Battery case

Abstract

The present invention addresses the problem of providing a battery case that can suitably accommodate an increase in thickness as well as an increase in size. A battery case (100) is made of metal and provided with an explosion-proof valve (2). The battery case (100) is characterized in that the explosion-proof valve (2) comprises: a folded part (11) that is continuous with a plate part (1) forming the battery case (100) and that is in a folded form; a thin plate part (12) that is continuous with the folded part (11) and that is located inward of the folded part (11); a thick plate part (13) that is continuous with the thin plate part (12) and that is formed thicker than the thin plate part (12) at the center of the explosion-proof valve (2); and a groove (14) for breaking that is provided in the thin plate part (12) and that breaks when a predetermined pressure is exerted thereon.

Description

[Technical field]

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

[0002] In secondary batteries such as lithium-ion secondary batteries, electrodes, electrolyte, etc. are housed inside a battery case. In such secondary batteries, if a malfunction causes internal gas to be generated in the battery case, the internal pressure may rise to an abnormal level. For this reason, the battery case is provided with an explosion-proof valve that can quickly release the internal gas when an abnormal pressure occurs.

[0003] Conventionally, this explosion-proof valve was manufactured separately from the battery case and then attached to the battery case by welding or the like. This resulted in a problem of a complicated manufacturing process and increased manufacturing costs. Therefore, in the manufacturing method of a battery case in Patent Document 1, instead of attaching the explosion-proof valve to the battery case later, the explosion-proof valve is formed directly on the surface (plate portion) that constitutes the battery case by forging, thereby simplifying the manufacturing process.

[0004] The explosion-proof valve for the battery case described in Patent Document 1 is formed by forging a thin plate part in the center, a rupture groove part is formed around the thin plate part, and a folded part is further formed on the outside of that. This allows the thin plate part and the folded part to absorb small pressure fluctuations applied to the battery case, and makes it possible to control the rupture groove part so that it does not rupture due to small pressure fluctuations. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-109222 A Summary of the Invention [Problem to be solved by the invention]

[0006] As the promotion of electric vehicles accelerates in the global market, particularly in China, Europe, and the United States, the capacity required for batteries is rapidly increasing in terms of electricity consumption, such as driving distance and charging and discharging efficiency. This has led to larger batteries, and correspondingly, the thickness of the battery cases is also increasing. When the battery case becomes larger, it becomes necessary to vent the internal gas more quickly than ever before when an abnormality occurs in the battery, and it is therefore necessary to enlarge the area of ​​the opening when an abnormality in pressure occurs.

[0007] In addition, when an explosion-proof valve is formed in a battery case by forging, the explosion-proof valve portion needs to be thinned, but there is a problem that the thinner the portion, the more excess material there is. In other words, the thicker the battery case is, the more excess material there is.

[0008] Therefore, an object of the present invention is to provide a battery case that can be suitably adapted to larger sizes and thicker walls. [Means for solving the problem]

[0009] The present invention, which solves such problems, is a metal battery case provided with an explosion-proof valve, which is characterized in that the explosion-proof valve has a folded-over portion that is continuous with the plate portion that constitutes the battery case and is formed by folding over, a thin plate portion that is continuous with the folded-over portion and is provided on the inside of the folded-over portion, a thick plate portion that is continuous with the thin plate portion and is formed in the center of the explosion-proof valve to be thicker than the thin plate portion, and a breaking groove portion that is provided in the thin plate portion and breaks when a predetermined pressure is applied to it.

[0010] According to the present invention, the thick plate portion is provided in the center of the explosion-proof valve, and can be used as a receiving portion for the material during forging. In addition, by providing the receiving portion for the material in the center, the forging is stable, and as a result, the thickness and shape of the outer periphery of the explosion-proof valve are easily stabilized, and the valve can be stably broken when a pressure abnormality occurs. This makes it possible to suitably accommodate larger and thicker battery cases.

[0011] Moreover, it is preferable that the folded portion and the thin plate portion have a circular or elliptical shape (including an oval shape). It is also preferable that the shape of the thick plate portion is similar to that of the folded portion and the thin plate portion.

[0012] According to the present invention, rupture can be achieved more stably when a pressure abnormality occurs.

[0013] It is also preferable that an arc-shaped recessed groove is formed on the outer side of the thick plate portion.

[0014] According to the present invention, by providing the recessed groove portion in addition to the breaking groove portion, the operating pressure and the breaking location can be easily controlled.

[0015] The thickness of the thick plate portion is preferably 1 / 1.1 to 1 / 2 of the thickness of the plate portion. Moreover, the area of ​​the thick plate portion is preferably 1 / 5 to 1 / 10 of the area of ​​the thin plate portion. Effect of the Invention

[0016] The battery case according to the present invention can be made large and thick. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing a battery case according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view showing the explosion-proof valve according to the first embodiment. [Diagram 3] FIG. 2 is a cross-sectional view showing the explosion-proof valve according to the first embodiment. [Figure 4] FIG. 2 is an enlarged cross-sectional view showing the explosion-proof valve according to the first embodiment. [Diagram 5] FIG. 2 is a flow diagram of a method for manufacturing a battery case member according to the first embodiment. [Figure 6] 4 is a half cross-sectional view showing an earlier stage of a base molding step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 7] 4 is a half cross-sectional view showing a latter stage of the base molding step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 8] 4 is a half cross-sectional view showing an earlier stage of a stretch-forming step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 9] 4 is a half cross-sectional view showing a latter stage of a stretch-forming step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 10] 4 is a half cross-sectional view showing a first stage of a folding step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 11] 5 is a half cross-sectional view showing a latter stage of a folding step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 12] 4 is a half cross-sectional view showing an earlier stage of a preliminary folding step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 13] 4 is a half cross-sectional view showing a latter stage of a preliminary folding step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 14] 4 is a half cross-sectional view showing an earlier stage of a main folding step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 15] 4 is a half cross-sectional view showing a latter stage of a main folding step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 16] 4 is a half cross-sectional view showing a breaking groove forming step in the manufacturing method for a battery case member according to the first embodiment. FIG. [Figure 17] FIG. 4 is a plan view showing an explosion-proof valve according to a second embodiment of the present invention. [Figure 18] FIG. 18 is a cross-sectional view taken along the line II in FIG. [Figure 19] FIG. 4 is a plan view showing an explosion-proof valve according to a third embodiment of the present invention. [Figure 20] 20 is a cross-sectional view taken along the line II-II of FIG. 19. [Figure 21] 20 is a cross-sectional view taken along the line III-III in FIG. 19. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [First embodiment] A battery case and a manufacturing method for a battery case member according to a first embodiment of the present invention will be described in detail with reference to the drawings. The following embodiments and modifications can be appropriately combined to form a configuration. As shown in FIG. 1, the battery case 100 is a hollow metallic container formed by joining a case 101 and a battery case lid 102 by welding or the like. The battery case 100 is formed of, for example, aluminum, an aluminum alloy, copper, a copper alloy, or the like.

[0019] Electrodes, an electrolyte, and the like are housed inside the battery case 100. The case 101 is rectangular in plan view and has a cylindrical shape with a bottom. The battery case lid 102 is a rectangular plate-like member that covers the opening of the case 101. Note that up / down, left / right, front / back are indicated according to the arrows in FIG. 1. These directions do not limit the directions of the present invention.

[0020] The battery case lid 102 includes a plate portion 1 and an explosion-proof valve 2. The explosion-proof valve 2 is integrally formed in the center of the plate portion 1, which is rectangular in plan view. The explosion-proof valve 2 is a valve that breaks when the internal gas reaches a predetermined pressure, and discharges the internal gas to the outside.

[0021] The explosion-proof valve 2 may be provided anywhere on the plate parts (such as the bottom plate, side plate, and lid plate) that constitute the battery case 100, but in this embodiment, the explosion-proof valve 2 is provided on the lid plate part (battery case lid 102). The shape of the battery case 100 is also merely an example, and other shapes such as a cylindrical shape, an elliptical cylindrical shape, or a polygonal cylindrical shape may also be used.

[0022] As shown in Fig. 2 and Fig. 3, the explosion-proof valve 2 includes a folded portion 11, a thin plate portion 12, a thick plate portion 13, a breaking groove portion 14, and a protruding portion 15. The folded portion 11 is continuous with the plate portion 1 and is folded flat. In this embodiment, the folded portion 11 is circular (ring-shaped) in a plan view. In this embodiment, the folded portion 11 has three layers, and the upper layers become thinner.

[0023] The thin plate portion 12 is a thin plate-like portion that is continuous with the folded-over portion 11 and is formed inside the folded-over portion 11. The plate thickness of the thin plate portion 12 is thinner than that of the plate portion 1. In this embodiment, the thin plate portion 12 has a circular shape in a plan view. The thickness of the thin plate portion 12 may be appropriately set according to the operating pressure when releasing the internal pressure. The thin plate portion 12 is formed at a height position approximately equal to the upper surface of the plate portion 1.

[0024] The thick plate portion 13 is a portion that is continuous with the thin plate portion 12 and is provided in the center of the explosion-proof valve 2. The plate thickness of the thick plate portion 13 is thicker than that of the thin plate portion 12. In this embodiment, the thick plate portion 13 has a circular shape in a plan view. The shape of the thick plate portion 13 is similar to that of the folded-over portion 11 and the thin plate portion 12. Since the thick plate portion 13 is provided in the center of the explosion-proof valve 2, it is easily subjected to the internal pressure of the battery case 100.

[0025] The shape of the thick plate portion 13 may be set as appropriate. The thick plate portion 13 may have a different shape from the folded-over portion 11 and the thin plate portion 12. The thickness of the thick plate portion 13 may be set as appropriate, but is preferably 1 / 1.1 to 1 / 2 the thickness of the plate portion 1. The area of ​​the thick plate portion 13 is preferably 1 / 5 to 1 / 10 the area of ​​the thin plate portion 12.

[0026] As shown in FIG. 4, the breaking groove portion 14 is formed on the upper surface of the thin plate portion 12 between the folded portion 11 and the protruding portion 15 (thick plate portion 13) over the entire circumferential direction. The breaking groove portion 14 has a circular shape in a plan view. The cross-sectional shape of the breaking groove portion 14 is not particularly limited, but is V-shaped in this embodiment. The depth of the breaking groove portion 14 (depth relative to the plate thickness dimension of the thin plate portion 12) may be appropriately set according to the operating pressure to be set. In addition, there may be multiple breaking groove portions 14.

[0027] As shown in Fig. 4, the convex portion 15 is a portion on the top surface of the thin plate portion 12 that convexes upward. The convex portion 15 is formed over the entire circumferential direction between the thick plate portion 13 and the breaking groove portion 14. The convex portion 15 has a circular (ring-shaped) shape in a plan view. The convex portion 15 is a portion that controls the strength of the thin plate portion 12. The convex portion 15 may protrude downward, may be provided in multiple rows, or may be omitted.

[0028] Next, a method for manufacturing a battery case member (battery case lid) according to this embodiment will be described. In this embodiment, the case of manufacturing the battery case lid 102 is illustrated as an example, but any part of the plate portion (member) that constitutes the surface of the battery case 100 may be used.

[0029] The manufacturing method for a battery case member includes a base forming step S1, a stretching step S2, a folding step S3, a preliminary folding step S4, a main folding step S5, and a breaking groove forming step S6, as shown in Fig. 5. In each step, the molding is gradually performed while changing the lower and upper dies having different shapes.

[0030] 6 and 7, the base molding step S1 is a step in which the metal plate K is pressed by the first lower die 31 and the first upper die 32 to form the thin portion K1a and the thick portion K1b. The first upper die 32 faces the first lower die 31 in the vertical direction. The first upper die 32 is convex toward the first lower die 31. In other words, the lower end surface of the outer portion 32b of the first upper die 32 is located slightly above the lower end surface of the inner portion 32a.

[0031] As shown in FIG. 7, when the metal plate K is pressed between the first lower die 31 and the first upper die 32, the first upper die 32 is convex, so that the material of the pressed metal plate K flows outward, and the thick-walled portion K1b of the metal plate K becomes thicker than the thin-walled portion K1a.

[0032] 8 and 9, the stretching process S2 is a process for processing the metal plate K to form the thin plate portion 12, the thick plate portion 13, and the cylindrical wall portion 18. In the stretching process S2, a stretching die 41 serving as an upper mold and a stretching punch 42 serving as a lower mold are used.

[0033] The stretching die 41 includes a recess 43 and a first cavity 44. The recess 43 is circular in plan view and includes a bottom surface 43a and a side surface 43b rising from the bottom surface 43a. The stretching die 41 also includes an end surface 45 extending outward from the side surface 43b. The inner diameter of the recess 43 is larger than the outer diameter of the stretching punch 42. The outer diameter of the stretching die 41 is smaller than the outer diameter of the thin-walled portion K1a of the metal plate K, and a first cavity 44, which is circular in plan view and recessed further from the bottom surface 43a, is formed near the center C of the recess 43. The first cavity 44 is a portion for forming the thick plate portion 13.

[0034] The stretching punch 42 is disposed opposite the stretching die 41, sandwiching the thin portion K1a of the metal plate K therebetween. The stretching punch 42 has a main body 46 and a pressing surface 46a. The main body 46 is cylindrical. The pressing surface 46a is provided at the tip of the main body 46. A recessed second cavity 48 having a circular shape in plan view is formed near the center C of the pressing surface 46a. The second cavity 48 faces the first cavity 44, and is a portion for forming the thick plate portion 13.

[0035] As shown in FIG. 8, the metal sheet K is pressed without being restrained while being sandwiched between the bottom surface 43a of the stretching die 41 and the pressing surface 46a of the stretching punch 42. As shown in FIG. 9, when the stretching punch 42 is further pressed into the stretching die 41, the thin wall portion K1a of the metal sheet K is further rolled and gradually becomes thinner, and the thin plate portion 12 is formed. At the same time, the outer periphery of the thin wall portion K1a is pressed downward by the side surface 43b and the end surface 45. A part of the excess material when the thin plate portion 12 is formed flows into the space formed by the first cavity 44 and the second cavity 48, and the thick plate portion 13 is formed, and the remaining material is gradually pushed out radially from the center of the stretching punch 42. The pushed out metal hits the side surface 43b of the recess 43 and is guided, and the moving direction is changed to the vertical direction and flows vertically downward. As a result, the thin plate portion 12, the thick plate portion 13, and the cylindrical wall portion 18 rising from the thin plate portion 12 are formed.

[0036] When forming the cylindrical wall portion 18, the material flows from the thin wall portion K1a to both the thick plate portion 13 and the cylindrical wall portion 18, forming a stable cylindrical wall portion 18. Since a stable cylindrical wall portion 18 can be formed at this stage, the subsequent forming steps can also be performed stably, the shape of the explosion-proof valve is stable, and the operating pressure is also stable.

[0037] If springback or the like occurs after the stretching step S2, a straightening step may be carried out to adjust the shape.

[0038] The folding step S3 is a step of forming a curved portion 19 which will ultimately become a folded portion, as shown in Figures 10 and 11. In the folding step S3, a second lower die 51 and a folding punch 52 are used.

[0039] The second lower die 51 has a flat pressing surface 51a. The folding punch 52 has a main body 56 and a peripheral wall 57. The peripheral wall 57 is a wall that protrudes downward from the main body 56 in a trapezoidal cross section and has a circular (ring-like) shape in a plan view. A second hole 59 that is circular in a plan view is formed inside the peripheral wall 57. The second hole 59 is a hollow portion for avoiding interference with the thick plate portion 13. In other words, the second hole 59 is formed with a depth that does not interfere with the thick plate portion 13. The peripheral wall 57 has a tapered surface 57b that is inclined so as to increase in diameter as it moves away from the pressing surface 57a. The outer diameter of the pressing surface 57a is smaller than the inner diameter of the cylindrical wall portion 18.

[0040] As shown in Fig. 10, in the folding process S3, the thin plate portion 12 is pressed downward by the pressing surface 57a and the tapered surface 57b of the peripheral wall portion 57, while the thin plate portion 12 is sandwiched between the pressing surface 51a of the second lower die 51 as shown in Fig. 11. As a result, the cylindrical wall portion 18 is bent while being slightly expanded outward, and the curved portion 19 is formed. At this time, the thick plate portion 13 is located in the hollow portion formed by the second hole portion 59 and the pressing surface 51a.

[0041] The pre-folding step S4 is a step of preliminarily folding the curved portion 19 while pushing and spreading it outward, as shown in Figures 12 and 13. In the pre-folding step S4, a second lower die 51 and a folding punch (first folding punch) 61 are used.

[0042] The second lower die 51 has the same form as described above. The folding punch 61 includes a main body 62 and a peripheral wall 63. The peripheral wall 63 is a wall that protrudes downward from the main body 62 in a trapezoidal cross section and has a circular (ring-like) shape in plan view. A second hole 64 that is circular in plan view is formed inside the peripheral wall 63. The second hole 64 is a hollow portion for avoiding interference with the thick plate portion 13. In other words, the second hole 64 is formed with a depth that does not interfere with the thick plate portion 13. The peripheral wall 63 is formed with a tapered surface 63b that is inclined so as to increase in diameter as it moves away from the pressing surface 63a. The inner angle formed by the tapered surface 63b and the pressing surface 63a is larger than the inner angle formed by the tapered surface 57b (see FIG. 10) and the pressing surface 57a. As shown in FIG. 12, the tapered surface 63b abuts against the tip of the curved portion 19 before being pressed.

[0043] As shown in Fig. 12, in the preliminary folding step S4, the curved portion 19 is preliminarily folded. That is, in the preliminary folding step S4, the second lower die 51 and the folding punch 61 are brought close to each other while pressing the tip of the curved portion 19 against the tapered surface 63b. As shown in Fig. 13, the approaching distance between the second lower die 51 and the folding punch 61 may be appropriately adjusted, and the pressing surface 63a of the peripheral wall portion 63 may be separated from the thin plate portion 12. The preliminary folding step S4 causes the curved portion 19 to be folded at a further incline.

[0044] 14 and 15, the main folding step S5 is a step of forming the folded portion 11. In the main folding step S5, a second lower die 51 and a folding punch (second folding punch) 71 are used.

[0045] The second lower die 51 has the same form as described above. The folding punch 71 has a flat pressing surface 71a and a second hole 72 formed near the center C of the pressing surface 71a. The second hole 72 is a hollow portion for avoiding interference with the thick plate portion 13. In other words, the second hole 72 is formed with a depth that does not interfere with the thick plate portion 13. The outer diameter of the folding punch 71 is sufficiently larger than the position of the tip of the curved portion 19.

[0046] As shown in Fig. 14, in the main folding step S5, the curved portion 19 is folded over completely. That is, in the main folding step S5, the second lower die 51 and the folding punch 71 are brought close to each other while pressing the tip of the curved portion 19 against the pressing surface 71a of the folding punch 71. This forms the folded portion 11 in which the curved portion 19 is folded over, as shown in Fig. 15. At this time, the thick plate portion 13 is located in the hollow portion formed by the second hole portion 72 and the pressing surface 51a.

[0047] The breaking groove forming step S6 is a step of forming the breaking groove 14 (see FIG. 3) as shown in Fig. 16. In the breaking groove forming step S6, a third lower die 91 and a third upper die 81 are used.

[0048] The third lower die 91 includes a main body 93, a peripheral wall 94, and a first hole 98. The peripheral wall 94 is a section with a rectangular cross section that protrudes upward from the main body 93 in a ring shape. The peripheral wall 94 faces a first protrusion 83 and a second protrusion 84, which will be described later. The first hole 98 is a hollow portion for avoiding interference with the thick plate portion 13. In other words, the first hole 98 is formed with a depth that does not interfere with the thick plate portion 13.

[0049] The third upper die 81 includes a main body 82, a first protrusion 83, and a second protrusion 84. The first protrusion 83 protrudes downward from an end surface 82a of the main body 82. The first protrusion 83 has a trapezoidal cross section, and the diameter decreases toward the bottom. The first protrusion 83 has a circular (ring-shaped) shape in a plan view. A second hole 87 is formed inside the first protrusion 83. The second hole 87 is a hollow portion for avoiding interference with the thick plate portion 13. In other words, the second hole 87 is formed with a depth that does not interfere with the thick plate portion 13.

[0050] The second protrusion 84 protrudes downward from an end surface 82a of the main body 82. The second protrusion 84 is provided on the outside of the first protrusion 83, has a trapezoidal cross section, and decreases in diameter downward. The second protrusion 84 has a circular (ring-shaped) shape in plan view. A protrusion 84a having a triangular cross section is formed on the tip surface of the second protrusion 84 for forming the breaking groove 14. A tapered surface 82b is formed on the outer circumferential surface of the main body 82, which is inclined so as not to interfere with the folded-over portion 11.

[0051] As shown in Fig. 16, in the breaking groove forming step S6, the thin plate portion 12 is sandwiched and pressed between the third lower die 91 and the third upper die 81 to form a breaking groove portion 14 on the upper surface of the thin plate portion 12. In addition, a convex portion 15 (see Fig. 3) is formed in the circumferential direction between the first protrusion 83 and the second protrusion 84. In this manner, the battery case lid 102 is formed. Note that the manufacturing method for the battery case member (battery case lid) is not limited to the steps and order described above, and the design can be modified as appropriate.

[0052] The manufacturing method of the battery case 100 and the battery case member (battery case lid) according to the present embodiment described above provides the following effects. Since the explosion-proof valve 2 has a thick plate portion 13 in the center, it can serve as a recipient for the material during forging. Furthermore, by providing a recipient for the material in the center, the material can be efficiently released, the thickness and shape of the thin plate portion 12 become more stable, and the thin plate portion 12 can be stably broken when abnormal pressure occurs. This makes it possible to suitably accommodate larger and thicker battery cases 100.

[0053] As in this embodiment, the folded-over portion 11, the thin plate portion 12, and the thick plate portion 13 are preferably circular. As in this embodiment, the shape of the thick plate portion 13 is preferably similar to those of the folded-over portion 11 and the thin plate portion 12. By using such a shape, stress concentration can be avoided, and the breakage can be more stable when abnormal pressure occurs.

[0054] Moreover, the width of the breaking groove portion 14 increases as it approaches the direction in which the internal pressure of the battery case 100 acts (upward in this embodiment). This allows the breaking groove portion 14 to easily deform in a direction in which the width of the breaking groove portion 14 increases when internal pressure acts, ensuring breakage.

[0055] In addition, since the present embodiment has the folded portion 11, even if the internal pressure fluctuates due to repeated charging and discharging of the battery, the change in the internal pressure is absorbed by the deformation of the folded portion 11 inward and outward of the battery case 100 (in the plate thickness direction of the battery case lid 102). As a result, excessive tensile stress is not applied to the breaking groove portion 14, so fatigue is unlikely to occur in the breaking groove portion 14. Therefore, the breaking groove portion 14 will not rupture except when the internal pressure reaches a level that exceeds the normal pressure increase during charging or due to an increase in environmental temperature. Therefore, the operating pressure of the explosion-proof valve 2 can be stabilized.

[0056] In addition, because the fracture groove 14 is formed in the easily deformable thin plate portion 12, when the thin plate portion 12 bulges outward (upward) of the case, the fracture groove 14 is first subjected to compressive stress and then subjected to tensile stress, causing the fracture groove 14 to rupture. Therefore, the fracture groove 14 is sure to rupture even if the thickness w (see FIG. 4) of the groove bottom is relatively thick. This increases the strength of the fracture groove 14, making it possible to prevent the fracture groove 14 from rupturing during the assembly of the secondary battery. This makes it easier to handle the battery case 100.

[0057] In addition, in this embodiment, since the structure is such that pressure is applied in two stages, namely, deformation of the folded-over portion 11 and rupture of the breaking groove portion 14, there are many parameters for setting the operating pressure, such as the thickness w and shape of the groove bottom of the breaking groove portion 14 and the shape of the thin plate portion 12, so that the operating pressure can be set to any level. Note that the thin plate portion 12 may have an overall curved shape, which makes the thin plate portion 12 more easily deformable and easier to absorb pressure.

[0058] In addition, in this embodiment, a thick folded portion 11 formed by folding is formed around the explosion-proof valve 2, so that the periphery of the explosion-proof valve 2 can be reinforced. Also, since the folded portion 11 can block heat caused by welding or the like, it is possible to reduce heat input to the explosion-proof valve 2 when welding the case 101 and the battery case lid 102. Also, since the folded portion 11 can be formed by simply folding the metal plate K, the manufacturing process is easy.

[0059] Furthermore, the second lower die 51 can be commonly used in the folding step S3, the preliminary folding step S4, and the main folding step S5, so that molding can be performed efficiently. Furthermore, in the stretch molding step S2, the thick plate portion 13 can be molded in the first cavity 44 and the second cavity 48 while performing backward extrusion molding. This allows the thick plate portion 13 to be easily molded while controlling excess material. Furthermore, after molding the thick plate portion 13, interference between the thick plate portion 13 and each molding die can be avoided, so that the thick plate portion 13 can be molded with high precision.

[0060] [Second embodiment] Next, a method for manufacturing a battery case and a battery case member (a battery case lid) according to a second embodiment of the present invention will be described. As shown in Fig. 17, the battery case lid according to the second embodiment differs from the first embodiment in that recessed grooves N, N are formed in the explosion-proof valve 2A. In this embodiment, the differences from the first embodiment will be mainly described.

[0061] As shown in Fig. 17 and Fig. 18, the explosion-proof valve 2A includes a folded portion 11, a thin plate portion 12, a thick plate portion 13, a breaking groove portion 14, and recessed groove portions N,N. The recessed groove portions N,N are grooves formed in an arc shape between the thick plate portion 13 and the breaking groove portion 14 and recessed downward. The recessed groove portions N,N are formed in positions that are line-symmetrical with respect to the thick plate portion 13. The shape, number, and arrangement of the recessed groove portions N,N can be set as appropriate, but in this embodiment, the curvature of the recessed groove portions N,N is the same as the curvature of the folded portion 11 and the thick plate portion 13.

[0062] Although specific illustration is omitted, for example, in the stretching step S2 or the breaking groove forming step S6, the concave and convex portions can be provided in the corresponding forming mold to form the concave groove portions N, N.

[0063] As in this embodiment, by providing the recessed grooves N,N in addition to the breaking groove 14, the operating pressure and the breaking location can be easily controlled. In other words, the shape, size, position, etc. of the recessed grooves N,N can be appropriately set according to the operating pressure and the breaking location. In addition, by making the curvature of the recessed grooves N,N the same as the curvature of the folded-over portion 11 and the thick plate portion 13, the operating pressure, the breaking location, etc. can be more easily controlled.

[0064] [Third embodiment] Next, a method for manufacturing a battery case and a battery case member (a battery case lid) according to a third embodiment of the present invention will be described. As shown in Fig. 19, the battery case lid according to the third embodiment differs from the first embodiment in that the explosion-proof valve 2B has an elliptical shape. In this embodiment, the differences from the first embodiment will be mainly described.

[0065] As shown in Fig. 19 to Fig. 21, the explosion-proof valve 2B includes a folded portion 11B, a thin plate portion 12B, a thick plate portion 13B, and a breaking groove portion 14B. The folded portion 11B, the thin plate portion 12B, the thick plate portion 13B, and the breaking groove portion 14B all have an elliptical shape in a plan view. The shape of the thick plate portion 13 is similar or approximately similar to the shapes of the folded portion 11B, the thin plate portion 12B, and the breaking groove portion 14B.

[0066] 20 and 21, the height dimension of the folded portion 11B is slightly larger on the short side (FIG. 21) than on the long side (FIG. 20). In the explosion-proof valve 2B, the long side of the folded portion 11 is less rigid and more easily deformed than the short side, so it tends to tear from the long side.

[0067] As in this embodiment, the explosion-proof valve 2B may be elliptical. When the explosion-proof valve 2B is elliptical, it has a tendency to break from the long side, and this characteristic can be utilized to control the operating pressure and the breaking point.

[0068] [Operating pressure test / durability test] Next, the working pressure test and the durability test will be described. Test specimens of the explosion-proof valve 2 of the first embodiment (a circular explosion-proof valve) and the explosion-proof valve 2A of the second embodiment (a circular explosion-proof valve having the concave grooves N, N) were prepared, and the working pressure was measured.

[0069] In the working pressure test, ten test specimens were prepared for each of the explosion-proof valves 2 and 2A, and the working pressure was measured. The average value of the working pressure of the explosion-proof valve 2 was 0.626 MPa, the maximum value was 0.642 MPa, and the minimum value was 0.618 MPa.

[0070] The average operating pressure of the explosion-proof valve 2A was 0.728 MPa, the maximum value was 0.758 MPa, and the minimum value was 0.672 MPa. Compared to the explosion-proof valve 2, the explosion-proof valve 2A had a higher operating pressure.

[0071] For the durability tests, four explosion-proof valve 2 test specimens and six explosion-proof valve 2A test specimens were prepared, and the pressure was increased and decreased 100,000 times (100,000 cycles) within a specified numerical range lower than the set operating pressure. As a result, no fractures were observed in either explosion-proof valve 2 or explosion-proof valve 2A. In addition, the operating pressure after the durability test was measured for each test specimen. For explosion-proof valve 2, the average value was 0.633 MPa, the maximum value was 0.640 MPa, and the minimum value was 0.626 MPa. For explosion-proof valve 2A, the average value was 0.706 MPa, the maximum value was 0.735 MPa, and the minimum value was 0.637 PMa. For both explosion-proof valve 2 and explosion-proof valve 2A, there was no significant change in the operating pressure before and after the durability test, and good results were obtained.

[0072] Although the embodiment of the present invention has been described above, appropriate design changes are possible within the scope of the present invention. For example, the cross-sectional shape of the breaking groove portion 14 may be other shapes than a V-shape. In addition, the preliminary folding step may be omitted, or the curved portion 19 may be folded three or more times. [Explanation of symbols]

[0073] 100 Battery case 101 cases 102 Battery case cover 1 plate part 2 Explosion-proof valve 11 Folding section 12 Thin plate part 13 Thick Plate Section 14 Breaking groove 41 Stretch forming die 42 Stretch forming punch 43 Recess 44 First Cavity 48 Second Cavity K Metal plate N Groove

Claims

1. A metal battery case provided with an explosion-proof valve, The explosion-proof valve is a folded portion formed by folding the plate portion contiguous to the plate portion constituting the battery case; A thin plate portion continuous with the folded portion and provided on the inside of the folded portion; A thick plate portion that is continuous with the thin plate portion, includes the center of the explosion-proof valve, and has a flat plate shape that is circular or elliptical in plan view and is formed thicker than the thin plate portion; a groove for breaking provided in the thin plate portion and breaking when a predetermined pressure is applied thereto; The folded portion and the thin plate portion have a circular or elliptical shape in a plan view, The thick plate portion has a shape similar to that of the folded portion and the thin plate portion, The battery case is characterized in that the plate thickness of the thick plate portion is 1 / 1.1 to 1 / 2 of the plate thickness of the plate portion.

2. 2. The battery case according to claim 1, wherein an arc-shaped recessed groove is formed on an outer side of the thick plate portion.

3. 2. The battery case according to claim 1, wherein the area of ​​the thick portion is 1 / 5 to 1 / 10 of the area of ​​the thin portion.

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