Battery case, secondary battery using the battery case, and method for manufacturing the battery case.

Abstract

The present invention provides a battery case and a method for manufacturing the battery case. [Solution] The battery case disclosed herein is a battery case for a secondary battery in which a gas discharge valve is provided on a single plane, wherein the gas discharge valve comprises a first thin-walled portion that is thinner than the thickness of the plane, and a second thin-walled portion formed on the surface of the first thin-walled portion and even thinner than the thickness of the first thin-walled portion, the surface of which has etching marks.

Description

Technical Field

[0001] The present disclosure relates to a battery case, a secondary battery using the battery case, and a method for manufacturing the battery case.

Background Art

[0002] In a battery case of a general secondary battery, a gas discharge valve is provided to prevent damage to the battery case due to expansion of the electrode body accompanying charge and discharge of the secondary battery. It has been proposed to form a thinner portion compared to other locations for the gas discharge valve so that the gas discharge valve can be surely operated even at a low internal pressure (for example, Patent Documents 1, 2, and 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a material for the battery case, a material having high hardness, such as a stainless steel material (SUS material), can be preferably used. However, when such a material is used, the operability of the gas discharge valve tends to decrease due to its high hardness. Therefore, it is necessary to form the thinner portion described above thinner to enhance the operation stability of the gas discharge valve. Here, the difficulty of processing due to the high hardness of the material, deformation of the material during processing, manufacturing aspects, cost aspects, etc. are cited as problems when forming a thinner portion for a material having high hardness.

[0005] In view of the above circumstances, this disclosure aims to provide a battery case equipped with a safety valve that operates normally near a specified operating pressure, a secondary battery using the battery case, and a method for manufacturing the battery case. [Means for solving the problem]

[0006] The battery case disclosed herein has a gas exhaust valve provided on a single plane. The gas exhaust valve comprises a first thin-walled portion that is thinner than the thickness of the plane, and a second thin-walled portion formed on the surface of the first thin-walled portion and even thinner than the thickness of the first thin-walled portion. The surface of the second thin-walled portion has etching marks.

[0007] With this configuration, first, the relatively thin second thin-walled section ruptures, followed by a continuous rupture of the first thin-walled section. This provides a battery case equipped with a gas discharge valve that has high operational stability.

[0008] In a preferred embodiment of the battery case disclosed herein, the battery case has a rectangular hexahedron shape, and an intersection point consisting of a plurality of slits is formed at the center of the rectangular plane, and the gas discharge valve is formed on the rectangular plane. Here, the second thin-walled portion is formed in the region including the intersection point on the rectangular plane. When the internal pressure inside the battery case rises, the internal pressure is most concentrated in the center of the surface of the battery case. Furthermore, if a plurality of slits are provided in the pressure-receiving surface and intersection points are formed between the plurality of slits, the internal pressure tends to concentrate at these intersection points. In other words, by providing a location where the internal pressure inside the battery case tends to concentrate when the internal pressure rises, and forming the second thin-walled portion of the gas discharge valve in the region including this location, the operability of the gas discharge valve can be suitably improved.

[0009] In one preferred embodiment of the battery case disclosed herein, the battery case is made of iron or an iron alloy steel. By using a material with high hardness as the material for the battery case, high stability against the expansion of the electrode body due to the charging and discharging of the secondary battery can be achieved.

[0010] In one preferred embodiment of the battery case disclosed herein, the first thin-walled portion is a press-formed portion, and the second thin-walled portion is formed within the press-formed portion in a plan view. By making the shape of the first thin-walled portion, which is located closer to the outer surface of the battery case, relatively large in a plan view, the pressure inside the battery case can be effectively relieved when the gas discharge valve is activated.

[0011] This disclosure makes it possible to provide a secondary battery equipped with the above-described battery case.

[0012] The secondary battery provided here has a gas release valve in the battery case that has high operational stability, which helps to suppress damage to the battery case when the electrode body expands due to the expansion of the electrode body during charging and discharging of the secondary battery.

[0013] The method for manufacturing a battery case disclosed herein is a method for manufacturing a battery case in which a gas exhaust valve is provided on a single plane. The gas exhaust valve comprises a first thin-walled portion that is thinner than the thickness of the plane, and a second thin-walled portion formed on the surface of the first thin-walled portion and even thinner than the thickness of the first thin-walled portion. The following steps are then performed: A pressing process in which the above-mentioned first thin-walled portion is formed by press working; Etching process to form the above-mentioned second thin-walled portion by etching; It includes. And, etching marks are present on the surface of the second thin section mentioned above.

[0014] With this configuration, even when using relatively hard materials, it is possible to manufacture a battery case with a gas exhaust valve that has high operational stability, in terms of material deformation, manufacturing aspects, and cost.

[0015] In a preferred embodiment of the method for manufacturing a battery case disclosed herein, the method further includes a slit forming step. The battery case has a rectangular parallelepiped shape, and an intersection formed by a plurality of slits is formed at the center of the rectangular plane. The gas discharge valve is formed on one surface of the rectangle. Here, the second thin portion is formed in a region including the intersection in the rectangular plane. When the internal pressure in the battery case rises, the internal pressure most easily concentrates on the central portion of the surface of the battery case. Further, when a plurality of slits are provided in the surface that receives the internal pressure and an intersection of the plurality of slits is formed, the internal pressure easily concentrates on the intersection. That is, when the internal pressure in the battery case rises, a location where the internal pressure particularly easily concentrates is provided, and by forming the second thin portion of the gas discharge valve in the region including the location, a battery case with suitably improved operability of the gas discharge valve can be manufactured.

[0016] In a preferred embodiment of the method for manufacturing a battery case disclosed herein, the battery case is made of a ferrous material or an alloy steel material of iron. By using a material with high hardness as the material of the battery case, it is possible to manufacture a battery case that can achieve high stability against the expansion of the electrode body accompanying the charge and discharge of the secondary battery.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a schematic perspective view of a secondary battery 100 according to an embodiment. [Figure 2] FIG. 2 is a perspective view of the secondary battery 100 in FIG. 1 with the top and bottom reversed. [Figure 3] FIG. 3 is a schematic cross-sectional view of a secondary battery 100 according to an embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view of a gas discharge valve 18 according to an embodiment. [Figure 5] FIG. 5 is a schematic plan view of a gas discharge valve 18 according to an embodiment. [Figure 6] FIG. 6 is a diagram schematically showing the operating mechanism of a gas discharge valve 18 according to an embodiment. [Figure 7]FIG. 7 is a schematic diagram showing the configuration of the electrode body 20 housed in the battery case 10 according to one embodiment. [Figure 8] FIG. 8 is a flow schematically showing a method for manufacturing the battery case 10 according to one embodiment. [Figure 9] FIG. 9 is a schematic cross-sectional view of a preferred aspect 118 of the gas discharge valve according to one embodiment. [Figure 10] FIG. 10 is a schematic plan view of a preferred aspect 118 of the gas discharge valve according to one embodiment. [Figure 11] FIG. 11 is a flow schematically showing a preferred aspect of a method for manufacturing a battery case according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, some embodiments of the technology disclosed herein will be described with reference to the drawings. In the following drawings, members and parts having the same function are denoted by the same reference numerals and will be described. Also, the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships. In addition, matters other than those specifically mentioned in this specification, which are necessary for the implementation of the technology disclosed here (for example, the general configuration and manufacturing process of a secondary battery that does not characterize the present disclosure), can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed here can be implemented based on the content disclosed in this specification and the common technical knowledge in the relevant field. Also, the following description is not intended to limit the present disclosure to the following forms.

[0019] In this specification, the notation "A to B" indicating a range means "A or greater and B or less." It also includes the meanings of "greater than A" and "less than B." Furthermore, in this specification, "secondary battery" is a term that refers to all energy storage devices that can be repeatedly charged and discharged by the movement of charge carriers between the positive and negative electrodes, and is a concept that encompasses so-called storage batteries (chemical batteries) such as lithium-ion secondary batteries and sodium-ion secondary batteries, and capacitors (physical batteries) such as lithium-ion capacitors (LICs). The main constituent materials of the secondary battery related to this disclosure will be described below. Note that conventionally known constituent materials of secondary batteries not described herein can be used.

[0020] 1. Battery case Figure 1 is a schematic perspective view of a secondary battery 100 according to one embodiment. Figure 2 is a view of the secondary battery 100 in Figure 1, but inverted vertically. Figure 3 is a schematic cross-sectional view of the secondary battery 100 according to one embodiment. The secondary battery 100 comprises a battery case 10 and an electrode body 20 housed inside the battery case 10. The positive electrode terminal 30 is electrically connected to the positive electrode 22 of the electrode body 20 via a positive electrode current collector (not shown) inside the battery case 10. The negative electrode terminal 40 is electrically connected to the negative electrode 24 of the electrode body 20 via a positive electrode current collector (not shown) inside the battery case 10. Although not shown, the secondary battery 100 further comprises an electrolyte housed inside the battery case 10. Each component will be described in order below.

[0021] 1. Battery case (1) Battery case 10 As shown in Figure 1, the battery case 10 is configured in a rectangular hexahedron shape, consisting of a case body 12 having openings 13 at both ends and a sealing plate 14 that seals the openings 13. The battery case 10 can be airtightly sealed and integrated by welding the sealing plate 14 along the edges of the openings 13 of the case body 12.

[0022] The case body 12 comprises a bottom wall 12c, a pair of elongated side walls 12b extending from the bottom wall 12c and facing each other, and a top surface 12a facing the bottom wall 12c. The bottom wall 12c is substantially rectangular in shape. The case body 12 is formed, for example, by bending a single metal plate into a cylindrical shape and joining the joints (for example, by welding). In this case, a welded joint 17 is located on the bottom wall 12c.

[0023] The width of the case body 12 (length in the Y direction in Figures 1, 2, and 3) may be 300 mm or more. By providing such a relatively large case, a relatively large electrode body can be housed inside the case body 12, thereby enabling the creation of a high-capacity secondary battery.

[0024] The width of the case body 12 (length in the Y direction in Figures 1, 2, and 3) may be 50 mm or less. By providing such a relatively small case, a relatively small electrode body can be housed inside the case body 12. In such a small battery, the increase in internal pressure of the battery case due to charging and discharging is relatively small, so it is necessary to further improve the operability of the gas discharge valve. The battery case according to one embodiment has high operational stability of the gas discharge valve and can therefore be suitably used in the manufacture of the above-mentioned small battery.

[0025] The sealing plate 14 seals the opening 13 of the case body 12. A positive terminal 30 and a negative terminal 40 are fixed to the sealing plate 14. The positive terminal 30 is located on one side of the battery case 10 in the width direction (the right side in Figures 1, 2, and 3). The negative terminal 40 is located on the other side of the battery case 10 in the width direction (the left side in Figures 1, 2, and 3). As shown in Figures 1, 2, and 3, the positive terminal 30 and the negative terminal 40 are exposed on the outer surface of the sealing plate 14.

[0026] The battery case 10 has a gas exhaust valve 18 on a single plane. In Figures 1 and 2, the gas exhaust valve 18 is located on the outer surface of the top surface 12a. The gas exhaust valve 18 is made of the same material as the case body 12, for example, a metal material such as iron, SUS430, SUS403, SUS420J2, SUS440C, SUS304, SUS316, SUS329J1, or SUS630.

[0027] As shown in Figures 1 and 2, the battery case 10 has one gas exhaust valve 18, but it may have two or more. The location where the gas exhaust valve 18 is provided is not limited to the top surface 12a; the gas exhaust valve 18 may also be provided on surfaces other than the top surface 12a, such as the long side wall 12b, the bottom surface 12c, the sealing plate 14, etc.

[0028] Figure 4 is a schematic cross-sectional view of a gas exhaust valve 18 according to one embodiment. As shown in Figure 4, the gas exhaust valve 18 comprises a first thin-walled portion 18a which is thinner than the thickness t4 of the plane on which the gas exhaust valve 18 is provided, and a second thin-walled portion 18b formed on the surface of the first thin-walled portion 18a which is even thinner than the thickness t1 of the first thin-walled portion 18a. The thickness t3 of the gas exhaust valve 18 is the sum of the thickness of the first thin-walled portion (t1) and the thickness of the second thin-walled portion (t2).

[0029] The thickness t1 of the first thin-walled section 18a refers to the thickness of the thinnest part of the first thin-walled section 18a. The same applies to the thickness t2 of the second thin-walled section 18b. Therefore, the location where the thickness t1 of the first thin-walled section 18a is measured is the boundary between the first thin-walled section 18a and the second thin-walled section 18b.

[0030] The gas exhaust valve 18 is formed by first creating the first thin-walled portion 18a by press working, and then creating the second thin-walled portion 18b by etching. Details of the gas exhaust valve 18 formation method will be described later.

[0031] Figure 5 is a schematic plan view of a gas exhaust valve 18 according to one embodiment. As shown in Figure 5, the shape of the gas exhaust valve 18 is circular in plan view, but its shape is not particularly limited. For example, it may be elliptical, rectangular, etc. in plan view. The area of ​​the location where the first thin-walled portion 18a is formed may be appropriately adjusted according to the operating pressure of the gas exhaust valve.

[0032] The shape of the second thin-walled portion 18b is not particularly limited, similar to the shape of the first thin-walled portion 18a, and may be, for example, an ellipse, a rectangle, etc., in plan view. It may be appropriately adjusted according to the area of ​​the location where the second thin-walled portion is formed, the operating pressure of the gas discharge valve, etc.

[0033] The thickness t1 of the first thin-walled portion is preferably 55% or more, more preferably 60% or more, and particularly preferably 65% ​​or more, when the total thickness t3 of the gas exhaust valve 18 is set to 100%, by increasing the amount of processing by press working, from the viewpoint of manufacturing suitably in terms of manufacturing and cost. However, if the thickness t1 of the first thin-walled portion 18a is too thin, that is, if the amount of processing by press working is large, deformation such as distortion and waviness of the material may occur during press working, and there is a risk that it will not be usable as a battery case. Therefore, the thickness t1 of the first thin-walled portion 18a is preferably 90% or less, more preferably 80% or less, and particularly preferably 70% or less, when the total thickness t3 of the gas exhaust valve is set to 100%.

[0034] The thickness t2 of the second thin-walled portion is preferably 45% or less, more preferably 40% or less, and particularly preferably 35% or less, when the total thickness t3 of the gas exhaust valve is taken as 100%, from the viewpoint of manufacturing efficiency and cost during gas exhaust valve formation. However, if the thickness of the second thin-walled portion is too thin, the amount of processing required in the etching process will be large, which will reduce manufacturing efficiency and cost. Therefore, the thickness t2 of the second thin-walled portion 18b is preferably 10% or more, more preferably 20% or more, and particularly preferably 30% or more, when the total thickness t3 of the gas exhaust valve is taken as 100%.

[0035] The charging and discharging of the secondary battery causes the electrode body to expand, increasing the internal pressure inside the battery case and activating the gas release valve. In other words, the internal pressure of the battery case becomes the operating pressure of the gas release valve. The operating pressure of the gas release valve 18 is typically 0.1 to 10 MPa, for example, 0.3 to 5 MPa or 1 to 3 MPa. Note that the operating pressure of the gas release valve refers to the pressure at which the second thin-walled section, which is more prone to damage, begins to fail.

[0036] Figure 6 is a schematic diagram showing the operating mechanism of a gas discharge valve 18 according to one embodiment. The arrows in Figure 6 indicate the internal pressure inside the battery case. In the gas discharge valve 18 according to one embodiment, the internal pressure inside the battery case 10 increases due to charging and discharging of the secondary battery (Figure 6(a)), and at the same time that the internal pressure inside the battery case 10 reaches the operating pressure of the gas discharge valve, the thinner second thin-walled portion 18b is damaged (Figure 6(b)). Subsequently, the first thin-walled portion 18a continues to receive internal pressure and is damaged (Figure 6(c)). As a result, the inside of the battery case 10 is depressurized.

[0037] In the gas discharge valve 18, etching marks 18c are present on the surface of the second thin-walled portion 18b. The etching marks are formed by the reaction between the material of the battery case 10 and the etching solution. That is, various reaction products can be generated on the surface of the second thin-walled portion depending on the combination of the material of the battery case and the etching solution. The analysis of the reaction products may be appropriately determined based on the reaction products that can be analyzed.

[0038] Furthermore, the method for distinguishing between the first and second thin-walled sections is not limited to the analysis of the reactants described above. For example, residual stress measurement, resistance measurement, thermal conductivity measurement, hardness measurement, brightness measurement, surface roughness measurement, visual evaluation, tactile evaluation, etc., may also be used.

[0039] In the gas discharge valve 18, the residual stress in the first thin-walled portion 18a may be greater than the residual stress in the second thin-walled portion 18b. Residual stress refers to the stress that remains within an object even after an external force is applied to deform it and then removed. In other words, residual stress affects the strength and durability of the material after processing. Generally, residual stress due to tension tends to decrease the strength of the material, while residual stress due to compression tends to improve the strength of the material. Furthermore, since residual stress is caused by applying an external force to an object and causing deformation, when comparing two objects with the same shape after processing, differences in residual stress may occur depending on whether or not deformation of the material occurs during processing, i.e., differences in processing methods.

[0040] Methods for measuring residual stress include, for example, X-ray stress measurement and electron backscatter diffraction (EBSD). Since the distribution of residual stress is not uniform within the material, residual stress is measured at 10 randomly selected locations in both the first and second thin-walled sections, and the average value calculated from these measurements is used as the residual stress in this specification.

[0041] Etching is a processing method that removes volume from a material through a chemical reaction between the material and an etching solution. In other words, within the etched surface, areas are created where reaction products between the material and the etching solution are formed. Since the composition of these reaction products differs from areas where no reaction products are formed, when comparing the resistance values ​​of a first thin-walled section and a second thin-walled section, a difference in resistance value dependent on the resistance value of the reaction products can be measured.

[0042] As described above, there is a change in the material composition between the etched surface and the unetched surface. Therefore, when comparing the thermal conductivity of the first thin-walled section and the second thin-walled section, a difference in thermal conductivity dependent on the thermal conductivity of the reactants can be measured.

[0043] As described above, there is a change in the material composition between the etched surface and the unetched surface. Therefore, when comparing the hardness of the first thin-walled section and the second thin-walled section, a difference in hardness dependent on the hardness of the reactants can be measured.

[0044] As described above, etching is a process in which reaction products between the material and the etching solution occur within the etched surface. In other words, the occupancy rate of metal atoms may differ between the etched surface and the unetched surface. Therefore, when comparing the brightness of the first thin-walled section and the second thin-walled section, a difference in brightness due to the difference in metallic luster can be measured.

[0045] As described above, etching is a process in which reaction products are generated between the material and the etching solution within the etched surface. In other words, there may be a difference in surface condition between the etched surface and the unetched surface. Therefore, when comparing the surface roughness of the first thin-walled section and the second thin-walled section, a difference in surface roughness due to the difference in surface condition can be measured.

[0046] Unlike the various analytical methods described above, visual and tactile evaluations are not quantitative, but they are methods that can qualitatively evaluate and distinguish different processed surfaces.

[0047] (2) Electrode body 20 Figure 7 is a schematic diagram showing the configuration of the electrode body 20 housed in the battery case 10. The electrode body 20 has a positive electrode 22 and a negative electrode 24. In this case, the electrode body 20 is a flat-shaped wound electrode body in which a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 are stacked via a strip-shaped separator 26 and wound around a winding axis WL.

[0048] As shown in Figure 7, the positive electrode 22 has a positive electrode core 22a and a positive electrode active material layer 22c formed on at least one surface (in this case, both surfaces) of the positive electrode core 22a.

[0049] The positive electrode core 22a is strip-shaped. The positive electrode core 22a is made of a conductive metal such as aluminum, aluminum alloy, nickel, or stainless steel. In this case, the positive electrode core 22a is a metal foil, specifically an aluminum foil.

[0050] As shown in Figure 7, the positive electrode active material layer 22c is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode core body 22a. The positive electrode active material layer 22c contains a positive electrode active material capable of reversibly intercalating and releasing charge carriers. The positive electrode active material preferably contains at least one of Ni, Co, and Mn, and for example, lithium transition metal composite oxides such as lithium nickel cobalt manganese composite oxide can be used. When the total solid content of the positive electrode active material layer 22c is taken as 100% by mass, the positive electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The positive electrode active material layer 22c may also contain optional components other than the positive electrode active material, such as conductive materials, binders, and various additives. As a conductive material, for example, carbon materials such as carbon black (e.g., acetylene black (AB)) can be used. As a binder, for example, PVdF can be used.

[0051] As shown in Figure 7, the multiple positive electrode tabs 22t protrude from the ends of the electrode body 20 in the long side direction Y. The multiple positive electrode tabs 22t are also provided at intervals along the longitudinal direction of the strip-shaped positive electrode 22. The shape of the tabs is rectangular in this example, but various other shapes (e.g., trapezoidal) can also be used. At least a portion of the positive electrode tab 22t has a region where the positive electrode core body 22a is exposed without the positive electrode active material layer 22c being formed.

[0052] As shown in Figure 7, the negative electrode 24 comprises a negative electrode core 24a and a negative electrode active material layer 24c formed on at least one surface (in this case, both surfaces) of the negative electrode core 24a.

[0053] The negative electrode core 24a is strip-shaped. The negative electrode core 24a is made of a conductive metal such as copper, copper alloy, nickel, stainless steel, etc. Here, the negative electrode core 24a is a metal foil, specifically a copper foil.

[0054] The negative electrode active material layer 24c is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode core 24a. The negative electrode active material layer 24c contains a negative electrode active material (for example, a carbon material such as graphite, a Si compound such as Si, SiO, etc.) that can reversibly occlude and release charge carriers. As the Si compound, silicon oxide represented by SiO x (0.05 < x < 1.95), lithium x Si y O z (x, y, z independently satisfy 0 ≤ x, y, z ≤ 1), lithium silicon oxide represented by Li 21 A lithium-containing lithium-silicon alloy represented by Si5, etc. can be used. When the total solid content of the negative electrode active material layer 24c is 100% by mass, the negative electrode active material may generally occupy 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The negative electrode active material layer 24c may contain optional components other than the negative electrode active material, such as a binder, a dispersant, various additive components, etc.. As the binder, for example, rubbers such as styrene-butadiene rubber (SBR) can be used. As the dispersant, for example, celluloses such as carboxymethyl cellulose (CMC) can be used.

[0055] When Si or a Si compound is used as the negative electrode active material, the large amount of charge carriers (such as lithium ions) inserted / deinserted per unit area makes it possible to provide a high-performance secondary battery with high capacity. When Si or a Si compound is used as the negative electrode active material, the large volume change associated with the insertion / deinsertion of charge carriers (such as lithium ions) can cause significant expansion of the electrode body during charging and discharging. In this case, if the operation stability of the gas discharge valve is poor, the battery case is prone to damage. However, the battery case according to this disclosure is equipped with a gas discharge valve with high operation stability and uses a material with high hardness as the material for the battery case, so damage to the battery case can be suppressed even when Si or a Si compound is used as the negative electrode active material.

[0056] As shown in Figure 7, the multiple negative electrode tabs 24t protrude from the end of the electrode body 20 in the long side direction Y. The multiple negative electrode tabs 24t are also provided at intervals along the longitudinal direction of the strip-shaped negative electrode 24. The shape of the tabs is rectangular in this example, but various other shapes (e.g., trapezoidal) can also be used. At least a portion of the negative electrode tab 24t has a region where the negative electrode core body 24a is exposed without the negative electrode active material layer 24c being formed.

[0057] The separator 26 is a component that insulates the positive electrode active material layer 22c of the positive electrode 22 and the negative electrode active material layer 24c of the negative electrode 24. The separator 26 is preferably a porous resin sheet made of polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 26 may also have a heat-resistant layer (HRL) containing an inorganic filler on the surface of the resin sheet. Examples of inorganic fillers include alumina, boehmite, aluminum hydroxide, and titania. Furthermore, it is preferable that an adhesive layer be provided on one or both sides of the separator 26. The adhesive layer improves adhesion to the positive electrode active material layer or negative electrode active material layer in contact with it. The adhesive layer contains, for example, polyvinylidene fluoride (PVdF) as an adhesive component. The adhesive layer may also contain inorganic particles such as alumina and boehmite. The adhesive layer may be provided on the surface of the resin sheet, or on the surface of the HRL.

[0058] (3) Electrolyte The non-aqueous electrolyte can be the same as conventional ones and is not particularly limited. The non-aqueous electrolyte contains, for example, a non-aqueous solvent and a supporting salt. The non-aqueous solvent contains, for example, carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, a fluorine-containing lithium salt such as LiPF6. However, the non-aqueous electrolyte may be in solid form (solid electrolyte) and integrated with the electrode group 20.

[0059] 2. Manufacturing method for battery cases Figure 8 is a schematic flowchart showing the manufacturing method of a battery case 10 according to one embodiment. The manufacturing method of the battery case 10 according to the first embodiment is a manufacturing method of a battery case according to the first embodiment and includes the following steps: a pressing step S10 in which the first thin-walled portion is formed by pressing; and an etching step S20 in which the second thin-walled portion is formed by etching. Each step will be described below.

[0060] (1) Pressing process S10 In the pressing process S10, a first thin-walled portion 18a is formed on one of the planes of the battery case 10 by press working. Press working is a processing method that deforms a material by applying external force. When press working is performed on metal materials, there are advantages in terms of manufacturing efficiency and cost. However, there is a disadvantage that deformation such as distortion and warping may occur in the metal material depending on the amount of processing. In the pressing process S10, press working is performed until such deformation does not occur, or until such deformation occurs but does not adversely affect the performance of the battery case. The press working method is not particularly limited and can include drawing, stretching, bending, coining, etc.

[0061] (2) Etching process S20 In etching step S20, a second thin-walled section 18b is formed by etching. Etching is a processing method that removes the volume of material by etching. Unlike the pressing step S10 described above, etching step S20 does not involve deformation of the material due to processing and has the advantage of enabling highly precise processing. However, it has disadvantages in terms of processing efficiency and cost. After the pressing step S10 described above, etching is performed on the region of the first thin-walled section 18a that includes the thinnest part. The etching method is not particularly limited and examples include isotropic etching and anisotropic etching.

[0062] Etching processes include, for example, wet etching, which utilizes the corrosion of materials with acidic or alkaline solutions. When performing wet etching, pretreatment is appropriately carried out, such as forming corrosion-preventive zones in areas where corrosion should be prevented, and creating liquid reservoirs to suitably retain the etching solution in the reaction area. Furthermore, wet etching is classified into isotropic etching and anisotropic etching depending on the difference in the reaction rate of the etching reaction.

[0063] In isotropic etching, the etching reaction proceeds in an isotropic direction, gouging the material. As a result, the cross-section of the material after etching is processed to have a curved surface. Isotropic etching can occur when the etching reaction rate is fast. On the other hand, in anisotropic etching, the etching reaction proceeds in a unidirectional direction. As a result, the cross-section of the material after etching is processed to have sharp edges. Anisotropic etching can occur when the etching reaction rate is slow.

[0064] The etching reaction rate can be adjusted by the crystal structure of the material, the type and concentration of the etching solution, and the temperature. The etching solution used for wet etching may be appropriately determined depending on the material to which the etching reaction is to be performed. The concentration and temperature of the etching solution may be appropriately determined according to the shape and thickness of the second thin-walled section to be formed.

[0065] As described above, in the manufacturing method of the battery case 10, press working and etching are combined when forming the gas exhaust valve 18. By doing so, press working and etching compensate for each other's disadvantages, making it possible to suitably manufacture a battery case with a thin wall thickness and a gas exhaust valve with high operational stability.

[0066] In the gas discharge valve 18 formed by the above manufacturing method, deformation of the material due to press working is observed in the first thin-walled portion 18a. Etching marks due to etching are observed in the second thin-walled portion 18b. For example, when etching is performed on a battery case made of SUS material with an aqueous ferric chloride solution, chlorides, i.e., iron chloride, chromium chloride, etc., which are constituent elements of the SUS material, may be observed as etching marks.

[0067] In one preferred embodiment of the battery case according to one embodiment, the battery case has a rectangular hexahedron shape, an intersection point consisting of a plurality of slits is formed at the center of the rectangular plane, and the gas discharge valve is formed on the rectangular plane. Here, the second thin-walled portion 118b is formed in the region including the intersection point 119b in the rectangular plane.

[0068] Figure 9 is a schematic cross-sectional view of a preferred embodiment 118 of the gas exhaust valve according to one embodiment. Figure 10 is a schematic plan view of a preferred embodiment 118 of the gas exhaust valve according to one embodiment. In Figures 9 and 10, only the gas exhaust valve of the secondary battery, which is a characteristic part of one embodiment, is shown, and the other parts are omitted because they have the same configuration as the secondary battery 100 of the embodiment described above.

[0069] When the internal pressure inside a secondary battery increases, the pressure is most concentrated at the center of the surface of the battery case. That is, if the surface receiving the internal pressure is rectangular, the internal pressure tends to concentrate at the intersection of the bisectors of the short and long sides. Furthermore, if slits are provided within the pressure-receiving surface, the internal pressure (hereinafter also referred to as linear pressure) tends to concentrate along the slits. If multiple slits are provided within the pressure-receiving surface and intersections are formed between the multiple slits, the internal pressure (hereinafter also referred to as point pressure) tends to concentrate even more at these intersections than at the linear pressure.

[0070] Therefore, by forming an intersection 119b consisting of multiple slits 119a at the center of the surface forming the gas exhaust valve 118, and further forming a second thin-walled portion 118b of the gas exhaust valve 118 in the region including the intersection 119b, the operational stability of the gas exhaust valve 118 can be suitably improved.

[0071] Figure 11 is a schematic flowchart showing a preferred embodiment of a method for manufacturing a battery case according to one embodiment. This manufacturing method is a preferred embodiment of a battery case according to one embodiment and includes the following steps: a slit forming step S100 for forming a slit on the planar surface of the battery case; a pressing step S110 for forming a first thin-walled portion by pressing; and an etching step 120 for forming a second thin-walled portion by etching. Each step will be described below.

[0072] In the slit formation process S100, the method for forming the slits 119a within the plane forming the gas discharge valve 118 is not particularly limited. For example, it may be press working, cutting, etching, etc. The number of slits 119a is sufficient as long as intersections 119b are formed, and at least two slits are required. The slits 119a should be formed to the extent that at least these intersections 119b are formed within the plane where they are formed. The depth of the slits 119a may be adjusted as appropriate according to the opening pressure of the gas discharge valve 118.

[0073] The pressing process S110 and the etching process S120 may be carried out in the same manner as the pressing process S10 and the etching process S20 in the manufacturing method of the battery case 10 according to the above embodiment.

[0074] In one preferred embodiment of the battery case according to one embodiment, the battery case is made of iron or an iron alloy steel. By using a material with high hardness for the battery case, damage to the battery case caused by the expansion of the electrode body due to the charging and discharging of the secondary battery can be suitably suppressed. Examples of materials for the battery case include iron, SUS430, SUS403, SUS420J2, SUS440C, SUS304, SUS316, SUS329J1, and SUS630.

[0075] Materials with high hardness, such as SUS material, offer high stability against the expansion of electrode bodies during charging and discharging, making them suitable for use as battery cases. However, due to their high hardness, such materials tend to be prone to malfunctions in the gas exhaust valve. Therefore, it is necessary to provide a thinner gas exhaust valve. If the thin-walled portion of the gas exhaust valve is to be formed even thinner by press working alone, the material may deform, such as warping or undulation, potentially rendering it unusable as a battery case. On the other hand, forming the gas exhaust valve by etching is inefficient in terms of manufacturing and cost. However, according to the battery case manufacturing method of one embodiment, the gas exhaust valve is formed by combining press working and etching, so even when using a material with high hardness, a thinner-walled portion can be suitably formed on the battery case.

[0076] In one preferred embodiment of the battery case according to one embodiment, the first thin-walled portion is a press-formed portion, and the second thin-walled portion is formed within the press-formed portion in a plan view. This allows for a relatively large area in a plan view of the first thin-walled portion, which is located closer to the outer surface of the battery case, thereby increasing the pressure relief area when the gas discharge valve ruptures, and thus enabling effective pressure relief within the battery case.

[0077] 3. Secondary battery According to a secondary battery using a battery case according to one embodiment, damage to the battery case caused by the expansion of the electrode body when the secondary battery is repeatedly charged and discharged can be suppressed.

[0078] <Evaluation Test> (1) Whether or not the material is deformed due to press working [1] Example 1 A SUS304 stainless steel sheet with a wall thickness of 0.65 mm was prepared. This SUS304 was press-formed at a press pressure of 40 GPa until its wall thickness was reduced to 0.2 mm. Afterward, the area around the press surface was visually inspected to confirm that no deformation such as distortion or waviness had occurred in the used SUS304.

[0079] [2] Comparative Example 1 The evaluation test was conducted in the same manner as in Example 1, except that the wall thickness after press working was set to 0.055 mm.

[0080] <Evaluation Results> (1) Whether or not the material is deformed due to press working The evaluation results are shown in Table 1.

[0081] [Table 1]

[0082] As shown in Table 1, in Example 1, with a deformation rate of 69%, no material deformation was observed around the press surface after press working. On the other hand, in Comparative Example 1, with a deformation rate of 92%, material deformation was observed around the press surface after press working.

[0083] Although a detailed explanation has been given above with specific embodiments, these are merely examples and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the embodiments described above.

[0084] As described above, this specification includes the disclosures set forth in the following sections. Section 1: A battery case for a secondary battery, in which a gas exhaust valve is provided on a single plane, The aforementioned gas discharge valve is A first thin-walled portion having a thickness thinner than the thickness of the aforementioned plane, A second thin-walled portion is formed on the surface of the first thin-walled portion and is even thinner than the thickness of the first thin-walled portion, Equipped with, The surface of the second thin section has etching marks. Battery case.

[0085] Section 2: The battery case has a rectangular hexahedron shape, and the gas discharge valve is formed on the rectangular plane. The battery case according to item 1, wherein the second thin-walled portion is formed in a region including the intersection of the angle bisector of the short side and the angle bisector of the long side in the rectangular plane.

[0086] Section 3: A battery case as described in item 1 or 2, made of iron or an iron alloy steel.

[0087] Section 4: The battery case according to any one of claims 1 to 3, wherein the first thin-walled portion is a press-formed portion, and the second thin-walled portion is formed within the press-formed portion in a plan view.

[0088] Section 5: A rechargeable battery equipped with a battery case as described in any one of items 1 to 4.

[0089] Item 6: A method for manufacturing a battery case in which a gas discharge valve is provided on a single plane, The aforementioned gas discharge valve is A first thin-walled portion having a thickness thinner than the thickness of the aforementioned plane, A second thin-walled portion is formed on the surface of the first thin-walled portion and is even thinner than the thickness of the first thin-walled portion, Equipped with, The residual stress in the first thin-walled section is greater than the residual stress in the second thin-walled section. The following steps: A pressing step in which the first thin-walled portion is formed by press working; An etching process to form the second thin-walled portion by etching; to include, A method for manufacturing battery cases.

[0090] Section 7: The method for manufacturing a battery case according to item 6, further comprising a slit forming step, wherein the battery case has a rectangular hexahedron shape, and the gas discharge valve is formed on one of the rectangular surfaces. The second thin-walled portion is formed in the region including the intersection point in the rectangular plane.

[0091] Section 8: A method for manufacturing a battery case according to item 6 or 7, wherein the battery case is made of iron or an iron alloy steel. [Explanation of symbols]

[0092] 10 Battery Case 12 Case body 12a Bottom wall 12b Long side wall 12c Top surface 13 Aperture 14 Sealing plate 15 Inlet 16 Sealing member 17. Welded joint 18 Gas discharge valve 18a 1st thin section 18b 2nd thin section 20 Electrode body 22 Positive electrode 22a Positive electrode core 22c Cathode active material layer 22t positive electrode tab 24 Negative electrode 24a Negative electrode core 24c negative electrode active material layer 24t negative electrode tab 26 Separators 30 Positive terminal 40 Negative terminal 100 Secondary battery 110 Battery Case 112 Case body 112a Bottom wall 112b long side wall 112c Top surface 113 Aperture 114 Sealing plate 115 Inlet 116 Sealing member 117 Welded joint 118 Gas discharge valve 118a 1st thin section 118b 2nd thin section 200 Secondary battery

Claims

1. A battery case for a secondary battery, in which a gas exhaust valve is provided on a single plane, The aforementioned gas discharge valve is A first thin-walled portion having a thickness thinner than the thickness of the aforementioned plane, A second thin-walled portion is formed on the surface of the first thin-walled portion and is even thinner than the thickness of the first thin-walled portion, Equipped with, The surface of the second thin section has etching marks. Battery case.

2. The aforementioned battery case has a rectangular hexahedron shape, At the center of the aforementioned rectangular plane, the intersection of multiple slits is formed. The gas exhaust valve is formed on the rectangular plane, The battery case according to claim 1, wherein the second thin-walled portion is formed in a region including the intersection point in the rectangular plane.

3. The battery case according to claim 1, which is made of iron or an iron alloy steel.

4. The battery case according to claim 1, wherein the first thin-walled portion is a press-formed portion, and the second thin-walled portion is formed within the press-formed portion in a plan view.

5. A secondary battery comprising the battery case described in any one of claims 1 to 4.

6. A method for manufacturing a battery case in which a gas discharge valve is provided on a single plane, The aforementioned gas discharge valve is A first thin-walled portion having a thickness thinner than the thickness of the aforementioned plane, A second thin-walled portion is formed on the surface of the first thin-walled portion and is even thinner than the thickness of the first thin-walled portion, Equipped with, The residual stress in the first thin-walled portion is greater than the residual stress in the second thin-walled portion. The following steps: A pressing step in which the first thin-walled portion is formed by press working; An etching step in which the second thin-walled portion is formed by etching; to include, A method for manufacturing battery cases.

7. The process further includes a slit formation step, The aforementioned battery case has a rectangular hexahedron shape, The intersection of multiple slits is formed at the center of the rectangular plane. The gas discharge valve is formed on one side of the rectangular shape. The method for manufacturing a battery case according to claim 6, wherein the second thin-walled portion is formed in a region including the intersection point in the rectangular plane.

8. The method for manufacturing a battery case according to claim 6 or 7, wherein the battery case is made of iron or an iron alloy steel.

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