and the inside of the pouch were washed with a solvent, and the volume was adjusted to 50 mL with the collected electrolyte. The Fe concentration of this adjusted volume was determined using ICP-MS (Agilent 7700x) and was recorded as the Fe elution amount.

[0185] The inventors prepared evaluation material of the size described above, and then reduced the amount of electrolyte to increase the ratio of the welded area to the amount of electrolyte. By using such evaluation material, it is possible to secure a welded area approximately 17 times larger than that of a PHEV2 battery case, enabling measurement of Fe elution amount by ICP-MS.

[0186] To confirm the effect of Ni addition to the base steel sheet, the ratio of Fe leaching was calculated within the same group, using the Fe leaching amount of evaluation material without Ni in the base steel sheet as a baseline. A Fe leaching ratio of 0.50 or less was considered acceptable. For samples No. 5-1 to 6-13, the Fe leaching ratio was calculated using the Fe leaching amount of No. 4-1 as a baseline.

[0187] The results obtained are summarized in Table 1-2 below.

[0188]

[0189]

[0190] (Test Example 2: Case of complete penetration welding) A verification was conducted inside the battery case to simulate a state in which the cut end surface is covered with weld metal, resulting in complete penetration welding.

[0191] Base steel sheets (manufactured by Nippon Steel Corporation) with Ni content varied within the range of 0 to 5.0 mass% were used. These base steel sheets were plated with a Ni-based coating using a Watt bath to achieve the desired amount of Ni adhesion, and then annealed to produce Ni-plated steel sheets that would serve as the material for the battery case.

[0192] The content (mass%) of each component other than Ni in the above-mentioned base steel sheet is as follows: C: 0.100 mass%, Si: 0.100 mass%, Mn: 0.50 mass%, Al: 0.005 mass%, P: 0.007 mass%, S: 0.2500 mass%, N: 0.020 mass%

[0193] Furthermore, in the description of the alloy components of the plating in Table 2-1 below, the notation "≤0.01" indicates that the content was "greater than 0% by mass and 0.01% by mass or less".

[0194] The Ni-plated steel sheet manufactured as described above was cut to a size of 10 mm x 66 mm. The two 66 mm edges of these sheets were butted together on a flat surface, and a welded material measuring (sheet thickness) x 20 mm x 66 mm was formed by laser welding. In this test example, full penetration welding was performed. The gap at the butt joint was approximately 50 μm. The width of the weld metal formed by this full penetration welding (weld width) is shown in Table 2-2 below.

[0195] The resulting weld material was examined using SEM-EPMA to observe the cross-section of the weld and determine the Ni concentration in the weld metal. The thickness of the oxide film was measured using the TEM method described earlier. The results are summarized in Table 2-2 below.

[0196] Next, these welded materials were electroplated with 5 μm thick nickel, except for a 4 mm x 50 mm area around the butt joint of the steel plates on the opposite side of the laser irradiation surface, to act as a mask for the electrolyte. The unmasked areas simulate the state in which the cut edge of the base steel plate is exposed inside the battery case. The structure of the evaluation material obtained in this way is schematically shown in Figure 9. In Figure 9, width W represents the width of the weld metal formed by full penetration welding (weld width).

[0197] As a comparative example, a Ni-plated steel sheet with a Ni content of 0% in the base steel sheet was cut to a size of 20 x 66 mm, and Ni masking was performed in the same manner as described above.

[0198] Using these evaluation materials, the amount of Fe eluted was measured in the same manner as in Test Example 1 above.

[0199] To confirm the effect of Ni addition to the base steel sheet, the ratio of Fe leaching was calculated using the Fe leaching amount of unwelded evaluation material as a baseline within a group with the same sheet thickness and Ni adhesion amount. Materials with an Fe leaching amount ratio of less than 2.50 were considered acceptable.

[0200] The results obtained are summarized in Table 2-2 below.

[0201]

[0202]

[0203] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0204] The embodiments disclosed herein are illustrative and not restrictive in all respects. The embodiments described above may be omitted, replaced, or modified in various ways without departing from the appended claims, the technical scope of the invention as described later, and the spirit thereof. For example, the constituent elements of the embodiments described above can be combined in any way without impairing their effects. Furthermore, such any combination will naturally yield the effects and benefits of each constituent element in the combination, as well as other effects and benefits that will be obvious to those skilled in the art from the description herein.

[0205] Furthermore, the effects described herein are merely descriptive or illustrative, and not limiting. In other words, the technology according to the present invention may produce other effects that will be apparent to those skilled in the art from the description herein, in addition to or in lieu of the effects described herein.

[0206] Furthermore, the following configurations also fall within the technical scope of the present invention. [1] A battery case for a lithium-ion battery using a Ni-plated steel sheet having a steel sheet as a base material and a Ni-based plating layer located on the steel sheet, wherein the Ni content of the steel sheet is in the range of 0.10 to 5.00 mass%, and the amount of Ni plating layer attached is 7.0 to 30.0 g / m² in terms of metallic Ni per side of the Ni-plated steel sheet. ２[1] A lithium-ion battery case wherein the battery case has a welded portion formed by welding the cut end faces obtained by cutting the Ni-plated steel sheet in the thickness direction, the Ni concentration in the weld metal constituting the welded portion is in the range of 1.0 to 8.0 mass%, and at least a part of the cut end face is covered with the weld metal. [2] The lithium-ion battery case according to [1], wherein the weld metal covers the entire surface of the cut end face. [3] The lithium-ion battery case according to [1] or [2], wherein the thickness of the steel sheet is in the range of 0.10 to 1.00 mm. [4] The lithium-ion battery case according to [1], wherein an Fe-Ni alloy oxide film is formed on the surface of the cut end face not covered with the weld metal, and the thickness of the oxide film is in the range of 10 to 50 nm. [5] A battery case for a lithium-ion battery according to [1] or [2], wherein an Fe-Ni alloy oxide film is formed on the surface of the weld metal in the welded part, and the thickness of the oxide film is in the range of 10 to 50 nm. [6] A battery case for a lithium-ion battery according to [1] or [2], wherein the steel plate is a steel plate having a chemical composition in mass% of: C: 0.001 to 0.250% Si: 0.002 to 0.100% Mn: 0.05 to 0.80% Ni: 0.10 to 5.00% Al: 0.005 to 0.050% P: 0.001 to 0.020% S: 0.0001 to 0.2500% N: 0.001 to 0.040%, with the remainder being Fe and impurities. [7] The steel sheet has a chemical composition in mass%, containing: C: 0.001 to 0.250%, Si: 0.002 to 0.100%, Mn: 0.05 to 0.80%, Ni: 0.10 to 5.00%, Al: 0.005 to 0.050%, P: 0.001 to 0.020%, S: 0.0001 to 0.2500%, N: 0.001 to 0.040%, and further containing one or more elements selected from the group consisting of element groups A to E below, with the remainder being Fe and impurities, as described in [1] or [2].[Element group A]: One or more elements selected from the group consisting of Sn: 2.0% or less, Ti: 1.0% or less, and Cu: 1.50% or less. [Element group B]: Nb: 0.200% or less. [Element group C]: Mo: 3.0% or less. [Element group D]: One or more elements selected from the group consisting of V: ​​0.10% or less, As: 0.10% or less, Sb: 0.50% or less, Ca: 0.050% or less, and Mg: 0.0500% or less. [Element group E]: B: 0.0030% or less. [8] A battery case for a lithium-ion battery according to [7], having a chemical composition containing element group A. [9] A battery case for a lithium-ion battery according to [7], having a chemical composition containing element group B.

[10] A battery case for a lithium-ion battery according to [7], having a chemical composition containing element group C.

[11] A battery case for a lithium-ion battery according to [7], having a chemical composition containing the element group D.

[12] A battery case for a lithium-ion battery according to [7], having a chemical composition containing the element group E.

[13] A battery case for a lithium-ion battery according to [1] or [2], wherein the Ni-based plating layer is a Ni plating layer.

[14] A battery case for a lithium-ion battery according to [1] or [2], wherein the Ni-based plating layer is a plating layer having a chemical composition in which, by mass%, Fe: 1.0 to 20.0%, with the remainder being Ni and impurities.

[15] A battery case for a lithium-ion battery according to [1] or [2], wherein the Ni-based plating layer is a plating layer having a chemical composition in which, by mass%, Fe: 1.0 to 20.0%, and further contains one or more elements selected from the group consisting of element groups F to H, with the remainder being Ni and impurities. [Element group F]: One or more elements selected from the group consisting of W: 50.0% or less, Co: 5.0% or less, and Mo: 30.0% or less [Element group G]: One or two elements selected from the group consisting of Sn: 0.1000% or less and Zn: 0.1000% or less [Element group H]: One or two elements selected from the group consisting of C: 0.01% or less and S: 0.01% or less

[16] A battery case for a lithium-ion battery according to

[15] , having a chemical composition containing the element group F.

[17] A battery case for a lithium-ion battery according to

[15] , having a chemical composition containing the element group G.

[18] A battery case for a lithium-ion battery according to

[15] , having a chemical composition containing the element group H.

[19] A battery case for a lithium-ion battery according to [1] or [2], wherein the welded part is a laser welded part.

[20] A lithium-ion battery having the battery case for a lithium-ion battery according to [1] or [2].

[0207] 1 Lithium-ion battery 3 Battery unit 5 Electrolyte 10 Battery case 11 Case body 13 Lid 15 Injection port 17 Injection port cover 21 Welded part 23 Joining part 31 End face 32 End face of body before welding 33 End face of lid before welding 100 Ni-plated steel sheet 101 Base steel sheet 103 Ni-based plating layer 201 Weld metal 203, 301 Oxide film

Claims

1. A battery case for a lithium-ion battery comprising a lid and a case body connected to the lid via a weld metal, wherein each of the lid and the case body is made of a Ni-plated steel sheet having a steel sheet as a base material and Ni-based plating layers located on two surfaces facing each other in the thickness direction of the steel sheet, the Ni content of the steel sheet is 0.1% by mass or more, and the amount of Ni-based plating layer attached is 7.0 g / m² in terms of metallic Ni per side of the Ni-plated steel sheet. ２ The above is true, and the Ni concentration in the weld metal is 1.0% by mass or more, and the lid, the weld metal, and the case body are arranged in order in the thickness direction of the lid, the battery case for a lithium-ion battery.

2. The battery case for a lithium-ion battery according to claim 1, wherein the weld metal is a fully penetrated weld metal that extends over the entire thickness of the case body.

3. The Ni content of the steel sheet is 5.0% by mass or less, and the amount of Ni-based plating layer deposited is 30.0 g / m² per side of the Ni-plated steel sheet, in terms of metallic Ni. ２ The battery case for a lithium-ion battery according to claim 1 or 2, wherein the Ni concentration in the weld metal is 8.0% by mass or less.

4. The battery case for a lithium-ion battery according to claim 1 or 2, wherein the thickness of the steel plate is in the range of 0.10 to 1.00 mm.

5. The battery case for a lithium-ion battery according to claim 1 or 2, wherein the battery case has an Fe-Ni alloy-based oxide film disposed on the base material of the case body at a position adjacent to the weld metal on the inner surface of the battery case, and the thickness of the oxide film is in the range of 10 to 50 nm.

6. A battery case for a lithium-ion battery according to claim 1 or 2, wherein an Fe-Ni alloy-based oxide film is disposed on the surface of the weld metal on the inner side of the battery case, and the thickness of the oxide film is in the range of 10 to 50 nm.

7. The battery case for a lithium-ion battery according to claim 1 or 2, wherein the steel sheet has a chemical composition in mass percent of: C: 0.001 to 0.250%, Si: 0.002 to 0.100%, Mn: 0.05 to 0.80%, Ni: 0.1 to 5.0%, Al: 0.005 to 0.050%, P: 0.001 to 0.020%, S: 0.0001 to 0.2500%, N: 0.001 to 0.040%, with the remainder being Fe and impurities.

8. The battery case for a lithium-ion battery according to claim 1 or 2, wherein the steel sheet contains, by mass%, C: 0.001 to 0.250%, Si: 0.002 to 0.100%, Mn: 0.05 to 0.80%, Ni: 0.1 to 5.0%, Al: 0.005 to 0.050%, P: 0.001 to 0.020%, S: 0.0001 to 0.2500%, and N: 0.001 to 0.040%, and further contains one or more elements selected from the group consisting of element groups A to E below, with the remainder being Fe and impurities. [Element Group A]: One or more elements selected from the group consisting of Sn: 2.0% or less, Ti: 1.0% or less, and Cu: 1.50% or less. [Element Group B]: Nb: 0.200% or less. [Element Group C]: Mo: 3.0% or less. [Element Group D]: One or more elements selected from the group consisting of V: ​​0.10% or less, As: 0.10% or less, Sb: 0.50% or less, Ca: 0.050% or less, and Mg: 0.0500% or less. [Element Group E]: B: 0.0030% or less.

9. The battery case for a lithium-ion battery according to claim 8, wherein the steel plate has a chemical composition containing the element group A.

10. The battery case for a lithium-ion battery according to claim 8, wherein the steel plate has a chemical composition containing the element group B.

11. The battery case for a lithium-ion battery according to claim 8, wherein the steel plate has a chemical composition containing the element group C.

12. The battery case for a lithium-ion battery according to claim 8, wherein the steel plate has a chemical composition containing the element group D.

13. The battery case for a lithium-ion battery according to claim 8, wherein the steel plate has a chemical composition containing the element group E.

14. The battery case for a lithium-ion battery according to claim 1 or 2, wherein the Ni-based plating layer is a Ni plating layer.

15. The battery case for a lithium-ion battery according to claim 1 or 2, wherein the Ni-based plating layer is a plating layer having a chemical composition in which, by mass%, Fe: 1.0 to 20.0%, with the remainder being Ni and impurities.

16. The Ni-based plating layer is a battery case for a lithium-ion battery according to claim 1 or 2, wherein the plating layer has a chemical composition in which, by mass%, Fe: 1.0 to 20.0%, and further contains one or more elements selected from the group consisting of the following element groups F to H, with the remainder being Ni and impurities. [Element group F]: One or more elements selected from the group consisting of W: 50.0% or less, Co: 5.0% or less, and Mo: 30.0% or less [Element group G]: One or two elements selected from the group consisting of Sn: 0.1000% or less, and Zn: 0.1000% or less [Element group H]: One or two elements selected from the group consisting of C: 0.01% or less, and S: 0.01% or less 17. The battery case for a lithium-ion battery according to claim 16, wherein the Ni-based plating layer has a chemical composition containing the element group F.

18. The battery case for a lithium-ion battery according to claim 16, wherein the Ni-based plating layer has a chemical composition containing the element group G.

19. The battery case for a lithium-ion battery according to claim 16, wherein the Ni-based plating layer has a chemical composition containing the element group H.

20. The battery case for a lithium-ion battery according to claim 1 or 2, wherein the welded part is a laser-welded part.

21. A lithium-ion battery having a battery case for a lithium-ion battery according to claim 1 or 2.

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