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

Abstract

To achieve superior safety and resistance to electrolytes. [Solution] The battery case for a lithium-ion battery according to the present invention comprises a case body that houses a battery unit having a positive electrode, a negative electrode and a separator, and an electrolyte containing a lithium salt, and a lid that seals the case body, wherein the material of the case body and the lid is steel having a chemical composition of mass%, containing Cr: 1.0~9.9%, Al: 0.5~10.0%, Mn: 0.1~5.0%, C: 0.002~0.100%, Si: 0.01~0.50%, P: 0.005~0.070%, S: 0.001~0.250%, N: 0.001~0.020%, B: 0.0001~0.0030%, with the remainder being Fe and impurities, and the battery case has a crimped portion where the case body and the lid are joined by a crimping process.

Description

Technical Field

[0001] The present invention relates to a battery case for a lithium-ion battery and a lithium-ion battery.

Background Art

[0002] In recent years, the applications of lithium-ion batteries have been rapidly expanding to power storage devices for power storage combined with new energy systems such as solar cells and wind power generation, and automotive batteries. Considering the application as an automotive battery, the material of the battery case of the lithium-ion battery is required to achieve both the lightness of the case itself and corrosion resistance.

[0003] As the corrosion resistance required for the battery case of a lithium-ion battery, in addition to the corrosion resistance of the outer surface of the battery case (the surface exposed to the atmosphere, etc., hereinafter referred to as "outer surface corrosion resistance"), the corrosion resistance against an electrolytic solution containing a lithium salt (for example, LiPF6, etc.) housed inside the battery case (hereinafter referred to as "electrolytic solution resistance") is considered. Therefore, as a material for the battery case of a lithium-ion battery, an aluminum material is often used as a material that can achieve the lightness of the battery case itself and has the above two types of corrosion resistance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the automotive lithium-ion battery market, there is a demand for increased capacity and energy density to improve the performance of electric vehicles, leading to a trend towards larger lithium-ion batteries (increasing the battery's volume). However, larger battery volumes tend to trap more heat. Therefore, if the lithium-ion battery's temperature rises excessively and leads to thermal runaway, the battery case could melt, exceeding the melting point of aluminum (approximately 660°C). Thus, as lithium-ion batteries become more widespread in automobiles, greater safety of the battery itself is essential.

[0006] From a safety perspective, as described above, it is conceivable to use a material with a higher melting point than aluminum to prevent the battery case from melting even if the lithium-ion battery experiences thermal runaway. One such material is steel. The melting point of steel is generally around 1500°C, although this depends on its chemical composition. Therefore, by using steel as the material for the battery case, it is possible to prevent the battery case from melting during thermal runaway, even if the lithium-ion battery itself is made larger.

[0007] On the other hand, regarding the corrosion resistance of lithium-ion battery cases, steel has traditionally been used as a material for various products and structures used in a variety of corrosive environments, such as high-temperature humid corrosion environments, atmospheric corrosion environments, condensation corrosion environments, tap water corrosion environments, drinking water corrosion environments, concrete corrosion environments, and seawater corrosion environments, and various technologies have been proposed to achieve excellent corrosion resistance.

[0008] For example, Patent Document 1 proposes a steel material that exhibits excellent corrosion resistance of processed parts even under various corrosive environments as described above. This steel material uses a steel containing Cr, Al, and Mg at specific concentrations as a base material, and has a metal layer that satisfies specific electrochemical conditions on the surface of the base material.

[0009] Considering the battery case of a lithium-ion battery, the inside of the lithium-ion battery contains a highly reactive compound called a lithium salt containing fluorine as the electrolyte. Furthermore, the environment inside the lithium-ion battery is an extremely unique corrosive environment, as it is exposed to both a strong oxidizing atmosphere and a strong reducing atmosphere within the confined space of the battery case. From the above perspective, even with steel materials intended to improve corrosion resistance under various corrosive environments, such as those described in Patent Document 1, there was still room for further improvement in terms of electrolyte resistance of the battery case in a lithium-ion battery.

[0010] Thus, when focusing on the battery case of a lithium-ion battery, there is currently no material that combines the safety required of a lithium-ion battery with the electrolyte resistance required for a battery case. Therefore, there is a strong demand for a lithium-ion battery case with superior safety and electrolyte resistance.

[0011] Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide a battery case for lithium-ion batteries and a lithium-ion battery that can achieve better safety and electrolyte resistance. [Means for solving the problem]

[0012] To solve the above problems, the inventors conducted diligent research and found that by using steel as the material for the battery case of a lithium-ion battery, which offers superior safety, it is possible to achieve better electrolyte resistance by keeping the chemical composition of the steel within a specific range. Based on these findings, the gist of the present invention is as follows:

[0013] (1) A battery case for a lithium-ion battery, comprising a battery unit having a positive electrode, a negative electrode and a separator, an electrolyte containing a lithium salt, a case body for housing the battery unit, and a lid for sealing the case body, wherein the material of the case body and the lid is, in mass%, Cr: 1.0~9.9%, Al: 0.5~10.0%, Mn: 0.1~5.0%, C: 0.002~0.100%, Si: A battery case for a lithium-ion battery, comprising steel having a chemical composition containing 0.01-0.50% of P, 0.005-0.070% of S, 0.001-0.250% of N, and 0.001-0.0030% of B, with the remainder being Fe and impurities, wherein the battery case has a crimped portion where the case body and the lid are joined by a crimping process. (2) A battery case for a lithium-ion battery, comprising a battery unit having a positive electrode, a negative electrode and a separator, an electrolyte containing a lithium salt, a case body for housing the battery unit, and a lid for sealing the case body, wherein the material of the case body and the lid is, in mass%, Cr: 1.0~9.9%, Al: 0.5~10.0%, Mn: 0.1~5.0%, C: 0.002~0.100%, Si: 0.01~0.50%, P: 0.005~ A battery case for a lithium-ion battery, comprising steel having a chemical composition of 0.070%, S:0.001~0.250%, N:0.001~0.020%, B:0.0001~0.0030%, and further containing one or more elements selected from the group consisting of element groups A to D below, with the remainder being Fe and impurities, wherein the battery case has a crimped portion where the case body and the lid are joined by a crimping process. [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]: One or two elements selected from the group consisting of Mo: 3.0% or less and Ni: 9.0% 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. (3) A battery case for a lithium-ion battery according to (1) or (2), wherein at least one of Cr fluoride or Al fluoride is present on the inner surface of the battery case in contact with the electrolyte. (4) A battery case for a lithium-ion battery as described in (1) or (2), wherein the thickness of the case body is 0.10 to 1.00 mm and the thickness of the lid is 0.10 to 1.00 mm. (5) The battery case for a lithium-ion battery according to (1) or (2), wherein the steel material is a steel material without a plating layer. (6) A battery case for a lithium-ion battery according to (1) or (2), wherein a sealing compound is present in the crimped portion. (7) A battery case for a lithium-ion battery according to (2), having a chemical composition containing the element group A. (8) A battery case for a lithium-ion battery according to (2), having a chemical composition containing the element group B. (9) A battery case for a lithium-ion battery according to (2), having a chemical composition containing the element group C. (10) A battery case for a lithium-ion battery according to (2), having a chemical composition containing the element group D. (11) A lithium-ion battery having a battery case for a lithium-ion battery as described in (1) or (2). [Effects of the Invention]

[0014] As described above, the present invention makes it possible to provide a battery case for lithium-ion batteries and a lithium-ion battery that have superior safety and electrolyte resistance. [Brief explanation of the drawing]

[0015] [Figure 1]It is an explanatory diagram schematically 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. [Figure 2A] It is an explanatory diagram schematically showing a battery case for a lithium-ion battery according to the embodiment and a lithium-ion battery using such a battery case. [Figure 2B] It is an explanatory diagram schematically showing a battery case for a lithium-ion battery according to the embodiment and a lithium-ion battery using such a battery case. [Figure 3] It is a schematic diagram for explaining the structure in the vicinity of the winding portion of a battery case for a lithium-ion battery according to the embodiment. [Figure 4] It is an explanatory diagram schematically showing the material of a battery case for a lithium-ion battery according to the embodiment.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0017] (Regarding Lithium-Ion Batteries) <Regarding the Overall Configuration of a Lithium-Ion Battery> First, referring to FIGS. 1 to 2B, the overall configuration of a lithium-ion battery according to an embodiment of the present invention will be described. FIGS. 1 to 2B are explanatory diagrams 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. In the following, for convenience, the description may be made using the coordinate system shown in FIG. 1.

[0018] As schematically shown in Figure 1, the lithium-ion battery 1 according to this embodiment comprises a battery unit 3 having a positive electrode, a negative electrode, and a separator, and an electrolyte 5 containing a lithium salt, all housed in a battery case 10 for the lithium-ion battery according to this embodiment (hereinafter simply abbreviated as "battery case 10"). Here, the battery case 10 according to this embodiment has a case body portion 11 and a lid portion 13.

[0019] [Regarding battery unit 3 and 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. Various types of lithium-ion batteries can be used for each component of the battery unit 3 as appropriate. Furthermore, the specific structure of the battery unit 3 is not particularly limited, and various structures can be adopted.

[0020] Furthermore, the specific shape and size of the battery unit 3 are not particularly limited. In Figure 1A, a battery unit 3 with a rectangular shape is shown for convenience, but the shape of the battery unit 3 may be cylindrical or any other shape.

[0021] Furthermore, the electrolyte 5 only needs to contain a lithium salt capable of generating lithium ions, and various electrolytes containing lithium salts (especially lithium salts containing fluorine) can be used as appropriate. Examples of such lithium salts include LiPF6, LiBF4, and LiN(SO2CF3)2 (also known as LiTFSI).

[0022] [About battery case 10] As shown in Figure 1, the battery case 10 in the lithium-ion battery 1 according to this embodiment houses the battery unit 3 and electrolyte 5 as described above, and is composed of a case body 11 and a lid 13.

[0023] The case body 11 of the battery case 10 is a hollow component having an internal space capable of housing the battery unit 3 and the electrolyte 5. The case body 11 is composed of a bottom surface (not shown) and side surfaces. In Figure 1A, the case body 11 has a rectangular bottom surface (not shown) and four side surfaces 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 13, as shown in Figure 1A.

[0024] In Figure 1, 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. Such a case body 11 can be manufactured, for example, by deep drawing of the steel material.

[0025] 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.

[0026] In the battery case 10 shown in Figure 1, 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 crimping. As a result, the case body 11 and the lid 13 of the battery case 10 are integrated. Subsequently, electrolyte 5 is injected into the inside of the battery case 10 through the liquid injection port 15 provided in the lid 13. After the liquid injection port 15 on the lid 13 is injected with the liquid injection port cover 17, and a sealing process using welding or blind rivets is 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 2A, a crimped portion 21 is formed at the joint between the body 11 and the lid 13, and a sealing portion 23 is formed at the joint between the lid 13 and the liquid injection port cover 17.

[0027] Here, various known methods can be used for the method of fastening the case body 11 and the lid 13 of the battery case 10, and for closing the lid 13 and the liquid injection port cover 17.

[0028] Furthermore, in Figures 1 to 2A, 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 (e.g., seam welding, laser welding, etc.).

[0029] For example, when forming the side surface of a case body 11 having a rectangular shape as shown in Figure 1, 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, which 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 material that will form the bottom surface can be welded to the side surface of the case body 11 obtained in the manner described above by laser welding or the like. In this case, the steel material 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 a welded portion 25 formed on the side surface of the case body 11, as schematically shown in Figure 2B.

[0030] Figure 3 is a schematic diagram illustrating the structure near the crimping portion of the battery case for a lithium-ion battery according to this embodiment. Figure 3 focuses on the cross-section when the battery case 10 is cut in the height direction of the battery case.

[0031] 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 crimped together. Subsequently, electrolyte 5 is injected through the injection port 15 provided in the lid 13, the injection port 15 is closed by the injection port cover 17, and the lid 13 is closed by the injection port cover 16. As a result, the battery case 10 of the lithium-ion battery 1 has a crimped section 21 and a sealing section 23 as shown in Figure 3.

[0032] In this embodiment, the specific structure of the crimping portion 21 in the battery case 10 is not particularly defined, and various known crimping methods can be applied in addition to the shape illustrated in Figure 3.

[0033] Furthermore, in the battery case 10 according to this embodiment, it is preferable that a sealing compound 27 is present in the crimping portion 21 in order to further improve the airtightness of the crimping portion 21. This makes it possible to prevent the electrolyte 5 held inside the battery case 10 from leaking out to the outside of the battery case 10, thereby further improving the safety of the lithium-ion battery 1 according to this embodiment.

[0034] Here, there are no specific requirements regarding the type of sealing compound 27 used during the crimping process. Various known sealing compounds can be appropriately selected depending on the size of the case body 11 and lid 13, the electrolyte 5 used, the crimping structure adopted, etc.

[0035] 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 1A to 3.

[0036] <Regarding the steel material used for the case body 11 and lid 13> Next, the steel materials used for the case body 11 and lid 13 of the battery case 10 according to this embodiment will be described in detail with reference to Figure 4. Figure 4 is a schematic explanatory diagram showing the materials for the battery case for lithium-ion batteries according to this embodiment.

[0037] As the material for the case body 11 and lid 13 according to this embodiment, steel material 100 as schematically shown in Figure 4 is used.

[0038] ≪About the chemical composition of steel material 100≫ The chemical composition of the steel material 100 according to this embodiment, in one embodiment, contains, by mass%, Cr: 1.0~9.9%, Al: 0.5~10.0%, Mn: 0.1~5.0%, C: 0.002~0.100%, Si: 0.01~0.50%, P: 0.005~0.070%, S: 0.001~0.250%, N: 0.001~0.020%, B: 0.0001~0.0030%, with the remainder being Fe and impurities.

[0039] Furthermore, according to another embodiment, the chemical composition of the steel material 100 in this embodiment is as follows: it contains, by mass%, Cr: 1.0~9.9%, Al: 0.5~10.0%, Mn: 0.1~5.0%, C: 0.002~0.100%, Si: 0.01~0.50%, P: 0.005~0.070%, S: 0.001~0.250%, N: 0.001~0.020%, B: 0.0001~0.0030%, and also contains one or more elements selected from the group consisting of element groups A to D below, with the remainder being Fe and impurities.

[0040] [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]: One or two elements selected from the group consisting of Mo: 3.0% or less and Ni: 9.0% 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.

[0041] [Cr:1.0~9.9% by mass] Cr is an element necessary for ensuring the corrosion resistance (more specifically, external corrosion resistance and electrolyte resistance) required for the battery case 10 in the steel material 100 according to this embodiment, and is included in a predetermined amount or more. If the Cr content in the steel material 100 is less than 1.0 mass%, the above-mentioned corrosion resistance cannot be guaranteed. For this reason, the Cr content in the steel material 100 is 1.0 mass or more. The Cr content is preferably 2.0 mass or more, and more preferably 3.0 mass or more.

[0042] On the other hand, if the Cr content of the steel material 100 exceeds 9.9 mass%, not only will the manufacturing cost of the battery case 10 increase, but the processability of the steel material 100 when processing it into the battery case 10 (case body 11 and lid 13) will decrease. A decrease in processability is undesirable because it reduces the yield of the battery case 10. Furthermore, if the Cr content of the steel material 100 exceeds 9.9 mass%, Cr carbides will form in the steel material 100, and the external corrosion resistance when the steel material 100 is processed into the battery case 10 will also decrease. For this reason, the Cr content of the steel material 100 should be 9.9 mass% or less. Preferably, the Cr content is 7.0 mass% or less, and more preferably 6.0 mass% or less.

[0043] [Al:0.5~10.0% by mass] Al is an element necessary to ensure the corrosion resistance (more specifically, external corrosion resistance and electrolyte resistance) required for the battery case 10 in the steel material 100 according to this embodiment, and is included in a predetermined or higher content. If the Al content in the steel material 100 is less than 0.5% by mass, the above-mentioned corrosion resistance cannot be guaranteed. Therefore, the Al content in the steel material 100 is 0.5% by mass or more. The Al content is preferably 0.8% by mass or more, and more preferably 1.0% by mass or more.

[0044] On the other hand, if the Al content of the steel material 100 exceeds 10.0 mass%, not only will the manufacturing cost of the battery case 10 increase, but the processability of the steel material 100 when processing it into the battery case 10 (case body 11 and lid 13) will decrease. A decrease in processability is undesirable because it reduces the yield of the battery case 10. Therefore, the Al content of the steel material 100 should be 10.0 mass% or less. Preferably, the Al content is 5.0 mass% or less, and more preferably 3.0 mass% or less.

[0045] [Mn:0.1~5.0% by mass] Mn is an element that lowers the Ac3 transformation point of steel material 100. By including Mn in steel material 100 at a predetermined level or higher, it becomes possible to control the Ac3 transformation point of steel material 100 within a desired range, thereby enabling appropriate control of the mechanical strength of steel material 100. In order to achieve this Ac3 transformation point control effect, the Mn content in steel material 100 should be 0.1% by mass or more.

[0046] Furthermore, Mn is a useful element as a deoxidizing agent for steel. The deoxidizing effect on steel can be achieved by setting the Mn content to 1.0 mass%. Therefore, in order to achieve both the Ac3 transformation point control effect and the deoxidizing effect, the Mn content in steel material 100 is preferably 1.0 mass% or more. The Mn content in steel material 100 is more preferably 2.0 mass% or more.

[0047] On the other hand, if the Mn content of the steel material 100 exceeds 5.0 mass%, the Ac3 transformation point control effect saturates, while the manufacturing cost of the battery case 10 increases, which is undesirable. Therefore, the Mn content of the steel material 100 should be 5.0 mass% or less. Furthermore, by setting the Mn content of the steel material 100 to 3.0 mass% or less, it is possible to maintain the workability of the steel material 100 while simultaneously exhibiting both the Ac3 transformation point control effect and the deoxidizing effect, which is preferable. The Mn content in the steel material 100 is more preferably 2.7 mass% or less.

[0048] [C:0.002~0.100% by mass] Since carbon (C) is an element that dissolves in steel and improves its strength, it is included in a predetermined amount or more. If the C content in steel material 100 is less than 0.002% by mass, the strength-improving effect described above cannot be achieved. Therefore, the C content in steel material 100 is 0.002% by mass or more. Furthermore, in order to achieve both the strength of the steel and the assurance of workability, the C content in steel material 100 is preferably more than 0.020% by mass, and more preferably 0.010% by mass or more. The C content in steel material 100 is even more preferably 0.020% by mass or more.

[0049] On the other hand, if the carbon content of the steel material 100 exceeds 0.100 mass%, carbon will form carbides in the steel, reducing the corrosion resistance of the steel material 100, which is undesirable. Also, when manufacturing battery cases for lithium-ion batteries, the case body may be made by welding, and from the viewpoint of welding, a lower carbon content is preferable. For this reason, the carbon content of the steel material 100 should be 0.100 mass% or less. Preferably, the carbon content of the steel material 100 is 0.050 mass% or less, and more preferably 0.030 mass% or less.

[0050] [Si:0.01~0.50% by mass] Since silicon (Si) is an element that improves the strength of steel, it is included in a predetermined amount or more. If the Si content in steel material 100 is less than 0.01% by mass, the strength-improving effect described above cannot be achieved. Therefore, the Si content in steel material 100 is set to 0.01% by mass or more. Furthermore, in order to achieve both the strength of the steel and the assurance of workability, the Si content in steel material 100 is preferably 0.10% by mass or more, and more preferably 0.25% by mass or more.

[0051] On the other hand, if the Si content in the steel material 100 is excessive, Si will concentrate on the steel surface during heating in the manufacturing process, reducing the electrolyte resistance of the manufactured steel material 100. This surface concentration of Si becomes noticeable when the Si content of the steel material 100 exceeds 0.50 mass%. Therefore, the Si content in the steel material 100 should be 0.50 mass% or less. To more appropriately ensure the electrolyte resistance of the steel material 100, the Si content in the steel material 100 is preferably less than 0.50 mass%, more preferably 0.40 mass% or less, and even more preferably 0.30 mass% or less.

[0052] [P:0.005~0.070% by mass] P is an element that is inevitably present in steel. While it is possible to reduce the P content in steel through dephosphorization during the steelmaking process, reducing the P content to less than 0.005% by mass would excessively increase the manufacturing cost of the steel, which is undesirable. From this perspective, the P content in steel material 100 is set to 0.005% by mass or more.

[0053] Furthermore, phosphorus (P) is an element that improves the strength of steel. The strength-improving effect of P becomes significant when the P content is 0.010% by mass or more, so it is preferable that the P content in steel material 100 is 0.010% by mass or more. More preferably, the P content in steel material 100 is 0.020% by mass or more.

[0054] On the other hand, if the P content of the steel material 100 exceeds 0.070 mass%, the strength of the steel material 100 improves too much, resulting in a decrease in workability, which is undesirable. Therefore, the P content of the steel material 100 should be 0.070 mass% or less. Preferably, the P content of the steel material 100 is 0.060 mass% or less, and more preferably 0.050 mass% or less.

[0055] [S:0.001~0.250% by mass] S is an element that is inevitably present in steel. While it is possible to reduce the S content in steel through desulfurization treatment in the steelmaking process, 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 steel material 100 is set to 0.001 mass% or more. Preferably, the S content of steel material 100 is 0.002 mass% or more, and more preferably 0.003 mass% or more.

[0056] On the other hand, if the S content of the steel material 100 exceeds 0.250 mass%, the steel material becomes brittle, which is undesirable. Therefore, the S content of the steel material 100 should be 0.250 mass% or less. Preferably, the S content of the steel material 100 is 0.100 mass% or less, and more preferably 0.010 mass% or less.

[0057] [N:0.001~0.020% by mass] N is an element that is inevitably present in steel. Reducing the N content to less than 0.001% by mass is undesirable because it excessively increases the manufacturing cost of the steel. Therefore, the N content in steel material 100 is set to 0.001% by mass or more. Preferably, the N content of steel material 100 is 0.002% by mass or more, and more preferably 0.003% by mass or more.

[0058] On the other hand, if the N content of the steel material 100 exceeds 0.020 mass%, nitrides and carbonitrides are formed in the steel, which degrades the quality of the steel, and is therefore undesirable. For this reason, the N content of the steel material 100 should be 0.020 mass% or less. Preferably, the N content of the steel material 100 is 0.010 mass% or less, and more preferably 0.005 mass% or less.

[0059] [B:0.0001~0.0030% by mass] B is an element that refines the recrystallized grains during annealing in the manufacturing of steel. Refining the recrystallized grains improves the rollability of the steel during cold rolling, thereby increasing the productivity of steel 100. This recrystallized grain refinement effect becomes significant when the B content of steel 100 is 0.0001% by mass or more. Therefore, the B content of the steel is set to 0.0001% by mass or more. Preferably, the B content of steel 100 is 0.0005% by mass or more, and more preferably 0.0010% by mass or more.

[0060] On the other hand, if the B content of steel material 100 exceeds 0.0030 mass%, the optimal rolling rate due to refinement decreases, and the productivity of steel material 100 decreases. For this reason, the B content of steel material 100 should be 0.0030 mass% or less. Preferably, the B content of steel material 100 is 0.0025 mass% or less, and more preferably 0.0020 mass% or less.

[0061] In the steel material 100 according to this embodiment, the remainder of the above Cr, Al, Mn, C, Si, P, S, N, and B is Fe and impurities. Here, "impurities" means components that are mixed into the steel material during the industrial production of steel material due to raw materials such as ore and scrap, or various factors in the manufacturing process, and are acceptable within a range that does not adversely affect the various properties of the steel material according to this embodiment.

[0062] Because the steel material 100 according to this embodiment has the above-described chemical composition, the steel material 100 according to this embodiment can exhibit even better electrolyte resistance.

[0063] Next, in a steel material 100 according to another embodiment of this invention, element groups A to D, which may be present in the chemical composition of such steel material 100, will be described in detail.

[0064] In addition, in the steel material 100 according to another embodiment of this embodiment, if at least one of the elements belonging to element groups A to D below is included, it is preferable that at least one of the elements belonging to element groups A to D below is included within the following content range, and the total content is 10.00% by mass or less.

[0065] By keeping the total content of elements belonging to element groups A to D to 10.00 mass% or less, it becomes possible to enjoy the effects exhibited by the addition of each element, as detailed below, without interfering with each other. The total content of elements belonging to element groups A to D is preferably 8.00 mass% or less, and more preferably 5.00 mass% or less.

[0066] ◇Element group A In another embodiment of the steel material 100 according to this embodiment, the element group A that the steel material 100 may contain will be described. At least one of the elements of element group A shown below may be contained in the steel material 100 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.

[0067] [Sn:0~2.0% by mass] In the steel material 100 according to this embodiment, it is possible to use it as a steel material 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 (particularly external corrosion resistance) of the steel material 100 under various corrosive environments. This effect of improving corrosion resistance is manifested when the Sn content in the steel material 100 is 0.1 mass% or more. Therefore, when Sn is included in the steel material 100, it is preferable that the Sn content be 0.1 mass% or more. More preferably, the Sn content in the steel material 100 is 0.2 mass% or more.

[0068] On the other hand, if the Sn content in the steel material 100 exceeds 2.0 mass%, the above-mentioned effect of improving corrosion resistance saturates, and the manufacturing cost of the steel material increases. Therefore, when Sn is included in the steel material 100, it is preferable that the Sn content be 2.0 mass% or less. More preferably, the Sn content in the steel material 100 is 1.0 mass% or less.

[0069] [Ti:0~1.0% by mass] In the steel material 100 according to this embodiment, it is possible that it does not contain Ti, so the lower limit of its content is 0 mass%. On the other hand, Ti is an element that suppresses the formation of Cr carbides by forming carbides with C in the steel material 100, thereby preventing a decrease in the corrosion resistance (particularly external corrosion resistance) of the steel material 100. This effect is manifested when the Ti content in the steel material 100 is 0.1 mass% or more. Therefore, when Ti is included in the steel material 100, it is preferable that the Ti content be 0.1 mass% or more. More preferably, the Ti content in the steel material 100 is 0.3 mass% or more.

[0070] On the other hand, if the Ti content in the steel material 100 exceeds 1.0 mass%, the effect of preventing the decrease in corrosion resistance described above becomes saturated, and the manufacturing cost of the steel material increases. Therefore, when Ti is included in the steel material 100, it is preferable that the Ti content be 1.0 mass% or less. More preferably, the Ti content in the steel material 100 is 0.7 mass% or less.

[0071] [Cu:0~1.50% by mass] In the steel material 100 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 (particularly external corrosion resistance) of steel materials containing Cr. This effect of improving corrosion resistance is exhibited when the Cu content in the steel material 100 is 0.01 mass% or more. Therefore, when Cu is included in the steel material 100, it is preferable that the Cu content be 0.01 mass% or more. More preferably, the Cu content in the steel material 100 is 0.02 mass% or more.

[0072] On the other hand, if the Cu content in the steel material 100 exceeds 1.50% by mass, the above-mentioned effect of improving corrosion resistance saturates, and the manufacturing cost of the steel material increases. Therefore, when Cu is included in the steel material 100, it is preferable that the Cu content be 1.50% by mass or less. More preferably, the Cu content in the steel material 100 is 1.00% by mass or less.

[0073] ◇Element group B In another embodiment of the steel material 100 according to this embodiment, the element group B that the steel material 100 may contain will be described. The elements of element group B shown below are elements that may be contained in the steel material 100 in place of a portion of the remaining Fe. [Element group B]:Nb:0.200% or less

[0074] [Nb:0~0.200% by mass] In the steel material 100 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. This toughness-improving effect is exhibited when the Nb content in the steel material 100 is 0.050 mass% or more. Therefore, when Nb is included in the steel material 100, it is preferable that the Nb content be 0.050 mass% or more. More preferably, the Nb content in the steel material 100 is 0.070 mass% or more.

[0075] On the other hand, if the Nb content in the steel material 100 exceeds 0.200 mass%, the carbides produced become coarser, and the toughness of the steel decreases. Therefore, when Nb is included in the steel material 100, it is preferable that the Nb content be 0.200 mass% or less. More preferably, the Nb content in the steel material 100 is 0.080 mass% or less.

[0076] ◇Element group C In another embodiment of the steel material 100 according to this embodiment, the element group C that the steel material 100 may contain will be described. At least one of the elements of element group C shown below may be contained in the steel material 100 in place of a portion of the remaining Fe. [Element group C]: One or two elements selected from the group consisting of Mo: 3.0% or less and Ni: 9.0% or less.

[0077] [Mo:0~3.0% by mass] In the steel material 100 according to this embodiment, it is possible that it does not contain Mo, 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 steel material 100. This effect of improving electrolyte resistance is exhibited when the Mo content in the steel material 100 is 0.2 mass% or more. Therefore, when Mo is included in the steel material 100, it is preferable that the Mo content be 0.2 mass% or more. More preferably, the Mo content in the steel material 100 is 0.5 mass% or more.

[0078] On the other hand, if the Mo content in the steel material 100 exceeds 3.0% by mass, the above-mentioned effect of improving electrolyte resistance saturates, and the manufacturing cost of the steel material increases. Therefore, when Mo is included in the steel material 100, it is preferable that the Mo content be 3.0% by mass or less. More preferably, the Mo content in the steel material 100 is 2.0% by mass or less.

[0079] [Ni:0~9.0% by mass] In the steel material 100 according to this embodiment, it is possible that it does not contain Ni, so the lower limit of its content is 0 mass%. On the other hand, Ni is an element that improves the electrolyte resistance of the steel material 100. This improvement in electrolyte resistance is manifested when the Ni content in the steel material 100 is 1.0 mass% or more. Therefore, when Ni is included in the steel material 100, it is preferable that the Ni content be 1.0 mass% or more. More preferably, the Ni content in the steel material 100 is 3.0 mass% or more.

[0080] On the other hand, if the Ni content in the steel material 100 exceeds 9.0% by mass, the above-mentioned effect of improving electrolyte resistance saturates, and the manufacturing cost of the steel material increases. Therefore, when Ni is included in the steel material 100, it is preferable that the Ni content be 9.0% by mass or less. More preferably, the Ni content in the steel material 100 is 6.0% by mass or less.

[0081] ◇Element group D In another embodiment of the steel material 100 according to this embodiment, the element group D that the steel material 100 may contain will be described. At least one of the elements of element group D shown below may be contained in the steel material 100 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.

[0082] [V:0~0.10% by mass] In the steel material 100 according to this embodiment, it is possible that it does not contain V, 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 steel material 100. This effect of improving the corrosion resistance of the processed part is manifested when the V content in the steel material 100 is 0.01 mass% or more. Therefore, when V is included in the steel material 100, it is preferable that the V content be 0.01 mass% or more. More preferably, the V content in the steel material 100 is 0.04 mass% or more.

[0083] On the other hand, if the V content in the steel material 100 exceeds 0.10 mass%, the above-mentioned effect of improving the corrosion resistance of the processed part saturates, and the manufacturing cost of the steel material increases. Therefore, when V is included in the steel material 100, it is preferable that the V content be 0.10 mass% or less. More preferably, the V content in the steel material 100 is 0.08 mass% or less.

[0084] [As:0~0.10% by mass] In the steel material 100 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 component obtained by processing the steel material 100. This effect of improving the corrosion resistance of the processed part is manifested when the As content in the steel material 100 is 0.01 mass% or more. Therefore, when As is included in the steel material 100, it is preferable that the As content be 0.01 mass% or more. More preferably, the As content in the steel material 100 is 0.02 mass% or more.

[0085] On the other hand, if the As content in the steel material 100 exceeds 0.10% by mass, the above-mentioned effect of improving the corrosion resistance of the processed part saturates, and the manufacturing cost of the steel material increases. Therefore, when As is included in the steel material 100, it is preferable that the As content be 0.10% by mass or less. More preferably, the As content in the steel material 100 is 0.06% by mass or less.

[0086] [Sb:0~0.50% by mass] In the steel material 100 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 component obtained by processing the steel material 100. This effect of improving the corrosion resistance of the processed part is manifested when the Sb content in the steel material 100 is 0.01 mass% or more. Therefore, when Sb is included in the steel material 100, it is preferable that the Sb content be 0.01 mass% or more. More preferably, the Sb content in the steel material 100 is 0.02 mass% or more.

[0087] On the other hand, if the Sb content in the steel material 100 exceeds 0.50 mass%, the above-mentioned effect of improving the corrosion resistance of the processed part saturates, and the manufacturing cost of the steel material increases. Therefore, when Sb is included in the steel material 100, it is preferable that the Sb content be 0.50 mass% or less. More preferably, the Sb content in the steel material 100 is 0.30 mass% or less.

[0088] [Ca:0~0.050% by mass] In the steel material 100 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 component obtained by processing the steel material 100. This effect of improving the corrosion resistance of the processed part is manifested when the Ca content in the steel material 100 is 0.001 mass% or more. Therefore, when Ca is included in the steel material 100, it is preferable that the Ca content be 0.001 mass% or more. More preferably, the Ca content in the steel material 100 is 0.005 mass% or more.

[0089] On the other hand, if the Ca content in the steel material 100 exceeds 0.050 mass%, the above-mentioned effect of improving the corrosion resistance of the processed part saturates, and the manufacturing cost of the steel material increases. Therefore, when Ca is included in the steel material 100, it is preferable that the Ca content be 0.050 mass% or less. More preferably, the Ca content in the steel material 100 is 0.010 mass% or less.

[0090] [Mg:0~0.0500% by mass] In the steel material 100 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 steel material 100. This effect of improving the corrosion resistance of the processed part is manifested when the Mg content in the steel material 100 is 0.0001 mass% or more. Therefore, when Mg is included in the steel material 100, it is preferable that the Mg content be 0.0001 mass% or more. More preferably, the Mg content in the steel material 100 is 0.0010 mass% or more.

[0091] On the other hand, if the Mg content in the steel material 100 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 material will increase. For this reason, when Mg is included in the steel material 100, it is preferable that the Mg content be 0.0500 mass% or less. More preferably, the Mg content in the steel material 100 is 0.0100 mass% or less.

[0092] [Method for measuring chemical components] The chemical composition of the steel material 100 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry). For the steel material 100 of interest, a position corresponding to 1 / 4 of the plate thickness d is identified along the plate thickness direction from the surface, and a measurement sample is taken from this position. When taking the measurement sample, it should be taken from a location sufficiently far from the crimped or welded parts (for example, at least 10 mm away from the ends of the crimped or welded parts). By performing measurements on the acquired measurement sample in accordance with JIS G 1258-1:2014, etc., the content of elements other than C, N, and O in the chemical composition of the steel material 100 can be determined.

[0093] The carbon content of the steel material 100 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 steel material 100 of interest can be determined by measuring a sample obtained in the same manner using the so-called inert gas fusion-thermal conductivity method. Furthermore, the oxygen content of the steel material 100 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.

[0094] As described above, by keeping the chemical composition of the steel material 100 used for the battery case 10 according to this embodiment within a specific range, it is possible to achieve not only superior external corrosion resistance but also superior electrolyte resistance. Therefore, by using the steel material 100 according to this embodiment, it is possible to use the steel material without plating layers as the material for the battery case 10, without having to newly apply various plating layers to the surface of the steel material 100. As a result, in this embodiment, the manufacturing cost of producing the battery case 10 can be further reduced.

[0095] The chemical composition of the steel material 100 according to this embodiment has been described in detail above.

[0096] Regarding the presence of fluoride on the inner surface of the battery case 10: As described above, the steel material 100 used for the case body 11 and lid 13 of the battery case 10 according to this embodiment contains Cr and Al in specific amounts as its chemical components. During the process from manufacturing the case body 11 and lid 13 of the battery case 10 using the above-mentioned steel material 100 to assembling them into a lithium-ion battery, a native oxide film containing oxides of Cr and Al is formed on the surfaces of the case body 11 and lid 13 due to the reaction of oxygen in the air with Cr and Al in the steel material 100. This native oxide film is often a thin film with a thickness of less than 0.01 μm. In addition, in the welded part 21 described earlier, an oxide film layer 205 is formed during welding.

[0097] On the other hand, lithium salts containing fluorine are generally used as the electrolyte for lithium-ion batteries. The highly reactive fluoride ions contained in the electrolyte react with the native oxide film or oxide film layer 205, causing the chromium oxides and aluminum oxides contained in the native oxide film or oxide film layer 205 to react with the fluoride ions, forming chromium fluoride (CrF3) or aluminum fluoride (AlF3). Thus, on the inner surface of the battery case 10 according to this embodiment, at least one of chromium fluoride or aluminum fluoride is present in the portion that comes into contact with the electrolyte.

[0098] The above-mentioned Cr fluoride and Al fluoride are stable compounds even with respect to lithium salts containing fluorine in the electrolyte. Because these fluorides are present on the surface of the portion of the battery case 10 that comes into contact with the electrolyte on its inner surface, the battery case 10 according to this embodiment exhibits superior electrolyte resistance.

[0099] Here, whether or not the above-mentioned Cr fluoride and Al fluoride are present in the portion of the battery case 10 that is in contact with the electrolyte on the inner surface can be determined by taking a measurement sample from the portion of the battery case 10 that is in contact with the electrolyte and performing the following measurements.

[0100] First, the lithium-ion battery having the battery case 10 of interest is completely discharged, and then the case body 11 or lid 13 is cut to separate the battery unit from the battery case 10. A 50 mm x 50 mm sample is taken from the obtained battery case 10, and the surface corresponding to the inner surface of the battery case 10 is analyzed by X-ray photoelectron spectroscopy (XPS). If peaks of CrF3 or AlF3 are present in the obtained F1s spectrum, it can be determined that Cr fluoride or Al fluoride was present. In the F1s spectrum, the peak around a binding energy of 685 eV can be considered to originate from CrF3, and the presence of such a peak indicates the presence of CrF3. Also, the peak around a binding energy of 686-689 eV can be considered to originate from AlF3, and the presence of a peak in this range indicates the presence of AlF3.

[0101] Regarding the thickness of the steel material 100 used for the case body 11 and lid 13: In the battery case 10 according to this embodiment, since the case body 11 and lid 13 are made of the steel material described above, it has superior mechanical strength compared to the conventionally used aluminum material. Therefore, even with a thin steel material 100, it is possible to satisfy the strength required for the battery case 10, enabling miniaturization (thinning) of lithium-ion batteries and reducing manufacturing costs.

[0102] More specifically, when the above-mentioned steel material 100 is used as the material for the case body portion 11, the thickness of the case body portion 11 is preferably in the range of 0.10 to 1.00 mm. More preferably, the thickness of the case body portion 11 is 0.25 mm or more. Furthermore, the thickness of the case body portion 11 is preferably 0.60 mm or less.

[0103] Furthermore, when the above-mentioned steel material 100 is used as the material for the lid portion 13, the thickness of the lid portion 13 is preferably in the range of 0.10 to 1.00 mm. More preferably, the thickness of the lid portion 13 is 0.30 mm or more. More preferably, the thickness of the lid portion 13 is 0.80 mm or less.

[0104] The case body 11 and the lid 13 may have the same thickness, or they may have different thicknesses.

[0105] Here, the thickness of the case body 11 and the lid 13 can be measured by taking a measurement sample measuring 10 mm x 20 mm in size in a plan view from approximately the center of the case body 11 and the lid 13, while avoiding the location of the welded part, then embedding and polishing it in resin and observing the cross-section.

[0106] The battery case and lithium-ion battery according to this embodiment have been described in detail above with reference to Figures 1A to 4.

[0107] (Regarding battery cases for lithium-ion batteries and manufacturing methods for lithium-ion batteries) Next, we will describe a battery case for a lithium-ion battery according to this embodiment and an example of a method for manufacturing a lithium-ion battery using such a battery case. In the following description, we will focus on the battery case 10 shown in Figures 1A and 2A.

[0108] Prior to the following explanation, it is assumed that the case body 11 and lid 13 of the battery case 10 have been manufactured using the plated steel sheet 100 as the material to achieve the desired shape.

[0109] 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.

[0110] In the manufacturing method of a 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 electrolyte 5 is injected into the battery case 10. Subsequently, the case body portion 11 and the lid portion 13 of the battery case 10 are joined using various crimping methods and sealing compounds, resulting in the formation of a crimped portion 21.

[0111] Here, the process of storing the battery unit 3 and electrolyte 5 as described above is preferably carried out under an inert gas atmosphere such as Ar or N2, 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 storing 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.

[0112] Furthermore, the joining process (sealing) 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, examples of inert gases include Ar gas, N2 gas, carbon dioxide gas, helium gas, or a mixed gas containing at least two of these gases.

[0113] More specifically, for example, the inert gas is blown into the internal space of the battery case 10 immediately before the crimping process. Then, during the crimping process, the inert gas is blown from above the battery case 10 while the crimping process is carried out. In this case, the amount of inert gas blown in should be 0.5 L / min or more, and the amount blown from above should be 20.0 L / min or more. This fills the internal space of the battery case 10 with inert gas, making it possible to create a situation where the surface of the weld metal 201 produced by welding is less likely to oxidize. Although there is no specific upper limit for the amount of gas blown in, in practice it is around 1.0 L / min. Similarly, although there is no specific upper limit for the amount blown from above, in practice it is around 50.0 L / min.

[0114] 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.

[0115] Furthermore, the specific conditions for the crimping process are not limited in any way; the conditions should be adjusted as appropriate according to the material used.

[0116] 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. [Examples]

[0117] (Example test) In the test example shown below, a case body, lid, and liquid injection port cover, as shown in Figure 1, were prepared, along with the battery unit shown below. These components were then assembled to create a lithium-ion battery.

[0118] <Steel materials used as raw materials> For the battery case, the main body, lid, and liquid injection port cover were made from steel materials (plate thickness: 0.25~1.00 mm, manufactured by Nippon Steel Corporation) having the steel composition shown in Tables 1-1 and 1-2 below. In Tables 1-1 and 1-2, blank spaces indicate that the corresponding element was not intentionally added. For comparison, commercially available aluminum plates (plate thickness: 0.60~1.00 mm) were also prepared separately.

[0119] [Table 1-1]

[0120] [Table 1-2]

[0121] The case body was manufactured by deep drawing, bending and seam welding, or bending and laser welding. When the side of the case body was manufactured using bending, the butted ends were welded together by laser welding to form a cylinder, and then the material that would form the bottom was joined to one end of the cylinder by crimping to form the case body. The welding conditions for each welding process are as follows.

[0122] Laser welding conditions A fiber laser welding machine is used. Shielding gas used: N2, Ar Output: 1.2~6.0kW Welding speed: 3-12 m / min Focus shift: 0mm For each sample, the conditions were adjusted within the above range to ensure that the material blended completely into the back surface. ≪Seam Welding Conditions≫ Overlap: Approximately 3 to 5 times the plate thickness, and seam welding was performed. Single-phase AC (50Hz), continuous power supply Contact surface shape: Flat Pressing force: 300 kgf (1 kgf is approximately 9.8 N.) Welding speed: 6-12 m / min

[0123] <Battery Unit> ◇Positive plate Lithium cobalt oxide was used as the positive electrode active material. This positive electrode active material was mixed with acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of lithium cobalt oxide:acetylene black:PVDF = 10:10:1. The mixture was then coated onto aluminum foil as an aqueous dispersion and dried. The resulting material was rolled to a predetermined thickness and cut to a predetermined size to form the positive electrode plate.

[0124] ◇ Negative electrode plate Amorphous carbon was used as the negative electrode active material. The amorphous carbon was dry-mixed with acetylene black, a conductive material, to form a mixture. Then, N-methyl-2-pyrrolidone (NMP), which is obtained by dissolving polyvinylidene fluoride, was uniformly dispersed in the mixture to create a paste with a mass ratio of carbon:acetylene black:PVDF = 88:5:7. The resulting paste was applied to a Cu foil, dried, rolled to a predetermined thickness, and then cut to a predetermined size to form the negative electrode plate.

[0125] ◇Separator A polyethylene microporous membrane was used as the separator.

[0126] <Electrolyte> As the electrolyte, a solution was used which consisted of a 1:1 volume mixture of ethylene carbonate and diethyl carbonate, to which 1 mol / L of lithium hexafluorophosphate was added (1M-LiPF6EC:DEC(1:1)).

[0127] <Lithium-ion battery manufacturing procedure> After sandwiching a separator between the positive electrode plate and the negative electrode plate obtained as described above, the assembly was wound to form an electrode unit. After crushing the battery unit into a shape that can be inserted into the internal space of the case body, the positive electrode plate was welded to the Al lead, and the negative electrode plate was welded to the Ni lead. The Al lead was welded to the positive electrode terminal provided on the lid, and the Ni lead was welded to the negative electrode terminal provided on the lid.

[0128] Thereafter, the case body and the lid were crimped in an atmosphere at a temperature of 25°C and a dew point of -40°C. After the crimping process, the obtained joined body was stored in an atmosphere at a temperature of 25°C and a dew point of -76°C for 24 hours or more to dry the inside of the battery and remove moisture.

[0129] After storage, the above electrolytic solution was injected through the liquid injection port provided on the lid in an atmosphere at a temperature of 25°C and a dew point of -76°C.

[0130] Thereafter, the liquid injection port provided on the lid was closed with a liquid injection port lid to obtain a completed lithium-ion battery. At each level shown in Tables 2-1 and 2-2 below, a plurality of completed lithium-ion batteries obtained in this way were produced and used as samples for the evaluation described below. In the crimping process, a sealing compound was used.

[0131] Thereafter, in an atmosphere at a temperature of 25°C and a dew point of -76°C, the obtained lithium-ion battery was charged at 3.6V. By such treatment, the moisture remaining in the battery was electrolytically removed.

[0132] <Confirmation of Cr fluoride and Al fluoride> For each sample obtained as described above, in accordance with the method described above, samples were cut out from the portion in contact with the electrolytic solution, and the presence or absence of Cr fluoride and Al fluoride was confirmed. The obtained results are summarized in Tables 2-1 and 2-2 below.

[0133] <Evaluation of the obtained lithium-ion battery> The obtained lithium-ion batteries were evaluated from the perspectives of external corrosion resistance, electrolyte resistance, and safety. The results are summarized in Tables 2-1 and 2-2 below.

[0134] [External corrosion resistance] For each sample prepared as described above, the seam between the case body and the lid was cut using a high-speed precision cutting machine to obtain corrosion resistance test specimens. The size of the corrosion resistance test specimens was set to 50 mm x 50 mm. A salt spray test (SST) as specified in JIS Z2371:2015 was performed on the obtained corrosion resistance test specimens for 5 hours, and the rate of red rust occurrence was calculated. The obtained red rust occurrence rates were evaluated according to the following evaluation criteria, with scores of "EX", "VG", and "G" being considered passing grades. ≪Evaluation Criteria≫ Rating "EX": Red rust occurrence rate is between 0% and less than 10%. "VG": Red rust occurrence rate is between 10% and less than 30%. "G": Red rust occurrence rate is between 30% and less than 50% "B": Red rust occurrence rate is 50% or higher.

[0135] [Electrolyte resistance] The lithium-ion batteries prepared as described above were held at 80°C for 1000 hours. After holding, a portion of the battery case was disassembled in an atmosphere of 25°C with a dew point of -76°C, and the electrolyte was collected using a pipette. The amount of metal leached from the obtained electrolyte (more specifically, the amount of Fe leached) was analyzed using a commercially available ICP mass spectrometer (Agilent 7700x ICP-MS, manufactured by Agilent Technologies, Inc.). The obtained metal leaching amounts were evaluated according to the following evaluation criteria, with scores of "EX," "VG," and "G" being considered passing grades. ≪Evaluation Criteria≫ Rating "EX": Metal elution amount is between 0 ppm and less than 10 ppm. "VG": Metal leaching amount is between 10 ppm and less than 20 ppm. "G": Metal leaching amount is between 20 ppm and less than 50 ppm. "B": Metal leaching amount is 50 ppm or more.

[0136] [Safety] The safety of the lithium-ion batteries manufactured as described above was verified by a fire spread test, which is detailed below. In the fire spread test, two lithium-ion batteries were prepared for each level shown in Table 2 below. These two lithium-ion batteries were charged to 4.3V using constant current and constant voltage charging to achieve a State of Charge (SOC) of 110%. The two lithium-ion batteries after charging were designated as the fire spread battery and the ignition battery, respectively.

[0137] A voltmeter was installed on both the ignition battery and the fire-contamination battery to measure the voltage of each battery during the test. A heater was also installed on the side of the ignition battery to allow for heating of the battery. The fire-contamination battery was heated to approximately 50°C using the heater. Then, using two dummy batteries, the batteries were arranged in the sequence (dummy battery / ignition battery / fire-contamination battery / dummy battery) so that adjacent batteries were in contact with each other. After arrangement, the ignition battery was heated to approximately 200°C at a heating rate of 10°C / min to forcibly ignite, and the state was maintained.

[0138] In this combustion test, the "time required from when the voltage of the ignition battery becomes 0V until the voltage of the combustion-affected battery becomes 0V" was defined as the "combustion time." For each lithium-ion battery prepared as described above, this combustion time was measured. The obtained combustion times were evaluated according to the following evaluation criteria, with a score of "G" being considered a pass. ≪Evaluation Criteria≫ Rating "G": Burning time was 60 seconds or more. "B": Burning time less than 60 seconds

[0139] [Table 2-1]

[0140] [Table 2-2]

[0141] As is clear from Tables 2-1 and 2-2 above, the samples corresponding to the embodiments of the present invention passed all evaluation results for external corrosion resistance, electrolyte resistance, and safety, while the samples corresponding to the comparative examples of the present invention failed at least one of the evaluation results for external corrosion resistance, electrolyte resistance, or safety.

[0142] 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.

[0143] 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.

[0144] 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 instead of the effects described above.

[0145] Furthermore, the following configurations also fall within the technical scope of the present invention. (1) A battery unit having a positive electrode, a negative electrode, and a separator, and an electrolyte containing a lithium salt, and a case body that houses them, A lid portion that seals the main body of the case, A battery case for a lithium-ion battery having, The material of the case body and the lid is, in terms of mass %, Cr: 1.0~9.9% Al: 0.5-10.0% Mn: 0.1~5.0%, C: 0.002~0.100%, Si: 0.01~0.50%, P: 0.005~0.070%, S: 0.001~0.250%, N: 0.001~0.020%, B: 0.0001~0.0030%, A steel material having a chemical composition in which it contains, with the remainder being Fe and impurities. A battery case for a lithium-ion battery, wherein the battery case has a crimped portion, which is a part where the case body and the lid are joined by a crimping process. (2) A battery unit having a positive electrode, a negative electrode, and a separator, and an electrolyte containing a lithium salt, and a case body that houses them, A lid portion that seals the main body of the case, A battery case for a lithium-ion battery having, The material of the case body and the lid is, in terms of mass %, Cr: 1.0~9.9% Al: 0.5-10.0% Mn: 0.1~5.0%, C: 0.002~0.100%, Si: 0.01~0.50%, P: 0.005~0.070%, S: 0.001~0.250%, N: 0.001~0.020%, B: 0.0001~0.0030%, A steel material having a chemical composition that contains, and further contains one or more elements selected from the group consisting of element groups A to D below, with the remainder being Fe and impurities. A battery case for a lithium-ion battery, wherein the battery case has a crimped portion, which is a part where the case body and the lid are joined by a crimping process. [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]: One or two elements selected from the group consisting of Mo: 3.0% or less and Ni: 9.0% 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. (3) A battery case for a lithium-ion battery according to (2), having a chemical composition containing the aforementioned group of elements A. (4) A battery case for a lithium-ion battery according to (2), having a chemical composition containing the aforementioned group of elements B. (5) A battery case for a lithium-ion battery according to (2), having a chemical composition containing the aforementioned element group C. (6) A battery case for a lithium-ion battery according to (2), having a chemical composition containing the aforementioned group of elements D. (7) A battery case for a lithium-ion battery according to any one of (1) to (6), wherein at least one of Cr fluoride or Al fluoride is present on the inner surface of the battery case in contact with the electrolyte. (8) The thickness of the case body is 0.10 to 1.00 mm. The battery case for a lithium-ion battery as described in any one of (1) to (7), wherein the thickness of the lid is 0.10 to 1.00 mm. (9) The aforementioned steel material is a steel material without a plating layer, a battery case for a lithium-ion battery according to any one of (1) to (8). (10) A battery case for a lithium-ion battery according to any one of (1) to (9), wherein a sealing compound is present in the crimped portion. (11) A lithium-ion battery having a battery case for a lithium-ion battery as described in any one of (1) to (10). [Explanation of Symbols]

[0146] 1. Lithium-ion battery 3 Battery Unit 5 Electrolyte 10 Battery Case 11. Case body 13, 13A Lid 15 Inlet 17 Injection port cap 21. Seam 23 Blockage Processing Unit 25 Welded section 27 Sealing Compound 100 steel

Claims

1. A battery unit having a positive electrode, a negative electrode, and a separator, and an electrolyte containing a lithium salt, and a case body that houses them, A lid portion that seals the main body of the case, A battery case for a lithium-ion battery having, The material of the case body and the lid is, in mass %, Cr: 1.0-9.9%, Al: 0.5-10.0%, Mn: 0.1 to 5.0%, C: 0.002-0.100%, Si: 0.01 to 0.50%, P: 0.005-0.070%, S: 0.001-0.250%, N: 0.001 to 0.020%, B: 0.0001 to 0.0030%, A steel material having a chemical composition in which it contains and the remainder is Fe and impurities, A battery case for a lithium-ion battery, wherein the battery case has a crimped portion, which is a part where the case body and the lid are joined by a crimping process.

2. A battery unit having a positive electrode, a negative electrode, and a separator, and an electrolyte containing a lithium salt, and a case body that houses them, A lid portion that seals the main body of the case, A battery case for a lithium-ion battery having, The material of the case body and the lid is, in mass %, Cr: 1.0-9.9%, Al: 0.5-10.0%, Mn: 0.1 to 5.0%, C: 0.002-0.100%, Si: 0.01 to 0.50%, P: 0.005-0.070%, S: 0.001-0.250%, N: 0.001 to 0.020%, B: 0.0001 to 0.0030%, A steel material having a chemical composition that contains, and further contains one or more elements selected from the group consisting of element groups A to D below, with the remainder being Fe and impurities. A battery case for a lithium-ion battery, wherein the battery case has a crimped portion, which is a part where the case body and the lid are joined by a crimping process. [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]: One or two elements selected from the group consisting of Mo: 3.0% or less and Ni: 9.0% 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.

3. The battery case for a lithium-ion battery according to claim 1 or 2, wherein at least one of Cr fluoride or Al fluoride is present on the inner surface of the battery case in contact with the electrolyte.

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

5. The battery case for a lithium-ion battery according to claim 1 or 2, wherein the steel material is a steel material without a plating layer.

6. A battery case for a lithium-ion battery according to claim 1 or 2, wherein a sealing compound is present in the crimped portion.

7. A battery case for a lithium-ion battery according to claim 2, having a chemical composition containing the aforementioned group of elements A.

8. A battery case for a lithium-ion battery according to claim 2, having a chemical composition containing the aforementioned element group B.

9. A battery case for a lithium-ion battery according to claim 2, having a chemical composition containing the aforementioned element group C.

10. A battery case for a lithium-ion battery according to claim 2, having a chemical composition containing the aforementioned element group D.

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

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